CA2012800C - Reliably detecting track crossings and controls associated therewith for track seeking in optic disk recorders - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A track-seeking apparatus of a disk recorder employs a track-crossing sensor to produce track-crossing signals. An oscillator is slaved to the sensor for supplying substitute track-crossing pulses in the absence of the sensor providing such pulses or when the radial velocity exceeds a threshold velocity. A velocity profile means alters the oscillator frequency so that the oscillator produces track-crossing pulses in accordance with the profile.

Description

2~2~

IN OPTICAL DISK RECORDERS

9 Background of the Invention 11 Disk recorders of either the magnetic or optical type employ 12 transducer positioning systems. Such positioning systems 13 often use a so-called velocity servo loop for long trans-14 ducer motions, termed seeks~ Such long transducer motions cause a sensing transducer to t~averse a large number o~
16 concentric circular record tracks on the disk re~ord member.
17 The velocity positioning servo loop is optimally switched to 18 a track-following position servo mode at a one-quarter track 19 pitch distance from a target track. Such a track following control may be favorably compared to "Stop-Lock" positioning 21 control in other servo positioning applications. Upon 22 reaching the target track, the track-following position 23 servo positions the transducer to faithfullY scan or follow 24 the target track. In a subsequent seek operation, the track following position loop is interrupted to return to either a 26 velocity loop, a second positioning loop or other form of 27 seek positioning servo control. It has been observed that ~2~

1 when inter-track spacing is reduced for obtaining higher 2 track densities, then reliable track counting during a 3 velocity seek becomes more acute. In particular, the so-4 called runout or eccentricity of rotation of the optical disk can cause false direction indicatlons and false count-6 ing of tracks such that a target track is not faithfully 7 reached. Accordingly, it is desired to provide for more 8 reliable counting and control of the velocity servo during a g seek operation in which a transducer transverses a plurality 10 of tracks.
11 , 12 In a seek operation, because of the high trac]c densities, 13 any asperity in the record medium surface can cause a track 14 not to be counted. Accordingly, it is desired to provide a svstem which obviates medium surface asperities from detract-16 ing from a successful track-seeking operation.

18 ~any optical recorders have the goal of high performance at 19 low cost. Tn some of these high performance optical record-ers, a so-called fine servo or fine actuator (also termed a 21 secondary head-arm) is carried on a primary transducer 22 carrying-arm which is radially moved by a so-called coarse 23 actuator. Typically, the fine actuator has high-frequency 24 response characteristics and provides for rapid and short distance positioning of the transducer with respect to a 26 track being followed or for moving from one track to a 27 second or target track. The coarse servo, which positions 28 the relatively large mass primarv or head-carrying head-arm, 29 typically has low-frequency characteristics for handling the longer moves. For optimizing the relationship for top 2~:L2~0 1 performance between the fine and coarse actuators, servo 2 systems also provide for relative positioning of the fine 3 actuator with respect to the coarse actuator to a central or 4 reference position. Such arrangements have been colloquial-ly called "~iggv-back" carriage servo systems.

7 Field of the Invention g The present invention relates to position control systems;
more particularlv, it relates to those position control 11 systems having reliable track counting apparatus and 12 methods~

14 Discussion o~ Prior Art 16 The application of such a piggy-back carriage svstem is not 17 limited to dis~ recorders. Actually, the concept was estab-18 lished many years ago ~or a pattern-following or template-19 controlled, coarse-fine positioning servo mechanism. See Gardiner USP 2,717,979. Such an arrangement enabled higher 21 production rates of a pattern-controlled machine, such as a 22 welding or cutting machine. The carried fine or secondary 23 actuator rapidly responds to sharp changes in the pattern, 24 such that the welding or cutting operation faithfully follows the guiding pattern template while overcoming only 26 minimal inertia of the pattern-control machine mechanisms.
27 Gardiner teaches that the fine actuator, which Gardiner 28 terms a topping servo, is to be controlled by -the absolute 29 positioning of the pattern template, while the coarse servo (Gardiner's main servo) is slaved or always follows 2~2~

1 positioning motions of the topping (fine) servo. Such an 2 arrangement means that the rapidly responding topping (fine) 3 servo controls the pattern-control machine, while the main 4 (coarse) servo follows the motions of the topping (fine) servo for maintaining the topping (fine) servo in an optimal 6 position with respect to the main (coarse) servo-controlled 7 carriage; this arrangement can maximize the range of opera-8 tion of the topping (fine) servo. This type of servo g arrangement is also shown in Mever USP 4,627,029.

11 McIntosh et al., USP 3,924,268 and Merrit et al. USP
12 4,513,332 show magnetic disk recorders having piggv-back, 13 head-positioning arrangements which are servo-position 14 controlled for optimlzing the relative position of the fine actuator with respect to a coarse actuator. Simmons USP
16 3,924,063 shows yet another coarse-fine control, wherein the 17 fine actuator is permitted to move over a predetermined 18 minimal distance before a coarse actuator operation is 19 invoked. van Winkle USP 4,191,981 shows fast and slow servo-positioning mechanism in a multiple magnetic disk 21 recorder in which the slow servo mechanism is slaved to a 22 fast servo mechanism. The latter arrangement is not a 23 piggy-back ar~angement in a true sense.

Another problem in track seeking is the reliable track 26 counting during the seek to ensure access to a target track 27 upon the first try. Defect accommod~tion or avoidance has 28 been practiced in the magnetic disk recorders for a long 29 time. For example Shoji et al. in USPs 4,406,000 and 4,414,655 show defect accommodation during a track following 2~ 283~

1 operation. Both of these references show employing the 2 current value of the track-following control signal for 3 maintaining the track following relationship while travers-4 ing a defect in the track. In fact the time out timer is used to determine the maximal length of time corresponding 6 to the size of the defect. This accommodation does not 7 suggest how to accommodate loss of track counts during a 8 high-speed, track-seek operation. Fujiie in USP 4,587,644 9 shows reducing track-following servo loop gain during occurrence of defects of the track being scanned.
11 .
12 Another problem in track seeking is the eccen-tricitv or run 13 out problem. When -the track-seek operation is relatively 14 slow wi-th respect to the rotational or lineal speed of the track heing crossed, then the runout may occur while the 16 radial motion is less than one track width. To assist in 17 accommodating such runout, the eccentricity is measured and 18 stored in a table, then the stored values are fed into the l9 positioning servo such that the positioning servo tends to follow the eccentricity. Such a runout compensator is shown 21 by Jacques et al., in USP 4,135,217. Another technique for 22 accommodating the runout condition is shown by Sordello in 23 USP 3,458,785. Sordello teaches that generating a 24 quadrature signal within a pattern recorded on the disk provides direction-indicating information. For example, a 26 first signal is generated which is alternating in accordance 27 with the rapidity of the seek. A second signal generated 28 from a second transducer scanning a second signal portion on 29 the disk surface provides a second alternating signal with 90 degrees phase change or quadrature, which unambiguously 2~2~

1 provides for direction indication. While the Sordello 2 technique provides a satisfactory system, it is e~pensive to 3 implement; in fact, the Sordello system is implemented in 4 those disk recorders having a dedicated servo surface.
~aving the quadrature signal recorded thereon is used to 6 guide a so-called comb-head supporting transducer for data 7 recording and reading on a plurality of co-rotating disks.
8 It is desired to avoid separate quadrature patterns on a g record surface.

11 Accordingly it is desired to provide Cor more faithful 12 tracking counting which therefore enables more faithful 13 seeking operations Summarv of the Invention 17 It is an object of the present invention to provide for 18 enhanced track counting and accommodation of defects during 19 track seeking operations.

21 In an optical disk recorder, or other positioning mecha-22 nisms, closely-spaced-apart, position-indicating, machine-23 sensible indicia are sensed and counted. The relative 24 movement is divided into first and second predetermined portions; such portions can be interleaved as will become 26 apparent. During a first predetermined portion, signals 27 directly derived from s,ensed indicia are supplied as indicia 28 signals to a motive means for controlling a relative motion.

1 A timed circuit, such as a variable-frequency oscillator 2 (VFO), phase-lock loop ~PLL~, other resonant circuit or 3 oscillating circuits including (astable multi-vibrators~ are 4 slaved to the indicia signals for generatinq timed signals.
During a second predetermined portion of the relative 6 movement, the timed signals are substi~uted for the indicia 7 signals for controlling the motor means.

9 In another aspect of the invention, whenever the speed during relative motion exceeds a predetermined reference 11 value, then the second predetermined portion is declared.
12 During the second predetermined portion, the timed signals 13 are used for controlling the motor means to the exclu~ion o~
14 the sensed indicia signals.

16 The foregoing and other objects, featur~s, and advantages of 17 the invention will be apparent from the following more 18 particular description of preferred embodlment o' the 19 invention, as illustrated in the accompanying drawings.

21 D ription of the Figures 23 Fig. 1 is a simplified and abbreviated showing of a position 24 and velocity detection circuits constructed in accordance with the present invention.

27 Fig. 2 is a simplified block diagram of an optical disk 28 recorder/player with which the servo system shown in Fig. 1 29 may be advantageously employed.

2 ~

1 Fig. 3 is a diagram showing the track-positioning portion of 2 the tracking and focusing circuits of Fig. 2.

-4 Fig. ~ shows a detail of the F'ig. 1 illustration which is a portion of the velocity circuits shown in Fig. 3.

7 Fig. 5 is a simplified showing the generation of a tracking 8 error signals (indicia signal and a quadrature signal).

Fig. 6 spatially illustrates the relationship of tracks to 11 the,signals generated in Fig. 5.

13 Fig. 7 is a detection window generations circuit usable in 14 the Fig. 4~illustrated circuits as a noise rejection cir-cuit.

17 Fig. 8 is a simplified and idealized set of signal waveforms 18 used for describing the, operation of the ~ig. 7-illustrated 19 circuit.
21 Fig. 9 shows a forward-reverse counting control for counting 22 tracks in the Fig. 1-illustrated system, including verifi-23 cation of the track count.

Fig. 10 shows a set of idealized signal waveforms used in 26 connection with the description of operation of Fig.

28 Fig. 11 shows a velocity signal smoothing circuit which 29 enhances operation of the illustrated system.

~2~

1 Detailed Description 3 Referring now more particularly to the appended drawing, 4 like numerals indicate like structural parts and ~eatures in the various figures. TES generator circuits 10 respond 6 jointly to a sensed TES supplied over line 63 (line 63 7 corresponds to a part of and is included in later described 8 line 57 of Fig. 2), as later described, and to a track count 9 of distance to go supplied by track position circuit 11 received over bus 12 to supply a corrected or valid TES
11 signal over line 13. The valid TES signal more faithfully 12 indicates track crossings than the indicia signal. The 13 valid TES si~nal on line 13 travels to track position 14 circuits 11 for effecting reliable track counting. A set of velocity circuits 14 respond to the valid TES signal on line 16 13 to generate a true velocity signal on line 15 for servo 17 circuits for controlling the motive means, as later 18 described. The line 15 velocity signal also travels to TES
19 generator circuits 10 for more validly producing a valid TES
signal. The actual track count to go is supplied not only 21 over cable 12 but over cable 12A for use in other parts of 22 the servo circuits. At the beqinning of each seek, the 23 value received over hus 59A is stored in the track position 24 circuits 11 to represent a predetermined numher of tracks to go (this value can be the number of tracks times two).

27 TES generator circuits 10 include a timed electrical circuit 28 for generating a valid TES signal which is used during 29 predetermined portions of the relative motion controlled by the positioning systems. At other times the sensed TES

~ 2~

1 signal supplied over line 63 is passed as an indicia signal 2 through T~S generator circuits 10 to become the valid T~S
3 signal on line 13.

An optical recorder with which the present invention mav be 6 advantageously emplo,ved is shown in Fig. 2. A magnetooptic 7 record disk 30 is mounted on spindle 31 for rotation by 8 motor 32. Optical head-carrying arm 33 on head-arm carriage g generally denoted by numeral 34, moves radially of disk 30.
A frame 35 of recorder suitably mounts carriage 34 for 11 réciprocating radial motions. The radial motions of car-12 riage 34 enable access to any one o~ a plurality of concen-13 tric tracks or circumvolutions of a spiral track Eor record-14 ing and recovering data on and from the disk. Linear actuator 36 suitablv mounted on frame 35, radially moves 16 carriage 34 for enabling track accessing. The recorder is 17 suitably attached to one or more host processors 37, such 18 host processors may be,control units, personal computers, 19 large system computers, communication systems, image process processors, and the like. Attaching circuits 38 provide the 21 logical and electrical connections between the optical 22 recorder and the attaching host processors 37.

24 Microprocessor 4n controls the recorder including the attachment to the host processor 37. Control data, status 26 data, commands and the like are exchanged between attaching 27 circuits 38 and microprocessor 40 via bidirectional bus 43.
28 Included in microprocessor 40 is a program or microcode-29 storing, read-only memory (ROM) 41 and a data and control signal storing random access memorv (RAM) 42.

2~2~

1 The optics of the recorder include an objective or focussing 2 lens 45 mounted for focussing and tracking motions on 3 head-arm 33 by fine actuator 46. This actuator includes 4 mechanisms for mo~ing lens 45 toward and away ~rom disk 30 for focussing and for radial movements parallel to carriage 6 34 motions; for example, for changing tracks within a range 7 of 100 tracks so that carriage 34 need not be actuated each 8 time a track adjacent to a track currentlv being accessed is 9 to be accessed. Numeral 47 denotes a two-way light path between lens 45 and disk 30.
11 , 12 In magnetooptic recording, magnet 48 (in a constructed 13 embodiment magnet 48 is an electromagnet) provides a weak 14 magnetlc steering field for directing the remnant magnetiza-tion direction of a small spot on disk 30 illuminated by 16 laser light from lens 45. The laser light spot heats the 17 illuminated spot on the record disk to a temperature above 18 the Curie point of the magnetooptic layer (not shown, but 19 can be an alloy of rare earth and transitional metals as taught by Chaudhari et al., US Patent 3,949,387). This 21 heating enables magnet 48 to direct the remnant magnetiza-22 tion to a desired direction of magnetization as the spot 23 cools below the Curie point temperature. Magnet 48 is shown 24 as oriented in the "write" direction, i.e., binary ones recorded on disk 30 normally are "north pole remnant magnet~
26 ization". To erase disk 30, magnet 48 rotates so the south 27 pole is adjacent disk 30. Magnet 48 control 49, which i.s 28 mechanically coupled to rotatable magnet 48 as indicated hy 29 dashed line 50, controls the write and erase directions.
Microprocessor 40 supplies control signals over line 51 to >
~2~

1 control 49 for effecting reversal of the recording direc-2 tion.

4 It is necessary to control the radial position of the beam following path 47, such that a track or circumvolution i5 6 faithfully followed and that a desired track or circum-7 volution is quickly and precisely accessed. To this end, - 8 focus and tracking circuits 54 control both the coarse g actuator 36 and fine actuator 46. The positioning of car-riage 34 by actuator 36 is precisely controlled by control 11 signals supplied by circuits 54 over line 55 to actuator 36.
12 Additionally, circuits 54 control signals travel over lines 13 57 and 58, respectively, for focus and fine tracking and 14 switching actions of fine actuator 46. Lines 57, 58 respec-tively carry a position error signal to circuits 54 and a 16 position control signal _rom circuits 54 to the focus and 17 tracking mechanisms of actuator 46. Sensor 56 senses the 18 relative position of fine actuator 46 to head-arm carriage 19 33.

21 The focus and tracking position sensing is achieved by 22 analyzing laser light reflected from disk 30 over path 47, 23 thence through lens 45, through one-half mirror 60 and to be 24 reflected by half-mirror 61 to a so-called "quad detector"
62. Quad detector 62 has four photo elements which respec-26 tively supply signals on four lines collectively denominated 27 by numeral 63 to focus and tracking circuits 54. Aligning 28 one axis of the detector 62 with a track center line, track 29 following operations are enabled. Focussing operations are achieved by comparing the light intensities detected by the .. . .. ..

1 follr photo elements in the quad detector 62. Focus and 2 tracking circuits 54 analyze the signals on lines 63 to 3 control both focus and tracking.

Recording or writing data onto ~isk 30 :is ne~t described.
6 It is assumed that magnet 48 is rotated to the desired 7 position for recording data. Microprocessor 40 supplies a 8 control signal over line 65 to laser control 66 for indicat-9 ing that a recording operation is to ensue. This means that laser 67 is energized by control 66 to emit a high-intensitv, 11 laser light beam for recording; in contrast, for reading, 12 the laser 67 emitted laser light beam is a reduced intensity 13 for not heating the laser illumlnated spot on dislc 30 above 14 the Curie point. Control 66 supplies its control signal over line 68 to laser 67 and receives a feedback signal over 16 line 69 indicating the laser 67 emitted light intensity.
17 Control 6~ ad~usts the light intensity to the desired value.
18 Laser 67, a semiconductor laser such as a gallium arsenide 19 diode laser, can be modulated by data signals so the emitted light beam represents the data to be recorded by intensity 21 modulation. In this regard, data circuits 75 (later des-22 cribed) supply data-indicating signals over line 78 to laser 23 67 for effecting such modulation. This modulated light beam 24 passes through polarizer 70 (linearly polarizing the beam), thence through collimating lens 71 toward half mirror 60 for-26 being reflected toward disk 30 through lens 45. Data 27 circuits 75 are prepared for recording by the microprocessor 28 40 supplied control signals over line 76. Microprocessor 40 29 in preparing circuits 75 is responding to commands for recording received from a host processor 37 via attaching æ~

~2~$~

l eircuits 38. Once data circuits 75 are prepared, data is 2 transferred direetly between host proeessor 37 to data 3 circuits 75 through attaehing cireuits 38. Data circuits 75 4 also includes ancillary circuits ~not shown) relating to disk 30 format signals, error deteetion and correekion and 6 the like. Cireuits 75, during a read or reeovery action, 7 strip the ancillary signals from the readback signals before 8 supply corrected data signals over bus 77 to host processor 9 37 via attaehing to 38.
11 Reading or reeovering data from disk 30 for transmission to 12 a host processor requires optieal and electrical proeessing 13 of the laser light beam Erom the disk 30. That port.ion of 14 the re1ected light (which has its linear polarization from polarizer 70 rotated by disk 30 reeording using the Kerr 16 effeet) travels along the two-wav light path 47, through 17 lens 45 and half-mirrors 60 and 61 to the data deteetion 18 portion 79 of the head-arm 33 optics. Half-mirror or beam 19 splitter 80 divides the reflected beam into two equal intensity beams both having the same refleeted rotated 21 linear polarization. The half-mirror 80 refleeted light 22 travels through a first polarizer 81, which is set to pass 23 onlv that refleeted light whieh was rotated when the remnant 24 magnetization on disk 30 spot being aecessed has a "north"
or binary one indieation. This passed light impinges on 26 photo eell 82 for supplying a suitable indieating signal to 27 differential amplifier 85. When the reflected light ~as 28 rotated by a "south" or erased pole direction remnant 29 magnetization, then polarizer 81 passes no or ver~ littl~
light resulting in no aetive signal being supplied by 20~2~0 1 photocell 82. The opposite opera~ion occurs by polarizer 83 2 which passes only "south" rotated laser light beam to photo 3 cell 84. Photocell 84 supplies its signal indicating its 4 received laser light to the second input of differential amplifier 8S. The amplifier 85 supplies the resulting 6 difference signal (data representing~ to data circuits 75 7 for detection. The detected signals include not only data 8 that is recorded but also all of the so-called ancillary 9 signals as well. The term "data" as used herein is intended to include any and all information-bearing signals, prefera-11 bly of the digital or discrete value type.

13 The rotational position and rotational speed of splndle 31 14 is sensed by a suitable tachometer or emitter sensor 90.
Sensor 90, preferably of the optical sensing type that 16 senses dark and light spots on a tachometer wheel (not 17 shown) of spindle 31, supplies the "tach" signals (digital 18 signals) to RPS circuit 91 which detects the rotational 19 position of spindle 31 and supplies rotational information-bearing signals to microprocessor 40. Microprocessor 40 21 employs such rctational signals for controlling access to 22 data storing segments on disk 30 as is widely practiced in 23 the magnetic data storing disks. Additionally, the sensor 24 90 signals also travel to spindle speed control circuits 93 for controlling motor 32 to rotate spindle 31 at a constant 26 rotational speed. Control 93 may include a crystal con-27 trolled oscillator for controlling motor 32 speed, as is 28 well known. Microprocessor 40 supplies control signals over 29 line 94 to control 93 in the usual manner.

2 ~

1 Fig. 3 illustrates the seeking and ~rack following portions 2 of focus and trac]sing circuits 54. The tracking and seeking 3 portions include fine actuator 46 positioning circuits 110 4 and coarse positioner 36 servo circuits 111. The coarse positioner circuits 111 operate such that the coarse actua-6 tor 36 always moves the head-arm to follow the motions of 7 fine actuator 46. Fine positioner circuits 110 actuate 8 actuator ~6 to move objective lens 45 such that a laser beam g traveling along light path 47 scans a single track during track following operations and moves radially across the 11 disk 30 for crossing the tracks during a track seek opera-12 tion. ~or track following operations track follow circuit 13 112 receives a sensed tracking error signal over line 63 14 from decoder 113 to provide track-following control si~nals over line 114. The line 114 control signal then traverses 16 electronic switch 115, entering at tra~k follow terminal 17 116, for controlling power output amplifier 117. Power 18 amplifier 117 supplies an actuating signal over line 57D to 19 actuator coil 46A of fine actuator 46. The drive current on line 57D causes the actuator ~6 to move radially along the 21 head-arm 33 for maintaining the position of the light beam 22 47 on a single track.

24 The quad detector 62 having independent photoresponsive elements A, B, C and D, arranged in a rectangular array, 26 provide tracking error indicating photo element signals -~o 27 decode circuit 113. The axis of the rectangle of quad 28 detector 62 lying between photoelements A, B and D, C is 29 aligned with the axis of the track being followed. Decode circuit 113 responds to the four photoelement signals to 20~2~0 1 provide a tracking error signal, as is well known and as 2 later described herein. ~n track follow circuit 112, the 3 tracking error signal actuates servo circuits in a known 4 manner. Operation of track follow circuit 112 is modified by a radial runout input received over line 118. A disk 6 profile is generated for the disk 30 which indicates that 7 the expected radial runout. Track follow circults 112 8 respond to the radial runout signal for modifying the g tracking error signal to anticipate the radial run out thereby providing more faithful track following. Addition-11 ally, relative position error sensor 56 mounted on head-arm 12 33 of carriage 34 senses relative displacement of actuator 13 46 and head-arm 33. It supplies a relative displacement 14 error signal RPE over line 58E, thence line 119, to track follow circuits 112 for compensating for modifying the TES
16 offset. Such offset is caused by relative mo-tion between 17 carriage 33 and fine actuator 46. This relative motion is 18 detected ~y sensor 56 and indicated as the RP~ signal which 19 is fed forward to track following circuits 112. Velocity seek loop circuits, generally denoted by numeral 123, 21 constitute all of the electronic circuits providing a signal 22 to the seek input terminal 124 of seek-follow switch 115.
23 Whenever a seek is instituted by microprocessor 40, elec-24 tronic switch 115 is moved from terminal 116 to terminal 124 for disconnecting the track follow circuit 112 from ampli-26 fier 117 and connecting the velocity servo loops circuits 27 123 to amplifier 117.

29 Circuits 123 xespond to several input signals for effecting the velocity-controlled seek. Track crossing circuit 125 `.f.b, , .. , ,: . ~,s,.~ ;. _ ., 2al~l281J 0 1 receives the sensed TES signal over line 63 for detecting 2 when the beam 47 is crossing a track on disk 30. Each time 3 a track crosslng is detected by circuit 125, an output 4 decrementing pulse is supplied to track counter 126 for decrementing one from the number o~ tracks to go. It may be ~ noted that in some embodiments a single track crossing is 7 represented by two zero crossings of the tracking error 8 signal on line 63. In some embodiments two pulses are g provided to the track counter for indicating a single track crossing. At the time microprocessor actuates circuits 123 11 to do a seek, the microprocessor ~0 supplies the number of 12 tracks to be crossed over bus 5~ ~part of line 59 oE Fiq.
13 2) presetting -track coun~er 126 for the upcomlng seek 14 operation. Track counter 126 continuously outputs the number of tracks-to-qo over bus 128 to velocity circuits 130 16 as well as to track crossing circuits 125. The track 17 crossing circuits 125 use the track count for verifying 18 accuracy of the number of tracks counted. Velocity circuits 19 130 resond to a velocity profile designed for the seek operation for genexating a reference signal and a measured 21 speed indicating signal. The speed reference signal sup-22 plied over line 132 is based upon the velocity profile 23 desired for the seek operation and the instant distance to 24 go. The measured speed signal is supplied over line 133 to be subtracted from reference signal on line 132 by sum 26 circuit 131. The resultant speed error signal supplied by 27 sum circuit 131 alters the operation of fine actuator 46 to 28 closelv follow the velocity profile. Operation of velocity 29 circuits 130 are described later.

2~$~

1 Circuits 123 also include a gain control circuit which 2 includes gain control switch 135 having its output terminal 3 connected to the seek terminal ]24 of switch 115. Switch 4 135 is actuated to an acceleratlon position 139 whenever microprocessor 40 supplies a SEEK signal over line 13~ (line 6 136 is shown as two different line portions in ~ig. 3 for 7 purposes of simplifying the drawing). The SEEK signal sets ~ flip-flop FF 137 to the inactive state causing FF 137 to g supply a switch actuating signal over line 138 to move switch 135 to connect acceleration terminal 139 to seek 11 terminal 124 of switch 115. Acceleration circuit ACC~L 140 12 provides high gain to the sum circuit 131 error signal; -that 13 is, the error signal is accentuated by ACCEL circuit 140 for 14 initially maximizing the drive power to actuator 46. Thi~
acceleration high gain portion minimizes the tim~ it takes 16 the fine actuator 46 to move beam 47 to a speed or velocity 17 corresponding to the desired velocity profile. Once the 18 velocity profile and the actual velocity are the same, then 19 detector circuit 141 detects a small error siqnal supplied by sum circuit 131. At this time, detector circuit 141 2~ resets FF 137 to the active state for supplying an activat-22 ing signal over line 138 for switching switch 135 from 23 terminal 139 to receive signals now from seek compensator 24 circuit COMP 142. Compensator circuit 142 is designed to maximize velocity servo operation whenever the reference 26 velocity profile and the measured velocity have a small 27 error condition. Compensator 142 continues to couple sum 28 circuit 131 through switch 135 to fine actuator 46 until the 29 end of the seek, which occurs at one-quarter track pitch from the target track. At this point, track follow circuit 2. ~

1 112 is again re-energized and the velocity circuits 123 are 2 disconnected from actuator 46.

4 Track capture, i.e., switching from track seeking to track following on the target track, is indicated by track co~nter 6 1~6 one-quarter track pulse supplied over line 145, resets 7 seek priming flip-flop 146 to the reset state. Initiall~
8 the SEE~ signal from microprocessor 40 on line l36 set FF
9 146 to the active state causing switch 115 to move from follow terminal 116 to seek terminal 124. Resetting ~F 146 11 at one-quarter track pitch-to-go from the target track 12 causes a deactivating slgnal to be supplied over line 147 13 for moving the switch 115 from seek terminal 124 back to the 14 follow terminal 116.

16 To assist in track capture, the dynamic range of power 17 amplifier 117 is momentarily increased for supplying a 18 maximal control signal over line 57D to actuator coil 46A.
19 This additional control current ensures fast capture but is not desired for faithful track following operations.
21 Accordingly, the one-quarter track pitch signal on line 145 22 actuates a monostable multivibrator, or other time delay 23 circuit MONO 148, to supply an actuating signal over line 24 149 to amplifier 117. This actuating signal causes t~e amplifier 117 dynamic range to be increased, electro~ical~
26 changing the dynamic range of amplifiers as is well ~ow~
27 and not further described for that reason.

29 It may be desired to verify that track counter 126 has faithfully counted the tracks, particularly when two puls~s TU988001 ~o 1 per track crossing are employed~ To this end, decode 2 circuit 113 supplies a signal which is the sum of all photo-3 currents from the elements of detector 62 over line 152 to 4 track counter 125. This sum sïgnal is in quadrature to the TES signal on line 63. Whenever the sum signal on line 152 6 has a maximum positive amplitude, then the beam 47 ls in the 7 center of a track being crossed. When two pulses per track 8 crossing are employed, this means that the numerical content g of track counter 126 should be even. If the track counter is odd, then the track count is changed by unity for 11 sinchronizing the track count to actual track crossings.
12 This paragraph completes -the description of circui.t 123.

14 The coarse positioner circuits 111 receive the relative position error signal RPE from detector 56 over line 58E.
16 Compensator and integrator COMP/INT 155 responds to the 17 error signal to suppl~r a smoothed and integrated error 18 signal to sum circuit 156. Sum circuit 156 compares the 19 error signal from compensator integrator 155 with a refer-ence signal (zero or ground reference potential) or supplv-21 ing a control signal through amplifier 157 causing actuator 22 to move head-arm to follow the motions of actuator 46. Such 23 following operations reduce the error signal sensed by 24 detector 56 in the relative movement of the head-arm 33 (carriage 34) and actuator 46 away from a reference position~
26 on head-arm 33 (not shown). During seek operations~ it is 27 desired to actuate coarse actuator 36 from moving head-arm 28 33 more quickly for limitin~ the relative position between 29 the fine and coarse actuators. To this end, the drive signal supplied to amplifier 117 for driving fine actuator 2~1~28~1~

1 46 is also supplied over line 159 to feedforward circuit 2 1580 Eeedforward circuit 158 is basically a gain control 3 and signa] smoothing circuit of any design. FeedforWard 4 cireuit circuit 158 supplies its output signal to sum circuit 156. The feedforward circuit 158 output signal is 6 added by sum circuit 156 to the signal from element 155 for 7 aetuating actuator 36 to maximal actuation, particularly 8 during acceleration mode. Thus, the fine servo loop during g acceleration phase passes the effects of circuit 140 to the coarse servo loop. Accordingl~7/ both the fine aetuator 46 11 and the coarse actuator 36 receive enhanced drive signals 12 during the acceleration phase for ensuring both actuators 36 13 and 46 accelera~e in a minimal time aecording ~o the desired 14 velocity profile.

16 Fig. 4 is a block diagram showing the track crossing cir-17 cuits 125, which aecommodate defeets or other error condi-18 tions during the track seeking operations. Electronic 19 switch 160 selects either a processed sensed tracking error signal produced zero axis crossings received by switch 160 21 over line 161 or substitute zero a~is crossing pulses 22 reeeived over line 162. Under certain operating conditions, 23 the line 162 pulses provide more reliable indications of 24 track erossings than the processed TES signal pulses. The substitute zero axis crossing pulses are supplied by a 26 phase-loek loop ~PLLJ 171, whieh is phase synchronized to 27 the processed TES pulses and frequency controlled in 28 accordance with the current velocity of the beam 47 crossing 29 the disk 30, 2~ i 2~

1 The processing of the received TES signal on line 63 into 2 zero crosslng pulses is first ~escribed. Plural band filter 3 166 band pass filters the line TES signal 207 (Fig. 6) in 4 accordance with current velocitv of the beam crossing disk 30. The current velocity, in the constructed embodiment, ls 6 ~he velocity profile of the seek. Such velocity profile is 7 digitally stored in velocitv profile ~PROM 164 as a table of 8 values. Track counter 126 supplles the number of tracks-to-9 go indication over bus 128 to EPROM 164 and to velocity circuits 130. The distance-to-go value actuates EPROM 164 11 to emit control signals over hus to select a pass band o, 12 plural band filter 166; for example, filter 166 may have 13 eight pass band.s, one of which ls selected at any given 1~ instant. The higher the velocity, the higher frequency and width of the pass band selected to process the line 63 TES
16 signal. The actual values and number of bands are best 17 empirically determined. The pass band filtered TES signal 18 travels over line 168 to zero axis crossing detector 167.
19 Detector 167 emits a train of pulses 231 (Fig. 8) corre-sponding to, zero axis crossings of TES signal 207, to line 21 161, thence switch 160. At low frequencies of pulses 169, 22 switch 160 passes the line 169 pulses as valid TES zero axis 23 crossing pulses over line 172 for decrementing track counter 24 126 and as an input to velocity measuring circuits 130.
26 The substitute zero axis crossing pulses on line 162 are PLL
27 171 output pulses. PLL 171 has a low-frequency response 28 characteristic, hence it does not respond to missing sensed 29 TES pulses on line 161 to provide defect accommodation as will become apparent. PLL 171 has the usual construction of 2~ 2~

1 a digital phase compare portion 175 which receives the line 2 161 pulses for phase compares with the line 162 pulses. I'he 3 phase error signal generated by phase compare portion 175 4 passes through the usual trans~er function 176 to phase control voltage controlled oscillator (VCO) 177. The 6 frequency of VCO 177 is controlled to represent the current 7 velocity of the beam 47 crossing disk 30. In a test embodi-8 ment, the current velocitv was derived from the measured 9 velocity signal on line 133 or from the velocity signal from ~PROM 164; both velocity-indicating signals, ~he measured or 11 the reference, were fed forward to frequency control VCO
12 177. The line 133 measured velocity signal has positive and 13 negative polarities, hence absolute value circuit 178 14 converts the bipol~r velocity signal to a unipolar (absolute value) signal traveling over line 179 to frequency control 16 VCO 177 to the current velocity. In the test embodiment, 17 the bus 16S carried reference velocity signal was alter-18 nately supplied for frequency controlling VCO 177. In a 19 commercial embodiment, either of the two velocity-indicating signals may be employed or the two signals ma~ be averaged 21 together for joint frequency control of VCO 177 23 Switch control 163 actuates switch 160 to couple the PLL 171 24 to line 172 whenever the radial velocity of the beam 47 exceeds a predetermined threshold indicated by a reference 26 signal on line 180. In the frequency domain, the threshold 27 is the track crossing frequency. Compare circuit 181 28 compares the line 179 measured velocity signal with the line 29 180 reference signal. When the measured velocity signal amplitude exceeds the reference signal amplitude, then TV988001 2~

1 compare circuit supplies a high-speed indicating signal over 2 line 182 to switch control circuit 163. Switch control 3 circuit 163 responds to the high-speed indicating signal to 4 actuate switch 160 to decouple line 161 from line 17~ and to couple line 162 to line 172. r~hen the line 179 measured 6 velocity signal decreases to be less than the line 180 7 reference signal, then compare circuit 181 switch control 8 163 responds to the compare circuit to actuate switch 160 to g recouple line 161 to line 172 for passing the processed sensed TES pulses as valid TES pulses.
11 .
12 Digital phase compare portion 175 produce phase error signal 13 can indicate a loss of phase synchronization between the 14 sensed TES ~ulses and the PI.L 171 output pulses. Switch control 163 includes a phase error detector (not shown) 16 operative during the high-speed portion of the seek for 17 indicating a loss of svnchronization; then switch control 18 163 actuates switch 160 to decouple line 162 from line 172 19 and recouple line 161 to line 172 for again passing the processed sensed TES pulses as valid TES pulses. Once a 21 loss of phase synchronization is detected, then the PLL 171 22 output pulses are not used during a current seek.

24 It has been found that PLL 171 enables the seeking operation to continue in an accurate manner over medium defects 26 extending over a relatively large number of tracks. While 27 no TES pulses are being sensed, digital phase compare 28 portion 175 did not indicate a loss-of-phase synchroniza-29 tion. The fed forward current velocity signal causes PLL
171 to velocity track the velocity profile such that when 2~ 2$0~

1 sensed TES pulses are again generated, the PT.L 171 operation 2 quickly regalns phase synchronization for continuing the 3 seek operation under its control. If phase synchronization 4 is not reestablished, then the sensed TES pulses on line 161 5 are used to complete the seek operation. It has been found 6 that PLL 171 enables seeking directly to a target track even 7 when large defects are encountered during the seek.
9 It is well known that each track crossing is indicated b~t two zero crossings of the tracking error signal. Track 11 counter 126 counts two such zero crossings for each trac]c 12 crosslng~ The center of a track is indicated by the numeri-13 cal contents of track counter portion 175 of -track counter 14 126 having an even count. This even or odd count ~he last or least significant digit of the counter) is supplied over 16 line 190 to verify count circuit 191. Verify count circuit 17 191 receives the sum (quadrature) signal over line 192 .or 18 comparison with the odd-even count of track counter portion 19 175. If the count is odd, unitv is subtracted from track counter 126 by a signal supplied from verif~ count circuit 21 191 over line 192. This minor change synchroni~es track 22 counter portion 126 numerical contents to the actual posi-23 tion of beam 47.

Fig. 5 is a simplified diagram of the circuits employed for~
26 generating the TES and quad signals respectively over lines 27 63 and 192. The light beam reflected from disk 30, when in 28 focus, impinges on the center of detector 62 as indicated by 29 dash-lined circle 204. Such an indication indicates true track following and true focus. As the beam 47 goes off 2 ~

1 center from the track being followed, then the impingement 2 of the beam 47 moves ~he circle 204 along an axis 205 of 3 detector 62; axis 2Q5 ls aligned with the track center lines 4 206 (Fig. 6). ~ll operations of decoder 113 are in analog signal form. TES signal 207 on line 63 is generated by two 6 sum circuits 210, 211 and differential amplifier 212. Sum 7 circuit 210 receives the sum of the photodetector elements A

8 and D electrical currents, respectively over lines 63A an~

9 63D, ~or summing same representing the total light received on one side of the axis 205 which corresponds to the phvsi-11 cal position of beam 47 radiallv o the trac~ being fol-12 lowed. Similarly, sum circuit 211 receives photocurrents 13 from photoelements B and C, respectivelv over lines 63B and 14 63C for supplying a second sum signal representative of the light received relative to the track being followe~.
16 Differential amplifier 212 compares the sum signals from 17 circuits 210 and 211 to generate the sensed TES signal 207 18 on line 63. Line 63 may be of the differential type wherein 19 two signal lines carry the TES signal in differential form.
Single-ended circuits may be employed as well. The quad 21 signal on line 192, which is in quadrature to the sensed TES
22 signal as will be explained with respect to Fig. 6, is 23 generated by sum circuit 213. Sum circuit 213 receives 24 photocurrents from all of the four elements A, B, C and D of detector 62, which provides a signal indicative of the total~
`26 light received.

28 Referring next to Fig. 6, a portion of the information-29 bearing surface of disk 30 is illustrated. The disk is formed with two sets of concentric rings, one set heing ~ 2~

1 mesas 215 and the second set being grooves 216. Beam 47 2 lmpinges on the outer surface consisting of the interleaved 3 grooves 216 and mesas 215. The track center lines 206 of 4 the three tracks illustrated in Fig. 6, lie along the center of the grooves. At the point of light beam impingement on 6 any track of disk 30, axis 205 is parallel to the respective 7 track center lines 206. When the beam 47 is focused into a 8 groove, the tracking error signal is at a zero crossing 9 position 220, i.e., when e,~actly centered, the sensed TES
signal should be at zero. As the beam moves radiallv from ll the,track center line (crosswise), then the amplitude o~ the 12 TES s;.gnal 197 changes as a sinusoid with the direction oE
13 change indicating the direction of tracking error. As the 14 beam 47 scans transversely (radially) across the grooves or tracks, the TES signal takes the sinusoidal shape wherein 16 zero axis crossings in a first direction signify crossing 17 track center lines 206, 193 and 194 as indicated bv dimen-18 sion line 220. Similarly, when the beam is crossing the 19 mesas 215, then the zero access crossing of TES signal 207 is in the opposite direction as at points 221. The quad 21 signal 224 on line 192 is displaced 90 degrees from the TES
22 signal 207. At the center of each track, quad signal 224 23 has a maximum positive amplitude (this applies to the 24 illustrative embodiment only), the polarity oE the signal may be inverted in other embodiments, whereas at the center 26 of the mesa.s, a negative potential maximum is reached 27 because of varying focus conditions, positive and negative 28 magnitudes may be different. Examination of Fig. 6 readily 29 shows the ninety degree or quadrature relationships between the sensed TES signal 207 and quad (sum) signal 2 4.

20~2~0 1 Referring again to Fig. 4, a noise rejection circuit 230 may 2 be interposed between line 161 and digital phase compare 3 portion 175. Figs. 7 and 8 illustrate such a noise rejec-4 tion circuit and its operation. During a seek operation, sensed TES zero crossing pulses 231 traveling over line 161 6 (Fig. 4) actuate ramp generator 241. The seek operation is 7 indicated by a seek signal received on line 136. Generator 8 241 outputs the ramp signal 243 over line 245 to a pair of 9 comparators 247 and 248. The desired velocity profile indicating digital signals provided over cable 165 are 11 con~rerted to analog form by DAC 250. The desired pro~ile is 12 supplied to generator 241 for indicating the slope of the 13 ramp 243. Comparator 247 compares the amplitu~e o~ ramp 14 signal ~3 with a reference signal supplied over line 255.
When the ramp amplitude equals the reference signal ampli-16 tude on line 255, a set or priming pulse 257 is supplied hy 17 comparator 247 to set check latch 260 to the active 18 condition; simultaneously, the set pulse S from comparator 19 247 triggers generator 241 to begin discharging, thereby identifying apex point 252.

22 A next succeeding sensed TES pulse '40 resets ramp generator 23 241 at point 274 returning ramp signal 243 to a reference 24 amplitude. A new ramp c~ycle then begins. This action is the usual operation when sensed TES pulses 231 are being 26 reliably generatedO

28 Latch 260 supplies the B and B signals detection defining 29 windows respectivel~ over lines 262 and 263. When latch 260 is in the reset condition, AND circuit 265 is enabled and it --.

~L281D~

1 passes a sensed TES pulse on line 161 as noise over line 2 266. On the other hand, when latch 260 is set to the active 3 condition, AND circuit 265 is disabled, while AND circuit 4 238 enabled to indicate a drop-out signal over line 269.
The other input to AND gate 268 is generated by comparator 6 248. Comparator 248 determines when the discharging of ramp 7 signal amplitude 243 falls below a certain reference signal 8 value received on line 275, i.e., no sensed T~S pulse 255 g had reactivated ramp generator 2il to again begin a ramp signal. For example, a drop out of the sensed TES pulses 11 occurred at point 272 of the sensed TES pulses. As a 12 result, the ramp signal 2~3 i9 not reset at point 273 on the 13 ramp signal 243. Instead ramp generator 2~1 continues to 14 discharge until a threshold va~ue indicated by the siqnal on line 275 is reached as indicated at 276. This point corre-16 sponds to comparator 248 supplying a drop-out pulse 280 over 17 line 281 which resets latch 260. Drop-out pulse 280 also 18 passes through AND circuit 268 to line 269. Lines 266 and 19 269 go to phase compare 175 for inhibiting its operation.

21 Switch control 163 is also partially illustrated. ~henever 22 the current velocity profile exceeds a predetermined speed 23 of the beam 47 laterally traversing the tracks, the PLL 171 24 pulses are selected as valid TES pulses, i.e., switch 160 is actuated by the line 169 signal. DAC 220 supplies the 26 velocity profile analog signal of comparators 255 and 256 of 27 compare circuit 181.

29 Fig. 7 also shows comparator 181 and a part of switch control 163. Comparator 286 compares the profile with a .... . .. . .

2~28~

1 reference signal supplied from DAC ~50 for indicatinq when 2 the velocity of the beam is less than the predetermined 3 value. The output signal of comparator 286 travels 0~7er 4 line 288 to AND circuit 290. The valid TES pulses supplied over line 172 times the setting of switch 160 control latch 6 291. As long as latch 291 is set, no enabling signal is 7 supplied over line 169 to switch 160 keeping line 161 8 coupled to line 172. On the other hand, when the velocity 9 profile indicates a velocity greater than the predetermined value, comparator 285 determines that the profile value 11 signal from DAC 250 is greater than the reference value 12 signal on line 293. Then, comparator 285 enables ~ND
13 circuit 295 to pass the valid TES pulses on line l72 to 14 reset latch 291 thereby providing a continuous select PLL
line 162 signal on line 169 keeping switch 160 in the 16 illustrated setting. As soon as the profile is reduced to 17 below the predetermined value, then latch 291 is again reset 18 to the inactive condition bY comparator 286. If a continu-19 ous phase sync loss signal from PLL 171 portion 175 is received over line 295, latch 291 stays in the reset state 21 for the remainder of the seek.

23 Figs. 9 and 10 show a track-crossing indicating circuit 24 which performs the function of verify count circuits 176 and supplies count input to a counter in track counter 175. The~
26 optical signals are retrieved from "quad" detector 62 as 27 shown in Fig. 5. The differential tracking error signal 28 (TES) on line 63 has a +TES signal 197 (Fig. 6) and a -TES
29 signal 270 (Fig. 9~; one signal being the complement of the other. The output signals of all four photo diodes A-D of 2~ 2~

1 detector 62 are scanned to create a sum or "quad" signal 198 2 (Fig. 10) having phase quadrature to TES signals 197 and 3 270. The quad and TES signals are combined to reliably 4 detect track crossings with an indication of relative direction of radial motion of the beam 47 to disk 30.

7 The block diagram of Fig. 9 is described with respect to the 8 signals shown in Fig. 10. The inputs A1, Cl are the TRS
9 signal 207 from differential amplifier 212 (Fig. 5). These inputs go to Schmitt triggers STl 300 and ST2 301, respec-11 tively. The Schmitt triggers have switchable hvsteresis 12 levels. The sw;tchable hvsteresi~s levels ellminate "plck 13 up" errors when track seeking at low radial v~locitles 14 (hysteresis increased) and drop outs when seeking at high velocities (hysteresis decreased). The baseline tracking 16 circuit (303) varies the reference level of the first 17 Schmitt triggers 300 and 301. Circuit 303 is only operative 18 at high seek velocities. A veloci-ty detector 304 compares 19 the desired velocity profile signal (a current velocity) on line 219 (DAC 250 of Fig. 7) with a reference value signal 21 on line 305 and determines wh~n to switch between different 22 hysteresis levels of the Schmitt triggers and a variable 23 reference level~

The quad signal 224 is used to detect retrograde motion 26 during a seek operation. Retrograde motion may occur 27 whenever disk runout is high or vibrations occur. The quad 28 signal has a 90-degree phase lag with respect to the TES
29 signal 207 when seeking radially inward versus a 90-degree phase lead when seeking radially outward. Output signals 1 308 and 309 respectively from AND 311 and AND 312 indicate 2 track crossings in respective opposite radial directions, 3 such as caused by a change in relative direction of moti~n 4 of the beam and track durinq a seek. A change in directi~
causes pulses which appeared at one output switch to the 6 other output. The quad signal 224 used to detect the 7 occurrence of retrograde motion is only used when seeking at 8 low velocities. Once the track crossing frequency is high, 9 this circuit path is gated off.
11 Baseline tracking circuits 303 and 313, respectively, 12 restore the baseline references for both the TES and quad 13 signals. The positive peak amplitude le~rel of the TES
14 signal 207 activates one of the Schmitt triggers, STl or ST2, 300 or 301. Triggers STl and ST2 each have asymmetry 16 which is accommodated by the complementary connections. The 17 time duration each peak level is stored varies as a function 18 of velocity (track-crossing frequencv). The baseline 19 reference voltages are connected to one leg of a comparator 315 (Schmitt trigger in the TES path). The other leg of the 21 comparator receives the quad signal 224. The outputs of the 22 comparator 315 are square wave B and b 316,317.

24 Fig. 10 shows two different runout conditions havin~ retro-grade motions. The solid line being one example and the 26 dotted line being the other example. The signal designated 27 as "Al" is the TES signal 207 and the one designated as "Bl"
28 is the ~uad signal 224. "AP" is defined as Al pulse occur-29 ring each positive-sloped zero crossing of the TES and "AN"
having pulses each time a negative zero crossing occurs. B2 TU9~8001 33 2 ~ 11 2 ~

1 and B2 are the in-phase and out-of-phase dlgital track 2 summing signals. The AND of AP+B2, ORed with the AND of 3 AN+2 produces track-crossing pulse at output ANDl for 4 indicating a radial outward motion of the beam. The AND of AP+B2 ORed with AND of AN+B2 produces track-crossing pulses 6 at output AND2 indicating a radial-inward motion of the 7 beam.

g In Fig. 9, gating logic 320 receives a direction signal from microprocessor 40 over line 321 which respectfully indicates 11 the,direc-tion of commanded seek direction radially inward or 12 radially outward. When a direction signal on line 321 13 indicates a radial].y-inward motion, then the radial impulses 1~ from AND circuit 282 are suhtracted from the numerical contents of track counter 26 which indicates distance to go, 16 while the radial-outward pulses from AND circuit 281 are 17 added to the counter 292 contents. In a similar manner, 18 when the direction signal on line 291 indicates a radial-19 outward motion, the pulses from AND circuit 281 are sub-tracted from the contents of counter 292, while the output 21 pulses from AND circuit 282 are added to the counter 292.
22 Reading the illustrated logic for achieving this simple 23 arrangement is well known. The output of AND circuits 311 24 and 312 represent the output signal of track-crossing circuit 125 which includes the illustrated NAND circuits and-26 the illustrated Schmitt triggers and baseline circuits. The 27 operation of NAND circuits is well known and the logic of 28 operation can be determined from inspection of Fig. 9.

2~2~

1 Referring next to Fig. 11, the illustrated velocity-state 2 estimator circuit is a preferred construction of velocity 3 circuits 130 which smoothes the measured velocity signal and 4 causes the measured velocity signal to change when a defect is being crcssed (no TES signal 207 is being produced) using 6 servo system parameters as will become apparent. This 7 smoothing provides a continuous analog-type velocity signal 8 throughout a seek operation even with significant defects.
g Such smoothing includes modeling the mechanical dynamic characteristics of the fine actuator and the relative-11 position error sensor 56. When the track-crossing frequencv 12 (high radial speed) durlng a SEEK exceeds a predetermined 13 threshold, digital ~elocity circuits 330 are emp]oyed for 14 generating the measured velocity signal on line 133. Such circuits may be the circuits shown in the co-pending appli-16 cation, supra; while at speeds below the track-cros~sing 17 frequency threshold, the TES signal on line 63 is employed 18 for measuring the radial velocity. The Fig. ll-illustrated 19 circuits selectivelv modify the measured velocity signal or the TES signal on line 63 tc supply a continuous analog-type 21 velocity-indicating signal on line 133.

23 In Fig. 11, summation circuit 400 receive.s three inputs to 24 be summed for providing the measured velocity signal on line 133. A first input signal is received from the fine actua--26 tor drive signal on line 57~ (the drive signal without the 27 radial runout compensation effect provided over line 118 28 lFig. 3). The fine actuator 46 drive current on line 57D is 29 modified in circuit 401 by a model of the force constant of fine actuator 46. A second input is the RPE signal on line 2~12g~0 1 58E that is modified by circuits ~02. In circuits 40?, the 2 RPE signal is modified by a model of the spring constant and 3 viscous damping constant of the fine actuator 46. The RPE
4 effect on summation circuit 400 is to subtract or counteract the other two inputs. In a practical embodiment, the 6 portions in circuits 402, respectively modelling the spring 7 constant and the viscous damping constant, may result in 8 separate summation inputs to the summation circuit 400. The 9 third input to summation circuit 400 on line 403 provides a timed velocity recalibration input from either velocity 11 cir$uits 330 or from the line 63 T~S signal 207, depending 12 upon the track-crossing frequency, as will become apparent.
13 The RPE error .signal from circuit 402 i.s subtractec1 ~rom the 14 sum of the first and third inputs, respectively, from circuits 401 and 403. Summation circuit 400 supplies its 16 sum signal through compensation circuit 404 which modifies 17 the summation circuit by an inverse of a model of the fine 18 actuator 46 mass value. Compensation circuit 404 supplies 19 its compensated signal through low-pass filter LP 405 to line 133.

22 The actual measured velocity calibration change of the 23 smoothed measured velocity signal on line 133 is timed to 24 coincide with the ends of respective velocity-measuring periods. Switch 410 times the modification of the estimated 26 measured velocity throughout the seek operation. The timing 27 is controlled by circuit 411 which holds electronic switch 28 410 closed for a predetermined period, such as by a mono-29 stable multivibrator indicated in circuit 411 by the word i'HOLD". Circuit 411 has four inputs into two AND function ~2~

1 circuit portions Al and A2. Circuit Al times the switch 410 2 whenever the digital velocity-measuring circuit 330 is being 3 implemented; i.e., above the track-crossing frequency 4 threshold. Below the track-crossing frequency threshold, when the TES signal on line 63 is used for generating the 6 velocity signal, AND circuit A2 controls the timing of 7 switch 410. An OR circuit "~R~ passes the outputs of ANn 8 circuits Al and A2 in a logic OR manner for actuating the 9 HOLD portion of circuit 411.

ll Circuit 411 is controlled by comparator circuit 412.
12 Comparator circuit 412 receives the reference velocitv 13 signal on line 132 (Fig. 3) for co~parison with a track-14 crossing frequency threshold value received over line 413.
Since the threshold signal on line 413 is a constant, it can 16 be provided by a voltage divider or other suitable voltage 17 or current source. Comparator circuit 412 is of the switch-18 ing type such that when the reference velocity on line 132 19 is less than the threshold signal on line 413, an actuating signal is supplied by comparator circuit 412 only over line 21 414; when the reference velocity signal on line 132 exceeds 22 the threshold signal on 413, then an actuating signal is 23 supplied over line 415. The reference velocity signal on 24 line 132 is representative of the track-crossing frequencvO
The actuating signal on line 414 is supplied to AND circuit 26 A2 for passing the track-crossing signals received from line 27 63 to actuate the "hold" portion of circuit 411 for closing 28 switch 410. AND circuit Al is enabled to pass the end of 29 measuring period signal on line 331 by the line 415 signal.
The line 331 signal is delayed by circuit 416 to compensate 2~280~

1 for circuit delays. When the digital velocity circuit 330 2 is providing the measured velocity signal on line 332, AND
3 circuit A1 is actuated at ~he end of each of the measuring 4 periods for timing the closure of calibrating switch 410.

6 Analog summation circuit 420 supplies the calibrate signal 7 through switch 410 as the third summation input on line 4~3 8 for analog summation circuit 400. Line 421 couples the 9 output of compensation circuit 404 as a suhtractive input into summation circuit 420. The actual measured signals are ll supplied to summation circuit 420 respectively through 12 either switch 422 or 425. Switch 422 is closed bv the line 13 415 actuating signal for passing the digital velocity 14 measured signal on line 332 as a positive summation signal to summation circuit 420. Therefo.re, when the seek speed or 16 velocity is greater than the threshold on line 413~ the 17 correction signal to summation circuit 400 is the difference 18 between the measured signal on line 332 from the digital 19 measuring circuit and the feedback signal on line 421.

21 When the seek speed is below the threshold value on line 22 413, the velocity measurement is as follows: The TES signal 23 207 on line 63 supplied though gain control block circuit 24 426 goes to switch 427, thence to sample and hold circuit S&H 428. Sample and hold circuit 428 receives the input TES
26 pulses on line 161 at each TES signal 207 zero crossing (two 27 zero crossings per track crossing). Electronic switch 425 28 remains closed when comparator 412 supplies the actuating 29 signal on line 414. Switch 410 supplies the timing control 2~1~8~

1 for the calihration of the measured velocity signal on line 4 Polarity corrections have to be provided for the velocity signal calculated from the line 63 TES signal 207. Refer-6 ring next to Fig~ 6, a portion of the grooved medium 30 is 7 shown with track center lines ~06 being in the grooves with 8 no tracks being on the mesas -15 intermediate the grooves.
g Tracking error signal 207 (TES signal on line 63) is shown in spatial relationship to the grooved media 30. An actual 11 track-crossing signal is represented by the vertical line 12 22Q and the ~ero crossings of TES signal 207 on the ~esas 13 are represented by numeral 221. Depending on th~ rel~tiv~
14 direction of motion with respect to the groove ~r track crossings 206, the polarity of the signal supplied to switch 16 427 varies. Accordingly, the actual relative direction of 17 the beam 47 as it crosses the tracks 206 have to be polarity 18 reversed. To achieve this, the outpl~ signal of gain-19 ad~usting circuit 426 is supplied over line 435 to direction circuit 436 which receives a direction indisating signal 21 over line 437. The direction indicating signal on line 437 22 is the actual direction as determined by the comparison of 23 the quadrature signal and the TES signal (Fig 9). Circuit 24 436 basically is a phase compare such that the control of switch 427 will always provide a properly-phased signal to 26 circuit S&H 428. ~ine 439 causes a polaritv inverted signal 27 from circuit 426 for supplying an inverted signal to termi-28 nal 440 of switch 427. The operation of the circuit is such 29 that when the beam is relatively moving across the tracks as seen in Fig. 6 from left to right, all signal crossings will 2~ 2~0(1 1 be positive. That is, the signal crossings at points 221 2 will be polarity inverted rather to have the same polarity 3 velocity-indicating signal in S&H 428. On the other hand, 4 when the beam movement is from right to left, the indicating S signals are reversed.

7 While the invention has been particularly shown and de-8 scribed with reference to preferred embodiment thereof, it 9 wlll be understood by those skilled in the art that various changes in form and details may be made therein without 11 departing from the spirit and scope Or the inventlon.

~U988001 40

Claims (15)

1. In a machine-effected method of operating a positioning mechanism having relatively movable first and second mem-bers, one of said members having closely-spaced-apart, position-indicating-machine-sensible indicia and another of said members having means for sensing said indicia, motive means coupled to said members for relatively moving same;
the improvement, including the machine-executed steps of:
sensing said indicia by said sensing means and generat-ing indicia signals for indicating said sensed indicia;
slaving a timed electrical circuit to said indicia signals for generating timed signals;
during a first predetermined portion of a relative movement of said members, applying only said indicia signals to said motive means for actuating the motive means to rela-tively move said members; and during a second predetermined portion of said relative movement, applying only said timed signals to said motive means for actuating the motive means to relatively move said members.

2. In the machine-effected method set forth in claim 1, the machine-executed steps of:
during said relative movement, sensing for and electri-cally indicating the relative velocity of said members;
establishing a reference velocity, comparing said electrically-indicated velocity with said reference velocity and indicating when said electrically-indicated velocity is greater than said reference velocity; and including third ones of said detection time periods in said second predetermined portion while said electrically-indicated velocity is greater than said reference velocity .

3. In the machine-effected method set forth in claim 2, the machine-executed steps of:
establishing and storing a velocity profile indicating a desired velocity throughout said relative movement; and altering the detection time period durations in an inverse ratio to the velocity of said velocity profile.

4. In the machine-effected method set forth in claim 3, the machine-executed steps of:
during said second predetermined portion, altering the frequency of the timed signal in a linear direct proportion to said velocity profile.

5. In the machine-effected method set forth in claim 4, the machine-executed steps of:
taking said desired velocity from the velocity profile and establishing a pass frequency band for the sensed signals such that the pass band frequencies are in a prede-termined direct ratio with said desired velocity; and filtering said sensed signals to lie only in said pass band such that any sensed signals outside the pass band are blocked and therefore not within said detection time periods.

6. In the machine-effected method set forth in claim 5, the machine-executed steps of:
modelling the servo system and changing the measured velocity in accordance with said modelling.

7. In the machine-effected method set forth in claim 5, wherein said first member is a transducer-carrying member movably mounted on a frame for reciprocating motions along a first lineal path, said second member is a record-member having record tracks extending transversely to said first lineal path and the members being relatively movably mounted for movements along said record tracks for enabling said sensing means to scan the respective record tracks, said record-member having grooves and mesas extending along said tracks, said sensing means including means for shining a light beam onto the record member and having detection means having four rectangularly arranged light sensing elements oriented such that one axis of the rectangle enclosing the four elements is aligned with the extend of the record-member tracks and includes means for generating the sensed signals by combining the signals from the elements on the respective sides of said axis and differencing the signals from the elements on the opposite sides of the axis and generating a quad signal by summing signals from all of the elements;
further including the machine-executed steps of:
counting the sensed signals such that an effective count of two represents transversal of one of said record tracks; and each time said quad signal amplitude indicates a current track crossing adjusting the count such that the count is even each time the quad signal signifies the beam impinges on a track.

8. In a machine-effected method of relatively moving first and second members, one of the members having closely spaced-apart, position-indicating, machine-sensible indicia and another of said members having means for sensing said indicia and producing indicia signals, motive means coupled to said members for relatively moving same;
the improvement including the machine-executed steps of:
during said relative movement, analyzing the indicia signals for electrically indicating the relative speed of movement as a sensed relative speed;
slaving a timed circuit to said indicia signals for generating timed signals;
comparing said sensed relative speed with a speed limit and indicating a first portion of said relative movement when the sensed relative speed is less than said speed limit and indicating a second portion of said relative movement when the sensed relative speed is greater than said speed limit; and supplying said indicia signals to said motive means only during said first portion and said timed signals to said motive means only during said second portion for actuating said motive means to control relative motion of said members during said relative movement.

9. In the method set forth in claim 8, the machine-executed steps of:
establishing and storing a speed profile for said relative movement which indicates desired speed as a func-tion of relative displacement during said relative movement;
indicating relative displacement of said members during said relative movement;
generating detection time periods for said indicia signals during said relative movement which varies in duration in an inverse ratio to one of the indicated speeds such that the detection time periods indicate the time of sensing for said indicia; and supplying only those indicia signals occurring during said detection times to said motive means.

10. In a positioning system having first and second rela-tively moveable members, said first member being a record member having elongated tracks in the record member, an optical transducer on the record member in optical communi-cation with the record member and its grooves, said members being mounted on a frame for first and second relative movements in first and second directions respectively along and transverse to said tracks, tracking circuit means operatively coupled to the transducer for receiving an indicia signal indicative of the current relative position of the transducer to one of said grooves along said second direction, motive means coupled to said members for rela-tively moving same along said second direction for moving said transducer from one record track on the record member to a second record track in the record member and displaced from the one record track along said second direction;
the improvement including, in combination:
a timed electrical circuit electrically connected to said transducer means for receiving said indicia signals and being slaved to said indicia signals for generating timed signals;
selection means for indicating first and second prede-termined portions of said relative movements in said second direction;
coupling means connected to said motive means, said timed electrical circuit, said transducer and said selection means for responding to said indications of the first and second portions to respectively supply said indicia signals and said timed signals to said motive means only during said respective first and second portions.

11. The invention set forth in claim 10, further including, in combination;
speed profile means and detection window generating means in said selection means;
distance means coupled to said transducer for receiving said indicia signals and generating an indication of rela-tive position of said members during said relative movement;
said speed profile means being coupled to said distance means for receiving said indication of relative position and generating therefrom an indication of desired speed of relative movement between said members;
said window generating means being coupled to said speed profile means and to said transducer for respectively receiving said desired speed indication and said indicia signals for generating a detection period indication during which occurrence of said indicia signals may be detected such that the detection period occurs when the transducer is scanning said tracks during said relative movement in the second direction, signal detection means in said window generating means jointly responsive to said detection window indication and to said indicia signals to indicate whether or not an indicia signal occurred during a detection window, said signal detection means being operatively connected to said coupling means to supply an indication of said first portion whenever said detection indicates an indicia signal occurred during the detection window and an indication of said second portion whenever said detection indicates an indicia signal did not occur during said detection window.

12. In the invention set forth in claim 11, further includ-ing, in combination:
speed means indicating a speed value;
means in said window generating means coupled to said speed profile means for receiving said desired speed indica-tion and coupled to said speed means for comparing said speed profile indicates a speed higher that the speed indicated by said speed value.

13. In the invention set forth in claim 11, further includ-ing in combination:
frequency band-pass means electrically interposed between said transducer and said window detection means and coupled to said speed profile means for responding to said speed profile indication to change the pass band in a direct ratio to the indicated speed.

14. In the invention set forth in claim 11, further includ-ing in combination:
distance means electrically connected to said trans-ducer for receiving said indicia signals and counting same at two counts per track crossing for indicating relative displacement of said members during said relative movement in said second direction;
amplitude indicating means electrically connected to said transducer for receiving a signal therefrom which is in phase quadrature to said indicia signal;
verify means electrically and logically interposed between said distance means and said amplitude indicating means for receiving said count and said alternating signal, and means in the verify means whenever said count is odd at a predetermined amplitude and polarity of said alternating signal to alter the count in the distance means by unity.

15. In the invention set forth in claim 14, further includ-ing, in combination:
multiple means in said signal detection means operative whenever said signal detection means receives a plurality of said indicia signals during any given one of said detection periods to indicate said second portion.