## 2 Materials and Methods
### Mechanical Design
#### 2.3.1 Robotic Arm  
The robotic arm is composed of 12 modules of six different sizes as shown in Figure 4. All the modules have the same length, but are in six different profiles to withstand the load due to the weight of the structure and the tension of the cables. In Table 2, for each module are reported the mass \(m\), the \(x\)-coordinate of the centre of mass with respect to its frame defined by the DH parameters \(CoM_{x}\), the link length \(l\), width \(w\), and height \(h\), and the pulley radius \(r\). Each link is composed of four metal rods connecting two consecutive joints and of four pairs of cross tie-rods that increase the link stiffness. Each joint angular position, whose limits are \([-\pi/3,\pi/3]\) rad, is measured by an AkSim2 magnetic absolute encoder supplied by Renishaw. This sensor has a resolution of 18 bits with an accuracy of 0.0017 rad. Each cable is fixed on both sides to a linear actuator and, passing through rollers made with IGLIDUR A350 assembled around two pairs of metal rods, transfers the power to the module through the friction between the pulley and the cable itself. The cables are made of a synthetic fiber called Zylon PBO [32]. This material was chosen because the more commonly used steel cables suffer from a few drawbacks mainly related to their weight per unit of length, their bending radius and difficulties in making simple and effective anchoring solutions. Table 3 compares the main characteristics of steel and Zylon PBO cables of equal diameter, 3 mm, highlighting that Zylon PBO cables present higher payload and lower mass density with respect to steel. Keeping in mind the necessity to operate at high temperatures, it is also important to point out that Zylon PBO fiber can withstand temperatures up to 650 \({}^{\circ}\)C. To ensure an efficient connection between the cable and the actuator, an eye splice is used to place a permanent loop in the end of a cable. This is an efficient method to connect a synthetic fiber rope to a fixed point without degrading the performances of the cable, retaining almost 100% of the specified rope tensile strength [33]. The splicing of the cable is shown in Figure 5. The components chosen to build the robotic arm (Zylon PBO cables, communication and power wires, sensors, and modules materials) all tolerate temperatures up to 105 \({}^{\circ}\)C.  
The robotic arm structure was dimensioned starting from a static analysis considering the robot in the worst-case configuration, where all the modules are parallel to the ground, and a 1 kg payload applied on its tip. In this configuration, all the forces and constraint reaction forces acting on the arm were evaluated using FEM analysis to fully validate the design of the robot. The FEM analysis was performed on the 1 st, 6 th, and 12 th module of the robotic arm and estimated a maximum total deformation of 0.350 mm, 0.257 mm, and 0.036 mm, respectively. Figure 6 reports the results on the 1 st module, which is the one subject to the highest load: (a) shows the forces and constraint reaction forces acting on the module; (b), (c), and (d) show the corresponding total deformation from different points of view, with a deformation scale factor of 71. In Figure 6, **A** refers to the sum of the constraint reaction forces due to the successor modules and the weight force, **B** represents the axis on