Version 1.0, August 31, 2001, Copyright, Hugh Jack 1993-2001
Motion of obstacles can cause significant path planning problems. Motion occurs in the form of rotation, and translation. In most path planners the only motions considered are for the payload and manipulator. In most cases an obstacle in the environment will experience both rotation and translation. This has devastating effects on all of the path planning methods, because some tough new requirements are added. The path planning systems must now incorporate a time scale factor, and keep an object description which includes a position, a velocity vector, and rotation vector. The method must also do the calculations to detect collisions and status at every instant of time as the system changes. With simplifications the problem may be reduced to a more manageable level. Obstacles may be categorized into motion categories; Static (un-moving), Deterministic (has predictable occurrence and positions), and Random (Freely moving, with no regular occurrence). All of these are of interest because most parts fixed in a workcell are Static, workpieces from feeders and conveyors are Deterministic, and human intruders are Random. Random obstacle motion usually occurs so quickly that path planning may only be able to escape the path of the obstacle, not compensate it. These motion strategies are often considered in the static and cyclic states, but the Random solutions are not implemented widely, except as safety measures.
Figure 2.6 Obstacle Motion Types
