Sonic path finder [2] alarms the blind when detecting the obstacle by the acoustic difference. However, it does not provide the accurate path but the position of an obstacle. MELDOG 
[3 I uses the artificial intelligence., unlike in the sonic path- finder. It can provide the accurate position of an obstacle 
using the ultrasound and laser sensors. But, in general, it is not only relatively large and heavy, but also requires fair 
amount of training. NavBelt[4] used an ultrasound sensor array instead of the steering signal for the robot controller 
and transmitted acoustic cues to the traveler's headphone. But this system also required long-period adaptation 
training even at a low speed. Guide cane [5] uses an array of ultrasound sensors, and is relatively small, light, and 
easy to use. MELDOG uses the local path, but guide cane uses both the local and the global paths for path planning. 
The global path planning is accomplished, when all the environmental information such as positions or shapes of 
obstacles is known. On the other hand, the local path planning is accomplished by the self-interpretation of the 
unknown environment. The global path planning needs to detect the location of robots, so-called "the map matching 
technique" with the ultrasound sensor or GPS [6]. Guide cane uses the absolute position method using GPS, and 
thus, detects the accurate position, regardless of time consuming process. But GPS method for the guide cane is less accurate in determining positions.