A novel low-profile shape memory alloy torsional actuator

Abstract

This paper presents low-profile torsional actuators applicable for mesoscale and microscale robots. The primary actuator material is thermally activated Ni-Ti shape memory alloy (SMA), which exhibits remarkably high torque density. Despite the advantages of SMAs for actuator applications-high strain, silent operation, and mechanical simplicity-the response time and energy efficiency limit overall performance. As an alternative to SMA wires, thin SMA sheets are used to fabricate effective yet compact torsional actuators. Also, instead of using conventional Joule heating, an external Ni-Cr heating element is utilized to focus heat on the regions of highest required strain. Various design parameters and fabrication variants are described and experimentally explored in actuator prototypes. Controlled current profiles and discrete heating produces a 20% faster response time with 40% less power consumption as compared to Joule heating in a low-profile (sub-millimeter) torsional actuator capable of 180 • motion.

Stretchable circuits and sensors for robotic origami

“…The actuator consists of an annealed SMA actuator and a heater [3]. The actuator module connects two adjacent tiles and applies a torque on the joint to actuate a fold.…”

“…The current choice of folding actuator is a custom shape memory alloy (SMA) sheet machined and annealed into a torsional actuator [3]. The low profile of the SMA torsional actuator conforms to the initial and final shape the robot.…”

A Hybrid Combining Hard and Soft Robots

“…electroactive polymers, 10 shape memory alloys, [11][12][13] and biosynthetic actuators. [14][15][16] Actuation of electroactive polymers requires high voltages, shape-memory alloys are relatively slow in rapid cycling, and while biosynthetic actuators have progressed far in the last decade, 14-16 they still require specialized biological processing techniques.…”

“…Our soft robots: i) are made of elastomeric materials (<1 MPa Young's modulus) with a variable stiffness that depends on the pneumatic pressurization; ii) can have a non-linear output motion and variable number of axes of motion; 11,12 and iii) require only a simple control system to achieve highly complex motions.…”

Cross-shaped twisting structure using SMA-based smart soft composite

“…Jung et al 11 showed that a thinner structure along with higher SMA eccentricity leads to a higher deflection of the actuator. Spinella et al 12 and Paik et al 13 developed twisting actuators with externally embedded SMA elements. However, Kim et al 14 were the first to realize a large twisting deformation of a structure through embedded SMA wire, but this twisting motion was coupled to a bending deflection.…”