Power assist control by repulsive compliance control of electric wheelchair

This paper describes a power assist control in pushing task by an electric wheelchair. Recently, wheelchairs are widely used in daily lives by disabled person in walking. To improve the function of wheelchair, a lot of studies of power assist control in electric wheelchair have been considered. In this paper, a new power assist control in pushing task is proposed as intelligent function of wheelchair. This is called a repulsive compliance control. In this strategy, reaction force of human input into object is estimated and is utilized to generate the power assist torque for wheels driving. The proposed approach brings a sophisticated function that makes it easy to carry out pushing task by wheelchair users. First, an acceleration estimation observer (AOB) and a disturbance observer (DOB) are employed. AOB can abstract human input as equivalent acceleration without force/torque sensor. DOB guarantees stability of whole control system. Second, a compliance control is constructed to generate the motion command of pushing task. The compliance control itself is passivity based control, and stable and flexible responses are expected. Here an assistance ratio is designed based on velocity control of wheelchair. Finally, to confirm the validity of the proposed approach in experiments, two test operations are implemented.