Devon Forney¹, Adonis Eid¹, Thiago Simiao¹, Amy Oxenrider¹, Jill Caruso², Mehdi Pourazady, Ph.D.¹, Mohamed Samir Hefzy, Ph.D., PE¹
1. Biomechanics and Assistive Technology Laboratory,
Dept. of Mechanical, Industrial and Manufacturing Eng., The University of Toledo, Toledo, Ohio
2. The Ability Center of Greater Toledo, Toledo, Ohio

ABSTRACT

Photo 1: A user moving a shopping cart attached to her wheelchair using the unit that was developed. (Click image for larger view)

The purpose of this project was to develop a device that enables a manual wheelchair user to safely move a shopping cart and/or a baby stroller.  Without such a device the user has no means by which to steer, or even hold on to a cart or stroller, as both hands are constantly needed to control the wheelchair.  The device consists of two flat aluminum plates, each sitting on three small swiveling casters and housing one of the rear wheels of the cart.  The problem of these wheels being fixed, which makes it nearly impossible for a wheelchair user to make a turn while pushing the cart, is thus eliminated by setting them on swiveling casters.  The two plates were held together by a cross member that has two pivoting connecting arms attached to it and to the front of the wheelchair.  Figure 1 shows an individual moving a shopping cart that is attached to her manual wheelchair using the device that was developed.  This figure demonstrates that the user hands are free to drive her manual wheelchair.

KEYWORDS:

wheelchair, shopping cart, baby stroller, spina bifida

BACKGROUND/STATEMENT OF THE PROBLEM

An individual (the “Client”) is affected by spina bifida (1).  This neural tube defect has left her with paraplegia of her lower extremities.  As a wheelchair user and mother of a one year old daughter, she finds it difficult to safely push her child’s stroller.  She currently moves the stroller forward by pushing it ahead of her, beyond her reach, creating a separation between the wheelchair and the stroller.  She then wheels herself forward to meet with the stroller again before pushing it forward once more.  The client repeats this procedure until she and the stroller have reached their destination.  This method has previously resulted in her child falling from the stroller and striking her head on the ground.  Another current option for pushing the stroller is for the client to constantly have one hand on the stroller’s handle, keeping the stroller in front of her and under control at all times.  With one hand on the stroller, however, she is then left with only one free hand to use in propelling and steering her wheelchair.  This makes it nearly impossible for her to maintain constant linear motion.  The Client has requested a device that would allow her to easily push her child’s stroller while keeping her baby safely within her reach at all times.  She requested that the device also allow her to push a shopping cart, as she is currently forced to do so with the same method that she uses to push her child’s stroller.  Specifically, she requires a device that will allow her to move a shopping cart or baby stroller in a safe and controlled manner while leaving her hands free to drive her manual wheelchair.  There are no devices presently available in the market which meet the needs of the Client.

METHODOLOGY/DESIGN

Design requirements, as set by the Client, included: 1.) the device should provide the Client with complete control over a shopping cart or baby stroller while offering increased maneuverability of both; 2.) the device should be able to quickly attach to, and detach from the wheelchair; 3.) it should be lightweight so that she can easily handle the device when it is detached from the wheelchair and not in use; 4.) it should be compact so that it does not add unneeded bulk to the wheelchair and possibly be collapsible so that she can store it in her vehicle at all times, and; 5.) it should be simple to operate and, if collapsible, easy to assemble and disassemble without the use of tools. 

Early in the project, it was realized that the greatest obstacle to overcome would be the maneuverability of the shopping cart or baby stroller when the Client attempted to make a turn.  Two different concepts were proposed.  The first was to attach a set of retractable arms to the wheelchair that would extend up to the handlebar of both the shopping cart and the baby stroller.  The second concept involved lifting the back wheels of the cart or the stroller off the floor and cradling them in a fixture that was attached to the wheelchair.

The second design concept was implemented because using retractable arms does not offer easy maneuverability.  Making turns with a shopping cart or baby stroller attached to the wheelchair would be incredibly difficult because of the cart or the stroller’s rear wheels.  The wheel configuration of a shopping cart and most baby strollers is such that the two front wheels are free to swivel around, unrestricted, with unlimited degrees of rotation.  The rear wheels, however, are fixed, allowing for only linear motion.  This configuration works well for individuals without disabilities who are able to walk behind the cart or stroller.  When making a left turn with a shopping cart, for example, a walking user turns the cart in such a way that the point of contact between the cart’s left rear wheel and the floor becomes the center of rotation of the cart.  The left rear wheel pivots at this point.  The two front wheels then swivel so that they, along with the cart’s right rear wheel, remain always tangent to radii about that center of rotation.  The cart is then free to make the turn with minimal resistance.  For a wheelchair user with the cart or stroller rigidly attached to the front of their wheelchair, however, the center of rotation of the turn is located directly between the rear wheels of the wheelchair.  Since the rear wheels of the shopping cart are fixed, it is impossible for them to position themselves tangent to a radius about the center of rotation of the turn.  They remain always perpendicular to their desired direction of movement.  The same is true for the wheels of a baby stroller.  The frictional resistance created at the rear wheels of a fully loaded shopping cart or a baby stroller containing a small child, as they attempt to move laterally across the ground during a turn, is far greater than the user should be expected to overcome.  For this reason, a design is needed that would eliminate such a situation by keeping the rear wheels of the shopping cart or baby stroller from making contact with the ground.    

The device that was developed was designed thus to lock the rear wheels of the shopping cart and raise them of the ground.  The device consists of two flat 11” x 9” x ¼” aluminum plates, one for each of the cart or stroller’s rear wheels.  A long narrow groove is cut out of the middle of each plate.  The rear wheels of the cart or stroller fit in these grooves and are each cradled in place by two pins.  Each grooved plate sits on three small swiveling casters.  By setting the rear wheels of the cart or stroller on swiveling casters, the problem of these wheels being fixed and making it nearly impossible for the wheelchair user to make a turn is eliminated. These two grooved plates are held together by a telescopic cross member.  The telescopic feature of this bar allows the device to accommodate the variation in widths that exists between different shopping carts and baby strollers.  Two pivoting connecting arms extend from the device’s cross member to the wheelchair.  Each connecting arm attaches to the front of the wheelchair by means of a small clamping block that tightens down around the tubular frame of the wheelchair.  The entire assembly weighs approximately thirteen pounds.

The device quickly attaches to, and detaches from, the wheelchair by means of two quick release pins, one per connecting arm.  The pins attach each connecting arm to one of the clamping blocks.  Only the clamping blocks remain connected to the wheelchair when the device is not in use.  The device is completely collapsible with four additional quick release pins holding the entire assembly together.

A three dimensional model of the device was created and refined using computer-aided drafting software.  The strength of the device was then evaluated using stress calculations for static loading conditions and confirmed through the use of finite element analysis software.  The material out of which to fabricate each component of the device and the sizes of those components were decided upon through the results of these calculations and analyses.  Once these details of the design were finalized, a prototype of the device was constructed.  Figure 1 shows the Client using the device to move a shopping cart while driving her manual wheelchair.

CONCLUSION

A device has successfully been designed and fabricated to allow a manual wheelchair user to easily push and maneuver a shopping cart or baby stroller in a safe and controlled manner while leaving the user’s hands free to drive their wheelchair.  The device attaches to, and detaches from the wheelchair quickly and easily.  Its design was kept lightweight and is collapsible with simple assembly and disassembly.  The total cost for manufacturing the device including parts and machining is under $450.

The device is currently being used by the Client on a regular basis.  She is very happy with it as it meets her needs.  Although this device was designed for one person in particular (the “Client”), it could be beneficial to any manual wheelchair users with needs similar to those of the Client. 

REFERENCES

1. Wikipedia, Spina Bifida, http://en.wikipedia.org/wiki/Spinal)bifida

ACKNOWLEDGEMENTS

This work was supported by grant BES-0625023 from the Research to Aid Persons with Disabilities Program from the BES Division of the NSF.

AUTHOR CONTACT INFORMATION  
[Corresponding Author]

c/o Mohamed Samir Hefzy
Biomechanics and Assistive Technology Laboratory
Department of Mechanical, Industrial and Manufacturing Engineering
The University of Toledo
Toledo, Ohio 43606
Phone: (419) 530.6086
E-mail: mhefzy@eng.utoedo.edu

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