JPH0673162B2 - Demagnetization test method for magnetic disk drive - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for testing a magnetic disk drive, and more particularly, to measuring the magnetic reduction of data recorded on a medium caused by accessing a magnetic head. The present invention relates to a demagnetization test method for determining the quality of a magnetic disk drive device.

(Prior Art) In a floppy disk drive that stores a date on a disk-shaped flexible recording medium by magnetic recording, there is a phenomenon that the read voltage from the magnetic head gradually decreases during use. This is generally called demagnetization phenomenon,
That is, the magnetic flux of the data on the track of the recording medium is reduced.

Next, the demagnetization phenomenon will be described with reference to FIG. FIG. 5 is a schematic view showing a contact surface between a magnetic head and a recording medium (floppy disk) in a floppy disk drive device. In the figure, when writing data to each track of the recording medium, the read / write head 5 writes the data and the erasing head 6 is driven to erase both sides of the just written data by DC. This is to keep the track width constant and to prevent mutual interference by providing a guard band between adjacent tracks.
Further, when reading data from each track, the read / write head 5 alone reads and the erasing head does not drive. When accessing the magnetic head to select a track, each track is traversed while the magnetic head is in contact with the recording medium. The demagnetization phenomenon usually occurs during this access. This demagnetization phenomenon occurs on the medium due to the residual magnetism of each core of the magnetic head, the magnetic flux concentration on the core due to the leakage magnetic field outside the magnetic head, the pressure applied to the recording medium by the magnetic head, and the structural defect of the magnetic head. Residual magnetic flux recorded in is affected and generated. As described above, the cause of the demagnetization phenomenon is on the side of the magnetic head of the apparatus, and particularly when the erasing head traverses each track during access, the recorded data on the track is gradually demagnetized.

Next, the state of the demagnetization phenomenon will be described with reference to the demagnetization curve of FIG. In the figure, the vertical axis represents the magnetic head output value (%),
The horizontal axis represents the number of times the magnetic head was accessed, and the magnetic head output value immediately after writing (D ₀ point) was set to 100%, and the change in the magnetic head due to the number of times of access was relatively expressed. As can be seen from the figure, the magnetic head output value gradually decreases as the number of accesses increases, and becomes almost saturated and constant at point D ₂ . That is, the demagnetization phenomenon occurs until the access count reaches D ₂ . The D ₂ point is about 5000 times of access. In the figure, C1, C2, and C3 are demagnetization curves for the respective magnetic disk drive devices. Figure 7 shows
It is explanatory drawing of the demagnetization rate of the demagnetization phenomenon by an access operation.
In the figure, (b1) is the head output voltage A immediately after data writing, that is, the output voltage at point D _{0 in} FIG.
(B2) is the head output voltage B after D ₂ accesses. Here, (AB) / A × 100 (%) is the demagnetization rate (the same as the magnetic head output value (%) in FIG. 6).

The demagnetization phenomenon described above is usually tested before shipping the magnetic disk device. This is done for the purpose of preventing the shipment of such a device, because if the demagnetization rate is large (if the demagnetization is severely reduced), a read error may occur and a failure may occur. When the demagnetization rate is set to about 70%, a device such as C3 in FIG. 6 is removed as a defective product.

Hereinafter, a conventional demagnetization test method will be described with reference to the flowchart shown in FIG. The recording medium used is a floppy disk having a plurality of concentric tracks, the outermost track being "00" and the innermost track being "39". First, access the track 38 with the magnetic head (step
81), data is written on the entire circumference of this track 38 (step 82). The track 38 is used because this track is close to the innermost circumference of the recording medium and the recording density is high, so that when the demagnetization rate becomes large, the data read error becomes the worst case. The output waveform immediately after being written to the track 38 is read (step 83), and this is stored in the memory as the output voltage A shown in FIG. 7 (b1). Next, the truck 38 is reciprocated between the trucks 37 and 39 with the truck 38 at the center (step 84). After repeating this round-trip access a specified number of times (n times), the magnetic head is tracked.
Return to step 38 to stop access (step 85). The output waveform of the magnetic head at this time is read (step 86), and this is taken as the output voltage B shown in FIG. 7 (b2). Then, the demagnetization rate is calculated from the output voltage A and the output voltage B stored in the memory (step 87), and as a result, the quality of the device is determined (step 88).

(Problems to be Solved by the Invention) However, the demagnetization test method described above has the following problems.

In the test method of measuring the demagnetization rate by reciprocating the specified number of times before and after a specific track, it takes a very long time to perform the necessary number of accesses, for example, the time required to reach point D ₂ shown in FIG. Takes about 5 minutes (accesses about 5,000 times). Further, since the reciprocal access operation by this test method is performed independently of the rotation of the recording medium,
A large number of axes must be required in order for the magnetic head to cross the entire circumference of the track in all directions. For this reason, productivity is not improved, which has been a bottleneck in mass production of magnetic disk drive devices.

Therefore, the aborted access at D _point shown in FIG. 6, it is also possible to adopt a method of estimating the demagnetizing factor of the final D ₂ points from demagnetizing factor at this time, to _a point D in this way It took about 2 minutes to reach the target, and there was a problem that the reliability of the measurement was lacking.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and provide a demagnetization test method for a magnetic disk drive, which has a short test time for generating a magnetic reduction of magnetic recording data and has excellent reliability.

(Means for Solving Problems) In order to solve the above problems, the present invention tests a magnetic disk drive as follows.

First, data is written to a specific track of a rotating recording medium, and an access operation in which the magnetic head reciprocates across the specific track is performed based on an index signal detected at least once per one rotation of the recording medium. It starts with a delay according to the designated number of times of access so as to access the predetermined area.

Then, after the specified number of accesses are completed, the output value of the magnetic head in the accessed specific track and the output value of the magnetic head in the unaccessed specific track are compared to determine the data written in the specific track. This is a demagnetization test method that measures the magnetic decrease and judges the quality of the magnetic disk drive by this measurement.

(Operation) According to the present invention, since the demagnetization test method for the magnetic disk drive device is configured as described above, the operation is as follows.

First, the recording medium is loaded into the magnetic disk drive, and data is written on a specific track of the rotating recording medium. The magnetic head starts an access operation, for example, a first access operation, which reciprocates and traverses the inner and outer tracks of the specific track around the specific track, after a delay of T1 time from the detection of the index signal. Then, the second access operation is started after a delay of, for example, 2 × T1 time from the detection of the next index signal. After that, the access from the third time to the specified number of times is started after the delay time corresponding to the number of times of access from the detection of the index signal as described above. In addition, the delay time is adjusted so that the above-mentioned specified number of accesses are performed only in a predetermined area of a specific track in which data is written. After the specified number of accesses, compare the output value of the magnetic head on the specific track that was accessed with the output value of the magnetic head on the specific track that was not accessed, and measure the magnetic decrease of the data written on the specific track. Then, the quality of the magnetic disk drive is determined based on this.

As described above, according to the present invention, since the access of the magnetic head is started with a delay according to the number of times of access based on the undex signal, it is possible to access the magnetic head in a certain track area without waste. As a result, the required number of accesses can be reduced. Therefore, the conventional problems can be solved.

(Example) Hereinafter, one example of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a flowchart of a demagnetization test method for a magnetic disk drive according to an embodiment of the present invention, and FIG. 2 shows a time chart of access of a magnetic head according to an embodiment of the present invention. FIG. 3 shows the connection between the demagnetization tester and the floppy disk drive when performing the procedure of FIG.
In FIG. 3, the demagnetization tester 1 is connected to a floppy disk drive device via a signal cable 3 and a power cable 4. The demagnetization test method according to the present embodiment delays the start of each access of the magnetic head according to the number of times of access, based on the index signal detected once per one rotation of the floppy disk. The demagnetization test method according to this embodiment will be described below with reference to the time chart of FIG. 2 according to the steps of the flowchart shown in FIG. In this test, the demagnetization of the track 38 is measured using a floppy disk having 40 tracks as a recording medium as in the conventional case.

Insert the floppy disk into the device and turn on the power to start the test. First, with respect to the rotating floppy disk, the magnetic head accesses the track 38 (step 11), and the data is written on one circumference of the track 38 (step 12). Next, the magnetic head is accessed to the track 37 (step 13), and the index signal comes in (step 14). The index signal is a signal output once per one rotation of the floppy disk, and is a pulse converted by detecting a hole on the floppy disk with light. This index signal is shown in FIG. In the figure, Tp indicates a cycle of one rotation. When the index signal is detected, the magnetic head is delayed by T1 time (step 15) and the track 39 is accessed (step 16). After the access, the magnetic head is held on the track 39 for TH1 time (step 17), and the track 37 is accessed again (step 18). Steps 15 to 15 above
The access operation up to 18 is shown in access (1) in FIG.

When the first access operation is completed in this way, the second access operation is then executed in accordance with steps 14 to 19 described above. This operation is shown as access (2) in FIG. As shown in the figure, track 37
When the next index signal arrives, the magnetic head located at position will be delayed by T2 time (T1 × 2) and then tracked.
39 is accessed. Subsequent operations are the same as the first access.

The third access is started T3 time after the pulse of the index signal after a delay of T1 time from the second access (access (3) in FIG. 2). Thereafter, similarly, the access is performed with a delay of Tn time (Tn = n × T1) until the round trip access reaches n times. The number of round trip accesses n, the access delay pitch T1 and the holding time TH1 are determined by experiments, and in the present embodiment, the n th track 37 to the track 39.
The time of access to the track 38 overlaps with the time of the first access from the track 39 to the track 37, and the entire magnetic head crosses the front half of one turn of the track 38. Therefore, the rear half of the track 38 is never crossed by the magnetic head (see FIG. 2). To access only the predetermined area of track 38, hold time TH1
Alternatively, it can be realized by adjusting the period Tp.

In this way, the n-th round trip access is performed (step 19), the magnetic head accesses the track 38 (step 20), and the output waveform is read there (step 2).
1). This output waveform diagram is shown in FIG. In the figure, (b1) is the head output voltage A immediately after writing data before the test starts.
(B2) shows the head output voltage B after the test. still,
As described above, the output waveform of (b2) is reduced to the output voltage B in the first half due to demagnetization due to access, and remains at the output voltage A in the latter half because it is not accessed. Therefore, the demagnetization factor is (A-
B) / A x 100 (%) can be calculated (Step 2
2) Then, by displaying this on the display of the demagnetization tester 1 shown in FIG. 4 (step 23), the quality of the disk drive device is judged (step 24).

As described above in detail, according to the present embodiment, the access operation for generating the demagnetization of the magnetic recording data is started with a delay depending on the number of times of access with the pulse of the index signal as a base point. The magnetic head can cross tracks without waste, and the number of times of access required is small. Further, in a 5-inch diameter floppy disk drive, experiments have confirmed that the demagnetization test is sufficient with T1 of 0.5 ms (access delay pitch in FIG. 2) and access count n of about 100 times. . In this case, since the pulse period Tp of the index signal is 200 ms, the test time may be about 20 seconds, which is shortened from the conventional 5 minutes to 20 seconds.

(Effect of the Invention) As described above in detail, according to the present invention, the access operation that causes the magnetic reduction of the data written in the specific track of the recording medium is delayed according to the number of accesses based on the index signal. I decided to start it, so
The magnetic head can access a predetermined area of a specific track without waste, and the number of times of access required is small. In addition, when measuring the magnetic decrease of the data written to a specific track, it is not necessary to store the output value of the magnetic head immediately after writing the data in the memory as in the conventional case, and the access to the specific track after the specified number of accesses is completed. It is possible to compare the output values of the respective magnetic heads in the read area and the non-accessed area. As a result,
It is expected that the test time will be shortened and the productivity of the magnetic disk drive will be improved.

[Brief description of drawings]

FIG. 1 is a flowchart of a demagnetization test method according to the present invention,
FIG. 2 is a time chart of access of a magnetic head according to the present invention, FIG. 3 is a diagram showing a configuration of a tester for carrying out the test method of the present invention, and FIG. 4 is a change of head output voltage according to the present invention. FIG. 5, FIG. 5 is an explanatory diagram of a magnetic head, FIG. 6 is a demagnetization curve diagram, FIG. 7 is a diagram showing changes in head output voltage due to a conventional access operation, and FIG. 8 is a conventional demagnetization test method. It is a flowchart of. 1 ... Demagnetization tester, 2 ... Floppy disk drive, 3 ... Signal cable, 4 ... Power cable.

Claims (1)

[Claims] 1. A magnetic head based on an index signal which is used to write data to a specific track of a rotating recording medium so that the magnetic head reciprocates across the specific track at least once per revolution of the recording medium. Starts with a delay according to the specified number of accesses to access a specified area of a specific track, and after the specified number of accesses is completed, the output value of the magnetic head on the accessed specific track and the specified value that was not accessed By comparing the output value of the magnetic head on the track to measure the magnetic decrease of the data written on the specific track, the quality of the magnetic disk drive is judged by this, and the decrease of the magnetic disk drive is characterized. Magnetic test method.