Micropositioning control of smart shape‐memory alloy‐based actuators

摘要

Purpose The purpose of this paper is to focus on the use of a nickel‐titanium (nitinol) shape memory alloy (SMA) wire (capable of showing strains of up to 8 per cent) as the active element that drives a flexible and lightweight micropositioning actuator. The purpose of this paper is to finely control the wire contraction, and as a result, the deflection of the actuator, with micrometric accuracies. Design/methodology/approach Different experimental platforms are built, all of them using the same nitinol wire as the active element. In all cases a current is applied to the wire to heat it up using the Joule effect, and in doing so cause the wire to transform from the martensite into the austenite. This phase transition has a non‐linear and hysteretic nature, so, finely controling wire's position requires a non trivial control strategy. A neural network used to compensate the hysteretic behaviour of the wire combined with proportional‐integral with antiwindup control strategy is implemented. Control experiments are carried out on a light robot gripper and on a single‐fingered experimental device. Findings It is found that the single‐fingered device could be used to better analyze the behaviour of the gripper. It is also found that the accuracy obtainable strongly depended on the position sensor used for the feedback, ranging from 3 μ m for an linear variable differential transformer sensor to 30 μ m for strain gauges mounted on the “fingers” of the grip. Originality/value This paper shows the viability of using SMA‐based actuators for lightweight applications, controllable with micrometric accuracies, without the need to place an extraordinarily large burden on the control system.