Design and rapid prototyping of a SMA based actuator

The geometry analysed in section 6.1, that had been optimized for another material and another type of actuation, shows few problems that make it unusable for the current project; the main features that must be changed to make it efficient for SMA actuation are:
* The maximum strain is too high for the current material; 2.5% ÷ 3% could be considered the maximum acceptable magnitude of the strain
* The element 3 in reference to figure 6.6 is affected by sensible P-Δ effects which cause instability
* The central element, which is used to close the gripper by hand, must be replaced by a place where locating the SMA actuating wire and a system that ensure the actuation of the mechanism

In addition to prevent these evident deficiencies, the optimization has the following goals:
* Maximize the pincers excursion
* Minimize the closure requirements in terms of force and displacements of actuation (since the SMA wires used can ensure a force of few kgf and their maximum axial deformation is about 3% of the total lenght of the wire)

As first step different geometries have been proposed and analysed in order to understand the relevance of each element and dimension of the gripper. Four different geometries have been proposed in this step of the design. The four proposals, illustrated in figure 6.7, are based on different mechanisms and are designed to maximize some features of the gripper. For each geometry few characteristic dimensions have been chosen and several analyses have been performed by varying them in order to build a relation between these dimensions and the features above-mentioned.