Geoffrey W. Vickers

Segmentation of a wrap-around model using an active contour

Abstract Segmentation in the past has been applied to single range maps, which are capable of modelling only the part of an object that is visible from the camera viewpoint. In the field of reverse engineering, there is a great need for the segmentation of complete wrap-around object models. In this paper, a new method is presented for segmenting a wrap-around wireframe model, which is created by interpolating and merging multiple range maps. A semi-automatic edge-based approach is used for the segmentation. Surface differential properties are estimated at each point in the model, and curvature extrema are identified as possible edge points. An energy-minimizing active contour is used interactively to link the edge points. The designer defines small closed contours within the regions to be segmented, and the contour is ‘inflated’ until it is trapped by the potentials at the edge points.

G1 continuity of B-spline surface patches in reverse engineering

When a clay model or industrial part is reverse engineered, B-spline surfaces are typically fitted to surface data points collected by a coordinate measuring machine, or, in more recent times, a laser scanner. The surface fitting procedure results in a patchwork of B-spline surfaces. Some of these patches may be required to blend smoothly with their neighbours to a specified degree of continuity. Past research on surface patch continuity has focused on Bezier surfaces. In the paper, some of those techniques are modified and applied to B-spline surfaces. An optimization method is presented which can achieve an approximate global G1 continuity of a given patchwork of B-spline surfaces. The method is illustrated by a complex physical model, which is digitized by a 3D laser scanner, and reverse engineered to create a smooth cad model.

Automated surface subdivision and tool path generation for 3 ½½-axis CNC machining of sculptured parts

As an innovative and cost-effective method for carrying out multiple-axis CNC machining, 3½½-axis CNC machining technique adds an automatic indexing/rotary table with two additional discrete rotations to a regular 3-axis CNC machine, to improve its ability and efficiency for machining complex sculptured parts. In this work, a new tool path generation method to automatically subdivide a complex sculptured surface into a number of easy-to-machine surface patches; identify the favorable machining set-up/orientation for each patch; and generate effective 3-axis CNC tool paths for each patch is introduced. The method and its advantages are illustrated using an example of sculptured surface machining. The work contributes to automated multiple-axis CNC tool path generation for sculptured part machining and forms a foundation for further research.

Free-form surface reconstruction for machine vision rapid prototyping

Prototyping is an essential step in the manufacture of many objects, both consumer and industrial. A fundamental step in this process is the definition of the 3-D form of the object shape, for example, a designers model created in clay or wood. A 3-D vision system (range sensor) offers the advantage of speed in defining shapes compared to a traditional tactile sensor. The viability of using range sensors is demonstrated by the development of a rapid prototyping system comprised of a laser-based range sensor and software that creates a computer model of the object. One particularly important area of application is the reverse engineering of models comprised of free-form surfaces. This is important in mold and die manufacture for aerodynamic and ergonomic object surfaces. Several methods of modeling free-form surfaces from irregular data are examined and a radial basis function approach is used in developing a self-contained, interactive software package utilizing the laser-generated range data.

Reverse engineering employing a 3D laser scanner: A case study

An important step in many manufacturing processes is the definition of the three-dimensional form of an objects shape. A common example is the definition of a designers model created in clay or wood. A three-dimensional laser scanner offers the advantage of speed and non-contact sensing compared to traditional touch probe sensing. The three-dimensional data produced have been used in a multi-patch reverse engineering program in order to model objects where many types of surface patches, such as quadric and free-form, are blended together on one object. The surface reconstruction algorithms have been demonstrated to provide accurate and smooth surfaces that are suitable for CAD database integration and CNC machine toolpath generation. The algorithms have been implemented in an interactive 3D surface modelling program that produces surfaces compatible with current CAD/CAM systems. The application of the technology to the reverse engineering of a typical injection moulded part is described.

Optimal toolpath pattern identification for single island, sculptured part rough machining using fuzzy pattern analysis

Abstract In the manufacture of sculptured parts from prismatic stock, rough machining dominates the machining time due to the significant shape difference between the stock and part. For the sculptured part rough machining using 2.5D milling or contour-map machining, the appropriate selection of a toolpath pattern for each cutting layer can significantly improve productivity and lead to lower production costs. In the paper, various feasible toolpath patterns are investigated. An intelligent approach for automatically identifying the most productive toolpath pattern for a given cutting layer is introduced. The study is focused on sculptured parts with a single island and no seriously nonconvex shape. The method is based on fuzzy cutting layer shape pattern clustering and recognition. An example is used to illustrate the method.

A multi-sensor approach to automating co-ordinate measuring machine-based reverse engineering

Abstract Co-ordinate measuring machines (CMMs) have been widely used in industry for reverse engineering. In an ideal reverse engineering system, the object would be automatically digitised, the data would be segmented into constituent surface patches, and an accurate solid model would be generated. However, at present, the time-consuming manual digitisation of many objects discourages the implementation of reverse engineering. As a major step toward attaining this goal, a charged coupled device (CCD) camera and a CMM touch probe digitiser are used together in a novel reverse engineering process. Neural network based stereo image processing is used to locate the object in the CMM work space, and to generate the CMM touch probe path. Precise data is then collected using the CMM touch probe, from which a CAD/CAM model can be constructed.

Curved surface machining through circular arc interpolation

Abstract In curved surface machining it is customary to represent and to generate the surface as a sequence of short linearly interpolated moves. Experimental measurements of such stop-start motion shows that full cutting speed is achieved typically for only ten percent of the machining time: the remaining time is spent in accelerating, decelerating, or pausing between instructions. An algorithm is presented which uses a recursive approach to maximize the number of circularly interpolated moves for surface generation. A reduction in machining time of up to 5:1 is demonstrated using this approach.

The definition and manufacture of compound curvature surfaces using G-surf

Abstract G-surf is a method for defining and machining the compound curvature surfaces encountered in many engineering applications. The surfaces are defined by orthogonal grids of B-spline space curves and machined with a cylindrical end-milling cutter inclined at predetermined angles to the surface normals. The approach proves to be very flexible and, as the cutter operates at a full and select cutting speed, gives an efficient means of material removal. Surface finish and cutter interference are both affected by cutter inclination to the surface normal and can be adjusted for optimum conditions. The interactive menu-driven package fits onto microcomputer installations and is suitable for small- to medium-size manufacturing companies.

A Multi-Sensor Approach for Rapid Digitization and Data Segmentation in Reverse Engineering

The development of a fully automated reverse engineering system currently faces two challenges; the time consuming digitization of the object due to the multi-view requirement of current industrial sensors and the conversion of copious amounts of 3-D cloud data into a compact form, compatible with CAD/CAM packages. An ideal reverse engineering system will automatically digitize the object from multiple viewpoints, segment the cloud data into constituent surface patches and generate an accurate solid model. The utilization of both a charged coupled device (CCD) camera and a 3-D laser digitizer, in the reverse engineering process, is a major step to attaining this goal. A neural network based segmentation algorithm is applied to stereo images for the location of the target object in the laser scanner work space and to generate the laser scanner path. The process automatically generates a description of an objects surface which can be exported to a CAD/CAM package for design or manufacturing applications.