Saskia Baltrusch

129 Chapter 5 design, the two top hinge joints are equipped with torsional springs (Figure 5B). This prevents the relatively heavy flexion/extension joint from pressing against the hip. Additionally, the two spring loaded joints counteract the tendency of the entire mechanism, to go into a singular configuration along the leg. In order to extend the range of motion even further, especially for lateral bending and axial rotations of the trunk, a spring loaded slider along the leg is added (Figure 4).The three hinge joints in combination with the linear joint, leaves the flexion- extension joint floating on both sides (“dual floating”). Potentially, this allows the flexion-extension joint to self-align. 2.3 Mechanical Implementation In the following, the design considerations of the passive Spexor exoskeleton (Figure 4) are described in more detail. Specifically, the physical interfaces, the spinal module, the misalignment compensation mechanisms, and the torque source at the hip. Physical Interfaces The pelvis structure, which connects the hip and the spinal part of the exoskeleton, is a custom made carbon fiber frame by Otto Bock HealthCare GmbH, consisting of two separate L-shaped structures that are clamped in the back. The pelvis structure is therefore adjustable in width. The mechanical loading of the pelvis structure is considerable. In order to prevent too large torsion angles of the structure, additional clamping of the ends of the overlapping structures was added (Figure 5A). The shoulder interface stems from a modified backpack (Karrimor Panther 65). An aluminum structure was added to mount the ball joint and to prevent the backpack from introducing unwanted slack into the system. The thigh interfaces are modified orthotics parts from Otto Bock HealthCare GMBH. Spinal Module In order to achieve a spinal range of motion of up to 60° in the sagittal plane, several different mechanisms were considered. Attempts to scale a 3D-printed multi-segmental prototype to torques of 20-30 Nm proved difficult due to high friction losses [37]. Therefore, a new concept consisting of multiple continuous carbon fiber beams under bending loads was developed (Figure 5A). Advantages of the continuous beams include, that the overall structure is light weight, 5