Industrial robot tool coordinate calibration method based on laser tracker assisted four-point method

Abstract

The invention relates to the technical field of coordinate calibration, in particular to an industrial robot tool coordinate calibration method using a laser tracker to assist a four-point method, which comprises the following steps of: feeding back accurate coordinates of a reference point through the laser tracker, feeding back a tail end position in real time by using the laser tracker, and providing accurate coordinate reference for using the four-point method. And the tail end can enter the reference point position more accurately, so that more accurate tool coordinates are obtained, and the calibration precision is effectively improved. Through assistance of the laser tracker, accurate coordinates of a target point can be fed back in real time, the problem of low calibration precision caused by visual inspection in a traditional method is avoided, the problem of needle point collision in calibration of a traditional four-point method is avoided, the calibration process is optimized, and the method has important significance for improving production efficiency and product quality. Therefore, the problem that an existing coordinate calibration method is low in calibration precision is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of coordinate calibration, and particularly to an industrial robot tool coordinate calibration method assisted by a laser tracker using the four-point method. Background Art

[0002] Industrial robots are widely used in fields such as handling, welding, and spraying, and play an important role in modern manufacturing. Positioning accuracy is an important indicator for evaluating the performance of industrial robots and has a crucial impact on the quality of production and processing. In order to clarify the pose transformation relationship between the tool and the industrial robot and improve the positioning accuracy, tool coordinate calibration must be carried out, that is, in the working space of the robot, determine the position of the tool center point in the robot base coordinate system.

[0003] Currently, the commonly used tool coordinate calibration methods can be divided into two categories: multi-point calibration methods and external reference methods. The multi-point calibration method is a commonly used tool coordinate calibration method, including the four-point method, six-point method, etc., and is usually used to calibrate the position or pose of the tool rotation center. The four-point calibration method selects a fixed point in the robot working space as a reference point, manually manipulates the robot to make the end effector tool of the industrial robot contact the fixed tip tool in four different postures. Through the pose data of the four points, the robot can automatically calculate the position of the tool center point using the built-in program. This method is simple, convenient, and easy to implement. Another type of external reference method uses precision measuring instruments, such as laser trackers, to calculate the tool coordinates by feeding back the precise coordinates of the reference point and combining the known link lengths of the robot. This method relies on precision equipment and has a long calibration time, but has high accuracy. Summary of the Invention

[0004] The purpose of the present invention is to provide an industrial robot tool coordinate calibration method assisted by a laser tracker using the four-point method, aiming to solve the problem of low calibration accuracy of the existing coordinate calibration methods.

[0005] To achieve the above purpose, the present invention provides an industrial robot tool coordinate calibration method assisted by a laser tracker using the four-point method, including the following steps:

[0006] Fix the target ball and the laser tracker;

[0007] Use the laser tracker to accurately locate the reference point and obtain the precise coordinates of the reference point;

[0008] Operate the industrial robot to make the target ball at the tool end reach the reference point, and use the laser tracker to record the initial position coordinates of the target ball at the reference point;

[0009] Operate the industrial robot to reach the reference point in three different postures, record the position coordinates of the target ball in each posture, and the z-axis angle intervals of the three postures are between 45 - 90° and not in the same plane;

[0010] Operate the industrial robot to make the tool axis along the z-axis direction of the spatial coordinate system, and reach the reference point in this posture, and record the position coordinates of the target ball;

[0011] According to the position coordinates of the target ball recorded in different postures, establish a system of equations and solve to obtain the tool coordinates.

[0012] Among them, in "fixing the target ball and the laser tracker", the following steps are included:

[0013] Firmly install the target ball at the tool end of the industrial robot;

[0014] Install the laser tracker at a predetermined position where the target ball can be accurately measured.

[0015] Among them, in "using the laser tracker to accurately locate the reference point and obtain the accurate coordinates of the reference point", the following steps are included:

[0016] Start the laser tracker and perform calibration and parameter initialization settings;

[0017] Use the laser tracker to accurately measure the preset reference point and obtain the coordinates of the reference point in the spatial coordinate system.

[0018] Among them, in "operating the industrial robot to make the target ball at the tool end reach the reference point and using the laser tracker to record the initial position coordinates of the target ball at the reference point", the following steps are included:

[0019] Control the industrial robot to make the target ball at the tool end reach the reference point;

[0020] Use the laser tracker to record the initial position coordinates of the target ball at the reference point.

[0021] Among them, in "operating the industrial robot to reach the reference point in three different postures, recording the position coordinates of the target ball in each posture, and the z-axis angle intervals of the three postures are between 45 - 90° and not in the same plane", the following steps are included:

[0022] Plan three different robot postures to ensure that the target ball can reach the reference point in each posture, and the z-axis angle intervals of the three postures are between 45 - 90°, and at the same time not in the same plane;

[0023] According to the planned postures, operate the industrial robot in sequence to make the target ball reach the reference point;

[0024] Use the laser tracker to record the position coordinates of the target ball in each posture.

[0025] Among them, in the step of "operating the industrial robot to make the tool axis along the z-axis direction of the space coordinate system, reaching the reference point position in this posture, and recording the position coordinates of the target ball", the following steps are included:

[0026] Adjust the posture of the industrial robot to make the tool axis along the z-axis direction of the space coordinate system;

[0027] Use a laser tracker to record the position coordinates of the target ball.

[0028] Among them, in the step of "establishing an equation set according to the recorded position coordinates of the target ball in different postures and solving to obtain the tool coordinates", the following steps are included:

[0029] Establish a mathematical equation according to the recorded position coordinates of the target ball in different postures and the position coordinates when the tool axis is along the z-axis direction;

[0030] Use numerical and analytical methods to solve the equation set to obtain the accurate position and direction of the tool coordinate system relative to the robot base coordinate system.

[0031] The industrial robot tool coordinate calibration method using the laser tracker-assisted four-point method of the present invention includes the following steps: fixing the target ball and the laser tracker; using the laser tracker to accurately locate the reference point to obtain the accurate coordinates of the reference point; operating the industrial robot to make the target ball at the tool end reach the reference point, and using the laser tracker to record the initial position coordinates of the target ball at the reference point; operating the industrial robot to reach the reference point in three different postures, recording the position coordinates of the target ball in each posture, and the z-axis angle intervals of the three postures are between 45 - 90° and not in the same plane; operating the industrial robot to make the tool axis along the z-axis direction of the space coordinate system, reaching the reference point position in this posture, and recording the position coordinates of the target ball; establishing an equation set according to the recorded position coordinates of the target ball in different postures and solving to obtain the tool coordinates. After obtaining the accurate coordinates of the reference point through the feedback of the laser tracker, the present invention then uses the laser tracker to real-time feedback the end position, providing a precise coordinate reference for using the four-point method, enabling the end to enter the reference point position more accurately, thereby obtaining more accurate tool coordinates, effectively improving the calibration accuracy. With the assistance of the laser tracker, the accurate coordinates of the target point can be real-time feedback, avoiding the problem of low calibration accuracy caused by visual observation in the traditional method, and avoiding the problem of tip collision in the traditional four-point method calibration, thereby optimizing the calibration process, which has important significance for improving production efficiency and product quality. Thus, the problem of low calibration accuracy of the existing coordinate calibration method is solved. Brief Description of the Drawings

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0033] Figure 1 It is a flowchart of an industrial robot tool coordinate calibration method using the laser tracker assisted four-point method provided by the present invention.

[0034] Figure 2 It is a flowchart of fixing the target ball and the laser tracker.

[0035] Figure 3 It is a flowchart of precisely positioning the reference point using the laser tracker to obtain the precise coordinates of the reference point.

[0036] Figure 4 It is a flowchart of operating the industrial robot to make the target ball at the tool end reach the reference point and using the laser tracker to record the initial position coordinates of the target ball at the reference point.

[0037] Figure 5 It is a flowchart of operating the industrial robot to reach the reference point in three different postures, recording the position coordinates of the target ball in each posture, and the z-axis angle intervals of the three postures are between 45 - 90° and not in the same plane.

[0038] Figure 6 It is a flowchart of operating the industrial robot to make the tool axis along the z-axis direction of the space coordinate system, reaching the reference point position in this posture, and recording the position coordinates of the target ball.

[0039] Figure 7 It is a flowchart of establishing an equation system based on the recorded position coordinates of the target ball in different postures and solving to obtain the tool coordinates.

[0040] Figure 8 It is a schematic diagram of the industrial robot, tool, target ball, and laser tracker.

[0041] In the figure: 1 - industrial robot, 2 - tool, 3 - target ball, 4 - laser tracker. Specific Embodiments

[0042] The following will describe in detail the embodiments of the present invention. The examples of the embodiments are shown in the drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions from beginning to end. The embodiments described below with reference to the drawings are exemplary and are intended to explain the present invention, but should not be construed as a limitation of the present invention.

[0043] Please refer toFigures 1 to 8 , the present invention provides an industrial robot tool coordinate calibration method using a laser tracker assisted four-point method, including the following steps:

[0044] S1 Fix the target ball 3 and the laser tracker 4;

[0045] S11 Firmly mount the target ball 3 at the end of the tool 2 of the industrial robot 1;

[0046] Specifically, select a suitable target ball 3 with good reflective properties on its surface so that the laser tracker 4 can accurately capture its position. The size of the target ball 3 should be appropriate, which can not only meet the measurement accuracy requirements but also not interfere with the movement of the industrial robot 1. Then, fix the target ball 3 at the end of the tool 2 of the industrial robot 1. The fixing method can be screw connection, magnetic adsorption or fixture, etc., to ensure that the target ball 3 will not loosen or shift during the movement of the robot. When fixing, try to make the center of the target ball 3 coincide with the center point of the tool 2 to improve the calibration accuracy.

[0047] S12 Install the laser tracker 4 at a predetermined position where the target ball 3 can be accurately measured.

[0048] Specifically, select a stable platform bracket to avoid movement or vibration during the measurement process, and install the laser tracker 4 on the stable platform bracket. The installation position covers the entire working space of the industrial robot 1 and is at the same time protected from external environmental factors (such as strong light, vibration, etc.). Ensure that the measurement beam of the laser tracker 4 can directly irradiate the surface of the target ball 3 and the target ball 3 is within the effective measurement range of the laser tracker 4. Adjust the height and angle of the laser tracker 4 so that its relative position with the target ball 3 meets the measurement requirements.

[0049] S2 Use the laser tracker 4 to accurately locate the reference point and obtain the accurate coordinates of the reference point;

[0050] S21 Start the laser tracker 4 and perform calibration and parameter initialization settings;

[0051] Specifically, turn on the power of the laser tracker 4, start the device for calibration operations, such as zero calibration, temperature compensation calibration, etc., to ensure the measurement accuracy. Initialize the parameter configuration of the laser tracker 4, including the measurement unit, data output format, communication interface settings.

[0052] S22 Use the laser tracker 4 to accurately measure the preset reference point and obtain the coordinates of the reference point in the space coordinate system.

[0053] Specifically, within the working space of the industrial robot 1, a reference point is preset. This reference point should have obvious features to facilitate the identification and measurement by the laser tracker 4. Activate the measurement function of the laser tracker 4 to precisely measure the reference point. The laser tracker 4 will real-time feedback the three-dimensional coordinate data of the reference point in the space coordinate system, including the coordinate values in the x, y, and z directions. Record these coordinate values as the reference data for subsequent calibration.

[0054] S3 Operate the industrial robot 1 to make the target ball 3 at the end of the tool 2 reach the reference point, and use the laser tracker 4 to record the initial position coordinates of the target ball 3 at the reference point;

[0055] S31 Control the industrial robot 1 to make the target ball 3 at the end of the tool 2 reach the reference point;

[0056] Specifically, according to the preset reference point coordinates, write the control program of the industrial robot 1 to enable it to automatically move near the reference point. Fine-tune the posture of the industrial robot 1 to make the target ball 3 at the end of the tool 2 coincide with the reference point. During the operation, collisions or damages to the target ball 3 or the reference point should be avoided as much as possible.

[0057] S32 Use the laser tracker 4 to record the initial position coordinates of the target ball 3 at the reference point.

[0058] Specifically, when the target ball 3 reaches the reference point, activate the measurement function of the laser tracker 4 to record the initial position coordinates of the target ball 3 at the reference point. These coordinate data should be consistent or very close to the coordinate data of the reference point, indicating that the target ball 3 has accurately reached the reference point. Save the recorded initial position coordinates of the target ball 3 in the control system of the industrial robot 1 as the basic data for subsequent calibration calculations.

[0059] S4 Operate the industrial robot 1 to reach the reference point in three different postures, record the position coordinates of the target ball 3 in each posture, and the z-axis angle intervals of the three postures are between 45 - 90° and not in the same plane;

[0060] S41 Plan three different robot postures to ensure that the target ball 3 can reach the reference point in each posture, and the z-axis angle intervals of the three postures are between 45 - 90°, and at the same time not in the same plane;

[0061] Specifically, according to the motion range and flexibility of the industrial robot 1, plan three different postures. In each posture, the target ball 3 at the end of the tool 2 can reach the reference point. Ensure that the z-axis angle intervals of the three postures are between 45 - 90°, which can form a three-dimensional reference frame to improve the calibration accuracy. At the same time, the three postures should not be in the same plane to avoid the linear correlation of data and ensure the reliability and stability of the calibration results.

[0062] S42 According to the planned posture, operate the industrial robot 1 in sequence to make the target ball 3 reach the reference point;

[0063] Specifically, operate the industrial robot 1 in sequence according to the three planned postures. In each posture, control the robot to make the target ball 3 at the end of the tool 2 reach the reference point. During the operation, keep the movement of the robot stable and accurate to avoid the target ball 3 deviating from the reference point due to movement errors.

[0064] S43 Use the laser tracker 4 to record the position coordinates of the target ball 3 in each posture.

[0065] Specifically, after the target ball 3 reaches the reference point in each posture, start the measurement function of the laser tracker 4 to record the position coordinates of the target ball 3 in this posture. Repeat this process to record the position coordinate data of the target ball 3 in the three postures respectively. Save the recorded position coordinate data of the target ball 3 in the control system of the industrial robot 1 to provide the necessary data support for subsequent calibration calculations.

[0066] S5 Operate the industrial robot 1 to make the axis of the tool 2 along the z-axis direction of the space coordinate system, and reach the reference point position in this posture, and record the position coordinates of the target ball 3;

[0067] S51 Adjust the posture of the industrial robot 1 to make the axis of the tool 2 along the z-axis direction of the space coordinate system;

[0068] Specifically, control the industrial robot 1 to adjust its posture to make the axis of the tool 2 parallel to the z-axis direction of the space coordinate system. Ensure that the parallelism error between the axis of the tool 2 and the z-axis is within the allowable range to improve the calibration accuracy. During the adjustment process, damage to the robot or the target ball 3 should be avoided.

[0069] S52 Use the laser tracker 4 to record the position coordinates of the target ball 3.

[0070] Specifically, when the axis of the tool 2 reaches the reference point along the z-axis direction, start the measurement function of the laser tracker 4 to record the position coordinates of the target ball 3 in this posture. These coordinate data will be used for subsequent calibration calculations to determine the exact position and orientation of the tool 2 coordinate system in space.

[0071] S6 Establish a system of equations based on the recorded position coordinates of the target ball 3 in different postures and solve it to obtain the tool 2 coordinates.

[0072] S61 Establish a mathematical equation based on the recorded position coordinates of the target ball 3 in different postures and the position coordinates when the axis of the tool 2 is along the z-axis direction;

[0073] Specifically, according to the transformation relationships among the base coordinate system of the industrial robot 1, the end flange coordinate system, and the coordinate system of the tool 2, as well as the recorded position coordinate data of the target ball 3 in different postures, a mathematical equation system is established. The equation system includes the position and orientation parameters of the coordinate system of the tool 2 relative to the base coordinate system of the robot. When establishing the equation system, the condition that the position coordinates of the target ball 3 should be equal when it reaches the reference point in different postures, as well as the special position relationship when the axis of the tool 2 is along the z-axis direction, should be considered.

[0074] The transformation relationships among the base coordinate system of the industrial robot 1, the end flange coordinate system, and the coordinate system of the tool 2 can be expressed as:

[0075]

[0076] Among them is the posture transformation matrix from the base coordinate system to the end flange coordinate system in the i-th posture of the industrial robot 1, is the position transformation vector from the origin of the base coordinate system to the origin of the end flange coordinate system, R ET is the posture transformation matrix from the end flange coordinate system to the coordinate system of the tool 2, t ET is the position transformation vector from the origin of the end flange coordinate system to the origin of the coordinate system of the tool 2, is the posture transformation matrix from the base coordinate system to the coordinate system of the tool 2, is the position transformation vector from the origin of the base coordinate system to the origin of the coordinate system of the tool 2.

[0077] From Equation (1), we can obtain

[0078]

[0079] When the tool 2 is in different postures, then:

[0080]

[0081] Since it is required in the implementation of the method that the target ball 3 reaches the same position t BT , that is Then Equation (3) can be transformed into:

[0082]

[0083] Then t ET :

[0084]

[0085] S62 uses numerical and analytical methods to solve the equation system to obtain the accurate position and orientation of the coordinate system of the tool 2 relative to the base coordinate system of the robot

[0086] Specifically, by solving the system of equations, the precise position and orientation parameters of the coordinate system of Tool 2 relative to the robot base coordinate system are obtained, including the position transformation vector and the attitude transformation matrix. These parameters will be used for the coordinate calibration of Tool 2 of the industrial robot 1 to ensure that the robot can accurately position and operate Tool 2 when performing tasks.

[0087] The technical solution calibrates the tool coordinates of the industrial robot by the laser tracker-assisted four-point calibration method, which can significantly improve the accuracy and efficiency of tool coordinate calibration. This is of great significance for improving the operation accuracy and efficiency of the industrial robot. The present invention is aimed at the tool coordinate calibration of the industrial robot and can be widely applied in the fields of industrial manufacturing, automated production lines, etc. At the same time, it can be extended to the performance detection of industrial robots to assist in the research and development of industrial robots. The technical solution has beneficial effects on the precise calibration of tool coordinates and the performance testing of industrial robots, and has broad market demand and good application prospects.

[0088] The industrial robot tool coordinate calibration method using the laser tracker-assisted four-point method provided by the present invention has the following beneficial effects:

[0089] (1) The industrial robot tool coordinate calibration method using the laser tracker-assisted four-point method provided by the present invention improves the calibration accuracy: after obtaining the precise coordinates of the reference points through the feedback of the laser tracker, the laser tracker is used to real-time feedback the end position, providing accurate coordinate reference for using the four-point method, enabling the end to enter the reference points more accurately, thereby obtaining more precise tool coordinates and effectively improving the calibration accuracy.

[0090] (2) The industrial robot tool coordinate calibration method using the laser tracker-assisted four-point method provided by the present invention optimizes the calibration process: with the assistance of the laser tracker, the precise coordinates of the target points can be real-time feedback, avoiding the problem of low calibration accuracy caused by visual observation in the traditional method and the problem of tip collision in the traditional four-point method calibration, thus optimizing the calibration process, which is of great significance for improving production efficiency and product quality.

[0091] The above-disclosed is only the preferred embodiment of the industrial robot tool coordinate calibration method using the laser tracker-assisted four-point method of the present invention. Of course, the scope of the rights of the present invention cannot be limited thereby. Those of ordinary skill in the art can understand all or part of the processes of realizing the above embodiments, and the equivalent changes made according to the claims of the present invention still fall within the scope covered by the present invention.

Claims

1. An industrial robot tool coordinate calibration method using a laser tracker-assisted four-point method, characterized in that: It includes the following steps: Fix the target ball and the laser tracker; Use the laser tracker to accurately locate the reference point and obtain the accurate coordinates of the reference point; Operate the industrial robot to make the target ball at the end of the tool reach the reference point, and use the laser tracker to record the initial position coordinates of the target ball at the reference point; Operate the industrial robot to reach the reference point in three different postures, record the position coordinates of the target ball in each posture, and the z-axis angle intervals of the three postures are between 45-90° and not in the same plane; Operate the industrial robot to make the tool axis along the z-axis direction of the space coordinate system, reach the reference point position in this posture, and record the position coordinates of the target ball; According to the recorded position coordinates of the target ball in different postures, establish a system of equations and solve to obtain the tool coordinates.

2. The industrial robot tool coordinate calibration method using the laser tracker-assisted four-point method according to claim 1, characterized in that: In "Fix the target ball and the laser tracker", it includes the following steps: Firmly install the target ball at the end of the tool of the industrial robot; Install the laser tracker at a predetermined position where the target ball can be accurately measured.

3. The industrial robot tool coordinate calibration method using the laser tracker-assisted four-point method as described in claim 1, characterized in that: In "Use the laser tracker to accurately locate the reference point and obtain the accurate coordinates of the reference point", it includes the following steps: Start the laser tracker and perform calibration and parameter initialization settings; Use the laser tracker to accurately measure the preset reference point and obtain the coordinates of the reference point in the space coordinate system.

4. The industrial robot tool coordinate calibration method using the laser tracker-assisted four-point method according to claim 1, characterized in that: In "Operate the industrial robot to make the target ball at the end of the tool reach the reference point, and use the laser tracker to record the initial position coordinates of the target ball at the reference point", it includes the following steps: Control the industrial robot to make the target ball at the end of the tool reach the reference point; Use the laser tracker to record the initial position coordinates of the target ball at the reference point.

5. The industrial robot tool coordinate calibration method using the laser tracker assisted four-point method according to claim 1, characterized in that: In "Operate the industrial robot to reach the reference point in three different postures, record the position coordinates of the target ball in each posture, and the z-axis angle intervals of the three postures are between 45-90° and not in the same plane", it includes the following steps: Plan three different robot postures to ensure that the target ball can reach the reference point in each posture, and the z-axis angle intervals of the three postures are between 45-90°, and at the same time not in the same plane; According to the planned postures, operate the industrial robot in sequence to make the target ball reach the reference point; Use the laser tracker to record the position coordinates of the target ball in each posture.

6. The industrial robot tool coordinate calibration method using the laser tracker-assisted four-point method according to claim 1, characterized in that: In "Operate the industrial robot to make the tool axis along the z-axis direction of the space coordinate system, reach the reference point position in this posture, and record the position coordinates of the target ball", it includes the following steps: Adjust the posture of the industrial robot to make the tool axis along the z-axis direction of the space coordinate system; Use the laser tracker to record the position coordinates of the target ball.

7. The industrial robot tool coordinate calibration method by the laser tracker assisted four-point method according to claim 1, characterized in that: In "According to the recorded position coordinates of the target ball in different postures, establish a system of equations and solve to obtain the tool coordinates", it includes the following steps: According to the recorded position coordinates of the target ball in different postures and the position coordinates when the tool axis is along the z-axis direction, establish a mathematical equation; Use numerical and analytical methods to solve the system of equations to obtain the accurate position and orientation of the tool coordinate system relative to the robot base coordinate system.

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