Saskia Baltrusch

121 Chapter 5 Kinematic compatibility in the frontal and transverse planes should also be considered. The Laevo system incorporates rotating elements in the chest pad, which to some degree fulfill the function of a differential transmission. The alignment for the legs is provided through the elasticity of a belt behind the waist. In comparison, the Robomate exoskeleton features more elaborated misalignment compensation for the hip, consisting of two hinge joints and one ball joint [10]. The same compensation mechanism is used for the trunk [10]. The BNDR does not include any mechanism to account for kinematic compatibility [11] other than the hip joints consisting of torsional springs. For the WMRD exoskeleton it is not clear, if any additional compensation mechanisms are integrated at the hip joint [12]. Two different models of the BackX exist, the model S and AC. The model S is similar in structure to the BNDR but features an additional adduction/abduction joint. The model AC, which features a rigid waist belt, also has an adduction/abduction joint and on top of that a joint at the base of the back structure to allow for lateral bending. A rotational joint at the top of the support strut enables axial rotation in the transverse plane. Soft, suit like structures have a relatively long history in back support devices [19]. The Personal Lift Augmentation Device (PLAD) was one of the pioneers in this field [19]. Like other exosuits, the forces are transmitted in tension only and no weight bearing structure parallel to the human exists. While the lack of rigid mechanic structures greatly enhances kinematic compatibility, the range of motion can still be a challenge [19]. Other devices, that use suit like structures are the Smart Suit Light (SSL) [20] the Passive Spine Exoskeleton [21], and the waist assist suit AB-Wear [22]. However, Inose et al. (2017) [22] raised concerns that their waist assist suit AB-Wear, without any rigid structure, might generate unwanted compression forces. To avoid these compression forces, they updated their design to include a flat spring mechanism in the back as a load bearing structure. As the mathematical model from Abdoli-Eramaki et al. (2007) [19] shows, suit like structures are able to reduce compression forces, as long as the force application of the suit occurs with a bigger lever arm, than that of the back muscles. However, the potential to reduce spinal compression forces is bigger, if an external, load bearing, “rigid” structure is present and thereby forces can be applied perpendicular to the back rather than tangential. 5