Surface inspection method

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 irradiating inspection light toward an inspection target, light reception means for receiving reflected light, or the inspection light reflected by the inspection target, and a 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 , Table relates to a surface inspection method.

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 the object to be inspected, a still image of the surface of the object to be inspected is acquired, and the presence or absence and shape of surface defects of the object to be inspected are detected by performing image analysis on this still image or comparing it with a reference image without defects (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 conventionally known surface inspection apparatuses using images, in order to detect fine 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 fine surface defects with high accuracy, it is necessary to handle large-sized images, and when inspecting a large number of objects to be inspected 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 high speed and capable of being manufactured with a simple configuration and at low cost, and a surface inspection method using the same.

Means for Solving the Problem

[0006] The inventors of the present invention 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 an object can be detected with high accuracy while the data volume is remarkably small and image processing is easy.

[0015] The surface inspection method according to an embodiment of the present invention proposes the following means. (1) The surface inspection method according to Aspect 1 of the present invention includes an irradiation step of irradiating the inspection light from a light source toward the subject while continuously and relatively changing the incident angle of the inspection light with respect to the subject, and detecting the surface defect of the subject based on an event detected asynchronously at a time when the luminance change of the reflected light reflected by the subject exceeds a preset threshold for each pixel and received independently for each pixel. , In the detection step, surface defects are detected from an event group composed of one or more of the stored events. By time-dividing the event group into event cycle groups for each period, the event group is divided into spatio-temporal voxels, the number of events in each voxel is counted, and a voxel with a count value equal to or greater than a certain value is defined as a surface defect voxel, including the process of It is characterized by this.

[0016] ( 2 ) The surface inspection method according to an aspect 2 of the present invention includes an irradiation step of irradiating the inspection light from a light source toward the subject while continuously and relatively changing the incident angle of the inspection light with respect to the subject, and detecting the surface defect of the subject based on an event detected asynchronously at a time when the luminance change of the measurement light generated by at least any one of transmission, refraction, and scattering in the subject and received independently for each pixel exceeds a preset threshold. , In the detection step, surface defects are detected from an event group composed of one or more of the stored events. By time-dividing the event group into event cycle groups for each period, the event group is divided into spatio-temporal voxels, the number of events in each voxel is counted, and a voxel with a count value equal to or greater than a certain value is defined as a surface defect voxel, including the process of It is characterized by this.

[0017] ( 3 ) The aspect 3 of the present invention 1 is characterized in that, in the detection step of the surface inspection method according to Aspect

[0018] ( 4Aspects of the present invention 4 In the surface inspection method of the aspect 2 in the detection step, based on the polarity of the difference in luminance of the reflected light, the surface defect of the object to be inspected is detected.

[0019] ( 5 Aspects of the present invention 5 In the surface inspection method of any one of the aspects 1 from 4 the light source includes a plurality of LEDs, and the LEDs are controlled to be lit one by one sequentially or a plurality of them are lit simultaneously. 。

Advantages of the Invention

[0020] According to the present invention, it is possible to provide a surface inspection apparatus capable of detecting the surface state of an object with high accuracy and high speed, and capable of being manufactured at low cost with a simple configuration, and a surface inspection method using the same.

Brief Description of the Drawings

[0021]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Modes for Carrying Out the Invention

[0022] Hereinafter, with reference to the drawings, a surface inspection apparatus and a surface inspection method according to an embodiment of the present invention will be described. The following embodiments 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 convenience of understanding the features of the present invention, and the dimensional ratios of the respective components are not necessarily the same as the actual ones.

[0023] (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 a test object 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 reflected light (measurement light) reflected by the test object M from the inspection light, and a control unit 14 that performs image processing and controls the operation of the light source unit 12.

[0024] The test object M for which the surface inspection apparatus 10 performs a surface state inspection, for example, a surface defect inspection, can be any material that can reflect the inspection light L1 emitted from the light source unit 12 on the surface, such as a metal material, a resin material with a smooth surface, or glass, as long as it has light reflectivity.

[0025] The stage 11 is a member that supports the test object M, and may have an angle adjustment mechanism or the like that can direct the surface of the test object M in an arbitrary direction.

[0026] 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 shape. Each LED 12b is controlled to turn on and off by the control unit 14, and a plurality of LEDs 12b, 12b... turn 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.

[0027] The light source unit 12 may be a light source capable of emitting inspection light L1 in an arbitrary wavelength range, such as white light, infrared light, ultraviolet light, etc., according to the object to be inspected M. In the present embodiment, LEDs 12b, 12b... capable of emitting white light are used as the light source unit 12.

[0028] The emission of the inspection light L1 from the light source unit 12 may be continuous or discontinuous. That is, in the present embodiment, the LEDs 12b, 12b... may be continuously turned on and off, or may be sequentially turned on and off discontinuously. When the inspection light L1 is emitted from the light source unit 12 discontinuously, control is performed by the control unit 14 so that the lighting and extinguishing of the light source unit 12 and the operation of the event-based camera 13 constituting the luminance change detection device described later are interlocked. When the inspection light L1 is emitted discontinuously, it is preferable to synchronize the light source unit 12 and the event-based camera (light receiving means) 13 by hardware or software.

[0029] 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 to illuminate, it may be spatially continuous or discontinuous.

[0030] The event-based camera 13 is an example of a luminance change detection device that is a light receiving means, and includes an event-based sensor, a memory that performs storage and update, and the like. The event-based camera 13 detects luminance changes for each pixel as events. 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.

[0031] 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.

[0032] Since the luminance change information output from the event-based camera 13 includes only information about pixels where luminance changes have occurred, for example, compared with image information including the luminance, color tone, etc. of all pixels obtained by imaging a test object with a CMOS camera, etc., the data capacity is extremely small, and data transfer and image processing are easy.

[0033] That is, the event-based camera 13 records only the time when an event occurs and the pixel position thereof. Since the pixel positions where such events occur are the positions where surface defects (scratches) are present in the surface inspection method described later, arithmetic processing for position identification becomes unnecessary.

[0034] The event-based camera 13 has a high temporal resolution capable of processing input light in a short time, has a wide dynamic range which is the ratio of the maximum value to the minimum value of the signals that can be processed, and has lower power consumption compared with general CMOS cameras and the like. Therefore, by using the event-based camera 13, it is possible to shorten the arithmetic time and significantly reduce the data storage capacity. For this reason, it becomes possible to configure the surface inspection device 10 at low cost by using an inexpensive notebook personal computer or the like as the control unit 14.

[0035] In this embodiment, an event-based camera 13 is used as the light-receiving means, i.e., the luminance change detection device, 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.

[0036] 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 caused by 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 pulse modulation can also be performed by software installed in the control unit 14 instead of by hardware such as a low-pass filter.

[0037] 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 the 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.

[0038] The control unit 14 performing 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.

[0039] In the control of the light source unit 12 as the displacement means of the control unit 14 in this 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, the 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 such that the plurality of LEDs 12b, 12b... arranged in a ring shape are sequentially turned on for one round.

[0040] By controlling the 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 object under inspection M can be changed. As a result, the incident angle of the inspection light L1 incident on the object under inspection M continuously changes by 360°.

[0041] 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 to turn on two or more of the LEDs arranged in a ring shape simultaneously and then turn them 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) can be turned on simultaneously, and then two facing LEDs 12b in positions sequentially shifted clockwise or counterclockwise can be turned on and off simultaneously.

[0042] 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 can be turned on simultaneously and then turned off, and then three LEDs 12b in positions sequentially shifted by 60° clockwise or counterclockwise can be turned on simultaneously and then turned off. In this way, the method of controlling the lighting and extinguishing of the plurality of LEDs 12b constituting the light source unit 12 is not limited, and the plurality of LEDs 12b can be turned on and off in any lighting pattern.

[0043] The surface inspection apparatus 10 configured as described above may be arranged, for example, such that the center of the inspection surface of the object M to be inspected, 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 on one optical axis S.

[0044] (Surface Inspection Method) Next, the operation of the surface inspection apparatus 10 of the first embodiment and the surface inspection method of this embodiment using the surface inspection apparatus 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 M to be inspected, for example, detecting surface defects, using the surface inspection apparatus 10, first, the object M is supported on the stage 11 such that the inspection surface of the object M faces the event-based camera 13. In this embodiment, a mirror-finished aluminum plate is used as the object M, and the surface defects of this aluminum plate are inspected.

[0045] Next, the control unit 14 is operated to control the light source unit 12, and the plurality of LEDs 12b, 12b... arranged in a ring are sequentially lit 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 lit LED 12b and enters the object M to be inspected. Then, the inspection light L1 that has entered the object M is reflected according to the surface state of the object M and enters the event-based camera 13 as reflected light L2.

[0046] 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 M to be inspected, may be set such that the displacement is a periodic movement. At this time, the period is T. For example, in the case of the light source unit 12 in which a plurality of LEDs 12b are arranged in a ring, when the LEDs 12b are sequentially lit and turned off one by one, the time required for one rotation is the period T. Alternatively, one light source may be periodically moved in a certain locus in free space, and in this case, the time required for the movement from the starting point to the end point is the period T.

[0047] Then, the event-based camera 13 records, as events, the pixel positions of the event-based sensor and the amount of change (difference) in luminance only when the luminance of the reflected light L2 by each of the LEDs 12b, 12b... changes.

[0048] For example, as shown in Fig. 2(a), when the inspection surface of the object M to be inspected 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. Further, 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.

[0049] That is, when the inspection surface of the object M to be inspected is smooth and has no surface defects such as unevenness, no matter which of the plurality of LEDs 12b, 12b... the inspection light L1 is emitted from, all are reflected at the same reflection angle θ and enter the event-based camera 13 as reflected light L2 having the same luminance. The event-based camera 13 does not record as events while the luminance of the incident reflected light L2 is the same.

[0050] That is, when there are no surface defects on the entire inspection surface of the object M to be inspected, 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 M is changed, no luminance change occurs, so no luminance change information is output from the event-based camera 13. Therefore, 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.

[0051] On the other hand, as shown in Fig. 2(b), when there is a surface defect Q such as unevenness on the inspection surface of the object M to be inspected, 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 entering the event-based camera 13 is in a state where its luminance is reduced compared to the reflected light on a smooth surface.

[0052] In addition, the inspection light L12 emitted from the LED12b2 arranged at a position different from the LED12b1 shown in FIG. 2(b) is diffusely reflected by the surface defect Q. However, since the incident angle with respect to the inspection object M is different from that of the inspection light L11, diffuse reflection with a scattering pattern different from that of the diffuse reflection by the LED12b1 occurs. As a result, the reflected light L22 incident on the event-based camera 13 has a different luminance from the reflected light on the smooth surface and the reflected light L21.

[0053] As described above, when there is a surface defect Q on the inspection surface of the inspection object M, if a plurality of LEDs 12b, 12b... arranged in a ring shape are sequentially turned on and then turned off, due to the difference in the incident angle of the inspection light L1 with respect to the inspection object M, diffuse reflection occurs in different patterns, and a luminance change occurs in the reflected light L2 continuously incident on the event-based camera 13.

[0054] That is, as shown in FIG. 3, in the normal part where there is no surface defect on the inspection object M and the abnormal part where there is a surface defect and unevenness occur, 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 the luminance.

[0055] The event-based camera 13 detects the luminance change for 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 inspection object 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.

[0056] When the control unit 14 sequentially lights all the LEDs 12b, 12b... and luminance change information is input, based on this luminance change information, it generates an enlarged image of the surface defect Q existing in the inspection object M by image processing software, and outputs it as a surface defect image to, for example, a display (detection step).

[0057] In such a detection step, 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 period 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 becomes equal to or greater than a certain value, the voxel is defined as a surface defect voxel.

[0058] And when 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 in the spatial vicinity cannot be made. Within the period T, spatial detection for each surface defect is performed. After the detection step, it is also possible to further execute tracking of the surface defect (tracking step).

[0059] In such a tracking step, when 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. As a result, it becomes possible to track the above-described surface defect in space-time.

[0060] Also, when the object to be inspected is moving at a constant speed by a belt conveyor or the like, it is also 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, the 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 becomes possible to process it in the same manner as when it is stationary. With the above configuration, the surface inspection can be performed by the surface inspection method using the surface inspection apparatus of the present embodiment.

[0061] As described above, according to the surface inspection apparatus and the surface inspection method of the present embodiment, for the object to be inspected for surface inspection, the inspection light is made incident at a plurality of different incident angles, and the luminance change of the obtained reflected light is detected by the luminance change detection device. With such a simple configuration, it becomes possible to easily detect the surface defects of the object to be inspected.

[0062] And, since the differential data of the luminance change used in the present embodiment has a significantly smaller data volume compared to the high-definition image data obtained by photographing the entire surface of the object to be inspected, even with a personal computer equipped with an inexpensive processor without using an expensive image processing device or the like, it is possible to 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 with a simple configuration at low cost.

[0063] Note that the luminance change of the reflected light used in the present embodiment is not limited to the macro luminance change across a plurality of pixels of the luminance change detection sensor that occurs due to surface defects (for example, dents) with relatively large unevenness on the surface of the object to be inspected, as described above.

[0064] For example, when the reflection due to fine irregularities is isotropic and the luminance changes within one pixel of the luminance change detection sensor cancel each other out, it is regarded as no luminance change. When the reflection due to the irregularities is anisotropic and a luminance change occurs within one pixel of the luminance change detection sensor, it is processed as having a luminance change. By doing so, surface defects with fine irregularities, such as scratches, can be detected with high precision.

[0065] (Surface inspection apparatus: Modification of the first embodiment) As a modification of the surface inspection apparatus of the first embodiment described above, the stage can also be configured to be rotatable by a rotating 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, as the inspected object supported by the stage rotates, the incident angle of the inspection light with respect to any region excluding the center point of the inspected object can be changed.

[0066] Thereby, when there is a surface defect in the inspected object, the luminance of the reflected light reflected from that region changes. By detecting the difference in such luminance changes with a luminance change detection device, such as an event-based camera, it becomes possible to inspect the surface state, such as surface defects existing in the inspected object, in the same manner as in the first embodiment described above. Such a modification of the first embodiment is suitable as a low-cost surface inspection apparatus for an inspected object that is a light-reflective disc, such as a metal wafer.

[0067] (Surface inspection apparatus: Second embodiment) FIG. 4 is a schematic diagram showing the configuration of the surface inspection apparatus according to the second embodiment of the present invention. The surface inspection apparatus 20 according to the second embodiment includes a conveyor 21 for placing a plurality of inspected objects 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 inspected object 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 inspected object M in one direction X.

[0068] The light source unit (light source) 22 is composed of one light source, and irradiates the inspection light L1 onto one inspection object M on the conveyor 21. The event-based camera 23 receives the reflected light L2 from the inspection object M irradiated with the inspection light L1. The control unit 24 controls the displacement means 25 to move the inspection object M along the one direction X at a set arbitrary moving speed.

[0069] In the surface inspection apparatus 20 having such a configuration, while one inspection object 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 inspection object M changes. However, when there are no surface defects such as unevenness on the surface of the inspection object M, the luminance of the reflected light L2 reflected from the surface of the inspection object M becomes uniform and does not change.

[0070] On the other hand, when there are surface defects such as unevenness on the surface of the inspection object M, while one inspection object M moves along the one direction 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 a luminance change with the event-based camera 23, the surface inspection of the inspection object M can be performed.

[0071] The surface inspection apparatus 20 of the present embodiment can be suitably used, for example, when arranged on a manufacturing line of parts having a glossy surface to continuously inspect the surface state of the manufactured parts.

[0072] (Surface Inspection Apparatus: Third Embodiment) The surface inspection apparatus according to 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 apparatus according to the second embodiment. The surface inspection apparatus 30 of this embodiment includes a light-transmissive stage 31 that supports the object M to be inspected, a light source unit (light source) 12 that emits inspection light L11, and an event-based camera (light-receiving means) 13 that is a luminance change detection device that receives measurement light L12 generated by at least any one of transmission, refraction, and scattering of the inspection light L11 by the object M2 to be inspected, and a control unit 14 that performs image processing and controls the operation of the light source unit 12.

[0073] The object M2 to be inspected for the surface state inspection, for example, the surface defect inspection, by the surface inspection apparatus 30 can be any object as long as it is a 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., having light transmissivity, light refraction property, and light scattering property. In this embodiment, a transparent resin material having light transmissivity is used as the object M2.

[0074] Note that the light transmissivity, 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, and scattering respectively, and is not limited to a state where the entire wavelength range of the inspection light causes transmission, refraction, and scattering.

[0075] The stage 31 is a member that supports the object M2 to be inspected. Such a stage 31 may be one that supports the entire one surface of the object M2 or a frame-shaped one that supports the peripheral edge of the object M2. When using a stage 31 that supports the entire one surface of the object M2, it may be made of a material that can transmit the measurement light L12.

[0076] The light source unit (light source) 12 of this embodiment is composed of, for example, a ring-shaped base material 12a with a plurality of LEDs 12b, 12b... arranged in a circular shape. Each LED 12b is controlled to be turned 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 this embodiment, a plurality of LEDs 12b, 12b... are controlled to be turned on and off one by one in a circular arrangement order.

[0077] A plurality of LEDs 12b, 12b... of such a light source unit (light source) 12 are arranged to be located outside the visual field region (angle of view) E of the event-based camera (light receiving means) 13. Thereby, detection of an event other than a change in luminance due to a surface defect of the object M2 to be inspected, that is, detection by the event-based camera (light receiving means) 13 as an event due to the lighting and extinguishing operations of the LEDs 12b, 12b... is prevented.

[0078] The visual field region (angle of view) E of the event-based camera 13 is adjusted 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 (angle of view).

[0079] A surface inspection method using the surface inspection apparatus 30 configured as described above will be described. When performing a surface inspection of, for example, a light-transmissive object M2 using the surface inspection apparatus 30, for example, when detecting a surface defect, 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 lit one by one in the clockwise direction for a certain period of time and then extinguished.

[0080] At this time, inspection light L1, which is white light, is emitted from each lit LED 12b and enters the object M2 to be inspected. Then, the inspection light L1 that has entered the object M2 is transmitted, refracted, and scattered according to the surface state of the object M2, and enters the event-based camera 13 arranged on the side opposite to the light source unit 12 through the object M2 as measurement light L12.

[0081] The event-based camera 13 records, as an event, the change amount (difference) in the pixel position and luminance of the event-based sensor only when the luminance of the measurement light L12 generated by the transmission, refraction, and scattering due to the surface defect of the object M2 changes for each of the LEDs 12b, 12b....

[0082] When the event-based camera 13 detects the luminance change for each pixel as an event, it records the pixel position, the amount of change (difference) in luminance, and the polarity as an event, and outputs them as an event signal to the control unit 14.

[0083] When the control unit 14 sequentially turns on and off all the LEDs 12b, 12b... and luminance change information is input, based on this luminance change information, it generates an enlarged image of the surface defect Q existing in the inspection object M2 by image processing software, and outputs it as a surface defect image to, for example, a display or the like. 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.

[0084] As described above, several embodiments of the present invention have been described. 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, and are also included in the invention described in the claims and the equivalent scope thereof.

Example

[0085] The effects of the present invention were verified. (Verification Example 1) In the verification, a surface inspection apparatus having the configuration shown in FIG. 1 was used. An event-based camera: EVK, manufactured by Prophesee S.A. (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. Inspection object: 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.

[0086] As shown in Fig. 5, dent scratches, linear scratches, and abrasion scratches were formed as surface defects on a stainless steel plate as the object to be inspected. Then, 60 white light LEDs were sequentially emitted toward this object to be inspected, and the reflected light was input to an 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 with event outputs of luminance change are displayed in white.

[0087] According to the results shown in Fig. 6, when the surface inspection apparatus of the present embodiment was used, the dent scratches, linear scratches, and abrasion scratches formed on the stainless steel plate were all clearly detected. Thereby, the effect of the surface inspection apparatus of the present embodiment could be confirmed.

[0088] (Verification Example 2) In the verification, a surface inspection apparatus having the configuration shown in Fig. 7 was used. Event-based camera: EVK, manufactured by Prophesee Co., Ltd. (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: A ring-shaped arrangement of 60 white light LEDs was used. Object to be inspected: A hollow box-shaped body made of acrylic resin (white light transmittance 95%). Abrasion scratches were formed on the surface. Control unit: A notebook personal computer installed with luminance image processing software was used.

[0089] 60 white light LEDs were sequentially emitted toward this object to be inspected, and the measurement light transmitted through the object to be inspected was input to an event-based camera. Then, luminance change information was output from the event-based camera. As a result, the abrasion 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

[0090] According to the surface inspection apparatus and the surface inspection method of the present invention, by inspecting the surface state of an object to be inspected based on luminance change information that is small in capacity and enables high-speed data processing as compared with a conventional image inspection apparatus, 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 Reference Numerals

[0091] 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. An irradiation step of irradiating the inspection light from a light source toward the object to be inspected while continuously and relatively changing the incident angle of the inspection light with respect to the object to be inspected; and a detection step of detecting a surface defect of the object to be inspected based on an event asynchronously detected at a time when the luminance change of the reflected light reflected by the object to be inspected, which is received independently for each pixel, exceeds a preset threshold value. The method includes at least: In the detection step, a surface defect is detected from an event group composed of one or more stored events, and the event group is time-divided into event period groups for each period, so that the event group is divided into spatio-temporal voxels, the number of events is counted in each of the voxels, and a voxel in which the count value becomes equal to or greater than a certain value is defined as a surface defect voxel. The surface inspection method is characterized by including the process.

2. An irradiation step of irradiating the inspection light from a light source toward the object to be inspected while continuously and relatively changing the incident angle of the inspection light with respect to the object to be inspected; and a detection step of detecting a surface defect of the object to be inspected based on an event asynchronously detected at a time when the luminance change of the measurement light generated by at least any one of transmission, refraction, and scattering by the object to be inspected, which is received independently for each pixel, exceeds a preset threshold value. The method includes at least: In the detection step, a surface defect is detected from an event group composed of one or more stored events, and the event group is time-divided into event period groups for each period, so that the event group is divided into spatio-temporal voxels, the number of events is counted in each of the voxels, and a voxel in which the count value becomes equal to or greater than a certain value is defined as a surface defect voxel. The surface inspection method is characterized by including the process.

3. The surface inspection method according to claim 1, wherein in the detection step, a surface defect of the object to be inspected is detected based on the polarity of the difference in luminance of the reflected light.

4. The surface inspection method according to claim 2, wherein in the detection step, a surface defect of the object to be inspected is detected based on the polarity of the difference in luminance of the measurement light.

5. The surface inspection method according to any one of claims 1 to 4, wherein the light source includes a plurality of LEDs, and the LEDs are controlled to be turned on one by one sequentially or a plurality of LEDs are turned on simultaneously.

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