Computer-aided Design Environment Research Articles

PARSIM: a parallel optimization tool

Current computer-aided control system design environments seldom support optimization methods for controller design in a truly interactive manner. A prototype tool, called PARSIM, supporting parallel processing, optimization, and a graphical user interface is presented, addressing many of the problems inherent in current approaches to multiobjective optimization-based design methods. An XWindows interface is used to simplify problem formulation and control the optimization processes. Using a previously developed interface, it is shown how the computational burden may be alleviated by parallel processing. >

Artificial neural network techniques for the estimation of thick-film resistance

Artificial neural network techniques are investigated as an alternative to parametric modelling for the estimation of fired thick-film resistor values. Multi-layer neural network models are constructed from resistor substrate test data. The connectionist models are developed through training procedures, allowing subsequent fired-value prediction. These non-parametric approaches do not require the functional form of the model to be known. The techniques are suitable for use in computer aided design environments.

Codisys: An integrated system for optimal structural design

In this paper a system for structural shape optimization named CODISYS is presented. This system allows us to obtain an automated design procedure for linear elastic structures by integrating structural analysis, sensitivity evaluation and mathematical programming methods in a Computer Aided Design environment. The integration of these different disciplines is a major aspect in shape optimal design. First of all, the paper provides a brief description of the integration strategy followed in this approach. Particular emphasis is given to creating an appropriate geometric model with suitable design variables and design variable linking procedures, as well as an automated mesh generation and adaptive mesh refinement based on a finite element error analysis. Some examples are used to show the power and generality of the system presented.

Approximation of quadratic Bézier curves by arc splines

The paths of cutting tools used in a computer-aided manufacturing environment are usually described by means of circular arcs and straight line segments. In a computer aided design environment, however, objects are often designed using B-splines or Bézier curves. This paper develops a simple technique to find an arbitrarily close approximation to a quadratic Bézier curve by a G 1 curve consisting of circular arcs.

A Generalized Approach to the Modelling of Modular Machines

This paper describes a method of graphically simulating modular machines within a computer aided design environment. This forms part of a much larger Science and Engineering Research Council (SERC) funded programme aimed at advancing modern practices when designing and building manufacturing machines. A generalized approach to the synthesis of the generic features of various kinematic motion pairs is presented and prismatic and revolute motion primitives generalized in their functional and geometric aspects. A hierarchical ring and tree data structure has been designed and implemented to comprehensively represent these motion pairs and to simulate their performance. More complex modular manufacturing machines can be represented using information from a library of up to three degree of freedom motion modules. Seven two degree of freedom motion primitives and twelve three degree of freedom motion primitives with articulation configurations have been analysed and included in the motion primitive library. The configuration of modular machines comprised of physically separate but logically connected distributed motion primitives are described. Examples of a two-finger industrial robot gripper and a three-finger industrial robot hand are used to demonstrate the general principles.

Validation of an automated system model generator

Modeling and simulation have always been highly useful techniques to use when designing, analyzing, or diagnosing an engineered system. Development of an appropriate model, in terms of accuracy, granularity, and complexity, has typically been the burden of the designer, analyst, or troubleshooter. It would naturally be advantageous if a model could be developed automatically, with the user supplying only some final minor refinements. The fact that most modern systems are designed in a computer-aided design (CAD) environment makes this a realistic prospect, because much of the data necessary for the model is already in electronic form. This article outlines a system called the automated knowledge generator (AKG), which embodies techniques that automatically create a model of an engineered system directly from its CAD representation, and describes the extensive testing process followed in order to validate its performance. >

Meta-Morphological Technique for a Multi-Parameter Design Index

Complex design and morphologic problems, consisting of multiple parameters, can be described, modelled and indexed using a meta-morphological technique presented here. All design and morphologic variables can be mapped in Euclidean n-dimensional space, where n is the number of variables. This meta-space contains all the possible solutions to the problem and each point in this solution n-space is a candidate solution. The desired solution, represented by a specific point in this space and coded (addressed) by its n-dimension Cartesian co-ordinates, is ranked by the hyper-distance of this point from the origin. The hyper-distance itself provides a design index (or hyper-index) of the solution and can be determined by the known hyper-Pythagorean theorem. The procedure is recursive and applies to complex design problems which are hierarchical and composed of problem-within-problem-within-problems. Here the parameters are composed of subparameters, and the solutions are correspondingly mapped in a recursive, fractal n-cube composed of sub-cubes composed of sub-sub-cubes. The total composite index is determined by the recursive application of the hyper-Pythagorean theorem and represents a quantification of the morphological complexity of the design. The model is independent of the design problem, and has attractive possibilities for application in computer-aided design environments. The application is shown with the hypothetical selection of a space frame from a number of alternatives.

An examination of the human factors support of NASA's safety directorate on the Space Station Processing Facility (SSPF) Kennedy space center, Florida

A Human Factors Engineering (HFE) pilot project undertaken by NASA on the Space Station Processing Facility (SSPF) at Kennedy Space Center, Florida, effectively demonstrates the advantage of using Human Factors to support NASA Safety. The project's goal is to reduce the causes of accidents by reducing error producing situations. The initial phase of this endeavor consisted of a review of design drawings for the SSPF, identifying all Human Factors (HF) concerns with special emphasis on those that affected personnel safety, payload protection, and operational efficiency. When drawings did not completely disclose how the facility's characteristics would fulfill operational needs, other facilities at KSC were visited to obtain insights that could be applied to the drawing critique. Overall, the drawing review revealed a broad range of HF and Safety concerns. When possible, these concerns were discussed with the appropriate engineering personnel to effect workable solutions. To date, some of these HF & Safety concerns have been resolved by incorporating HF principles. Thus, this project has reduced potential problems that can contribute to accidents and costly delays, such as the Magellan Spacecraft Incident in October of 1988. In addition, this project has led to the evaluation of candidate methods for the implementation of HF. Among these, a means of conducting HF evaluations during Engineering Phototyping in a Computer Aided Design environment. This innovative technique is anticipated to demonstrate the Safety advantage and substantial cost savings of incorporating HF principles.

Through the looking glass — why no wonderland? Computer applications in architecture in the USA

one objective of the paper is to survey computer-aided design activities in the USA as they apply to architectural design. Normally, such reviews limit their focus to software, and possibly hardware, developments. However, the economic and institutional environments of a country largely determine the rate and direction of research and its application, and this is especially true of computer-aided design. Thus, a second objective of the paper is to place the current efforts in the USA within this wider context. A survey is attempted, not only of the innovative research and applications of computers in architectural design, but also the context in which these developments have been taken place. Also surveyed are the changes in the environment for computer-aided architectural design that have been proposed or are taking place.

Representation of process system knowledge through component constraint descriptions

Automated development of models for use in computer simulations of engineered systems (e.g. electronic, power, thermal, process systems, etc.) can represent a significant advantage to system designers and troubleshooters. The fact that most modern systems have been designed in Computer-Aided Design (CAD) environments represents a unique opportunity for automatically generating a model from the electronic representation of a system. Models generally require definition of the system structure (i.e. component connectivity) and of the behavioral description of its components. With some exceptions, determination of the system connectivity from a CAD representation is a relatively uncomplicated procedure. However, the assignment of a functional behavior to each component of the system depicted in the CAD representation is a significant problem. This is because behavioral information is usually not included in the CAD representation of the system, as it is not required by the typical users of the CAD graphic output. The overall issue addressed in this paper, therefore, is the determination of the correct behavioral attributes for the components making up the modeled system. This will be addressed through the identifcation and matching of system components to elements of an external base of generic component knowledge. The components' behavioral representation (i.e. transfer function) will be set equal to that of its matching element in this external database. The compatibility of a hard-to-identify system component with its (known) neighboring components can be used to shed some light on its identity. Component compatibility can also be used to determine correct connectivity when that defined by the CAD database is incorrect. This compatibility can be determined through the use of domain (system) knowledge, in the form of system theory and/or practice. The representation of this knowledge as a series of constraints is the focus of this paper. Verification of this technique using a testbed system is also reported here.

Wolverines: standard cell placement on a network of workstations

The authors point out that a typical computer-aided design environment consists of a number of workstations connected together by a high-speed local area network. A placement program that makes use of this distributed computing environment to achieve linear speedup without sacrificing the quality of the results obtained by the serial version of the program is presented. The placement program is based on the genetic algorithm, which is a heuristic search method inspired by biological evolution models. The parallel implementation has other desirable features such as the ability to operate in a heterogeneous network environment and dynamic and static load balancing. The implementation of the placement program and detailed experimental studies of the behavior of the algorithm with various parameter settings, network capabilities, and communication patterns are described.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Computer-aided modeling and evaluation of reconfigurable VLSI processor arrays with VHDL

The authors present an integrated computer-aided design environment, the VAR (VHDL-based array reconfiguration) system, for the tasks of design, reconfiguration, simulation, and evaluation in an architecture modeled by VHDL. An easily diagnosable and reconfigurable two-dimensional defect-tolerant processing element (PE) switch lattice array is used as an example to illustrate the methodology of VAR. VAR allows the designers study and evaluate fault diagnosis and reconfiguration algorithms by inserting faults, which are generated based on manufacturing yield data, into the array and then locating the fault PEs as well as simulating the reconfiguration process. Thus, VAR can assist the designers in evaluating the different combinations of fault patterns, fault diagnosis algorithms, and reconfigurable architectures through a complete set of figures of merit which aim at architectural improvements. Extensive simulation and evaluation have been performed to demonstrate and support the effectiveness of VAR. >

Regular VLSI architectures for multiplication modulo (2/sup n/+1)

The authors describe VLSI architectures for multiplication modulo p, where p is a Fermat prime. With increasing p, ROM-based table lookup methods become unattractive for integration due to excessive memory requirements. Three novel methods are discussed and compared to ROM implementations with regard to their speed and complexity characteristics. The first method is based on an (n+1)*(n+1)-bit array multiplier, the second on modulo p carry-save addition, and the third on modulo (p-1) carry-save addition using a bit-pair recoding scheme. All allow very high throughputs in pipelined implementations. While the former is very convenient for CAD (computer-aided design) environments providing a pipelined multiplier macrocell, the latter two are well-suited to full-custom implementation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The Making of Exces - A Software Engineering Perspective

Abstract This paper is concerned with the software engineering aspects of the development of eXCeS (Extended X-based Control Engineering workStation) - an integrated computer-aided design environment for control engineering. The requirements of such an environment are analysed and major implementation issues including modularised infrastructure, standard ‘look and feel’ and uniform and extensible data environment are discussed. The eXCeS environment takes account of each of these issues in order to provide a user interface which meets the needs of control engineers, incorporates the latest developments in user interface technology and provides a platform for a wide spectrum of software products for computer-aided control system design.

Linearization techniques for nth-order sensor models in MOS VLSI technology

The authors present new linearization techniques and introduce novel circuits for second- and third-order sensor models. Furthermore, a general framework as well as circuit techniques for linearization of sensor models of any order are presented. The new techniques are based on subtle circuit design of simple and compact multiplier/divider and vector multiplier circuits that comprise op-amps and MOS transistors. The design is programmable using DC control voltages and is capable of implementing different values of model parameters using identically sized devices without altering physical circuit layout. The resulting continuous-time signal processing circuits are completely compatible with MOS VLSI technology and easy to incorporate in a computer-aided design environment. The circuit design details are given and nonideal effects due to op-amp dynamics and MOS parasitic capacitances are investigated. Experimental results for the new second-order sensor models, obtained from a MOSIS 2- mu m CMOS process test chip, and SPICE simulation results of third-order models verify the validity of the proposed linearization techniques. >

The structural optimization system CAOS

CAOS is a system for structural shape optimization. It is closely integrated in a Computer Aided Design environment and controlled entirely from the CAD-system AutoCAD. The mathematical foundation of the system is briefly presented and a description of the CAD-integration strategy is given together with an example.

Structural shape optimization integrated with CAD environment

The research work presented here is based on the concept of the integration of optimization techniques and numerical analysis with the finite element method (FEM) and computer-aided design (CAD). A microcomputer aided optimum design system, MCADS, has been developed for general structures. Certain techniques to be discussed in the paper, e.g. the semi-analytical method for design sensitivity analysis, optimization analysis modelling for shape design, application oriented user interfaces and the coupling of automated optimization and user intervention have rendered MCADS pratical and versatile in applications for engineering structures. The above techniques and an application are presented in this paper.

Tight Coupling of Microcomputers in a CAD Environment

The integration of microcomputers into a networked CAD environment involving host computers and workstations is discussed. “Integration” here refers to the tight coupling of microcomputers in the execution of a CAD (Computer‐Aided Design) or CG (Computer Graphics) program. The emphasis of the paper is placed on the proposed hardware and software architecture where the application or development of in‐house software plays the major role. The evolution of CAD hardware is first reviewed, after which the hardware configuration and software details of current implementation are described, and finally some system performance data are presented. It is demonstrated that the introduction of microcomputers into a networked environment provides a versatile and economic solution toward the promotion of CAD applications.

Model Based Rigid Body Guidance in Presence of Nonconvex Geometric Constraints

This paper presents an efficient algorithm for guidance of a convex rigid body in-between nonconvex polygonal objects in a Computer-Aided Design (CAD) environment. A shrinking procedure is used that separates the kinematic from the shape constraints by reducing the problem to that of guidance of a line segment in an expanded environment. A slicing technique together with an algorithm for decomposition of the interface channel between the nonconvex objects is used to generate the motion program for the line segment. The results can be applied to model based guidance of mobile robots or automatic motion planning for robot manipulators.

A Separating Channel Decomposition Algorithm for Nonconvex Polygons With Application in Interference Detection

An algorithm for efficient decomposition of interface channels between nonconvex polygons in a Computer-Aided Design (CAD) environment is presented. This algorithm forms the computational basis for the solution of several design automation problems. In this paper, the channel decomposition algorithm is presented and applied to the problem of interference detection between nonconvex polygons. The resulting interference detection algorithm does not require preprocessing of the data and uses a simple data structure. In a companion paper (Ku and Ravani, 1989), the rigid channel decomposition algorithm is applied to the problem of model-based rigid-body guidance in presence of geometric constraints.