Force Sensorless Power Assist Control for Wheelchairs Considering Caster Effects

Power Assist Wheelchair (PAW) has being developed for users and caregivers in current high aging society. As a human-machine system, it is important for PAW to sense the human force and operation. In this paper, a Disturbance Observer (DOB) based force estimator is applied to PAW to estimate external forces including the human force, the rolling resistance and the sliding resistance. The rolling resistance can be compensated using the Static and Coulomb friction model easily. When the directions of PAW is changed, a caster orientation observer is applied to detect the movement of the casters firstly, aiming to reduce the influence on the entire system by the sliding force. Then the sliding resistance is compensated. By compensating rolling resistance and sliding resistance, the human force can be estimated correctly during both straight forward and turning around. Simulation and experimental results demonstrate the validity of the proposed method.