High performance control for graceful motion of an intelligent wheelchair

To be acceptable to human drivers, the motion of an intelligent robotic wheelchair must be more than just collision-free: it must be graceful. We define graceful motion as being safe, comfortable, fast and intuitive. In this paper, we quantify these properties of graceful motion, providing formal evaluation criteria. We propose a method for graceful motion and present implementation results for the task of driving through a narrow doorway, evaluated on a simulated model of the wheelchair. We use B-splines to specify an intuitive path to a goal, and then describe path-following control law for a differential- drive wheeled vehicle to follow that path within velocity and acceleration bounds. Existing methods typically respond to tight clearances with very slow motion which is not graceful. Our results show that, starting from a set of representative poses, the wheelchair passes through the door at near maximum speed, staying close to the mid-line of the doorway. The velocity of the wheelchair reflects the curvature of the path rather than the closeness of the door edges, so it can move smoothly, safely, and quickly through the doorway. Thus, this paper makes two contributions - first it introduces the concept of graceful motion and provides quantitative measures for the same, and second, it proposes a method for graceful motion and demonstrates it on a specific task.

I. Introduction

An intelligent wheelchair that navigates safely through the environment without requiring constant control from its human driver can reduce driving-stress and increase mobility of a disabled person [1], [2]. The ability of the wheelchair to gracefully perform common navigation tasks such as going through a door, going up and down ramps, and turning sharp corners is an important factor in ensuring the comfort of the human driver.