Accurate Position Tracking Control of SMAAs Based on Low-Complexity Self-Sensing Model and Compound Control Strategy

Abstract

Shape memory alloy actuators (SMAAs) exhibit high strain, high power-to-weight ratio, and self-sensing ability, which are promising characteristics for application in micro-actuator systems. However, the complex self-sensing and nonlinear hysteresis characteristics of shape memory alloy (SMA) seriously affect the position tracking accuracy of SMAAs. In order to realize the accurate position tracking of the SMAAs without sensors, this article proposes a low-complexity self-sensing of modeling methods, which does not require complex mechanical structure, specific prestress, and complex mathematical models. Furthermore, a compound control strategy of generalized Prandtl–Ishlinskii (GPI) inverse model and fuzzy-proportional–integral derivative (PID) was presented to compensate the nonlinear hysteresis and time-varying characteristics of SMAAs. First, macroscopic and microcosmic characteristics of SMA were analyzed to explain the negative effect of the rhombohedral ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}$ </tex-math></inline-formula> ) phase on the self-sensing characteristics of SMA. Second, a NiTi-based SMA wire without <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}$ </tex-math></inline-formula> phase was selected as a self-sensing modeling object by comparative evaluation experiments, which has similar linear self-sensing properties under various pretension force conditions, a self-sensing model containing only quadratic polynomials is constructed by an offline identification. Third, a fuzzy-PID controller is designed based on the transfer function obtained from the SMAA’s system identification, further, a nonlinear hysteresis feedforward compensation controller is designed based on the GPI model. Finally, comparative experiments with the compound controller and fuzzy-PID controller for multistep and sinusoidal position tracking responses were performed, and the experimental results show that the proposed compound controller has a faster response and higher control accuracy in position tracking control.