A motion distance measuring device and calibration method for an industrial robot

Abstract

The present invention discloses a motion distance measuring device and calibration method for an industrial robot. The measuring device in the present invention comprises a motion distance measuring component, a measuring rod, and a supporting tripod. The motion distance measuring component uses a laser displacement sensor to measure the distance, and the distances at both ends of the motion distance measuring component are fixed values. The motion distance measuring device designed by the present invention is used to measure the actual distances of multiple movements of the standard ball position at the end of the robot, and a distance error equation is established to solve the error parameter value to calibrate the distance error of the robot. Compared with the traditional calibration method using a laser tracker, the present invention has the advantages of low cost, high measurement accuracy, and easy to carry, and can meet the robot calibration requirements. In addition, compared with the contact measuring device, the non-contact type does not have the problem of robot calibration failure caused by errors in the device itself due to wear during use, and can better ensure the normal operation of the industrial robot.

Description

Technical Field

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

[0002] Industrial robots play a very important role in automated production. However, during the use of robots, errors in workpiece size, assembly, deformation, wear, etc. make the robot's accuracy unable to meet the operation requirements, resulting in reduced quality of robot task completion. Therefore, it is very necessary to improve the posture accuracy of industrial robots and correct the error model parameter values ​​of robots.

[0003] At present, laser trackers are generally used to measure the end position of the robot in industrial robot calibration. Although the laser tracker has high calibration accuracy, it is expensive and not suitable for most small enterprises on the market. Although the cost of vision-related measurement equipment or wire-drawing measurement systems is relatively low, they have low measurement accuracy and cannot meet the robot calibration requirements. In addition, Chinese patent publication No. CN 118305794 A discloses a robot calibration device and method. The calibration device requires manually adjusting the slider on the guide rail to make the standard ball close to the ball seat in order to measure the distance between the two standard balls. The operation is inconvenient, depends on the proficiency of the device, and the contact measurement is prone to wear. Summary of the invention

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

[0005] In a first aspect, the present invention provides a motion distance measuring device for an industrial robot, comprising a motion distance measuring component and a supporting tripod, the two being connected by a measuring rod;

[0006] The motion distance measurement assembly includes six laser displacement sensors and two mounting brackets;

[0007] Three laser displacement sensors are installed on each mounting bracket; the measuring line of the vertically mounted laser displacement sensor is directed upward; the measuring lines of the two horizontally placed laser displacement sensors are located in the same plane as the top of the mounting bracket and the angle between the two measuring lines is 90°; the measuring lines of the three laser displacement sensors are perpendicular to each other and intersect at one point.

[0008] In a second aspect, the present invention provides a calibration method for an industrial robot, specifically:

[0009] Step 1, control the end tool of the industrial robot to move to the vicinity of the origin of the first measurement coordinate system of the motion distance measuring device, and record the first measurement value of the laser displacement sensor and the first nominal joint angles of the six joints at this time;

[0010] Based on the nominal homogeneous transformation matrix and the first nominal joint angle to obtain the first nominal three-dimensional coordinate value of the end tool in the base coordinate system ;

[0011] Step 2, control the industrial robot to move the terminal standard ball to the vicinity of the origin of the second measurement coordinate system of the motion distance measurement device, and record the second measurement value of the laser displacement sensor and the second nominal joint angles of the six joints at this time;

[0012] Based on the nominal homogeneous transformation matrix and the second nominal joint angle to obtain the second nominal three-dimensional coordinate value of the end tool in the base coordinate system. ;

[0013] Step 3: Based on the first nominal 3D coordinate value and the second nominal 3D coordinate value Get the nominal distance value of the end tool in the base coordinate system ;

[0014] Obtaining an actual measured distance value based on the first measurement value of the laser displacement sensor and the second measurement value of the laser displacement sensor ;

[0015] Step 4: Each time the posture of the motion distance measuring device is adjusted once, steps 1 to 3 are repeated, and the posture of the motion distance measuring device is adjusted m times in total to obtain m measurement results;

[0016] Step 5: Based on the actual measured distance value Distance to nominal value The difference between them is used to establish the distance error model between two consecutive points;

[0017] Step 6: Use the optimization algorithm to perform parameter identification, obtain the actual kinematic error parameter value, and load the error parameter value into the industrial robot controller to complete the distance error calibration.

[0018] Compared with the traditional calibration method using a laser tracker, the present invention has the advantages of low cost, high measurement accuracy, and easy portability, and can meet the robot calibration requirements. In addition, compared with the contact measurement device, the non-contact type does not have the problem of robot calibration failure caused by errors in the device itself due to wear during use, which can better ensure the normal operation of industrial robots. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1A schematic diagram of the technical principle of the calibration method of an embodiment of the present application;

[0020] Figure 2 is a schematic diagram of a measuring rod and a motion distance measuring assembly;

[0021] Figure 3 Schematic diagram of motion distance measurement component and three-coordinate measuring machine. DETAILED DESCRIPTION

[0022] 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.

[0023] like Figure 1 and Figure 2 As shown, the embodiment of the present application provides a motion distance measuring device for an industrial robot, which comprises a motion distance measuring assembly, a measuring rod 4, and a supporting tripod 9. The motion distance measuring assembly comprises six laser displacement sensors 2 and mounting brackets 3-1 and 3-2.

[0024] Three laser displacement sensors are installed on the mounting brackets on both sides of the measuring rod 4, and the mounting brackets on both sides are connected by invar. The motion distance measurement assembly is fixed on the measuring rod using an external hexagonal bolt 10. A vertically mounted laser displacement sensor is installed on each mounting bracket, and its measuring line is directed upward; the measuring lines of two horizontally placed laser displacement sensors are located in the same plane as the top of the mounting bracket, and the angle between the two measuring lines is 90°; the measuring lines of the three laser displacement sensors are perpendicular to each other and intersect at one point. There are also evenly distributed triangular bolt holes 5 on both sides of the measuring rod, which are used to match the external hexagonal bolts 10.

[0025] Based on the above-mentioned motion distance measurement component, the embodiment of the present application also establishes a coordinate system of the motion distance measurement component, takes the intersection of the laser beams of the three laser displacement sensors as the origin, and establishes a first measurement coordinate system and a second measurement coordinate system with the direction away from the laser displacement sensor as the axis direction.

[0026] Preferably, the Manfrotto brand model MKBFRTC4-BH is used as the supporting tripod, the invar length is 600mm, and it is processed by high-precision CNC integration, with a length of 97mm, a width of 97mm, and a height of 71.1mm. The laser displacement sensor model is Omron's ZX1-LD50.

[0027] Furthermore, to improve the measurement accuracy, Figure 3As shown, the embodiment of the present application also places the motion distance measurement component on the three-dimensional coordinate measuring machine 12 platform for calibration, and the calibration steps are as follows:

[0028] Step 1: Use the ball handle fixture 14 to fix the standard ball and establish the coordinate measuring machine coordinate system.

[0029] Step 2: Move the ball handle fixture to place the standard ball near the origin of the first measurement coordinate system of the motion distance measurement component, and obtain the first group of three laser displacement sensor measurement values.

[0030] Step 3: Control the three-dimensional coordinate measuring machine probe 13 to contact the standard ball, and obtain the three-dimensional coordinate value of the center of the standard ball in the three-dimensional coordinate measuring machine coordinate system.

[0031] Step 4: Move the ball handle fixture to place the standard ball near the origin of the second measurement coordinate system of the motion distance measurement component, and obtain the second set of three laser displacement sensor measurement values.

[0032] Step 5: Control the probe of the three-dimensional coordinate measuring machine to contact the standard ball, and obtain the three-dimensional coordinate value of the center of the standard ball in the coordinate system of the three-dimensional coordinate measuring machine.

[0033] Step 6: Calculate the distance between the centers of the standard balls measured twice by the three-dimensional coordinate measuring machine according to the three-dimensional coordinate values ​​of the centers of the standard balls in steps 3 and 5.

[0034] Step 7: Repeat steps 2 to 6 for a total of n times to obtain 6×n sensor measurement values ​​and n standard ball center distance values.

[0035] Step 8: According to step 7, the data is obtained, 6×n laser displacement sensor measurement values ​​are used as input, and n standard ball center distance values ​​are used as output. The BP neural network is used to calibrate the distance error of the motion distance measurement component.

[0036] Step 9: Write the result of BP neural network fitting into the lower computer of the motion distance measurement component to complete the calibration of the motion distance measurement component.

[0037] In a preferred embodiment, the ball handle fixture is moved to place the standard ball near the origin of the first measurement coordinate system, and the laser displacement sensor measurement value is recorded. At the same time, the three-dimensional coordinates of the center of the standard ball in the coordinate measuring machine coordinate system are recorded. , where the radius of the standard ball is R, the radius of the ruby ​​probe of the three-dimensional coordinate measuring machine is r, and n is the number of measurements. The measurement value of the laser displacement sensor is recorded once in the first and second measurement coordinate systems respectively, which is counted as one measurement.

[0038] In a preferred embodiment, the ball handle fixture is moved to place the standard ball near the origin of the second measurement coordinate system, and the laser displacement sensor measurement value is recorded. , and at the same time control the three-dimensional coordinate measuring machine probe to contact the standard ball and record the three-dimensional coordinate value of the center of the standard ball at this time , where n is the number of measurements, and recording the measurement value of the laser displacement sensor once in the first and second measurement coordinate systems is counted as one measurement.

[0039] The three-dimensional coordinates of the center of the standard ball measured by a three-dimensional coordinate measuring machine , Calculate the distance to the center of the sphere:

[0040] ;

[0041] Furthermore, the laser displacement sensors on the mounting brackets on both sides measure the , As input, the distance from the center of the sphere As output, a three-layer BP neural network with 8 neurons in the hidden layer is used to calibrate the motion distance measurement component.

[0042] Preferably, the three-coordinate measuring machine is Hexagon's Leitz PMM-C, the motion distance measurement component calibration times n is 100 times, the three-coordinate measuring machine probe ruby ​​diameter is 2mm, the standard ball with handle standard ball diameter is 25mm, the measuring rod is 1000mm long, 50mm wide, and 20mm thick invar.

[0043] The embodiment of the present application also provides a calibration method for an industrial robot. The industrial robot 1 is a KUKAKR10 R1100 six-axis serial robot. To achieve the expected effect, the calibration method for the industrial robot is obtained using the aforementioned calibrated motion distance measuring device. The specific steps are as follows:

[0044] Step 1: Establish the industrial robot base coordinate system and the first to sixth joint coordinate systems of the industrial robot.

[0045] Step 2: Install the standard ball 11 with a handle on the sixth joint of the robot to establish the end tool coordinate system; the standard ball is made of ceramic material.

[0046] Step 3: Establish the kinematic MD-H model of adjacent joints of the robot and obtain the transformation relationship between the adjacent joint coordinate systems.

[0047] Step 4: Calculate the homogeneous transformation matrix of adjacent joint errors based on differential motion.

[0048] Step 5: According to steps 1 to 3, establish the nominal homogeneous transformation matrix of the robot end tool coordinate system relative to the base coordinate system.

[0049] Step 6: According to steps 1 to 4, establish the actual homogeneous transformation matrix of the robot end tool coordinate system relative to the base coordinate system.

[0050] Step 7: Calculate the error homogeneous transformation matrix of the robot end tool coordinate system relative to the base coordinate system according to steps 5 and 6, and further obtain the position error matrix.

[0051] Step 8: Control the standard ball at the end of the industrial robot to move to the vicinity of the origin of the first measurement coordinate system of the motion distance measurement device, and record the measurement value of the laser displacement sensor and the nominal joint angles of the six joints at this time.

[0052] Step 9: Control the industrial robot to move the terminal standard ball to the vicinity of the origin of the second measurement coordinate system of the motion distance measurement device, and record the measurement value of the laser displacement sensor and the nominal joint angles of the six joints at this time.

[0053] Step 10: According to step 8, the nominal joint angle is substituted into the nominal homogeneous transformation matrix in step 5 to obtain the nominal three-dimensional coordinate value of the end tool, i.e., the standard ball, in the base coordinate system.

[0054] Step 11: According to step 9, the nominal joint angle is substituted into the nominal homogeneous transformation matrix in step 5 to obtain the nominal three-dimensional coordinate value of the end tool, i.e., the standard ball, in the base coordinate system.

[0055] Step 12: According to step 10 and step 11, the nominal distance value of the end tool, i.e., the standard ball, in the base coordinate system is calculated.

[0056] Step 13: According to step 8 and step 9, the measurement values ​​of the six laser displacement sensors are written into the lower computer of the motion distance measurement component to obtain the actual measured distance value.

[0057] Step 14, adjust the attitude adjustment handle of the supporting tripod, and adjust the motion distance measurement component together with the measuring rod to different postures; among which the adjustment handle 6 is used to adjust the pitch angle attitude around the Y axis, the adjustment handle 7 is used to adjust the rotation angle attitude around the X axis, and the adjustment handle 8 is used to adjust the deflection angle attitude around the Z axis.

[0058] Step 15, repeat steps 8 to 14, and measure m times in total to obtain 2×6×m nominal joint angle values, 2×m nominal end standard ball three-dimensional coordinate values, m segments of nominal distance values, and m segments of actual measured distance values; the value of m can be selected as 30.

[0059] Step 16: Use the distance constraint, that is, the difference between the actual measured distance value and the nominal distance value, to establish a distance error model between two consecutive points.

[0060] Step 17: Use an optimization algorithm to perform parameter identification, obtain actual kinematic error parameter values, and write the error parameter values ​​into the industrial robot controller to complete distance error calibration.

[0061] Furthermore, the transformation relationship of the adjacent joint coordinate systems is the nominal homogeneous transformation matrix of the adjacent joints: ,in Indicates joint, ;

[0062] The nominal homogeneous transformation matrix of the robot end tool coordinate system relative to the base coordinate system is represented as: ;

[0063] Therefore, the actual homogeneous transformation matrix of the robot end tool coordinate system relative to the base coordinate system is represented as: ;

[0064] in is the homogeneous transformation matrix of adjacent joint errors.

[0065] Furthermore, the error homogeneous transformation matrix of the robot end tool coordinate system relative to the base coordinate system can be obtained: ;

[0066] From the error homogeneous transformation matrix we get The first three rows of the fourth column get the position error matrix ,Right now: ;

[0067] in, The error homogeneous transformation matrix is ​​expressed as The first three rows of the fourth column of represents the position error Jacobian matrix, represents the error parameter vector , superscript N indicates nominal value, R indicates actual value, and superscript T indicates transposition. represents the joint torsion angle, Indicates the connecting rod length, represents the joint rotation angle, represents the connecting rod offset, Indicates the rotation angle around the Y axis.

[0068] In a preferred embodiment, the robot is controlled to move the end tool, i.e., the standard ball, to the vicinity of the origin of the first measurement coordinate system of the motion distance measurement component, and the first measurement value of the laser displacement sensor is recorded at this time. 、The robot's six nominal first joint angles , where the superscript N represents the nominal value, m represents the number of robot measurements, and records the laser displacement sensor measurement value of the standard ball at the end of the robot in the first and second measurement coordinate systems as one measurement number, 1 represents the first measurement coordinate system, It represents the nominal joint angle of joint 1 measured for the mth time, and the remaining nominal joint angles are similarly measured.

[0069] In a preferred embodiment, the teaching pendant is controlled to move the standard ball at the end of the robot to the vicinity of the origin of the second measurement coordinate system of the motion distance measuring device, and the second measurement value of the laser displacement sensor at this time is recorded. 、The robot's six second nominal joint angles ; Wherein, the superscript N represents the nominal value, m is the number of robot measurements; the number of measurements is the number of laser displacement sensors measuring the standard ball at the end of the robot in the first and second measurement coordinate systems, 2 represents the second measurement coordinate system, It represents the nominal joint angle of joint 1 measured for the mth time, and the remaining nominal joint angles are similarly measured.

[0070] According to the first nominal joint angle, substitute the nominal homogeneous transformation matrix , calculate and obtain the nominal three-dimensional coordinate value of the end tool, i.e. the standard ball, in the base coordinate system , where m is the number of robot measurements; the value of the laser displacement sensor measuring the standard ball at the end of the robot in the first and second measurement coordinate systems is counted as one measurement.

[0071] According to the second nominal joint angle, substitute the nominal homogeneous transformation matrix , calculate and obtain the nominal three-dimensional coordinate value of the end tool, i.e. the standard ball, in the base coordinate system , where m is the number of robot measurements; the value of the laser displacement sensor measuring the standard ball at the end of the robot in the first and second measurement coordinate systems is counted as one measurement.

[0072] Furthermore, the nominal distance value of the end tool, i.e. the standard ball, in the base coordinate system can be calculated , where m is the number of robot measurements; the value of the laser displacement sensor measuring the standard ball at the end of the robot in the first and second measurement coordinate systems is counted as one measurement, and the superscript N represents the nominal value.

[0073] Furthermore, the sensor measurement value , Write to the motion distance measurement component lower computer to obtain the actual measured distance value , where m is the number of robot measurements; the value of the laser displacement sensor measuring the standard ball at the end of the robot in the first and second measurement coordinate systems is counted as one measurement, and the superscript R represents the nominal value.

[0074] By adjusting the attitude adjustment handle on the supporting tripod, the motion distance measurement component together with the measuring rod is adjusted to different postures; the measurement is repeated m times to obtain 2×6×m nominal joint angle values, 2×m nominal end standard ball three-dimensional coordinate values, m segments of nominal distance values, and m segments of actual measured distance values.

[0075] Going a step further, distance constraints are used to calculate the actual measured distance value Distance to nominal value The difference between them is used to establish the distance error model between two consecutive points. ;

[0076] in ;

[0077] Finally, an optimization algorithm is used to solve the kinematic error parameter value by combining the pseudo-inverse method with regularization. The actual kinematic error parameter value obtained is written into the robot controller to complete the robot distance error calibration.

[0078] 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 calibration method for an industrial robot, characterized in that The steps of this method are as follows: Step 1, control the end tool of the industrial robot to move to the vicinity of the origin of the first measurement coordinate system of the motion distance measuring device, and record the first measurement value of the laser displacement sensor and the first nominal joint angles of the six joints at this time; Based on the nominal homogeneous transformation matrix and the first nominal joint angle to obtain the first nominal three-dimensional coordinate value of the end tool in the base coordinate system ; Step 2, control the industrial robot to move the terminal standard ball to the vicinity of the origin of the second measurement coordinate system of the motion distance measurement device, and record the second measurement value of the laser displacement sensor and the second nominal joint angles of the six joints at this time; Based on the nominal homogeneous transformation matrix and the second nominal joint angle to obtain the second nominal three-dimensional coordinate value of the end tool in the base coordinate system. ; Step 3: Based on the first nominal 3D coordinate value and the second nominal 3D coordinate value Get the nominal distance value of the end tool in the base coordinate system ; Obtaining an actual measured distance value based on the first measurement value of the laser displacement sensor and the second measurement value of the laser displacement sensor ; Step 4: Each time the posture of the motion distance measuring device is adjusted once, steps 1 to 3 are repeated, and the posture of the motion distance measuring device is adjusted m times in total to obtain m measurement results; Step 5: Based on the actual measured distance value Distance to nominal value The difference between them is used to establish the distance error model between two consecutive points; Step 6: Use the optimization algorithm to perform parameter identification, obtain the actual kinematic error parameter value, and load the error parameter value into the industrial robot controller to complete the distance error calibration; The motion distance measuring device comprises a motion distance measuring component and a supporting tripod, which are connected by a measuring rod, and the motion distance measuring component comprises six laser displacement sensors and two mounting brackets; three laser displacement sensors are respectively mounted on each mounting bracket; the vertically mounted laser displacement sensor has its measuring line directed upward; the two horizontally placed laser displacement sensors have their measuring lines located in the same plane as the top of the mounting bracket and the angle between the two measuring lines is 90°; the measuring lines of the three laser displacement sensors are mutually perpendicular and intersect at one point; It also includes establishing a first measurement coordinate system and a second measurement coordinate system with the intersection of the laser beams of the three laser displacement sensors as the origin and the direction away from the laser displacement sensors as the axis direction.

2. The calibration method of an industrial robot according to claim 1, characterized in that: The nominal homogeneous transformation matrix Obtained in the following way: Establish the industrial robot base coordinate system, the first to sixth joint coordinate systems, and the end tool coordinate system; Based on the kinematic model of adjacent joints, the nominal homogeneous transformation matrix of adjacent joints is obtained And the error homogeneous transformation matrix of adjacent joints ; According to the nominal homogeneous transformation matrix of the base coordinate system and adjacent joints , obtain the nominal homogeneous transformation matrix of the robot end tool coordinate system relative to the base coordinate system .

3. The calibration method of an industrial robot according to claim 2, characterized in that: The distance error model between two consecutive points : ； in The function is related to the position error Jacobian matrix, represents the error parameter vector.

4. The calibration method of an industrial robot according to claim 3, characterized in that: The error parameter vector is transformed by the error homogeneous matrix get.

5. The calibration method of an industrial robot according to claim 2, characterized in that: Also included is an error homogeneous transformation matrix based on the adjacent joints And the nominal homogeneous transformation matrix of the robot end tool coordinate system relative to the base coordinate system , obtain the actual homogeneous transformation matrix of the robot end tool coordinate system relative to the base coordinate system ; Calculate the error homogeneous transformation matrix of the robot end tool coordinate system relative to the base coordinate system , and obtain the position error matrix.

6. The method for calibrating an industrial robot according to claim 5, characterized in that: The position error matrix : ； in Represents the first three rows of the fourth column of the error homogeneous transformation matrix, represents the position error Jacobian matrix, represents the error parameter vector.

7. A motion distance measuring device for an industrial robot, applied to the method according to any one of claims 1 to 6, comprising a motion distance measuring assembly and a supporting tripod, the two being connected by a measuring rod, characterized in that: The motion distance measurement assembly includes six laser displacement sensors and two mounting brackets; Three laser displacement sensors are installed on each mounting bracket; the measuring line of the vertically mounted laser displacement sensor is directed upward; the measuring lines of the two horizontally placed laser displacement sensors are located in the same plane as the top of the mounting bracket and the angle between the two measuring lines is 90°; the measuring lines of the three laser displacement sensors are perpendicular to each other and intersect at one point.

8. The motion distance measuring device of an industrial robot according to claim 7, characterized in that: It also includes establishing a first measurement coordinate system and a second measurement coordinate system with the intersection of the laser beams of the three laser displacement sensors as the origin and the direction away from the laser displacement sensors as the axis direction.

9. The motion distance measuring device of an industrial robot according to claim 8, characterized in that: The motion distance measuring device is calibrated using a three-coordinate measuring machine to improve its measurement accuracy.

10. The motion distance measuring device of an industrial robot according to claim 9, characterized in that: BP neural network is used to calibrate the distance error of the moving distance measurement component.

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