JPH0236896B2 - JIKUTAISHOBUTSUTAINOKETSUKANKENSASOCHI - Google Patents

Description

[Detailed Description of the Invention] [Technical Field] The present invention involves photographing an object to be inspected with a TV camera and processing the image signal of the TV camera to inspect the presence or absence of defects in the object to be inspected. The present invention relates to a defect inspection apparatus for an axially symmetrical object, and particularly for inspecting an axially symmetrical object as an object to be inspected for defects.

[Background technology]

Conventionally, there is a pattern matching method as a method of inspecting products of various shapes for defects using a TV camera. In this method, the pattern of a non-defective product is memorized in advance and compared pixel by pixel with an image of the product to be inspected for defects, but in reality, the positions of the reference pattern and target pattern are different. Therefore, it is necessary to repeat the process many times while changing the position of one of the images, which has the disadvantage of increasing processing time.In addition, it is necessary to provide frame memory for two screens, which is expensive, so it is not practical. Generally speaking, processing up to binary images was the limit.

Furthermore, if the object to be inspected for defects is limited to axially symmetrical objects, comparisons can be made around the axis of symmetry, eliminating the need for a reference pattern. Since the symmetrical addresses on both sides of the symmetrical address are calculated and compared one after another, there is still the problem that the processing takes time.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a defect inspection device for an axially symmetrical object that can detect defects in an axially symmetrical object at high speed with a simple configuration.

[Disclosure of the invention]

Example 1 Figure 1 shows a monitor image when an axially symmetrical object is photographed with a TV camera. In the figure, the cross-hatched area is the background, and the level is sufficiently low (dark). The axis of symmetry is located near the center of the screen, as shown by the dashed line.
It is assumed that the axially symmetrical object to be inspected has a shape as shown by the hatched area and the white area in the figure and is symmetrical in the horizontal direction, and its rotational deviation is so small that it can be ignored. FIG. 2 shows the configuration of a first embodiment of the present invention. This circuit operates by scanning the image signal of the TV camera output twice, which is obtained as a "video input". First, during the first scan, the image signal is binarized by the analog comparator 1 as shown in FIG. At this time, since the background is sufficiently dark, the slice level is set to a voltage level at which the entire object becomes white "1" and the background becomes black "0". The timing control unit 2 determines the address X _A of the point of change from “0” to “1” in one horizontal period,
Detect the address X _B of the change point from "1" to "0" and set the midpoint (X _A + X _B ) as the address X _C of the axis of symmetry.
It is constructed with a pixel counter and an adder/divider for determining the . Next, in the second scanning of the image signal, the image signal is A/D converted by the A/D converter 3 and input to the FIFO/LIFO 4.
FIFO/LIFO4 has two modes.
In FIFO mode, the data that goes in first comes out first, so it functions like multiple shift registers. Also, in LIFO mode, the data that entered last is output first. Therefore, when in FIFO mode, it is a data-flowing buffer, and the contents of the buffer are read out from the moment the switch is made to LIFO mode. The timing of this switching is determined by the symmetrical axis address X _C from the timing control section 2.
Then, the FIFO/FIFO that was initially in FIFO mode
LIFO4 becomes LIFO mode and outputs the data before _address In such a case, the waveforms are the same, and even if the latter data is subtracted from the former data by the subtracter 5, the value will be only about that of noise. However, if the axially symmetrical object has a defect such as dirt or deformation, the difference between the subtraction results will be large, and this can be detected by the digital comparator 7 via the integrator 6 or adder as required. The period for this determination starts from the address X _C and is slightly longer than X _C −X _B (or X _A −X _C ), and the timing control unit 2 specifies (gates) the period.

Embodiment 2 FIG. 4 shows the configuration of a second embodiment of the present invention,
In the first embodiment described above, A/
In contrast to the configuration in which the image data output from the D converter 3 is subtracted and the digital comparator 7 compares whether the subtracted value exceeds a set value, this second embodiment The correlation between the output waveform data of the FIFO/LIFO 4 and the image data output from the A/D converter 3 is determined by a correlator 8, and the output of this correlator 8 is determined by a digital comparator 7. Thus, the correlator 8 is composed of a correlation IC having a configuration as shown in the block diagram of FIG.
The correlation for each bit is calculated using correlator units 0 to n, which correspond to the number of bits n of LIFO4 output), and the correlation is calculated for each bit by SUM1 to n, which is one less than the number n of bits mentioned above. The output of the correlator unit is weighted by shifting it to the left as the output increases, and the output of SUMn is obtained as the output of the correlator 8.

〔Effect of the invention〕

Since the present invention is configured as described above, the phase of the axis of symmetry of an axisymmetric object is automatically measured in the first frame, eliminating the need for highly accurate positioning and simplifying defect inspection operations. In addition to having the effect of simplifying the process, it also has the effect that defects of any shape can be detected with the same process, regardless of the shape of the object, as long as the object is axially symmetrical.
Furthermore, the structure is simple, no image memory is required, and the cost can be reduced. Furthermore, since the process can be performed in two frames of scanning time, it has the effect of enabling high-speed processing.

[Brief explanation of drawings]

Fig. 1 is a monitor screen diagram of an axially symmetrical object according to an embodiment of the present invention, Fig. 2 is a block circuit diagram of the same as above, and Fig. 3
The figure is a monitor screen diagram of the binarized axisymmetric object as above, FIG. 4 is a block circuit diagram of the second embodiment of the present invention, and FIG. 5 is an internal block diagram of the correlator as above. FIFO/LIFO.

Claims (1)

[Claims] 1. A TV camera that photographs an axially symmetrical object;
comprising means for measuring the position of the axis of symmetry of the axially symmetrical object in the first frame of the image signal output from the TV camera; and a memory for storing the image signal of the second frame up to the position of the axis of symmetry; Defect inspection of an axially symmetrical object, characterized in that asymmetry due to a defect is detected by comparing a signal after the symmetry axis of the frame-th image signal with a stored image signal read out reversely from the memory. Device. 2 FIFO/ which converts the image signal into A/D and inputs it
The memory is configured with LIFO, and image data is stored in FIFO mode, and the above image data is read out in LIFO mode by the output of the address counter where the symmetry axis position is set, and the read stored image data and image signal are 2. A defect inspection device for an axially symmetrical object according to claim 1, wherein a difference from A/D converted image data is detected and this difference is compared with a preset threshold value. 3. A patent claim characterized in that asymmetry due to a defect is detected by calculating the correlation between the signal after the symmetry axis of the second frame image signal and the stored image signal read out from the memory in reverse. A defect inspection device for an axially symmetrical object according to item 1.