JP2830850B2 - Protection method for off-track in magnetic disk device and magnetic disk device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protection method for off-track in a magnetic disk drive and a magnetic disk drive.

[0002]

2. Description of the Related Art In a servo system of a magnetic disk drive, a servo surface servo system in which only one of a plurality of disk surfaces is used exclusively for servo information, and a direction crossing a data recording track on each disk surface (in a radial direction of the disk). ), There is a sector servo system in which about 30 to 100 wedge-shaped areas (servo sectors) in which servo information is recorded are provided at regular intervals at one time.

In recent years, the track density has been increased, and in a servo surface servo which performs positioning based on the position information of a servo head on a dedicated servo surface, a mechanical off track due to a temperature difference and a dimensional distortion between the servo head and the data head cannot be ignored. Since off-tracking occurs, position information of the head itself used for reading and writing can be obtained, and sector servos that do not cause off-tracking as described above are mainly used.

In order to realize a higher recording density of a magnetic disk drive, a head in which a thin film head for writing and a magnetoresistive head (hereinafter referred to as MR head) having high reading sensitivity are combined instead of a thin film head for both reading and writing. Has begun to be used. However, in MR heads, a phenomenon called Barkhausen noise may occur due to magnetic distortion due to instability of magnetic domains of the magnetic material of the head. Due to this phenomenon, the degree of vertical asymmetry of the read waveform of the MR head changes, the off-track profile (off-track amount vs. output amplitude characteristic) of the MR head suddenly changes, and the error in the position information of the sector servo increases. There is a problem that accurate positioning cannot be performed. FIG. 2 shows an example of a change in the off-track profile.
(B) is an example at the time of abnormality. Conventionally, as a measure against Barkhausen noise, a defect is selected as a defect at the stage of a single head inspection.

[0005]

The above-mentioned prior art has the following problems.

[0006] It is difficult to select the head by the unit inspection, and there is a case where the inspection is omitted. If the phenomenon of Barkhausen noise occurs while using such a head, there remains a problem that data is written at an off-track position. This is because even if the off-track is detected immediately after the head characteristics suddenly change and write protection (write protection) can be performed, if the head characteristics do not return to the original position, erroneous position information having an error after the characteristics change will be lost. This is because positioning is performed reliably, and even if the track is off-track from the original position, it appears that the positioning is correct.

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, an object of the present invention is to provide a method of protecting a magnetic disk device against off-track and a magnetic disk device.

[0008]

According to the present invention, there is provided a method for protecting against off-track in a magnetic disk drive, comprising the steps of: providing position information for head positioning servo read by a magnetoresistive head; A step of detecting the position taken out from the read / write circuit means, a step of detecting that the mechanical shock has exceeded an allowable value using a shock sensor, and a step of monitoring the output from the position detection means to detect the center of the track and the center of the head. If the off-track is detected as a misalignment, and if the off-track is detected and no mechanical shock is detected at that time, it is determined that the positional information is disturbed due to fluctuations in the magnetic characteristics of the magnetoresistive head, and the magnetoresistive effect is determined. Activating means for restoring the magnetic properties of the mold head to a normal state.

A magnetic disk drive according to the present invention comprises a composite head of a write thin film head and a read magnetoresistive head, an actuator for driving the composite head and a head support mechanism for moving the composite head. A magnetic disk drive having an actuator driving means for driving an actuator and a read / write circuit means for performing a read / write operation of a composite head, wherein a read / write circuit reads head position servo position information read by a magnetoresistive head. Position detecting means to be taken out from the means, a shock sensor for detecting external vibration shock, mechanical shock detecting means for detecting that the mechanical shock exceeds an allowable value using the shock sensor, and an output from the position detecting means To detect the off-track, which is the misalignment between the center of the track and the center of the head. If a mechanical shock is not detected at that time, it is determined that the positional information is disturbed due to a change in the magnetic characteristics of the magnetoresistive head, and a means for returning the magnetic characteristics of the magnetoresistive head to a normal state is provided. Microprocessor means for activating.

In order to perform an operation of recovering from the Barkhausen noise state by using a shock sensor to determine whether the cause of off-track is an external vibration or a suspicion of Barkhausen noise and to recover from the Barkhausen noise state. It is possible to prevent an accident in which data is written at a position off-track due to Hausen noise.

[0011]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of a magnetic disk drive according to an embodiment of the present invention, and the configuration will be described based on the block diagram.

The disk 2 attached to the spindle motor 1 rotates, and data is read and written on the disk surface by the magnetic head 3. The magnetic head 3 is a composite head of a write thin film head and a read MR head. The magnetic head 3 is attached to a head support mechanism (hereinafter, referred to as a carriage) 4 and is movable in and out on the disk surface. The magnetic head 3 and the carriage 4 are driven by an actuator 5. The magnetic head 3 is connected to read / write circuit means (hereinafter, referred to as R / W circuit means) 11, and a read / write (read / write) operation is performed by this circuit. The position information of the sector servo is extracted from the R / W circuit unit 11 by the position detection unit 12. Based on this position information, the microprocessor means 10 performs calculations necessary for positioning control, and controls the actuator driving means 13 to cause the position of the magnetic head 3 to follow the data track.

A shock sensor (mechanical shock detector) 6 is provided to detect whether or not there is an external vibration and shock. Changes, and the flip-flop 9 is set. The output of the flip-flop 9 inhibits the write operation (write operation) of the R / W circuit means 11. Further, the microprocessor means 10 monitors the output of the position detection means 12 to determine whether or not the track has been off-tracked. If it is determined that the track is off-track, the write operation of the R / W circuit means 11 is prohibited.

Next, the operation of the magnetic disk drive according to the embodiment of the present invention will be described.

If, during data writing, Barkhausen noise is suddenly generated in the magnetic head due to the influence of the magnetic field due to the write operation and an output fluctuation such as off-track appears, the position is detected by the position detecting means 12 at regular time intervals. . If the microprocessor means 10 determines that the track is off-track based on the output of the position detection means 12, the cause is not limited to Barkhausen noise, but may be external vibration and impact. The microprocessor means 10 checks the output of the flip-flop 9 and discriminates whether off-track has occurred due to external vibration and shock or whether or not off-track has occurred with a small vibration and shock. It is determined that there is a possibility of the recovery, and the recovery operation is performed.
Microprocessor means 1
After recognizing that the flip-flop 9 is set, 0 shifts to an operation of retrying the interrupted write operation. At that time, the flip-flop 9 is reset, and it is confirmed that the vibration and the impact have been settled. The write protection operation by the shock sensor against the vibration impact is described in, for example, Japanese Patent Application Laid-Open No. Hei 6-187718.

Note that write protection is not performed except at the time of writing, but it is necessary to check off-track and external vibration / shock in the sense of Barkhausen noise in the same way as during writing. For example, if Barkhausen noise occurs immediately after writing, rewriting is not necessary because the writing has been completed normally, but it is necessary to recover from the Barkhausen noise generation state. Check.

When suddenly off-tracking during positioning,
It is not possible to distinguish whether the off-track is caused by external vibration or shock or by head characteristics abnormality such as Barkhausen noise. Therefore, the shock on the base of the magnetic disk drive or the printed circuit board cannot be recognized. If the sensor is installed and the output of the shock sensor exceeds the shock detection level (± Vref7) which is a preset threshold level when off-track occurs, it is judged that the shock has occurred due to external vibration shock A simple retry is performed.If the output of the shock sensor does not exceed the threshold level, it is considered that Barkhausen noise has occurred during positioning, and the head is returned to normal. In the write-off area provided outside the area (for example, the innermost position), It is the door operation, since by reducing the magnetic distortion by passing a write current to the head, so that moves to the normal retry operation. At this time, whether or not the head has recovered to a normal state can be determined by, for example, performing a read margin measurement for off-track by a self-diagnosis function.

The recovery process of the magnetic head takes time,
Since the overhead until the retry ends increases,
By using the present invention, it is possible to omit a head recovery process that is not required in off-track due to a normal mechanical impact, and it is possible to reduce retry.

[0019]

As described above, the first effect of the present invention is that the two factors of off-track, Barkhausen noise and mechanical shock, can be distinguished. Since the off-track due to Barkhausen noise is identified and the abnormal state is recovered, it is possible to prevent an accident of writing data at the off-track position due to Barkhausen noise.

The second effect is that, since the factors can be distinguished, the recovery process for Barkhausen noise can be omitted in the case of vibration and impact, so that the retry time can be shortened.

[Brief description of the drawings]

FIG. 1 is a block diagram of a magnetic disk drive of the present invention.

FIG. 2 is a diagram showing the influence of Barkhausen noise on off-track profile characteristics of an MR head. (A) Indicates a normal state. (B) Indicates an abnormal time.

[Explanation of symbols]

 1 spindle motor 2 disk 3 magnetic head 4 head support mechanism (carriage) 5 actuator 6 shock sensor 7 impact detection level 8 comparator 9 flip-flop 10 microprocessor means 11 read / write circuit means (R / W circuit means) 12 position detection means 13 Actuator driving means

Claims (2)

(57) [Claims] 1. A method of protecting against off-track in a magnetic disk drive, comprising: a position detecting step of extracting position information for a head positioning servo read by a magnetoresistive head from a read / write circuit means; and a machine utilizing a shock sensor. A step of detecting that the impact exceeds an allowable value; anda step of monitoring an output from the position detecting means to detect an off-track which is a misalignment between the center of the track and the center of the head. If no mechanical shock is detected at this time, it is determined that the positional information is disturbed due to a change in the magnetic characteristics of the magnetoresistive head, and means for returning the magnetic characteristics of the magnetoresistive head to a normal state is activated. And a method for protecting against off-track in a magnetic disk drive. 2. An actuator for driving a composite head of a thin-film head for writing and a magnetoresistive head for reading, an actuator for driving the composite head and a head support mechanism for moving the composite head, and A magnetic disk drive comprising: an actuator driving means for driving; and a read / write circuit means for performing read / write operations on the composite head, wherein the read / write circuit reads head position servo position information read by the magnetoresistive head. Position detecting means for taking out from the means; a shock sensor for detecting an external vibration shock; mechanical shock detecting means for detecting that a mechanical shock exceeds an allowable value using the shock sensor; Monitoring the output of the off-track to detect the off-track which is the displacement between the center of the track and the center of the head. If a mechanical shock is not detected at that time, it is determined that positional information is disturbed due to a change in magnetic characteristics of the magnetoresistive head, and the magnetic characteristics of the magnetoresistive head are returned to a normal state. A microprocessor means for activating the means.