Scheduling of Parallel Computation for a Computer-Controlled Mechanical Manipulator

The physical compactness of the microcomputer has made it feasible to mount the controller and the mechanical manipulator together as a single unit. By using a computer with multiple central processing units (CPU's), parallel computations may be executed to achieve a minimum computing time so that a real-time control is possible. The parallel processing system utilizes one CPU for each link of the manipulator. Because of the dynamic coupling between adjacent links, precedence relations appear among the subtasks to be executed in CPU's. Under the series-parallel precedence constraints a method of "variable" branch-and-bound has been developed which determines an optimum ordered schedule for each of the CPU's. It consists of, alternatively, forward and backward search procedures with an aid of pushdown-stacks. In each forward search procedure, it seeks the currently feasible schedule with shorter computing time which updates the upper bound of the optimum schedule, while in each backward search procedure it discards those schedule-branches that will not provide improvements. A Fortran program has been written for a manipulator based on the Newton-Euler formulation of dynamic equations and is applied to the Stanford manipulator as an illustration.