Contact characteristics of cycloid planetary gear drives considering backlashes and clearances

The cycloid planetary gear reducers in so-called Cyclo-type design are developed for a long time and already used in many applications. However, the analysis of performance under some extreme conditions becomes more important because the demand for accuracy increases. Among them, bearing clearance play a significant role for contact characteristics of the drives. It is not only because the transmission accuracy can be affected, but also because the load capacity of bearings would be reduced accordingly. Because of presence of bearing clearances, the cycloid disc is floating with three degree of freedom in the planar mechanism. This condition will cause more complicate in the load analysis for multiple contact pairs. The aim of the paper is thus to analyse contact characteristics of the relevant contact pairs in the Cyclo-type gear drives considering not only the influences of the crank bearing and the pin-hole clearances, but also profile modification of cycloid flank. A computerized loaded tooth contact analysis (LTCA) approach based on influence coefficient method is proposed in the paper for analysis of Cyclo-type drives having clearances. The effects of the clearances on contact characteristics are afterwards analysed by using an example from industry. The variation of shared load, contact stress on each individual cycloid tooth and on bearing roller, as well as the load of pin-hole are simulated with comparison of three different amounts of bearing clearance. The results show that the bearing clearances affect the loads acting on the pins of the-pin-shaft more strongly than the bearing, and have almost no significant influence on the contact with the pins of the pin wheel. The pin-hole clearance has less influences on the acting loads on the contact pairs, but affects significantly the peak-to-peak value of transmission errors.