JPH03102683A - Magnetic disk device - Google Patents

Abstract

PURPOSE:To effectively compensate the positioning of a head even under the high frequency that a disk and a housing are differently moved by providing a means, which compensates mechanical transmitting function between the housing and the disk, between the output signal part of an acceleration detection means and a composition part. CONSTITUTION:The acceleration detection means 6 is attached to the housing 16. The positioning signal DELTAP of the head 13 is generated from a control head by a positioning control part 3. A compensation signal DELTAS in proportion to the signal outputted by the sensor 6 is generated by an oscillation follow-up control part 7. Both signals DELTAP and DELTAS are composed by the composition part 8 and the control of acceleration feed forward is executed. Then, the compensation means 29 provided between the output signal part of the acceleration detection means 6 and the composition part 3 compensates the mechanical transmitting function between the housing 16 and the disk 10. Thus, not only under a low frequency but also under the high frequency that the disk 10 and the housing 16 are differently moved, the positioning of the head 13 is effectively compensated.

Description

[Detailed Description of the Invention] [Summary] Regarding magnetic disk drives, the present invention relates to a magnetic disk device that can effectively compensate for head positioning not only at low frequencies but also at high frequencies where the disk and the housing move differently. A spindle that rotates with a plurality of magnetic disks attached thereto, a plurality of magnetic heads that include a control head and exchange data with each of the disks, and a motor that accesses the heads; A positioning control unit generates a positioning signal of the head according to a position signal from the control head, and is proportional to the output signal of the sensor. In a magnetic disk drive that performs acceleration feedforward control, a vibration tracking control section generates a compensation signal, and a combination section combines both signals to perform acceleration feedforward control. A compensating means for compensating the mechanical transfer function between the housing and the disk is provided between the two.

[Industrial application field]

The present invention relates to a magnetic disk device, and more particularly to a magnetic disk device with improved head positioning accuracy. In recent years, magnetic disk drives used as external storage devices for computer systems have rapidly increased in capacity and speed, and recording track widths have also become denser. A head that reads/writes information from a disk must be accurately positioned on a predetermined track of the disk. However, in such a magnetic disk drive, when a seek is performed on the disk to position the head, the reaction force causes the housing of the magnetic disk drive to vibrate, and the rotating shaft is attached to the housing. The magnetic disk inside also vibrates. As a result, a head positioning error occurs due to mechanical vibration of the housing, and a solution to this problem is desired.

[Conventional technology]

Figure 9 shows the structure of a conventional magnetic disk drive. In the same figure (8), 1 is a magnetic disk unit, in which a magnetic disk 10 as an information storage medium is rotated around a rotating shaft 11 by a spindle motor 12.
The magnetic head 13 is attached to the accessor 140 of the voice coil motor unit 14, and is moved (seek) in the radial direction of the magnetic disk 10 by the coil 141 and magnet 142.
These are housed in the housing l6. Reference numeral 2 denotes a speed control section, which generates a speed error signal Δ■ based on a position signal PS generated by a servo signal from the magnetic head 13. Reference numeral 3 denotes a positioning control section, which converts the position signal PS into a P-I-D ( 4 is a control unit that generates a positioning signal ΔP from a signal obtained by applying a low-pass filter to the processed signal (proportional, integral, differential) and the detection signal i, and 4 is a control unit that controls the speed control unit 2 in response to a movement instruction from the outside. 5 is a changeover switch that controls to generate a speed error signal ΔV to control the speed of the voice coil motor 14, and also generates a coarse/fine switching signal MS in the vicinity of the target position to operate a changeover switch to be described later; Switching is performed according to the coarse/fine switching signal MS, and in the coarse instruction, the speed error signal ΔV is given to the voice coil motor 14, and in the fine instruction, the positioning signal ΔP is given to the voice coil motor 14. This is a power amplifier that amplifies the power of the output of the changeover switch 5 and supplies it to the voice coil motor 14.

In such a magnetic disk device, as shown in FIG. 9(B), when a movement instruction is given from the outside, the control unit 4
The amount of movement to the target position is calculated and given to the speed control section 2.

The speed control unit 2 generates a reference speed Vc from the movement amount according to a speed function such as a trapezoidal curve, compares it with the actual speed Vr obtained from the position signal PS from the magnetic head l3, and generates a speed error signal Δ.
Generates V. Since the control unit 4 instructs the coarse mode, the changeover switch 5 is connected to the a side, and the speed error signal Δ■ is given to the voice coil motor 14, whereby the voice coil motor 14 and the magnetic head 13 are set to the trapezoidal mode. It moves toward the target position (target cylinder) according to the speed curve by speed control. The control unit 4 receives the position signal P
When it is detected by S that the target position has been reached, the coarse/fine switching signal MS instructs the fine mode, and the changeover switch 5 is connected to the b side. The position control unit 3 generates a positioning signal ΔP from the position signal PS, and the positioning signal ΔP is given to the voice coil motor l4.
Positioning and position holding control are performed.

Then, after switching to the fine mode, when the control unit 54t detects that the position signal PS is within the allowable range, it sends a sequence signal indicating completion of positioning to the upper layer, and if it is a magnetic disk, the target Cylinder lead/
Run the light. To maintain the position during reading/writing, the position control unit 3 generates a positioning signal ΔP from the position signal PS obtained from the servo signal SvS read by the magnetic head 13, and controls the position of the head 13 from the track. I was trying to prevent this.

However, the cause of the positional deviation of the head 13 is the first one.
The second reason is the positioning accuracy of the position control unit 3, and the second reason is vibration due to mechanical factors within the position control loop. Both of these can be improved by improving the followability of the position control unit 3, but there are problems such as oscillation due to resonance of the mechanism, and there is a limit to the improvement of followability, and it is difficult to maintain position on the order of submicrons or less. The problem was that it was difficult. In particular, regarding the vibration of the mechanism due to mechanical factors, it is 1 (10 Fl
In the case of low-frequency vibrations below z, the off-track amount (positional deviation amount) is larger than that of Takagi even for the same disturbance, and there is a problem in that the off-track amount cannot be reduced with the conventional technology.

Therefore, the present inventors have proposed a magnetic disk device that can reduce head track position deviations caused by mechanical vibrations (see Japanese Patent Laid-Open No. 64-43881 and Japanese Patent Laid-Open No. 64-73579). In these devices, the 9th
An acceleration sensor 6 is provided in a housing 6 of the conventional device shown in the figure, and the acceleration in the seek direction of the head 13 of a housing 16 housing a magnetic disk 10 and a positioning section (magnetic head 13 and voice coil motor 14) 15 is detected. I am trying to have it detected. In the device disclosed in Japanese Patent Application Laid-Open No. 64-43881, a compensation signal proportional to the detection output of the acceleration sensor 6 is generated to eliminate mutual interference during seek by a plurality of independently moving head positioners. Also, JP-A-64
In the device disclosed in Publication No. 73579, the detection output of the acceleration sensor 6 is manually inputted to a vibration tracking control section that includes a low-pass filter that has a flat phase characteristic in the vibration frequency band and has a small gain in the high frequency range, so that the detection output can be reduced. A vibration follow-up signal ΔS is generated from the frequency command, and this is combined with the positioning signal ΔP of the positioning control unit 3 to control the head moving unit 14, thereby performing so-called feedforward control. As a result, the mechanical vibration of the mechanism is detected, and the head l3 follows the movement of the magnetic disk 10, so that off-track of the head 13 is reduced.

As the low-pass filter in the device disclosed in Japanese Patent Application Laid-Open No. 64-73579, a second-order filter with damping characteristics as shown in FIGS. 8(A) and 8(B) was used. In other words, the low frequency vibration region 1(10~3(1
ff range of about 0 Hz, i.e. 1 of the cutoff frequency
At frequencies of 73 to 1/10, the gain is high and the phase is flat (almost O), while at high frequencies (for example, around 10 kHz) the gain is low and the phase is inverted, sufficiently cutting noise due to resonance of the sensor 6, etc. It is possible,
A second-order filter with a damping coefficient Q of 1.5 to 2, centered around 1.76, was used. [Problems to be Solved by the Invention] The magnetic disk device proposed by the present inventors basically detects the mechanical vibration of the mechanism section using the acceleration sensor 6 attached to the housing 16 and detects the movement of the head L3. Since it is a compensation method (feedforward control), it has a great practical effect and has great utility value. However, as a result of further research by the present inventors, it has been found that the above-described magnetic disk device includes factors that cause some errors in detecting the movement of the disk 10 using the housing 16. I found out. In other words, it was found that the compensation proposed by the present inventors cannot be applied at high frequencies where the disk IO and the housing 16 move differently, and there is a problem in that the above-mentioned compensation is effective only at low frequencies. ．． in fact,
The spindle system of a magnetic disk device often has a resonance point at a frequency of several 1 (10 Hz), and the above-mentioned control at this frequency is not effective.Of course, there is no problem if the movement of the disk itself can be detected, but the There is a problem in that it is practically difficult to detect the acceleration in the sea/west direction.

The purpose of the present invention is to solve the problems of magnetic disk drives that execute feedforward control, which the inventors have already proposed, and It is an object of the present invention to provide a magnetic disk device that can effectively compensate head positioning even in terms of frequency.

[Means to solve the problem]

FIG. 1 shows the structure of a magnetic disk drive according to the present invention that achieves the above object. In FIG. 1, a spindle 12 rotates with a plurality of magnetic disks 10 attached thereto, a plurality of magnetic heads 13 include a control head and exchange data with each of the disks IO, and a motor 14 rotates with a plurality of magnetic disks 10 attached thereto. be accessed. A housing 16 accommodates these, and the acceleration detection means 6 is attached to this housing 16. Furthermore, the positioning control section 3 controls the head 1.
The vibration tracking control section 7 generates a compensation signal ΔS proportional to the output signal of the sensor 6, and the combining section 8 generates a positioning signal ΔP based on the position signal from the control head. Acceleration feedforward control is then performed. In such a magnetic disk drive, the compensation means 29 provided between the output signal section of the acceleration detection means 6 and the synthesis section 8 compensates for the mechanical transfer function between the housing 6 and the disk 10.

Note that the compensating means 29 is preferably a low-pass filter having a damping larger than the damping of the spindle mechanical resonance.

(Function) According to the magnetic disk device of the present invention, the acceleration of the casing detected by the acceleration sensor attached to the casing of the magnetic disk device is adjusted to the O of the transfer function of the disk by the compensation circuit.
Since the deviation from B is corrected, O of the disk transfer function at the feedforward compensation value is
The deviation from dB is canceled, and the acceleration of the casing detected by the acceleration sensor becomes equivalent to the actual acceleration of the disk.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 2 shows the structure of an embodiment of a magnetic disk device that performs feedforward control according to the present invention, and the same components as those of the conventional magnetic disk device shown in FIG. 9 are designated by the same reference numerals. This will be explained below. 20 is a reference speed generation circuit, which generates a reference speed Vc according to a trapezoidal speed curve according to the amount of movement from the control unit 4; 21 is a speed signal generation circuit, which generates a position signal PS and a power amplifier 5;
An error signal generating circuit 22 generates a detection current i of 0 or an actual speed Vr, which takes the difference between the reference speed Vc and the actual speed Vr and generates a speed error signal Δ■.
It is given to

30 is a low-pass filter that cuts a high frequency part of the position signal PS; 31 is an integrating circuit that integrates the position signal PS from the low-pass filter 30;
2 is an amplifier that proportionally amplifies the position signal PS from the low-pass filter 30; 33 is a differentiation circuit that differentiates the position signal PS from the low-pass filter 30; 35 is a low-pass filter; The sum of the output of the differentiating circuit 33 and the detected current i is taken to cut high frequency signals. 34 is a sum circuit which sums the output of the integrating circuit 31, the output of the amplifier 32, and the output of the low-pass filter 35, generates a positioning signal ΔP, and outputs it to the changeover switch 5.

40 is a position detection circuit that detects the position from the position signal PS; 41 is a microprocessor (MPU) that receives a seek command and a target cylinder from a higher level and performs seek control; The detected position and the actual speed Vr of the speed signal generation circuit 2l are inputted, and the movement amount to the target cylinder is calculated and the reference speed generation circuit 20
It outputs a coarse/fine switching signal MS to the selector switch 5 and a switch circuit to be described later, and upon completion of the seek, a seek end signal is issued to the upper level.

Reference numeral 70 denotes a high-pass filter, which serves as a filter circuit for removing the DC offset of the output of the acceleration detection sensor 6, and is composed of an operational amplifier 70a, a capacitor C1, and a resistor R1, as shown in FIG. 4(A). 71 is a low-pass filter that extracts only the necessary band of the output of the acceleration sensor 6.
This is a low-pass active filter that uses an operational amplifier 71a and a CR passive element, as shown in Figure 4 (A), to cut Takagi noise. It uses a first-order filter with damping (L = 9
The frequency characteristics of this low-pass filter 7l when 80 Hz and Q=1, 76 are shown in FIG. The gain setting unit 72 sets the convolution gain with the positioning signal ΔP and outputs the vibration follow-up signal ΔS, and as shown in FIG. It is an amplifier consisting of R6, and the gain can be set by the ratio of resistors R2 and R3 between resistor R5 and low-pass filter 71. 29 is a compensation circuit, and vibration follow-up signal ΔS
80 is a switch circuit which compensates for the error in the transfer function of the magnetic disk 10 included in the transfer function and outputs a compensated vibration follow-up signal ΔS', which is turned on/off by the coarse/fine switching signal MS from the MPU 41. It outputs a compensated vibration follow-up signal ΔS' to the synthesis section (addition fs) 8.

Reference numeral 9 denotes a position signal generator, which generates a sine wave servo signal obtained by the magnetic head 13 reading a servo signal recorded on the servo surface of the magnetic disk 10 (for example, the bottom surface of the second magnetic disk 0 in the figure). The AGC amplifier 90 generates the position signal PS from the signal SVS and performs AGC III control (automatic gain control) of the servo signal SvS, and the position signal detection unit outputs a sine wave position signal PS from the AGC-controlled servo signal. It has a circuit 91.

The operation of the embodiment configured as described above is almost the same as that of the conventional magnetic disk device shown in FIG. , the detection signal from the acceleration sensor 6 is transmitted to the vibration tracking control section 7 and the compensation circuit 29.
The only point is that the signal is compensated by , is added to the alignment section 8 , and is added to the positioning signal ΔP from the positioning control section 3 .

FIG. 3 is a block diagram showing signal transmission characteristics depending on the number of transmission intervals of the magnetic disk device of FIG. 2.

In this system, a controller 3' corresponds to the positioning control section 3 of FIG. 2, and a head positioning signal PS is input to this controller 3', and a head positioning current (2) is generated. is output. In this system, Bl is the force constant of the motor, 1/m is the actuator of the voice coil motor, G ff (S) is a transfer function indicating the vibration characteristics of the housing of the magnetic disk drive, and G4 (S) is The transfer function that indicates the vibration characteristics of the spindle (disk), 1/S" is the transfer function that converts acceleration into displacement, F2., is the disturbance applied to the housing from the outside, and Hf is the feed from the acceleration sensor attached to the housing. The figure shows a gain setter for the forward control signal.In this system, the vibration characteristics of the housing (transfer function C-1 of the housing) caused by the motor's reaction force -81 and the disturbance Fpar applied to the housing from the outside. S)> is detected by the acceleration sensor attached to the housing, and the disk transfer function G, (S) is applied to the positioning signal whose gain is set by the gain setting device 11f.
The error due to the deviation from OdB of the transfer function G 4 (S
) '1,
This is intended to cancel out the effects of vibrations in the vertical direction of the magnetic disk in the head.

Here, the error due to the deviation of the transfer function G 4 (S) of the disk from OdB will be explained with respect to the transfer function G 4 (S)'. Vibrations generated in the magnetic disk 10 due to the reaction force generated by the voice coil motor during seek should originally be detected after the disk transfer function G 4 (S) shown in FIG. 3. However, since the actual vibration (acceleration) of the magnetic disk 10 cannot be detected, the acceleration sensor 6
is used to input the transfer function G 3 (S) of the housing 16 to the gain setter Hf. For this reason, errors due to the transfer function between the housing and the disk (shown by the solid line in Figure 5)
Therefore, the OdB of the disk transfer function G 4 (S) is applied to the positioning signal whose gain is set by the gain setting device 11f.
If feedforward control is performed without compensating for errors due to deviation from the transfer function 64(S), feedforward control will not be performed near 15082, which is the original purpose, as shown by the solid line in Figure 7. Characteristics of time (
Although it is practically sufficient to obtain an effect of slightly less than 30 dB compared to the broken line), the effect decreases as the frequency increases.
8 (It can be seen that at the spindle resonance point around 10 Hz, there is a slight reverse effect.

In this way, although the disk acceleration should originally be detected after the disk transfer function 0 4 (S),
Transfer function G of the casing: If I (S) is the acceleration of the disk, Od of the disk transfer function G 4 (S)
A deviation from B causes undercompensation, resulting in an error. This compensation error increases as it approaches spindle resonance, and reaches its maximum value at the spindle resonance point. In order to cancel this error, in this embodiment m is the mass of the positioner and Bj! as the force constant of the positioner,
The following formula, Hf = 1/B l-m-G4(S)...
By giving the detected value of the acceleration sensor a feedback gain of (2), the above-mentioned error can be theoretically completely canceled. What provides this feedback gain is the compensation circuit 29 in FIG.
This compensation circuit 29 is realized by inserting a low-pass filter G 4 (S)' having exactly the same characteristics as the transfer function G 4 (s) indicating the vibration characteristics of the disk into the feedback loop as a simulator. And, with this low-pass filter G 4 (S)',
The influence of the transfer function G 4 (S), which indicates the vibration characteristics of the disk, is completely canceled. Specifically, this transfer function G
4 (S)', M2 is the mass of the spindle disk, C2 is the damping of the spindle disk, and K! Assuming the stiffness of the spindle/disk (bearing or shaft stiffness), the following formula is given, Ga −xi(s)/x+(s)
= (Cz +Kz) / (ToS” +CS 10K
g) Given by −■. Figure 4 shows this low-pass filter c. FIG. 2 is a circuit diagram showing an example of the configuration of (s)'. low pass filter c a
(s)' is different from a general second-order filter and has a special transfer function, so it is an operational amplifier O that includes integral feedback.
P, ~OP, resistors R1~R, and capacitors CI~C
3. Here, the constants of the resistors R, ~Rh and the capacitors 01~C3 are the following formula, which is a nondimensionalized form of the formula (2):
J+6)n")m
2(Mz"Kz)""), ω, = (R4 /Rl
Book R! *Rs*(,*C,)l/xζ"" Rz/ 2
'k (R6*cl, / R +*Rff*Rs*C
3) Select constants so that “”.

In addition, in this way, the low-pass filter G 4 (S)'
Although the simulator is theoretically perfect, in practice, the mechanical vibration characteristics tend to vary due to temperature changes and variations, as shown in Figure 5. That is, even if the characteristics of the low-pass filter G 4 (S)' are set as shown by the solid line, they may deviate as shown by the broken line. Generally, the damping constant ζ of the spindle is quite small, and when a low-pass filter set to this value is used, ω. If it deviates in either direction, the control effect will be greatly affected. That is, if an attempt is made to completely cancel the spindle resonance, a change in the parameters will have a large effect as described above. Therefore, instead of canceling the spindle resonance completely, as shown in Figure 6, we use a low-pass filter with a large damping constant ζ to cancel the tail part of the peak without compensating for the peak itself. low-pass filter c. (s)' is set so that the tail portions of both peaks can be compensated for even if the mechanical characteristics change due to temperature or the like, as shown by broken lines A and B in FIG.

FIG. 7 shows the effect of the low-pass filter ca (s)' when the damping constant ζ is set to a large value in comparison with the characteristics of a conventional magnetic disk drive. The broken line in this figure is the characteristic when the above-mentioned feedforward control is not performed, the solid line is the characteristic when the conventional feedforward control is performed, and the dashed line is the characteristic of the feed of the present invention with a large damping constant ζ. This is the characteristic when forward control is performed. As can be seen from this figure, when the feedforward control of the present invention is executed, the normal compensation in the low frequency region around 150112 results in 30d
The effect, which was only a little B, is now more than 60 dB, and 8 (at the spindle resonance point around 10 Hz,
It can be seen that although the effect has decreased slightly, it is significantly improved compared to the conventional method. In this way, by increasing the damping constant ζ of the low-pass filter G 4 (S)', it was possible to realize a control system that is robust against changes in vibration parameters. [Effects of the Invention] As explained above, according to the magnetic disk device of the present invention, positioning accuracy higher than that of the conventional technology is ensured at low frequencies, and even at high frequencies where the disk and the casing move differently, head positioning accuracy is ensured. This has the effect that positioning compensation can be effectively performed.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the principle of the magnetic disk device of the present invention, and FIG.
The figure shows a configuration diagram of one embodiment of the magnetic disk device of the present invention, FIG. 3 is a block diagram showing signal transfer characteristics based on the transfer function of the device of FIG. 2, and FIG. 3 shows the low-pass filter of FIG. 2. 4(A) is a circuit diagram showing an example of the structure of the vibration tracking control section in FIG. 2, and FIG. 4(B) is a circuit diagram showing an example of the compensation circuit in FIG. 2. Figure 5 is a characteristic diagram showing the temperature change of a low-pass filter, Figure 6 is a characteristic diagram of a low-pass filter with a large damping constant, and Figure 7 shows the effect of the low-pass filter of the present invention with a large damping constant. Figure 8 shows a comparison with the characteristics of conventional magnetic disk devices.
The figure is a characteristic diagram of a low-pass filter used in the vibration follow-up control section of FIG. 2, and FIGS. 9(^) and (B) are explanatory diagrams showing the configuration and control characteristics of a conventional magnetic disk device. 1... Magnetic disk unit, 2... Speed control section,
3...Positioning control section, 4...Il control section, 6...
- Acceleration sensor, 8... Synthesis unit, 10... Magnetic disk, 11... Rotating shaft, 12... Spindle motor, 13... Ift air head, 14... Voice coil motor, 16 . . . Case (housing), 21 . . . Low-pass filter, 29 . . . Compensation means (circuit), 50.
··Power Amplifier. Diagram for explaining the principle of the present invention 1 Configuration example of the vibration tracking control ms shown in FIGS. B) Mouth-pass filter characteristic diagram Explanatory diagram of conventional technology

Claims (1)

[Claims] 1. A spindle (12) that rotates with a plurality of magnetic disks (10) attached thereto, and a plurality of magnetic heads (12) that include a control head and exchange data with each of the disks (10). 13), a motor (14) for accessing this head (13), and a casing (16) that houses these.
and an acceleration detection means (6) attached to this housing (16), and a positioning signal (
The positioning control section (3) generates ΔP) based on the position signal from the control head, and the vibration tracking control section (7) generates a compensation signal (ΔS) proportional to the output signal of the sensor (6), which is then synthesized. In a magnetic disk drive that performs acceleration feedforward control by synthesizing both signals (ΔP) (ΔS) in a section (8), the output signal section of the acceleration detecting means (6) and the synthesizing section (
8) A magnetic disk drive characterized in that a compensation means (29) is provided between the housing (16) and the disk (10) for compensating the mechanical transfer function between the housing (16) and the disk (10). 2. The magnetic disk device according to claim 1, wherein the compensating means (29) is a low-pass filter having damping larger than damping of spindle mechanical resonance.