Vast DOF Wet Shape Memory Alloy Actuators Using Matrix Manifold and Valve System

Abstract

A system is presented for allowing a large number of fast and powerful actuators to be placed within a compact volume. Shape Memory Alloy (SMA) wires on the order of 0.25 mm in diameter are embedded within a large array of compliant, fluid-filled vessels on the order of 1 mm in diameter. The SMA wires are contracted using resistive heating. However, the fluid flowing through these vessels allows the SMA wires to be rapidly cooled by convection without adding too much weight to the system. Thus the power to weight ratio is still higher than conventional actuators (i.e. greater than 1kW/kg) while the speed of response is significantly higher (greater than 1 Hz) than is normally achievable with dry SMA actuators. By arranging these wet SMA actuators in a two-dimensional matrix, the electric current and fluid flow can be controlled by one-dimensional manifolds of electric switches and fluidic valves located at either end. For a system with N2 actuators, only 2N switches and valves are required, thus making the system easily scalable to a vast number of actuators. This paper presents the design and experimental analysis of a prototype for this system, which contains 16 actuators in a volume measuring only 100 mm × 100 mm × 200 mm. Tendon cables can be attached to each actuator to distribute the actuation to the various extremities of a robot or machine. Each actuator is capable of up to 8 mm linear stroke, generating a force on the order of 10 N. The force can be increased by using a thicker SMA wire or by connecting multiple actuators to a tendon cable in parallel. Even though the actuators are located physically in parallel, they can be connected to a tendon cable in a mechanically serial configuration in order to increase the total stroke by up to 8 times. Although the matrix manifold and valve (MMV) system allows only a subset of the actuators to be addressed simultaneously, this system would be ideal for robots or machines where the number of actuators required is large but only a fraction are needed at any given time.