Development of an add-on drive mechanism for improving motion performance of a manual wheelchair

In the previous work, we have developed a five-wheeled wheelchair composed by a manual wheelchair with an active-caster drive system. Since an active-caster generates active traction force with an arbitrary direction and magnitude, two degrees of freedom (2DOF) motion, translational motion and pivot turn motion, can be controlled independently despite of a single-wheel drive system. Moreover, by changing the height of the drive wheel relative to the wheelchair frame using linear actuator, this wheelchair can be switched to two drive modes, namely rear-like drive and front-like drive mode. In this study, we propose a step climbing method and develop a novel add-on drive mechanism. The proposed five-wheeled wheelchair has five points of contact with the ground. By the hovering motion of the front casters, the wheelchair can perform a static wheelie maneuver, which can be maintained by the large wheels and drive wheel. We apply this stability to the step climbing motion of the front casters. Similarly, by the stability of the three-point-contact, the large wheels hover from the ground and pass over a step. Additionally, the drive wheel is lifted onto the step by cooperative control of the linear actuator and drive wheel. We confirm the designing condition for developing an add-on drive mechanism to realize not only the step climbing method but also the drive mode change function. Also, we confirm the validity of the proposed step climbing method by comparing with a method which uses only the traction force of the drive wheel. After the prototype is built, we confirm that users can climb over a step by the proposed method and mechanism.