Most autonomous mobile robots view things only in front of them, and as a result, they may collide with objects moving from the side or from behind. To overcome this problem, an Active Omni-directional Range Sensor System has been built, that can obtain an omni-directional depth map through the use of a laser conic plane and a conic mirror. In the navigation of the mobile robot, the proposed sensor system makes a laser conic plane by rotating the laser point source at high speed; this creates a two-dimensional depth map, in real time, once an image has been captured. Object-recognition is made possible by using a three-dimensional depth map acquired from a combination of previously obtained two-dimensional depth maps. The experimental results show that the proposed sensor system is very efficient, and can be utilized For object-recognition and navigation of a mobile robot in an unknown environment. (C) 1998 Elsevier Science Ltd. All rights reserved.