On the surface, thecable harness design process is straightforward. A closer examination will show, however, that it contains a complex set of dependencies between the design features and activities. The cable designers must work with multiple perspectives while interacting with structural, electrical, and package designers and production engineers. The design task is a a typical configuration design problem, in which the designer must first select a design from a large search space of possible configurations before deciding on parametric variations for each configuration. One aspect of this is shown in the selection of cable configuration for a give wiring requirement.
To construct the agent-framework for this problem, we started by
decomposing the problem into top level tasks, each of which is
addressed by an agent. The problem domain also is decomposed into
multiple layers of features, which we call the domain
model. Each
agent has a user interface, a local model, and local knowledge
base. Each agent maintains its internal view of the design domain,
and interacts with other agents via feature
mapping. This led to the following architecture, in which the
"central node" maintains a list of input and output features for each
agent, and thus manages the flow of messages
whenever an agent publishes or requests information.
The FirstLink framework was based on an extensive study of the actual design process at Lockheed. We have confirmed from our development efforts that this problem domain provides a suitable testbed for studying the agent-assisted, collaborative design precess for the following reasons:
The following literature describes in depth both the cable design domain and
the applied agent-framework:
AI/EDAM Abstract and
AI/EDAM'94 article or
CIE Abstract and
CIE'92 article
.
2. Cable harness components
A harness is an assembly of
connectors, bundles, and transitions.
3. Cable configurations
Many different configurations can
satisfy a given set of electrical specifications.
4. Design dependencies
Interdependent subtasks makes cable design
particularly challenging for a team of designers.
5. Design aspects
The harness can be viewed from several basic
perspectives: function (electrical specifications), configuration (the
harness as an assembly with sub-assemblies and parts), and geometry
(the paths taken through space and the spaces that can be occupied.
Decomposing the problem according to these perspectives can simplify the
design process.
6.
The First-Link agents
The top level decomposition of the
harness leads to the set of agents that comprise First-Link: the cable
(configuration) editor, the environment editor, the free space manager
(router), and the component selector.
7. Project scope
The First-Link system is designed to interface
with electronics package and vehicle structural design upstream, and
with production planning system downstream.
8. Agent construction
Each agent has a user interface,
a local model, and local knowledge base. Agents convert their
local features to global features in the domain model for
publishing/retrieving changes.
9.
Facillitator (Central node)
A central node or facilitator
maintains a directory of which agent(s) are associated with domain
features.
10. Example of an agent: Cable Editor
We indicate some common properties of the
agents with the Cable Editor.
11. Example: local model
Like other agents, the cable editor
maintains its internal view of the world. In this case, the agent applies its
internal set of rules to ensure that the wire count in each bundle remains
correct as the user (or another agent manipulates the cable topology. One of
its tasks is to recompute the approximate bundle diameters based on the
wire-counts.
12.
Example of internal operations
Internally, it uses a set of simple, low-level
operations to derive a new cable topology.
13. Example of a user-level operation
A "swap-bundle" operation is
an example of a high-level, composite operation that a human might invoke
to transform the cable's topology.
14.
Agents and feature abstraction
One benefit that the agent-based
implementation provides is that the designers can now act on high-level
features and operations without the danger of ignoring the details. The
agents ensure that proper operations are applied to the elements of its
internal model. The communication between different agents and the human
users is done using high-level features. For the details of implementation
framework, see
"An Agent-Based Approach to Cable Harness Design."
NEXT-LINK - This is the Lockheed sponsored continuation of the First-Link project. Current research is SHARE sponsored.
ACaPS - This is a related Lockheed project to provide an Agile Cable Production Service.
CABLER - This is an off-shoot of the First-Link project which focuses on interactive 3D routing issues.
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Hisup Park
