An Integrated Path Planning and Control Framework for Nonholonomic Unicycles

In this paper, navigation and control of autonomous mobile unicycle robots in a complex and partially known obstacle-ridden environment is considered. The unicycle dynamic model used has two differentially-driven wheels, with the two wheel motor torques as the system input. Two novel controllers are derived which stabilize the robot within a surrounding disk-shaped area (henceforth called a bubble) of arbitrary size for any initial velocities. The first controller takes the unicycle to the center of its bubble while the second corrects its orientation. The torque-levels can be controlled by adjusting gains. The control laws are independent of inertial parameters. An existing global planner is used by each robot to create a string of bubbles connecting its start point to its goal point, with each bubble’s size indicative of the radial obstacle-clearance available from its center. Each robot then uses its local bubble-controllers to follow its global planned path. This method is then extended to an experimental setup of multiple robots, each equipped with proximity sensors. The same algorithm is run on each robot in a distributed manner with no information sharing. Results are presented to illustrate the robustness of the system.