JPS6338083B2 - - Google Patents

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 to 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 a time-divided manner. There are two ways to do this: one is to scan at a constant velocity using a polygon, and the other is to scan at a constant velocity using a vibrating mirror. The method of performing constant-velocity scanning with polygons is simple by configuring polygons and Fθ lenses or Fθ mirrors, which makes it easy to determine the addresses for dividing lines, but optical accuracy is limited. are complex and very expensive. In the method of constant velocity scanning using a vibrating mirror, sin pulse vibration is used to increase the scan speed due to the responsiveness of the vibrating mirror. 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 of the scan width has a speed close to 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 response of the vibrating mirror or variations in scan speed, and can use the entire scan width as a detection line. It is to provide.

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 vibrating mirror 2 that is driven by a sine wave and linearly scans the beam from the laser 1 within a certain angle θ, and a vibrating mirror 2 that scans the beam scanned by the vibrating mirror 2. Fθ lens 3 for parallel light and this Fθ lens 3
a half mirror 5 that divides the parallel light emitted from the
a position sensor 6 that detects the reflected light from the Fθ lens 3; a photodiode 7 that serves as a light receiving element that receives the reflected light from the object to be measured 4 of the transmitted light through reflection by the half mirror 5; A circuit for correcting the frequency of the detection output of the photodiode 7 using the output from the position sensor 6 is provided. This circuit is shown in FIG. In the figure, 8' is an A/D converter, 9' is an address signal generator, 12 is an amplifier, 13 is a voltage variable high-pass filter, 10' is a binarization circuit, 11' is a data processing circuit, and 14 is a differential circuit. The circuit 15 is an absolute value circuit.

The operation will be explained. The spot light that is scanned not at a constant velocity but at a sine wave is received by the position sensor 6 and outputs a voltage corresponding to the scanning location. By A/D converting this voltage, for example, in the case of an 8-bit A/D converter, the voltage is divided into 255 steps from 0. The signal from the photodiode 7 is then binarized and processed. By providing this address signal to its representative detection signal, it is divided by 256 in the case of 8 bits at equal distances over the entire scan width. The address division ratio is determined by the number of bits of the A/D converter 8'. The output of the photodiode 7 is corrected by the scan speed before being binarized. That is, the output from the position sensor 6 is A/D converted and used as an address signal, and the output from the position sensor 6 is differentiated to convert the position sensor output signal of V _p sin θ to a velocity of V _p cos θ. Then, the voltage converted to the scan speed is inputted into the absolute value circuit 15, and the
Convert to the signal shown in . An optical signal reflected from the object to be measured 4 is converted into an electrical signal by a photodiode 7 and amplified by an amplifier 12. The amplified signal is sent to a high-pass filter 13 whose cutoff frequency is changed by an external voltage. high pass filter 1
3, in response to the signal shown in FIG. 4B, the cutoff frequency varies from f _c min to f _c max as shown in FIG. 4 c. In the output signal from the photodiode 7, the frequency component of the raw signal varies depending on the scan speed even if the defect is the same, depending on the location of the defect, whereas the constant of the high-pass filter 13 is set to the scan speed. By changing them together, there will be no difference in detection depending on location.
In this way, the shortcomings of the vibrating mirror 2, such as response delay and speed variations due to position due to sine wave scanning, can be avoided by using the position sensor 6 to set accurate addresses and by adjusting the photo speed according to the scanning speed. By correcting the output of diode 7, this became 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.

As described above, the surface defect detection device of the present invention creates a light scanning means using a vibrating mirror and a lens for obtaining parallel light beams, and uses a position sensor to correct the output of the light receiving element using the differentiated velocity signal. 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]

Figure 1 is an explanatory diagram showing the problem of conventional sine wave drive.
FIG. 2 is a perspective view of an embodiment of the present invention, FIG. 3 is a circuit block diagram thereof, and FIG. 4 is an explanatory diagram of its operation. 1...Laser, 2...Vibration mirror, 3...Fθ lens,
4...Object to be measured, 6...Position sensor, 7...Photodiode (light receiving element), 8...A/D converter, 9...Address signal generator, 10...Binarization circuit, 11, 11'...Data processing circuit .

Claims (1)

[Claims] 1. A laser, a vibrating mirror that is driven by a sine wave and linearly scans the light beam from the laser over a certain angle range, a lens that converts the beam scanned by the vibrating mirror into parallel light, and a parallel beam emitted from this lens. a half mirror that divides the light into two and irradiates the transmitted light onto the measured object; a position sensor that detects the reflection plate from the lens of the half mirror; and a position sensor that detects the reflection plate of the transmitted light from the measured object. a light receiving element that receives light through reflection by a half mirror; an address signal generation circuit that obtains an address signal from the output of the position sensor via an A/D conversion circuit; the output of the light receiving element is inputted and cut off by a control voltage; A variable voltage high pass filter that changes frequency and the output of this high pass filter are
a binarization circuit that converts the output into a value; a differentiation circuit that differentiates the output of the position sensor to obtain a speed signal; an absolute value circuit that obtains the absolute value of this speed signal and uses it as a control voltage for the high-pass filter; A surface defect detection device comprising a data processing circuit that determines the presence and position of a defect on an object to be measured from a binary signal and the address signal.