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

Although shape memory alloys (SMAs) are increasingly exploited to build actuators for many applications, these materials are basically confined to the field of linear devices. By contrast, SMA technology is virtually unexplored for the construction of compact rotary actuators, which can provide high output torque and significant rotations.

This work is focused on the design, the optimization and the simulation of a rotary SMA actuator purposely conceived to maximize torque and angular stroke while limiting overall size and electric consumption.

The design process complies with a Quality Function Deployment approach. Starting point of the procedure is the House of Quality, which is built around the customer needs identified for the  commodity field of automatic roll-up shutters. Output of the House of Quality are the technical specifications that the actuator must satisfy in order to overcome existing competitors in the selected field.

Following the House of Quality, a structured conceptual design procedure is presented, leading to a portfolio of concepts which are evaluated systematically with respect to the customer needs. The selected concept is a rotary actuator based on a modular architecture: several identical stages are assembled axially to achieve the desired angular stroke. Each stage is made of SMA springs, which act circumferentially on  two coaxial disks to produce their relative rotation.

An electro-thermo-mechanical model of this design is developed to optimize the basic module. Output torque and overall rotation are maximized while total size and electrical consumption are simultaneously minimized. Built on the optimum parameters, a dynamic model of the device is proposed, able to simulate the actuator under arbitrary external loading.

The disclosed rotary SMA actuator shows excellent performance in terms of output torque,  electrical consumption and total size. Capitalizing on the modular architecture, the angular stroke is easily adjusted to meet the requirements of many applications.