JPS62195511A - Magnetic disk defect detecting device - Google Patents

Abstract

PURPOSE:To detect whether or not there is a flaw in a magnetic disk surface in a short time by providing an optical head made of a light transmissive material on a magnetic disk and detecting variation in the intensity of interference light between the surfaces of the optical head and magnetic disk. CONSTITUTION:Projection light 9 from a laser light source 1 is reflected by a beam splitter 2 and converged on the surface 8a of the magnetic disk 8 by a lens 3 through the optical head 4 made of the light transmissive material. The light incident on the head 4 is reflected by the top surface 4a and reverse surface 4b of the head 4 and the disk top surface 8a and the reflected light becomes multiple interference light 10, which is converged on a photoelectric converter 7 through a lens 6. When the disk 8 is rotated and the head 4 is moved radially, the multiple interference varies in light intensity in the presence of even a slight flaw in the surface of the disk 8 and the variation is detected in the form of the electric output of the converter 7. Consequently, whether the disk has a flaw or not is judged in a short time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an apparatus for detecting defects such as scratches and dust on the surface of a magnetic disk that performs magnetic recording and reproduction.

[Conventional technology]

Conventionally, the defects have been detected using equipment and procedures that are substantially the same as those used in actual use. That is, the magnetic disk to be detected is set in a known defect detection device 1 having magnetic recording and reproducing capabilities (hereinafter this device will be referred to as a US-based device), and the magnetic disk of the US-based device is first used to perform recording and reproducing. playback,
By monitoring the strength of the electrical signal during playback, we determined whether the surface had defects such as scratches due to force. If there is a scratch, the signal will not be recorded properly, and the strength of the electrical signal will drop rapidly at that location, resulting in so-called dropout.

Next, the recorded portion is erased, further reproduction is performed, and the electrical signal output is monitored. In areas where there are scratches on the surface and are not erased properly, the previously recorded state remains, so the electrical signal output suddenly drops, resulting in a so-called drop-in.

In this way, the U.S.-based equipment detects defects such as falsification and dust on the magnetic disk surface by measuring dropout and dropin. Such operations are performed over the entire surface of the magnetic disk to be detected, and it is inevitable that it takes time to judge the presence or absence of scratches due to recording, reproduction, erasure, and reproduction for each portion.

[Problem that the invention seeks to solve]

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic disk defect detection device f that solves the drawback of conventional disc devices that it takes time to detect scratches on the surface of a magnetic disk.

[Means to solve the problem]

In order to achieve this objective, the present invention utilizes the original microgap measuring device m of Japanese Patent Application No. 59-233067, which was previously proposed by the inventor of the present invention. I will give an overview of the basics of the device. Figure 3 is an explanatory diagram of its principle. 1 is a laser light source, 2 is a beam splitter, 3 is a lens, 4 is an optical head made of a transparent material, 7 is a photoelectric converter, 5 is an object to be measured, and I is This is the minute gap you want to measure. The yri diagram is an exaggeration, but in reality it can be achieved by about 0.1 to 1 μm. Coherent light emitted from a laser light source 1 is reflected by a beam splitter 2, and is focused by a lens 3 onto a surface to be measured 5a of an object to be measured 5 through a translucent optical head 4.

The light incident on the optical head 4 is the upper surface 4 of the optical head 4.
The light is reflected by three surfaces: a, the lower surface 4b, and the surface to be measured 5a of the object to be measured 5, and is focused on the photoelectric converter 7 by the lens 6. When the object to be measured changes and the minute gap I to be measured changes, the light intensity due to the multiple interference of the reflected light L2 changes, and this change is taken into consideration for a magneto-optical disk.

That is, in the present invention, an optical head made of a translucent material is arranged on a magnetic disk to be detected, and coherent light is incident from above the optical head, and three surfaces of the optical head, the upper surface, the lower surface, and the surface to be detected, are illuminated. The change in the intensity of the multiple interference light reflected by the sensor is now detected.

With this configuration, when we measure the intensity change of the interference light by moving the optical head along the diameter of the magnetic disk while rotating the magnetic disk within its plane, we find that if there are slight scratches on the surface of the magnetic disk. However, the intensity of the interference light changes rapidly, and we were able to quickly identify defects in the magnetic surface that cause drop-outs and drop-ins.

(X Example) Figure 1 shows an example of the present invention.The incident light 9 from the laser light source 1 is reflected by the beam splitter 2, and the surface of the magnetic disk 8, which is the object to be detected, is reflected by the lens 3. The light enters from the optical head 41m so as to be focused on point 8a.The spit diameter is about 100μ.The optical head is made of a translucent optical material, and its size is 6m long and 4cm thick. 2B was used.This was applied to the magnetic disk to be measured at 16 to 20
I pressed it down with a gram weight. After this configuration, while rotating the magnetic disk at 30 or-p-m within its plane (the rotating means is not shown), the optical head is rotated along the diameter of the magnetic disk at a angle of 100 μm in one rotation time of the magnetic disk. Moved by pitch. (Moving means not shown) The incident light beam 9 is reflected by the upper and lower surfaces 4a, 4b of the optical head and the magnetic disk surface 8a as shown in FIG.
9b and 9c become multiple interference light 10. When this change in intensity was measured using a photoelectric converter, it was found that even when there was a slight scratch on the surface of the magnetic disk, which was the object to be detected, there was a large change, and it was possible to determine the presence or absence of a scratch on the disk surface.

[Invention-Imraku effect]

As explained above, the present invention has a configuration in which an optical head made of a light-transmitting material is arranged on a magnetic disk, and a change in the intensity of interference light between the surfaces of the optical head and the magnetic disk is detected.
It has the feature of being able to detect the presence or absence of scratches on the surface of a magnetic disk in a short time.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention. FIG. 2 is a diagram showing the state of light reflection on the optical head and the magnetic disk surface in the present invention. FIG. 3 is a diagram explaining the principle of the micro gap measuring device. 1...Laser light disappears 3.6...Lens 4...
・Optical head 7...Photoelectric converter 8...Magnetic disk Figure 1 Figure 2

Claims (1)

[Claims] (1) In a device that detects defects such as scratches and dust on the surface of a magnetic disk that performs magnetic recording and reproduction, an optical head made of a transparent material placed on the magnetic disk that is the object to be detected; means for projecting coherent light over the entire detected surface of the detected object through the optical head; and a means for projecting coherent light from the upper and lower surfaces of the optical head and the surface of the magnetic disk that is the detected surface; 1. A magnetic disk defect detection device comprising: means for measuring the intensity of light due to multiple interference and detecting defects on the surface of the magnetic disk from changes in the intensity of the measurement light depending on the position of the detection surface.