JPH0438777A - Head positioning controller - Google Patents

Abstract

PURPOSE:To improve accuracy for positioning a head by providing a notch filter having an amplitude attenuation ratio at a specified value in a precise positioning control part. CONSTITUTION:In a velocity control part 20 to coarsely position a head 73, an error signal generating circuit 23 generates a velocity error signal V by subtracting reference velocity Vc and real velocity Vr and applies it to a change over switch 50. A positioning control part 30 to precisely position the head 73 is equipped with a notch filter 31, which amplitude attenuation ratio is higher than 6dB and lower than 20dB, reducing phase turning and being immune to the temperature change or dispersion, etc., of mechanical resonance. Thus, since the cutoff characteristic of the filter is made smooth, there is an effect to the decrease of an amplitude even when deviating from the mechanical reso nance frequency and the central frequency of filter, and further, phase turning at that time can be suppressed small.

Description

[Detailed Description of the Invention] [Summary] Regarding a head positioning control device, it is possible to secure as high a loop gain as possible even if the mechanical resonance point of a disk device changes, and to minimize phase rotation.
The purpose of this device is to provide a head positioning control device that can improve head positioning accuracy.The housing includes a plurality of rotating disks attached to a spindle, and a control head that transfers data from each disk. A head positioning control device for a disk drive including a plurality of heads including a plurality of heads and a motor for accessing the heads, the precision positioning control unit generating a precision positioning signal for the motor having an amplitude attenuation ratio of 6 dB.
A notch filter of 20 dB or less is provided.

In this notch filter, S is a Laplace operator, K is a constant, ζ is a damping constant, and ω. It can be constructed from a filter with a transfer function where is the notch frequency, and the damping constant ζ and the value of the constant are ζ-0.3 to 0.7.
, K=0.1 to 0.5.

[Industrial application field]

The present invention relates to a head positioning control device, and more particularly to a head positioning control device that improves the positioning accuracy of a head of a disk device widely used as an external storage device for electronic computers.

Generally, file storage devices such as magnetic disk devices and optical disk devices are used as external storage devices for computer systems. In recent years, disk devices have been rapidly increasing in capacity and speed, and recording track widths have also become denser.

In such a disk device, the head that reads/writes information from the disk must be accurately positioned on a predetermined track of the disk, but it is necessary to minimize positional errors due to various disturbances. In order to do this, it is necessary to make the loop gain of the control system sufficiently large. However, since it is difficult to make the resonant frequency of the motor that moves the head at high speed sufficiently high, increasing the loop gain causes the control system to become unstable, and a solution to this problem is desired.

[Conventional technology]

FIG. 6 shows the configuration of a conventional magnetic disk device. In the figure, 70 is a magnetic disk unit, and a spindle 71 to which a plurality of magnetic disks 72 as information storage media are attached is rotated by a spindle motor 75, and a magnetic head 73 is attached to a rotating shaft 76 of a voice coil motor 74. It is attached to the tip of a protruding arm and is moved (seek) in the radial direction of the magnetic disk 72 by a coil 77 and a magnet 78, and is housed in a housing 79. The magnetic disk unit 70 is driven by a head positioning control device including a speed control section 20, a positioning control section 30, a control section 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 generated by the servo signal from the magnetic head 73, and the positioning control unit 30 generates a signal obtained by processing the position signal PS by P-ID (proportional, integral, differential) and A positioning signal ΔP is generated from a signal obtained by applying a low-pass filter to the detection signal j. Further, when a movement instruction is given from the outside, the control unit 40
The amount of movement to the target position is calculated, the speed control section 20 is controlled to generate a speed error signal ΔV, and the voice coil motor 7
4, a core-on/fine switching signal MS is generated near the target position, and a change-over switch 50, which will be described later, is operated. The changeover switch 50 is switched in response to the core on/fine switching signal MS, and gives a speed error signal Δ■ to the voice coil motor 74 in the coarse instruction, and gives a positioning signal ΔP to the voice coil motor 74 in the fine instruction. Furthermore, power amplifier 60
power amplifies the output of the changeover switch 50 and applies it to the voice coil motor 74 to drive it.

In this way, a method is used for positioning the head by reading position information written on the disk 72 with the head 73 and feeding it back. In order to reduce position errors due to various disturbances, the loop gain of the control system is generally increased.

However, if the weight of the voice coil motor 74 is reduced in order to move the head at high speed, it becomes difficult to make the resonance frequency of the voice coil motor 74 sufficiently high. Conversely, the problem arises that the control system becomes unstable. That is, when the resonant frequency becomes low, a problem arises in that vibration impairs positioning accuracy.

To solve this problem, a notch filter has conventionally been generally used in the positioning control section 30.

(For example, see Japanese Patent Application Laid-Open No. 61-224185.) If we look at the open-loop transfer function of a magnetic disk device, this is the 7th round transfer function.
This is to electrically cancel out the peak of gain that occurs at a certain frequency due to mechanical resonance, as shown in Figure (a). For this reason, the notch filter is
As shown in b), this filter has a characteristic of having a valley at the mechanical resonance frequency ω. By passing the signal through this notch filter, it becomes possible to suppress the gain at the mechanical resonance point ω, as shown in FIG. 7(C). This notch filter uses an analog filter called a twin T-type circuit, which is constructed using an operational amplifier, a plurality of resistors, and a capacitor, as shown in FIG.

[Problem to be solved by the invention]

However, although it is possible to suppress the gain at the mechanical resonance point using this notch filter, it is possible to suppress the gain at the mechanical resonance point;
As shown in b), at the center frequency ω7 of the notch,
The phenomenon of phase shift due to the notch filter (hereinafter referred to as phase circumference) increases, which tends to reduce the low-frequency phase margin, making the control system more likely to become unstable. The problem was that it was difficult to take the In other words,
Increasing the loop gain sufficiently above the mechanical resonance point means that conventional notch filters are not very successful.

In addition, as shown in Figure 9(a), the notch filter has a steep notch cutoff characteristic, so if the mechanical resonance point varies due to temperature change, aging, or individual differences, the notch center frequency ω7 There is also the problem that the notch filter does not match the mechanical resonance point, making a large difference in the effectiveness of the notch filter, and making stable operation difficult.

For example, in a conventional notch filter, if the mechanical resonant frequency and the notch center frequency ωa match, the effect can be more than 30 dB, but if the mechanical resonant frequency is slightly different from the notch center frequency ω7, If it deviates, there is a problem that the effect decreases rapidly.

It is an object of the present invention to solve the problems in the conventional helad positioning control device of a disk device, to ensure as high a loop gain as possible even if the mechanical resonance point of the disk device changes, to reduce phase rotation, and to achieve head positioning accuracy. An object of the present invention is to provide a head positioning control device that can improve the performance.

[Means to solve the problem]

The configuration of a magnetic disk device of the present invention that achieves the above object is shown in FIG. As shown in this figure, the head positioning control device of the present invention includes, in a housing 10, a plurality of disks 12 attached to a spindle 11 to rotate, and a control head that transfers data to each disk 12. This is a head positioning control device for a disk drive 1 that includes a plurality of heads 13 and a motor 14 that accesses the heads 13.The head positioning control device for a disk drive 1 includes a plurality of heads 13 and a motor 14 that accesses the heads 13. The coarse positioning control section 2 generates the signal Δ■, the processed signal of the position signal ps, and the detected value i of the drive signal of the motor 14 determines the position of the motor 14.
A precision positioning control section 3 that generates a signal ΔP for precision positioning, a motor drive section 6 that drives a motor 14 based on signals from the coarse positioning control section 2 or the precision positioning control section 3, and A switching section 5 connects one of the positioning control sections 3 to the motor drive section 6, and when a movement instruction is given from the outside, the switching section calculates the amount of movement to the target position and connects the coarse positioning control section 2 first. (5) to the motor drive unit 6, and when the head 13 reaches the vicinity of the target position, connects the precision positioning control unit 3 to the motor drive unit 6 via the switching unit 5. The positioning control section 3 is characterized by being provided with a notch filter (7) having an amplitude attenuation ratio of 6 dB or more and 20 dB or less. Furthermore, the notch filter 7 can be configured with a transfer function as follows, where S is a Laplace operator, K is a constant, ζ is a damping constant, and ω0 is a notch frequency, and the damping constant ζ and the value of the constant are ζ −0.3 to 0.7,
It can be configured as K=0.1 to 0.5.

C effect] According to the head positioning control device of the present invention, since the cutoff characteristic of the filter is gentle, it is effective in reducing the amplitude even when the mechanical resonance frequency deviates from the center frequency of the filter. The phase circumference of can also be kept small.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 2 shows the configuration of an embodiment of the magnetic disk device of the present invention, and the same components as those of the conventional magnetic disk device shown in FIG. 6 will be described with the same reference numerals.

The configuration of the magnetic disk unit 70 of this embodiment is the same as the conventional one, and a plurality of magnetic disks 7 are mounted on a spindle 71 rotated by a spindle motor 75 in a housing 79.
A magnetic head 73 driven by a voice coil motor 74 reads and writes data onto the magnetic disk 72 . This magnetic disk unit 70 includes a position signal generation section 90, a speed control section 20
, positioning control section 30, control section 40, changeover switch 50
, and a power amplifier 60.

The position signal generating section 90 operates on the servo surface of the magnetic disk 72 (
For example, the position signal PS is generated from the sine wave servo signal SVS obtained by the magnetic head 73 reading the servo signal recorded on the bottom surface of the second magnetic disk 72 in the figure. AGC (automatic gain control)
an AGC amplifier 91 that performs
2.

A reference speed generation circuit 21 in the speed control section 20 that performs rough 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 section 40, and a speed signal generation circuit 22 The actual speed Vr is generated from the position signal PS and the detection current i of the power amplifier 60. The error signal generation circuit 23 then outputs the reference speed Vc and the actual speed Vr.
The difference between the speed error signal ΔV and the speed error signal ΔV is generated and applied 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 rotation of the position signal PS and reduces mechanical resonance, a low-pass filter 32 that cuts high-frequency components of the position signal PSO, and a low-pass filter 32 that reduces the phase rotation of the position signal PS and reduces mechanical resonance. Signal integration circuit 33, proportional amplification circuit 3
4. Differentiating circuit 35, low-pass filter 37 that adds the output of the differentiating circuit 35 and the detected current i and cuts high frequency components.
, and the output of the integrating circuit 33, the output of the amplifier 34, and the output of the low-pass filter 37 to obtain the positioning signal ΔP.
There is also a sum circuit 36 which generates and outputs it to the changeover switch 50.

The control unit 40 also includes a position detection circuit 41 that detects the position of the head 73 from a position signal PS, and performs seek control in response to a seek command and a target cylinder from a higher level. Speed signal generation circuit 2
A microprocessor to which the actual speed Vr from 2 is input (
MPU) 42. This MPU 42 calculates the amount of movement to the target cylinder and outputs it to the reference speed generation circuit 21, generates a coarse/fine switching signal MS and outputs it to the changeover switch 50, and furthermore, upon completion of the seek, selects the upper position. emit a signal.

The head positioning control device in the magnetic disk device of the embodiment configured as described above is significantly different from conventional devices because the positioning control section 30 has fewer phase components in place of a notch filter, and is more sensitive to temperature changes due to mechanical resonance. The point is that a filter 31 that is resistant to variations is provided. In contrast to the conventional notch filter, which is expressed by the transfer function shown by the following formula (2), this filter 31 is expressed by the transfer function shown by the following formula (2) (where ω is the two-notch frequency, ζ is the damping constant, and S nira plus operator). The filter 31 of this embodiment has a transfer function expressed by the following formula (■) where K is an amplitude ratio.A filter that realizes the transfer function expressed by this formula (■) is, for example, an analog circuit as shown in FIG. 3(a). As shown,
It is realized with a bifarad circuit using four operational amplifiers and multiple resistors and capacitors. Furthermore, in the digital circuit, as shown in FIG. 3(b), a digital arithmetic circuit (DSP) Di can be used and realized as a digital filter using 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:
2 1-Z-' It is expressed as a discrete system transfer function after Z-transformation.

By the way, all the coefficients of Equation 0 and Equation 0 obtained by Z-transforming Equation (2) are non-O. Therefore, as long as the coefficients are calculated in advance, the calculation time during execution is completely the same for both 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 the gain characteristics and phase characteristics of the filter of the present invention configured as shown in FIG. 3. As shown in this figure, in the filter 31 used in the head positioning control device of the present invention, the gain does not fall sharply with respect to the notch frequency ω7. Furthermore, the phase rotation around the notch frequency ωa is small. The conditions for constructing such a stable notch filter are: (1) The phase rotation due to the notch in the servo band of zero cross frequency ω5 is approximately 8 degrees or less, (2) The phase rotation due to the notch in the servo band of zero cross frequency ω5 is 2 to 3 times the zero cross frequency ω5. Notch frequency ω
7, and in the conventional notch filter, this (11, (2)
It is impossible to achieve both, and if only condition (2) is used, the phase rotation would be 20'.

The conditions for the filter 31 of the present invention to satisfy the above conditions can be expressed using the above-mentioned formula (2), where the value of K is in the range of 0.1 to 0.5 (the amplitude of the filter obtained by dividing the notch frequency amplitude by the general amplitude). Attenuation ratio is 20dB to 6dB), damping constant ζ is 0
．． It is 3 to 0.7.

FIG. 5 (aL) (b) and (C) respectively show that in the positioning control unit 30 of the head positioning control device shown in FIG. (C) When a notch filter having a transfer function shown by the equation Gain characteristics (GF
), and the open-loop phase characteristics (denoted by PO) and gain characteristics (denoted by G) of the positioning control unit 30.

This figure shows the simulation results for (shown in ). Here, the resonance point of the mechanical system is set to 1.5 kl (z, servo band ω, (gain zero cross frequency) is 700 Hz, and the notch frequency ω7 of the conventional notch filter and the filter of the present invention is intentionally set to the resonance point of the mechanical system. 1.6kHz shifted from
I made it z.

Here, the stability conditions for the control system are - boat fishing, gain is Od
The phase when it becomes B is the phase margin PM, and the phase is 180
When the gain when the rotation angle is rotated by 1° is taken as the gain margin GM, the following formulas are satisfied: Phase margin PM ≧ 20 to 30° Gain margin GM ≧ 6 dB. Therefore, when examining the phase margin PM and gain margin GM in each case in Fig. 5, (however,
Both were set to ζ-0.5. ) From this table, in case (a) without a filter, the gain margin GM is small and somewhat unstable. On the other hand, in case (C) when the filter of the present invention is used, the gain margin GM increases by 4 dB, and the phase margin PM &Y is slightly decreased compared to the case without the filter, but it can be determined that it is sufficiently stable. However, when using a conventional notch filter (b)
Then, due to the phase of the filter, the phase margin PM
is significantly reduced, and even though the peak amplitude due to resonance of the mechanical system is suppressed, the resultant gain margin GM is almost the same as in case (a) without a filter due to the surroundings of the filter phase, making it unstable in practice. This is a level that can be said to be.

As described above, by applying the present invention to an actuator having mechanical resonance, it is possible to achieve further stability even if the gain of the servo system is increased, and positioning accuracy can be improved. It can be seen that this is very effective when applied to magnetic disk drives, which have recently seen a remarkable increase in density.

〔Effect of the invention〕

As explained above, according to the head positioning control device of the present invention, it is possible to secure as high a loop gain as possible even if the mechanical resonance point of the disk device changes, and to improve the head positioning accuracy with less phase rotation. There is an effect that it can be done.

[Brief explanation of the drawing]

FIG. 1 is a diagram explaining the principle of the head positioning control device of the present invention, FIG. 2 is a configuration diagram of an embodiment of the head positioning control device of the present invention, and FIG. 3(a) is an analog circuit of the filter in FIG. 2. FIG. 3(b) is a circuit diagram showing an example of the configuration of the filter in FIG. 2 using a digital circuit. FIG. 4(aLO)) shows the gain and phase characteristics of the filter of the present invention. Figures 5(a), (g), and (C) are characteristic diagrams showing the effects of the head positioning control device of the present invention in comparison with a conventional device, and Figure 6 is a characteristic diagram of the conventional magnetic A block diagram showing the configuration of a disk device. Figures 7 (a), (b), and (C) are diagrams showing the characteristics and effects of a conventional notch filter. Figure 8 shows an example of the configuration of a conventional notch filter. The circuit diagram and FIGS. 9(a) and 9(b) are characteristic diagrams showing the gain and phase characteristics of a conventional notch filter. 20... Speed control section, 30... Positioning control section, 31... Filter of the present invention, 40... Control section, 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. (a) A diagram showing the effects of the present invention in comparison with the conventional one. Figure 5. Characteristics of notch filter No. 9 UjJ

Claims (1)

[Claims] 1. In a housing (10), one or more disks (12) are attached to a spindle (11) and rotate, and a plurality of heads (13) for reading and writing to each disk (12) are provided. ) and a motor (14) that accesses this head (13).
A head positioning control device for a disk device (1) comprising: a precision positioning control section (3) that generates a precision positioning signal (ΔP) to a motor (14);
A header positioning control device comprising a notch filter (7) having an amplitude attenuation ratio of 6 dB or more and 20 dB or less. 2. The notch filter (7) has the following formula: H(s)={s^2+K(2ζω_0)s+ω_0^2, where s is a Laplace operator, K is a constant, ζ is a damping constant, and ω_0 is a notch frequency.
}/{s^2-2ζω_0s+ω_0^2}, and its damping constant ζ and constant K have the following values: ζ=0.3~0.7 K=0.1~0.5 The head positioning control device according to claim 1, characterized in that: