An active-caster drive system for motorizing a manual wheelchair

An external motorize system with an active-caster is presented in this paper. The external motorize system is for driving a manual (hand propelled) wheelchair by electric power by mounting the external device with electric motors, a set of batteries, a joystick and motor controllers on a manual wheelchair. In spite of a single drive wheel, 2DOF of the wheelchair with an active-caster drive system can be controlled independently without any constraint, such as the orientation of the drive wheel which is well known as a non-holonomic constraint. A kinematic model of the wheelchair and that with an active-caster drive system are analyzed and a control method for propelling the wheelchair by using a 2DOF joystick is derived. Based on the kinematic model, a prototype mechanism of the active-caster is designed and mounted on a manual wheelchair to realize the motorized manual wheelchair. In the experiments, the independent 2DOF motion can be achieved by the control of the active-caster in which the wheelchair shows successful translation and rotation motions which includes flip motion of the active-caster mechanism.