JPH1049801A - Magnetic disc check apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To check even a large capacity magnetic disc with high accuracy. SOLUTION: A magnetic head 10 writes the predetermined signal to a magnetic disc and also reads the signal stored n the magnetic disc. An envelope generating circuit 14 generates an envelope signal of the readout signal. A low-pass filter 16 cuts a high frequency element of this envelope signal. A slice level circuit 18 amplifies an output signal of the low-pass filter with the predetermined amplification factor to generate a slice level signal. This amplification factor may be changed depending on the measuring condition of a magnetic disc. A comparator 20 compares a slice level signal and envelope signal. The comparator 20 can provide a response with relatively higher accuracy because the signal is not a readout signal but its envelope signal and it is lower than the readout signal in the frequency. An error processing circuit 22 specifys an error part of the readout signal from an output signal of the comparator 20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for inspecting a magnetic disk medium of a magnetic disk drive, and more particularly to a magnetic disk inspection apparatus suitable for inspecting a large-capacity magnetic disk.

[0002]

2. Description of the Related Art Computers and other computers use large-capacity storage devices for storing software and the like. At present, as this mass storage device,
A magnetic disk device fixed to a computer is mainly used, and is generally called a hard disk device. In a magnetic disk drive, a magnetically recordable disk is rotated by a spindle motor, and data is magnetically written to and read from the magnetic disk medium by a magnetic head. The capacity of the magnetic disk device is a type using several 3.5-inch disks, and a large capacity of several gigabytes is currently realized.

FIG. 4 shows a conventional magnetic disk inspection apparatus.
It is a block diagram showing an example. Various inspections are performed on the magnetic disk used in the magnetic disk device. One of these checks is a missing error check. The calibrated magnetic head 10 writes a signal of a predetermined frequency on a predetermined track of a magnetic disk to be inspected (not shown), and then reads the signal along the track. Missing error inspection is to determine whether or not there is a portion (error) in which the read signal is smaller than a specified value to check for defects such as scratches on the disk surface.

[0004] The magnetic head 10 writes, for example, a rectangular wave signal having a predetermined cycle and amplitude on a magnetic disk.
At this time, if the disk is in an ideal state, the read signal also has the same cycle as the write signal, and has a waveform obtained by differentiating the write signal. A read signal from the magnetic head 10 is amplified to an appropriate amplitude by an amplifier (amplifier) 12. This read signal is input to one input terminal of the comparator 20. The read signal is also input to the peak detection circuit 15.

FIG. 5 shows a readout signal A, an output waveform B of the peak detection circuit 15 and a slice level signal C observed using a waveform measuring device such as an oscilloscope.
As shown in FIG. 5, the output signal B of the peak detection circuit 15
Detects the peak value of the read signal A, and then the voltage value gradually decreases according to the time constant. Here, the output voltage B of the peak detection circuit 15 is referred to as a peak voltage signal. The slice level circuit 18 receives the peak voltage signal B, amplifies it at an amplification factor according to the inspection condition, and generates a slice level signal C for error determination (error determination reference signal).

The comparator 20 compares the read signal A and the slice level signal C. Since the read signal has the same known period T as the write signal, the amplitude of the read signal A should ideally exceed the slice level in synchronization with the period T. Therefore, if there is an amplitude portion (time point t0 in FIG. 5) that does not exceed the slice level signal C in synchronization with the cycle T, it can be determined that the portion is a defective portion. In addition, since sufficient accuracy can be obtained even if an error is determined by regarding the sign of the read signal as substantially symmetrical, a comparison is made only for half waves. The error processing circuit 22 detects an error of the read signal and specifies an error detection position from the output signal of the comparator 20. The processing result is sent to a microprocessor (not shown) or the like for processing.

[0007]

As the recording density of today's magnetic disks increases, the frequency of the write signal, and hence the read signal, has increased. However, in the circuit shown in FIG. 4, the comparator 20 directly compares the read signal with the slice level signal, and when the frequency of the read signal increases, the response speed of the comparator 20 can correspond to this. Without
The accuracy of the error determination is reduced. Therefore, it is necessary to cope with an increase in the density of a magnetic disk so that an error determination can be performed with high accuracy even for a read signal of a high frequency.

[0008]

According to the magnetic disk inspection apparatus of the present invention, first, a predetermined signal is written to a magnetic disk by a magnetic head, and a signal written to the magnetic disk is read. Note that writing and reading may be performed by independent magnetic heads. According to this, reading can be performed immediately after writing and inspection can be performed. The envelope generating means generates an envelope signal of the read signal read by the signal reading means. The low-pass filter cuts the high frequency components of the envelope signal. The amplification means amplifies the output signal of the low-pass filter means at a desired amplification factor. This amplification factor may be changed according to the inspection conditions of the magnetic disk. The comparison means is
The output signal of the amplifying means is compared with the envelope signal, and the error processing means specifies an error portion of the read signal from the output signal of the comparing means.

The read signal passes through the low-pass filter means and the amplifying means, but the order may be reversed. However, because of the problem of the response speed of the amplifying means, it is generally better to pass the low-pass filter means first.

The error detection scale may be changed by changing the detection response speed of the envelope detection means. In other words, if the detection response speed is increased, a finer change in the amplitude of the read signal is followed, so that a finer change in the disk surface is detected. Can be ignored and the inspection performed. Note that an automatic gain control circuit can be used as the low-pass filter means.

According to the present invention, what the comparing means compares with the reference signal (slice level signal) is not the read signal, but the envelope signal of the read signal, unlike the related art. Therefore, since the frequency of the envelope signal is lower than the frequency of the read signal, the error determination can be performed with relatively higher accuracy than the frequency of the read signal.

[0012]

FIG. 1 is a block diagram showing an example of a magnetic disk inspection apparatus according to the present invention. Components corresponding to those of the conventional example will be described with the same reference numerals. Magnetic head 10
, Use a pre-calibrated one. Magnetic head 10
Writes a predetermined signal (for example, the above-described rectangular wave) having a known frequency and amplitude on a predetermined track of a magnetic disk (not shown) to be inspected. The magnetic head 10 reads out the written signal. In FIG. 1, writing and reading are performed by the same magnetic head, but may be performed by independent magnetic heads. According to this, reading can be performed immediately after writing and inspection can be performed. The read signal is
The signal is amplified by the amplifier 12 to an appropriate amplitude.

The envelope detection circuit 14 includes an amplifier 12
Detects the envelope of the readout signal output by the controller and generates an envelope signal. FIG. 2 shows how the envelope is detected from the read signal A. The envelope detection circuit 14 basically generates an envelope (envelope) signal by tracing all the peaks of the amplitude of the readout signal, as indicated by the solid line a. By the way, since the sign of the read signal can be regarded as substantially symmetrical, only a half wave of the read signal is sufficient for the inspection. Therefore, for simplicity, the read signal may be half-wave rectified, and then the high-frequency component may be cut by a low-pass filter to generate an envelope signal.

Although it has been described above that all of the peaks of the amplitude of the read signal are basically traced, in reality, the response speed of the envelope detection circuit 14 is changed to change the amplitude of the read signal in accordance with the frequency of the read signal. You can set whether to trace all peaks or ignore them to some extent. Taking the above-described configuration using the half-wave rectification and the low-pass filter as an example, if the threshold of the high frequency cut off (filtered) by the low-pass filter is increased, all the peaks of the amplitude can be traced. By lowering the threshold of the frequency to be performed and removing even the lower frequency components, it can be ignored to some extent. A dashed line b in FIG. 2 shows an example in which the response speed of the envelope detection circuit 14 is reduced so that small changes are ignored to some extent.

The problem of the response speed of the envelope detection circuit 14 is a problem of the inspection scale of how finely the magnetic disk is inspected. If the detection response speed of the envelope detecting means is increased, finer changes in the magnetic disk surface appear in the envelope signal, so that the magnetic disk surface is inspected on a smaller scale. The extent of this scale depends on the inspection conditions. Of course, there is a case where it is not necessary to perform inspection on a scale smaller than necessary. In this case, an envelope signal indicated by a broken line b rather than a solid line a may be used.

The envelope signal thus generated is:
The signal is input to one input terminal of the comparator 20 and is also input to a reference signal generation circuit (reference signal generation means) 19. The reference signal generation circuit 19 includes a low-pass filter 16 and a slice level circuit 18. The low-pass filter 16 cuts high frequency components of the envelope signal. The slice level circuit (amplifying means) 18
The envelope signal is amplified at a desired amplification factor. The output signal of the reference signal generation circuit 19 is called a slice level signal, is applied to the other input terminal of the comparator 20, and is compared with the envelope signal of the read signal.

The comparator 20 compares the slice level (reference) signal and the envelope signal. At this time, if the read signal is an ideal one as in the conventional example, the envelope signal of the envelope signal is changed according to the period T of the read signal. The level should exceed the slice level. Therefore, the error processing circuit 22 samples the output signal of the comparator 20 in accordance with the period T of the read signal. If there is a portion where the envelope signal is lower than the slice level signal, this is a portion where the read signal cannot be read normally, and it can be determined that there is some defect such as a scratch on the corresponding magnetic disk surface. That is, the slice level signal functions as a reference signal for error determination for determining whether the signal is defective.

A solid line d and a broken line e shown in FIG. 3 are signals obtained after the envelope signal c has passed through the reference signal generating circuit 19, but they have different threshold values of the frequency cut by the low-pass filter 16. That is, the solid line d
Is cut (filtered) from the lower frequency. At this time, if the solid line d is used as the slice level signal, it is possible to accurately detect the dent of the envelope signal as shown at the time point t1, that is, the error position of the read signal. Note that the solid line d can also be obtained by passing the envelope signal through an automatic gain control circuit (AGC). However, using a low-pass filter can be realized with a simple and inexpensive configuration.

Although the envelope signal is input to the slice level circuit 18 after being input to the low-pass filter 16 in FIG. 1, the order may be reversed. Generally, there is a problem with the response speed of the slice level circuit (amplifying means). Therefore, it is only necessary to pass the read signal through the low-pass filter circuit 16 first and then through the slice level circuit 18. is there.

The setting of the amplification factor of the slice level circuit may be changed according to the inspection conditions. That is, if the criterion of failure is strict, the amplification rate should be lowered to lower the slice level, and if the criterion is loosened, the amplification rate should be higher and the slice level should be higher.

It should be noted that, in the present invention, what the comparator 20 compares with the slice level signal is not the readout signal but the envelope signal of the readout signal unlike the related art. Since the envelope signal has a much lower frequency than the read signal, even if the frequency of the read signal is high,
That is, even when the recording density of the magnetic disk is high, the comparator 20 can compare with the slice level signal and make an error determination by responding with relatively sufficiently high accuracy as compared with the related art.

The error processing circuit 22 detects an error portion of the read signal from the output signal of the comparator 20, and specifies an error position on the magnetic disk. The processing result is sent to a microprocessor (not shown) and used for some processing such as data storage.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the present invention.

FIG. 2 is a diagram illustrating a difference in envelope generation depending on a response speed of an envelope circuit according to the present invention.

FIG. 3 is a diagram illustrating a difference in slice level due to a difference in cut frequency of a low-pass filter according to the present invention.

FIG. 4 is a block diagram showing an example of a conventional magnetic disk inspection device.

5 is a diagram showing a peak voltage signal and a slice level signal of the circuit shown in FIG.

[Explanation of symbols]

 Reference Signs List 10 magnetic head (writing means, reading means) 12 amplifier 14 envelope detection circuit 15 peak detection circuit 16 low-pass filter means 18 slice level circuit (amplification means) 19 reference signal (slice level) generation circuit 20 comparator 22 error processing circuit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location G11B 20/18 572 G11B 20/18 572B 572F

Claims (6)

[Claims] 1. An apparatus for inspecting a magnetic disk, comprising: writing means for writing a predetermined signal on the magnetic disk; signal reading means for reading the signal written on the magnetic disk; Envelope generating means for generating an envelope signal of the read signal; reference signal generating means having low-pass filter means for cutting high-frequency components of the envelope signal; and amplifying means for amplifying the envelope signal at a desired amplification factor; Magnetic means comprising comparing means for comparing the reference signal output from the reference signal generating means and the envelope signal, and error processing means for specifying an error portion of the read signal from the output signal of the comparing means. Disk inspection device. 2. An apparatus for inspecting a magnetic disk, comprising: a writing unit for writing a predetermined signal on the magnetic disk; a signal reading unit for reading the signal written on the magnetic disk; Envelope generating means for generating an envelope signal of the read signal; low-pass filter means for cutting high-frequency components of the envelope signal; amplifying means for amplifying an output signal of the low-pass filter means at a desired amplification factor; A magnetic disk inspection apparatus, comprising: comparison means for comparing the output signal of the amplification means and the envelope signal; and error processing means for specifying an error portion of the read signal from the output signal of the comparison means. 3. The magnetic disk inspection apparatus according to claim 1, wherein an error detection scale is changed by changing a detection response speed of the envelope detection means. 4. The magnetic disk inspection apparatus according to claim 1, wherein an amplification factor of the amplification means is changed according to inspection conditions of the magnetic disk. 5. An apparatus according to claim 1, wherein an automatic gain control circuit is used as said low-pass filter means.
5. The magnetic disk inspection device according to 3 or 4. 6. The comparison means uses the envelope signal, which is the envelope of the read signal, for comparison, thereby making it possible to determine an error with relatively high accuracy compared to the frequency of the read signal. The magnetic disk inspection device according to claim 1, 2, 3, 4, or 5, wherein