A sizing and grading method for better footwear fit and comfort

Abstract

Footwear has been developed and improved through the long human history. Nowadays, footwear not only provides basic protection and support function for the foot, but also reflects other characteristics related to the designers and wearers, for example, fashion and culture. Different types of footwear may have different emphasis on function or aesthetic aspects; nonetheless, as wearable products, fit and comfort of the footwear is among the most important customer needs. The definition of fit and comfort is rather complicated and involves various factors in both subjective and objective aspects. One of the concepts related to footwear fit and comfort is the compatibility between the foot and the footwear, which can be analysed through the dimensions and shapes of the foot and the footwear. The dimensions and shapes of the foot vary with multiple factors, including gender, age, ethnicity, and influenced by load and environment. The dimensions and shapes of the footwear are determined by shoe lasts, which are decided by sizing and grading systems. Similar to the variation of the foot sizes and shapes, the sizing and grading systems also vary in countries and regions with different standards and rules. The lack of unification results in confusion in footwear production and consumption. Moreover, the foot measuring methods and tools have been rapidly developed in past few decades, from 2D anthropometric easements to 3D scanning and modelling, yet current sizing and grading rules are mostly based on past empirical experience in the industry. Although recent research provides several possible improvement directions for sizing and grading, work still needs to be done to build a scientific and practical system that can be adopted in industrial production. This research aims at developing a scientific footwear sizing and grading method based on 3D foot scanning data. During this study, 3D foot data of 505 Chinese female participants were analysed in total. The data were scanned by portable 3D scanner (Microsoft Kinect) and processed with point cloud editing software and Matlab. Models were created for three different sizing and grading methods to calculate their average errors: the traditional anthropometric sizing and grading methods, methods using Principal Component Analysis (PCA) for sizing and grading, and methods using anthropometric sizing and PCA grading, combining the 3D analysis with traditional measurements to build a more practical method. The errors were used to evaluate the accuracy of the sizing and grading systems, which indicated the corresponding fit and comfort of the systems. The influences of different shoe styles on the sizing and grading were also analysed by composing the errors within different foot regions. Results showed that the anthropometric sizing and PCA grading method has satisfying performance under heel centreline alignment, and can provide better fit and comfort than the traditional method. The analysis on the three styles also indicated that the compatibility between the foot and footwear is easier to achieve at the lower region near the sole, than the instep and ankle part. This research combined the modern 3D technology with the traditional foot measurement rules to evaluated and developed the new sizing and grading system. The scientific analysis based on the 3D modelling on the foot shape and dimensions helped achieve better fit and comfort, considering different shoe styles.