Saskia Baltrusch

130 Chapter 5 compact and comparatively simple. However, one of the main disadvantages is, that excessive loading breaks the beams. The peak stresses occur at the base of the beam, therefore special attention was payed to the fixation at the base. The beams are clamped in a structure made out of 3D printed ABS plastic embedded in an aluminum structure. At the base of the structure, the ABS plastic is modeled in such a way that the plastic follows the bending curve of the beam. The active length of the beam can be individually adjusted to the size of the user. The beams are cut to a length of 600 mm and are 4 mm in diameter. Three beams in parallel are used to provide a torque in the range of 30 Nm (Figure 5A). In order to dimension the beams, linear and non-linear models were used. The linear model follows a text book approach and is described in the following. Readers interested in the non-linear models are referred to [38]. Figure 5: Elastic spinal module (A) . Three carbon fiber beams (D = 4 mm) provide the necessary flexibility to allow for the required range of motion, while providing a restoring torque when bent; Three parallel hinge joints (B) . This mechanism is on the one hand used to compensate for misalignment and on the other hand to provide a good fit. Torsional springs are mounted on the top two joints to avoid singularities and increase comfort; Misalignment compensation mechanism hip and torque source hip (C) . The torque, that is generated by the actuator is transmitted through the misalignment compensation mechanism.