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RI Seminar -- John Lloyd


This talk will describe elements of the presenter's work in sensor-driven robotcontrol.

First, a quick overview will be given of the Multi-Robot Control C Library (Multi-RCCL), which provides an environment for sensor-driven robot programmingin a UNIX (or UNIX-like) environment. The system provides primitives for specifying various types of robot motions and, in particular, allowing them to track time-varying targets. This latter capability has allowed Multi-RCCL to serve as a research platform for such applications as force and compliant control, telerobotics, and visual servoing.

The next part will discuss how the Multi-RCCL trajectory generator creates smooth motions by blending together adjacent path segments, removing excess acceleration based on an estimate of the difference in path velocities. Since this method requires no advance knowledge of the path segments, it is well suited for situations where the paths are changing with time. The method can also be used to adjust the spatial shape of the transition curve (such as to have it pass around or through the transition ``via point''), which is useful in handling different types of geometric tasks.

The talk will conclude by describing some of the presenter's work on kinematic singularities. These are bothersome places in the manipulator workspace where the Jacobian loses rank and following a Cartesian path can cause unbounded joint velocities and accelerations. Since it is common for paths which are modified on-line to wander into singularities, proper handling of these situations is important. Usual approaches to this problem involve limiting the joint velocities at the expense of deviating from the desired path. The presenter has developed an alternate approach, mainly applicable to simpler non-redundant robots, in which the trajectory is time-scaled (in real-time) so as to bound both the joint velocities and accelerations without deviating from the desired path. This will be illustrated for the cases of the elbow and shoulder singularities of a PUMA-like manipulator.


John Lloyd is the author of Multi-RCCL, a system for programming robots in a UNIX workstation environment. He has worked as a consultant for the Jet Propulsion Laboratory, General Electric, and several universities. His research interests include robot programming, kinematics, trajectory generation, and motion planning, as well as real-time systems and computer graphics. He is currently completing his Ph.D. at McGill University on the subject of robot trajectory generation near kinematic singularities.

Host                   Ralph Hollis (rhollis@cs.cmu.edu)
Appointments     Mary Anne Cowden (mac@cs.cmu.edu)

Christopher Lee | chrislee@ri.cmu.edu
Last modified: Thu Oct 13 18:36:07 1994