Rotary calibration method based on XYR axis platform
By adopting a rotation calibration method based on the XYR axis platform in the rotation center calibration, the Y-moving axis and the X-moving axis make the suction plate Mark point calibrate in the field of view of the camera, the problems of camera position consistency and the XY-axis immovable problems in the prior art are solved, and flexible calibration and highly accurate rotation center calibration are achieved.
Patent Information
- Application Number
- CN202411889584.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-20
- Publication Date
- 2025-05-06
AI Technical Summary
The existing rotary center calibration method requires ensuring that the calibration timed photography position is consistent with the application photography position, and the XY axis cannot move during calibration and cannot be compatible with the situation where the nozzle Mark point exceeds the camera's field of view during rotation.
The rotation calibration method based on the XYR axis platform is adopted, and the Y-moving axis and the X-moving axis are used to calibrate the Mark points of the suction plate in the field of view of the camera, and mechanical coordinates are used instead of pixel coordinates for calibration calculation.
It realizes flexibility in taking photos during calibration and use, avoids the problem of pixel coordinate origin offset, and is compatible with the situation where the nozzle Mark point exceeds the camera's field of view, improving calibration flexibility and accuracy.
Smart Images
Figure CN119927898A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of visual positioning, and in particular relates to a rotation calibration method based on an XYR axis platform. Background Art
[0002] Rotation center calibration refers to the process of determining the rotation center of the manipulator or robot end effector in machine vision applications. The rotation center is a key parameter used to accurately control the manipulator's grasping action when the manipulator or robot's end tool center does not coincide with its own rotation center. In actual machine vision applications, the manipulator or robot needs to grasp materials, but the angle of the material may be different each time. If the manipulator's end tool center does not coincide with its own rotation center, the rotation center needs to be calibrated. Calibrating the rotation center ensures that the manipulator can accurately align with the target position when grasping and placing materials, thereby improving the accuracy and stability of the operation.
[0003] In the commonly used rotation center calibration method, while ensuring that the camera and nozzle XY axis are stationary, only the nozzle's R axis is rotated, the nozzle is rotated to an angle and a photo is taken, then the nozzle Mark point center is located and the data is recorded. After repeating the above actions until enough data is collected, a circle is fitted through these positioning data, and its center is the nozzle's rotation center. The output rotation center coordinates are pixel coordinates with the upper left corner of the image at the photo position as the origin. When used for positioning, the XY offset caused by the product rotation can be compensated by the product angle and the calibrated nozzle rotation center.
[0004] Based on the above content, the commonly used rotation calibration generally has the following disadvantages: 1. When in use, it is necessary to ensure that the camera position (i.e., X and Y axis position) during calibration is consistent with the product camera position during application, otherwise it will cause the pixel coordinate origin to shift and affect the rotation center of the calibration. 2. During calibration, it is necessary to ensure that only the R axis can be rotated during the calibration process, and the X and Y axes cannot be moved. Therefore, it is not compatible with the situation where the nozzle mark point may exceed the camera's field of view during the rotation process. Summary of the invention
[0005] The purpose of the present invention is to provide a rotation calibration method based on an XYR axis platform to solve the technical problems described in the background technology.
[0006] A rotation calibration method based on an XYR axis platform, characterized in that: it is applied to an XYR axis platform, the XYR axis platform is equipped with a Y movable axis and an X movable axis, the Y movable axis is rigidly connected to a suction plate, the X movable axis is rigidly connected to a camera, the size of the suction plate is larger than the field of view of the camera, and during the R-axis rotation calibration of the suction plate, when the suction plate Mark point exceeds the camera field of view, the Y movable axis drives the suction plate to move in the Y-axis direction and the X movable axis drives the camera to move in the X-axis direction, so that the suction plate Mark point is within the camera field of view, thereby performing calibration.
[0007] Furthermore, the calibration calculation uses the mechanical coordinate origin of the XY axis instead of the pixel coordinate origin, that is, when recording the rotation calibration data, the pixel coordinates of the camera are converted into mechanical coordinates through a 9-point calibration matrix, and the position of the Mark point of the suction plate in the mechanical coordinate system is calculated in combination with the photographing position.
[0008] Furthermore, the calibration process includes the following steps: S1, the suction plate rotates to a preset angle; S2, XY axis moves to the shooting position of the angle to take a picture; S3, calculate the distance from the Mark point of the suction plate to the optical center of the camera; S4, move the suction plate mark point to the optical center of the camera; S5, record the X-axis coordinate and Y-axis coordinate at this time; S6. Change the preset angle and repeat the above steps S1-S5 to record a number of points. After fitting a circle through these points, calculate the center of the circle, which is the final calibrated rotation center.
[0009] Furthermore, the rotation center is a rotation center of a corresponding relationship between the shooting point of the camera and the rotation of the suction plate. When in use, by obtaining the shooting position of a certain point on the suction plate, the shooting position after the suction plate is rotated by any angle can be obtained through the rotation center, so as to obtain the rotation calibration matrix of the solution by calculating the compensation value of the shooting position.
[0010] Furthermore, the pre-rotation angle θ and the calibrated rotation center xy of the suction plate are obtained, and then the Mark point on the product is located. The new photographing position of the Mark point on the product after rotating the preset angle is calculated by the current photographing position × rotation change matrix, and the camera is moved to the new photographing position to take a photo, so that the position of the Mark point at the new photographing position is consistent with the position of the Mark point before rotation. The specific formula is as follows: ; P1: New product photo taking location; P0: Current product photo taking position; The rotation matrix for rotating by angle θ around xy.
[0011] According to the technical solution described above: First, no matter where the Mark point is selected on the suction plate, the rotation center calculated according to the calibration method is the intersection of the camera center and the suction plate rotation center. The selection of the Mark point position will only change the radius of the rotation calibration circle, and will not change the position of the rotation center. Secondly, according to geometric calculations, it can be known that the calculated rotation center will not change with the movement of the XYR axis, and will only be affected by the camera optical center and the suction plate rotation center. In addition, since the camera is rigidly connected to the X moving axis and the suction plate is rigidly connected to the Y moving axis, the camera optical center and the suction plate rotation center will not change, so that the calculated rotation center is a fixed point. Therefore, whether in calibration or use, the shooting position can be set arbitrarily without restriction. In summary, the present invention achieves the following beneficial effects: 1. When in use, the photo taking position may be different from the photo taking position during calibration; 2. When calibrating, you don’t need to consider the camera field of view. Even if the selected mark point is beyond the camera field of view during rotation, you can move the XY axis to make the mark point within the camera field of view; 3. In the commonly used rotation calibration method, after calibration, the product's photographing position is determined and cannot be changed. If the photographing position is modified later, it must be recalibrated. Therefore, compared with the commonly used rotation calibration method, the rotation calibration method of the present invention can change the product's photographing position arbitrarily without being affected after rotation calibration; 5. In the commonly used rotation calibration method, since the pixel coordinates are used as the origin, the XY axis cannot move during the rotation calibration process. This has a certain field of view limitation for the calibration of a suction plate or nozzle with a relatively large size. In the commonly used rotation calibration method, the rotation calibration method of the present invention uses the mechanical coordinates as the origin during the calibration process, so the XY axis can move arbitrarily without affecting the calibration result. BRIEF DESCRIPTION OF THE DRAWINGS
[0012] In order to more clearly illustrate the specific implementation of the present invention, the following is a brief description of the drawings and reference numerals required to be used in describing the specific implementation.
[0013] Figure 1 This is a working state diagram of a common rotation center calibration method; Figure 2 This is a schematic diagram of the structure layout of a common XYR mechanical platform; Figure 3 It is a schematic diagram of the structure layout of the XYR axis platform claimed in the present invention; Figure 4 It is a geometric position diagram of the box simulation suction plate when it rotates -60°, -40°, -20°, 0°, 20°, 40°, 60°, 80°, and 100°; Figure 5 yes Figure 4 Remove the box (suction plate) and keep the geometric diagram of the line connecting the box's rotation center and the suction plate Mark center. DETAILED DESCRIPTION
[0014] In order to make the objectives, technical solutions and advantages of the present invention more clear, an explanation is given below with reference to the accompanying drawings.
[0015] like Figure 1 As shown, in the common rotation center calibration method, while ensuring that the camera and the nozzle XY axis are stationary, only the R axis of the nozzle is rotated, and the nozzle is rotated to an angle to take a photo, and then the nozzle Mark point center is located and the data is recorded. Repeat the above actions until enough data is collected, and then a circle is fitted through these positioning data, and its center is the rotation center of the nozzle. The output rotation center coordinates are pixel coordinates with the upper left corner of the image at the photo position as the origin. When used for positioning, the XY offset caused by the rotation of the product can be compensated by the product angle and the calibrated nozzle rotation center. In the commonly used rotation calibration, when it is used, it is necessary to ensure that the photo position (i.e., X, Y axis position) during calibration is consistent with the product photo position during application, otherwise it will cause the pixel coordinate origin to shift and affect the calibrated rotation center. In addition, during calibration, it is also necessary to ensure that only the R axis can be rotated during the calibration process, and the XY axis cannot move. Therefore, it is not compatible with the situation where the nozzle Mark point may exceed the camera field of view during rotation.
[0016] In common XYR mechanical platforms, such as Figure 2 As shown, the XY movable axis in the XYR mechanical platform is rigidly connected to the suction nozzle, that is, the XYR mechanical platform drives the suction nozzle to move along the XY axis by driving the XY movable axis, and the camera is fixed to the bottom plate in the XYR mechanical platform, and the bottom plate cannot move along the XY axis.
[0017] In order to understand the common rotation center calibration methods, you can further refer to the document "Calibration and use of rotation center using Halcon 9-point calibration".
[0018] In view of the above common rotation center calibration methods, this specific implementation provides a rotation calibration method based on an XYR axis platform.
[0019] like Figure 3As shown, the XYR axis platform is equipped with a Y movable axis and an X movable axis, the Y movable axis is rigidly connected to a suction plate, the Y movable axis can drive the suction plate to move along the Y axis, and the suction plate can only move along the Y axis, the X movable axis is rigidly connected to a camera, the X movable axis can drive the camera to move along the X axis, and the camera can only move in the X direction; the size of the suction plate is larger than the field of view of the camera, and during the R-axis rotation calibration of the suction plate, when the suction plate Mark point exceeds the camera field of view, the Y movable axis drives the suction plate to move along the Y axis and the X movable axis drives the camera to move along the X axis, so that the suction plate Mark point is within the camera field of view, thereby performing calibration.
[0020] Since the XYR axes need to move during the calibration process, the calibration calculation method uses the mechanical coordinate origin of the XY axes instead of the pixel coordinate origin. That is, when recording the rotation calibration data, the camera's pixel coordinates are converted to mechanical coordinates through a 9-point calibration matrix, and the position of the Mark point of the suction plate in the mechanical coordinate system is calculated in combination with the shooting position.
[0021] The calibration process includes the following steps: S1, the suction plate rotates to a preset angle; S2, XY axis moves to the shooting position of the angle to take a picture; S3, calculate the distance from the Mark point of the suction plate to the optical center of the camera; S4, move the suction plate mark point to the optical center of the camera; S5, record the X-axis coordinate (the axis where the camera is located) and the Y-axis coordinate (the axis where the suction plate is located) at this time; S6. Change the preset angle and repeat the above steps S1-S5 to record a number of points. After fitting a circle through these points, calculate the center of the circle, which is the final calibrated rotation center.
[0022] Furthermore, the rotation center is not the rotation center of the suction plate, but the rotation center of a corresponding relationship between the shooting point of the camera and the rotation of the suction plate. When in use, by obtaining the shooting position of a certain point on the suction plate, the shooting position after the suction plate rotates at any angle can be obtained through the rotation center, so as to obtain the rotation calibration matrix of the solution through the calculated compensation value of the shooting position.
[0023] Compared with the common rotation center calibration method, the above scheme is also different in usage. The commonly used rotation calibration matrix is used to calculate the compensation value of the pixel position of the product positioning, while the rotation calibration matrix of the above scheme is used to calculate the compensation value of the camera position.
[0024] To further demonstrate the specific calculation logic, the following geometric proof is listed: like Figure 4 As shown, Figure 4 The boxes in the figure are the simulated suction plate when rotating at -60°, -40°, -20°, 0°, 20°, 40°, 60°, 80° and 100°. The suction plate positions at different angles are marked with different colors. The suction plate at 0 degrees is marked with a red solid line, and two points are marked at the same time (the suction plate Mark center and the suction plate rotation center). The suction plates at other angles are calculated with reference to the suction plate at 0 degrees. Since the suction plate Mark center is moved to the camera center every time during calibration, the suction plate Mark center must fall on the line parallel to the X axis (herein referred to as: camera optical center line). In addition, since the suction plate only has a Y axis, the suction plate rotation center must fall on the line parallel to the Y axis (herein referred to as: suction plate rotation center line) every time the suction plate moves.
[0025] For the convenience of observation, Figure 5 As shown, remove the frame of the suction plate (suction plate), only keep the line connecting the suction plate rotation center and the suction plate Mark center, and mark the intersection of the corresponding camera axis coordinates (X moving axis) and the suction plate axis coordinates (Y moving axis) (these intersections are the XY axis position data we recorded), and then connect these coordinate points with arcs. At this point, you will find that these points form a circle (this is a geometric theorem), the center of this circle is exactly the intersection of the line connecting the camera optical center and the line connecting the suction plate rotation center, and the radius is exactly the distance from the suction plate Mark point to the suction plate rotation center.
[0026] In summary, according to the above rules, firstly, no matter where the Mark point is selected on the suction plate, the rotation center calculated according to the calibration method is the intersection of the camera center and the suction plate rotation center. The selection of the Mark point position will only change the radius of the rotation calibration circle, and will not change the position of the rotation center. Secondly, according to the above geometric calculation, it can be known that the calculated rotation center will not change with the movement of the XYR axis, and is only affected by the camera optical center and the suction plate rotation center. In addition, since the camera is rigidly connected to the X moving axis and the suction plate is rigidly connected to the Y moving axis, the camera optical center and the suction plate rotation center will not change, so that the calculated rotation center is a fixed point. Therefore, whether during calibration or use, the photo position can be set arbitrarily without restriction.
[0027] When applied, obtain the pre-rotation angle θ and the calibrated rotation center xy of the suction plate, then locate the Mark point on the product, calculate the new shooting position of the Mark point on the product after rotating the preset angle by the current shooting position × rotation change matrix, move the camera to the new shooting position to take a picture, so that the position of the Mark point at the new shooting position is consistent with the position of the Mark point before rotation, specifically as follows: ; P1: New product photo taking location; P0: Current product photo taking position; The rotation matrix for rotating by angle θ around xy.
[0028] Based on the comparison between the above scheme and the common rotation center calibration method: 1. After the rotation calibration, the product photo position can be changed arbitrarily without being affected by the above scheme; in the commonly used rotation calibration method, after calibration, the product photo position is determined and cannot be changed. If the photo position is modified later, it must be recalibrated. 2. During the calibration process of the above scheme, the XY axis can be moved. Since the calibration method uses the mechanical coordinates as the origin, the XY axis can be moved arbitrarily without affecting the calibration results; while in the commonly used rotation calibration method, since the pixel coordinates are used as the origin, the XY axis cannot be moved during the rotation calibration process, which has certain limitations for the calibration of larger suction plates or nozzles.
[0029] In addition, in the above scheme, the photographing position during use may be different from the photographing position during calibration. The camera field of view does not need to be considered during calibration. Even if the selected Mark point exceeds the camera field of view during rotation, the Mark point can be moved within the camera field of view by moving the XY axis.
Claims
1. A rotation calibration method based on an XYR axis platform, characterized in that: The XYR axis platform is equipped with a Y movable axis and an X movable axis, the Y movable axis is rigidly connected to a suction plate, the X movable axis is rigidly connected to a camera, the size of the suction plate is larger than the field of view of the camera, and when the suction plate is calibrated during R-axis rotation, when the suction plate Mark point exceeds the camera field of view, the Y movable axis drives the suction plate to move in the Y-axis direction and the X movable axis drives the camera to move in the X-axis direction, so that the suction plate Mark point is within the camera field of view, thereby performing calibration.
2. The rotation calibration method based on the XYR axis platform according to claim 1, characterized in that: The calibration calculation uses the mechanical coordinate origin of the XY axis instead of the pixel coordinate origin. That is, when recording the rotation calibration data, the pixel coordinates of the camera are converted into mechanical coordinates through a 9-point calibration matrix, and the position of the Mark point of the suction plate in the mechanical coordinate system is calculated in combination with the shooting position.
3. The rotation calibration method based on the XYR axis platform according to claim 2, characterized in that: The calibration process includes the following steps: S1, the suction plate rotates to a preset angle; S2, XY axis moves to the shooting position of the angle to take a picture; S3, calculate the distance from the Mark point of the suction plate to the optical center of the camera; S4, move the suction plate mark point to the optical center of the camera; S5, record the X-axis coordinate and Y-axis coordinate at this time; S6. Change the preset angle and repeat the above steps S1-S5 to record a number of points. After fitting a circle through these points, calculate the center of the circle, which is the final calibrated rotation center.
4. The rotation calibration method based on the XYR axis platform according to claim 3, characterized in that: The rotation center is a rotation center of a corresponding relationship between the shooting point of the camera and the rotation of the suction plate. When in use, by obtaining the shooting position of a certain point on the suction plate, the shooting position after the suction plate is rotated at any angle can be obtained through the rotation center, so as to obtain the rotation calibration matrix of the solution by calculating the compensation value of the shooting position.
5. The rotation calibration method based on the XYR axis platform according to claim 4, characterized in that: Get the pre-rotation angle θ and the calibrated rotation center xy of the suction plate, then locate the Mark point on the product, calculate the new shooting position of the Mark point on the product after rotating the preset angle by the current shooting position × rotation change matrix, move the camera to the new shooting position to take a picture, so that the position of the Mark point at the new shooting position is consistent with the position of the Mark point before rotation, specifically as follows: ； P1: New product photo taking location; P0: Current product photo taking position; The rotation matrix for rotating by angle θ around xy.