Celesstin, a system that converts mechanical engineering drawings into a format suitable for CAD, is described. Celesstin integrates several modules in a blackboard-based interpretation system. Once a drawing has been digitized, a first processing step separates the text and the dimensioning lines from the pure graphics part. Celesstin vectorizes the graphics part and assembles the resulting lines into blocks, the basic elements for the technical entities that it creates. The result is transferred to the CAD system. Celesstin tries to match the extracted entities with the corresponding models from the CAD library. It puts the remaining blocks and lines into different layers of the CAD description. The system is based on the assumption that even when the vectorized drawing is distorted, it can be correctly interpreted by using knowledge about the representation rules used in technical drawings and about the manufacturing technology associated with the represented objects. >

Celesstin: CAD conversion of mechanical drawings

A successful implementation of the Model-Based Enterprise concept (MBE) requires maximizing the potential benefits of annotated 3D models. The foundations of the MBE model are established by digital product definition data practices, which are currently regulated by standards such as ASME Y14.41-2003 and ISO 16792:2006. At the center of the MBE concept is the notion of CAD model reusability, which relies on the idea that 3D CAD models can be reused both throughout the entire product lifecycle and as a starting point for future development of new products. In this context, a critical aspect of CAD model reuse is the proper identification and understanding of the geometric design intent that is usually expressed implicitly within the CAD model. In this work, we present a method to communicate geometric design intent explicitly by overloading and extending the scope of the current annotation instruments available in the MBE approach. We propose a new broader type of model annotation that we call “extended annotation”, where design information is represented both internally within the 3D model and externally, on a separate repository. This structure naturally demands additional mechanisms to support the interaction of users with the information. In order to manage the information stored in these extended annotations effectively, we implemented an annotation manager that automatically synchronizes the dual representation of the annotations. To reduce the visual clutter in the 3D model, the software provides powerful filtering, editing, and visualization capabilities, giving users complete control of the information stored in the model. Finally, a study was conducted with 60 participants to evaluate the performance of the proposed model and the usability of the annotation manager. Results show a statistically significant benefit of using the extended annotation system, suggesting the use of this model as a valuable approach to improve design intent communication.

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Extended 3D annotations as a new mechanism to explicitly communicate geometric design intent and increase CAD model reusability

A functional feature modeling method

Computer-aided design (CAD) is a ubiquitous tool that today's students will be expected to use proficiently for numerous engineering purposes. Taking full advantage of the features available in modern CAD programs requires that models are created in a manner that allows others to easily understand how they are organized and alter them in an efficient and robust manner. The results of a class-based exercise are presented to examine the role of model attributes on model creation, alteration, and student perception. Two popular CAD programs are used for the exercise: SolidWorks and Pro|Engineer. General results from both programs are reported. Fewer more complex features are found to be correlated with reduced modeling time. Simple features are shown to be positively correlated with the number of features retained without change. More complex features are found to be negatively correlated with the number of new features. Student perceptions of model quality and intuitiveness are positively correlated with the amount of feature reuse. Student survey data shows a preference for simpler features, the naming of features, and the use of reference geometry. The results do not allow for a generic approach regarding feature complexity to be prescribed. Overall, properly conveying design intent is shown to be positively correlated with design retention and negatively correlated with alteration time.

An educational exercise examining the role of model attributes on the creation and alteration of CAD models

Current computer-aided design systems excel at recording the final design solution for an engineering problem; however, they are not as adept at capturing the individual designer's rationale, knowledge or the process used during the design session. Being able to access this information will give insight into the reasons why key design decisions were made which, in turn, will support engineers who have to make revisions to the product in the future. Therefore, it would be beneficial if CAD systems were able to record design knowledge automatically. The research in this paper attempts to address this issue with a system that unobtrusively captures design processes and design knowledge by logging individual designer behaviour and system interactions while a CAD system is being used; user trials generated around 700 log files that were then analysed to extract these. In addition, various CAD system-independent representations were output to give a visual and formal representation of the processes that occurred. Overall, although carried out within a constrained design environment, this early knowledge capture work demonstrates the potential for automated knowledge capture and subsequent representations within CAD environments as well as the feasibility of design information push.

Automated design knowledge capture and representation in single-user CAD environments

Design intent has received much attention in numerous disciplines ranging from mechanical engineering design, software engineering to human-computer interaction research. While it is universally acknowledged that knowing design intent is extremely useful, there is still a lack of both support for frameworks for design intent and widespread use in engineering. Design groups looking to use the latest design intent systems and tools face the problem that the bulk of their product data resides in unintelligent 2D drawings. There exists a need to propagate the design intent present in these 2D drawings to a structured, intelligent, reusable format. This paper tries to understand what design intent is in the domain of 2D CAD drawings by providing a definition for it along with a survey of research and literature in the area of design intent. The paper also focuses on the importance, capture, representation and retrieval of design intent from 2D CAD drawing.

Design Intent in 2D CAD: Definition and Survey

There exist numerous design intent systems that convert captured information into structured design intent while providing intent representation and retrieval. These systems woefully neglect the design intent that is present in legacy CAD such as 2D drawings and 3D models. We address the issues that arise when dealing with the capture, representation and retrieval of design intent from the legacy CAD data. A definition for design intent in the CAD domain is presented which forms the basis of the proposed approach. The approach uses a unique context-based inference system to capture design intent from legacy CAD data. A brief explanation of context is provided along with the advantages of using context for this task. The need and use of an inference system is detailed. Additionally a prototype system is implemented to address these issues from a software system point of view.

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Using a Context-based Inference Approach to Capture Design Intent from Legacy CAD

Over the last two decades, the mechanical CAD industry has witnessed the development of many powerful 3D CAD software products built upon proprietary geometric kernals. The ISO 10303 STEP standard was developed, with the Application Protocol (AP 203) in particular, to provide a medium for product data exchange of lower-level geometry of mechanical parts and assemblies. A recent version, AP203 Edition 2, introduced the exchange of product data using a hybrid model containing construction history, GD&T, parameters and other high-level content. This paper presents an interpretation of the schema definitions provided under the current standard, presents a generic approach to map feature history data between CAD systems, discusses an implementation of this approach for data translation, and discusses the issues in the standard realized during this effort.

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Experience in Development of Translators for AP203 Edition 2 Construction History

Design is a difficult, complex subject. Many believe that it can only be learned by doing – gaining experience by designing artefacts. In this paper we propose that experienced designers make their life simpler by implicitly recognizing that their design problem lies within a context and by recognizing the particular context in which a problem lies. In our view context include such things as the branch of industry, the country, the company, the domain of the problem and the functions, objectives, constraints and design principles involved in the design problem. Implicitly recognizing the context simplifies the problem by constraining the number of variables. In particular the part of the context formed by the domain of the problem constrains the number of flows (the nouns associated with the active verb functions) and functions (i.e. active verbs that are relevant to that problem. We present a series of taxonomies that decompose the engineering domain down to sub-sub-sub-domains and show that both the nouns and the action verbs are constrained within the sub-sub-sub-domains by a large percentage (>50%). We discuss the implications of this finding for a variety of topics including design education and design automation.

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Ganeshram R. Iyer

Papers

Design Intent in 2D CAD: Definition and Survey

Using a Context-based Inference Approach to Capture Design Intent from Legacy CAD

Experience in Development of Translators for AP203 Edition 2 Construction History

Using Domains to Constrain Design Variables