A Power Flow Analysis and Control Methodology for Cycloid Gear Train in Precision Transmission

Abstract

Cycloid gear is a special type of gear used in precision transmission system. For example, the mechanical watch movement requires not involute gear train but cycloid gear train owing to the very small size and large transmission ratio, in which the gear modules vary from 0.12mm to 0.0625mm and the maximum transmission ratio is 12. As we all know, the mechanical watch is a precise machine and the power transfer in the watch main train should be kept stable for the timekeeping performance. A three dimensional (3D) model of gear main train system, which includes all the gears, pinions and escapement, is developed. The multi-body dynamic simulation technique is utilized to analyze the influence of torque transmission fluctuation in the cycloid gear train on the vibration cycle of escapement in detail. In practical meshing condition, the misalignment errors are inevitable, the influence of which is obvious due to the gear module in main train is very small. All possible misalignment errors in cycloid gear train are analyzed in the analysis model. Algorithm for computing torque transmission (power flow) is presented, which is directly based on multi-body simulation result and is different from other approximation methods. Thus with the influence of misalignment errors, the variance of torque transmission is calculated. For reducing the cycloid gear train’s sensitivity to misalignment errors and achieving the precision transmission, the combined wheel tooth modification approach is put forward, i.e. wheel tooth modification in profile direction and in longitudinal direction. It could be seen clearly that with the combined wheel tooth modification, the fluctuation of torque transmission in the cycloid gear train is decreased and the transmission efficiency is improved.