GB2231686A

GB2231686A - Controlling magnetic disk apparatus

Info

Publication number: GB2231686A
Application number: GB9006377A
Authority: GB
Inventors: Makoto Nishimura
Original assignee: Tokico Ltd
Current assignee: Tokico Ltd
Priority date: 1989-05-19
Filing date: 1990-03-21
Publication date: 1990-11-21
Also published as: DE4009476A1; GB9006377D0; JPH02306479A

Description

MAGNETIC DISK APPARATUS CONTROL DEVICE

Field of the InMention

The present invention pertains to control devices for magnetic disks and the like.

Background Art

Winchester drives are a well known example of magnetic disk data storage devices. Winchester drives are magnetic disk drives composed of multiple disks mounted on a unitary spindle. In such drives, a motor causes the disks to rotate in unison at a fixed rotational velocity via the spindle. As the disks rotate, magnetic data may be written to and read from a series of concentric tracks on their surfaces. In general, these devices employ a servo-surface servo control system which permits accurate, high speed data access, as well as accurate and stable control of the rotating disks.

In such a drive, the lower surface of the lowermost disk often serves as the servo-surface which contains read-only servo data, while the upper surface of the same disk as well as both surfaces of all the remaining disks serve as readwrite data surfaces. Data is read from all surfaces and written to the data surfaces by magnetic heads which can be moved to a target position over a respective disk surface by means of a voice coil motor (VCM) or similar drive means, thereby becoming positioned over a target track. Magnetic head movement is approximately linear, in a radial orientation with respect to the magnetic disks and is governed by control circuitry which is part of the drive equipment, based on the above mentioned servo data. In this way, a magnetic head becomes positioned over a target track out of the many concentric rotating tracks on the respective disk surface.

The necessary radial displacement of a magnetic head in order to reach the correct position over the target track is calculated from data based on the target position and the current position. Based on the displacement calculated as described above, a target head velocity is read from a velocity table (containing an array of the above mentioned displacement values correlating with corresponding velocity data indicating the head velocity required to realize that displacement) in ROM. On the basis of the target-head. velocity thus determined, feedback control of the drive current supplied to the above mentioned VCM is carried out, thereby effecting head towards the target position movement. Accordingly, until the target ve locity of the magnetic head read from the above mentioned velocity table is actually attained by the moving magnetic head, acceleration control is carried out. After the target speed has been reached, deceleration control of the magnetic head is carried out.

With the servo-face servo system described above, because the apparatus employs a dedicated servo-surface, it is possible to sample the servo data from the servo face nearly continuously, each sampling taking place over some several microseconds. Thus tracking adjustments can Ize make nearly instantaneously, and fine control of tracking movements can be accomplished.

In recent years, a data-face servo system has been developed in which the servo data is included on the same disk surfaces that are used for recording data, occurring for example at intervals along the length of a circular track. By eliminating the servo-face, more disk space is made available for recording data. However, with such a system, since the servo data is included on the same disk surfaces on which data is recorded, the servo data occurs at a much lower density than on the dedicated servo-surface of a conventional winchester drive. Accordingly, a considerable length of - 1) - time, on the order of several hundreds of microseconds is required to sample the servo data.

With such a data-face servo system, if there is even one mis-sampling of the servo data during a high speed radial movement of the magnetic head, speed control carried out based on an inappropriate velocity value read from thevelocity table based on erroneous servo data continues over a relatively long period of time at least until the next servo data sampling (several hundreds of microseconds). As a result, there is a much greater tendency for the movement of the magnetic heads to become unstable. Additionally, deceleration control of the magnetic heads cannot be carried out at high speeds.

Summary of the InventiQU

In consideration of the above difficulties, it is an object of the present invention to provide a magnetic disk apparatus control device by means of which control of the drive means for the magnetic heads can reliably be carried out stably and at high speeds.

In order to achieve this object, as-shown in Fig. 1, the--.--,. present invention includes: a remaining displacement calculation means A for determining the remaining displacement n which is the difference between the current magnetic head position and the target head position; a velocity data memory means B for outputting standard velocity data corresponding to the remaining displacement n determined by the remaining displacement calculation means A; a velocity calculation means C for calculating movement velocity of the above mentioned magnetic head based on data indicating the current position of the magnetic head read out from the magnetic disk; and a drive current calculation means D for calculating the value for the drive current to be supplied to the above mentioned drive means based on the above mentioned g remaining displacement n, the standard velocity data, and the magnetic head movement velocity.

With such a magnetic disk apparatus control device, standard velocity data corresponding to the remaining displacement n and the actual movement velocity of the magnetic head are supplied to the drive current calculation means D,- whereby the drive current calculation means D determines the appropriate drive current to be supplied to the drive means, thereby achieving accurate, reliable and stable high speed control of the drive means for the magnetic heads.

Further, with the magnetic disk apparatus control device as described above, when the remaining displacement n is relatively large, feed forward control can be carried out, and when the remaining displacement n is small, feed back control can be carried out. Thus seek operations.can be carried out accurately, and at high velocity. For this reason, with the apparatus of the present invention, even when used as a data-face servo system which entails relatively long servo data sampling periods, the magnetic heads can be stably controlled.

Brief Description of the Drawin_gz

Fig. 1 is a functional block diagram showing the structure of the present invention.

Fig. 2 is a block diagram of the control system of the present invention.

Fig. 3 is an oblique view schematically showing a magnetic disk incorporated in the present invention.

Fig. 4 is a overhead view showing a data track in detail from the magnetic disk shown in Fig. 3.

i Fig. 5 is a waveform chart for showing some of the characteristics of the servo data read out from the magnetic disk shown in Fig. 3.

Figs. 6 (a) and (b) are the charts showing control characteristics of the magnetic disk apparatus control device of the present invention.

Description of the Preferred Embodiments of the Invention

In the following sections, one preferred embodiment of the present invention will be described with reerence to Figs. 1 through 6.

First of all, with reference to Figs. 3 and 4, the format of the servo data will be described.

In addition to ordinary data, a plurality of servo sectors 2 (for example 45) are providedon magnetic disk 1 a:t equal intervals in a radial orientation, as shown in F ig. 3. Servo data is written in these servo sectors 2 according to the'format shown in Fig. 4. As shown in Fig. 4,. the_servo sectors 2 of each tack are provided with an address mark AM, a gray area indicating the track position, and an odd-even area more precisely indicating the position on the track, that is, whether the magnetic head is positioned at the center of the track or not.

In the next section, the make up of the control circuit will be described with reference to Fig. 2.

The magnetic head 3 disposed opposing the recording surface of the magnetic disk 1 reads data from the disk surface and outputs a difference signal (Dx - Dy). This difference signal (Dx - Dy) is then supplied to head amplifier 4 where it is amplified to yield a position signal - 5 F+. The output from the head amplifier 4 is then supplied to digital signal processor DSP via gate array GA1. The difference signal (Dx - Dy) from the magnetic head 3, as well as the corresponding position signal F+ output from the he-ad am-olifier 4 characteristically vary as shown in Fig. 5 as each bit passes.

The grey code (16 bits) written in the grey area of the servo sector (see fig. 4) is read by the magnetic head 3, and via head amp 4, supplied to gate array GA1._ In gate array GA1, the grey code is then written to an internal grey code register from which it is supplied to digital terminals P20 to P27 of the digital signal processor DSP as cylinder position data CYL eight bits at a time.

Also, the digital signal processor DSP computes the movement distance of the magnetic head from the current cylinder position supplied from the gray code register in the gate array GA1 and the target cylinder position. Together with this, the digital signal processor DSP receives standard velocity data corresponding to the computed movement distance from a velocity table data previously stored in ROM (read only memory) from which it calculates a feed-forward control signal according to a formula to be described later.

1 The signal from the odd-even area included in the position signal F+ is converted into a position error ' difference signal PE in a CE-DET circuit, which is.then supplied to an analog input terminal AN1 in the digital signal processor DSP. That is, by causing the magnetic head 3 to read the odd-even signal written in the servo sector at a phase difference of a half cycle, the position error signal PE is supplied to the analog input terminal AN1 in proportion to the extent of deviation from the track center by the magnetic head 3.

The digital signal processor DSP digitally processes the position signal supplied from the magnetic head 3 and outputs control signals from terminals DAC1 and DAC2 to provide feed forward control or feed-back control to the voice coil motor J VCM which serves as a drive means for the magnetic head 3. These control signals are amplified by amplifier Al and supplied to a operator A2 as a drive current command value IT, which is then supplied to a VCM driver 5 after having been amplified by the predetermined gain K2. The VCM driver 5 controls the drive current of the VCM according to the drive current command value IT, by which the voice coil 6 in the VCM is driven at a predetermined speed. Furthermore, the signal that indicates the drive current of the VCM driver 5 is supplied to the operator A3, after which it is supplied to the analog input terminal AN2 in the digital signal processor DSP as a current feed-back signal IFB after having been amplified by a predetermined gain K3. Using the velocity data obtained by integrating the signal IFB supplied to the terminal AN2, based on position data, the velocity calculated by digital signal processor DSP is corrected, whereby the velocity is more accurately obtained.

The drive current command value IT is also supplied directly to an analog input terminal ANO of the digital signal processor DSP to be used as a reference voltage Vref' for the above described velocity correction.

With the control circuit constructed as described above, the' voice coil motor VCM is controlled by feed-back control in accordance with the characteristics shown in Fig. ((a), and by feed-forward control in accordance with the characteristics shown in Fig. 6(b), and is thereby controlled so as to cause the magnetic head 3 to move to the target position.

In other words, when the seek operation is directed, the digital signal processor DSP reads in from gate array GA1 the grey area position data supplied from the magnetic head 3, then calculates the distance between the current position and the target position, and forms from this distance the drive current command value IT which is calculated using the formula:

IT = K1 { (a - b) f (n) + C (1 f (n)} Equ. 1 where a is the standard velocity from the velocity table corresponding to the distance of the magnetic head 3 from the target position, b is the actual velocity calculated by the' digital signal processor DSP according to the position data from gate array GA1, n is the number of tracks remaining between the number of the current track and that of the target track, that is, n indicates the distance between the current position and the target position of the magnetic head 3, C is the target current, and K1 is the gain. f(n) is a servo coefficient which is a function of the tracks n remaining for the movement which gradually increases as the remaining tracks decreases, and is defined such that abs(f(n)).:::-:,. 1. The remaining tracks n takes a value such that 0 j n nj, where nj is the"total track movement, that is the difference between the track number at the start of magnetic head 3 movement and the target track number.

It can be seen from Equ. 1 above that immediately after the start of the movement of the magnetic head 3 when the number of the remaining tracks n is large and f(n) is very small, the drive current command value IT comes to be approximately equal to Kl"C. Thus as shown in Fig. 6(b),-a n approximately constant target current C is supplied to.the voice coil motor VCM at the onset of magnetic head j movement. In Fig. 6(a) where the solid line indicates target velocity a, the brokenline shows that the actual velocity b is rapidly rising towards the target velocity a at the onset of magnetic head 3 movement. Then, when the target velocity a is attained at point Pl, drive current is supplied in the reverse direction to the voice coil motor VCM as shown in Fig. 6(b), and the magnetic head 3 decelerates. Then, based on the position data CYL supplied from the gate array GA1, target velocity a is read out, and as control is carried out according to Equ. 1, the magnetic head 3 gradually moves to the vicinity of the target track. Furthermore, when the 4 number of the remaining tracks n falls below a predetermined value at point P2, f(n) approaches zero, and the drive current command value IT comes to be approximately equal to Kl(a - b). Moreover, at point P3 when the target velocity a comes to equal 0, drive current command value IT becomes zero and the VCM stops. Also, together with this kind of feedback control carried out in the vicinity of the target position, by controlling the drive current command value IT so that the position error signal PE supplied to terminal AN1 is less than a reference value, it is also possible to position the magnetic head 3 at the center of the target track. This is inputted into the terminal AN1, below the reference value, and feed-back control can be made in the vicinity of the target position.

To summarize the above-described control operations:

(1) In the region where f(n) is small, feed-forward control is carried out because the drive current command value IT is mainly dependent on [1 f(n)] which is-not influenced by the actual speed b.

(2)' In the-region where f(n) is large, feed-back control is carried out because the drive current command value IT is mainly dependent on [(a - b) f(n)l which is influended by the actual speed b.

1

Claims

What is claimed is:

1. A magnetic disk apparatus control device comprising:' a drive means for driving a magnetic head; a remaining displacement calculation means for determining a remaining displacement n which is the difference between a current magnetic head position and a target head position; a velocity data memory means for outputting standard velocity data corresponding to said remaining displacement n determined by said remaining displacement calculation meanst- a velocity calculation means for calculating movement velocity of said magnetic head based on data indicating a current position of said magnetic head read out from'a magnetic disk; and a drive current calculation means for calculating a value for a drive current to be supplied to said.drive means based on said remaining displacement n determined by said remaining displacement calculation means, said standard velocity data output from said velocity data memory means, and said magnetic head movement velocity determined by said velocity calculation means.

A magnetic disk apparatus control device in accordance with Claim 1 above in which in said drive current calculation means, said drive current supplied to said drive means is calculated by obtaining a first value by multiplying the difference between said standard velocity data and said magnetic head movement velocity by a function of said remaining displacement; obtaining a second value by subtracting said function of said remaining displacement from 1, and multiplying the difference thereby obtained by a first constant; and adding said first value and said second value and multiplying the sum thereby obtained by a second constant.

A magnetic disk apparatus control device in accordance with Claim 2 above in which said function of said remaining displacement is such that when said magnetic head is in the vicinity of said target posit-ion, the value of said function of said remaining displacement becomes large.

4. The fflagnetic disk apparatus control device substantially as herein ddEtibdd with reference to and as shown in the accompanying drawings P--b'ished 1990 at The Pazen Office. SzateHouse-66 71 High Holborn. LcndonWC1R4TP. Further copies maybe obtainedfrom The Patent Office. Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Multiplex techWques ltd, St Mary Cray. Kent, Con. 1187