EPA toolbox documentation home
What is EPA?
EPA (Exploring Possible Architectures) is a computational method for representing and exploring the "design spaces" of product architectures. It can help designers consider wider ranges of architectures and potentially help them identify architectures of higher quality.
The most up-to-date implementation of EPA is as a "toolbox" for CAM. A screenshot of the EPA toolbox in use is shown below.
(click picture to enlarge it)
In EPA, "Product architectures" are defined as the abstract conceptual structures that underlie engineering artefacts - similar to the design "concept", "configuration", "product structure" or "topology". Because product architectures are fundamentally qualitative, their design space cannot be explored using conventional numerical engineering techniques. In practice, architectures for new designs are frequently generated using informal processes such as brainstorming, or by reusing existing architectures with only small changes. EPA aims to help designers explore the product architecture "design space" more systematically and more thoroughly, thereby identifying novel and better architectures for a product (in whatever way "better" is defined).
Overview of the approach
EPA models a single product architecture as a set of "components" linked by "connections" - i.e. a network or graph. However, the "components" and "connections" may not correspond directly to individual "pieces of metal": components may be assemblies of many parts (e.g. a jet engine) or may be "organs" composed of features from multiple parts (e.g. a handle), while connections may include flows (e.g. of energy, materials or signals), spatial interactions (e.g. "contains" or "is above"), and assignment relations (e.g. "is composed of") as well as pure structural connections such as "attached to".
Components and connections themselves are then assigned "types" to identify their equivalence at the architecture level, although the detailed design of two components of the same type may be very different in practice. Types may be organised in a generalisation/specialisation hierarchy to reflect higher-order similarities between components; high-level types may be marked "abstract" (rather than "concrete") to indicate they are too generic to be instantiated.
The set of component and connection types (the ontology) then defines the structure of the "design space" for product architectures for a particular problem - however, not every combination of components of those types will "make sense" or be "realisable". Therefore, declarative Network Structure Constraints are used to define what makes a realisable architecture. See EPA modelling for more details of the modelling constructs and their use in practice, and Information for users for a general explanation of model construction in CAM.
Using this information, realisable architectures can be synthesised computationally. Synthesis can start either "from scratch" or from a specified architecture as a start point, The current implementation of EPA uses state-space search; details are given in EPA synthesis.
Finally, synthesised architectures can either be browsed individually or evaluated or classified using structural characteristics; see EPA interpretation for further details of the EPA-specific mechanisms, and How to use charting functionality for an explanation of the CAM charting functionality.
More details of the method are given in the publications listed under "Further information" below.
Strengths and weaknesses of EPA
Strengths: quick, simple, concrete, flexible, can cope with existing archs, graphical, declarative
Weaknesses: limited syntax, computational cost of synthesis can be an issue for large problems
Preliminary evaluation studies (reported in the papers listed at the bottom of this page) have suggested EPA can be both usable and useful, both directly and through giving designers a better understanding of what is and is not possible in the design problem they are facing.
Instructions on using EPA in CAM
Installing EPA: Since the EPA toolbox is not part of the standard CAM distribution, it must be installed manually:
- Download the zipped EPA toolbox files and unzip to somewhere convenient (e.g. the desktop).
- Copy/move the "EPAPalettev2" folder into the "palette" directory of your CAM installation.
- Copy/move the "epa-core.jar" ,"dataset-saving.jar","icon-designer.jar" files into the "modules" directory of your CAM installation.
- Restart CAM - you should now be able to create workbooks of type "EPAPalettev2" and there should be an "EPA architecture synthesis" entry on the "Tools" menu.
Modelling design spaces: EPA modelling
Synthesising architectures: EPA synthesis
Hints on applying EPA to a design problem: EPA hints and tips
A full description of the approach and its application procedure is available here
A number of architecture design problems have been modelled using EPA, either to illustrate the use of the method or for research purposes, as listed below. Some of the models are available for download; if you are interested in other models, please contact David Wyatt. Downloadable models also state the changes to the default synthesis settings that must be made to synthesise architectures; the meanings of the synthesis settings are discussed in EPA synthesis.
- Ten green bottles (Adding components: 10; Adding connections: 10)
- Aeroplane topology (Workbook containing architecture schema: schema)
- Gear trains (Adding components: 3; Adding connections: 5)
- Hydrocarbons (Adding components: 8 (breadth-first); Adding connections: 7)
- Vacuum cleaners: full architecture, airflow path, cyclone incorporation (Synthesis start point: From workbook - Sanyo SC-N200; Adding components: 3 (stochastic, 1000 runs); Adding connections: 6 (stochastic, 1 run))
- Bicycle lighting systems
- Diesel engine component mounting arrangements
- Domestic hot water systems
- Hybrid power trains
- Hydraulic systems
- Respiratory systems
The EPA method and software implementation arises from work carried out by David Wyatt in his PhD research project "Supporting Product Architecture Design". Further details of the method may be found in the following publications:
WYATT, D. F., WYNN, D. C., JARRETT, J. P. and CLARKSON, P. J. (2011) 'Supporting Product Architecture Design Using Computational Design Synthesis with Network Structure Constraints' Research in Engineering Design, DOI: 10.1007/s00163-011-0112-y
WYATT, D. F., WYNN, D. C. and CLARKSON, P. J. (2009) 'A computational method to support product architecture design' Proceedings of the ASME International Mechanical Engineering Congress and Exposition (IMECE 2009), Lake Buena Vista, Florida, USA, 13-19 November 2009
WYATT, D. F. PhD thesis