Session: 04-07: Shape Memory Alloy Enabled Mechanisms II

Paper Number: 90552

90552 - Control of Rotatory Decoupled Antagonistic SMA Actuators 

SMA actuators are available in a wide variety of designs and constructions. The two-way effect is often used in order to achieve a repeatable actuator behaviour. For this, a restoring force is required for the SMA material. In many applications a spring or an inertial mass is responsible for the restoring force. The so-called antagonistic construction, in which two SMA control elements work against each other, is a special design because there is no need for an additional “passive” restoring force [1]. A disadvantage of this structure is that after activating one of the SMA elements, the return movement cannot be carried out directly by the antagonistic partner. The delay caused by waiting for the first SMA element to cool down leads to longer cycle times.

To compensate for this disadvantage of the antagonistic structure, a decoupled structure has been developed. The actuator construction was designed in such a way that the antagonistic SMA partner is decoupled from the first SMA element when it is active [2]. This enables the actuator to move back quickly regardless of the state of the first SMA control element. The developed linear actuator is used for valve applications at high ambient temperatures [3].

This work deals with the construction as well as the control of two rotatory decoupled antagonistic SMA actuators. The motivation for this development is a demonstrator setup to illustrate this new special decoupled antagonist setup. The first actuator should enable a 90 ° rotation in order to display the potential of an actuator in a production line. A gear drive is used to convert the 2 mm stroke of the SMA wire into rotation. The antagonistic wire serves as a coupling element between the two movable elements. The second actuator contains a bistable element [4] to illustrate another type of actuator structure. This bistable element serves as output device of the actuator and is intended to accelerate a device impulsively.

In both cases a quick back and forth movement can be realized. A circuit board was developed to control the actuators. Different electrical resistances of the various installed wires require different energies for phase conversion [5]. In this case, faster activation of higher energy pulses is also possible [6]. The different amounts of energy for the individual SMA wires are controlled via a PWM. In order to determine the correct PWM parameters, measurements were carried out to ensure fast activation.

[1]  S. Langbein und A. Czechowicz, “Konstruktionspraxis Formgedächtnistechnik.” Springer Fachmedien Wiesbaden, 2013.

[2]   R. Britz, P. Motzki, and S. Seelecke, “THERMAL ACTUATOR ARRANGEMENT HAVING IMPROVED RESET TIME,” WO2021052933A1, 2019.

[3]   Britz, R, Seelecke, S, Rizzello, G, & Motzki, P. "Decoupled Antagonistic SMA Actuator for Valve Applications." Proceedings of the ASME 2020 Conference on Smart Materials, Adaptive Structures and Intelligent Systems. ASME 2020 Conference on Smart Materials, Adaptive Structures and Intelligent Systems. Virtual, Online. September 15, 2020. V001T02A001. ASME.

[4]   P. Motzki and S. Seelecke, “Bistable Actuator Device Having A Shape Memory Element,” US 2019/0203701 A1, 2019.

[5]   SAES Group: SmartFlex Brochure, Data Sheet [Online]. Available: https://www.yumpu.com/en/document/fullscreen/62284379/brochure-smartflex .

[6]   P. Motzki, T. Gorges, M. Kappel, M. Schmidt, G. Rizzello and S. Seelecke: High-Speed and High Efficiency Shape Memory Alloy Actuation, Smart Materials and Structures, vol. 27, no. 7, p. 075047, 2018.

Presenting Author: Tom Gorges Intelligent Material Systems Lab, Center for Mechatronics and Automation Technology (ZeMA gGmbH), Saarbrücken, Germany