Saskia Baltrusch

128 Chapter 5 Additionally, a wide range of sizes should be fitted. Based on a simple kinematic model of the human hip and the exoskeleton the workspace in the frontal plane is estimated. Anthropomorphic data from [30] and range of motion estimates from [35] are used to estimate the human workspace (Figure 2F and for more detail Figure S2). The kinematic equations are provided in the Supplementary Material. Previous research on misalignment compensation around the internal/ external degree of freedom of the hip indicated, that preventing the thigh cuffs from rotating around the thigh is challenging [16]. Especially, when additional compensatory degrees of freedom are introduced. The kinematic structure of the here presented exoskeleton allows for no rotation in the transverse plane, meaning the internal/external degree of freedom is blocked. However, because it is challenging to connect to the thigh in a way, that no rotation around the thigh axis occurs, we decided to use this to our advantage and implement the compensation of the internal and external rotation of the hip this way: the exoskeleton structure stays rigid and the leg rotates inside the not too much tightened cuff. The presence of large muscle groups and compliant tissues of the leg further simplify this approach. Next to the problem to compensate for misalignment, the fitting of the exoskeleton on the hip is essential, especially, if the exoskeleton should not be protruding. One mechanism, that can be used to accommodate a wide range of different waist to hip widths, is one that consists of three parallel joints in series (Figure 5B). Incidentally, this mechanism can also be used to compensate for a small amount of misalignment. In the design of a controlled-brake orthosis [36] and later in the Robomate [10] a similar structure is used. The difference to our design is though, that in our case, the three compensatory joints are placed above the flexion-extension joint (Figure 4). This allows us to use the mechanism additionally for fitting purposes and place the connection to the pelvis very close to the body. Further, this configuration avoids collisions of the exoskeleton with the leg, which could potentially occur for large abduction angles in the controlled-brake orthosis or Robomate exoskeleton. However, this approach also comes with potential disadvantages. By placing the typically actuated and somewhat heavy flexion–extension joint below the three hinge joints for misalignment, the weight of the structure tends to rest against the skin of the wearer. Exerting a compression force at the hip. This might become a source of discomfort, especially if the actuator is heavy. Therefore, in the presented