Adaptive Impedance Control in Bilateral Telerehabilitation with Robotic Exoskeletons

Telerehabilitation with Robotic Exoskeletons is an emerging technology aimed at assisting to restore patients’ mobility using a master and slave robotic system. Some of the main challenges for achieving good tracking performance, stability and transparency in telerehabilitation are nonlinearities, uncertain and time-varying parameters in the robot and human models, and communication delays. Additionally, a paramount challenge for this technology is ensuring safe and compliant interaction between the robots and the human operators. This paper presents a novel control approach utilized during unilateral and bilateral teleoperation which address these challenges. An Adaptive Impedance Controller is designed using Lyapunov-based methods for the master exoskeleton while a Proportional-Derivative Impedance Controller is implemented on the slave exoskeleton. Subsequently, a torque limiter technique was implemented on the master side to ensure stability in the presence of time delays. The advantages of these controllers are that they address unknown dynamics, incorporate designed impedance response for rehabilitation applications, and are simple to implement. Simulations for two two-degree-of-freedom robotic exoskeletons are provided to demonstrate the effectiveness of these methods in both passive and assistive telerehabilitation modes, and with time delays.