Design and Control of a Series-Parallel Elastic Actuator for a Weight-Bearing Exoskeleton Robot

Area of Science:

• Robotics
• Biomechatronics
• Mechanical Engineering

Background:

• Weight-bearing exoskeletons require actuators with high force output, compliance, and low weight for safe human interaction.
• Existing actuators often struggle to balance these competing demands, limiting exoskeleton performance.

Purpose of the Study:

• To design and validate a series-parallel elastic actuator (SPEA) for the PALExo exoskeleton robot.
• To achieve high force output, adjustable compliance, and variable stiffness for dynamic locomotion phases.

Main Methods:

• A series-parallel elastic actuator (SPEA) was developed, incorporating a gas spring for force adjustment and a series elastic module (SEM) for variable stiffness.
• A force controller was designed, integrating dynamic compensation with a cascade control structure, including an inner velocity loop and a disturbance observer.
• Experimental validation was performed to assess the controller's performance and adaptability.

Main Results:

• The designed SPEA successfully met the demanding requirements for the PALExo exoskeleton.
• The force controller demonstrated effective dynamic compensation and adaptability to the SEM's varying stiffness.
• Experimental results confirmed the actuator's capability to provide sufficient force with high compliance.

Conclusions:

• The developed SPEA and its force controller are well-suited for weight-bearing exoskeleton applications.
• The variable stiffness SEM allows adaptation to different locomotion phases, enhancing exoskeleton functionality.
• This research contributes to the advancement of compliant and powerful actuators for human-interactive robots.