JPH0317875A - Head positioning circuit for magnetic disk device - Google Patents

Abstract

PURPOSE:To stably perform positioning control by judging the position of a magnetic head with an absolute address counter, and varying the gain of a position signal with a variable gain amplifier by selecting an appropriate correction value with a read-only memory. CONSTITUTION:A track pulse signal 2, a forward signal 3, a reverse signal 4, and a reset signal are inputted to the absolute address counter 6 of a variable gain circuit 14, and the counter 6 judges the current position of the magnetic head, and outputs a correction value address signal 7 to select the correction value of the power constant of a voice coil motor. The read-only memory 8 receives the selection signal 7, and outputs the correction value of the power constant suitable for the current position of the magnetic head as a digital correction value signal 9. The correction value signal 9 is supplied to the variable gain amplifier 12 via a D/A converter 10, and changes the gain of the amplifier 12, and the position signal 1 is outputted as a correction position signal 13. Thus, the positioning control can be stably performed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a head positioning circuit for a magnetic disk device.

[Prior Art] Conventionally, a head positioning circuit of this type of magnetic disk device uses a voice coil motor to move a magnetic head and position it on a target track.

This voice coil motor is driven by a drive current output by a power amplifier. Information regarding the position of the magnetic head is given by a position signal obtained by the magnetic head reading position information written on the servo surface and demodulating the read position information. During a position control operation to hold the magnetic head on a target track, a position signal is fed back to the power amplifier input to form a closed position control loop. FIG. 3 shows a block diagram of a position control loop of a conventional head positioning circuit. The signal flow will be explained using FIG. 3.

(1) The target position signal 15 and the feedback position signal 29 are input to the comparator A.

(2) The position deviation signal 16 is output from the comparator A to the position signal demodulation circuit 17.

(3) Position signal 1 is output from position signal demodulation circuit 17 to compensation circuit 18.

(4) One compensation position signal is output from the compensation circuit 18 to the power amplifier 20.

(5) 2 l of current is output from the power amplifier 20 to the voice coil motor 22.

(6) The force signal 23 is output from the voice coil motor 22 to the movable part 24.

(7) The acceleration signal 25 is output from the movable part 24 to the integrator 26.

(8) The measured speed signal 27 is output from the integrator 26 to the integrator 28.

(9) Two feedback position signals are output from the integrator 28.

The oven lube transfer function G (s
) is G(s)=K1・KC(S〉・KA−KP・1/M・
1/S2 (s=jω, K: force constant, M: movable part mass).

The frequency fc (oven-lube crossover frequency) at which the oven-lube gain IG(s)l of the oven-lube transfer function G(s) is 1 is fc-1/2π・(Kt
-KA "Kp/M)", and when the values of K, , M change, the value of fc also changes. Also, as shown in Figure 4,
The force constant KP of the voice coil motor has position dependence 30, but conventional positioning methods do not take into account the position dependence 30 of the force constant KF of the voice coil motor, and the average value of the force constant K is 31 It is designed based on. Therefore, depending on the position of the voice coil, the average force constant is 31
Errors 32, 33, and 34 from the position become large, and the open-lobe transfer function fc changes depending on the track position.

[Problems to be Solved by the Invention] In the head positioning circuit of the conventional magnetic disk drive described above, the force constant K of the voice coil motor differs depending on the position. In a truck, the oven lube gain during positioning becomes small, resulting in a large transient response and a small holding force against external forces. In addition, in tracks with a large force constant KF, that is, tracks with a large frequency fc, the open-lube gain during positioning becomes large, which amplifies mechanical resonance of moving parts, magnetic heads, etc., and makes the position control loop unstable. , it has the disadvantage of oscillation.

SUMMARY OF THE INVENTION An object of the present invention is to provide a head positioning circuit for a magnetic disk drive that has a transient response at a constant small level, has a large holding force against external forces, and can perform stable positioning control.

[Means for Solving the Problems] In order to achieve the above object, a head positioning circuit for a magnetic disk device according to the present invention has the following features.

That is, the present invention provides a head positioning circuit for a magnetic disk device that positions a magnetic head at a target position by a closed loop control method using a position signal representing a change in the position of the magnetic head as a feedback signal. an absolute address counter that outputs a correction value address selection signal for selecting a correction value for the force constant of the voice coil motor; a read-only memory that outputs a constant correction value as a digital correction value signal; a DA converter that receives the digital correction value signal, converts it into an analog correction value signal, and outputs the analog correction value signal; A position deviation signal obtained from the error between the magnetic target position signal and the feedback signal is received, the gain is changed by the analog correction value signal, the position deviation signal is amplified by this gain, and a corrected position signal is generated. It is characterized by having a variable gain amplifier that outputs as follows.

[Effect] The force constant of a voice coil motor is position dependent.

If the amplifier gain is adjusted taking this position dependence into account,
Stable head positioning control is possible. In this invention, the following steps are taken.

The absolute address counter confirms the current position of the magnetic head. Then, a correction value address selection signal for selecting a correction value for the force constant of the voice coil motor corresponding to the current position of the magnetic head is output to the read-only memory.

Based on this correction value address selection signal, the read-only memory selects an appropriate correction value from among the force constant correction values stored in advance, and outputs the correction value to the DA converter as a digital correction value signal. . The DA converter converts the digital correction value signal into an analog correction value signal and outputs this signal to the variable gain amplifier. The variable gain amplifier receives the analog correction value signal and the position deviation signal, corrects the position deviation signal using the analog correction value signal, and outputs a corrected position signal as a result.

As described above, the magnitude of the corrected position signal can be changed depending on the position dependence of the force constant.

[Example] Next, an embodiment of this system will be described with reference to the drawings.

FIG. 1 shows a variable gain circuit 1 used in an embodiment of the present invention.
4 is a block diagram of FIG. In this embodiment, a variable gain circuit is used as part of the head positioning circuit of a magnetic disk drive.

The absolute address counter 6 of the variable gain circuit 14 receives a track pulse signal 2, a forward signal 3, and a reverse signal 4.
and reset signal 5 are sent.

The absolute address counter 6 determines the current position of the magnetic head and outputs a correction value address selection signal 7 to the read-only memory 8 for selecting a correction value for the force constant K of the voice coil motor corresponding to the position of the magnetic head. do. Based on the correction value address selection signal 7, the read-only memory 8 selects a value suitable for the current position from among the correction values of the force constant KF stored in advance, and outputs the digital correction value signal 9.
is output to the DA converter 10. The DA converter 10 performs DA conversion on the digital correction value signal 9 and outputs the converted signal as an analog correction value signal 11 to the variable gain amplifier 12 .

In addition to the analog correction value signal 11, the position signal 1 is also input to the variable gain amplifier 12. The variable gain amplifier 12 is
Depending on the position of the magnetic head, where the force constant KF is smaller than its average value, the position signal 1 is amplified with a gain K greater than the gain 1, which corresponds to the analog correction value signal 11.

Also, where the force constant K is larger than its average value,
Conversely, it is amplified with a gain K smaller than the gain 1.

Then, a corrected position signal 13 is output.

FIG. 2 shows a block diagram when the variable gain circuit 14 having the above function is added to the position control loop of the magnetic head.

The difference between FIG. 2 and the prior art shown in FIG. 3 is that a variable gain circuit 14 is inserted between a position signal demodulation circuit 17 and a compensation circuit 18. As for the signal flow, the following is added in place of operation (3) of the prior art.

(3-1) Position signal 1 is output from the position signal demodulation circuit 17 to the variable gain circuit 14.

(3-2) The corrected position signal 13 is output from the variable gain circuit 14 to the compensation circuit 18.

In FIG. 2, the same reference numerals are used for circuits, signals, etc. that are the same as in the prior art.

The oven Lube transfer function G (s) for position control in the block diagram of Fig. 2 is as follows: G(s> -K+ - K - Kc(s)・KA
− Kp − 1/M·1/s2 (s−jω, K: force constant, M: mass of moving part).

The frequency fc (open loop crossover frequency) at which the oven loop gain IG(s)l of the oven loop transfer function G(s) becomes 1 is fc-1/2π・(K+
・K-KA-K, / M) l/2. This fc has a constant fc value regardless of changes in the force constant KF. This is because the gain K of the variable gain amplifier is determined so that K and -K are always constant. Therefore, when positioning the magnetic head on the target track, the transient response remains at a constant small level regardless of the track position, and the holding force against external forces also increases.

As a result, stable positioning control of the magnetic head can be performed.

[Effect of the Invention] As explained above, in this invention, the absolute address counter judges the (U position) of the magnetic head, and the read-only memory that receives this judgment result corrects the force constant stored in advance. An appropriate correction value is selected from among the values.Then, based on this correction value, the variable gain amplifier changes the gain of the position signal.

By doing this, the open-lube gain G(s)l of the open-lube transfer function G(s) for position control is
The frequency fc at which 1 becomes 1 can be kept constant regardless of changes in the force constant. As a result, when the present invention positions the magnetic head on the target track, the transient response is kept at a constant small level regardless of the track position, and the holding force against the outside is also increased, making it possible to perform stable positioning control. effective.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a variable gain circuit according to an embodiment of the present invention, Fig. 2 is a block diagram of a position control loop of this embodiment, Fig. 3 is a block diagram of a conventional position control loop, and Fig. 4 is a block diagram of a conventional position control loop. FIG. 3 is an explanatory diagram showing the position dependence of the force constant of a voice coil motor. 1... Position signal 6... Absolute address counter 7... Correction value address selection signal 8... Read only memory 9... Digital correction value signal 10... DA converter 11... Analog correction Value signal 12...Variable gain amplifier 13...Corrected position signal 15...Target position signal 16...Position deviation signal 29...Return position signal

Claims (1)

[Scope of Claims] In a head positioning circuit of a magnetic disk device that positions a magnetic head at a target position by a closed loop control method using a position signal representing a change in the position of the magnetic head as a feedback signal, the current position of the magnetic head is an absolute address counter that outputs a correction value address selection signal for selecting a correction value for the force constant of the voice coil motor; a read-only memory that outputs a constant correction value as a digital correction value signal; a DA converter that receives the digital correction value signal, converts it into an analog correction value signal, and outputs the analog correction value signal; Receives a position deviation signal obtained from the error between the target position signal of the magnetic head and the feedback signal, changes the gain according to the analog correction value signal, amplifies the position deviation signal with this gain, and outputs it as a corrected position signal. 1. A head positioning circuit for a magnetic disk device, comprising a variable gain amplifier.