There mingle in the contemporary field of robotics a great many disparate currents of thought from a large variety of disciplines. Nevertheless, a largely unspoken understanding seems to prevail in the field to the effect that certain topics are conceptually distinct. In general, methods of task planning are held to be unrelated to methods of control. The former belong to the realm of geometry and logic whereas the latter inhabit the earthier domain of engineering analysis; geometry is usually associated with off-line computation whereas everyone knows that control must be accomplished in real-time; the one is a “high level” activity whereas the other is at a “low level”. This article concerns one circle of ideas that, in contrast, intrinsically binds action and intention together in the description of the robot’s task. From the perspective of task planning, this point of view seeks to represent abstract goals via a geometric formalism which is guaranteed to furnish a correct control law as well. From the perspective of control theory, the methodology substitutes reference dynamical systems for reference trajectories. From the point of view of computation, less is required off-line, while more is demanded of the real-time controller. From the historical perspective, these techniques represent the effort of engineers to avail themselves of natural physical phenomena in the synthesis of unnatural machines.
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