JPS5924202A - Surface defect detector - Google Patents

Abstract

PURPOSE:To enable the use of the scan width entirely for a detection line with an accurate address setting having a simple structure by arranging a light scanning means comprising an oscillation mirror and a lens for obtaining a parallel light while a position sensor is used to correct frequency in the output of a light receiving element. CONSTITUTION:A circuit comprises an A/D convertor 8, an address signal generator 9, binary coding circuit 10 and a data processing circuit 11. A spot light not of equal velocity but subjected to a scanning by a sine wave is received with a position sensor 6 and a voltage is outputted corresponding to the scanning. The voltage is converted to digital from analog and divided into 0-255 levels, for example, when an 8 bit A/D converter 8 to binary coding a signal from a photo diode 7. When a representative detection signal is provided with this address data, it is divided into 256 where it is 8 bit at an even distance with respect to the entire scan width. The address division ratio is determined by the number of bit the A/D converter 8 has.

Description

[Detailed description of the invention] The present invention relates to a surface defect detection device.

Conventionally, as a method for detecting defects in sheet-like objects, a method has been adopted in which defects are detected by scanning focused light into a spot and photoelectrically converting the reflected light and transmitted light. In order to process this data with high precision, it is necessary to scan the light at a constant speed and set scan line addresses in time divisions. There are two methods for doing this: 1. A method in which a polygon is scanned at a constant speed, and 2. A method in which a vibrating mirror is used to perform a constant speed scan. The method (3) of scanning polygons at a constant speed consists of polygons and Fθ lenses or FO mirrors, which allows for easy uniform speed scanning, making it easy to determine the addresses for dividing lines.
It is complex, requiring optical precision, and is also very expensive. ■The method of constant speed scanning with a vibrating mirror requires s1 to increase the scanning speed due to the responsiveness of the vibrating mirror, etc.
It becomes a Hals vibration. However, as shown in FIG. 1, there is a limit to the scan width l that can actually be used with sine waves.

That is, since approximately half the width of the hole yang has a speed close to a constant velocity to some extent, this portion is used for detection. .

Therefore, an object of the present invention is to provide a surface defect detection device that allows accurate address setting with a simple configuration, does not affect the responsiveness of a vibrating mirror or fluctuations in scan speed, and can use the entire scan width as a detection line. That's true.

An embodiment of this invention is shown in FIGS. 2 to 4. That is, this surface defect detection device consists of a laser 1, a oscillating mirror 2 that linearly scans the ray 'k from the laser 1 using a sine wave drive, and a ray scanned by the oscillating mirror 2. Fθ lens 3 that makes parallel light
A half mirror 5 divides the parallel light emitted from the Fθ lens 3 into two and irradiates the transmitted light onto the measured object 4, and a position sensor 6 detects the reflected light from the Fθ lens 3 of the half mirror 5. 1. A photodiode 7 serving as a light-receiving element that receives the reflected light from the object to be measured 4 of the transmitted light through reflection by a half mirror 5; and a correction circuit. This circuit is the third
As shown in the figure, it has an A/D converter 8, an address signal generator 9, a binarization circuit 10, and a data processing circuit 11.

Because of this configuration, the spot light being scanned at a constant velocity (sin wave) is received by the position sensor 6, and a voltage corresponding to the scanning location is output.This voltage Th A/D By converting, for example, an 8-bit A/D converter 8 is divided into 255 steps from 0 (Fig. 4).
The signal from the photodiode 7 is binarized and processed.

By providing this address data to the representative detection signal, it is divided into 256 in the case of 8 bits with equal path deviation for the entire scan width. The address division ratio is A/
It is determined by the bit number of the D converter 8. In this way, the shortcomings of the vibrating mirror 2, such as response delay and speed variations depending on the position of the sine wave scan, can be avoided.
Since the use of the position sensor 6 makes it easy to set an accurate address, this problem is no longer a problem. In this way, accurate address setting is possible with a simple configuration, and the response of the vibrating mirror 2 and fluctuations in scan speed are not affected, and the entire scan width can be used as a detection line.

5 and 6 show modified examples of the circuit for correcting the output cuff of the photodiode shown in FIG. 2 using the output of the position sensor 6. In FIG. In Fig. 5, 8' is an A/D converter;
9' is an address signal generator, 12 is an amplifier, 13 is a voltage variable bypass filter, 10' is a binarization circuit, 11'
1 is a data processing circuit, 14 is a differentiation circuit, and 15 is an absolute value circuit.

The operation will be explained. The output from the position sensor 6 is A/D converted to be used as an address signal, and the position sensor output signal of vp8inθ is differentiated to v,
, and one that converts to a velocity of cos θ.

Then, the voltage converted to the scan speed is input to the absolute value circuit 15 and converted into a signal as shown in FIG. 6(8). An optical signal reflected from the object to be measured 4 is converted into electricity by a photodiode 7 and amplified by an amplifier 12. The amplified signal is sent to a bypass filter 13 whose cutoff frequency is changed by an external voltage (5). The bypass filter 13 receives the signal shown in FIG. 6(B) and changes its cutoff frequency to f as shown in FIG. 6(C).
omin to f. Variable up to max. In the output signal from the photodiode 7, the frequency component of the raw signal changes depending on the scan speed depending on the location of the defect even if it is the same defect, whereas the constant of the bypass filter 13 is set to the scan speed. By changing them together, there will be no difference in detection depending on location. The rest is the same as the first embodiment.

As described above, the surface defect detection device of the present invention has a light scanning means made up of a vibrating mirror and a lens for obtaining parallel light beams, and uses a position sensor e to correct the frequency of the output of the light receiving element. This has the advantage of allowing accurate address setting with a simple configuration, without affecting the response of the vibrating mirror or fluctuations in scan speed, and allowing the entire scan width to be used as a detection line.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the conventional sine wave drive problem, (6
) FIG. 2 is a perspective view of one embodiment of the present invention, FIG. 3 is a circuit block diagram thereof, FIG. 4 is an explanatory diagram of its operation, FIG. 5 is a circuit block diagram of another embodiment, and FIG. 6 (A) ~ (F)
is an explanatory diagram of its operation. 1...Laser, 2...Vibration mirror, 3...Fθ lens, 4...M measurement object, 6...Position sensor,
7... Photodiode (light receiving element), 8.8'...
・A/D converter, 9...address signal generator, 1
0.10'... Binarization circuit, 11, 11'... Data processing circuit (7)

Claims (1)

[Claims] A laser, a vibrating mirror that is driven by a sine wave and linearly scans the light beam from the laser within a certain angle range, a lens that converts the light beam scanned by the vibrating mirror into parallel light, and the parallel light emitted from this lens. a half mirror that divides the transmitted light into two and irradiates the measured object with transmitted light; a position sensor that detects the reflected light from the lens of the half mirror; and a position sensor that detects the reflected light of the transmitted light from the measured object. A surface defect detection device comprising: a light receiving element that receives light through reflection by a light receiving element; and a circuit that corrects the frequency of the detection output of the light receiving element using the output from the position sensor.