Adaptive Energy Reference Time Domain Passivity Control of Haptic Interfaces

Haptic devices are designed to assist humans in operating tasks in a remote or virtual environment. The passivity-based controllers feed back the forces from the environment while maintaining stability. This article presents the adaptive energy reference time domain passivity approach to overcome the sudden force change inherent in the conventional time domain passivity approach (TDPA). The main advantage of the proposed method is that it can be applied to the haptic interfaces interacting with delayed unknown environments without increasing conservatism compared to the conventional TDPA with or without energy reference. The adaptive energy reference is learned at each interaction by a passive estimation of the haptic interface energy. The energy reference is found using force and velocity data, which does not need the foreknowledge of the environment dynamic model parameters and time delay. Therefore, the designed controller can adapt to different environments and time delays. The proposed method is evaluated in both simulation and experimental setups where the parameters of the environments are unknown to the controller. It is shown that the sudden change in force is decreased compared to the conventional TDPA for haptic interface with or without time delay in the system.