Experimental testing of a modular flexible actuator based on sma wires

A flexible finger made up of three actuator modules based on shape memory wires (SMA) is experimentally studied in this research. A module is composed by few simple components: a plastic body and SMA wires. The body is a thin cylinder with a lower and upper base and two intermediate disks. Three equidistant SMA wires are longitudinally placed and allow the module to bend in any direction when one or more wires are actuated. The motion of the module is performed with the heating and cooling of the wire and the central rod exerts bias force, necessary to the stretching of the wire to the original length. Two test benches were built to perform both positioning tests and force tests. To evaluate the actuator workspace different tests were performed, with different power supply, heating and cooling time, actuation sequence. Force tests were performed with different distance between the undeformed finger and the obstacle. The results achieved with this first prototype are encouraging since the finger shows stable and correct operation. The planar projection of the workspace is a circle of about 30-40 mm of radius and exerted force is similar to mathematical model results (about 1 N at 5 mm). These results are encouraging, even though, probably due to manufacturing imperfections and frictions, the movement is not very regular along the various directions.