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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

	Block on Ground	Conveyor	Bullet
	Static	Deterministic	Random
			(Unpredictable Motion)
	(No Motion)	(Predictable Motion)
	40.2.7 ROBOT COORDINATION

If only a single robot may be used in a workcell, then bottlenecks will soon arise. When two robots are placed in close proximity, they can produce more bottlenecks, thus they must be given some scheme for avoiding each other. If these robots are to cooperate then a complete and integrated cooperation strategy is required. These strategies require some sort of status link between both manipulators. To make sense of the status of the other robot, it is also necessary to have algorithms for path planning in the Deterministic environment. This algorithm relies upon a proper moving obstacle path planning scheme being developed first. It is possible to use assumptions, or an engineered environment to allow robot coordinations, without the extensiveness of a complete coordination algorithm.