Modeling of Wire-on-Drum Shape Memory Actuators for Linear and Rotary Motion

Abstract

The article presents the analytical model of a linear/rotary solid-state actuator formed by a shape memory wire wound over a cylindrical drum. The model assumes a bilinear w temperature) and a linear elastic response in the austenitic state (high temperature). Based on simple equilibrium conditions, the model calculates the stress and strain distributions in the wire when subjected to a constant external backup force and undergoing frictional sliding forces at the contact with the drum. Closed-form expressions are supplied for the stroke produced by whatever actuator geometry and are validated numerically against finite element results. For a particular actuator configuration, the analytical forecasts are also checked experimentally on a proof-of-concept prototype. The analytical model shows that large strokes (up to one-half of the drum’s diameter) are achieved if the frictional coefficient is kept below 0.01. Rolling-contact architectures or sonic-pulse excitations of the drum are discussed as technical solutions to obtain such low friction values

Characterization and Lubrication of Tube-Guided Shape-Memory Alloy Actuators for Smart Textiles

“…A proposed solution to this challenge is to use a long SMA wire, and wind it back and forth inside or circumferentially around the orthotic in question, such that while the SMA length is large, the device length remains small. SMAs wound on the surface of drums, for example, have been predicted to deliver strokes as high as 50% of drum radius, provided that friction is kept low [10]. In practice, these low frictions have been achieved using rolling-contact architectures such as ball-bearings, allowing for experimental strokes of 20% of drum radius [10].…”

“…SMAs wound on the surface of drums, for example, have been predicted to deliver strokes as high as 50% of drum radius, provided that friction is kept low [10]. In practice, these low frictions have been achieved using rolling-contact architectures such as ball-bearings, allowing for experimental strokes of 20% of drum radius [10]. However, this solution is somewhat complicated, requiring a large number of bearings in a small volume to support the SMA wire.…”

Smart materials: Properties, design and mechatronic applications

“…Examples of application of the methods are found in the technical literature. [123][124][125][126][127][128][129] Basic design methods of the main architectures. To design SMA actuators, a material model must describe the mechanical behaviour of the alloy in two temperature ranges: below the temperature M f , at which the austenite-martensite transformation is finished (OFF or deactivated or cold state) and above the temperature, A f , at which the martensite-austenite transformation is completed (ON or activated or hot state).…”

A Rotary Actuator Using Shape Memory Alloy (SMA) Wires

“…By combining the SMA wire as a driver and the flexural mechanism as a load transmitter, high precision rotary motion is achieved without friction/backlash. Bloch, Mammano and Dragoni achieved the rotary motion by winding an SMA wire around a rotational accumulator or a cylindrical drum [17], [18]. Spinella et al developed a compact shape memory rotary actuator consisting of an outer chassis, an inner rotor, four SMA helical springs, and conventional spring to reduce the torque ripple [19].…”