An Accurately Controlled Antagonistic Shape Memory Alloy Actuator with Self-Sensing

Abstract

With the progress of miniaturization, shape memory alloy (SMA) actuators exhibit high energy density, self-sensing ability and ease of fabrication, which make them well suited for practical applications. This paper presents a self-sensing controlled actuator drive that was designed using antagonistic pairs of SMA wires. Under a certain pre-strain and duty cycle, the stress between two wires becomes constant. Meanwhile, the strain to resistance curve can minimize the hysteresis gap between the heating and the cooling paths. The curves of both wires are then modeled by fitting polynomials such that the measured resistance can be used directly to determine the difference between the testing values and the target strain. The hysteresis model of strains to duty cycle difference has been used as compensation. Accurate control is demonstrated through step response and sinusoidal tracking. The experimental results show that, under a combination control program, the root-mean-square error can be reduced to 1.093%. The limited bandwidth of the frequency is estimated to be 0.15 Hz. Two sets of instruments with three degrees of freedom are illustrated to show how this type actuator could be potentially implemented.

A fuzzy PID-controlled SMA actuator for a two-DOF joint

“…As noted by Lan and Fan 9 as well as in our previous work, 24 under convenient pre-strain, the heating and cooling paths are already quite close, and a polynomial model with one-to-one mapping is sufficient to describe the paths. In this experiment, the MATLAB ''polyfit'' function was used to obtain the coefficients of the polynomials.…”

“…Within the antagonistic pair of SMA wires actuator, enough pre-strain could also maintain enough inner stress between the wires, which minimized the hysteresis gap with the same principle. Based on our previous study 24 of the pair of SMA wires actuator, it is concluded that the hysteresis gap between the heating and cooling curves is directly influenced by real-time internal force. With correct pre-strain, the hysteresis gap might be minimized.…”

“…Our previous studies of the S-R curve of the SMA wires proved that an appropriate pre-tension force could make the heating and cooling paths nearly overlap, 24 and it was simple to construct a polynomial model to apply the feedback control. Within the antagonistic pair of SMA wires actuator, enough pre-strain could also maintain enough inner stress between the wires, which minimized the hysteresis gap with the same principle.…”

“…Further research on the use of an antagonistic pair of SMA wires in an actuator with nonlinear stress has shown improved accuracy by limiting inner stress to a narrow range. 24 Yet, this is harder to achieve within more complicated structures, as shown in Fig. 1.…”

Three-Dimensional Hysteresis Modeling of Robotic Artificial Muscles with Application to Shape Memory Alloy Actuators

“…Note that the resistance of the actuator might also undergo mild changes during phase transition, the change is less than 15% [29] and is considered to be constant in this work. Under a constant (quasi-static) voltage V , the steady-state temperature T can be computed as…”