GB2248935A

GB2248935A - Surface inspection device

Info

Publication number: GB2248935A
Application number: GB9120957A
Authority: GB
Inventors: Hajime Yoshida
Original assignee: Hajime Industries Ltd
Current assignee: Hajime Industries Ltd
Priority date: 1990-10-09
Filing date: 1991-10-02
Publication date: 1992-04-22
Also published as: DE4133315A1; JPH04147045A; CA2052905A1; JPH06103276B2; GB9120957D0; AU8562991A; FR2667686A1

Abstract

An object is irradiated, transmission or reflection light therefrom is picked up by a video camera, and an image signal is electronically processed to detect defects on the object. An image signal is extracted whose contrast of light and shade exceeds a preset value, converted into a digital signal, and stored in a memory (Fig. 1A). A histogram (Fig. 1C) of the digital signals in the horizontal or vertical direction of the image is formed, and a filter produces a waveform (Fig. 1D). Parts of the waveform that exceed a preset threshold TH are extracted, and a center line of each extracted part is obtained. A window 6 scans the memory in the vertical direction until it coincides with the center line of the extracted waveform image. A judging circuit decides that there is a defect whenever there are more signal counts than a preset value in the window. Horizontal and vertical histograms may be formed to locate possible flaws without needing to scan the window 6. <IMAGE>

Description

2243?15 8 TITLE: SURFACE INSPECTION DEVICE

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to surface inspection device. Description of the Prior Art

In the modern industrial fields, substitution to manual inspection for parts or the like by visual sense, is increasing by setting up automatic inspection devices that utilize video camera and electronic processors. As objects of inspection, there are raw materials, plain material, half products, completed products, etc., where various surface inspection devices that detect the surface flaws such as differences in shape or appearance, dimensions or defects, are prpposed and practically used.

The surface inspection devices for objects of the prior art, irradiate illuminating light on the inspected object, catch the transmission light or reflection light from the inspected object by the video camera and convert the light to the image signal, and detect the defect by process analysis of the image signal by an electronic processor containing a computer or the like.

In this case, the image signal as caught by the video camera is an analog signal, and in order to make the electronic processing easy, conversion of the analog signal to the digital signal by the use of A/D converter or the like is the general practice. Further, if the entire data on gray scale which is the light and shade of the image, is attempted to be processed, it means that enormous data volume must be processed which makes the device complicated, and long processing time are necessary that make it impractical.

1 Accordingly, the presently used inspection devices separate the light and shade of an image into binary values by a threshold value, by which the processing is simplized as practiced on the majority of devices in practical use. Otherwise, the gray scale is confined into few stages and digitized for processing on devices as noted in some cases.

For instance, in the case that surface defects on the inspected object are to be detected, various problems are encountered. As to the inspected objects, there are variations such as, metal plates, metal strips or glass, plastic containers, paper or plastic rolled material, etc., and it is substantially difficult to extract the defect only from the surface and detect the same. That is to say that upon picking up the inspected object by a video camera, not only will the defects be picked up as variance of the light and shade but the base material surface course roughness or subtle wrinkles that are not defects, as well as slight trace of dirtiness will at the same time be picked up as variance in the light and shade, which cannot be distinguished from the defects.

Such surface coarseness, wrinkles or slight traces of dirty can be said to be "noise,, in the image for the video camera and the detection of only the defects from among such noise in a simple manner was a difficult problem.

Various methods are offered in order to resolve such problems. As one effective means among such offers, there is the method to divide the picture screen into many small zones, measure the differences of light and shade within each small zone so that whenever there is a variance exceeding a preset value, judgement that a defect exists there is made.

The portion with noise like variance of light and shade is 2 small within each small zone, whereas the variance of light and shade is great within the zone where defects exist, so that it is easy to segregate the defect from noise and make a judgement. It is needless to say that the size of the zones for division may be adequately determined based upon the size of the defect to be detected.

However, although the method of defect detection by division of the picture screen into many small zones is a very effective means, because it is necessary to scan and make judgements for each of the small zones across the entire picture screen, a great processing time is required to make judgement of the entire frame.

OBJECTS AND SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide an improved surface inspection device which can obviate the shortcomings encountered with the prior art.

According to an aspect of the present invention, there is provided a surface inspection device in which an inspected object is irradiated by a light source, transmission light or reflection light therefrom is picked up by a video camera and an image signal from the video camera is imageprocessed by an electronic processor to thereby detect defects on the inspected object, comprising:

a) an image signal extracting means for extracting from among the image signals of the video camera, an image signal whose contrast of light and shade exceeds a preset value; b) an A/D converter for converting said image signal into digital signal; c) a memory for storing said digital signal; d) a histogram formation means for producing a histogram 3 signal of the entire digital signals in the horizontal or vertical direction of the image; e) a lowpass filter for producing a waveform signal by removing high frequency components of said histogram signal; f) a signal extracting means for extracting a part of said waveform signal that exceeds a preset threshold value) g) vertical or horizontal position setting means for obtaining a center line of said extracted part of said waveform signal in the vertical or horizontal direction of an image; h) a window setting means for setting a small window on a picture screen with a preset size that allows defect detection; i) a window address setting means for scanning the memory in which the digital signal is stored by S-aid window in the vertical direction in a manner that the center of said window coincides with the center line of the image as obtained from the extracted waveform signals in the vertical or horizontal direction; and j) a judging means for judging that there exists a defect when said memory is scanned by said window, whenever there are more digital signal counts exceeding a preset value in said window, or whenever the areas of the digital signal clot in said window is larger.

According to another aspect of the invention, there is provided a surface inspection device in which an inspected object is irradiated by a light source, transmission light or reflection light therefrom is picked up by a video camera and an image signal from the video camera is image- processed by an electronic processor to thereby detect defects on the inspected object, comprising:

a) an image signal extracting means for extracting from 4 among the image signals of the video camera, an image signal whose contrast of light and shade exceeds a preset value; b) an A/D converter for converting said image signal into digital signal; c) a memory for storing said digital signal; d) histogram formation means for producing histbgram signals of the entire digital signals in the horizontal and vertical directions of the image; e) lowpass filters for producing waveform signals by removing high frequency components of said histogram signals; f) signal extracting means for extracting a part of each of said waveform signals that exceeds a preset threshold value; g) vertical and horizontal position setting means for obtaining center lines of said extracted parts of said waveform signals in the vertical and horizontal directions of an image; h) a window setting means for setting a small window on a picture screen with a preset size that allows defect detection; i) means for obtaining a position at which the vertical and horizontal center lines provided from said waveform signals intersect each other and making the center of said window coincident with said intersecting position; and j) a judging means for judging that there exists a defect when said memory is scanned by said window, whenever there are more digital signal counts exceeding a preset value in said window, or whenever the areas of the digital signal clot in said window is larger.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the object, features and advantages of the invention can be gained from a consideration of the following detailed description of the preferred embodiments thereof, in conjunction with the figures of the accompanying drawings, wherein:

Fig. 1 is a schematic diagram in order to explain the basic theory of the present invention; Fig. 2 and Fig. 3, which are respectively formed of Figs. 2A, 2B and Figs. 3A, 3B drawn on two sheets of drawings so as to permit the use of a suitably large scale, are block diagrams that respectively illustrate embodiments of the present invention; and Fig. 4 is a schematic diagram in order to explain the function of the embodiment on Fig. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An explanation of the present invention shall be made in reference with the drawings. The basic theory of the present invention shall be explained in reference with Figs. 1A to 1E.

In the present invention, in the picture screen of the video camera on which the image of the surface of an object to be inspected is displayed, its portion where there exists a change of light and shade is converted into a digital signal.

In doing so, the analog signal of the portion of the picture screen containing the variance of light and shade may be binary valued by using a preset threshold value and then converted to digital signal, or by processing the analog signal of the light and shade variance portion in differentiation fashion to form a waveform. on the boarder of light and shade and then similarly make it a digital signal. The digital signals over the entire picture screen are stored in a memory.

Fig. 1A shows the above digital signals as scattered in the responsive areas of a memory that memorizes the digital signals and corresponds to the picture screen of the video camera or picture screen 1 shown by dots. Roughly spotted black dots 2 6 within the picture screen 1 are the converted signals of the light and shade variances by coarseness or traces of slight dirtiness that exist on the surface of the inspected object as other than defects as above described which are the so called noise that are obstacles in the defect judgements.

on the other hand, dense black dots 3 and 3A in the screen 1 are the digital signals responding to the flaws or defects that are to be detected and many black dots are assembled here.

Fig. 1B shows the digital signals on a single scanning line, which is the line X - X' on picture screen 1, by which it is obvious that the defect or noise cannot be segregated if the digital signals are detected as they are. However, by dividing the picture screen 1 into small zones as shown on Fig. 1A (in this case, the division is vertically 4, horizontally 6), and by counting the number of black dots within each zone, it is apparent that the noise and defect can be segregated and discriminated.

At the present invention, the histogram of the digital signals (black dots) of each horizontal scanning line on picture screen 1 is formed throughout the vertical direction on picture screen 1. This histogram shows the distribution status of the entire digital signals that appear in the horizontal direction on picture screen 1. Fig. 1C illustrates this histogram.

As the next step, the histogram as formed with the digital signals and shown on Fig. 1C is passed through a low pass filter to remove the high frequency components thereof, and is formulated into a waveform signal. Fig. 1D, shows this waveform signal of the converted digital signals.

In order to segregate the defects from the noise of dirty, etc., the waveform signal as shown on Fig. 1D is sliced by 7 a preset threshold value TH, find the position of the waveform signal portion that exceeds the threshold value, and obtain a center line CN in vertical direction for the image at this position. In the case on Fig. 1D, the portions of the waveform signal that exceed the threshold value TH are 2 places, so that the above center lines will be CN 1, CN 2. Further, 'the reason that the histogram as formed by digital signals was shaped to the waveform signal by the lowpass filter, was to make it easy to. obtain the center line of the digital signal clot. Also, it is needless to say that the number of the center lines (CN) as obtained as above becomes different dependent on the distribution of the digital signals in the histogram and on the manner in -which the threshold value TH is set.

As shown on Fig. 1E, the picture screen 1 of the memory that memorizes digital signals is scanned by moving a preset small zone window 6 along the center line (CN) in the direction from, for example, the upper side to lower side and whenever there is more digital signals than a preset number in window 6, or when the area of the clot of digital signals in the window 6 is large, a judgement that there is abnormality or a defect is made. The window 6 is a single one with a preset size.

Fig. 2 is a block diagram that illustrates an embodiment that practices the basic theory of the present invention. At the example on Fig. 2, an image signal a from a video camera 10 that picks up an inspected object (not shown) is input to a preamplifier 11. The preamplifier 11 supplies an amplified image signal b to -an image signal extractor 13 and synchronizing signal separator 12. The image signal extractor 13 formulates a extracted signal c by the image signal portion that exceeds a preset threshold value TH1 set by a threshold value setting unit 8 13A. The image signal extractor 13 is such as a comparator which extracts the specific image signal c based on the threshold value TH1. This extracted image signal c is input to an A/D converter 14 and is converted to a digital signal d. Such converted digital signal d by the A/D converter 14 is input to a memory 16 through a fixed contact point X and a movable contact A of conversion switch 15.

The synchronizing signal separator 12 consists of vertical synchronizing signal separator 12v and horizontal synchronizing signal separator 12h, which respectively separates a vertical synchronizing signal v and horizontal synchronizing signal h from the amplified image signal b that the video camera 10 has picked up. These vertical and horizontal synchronizing signals v and h are input to an image address generator 17. The image address generator 17 generates an address signal e. This address signal e is input to memory 16 through a fixed contact X' and movable contact A of conversion switch 15A to control the vertical and horizontal addresses of memory 16 so that the digital signal d is memorized in the memory 16 in synchronism with the image signal a that the video camera 10 has caught.

on the other hand, the digital signal d that is output from the A/D converter 14 is input to a horizontal histogram formulator 18 to make a horizontal histogram signal f of digital signal d (refer to Fig. 1C) which is then input to a lowpass filter 19 to obtain a waveform signal g (refer to Fig. 1D). At the same time, the aforementioned vertical synchronizing signal vand horizontal synchronizing signal h are input to the histogram formulator 18 and lowpass filter 19 respectively in order to accurately formulate the histogram signal f and waveform signal g.

9 The waveform signal _q is supplied to a signal extractor 20, by which a signal -i (see Fig. 1D) exceeding a preset threshold value TH2 set by a threshold value setter 20A is extracted from the waveform signal _q. This signal i is input to a vertical position setter 21, so that the center point of this signal i in the vertical direction of the image of the waveform signal g is obtained. Also, to the vertical position setter 21, the vertical synchronizing signal v and the horizontal synchronizing signal hare input, in order to control the vertical position setter 21 such that the center point is set at the correct positl:On on the picture screen and the vertical position signal.1 is derived from the setter 21.

In Fig. 2, 22 is a window setter which receives the vertical and horizontal synchronizing signals v and h and outputs window setup signal k so that a small dimentioned window 6 with a size that encloses the desired defect to be detected is setup. 23 is a window address generator, which by receiving the vertical position signal j, window setup signal k, vertical and horizontal synchronizing signals v and h, outputs such window address signal 1 that enables the window 6 at a given vertical scan position to vertically scan the digital signal d as memorized in memory 16, which address signal 1 is output to the other fixed contact Y1 of the conversion switch 15A. Switches 15 and 15A are interlocked, fixed contact X and X' thereof are in signal intake mode to memory 16, while the other fixed contacts Y and Y' thereof are in judgement mode.

In this manner, switches 15 and 15A are placed in the signal intake mode to the memory 16, and the entire image digital signals d are stored in memory 16. Then, the switches 15 and 15A are switched to judgement mode, and the window 6 is operated to scan the screen 1 only in the setup vertical direction as shown in Fig. 1E, such result is judged by a judgement circuit 24 to detect the defects 3, 3A.

The above explains an example case of function by seeking the horizontal histogram, but it is apparent that by seeking the vertical histogram in the place of horizontal histogram, and by scanning the window horizontally, the same function and effects can be obtained. In such case, the horizontal histogram formulator 18 can be the vertical histogram formulator, and the vertical position setter 21 can merely be changed to a horizontal position setter so that the specific duplicated explanation thereof shall be omitted.

Further, Fig. 3 is a block diagram of another embodiment of the present invention. On Fig. 3 the same symbols as those of Fig. 2 point to the same parts. The difference in Fig. 3 to Fig. 2 is that at the example on Fig. 3, a set of horizontal and vertical histograms are simultaneously formulated.

For this reason, in the case of Fig. 3, a vertical histogram formulator 18B, low pass filter 19B, signal extractor 20B and threshold value setter 20C are installed together to the case of Fig. 2.

The functional difference in the case of Fig. 3 compared to the case of Fig. 2 is that on the embodiment of Fig. 3, the vertical position setter 21 in case of Fig. 2 becomes a horizontal and vertical position setter 21B that simultaneously controls the horizontal position and the vertical position, while the window address setter 23 generates a window address signal to address the window 6 at the cross point of the horizontal position and vertical position.

Fig. 4 illustrates this status, in which at crossing points 11 between the vertical direction center lines CN1 and CN2 that are obtained from the horizontal histogram and the horizontal direction center lines CN3 and CN4 that are obtained from the vertical histogram, the window 6 is consecutively setup thereby carry out the judgement.

By this method, rather than scanning with the window, judgement is made by simply moving the window consecutively to the cross points so that it features a very short overall judgement processing time.

As for the explanation of the other portions on Fig. 3, the functions will be exactly the same to the case on Fig. 2 and explanations therefore shall be omitted.

Also, although the functions of the present invention have been made in reference to block diagrams, it is generally the practice to carry out the present invention by computer processings respectively, and it is apparent that anyone with ordinary skill in the art can easily achieve such above mentioned functions by software programming.

It also is not necessary to be bond by the rectangular shape of the window, and depending upon the purpose it can be of a special shape, and it is needless to say that freely arranged setups by the detection purposes such as judgement processing within the window can be by the count of the extract signal numbers or the clot status or shape of the extracted signal as the basis for judgement.

The present invention obviates such shortcomigs in the processing time by the conventional methods, and enables an extremely fast practice by a unique method of window processing on the picture screen, and offers enormously huge merit by making it possible to use this type of device on highspeed production 12 lines. Further, it is not necessary to encounter complicated compositions, but the device can be manufacted most conveniently.

It should be understood that the above description is presented by way of example on the preferred embodiments of the invention and it will be apparent that many modifications and variations thereof could be effected by one with ordinary skilled in the art without departing from the spirit and scope of the novel concepts of the invention so that the scope of the invention should be determined only by the appended claims.

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Claims

1. A surface inspection device in which an inspected object is irradiated by a light source, transmission light or reflection light therefrom is picked up by a video camera and an image signal from the video camera is image-processed by an electronic processor to thereby detect defects on the inspected object, comprising:

a) an image signal extracting means for extracting from among the image signals of the video camera, an image signal whose contrast of light-and shade exceeds a preset value; b) an AID converter for converting said image signal into digital signal; c) a memory for storing said digital signal; d) a histogram formation means for producing a histogram signal of the entire digital signals in the horizontal or vertical direction of the image; e) a lowpass filter for producing a waveform signal by removing hich frequency components of said histogram signal; f) a signal extracting means for extracting a part of said waveform sianal that exceeds a preset threshold value; g) vertical or horizontal position setting means for obtaining a center line of said extracted part of said waveform signal in the vertical or horizontal direction of an image; h) a window setting means f or setting a small window on a picture screen with a preset size that allows defect detection; i) a window address setting means for scanning the memory in which the digital signal is stored by said window in the vertical direction in a manner that the center of said window coincides with the center line of the image as obtained from the extracted waveform signals in the vertical or horizontal direction; and j) a judging means for judging that there exists a defect when said memory is scanned by said window, whenever there are more digital signal counts exceeding a preset value in said window, or whenever the areas of the digital signal clot in said window is larger.

2. A surface inspection device in which an inspected object is irradiated by a light source, transmission light or reflection light therefrom is picked up by a video camera and an image signal from the video camera is image-processed by an electronic processor to thereby detect defects on the inspected object, comprising:

a) an image signal extracting means for extracting from among the image signals of the video camera, an image signal whose contrast of light and shade exceeds a preset value; b) an A/D converter for converting said image signal into digital signal; c) a memory for storing said digital signal; d) histogram formation means for producing histogram signals of the entire digital signals in the horizontal and vertical directions of the image; e) lowpass filters for producing waveform signals by removing high frequency components of said histogram signals; f) signal extracting means for extracting a part of each of said waveform signals that exceeds a preset threshold value; g) vertical and horizontal position setting means for obtaining center lines of said extracted parts of said waveform signals in the vertical and horizontal directions of an image; h) a window setting means for setting a small window on a picture screen with a preset size that allows defect detection; 1 i) means for obtaining a position at which the vertical and horizontal center lines provided from said waveform signals intersect each other and making the center of said window coincident with said intersecting position; and j) a judging means for judging that there exists a defect when said memory is scanned by said window, whenever there are more digital signal counts exceeding a preset value in said window, or whenever the areas of the digital signal clot in said window is larger.

3. A surface inspection device-according to claim I further comprising a synchronizing signal separating means for receiving the image signal and separating therefrom vertical and horizontal synchronizing signals which are supplied to said histogram formaticn means, said lowpass filter, said vertical or horizontal position setting means said window setting means and said window address setting means, respectively.

4. A surface inspection device according to claim 2 further comprising a synchronizing signal separating means for receiving the image signal and separating therefrom vertical and horizontal synchronizing signals which are supplied to said histogram formation means, said lowpass filter, said vertical and horizontal position setting means said window setting means and said window address setting means.

5. A surface inspection device as claimed in claim 1, wherein the shape of said small window is selected to be rectangular.

6. A surface inspection device as claimed in claim 2, wherein the shape of said small window is selected to be rectangular.

7. A surface inspection device according to claim 3 further 16 comprising an address generating means for receiving the vertical and horizontal synchronizing signals and generating an address signal to control addresses of said memory.

8. A surface inspection device according to claim 4 further comprising an address generating means for receiving the vertical and horizontal synchronizing signals and generating an address signal to control addresses of said memory.

9. A surface inspection device according to claim 7 further comprising a first switching means connected between said A/D converter and said memory and a second switching means connected between said address generating means and said memory, said first and second switching means being operated in an interconnected fashion.

10. A surface inspection device according to claim 8 further comprising a first switching means connected between said A/D converter and said memory and a second switching means connected between said address generating means and said memory, said first and second switching means being operated in an inter-connected fashion.

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