High-precision absolute positioning calibration system and method for rotary joint robot

Abstract

The invention discloses a high-precision absolute positioning calibration system and method for a rotary joint robot, and relates to the technical field of robot positioning precision calibration, the high-precision absolute positioning calibration system comprises a model building module, an information acquisition module, a data analysis module and a pose calibration module, and the model building module builds a kinematics model of the robot through a DH modeling method; and a parameter identification algorithm is used for performing error compensation on the kinematic model, and the information acquisition module acquires position information of an end effector of the robot by using a position sensor and calculates all joint angle values of the robot under the actual pose according to the change of the light position. The method has the beneficial effects that the position information of the end effector of the robot is translated and obtained, all joint angle values of the robot under the actual pose are calculated and recorded in combination with the laser beams with the same emission path of the laser, the relation between all the shaft joints of the robot can be better represented, and the precision of the robot is improved. Zero deviation self-calibration and space pose self-calibration of the robot end effector are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of robot positioning accuracy calibration, in particular to a high-precision absolute positioning calibration system and method for a rotary joint robot. Background Art

[0002] With the development of science and technology, automated and intelligent production has become the mainstream. The position of robots in industrial production is unshakable, and the research on robot calibration technology is increasing. At present, the research on rotary joint robots generally goes through the following steps. First, the kinematic model is established, then the actual posture measurement of the end is carried out, then the error to be solved is determined and the parameters are identified, and finally the error compensation is performed to make the rotary joint robot reach the ideal posture, thus completing the robot calibration. When conducting robot research, it is necessary to describe the conversion relationship between the robot rods and joints. In the field of robot research, the DH (Denavit-Hartenberg) modeling method is often used. The DH modeling method is a common method for establishing robot kinematic models, and various robot modeling can be solved by it. However, the kinematic model established using the DH method is not perfect. In the case of two adjacent parallel joints of the robot, the subsequent parameter identification work cannot be carried out smoothly due to the singularity problem.

[0003] The end positioning accuracy of the rotary joint robot is divided into repeated positioning accuracy and absolute positioning accuracy. Due to the influence of mechanical processing, assembly and other aspects, the absolute positioning accuracy is low. In order to solve this problem, calibration technology is needed to improve the absolute positioning accuracy of the robot. Calibration technology is divided into open-loop calibration technology and closed-loop calibration technology according to whether it relies on external measuring instruments. The cost of open-loop calibration technology is relatively high. It relies on external measuring equipment to measure the actual position of the end of the robot, such as using a laser measuring instrument to measure the actual position of the end; closed-loop calibration technology is mainly divided into physical constraint calibration technology and visual calibration technology.

[0004] Therefore, in order to enable the robot to calmly face various complex and narrow environments, how to use calibration technology to improve the absolute positioning accuracy of the robot and compensate for errors caused by factors such as machining errors, assembly errors and parts wear is a technical problem that needs to be solved urgently. Summary of the invention

[0005] The purpose of this section is to provide a high-precision absolute positioning calibration system and method for a rotary joint robot, which can calibrate and improve the absolute positioning accuracy of the robot's end effector.

[0006] To solve the above technical problems, the present invention provides the following technical solutions: a high-precision absolute positioning calibration method for a rotary joint robot, comprising the following steps: S100, establishing a kinematic model of the robot through the DH modeling method, and using a parameter identification algorithm to perform error compensation for the kinematic model; S200, using a position sensor to obtain the position information of the robot's end effector, and calculating all joint angle values ​​under the actual posture of the robot according to changes in the light position; S300, analyzing the geometric relationship between the position of the robot's end effector and the corresponding joint angle value, and performing self-calibration of the zero-position deviation of the robot's end effector; S400, obtaining the rotation transformation matrix according to the quaternion method, calculating the translation vector between the coordinate systems, and performing self-calibration of the spatial posture of the robot's end effector.

[0007] As a preferred solution of the high-precision absolute positioning and calibration method of the rotary joint robot described in the present invention, wherein: in S100, a three-dimensional coordinate system is established at each joint of the robot, the joint axis and the common perpendicular line between two adjacent joints are respectively used as the two axes of the three-dimensional coordinate system, and the intersection of the two axes is used as the origin of the three-dimensional coordinate system. The error value of the kinematic model is solved by a parameter identification algorithm, and the optimal solution is calculated as a correction value to replace the corresponding parameters in the kinematic model.

[0008] As a preferred solution of the high-precision absolute positioning and calibration method of the rotary joint robot described in the present invention, in which: in S200, the specific steps are as follows: S201, a laser beam is emitted by a laser installed on the end effector of the robot, the laser beam is incident from the center of the position sensor, and is reflected at the center of another position sensor, and the position of the end effector of the robot is recorded as P1, and all joint angle values ​​are collected at the same time; S202, the end effector of the robot is translated based on the P1 position, recorded as the P2 position, and a laser beam with the same path is emitted by the laser, and all joint angle values ​​are collected at the same time; S203, using the same method as above, multiple positions are set, and all joint angle values ​​at the corresponding positions are collected and recorded.

[0009] As a preferred solution of the high-precision absolute positioning and calibration method of the rotary joint robot described in the present invention, wherein: in S300, the robot end effector is made to reach a specific posture, and the homogeneous transformation matrices of all joints are rewritten according to the zero-position deviations of all joints of the robot. The posture conversion matrix is ​​obtained by combining the zero-position deviations of each joint, and a group of equations is established according to the geometric relationship. The robot joint offsets are then obtained by optimizing the solution through the parameter identification algorithm. Finally, the parameters in the kinematic model are modified according to the offsets of each joint to obtain the correct robot forward kinematics model parameters.

[0010] As a preferred solution of the high-precision absolute positioning and calibration method of the rotary joint robot described in the present invention, wherein: in S400, the positive kinematic homogeneous transformation matrices corresponding to multiple positions of the robot are obtained again according to the zero-position deviation, and the unit direction vector of the laser beam relative to the coordinate system is obtained according to the positions of P1 and P2 in the workpiece space coordinate system, and then the unit direction vector of the reflected laser beam relative to the robot base coordinate system is calculated according to the spatial posture of P1 and P3 relative to the robot base coordinate system.

[0011] As a preferred solution of the high-precision absolute positioning and calibration system for the rotary joint robot described in the present invention, it includes: a model building module, an information collection module, a data analysis module and a posture calibration module.

[0012] As a preferred solution of the high-precision absolute positioning calibration system for the rotary joint robot described in the present invention, the model building module builds the kinematic model of the robot through the DH modeling method, and uses the parameter identification algorithm to perform error compensation of the kinematic model.

[0013] As a preferred solution of the high-precision absolute positioning and calibration system for the rotary joint robot described in the present invention, the information acquisition module uses a position sensor to obtain the position information of the robot's end effector, and calculates all joint angle values ​​in the actual posture of the robot based on the change in the light position.

[0014] As a preferred solution of the high-precision absolute positioning and calibration system for the rotary joint robot described in the present invention, the data analysis module is used to analyze the geometric relationship between the position of the robot's end effector and the corresponding joint angle value, and to perform self-calibration of the zero-position deviation of the robot's end effector.

[0015] As a preferred solution of the high-precision absolute positioning and calibration system for the rotary joint robot described in the present invention, the posture calibration module obtains the rotation transformation matrix according to the quaternion method, calculates the translation vector between the coordinate systems, and performs spatial posture self-calibration of the robot's end effector.

[0016] Beneficial effects of the present invention:

[0017] 1. By translating and acquiring the position information of the robot's end effector, combined with the laser beam with the same laser emission path, all joint angle values ​​under the actual posture of the robot are calculated and recorded, which can better represent the relationship between the various axis joints of the robot and realize the zero-position deviation self-calibration and spatial posture self-calibration of the robot's end effector.

[0018] 2. By adopting a dual PSD-based calibration device, a kinematic model of the robot is established and a calibration algorithm is derived. Then the mechanical part is designed, including the flange and PSD fixture connected to the end of the robot. For the circuit part, a circuit board needs to be designed that can realize functions such as analog calculations, signal processing, and communication with industrial computers. Finally, programming is performed according to the calibration process, which can effectively compensate for the end position error caused by various factors. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. The drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creativity and labor. Among them:

[0020] Figure 1 It is a schematic flow chart of the high-precision absolute positioning calibration method of the rotary joint robot of the present invention. DETAILED DESCRIPTION

[0021] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below with reference to the accompanying drawings.

[0022] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from this description. The "embodiment" referred to here refers to a specific feature, structure or characteristic that may be included in at least one implementation of the present invention.

[0023] Embodiment 1

[0024] Reference Figure 1 This embodiment provides a high-precision absolute positioning and calibration system for a rotary joint robot, which specifically includes the following steps: S100, establishing a kinematic model of the robot through the DH modeling method, and using a parameter identification algorithm to compensate for the error of the kinematic model; S200, using a position sensor to obtain the position information of the robot's end effector, and calculating all joint angle values ​​under the actual posture of the robot according to the change in the light position; S300, analyzing the geometric relationship between the position of the robot's end effector and the corresponding joint angle value, and performing self-calibration of the zero-position deviation of the robot's end effector; S400, obtaining the rotation transformation matrix according to the quaternion method, calculating the translation vector between the coordinate systems, and performing self-calibration of the spatial posture of the robot's end effector.

[0025] In this application, the least squares method is used as the parameter identification algorithm. Parameter identification is a key step in robot calibration. Before performing parameter identification, it is necessary to first determine the parameters that should be identified, which generally refers to the error values ​​to be solved in the error model. A set of equations is established based on geometric relationships, and the error values ​​are optimized with the help of parameter identification algorithms. The kinematic model parameters are changed based on these optimal solutions. The use of parameter identification algorithms greatly improves the accuracy and efficiency of robot calibration.

[0026] The quaternion method is a mathematical method used to describe rotation and posture in three-dimensional space. It uses the multiplication and operation rules of quaternions to concisely and efficiently handle the rotation problem of rigid bodies. It is widely used in vector operations in three-dimensional space.

[0027] In S100, a three-dimensional coordinate system is established at each joint of the robot. The joint axis and the common perpendicular line between two adjacent joints are used as the two axes of the three-dimensional coordinate system, and the intersection of the two axes is used as the origin of the three-dimensional coordinate system. The error value of the kinematic model is solved through the parameter identification algorithm, and the optimal solution is calculated as the correction value to replace the corresponding parameters in the kinematic model.

[0028] Use the right-hand rule to determine the joint axis as the Z axis of the three-dimensional coordinate system. When two adjacent joint axes are parallel, the common perpendicular line intersecting the Z axis is defined as the X axis. When two adjacent axes are not parallel, the perpendicular line of the plane formed by the two axes is defined as the X axis. According to the positional relationship between the three axes of the coordinate system, the intersection of the X and Z axes is set as the origin, and the Y axis can be obtained.

[0029] In S200, the specific steps are as follows: S201, a laser beam is emitted by a laser installed on the end effector of the robot. The laser beam is incident from the center of a position sensor and reflected at the center of another position sensor. The position of the end effector of the robot is recorded as P1, and all joint angle values ​​are collected at the same time; S202, the end effector of the robot is translated based on the P1 position, recorded as the P2 position, and a laser beam with the same path is emitted by a laser, and all joint angle values ​​are collected at the same time; S203, multiple positions are set using the same method as above, and all joint angle values ​​at the corresponding positions are collected and recorded.

[0030] In S300, the robot end effector is made to reach a specific posture. According to the zero-position deviation of all joints of the robot, the homogeneous transformation matrix of all joints is rewritten. The posture conversion matrix is ​​obtained by combining the zero-position deviation of each joint. A set of equations is established according to the geometric relationship. The robot joint offset is then obtained by optimizing the solution through the parameter identification algorithm. Finally, the parameters in the kinematic model are modified according to the offset of each joint to obtain the correct parameters of the robot forward kinematic model.

[0031] The zero deviation is added to the joint homogeneous transformation matrix to obtain the posture transformation matrix of the robot's end coordinate system in the robot's base coordinate system. The equations are written according to the geometric relationship, and then the LM algorithm (i.e., Levenberg-Marquardt algorithm, an iterative optimization algorithm for nonlinear least squares problems) is used to optimize the solution to obtain the robot's joint offsets. Finally, the parameters in the kinematic model are modified according to the offsets of each joint to obtain the correct robot forward kinematics model parameters and control the robot to reach the true posture.

[0032] In S400, the forward kinematic homogeneous transformation matrices corresponding to multiple positions of the robot are obtained based on the zero-position deviation, and the unit direction vector of the laser beam relative to the coordinate system is obtained based on the positions of P1 and P2 in the workpiece space coordinate system. Then, based on the spatial postures of P1 and P3 relative to the robot base coordinate system, the unit direction vector of the reflected laser beam relative to the robot base coordinate system is calculated.

[0033] Embodiment 2

[0034] This embodiment provides a high-precision absolute positioning and calibration system for a rotary joint robot, which specifically includes a model building module, an information collection module, a data analysis module and a posture calibration module.

[0035] The model building module establishes the robot's kinematic model through the DH modeling method and uses the parameter identification algorithm to compensate for the error of the kinematic model.

[0036] The information acquisition module uses the position sensor to obtain the position information of the robot's end effector, and calculates all joint angle values ​​in the actual position of the robot according to the changes in the light position.

[0037] The data analysis module is used to analyze the geometric relationship between the position of the robot end effector and the corresponding joint angle value, and to perform self-calibration of the zero position deviation of the robot end effector.

[0038] The posture calibration module obtains the rotation transformation matrix based on the quaternion method, calculates the translation vector between coordinate systems, and performs spatial posture self-calibration of the robot's end effector.

[0039] In this application, the positioning accuracy of the robot is calibrated, which requires the use of an industrial robot, a flange, a semiconductor laser, a PSD position sensor, a PSD fixture, a signal calculation and processing circuit board, an industrial computer and a robot controller.

[0040] The laser is fixed on the end effector of the industrial robot through a flange. The PSD fixture is used to install two PSD position sensors. The laser moves with the end of the manipulator and is fixed on the end effector of the robot through a flange. The laser beam is incident from one PSD and reflected on another PSD. The precise position of the laser spot is obtained through the operation circuit and the information processing circuit and handed over to the industrial control computer. Among them, the signal processing circuit and the industrial control computer.

[0041] The industrial control computer calculates the corresponding control quantity and gives it to the robot controller, which directly drives the robot end effector to move, and obtains precise laser spots and reflected spots at the surface center points of the two PSD position sensors to form virtual line constraints.

[0042] Importantly, although only a few embodiments are described in detail in this disclosure, it should be readily understood by those who refer to this disclosure that many modifications are possible without substantially departing from the subject matter described in this application, such as the size, structure, shape and proportion of the various elements, as well as temperature, pressure, mounting arrangements, use of materials, color, directional changes, etc.; for example, an element shown as integrally formed may be composed of multiple parts or elements, and the position of the element may be inverted or otherwise changed; therefore, all such modifications should be included within the scope of the present invention, and other substitutions, modifications, changes and omissions may be made in the design, operating conditions and arrangement of the exemplary embodiments without departing from the scope of the present invention.

Claims

1. A high-precision absolute positioning calibration method for a rotary joint robot, characterized in that: The following steps are involved: S100, establishing a kinematic model of the robot by using a DH modeling method, and using a parameter identification algorithm to perform error compensation on the kinematic model; S200, using a position sensor to obtain position information of the robot end effector, and calculating all joint angle values ​​of the robot in actual position according to the change of light position; S300, analyzing the geometric relationship between the position of the robot end effector and the corresponding joint angle value, and performing self-calibration of the zero position deviation of the robot end effector; S400, obtaining the rotation transformation matrix according to the quaternion method, calculating the translation vector between the coordinate systems, and performing the spatial posture self-calibration of the robot end effector.

2. The high-precision absolute positioning calibration method for a rotary joint robot according to claim 1, characterized in that: In S100, a three-dimensional coordinate system is established at each joint of the robot. The joint axis and the common perpendicular line between two adjacent joints are used as the two axes of the three-dimensional coordinate system, and the intersection of the two axes is used as the origin of the three-dimensional coordinate system. The error value of the kinematic model is solved through the parameter identification algorithm, and the optimal solution is calculated as the correction value to replace the corresponding parameters in the kinematic model.

3. The high-precision absolute positioning calibration method for a rotary joint robot according to claim 1, characterized in that: In S200, the specific steps are as follows: S201, a laser beam is emitted by a laser installed on the end effector of the robot. The laser beam is incident from the center of a position sensor and reflected from the center of another position sensor. The position of the end effector of the robot is recorded as P1, and all joint angle values ​​are collected at the same time; S202, based on the P1 position, the robot end effector is translated to the P2 position, and a laser beam with the same path is emitted by the laser, and all joint angle values ​​are collected at the same time; S203, using the same method as above, set multiple positions, and collect and record all joint angle values ​​at the corresponding positions.

4. The high-precision absolute positioning calibration method for a rotary joint robot according to claim 3, characterized in that: In S300, the robot end effector is made to reach a specific posture. According to the zero-position deviation of all joints of the robot, the homogeneous transformation matrix of all joints is rewritten. The posture conversion matrix is ​​obtained by combining the zero-position deviation of each joint. A set of equations is established according to the geometric relationship. The robot joint offset is then obtained by optimizing the solution through the parameter identification algorithm. Finally, the parameters in the kinematic model are modified according to the offset of each joint to obtain the correct parameters of the robot forward kinematic model.

5. The high-precision absolute positioning calibration method for a rotary joint robot according to claim 4, characterized in that: In S400, the forward kinematic homogeneous transformation matrices corresponding to multiple positions of the robot are obtained based on the zero-position deviation, and the unit direction vector of the laser beam relative to the coordinate system is obtained based on the positions of P1 and P2 in the workpiece space coordinate system. Then, based on the spatial postures of P1 and P3 relative to the robot base coordinate system, the unit direction vector of the reflected laser beam relative to the robot base coordinate system is calculated.

6. High-precision absolute positioning calibration system for rotary joint robots, characterized in that: It includes a model building module, an information collection module, a data analysis module and a posture calibration module.

7. The high-precision absolute positioning calibration system for a rotary joint robot according to claim 6, characterized in that: The model building module builds the robot's kinematic model through the DH modeling method, and uses a parameter identification algorithm to perform error compensation for the kinematic model.

8. The high-precision absolute positioning calibration system for a rotary joint robot according to claim 6, characterized in that: The information acquisition module uses a position sensor to obtain the position information of the robot's end effector, and calculates all joint angle values ​​of the robot in its actual position according to the change in the light position.

9. The high-precision absolute positioning and calibration system for a rotary joint robot according to claim 6, characterized in that: The data analysis module is used to analyze the geometric relationship between the position of the robot end effector and the corresponding joint angle value, and to perform self-calibration of the zero position deviation of the robot end effector.

10. The high-precision absolute positioning calibration system for a rotary joint robot according to claim 6, characterized in that: The posture calibration module obtains the rotation transformation matrix according to the quaternion method, calculates the translation vector between the coordinate systems, and performs the spatial posture self-calibration of the robot end effector.

Images