Biomecánicamente - Reinventing the crutch

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Tuesday, 13 January 2015 15:22

Reinventing the crutch ^Featured

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Ignacio Bermejo Bosch (*), (**), Francisco Sánchez Rodríguez-Acosta (***), José Navarro García (*), Laura Martínez Gómez (*),Sandra Alemany Mut (*), Javier Ferris Oñate (*), Raquel Marzo Roselló (*), Jaime Prat Pastor (*)(**)

Instituto de Biomecánica de Valencia (*)

CIBER de Bioingeniería, Biomateriales y Nanomedicina (CIBER-BBN) (**)

FORTA (***)

The current competitive strategy, based on the reduction of the prices of products coming from foreign markets, is a challenge which Spanish companies must transform into opportunities for innovation. This is the case of the euroCrutch®, designed by the company FORTA. This crutch was conceived to offer maximum performance in terms of safety, functionality, usability, convenience and sustainability, while maintaining a highly competitive price.

INTRODUCTION

Elbow crutches are an assistive device whose main functions are to facilitate walking by increasing stability, extending the support base and/or reducing the load on one or both of the lower limbs.

Currently, many companies are producing these products in areas with extremely low labor costs, such as Asian countries, in order to reduce production costs as far as possible. Moreover, the current world financial crisis means that purchase price is one of the most important factors when it comes to purchasing these products. At the same time, other trends are emerging, such as those related to the users' desire to increase their independence and comfort, respect for the environment, safety, etc.

In light of all this, the company FORTA decided to develop the euroCrutch®. The aim of this crutch is to meet the demands of current consumers, while maintaining prices that are competitive with other products originating from the Asian market.

THE CONCEPT OF THE EuroCrutch®

In the past, FORTA developed a line of wheelchairs manufactured using polymeric materials which have, to date, been highly successful. Based on the know-how generated, FORTA has developed the concept of the euroCrutch®, a healthcare product completely manufactured using recycled molded plastic, with the following characteristics:

♦ More automated manufacturing process than that used in current methods.

♦ Environmentally-friendly, thanks to the use of recycled materials.

♦ The crutch makes much less noise when hitting the floor than conventional ones.

♦ The jolt experienced by the user when using the crutch is much lighter.

♦ The crutch can be used around metal detectors or nuclear magnetic resonance systems, etc., as it contains no metallic elements.

♦ The structural resistance of the crutch is guaranteed.

♦ The product's esthetics are in line with current design trends.

CHALLENGE OF THE PROJECT

The concept of the euroCrutch® was so different from conventional products that its development posed a challenge for FORTA, which could not resort to previously used experiments to predict its mechanical behavior since 1) the materials used have characteristics which are very different from those used in conventional crutches, and 2) the manufacturing process means that the design of the crutch cannot resemble those used in conventional products.

In fact, the initial prototypes supplied by the company entrusted with the manufacture thereof did not pass the regulatory testing (Figure 1), bending out of shape excessively, owing to which they failed to cover the necessary safety and functionality requirements.

Figure 1.Mechanical trial with the initial prototype. From left to right: without load, with the maximum load withstood, the instant of breakage.

To overcome this challenge, the collaboration of Instituto de Biomecánica de Valencia (IBV) was sought with a view to redesigning the crutch, taking into account the criteria of safety, functionality, usability, comfort and sustainability initially set, while maintaining the manufacturing process designed by the company.

DEVELOPMENT

A detailed mechanical analysis of the situation was performed (Figure 2), taking into account the geometric non-linearities produced when the crutch bent out of shape. The conclusions from the analysis made it possible to highlight the design’s weak points and to propose a new structural design. Through this study the characteristics of resistance and minimum rigidity required by the section of the crutch were obtained, which helped in the subsequent geometric design thereof.

Figure 2.Approach to mechanical analysis.

Work was conducted on the product's appearance in order to transform its esthetics into an added value, and a new design incorporating the conclusions from these prior studies was proposed (Figure 3).

Before proceeding to the manufacture of the crutch, a new structural analysis was performed, this time using Computer Aided Engineering (CAE) techniques. The use of one of the most powerful versions of these tools, the Finite Element Method (FEM), meant that the design could be optimized to reduce the material used as far as possible (Figure 4), while guaranteeing the necessary strength and rigidity through the optimal sizing of the different thicknesses. The benefits of this are twofold: on the one hand, it reduces manufacturing costs and, hence, allows lower purchase prices; on the other hand, the crutch is also lighter, making it easier to use and transport.

Figure 4.Structural analysis using the Finite Element Method

Once the definitive design had been virtually assessed, the manufacturing company proceeded to design and build the injection molds to manufacture the new crutch design. After the manufacture of the initial units, they were subjected to the UNE-EN ISO 11334-1 test. This test, for evaluating the static load and fatigue resistance, was easily passed by the euroCrutch® (Figure 5).

Figure 5.Mechanical test with the definitive design.

CONCLUSIONS

This project has made it possible to develop an elbow crutch which can be manufactured using 100% recyclable materials using injection molds, resulting in products with a highly competitive price.

The use of Computer Assisted Engineering techniques has facilitated the optimization of the crutch's geometry, minimizing the quantity of material used (lower cost and weight), whilst guaranteeing suitable resistance.

Moreover, know-how related to design and ergonomics has made it possible to produce a product adapted to the characteristics of users in a wide range of sizes, while maintaining a stable appearance.

In short, the work of FORTA, the manufacturers and the Instituto de Biomecánica de Valencia (IBV) has made it possible to produce a new commercial product, with a design based on new market trends and adapted to users' requirements. This has made it possible to introduce a new concept of a crutch into a saturated market, at a highly competitive price, providing users with high added value.