JPH0142073B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides the ability to
The present invention relates to a method for inspecting servo pattern writing intervals for magnetic disks, which can accurately determine whether or not written servo pattern intervals are acceptable.

When manufacturing a magnetic disk, it is necessary to inspect whether the servo patterns used for head positioning, etc. written on the servo surface are correctly written at predetermined intervals to determine whether or not the disk is acceptable. To measure the writing interval of this servo pattern, the method of converting time into voltage using an integrator or the like and comparing it with a preset reference voltage is to convert the interval of several μs to within several tens of nanoseconds. Difficult to measure with desired accuracy. In addition, a method is generally used to measure the interval (time) between pattern reading times using an ultra-high-speed digital oscillator and a counter of about 100 MHz, but even with this method, if the disk rotation speed during inspection is not the standard or the rotation speed during writing is If the speed is different, accurate measurements cannot be made. Therefore, in the past, expensive and large-scale equipment was required to accurately inspect the servo pattern writing interval.

An object of the present invention is to provide a servo pattern writing interval inspection method that can correctly determine whether the written servo pattern interval is acceptable even if the disk rotational speed at the time of inspection is somewhat different from the rotational speed at the time of writing or the reference rotational speed. There is a particular thing.

In order to achieve the above object, in the present invention,
A servo pattern written on one track is read out to the head under normal disk rotation, and a PLL (phase locked loop) is applied to this read signal.
The oscillation of the VCO (voltage controlled oscillator) inside is pulled in,
A servo pattern created by generating a clock pulse at an interval that accurately divides the time required for the disk to rotate once at the rotational speed during reading by a specific integer, and using this clock as a reference signal to read out a certain servo pattern. We decided to measure the time from the time of generation to the time of generation of pattern pulses for the next servo pattern. In other words, although the absolute value of the clock pulse interval (time) described above varies in accordance with fluctuations in the rotational speed, the absolute value of the pattern pulse generation interval (time) is also affected by the rotational speed in exactly the same way. This is because, if measured by the pulse count of such clock pulses, the intervals between the servo patterns written on the disk should always be the same value regardless of fluctuations 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,
3600 rpm), 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, there is no problem such as the clock going out of order while measuring the interval between the target servo patterns.
In actuality, the interval between pattern pulses is measured by converting the phase difference between the gate pulse created in synchronization with the clock and the pattern pulse for one servo pattern read within this gate pulse into a voltage using an integral hold circuit. Using this as a reference voltage, the phase difference between the gate pulse, which was similarly created by delaying the gate pulse by a predetermined number of clocks, and the pattern pulse for the next pattern after the pattern was converted into a voltage using another integral hold circuit. is used as the voltage to be tested, and whether or not the writing interval between the two servo patterns is acceptable is determined based on whether the difference between these two voltage values is 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 (integer) 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 portion corresponding to the fraction of the clock in an analog manner, gate pulses are generated for each of the two servo patterns in synchronization with the clock, and these are The phase difference between the gate pulse 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 judged to have passed. This predetermined tolerance value is equivalent to more than ten nanoseconds.

The following will explain FIG. 1, which is a circuit block diagram of an embodiment of the present invention, and FIG. 2, which shows the waveforms and timings of each signal therein. For example, signal a is written in FIG. 1, and the corresponding waveform is shown in FIG. The servo pattern is read out by the head and the signal a amplified by the amplifier is as shown in FIG. The signal b, which is converted into a digital pulse through a peak detection circuit, is as shown in FIG. This signal is input to a pattern synchronization signal generation circuit consisting of a PLL, and the oscillation of the VCO in the PLL is drawn into this input. In this way, the pattern synchronization signal generation circuit generated (pulled into the input
The signal c (generated by the VCO in the PLL) is a clock corresponding to the disk rotation, which is the essence of the present invention.
Based on this clock, various gate signals are created by the check timing creation circuit shown in FIG. On the other hand, the signal b is passed through a pulse generating circuit to be 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 such patterns are written on one track of the disk. ing. Note that the signal d in FIG. 2 and the symbol α' in the diagram of pattern pulses indicate the next set of α pulses. As shown in FIG. 1, a phase difference detection circuit A detects a phase difference _T1 between a gate (so-called measurement window) A created by a check timing creation circuit and a pattern pulse α. This is converted into a voltage e by an integral hold circuit A, which is regarded as a reference voltage, and an upper limit V _H (f) and a lower limit V _L (g) are created by adding and subtracting a tolerance, so to speak, to this voltage. Next, the phase difference between gate B and pattern pulse β created after a predetermined clock (corresponding to the original or intended interval between pattern pulses α and β) is detected by phase difference detection circuit B, and this is integrated and held. Convert it to voltage h in circuit B, use it as the voltage to be tested V, check whether V < V _H with the upper limit comparator, check whether V _L < V with the lower limit comparator, and check the results as an error. If V _L < V < V _H , then the time interval between pattern pulses α and β will be the corresponding servo pattern writing (distance) on the disk.
The interval is considered pass, otherwise it is judged as fail. Note that the phase detection circuit D and the integral hold circuit D in FIG. 1 are for the pattern pulse α'.

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

[Brief explanation of drawings]

Figure 1 is a circuit block diagram of an embodiment of the present invention, Figure 2 is a circuit block diagram of an embodiment of the present invention.
The figure is a diagram showing signals in the circuit.

Claims (1)

[Claims] 1. In the write interval inspection of servo patterns for magnetic disks, the servo pattern written on one track is read out to the head 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 the disk to rotate once at the rotation speed of The phase difference with a pattern pulse created from one pattern is converted into a voltage by an integral hold circuit, and the reference voltage is used;
Similarly, the phase difference between the gate pulse created after a predetermined clock and the pattern pulse for the next pattern of the pattern is converted into a voltage by another integral hold circuit and used as the voltage to be tested; the difference between the reference voltage and the voltage to be tested A method for inspecting a servo pattern writing interval for a magnetic disk, characterized in that whether the writing interval between the two patterns is acceptable or not is determined based on whether or not the writing interval is within a predetermined value.