3D MODELLING AND RAPID PROTOTYPING OF LASTS USED TO OBTAIN SPECIAL FOOTWEAR FOR PATIENTS WITH ARTHRITIS

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Timothy Grant
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1 3D MODELLING AND RAPID PROTOTYPING OF LASTS USED TO OBTAIN SPECIAL FOOTWEAR FOR PATIENTS WITH ARTHRITIS MARIANA PĂŞTINĂ 1, AURA MIHAI 1 1 Gh.Asachi Technical University of Iaşi, Romania, mpastina@tex.tuiasi.ro, amihai@tex.tuiasi.ro The aim of this study was to develop principles of 3D modelling of lasts used to obtain special footwear for patients with locomotion disabilities caused by arthritis. The design process and manufacture process of a personalized last are the first steps in achieving the right type of footwear for patients with arthritis. The footwear shape and dimensions are influenced by the last s shape and dimensions. A last that is designed without a scientific basis, without considering the consumer s foot individual conformation, will lead to an unsuitable footwear product. The compatibility between the foot and the last represents the key element for this kind of activity. Whatever method is used, the shape of the last is given by the shape of the foot and its dimensions (length, widths and girths). These foot dimensions are modified and transformed into last s dimensions using 3D modelling software. The advantage of 3D modelling procedure is that it allows us to interactively visualize and to modify the last according to the patient s scanned foot shape. After the last, perfectly adapted to a foot with arthritis, has been created, it can be exported and sent to a 3D printer. Here, a prototype will be obtained and it can be used to design other lasts or to make the footwear directly on it. Keywords: foot, arthritis, last, footwear, 3D modelling. INTRODUCTION When they purchase a footwear product, the consumers are looking for two main characteristics: footwear appearance and its dimensional comfort. The footwear that does not correspond to the foot shape and dimensions and does not take over/absorb the foot modifications that appear while walking is the main cause for prevalence and evolution of structural and functional foot anomalies. Thus, the health of the entire body is affected, too [1]. The notion of last s shape/dimension fitted to the foot is not well defined. Further research is needed to assess the last design and its industrial application in footwear industry. The lack of information in this area determines the footwear producers to select the last on empiric basis. By doing this, a lot of physical prototypes that suffer a series of adaptations and adjustments based only on designer s experience are required. The 3D scanning technologies and CAD solutions developed in the recent years allow us to reconsider the last s design process and provide both useful tools for designing personalized footwear and lasts [2, 3]. Arthritis patients frequently present foot modifications that lead to severe walk difficulties and orthostatism. The meaning of arthritis is joint inflammation and causes pain, stiffness, swelling, tenderness, redness, warmth in the joints. Any part of the body has the risk of been inflamed from arthritis. There are registered more than 100 forms of arthritis and rheumatism and the most common forms are: Osteoarthritis the most common form of arthritis; Rheumatoid arthritis, RA a type of inflammatory arthritis. Some of the major causes of arthritis are: age, heredity, overuse of a joint, injury, infection, tumor necrosis factor [4]. Foot problems appear in almost 89% of patients with rheumatoid arthritis and the important changes involve mechanical stress. The most known manifestations are hallux 283

2 valgus, valgus heel deformity and lesser toe deformities, causing severe foot pain and reduced mobility. In order to improve life quality of patients with arthritis and to relieve their pain, a palliative foot care, special footwear and orthotics are necessary [5]. Fitted footwear could solve most of the patients problems. Some clinical and practical observations regarding special footwear requirements for diabetic subjects have been registered: the material used for manufacturing must be soft, extensible, permeable, excluding synthetics; the inner joining seams must be avoided, especially in the affected area; the width must be larger; the toe puff must be higher and wider; the closing system must be adjustable; the insole must accommodate high plantar pressures; the insole cover must be detachable; the flexible sole and the orthopedic heel are used; the classic design is preferred; the high boots are recommended in case of ankle s instability [1]. METHOD Designing a new last is firstly based on foot anthropometrics and biomechanics. There are restrictive factors affecting the last s shape and dimensions: acceptable limits of foot tightening by the footwear, the modification of foot dimensions while walking, footwear constructive type, material characteristics, and footwear manufacturing technology. Also, we have to take care of the general design requirements of the footwear. The footwear is considered to be comfortable when, throughout its shape and inner dimensions, it helps the foot to achieve its functions. 3D Modelling of the Last Nowadays, two methods are used for designing the last: classic and computerized (3D). The classic method consists in designing and modelling a last by using 2D patterns and values of foot anthropometrics. The computerized method consists in 3D interactive modelling of the last; this method has the advantage of simulating the new last before its physical manufacturing. The development of computer techniques allows for using specialized software, like the ones of CRISPIN-DELCAM: OrthoLast, OrthoModel, OrthoDesign, OrthoTech. For this study, the Crispin-OrthoLast software has been used. The technique of transforming an initial 3D structure into a new one, named Free- From Deformation of Solid Geometric represents one of the graphic procedures which modify a 3D structure by moving the grid s basic points [6]. This method was used by Mochimaru et al., who highlighted the difference between two 3D shapes using a deformed test grid. Two structures described by normal shapes were used in order to obtain the new deformed built grid for grading the lasts [7]. The present study suggests a new procedure of lasts modification, by re-designing it, according with the data obtained from 3D scanning of an arthritic foot. This procedure implies several stages: 1) scanning the foot; 2) importing an initial last from data base; 3) comparing the foot against initial last; 4) modifying the last according to foot shape. The patient s foot has been scanned by using a 3D foot scanning system; namely the INFOOT USB Standard Model IFU-S-01, provided with 8 progressive ¼ CCD cameras and four laser instruments, class 1M. The initial last has been selected according to the information received regarding size and width of the patient s foot. 284

The initial last imported from data base (Figure 1) is subject to an interactive comparing process against the

On these lines, by using the Compare module of OrthoLast-Delcam Crispin software, the two 3D shapes (foot and

The initial last imported from data base Figure 2.

align them in the same plane (Figure 2).

Before the modifying process starts the last and the foot are aligned so that they are overlapping in as many

The two shapes have different appearances: draft solid for foot and gridded solid for last.

3 The initial last imported from data base (Figure 1) is subject to an interactive comparing process against the scanned foot. On these lines, by using the Compare module of OrthoLast-Delcam Crispin software, the two 3D shapes (foot and last) were brought together in the same screen (Figure 2). Figure 1. The initial last imported from data base Figure 2. Last s alignment with the foot The initial last and the foot are successively moved and rotated in order to align them in the same plane (Figure 2). The chosen last must have appropriate size to the foot, a small heel height and a rounded toe. Before the modifying process starts the last and the foot are aligned so that they are overlapping in as many points as possible (Figure 3). The two shapes have different appearances: draft solid for foot and gridded solid for last. By overlapping, the differences between the foot and the last can be seen; therefore the last will be modified in those specific areas. Figure 3. Last and foot overlap Figure 4. Last s width modification Last modifications were made, step by step, on lengths, widths, toe girth, instep girth, heel height, toe spring, and other increments. The result is a last adapted to the conformational particularities of the subject (Figures 4, 5, 6). Figure 5. Length modification Figure 6. Ankle s girth modification 285

The shape of the last in the toe area is very important, especially in case of anomalies like claw toes and hammertoes; that is why we used templates, designed in a 2D stage that will give the

Last s modification in the toe area using the template It can be seen that there should not be a total identity between the foot and the last.

4 The shape of the last in the toe area is very important, especially in case of anomalies like claw toes and hammertoes; that is why we used templates, designed in a 2D stage that will give the required shape to toe cap (Figures 7, 8). Figure 7. The template for the toe cap Figure 8. Last s modification in the toe area using the template It can be seen that there should not be a total identity between the foot and the last. When the foot gets inside the footwear, it is constrained to modify its shape and dimensions among certain admissible limits of tightening. For an arthritic foot, these constraints have to be as few as possible, especially in the affected areas. Thus, a low level of tightening the foot by footwear is determined, and therefore it reduces the risk of high pressures on specific foot surface. Rapid Prototyping of the Last Virtual prototypes for the last will be obtained using a 3D printer from Z Corp. Thus ZEdit software is used, which provides powerful tools for modifying and highlighting the constructive characteristics of virtual model, so that the physical model will be exactly like the one designed. ZPrint uses software specially made to manipulate, modify and visualize easily the 3D models before the printing process. The program is launched and then the model is imported in ZPrint. The extensions that the software will recognize are the following:.zbd,.zpr,.stl,.wrl,.ply,.3ds,.gis,.sfx. After choosing the last, we have to select the measuring unit we need, it will maintain the same position and orientation and the type of powder that will be used. After validating the options, the model will be visualized (Figure 9). Figure 9. Last s visualization in ZPrint The ZPrint software allows us to modify the thickness, the size and so on, but these changes can be made only in the test session, because, when a prototype is make, this has to have some specific dimensions, the only thing that we can change is the position. If the models are ready, we have to choose which printer will be used and before the start of the printing process, there are some very important things to be checked, if all 286

the components were verified and ready, if there is enough powder in the construction box, if the powder is the right one for our model, if the immersion

RESULTS This study proposed a method of 3D last modelling in order to obtain the shape of lasts specially designed for patients with arthritis.

The software used, OrthoLast form Crispin- Delcam has an important function, Export, which allows the data to be saved with other extensions like.lst,.

Figure 10. Final shape of the modified last (with the foot inside) Figure 11.

5 the components were verified and ready, if there is enough powder in the construction box, if the powder is the right one for our model, if the immersion solution is in the required quantity, if all the recipients were carefully cleaned and if the printer is Online to be recognized by the computer. RESULTS This study proposed a method of 3D last modelling in order to obtain the shape of lasts specially designed for patients with arthritis. Applying all the modifications to the last and comparing it with the foot, the final shape is obtained (Figures 10 and 11). The software used, OrthoLast form Crispin- Delcam has an important function, Export, which allows the data to be saved with other extensions like.lst,.iges,.pat and.stl, which may be transmitted to a 3D printer and a prototype can be obtained, or to a CNC machine where a real last can be manufactured. Figure 10. Final shape of the modified last (with the foot inside) Figure 11. Final shape of the modified last Using the 3D printer 310 Plus from Z Corporation (Figure 12.) and the ZEdit software, the last for the foot of a patient with arthritis was obtained the re-designed (Figure 13). Figure 12. The ZPrinter 310 Plus Figure 13. The last obtained with the 3D printer 287

6 CONCLUSIONS A series of modifications on last is suggested regarding the conformational particularities of the subject. The last s modelling process follows up the foot measurements for the toe girth, the length, width and the toe cap increment, therefore a fitted and adapted last could be obtained. A special last, fully adapted to an arthritis foot, was created by using the 3D computer-based technologies. The 3D modelling procedure allows us to interactively visualize and to modify the last according to the patient s scanned foot shape. The last prototype was obtained on a 3D printer and this one can be used to design other lasts or to make the footwear directly on it. Future research is required in order to analyze the patient s condition while wearing the footwear specially made on the proposed last which has been modified according to the procedure described above. REFERENCES Mălureanu, G., Mihai, A. (2003), Footwear Design Basics, Performantica Publishing House, Iasi. Sikyung, K., Mazumder, M.M.G., Park, S.J. (2007), A Conformal Mapping Approach for Shoe Last Design, in Frontiers in the Convergence of Bioscience and Information Technologies, , Digital Object Identifier /FBIT Zhao, J., Xiong, S., Bu, Y., Goonetilleke, R.S. (2008), Computerized Girth Determination for Custom Footwear Manufacture, Computers and Industrial Engineering, 54(3), Kumar, A., Arthritis, available at accessed at Williams, A.E., Bowden, A.P. (2004), Meeting the Challenge for Foot Health in Rheumatic Diseases, The Foot, 14, , available at accessed at Sederberg, T.W. (1986), Free-From Deformation of Solid Geometric Models, Proceedings of ACM and GGRAPH'86, Computers & Graphics, 20(4), Mochimaru, M. et al. (2000), Analysis of 3D Human Foot Forms Using the FFD Method and its Application in Grading Shoe Last, Ergonomics, 43(9),

Bunions / Hallux Valgus deviation of the big toe

Bunions / Hallux Valgus deviation of the big toe A bunion (hallux valgus) is a deformity of the base joint of the big toe. The cause is not clear in many cases. The deformity may cause the foot to rub