Monocular vision centering method for reactor probe assemblies

Abstract

This invention relates to the field of nuclear power plant equipment replacement and discloses a monocular vision alignment method applicable to reactor detector assemblies. First, the image coordinates of the reactor detector assembly's center are acquired. Then, based on the distance between the plane where the camera is located and the plane where the reactor detector is located, the world coordinates of the reactor detector assembly's center are obtained. Next, based on the distance between the world coordinates of the reactor detector assembly's center and the camera's optical axis, the camera movement is adjusted. Once the camera's optical axis coincides with the center of the reactor detector assembly, the center of the mechanical gripper is adjusted to coincide with the center of the reactor detector assembly based on the coordinate offset between the camera's optical axis and the center of the mechanical gripper. This invention eliminates the need for external parameter calibration by placing calibration objects inside the reactor, and the method is simple, highly feasible, and very suitable for reactor detector assembly replacement scenarios in nuclear power plants.

Description

Technical Field

[0001] This invention belongs to the field of visual calibration technology, and relates to visual alignment between reactor detector components and robotic grippers during the replacement of equipment in nuclear power plants. In particular, it relates to a monocular visual alignment method suitable for reactor detector components. Background Technology

[0002] To achieve optimal power density distribution and improve operational safety, a core measurement system is used to measure critical parameters such as neutron flux and temperature within the reactor in real time and with precision. Due to lifespan limitations, the detector assemblies used in this system need to be replaced every two refuelings. Figure 1 The diagram shows the mechanical structure of an automated device used for picking up and replacing detector components.

[0003] from Figure 1 As can be seen from the diagram, the automated equipment for grabbing and replacing detector components includes a grabbing device 01 and a drive mechanism for controlling the grabbing device to move along the X-axis and Y-axis. The grabbing device 01 includes a mechanical gripper 011, a camera 012, and a compression device 013. The mechanical gripper 011 is used to grab the reactor detector components, the camera 012 is used to acquire images containing the reactor detector components, and the compression device 013 is used to compress the reactor core waste for storage. The drive mechanism includes an X-track 02 and a Y-track 03 installed at both ends of the X-track and sliding perpendicularly to the X-track. The grabbing device 01 is mounted on a railcar located on the X-track. The railcar is driven by an X-axis motor 04 to move along the X-track, and the X-track is driven by a Y-axis motor 05 to move along the Y-track.

[0004] However, due to the unique environment of the reactor, it is impossible to place calibration objects inside the reactor for external parameter calibration, and the accuracy of controlling the movement of the track vehicle and X-track via motors is limited. Therefore, it is difficult to achieve effective alignment between the mechanical gripper and the reactor detector assembly. Summary of the Invention

[0005] To address the aforementioned problems in the existing technology, the present invention aims to provide a monocular vision alignment method suitable for reactor detector components, which first aligns the camera optical axis with the center of the reactor detector component from multiple angles, and then aligns the mechanical gripper with the center of the reactor detector component.

[0006] To achieve the above objectives, the present invention provides a monocular vision alignment method suitable for reactor detector assemblies, comprising the following steps:

[0007] S1 acquires images containing reactor detector components via a camera;

[0008] S2 uses a template matching algorithm to obtain the reactor detector components in the image;

[0009] S3 obtains the world coordinates of the reactor detector assembly center based on the image coordinates of the reactor detector assembly center and the distance between the plane where the camera is located and the plane where the reactor detector is located;

[0010] S4 determines whether the projected coordinate distance between the world coordinates of the reactor detector component and the camera optical axis is greater than a set threshold. If yes, proceed to step S5; otherwise, proceed to step S6.

[0011] S5 Driven by the driving mechanism, the camera moves, and during the movement, the distance between the plane where the camera is located and the plane where the reactor detector is located is measured, and then returns to step S1;

[0012] S6 takes the deviation between the camera optical axis and the center coordinates of the reactor detector assembly as input, controls the drive mechanism through the PID controller, and then controls the camera to move so that the camera optical axis coincides with the center of the reactor detector assembly; then proceed to step S7.

[0013] Based on the coordinate offset between the camera optical axis and the center of the mechanical gripper, the S7, driven by the drive mechanism, moves the mechanical gripper by an offset amount, so that the center of the mechanical gripper coincides with the center of the detector component.

[0014] In step S2 above, the Linemod template matching algorithm is used to obtain the reactor detector component from the image and obtain the center image coordinates of the reactor detector component.

[0015] In step S3 above, the coordinates of the reactor detector assembly center image are transformed to the world coordinate system according to the following formula to obtain the corresponding world coordinates:

[0016]

[0017] In the formula, (X W Y W P represents the world coordinates of the center of the reactor detector assembly. W , (X C Y C P represents the image coordinates of the center of the reactor detector assembly. C , f represents the distance between the plane where the camera is located and the plane where the reactor detector is located during the nth measurement. x f y These represent the camera's focal length on the x and y axes, respectively.

[0018] The acquisition method is as follows: the camera is moved a fixed length B, and the coordinates P of the center of the reactor detector assembly are recorded before and after the movement. aand P b According to the formula: Obtain the coarse measurement height value H n In the formula, f is the focal length of the camera along the direction of movement. Since there is an error in each height measurement, this invention is designed to remeasure the height H every 10mm of movement. n And H is calculated using the following formula. n Update and fix: In the formula, This represents the result of the (n-1)th measurement, and N represents the total number of calculations.

[0019] In step S5 above, during the movement, the distance between the plane where the camera is located and the plane where the reactor detector is located is measured according to the method given above.

[0020] In step S6 above, a PID controller already disclosed in the art can be used to control the drive mechanism, thereby controlling the movement of the camera optical axis so that the camera optical axis coincides with the center of the reactor detector assembly.

[0021] In step S7 above, the coordinate offset L between the camera optical axis and the center of the mechanical gripper can be measured during the installation process of the camera and the mechanical gripper. After the camera optical axis coincides with the center of the detector assembly, the mechanical gripper center can be made to coincide with the center of the reactor detector assembly simply by moving the offset L.

[0022] This invention first obtains the image coordinates of the center of the reactor detector assembly, then obtains the world coordinates of the center of the reactor detector assembly based on the distance between the plane where the camera is located and the plane where the reactor detector is located; subsequently, it adjusts the camera movement based on the distance between the world coordinates of the reactor detector assembly center and the camera's optical axis; once the camera's optical axis coincides with the center of the reactor detector assembly, it adjusts the center of the mechanical gripper to coincide with the center of the reactor detector assembly based on the coordinate offset between the camera's optical axis and the center of the mechanical gripper. Compared with the prior art, the high-precision monocular vision alignment method for reactor detector assemblies provided by this invention has the following beneficial effects:

[0023] 1) The present invention first adjusts the camera optical axis to coincide with the center of the reactor detector assembly, and then adjusts the mechanical gripper center to coincide with the center of the reactor detector assembly based on the coordinate offset between the camera optical axis and the center of the mechanical gripper. This not only ensures the alignment accuracy between the center of the mechanical gripper and the center of the reactor detector assembly, but also makes the adjustment target clear and improves the alignment efficiency.

[0024] 2) In the process of aligning the camera optical axis with the center of the reactor detector assembly, the present invention can further improve the alignment accuracy between the camera optical axis and the center of the reactor detector assembly by correcting the distance between the plane where the camera is located and the plane where the reactor detector is located.

[0025] 3) During the process of aligning the camera optical axis with the center of the reactor detector assembly, the present invention also incorporates a PID controller to further improve the alignment accuracy between the camera optical axis and the center of the reactor detector assembly;

[0026] 4) This invention does not require the placement of calibration objects in the reactor for external parameter calibration, and the method is simple and highly feasible, making it very suitable for the replacement of reactor detector components in nuclear power plants. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of an automated device used for grasping and replacing detector components; in the diagram, 01-grabbing device, 011-mechanical gripper, 012-camera, 013-compression device, 02-X track, 03-Y track, 04-X-axis motor, 05-Y-axis motor.

[0028] Figure 2 This is a schematic diagram of the high-precision monocular vision alignment method for reactor detector components provided by the present invention. Detailed Implementation

[0029] The technical solutions of various embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Example

[0031] The monocular vision alignment method for reactor detector assemblies provided in this embodiment can be applied to... Figure 1 The presented automated equipment for grasping and replacing detector components aligns the mechanical gripper with the center of the reactor detector component. However, the mechanical gripper is difficult to calibrate. Furthermore, the relative positions of the camera and the mechanical gripper are fixed after installation in the gripper device. Therefore, this invention first aligns the camera's optical axis with the center of the reactor detector component, and then aligns the mechanical gripper with the center of the reactor detector component.

[0032] The monocular vision alignment method for reactor detector assemblies provided in this embodiment, such as Figure 2 As shown, it includes the following steps:

[0033] S1 uses a camera to capture images containing reactor detector components.

[0034] In this step, based on the location of the target reactor detector assembly, the X-axis and Y-axis motors in the drive mechanism, the railcar and / or the X-track can be used to move the grasping device to the target area; then, the camera can capture images containing the reactor detector assembly.

[0035] S2 uses a template matching algorithm to obtain the reactor detector components in the image.

[0036] In this step, the Linemod template matching algorithm is used to extract the reactor detector component from the image and obtain the center image coordinates of the reactor detector component. For details on the operation of the Linemod template matching algorithm, please refer to "Gradient Response Maps for Real-Time Detection of Textureless Objects".

[0037] S3 obtains the world coordinates of the reactor detector assembly center based on the image coordinates of the reactor detector assembly center and the distance between the plane where the camera is located and the plane where the reactor detector is located.

[0038] In this step, the plane of motion of the grasping device and the reactor detector assembly are parallel according to the plane sputtering. The transformation relationship between the center image coordinates of the reactor detector assembly and world coordinates is shown in the following formula:

[0039]

[0040] In the formula, (X W Y W P represents the world coordinates of the center of the reactor detector assembly. W , (X C Y C P represents the image coordinates of the center of the reactor detector assembly. C , f represents the distance between the plane where the camera is located and the plane where the reactor detector is located during the nth measurement. x f y These represent the camera's focal length on the x and y axes, respectively.

[0041] Using the above formula, the world coordinate system of the reactor detector assembly center can be obtained based on the image coordinates of the reactor detector assembly center.

[0042] The above That is, the result obtained in step S5 of the previous iteration. For the initial time (n=0), the initial distance between the plane where the camera is located and the plane where the reactor detector is located can be given according to the initial position of the grasping device.

[0043] Based on the principle of binocular ranging, the coordinates P of the reactor detector assembly center can be recorded before and after the camera moves a fixed length B. a and P b According to the formula: Obtain the coarse measurement height value H n In the formula, f is the focal length of the camera along the direction of movement. Since there is an error in each height measurement, this invention is designed to remeasure the height H every 10mm of movement. n And H is calculated using the following formula. n Update and fix: In the formula, This represents the result of the (n-1)th measurement, and N represents the total number of calculations during the iteration process.

[0044] S4 determines whether the distance between the world coordinates of the reactor detector component and the projected coordinates of the camera optical axis is greater than a set threshold. If yes, proceed to step S5; otherwise, proceed to step S6.

[0045] The threshold given in this step is 10mm. When the projected coordinate distance between the world coordinates of the reactor detector assembly and the camera optical axis is greater than 10mm, it means that it is still within the mechanical motion precision control range and can continue to be adjusted by mechanical motion; when the projected coordinate distance between the world coordinates of the reactor detector assembly and the camera optical axis is not greater than 10mm, it means that it has exceeded the mechanical motion precision control range and it is difficult to achieve the centering adjustment of the camera optical axis and the reactor detector assembly.

[0046] S5: Driven by the driving mechanism, the camera moves, and during the movement, the distance between the plane where the camera is located and the plane where the reactor detector is located is measured, and then returns to step S1.

[0047] In this step, as described earlier, the X-axis and Y-axis motors in the drive mechanism drive the railcar and / or the X-track to move the gripping device, and the camera moves with the gripping device. During the movement, the distance between the plane where the camera is located and the plane where the reactor detector is located in the current iteration is measured according to the method given above.

[0048] S6 takes the deviation between the camera optical axis and the center coordinates of the reactor detector assembly as input, controls the drive mechanism through the PID controller, and then controls the camera to move so that the camera optical axis coincides with the center of the reactor detector assembly; then proceeds to step S7.

[0049] Using the deviation between the camera's optical axis and the center coordinates of the reactor detector assembly as input, a PID controller, already disclosed in the art, is employed to control the X-axis and Y-axis motors in the drive mechanism. The railcar and / or X-track moves the gripping device, thereby controlling the movement of the camera's optical axis to ensure it coincides with the center of the reactor detector assembly. For the PID controller, see "Directional stability of automatically steered bodies".

[0050] Based on the coordinate offset between the camera optical axis and the center of the mechanical gripper, the S7, driven by the drive mechanism, moves the mechanical gripper by an offset amount, so that the center of the mechanical gripper coincides with the center of the detector component.

[0051] In this step, the coordinate offset L between the camera optical axis and the center of the mechanical gripper can be measured during the installation of the camera and the mechanical gripper. Once the camera optical axis coincides with the center of the detector assembly, the mechanical gripper center can be made to coincide with the center of the reactor detector assembly simply by moving the offset L.

[0052] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of this invention.

Claims

1. A monocular vision alignment method suitable for reactor detector assemblies, characterized in that, Includes the following steps: S1 acquires images containing reactor detector components via a camera; S2 uses a template matching algorithm to obtain the reactor detector components in the image; S3 obtains the world coordinates of the reactor detector assembly center based on the image coordinates of the reactor detector assembly center and the distance between the plane where the camera is located and the plane where the reactor detector is located; S4 Determine whether the projected coordinate distance between the world coordinates of the reactor detector component and the camera optical axis is greater than a set threshold. If yes, proceed to step S5; otherwise, proceed to step S6. S5 Driven by the drive mechanism, the camera moves, and during the movement, the distance between the plane where the camera is located and the plane where the reactor detector is located is measured, and then the process returns to step S1; S6 takes the deviation between the camera optical axis and the center coordinates of the reactor detector assembly as input, controls the drive mechanism through the PID controller, and then controls the camera movement to make the camera optical axis coincide with the center of the reactor detector assembly. Then proceed to step S7; Based on the coordinate offset between the camera optical axis and the center of the mechanical gripper, the mechanical gripper can be moved by the drive mechanism to make the center of the mechanical gripper coincide with the center of the detector component.

2. The monocular vision alignment method for reactor detector assemblies according to claim 1, characterized in that, In step S2, the Linemod template matching algorithm is used to obtain the reactor detector component from the image and obtain the center image coordinates of the reactor detector component.

3. The monocular vision alignment method for reactor detector assemblies according to claim 1, characterized in that, In step S3, the coordinates of the reactor detector assembly center image are transformed to the world coordinate system according to the following formula to obtain the corresponding world coordinates: ； In the formula, ( X W , Y W ) represents the world coordinates of the center of the reactor detector assembly, ( X C , Y C () represents the image coordinates of the center of the reactor detector assembly. This represents the distance between the plane where the camera is located and the plane where the reactor detector is located during the nth measurement. f x , f y These respectively represent the camera at x , y Focal length on the axis.

4. The monocular vision alignment method for reactor detector assemblies according to claim 3, characterized in that, The acquisition method is as follows: the camera is moved by a fixed length B, and the coordinates of the center of the reactor detector assembly are recorded before and after the movement. P a and P b According to the formula: The coarse height value was obtained. H n In the formula f The focal length of the camera along the direction of movement; And through the following formula H n Update and fix: In the formula, This represents the result of the (n-1)th measurement. N This indicates the total number of calculations.

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