JPS61274204A - Method for detecting magnetic disk surface roughness - Google Patents

Abstract

PURPOSE:To improve inspection efficiency by making use of the fact that irregularities on magnetic disks are prone to occur on concentric cylinders, and by detecting surface irregularities using the changes in the average read output for each track. CONSTITUTION:A 1MHz magnetizing inversion signal is written on all the tracks of magnetic disk 10 by write circuit 7 through switching circuit 8 and magnetic head 9. Read circuit 11 rotates the disk 10 at a speed of 3,600rpm and drives magnetic head 9 in steps over each track by control circuit 12, which determines positioning of the head, and stepping motor 3. Magnetic head 9 switches to read circuit 11 and measures the average read output for each track through circuit 8. No.1 storage unit 14 stores the variation characteristics of the average read output in the radial direction for each track of the magnetic disk. The output from smoothing circuit 15 is stored in No.2 storage unit 16 to serve as the reference characteristic. The quality of the surface finish of the magnetic disk is judged by calculation circuit 17 through the comparison made by comparison circuit 18 of the reference characteristic with the variation characteristic stored in unit 14, which is then compared with a preset permissible limit value.

Description

[Detailed Description of the Invention] [Summary] A method for inspecting the surface roughness of a magnetic disk, which is carried out as part of the inspection of a magnetic disk. This enables non-destructive testing and improves testing efficiency.

[Industrial application field]

The present invention relates to a magnetic disk surface roughness inspection method.

A magnetic disk is, for example, a light alloy disk on which a magnetic recording film of magnetic iron oxide powder or the like is formed by a method such as spin coating.

Light alloy discs are usually finished by precision grinding, and after cleaning, a magnetic recording film is coated to a thickness of about 1 micron and finished by roughing.

However, on the surface of a precision-ground light alloy disc, very fine concentric grinding marks remain.

Even if the unevenness is less than the allowable value, when a magnetic recording film is applied thereto, the unevenness increases, and even after finishing the lapping, the unevenness exceeding the allowable value may remain in the form of concentric circles.

Therefore, the surface roughness is inspected prior to incorporation into a magnetic disk drive, and it is desirable that this inspection be performed reliably and efficiently.

[Conventional technology]

Conventionally, a method using a stylus tester has been used to test the surface roughness of magnetic disks.

[Problem that the invention seeks to solve]

In the above conventional example, the surface of the magnetic disk is traced using a sensitive stylus, which not only takes a long time and is inefficient, but also damages the surface of the magnetic film with the stylus. Destructive inspection will have to be done.

Therefore, there is a problem that 100% inspection is not possible.
An object of the present invention is to propose a method for inspecting the surface roughness of a magnetic disk, which not only increases inspection efficiency but also enables 100% inspection.

[Means for solving problems]

FIG. 1 is a diagram showing the principle of the present invention.

1 is a writing process in which a magnetization reversal signal of a constant period is written to all tracks of a magnetic disk.

2 is a measuring step for measuring the average read output for each track of the magnetic disk to which the magnetization reversal signal has been written in writing step 1;

3 is a change characteristic generation step for generating a change characteristic of the average read output for each track in the magnetic disk radial direction.

4 is a smoothing step for generating a reference characteristic by smoothing the change characteristic generated in the change characteristic generation step 3;

5 is a quality determination step in which the quality of the surface roughness of the magnetic disk is determined by comparing the change characteristics with a preset allowable limit.

[Effect]

The present invention focuses on the fact that, as described above, the unevenness of a magnetic disk tends to occur concentrically, and detects the unevenness based on the change in the average read output for each trunk.

FIG. 2 is a diagram showing an example of the change characteristics of the average readout output obtained in measurement step 2, and the vertical axis is the readout output (mV
pρ), and the horizontal axis is the radius (mm) of the magnetic disk.

In the illustrated example, singular points such as ■, ■, and ■ can be seen, but as a result of measurement using the conventional method, irregularities of 0.2 to 0.3 microns in the radial direction were confirmed in these parts. .

〔Example〕

FIG. 3 is a configuration diagram of the embodiment.

Reference numeral 7 denotes a write circuit used in the write process 1, and the write circuit 7 is used to write data through a switching circuit 8 and a magnetic heald 9.

A 1 MHz magnetization reversal signal is written to all trunks of the magnetic disk 10.

Reference numeral 11 denotes a reading circuit used in the measurement step 2, which rotates the magnetic disk 10 at 3,600 revolutions per minute, and tracks the magnetic helad 9 by a control circuit 12 for magnetic head positioning control and a stamping motor 13. The magnetic head 9 and switching circuit 8 measure the average readout output for each reading.

Reference numeral 14 denotes a first storage section used in the change characteristics generation step 3, which stores the change characteristics of the average read output for each track obtained by the reading circuit 11 in the magnetic disk radial direction.

15 is a smoothing circuit used in the smoothing step 4, and its output is stored in the second storage section 16 as a reference characteristic.

17 sets an upper limit reference characteristic by adding a voltage corresponding to a preset allowable limit using the reference characteristic stored in the second storage unit 16 as a reference.

Further, a lower limit reference characteristic is set by regular subtraction, and the set upper and lower limit reference characteristics are stored in the second storage unit 16.

Reference numeral 18 denotes a verification circuit used in the pass/fail judgment process, which compares the change characteristics stored in the first storage section 14 with the upper and lower limit reference characteristics stored in the second storage section 16 to determine the surface roughness of the magnetic disk. Determine whether the quality is good or bad.

That is, as shown in FIG. 4, the variation characteristic A is generated in the variation characteristic generation step 3, the reference characteristic B is obtained in the smoothing step 4, and the upper limit C and lower limit of the allowable limit are obtained from the reference characteristic B. .

Then, in the pass/fail judgment step 5, the variation characteristic A is compared with the upper limit C and the lower limit of the allowable limit, and the variation characteristic A is compared with the upper limit C and the lower limit of the allowable limit.
Alternatively, a portion exceeding the lower limit (hunting portion) is detected, and whether or not the magnetic disk 10 is uneven is determined based on its presence or absence.

In the configuration shown in FIG. 3, the write circuit 7, switching circuit 8, magnetic head 9, read circuit 11, control circuit 12, stepping motor 13, etc. can all be the same components of the magnetic disk device as they are.

〔Effect of the invention〕

As explained above, according to the second aspect of the present invention, since a destructive test is not required, a 100% test is possible, and the test can be performed in a shorter time than in the conventional example.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the principle of the present invention. FIG. 2 is an explanatory diagram of the action. FIG. 3 is a configuration diagram of the embodiment. FIG. 4 is an explanatory diagram of the embodiment. In the figure. 1 is the writing process, 2 is the measurement process. 3 is a change characteristic generation process, and 4 is a smoothing process. 5 is a pass/fail judgment process, and 7 is a write circuit. 9 is a magnetic head, 10 is a magnetic disk. 11 is a reading circuit, and 15 is a smoothing circuit.

Claims (1)

[Claims] Write a magnetization reversal signal of a constant period on all tracks of a magnetic disk (1), measure the average read output for each track of the magnetic disk to which the magnetization reversal signal is written (2), Generating (3) a variation characteristic of the average read output for each track in the magnetic disk radial direction, smoothing (4) the generated variation characteristic to generate a reference characteristic, and subjecting the variation characteristic to a preset tolerance. Determine the quality of the surface roughness of the magnetic disk by comparing it with the limit (5
) A magnetic disk surface roughness inspection method characterized by: