Position error calibration device and calibration method of industrial robot

Abstract

The invention discloses a position error calibration device and calibration method of an industrial robot. The position error calibration device comprises a laser ranging assembly used for measuring three-dimensional coordinates of a target ball at the tail end of a robot, and the laser ranging assembly comprises a laser interferometer, a spectroscope, a two-dimensional position sensitive detector and a shell; the two-dimensional moving platform is used for moving the laser ranging assembly in the X-axis direction and the Y-axis direction, and the two-dimensional moving platform comprises a lead screw sliding block module and a grating ruler in the X-axis direction and the Y-axis direction; and the supporting device is used for fixing and supporting the two-dimensional moving platform, so that the two-dimensional moving platform can stably work in a three-dimensional space. Compared with a laser tracker, conversion between a spherical coordinate system and a rectangular coordinate system is not needed, and therefore the amplification effect of the angle error of the inner circle grating of the laser tracker can be avoided. The three-dimensional coordinate value of the reflection target ball under the measurement coordinate system can be directly measured, the calibration effect is good, and the calibration requirement of the industrial robot can be met.

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. Using the measurement value fed back by the two-dimensional position sensitive detector, adjust the slider position of the two-dimensional mobile 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 ruler in the X-axis and Y-axis directions as the X and Y coordinate values ​​of the center of the target ball;

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

[0014] Step 5. Record the joint 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 angle data, a position error model is established, and the robot kinematic model parameters are identified using an optimization algorithm;

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

[0017] Beneficial effects of the invention: The invention proposes 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. The device is expected to reduce the calibration cost of industrial robots and has high calibration accuracy, meeting the needs of enterprises for low-cost, high-precision calibration devices for industrial robots. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A calibration 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 a laser ranging component in an embodiment of the present application;

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

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

[0022] Figure 5 This is a schematic diagram of the electric control in the embodiment of the present application;

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

[0024] In the figure: 1. Industrial robot; 2. Reflective target sphere; 3. Experimental table; 4. Support tripod; 5. Laser ranging component housing; 6. Laser interferometer; 7. Laser interferometer bracket; 8. Spectrometer; 9. Spectrometer bracket; 10. Two-dimensional position sensitive detector (PSD); 11. Y-axis module motor; 12. Y-axis module base; 13. Y-axis module slider; 14. Y-axis grating scale; 15. Y-axis grating scale reading head; 16. Y-axis lead screw; 17. X-axis module motor; 18. X-axis module base; 19. X-axis module slider; 20. X-axis grating scale; 21. X-axis grating scale reading head; 22. X-axis lead screw. DETAILED DESCRIPTION

[0025] For ease of understanding, the present invention is further described in detail below in conjunction with specific embodiments and drawings. The present invention is not limited to the embodiments described herein, and the purpose of providing the embodiments is to make the disclosure of the present invention more thoroughly and comprehensively understood. Obviously, the embodiments described are only some embodiments of the present invention, rather than all embodiments.

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

[0027] The laser distance measuring component includes a laser interferometer, a spectroscope, a two-dimensional position sensitive detector (PSD) and a laser distance measuring component housing, and the laser interferometer is used to measure the distance; the two-dimensional mobile platform includes an x-axis direction screw slider module, an x-axis direction grating ruler, an x-axis direction grating ruler reading head, a y-axis direction screw slider module, a y-axis direction grating ruler, and a y-axis direction grating ruler reading head, and the sliders of the x-axis and y-axis direction screw slider modules are used to move in the x-axis and y-axis directions, and the x-axis and y-axis direction grating rulers measure the moving distances in the x-axis and y-axis directions. The position error calibration device designed by the present invention is used to measure the position of the target ball at the end of the robot in the robot workspace for multiple times, and a position error model is established to solve the error parameters to calibrate the robot position error.

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

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

[0030] The x-axis grating ruler 20 and the x-axis grating ruler reading head 21 are fixed to the x-axis module base 18 and the side of the slider respectively; the y-axis grating ruler 14 and the y-axis grating ruler reading head 15 are fixed to the y-axis module base 12 and the side of the slider respectively. Figure 4 .

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

[0032] In this embodiment, the industrial robot is a KUKA KR10 R1100 six-axis industrial robot, and a reflective target ball matched 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. The Manfrotto brand model MKBFRTC4-BH is used as a supporting tripod, the precision vibration isolation equipment of Hawk Optical Instrument (Beijing) Technology Co., Ltd. is used as the experimental table, the laser interferometer is Renishaw XL-80, the spectroscope is Chuanglai Optoelectronics CL-PZ-LJ010062, the two-dimensional position sensitive detector (PSD) is Hamamatsu S5991-01, the grating ruler is DITRON DC10-400mm, and the module slider is Kashima Transmission KTH10-1605.

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

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

[0035] Step (2): Control the target ball at the end 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 control 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 rulers at this time as the x and y coordinate values ​​of the center of the current end target ball;

[0037] In one embodiment, the measured values ​​of the grating ruler in the x-axis direction and the y-axis direction are recorded as , the superscript R indicates the actual value.

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

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

[0040] Step (5), record the six joint angle data of the robot in the current state;

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

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

[0043] Step (7): Based on the obtained coordinate values ​​of the target ball (x, y, z) of the M groups of robot ends and the 6×M robot joint angle values, the homogeneous transformation matrix of the robot end coordinate system relative to the base coordinate system is established according to the MD-H model and the position error model is derived. The nominal MD-H parameter values ​​of the robot's six joints are substituted into the position error model, and the robot kinematic model parameters are identified using the optimization algorithm to obtain the calibrated MD-H model parameters.

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

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

[0046] in, Indicates the number of robot joints; is the joint torsion angle, Axis and Between the axes The angle of the axis; is the connecting rod length, indicating Axis and Along the axis The distance between the axes; is the joint rotation angle, indicating Axis and Between the axes The angle of the axis; is the connecting rod offset, indicating Axis and Between the axes The distance between the axes; Indicates rotation; Indicates translation; Indicates the robot The joint coordinate system axis; Indicates the robot The joint coordinate system axis;

[0047] Step (7-2) is based on the homogeneous transformation matrix of the robot's adjacent joints in step (7-1) , establish the total homogeneous transformation matrix (i.e., the second homogeneous transformation matrix) of the robot's end coordinate system relative to the base coordinate system: ;

[0048] Step (7-3) establishes the homogeneous transformation matrix (i.e., the third homogeneous transformation matrix) of the robot end tool coordinate system relative to the robot sixth joint coordinate system: ,in, Respectively, relative to axis, axis, Translation of the axis;

[0049] Step (7-4) establishes the homogeneous transformation matrix (i.e., the fourth homogeneous transformation matrix) of the robot base coordinate system relative to the measurement coordinate system of the position error calibration device: ;in, , , Respectively represent the axis, axis, Axis rotation angle, Respectively, relative to axis, axis, Translation of the axis;

[0050] Step (7-5) establishes the homogeneous transformation matrix (i.e., the fifth homogeneous transformation matrix) of the robot end tool coordinate system relative to the measurement coordinate system of the position error calibration device: ;

[0051] Step (7-6) is based on the homogeneous transformation matrix of step (7-5) , take the homogeneous transformation matrix The first 3 rows of the last column of the robot are the 24 MD-H model parameter values ​​and homogeneous transformation matrix of the robot's 6 joints 3 parameters, homogeneous transformation matrix The robot position error model is derived by taking the derivatives of 6 parameters of 33 model parameters: ;in 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: .

[0052] Furthermore, the 33 model parameters are: .

[0053] Step (7-7) is based on the target ball at the end of robot group M Coordinate values, 6×M robot joint angle values ​​and position error model , the nominal values ​​of 33 parameters, the end target balls of group M Coordinate values ​​and 6×M robot joint angle values ​​are substituted into the position error model , taking advantage of the extended Kalman EKF to reduce noise and the least squares method to quickly solve nonlinear problems, the optimization algorithm combining the extended Kalman EKF with LM is used to identify the robot kinematic model parameters and obtain the actual MD-H model parameters after calibration.

[0054] Step (8), the calibrated MD-H model parameters are compensated to the robot controller to complete the robot position error calibration.

[0055] Based on the same concept as the above method, an embodiment of the present application further provides a computer-readable storage medium, including instructions, which, when executed on a computer, enables the computer to execute the position error calibration method of the industrial robot.

[0056] Based on the same concept as the above method, an embodiment of the present application also provides an electronic device for calibrating the position error of an industrial robot, including a memory, a processor, and a computer program stored in the memory and capable of running on the processor. When the processor executes the computer program, the position error calibration method of the industrial robot is implemented.

[0057] In summary, compared with the laser tracker, the present application does not require the transformation between the spherical coordinate system and the rectangular coordinate system in terms of working principle, thereby avoiding the amplification effect of the angle error of the circular grating in the laser tracker. The position error calibration device can directly measure the three-dimensional coordinate value of the reflective target sphere 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 the laser tracker on the market.

[0058] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the embodiments here. All obvious changes or modifications derived from the technical solution of the present invention are still within the protection scope of the present invention.

Claims

1. A position error calibration device for an industrial robot, characterized in that: include: 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; 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; The supporting device is used to fix and support the two-dimensional mobile platform so that it can work stably in three-dimensional space.

2. The position error calibration device for an industrial robot according to claim 1, characterized in that: The laser interferometer and the beam splitter of the laser ranging assembly are respectively fixed on the bracket inside the shell, and the two-dimensional position sensitive detector is fixed at the lower end of the beam splitter bracket. The 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 sphere.

3. The position error calibration device for an industrial robot according to claim 1 or 2, characterized in that: The lead screw slider modules in the X-axis and Y-axis directions of the two-dimensional mobile platform are respectively equipped with a grating ruler and a grating ruler reading head for accurately measuring the moving distance in the X-axis and Y-axis directions.

4. The position error calibration device for an industrial robot according to claim 1 or 2, characterized in that: The supporting device is a tripod structure, which is used to stably support the two-dimensional mobile platform and ensure its positioning accuracy in three-dimensional space.

5. A method for calibrating the position error of an industrial robot, characterized in that: The following steps are involved: 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; Step 2. Control the target ball at the end of the robot to move to multiple preset positions in the workspace; Step 3. Using the measurement value fed back by the two-dimensional position sensitive detector, adjust the slider position of the two-dimensional mobile 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 ruler in the X-axis and Y-axis directions as the X and Y coordinate values ​​of the center of the target ball; Step 4. Obtain the Z coordinate value of the center of the target sphere according to the distance between the laser beam and the center of the target sphere recorded by the laser ranging component; Step 5. Record the joint 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 angle data, a position error model is established, and the robot kinematic model parameters are identified using an optimization algorithm; Step 7. Compensate the identified kinematic model parameters to the robot controller to complete the position error calibration.

6. The method for calibrating the position error of an industrial robot according to claim 5, characterized in that: In step 6, the extended Kalman filter algorithm is used to perform noise reduction on the measurement data, and the LM algorithm is combined to optimize and identify the robot kinematic model parameters to improve the calibration accuracy and robustness.

7. The method for calibrating the position error of an industrial robot according to claim 6, characterized in that: In step 6, a homogeneous transformation matrix of the robot end coordinate system relative to the base coordinate system is established based on the MD-H model, and a position error model is derived, which specifically includes: According to the MD-H model parameters, the first homogeneous transformation matrix of the adjacent joints of the robot is established; Based on the first homogeneous transformation matrix, a second homogeneous transformation matrix of the robot end coordinate system relative to the base coordinate system is established; Establishing the third homogeneous transformation matrix of the robot end tool coordinate system relative to the robot sixth joint coordinate system; Establishing the fourth homogeneous transformation matrix of the robot base coordinate system relative to the measurement coordinate system of the position error calibration device; Obtaining a 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 few rows of the last column of the fifth homogeneous transformation matrix, and derive the MD-H model parameters, the third homogeneous transformation matrix parameters, and the fourth homogeneous transformation matrix parameters to derive the position error model, which is used to describe the deviation between the actual coordinate value and the nominal coordinate value of the terminal target ball.

8. The position error calibration method of an industrial robot according to claim 7, characterized in that: The first homogeneous transformation matrix is ​​expressed as: ； in, Indicates the number of robot joints; is the joint torsion angle, Axis and Between the axes The angle of the axis; is the connecting rod length, indicating Axis and Along the axis The distance between the axes; is the joint rotation angle, indicating Axis and Between the axes The angle of the axis; is the connecting rod offset, indicating Axis and Between the axes The distance between the axes; Indicates rotation; Indicates translation; Indicates the robot The joint coordinate system axis; Indicates the robot The joint coordinate system axis.

9. A computer-readable storage medium, comprising instructions, which, when executed on a computer, enables the computer to execute the position error calibration method for an industrial robot as claimed in any one of claims 5 to 8.

10. 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, the position error calibration method of the industrial robot according to any one of claims 5 to 8 is implemented.

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