JP2835763B2 - Magnetic disk drive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] A magnetic disk drive capable of high-precision positioning is intended to correct an error of a servo signal, and a servo unit of a minimum unit in a circumferential direction of the servo signal. One or both of the front and rear regions are provided with a magnetic disk in which error information indicating the error of the servo signal is written so that it can be read during on-track.

[Industrial applications]

The present invention relates to a magnetic disk drive that enables highly accurate positioning.

The magnetic disk drive is required to be reduced in size and increased in capacity, and the recording density is increased accordingly, so that the track density is also increased. For such a high-density track, it is necessary to accurately position the magnetic head with respect to the target track, and there is a demand for an improvement in the positioning accuracy by a high-quality servo signal.

[Conventional technology]

In order to position the magnetic head on the target track of the magnetic disk, a servo signal is written on the magnetic disk in advance, and the servo signal is written on the entire recording surface of the magnetic disk. And a sector servo method in which a servo signal is written for each sector of the magnetic disk.

When positioning the magnetic head on the target track of the magnetic disk, for example, by a control unit such as a microprocessor, an actuator such as a voice coil motor is controlled according to the difference between the current track position and the target track position of the magnetic head, The magnetic head is moved toward the target track, and by counting the track cross pulses obtained from the servo signal read by the magnetic head, the number of tracks and the position signal of the difference between the current track position and the target track position are used. When it is determined that the magnetic head has moved to the target track position, the magnetic head is positioned at the center of the target track by the position signal obtained from the servo signal. Then, data writing or data reading is performed.

[Problems to be solved by the invention]

In a conventional magnetic disk drive, positioning control is performed using a servo signal read by a magnetic head. This servo signal also includes an error component during formation (writing). In the case of high-density tracks, positioning errors cannot be ignored.

Writing of the servo signal to the magnetic disk is performed by measuring the position of the magnetic head using a laser distance measuring device or the like and positioning the magnetic head at a predetermined position on the magnetic disk because there is no information indicating the track position. Things. In this case, the track on which the servo signal has been written is deviated from the ideal state due to the influence of vibration due to the rotation of the magnetic disk or the like.

For example, when a part of the track is linearly developed and exaggerated, as shown in FIG. 6, the actual track center 62 is in the radial direction due to the rotational vibration of the magnetic disk or the like, as shown in FIG. Will fluctuate. Reference numeral 60 denotes an example of a servo signal magnetic head.

When the radial variation of the actual track center 62 with respect to the ideal track center 61 increases, as shown in FIG.
Part of the track area overlaps as indicated by 71, and the error increases. Generally, the fluctuation of the actual track center 62 due to the rotational vibration of the magnetic disk is similar to each track along the circumference. That is, as shown in FIG. 8, the track area fluctuates in parallel with respect to the ideal track center 61.

As described above, even when a high-precision servo signal writing device is used, the magnetic field is not affected by the vibration of the bearing of the spindle to which the magnetic disk is fixed or the vibration of the mirror of the laser distance measuring device for positioning the magnetic head. The track due to the servo signal written on the disk fluctuates with respect to the ideal track center 61. Therefore, when the servo signal is read to control the positioning of the magnetic head, the positioning error for the high-density track becomes large. was there.

An object of the present invention is to correct an error of a servo signal.

[Means for solving the problem]

The magnetic disk drive of the present invention writes error information of a servo signal together with a servo signal on a magnetic disk, and will be described with reference to FIG.

The error information 2 indicating the error of the servo signal 1 is written in one or both areas before and after the servo frame of the minimum unit in the circumferential direction of the servo signal 1 so as to be able to be read during on-track. The magnetic disk 3 includes a spindle motor 6.
And the magnetic head 4 is positioned at the target track by an actuator 5 such as a voice coil motor.

In the case of the servo surface servo system, the servo signal 1 and the error information 2 thereof are written alternately. In the case of the sector servo system, the servo signal 1 and the error information 2 are written in the servo area. Will be.

[Action]

When writing data to or reading data from the magnetic disk 3, the servo signal 1 is read to position the magnetic head 4 on the target track, but the error information 2 of the servo signal 1 is read. Thus, the error can be corrected corresponding to the servo frame.

Therefore, for the magnetic disk 3 having a high density track,
The magnetic head 4 can be accurately positioned.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 2 is a block diagram of an embodiment of the present invention, in which 11 is a single or plural magnetic disks rotated by a spindle motor 23, 12 ₁ and 12 ₂ are magnetic heads, 13 is a voice coil motor and the like. Actuators, 14-15 are amplifiers,
16 is a signal writing circuit, 17 is a demodulation circuit, 18 is an AD converter (A /
D), 19 is a servo signal writing control unit, 20 is a DA converter (D /
A) and 21 are a read / write control circuit, 22 is a motor control circuit, and 24 is a main control unit composed of a microprocessor or the like.

A signal writing circuit 16 and a servo signal writing control unit 19 are shown as an explanatory configuration for writing a servo signal and error information on the magnetic disk 11, but are omitted in a general magnetic disk device. The laser distance measuring device or the like for controlling the positioning of the magnetic head 12 ₁ when writing servo signals and the error information is omitted.

The spindle motor 23 is controlled by the motor control circuit 22 to rotate the magnetic disk 11 at a constant rotational speed, for example, 3600.
When the servo signal and the error information are already written on the magnetic disk 11 as shown in FIG. ₁ , the servo signal and the error information are read out by the magnetic head 121 and the amplifier is rotated. The signal is amplified by 15 and applied to the demodulation circuit 17, and the demodulated servo signal is converted into a digital signal by the AD converter 18 and applied to the main control unit 24.

When the magnetic head 12 ₂ reads the write or data of the data, the target track to the main control unit 24 is supplied, the main controller 24, the current track position and the target track position of the magnetic head 12 _1, 12 ₂ The target speed is set on the basis of the difference between the drive signals and the magnetic heads 12 ₁ and 12 ₂ are applied to the drive signal DA converter 20 so as to reach the target speed, and the converted analog signal is amplified by the amplifier 14 so that the drive current And the magnetic heads 12 ₁ and 12 ₂ are supplied to the actuator 13 and moved toward the target track. Then, a track cross pulse is formed based on the demodulated servo signal, and the track cross pulse is counted. When the difference between the current track position and the target track position of the magnetic head becomes zero or less than a predetermined value, the demodulated servo signal is generated. The position signal is corrected based on the error information.

Therefore, the magnetic heads 12 ₁ , 12
₂ to position the, via the read write control circuit 21, read write or data of the data by the magnetic head 12 ₂ is performed.

For example, as shown in FIG. 3, when the minimum unit in the circumferential direction of the servo signal is a servo frame A, the error information B corresponding to the servo frame A is converted into the on-track state as shown in FIG. Is written so that it can be read by the magnetic head 12. Magnetic head 12
Has a width wider than the track width in the case of a servo head that reads a servo signal of a servo method on a servo surface, but has a width smaller than the track width as shown in the case of a data head that reads data. Things.

In the servo surface servo method, a set of a servo frame A and error information B is formed along the circumferential direction as AB, AB,.
・ ・ Or written like BA, BA, ... In the case of the sector servo method, a data area and a servo area of the servo frame A and the error information B are formed for each sector.

Further, as shown in FIG. 4, it is also possible to record the error information separately for the mating of the data track. For example, error information B _n , B _{n + 1} , B _{n + 2} ,... Indicating the error of the servo signal with respect to the data tracks C _n , C _{n + 1} , C _{n + 2} ,. Are written so that they can be sufficiently read even when they are off the center of the data tracks C _n , C _{n + 1} , C _{n + 2} ,. This shows a case where error information corresponding to a track is written and error information corresponding to an even track is written in a subsequent area. In the servo surface servo method, a head having a core width larger than a track width, which is generally called a double core width, is used. Therefore, the area of the error information B may be formed to be four times the data track width in some cases. Incidentally, in the case of the servo surface servo system, the servo frame A, the odd track error information and the even track error information are repeatedly written, and in the case of the sector servo system, the track C of the data area is formed as shown in the figure. Will be.

Further, as shown in FIG. 5, error information can be written in the area before and after the servo frame A. That is, the error information corresponding to the odd-numbered track is provided in the area before the servo frame A.
_Bn , _{Bn + 2} ,... Can be written, and error information _{Bn + 1} , _{Bn + 3} ,. Also in this case, in the case of the servo surface servo system, the odd track error information, the servo frame A and the even track error information are repeatedly written, and in the case of the sector servo system, the track C in the data area is Will be formed.

The above-described writing of the servo signal and error information is performed, for example, by
This is performed as follows.

(A) A servo signal is written by a servo signal writing device. In the case of the servo surface servo method, an area in which the error information B is to be written is written in a servo frame A, or the error information B can be overwritten. Therefore, a servo signal can be written to the entire surface. In the case of the sector servo method, a servo signal is written in a servo area for each sector.

(B) Next, a servo pattern for reproducing the reference track line is written in a region that does not interfere with the servo signal previously written by a predetermined magnetic head that can be fixed to the surface plate of the servo signal writing device. Playback of this reference track line
This is performed by a dedicated circuit. In the case of the sector servo method, it is conceivable that an area for writing a servo pattern for a reference track line cannot be obtained. Reading may be performed by a head. Although the servo pattern for the reference track line can be written on the data surface of the magnetic disk, it is preferable to write it on the same surface as the magnetic disk surface for which error information is to be obtained.

(C) Next, a servo pattern for a reference track line is reproduced by the predetermined magnetic head and filtered to obtain a reference track line. In this case, the filtering process is performed to obtain a smooth track line that does not include a component equivalent to noise because the error factor is included even by the predetermined magnetic head.
This filtering includes averaging and low-pass filtering.

(D) Next, the value of the reference track line is stored corresponding to the servo frame.

(E) Next, the device head (the magnetic head 12 as a magnetic disk device) and the value of the track line of the predetermined magnetic head are read at the same timing corresponding to the servo frame, and the reference in (d) is read. Error information is obtained from the value of the track line.

The error Rx from the track line at the time of on-track is obtained by the following equation: Rx = (Rd−Rc) − (Rb−Ra) (1) Note that Ra is the disk radius of the reference track line, Rb is the disk radius of the predetermined magnetic head and the track line at that time, Rc is the disk radius of the ideal track line of the servo frame, and Rd is the disk radius of the current track line of the servo frame. Radius.

(Rd-Rc) is obtained from the servo signal read by the device head, and (Rb-Ra) is a correction term considering that the reference track line at the time of measurement is affected by vibration. is there.

(F) Next, the error information is written as digital information in an adjacent area of the corresponding servo frame. This error information is
The error information is written in the on-track state, and the error information can be written using the area before or after the servo frame or both the front and rear areas.

By the above-described processing, the servo signal and the error information are written on the magnetic disk 11. When the servo signal and the error information are read out and the positioning control of the magnetic head is performed, the servo signal and the error information must be read in advance in FIG. Since the servo frame A and the error information B are written in the pattern shown in FIG. 4 or FIG. 5, for example, in the case shown in FIG. Servo frame A
Error information read from the area after
In the case shown in FIG. 5, the error information read from the area before the servo frame A is used. Then, the deviation amount ΔR from the reference track line is obtained as follows.

ΔR = Rs−K · Rx (2) where Rs is a shift amount between a track line obtained from a servo frame and an ideal track line, and K is a correction amount of a gain between Rs and Rx. In this case, the error Rx is previously set to (−
Rx), equation (2) can be expressed as follows: ΔR = Rs + K · Rx (3)

In a digital servo system, since K · Rx is a digital value, Rs can be AD-converted to easily determine the deviation ΔR. In the analog servo system, Rx
Is converted to DA, and the gain K is corrected and Rs
By performing an analog calculation on the shift amount ΔR, the shift amount ΔR can be obtained.

〔The invention's effect〕

As described above, according to the present invention, the error information 2 indicating the error of the servo signal 1 is written in the area before, after, or both before and after the servo frame of the minimum unit in the circumferential direction of the servo signal 1. Since the magnetic disk 3 is provided, the error information 2 is read by the magnetic head 4 during on-track, so that the error of the servo signal 1 can be corrected and the magnetic head 4 can be accurately positioned on the target track. .

Accordingly, high-precision position information can be obtained even for the magnetic disk 3 having a high-density track, and there is an advantage that data reliability can be improved by accurate positioning.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining the principle of the present invention, FIG. 2 is a block diagram of an embodiment of the present invention, FIGS. 3, 4, and 5 are explanatory diagrams of servo signals and error information, and FIG. FIG. 7 is an explanatory view of the variation of the track center, FIG. 7 is an explanatory view of the overlap area, and FIG. 8 is an explanatory view of the parallel track. 1 is a servo signal, 2 is error information, 3 is a magnetic disk, 4
Denotes a magnetic head, 5 denotes an actuator, and 6 denotes a spindle motor.

Claims (1)

(57) [Claims] An error information (2) indicating an error of the servo signal (1) is provided in one or both areas before and after a minimum unit servo frame in a circumferential direction of the servo signal (1). A magnetic disk drive comprising a magnetic disk (3) written so as to be readable during on-track.