JP2970679B2 - Head positioning control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] Regarding a head positioning control device, it is possible to secure a loop gain as high as possible even when a mechanical resonance point of a disk device changes, to reduce a phase rotation, and to improve head positioning accuracy. In order to provide a head positioning control device, in a housing, a plurality of disks mounted on a spindle and rotating, a plurality of heads including a control head for exchanging data with each disk, and allowing the heads to access A head positioning control device for a disk drive equipped with a motor, wherein a precision positioning control unit that generates a signal for precise positioning with respect to the motor has an amplitude attenuation ratio of 6 dB.
A notch filter of not less than 20 dB or less is provided. This notch filter has s as a Laplace operator, K as a constant, ζ
Is the damping constant and ω ₀ is the notch frequency. , And the values of the damping constant 定 数 and the constant K are set as follows: ζ = 0.3 to 0.7, K =
Configure as 0.1-0.5.

[Industrial applications]

The present invention relates to a head positioning control device, and more particularly, to a head positioning control device with improved head positioning accuracy of a disk device widely used as an external storage device of an electronic computer.

Generally, as an external storage device of a computer system,
File storage devices such as magnetic disk devices and optical disk devices are used. In recent years, the capacity and speed of this disk device have been rapidly increased, and the recording track width has also been increased. In such a disk device, a head for reading / writing (read / write) of information from / to the disk must be accurately positioned on a predetermined track of the disk, but the position error is reduced with respect to various disturbances. In order to achieve this, it is necessary to increase the loop gain of the control system sufficiently. However, since it is difficult to sufficiently increase the resonance frequency of the motor that moves the head at high speed, there is a problem that the control system becomes unstable when the loop gain is increased, and this solution is desired.

[Conventional technology]

FIG. 6 shows the configuration of a conventional magnetic disk drive. In the figure, reference numeral 70 denotes a magnetic disk unit, and a spindle 71 on which a plurality of magnetic disks 72 as information storage media are mounted is rotated by a spindle motor 75, and a magnetic head 73 is mounted on a rotating shaft 76 of a voice coil motor 74. It is attached to the tip of the protruding arm and is moved (seeked) in the radial direction of the magnetic disk 72 by the coil 77 and the magnet 78, and these are housed in the housing 79. And this magnetic disk unit 70
Is driven by a head positioning control device including a speed control unit 20, a positioning control unit 30, a control unit 40, a changeover switch 50, and a power amplifier 60.

The speed control unit 20 generates a speed error signal ΔV based on the position signal PS based on the servo signal from the magnetic head 73, and the positioning control unit 30 processes the position signal PS by PID (proportional, integral, differential). A positioning signal ΔP is generated from a signal obtained by applying a low-pass filter to the signal and the detection signal i. Also,
When an external movement instruction is given, the control unit 40 calculates the amount of movement to the target position, controls the speed control unit 20 to generate a speed error signal ΔV, and controls the speed of the voice coil motor 74. A coarse / fine switching signal MS is issued in the vicinity of the target position, and a changeover switch 50 described later is operated. The changeover switch 50 is switched in response to the coarse / fine switching signal MS, and applies a speed error signal ΔV to the voice coil motor 74 when the coarse instruction is given, and applies a positioning signal ΔP to the voice coil motor 74 when the fine instruction is given. Further, the power amplifier 60 amplifies the power of the output of the changeover switch 50 and supplies it to the voice coil motor 74 to drive it.

As described above, a method of reading the position information written on the disk 72 with the head 73 and feeding it back is used for positioning the head. The loop gain of the control system is generally increased in order to reduce the position error with respect to various disturbances. However, if the weight of the voice coil motor 74 is reduced to move the head at high speed, it becomes difficult to sufficiently increase the resonance frequency of the voice coil motor 74.In this state, if the loop gain is increased to increase the positioning accuracy, On the contrary, the problem that the control system becomes unstable occurs. That is, when the resonance frequency becomes low, there is a problem that the vibration hinders the positioning accuracy.

In order to solve this problem, a notch filter is generally used in the positioning control unit 30 conventionally. (See, for example, Japanese Patent Application Laid-Open No. 61-224185.) When looking at the loop transfer function of a magnetic disk drive, as shown in FIG. This is for electrically canceling the operation. Therefore, the notch filter is as shown in FIG. 7 (b).
This is a filter having such a characteristic that it has a valley at the mechanical resonance frequency ω. Then, by passing through the notch filter, the gain at the mechanical resonance point ω can be suppressed as shown in FIG. 7 (c). As the notch filter, an analog filter called a twin T-type circuit constituted by using an operational amplifier and a plurality of resistors and capacitors as shown in FIG. 8 is used.

[Problems to be solved by the invention]

However, although the gain at the mechanical resonance point can be suppressed by this notch filter, FIG.
As shown in (b), at the center frequency ω _n of the notch, the phenomenon that the phase shifts due to the notch filter (hereinafter referred to as “around the phase”) increases, and the direction of decreasing the low-frequency phase margin tends to decrease, and the control system becomes unstable. Therefore, there is a problem that it is difficult to obtain a control band close to the mechanical resonance point. In other words, increasing the loop gain sufficiently with respect to the mechanical resonance point does not work very well with the conventional notch filter.

The notch filter is, as shown in FIG.
Because the cut-off characteristics of the notch are steep, if the mechanical resonance point varies due to temperature changes, aging, or individual differences, the center frequency ω _n of the notch does not match the mechanical resonance point, and the effect of the notch filter However, there is also a problem that stable operation is difficult.

For example, in a conventional notch filter, when the center frequency omega _n mechanical resonance frequency and the notch match,
Although the effect take more than 30dB, and shifts the mechanical resonance frequency is even a little from the center frequency ω _n of the notch, there is a problem that the effect is reduced sharply.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems in the conventional head positioning control device for a disk drive, to ensure a loop gain as high as possible even when the mechanical resonance point of the disk drive changes, and to reduce the phase rotation and reduce the head positioning accuracy. It is an object of the present invention to provide a head positioning control device that can improve the head position.

[Means for Solving the Problems] FIG. 1 shows the configuration of a magnetic disk drive of the present invention that achieves the above object. As shown in this figure, a head positioning control device of the present invention includes a plurality of disks 12 attached to a spindle 11 and
12. A head positioning control device for a disk drive 1 comprising a plurality of heads 13 including a control head for exchanging data with a motor 12, and a motor 14 for accessing the head 13, wherein a position signal of the head 13 from the control head is provided. A coarse positioning control unit 2 for generating a signal ΔV for coarse positioning of the motor 14 based on the PS, and a signal Δ for fine positioning of the motor 14 based on the processing signal of the position signal PS and the detected value i of the driving signal of the motor 14.
The motor is driven by a signal from the fine positioning control unit 3 which generates the P and the coarse positioning control unit 2 or the fine positioning control unit 3.
14, a switching unit 5 for connecting either the coarse positioning control unit 2 or the fine positioning control unit 3 to the motor driving unit 6, and when a movement instruction is given from the outside, the motor moves to the target position. , The coarse positioning control unit 2 is connected to the motor drive unit 6 via the switching unit (5) first,
A control unit 4 for connecting the precision positioning control unit 3 to the motor drive unit 6 via the switching unit 5 when the head 13 reaches the vicinity of the target position;
A notch filter (7) of B or more and 20 dB or less is provided. The notch filter 7 has s as a Laplace operator, K as a constant, ζ as a damping constant, and ω ₀ as a notch frequency. And the value of the damping constant ζ and the constant K are expressed as follows: ζ = 0.3 to 0.7, K = 0.1
Can be configured as ~ 0.5.

[Action]

According to the head positioning control device of the present invention, since the cut-off characteristic of the filter is gentle, even if it deviates from the mechanical resonance frequency and the center frequency of the filter, it is effective in reducing the amplitude. Can also be kept small.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 2 shows the configuration of an embodiment of the magnetic disk drive of the present invention. The same components as those of the conventional magnetic disk drive shown in FIG. 6 are denoted by the same reference numerals.

The configuration of the magnetic disk unit 70 of this embodiment is the same as that of the related art, and a plurality of magnetic disks 72 are mounted on a spindle 71 rotated by a spindle motor 75 in a housing 79. Is read and written by a magnetic head 73 driven by a voice coil motor 74. And this magnetic disk unit 70
Position signal generator 90, speed controller 20, positioning controller 30,
It is driven by a head positioning control circuit including a control unit 40, a changeover switch 50, and a power amplifier 60.

The position signal generating section 90 converts the servo signal recorded on the servo surface of the magnetic disk 72 (for example, the lower surface of the second magnetic disk 72 in the figure) from a sine wave servo signal SVS obtained by reading the magnetic head 73 with the servo signal. A position signal PS is generated,
AGC amplifier 9 that performs AGC (automatic gain control) of servo signal SVS
1 and a position signal detection circuit 92 that outputs a sine wave position signal PS from the AGC servo signal.

The reference speed generation circuit 21 in the speed control unit 20 that performs coarse positioning of the head 73 generates a reference speed Vc according to a trapezoidal speed curve according to the amount of movement from the control unit 40, and the speed signal generation circuit 22 An actual speed Vr is generated from the position signal PS and the detection current i of the power amplifier 60. Then, the error signal generation circuit 23 calculates the difference between the reference speed Vc and the actual speed Vr, generates a speed error signal ΔV, and gives the speed error signal ΔV to the changeover switch 50.

The positioning control unit 30 that performs precise positioning of the head 73 includes a filter 31 that reduces the phase signal PS around the phase and reduces mechanical resonance, a low-pass filter 32 that cuts high-frequency components of the position signal PS, and a low-pass filter 32.
Signal, integration circuit 33, proportional amplification circuit 34, differentiation circuit 3
5. A low-pass filter 37 for taking the sum of the output of the differentiating circuit 35 and the detection current i to cut off the high-frequency component; Switch 50
And a sum circuit 36 which outputs the sum.

The control unit 40 also includes a position detection circuit 41 that detects the position of the head 73 from the position signal PS, and performs seek control in response to a seek command and a target cylinder from a higher order. There is a microprocessor (MPU) 42 to which the actual speed Vr from the speed signal generation circuit 22 is input. The MPU 42 calculates the amount of movement to the target cylinder and outputs it to the reference speed generating circuit 21. The MPU 42 also generates a coarse / fine switching signal MS and outputs it to the changeover switch 50. Emits a signal.

The head positioning control device in the magnetic disk device of the embodiment configured as described above is greatly different from the conventional device in that the positioning control unit 30 has a small phase rotation in place of the notch filter, and has a temperature change due to mechanical resonance and the like. The point is that a filter 31 that is strong against variations and the like is provided. This filter 31 is a conventional notch filter having a transfer function represented by the following equation: (Where ω _{0 is a} notch frequency, ζ is a damping constant, and s is a Laplace operator.) On the other hand, the filter 31 of this embodiment is represented by the following equation, where K is an amplitude ratio. Transfer function, It is represented by

The filter that realizes the transfer function represented by this equation is
For example, as shown in FIG. 3A, an analog circuit is realized by a biquad circuit using four operational amplifiers A1 to A4 and a plurality of resistors and capacitors. Also,
In the digital circuit, as shown in FIG. 3 (b), a digital operation circuit (DSP) D1 can be used and can be realized as a digital filter by software. In this case, an A / D converter D2 is required on the input side, and a D / A converter D3 is required on the output side. The algorithm of this digital filter is as follows: A transfer function of a discrete system that has been subjected to a Z-transform such as Indicated by

By the way, all of the coefficients of the expression and the expression obtained by Z-transformation are all non-zero. Therefore, if only the coefficients are calculated in advance, the operation time at the time of execution does not change at all between the conventional filter and the filter of the present invention. Therefore, it can be seen that the filter 31 used in the present invention is actually suitable for a digital servo system.

FIG. 4 shows gain characteristics and phase characteristics of the filter of the present invention configured as shown in FIG. As shown in this figure, the filter 31 used in the head positioning control apparatus of the present invention, the gain of the fallen way is not steep relative to the notch frequency omega _n. Then, a small phase around in the vicinity notch frequency omega _n. Conditions for constructing such a stable notch filter are as follows: (1) the phase rotation due to the notch in the servo band of the zero cross frequency ω _s is about 8 ° or less, and (2) the zero cross frequency ω _s of 2-3. There is a notch frequency ω _n twice, and in the conventional notch filter, (1) and (2)
It was impossible to achieve both, and if only the condition (2) was used, the phase rotation was about 20 °.

If the condition of the filter 31 of the present invention for satisfying the above condition is expressed by the above equation, the value of K is in the range of 0.1 to 0.5 (the amplitude attenuation ratio of the filter obtained by dividing the notch frequency amplitude by the general amplitude is 20 dB to 6dB) and the damping constant 0.3 is 0.3 to 0.7.

FIGS. 5 (a), (b) and (c) show the case where (a) the filter 31 is not provided and (b) the filter 31 in the positioning control unit 30 of the head positioning control device shown in FIG.
When a notch filter having a transfer function represented by the conventional equation is used for (c), the phase characteristic of the filter when the filter of the present invention having the transfer function represented by the equation is used for the filter 31 (indicated by PF) 3 shows simulation results of the gain characteristics (indicated by GF) and the open-loop phase characteristics (indicated by PO) and gain characteristics (indicated by GO) of the positioning control unit 30. Here, the resonance point of the mechanical system is set to 1.5 kHz.
z, servo bandwidth ω _b (zero cross frequency of gain) 700Hz
The notch frequency ω _n of the conventional notch filter and the filter of the present invention is deliberately shifted from the resonance point of the mechanical system.
6 kHz.

Here, the stability condition of the control system is generally that the gain is 0d
When the phase at B becomes the phase margin PM and the gain when the phase is turned by 180 ° is the gain margin GM, the phase margin PM ≧ 20 to 30 ° and the gain margin GM ≧ 6dB. Therefore, when the phase margin PM and the gain margin GM were examined in each case in FIG. 5, the results shown in the following table were obtained.

According to this table, when there is no filter (a), the gain margin GM is small, and it is somewhat unstable. On the contrary,
When the filter of the present invention is used (c), it can be determined that the gain margin GM is sufficiently stable although the gain margin GM is increased by 4 dB and the phase margin PM is slightly reduced as compared with the case without the filter. However, in the case of using the conventional notch filter (b), the phase margin PM is greatly reduced due to the phase around the filter, and the peak amplitude due to the resonance of the mechanical system is suppressed. As a result, the gain margin GM is almost the same as the case (a) without the filter, and is at a level that can be said to be practically unstable.

As described above, by applying the present invention to an actuator having mechanical resonance, even if the gain of the servo system is increased, the stability can be further improved, and the positioning accuracy can be improved. It can be seen that this is very effective if applied to a magnetic disk device whose density has been remarkably increased recently.

〔The invention's effect〕

As described above, according to the head positioning control device of the present invention, it is possible to ensure the highest possible loop gain even when the mechanical resonance point of the disk device changes, to reduce the phase rotation, and to improve the head positioning accuracy. There is an effect that can be.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining the principle of a head positioning control device according to the present invention, FIG. 2 is a block diagram of an embodiment of the head positioning control device according to the present invention, and FIG. 3 (a) is an analog circuit of the filter shown in FIG. FIG. 3 (b) is a circuit diagram showing a configuration example of a digital circuit of the filter of FIG. 2, and FIGS. 4 (a) and (b) are gains and phases of the filter of the present invention. 5 (a), 5 (b) and 5 (c) are characteristic diagrams showing the effect of the head positioning control device of the present invention in comparison with a conventional device, and FIG. 6 is a conventional magnetic disk. 7 (a), 7 (b) and 7 (c) are diagrams showing the characteristics and effects of a conventional notch filter, and FIG. 8 is a circuit showing a configuration example of a conventional notch filter. Figures 9 (a) and 9 (b) show the gain and phase characteristics of a conventional notch filter. A be characteristic diagram. 20: speed control unit, 30: positioning control unit, 31: filter of the present invention, 40: control unit, 50: changeover switch, 60: power amplifier, 70: magnetic disk unit, 71: Spindle, 72: Magnetic disk, 73: Magnetic head, 74: Voice coil motor, 75: Spindle motor.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G11B 21/10

Claims (2)

(57) [Claims] 1. A housing (10) having at least one rotating disk (12) mounted on a spindle (11) and a plurality of heads (13) for reading and writing each disk (12).
A head positioning control device for a disk drive (1) including a motor (14) for accessing the head (13), wherein a precision positioning control unit for generating a signal (ΔP) for precise positioning with respect to the motor (14) (3) The amplitude attenuation ratio is 6d
A heading positioning control device comprising a notch filter (7) of B or more and 20 dB or less. 2. The notch filter (7), wherein s is a Laplace operator, K is a constant, ζ is a damping constant, and ω ₀ is a notch frequency. 2. The head positioning control device according to claim 1, wherein the filter comprises a filter having the following transfer function, and the values of the damping constant ζ and the constant K are ζ = 0.3 to 0.7 K = 0.1 to 0.5.