Design and fabrication of an innovative active bending articulation based on shape memory alloy wires

As a result of their unique manipulability and scalability, continuum robots are used in challenging areas such as medical, industrial inspection, and repair. The mechanical structures, conventionally adopted for the realization of endoscopes, consent the continuum robots to modify their structure in complex shapes without the aid of joints or rigid links. However, their actuation is made complex and often not efficient because bulky actuators are used compared to the total dimensions of the robot. Some examples may be the numerous motors needed to pull the cables that act as tendons for tentacle arms or compressors to produce compressed fluid and the activation of the soft pneumatic or hydraulic system. The integration of Shape Memory Alloy wires as actuator elements into the moving structure represents a promising approach to the miniaturization of robotic endoscopic structures.

In this paper, a novel endoscope concept based on SMA wires is presented. It consists of a modular expandable structure able to bend with constant curvature in all spatial directions. To achieve complete mobility freedom, a minimum number of three SMA wires symmetrically arranged is required. The bending motion along the robot length follows an elastic deformation pattern dictated by a neutral core. The modules designed for the articulation are coupled to each other and generate an elementary movement between them and, consequently, a localized flexing of the core. After the manufacturing of the modules and their assembly, a high bending angle relative to the length is observed.