Double closed-loop cascade control for lower limb exoskeleton with elastic actuation.

Area of Science:

• Robotics
• Biomechanics
• Control Systems Engineering

Background:

• Series Elastic Actuators (SEAs) offer advantages like stable torque control and impact resistance, making them suitable for exoskeleton applications.
• A critical challenge in exoskeleton design is achieving seamless human-exoskeleton movement coordination.
• Existing control methods may not fully leverage SEA capabilities for intuitive human-robot interaction.

Purpose of the Study:

• To propose and validate a novel double closed-loop cascade control strategy for lower limb exoskeletons equipped with SEAs.
• To investigate the actuation performance of SEAs within an integrated exoskeleton control system.
• To demonstrate stable and coordinated movement between a human pilot and the exoskeleton.

Main Methods:

• Developed a double closed-loop cascade control system comprising an inner SEA torque loop and an outer contact force loop.
• Integrated internal sensors (encoders, resolvers) for joint angle measurement and external sensors (pressure sensors) for contact force detection.
• Analyzed SEA actuation performance using a motor velocity loop within the SEA torque control.
• Established a control model based on combined internal and external sensor feedback signals.

Main Results:

• Preliminary experimental results demonstrate stable exoskeleton movements with a human pilot.
• The proposed double closed-loop cascade control method effectively facilitates human-exoskeleton coordination.
• The feasibility of using SEAs in exoskeleton robots and the effectiveness of the control strategy were verified.

Conclusions:

• The double closed-loop cascade control method is effective for achieving stable and coordinated movements in lower limb exoskeletons with SEAs.
• This control approach enhances human-exoskeleton interaction, paving the way for more intuitive and responsive robotic assistance.
• Series Elastic Actuators are a viable and beneficial component for advanced exoskeleton designs.