A low-cost, installation convenient, continuously
　　accurate and multi-sensor based localization system
　　for a mobile robot
　　was introduced. A gyroscope based dead reckoning
　　system was firstly employed to provide momentary but
　　real-time heading and
　　position information for the robot. Then, a novel
　　scanning laser and ultrasonic absolute positioning
　　system was developed to
　　eliminate the accumulative error in dead reckoned
　　robot heading and position. The robot has a fixed
　　base station where the robot can
　　recharge itself. A scanning laser and an ultrasonic
　　transmitter were mounted on the base station to
　　measure the robots angle and
　　distance relative to it. Another scanning laser was
　　mounted on the robot to measure the base stations
　　relative angle in the robots
　　frame. The base station and the robot were wirelessly
　　connected through radio frequency (R.F). This method
　　was implemented on a
　　lawn robot. Experimental results show that the lawn
　　robot can work continuously for a long period of time
　　within thirty meters away
　　from the base station without losing its position.