In times of increasingly complex overall technical systems and the associated component integration, there is a need to downsize existing components. Due to their high energy density, shape memory alloy (SMA) actuators offer the possibility of developing lightweight and compact systems. These actuators are available in a variety of shapes, e.g., wires. A challenge for shape memory alloy wire actuators arises in the design. SMA actuator wires can typically generate a stroke of 2-4%. One possibility to integrate a certain length for the required actuator stroke without additional elements (e.g., levers) is the deflection of the wire. It can be observed, however, that the lifetime of the deflected wires is significantly shorter than in the non-deflected state, despite the same external mechanical stress and actuator stroke. It is also expected that cracks occur at the deflected points where the mechanical stress is high. Therefore, investigations on the influence of the deflections on the lifetime of SMA wires are necessary. In this paper, a test set-up for deflected SMA wires is developed, which is a modular extension of an existing lifetime test rig for SMA actuator wires. The focus of the setup is the ability of parameter variations to determine their influence on lifetime behavior. Potential influencing factors which are investigated are the deflection radius, the actuator elongation, the deflection path, and the wire diameter. The setup is validated in terms of friction and bending stiffness.
This research work focuses on the development of a dynamic flapping wing actuation mechanism for bat-like micro drone, based on Shape Memory Alloy (SMA) wires combined with compliant beam joints. The SMA wires' unique properties enable the robot to achieve wing flapping, mimicking movements of natural bat wings, with almost zero cost in terms of weight and occupied volume. The idea is to implement SMAs in an agonist-antagonist muscle-like configuration, paired with compliant beam joints at the shoulders of the wings, exploiting the resonance frequency of the beam and wing inertia. The study utilizes 50 micrometer diameter SMA wires strategically integrated into the bat structure, which has a total weight (considering body, actuators, and electronics besides power supply) of approximately 20 grams. The results demonstrate that the drone can achieve a substantial wing-span flapping amplitude of 80° at a frequency of 5 Hz without the need for any external cooling systems. This achievement is particularly significant given the well-known limitations of SMAs in high-frequency actuation tasks. By exploiting the resonance of the compliant beam joint, designed to have a specific natural frequency, the drone also features improved energy efficiency at the designated flapping speeds, comparing to a normal hinge joint. In conclusion, the research showcases the large potential of SMA micro-wires in enhancing performance and characteristics of robotic bio-inspired systems, particularly when combined with mechanical structures which can help overcome its limits. The achievement opens doors to significant improvements in the field of flying biomimetic micro-structures, promising exciting possibilities for future applications in surveillance, exploration, and environmental monitoring.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.