This work presents a novel actuator system consisting of a combination of shape memory alloy (SMA) wires with electrostatic clutches. The proposed combination of smart material systems stems from the need to reduce the energy consumption of SMA based actuators while leveraging their high energy densities in compact actuation systems. To this end, large actuation forces provided by SMA wires are combined with the highly energy-efficient actuation of electrostatic clutches. The actuation of the SMA wire generates the desired motion after which the activation of the clutch and deactivation of the SMA wire ensures that the desired position is held in an energyefficient manner. A retractable electro-adhesive tubular clutch was chosen for our testing due to its enclosed nature and ease of fabrication. A characterization setup is also developed and used to demonstrate the feasibility of our new actuator concept. The tests show that a 254 μm SMA wire has an energy consumption rate of about 850.7 mJs−1 as compared to less than 31.3 mJs−1 for the clutch, which results in an energy savings rate of over 800 mJs−1 for position holding tasks.
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.
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