A high-rate shape memory alloy actuator for aerodynamic load control on wind turbines

Abstract

This paper discusses the development of a high rate shape memory alloy (SMA) driven actuator. The concept of the actuator was developed to act as aerodynamic load control surface on wind turbines. It was designed as a plate or beam-like structure with prestrained SMA wires embedded off its neutral axis. Moreover, the SMA material was embedded in channels through which air was forced to actively cool the wires when the recovery load was to be released. Wires were implemented on both sides of the neutral axis to deflect the beam in both directions. Thermal analysis of the cooling channels showed that they increased the cooling up to tenfold in comparison to the same set-up without forced convection. Subsequently a fuzzy logic controller was designed to control the thermo-mechanical system. The inputs were the error between the deflection and the set point, the value of the set point and the time derivative of the set point. The output consisted of two signals to the valves that controlled the flow through the channels and a signal heating signal that was split to both sets of wires, depending on its sign. The controller was tested on an antagonistic set-up, through which a similar thermo-mechanic behaviour as with the actuator was obtained, but eliminating the beam dynamics. The results were satisfactory; an actuation bandwidth of 1Hz was attained. Subsequently, the controller was tested on the actuator. With increasing actuation frequency, until 0.6Hz a relatively small error between the set point and the actual deflection was observed. Above that frequency the error increased, but also the sinusoidal response was lost. This is believed to be due to snap-through behaviour around the neutral position of the actuator. This was substantiated by the apparent inability of the actuator to track the set point around the neutral position in tracking a composite sinusoidal set point.

Silent Pumpers: A Comparative Topical Overview of the Peristaltic Pumping Principle in Living Nature, Engineering, and Biomimetics

“…Shape memory alloy (SMA) springs or coils might be good actuators for artificial esophagi or some peristaltic pump applications, but they are inapplicable in cooling systems due to their thermoresponsiveness (see Figure a,b). SMAs are typically actuated electrically, where an electric current results in Joule heating . Cooling and reshaping occur slowly by free convective heat transfer to the ambient environment.…”

Bio-inspired annelid robot: a dielectric elastomer actuated soft robot

“…Unfortunately, due to the thermo-mechanic actuation principle, i.e. deformation actuated by heating and cooling, SMA is neither energetically nor temporally efficient [8][9][10]. As a result, velocity of the SMA-based robots is limited.…”

Functional properties and morphology of NiTi articulated actuation elements during thermo-mechanical cyclic tests

“…The deformation of the martensite phase is usually achieved by the application of an external load able to promote the re-orientation of martensite variants (de-twinning); during detwinning, the high mobility of the martensite variant interfaces minimises the strain energy and allows for high deformation. The shape recovery obtained after heating de-twinned martensite is normally used to promote mechanical work, and it finds several interesting applications in the field of actuation [3][4][5][6][7][8][9][10][11].…”