Encyclopedia of Computer Science and Technology

98 computer-aided design and manufacturingfind the most efficient route for a person traveling to a numberof cities to visit each of the cities.Mathematicians therefore categorize the complexity ofproblems as P (solvable in a polynomial period of time),EXP (requiring an exponential time), or an intermediateclass NP, which means “nondeterministic polynomial.” AnNP problem is one that can be solved in polynomial time ifone is able to guess (and then verify) the answer. The TravelingSalesman Problem is believed to be in the NP class.While abstruse, the study of computability and complexityhas important implications for practical applications.For example, determining the complexity of a cryptographicalgorithm can help determine whether the resultingencryption is strong enough to withstand the efforts of afeasible attacker.Further ReadingBoolos, George S., John P. Burgess, and Richard C. Jeffrey. Computabilityand Logic. 4th ed. New York: Cambridge UniversityPress, 2002.Jones, Neil D. Computability and Complexity: From a ProgrammingPerspective. Cambridge, Mass.: MIT Press, 1997.Sipser, Michael. Introduction to the Theory of Computation. 2nd ed.Boston: Thomson Course Technology, 2006.computer-aided design and manufacturing(CAD/CAM)The use of computers in the design and manufacturing ofproducts revolutionized industry in the last quarter of the20th century. Although computer-aided design (CAD) andcomputer-aided manufacturing (CAM) are different areasof activity, they are now so closely integrated that they areoften discussed together as CAD/CAM.Computer-Aided DesignIn 1950, science fiction writer Robert Heinlein had hisfuture inventor create “Drafting Dan,” an automated draftingsystem that would enable designers to turn their ideasinto manufacturing plans in a fraction of the time requiredfor the hand preparation of schematics and parts lists. Bythe 1960s, engineers had developed the first computerassisteddesign programs, running on terminals attached tomainframe computers.The activity of a CAD workstation centers on the creationof geometrical models (first 2D, then 3D). With theaid of models, a virtual representation of the product beingdesigned can be built up. With its knowledge of geometricaland physical relationships, routines in the CAD system canperform not only measurement of dimensions and mass butalso structural analysis. (In some cases CAD can be interfacedwith systems that provide full-blown simulation ofthe effects of stresses, heat, and other factors.)The growth of desktop computing power in the 1980sand 1990s moved CAD from the mainframe to the high-endworkstation (such as those built by Sun Microsystems) andeven to high-end personal computers. The growing processingpower also meant that the geometric models couldbecome more sophisticated, including solid models withrealistically rendered surfaces rather than just wireframes.The model of surfaces can include such factors as reflectivity,friction, or even aerodynamic characteristics. In designinga product (or a subsystem of a product), engineers cannow use simulation software to determine how well a groupof parts in a complex assembly (such as a car’s steeringmechanism) will perform. The ability to get detailed data inreal time means that the CAD operator can work in a feedbackloop in which the design is incrementally refined untilthe required parameters are met.This growing modeling capability has been combinedwith the use of detailed databases containing the standardparts used in a particular industry or application.Libraries of templates allow the designer to “plug in” standardassemblies of parts and then modify them. The databasescan also be used with algorithms that can assist thedesigner in optimizing the design for some desired characteristic,such as strength, light weight, or lower cost.Recent systems even have the capability to set “strategic”design goals for a whole family of products and to identifyparticular optimizations that would help each part or subsystemachieve those goals.Computer-aided ManufacturingThe automated fabricating of products on the factory floororiginally developed independently of computer-aideddesign. Numerically controlled machine tools and lathes canbe programmed using specialized languages such as APT(Automatically Programmed Tool) or more recently, througha system that uses a graphical interface. Advances in patternrecognition and other artificial intelligence techniques havebeen used to improve the ability of the automatic tool toidentify particular features (such as holes into which boltsare to be inserted) and to properly orient surfaces. At somepoint the programmability and flexibility of the system withregard to its ability to manipulate the environment gives itthe characteristics of a robot (see robotics).Integration of CAD and CAMAs CAD systems became more capable, it soon became evidentthat there could be substantial benefits to be gainedfrom integrating the design and manufacturing process.The CAD software can also output detailed parts andassembly specifications that can be fed into the CAM process.In turn, manufacturing considerations can be appliedto the selection of parts during the design process.The integration of design, simulation, and manufacturingcontinues. The goal is to give the engineer aseamless way to “tweak” a design and have a number ofsimulation modules automatically depict the effects of thedesign change. In essence, the designer or engineer wouldbe working in a virtual world that accurately reflects thephysical constraints that the product will face in the realworld.The automation of the design and manufacturing processhas been mainly responsible for the increasing productivityof modern factories. Factories using traditional methods inproducing complex products such as automobiles or con-