Saskia Baltrusch

181 Chapter 7 of two passive elements, connected in series, with misalignment compensation mechanisms, that generate an extension torque around the hip and the L5S1 joint: 1) a pair of passive spring-based, hip joint actuators (MACEPPA 2.0) at the outside of the upper leg (Figure 1a) and 2) an elastic spinal module at the level of L5S1 and up (Figure 1b). The spring-based hip actuators were designed to be continuously adjustable. Each actuator can generate a support torque between 10 Nm and 30 Nm, hence total peak torque can reach 60 Nm (both sides). The pre-tension of the springs in the hip actuators can be adjusted to change the provided support torque. The spinal structure comprises a ball joint, a linear slider and elastic carbon fiber beams. By adapting the thickness and number of beams, the stiffness of the spinal module can be adjusted. With three beams with a diameter of 4.7 mm, the current spinal model can generate peak torques of up to 50 Nm. Figure 2 presents the angle-torque relationship of both actuators, measured in a previous study [23]. An additional feature of the exoskeleton is the implementation of a clutch (Figure 1c), which can be switched on and off. If switched on, the clutch engages the springs in both hip actuators. If switched off, the actuators stay unengaged and do not provide a support torque to the user, allowing for unobstructed hip flexion. Figure 1 : The SPEXOR exoskeleton was designed to reduce peak and cumulative load on the low back by providing an extension moment around the low back with the help of two passive, in series connected elements: two spring-based hip actuators (a) and an elastic spinal module (b). The implemented clutch allows disengagement of the passive hip actuators (c). 7