The IBV participates in this project with a group of partners with the purpose of defining the non-geometrical requirements for customized products. When trying to satisfy user comfort, it is not only necessary to consider the geometrical requirements and a good product fit, moreover it is necessary to consider non-geometrical requirements that define the interaction in the zones of contact such as, pressure distribution between the product and the human body, or the comfort felt by the user while he is using the product.
Furthermore a methodology has been developed using rapid manufacturing which permits the manufacturing of product parts from CAD designs.
Seven different products are being looked at in the Custom-Fit project, although the one that has drawn the most attention is the motorbike helmet as it is a product with a high rate of usage but a distinct absence of comfort. The helmets studied in this project have been supplied by the company MAVET (Italy). In this article the steps followed in the project are going to be shown and you will see the development of a customized helmet that is far more comfortable for the motorcyclist to wear.
The objective of the project is the successful development of a process or a group of actions to customize products with the purpose of making them more comfortable for the users. Although the process is used to demonstrate the possibility of helmet customization, the supply of the product to the shop has not yet been defined. Moreover, the methodology is being studied by the normalization commission because at the moment it is not possible to approve the helmets without conducting a physical test on them, so for the moment it is not possible to supply customized helmets with a reasonable cost and short production time. Therefore a methodology of virtual evaluation has been developed for the helmets in order to replace the current test, but this work exceeds the importance of this article.
As we have mentioned the objective is the satisfaction of the motorcyclist with regard to helmet comfort. So as to achieve this, the geometrical data of the user’s head and the registered non-geometrical information, by means of the pressure distribution on the interior of the helmet accompanied by the perception of comfort of the head’s zones, will be used.
MATERIAL AND METHODS
The study of comfort satisfaction of a single motorbike helmet is not easy and during the first phases of the project more than 120 variables were examined (geometrical and non-geometrical) which can affect comfort. Once examined, the pressure distribution through the interaction between the user’s head and the helmet was identified as the most important variable, according to the different morphologies of users’ heads and the little existing variation in the interior of the helmets. The climatic comfort of the helmets was also identified, but finally it was decided to analyze this in future projects. The helmet manufacturer which took part in the project had 6 different sizes of the same product, nevertheless in each one of the sizes a unique morphology of the interior of the helmet existed, it had been defined by means of the geometrical variable of the head circumference. This dimension has been used for years to develop the different sizes and it is considered very important to avoid the movement of the helmet when it is worn, but user comfort has not been obtained very often with this single dimension.
In the designed methodology the dimensions of the head (geometrical variables) have been used, as has the pressure distribution between the head and the helmet, and the feelings/opinions of the user (non-geometrical variables).
The study has been developed by means of the participation of 6 users. To record the geometrical variables a three-dimensional scanner was used, with which the user’s head was scanned, getting a total of 5 dimensional variables. In order to obtain the non-geometrical information about the pressure between the helmet and the user’s head a recording system of static pressures was used. So as to determine the comfort feelings of the user a questionnaire based on 5 levels of comfort was developed, after locating 6 important zones on the head.
Once the variables to be recorded were defined, the users started the first test with the helmets. The company supplied a helmet model in 6 different sizes (there were 2 exterior parts of the helmet and with the modification of the interior liner of the helmet the 6 sizes were achieved). The following procedure was used; each subject tried on the available helmets (XS, S, M, L, XL, XXL) and decided which one of them fitted better. Then the helmet was taken off and the user’s head was measured. After this, the subject wore the chosen helmet again and the interaction pressures were recorded. Moreover a questionnaire about the comfort felt on the different zones of the head was answered. Then after trying out the helmet with the size which the subjects felt more comfortable in, they tried on a helmet, one size smaller, and the procedure was carried out again, the pressure distribution and the information about the comfort felt on the different zones of the head was recorded. The objective of this was to discover how the smaller sized helmet increased the pressure and its correlation with the increase in discomfort felt.
The first part of the study finished with the reviewing of all the information collected. The results of the pressure distribution, the head geometry and its correlation with the comfort felt were all analyzed.
The susceptible part of the helmet that needed to be modified had been defined; however this would not affect product security, as only the part in contact with the user’s head would be modified.
With all the generated information the manufacture of the customized helmets was proposed, developing first the file CAD of the users head and the commercial helmet, and then the modifications in the design of the interior part of the helmet were made in accordance with the non-geometrical information recorded in the previously mentioned test. Once the interior parts of the customized helmets were manufactured, the tests with the users were repeated following the same protocol as before.
The analysis of the results of the first test did not show any significant correlation between the absolute recorded pressures and the comfort felt by the user. This indicated that the sensitivity of the pressure on the user’s head had not been considered and so the analysis was more difficult. Moreover the test with the helmet one size smaller increased the pressure and stopped the helmet fitted correctly. Along with all of this, the surface contact and the interaction between the helmet and the head were analyzed without paying attention to the absolute levels of the recorded pressures.
The hypothesis to improve the comfort through the development of the interior of the helmets was to increase the surface contact between the helmet and the user’s head (without reducing the helmet’s ventilation system), so as to reduce the pressure high peaks. And then compare the relative decrease of pressure between the helmet and the user head during interaction.
Figure 6. Pressure maps of the three helmets: correct size, smaller size and customized helmet.
The results of the comfort evaluation showed that in 5 of the 6 helmets the comfort increased with the customized helmet. In one case customization was impossible without increasing the size of the helmet due to the head geometry so the comfort didn’t improve.
Looking at the results, they demonstrate that the customization of products is a good way to improve comfort, but in this test only the mechanical comfort was studied and the thermal comfort should be studied in future projects. Moreover the study did not allow for the testing of the helmets in real conditions (driving).
On the other hand the viability of the project has been demonstrated, but it has not been possible to implement the distribution of helmets in the shops. So, it is necessary to continue working on the supply of the customized product in relation to time and reasonable cost.
There is a point that has not been evaluated in the project. This was the case where it was necessary to increase the helmet size in order to improve comfort but in the end no increase was achieved. Motorcyclists do not like big helmets; they do not perceive them as aesthetically pleasing, so is necessary to pay attention to how to customize helmets and when it is necessary to increase the size in order to change how the user feels.
Thanks to the European Commission, the members of Custom-Fit and especially to the MAVET Company (Dainese) for their collaboration on the project.
For more information, visit www.custom-fit.org
By David Rosa Mañez, Francisco Payá Gisbert.
Instituto de Biomecánica de Valencia
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