Relaxing Conservatism for Enhanced Impedance Range and Transparency in Haptic Interaction

The Time Domain Passivity Approach (TDPA) has been accepted as one of least conservative tools for designing stabilizing controllers in haptics and teleoperation, but it still suffers from conservatism because it is based on passivity. Additionally, high-frequency, immediate control actions lead to a degradation of transparency. In this paper, we propose a method to relax the conservatism of haptic interaction and enhance stable impedance range while maintaining high transparency. Based on the observation of energy exchange behavior in pressing and releasing paths in haptic interaction, we introduce an energy cycle as a completion of a pressing and releasing path. With this new concept, we compare the energies at the end of each energy cycle to estimate the energy generation and inject adaptive damping to regulate it over upcoming cycles. Because we wait a pressing-releasing cycle is completed, we allow energy to be generated, but we regulate the amount of generated energy over upcoming cycles by injecting adaptive damping. In this way, we perform low-frequency control actions on system dynamics. These in turn enable us to achieve high transparency. We show the validity of the proposed approach through several simulations and experiments, and show that it enhances the stable impedance range and transparency compared to the TDPA.