Designing compliant mechanisms composed of shape memory alloy and actuated by induction heating

Abstract

Shape memory alloys (SMAs) are a type of smart materials that reacts mechanically to heat. Due to their complex behavior, they are often used in a simple geometry such as wires. This constrains the output displacement of the alloy to a simple linear contraction of the wire. When a different output displacement is desired, the SMA is coupled to a mechanism that transforms the motion, degrading the compactness of the whole system. To alleviate such issues, we propose fabricating, directly in SMA, a compliant mechanism that performs complex output motions and thus improves integration. The first part of this paper presents a method to design such systems. When coupled with a bias-spring and a heating system, these mechanisms form a full actuator. The conventional heating system relies on Joules losses coming from direct electric conduction through the alloy. However, now that the SMA has a complex shape, passing a current through it becomes an arduous task requiring multiple electrodes making the system cumbersome and deteriorating its integrability. Magnetic induction heating is proposed to tackle this limitation, heating the mechanism without contact and conserving a compact actuator.

Shape Memory Alloy (SMA) Actuators: The Role of Material, Form, and Scaling Effects

“…Also, the photolithography and deposition processes can join soft or hard materials with SMAs (such as a compliant frame or bimetallic design). [ 132 ] Although the above approaches allow small SMAs to exhibit high actuation speeds and various actuation modes, precise motion and force control still remain challenging. Compared to lead zirconate titanate (PZT) actuators, which are representative of small‐scale actuators, SMAs are lacking in terms of precise control and a simple powering system.…”

Elasto-Kinematics and Instantaneous Invariants of Compliant Mechanisms Based on Flexure Hinges

“…It is worth pointing out that distributed loads are usually omitted in studies regarding flexure hinges, as most of the forces are exchanged at the extremes. In this paper, we include this type of loads because there are some applications in which compliant mechanisms are driven using a distribution of smart materials (e.g., piezoelectric actuators [60] or shape memory alloys [61]); in these cases, the effect of smart-material actuators manifests as distributed loads.…”