Reduction of Odometry Errors in Over-constrained Mobile Robots1

This paper presents an analysis of odometry errors in over-constrained mobile robots, that is, vehicles that have more independent motors than degrees of freedom. Based on our analysis we developed and examined three novel error-reducing methods. One method, called “Fewest Pulses” method, makes use of the observation that most terrain irregularities, as well as wheel slip, result in an erroneous over-count of encoder pulses. A second method, called “Cross-coupled Control,” optimizes the motor control algorithm of the robot to reduce synchronization errors that would otherwise result in wheel slip with conventional controllers. The third method is based on so-called Expert Rules. With this method readings from redundant encoders are compared and utilized in different ways, according to predefined rules. In the work described here we implemented our three error reducing methods on a modified Pioneer AT skid-steer platform and compared their odometric accuracy. The results in this paper point to clear advantages of the Expert Rulebased method over the other tested methods.