KR19980051179A - Surface defect signal correction method - Google Patents

Abstract

The present invention relates to a surface defect signal correction method, and more particularly, to provide a surface defect signal correction method for improving the detection capability of the surface defect through the background correction of the object surface.

According to the present invention, a light detector (3), a light filter (2), a spatial filter (5), which detects a light beam reflected from the light filter (2) among the light beams scanned by the laser (1) on the object surface (8), Photodetectors (9, 12, respectively) for sensing light rays reflected on the object surface (8) after passing through the aperture (6), the large lens (7) and / or the small lens (10), and the photodetectors ( Input the signals generated from them through the computer 4 interfaced with 3, 9, and 12, and measure the reference signal, the ground signal, and the defect signal, respectively, and correct the surface signal by using these measurements. The gist of the method for compensating surface defect signals for calculating signals is provided.

Description

Surface defect signal correction method

The present invention relates to a method for correcting a surface defect signal, and more particularly, to a method for correcting a surface defect signal by performing background correction on an object surface.

In general, the surface of the object not only has various surface defects such as scratches, scabs, pinch trees, etc. due to rolling during the manufacturing process, but also various forms of rust during storage. Occurs. The detection of such surface defects with the naked eye involves various difficulties and reliability problems, and thus, surface defect inspection techniques using lasers have been used. Known techniques for surface defect detection include U.S. Patent No. 4,298,808, Japanese Patent No. 61-25042, and Small 61-45914. These methods only detect reflected light from the object surface without considering background correction, thus detecting fine surface defects. The disadvantage is that the performance is very low.

Accordingly, the present invention obtains a defect signal by using the reflected light of a thin laser beam sensitive to minute changes in the surface, such as surface defects, in order to improve the problems of the prior art, the surface defect does not respond well, but the state of the overall surface It is an object of the present invention to provide a method for correcting a surface defect signal that improves detection capability of surface defects by measuring reflected light of a laser beam having a large cross-sectional area having a different reflectance.

1 is a block diagram of a surface defect signal correction apparatus according to the present invention

2 is a flow chart for correcting the surface defect signal of the present invention (FLOW CHART)

3 is a surface defect signal flaw graph as a comparative example

Figure 4 is a surface defect signal flaw detection graph of an embodiment of the present invention

* Explanation of symbols for main parts of the drawings

3, 9, 12 ... photodetector 7 ..... large lens

8 ............. Object surface 10 .... Small lens

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

The present invention controls the light filter 2 for dividing the light beams scanned from the laser 1 onto the object surface 8, the space filter 5 for diffusing the light beams passing through the light filter, and the light beams passing through the space filter. A diaphragm (6), a large lens (7) for making the rays passing through the aperture into parallel rays, a photodetector (3, 9, 12) for detecting the rays, and a computer (4) interfaced with the photodetector. In the method for correcting the defect signal on the surface of the object by using a surface defect signal correction device, the optical detector for detecting the light beam reflected by the light filter 2 of the laser beam by the computer ( 3) Measuring the reference signal by inputting the signal generated from 3), and after passing through the light filter (2), the spatial filter (5), the aperture (8) and the large lens (7) and the reflected light on the surface of the object The background signal is input by inputting the signal generated from the optical detector A photodetector 12 for measuring and detecting the light reflected on the surface of the object after passing through the small lens 10 having a diameter smaller than the width of the parallel light and having a long focal length at the bottom of the large lens 7. Measuring a defect signal by inputting a signal generated from the signal; and calculating the corrected defect signal by calculating the measured reference signal, the ground signal, and the defect signal by the computer 4; It relates to a signal correction method.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

In the surface defect signal correcting apparatus according to the present invention, as shown in FIG. 1, the light beam generated by the laser 1 passes through the light shader 2, and a part thereof is an optical detector for measuring a reference output signal of the laser beam. Incident on (3), the output signal generated by this photodetector is input to the computer (4).

A portion of the laser beam passes through the light filter 2 and diffuses in the spatial filter 5, and then through the aperture 6, parallel rays are made by the large lens 7, and then the surface 8 of the object to be measured. Is reflected from. The reflected light beam is incident on the photodetector 9, and the output signal generated by the photodetector 9 is input to the computer 4 to be used for background correction of the defect signal.

On the other hand, a small lens 10 whose diameter is smaller than the width of the parallel beam and the focal length is placed in the parallel beam that has passed through the large lens 7. The light rays passing through the small lens 10 are focused on the object surface 8 and then reflected or scattered, enter the photodetector 12 via the aperture 11, and are used as a defect signal.

The computer 4 receives an output signal from the interfaced photodetectors 3, 9, and 12, calculates a correction, and outputs a defect signal.

In the method for correcting the surface defect signal of the present invention, as shown in FIG. 2, first, an optical detector which detects light reflected by the light filter 2 of light beams scanned from the laser 1 to the object surface 8. Input the signal generated from (3) to receive a reference signal from the laser (1) at the same time with the light filter (2), spatial filter (5), aperture (6), large lens (7) or / and small After passing through the lens 10, the signal generated from the photodetectors (9 and 12, respectively) for detecting the light rays reflected on the object surface 18 is input to receive a background signal and a defect signal, and the photodetectors 3, 9, 12) through a computer interfaced with.

Next, as shown in Equation 1 below, the corrected defect signal can be calculated from the correlation between the reference signal, the background signal, and the defect signal.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example

3 is a comparative example of surface defect inspection using a laser. The horizontal axis shows the length of the laser beam scanned on the surface of the object, and the vertical axis shows the intensity of the signal beam. Figure 3a is a scratch (SCRATCH), Figure 3b is a pinch tree (PINCH TREE), Figure 3c is a defect signal for the linear SCAP (LINE SCAB), the defect signal is reflected by the sum of the reflected light from the surface of the normal object Defective signals are not clear, and surface defects are difficult to detect, especially for surface defects with small signal waveforms.

4 is an embodiment of surface defect inspection by the method of the present invention. As in FIG. 3, FIG. 4A shows a scratch, FIG. 4B shows a pinch tree, and FIG. 4C shows a defect signal for a linear cap. Since the background signal appears in the corrected state in the surface defect signal, it can be seen that even a small surface defect signal waveform can be easily detected.

As described above, the present invention makes it possible to easily detect the minute surface defect signal by correcting the background signal of the object in order to improve the problems of the prior art.

Claims (2)

A light filter 2 for splitting light beams scanned from the laser surface 1 onto the object surface 8, a space filter 5 for diffusing light beams passing through the light filter, and an aperture for adjusting light beams passing through the space filter ( 6) a large lens 7 which makes the light beams passing through the aperture into parallel light beams, photodetectors 3, 9 and 12 for sensing the light beams and a computer 4 interfacing with the light detectors. In the method for correcting the defect signal on the surface of the object using a surface defect signal correction device, Optical detector (3) for detecting the light beam reflected by the light shingler (2) of the laser beam by the computer (4) The reference signal is measured by inputting the signal generated from the sensor, and the beam reflected through the light filter 2, the space filter 5, the aperture 8, and the large lens 7 is detected. Input the signal generated from the optical detector (9) to measure the background signal, At the same time, it is generated from the light detector 12 which is located under the large lens 7 and passes through the small lens 10 whose diameter is smaller than the width of the parallel beam and the focal length is long, and then detects the reflected light on the object surface. Measuring a defect signal by inputting the received signal, and calculating the corrected defect signal by calculating the measured reference signal, the ground signal, and the defect signal by the computer (4). . The method of claim 1, wherein the equation for calculating the corrected defect signal is Surface defect signal correction method characterized in that.