Showing papers in "Computer-aided Design in 1978"
TL;DR: The method is presented as a generalization of a recursive bicubic B-spline patch subdivision algorithm, which generates surfaces that approximate points lying-on a mesh of arbitrary topology except at a small number of points, called extraordinary points.
Abstract: This paper describes a method for recursively generating surfaces that approximate points lying-on a mesh of arbitrary topology. The method is presented as a generalization of a recursive bicubic B-spline patch subdivision algorithm. For rectangular control-point meshes, the method generates a standard B-spline surface. For non-rectangular meshes, it generates surfaces that are shown to reduce to a standard B-spline surface except at a small number of points, called extraordinary points. Therefore, everywhere except at these points the surface is continuous in tangent and curvature. At the extraordinary points, the pictures of the surface indicate that the surface is at least continuous in tangent, but no proof of continuity is given. A similar algorithm for biquadratic B-splines is also presented.
2,137 citations
TL;DR: In this article, the behaviour of the limits surface defined by a recursive division construction can be analyzed in terms of the eigenvalues of a set of matrices, and suggestions for the further improvement of the method are made.
Abstract: The behaviour of the limits surface defined by a recursive division construction can be analysed in terms of the eigenvalues of a set of matrices. This analysis predicts effects actually observed, and leads to suggestions for the further improvement of the method.
971 citations
TL;DR: In this paper, a fast algorithm is described to compute the necessary cutting paths for machining arbitrarily shaped areas (pockets) bounded by straight lines and arcs, implemented in the SAAB-Adapt processor.
Abstract: Machining mechanical parts requires a great deal of area cleaning, i.e. cutting away all material within given boundaries. This paper describes a fast algorithm, implemented in the SAAB-Adapt processor, to compute the necessary cutter paths for machining arbitrarily shaped areas (pockets) bounded by straight lines and arcs.
187 citations
TL;DR: In this paper, a theory to explain how dimensions and views combine to specify the shape of a mechanical component is presented, and a method to determine whether a component is under, over, or exactly defined by a given dimensioning scheme is proposed.
Abstract: The paper sets forth a theory to explain how dimensions and views combine to specify the shape of a mechanical component. It provides a method to determine whether a component is under, over, or exactly defined by a given dimensioning scheme. Measures for assessing the quality of a scheme are proposed. A solution is offered to a problem of tolerancing: given a toleranced dimensioning scheme, find the resulting tolerances between undimensioned parts of a component.
162 citations
TL;DR: In this article, the authors propose a method to detect and eliminate fouling by simulating the changing billet shape and the moving cutting assembly, and apply the program to the initial toolpath and subsequent defouling toolpaths until a final toolpath is reached.
Abstract: When a 3D object is milled from a billet by a cutting assembly (tool and an associated cutting head), a common hazard, particularly if the cutting is under numerical control, is that this assembly may collide with (foul) the partly cut billet. Fouling may be detected and eliminated by simulating the changing billet shape and the moving cutting assembly: fouling is detected when billet and cutting assembly models occupy the same model space. The principal method of removing fouling is to modify the billet by removing those parts that would subsequently foul. Alternatively, the cutter assembly may be modified by fitting a longer tool, whose length is calculated to lift the cutter assembly above any part of the billet causing fouling. For premodifying billets, the program records the parts of the billet causing fouling and calculates a cutter path to remove these. Since this preliminary cut may itself cause fouling, the program is applied recursively to the initial toolpath and subsequent defouling toolpaths until a final toolpath is reached that does not cause fouling. These preliminary toolpaths are then executed in the reverse order of their generation. The method assumes that the final shape has a single height above every point of its base, and is therefore limited to shapes that do not have undercutting.
76 citations
TL;DR: A CAD method is presented for converting existing continuous-data control systems into digital control systems by means of a digital controller that is synthetized by matching the frequency response of the digital control system to that of the continuous- data system with a minimum weighted mean-square error.
Abstract: A CAD method is presented for converting existing continuous-data control systems into digital control systems by means of a digital controller The digital controller is synthetized by matching the frequency response of the digital control system to that of the continuous-data system with a minimum weighted mean-square error A formula for computing the parameters of the digital controller is obtained as a result The design technique is illustrated with a numerical example and a comparison with previous methods is also presented
45 citations
TL;DR: Parametrized polynomial spline curves are defined by an S-polygon, but locally they are Bezier curves defined by a B- polygon, and two algorithms are given which construct one polygon from the other and vice versa.
Abstract: Parametrized polynomial spline curves are defined by an S-polygon, but locally they are Bezier curves defined by a B-polygon. Two algorithms are given which construct one polygon from the other and vice versa. The generalization to surfaces is straightforward. This may be of some interest in CAD because of the good local properties of the B-polygon
44 citations
TL;DR: SLIP (symbolic layout interpreted for polycells) is a program which uses symbolic layout information to generate NMOS polycells (standard cells) for small-scale and medium-scale integrated circuits.
Abstract: SLIP (symbolic layout interpreted for polycells) is a program which uses symbolic layout information to generate NMOS polycells (standard cells) for small-scale and medium-scale integrated circuits. At the input level, the designer works with symbolic nodes and lines representing transistors, loads, interlayer contacts and connections. The relative locations of the nodes and lines are then used to generate a hard-coordinate mask description. The mask description is generated by first translating the relative location information of the symbolic layout into an initial legal mask layout. The mask layout is then compacted using a shear-line compaction technique. The program is written in the C programming language and is currentky running on a Hewlett-Packard 21 MX minicomputer.
41 citations
39 citations
TL;DR: It is shown how the result can be automatically obtained by distorting an auxiliary triparametric set of references by using the principle of an approximate method for high-order curves and surfaces.
Abstract: When the shape of an object has been numerically defined, it is sometimes necessary to distort it to improve either its technical performance or its aesthetic appearance. After briefly recalling the major properties of space curves and surfaces defined by Bernstein polynomials, it is shown how the result can be automatically obtained by distorting an auxiliary triparametric set of references. The principle of an approximate method for high-order curves and surfaces is explained.
29 citations
TL;DR: The design of man-computer dialogue requires the underlying theoretical framework of basic concepts present in other applied arts, and nonverbal communication should be exploited to widen the rather limited ‘bandwidth’ of current computer terminals.
Abstract: The design of man-computer dialogue requires the underlying theoretical framework of basic concepts present in other applied arts. Four basic aspects of man-computer interaction are predictability, implication (the extensive use made by humans of context), experimentation (the importance of trial and error procedures) and motivation (the part played by feelings such as trust, hostility etc.). Nonverbal communication should also be exploited to widen the rather limited ‘bandwidth’ of current computer terminals.
TL;DR: A method for imposing a good parametrization on a curve constructed by Bezier's method and based on B-splines is described.
Abstract: Sections of parametric surfaces defined by equally spaced parameter values can be very unevenly spaced physically. This can cause practical problems when the surface is to be drawn or machined automatically. This paper describes a method for imposing a good parametrization on a curve constructed by Bezier's method and based on B-splines. The extension of the method to the parametrization of surfaces is considered briefly.
TL;DR: In this paper, a dynamic model for predicting the thermal behavior and energy consumption of a full-scale building has been developed, which can include most of the design and climatological factors affecting the building.
Abstract: A dynamic model for predicting the thermal behaviour and energy consumption of a full-scale building has been developed. The model can include most of the design and climatological factors affecting the building. The time-dependent equation for the heat flow through the walls is converted into an implicit scheme and solved numerically. Special effort has been devoted to producing a model capable of aiding the architect during the various steps of building design, so as to approach thermal comfort with minimal energy consumption. The results are presented in graphical form, which allows the architect to detect easily the crucial factors in the thermal performance of the building.
TL;DR: An algorithm is described for displaying curved surfaces with their hidden parts removed that calculates a number of points on a surface at which the surface disappears from view, and joins the points to form a piecewise smooth ‘critical boundary’.
Abstract: An algorithm is described for displaying curved surfaces with their hidden parts removed. The algorithm calculates a number of points on a surface at which the surface disappears from view, and joins the points to form a piecewise smooth ‘critical boundary’. With a knowledge of this critical boundary, the task of displaying the visible parts of the surface becomes simple.
TL;DR: The algorithm produces a piecewise linear curvature profile, thus the resultant curve consists of parts of Cornu spirals, and a FORTRAN program based on this algorithm can provide many substantially different solutions to any given problem.
Abstract: A new algorithm for fitting a smooth curve through two datapoints, to meet specified tangent direction and curvature requirements at these datapoints, is described. The algorithm produces a piecewise linear curvature profile, thus the resultant curve consists of parts of Cornu spirals. It does this by blending some basic forms defined in the paper. A FORTRAN program based on this algorithm can provide many substantially different solutions to any given problem. It can either be incorporated in a linear curvature spline package or used in an interactive system for designing spans or splines.
TL;DR: In this paper, the authors consider some of the problems in applying computer aid to the sequential processes of initial design, detailing, planning, piece-part manufacture and assembly, especially in modelling and in user-oriented interactive input of design parameters and insight-giving output of analysis results.
Abstract: While considerable success has attended the application of CAD in the electronics, aerospace, ship, offshore structure and other industries, less progress has been reported in general mechanical engineering; yet the opportunities are great and the CAD idea started in mechanical engineering. This paper considers some of the problems in applying computer aid to the sequential processes of initial design, detailing, planning, piece-part manufacture and assembly. Recent achievements in separate parts of this process are identified, especially in modelling and in user-oriented interactive input of design parameters and insight-giving output of analysis results. Case histories are mentioned and possibilities for a cost-effective solution to the CAD/CAM problem in medium-sized engineering companies are discussed.
IBM1
TL;DR: An overview of work in the area of macromodeling can be found in this article, where a recent progress in macroanalysis is discussed, such as the latent approach, which is a method which takes advantage of the natural small activity in large systems.
Abstract: Macromodelling is a new area of circuit theory which has gained importance with the advent of large scale integration for semiconductor chips. These integrated circuits require an analysis capability which far exceeds presently available computer-aided network analysis programs. This paper gives an overview of work which pertains to the area of macromodelling. Also, recent progress in macroanalysis is discussed, such as the latent approach, which is a method which takes advantage of the natural small activity in large systems.
TL;DR: In this paper, a finite element method based on the weighted residuals principle is used for the description of the generation and the unidirectional propagation of waves in a channel due to the temporal vibration of some cross sections of it (lateral earth motion due to landslide on the channel bank).
Abstract: The finite element method based on the weighted residuals principle is used for the description of the generation and the unidirectional propagation of waves in a channel due to the temporal vibration of some cross sections of it (lateral earth motion due to landslide on the channel bank). The deriving algebraic system is solved by iterations. The integration in time is achieved by a leap frog finite differences scheme for the computation of surface elevation and velocity functions. The finite element model is applied on a typical channel and several controls on the obtained solutions proves the descriptive capacity of the model.
TL;DR: In this paper, a spline algorithm that uses arc length as parameter and generates a curve in terms of the quantities "relative curvature" and "relative torsion" is described.
Abstract: A new spline algorithm that uses arc length as parameter and generates a curve in terms of the quantities ‘relative curvature’ and ‘relative torsion’ is described. The tangent and curvature vectors at each datapoint are estimated and the spline is built up span by span. This allows local changes without affecting the whole curve and facilitates the incorporation of derivative discontinuities. Unless discontinuities are specifically requested, the solution obtained is curvature continuous.
TL;DR: In this article, a technique is described for determining the patch or patches intersected by a vector, given the patches intersecting by a single plane containing the intersecting vector, and the distance to the multipatch surface obtained.
Abstract: A previously reported method for finding the points of intersection of a vector and a parametric surface patch is examined. However, before the point of intersection of a vector and a patch can be determined, it is necessary to find the patch (or patches) on a multipatch surface intersected by the vector. A technique is described for determining the patch or patches intersected by a vector, given the patches intersected by a single plane containing the intersecting vector. Once these have been found, the point of intersection can be determined and the distance to the multipatch surface obtained.
TL;DR: The principles of the basic algorithms of the MASOB computer program can be used for recognizing the topology and parameters of a lumped-parameter network matched to the integrated circuits, written in FORTRAN.
Abstract: Technological data and geometric dimensions of mask patterns define the properties of integrated circuits. These parameters cannot, however, be used directly to analyse the circuits. The MASOB computer program can be used for recognizing the topology and parameters of a lumped-parameter network matched to the integrated circuits. The network can then be readily analysed. Silicon gate MOS technology is assumed. The paper presents the principles of the basic algorithms of the MASOB computer program, written in FORTRAN, and an example of application.
TL;DR: In this article, it was shown that a three-dimensional cubic segment can be specified completely by its end points, end slopes and one intermediate point, which is called the intermediate point.
Abstract: A parametric cubic segment may be specified in many ways but most specifications require quantities peculiar to the parametric representation rather than the geometric properties of the curve segment. This paper shows that a three-dimensional cubic segment is specified completely by its end points, end slopes and one intermediate point.
TL;DR: A structure for automated architectural sketch design is outlined, its theoretical basis is examined, and some general features of its computer implementation are indicated.
Abstract: This paper outlines a structure for automated architectural sketch design, examines its theoretical basis, and indicates some general features of its computer implementation. Design goals are identified as fulfilling a central role in the creation of suitable mechanisms for generating, evaluating and selecting design solutions. It is suggested that these mechanisms should operate at each of the levels of a hierarchial architectural sketch design decision-making structure.
TL;DR: In this article, mean tangent rotation angles are used in the intrinsic-curve design method which defines curves for CAD by specifying curvature and/or torsion profiles, and makes use of ψ to derive approximate formulas for fast integration of curvature profiles.
Abstract: Stationary values of mean tangent rotation angles are used in the intrinsic-curve design method which defines curves for CAD by specifying curvature and/or torsion profiles. This paper discusses these mean angles ( ψ and φ ) and makes use of ψ to derive approximate formulas for fast integration of curvature profiles.
TL;DR: An editor is described for creating and modifying free-form surfaces with the essential features of a large-scale implementation, with the capability of utilizing many new surface forms that have not yet been tried in actual applications.
Abstract: An editor is described for creating and modifying free-form surfaces. A modular system was developed in order to provide the researchers with a facility for communicating design ideas and new mathematical forms through an interactive graphical interface to a computer-based model. To achieve this it was necessary to invent a new graphical construct called a ‘spider’ for inputting three-dimensional parameters. This experimental system has the essential features of a large-scale implementation, with the capability of utilizing many new surface forms that have not yet been tried in actual applications.
TL;DR: The TOPES (telephone office planning and engineering system) as discussed by the authors is a computer-aided interactive graphics system that addresses the sequence of steps in planning and designing office space has been developed for Bell System planning engineers.
Abstract: A computer-aided interactive graphics system that addresses the sequence of steps in planning and designing office space has been developed for Bell System planning engineers. TOPES (telephone office planning and engineering system) is currently in use for planning and engineering Bell System equipment buildings. It is used for tasks ranging from graphics editing and interactive graphics teleconferencing to creating drawings files capable of supplying equipment engineering data, equipment inventories and other planning information.