Investigation of methods for quantifying sitting postures in cars

Abstract: Understanding and being able to quantify sitting postures is a central asset in car safety evaluations. This is due to the fact that passengers can choose a range of different sitting positions. Studying and understanding how passengers choose to sit to obtain some comfort is important for increased safety in futures cars and is particularly challenging facing a heterogeneous population. Data is also needed to improve the accuracy of virtual crash simulations. In addition, more recently the development of autonomous cars has made it important to be able to quantify how passengers choose sit as new behaviors may emerge when there is no responsible driver in the car. The aim of this master thesis has been to find a measuring method that measures the posture of a passenger in a car seat. Focus has been on the orientation of the passenger's pelvis as the interaction of this structure with the lap-belt is a central part of occupant restraint system. A literature review was conducted to gain knowledge of the ergonomic aspects of this project and to review the different technologies that could be used to quantify passengers' sitting postures. The requirements of the measuring method were defined, different technologies were tested and a few concepts were selected. The concept in focus was a 3D motion capture system developed by Xsens. It was tested in three different experiments on a total of 30 test persons. In the first experiment, the accuracy of the Xsens equipment was verified by comparing it to a recognized method used to measure sitting postures statically in cars. Results showed that the two methods corresponded well. In the second experiment, the possibility of determining the orientation of the passenger's pelvis when knowing the position of the shoulder and the knee was tested. Such a connection would have facilitated the quantification of sitting postures but could not be found. Results showed that the human body is interconnected in a complex way and that it is difficult to draw general conclusions that apply to all body types. In the third experiment, the Xsens equipment was tested during a drive. The equipment performed well in a dynamic environment but a compensation for the movement of the car is needed. To conclude, a measuring method that measures the posture of a passenger in a car seat was found and evaluated. It can measure the pelvic orientation. It is a precise method if the calibration is carefully done and the sensors stay in place.