Jonathan Corney

Method for finding holes and pockets that connect multiple faces in 2 1/2D objects

Abstract Given a boundary representation, the problem of identifying sets of faces that bound holes and pockets in 2 1/2D objects is relatively trivial when they emanate from a single face, because the edges of the depression form an inner loop of convex edges. There are, however, many components in which a hole or pocket is present, and yet defines no inner loop on any face; in other words, it has a nonunique entrance face. The paper describes an algorithm, based on the manipulation of a face—edge graph, for identifying sets of faces in a 2 1/2D object that bound holes or pockets with unique or nonunique entrance faces. The algorithm also determines the perimeter of the projected area enclosed by each hole or pocket in a specific direction. This information is of direct use in the manufacture of the component.

Delta-volume decomposition for multi-sided components

Abstract The subdivision of the removal, or delta-volume, of a machined component into meaningful volumes suitable for efficient machining is at present a complex and time-consuming task. An algorithm is presented for recognizing CNC machining volumes from 3D boundary representation solid models. The 2.5D volumes identified are associated with generic depressions and protrusions. The novelty of the algorithm lies in the fact that its success does not depend upon a pre-defined library of features and that it guarantees the accessibility of the volumes found.

Factors affecting user performance in haptic assembly

Current computer-aided assembly systems provide engineers with a variety of spatial snapping and alignment techniques for interactively defining the positions and attachments of components. With the advent of haptics and its integration into virtual assembly systems, users now have the potential advantage of tactile information. This paper reports research that aims to quantify how the provision of haptic feedback in an assembly system can affect user performance. To investigate human–computer interaction processes in assembly modeling, performance of a peg-in-hole manipulation was studied to determine the extent to which haptics and stereovision may impact on task completion time. The results support two important conclusions: first, it is apparent that small (i.e. visually insignificant) assembly features (e.g. chamfers) affect the overall task completion at times only when haptic feedback is provided; and second, that the difference is approximately similar to the values reported for equivalent real world peg-in-hole assembly tasks.

The CAD/CAM Interface: A 25-Year Retrospective

The vision of fully automated manufacturing processes was conceived when computers were first used to control industrial equipment. But realizing this goal has not been easy; the difficulties of generating manufacturing information directly from computer aided design (CAD) data continued to challenge researchers for over 25 years. Although the extraction of coordinate geometry has always been straightforward, identifying the semantic structures (i.e., features) needed for reasoning about a components function and manufacturability has proved much more difficult. Consequently the programming of computer controlled manufacturing processes such as milling, cutting, turning and even the various lamination systems (e.g., SLA, SLS) has remained largely computer aided rather than entirely automated. This paper summarizes generic difficulties inherent in the development of feature based CAD/CAM (computer aided manufacturing) interfaces and presents two alternative perspectives on developments in manufacturing integration research that have occurred over the last 25 years. The first perspective presents developments in terms of technology drivers including progress in computational algorithms, enhanced design environments and faster computers. The second perspective describes challenges that arise in specific manufacturing applications including multiaxis machining, laminates, and sheet metal parts. The paper concludes by identifying possible directions for future research in this area.

Automated design process modelling and analysis using immersive virtual reality

The capture of engineering design processes and associated knowledge has traditionally been extremely difficult due to the high overhead associated with current intrusive and time-consuming manual methods used in industry, usually involving interruption of the designer during the design task and relying on them to remember how a design solution was developed after the event. This paper presents novel research which demonstrates how the detailed logging and analysis of an individual designers actions in a cable harness virtual reality (VR) design and manufacturing system permits automated design task analysis with process mapping. Based on prior research, which utilised user-logging to automatically analyse design activities and generate assembly plans, this work involves the automatic capture of extracted design knowledge embedded within the log files and subsequently represented using IDEF0 diagrams, DRed graphs, PSL, XML, annotated movie clips and storyboard representations. Using this design knowledge, an online help system has been demonstrated which helps users to carry out design tasks similar to those performed previously by expert users. This is triggered by monitoring the designers actions and functions in real time and pushes knowledge and advice to the user which was captured from experts and subsequently formalised during earlier design sessions.

Edge-based identification of DP-features on free-form solids

Numerous applications in mechanical CAD/CAM need robust algorithms for the identification of protrusion and depression features (DP-features) on geometric models with free-form (B-spline) surfaces. This paper reports a partitioning algorithm that first identifies the boundary edges of DP-features and then creates a surface patch to cover the depressions or isolate the protrusions. The novelty of the method lies in the use of tangent continuity between edge segments to identify DP-feature boundaries that cross multiple faces and geometries.

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

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 designers 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.

Algorithms for the physical rendering and assembly of octree models

Hierarchical decomposition techniques are well established for the representation of 2D images, the calculation of distance maps, and the modelling of volume data. However, recent work has suggested that their use can be extended to the manufacture of physical objects for low cost prototyping and visualization. This paper details various decomposition and assembly planning routines created to support this process. Specifically the decomposition methods are described to generate octants appropriate for the physical assembly process. Having established methods for generating suitable octrees, three different algorithms for planning the assembly of octrees are presented. The comparative performance of these different approaches is discussed.

The Heriot-Watt FeatureFinder: CIE97 results

This paper describes the functionality of a Feature Recognition system, known as FeatureFinder. The systems algorithm has been developed from a graph-based approach to feature recognition and is now capable of identifying a variety of features on a wide range of machined components. The system has been designed to be used within a solids machining package and identifies features from a specified tool approach direction. The paper details the result of applying the algorithm to the CIE97 test pieces. Features are identified on all of the components and the paper concludes with a brief description of on-going work designed to extend the range of components FeatureFinders algorithm can analyse.

Assessment of a Haptic Virtual Assembly System that uses Physics-based Interactions

Assembly is one of the most extensively studied manual processes in manufacturing. Using design for assembly (DFA) methodologies relative times of real-world assembly tasks such as manipulation and insertion can be quantified. However, it is unclear if similar values can be reflected in a virtual assembly system? This question forms the rationale for the peg-in-hole assembly task addressed in this study. Although almost simplistic in nature, assembling a peg into a hole addresses three fundamental states in an assembly process -picking, placing and motion within an environment. The objective here is to investigate assembly performance in the virtual environment using a force feedback haptic device benchmarked against previously quantified data. Inclusive, is a kinematic evaluation of task performance for peg-in-hole manipulation based on geometric and force conditions.