Path planning for two planar robots moving in unknown environment

The authors investigate the problem of planning a collision-free path for a 5-link closed chain, which represents two planar robot manipulators cooperatively carrying a small object 2-D workspace that is filled with unknown stationary obstacles. It is assumed that the shapes of the obstacles are arbitrary, their positions are not known, and any point on the robots is subject to collision. The path of the closed chain is planned continuously, based on the arms´ start position, target position, current position, and the sensory feedback. The configuration space of the closed chain is divided into two 2-D subspaces. In each 2-D subspace, a connected free space is denoted as a free region. Within each free region, Lumelsky´s algorithm Bug2 is adopted to find the collision-free path. The connectivity between free regions is discussed. A systematic search method is used to determine if there is an unvisited free region when no collision-free path can be found in visited free regions. The proposed algorithm is nonheuristic and converges