JPH0519642B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention is an apparatus for optically detecting surface defects of a material to be inspected that rotates around its axis and has a circular outer periphery. Even if the direction of specular reflection of the light irradiated onto the circumferential surface of the inspected material changes in the circumferential direction due to deformation of the inspected material, such as bending or uneven thickness, surface defects can be detected without causing false detection or deterioration of detection accuracy. related to a device for

[Prior art]

2. Description of the Related Art Optical detection devices are available as devices for detecting surface defects in materials with circular outer peripheries, such as steel bars and threaded steel pipes.
As shown in Fig. 7, this device directly irradiates a laser beam from a laser projector 2 onto the circumferential surface of a steel pipe 1 that is being rotated or spirally fed, or it is applied to a rotating or oscillating optical scanner 4 and the laser beam is reflected from the beam. Light is irradiated to scan the steel pipe 1 in the axial direction. Since the steel pipe surface is not a perfect mirror surface, the irradiated light is reflected with a certain degree of spread centered on the specular reflection direction, but the specular reflection light is mainly used for defect detection. 30 and 31, and detects a surface defect on the steel pipe 1 using the amount of light received as a criterion, and when a surface defect exists at the laser beam irradiation position of the steel pipe 1, the direction of the specularly reflected light is detected. This method utilizes the fact that the amount of light received by the light receivers 30 and 31 changes as the light changes.

However, when using this device, when the steel pipe 1 is not a perfect circle or is bent, for example, as shown in FIG. In some cases, this has led to incorrect inspections and a decrease in defect detection accuracy. That is, this is because the direction of specularly reflected light from the steel pipe 1 changes due to the rotation of the steel pipe 1 or the roll 35, especially in the circumferential direction, and when it comes off the light receivers 30 and 31 provided at predetermined positions. This is because the light receivers 30 and 31 are unable to detect this at this time, resulting in an erroneous determination that the amount of light received has decreased due to the presence of a surface defect. Further, even if the specularly reflected light does not deviate from the light receivers 30 and 31, the center of the diffused reflected light and the center of the light receiver may not match, resulting in a decrease in the level of the amount of received light, resulting in an erroneous determination.

〔the purpose〕

The present invention has been made in view of the above circumstances, and its purpose is to scan and irradiate a beam light in the axial direction onto the circumferential surface of a material to be inspected which rotates on its axis and has a circular outer periphery, and from there. Detection accuracy can be improved even when the direction of the specularly reflected light changes due to factors other than the surface defects of the inspected material, such as the roundness of the inspected material, the bending of the inspected material, the bending of the roll for rotational drive, uneven thickness, etc. An object of the present invention is to provide an optical surface defect detection device capable of inspecting surface defects without degrading the surface quality.

[Structure of the invention]

The surface defect detection device according to the present invention includes means for rotating an inspected material having a circular outer periphery around its axis, and a light projecting means for scanning a beam light on the axially longitudinal circumferential surface of the inspected material being rotated around its axis. , a surface defect detection device comprising: a light receiver that captures reflected light from the circumferential surface of the inspected material; A plurality of follow-up light-receiving parts arranged in parallel in the circumferential direction of the material to be inspected with their surfaces facing in the same direction as the light-receiving parts and capturing the reflected light, and a circuit for sample-holding signals from the follow-up light-receiving parts; , a differential amplifier into which the sample value held in the circuit is input for a predetermined period, and a light receiver or a specularly reflected light directed to the light receiver in the circumferential direction of the material to be inspected so that the output of the differential amplifier satisfies predetermined conditions. In the case of a light receiver equipped with a guiding light guide, the light receiver is provided with a drive unit that changes the position of the light guide, and the light receiver or the light guide is moved so that the defect detection light receiving unit can capture the specularly reflected light. It is characterized by providing a means for following.

〔Example〕

The present invention will be specifically explained below based on the drawings. FIG. 1 is a schematic diagram showing an embodiment of the present invention, and in the figure, reference numeral 1 denotes a steel pipe, which is a material to be inspected, which is spirally fed in the axial direction by a transfer device and an axial rotation means (not shown). Above the steel pipe 1,
An optical scanner 4 is installed, which is a mirror surface body with an appropriate area and constitutes a light projecting means that receives light and scans the reflected light in the axial direction. It is tilted and can be rotated back and forth at a constant angular velocity around the reflection point by the optical scanner controller 5.

A laser projector 2 is installed at the same height position, slightly away from the optical scanner 4, with its light projection window facing the optical scanner 4, and the laser light generated by the laser projector 2 is horizontally irradiated onto the optical scanner 4. ,
Here, it is reflected downward, and the reflected light is scanned onto the surface of the steel pipe 1 below the optical scanner 4 in its axial direction.

A rectangular cylindrical light receiver 3 is directed to the scanning area on the steel pipe 1 and is designed to follow the optical path of the reflected light for inspection. , a guide rail 11 is provided in an arc shape concentric with the steel pipe 1 at a distance from the steel pipe 1, and a guide rail 11 having a rack formed on the outer circumference is inserted through the hole, and is provided so as to be rotatable around the steel pipe 1 through the guide rail 11. There is.

A worm gear 12 that is screwed into the rack of the guide rail 11 and a servo motor 9 that rotationally drives the worm gear 12 are attached to the light receiver 3.
The receiver 3 is connected to a worm gear 12 by a servo motor 9.
It moves by being rotated. As a mechanism for moving the light receiver 3, various other mechanisms can be used.

FIG. 2 is a sectional view of the light receiver 3 seen from the light input side. The light receiver 3 has a cylindrical shape, and has a light receiving section 3a for detecting surface defects on one side, and a top and bottom light receiving section 3a on the other side. Light receiving sections 3b and 3c for tracking are provided separated by a distance a and facing in the same direction.

The light receiving section 3a detects surface defects based on the amount of specularly reflected light received from the steel pipe 1, and has a built-in photoelectric conversion element, which outputs the amount of received light as an electrical signal according to its level. The output signal is given to the defect detector 10. Defect detector 10 detects surface defects based on input signals.

The light receiving sections 3b and 3c detect changes in the circumferential direction of the specularly reflected light of the reflected light from the steel pipe 1, and similarly have a built-in photoelectric conversion element and output electric signals at a level corresponding to the amount of light received. The output signals are supplied to sample and hold circuits 6 and 7, respectively.

The optical scanner controller 5 outputs a drive signal for reciprocating the optical scanner 4, and uses this drive signal to output a hold command signal, for example, a little later than the start of forward movement. The output signal is supplied to sample and hold circuits 6 and 7.

When the hold command signal is input, the sample and hold circuits 6 and 7 hold the signals from the light receiving sections 3b and 3c at that time for a predetermined period until the next hold command signal is input, and hold these signals to the differential amplifier. 8 for a predetermined period of time, stable tracking can be achieved even if the amount of light incident on the tracking light receiver becomes extremely small due to optical scanning. That is, specifically, each held signal is output to the differential amplifier 8, the differential amplifier 8 amplifies the difference between the two input signals, and outputs the amplified signal to the servo amplifier 13, which in turn amplifies the difference between the two input signals. The servo motor 9 is controlled to rotate the required amount in a direction to make the output of the dynamic amplifier 8 zero.

Due to the rotation of the servo motor 9, the light receiver 3 is connected to the steel pipe 1 via the worm gear 12 and the guide rail 11.
is moved in the circumferential direction.

[Effect]

Next, the operation of the apparatus of the present invention will be explained. steel pipe 1
When the laser beam irradiation position on the steel pipe 1 changes due to bending or uneven thickness, and the direction of the reflected light from there changes, for example, downward in the circumferential direction, the lower light receiving part 3c The upper light receiving section 3b receives a large amount of reflected light, and the upper light receiving section 3b receives a small amount of reflected light.

The tracking light receiving sections 3b and 3c each sample and hold an electrical signal at a level corresponding to the amount of light received, that is, the level of the light receiving section 3b is lower than that of the light receiving section 3c.
When the sample and hold circuits 6 and 7 receive the hold command signal from the optical scanner controller 5, they hold the respective output signals of the light receiving sections 3b and 3c, and this signal is input to the next hold command signal. output to the differential amplifier 8.

The differential amplifier 8 outputs the difference signal, that is, both light receiving sections 3
Servo amplifier 1 amplifies the level difference between b and 3c.
Based on the input signal, the servo amplifier 13 rotates the servo motor 9 and operates to move the light receiver 3 below the guide rail 11.

As a result, the light receiver 3 is rotated downward, and the same amount of reflected light enters the light receiving sections 3b and 3c.

Therefore, even if there is a change in the laser beam irradiation position on the steel pipe 1 due to bending or uneven thickness of the steel pipe 1 or the rotating roll 35, the light receiving part 3a detects the direction of reflection of the specularly reflected light from the steel pipe 1 due to surface defects. It can follow directional changes other than changes, and can detect defects on the surface without erroneous inspection or deterioration of detection accuracy.

Although the above explanation uses laser light,
The present invention is not limited to this, but can also be applied to systems that use other beams of light.

Further, in the above description, two light receiving sections for tracking are used, but the present invention is not limited to this, and three or more may be used.

For example, using three as shown in FIG. 4 is effective when the reflected energy distribution of reflected light is concentrated at the center. In other words, in such a case, 2
When using multiple light receiving sections, a slight change in the direction of the reflected light will cause a large change in the amount of light on the tracking light receiving section.
Therefore, the position of the light receiver must be controlled frequently, and in extreme cases, oscillation may occur. On the other hand, when using three light receiving parts, the light receiving parts 3b, 3c,
The output electrical signals of 3d are held in sample-and-hold circuits 6, 7, and 21, respectively, and applied to differential amplifiers 22, 23, and 24, and when the input signal from the central light receiving section 3c is below the set level, The switching transistor 26, which is controlled to be turned on or off by the output of the differential amplifier 23, is turned off to stop the differential amplifiers 22 and 24. This allows tracking to be stopped when the direction of reflected light changes significantly. When the set level is exceeded, the differential amplifiers 22 and 2 are set so that the reflected light always enters the central light receiving section 3c.
The servo amplifier 13 supplies the output signal of 4 to the differential amplifier 25 to make the signal to be outputted from now on zero.
The oscillation phenomenon can be prevented by controlling the rotation of the servo motor 9. Note that even when two light receiving sections are used, control may be performed so that tracking is stopped when the amount of light received by both light receiving sections becomes less than a predetermined value.

Furthermore, in the above explanation, the light receiver itself is moved in accordance with the change in the direction of the reflected light, but the present invention does not do this, but instead includes a flexible structure on the light incident side of the light receiver 3, as shown in FIG. It goes without saying that the light receiver 3 can be kept stationary by attaching a light guide 14 having a light guide 14 and guiding the light with the light guide 14 and moving the tip of the light guide 14 to the optical path of the reflected light.

Furthermore, the present invention is of course capable of inspecting not only steel pipes but also other general materials having a circular outer periphery, such as screw materials.

〔effect〕

As described in detail above, the present invention changes the direction of the reflected light by changing the light irradiation position on the surface of the inspected material due to bending of the inspected material or a device for rotating or transporting the inspected material. Even if the amount of light incident on the device is extremely small, it can be stably tracked, and the light receiver or the light guide provided to guide the specular reflection accurately tracks and receives the specular reflection, so
This has an excellent effect of preventing false detection and deterioration of detection accuracy.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing an embodiment of the present invention, Figure 2 is a schematic diagram showing an embodiment of the present invention.
3 and 4 are schematic cross-sectional views showing examples of the arrangement of the defect detection light receiving section and the tracking light receiving section of the present invention,
FIG. 5 is a circuit diagram in the case of FIG. 4, FIG. 6 is another embodiment of the present invention, and FIGS. 7 and 8 are explanatory diagrams of the prior art. DESCRIPTION OF SYMBOLS 1... Steel pipe, 2... Laser emitter, 3... Light receiver, 3a... Light receiving part for detection, 3b, 3c, 3d...
...Following light receiving section, 8, 22, 23, 24, 25...
... Differential amplifier, 9 ... Servo motor, 13 ... Servo amplifier, 14 ... Light guide.

Claims (1)

[Scope of Claims] 1. A means for rotating an inspected material having a circular outer periphery around its axis, a light projection means for scanning a beam light on the axially longitudinal circumferential surface of the inspected material being rotated around its axis, and an inspected object. A surface defect detection device comprising: a light receiver that captures light reflected from the circumferential surface of a material; a circuit that includes a plurality of tracking light receiving sections that are arranged in parallel in the circumferential direction of the material to be inspected in the same direction as the light receiving sections and captures the reflected light, and that samples and holds signals from the tracking light receiving sections; a differential amplifier into which the held sample value is input for a predetermined period of time; and a light guide that guides specularly reflected light to a photoreceiver or the receiver in the circumferential direction of the material to be inspected so that the output of the differential amplifier satisfies predetermined conditions. and a drive unit that changes the position of the light guide, and causes the light receiver or the light guide to follow this so that the defect detection light receiving unit can capture the specularly reflected light. A surface defect detection device characterized by comprising means.