JPS62228148A - Detection of surface flaw - Google Patents

Abstract

PURPOSE:To optically detect the surface flaw present on the surface of an object to be inspected with good accuracy, by detecting the flaw on the basis of the data row in the arrangement direction of scanning circles after optical scanning. CONSTITUTION:The laser beam emitted from laser beam source 1 is incident on the surface 6 of a disc 5 through a polarizing beam splitter 2 and the reflected beam R from said surface 6 passes through the splitter 2 to be received by a bright point position detector 7. The signal VD successively outputted from the detector 7 is stored in a memory 44 through a preamplifier 41, a band-pass filter (BPF) 42 and an A/D converter 43 in the form corresponding to the scanning position of the beam L on the surface 6. Therefore, beam receiving data about the scanning circle arrangement consisting a plurality of concentric scanning circles are successively stored in the memory 44. Next, these beam receiving data are read along the arrangement direction of the scanning circles from the memory 44. On the basis of this data row in the radius direction, level variation is determined as a clear changed. Therefore, the presence of a surface flaw can be detected with good accuracy in a signal processing circuit 45.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention optically detects surface defects existing on the surface of an object to be inspected that has rotational symmetry around a predetermined axis of symmetry, such as a disk or drum. The present invention relates to a surface defect detection method.

(Conventional technology and its problems) The quality of aluminum magnetic disks, optical disks, copying machine drums, etc. is greatly affected by surface defects such as minute scratches on the surface. In addition to processing the surface with extreme precision, it is necessary to detect the extent to which surface defects exist on the processed surface. Among such surface defect detection methods, a typical non-destructive method is an optical detection method, and many methods of this type have been proposed in the past.

In this case, since the object to be inspected has rotational symmetry about a predetermined axis of symmetry, for example, for the disk 60 shown in FIG. 8, the disk 60 is rotated in the α direction about the axis of symmetry P. By doing so, while optically scanning the surface with the laser beam L, the reflected light R is received.
Obtain light reception data for scanning circle C. Next, the disk is translated in the X direction shown in the figure to perform scanning along another concentric scanning circle C', and by repeating this process, light reception data for the entire surface of the disk is acquired.

Using these received light data, a continuous received light data string is formed in the input order, that is, along the circumferential direction of the scanning circle C, and surface defects are detected based on the level fluctuation state of this received light data string.

However, an object to be inspected with such rotational symmetry is
Even during surface processing, processing is performed along the circumferential direction around the axis of symmetry (for example, diamond turning), so only very gradual changes in shape occur in the circumferential direction, and there is no possibility of shape changes or surface defects. Generation occurs primarily along the radial direction. For this reason, there is a problem in that the method of performing detection processing based on the received light data sequence along the circumferential direction of the scanning circle C as described above cannot accurately detect surface defects.

(Object of the Invention) The present invention is intended to overcome the above-mentioned problems in the prior art. It is an object of the present invention to provide a surface defect detection method that can optically accurately detect surface defects existing on the surface of an object to be inspected.

(Means for Achieving the Object) In order to achieve the above-mentioned object, the present invention first irradiates the surface of the object to be inspected with rotational symmetry with a light beam while moving the object to be inspected around its axis of symmetry. The surface of the object to be inspected is optically scanned along a scanning circle around the axis of symmetry by rotating the object to be inspected, and the light reception data obtained by receiving the reflected light from the surface of the object to be inspected is stored in correspondence with the scanning position. By sequentially repeating the process of storing data in the object while relatively translating the light beam and the object to be inspected, a plurality of scanning circles (a plurality of concentric circles in the case of a disk) on the surface of the object to be inspected can be scanned. Each light reception data is stored in the storage means.

Then, the light reception data is read out from the storage means along the arrangement direction of the plurality of scanning circles (for example, the radial direction in the case of a disk) to obtain a light reception data string for the arrangement direction, and based on this light reception data string, Detecting the surface defects.

(Example) A. Purpose of Implementation - Figure 1 is a schematic diagram of an apparatus used in a surface defect detection method which is an embodiment of the present invention. The configuration of this device is an optical system,
It is broadly divided into a scanning mechanism and a signal processing system, and among these, various conventional methods can be adopted as appropriate for the optical system.
In this embodiment, a novel photodetection principle is adopted in order to perform detection with higher precision. Therefore, in the following, the configuration and operation of the optical system will be explained first with reference to FIG. 1.

In the figure, a laser beam L emitted from a laser light source 1 becomes linearly polarized light by a polarizing beam splitter 2, passes through a 174-wave plate 3 and a focusing lens 4 with a focal length f, and exits from this lens 4 with a focal length f. The light is incident on the surface 6 of a disk 5 as an object to be inspected at a certain position. Here, this surface 6 is a surface processed along the circumferential direction around the symmetry axis P of this disk 5. Then, reflected light (reflected beam) R obtained by reflecting this laser beam L on the disk surface 6 passes through the lens 4 and the quarter-wave plate 3 again and enters the polarizing beam splitter 2 again.

Since the reflected light R at this point has passed through the 174-wave plate 3 twice, its polarization direction has been rotated by 90° with respect to the irradiated laser beam L. therefore,
The reflected light R passes through the polarizing beam splitter 2 as it is and is received by the light receiving surface 8 of the bright spot position detector 7.

By the way, in this case, the disk surface 6 is flat,
There are no defects or irregularities, and the disk surface 6 is a plane perpendicular to the direction of incidence of the laser beam L (hereinafter referred to as the "reference plane").
, the reflected light R is reflected in the same direction as the incident direction of the laser beam L, and passes through the polarizing beam splitter 2 after traveling in the opposite direction along the incident path of the laser beam L.
pass through. As shown in FIG. 2, which is a partial diagram of FIG. 1, the reflected light R8 is reflected by x on the light receiving surface 8 of the bright spot position detector 7. The light enters the reference position shown as a bright spot.

On the other hand, as shown in FIG.
2 and the reference surface 6a is θ, the reflected light R is reflected at a deflection angle of 2θ with respect to the incident laser beam. Then, the reflected light R after passing through the lens 4 becomes parallel to the incident laser beam, but there is a polarization of Δx=f-jan(2θ) ・(1) with respect to the incident laser beam. It is causing the rank. Therefore, in this case, the reference position X on the light receiving surface 8. The reflected light R will be incident at a position deviated by ΔX from . Therefore, by detecting this ΔX, it becomes possible to obtain the inclination angle θ from equation (1). In addition, since the inclination angle θ is minute in the case of minute bites or undulations on a precision machined surface, the approximate expression for the above equation (1) is Δx#f・2θ ・・
- (2) can be used.

In this way, the amount of deviation ΔX is determined by the inclination angle θ of the bite defect 21, etc.
Since the amount reflects the amount of deviation ΔX, it is possible to determine the surface condition of the disk surface 6 based on this amount of deviation ΔX. At this time, in order to detect minute changes in the amount of deviation ΔX as precisely as possible, the bright spot position detector 7 is
It is desirable to use a light-receiving surface whose light-receiving surface 8 is a continuous light-receiving surface.

Therefore, in this embodiment, a sensor known as a semiconductor device detector (hereinafter referred to as PSD) is used as the bright spot position detector 7. FIG. 3(a) shows the light-receiving surface 8 of the bright spot position detector 7 constructed using one-dimensional PSD among such PSDs.
By taking the ratio of the photocurrent values taken out from each of b, a signal corresponding to the deviation amount ΔX of the received bright spot SP is obtained.Signal level ■ in FIG. Bind and output. In this operation, since the light-receiving surface 8 is not a collection of discrete elements but has a continuous spread, the light-receiving position can be detected with high precision.

B. One Scan in Example J and J Next, the scanning mechanism in this example will be explained.

In this embodiment, when optically scanning the disk surface 6, the disk 5 is moved by the disk moving AM mechanism 30 shown in FIG. 1, and the optical system is kept fixed. In this disk moving mechanism 30, a motor 33 is provided on a base 31, and a feed screw 35 extending from the motor 33 allows
The slide table 32 provided on the base 31 is
The disk 5 is translated in a horizontal direction perpendicular to the circumferential direction (X direction in the figure). This motor 3
3 is provided with an encoder 34 that detects its rotation angle.

Further, a motor 37 to which another encoder 36 is attached is fixed on this slide table 32, and a disk holder (
(not shown) holds the disk 5 horizontally. The motor 37 rotates the disk 5 in the α direction in the figure.

Therefore, for example, by driving the motor 37, the disk 5
If the other motor 33 is rotated by a predetermined angle each time the motor 33 rotates 360 degrees, the laser beam L will be directed to the disk surface 6.
will be scanned concentrically. Moreover, if the two motors 33, 37 are rotated simultaneously, the disk surface 6 will be scanned in a spiral manner. In this embodiment, it is assumed that the former is the case.

Signal Processing in Embodiment C1 Next, while performing such scanning, signals V are output one after another from the bright spot position detector 7 in Figure @1.

The processing will be explained. This signal V. is amplified by a preamplifier 41 in FIG. 1, and then provided to an A/D converter 43 via a bandpass filter 42.

The signal obtained in this way is transmitted to the A/D converter 43.
After being A/D converted and numbered at predetermined intervals of rR11, it is stored in the memory 44.

For this storage, encode signals from encoders 34 and 36 are applied to address generator 47, and address generator 47 specifies a write address according to these encode signals. Therefore, in the memory 44,
The received light data is stored in a U-shape corresponding to the scanning position of the laser beam L on the disk surface 6.

These processes are sequentially repeated while the disk 5 is translated, and therefore, the light reception data regarding the scanning circle array consisting of a plurality of concentric scanning circles is sequentially stored in the memory 44.

Figure 4 shows the received light data stored in this way.
It is a diagram shown in input order (that is, scanning order). Therefore, the horizontal axis indicates the rotation angle α of the disk detected by the encoder 36.

In addition, (a) to (e) of the same figure respectively show (N-1) of the concentric scanning concentric circles on the disk surface 6 shown in FIG.
)th scanning circle CN-1 to (N+3)th scanning circle C
It shows the fluctuation of the light reception level up to N+3. As can be seen from this figure, the level fluctuation of the received light data on the same scanning circle is quite small.

In this way, when the capture and storage of the light reception data for the entire disk surface 6 is completed, next, the memory 4
4, the above-mentioned light reception data is transferred to the scanning circle (..., C, C,...
..., CN+3...) along the arrangement direction N-IN, that is, along the radial direction of the disk 5.

This operation is performed from the address generator 47 to sampling points aN-1°aN, . . . along the direction in FIG.
This is achieved by sequentially generating storage addresses of .

FIG. 6 shows the sampling points aN-1 and aN.

... is the angle line α in Figure 4. If it is above,
FIG. 6 is a diagram showing a radial data string read out by the method described above. As can be seen by comparing Figures 5 and 6, level fluctuations are quite clear in the data array in the radial direction (Figure 6), unlike the data array in the circumferential direction of the scanning circle (Figure 5). This is seen as a significant change.

Therefore, in the signal processing circuit 45 of FIG. 1, the signal based on the data string of FIG. 6 is compared and
By performing this discrimination, the presence of surface defects such as scratches can be detected. This detection result is output to a desired output device 46 such as a display device or a recording device to be displayed or recorded.

Such readout and signal processing are performed in each radial direction of the disk surface 6, but the position where a defect exists can also be outputted if necessary.

(Modifications) Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and for example, the following modifications are possible.

■ In the above embodiment, a disk was considered as the object to be inspected, but in the case of a drum 49 as shown in FIG. 7(a), the scanning circle on the drum 49 is The received light data is stored while optically scanning along the axis of symmetry P, and this operation is repeated by performing translation in the Y direction along the axis of symmetry P. Then, the received light data is read out along the direction Y, and
A data string regarding the direction is obtained and defect detection is performed based on this.

The same applies to the object to be inspected 50 having a conical surface as shown in FIG. The reading is performed along the following lines.

Therefore, what these methods have in common is that a data string is obtained by reading received light data along the direction in which the scanning circles are arranged.

(2) In the above embodiment, a light receiving system using a PSD is used, but any conventional technique for detecting the intensity of specularly reflected light or scattered light may be used as the light receiving system.

Furthermore, even when using a PSD, as shown in Fig. 3(b), a set of electrodes (X, Xb), (Y, Y
,) using a two-dimensional PSD with a and the respective outputs v and v (V, "b"
) a b +V may be determined and used as the received light data.

Furthermore, since the object to be inspected and the light beam need only be translated relatively, the object to be inspected may not be translated, but the optical beam may be translated.

As mentioned above, if the object to be inspected is rotated and translated at the same time, scanning will be performed not in a perfect circle but in a spiral. Think of it as scanning along the .

Therefore, in such a case, one rotation of the spiral is treated as a scanning circle, and detection is performed based on a data string in the arrangement direction of the scanning circle.

(Effects of the Invention) As explained above, according to the present invention, since defect detection is performed based on a data string regarding the arrangement direction of scanning circles in which optical scanning is performed, data regarding the direction in which defects are likely to occur is obtained. Therefore, it is possible to obtain a surface defect detection method that can optically and accurately detect surface defects present on the surface of an object to be inspected that has rotational symmetry.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a device used in an embodiment of the present invention, FIG. 2 is a partial diagram of FIG. 1, FIG. 3 is a diagram showing the light receiving surface of the PSD, and FIG. FIG. 5 is a diagram showing the variation of received light data in the circumferential direction. FIG. 5 is a diagram showing the relationship between the scanning circle and data read in the disk radial direction. FIG. FIG. 7 is an explanatory diagram of processing for an object to be inspected having a shape other than a disk, and FIG. 8 is a diagram illustrating a general scanning method for detecting surface defects of a disk. 1... Laser light source, 5... Disk, 7...
Bright spot position detector, 30...disk transfer! 1llll! a
Structure, 33.37...Motor, 34.36...Encoder, 44...Memory, 47...Address generator, L...Laser beam, R...Reflected light Figure 3, Figure 2 Figure 5 Figure 4 Figure 1 --Sid OO Figure 6

Claims (1)

[Claims] (1) A method for optically detecting a surface defect present on a surface of an object to be inspected that has rotational symmetry about a predetermined axis of symmetry and is machined along a circumferential direction about the axis of symmetry. , a process of optically scanning the surface of the object to be inspected along a scanning circle around the axis of symmetry by rotating the object to be inspected about the axis of symmetry while irradiating the surface of the object to be inspected with a light beam; , a process of storing light reception data obtained by receiving reflected light from the surface of the object to be inspected in a storage means while corresponding to a scanning position, by relatively translating the light beam and the object to be inspected. By sequentially repeating the above, each light reception data for a plurality of scanning circles on the surface of the object to be inspected is stored in the storage means, and the light reception data is stored from the storage means along the arrangement direction of the plurality of scanning circles. 1. A surface defect detection method, comprising: reading out data to obtain a light reception data string for the arrangement direction, and detecting the surface defect based on the light reception data string.