Abstract
The primary aim of this dissertation is to provide a platform and format-neutral exchange mechanism for Layered Manufacturing (LM) and Telemanufacturing. The current exchange standard is the Stereolithography (STL) file format. The format is notoriously prone to error and frequently causes problems during the process-planning stage. The format exclusively uses a triangular boundary representation as a mathematical model and therefore lacks accuracy for models that exhibit curved features [Van00]. The goal of this thesis is therefore two-fold. Firstly, a short-term solution needs to be implemented as a stopgap measure, while a long-term solution is realised. The long-term solution will hopefully fill the communication gap caused by the STL format.
A short-term solution needs to extend the capabilities of the STL format. This will compensate for the discrepancies and will allow the STL format to keep up with the requirements of the industry, while a more permanent solution is developed. In this thesis, a stopgap measure in the form of STL-Extended is proposed. STL-Extended or STL-E is a technique that redefines the semantic properties of redundant information in the existing STL file. This allows additional information to be embedded within a STL file and facilitates the storage of models more accurately. The main aim of STL-E is to remain backwards compatible with legacy hardware and software. Although this does not address the flaws that the format exhibits, it provides the most transparent integration possible.
A long-term solution is proposed in the form of the Data Exchange Framework for Layered Manufacturing (DEF4LM or just DEF). This is not a new LM file format, but a platform that would allow any format that is used by the industry to potentially become an exchange standard between designer and bureau. In essence, the platform redefines the mathematical model (representation technique) as the common denominator between abstractions, as opposed to the computer model (file format).
DEF4LM constitutes a four-layer architecture, which includes the Data Layer, Implementation Layer, System Layer and the Application Layer. The Data Layer represents the actual computer model being used and serves as the carrier medium for the model. The Implementation Layer consists of a descriptor and a properties file. These two elements are used to describe the syntax and the semantics of a specific file format. The various data structures are extracted and passed to the System Layer, which in turn, passes the extracted data structures to the Application Layer. The Application Layer includes the LM process-planning system, as well as the hardware and controlling software.
A complementary study also conducted as part of this thesis, investigates the feasibility of a genetic algorithm to generate tool-paths for extrusion-based LM technology. The technique evolves unique tool-paths and is guided by a fitness function that includes elements that optimise for surface quality and material deposition.
Prof. E.M. Ehlers