Saskia Baltrusch

124 Chapter 5 Table 1: Range of motion of the hip, lumbar spine and the combination of the two: trunk angle [35]: The definitions of the flexion angles (*) are shown in Figure 2A. Note, 33% of the trunk flexion (Figure 2A (c)) originates from the lumbar spine (Figure 2A (b)). Kinetic Requirements Due to its location at the base of the back, the peak torque in the human spine is generated a the lumbo-sacral joint (L5-S1). Biomechanical linked segment models [31] suggest that peak torques of up to 254 Nm are generated around L5-S1 while lifting a load of 15.7 kg. Especially in the design of a passive exoskeletons, any attempt to compensate for the full dynamic torque at L5-S1 would lead to an exoskeleton that hinders its user most of the time. Therefore, designers often decide to compensate for a fraction of the full dynamic torque, which ranges typically between 20 and 30 Nm for purely passive devices [19]. More complex, optimization based models indicate, that torque requirements for a passive back support exoskeleton could be as low as approximately 20 Nm [32]. However, the toques of an active system for the lumbar spine and hip are significantly higher. In the optimization, the active torques were saturated to 67 Nm. 2.2 Concept Based on the requirements above there were two main design goals: kinematic compatibility and the support torque in the same order of magnitude as in passive back support exoskeletons of approximately 20–30 Nm, should be transmitted. Here, first the concept for the spinal part is described, followed by the concept for the hip part.