Research On Decelerator Based On Two-stage Planetary Roller Screw

With the increasing demand of industrial robots, the research of a new robot joint decelerator with high efficiency, low cost, and simple structure is of great significance. A new joint decelerator used in industrial robot is studied in this paper. Since planetary roller screw has high thrust, high precision, high frequency response, long lifetime and other characteristics, the transmission state, contact stiffness, transmission efficiency and load sharing characteristic is discussed based on the structural parameters of PRS. The rationality of the design scheme is verified by the virtual prototype model.The working principle of PRS-decelerator and performance index is analyzed, then to establish the symmetric structure design. Establishing the parametric design model of PRS-decelerator according to the performance index analysis. The motion relationship between the chief components is analyzed by using inversion method of planetary gear system and combined with transmission characteristics. The ratio design formula of PRS-decelerator is deduced, and it is related with a series of structure parameter. The situation of whether considering sliding between roller and screw is discussed based on the planetary gear train reversal method. Then setting space Cartesian coordinate system to describe the position and velocity on contact point exists between screw/roller and nut/roller, respectively. Analyzing the continuous sliding mode according to the sliding speed, which is obtained by considering elastic deformation.Combined with traditional Hertz elastic contact theory and M-B model, then reconstruct the surface contact coefficient, building a screw pair rough surface contact mechanical model, and axial contact stiffness model is established by force analysis at the contact point, providing a numerical method for evaluating the stiffness of the PRS-decelerator. Analyzing the reasons of energy lose during working, then friction torque model is established based on elastic lag, roller spin sliding and lubrication viscous resistance. The transmission efficiency is improved by increasing the helix angle, the contact angle, roller thread number and the axial load appropriately.In addition, the finite element analysis of the screw pair contact situation is completed by ANSYS software, and the axial contact load distribution is obtained. Then the best tooth angle range and the optimal relationship of material elastic modulus between roller and screw is obtained to improve the load sharing characteristics.