Dynamic analysis of a three-axis robot wrist and optimization of its structure

A Multi-axis wrist as an end effecter of an industrial robot provides high flexibility to perform various tasks such as welding, cutting, painting and others. Recently, a new three-axis wrist has been developed for gantry-type robots whose payload is 250N. In designing such a wrist, structure analysis including statics and dynamics should be carried out to guarantee the performance of the wrist motion, also structure optimization is needed for reducing its weight. For the purpose, this paper presents a method of both the structure analysis and the optimization for the three-axis wrist. Firstly, dynamic analysis is carried out to find the wrist position yielding the maximum external torque. Also, static analysis is carried out to find the stress distribution and deformation under the maximum external torque. Secondly, optimization using a genetic algorithm is carried out to reduce the wrist weight. Specifically, the thicknesses of three pads constituting the upper body are selected as the design variables. The structure analysis results show that the three-axis wrist designed satisfies the design criteria, also the optimization result shows that the weight of the wrist designed can be reduced to a degree while satisfying the condition of the allowable stress.