Sonic path finder [2] alarms the bl

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.