Transmission Error of Modular Robotic Joint

摘要

This paper deals with the accuracy problem of a type of joint module with two rotary degrees of freedom used in a modular robot system. The error investigation concentrates on its differential gear mechanism. By dividing the gearing error into the gear transmission error due to effective eccentricity and the lost motion error due to effective backlash, errors in two output angles (i. e., joint angles) are modeled based on the engaging principle of two bevel gears. Effective eccentricity due to the tolerances in the bearing system is then determined using the geometry between the bearing and the bevel gear. By taking into account the random nature of tolerances, stochastic characteristics of the output angles' errors are calculated under the assumption that eccentricity is distributed uniformly within a circle of tolerance. On the basis of the above stochastic error formulas, an optimal method and a simplified method are proposed for allocating the tolerances. In this paper, the concrete structure of the modular joint is examined to illustrate error estimation and tolerance allocation. Finally some conclusions are drawn for improving the accuracy of this type of modular joint.