Veterans Affairs

Collapsible wheelchair with offset push rim for improved biomechanics, stability, and transfers

Decoupling of the push rim and drive wheels allows for optimal positioning of the shoulders, enables gearing for improved locomotion, and creates better options for moving in and out of the chair

Medical & Biotechnology

The most common form of a wheelchair utilizes a push rim connected directly to the drive wheels. A user is able to propel the wheelchair by pushing the rims with their hands, thereby rotating the wheel an equal angle. The common wheelchair is elegant in its simplicity.

However, the inherent mechanical coupling of the push rim and the wheel requires that they are placed in the same fore-aft position, which may lead to reduced stability of the wheelchair as well as shoulder problems for the user.

In setup the clinician must balance these concerns – on one hand, the clinician would like to move the push rims forward to promote a better positioning of the shoulders for propulsion. On the other hand, the axle of the wheels must remain behind the center of gravity to reduce the likelihood that the wheelchair will tip over backward.

The positioning of the push-rim and wheel also makes moving in and out of the wheelchair difficult. For example, the user must position the wheelchair at an angle with a bed or other transfer surface in order to use a transfer board. Without a transfer board, the person must elevate their body a significant distance to clear the wheel of the chair.

To address these concerns, researchers at the Department of Veterans Affairs have developed a new collapsible manual wheelchair system that decouples the push rims from the drive wheels and reconnects them using a belt drive or chain drive transmission, thus allowing for optimal stability and better shoulder positioning for propulsion. Decoupling also allows the push rims to be rotated towards the back of the chair thereby moving them out of the way for easier transfers. The setup further enables the use of multispeed fixed-gear hubs for easier propulsion on different terrain.

Businesses can develop the design into products by licensing US patent 9,980,863, which is related to US patents 9,795,522; 9,445,958; and 8,905,421, and US patent applications 20170007476 and 20190133854, as well as two pending international patents.

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