Method for detecting double-sided complete isopathic confocal imaging of grain based on time difference resolution

Abstract

The present invention discloses a double-sided complete equal-optical-path confocal imaging detection method for grains based on time difference resolution, which is characterized by comprising: a CMOS or CCD camera, a telecentric imaging lens, a front prism image transfer subsystem, a semiconductor grain, and a transparent stage for holding the semiconductor grain, which are sequentially arranged in the direction of the optical path, and the images of the adjacent surfaces of the semiconductor grains taken independently by the camera at different time points are used to realize the complete equal-optical-path confocal imaging detection of the adjacent surfaces of the semiconductor grains. The detection method of the present invention realizes the double-sided complete equal-optical-path confocal imaging detection by shooting twice at different time points, and the working distance of the double-sided imaging detection optical path can be flexibly selected according to the needs, and the overall structure is simple and convenient for assembly and debugging.

Description

Technical field:

[0002] The invention belongs to the field of optical detection and machine vision, and in particular relates to a grain double-sided complete equal-optical-path confocal imaging detection method based on time difference resolution. Background technology:

[0004] The main optical technical problems that need to be solved by the device and method for simultaneous defect detection on opposite or adjacent surfaces of grains include equal optical path confocal imaging of the double-sided detection light path. The existing authorized patents and patent applications all use a large-field telecentric imaging lens to solve the confocal and resolution problems caused by the optical path difference between the double-sided imaging light paths. For example, the patent applications (application numbers 2019113692573 and 2020101330447) solve the method of simultaneous equal optical path confocal imaging and equal illumination illumination detection of opposite surfaces of grains, such as Figure 1 , as shown in 2, and Figure 3 The proposed optical detection device and method solve the problem of simultaneous quasi-equi-optical confocal imaging of adjacent surfaces of the grains. However, there is still an optical path difference △ between the adjacent double-sided imaging optical paths, such as Figure 3 As shown in the figure, this optical path difference depends on the side length a of the grain and the distance d between the two-sided images, that is, △=a+d. For smaller grains, its value is usually 2~3mm. This small optical path difference can be compensated by selecting a telecentric imaging lens with a corresponding depth of field. However, when the size of the grain to be detected increases, the optical path difference △ and the object field of view VOF=△+a of the required telecentric imaging lens will also increase. A telecentric imaging lens with a large field of view and a large depth of field must be used, which will increase the cost of the telecentric imaging lens accordingly. Therefore, it is necessary to find a new way to detect the adjacent surfaces of the grains with completely equal optical path confocal imaging. Summary of the invention:

[0006] In view of the above problems existing in adjacent surface detection, the present invention proposes a double-sided grain complete equal-optical-path confocal imaging detection method based on time difference resolution, which is conducive to realizing double-sided complete equal-optical-path confocal imaging detection.

[0007] The invention discloses a method for detecting double-sided complete equal-optical-path confocal imaging of grains based on time difference resolution, which is characterized by comprising a CMOS or CCD camera, a telecentric imaging lens, a front prism image transfer subsystem, a semiconductor grain and a transparent stage for holding the semiconductor grain, which are sequentially arranged in the direction of the optical path. The images of the adjacent surfaces of the semiconductor grains are independently taken by the camera at different time points to realize complete equal-optical-path confocal imaging detection of the adjacent surfaces of the semiconductor grains.

[0008] The front prism image transfer subsystem includes a cubic beam splitter, and a side right-angle image transfer prism and a top right-angle image transfer prism respectively arranged on the optical path between the semiconductor crystal grain and the cubic beam splitter. The side right-angle image transfer prism and the top right-angle image transfer prism are respectively located on the front side of the semiconductor crystal grain and directly above the top surface. The cubic beam splitter and the top right-angle image transfer prism are at the same horizontal height. The side right-angle image transfer prism and the cubic beam splitter are located directly below the telecentric imaging lens. The first right-angle surface of the side right-angle image transfer prism is opposite to the first surface of the cubic beam splitter, and the second right-angle surface of the side right-angle image transfer prism is opposite to the side surface of the semiconductor crystal grain. The inclined surface of the side right-angle image-turning prism is tilted to the optical axis of the telecentric imaging lens, and the two right-angle surfaces of the top right-angle image-turning prism are respectively opposite to the top surface of the semiconductor crystal grain and the second surface of the cubic beam splitter; a first illumination light source is provided between the top right-angle image-turning prism and the semiconductor crystal grain, and a second illumination light source is provided between the side right-angle image-turning prism and the semiconductor crystal grain. The top surface and the side surface of the semiconductor crystal grain are respectively imaged on the camera sensor surface with single optical path and equal optical path through the right-angle image-turning prism and the cubic beam splitter at different time points, so that independent images of both surfaces are obtained on the CMOS or CCD camera at different time points.

[0009] Furthermore, the first illumination light source and the second illumination light source are coaxial illumination light sources.

[0010] Furthermore, the first illumination light source, the second illumination light source and the CMOS or CCD camera are electrically connected to a signal controller to control the light source and the camera.

[0011] Furthermore, the size of the top right-angle image-transmitting prism is 15*15*15mm, the size of the side right-angle image-transmitting prism is 15*15*15mm, and the size of the cubic beam splitter is 15*15*15mm.

[0012] Furthermore, the working distances of the semiconductor crystal grain top imaging light path and the side imaging light path can be determined according to the working distance of the telecentric imaging lens and the size of the stage.

[0013] Furthermore, the frame rate μ of the CCD or CMOS camera is selected to be greater than twice the semiconductor grain transmission frequency f, and the interval △t between the top and side shooting satisfies , the camera object field of view VOF ≥ semiconductor grain side length a + △t * stage transfer rate υ; the images of the two adjacent surfaces completely overlap in the direction perpendicular to the optical axis A of the telecentric imaging lens, and are both output from the middle of the end face of the cubic beam splitter. The position difference between the two images in the thickness direction of the front prism image transfer subsystem is: △t*υ.

[0014] Furthermore, the stroboscopic duration τ1 of the first illumination light source satisfies: the camera exposure time ψ<τ1<△t.

[0015] Furthermore, the stroboscopic duration τ2 of the second illumination light source satisfies: the camera exposure time ψ<τ2<△t.

[0016] The present invention is based on the grain double-sided complete equal optical path confocal imaging detection method of time difference resolution:

[0017] ① Two shots at different time points realize double-sided complete equal optical path confocal imaging detection, that is, △=0;

[0018] ②The working distance of the double-sided imaging detection optical path can be flexibly selected according to needs, and the overall structure is simple and easy to assemble and debug;

[0019] ③ Double-sided lighting uses independent lighting sources to achieve equal illumination;

[0020] ④ The increase in the object field of view of the telecentric imaging lens for double-sided imaging detection is equal to the displacement of the grain within two consecutive exposure times △t. Description of the drawings:

[0022] Figure 1-3 It is an existing optical device for detecting adjacent surfaces of semiconductor grains;

[0023] Wherein 1 is a black and white camera, 2 is a telecentric imaging lens, 3a or 3b is an image transfer prism, 3 is an image combining optical element, 4 is a semiconductor crystal, 5 is a transparent stage, 6 or 6a or 6b is an image transfer prism, 7 or 7a or 7b is a light source;

[0024] Figure 4 It is a schematic diagram of the structure of the device of the present invention;

[0025] Figure 5 Schematic diagram of an embodiment of the device of the present invention;

[0026] Figure 6 It is a control principle block diagram of the signal controller, the first and second lighting sources and the camera. Specific implementation method:

[0028] The present invention is a method for detecting double-sided complete equal-optical-path confocal imaging of grains based on time difference resolution, comprising a CMOS or CCD camera 1, a telecentric imaging lens 2, a front prism image transfer subsystem K, a semiconductor grain 6 and a transparent stage 5 for holding the semiconductor grain, which are sequentially arranged in the direction of the optical path. The images of the adjacent surfaces of the semiconductor grains taken independently at different time points by the camera 1 are used to realize complete equal-optical-path confocal imaging detection of the adjacent surfaces of the semiconductor grains.

[0029] The front prism image transfer subsystem K includes a cubic beam splitter 3, and a side right-angle image transfer prism 4b and a top right-angle image transfer prism 4a respectively arranged on the optical path between the semiconductor crystal grain 6 and the cubic beam splitter 3. The side right-angle image transfer prism and the top right-angle image transfer prism are respectively located on the front side of the semiconductor crystal grain 6 and directly above the top surface, and the cubic beam splitter and the top right-angle image transfer prism are at the same horizontal height; the side right-angle image transfer prism and the cubic beam splitter are located directly below the telecentric imaging lens, the first right-angle surface 01 of the side right-angle image transfer prism is opposite to the first surface 03 of the cubic beam splitter, and the second right-angle surface 02 of the side right-angle image transfer prism is opposite to the first surface 03 of the cubic beam splitter, and the second right-angle surface 02 of the side right-angle image transfer prism is opposite to the semiconductor crystal grain 6. The side surfaces are opposite to each other, and the inclined surface of the side right-angle image-turning prism is inclined to the optical axis A of the telecentric imaging lens. The two right-angle surfaces of the top surface right-angle image-turning prism are respectively opposite to the top surface of the semiconductor crystal grain and the second surface 04 of the cubic beam splitter; a first illumination light source 7 is provided between the top surface right-angle image-turning prism and the semiconductor crystal grain, and a second illumination light source 8 is provided between the side surface right-angle image-turning prism and the semiconductor crystal grain. The top surface and the side surface of the semiconductor crystal grain are respectively imaged on the camera sensor surface with single optical path and equal optical path through the right-angle image-turning prism and the cubic beam splitter at different time points, so that independent images of the two sides are obtained at different time points on the CMOS or CCD camera.

[0030] The cubic beam splitter 3 can also be called a cubic beam splitter / image combiner, which is a common optical device. A beam splitter film with a transmission and reflection ratio of 50%:50% is plated on the inclined surface of a right-angle prism, and the inclined surfaces of two right-angle reflection prisms are glued together.

[0031] Furthermore, for a reasonable design, the first illumination light source and the second illumination light source are coaxial illumination light sources.

[0032] Furthermore, the first illumination light source 7, the second illumination light source 8 and the CMOS or CCD camera 1 are electrically connected to the signal controller 9 to realize the control of the light source and the camera. The control method is as follows: when the semiconductor crystal grain enters the object field of the camera, the signal controller receives the crystal grain positioning signal, and then sends a trigger signal to make the second illumination light source coaxial on the side strobe to illuminate the side of the crystal grain and control the camera to take side imaging photos at the same time, and then send the imaging picture to the industrial computer for image processing and detection; after an interval △t, the crystal grain is transferred to a small position (i.e., the thickness direction of the front prism image transfer subsystem) along the thickness direction of the front prism image transfer subsystem. Figure 4 The signal controller sends a trigger signal to the first illumination light source coaxial with the sky surface for stroboscopic illumination, illuminating the grain sky surface and controlling the camera to take pictures of the sky surface at the same time, and then sends the image to the industrial computer for image processing and detection.

[0033] The size of the above-mentioned right-angle image-transmitting prism on the top is 15*15*15mm, the size of the right-angle image-transmitting prism on the side is 15*15*15mm, and the size of the cubic beam splitter is 15*15*15mm. Figure 5 Parameters of a preferred embodiment are given in the figure, wherein the positions of the first illumination light source and the second illumination light source can be adjusted according to actual needs.

[0034] The working distances of the semiconductor crystal grain top imaging optical path and the side imaging optical path can be determined according to the working distance of the telecentric imaging lens and the size of the stage.

[0035] Furthermore, the frame rate μ of the CCD or CMOS camera is selected to be greater than twice the semiconductor grain transmission frequency f, and the interval △t between the top and side shooting satisfies , the camera object field of view VOF ≥ semiconductor grain side length a + △t * stage transfer rate υ; the images of the two adjacent surfaces completely overlap in the direction perpendicular to the optical axis A of the telecentric imaging lens, and are both output from the middle of the upper end surface 05 of the cubic beam splitter, in the thickness direction of the front prism image transfer subsystem (i.e. Figure 4 The position difference between the two images (in the direction perpendicular to the paper plane) is: △t*υ.

[0036] The stroboscopic duration τ1 of the first illumination light source satisfies: camera exposure time ψ<τ1<△t; the stroboscopic duration τ2 of the second illumination light source satisfies: camera exposure time ψ<τ2<△t.

[0037] The detection method and steps of this patent application are as follows:

[0038] ① Install the front prism image transfer subsystem above and to the side of the transparent stage, and adjust the horizontal and vertical positions of the front prism image transfer subsystem (including the cubic beam splitter, the side right-angle image transfer prism and the top right-angle image transfer prism) so that when the transparent stage is stationary, the double images of the adjacent surfaces are emitted from the center of the upper end face 05 of the cubic beam splitter;

[0039] ② Connect the stroboscopic signal control lines of the first and second illumination sources and the camera shooting trigger signal line to the signal controller;

[0040] ③ Start the transparent stage to transport the semiconductor crystal grains. When the semiconductor crystal grains enter the camera's object field of view, the signal controller receives the crystal grain positioning signal, and then sends a trigger signal to make the second coaxial illumination light source on the side strobe to illuminate the side of the crystal grain and control the camera to take side imaging photos at the same time, and then send the imaging pictures to the industrial computer for image processing and detection;

[0041] ④ After an interval of △t, the crystal moves a small segment along the thickness direction of the front prism image transfer subsystem: △t*υ, and the signal controller sends a trigger signal to the first illumination light source coaxial with the sky surface for stroboscopic illumination, illuminating the crystal surface and controlling the camera to take photos of the sky surface, and then sends the image to the industrial computer for image processing and detection;

[0042] ⑤ After the industrial computer completes the image processing and detection of the sky surface, it sends the corresponding operation instructions of the processing results to the signal controller for storage. When the grains are transferred to the sorting station through the glass stage, the instructions are sent for sorting;

[0043] ⑥ Repeat steps ③-⑤ to identify, detect and sort the adjacent surface defects of each grain.

[0044] Assuming that the size of the grain is 2.10*1.32*1.32mm, the transmission frequency is 10Pcs / s, the stage transmission rate is 70mm / s, and a camera with a target size of 2 / 3" and a frame rate of 50 frames / s can meet the use requirements. Assuming that the double-sided shooting time interval △t=25ms, there is a displacement of about 1.75mm in the grain when shooting the top and side surfaces.

[0045] The working distances of the top and side surfaces are 12.5 and 35 respectively (the distance from the right angle surface of the prism to the center of the grain).

[0046] The grain double-sided complete equal-optical-path confocal imaging detection method based on time difference resolution of the present invention has the following advantages:

[0047] ① Two shots at different time points realize double-sided complete equal optical path confocal imaging detection, that is, △=0;

[0048] ②The working distance of the double-sided imaging detection optical path can be flexibly selected according to needs, and the overall structure is simple and easy to assemble and debug;

[0049] ③ Double-sided lighting uses independent lighting sources to achieve equal illumination;

[0050] ④ The increase in the object field of view of the telecentric imaging lens for double-sided imaging detection is equal to the displacement of the grain within two consecutive exposure times △t.

[0051] Double images of adjacent faces of semiconductor grains are formed on the cubic beam splitter and the double images are in the horizontal direction ( Figure 4 However, when the semiconductor crystal grain on the glass turntable (transparent stage) passes under the front prism image transfer subsystem, the signal controller controls the first and second illumination light sources corresponding to the side and top surfaces in turn within the △t time interval to illuminate the surface of the crystal grain and control the camera to form images twice at the same time, so that two shots are taken in quick sequence to realize defect detection on adjacent surfaces of the crystal grain.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or some technical features can be replaced by equivalents without departing from the spirit of the technical solution of the present invention, which should be included in the scope of the technical solution for protection of the present invention.

Claims

1. A method for detecting grain double-sided complete equal optical path confocal imaging based on time difference resolution, characterized in that: The method comprises a CMOS or CCD camera, a telecentric imaging lens, a front prism image transfer subsystem, a semiconductor crystal grain and a transparent stage for holding the semiconductor crystal grain, which are sequentially arranged in the direction of the optical path. The images of the adjacent surfaces of the semiconductor crystal grain are independently photographed by the camera at different time points to realize complete equal optical path confocal imaging detection of the adjacent surfaces of the semiconductor crystal grain. The front prism image transfer subsystem includes a cubic beam splitter, and a side right-angle image transfer prism and a sky right-angle image transfer prism respectively arranged on the optical path between the semiconductor crystal grain and the cubic beam splitter, the side right-angle image transfer prism and the sky right-angle image transfer prism are respectively located on the positive side of the semiconductor crystal grain and directly above the sky surface, and the cubic beam splitter and the sky right-angle image transfer prism are at the same horizontal height; the side right-angle image transfer prism and the cubic beam splitter are located directly below the telecentric imaging lens, the first right-angle surface of the side right-angle image transfer prism is opposite to the first surface of the cubic beam splitter, the second right-angle surface of the side right-angle image transfer prism is opposite to the side surface of the semiconductor crystal grain, and the oblique surface of the side right-angle image transfer prism is inclined to the optical axis of the telecentric imaging lens The two right-angled surfaces of the top right-angle image-turning prism are respectively opposite to the top surface of the semiconductor crystal grain and the second surface of the cubic beam splitter; a first illumination light source is provided between the top right-angle image-turning prism and the semiconductor crystal grain, and a second illumination light source is provided between the side right-angle image-turning prism and the semiconductor crystal grain. The top surface and the side surface of the semiconductor crystal grain are respectively imaged on the camera sensor surface with a single optical path and equal optical path through the right-angle image-turning prism and the cubic beam splitter at different time points, and independent images of the two surfaces are obtained on the CMOS or CCD camera at different time points; the frame rate μ of the CCD or CMOS camera is selected to be greater than twice the transmission frequency f of the semiconductor crystal grain, and the shooting interval △t between the top surface and the side surface satisfies , the camera object field of view VOF ≥ semiconductor grain side length a + △t * stage transfer rate υ; the images of the two adjacent surfaces completely overlap in the direction perpendicular to the optical axis A of the telecentric imaging lens, and are both output from the middle of the end face of the cubic beam splitter. The position difference of the two images in the thickness direction of the front prism image transfer subsystem is: △t*υ; The detection steps are as follows: ① Install the front prism image transfer subsystem above and to the side of the transparent stage, and adjust the horizontal and vertical positions of the front prism image transfer subsystem so that when the transparent stage is stationary, the double images of adjacent surfaces are emitted from the center of the upper end face of the cubic beam splitter; ② Connect the stroboscopic signal control lines of the first and second illumination sources and the camera shooting trigger signal line to the signal controller; ③ Start the transparent stage to transport the semiconductor crystal grains. When the semiconductor crystal grains enter the camera's object field of view, the signal controller receives the crystal grain positioning signal, and then sends a trigger signal to make the second coaxial illumination light source on the side strobe to illuminate the side of the crystal grain and control the camera to take side imaging photos at the same time, and then send the imaging pictures to the industrial computer for image processing and detection; ④ After an interval of △t, the crystal moves a small segment along the thickness direction of the front prism image transfer subsystem: △t*υ, and the signal controller sends a trigger signal to the first illumination light source coaxial with the sky surface for stroboscopic illumination, illuminating the crystal surface and controlling the camera to take photos of the sky surface, and then sends the image to the industrial computer for image processing and detection; ⑤ After the industrial computer completes the image processing and detection of the sky surface, it sends the corresponding operation instructions of the processing results to the signal controller for storage. When the grains are transferred to the sorting station through the glass stage, the instructions are sent for sorting; ⑥ Repeat steps ③-⑤ to identify, detect and sort the adjacent surface defects of each grain.

2. The method for detecting grain double-sided complete equal optical path confocal imaging based on time difference resolution according to claim 1 is characterized in that: The first illumination light source and the second illumination light source are coaxial illumination light sources.

3. The method for detecting grain double-sided complete equal optical path confocal imaging based on time difference resolution according to claim 1, characterized in that: The first illumination light source, the second illumination light source and the CMOS or CCD camera are electrically connected to a signal controller to control the light source and the camera.

4. The method for detecting grain double-sided complete equal optical path confocal imaging based on time difference resolution according to claim 1, characterized in that: The size of the top right-angle image-transfer prism is 15*15*15mm, the size of the side right-angle image-transfer prism is 15*15*15mm, and the size of the cubic beam splitter is 15*15*15mm.

5. The method for detecting grain double-sided complete equal optical path confocal imaging based on time difference resolution according to claim 1, characterized in that: The working distances of the semiconductor crystal grain top imaging light path and the side imaging light path can be determined according to the working distance of the telecentric imaging lens and the size of the stage.

6. The method for detecting grain double-sided complete equal optical path confocal imaging based on time difference resolution according to claim 1, characterized in that: The stroboscopic duration τ1 of the first illumination light source satisfies: the camera exposure time ψ<τ1<△t.

7. The method for detecting grain double-sided complete equal optical path confocal imaging based on time difference resolution according to claim 1, characterized in that: The stroboscopic duration τ2 of the second illumination light source satisfies: the camera exposure time ψ<τ2<△t.

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