JPS63188873A - Head positioning servo mechanism for magnetic disk device - Google Patents

Abstract

PURPOSE:To decrease the transient response of a head positioning servo by subtracting an external disturbance cancelling signal and a speed signal from the driving current signal of a servo motor, integrating the result and adding the external cancelling signal being the result of subtracting the speed signal from a speed estimating signal obtained in this way. CONSTITUTION:A current detector 2 detects the driving current J1 of the servo motor 9 and a speed detector 3 detects the speed signal U0 of the motor 9 from the signal of a disk face written with a bit of position information. When any external disturbance exists, a difference is caused between the signal U0 and the speed estimating signal U1, the external disturbance cancelling signal F is caused in the output of an error amplifier 6 and the signal is fed to a power amplifier 1 via an adder 7. A speed signal the inverse of U0 produced from the polarity inverting circuit 8 eliminates the current signal component against the dynamic friction proportional to the speed in existence in the correction current detection signal J2 fed to an integrating device 5 to eliminate the effect of the dynamic friction onto the response of the signal F. Thus, the transient response of the head positioning servo mechanism is decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a head positioning servo mechanism 1 for a magnetic disk device.

[Conventional technology]

An ideal magnetic disk drive uses a servo motor that generates a force proportional to the drive current to move and position a head attached to a movable part to a target track using a closed-loop servo system. The only force that is applied to the moving part is the force generated by the servo motor, and from a mechanical point of view, the acceleration (=proportional), which is once integrated, is the velocity of the moving part (=proportional, 2 The relationship holds that the integral is proportional to the displacement of the moving part, that is, the head.However, in an actual magnetic disk drive, the moving part is affected by the wind generated by the rotation of the disk, and by the wind that connects the head and the circuit. The bending force of flexible cables used in 9 External forces such as gravity act.

That is, the force acting on the movable part is a composite force that is the sum of the force generated by the servo motor and the external force. In order to control the position of the head correctly, assuming there is no external force (= accelerating the moving part).

Signal components necessary for deceleration (= In addition, in order to avoid being affected by external forces, a signal component that counteracts the external forces must be added to the drive current.

As a way to provide a signal to cancel this external force.

Conventionally, there are two methods: adding a DC offset voltage to the position control loop and adding a circuit that integrates two position errors, but the method of adding a DC offset voltage has drawbacks such as not being able to deal with variations in external force from device to device. The method of integrating the υ99 position error has the disadvantage of slow response.

These shortcomings have been removed. A method for generating a disturbance cancellation signal is disclosed in Japanese Patent Application Laid-Open No. 59-146485 entitled "Head Positioning Servo Mechanism for Magnetic Disk Devices." In the positioning servo mechanism.

A current detection signal amplifier, an integrator, and an error amplifier are connected in cascade, and the output of the error amplifier, which serves as a disturbance cancellation signal, is fed back to the current detection signal amplifier to form a minor loop, and a speed signal is further applied to the error amplifier to generate a speed signal. A disturbance cancellation signal generation circuit is configured to extract the error between the output of the integrator and the output of the integrator. The operation of the disturbance cancellation signal generation circuit is as follows.

As mentioned above, the current detection signal contains a component that is originally necessary to control the moving part and a component that is generated to counter external force, so the integral output is the integral of both, and is equal to the speed of the moving part. is not proportional.If we extract the disturbance cancellation signal as the error component between the integrator output and the speed signal, we get
This corresponds to a component occurring to counteract the external force included in the current detection signal. Therefore, if the disturbance cancellation signal is fed back to the current detection signal amplifier, the output of the current detection signal amplifier will contain only the components originally necessary to control the moving parts, and the change in the integrator output signal will be proportional to the speed signal. .

By using this positioning servo mechanism.

The problems with the method of applying the DC offset voltage and the method of integrating the positional deviation described above could be solved to a certain extent.

[Problem that the invention seeks to solve]

However, the response speed to disturbance in the positioning servo mechanism can be increased by increasing the gain intersection frequency of the open loop transfer function of the minor lube of the disturbance cancellation signal generation circuit, but there is a limit due to the stability of the entire two positioning servo loops. On the other hand, the external force applied to the moving part (= dynamic frictional force that changes in proportion to the speed of the moving part) is included.

The dynamic friction force is particularly high in small magnetic disk drives. Since the movable part is accelerated and decelerated during the cranking operation, the dynamic frictional force changes greatly, which causes a problem in that the response of the external force cancellation signal generation circuit is delayed.

The present invention attempts to solve these problems with the conventional devices, and aims to provide a magnetic disk device that does not require adjustment and has a small transient response.

[Means for solving problems]

The head positioning servo mechanism of the magnetic disk drive of the present invention has a servo motor that generates a force proportional to the drive current, and uses a closed-loop servo system (which positions the head on any target track among a plurality of data tracks. In the head positioning servo mechanism of a magnetic disk device, a power amplifier that supplies a proportional drive current to a servomotor, a means for detecting the drive current of the servomotor, and a means for detecting the speed of the servomotor are used. The integrator (:I) is proportional to the current detection signal obtained by the current detection means to the disturbance cancellation signal which is the output signal of the error amplifier and the speed signal obtained by the speed detection means. The error amplifier amplifies the error obtained by subtracting the speed signal obtained by the speed detection means from the speed estimation signal obtained as the output of the integrator. The input of the power amplifier includes a disturbance cancellation loop configured to add the disturbance cancellation signal.

〔Example〕

Next (=2) The present invention will be explained with reference to the drawings.

FIG. 1 is a circuit diagram of an embodiment of the present invention.

This figure differs from the circuit example in Japanese Patent Laid-Open No. 59-14<5'485 mentioned above in that a polarity inversion circuit 8 is added. In Figure 1 (=, 1 is a power amplifier, 2 is a current detector, 6 is a speed detector, and 9 is a motor. 4, 5.6,
7.8 is an operational amplifier, and 4 generates J and -F from the current detection signal J1 and the disturbance cancellation signal F. 5 is an integrator, and 6 is an error U1-U from the speed estimation signal U1 obtained as the output of the integrator 5 and the speed signal UO.
7 is an addition circuit that adds the main control signal E and disturbance cancellation signal F to bring the position and speed closer to the target value, and 8 is a polarity inversion circuit that inverts the polarity of the speed signal Uo. It consists of

X represents position (displacement) and +J2 is a corrected current detection signal. The integration time constant of the integrator 5 advances so that its output, the speed estimation signal U1, is at the same level as the speed signal Ua!
It shifts. The speed detector 3 demodulates the readout signal from the disk surface (servo surface) on which 9 position information is written, and generates a 900°
In the two-phase servo system 1-, in which two position signals with different phases are obtained, it is assumed that a speed signal is created by differentiating these two position signals and sequentially switching and selecting the polarity so that the polarity becomes constant. There is.

In an ideal state with no disturbance, the speed signal Uo and the speed estimation signal U
A difference of 1 is zero, and the disturbance cancellation signal applied from the error amplifier 6 to the adder 7 is also zero.

The operational amplifier circuits 4, 5, 6, and 8 have no effect on the main control. When there is a disturbance, a difference occurs between the speed signal UD and the speed estimation signal U1, and a disturbance cancellation signal F is generated at the output of the error amplifier O, which is then sent to the power amplifier 1 via the adder 7.
The main control signal E is not affected by disturbances. Speed signal −Uo output from polarity inversion circuit 8
removes the current signal component that opposes the dynamic friction force proportional to the speed present in the modified current detection signal J2 applied to the integrator 5, and can eliminate the influence of the dynamic friction force on the response of the disturbance cancellation signal F.

〔Effect of the invention〕

As explained above, the present invention can cancel the effects of disturbances by adding a simple circuit, and automatically follows the disturbances without being affected by the large dynamic friction force of the movable part. Therefore, it is possible to obtain a magnetic disk device that does not require adjustment and has a small transient response.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. Explanation of symbols: 1...Power amplifier, 2...Current detector, 3...Speed detector, 4...J, -F creation circuit. 5... Integrator, 6... Error amplifier, 7... Addition circuit. 8... Polarity inversion circuit, 9... Motor, E... Main control signal, F... Disturbance cancellation signal, Jl... Current detection signal. J2...Corrected current detection signal +UQ...Speed signal +U
i... Speed estimation signal, X... Position (displacement).

Claims (1)

[Claims] 1. A head positioning servo mechanism for a magnetic disk device that has a servo motor that generates a force proportional to the drive current and positions the head to an arbitrary target track among a plurality of data tracks using a closed-loop servo system. The integrator includes a power amplifier that supplies a drive current proportional to the input voltage to the servo motor, a means for detecting the drive current of the servo motor, a means for detecting the speed of the servo motor, an integrator, and an error amplifier. A signal obtained by subtracting a disturbance cancellation signal which is an output signal of the error amplifier and a signal proportional to the speed signal obtained by the speed detection means from the current detection signal obtained by the current detection means is input, and the error amplifier calculates the integral a disturbance configured to amplify the error obtained by subtracting the speed signal obtained by the speed detection means from the speed estimation signal obtained as the output of the power amplifier, and to add the disturbance cancellation signal to the input of the power amplifier. A head positioning servo mechanism for a magnetic disk device, characterized by including a cancellation loop.