Dynamic error modeling, analysis and compensation of planar flexible multilink mechanism for high-speed precision presses considering the thermal expansion effect of sliding and angular contact ball bearings

In order to study the dynamic position accuracy of bottom dead point (BDP) for multilink high-speed precision presses (MHSPPs), it's essential to develop a dynamic model of planar multilink mechanism. Traditional dynamic error models (DEMs) always neglect the thermal effect of angular contact ball bearing (ACBB), which reduces the prediction accuracy of DEM for multilink transmission mechanisms. To overcome the shortcomings of the previous models, a new contact model of revolute clearance joint considering thermal expansion effect is proposed in this paper. Then, a thermal network model (TNM) of ACBB lubricated by grease is built and the stiffness of ACBB considering the thermal expansion effect is derived. On this basis, an improved DEM of planar flexible multilink mechanism with clearance considering the thermal expansion effect of ACBB is developed. And the influence of crankshaft speed, contact angle of ACBB and clearance size on the position error of slider's BDP based on the improved DEM is analyzed. Compared to the simulation from traditional models, the simulated slider's BDP position error from the improved DEM agrees better with experimental data, which verifies the correctness of the proposed model. It's demonstrated that the punching force and thermally induced variable stiffness of bearing lead to a significant increase in the slider's BDP position error, which reduces the machining precision of MHSPP. Moreover, a novel compensation algorithm based on the improved DEM with online modification is proposed. Test results show that the root mean square (RMS) and maximum absolute values of the slider's BDP position error after compensation under no load condition are reduced by 98.06% and 96.20%, respectively, and can be reduced by 98.11% and 96.36%, respectively.

Automated summary

This paper proposes a novel contact model and a thermal network model considering the thermal expansion effect, as well as an improved dynamic error model for multilink mechanisms. The correctness of the proposed model is verified by analyzing the influence of parameters on the position error of the bottom dead point. The study demonstrates that the punching force and thermally induced variable stiffness significantly increase the position error of the bottom dead point, reducing the machining precision. Additionally, a compensation algorithm based on the improved dynamic error model with online modification is proposed, effectively reducing the position error of the bottom dead point.