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

Flexible Fingers Based on Shape Memory Alloy Actuated Modules

To meet the needs of present-day robotics, a family of gripping flexible fingers has been designed. Each of them consists of a number of independent and flexible modules that can be assembled in dierent configurations. Each module consists of a body with a flexible central rod and three longitudinally positioned shape memory alloy (SMA) wires. When heated by the Joule eect, one to two SMA wires shorten, allowing the module to bend. The return to undeformed conditions is achieved in calm air and is guaranteed by the elastic bias force exerted by the central rod. This article presents the basic concept of the module and a simple mathematical model for the design of the device. Experimental tests were carried out on three prototypes with bodies made of dierent materials. The results of these tests confirm the need to reduce the antagonistic action of the inactive SMA wires and led to the realization of a fourth prototype equipped with an additional SMA wire-driven locking/unlocking device for these wires. The preliminary results of this last prototype are encouraging

Three-Fingered Gripper with Flexure Hinges Actuated by Shape Memory Alloy Wires

A three-fingered gripper with flexure hinges actuated by shape memory alloy (SMA) wires was designed and prototyped. The aim of the work was the manipulation of small, almost cylindrical objects, e.g. test tubes, by a device having small overall dimensions. A parametric study of four different, but similar, fingers was conducted with the aim of obtaining a solution with a good amplification ratio and a gripping force almost constant during closure. The use of flexure hinges simplifies the design, but limits the finger range of motion. Moreover, it was possible to find a configuration with sufficient work space. Once the finger geometry was defined, the whole hand was then designed with the aim of producing a compact hand contained in a cylindrical volume (d 65 x h 65 mm), and the first prototype was built. Preliminary tests demonstrated its good dimensioning and the success of some technological solutions. The experimental transmission ratio was almost the same as the theoretical one. Some drawbacks have been highlighted, such as a reduced range of motion and incomplete backstroke; future studies will deal with them