Subspace-oriented energy distribution for the Time Domain Passivity Approach

The Time Domain Passivity Control Approach (TDPA) is a powerful tool to guarantee passive interaction between a robot and its environment. Rather than establishing fixed control parameters to keep the system stable in any possible environment, the TDPA observes the energy flow due to the interaction and applies a dissipative term in the case the interaction becomes active. In a robot manipulator the rationale behind the Passivity Controller requires a criterion on how to distribute the energy to be dissipated among the multiple joints and must be adjusted according to the general control goal of the application. This paper presents a method for distributing the dissipation between decoupled subspaces of a redundant manipulator, prioritizing dissipation in the null-space. The method allows to preserve passivity while avoiding disturbance of the general control goal defined in the task-space. Thus the general control goal can, to some extent, be as well decoupled from passivity considerations and thus a less conservative controller can be achieved. The approach is sustained with a numerical simulation.