3D Modelling Of Customized Lasts Based On Anthropometric Data Acquired From 3D Foot Scanning - One Study Case

Abstract

Designing and manufacturing personalized lasts are the first steps in obtaining the right fitted footwear for various users, especially for sport or/and medical purposes. The accurate dimensional relationship between foot and last represents the key element for this activity. The critical shape of the last should always be determined by the shape of the foot and the cumulative relationship between lengths, widths, heights and girths, whatever method is used, Some corrections and constraints must always be considered because the shoe-last is not identical to the foot. The foot anthropometric measurements are modified based on biomechanical constraints and technological limitations and they are interactively transformed into last’s dimensions by using 3D modelling. The present study brings together the modern scanning technique with the new methodology for modifying a reference last, and it is aimed to explore the philosophy of re-designing functional lasts. It also tests and highlights the limits of the actual methodology for shoe-last virtual prototyping based on anthropometric data acquired from one commercially available 3D foot scanning system.

1. Introduction

When purchasing footwear, consumers are looking for two main features: style and comfort. Footwear products that do not correspond dimensionally to the foot shape, and also do not take over the foot modifications while standing or walking, represent the main cause for prevalence and evolution of structural and functional foot anomalies (Dahmen R et.al. 2001, Williams A.E. et.al. 2011). Moreover, the health of the entire body, as well as the human performance, could be affected. Customized footwear for different uses, including the medical and sports ones, is an important market niche (Uccioli L. 2006, Jones J., and Wimpenny D. 2009). Personalized footwear based on customized lasts could solve some of the foot problems related to sizing, poor fitting or perceived a lack of comfort (Lee Au E.Y. et.al 2011, Liu S. et.al 2011, Luximon A. et.al 2012).

The footwear shape and its inner space are both influenced by the shape and dimensions of the technological lasts (Chung-Shing W., 2010). Often, several physical prototypes that go through a series of adaptations and adjustments are required. The virtual prototype can be created, analysed and modified long before producing a physical prototype. This technology diminishes the time for testing the physical prototype; also other designing problems may be resolved in the virtual prototyping stage. The main advantages are given by reducing time and costs for trials of the new products (Wang Z. et all, 2009).

There is an increasing demand for industrial applications of systems digitizing the human body, and there are markedly available innovative solutions regarding affordable imaging techniques, such as laser scanners, multiple video cameras, motion capture systems or projector-camera sets. The 3D images are transformed into digital forms, and the process of designing new products includes new stages, such as modelling and simulation for the virtual prototype. Virtual prototyping suggests new opportunities both for researchers and for customized footwear businesses (Telfer S. and Woodburn J., 2010). While the manual measuring of the foot introduces errors caused by the skills of the person who takes the measurements, the automatic measurement from a scanning device could offer error-free data (Witana C.P et.al. 2006).

Nowadays, the lasts can be rapidly designed due to the recent developments in computer-aided design (CAD) technologies (Wang J. et.al 2011). The computerized method consists in the 3D modelling of the last; this method has the advantage of simulating the new shape before a physical last prototype is manufactured. When a last is interactively or/and automatically modified, the new changes are carried out while the designers visualize their models at every step; thus, the entire shoe-last designing process is less time consuming. Because of some limits in using commercially available CAD systems, most of the shoe-last designers still prefer manual methods (Luximon A., Luximon Y, 2009). The mixed techniques for designing new lasts use combinations between computer-aided designing based on modelling software and manual methods based on lasts construction type grouping and/or 2D templates (Sederberg, T.W. 1986). Regardless of the method, important design features determine how the required fitting conditions are achieved; also, the dimensional design restrictions should refer to the technological constraints of lasts manufacturing (Luximon A., Luximon Y, 2009).

Designing new lasts and re-designing existing ones are based on foot anthropometric. There are certain restrictive factors affecting the last’s shape and its dimensions: acceptable limits of foot tightening by footwear, modification of foot dimensions while walking (biomechanics), footwear constructive type, physical and mechanical properties of materials, and footwear manufacturing technology. Also, one has to consider the general design requirements of the footwear. The footwear is comfortable when, throughout its inner volume and dimensions, it allows the foot to achieve its protective, biomechanical and orthopaedic functions (Sikyung K. et.al 2007, Pastina M., Mihai A., 2010; Pastina M., Mihai A., 2011; Ionesi et. all, 2014).

2. Method

The paper presents one case study, but the hereby described method, as well as the developed methodology for analyzing the final results of the modelling process, can be replicated and applied for any new study case. The high degree of interaction between practitioner/designer and its computer, as well as the high level of customization are the main advantages of this re-designing process. Five working stages are considered in order to obtain the modified last: 1) scanning of the foot; 2) positioning of the anatomical points on foot; 3) measurement/calculation of the main anthropometric measurements; 4) comparison of the foot against the reference last; 5) modification of the last according to the foot shape.

3. Results

When wearing shoes, the foot is constrained to modify its shape and dimensions among certain admissible limits of tightening. The constructive dimensional parameters of last provide limits of tightening the foot by footwear. As a result, a lower level of tightening the foot by footwear that will reduce the risk of high pressures on concrete foot surfaces is one functional requirement in this study case (Andrews K.L. 2011, Dahmen R., et.al. 2001).

Table 1 shows the obtained data from 3D interactive modifications on dimensional parameters by following up nine successive steps. Each step is based on the results obtained in the previous step. When one parameter is modified, the entire range of the studied parameters is collected. While the modelling process advances, there can be determined paired relationships among sets of parameters that characterize the shape of last at each step of modification. Also, the set of dimensional parameters for the resulting last could be compared against the initial one.

The dimensional parameters of the last, both the interactively modified parameters and the outcome parameters have different values on successive steps of modification. For comparing on a common basis the range of variations (increase or decrease) for each parameter, following calculus has been considered:

Di = (Pi/Pi-1–1) * 100 (%), (1)

Where:

i –step of modification, i = 1, 2, 3, 4, 5, 6, 7, 8, 9

Di –increase or decrease of modified parameter on step i,, in %

Pi –value of modified parameter on step i, in mm

Pi-1 –value of modified parameter on step i-1 (previous step), in mm

Di variations are calculated against the previously obtained values; thus, the dependencies between two successive modified lasts can be progressively noticed and quantified. Additionally, after the final iteration is performed (corresponding to the 9th step), the variation is calculated with the same relation (Eq. 1), by comparing final obtained parameters with parameters of the reference last.

Because the order of modifying the last was empirically established, a mathematical method is proposed by the authors using a DSM matrix. The right method will be the one in which the last’s parameters are closer to the scanned foot.

DSM matrix design was firstly described by Yassine in 1999, being developed and applied later in many fields (Mihai A. et al. 2009). In this type of analysis, three steps are followed:

1. The product is decomposed in elements and the relationships and connections between them are established;

2. The identified elements are written in the same order in a matrix. The connection between elements is marked inside the matrix;

3. The matrix is transformed using special algorithms in a low triangular shape by arranging rows such that the marked points are located close to the diagonal of the matrix. A specialized software facilitates and simplifies the procedure.

In our case, the algorithm used is the one A. Kusiak et al., developed in 1994 and available at: http://css.engineering.uiowa.edu/~ankusiak/process-model.html was used.

Based on the obtained results, the initial last will be modified respecting the order given by the DSM matrix. The results can be seen in the table below:

The results of the two methods, empirically one and DSM method are presented in the table below.

Comparing the results obtained in both cases, the empirical method and the DSM method, lower deviation from the initial last are obtained in the user defined order: SL > LW > BG > IUG > HH > HW > HC > TS > TT. Research is recommended to continue, for testing another order for the parameters.

All successive modifications on the empirical method are made considering the foot’s anthropometric measurements and the dimensional parameters of the reference last (Table 5). The result is an adapted last to the subject’s foot (Fig. 8).

4. Discussions

The relations between human foot and last is critical for designing new footwear, lasts or footwear bottom components as insoles, soles, orthoses, etc., as well as their manufacturing (Chung-Shing W., 2010). Lasts give the fitting volume and the inner dimensions of footwear. A last designed on empirical trials, without a scientific basis towards the consumer’s foot specific conformation, will lead to a less comfortable product (Lee Au E.Y. and Goonetilleke R.S., 2007). Furthermore, inappropriate footwear could cause irreversible changes on foot and/or on gait patterns (Wegener et al. 2011). The concept of shoe-last tailored to support foot’s modification during human body locomotion is not precisely and finally defined yet. Complete customization of lasts and footwear is still under development, but some promising results have demonstrated clear good practices of how CAD/CAM systems for simulations and modelling can be employed to bring innovative solutions in the footwear industry (Azariadis P. et.al. 2010, Ruperez M.J. et.al. 2010, Xiao M. et.al. 2011). Further research is needed to assess entirely customized lasts and customized footwear. The lack of information in this area still determines the designers to select the last just based on empirical approaches gained from previous experiences (Wang Z. et al, 2009).

The described method, as well as the developed methodology for analyzing the final results of the modelling process, could be replicated and applied for any new study case. In order to obtain the modified last, five working stages have been followed up: 1) scanning the foot; 2) positioning the anatomical points on foot; 3) measuring/calculating the main anthropometric measurements; 4) comparing the foot against the reference last; 5) modifying the last towards the foot shape.

The studied case refers to a subject (47-year-old, female, diagnosed with arthritis and incipient stages of Hallux-Valgus) having visibly identified foot problems that ask for a careful interpretation of the design features based on anthropometric data, biomechanics and orthopaedic requirements. Several initial stages of structural modification related with arthritic feet have been identified on this subject, especially in the forefoot area.

The obtained data from 3D interactive modifications on dimensional parameters follows up nine successive steps. Each step is based on the results obtained in the previous step. When one parameter is modified, the entire range of the studied parameters is collected. While the modelling process advances, there are determined paired relationships among sets of parameters that characterize the shape of last at each step of modification.

The dimensional parameters of the last, both the interactively modified parameters and the outcome parameters have different values on successive steps of modification.

Each modification on a parameter brings changes to the other parameters. The designer has to follow each change, so that at the end, the last will be proper to the subject’s foot. This research has indicated that modifying last’s parameters are not enough for designing a customized last, the relationship between parameter has to be taken into account. The limitation of this paper given by the fact that some foot area could be tightened while wearing a footwear product, and to know if these are acceptable, the subject has to wear a shoe designed on these specific lasts.

5. Conclusions

This research follows up an extended and integrated application on combining CAD techniques for 3D shoe-last modelling with 3D foot scanning and measuring procedures. Both 3D scanning and 3D virtual modelling in the practice of designing fully customized lasts for special purposes are analyzed and presented as grounded related results for further innovation and development on software applications in the footwear industry. The present study brings together the modern scanning technique with the new methodology for modifying a reference last through interactive 3D modelling. Thus, it aims to go deeply into re-designing process of functional lasts based on anthropometric data obtained from 3D foot scanning. This research emphasizes the necessity of reuniting various modelling methods and scanning techniques into a new common standardized approach that should make the data transforming process more easily and precisely.

Declarations

Ethics approval Not applicable.

Consent to participate All authors have approved to participate.

Consent for publication The manuscript is approved by all authors for publication.

Conflict of interest The authors declare that they have no conflict of interest.

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