Damper-controlled switch for SMA motion smoothing

Luntz, J.; Gonzalez, R.; Aguayo, C.; Brei, D.; Utter, Brent; Johnson, N. L.; Alexander, P. W.

Damper-controlled switch for SMA motion smoothing

Abstract

While the use of SMA-actuated devices continues to grow in many industries, current device limitations pose a
challenge to successful adoption for certain classes of applications. SMA-actuated devices typically demonstrate motion
with non-constant velocity due to the non-linear thermo-mechanically coupled behavior of SMA material transformation,
and motion sensitivity to external factors such as voltage and load. This variation in motion can lead to the perception of
poor device quality, limiting SMA-actuated devices to applications hidden from the sight of the product user, or requiring
them to be augmented with higher cost controls to improve the motion quality. Therefore, a need exists for simple, passive,
low-cost device technologies that enable the designer to prescribe desired motion characteristics with relative insensitivity
to fluctuation in operating conditions. This paper presents a Damper Controlled Switch (DCS) mechanism that delivers
constant velocity and relative insensitivity to operating conditions when combined with a standard SMA wire actuator.
The DCS includes a damper that acts against a spring to open a switch when the velocity exceeds a tunable threshold. To
validate the ability of the DCS to provide the desired motion quality, experiments were conducted comparing the normal
motion of the SMA actuator to the motion produced when the same actuator was fitted with a DCS prototype. The addition
of the DCS produced nearly constant actuator velocity, performing significantly better than the SMA actuator alone. The
tunability of the DCS was demonstrated producing a wide range of attainable constant velocities. Finally, a set of
experiments explored the DCS’s sensitivity to voltage and load, indicating a low sensitivity to a wide range of operating
parameters for which the operating limits were identified. The DCS represents a simple, compact technology based on
passive, low-cost components, providing a very practical solution that will enable integration of SMA-actuated devices
into a broader class of applications.

Title	Damper-controlled switch for SMA motion smoothing
Creator	Luntz, J.
	Gonzalez, R.
	Aguayo, C.
	Brei, D.
	Utter, Brent
	Johnson, N. L.
	Alexander, P. W.
Publisher	Proceedings of the SPIE
Academic Department	Mechanical Engineering
Division	Engineering
Organization	Lafayette College
Date Issued	April 16, 2014
Date Available	2020-01-28
Type	Article
Language	English
Keyword	Shape Memory Alloy
	Actuator
	Motion Quality
	Device Performance
Bibliographic Citation	Aguayo, C., et al. (2014 Apr 16) "Damper-controlled switch for SMA motion smoothing. Proceedings of the SPIE 9059: 90590H
Standard Identifier	DOI 10.1117/12.2052871
Standard Identifier	Handle 10385/kd17ct23n
Permalink	http://hdl.handle.net/10385/kd17ct23n
Rights Statement	In Copyright
Rights Holders	SPIE