Novel laser processed shape memory alloy actuator design with an embedded strain gauge sensor using dual resistance measurements. Part I: Fabrication and model-based position estimation

Abstract

Shape memory alloys have sparked great amount of interest in the field of actuation over the past decades. Until now, sensorless position estimation of SMA actuators under dynamic unknown applied stresses has not been feasible due to the complexity of the system and the number of unknown parameters which the proposed extra information obtained from the embedded sensor solves. In this paper, a novel laser processed NiTi shape memory alloy (SMA) actuator is proposed containing two different material compositions in one monolithic piece of actuator wire. Each of these compositions behaves differently at room temperature, one exhibits a shape memory effect (SME) for actuation, and the other is pseudo-elastic (PE) which is used to enable an embedded sensor. Fabrication of the wire included laser processing, heat-treatment, and cold-working procedures. The actuator wire was subsequently trained to stabilize its properties using iso-stress thermal cycling. Additionally, a novel model-based sensorless position estimation algorithm is presented. Proposed model can estimate the position of the actuator under varying applied stresses with an approximate accuracy of 95% only using dual resistance measurements across the two different material compositions. The proposed actuator has significant application in robotics, wearables, haptics, automotive, and any other application which the mechanical load is not known in advance.