Semi-autonomous Navigation of a Robotic Wheelchair

Abstract

The present work considers the development of a wheelchair for people with special needs, which is capable of navigating semi-autonomously within its workspace. Such a system is expected to prove useful to people with impaired mobility, who may have limited fine motor control of the upper extremities. Among the implemented behaviors of this robotic system are the avoidance of obstacles, the motion in the middle of the free space and the following of a moving target specified by the user (e.g. follow a person walking in front of the wheelchair). The wheelchair is equipped with sonars, which are used for distance measurement in preselected critical directions, and with a panoramic camera (with a 360 degree field of view), which is used for following a moving target. After suitably processing the color sequence of the panoramic images using the color histogram of the desired target, the orientation of the target with respect to the wheelchair is determined, while its distance is determined by the sonars. The motion control laws developed for the system use the sensory data and take into account the nonholonomic kinematic constraints of the wheelchair, in order to guarantee certain desired features of the closed--loop system, such as stability, while preserving their simplicity, for ease in implementation. An experimental prototype has been developed at ICS--FORTH, based on a commercially--available wheelchair, where the sensors, the computing power and the electronics needed for the implementation of the navigation behaviors and of the user interfaces (touch screen, voice commands) were developed as add--on modules