CA1109558A - Data storage apparatus - Google Patents
Data storage apparatusInfo
- Publication number
- CA1109558A CA1109558A CA290,791A CA290791A CA1109558A CA 1109558 A CA1109558 A CA 1109558A CA 290791 A CA290791 A CA 290791A CA 1109558 A CA1109558 A CA 1109558A
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- CA
- Canada
- Prior art keywords
- signal
- servo
- data
- linear
- circuit
- 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
-
- 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
- G11B5/58—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 for the purpose of maintaining alignment of the head relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
- G11B5/596—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 for the purpose of maintaining alignment of the head relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for track following on disks
- G11B5/59688—Servo signal format patterns or signal processing thereof, e.g. dual, tri, quad, burst signal patterns
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- Engineering & Computer Science (AREA)
- Signal Processing (AREA)
- Moving Of The Head To Find And Align With The Track (AREA)
- Control Of Position Or Direction (AREA)
- Moving Of Head For Track Selection And Changing (AREA)
Abstract
ABSTRACT
Data storage apparatus of the type employing a stack of rotatable storage disks accessible by a plurality of data heads ganged for movement over the data surfaces. The position of a data head during track following operations over a selected data surface being controlled by a hybrid servo signal consisting of low frequency components of position information signals derived from servo sectors around the data track being followed added to which are high frequency components of continuous position information signals derived either from a dedicated servo surface forming part of the stack or from an external position transducer. The continuous position information being provided by a servo trans-ducer, which is also ganged to the data heads, in the form of two cyclic quadrature signals (90° out of phase with each other) each having portions which are linear and co-extensive over the whole range of head displacement. The apparatus including servo control circuits for detecting during data track following position (caused for example by temperature variations or mechanical vibrations) beyond the linear region of the correspond-ing one of the two quadrature signals supplying the high frequency components and, upon such detection, switching to an adjacent linear portion of the other signal, or the inverse of the other signal, to either of which has been added an appropriate d.c. offset so that the linear portion of this other signal becomes an effective extension of the linear portion of the continuous servo signal corresponding to the data track being followed. By this means the a.c. gain of the servo circuits is maintained constant thereby improving the servo loop performance.
Data storage apparatus of the type employing a stack of rotatable storage disks accessible by a plurality of data heads ganged for movement over the data surfaces. The position of a data head during track following operations over a selected data surface being controlled by a hybrid servo signal consisting of low frequency components of position information signals derived from servo sectors around the data track being followed added to which are high frequency components of continuous position information signals derived either from a dedicated servo surface forming part of the stack or from an external position transducer. The continuous position information being provided by a servo trans-ducer, which is also ganged to the data heads, in the form of two cyclic quadrature signals (90° out of phase with each other) each having portions which are linear and co-extensive over the whole range of head displacement. The apparatus including servo control circuits for detecting during data track following position (caused for example by temperature variations or mechanical vibrations) beyond the linear region of the correspond-ing one of the two quadrature signals supplying the high frequency components and, upon such detection, switching to an adjacent linear portion of the other signal, or the inverse of the other signal, to either of which has been added an appropriate d.c. offset so that the linear portion of this other signal becomes an effective extension of the linear portion of the continuous servo signal corresponding to the data track being followed. By this means the a.c. gain of the servo circuits is maintained constant thereby improving the servo loop performance.
Description
S~i8 1 The inventi,on relates to data storage apparatus and is a modification of or improYemen-t in the invention described and claimed in U.S.. Patent No, 4,072~990~ issued February 7, 1978 to W.J~P. Case~ et al~ and entitled Servo Positioning System for Data Storage Apparatus.
In the aforesaid U.S. patent, data storage apparatus is described and claimed comprising a stack of recording disks mounted for rotation on a drive spindle, a plurality of recording and playback data heads each associated with a corresponding one of a plurality of data surfaces on the disks for performing transducing operations on data tracks thereon, each data track consisting of data sectors for recording and/or playback of data thereon by a data head alternating with servo sectors containing pre-recorded data track position information for that track readable by the same data head, a ; servo head ganged for movement with the data heads and associated with servo tracks pre-recorded on a servo surface on one of the disks, the servo tracks being distinct from the servo sectors on the data tracks and providing continuous data track position information readable by the servo head, and servo control circuits operable during track access operations in response to position information signals from the servo surface alone to control movement of the data heads across tracks and operable during track following operations in response to a hybrid signal composed of signals derived from the servo~sectors on the data surface including the track being followea and high frequency components of position lnformation signals derived from the servo surfaca.
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Although the s~stem described in the parent speci~ication represents a marked improvement over previous systems, it too suffers ~rom a disadvantage caused by the cyclic nature and hence the non-linearity of the position information signals, or position error signals (PES) as they are often called, used to control the servo. The problem exists as a result of disturbances which effect the mechanical stability of the apparatus and can lead to the servo head being considerably displaced from its true on-track position over the associated servo track, despite the data head being accurately positioned over the data track being followed.
Under these circumstances it is possible for the servo head to be so far off track that the posltion information or position error signals being supplied by the servo head are from the non-linear part of the signal. That is, they do not exhibit a linear relationship with respe t to displacement Erom the servo on-track position. Accordingly since the high ~requency components of this signal are required to form the hybrid servo signal used during track following operations, the gain of the servo circuits àt high frequencies varies with changing displacement from the servo on-track position~
Since these servo head displacements are caused largely by external disturbances such as temperature variations or shocks and vibrations as well as internal influencing factors such as eccentricity and tilt o~ disks on the disk spindle they are largely uncontrollable. The continuous and unpred-ictable changing in gain of the UK9-76~013 -3 ~' . .
.- .: ,. - - ' : :-: .. ' , . , . - .:
s~
servo circui.ts.can lead to loop instabilit~ and~ox increased head settle time ~oth o~ wh~ch are undesirable features.
According to the in~ention therefore, data storage apparatus compxises a stack of recording disks mounted for rotation on a drive spindle r a plurality of recording and playback heads each associated with a corresponding one of a plurality of data surfaces on the disks for performing transducing operations in data tracks thereon, each data track consisting of da~a sectors for recording and/or play-back of data thereon by a data head alternating with servo sectors containing pre recorded data track position inform--; atiOn for that track readable by the same data head, a servo transducer ganged for movement with the data heads and associated with servo means providing continuous cyclic data track position information having substantially linear portions each indicating by its magnitude and polarity the degree and direction of off-set of the servo transducer from the end of an increment of movement equal to the distance between successive data tracks, modifying means for receiving said continuous data track position information signals supplied thereto and operable to supply modified position information signals at its output which are substantially linear with respect to displacement from one to another servo track over their entire range, and servo control circuits operable during track access operations in response to position information signals from the servo surfaces alone to control movement of the data heads across tracks and operable during track following operations in response : ' ' i.' ' ', ~ . ,, . .:
5~
to a hybrid si~nal composed of si~nals derived from the servo sectors on the data surface including the track being followed and high frequency components of modified signals supplied at the output to the modifying means.
In order that the invention may be fully understood preferred embodiments will now be described with reference to the accompanying drawings.
In the drawings:~
Figure 1 shows in block form, data storage apparatus as described and claimed in the parent application;
Figure 2 shows normal and quadrature position error signals and logic waveforms derived therefrom;
Figure 3 shows a circuit according to one embodiment of the invention for effectively extending the linear region of the normal signal shown in Figure 2;
Figure 4 shows a circuit according to another embodiment of the invention for providing the hybrid position error signal required during track following operations and also for effectively extending the linear region of the normal signal.
~ Figure 1 shows in block form data storage apparatus descrlbed and claimed in the parent specification. In the figure, a stack of magnetic recording disks 1 are mounted for rotation on a central spindle 2. Pre~recorded servo tracks 3 are provided over one surface of one of the disks and are read by an associated servo head 4. Since this sur~aoe contains onl~ servo information it is referred to as a dedicated servo surface. The dedicated servo surface contains continuous information regarding the posi-.
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tion of data tracks on th~ remainin~ sur~ace o~ the disks which are accessed by a number o~ data recording and playback heads 5, one being provided for each of the remaining disk surfaces. The data heads 5 and the servo head 4 are all ~anged together for movement to and fro over the disk surface by actuator mechanism 6.
During track access operations, the continuous position error signals derived by the servo head 4 are passed through pre-amplifier 9 and AGC amplifier 10 to servo control circuit ll which also receives the address and polarity of the destin-ation track for each track access operation ~rom an external ; Control system 12. From this information the servo circuits produce the necessary drive currents for the actuator mech-anism 6 to coarsely position the data heads over the desired destination track.
During track following operations the fine po~ition error signals required to maintain the data head accurately on-track are derived from servo information pre~recorded in sectors around the data track itself. Data and servo information read by a selected data head 5 is passed through pre-amplifier 7 and AGC amplifier 8 to servo control circuit ll. Here the d.c. and low frequency components of the sectored servo in~ormation from the data head is combined in the servo control circuits ll with high frequency inform~
ation derived from the dedicated servo surface. The resulting hybrid signal of wide bandwidth is then used to produce suitable drive currents to control the actuator 6 in closed loop mode to hold the data head -track following the selected data track~ Details of construction and operation of the circuits shown in U ~ 76-013 - 6 -s~
1 Figure 1 are fully described in the parent ~pecification.
The position error signals derived by the servo head 4 reading the pre-recorded servo information 3 on the dedicated servo surface are shown in Figure 2. Two types of servo tracks recorded on the disk yive rise to these two position information signals which are called normal (waveform N) and quadrature or displaced (waveform (~). The production of these signals is fully described in U.S. Patent No. 4,068~269, issued January 10, 1978 which is referred to in the above-noted U.S. Patent No.
4, 072, 990. As the servo head accesses the disk, the normal and quadrature signals change in a cyclic manner passing through the waveform centre line which in this case is zero volts as the servo head crosses the associated normal or quadrature servo tracks on the disk and reaches a maximum voltage mid-way between tracks. The zero crossings, or on-track positions 0,1,2,..., of the normal signal (waveform N) are p~e-recorded to coincide with corresponding data head on-track positions.
AS has been previously explained however disturbances to the apparatus often upset the mechanical stability and prevent ; this the servo head on-track position from coinciding with the data on-track position.
The nature of the particular servo patterns recorded on the dedicated disk surface is such that the resulting position information signals derived from a single track are substant-ially linear over a range o~ ~1/4 of a track width about the on-track position. Such a position is known for example as Pl on Figure 2. Thus, provided the displacement of the servo head during data track following ,.. ,~
~ ~ ,t ,, operations does not exceed ~ of a track width the vol~age generated per uni~ displacement is constant and the gain of the servo control cîrcuits is also constant at the desired value. If, however, the displaoement is such that the ser~o head becomes off-set from its on-track position P1 by more than ~ ~of a track width so that during track following operations it lies at position P2'for example, f t'hen changes in position error voltage will no longer be linear with respect to changes of position about P2 and the servo position loop performance wlll be drastically degraded.
The problem is solved in a manner now to be described and involves using the quadrature position erroC signal not normally used during track following operation to effec-tively extend the linear region of the normal error signal beyond the +% track range thereby maintaining `
the a.c. gain of the servo circuits oonstant over the entire ~~ displacement range which may occur during track followi,~g ' . , . . :
operations.
The particular servo pattern employed has the advantage that the linear- portion of the quadrature waveform Q
commences when the linear portion of'the normal waveform .
N ends and vice versa. Thus, by applying a d.c. Q~f set to the quadra~ure position error signal w;th or without inversion of the signal, as will b~ seen later, the linear region of t'he normal signal can be extended as shown for example by the dotted waveform Q' in Figure 2. Now with the head displaced to position P2 its po'sition error voltage P2i is still linear wIth respect to head dispIacemRnt and the a.c.
gain of the circuit is constant.
UK9-76-~13 ' - ~ -.
55~
Th~ Qnd of ~he ltneqr reglon of ~ho nonmal ~rror ~Ignal Ts roadlly d~termined by dotectlng whon ~ho magnTtuda of th~ normal error slqnal N oxto~ds ~ha~ of tho quadraturo crror slgnal Q. ~hen thts is ~h~ case, the quadrature ~rror slgn~l plus ~ d.c. off~ot 15 u~d to of~ectlYely oxeend the ltnoar r~glon of the nor~a1 ~rror 9 I gfla I ~ .
Tho polarlty of th~ roqulred quadrature and of~-s~t volt-~ge 1~ dotormlned by th~ polarlty o~ the nor~al error ~Ignal to be extended and the dlrectlon of dlsplacement ~Ithcr l~ft ar rlgh~ fro~ the on-track posi~lon. Thus, re~rrlng to Flgurs 2 ~h1~h shows posltion Pl as eh~
~n-track po~ltlon for an ev~n-nu~be~ed track 2 ~he follow-lng truth tabl~ gl~es tho ~our poss1bio oandittons r~qutred to oxtond tho lln~ar reg10n o~ rhe normal s~qn~1. The roqutred polar1ty of quadra~ure and d.c. of~-se~ is atven In oach caso toga~hsr ~Ith the loglc 1eYq1$ needod to control 3wl ~ch1ng fro~ nor~al llnoar reglon to s~tanded llnear ragion.
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U~9-76-o 1 3 _ ~ _ ,.
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TRACK DIRECTION OF LOGIC LEVELS
POLARITY DI$RLACEMENT SIGNAL REQUI~ED N O Q.~N Q+N
. . ..
ODD LEFT Q + OFFSET 1 0 ODD RIGHT ~Q - OFFSET 0 1 0 ~ EVEN LEFT Q ~ OFFSET 1 1 0 : EVEN RIGHT -Q + OFFSET 1 0 _' .
~ . _. .__ Thus, in the event of a left hand displacement of a head in excess of a quarter of a track from track following an odd-numbered track the signal required to extend the normal linear region is the quadrature signal Q plus a d.c. oEf-set of approp-riate magnitude. Inspection of Figure 2 shows that the mag-nitude of the d.c. off-set required is twice the voltage V
(Figure 2) of the quadrature and normal signals when they are of equal magnitude. For a right hand displacement in excess of a quarter of a track from an odd polarity track, the signal required is the inverted quadrature signal quadrature signal -Q plus a negative d.c. off-set. Similarly a left hand displacement from an even-numbered track requirés the quadrature signa~ Q plus a negative d.c. off-set and a right hand displacement requires the inverted quadrature signal -Q plus~a positive d.c. o~f-set.
~ The loyic levels used to indicate head displacements in excess o~ one quarter of a track in either direction .
~rom the on-traak positions of odd or even numbered tracks are identi~ied in the truth table and the waveforms showing the logic levels derived from the position error slgnals UK9~76~013 -10-1~ .
. ' . . ', ~ . .
9,Si5i~
Q and N are shown and identifiea in Figure 2. The generation of these logic levels ~rom the position error signals is achieved by standard comparison circuits which will not be described here~
By exclusively OR~ing the (Q~N) signal with (Q~N) a signal A having up levels corresponding to the non-linear portions of the normal error signal is produced. Also the required polarity of the quadrature signal is given by exclusively OR-ing the (N>O) signal with the polarity signal from the control system which is at its up level for track accesses to even-numbered tracks and at its down level for accesses to odd numbered tracks. The EVEN signal as it is called lS quite conventionally supplied from the control system 12 at the start of an access operation as previously mentioned.
A circuit for switching from the normal linear region to ex-~ended linear region when displacement in excess of the normal linear region occurs is shown in Figure 3. The circuit consists of a standard three-channel operational amplifier 13, the appropriate channels being selected by a positive level on one of three corresponding channel select lines 14, 15 and 16. The normal position error signal N
is applied to input terminal 17, and thence to the positive input of ~hannel 1 of the amplifier 13. The quadrature position error signal Q is applied at input 18, and then to the positive input of channel 2 through resistor R and to the negative input of channel 3 through an identical resistor R. The of f -set voltage V~ equal to UK9~76~013 -11-, s~
twice the cross~over voltage of -the quadrature and normal signals, is applied as a positive voltage to input 19 if the track being followed is an odd-numbered track or as a negatlve voltage of the same magnitude if an even-numbered track is being ~ollowed. The polarity o~ the off-set voltage is switched under control of the EVEN signal from the control circuit 12 and since it is quite conventional is not shown or described. The off-set voltage is added to the signals applied to the positive input of channel 2 and the negative input of channel 3.
During operation, the normal error signal N, supplied to input 17, is transmitted to the output 20 by logic selection of channel 1 during the linear region of the normal Signal that is during the down-level of signal A (Figure 2).
At all other times the quadrature signal supplied to input 18 is transmitted to output 20 with positive or nega~ive d.c.
off-set voltage V by logic selection of channel 2, or inverted and transmitted to output 20 again with positive or negative off-set voltage V added by logic selection of channel 3.
Logic circuits consisting of XOR gates 21 and 22, AND
gates 23 and 24, and inverters 25 and 26 supplied with the appropriate logic signal levels perform the channel selection.
Accordingly the non-linear region of the normal signal is provided by applying the (Q-N)~ 0 signal to input 27 and the (Q+N)> to input 28 of XO~ 21, the output o~ which is at an up-level at all times except ~ 76-013 - 12 9S~i~
during the linear region of the normal signal N~ This signal, after inversion by inverter 25, is used therefore to select . channel 1 during the linear re~ion of the normal signal and to : enable AND gates 23 and 24 during the non-linear regions.
Further the track polarity signal (EVEN) from the control system is applied to input 29 and the s.ignal ~N~0) to input 30 of XOR 22 to select the appropriate channel 1 or 2 through AND~gates 23 and 24. Thus for an EVEN track for example with a left hand displacement (N~0) wili be negative and the output from XOR 22 will be at an up level selecting channel 2 via AND~gate 23. The output on line 20 will therefore be the linear region of the quadrature signal with a negative d.c.
off-set as shown in the above truth table. The other possible conditions can be easily verified with re~erence to the truth table and the waveforms shown in Figure 2 and further descrip-tion for an understanding of the invention i5 not necessary.
In order to avoid discontinuities in the extended linear region signal at the point where the quadrature plus off-set is switched in it is necessary that the off-set voltage is accurately equal to twice the voltage of the normal and : quadrature signals cross-over voltage as previously explained.
The o~f-set voltage can o~ course be produced to any desired accuracy but the magnitude of the cross-over voltage is not constant being subject to change in response to indeterminate circuit tolerances. Thus the circuit shown in Figure 2 suf~ers from the disadvantage that discontinuities can occur durlng cross-over from l.inear normal to extended linear quadrature. It is UK9-76-013 -13- ;
-, ne~essary to therefore incor~orate a ~eedback loop in the circuit which controls the servo signal gain control so as to normalize the cross-over voltage to half the d.c. off-set. The next embodiment to be described takes advantage of the a~c. coupling of the dedicated error signal inherent in the hybrid circuit described in the parent specification to provide a solution ~o this problem.
Figure 4 shows a circuit for generating the hybrid servo signal used for track following with the extended linear region feature. The selection o~ the polarity of the quadrature signal Q applied to terminal 31 is made in this case by a two channel operational amplifier 32 which acts as a switchable inver~erO The quadrature signal is passed unchanged through channel l selected by the up level of the ~N 0) signal applied to terminal 33 after inversion by inverter 34 and inverted via channel 2 selected directly by the up-level of the (N 0) signal. The normal position error signal N is supplied to input terminal 35 and the data head position error signals from the sectored servo ; 20 information associated with the track being followed is supplied to input terminal 36. Capacitors Cl and Resistors Rl connected as shown serve as high pass filters for the quadrature and normal signals from the dedicated surface and as a low pass filter for the sectored servo information from the data aurface. A hybrid quadrature position error signal is thereby produced at node Q and a hybrid normal position error signal is produced at node N. To incorporate the extended linear region function it is neces-sary to switch between these two signals without introducing 3Q a discontinuity. This is achieved by means of the switches UK9~7 ~ 13 -14-::. , : . , :
~ ~ \
. Sl and S2. ~s sho~n in the .Figuxe~ the. circuit is shown in the normal linear region mode with Sl closed and S2 open. During this time the hybrid normal signal is supplied direct to the positive input of the amplifier 39 and appears as a version N' on the output line 40. By virtue of the feedback path around amplifier 40, this buffered hybrid position error si~nal N' appearing during the normal linear region forces the voltage of the Q node which is connected to the negative input of operational amplifier 39 via closed switch Sl to be e~ual to the voltage of the N node. Now, when the normal position error signal reaches the limit of its linear region Sl opens and S2 closes under control of logic Signal applied to input 42. Under these circumstan~es the hybrid quadrature signal which is applied to the positive input of amplifier 41 appears as a buffered v~rsion Q' from its output 42.; By virtue of the ~eedback path around amp lifier 41 the buffered signal Q' now drives the N node which is connected to:the negative input of operational amplifier 41 via closed switch S2 to acquire the voltage of the Q node.
Since the voltage at Q was previously forced to be equal to the voltage at N the d~co off-set of re~uired magnitude is automatically provided with no discontinuity at the change over point. The extended linear region hybrid error signal now appears at both the N and Q nodes. The logic signal for closing Sl and for opening S2 is the linear region signal (-A) appearing from inverter 25 in Figure 3 which is applied to input 43. Thè connection is shown in dotted outline in Figure 3. Finally, it should be no~ed that the operation o~ the circuit shown in Figure 4 using the two channel amplifier 3I together with the two additianal , .
amplifiers 39 and 41 fulfill the conditions set out in the truth table above as well as providin~ the required frequency mix of the hybrid position error signal.
A problem well known in multiple switching circuits such as that shown in Figure 4 is an unwanted build up of cnarge on the capacitors as a result of multiple switching and accumulation of small off-set error voltages existing in the amplifiers and switches. As will be apparent to those familiar with such circuits this problem can readily be ~esolved in a conventional manner by applying hysteresis to the logic comparators which produce the switching signal on line 42 for switches Sl and S2.
Description of this well known technique is not necessary for the understanding of the invention and i5 not included in this specification.
In the embodiments described to illustrate the present invention~ the continuous position information is derived from servo tracks pre-recorded on a dedicated servo surface of the stack of disks. It should be understood that the invention is equally applicable where the data head position information is derived from other means for example an optical or inductive transducer cooperating with independent devices con~ainlng data track position informa-tion.
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U ~-76-OL3 -16-. ., -, . . .
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In the aforesaid U.S. patent, data storage apparatus is described and claimed comprising a stack of recording disks mounted for rotation on a drive spindle, a plurality of recording and playback data heads each associated with a corresponding one of a plurality of data surfaces on the disks for performing transducing operations on data tracks thereon, each data track consisting of data sectors for recording and/or playback of data thereon by a data head alternating with servo sectors containing pre-recorded data track position information for that track readable by the same data head, a ; servo head ganged for movement with the data heads and associated with servo tracks pre-recorded on a servo surface on one of the disks, the servo tracks being distinct from the servo sectors on the data tracks and providing continuous data track position information readable by the servo head, and servo control circuits operable during track access operations in response to position information signals from the servo surface alone to control movement of the data heads across tracks and operable during track following operations in response to a hybrid signal composed of signals derived from the servo~sectors on the data surface including the track being followea and high frequency components of position lnformation signals derived from the servo surfaca.
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Although the s~stem described in the parent speci~ication represents a marked improvement over previous systems, it too suffers ~rom a disadvantage caused by the cyclic nature and hence the non-linearity of the position information signals, or position error signals (PES) as they are often called, used to control the servo. The problem exists as a result of disturbances which effect the mechanical stability of the apparatus and can lead to the servo head being considerably displaced from its true on-track position over the associated servo track, despite the data head being accurately positioned over the data track being followed.
Under these circumstances it is possible for the servo head to be so far off track that the posltion information or position error signals being supplied by the servo head are from the non-linear part of the signal. That is, they do not exhibit a linear relationship with respe t to displacement Erom the servo on-track position. Accordingly since the high ~requency components of this signal are required to form the hybrid servo signal used during track following operations, the gain of the servo circuits àt high frequencies varies with changing displacement from the servo on-track position~
Since these servo head displacements are caused largely by external disturbances such as temperature variations or shocks and vibrations as well as internal influencing factors such as eccentricity and tilt o~ disks on the disk spindle they are largely uncontrollable. The continuous and unpred-ictable changing in gain of the UK9-76~013 -3 ~' . .
.- .: ,. - - ' : :-: .. ' , . , . - .:
s~
servo circui.ts.can lead to loop instabilit~ and~ox increased head settle time ~oth o~ wh~ch are undesirable features.
According to the in~ention therefore, data storage apparatus compxises a stack of recording disks mounted for rotation on a drive spindle r a plurality of recording and playback heads each associated with a corresponding one of a plurality of data surfaces on the disks for performing transducing operations in data tracks thereon, each data track consisting of da~a sectors for recording and/or play-back of data thereon by a data head alternating with servo sectors containing pre recorded data track position inform--; atiOn for that track readable by the same data head, a servo transducer ganged for movement with the data heads and associated with servo means providing continuous cyclic data track position information having substantially linear portions each indicating by its magnitude and polarity the degree and direction of off-set of the servo transducer from the end of an increment of movement equal to the distance between successive data tracks, modifying means for receiving said continuous data track position information signals supplied thereto and operable to supply modified position information signals at its output which are substantially linear with respect to displacement from one to another servo track over their entire range, and servo control circuits operable during track access operations in response to position information signals from the servo surfaces alone to control movement of the data heads across tracks and operable during track following operations in response : ' ' i.' ' ', ~ . ,, . .:
5~
to a hybrid si~nal composed of si~nals derived from the servo sectors on the data surface including the track being followed and high frequency components of modified signals supplied at the output to the modifying means.
In order that the invention may be fully understood preferred embodiments will now be described with reference to the accompanying drawings.
In the drawings:~
Figure 1 shows in block form, data storage apparatus as described and claimed in the parent application;
Figure 2 shows normal and quadrature position error signals and logic waveforms derived therefrom;
Figure 3 shows a circuit according to one embodiment of the invention for effectively extending the linear region of the normal signal shown in Figure 2;
Figure 4 shows a circuit according to another embodiment of the invention for providing the hybrid position error signal required during track following operations and also for effectively extending the linear region of the normal signal.
~ Figure 1 shows in block form data storage apparatus descrlbed and claimed in the parent specification. In the figure, a stack of magnetic recording disks 1 are mounted for rotation on a central spindle 2. Pre~recorded servo tracks 3 are provided over one surface of one of the disks and are read by an associated servo head 4. Since this sur~aoe contains onl~ servo information it is referred to as a dedicated servo surface. The dedicated servo surface contains continuous information regarding the posi-.
UR9-76~013 ~ 5 ~
', , .: . . .:. : ,. . . .
~g~
tion of data tracks on th~ remainin~ sur~ace o~ the disks which are accessed by a number o~ data recording and playback heads 5, one being provided for each of the remaining disk surfaces. The data heads 5 and the servo head 4 are all ~anged together for movement to and fro over the disk surface by actuator mechanism 6.
During track access operations, the continuous position error signals derived by the servo head 4 are passed through pre-amplifier 9 and AGC amplifier 10 to servo control circuit ll which also receives the address and polarity of the destin-ation track for each track access operation ~rom an external ; Control system 12. From this information the servo circuits produce the necessary drive currents for the actuator mech-anism 6 to coarsely position the data heads over the desired destination track.
During track following operations the fine po~ition error signals required to maintain the data head accurately on-track are derived from servo information pre~recorded in sectors around the data track itself. Data and servo information read by a selected data head 5 is passed through pre-amplifier 7 and AGC amplifier 8 to servo control circuit ll. Here the d.c. and low frequency components of the sectored servo in~ormation from the data head is combined in the servo control circuits ll with high frequency inform~
ation derived from the dedicated servo surface. The resulting hybrid signal of wide bandwidth is then used to produce suitable drive currents to control the actuator 6 in closed loop mode to hold the data head -track following the selected data track~ Details of construction and operation of the circuits shown in U ~ 76-013 - 6 -s~
1 Figure 1 are fully described in the parent ~pecification.
The position error signals derived by the servo head 4 reading the pre-recorded servo information 3 on the dedicated servo surface are shown in Figure 2. Two types of servo tracks recorded on the disk yive rise to these two position information signals which are called normal (waveform N) and quadrature or displaced (waveform (~). The production of these signals is fully described in U.S. Patent No. 4,068~269, issued January 10, 1978 which is referred to in the above-noted U.S. Patent No.
4, 072, 990. As the servo head accesses the disk, the normal and quadrature signals change in a cyclic manner passing through the waveform centre line which in this case is zero volts as the servo head crosses the associated normal or quadrature servo tracks on the disk and reaches a maximum voltage mid-way between tracks. The zero crossings, or on-track positions 0,1,2,..., of the normal signal (waveform N) are p~e-recorded to coincide with corresponding data head on-track positions.
AS has been previously explained however disturbances to the apparatus often upset the mechanical stability and prevent ; this the servo head on-track position from coinciding with the data on-track position.
The nature of the particular servo patterns recorded on the dedicated disk surface is such that the resulting position information signals derived from a single track are substant-ially linear over a range o~ ~1/4 of a track width about the on-track position. Such a position is known for example as Pl on Figure 2. Thus, provided the displacement of the servo head during data track following ,.. ,~
~ ~ ,t ,, operations does not exceed ~ of a track width the vol~age generated per uni~ displacement is constant and the gain of the servo control cîrcuits is also constant at the desired value. If, however, the displaoement is such that the ser~o head becomes off-set from its on-track position P1 by more than ~ ~of a track width so that during track following operations it lies at position P2'for example, f t'hen changes in position error voltage will no longer be linear with respect to changes of position about P2 and the servo position loop performance wlll be drastically degraded.
The problem is solved in a manner now to be described and involves using the quadrature position erroC signal not normally used during track following operation to effec-tively extend the linear region of the normal error signal beyond the +% track range thereby maintaining `
the a.c. gain of the servo circuits oonstant over the entire ~~ displacement range which may occur during track followi,~g ' . , . . :
operations.
The particular servo pattern employed has the advantage that the linear- portion of the quadrature waveform Q
commences when the linear portion of'the normal waveform .
N ends and vice versa. Thus, by applying a d.c. Q~f set to the quadra~ure position error signal w;th or without inversion of the signal, as will b~ seen later, the linear region of t'he normal signal can be extended as shown for example by the dotted waveform Q' in Figure 2. Now with the head displaced to position P2 its po'sition error voltage P2i is still linear wIth respect to head dispIacemRnt and the a.c.
gain of the circuit is constant.
UK9-76-~13 ' - ~ -.
55~
Th~ Qnd of ~he ltneqr reglon of ~ho nonmal ~rror ~Ignal Ts roadlly d~termined by dotectlng whon ~ho magnTtuda of th~ normal error slqnal N oxto~ds ~ha~ of tho quadraturo crror slgnal Q. ~hen thts is ~h~ case, the quadrature ~rror slgn~l plus ~ d.c. off~ot 15 u~d to of~ectlYely oxeend the ltnoar r~glon of the nor~a1 ~rror 9 I gfla I ~ .
Tho polarlty of th~ roqulred quadrature and of~-s~t volt-~ge 1~ dotormlned by th~ polarlty o~ the nor~al error ~Ignal to be extended and the dlrectlon of dlsplacement ~Ithcr l~ft ar rlgh~ fro~ the on-track posi~lon. Thus, re~rrlng to Flgurs 2 ~h1~h shows posltion Pl as eh~
~n-track po~ltlon for an ev~n-nu~be~ed track 2 ~he follow-lng truth tabl~ gl~es tho ~our poss1bio oandittons r~qutred to oxtond tho lln~ar reg10n o~ rhe normal s~qn~1. The roqutred polar1ty of quadra~ure and d.c. of~-se~ is atven In oach caso toga~hsr ~Ith the loglc 1eYq1$ needod to control 3wl ~ch1ng fro~ nor~al llnoar reglon to s~tanded llnear ragion.
.
U~9-76-o 1 3 _ ~ _ ,.
.
.. . ... ........ . .. . . . . . ... ..
3~ ;8 ....... . ` ` - `~
TRACK DIRECTION OF LOGIC LEVELS
POLARITY DI$RLACEMENT SIGNAL REQUI~ED N O Q.~N Q+N
. . ..
ODD LEFT Q + OFFSET 1 0 ODD RIGHT ~Q - OFFSET 0 1 0 ~ EVEN LEFT Q ~ OFFSET 1 1 0 : EVEN RIGHT -Q + OFFSET 1 0 _' .
~ . _. .__ Thus, in the event of a left hand displacement of a head in excess of a quarter of a track from track following an odd-numbered track the signal required to extend the normal linear region is the quadrature signal Q plus a d.c. oEf-set of approp-riate magnitude. Inspection of Figure 2 shows that the mag-nitude of the d.c. off-set required is twice the voltage V
(Figure 2) of the quadrature and normal signals when they are of equal magnitude. For a right hand displacement in excess of a quarter of a track from an odd polarity track, the signal required is the inverted quadrature signal quadrature signal -Q plus a negative d.c. off-set. Similarly a left hand displacement from an even-numbered track requirés the quadrature signa~ Q plus a negative d.c. off-set and a right hand displacement requires the inverted quadrature signal -Q plus~a positive d.c. o~f-set.
~ The loyic levels used to indicate head displacements in excess o~ one quarter of a track in either direction .
~rom the on-traak positions of odd or even numbered tracks are identi~ied in the truth table and the waveforms showing the logic levels derived from the position error slgnals UK9~76~013 -10-1~ .
. ' . . ', ~ . .
9,Si5i~
Q and N are shown and identifiea in Figure 2. The generation of these logic levels ~rom the position error signals is achieved by standard comparison circuits which will not be described here~
By exclusively OR~ing the (Q~N) signal with (Q~N) a signal A having up levels corresponding to the non-linear portions of the normal error signal is produced. Also the required polarity of the quadrature signal is given by exclusively OR-ing the (N>O) signal with the polarity signal from the control system which is at its up level for track accesses to even-numbered tracks and at its down level for accesses to odd numbered tracks. The EVEN signal as it is called lS quite conventionally supplied from the control system 12 at the start of an access operation as previously mentioned.
A circuit for switching from the normal linear region to ex-~ended linear region when displacement in excess of the normal linear region occurs is shown in Figure 3. The circuit consists of a standard three-channel operational amplifier 13, the appropriate channels being selected by a positive level on one of three corresponding channel select lines 14, 15 and 16. The normal position error signal N
is applied to input terminal 17, and thence to the positive input of ~hannel 1 of the amplifier 13. The quadrature position error signal Q is applied at input 18, and then to the positive input of channel 2 through resistor R and to the negative input of channel 3 through an identical resistor R. The of f -set voltage V~ equal to UK9~76~013 -11-, s~
twice the cross~over voltage of -the quadrature and normal signals, is applied as a positive voltage to input 19 if the track being followed is an odd-numbered track or as a negatlve voltage of the same magnitude if an even-numbered track is being ~ollowed. The polarity o~ the off-set voltage is switched under control of the EVEN signal from the control circuit 12 and since it is quite conventional is not shown or described. The off-set voltage is added to the signals applied to the positive input of channel 2 and the negative input of channel 3.
During operation, the normal error signal N, supplied to input 17, is transmitted to the output 20 by logic selection of channel 1 during the linear region of the normal Signal that is during the down-level of signal A (Figure 2).
At all other times the quadrature signal supplied to input 18 is transmitted to output 20 with positive or nega~ive d.c.
off-set voltage V by logic selection of channel 2, or inverted and transmitted to output 20 again with positive or negative off-set voltage V added by logic selection of channel 3.
Logic circuits consisting of XOR gates 21 and 22, AND
gates 23 and 24, and inverters 25 and 26 supplied with the appropriate logic signal levels perform the channel selection.
Accordingly the non-linear region of the normal signal is provided by applying the (Q-N)~ 0 signal to input 27 and the (Q+N)> to input 28 of XO~ 21, the output o~ which is at an up-level at all times except ~ 76-013 - 12 9S~i~
during the linear region of the normal signal N~ This signal, after inversion by inverter 25, is used therefore to select . channel 1 during the linear re~ion of the normal signal and to : enable AND gates 23 and 24 during the non-linear regions.
Further the track polarity signal (EVEN) from the control system is applied to input 29 and the s.ignal ~N~0) to input 30 of XOR 22 to select the appropriate channel 1 or 2 through AND~gates 23 and 24. Thus for an EVEN track for example with a left hand displacement (N~0) wili be negative and the output from XOR 22 will be at an up level selecting channel 2 via AND~gate 23. The output on line 20 will therefore be the linear region of the quadrature signal with a negative d.c.
off-set as shown in the above truth table. The other possible conditions can be easily verified with re~erence to the truth table and the waveforms shown in Figure 2 and further descrip-tion for an understanding of the invention i5 not necessary.
In order to avoid discontinuities in the extended linear region signal at the point where the quadrature plus off-set is switched in it is necessary that the off-set voltage is accurately equal to twice the voltage of the normal and : quadrature signals cross-over voltage as previously explained.
The o~f-set voltage can o~ course be produced to any desired accuracy but the magnitude of the cross-over voltage is not constant being subject to change in response to indeterminate circuit tolerances. Thus the circuit shown in Figure 2 suf~ers from the disadvantage that discontinuities can occur durlng cross-over from l.inear normal to extended linear quadrature. It is UK9-76-013 -13- ;
-, ne~essary to therefore incor~orate a ~eedback loop in the circuit which controls the servo signal gain control so as to normalize the cross-over voltage to half the d.c. off-set. The next embodiment to be described takes advantage of the a~c. coupling of the dedicated error signal inherent in the hybrid circuit described in the parent specification to provide a solution ~o this problem.
Figure 4 shows a circuit for generating the hybrid servo signal used for track following with the extended linear region feature. The selection o~ the polarity of the quadrature signal Q applied to terminal 31 is made in this case by a two channel operational amplifier 32 which acts as a switchable inver~erO The quadrature signal is passed unchanged through channel l selected by the up level of the ~N 0) signal applied to terminal 33 after inversion by inverter 34 and inverted via channel 2 selected directly by the up-level of the (N 0) signal. The normal position error signal N is supplied to input terminal 35 and the data head position error signals from the sectored servo ; 20 information associated with the track being followed is supplied to input terminal 36. Capacitors Cl and Resistors Rl connected as shown serve as high pass filters for the quadrature and normal signals from the dedicated surface and as a low pass filter for the sectored servo information from the data aurface. A hybrid quadrature position error signal is thereby produced at node Q and a hybrid normal position error signal is produced at node N. To incorporate the extended linear region function it is neces-sary to switch between these two signals without introducing 3Q a discontinuity. This is achieved by means of the switches UK9~7 ~ 13 -14-::. , : . , :
~ ~ \
. Sl and S2. ~s sho~n in the .Figuxe~ the. circuit is shown in the normal linear region mode with Sl closed and S2 open. During this time the hybrid normal signal is supplied direct to the positive input of the amplifier 39 and appears as a version N' on the output line 40. By virtue of the feedback path around amplifier 40, this buffered hybrid position error si~nal N' appearing during the normal linear region forces the voltage of the Q node which is connected to the negative input of operational amplifier 39 via closed switch Sl to be e~ual to the voltage of the N node. Now, when the normal position error signal reaches the limit of its linear region Sl opens and S2 closes under control of logic Signal applied to input 42. Under these circumstan~es the hybrid quadrature signal which is applied to the positive input of amplifier 41 appears as a buffered v~rsion Q' from its output 42.; By virtue of the ~eedback path around amp lifier 41 the buffered signal Q' now drives the N node which is connected to:the negative input of operational amplifier 41 via closed switch S2 to acquire the voltage of the Q node.
Since the voltage at Q was previously forced to be equal to the voltage at N the d~co off-set of re~uired magnitude is automatically provided with no discontinuity at the change over point. The extended linear region hybrid error signal now appears at both the N and Q nodes. The logic signal for closing Sl and for opening S2 is the linear region signal (-A) appearing from inverter 25 in Figure 3 which is applied to input 43. Thè connection is shown in dotted outline in Figure 3. Finally, it should be no~ed that the operation o~ the circuit shown in Figure 4 using the two channel amplifier 3I together with the two additianal , .
amplifiers 39 and 41 fulfill the conditions set out in the truth table above as well as providin~ the required frequency mix of the hybrid position error signal.
A problem well known in multiple switching circuits such as that shown in Figure 4 is an unwanted build up of cnarge on the capacitors as a result of multiple switching and accumulation of small off-set error voltages existing in the amplifiers and switches. As will be apparent to those familiar with such circuits this problem can readily be ~esolved in a conventional manner by applying hysteresis to the logic comparators which produce the switching signal on line 42 for switches Sl and S2.
Description of this well known technique is not necessary for the understanding of the invention and i5 not included in this specification.
In the embodiments described to illustrate the present invention~ the continuous position information is derived from servo tracks pre-recorded on a dedicated servo surface of the stack of disks. It should be understood that the invention is equally applicable where the data head position information is derived from other means for example an optical or inductive transducer cooperating with independent devices con~ainlng data track position informa-tion.
.
.,., .", .. .
U ~-76-OL3 -16-. ., -, . . .
. .
': , . ' . . . . .
Claims (9)
1. A servo system in a disk drive for accessing selected data tracks on disk surfaces and for following selected data track as the disk surfaces are rotated, one of such disk surfaces being dedicated to servo information, and the other surfaces having data information with servo information sectors in the data tracks, having accessing means including movable magnetic heads coupled to an actuator that is responsive to servo signals comprising:
means for generating a first continuous position signal having high frequency components derived from the dedicated servo disc surface, said continuous position signal including linear and non-linear signal portions;
means for modifying said non-linear signal portions to linear signal portions in response to sensed d.c. voltage levels of previous linear signal portions preceding the non-linear signal portions;
means for generating a second position signal having d.c.
and low frequency components derived from data surface servo information:
means for forming a hybrid position signal from said modified and second position signals; and servo control circuit means for controlling the movement of said accessing means relative to the data track being followed in response to said hybrid position signal.
means for generating a first continuous position signal having high frequency components derived from the dedicated servo disc surface, said continuous position signal including linear and non-linear signal portions;
means for modifying said non-linear signal portions to linear signal portions in response to sensed d.c. voltage levels of previous linear signal portions preceding the non-linear signal portions;
means for generating a second position signal having d.c.
and low frequency components derived from data surface servo information:
means for forming a hybrid position signal from said modified and second position signals; and servo control circuit means for controlling the movement of said accessing means relative to the data track being followed in response to said hybrid position signal.
2. Data storage apparatus as in claim 1, in which the continuous data track position information signal read by the servo transducer is represented by a plurality of cyclic electrical signals displaced in phase relative to one another, successive crossings of the centerline of each signal repres-enting successive increments of movement of the servo head along a predetermined path, each signal having a linear portion extending on each side of its centerline crossing which indicates by its magnitude and direction the degree and direction of offset of the servo head from the end of the increment of movement represented by that centerline crossing.
3. Data storage apparatus as in claim 2, in which the number and phase displacement of the cyclic electrical signals are such that said extending linear portions are sequentially generated during a track access operation and taken together represent the entire movement of the data head across the data tracks.
4. Data storage apparatus as in claim 3, in which said modifying means includes means for detecting the end of a selected linear portion of said continuous position information signal and means effective thereafter for selecting the polarity and adjusting the dc level of the immediately adjacent linear portion of a cyclic electrical signal so that it becomes an extension of said selected linear portion.
5. Data storage apparatus as in claim 1, in which the continuous data track position information read by the servo head is represented by a normal cyclic electrical signal and a quadrature cyclic electrical signal displaced in phase 90° from said normal signal, each of such cyclic signals having linear portions.
6. Data storage apparatus as in claim 5, in which said modifying means includes means for detecting the end of a linear portion of a normal cyclic electrical signal and there-after for selecting the polarity and for adjusting the dc level of the quadrature cyclic electrical signal, so that a linear portion of the quadrature signal becomes an extension of the linear portion of the normal signal.
7. Data storage apparatus as in claim 5, in which the detecting means comprises logic circuits operable in response to voltage levels of said cyclic electrical signals.
8. Data storage apparatus as in claim 6, in which the modifying means includes a first circuit for generating a first hybrid signal from signals derived from the servo sectors and high frequency components of normal signals;
a second circuit for generating a second hybrid signal from said signals derived from the servo sectors and high frequency components of quadrature signals;
a first feedback path connected by a first switch during the linear period of the normal signal from the output of the first circuit to the input of the second circuit, so that the input voltage of the second circuit follows the output of the first circuit; and a first storage device connected to the input of the second circuit for storing the voltage thereon;
a second feedback path connected by a second switch during the nonlinear period of the normal signal from the output of the second circuit to the input of the first circuit, so that the input voltage of the first circuit follows the output voltage of the second circuit, and a second storage device connected to the input of the first circuit for storing the voltage thereon, whereby during track following operations, the modified data track position signal is obtained from the output of either the first or the second circuit.
a second circuit for generating a second hybrid signal from said signals derived from the servo sectors and high frequency components of quadrature signals;
a first feedback path connected by a first switch during the linear period of the normal signal from the output of the first circuit to the input of the second circuit, so that the input voltage of the second circuit follows the output of the first circuit; and a first storage device connected to the input of the second circuit for storing the voltage thereon;
a second feedback path connected by a second switch during the nonlinear period of the normal signal from the output of the second circuit to the input of the first circuit, so that the input voltage of the first circuit follows the output voltage of the second circuit, and a second storage device connected to the input of the first circuit for storing the voltage thereon, whereby during track following operations, the modified data track position signal is obtained from the output of either the first or the second circuit.
9. Data storage apparatus as in claim 8, in which the modifying means includes logic means for selecting the polarity of the quadrature signal required to form the extension of the linear portion of the normal signal.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB53582/76A GB1520350A (en) | 1976-12-22 | 1976-12-22 | Data storage apparatus |
| GB53582 | 1977-12-22 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1109558A true CA1109558A (en) | 1981-09-22 |
Family
ID=10468305
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA290,791A Expired CA1109558A (en) | 1976-12-22 | 1977-11-14 | Data storage apparatus |
Country Status (10)
| Country | Link |
|---|---|
| US (1) | US4115823A (en) |
| JP (1) | JPS58112B2 (en) |
| BR (1) | BR7708548A (en) |
| CA (1) | CA1109558A (en) |
| DE (1) | DE2755652C2 (en) |
| ES (1) | ES464537A1 (en) |
| FR (1) | FR2375688A1 (en) |
| GB (1) | GB1520350A (en) |
| IT (1) | IT1126221B (en) |
| NL (1) | NL7713945A (en) |
Families Citing this family (38)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4208679A (en) * | 1978-02-28 | 1980-06-17 | Digital Equipment Corporation | Transducer positioning system for rotating disk drive units |
| DE2841381A1 (en) * | 1978-09-22 | 1980-03-27 | Siemens Ag | CIRCUIT ARRANGEMENT FOR THE POSITION CONTROL OF A DATA HEAD IN A DISK STORAGE |
| US4246536A (en) * | 1978-09-29 | 1981-01-20 | International Business Machines Corporation | Electronic velocity measurement device |
| JPS56157506A (en) * | 1980-05-09 | 1981-12-04 | Fujitsu Ltd | Positioning device |
| US4383209A (en) * | 1980-10-15 | 1983-05-10 | Minnesota Mining And Manufacturing Company | Control system for transducer positioning motor |
| US4377827A (en) * | 1980-11-10 | 1983-03-22 | Memorex Corporation | Servo positioning control system for a data storage apparatus |
| US4390912A (en) * | 1980-11-12 | 1983-06-28 | Digital Equipment Corporation | Transducer positioning system and data disk therefor |
| US4405956A (en) * | 1981-04-22 | 1983-09-20 | Xerox Corporation | Tracking apparatus for read/write head |
| US4532562A (en) * | 1981-04-24 | 1985-07-30 | Iomega Corporation | Servo control of seek operation in magnetic disk drive |
| US4439800A (en) * | 1981-04-24 | 1984-03-27 | Iomega Corporation | Servo control of seek operation in magnetic disk drive |
| US5115360A (en) * | 1982-05-10 | 1992-05-19 | Digital Equipment Corporation | Embedded burst demodulation and tracking error generation |
| US5153786A (en) * | 1982-05-10 | 1992-10-06 | Digital Equipment Corporation | Extended range servo system for positioning a disk drive head over a selected track |
| US5109307A (en) * | 1982-05-10 | 1992-04-28 | Digital Equipment Corporation | Continuous-plus-embedded servo data position control system for magnetic disk device |
| US5220468A (en) * | 1982-05-10 | 1993-06-15 | Digital Equipment Corporation | Disk drive with constant bandwidth automatic gain control |
| US5136440A (en) * | 1982-05-10 | 1992-08-04 | Digital Equipment Corporation | Track identification and counting in a disk drive positioning system |
| US5187619A (en) * | 1982-05-10 | 1993-02-16 | Digital Equipment Corporation | High speed switched automatic gain control |
| US5153787A (en) * | 1982-05-10 | 1992-10-06 | Digital Equipment Corporation | Combination embedded and dedicated servo system including embedded servo waiting |
| US5099367A (en) * | 1982-05-10 | 1992-03-24 | Digital Equipment Corporation | Method of automatic gain control basis selection and method of half-track servoing |
| US5115359A (en) * | 1982-05-10 | 1992-05-19 | Digital Equipment Corporation | Fault tolerant frame, guardband and index detection methods |
| US5202802A (en) * | 1982-05-10 | 1993-04-13 | Digital Equipment Corporation | Methods of writing and detecting dibit servo encoding |
| ATE39588T1 (en) * | 1982-05-10 | 1989-01-15 | Digital Equipment Corp | POSITIONING CONTROL SYSTEM WITH BOTH CONTINUOUS AND INSERTED SERVO INFORMATION FOR A MAGNETIC DISK MEMORY. |
| US5095471A (en) * | 1982-05-10 | 1992-03-10 | Digital Equipment Corporation | Velocity estimator in a disk drive positioning system |
| US4551776A (en) * | 1982-12-20 | 1985-11-05 | International Business Machines Corporation | Automatic reference adjustment for position error signal on disk file servo system |
| JPS59117830U (en) * | 1983-01-31 | 1984-08-09 | 日野自動車株式会社 | Marine internal combustion engine |
| US4535372A (en) * | 1983-06-29 | 1985-08-13 | Storage Technology Corporation | Position tracking servo control systems and methods |
| EP0240745A3 (en) * | 1983-08-31 | 1987-11-19 | Memorex Corporation | Disk drive servo techniques |
| JPS60193176A (en) * | 1984-03-13 | 1985-10-01 | Toshiba Corp | Head positioning system |
| US4700244A (en) * | 1986-02-14 | 1987-10-13 | Hewlett-Packard Company | Process and system for compensating for information shifts on disc storage media |
| GB2188720B (en) * | 1986-04-04 | 1990-12-19 | Data Recording Instr Co | Improved position control system |
| US4688118A (en) * | 1986-07-01 | 1987-08-18 | Hewlett-Packard Company | Servo gain compensation in a disc drive |
| US5111349A (en) * | 1989-02-07 | 1992-05-05 | Alps Electric (Usa), Inc. | Digital servo system for moving body by a distance equal to an integral multiple of a predetermined pitch |
| JPH0373476A (en) * | 1989-05-17 | 1991-03-28 | Mitsubishi Electric Corp | Recording device |
| KR930012164B1 (en) * | 1991-11-09 | 1993-12-24 | 주식회사 금성사 | Auto-trackiing error detecting method and apparatus of vcr |
| JP2608220B2 (en) * | 1992-01-31 | 1997-05-07 | 富士通株式会社 | Position sensitivity adjustment method for magnetic disk drive |
| US6266205B1 (en) | 1998-03-10 | 2001-07-24 | Maxtor Corporation | Parallel servo with ultra high bandwidth off-track detection |
| US6606216B1 (en) | 1999-05-05 | 2003-08-12 | Maxtor Corporation | Transducer head with separate data and servo read elements |
| US8498695B2 (en) | 2006-12-22 | 2013-07-30 | Novadaq Technologies Inc. | Imaging system with a single color image sensor for simultaneous fluorescence and color video endoscopy |
| CN101964613B (en) * | 2010-10-22 | 2013-04-10 | 西安立明电子科技有限责任公司 | Automatic tracking system for solar photoelectric plate |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3534344A (en) * | 1967-12-21 | 1970-10-13 | Ibm | Method and apparatus for recording and detecting information |
| US3742470A (en) * | 1971-12-30 | 1973-06-26 | Information Storage Systems | Memory disc pack drive having accurate read/write head positioning |
| US3812533A (en) * | 1972-12-22 | 1974-05-21 | Vermont Res Corp | Information storage unit transducer positioning system |
| DE2364784A1 (en) * | 1973-12-27 | 1975-07-03 | Ibm Deutschland | TRACK FOLLOWING CONTROL FOR A MAGNETIC DISC MEMORY |
| US3893180A (en) * | 1974-01-02 | 1975-07-01 | Honeywell Inf Systems | Transducer positioning system |
| US4032984A (en) * | 1975-04-28 | 1977-06-28 | Burroughs Corporation | Transducer positioning system for providing both coarse and fine positioning |
| GB1503971A (en) * | 1975-05-15 | 1978-03-15 | Ibm | Positioning system for data storage apparatus |
| GB1503972A (en) * | 1975-07-24 | 1978-03-15 | Ibm | Data storage apparatus |
-
1976
- 1976-12-22 GB GB53582/76A patent/GB1520350A/en not_active Expired
-
1977
- 1977-06-27 US US05/810,328 patent/US4115823A/en not_active Expired - Lifetime
- 1977-11-10 FR FR7734665A patent/FR2375688A1/en active Granted
- 1977-11-14 CA CA290,791A patent/CA1109558A/en not_active Expired
- 1977-11-28 ES ES464537A patent/ES464537A1/en not_active Expired
- 1977-12-09 JP JP52147304A patent/JPS58112B2/en not_active Expired
- 1977-12-12 IT IT30572/77A patent/IT1126221B/en active
- 1977-12-14 DE DE2755652A patent/DE2755652C2/en not_active Expired
- 1977-12-16 NL NL7713945A patent/NL7713945A/en not_active Application Discontinuation
- 1977-12-21 BR BR7708548A patent/BR7708548A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| BR7708548A (en) | 1978-08-15 |
| GB1520350A (en) | 1978-08-09 |
| JPS5395005A (en) | 1978-08-19 |
| US4115823A (en) | 1978-09-19 |
| DE2755652A1 (en) | 1978-06-29 |
| DE2755652C2 (en) | 1986-07-03 |
| NL7713945A (en) | 1978-06-26 |
| FR2375688A1 (en) | 1978-07-21 |
| JPS58112B2 (en) | 1983-01-05 |
| ES464537A1 (en) | 1978-09-01 |
| IT1126221B (en) | 1986-05-14 |
| FR2375688B1 (en) | 1980-08-22 |
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