Autonomous/Semi-Autonomous Navigation System of a Wheelchair by Active Ultrasonic Beacons

This paper describes the autonomous and semiautonomous navigation system of a powered wheelchair for disabled people and nursing staffs. In order to detect its position reliably, this system utilizes active ultrasonic beacons on ceiling. 2 receivers on a wheelchair measures the time-of-flight of the ultrasonic pulses from 2 beacons. Since the distances from only 1 beacon can be obtained at once, the position should be dynamically estimated with its movement in a measurement interval during navigation. Three types of navigation mode by this positioning system are also proposed to assist users. "Automatic transfer mode" guides a wheelchair to a target position autonomously. "Operation assistance mode" helps a user's operation by moving a wheelchair straight toward a commanded direction. "Selective semi-automatic mode" runs path networks selecting a desired direction at each branch point. These navigations were practically succeeded. 1 I n t r o d u c t i o n Elderly population is increasing rapidly today and it has been a critical problem in our society. Since nursing staffs for elderly or disabled people are not enough and their work is very hard, assistance by effective technologies is strongly requested. Considering the mobility assistance for disabled people with motor problems, the autonomous transfer system by a powered wheelchair is needed in hospitals or nursing homes instead of a nursing staff to navigate a wheelchair. The assistant system to reduce the operation effort of a wheelchair is also required for disabled users to move independently, especially when they have disability to operate a normal joystick well or they use some interfaces by chin, electromyogram, voice, etc. Several autonomous navigation systems of a wheelchair [1]-[4] or a mobile robot have been proposed. Though the 0 7 8 0 3 5 8 8 6 4 / 0 0 1 5 1 0 . 0 0 © 2 0 0 0 IEEE 1 ID 2 @ ID 1 I D 3 @ Ultrasonic beacons \ \ \ Ultrasonic pulse on ceiling \ \ Control by , l Joystiq IO¢o e , 2 Receivers . ~ Position O) ~ l ~ t ' . 2 wheels ~ r w i t h 2 encoders V for odometry Figure 1: Navigation system using ultrasonic beacons highest way is the "intelligent" control to recognize environment by vision, sonar, and so on, it doesn't have sufficient reliability and robustness now. Therefore, the methods using artificial landmarks have been developed to navigate them easily and reliably [5][6]. In the human-machine coexisting environment, landmarks and navigation system should be harmless and not be obstructive to human [7]. We have been developing a reliable, safe and inexpensive positioning system using active ultrasonic beacons mounted on a ceiling for an indoor mobile robot [8]. In this paper, we apply this system to a powered wheelchair and propose the autonomous navigation to transfer it and semi-autonomous navigation to assist a user to operate it easily by utilizing active ultrasonic beacons in house. Of course, the function of obstacle avoidance is necessary for safety, however, we do not deal with it and we focus on basic system of navigation in this paper.