. IntroductionOne of the many features needed to support the activities of autonomous systems is the ability to plan motion. Motion planning enables a robot to move in its environment securely and to accomplish a given task. In dynamic environments, the necessary adaptation of the robot motion is provided by closed control loops comprising sensing, planning, and acting, which have very short cycle times. One approach for realizing intelligent and reactive robotic systems is to integrate the planning algorithms into the control loop. Unfortunately, sound planning algorithms are complex and need long execution times. To still pursue this approach, a reduction in planning time is required. New parallel computing architectures with high computing power look promising.One could object that the motion planning problem in general can become very complex for increasing degrees of freedom (DOF) of the robot and is still intractable, even for a parallel computer. On the other hand, the aim of parallel processing is not to reduce the intractability of complex problems, but to reduce the solution time for given problems, or to increase their solution quality. Also, it is important to approximate the general problem by a simplified, but still realistic problem. This is independent or whether sequential of parallel processing is used.Thus, an important task is the parallelization of existing problem solutions in robotics so that they are suitable for highly computational parallelism. In several cases, fundamentally new algorithms have to be designed, so that a parallelization is feasible. The paper [28] reviews the research performed thus far in designing and implementing parallel algorithms for robotics. One of the key findings is that, in the subareas of manipulation and task planning, not much work has been published concerning parallel algorithms. Several parallel motion planing algorithms have been suggested however, which are reviewed in the rest of this paper.
. Motion Planning ApproachesSequential motion planning approaches have been classified in: skeletons, cell decompositions, potential fields, and mathematical programming [16]. In the skeleton approach, the free configuration space (free C-space), i.e., the set of feasible motions, is retracted, reduced to, or mapped onto a network of one-dimensional (1D) lines. In the cell decomposition approach, the free C-space is decomposed into a set of simple cells, and the adjacency relationships among the cells are computed.To structure the parallel approaches, these keywords are modified by exchanging "skeletons" and "cell decompositions" with graph-based and grid-based approaches. The parallel ancillary algorithms, which are necessary to fulfill the planning task, are omitted due to space limitations.
Graph-based ApproachesThe graph-based approaches include irregular skeletons and object-dependent cell decompositions. These approaches consist of two basic phases. The first phase is associated with the construction of a graph representing relations between free space. Aft...