Towards human-knee orthosis interaction based on adaptive impedance control through stiffness adjustment

Area of Science:

• Robotics
• Rehabilitation Engineering
• Biomechanics

Background:

• Powered, wearable lower limb orthoses are crucial for rehabilitation, enabling challenging locomotor tasks.
• Assist-as-needed strategies, like adaptive impedance control, are key for effective repetitive training.

Purpose of the Study:

• To implement and evaluate an adaptive impedance control strategy for a human-knee orthosis.
• To enhance user comfort, natural motion, and kinematic freedom during gait training.

Main Methods:

• Software control of robotic stiffness based on gait cycle and speed.
• Estimation of stiffness using interaction torque-angle characteristics from experimental data.
• Comparison of adaptive control with trajectory tracking control using five healthy subjects.

Main Results:

• Adaptive control strategy demonstrated more comfortable and natural motion compared to trajectory tracking.
• Increased kinematic freedom was observed, allowing greater user contribution to gait.
• Speed-stiffness dependency was evident, particularly at higher user-demanded stiffness levels.

Conclusions:

• Adaptive impedance control in lower limb orthoses improves user experience and training effectiveness.
• This strategy facilitates user participation and natural movement during rehabilitation.
• Future work includes gravitational compensation and real-time dynamic property control.