Content area
Contour error is the deviation between the actual displacement and reference trajectory, which is directly related to the machining accuracy. Contour error compensation poses substantial challenges because of the time-varying, nonlinear, and strongly coupled characteristics of parallel machining modules. In addition, the time delay in the system reduces the timeliness of the feedback data, thereby making online contour error calculations and compensation particularly difficult. To solve this problem, the generation mechanism of the time delay of the feedback data and contour error is revealed, and a systematic method for the identification of the time-delay parameter based on Beckhoff's tracking error calculation mechanism is proposed. The temporal alignment between the position commands and feedback data enables the online calculation of the contour error. On this basis, the tracking error of the drive axes (an important factor resulting in end-effector contour errors) is used for the contour error calculation. Considering the ambiguous parameter-setting logic of the servo drive, the servo parameter is calculated in reverse using the steady-state error to obtain the tracking error model of the drive axes. Furthermore, combined with the system time-delay model, an online correction method for the tracking error estimation model is established. To achieve an accurate mapping of the drive-axis tracking error and end-effector contour error, a bounded iterative search method for the nearest contour point and online calculation model for the contour error are respectively established. Finally, an online compensation controller for contour error is designed. Its effectiveness is verified by a machining experiment on a frame workpiece. The machining results show that the contour error reduces from 68 μm to 45 μm, and the finish machining accuracy increases by 34%. This study provides a feasible method for online compensation of contour error in a system with time delay.
Details
Axes (reference lines);
Accuracy;
Contours;
Time lag;
Workpieces;
Control algorithms;
End effectors;
Feedback;
Error correction;
Machining;
Controllers;
Machine tools;
Servoamplifiers;
Design;
Error analysis;
Methods;
Error reduction;
Modules;
Machining centres;
Tracking errors;
Error compensation;
Efficiency
; Xie, Zenghui 2 ; Liu, Xinjun 2 1 Tsinghua University, State Key Laboratory of Tribology in Advanced Equipment, Beijing, China (GRID:grid.12527.33) (ISNI:0000 0001 0662 3178)
2 Tsinghua University, State Key Laboratory of Tribology in Advanced Equipment, Beijing, China (GRID:grid.12527.33) (ISNI:0000 0001 0662 3178); Tsinghua University, Beijing Key Laboratory of Transformative High-end Manufacturing Equipment and Technology, Department of Mechanical Engineering (DME), Beijing, China (GRID:grid.12527.33) (ISNI:0000 0001 0662 3178)