FI86778C - MAGNETSKIVSTATION - Google Patents

Description

86778

Magnetic Disk Drive

The invention relates to a magnetic disk drive comprising a disk assembly having at least one data surface with annular dataurs comprising sectors each containing a data field and a servo field containing internal servo signals, an internal signal of the internal signal to detect servo signals and position the read / write head of the head setting system over the selected data track, the internal servo signals in each servo field being included in circumferentially spaced segments adjacent to the center-15 line of the data track including the servo field and located on opposite sides of the centerline.

A magnetic disk device, commonly referred to as a "disk drive", is a memory device used in a computing system to store traceable digital data 20 in magnetic form. The data is stored on a rotating magnetic disk in a series of concentric circular patterns called "grooves." The read / write head is mounted on a conveyor which moves the head radially to bring it to the desired groove and then maintains it in place above that groove so that the head can store a series of data bits or alternatively trace a series of bits from the groove as the groove rotates below the head. High-capacity disk drives comprise a plurality of disks of that type mounted to rotate 30 together about a single axis. At least one separate read head is used for each disk surface, with all ends mounted on the same conveyor to provide a comb-like arrangement in which the ends move in and out as a unitary system.

35 The conveyor on which the read-write heads are mounted 2 86778 is included in the servo system, which performs two separate functions when moving the conveyor. One of them is the "search" or "access" function, in which the servo system moves the read head to the selected groove from the previous 5 grooves, which may be located at the end of many grooves. When the head reaches the desired groove, the servo system initiates a "groove tracking" function in which it accurately positions the head over the centerline of the selected groove and maintains it at that location as subsequent portions of the groove pass past the head.

10 Searching and career tracking activities place different demands on the servo system. During the retrieval operation, the conveyor must be moved as fast as possible to minimize the time required for this operation. Speed accuracy is also important to create a speed trajectory and good arrival characteristics. On the other hand, during the career tracking function, position accuracy is the most important factor. The accuracy with which the read-write head can be made to follow the center line of the groove is a determining factor in view of the groove density of the disc. In other words, the closer the head can be made to follow the center lines of the grooves, the closer the grooves can be placed to each other.

The head positioning servo system senses the position of the read / write head using servo signals stored in the grooves on the plates. In a conventional arrangement, the servo signals are stored on a special servo surface, i.e. a surface containing only these signals. In another conventional arrangement, the servo signals are included in the data. This means that they are stored in the servo fields at the beginning of the data trackers. Internal servo signals are able to provide more accurate data end location information than specific servo signals. However, because they are separated from each other by the number of data sectors on the data track, they are sampled periodically at a relatively low frequency. They are thus unable to provide position signals with high frequency components. On the other hand, the servo signals in each groove on a particular servo surface are substantially continuous and thus are able to provide location information with a substantially 5 wider frequency band.

U.S. Patent Nos. 4,115,823 to Commander, et al. and 4,072,990 to Case, et al. shows a servo control system that uses both internal servo signals and signals from a specific servo surface. Signals from a specific servo surface are used during career search operations. During groove tracking operations, the system combines the signals from both sources into a "hybrid" position error signal that is used to control the position of the read / write head. A hybrid signal is a combination of the low frequency components of an internal servo signal with the high frequency components of a particular servo signal. This allows a wideband hybrid position error signal while maintaining the accuracy provided by the low frequency components of the internal signals. However, this arrangement does not achieve the positioning accuracy required for higher groove density, which in turn is desired in newer high performance disk systems.

The main object of the present invention is to provide a multi-disk disk drive with an improved head positioning system capable of positioning data heads within a relatively small error.

A more specific object of the invention is to provide a disk drive in which the head positioning system utilizes both special and internal servo data.

Another object of the invention is to provide a disk drive of the above type which is able to closely follow the center lines of the data grooves and which is thus capable of a relatively high groove density.

It is a further object of the invention to provide a disk drive of the type of the present invention in which servo data can be stored at a relatively low cost.

This is achieved by a magnetic disk station characterized according to the invention in that the internal signal detector includes first and second amplitude sensors for detecting the respective amplitudes of the detected servo signal segments and an automatic gain control circuit including first and second attenuators connected to receive the respective outputs of the amplitude sensors. selectively switchable to change its output between maximum and minimum attenuation, means for summing the attenuator outputs, means for comparing the output of the adder means to a reference level, means responsive to the output of the comparator means for switching attenuators according to whether the sum is greater or less than the reference level, thus maintaining attenuation at the reference level and means for reducing the attenuator outputs in the form of an internal groove signal error-2 0, which main setting system responds to said internal groove signal error.

The disk drive shown here includes many features that accomplish the above objectives. First, instead of combining only the low frequency components of the internal servo signal with the high frequency components of the special servo signal, the entire internal servo signal is combined with the high frequency components of the special servo signal to provide a hybrid or combined groove error signal used in the servo system.

The invention is further characterized by the use of high frequency bursts as internal servo signals. More specifically, each sector of the data track begins with an internal servo field containing a first high frequency burst 35 flanking the groove centerline on one side and then a second high frequency burst flanking the centerline on the opposite side. Thus, as the servo field travels under the read-write head, the head first senses one burst and then another. If the head is located aside from the desired centerline location, the received amplitude of the first burst is greater than the received amplitude of the second burst, and it is this difference that is used as the internal position error servo signal.

This type of internal servo signal has been used in the past but has not been used, as far as is known to the applicant, in connection with a specific servo surface. This provides an important advantage due to the fact that the positions of the servo bursts in the circumferential direction do not have to be kept within strict tolerances, as will be explained below. Thus, internal servo signals can be written to a data surface on the same disk drive that reads and writes data to these surfaces. This means that a disk assembly with a pre-stored special servo surface can be mounted on the station and the station can then use the servo information from the special plate to radially position the ends on the data surfaces and schedule the writing of internal servo bursts. With other types of internal servo formats, the servo signals must be located in a circumferential direction with a high accuracy, but the vibration of the data heads relative to the servo head prevents that accuracy from being achieved. Therefore, both special and internal servo information must be stored in advance on a very expensive machine designed for this purpose.

The station is further characterized by the use of novel types of automatic gain control circuits for servo signal detection, as described below. These gain control circuits provide wide bandwidths in the gain control loops, and thus high-gain loops can be used to monitor variations in the intensities of the stored servo signals.

The drive also includes several other features, which are described below.

Figures 1A and 1B show a diagram of a disk drive according to Embodiment 5 of the invention.

Figure 2 schematically shows the arrangement of internal servo signals on the data surface.

Figures 3A and 3B include a circuit diagram of the internal serodata demodulator of Figure IB.

Figure 4 shows several timing diagrams of the circuits of Figures 3A and 3B.

Figures 1A and 1B show in block diagram form a disk drive including a head positioning system according to an embodiment of the present invention. The multi-plate 15 plate size assembly 10 comprises a plurality of stacked magnetic plates 12, 14 and 16 mounted at equal distances from each other for rotation about an axis 18. The mobile conveyor 20 supports a set of read-write heads or transducers 22-26 mounted on the Luke-20 ground or to write data from the upper and lower surfaces of the plates 12 and 14 and the upper surface of the plate 16. The conveyor also supports a reading head 27 mounted to read servo information stored on the bottom surface of the plate 16, this surface being a special servo surface.

The conveyor 20 is moved toward and away from the electromagnetic actuator 28 to position the respective transducers radially inwardly and outwardly with respect to the plates 12, 14 and 16 to obtain magnetically stored information from selected circular grooves 30 in the plates. The grooves are selected in the control of the general control unit 30 of the station, which receives a command from the data processing system to which the disk system shown is connected. The drive control unit typically receives instructions to read or write data in the selected groove 35 on the selected data surface of the disk assembly 20. The present invention relates to a servo system that moves a read / write head to a selected groove and maintains it in place above the centerline of that groove during read or write operation.

More specifically, referring further to Figure 1B, data converters 22-26 are connected to the head selection and amplifier unit 32 by a series of wires 34. The unit 32 selects a data surface in the disk assembly 10 by connecting one of the data heads 22-26 in response to the head 10 selection signals from the station control unit 10. The unit 32 is also connected to read-write circuits 33 which transmit data from the disk assembly 10 to the data processing system during read operations and in the opposite direction during write operations. Circuits 34 also provide an automatic gain control signal for circuit 32. During both write and read operations, internal servo signals are read from the selected data track and unit 32 directs them to internal servo data demodulator 36.

At the same time, the output of the servo converter 27 is fed to a conventional preamplifier 38, the output of which in turn is fed to a special servodata demodulator 40. The output of the demodulator 40 appears substantially time-multiplexed to the four conductors 42A-42D. These specific groove location signals are applied to the location evaluation circuit 44 along with the internal groove error signal from the demodulator 36. The output of the position error circuit 44 is a combined groove error signal (COMPOSITE TE) which, after the modifications disclosed herein, is fed to a power amplifier 46 which controls the actuator 28 to close the servo loop and bring the data head to the desired groove and maintain it in the centerline of this groove.

More specifically, the combined groove error signal from the location estimator 44 is summed in the adder 48 with the output of the low frequency amplifier unit 50 and the position offset 86778 8 correction signal from the digital analog converter 52. The input of the converter 50 is a digital jitter and bias correction signal conducted by the station control unit 30 in the manner described below. The output of adder 48, in turn, is applied via state switch 5 to second adder 56. Adder 56 adds to the groove error signal a speed feedback signal provided by speed evaluation circuit 58 and a speed command derived by digital analog converter 60 from signals provided by station control unit 30. 10 The output of 56 is passed through a limiting amplifier 62 and a frequency compensation circuit 64 before being fed to a power amplifier 46.

During the search operations, the switch 54 is open so that the input of adder 56 consists only of (1) a speed command signal from station control unit 30 and (2) a speed feedback signal from speed evaluation circuit 58 subtracted from speed command signal by adder 56 to provide a speed error feedback signal. .

The station control unit 30 provides a speed command based on the distance of the servo inverter from the groove into which it is being moved, as is known in the art. This distance, which may be called coarse position information, is provided by the track difference counter 66 66, which is initially loaded by the station control unit 30 with the number of tracks to be crossed when moving on the selected track. The counter thus counts down in response to the groove crossing pulse sent by the groove detection unit 68 each time the servo head 27 traverses the groove over the mat-30 to the destination groove. The groove detection unit 68 in turn responds along conductors 42B-42D to the output signals from the special servodata demodulator 40.

When the selected groove is approached, the switch 54 is closed and remains closed during the next groove follow-up operation, so that the adder 56 receives the combined groove error signal from the position estimating circuit 44 as it has been transformed in the adder 48. During this mode of operation, the digital-to-analog converter 60 does not receive any command from the station control unit 30. However, the evaluation circuit 58 provides a rate feedback signal.

The speed estimating circuit 58 derives its speed signal from the specific servo position signals up to the conductors 42A-42D during the search operations and from the combined groove error signal 10 provided by the position estimating circuit 44 during the groove tracking operations. It is switched to these two operating modes by a control signal obtained from the station control unit 30, as shown in Fig. 1A.

The thought signals for the station are passed to the phase count-15 unit 70. The unit 70 provides in particular suitable thought signals for the operation of the servodemodulators 36 and 40.

Figure 2 shows the format of the internal servoinformation on the data track with one of the data pins 20 of the disk assembly 10. The sets of dataurs are indicated by their centerlines 250, 251, etc. Each groove contains a series of sectors, each containing a servo field 254 followed by a data field 256. The servo field 254 contains two sets of servo signal blocks denoted by "X" and "Y". 25 Each block is centered on the edge of a groove (not shown), has a width equal to one groove, and thus covers the distance between the center lines of two adjacent grooves. The X-blocks are centered on alternating groove edges and the Y-blocks are centered on alternating edges that rotate with respect to the X-blocks. Thus, as the disk rotates below the lu-ku write head 262 located above the groove centerline, a portion of the X servo block passes below the head, followed by a portion of the Y servo block. The system determines the radial position of the head 262 with respect to the centerline 251, ensuring the relative 10 s * 778 portions of the widths of the X and Y blocks under the head 35.

More specifically, each X or Y servo block contains a magnetically stored high frequency burst. The amplitude 5 of the burst received by the head 262 from the X-block is compared with the next amplitude received by the Y-block. The equality of these two amplitudes indicates that the head is centered on the centerline 251; if they are different, the magnitude of the difference in expressed amplitudes is a measure of the deviation from the centerline of head 262.

It should be noted that when the head 262 is positioned above a pair of numeric grooves, such as above the groove 251, the X servo blocks are radially outer blocks with respect to the groove centerline and the Y blocks are radially inner blocks. Conversely, when the end 262 is positioned above the even-numbered groove, the Y-blocks are outer blocks and the X-blocks are inner blocks. This gives the direction of the position error signal derived from the X and Y blocks depending on whether the groove is even or odd numeric, a factor that is taken into account in the operation of the internal servo detector 36.

It is obvious that the X and Y servo blocks in Fig. 2 do not have to be placed in the circumferential direction with high accuracy. They should be spaced apart by a distance greater than the width of the gap 25 at the magnet 252 so that the end does not receive energy from the X-block at the same time as it receives energy from the Y-block. In addition, there should be a dead zone before the X-blocks and after the Y-blocks, so that the end 262 does not receive any other signal when it receives the X-block signals and the Y-block signals. In addition to this, the circumferential arrangement of these servo blocks has relatively wide tolerances, so they depend on the requirements set by the timing signals used to express the servoinformation.

35 An important feature resulting from this arrangement 86778 11 is the ability to use the disk drive itself to store internal servo signals. A high-precision servo recording system only needs to be used to record signals on a special servo surface. The signals 5 received from this surface can be used by the station itself to store internal servo information for the other data stacks.

Fig. 3 is a circuit diagram of a detector 36 that detects internal servo signals and generates an internal position error signal 10 in response thereto. The plurality of timing signals used in Figure 3 have been generated by decoder 262, the input of which is the contents of the counter 186 of Figure 10. The timing of these signals and the signals produced by demodulator 36 is shown in Figure 4.

Referring to Figure 3, input from demodulator 36, head selection, and amplifier unit 32, passes through adder 264 to input amplifier 266. The output of amplifier 266 is passed through LC tank circuit 268 having a resonant frequency equal to the signal burst frequency included in each of X and Y. to the servo data block (Figure 2). Tank circuit 268 is turned on and off by a reset LC tank signal from decoder 262, this signal effectively shorting the tank circuit at times other than the arrival times of the X and Y bursts, as shown in Figure 4. The output format of tank circuit 268 is also shown in Figure 4. .

The output of the tank circuit 268 passes through an amplifier 270 to a full-wave rectifier 272, the output of which is filtered by a low-pass filter 274. The filtered signal then passes through a resettable integrator 278 of the switch 276, with the typical output of the integrator shown in Figure 4. 282 and 284 pairs. If the servo burst included in the integrator 278 is from the outer block, it is sampled and held in circuit 282. If it is from the inner block, it is held in circuit 284. Thus, at the end of each internal servo field, the sampling and hold circuits 282 and 284 contain updated voltages corresponding to the 5 sensed amplitudes in the outer and inner servo blocks in the data groove in which the selected data end is positioned.

The contents of the sampling and holding circuits are passed through buffer amplifiers 286 and 288 to an automatic gain control circuit, generally indicated at 10 290. After the gain correction by circuit 290, they are subtracted at a difference amplifier 292, the output of which generates an internal groove error signal.

More specifically, referring further to Figure 3, in the automatic gain control circuit 290, the outer 15 and inner signals pass through switch attenuators 294 and 296 and buffer amplifiers 302 and 304. The outputs of the buffer amplifiers are fed to a differential amplifier 292. They are also fed to an adder 306, which compares the sum of their voltages with the reference voltage. The voltage comparator 20 308 sets its output whenever the sum of the output voltages of the buffer amplifiers 302 and 304 exceeds the reference voltage. In response to the setting level, the switch station 310 switches the attenuators 294 and 296 to their attenuation state. With the attenuators shown, each comprising a series resistor and a bypass switch, this drops the attenuator output voltages to zero. The output voltages of the low-pass filters 298 and 300 then begin to decrease, and when their sum becomes less than the reference voltage applied to the adder 306, the comparator resets its output. As a result, the dampers 294 and 296 are connected to their non-damping state, so that the output voltages of the low-pass filters 298 and 300 begin to increase again.

In operation, attenuators 294 and 296 periodically reciprocate between their attenuation and non-attenuation states 35, the frequency at which this switching occurs 86678 13 depending on the time constants of the low pass filters 298 and 300 and the dead range of the comparator 308. The comparator 308 preferably has a negligible dead band and, as a result, attenuators 294 and 296 are switched at a high frequency, for example at a frequency of 1-5 MHz. The gain control circuit 290 thus has a fast response, typically several microseconds, to change the input signal states and, in addition, can accommodate a large range of input signal levels.

Claims (1)

86778 Claim A magnetic disk drive including a disk assembly (10) having at least one data surface (16) having 5 annular data grooves containing sectors each containing a data field (256) and a servo field (254) containing internal servo signals. a signal detector for detecting internal servo signals and positioning the read / write head of the head setting system over the selected data groove, the internal servo signals in each servo field being included in circumferentially spaced segments adjacent to the data groove centerline, the groove including the centerline on opposite sides, characterized in that the internal signal detector includes a first (282) and a second amplitude tur (284) for detecting the respective amplitudes of the detected servo signal segments and an automatic gain control circuit (290) comprising the first 20 (294) and second (296) attenuators connected to receive the respective outputs of the ground amplitude sensors (282, 284), the attenuators (294, 296) being selectively switchable to change their output between maximum and minimum attenuation, means (306) for summing the attenuator outputs 25 , means (308) for comparing the output of the adder means (306) to a reference level, means responsive to the output of the reference means (308) for connecting attenuators (294, 296) according to whether the sum is greater than or less than the reference level while maintaining the attenuator output voltage substantially at said reference level; (292) for reducing the outputs of the attenuators to generate an internal groove signal error, the main setting system responding to said internal groove signal error. 15 86778 Drives for magnetic rock, single-core and single-core (10) with data and data (16), up to 5 circuits with circular data set, with non-internal data, single data and data (256) and servo (254) in the case of in-service servo-signalers, the detector for in-line servo-signaling detectors for the detection of in-service servo-signalers and in the field of operation of the 10-inch system for switching the output of the power supply to the on-board servo signal , a single signal at the center of the data line, a single spAr internal servofallet, and a single signal at the center of the signal line at the center line, the reverse signal, a detector for the signal amplifier at the same level (282) from the second (282) and above amplitude -tuder hos avkända servosignalsegmenter och en automatisk 20 förstärkningsregl special ring (290), in which the span (294) and the spool (296) are selected from the amplitude of the amplifier (282, 284), the splitter (294, 296) can be selected from the splitter to the max. and with a minimum of 30, (306) for summer heating with the same temperature, the medium (308) for the summer with high pressure (306) for the summer with high temperature (306) for the summer with the summer (308) , 296) is an increase in the sum of the amounts of the same and the same value as in the case of the same number of parts (292) in the case of the same number of parts, (292) for the subtraction of the result. reader for these spArsignalfel.