JPH02177182A - Magnetic disk device - Google Patents

Abstract

PURPOSE:To detect the run-away of a magnetic head between plural cylinders by detecting it in comparing a delayed digital difference signal with an undelayed digital difference signal. CONSTITUTION:A digital difference signal generating circuit 1 is the circuit for making an absolute value of a difference between target cylinder and present cylinder position signals (a) and (b), and a delay circuit 2 is for delaying a digital difference signal (c) and outputting it as the delayed digital difference signal (d), which is the outputted to a comparison circuit 3, where a run-away detecting signal (d) is sent out by the comparison circuit 3. That is, at the time of the run-away, since the absolute value of the difference between the present cylinder and target cylinder position signals becomes larger in course of time from the time when the present cylinder goes over the target cylinder, the value of the digital difference signal (c) becomes larger than the delayed digital difference signal (d) so that the run-away is detected out. By this method, the run-away can be detected in a position moved by a few cylinders from the target cylinder.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a magnetic disk drive, and more particularly to a magnetic disk drive having a servo circuit that performs a positioning seek operation using a position signal read from a servo surface.

[Prior Art] Conventionally, this type of magnetic disk drive operates a counter using a track crossing pulse signal generated from a position signal read from a servo surface as a clock, and calculates the distance Il! between the target cylinder and the current cylinder. (remaining seek length) was detected in real time and the seek operation was performed.

[Problem to be solved by the invention]

In the above-mentioned conventional magnetic disk drive, if the servo circuit breaks down or malfunctions during seek, the magnetic head starts running out of control as soon as it crosses the target cylinder, and the farther it is from the target cylinder, the faster the seek speed becomes and the inner stopper Otherwise, it may collide with the outer stopper, damaging the magnetic medium or causing a head crash.Also, if the servo pattern is erased during seek, it may not be able to stop at the target cylinder and may run out of control. be.

(Means for Solving the Problems) A magnetic disk drive of the present invention includes a digital difference signal generating means for obtaining a digital difference signal indicating the distance between a target cylinder and a current cylinder, and all or part of the difference signal of the digital difference signals. a delay means for delaying the digital difference signal; a digital comparison means for comparing the delayed digital difference signal and the undelayed digital difference signal; and when the absolute value of the undelayed digital difference signal is greater than the absolute value of the delayed digital difference signal It has means for determining a runaway state.

[For production]

In a normal seek, the value of the undelayed digital difference signal will never be greater than the delayed digital difference signal because the current cylinder never exceeds the target cylinder.

However, during runaway, the absolute value of the difference in distance between the current cylinder and the target cylinder increases as time passes from the point at which the current cylinder exceeds the target cylinder, so the value of the undelayed digital difference signal changes to the delayed digital difference signal. It becomes larger than the difference signal, and runaway of the magnetic head is detected.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of essential parts of an embodiment of a magnetic disk device of the present invention.

The target cylinder position signal a is normally input manually through an interface, and is input to the digital difference signal generation circuit 1. The current cylinder position signal is the output of an up/down counter (not shown) and is input to the digital difference signal generating circuit 1 together with the target cylinder position signal a. The digital difference signal generation circuit 1 is a circuit that generates the absolute value of the difference between the position signals a and b between the target cylinder and the current cylinder. Digital difference signal C which is the output signal of digital difference signal generation circuit l
is a signal whose value decreases as the current cylinder approaches the target cylinder, is 0 on the target cylinder, and increases in value from the point at which it exceeds the target cylinder, and is inputted to the comparator circuit 3 and the delay circuit 2. 8 extension circuit 2 is a digital difference signal C
is delayed and output as a delayed digital difference signal d. The delayed digital difference signal d is output to the comparison circuit 3. Comparison circuit 3 is a magnitude comparator,
The digital difference signal C and the delayed digital difference signal d are compared, and when the digital difference signal C becomes larger than the delayed digital difference signal d, a runaway detection signal d is sent out.

In normal seek, the current cylinder does not exceed the target cylinder, so the value of the digital difference signal C does not become larger than the delayed digital difference signal d. Therefore, the runaway detection signal d is not sent during normal seek. During runaway, the absolute value of the difference between the position signals of the current cylinder and the target cylinder increases as time passes from the time when the current cylinder exceeds the target cylinder, so the value of the digital difference signal C becomes a delayed digital difference signal. d, and runaway is detected.

With this detection signal, it is possible to cut off the power amplifier's power or stop the seek with firmware to prevent it from colliding with the inner stopper or actor stopper.

In this example, everything is made up of hardware, but
It is also possible to replace it with microprocessor means. Instead of the digital difference signal generation circuit 1, a microprocessor can be used to calculate the difference between the signals a and b. Further, the delay means and the comparison means can be implemented by reading the difference signal twice with a microprocessor, comparing the values, and determining a runaway when the value read later is larger. Further, the delay circuit 2 may delay only the lower bits of the digital difference signal C.

(Effects of the Invention) As explained above, the present invention compares the delayed digital difference signal and the undelayed digital difference signal between the target cylinder position signal and the current cylinder position signal, and calculates the number of cylinders from the point where the runaway starts. By detecting runaway of the magnetic head during seek, the magnetic head may be too fast to seek and pass the target cylinder, or may not be able to stop at the target cylinder due to an external shock and run out of control, or the servo may be damaged during seek. There is an effect that when the pattern is erased and the cylinder cannot stop at the target cylinder position and the cylinder runs out of control, the runaway can be detected at a position several cylinders away from the target cylinder.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of essential parts of an embodiment of a magnetic disk device of the present invention. 1......Digital difference signal generation circuit. 2...Delay circuit. 3...Comparison circuit, a...Target cylinder position signal, b-...
...Current cylinder position signal. e-...Digital difference signal, d-...
・・・Delayed digital difference signal, e −・・・・・−
・Runaway detection signal. Patent applicant: Ibaraki NEC Co., Ltd.

Claims (1)

[Claims] 1. Digital difference signal generating means for obtaining a digital difference signal indicating the distance between the target cylinder and the current cylinder in a magnetic disk drive having a servo circuit that positions the magnetic head and performs seek operations using position signals read from the servo surface. a delay means for delaying all or part of the digital difference signal; and a digital comparison means for comparing the delayed digital difference signal and the non-delayed digital difference signal.
A magnetic disk drive comprising means for determining a runaway state of a magnetic head when the absolute value of an undelayed digital difference signal is greater than the absolute value of a delayed digital difference signal.