Regenerative brake control of cycling wheelchair with passive behavior

In this study, we propose a cycling wheelchair that assists the movement of patients with impairment of lower extremities. The wheelchair is a pedal-driven system, similar to a bicycle, moved by the pedaling force of the patient's legs. Although the lower extremities of patients are impaired, they can use both legs to smoothly rotate the pedal. However, there are several barriers to use the cycling wheelchair in an outdoor environment such as steep slopes, steps, and obstacles. In this study, we develop a cycling wheelchair controlled by a regenerative brake system. The braking control provides several assistive functions including velocity control, gravity compensation, and step/obstacle avoidance. The regenerative brake system can also charge a battery during the braking control. However, in situations such as steep-slope climbing and emergency stopping, the regenerative brake cannot generate the required force/moment and an active control is required. In these situations, the control mode is altered from braking to active, and the assistive functions are invoked using the energy charged by the braking control. For safety reasons, we propose a passive motion control method of the cycling wheelchair, even if the wheelchair operates under active control. The proposed cycling wheelchair is validated in a series of experiments in this study.