JPS62140007A - pattern detection device - Google Patents

Abstract

PURPOSE:To obtain a stable binarized output signal by enabling automatic operation without operator's adjustment, by automatically correcting the variation of a signal without receiving restriction from an apparatus or a subject. CONSTITUTION:From video signal input S1, the max. value corresponding to a copper foil level is detected by a detector 1 and the min. value corresponding to a base material level is detected by a detector 2 and the arbitrary intermediate value of the signals from both of them is set as one input of a comparator 4 through a dividing circuit 3 and compared with the signal S1 to be binarized. Further, a pattern detection part 5 detecting the presence of a copper foil pattern from the signal S1 is provided. Only when the output of the detection part 5 judged 'pattern presence', the max. and min. values are sampled and, when judged' pattern absence', the max. and min. values at that time are held and, next, binarization is performed on the basis of a definite threshold value until a pattern is obtained. By this method, even when the frequency of appearance of the copper foil pattern is low, the threshold value is stable and accurate binarization can be performed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a pattern detection device, and more particularly to a pattern detection device suitable for outputting all binary output signals in image recognition and image processing.

[Background of the invention]

There are two methods for binarizing video signals from visual sensors such as television cameras and CCD sensors: fixed binarization and floating binarization, which are used depending on the purpose.

Fixed binarization is the basic technology of binarization, and is widely used for various purposes. has been done. However, there are cases where a small signal superimposed on a large signal cannot be detected, and floating binarization is used as a method to solve this problem. In floating binarization, an image signal equivalent to a spatially shifted image signal is obtained by applying an electrical delay to the input video signal, and the image signal is compared with the original signal.

As a result, spatial differentiation has been performed, and even minute fluctuations in the original signal can be reliably detected. However, since fine irregularities are emphasized, it may be inappropriate depending on the application, and fixed binarization is not used in many cases.

Hereinafter, fixed binarization will be explained as an example of conventional technology. However, the explanation will be given using two examples of printed circuit board patterns as image examples. What about printed circuit boards? , a copper foil pattern is placed on the edge base material, and when the surface is irradiated with light, the video signal is modulated because the reflectance is different between the steel foil and the base material, and the copper foil part receives a high signal. A low signal level can be obtained from the base material part. In this case, in order to binarize the signal by fixed binarization, the original signal can be binarized by setting the threshold value between the signal level of the copper foil and the signal level of the base material. When detecting fluorescence from the base material, the signal levels of the copper foil and the base material are reversed, but the same method can be applied for binarization.

However, fixed binarization has the following drawbacks.

(1) If the amount of light, the sensitivity of the detector, the reflectance of the subject, and the fluorescence characteristics change, the copper foil level and base material level of the signal will change, and even if the optimal threshold is set at the beginning, over time Its value fluctuates. Therefore, the operator must adjust the threshold to the optimum value while checking the video signal each time.

(2) If there are local variations in the reflectance or fluorescence characteristics of the subject, the signal level of the copper foil or base material will fluctuate during the inspection of the same subject, resulting in areas that cannot be binarized locally. Occur.

For these reasons, devices using conventional techniques that binarize images are subject to significant restrictions from the device and the object to be measured, and frequent adjustments by the operator are indispensable.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a pattern detection device that can automatically correct signal fluctuations without being subject to restrictions imposed by the device or a subject, and can be fully operated automatically without operator adjustment.

[Summary of the invention]

The features of the present invention include a maximum value detection section that detects the maximum value of an output signal obtained by amplifying a signal from a visual sensor such as a television camera or a COD sensor, and a minimum value detection section that detects all minimum values.
a dividing circuit that obtains an arbitrary intermediate value of the output signals of the maximum value detection section and the minimum value detection section; a comparator that compares the output signal of the division circuit with the amplified output signal; A pattern detection section is provided for detecting the presence or absence of a pattern from the output signal of the comparator, and the sample or hold operation of the maximum value detection section or the minimum value detection section is controlled by the output signal of the pattern detection section for the comparison. The main point is that the configuration is such that an optimal binarized output signal is sent out from the device.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail with reference to the embodiments shown in FIG. 1 and FIGS. 7 to 9, and FIGS. 2 to 6.

FIG. 1 is a block diagram showing an embodiment of the pattern detection apparatus of the present invention, and the explanation will be given by taking a case where the object to be inspected is a printed circuit board as an example. In FIG. 1, 1 is a maximum value detection unit that detects the maximum value corresponding to the copper foil level from the video signal S1, and 2 is a minimum value detection unit that detects all minimum values corresponding to the base material level from St. An arbitrary intermediate value of the signal is inputted to one side of the comparator 4 via the dividing circuit 3, and is compared with the video signal Sr to be binarized.

Further, a pattern detecting section 5 is provided which detects the presence or absence of a pattern from the video signal Sr, thereby capturing the maximum value and minimum value data only when there is a pattern, and holding the previous value when there is no pattern. 6 is a binary signal output terminal.

FIG. 2 is a diagram for explaining the entire operation of FIG. 1. Second
If there is a copper foil pattern as shown in Figure 2(a), the video signal will be as shown in Figure 2(b), and the outputs of maximum value detection section 1 and minimum value detection section 2 will be indicated by broken lines, respectively. become that way. The threshold value, which is the intermediate value between the two, becomes as shown by a dashed line, and the output signal of the binarization becomes as shown in FIG. 2(C).

3 and 4 are diagrams each showing an example where the signal strength varies locally in the case of FIG. 2, and FIG. 3 is a case according to the present invention, and the threshold value is shown in FIG. As shown by the dashed line, the change in signal level is almost followed, and an accurate binary output signal is obtained as shown in FIG. 3(b). On the other hand, Fig. 4 shows the conventional case, where the threshold is constant as shown by the dashed line in Fig. 4(a), and as a result, the binarization does not occur in the center as shown in Fig. 4(b). The output signal will be inaccurate,
The line width may become narrower or may not be detected.

In this way, if the maximum and minimum values are taken independently and the intermediate value between them is selected as the threshold, the optimal threshold will always be set even if the signal changes for the reasons mentioned above, and the accurate 2nd value will be set.
A digitized output signal is obtained.

However, the following problem arises. In other words, there is no problem if the appearance frequency of copper foil patterns is high, but if this is low,
The detection level of the copper foil pattern gradually attenuates. FIG. 5 is a diagram showing an example of this. Specifically, Figure 5 (
As shown in Figure 5 (a), in a situation where a few copper foil lines are running on a wide board, the maximum value indicating the copper foil level or the threshold proportional to it will attenuate as shown in Figure 5 (b). I end up. When the maximum value (or threshold) attenuates and there is no difference between it and the video signal, the comparator 4 responds to even a small amount of noise on the video signal, resulting in superimposed noise as shown in Figure 5 (C). A binarized output signal is obtained. In order to prevent this, it is possible to follow the threshold value with a time constant that is larger than the pattern appearance interval, but in this case,
Conversely, it becomes impossible to accurately binarize the video input signal of a board in which the copper foil signal level of the video signal fluctuates rapidly.

Therefore, in the present invention, as shown in FIG. 1, the video input signal S! A pattern detection unit 5 is provided to detect the presence or absence of a copper foil pattern from the pattern detection unit 5, and only when the output of the pattern detection unit 5 is determined to be “pattern present”, the maximum value and minimum value are sampled, and it is determined that “pattern is absent”. In this case, the maximum and minimum values at that point are held, and binarization is performed using a constant threshold until the next pattern is obtained. In this way, even when the appearance frequency of copper foil patterns is low, the threshold value remains stable and accurate binarization can be performed.

Figure 6 is a diagram for explaining the operation at that time.In the case of a copper foil pattern as shown in Figure 6(a), Figure 6(b)
At point P, release the hold of maximum and minimum value detection and capture the maximum and minimum values. Maximum value.

The minimum value starts to decay with the above-mentioned time constant, but at point Q, it is determined that there is no pattern based on the output of the pattern detection section 5, and it is held again. The threshold value changes as well. The binarized output signal is as shown in FIG. 6(c), and no malfunction occurs due to noise.

FIG. 6(d) shows the hold and sample states.

With this method, even images with few copper foil patterns can have a maximum value of 1.
It is possible to hold the threshold value for a long time without sacrificing the response speed for small values.

FIG. 7 is a circuit diagram showing an example of a specific circuit of the pattern detection section 5 of FIG. 1. Bias power supply 7, Figure 3 (
The voltage is set to a level that does not affect the baseline noise in b), and when the video signal is compared with the human power Sr by the comparator 8, a pulse signal is output if there is a copper foil pattern. If the one-shot multi 9 is equipped with the IJ function, it will output a pulse of a certain width when a pulse signal is input to the input, so the next input pulse will be output while the output is at 'H'. As long as the output is input, the output remains in the "H" state. In other words, the output becomes "L" only when the copper foil pattern does not appear for a certain period of time, so the one-shot multi-9
It is possible to determine whether there is a copper foil defect or not based on the output state of the output.

FIG. 8 is a block diagram showing another embodiment of FIG. 1 in which the output signal of the comparator 4 is used as the input signal of the pattern detection section 5. In this case, the comparator of FIG. 8
becomes unnecessary.

FIG. 9 is a circuit diagram showing an example in which FIG. 8 is developed into a specific circuit.

As described above, according to the embodiment of the present invention, in the case of a printed circuit board, the copper foil level and the base material level are independently detected,
The threshold value is calculated from these values, and the maximum and minimum values are taken in only when there is a copper foil pattern, and in other cases, all the previous values are retained, so reflectance, staining, light intensity, etc. Even if the loss width of the video signal fluctuates greatly due to changes, a stable binary output signal can be obtained. in particular,
When recognizing the pattern of a printed circuit board, with the conventional technology, only all land boards (boards with a land provided at each grid point) could be binarized with high precision, but according to the embodiment of the present invention, An effective land board (a board in which lands are provided only at grid points where lines run) can also be binarized with high precision.

In the above embodiments, the case of a copper foil pattern of a printed circuit board was explained as an example, but it goes without saying that the present invention is applicable to all cases where an image signal is to be binarized. In particular, copper foil pattern/mask pattern of printed circuit board, I
C/LSI (7) Great effects can be obtained when used in binary signal conversion of images that require high geometric precision, such as wafer patterns and mask patterns.

Furthermore, although the case has been explained using hardware as an example, it is quite possible to perform similar processing using software.

〔Effect of the invention〕

As explained above, according to the present invention, signal fluctuations can be automatically corrected without restrictions imposed by the device or the subject, and automatic operation can be performed without operator adjustment.
Even if the amplitude of the video signal fluctuates sharply due to changes in the amount of light, etc., a stable binary output signal can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the pattern detection device of the present invention, FIG. 2 is a diagram for explaining the operation of FIG. 1,
Figures 3 and 4 are diagrams showing examples of where the signal strength varies locally in the case of Figure 2, respectively, and Figure 5 is a case where the copper foil pattern appears less frequently and the detection level gradually attenuates. FIG. 6 is a diagram for explaining the operation when the appearance frequency of copper foil patterns is low. FIG. 7 is a diagram showing an example of a specific circuit of the pattern detection section of FIG. 1. Circuit diagram, 8th
The figure is a block diagram showing another embodiment of Fig. 1 in which the output signal sound of the comparator is used as the input signal of the pattern detection section, and Fig. 9 is an example in which Fig. 8 is developed into a concrete circuit. FIG. 2 is a circuit diagram showing an example. 1... Maximum value detection section, 2... Minimum value detection section, 3...
- Division circuit, 4... Comparator, 5... Pattern detection section, 7... Bias power supply, 8... Comparator, 9... One-shot multi.

Claims (1)

[Claims] 1. A maximum value detection unit that detects the maximum value of an output signal obtained by amplifying a signal from a visual sensor such as a television camera or a CCD sensor; a minimum value detection unit that detects the minimum value; a dividing circuit for obtaining an arbitrary intermediate value of the output signals of the value detecting section and the minimum value detecting section; a comparator for comparing the output signal of the dividing circuit with the amplified output signal; and a comparator for comparing the amplified output signal or the comparison. a pattern detection section that detects the presence or absence of a pattern from the output signal of the pattern detection section, and controls the sample or hold operation of the maximum value detection section or the minimum value detection section by the output signal of the pattern detection section, and controls the sample or hold operation of the maximum value detection section or the minimum value detection section to A pattern detection device characterized by having a configuration that sends out a more optimal binarized output signal. 2. The pattern detecting section includes a timer that inputs the output signal of the comparator, and the output of the timer controls sampling or holding operations of the maximum value detecting section and the minimum value detecting section. A pattern detection device according to claim 1.