Why can't robots perform tasks accurately according to their repetitive positioning accuracy? In robot motion control systems, the deviation of various coordinate systems is a key factor affecting the robot's motion accuracy and repeatability. The following is a detailed analysis of various coordinate system deviations:
1、 Base coordinates
The base coordinate is the benchmark for all coordinate systems and the starting point for establishing the kinematic model of the robot. When building a kinematic model on software, if the setting of the base coordinate system is not accurate, it will lead to the accumulation of errors in the entire system. This type of error may not be easily detected during subsequent debugging and use, as the software may have already undergone corresponding compensation processing internally. However, this does not mean that the setting of the base coordinates can be ignored, as any small deviation can have a significant impact on the motion accuracy of the robot.
2、 DH coordinates
The DH coordinate (Denavit Hartenberg coordinate) is the reference for each axis rotation, used to describe the relative position and posture between the joints of the robot. When building a robot kinematic model on software, if the direction of the DH coordinate system is set incorrectly or the linkage parameters (such as length, offset, torsion angle, etc.) are incorrect, it will cause errors in the calculation of the homogeneous transformation matrix. This type of error will directly affect the robot's motion trajectory and posture. Although it may not be easily detected during debugging and use due to internal compensation mechanisms in the software, in the long run, it will have adverse effects on the robot's motion accuracy and stability.
3、 Joint coordinates
Joint coordinates are the benchmark for joint motion, closely related to parameters such as reduction ratio and origin position of each axis. If there is an error between the joint coordinate system and the actual value, it will lead to inaccurate joint motion. This inaccuracy may manifest as phenomena such as lagging, leading, or shaking in joint motion, seriously affecting the motion accuracy and stability of the robot. To avoid this situation, high-precision laser calibration instruments are usually used to accurately calibrate the joint coordinate system before the robot leaves the factory, ensuring the accuracy of joint motion.
4、 World coordinates
The world coordinates are the benchmark for linear motion and are related to factors such as reduction ratio, origin position, and linkage parameters. If there is an error between the world coordinate system and the actual value, it will lead to inaccurate linear motion of the robot, thereby affecting the posture maintenance of the end effector. This inaccuracy may manifest as phenomena such as end effector deflection, tilt, or offset, seriously affecting the robot's operational effectiveness and safety. Therefore, before the robot leaves the factory, it is also necessary to use laser calibration instruments to accurately calibrate the world coordinate system to ensure the accuracy of linear motion.
5、 Workbench coordinates
Workbench coordinates are similar to world coordinates and are also used to describe the relative position and posture of robots on the workbench. If there is an error between the coordinate system of the workbench and the actual value, it will cause the robot to be unable to move accurately in a straight line along the set workbench. This inaccuracy may manifest as the robot shifting, swaying, or unable to reach the designated position on the workbench, seriously affecting the robot's operational efficiency and accuracy. Therefore, when integrating robots with workbenches, precise calibration of the workbench coordinate system is required.
6、 Tool coordinates
Tool coordinates are the benchmarks that describe the position and orientation of the tool end relative to the robot's base coordinate system. If there is an error between the tool coordinate system and the actual value, it will result in the inability to perform accurate trajectory motion based on the calibrated end point during the attitude transformation process. This inaccuracy may manifest as tool tilting, tilting, or inability to accurately reach the designated position during the operation process, seriously affecting the accuracy and efficiency of the robot's work. In situations where high-precision tool coordinates are required, the 23 point method can be used to calibrate the tool and origin to improve overall motion accuracy. This method ensures the accuracy of the tool coordinate system by conducting multiple measurements and calibrations at different positions and orientations, thereby improving the robot's operational accuracy and repeatability.
The deviation of various coordinate systems has a significant impact on the motion accuracy and repetitive positioning ability of robots. Therefore, in the design, manufacturing, and debugging process of robot systems, it is necessary to attach great importance to the calibration and accuracy control of various coordinate systems to ensure that robots can accurately and stably complete various tasks.
Post time: Dec-03-2024
