JP2646643B2 - Head positioning device for disk drive - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a head positioning device applied to a disk drive device such as a floppy disk and a hard disk.

[Conventional technology]

Conventionally, a head positioning device for a disk drive of this type is shown in FIGS. 15 and 16. FIG. In this method, data is written to and read from a data recording disk 1 by a head 2. The disk 1 is rotated by a disk drive motor 3. The head 2 is mounted on a carriage 4 movable in the radial direction of the disk 1. And the carriage 4
It is driven by a carriage driving motor 5. Here, the head 2 is provided with a servo disk 1 'coaxially with the disk 1 so as to be accurately positioned at the center of a track to be accessed on the disk 1, and reads a servo signal from the servo disk 1'. Is controlled by a surface servo system having a configuration in which a head 2 'is mounted on the carriage 4.

The servo signal S of the servo disk 1 'is formed by alternately recording different frequencies such as frequencies f _P1 and f _P2 on the servo surface as shown in FIG. 16 (A). The recording state of the servo signal S is represented by n, n + 1, n + 2 formed on the recording surface of the disk 1 as shown in FIG.
.. Correspond to the center of the data track T of the servo signal S. Therefore, the servo signal S reproduced from the head 2 ′ is obtained as the position error signal (PES) of the head 1 with f _P2 −f _P1 . That is, the point where f _P2 −f _P1 is zero corresponds to the center position of the data track T.

In order to move the head 1 from a distant track to a target track for access, the head 1 adopts two modes of high-speed movement (seek mode) and control for accurately positioning on the target track (following mode). Is common.

The seek mode is achieved by the control system shown in FIG. K is a gain constant, A is an actuator section of the carriage driving motor 5, the carriage 4, and the head 2, and is composed of a feedback system 6 based on a preset reference speed S _R (Track / ms). Therefore, the speed S _{V of the} head 2 (Trac
k / ms) is accelerated by the carriage driving motor 5 to the reference speed S _R as shown in FIG. 19, and after reaching the target speed at the reference speed S _R , the vehicle approaches the target track. Is decelerated. The start position of this deceleration operation is managed by counting the number of tracks passed by the head 2. The following mode is achieved by the control system shown in FIG. Reference numeral 7 denotes a PID compensating circuit (proportional-integral-differential compensating circuit). The PID compensating circuit 7 comprises a feedback path 8 based on the center position of the track T obtained from the position error signal. Therefore, when the head 2 reaches the target track in the seek mode, the displacement of the head 2 'is controlled to be zero by the reproduction signal with respect to the center position obtained from the head 2', and is located at the center of the target track. Here, the PID compensation circuit 7 is obtained by adding an integral operation and a differential operation to the proportional operation of the control system, eliminates a residual deviation (offset) due to disturbance by the integral operation, and adds a differential operation to the instability due to the integral operation. This is to stabilize.

[Problems to be solved by the invention]

However, conventionally, in a head positioning following mode, a gimbal sheet (not shown) for attaching the carriage 4 and the head 2 to the carriage 4 during a servo loop is included. Therefore, the servo band is limited by the occurrence of the resonance phenomenon. Accordingly, there is a problem that necessary servo stiffness cannot be obtained and the servo is susceptible to vibration and shock from disturbance. Also, if the servo band is increased until the resonance problem is solved and stiffness is obtained, the servo system is affected by the noise of the position error signal,
There is a problem that the positioning accuracy is deteriorated.

The present invention has been made in view of the above-described problems, particularly in a following mode in which head positioning accuracy is required. An object of the present invention is to provide a head positioning device for a disk drive device positioned at the center of a track.

[Means for solving the problem]

A head positioning device for a disk drive device according to the present invention includes a carriage for moving a head in a radial direction of a disk to be rotated, a carriage drive motor for driving the carriage, and a rotation angle of the carriage drive motor. An encoder for detecting displacement or angular velocity, seek control for moving the head at a high speed from a distant track to a target track, and moving the head reaching the target track position to a predetermined position on the track. In a disk drive device that performs following control for positioning, the encoder is directly connected to the carriage drive motor,
First calculating means for calculating an absolute value speed in the track width direction of the head based on an output signal of the carriage driving motor rotated at the time of positioning the head at a predetermined position; Error signal detecting means for obtaining a position error signal with respect to a predetermined position; and second means for calculating a position error between the head and the predetermined position on the track based on an output signal of the error signal detecting means. And a third means for calculating the difference between the absolute velocity and the position error.
If there is a difference in the calculation result of the third calculation means during the following control, the rotation of the carriage driving motor is controlled so that the difference becomes zero. It is characterized by doing so.

[Action]

In the above configuration, there is provided a control loop for detecting the angular velocity of the drive shaft of the carriage drive motor based on the output signal of the encoder directly connected to the carriage drive motor, and using the detected output as a head follow-up. In the following mode, a servo system having a high resistance to vibrations and shocks, that is, a high stiffness servo system can be realized, and the servo system has a closed loop characteristic in which the gain is reduced with respect to a high frequency. Not affected. Further, a precise following control is performed by calculating a difference between an absolute value speed of the head in the track width direction and a position error of the head relative to a predetermined position of the target track.

〔Example〕

 Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a servo circuit for the following mode.
Reference numeral 10 denotes a driven portion such as the head 2, the carriage 4, and the like, which is driven by the carriage driving motor 5. 11
Is an encoder for detecting the angular displacement or angular velocity of the motor 5 connected to the carriage driving motor 5 and having an amplifier for sending a detection voltage to the output side. Reference numeral 12 denotes a moiré sensor which is formed integrally with the magnetic head and detects a position error with respect to the center of the track, has an amplifier, and sends out a detection voltage to an output side. Reference numeral 13 denotes an analog / digital signal converter (hereinafter, referred to as an A / D converter), which converts a detection voltage obtained at the output side of the encoder 11 and the moiré sensor 12 into a digital signal. 14
Is a switch connected between the output side of the encoder 11 and the moiré sensor 12 and the A / D converter 13, and selectively connects the output side of the encoder 11 and the output side of the moiré sensor 12 to the A / D converter 13. Connect to the input side.
Reference numeral 15 denotes a digital signal processor, 16 denotes a digital / analog signal converter (hereinafter referred to as a D / A converter), and an A / D converter 13 is connected to the input side of the digital signal processor 15 and the output side Is connected to a DA converter 16. Reference numeral 17 denotes a drive circuit for driving the motor 5 connected to the output side of the DA converter 16. With this configuration, the encoder 11,
The detection voltage of the moiré sensor 12 is converted into a digital signal, processed by the digital signal processor 15, converted into an analog signal again, supplied to the motor 5 as a control current, and controlled in the following mode.

Digital signal processor for following servo
An arithmetic circuit 18 for calculating an absolute value speed based on a digital signal obtained from the encoder 11 side, an arithmetic circuit 19 for performing a calculation of a position error signal based on the digital signal obtained from the moire sensor 12 and , A band amplification filter 20 and an addition circuit 21. Then, the arithmetic circuit 18
Is supplied to the negative input side of the adder circuit 21 and the arithmetic circuit 19
Is supplied to the positive input side of the adder circuit 21 via the band amplification filter 20. Reference numeral 22 denotes an addition circuit connected to the input side of the moiré sensor 12. The current input signal Y of the head obtained from the driven unit 10 is supplied to the negative input side, and the center position signal of the track is supplied to the positive input side. R is supplied.

FIG. 2 shows a seek mode servo circuit. Driven part
10 is driven by a motor 5. The encoder 11 is connected to the motor 5. The moiré sensor 12 is connected to the driven part 10. These encoders
11, A / D converter 13 is provided on the output side of moire sensor 12.
Is connected. A digital signal processor 15 is connected to the output side of the A / D converter 13. A D / A converter 16 is connected to the output side of the digital signal processor 15. The motor 5 is connected to the output side of the D / A converter 16 via a drive circuit 17.

Digital signal processor 15 in seek mode
An arithmetic block in the arithmetic circuit 26 for calculating and detecting the current speed of the motor based on the digital signal obtained from the encoder 11 side, and calculates the current position of the head 2 based on the digital signal obtained from the moire sensor 12 side It comprises an arithmetic circuit 27 for detection, a reference speed signal generating circuit 28, an adding circuit 29, and a constant circuit 30 for a gain constant K. The output of the operation circuit 26 is supplied to the negative input side of the addition circuit 29, the output of the operation circuit 27 is supplied to the reference speed signal generation circuit 28, and the output of the reference speed signal generation circuit 28 is , And the output of the adder circuit 29 is supplied to a constant circuit 30.

FIGS. 3A, 3B and 3C show a floppy disk drive applied to an embodiment of the present invention. Reference numeral 40 denotes a base on which the carriage 4 is slidably mounted. Reference numeral 41 denotes a drive shaft connected to the carriage drive motor 5. The rotational force of the drive shaft 41 is converted via the steel belt 42 so that the carriage 4 moves linearly. The carriage 4 is provided with an upper arm 43,
The head 2 is mounted on the carriage 4 and the upper arm 43 via a gimbal sheet 44. Numeral 45 denotes a floppy disk cartridge, in which a floppy disk 46 is mounted, and data is recorded and reproduced by the head 2. In the carriage driving motor 5, a rotary encoder 11 provided directly connected to the motor shaft is arranged. As shown in FIG. 4, the output of the encoder 11 has a 90-degree phase difference between the A phase and the B phase.
The output waveform of the phase is transmitted. The cycle is 420 cycles per rotation.

Next, the stiffness of the servo system in one embodiment of the present invention will be analyzed.

The differential equation of the actuator is as the following equation (1).

Jθ + Td = Kti (1) where J: moment of inertia of motor 5 and carriage 4 (g cm sec ² ) Td: disturbance torque (g cm) Kt: torque constant (g cm / A) i: drive current (A).

When the equation (1) is Laplace transformed, the following equation (2) is obtained.

JS ² + Td = KtI (where, is the Laplace transform of θ) FIG. 5 shows the above equation (2) in a block diagram. FIG. 6 is obtained by equivalently converting FIG. FIG. 7 shows the following servo system of the present invention with reference to FIG.

Here, R: track center position signal E: off, track Y; head displacement Y ₁ : angular displacement of motor 5 D: compensation circuit of servo system Kb: gain of speed feedback system using encoder P: gain of motor 5 This is a transfer function from the displacement of the rotation angle to the displacement of the head 2.

 Next, the following equation is obtained.

E = R−Y = R−Y ₁ P (3) Y ₁ Kbs = U (4) From equation (3) From equations (4) and (5) FIG. 8 is obtained from FIG. 7 and equation (6).

Next, FIG. 9 is equivalently transformed to obtain FIG. Here, the high stiffness in question means that the magnitude of the off-track E with respect to the disturbance torque Td is small. Therefore, the transfer function of E / Td may be considered. Therefore, since the behavior of the off-track E with respect to the disturbance torque Td is observed, the track center position signal R is set to 0.

As a result, FIG. 10 is obtained. When FIG. 10 is equivalently exchanged, FIG. 11 is obtained. Here, if C and G are one block, FIG. 12 is obtained. Loop α in FIGS. 7 and 11
Is a speed feedback loop using the encoder 11, and the loop β is a head 2 based on the displacement of the rotation angle of the motor 5.
Is a loop including P, which is a transfer function up to the displacement of.

On the other hand, from FIG. Becomes

In equation (7), when (i) CG = circular transfer function >> 1 (Ii) When CG <1 Becomes

Here, since the gain of the block G is given,
From the equation (8), it can be seen that the gain of the transfer function of the block C should be increased in order to improve the stiffness.

On the other hand, the relationship between the transfer function of the block C and the loop α and the loop β shown in FIG. 7 is as shown in FIG. or,
The block diagram of the conventional PID servo system shown in FIG. 18 is also shown in FIG.
Takes the same form as the figure, but with a carriage 4 having a low resonance frequency.
In the loop, and the loop gain is limited to a lower level than in the case of the present invention. Therefore, the gain of the block C in FIG. 12 is low.

On the other hand, in the present invention, since the loop α does not include P, which is a transfer function from the displacement of the rotation angle of the motor 5 to the displacement of the head 2, the gain can be set high, and the gain of the loop β accordingly increases. Can be set. Therefore, the stiffness can be improved and a servo system with high stiffness can be obtained. Here, the loop α has a role of stabilizing the loop β. When the loop gain of the loop α is set high, the loop gain of the loop β can be increased due to the nature of the servo system.

Reduction of the influence of noise on the position error signal on the disk will be described with reference to FIGS. 13 and 14. FIG. 13 shows the closed-loop transfer characteristic of the conventional PID servo system when the servo band (frequency fc at which the gain becomes −3 dB when the frequency is increased in the closed-loop transfer function) is the same. FIG. 14 shows the closed-loop transfer characteristics of the present invention. Thirteenth
Comparing the characteristics of FIG. 14 and FIG. 14, the attenuation of the gain at a high frequency exceeding the servo band is faster in FIG. 14 of the present invention. This means that it does not respond to high frequency noise. That is, according to the present invention, the servo system does not respond to high-frequency noise and is not easily affected by the noise.

In the reference speed followability in the seek mode, the speed connection loop (loop γ) in FIG. 2 does not include the peripheral mechanism of the carriage 4 having a low resonance frequency. Therefore, the loop gain can be set high. Therefore, the ability of the servo system to follow the reference speed can be improved,
Variations in speed when switching from the seek mode to the following mode can be suppressed, and stable settling can be realized.

In the above-described embodiment of the present invention, the disk drive device is used for a floppy disk, but it goes without saying that the disk drive device may be used for a disk such as a hard disk.

〔The invention's effect〕

As described above, according to the present invention, the rotational angular displacement or angular velocity of the carriage driving motor is detected based on the output signal of the encoder directly connected to the carriage driving motor,
Since the following control is performed based on the detected signal, a servo system that is resistant to vibration and impact, that is, has high stiffness can be realized. In addition, since the servo system has a closed loop characteristic in which the gain decreases with respect to a high frequency, the servo system is not affected by high frequency noise. In addition, following control is performed using a difference signal between the absolute value speed of the head in the track width direction and the error position of the head with respect to the track, and this difference signal is generated from a signal irrelevant to the phase. Therefore, from this point, an effect such as realization of a servo system resistant to noise is achieved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a servo circuit for a following mode in one embodiment of the present invention, FIG. 2 is a block diagram showing a servo circuit for a seek mode in one embodiment of the present invention, and FIGS. 4 (B) and (C) are a plan view, a side view and a front view of a floppy disk drive applied to an embodiment of the present invention, and FIG. 4 shows an output obtained from an encoder according to an embodiment of the present invention. Waveform diagrams, Figs. 5 to 12
FIG. 1 is a block diagram provided for analyzing the stiffness of a servo system in one embodiment of the present invention, FIG. 13 is a closed loop transfer characteristic diagram of a conventional servo system, and FIG. FIG. 15 is a sectional view of a conventional disk drive, and FIG.
(B), (C) Explanatory drawing which shows the surface servo in FIG. 15,
FIG. 17 is a block diagram of a control system in a conventional seek mode, FIG. 18 is a block diagram of a control system in a conventional following mode, and FIG. 19 shows a relationship between a reference speed and a head speed in a seek mode. It is a graph. DESCRIPTION OF SYMBOLS 1 ... Disc 2 ... Head 3 ... Disk driving motor 4 ... Carriage 5 ... Carriage driving motor 6,8 ... Feedback path 10, 10 Driven part 1,
1 ... Encoder, 12 ... Moire sensor, 15 ... Digital signal processor, 41 ... Drive shaft, 45 ... Floppy disk cartridge.

Claims (1)

(57) [Claims] 1. A carriage for moving a head in a radial direction of a disk to be rotated, a carriage driving motor for driving the carriage, and detecting a rotational angular displacement or angular velocity of the carriage driving motor. And a seek control for moving the head at high speed from a distant track to a target track, and a following control for positioning the head that has reached the target track position at a predetermined position on the track. In the disk drive device, the encoder is directly connected to the carriage driving motor, and the absolute value of the head in the track width direction based on the output signal of the carriage driving motor rotated when the head is positioned at a predetermined position. First calculating means for calculating a speed;
Error signal detection means for obtaining a position error signal between the head and a predetermined position on the track; and a position error between the head and a predetermined position on the track based on an output signal of the error signal detection means. Second calculating means for calculating
A third calculating means for calculating a difference between the absolute speed and the position error; and, if a difference occurs in the calculation result of the third calculating means during the following control, the difference is calculated. Wherein the rotation of the motor for driving the carriage is controlled so as to be zero.