Abstract
The Dynamic Errors (DEs) of individual axes present Time-dependent Characteristics (TDCs) because the setpoints, as the input of the servo feed system, change in velocity, acceleration and jerk during the feed motion. Deep insight into the TDC contributes to the effective control of DEs. However, up to now, mechanism analysis about the TDCs of DEs are indistinct and inadequate due to a lack of analysis on the TDC of setpoint frequency. So, in this study, the mechanism of the TDC of DE is investigated by extracting the TDC of setpoint frequency. Firstly, the servo dynamics model is established for presenting the DE and its respective components, the Dynamic Error Inside Servo-loop (DEIS) (tracking error) and the Dynamic Error Outside Servo-loop (DEOS) under to and fro motions. Secondly, time–frequency analysis is carried out on the setpoints of the to and fro motions to present a TDC of setpoint frequency which is described as the Time-dependent Setpoint Bandwidth (TDSB) and the Time-dependent Potential Excitation (TDPE). Finally, the correlation between the TDSBs and DEISs and the correlation between the TDPEs and DEOSs are investigated, respectively. On these bases, the mechanism of the TDC of DE is analyzed. The results show that the TDSB, which is related to the acceleration of setpoints, accounts for the TDC of the DEIS; that the TDPE, which is related to the jerk of setpoints, accounts for the TDC of the DEOS in vibration-form; and that the TDC of transient-form DEOS is determined by the change in acceleration of the setpoints.
Highlights
The basic function of multi-axis CNC machine tools is to drive the tool and workpiece in order to accurately realize the desired tool trajectory. This basic function needs to be executed by both the CNC system and the servo feed systems
To guarantee the accuracy of the actual trajectory, both the deviation from the setpoints trajectory to the tool trajectory and the deviation of the actual trajectory from the setpoints trajectory should be guaranteed by the interpolation of the CNC system and the control of servo feed systems
When it comes to the interpolation of the CNC system, deviation is limited by setting geometric constraints such as chord error
Summary
The basic function of multi-axis CNC machine tools is to drive the tool and workpiece in order to accurately realize the desired tool trajectory. To guarantee the accuracy of the actual trajectory, both the deviation from the setpoints trajectory to the tool trajectory and the deviation of the actual trajectory from the setpoints trajectory should be guaranteed by the interpolation of the CNC system and the control of servo feed systems. The DEOS is the deviation the effector end position from the motor rotor encoder detection positio6no.f 2T0he con block diagram presents a basic control framework which only concludes popular cont lers in practice to improve servo performance and control the DEs. Under the controll the tyifnoprpmircsaacatlnicdfeoctrhomairmascptaernorivsdeticcseohrfvaDorEapscectrafeonrribmsetaiinlclcueostafrnaDdteEdco.sntcraonl thbeeDiEllsu. Based on the verified dynamic model, the DEIS and DEOS could be analyzed, and the results are described
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