Evaluation of Helmet Comfort Based on Flexible Pressure Sensor Matrix.

The helmet comfort has been a focus in infantry equipment fitting evaluation, and has not been solved well for decades. In order to evaluate the stability and comfort of helmets, this paper proposed a novel helmet comfort evaluation method, combined with quantitative analysis and subjective rating. We demonstrated the helmet pressure acquisition system, and we also presented the data analysis and display system. Helmet pressure data between the skins of the wearer and the cushion pads lying in the helmet inner liner was collected by using a pressure headgear, which was composed by a matrix of flexible pressure sensors. The system includes the head pressure sensing matrix composed of more than one hundred flexible pressure sensors, pressure data analysis and display module, and helmet comfort evaluation module. We carefully chose the head model according to the latest anthropometry industrial standards, in which the head dimensions were illustrated in details. We used Geomagic, a popular re-engineering soft package in computer graphics, to construct the head model on which we would put the pressure sensing matrix. The original resistance values of the pressures were transferred by A/D conversion circuit from analog to digital numbers and then output to the data analysis module. In this way, the pressure data of each sensor in the helmet inner liner was collected. We asked several experts to rate the helmet comfort and then used Analytic Hierarchy Process (AHP) to calculate the final comfort score. In the criterion layer of AHP technique, we proposed four criteria, i.e., duration-related metrics, pressure amplitudes, pressure distribution and pressure stability. Finally, the pressure distribution image was showed on the computer by using the Graphic class in C#. Experimental results showed quite good agreement between our evaluation score and the subjective feeling of the subjects. The proposed technique makes the pressure data measurement more intuitive and efficient, and it is quite convenient to analyze and evaluate the factors affecting the ergonomics of the helmet, to optimize the safety and fitting of the helmet rationally. It's also expected to expand this technique in other human body wearable products, such as goggles, glasses, ear-phones and neck brace.