Localization of center of gravity of helmet systems in the human anatomical frame using 3D laser scanners

Abstract

Introduction: An accurate assessment of the Center of Gravity (CoG) and mass properties of aircrew helmets and helmet-mounted devices is an essential requirement to predict neck injury potential. Conventionally, trifilar pendulum method is used for the assessment of CoG shift and calculation of force moment and mass moment. In this study, a new procedure is described to obtain a more precise measurement of the CoG of the helmet as well as the combined head and helmet system. Material and Methods: Measurement of the helmet mass and CoG properties was done using a trifilar pendulum and the geometrical properties of the helmet and head were obtained using a 3D laser scanner. The required coordinate transformations from the laboratory frame to the anatomical frame using the 3D scanner as a coordinate digitizer. The head sizes used in the calculations ranged from small female head to large male head and a single average head CoG position was used to calculate the combined head and helmet CoG. Results: The error of the 3D scanner method for combined head and helmet CoG measurement as compared to the trifilar pendulum method varied between 0.3 mm and 0.4 mm with an average error of 0.4 mm. This method could also successfully calculate the combined CoG of the helmet on various head sizes ranging from small female to large male heads. Conclusion: The 3D laser scanner-based CoG measurement gave similar results as compared to the present method of CoG measurement when the medium-sized anthropomorphic test dummy head was considered. The localization of helmet CoG in the anatomical frame would allow more accurate measurements of force moment and mass moment. The same methodology could also be used to calculate the combined head and helmet CoG of different head and helmet masses.