GB2235070A

GB2235070A - Controlling velocity of magnetic disk reader

Info

Publication number: GB2235070A
Application number: GB9013384A
Authority: GB
Inventors: Makoto Nishimura
Original assignee: Tokico Ltd
Current assignee: Tokico Ltd
Priority date: 1989-06-20
Filing date: 1990-06-15
Publication date: 1991-02-20
Also published as: GB9013384D0; DE4019657A1; JPH0323570A

Abstract

A velocity signal creation circuit 15 generates velocity signals SV to indicate a movement velocity of a servo head 3, according to the servo information SI which the servo head reads from a magnetic disk 1. These velocity signals are supplied to an amplifier 25 that has a gain of one time and an amplifier 26 that has a gain of K times (K>1). These output signals are supplied to a switching circuit 27 which selectively outputs the velocity signal amplified by either one of the amplifiers. A CPU 13 supplies the servo head with the velocity command value to indicate a movement velocity for the servo head to reach the target position when it moves to the target position. It also multiplies the velocity command value to K times when the distance between the current position and the target position of the servo head reaches the previously set remaining movement distance N. Furthermore, it outputs the control signal B to the switching circuit. When the control signal B is supplied, the switching circuit outputs the K times velocity signal to the servo system to control the servo head position. <IMAGE>

Description

k, Magnetic Disk Storage Device

Background of the Invention

Field of the Invention

The present invention relates to a magnetic disk device suitable for use in an external computer storage device.

Prior Art

The conventional magnetic disk device, designed to reach a target position, has been structured in such a way that its servo head is controlled through a proportional integral derivative (PID) control based on the deviation of a movement velocity of the servo head and the target velocity of that.

Fig. I is a block diagram that shows a configuration of the conventional magnetic disk device. In the figure, a servo information SI initially written on the servo face of a disk 1 is read by a servo head 3 attached to the tip of a head arm 2. The servo information SI, as shown in Fig. 2 (a), consists of the magnetic patterns of N, R, Q and Q to obtain positional information from the servo head 3, a timing clock to receive the positional information, and servo sink bits required to make up unique patterns. Fig. 2 (b) shows waveforms, each of which is read by, for example, the servo head 3 each time it is in positions, D, A, B or C (shown in Fig. 2 (a)). The servo information (SI) read out by the servo head 3 is supplied to an AGC 6 (auto gain controller) through a head amplifier 4 and a filter 5 shown in Fig. 1. The servo information (SI) outputted from the AGC 6 is supplied to a window pulse generator 9 and a VCO 10 (voltage control oscillator) through a SYNC separator 7 and a phase detector 8. The window pulse generator 9 sorts out the positional information and the unique patterns from the servo information (SI). The servo information (SI) is also supplied to a position demodulator 11. The latter serves to obtain a positional signal for the servo head 3 from the servo information (SI).

1 The unique pattern sorted out by the window pulse generator 9 is supplied to the position demodulator 11 and the unique pattern detection circuit 12. The latter detects Indexes and guard bands, which are supplied to a central processing unit 13 (CPU).

On the one hand, the position demodulator 11 generates a positional signal made up of N phase and Q phase, which differ by 900 to each other, based on the unique pattern outputted by the window pulse generator 9 and the servo information (SI) outputted by the AGC 6. (Refer to Figs. 3 (d) and (e).). This signal is applied to a velocity signal creation circuit 15 and a position signal creation circuit 16. The velocity signal creation circuit 15 generates a velocity signal (SV1) according to the positional signal. (Refer to Fig. 3 (b).) The position signal creation circuit 16 generates a position signal multiplied by four. (Refer to Fig. 3 (f).) The pulse width of this position signal corresponds to the feed amount of one track, with the pulse center value corresponding to the center position of each track. This position signal is converted to digital signals of 0 C and 0 D (refer to Figs. 3 (h) and (I)), and is then supplied to the CPU 13.

Next, an explanation is given to a seek operation to move the servo head 3 to the target position (target track). First, when a seek command (shown in Fig. 3 (a)) is applied into the CPU 13. The CPU 13 then outputs a control signal A (shown in Fig. 1) that switches the servo control system from a position control mode for tracking the operation of the track, to a velocity control mode that enables a seek operation (refer to Fig. 3 (c)) and outputs a velocity command value VD (refer to Fig. 3 (b)). This velocity command value VD is supplied to a digital-analog converter (DAC) 18 through a latch circuit 17. The DAC 18 converts the velocity command value VD to a object velocity signal SV2 of an analog signal, the object velocity signal SV2 being supplied to an addition point 19. In addition, the control signal A is supplied to a switching circuit 20, which is changed over from the position signal creation circuit 16 2 11 side to the velocity signal creation circuit 15 side. Thus, the addition point 19 obtains a deviation signal as a result of the velocity signal SV, outputted from the velocity signal creation circuit 15 and the object velocity signal SV2. This deviation signal is supplied to a voice coil motor (VCM) driver 22-through a phase compensation circuit 21. The VCM driver 22 drives a VCM 23, while a head arm 2 swings and the servo head 3 moves on the disk 1. When the servo head 3 reaches the object position, the switching circuit 20 changes over to the position signal creation circuit 16 side (refer to Figs. 3 (b) and (c)), and the servo control system is transferred to the position control mode.

As described, the conventional disk device reduces the servo head movement velocity as it approaches the object position, which finally reaches zero when the servo head arrives at the object position. In the lower velocity range where the servo head movement velocity is reduced (as shown in Fig. 3 (b)), the dynamic range decreases, resulting in larger errors due to an offsetting effect and worsened velocity control. The DAC to generate the object velocity signal SV2 is normally made of eight bits, because of cost. For this reason, the resolution of the object velocity signal SV2 is restricted to 1/256 of the maximum value. Therefore, the smaller the velocity command value VD, the relatively larger the variation of the object velocity signal SV2 per bit, relative to the velocity signal SV1. Thus, no precise velocity control is possible in the lower velocity range where the movement velocity approaches zero, even if the velocity signal SV, at the servo head is fed back correctly. As a result, the above-mentioned switching from the velocity control mode to the position control mode will not be carried out as desired, the setting time for the servo head 3 is worsened, and the access time performance is degraded.

Summary of the Invention

The present invention is made in consideration of the above-mentioned problems, with an aim of providing a magnetic disk device which enables controlling velocity precisely in 3 the lower servo head velocity range, and can position the servo head at a high speed.

For this reason, the present invention provides a magnetic disk device which is equipped with the following: magnetic head to read the servo information on the disk; a velocity signal generating means to generate a velocity signal to indicate a movement speed of the magnetic head; a gain controlling means to amplify and output the velocity signal. The disk is furthermore equipped with a controlling means which serves the following functions. First, it outputs a velocity command value when the magnetic head is moved to a target position, and multiplies to K (K>l) the velocity command value when a distance from the current position of the magnetic head to the target position reaches the Initially set remaining movement distance N. Moreover, it outputs a control signal to the gain controlling means, the gain controlling means switching the gain from one time to K times when the control signal is supplied. To explain, as soon as the distance between the current position and the target position of the magnetic head reaches the initially set remaining movement distance during the magnetic head moving to the target position (based on the velocity signal outputted by the velocity signal creation means) the controlling means multiplies the velocity command value by K, and outputs the control signal to the gain controlling means. The gain controlling means switches the gain from one time to K times when the control signal is supplied, and outputs the velocity signal, which makes it K times.

These arrangements enhance the above-mentioned resolution of the control system, enable the precise control of the magnetic head velocity, and realize the positioning of the magnetic head at high velocity.

Brief Description of the Drawings

Fig. 1 is a block diagram that shows the servo system structure in a magnetic disk device.

Fig. 2 is a servo signal waveform chart that describes the operation of the magnetic disk device.

4 1 1 1 Fig. 3 is a timing chart that describes the operation of the magnetic disk device.

Fig. 4 is a block diagram that shows a structure of one embodiment of the present invention.

Fig. 5 is a waveform chart that describes the velocity signal and the object velocity signal, explaining the operation of the magnetic disk device according to the embodiment of the present invention.

Description of a Favorable Embodiment of the Invention

Explanations are given to an embodiment of the present invention with reference to the drawings.

Fig. 4 is a block diagram that shows a structure of one embodiment of the present invention. The parts in the figure that correspond to the parts of the conventional magnetic device (shown in Fig. 1) are given the same numerals, and are not explained in this document.

In the figure, part 25 is an amplifier that has one time gain. Part 26 is an amplifier that has a K time gain (K>1). The input terminals in the amplifier 25 and the amplifier itself 26 are interconnected, and the input terminals are designed so that the velocity signal SV1 outputted from the velocity signal creation circuit 15 is supplied. Part 27 is a switching circuit, which supplies either one of the output signals outputted from the amplifiers 25 or 26 to one end of the switching circuit 20.

Next, the seek operation of the above structure is explained. First, when a seek command is inputted into the CPU 13 in the similar manner with in the magnetic disk device (shown in Fig. 1), the CPU 13 outputs the predetermined control signals A and B to each of the switching circuits 20 and 27. The switching circuit 20 changes over to the switching circuit 27 side from the position signal creation circuit 16 side in response to the control signal A, and the switching circuit 27 changes over to the amplifier 25 side from the amplifier 26 side in response to the control signal B. In this case, the switching circuit 27 may be switched i k initially to the amplifier 25 side using an initialization. The CPU 13 outputs the velocity command value VD (refer to Fig. 5 for time t=O), while the velocity command value VD is converted to the analog object velocity signal SV2, and is supplied to the addition point 19. On the one hand, the velocity signal SVI, outputted from the velocity signal creation circuit 15, passes through the amplifier 25 and, while holding the original gain, is supplied to the addition point 19 through the switching circuit 27 As a result, the addition point 19 obtains a velocity deviation between the velocity signal SV, and the object velocity signal SV2. Therefore, the servo head 3 moves on the disk 1 at a velocity according to the velocity deviation, as shown by the solid lines in Fig. 5. When the distance between the current position and the target position of the servo head 3 reaches the initially set remaining movement distance N (refer to Fig. 5), the CPU 13 outputs the control signal B to the switching circuit 27. Upon receiving the control signal B, the switching circuit 27 changes over to the amplifier 26 side having K time gain, according to the control signal B. As the control signal B is outputted, the velocity command value VD is simultaneously multiplied to K, as in the case of the gain in the amplifier 26. Thus, by multiplying to K the velocity command value VD from the CPU 13, the dynamic range of the object velocity signal BV2 expands, and the resolution is enhanced (refer to Fig. 5) to achieve precise velocity control. Furthermore, when the servo head 3 arrives at the target position, the switching circuit 20 changes over to the position signal creation circuit 16 side in response to the control signal A, and the switching circuit 27 changes over to the side of the amplifier 25 that has one time gain. That is, the servo control system (shown in Fig. 4) is changed over from the velocity control mode to the position control mode.

The above-mentioned velocity signal creation circuit 15, the position signal creation circuit 16, the latch circuit 17 and the DAC 18 may all be contained in one LS1 chip. In this case, use a differentiator in the velocity signal creation 6 1 X circuit 15 (not shown) a switched capacitor differentiator is preferable. A switched capacitor differentiator has its gain changed when the clock frequency for operating the switched capacitor differentiator is varied. Therefore, using a switched capacitor differentiator provides the advantage of simplifying the circuitry and reducing errors.

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Claims

What is claimed is:

1. A magnetic disk device which is characterized by having:

(a) magnetic head for reading a servo Information on a disk; (b) velocity signal creating means for generating a velocity signal to indicate a movement velocity of said magnetic head; (c) controlling means for outputting a velocity command value when said magnetic head is moved to a target position; multiplying to K (K>l) said velocity command value when a distance from the current position of the magnetic head to the target position reaches the initially set remaining movement distance N; outputting a control signal; and (c) gain controlling means for receiving the control signal and amplifying and outputting said velocity signal, as switching the gain from one time to K times when the control signal is supplied.

2. A magnetic disk device according to claim 1, which is further characterized in that said velocity signal creating means is contained in one LSI chip together with the other circuits.

3. A magnetic disk device according to claim 1, which is further characterized in that said velocity signal creating means comprises a switched capacitor differentiator for changing the gain when the operation clock frequency is varied.

4. A magnetic disk device according to claim 1, which is further characterized in that said gain controlling means comprises a switching circuit, a first amplifier having a gain of one time, and a second amplifier having a gain of K times, and said gain controlling means selectively outputs either one of the output signals outputted from said first amplifier or said second amplifier when said control signal is supplied.

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5. A magnetic disk device according to claim 1, which is further characterized in that said controlling means is a central processing unit which operates according to the previously stored programs.

6. The magnetic disk device substantially as herein described with reference to and as shown in the accompanying drawings.

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