The Assisted Chair Project

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The idea behind this project is to make a wheelchair with a moveable base that makes standing up and sitting down easier for people with physical disabilities, or elderly people. A wheelchair is ideal as it provides mobility as well as being suited for such a medical application due to its ergonomics. It uses a standard wheelchair upon which modifications are made. The base is replaced with one designed by the team which makes use of a four-bar linkage mechanism to provide rotational movement of the base. The backrest and armrests are also linked to the movement of the base and move with it to aid in standing up. The mechanism is driven by a hydraulic cylinder that is connected to a pneumatic system. The entire system is placed onto a base that is fixed to the bottom frame of the wheelchair.

Prior to the mechanical design of the wheelchair, an analysis of the motion had to be carried out in order to identify the limits of mechanical movement. An ergonomics study was carried out with the goal of understanding how elderly people move. The results of the study were then verified via motion analysis using high-speed video capture. This motion was then mapped in an X-Y coordinate system and equations of motion were obtained based on the mapped points. This mapping of motion provided the team with the parameters that the mechanism had to meet.

The next step was to shortlist an appropriate mechanism. The mechanism had to be safe and have a steady and smooth movement to reduce risk. Among the various ideas that were discussed, the chosen mechanism was a combined hydraulic-pneumatic system. Hydraulic systems are more complex, but allow for much smoother movement, whereas pneumatic systems are less complex and require less power. The simpler pneumatic system is used to drive the more complex hydraulic cylinder that powers the mechanism.

As the desired target market of this wheelchair is persons with limited mobility, safety is of the utmost importance. As a result, the braking system of the wheelchair has been upgraded, and instead of using standard wheelchair brakes, a system is created that is adapted from a motorcycle's brake system. This ensures that the stopping force is large enough to prevent the wheelchair from moving while the base is in motion. The brakes are linked to the cylinder in a manner that the cylinder will not activate unless the brakes are applied.

The final product is a system that is capable of providing the user a safe and controlled way by which they are able to confidently stand up without having to rely fully on their own strength.

Topics

Exhibitors
Ian Ireland,
Mohammed Talib Ali Rizvi,
Asjad Alvi

Advisor(s)
Dr. Ghalib Kahwaji at RIT Dubai

Organization
Senior Design II


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