Linear motion is rather common in the industry, and linear electric motors (LEMs) can provide it directly (without a mechanical transmission) through electromagnetic field forces. LEMs may be considered counterparts of rotary electric machines, but specific topologies lead to characteristics that differ (in some cases notably) from those of the latter. This paper attempts an overview on recent progress of LEMs, from innovative topologies to advanced modeling, design, and control, with case studies and examples related to specific industrial applications from people movers to small compressors solenoids, speakers, and microphones.

Linear Electric Machines, Drives, and MAGLEVs: An Overview

The field of energy harvesting has grown concurrently with the rapid development of portable and wireless electronics in which reliable and long-lasting power sources are required. Electrochemical batteries have a limited lifespan and require periodic recharging. In contrast, vibration energy harvesters can supply uninterrupted power by scavenging useful electrical energy from ambient structural vibrations. This article reviews the current state of vibration energy harvesters based on magnetostrictive materials, especially Terfenol-D and Galfenol. Existing magnetostrictive harvester designs are compared in terms of various performance metrics. Advanced techniques that can reduce device size and improve performance are presented. Models for magnetostrictive devices are summarized to guide future harvester designs.

http://iopscience.iop.org/article/10.1088/1361-665X/aa8347/pdf

Review of magnetostrictive vibration energy harvesters

The supercoiled polymer (SCP) actuator is a recently discovered artificial muscle that demonstrates significant mechanical power, large contraction, and good dynamic range in a muscle-like form factor. There has been a rapid increase of research efforts devoted to the study of SCP actuators. For robotics, SCP actuators overcome specific challenges of artificial muscles such as shape memory alloy wires, where limited strain and slow dynamics, and power consumption had limited their use. It is known that hysteresis nonlinearity results from coiling the threads, and can cause up to 30% strain difference under the same voltage; however, no work has been reported to characterize the hysteresis in SCP actuators. In this paper, three new models are formulated to characterize the hysteretic relationship between three coupled variables (voltage input, strain, and load) of an SCP actuator, namely, the augmented generalized Prandtl-Ishlinskii model, the augmented Preisach model, and the augmented linear model. By incorporating the relationship between hysteresis curves and loading forces, the proposed models can efficiently characterize the hysteresis. Open-loop position control is further realized through inverse compensation. Experimental results show that the proposed schemes can effectively estimate and compensate the hysteresis. For the first time, the hysteresis characterization and compensation of SCP actuators are successfully demonstrated, such that accurate robot control can be realized.

Modeling and Inverse Compensation of Hysteresis in Supercoiled Polymer Artificial Muscles

Excessive vibrations in civil and mechanical systems can cause structural damage or detrimental noise. Structural vibrations can be mitigated either by attenuating energy from vibration sources or isolating external disturbance from target structures. Magnetostrictive materials coupling mechanical and magnetic energies have provided innovative solutions to vibration control challenges. Depending on the system’s tunability and power consumption, the existing vibration control strategies are categorized into active, passive, and semi-active types. This article first summarizes the unique properties of magnetostrictive materials that lead to compact and reliable vibration control strategies. Several magnetostrictive vibration control mechanisms together with their performance are then studied using lumped parameter models. Finally, this article reviews the current state of vibration control applications utilizing magnetostrictive materials, especially Terfenol-D and Galfenol.

https://iopscience.iop.org/article/10.1088/1361-665X/aadff5/pdf

Review of magnetostrictive materials for structural vibration control

Robotic artificial muscles are compliant and can generate straight contractions. They are increasingly popular as driving mechanisms for robotic systems. However, their strain and tension force often vary simultaneously under varying loads and inputs, resulting in three-dimensional hysteretic relationships. The three-dimensional hysteresis in robotic artificial muscles poses difficulties in estimating how they work and how to make them perform designed motions. This study proposes an approach to driving robotic artificial muscles to generate designed motions and forces by modeling and compensating for their three-dimensional hysteresis. The proposed scheme captures the nonlinearity by embedding two hysteresis models. The effectiveness of the model is confirmed by testing three popular robotic artificial muscles. Inverting the proposed model allows us to compensate for the hysteresis among temperature surrogate, contraction length, and tension force of a shape memory alloy (SMA) actuator. Feedforward control of an SMAactuated robotic bicep is demonstrated. This study can be generalized to other robotic artificial muscles, thus enabling muscle-powered machines to generate desired motions.

http://iopscience.iop.org/article/10.1088/1361-665X/aaa690/pdf

Three-dimensional hysteresis compensation enhances accuracy of robotic artificial muscles

Design and modeling of a bi-laminate, Galfenol-driven composite beam is presented in which the elasticity of the adhesive layer is considered. The optimal thickness ratio necessary to maximize the tip deflection is found by minimization of the internal energy of the beam. Model simulations show that use of a substrate material with high modulus leads to larger tip deflections. Stainless steel was therefore utilized as substrate in the experiments. In order to reduce eddy currents, a laminated silicon steel frame was employed to magnetize the beam. A dynamic model is proposed by coupling the structural dynamics of the beam and adhesive layer with the magnetostriction generated by the Galfenol layer. The latter is described with a linear piezomagnetic law with uniform magnetic field distribution along the length of the beam. Galerkin discretization combined with Newmark numerical integration are employed to approximate the dynamic response of the beam. The model is shown to describe both the transient and s...

Optimization and Dynamic Modeling of Galfenol Unimorphs

This article presents a fully coupled, nonlinear model for the dynamic response of Galfenol-driven unimorph actuators in a cantilever configuration. The hysteretic magnetomechanical behavior of Gal...

Nonlinear model for Galfenol cantilevered unimorphs considering full magnetoelastic coupling

A fully coupled simulation framework is developed to predict the dynamic characteristics of the permanent magnet (PM) contactors. Dynamic inductance, magnetic field distribution, and mechanical motion are solved by coupling the electric, magnetic, and mechanical governing equations. The equations are developed in the weak forms and the Weak Form Partial Differential Equation module of Comsol Multiphysics is employed to solve the equations. Influence of PM is taken into account by considering the remanent flux as a static potential. The electromagnetic variables and mechanical variables can be solved in the same discrete time period, which gives much higher calculation efficiency than the existing method. The simulation results show that the framework can predict the changing of the inductance, closing displacement, and excitation current in the time domain. Comparative experiments have been conducted to verify the simulations. Physical measurements show that the dynamic closing process of the contactor can be captured by the model with good precisions.

A Fully Coupled Framework of Predicting the Dynamic Characteristics of Permanent Magnet Contactor

Impact force sensing with magnetostrictive Fe-Ga alloys

On active bending structures, the actuation direction and the excitation field direction are not the same. Simple lumped parameter models are inadequate to describe the relationship between output displacement and input field. In this paper, a dynamic distributed parameter model is presented to describe the system dynamics of a galfenol bending actuator. To consider nonlinearities and hysteresis in bending, a nonlinear magnetomechanical model is developed to characterize the hysteretic magnetostriction generated by the galfenol layer. A dynamic real-time control strategy is proposed to compensate for hysteresis. A nonlinear inverse filter is constructed to linearize the hysteresis based on the proposed distributed parameter model. In order to increase the calculation efficiency, a new iteration method is proposed to calculate the filter. The iteration stepsize of the input field can be adaptively updated according to the inverting error. Simulation results show that significant enhancement of convergence efficiency can be achieved by using the proposed method compared with the existing fixed step size method. Experiments have been conducted to verify the real-time control strategy.

https://iopscience.iop.org/article/10.1088/0964-1726/25/3/035046/pdf

Liang Shu

Papers

Optimization and Dynamic Modeling of Galfenol Unimorphs

Nonlinear model for Galfenol cantilevered unimorphs considering full magnetoelastic coupling

A Fully Coupled Framework of Predicting the Dynamic Characteristics of Permanent Magnet Contactor

Impact force sensing with magnetostrictive Fe-Ga alloys

Modeling of galfenol bending actuator considering nonlinear hysteresis and dynamic real-time control strategy