Intrinsically Multistable Soft Actuator Driven by Mixed-Mode Snap-Through Instabilities.

Area of Science:

• Soft robotics
• Materials science
• Mechanical engineering

Background:

• Actuators using snap-through instabilities offer rapid response and low energy needs for reconfigurable structures.
• Current designs often require multiple bistable units, and achieving multistability in a single unit is a significant challenge.

Purpose of the Study:

• To develop a single soft actuator unit capable of intrinsic multistable shape reconfiguration.
• To explore the use of shape memory alloy (SMA) and mixed-mode elastic instabilities for achieving multiple stable states.

Main Methods:

• A soft actuator was designed using a pre-stretched elastic membrane between elastomeric frames with embedded SMA coils.
• Mixed-mode elastic instabilities and SMA activation sequences were employed to control shape transitions.
• Energy minimization principles guided the identification of actuation sequences for stable state transitions.

Main Results:

• The developed actuator unit demonstrated six stable states: two pure bending and four bend-twist configurations.
• Rapid transitions between all six states were achieved within hundreds of milliseconds by controlling SMA activation.
• Bending and twisting angles were systematically recorded across various prestretch ratios.

Conclusions:

• The presented soft actuator achieves intrinsic multistability, offering a significant advancement over multi-unit designs.
• The actuator's ability to rapidly transition between multiple states opens possibilities for advanced applications.
• Demonstrated applications include confined space visual inspection, photovoltaic energy harvesting, and agile crawling robots.