In order to produce the first prototype, a 3D model of the device was designed by using a 3D CAD software. Each tube of the structure was modelled according to the above-defined dimensions. All of them had transversal section as described for FEM model, except for those inserted in the tips, which were smaller (external diameter of 26 mm) and presented four vertically equidistant holes on their lateral surface, in order to create a telescopic joint for the regulation of the height of the walking frame. Then, joints were designed using relevant angles according to the results of the FEM simulation (Figure 1a). Tips, showed in Figure 1b, are characterized by a no slip surface (Figure 1c). The non-slip feature was obtained by designing grooves (which increase the contact surface under pressure) in order to make tips able to provide enough friction forces. The height-regulation mechanism, showed in Figure 1d, is based on a flexible ring and a pin, which fits the hole properly made on the leg-tubes of the device. Handles were designed in an ergonomic way (figure 1e). Each of them was modelled to be fabricated in two half pieces connectable by specific bolts, in order to simplify its assembly on the relative tube.

_{Figure 1: CAD model of (a) the 3-entry joint designed with “ad hoc” angles, (b) tip with grooves, (c) non-slip terminal part for the tip, and (d) half of an handle, with the UBORA logo}

The design of the various components (apart from tubes) were optimized to be 3D printed using the Fused Deposition Modelling (FDM) technology. Relevant dimensions are provided in Figure 2 and Table 1.

_{Figure 2 - Walking frame CAD model}

_{Table 1 - Relevant dimensions for frame components}