Wet SMA Actuator Array With Matrix Vasoconstriction Device

Abstract

A new mechanism for controlling arrays of Shape Memory Alloy (SMA) muscle wires has been developed. Similar to previous work, SMA wires on the order of 0.25 mm in diameter are embedded in a network of compliant fluid filled vessels on the order of 1 mm in diameter. Hot and cold water are delivered through the vascular network to convectively heat and cool the SMA muscles, causing them to contract and extend. By arranging the muscles or actuators in a 2D array, n2 actuators can be controlled using 2n valves, where the valves control the flow to and from rows and columns of actuators. However, unlike the previous Matrix Manifold and Valve system (MMV), the fluid flows to the actuators are now controlled using a Matrix Vasoconstriction Device (MVD). The MVD is capable of constricting combinations of the vessels, which are arranged in rows and columns. The MVD does not introduce any fluidic resistance to the network until constricted, allowing for larger flow rates and faster muscle cycling. The MVD system architecture also removes undesired dynamic effects stemming from fluidic capacitance which were suffered by the MMV. An array of 16 muscle wires has been experimentally implemented using an MVD with 8 control inputs. The MVD has been constructed in a 50 mm × 50 mm × 60 mm volume, and the overall length of the actuators is 500 mm. The system will drive each SMA wire at a rate of 2 Hz with a force of 10 N and a stroke of 10 mm. The system could control a robotic hand with up to 16 DOF and fit within the size of a human forearm.