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

NSF/RCV-0413242仿生机器人系统固态形状-记忆-合金阵列执行器的分段二进制控制麻省理工学院麻省理工学院哈里·浅田提出了一种设计和控制形状记忆合金(SMA)执行器的新方法。形状记忆合金线材被分成多个线段，其热状态作为一组有限状态机单独控制。这种新方法不是向整个SMA焊丝驱动电流并基于模拟应变-温度特性控制焊丝长度，而是控制单个线段的二元状态(热或冷)，从而控制与加热线段的数量成比例的总位移，即奥氏体相。虽然SMA的固有特性具有高度的非线性和不确定性，并且具有明显的滞环特性，但是这种分段二进制控制(SBC)具有健壮性和稳定性，提供了类似于步进电机的特性。该项目的三个主要目标是：利用形状记忆合金固有的迟滞特性，开发出一种提高响应速度和功耗的有效方法。不是持续保持高温，而是将温度拉回到一个中间的“保持”温度，该温度大大低于奥氏体精加工(Af)温度，但足够高以保持奥氏体态。具有独立热状态的多个段的协调允许快速响应，即使对于粗的SMA线也具有零延迟时间。通过将形状记忆合金丝排列成二维阵列，将形状记忆合金丝的分段结构扩展到多轴致动器阵列。为了以协调的方式激活机器人机构的多个连杆，使用二维分割方法来简化和协调多轴控制。将该方法应用于五指机械手，利用Peltier效应热电器件对SMA丝进行选择性局部加热和冷却，利用10轴SMA执行器阵列，能够采取多种姿势。将组成一个由本科生(来自机械、电气和材料工程系)组成的跨部门研究团队来实施这一跨学科项目。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一门新的本科生机器人学课程中。

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.