Design, modelling and control of a micro-positioning actuator based on magnetic shape memory alloys

Abstract

This paper presents an actuator based on magnetic shape memory alloys (MSMAs) suitable for precise positioning in a wide range (up to 1 mm). The actuator is based on the spring returned operating mode and uses a Smalley wave spring to maintain the same operating parameters of a classical coil spring, while being characterized by a smaller dimension. The MSMA element inside the actuator provides a deformation when excited by an external magnetic field, but its behavior is characterized by an asymmetric and saturated hysteresis. Thus, two models are exploited in this work to represent such a non-linear behavior, i.e., the modified and generalized Prandtl-Ishlinskii models. These models are particularly suitable for control purposes due to the existence of their analytical inversion that can be easily exploited in real time control systems. To this aim, this paper investigates three closed-loop control strategies, namely a classical PID regulator, a PID regulator with direct hysteresis compensation, and a combined PID and feedforward compensation strategy. The effectiveness of both modelling and control strategies applied to the designed MSMA-based actuator is illustrated by means of experimental results.

A Modified Prandtl-Ishlinskii Hysteresis Modeling Method with Load-dependent Delay for Characterizing Magnetostrictive Actuated Systems

“…The output displacement amplitude of the magnetostrictive actuated system thus shows more significant contributions of dynamics of the actuator under higher frequency excitations. Specifically, the displacement-current characteristics of the magnetostrictive actuator without load for different discrete frequency can also be described by rate-dependent PI model (Minorowicz et al, 2016) well by involving the input frequency in the play operator. However, the RDPI model is not capable of describing the situation with actuating loads especially under high frequency.…”

“…This property of the magnetostrictive material has been used for developing micro-actuating/positioning devices. Compared with other smart material-based actuators such as piezoelectric (Chen and Ozaki, 2011), SMA (Jani et al, 2014) and MSMA (Minorowicz et al, 2016), the magnetostrictive actuators exhibit relatively large force and deflection with micrometre resolution over a broad frequency range. Such actuators have thus been explored for various applications such as active vibration control and high-speed precision machining (Braghin et al, 2011;Chen and Liu, 2013).…”

“…The magnetostrictive material-based actuators, however, exhibit dominant nonlinearities between the input magnetic field (current) and the actuation force (displacement) (Cao et al, 2006), similar to other smart material-based actuators (Song et al, 2005;Liu et al, 2015;Minorowicz et al, 2016). Such nonlinearities limit the actuating precision and performance, and may cause undesirable inaccuracies or oscillations in the output, specifically when used in a closed loop system (Smith, 2005).…”

“…Based on the classical PI model, a few studies have presented different extensions of the classical PI model to describe asymmetric, saturated and rate-dependent hysteresis characteristics observed in some smart materials based actuators (Su et al, 2009;Zhang et al, 2013;Minorowicz et al, 2016). For example, the generalized Prandtl-Ishlinskii model (GPIM) being constructed by asymmetric hysteresis operator and modified Prandtl-Ishlinskii model (MPIM) being built by classical PI model combining with dead-zone operators are used to express the asymmetric and saturated hysteresis in magnetic shape memory alloys based actuators (Minorowicz et al, 2016).…”

“…For example, the generalized Prandtl-Ishlinskii model (GPIM) being constructed by asymmetric hysteresis operator and modified Prandtl-Ishlinskii model (MPIM) being built by classical PI model combining with dead-zone operators are used to express the asymmetric and saturated hysteresis in magnetic shape memory alloys based actuators (Minorowicz et al, 2016). The input rate-dependence of the hysteresis nonlinearity has been mostly characterized by introducing a dynamic density function to the classical PI and Preisach models (Li et al, 2014).…”