Segmented Binary Control of Solid-State Shape-Memory-Alloy Array Actuators for Biologically Inspired Robotic Systems

NSF/RCV-0413242固态形状记忆合金阵列致动器的分段二进制控制，用于生物启发的机器人系统H. Harry Asada，P.I.马萨诸塞州理工学院提出了形状记忆合金（SMA）致动器设计和控制的新方法。SMA丝被分成许多段，它们的热状态作为一组有限状态机被单独控制。代替驱动电流到整个SMA线和基于模拟应变-温度特性控制线长度，新方法控制各个段的二元状态（热或冷），从而控制与加热段的数量成比例的总位移，即奥氏体相。虽然形状记忆合金的固有特性是高度非线性和不确定性与一个突出的滞后，这种分段二进制控制（SBC）是鲁棒性和稳定性，提供类似于步进电机的特性。该项目的三个主要目标是：一个有效的方法，提高响应速度和功耗开发利用SMA固有的滞后。代替持续保持高温，温度被拉回到中间“保持”温度，该温度显著低于奥氏体结束（Af）温度，但足够高以保持奥氏体状态。具有独立热状态的多个段的协调允许具有零延迟时间的快速响应，即使对于粗SMA线也是如此。SMA线的分段架构扩展到多轴致动器阵列，通过将它们排列在一个二维阵列。使用二维分割方法来简化和协调多轴控制，以便以协调的方式激活机器人机构的多个连杆。该方法被应用到一个五指机器人手能够采取各种姿态与10轴SMA致动器阵列使用Peltier效应热电器件的SMA线的选择性局部加热和冷却。跨部门的研究团队的本科生（来自机械，电气和材料工程部门）将形成进行这个跨学科的项目。一名专门研究机器人执行器的博士生将把新的执行器技术和生物启发的机器人带到新的本科机器人课程中。

NSF/RCV- 0413242Segmented Binary Control of Solid-State Shape-Memory-AlloyArrayActuators for Biologically Inspired Robotic SystemsH. Harry Asada, P.I.Massachusetts Institute of TechnologyA new approach to the design and control of shape memory alloy (SMA) actuators is presented. SMA wires are divided into many segments and their thermal states are controlled individually as a group of finite state machines. Instead of driving a current to the entire SMA wire and controlling the wire length based on the analogue strain-temperature characteristics, the new method controls the binary state (hot or cold) of individual segments and thereby controls the total displacement proportional to the number of the heated segments, i.e. austenite phase. Although the inherent property of SMA is highly nonlinear and uncertain with a prominent hysteresis, this Segmented Binary Control (SBC) is robust and stable, providing characteristics similar to a stepping motor. Three major aims of the projects are:An efficient method for improving speed of response and power consumption is developed by exploiting the inherent hysteresis of SMA. Instead of keeping high temperature continually, the temperature is pulled back to an intermediate "hold" temperature that is substantially lower than the Austenite Finish (Af) temperature but is high enough to keep the austenite state. Coordination of the multitude of segments having independent thermal states allows for fast response with zero latency time even for thick SMA wires. The segmented architecture of SMA wires is extended to a multi-axis actuator array by arranging them in a two-dimensional array. The multi-axis control is streamlined and coordinated using a two-dimensional segmentation method in order to activate multiple links of a robot mechanism in a coordinated manner. The method is applied to a five-fingered robotic hand capable of taking a variety of postures with a 10-axis SMA actuator array using Peltier effect thermoelectric devices for selective local heating and cooling of SMA wires.An inter-departmental research team of undergraduate students (from mechanical, electrical, and materials engineering departments) will be formed to conduct this interdisciplinary project. One doctoral student specializing in robotic actuators will bring the new actuator technology and biologically inspired robots to a new undergraduate robotics course.