A smart soft actuator using a single shape memory alloy for twisting actuation

Abstract

Recently, robots have become a topic of interest with regard to their functionality as they need to complete a large number of diverse tasks in a variety of environments. When using traditional mechanical components, many parts are needed to realize complex deformations, such as motors, hinges, and cranks. To produce complex deformations, this work introduces a smart soft composite torsional actuator using a single shape memory alloy (SMA) wire without any additional elements. The proposed twisting actuator is composed of a torsionally prestrained SMA wire embedded at the center of a polydimethylsiloxane matrixthat twists by applying an electric current upon joule heating of the SMA wire. This report shows the actuator design, fabrication method, and results for the twisting angle and actuation moment. Results show that a higher electric current helps reach the maximum twisting angle faster, but that if the current is too low or too high, it will not be able to reach its maximum deformation. Also, both the twisting angle and the twisting moment increase with a large applied twisting prestrain, but this increase has an asymptotic behavior. However, results for both the width and the thickness of the actuator show that a larger width and thickness reduce the maximum actuation angle of the actuator. This paper also presents a new mechanism for an SMA-actuated active catheter using only two SMA wires with a total length of 170 mm to bend the tip of thecatheter in multiple directions. The fabricated active catheter's maximum twisting angle is 270°, and themaximum bending curvature is 0.02 mm −1 .

Twist again: Dynamically and reversibly controllable chirality in liquid crystalline elastomer microposts

“…Microstructures with controllable bending, twisting, and chirality can be used to greatly expand the range of motion exhibited by microscopic robots and devices (37). This degree of structural reconfiguration is also valuable for creating shape-changing biomedical devices and microactuators (16).…”

A novel design of shape-memory alloy-based soft robotic gripper with variable stiffness

“…The SMA wire (55 wt% Ni, 45 wt% Ti, Flexinol, Dynalloy) with the diameter of 0.38 mm and the austenite start temperature (A s ) of 68 C is used as a tendon to drive the soft gripper to generate bending deformation due to its high power-to-weight ratio, large life cycles, low noise, and low driving voltages. 31,32 The paraffin as a variable stiffness material is selected to modulate the stiffness of the embedded variable stiffness joint due to the large range of stiffness change between its liquid and solid states, easy fabrication of the variable stiffness joint by molding method and its nontoxicity. The transformation temperature of the paraffin is its melting point (T m ) of 58 C. At ambient temperature (25 C), the paraffin at solid state is stiff corresponding to the robotic finger joint at high stiffness.…”

Materials as Machines

“…SMAs in a wire geometry are particularly suited for tensile actuation due to their comparatively higher efficiency (by weight) and uniformity of generated stress over the cross‐sectional area of the device. Numerous wire‐based actuators have been described 36,39–42. For example, Allen et al employ a Nitinol wire embedded with a polycaprolactone (PCL) rod, both of which are encapsulated in a silicone rubber to form a composite actuator ( Figure a) 43.…”