Modeling of Shape Memory Alloy Actuated System Using a Modified Rate-dependent Prandtl-Ishlinskii Hysteresis Model

Shape memory alloys (SMAs) are widely used as actuators to construct various robotics systems, such as, minimally invasive surgery robots, micro in-pipe robots and biomimetic micro robots. However, the nonlinear hysteresis behaviors in SMA actuators seriously degrade the control accuracy and desired performances of SMA-actuated control systems. In this paper, an experimental platform based on SMA actuator is conducted. To make the platform capable of achieving precise control, the complex hysteresis characteristics of the SMA actuators are studied. The SMA actuator in this study exhibits complicated nonlinear properties with saturation nonlinearity and asymmetric hysteresis influenced by both the duty cycle of the input voltage and the load mass, which are different from the classical rate-dependent hysteresis behaviors. To explore the nonlinear properties of the SMA actuated system, open-loop experiments under different duty cycles and loads are testified, and a modified Rate-dependent Prandtl-Ishlinskii (RDPI) model is developed to enhance modeling abilities. Fitting effects of the modified RDPI model is validated by the comparison between the modeling output and experimental data.