**7. Discussion**

The need to create flexible and versatile gripping hands has led to the creation of a flexible module operated by SMA wires, which can be the basic "brick" with which to assemble many different solutions.

A simple mathematical model was implemented with the aim of theoretically describing the behavior of the device and evaluating its working space.

Based on the results obtained, three devices with the same geometry were developed using three different materials. Experimental tests were conducted on these three prototypes, which allowed the evaluation of the workspace and highlighted some advantages and disadvantages. The working space of prototype A proved to be adequate, but the module was damaged at some points due to the low melting temperature of the nylon. With prototype B, this limit was avoided because the PTFE the central module was made of has a high melting temperature. However, despite a similar nominal elastic module, it showed a reduced working space. Therefore, by accepting an increased difficulty in assembling the module, a solution was conceived, thanks to which large working spaces were obtained and no overheating problems were encountered. This solution (prototype C) involved the use of different materials for the disks and for the central shaft, respectively in PEEK1000 and LIM, but a limitation was introduced by the difficulty in returning to the undeformed condition and a consequent non-repeatability of the tests.

Prototypes B and C were also tested for the evaluation of the influence of the presence of inactive SMA on the work space amplitude, conducted by simply removing these wires and verifying the bending of the central module along the main and secondary directions in the presence of one or two active wires. The results of these tests led to the design of a further prototype. Here, in prototype D, each module had a device for locking/unlocking the SMA wires, governed in turn by an additional SMA wire. Results from the tests on this last prototype are encouraging because its workspace was greater than the workspace of the prototype without a locking/unlocking device.

However, further improvements could be obtained by reducing the sliding friction observed in the new device and by solving some pre-tension and alignment issues. The former could be reduced by taking into consideration other materials for the realization of the gripper/cylinder coupling having a lower friction coefficient, and having greater care for surface roughness. The latter are being resolved through the implementation of appropriate assembly equipment.

**Author Contributions:** Conceptualization, D.M. and T.R.; methodology, D.M. and T.R.; software, D.M.; validation, D.M.; writing—original draft preparation, D.M.; writing—review and editing, D.M.; supervision, T.R.

**Funding:** This research received no external funding.

**Conflicts of Interest:** The authors declare no conflict of interest.
