Extending functionality of RF Ultrasound positioning system with dead-reckoning to accurately determine mobile robot´s orientation

In this paper we show how to accurately track position and orientation of a mobile robot using positioning only RF Ultrasound transceiver system and dead-reckoning. The solution is based on geometrical displacement of the positioning device from the axis of rotation of the robot which brings dependency in position of the device and robot´s orientation and enables the correction of the absolute orientation of the robot. Estimation is done via Extended Kalman Filter with variable discretization time because of stochastic nature of measurement arrival times. We describe and analyze the main sources of noise in odometry and position device readings. We also suggest the method for measurement outlier elimination derived from empirical measurement analysis. Experimental verification of the proposed method is presented that yields position error aprox. 1±2.5 centimeters and 1±2 degrees.