A comparative analysis of three self-balancing wheelchair balancing mechanisms.

In the last 20 years, three different basic, dynamic balancing designs have been proposed for a self-balancing wheelchair (SBW) that allows the wheelchair user to transition from driving on all four wheels to driving while balanced on the two large rear wheels. The dynamic performance of these three SBW designs, the hanging pendulum counterweight (HPC), the single inverted pendulum (SIP), and the double inverted pendulum (DIP), are compared when controlled by a common state space controller. The four dynamic performance considerations of stability, driver dynamic stress, maneuverability and technical requirements were used to compare these designs while performing the following five tests: 1) transition from four-wheel to two-wheel, balancing mode; 2) stationary, self-balancing stability when subjected to an impact disturbance; 3) movement initiation, and stopping while balancing; 4) response to impact disturbances while moving; and 5) stability on low traction surfaces. In addition, the movement initiation and stopping test was repeated with increased chair mass and inertia to investigate the sensitivity of model performance to changes in model parameters. After comparing the three models it was determined that the HPC mechanism is the best choice for further development based on the criteria of stability, driver dynamic stress, maneuverability, and technical requirements. The HPC ranked equal or better compared to the SIP and DIP on 15 of 29 stability and performance factors. It was also the only design that was stable for all normally expected driving conditions.