A Teleoperation System with Impedance Control and Disturbance Observer for Robot-Assisted Rehabilitation

TL;DR

This work addresses robot-assisted rehabilitation by enabling safe, compliant teleoperation through a bilateral system that couples impedance control with a nonlinear disturbance observer (NDOB) to compensate dynamic uncertainties. The approach supports trajectory tracking, physical human-robot interaction (pHRI), force feedback rendered via a virtual spring, and record-replay of therapist demonstrations, all within a single control framework. Experiments on two 2-DOF Quanser rehab robots demonstrate accurate tracking across multiple trajectories, effective pHRI, and robust force rendering without force sensors. The proposed architecture has practical potential to reduce therapist workload and enable home-based rehabilitation, while maintaining accuracy and safety across varied rehabilitation tasks.

Abstract

Physical movement therapy is a crucial method of rehabilitation aimed at reinstating mobility among patients facing motor dysfunction due to neurological conditions or accidents. Such therapy is usually featured as patient-specific, repetitive, and labor-intensive. The conventional method, where therapists collaborate with patients to conduct repetitive physical training, proves strenuous due to these characteristics. The concept of robot-assisted rehabilitation, assisting therapists with robotic systems, has gained substantial popularity. However, building such systems presents challenges, such as diverse task demands, uncertainties in dynamic models, and safety issues. To address these concerns, in this paper, we proposed a bilateral teleoperation system for rehabilitation. The control scheme of the system is designed as an integrated framework of impedance control and disturbance observer where the former can ensure compliant human-robot interaction without the need for force sensors while the latter can compensate for dynamic uncertainties when only a roughly identified dynamic model is available. Furthermore, the scheme allows free switching between tracking tasks and physical human-robot interaction (pHRI). The presented system can execute a wide array of pre-defined trajectories with varying patterns, adaptable to diverse needs. Moreover, the system can capture therapists' demonstrations, replaying them as many times as necessary. The effectiveness of the teleoperation system is experimentally evaluated and demonstrated.

Figures (8)

• Figure 1: Block diagram of control schemes for the proposed teleoperation system. The dashed line means a linked switch. The output of NDOB $\tau_{\tt M,NDOB}$ and $\tau_{\tt S,NDOB}$ are the estimation of the lumped uncertainties $\tau_{\tt M,disturb}$ and $\tau_{\tt S,disturb}$, respectively.
• Figure 2: Schematic of the 2-DOF planar upper-limb rehabilitation robot (black, white) and frame attachment to each joint. Frame {0} is the base frame while frame {3} is the end-effector (EE) frame. $L_1, L_2$ are link lengths. $q_1, q_2$ are joint angle variables.
• Figure 3: Workspace of the master robot and the second robot.
• Figure 4: Exp.1 results of individual performance of the two robots by implementing impedance controller with or without NDOB.
• Figure 5: Exp.2 results of the teleoperation system performance on trajectory tracking tasks. The master robot tracks a pre-defined trajectory while the second robot follows the master robot.