Abstract: A dynamic model for underactuated robots with link flexibility is presented using finite element method. Based on this model, the dynamic coupling effects are analyzed, including the acceleration coupling between active joints and passive ones, the dynamic coupling between passive joints and driving torques. A new index is proposed to describe the dynamic cou-pling between the elastic deformations of flexible links and the active as well as the passive joints, respectively. Comparing the simulation results of acceleration and torque coupling of un-deractuated flexible system with those of the rigid system, it has been shown that the former system can obtain greater coupling values at the certain actuator configuration. The flexible system can supply a better energy transmission at this configuration. Therefore, the results indicate that the elastic deformations of flexible links have important influence on the dynamic characteristics of the system. The dynamic coupling effects are of significance in structure design, configuration design, actuator placement and control of underactuated robots system.

Key words: Coupling, Dynamics Modeling, Flexibility, Underactuated robot