JPS5883370A - Inspecting method for writing intervals of servo pattern for magnetic disk - Google Patents

Abstract

PURPOSE:To decide on whether intervals of servo patterns on a magnetic disk are normal or not without reference to fluctuation in turning speed, by deciding on whether a writing interval between two patterns is normal or not on the basis of whether the difference between a reference voltage and a voltage to be detected is a value within the prescribed range or not. CONSTITUTION:In a normal disk rotation state, servo patterns written on one track are read out by a heat, and a VCO in a PLL is oscillated to the read signal to generate clock pulses at intervals obtained by dividing the time for one readout-speed turn of the disk by a specific integer accurately and equally. On the basis of this clock, the time from the pattern pulse generation point by the read signal of some servo pattern to the pattern pulse generation point corresponding to a next servo pattern is measured. Then, the properiety of writing intervals between respective patterns is decided on according to whether the difference between a reference voltage and a voltage to be detected is less than a value in the prescirbed range or not.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a servo pattern writing method for a magnetic disk that can correctly determine whether or not the written servo pattern interval is acceptable even if the disk rotational speed at the time of inspection is slightly different from the rotational speed at the time of writing or the standard rotational speed. This invention relates to an interval inspection method.

When manufacturing a magnetic disk, it is necessary to inspect whether the servo patterns used for head positioning and the like written on the servo surface are correctly written at predetermined intervals to determine whether or not the magnetic disk is acceptable.

To measure the writing interval of this servo pattern, the time is converted into a voltage sum using an integrator, etc., and compared with a preset reference voltage to determine the interval. It is difficult to measure with the desired accuracy. In addition, ultra-high-speed digital generation aS of approximately 100MHz
A commonly used method is to measure the interval (time) between pattern reading times according to and Kakunta, but even with this method, if the disk rotational speed at the time of inspection is different from the standard or rotational speed at the time of writing, it is not accurate. measurements cannot be made. Therefore, in the past, accurate inspection of servo pattern writing intervals required expensive, large-scale equipment.The purpose of the present invention is to detect disk rotational speeds that are slightly different from the writing or standard rotational speeds during inspection. It is an object of the present invention to provide a servo pattern writing interval inspection method that can correctly determine the pass/fail of the written servo pattern interval even if the interval is different.

In order to achieve the above object, the present invention causes a head to read out a servo pattern written on one track under normal disk rotation, and uses this read signal to perform a PLL.
The oscillation of the VCO (voltage controlled oscillator) in the (phase-locked loop) is pulled in, and clock pulses are generated at intervals that accurately divide the time required for one rotation of the disk at the rotation speed during reading by a specific integer. Using this clock as a reference, we decided to measure the time until the pattern pulse generation point for the servo pattern using a signal read from a certain servo pattern. In other words, although the absolute value of the clock pulse interval (time) mentioned above varies according to the variation in rotational speed, the absolute value of the pattern pulse generation interval (time) is also affected by the rotational speed in exactly the same way. If measured by the pulse count of the clock pulse related to
This is because the intervals between servo patterns written on the disk should always be the same regardless of variations in the disk rotation speed. In addition, the disk has a considerably high rate of inertia, and rotates at a considerably high speed (for example, 3.60 Or?ff
1) Because of this, the fluctuations in rotational speed that occur during steady operation take an extremely long time compared to the (time) interval between the servo patterns that we are currently trying to measure, and occur extremely slowly. Therefore, the objective is to There will be no problems such as irregularities occurring while measuring the intervals between servo patterns. Note that the actual measurement of the interval between pattern pulses is based on the gate pulse created in synchronization with the clock and the C no.
? ” The phase difference between the pattern pulse for one servo pattern read out during the gate pulse is converted into a voltage by an integral hold circuit, and the reference voltage is used as the reference voltage. It is decided whether or not the writing interval between the two servo patterns is acceptable or not based on whether the pulse and the pattern pulse for the pattern following the pattern are within a predetermined value.

This is because if the writing intervals of these servo patterns are correct, the interval between pattern pulses created by reading them should be exactly a predetermined (integral) multiple of the clock according to the present invention, but in reality It is unavoidable that some error will occur, so in order to measure the error part corresponding to the fraction of the clock in an analog way, for the two servo patterns,
Each generates a gate pulse in synchronization with the clock,
The phase difference between these gate pulses and each pattern pulse was converted into a voltage using separate integral hold circuits and compared, and if the voltage difference was within a predetermined value, the test was determined to pass. This predetermined tolerance value is more than ten aSS1.

Below, FIG. 1 is a circuit block diagram of an embodiment of the present invention,
FIG. 2, which shows the waveforms and timings of each signal therein, will be explained. For example, signal 1 is written in FIG. 1, and the corresponding waveform is shown in FIG.

The signal a obtained by reading out the servo pattern with the head and amplifying it with the amplifier is as shown in FIG. The signal obtained by converting this signal into a gagetal pulse through a peak detection circuit is shown in FIG. This signal is synchronized with a pattern consisting of PLL @
This input is input to the thought generation circuit, and the oscillation of vCo in the PLL is drawn into this human power. The signal C thus generated in the pattern synchronization signal generation circuit (generated by vCO in the PLL drawn into the input) corresponds to the rotation of the disk, which is the essence of the present invention. Based on this clock, various gate signals are created by the check tie construction circuit shown in FIG. On the other hand, the signal d is passed through a pulse generating circuit and converted into a signal d, that is, a pattern pulse. As shown in FIG. 2, in this embodiment, servo patterns α, β, and γ provided at predetermined irregular intervals form one set, and thousands of sets of patterns are written on one track of the disk. It is rare. In addition, α' is shown in the diagram of signal d and pattern pulse in Figure 2.
indicates the next set of α pulses. As shown in FIG. 1, a phase difference T between the gate (so-called measurement window) A created by the check timing creation circuit and the pattern pulse α is detected by a phase difference detection circuit (A). This is converted into a voltage (e)K by an integral hold circuit (A), and this is regarded as a reference voltage.
Create YH(f) and lower limit VL(g).

Next, the phase difference between the pattern pulse β and the pattern pulse β created after a predetermined clock (corresponding to the original or intended interval between the pattern pulses α and β) is detected by the phase difference detection circuit (B). is converted into a voltage (h) by the integral hold circuit CB), and this is set as the voltage to be tested, V. The upper limit comparator checks whether ■〈vH, and the lower limit comparator checks whether V, <V. , then the time interval between the pattern pulses α and β, and therefore the writing (distance) interval of the servo pattern on the disk corresponding to these, is determined to be a pass, otherwise it is determined to be a fail. Note that the phase detection circuit (D) in FIG.
The integral hawked circuit CD) is for pattern pulse α'.

As described above, according to the present invention, it is possible to determine whether the interval between servo patterns written on a magnetic disk is acceptable or not, without being affected by fluctuations in the rotational speed of the disk, and with relatively inexpensive equipment.

[Brief explanation of drawings]

FIG. 1 is a circuit block diagram of an embodiment of the present invention, and FIG. 2 is a diagram showing signals in the circuit. Agent: Patent Attorney Takeo Agata Figure 1 Figure 2

Claims (1)

[Claims] In testing the writing interval of servo patterns for magnetic disks, the head reads out the servo pattern written on one track under normal disk rotation; the oscillation of the VCO in the PLL is drawn into this read signal, and the readout Clock pulses are generated at intervals that accurately divide the time required for one rotation of the disk at the rotational speed of The phase difference between one pattern f) and the pattern pulse created from s is converted into a voltage by an integral hold circuit, which is used as a reference voltage; similarly, the gate pulse created after a predetermined clock and the pattern next to the above pattern are used. The phase difference between the pattern pulse and the reference voltage is converted into a voltage by another integral hold circuit and used as the voltage to be tested;
A servo pattern writing interval inspection method for a magnetic disk, characterized in that it determines whether the writing interval between patterns is acceptable or not.