Theoretical analysis and performance prediction of a NN-type precision cycloidal reducer

The NN-type precision cycloidal reducer is widely applied in industrial robots, machine tools, and automatic machinery where precision positioning is required, due to its high transmission ratio in a compact size leading to higher power density. However, the performance prediction and design criterion of this two-stage cycloidal drive is limited and less extensive. To this end, the method of theoretical analysis and performance prediction of the NN-type precision cycloidal reducer is proposed with consideration of friction and clearance in the cycloidal-pin gear pairs. Firstly, the mechanism and operating principle of the NN-type precision cycloidal reducer are introduced, and the calculation method of its transmission ratio is given. Then, the unloaded tooth contact and load distribution analysis models are established to predict the load distributed on pins, torsional meshing stiffness, maximum contact stress, transmission efficiency, and loaded transmission error. With this, the transmission performances of two cases with the same transmission ratio are compared under different tooth number combinations of two-stage gear pairs. The influences of tooth clearances and applied torque are also discussed through case studies. This study gives a theoretical foundation for assessing the transmission performance and can be used to assist the optimal design of NN-type precision cycloidal reducers.