The influence of dynamic error outside servo-loop on the trajectory error

Abstract

The moon-shaped trajectory is designed as to study the influence of dynamic error outside servo loop (DEOS) on the trajectory error of CNC machine tool. Firstly, the system identification method is used to build up the transfer function from the setpoint position (SP) to the linear encoder feedback position (LEFP), as well as the transfer function from the SP to the effector end position (EEP). Inputting the setpoints of the moon-shaped trajectory into these transfer functions, the LEFP and EEP can be predicted. Secondly, the setpoint trajectory, trajectory at LEFP, and trajectory at EEP are generated by D-H method. In addition, the trajectory errors are solved. Finally, the influence of DEOS on the trajectory error at EEP is investigated. The results show that there is a clear difference between the trajectory error at LEFP and the trajectory error at EEP, which causes the moon-shaped trajectory to be overcut and undercut. At a feed rate of 10000 mm/min, the difference between the two errors can reach a maximum of 0.03 mm. The main reason for the inconsistency is that the DEOS causes the trajectory at LEFP and the trajectory at EEP to not coincide.