Modelling and Torque Control of an Non-Linear Friction Inverted Pendulum driven with a Rotary Series Elastic Actuator

Rotary Series Elastic Actuators (RSEA) are one of the most appropriate actuation methods for legged locomotion. RSEA systems have been shown a large shock tolerance and introduce additional dynamics behavior which are useful to achieve walking or running comportment. In this paper, a modelling and torque control analysis of a Rotary Series Elastic Actuator (RSEA) for an inverted pendulum with non-linear frictions are studied. Here, two different controllers; Torque PID+FF (Feed-Forward) controllers without friction estimation model and with friction estimation model were developed. The inputs of the two controllers are the deflection position errors and the rate of deflection position errors of the RSEA. The feedforward inverse model was used in the PID+FF controller. The feedforward technics and the integral action are used to reduce the steady state error of the control system. The PID parameters were optimized using a Genetic Algorithm (GL). In order to have more robust controller, a Non-Linear Friction Estimation Model (NLFEM) was used in PID+FF controller. The experimental results showed that the torque and trajectory tracking of RESA is satisfactory and overall the inverted pendulum stability has improved using the PID+FF with NLFEM.