Biometrics in wearable products: Reverse Engineering and numerical modeling

The Reverse Engineering (RE) techniques and the Finite Element Modelling (FEM) are widely used tools in many scientific fields. They were firstly developed for the mechanics but in the last times became common for other disciplines. In the thesis these techniques are used for the customization of the wearable products. It is possible to observe that the geometry of whatever wearable product is fundamental for the comfort. In particular, starting from the need of wearable product it is possible to analyse the relative body part and to study the products most appropriate interface geometry to maximize the comfort. The related disciplines are biometrics, biomechanics and anthropometry. In the thesis four different non-contact RE techniques are taken into account: shape from stereo, shape from silhouette, shape from laser and range finding. The first instrument which has been developed is based on the multi stereo vision, focusing the attention to the data filtering and to the generation of the solid model represented by mesh. The second instrument is based on the model generation starting from the silhouette. These two techniques are compared to another laser instrument available on the market. The tolerance on the reconstruction give an error on the total length of the foot of about 2 mm. The tolerance is acceptable for the study of a footwear product anyway it is not sufficient for a scientific research. For this reason a fourth RE system based on range finding is studied. A lot of possible methods were analysed, the multifrequencies, belonging as Fringe Projection Profilometry (FPP) group, has been considered the best compromise between precision, accuracy and elaboration times. An instrument has been developed which in few seconds performs the reconstruction using common, cheap products such as a projector and a camera. The use of the aforementioned RE techniques allowed to adequately reconstruct the geometrical model of the foot, then the deformation of the foot is studied using a Finite Element Analysis (FEA). A model characterized by nearly 200000 elements has been developed. The deformations are congruent with literature data. Anyway, considering the complex validation process of the FE model, caused by the difficulties on measuring the real displacement of the foot under loading condition, a direct matching between the acquired geometry and the final shape of the wearable product has been preferred. A function, capable to analyse the fitting between foot and shoe, through a coefficient called comfort index has been developed.