Industrial robot calibration device and method based on structured light system and hemispherical target

Abstract

The application discloses an industrial robot calibration device and method based on a structured light system and a hemispherical target. The application takes a double target fixed at both ends of a rigid ruler and composed of at least three precise standard hemispheres as a calibration reference, combines a structured light three-dimensional measurement technology, constructs a double-constraint calibration algorithm based on fixed distances and fixed relative postures, and realizes calibration of kinematic parameters of an industrial robot. Through a low-cost structured light system and a standardized double-hemispherical target reference element, high-precision standards required by calibration of the industrial robot are met, the calibration operation threshold and equipment cost are greatly reduced, and stable and reliable constraint conditions are provided for identification of kinematic parameters of the industrial robot.

Description

Technical Field

[0001] This invention belongs to the field of robot calibration technology, specifically relating to an industrial robot calibration device and method based on a structured light system and a hemispherical target. Background Technology

[0002] Industrial robots are widely used in modern manufacturing for high-precision tasks such as welding, handling, and assembly. Their absolute positioning accuracy is a key performance indicator for ensuring work quality and reliable production. However, due to factors such as manufacturing tolerances, joint transmission errors, and mechanical wear during long-term operation, there is a significant error between the actual pose of the end effector and the theoretical pose based on an ideal kinematic model. Therefore, regular and efficient calibration of industrial robots to correct their kinematic parameters is a necessary step to improve their absolute positioning accuracy and ensure work quality.

[0003] Traditional industrial robot calibration methods primarily rely on high-precision external measuring equipment, such as laser trackers and binocular vision systems. These methods typically require fixing one or more targets to the robot's end effector and tracking their motion trajectory using an external measurement system to obtain the robot's actual pose in three-dimensional space. By comparing the actual measured pose with the calculated theoretical pose, parameter identification algorithms are used to inversely solve for the robot's kinematic model error parameters, thereby compensating for the model's errors.

[0004] Chinese invention patent CN117381772A discloses a calibration method for industrial robots based on a laser interferometer. This invention adjusts the multi-axis positions and angles of the laser interferometer, interferometer, and reflector to achieve stable laser interference, and controls the robot to move along a preset circular trajectory. The radial length of the tool coordinate system relative to the reference system is measured using the laser interferometer, and the azimuth and polar angles are measured using a dual-angle encoder, converting the spherical coordinates to Cartesian coordinates as measurement data. However, this solution is not only costly but also has the following drawbacks: it requires precise calibration of the multi-axis positions of the laser interferometer, interferometer, and reflector to ensure stable light interference; the optical path adjustment process is cumbersome, demanding high levels of operator skill; debugging is difficult and time-consuming; and the calibration trajectory is limited to a circle, with the device structure designed for the laser interferometer's optical path. For high-load, long-stroke robots, the guide rail length and optical path layout need to be readjusted, resulting in poor adaptability. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides an industrial robot calibration method and apparatus based on a structured light system and a hemispherical target.

[0006] The industrial robot calibration method based on a structured light system and a hemispherical target in this invention includes the following steps: The structured light system comprises a first industrial camera, a second industrial camera, and a projector.

[0007] The structured light system is fixed to the end flange of the industrial robot. A scale with a first target and a second target fixed at both ends is set in the working space of the industrial robot. The first target and the second target each include a flat plate and at least three standard hemispheres installed on it. The spatial distance between the center points of the two targets and the relative attitude of the local coordinate system of the two targets are pre-calibrated reference values.

[0008] Adjust the pose of the scale, control the industrial robot to drive the structured light system to align with the first target and the second target respectively, and collect images of each target; obtain the three-dimensional point cloud of each target surface based on the structured light three-dimensional reconstruction, extract the center coordinates of each standard hemisphere through point cloud processing, combine the current joint rotation data of the industrial robot, and obtain the pose parameters of the local coordinate system of the two targets relative to the base coordinate system of the industrial robot through coordinate system transformation.

[0009] Repeat the above steps to obtain pose parameters under N different scale poses;

[0010] Based on the N pose parameters, and with the pre-calibrated spatial distance between the center points of the two targets and the relative attitude of the local coordinate systems of the two targets as constraints, an objective function containing position distance error terms and attitude distance error terms is constructed. The kinematic model parameters of the industrial robot and the tool offset parameters of the structured light system are optimized and solved to complete the calibration of the industrial robot.

[0011] In some embodiments, the first target and the second target each include four standard hemispheres, each standard hemisphere being distributed in a square on the plate. The standard hemispheres are made of matte ceramic material and have a sphericity better than 5 μm.

[0012] In some embodiments, the extraction of the center coordinates of each standard hemisphere through point cloud processing includes:

[0013] The three-dimensional point cloud is segmented using a Euclidean clustering algorithm, and a subset of the surface point cloud of each standard hemisphere is extracted by combining the known diameter information of the standard hemisphere.

[0014] The RANSAC algorithm is used to remove outlier noise points from the point cloud.

[0015] The least squares method is used to fit the effective point cloud of each standard hemisphere surface to obtain the three-dimensional coordinates of the center of each standard hemisphere.

[0016] In some embodiments, obtaining the pose parameters of the target's local coordinate system relative to the industrial robot's base coordinate system through coordinate system transformation includes:

[0017] Based on the standard DH kinematic modeling method, the homogeneous transformation matrix of the end flange coordinate system relative to the robot base coordinate system is calculated according to the current joint angle data and nominal DH parameters of the industrial robot.

[0018] Based on the pre-defined tool position offset vector and tool attitude offset vector of the structured light system, construct the homogeneous transformation matrix of the structured light system measurement coordinate system relative to the robot end flange coordinate system;

[0019] Based on the structured light 3D reconstruction results, the homogeneous transformation matrix of the target's local coordinate system relative to the measurement coordinate system is obtained;

[0020] The homogeneous transformation matrix of the target's local coordinate system relative to the robot's base coordinate system is obtained through coordinate system transformation, and the position and attitude parameters are extracted from it.

[0021] In some embodiments, when acquiring images of each target, the rotation angles of each joint of the industrial robot are adjusted to ensure that the axis of the structured light system is at an angle of less than 40 degrees to the plane of the corresponding target plate.

[0022] In some embodiments, in the objective function, the position distance error term and the attitude distance error term are multiplied by the position distance error weighting coefficient and the attitude distance error weighting coefficient, respectively, and then summed to achieve a balance between the magnitudes of the position distance error and the attitude distance error.

[0023] The industrial robot calibration device based on a structured light system and a hemispherical target in this invention is used to implement the above method, including:

[0024] The structured light system includes a first industrial camera, a second industrial camera, and a projector, wherein the structured light system is fixed to the end flange of an industrial robot.

[0025] The first target and the second target are respectively fixed at both ends of the scale, and each includes a flat plate and at least three standard hemispheres mounted on it. The center points of the first target and the second target have a pre-calibrated spatial distance, and the local coordinate system of the first target and the local coordinate system of the second target have a pre-calibrated fixed relative posture.

[0026] A support component is used to place the scale and the first and second targets at both ends of it within the workspace of the industrial robot, and to adjust the pose of the scale.

[0027] The structured light system is used to align with the first target and the second target respectively under the drive of the industrial robot to obtain the three-dimensional point cloud data of each target. The first target and the second target serve as calibration references, and based on the pre-calibrated spatial distance and fixed relative posture, a dual constraint condition is formed to calibrate the kinematic parameters of the industrial robot.

[0028] In some embodiments, the first target and the second target each include four standard hemispheres, each standard hemisphere being distributed in a square on the plate. The standard hemispheres are made of matte ceramic material, have a sphericity better than 5 μm, a diameter of 12 mm, and the center of each standard hemisphere is located on the surface of the plate.

[0029] In some embodiments, the pre-calibrated spatial distance is a fixed distance between the center points of the two targets, and the pre-calibrated fixed relative attitude includes the fixed relative roll angle of the local coordinate system of the two targets about the X-axis, the fixed relative pitch angle about the Y-axis, and the fixed relative yaw angle about the Z-axis.

[0030] In some embodiments, the support assembly includes a multi-functional rotating base, which includes a ball joint and a ball joint locking handle, enabling multi-angle adjustment within a range of ±30° to drive the ruler and the first and second targets to rotate around the X-axis, Y-axis, and Z-axis, thereby achieving spatial attitude adjustment.

[0031] The beneficial effects of this invention are as follows: This invention uses a double target, each consisting of at least three precision standard hemispheres, fixed at both ends of a rigid ruler as a calibration reference. Combined with structured light 3D measurement technology, it constructs a dual-constraint calibration algorithm based on fixed distance and fixed relative posture, thus realizing the calibration of kinematic parameters of industrial robots. Through a low-cost structured light system and standardized double-hemispherical target reference components, the high-precision standards required for industrial robot calibration are met, significantly reducing the calibration operation threshold and equipment cost. Simultaneously, it provides stable and reliable constraints for the identification of industrial robot kinematic parameters.

[0032] Actual measurements show that, using the device and method of this embodiment, the absolute position positioning accuracy of the six-axis industrial robot after calibration is ≤1.5mm, the absolute attitude positioning accuracy is ≤0.0019rad, the hardware cost of the entire calibration device is ≤40,000 yuan, and the single calibration cycle is usually ≤1.5 hours. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the overall structure of the calibration device of the present invention;

[0034] Figure 2 This is a partially enlarged schematic diagram of the calibration instrument combination device of the present invention;

[0035] Figure 3This is a partially enlarged schematic diagram of the scanning system of the present invention;

[0036] Figure 4 This is a schematic diagram of the local coordinate system of the first target of the present invention;

[0037] Figure 5 This is the original point cloud data of the first target in the test case. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0039] Example 1: As Figure 1 and Figure 2 As shown, this embodiment provides an industrial robot calibration device based on a structured light system and a hemispherical target. The device includes a tripod 3, a lifting platform 4, a multi-functional rotating base 5, an optical axis fixing seat 10, a scale 11, a first target 12, a second target 16, a first industrial camera 14, a second industrial camera 17, and a projector 15.

[0040] Furthermore, the tripod 3 is a Black Ant DVHZ-306 heavy-duty tripod, which includes a tripod body and a fixed base, used to stably install the entire device next to the industrial robot, ensuring that the first target 12 and the second target 16 are both located within the working space of the industrial robot.

[0041] The lifting platform 4 is a Weiyuan Precision ZT410MS120 manual lifting platform, with a platform size of 120mm×120mm and a lifting stroke of 120mm. It is used to adjust the position of components such as the scale 11 and the target in the vertical direction (Z-axis direction). The lifting platform 4 is fixed on the tripod 3 and is equipped with a lifting locking handle 8.

[0042] The multi-functional rotating base 5 is a SECCO SK-293 universal rotating base, which is fixed to the platform of the lifting platform 4. This multi-functional rotating base 5 has a ball joint 9 and a ball joint locking handle 7, enabling multi-angle adjustment of the X, Y, and Z axes within a range of ±30°. The multi-functional rotating base 5 has a clamping capacity ranging from 20mm to 80mm in width and 0mm to 25mm in thickness. Its top clamps and fixes the optical axis fixing seat 10, which can be secured using the caliper locking handle 6.

[0043] Furthermore, the optical axis fixing seat 10 is used to fix the scale 11 and the target, and its model is SK-30.

[0044] The scale 11 is made of Invar steel with a length of 1000mm, a diameter of 30mm, and a low coefficient of thermal expansion. Each end of the scale 11 has a 100mm long flat section with a plane dimension of 30mm × 10mm. Each flat section has two M6 screw holes with a hole spacing of 50mm, which are used to fix the first target 12 and the second target 16 respectively.

[0045] The first target 12 and the second target 16 have the same structure, each including a flat plate and four standard hemispheres 13 mounted on the plate. The flat plate is made of matte aluminum alloy and measures 200mm × 200mm × 10mm. Four mounting holes are machined on the plate, evenly distributed in a square with sides of 100mm. The standard hemispheres 13 are precision standard spheres made of matte ceramic material, each with a diameter of 12mm and a sphericity better than 5μm. Each standard hemisphere 13 is fixedly connected to the mounting holes on the plate via an M4 threaded base, ensuring that the center of each hemisphere is located on the surface of the target plate (at a height of 0mm).

[0046] Furthermore, the structured light system 2 is fixed to the end flange of the industrial robot 1. In this embodiment, the structured light system 2 uses a Hikvision MV-DPS-200P-02 structured light stereo camera, whose point cloud accuracy can reach 0.03mm. The structured light system 2 internally includes the first industrial camera 14, the second industrial camera 17, and a projector 15, wherein the projector 15 is located between the first industrial camera 14 and the second industrial camera 17. When fixed to the robot end, the axis of the projector 15 is perpendicular to the surface of the end flange of the industrial robot, see... Figure 3 .

[0047] Before calibrating an industrial robot, it is necessary to complete the distance calibration of the center points of the targets at both ends of the scale and the determination of the local coordinate system of the targets.

[0048] For the first target 12, the center of the standard hemisphere A1 is taken as the origin of its local coordinate system (i.e., the center point of the first target), and this origin serves as the reference position of the local coordinate system. The x-axis is defined to pass through this origin, and its direction is the direction of the line connecting this origin to the center of the standard hemisphere A3. The direction of the y-axis is defined as the direction perpendicular to the x-axis from the center of the standard hemisphere A2, and the y-axis also passes through this origin. The z-axis is determined by the right-hand rule based on the determined x-axis and y-axis, thus establishing the local coordinate system of the first target, see [link to relevant documentation]. Figure 4 .

[0049] For the second target 16, the center of the standard hemisphere B1 is taken as the origin of its local coordinate system (i.e., the center point of the second target), and this origin serves as the reference position of the local coordinate system of the second target. The x-axis is defined to pass through this origin, and the direction of the x-axis is the direction of the line connecting this origin to the center of the standard hemisphere B3. The direction of the y-axis is defined as the direction perpendicular to the x-axis from the center of the standard hemisphere B2, and the y-axis also passes through this origin. The z-axis is determined by the right-hand rule based on the determined x-axis and y-axis, thus establishing the local coordinate system of the second target.

[0050] Two targets each define a center point based on the location of the center of a standard hemisphere on each target. The coordinates of the centers of the hemispheres on the two targets are pre-calibrated by a coordinate measuring machine. The distance between the two center points (i.e., the origins of the two local coordinate systems) is denoted as... The relative attitude rotation angle between the two target local coordinate systems is denoted as... ,in Let X be the fixed relative roll angle of the two targets' local coordinate systems about the X-axis. For a fixed relative pitch angle about the Y-axis, This is a fixed relative yaw angle about the Z-axis. The aforementioned distance... and relative attitude rotation angle The coordinate measuring machine is used for pre-calibration as the calibration reference value.

[0051] Based on the above-described device, this embodiment also provides an industrial robot calibration method based on a structured light system and a hemispherical target. Before calibration begins, the following parameters need to be determined in advance:

[0052] The offset of the coordinate system reference point of the structured light system relative to the origin of the coordinate system of the end effector joint of the industrial robot (i.e., the center point of the end flange) is denoted as the tool position offset vector. ,in , , These represent the translational offsets along the X, Y, and Z axes of the robot's end effector joint coordinate system, respectively.

[0053] The Euler angles of the orientation offset of the structured light system's coordinate system relative to the coordinate system of the industrial robot's end effector joint are denoted as the tool orientation offset vector. ,in Let be the roll angle of the two coordinate systems about the X-axis. Let Y be the pitch angle about the Y-axis. The yaw angle is about the Z-axis.

[0054] The aforementioned tool offset vector was estimated using a manual measurement method to obtain a rough initial value (as a nominal value).

[0055] During the calibration of an industrial robot, the scale should be in N poses sequentially (N is usually an integer between 15 and 30), and the nominal parameters of the industrial robot's kinematic model are known. Initialize i=1 and perform the following steps:

[0056] Step S1: Pose Adjustment

[0057] Adjust the height of the lifting platform 4 and the angle of the multi-functional rotating base 5 so that the scale 11 is in the required i-th position, ensuring that the first target 12 and the second target 16 are both within the reach of the industrial robot.

[0058] Step S2: First target image acquisition and 3D reconstruction

[0059] The industrial control computer controls the industrial robot to move the structured light system 2 to the vicinity of the first target 12, and adjusts the rotation angles of each joint of the industrial robot to ensure that the axis of the structured light system is at an angle of less than 40 degrees to the plane where the flat plate of the first target 12 is located. The projector 15 projects striped structured light, and the first industrial camera 14 and the second industrial camera 17 simultaneously acquire the distorted striped images of the first target 12.

[0060] Based on the image data obtained from the structured light system, the phase measurement profilometry (PMP) technique based on the binocular structured light system is used to perform phase principal value calculation, multi-frequency phase unwrapping and stereo matching on the multi-frequency phase-shifted fringe images acquired by the left and right cameras. Combined with the pre-calibrated internal and external parameters of the structured light system, the three-dimensional point cloud of the surface of the first target 12 is reconstructed.

[0061] The Euclidean clustering segmentation algorithm is adopted, and combined with the known diameter information of the standard hemisphere, the reconstructed point cloud is sequentially subjected to pass-through filtering, statistical denoising, and clustering segmentation. The background point cloud of the target plate and environmental noise points are removed, and the surface point cloud subsets of each standard hemisphere are extracted to achieve the segmentation of the surface point cloud of each standard hemisphere.

[0062] The RANSAC (Random Sample Consensus) algorithm combined with the least squares spherical fitting algorithm is used. First, the RANSAC algorithm is used to remove outlier noise points in the point cloud. Then, the least squares method is used to fit the effective point cloud on the surface of each hemisphere to obtain the three-dimensional coordinates of the center of each standard hemisphere.

[0063] Step S3: Calculation of the pose of the first target

[0064] When the industrial robot drives the structured light system to acquire the image of the first target in the i-th pose, the joint rotation angles of each joint of the industrial robot are recorded. ,in (j=1,2,...,6) represents the joint angle of the j-th joint of the industrial robot during the i-th acquisition of the first target.

[0065] The homogeneous transformation matrix of the link j coordinate system relative to the link j-1 coordinate system is obtained based on the standard DH (Denavit-Hartenberg) kinematic modeling method:

[0066]

[0067] in For the length of the connecting rod, For connecting rod torsion angle, For link offset, This refers to the joint angle.

[0068] The currently measured joint angle Substituting into the above formula, and combining it with the robot's known nominal DH parameters ( ~ , ~ , ~ By multiplying six adjacent transformation matrices, the homogeneous transformation matrix of the end flange coordinate system relative to the robot base coordinate system is obtained:

[0069] .

[0070] Then, from the tool position offset vector and tool attitude offset vector The homogeneous transformation matrix of the structured light system measurement coordinate system relative to the robot end effector flange coordinate system is constructed. Simultaneously, the homogeneous transformation matrix of the local coordinate system of the first target relative to the measurement coordinate system is directly obtained through structured light 3D reconstruction. .

[0071] Finally, through coordinate system transformation, the homogeneous transformation matrix of the first target's local coordinate system relative to the robot's base coordinate system is obtained. Extract the position parameters of the first target's local coordinate system relative to the robot's base coordinate system at the i-th pose. and attitude parameters ,in , , Let X, Y, and Z be the coordinates of the origin of the local coordinate system of the first target at the i-th pose along the X, Y, and Z axes of the robot's base coordinate system. Let X be the roll angle of the first target's local coordinate system about the robot's base coordinate system X-axis in the i-th pose. Let Y be the pitch angle about the Y-axis. The yaw angle is about the Z-axis.

[0072] Step S4: Second target image acquisition and 3D reconstruction

[0073] The industrial control computer controls the industrial robot to move the structured light system 2 to the vicinity of the second target 16, and adjusts the rotation angles of each joint of the industrial robot to ensure that the axis of the structured light system is at an angle of less than 40 degrees to the plane where the flat plate of the second target 16 is located. The projector 15 projects striped structured light, and the first industrial camera 14 and the second industrial camera 17 simultaneously acquire the distorted striped images of the second target 16.

[0074] Using the same method as in step S2, the second target is reconstructed in three dimensions, segmented in three dimensions, and fitted with the center of the sphere to obtain the three-dimensional coordinates of the center of each standard hemisphere on the second target.

[0075] Step S5: Calculation of the pose of the second target

[0076] The joint angles of each joint of an industrial robot are denoted as... ,in (j=1,2,...,6) represents the joint angle of the j-th joint of the industrial robot during the i-th acquisition of the second target.

[0077] Using the same coordinate system transformation method as in step S3, the homogeneous transformation matrix of the second target local coordinate system relative to the robot base coordinate system is obtained. Extract the position parameters of the second target's local coordinate system relative to the robot's base coordinate system at the i-th pose. and attitude parameters ,in , , Let X, Y, and Z be the coordinates of the origin of the local coordinate system of the second target along the X, Y, and Z axes of the robot's base coordinate system, respectively, in the i-th pose. Let X be the roll angle of the second target's local coordinate system about the robot's base coordinate system X-axis in the i-th pose. Let Y be the pitch angle about the Y-axis. The yaw angle is about the Z-axis.

[0078] Step S6: Loop Collection

[0079] Let i = i + 1, and repeat steps S1 to S5 until the above steps and data acquisition for the corresponding N scale poses are completed.

[0080] Step S7: Parameter optimization solution

[0081] The kinematic model parameters and tool offset vector of the industrial robot are optimized using an optimization algorithm. The variables to be optimized are defined as follows:

[0082]

[0083] in This includes the errors of 24 DH kinematic parameters for a 6-axis industrial robot (for the j-th joint (j=1,2,...,6)). For link length error, For connecting rod torsion angle error, For link offset error, (for joint angle error) The error is the tool position offset vector of the structured light system. This represents the error in the tool attitude offset vector of the structured light system.

[0084] Construct the optimization objective function:

[0085]

[0086] Among them, the position distance error term This represents the spatial distance between the center points of the two targets, calculated using the robot's kinematics model, and the pre-calibrated reference length at the i-th pose. The difference is calculated using the following formula:

[0087]

[0088] Attitude distance error term This represents the relative attitude Euler angles between the two target local coordinate systems calculated by the robot kinematics model at the i-th pose, and the pre-calibrated fixed relative attitude of the reference. The difference vector is calculated using the following formula:

[0089]

[0090] This indicates the calculation of the attitude distance error term. The sum of squares of the elements in a vector.

[0091] The unit of positional distance error is millimeters (mm), with a typical order of magnitude of 0.01mm-1mm; the unit of attitude distance error is radians (rad), with a typical order of magnitude of 0.001rad-0.01rad. Due to the difference in units and orders of magnitude, a weighting coefficient for positional distance error is introduced. and attitude distance error weighting coefficient This addresses the issue of inconsistent magnitudes between position distance error and attitude distance error, achieving a "balanced magnitude of error contribution" between the two during optimization. It ensures the optimization model's ability to accommodate both position and attitude distance accuracy.

[0092] During optimization, the nominal values ​​of the kinematic model parameters of the industrial robot and the nominal value of the tool pose offset vector are used as the initial values ​​of the parameters to be optimized. The objective function is optimized and solved to obtain the kinematic parameter error values ​​that minimize the position distance error and the attitude distance error.

[0093] Verification example: such as Figure 5 As shown, the original point cloud data of the first target in a certain pose was collected. The coordinates of the center of the standard hemisphere fitted by structured light in 20 different poses are shown in Tables 1-1 and 1-2:

[0094] Table 1-1 Table 1-2

[0095] The following are the positional distance errors (mm) of the industrial robot before and after calibration according to this application (30 verification points):

[0096] Table 2

[0097]

[0098] The data from the 30 verification points in the table show that after calibration, the average position distance error of the robot decreased from 4.129 mm to 1.093 mm, and the maximum position error was 1.476 mm, all of which meet the technical specification of ≤1.5 mm.

[0099] The following are the industrial robot attitude distance error (rad) data before and after calibration using this application (30 verification points):

[0100] Table 3

[0101]

[0102] Table 3 shows that after calibration, the average attitude distance error decreased from 0.01325 rad to 0.00173 rad, and the maximum attitude error was 0.00181 rad, all meeting the technical requirement of ≤0.0019 rad. Traditional methods usually cannot guarantee both position accuracy and attitude accuracy at the same time. However, this application achieves a significant improvement in both position accuracy and attitude accuracy by introducing a dual-target relative attitude constraint.

[0103] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An industrial robot calibration method based on a structured light system and a hemispherical target, wherein the structured light system includes a first industrial camera, a second industrial camera, and a projector, characterized in that, Includes the following steps: The structured light system is fixed to the end flange of the industrial robot. A scale with a first target and a second target fixed at both ends is set in the working space of the industrial robot. The first target and the second target each include a flat plate and at least three standard hemispheres installed on it. The spatial distance between the center points of the two targets and the relative attitude of the local coordinate system of the two targets are pre-calibrated reference values. Adjust the position and pose of the scale, and control the industrial robot to drive the structured light system to align with the first target and the second target respectively, and collect images of each target; The three-dimensional point cloud of each target surface is obtained based on structured light three-dimensional reconstruction. The center coordinates of each standard hemisphere are extracted through point cloud processing. Combined with the current joint rotation data of the industrial robot, the pose parameters of the two target local coordinate systems relative to the industrial robot base coordinate system are obtained through coordinate system transformation. Repeat the above steps to obtain pose parameters under N different scale poses; Based on the N pose parameters, and with the pre-calibrated spatial distance between the center points of the two targets and the relative attitude of the local coordinate systems of the two targets as constraints, an objective function containing position distance error terms and attitude distance error terms is constructed. The kinematic model parameters of the industrial robot and the tool offset parameters of the structured light system are optimized and solved to complete the calibration of the industrial robot.

2. The method according to claim 1, characterized in that, The first target and the second target each include four standard hemispheres, each of which is distributed in a square on the plate. The standard hemispheres are made of matte ceramic material and have a sphericity better than 5μm.

3. The method according to claim 1 or 2, characterized in that, The extraction of the center coordinates of each standard hemisphere through point cloud processing includes: The three-dimensional point cloud is segmented using a Euclidean clustering algorithm, and a subset of the surface point cloud of each standard hemisphere is extracted by combining the known diameter information of the standard hemisphere. The RANSAC algorithm is used to remove outlier noise points from the point cloud. The least squares method is used to fit the effective point cloud of each standard hemisphere surface to obtain the three-dimensional coordinates of the center of each standard hemisphere.

4. The method according to claim 3, characterized in that, The process of obtaining the pose parameters of the target's local coordinate system relative to the industrial robot's base coordinate system through coordinate system transformation includes: Based on the standard DH kinematic modeling method, the homogeneous transformation matrix of the end flange coordinate system relative to the robot base coordinate system is calculated according to the current joint angle data and nominal DH parameters of the industrial robot. Based on the pre-defined tool position offset vector and tool attitude offset vector of the structured light system, construct the homogeneous transformation matrix of the structured light system measurement coordinate system relative to the robot end flange coordinate system; Based on the structured light 3D reconstruction results, the homogeneous transformation matrix of the target's local coordinate system relative to the measurement coordinate system is obtained; The homogeneous transformation matrix of the target's local coordinate system relative to the robot's base coordinate system is obtained through coordinate system transformation, and the position and attitude parameters are extracted from it.

5. The method according to claim 1, characterized in that, When acquiring images of each target, adjust the rotation angle of each joint of the industrial robot to ensure that the axis of the structured light system is at an angle of less than 40 degrees to the plane of the corresponding target plate.

6. The method according to claim 1 or 5, characterized in that, In the objective function, the position distance error term and the attitude distance error term are multiplied by the position distance error weighting coefficient and the attitude distance error weighting coefficient, respectively, and then summed to achieve a balance between the magnitudes of the position distance error and the attitude distance error.

7. An industrial robot calibration device based on a structured light system and a hemispherical target, used to implement the method according to any one of claims 1-6, characterized in that, include: The structured light system includes a first industrial camera, a second industrial camera, and a projector, wherein the structured light system is fixed to the end flange of an industrial robot. The first target and the second target are respectively fixed at both ends of the scale, and each includes a flat plate and at least three standard hemispheres mounted on it. The center points of the first target and the second target have a pre-calibrated spatial distance, and the local coordinate system of the first target and the local coordinate system of the second target have a pre-calibrated fixed relative posture. A support component is used to place the scale and the first and second targets at both ends of it within the workspace of the industrial robot, and to adjust the pose of the scale. The structured light system is used to align with the first target and the second target respectively under the drive of the industrial robot to obtain the three-dimensional point cloud data of each target. The first target and the second target serve as calibration references, and based on the pre-calibrated spatial distance and fixed relative posture, a dual constraint condition is formed to calibrate the kinematic parameters of the industrial robot.

8. The calibration device according to claim 7, characterized in that, The first target and the second target each include four standard hemispheres, each of which is distributed in a square on the plate. The standard hemispheres are made of matte ceramic material, have a sphericity better than 5μm, a diameter of 12mm, and the center of each standard hemisphere is located on the surface of the plate.

9. The calibration device according to claim 7 or 8, characterized in that, The pre-calibrated spatial distance is a fixed distance between the center points of the two targets. The pre-calibrated fixed relative attitude includes the fixed relative roll angle of the local coordinate system of the two targets around the X-axis, the fixed relative pitch angle around the Y-axis, and the fixed relative yaw angle around the Z-axis.

10. The calibration device according to claim 9, characterized in that, The support assembly includes a multi-functional rotating base, which includes a ball joint and a ball joint locking handle, enabling multi-angle adjustment within a range of ±30° to drive the ruler and the first and second targets to rotate around the X-axis, Y-axis, and Z-axis, thereby achieving spatial attitude adjustment.

Images