JP5928231B2 - Surface defect inspection method - Google Patents

Description

  The present invention relates to a surface defect inspection method for inspecting a surface defect of a metal plate (including a metal strip).

In the hot dip galvanizing line (hereinafter abbreviated as CGL) in the metal plate manufacturing process, after immersing the metal plate in the hot dip zinc bath to give zinc to the surface, the air is metalized by a wiping nozzle directly above the zinc bath. The amount of zinc adhesion is controlled by spraying on the plate surface.
The amount of zinc adhered by the wiping nozzle is controlled by adjusting the pressure of air to be blown, the distance between the nozzle and the metal plate, the nozzle height (distance between the zinc bath and the nozzle), and the like. However, when the target value of the zinc adhesion amount is small and the gas squeezing by the wiping nozzle is large, or when there is equipment abnormality such as clogging of the wiping nozzle, the air from the wiping nozzle melts the zinc bath surface. It tends to cause a situation where zinc is scattered.
When the scattered molten zinc adheres to the surface of the metal plate, the plating thickness of the scattered zinc adhering portion becomes thicker than the normal portion. This abnormal part is usually called “splash” and not only deteriorates the surface appearance of the metal plate, but also causes damage to the press die during press processing in a consumer such as an automobile manufacturer. It is a problem.

  As a conventional quality control technique in the metal plate manufacturing process, for example, there is a technique disclosed in Patent Document 1. This technique is based on detection means for detecting the surface condition of a steel sheet, comparison means for comparing a signal obtained by the detection means with a predetermined reference value, and a surface defect name based on the surface defect signal obtained by the comparison means. And a calculation means for calculating a defect grade.

JP 2000-28547 A

Since the above-mentioned CGL has a high line speed, surface appearance inspection is mainly performed with an optical surface defect meter. In the optical surface defect meter, the surface of the metal plate is irradiated from the projector, the reflected light is detected by the receiver, the difference in brightness between the normal and abnormal parts, the size of the abnormal part, etc. (Degree of harmfulness of sputum).
However, when the surface defect is splash, the plating thickness is thick, but the surface appearance is often not much different from the normal part, and it is mild (less harmful) by the surface defect meter. There is a problem that the product is shipped as a defect.

  In the present invention, in view of the problems of these prior arts, when the surface defect is splash, it is determined that the defect is a severe defect, thereby stopping the shipment of the product and causing the product outflow having a splash part to the consumer. An object of the present invention is to provide a surface defect inspection method capable of preventing damage to a press die by preventing the damage.

  The above problems can be solved by the following invention.

[1] A surface defect inspection method using an optical surface defect meter for inspecting a surface defect of a metal plate,
Receive images of the front and back of the metal plate,
Detect front and back flaws by image processing of received images,
Perform a primary determination as to whether the detected defect grade of the flaw is mild or severe,
A surface defect inspection method, characterized in that, when wrinkles are detected at substantially the same position on the front surface and the back surface of those determined to be mild and primary, the surface is determined to be severe and secondary.

[2] In the surface defect inspection method according to [1] above,
In the primary determination,
Based on the heel length, heel width, heel area, and heel brightness, the defect grade of the heel is performed,
In the secondary determination,
Set a circumscribed rectangle containing a slight surface defect as a front area, set a front tolerance area by adding a predetermined tolerance to this,
Set a circumscribed rectangle containing a mild backside flaw as a backside area,
A surface defect inspection method, characterized in that if there is a portion where both the front side allowable area and the back side area overlap in position, it is determined to be severe.

  According to the present invention, when the surface defect is a splash, it is determined as a severe defect. Therefore, the shipment of the product is stopped and the splash outflow to the consumer is prevented, thereby pressing the consumer. It is also possible to prevent damage to the press die during processing.

It is a figure which shows an example of the processing flow of the surface defect inspection method which concerns on this invention. It is a figure which shows the example at the time of determining with "mild" similarly to the primary determination by secondary determination. It is a figure which shows the example at the time of determining with "severity" different from primary determination by secondary determination. It is a figure which shows the system structural example to which the surface defect inspection method which concerns on this invention is applied. It is a figure which shows the apparatus structural example of an optical apparatus.

  The splash defect part is thicker than the normal part, and as a result, the front and back surfaces of the defect part come into contact with the transport roll more strongly during the CGL plate, but the appearance is mild. The present inventors have conceived the present invention based on the knowledge of the present inventors that defects appear at substantially the same position on the back surface.

  That is, when a defect is recognized at approximately the same position on the front and back surfaces by the front surface defect meter, even if the front and back surfaces are determined to be light in the primary determination, the secondary determination is determined as severe and redetermined. I devised a "front / reverse judgment logic".

  If it is re-determined as severe by this “front and back side detection logic”, the product shipment will be stopped, preventing the product from having a splash defect to the customer and preventing the press die from being damaged by the customer. can do. This “front / reverse penetration determination logic” is effective not only for splash defects but also for blister defects such as blisters.

  FIG. 1 is a diagram showing an example of a processing flow of a surface defect inspection method according to the present invention. First, in Step 01, reflected light from the surface of the metal plate is received by the CCD camera, and an image taken by the CCD camera is received. Imaging with a CCD camera is performed on both the front surface (hereinafter also referred to as the front surface) and the back surface (hereinafter also referred to as the back surface) of the metal plate.

Next, in Step 02, wrinkles are detected by image processing of the received image. For pixels in which the signal intensity (luminance) of the image exceeds a preset threshold value (minimum evaluation section on the surface of the metal plate), continuous pixels in the longitudinal direction (y direction) and the plate width direction (x direction) are connected, Think of it as one trap. This process is performed on each front surface and back surface, surface defects (hereinafter, also referred to as front scratches) and the back surface flaws (hereinafter also reverse flaw hereinafter) to.

  In Step 03, the primary determination, that is, the defect grade determination for the front and back defects is performed. The defect grade of the defect is determined based on the defect length (the length in the y direction), the defect width (the length in the x direction), the defect area, and the defect luminance.

  After the above primary determination, in the present invention, in Step 04, it is determined whether the defect grade is “mild” or “severe”. Here, the “severe” judgment is maintained without passing through the secondary judgment shown below for the front face for which the defect grade is judged as “severe” (Step 10).

  For a front with a “minor” defect grade, in Step 05, a circumscribed rectangle containing the front is set as the front area. Further, in Step 07, a predetermined allowable range (for example, length A at the front end in the longitudinal direction of the front ridge area, length B at both sides in the plate width direction, see FIGS. 2 and 3 described later) Set the front tolerance area with) added.

  Then, in the case of a back surface with a defect grade of “mild”, a back surface area is set in Step 06 as in Step 05.

  Next, in Step 08, it is determined whether or not there is a portion where both the front side allowable area and the back side area overlap in position. If there is no part where both areas overlap in position, it is determined as “mild” (Step 09) as in the primary determination, and if there is a part where both areas overlap in position, it is determined as “severe” ( Step10).

  In the above, an example of the position comparison between the front area and the back area has been described, but the back area is set from the back area, and the determination is made by comparing the position between the back area and the front area. You may make it do.

  FIG. 2 is a diagram illustrating an example in which “mild” is determined in the secondary determination similarly to the primary determination. This is a case in which there is no overlapping portion between the front tolerance area and the back area. In this case, it is determined that the defect is “mild”.

  Unlike this, FIG. 3 is a diagram illustrating an example of a case where “secondary determination” is determined to be “severe” different from the first determination. Since there is an overlapping portion between the front side allowable area and the back side area, it is determined as a “severe” defect.

  As shown in FIG. 3, when it is secondarily determined as “severe”, that is, a severe defect (harmful defect), shipment of the product is stopped. Thereby, the product outflow which has a splash part to a consumer can be prevented, and the press die damage by a consumer can also be prevented.

  Embodiments to which the present invention is applied will be described below.

  FIG. 4 is a diagram showing a system configuration example to which the surface defect inspection method according to the present invention is applied. Furthermore, FIG. 5 is a diagram illustrating a device configuration example of the optical device. In the figure, 1 is a steel plate, 10 is an optical device, 11 is a linear light source, 12 is a CCD camera, 20 is a signal processing system, 21 is a preprocessing device, 22 is an image processing device, 23 is a defect determination device, and 24 is Each light quantity control device is shown.

  The overall configuration includes an optical device 10 and a signal processing system 20, as shown in FIG. The optical device 10 includes a linear light source 11 that applies light to the steel plate 1 and a CCD camera 12 that receives reflected light from the steel plate 1. The CCD cameras 12 are arranged side by side in the width direction of the steel plate 1.

  The image pickup signal from the CCD camera 12 is sent to the signal processing system 20. First, the preprocessing device 21 performs averaging processing, shading correction, and visual field synthesis, and the image processing device 22 adjusts the peak luminance and the like. The defect is extracted from the feature amount.

  The next defect determination apparatus 23 is an apparatus for performing the above-described surface defect inspection method of the present invention. Here, the species / grade is determined. The light quantity control device 24 controls the intensity of the light quantity of the linear light source based on the signal processing result from the imaging signal from the CCD camera 12.

  The system described above was installed in a CGL line for producing a hot-dip galvanized steel sheet to prevent product outflow having a splash part to consumers. As a result, there has been no damage to customer press dies due to products with a splash part, which has occurred twice a year. Reduced press die repair costs and improved customer reliability.

DESCRIPTION OF SYMBOLS 1 Steel plate 10 Optical apparatus 11 Linear light source 12 CCD camera 20 Signal processing system 21 Preprocessing apparatus 22 Image processing apparatus 23 Defect determination apparatus 24 Light quantity control apparatus

Claims (2)

A surface defect inspection method using an optical surface defect meter for inspecting a surface defect of a metal plate plated with molten zinc ,
Receives the image obtained by photographing the front and back surfaces of the metal plate,
Detect front and back flaws by image processing of received images,
Perform a primary determination as to whether the detected defect grade of the flaw is mild or severe,
A surface defect inspection method characterized in that, when a wrinkle is detected at substantially the same position on the front surface and the back surface among those determined to be mild and primary, the wrinkle is a splash defect and secondarily determined to be severe. The surface defect inspection method according to claim 1 ,
In the primary determination,
Based on the heel length, heel width, heel area, and heel brightness, the defect grade of the heel is performed,
In the secondary determination,
Set a circumscribed rectangle containing a slight surface defect as a front area, set a front tolerance area by adding a predetermined tolerance to this,
Set a circumscribed rectangle containing a mild backside flaw as a backside area,
A surface defect inspection method, characterized in that if there is a portion where both the front side allowable area and the back side area overlap in position, it is determined to be severe.