Title:
An Agent-Based Approach to the Design of Rapidly Deployable Fault Tolerant Manipulators
An Agent-Based Approach to the Design of Rapidly Deployable Fault Tolerant Manipulators
Authors
Paredis, Christiaan J. J.
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Abstract
There exists a need for manipulators that are more flexible and reliable than the current fixed
configuration manipulators. Indeed, robot manipulators can be easily reprogrammed to perform
different tasks, yet the range of tasks that can be performed by a manipulator is limited
by its mechanical structure. In remote and hazardous environments, such as a nuclear facility
or a space station, the range of tasks that may need to be performed often exceeds the
capabilities of a single manipulator. Moreover, it is essential that critical tasks be executed
reliably in these environments.
To address this need for a more flexible and reliable manipulator, we propose the concept of
a rapidly deployable fault tolerant manipulator system. Such a system combines a Reconfigurable
Modular Manipulator System (RMMS) with support software for rapid programming,
trajectory planning, and control. This allows the user to rapidly configure a fault
tolerant manipulator custom-tailored for a given task. This thesis investigates all aspects
involved in such a system. It describes an RMMS prototype which consists of seven manipulator
modules with a total of four degrees-of-freedom. The reconfigurability of the hardware
is made transparent to the user by the supporting control software that automatically
adapts itself to the current manipulator configuration. To achieve high reliability, a global
fault tolerant trajectory planning algorithm is introduced. This algorithm guarantees that a
manipulator can continue its task even when one of the manipulator joints fails and is immobilized. Finally, all these aspects are considered simultaneously in the task based design
software, that determines the manipulator configuration, its base position, and the fault tolerant
joint space trajectory that are optimally suited to perform a given task.
The most important contribution of this thesis is a novel agent-based approach to solve the
task based design problem. The approach is based on a genetic algorithm for which the
modification and evaluation operations are implemented as autonomous asynchronous
agents. Specific design knowledge about the task based design problem has been included in
the agents, resulting in a significant reduction of the size of the design space and of the cost
of evaluating a candidate design. Furthermore, thanks to their autonomous and asynchronous
nature, these agents can be easily executed distributedly on a network of workstations.
The flexibility and performance of the agent-based implementation, combined with the
problem specific knowledge included in the modification and evaluation agents results in a
powerful new approach to task based design of rapidly deployable fault tolerant manipulators.
Finally, the thesis presents a performance analysis of the agent-based design framework by
comparing its results with those of exhaustive search, random search, and multiple restart
statistical hill-climbing. This analysis is performed for three examples, including a comprehensive
example of a satellite docking operation with a fault tolerant modular manipulator
mounted in the cargo bay of the space shuttle.
Sponsor
Department of Energy (Grant #DE-F902-
89ER14042)
Sandia National Laboratories (Contract #AL–3020)
The Robotics Institute at Carnegie Mellon University
Sandia National Laboratories (Contract #AL–3020)
The Robotics Institute at Carnegie Mellon University
Date Issued
1996-08
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