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Design Innovation Paper

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

[+] Author and Article Information
Giovanni Scirè Mammano

Department of Engineering Sciences and Methods,
University of Modena and Reggio Emilia,
Reggio Emilia I-42122, Italy

Eugenio Dragoni

Department of Engineering Sciences and Methods,
University of Modena and Reggio Emilia,
Reggio Emilia I-42122, Italy
e-mail: eugenio.dragoni@unimore.it

2Corresponding author.

Contributed by the Design Innovation and Devices of ASME for publication in the JOURNAL OF MECHANICAL DESIGN. Manuscript received March 26, 2016; final manuscript received July 28, 2016; published online October 6, 2016. Assoc. Editor: Massimo Callegari.

J. Mech. Des 139(1), 015001 (Oct 06, 2016) (9 pages) Paper No: MD-16-1243; doi: 10.1115/1.4034401 History: Received March 26, 2016; Revised July 28, 2016

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.

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Figures

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Fig. 1

Concept of the single-stage rotary motor

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Fig. 2

Example of a three-stage rotary motor

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Fig. 3

Material model of the SMA wire in austenitic and martensitic states

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Fig. 4

CAD model of the optimized motor

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Fig. 5

Prototype of the optimized motor: (a) view from the spring side and (b) view from the electronic board side

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Fig. 6

Schematics of the power converters for the SMA wires

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Fig. 7

Three-dimensional CAD model of the prototype motor mounted on the test bed (a) and experimental setup (b)

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Fig. 8

Activation sequence used for the speed testing

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Fig. 9

Comparison between theoretical and experimental rotary stroke of the single module for given external torques

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Fig. 10

Transient shaft rotation for a single module supplied with a current step of 800 mA under several external torques

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Fig. 11

Effect of drum diameter on the transient shaft rotation of a free single module supplied with a current step of 800 mA

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Fig. 12

Transient shaft rotation with two modules supplied simultaneously (800 mA each) under several external torques

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Fig. 13

Comparison of transient shaft rotation for single-stage and two-stage activation of the motor under external torques of 0 Nmm and 20 Nmm

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Fig. 14

Average rotational speed of the motor as a function of the applied torque for several operating modes (ψ = 0, 0.4, 0.8, and 1) and supply time tphase = 500 ms

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Fig. 15

Average rotational speed of the motor as a function of the applied torque for several operating modes (ψ = 0, 0.4, 0.8, and 1) and supply time tphase = 1000 ms

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