Constraint-based reverse engineering of assemblies using design and measurement intents

Reverse engineering is a methodology for generating a design on the basis of an existing physical part in the absence of the original design information. One of the major difficulties in reverse engineering (RE) is to acquire reliable and accurate geometric models because an existing part frequently contains deviations from its original geometry due to wear and distortion of surfaces, tolerances applied, process capabilities, etc.; This dissertation presents a new systematic approach to apply the reverse engineer's knowledge and understanding about product design and measurement operations to reverse engineering of assemblies, focusing on generation of geometric models. Based on the recent research in constraint-based design and feature modeling, the use of geometric constraints is proposed to represent information obtained from the reverse engineer and to utilize that information in constructing geometry during the RE process.; The procedure begins with the reverse engineer hypothesizing design and measurement intents and translating these into geometric constraints. These inputs are represented in a constraint graph. Optimization models are used to fit surfaces to measurement data, to assist in validating the provided constraints, and to generate part surfaces that best satisfy the constraints and the measurements. These mathematical surface definitions can then be used to build geometric models in a CAD system.; The methodology is demonstrated by using a simple assembly with actual point samples acquired on a coordinate measuring machine. In addition, experiments were performed with simulated point samples to investigate the characteristics of the methodology. Both the demonstration and the experimentation show that geometry determined by the methodology successfully preserves such geometric properties as parallelism and perpendicularity as well as assembly-related dependencies.; The constraint-based procedure provides a systematic way to combine design intents with measured surface data from a part or an assembly such that the RE process can produce part CAD models that more accurately represent the originally intended geometries.