Analysis of 3-D human foot forms using the Free Form Deformation method and its application in grading shoe lasts

Abstract

An effective way to design well-fitting products is to analyse human body forms and to classify them into several groups. In the present study, a new method is proposed to analyse human body forms using the FFD (Free Form Deformation) technique. The FFD method is a way to deform the shapes of object smoothly by moving control lattice points set around the object. The reference body form is automatically deformed to coincide with the other body forms using the FFD method. The dissimilarity is defined by the movements of the control lattice points. The foot forms of 56 Japanese adult females were analysed with this method, and distributions for them were calculated using multi-dimensional scaling. The first axis contrasts feet with high dorsal arches and low dorsal arches, and the second axis is related to the antero-posterior proportion of the foot. As an application of the present method, a last of width EEEE was designed from an existing last of width E by applying the control lattice points that converted a representative foot of width E into a foot of width EEEE. The new EEEE width last reflected the allometric differences between narrow and wide feet better than one obtained by a conventional method. It was found that the present method with FFD is not only useful for classifying 3-D human body forms, but also has potential as applications for designing well-fitting products.

Automation of the shoe last grading process according to international sizing systems

“…Traditionally, the most frequently used measures for the determination of sizes were foot length and ball girth. However, different studies [4] have demonstrated that the increase in foot length and ball girth is not proportional. Furthermore, girth measures (ball, waist and instep) are largely correlated to each other and to other measures, except for foot length.…”

“…This approach did not describe in detail the equations employed to grade the last, but highlighted that the grading is performed proportionally. As mentioned above, several studies concluded that there is little correlation between length increase and ball girth increase [4], therefore, it would be necessary to analyse the results of the proposed method to check the adaptation of the resulting last to the user's foot.…”

“…Among them, there are systems that provide information to generate sizes according to certain morphological features of the foot [1,2] and others that automatically generate the last from a reference template [4,5,6,7,8,9] obtained by using a CAD tool or by 2D or 3D scanning.…”

“…Given that the latter dimension is established by polar coordinates, too large grading causes corner rounding, so it is necessary to produce a new master for every 3 sizes. Furthermore, feet do not grow linearly in all their dimensions, since the ratio between foot length and ball girth increase is really small [4]. Therefore, accurate techniques are required for the automatic generation of the various sizes starting from a base last and taking into account the morphological features of feet.…”

“…Therefore, accurate techniques are required for the automatic generation of the various sizes starting from a base last and taking into account the morphological features of feet. The latest CAD/CAM advances have led to different shoe last grading, design [4,5,6,7,8] and manufacturing approaches starting from the designed models.…”