具溫度自補償形變感測與致動功能之液晶高分子材料特性與元件

Abstract

本研究提出一具形變感測功能之微型液晶高分子致動器，可透過兩電源輸入端達到同時致動與形變感測之功能。此致動器是利用微機電製程技術與真空抽濾技術製作而成之雙層結構，分別為液晶高分子層與混有石墨與奈米碳管之液晶高分子導電層。當通以一驅動電壓時，高分子導電層因焦耳加熱而迅速升溫並加熱整體元件。液晶高分子能於受溫度變化之刺激而產生良好可逆形變，從而達到元件致動之效果。此外，本研究之高分子導電層為一特定比例之石墨與奈米碳管均勻混合而成。透過兩者電阻溫度係數之中和，能使元件之電阻值不易隨溫度變化，達到溫度自補償之功能。因此，藉由量測電阻之變化即可推算元件之形變，使元件亦為一應變感測器。除此之外，本研究展示一由兩致動器組裝成之微型手爪，並展示其致動夾取與感測重量之特性。此元件展現了優異之致動力道，能抓取、移動與放置自身重量約五十倍之物品。元件抓取物品時，可透過量測元件受物品重力作用而拉伸時之電阻變化，達到預測夾取物品重量之感測能力。此微形致動器於實現多項感測回饋能力與實際應用情境中具有極大的潛力。

In this study, we present a miniaturized liquid crystal elastomer(LCE)-based micro-actuator with sensing capability. The proposed device is a bilayer structure consisting of an insulating layer and a conductive layer and can be realized with a standard soft-lithography technique and a novel two-step vacuum filtration process. The insulating layer is made of liquid crystal elastomer (LCE) and the conductive layer is composed of graphite microparticles and carbon nanotubes dispersed in LCE matrix. The actuation of the bilayer structure is generated by applying a voltage across the two input terminals of the conductive composite film. The temperature elevation caused by Joule heating induces the LC-to-isotropic phase transition phenomenon of LCE and results in the deformation of the LCE layer. Besides, by optimizing the ratio of graphite microparticles and carbon nanotubes (CNTs) in the composite films, the strain sensing and the electrothermal stimulation of the composite can be decoupled. Consequently, the conductive composite film is capable of serving as an electrothermal heater for actuating the device as well as a piezoresistive strain gauge for detecting the motion of the device. A gripper consisting of two proposed LCE actuators was implemented. The measured results indicate that the gripper exhibits excellent actuating force and is capable of gripping, lifting, and placing objects that are about fifty times its weight. In addition, it was also demonstrated that the weight of the lifted object can be estimated by measuring the resistance variation of the composite film as it is stretched by the weight of the object. The relationship between the resistance change of the composite film and the object weight was also obtained. The proposed simple approach of integrating self-sensing capability on a LCE-based actuating material is promising for developing intelligent soft robots.