JPH02202391A - Servo circuit for disc mechanism - Google Patents

Abstract

PURPOSE:To rise the acceleration current well and to realize high speed access by switching the gain of a speed control/position control switching circuit ar ranged in the servo loop of an amplifier circuit located at the post stage of a circuit for determining the frequency characteristic of the servo loop to a higher level during the interval between start of seeking operation and finish of acceleration. CONSTITUTION:A servo logic 20 provides target speed data to a target speed generating circuit 22 thus feeding a target speed voltage E1 to a velocity error circuit 14 through a switch 24-1. Since an actual speed voltage E2 to be fed from a speed signal forming circuit 38 is zero under initial state, a differential signal E is maximized and fed through a switch 16-1 to the amplifier 50 in a speed control/position control switching circuit 16. The differential signal E is amplified through the amplifier 50 with a higher gain G to be determined by a resistor R8, and seek current is produced through a power amplifier 28 according to the differential signal E thus feeding acceleration current to the voice coil 10 of a disc mechanism 30.

Description

[Detailed Description of the Invention] [Summary] Regarding a servo circuit that controls the speed by flowing a seek current to a voice coil motor according to the difference between a target speed and an actual speed, the acceleration/deceleration period of the seek current is the cutoff frequency of the servo loop. The purpose of this is to start up the accelerating current well and access it at high speed even when the difference theta approaches The gain of the switching circuit for speed control and position control provided in the servo loop is configured to be switched to a higher gain until the end of the process.

[Industrial Application Field] The present invention relates to a servo circuit for a disk device that controls the speed of a head mounted on a carriage toward a target track position by flowing a seek current to a voice coil motor in accordance with the difference between a target speed and an actual speed. .

In recent years, the speed of the seek operation for accessing the head of a disk device to a target track position has been increasing, and as a result, the speed of the so-called 1-difference seek operation for moving the head to an adjacent track position has also increased significantly. A servo circuit with high acceleration responsiveness commensurate with the increased speed of this 1-difference seek is required.

[Prior art] FIG. 4 is a configuration diagram of a conventional circuit.

In FIG. 4, 20 is a servo logic using an MPU, which, when accessed from a host device, generates target speed data based on the amount of difference to the target track position at that time and various types of data necessary for seek operations. Generates control signals.

Target speed data from the servo logic 20 is given to a target speed generation circuit 22, which generates a target speed voltage E1 through D/A conversion. This target speed voltage E1 has different polarity between forward control and reverse control. Further, the target speed E1 maintains a predetermined maximum speed level if the difference amount is above a predetermined value, and when it becomes below the predetermined difference amount,
The target speed level decreases in proportion to, for example, the square value of the difference amount, and the target speed voltage E1 becomes the minimum speed level during one difference seek.

The target speed voltage E1 from the target speed generation circuit 22 is selected by the forward/reverse switching circuit 24 according to the control direction at that time, and is applied to the velocity error circuit 14 at the next stage.

The velocity error circuit 14 takes the difference between the target speed voltage E1 inputted through the resistor R1 or R2 and the actual speed voltage E2 inputted through the resistor R3, and outputs E as a difference signal through the amplifier 26.

Here, the amplifier 26 includes a resistor RO and a capacitor C in the feedback circuit.
Ro and C are connected in parallel, and the frequency characteristics of the velocity error circuit 14, that is, the frequency characteristics of the servo loop, are
o It is determined by which time constant.

The difference signal ΔE from the velocity error circuit 14 is on the velocity side w
J/position control switching circuit 16.

The speed control/position control switching circuit 16 is switched to speed control, that is, coarse control, at seek stars 1 to 1, and amplifies the difference signal E from the velocity error circuit 14 with a built-in amplifier and outputs it to the power amplifier 28.

The difference amount with respect to the target track in this speed control is monitored by the servo logic 20, and when the difference amount reaches zero, the position control is switched to fine control, and the position control is performed so that the head traces the target track. do.

The power amplifier 28 supplies a drive current, that is, a seek current, according to the input control voltage to the voice coil motor 10 of the disk mechanism 30, and the voice coil motor 10 drives the head mounted on the head carriage 32 in the radial direction of the disk medium 34. and access the target track position.

The reproduced signal from the head 12 is converted into a position signal by a position signal demodulation circuit 36, and is provided to a speed signal generation circuit 3B. Further, the speed signal generation circuit 38 is given a current detection detection signal from a current detection circuit 40 provided in the power amplifier 28. Therefore, the velocity signal generation circuit 38 generates the actual velocity voltage E2 by differentiating the position signal ((q) velocity signal, integrating the current signal and adding 1q) signal with each predetermined gain, and calculates the velocity error. Returns to circuit 14.

By the way, in the conventional speed control servo circuit shown in FIG. 1, a resistor Ro and a capacitor C are used.

The cutoff frequency f1 in the frequency characteristic of the velocity error circuit 14 determined by the frequency characteristic of the velocity error circuit 14 needs to be set smaller than the frequency f2 of the gain peak of the mechanical frequency characteristic (x/i>) in the disk mechanism 30. where i is the current flowing through the motor.

FIG. 5(a) shows the mechanical frequency characteristics of the disk mechanism 30, where the frequency r2 is the torsional resonance point of the servo arm. Further, FIG. 5(b) shows the frequency characteristics of the velocity error circuit 14, and the cutoff frequency f1 is determined by the time constants of RO and GO.

In a servo loop having such an electrical cutoff frequency f1 and a mechanical frequency f2, if the velocity error circuit 14 is provided with a cutoff frequency f1 higher than the frequency f2 which is the torsional resonance point of the servo arm, mechanical shooting will occur. is lost during seek, and it is not possible to improve the flying stability of the head or the stability of the head after fine switching.

Therefore, in the conventional device, the velocity error circuit 14
The cutoff frequency f1 is set to be lower than the frequency f2 of the gain peak of the mechanical characteristics, and specifically, a relationship of the order of f2=1.5·f1 to 2·fl is established.

[Problems to be Solved by the Invention] However, in such conventional servo circuits, in one-difference seek which requires high-speed access, the cycle of the seek current consisting of an acceleration period and a deceleration period is has a value close to the cutoff frequency f1 of the velocity error circuit, and the rise of the seek current during acceleration is limited by the cutoff frequency and becomes dull, causing a problem that a sufficient acceleration current cannot be obtained.

That is, as is clear from the change in the seek current shown together with the position signal in Fig. 6, the cutoff frequency f1 is determined by the cycle of the seek current, which is one cycle of the acceleration period and deceleration period of one difference seek. Since the values are close to each other, if the cutoff frequency were sufficiently high, the seek current would quickly rise as shown by the broken line and sufficient acceleration could be obtained, but the seek current becomes dull as shown by the solid line.

Therefore, a device that can reach the target track position at time t1 ends up reaching the target track position with a delay time as shown at time t2, making it difficult to speed up access for one-difference seek.

The present invention has been made in view of such conventional problems, and it is possible to improve the acceleration current even when the acceleration/deceleration period of the seek current approaches the cutoff frequency of the servo loop, as in the case of 1-difference seek. The object of the present invention is to provide a servo circuit for a disk device that achieves high-speed access upon startup.

Specifically, since the frequency characteristics of the servo loop are set by the velocity error circuit, a gain switching circuit 18 is provided in the amplifier provided in the speed control/position control switching circuit that is installed following the velocity error circuit. .

[Means to solve the problem] FIG. 1 is a diagram explaining the principle of the present invention.

First, the present invention provides a difference signal Δ between the target speed E1 and the actual speed E2.
The present invention is directed to a servo circuit of a disk device equipped with a servo loop that supplies a seek current according to E to a voice coil motor 10 to control the speed of a carriage-mounted head 12 toward a target track position.

Regarding such a servo circuit, in the present invention, the amplifier circuit 16 located after the amplifier circuit 14 that determines the frequency characteristics of the servo loop is provided with a predetermined gain G1 from a seek start to the end of acceleration. A gain switching means 18 for switching to G2 is provided.

[Function] In the servo circuit of the disk drive according to the present invention having such a configuration, even if the current cycle of acceleration/deceleration during one differential shift becomes a value close to the cutoff frequency of the amplifier, the acceleration period In order to forcibly increase the gain of the servo loop to a high gain after the circuit section that determines the frequency characteristics of the servo loop, the accelerating current is quickly raised to the first part of the servo loop without being constrained by the off-frequency. It can be sufficiently accelerated, and one-difference seek can be accessed at a higher speed.

[Embodiment] FIG. 2 is a block diagram showing an embodiment of the present invention.

In FIG. 2, the servo loop of the present invention includes a servo logic 20, a target speed generation circuit 22, a forward/reverse switching circuit 24, a velocity error circuit 14, a speed control/position control switching circuit 16, and a current detection circuit 40. It is composed of a power amplifier 28, a voice coil motor 10, a head carriage 32, a disk mechanism 30 including a head 12 and a disk medium 34, a position signal demodulation circuit 36, a speed signal generation circuit 38, and an acceleration end detection circuit 42.

The velocity error circuit 14 takes the difference between the reverse or forward target speed voltage E1 from the target speed generation circuit 22 inputted via the forward/reverse switching circuit 24 and the actual speed voltage E2 given from the speed signal generation circuit 38, and calculates the difference. Generates signal ΔE. This velocity error circuit 14 is provided with an amplifier 26, and a resistor Ro and a capacitor Co are connected in parallel to the feedback circuit of the amplifier 26.
The frequency characteristics of the velocity error circuit 14, that is, the frequency characteristics of the servo loop are determined by the time constants of Mechanical cutoff frequency f2 determined by the stopping point
The frequency is set to a low value.

A speed control/position control switching circuit 16 provided subsequent to the velocity error circuit 14 has a changeover switch 16- turned on by a coarse mode signal (speed control mode signal) 04.
1 and fine mode signal (position control mode signal) C5
The changeover switch 16 - 2 is equipped with a changeover switch 16 - 2 that is turned on by the changeover switch 16 - 2 , which inputs the difference signal ΔF output from the velocity error circuit 14 via the changeover switch 16 - 1 , and inputs a position signal from a position signal generation circuit (not shown) to the changeover switch 16 . -2. The output of the selector switch 16-1 is the resistor R5
Also, the output of the selector switch 16-2 is connected to the resistor R6.
The signal is input to the amplifier 50 via. The amplifier 50 has a feedback circuit connected in parallel with a resistor R8 and a resistor R9, and a gain changeover switch 18-1 is connected in series with one of the resistors R9.

The gain changeover switch 18-1 is normally on, and therefore the gain G1 of the amplifier 50 in a steady state is determined by the parallel resistance values of the resistors R8 and R9. On the other hand, when the gain selector switch 18-1 is turned off to disconnect the resistor R9 from the feedback circuit, the gain of the amplifier 50 becomes a gain G2 higher than that determined by the resistor R8.

The gain changeover switch 18-1 is controlled on and off by a D-FF 18-2 provided as gain changeover control means. The acceleration end signal C2 from the acceleration end detection circuit 42 is applied to the clock terminal CLK of the D-FF 18-2, and the acceleration end signal C2 is inputted to the D terminal via a capacitor. Further, a reseek start pulse P2 is inputted from the servo logic 20 to the clear terminal CLR.

Therefore, in the steady state, the D-FF'18-2 is placed in a reset state, and the seek acceleration signal C3, which outputs 0, is at the L level, so the gain changeover switch 18-1 is turned on and the resistors R8 and R9 are turned on. The gain G1 in the steady state is set in the amplifier 50 by the parallel resistance value. When the servo logic 20 generates the seek start pulse P in response to access from the host device, the D-FF 18-2 is cleared, the seek acceleration signal @C3 as the Q output becomes H level, and the gain changeover switch 18-1 is turned on. By turning off, the resistance R
9 is disconnected from the feedback circuit and amplifier 50 is switched to the higher gain G2. The D-FF 18-2 reset by the seek start pulse P is then set again by the acceleration end signal C2 from the acceleration end detection circuit 42, and when the acceleration signal C3 returns to L level, the gain changeover switch 18-1 Turn on the original gain G1 again.
I'm trying to change it back to .

Next, the operation of the embodiment shown in FIG. 2 will be explained with reference to the operation timing chart shown in FIG.

In FIG. 3, it is assumed that the servo logic 20 receives access from a host device at time t1 and starts forward control, for example. That is, the servo logic 20 supplies target speed data according to the difference for the target track at that time to the target speed generation circuit 22, and the target speed generation circuit 22 generates a target speed voltage by AD conversion. Since the forward side changeover switch 24-1 of the forward/reverse changeover circuit is turned on by the forward control command from the changeover switch 2.
A target velocity voltage E1 for forward control is supplied to the velocity error circuit 14 via the output terminal 4-1.

In the initial state, since the actual speed voltage E2 from the speed signal generation circuit 38 is zero, the velocity error circuit 1
The difference signal ΔE outputted from the amplifier 26 provided at 4 becomes the maximum level, and is sent to the amplifier 50 of the speed control/position control switching circuit 16 through the changeover switch 16-1, which is turned on by the coarse mode signal C4, to the maximum level. The difference signal ΔE is input. At this time, the gain changeover switch 18-1 provided in the feedback circuit of the amplifier 50 changes so that the D-FFI 8-2 is set at time t1.
Since it is in a reset state upon receiving the seek start pulse P from the servo logic 20, it is switched off upon receiving the seek acceleration signal C3 which becomes O=H level, and is determined by the resistor R8 by disconnecting the resistor R9 from the feedback circuit. It is set to a higher gain G2.

Therefore, the difference signal ΔF from the velocity error circuit 14 is amplified by the higher gain G determined by the resistor R8 in the amplifier 50, and the power amplifier 28 generates a seek current according to the difference signal ΔE to drive the voice coil motor of the disk mechanism 30. An accelerating current is applied to 10.

The voice coil motor 10, which receives the accelerated seek current from the power amplifier 28, starts speed control to move the head 12 toward the target track position on the disk medium 34 using the carriage 32, and as a result of this speed control, the position changes. Position signal from signal demodulation circuit 36 and power amplifier 28
Servo control is performed in which the speed signal generation circuit 38 generates an actual speed voltage E2 based on the current detection signal from the current detection circuit 40 provided in the servo control circuit 38 and feeds it back to the velocity error circuit 14.

When the actual speed voltage E2 increases due to this servo control and reaches the target speed voltage E1, E becomes zero voltage in the difference signal from the amplifier 26, so the acceleration end detection circuit 42 detects reaching this zero voltage. Then, as shown at time t2 in FIG. 3, the acceleration end signal C2 for the D-FF 18-2 is raised to the H level, and the D-FF 18, which has been in the reset state until then, is raised to the H level.
-2 is returned to the set state again at the time of detection of end of acceleration. Therefore, the seek acceleration signal C3, which becomes 0 output, returns from the H level to the L level, and the gain changeover switch 18-1
When turned on, the resistor R9 is connected to the feedback circuit and the original gain G1 is restored.

That is, the amplifier 50 switches the normal gain G1 to the higher gain G2 from the start of the seek to the end of acceleration.

After the acceleration ends at time t2, deceleration control is performed based on the difference signal ΔE between the target speed voltage E1 and the actual speed voltage E2,
At time t3, the difference amount with respect to the target track becomes zero, the changeover switch 16-2 is turned on by the fine mode signal C5 from the servo logic 20, and position control (fine control) is performed to control the head to trace the target track. Switch to .

For such a one-difference seek of the present invention, the fourth
In the conventional 1-difference seek shown in the figure,
Velocity error circuit] Under the influence of the cutoff frequency f1 in the frequency characteristic determined by the time constant of the resistor RO and capacitor Co provided in 4, as shown in Fig. 3, regarding the seek current with the gain of the conventional servo loop constant. During the acceleration period, the rise of the seek current slows down,
If the seek operation is started at time t1, the seek time T1 is longer than the seek time T1 of the present invention and extends to time t4.
It takes 2.

On the other hand, in the present invention, even if the cycle of the acceleration/deceleration period of the seek current in one difference seek approaches the cutoff frequency f1 of the servo loop, the velocity error circuit 14 in the subsequent stage of the velocity error circuit 14 that determines the frequency characteristics of the servo loop In order to switch the gain of the amplifier 50 provided in the speed control/position control switching circuit 16 located in the acceleration period to a higher gain during the acceleration period, the rise of the seek current during the acceleration period is made good without being limited by the frequency characteristics of the servo loop. By achieving sufficient acceleration, the access time for one difference seek can be significantly shortened and high-speed access can be achieved.

Incidentally, in the above embodiment, the velocity error circuit 14
Since a circuit element that determines the frequency characteristics of the servo loop is provided in the servo loop, a gain switching means is provided in the speed control/position control switching circuit 16 which is a subsequent stage of the velocity error circuit 14, but the present invention is not limited to this. First, a gain switching means for switching to a higher gain than the steady gain is provided in an appropriate amplifier circuit located after the amplifier circuit that determines the frequency characteristics in the loop of the servo circuit from the start of the seek to the end of acceleration. Of course, it is fine to do so.

As explained above, according to the present invention, even in a 1-difference seek where the acceleration/deceleration period of the seek current is close to the cutoff frequency of the servo loop, the forced In order to increase the gain of the servo loop, the accelerating current can be quickly started and sufficiently accelerated without being restricted by the cutoff frequency of the servo loop, making 1-difference seek even faster access. can do.

[Brief explanation of the drawing]

FIG. 1 is a diagram explaining the principle of the present invention; FIG. 2 is a configuration diagram of an embodiment of the present invention; FIG. 3 is an operation timing chart of the present invention; FIG. 4 is a configuration diagram of a conventional circuit; FIG. 5 is a conventional device Figure 6 is an explanatory diagram of the conventional 1-difference seek operation. [Effects of the Invention] In the figure, 10: Voice coil motor 12: Head 14: Velocity error circuit (amplifier circuit) 16: Speed control/position control switching circuit (amplifier circuit) 18 Gain switching means 18-1 Gain switching switch 18- 2: D-FF 20: Servo logic (MPU) 22: Forward/reverse switching circuit 24: Target speed generation circuit 28: Power amplifier 30: Disk mechanism 32: Carriage 34: Disk medium 36: Position signal demodulation circuit 38: Speed signal create circuit

Claims (2)

[Claims] (1) Difference signal between target speed (E1) and actual speed (E2) (
The voice coil motor (10
) in a servo circuit of a disk device that is equipped with a servo loop that controls the speed of a carriage-mounted head (12) toward a target track position, an amplifier circuit (1) that determines the frequency characteristics of the servo loop.
4) A preset gain (
A servo circuit for a disk device, characterized in that it is provided with gain switching means (18) for switching G1) to a larger gain (G2). (2) The gain switching means (18) is provided in a speed control/speed control switching circuit (16) provided after a velocity error circuit (14) that determines the frequency characteristics of the servo loop. 1. The servo circuit of the disk device according to item 1.