Tracking control of time-varying knee exoskeleton disturbed by interaction torque

Area of Science:

• Robotics
• Biomechanics
• Control Systems

Background:

• Knee exoskeletons assist individuals with lower-extremity impairments by compensating for joint movement.
• Controlling these devices is challenging due to time-varying parameters and interaction torques from the wearer.
• These disturbances affect the exoskeleton's dynamic behavior and tracking accuracy.

Purpose of the Study:

• To propose a novel control strategy for knee exoskeletons with time-varying coefficients and interaction torque disturbances.
• To ensure exponential convergence of tracking errors for joint angle control.
• To demonstrate robustness against interaction torques, maintaining bounded tracking errors.

Main Methods:

• Development of a new control strategy for knee exoskeleton systems.
• Mathematical modeling to account for time-varying inertial and viscous coefficients.
• Inclusion of interaction torque as a disturbance in the control design.
• Simulation and experimental validation of the proposed controller.

Main Results:

• The proposed controller achieves exponential convergence of the knee exoskeleton's joint angle tracking error to zero.
• The control strategy demonstrates robustness, ensuring bounded tracking errors even with interaction torque.
• Simulations and experiments confirm the controller's effectiveness and efficiency.

Conclusions:

• The novel control strategy effectively manages time-varying parameters and interaction torques in knee exoskeletons.
• The approach offers superior performance compared to existing methods like the gradient dynamic (GD) approach.
• This work advances the accuracy and reliability of assistive knee exoskeleton control systems.