JPH0495862A - Ceramic defect detector - Google Patents

Abstract

PURPOSE:To detect a defect existing on a surface or inside simply, securely and non-destructively by applying a convergent light beam on one of faces and sensing transmitted light from a position distant from a convergence center position of the light. CONSTITUTION:A laser beam emitted from a laser generator 11 is, via a light focusing device 12, focused on a rear unit of ceramic 14 which is placed on a mount 13, while transmitted light 15 which has passed through the ceramic 14 forms an image 16 and detected 17 at the laser beam level through a measurement window at a position distant from a convergence center position. Since the mount 14 rotates and moves with the ceramic 14 mounted thereon at this time, the measurement window part is displaced according to the movement. When there is a defect as a sufficiently large crack on the crack on the ceramic, light incident to the defect is reflected and refracted to depart from a scattered state and a state of an intensity distribution changes, so that the measurement of a change in the detection level allows the ceramic defect to be detected simply, securely and non-destructively.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a ceramic defect detection device that non-destructively detects defects such as cracks existing on the surface or inside of a ceramic.

[Prior Art] For example, it is known that a plurality of PZT elements known as piezoelectric elements are stacked with electrode layers in between to form an actuator that controls expansion by controlling applied voltage. When configuring an actuator with such a configuration, if there is a current leak in even one of the PZT elements used in a large number of stacked layers, high voltage cannot be applied (and the function of the actuator is impaired). There is nothing (naru).

Therefore, for example, when 80 PZT elements are stacked to form an actuator, the quality level of each PZT element is required to be two orders of magnitude higher in reliability than the quality level of the actuator.

However, since a ceramic such as a PZT element is a brittle material, microscopic racks are occasionally generated due to various stresses applied during the processing process, which lowers the dielectric strength of the element and causes current leakage.

It is also known that when ceramic, which is a brittle material, is used as a structural material, minute defects (cracks, foreign objects, etc.) existing on its surface or inside can become a starting point for concentrated stress, easily leading to fracture.

Therefore, in the technical field related to ceramics, it is widely desired to establish a technology that non-destructively and reliably detects the presence or absence of defects on the surface or inside of ceramics using simple equipment. .

Non-destructive testing methods such as X-rays, ultrasonic waves, and dyeing are known as means for detecting defects in such ceramic materials. However, with inspection methods that detect defects by transmitting X-rays, it is difficult to detect, for example, meandering, narrow cracks, and X-rays that have a negative impact on the human body are used. Therefore, management and operation regarding safety is also complicated. In flaw detection methods that use ultrasonic waves, even if defects can be discovered, it is difficult to determine the type of the defect. In addition, erroneous detection may occur due to contamination of the ultrasonic propagation medium (water, alcohol, etc.), so management of the medium is also required. Furthermore, in the case of dyeing flaw detection, it is impossible to detect internal defects, and even for surface defects, the dyeing, drying, cleaning, and inspection processes are complicated.
If the surface is rough, the staining solution may remain and cause false detections, which limits its applicability.

[Problems to be Solved by the Invention] This invention has been made in view of the above points, and is capable of easily and reliably removing defects without being concerned about the location or shape of the defect inside or on the surface. The present invention aims to provide a non-destructive ceramic defect detection device capable of detecting the presence of.

[Means for Solving the Problem] A ceramic defect detection device according to the present invention applies focused laser light, for example, to one surface of a ceramic that is an object to be inspected, and identifies the defect from the focused center position of the laser light. The laser light that has passed through the ceramic is detected by a detection means set at a distance, and the level of the laser light that has passed through the ceramic is detected. In this case, the detection position of the ceramic detected by the detection means is moved and changed with respect to the focusing center position of the laser beam, and the state of change in the detection level is measured.

[Function] In the ceramic defect detection device configured as described above, when the position on the ceramic detected by the detection means is changed in relation to the focus center position of the laser beam, cracks etc. existing in the ceramic can be detected. In relation to the defect position, the intensity of the laser light that has passed through the ceramic changes, and the level of the laser light detected by the detection means set at the specified position changes.

For example, when the defect position approaches the position of the detection means from the outside in the direction of the focus center position of the laser beam, when the defect position arrives at the position immediately in front of the detection means, the laser beam is reflected by the defect and leveled. becomes higher. When the defect position and the position of the detection means match, the laser beam is not incident on the detection means, and the detection level decreases. That is, defects in the ceramic can be reliably detected by observing changes in the detection level in the detection means.

[Embodiments of the invention] Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows the basic configuration, which includes a laser generator 11, which is a type of means for generating and irradiating strong light. Laser light emitted from this laser generator 11 is focused on the back surface of a ceramic 14 set on a mounting table 13 including a driving device via a light focusing device 12 such as an optical lens. Transmitted light 15 transmitted through this ceramic 14
is imaged by an imaging device 16 such as a lens, and a detector 17
The level of the focused laser light is detected and converted into an electrical signal. The signal detected by this detector 17 is input to a control circuit 18 constituted by a computer or the like, is digitally stored and processed as appropriate, and is subjected to defect detection processing. This control circuit 18 drives and controls the mounting table 13 on which the ceramic 14 is placed, and also controls the laser generator 11.

Here, the mounting table 13 is rotated and linearly moved with the ceramic 14 placed thereon, and as shown in FIG.
A measurement window B is set at a position separated by a specified distance Xo from this center position.

In this case, the ceramic 14 is moved by the mounting table 13, and in the detector 17 where the light that has passed through the ceramic 14 forms an image, the laser that has passed through the measurement window, which is a part that changes as the ceramic 14 moves, is Allow the light intensity to be detected.

FIG. 3 shows a more specific configuration, in which laser light is generated by a semiconductor laser 111, and this semiconductor laser 111 is driven by a laser control circuit 112 that receives control commands from a control circuit 18. . The mounting table 13 includes, for example, a ring-shaped rotation stage 132 driven by a motor 131.
A transparent plate 133 is placed on top of 32. Then, a plate-shaped ceramic 14 is placed on top of this transparent plate 133. The rotation of the motor 131 is controlled by a motor control circuit 134 commanded by the control circuit 18, and the ceramic 14 is set to be rotatable at any angle by the rotation of the motor 131.

Although the details are not shown, the semiconductor laser 111 is equipped with a focusing lens at its tip, and the output laser beam focused by this focusing lens is irradiated onto the back surface of the ceramic 14 from below the rotation stage 132. . In this case, for example, spot illumination with a half width of about 100 μm is performed.

The imaging device af1B includes an objective lens 161 and a lens barrel 162.
The laser beam transmitted through the ceramic 14 is imaged on the light receiving surface of a CCD camera 171 forming a detector. That is, this CCD camera 171
1 lens barrel 162 and objective lens 181 constitute a microscope equipped with a video camera, and the focus of this microscope is set on the surface of the ceramic 14.
After converting the surface brightness of the ceramic 14 into a digital value, it is stored in a storage device of a computer constituting the control circuit 18.

FIG. 4 shows an image taken by the CCD camera 171, which shows the set measurement field of view (for example, about 1.5 + a
A light source 20 that focuses a laser beam is set at the center of w2), and several measurement windows 211, 212, . . . are set at positions slightly away from this light source 20.

Then, the luminance data of the constituent pixels of each window 211, 212, . . . are averaged and used as a detection signal.

In this state, the rotation stage 132 is rotated at specified rotation angles, for example, at intervals of 0.5'', and average luminance data corresponding to each rotation angle is plotted and used as measurement data.

In the apparatus shown in FIG. 3, the image taken by the camera 171 must be stored for each rotation angle, and the average brightness within each window must be calculated.

Therefore, measurement may take time.

FIG. 5 shows an embodiment that takes these points into consideration. Laser light generated from a semiconductor laser 111 and focused is reflected by a mirror 31 onto the outer periphery of a ceramic 14 placed on a rotary table 30. and irradiate it. And ceramic 14
The light that has passed through is focused on a photodiode 172 of a size corresponding to the measurement window, and this diode 17
A signal corresponding to the laser light level detected in step 2 is appropriately amplified by an amplifier 32 and output.

As shown in FIG. 6A, even in the ceramic 14 without defects, pores 35 are present, for example.

Therefore, when the focused laser beam is irradiated, the incident light is scattered by the pores 35, becomes scattered light, and passes through the ceramic 14 while being attenuated. Therefore, the intensity distribution per unit area of the light transmitted through the ceramic 14 on the ceramic surface is strongest at the focal point of the incident laser beam, as shown in (B) in the same figure, and gradually increases as the distance from this central position increases. It is attenuating.

Furthermore, as shown in FIG. 7(A), if there is a rack-like defect 36 that is sufficiently larger than the pore 35, the scattered light incident on the defect 36 will be reflected and refracted at the defect 3B. As a result, the scattering state deviates from that shown in FIG. 6, and the intensity distribution of the light transmitted through the ceramic 14 becomes as shown in FIG. 7(B).

In other words, the light that hits the surface of the defect 36 is reflected by the surface of the defect 36, resulting in a different state of attenuation curve from the central position, and furthermore, at the position where the defect 36 exists, the transmitted light level drops sharply. .

Therefore, the ceramic 14 placed on the mounting table I3 is
When the center position of the focused laser beam is moved, that is, when the relative distance between the position of the defect 36 and the center position of the incident light is changed, the state of the intensity distribution of the transmitted light shown in FIG. changes.

Figure 8 shows the distance Xol with respect to the focusing center position of the laser beam.
This figure shows the state of the transmitted light intensity distribution when the ceramic 14 is moved with a photodetector 40 such as a photodiode that detects the light transmitted through the position where the light passes through the li. The position of the defect 36 is located outside the light focusing center l with respect to the detector 40. In this state, the light from the focusing center I is reflected by the defect 36 and detected by the detector 4.
0, and the detector 40 detects a signal at a level slightly higher than the level of the attenuation curve corresponding to the distance Xo.

Specifically, light coming from the left side of the figure is scattered by the defect 36, making the left side slightly brighter and the right side darker. At this time, the output of the detector 40 is increased due to the influence of the left side becoming brighter. This phenomenon only occurs due to the presence of defects 36 such as cracks.

From this state, the ceramic 14 is moved as shown by the arrow, and the position of the defect 36 is changed as shown in (B) of the same figure.
If the laser beam is moved to a position close to the focusing center l of the detector 40, the laser beam is blocked by the defect 3B, and the detector 4
The amount of incident light relative to 0 becomes low, and the detection level decreases. When the defect 36 crosses the window by the detector 40,
The light that should be incident on the detector 40 is scattered by the defect 3B, reducing the average brightness of the window portion.

As shown in (C) of the figure, when the defect 36 is moving between the focusing center I, that is, between the light source and the detector 40,
The light incident on the detector 40 is always scattered by the defect 36, and the brightness detected by the detector 40 remains in a reduced state.

When the defect 36 passes through the focusing center I of the laser beam as shown in FIG. Therefore, a state equivalent to the case where no defect exists appears, and the average brightness of the light detected by the detector 40 increases slightly. Further, the ceramic 14 is moved (
E) As shown in the figure, when the defect 36 passes through the focusing center I, the light scattered by the defect 36 is added to the light source, and the intensity of the light detected by the detector 40 increases slightly.

That is, light coming from the right side of this figure is scattered by the defect 36, and the right side becomes slightly brighter, while the left side becomes darker. In this case, the bright portion on the right side influences the position of the detector 40, and the level of the signal detected by this detector 40 increases. Such a phenomenon occurs only due to the presence of defects 36 such as cracks. And defect 3
6 or further away from the focusing center I, only the light from the light source at this focusing center is detected by the detector 40.

Therefore, when the ceramic 14 is moved as shown in (A) to (E), the change pattern of the brightness level detected by the detector 40 becomes as shown in CF in the same figure, and the defect is detected. A unique pattern is expressed when 36 exists. The signal pattern shown in Figure (F) is not caused by dust or foreign matter on the surface. In this signal pattern, points a to e are shown in (A) to (A), respectively.
E) Each corresponds to the state shown in the figure.

The two peak points a and e that appeared in this signal pattern
is caused by an increase in scattered light due to the defect 36, whereas the depressed portion at the 0 point occurs because the defect 36 blocks transmitted light attempting to reach the position of the detector 40. Therefore, the distance at which this light is blocked is determined only by the distance between the spot light from the focused light source and the detector 40, and the defect 36 can be determined based on the amount of change ΔI in the signal level and the signal width. This can be clearly distinguished from other pseudo defects (dust, abnormal surface roughness, etc.).

Alternatively, discrimination can be made by detecting only the pattern shown in Figure (F) using pattern recognition technology.

FIG. 9 shows an actual example of a defect detection signal pattern.

FIG. 10 shows that the amount of intensity change ΔI of the detection signal pattern that detected the defect 36 corresponds to the light source and detector 4 corresponding to the focal center position.
It shows that it has a maximum value at a position relative to 0.

Assuming that the amount of light emitted from the light source is constant, the intensity of the scattered light that the detector 40 receives from the light source and the amount of change in intensity ΔI increase exponentially as the detector 40 approaches the light source. However, when the detector 40 approaches within the range of the light spread of the light source, the scattering of light accompanying the movement of the defect 36 does not necessarily block the propagation of the light to the detector 40. Although the intensity increases, the intensity change amount ΔI does not increase. As the detector 40 comes closer to the light source, the intensity of the scattered light further increases, but conversely, the amount of change in intensity ΔI decreases more and more. Therefore, the intensity change amount ΔI of the defect detection signal is maximum only at the outer periphery of the spread of the light source.

FIG. 11 shows the relationship between the distance XO between the light source and the detector 40 and the signal width.

detecting defects by light transmitted through the ceramic;
It has also been known for a long time to detect changes in the amount of light using a photodetector, but in the device shown in the example,
The defect 36 is irradiated with light and the defect 36 is moved, and the pattern of change in the amount of light detected by the detector 40 is observed.

The presence of defects 40 such as cracks is then observed depending on the condition of this signal pattern, so that only crack defects can be clearly distinguished from surface dust, foreign matter, etc. and detected.

[Effects of the Invention] As described above, according to the defect detection device of the present invention, defects such as cracks existing inside a ceramic can be clearly and easily identified and detected by a non-destructive method. Therefore, it can be effectively used for quality control of various ceramic element members.

[Brief explanation of drawings]

FIG. 1 is a block diagram schematically illustrating a ceramic defect detection device according to an embodiment of the present invention, FIG. 2 is a diagram illustrating the relationship between a measurement laser beam and a measurement window, and FIG. 3 is a more detailed diagram. FIG. 4 is a diagram illustrating the state of the image of the CCD camera in this embodiment. FIG. 5 is a configuration diagram illustrating another embodiment. FIG. Diagram explaining the state of light scattering in ceramic, No. 7
The figure is a diagram explaining the state of light scattering when a defect exists in the ceramic, and (A) to (E) in Figure 8 are diagrams showing the intensity pattern of transmitted light when the defective part is moved, respectively. (F) in the figure shows the detection signal pattern, No. 9
The figure shows a specific example of a signal pattern.
FIG. 1 is a diagram illustrating the relationship of signals to the position of a detector. 1 laser generator, 111... semiconductor laser, 12...
- Light focusing device, 13... Mounting table, 14... Ceramic (object to be detected), 15... Transmitted light, 16... Imaging device, 17.40... Detector, 171 - CCD Camera, 172...Photodiode, 18...Control circuit. Applicant's representative Patent attorney Takehiko Suzue Figure Figure 4 Figure Figure 6 Figure Travel distance X Figure 9 Figure 10

Claims (1)

[Scope of Claims] A light generating means for generating light; a light focusing means for focusing the light generated by the means on one surface of a ceramic which is a detected object; a detection means for detecting a position a specified distance away from the center of light convergence and converting it into a signal corresponding to the detection level; A control means for moving and changing the ceramic according to the position thereof, and a change in light intensity detected by the detection means is measured as the detection position of the ceramic changes. Device.