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Title: Study on thermally activated coiled linear actuators made from polymer fibers
Authors: Peng, Zehua
Degree: M.Phil.
Issue Date: 2018
Abstract: Considerable research is currently underway to develop a variety of actuator technologies for applications including factory floor automation, automatic control systems, humanoid robots, micro-surgical manipulators, as well as fluidic and textile applications. The conventional actuators, including electric motors, hydraulic motors, and pneumatic motors, are generally excellent in certain respects such as high energy density, fast dynamic response, and extremely high torque. But overall, such actuators can be rather complex and bulky to be miniaturized. Actuators made from piezoelectric materials complement traditional actuator technologies by enabling relatively fine positioning. However, they are rigid and require strong electric field, making them inappropriate for muscle-like applications. Recently, a novel thermally activated actuator with self-coiled structure, constructed from common polymer fibers through an easy and effective manufacturing method, has been shown to produce large stroke when heated together with promising performance in terms of actuating energy and power densities. However, related research has been concentrated on actuators made from semi-crystalline polyamide fibers and there is lack of information on comprehensive performance evaluation in published works. In this study, the actuating mechanism and fabrication procedure of the actuator made from semi-crystalline polyester fibers are elaborated. Key parameters for fabrication are identified and analyzed. Isotonically, isothermally, and isometrically thermomechanical characterizations are conducted on coiled actuators based on polyester fiber, which is particularly promising through multiple material characterization techniques, to provide performance evaluation protocol for the future engineering applications. Based on the experimental results, the influence of critical parameters of the actuator, i.e. spring index, temperature and heating rates, as well as applied load during thermal actuation, on actuating performance is demonstrated. The polyester fiber-based actuator shows the ability to produce up to 15.6 % actuation stroke against 125-g load upon heating. Specific work done of 0.85 kJ/kg together with mean power density of 0.21 kW/kg are conservatively achieved, which are comparable to reported works. Moreover, electrothermal actuation is tentatively investigated with two methods. The Joule heating activated actuators made from commercial silver-plated polyamide yarn merit simple fabrication, stable structure, excellent actuation performance and be hence studied emphatically. Finally, comparison of the two approaches is made and required improvements are proposed. With the silver-plated polyamide yarns, the actuator is successfully electrothermally driven by using Joule heating, achieving 14.4 % stroke under 1.7 MPa stress from room temperature to 129 ℃, corresponding to specific mechanical energy of 0.39 kJ/kg.
Subjects: Hong Kong Polytechnic University -- Dissertations
Actuators -- Materials
Pages: viii, 143 pages : color illustrations
Appears in Collections:Thesis

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