Shape Memory Alloy (SMA) Actuator With Embedded Liquid Metal Curvature Sensor for Closed-Loop Control

Area of Science:

• Robotics
• Materials Science
• Sensor Technology

Background:

• Shape memory alloy (SMA) actuators are vital for soft robot locomotion but prone to overheating and degradation due to premature electrical stimulation.
• Existing SMA actuators lack integrated feedback mechanisms to monitor mechanical recovery between activation cycles.

Purpose of the Study:

• To develop a novel soft robot actuator with an integrated curvature sensor to enable controlled, continuous actuation.
• To prevent overheating and degradation in SMA-powered soft robots by ensuring full mechanical recovery between cycles.
• To provide feedback for precise control, including partial actuation for low-power applications.

Main Methods:

• Fabrication of a soft actuator using a pre-stressed elastomer film embedded with shape memory alloy (SMA) and a liquid metal (LM) curvature sensor.
• Integration of a capacitive LM sensor for real-time measurement of actuator bending curvature.
• Implementation of a closed-loop "bang-bang" controller utilizing sensor feedback to manage SMA activation cycles.

Main Results:

• The embedded LM sensor accurately measures bending curvature without compromising the actuator's mechanical properties.
• The closed-loop controller successfully ensures full actuator relaxation before subsequent activation, enabling dynamic adaptation of activation frequency.
• Demonstrated capability for continuous, cyclic actuation and precise partial actuation using sensor feedback for low-power scenarios.

Conclusions:

• The developed soft actuator with an integrated LM curvature sensor effectively addresses the limitations of traditional SMA actuators.
• This innovation allows for enhanced durability, controlled continuous motion, and versatile partial actuation in soft robots.
• The system provides a robust solution for reliable and adaptable soft robotic locomotion.