JPH06236504A - Magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To decrease the read errors by the off-track of a magnetic disk device. CONSTITUTION:Data S is written with the off-track delta1 (core center 15) from a track center 16 by a head 4 of a track width (core width) TW. The ratio of a noise to a read out signal S is determined by the read out width TN/signal read out width TS of the noise N and is given by a write blotting quantity W, erase blotting quantity DELTAE and delta=delta1+delta2 as shown in Fig., if there is the noise N by the imperfect erasure of the previous writing signal when reading is executed by the off-track delta. The imperfectly erased noise N is erased by DC erasing while the head is offset to positive and negative and thereafter, rewriting/reading are executed if there are the write or read errors (correctable errors and read retry) of the specified number of times or above to the same track. As a result the noise read out width TN is made zero, the S/N is improved and the error generation rate is lowered.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording / reproducing device such as a magnetic disk device, and more particularly to a magnetic recording / reproducing device capable of reducing the occurrence rate of read errors caused by deterioration of positioning accuracy of a magnetic recording / reproducing head.

[0002]

2. Description of the Related Art Generally, in a magnetic recording / reproducing apparatus such as a magnetic disk apparatus, one of the main causes of a read error of recorded data is off-track due to deterioration of positioning accuracy of a magnetic head.

As a countermeasure against this, conventionally, for example, JP-A-3-
As described in Japanese Patent No. 17874 (Reference 1),
An apparatus for correcting the off-track by gradually increasing the offset amount of the reproducing head alternately to the inner circumference side or the outer circumference side according to the output decrease amount of the read voltage of the data signal due to the off-track, and Japanese Patent Laid-Open No. 3-252912. As described in 2), there is known a device in which the size and shape of the magnetic material for the shield of the MR head is improved in order to reduce the noise caused by the induced electromotive force due to off-track.

[0004]

The main cause of a read / write error caused by off-track is that the S / N ratio is deteriorated by reading the unerased noise of previously written data. This kind of unerased noise is
This occurs because the amount of off-track at each write track position varies once, and increases as the number of writes to the same track increases. However, the above-mentioned Document 1 relates to the off-track correction of the read magnetic head when the read voltage decreases, and the above-mentioned Document 2 relates to the read magnetic head of the structure for shielding the noise magnetic field generated due to the off-track. The prior art in the literature does not consider anything about eliminating the unerased noise itself, which is the root cause of the above read error, and simply treats the generated noise as little as possible in a symptomatic manner. It was only taking measures against other small secondary causes. For this reason, the conventional technique has a problem in that the effect of the noise left unerased cannot be fundamentally removed, and a head having a special structure is required to remove the effect of the noise.

Therefore, an object of the present invention is to solve the above-mentioned problems of the prior art, and to eliminate the unerased data itself and the noise itself, which is the main cause of the error due to the off-track, to reduce the error occurrence rate due to the off-track. Lower,
Another object is to provide a highly reliable magnetic recording / reproducing device.

[0006]

In order to achieve the above-mentioned object, the present invention requires that the same track has been written (written) more than a specified number of times (specified update number of times) or a read (read) error has occurred. Erasure of a previously written signal is provided with means for detecting occurrence, and means for erasing (erasing) with the magnetic head by off-tracking the magnetic head in the positive or negative direction when this detection is made. Then, the remaining part is erased.

Here, when a read error occurs, it means when a correctable error (error that can be corrected by ECC) has occurred or when a read retry has occurred. This read retry is performed when an uncorrectable error (an uncorrectable error) occurs in the first read. At this time, the read conditions such as the slice level and phase of the read signal are variously changed. Read retry is also performed, which may eventually result in no read error or a collectable error.

When (a) the writing is performed more than the specified number of times, (b) the correctable error occurs, or (c) the read retry occurs, the offset erase is performed.

The means for erasing by offsetting is constructed so that the offset erasing is performed in the following order (1) to (4). That is, (1) the corresponding track data is temporarily saved in the cache memory or a spare track in the magnetic recording / reproducing apparatus (magnetic disk apparatus). (2) In the corresponding track, the magnetic head is off-tracked in the inner or outer direction (in the positive or negative direction), and the unerased noise of the previously written data is erased by direct current (DC erase). (3) The data saved in the memory or the like is rewritten to the corresponding track. (4) Reread the relevant track, and if an error occurs, until no error occurs,
The above steps (2) and (3) are repeated. in this case,
At the time of rewriting, the off-track amount can be kept fixed, or the off-track amount can be changed little by little (for example, gradually increased).

It is also possible to automatically erase the noise portion (remaining erased portion) of the track based on the detection when writing is detected more than the specified number of times.

The erasing of the unerased portion can be performed in a waiting state (idle state, waiting state) for a data read or write command.

[0012]

The operation based on the above configuration will be described.

According to the present invention, when the writing is performed a specified number of times or more on the same track, or when a read error occurs (when a collectable error occurs or a read retry occurs), the magnetic head is removed. Since the unerased portion of the previously written signal is erased by offtracking in the positive or negative direction, the noise due to the unerased portion can be reduced to almost zero. As a result, the S / N ratio at the time of reading the signal can be remarkably increased, and the bit error occurrence rate can be suppressed as low as possible.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIGS.
Will be described.

FIG. 2 is a sectional view of a mechanical portion of a magnetic disk device according to an embodiment of the present invention. In FIG. 2, the magnetic disk device forms a magnetic disk chamber by a housing composed of a housing 6 and a base 12. The structure of the magnetic disk chamber will be described below.

The spindle 3 is directly connected to the motor 1, and a plurality of magnetic disks 2 are mounted on the spindle 3 to form a magnetic disk drive section. The magnetic disk drive section is fixed to the housing 6. Has been done.
The plurality of magnetic heads 4 are respectively provided with a plurality of head arms 5.
Is supported by the tip. The head arm 5 is supported by a carriage 7, and the carriage 7 is supported by a ball bearing 8 so that linear movement is possible, and the ball bearing 8 is guided by a rail 9. The rail 9 is fixed to the housing 6. A coil 10 is attached to the other end of the carriage 7, and a magnetic circuit 11 is attached to a base 12 around the coil. Coil 10
The magnetic circuit 11 forms a so-called voice coil motor (hereinafter referred to as VCM), and when a current is applied to the coil 10, thrust is generated in the coil. With the above construction, the magnetic head 4 is allowed to move linearly in the horizontal direction in the radial direction of the magnetic disk, and is positioned by the motor 1 at a desired track of the magnetic disk 2. This positioning operation is performed by servo control. The positioned magnetic head 4 writes information on the magnetic disk 2 and reads information on the magnetic disk 2. In this way, the magnetic disk device functions as an information storage device.

The magnetic disc chamber is connected to the outside air via the breathing filter 13.

The present invention intends to reduce the read / write error occurrence rate due to off-track by DC erasing (erasing direct current) the previously written unerased noise of data in such a magnetic disk device. That is.

FIGS. 3A to 3C show the principle of read error occurrence due to off-track. The track width (core width) is T _W for a track where data is overwritten many times.
A model diagram when data is written in the magnetic head 4 such that the center 15 of the core width shifts from the regular track center 16 to, for example, δ _{1 off} track to the right side is shown in FIG.

When data is written in the track width (core width) T _W , the writing blur amount of the width ΔW and the Δ
An erasing blur amount of the width E occurs. The ΔW portion is a portion that contributes to the reproduction of the signal together with the signal portion S. Width Δ
The remaining portion of E except ΔW is an erase portion having neither signal (data) nor noise. Furthermore, on both the left and right outer sides of the erase portion, there are noise portions N whose boundaries are the remaining unerased old data written with the maximum positive and negative (right and left) offtrack.

Next, FIG. 3B shows a model diagram when δ ₂ offset is set in the same track and data is read by a magnetic head having a core width T _W. FIG. 3B shows a case of off-tracking to the left. The signal read width in this case is T
_{If S} and the noise read width are T _N and δ = δ ₁ + δ ₂ , then T _S = T _W − (δ ₁ + δ ₂ ) + ΔW = T _W −δ + ΔW T _N = (δ ₁ + δ ₂ ) −ΔE = δ −ΔE. Here, the error rate is closely related to T _N / T _S, it is possible to lower the error rate the lower the T _N / T _S.

FIG. 3C shows a model diagram of the present embodiment when data is rewritten by off-tracking in both positive and negative directions (left and right directions) to perform DC erase and rewriting the data in FIG. 3B. . In this case, since T _N = 0, the error occurrence rate can be drastically reduced. In this case, the off-track amount is variously changed in consideration of the relative shaking of the head with respect to the track width direction and the track pitch so that the adjacent track can be erased to the maximum extent without erasing the adjacent track.
For example, when the first off-track / DC erase is insufficient, the second off-track amount is increased to perform the DC erase, and the off-track amount is gradually increased to perform the erase.

FIG. 4 shows the relationship between the off-track amount at the time of reading / writing and the error occurrence rate, which is obtained by simulation. The horizontal axis of FIG. 4 is the off-track amount (μm) and the vertical axis is the bit error occurrence rate (probability). For example, “1E-08” is 1 × 10 (−8) th power, “1E−
“9” represents 1 × 10 to the power of (−9). As can be seen from this figure, the method of the present invention for DC erasing noise can significantly reduce the error occurrence rate.
It can be seen that this effect becomes more remarkable as the off-track becomes larger.

FIG. 1 shows a flow chart of an embodiment of an erase method using the magnetic disk device of the present invention.

First, the power source of the apparatus is turned on (step 10).
1) Initialization is performed (step 102). Next, a read operation or a write operation is performed for each track, and the read number and write number for each track are stored (step 103). Therefore, it has a counter for recording the number of writes for each track and a counter for recording the number of retries of the currently read track. In the figure, I (T _K ) is the number of writes, k (= 0, 1,
... n) is the track number, N is the total number of tracks, J is the number of reads, W is the specified number of writes, and R is the specified number of reads.

This apparatus has the following three conditions (a)-
If any of (c) is satisfied, the DC of the corresponding track
Erase. (A) Write count for each track (data update count)
When the number of the counter recording I (h) is equal to or larger than the preset value N (steps 104 to 106). (B) When a correctable error (error that can be corrected by ECC, etc.) occurs (step 114). That is, the read operation for a certain track is repeated R times a predetermined number of times while sequentially changing the offset amount (steps 115 and 116), during which a correctable error occurs. When the correction by the ECC is impossible even after the reading is repeated a predetermined number of times, the read / write is stopped as an uncorrectable error (step 117). (C) When a readable read retry finally occurs (step 113 or the like). That is, when the read operation for a certain track is correctly performed once (steps 112 and 113),
The process proceeds to the next track (103), but when an uncorrectable error occurs, read retry is performed many times. In this case, when various read conditions such as the slice level and phase of the read signal are changed, the data may be finally read (no read error or correctable error).

DC erase of noise is performed by the following (1)-
The process is performed in the order of (4) (steps 107 to 110). (1) The corresponding track data is temporarily saved in a memory such as a cache (step 107). (2) At the corresponding track, the head is off-tracked in both positive and negative directions, and the unerased noise of the previously written data is DC erased (step 108). (3) The data saved in the memory is rewritten to the corresponding track (step 109). (4) Re-read the corresponding track, and if an error occurs, repeat (2) and (3). In this case, the off-track amount is changed little by little at the time of rewriting (step 110). (5) In the DC erase, if the idle state (standby state) in which the read / write command is not issued is aimed at, the performance such as the processing speed of the device is not deteriorated and the efficiency is good.

The amount of off-track during DC erase is
It is desirable to make it as large as possible without deleting adjacent data.

According to the above embodiment, as shown in FIG. 4, the off-track 1 μm has a relatively inexpensive and simple structure.
The error occurrence rate can be reduced to 4 digits (10 −4) and 2 μm to 9 digits (10 −9), and practically the error occurrence due to off-track can be made almost zero.

[0030]

As described in detail above, according to the magnetic recording / reproducing apparatus of the present invention, when the same recording track is written a specified number of times or more, a correctable error occurs or a read operation is performed. When the retry occurs, the magnetic head is off-tracked in the positive or negative direction to erase the unerased portion of the previously written signal, so without using special expensive equipment like the conventional one, With a simple structure, the unerased portion that is the cause of noise is removed from the root, and even if there is off-track when reading a signal, the S / N at this reading is improved,
The effect that the bit error occurrence rate can be reduced as much as possible is obtained.

[Brief description of drawings]

FIG. 1 is a flowchart showing a procedure of an erasing method according to an embodiment of a magnetic recording / reproducing apparatus of the present invention.

FIG. 2 is a sectional view of a magnetic disk device according to an embodiment of the present invention.

FIG. 3 is a diagram for explaining the principle of error occurrence due to off-track.

FIG. 4 is a diagram showing a relationship between off-track and an error occurrence rate.

[Explanation of symbols]

 1 Motor 2 Magnetic Disk 3 Spindle 4 Magnetic Head 5 Head Arm 6 Housing 7 Carriage 8 Ball Bearing 9 Rail 10 Coil 11 Magnetic Circuit 12 Base 13 Absorption Filter

Claims (1)

[Claims] 1. A means for detecting that writing has been performed a specified number of times or more on the same track, or a read error has occurred, and when this is detected, the magnetic head is off-tracked in the positive or negative direction. A magnetic recording / reproducing apparatus comprising means for erasing with a magnetic head, and erasing the previously written signal and erasing the remaining portion.