WO2015173575A1

WO2015173575A1 - Print removal devices and methods

Info

Publication number: WO2015173575A1
Application number: PCT/GB2015/051426
Authority: WO
Inventors: David Ricardo LEAL-AYALA; Juan-Leonardo MARTINEZ-HURTADO; Anthony R Dunn
Original assignee: Reduse Limited
Priority date: 2014-05-16
Filing date: 2015-05-14
Publication date: 2015-11-19

Abstract

We describe a print removal device, the device comprising: a paper feed system to receive and feed printed paper though the device; a print removal head having a controllable laser output for removing print from said paper; and a head drive system to scan said print removal head over said paper as said paper is fed through the device; wherein said print removal head further comprises a sensor, mounted to be scanned over said paper in conjunction with said head and configured to operate in tandem with said laser output; the device further comprising a control system, coupled to said sensor and to control said laser output, wherein said control system is configured to control said laser output to irradiate said paper to remove print from said paper in response to detection of said print by said sensor as said head is scanned over said paper.

Description

Print Removal Devices and Methods

FIELD OF THE INVENTION This invention relates to apparatus and methods for removing print from paper ("unprinting"), and for marking unprinted paper as unprinted.

BACKGROUND TO THE INVENTION We have previously described a combination of laser pulse length and wavelength which optimises the removal of toner ink from white paper, in Leal-Ayala D.R. and Allwood J.M., "Paper re-use: Toner-print removal by laser ablation", International Conference on Digital Printing Technologies (2010), pages 6-9; and also in Leal-Ayala, D. R., Allwood, J. M., Schmidt, M., & Alexeev, I. (2012), "Toner-print removal from paper by long and ultrashort pulsed lasers", Proceedings of the Royal Society A: Mathematical, Physical and Engineering Science, 468(2144), 2272-2293. Figure 8, which is taken from the Proc. Roy. Soc. paper, illustrates the relationship between wavelength, pulse length and paper damage, showing that the optimum wavelength is in the visible, around the green, and that the optimum pulse length is in the range 10ps - 40ns. Further background prior art can be found in US8693064B and US2004/0080787; JP2005/292747A also appears to describe a paper sheet regenerating device.

Despite this general background, there is need to solve various practical engineering problems in order to make a practical, low-commercial device.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is therefore provided a print removal device, the device comprising: a paper feed system to receive and feed printed paper though the device; a print removal head having a controllable laser output for removing print from said paper; and a head drive system to scan said print removal head over said paper as said paper is fed through the device; wherein said print removal head further comprises a sensor, mounted to be scanned over said paper in conjunction with said head and configured to operate in tandem with said laser output; the device further comprising a control system, coupled to said sensor and to control said laser output, wherein said control system is configured to control said laser output to irradiate said paper to remove print from said paper in response to detection of said print by said sensor as said head is scanned over said paper.

Embodiments of the above described print removal device avoid the need for complex and expensive image processing and instead use an arrangement with a direct functional coupling between the print sensing and laser ablation: in embodiments the ablation head is scanned and as it is scanned an optical detection system on the head detects the print and directly controls the laser (optionally compensating for a short time delay). This quasi-direct control avoids the need for 2D image capture and processing thus potentially providing a substantial cost saving and improved unprinting speed. Preferably, but not essentially, the print sensor is mounted on the print removal head, and preferably the sensor is directed towards a region close to the region of laser ablation. In embodiments a delay device, preferably memory but in principle a counter or timer, provides a delay between print detection and laser ablation to compensate for the lateral displacement between the sensing and ablation and the consequent delay due to head movement. Where the spacing between the sensing and ablation is more than one ablation pixel, memory may be employed to store the one or a few intermediate pixels to provide a first in - first out buffer for the ablation data.

In preferred embodiments the paper feed system feeds paper past the head in a first, feed direction and the head is scanned in a second, perpendicular, scanning direction. Alternatively, however, the paper may be fed stepwise through the device, in which case the head may be scanned into perpendicular directions rather than just in a single direction. In embodiments the paper feed system feeds paper through the device from an input port to an output port but in other arrangements an input and/or output paper tray or hopper may be internal and the paper feed system may feed the paper internally through the device.

The laser may be mounted within the device and the laser output is provided to the print removal head via transmission optics, for example a fibre optic, but in other embodiments the laser is mounted on the print removal head. The laser may be a continuous laser or a pulse laser; in the former case a shutter may be employed to control the laser output for selective unprinting. In some preferred embodiments two print sensors are provided, one for either side of the laser output (in the scanning direction) so that the head may be operated bi- directionally for increased scanning speed. Thus in embodiments the head drive system is arranged to scan the head in a substantially continuous boustrophedonic motion. Preferably in such an arrangement the head drive is arranged so that the head overshoots the boundary of the paper slightly at each side so that the relevant sensor is correctly positioned for the start of the next scanning pass across the paper. Preferably the head is moved at a rate no greater than the product of a pixel dimension in the scanning direction and the frequency of operation of the laser - that is preferably the scanning speed is matched to the frequency of laser operation. Preferably the laser output provides a peak laser pulse power of at least 30KW, more preferably at least 50kW, 80KW or 90KW, over the area of an unprinting pixel.

In embodiments the device is configured to unprint both sides of a sheet of paper simultaneously. It is preferable for the paper to be supported in the unprinting region and in embodiments double-sided unprinting is achieved by providing a paper support with a slot longitudinally aligned along the scanning direction so that a second print removal head under the paper can sense and ablate print.

Optionally the unprinter may include an additional sensor, for example a 1 D line sensor, to sense the presence of an entire blank line along the scanning direction. When such a blank line is sensed the control system can control the paper feed system to skip past the blank line. This can speed up the unprinting process since a typical printed page will often include many blank lines.

In a related aspect the invention provides a method of removing print from paper, the method comprising: providing a print removal head having a controllable optical output for removing print from paper; moving printed paper and said print head relative to one another in a first direction; scanning said print removal head relative to said paper in a second direction perpendicular to said first direction; scanning a sensor in tandem with said print removal head in said second direction; and controlling said optical output to irradiate said paper to remove print from said paper in response to detection of said print by said sensor as said head is scanned relative to said paper. The invention further provides a print removal device, the device comprising: a print removal head having a controllable optical output for removing print from paper; means for moving printed paper and said print head relative to one another in a first direction; means for scanning said print removal head relative to said paper in a second direction perpendicular to said first direction; means for scanning a sensor in tandem with said print removal head in said second direction; and means for controlling said optical output to irradiate said paper to remove print from said paper in response to detection of said print by said sensor as said head is scanned relative to said paper.

Operation of a print removal device such as that previously described results primarily in ablated toner particles, as well as some water vapour and carbon dioxide. By way of example, for black toner the ablated toner typically comprises a mixture of polymer (polyester) resin and pigment; the pigment typically comprises iron oxide. The ablated material comprises nanoparticles, typically with a median maximum dimension of less than 1000nm, 500nm, or 200nm. For example typical ablated toner particles comprise iron oxide with a size distribution extending over the range 10nm to 200nm, typically with a peak in the 10-20nm range. It is therefore important in embodiments of the device to include a particle removal system, for safety and, potentially, also reuse of the ablated toner material.

Thus in a further aspect the invention provides a print removal device, the device comprising: a paper feed system to receive and feed printed paper through the device; a print removal head having a laser output for removing print from said paper; and a particle removal system to capture nanoparticles from said removing of said print.

In a preferred embodiment the particle removal system comprises an inlet nozzle mounted on the print removal head (or at least to move together with the head) and directed towards the point of removal of the print by the laser. This inlet nozzle may then be connected to a suction device and to a nanoparticle receptacle or bag, preferably incorporating a nanoparticle filter such as an HEPA filter to remove nanoparticles from the discharged air.

In preferred embodiments the nanoparticle receptacle bag has a self-sealing air inlet, for safe handling. In one arrangement this is provided by a set of moveable leaves which engage with a male member of an air duct of the particle removal system - so that the receptacle or bag can be pushed over the air-duct to form a sealed coupling. Preferably the end of the air-duct has an asymmetric cross-sectional shape which matches a corresponding shape defined by the pattern of moveable leaves or flaps (or other sealing arrangement), to reduce the risk of accidental opening of the receptacle or bag. In another approach the self-sealing arrangement comprises a displaceable sealing member which is displaced to open the air inlet on attachment of the receptacle or bag and which is displaced to close the air inlet when the receptacle/bag is removed. In a simple embodiment the receptacle/bag may have an attachment portion with a moveable shutter which slides out of the way when the attachment portion is slid across the end of the relevant air duct.

The skilled person will appreciate that features of the above described aspects and embodiments of the invention can be combined in the permutation.

In a still further aspect the invention provides a print removal device, the device comprising: a paper feed system to receive and feed printed paper though the device; a print removal head having a controllable laser output for removing print from said paper; and a head drive system to scan said print removal head over said paper as said paper is fed through the device; a point or line sensor for sensing print on said paper; means for providing relative motion between said paper and said sensor; and a control system, coupled to said sensor and to control said laser output, wherein said control system is configured to control said laser output to irradiate said paper to remove print from said paper in response to detection of said print by said sensor as said head is scanned over said paper.

In embodiments, the laser may be remote from the print removal head and the laser light provided to the print removal head for removing print. In embodiments the sensor may be a line sensor for sensing a line of print (along the scanning direction). The control system may then comprise a buffer to store one or more lines of sensed unprinting pixels prior to the line of print arriving at the print removal head. Optionally the control system may then be configured to control the paper feed system responsive a signal from the sensor to skip past a blank line on the paper. For avoidance of doubt, a blank line is a mostly blank line, a partially blank line, or a blank remainder of a line. Again, features from other previously described aspects/embodiments of the invention may be included in the device.

Marking unprinted paper as 'unprinted':

According to a further aspect of the present invention, there is provided an unprinter including a printer or other marking device to mark unprinted paper as unprinted.

Broadly speaking, an "unprinter" is a system or apparatus which comprises a laser device in combination with a positioning sensor to effectively remove (i.e. 'unprint') toner print from an item of media (e.g. paper). Toner particles are removed from paper by laser ablation. The unprinter system and the process to 'unprint' toner print are described in more detail below. Preferably, such unprinted items of media may be marked with a label, message and/or code to indicate that the items have been unprinted. More preferably, such marks are permanent and/or not unprinted during any subsequent procedures to unprint the items of media.

The mark may be provided in a margin or along an edge of the item of media. Additionally or alternatively, the mark may be provided as a watermark-style mark covering a substantial area of the item of media. Thus, in embodiments, the printer or other marking device comprises a marking device to mark more than 20%, 25% or 50% of an area of an item of unprinted media. In other embodiments, the printer or other marking device comprises a marking device to mark substantially all of an area of an item of unprinted media. The watermark may be applied using ink which cannot be removed during subsequent unprinting of the item of media.

In embodiments, the printer or other marking device comprises a printer configured to print a code or message on an item of unprinted media. The mark may be applied using any one of the following techniques: a stamp (e.g. tampography or transfer printing), and inkjet print head, or thermal transfer head. A mark may be applied to an item of unprinted media each time it is unprinted (i.e. a tally mark), or only the first time an item of media is unprinted. Tampography or print stamps may be used to apply a simple mark to an item of unprinted paper, and may be used to mark an item of media the first time it is unprinted. The mark may be a machine readable code, or a machine identifiable mark, and/or may combine machine-readable code with an alphanumeric message. Thus, in embodiments, the code or message applied to an item of unprinted media comprises a machine-readable part, and preferably further comprises a configurable human- readable part. The machine-readable part may enable a printer to distinguish between 'new' paper and 'unprinted' paper. This may enable a printer to check that the paper being fed through the printer for a print job matches the type of paper selected by a user, prior to it being printed upon. Additionally or alternatively, the machine-readable part may enable an unprinter to check how many times an item of media has been unprinted previously, prior to performing the unprinting process. This may be important if there is an upper limit on the number of times an item of media can be unprinted (e.g. for quality purposes). The human-readable part may be configurable to provide a particular message, such as, but not limited to, "this is unprinted paper", or "unprinted by Reduse Ltd".

In embodiments, the code or message comprises data indicating a count of the number of times the media has been unprinted. The count may be provided by tally marks applied to the media each time it is unprinted. In embodiments, the code or message is printed in one or more margins of said unprinted media. Advantageously, the mark is applied to a small area of an unprinted item of media such that the majority of the item of media to be reused for printing.

In embodiments, the code or message includes a header such that the code or message is readable when the media in each of any orientation. Headers may be provided on either side of the code or message, and preferably, the headers are asymmetric or dissimilar, such that the headers can be used to determine which way round the unprinted item is oriented. In embodiments, the unprinter comprises a duplexing unit to reverse an item of media to read the code or message on one or both sides of the item of unprinted media. Advantageously, the duplexing function may enable the unprinter to read a mark on an item of media regardless of which side the mark is on, and a user of the unprinter does not need to provide the unprinter with items of media in a particular orientation. In embodiments, the unprinter further comprises at least one sensor coupled to a processor to detect the mark on the unprinted media, and to control the unprinter response to the detection. Preferably, the control comprises controlling operation of the printer or other marking device. For example, if the printer/marking device comprises a tampo stamp which is capable of applying a pre-defined mark (and not a tally mark), and if the sensor detects a mark on the unprinted media, the control comprises sending a command to the printer/marking device not to engage. If the printer/marking device is capable of applying a tally mark, the control comprises sending a command to the printer to engage and apply a mark. If the sensor does not detect a mark on an item of media (because it has not previously been unprinted), the control comprises printing a mark on the media item prior to unprinting the media. In embodiments, the at least one sensor is configured to detect the number of times each side of the media has been unprinted, and the control comprises a decision as to whether to proceed with unprinting the media. For example, if an organisation sets the upper limit in the number of times an item of media can be unprinted, the control determines proceeding with the unprinting process if the sensor detects the upper limit has not been reached, or ejecting the item of media (e.g. for ordinary recycling) if the sensor detects the upper limit has been reached or will be exceeded.

In embodiments, further comprising a plurality of out-feed trays to collect said unprinted media, wherein the at least one sensor is further configured to determine unprinted media density, and wherein said control comprises a decision as to which of said plurality of out-feed trays to direct said unprinted media to dependent on said determined density of said unprinted media. The density (e.g. grams per square meter, or GSM) of an item of media may be used to direct the items of media to particular out- feed trays so that the unprinted items of media are filtered according to density. Advantageously, by filtering the unprinted paper in this way, the unprinted items of media can be passed to a printer (manually by a user or automatically in a combined unprinter and printer system) which is capable of printing items of media of particular densities. According to a further aspect of the invention, there is provided a printer comprising a sensor coupled to a processor to detect a mark identifying media for printing as unprinted media, and to control said printer responsible to said detection. In embodiments, the control comprises a decision as to whether to proceed with printing. For example, if a user selects 'new' paper (i.e. paper which has never been unprinted or printed upon), for a particular print job, the printer uses paper from the 'new' paper infeed tray. The printer may be configured to check that the paper in the new paper infeed tray is not actually unprinted paper. This check may be performed via a mark-reading module or sensor arrangement coupled to the printer. If no mark is found on the 'new' paper, the print job is completed. If a mark is found on the 'new' paper, the paper may be diverted to a recycling bin or to an unprinted-media infeed tray. This may be important if a user or organisation has to comply with certain requirements controlling how or when unprinted media may be used for printing (e.g. for internal use only).

In a further aspect of the invention, there is provided a method of providing unprinting information on unprinted paper, the method comprising: printing a mark providing unprinting information on printed paper; sending said printed paper to an unprinter for unprinting; capturing an optical image of said printed paper for unprinting; and unprinting said printed paper.

In embodiments, printing of the mark is performed by a mark-printing module. In embodiments, the mark-printing module comprises any one of the following: a tampography stamp, a thermal transfer printing device, an inkjet printing device or a laser printer.

In a further aspect of the invention, there is provided a system for re-using paper, the system comprising: an unprinter to accept printed paper as an input, and to output unprinted paper; a printer to accept said unprinted paper for printing; wherein said unprinter comprises a system to mark said unprinted paper as unprinted; and wherein said printer comprises a system to detect said marking of said unprinted paper as unprinted. In embodiments, the unprinter further comprises a system to detect said marking of said unprinted paper. Thus, marks may be detected via the unprinter system and/or the printer system. In the former case, this enables the unprinter to determine how many times an item of media has been unprinted previously (in case there are thresholds, as mentioned above), while in the latter case, the printer may check an item of media is the correct type (i.e. unprinted or 'new') prior to performing a print job.

In embodiments, a printer driver of said printer, or said printer control system may maintain a log that records use of said unprinted paper responsive to said detection or when configured to associate an in-feed tray with unprinted media. This may enable statistics to be accumulated related to number or the ratio of new to Unprinted paper which may be used to encourage increased reuse of paper. In the preferred embodiment a modified printer driver is used to both encourage increased use of unprinted paper and provide statistics on a user's performance.

In a further aspect of the invention, there is provided a method of determining a measure of unprinting performance, the method comprising: capturing an optical image of part or all of an item of unprinted media; and generating a set of one or more unprinting metrics from said optical image. The unprinting performance may advantageously enable a quality check of unprinted items to be performed prior to being provided to a printer.

In embodiments, the measure comprises a pass/fail measure for said unprinted media. In embodiments, the method further comprises assessing the quality of the unprinted media and its suitability for being used again by scoring the collective visual impact of any artefacts left on the media after unprinting. The method comprises identifying one or more print marks, stains or extraneous marks on said item of unprinted media; and scoring the visual impact of the identified marks or stains to provide one or more metrics indicative of the suitability for reuse of said item of unprinted media. Preferably, the method of scoring the identified marks or stains comprises: characterising the identified marks or stains into one or more categories or types; applying one or more weighting values to said identified marks or stains; computing aggregated unprinting metrics; and determining if said aggregated unprinting metrics are above or below a threshold quality value. The type of marks may be left-over artefacts from ink or toner print that may be single dots, clusters of dots, lines or curves of printed matter which have not been successfully removed during the unprinting process. They may also be stains (e.g. food or drink stains), pen or pencil annotations, holes from where staples have been removed, etc. Thus, some marks cannot be unprinted and some print may have not been completely unprinted.

In embodiments, the weighting values comprise a weighting value for each mark category or type, and/or a weighting value for colour. In embodiments, the unprinted media is characterised as suitable for reuse if said aggregated unprinting metrics for said unprinted media are acceptable relative to a threshold quality value.

In a related aspect of the invention, there is provided a non-transitory data carrier carrying processor control code to implement the above-described methods.

In a related aspect of the invention, there is provided a printer, unprinter or computer storing processor control code to implement the above-described methods. In a further aspect of the invention, there is provided a combined printer and unprinter system, comprising: a media printing system; a media unprinting system; and at least one shared media path or receptacle linking both said unprinting system and said printing system, such that said printing system is able to print on unprinted media generated from said unprinting system.

In embodiments, the combined printer and unprinter further comprises an unprinted media evaluation system to evaluate said unprinted media to determine suitability for re-use. It is generally desirable to encourage use of recycled materials to reduce waste and cost in purchasing new paper.

Thus in a further aspect the invention provides a printer driver for unprinted media, the printer driver comprising: an input to receive document data for printing; an output to provide printer data for driving a printer to print a document defined by the document data; and a conversion module, coupled between the input and output to convert the document data to printer data; wherein said printer driver is configured to: receive said document data, and in response: display a user prompt for the user to select unprinted media for printing: receive a user command to select unprinted media; and output control data for selecting said unprinted media for printing.

Broadly speaking embodiments of the printer driver, which may be used in any of the systems described herein incorporating a printer, encourage use of unprinted paper by displaying a prompt at the moment when the user is commanding the act of printing. Further, the inventors have recognised that it is particularly advantageous to incorporate such a prompt into a printer driver for unprinted paper because this provides the correct message timing and also provides an efficient mechanism for intercepting a range of printing acts initiated from a range of different applications. In some particularly preferred embodiments the printer driver provides a simple 'yes/no' interface for a user input signal, for example, providing a button to click, preferably as a single-click operation, so as to provide a minimum of impediment to the user in selecting use of unprinted paper or other media. In one preferred embodiment the printer driver is configured so that this option is provided but does not override any existing defaults so that when the option to use unprinted paper is chosen, unprinted paper is used for that printing event but the system then defaults back to the previous paper (or other media) selection. It will be recognised, however, that alternative modes of operation may be employed. In some preferred embodiments the user prompt to employ unprinted paper (or other media) changes from one instance of displaying the prompt to another. Thus the appearance, for example, colour of the prompt message could change and/or the content of the message could change. For example the message content could be selected from a set of different message contents or the message content may be updated from one message to another, for example by incorporating information based on stored usage statistics for unprinted paper. In broad terms a changing message is useful because a static message can, with repeated presentation, not be noticed by a user. Examples of messages that may be presented include, but are not limited to: messaging to direct the user to comply with a paper (media) usage policy; messaging including statistics and/other information about one or more benefits of using unprinted paper to the environment and/or business; motivational messages; messages comprising news, links to articles, or other content, for example sport. In some embodiments some or all of the message data comprising a message may be retrieved from a server; additionally or alternatively a local message store may be provided.

In some preferred embodiments the display of the user prompt/messaging is conditional upon application of one or more unprinted paper/media use rules. In a simple case such a use rule may comprise, for example, prompt the user to use unprinted paper/media if unprinted paper/media not already set as the default. Additionally or alternatively, in a more sophisticated approach the display of a prompt may be made dependent upon document characterising data characterising the nature or content of the document. For example documents intended for external use, such as letters, may use new or virgin paper whereas documents intended for internal use may employ unprinted paper/media. Such a determination may be made based upon use of a template, for example, a memo template, a letter template, etc., and/or metadata associated with the document, for example document properties and/or may be inferred from the content of the document data to be printed - for example a letter will generally incorporate an address and a date and maybe sent for printing on, say, 'letter' rather than Ά4' paper size in a similar way an internal document may be identified, for example, by inclusion of the word 'memo' or simply by not being identified as an external document. The skilled person will appreciate that there are many ways in which the nature of a document may be determined to provide document characterising data which could be used to apply an unprinting paper use rule. The invention further contemplates using a similar approach to prompt the use of one or more additional environmentally friendly options, such as the use of double sided paper.

In some embodiments the printer driver is further configured to add paper reuse data to the information to be provided in the printed document, either by printing additional information on the document or by omitting parts of the document data designated for printing. For example in the latter case a water mark may be printed by applying the watermark so as to overwrite the printed document. Alternatively a water mark could be printed and/or paper margins could be employed for printing. In broad terms, in embodiments the printer driver may add data to the image spooled to the printer to be displayed or marked on the media, for example related to the user's performance or other statistics or to provide one or more messages.

Preferred embodiments of the printer driver also capture and cause to be stored, locally and/or remotely, information relating to use of unprinted paper/media and, optionally, use relating to other media. In this way the use or proportion of use of unprinted media can be measured and used, for example by a reporting system for reporting to the user, management or a third party and/or made visible to the user and/or management and/or a third party. Thus in some preferred embodiments the printer driver is coupled to a reporting system typically, but not essentially, on a remote machine coupled to the printer driver via a network. The reporting system gathers data provided by the printer driver relating to use of unprinted media and provides reporting data, which may be employed as previously described. Such a system can be used, for example, to encourage competition amongst users and/or data sharing and can thus drive behavioural change.

Broadly speaking, embodiments of the printer driver use a print driver as described not merely to select printer options but also to drive behavioural change. Thus in embodiments, in order to motivate individuals into behavioural change, the printer driver is configured for providing one or more of the following:

1. Making an individual's performance and actions measurable and visible or at least making it known to the user that their performance can be measured.

2. Timely positive messages and prompting of people to act in a particular way when they may otherwise forget because they are busy or focused on other priorities.

3. Minimally intrusive changes to people's workflow so that they are prepared to accept the suggestions and make minor alterations to habits.

4. Facilitating monitoring against targets, reporting of improvement, competition with peers and other groups especially when coupled to positive personal or team rewards and recognition.

5. Provide management teams with performance data so that training and encouragement can be targeted and so that improvement can be recognised. In embodiments, the media unprinting system and the media unprinting system are provided in a single device.

The invention also provides processor control code for a controller to implement the above-described devices and methods, in particular on a data carrier such as a disk, CD- or DVD-ROM, programmed memory such as read-only memory (Firmware), or on a data carrier such as an optical or electrical signal carrier. Code (and/or data) to implement embodiments of the invention may comprise source, object or executable code in a conventional programming language (interpreted or compiled) such as C, or assembly code. As the skilled person will appreciate such code and/or data may be distributed between a plurality of coupled components in communication with one another.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is diagrammatically illustrated, by way of example, in the accompanying drawings, in which:

Figures 1 a to 1 c show, respectively, a perspective view of an unprinter according to an embodiment of the invention, a perspective view of a first example of an unprinter head, and a perspective view of a second example of an unprinter head;

Figures 2a to 2c show, respectively, a side view of a paper feed system, a view from above of the paper feed system, and an illustration of paper positioning under the unprinting head; Figure 3 shows a vertical cross-section view through an unprinting head according to an embodiment of the invention;

Figures 4a to 4c show, respectively, a laser system for the head of Figure 3, a toner detection system for the head of Figure 3, and a head positioning system; Figure 5 illustrates, schematically, an optical sensor for toner detection for the unprinting head of Figure 3;

Figures 6a to 6d show, respectively, evolution of a toner sensing signal as the unprinting head is scanned over printed paper, a schematic illustration of an unprinting pixel and laser spot, unprinting pixel geometry/definitions, and a flow diagram of an unprinting procedure implemented by an unprinter controller in an embodiment of the invention; Figure 7 shows an ablated toner extraction system according to an embodiment of the invention;

Figure 8 shows examples of wavelength and pulse length operating regions illustrating a preferred region of operation for unprinting;

Figure 9 shows a variant of an unprinter employing a line/array sensor for detecting printed toner;

Figure 10 shows example configurations in which the laser is mounted separately to the unprinting head; and

Figure 11 shows an example of a preferred unprinting scan pattern in embodiments of the invention; Figures 12a to 12c show cross-sectional views through an embodiment of an unprinter according to the invention illustrating, in particular, a colour toner residue collection system;

Figs. 13a, 13b and 13c show schematics of codes and messages printed on unprinted paper;

Fig. 14 illustrates an example of a message printed on an unprinted sheet of paper;

Fig. 15 is a flow diagram illustrating example steps to detect media weight and marks from previous Unprinting, to unprint paper, generate quality metrics related to the unprinted media, mark a message on the unprinted paper and deliver the unprinted media to an appropriate out-feed tray;

Fig. 16a is a flow chart illustrating example steps to detect the density of media being unprinted;

Fig. 16b is a circuit diagram to detect media on entry, determine density of items of media and detect codes marked on the media; Fig. 16c illustrates current ramping to first determine density of an item of media and then detect any marks on the item;

Fig. 17 is a flow chart illustrating example steps to use unprinted media for printing; Figs. 18a and 18b respectively show example dialogue boxes to prompt a user to use unprinted paper when printing, and to provide a user with their unprinting statistics;

Figs. 19a and 19b respectively show a perspective view and a plan view of an Unprinting device with features for printing a message or mark on unprinted media and for reading marks on unprinted media;

Fig. 20 is a flow chart of the steps to check the quality of an unprinted item of media; and Fig. 21 shows a schematic of a computer system to check the quality of an unprinted item of media.

DETAILED DESCRIPTION OF THE DRAWINGS System for removing toner print from paper

Broadly speaking we will describe a system that uses a laser device in combination with a positioning sensor for effectively removing toner print from paper. We will also describe a method for detecting the location of toner particles in the form of printed features (e.g. characters or images) on the surface of paper and then removing them by laser ablation. The laser ablation of toner particles is a process that consumes less energy than paper recycling. The laser system is selected to produce the high energy radiation required to remove toner particles without paper damage or discolouration. The high energy light is preferably directed through vacuum sealed optics to a toner containing surface. The positioning of the printed surface under the laser radiation is preferably done by a positioning system that includes a scanning device that feeds data to an algorithm that then positions the target area. The positioning sensor detects the position of the toner on a white paper background by means of light reflection. The positioning may be done by mechanical means by a paper feeding system and then by moving the laser system to the required location along the paper.

We will first outline the various aspects of an example unprinter, then describe these in more detail. Thus Figure 1a shows an unprinter 100 according to an embodiment of the invention. The unprinter comprises a laser power unit 1 providing power to a laser source 3. The laser is cooled by laser cooling unit 13. An unprinter head of the device also includes a toner position detector 4 and an air extraction model 5; the head is moved by a servo motor 6. A stepper motor 7 drives the paper feed which loads paper from input tray 1 1 and transports the paper over paper feed rollers 10. The unprinter is powered by a main power unit 12 and controlled by a controller 9, which interfaces to a visual display/user interface 8. The controller may comprise a processor operating under control of processor control code stored in non-volatile memory to implement and control the operations described later. The unprinter also includes an ablated toner extraction system 2. Figure 1 b shows details of the unprinting head, in this example comprising a laser source 1 and laser optics 2 focusing the laser onto the region of an unprinting pixel. The head includes a toner detector/sensor 3 and a head support 4 for mounting and positioning the head. In preferred embodiments a toner particle extraction nozzle is also provided (not shown in Figure 1 b). Figure 1 c shows an alternative arrangement in which a toner detector/sensor 3 is located to either side of the laser ablation region.

Figure 2a shows the paper feed system; comprising paper feed rollers 1 to transport paper from an input tray 2. The rollers 1 are driven by a stepper rotor (shaft) 3 and chain 4. In Figure 2b reference numeral 3 labels the unprinting scanning access and reference numeral 4 an input paper tray sensor. Figure 2b also shows a second sensor 5 adjacent to the unprinting axis (X), and a paper exit sensor 6. In Figure 2c reference numeral 2 labels a guide rail for the unprinting head and reference numeral 3 labels a belt drive for moving the head in the X direction, transverse to the direction of paper feed; paper is moved in the Y direction 4.

Figure 3 illustrates components of an example unprinting head comprising, as before, a laser source 1 , laser optics 2, toner sensor 3, and head guide/stage support 4.

Figure 4a illustrates an example unprinting head incorporating a laser source 1 coupled to laser optics 2 (preferably under vacuum), which include a focusing lens 3 to focus the optical output 4 onto a target on printing area 6 of paper 5. A cable 7 connects the laser 1 to a power supply and electronic control unit.

Referring to Figure 4b, an example toner detection system comprises an LED emitter 2 and photodiode 3 supported on a mount 1 and defining an optical path 4 for detecting toner over a target unprinting region 6 on paper 5. An electrical connection 7 couples a sensor to a power supply and the unprinter controller.

Figure 4c shows the head positioning system comprising head support/positioning rods 1 , 2, a support wheel 3 running in a guide 5 on the lower rod 2 (wheel 3 provides support but in embodiments is not used to drive the head). The head is driven laterally by a belt 8 which engages with a 2 stroke mount 4 and is driven by motor 7.

Figure 5 shows a simplified schematic diagram of the toner sensor of Figure 4b.

Figure 6a illustrates the evolution of a signal at successive points (1), (2) and (3) as the head moves across the surface of paper 9 bearing toner in region 8. The toner detection area of the sensor is labelled 7; at stages (1), (2) and (3) the detection area is respectively free from toner, partially covered by toner, and fully covered by toner. The sensor is calibrated to zero for a signal from the region of the paper free from toner as indicated by level 4; the signal level increases 5 as the paper is displaced in the X (or Y) direction over the toner, increasing to a maximum 6 when the detection area is entirely covered by toner. Figure 6b illustrates a region of paper 1 showing the laser spot area 2 (the toner detection area preferably corresponds), and an unprinting pixel 3.

Figure 6c illustrates the labelling of unprinting pixels, described further later, and Figure 6d shows a (simplified) unprinting procedure, referring to the coordinates shown in Figure 6c. Thus the paper feed system passes paper through the device, unprinting pixels in the scanning head movement direction (index j), and unprinting rows of pixels in the paper feed direction (index i). The controller successively increments over the pixels, determines whether toner is present, if so unprinting, if not incrementing to the next pixel, finally outputting the unprinted paper.

Figure 7 shows an ablated toner extraction system, with a schematic illustration of an intake nozzle 1 having an air conduit to a fan 2, and thence to a HEPA filter porous bag 3 and exhaust port 4. Preferably the porous bag 3 has a self-sealing closure 3a, for example comprising a shutter displaced when the bag is fitted as shown in the inset sketch and/or comprising a set of moveable flaps or leaves opened when the bag is fitted.

Figure 8 is taken from the Leal et al paper (ibid).

Figure 9 shows a variant of the unprinter in which, rather than the toner sensor being mounted on the head, a line or array-type toner sensor 6 is provided to sense an entire row of pixels in the head scanning direction. The line sensor 6 is prior to the unprinting head in the paper feed direction; as illustrated paper 4 is carried by rollers 1 from sensor 6 towards unprinting head 5 mounted on guide rail 2, driven by belt 3.

Figure 10 illustrates a variant of the unprinter in which the laser source 1 is remote from the unprinting head and coupled to the head by, for example, an optical fibre 4 or a flexible arm 5 with internal guide mirrors 6. The unprinting head comprises laser optics 2 (preferably under vacuum) including a focusing lens 3.

Figure 11 illustrates scanning of the unprinting head in one embodiment, in which the head scans alternately in opposite directions along the unprinting axis. Thus in this example preferably the head has a pair of sensors for sensing toner, 1 to either side of the ablation output. Figures 12a to 12c show cross-sectional views through an embodiment of an unprinter according to the invention illustrating, in particular, separate, removable, black and colour toner residue collection receptacles. The optical toner sensing system may be configured to distinguish black (on white) toner from colour printing and means may be provided to selectively provide ablated toner to either a black or a colour toner receptacle, for example by selectively activating one of two different suctions devices (fans) for each of the two collection systems (which may have a separate or shared collection nozzle). It will be appreciated that although we have described separate black and colour toner collection, more generally a selective toner collection system may separately collect between any two different, distinguishable types of toner.

Now, referring again to Figure 1 , embodiments of the 'unprinter' preferably comprise three main systems within an enclosure, which is preferably substantially light-proof for safety: i. the laser system, which conducts the laser radiation to the surface of the printed paper;

ii. the positioning system, which ensure that the laser radiation is directed to a previously scanned area containing toner on the surface of the paper; and iii. the vaporized toner removal system, which continuously absorbs and filters any possible residues from the process.

The laser and positioning systems are the core unprinting mechanism; these systems work together and are mechanically guided by their own positioning mechanisms. The enclosure contains those systems together with the required electronics for them to function. The three main systems are described in turn below.

Laser system:

The laser system comprises a laser source; experiments have shown that this may have a relatively low pulse energy, and pulse energy of greater than 0.1 mJ can be suitable (for example a pulse energy of 0.37 mJ was found effective in laboratory tests). The skilled person will appreciate that since pulse energy divided by the pulse length defines the peak power, low peak pulse energies are preferably used together with short pulses. The skilled person will further appreciate that the energy fluence, also known as energy density, is generally chosen to suit the laser spot area. In embodiments, removal of toner has been achieved with energy fluence as low as 0.1J/cm² while optimal removal is achieved for energy fluence (density) between 1.0 and 1.6 J/cm². Nonetheless for speed/larger unprinting pixel sizes a higher energy pulsed laser may be preferred, for example with a pulse energy of at least 200mJ, preferably 400m J up to 1200m J or 1300m J or greater. The laser may be, for example: a Q-switched Nd:YAG laser (532nm or 1064nm), a Q-switched ruby laser (694nm), a Q-switched alexandrite laser (755nm), an argon laser, a carbon dioxide laser, an Er:YAG laser, a fiber laser, a semiconductor laser, a diode laser, or a combination thereof. Preferably a Q-Switched laser with peak output wavelength around 532nm is used. The output wavelength(s) is/are preferably situated at a value or values corresponding to one or more wavelengths highly absorbed by toner particles. A preferred wavelength may be selected in combination with a laser pulse duration according to the graph in FIG 8 (Leal et al., ibid). The wavelength is preferably in the range 250nm to 1200nm (for example 266nm to 1064nm), and the pulse duration may be from 1 ps to 20ns, preferably 10ps to 10ns, and more preferably 4ns to 8ns for 532nm. These values help to preserve paper whiteness and the integrity of the cellulose fibres (see Leal-Ayala et al., ibid).

The laser beam is directed through an optical path to a target surface containing toner particles on printed paper. These optics are preferably assembled at low pressures (vacuum) <500mbar, preferably <200mbar to avoid air ionization and improve optical transmission. The optics guide the laser beam from the laser source to the surface of the printed paper, and define an illumination area on its surface. The laser beam is focused by a focusing lens (FIG4A:3) onto the surface containing print. The area of the laser spot is determined by the distance from the paper at which the lens is positioned; the area of the laser spot corresponds to a circle with a diameter selected from 1 mm to 5cm, and preferably 5mm for total area of 19.6mm². In principle, however, smaller sizes, for example down to 0.01 mm or less, may be employed - smaller spot sizes may, for example, help to increase unprinting resolution. The size (diameter) of the laser spot area may be chosen in accordance with the laser power output provided by the laser system. Positioning system: The positioning system of the unprinter comprises the toner position detector, the laser positioning mechanism, the paper feeding system and a scanner signal processing to coordinate the actions of these elements for successful removal of print. The integrated unprinting action mechanism is coordinated by an algorithm as follows: position the detection system over a given area of the paper; if toner print is detected store value and continue process until laser system is positioned onto the previously scanned location; if print was detected there fire laser and unprint. The algorithm finishes when the entire printed surface has been scanned and unprinted. The detection of toner print on the surface is done by the toner position detector. The position is stored and the displacement of the unprinting head in the X and Y directions over the paper surface (FIG 2B), is performed by the laser positioner and the feeding system respectively. Fig 2c shows the paper positioning under the unprinting head in the X and Y directions.

The laser system includes a positioning system to determine the position of toner particles on the target surface. In embodiments this comprises a light emitting element and a light detecting element and optical components to align the light paths (FIG 4B). The light emitting element preferably comprises a light emitting diode (LED) with peak wavelength emission selected from 600nm to 2000nm, preferably a peak wavelength emitted at the peak sensitivity wavelength of the detecting element. The detecting element is preferred to have peak sensitivity values in the near infrared or visible red light from 600nm to 2000nm. The detecting element may comprise one or more InGaAs photodiodes (sensitivity range 700nm to 1700nm), PIN photodiodes (max response 940nm), side-looking infrared detectors, or phototransistors. A preferred combination comprises a photodiode with peak sensitivity at 940+/-20nm and an LED infrared emitter with peak emitting wavelength at 940+/-20nm. Both the emitter and detector are preferably geometrically arranged as in the configuration shown in FIG4B. The detector and emitter are inclined at an angle selected from 0° to 60° from the normal to the surface of the paper. The angle and distance from the paper surface determine the target unprinting area (FIG4B:6). A configuration is preferred in which the inclination angle of the light emitter and detector is -30° from a normal to the surface of the paper in opposite direction to each other. The scanning may also be adjusted by means of optical elements accompanying the emitter and detector, such as lenses. The area is selected in accordance to the unprinting laser spot area. In embodiments the unprinting laser spot area may have a maximum dimension (or diameter for a circular spot) in the range 1 mm to 3cm and may be, for example, a circle of 5mm diameter with 19.6mm² area. In principle however the maximum dimension, or diameter for a circular spot, may be smaller, for example down to 0.01 mm (in principle a diffraction limited spot), or larger, for example up to 5cm or more (depending upon the laser power). The combination of photodetector and photo emitter can be substituted by integrated optical detector/phototransistor. The presence or absence of toner on the surface of the paper is detected by the difference in signal detected from the photodetector after the emitted light has been reflected from the surface of the paper. The signal is transmitted by means of electrical connections to the main control unit via an electronic circuit similar to, but not limited to, the one depicted in FIG5. The intensity of the signal is calibrated to 0 for a white paper surface containing no printed tonner. As the toner print is positioned in the area of detection of the toner detection system, the reflected light from the white paper surfaces decreases in intensity due to the darkness of the toner print. This results in an increase of the signal as illustrated in FIG6. When there is no toner the signal is set to 0 (S=0, FIG6:1), whereas when all the surface of the detection area is covered by tonner the signal will acquire a maximum value (S=Max, FIG6:3). Values in between (Max...O) correspond to an area partially covered by toner print (FIG6:2).

The laser head of the laser unit is positioned on a guiding stage (FIG4C). The stage comprises two guides for cylindrical rods or guiding rails (10mm diameter) attached to the main body of the unprinter. One of them includes a support wheel to support the weight of the unprinting head mechanically attached to this laser positioner (FIG4C:3,5). The laser positioner is attached to a toothed belt (FIG4B:8) to drive the unprinter head along the width of the paper sheet. The unprinter dimensions are preferable compatible with an A4 paper size but are not limited to this and may be selected from standard sizes of A series, B series, C series or US series (e.g. legal, letter, envelope, A3, A2, B3, B4, B2). The carriage and unprinter dimensions may be defined in accordance with these paper sizes. A rubber toothed band is driven by a motor which is fixed on the side of the paper feeding system (FIG4B:7). The belt material is preferably a fabric or woven steel wires embedded in an elastic material. The wire or fabric reinforcement reduces elasticity horizontally for a precise positioning of the unprinting head. This movement is defined as the movement along the X direction while the movement of the paper sheet by the feeding system provides movement in the Y direction (FIG 2B).

For the signal processing it is useful to define certain geometrical measures. The area given by the laser optics and toner detection system corresponds to a circle of diameter 'D' and defined as Α=(πϋ²/4). In order to ensure complete removal of toner print under the area of incidence of the laser beam, an square area smaller than the laser spot area is defined as an 'unprinting pixel' and called 'U' hereafter. These definitions are graphically depicted in FIG6B. The square area U (FIG6B:3) is entirely contained in the laser or detection system area such as the centre of the square U and circle A (FIG6B:2) are the same point. The area U is preferable -63% of the area A. The sides of the square 'U measure D/2^{1 2} or less, preferably the dimensions that match -63% of the area of the circle. The dimensions of the printed paper are defined in terms of the unprinting pixels as depicted in FIG6C. The rectangular piece of paper is divided into a grid of unprinting pixels, the number of unprinting pixels in the X direction of the paper is defined as 'n' and the number of unprinting pixels in the Y direction is defined as 'k'. The location of an unprinting pixel along the X direction is defined as the i^th position and the location along the Y direction as the j^th position. A given unprinting pixel can be described in unprinting coordinates as Xi.y as highlighted in FIG6C.

The main control unit processes the information from all the unprinter components and executes the required actions for successful unprinting as follows: The paper is fed to the unprinter and the toner detector in the unprinted head is positioned on the first unprinting pixel (i.e. Xi ,yi), the detector is moved along the Y axis and X axis by the motors described in the paper feed system and laser position system sections respectively. The paper feed sensors establish the edges of the paper and then the toner detector area is centred on the unprinting pixel. From that point the displacement of the paper and unprinting head proceeds in steps of distance L along X and Y. The toner detector system first records the signal information from the current unprinting pixels, then stores it and continues. When the laser head is positioned on the pixel that produced S>0 the laser beam is triggered and all the toner on the area is removed. In the illustrated embodiment the centre of the laser spot area is 5 unprinting pixels apart from the toner detection area (5D/2^{1 2}). These steps are coded into an algorithm contained in the control unit which stores all the geometries ensuring that all surface of the paper has been scanned and unprinted. Unpnnting parameters

The unprinting parameters used for unprinting are defined as follows: An unprinting energy density (UED) is defined as the unprinting intensity (/_u) divided by the unprinting speed (V_pix):

UED=i V_pix where l_u is the laser intensity in terms of the pixel area defined above (l_uo l) and defined as: and,

l_u=PP/A_pix where PP is the laser peak power given by the laser pulse energy E divided by the pulse length pi of the laser as:

PP=E/pl

Laser energy parameters E are typically provided by the laser manufacturer in millijoules mJ and pulse lengths pi in nanoseconds ns respectively. The unprinting speed V_pix is the pixel length L (defined in function of the laser spot area diameter D) multiplied by the laser frequency f:

V_pix=f-L

Example parameters are Ω= 150μΐΎ and f= 15Hz with pl=4ns and E/A= 1.6J/cm². The diameter may be small, for example down to 0.01 mm (diffraction limited spot), or larger, for example up to 5cm or more (depending upon the laser power). The frequency of operation may be, for example, from 1Hz up to 1MHz or more.

In embodiments the unprinter V_pix preferred parameter range is 0.1mm/s to 2x10⁶mm/s; in embodiments the unprinter has a characteristic UED from about 0.08kWs/mm³ to 1x10-¹¹kWs/mm³. Paper feed system:

1. Overview: the unprinting device in one embodiment has a line along which un- printing takes place, described in this document as the unprinting axis [FIG2B:3], beneath the unprinter head [FIG2B:3]. A page passes through the un-printing axis a line (of unprinting pixels) at a time. Paper is transported from the input tray across the un-printing axis by a set of, for example, eight plastic rollers located on the sides of the paper path (four on each side), as shown in FIG2A: 1 and FIG2B: 1. Paper motion through the un-printing axis is a succession of linefeed - stop actions to each new line. This allows the unprinter head [FIG1AB] on its carriage to detect and un-print one line per pass. The width of the line is determined by the laser spot area (See "Laser optics" section).

2. Feeder mechanism: the eight rollers [FIG2A: 1 and FIG2B: 1] are simultaneously rotated by the action of a cog chain [FIG2A:4] that engages with the DC stepper motor shaft [FIG2A:3]. To insert a page the feeder system first needs to detect the presence of paper in the input tray to start the process. After this the feed rollers pick the page up and propel it forward in a continuous movement until reaching the un-printing area, where a signal is produced to switch from continuous to linefeed - stop motion for un-printing.

3. Motor drive: in one embodiment the motor drive for the feed rollers is provided by a stepper motor [FIG1AA:7] capable of producing short steps to move the paper in lines not wider than the laser spot area width (See "Laser optics" section).

4. Control sequence and sensors: in one embodiment three sensors provide the intelligence required to control the paper feed system: i) an electro-mechanical limit switch located at the paper input tray to mechanically detect the presence of paper and trigger an electrical signal [FIG2B:4]; ii) an infrared photo-emitter and detector pair located near the unprinting axis [FIG2B:3] to detect the presence of paper in this area to switch from continuous paper feed movement to line by line step movements [FIG2B:5]; iii) and a second infrared photo- emitter and detector pair located at the exit of the paper path to notify the system about the end-of the unprinting operation [FIG2B:6]. This provides the useful feedback on what the paper path is doing and helps to coordinate the activation of the paper feed motor. The command sequence is the following: i) un-printing sequence activated by user; ii) paper detection process: if positive activate main feed motor in continuous movement mode, if negative wait; iii) when feed motor is activated wait for un-printing area detection signal to switch into line by line step movement; iv) wait for paper-out signal to finalise process and switch-off main feed motor.

5. Paper input tray: in one embodiment the paper input tray is where paper is deposited prior to unprinting [FIG1AA: 1 1]. When the unprinting sequence is initiated, paper is propelled into the machine in a linear movement, starting at the paper input tray [FIG1A: 1 1], located at the front of the machine, through the opening at the front of the unprinter, across the unprinting axis [FIG2B:3], and out through the back of the unprinter. This movement has enough clearance at the back to avoid a collision between the exiting paper and external objects. Vaporised toner residues extraction system

The toner residues extraction system in one embodiment has five main components [FIG7], as follows: 1. An intake nozzle embedded in the unprinting head [FIG7: 1];

2. An electric motor and fan [FIG7:2];

3. A HEPA filter porous bag capable of capturing particles of down to 10 nm diameters [FIG7:3]; in preferred embodiments the filter captures particles in a size (average lateral dimension) range of 10nm to 200nm;

4. An exhaust port [FIG7:4];

5. A housing that contains all components [FIG7:5].

The DC motor is attached to the fan [FIG7:2], which has angled blades that force air forward as they turn, toward the exhaust port. Captured toner particles from the unprinting area are driven forward through the intake nozzle [FIG1A:5] and captured in the porous bag [FIG7:3] before air flows out of the housing [FIG7:5] through the exhaust port [FIG7:4]. The fan creates suction, creating a partial vacuum inside the toner residues extraction system, sucking ambient air into the intake nozzle because of the pressure difference. The HEPA filter porous bag [FIG7:3] acts as an air filter, allowing air to pass but small collecting the toner debris. Unprinter housing

The unprinting device in one embodiment has 13 main components within a common housing [FIG1A], as follows:

1. Laser power unit [FIG1A:1]: this power supply provides the voltage for the laser tubes contained within the laser head [FIG1A:3], with a highly regulated current output to ensure optical stability. The power supply adjusts laser tube voltage to maintain a fixed discharge current. The core component of the power supply is a transformer connected backwards to step-up voltage.

2. Vaporised toner residues extraction system [FIG1A:2]: this is the system in charge of collecting and filtering out toner residues generated during the unprinting process. More details given in "Vaporized toner residues extraction system" section.

3. Laser source [FIG1A:3 and FIG1AB:1]: This component is the part of the laser system where the laser beam is generated and fired during unprinting. More details in the "laser system section".

4. Toner position detector [FIG1A:4 and FIG1AB:3]: This component is part of the laser system. It determines the position of the toner on the paper to control the laser firing process. More details in the "laser system section".

5. Air extraction nozzle [FIG1A:5]: This component is part of the toner residues extraction system [FIG7]. It has an opening at the end of the intake port where air enters the passageway that conducts it towards the porous bag for filtration. More details in the "Vaporised toner residues extraction system" section.

6. Laser guide servomotor [FIG1A:6]: this servomotor allows for precise control of angular position, velocity and acceleration. Preferably this comprises a brushless DC electric motor coupled to a sensor for position feedback and a closed-loop controller. This servomotor controls the motion and positioning of the laser system in the unprinting area.

7. Paper feed rollers DC stepper motor [FIG1A:7]: a brushless DC stepper motor divides a full rotation into a number of steps by having multiple electromagnets arranged around a central gear-shaped piece of iron. An external microcontroller energises the electromagnets to attract the gear's teeth by magnetic attraction, effectively rotating the gear step by step. This allows the motor to rotate and hold its position in an easy way, without the need for any feedback sensor, effectively controlling the paper's feed into the unprinting area by propelling the paper forward in small line by line steps. This motor provides motion for the eight paper feed rollers during unprinting.

8. Electronic visual display [FIG1A:8]: this is an active liquid crystal display that works as the interface between the user and the machine. A series of options are given to the user through this display before commencing the unprinting sequence, triggered by the user through the display.

9. Main control unit [FIG1A:9]: this unit contains the electronic systems required to control all aspects of the machine: i) display electronics; ii) laser system control; iii) paper feed system control; iv) and vaporised toner residues extraction system. It is mainly composed of one or more microprocessors programmed with the command sequences to coordinate all these functions.

10. Paper feed rollers [FIG1A:10]: These components are part of the paper feed system [FIG2A: 1 and FIG2B: 1]. They are responsible for transporting paper from the input tray into the unprinting area. More details in the "Paper feed system" section.

11. Paper input tray [FIG1A:11] This component is part of the paper feed system [FIG2A:2 and FIG2B:2]. It is the area where paper is initially located prior to the beginning of the unprinting process. More details in the "Paper feed system" section.

12. Main power unit [FIG1A:12]: This power supply provides the voltage for all peripheral components of the machine, including: i) the laser system servomotor; ii) the paper feed system DC motor controlling the rollers; iii) the vaporised toner residues extraction system fan; iv) other electronic components such as sensors and the electronic display.

13. Laser cooling unit [FIG1A:13]: The laser unit generates heat that should be removed from the laser system to avoid overheating. An ambient cooling system is preferably added for this purpose, comprising, for example, a high- performance copper heat exchanger for use with water, integrated with a fan, pump, and a tank in a metal chassis.

In another configuration, the toner detection system is detached and separate from the unprinting head and comprises a linear array of detectors that scan along the paper X direction as shown in FIG9. The values for each unprinting pixel are stored and processed, feeding the toner position to the laser system on the moving unprinting head. Then, the control unit directs the paper to under the laser system via the feed system using the same algorithm. Finally, the laser is triggered removing the ink on the selected pixels.

The positioning detection system may comprise a commercial optical detector such as the Fairchild Semiconductor QRD1 13/4 reflective object sensor. In embodiments it is located on the unprinting head or on the array described above. In embodiments the light emitter of the detection system comprises a low power red laser.

The high power laser light may be generated adjacent the laser power supply unit and guided to the laser optics on the unprinter head from this external source by means of an optical fibre, collimated fibre, or mirrors inside a guiding arm comprising hollow tubes, as depicted on FIG10.

The toner detection system is place on the X axis of displacement aligned with the laser head, and preferably on both sides of the head, so that when the laser head is driven by the positioning motors, the detection system simultaneously detects the toner ink on the paper surface as it moves from -X to +X. Thus in embodiments the unprinter head contains two toner print sensors located one on each side of the unprinting optical output along the unprinting axis, and the head moves sidewise scanning in the +X direction and in the -X direction as shown in FIG11.

We now describe the functional operation of an embodiment of the unprinter. The user instigated functions are as follows:

1. The user switches the machine ON (or wakes the machine up).

2. The user loads printed paper in the input paper tray (component 11 in FIG 1a).

3. The user interacts with the user interface (component 8 in FIG 1 a, e.g. electronic display, mechanical button, or voice recognition) to give the command that executes the unprinting sequence. 4. After the end of the unprinting sequence, the user collects the paper from the paper output tray (for example, behind the machine).

At start-up and during unprinting operation in one embodiment the Unprinter performs a sequence of functions as follows:

1. When the user switches on the machine (or wakes it up), the unprinter checks the status of all peripheral systems, i.e. the control unit sends an activation signal and then expects to receive and read a return signal from all unprinter components, which are provided with a feedback loop. An activation signal is sent to all systems (laser, air extraction, paper feed system, laser positioning system) to check ON status. If all systems return an ON signal, the user interface displays a READY message.

2. The loading tray holds paper (which may be of different sizes, but one size at a time) in a position where the paper feed system can load the paper to the machine.

The paper tray has an adaptable size switch. The position of this switch (which is moved according to the paper size) defines the number of pixels that is contained within one page based on the coordinates "n" and "k" (See FIG 6C). 3. When the unprinter receives an unprinting command the user interface sends command to the main electronic control unit system which then checks that conditions for unprinting are met:

i. Paper tray contains paper: The control unit checks the status of the sensor (electromechanical switch or optical) located at the paper input tray. If tray contains paper then the signal is ON, if not then it is OFF. If the signal is OFF the control unit sends the user interface a message prompting to load paper on tray (display, light, or sound). If the signal is ON check next condition. ii. Check laser status and position laser head to initial position: Check for laser power unit status (ON, OFF). If OFF turn ON and message user to wait while the optimum laser operation temperature is reached. If ON proceed to next step: Send signal to laser positioning rotor to position laser in reference start position (outside first pixel area -10L [L is defined below], at coordinates ΧΟ,ΥΟ [Fig 6c]) iii. Check paper feed rotors (Fig 1) for ON signal (if OFF send error message). If ON go to next step. iv. Check laser positioning rotor for ON signal (if OFF send error message). If ON go to next step. v. Check air extraction system (Fig 7) for ON signal (if OFF send error message). If ON, go to the next step. vi. If all previous steps OK send ON signal, proceed to next step.

4. Air extractor begins continuous extraction: The ON signal continues and the air extractor operates until an OFF signal is received. 5. Paper loading to unprinting area (Fig 2b): The paper feed rotor starts to operate in continuous mode: the plastic rollers on the sides start displacing a sheet of paper at a time until the front edge of the sheet of paper reaches the unprinting axis sensor (electromechanical or optical, see component 5 in Fig 2b, or Fig 11) to indicate sheet is at the right position. If paper is not detected (OFF) keep feeding with rollers, if OFF is received after a given warning length then send error. If paper is detected (ON) proceed to next step.

6. Start unprinting sequence (algorithm, see FIG6D). a. The laser positioning rotor starts to operate continuously at a given speed which is no greater than the laser frequency (pulses per second, f) multiplied by pixel length "L" (where pixel length "L" is preferably smaller than the laser spot size

L < ^= , and the pixel area is less than 63% of the laser spot area).

V2 b. When toner detector on laser head is over the first pixel (X1 , Y1) a signal

reading (S) is taken (see FIG6) and compared to a reference signal (SO) corresponding to a not printed area (alternatively, the user previously executes calibrate command and inputs a not printed paper sheet with the same characteristics as the desired printed sheet to unprint to record SO). c. If S-S0> 0 a signal is sent to the control unit which starts a counter that triggers the laser after the laser head has moved by 5 pixels (the laser is spaced 5 pixel lengths apart from toner sensor, see FIG3). This acquisition process continues until 'n' pixels have been scanned for toner (X1...n, Y1). d. Then the motor continues to the END position (n+10 pixels), when this position is reached a signal is sent to the control unit which in return sends a signal to the paper feed system to move the paper forward by activating rotors and displacing the paper one pixel length e. Then, the laser positioning system rotor moves until the second toner sensor (on the other side of laser head) is positioned over the pixel corresponding to (Xn, Y2). The signal is sampled and the laser positioning rotor moves, scanning all pixels in the X direction until the start position is reached again, then the laser head is moved to the starting, reference position. f. The process repeats (move, scan, move, unprint) until pixel (Xn, Yn) is reached (Fig 11). When unprinting is complete a paper extraction action is executed.

7. Paper extraction: Send signal to paper feed rotor to displace paper out until outlet paper sensor stops detecting paper (if outlet sensor has not detected paper by the last pixel Xn, Yn, keep moving rotor until paper is detected and then continue until paper stops been detected again).

8. Repeat steps 3 onward until input paper tray sensor is OFF.

9. Control unit displays "Ready" message in the user interface, switches fan OFF and starts timer to switch main power OFF after X minutes of the machine being idle.

Thus, broadly speaking, embodiments of the invention provide a laser system that works in combination with a sensor/positioning system. The sensor/positioning system processes spatial information defining the location of colour toner on a white paper surface. The area where toner is detected is then placed under the axis of the unprinting head and under the ablation spot of a high energy laser for removal. The laser light is preferably guided through high transmission optics for minimal energy loss. The dark toner on white background is detected by means of light reflection by a position scanner system, preferably comprising an incident light source and a photodetector. The incident light source may be a NIR (near infrared) LED with a focusing lens that provides a fixed illumination area. In embodiments light is reflected from the surface of the paper at an angle to meet the photodetector. The photodetector may comprise a single pixel detector spatially arranged to scan over a fixed area for later ablation. The spatial information may be processed by an algorithm that positions the laser system along the paper and the paper itself by means of a paper feed system, for example a roller, for ablation of the detected toner.

Marking unprinted paper as 'imprinted'

Thus far, we have described systems and methods for unprinting printed media such as paper. Turning now to Figs. 13a-c, we describe how unprinted paper may be marked with a label, message and/or code to indicate that the paper has been unprinted.

As described above, an unprinter removes the print (e.g. ink and/or toner) from previously printed items of media, resulting in items of media that no longer have print on them, such that they are suitable for printing again. For example, the items of unprinted media could be used for printing in an office laser printer.

The unprinting process ideally produces an unprinted item of media which is substantially print-free and unblemished (i.e. substantially free of marks). However, the unprinting process may not be perfect - it is possible that the unprinted media will retain marks from, for example:

• Areas of the items of media that were not completely successfully unprinted; · Marks or annotations made by a user on the item of media, using e.g. highlighters, pens, or pencils, which cannot be removed by the unprinting process;

• Marks from contact with other substances, for example spilled coffee, or dirt;

• Holes from where staples have been removed;

· Creases from handling the previously printed item of media. Thus, it is desirable to perform a check of an unprinted item of media before it is reused (e.g. used for printing), so that items of unprinted media which contain too many marks are not reused. Preferably a quality check is performed on all unprinted items of media. The quality of each unprinted item of media may be determined by imaging the item of media and identifying or categorising and scoring any marks on the unprinted item - this quality check process is described in more detail below, with reference to Fig. 20. Preferably, unprinted paper and paper which has never been printed on before ('new' paper), are loaded into a printing device in separate in-feed trays. It may be desirable to use one in-feed tray for 'new' paper, and a separate in-feed tray for unprinted paper, so that a user can select between the two types of paper for a print job. (In this context, 'new' media refers to all items of media which have not been printed on (and therefore, have not been unprinted). 'Unprinted' media refers to items of media which have been printed, and have been through the unprinting process to remove print.) Checking items of media to determine if they are unprinted or 'new' before they are used makes it possible to determine if the unprinted paper has been loaded into the correct in-feed tray of a printer. If unprinted paper is identified as being loaded in the 'new' paper in-feed tray, then the unprinted paper could be discarded and/or manually moved to the 'unprinted' paper in-feed tray, to avoid it being used in error. As explained in more detail below, organisations may wish to control how 'unprinted' paper is used, and thus, such a check prior to using unprinted paper may be important. Organisations may have concerns about the re-use of items of media (e.g. the re-use of unprinted paper), if the items of media were previously printed with confidential information. Thus, being able to identify paper which has been unprinted may be useful so that organisations can decide whether the unprinted media can be used, and/or so organisations can define rules about what sorts of printed communications the unprinted media can be used for (e.g. for internal memos only). Some organisations may be happy to mix new media and unprinted media, whereas others may choose to separate new media from unprinted media. As mentioned above, new paper and unprinted paper may be loaded into a printer via separate paper in-feed trays, to help control which type of media is being used for a print job. The ability to identify unprinted media, and in particular, the ability to specify whether unprinted or new paper is to be used for print jobs, may also enable organisations to determine how much 'new' paper they use and how much unprinted paper they use. For example, collecting data on the number of times new paper and unprinted paper are used (via a printer driver, for instance), could help an organisation to determine how 'green' or energy efficient the organisation is and to assess progress.

Figs. 13a, 13b and 13c each show a schematic of marks that are applied to unprinted media in order to identify unprinted media as unprinted. The illustrated marks are merely examples of marks or messages that could be used to identify unprinted paper. The marks allow a user to readily distinguish between 'new' paper and 'unprinted' paper, as only unprinted paper will be marked. In embodiments, the mark 130 is a machine readable code, or a machine identifiable mark such as a shape, pattern or code containing information such as a linear or 2D barcode (e.g. a Quick Response code encoding a URL to the Reduse Ltd website). Additionally or alternatively, the mark combines a pattern or code with an alphanumeric message, as shown in Fig. 13a. A mark 130 may comprise a machine-readable part 132 and a user-readable part 134. The machine-readable part enables a printer to distinguish between 'new' paper and 'unprinted' paper. This enables a printer to check that the paper being fed through the printer for a print job matches the type of paper selected by a user, prior to it being printed upon (as explained in more detail below).

The machine-readable part 132 comprises one or more headers preceding the body data and/or preceding the user-readable part 134. As shown in Fig. 13a, the headers on either side of the data portion of the machine-readable part are preferably asymmetric or dissimilar. This helps to determine which way round unprinted paper is oriented as it passes through a printer. This allows the mark to be decoded from the unprinted paper in any orientation of the paper. The machine-readable part 132 may comprise a code, pattern or shape, which is used to identify an item of media as unprinted. For example, the machine-readable part could be a simple printed shape (e.g. a block) used to keep a tally of the number of times an item of media has been unprinted. Fig. 13a shows the area in which such simple marks can be printed, while Figs. 13b and 13c show variations of the marks which can be applied in this area. The data may be in the form of a Non-Return-to-Zero (NRZ) code. The user-readable part 134 is a configurable message. In Figs. 13b and 13c, the configurable message 134 is shown as "Reused Paper | Lower Carbon | Lower Cost", though this is merely an example and the skilled person would understand that the user-readable part may be used to convey any information or message to a user.

The mark 130 may be used to promote reuse of paper (i.e. to encourage unprinting and use of unprinted paper). Thus, the user-readable part 134 of the mark may be used to:

• provide information about the device used to unprint an item of media, e.g. via a message such as "Unprinted by Reduse"

• encourage or reward reuse of paper, e.g. via a message such as "ABC Corporation is proud to reuse paper using Unprinting from Reduse"

• provide information regarding the energy or C0₂ saved over a period of time, or by a team or individual, e.g. via a message such as "ABC Corporation saved 23tonnes of C0₂ using Unprinted paper on 2014 Q1"

• warn or advise how an item of unprinted media should be used, e.g. via a message such as "This document is printed on unprinted media: Not for issue outside of the ABC Corp." For example, organisations may wish to restrict the use of unprinted media to internal use only, particular if the item of media was previously printed with highly confidential information. Such a warning may be used as a precautionary measure in case it is possible to determine what was previously printed.

In embodiments, the mark 130 is applied to an item of media (e.g. a piece of paper) when the paper has been unprinted using the above-described unprinting techniques and apparatus. Thus, a sheet of paper is unprinted and, after the unprinting is complete, the unprinted paper is marked with mark 130. Thus, the unprinted sheet is readily identifiable as an unprinted item. This is useful information to provide users who wish to differentiate between 'new' paper and 'unprinted' paper when printing. For example, in some situations a user may wish to use a 'new' sheet of paper (e.g. for official letters or documents), while in other situations (e.g. for company memos or internal use) 'unprinted' paper may be preferred. The marks 130 on items of unprinted media enable a user to easily distinguish between new and unprinted paper, and also enable a printer to distinguish between them.

The mark 130 may be used to provide information or statistics on the number of times a particular item of media (e.g. a sheet of paper) has been unprinted. This may enable the unprinter to track the number of times a particular item of media has been unprinted. As mentioned earlier, the machine-readable portion 132 of the mark 130 may comprise a tally of the number of times an item of media has been unprinted. This information may enable an organisation to track and promote their efforts to recycle paper or lower their carbon footprint. The tally may be updated each time an item is unprinted. Each side of an item of media such as a piece of paper may have an independent tally and this may be used to preferentially orientate media with the least used side on top. The mark 130 is applied to an item of media using any one of the following techniques: a stamp (e.g. tampography or transfer printing), an inkjet print head, or thermal transfer head. Tampography or print stamps are used to apply a simple mark to an item of unprinted paper. Such a mark may be printed only once, regardless of how many times the item of media is unprinted, or may be printed each time the item is unprinted to form a tally by offsetting from previous mark(s) each time..

Fig. 14 illustrates an example of a mark 130 applied to an unprinted item of media 136 (e.g. a sheet of paper). The mark 130 is shown as being provided in a margin or along an edge of the item of media, but the mark 130 may be provided in additional or alternative locations. For example, the configurable message part of a mark may be provided as a watermark-style mark covering a substantial area of the item of media, e.g. covering more than 20%, 25% or 50% of the item of media. The watermark is applied using ink which cannot be removed during subsequent unprinting of the item of media. The illustrated sheet of unprinted paper 136 is shown as having print 138 thereon. In embodiments, the mark 130 is applied to the unprinted paper 136 after it has been unprinted, and prior to it being used for reprinting. This enables unprinted items of media to be distinguished from 'new' media prior to being used for a print job.

Turning now to Figs. 19a and 19b, these respectively show a perspective view and a plan view of a device 190 which is a module for Unprinting and incorporates items for printing a message or mark on unprinted media and for reading marks on unprinted media. The device 190 may be part of an unprinter (as shown in Fig. 1 a). The device 190 incorporates a mark-printing module 196, to apply a mark to an item of media 192 which is to be unprinted. An item of media 192 is fed through the device 190 from right to left in Fig. 19a. Paper is transported through the device 190 one sheet at a time. A mark-reading module 198 is used to detect marks on the sheet of paper. The mark- reading module 198 is described in more detail below. If a mark is detected (indicative of the sheet of paper having been unprinted previously), the mark-printing module 196 may be engaged to apply a mark as described above to the unprinted paper. Alternatively, in embodiments where the mark-printing module 196 comprises a tampo or print stamp, the mark-printing module 196 may not be engaged if a mark has already been applied to the sheet of paper or may be offset from previous marks to form a tally. The sheet of paper may be marked before or after unprinitng takes place. Preferably the paper moves through the device 190 and is scanned by a page wide line scanner or contact image sensor 200, prior to being unprinted. (The unprinting process is described in detail above.) The page wide line scanner or contact image sensor 200 may operate either independently or in cooperation with a light source such as an LED on the opposite side of the paper in order to read the marks instead of or as well as mark reading module 198.

The mark-printing module 196 comprises a print head and a print head service station 194, which caps the print head when not in use. The mark-printing module is configured to print any one of the following (or a combination of one or more of the following):

• Marks comprising basic blocks or barcodes easily recognisable with low cost sensors;

• Delimited or prefixed codes indicating the number of cycles of unprinting for that item of media;

· One or more headers to delimit the information field (e.g. the data part of the machine-readable part 132 and the user-readable part 134), allowing it to be orientated;

• A human-readable message. The mark-reading module 198 of the device 190 may comprise one or more sensors (e.g. reflective line sensors), CCD imagers or one or multiple line-of-sight or reflective opto-couplers to read the mark(s). The one or more sensors may each comprise an LED and photo-detector. In the embodiment shown in Figs. 19a and 19b, the mark- reading module 198 comprises at least one sensor arranged in the device 190 to detect marks along one edge of an item of media as it feeds through the device. Each sensor comprises two parts: one part arranged above the track for item of media and the other part arranged below the track for items of media. The part above the track may comprise a light source and the part below the track may comprise a detector, or vice versa. These may of course be substituted for reflective opto-couplers both above and below the media or on one side only which would require the media to be turned over in a duplex module in order to read first one side and then the other side.

An item of media could be presented to the mark-reading module 198 in any orientation. In preferred embodiments, for each edge of an item of media, one or more sensors (acting in cooperation), may be provided such that they are arranged to sense marks along one or more margins of an item of media simultaneously, to determine if an item of media has been unprinted previously. Items of unprinted media may be provided to the mark-reading module 198 the 'right way up' (i.e. the mark is on the upper surface of the unprinted paper) or 'upside down' (i.e. the mark is on the lower surface of the unprinted paper). To ensure that marks are detected regardless of the orientation in device 190, the mark-reading module 198 comprises sensors arranged to scan for a mark 130 on either side/surface of an item of media. Additionally or alternatively, the device 190 may be supplemented with a duplex function, such that an item of media can be reversed to scan both sides/surfaces of the item.

Since items of unprinted media may be fed-through the mark-reading and mark-printing device 190 in any orientation, in embodiments the mark-reading modules 198 are configured to detect marks to items of media on either side/surface of the item, and along any edge. In some preferred embodiments there need only be one print head that prints on only one side and edge, although the unprinter reads all sides and edges in a single pass.

Consider, now an example where a sheet of paper is determined by the mark-reading module 198 not to have any marks thereon to indicate the sheet has been previously unprinted. The mark-printing module 196 may be configured to apply a 'long mark' such as that shown in Fig. 13b. The 'long mark' includes the configurable message, and the machine-readable part 132, which comprises a tally mark indicating the sheet has been (or will be) unprinted. On subsequent passes through device 190, the sheet of paper may simply be marked with a tally mark on whichever edge is presented to the mark-printing module 196, which could be the same edge as that having the 'long mark', the opposite edge or an edge on the other side of the sheet. This has the advantage that a mark can be applied on an unprinted sheet of paper on any edge and it is not necessary to ensure the sheet of paper is fed-through the device 190 in a particular orientation or to have more than one print marking module.

In embodiments where a tally mark or code may be applied on any edge and any side of the unprinted paper, the mark-reading module(s) 198 may be configured to read marks along each edge and on both sides of unprinted items of media. The one or more tallies may be totalled by side or media item. This is important if organisations set an upper limit on the number of times an unprinted item of media can be reused for printing (which may be desirable as the quality of the paper may decrease as the number of times it is reused increases). For example, if an organisation sets the upper limit to be eight, if the summation of tallies read by mark-reading module(s) 198 determines there are fewer than eight tally marks on the item of media, the item is marked and may be reused. However, if the mark-reading module 198 determines there are eight or more tally marks, the item of media is no longer suitable for re-use (according to the organisation) and is ejected for ordinary recycling. A further advantage of marking items of media on any side is to track how many times each side has been unprinted. For example, a sheet of paper which has been printed single-sided can be unprinted and the other side can be presented uppermost for a subsequent print job. The 'unprinted' mark can be applied to the side of the sheet which has been (or is about to be) unprinted. In subsequent passes through device 190, the total number of marks on each side of the sheet can be determined by the mark-reading module(s) 198. If the sheet has been printed (and unprinted) on one side more often than on the other side, an unprinter may be configured to reverse the sheet of paper to the side least used before it is provided to the infeed tray of a printer, to help balance usage. Consequently, organisations could set re-usage thresholds for each side of a sheet of paper. In embodiments, the mark-reading module 198 is combined with the contact image sensor 200. The contact image sensor 200 alone may read the marks the media on the same side as the sensor. Additionally, a light source may be provided below the paper track of device 190 to illuminate through items of media directly below the contact image sensor 200 allowing marks on either side to be detected by modulation of the light source. The sensor 200 therefore functions as the sensing part of the mark- reading module 198. This arrangement has the advantage that fewer components are required to provide the mark-reading functionality of device 190, which may reduce costs and manufacturing complexity. In an alternative embodiment a second contact image sensors may be deployed on the other side of the media.

The mark-reading module may optionally be used to determine the density of each item of media as well as to detect marks. Information regarding the weight or density (e.g. grams per square meter) of an item of media may be used to filter out items of media for example in order to provide a stack of unprinted media which is comprised of only standard weight paper, typically 80gsm. Advantageously, by filtering out paper over a certain threshold density, energy is not used to unprint the paper that is not required. Instead, these non-conforming items can be recycled in the ordinary manner. The mark-reading module may also use the density measurement process to detect if more than one item of media has been picked in the paper feeder whereupon it may be diverted to a waste bin. Additionally or alternatively, the thickness/weight of an item of media may be determined using separate sensors, or a separate thickness-determining module comprising sensors arranged to determine the thickness.

Fig. 16a shows a flow chart illustrating example steps to detect the density (g.s.m.) of media being unprinted. The weight or thickness is determined via a sensor, such as an LED and photo-detector pair (as shown in Fig. 16b). As mentioned above, the light source and detector pair may be those used in the mark-reading module. An item of media may be provided between the LED and photo-detector, such that detection by the photo-detector is interrupted or the light detected is reduced. Such detection may enable the density of the item of media to be determined. Fig. 16c illustrates how the mark-reading module can be used to first to detect the edge of the media, then determine the density of an item of media, and then detect any marks on the item. The current (l_v) supplied to a light source (e.g. an LED) on one side of an item of media is ramped up when an item of media has been detected by an edge detector, as described earlier. The current is increased until the light is detected by a photo- detector located on the other side of the item of media (as shown in Fig. 16b). The current required for photo-detection is a particular level for standard paper (80gsm), and is higher for denser paper (e.g. 120gsm). (If the current is ramped above a threshold level and no signal indicating detection is provided by the photo-detector, the item of media is determined to be too dense and is ejected prior to or after unprinting, as mentioned earlier.) Once the density of the sheet of paper is known, the current level is fixed for the mark-detection process. Ink/toner on the sheet of paper will block some or all of the light and the sequence of blocked and transmitted light indicates a mark on the sheet of paper.

Fig. 15 is a flow diagram illustrating example steps to unprint paper and apply a mark to unprinted paper. The process begins by detecting that an item of media (e.g. a sheet of paper) has been fed into an unprinter. A scanner or mark-reading module, as described above, checks the paper for a mark and reads the mark to extract data related to that sheet of paper (e.g. the number of times it has been unprinted). In embodiments, the scanning device of an unprinter may be used to read the mark (e.g. the scanning mechanism described earlier or the contact image sensor 200). In some cases, the paper may not have been unprinted previously, and thus, there will be no mark to read. Optionally, the density or thickness of the unprinted media may be determined, as mentioned earlier. In this embodiment, the density/weight is determined before unprinting media items, to filter out media which is not required, and thus, the process flow shown in Fig. 16a is performed.

If the mark-reading module determines that the paper has been unprinted previously, the unprinter is configured to apply special settings that instruct the unprinting mechanism to ignore, modify or supplement the mark on the paper during the unprinting process. If the mark-reading module determines that the paper has not been unprinted previously (e.g. because there is no mark on the paper), the unprinter may be configured to generate and apply a mark to the paper. Although Fig. 15 shows that the mark is applied to the paper immediately after checking for a mark, it will be understood that a mark could be applied to the paper at any stage of the unprinting process, such as, for example, after the paper has been unprinted. Thus, in embodiments, a message or tally mark may be applied to an item of media after the unprinting process is completed. The mark may be applied by the unprinter if it comprises a printing function, or by a printing station or module coupled to the unprinter.

Next, the Unprinting step is carried out followed by imaging/scanning the item of media to determine the quality of the unprinted item.

The unprinter may apply an algorithm or series of checks to determine if an item of media has been successfully unprinted. (This process is described in more detail below with reference to Fig. 20.) If the unprinted media passes these checks, the media continues through the process to determine if it is suitable to be reused. If the media item fails the check, the media item may go through the unprinting process again, or alternatively, may be outputted from the unprinter so that it may be recycled using conventional recycling techniques, or may simply be thrown away/discarded as waste.

The weight/thickness of a successfully unprinted item of media may be checked, or referenced from an earlier check, at the end of the process to determine whether it is standard or non-standard paper. For example, the print function or print module coupled to the unprinter may only be configured to handle certain thickness of paper. Paper is diverted to different outfeed trays depending on the density of the paper - standard paper (80gsm) is diverted to a separate outfeed tray to non-standard paper (e.g. high quality 120gsm paper). Separating the unprinted media at this stage allows the correct paper type to be used in a subsequent printing job, as unprinted paper from the separate outfeed trays can be manually or automatically transferred to the appropriate, separate infeed trays of a printer.

As mentioned earlier, the quality of the unprinting is preferably checked prior to reusing items of media. Fig. 20 is a flow chart of the example steps to check the quality of an unprinted item of media. First, in step S200, an image of the item of media that has just been unprinted is obtained (e.g. via the same or a further page wide line scanner or contact image sensor used to image items of media before unprinting). The image is analysed for stray marks on the unprinted sheet of paper to determine if the sheet is suitable for reuse before progressing to the next stages in Fig. 15 (selection based on media density and quality of output). If stray marks are detected in the image, the marks are characterised (S202) into different types of mark. Example types of mark (or category) include: single/few dots; clusters of close dots; lines or curves; areas of shading from previous images or for example due to exposure to sunlight.

The next step, S204, is to score each type of mark, by for example, whether the marks appear as dots or small clusters of dots, medium-sized clusters, large clusters, lines/curves, multiple instances of these in close proximity, etc. The score for each type may include colour attributes of the mark, e.g. if the mark is cyan, magenta, yellow, red, green, blue, black or has specific colour attributes according to a recognised system of colour measurement or human perception to colour.

Weightings are applied to each mark based on pre-determined weightings for each mark type (S206) and each colour (S208). The weightings may be applied simultaneously. For example, if the mark type is a dot/small cluster of dots, the weighting may be lower than for medium clusters. Similarly, certain colours (e.g. yellow) are weighted lower than other colours (e.g. black) because of the overall visibility of such colours. Table 1 below shows examples of weightings applied at this stage in the quality check process.

Once the weightings have been applied, aggregated unprinting performance metrics are calculated (S210) for each mark type identified on the sheet of paper. The total for each mark type (or category) is tallied, adjusted by the applied weighting factors (S214). One or more pre-defined threshold quality values are applied (S214) to the calculated metrics. If the unprinted media metrics do not achieve the pass level for the pre-defined threshold values, the media item fails the quality check and is rejected (S218). The rejected item of unprinted media may be passed back to the unprinter for further unprinting, or may be recycled in the ordinary manner. If the unprinted media metrics achieve the pass level for the pre-defined threshold quality values, the unprinted media passes the quality check and is identified as suitable for printing (S216). The unprinted item then moves to the next stages (selection based on media density and quality of output) in the process of Fig. 15.

Table 1 : example weightings Mark type or Weighting Reasoning

Claims

CLAIMS:

1. A print removal device, the device comprising:

a paper feed system to receive and feed printed paper though the device;

a print removal head having a controllable laser output for removing print from said paper; and

a head drive system to scan said print removal head over said paper as said paper is fed through the device;

wherein said print removal head further comprises a sensor, mounted to be scanned over said paper in conjunction with said head and configured to operate in tandem with said laser output;

the device further comprising a control system, coupled to said sensor and to control said laser output, wherein said control system is configured to control said laser output to irradiate said paper to remove print from said paper in response to detection of said print by said sensor as said head is scanned over said paper.

2. A print removal device as claimed in claim 1 wherein said head is scanned in a scanning direction and wherein said sensor is displaced from a position of said laser output along said scanning direction.

3. A print removal device as claimed in claim 2 comprising two said sensors, one displaced to each side of said laser output along said scanning direction, and wherein said head drive system is arranged to scan said head bi-directionally along said scanning direction.

4. A print removal device as claimed in claim 2 or 3 wherein said control system comprises a delay device to control said laser output to fire after a delay from detection of said print on said paper by said sensor or sensors.

5. A print removal device as claimed in any preceding claim wherein said head drive system is configured to scan said head at a rate no greater than the product of a pixel dimension in a scanning direction of said head and a frequency of operation of said laser.

6. A print removal device as claimed in any preceding claim wherein said controllable laser output provides a peak laser pulse power of at least 30KW over the area of a unprinting pixel.

7. A print removal device as claimed in any preceding claim wherein said head drive system is configured to scan said head in a substantially continuous boustrophedonic motion.

8. A print removal device as claimed in any one of claims 1 to 7 further comprising a paper support having a slot longitudinally aligned along said scanning direction and a second said head beneath said slot, such that the device is configured to remove print from both sides of said paper simultaneously.

9. A print removal device as claimed in any preceding claim further comprising an additional sensor to sense a blank line along said scanning direction, wherein a said blank line comprises a line without print on said paper; and a blank line skipping controller to control said paper feed system to skip past an identified blank line.

10. A method of removing print from paper, the method comprising:

providing a print removal head having a controllable optical output for removing print from paper;

moving printed paper and said print head relative to one another in a first direction;

scanning said print removal head relative to said paper in a second direction perpendicular to said first direction;

scanning a sensor in tandem with said print removal head in said second direction; and

controlling said optical output to irradiate said paper to remove print from said paper in response to detection of said print by said sensor as said head is scanned relative to said paper.

1 1. A print removal device, the device comprising:

a print removal head having a controllable optical output for removing print from paper; means for moving printed paper and said print head relative to one another in a first direction;

means for scanning said print removal head relative to said paper in a second direction perpendicular to said first direction;

means for scanning a sensor in tandem with said print removal head in said second direction; and

means for controlling said optical output to irradiate said paper to remove print from said paper in response to detection of said print by said sensor as said head is scanned relative to said paper.

12. A print removal device, the device comprising:

a paper feed system to receive and feed printed paper though the device;

a print removal head having a laser output for removing print from said paper; and

a particle removal system to capture nanoparticles from said removing of said print.

13. A print removal device as claimed in claim 12 further comprising a head drive system to scan said print removal head over said paper as said paper is fed through the device; and wherein said particle removal system comprises an inlet nozzle, mounted to move in tandem with said print removal head, and directed towards a point of removal of said print by said laser.

14. A print removal device as claimed in claim 12 or 13 wherein said particle removal system comprises a removable receptacle or bag, preferably incorporating a nanoparticle filter.

15. A print removal device as claimed in claim 14 wherein said receptacle or bag has self-sealing air inlet configured to self-seal on removal of said receptacle or bag from said particle removal system.

16. A print removal device as claimed in claim 16 wherein said self-sealing air inlet comprises plurality of moveable leaves configured to engage with a male member of an air duct of said particle removal system.

17. A print removal device as claimed in claim 15 or 16 wherein said self-sealing air inlet is configured to engage with a male member of an air duct of said particle removal system, and wherein said male member and said self-sealing inlet each have a matching, non-symmetrical cross-sectional shape.

18. A print removal device as claimed in claim 15, 16 or 17 wherein said self- sealing air inlet comprises a displaceable sealing member, configured to be displaced to open the air inlet on attachment of said air inlet to an air conduit of said particle removal system and to be displaced to close the air inlet on removal of said receptacle or bag.

19. A self-sealing receptacle or bag for the print removal device of any one of claims 12 to 18, wherein said receptacle or bag has self-sealing air inlet configured to self-seal on removal of said receptacle or bag from said particle removal system.

20. The print removal device as claimed of any one of claims 1 to 9 and 1 1 , further comprising a particle removal system to capture nanoparticles from removal of said print, in particular wherein said particle removal system comprises an inlet nozzle, mounted to move in tandem with said print removal head, and directed towards a point of removal of said print by said laser.

21. A print removal device, the device comprising:

a paper feed system to receive and feed printed paper though the device;

a point or line sensor for sensing print on said paper;

means for providing relative motion between said paper and said sensor; and a control system, coupled to said sensor and to control said laser output, wherein said control system is configured to control said laser output to irradiate said paper to remove print from said paper in response to detection of said print by said sensor as said head is scanned over said paper.

22. A print removal device as claimed in claim 21 wherein said sensor comprises a line sensor for sensing a line of print on said paper and wherein said control system comprises a buffer to store one or more lines of sensed unprinting pixels prior to said line of print arriving at said print removal head.

23. A print removal device as claimed in claim 21 or 22 wherein said control system is configured to control said paper feed system responsive a signal from said sensor to skip past a blank line on said paper.

24. The print removal device as claimed in claim 21 , 22 or 23, further comprising a particle removal system to capture nanoparticles from removal of said print, in particular wherein said particle removal system comprises an inlet nozzle, mounted to move in tandem with said print removal head, and directed towards a point of removal of said print by said laser.

25. An unprinter including a printer or other marking device to mark unprinted paper as unprinted.

26. An unprinter as claimed in claim 25 wherein said printer or other marking device comprises a marking device to mark more than 20% of an area of an item of unprinted media.

27. An unprinter as claimed in claim 25 wherein said printer or other marking device comprises a marking device to mark substantially all of an area of an item of unprinted media.

28. An unprinter as claimed in claim 25 wherein said printer or other marking device comprises a printer configured to print a code or message on an item of unprinted media.

29. An unprinter as claimed in claim 28 wherein said code or message comprises a machine-readable part.

30. An unprinter as claimed in claim 28 or 29 wherein said code or message comprises a configurable human-readable part.

31. An unprinter as claimed in claim 28, 29 or 30 wherein said code or message comprises data indicating a count of the number of times the media has been unprinted.

32. An unprinter as claimed in any one of claims 28 to 31 wherein said code or message is printed in one or more margins of said unprinted media.

33. An unprinter as claimed in any one of claims 28 to 32 wherein said code or message includes a header such that the code or message is readable when the media in each of two opposite orientations.

34. An unprinter as claimed in claim 33 further comprising a duplexing unit to reverse said media to read the code or message on one or both sides of the item of unprinted media.

35. An unprinter as claimed in any one of claims 25 to 34 further comprising at least one sensor coupled to a processor to detect said mark on said unprinted media and to control said unprinter response to said detection.

36. An unprinter as claimed in claim 35 wherein said control comprises controlling operation of said printer or other marking device.

37. An unprinter as claimed in claim 35 or 36 wherein said at least one sensor is configured to detect the number of times each side of the media has been unprinted, and wherein said control comprises a decision as to whether to proceed with unprinting said media.

38. An unprinter as claimed in any one of claims 35 to 37 further comprising a plurality of out-feed trays to collect said unprinted media, wherein the at least one sensor is further configured to determine unprinted media density, and wherein said control comprises a decision as to which of said plurality of out-feed trays to direct said unprinted media to dependent on said determined density of said unprinted media.

39. A printer comprising a sensor coupled to a processor to detect a mark identifying media for printing as unprinted media, and to control said printer responsible to said detection.

40. A printer as claimed in claim 39 wherein said control comprises a decision as to whether to proceed with printing.

41. A method of providing unprinting information on unprinted paper, the method comprising:

printing a mark providing unprinting information on printed paper;

sending said printed paper to an unprinter for unprinting;

capturing an optical image of said printed paper for unprinting; and

unprinting said printed paper.

42. A method as claimed in claim 41 wherein printing said mark is performed by a mark-printing module.

43. A method as claimed in claim 42 wherein said mark-printing module comprises any one of the following: a tampography stamp, a thermal transfer printing device, an inkjet printing device, or a laser printing device.

44. A system for re-using paper, the system comprising:

an unprinter to accept printed paper as an input, and to output unprinted paper; a printer to accept said unprinted paper for printing;

wherein said unprinter comprises a system to mark said unprinted paper as unprinted; and

wherein said printer comprises a system to detect said marking of said unprinted paper as unprinted.

45. A system as claimed in claim 44 wherein said unprinter further comprises a system to detect said marking of said unprinted paper.

46. A system as claimed in claim 44 or 45 wherein a printer driver of said printer, or said system to detect said marking, is configured to log use of said unprinted paper.

47. A system as claimed in claim 46 wherein the printer driver of said printer prompts a user to select a media type for said printing.

48. A method of determining a measure of unprinting performance, the method comprising:

capturing an optical image of part or all of an item of unprinted media; and generating a set of one or more unprinting metrics from said optical image.

49. A method as claimed in claim 48 wherein said measure comprises a pass/fail measure for said unprinted media.

50. A method as claimed in claim 48 or 49 further comprising:

identifying one or more print marks, stains or extraneous marks on said item of unprinted media; and

scoring the visual impact of the identified marks or stains to provide one or more metrics indicative of the suitability for reuse of said item of unprinted media.

51. A method as claimed in claim 50 wherein scoring the one or more identified marks or stains comprises:

characterising said identified marks or stains into one or more categories or types;

applying one or more weighting values to said identified marks or stains;

computing aggregated unprinting metrics; and

determining if said aggregated unprinting metrics are above or below a threshold quality value.

52. A method as claimed in claim 51 wherein said weighting values comprise a weighting value for each mark category or type, and/or a weighting value for colour.

53. A method as claimed in claims 51 or 52 wherein said unprinted media is characterised as suitable for reuse if said aggregated unprinting metrics for said unprinted media satisfy said threshold quality value.

54. A non-transitory data carrier carrying processor control code to implement the method of any one of claims 48 to 53.

55. A printer, unprinter or computer storing processor control code to implement the method of any one of claims 48 to 53.

56. A combined printer and unprinter system, comprising:

a media printing system;

a media unprinting system; and

at least one shared media receptacle linked to both said unprinting system and said printing system, such that said printing system is able to print on unprinted media generated from said unprinting system.

57. A combined printer and unprinter as claimed in claim 56 further comprising an unprinted media evaluation system to evaluate said unprinted media to determine suitability for re-use.

58. A combined printer and unprinter as claimed in claim 56 or 57 wherein the media unprinting system and the media unprinting system are provided in a single device.

59. A printer driver for unprinted media, the printer driver comprising:

an input to receive document data for printing;

an output to provide printer data for driving a printer to print a document defined by the document data; and

a conversion module, coupled between the input and output to convert the document data to printer data;

wherein said printer driver is configured to:

receive said document data, and in response:

display a user prompt for the user to select unprinted media for printing:

receive a user command to select unprinted media; and

output control data for selecting said unprinted media for printing.

60. A printer driver as claimed in claim 59 wherein said user command comprises a "yes/no" user input signal to select said unprinted media.

61. A printer driver as claimed in claim 60 wherein in response to a "yes" user signal the printer driver is configured to select said unprinted media once, for the current print job, and then revert to a previous media selection.

62. A printer driver as claimed in claim 59, 60, or 61 wherein said user prompt is configured to alter in appearance from one instance of displaying said user prompt to another.

63. A printer driver as claimed in claim 62 further comprising retrieving data for said user prompt from a server.

64. A printer driver as claimed in any one of claims 59 to 63 wherein said printer driver is configured to determine whether unprinted media is selected prior to displaying said user prompt, and wherein display of said user prompt is conditional upon the application of one or more unprinted media use rules.

65. A printer driver as claimed in any one of claims 59 to 64 wherein said printer driver is configured to add media reuse data to said printer data, wherein said media reuse data comprises data defining additional information to be provided in said printed document, such that an information content of said document data, when printed, is modified by said media reuse data.

66. A printer driver as claimed in any one of claims 59 to 65 further comprising a communications output to provide data on use of unprinted media, and wherein a reporting system is coupled to the data provided to report information on use of unprinted media gathered from the printer driver.

67. A method of performing unprinting of printed items of media and previously unprinted items of media, substantially as hereinbefore described with reference to Fig. 15.

68. A method of printing on previously unprinted items of media substantially as hereinbefore described with reference to Fig. 17.

69. A method of checking the quality of unprinted items of media substantially as hereinbefore described with reference to Fig. 20.