JPS6336458B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a defect inspection apparatus that irradiates the surface of a rod or tubular object to be inspected with light, converts the reflected light component into an electrical signal, and inspects the object for defects. Conventionally, a defect inspection apparatus equipped with an optical system as shown in FIG. 1a has been used to detect surface defects on paper or steel plates. In the figure, reference numeral 10 indicates a steel plate as an object to be inspected that is fed in the direction of arrow A, and a light beam from a light source 1 that emits a linearly polarized light beam is applied to the surface of the steel plate 10, driven by a high-speed motor 2. The rotating polygon mirror 3 is scanned between pp' in the width direction, and the reflected light is received by the photoelectric converter 4 via the condenser lens 4, and the optical signal that changes depending on the defects on the steel plate surface is converted into electricity. Treat it as a change in the signal,
It detects defects. Moreover, FIG. 1b is a view of the steel plate 10 in the direction of arrow B,
The light-emitting optical system that irradiates the light beam and the light-receiving optical system that receives the reflected light beam are arranged at different positions in the steel plate traveling direction so as to have an incident angle θ ₁ and a reflection angle θ ₂ , respectively. When such a conventional defect inspection device is used to irradiate a light beam onto the surface of a welding rod having a circular cross section and inspect for shape defects, the defect detection accuracy does not fully meet our requirements. The first reason is that when scanning a spot light on the surface along the axis while rotating a welding rod with a circular cross section for work efficiency, the second reason is related to the difference in the diameter of the welding rod or the rotation accuracy. As shown in the figure, it is sometimes difficult for the reflected light to accurately reach the light receiving optical system, which makes it difficult to identify shape defects. The second reason is that welding rods are made by combining various materials by firing, etc., so the surface is not flat and reflects spot light diffusely, and even if there are shape defects such as depressions, the reflected light intensity will be low. This is because there is no significant difference in the The third reason is that the relative spacing between the light-emitting optical system and the light-receiving optical system is relatively narrow;
Due to the small incident angle θ ₁ and reflection angle θ ₂ shown in , surface contamination such as rust that easily occurs on sintered materials and depressions have almost the same reflection characteristics, making it difficult to function as a welding rod. This is due to an increase in the proportion of dirt that has little effect on shape defects. The present invention has been made in view of the above points, and an object of the present invention is to provide a defect inspection device that greatly improves the accuracy of detecting shape defects in a rod or tubular object to be inspected having a diffused reflection surface. Hereinafter, one embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 3a is a plan view showing the structure of an embodiment of the present invention, and FIG. 3b is a side view thereof. In the figure, 1 is a light source that emits linearly polarized light, 2 is a high-speed motor, 3 is a rotating polygon mirror with a plane mirror placed on each surface of the rotating polygon, and 4 is a screen that displays the image of the welding rod 11, which is the object to be inspected. 6 a lens, 5 a photoelectric converter that corresponds to the luminous intensity of the welding rod imaged on the screen 6 and converts it into an electrical signal, 7 a preamplifier, 8 a main amplifier, and 9 an amplifier 7. , 8 are shown, respectively. Here, the light emitting optical system including the rotating polygon mirror 3 and the light receiving optical system including the lens 4, the photoelectric converter 5, and the screen 6 are provided on one plane including the welding rod 11, and They are arranged at different positions in the axial direction of the welding rod 11 so that the incident angle θ ₁ and the reflection angle θ ₂ are approximately 30° to 70°. The operation of this embodiment configured as described above will be explained below. First, by scanning the spot light along the axial surface of the welding rod 11 while rotating it, the entire circumferential surface of the welding rod will be inspected. Originally, giving rotation to the welding rod and feeding it to various inspection processes has been widely adopted as a means to improve inspection efficiency. The welding rod can be inspected by simply scanning the surface along the axis of the welding rod through the welding rod. Since this scanning speed is extremely high compared to the rotation speed of the welding rod, the entire length and circumference of the surface is scanned during one rotation of the welding rod. In other words, the light receiving optical system forms an image of the welding rod on the screen, and by measuring the luminous intensity, the entire surface of the welding rod can be inspected for defects. This means that the incident angle θ ₁ and reflection angle θ ₂ of the transmitted and received light beam are kept at 30 degrees to 70 degrees even if the scanning position of the spot light is at the end of the welding rod. There is.
In other words, by arranging the two optical systems that transmit and receive light on a plane that passes through the axis of the welding rod and giving them the above-mentioned reflection angle, the light that fluctuates due to the difference in the diameter of the welding rod or the rotation accuracy can be reduced. It is possible to keep the reflection range narrow. This will be explained in more detail. For example, if the light-emitting optical system and the light-receiving optical system are arranged at different positions in the moving direction of the steel plate as shown in Figure 1a, if these optical systems are arranged in the circumferential direction of the rotating welding rod, the second As is clear from the figure, a deviation in the diameter or rotational position of the welding rod greatly changes the reflection direction of the light beam, making it difficult for the light beam to reach the light receiving optical system.
On the other hand, in the embodiment shown in FIG. 3, even if there is a slight deviation in the diameter or rotational position of the welding rod, the direction of reflection of the light beam will not change significantly.
The first reason that affected the shape defect detection accuracy described above can be eliminated. Next, the light-receiving optical system in this embodiment does not make the light beam reflected by the surface of the welding rod directly enter the photoelectric converter, but instead images the surface to be inspected of the welding rod on the screen 6, and this image-forming surface The photoelectric converter 5 captures the average luminous intensity of the light, and in this sense, it is possible to easily determine the condition of the surface of the welding rod whose surface to be inspected is a light diffusing surface. Therefore, the second reason that affected the shape defect detection accuracy described above can be eliminated. Furthermore, in this example, it is necessary to separate the two optical systems from each other so that the angle of incidence or reflection exceeds 30 degrees, but this prevents dirt such as rust occurring on the surface of the welding rod and the shape of the welding rod. This makes it easy to distinguish it from defects. This will be explained with reference to FIGS. 4 and 5. FIG. 4 shows an example of the reflected light when the light ray L is almost perpendicularly incident on the welding rod surface _11a , as an example where the light emitting optical system and the light receiving optical system are extremely close together (the incident angle θ 1 and the reflection angle θ ₂ are small). The distribution is shown in which X represents the normal welding rod surface and has the highest reflectance. Next, Y is the distribution of reflected light on the surface 11a contaminated with rust or the like, which is weaker by the amount of light absorbed compared to a normal surface. Further, Z is the distribution of reflected light from the depressed surface 11b, which is a surface defect, and this is almost similar to the characteristic Y. Merely measuring the luminous intensity of these characteristics Y and Z indicates that the stain is due to rust, etc., or
It can be seen that it is difficult to identify whether it is a shape defect or not. On the other hand, Figure 5 shows the distribution of reflected light when the light emitting optical system and the light receiving optical system are sufficiently separated and the angle of incidence or reflection is increased as in this example, and shows the distribution of reflected light when the welding rod is normal. The distribution X of the surface and the distribution Y of the surface contaminated by rust etc. are extremely similar in distribution characteristics, although there is a slight difference in the reflected light intensity. However, the distribution Z of light reflected from the recessed surface is clearly distinguished from the above-mentioned X and Y, although its characteristics change depending on the curvature of the recessed surface and the angle of incidence. Therefore, the luminous intensity of a depressed surface, which is a shape defect, is much weaker than that of a normal surface or a surface contaminated by rust, etc., making it easier to adjust the wave height discriminator 9 and to reduce the intensity of the welding rod. A welding rod that is simply dirty and has almost no effect on its functionality can be determined as a good product. This also eliminates the third reason that affects the shape defect detection accuracy described above. A comparison of the detection rate of shape defects between the defect inspection apparatus according to this embodiment and other inspection apparatuses is as follows. First, 325 welding rods with visually confirmed shape defects and 325 welding rods with surfaces contaminated by rust or the like are prepared. After mixing these welding rods, the discrimination level is adjusted so that 90% or more of the welding rods with shape defects are extracted, that is, 293 or more welding rods. Table 1 shows the proportion of welding rods with contamination expressed as an excess detection rate.

[Table] However, defect detection rate = number of shape defects detected by the device /
Total number of shape defects (325) x 100 [%]...(1) Excess detection rate = Number of dirty surfaces detected as shape defects / Total number of shape defects (325) x 100 [%]
(2) As is clear from Table 1, while the conventional device had an excessive detection rate of 38%, the device of this embodiment was able to suppress it to only 6%. As is clear from the above description, according to the defect detection device of the present invention, even if the rod or tubular object to be inspected is rotated for work efficiency, shape defects and surface contamination due to rust etc. can be optically detected. In addition to finding and reliably identifying differences depending on the system layout,
Even if the surface of these objects to be inspected is a surface that reflects light diffusely, the light-receiving optical system focuses the image on the screen, so
Shape defects can be easily detected and detection accuracy can be greatly improved. The defect inspection device of the present invention is also capable of inspecting the surface condition of not only a cylindrical object with the above-mentioned diffused reflection surface but also a cylindrical object with a flat outer surface by adjusting the detection level of the wave height discriminator. It is.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a conventional defect inspection device.
Figure 2 is a diagram for explaining the operation of the device, Figure 3
The figure shows the configuration of an embodiment of the defect inspection apparatus according to the present invention, and FIGS. 4 and 5 are diagrams for explaining the operation of the embodiment. 1... Light source, 2... High speed motor, 3... Rotating polygon mirror, 4... Lens, 5... Photoelectric converter, 6...
Screen, 7... Preamplifier, 8... Main amplifier, 9... Wave height discriminator, 10... Steel plate, 11...
Welding rods.

Claims (1)

[Claims] 1 In a defect inspection device that irradiates the surface of a rod or tubular object to be inspected with light and converts the reflected light component into an electrical signal to inspect defects in the object to be inspected, a first optical system that scans a spot light in the axial direction of the object to be inspected at an incident angle of 30 degrees to 70 degrees; The first optical system is located at a position spaced apart in the axial direction of the object to be inspected, and at a position that receives reflected light from the object to be inspected at a reflection angle of 30 degrees to 70 degrees. a second photoelectric converter that includes a screen, forms an image of the object to be inspected on the screen, and converts the luminous intensity of the imaged portion into an electrical signal;
A defect inspection device characterized by comprising an optical system.