Coventry University (HDTI, School of Art and Design and SGI), West Midlands Rehabilitation Centre, Kings College Hospital NHS Foundation Trust, Betsi Cadwaladr University Health Board and Abertawe Bro Morgannwg University Health Board
Wheelchairs that are not appropriately modified to meet client requirements, lifestyle and environments can be prone to tipping, sliding and loss of traction. The project aimed to design, develop and evaluate a system for assessing the stability and performance of wheelchairs before they are released to the client and used in the community.
The resulting system measures the centre of gravity of the client:wheelchair system and maps the stability points. This information can then be used to inform the tuning of the wheelchair and used predictively to model the effect of changes to the wheelchair on the performance and stability.
Traditionally wheelchair stability in the UK is tested through a ramp test. The wheelchair and client are positioned on a ramp to see whether the chair tips when positioned facing upwards, downwards, and sideways at an angle of 12° or 16°. Reports from patients suggest that they can feel vulnerable during the test, and it requires significant physical effort from the prescriber.
In order to improve stability assessment beyond these pass/fail tests, it was aimed to explore the use of load cell technology (widely used in vehicle stability testing) to measure the weight distribution of the wheelchair and occupant and use this to model and predict stability.
Wheelsense® (patent WO2015004454 (A1)) is a computer-based system incorporating force-measurement technology within a custom made rig. It calculates the centre of gravity, and maps the stability points of the user-wheelchair system. The design incorporates:
- A folding platform-based weighing system
- Underlying mathematical modelling and electronics
- Software and graphical user interface.
For portability, the platform was designed as a foldable four quadrant frame linked with suitable hinges so that it could be transported by car and used in a clinic, or out in the community. The platform senses the wheelchair wheel and castor position and determines dimensional information. The assessment procedure involves 3 easy steps whereby the wheelchair is moved sequentially into position on the platform and sensor data collected. The resulting stability mapping is presented to the wheelchair prescriber on a Wi-Fi connected tablet computer to inform their tuning of the wheelchair.