JPS59177767A - Access control circuit - Google Patents

Abstract

PURPOSE:To detect the runaway of a head moving means and to prevent a magnetic disc and a head from being damaged by integrating current flowing into a voice coil motor (VCM) in a head moving means and monitoring the output. CONSTITUTION:A real speed detecting circuit 1 detects the moving speed of the head. A speed instruction generating circuit 2 generates a head moving speed under control from the host device. An operational amplifier 3 comares a signal from the speed detecting circuit 1 with a signal from the speed instrction generating circuit 2 and outputs the difference. Receiving the signal from the operational amplifier 3, a power amplifier 4 makes current flow into a VCM5. When the output signal of the real speed detecting circuit 1 exceeds a set value i.e. the runaway state is generated, a real speed detection type runaway detecting circuit 6 turns off the power amplifier 4 and interrupts current supply to the VCM5. A current integration type runaway detecting circuit 7 integrates the current flowing into the VCM5, and when the integrated value exceeds a set value, turns off the power amplifier 4 and interrupts current supply to the VCM5.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an access control circuit for a magnetic disk device, and in particular has a runaway detection function to prevent damage to a magnetic head and the magnetic head due to a runaway collision of a head moving mechanism. Related to access control circuits.

[Background of the invention]

Generally, a magnetic disk storage device includes an access control circuit having a runaway detection function for detecting runaway of a head moving mechanism. An example of an access control circuit according to the prior art is shown in FIG. This access control circuit includes a speed command generation circuit 2 that generates a speed command signal to drive the voice coil motor (hereinafter referred to as α) 5 of the head moving mechanism according to instructions from a host device, and a speed command generation circuit 2 that generates a speed command signal that drives the voice coil motor (hereinafter referred to as A differential amplifier 5 which inputs an actual speed signal 12 outputted from an actual speed detection circuit 1 (to be described later) to a positive (plus) terminal and amplifies the difference between these signals by inputting an actual speed signal 12 output from an actual speed detection circuit 1 (to be described later) to a minus (-) terminal, and the output of the amplifier B. Power amplifier 4 amplifies and supplies drive current to VCM5
A runaway detection circuit 6 receives the actual speed signal 12 and detects runaway of the VCM 5, and a servo head (not shown) receives the VCM current waveforms 16 and 14 supplied to the previous day's power amplifier 4 to one side. The actual device detection circuit 1 receives the position error signal read out and demodulated from the VCM 5 and detects the actual speed of the VCM 5. Note that the runaway detection circuit 6 does not have a function of simply detecting whether the signal 12 exceeds a predetermined value.

The actual speed detection circuit 1 has a position error signal and a VCM5 (
This circuit detects the moving speed of the head from the current flowing through the voice coil motor (voice coil motor), and the detected moving speed (v) of the head is proportional to the integral value of the current (i) flowing through the VCM5, and v- kfidt (k is the coefficient of the device), and the speed can be detected just by integrating the current, but it is difficult to compensate for disturbances (frictional force, etc.) acting on the head.
By differentiating the position error signal x (X), the velocity of v-La t (L is the coefficient of the device) can be detected. Since the differential of the error signal detects the movement of the position of the head, it is not affected by disturbances, so the detection accuracy is good. When the servo head moves on the track, the position error signal has a sinusoidal waveform as shown in FIG. The servo head is directly above the track (
TC), the position error peak is 0, and when it is in the middle of the truck and the trunk, it has a positive or negative peak. Therefore, the actual speed detection circuit 1 differentiates the position error signal at the linear portion LN of the waveform shown in FIG.
At the location L, the currents 16 and 14 flowing through the VCM 5 are integrated and mixed by a certain coefficient to detect the actual speed. A speed command generation circuit 2 generates a target speed at which the head moves according to a command from a host device. The operational amplifier 6 compares the actual speed signal that is the output of the actual speed detection circuit 1 and the target speed signal that is the output of the speed command generation circuit 2, and outputs the difference.

The power amplifier 4 outputs VCM according to the output signal of the operational amplifier 3.
A current is applied to 5 to move the head. Next, FIG. 6 shows the valley waveform during normal access. Speed command generation circuit 2
The target speed signal 11 output from the actual speed detection circuit 1 is compared with the actual speed signal 12 output from the actual speed detection circuit 1, and a current 16 is caused to flow through the VCM 5.

When the target speed signal 11 and the actual speed signal 12 match at point a, the VCM current 16 becomes almost 0, acceleration ends and the speed becomes constant, and deceleration starts from point b, when the actual speed signal 12 becomes 0. Access ends.

Next, if the head accelerates beyond the maximum speed of the device due to a failure in the speed command generation circuit 2, operational amplifier 6, etc., the actual speed detection circuit 1 is operating normally, so the actual speed signal 1
2 is detected by an actual speed detection type runaway detection circuit 6, the power amplifier 4 is turned OFF, and the current flowing to the LVCM 5 is cut off to prevent the head moving speed from increasing further.

However, in the case of a failure in the actual speed detection circuit 1, for example, when the position error signal is not input normally, the current integration of the VCM 5 only performs the nonlinear part of the position error signal, so a normal actual speed signal 12 is detected. Can not. At this time, the actual speed detection type runaway circuit 6 cannot detect the increase in head movement speed, and the head continues to increase speed and hits the stopper, etc., resulting in damage to the magnetic disk, head, etc. Something happened. Such an access control circuit is described in, for example, Japanese Unexamined Patent Publication No. 57-6470.

[Purpose of the invention]

The object of the present invention is to use a current integral type runaway detection circuit to detect runaway when the head movement mechanism runs out of control and cannot be detected by the conventional actual speed detection type runaway detection circuit, thereby preventing damage to the magnetic disk and head. The object of the present invention is to provide an access control circuit that can

[Summary of the invention]

The present invention focuses on the fact that when the head moving mechanism goes out of control, the speed will be abnormal if current continues to flow in α, and the VCM
The relationship between the current i flowing through the head and the moving speed ■ of the head is v=
By utilizing the fact that "kj" idt (k is the coefficient of the device), by integrating the current flowing through the VCM and monitoring its output, runaway of the head movement mechanism is detected and damage to the magnetic disk and head is detected. The aim is to prevent such collisions.

[Embodiments of the invention]

Embodiments of the present invention will be described in detail below with reference to the drawings.

(ll) Structure of Embodiment A block diagram of an embodiment of the present invention is shown in FIG. 4. The actual speed detection circuit 1 detects the moving speed of the head. The speed command generation circuit 2 Generates movement speed.

Operational amplifier 6 compares the signal from actual speed detection circuit 1 and the signal from speed command generation circuit 2, and outputs the difference. The power amplifier 4 receives the signal from the operational amplifier 6 and outputs V
Apply current to CM5. The actual speed detection type runaway detection circuit 6 looks at the output signal of the actual speed detection circuit 1, and turns off the power amplifier 4 and cuts off the current of the VCM 5 when the output signal exceeds a certain set value, that is, when a runaway state occurs.

The current integral type runaway detection circuit 7 integrates the current flowing through the VCM 5, and when the value exceeds a certain set value, turns off the power amplifier 4, and cuts off the current flowing through the VCM 5.

(2) Operation of the embodiment Upon receiving a head movement command from the host device, access is started. A current 14 is applied to the VCM 5 to accelerate it, but the actual speed signal cannot be detected normally because the actual speed detector 1 is out of order.
3) in the figure, the VCM current 14 does not become zero and continues to accelerate. However, when the current integration type runaway detection circuit 7 integrates the VCM current 14, the current integral waveform 15 shown in FIG. 5 is obtained. When the integral waveform 15 exceeds the set runaway detection level 16 of the device, the power amplifier 4 is turned off.
, cut off the current of VCM5 and suppress further acceleration.

(3) Effects of Example In a disk drive device with a maximum head movement speed of 1.4 m/s, when this circuit with the runaway detection level set to 1.8 m/s is operated, the actual head speed is 1. .9m
/s, the circuit worked and was able to prevent damage to the magnetic disk and head.

〔Effect of the invention〕

As described above, according to the present invention, by directly detecting the current flowing in the VCM and integrating this current, the VC
This has the effect that the actual speed of M can be detected even if the actual speed detection circuit fails.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an access control circuit according to the prior art, and FIG. 2 is a diagram showing a position error signal when the servo head moves in the circuit of FIG. 1. FIG. 3 is a diagram showing the target speed signal, actual speed signal, and seven current waveforms during normal access. FIG. 4 is a block diagram of one embodiment of the access control circuit of the present invention. FIG. 5 is a diagram showing the ■χ current waveform and the integrated waveform of the VCM current at the time of runaway in the circuit of FIG. 4. DESCRIPTION OF SYMBOLS 1... Actual speed detection circuit, 2... Speed command generation circuit, 6... Operational amplifier, 4... Power amplifier, 5... VCM, 6... Actual speed detection type runaway detection circuit, 7...Current integral type runaway detection circuit, 11...Target speed signal, 12...Actual speed signal,
16 and 14... VCM torrent waveform, 15... VCM current integral waveform, 16... Runaway detection level. Figure 1 Figure 20 Third Country'$ 40 The Ginmon Gate of the Evening

Claims (1)

[Claims] A head access control circuit for a magnetic disk drive device comprising a power amplifier that generates a drive current for driving a voice coil motor, and an actual speed detection circuit that detects the actual speed of a head driven by the power amplifier. A head access device comprising: a current integrating type runaway detection circuit that detects the actual speed of the head by integrating the drive current that drives the head, and instructs to stop driving the power amplifier when the actual speed is equal to or higher than a predetermined value. control circuit.