A Passivity-Based Approach for Stable Patient-Robot Interaction in Haptics-Enabled Rehabilitation Systems: Modulated Time-Domain Passivity Control

In this paper, a novel passivity-based technique is proposed to 1) analyze and 2) guarantee the stability of haptics-enabled robotic/telerobotic systems when there is a possibility of having a source of nonpassivity (namely, a nonpassive environment) in addition to the conventional nonpassive component in teleoperation systems (namely, a delayed communication channel). The need for the proposed technique is motivated by safe and optimal implementation of the haptics-enabled robotic, cloud-based, and remote rehabilitation systems. The objective of the controller proposed in this paper is to perform minimum alteration to the system transparency, in a dynamic and patient-specific manner, by utilizing quantifiable biomechanical capability of the user's limb (i.e., excess of passivity) in dissipating interactive energies to guaranteeing human-robot interaction safety, in the context of the strong passivity theorem. The proposed controller is named modulated time-domain passivity control (M-TDPC) approach and is a new member of the family of the state-of-the-art TDPC techniques. Simulations and experimental results are presented in support of the proposed technique and the developed theory.