Improved Free Motion Performance for TDPA-Passivated Position-Force Measured Teleoperation Architectures

Abstract

Passivity-based methods are widely used in tele-operation to guarantee stability, especially for the widely used Position-Force measured (PFm) architecture. Among them, Time Domain Passivity Approach (TDPA) achieves stability through passivation, generating a dissipation action that degrades the reference signals and thus, the performance of the system. Whereas passivization is necessary to ensure stability during contact, in free motion, it acts just as a disturb, without having a real impact on stability. In fact, during free motion the force feedback is zero, i.e. the teleoperation loop is not closed and thus, a stabilization action is not needed. Therefore, this paper proposes a formal demonstration that passivation is not needed during free motion. Accordingly, the paper introduces a new formulation of the TDPA to take into account the free motion condition. A one-degree-of-freedom case study is then proposed to provide a simple example to instantiate the formalism and to show the advantages of the proposed method, that achieve an almost total cancellation of the drift during free motion. Finally, the paper discusses the limitations of the method in real-case scenarios. In particular, how the inertia of tools mounted after the force sensors can affect the measurements and the perception of the system.