Development of a novel manipulator system using thermoelectrically driven SMA actuators

采用热电驱动形状记忆合金作动器，研制了一种重量轻、响应快的新型机械手系统。■实验研究了形状记忆合金（SMA）的恢复力与温度和约束条件的关系。基于SMA中约束应变相关的应力分布，提出了描述恢复力变化的数学模型。为了考虑SMA非均匀相变过程中的多个相域，我们在模型中引入了独立相分数，从而能够模拟SMA致动器在真实热环境中的力学行为。该模型用于温度输入的SMA致动器的机械输出控制是有效的。■利用类似的概念，建立了考虑温度和相变滞后变化的SMA致动器自由变形行为模型。因此，可以通过温度控制来控制SMA致动器的自由变形。■制作了热电元件驱动的SMA机械手原型。提出了一种SMA温度闭环控制方法。在PID温度控制下，超调量和稳态误差足够小，可以得到精确的机械输出，如自由变形和抓握力。这个手指状的机械手可以抓住比它重10倍的物体。热电元件的使用将机械手的响应时间减少到自然冷却的三分之一。

A novel manipulator system which has the features of light weight and rapid response has been developed using thermoelectrically driven shape memory alloy actuator.■The dependencies of recovery forces of shape memory alloy (SMA) on the temperature and restraining conditions were experimentally investigated. Mathematic model to describe the recovery force changes was proposed based on the restraining strain related stress distribution in SMA. To account the multiple phase domains during an inhomogeneous transformation in SMA we introduced independence phase fraction into the model, so that the mechanical behavior of SMA actuators in a real thermal ambience was able to be simulated. The model has been proven valid for the control of mechanical output of SMA actuators with temperature inputs.■With the similar concept a model to describe the free deformation behavior of SMA actuators was established with the dependencies on the hysteretic changes of both the temperature and phase transformation being taken into account. In consequence, the free deformation of SMA actuators was able to be controlled by the temperature control.■SMA manipulators driven by thermoelectric elements were prototyped. A closed-loop control of the temperature in SMA was developed. With the PID temperature control the overshoot and the steady-state error were sufficiently small, leading to the precise mechanical outputs like free deformation and grasping forces. The finger-like manipulator can grasp subjects of 10 times as heavy as its weight. The use of thermoelectric elements decreased the response time of the manipulator to one third of that in natural cooling.