High speed stereo visualization of hair-skin dynamics

Philips has a huge electric shaving market and in order to compete at the fore fronts, the shave needs to be as close as possible without compromising on the comfort of the customer. Hair and skin manipulation (HSM) are vital factors that prepare the skin and hair for a smooth and efficient shave. While several efforts have been laid down in quantifying the 'closeness' in shave or to find the exact length of the beard before and after shaving, the most popular and confident approach has been a simple user perception. In order to obtain a more confident number it is required to build an optical setup which can both qualitatively visualize and quantitatively derive 3D data to assess the HSM process. Thus the work described in this project is towards the design and construction of an opto-mechanical setup that can simulate the shaving process and simultaneously capture high-speed videos of the HSM process happening on the beard. Stereo imaging with two high speed cameras was chosen as the working principle of the setup such that it is suitable to extract 3D data from the hairs. Semi automatic software helps in manually detecting the coordinates of the hairs and through it, its length and its angles with respect to skin. The entire setup is calibrated with a dummy hair-skin phantom and an error analysis is done to determine the accuracy of the set up. In house manipulation concepts were put together as six module geometries each with varying parameters of interest. These modules were mounted on to the 3D setup and similar to shaving speed strokes were made on three regions of interest - cheek, neck and chin. A total of 40 single hairs were targeted (two strokes each) and experiments were done in unmanipulated state and in manipulated state by the modules to see the exact influence of the modules. The results show the best geometry of the module has 76% hair manipulation efficiency with an average hair lift of 108mum. While cheek is the best place for manipulation, chin is the toughest place as it is hard to follow contour in that region. It is found that the module does not have uniform contact with the skin and this affects the results as the hairs need to be attacked at their root level. Taking into consideration, only the most efficiently manipulated hairs the average hair lift is found to be 105mum and the average remaining stubble (virtual) would be -36mum. This project lays the foundation for accurately measuring the 3D data of a hair while manipulating hair and skin with close to shaving speed strokes. The setup can be adapted to several shaving systems to study their manipulation features. The project also provides us with knowledge on the current HSM module design and its possible extension in the future.