Position error calibration device and calibration method for an industrial robot

Abstract

The present invention discloses a position error calibration device and a calibration method for an industrial robot. The position error calibration device in the present invention includes a laser ranging component for measuring the three-dimensional coordinates of the target ball at the end of the robot. The laser ranging component includes a laser interferometer, a beam splitter, a two-dimensional position sensitive detector, and a housing; a two-dimensional moving platform for moving the laser ranging component in the X-axis and Y-axis directions. The two-dimensional moving platform includes a lead screw slider module and a grating scale in the X-axis and Y-axis directions; a supporting device for fixing and supporting the two-dimensional moving platform so that it can work stably in three-dimensional space. Compared with a laser tracker, the present invention does not require transformation between a spherical coordinate system and a rectangular coordinate system, thereby avoiding the amplification effect of the angle error of the inner circle grating in the laser tracker. The present invention can directly measure the three-dimensional coordinate values of the reflecting target ball in the measurement coordinate system, has a good calibration effect, and can meet the calibration requirements of industrial robots.

Description

Technical Field

[0001] The invention belongs to the technical field of metrology and calibration, and relates to a position error calibration device and a calibration method for an industrial robot. Background Art

[0002] Current industrial robots have extremely high repeatability, but their absolute positioning accuracy may decrease during use and is far lower than the repeatability, making them unable to meet the application requirements of continuous high-precision operations. Therefore, the key to improving absolute positioning accuracy is to establish a mathematical model to calibrate and compensate for the errors that affect the absolute positioning accuracy of the robot.

[0003] At present, the calibration tools used for industrial robots are mainly laser trackers. Although the laser trackers on the market have high measurement accuracy, they are expensive. In addition, the working principle of the laser tracker in measuring three-dimensional coordinates is the transformation between the spherical coordinate system and the rectangular coordinate system. The error of its angle sensor has an amplifying effect, which significantly reduces the accuracy of the transformed three-dimensional coordinates. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a position error calibration device and a calibration method for an industrial robot.

[0005] A first aspect of the present invention provides a position error calibration device for an industrial robot, comprising:

[0006] A laser ranging component is used to measure the three-dimensional coordinates of the target ball at the end of the robot. The laser ranging component includes a laser interferometer, a spectroscope, a two-dimensional position sensitive detector and a shell;

[0007] A two-dimensional mobile platform, used to move the laser distance measurement component in the X-axis and Y-axis directions, and the two-dimensional mobile platform includes a lead screw slider module and a grating ruler in the X-axis and Y-axis directions;

[0008] The supporting device is used to fix and support the two-dimensional mobile platform so that it can work stably in three-dimensional space.

[0009] A second aspect of the present invention provides a method for calibrating a position error of an industrial robot, comprising the following steps:

[0010] Step 1. Install the target ball at the end of the robot, and start the laser ranging component to emit a laser beam to aim at the target ball;

[0011] Step 2. Control the target ball at the end of the robot to move to multiple preset positions in the workspace;

[0012] Step 3. Use the measurement values fed back by the two-dimensional position-sensitive detector to adjust the slider position of the two-dimensional moving platform, align the laser beam with the center of the two-dimensional position-sensitive detector, and record the readings of the grating scales in the X-axis and Y-axis directions as the X and Y coordinate values of the target ball center;

[0013] Step 4. Obtain the Z coordinate value of the target ball center according to the distance between the laser beam and the target ball center recorded by the laser ranging component;

[0014] Step 5. Record the joint rotation angle data of the robot at each position;

[0015] Step 6. Based on the recorded three-dimensional coordinate values of the target ball and the joint rotation angle data, establish a position error model, and use an optimization algorithm to identify the parameters of the robot kinematic model;

[0016] Step 7. Compensate the identified kinematic model parameters to the robot controller to complete the position error calibration.

[0017] Advantages of the present invention: The present invention provides a position error calibration device and method, which avoids the transformation between the spherical coordinate system and the rectangular coordinate system in the working principle and can directly obtain the three-dimensional coordinates in the rectangular coordinate system. This set of devices is expected to reduce the calibration cost of industrial robots and has high calibration accuracy, meeting the needs of enterprises for low-cost and high-precision calibration devices for industrial robots. Brief Description of the Drawings

[0018] Figure 1 It is a calibration schematic diagram of an industrial robot position error calibration device according to an embodiment of the present application;

[0019] Figure 2 It is a front view schematic diagram of the laser ranging component in an embodiment of the present application;

[0020] Figure 3 It is a side view schematic diagram of the laser ranging component in an embodiment of the present application;

[0021] Figure 4 It is a schematic diagram of the two-dimensional moving platform in an embodiment of the present application;

[0022] Figure 5 It is an electrical control schematic diagram in an embodiment of the present application;

[0023] Figure 6 It is a schematic diagram of the method flow in an embodiment of the present application;

[0024] In the figure: 1. Industrial robot; 2. Reflective target ball; 3. Test bench; 4. Support tripod; 5. Laser ranging component housing; 6. Laser interferometer; 7. Laser interferometer support; 8. Beam splitter; 9. Beam splitter support; 10. Two-dimensional position sensitive detector (PSD); 11. Y-axis direction module motor; 12. Y-axis direction module base; 13. Y-axis direction module slider; 14. Y-axis direction grating scale; 15. Y-axis direction grating scale reading head; 16. Y-axis direction lead screw; 17. X-axis direction module motor; 18. X-axis direction module base; 19. X-axis direction module slider; 20. X-axis direction grating scale; 21. X-axis direction grating scale reading head; 22. X-axis direction lead screw. Detailed implementation manner

[0025] For the convenience of understanding, the following will further elaborate on the present invention in combination with specific embodiments and the accompanying drawings. The present invention is not limited to the embodiments described in the text. The purpose of providing the embodiments is to make the disclosure content of the present invention more thoroughly and comprehensively understood. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0026] This application proposes a position error calibration device and calibration method for an industrial robot. The calibration device includes a laser ranging component, a two-dimensional moving platform, and a support tripod.

[0027] Among them, the laser ranging component consists of a laser interferometer, a beam splitter, a two-dimensional position sensitive detector (PSD), and a laser ranging component housing, and the laser interferometer is used for distance measurement; the two-dimensional moving platform consists of an X-axis direction lead screw slider module, an X-axis direction grating scale, an X-axis direction grating scale reading head, a Y-axis direction lead screw slider module, a Y-axis direction grating scale, and a Y-axis direction grating scale reading head. The sliders of the X-axis and Y-axis direction lead screw slider modules are used for moving in the X-axis and Y-axis directions, and the X-axis and Y-axis direction grating scales measure the moving distances in the X-axis and Y-axis directions. The position error calibration device designed by the present invention measures the position of the end target ball of the robot in the robot working space multiple times, and establishes a position error model to solve the error parameters for calibrating the robot position error.

[0028] As Figure 1 、 Figure 2 and Figure 3 shown, in an embodiment, the laser interferometer 6 and the beam splitter 8 are respectively fixed on the laser interferometer support 7 and the beam splitter support 9 inside the laser ranging component housing 5, and the two-dimensional position sensitive detector 10 (PSD) is fixed at the lower end of the beam splitter support to form the laser ranging component.

[0029] The z-axis measurement value of the laser ranging component is the distance from the laser ranging component to the center of the reflection target ball 2 at the end of the industrial robot 1 (placed on the experimental bench 3). The laser ranging component is fixed on the x-axis module slider 19 of the x-axis lead screw 22 (driven by the x-axis module motor 17) and moves left and right with the slide table. The base of the x-axis lead screw module slider is fixed on the y-axis module slider 13 of the y-axis lead screw 16 (driven by the y-axis module motor 11) and moves up and down with the slider.

[0030] The x-axis grating scale 20 and the x-axis grating scale reading head 21 are respectively fixed on the x-axis module base 18 and the side of the slider; the y-axis grating scale 14 and the y-axis grating scale reading head 15 are respectively fixed on the y-axis module base 12 and the side of the slider, as shown in Figure 4 .

[0031] The base of the y-axis lead screw slider module is fixed on the support tripod 4 to realize the assembly of the position error calibration device and the measurement of the three-dimensional coordinate values.

[0032] In this embodiment, the industrial robot is a KUKA KR10 R1100 six-axis industrial robot. A reflection target ball that cooperates with a domestic six-degree-of-freedom laser tracker is used as the end target ball of the industrial robot, and the robot is controlled to move the end target ball 100 times in total. The support tripod is of the Manfrotto brand model MKBFRTC4-BH, the experimental bench is a precision vibration isolation device of Hawk Optoelectronics (Beijing) Technology Co., Ltd., the laser interferometer is a Renishaw XL-80, the beam splitter is a CL-PZ-LJ010062 of Chuanglai Optoelectronics, the two-dimensional position sensitive detector (PSD) is a Hamamatsu S5991-01, the grating scale is a DC10-400mm of DITRON, and the module slider is a KTH10-1605 of Jiada Transmission.

[0033] As Figure 5 and Figure 6 shown, on the other hand, the present application proposes a position error calibration method for an industrial robot. To achieve the expected effect, a measurement coordinate system, an end tool coordinate system of the position error calibration device, the first to sixth joint coordinate systems, a base coordinate system and a position error model of the industrial robot are established based on the MD-H model and the partial differential theory, and the industrial robot calibration method using the aforementioned position error calibration device is used. The specific steps are as follows:

[0034] Step (1): Install and fix a target ball at the end of the robot, start the laser ranging component to emit laser and roughly aim at the target ball, and let k = 1.

[0035] Step (2): Control the end target ball of the robot to move to the kth position in the robot workspace.

[0036] Step (3): According to the feedback of the measurement value of the two-dimensional position-sensitive detector (PSD), adjust the sliders of the x-direction module and the y-direction module so that the refracted laser beam is aligned with the center of the two-dimensional position-sensitive detector (PSD), and record the readings of the two grating scales at this time as the x and y coordinate values of the current end target ball center;

[0037] In one embodiment, the measured values of the grating scales in the x-axis direction and the y-axis direction are denoted as , and the superscript R represents the actual value.

[0038] Step (4): Record the distance of the end target ball of the robot according to the laser ranging component as the current z coordinate value;

[0039] In one embodiment, the distance of the end target ball is , and at this time, the actual coordinate value of the end target ball center is obtained .

[0040] Step (5): Record the six joint rotation angle data of the robot in the current state;

[0041] In one embodiment, the six joint rotation angle data are , and the superscript N represents the nominal value.

[0042] Step (6): Determine whether k is less than M. If so, let k = k + 1 and return to Step (2); otherwise, proceed to the next step.

[0043] Step (7): Based on the obtained M groups of end target ball (x, y, z) coordinate values of the robot and 6×M robot joint angle values, establish a homogeneous transformation matrix of the end coordinate system of the robot relative to the base coordinate system according to the MD-H model and derive a position error model. Substitute the nominal MD-H parameter values of the 6 joints of the robot into the position error model, and use an optimization algorithm to complete the identification of the kinematic model parameters of the robot to obtain the calibrated MD-H model parameters.

[0044] In one embodiment, Step (7) specifically includes:

[0045] Step (7-1): According to the four-parameter MD-H model, establish the homogeneous transformation matrix of adjacent joints of the robot (i.e., the first homogeneous transformation matrix):

[0046] ;

[0047] Among them, represents the number of robot joints; is the joint twist angle, indicating the angle between the axis and the axis about the axis; is the link length, indicating Axis and The distance along the axis between the axes; Is the joint rotation angle, representing Axis and The angle between the axes with respect to the axis; Is the link offset, representing Axis and The distance between the axes with respect to the axis; Represents rotation; Represents translation; Represents the th joint coordinate system of the robot axis; Represents the th joint coordinate system of the robot axis;

[0048] Step (7-2) Based on the homogeneous transformation matrix of adjacent joints of the robot in step (7-1) , establish the total homogeneous transformation matrix of the end coordinate system of the robot relative to the base coordinate system (i.e., the second homogeneous transformation matrix): ;

[0049] Step (7-3) Establish the homogeneous transformation matrix of the end tool coordinate system of the robot relative to the sixth joint coordinate system of the robot (i.e., the third homogeneous transformation matrix): , where Respectively represent relative to axis,[[]] axis,[[]] axis translation;

[0050] Step (7-4) Establish the homogeneous transformation matrix of the base coordinate system of the robot relative to the measurement coordinate system of the position error calibration device (i.e., the fourth homogeneous transformation matrix): ; Among them , , Respectively represent the rotation angles around the axis,[[]] axis,[[]] axis, Respectively represent relative to axis,[[]] axis,[[]] axis translation;

[0051] Step (7-5) Establish the homogeneous transformation matrix of the end tool coordinate system of the robot relative to the measurement coordinate system of the position error calibration device (i.e., the fifth homogeneous transformation matrix): ;

[0052] Step (7-6) is based on the homogeneous transformation matrix of step (7-5). , take the first 3 rows of the last column of the homogeneous transformation matrix , and take the derivative of the 24 MD-H model parameter values of the 6 joints of the robot, the 3 parameters of the homogeneous transformation matrix , and the 6 parameters of the homogeneous transformation matrix , a total of 33 model parameters, and derive the robot position error model: ; where is the difference between the actual coordinate value and the nominal coordinate value of the center of the end target ball, is the position error Jacobian matrix, is the position error parameter vector: .

[0053] Furthermore, the 33 model parameters are respectively: .

[0054] Step (7-7) is based on the M groups of end target balls of the robot coordinate values, 6×M robot joint angle values and the position error model , substitute the nominal values of the 33 parameters, the coordinate values of the M groups of end target balls , and the 6×M robot joint angle values into the position error model , utilize the advantages of the extended Kalman EKF to reduce noise and the least squares method to quickly solve nonlinear problems, and adopt an optimization algorithm combining the extended Kalman EKF and LM to identify the kinematic model parameters of the robot, and obtain the calibrated actual MD-H model parameters.

[0055] Step (8), compensate the calibrated MD-H model parameters into the robot controller to complete the robot position error calibration.

[0056] Based on the same concept as the above method, the embodiment of the present application also provides a computer-readable storage medium, including instructions, which when running on a computer, cause the computer to execute the position error calibration method of the industrial robot described above.

[0057] Based on the same concept as the above method, the embodiment of the present application also provides an electronic device for position error calibration of an industrial robot, including a memory, a processor, and a computer program stored in the memory and capable of running on the processor, and when the processor executes the computer program, it implements the position error calibration method of the industrial robot described above.

[0058] In summary, compared with the laser tracker, the present application does not need to perform the transformation between the spherical coordinate system and the rectangular coordinate system in terms of the working principle, thereby avoiding the amplification effect of the angular error of the inner circular grating in the laser tracker. The position error calibration device can directly measure the three-dimensional coordinate values of the reflected target ball in the measurement coordinate system, has a good calibration effect, and can meet the calibration requirements of industrial robots. In addition, the cost will also be lower than that of the laser trackers on the market.

[0059] Obviously, the above-mentioned embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limiting the embodiments of the present invention. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is impossible to list all the embodiments here. Any obvious changes or variations derived from the technical solutions of the present invention still fall within the protection scope of the present invention.

Claims

1. A method for calibrating the position error of an industrial robot, which uses a position error calibration device. The device includes: A laser ranging component for measuring the three-dimensional coordinates of the target ball at the end of the robot. The laser ranging component includes a laser interferometer, a beam splitter, a two-dimensional position sensitive detector, and a housing; A two-dimensional moving platform for moving the laser ranging component in the X-axis and Y-axis directions. The two-dimensional moving platform includes a lead screw slider module and a grating scale in the X-axis and Y-axis directions; A support device for fixing and supporting the two-dimensional moving platform so that it can work stably in three-dimensional space; It is characterized in that the method includes the following steps: Step 1. Install a target ball at the end of the robot and start the laser ranging component to emit a laser beam to align with the target ball; Step 2. Control the target ball at the end of the robot to move to multiple preset positions in the working space; Step 3. Use the measurement values feedback by the two-dimensional position sensitive detector to adjust the slider position of the two-dimensional moving platform so that the laser beam is aligned with the center of the two-dimensional position sensitive detector, and record the readings of the grating scales in the X-axis and Y-axis directions as the X and Y coordinate values of the target ball center; Step 4. Obtain the Z coordinate value of the target ball center according to the distance between the laser beam and the target ball center recorded by the laser ranging component; Step 5. Record the joint rotation angle data of the robot at each position; Step 6. Based on the recorded three-dimensional coordinate values of the target ball and the joint rotation angle data, establish a position error model, and use an optimization algorithm to identify the parameters of the robot kinematic model; Step 7. Compensate the identified kinematic model parameters to the robot controller to complete the position error calibration; In the said Step 6, the extended Kalman filter algorithm is used to denoise the measurement data, and the LM algorithm is combined to optimize and identify the parameters of the robot kinematic model to improve the calibration accuracy and robustness; In the said Step 6, based on the MD-H model, a homogeneous transformation matrix of the end coordinate system of the robot relative to the base coordinate system is established, and a position error model is deduced, specifically including: According to the MD-H model parameters, establish the first homogeneous transformation matrix of adjacent joints of the robot; Based on the first homogeneous transformation matrix, establish the second homogeneous transformation matrix of the end coordinate system of the robot relative to the base coordinate system; Establish the third homogeneous transformation matrix of the end tool coordinate system of the robot relative to the sixth joint coordinate system of the robot; Establish the fourth homogeneous transformation matrix of the base coordinate system of the robot relative to the measurement coordinate system of the position error calibration device; Obtain the fifth homogeneous transformation matrix of the end tool coordinate system relative to the measurement coordinate system from the second homogeneous transformation matrix, the third homogeneous transformation matrix, and the fourth homogeneous transformation matrix; Take the first several rows of the last column of the fifth homogeneous transformation matrix, and take the derivatives of the MD-H model parameters, the third homogeneous transformation matrix parameters, and the fourth homogeneous transformation matrix parameters to deduce the position error model, which is used to describe the deviation between the actual coordinate value and the nominal coordinate value of the end target ball.

2. The position error calibration method of the industrial robot according to claim 1, characterized in that: The said first homogeneous transformation matrix is expressed as: Among them, i represents the number of robot joints; α i-1 is the joint twist angle, representing the angle between the z i-1 axis and the z i axis about the x i-1 axis; a i-1 is the link length, representing the distance along the x i-1 axis between the z i axis and the z i-1 axis; θ is the joint rotation angle, representing the angle between the x i-1 axis and the x i axis about the z i axis; d is the link offset, representing the distance between the x i-1 axis and the x i axis about the z i axis; rot represents rotation; trans represents translation; x i-1 represents the x-axis of the (i - 1)-th joint coordinate system of the robot; z i represents the z-axis of the i-th joint coordinate system of the robot.

3. The method for calibrating the position error of an industrial robot according to claim 1, characterized in that: The laser interferometer and the beam splitter of the laser ranging component are respectively fixed on the brackets inside the housing. The lower end of the beam splitter bracket is fixed with a two-dimensional position sensitive detector. A laser beam is emitted by the laser interferometer and reflected by the beam splitter to the two-dimensional position sensitive detector to obtain the Z-axis coordinate value of the center of the target ball.

4. The position error calibration method of the industrial robot according to claim 1 or 3, characterized in that: The lead screw slider modules in the X-axis and Y-axis directions of the two-dimensional moving platform are respectively equipped with grating scales and grating scale reading heads for accurately measuring the moving distances in the X-axis and Y-axis directions.

5. The method for calibrating the position error of an industrial robot according to claim 1 or 3, characterized in that: The supporting device is a tripod structure for stably supporting the two-dimensional moving platform and ensuring its positioning accuracy in three-dimensional space.

6. A computer-readable storage medium includes instructions that, when run on a computer, cause the computer to execute the position error calibration method of the industrial robot according to any one of claims 1-5.

7. An electronic device for calibrating the position error of an industrial robot, comprising a memory, a processor, and a computer program stored in the memory and capable of running on the processor, characterized in that: When the processor executes the computer program, it implements the position error calibration method of the industrial robot according to any one of claims 1-5.

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