JPH0447256A - Inspecting apparatus for surface defect of sheet - Google Patents

Abstract

PURPOSE:To improve the precision in detection of the end of a work piece to be inspected and to lessen regions of the opposite ends of the workpiece being insensitive for inspection, by comprising a detecting circuit using fixed binary-coding jointly with differential binary-coding in detection of the end of the workpiece. CONSTITUTION:A video output signal (a) of a one-dimensional CCD camera 5 is inputted to a differentiating circuit 10 and a fixed binary-coding circuit 11 and it is converted into a video signal differentiation signal (bb) and a video signal fixed binary- coding signal (cc) in these circuits and outputted therefrom. In regard to the differentiated waveform (bb) of the signal (a), a defect detecting circuit 12 reckons it to be a defect signal (b) as to its point being a set threshold value Ld or below or Ld<+> or above. In a window circuit 13, the first point Pe being a set threshold value Lp or below on the above-mentioned differentiated waveform (bb) in a section '1' of the signal (cc) binary-coded at a fixed threshold value Le of the signal (a) is taken as the end E of a workpiece, and thereafter a detection region signal (c) from a section corresponding to the width W of the workpiece and taken as a detection region is generated and outputted. In a defect determining circuit 14, the result (d) of determination is produced by the logical product of the signal (c) and the signal (b) and outputted therefrom.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a sheet surface defect inspection device, and particularly to a sheet surface defect inspection device for inspecting the presence or absence of defects such as indentations and scratches on the surface of rolled metal or the like.

[Conventional technology]

Conventionally, a fixed binarization method has been adopted for detecting the end of a workpiece to be inspected in this type of defect inspection apparatus.

[Problem to be solved by the invention]

Conventional sheet surface inspection equipment uses dark-field illumination arranged to image defects as bright spots, so the brightness distribution at the edge of the sheet is lower than with regular reflection illumination, and when the sheet is fed, Level fluctuations caused by undulations and deviations are large. Therefore, the workpiece end position determined by the fixed binarization method has a large error, and in practice, there is a drawback that a large dead area in which defect detection is not performed must be set for both ends of the workpiece.

[Means to solve the problem]

The sheet surface defect inspection apparatus of the present invention includes: a differentiation circuit that differentiates a video output signal of a one-dimensional CCD camera and outputs a differential signal; a defect detection circuit that detects a defect location based on the differential signal; a window circuit that determines the end of the workpiece to be inspected by ANDing a fixed binary signal of the fixed binary signal and a signal obtained by binarizing the differential signal and generates an inspection area signal corresponding to the width of the workpiece; the defect detection circuit and the window circuit; and a defect determination circuit that performs defect determination based on the logical product of signal outputs.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention.

The video output signal a of the one-dimensional CCD camera 5 is sent to the differentiating circuit 10.
are input to the fixed binarization circuit 11, and the video signal differential b
b and the video signal are converted into fixed binary CC and output.

The defect detection circuit 12 binarizes the video signal differential bb and outputs a defect signal S. The window circuit 13 inputs the video signal differential bb and the video signal fixed binary conversion CC, and outputs a detection area signal C. The defect determination circuit 14 calculates and outputs a determination result d, which is a logical product of the defect signal (x) and the inspection area signal (C).

FIG. 2 is a signal waveform diagram illustrating details of signal processing in each circuit of the control system. The horizontal axis indicates the image sensor and the corresponding position on the workpiece, and the vertical axis indicates the signal voltage or logical value.

It is assumed that the defect detection circuit 12 detects a defect signal at a point that is less than or equal to a set threshold value Ld or more than Ld+ with respect to the differential waveform bb of the video output signal a. In the window circuit 13, the first point Pe below the set threshold Lp on the aforementioned differential waveform bb in the "1" section of the signal CC binarized with the fixed threshold Le of the video output signal a is defined as the work end E, and thereafter. A detection area signal C whose detection area is a section corresponding to the workpiece width W is generated and output.

The defect determination circuit 14 generates and outputs a determination result d by ANDing the detection area signal C and the defect signal S.

As can be seen from the waveform of the video output signal a, the rise of the signal is not large enough at the edge of the workpiece, so when simply binarizing with a fixed threshold, for example Le, the workpiece edge E1, which is closer than the true workpiece edge E, is I judge that. However, in the control circuit of the present invention, since the edge position E is determined by ANDing with the differential signal bb, the error of ±1 to 2 pixels is sufficiently small compared to the workpiece edge position detection error caused by fixed binary conversion of about ±5 pixels. Detection is possible within

〔Effect of the invention〕

As explained above, the present invention improves the workpiece edge detection accuracy by including a detection circuit that uses both fixed binary conversion and differential binary conversion in detecting the ends of the workpiece to be inspected, and reduces the inspection insensitive area at both ends of the workpiece. It has the effect of being able to

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG. 2 is a signal waveform diagram. 5... One-dimensional CCD camera, 10... Differential circuit, 1
1... Fixed binarization circuit, 12... Defect detection circuit, 1
3...Window circuit, 14-way defect determination circuit.

Claims (1)

[Scope of Claims] A differentiation circuit that differentiates a video output signal of a one-dimensional CCD camera and outputs a differential signal, a defect detection circuit that detects a defective location based on the differential signal, and fixation of the video output signal. a window circuit that determines the end of a workpiece to be inspected by ANDing a binary signal and a signal obtained by binarizing the differential signal and generates an inspection area signal corresponding to the width of the workpiece; and signals of the defect detection circuit and the window circuit. A sheet surface defect inspection device comprising: a defect determination circuit that performs defect determination based on output logical product. 2. The sheet surface according to claim 1, wherein the first point below a threshold set for the differential signal is defined as the workpiece end, and thereafter the section corresponding to the workpiece width is calculated by counting the number of output bits of a one-dimensional CCD camera. Defect inspection equipment.