Increasing the Energy Efficiency of NiTi Unimorph Actuators With a 3D-Printed Passive Layer

This work demonstrates two strategies to reduce the energy required for actuation of thin film NiTi unimorph actuators with 3D printed polymeric passive layers. First, by taking advantage of 3D printing, a low mass and high stiffness passive layer can be used to achieve faster heating/cooling rates. This ultimately reduces the time and energy required to achieve a threshold temperature. The second approach uses higher currents for shorter periods of time to reach a predefined operational temperature with less energy. Using a well-designed 3D printed passive layer combined with pulsed actuation results in a decrease in the required input energy per cycle of approximately 83% while improving the mechanical work output by about 50% when compared to actuators with a solid passive layer driven at a lower current. The actuators were tested using currents up to 19 mA, aiming for a 95 °C change in the temperature of the NiTi layer. The proposed strategies have been shown to enhance the energy efficiency of the electrothermally heated NiTi unimorph microactuators by up to 803%. [2020-0204].

I. Introduction

When designing microactuators for battery-powered systems, it is important to balance multiple objectives including energy efficiency, actuator impedance, and actuator force-displacement characteristics. Electrothermal microactuators are attractive due to high forces and displacements that can be generated via Joule heating at relatively low voltages that match existing battery technologies. These actuators have found use in various applications such as micro-mirrors [1], micro-grippers [2], micro-motors [3], and microrobots [4]–[8]. However, in comparison to electrostatic and piezoelectric actuation, electrothermal actuators trade off energy efficiency (defined as mechanical work output divided by electrical energy input) for the benefit of low voltage actuation [9].