Trajectory Planning: Pick-and-Place Operations
The motions undergone by robotic mechanical systems should be, as a rule, as smooth as possible; i.e., abrupt changes in position, velocity, and acceleration should be avoided. Indeed, abrupt motions require unlimited amounts of power to be implemented, w
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Trajectory Planning: Pick-and-Place Operations
6.1 Introduction The motions undergone by robotic mechanical systems should be, as a rule, as smooth as possible; i.e., abrupt changes in position, velocity, and acceleration should be avoided. Indeed, abrupt motions require unlimited amounts of power to be implemented, which the motors cannot supply because of their physical limitations. On the other hand, abrupt motion changes arise when the robot collides with an object, a situation that should also be avoided. While smooth motions can be planned with simple techniques, as described below, these are no guarantees that no abrupt motion changes will occur. In fact, if the work environment is cluttered with objects, whether stationary or mobile, collisions may occur. Under ideal conditions, a flexible manufacturing cell is a work environment in which all objects, machines and workpieces alike, move with preprogrammed motions that by their nature, can be predicted at any instant. Actual situations, however, are far from being ideal, and system failures are unavoidable. Unpredictable situations should thus be accounted for when designing a robotic system, which can be done by supplying the system with sensors for the automatic detection of unexpected events or by providing for human monitoring. Nevertheless, robotic systems find applications not only in the well-structured environments of flexible manufacturing cells, but also in unstructured environments such as exploration of unknown terrains and systems in which humans are present. The planning of robot motions in the latter case is obviously much more challenging than in the former. Robot motion planning in unstructured environments calls for techniques beyond the scope of those studied in this book, involving such areas as pattern recognition and artificial intelligence. For this reason, we have devoted this book to the planning of robot motions in structured environments only.
Electronic supplementary material The online version of this article (doi: 10.1007/978-3-31901851-5_6) contains supplementary material, which is available to authorized users. J. Angeles, Fundamentals of Robotic Mechanical Systems: Theory, Methods, and Algorithms, Mechanical Engineering Series 124, DOI 10.1007/978-3-319-01851-5__6, © Springer International Publishing Switzerland 2014
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6 Trajectory Planning: Pick-and-Place Operations
Two typical tasks call for trajectory planning techniques, namely, • pick-and-place operations (PPO), and • continuous paths (CP). We will study PPO in this chapter, with Chap. 11 devoted to CP. Moreover, we will focus on simple robotic manipulators of the serial type, although these techniques can be directly applied to other, more advanced, robotic mechanical systems.
6.2 Background on PPO In PPO, a robotic manipulator is meant to take a workpiece from a given initial pose, specified by the position of one of its points and its orientation with respect to a certain coordinate frame, to a final pose, specified likewise. However, how the object move
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