Analysis of position tracking in torque control of humanoid robots considering joint elasticity and time delay

This study investigates the position tracking performance of torque controlled humanoid robots in the presence of joint elasticity and time delay in torque command. One of the main purposes using torque control for humanoid robots is to achieve compliant behaviors on uncertain external disturbance such as uneven terrain and interaction with human. On the other hand, high performance of position tracking is also required to implement motion control of robots. In this study, the effects of joint elasticity and time delay in torque command area investigated in terms of position tracking. First, a joint model is derived and validated, which reflects the elasticity and time delay. Frequency response analysis is exploited to theoretically evaluate the performance of the control system for position tracking. This joint model with the elasticity and time delay is used to estimate the limitations in the controller design for our torque controlled humanoid robot. Theoretical analysis and its comparison with experimental results demonstrate that the joint elasticity and time delay significantly affect the system performance.