JPH03192584A - Magnetic disk device - Google Patents

Abstract

PURPOSE:To improve the suppression rate of a position deviation by inputting a position deviation signal to a position deviation correction circuit and adding a correction signal outputted from the position deviation correction circuit to a position deviation generating circuit. CONSTITUTION:A position deviation correction circuit 15 consists of a closed loop circuit 16 and a proportion element 17. A dead time element 18 is provided so as to apply positive feedback of the output to the input side. The element 18 delays a position deviation E(S) by a disk fundamental rotation period L and outputs the result. Since the output of the element 18 is fed back positively to the input side, the open loop gain is infinite at a frequency k/L being a multiple of (k) of a disk rotation frequency 1/L. The element 17 outputs a signal at a multiple of K of an input signal. Thus, the suppressing rate of the control is improved by nearly 50 - 60dB.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic disk device equipped with a magnetic head positioning mechanism using servo control, and particularly to a magnetic disk device that has excellent followability of a magnetic head against track runout. Regarding.

``Prior Art'' FIG. 4 is a block diagram showing a schematic configuration of a conventional magnetic disk device equipped with a head positioning mechanism using a sector servo control method.

In this figure, reference numeral 1 denotes a magnetic disk, and a large number of concentric tracks are formed on the surface of the magnetic disk 1. Each of the above tracks is divided into multiple sectors, and each sector is a data sector into which various data are written.
It consists of a field and a servo field in which servo information is written. Further, 2 is a rotating shaft of a spindle motor, and 3 is a magnetic head that scans the above-mentioned track during rotation and reads and writes data and servo information. As described above, data fields and servo fields are alternately set in each track, so servo information is intermittently provided. 4 is a carrier that supports the magnetic head 3;
5 is a VCM (voice coil motor) that directly drives the carrier 4; Further, 6 is a CPU (central processing unit) that controls each part of the device and also functions as a compensator (PID controller) to be described later; 7 is a spindle motor control circuit that controls the rotational drive of the spindle motor; 8
is a position signal generation circuit (servo demosimulator) that generates a position signal indicating the current position of the magnetic head 3 based on servo information read from the magnetic head 3. 9 is C
The positioning circuit IO corrects the positional deviation of the magnetic head 3 by controlling the current applied to the VCM 5 based on the current command from the PU 6, and is a recording/reproducing circuit that creates a recording/reproducing signal.

FIG. 5 is a block diagram showing how signals are transmitted in a servo control system applied to the conventional magnetic disk device.

In this figure, 11 amplifies the control amount C(S) output from the controlled system 12, and the feedback amount B
Feedback amplification element to be fed back as (S), 13
is the feedback I from the target value (target position γ(S))
By subtracting B (S), the positional deviation E (S
), 14 is the positional deviation E (S)
PID to the controlled system 12 based on the supply of
It is a compensator that performs (proportional-integral-derivative) control operation. Note that the VCM 5 and the carrier 4 are the control target system 12 described above. Ideally, the track TR on the disk surface is formed in a perfect circle, but in reality, as shown in FIG. 4, undulations may occur due to eccentricity of the magnetic disk 1. It's normal. FIG. 3(a) is a signal waveform showing track runout when servo control is not performed.

Therefore, in the above servo control method, in order to follow the undulating track TR, the amount of track deflection is considered to be the above target position γ(S).

In the servo control system with the above configuration, the integral compensation time constant of the compensator 14 is set to be less than or equal to the basic disk rotation period, thereby suppressing vibrations around the disk basic rotation frequency. It was also able to follow track vibrations.

"Problems to be Solved by the Invention" By the way, in the above-mentioned conventional magnetic disk device, the suppression rate near the basic disk rotation frequency is at most 10~
It was only about 20 dB (the signal waveform is shown in FIG. 3(b)). In order to increase the suppression rate, the gain of the compensator 14 is forcibly increased.

Since the compensator 14 is located in the (main) loop, there is a problem that the stability of the servo control system deteriorates.

This invention solves the above problem by focusing on the fact that components of track runout near the disk basic rotational frequency have high reproducibility (repeatability) caused by eccentricity of the magnetic disk l. It was done in order to
It is an object of the present invention to provide a magnetic disk device that has excellent track followability without deteriorating the stability of a servo control system.

“Means for solving the problem” Claims to solve the above problem! The described invention includes a positional deviation generation circuit that generates a positional deviation signal representing the amount of positional deviation of the magnetic head from the center of the track, and a positioning of the magnetic head based on the positional deviation signal supplied from the positional deviation generation circuit. A dead time element that delays an input signal by a time equal to the basic rotation period of the magnetic disk and outputs it, and a feedback element that positively feeds back the output of the dead time element to its own input side. and a proportional element that multiplies the output signal of the closed loop circuit by K (K is a positive number), and inputs the position deviation signal to the position deviation correction circuit. In addition, the correction signal outputted from the positional deviation correction circuit is added to the apparatus deviation signal formed from the positional deviation generation circuit, and the resultant signal is supplied to the servo control circuit.

The invention according to claim 2 includes a positional deviation generation circuit that generates a positional deviation signal representing the amount of positional deviation of the magnetic head from the center of the track, and a positional deviation generation circuit that generates a positional deviation signal representing the positional deviation amount of the magnetic head from the center of the track. a servo control circuit that performs positioning; , n delay devices that delay the input signal by a time equal to the sampling period and output the signal are connected in cascade to form a closed loop circuit, and the position error signal that has passed through the sampler is connected to the input side of the first stage delay device. A closed-loop delay circuit has an input terminal that takes in the output terminal of the closed-loop delay circuit and has an output terminal on the output side of the final stage delay device, and the output signal of the closed-loop delay circuit output from the output terminal of the closed-loop delay circuit is multiplied by (K is positive A position deviation correction circuit is provided, which includes a proportional element that holds the output signal of the proportional element, and a zero-order hold element that holds the output signal of the proportional element, and the position deviation correction circuit manually inputs the position deviation signal, The present invention is characterized in that the output signal of the positional deviation generation circuit is added to a device deviation signal constituted by the positional deviation generation circuit and the resultant signal is supplied to the servo control circuit.

"Operation" According to the configuration described in claim 1, by passing the positional deviation signal through the closed loop circuit, the disk basic rotation frequency component of the positional deviation signal is determined to
The previous cycle, 2 cycles before, ..., N cycles before are multiplexed, and a feedforward control effect can be obtained, so there is no need to forcefully increase the gain of the servo control circuit.
The component can be suppressed. Therefore, it is possible to prevent the servo control system from becoming unstable.

Also, in the configuration according to claim 2, the multiplexed disk fundamental rotation frequency component can be obtained by passing the position error signal through the closed loop delay circuit, so that the same effect as in the configuration according to claim 1 can be obtained. Obtainable.

"Embodiments" Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First Embodiment) FIG. 1 is a block diagram showing a state of signal transmission in a servo control system applied to a magnetic disk device which is an embodiment of the invention as claimed in claim 1. Figure 1 1! 5, the same reference numerals are given to the parts corresponding to those shown in FIG. 5, and the explanation thereof will be omitted.

Note that the schematic configuration of the magnetic disk device applied to this example is the same as the conventional schematic configuration shown in FIG.

The magnetic disk device applied to this example differs from the conventional one described above in that a position error correction circuit 15 is added in parallel between the summing point 13 and the compensator 14 in the servo control system. It is a point.

This position deviation correction circuit 15 is composed of a closed loop circuit 16 and a proportional element! It consists of 7. The closed loop circuit 16 is
It is constituted by a dead time element I8 configured to provide positive feedback of its output to the input terminal. This dead time element I8 is based on the input signal (i.e.
This is an element that outputs the positional deviation E(S)) after being delayed by the basic rotation period of the disk. As mentioned above, the dead time element 18 has its output positively fed back to its input side, so that at /L, the frequency is k (k is a positive integer) times the disk basic rotation frequency 1/L. Open loop gain becomes infinite. The proportional element 17 is an element that outputs a signal twice the magnitude (value) of the input signal.

The operation of this example is as follows.

Immediately after servo control starts, only the same characteristics as conventional servo control can be obtained. This is because the transfer function is e-8L
This is because there is a dead time element. Therefore, immediately after the start, the positional deviation E(S) has the signal waveform shown in FIG. 3(b). However, after L time has elapsed from the start, the positional deviation E (S) is as shown in Fig. 3(c).
The signal waveform becomes as shown in , and is significantly suppressed. This is because the track runout is mostly composed of a /L component at a frequency k (k is a positive integer) times the disk basic rotational frequency 1/L. Furthermore, after the elapse of L time, the positional deviation E(s) has the signal waveform shown in FIG. 3(d). Furthermore, after the elapse of L time, the positional deviation E(s) is
The signal waveform is shown in FIG. 3(e).

As mentioned above, according to the servo control method of this example, learning control (Fig. 3 (b) to (e)) is performed, thereby improving the control suppression rate to about 50 to 60 dB. I can do it.

Furthermore, since the gain of the compensator 14 is not forced to increase, stability can always be maintained.

Furthermore, even if a disturbance D (S) is applied to the controlled system 12, it can be suppressed to the same extent as above.

(Second Embodiment) FIG. 2 is a block diagram showing the configuration of a position deviation correction circuit of a servo control system applied to an embodiment of the invention as claimed in claim 2.

The difference between the position deviation correction circuit of this example and the position deviation correction circuit 15 of the first embodiment is the position deviation correction circuit of the first embodiment! 5 has an analog configuration, whereas the position deviation correction circuit in this example has a digital configuration.

In FIG. 2, I9 is a position deviation correction circuit, and this position deviation correction circuit 19 is composed of a sampler 20, a closed loop delay circuit 211, a proportional element 22, a zero-order hold element 23, a summing point 24, etc. . The sampler 20 has a positional deviation E(s) at each sampling interval T.
Operates a switch that allows the passage of sampling interval T
is determined as L/n when the number of sectors of the magnetic disk l is rnJ and the disk basic rotation time is rLJ. In this example, the number of sectors is set to about 40, and the sampling interval T is set to about 400 μsec. Also, the above closed loop delay circuit 2! is the addition point 2
5 and n delay elements 26.2B, . These delay elements 26, 26°, etc. all have the same configuration and delay the input signal by the same time as the sampling interval T. These delay elements 26, 26 .・
... are connected in cascade, and the final stage delay element 26
The output signal from the summing point 25 is positively fed back to the first stage delay element 26. The summing point 25 adds the output signal of the final stage delay element 26 that has been positively fed back and the positional deviation E(s) that has passed through the sampler 20, and supplies the result to the first stage delay element 26. . The proportional element 22 doubles the output signal from the final stage delay element 26. The zero-order hold element 23 holds the output signal from the proportional element 22 during the sampling period. The above addition point 24 is the zero-order hold element 2
The compensator 14 adds the output signal from 3 and the device deviation E(s) consisting of the summing point 13 (FIG. 1).
(Figure 1).

In the above configuration, when the closed-loop delay circuit 21 receives the position deviation E(s) via the sampler 20, the closed-loop delay circuit 21 sequentially converts the position deviation E(s) into n delay elements 26, 26, . Let it pass. In this way, the positional deviation E(s) that has passed through the final stage delay element 26 is delayed by an amount equivalent to the basic rotation period of the disk. The output signal from the final stage delay element 26 is positively fed back and is again input to the first stage delay element 26.

After that, the delay and positive feedback are repeated sequentially, and in the end, before L time,
A signal on which the positional deviations E(s) of 2L hours before, . . . are superimposed is output as an output signal of the closed-loop delay circuit 21. This output signal is doubled in a proportional element 22, held in a zero-order hold element 23, and returned to the main loop via a summing point 24.

Also with the configuration of the second embodiment, learning control similar to that shown in FIG. 3 is performed, and the positional deviation E(s) is suppressed.

The configuration of the second embodiment has the advantage that it is easier to create the dead time element 18 having a time constant (as compared to the first embodiment).

In the second embodiment, if the main loop itself is a discrete system, the sampler 20 and zero-order hold element 23 in the position error correction circuit 19 are unnecessary.

Further, in the above-mentioned embodiments, the case of the sector servo method was explained, but it can also be applied to the servo surface servo method. For example, 1 of the basic rotation period of the disk.
This is possible if discretization is performed using a sampler that operates at /n (n is the number of sectors).

"Effects of the Invention" As explained above, according to the magnetic disk drive of the invention as set forth in claim 1 or 2, by performing learning control, the suppression rate of positional deviation can be increased from 10 to 20 dB to 5 dB.
It can be improved to about 0 to 60 dB, that is, to about 100 times.

Furthermore, since the gain of the compensator is not forced to increase, it is possible to always reduce track runout caused by rotation of the magnetic disk in a stable state.

Further, since the loop gain is not increased, oscillation caused by mechanical resonance of a drive system such as a VCM does not become a problem, and the design is easy.

Further, even if a disturbance is applied to the controlled system, it can be suppressed in the same way as track shake.

Because of the above effects, it is possible to increase the density of tracks.

[Brief explanation of drawings]

Figure 1 is a claim! FIG. 2 is a block diagram for explaining the state of signal transmission in a servo control system applied to magnetic disk loading, which is an embodiment of the invention as claimed in claim 2. FIG. 3 is a track runout waveform diagram for explaining the track runout in the embodiment of the present invention, and FIG. 4 is a diagram showing a conventional magnetic disk drive. FIG. 5 is a block diagram showing a state of signal transmission in a servo control system applied to a conventional magnetic disk. ■...Magnetic disk, 3...Magnetic head, 5...VCM, 6...CPU (
central processing unit), 8...position signal generation circuit, 9
...Positioning circuit, 12...Controlled system, 13...Addition point (position deviation generation circuit), 14...Compensator (servo control circuit) )
, 15.19...Position deviation correction circuit, 16...
...Closed loop circuit, 17.22...Proportional element, 18...Dead time element, 20...
Sampler, 21...Closed loop delay circuit, 23.
...Zero-order hold element, 24.25...
Addition point, 26...delay element (delay unit),
γ(S)...Target position, B(S)...
・Feedback amount, E (S)...Position deviation (position deviation signal), C(S)...Control amount, TR
······truck.

Claims (2)

[Claims] (1) A position deviation generation circuit that generates a position deviation signal representing the amount of positional deviation of the magnetic head from the center of the track, and a servo that positions the magnetic head based on the position deviation signal supplied from the position deviation generation circuit. A magnetic disk device equipped with a control circuit, comprising a dead time element that delays an input signal by a time equal to the basic rotation period of the magnetic disk and outputs it, and a feedback element that positively feeds back the output of the dead time element to its own input side. A position deviation correction circuit including a closed loop circuit and a proportional element that multiplies the output signal of the closed loop circuit by K (K is a positive number) is provided, and the position deviation signal is input to the position deviation correction circuit, and A magnetic disk drive characterized in that a correction signal outputted from the positional deviation correction circuit is added to a positional deviation signal outputted from the positional deviation generation circuit and the resultant signal is supplied to the servo control circuit. (2) A position deviation generation circuit that generates a position deviation signal representing the amount of positional deviation of the magnetic head from the center of the track, and a servo that positions the magnetic head based on the position deviation signal supplied from the position deviation generation circuit. In a magnetic disk device equipped with a control circuit, 1/n (n is a positive integer) of the basic rotation period of the magnetic disk.
A sampler that passes the position error signal every sampling period equal to n, and n delay devices that delay the input signal by a time equal to the sampling period and output the signal are connected in cascade to form a closed loop circuit, and a first stage a closed loop delay circuit having an input end for taking in the position error signal that has passed through the sampler on the input side of the delay device, and an output end on the output side of the final stage delay device; The output signal of the closed loop delay circuit is multiplied by K times (
A position deviation correction circuit is provided, which is composed of a proportional element (K is a positive number) and a zero-order hold element that holds the output signal of the proportional element, and the position deviation signal is input to the position deviation correction circuit. and adding a correction signal output from the position deviation correction circuit to a position deviation signal output from the position deviation generation circuit and supplying the resultant to the servo control circuit.