JPH0458903B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a surface defect inspection method capable of optically inspecting products for surface defects at high speed.

(Prior Art) As shown in FIG. 3, in a conventional automatic inspection method for surface defects on plate glass, steel plates, etc., a line image that is stood perpendicular to the moving direction of the product is detected by a CCD line sensor using a lens 50. 51, and its output signal is converted into a binary signal by an A/D conversion circuit 52, which is connected to a clock signal from a clock signal generator 53 by an AND circuit 54 and output, and is detected by a rotary encoder 55 or the like. Outputs the position information and sends both signals to RAM5 at the same time.
6, the microcomputer 57
The usual method was to perform arithmetic processing and determine whether it was good or bad. However, such a CCD line sensor 5
In recent years, 1024 to 5000 bits have been used in terms of inspection accuracy and inspection field of view, so each row of the RAM 56 has 1024 to 5000 bit defects per scan, as shown in Figure 4. Bit information and defect position information are imported, and the amount of information becomes so huge that it takes too long to process on a normal microcomputer, and it is too large and expensive to use for online inspection at a factory. There was a problem that forced me to use a computer.

(Problems to be solved by the invention) The present invention solves the conventional problems as described above,
It was developed with the aim of creating a surface defect inspection method that allows for high-speed online inspection of surface defects on products using an ordinary microcomputer without reducing inspection accuracy or reducing the inspection field of view.

(Means for Solving the Problems) The present invention focuses on forming a line image in a direction perpendicular to the moving direction of a product on a CCD line sensor, and converting the output signal into a binary value using an A/D conversion circuit. Each time a defective pulse occurs, a gate signal with a sufficient number of bits to include the defect tolerance value is generated from the rise of the first pulse, and three gates are simultaneously opened, and defective bit information is transmitted from the first gate. is characterized in that the positional information in the width direction of the product is loaded into the RAM from the second gate, and the positional information in the moving direction of the product is loaded into the RAM from the third gate, and then arithmetic processing is performed.

(Example) Next, the present invention will be explained in detail with reference to FIGS. 1 and 2. Reference numeral 1 indicates a plate-shaped product to be inspected, which is moved at a constant speed in the direction of the arrow. 2 is the imaging lens of the camera, which captures a line image in the direction perpendicular to the moving direction of the product 1 to the CCD line sensor 3.
image on top. The analog video signal obtained by this CCD line sensor 3 is binarized by an A/D conversion circuit 4, and then converted to a clock signal generator 5.
Similar to the conventional method, the signal is combined with the clock signal for driving the CCD generated by the AND circuit 6 and converted into a pulse. However, in the conventional method, as shown in Fig. 4, the CCD line sensor 3
In contrast, in the present invention, as shown in FIG. 2, the amount of defective bit information that is captured into the RAM is greatly reduced, as opposed to the case where the information covering all bits of the data is directly captured into the RAM as defective bit information. The reason for this is as follows.

In other words, defects in the appearance of products are generally classified into major defects and minor defects. Major defects are defects that have a fatal impact on quality characteristics and defects whose size exceeds the defect tolerance value, and minor defects are defects that have a fatal impact on quality characteristics. A defect is a defect whose size exceeds the allowable number determined for each type even if the size is less than the allowable defect value. Therefore, it is sufficient that the defective bit information to be loaded into the RAM and processed has a necessary and sufficient number of bits to include the above defect tolerance value, and defective bit information that exceeds this defect tolerance value is uniformly weighted. Since it will be treated as a defect, there is little point in importing it into RAM. However, since a plurality of light defects may exist in one line image, it is necessary to accurately count the number of defects.

Therefore, in the present invention, each time a defective pulse is generated from the AND circuit 6, the monostable circuit 7 generates a gate signal with a necessary and sufficient number of bits to cover the above defect tolerance value from the rise of the first pulse. The gates 8, 9, and 10 are simultaneously opened by the number of bits of the gate signal. The first gate 8 sends defective bit information to the RAM 11, and the second gate 9 sends position information in the width direction of the product.
The third gate 10 sends position information in the moving direction of the product to the RAM 11, respectively. The position information in the width direction of this product is obtained by dividing the clock signal for driving the CCD into 1/64, for example, by a frequency dividing circuit 12, and counting it by a counter 13 to divide the width direction of the product 1 into about 16 parts. This indicates in which division the defect exists. In addition, the position information in the moving direction of the product is obtained from the start pulse from the scan start pulse generator 14 of the CCD line sensor by the frequency dividing circuit 15.
The frequency is divided as necessary, and counted by a counter 16 to indicate the number of scans in which a defect was detected. The number of bits of each piece of information that is loaded into the RAM 11 in this way is usually 1/2 of the total number of bits of the CCD line sensor.
For example, if a 2048-bit CCD line sensor 3 is used, 128 bits is sufficient for the defective bit information, and if the position information in the width direction is divided into 16 divisions, it will be 4 bits in binary. It is sufficient to obtain 10 bits of position information in the direction of movement, so a total of 142 bits is sufficient. Therefore, the number of bits of information to be loaded into the RAM 11 is about 7/100 compared to the conventional method, and the microcomputer 17 can perform arithmetic processing at a sufficiently high speed to determine pass/fail. . It goes without saying that when defective pulses occur at multiple locations in one line image, information is captured each time. Further, the present invention can be used as is for inspecting not only plate-shaped products but also circular products.

(Effects of the Invention) As is clear from the above description, the present invention has the following advantages:
Since we were able to significantly reduce the number of bits of information loaded into RAM compared to conventional methods, it is possible to perform arithmetic processing at a speed sufficient for use in online factory inspections using a normal microcomputer. Moreover, it is no different from conventional methods in terms of inspection accuracy and inspection field of view. Therefore, the present invention can greatly contribute to the development of industry by solving the problems of conventional surface defect inspection methods of this type.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of a circuit used to implement the present invention, FIG. 2 is a diagram showing an example of bit information allocation for one row of RAM, and FIG. 3 is a diagram showing a circuit used to implement the conventional method. The block diagram shown in FIG. 4 is a diagram showing an example of allocation of bit information to the RAM. 3...CCD line sensor, 4...A/D conversion circuit, 8...first gate, 9...second gate, 10...third gate, 11...RAM.

Claims (1)

[Claims] 1 A line image perpendicular to the moving direction of the product is formed on a CCD line sensor, and the output signal is binarized by an A/D conversion circuit and then converted into pulses, and the first pulse is generated every time a defective pulse occurs. From the rising edge of , a gate signal with a sufficient number of bits to cover the defect tolerance value is generated to simultaneously open three gates, and defective bit information is transmitted from the first gate.
From the second gate, position information in the width direction of the product is transmitted.
A surface defect inspection method characterized in that positional information in the moving direction of the product is loaded into RAM from the third gate and then subjected to arithmetic processing.