1. Introduction
There are many guidance systems for visually impaired travelers to navigate quickly and safely against obstacles and other hazards faced. Recent statistical data [ 11 reported that there were 46,000 blind persons in Korea, 1999. Ingeneral, the blind travels using a white cane or carries a guidance dog. But, the guidance dog is very expensive for the blind and hard to maintain. Therefore, most blind use white canes without the information of environmental
situation. The most important function for the blind persons is to get information on the shape of the road and the position of obstacles when they are in unknown places. With this information, they need to arrive at their destinations,
avoiding unexpected obstacles. Many robot technologies have been applied to guide the blind and some are commercially available.