Saskia Baltrusch

144 Chapter 5 5 Discussion A passive back support exoskeleton for industrial applications, that preserves the natural range of motion of the user was designed and tested. The exoskeleton uses misalignment compensation for both the lumbo-sacral (L5-S1) joint and the hip joint. We have demonstrated, that using flexible beams as a back interface increases the trunk range of motion by more than 25% (24.5°) compared to its rigid counterpart in the sagittal plane (Figure 11). With the flexible beams, the range of motion is only decreased by 10% (13°) compared to not wearing an exoskeleton at all. An average range of motion of 117° in the sagittal plane was measured in the prototype with the flexible beam as spinal interface. Compared to the design goal of 60° flexion-extension in the sagittal plane of the Robomate exoskeleton [10] that is an increase of almost 100% (57°). Encouraging are also the results, that an angle agreement between the exoskeleton and the human of more than 70% was achieved if the full set of misalignment compensating mechanisms is enabled (Figure 11). Meaning, that the angles of the exoskeleton are only around 30% smaller than the corresponding angles of the human. Of special interest here is, that both the lumbar and the hip angle are 30% reduced compared to the human angles. In this case, no literature values to compare to are available. The Back Support Muscle Suit is one of the few designs that also includes a flexion-extension joint for the lumbar spine [14]. However, no data was published on how big the contributions of these individual angles were, while wearing the device. The angle agreement results are especially striking, if we compare these results to the case of the rigid exoskeleton (Figure 11): The agreement between the lumbar angles is as low as one percent. Meaning, that the exoskeleton structure accounted for only one percent of the lumbar angle in the human. However, this discrepancy is to some degree compensated by the hip angle, which agrees by more than 90% in this case. For the overall trunk flexion however, the difference is still a 50% discrepancy between the exoskeleton trunk angles and the human trunk angle. The flexible exoskeleton structure produces a torque of up to 25 Nm, which places it in a similar range as state of the art passive exoskeletons such as the PLAD, which produces torque of up to 27.5 Nm. With the rigid aluminum tube as spinal structure, a torque of up to 40 Nm can be produced, however, at the