Hingenious 2.0 (Missouri Science & Technology)


Wheelchair Attachment

Damien Rolfes, Brock Curtis, Jake Long, Samantha Klump, & Chad Stanley

Abstract

Wheelchairs are used to accommodate people with a wide variety of mobility issues, some of which involve the user being completely dependent on the wheelchair for day to day living. One danger that is feared by all wheelchair users is that of tipping over. The solution that is currently on the market is a cambered wheel design. While this does solve the problem, it is expensive and not universally adaptable for the standard model wheelchair. In most cases, this concept also requires the purchase of an entirely new wheelchair which, in turn, may leave the user with the wrong wheelchair at the wrong time. The final design and the one that has been implemented is an inexpensive attachment that adds an extra wheel to each side to effectively widen the wheelbase and add lateral stability.

Background

The objective of this project is to create a personal assistance device for the RESNA (Rehabilitative Engineering and Assistive Technology Society of North America) design competition that will help an individual with a disability achieve greater independence. One of the main problems facing a person in a wheelchair is sideways tipping. If a person in a wheelchair is on a steep incline it is easy to tip over. The current implemented solution is a cambered wheel design, and while this does solve the problem it is also very expensive. It also requires the purchase of an entirely new wheelchair.

There isn’t a big variety of products that fix this problem, the only one being the cambered wheel design. Figure 1 shows a few basic designs that incorporate cambered wheels. Figure 2 shows the cambered design in comparison to the traditional wheelchair design. While this design does sufficiently solve the problem, it does require the user to buy an entirely new wheelchair. On top of that, these wheelchairs cost $2000 and up, where the average normal wheelchair only costs a few hundred dollars.

Figure 1: Cambered Wheelchairs

Figure 2: Camber vs. Non-Camber

Problem Statement

The goal of this project is to prevent the lateral tipping of a wheelchair.

Design and Development

The Hingenious 2.0 design incorporates a cross bar that allows it to attach to the longitudinal side span of the wheelchair. This reduces the amount of space taken up by the attachment and increases the structural integrity of the overall design. Having this cross bar allows the attachment to fold up with the collapsible wheelchair making the design work with the factory function. This design also incorporates a simple and easy to use locking mechanism for easy user operation. When the attachment is stowed away, it is completely out of the way taken up only unused space. The design of the outer clamp allows the caster wheel to be lifted off the ground 0.5 in. so that it doesn’t interfere with normal use. In addition, when the wheelchair needs to be folded up, the outriggers can be removed and the pin in the middle of the cross bar allows it to fold with the wheelchair. Figures 3-4 depict Hingenious 2.0 in the deployed and stowed positions, with a close-up of the clamp portion.

Figure 3: Hingenious 2.0 – Deployed

Figure 4: Hingenious 2.0 – Stowed

Advantages of this design include the ability to attach to any wheelchair, easily removable, can be stowed away when not used, and doesn’t require any modification to the existing wheelchair (only installation). Disadvantages include custom installation and the attachment slightly reduces the usable arm space during wheelchair operation.

Evaluation

The only prior art that addresses this problem is the cambered wheeled wheelchair which costs significantly more than a conventional one. The use of the Hingenious 2.0 design will accomplish the same concept as the slanted wheel design when utilized on a conventional wheelchair allowing for more control on surfaces. The cost is notably cheaper than buying a new wheelchair and does not alter the structure of the current design. Hingenious 2.0 is available for use on most manual wheelchairs with slight alterations on mounting depending on wheelchair model and size. The design also does not alter the overall width of the wheelchair when stowed away. Along with this, Hingenious 2.0 also allows for a one time installation allowing for a permanent fixture that can be used when needed and conveniently retracted when the owner is not on steep or unleveled surfaces. This design allows for the consumer to use their standard wheelchair without the added strain of pushing the cambered wheels.

Finite Element Analysis

Figure 5 shows the results of the FEA for a static load of 200 lbf normal to the ramp. It can be seen from the analysis that the highest stress that the part will see is around 13200 psi in compression. This gives a factor of safety of 3.85 for this load when using AISI 1018 cold drawn carbon steel. However, because this load is nearly twice the calculated load of 108 lbs (see Section 9: Design and Analysis), the actual factor of safety is significantly higher. In addition, this was calculated for a ramp angle of 20°, which is 2.5 times the ADA recommended angle of just 8°.

Figure 5: FEA for static load

Robustness

If the wheelchair is submitted to a “torsional” tipping condition, where only the caster of the attachment and either the front or back wheels are in contact with the ground, the attachment will experience an angled load. Figure 6 shows this angled load. In this condition, the maximum stress is 30000 psi, giving a factor of safety of 1.76. This analysis can be seen in Figure 7.

Figure 6: Angled Load

Figure 7: Results of angled load

Figure 8: Exploded View of Assembly

Discussion and Conclusion

This attachment, known as Hingenious 2.0, does not interfere with normal operation of the wheelchair and will be able to fold with the wheelchair for storage purposes. The design is easily adaptable for most wheelchair models along with a variety of sizes. Hingenious 2.0 also provides for easy deployment at the user’s discretion which is useful when fitting through tighter doorways/spaces. This allows the user to have a safe, inexpensive alternative to a cambered chair.

 

 

 

 

 

 

 

 

 

References

“ADA Standards.” Http://www.ada.gov/stdspdf.htm. U.S. Department of Justice. Web

CAD Modeling – Solidworks 2011. Computer software. Www.solidworks.com. Vers. 2011. Dassault Systemes. Web.

FEA – Autodesk Simulation Mechanical 2012. Computer software. Usa.autodesk.com. Autodesk, Inc. Web.

GANTT and Pugh Chart – Microsoft. Microsoft Excel. Redmond, Washington: Microsoft, 2010. Computer Software.

Photos:

Cambered Vs. Non-Cambered Wheelchair. Digital image. Http://www.streetsie.com/manual-wheelchair-design-production/. MAd Spaz Club. Web

Front View of Cambered Wheelchair. Digital image. Http://www.melrosewheelchairs.com/index.php?main_page=page&id=9. Melrose Chairs. Web.

Purple Cambered Wheelchair. Digital image. Http://emedicine.medscape.com/article/318092-overview. WebMD LLC. Web.

Red Cambered Wheelchair. Digital image. Http://www.caremedicalsource.com/Shop/WheelChairs/Sport-Wheelchairs/Quickie-All-Court-Wheelchair. Care Medical Source. Web.

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