Phase Lag Bounded Velocity Planning for High Performance Path Tracking

We propose an algorithm for planning the velocity of a vehicle on a pre-planned path applicable to differentially steered, zero turn radius, mobile robots with symmetric mass distribution about the turn axis. This approach uses estimates of path curvature to maintain tracking precision in the vehicle's heading controller. The longitudinal speed of the vehicle is restricted to limit the bandwidth of the input forcing function (the path). As a result, we guarantee bounds on the driving frequency in the heading controller so that the robot stays close to the intended path. The result allows the robot to use the full performance envelope of the drive motors and provides a principled means of regulating precision and time performance during path traversal. Evaluation of the technique is conducted in simulation and in real experiments on the UMass uBot. Results indicate that the proposed velocity planner can make full use of motor performance and reduces path tracking error and traversal times relative to constant velocity plans.