Equipping New SMA Artificial Muscles With Controllable MRF Exoskeletons for Robotic Manipulators and Grippers

Shape memory alloy (SMA) wires are one of the widely used materials for soft artificial muscles. However, SMA artificial muscles have two problems, including limited load holding ability due to their soft nature and slow response due to their long cooling time. The main contributions of this article are the developments of a controllable magnetorheological fluid (MRF) exoskeleton and a fast-response magnetorheological elastomer-SMA artificial muscle as effective approaches to solve the above-mentioned problems. The controllable MRF exoskeleton provides variable stiffness so that it can be flexible enough to allow the manipulator to bend as required while stiff enough to hold up heavy loads. This new artificial muscle accelerates the cooling speed of SMA wire to shorten its recovery time. Our tests proved that this new artificial muscle, compared with conventional SMA artificial muscles, could improve the recovery speed by up to 333%. The new artificial muscle and the MRF exoskeleton assembled a robotic manipulator and then a robotic gripper with three of those manipulators. The experimental tests verified that the loading capability of the new gripper had increased by 440% compared to the pure SMA gripper.