JPH08102155A - Offset format for magnetic disk device - Google Patents

Abstract

PURPOSE: To shorten the head changeover time by unnecessitating a head moving operation which used to happen due to off-track of a head at the time of changing heads. CONSTITUTION: The device is composed of a demodulation circuit part 4 for demodulating servo information and generating a position signal and a drive control microcmputer 5 for calculating an off-track amt. from the position signal and sending the off-track amt. as data to a data circuit part 6 and also giving an offset to a VCM control circuit part 8. By this constitution, a head at the changeover destination is not required to move from its present following position. Thus, since the head changeover time can be shortened, drastical shortening of this time can be expected for file transfer processing, etc., where the head changeover is frequently performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic disk device having servo information on its data surface, and more particularly to a technique effective in reducing access time when switching heads.

[0002]

2. Description of the Related Art Generally, in a magnetic disk device, servo information for positioning is written on the surface of a recording medium, a relative position error between a head and a track is detected based on this information, and feedback is applied. Servo control is performed. Servo information is usually a servo track writer (equipment)
Written by

The position of the head when writing servo information,
After the device is assembled, the position of the head is displaced. Possible causes include the base distortion of the HDA (head disk assembly) when it is fixed to the servo track writer, the deformation of the head bar when the servo track writer control component is attached, etc., and the positional deviation may be several μm. .

When there is a positional deviation between the written servo information and the head, the servo control works so as to move the head to the position where the servo information is written, so that the head moving operation occurs each time the head is switched. , It takes time to finish switching heads.

Conventionally, the head switching time has been shortened by devising how to read or write data depending on how close the head is to the following center point after head switching. In addition, a technique of performing a skew at the time of formatting according to the head switching time has been studied.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to eliminate the head moving operation that occurs when the head is switched, and to shorten the head switching time.

[0007]

In order to achieve the above object, the initial off-track amount is measured in advance for each head and recorded as the initial off-track value.

When the head is switched, servo control is performed using the head off-track value of the switching destination as an offset value.

[0009]

In a recent magnetic disk device, a management area is provided on the data side, and a program for operating the device and parameters peculiar to the device are written. When the device is started, the information in the management area is read. After copying to RAM and starting up, the device is moved by the information in RAM. Further, on the data surface, an ID field, a data field and the like are written to enable reading and writing, and formatting (also called initialization or initialization) for forming a track format is performed.

In the present invention, the initial off-track amount of each head is measured and written as the initial off-track value for each head in the management area of the data surface.

When performing the formatting, since the initial off-track value is given to the control system as an offset when the head is switched, the head does not need to move from the current position,
Head switching can be done in a short time.

[0012]

Embodiment This embodiment will be described below with reference to FIG.

The HDA 1 is mounted on a servo track writer before being assembled as a device, and servo information is written on the disk 2 in the HDA 1. The servo information written on the disk 2 is read by the head 3 and is demodulated by the demodulation circuit 4
To form a position signal. The drive control microcomputer 5 calculates the off-track value from the position signal and writes the value on the disk 2 through the head 3 by the data write circuit 6. Similarly, the off-track value is measured for a plurality of heads and written on the disk 2. (The best place to write is in the management area of the disk 2, but there is no problem in other places. The reference value when calculating the off-track value is based on the measured value of a specific head (any) The drive control microcomputer 5, which has received the formatting command from the HOST 7, sends the off-track value of the head of the switching destination as an offset to the VCM control circuit 8 in addition to other transfer data when the head is switched, and the head 3 Format while offsetting.

FIG. 2 shows a position signal response when the head is switched. The change in command comp is the head switching time. When the head A and the head B are misaligned, when the head A is switched to the head B, the servo control system controls the head B to follow the center of the servo information. Since the read / write permission is determined to be within a certain value from the center, it takes T _{1 to} switch the head.

FIG. 3 shows the response of the position signal when the present invention is applied.

Since the position does not move before and after the head is switched, the head is switched only by the overhead time of the command and the time of T ₂ is shorter than T ₁ .

When the offset is used for the formatting as described above, since the head does not move when the head is switched, the switching time becomes short and the access time is reduced.

[0018]

According to the present invention, the head at the head switching destination does not have to move from the present following position, and the time required for head movement becomes zero.

Before the present invention, the head switching time was about 1.5 ms for a head having an off-track of about 3 μm, but after the implementation, it was 0.7 ms or less, and the switching time was greatly shortened. As a result, the access time is reduced, and in particular, the head switching is frequently performed, formatting, file transfer processing, file inspection processing, etc. are greatly shortened and performance is improved.

[Brief description of drawings]

FIG. 1 is a control circuit block diagram.

FIG. 2 is a position response at the time of switching heads before implementing the present invention.

FIG. 3 is a position response at the time of switching heads after implementing the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... HDA (head disk assembly), 2 ... Disk, 3 ... Head, 4 ... Position demodulation circuit, 5 ... Drive control microcomputer, 6 ... Data write circuit, 7 ... HOST, 8 ... VCM control circuit.

Claims (2)

[Claims] 1. A plurality of recording media and a plurality of heads for recording and reproducing are mounted on the surfaces of the recording media, and positioning is performed based on servo information written on the surfaces of each recording medium. In a servo-type magnetic disk device, an offset format method that enables faster head switching by performing formatting while considering the initial off-track of the head when formatting the data surface. 2. A magnetic disk drive according to claim 1, wherein the initial off-track of the head is measured in advance and written on the surface of the recording medium.