Feedback linearization and simultaneous stiffness-position control of robots with antagonistic actuated joints

In this paper, the dynamic model of a robot with antagonistic actuated joints is presented, and the problem of full linearization via static state feedback is analyzed. The use of transmission elements with nonlinear relation between the displacement and the actuated force allows to control both the position and the stiffness of each joint. The main advantage of this actuation modality is that the achieved stiffness becomes a mechanical characteristic of the system and it is not the result of an immediate control action as in the classical impedance control scheme (Davison, 2003). Different examples of implementation of this kind of devices are known in literature, even if limited to one single joint (Kjita et al., 2003; Laumond and Kineocam, 2006; Mansard and Chaumette, 2004 and 2006) and the application of antagonistic actuated kinematic chains in the field of robotic hand design is under investigation (Stasse et al., 2006). After a brief review of the dependence of the properties of antagonistic actuation on the transmission elements characteristics, a scheme for simultaneous stiffness-position control of the linearized system is presented. Finally, simulation results of a two-link antagonistic actuated arm are reported and discussed.