JPH0332733B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a defect detection method for detecting defects such as partial defects and holes in a plate-shaped object by optically manipulating the defects.

When a plate-shaped object is passed between the light source array and the light-receiving element array, if the plate-shaped object has defects such as partial defects or holes, the light from the light source will not be blocked by the plate-shaped object. Since it hits several light receiving elements, it is possible to know whether there is a defect in the plate-shaped object from the output signal of the light receiving elements. FIG. 1 shows the known principle configuration of this type of defect detection device.

In the apparatus shown in FIG. 1, n light sources 1a to 1
n light receiving elements 2a facing a light source array consisting of n
A light receiving element array consisting of ~2n is provided. In this example, n light sources and light receiving elements are provided in a one-to-one relationship, but the number of light sources may be different from the number of light receiving elements, and in extreme cases, it may be one. . The plate-shaped sample 3 moves in the direction of arrow and passes between the light source array and the light receiving element array while blocking light. The output signals of the light receiving elements 2a to 2n are input to the signal processing device 4 and processed for defect detection. If defects such as a missing portion 3a or a hole 3b are present in the sample 3, when these defective portions pass between the light source and the light receiving element, light hits the light receiving element, causing a change in the output of the light receiving element. Based on this change, the signal processing device 4 detects a defect and outputs the detection result to the output device 5.

An example of a defect determination circuit provided in the signal processing device 4 is shown in FIG. This circuit includes a comparator 5, which compares the output signal S of the light receiving element 2 with a reference voltage So generated by a reference power source 6. If the characteristics of the light receiving element 2 are such that, for example, the output signal S increases as the light increases, the comparator 5 determines that there is a "defect" when S>So and outputs, for example, a 〓1'' signal. do.

However, such conventional defect detection methods have
There is a drawback that the detection accuracy depends only on the setting accuracy of the reference voltage So. In other words, during initial adjustment such as during equipment installation, the reference voltage So is adjusted for each light-receiving element to account for variations in the output characteristics of the light-receiving element due to manufacturing variations in the element or differences in the environment in which the element is placed. I have to do it. Further, when the output characteristics of the light receiving elements change due to aging, it becomes necessary to readjust the individual reference voltages So. These drawbacks may not be a big problem if the plate-like object being investigated is completely opaque, but cannot be ignored if it is translucent or has a fine mesh structure (such as seaweed). .

An object of the present invention is to provide a highly accurate defect detection method that eliminates the above-mentioned drawbacks, is easy to adjust and manage, and is not affected by variations in characteristics among a plurality of light receiving elements.

In order to achieve this object, according to the present invention, a defect detection method detects defects in a sample from output data of each light receiving element obtained by optically scanning a plate-shaped object as a sample with a plurality of m light receiving element arrays. In the method, all m pieces of data D(i) (where i = 1, 2, ..., m) sequentially obtained from each light receiving element during one scanning cycle of the light receiving element array are stored, The sum of m pieces of data _n 〓 ⁱ⁼¹ D(i) is calculated, and the result is multiplied by k/m to calculate k, which is equivalent to a constant k times the average value of m pieces of data. Regarding each stored data D(i) |D(i)−
D(i+1)| is calculated, and this |D(i)−D(i+1)
It is characterized by determining the presence or absence of defects in the sample by comparing the magnitude of | and k, and if there is even one case where |D(i)-D(i+1)|>k, It is determined that there is a defect.

That is, the principle of the present invention will be explained in more detail below based on the graph of FIG. In the same figure a, if D(i) is now assumed to be D(3) and D(4) is judged as "defective part", the tolerance range is plus or minus with respect to D(3). It is represented by the threshold value K (hatched part in the figure). On the other hand, the judgment value compared with this |D(i)-D(i+1)|, that is, |D(3)-D(4)| It corresponds to A. Therefore, if we compare the positive threshold value B of the hatched part, which is the allowable range, with the judgment value A, then A
>B, the judgment value exceeds the threshold and there is a "defective"
It is judged that. Next, if D(i) is assumed to be the "defect part" D(4), the reference point of the threshold value is D(4), and the comparison is made with the threshold value B' on the negative side of the tolerance range |D(4) )-D
(5) It is performed between the judgment value represented by |.

In this way, the threshold value of the present invention is set based on the value to be compared at each point in time, so the threshold value is affected by variations in the output of the entire element that occur when a single light source is used. Never.
This is due to the fact that the determination value is the absolute value of the difference in output, but the constant k of the threshold value cannot be overlooked as it is accompanied by the above effect.

That is, the constant k determines the permissible range and is set in advance depending on the individual conditions in the measurement. These conditions include the accuracy of the equipment and the characteristics of the object to be measured. An example of the former is the variation in output due to the element being composed of a solar cell, and an example of the latter is the accuracy of the object to be measured. The variation in output is due to the fact that the material is edible glue.In the example in Figure 4, k≒
By setting k to 0.5, variation in the output of each element was dealt with, but if this variation is small, it is preferable to decrease k to narrow the width of the tolerance range and increase the detection sensitivity of defective parts.

The above explains that the present invention is not affected by variations in output, but the present invention also takes into account aging of the element, and this is shown in Fig. 3b.
The explanation will be based on.

That is, this figure shows an example in which the output of the element shown in FIG. 3a has decreased overall due to aging.

As above, considering D(3) and D(4) as an example,
It can be seen that the determination value |D(3)−D(4)| also becomes smaller as the output of the element decreases. If the threshold value is set as in the conventional case, the defect represented by the output value D(4) will not be detected. However, the threshold value in the present invention includes the average of the overall output values as a variable, and the output value of the element and the threshold value have a close relationship. Therefore, if the overall output of the element decreases, the threshold value also decreases accordingly, and the hatched area in the figure corresponds to the allowable range in this case. Therefore, as in FIG. 3a, D(4) is detected as a defective portion.

The present invention is constructed based on such a principle. Next, an example of an apparatus for carrying out the present invention will be explained based on FIG. 4.

The light receiving element 11 inputs an output signal S corresponding to the input light to the A/D converter 12. On the other hand, a frequency divider 13 divides the frequency of the fixed-frequency reference pulse by 1/q to generate a system timing pulse.
That is, the frequency divider 13 outputs a start signal pulse T every q reference pulses to operate the system once every q reference pulses. By changing the value of q, the operating speed of the system can be adjusted, and in some cases, the frequency divider 13 can be omitted. A/D converter 12 is frequency divider 1
3 through the AND gate 10, and outputs a conversion end signal EOC and a data signal D when the conversion operation is completed.
These data signals D are sent to m registers 21, 2.
2, ... and are stored sequentially. Control for sequential storage is provided in each register by AND
This is done by gates A1, A2, .

The output pulses of the frequency divider 13 are counted by a counter 14 from an initial value of zero. The binary output signal X of the counter 14 is processed by the decoder 15 from 1 to m _+1.
is decoded into a control signal Y. Here, the i-th control signal turns on, that is, becomes a "1" signal only when the binary output of the counter 14 is equal to i. Therefore, the decoder 15 outputs "1" signals in order from 1 to m ₊₁ . Registers 21, 22,...
Among them, the i-th register has an AND gate A1,
Due to the action of A2, the value of the signal S A/D-converted by the A/D converter 12 is written only when the conversion end signal EOC=1 and the i-th control signal=1. In other words, the i-th A/D converted signal S
The data D(i) is stored in the i-th register, and finally the data of the signal S that has been A/D converted m times is written in registers 21, 22, . . . in chronological order. These m conversions correspond to the light receiving element 11 scanning from one end of the sample to the other end.

The next timing after completing the measurement of the signal S m times,
In other words, the m ₊₁ output of the decoder 15 becomes 〓1'', the series of operations related to A/D conversion is completed, and the system operation moves to the next stage. That is, the addition is performed by the control signal m ₊₁ . As adder 16 is started, AND gate 10 is blocked and counter 14 is held.
The sum of data D(i) written in 1, 22, . . . is calculated. If the conversion data of the A/D converter 12 is D(i), D(2)..., Dm in chronological order, then the adder 1
The operation performed by 6 is _n 〓 ⁱ⁼¹ D(i).

A subtracter 3 is provided for each of the two adjacent sets of registers 21, 22 and the following registers 22, 23...
1, 32, ... are provided, and each subtracter calculates the difference D(1)-D(2), D(2)-D between the data stored in both registers, respectively.
(3),..., calculate D(m-1)-D(m). These differences are determined by the absolute value forming circuit 4 placed after each subtractor.
Absolute value |D(1)−D(2)|,| by 1, 42, ...
It is converted into D(2)-D(3)|,..., |D(m-1)-Dm|.

The output ΣD(i) of the adder 16 is
multiplied by k/m, where k/mΣD(i)=k{1/mΣD(i)}
=k D is calculated. Here, k is determined according to individual conditions as described above, and =
1/mΣD(i) means the average value of all data.

The value k of the output signal of the multiplier 17 and the value of the output signal of each absolute value forming circuit 41, 42, ... |D(i)-D
A magnitude comparator with (i ₊₁ )| is performed using 51, 52, . Each comparator is k<|D(i)−D(i ₊₁ )|
If so, the output signal Bi becomes 〓1'', and a 〓1'' signal representing a defect in the sample is outputted as a system output via the OR gate 18. Note that the above calculations can also be executed by a microcomputer or the like.

The above circuit operation can be summarized as follows.

First, the sample is scanned from one end to the other, and the output of the light receiving element 11 is A/D converted m times. Let the conversion results be D(1), D(2), . . . D(m)=D(i). D(i) corresponds to the scanning result at a position of W·i/m, where W is the lateral distance (width) from one end of the sample to the other. After taking m pieces of data, calculate k times the average value of the data, that is, k=k{1/mΣD(i)}.

On the other hand, calculate |D(i)−D(i ₊₁ )|, compare the magnitude of the calculation result with k, and find even one |D(i)−D
If (i ₊₁ )|>k, it is determined that this is due to the passage of a defective part, and a signal indicating "defective" is output.

According to the detection method of the present invention described above, the amount of change in data |D(i)−D(i ₊₁ )| is used as a determination value for the presence or absence of a defect, and the constant times k of the average value of data is determined. By using it as a time threshold, variations in multiple elements and changes over time become irrelevant to detection accuracy, which has the advantage of providing high accuracy while eliminating the need for troublesome adjustment work for each light-receiving element. . In addition, the above judgment value is not just the absolute value of data D(i), but the absolute value of the difference with the next data |D(i)-D(i ₊₁ )| is used as judgment data, so that the device side There is an advantage that the threshold value is not affected by the slope of the overall output caused by the accuracy of .

[Brief explanation of the drawing]

Fig. 1 is a layout diagram showing the basic structure of a known defect detection device, Fig. 2 is a block diagram showing the basic structure of the signal processing circuit portion of Fig. 1, and Figs. 3 a and b explain the principle of the present invention. FIG. 4 is a block diagram showing an example of an apparatus for carrying out the present invention. 3...Sample, 11...Photodetector, 12...A/
D converter, 16... Adder, 17... Multiplier, 2
1, 22... register, 31, 32... subtractor,
41, 42... Absolute value forming circuit, 51, 52...
Comparator.

Claims (1)

[Scope of Claims] 1. In a defect detection method for detecting defects in a sample from output data of each light-receiving element obtained by optically scanning a plate-shaped object as a sample with a light-receiving element array consisting of a plurality of m light-receiving elements. , all m pieces of data D(i) (where i=1, 2, ..., m) sequentially obtained from each light receiving element during one scanning cycle of the light receiving element array are stored, and the stored m Sum of data _n 〓 ⁱ⁼¹ D(i) is calculated, and the result is multiplied by k/m to calculate k, which is equivalent to a constant k times the average value of m data. Calculate |D(i)-D(i+1)| for data D(i), and calculate |D(i)
A method for detecting a defect in a plate-shaped object, characterized in that the presence or absence of a defect in the sample is determined by comparing the magnitude of -D(i+1)| with the k.