Modeling and analysis of static wheelie of a five-wheeled wheelchair for climbing over a step

In this paper, we propose an unique step climbing method for a manual wheelchair with an add-on drive unit. We have proposed the active-caster drive system for an add-on drive unit for a manual wheelchair since it can generate velocity vector in arbitrary direction with an arbitrary magnitude. The active-caster enables a wheelchair user to control 2DOF of the wheelchair motion in a same manner of a standard electric wheelchair with a 2DOF joystick. By installing the active-caster drive system on a manual wheelchair, it forms a five-wheeled wheelchair. The relative position between the active-caster and the wheelchair frame can be varied since the drive unit is mounted on the frame with a link whose relative angle can be varied, namely an actuated pin joint connection. By using this DOF, we realize “static wheelie” motion for lifting up front casters to climb up a step, which is not a dynamic motion but statically stable at all times. Therefore the proposed function might be able to enhance the safety of a wheelchair for disabled or handicapped persons. In this paper, a static model of a wheelie motion of the proposed five-wheel wheelchair is analyzed. By the analysis, it is clarified that braking of the main wheels of the manual wheelchair would be very effective for realizing static wheelie by minimum traction force of the drive wheel. During the wheelie, the wheelchair contacts to the ground by three wheels, two big wheels and the active-caster, the configuration is relatively stable compared with a dynamic wheelie balancing with two wheels. By this three-wheel-contact configuration, it can also stably move on the floor by the drive wheel with releasing the brakes for the main wheels. By the analysis, the location of the pin joint for supporting the drive wheel on the wheelchair frame will be suggested for realize the static wheelie. To verify the proposed wheelie method, a prototype five-wheeled wheelchair is designed and tested. In the experimen- al section, it will be presented that the manual wheelchair with a human operator can present static wheelie and stable translation motion with three-wheel-contact configuration.