Self-Sensing Actuation and Control with Shape Memory Alloys

Cate Brinson、Michael Peshkin、Bruce Wilson西北大学形状记忆合金(SMA)已被用于各种驱动、能量吸收和传感应用。这种材料的关键特征是它能够承受看似塑性的大应变，然后在移除载荷或加热材料时恢复这些应变。这种独特的能力是由于奥氏体和马氏体之间的可逆热弹性相变而产生的。该关键功能允许SMA充当非常紧凑的执行器。由于形状记忆合金既可用于材料强化，又可用于吸能，因此在智能结构领域引起了人们的极大兴趣。此外，在占据如此小的体积的同时，没有其他材料或装置能够在大的位移上产生显著的拉力。许多SMA的第二个有用特征是随着应变的变化而改变电阻率。当SMA经历应变时，电阻率的变化使调查人员能够将它们用作粗略的位置传感器。这种粗糙是由于电阻率与材料状态之间的复杂关系以及它与机械载荷和温度的耦合造成的。考虑到上述材料特性，形状记忆合金可以实现经济、高功率密度的自感知驱动(SSA)。然而，由于形状记忆合金驱动和传感的非线性、对形状记忆合金热机械响应的不完全了解以及缺乏合适的控制模型，导致这种有用的材料作为执行器、传感器和形状记忆合金没有得到充分的利用。在这项研究中，重点将致力于(1)改善SMA在传感和控制环境中的特性，(2)改进材料建模，(3)开发基于模型的控制算法，以及(4)用硬件演示这些算法，以促进对SMA作为执行器、传感器和SSA的理解和应用范围。

Cate Brinson, Michael Peshkin, Bruce Wilson Northwestern University Shape memory alloys (SMAs) have been used in a variety of actuation, energy-absorbing, and sensing applications. The key feature of this material is its ability to undergo large seemingly-plastic strains and subsequently recover these strains when a load is removed or the material is heated. This unique ability occurs due to a reversible thermoelastic phase transformation between austenite and martensite. The key feature allows SMAs to serve as very compact actuators. As SMAs can be used for both material-stiffening and energy-absorption, they have generated much interest in the smart structures field. Further, no other material or device can generate significant tensile forces over a large displacement while occupying such a small volume. A second useful feature of many SMAs is a change in resistivity with a change in strain. The change in resistivity as an SMA undergoes strain has enabled investigators to use them as coarse position sensors. The coarseness is due to a complex relationship between resistivity and the material state and its coupling with mechanical load and temperature. Given the material characteristics above, economical, power-dense self-sensing-actuation (SSA) can be achieved with shape memory alloys. However, the nonlinear nature of SMA actuation and sensing, incomplete understanding of SMA thermomechanical response and the lack of suitable models for control result in an under-utilization of this useful material as an actuator, sensor, and SSA. In this research, a focused effort will be targeted at (1) improving the characterization of SMAs for a sensing and control context, (2) refining material modeling, (3) developing model-based control algorithms, and (4) demonstrating these in hardware to advance the understanding and range of applications of SMAs as actuators, sensors, and SSAs.