Surface inspection device

Abstract

To provide a surface inspection device which is capable of accurately and quickly detecting the surface condition of an object, has a simple configuration, and can be manufactured at low cost, and to provide a surface inspection method using the same.SOLUTION: A surface inspection device is provided, comprising a light source for radiating inspection light toward an inspection target, light reception means for receiving reflected light, or the inspection light reflected by the inspection target, and displacement means for relatively changing the angle of incidence of the inspection light to the inspection target, where the light reception means is a luminance change detection device configured to output a difference in luminance of the reflected light.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a surface inspection apparatus.

Background Art

[0002] Surface inspection apparatuses for detecting surface defects of an object and the like have been put into practical use in various configurations. Generally, inspection light is irradiated onto a test object, and a still image of the surface of the test object is acquired. By analyzing this still image or comparing it with a defect-free reference image, it is known to detect the presence or absence of surface defects of the test object and their shapes (see, for example, Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in a conventionally known surface inspection apparatus using an image, in order to detect minute surface defects with high accuracy, a high-resolution camera, a high-performance processor for handling large-sized images, etc. are required, and there has been a problem that the apparatus cost is high. Further, in order to detect minute surface defects with high accuracy, it is necessary to handle large-sized images, and when inspecting a large number of test objects in a short time, a large-scale and high-cost inspection apparatus has been required.

[0005] The present invention has been made in view of the above problems, and an object thereof is to provide a surface inspection apparatus capable of detecting the surface state of an object with high accuracy and at high speed, and capable of being manufactured with a simple configuration at low cost.

Means for Solving the Problems

[0006] The inventors irradiate inspection light while changing the irradiation angle toward the subject, and by using the differential data of the luminance change of the reflected light reflected by this subject, compared with the image data used in the conventional surface inspection apparatus, it has been found that the surface state of the object can be detected with high accuracy while the data volume is significantly smaller and image processing is easy.

[0007] The present invention has been made based on the above-described findings, and in order to solve the above-described problems, a surface inspection apparatus according to an embodiment of the present invention proposes the following means. (1) The surface inspection apparatus according to aspect 1 of the present invention includes a light source unit including a plurality of light sources that irradiate inspection light toward a subject, a light receiving means that receives the reflected light reflected by the subject from the inspection light, and displacement means that relatively changes the incident angle of the inspection light with respect to the subject. The light receiving means is a luminance change detection device that outputs an event as a luminance difference asynchronously at a time when the luminance change of the received reflected light exceeds a preset threshold for each pixel, and the center of the inspection surface of the subject, the center of the light source unit, and the optical axis of the light receiving means are all arranged so as to be aligned on one optical axis.

[0008] (2) The surface inspection apparatus according to aspect 2 of the present invention includes a light source unit including a plurality of light sources that irradiate inspection light toward a subject, and a light receiving means that is arranged on the side opposite to the light source via the subject and receives the measurement light generated by at least any one of transmission, refraction, and scattering of the inspection light by the subject. Displacement means for relatively changing the incident angle of the inspection light with respect to the subject, and the light receiving means is a luminance change detection device that outputs an event as a luminance difference asynchronously at a time when the luminance change of the received measurement light exceeds a preset threshold for each pixel, and the center of the inspection surface of the subject, the center of the light source unit, and the optical axis of the light receiving means are all arranged so as to be aligned on one optical axis.

[0009] (3)Aspect 3 of the present invention is characterized in that, in the surface inspection apparatus of Aspect 1, the light receiving means is a luminance change detection device that outputs the polarity of the difference in luminance of the reflected light.

[0010] (4)Aspect 4 of the present invention is characterized in that, in the surface inspection apparatus of Aspect 2, the light receiving means is a luminance change detection device that outputs the polarity of the difference in luminance of the measurement light.

[0011] (5)Aspect 5 of the present invention is characterized in that, in the surface inspection apparatus of any one of Aspects 1 to 4, the displacement means changes the emission angle of the inspection light emitted from the light source unit.

[0012] (6)Aspect 6 of the present invention is characterized in that, in the surface inspection apparatus of any one of Aspects 1 to 5, the displacement means changes the position of the object to be inspected with respect to the light source unit.

[0013] (7)Aspect 7 of the present invention is characterized in that, in the surface inspection apparatus of any one of Aspects 1 to 6, the wavelength of the light source is in the wavelength region of infrared light.

[0014] (8)Aspect 8 of the present invention is characterized in that, in the surface inspection apparatus of Aspect 3 or 4, the luminance change detection device is an event-based camera.

Advantages of the Invention

[0015] According to the present invention, it is possible to provide a surface inspection apparatus that can detect the surface state of an object with high precision and high speed, and can be manufactured at low cost with a simple configuration.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Mode for Carrying Out the Invention

[0017] Hereinafter, with reference to the drawings, a surface inspection apparatus according to an embodiment of the present invention will be described. Note that the embodiments shown below are specifically described to better understand the gist of the invention, and do not limit the present invention unless otherwise specified. In addition, the drawings used in the following description may show the main parts enlarged for the sake of clarity of the features of the present invention, and the dimensional ratios of the respective components are not necessarily the same as the actual ones.

[0018] (Surface Inspection Apparatus: First Embodiment) The surface inspection apparatus according to the first embodiment of the present invention will be described. FIG. 1 is a schematic diagram showing the basic configuration of the surface inspection apparatus according to the first embodiment. The surface inspection apparatus 10 of the present embodiment includes a stage 11 that supports the object to be inspected M, a light source unit (light source) 12 that emits inspection light, an event-based camera (light receiving means) 13 that is a luminance change detection device that receives the reflected light (measurement light) reflected by the object to be inspected M by the inspection light, and a control unit 14 that performs image processing and controls the operation of the light source unit 12.

[0019] The inspection object M to be inspected for its surface condition, for example, surface defects, by the surface inspection apparatus 10 can be any object made of a material capable of reflecting the inspection light L1 emitted from the light source unit 12, such as a metal material, a resin material with a smooth surface, or glass, as long as it has light reflectivity.

[0020] The stage 11 is a member that supports the inspection object M and may have an angle adjustment mechanism or the like that can orient the surface of the inspection object M in any direction.

[0021] The light source unit (light source) 12 of the present embodiment is composed of, for example, a ring-shaped base material 12a with a plurality of LEDs 12b, 12b... arranged in a circular pattern. The lighting and extinguishing of each LED 12b are controlled by the control unit 14, and a plurality of LEDs 12b, 12b... are lit and extinguished in an arbitrary lighting pattern. In the present embodiment, a plurality of LEDs 12b, 12b... are controlled to be lit and extinguished one by one in order in a circular pattern.

[0022] The light source unit 12 may be any light source that can emit inspection light L1 in an arbitrary wavelength range, such as white light, infrared light, or ultraviolet light, according to the inspection object M. In the present embodiment, LEDs 12b, 12b... capable of emitting white light are used as the light source unit 12.

[0023] The emission of the inspection light L1 from the light source unit 12 may be continuous or non - continuous. That is, in the present embodiment, the LEDs 12b, 12b... may be continuously lit and extinguished, or may be sequentially lit and extinguished discontinuously. When the emission of the inspection light L1 from the light source unit 12 is performed discontinuously, control is performed by the control unit 14 so that the lighting and extinguishing of the light source unit 12 are interlocked with the operation of the event - based camera 13 that constitutes the luminance change detection device described later. When the emission of the inspection light L1 is performed discontinuously, it is preferable to synchronize the light source unit 12 and the event - based camera (light receiving means) 13 by hardware or software.

[0024] Regarding the emission of the inspection light L1 mentioned here, whether it is continuous or discontinuous, in addition to the temporal continuity as described above, depending on whether the LEDs 12b, 12b... are formed intermittently or continuously, whether the emitted light uniformly illuminates the space or locally changes the irradiation position in the space for illumination, it may be spatially continuous or discontinuous.

[0025] The event-based camera 13 is an example of a luminance change detection device as a light receiving means, and includes an event-based sensor, a memory for performing storage and update, etc. The event-based camera 13 detects the luminance change for each pixel as an event. That is, when the luminance change of the received light exceeds a preset threshold value, the event-based camera 13 outputs an event (coordinates, polarity, time) as an event signal. Such operations are performed independently and asynchronously for each pixel.

[0026] Based on such event signals, the event-based camera 13 outputs the pixel coordinates where the luminance has changed, the degree of luminance change (difference), and the polarity (whether the luminance has changed to be higher or lower) to the control unit 14 as luminance change information asynchronously at an arbitrary timing.

[0027] Since the luminance change information output from the event-based camera 13 only includes information on the pixels where the luminance change has occurred, for example, compared with the image information including the luminance, color tone, etc. of all pixels obtained by imaging the object to be inspected with a CMOS camera, the data capacity is extremely small, and data transfer and image processing are easy.

[0028] That is, the event-based camera 13 records only the time when the event occurs and the pixel position thereof. Since the pixel position where such an event occurs is the position with a surface defect (scratch) in the surface inspection method described later, the arithmetic processing for position identification becomes unnecessary.

[0029] The event-based camera 13 has a high temporal resolution capable of processing input light in a short time, a wide dynamic range which is the ratio of the maximum value to the minimum value of the processable signals, and low power consumption compared to general CMOS cameras and the like. Therefore, by using the event-based camera 13, it becomes possible to shorten the calculation time and significantly reduce the data storage capacity. For this reason, as the control unit 14, it becomes possible to configure the surface inspection device 10 at low cost using an inexpensive notebook personal computer or the like.

[0030] In the present embodiment, the event-based camera 13 is used as the luminance change detection device which is the light receiving means, and the difference and polarity of the luminance of the incident light are output as luminance change information. However, the luminance change detection device is not limited to the event-based camera 13. For example, when a luminance difference camera is used as the luminance change detection device, the difference in the luminance of the incident light is output as luminance change information. Thus, any sensor device capable of detecting at least the pixel position and the difference in its luminance change can be applied regardless of its configuration.

[0031] The event-based camera (light receiving means) 13 may further include a low-pass filter (LPF). When the lighting of the light source unit 12 is controlled by pulse modulation, events due to noise components of the pulse modulation can be removed by removing high-frequency signals above a certain level with a low-pass filter. Note that the removal of such noise components of the pulse modulation can also be performed by software installed in the control unit 14 instead of by hardware such as a low-pass filter.

[0032] The control unit 14 constitutes a displacement means for continuously changing the incident angle of the inspection light L1 from the light source unit 12 to the inspection object M by performing lighting control and extinguishing control of a plurality of LEDs 12b, 12b,.... Further, the control unit 14 constitutes an image processing means for visualizing a portion where the luminance has changed based on the luminance change information output from the event-based camera 13 and outputting it as a surface defect image to a display or the like. Further, the control unit 14 constitutes a storage means (memory). The storage means stores, for example, information output from the event-based camera 13.

[0033] The control unit 14 that performs such processing may be composed of, for example, a computer (PC) installed with image processing software capable of processing luminance information, an interface, a display, etc. Further, the control unit 14 can also be composed of an FPGA "Field Programmable Gate Array" or the like.

[0034] In the control of the light source unit 12 as the displacement means of the control unit 14 in the present embodiment, first, after turning on any one of the LEDs 12b for a certain period of time from the start of the inspection, it is turned off. Next, after turning on the LED 12b adjacent to the turned-on LED 12b for a certain period of time, it is turned off. In this way, a plurality of LEDs 12b, 12b,... arranged in a ring shape are controlled to be turned on one by one in the clockwise direction, for example, for a certain period of time and then turned off. The lighting of the LED 12b may be sequentially lighting a plurality of LEDs 12b, 12b,... arranged in a ring shape for one round.

[0035] By controlling a plurality of LEDs 12b, 12b,... constituting the light source unit 12 by the control unit 14 as described above, the emission angle of the inspection light L1 emitted from the light source unit 12 with respect to the inspection object M can be changed. As a result, the incident angle of the inspection light L1 incident on the inspection object M continuously changes by 360°.

[0036] In addition, as another control of the light source unit 12 as the displacement means of the control unit 14, the control unit 14 may control so that two or more LEDs arranged in a ring shape are lit simultaneously and then turned off. For example, among the LEDs 12b, 12b arranged in a ring shape, two LEDs 12b in a facing position relationship (a position relationship of 0 degrees or 180 degrees) are lit simultaneously, and then two facing LEDs 12b in positions sequentially shifted clockwise or counterclockwise are lit and turned off simultaneously.

[0037] Alternatively, among the LEDs 12b, 12b arranged in a ring shape, three LEDs 12b in a position relationship of 0 degrees, 120 degrees, and 360 degrees are lit simultaneously and then turned off, and then three LEDs 12b in positions sequentially shifted by 60° clockwise or counterclockwise are lit simultaneously and then turned off. In this way, the method of lighting control and extinguishing control of the plurality of LEDs 12b constituting the light source unit 12 is not limited, and the plurality of LEDs 12b can be lit and extinguished in any lighting pattern.

[0038] The surface inspection device 10 having the above configuration may be arranged, for example, on one optical axis S such that the center of the inspection surface of the object to be inspected M, the center of the ring of the base material 12a of the light source unit 12, and the optical axis of the event-based camera 13 are aligned.

[0039] (Surface inspection method) Next, the operation of the surface inspection device 10 of the first embodiment and the surface inspection method of this embodiment using the surface inspection device 10 will be described. FIG. 2 is a schematic diagram showing the state of reflection of inspection light on the object to be inspected. When performing a surface inspection of an arbitrary object to be inspected M, for example, detecting a surface defect, using the surface inspection device 10, first, the object to be inspected M is supported on the stage 11 so that the inspection surface of the object to be inspected M faces the event-based camera 13. In this embodiment, a mirror-finished aluminum plate is used as the object to be inspected M, and the surface defect of this aluminum plate is inspected.

[0040] Next, the control unit 14 is operated to control the light source unit 12, and a plurality of LEDs 12b, 12b... arranged in a ring shape are sequentially turned on one by one in the clockwise direction for a fixed time and then turned off (irradiation step). At this time, inspection light L1, which is white light, is emitted from each of the turned-on LEDs 12b and enters the object under inspection M. Then, the inspection light L1 that has entered the object under inspection M is reflected according to the surface state of the object under inspection M and enters the event-based camera 13 as reflected light L2.

[0041] Note that the control unit 14, which is a displacement means for relatively changing the incident angle of the inspection light L1 with respect to the object under inspection M, may be set so that the displacement becomes a periodic movement. At this time, let the period be T. For example, in the case of the light source unit 12 in which a plurality of LEDs 12b are arranged in a ring shape, when the LEDs 12b are sequentially turned on and off one by one, the time required for one rotation becomes the period T. Alternatively, one light source may be periodically moved along a certain locus in free space, and at this time, the time required for the movement from the starting point to the end point becomes the period T.

[0042] Then, the event-based camera 13 records, as events, the pixel position and the amount of change (difference) in luminance of the reflected light L2 by each of the LEDs 12b, 12b... only when the luminance of the reflected light L2 changes.

[0043] For example, as shown in Fig. 2(a), when the inspection surface of the object under inspection M is smooth and has no surface defects such as unevenness, the inspection light L11 emitted from the LED 12b1 is reflected at the reflection angle θ and enters the event-based camera 13 as the reflected light L21. Also, the inspection light L12 emitted from the LED 12b2 arranged at a position different from the LED 12b1 shown in Fig. 2(a) is reflected at the reflection angle θ and enters the event-based camera 13 as the reflected light L22.

[0044] That is, when the inspection surface of the object under inspection M is smooth and has no surface defects such as unevenness, all of the inspection lights L1 emitted from any of the plurality of LEDs 12b, 12b... are reflected at the same reflection angle θ and enter the event-based camera 13 as reflected lights L2 with the same luminance. The event-based camera 13 does not record it as an event while the luminance of the incident reflected light L2 is the same.

[0045] That is, when there are no surface defects on the entire inspection surface of the object under inspection M, even if the plurality of LEDs 12b, 12b... arranged in a ring shape are sequentially lit and the incident angle of the inspection light L1 with respect to the object under inspection M is changed, no luminance change occurs. Therefore, no luminance change information is output from the event-based camera 13. Thus, when no luminance change information is output from the event-based camera 13 even if all the LEDs 12b, 12b... are sequentially lit, the control unit 14 outputs that there are no surface defects.

[0046] On the other hand, as shown in Fig. 2(b), when there are surface defects Q such as unevenness on the inspection surface of the object under inspection M, the inspection light L11 emitted from the LED 12b1 shown in Fig. 2(b) is diffusely reflected by the surface defect Q, and the reflected light L21 incident on the event-based camera 13 is in a state where its luminance is lower compared to the reflected light on a smooth surface.

[0047] Also, the inspection light L12 emitted from the LED 12b2 arranged at a position different from the LED 12b1 shown in Fig. 2(b) is diffusely reflected by the surface defect Q, but since the incident angle with respect to the object under inspection M is different from that of the inspection light L11, diffuse reflection with a scattering pattern different from the diffuse reflection by the LED 12b1 occurs. As a result, the reflected light L22 incident on the event-based camera 13 has a luminance different from that of the reflected light on a smooth surface and the reflected light L21.

[0048] Thus, when there is a surface defect Q on the inspection surface of the object under inspection M, if a plurality of LEDs 12b, 12b... arranged in a ring shape are sequentially lit and then turned off, due to the difference in the incident angle of the inspection light L1 with respect to the object under inspection M, specular reflection occurs in different patterns, and a luminance change occurs in the reflected light L2 that continuously enters the event-based camera 13.

[0049] That is, as shown in FIG. 3, in the normal part of the object under inspection M where there is no surface defect and the abnormal part where there is a surface defect and unevenness occurs, the normal distribution of the reflected light is different. Therefore, due to such a difference in the normal distribution, the reflection characteristics of the reflected light are different between the normal part and the abnormal part. Such a difference in the reflection characteristics is detected as the difference and polarity of luminance.

[0050] The event-based camera 13 detects the luminance change of each pixel as an event. The event-based camera 13 detects the luminance change of the reflected light L2 due to the surface defect Q as an event. That is, when the luminance change of the received light exceeds a preset threshold value, the event-based camera 13 records the pixel position, the change amount (difference) of the luminance, and the polarity of the event-based camera 13 as an event, and outputs it to the control unit 14 as an event signal. The position of the pixel included in this event signal is data corresponding to the position (coordinates) where the surface defect Q exists on the inspection surface of the object under inspection M, and the change amount (difference) of the luminance is data corresponding to the shape (such as the depth of unevenness) of the surface defect Q. Note that such an operation of the event-based camera 13 is performed independently and asynchronously for each pixel.

[0051] When the control unit 14 sequentially lights all the LEDs 12b, 12b... and the luminance change information is input, based on this luminance change information, it generates an enlarged image of the surface defect Q existing on the object under inspection M by image processing software, and outputs it as a surface defect image to, for example, a display (detection step).

[0052] In such a detection process, surface defects are detected from an event group composed of one or more stored events. For example, this event group is time-divided into event cycle groups for each period T, and spatially divided into a grid based on xy coordinates. As a result, the event group is divided into spatio-temporal rectangular parallelepipeds (voxels). The number of events in each voxel is counted, and when the count value exceeds a certain value, the voxel is defined as a surface defect voxel.

[0053] If other voxels that are spatially adjacent to the voxel are surface defect voxels, they are connected as surface defect voxels related to the same surface defect. And such connection processing is repeatedly executed until the connection of spatial neighbors cannot be made. Within the period T, spatial detection for each surface defect is performed. After the detection process, it is also possible to further perform tracking of surface defects (tracking process).

[0054] In such a tracking process, if a surface defect detected at a certain time is a surface defect detected before that time, it is tracked as the same surface defect. For the connected surface defect voxel group described above, surface defect voxels that are temporally adjacent are searched for, and the surface defect voxels are connected in the time axis direction. This makes it possible to track the above-described surface defects in space-time.

[0055] Also, when the object to be inspected is moving at a constant speed by a belt conveyor or the like, it is preferable to execute a correction process as a preprocessing process of the detection process. In this correction process, based on the known moving speed, the coordinates (pixel positions) of all events stored in the storage means of the control unit 14 are corrected. Then, with reference to an arbitrary time, according to the difference from the occurrence time of each event, a coordinate correction amount is calculated using the difference time and the moving speed. The coordinates are corrected by subtracting this coordinate correction amount from the coordinates of the event. By such a correction process, even for an object to be inspected moving at a constant speed, it is possible to process it in the same way as when it is stationary. With the above configuration, surface inspection can be performed by the surface inspection method using the surface inspection apparatus of the present embodiment.

[0056] As described above, according to the surface inspection apparatus and the surface inspection method of the present embodiment, inspection light is incident on an inspection object to be surface-inspected at a plurality of different incident angles, and a simple configuration in which the luminance change of the obtained reflected light is detected by a luminance change detection device enables easy detection of surface defects of the inspection object.

[0057] And, since the differential data of the luminance change used in the present embodiment has a significantly smaller data volume compared to high-definition image data obtained by photographing the entire surface of the inspection object, even a personal computer equipped with an inexpensive processor without using an expensive image processing device or the like can perform image processing and image output of surface defects, and a surface inspection apparatus capable of detecting surface states such as surface defects can be realized at low cost with a simple configuration.

[0058] Note that the luminance change of the reflected light used in the present embodiment is not limited to a macro luminance change that occurs in a plurality of pixels of the luminance change detection sensor due to surface defects (for example, dents) caused by relatively large unevenness on the inspection object, as described above.

[0059] For example, by treating the case where the reflection due to fine unevenness is isotropic and the luminance changes cancel each other out within one pixel of the luminance change detection sensor as no luminance change, and the case where the reflection due to unevenness is anisotropic and a luminance change occurs within one pixel of the luminance change detection sensor as having a luminance change, surface defects with fine unevenness, such as scratches, can be detected with high accuracy.

[0060] (Surface inspection apparatus: Modification example of the first embodiment) As a modification example of the surface inspection apparatus of the first embodiment described above, the stage can also be configured to be rotatable by a rotation device (displacement means) or the like. In this case, the light source may be fixedly provided at one location. Even with such a configuration, for the inspection light emitted at a uniform emission angle, the incident angle of the inspection light with respect to an arbitrary region excluding the center point of the inspection object can be changed by rotating the inspection object supported by the stage.

[0061] Thus, when there are surface defects on the object to be inspected, the luminance of the reflected light reflected from that area changes. By detecting the difference in such luminance changes with a luminance change detection device, for example, an event-based camera, it becomes possible to inspect the surface state such as surface defects present on the object to be inspected, similar to the first embodiment described above. Such a modification of the first embodiment is suitable as a low-cost surface inspection device for an object to be inspected that is a light-reflective disc, for example, a metal wafer.

[0062] (Surface inspection device: Second embodiment) FIG. 4 is a schematic diagram showing the configuration of the surface inspection device according to the second embodiment of the present invention. The surface inspection device 20 according to the second embodiment includes a conveyor 21 for placing a plurality of objects to be inspected M in one direction, a light source unit (light source) 22 for emitting inspection light, an event-based camera (light receiving means) 23 that is a luminance change detection device for receiving the reflected light (measurement light) when the inspection light L1 is reflected by the object to be inspected M, a control unit 24 that performs image processing and controls the operation of the light source unit 12, and a displacement means 25 that drives the conveyor 21 to move the placed object to be inspected M in one direction X.

[0063] The light source unit (light source) 22 is composed of one light source and irradiates one object to be inspected M on the conveyor 21 with the inspection light L1. The event-based camera 23 receives the reflected light L2 from the object to be inspected M irradiated with the inspection light L1. The control unit 24 controls the displacement means 25 to move the object to be inspected M along the one direction X at an arbitrarily set moving speed.

[0064] In the surface inspection device 20 configured in this way, while one object to be inspected M moves along the one direction X within the irradiation range of the inspection light L1, the incident angle of the inspection light L1 with respect to the object to be inspected M changes. However, when there are no surface defects such as unevenness on the surface of the object to be inspected M, the luminance of the reflected light L2 reflected from the surface of the object to be inspected M becomes uniform and does not change.

[0065] On the other hand, when there are surface defects such as unevenness on the surface of the object M to be inspected, while one object M to be inspected moves along the one-way X within the irradiation range of the inspection light L1, the inspection light L1 is diffusely reflected by this crystal defect, and the luminance of the reflected light L2 changes. By detecting such luminance changes with the event-based camera 23, the surface inspection of the object M can be performed.

[0066] The surface inspection device 20 of the present embodiment can be suitably used, for example, when arranged on a manufacturing line of parts with a glossy surface to continuously inspect the surface state of the manufactured parts.

[0067] (Surface Inspection Device: Third Embodiment) The surface inspection device of the second embodiment of the present invention will be described. Note that the same components as those in the first embodiment are denoted by the same reference numerals, and redundant descriptions are omitted. FIG. 7 is a schematic diagram showing the basic configuration of the surface inspection device of the second embodiment. The surface inspection device 30 of the present embodiment includes a light-transmissive stage 31 that supports the object M to be inspected, a light source unit (light source) 12 that emits the inspection light L11, and an event-based camera (light receiving means) 13 that is a luminance change detection device that receives the measurement light L12 generated by at least any one of transmission, refraction, and scattering of the inspection light L11 by the object M2, and a control unit 14 that performs image processing and controls the operation of the light source unit 12.

[0068] The object M2 to be inspected for the surface state inspection, for example, the surface defect inspection, by the surface inspection device 30 can be any material that can transmit, refract, and scatter the inspection light L11 emitted from the light source unit 12, for example, a transparent or translucent glass, resin material, etc., as long as it has light transmissivity, light refractivity, and light scattering properties. In the present embodiment, a transparent resin material having light transmissivity is used as the object M2.

[0069] Note that the light transmittance, light refraction property, and light scattering property mentioned here only need to be in a state where at least a part or all of the wavelength range of the inspection light causes transmission, refraction, or scattering respectively, and are not limited to a state where all of the wavelength range of the inspection light causes transmission, refraction, or scattering.

[0070] The stage 31 is a member that supports the object to be inspected M2. Such a stage 31 may be one that supports the entire surface of the object to be inspected M2 or a frame-shaped one that supports the peripheral edge of the object to be inspected M2. When using a stage 31 that supports the entire surface of the object to be inspected M2, it may be made of a material that allows the measurement light L12 to pass through.

[0071] The light source unit (light source) 12 of the present embodiment is composed of, for example, a plurality of LEDs 12b, 12b... arranged in a circular pattern on a ring-shaped base material 12a. Each LED 12b is controlled to turn on and off by the control unit 14, and a plurality of LEDs 12b, 12b... are turned on and off in an arbitrary lighting pattern. In the present embodiment, a plurality of LEDs 12b, 12b... are controlled to turn on and off one by one in a circular arrangement order.

[0072] A plurality of LEDs 12b, 12b... of such a light source unit (light source) 12 are arranged outside the visual field region (field angle) E of the event-based camera (light receiving means) 13. Thereby, detection of events other than the luminance change due to surface defects of the object to be inspected M2, that is, the event-based camera (light receiving means) 13 is prevented from detecting an event due to the on / off operation of the LEDs 12b, 12b....

[0073] The event-based camera 13 adjusts the visual field region (field angle) E by the installation position and the filter so that a plurality of LEDs 12b, 12b... of the light source unit (light source) 12 do not enter the visual field region (field angle).

[0074] A surface inspection method using the surface inspection apparatus 30 having the above configuration will be described. When performing a surface inspection of, for example, a light-transmissive inspection object M2, such as detecting surface defects, using the surface inspection apparatus 30, the control unit 14 is operated to control the light source unit 12, and a plurality of LEDs 12b, 12b... arranged in a ring shape are sequentially turned on one by one for a fixed time in the clockwise direction and then turned off.

[0075] At this time, inspection light L1, which is white light, is emitted from the lit individual LEDs 12b and enters the inspection object M2. Then, the inspection light L1 that has entered the inspection object M2 undergoes transmission, refraction, and scattering according to the surface state of the inspection object M2, and enters the event-based camera 13 arranged on the side opposite to the light source unit 12 through the inspection object M2 as measurement light L12.

[0076] The event-based camera 13 records the pixel position and the amount of change (difference) in luminance of the event-based sensor as events only when the luminance of the measurement light L12 generated by the transmission, refraction, and scattering of each of the LEDs 12b, 12b... due to surface defects of the inspection object M2 changes.

[0077] When the event-based camera 13 detects a luminance change for each pixel as an event, it records the pixel position, the amount of change (difference) in luminance, and the polarity as events and outputs them to the control unit 14 as event signals.

[0078] When all the LEDs 12b, 12b... are sequentially turned on and off and luminance change information is input, the control unit 14 generates an enlarged image of the surface defect Q existing in the inspection object M2 using image processing software based on this luminance change information, and outputs it as a surface defect image to, for example, a display. With the configuration as described above, surface inspection can be performed by the surface inspection method using the surface inspection apparatus 30 of the third embodiment.

[0079] As described above, several embodiments of the present invention have been explained. However, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, as well as in the invention described in the claims and the equivalent scope thereof.

Example

[0080] The effects of the present invention were verified. (Verification Example 1) For the verification, a surface inspection apparatus having the configuration shown in FIG. 1 was used. An event-based camera: EVK, manufactured by Prophesee Co., Ltd. (equipped with a 25 mm objective lens) was used. Light source unit: One in which 60 white light LEDs are arranged in a ring shape was used. Specimen: A stainless steel plate with a mirror-finished surface (white light reflectance 95%) was used. Control unit: A notebook personal computer installed with luminance image processing software was used.

[0081] As shown in FIG. 5, dent scratches, linear scratches, and rubbing scratches were formed on the stainless steel plate, which is the specimen, as surface defects. Then, 60 white light LEDs were sequentially emitted toward this specimen, and the reflected light was input to the event-based camera. Then, luminance change information was output from the event-based camera. FIG. 5 shows a photograph of the inspection result in which pixels having event outputs of luminance change are displayed in white.

[0082] According to the results shown in FIG. 6, when the surface inspection apparatus of the present embodiment was used, all of the dent scratches, linear scratches, and rubbing scratches formed on the stainless steel plate were clearly detected. Thereby, the effect of the surface inspection apparatus of the present embodiment could be confirmed.

[0083] (Verification Example 2) For the verification, a surface inspection apparatus having the configuration shown in FIG. 7 was used. Event-based camera: EVK, manufactured by Prophesee S.A.S. (equipped with a 25 mm objective lens) was used. The detection angle of view was adjusted so that the white light LEDs in the light source unit did not enter the field of view. Light source unit: One with 60 white light LEDs arranged in a ring shape was used. Inspected object: A hollow box-shaped body made of acrylic resin (white light transmittance 95%). Scratches were formed on the surface. Control unit: A notebook computer installed with luminance image processing software was used.

[0084] The 60 white light LEDs were sequentially lit toward this inspected object, and the measurement light transmitted through the inspected object was input into the event-based camera. Then, luminance change information was output from the event-based camera. As a result, the scratches formed on the hollow box-shaped body made of acrylic resin were clearly detected. Thereby, the effect of the surface inspection apparatus of the present embodiment could be confirmed.

Industrial Applicability

[0085] According to the surface inspection apparatus of the present invention, compared with the conventional image inspection apparatus, by inspecting the surface state of the inspected object based on luminance change information that is small in capacity and enables high-speed data processing, a surface inspection apparatus capable of high-speed inspection can be realized with a simple configuration and at low cost. Therefore, the present invention has industrial applicability.

Explanation of Signs

[0086] 10…Surface inspection apparatus 11…Stage 12…Light source unit (light source) 13…Event-based camera (light receiving means) 14…Control unit (displacement means)

Claims

1. a light source unit including a plurality of light sources for irradiating an inspection light onto an object under inspection, a light receiving means for receiving light reflected from the object under inspection, and a displacement means for relatively changing an incident angle of the inspection light with respect to the object under inspection, the light receiving means is a luminance change detection device that asynchronously outputs an event as a luminance difference at a time when a luminance change of the received reflected light exceeds a preset threshold independently for each pixel, A surface inspection device characterized in that the center of the inspection surface of the object to be inspected, the center of the light source unit, and the optical axis of the light receiving means are all arranged to be aligned on a single optical axis.

2. a light source unit consisting of a plurality of light sources for irradiating an inspection light to an object under inspection; a light receiving means arranged on the opposite side of the object under inspection from the light source and for receiving measurement light generated by at least one of transmission, refraction, and scattering of the inspection light in the object under inspection; and a displacement means for relatively changing an incident angle of the inspection light with respect to the object under inspection; The light receiving means is a luminance change detection device that asynchronously outputs an event as a luminance difference at a time when a luminance change of the received measurement light exceeds a preset threshold value independently for each pixel, A surface inspection device characterized in that the center of the inspection surface of the object to be inspected, the center of the light source unit, and the optical axis of the light receiving means are all arranged to be aligned on a single optical axis.

3. 2. A surface inspection apparatus according to claim 1, wherein said light receiving means is a luminance change detection device that outputs a polarity of a difference in luminance of said reflected light.

4. 3. A surface inspection apparatus according to claim 2, wherein said light receiving means is a luminance change detection device that outputs a polarity of a difference in luminance of said measurement light.

5. 5. The surface inspection device according to claim 1, wherein the displacement means changes an emission angle of the inspection light emitted from the light source section.

6. 5. The surface inspection apparatus according to claim 1, wherein the displacement means changes a position of the object to be inspected relative to the light source unit.

7. 5. The surface inspection device according to claim 1, wherein the wavelength of the light source is in the infrared wavelength region.

8. 5. The surface inspection apparatus according to claim 3, wherein the luminance change detection device is an event-based camera.

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