Measurement and correction of systematic odometry errors in mobile robots

Odometry is the most widely used method for determining the momentary position of a mobile robot. In most practical applications odometry provides easily accessible real-time positioning information in-between periodic absolute position measurements. The frequency at which the (usually costly and/or time-consuming) absolute measurements must be performed depends to a large degree on the accuracy of the odometry system. This paper introduces practical methods for measuring and reducing odometry errors that are caused by the two dominant error sources in differential-drive mobile robots: (a) uncertainty about the effective wheelbase and (b) unequal wheel diameters. These errors stay almost constant over prolonged periods of time. Performing an occasional calibration as proposed here will increase the robot's odometric accuracy and reduce operation cost because an accurate mobile robot requires fewer absolute positioning updates. Many manufacturers or end-users calibrate their robots, usually in a time-consuming and non-systematic trial and error approach. By contrast, the method described in this paper is systematic, provides near-optimal results, and it can be performed easily and without complicated equipment. Experimental results are presented that show a consistent improvement of at least one order of magnitude in odometric accuracy (with respect to systematic errors) for a mobile robot calibrated with our method. Some parts of the material in this paper were presented at the 1995 International Conference on Intelligent Robots and Systems (IROS '95), Pittsburgh, Pennsylvania, August 5-9, 1995; some other parts were presented at the 1995 SPIE Conference on Mobile Robots, Philadelphia, October 22-26, 1995.