JPH03186739A - Detecting circuit for damage of outside peripheral end part of magnetic disk substrate - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a circuit for detecting damage existing at the outer peripheral edge of a magnetic disk substrate.

[Prior Art] A hard magnetic disk used as a recording medium for a computer system is manufactured by using an aluminum disk as a substrate and coating the substrate with a magnetic medium. If such a magnetic disk substrate is damaged during handling such as polishing, the surface to which the medium is applied (hereinafter simply referred to as the medium surface) naturally becomes unusable, and the substrate is polished again to make it a good product.

[Problem to be solved] In -1-, when handling a magnetic disk substrate, other substrates and other substrates may be exposed to the surface and side surface of the outer peripheral edge of the substrate (hereinafter simply referred to as the outer peripheral edge), excluding the medium surface. Damage may occur due to collision with mechanical parts, etc. In the past, no particular attention was paid to damage to the outer edge of the outer periphery, as it was thought that it was not directly related to the storage medium, but recently, with the advancement of recording density and the miniaturization of magnetic heads! ! With the progress of spearing, damage to the ends has become a problem.

FIG. 3(a) shows an example of damage to the outer peripheral edge, where it is assumed that uneven damage 1b has occurred on the outer peripheral edge 1a of the magnetic disk substrate 1 for some reason. In Figure (b), when the magnetic head 2 makes a seek movement with respect to the magnetic disk substrate 1, the magnetic head 2 collides with the convex part of the damage 1b, and the magnetic head 2 is damaged or an abnormality occurs in its function. There may be problems such as To explain this point in detail, the outer peripheral edge 1a of the magnetic disk substrate is chambered at an appropriate angle, and the magnetic helad 2 passes through the outer peripheral edge 1a with almost no gearing with the surface of the substrate 1. It operates at a slight i'7 L L due to the rotation of the magnetic disk on the medium surface, so even a slight protrusion on the outer peripheral edge will cause a problem. Particularly in recent thin-film heads, the gap has become even smaller, creating a serious problem. It should be noted that if damage occurs on the side surface, it does not seem to be directly related to the seek movement of the magnetic head mentioned above, but in the event of misalignment, damage to the side surface is not limited to only the side surface, but also affects a part of the chamber at the outer edge. As a result, unevenness appears, which also impedes the seek movement of the magnetic head. It is difficult to visually inspect such damage at the outer peripheral end, and a suitable inspection device is desired.

Now, conventionally, the medium surface of a magnetic disk substrate has been inspected for defects such as scratches and attached microscopic dust using a surface inspection device, and also for concave defects that are shallow in depth relative to the area. Detection methods and equipment have also been established.

Therefore, it is efficient to use these inspection devices or detection methods to inspect the surface and detect damage to the outer peripheral edge. However, inspections for defects and dust are aimed at minute objects on the order of microns or submicrons.
Compared to this, the unevenness of the outer peripheral end portion is somewhat large, which is not appropriate. However, it is believed that detection devices for concave defects are available.

FIGS. 4(a) and 4(b) show an apparatus for detecting concave defects. In FIG. 4(a), a laser beam T is projected obliquely onto the surface of the magnetic disk substrate 1 in the direction of arrow C. Scan to. On the other hand, a pinhole plate 3 is provided in the direction of the surface emitted light of the beam T, and when the surface is the back surface, the reflected light passes through the pinhole and is received by the light receiving element 4, but there is a concave surface on the surface. When there is a defective IC, the direction of specularly reflected light changes and is blocked by the pinhole plate 3, so that the light is not received by the light receiving element. Figure (b) shows an example of the detection signal Ss obtained from the light-receiving element 4, and the part corresponding to the concave defect 1C has a low level.
-'I-shaped large defect is detected. In this case, the detection sensitivity is better as the pinhole diameter φd is smaller, but +1!
]-shaped defect IC has a rather wide area and relatively shallow depth, so the diameter φd is considered to be commensurate with this. The detection signal obtained by applying this method has a slow waveform change and has unsatisfactory detection accuracy. Therefore, it is necessary to add an appropriate circuit to obtain a waveform that changes more sharply than such a detection signal.

Furthermore, since damage to the outer peripheral edge requires different countermeasures than gate-like defects on the surface of the medium, it is also necessary to output these separately.

The present invention has been made in view of the above (1), and includes adding a necessary circuit to a concave defect detection device provided in a magnetic disk surface calibration device, and by adding a necessary circuit to a concave defect detection device to distinguish concave defects from concave defects. The purpose is to provide a method for detecting damage.

[Means for Solving the Problems] The present invention projects a laser beam obliquely onto the surface of a magnetic disk substrate, and specularly reflected light of the laser beam is transmitted through a pinhole and received by a light receiving element. , a detection circuit for detecting damage to the outer peripheral edge of a magnetic disk, which is added to a defect detection device that detects concave defects on the surface of the medium using a detection signal indicating a change in direction of specularly reflected light output from a light receiving element, A switch and a differentiation circuit are provided for inputting and differentiating the above-mentioned detection signal for the outer peripheral edge of the disk substrate, and damage to unevenness existing at the outer peripheral edge is detected by the differential signal output from the differentiating circuit.

[Function] In the outer peripheral edge damage detection circuit having the configuration I below, the detection signal of the specularly reflected light of the laser beam obtained by the conventional portal defect detection device is input to the differentiating circuit via the switch and is changed. A steep differential signal is output, and the gate convex damage at the outer peripheral edge can be detected with high accuracy using this differential signal. In this case, since the switch is connected to the outer peripheral edge, data on outer peripheral edge damage can be changed to distinguish it from concave defects.

[Example 1] Figures 1(a) and 1(b) show an embodiment in which a detection circuit for detecting damage to the outer peripheral edge of a magnetic disk according to the present invention is added to a conventional concave defect detection device. , the concave defect detection device is similar to that shown in FIG. The light passes through the hole and is received by the light receiving element 4, and a detection signal Ss is output.

Since the scanning of the laser beam T is performed in the radial direction 11 from the center of the substrate 1, the switch 5 is switched by the switching signal tQ at an appropriate position on the outer circumferential edge, and the detection signal Ss at the outer circumferential edge is sent to the differential circuit. Enter 6. Differential circuit 6
is constituted by a bypass filter, for example, and the detection signal Ss
The differential A, which has a steeper change, Sr, is extracted and output. Figure (b) shows an example of the differential bow Sr. Differential signal Sr
is input to the damage detection circuit 7, and the uneven damage 1b on the outer peripheral edge is detected using an appropriate voltage vr as a threshold value.

FIG. 2 shows the configuration of an embodiment in which the outer peripheral edge damage detection circuit shown in FIG. 1(a) is added to the conventional magnetic disk surface inspection apparatus. First, a conventional surface inspection device will be explained. A laser beam T from a light source 8a of a light projecting section 8 is focused by a focusing lens 8b and projected obliquely onto the surface of a rotating magnetic disk substrate 1 to be inspected. Scanning is performed by rotation. On the other hand, the light regularly reflected by the surface and the light scattered by defects on the surface are collected by the condensing lens 9a of the light receiving system 9 and transmitted through the half mirror 9a. The transmitted regularly reflected light is blocked by the stopper 9c, and only the scattered light is input to the photomultiplier tube 9d, and a defect signal St is output. As in FIG. 1(a), the specularly reflected light split by the half mirror 9b is transmitted through the pinhole of the pinhole plate 3 and input to the light receiving element 4, where it is converted into a detection signal Ss for a concave defect on the surface. . This signal passes through the switch 5, and together with the defect signal St written in L, the surface defect detection circuit lO
The data is inputted to the input section a, and flaws, attached foreign matter, and concave defects are detected, data is processed by the microprocessor 10b, and the data is output to the output section 10c. On the other hand, a switching signal t□ indicative of the outer peripheral edge is given to the switch 5 from the microprocessor IOb, and the detection signal Ss for this portion is input to the differentiation circuit 6 and differentiated, and the damage detection circuit 7 outputs the differentiation signal Sr as appropriate. Damage to the outer peripheral edge is detected using a suitable threshold value, and the data is processed by the microprocessor lOb and output to the output unit IOc.

[Effects of the Invention] As is clear from the explanations 1-6 below, the circuit for detecting damage to the outer peripheral edge of a magnetic disk substrate according to the present invention utilizes the fact that the direction of the laser beam emitted from the surface changes depending on the four surfaces. This device adds a switch and a differential circuit to the conventional concave defect detection device, captures the detection signal at the outer edge, creates a differential signal, and detects damage at the outer edge separately from the concave defect. When applied to a conventional magnetic disk substrate inspection apparatus, it is possible to inspect not only surface defects but also damage on the outer peripheral edge at once, and has a great effect in efficiently inspecting.

[Brief explanation of drawings]

FIGS. 1(a) and (b) are a block diagram and a differential signal waveform diagram of an embodiment of a detection circuit for detecting damage to the outer peripheral edge of a magnetic disk substrate according to the present invention, and FIG. 2 is a diagram of FIG. 1(a). A configuration diagram in which a detection circuit is added to a conventional magnetic disk inspection device.
FIGS. 3(a) and (b) are illustrations of damage to the surface and side surface of the outer peripheral edge of the magnetic disk substrate and hindrance to the seek movement of the magnetic head, and FIGS. 4(a) and (b) are FIG. 2 is an explanatory diagram of a conventional portal defect detection method and a detection signal. 1...magnetic disk) & plate, 1a...outer peripheral end, 1
b... Damage to outer peripheral end, IC...11. 'L-shaped defect, 2... Magnetic head, 3... Pinhole plate, 4... Light receiving element, 5... Switch, 6
...differentiation circuit, 7.damage detection circuit, 8.
...Light projection system, 8a...Light source, 8b...
Focusing lens, 9... Light receiving system, 9a... Condensing lens, 9b... Half mirror-9c... Stopper, 9d... Photomultiplier tube, 10a... Surface defect detection circuit, tab. ...Microprocessor, 10c...Output section.

Claims (1)

[Claims] (1) A laser beam is projected obliquely onto the surface of a magnetic disk substrate, and the specularly reflected light of the laser beam is transmitted through a pinhole and received by a light receiving element, and the above is output from the light receiving element. The detection signal for the outer peripheral edge of the magnetic disk substrate is input to a defect detection device that detects a concave defect on the medium surface of the magnetic disk substrate using a detection signal indicating a change in direction of the specularly reflected light, and the detection signal is differentiated. ,
1. A detection circuit for detecting damage to an outer peripheral edge of a magnetic disk substrate, the circuit further comprising a switch and a differentiating circuit, and detecting damage to irregularities existing at the outer peripheral edge using a differential signal output from the differentiating circuit.