Quality inspecting method and apparatus for detecting defects in magnetic disks by dividing a plurality of concentric tracks into numbered sectors

A magnetic disk inspection apparatus for recording and reproducing inspection signals onto and from each track on a magnetic disk, in which the inspection signals are recorded and reproduced automatically without a manual operation onto and from the magnetic disk, the maximum value is detected from the reproduction signals on the basis of the sampling signal, the average value of the maximum values is calculated for each sector, the difference between the average values in the same sector number of the adjacent tracks is determined, the change ratio based on this difference is calculated and quality of the magnetic disk is judged on the basis of this change ratio.

BACKGROUND OF THE INVENTION 
The present invention relates to a magnetic disk inspection apparatus and 
more particularly, to a magnetic disk inspection apparatus which records 
and reproduces an inspection signal onto and from each track on a magnetic 
disk and inspects quality of the magnetic disk on the basis of the 
reproduction signal. 
In magnetic disks in general (hereinafter referred to as a "disk(s)", 
inspection whether or not a recorded signal can be reproduced correctly is 
conducted and an inspection method referred to as "radial modulation 
measurement" is included among the inspection methods. 
This inspection is made particularly for evaluating whether or not the disk 
can be used as a servo disk. An inspection signal is recorded in place of 
a servo signal onto a blank disk onto which no recording is made, this 
inspection signal is then reproduced and the reproduction signal is 
inputted to an oscilloscope. 
Next, an inspector has the reproduction waveform of the reproduction signal 
displayed on the oscilloscope and determines the peak values of a 
plurality of reproduction signals for each track. 
The inspector inputs the peak value to processing unit such as a personal 
computer so as to calculate an average value for each sector of each 
track. In the case of this inspection, the difference between the average 
values in the same sector of adjacent tracks is determined. Suitable 
processing is conducted on this difference and the result of the 
processing is compared with predetermined allowable value so as to judge 
quality of the disk. 
In accordance with the conventional inspection method described above, 
however, the inspector must carry out a series of manual operations of 
inputting the reproduction signals to the oscilloscope, observing the 
reproduction waveforms to detect the peak values, etc, and inputting the 
peak values, etc, to the personal computer or the like for processing. 
Accordingly, there arise problems that an extremely long time is necessary 
for the inspection and the inspection itself is troublesome. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a magnetic disk 
inspection apparatus which can inspect quality of magnetic disks 
automatically. 
It is another object of the present invention to provide a magnetic disk 
inspection apparatus for inspecting radial modulation of magnetic disks 
automatically. 
In order to accomplish the object described above, the present invention 
provides a magnetic disk inspection apparatus for recording and 
reproducing inspection signals onto and from each track on a magnetic disk 
fitted to a spindle and inspecting quality of the magnetic disk on the 
basis of the reproduced inspection signals which apparatus comprises 
sampling signal generation means for generating a sampling signal in 
accordance with the rotation of the spindle; maximum value detection means 
for detecting a maximum value from the inspection signals reproduced from 
the magnetic disk in synchronism with the sampling signal; average value 
calculation means for calculating the average value of the maximum values 
detected by the maximum value detection means for each sector on the 
track; change ratio calculation means for determining the difference 
between the average values in the same sector number of adjacent tracks 
and calculating a change ratio based on this difference; and quality 
judgement means for judging quality of the magnetic disk on the basis of 
the change ratio. 
According to the construction described above, inspection signals are 
recorded onto each track on a magnetic disk by means such as a magnetic 
head and the inspection signals are then reproduced. In this instance, 
maximum value detection means detects the maximum value of the inspection 
signals from among the reproduction signals in synchronism with the 
sampling signal generated by sampling signal generation means, and average 
value calculation means calculates an average value of the maximum values 
for each sector on each track. 
Next, change ratio calculation means determines the difference between the 
average values in the same sector number of adjacent tracks from the 
average values determined by the average value calculation means and 
calculates a change ratio based on this difference. A method of 
calculating the change ratio includes a method which divides the 
difference obtained by the method described above by the sum of the 
average values in the same sector of adjacent tracks and other methods can 
of course be employed. 
Finally, quality judgement means judges quality of the magnetic disk on the 
basis of the change ratio calculated by the change ratio calculation means 
described above. For example, if the change ratio exceeds a predetermined 
allowable value, the disk is judged to be "rejectable (disapproved)" and 
if it is within the allowable value, the disk is judged to be "acceptable 
(approved)".

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Hereinafter, an embodiment of the magnetic disk inspection apparatus in 
accordance with the present invention will be explained with reference to 
the accompanying drawings. 
FIG. 1 is a block diagram showing the configuration of the magnetic disk 
inspection apparatus of this embodiment. 
In the drawing, no data, no signal, etc is recorded onto a disk as an 
object of inspection and this disk 1 is fitted to a spindle 2 of the 
present apparatus at the time of inspection and is rotated. 
The apparatus of the present invention is provided with a magnetic head 3 
for recording and reproducing an inspection signal onto and from the disk 
1 described above, a carriage 4 for supporting the magnetic head 3, a 
driver circuit 5 for moving and rotating both of the carriage 4 and the 
spindle 2 described above, and a sampling signal generation circuit 6 for 
generating sampling signals with a predetermined period in accordance with 
the rotation of the spindle 2. 
Furthermore, the present apparatus includes an amplifier 7 for amplifying a 
reproduction signal outputted from the magnetic head 3, a peak detector 8 
for detecting a maximum value of reproduction signals obtained through the 
amplifier 7 in synchronism with a sampling signal outputted from the 
sampling signal generator 6, an A/D convertor 9 for converting the maximum 
value outputted from the peak detector 8 to a digital value, an average 
calculater 10 for adding and holding temporarily the maximum value to and 
in a register or the like, and calculating an average value by dividing 
the sum of the maximum values added to and held by the register by the 
number of samplings for each sector in synchronism with a sector signal 
having a period equivalent to the periods of several sampling signals for 
each track, a memory 11 for storing sequentially the average value 
described above and a later-appearing change ratio, and a central 
processing unit 12 (hereinafter referred to as "CPU") for sending an 
instruction to each circuit through a bus 13, controlling the operation of 
each circuit, calculating the average value described above in a 
later-appearing method and making judgement on the basis of the result of 
the calculation. Incidentally, the register of the average calculater 10 
is constructed in such a fashion that it is reset after the average value 
of the current sector has been stored in the memory 11 and the average 
value of the next sector is determined so that the average value of the 
latest sector can be obtained. 
The alternative sequence can be realized by the configuration to store 
directly value outputted from the A/D convertor 9 in the memory 11 instead 
of the register of the average calculator 10 and to determine an average 
value by the CPU 12. 
In the same sector number m of adjacent tracks n and n+1 as shown in FIG. 
2, for example, the CPU 12 has the functions of determining the difference 
and sum of the average values V(n, m), V(n+1, m) of the maximum values of 
the reproduction signals in that sector m and then dividing the difference 
by the sum as expressed by the following formula: 
##EQU1## 
or in other words, the function as change ratio calculation means for 
calculating the change ratio between the adjacent tracks, and the function 
of quality judgement means for comparing the change ratio with a 
predetermined allowable value and judging quality of the magnetic disk 
according to whether or not a predetermined proportion or a predetermined 
number of change ratios exceeding the allowable value exist. In order to 
let the CPU 12 function as the change ratio calculation means and the 
quality judgement means, a microprogram to exhibit the function described 
above is stored in a programmable ROM, or the like, that is not shown in 
the drawing. 
Next, the function of the present apparatus will be explained with 
reference to FIG. 3 showing the operations of the present apparatus, FIG. 
4 showing the processing inside the CPU and FIG. 5 showing the waveforms 
of various signals. 
To begin with, when the disk 1 is fitted to the spindle 2 of the present 
apparatus, an inspection start instruction is outputted from the CPU 12 to 
each circuit through the bus 13. 
On receiving the inspection start instruction, the driver circuit 5 rotates 
the spindle 2 and when the spindle attains a predetermined rotation speed, 
the driver circuit 5 drives the carriage 4 so that the magnetic head 3 is 
moved to a first track (ST1 in FIG. 3) and inspection signals are recorded 
on a full circumference of the track through the magnetic head 3 by a 
record/reproduction circuit not shown in the drawing (ST2 in FIG. 3). 
Next, readout instruction of the inspection signals is outputted from the 
CPU 12 and the inspection signals recorded onto the magnetic disk 1 are 
reproduced (ST3 in FIG. 3 ). Incidentally, the reproduced inspection 
signals have an envelop such as shown in FIG. 5(a) and when the waveform 
of its portion A is enlarged, it can be understood that it is a waveform 
having variance of amplitude as shown in FIG. 5(b). 
The reproduction signals are amplified by the amplifier 7 and are inputted 
to the peak detector 8. The peak detector 8 detects a maximum value (peak 
value) included in that portion of the waveform of the reproduction 
signals shown in FIG. 5(b) that spans a sampling interval shown in FIG. 
5(c) (ST4 in FIG. 3). 
This maximum value is inputted to the A/D convertor 9 and is digitized 
there (ST5 in FIG. 3). 
The digitized maximum value is inputted to the average calculater 10, which 
adds and holds temporarily the maximum value in a register or the like, 
calculates an average value by dividing the sum of maximum values added 
and held in the register for each sector by the number of samplings in 
synchronism with a sector signal equivalent to several sampling signals 
and shown in FIG. 5(e) for the sampling signals shown in FIG. 5(d), and 
outputs its average value (ST6 in FIG. 3). 
The average value outputted from the average calculater 10 is sent to, and 
stored in, the memory 11 through the bus 13 for each sector under the 
state where it is synchronized with a sector signal by the control of the 
CPU 12 (ST7 in FIG. 3). 
After the processing described so far is completed for the first track, the 
CPU 12 detects a maximum value in synchronism with the sampling signal for 
the next track in the same way as described above, gives an instruction so 
as to calculate the average value of the maximum values for each sector 
and to store the average value in the memory 11 and executes sequentially 
the above-mentioned processing for each track (ST2-9 in FIG. 3). 
Thereafter, the CPU 12 judges whether or not average values of a sector for 
two tracks are stored in the memory 11 (ST8 in FIG. 3) and if average 
values for the two tracks are not stored in the memory ("NO" at ST8 in 
FIG. 3), the CPU 12 gives an instruction to move to the next track and to 
execute a series of processings described above (ST9 in FIG. 3). 
In contrast, if average values for the two tracks is stored in the memory 
11 ("YES" at ST8 in FIG. 3), the CPU 12 executes calculation of a change 
ratio for the radial modulation measurement and the processing of quality 
judgement in parallel with the processing described above (ST10 in FIG. 
3). 
In other words, the CPU 12 reads out an average value for each sector that 
is stored in the memory 11, determines the difference and sum of average 
values in the same sector number of the adjacent tracks and calculates the 
change ratio between the adjacent tracks for each sector from these 
difference and sum in accordance with the afore-mentioned formula (ST101 
in FIG. 4). 
The CPU 12 stores a change ratio calculated for each sector in the memory 
11, compares a change ratio as to whether or not it exceeds a 
predetermined allowable value for each sector (ST102 in FIG. 4) and stores 
also the result of comparison in the memory 11. For example, a change 
ratio is calculated and outputted as 0.5% for a first sector, 0.4% for a 
second sector, 0.3% for a third sector, and so forth between the adjacent 
tracks n and n+1, and these change ratios are compared with an allowable 
value which is set to 0.4%, for example. 
If a change ratio exceeding the allowable value is found as a result of the 
comparison ("NO" at ST102 in FIG. 4), whether or not such change ratios 
exist in not less than a predetermined proportion or in a predetermined 
number and whether the inspection is to be continued or stopped is decided 
in accordance with the result (ST103 in FIG. 4). 
In other words, if the change ratios exceeding the allowable value exists 
in not less than a predetermined proportion ("YES" at ST103 in FIG. 4), 
the magnetic disk is judged immediately to be "rejectable (disapproved)" 
(ST106 in FIG. 4) and the inspection is terminated. On the other hand, if 
the change ratio is smaller than the allowable value ("YES" at ST102 in 
FIG. 4) or if change ratio exceeding the allowable value does not 
constitute the predetermined proportion described above ("NO" at ST103 in 
FIG. 4), the procedures ranging from the calculation of a change ratio to 
the judgement are repeated sequentially for the next sector (ST101-ST104 
in FIG. 4). 
After the processings described above are completed for the final sector 
for each track ("YES" at ST104), whether or not the track is the final 
track is judged (ST105 in FIG. 4) and if the processing is not completed 
for the final track ("NO" at ST105 in FIG. 4), processing is moved to the 
next track (ST9 in FIG. 3) and the previous processing is repeated 
(ST2-ST9 in FIG. 3). 
On the other hand, when the processing is completed for the final track 
("YES" at ST105 in FIG. 4), quality of the disk is judged in accordance 
with the results of comparison that have so far been compared, stored in 
the memory and totaled (ST106 in FIG. 4). In this case, since a change 
ratio exceeding the allowable value does not exist in a proportion 
exceeding the predetermined proportion or in the number exceeding the 
predetermined number and since this inspection process is continued and 
completed for the final track the CPU 12 may judge this disk to be "good 
(approved)", but may also judge quality of the disk by processing the data 
of the change ratio stored in the memory 11 to prepare a histogram, 
displaying the histogram on a display device such as a CRT, not shown in 
the drawing, and judging the disk from its distribution. 
Accordingly, since the inspection referred to as "radial modulation 
measurement" is effected automatically without a manual operation in 
accordance with the present apparatus, it is not necessary for the 
inspector to observe the waveform of the reproduction signal on the 
oscilloscope, to determine the peak value from the waveform and to make 
operation using a personal computer, or the like. Therefore, the 
inspection time can be shortened and the trouble of inspection can be 
eliminated. 
If change ratios exceeding the allowable value exist in a proportion or 
number exceeding a predetermined proportion or number, the present 
apparatus judges the disk to be "rejectable (disapproved)" and terminates 
the inspection. Therefore, the inspection time can be further shortened. 
Incidentally, in this embodiment, the CPU compares a change ratio with an 
allowable value and when the change ratios exceeding the allowable value 
exist in not less than the predetermined proportion or in the 
predetermined number, the inspection of this disk is stopped 
automatically. In the present invention, it is possible to set the 
predetermined proportion or the predetermined number to 0% or 0, to judge 
immediately the disk to be "rejectable (disapproved)" when a change ratio 
exceeding the allowable value described above exists, and to stop the 
inspection of the disk. 
As described above, in the inspection in accordance with the present 
invention, the inspection signals are recorded and reproduced 
automatically without a manual operation onto and from the magnetic disk, 
the maximum value is detected from the reproduction signals on the basis 
of the sampling signal, the average value of the maximum value is 
calculated for each sector, the difference between the average values in 
the same sector of the adjacent tracks is determined, the change ratio 
based on this difference is calculated and quality of the magnetic disk is 
judged on the basis of this change ratio. Accordingly, it is not necessary 
for the inspector to observe the waveform of the reproduction signal on 
the oscilloscope, to determine the peak value from the waveform and to 
process the peak value by the personal computer, or the like. Therefore, 
the inspection time can be shortened and the trouble of the inspection can 
be eliminated.