When standard voltage levels commonly adopted in industry are used to activate thermal shape memory alloy (SMA) wire actuators, they often result in very high electrical currents which may eventually damage or destroy the actuators. To improve performance of SMA wire actuators operating in industrial environments, in this paper we investigate a novel, fast and energy-efficient actuation strategy based on short pulses in the millisecond range. The use of higher voltages leads to a highly dynamic activation process, in contrast to commonly used quasi-static activation based on low-voltage. A test setup is designed to examine the effects of the control parameters (i.e., supply voltage, activation pulse duration, SMA wire pre-tension and wire diameter) on the measured displacement and force output of the SMA wire. It is shown that actuation times in the range of 20 ms and strokes of more than 10% of the SMA wire length can be reached. Additionally, energy savings of up to 80% with respect to conventional quasi-static actuation are achieved. Possible applications for this activation method are release mechanisms, switches or safety applications.

The thermal shape memory effect describes the ability of a deformed material to return to its original shape when heated. This effect is found in shape memory alloys (SMAs) such as nickel-titanium (NiTi). SMA actuator wire is known for its high energy density and allows for the construction of compact systems. An additional advantage is the so-called “self-sensing” effect, which can be used for sensor tasks within an actuator-sensor-system. In most applications, a current is used to heat the SMA wires through joule heating. Usually a current between zero and four ampere is recommended by the SMA wire manufacturers depending on the wire diameter. Therefore, supply voltage is adjusted to the SMA wire’s electrical resistance to reach the recommended current. The focus of this work is to use supply voltages of magnitudes higher than the recommended supply voltages on SMA actuator wires. This actuation method has the advantage of being able to use industry standard voltage supplies for SMA actuators. Additionally, depending on the application, faster actuation and higher strokes can be achieved. The high voltage results in a high current in the SMA wire. To prevent the wire from being destroyed by the high current, short pulses in the micro- and millisecond range are used. As part of the presented work, a test setup has been constructed to examine the effects of the crucial parameters such as supply voltage amplitude, pulse duration, wire diameter and wire pre-tension. The monitored parameters in this setup are the wire displacement, wire current and force generated by the SMA wire. All sensors in this setup and their timing is validated through several experiments. Additionally, a highspeed optical camera system is used to record qualitative videos of the SMA wire’s behavior under there extreme conditions. This optical feedback is necessary to fully understand and interpret the measured force and displacement signals.

Alternating voltage is available in many environments for actuators. Due to the fact that a lot of actuators cannot directly handle this type of supply voltage, such as shape memory alloy (SMA) actuators, the voltage is usually converted to direct current. In the case of SMA actuators, the supply voltage often even has to be adjusted to the electrical resistance of each particular actuator. Due to high energy potential in AC supplies, conventional activation for SMA actuators over several seconds is not possible. In this study a control procedure for SMA wire actuators with high AC voltage supply is presented, which allows very flexible and versatile control of SMA wires. In addition two different types of activation are distinguished in an experimental study: one-time activation and activation over a longer period of time. The objective of the one-time activation is to reach a given actuator displacement. The activation over time is intended to hold a given position. The results of this series of experiments are presented and the resulting energy saving potential in high voltage SMA activation is observed.

For repeated actuation in shape memory alloy (SMA) actuators, a restoring force is needed to return to the initial starting position after activation. Therefore, SMA wires are often coupled with mechanical springs, which lengthen said wires again after activation through heating and resulting contraction. In more advanced SMA actuation systems a second SMA wire is used as an actively controllable restoring element instead of passively working spring forces. A disadvantage of these antagonistic SMA actuator systems is that after activation of the first SMA wire, the return movement cannot be carried out immediately by the antagonistic partner. This delay caused by the first SMA wire’s cooling time leads to longer cycle times. To compensate for this disadvantage, a decoupled antagonistic SMA actuator has been developed. This enables the actuator to move back to its initial position immediately, regardless of the state of the antagonistic SMA wire. This work deals with the construction as well as the control of two rotatory decoupled antagonistic SMA actuators. The first actuator enables a 90° rotational movement through 2 mm of SMA wire stroke via a gear drive. The second actuator contains a bistable element to enable two energy-free switching positions. This bistable element serves as output device of the actuator and an output stroke of 8 mm is realized by an SMA wire stroke of 1.9 mm.