Multi-axial Coupling Effects in the Human Hand-Arm-System: The Influence of Grip and Push Forces on the Vibration Behaviour

The human hand-arm system (HAS) is excited multi-axially by hand-held tools, which leads to superimposed vibration loads. The state of research assumes that vibrations in the HAS act along one axis without influencing the orthogonal directions. However, it also suggests that there are coupling effects between the directions of the HAS, but there is still a lack of studies on this topic. In addition, grip and push forces, which vary during the use of hand-held tools, affect the vibration properties of the HAS to different degrees in certain frequency ranges. The aim of this investigation is to analyze the vibration behavior of the HAS in the directions orthogonal to the direction of excitation, taking into account varying grip and push forces. For this purpose, an experimental study was carried out on six subjects with four levels of grip and push forces. The results show that a single-axis excitation along the lower arm causes a multi-axial vibration response of the HAS. The vibration behavior orthogonal to the excitation direction differs both from each other and from the behavior with direct excitation. The vibration behavior measured in the orthogonal directions is dependent on grip and push forces. ... mehrThe results indicate a complex, non-linear coupling of the axes of the HAS, which should be addressed in existing studies to realistically assess the vibration load of hand-held tools. With these findings existing models of the HAS, which are only valid in the direction of excitation, can be extended to include coupling effects. This allows 3D models of the HAS to be developed, which can be used to predict and analyze hand-arm vibrations.