CA1110359A - Servo system for track accessing and track following in a disk drive - Google Patents
Servo system for track accessing and track following in a disk driveInfo
- Publication number
- CA1110359A CA1110359A CA314,763A CA314763A CA1110359A CA 1110359 A CA1110359 A CA 1110359A CA 314763 A CA314763 A CA 314763A CA 1110359 A CA1110359 A CA 1110359A
- Authority
- CA
- Canada
- Prior art keywords
- track
- signals
- magnetic head
- servo
- servo system
- 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.)
- Expired
Links
Classifications
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/48—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed
- G11B5/54—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed with provision for moving the head into or out of its operative position or across tracks
- G11B5/55—Track change, selection or acquisition by displacement of the head
- G11B5/5521—Track change, selection or acquisition by displacement of the head across disk tracks
- G11B5/5526—Control therefor; circuits, track configurations or relative disposition of servo-information transducers and servo-information tracks for control thereof
- G11B5/553—Details
- G11B5/5547—"Seek" control and circuits therefor
Abstract
Abstract of the Disclosure Digital position error signals from a position detector and a track increment generator are summed and applied to a compensator which is responsive to these signals during the sampling of servo sectors on the tracks of a magnetic disk of a magnetic disk store to regulate the position of a magnetic head for track selection and track following. Track selection is effected with an acceleration phase, a constant velocity phase, and a deceleration phase, and overshooting of the magnetic head at the ends of the acceleration and deceleration phases is avoided by digital modification signals read out, from read-only memories in the track increment generator, to the compensator.
The digital position error signal from the track increment generator can be combined with the output of a track crossing detector.
The digital position error signal from the track increment generator can be combined with the output of a track crossing detector.
Description
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Device for regulating the magnetic head position during track selection ... . .
and track following of the ma~netic head f a magnetic disk storage The invention concerns a device for regulating the magnetic head position during track selection and track following of the magnetic head of a magnetic disk storage, which can be positioned to selectable track addresses of a magnetic disk, with regulation of the magnetic head position by servo marks arranged on the magnetic disk in servo sectors of the recording tracks in the form of a mark pattern, the sampling of which permits left/right deviations of the magnetic head from tha center lQ of a data track to be represented by a position error voltage of a position detector, which increases positively/negatively proportional to the degree of deviation and by means of which in a compensator a regulating voltage driving the positioning motor of the magnetic head can be generated, and with a switching device synchronized with the disk rotation and which upon sampling of the servo sectors by means of the magnetic head feeds the sampled servo signals at predetermined time intervals to a servo circuit, and with a track follower circuit designed as a servo regulating loop and which is regulable by servo signals and controllable by address and clock signals.
It is kno~l, as described in US Patent 3,753,869, to design a positioning device for the access arm of the magnetic head of a magnetic disk storage in such a manner that the access arm, as the magnetic head is positioned to a selected track addresst is driven by a motor, whose speed during the positioning motion of the magnetic head is regulable by a servo device.
This servo device effects an initial acceleration, a subsequent uniform speed, and a delaying of the access arm at the end of the positioning path before the magnetic head reaches the track address. The speed regulat-GE9-77-011 ~3~
3.~;9 ion of the access arm is enaured by the tachometer of a serYo circuit which, when the selected track address is reached, is dîsconnected by the magnetic head from the drive motor of the access arm. Simultaneously, the motor of the access arm is switched on in a servo regulating circuit which causes the magnetic head to be guided over the center of the recording track. The servo and dat~ marks are recorded on different surfaces of the magnetic disk storage. The servo marks of a first disk surface are sampled by a servo magnetic head and the data marks of a second disk surface by a data magnetic head. Both magnetic heads are associated with different but join-tly driven access arms positioning the magnetic heads to a selected track address.
The disadvantage of the known device is that the arrangement of the servo and data marks on different disk surfaces, as a result of the positioning mechanism, lead to differences between the servo and the data magnetic head. The tolerance values of these positional differences are so high that they limit the density of the addressable recording tracks of a magnetic disk storage.
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It is also known, as described in US Patent 3,185,972, to regulate the track following of the magnetic head of a magnetic disk storage by means of servo signals sampled on servo marks which are recorded in servo sectors of the recording tracks. The servo sectors are arranged at uniform angular distances between the data sectors of the magnetic disk. The sampling of the data and servo sectors of a magnetic disk is effected by a single magnetic head positioned to a selected recording track by means of a carrier arm. For this purpose the servo circuit is controlled by a switch-ing device synchroni~ed with the disk rotation and which, as the servosectors are sampled by the magnetic head, applies the sampled servo signals at predetermined time intervals to the magnetic head.
The known device makes it possible to associate the servo and data magnetic head with a single magnetic head carrier arm, so that as a result of this simplification of the positioning mechanism, position differences between data and servo magnetic head are eliminated, thus increasing the density of the selectable recording tracks. However, the known device has the dis-advantage :~
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that for track selection and track follo~ing of the m~gnetic head different drive systems are required, which leads to an increase in the mass moment of inertia of the moved elements and to a reduction in the positioning speed of the magnetic head.
It has also been proposed, as described in U.S. Pa-tent No. 4,120,505 and assigned to the same assignee to design a device for regulating the magnetic head posi~ion during track selection and track following of the magnetic head of a magnetic disk storage in such a manner that the same drive system can be used both for the access motion of the magnetic head and for its position control during track following. In the case of the magnetic disk storage of the proposed type~ the servo marks for regulating the track following of the magnetic head are recorded in servo sectors of a disk surface. At the beginning of an access motion of the magnetic head the drivé motor of the magnetic head carrier arm, effecting the radial advance motion of the magnetic headg is connected to a constant drive voltage during ~ ~ -an acceleration phase. The duration of the acceleration phase is controlled by clock signals which are sampled by a special, permanently arranged mag-netic head of a recording track and which are utilized for the control of the switching periods of the data and servo sectors. After sampling of a ~o particular number of servo sectors, the drive motor of the magnetic head carrier arm is connected to a servo regulating circuit for a particular period of time during which the speed of the magnetic head carrier arm is constant. After completion of the access motion of the magnetic head, said servo regulating circuit is also used to regulate the track following. For ~he duration of a particular number of servo sectors, the servo marks, by means of which the radial position of the magnetic head is indicated by a position signal during each sector time9 are sampled by the servo and d~ta magnetic head for the duration of a sector time. Via the regulating `
circuit~ this position signal produces an acceleration or deceleration 3Q component of the drive signal, depending upon whether at the tLme of sampling a leading or lagging track deviation of the magnetic head from the center of a data track is detected. At the end of the period in which the access speed is constant~ the drive motor is disconnected ~rom the regulat-ing circuit and connected to a constant voltage decelerating the magnetic head and whose sign is opposite to the sign of the constant drive voltage GE9-77-011 ~5~
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to which the drive motor was connectea auring the acceleration phase. After a par~icular n~lmber of servo sectors has been passed9 the magnetic head is arrested on a selected recording track as a result of this. After the address position has been reached, the drive for the radial advance of the magnetic head is connected to the regulating circuit for track following The proposed device offers the possibility to utilize the drive o~ a magnetic head carrier arm both for the duration of an access motion and, after the address position has been reached, for the regulation of track following.
There is, howe~er, the disad~antage that the switching processes of the drive voltage lead to a discontinuous course of the drive force acting on the drive motor of the magnatic head carrier arm, so that oscillations of the moved mass parts reduce the positioning accuracy and the positioning speed of the magnetic head.
It is the object of the present invention to design a device for regulating the magnetic head position during track selection and track following of the magnetic head of a magnetic disk storage ;n such a manner that the components of a joint regulating circuit can be used both for the access motion and for track following of the magnetic head~ without the magnetic head being subaect to detrimental oscillations.
The problem is-solved in accordance with the present invention by digital position error signals, derived from the position detector, beirlg applied to the first input of a su~ming circuit, and by digital position control signals sampled by a track increment ~enerator with the aid of clock and address signals being fed to a second input o~ said su~ming circuit, the output of which is connected to the compensator to which during the sampling period of a servo sector a digital position signal generated by the su~ming circuit and a digital modification signal sampled on the read-only memory of the track increment generator can be applied.
By means of the described device it is possible to generate in the current circuit of the drive motor of a magnetic head carrier arm from the sum of the digital position error and position control signals a drive current :. : . : ~ ,. .: , : .. - . ..... ;
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in accordance with a predetermlned program sequence in such a manner that discontinuities of the drive motion of the magnetic head are avoided.
More particularly, there is provided:
A servo system for a disk drive having a magnetic disk recorded with data signals and with interleaved servo signals, a magnetic head for sensing ~aid data and servo signals and a motor for driving said head to access data tracks on said disk comprising:
a position detector for providing first position error signals in response to sensed servo signals;
a track increment generator for generating second posi-tion error signals under control of clock and address signals;
a summing circuit coupled to said position detector and to said track increment generator for sumning said first and second error signals and for producing a combined position error ~ignal; and .
: a compensator coupled to said summing circuit and to ~:
said track increment generator for providing a compensating signal to said drive motor o~ ~aid accessing head.
The invention ~ill be describ~d in det~l by ~e~ns of illu~trations, Fig. 1 shows the total ~rrangement of a device for regulating the ms~netic head po~ition o~ a msgnetic di~k ~tor~e during tr&ck selection ~cd trsck ~ollowing in the form of ~ block dia~3ram, Fig. 2 shows the recording patter~ o~ servo mark~ recorded in the ser~o ~:
sector of a ~etic di~k, Fig. 3 ~hows the cour~e of the digital output 0ignQl of the ~/d converter illustrated in FiB. 19 ~hich i3 produced by poBitio~ ;
errors Or the ~ervo and dats nQ8~etic head, Fi~. 4 ~ho~rs the cour~e o~ the diglt~l 13i~1R15 o:f' a track incr~ent gener3tor, which ~re introduceB into the rezulQting circuit ~or the track followlng o~ the ma6~etic head a~d ~hich ~re summed to the digit~l position error ~ignQl~ Or the tr~c~ follower ro6ulsting circuit, ~ , :
-7a-3~3 Fi~s . 5B to 5d show the diagrams of the position error, position control, position hnd compensating voltages of the ~ervo ~nd datA msgnetic head during an access ~otion in ~unctional d0pendence of the time -- expressed bJ the number Or s~mpled ~ervo sectors, Fig. 6 shows the switching elements of a track incr~ment generator in the ~or~ of a block di~4rAm, Fig. 7 sbows another e~bodiment of ~ device for re6ulating the ~gnetic head position during trsck selection and trsck rollo~ing Or the netic hesd of a ~sgnetic disk stor~ge in the ~orm of a block .--' '; ' ~,' ' .",.' . ' . ,: , .
The magnetic disk 1 of a magnetic disk storage sho~m in Fie. 1, which is rotatably supported on the hub 2, is rotated clockwise b~ a drive motor not shown. The magnetic head 5 fixed to a magnetic head carrier 4 of a magnetic head carrier arm 12 can be optionally positioned in a radial direct-ion to concentric recording tracks of the magnetic disk 1 by means of a drive motor 13. The surface of the magnetic disk 1 is divided into a random number of data sectors D and servo sectors S in which data and servo signals, respectively, are recorded in the associated angular areas. On the outer circumference o~ the magnetic disk 1 clock signals, which can be sampled by a fixed clock magnetic head 6, are recorded in a clock track. The clock signals sampled by the clock magnetic head 6 are converted into time control signals by means of the switching device 70 Said time control signals are fed to an input of the data input/output 8 via line 25. The magnetic clock generation can be replaced by optical clock generation o~ a known kind. The time control signals trans~erred by line 25 determine the time control signals, by means of which during the "D sector times" the inputloutput signals transferred between the magnetic head 5 and the data inputtoutput 8 via line 26 are fed from and to the output line 9, ~he switching device 7 also produces time control signals which on the output line 10 during the "S sector times" control the sampling o~ the servo sectors S on the magnetic disk 1. From the output line 11 of the switchin~ device 7 clock signals for the generation of position control signals are derived ~which are used to control the drive motor 13 o~ the mag~etic head carrier arm 12.
The drive motor 13 o~ the magnetic head carrier arm 12 is connected to track follower rejgulating circuit to which, via the line 27, as the servo sectors S pass magnetic head 5, servo signals sampled on servo marks are applied. ~y means of a position detector 15 track deviations of the magnetic head 5 from the center of a data track are detected and converted into corresponding position error signals. Via an analogue-to-digital converter these po~ition error signals are converted into digital position error signals Pl indicating a position error and which are ~ed to a first input o~
a summing circuit 17. ~o a second input of the summing circuit 17 digital position signals P2 are applied which are eenerated b~ the track increment GE 9'77 011 3~
generator 21. Generation of the position control si~nals P2 is effected under the control of clock signals which are derived from the switching device 7 and are fed to a first input line 22 of the track increment generator 21.
Via a second input line 23, the track increment generator 21 receives address signals determining a ~elected recording track of the magnetic disk 1 to which the magnetic head 5 is po~itionable in a free QCC9SS motion. By the summing circuit 17 the digital position error signals P1 and the digital posit-ion control signals P2 are summed to position control signal6 P which are applied to a first input of the compensator 18. To a second input 20 of the compensator 18 "S sector time" control signals are applied~ by means of which K signals are generated each time a servo sector passes the ma~netic head 5. Said K signals represent digital compensation values of the position control signals P. ~hese compensation signals remain constant for the time during which the subse~uent data sector D passes the magnetic head. The digitalcompensation signals K derived from the output of the compensator 18 are convert-ed by a digital-to-analogue converter 19 into corresponding analogue signals andare transferred from line 24, ViQ a power amplifier 14, to the drive motor 13 of the magnetic head carrier arm 12. During the access time, said magnetic head carrier arm causes the magnetic head 5 to ~e positioned in a motional pathg the positions o~ which, as shown in Fig. 5, are time-depend-ent, according to the number of servo sectors sampled by the ma~netic head 5. The path/time diaOE am determined by the track increment generator 21 is divided into an A time, in which ~n acceleration path is covered, into a~subsequent B time, in which a constant speecL path is covered, and into a C time in which a deceleration path i8 co~ered. ~
i The servo marks recorded on the ma~netic disk 1 in the servo sectors S may be seen from Fig. ?~ In a servo sector S~ limited on both sides by data sectors D, magnetic servo marks of opposite polarity and opposite phase position, respectively, are recorded. Two different servo marks each of`
opposite polarity, which are recorded on both sides of a track line at the same track width W2, form a servo track of the track width W1. A data track in the data tracks D has the track width W2. It ~orms in each case the continuation of one track half of the track halves of a servo track of the trackwidth W1 recorded in servo sector S. Each data track is limited by two track lines E between which the center line 0 of a data track extends. The servo ::: : :. ~ : .
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and data magnetic head 5~ ~ixed to the magnetic head carrier 12 option-ally positiona~le by means of the drive motor 13~ has the track width W2.
In the normal, error-free sampling position the magnetic head 5 is excactly over the center line of a servo track and the center line 0 o~ a data track, respecti~ely. Deviations o~ the magnetic head position ~rom this center position either in the region o~ the positive or in the region of the neeative polarity o~ the servo marks lead to position error signals. ~he position error signals continue to indicate track deviations o~ the magnetic head, i~ thelatter at maximum track deviation ~rom the normal position is deMected either into the positive marking range or into the negative marking range of the ser~o marks on both sides o~ a track line 0, as illustrated by broken lines.
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~he course of a position error voltage P1 ma~ be seen ~rom the illustration in accordance with Fig. 3. If the track position o~ the magnetic head 5 between the two track lines E1 and E2 limiting a data track changes, a linearl~ descending course of the position error ~oltage occurs, which is a ~unction o~ the track position and whose signal value is 0 when the magnetic head is accurately centered over the center line 0. In this normal position the magnetic head 5 samples equall~ large track halves of the positive and the negative servo marks, the signal components of which cancel each other upon sampling. In the position in which the magnetic head 5 exclusively records the signal component of the positive polarity of the servo marks, the position error signal P1 re~ches its positive maximum value. ~n the opposite marginal position in which the magnetic head 5 exclusively records the signal i component of the negative polarity o~ the servo marks, the position error ~ signal P1 reaches its negative maximum value. ~he compensator o~ a track ; ~ollower regulating circuit operates in ~uch a manner that upon the occurrence of a position error signal P1 in the regulating circuit it generates a compensation signal which decreases the position error, thus stabilizing the position o~ the magnet;c head over the center line 0 o~ the recording track.
Fig. 4 shows the path/time diagram o~ the magnetic head 5 which is ~ollowed as a result of an access motion o~ the magnetic head to the selected record-ing track of the track address n25 of the magnetic disk 1. During the time 3~
in which 6 servo sectors pass the magnetic head 5, the latter is accelerated during the A time. In this period of time the magnetic head 5 crosses six recording tracks. The subsequent B time, in which the magnetic head 5 is moved at a constant speed, has a duration corresponding to the sampling time of four servo sections, i.e., the period lasts up to the sampling of the tanth servo sector. During this period of time, three recording tracks are crossed during the time in which one servo sector passes the magnetic head. At the end o~ this speed period the magnetic head reaches the track address nl8. ~his is followed b~ the C time in which the access motion of the ma~netic head 5 is de-celerated during the sampling time of six servo sectors. ~t the end of the de-celeration path9 in the course o~ which the magnetic head 5 crosses seven record-ing tracks, the head reaches the track address n25 preselected b~ addressing. Inthis track position the access motion of the magnetic head ends, so that the position control signals P2 generated on the output of the track increment generator 21 of Fig. 1 and controlling the access motion are interrupted.
As a result, the track selection regulating circuit is switched to regulate the position o~ the magnetic head 5 ~or track following over the center o~
the recording track n25.
The signal/time diagram illustrated in Fig. 5a shows the dependence of the digital position signals P generated on the output of the summing circuit 17 which is shown in Fig. 1. ~y means o~ the compensQtor 18, digital K signals corresponding to the position signals P are generated. ~y means o~ the d/a converter, said K signals are converted into analogue signals feeding the drive motor 13. The digital position signal P shown in Fig. 5a is obtained by summing in the summing circuit 17 the digital position error signal P1 of Fig. 5c to the digital position control signal P2 of Fig. 5d. Upon crossing the recording tracXs n1 to n25, the magnetic head 5 is accelerated in the acceleration path during the time in which the servo sectors S1 to S6 pass the magnetic head. For this purpose, the track increment generator 21 generates position control signals P2 in accordance with a given program, which in the direction of movement of the access path have constant digital values for the duration of one or several track crossings.
This determines the course o~ the digltal position signals P. By means of the compensator ?8, a corresponding digital compensation signal K, illustrat-ed in Fig. 5b, is generated. Said signal drives the magnetic head in the `', ~.. .. : : .. ,, ,, : .
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direction o~ the target address of the recording track n25, since the track follower regulating circuit because o~ detuning as a result o~ the added component of the position control signal P2 cannot ef~ect a zero compensation for stabili~ing the position o~ the magnetic head in the center of the re-cording track nl. ~he po~ition control signal~ P2 are dimensioned in accord-ance with a given program in such a manner that the magnetic head 5 passes the acceleration path o~ Fig. 4 ~or the duration of the A time until the track address n6 is reached.
As the magnetic head enters the constant speed phase of the B time, position error signals P1 are trans:~erred to the su~ming circuit 17 only i~ during the time in which a data sector D passes the magnetic head, the latter does not have to cross all -the recording tracks. At the end of the B time, the magnetic head has reached the track address n18.
In the subsequent deceleration phase, position control signals P2 having an opposite polarity to the position control signals P2 active in the acce~
leration phase are derived from track increment generator 21. ~hese control signals generate negative acceleration forces, so that the magnetic head 5 in the C time ~ollows the deceleration path o~ Fig 4 until the selected track addresses n25 ha~e been reached. During the C time the position signal P
generates a compensation signal K which stops the magnetic head.
At the end of the A time and at the end of the C time modi~ication signals M
are trans~erred in each case from an output o~ the track increment generator 21 to an input o~ the compensator 18, so that the compensation signal K stor-ed in the compensator is changed in such a manner that the magnetic head 5 is transferred to the subsequent motional state without overshooting.
~y means of the compensator i8, compensation signals K are computed from the position signals P. These compen~ation signals are obtained in accordance with the ~ollowing algorithm:
K(T) = const. P(T) + a1 P(T-1) + a2 P(T-2) + .... 3 - b1 K(T-1) + b2 K(T-2) . ..~
. . , ;
.. :, : . : .: , . ..
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where P(T) and K(T) represent position and compensation signals at the sampling times T and at the preceding sampling points (T-1), (T-2) ..., respectively.
The constants al ... an and b1 ..0 bn are a function of the characteristics of the regulating system, such as mass, threshold frequency, frictional losses, and the electrical time constants of the energizing voltage. They determine the transfer function o~ a linear controlled system7 as describ-ed in detail in chapter 7.2., pp. 147 and 148, of the book "Sampled-Data Control System" by J.R. Ragazzini et al, McGraw-Hill Book Comp., Inc.~ 1958.
Fig. 6 shows the individual switching elements o~ the track increment generat-or 21 illustrated in Fig. 1. Said generator compri3es a control device 31, to on0 input line 22 o~ which clock signals ~rom the output line 11 of the switch-ing device 7 o~ Fie. 1 are applied. To the aecond input line 23 addres6 signalsare applied, indicating to which recording track on the magnetic disk 1 the magnetic head 5 is to be positioned. Aæ a function of the clock and address signals applied via the input lines 22 and 23 the control device 31 generates control signals which at the different A, B, and C times are trans~erred to a read-only memory 28, 29, and 30 via the different output lines of the control device. Said read-only memories contain storage values for the track incre-ments, which can be sampled in accordance with a particular progr~m. For generating the digital P2 position control signals, the track increments are transferred to an output line in a predetermined time sequence. Via another output line of the track increment generator 21~ the modi~ication signals M
generated at the end of the A time ana the C time are transferred to an input o~the compens~tor 18. The A, B, and C control 3ignals are made available as a function o~ the entered address in accordance with a particular program controlling the acceleration, the constant speed~ and the deceIeration of the magnetic head 5. Thus, it can be assumed, ~or exampleg that deviating from the addressing o~ the magnetic head 5 to the recording track n25, in accordance with the embodiment described by means of the illustration of Figs. ~ and 5, the magnetic head 5 is to be addressed to the recording track n28. In this case it is merely necessary to extend the B time of the constant speed range by one sector interval with the aid of the control device 31. In accordance with the given prerequisites, it is assumed that the position control signals P2 derived from the read-only memory 33 effect a speed of the magnetic head 5, which equals three track crossings per sector interval. Extensions of the B
time by one sector interval each thus lead to recording tracks n28, n31, : :: , - ,: . , : :: :~ ;:.: :": : : . :, :;
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n34 ... or, in the case of reductions in the B time by one sector interval, to recording tracks n22~ n18~ nl5 to be optionally addressed. The inter-mediate values of said address se~uence3 e.g., o~ the recording tracks 26 and 27, can be set at equal track increment values sampled on the read-only memory 29, if the acceleration of the A time or the deceleration of the C time are extended by one or two sector intervals. If the recording track n26 is selected, it can be assumed, ~or example, that the magnetic head 5 reaches the necessary access speed o~ three track crossings per sector interval in the constant speed range after seven rather than six sector intervals. For this purpose it is necessary that the A time of the acceleration phase comprises seven sector intervals, and that the position control values sampled on the re&d-only memory 28 are changed. The magnetic head can be correspondingly positioned to the selected recording track n27 when the A time comprises seven sector intervals and the C time eight sector intervals. The position control values sampled on the read~only memory 30 must also be changed for this purpose9 so that the magnetic head 5 having a positioning speed of three track crossings per sector interval in the constant speed range reaches the zero value in the extended B time. The sampling of the track increment ~alues necessary for a predetermined track addressing of the magnetic head and the dimensioning of the A, B~ and C times necessary for this purpose is ensured by means of the address value entered via the line 23.
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Fig. 7 shows a further alternative for generating the position control sign~ls which ~or the purpose~of performing a track access motion of a magnetic head are introduced into the track follower regulating circuit of the magnetic head. The device is operated in such a manner that the digital position ; -control signals P2 derived from the output o~ the track increment generator 21' are added by the adder 33 for each track crossing and are fed to an input of the summing circuit 32. From an output of the compensator 1~' and an output of the a/d converter 16' signals H and L are transferred to the inputs of the track change detector 3~ via one line each. The output signal F of the track change detector 34, whose value is proportional to the number of record-ing tracks crossed by the magnetic head 5, is transferred to a second input o~
the summing circuit 32.
': '' ' `, ' ` : '' ~ ' ': . ':' The position control and track change signals applied to both inputs of the su~ming circuit 32 have opposite signs, so that on the output of the summing circuit 32 the difference between the two input signals is entered in the form of the control si~nal G into the track follower regulating circuit, in order to be summed with the position error signal P1 in the summing circuit 17'. The function of the position detector 15' connected to the line 27' and of the d/a converter connected to the line 24' corresponds to the description of the circuit elements 15 and 19 according to Fig. 1.
Signals P1, P2, P, M, K9 F, G, H, and L described by means of Figs. 1 and 7 are multi-position, preferably binary-coded, digitaI sienals. ~y means of the device described with the aid of Fig. 7, the direction o~ the access motion of the magnetic head can be detected in the case of an address operation mode, so that erroneous positioning of the magnetic head is avoided.
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Device for regulating the magnetic head position during track selection ... . .
and track following of the ma~netic head f a magnetic disk storage The invention concerns a device for regulating the magnetic head position during track selection and track following of the magnetic head of a magnetic disk storage, which can be positioned to selectable track addresses of a magnetic disk, with regulation of the magnetic head position by servo marks arranged on the magnetic disk in servo sectors of the recording tracks in the form of a mark pattern, the sampling of which permits left/right deviations of the magnetic head from tha center lQ of a data track to be represented by a position error voltage of a position detector, which increases positively/negatively proportional to the degree of deviation and by means of which in a compensator a regulating voltage driving the positioning motor of the magnetic head can be generated, and with a switching device synchronized with the disk rotation and which upon sampling of the servo sectors by means of the magnetic head feeds the sampled servo signals at predetermined time intervals to a servo circuit, and with a track follower circuit designed as a servo regulating loop and which is regulable by servo signals and controllable by address and clock signals.
It is kno~l, as described in US Patent 3,753,869, to design a positioning device for the access arm of the magnetic head of a magnetic disk storage in such a manner that the access arm, as the magnetic head is positioned to a selected track addresst is driven by a motor, whose speed during the positioning motion of the magnetic head is regulable by a servo device.
This servo device effects an initial acceleration, a subsequent uniform speed, and a delaying of the access arm at the end of the positioning path before the magnetic head reaches the track address. The speed regulat-GE9-77-011 ~3~
3.~;9 ion of the access arm is enaured by the tachometer of a serYo circuit which, when the selected track address is reached, is dîsconnected by the magnetic head from the drive motor of the access arm. Simultaneously, the motor of the access arm is switched on in a servo regulating circuit which causes the magnetic head to be guided over the center of the recording track. The servo and dat~ marks are recorded on different surfaces of the magnetic disk storage. The servo marks of a first disk surface are sampled by a servo magnetic head and the data marks of a second disk surface by a data magnetic head. Both magnetic heads are associated with different but join-tly driven access arms positioning the magnetic heads to a selected track address.
The disadvantage of the known device is that the arrangement of the servo and data marks on different disk surfaces, as a result of the positioning mechanism, lead to differences between the servo and the data magnetic head. The tolerance values of these positional differences are so high that they limit the density of the addressable recording tracks of a magnetic disk storage.
~ .
It is also known, as described in US Patent 3,185,972, to regulate the track following of the magnetic head of a magnetic disk storage by means of servo signals sampled on servo marks which are recorded in servo sectors of the recording tracks. The servo sectors are arranged at uniform angular distances between the data sectors of the magnetic disk. The sampling of the data and servo sectors of a magnetic disk is effected by a single magnetic head positioned to a selected recording track by means of a carrier arm. For this purpose the servo circuit is controlled by a switch-ing device synchroni~ed with the disk rotation and which, as the servosectors are sampled by the magnetic head, applies the sampled servo signals at predetermined time intervals to the magnetic head.
The known device makes it possible to associate the servo and data magnetic head with a single magnetic head carrier arm, so that as a result of this simplification of the positioning mechanism, position differences between data and servo magnetic head are eliminated, thus increasing the density of the selectable recording tracks. However, the known device has the dis-advantage :~
GE9-77-011 ~4~
3~
that for track selection and track follo~ing of the m~gnetic head different drive systems are required, which leads to an increase in the mass moment of inertia of the moved elements and to a reduction in the positioning speed of the magnetic head.
It has also been proposed, as described in U.S. Pa-tent No. 4,120,505 and assigned to the same assignee to design a device for regulating the magnetic head posi~ion during track selection and track following of the magnetic head of a magnetic disk storage in such a manner that the same drive system can be used both for the access motion of the magnetic head and for its position control during track following. In the case of the magnetic disk storage of the proposed type~ the servo marks for regulating the track following of the magnetic head are recorded in servo sectors of a disk surface. At the beginning of an access motion of the magnetic head the drivé motor of the magnetic head carrier arm, effecting the radial advance motion of the magnetic headg is connected to a constant drive voltage during ~ ~ -an acceleration phase. The duration of the acceleration phase is controlled by clock signals which are sampled by a special, permanently arranged mag-netic head of a recording track and which are utilized for the control of the switching periods of the data and servo sectors. After sampling of a ~o particular number of servo sectors, the drive motor of the magnetic head carrier arm is connected to a servo regulating circuit for a particular period of time during which the speed of the magnetic head carrier arm is constant. After completion of the access motion of the magnetic head, said servo regulating circuit is also used to regulate the track following. For ~he duration of a particular number of servo sectors, the servo marks, by means of which the radial position of the magnetic head is indicated by a position signal during each sector time9 are sampled by the servo and d~ta magnetic head for the duration of a sector time. Via the regulating `
circuit~ this position signal produces an acceleration or deceleration 3Q component of the drive signal, depending upon whether at the tLme of sampling a leading or lagging track deviation of the magnetic head from the center of a data track is detected. At the end of the period in which the access speed is constant~ the drive motor is disconnected ~rom the regulat-ing circuit and connected to a constant voltage decelerating the magnetic head and whose sign is opposite to the sign of the constant drive voltage GE9-77-011 ~5~
, ....
i3~
to which the drive motor was connectea auring the acceleration phase. After a par~icular n~lmber of servo sectors has been passed9 the magnetic head is arrested on a selected recording track as a result of this. After the address position has been reached, the drive for the radial advance of the magnetic head is connected to the regulating circuit for track following The proposed device offers the possibility to utilize the drive o~ a magnetic head carrier arm both for the duration of an access motion and, after the address position has been reached, for the regulation of track following.
There is, howe~er, the disad~antage that the switching processes of the drive voltage lead to a discontinuous course of the drive force acting on the drive motor of the magnatic head carrier arm, so that oscillations of the moved mass parts reduce the positioning accuracy and the positioning speed of the magnetic head.
It is the object of the present invention to design a device for regulating the magnetic head position during track selection and track following of the magnetic head of a magnetic disk storage ;n such a manner that the components of a joint regulating circuit can be used both for the access motion and for track following of the magnetic head~ without the magnetic head being subaect to detrimental oscillations.
The problem is-solved in accordance with the present invention by digital position error signals, derived from the position detector, beirlg applied to the first input of a su~ming circuit, and by digital position control signals sampled by a track increment ~enerator with the aid of clock and address signals being fed to a second input o~ said su~ming circuit, the output of which is connected to the compensator to which during the sampling period of a servo sector a digital position signal generated by the su~ming circuit and a digital modification signal sampled on the read-only memory of the track increment generator can be applied.
By means of the described device it is possible to generate in the current circuit of the drive motor of a magnetic head carrier arm from the sum of the digital position error and position control signals a drive current :. : . : ~ ,. .: , : .. - . ..... ;
:: : :~: . ;
:: :: . . , : .
35~
;
in accordance with a predetermlned program sequence in such a manner that discontinuities of the drive motion of the magnetic head are avoided.
More particularly, there is provided:
A servo system for a disk drive having a magnetic disk recorded with data signals and with interleaved servo signals, a magnetic head for sensing ~aid data and servo signals and a motor for driving said head to access data tracks on said disk comprising:
a position detector for providing first position error signals in response to sensed servo signals;
a track increment generator for generating second posi-tion error signals under control of clock and address signals;
a summing circuit coupled to said position detector and to said track increment generator for sumning said first and second error signals and for producing a combined position error ~ignal; and .
: a compensator coupled to said summing circuit and to ~:
said track increment generator for providing a compensating signal to said drive motor o~ ~aid accessing head.
The invention ~ill be describ~d in det~l by ~e~ns of illu~trations, Fig. 1 shows the total ~rrangement of a device for regulating the ms~netic head po~ition o~ a msgnetic di~k ~tor~e during tr&ck selection ~cd trsck ~ollowing in the form of ~ block dia~3ram, Fig. 2 shows the recording patter~ o~ servo mark~ recorded in the ser~o ~:
sector of a ~etic di~k, Fig. 3 ~hows the cour~e of the digital output 0ignQl of the ~/d converter illustrated in FiB. 19 ~hich i3 produced by poBitio~ ;
errors Or the ~ervo and dats nQ8~etic head, Fi~. 4 ~ho~rs the cour~e o~ the diglt~l 13i~1R15 o:f' a track incr~ent gener3tor, which ~re introduceB into the rezulQting circuit ~or the track followlng o~ the ma6~etic head a~d ~hich ~re summed to the digit~l position error ~ignQl~ Or the tr~c~ follower ro6ulsting circuit, ~ , :
-7a-3~3 Fi~s . 5B to 5d show the diagrams of the position error, position control, position hnd compensating voltages of the ~ervo ~nd datA msgnetic head during an access ~otion in ~unctional d0pendence of the time -- expressed bJ the number Or s~mpled ~ervo sectors, Fig. 6 shows the switching elements of a track incr~ment generator in the ~or~ of a block di~4rAm, Fig. 7 sbows another e~bodiment of ~ device for re6ulating the ~gnetic head position during trsck selection and trsck rollo~ing Or the netic hesd of a ~sgnetic disk stor~ge in the ~orm of a block .--' '; ' ~,' ' .",.' . ' . ,: , .
The magnetic disk 1 of a magnetic disk storage sho~m in Fie. 1, which is rotatably supported on the hub 2, is rotated clockwise b~ a drive motor not shown. The magnetic head 5 fixed to a magnetic head carrier 4 of a magnetic head carrier arm 12 can be optionally positioned in a radial direct-ion to concentric recording tracks of the magnetic disk 1 by means of a drive motor 13. The surface of the magnetic disk 1 is divided into a random number of data sectors D and servo sectors S in which data and servo signals, respectively, are recorded in the associated angular areas. On the outer circumference o~ the magnetic disk 1 clock signals, which can be sampled by a fixed clock magnetic head 6, are recorded in a clock track. The clock signals sampled by the clock magnetic head 6 are converted into time control signals by means of the switching device 70 Said time control signals are fed to an input of the data input/output 8 via line 25. The magnetic clock generation can be replaced by optical clock generation o~ a known kind. The time control signals trans~erred by line 25 determine the time control signals, by means of which during the "D sector times" the inputloutput signals transferred between the magnetic head 5 and the data inputtoutput 8 via line 26 are fed from and to the output line 9, ~he switching device 7 also produces time control signals which on the output line 10 during the "S sector times" control the sampling o~ the servo sectors S on the magnetic disk 1. From the output line 11 of the switchin~ device 7 clock signals for the generation of position control signals are derived ~which are used to control the drive motor 13 o~ the mag~etic head carrier arm 12.
The drive motor 13 o~ the magnetic head carrier arm 12 is connected to track follower rejgulating circuit to which, via the line 27, as the servo sectors S pass magnetic head 5, servo signals sampled on servo marks are applied. ~y means of a position detector 15 track deviations of the magnetic head 5 from the center of a data track are detected and converted into corresponding position error signals. Via an analogue-to-digital converter these po~ition error signals are converted into digital position error signals Pl indicating a position error and which are ~ed to a first input o~
a summing circuit 17. ~o a second input of the summing circuit 17 digital position signals P2 are applied which are eenerated b~ the track increment GE 9'77 011 3~
generator 21. Generation of the position control si~nals P2 is effected under the control of clock signals which are derived from the switching device 7 and are fed to a first input line 22 of the track increment generator 21.
Via a second input line 23, the track increment generator 21 receives address signals determining a ~elected recording track of the magnetic disk 1 to which the magnetic head 5 is po~itionable in a free QCC9SS motion. By the summing circuit 17 the digital position error signals P1 and the digital posit-ion control signals P2 are summed to position control signal6 P which are applied to a first input of the compensator 18. To a second input 20 of the compensator 18 "S sector time" control signals are applied~ by means of which K signals are generated each time a servo sector passes the ma~netic head 5. Said K signals represent digital compensation values of the position control signals P. ~hese compensation signals remain constant for the time during which the subse~uent data sector D passes the magnetic head. The digitalcompensation signals K derived from the output of the compensator 18 are convert-ed by a digital-to-analogue converter 19 into corresponding analogue signals andare transferred from line 24, ViQ a power amplifier 14, to the drive motor 13 of the magnetic head carrier arm 12. During the access time, said magnetic head carrier arm causes the magnetic head 5 to ~e positioned in a motional pathg the positions o~ which, as shown in Fig. 5, are time-depend-ent, according to the number of servo sectors sampled by the ma~netic head 5. The path/time diaOE am determined by the track increment generator 21 is divided into an A time, in which ~n acceleration path is covered, into a~subsequent B time, in which a constant speecL path is covered, and into a C time in which a deceleration path i8 co~ered. ~
i The servo marks recorded on the ma~netic disk 1 in the servo sectors S may be seen from Fig. ?~ In a servo sector S~ limited on both sides by data sectors D, magnetic servo marks of opposite polarity and opposite phase position, respectively, are recorded. Two different servo marks each of`
opposite polarity, which are recorded on both sides of a track line at the same track width W2, form a servo track of the track width W1. A data track in the data tracks D has the track width W2. It ~orms in each case the continuation of one track half of the track halves of a servo track of the trackwidth W1 recorded in servo sector S. Each data track is limited by two track lines E between which the center line 0 of a data track extends. The servo ::: : :. ~ : .
:~
3~
and data magnetic head 5~ ~ixed to the magnetic head carrier 12 option-ally positiona~le by means of the drive motor 13~ has the track width W2.
In the normal, error-free sampling position the magnetic head 5 is excactly over the center line of a servo track and the center line 0 o~ a data track, respecti~ely. Deviations o~ the magnetic head position ~rom this center position either in the region o~ the positive or in the region of the neeative polarity o~ the servo marks lead to position error signals. ~he position error signals continue to indicate track deviations o~ the magnetic head, i~ thelatter at maximum track deviation ~rom the normal position is deMected either into the positive marking range or into the negative marking range of the ser~o marks on both sides o~ a track line 0, as illustrated by broken lines.
:
~he course of a position error voltage P1 ma~ be seen ~rom the illustration in accordance with Fig. 3. If the track position o~ the magnetic head 5 between the two track lines E1 and E2 limiting a data track changes, a linearl~ descending course of the position error ~oltage occurs, which is a ~unction o~ the track position and whose signal value is 0 when the magnetic head is accurately centered over the center line 0. In this normal position the magnetic head 5 samples equall~ large track halves of the positive and the negative servo marks, the signal components of which cancel each other upon sampling. In the position in which the magnetic head 5 exclusively records the signal component of the positive polarity of the servo marks, the position error signal P1 re~ches its positive maximum value. ~n the opposite marginal position in which the magnetic head 5 exclusively records the signal i component of the negative polarity o~ the servo marks, the position error ~ signal P1 reaches its negative maximum value. ~he compensator o~ a track ; ~ollower regulating circuit operates in ~uch a manner that upon the occurrence of a position error signal P1 in the regulating circuit it generates a compensation signal which decreases the position error, thus stabilizing the position o~ the magnet;c head over the center line 0 o~ the recording track.
Fig. 4 shows the path/time diagram o~ the magnetic head 5 which is ~ollowed as a result of an access motion o~ the magnetic head to the selected record-ing track of the track address n25 of the magnetic disk 1. During the time 3~
in which 6 servo sectors pass the magnetic head 5, the latter is accelerated during the A time. In this period of time the magnetic head 5 crosses six recording tracks. The subsequent B time, in which the magnetic head 5 is moved at a constant speed, has a duration corresponding to the sampling time of four servo sections, i.e., the period lasts up to the sampling of the tanth servo sector. During this period of time, three recording tracks are crossed during the time in which one servo sector passes the magnetic head. At the end o~ this speed period the magnetic head reaches the track address nl8. ~his is followed b~ the C time in which the access motion of the ma~netic head 5 is de-celerated during the sampling time of six servo sectors. ~t the end of the de-celeration path9 in the course o~ which the magnetic head 5 crosses seven record-ing tracks, the head reaches the track address n25 preselected b~ addressing. Inthis track position the access motion of the magnetic head ends, so that the position control signals P2 generated on the output of the track increment generator 21 of Fig. 1 and controlling the access motion are interrupted.
As a result, the track selection regulating circuit is switched to regulate the position o~ the magnetic head 5 ~or track following over the center o~
the recording track n25.
The signal/time diagram illustrated in Fig. 5a shows the dependence of the digital position signals P generated on the output of the summing circuit 17 which is shown in Fig. 1. ~y means o~ the compensQtor 18, digital K signals corresponding to the position signals P are generated. ~y means o~ the d/a converter, said K signals are converted into analogue signals feeding the drive motor 13. The digital position signal P shown in Fig. 5a is obtained by summing in the summing circuit 17 the digital position error signal P1 of Fig. 5c to the digital position control signal P2 of Fig. 5d. Upon crossing the recording tracXs n1 to n25, the magnetic head 5 is accelerated in the acceleration path during the time in which the servo sectors S1 to S6 pass the magnetic head. For this purpose, the track increment generator 21 generates position control signals P2 in accordance with a given program, which in the direction of movement of the access path have constant digital values for the duration of one or several track crossings.
This determines the course o~ the digltal position signals P. By means of the compensator ?8, a corresponding digital compensation signal K, illustrat-ed in Fig. 5b, is generated. Said signal drives the magnetic head in the `', ~.. .. : : .. ,, ,, : .
h 3~
direction o~ the target address of the recording track n25, since the track follower regulating circuit because o~ detuning as a result o~ the added component of the position control signal P2 cannot ef~ect a zero compensation for stabili~ing the position o~ the magnetic head in the center of the re-cording track nl. ~he po~ition control signal~ P2 are dimensioned in accord-ance with a given program in such a manner that the magnetic head 5 passes the acceleration path o~ Fig. 4 ~or the duration of the A time until the track address n6 is reached.
As the magnetic head enters the constant speed phase of the B time, position error signals P1 are trans:~erred to the su~ming circuit 17 only i~ during the time in which a data sector D passes the magnetic head, the latter does not have to cross all -the recording tracks. At the end of the B time, the magnetic head has reached the track address n18.
In the subsequent deceleration phase, position control signals P2 having an opposite polarity to the position control signals P2 active in the acce~
leration phase are derived from track increment generator 21. ~hese control signals generate negative acceleration forces, so that the magnetic head 5 in the C time ~ollows the deceleration path o~ Fig 4 until the selected track addresses n25 ha~e been reached. During the C time the position signal P
generates a compensation signal K which stops the magnetic head.
At the end of the A time and at the end of the C time modi~ication signals M
are trans~erred in each case from an output o~ the track increment generator 21 to an input o~ the compensator 18, so that the compensation signal K stor-ed in the compensator is changed in such a manner that the magnetic head 5 is transferred to the subsequent motional state without overshooting.
~y means of the compensator i8, compensation signals K are computed from the position signals P. These compen~ation signals are obtained in accordance with the ~ollowing algorithm:
K(T) = const. P(T) + a1 P(T-1) + a2 P(T-2) + .... 3 - b1 K(T-1) + b2 K(T-2) . ..~
. . , ;
.. :, : . : .: , . ..
3~
where P(T) and K(T) represent position and compensation signals at the sampling times T and at the preceding sampling points (T-1), (T-2) ..., respectively.
The constants al ... an and b1 ..0 bn are a function of the characteristics of the regulating system, such as mass, threshold frequency, frictional losses, and the electrical time constants of the energizing voltage. They determine the transfer function o~ a linear controlled system7 as describ-ed in detail in chapter 7.2., pp. 147 and 148, of the book "Sampled-Data Control System" by J.R. Ragazzini et al, McGraw-Hill Book Comp., Inc.~ 1958.
Fig. 6 shows the individual switching elements o~ the track increment generat-or 21 illustrated in Fig. 1. Said generator compri3es a control device 31, to on0 input line 22 o~ which clock signals ~rom the output line 11 of the switch-ing device 7 o~ Fie. 1 are applied. To the aecond input line 23 addres6 signalsare applied, indicating to which recording track on the magnetic disk 1 the magnetic head 5 is to be positioned. Aæ a function of the clock and address signals applied via the input lines 22 and 23 the control device 31 generates control signals which at the different A, B, and C times are trans~erred to a read-only memory 28, 29, and 30 via the different output lines of the control device. Said read-only memories contain storage values for the track incre-ments, which can be sampled in accordance with a particular progr~m. For generating the digital P2 position control signals, the track increments are transferred to an output line in a predetermined time sequence. Via another output line of the track increment generator 21~ the modi~ication signals M
generated at the end of the A time ana the C time are transferred to an input o~the compens~tor 18. The A, B, and C control 3ignals are made available as a function o~ the entered address in accordance with a particular program controlling the acceleration, the constant speed~ and the deceIeration of the magnetic head 5. Thus, it can be assumed, ~or exampleg that deviating from the addressing o~ the magnetic head 5 to the recording track n25, in accordance with the embodiment described by means of the illustration of Figs. ~ and 5, the magnetic head 5 is to be addressed to the recording track n28. In this case it is merely necessary to extend the B time of the constant speed range by one sector interval with the aid of the control device 31. In accordance with the given prerequisites, it is assumed that the position control signals P2 derived from the read-only memory 33 effect a speed of the magnetic head 5, which equals three track crossings per sector interval. Extensions of the B
time by one sector interval each thus lead to recording tracks n28, n31, : :: , - ,: . , : :: :~ ;:.: :": : : . :, :;
,; :
k3.5~
n34 ... or, in the case of reductions in the B time by one sector interval, to recording tracks n22~ n18~ nl5 to be optionally addressed. The inter-mediate values of said address se~uence3 e.g., o~ the recording tracks 26 and 27, can be set at equal track increment values sampled on the read-only memory 29, if the acceleration of the A time or the deceleration of the C time are extended by one or two sector intervals. If the recording track n26 is selected, it can be assumed, ~or example, that the magnetic head 5 reaches the necessary access speed o~ three track crossings per sector interval in the constant speed range after seven rather than six sector intervals. For this purpose it is necessary that the A time of the acceleration phase comprises seven sector intervals, and that the position control values sampled on the re&d-only memory 28 are changed. The magnetic head can be correspondingly positioned to the selected recording track n27 when the A time comprises seven sector intervals and the C time eight sector intervals. The position control values sampled on the read~only memory 30 must also be changed for this purpose9 so that the magnetic head 5 having a positioning speed of three track crossings per sector interval in the constant speed range reaches the zero value in the extended B time. The sampling of the track increment ~alues necessary for a predetermined track addressing of the magnetic head and the dimensioning of the A, B~ and C times necessary for this purpose is ensured by means of the address value entered via the line 23.
.
Fig. 7 shows a further alternative for generating the position control sign~ls which ~or the purpose~of performing a track access motion of a magnetic head are introduced into the track follower regulating circuit of the magnetic head. The device is operated in such a manner that the digital position ; -control signals P2 derived from the output o~ the track increment generator 21' are added by the adder 33 for each track crossing and are fed to an input of the summing circuit 32. From an output of the compensator 1~' and an output of the a/d converter 16' signals H and L are transferred to the inputs of the track change detector 3~ via one line each. The output signal F of the track change detector 34, whose value is proportional to the number of record-ing tracks crossed by the magnetic head 5, is transferred to a second input o~
the summing circuit 32.
': '' ' `, ' ` : '' ~ ' ': . ':' The position control and track change signals applied to both inputs of the su~ming circuit 32 have opposite signs, so that on the output of the summing circuit 32 the difference between the two input signals is entered in the form of the control si~nal G into the track follower regulating circuit, in order to be summed with the position error signal P1 in the summing circuit 17'. The function of the position detector 15' connected to the line 27' and of the d/a converter connected to the line 24' corresponds to the description of the circuit elements 15 and 19 according to Fig. 1.
Signals P1, P2, P, M, K9 F, G, H, and L described by means of Figs. 1 and 7 are multi-position, preferably binary-coded, digitaI sienals. ~y means of the device described with the aid of Fig. 7, the direction o~ the access motion of the magnetic head can be detected in the case of an address operation mode, so that erroneous positioning of the magnetic head is avoided.
; ~
. ,, : : . : ". . . ~ : .
:' ' ,: ~,-,,: .,: "
.
Claims (7)
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A servo system for a disk drive having a magnetic disk recorded with data signals and with interleaved servo signals, a magnetic head for sensing said data and servo signals and a motor for driving said head to access data tracks on said disk comprising:
a position detector for providing first position error signals in response to sensed servo signals;
a track increment generator for generating second posi-tion error signals under control of clock and address signals;
a summing circuit coupled to said position detector and to said track increment generator for summing said first and second error signals and for producing a combined position error signal; and a compensator coupled to said summing circuit and to said track increment generator for providing a compensating signal to said drive motor of said accessing head.
a position detector for providing first position error signals in response to sensed servo signals;
a track increment generator for generating second posi-tion error signals under control of clock and address signals;
a summing circuit coupled to said position detector and to said track increment generator for summing said first and second error signals and for producing a combined position error signal; and a compensator coupled to said summing circuit and to said track increment generator for providing a compensating signal to said drive motor of said accessing head.
2. A servo system as in claim 1, wherein said track increment generator includes a plurality of read-only memories that are sampled during respective phases of said track access mode of said magnetic head.
3. A servo system as in claim 1, including a clock control unit for providing clock signals for generating position control signals to control the drive motor for said magnetic head.
4. A servo system as in claim 1, including an analog to digital converter coupled to the output of said position detector for providing digital position error signals to said summing circuit.
5. A servo system as in claim 1, including a digital to analog converter coupled to the output of said compensator for providing an analog compensating signal to said head drive motor.
6. A servo system as in claim 1, including a track crossing detector coupled to the output of said compensator, an adder coupled to the output of said track increment generator, and a second summing circuit coupled to the output circuits of said track crossing detector and said adder, the output of said second summing circuit being coupled to an input circuit of said first recited summing circuit.
7. A servo system as in claim 6, wherein said compen-sator, said track crossing detector and said summing circuits are in a closed loop.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19772759066 DE2759066A1 (en) | 1977-12-30 | 1977-12-30 | DEVICE FOR REGULATING THE MAGNETIC HEAD POSITION DURING THE TRACK SELECTION AND THE TRACK SEQUENCE OF THE MAGNETIC HEAD OF A MAGNETIC DISC MEMORY |
| DE27590665 | 1977-12-30 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1110359A true CA1110359A (en) | 1981-10-06 |
Family
ID=6027817
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA314,763A Expired CA1110359A (en) | 1977-12-30 | 1978-10-30 | Servo system for track accessing and track following in a disk drive |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US4217612A (en) |
| JP (1) | JPS5495214A (en) |
| CA (1) | CA1110359A (en) |
| DE (1) | DE2759066A1 (en) |
| FR (1) | FR2413746A1 (en) |
| GB (1) | GB2011654A (en) |
| IT (1) | IT1202807B (en) |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3185972A (en) * | 1961-10-10 | 1965-05-25 | Ibm | Transducer positioning system utilizing record with interspersed data and positioning information |
| FR83053E (en) * | 1961-10-10 | 1964-06-05 | Ibm | Data storage device |
| US3691543A (en) * | 1971-02-08 | 1972-09-12 | Ibm | Positioning system including servo track configuration and associated demodulator |
| US3737883A (en) * | 1971-08-18 | 1973-06-05 | Information Storage Systems | Linear positioning apparatus for memory disc pack drive mechanisms |
| US3881184A (en) * | 1974-05-28 | 1975-04-29 | Ibm | Adaptive digital servo system |
| US3924268A (en) * | 1974-08-05 | 1975-12-02 | Ibm | High density track follower control system for magnetic disk file |
| US4048660A (en) * | 1975-12-23 | 1977-09-13 | International Business Machines Corporation | Record track following and seeking |
| DE2558359A1 (en) * | 1975-12-23 | 1977-07-07 | Ibm Deutschland | ADJUSTING DEVICE FOR THE ACCESS ARM OF THE MAGNETIC HEAD OF A MAGNETIC DISK MEMORY |
| US4135217A (en) * | 1976-11-02 | 1979-01-16 | Xerox Corporation | Utilization of stored run-out information in a track following servo system |
-
1977
- 1977-12-30 DE DE19772759066 patent/DE2759066A1/en not_active Withdrawn
-
1978
- 1978-10-30 CA CA314,763A patent/CA1110359A/en not_active Expired
- 1978-11-27 US US05/963,701 patent/US4217612A/en not_active Expired - Lifetime
- 1978-11-30 FR FR7834438A patent/FR2413746A1/en not_active Withdrawn
- 1978-12-01 JP JP14798478A patent/JPS5495214A/en active Pending
- 1978-12-12 IT IT30726/78A patent/IT1202807B/en active
- 1978-12-20 GB GB7849278A patent/GB2011654A/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| FR2413746A1 (en) | 1979-07-27 |
| US4217612A (en) | 1980-08-12 |
| DE2759066A1 (en) | 1979-07-12 |
| GB2011654B (en) | |
| JPS5495214A (en) | 1979-07-27 |
| IT7830726A0 (en) | 1978-12-12 |
| IT1202807B (en) | 1989-02-09 |
| GB2011654A (en) | 1979-07-11 |
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