JP2002202264A - Method and device for appearance inspection - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance inspection accuracy, for preventing erroneous determination, and the like, by eliminating a problem caused by illumination. SOLUTION: This device is equipped with a work holding/conveying mechanism 2 capable of conveying/stopping a spherical component 1 held thereon, a ring lighting system 3 for irradiating the component at a stop from its periphery, a television camera 5 for observing the component from its top surface side, and an image processing means for determining surface defects of the component. The lighting system is constructed by layering a plurality of ring lighting units each having a multitude of LED light sources separately disposed in the circumferential direction. One of the units is set up so that its irradiation directions to the surface of the component are perpendicular to the optical axis of the camera. Another of the units is set up so that its irradiation directions cross the optical axis at a fixed inclination angle from a position displaced to the anti-camera side. An individual irradiation system is used wherein the LED light sources are sequentially turned on/off. As defect determination criteria, luminance difference determination criteria are used which are individually set for each of coaxial ring-like belt-shaped measurement areas of a constant width zoned along the surface of the component.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an appearance inspection method and apparatus for inspecting a surface defect of a component having a curved surface or the like,
In particular, the present invention relates to an appearance inspection method and an appearance inspection apparatus suitable for inspecting minute defects of a spherical component.

[0002]

2. Description of the Related Art For example, a hard disk drive built in a computer or the like has a diameter of 2 m as a ball bearing.
A ceramic ball as small as about m is applied. After firing and before surface finishing,
It is common to inspect for the presence of undesirable surface defects (for example, scratches having a length of 0.5 mm or more).

Conventionally, when inspecting the surface defects of such spherical parts and the like, appearance inspection using a television camera has been frequently used. As the appearance inspection method, usually, an inspection object is observed by a television camera under illumination, and a video signal from the television camera is input to an image processing device to perform image processing, and appears on the surface of the inspection object. The brightness difference of the shadow is calculated and output to the display device as, for example, a two-dimensional image. The brightness difference in this image is compared with a certain determination criterion, and if a flaw or the like having a length equal to or more than a certain length has occurred, this is determined as a defect.

Conventionally, such an appearance inspection method for inspecting the occurrence of surface defects on an object to be inspected, particularly a spherical component, etc., has been carried out under various illuminations, such as dome illumination, ring illumination, and strobe illumination. Have been applied.

The dome lighting is a method of arranging an inspection object inside a dome-shaped lighting device and uniformly irradiating the entire surface of the inspection object. However, with this dome illumination, the entire surface including the defect portion of the inspection object is uniformly illuminated, so that it is difficult to obtain a brightness difference of a shadow that can be determined as a defect by image processing.

[0006] Ring illumination is a method of arranging an inspection object at a center position of a ring-shaped illuminating device and simultaneously irradiating the inspection object from a peripheral portion. In this ring illumination, since the illumination width is limited to some extent, the shadow is easier to observe clearly than the dome illumination, but depending on the position where the defect occurs, the detection state may change and it may not be possible to judge,
It is difficult to detect defects stably.

Further, the strobe lighting is a method in which, for example, an object to be inspected is freely dropped while illuminating the object to be inspected with the strobe light. In the method using the strobe illumination, it is difficult to obtain a luminance difference at which a defect can be determined as in the case of the dome illumination, and the posture of the falling inspection object changes, resulting in a decrease in measurement accuracy.

[0008]

As described above, in the illumination method applied in the conventional appearance observation inspection,
In the case of dome illumination, it is difficult to obtain a difference in the brightness of shadows that can be determined due to uniform illumination.In the case of ring illumination, the detection state changes depending on the defect occurrence position, making it difficult to detect defects stably. There are various difficulties, such as difficulty in obtaining a determinable luminance difference, and a decrease in measurement accuracy due to a change in the posture of the inspection object. Problems such as a decrease in inspection accuracy and a risk of erroneous determination have occurred.

The present invention has been made in view of such circumstances, and solves problems caused by illumination by improving an illumination method and a luminance difference determination method, thereby improving inspection accuracy.
It is an object of the present invention to provide a visual inspection method capable of preventing erroneous determination and the like.

[0010] Another object of the present invention is to provide an appearance inspection apparatus most suitable for implementing the above method.

[0011]

In order to achieve the above object, according to the first aspect of the present invention, an inspection object having a curved surface is placed at the center position of ring illumination, and the inspection object to be irradiated is set on a television camera. A visual inspection method for determining a surface defect of the inspection object based on a luminance difference obtained by image processing of an input signal from the television camera, wherein the ring illumination is used for a curved surface of the inspection object. The irradiation direction is set to at least one of a direction orthogonal to the optical axis of the television camera or a direction intersecting with a fixed inclination angle from a position displaced toward the television camera side, and the irradiation method is set to a peripheral direction. The present invention provides an appearance inspection method characterized by employing an individual irradiation method by sequentially blinking from a large number of light sources divided in a direction.

According to a second aspect of the present invention, in the appearance inspection method of the first aspect, the defect determination by the image processing is individually set for each band-shaped measurement area having a constant width divided along the curved surface of the inspection object. Provided is an appearance inspection method characterized in that the method is performed using a luminance difference determination criterion.

According to a third aspect of the present invention, there is provided an appearance inspection method according to the first or second aspect, wherein the ring illumination is an LED ring illumination.

According to the fourth aspect of the present invention, the spherical component is placed at the center position of the ring illumination, the illuminated spherical component is photographed by a television camera, and a luminance difference obtained by image processing of an input signal from the television camera. An appearance inspection method for determining a surface defect of the spherical component based on the direction of irradiation of the surface of the spherical component by the ring illumination, a direction orthogonal to the optical axis of the television camera, and the anti-TV camera side The direction is set to two directions, that is, the direction intersecting at a fixed inclination angle from the displaced position, and the irradiation method is an individual irradiation method by sequentially blinking from a large number of LED light sources arranged in a circumferential direction. The defect judgment by the processing is performed by using the brightness difference judgment standard individually set for each coaxial ring-shaped fixed width band measuring area divided along the surface of the spherical part. It provides a visual inspection method characterized by performed.

According to the fifth aspect of the present invention, a work holding and conveying mechanism capable of holding and conveying and stopping a spherical part with at least half of the surface exposed, and stopping at the visual inspection position by the work holding and conveying mechanism. A ring illumination device that irradiates the formed spherical part from the periphery thereof, a control unit that drives and controls the work holding / transporting unit and the illumination device, and a television camera that observes the spherical part from the top side thereof,
Image processing means for performing image processing on an input signal from the television camera to calculate a surface luminance difference of the spherical component, and determining a surface defect of the spherical component based on a predetermined criterion; The device has a configuration in which a plurality of ring illumination units having a large number of LED light sources arranged in the circumferential direction are stacked, and at least one of the units has an irradiation direction with respect to the surface of the spherical component of the television camera. It is set in a direction perpendicular to the optical axis, and at least the other units are set in a direction intersecting at a fixed inclination angle from a position where the irradiation direction with respect to the surface of the spherical part is displaced toward the television camera side, and The irradiation method is set as an individual irradiation method by sequentially blinking from a large number of LED light sources divided and arranged in the circumferential direction. The defect inspection criterion uses a brightness difference criterion individually set for each coaxial ring-shaped band-shaped measurement area having a constant width that is sectioned along the surface of the spherical component. provide.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of an appearance inspection apparatus and method according to the present invention will be described with reference to the drawings. In this embodiment, a case will be described in which a spherical component such as a fine ceramic ball is applied as an inspection target.

FIG. 1 is a system diagram schematically showing the overall configuration of a visual inspection apparatus according to this embodiment. This appearance inspection device is roughly divided into a work holding and transporting mechanism 2 for holding and transporting the spherical component 1, a ring illumination device 3, an operation panel 4 having control means for driving and controlling these components, a television camera 5, an image processing device 6, and a display device. 7 and the like.

The work holding and transporting mechanism 2 is configured to be able to hold the spherical component 1 from below with the half or more surface exposed and transport and stop it at the inspection position. That is, the work holding and transporting mechanism 2 is configured by attaching a plurality of work holding mechanisms 10 to a transporting mechanism 9 such as an endless belt driven by a driving mechanism 8 such as a motor. Each of the workpiece holding mechanisms 10 includes a support cylinder 11 on which the spherical component 1 can be removably mounted, an air chuck 12 for sucking and holding the spherical component 1 downward, and positioning for supporting these on the transport mechanism 9 so as to be able to move up and down. Air cylinder 13 and the like.

The drive mechanism 8, the air cylinder 13, the air chuck 12 and the like of the work holding and transporting mechanism are composed of a sequencer 4a as a drive control device provided on the operation panel 4.
Via a driver 4b. By these control operations, the plurality of spherical parts 1 are sequentially conveyed to the inspection position, rise to the inspection position of the predetermined height shown in FIG. 1 and stop, and are lowered and discharged after the inspection. .

The ring illuminating device 3 irradiates the spherical part 1 stopped at the inspection position from the periphery thereof, and the spherical part 1 is fixedly installed at a portion arranged at the center shown in FIG. The ring illuminating device 3 includes a pair of ring illuminating units (an upper ring illuminating unit 14 and a lower ring illuminating unit 15) stacked and arranged in upper and lower two stages, and is connected to different power sources 16 and independently driven. You.

FIG. 2 is an enlarged sectional view showing the ring illumination device 3, and FIG. 3 is a plan view of FIG. As shown in these drawings, the upper ring illumination unit 14 and the lower ring illumination unit 15 are each provided with a large number of lamp light sources, for example, L on the inner peripheral surfaces of ring-shaped support frames 16 and 17.
The ED light sources 18 and 19 are mounted at equal intervals in the circumferential direction, and these LED light sources 18 and 19 share and irradiate the substantially upper half surface of the spherical component 1 arranged at the inspection position. I have. That is, the upper ring illumination unit 14
Each LED light source 18 has an irradiation direction to the surface of the spherical component 1 set in a direction orthogonal to the optical axis A of the television camera 5. For example, when the optical axis A is vertical, the LED light It is designed to irradiate horizontally toward the top. Further, each LED light source 19 of the lower ring illumination unit 15 has a predetermined inclination angle (for example, an elevation angle of 10 to 30 °) from a position where the irradiation direction on the surface of the spherical component 1 is displaced toward the television camera side (downward in FIG. 2). ) Is set in a direction crossing the optical axis A of the television camera 5. Each LED light source 19 of the lower ring illumination unit 15 illuminates a peripheral portion of the upper half surface of the spherical component 1 except for a top portion.

The LED light sources 18 and 19 of these ring illumination units 14 and 15 are connected to the respective power supplies 16 shown in FIG. 1 via switches (not shown) and the like. The blinking order irradiation time and the like are controlled by the sequencer 4a and the driver 4b.
In the present embodiment, for example, first, the lower ring illumination unit 15 and then the upper ring illumination unit 14 are used, and the respective LED light sources 18 and 19 are sequentially turned on and off along the circumferential direction, and flicker. It has become.
That is, the irradiation method of the LED light sources 18 and 19 is switched at a high speed (for example, 0.2 seconds) so that the individual irradiation method by the sequential blinking is set.

The television camera 5 shown in FIG. 1 is arranged vertically above the spherical part 1 at the stop position of the spherical part 1, and the whole view of the spherical part 1 is observed from the top side by the downward viewing lens portion 5a. You can do it. This television camera 5 is connected to the image processing device 6,
An image signal of the spherical component 1 observed by the television camera 5 is input to the image processing device 6. In the image processing device 6, the surface luminance difference of the spherical component 1 is calculated by image processing of the input signal, and the spherical component 1 is determined based on a predetermined criterion.
Of the surface defect is determined. Then, the determination result is output to the display device 7. The image processing device 6 will be described in detail later. As a defect determination criterion, a brightness difference determination criterion individually set for each coaxial ring-shaped band-shaped measurement area divided along the surface of the spherical component 1 is used. .

Next, an appearance inspection method according to the present embodiment implemented by the above-described apparatus configuration will be described with reference to FIGS.

FIG. 4 is a flowchart showing the procedure of the appearance inspection method according to the present embodiment. As shown in FIG. 4, after the start, the spherical part 1 as a work is introduced to the inspection position (S1: Work inspection position introduction). After this, each LE of the lower ring illumination unit 15 of the ring illumination device 3
The D light sources 19 are sequentially turned on (S2: ring illumination (1) O
N), the image signal from the television camera 5 is transmitted to the image processing device 6
(S3: Image input (1) ON). And
When all image inputs are performed, the ring illumination (1) is turned off.
F (S4), the image processing device 6 performs image processing to determine a defect in the peripheral portion of the surface of the spherical component 1 (S5: inspection (1)), and displays the determination result on the display device 7
Is output to

When the end of the inspection (1) is confirmed by the above steps (S6: YES), the illumination is switched. That is, each LED light source 18 of the upper ring illumination unit 14 of the ring illumination device 3 is sequentially turned on (S7: ring illumination (2) ON), and an image signal from the television camera 5 is input to the image processing device 6. (S8: Image input (2)
ON). When the image input is all performed, the ring illumination (2) is turned off (S9), and the image processing in the image processing device 6 determines the defect of the top portion of the surface of the spherical component 1 (S10: Inspection (2) )), And the determination result is output to the display device 7. Then, when the end of the inspection (2) is confirmed (S11: YES), the work is discharged (S12), and one process ends. Thereafter, the steps are performed for a predetermined number of inspections by introducing the next work.

In the above steps, only the appearance inspection of the upper half surface of each spherical component 1 is performed. Therefore, in the present embodiment, a second device (not shown) capable of receiving the discharged work is provided. In the second device, for example, the work holding and conveying mechanism 2 shown in FIG. The same operation as described above may be performed by adopting a mechanism for holding the lower half of the device. Thereby, the appearance inspection of the entire surface of each spherical component 1 can be performed.

Next, the illumination and defect determination in the above inspection process will be specifically described with reference to FIGS. FIG. 5 is an enlarged view showing an example of a spherical part 1 having a defect such as a scratch in a partial cross section. 6 and 7 are explanatory diagrams showing examples of input images in the image processing device 6.

The spherical part 1 shown in FIG. 5 is a ceramic ball as a ball bearing used for a hard disk drive built in a computer or the like, and has a diameter of about 2 mm.
belongs to. In the spherical component 1, defects 101 and 102 such as scratches are generated at two locations, that is, a peripheral portion around a central portion and a vicinity of a top portion.

FIG. 6 is an explanatory view exemplifying an input image when the lower ring illumination unit 15 illuminates the peripheral portion of the spherical component 1 in steps S2 to S4 described above. As shown in FIG. 6, when the spherical component 1 is viewed from above, the peripheral portion is illuminated by each LED light source 19 of the lower ring illumination unit 15 to become a bright area 103a, while the central part of FIG. The area near the top of the spherical component 1 is a dark shaded area 103b indicated by oblique lines.
In these 103a and 103b, boundary lines a to e
As shown by, the luminance range is different for each concentric band-shaped area (area) having a predetermined width in order from the peripheral side toward the center side. Therefore, a defect determination criterion based on a luminance difference serving as a criterion for defect determination is set for each of these luminance ranges as described above. In FIG. 6, the entire circumferential direction of the image of the spherical component 1 is shown with uniform brightness. However, in practice, each LED light source 19 blinks instantaneously to the adjacent one instantaneously. Bright areas 103 sequentially along the circumferential direction
a will move.

As shown in FIG. 6, when the light is radiated from obliquely below the defect 101, a shadow 101a clearly appears in the dent portion on the irradiation side, and the light of the dent shines. Since the luminance difference is significantly different from the opposite side portion and the non-defect portion, the length of the defect 101 can be determined with high accuracy by using the determination criteria individually defined for each area. If it is determined that the product is defective, for example, "NO" is displayed on the display device 7 shown in FIG.

In this case, as described above, depending on the lower ring illumination unit 15, only the outer peripheral side of the image in the image is a detectable area, the top (the center in FIG. 6) is a dark area, and the luminance difference Is not obtained and the top defect 102
Cannot be detected. In this inspection, the purpose is to detect minute defects. The minute defect appears as a shadow on the periphery thereof as shown by 101a by illumination from below, and the brightness of the shadow at this time varies depending on the depth of the defect. The defect depth can also be determined from this luminance difference. Further, in order to detect a change in luminance difference as accurately as possible, comparative inspection areas in image processing are arranged on concentric circles as shown by boundary lines a, b, and c in FIG. By setting so as to match the shading of the surface arc, it is possible to make a more accurate determination.

FIG. 7 is an explanatory diagram specifically showing an example of an input image in steps S7 to S9. Here, an image when the top of the spherical component 1 is illuminated from the horizontal direction by the upper ring illumination unit 14 is shown. An inspection near the top (the center in FIG. 7) that could not be inspected by the irradiation of the lower ring illumination unit 15 can be performed.

Here, contrary to the case of FIG. 6, the peripheral portion becomes the dark region 104b and cannot be inspected. However, shading can be obtained for the central portion 104a. Thus, the defect 102 at the top of the spherical component 1 can be determined by the same phenomenon and method as described above.

According to the method described in the above embodiment, an appearance inspection was conducted on an actual fired product of a ceramic ball (having a diameter of about 2 mm). It was confirmed that a flaw having a thickness of 0.5 mm or less, for example, about 0.3 mm can be easily found.

Therefore, according to the present embodiment, the direction of irradiation of the surface of the spherical component 1 by the ring illuminating device 3 is fixed at a certain angle from the direction orthogonal to the optical axis of the television camera 5 and the position displaced toward the television camera side. By setting the direction to intersect at an angle, and by setting the irradiation method to an individual irradiation method by sequentially blinking from a large number of light sources divided in the circumferential direction, the brightness of the shadow can be clearly expressed, whereby The effect that the detection capability of the surface defect of the spherical part 1 can be improved is produced.

Further, the defect judgment by the image processing is performed by using the luminance difference judgment standard individually set for each of the band-shaped measurement areas having a constant width which is divided along the curved surface of the spherical part 1, thereby obtaining the surface of the spherical part 1. When detecting a defect by image processing, by switching the inspection illumination and distributing the measurement area for each illumination, the measurement accuracy can be improved.

In the present embodiment, an LED light source is used as the ring illumination device 3. However, this focuses on the advantages that a high light quantity can be obtained effectively and that high-speed switching can be easily and reliably performed. It was done. However, it is also possible to apply a halogen lamp or other various lighting devices as needed.

In the present embodiment, a spherical part is applied. However, in the present invention, an object to be inspected having a curved surface, which cannot be sufficiently inspected by the conventional method, may be appropriately applied to the present invention. It can be applied as an object.

Various other modifications or applications are also possible. For example, it is also possible to stack three or more ring illumination units, and to carry out various changes in the work holding / transporting mechanism in accordance with the inspection object or the like, to change the irradiation order, or to change the optical axis of the television camera. It is also possible to use only one of the direction perpendicular to the camera or the direction intersecting at a fixed inclination angle from the position displaced toward the television camera side.

[0041]

As described above, according to the present invention, by improving the illumination method and the luminance difference determination method, the conventional problems caused by illumination can be solved, the inspection accuracy can be improved, and erroneous determination can be prevented. .

[Brief description of the drawings]

FIG. 1 is a system configuration diagram showing one embodiment of a visual inspection device according to the present invention.

FIG. 2 is an enlarged view of a lighting device in the appearance inspection device shown in FIG.

FIG. 3 is a plan view of the lighting device shown in FIG. 2;

FIG. 4 is a flowchart showing the procedure of the same appearance inspection method according to the embodiment;

FIG. 5 is an enlarged view showing a spherical part to be inspected according to the embodiment in a partial cross section.

6 is an explanatory diagram showing an input image of a first inspection when inspecting the spherical part of FIG. 5 by the method of FIG. 4;

FIG. 7 is an explanatory view showing an input image of a second inspection when inspecting the spherical part of FIG. 5 by the method of FIG. 4;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Spherical part (inspection object) 2 Work holding and transporting mechanism 3 Ring illumination device 4 Operation panel 5 TV camera 6 Image processing device 7 Display device 14 Upper ring illumination unit 15 Lower ring illumination unit 18, 19 LED light source

Claims (5)

[Claims] 1. An inspection object having a curved surface is placed at a center position of a ring illumination, and the inspection object to be irradiated is photographed by a television camera, and a luminance difference obtained by image processing of an input signal from the television camera is calculated. An appearance inspection method for determining a surface defect of the inspection object based on the irradiation direction of the ring illumination on the curved surface of the inspection object, in a direction orthogonal to an optical axis of the television camera or in a direction opposite to the television camera. It should be set in at least one of the directions intersecting at a fixed inclination angle from the displaced position, and the irradiation method should be an individual irradiation method by sequentially blinking from a number of light sources divided and arranged in the circumferential direction. Features a visual inspection method. 2. The appearance inspection method according to claim 1, wherein
An appearance inspection method, wherein a defect determination by image processing is performed using a luminance difference determination criterion individually set for each band-shaped measurement area having a fixed width divided along a curved surface of an inspection object. 3. The appearance inspection method according to claim 1, wherein the ring illumination is an LED ring illumination. 4. A spherical component is placed at the center position of ring illumination, the spherical component to be illuminated is photographed by a television camera, and the spherical component is determined based on a luminance difference obtained by image processing of an input signal from the television camera. An appearance inspection method for determining a surface defect, wherein the direction of irradiation of the surface of the spherical component by the ring illumination, a direction perpendicular to the optical axis of the television camera, a fixed position from the position displaced to the television camera side. And two directions of intersecting with the inclination angle, and the irradiation method is an individual irradiation method by sequentially blinking from a large number of LED light sources arranged in the circumferential direction, and further, defect determination by image processing is performed. The determination is performed using a brightness difference determination standard individually set for each coaxial ring-shaped fixed-width band-shaped measurement area divided along the surface of the spherical component. Appearance inspection method. 5. A workpiece holding / transporting mechanism capable of holding and transporting and stopping a spherical component while at least half of the surface is exposed, and a spherical component stopped at an appearance inspection position by the workpiece holding / transporting mechanism. A ring illuminating device for irradiating the workpiece, a control unit for driving and controlling the work holding / transporting unit and the illuminating device, a television camera for observing the spherical part from the top side, and an image processing for an input signal from the television camera. Image processing means for calculating a surface luminance difference of the spherical component, and determining a surface defect of the spherical component based on a predetermined criterion. A plurality of ring illumination units having LED light sources are stacked, and at least one of the ring illumination units is configured to irradiate the surface of the spherical component with light. Is set in a direction orthogonal to the optical axis of the TV camera, and at least another unit is set in a direction intersecting at a fixed inclination angle from a position where the irradiation direction with respect to the surface of the spherical component is displaced toward the anti-TV camera side. And the irradiation method is set as an individual irradiation method by sequentially blinking from a large number of LED light sources divided in the circumferential direction. A brightness difference criterion individually set for each coaxial ring-shaped band-shaped measurement area having a constant width, which is divided along the line.