EP1676030A2 - Apparatus and method for low cost control of shape memory alloy actuators - Google Patents
Apparatus and method for low cost control of shape memory alloy actuatorsInfo
- Publication number
- EP1676030A2 EP1676030A2 EP04782960A EP04782960A EP1676030A2 EP 1676030 A2 EP1676030 A2 EP 1676030A2 EP 04782960 A EP04782960 A EP 04782960A EP 04782960 A EP04782960 A EP 04782960A EP 1676030 A2 EP1676030 A2 EP 1676030A2
- Authority
- EP
- European Patent Office
- Prior art keywords
- shape memory
- memory alloy
- actuator
- actuation
- parameter
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
- C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C1/00—Making non-ferrous alloys
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
- C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
- C22F1/006—Resulting in heat recoverable alloys with a memory effect
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
- F03G—SPRING, WEIGHT, INERTIA OR LIKE MOTORS; MECHANICAL-POWER PRODUCING DEVICES OR MECHANISMS, NOT OTHERWISE PROVIDED FOR OR USING ENERGY SOURCES NOT OTHERWISE PROVIDED FOR
- F03G7/00—Mechanical-power-producing mechanisms, not otherwise provided for or using energy sources not otherwise provided for
- F03G7/06—Mechanical-power-producing mechanisms, not otherwise provided for or using energy sources not otherwise provided for using expansion or contraction of bodies due to heating, cooling, moistening, drying or the like
- F03G7/065—Mechanical-power-producing mechanisms, not otherwise provided for or using energy sources not otherwise provided for using expansion or contraction of bodies due to heating, cooling, moistening, drying or the like using a shape memory element
Definitions
- This invention relates generally to shape memory alloy actuators. More particularly, this invention relates to an apparatus and method for a low cost shape memory alloy actuator using measured actuation parameter feedback.
- SMAs shape memory alloys
- SMA actuators are finding unique applications in a variety of industries. Many of these applications require precise control over SMA actuator position or actuation speed. Various applications also require control over other actuation properties, such as end-of-travel limit- stops or overheat protection to prevent damage to the SMA actuator.
- actuation properties such as end-of-travel limit- stops or overheat protection to prevent damage to the SMA actuator.
- it is often desirable that the SMA actuator has a small footprint, so that it may be used for limited-space applications, which require miniature or reduced-sized actuation mechanisms.
- the invention includes a method of controlling a shape memory alloy actuator by applying power to the shape memory alloy actuator.
- a measured actuation parameter is obtained from the shape memory alloy actuator.
- An operational characteristic parameter is derived based upon the power and the measured actuation parameter.
- An actuation state parameter is identified from the operational characteristic parameter. The actuation state parameter is used to modify the control of the shape memory alloy actuator.
- the invention also includes a mechanical actuator.
- the mechanical actuator has a shape memory alloy.
- a controller is connected to the shape memory alloy.
- the controller is adapted to apply power to the shape memory alloy, derive an operational characteristic parameter based upon a measured actuation parameter, identify an actuation state parameter from the operational characteristic parameter; and alter the application of power to the shape memory alloy based upon the actuation state parameter.
- the invention relies upon components that are typically already present in a shape memory alloy actuator. Therefore, the invention can be implemented at a relatively low cost.
- the various techniques of the invention provide designers with a variety of strategies for optimizing a given low cost shape memory alloy actuator.
- Figure 4 illustrates the relationship between resistance, collector voltage, and base current; the apparatus illustrated in Figure 3 uses this relationship to derive an operational characteristic parameter used in accordance with an embodiment of the invention.
- Figure 7 illustrates the relationship between resistance, time, and collector current; the apparatus of Figure 6 uses this relationship to derive an operational characteristic parameter used in accordance with an embodiment of the invention.
- Figure 8 illustrates the relationship between actuator position, input power, and position sensors utilized in accordance with another embodiment of the invention.
- the actuator output is fed back to the controller 120 as a measured actuation parameter 140.
- This measured actuation parameter 104 is typically a subset of the overall actuator output 150 and therefore may be delivered through a signal path that is different than the actuator output signal path.
- the invention relies upon standard measurements (i.e., measured actuation parameters) to make actuator control decisions.
- these measurements are not used directly, rather they are used to deduce additional parameters, such as operational characteristic parameters and then actuation state parameters, which are then used in the control process.
- additional parameters may be computed using relatively small physical and computational resources, which are implemented at low cost.
- the invention affords enhanced signal processing, while still affording the benefits of low cost and a small form factor.
- FIG. 3 illustrates an apparatus 300 to measure the resistance of a shape memory alloy (SMA) element 350 for actuation control according to one embodiment of the present invention.
- SMA element 350 is connected in series between a positive voltage 310 and the collector 332 of an npn-type bipolar junction transistor 330.
- the emitter 336 of bipolar junction transistor 330 is connected to ground 320.
- the bipolar junction transistor 330 is controlled by microcontroller 305, which provides a base current to base 334 of bipolar junction transistor 330 via output pin 309 using a programmable current source.
- Input pin 307 of microcontroller 305 is connected between SMA element 350 and collector 332. Power for microcontroller 305 is not shown, but may be provided by positive voltage 310 and ground 320 or by another source.
- the apparatus 300 depicted in Figure 3 operates in the following manner. First, a collector voltage signal from collector 332 is input to microcontroller 305 via input pin 307. The collector voltage signal is compared by comparator module 315 to a pre-determined threshold voltage signal. The collector voltage signal is then converted by analog-to-digital converter (ADC) module 325 to a digital voltage signal using an analog-to-digital conversion technique. Observe that the ADC 325 may be omitted since the comparator 315 operating with DAC 345 and processor 335 can implement the same function. If the collector voltage signal is less than or equal to the threshold voltage signal, processor module 335 processes the digital voltage signal to determine the resistance of SMA element 350.
- ADC analog-to-digital converter
- the programmable current source associated with output pin 309 comprises a digital- to-analog converter (DAC) module 345 integrated with microcontroller 305, according to one embodiment of the present invention.
- microcontroller 305 does not comprise integrated DAC module 345, and a secondary digital-to-analog current converter of n bit-depth is implemented by connecting n output pins of microcontroller 305 through n resistors in parallel to the base 334 of bipolar junction transistor 330.
- the secondary digital- to-analog current converter of n bit depth may also be used in conjunction with an integrated digital-to-analog current converter to provide hardware gain scaling or offset adjust. Alternatively, gain scaling or offset adjust may be provided in software by microcontroller 305.
- the threshold voltage signal is the minimum voltage detectable by microcontroller 305 for input pin 307.
- input pin 307 functions as comparator module 315.
- microcontroller 305 reads and converts successive collector voltage signals to digital voltage signals until a collector voltage signal falls below the minimum voltage for input pin 307.
- microcontroller 305 may process the value of the last collector voltage signal detected to determine the resistance of the SMA element 350.
- the comparison may be performed by discrete components or combinations thereof external to microcontroller 305, or performed in software by microcontroller 305.
- Figure 4 illustrates the relationship between resistance, collector voltage, and base current of apparatus 300. Recall that the base current is known, since it is generated by the microcontroller 305. The collector voltage, a measured actuation parameter, is also known, since it was acquired using the previously described techniques. The relationship of Figure 4 is also known empirically and is available (e.g., as a look-up table) for this embodiment of the invention. With the base current and the collector voltage known, a resistance value can be derived based upon the information of Figure 4. This resistance value, which is an operational characteristic parameter, can then be used to produce an SMA position value. Known techniques for mapping an SMA resistance value to an SMA position are implemented by the microcontroller 305 to produce an actuation state parameter (i.e., position in this example), which may then be used to alter the control of the SMA actuator, if necessary.
- an actuation state parameter i.e., position in this example
- the resistance of SMA element 350 may also be calculated from the generic equation for a bipolar junction transistor:
- Bipolar junction transistors 530 and 541 are controlled by microcontroller 505, which provides a base current to base 534 and base 539 of bipolar junction transistors 530 and 541, respectively, using a programmable current source via output pin 509.
- a programmable current source via output pin 509.
- separate programmable current sources may be used to provide base currents to bipolar junction transistors 530 and 541.
- Input pin 507 of microcontroller 505 is connected between SMA element 550 and collector 532 of bipolar junction transistor 530.
- Input pin 508 of microcontroller 505 is connected between reference resistor 555 and collector 537 of bipolar junction transistor 541. Power for the microcontroller 505 can be provided by positive voltage 510 and ground 520 or be provided by another source.
- the apparatus 500 depicted in Figure 5 operates similarly to apparatus 300 described previously in connection with Figure 3, with the following additional features.
- Microcontroller 505 is adapted to read the voltage at collector 537 of second bipolar junction transistor 541 concurrently with the voltage at collector 532 of first bipolar junction transistor 530.
- the voltage at collector 537 of second bipolar junction transistor 541 is a function of the current through reference resistor 555. Because the resistance of reference resistor 555 is known, it is possible to determine the gain of the second bipolar junction transistor 541 using Equation 1 discussed previously in connection with Figure 4.
- the gain of the second bipolar junction transistor 541 is a function of environmental factors such as change in temperature or voltage supply.
- microcontroller 505 may use information regarding the gain of the second bipolar junction transistor 541 to calibrate first bipolar junction transistor 530 and compensate for environmental factors.
- the microcontroller 505 may be configured to switch positive voltage 510 between bipolar junction transistors 530 and 535, whereby the voltage at collector 537 is not read concurrently with the voltage at collector 532, but is instead read sequentially or occasionally depending upon the specific application.
- Microcontroller 505 can also be configured to switch between bipolar junction transistors 530 and 541 using an alternate circuit, including but not limited to using additional transistors to control current flow to one or both transistors 530 and 541. It is to be appreciated that while the current embodiment is described utilizing npn-type bipolar junction transistors, other transistor types such as pnp-type bipolar junction transistors or field-effect transistors may also be implemented without departing from the scope of the invention.
- timer module 615 can alternatively be implemented in software by microcontroller 605, or implemented using discrete components or combinations thereof external to microcontroller 605.
- the pnp-type bipolar junction transistor 641 remains saturated as base current continues to flow from the base 639 of pnp- type bipolar junction transistor 641 through base resistor 660 into the feedback capacitor 680.
- a measured actuation parameter in the form of a start of cycle and end of cycle location limiter may be used to derive operational characteristic parameters in the fo ⁇ n of start and finish positions, which may then be used to identify an actuation state parameter, such as cycle duration.
- FIG. 8 illustrates the relationship between actuator position, input power, and start and finish position sensors.
- Tpon is the time when input power is applied to the SMA element; Tas is the time the actuator begins to move from a start position; Tae is the time the actuator reaches the end of travel; Tpoff corresponds to when input power is cut to allow the actuator to return; Tars is the time when the actuator starts returning; Tare corresponds to the time the actuator completes its return to the start position; P0 is a start-of-travel sensor adapted to detect when the actuator begins to move; and PI is an end-of-travel sensor adapted to detect when the actuator reaches the end of travel.
- Figure 8 illustrates the actuator motion in a linear fashion, this motion is often non-linear for many actuators.
- Figure 8 illustrates an actuator that returns automatically when power is cut, although a similar figure could be shown for actuators that need some form of power to return.
- the various times at which point the actuator achieves the above labels for a given application depends on many factors, many of which are environmental. For example, if the input power source fluctuates (e.g. batteries that drain over time), then this may affect the times. In actuators that are highly affected by environmental temperature, such as SMA actuators, then variations in temperature or simply air flow (e.g. the air conditioner just switched on) can radically affect these times. Variation in friction and load on an actuator or other tolerance changes from one product to another can also affect these times.
- the control process can make adjustments to compensate for many of these factors so as to achieve a consistency of motion.
- the technique associated with Figure 8 may alternatively be implemented by measuring the time between providing power to the SMA element and complete actuation of the SMA element.
- This embodiment of the present invention requires the SMA element to go through a complete actuation cycle before calculating the actuation speed. Consequently, control of the actuation speed is limited by the time required to complete at least one actuation cycle.
- the actuation speed based on the take-off time or fall-off time can be determined during an actuation cycle, so that control of the actuation speed can occur during the first actuation cycle, allowing the control process to quickly adjust the actuation speed so as to achieve a consistency of motion.
- control process is able to respond more quickly to changes in environmental factors, such as temperature or power supply variation, to maintain the desired actuation speed.
- a new take-off time may be estimated from a previous take-off time measurement and used to adjust when power is supplied to the SMA element actuator during subsequent cycles so that the actuator moves at the specific time.
- the process associated with Figure 8 can also be implemented by measuring the take-off time or fall-off time using the resistance of the shape memory alloy element, without the need of position sensors, such as the start-of-travel sensor P0 and end-of-travel sensor PI. Since resistance of the SMA element varies with position, it is possible to determine Tas (the time the actuator begins to move) by monitoring the resistance of the SMA element over time until a maximum resistance value, corresponding to start of actuation after power is applied, is achieved. The time it takes to achieve this maximum resistance value can be used to calculate the take-off time without a physical start-of-travel sensor.
- a technique of time-domain resistance analysis of an SMA element such as the technique described in commonly owned U.S. Patent No. 6,574,958, is used to determine both start and end-of-travel by monitoring the rate of change of the SMA resistance rather than the absolute value of the SMA resistance.
- Monitoring the rate of change of the SMA resistance has the advantage of not being dependent upon variation of SMA resistance due to type or extended use, and yields additional information regarding actuation characteristics, such as load on the actuator, overall performance of SMA element, or damage sustained by the SMA element.
- Monitoring the rate of change of the SMA resistance may be accomplished using any of the techniques described herein to measure the resistance of an SMA element or using any other technique known in the art, and control of actuation speed or other actuation characteristics may be achieved according to the methods and embodiments for actuation control of a shape memory alloy element using actuation feedback according to the present invention.
- Additional advantages of some embodiments of the present invention include automatic compensation of fluctuation in actuation load.
- the use of resistance for position measurement depends upon the relationship between resistance and percentage of transformation of the SMA element. Transformation of the SMA element depends, in turn, on both the temperature and mechanical load of the actuator. As the load on the actuator increases, the resistance of the SMA element increases in response.
- the actuator power source can play a critical role in determining how the actuator will respond to load fluctuations.
- the power drawn by the SMA element is inversely proportional to its resistance.
- the resistance increases due to a fluctuation in load, the resulting power drop will cause a drop in actuator temperature, and the resistance will further increase. This is equivalent to positive feedback due to fluctuation in actuator load, and is an unstable condition, which can result in the actuator moving away from a desired position.
- the power drawn by the SMA element is directly proportional to its resistance.
Abstract
Description
Claims
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US50057603P | 2003-09-05 | 2003-09-05 | |
US50612703P | 2003-09-25 | 2003-09-25 | |
PCT/US2004/028570 WO2005026539A2 (en) | 2003-09-05 | 2004-09-03 | Apparatus and method for low cost control of shape memory alloy actuators |
Publications (2)
Publication Number | Publication Date |
---|---|
EP1676030A2 true EP1676030A2 (en) | 2006-07-05 |
EP1676030A4 EP1676030A4 (en) | 2007-01-24 |
Family
ID=34316449
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP04782960A Withdrawn EP1676030A4 (en) | 2003-09-05 | 2004-09-03 | Apparatus and method for low cost control of shape memory alloy actuators |
Country Status (3)
Country | Link |
---|---|
US (1) | US20060048511A1 (en) |
EP (1) | EP1676030A4 (en) |
WO (1) | WO2005026539A2 (en) |
Families Citing this family (25)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US7484528B2 (en) * | 2004-12-23 | 2009-02-03 | Alfmeier Prazision Ag Baugruppen Und Systemlosungen | Valve |
DE102005045395A1 (en) * | 2005-09-23 | 2007-03-29 | Robert Bosch Gmbh | Method and device for length control of an actuator |
DE102006005268A1 (en) * | 2006-02-02 | 2007-08-16 | Viessmann Modellspielwaren Gmbh | Miniature model operating method for use in e.g. vehicle, involves pressurizing shape memory alloy unit with electrical energy for generation of drive force and controlling energy supply to unit based on parameter e.g. temperature of unit |
KR101353158B1 (en) | 2006-03-30 | 2014-01-22 | 캠브리지 메카트로닉스 리미티드 | Camera lens actuation apparatus |
KR20090129986A (en) * | 2007-02-12 | 2009-12-17 | 캠브리지 메카트로닉스 리미티드 | Shape memory alloy actuation apparatus |
ATE553591T1 (en) * | 2007-04-23 | 2012-04-15 | Cambridge Mechatronics Ltd | MEMORY ALLOY ACTUATOR |
US7974025B2 (en) * | 2007-04-23 | 2011-07-05 | Cambridge Mechatronics Limited | Shape memory alloy actuation apparatus |
JP4952364B2 (en) * | 2007-05-07 | 2012-06-13 | コニカミノルタオプト株式会社 | Drive unit and movable module |
WO2009056822A2 (en) * | 2007-10-30 | 2009-05-07 | Cambridge Mechatronics Limited | Shape memory alloy actuation apparatus |
EP2233739A1 (en) * | 2007-11-12 | 2010-09-29 | Konica Minolta Opto, Inc. | Shape memory alloy drive device |
US8756933B2 (en) * | 2007-12-03 | 2014-06-24 | Cambridge Mechatronics Limited | Control of a shape memory alloy actuation apparatus |
JP4539784B2 (en) * | 2008-01-15 | 2010-09-08 | コニカミノルタオプト株式会社 | Shape memory alloy drive unit |
GB2474173B (en) | 2008-07-30 | 2011-11-09 | Cambridge Mechatronics Ltd | Shape memory alloy actuation apparatus |
WO2010029316A2 (en) | 2008-09-12 | 2010-03-18 | Cambridge Mechatronics Limited | Optical image stabilisation |
JP5548211B2 (en) * | 2008-10-29 | 2014-07-16 | ケンブリッジ メカトロニクス リミテッド | Control of shape memory alloy actuator device |
TWI461826B (en) * | 2010-06-25 | 2014-11-21 | Hon Hai Prec Ind Co Ltd | Shutter structure |
WO2012038703A2 (en) | 2010-09-22 | 2012-03-29 | Cambridge Mechatronics Limited | Optical image stabilisation |
US8733097B2 (en) | 2011-03-16 | 2014-05-27 | GM Global Technology Operations LLC | Multi-stage actuation for an active materials-based actuator |
GB201220485D0 (en) | 2012-11-14 | 2012-12-26 | Cambridge Mechatronics Ltd | Control of an SMA actuation apparatus |
WO2017197336A1 (en) | 2016-05-12 | 2017-11-16 | Auburn University | Dual measurement displacements sensing technique |
GB201610039D0 (en) | 2016-06-08 | 2016-07-20 | Cambridge Mechatronics Ltd | Dynamic centring of SMA actuator |
GB2555655A (en) * | 2016-11-08 | 2018-05-09 | Eaton Ind Ip Gmbh & Co Kg | Valve assembly and method for controlling a flow of a fluid using a shape memory alloy member |
DE102016225519B4 (en) | 2016-12-20 | 2019-03-28 | Conti Temic Microelectronic Gmbh | Pneumatic valve |
DE102018216876B4 (en) | 2018-10-01 | 2022-10-27 | Conti Temic Microelectronic Gmbh | pneumatic valve |
CN113484969B (en) * | 2021-06-23 | 2022-05-20 | 广东海德亚科技有限公司 | SMA wire drive structure, closed-loop control method thereof and electronic equipment |
Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
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US4553393A (en) * | 1983-08-26 | 1985-11-19 | The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration | Memory metal actuator |
US4930494A (en) * | 1988-03-09 | 1990-06-05 | Olympus Optical Co., Ltd. | Apparatus for bending an insertion section of an endoscope using a shape memory alloy |
US5921083A (en) * | 1992-07-30 | 1999-07-13 | Brotz; Gregory R. | Tri-clad thermoelectric actuator |
US20010025477A1 (en) * | 2000-03-23 | 2001-10-04 | Yoshihiro Hara | Control mechanism with actuator employing shape memory alloy and method for adjusting servo control of the control mechanism |
US6574958B1 (en) * | 1999-08-12 | 2003-06-10 | Nanomuscle, Inc. | Shape memory alloy actuators and control methods |
Family Cites Families (5)
Publication number | Priority date | Publication date | Assignee | Title |
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JPH0686866B2 (en) * | 1985-08-16 | 1994-11-02 | キヤノン株式会社 | Shape memory alloy actuator |
US5619177A (en) * | 1995-01-27 | 1997-04-08 | Mjb Company | Shape memory alloy microactuator having an electrostatic force and heating means |
US5685149A (en) * | 1995-11-14 | 1997-11-11 | Tcam Technologies, Inc. | Proportionally controlled thermochemical mechanical actuator |
US6543224B1 (en) * | 2002-01-29 | 2003-04-08 | United Technologies Corporation | System and method for controlling shape memory alloy actuators |
US6834835B1 (en) * | 2004-03-12 | 2004-12-28 | Qortek, Inc. | Telescopic wing system |
-
2004
- 2004-09-03 WO PCT/US2004/028570 patent/WO2005026539A2/en not_active Application Discontinuation
- 2004-09-03 EP EP04782960A patent/EP1676030A4/en not_active Withdrawn
- 2004-09-03 US US10/934,037 patent/US20060048511A1/en not_active Abandoned
Patent Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4553393A (en) * | 1983-08-26 | 1985-11-19 | The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration | Memory metal actuator |
US4930494A (en) * | 1988-03-09 | 1990-06-05 | Olympus Optical Co., Ltd. | Apparatus for bending an insertion section of an endoscope using a shape memory alloy |
US5921083A (en) * | 1992-07-30 | 1999-07-13 | Brotz; Gregory R. | Tri-clad thermoelectric actuator |
US6574958B1 (en) * | 1999-08-12 | 2003-06-10 | Nanomuscle, Inc. | Shape memory alloy actuators and control methods |
US20010025477A1 (en) * | 2000-03-23 | 2001-10-04 | Yoshihiro Hara | Control mechanism with actuator employing shape memory alloy and method for adjusting servo control of the control mechanism |
Non-Patent Citations (1)
Title |
---|
See also references of WO2005026539A2 * |
Also Published As
Publication number | Publication date |
---|---|
US20060048511A1 (en) | 2006-03-09 |
EP1676030A4 (en) | 2007-01-24 |
WO2005026539A3 (en) | 2006-08-24 |
WO2005026539A2 (en) | 2005-03-24 |
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