  In this letter, we investigate the formation control problem of mobile robots
moving in the plane where, instead of assuming robots to be simple points, each
robot is assumed to have the form of a disk with equal radius. Based on
interior angle measurements of the neighboring robots' disk, which can be
obtained from low-cost vision sensors, we propose a gradient-based distributed
control law and show the exponential convergence property of the associated
error system. By construction, the proposed control law has the appealing
property of ensuring collision avoidance between neighboring robots. We also
present simulation results for {a team} of four circular mobile robots forming
a rectangular shape.
