Calculation of Human Arm Stiffness using a Biomechanical Model

A novel hand-arm system (HASy), being developed in DLR as an anthropomorphic system, requires as an input parameter the realistic instantaneous joint stiffness of human upper limb in different postures and movements. Because muscles in our musculokeletal system are the active component (actuator), joint stiffness is driven by muscle stiffness. In this thesis, the theoretical fundamentals in extracting skeletal muscle stiffness from Delft ShoulderElbow Model (DSEM), a 3D finite element model of human upper limb, are presented in this thesis. The basics of musculoskeletal biomechanics and also skeletal muscle properties were studied in order to understand the arm stiffness, especially the skeletal muscle stiffness. In order to complete the discussion of human arm stiffness, the three parameters contributing to arm stiffness, namely the end-point stiffness, the joint stiffness, and the muscle stiffness, were reviewed and their relationship with each other is discussed. Firstly, the mapping from muscle stiffness to joint stiffness will need to be done because HASy requires the joint stiffness value. Second, the most available arm stiffness research deals with end-point stiffness. Thus, knowing the corresponding end-point stiffness from the calculated muscle stiffness is good for future data validation. Finally, the potential applications of this study are proposed. This study has implication in both robotics and biomechanics fields. In fields of robotics, specific application in HASy and also the possible application in general robotics are discussed briefly.