Conceptual Design and Simulation of a Compact Shape Memory Actuator for Rotary Motion

Abstract

This work describes the conceptual design, the modelling, the optimization, the detail design and the virtual testing of a shape memory actuator purposely conceived to maximize torque and angular stroke while limiting overall size and electric consumption. The chosen design, achieved by means of a Quality Function Deployment approach, features a fully modular concept in which an arbitrary number of identical modules are assembled to produce the desired angular stroke and output torque. The basic module contains shape memory springs that actuate the device and also a conventional spring that reduces the torque ripple. Following the concept generation stage, a thermo-electromechanical model is developed and a numerical optimization performed, aimed at minimizing the electrical consumption of the actuator. Finally, the device is designed in detail and the actuator is tested virtually. Thanks to the proposed modular construction and the use of a conventional balancing spring, the device shows better performances than known rotary shape memory actuators in terms of rotation, torque and customization.

Optimum Mechanical Design of Binary Actuators Based on Shape Memory Alloys

“…(19) shows that for each combination of s 1 and s F the stroke increases monotonically when parameter s 2 decreases, implying a more flexible bias spring. Both equations (18) and (19) prove that meaningful strokes (Δx>0) are only possible if parameter s F is lower than s Fcr of equation (10). Section 3.3 shows that the binary actuator with a SMA spring backup gives the best performances in terms of output characteristic, both respect to elastic backup and bias force backup.…”

“…(7); ─ the value of s0 is calculated using definition (6); ─ the lowest affordable value of parameter s2 is chosen (to exploit the primary spring), or the optimal value (21) is adopted (to conserve overall space). If the parameters ml1 and ml2 cannot be determined, expression (31) can be used for a suboptimal design; ─ the maximum deflection of the primary spring, LC-L01, is retrieved from (19); ─ the cold stiffness, K1SC, of the spring is calculated from eq. (4); ─ the pre-stretch of the system, p, is calculated from (17); ─ the stiffness of the traditional spring, KC, is calculated from eq.…”

“…This section introduces a compensation system to store available power from the SMA element in high force positions and then return this power in low force positions [19]. The same principle was successfully applied for electroactive polymer actuators by introducing compliant mechanisms [27].…”

“…Among the proposed actuator there is lack of simple design instruments to provide basic information to the designer, either due to specific constraints of application or due to the high complexity of the thermomechanical material models used. In order to answer for an analytical design methodology, the author described in several technical publications a set of equations useful for linear [18] and rotary application [19]. The authors developed the design equations both for SMA actuators under a general system of external forces [20] and produced the design formulae to increase the output stroke thanks to negative stiffness compensators [21].…”

Cross-shaped twisting structure using SMA-based smart soft composite

“…Jung et al 11 showed that a thinner structure along with higher SMA eccentricity leads to a higher deflection of the actuator. Spinella et al 12 and Paik et al 13 developed twisting actuators with externally embedded SMA elements. However, Kim et al 14 were the first to realize a large twisting deformation of a structure through embedded SMA wire, but this twisting motion was coupled to a bending deflection.…”