Distributed Robot Architectures (DIRA)

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The Carnegie Mellon
Field Robotics Center

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Overview
The primary objective of this project is to develop fundamental capabilities that enable multiple, distributed, heterogeneous robots to coordinate tasks that cannot be accomplished by the robots individually. The basic concept is to enable individual robots to act independently, while still allowing for tight, precise coordination when necessary. Individual robots will be highly autonomous, yet will be able to synchronize their behaviors, negotiate with one another to perform tasks, and "advertise" their capabilities. The proposed architecture supports the ability of robots to react to changing and/or previously unknown conditions by replanning and negotiating with one another if the new plans conflict with previously planned-upon cooperative behaviors. The resulting capability will make it possible for teams of robots to undertake complex coordinated tasks, such as assembling large structures, that are beyond the capabilities of any one of the robots individually. Emphasis will be placed on the reliability of the worksystem to monitor and deal with unexpected situations, and flexibility to dynamically reconfigure as situations change and/or new robots join the team. This project is a multi-center collaboration with participation from Johnson Space Center (JSC)/TRACLabs and the National Institute of Standards and Technology (NIST). CMU will focus on algorithms for distributed task execution, task negotiation, planning under uncertainty, and algorithms specific to the domain of multi-robot assembly and construction.
Challenges
The main technical challenge of the project is to develop an architectural framework that permits a high degree of autonomy for each individual robot, while providing a coordination structure that enables the group to act as a unified team. Our approach is to extend current state-of-the-art hierarchical, layered robot architectures being developed at CMU (TCA), TRACLabs (3T) and NIST (RCS) to support distributed, coordinated operations. Our proposed architecture is highly compatible with these single-agent robot architectures, and will extend them to enable multiple robots to handle complex tasks that require a fair degree of coordination and autonomy. Research issues include: Developing communication protocols that will support sophisticated interaction between robots, including the ability to negotiate and distribute tasks, monitor progress in a distributed fashion, and distribute sensing and control among a heterogeneous group of robots; Dealing with asynchronous timing issues introduced by distributing the control, data bandwidth limitations, and issues of reliability (e.g., dealing with situations where robots, or communication channels, break down); Developing task-specific algorithms that take advantage of the architectural framework to enable teams of robots to achieve tasks that no single robot could achieve. The architectural approach will be validated by an increasingly complex series of demonstrations in the area of multi-robot assembly with a heterogeneous team of robots. The "team" will include the NIST Robocrane, a roving eye, and a mobile manipulator.
Visual Servoing
	Since assembly operations require high precision, we use visual servoing to perform mating operations. Proof of principle servoing has been demonstrated with a desktop mounted manipulator and a roving eye (stereo cameras mounted on a mobile robot). The visual servoing determines the relative 6-DOF pose between two fiducial markers and determines a correction to reduce the difference between current relative pose and the desired one. More information about XVision, the image library that we use
The Robots
	Gross Motion Robocrane is a large gantry type, inverted Stewart platform capable of manipulating large loads. We use Robocrane for gross manipulation. Visit NIST for more information
	Mobile Manipulator We use Bullwinkle, a mobile robot built by RWII, to host a small five degree-of-freedom arm that is capable of fine manipulation. The robot is a four wheel, skid steered machine equipped with onboard computing and inertial sensing. Visit RWII for more information
The Simulator
	We are developing a simulator that will allow us to test robot planning and architectural issues. It models robot mechanisms and sensors such as stereo vision. The simulator will enable testing of algorithms in repeatable configuration and in configurations that are not easy to create physically. The system that drives our robot testbed can be attached to the simulator through an identical interface.