Continuous Rotary Motor Actuated by Multiple Segments of Shape Memory Alloy Wires

Shape memory alloys have recently gained attention for applications in motor driving components. The most expressive advantage of shape memory alloy components in that type of application is the high torque to motor weight ratio. Considering the importance of these studies, this article presents the design, manufacture, and theoretical and experimental analyses of a rotary motor driven by Ni–Ti shape memory alloy mini springs. The adopted motion mechanism allows the motor to run in continuous and bidirectional rotation mode, where speed and torque are determined by a drive sequence. A simplified analytical model was implemented, considering the thermomechanical characteristics of the shape memory alloy springs. Experimental tests with and without electrical drives were performed using properly designed electronic measurement instrumentation. The principal scientific contribution of this work is the demonstration of the motor’s functionality and torque generation. An energy density index of 1.41 × 10−3 Nmm/mm3 was attained, which is higher to those of other similarly constructed motors in the literature.

Download Full-text

Modelling and Validation of a Rotary Motor Combining Shape Memory Wires and Overrunning Clutches

Volume 1: Development and Characterization of Multifunctional Materials; Modeling, Simulation and Control of Adaptive Systems; Structural Health Monitoring; Keynote Presentation ◽

10.1115/smasis2014-7406 ◽

2014 ◽

Author(s):

Giovanni Scirè Mammano ◽

Eugenio Dragoni

Keyword(s):

Shape Memory Alloy ◽

Shape Memory ◽

Electrical Activation ◽

Constant Force ◽

Experimental Characterization ◽

Low Friction ◽

The Wire ◽

Rotary Motor ◽

Static Simulation

The paper presents the conceptual design, modeling and prototyping of a novel rotary motor based on shape memory alloy (SMA) wires. The basic architecture of the device capitalizes on a SMA wire wound around a low-friction cylindrical drum. The backup force to the SMA wire is provided by a beam spring which generates a nearly-constant force tangential to the drum. The electrical activation of the wire produces a contraction of the wire, hence a rotation of the drum fitted to the shaft through an overrunning clutch (free wheel). Thanks to the overrunning clutch, during the backup phase (recoiling of the wire), the drum rotates backward while the shaft does not move. Spurious backward movements of the shaft are contrasted by a second overrunning clutch linking the shaft to the frame. The paper presents a model for the quasi-static simulation of the motor and the experimental characterization of a prototype device featuring three active drums, a rotary sensor and an angular brake to apply the external load.

Download Full-text

Design and Characterization of a Continuous Rotary Minimotor Based on Shape-Memory Wires and Overrunning Clutches1

Journal of Mechanical Design ◽

10.1115/1.4034401 ◽

2016 ◽

Vol 139 (1) ◽

Cited By ~ 4

Author(s):

Giovanni Scirè Mammano ◽

Eugenio Dragoni

Keyword(s):

Shape Memory Alloy ◽

Shape Memory ◽

Low Friction ◽

Maximum Torque ◽

Output Torque ◽

Large Rotations ◽

Rotary Motor ◽

High Output ◽

Unidirectional Motion

An attractive but little explored field of application of the shape-memory technology is the area of rotary actuators, in particular for generating endless motion. This paper presents a miniature rotary motor based on shape-memory alloy (SMA) wires and overrunning clutches, which produces high output torque and unlimited rotation. The concept features an SMA wire tightly wound around a low-friction cylindrical drum to convert wire strains into large rotations within a compact package. The seesaw motion of the drum ensuing from repeated contraction–elongation cycles of the wire is converted into unidirectional motion of the output shaft by an overrunning clutch fitted between drum and shaft. Following a design process developed in a former paper, a six-stage prototype with size envelope of 48 × 22 × 30 mm is built and tested. Diverse supply strategies are implemented to optimize either the output torque or the speed regularity of the motor with the following results: maximum torque = 20 Nmm; specific torque = 6.31 × 10−4 Nmm/mm3; rotation per module = 15 deg/cycle; and free continuous speed = 4.4 rpm.

Download Full-text