Fabrication and Model Based Position Estimation of Novel Laser Processed Shape Memory Alloy Actuator with an Embedded Strain Gauge Sensor

Abstract

Shape Memory Alloys have sparked great amount of interest in the eld 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 thesis, a novel laser processed NiTi Shape Memory Alloy (SMA) actuator is proposed containing two di erent material compositions in one monolithic piece of actuator wire. Each of these compositions behaves di erently at room temperature, one exhibits a shape memory e ect (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 di erent material compositions. The proposed actuator has signi cant application in robotics, wearables, haptics, automotive, and any other application which the mechanical load is not known in advance. Two simple position and force controller schemes using the proposed dual-resistance measurement position (and force) estimation are discussed and the control results presented. The proposed position estimation algorithm is used for the feedback-signal of a simple PID position and force controller scheme. Moreover, another novel sensorless position estimation of SMA actuator wires are presented using the power measurement of the standing wave cause by the re ection of a high-frequency signal at an un-terminated end.