JPS5883238A - Method and device for detection of surface defect of object - Google Patents

Abstract

PURPOSE:To detect the surface detects of objects accurately and easily by delaying the delay signals obtained by delaying electric signals by at least one scanning, further with plural stages of delay elements, adding and averaging the outputs of the respective delay elements, and comparing the electric signals under scanning with the added and averaged signal. CONSTITUTION:The electric signal E1 from a photoelectric converter 100 is amplified with an amplifier 101 which outputs a video signal E2. The signal E2 is inputted to a comparator 103 and a delay circuit 104. The circuit 104 is constituted by cascade connection of (n) pieces of delay elements d1-dn. One piece of the element di (i=1-n) can delay the signal E2 by as much as one scanning from the current rotary slit to the next rotary slit. The signal E2 is delayed by as much as (n) scanning with the delay circuit 104. The delay signal F via the circuit 104 is further inputted to a delay circuit 105 and total N pieces of delay signals G1-GN are drawn out individually from N pieces of delay elements D1-DN, and are inputted to an adder 106. The adder 106 adds the received signals G1-GN, and outputs the average value thereof from its output part. The output is inputted to a comparator 103, whereby the influence upon the average value signal is decreased and fine defects are detected.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for detecting surface defects on an object, and in particular, to detecting defects such as surface scratches on a metal workpiece using a photoelectric converter such as a photomultiplier tube. The present invention relates to a method of detecting electrical signals by converting them into electrical signals, and a device used to carry out the method.

The prior art of such a detection method is disclosed in Japanese Patent Application Laid-Open No. 55-667.
It is disclosed in Publication No. 40. This prior art is
As shown in FIG. 1, the surface of, for example, a cylindrical test object 3 is uniformly illuminated through an illumination optical system consisting of a light source 1 and a condensing lens 2, and a half mirror 4, an imaging lens 5, A real image of the object 3 is formed on the front surface of a photoelectric conversion means such as a photomultiplier tube 9 through an imaging optical system such as a condensing lens 6, and a fixed slit 6, a rotating slit 7, etc. in the imaging optical system are formed. The object 3 passed through the fixed slit 6 by a scanning mechanism consisting of
scans the real image of
This electrical signal is then input into an electrical circuit as shown in FIG. 2 to determine and detect the presence or absence of defects on the surface to be inspected. Next, the configuration and operation of the prior art electric circuit shown in FIG. 2 will be explained. As described above, the electrical signal is output from the photoelectric conversion unit 10 including the photomultiplier tube 9 and the like, which receives light related to the real image of the object and converts it into an electrical signal. . The electrical signal is amplified by an amplifier 11. The waveform of the electrical signal A amplified by the amplifier 11 has the following characteristics, as shown in FIG. Contains signals with high frequency components.

On the other hand, when this electric signal A is passed through a low-pass filter 12, a signal B is obtained in which high frequency component signals caused by the fine structure of the surface of the object to be inspected are removed. by the way,
The low-pass filter 12 connects the amplifier 11 to generate an electrical signal B for determining the presence or absence of defects on the surface to be inspected.
It is inserted in the latter stage, but due to the frequency cut characteristics of the low-pass filter itself, the original electrical signal A
Compared to No. A, there is a possibility that it cannot be used as a signal for determining the presence or absence of defects on the surface of the object to be inspected.

Therefore, in the circuit of the prior art, in order to prevent this delay, a ζ delay circuit 13 is inserted between the comparator circuit 14 and the low-pass filter 12, and the original electrical signal A is passed through the delay circuit 13. electrical signal C that is in phase with
This electrical signal C is compared with the original electrical signal A by a comparison circuit 14 to determine whether there is a defect on the surface to be inspected. However, in the prior art electrical circuit having such a configuration, as shown in FIG. 3, the electrical signal AO corresponding to the defect on the surface to be inspected contained in the original electrical signal A
The electrical signal CO corresponding to the electrical signal AO of the electrical signal C rotated next from the level with respect to the test surface currently being scanned by the rotating slit 7 is also a signal processed from the signal from the previous scan. Therefore, as shown in the electrical signals GO1 to C05 in FIG. 3, the level is gradually increased.

As a result, the level of the electrical signal AO corresponding to the defect on the surface to be inspected remains below the level of the electrical signal CO; 1.
In the comparison circuit 14, the presence or absence of a defect on the surface to be inspected cannot be determined by comparing the electrical signal AO included in the original electrical signal A with the electrical signal C. Furthermore, since the electric signal C is a signal that has passed through the low-pass filter 12'fI, the portion of the electric signal C at D and 6 in FIG. over a very wide range of frequencies due to the diversity of defects corresponding to defects on the surface to be examined that may be too smooth and therefore included in the peripheral part to the original electrical signal. In such cases, the purpose of using a low-pass filter is to solve the above-mentioned technical problems and provide a detection method and device that can easily and accurately detect the presence or absence of defects on the surface to be inspected. That's true.

FIG. 4 is a block diagram of a signal processing circuit according to an embodiment of the present invention. In the embodiments of the present invention, an illumination optical system that illuminates the surface of the test object, an imaging optical system that forms a real image of the test object,
The photoelectric conversion system that converts the light related to the real image into an electrical signal and the scanning mechanism may be those shown in FIG. 1 described above. In particular, it is clear from the description of the embodiments of the present invention that an image pickup tube or the like may be used as other examples of the photoelectric conversion system and the scanning mechanism. An electrical signal (hereinafter referred to as a video signal) E+ is output from a photoelectric converter 100 that converts light related to a real image of the surface of the object into an electrical signal. Amplifier 101
amplifies the video signal E- and outputs the video signal E2.

Similar to the electrical signal A in Fig. 3, the video signal E-2 contains a signal with a high frequency component according to the fine structure of the object surface, such as defects and finishing roughness on the object surface. There is.

Such a video signal E2 is input to the comparison circuit 103 and also to the delay circuit 104.

The delay circuit 104 includes delay elements (for example, BBD manufactured by Matsushita Electronics Co., Ltd.) d+~ for delaying the video signal E2.
dn, as shown in FIG.
Consists of cascade connections. One delay element di(
1=1 to n) is a video signal E2'fr:, which can be delayed by one scan from the current rotation slit to the next rotation slit. Therefore, the video signal E2 is By passing through the circuit 104, it is delayed by n scans. In this way, the delay circuit 10
4 (the signal in this case is hereinafter referred to as a delayed signal) F is further connected to a circuit 105 similar to the delay circuit 104.
A total of N from each of N delay elements D1 to DN constituting
The delayed signals 01 to GN are individually taken out. Each of these delayed signals 01-GN is individually input to adder 106.

The adder 106 receives these delayed signals 01 to GN.
f: Add and output the average value from the output section. As a result, the output of the adder 106 is the average value of the delayed signals for N scans, and this output is further input to the gain setter 107 to set the gain, and then compared. It is input to circuit 10g. In this embodiment, the delay time is set in accordance with the rotational speed of the rotating slit, and therefore, if the rotating slit has uneven rotation, it becomes difficult to accurately set the delay time. Therefore, in order to avoid this and synchronize the original video signal and the delayed signal, a synchronization signal H is input from the photoelectric converter 100 to the flip-flop circuit 108 in response to the change in the rotation speed of the rotating slit. The flip-flop output of this flip-flop circuit 108 is inputted to a PLL (abbreviation for phased lock loop) @ path 109 surrounded by a broken line, and its PTI
, the outputs of the L circuits 109 are input to delay circuits 104 and 105. This PLL circuit 109 includes a phase comparison circuit 110, a low-pass filter 111, a voltage controlled oscillator 11
2 and a counter 113.

Note that the output of the counter 113 is temporarily
After being input to a flip-flop circuit 114 located outside of ing. In this manner, the PLL circuit 109 and the above-mentioned electric circuit configured in this manner have the amplifier 1
01 and the comparator 103, without using a low-pass filter, in order to detect the presence or absence of defects on the surface of the test object.
Since delay circuits 104 and 105'ii are used,
As shown in FIG. 8, the signals E21 to E25 corresponding to defects on the surface of the object to be inspected for each scan, which are included in the video signal E2, are rarely present, and therefore, in the comparison circuit 103, the video signals The signals E2+ to E2 included in E2
5 can be detected by comparing it with the average value signal I.

FIG. 6 is a circuit block diagram of another embodiment of the present invention, in which parts similar to and corresponding to those in FIG. 4 are given the same reference numerals. What should be noted is the amplifier 101 and the comparator circuit 10.
Delay circuits 104 and 105 are inserted between 3 and 3, and each of the delay elements d1 to cln constituting the delay circuit 104 shown in FIG. 7 is individually connected as an input to an adder 106, Further, the final stage delay element dn in the delay circuit 104 is connected to the first delay element D1 in the next stage delay circuit 105, and the final stage delay element D in the delay circuit 105 is connected to the first delay element D1 in the next stage delay circuit 105.
N means that the input is connected to the comparator circuit 103 as is. The adder 106 is connected to the comparator circuit 103 via the gain setter 107, as shown in FIG. Therefore, in the electric circuit of this embodiment having such a configuration, the video signal E2 is transmitted through the delay circuit 10.
4, the signals from each delay element d1 to dn are first added as they are in an adder 106 and outputted from the adder 106 as an average value of video signals for n scans. The video signal E2 input from the delay circuits 104 and 105 to the comparison circuit 103 is input to the comparison circuit 103 after being delayed as a delay signal F in the delay circuit 104 and as a delay signal G in the delay circuit 105. .

Therefore, also in the electric circuit shown in FIG. 6, it is possible to accurately detect the above-mentioned video signals E2+ to E25 corresponding to defects on the surface of the object to be inspected.

As explained above, according to the present invention, the electric signal related to the real image of the surface of the object to be inspected is delayed by at least one scan using the delay element, so that the electric signal corresponding to the defect on the surface of the object to be inspected is delayed. Even if the level is gradually changed, the influence on the determination signal (average value signal) that is compared with the electric signal to determine the presence or absence of a defect on the surface of the object to be inspected can be greatly reduced. Further, since a low-pass filter is not used unlike the prior art, it is possible to avoid difficulties in setting the frequency cut characteristics of the low-pass filter. In particular, in the present invention,
Since the configuration is configured such that each output of each delay element is averaged and compared with the average signal, unique effects such as being able to detect minute defects are produced.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a device for optically detecting the condition of the surface of a test object and converting it into an electrical signal, FIG. 2 is a block diagram of a signal processing circuit of the prior art, and FIG. FIG. 4 is a block diagram of a signal processing circuit according to an embodiment of the present invention, FIG. 5 is a detailed circuit block diagram of its main parts, and FIG. 6 is a diagram showing signal waveforms according to the prior art. FIG. 7 is a block diagram of a signal processing circuit according to an embodiment of the present invention, FIG. 7 is a detailed circuit block diagram of the main part thereof, and FIG. 8 is a diagram showing signal waveforms according to the present invention. 100...Photoelectric conversion unit, 101...-Amplifier, 103
...Comparison circuit, 104/105...Delay circuit, 10
6... Adder, 107... Gain setting device, d1 to dn
, DI to DN...Delay element Fig. 2 Fig. 3

Claims (3)

[Claims] (1) In a method of scanning a real optical image of an object to be inspected and converting it into an electrical signal, and detecting surface defects on the object based on the waveform of the electrical signal, a delay obtained by delaying the electrical signal by at least one scan. By further delaying the signal through multiple stages of delay elements, adding and averaging the outputs of each of the delay elements, and comparing the electrical signal related to the current scanning with the signal related to the added average. A method for detecting surface defects on objects. (2) A method of scanning a real optical image of an object to be inspected and converting it into an electrical signal, and detecting surface defects on the object based on the electrical signal waveform, the electrical signal being delayed through a plurality of stages of delay elements; An average value of the outputs of each of the delay elements is calculated, and the output from the final stage of each delay element is further delayed by at least one scan to obtain a delayed signal, and the signal related to the average value and the A method of detecting surface defects on an object by comparing with delayed signals. (3) In a device that scans an optical real image of an object to be inspected and converts it into an electrical signal, and detects a surface defect on the object based on the waveform of the electrical signal, at least one a first delay circuit that delays the electrical signal by a scanning amount; a second delay circuit that includes multiple stages of delay elements that delay the electrical signal directly or the delayed signal of the first delay circuit; It is characterized by comprising an adder that adds and averages the outputs of each of the delay elements, and a comparator that compares a signal related to the output of the adder and the electrical signal or the output signal of the first delay circuit. Object surface defect detection device.