Abstract: The joint of cooperative robot is the main source of the total weight of cooperative robot, and its core part is the transmission system composed of motor and harmonic reducer, which determines the weight and performance of the whole joint. The key to realize lightweight design of joints is to optimize the selection of motors and reducers. In order to solve the problems of heavy structure and high-power consumption of cooperative robot, an optimal selection method of joint transmission system based on scaling law was proposed. First, the dynamic model of the joint drive system was established and the selection conditions of the motor and reducer were determined. Then, the optimization function aiming at minimizing the mass of the motor and reducer was constructed. Since the proposed optimization function involved many parameters needed to be simplified, a method of scaling law was proposed. The optimization function was simplified to be composed of only two parameters of motor locked-rotor torque and reduction ratio. The correctness of scaling law was verified by the actual data of motor and reducer. Finally, in order to verify the effectiveness of the proposed optimization selection method, simulation experiments and actual experiments were carried out with reference to the commercially available joint performance parameters, and the final design of the joint was completed. The results show that the weight of the motor and reducer obtained by this selection method is reduced by about 20% compared with the original design mass of the joint in the simulation experiment, which verifies the effectiveness of this method. In the actual type selection test, the total weight of the selected motor and reducer is reduced by 18% compared with the original design, which further verifies that the method can meet the design requirements of joint lightweight.
Key words:  mechanical transmission mechanism; joint module; transmission system optimization; lightweight design; gear reducer; scaling law; optimization function