Development of a novel manipulator system using thermoelectrically driven SMA actuators

利用热电驱动的形状记忆合金驱动器，研制了一种重量轻、响应快的新型机械臂系统，实验研究了形状记忆合金恢复力随温度和约束条件的变化规律。基于形状记忆合金中约束应变相关的应力分布，建立了描述恢复力变化的数学模型。为了考虑形状记忆合金非均匀相变过程中的多相区，我们在模型中引入了独立相分数，从而能够模拟形状记忆合金致动器在真实热环境中的力学行为。该模型对具有温度输入的形状记忆合金作动器的机械输出控制是有效的，利用相似的概念，建立了描述形状记忆合金作动器自由变形行为的模型，该模型同时考虑了温度和相变滞后变化的相关性。因此，可以通过温度控制来控制SMA执行器的自由变形。提出了一种形状记忆合金温度的闭环控制方法。采用PID温度控制，超调量和稳态误差足够小，实现了自由变形和抓持力等精确的机械输出。这个手指状的机械手可以抓住重量10倍于其重量的物体。热电元件的使用将机械手的响应时间减少到自然冷却时的三分之一。

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.