Identification for Control of Variable Impedance Actuators

Development of Variable Impedance Actuators (VIA) is a recent evolution in robotics to face hallenges as adaptability to the environment, energy saving, safety and robustness. VIA allow to change the impedance of the limbs of a robot using physical elastic and dissipative elements rather than through traditional Impedance Control. This leads to the problem of controlling a VIA, one important aspect of this problem lies in the absence of sensors able to measure on-line the mechanical impedance of a system. This thesis deals with the problem of impedance parameters observation in a VIA robot. This in order to develop an instrument to be used in implementing real closed-loop control of impedance of a VIA. After an introduction to VIA and traditional impedance measurement techniques, we follow an innovative approach to derive an observer able to estimate in real-time the impedance of a VIA. In particular three observers are presented: a nonparametric stiffness observer, a parametric stiffness observer, and an impedance observer able to estimate either non-linear time-varying stiffness, as long as linear damping and inertia coefficients. Derivation of the algorithms is shown and both simulation and experimental results are presented to support the thesis.