The skeleton of the walker is made of tubes linked together with specific joints obtained by FDM. Figure 1 shows the tubes are joint together.
Figure 1 - Walking frame CAD model
Each tube was laminated by assembling three different kind of layers (called skin) of carbon fiber composite. In particular (from the ext. to the int.) the choice was: 200 g plain 0°, 300 g unidirectional 0°, 414 g twill 45°, combination that allows to optimize the mechanical strength of the component according to the expected stress distribution. Laminating the carbon fiber requires to use a mold which is exactly the negative of the piece of interest and it was made of carbon fiber composite, too. After lamination, each component was cured at controlled temperature and pressure in an autoclave to ensure its stabilization.
Joints, the core part of the tip and the height-regulation mechanism (Figure 2) were 3D printed in ABSplus using a Stratasys Fortus 3D printer (FDM technology) available at the Bioengineering and Robotics Research Center E. Piaggio (University of Pisa).
Figure 2 - 3D printed joints (a), the core part of tip with the no slip terminal part (b) and height-regulation mechanism (c)
The handles (Figure 3a) and the terminal part of the tips (Figure 3b) were 3D printed in thermoplastic polyurethane (TPU) using the Creality cr10 3D printer (FDM technology).
Figure 3 - TPU printed components: a handle (a) and the terminal part of the tip (b)
All the printed parts were glued together with the tube using a resin-based glue which needs UV-curing to solidify. Fabrication phases with the students at work and the final prototype are shown in Figure 4.
Figure 4 - Fabrication phases with students at work and, in the bottom line, the final prototype