Tilt location selection is an important part of choosing the correct chair configuration for a user. The location of the tilt pivot will determine various aspects of tilt. There are trade-offs, so it is important to know what you are looking for. Two of the most common tilt pivot locations are center-of-gravity pivots and knee pivots.
A center-of-gravity pivot (COG) is exactly what it sounds like. The seating portion of the chair pivots around the user’s center of gravity. This pivot location is achieved in two ways, either a simple pivot is located at the location of the center of gravity, or a system of curved rails is used to create a virtual pivot about this point. The curved rails allow for side access, but require more maintenance and cleaning to retain functionality, while the simple pivot solution will restrict side access somewhat but will require negligible amounts of maintenance.
PDG Fuze T50
Either approach results in very low handle loads when tilting and keeps the seating portion of the chair free of interference with the rear wheel axles, resulting in a narrower overall chair width.
Wheelchairs with pivots at or close to the knee have very different characteristics than center-of-gravity pivot chairs. Keeping the tilt location close to the knee allows for foot propulsion even while in tilt, and also will allow the user to be rolled up to a table even while in tilt. The distance of the pivot to the knee will also affect the tilt angle, with pivots very close to the knee not being able to achieve 45° of tilt but with the trade-off of having almost no knee movement.
PDG Stellar GLT
Since these tilt systems have a moving center-of-gravity, they require gas springs to cancel out the user’s weight, making tilting the chair without an occupant quite difficult. However, a properly set up chair will have minimal force input required when tilting with an occupant. An added benefit to this system is the shock absorbing characteristics of the gas-spring. This will provide a smoother overall ride and will also help soften the forces of more agitated users.
Written by Jim Formby, Senior Mechanical Design Engineer at PDG Mobility
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