Bulletin of the JSME Journal of Advanced Mechanical Design, Systems, and Manufacturing Vol.11, No.6, 2017 Paper No.17-00213 © 2017 The Japan Society of Mechanical Engineers [DOI: 10.1299/jamdsm.2017jamdsm0077] 1. Introduction The demand on gear drives of automation machinery increases recently, so as to reduce the labor cost and to improve the productivity. Precise motion and high power transmission are the essential requirements for development of such the gear drives. Among various types of gear drives, the reducers combined with involute and cycloid planetary gears play an important role to fulfill this requirement. This type of gear drives, i.e., so-called RV-drives (Fig. 1), has not only the advantage in high gear ratio, but also the good performances to share the transmitted load and to absorb the shock because of multiple tooth-pairs in contact. The conventional involute planetary gear, by contrast, can not fulfill the extreme requirements. Besides the geometrical design of the tooth profiles for the backlash and the transmission accuracy, the load analysis is the most important issue for successful application of such the drives. Two essential tasks must be handled for the analysis. First, the statically indeterminate contact problem of multiple tooth pairs should be solved. Second, the influences of the stiffness of components, the friction, the flank modification and the assembly/manufacturing errors on acting loads should be considered in the analysis model. Some calculation approaches for load analysis of the mentioned cycloid planetary gear drives can be fund in some but a little research papers. For example, Dong et al. (1996) proposed a calculation approach for calculating the acting forces in the cycloidal gear drive, where the bearing stiffness is assumed as the same. Blanche and Yang (1989, 1990) analyzed the influence of the manufacturing errors on the transmitted load and transmission errors. Hidaka et al. (1994) proposed an analytical method to analyze the influence of manufacturing errors. The analytical approach is later compared with FEM analysis by Ishida et al. (1996). Gorla et al. (2008) develop a simplified approach to analyze the 1 A study on loaded tooth contact analysis of a cycloid planetary gear reducer considering friction and bearing roller stiffness Ching-Hao HUANG* and Shyi-Jeng TSAI* *Department of Mechanical Engineering, National Central University No. 300, Zhongda Rd., Zhongli District, Taoyuan City 32001, Taiwan E-mail: sjtsai@cc.ncu.edu.tw Received: 10 April 2017; Revised: 17 May 2017; Accepted: 31 May 2017 Abstract The cycloid planetary gear drives designed in the so-called RV-type play an important role in precision power transmission. Not only the high reduction ratio, but also the shock absorbability is the significant advantage. However, the load analysis of such the drive is complicated, because the contact problem of the multiple tooth pairs is statically indeterminate. The aim of the paper is thus to propose a computerized approach of loaded tooth contact analysis (LTCA) based on the influence coefficient method, either for the contact tooth pairs of the involute stage or of the cycloid stage. The contact points are determined based on the instant center of velocity in the model. On the other hand, the shared loads of multiple contact tooth pairs are calculated numerically with a set of equations according to the relations of deformation-displacement and load equilibrium. The coupled influences of the loads acting on the involute and the cycloid tooth pairs are also analyzed considering the friction on the contact tooth flanks as well as the stiffness of the supporting bearings for the cycloid discs. With an industrial example, the contact pattern with distributed contact stresses and the shared load of each contact tooth pair during operation are simulated with aid of the proposed approach. The transmitted torques on the crankshaft, the displacements of the main components and the efficiency of each stage calculated accordingly are also illustrated in the paper. Keywords: Loaded tooth contact analysis, Cycloid planetary gear reducer, Bearing roller stiffness, Friction, Load sharing, Contact stress