Toward the ideal mechanical engineering design support systemDavid G.UllmanAbstract This paper details the progress toward the development oftheidealmechanical engineering design support system.It attempts to look at the gap between the needs of a mechanicalengineerandwhatis currently available onCAD systems Since the tern：CAD emphasizes that the computer is an aid to the human designer，this paper is designer centric it is based heavi~on the activities performed by designers and the types ofinformation developed by then：Seventeen goals for the ideal mechanical design support system are listed These are directed at the types ofinfor mation developed during the design process and the activ ities used to develop them For each of the seventeen，background information，the current state of the art，and opportunities for future development are itemizedKeywords Mechanical engineering design，CAD，Support system1IntroductionThis paper summarizes the progress made toward the development of the ideal mechanical engineering design support system For nearly 30 years，computer aided de sign(CAD)systems have been touted by their developers as systems that support engineering designers developing products CAD systems have had a major impact on how design is accomplished in the workplace This being said，there is amazingly little ibrmal research on the effects of these systems on the designers and on the final products‟This paper presents a structure for discussing these effectsIn doing so、lt summarizes what is known and what needs co be studied Finally、it discusses how CAD systems have evoh,edto supportincreasingportions ofthe activitiesthat are used to develop products.The term CAD emphasizes that the computer ls an aid to the human designer，so this paper is designer centric it is based heavily on the activities pertbrmed by designers and the types ofintbrmation developed by them in many ways，this is an update of two earlier papers，‘‘The importance of drawing in the mechanical design process”[29 J and“issues critical to the development of design history，design ratio nale and design intent systems”【311 The latter paper developed 13 outstanding issues that needed to be resolvedto realize the capture and query ofengineering design intormation as a potential lor lmprovmg the design processand the reuse ofdesign Intormation.The tbundation for the first paper was the study of the marks made on paper by nve mechanical design engineers of varying backgrounds and experience They were each given the initial specifications tbr one of two t~irly simple，yet realistic，mechanical design problems taken from professional practice The engineers were requested to think aloud as they soh,ed the problems Their verbal reports、drawings，and gestures were video and audio taped for aperiod of6 10 h The taped data were then transcribed to ob tain a……protocol”of the design session Each designer made numerous drawings during his or her solution of the problem A11 0fthesewere on paper CAD systemswere not usedinthe studgbecausenone ofthedesigners usedCADln their daily practice，and its use would have added another variable to an already complex experiment.From the more than 40 h ofdata taken，15 sections were selected that represented typical conceptual，layout，detail and selection design for each subject The 15 sections of protocol data consisted of 174 rain of data The data were analyzed to explore the observations that drawings are usedto：1 Archive the geometric torm of the design2 Communicate ldeas between designers and between the designers and manufacturing personnel3 Act as an analysis tool Often，missing dimensions and tolerances are calculated on the drawing as it ls developed4 Simulate the design5 Serve as a completeness checker As sketches or other drawings are being made，the details left to be designed become apparent to the designer This，in ett)ct，helps establish an agenda of design tasks leL to accomplish6 Act as an extension of the designer‟s short term memory Designers often unconsciouslv make sketches to help them remember ldeas that they might otherwise torgetThe 1990 paper refined and supported these observa tions AdditionalIv，although the subiects did not use CAD systems，the resuhs suggested that：1 CAD systerns nl[ist allow tbr sketching lnput2 CAD systerns nlust allow for a variety of Interfaces tbr the designer This does not mean more ways to define a circle、but an eftort to match the interface and the im age on the CAD system to that needed by the designer3 CAD systems iiltlSt recognize domain dependent features and treat them as entities4 CAD tools need to be able to manage constraints(even abstract and tkmctional constraints)and ensure their satistaction、as it is evident that human designers are cognitively limited in this ability Since that paper was written，CAD systerns have matured and have addressed、at least to some degree、all南ur of the conclusions iIowever，even the most recent systems are a ong way tbom the ideal mechanical engineering design support system In this paper，the ideal system will be described and progress toward this ldeal discussed2A model of design problem solvingit may someday be possible for a designer to put on a ‘‘thinking cap”that can take his or her thoughts and de elop a hardware reDresen【atlon Research on under standing cognitive processes，CAD，and rapid prototyping ls certainly moving ln that direction This ideal implies that we can tbrmtflate concepts Jn our heads that are sumciently well tormed to warrant hardware It also as sumes that CAD systems are suflicientlg developed to take our thoughts and manage the evolution of parts and as semblies CAD system development will require an tin derstanding of the cognitive workings of designers so that the transition tbom thought to representation is possibleTo explore what ls known about this link、consider the relationship between the human problem soh,er and the external environment shown in Fig 1 This figure ls based on the model developed bv Newell and Simon『20l and ls called the information processing system(IPS)The figure is a simple……map‟‟ofw here information about the design is developed and stored The figure shows an internal，human problem solving environment(inside the mind of the designer)and an external environment(outside the mind of the designer)Within the designer，two locations correspond to the two different kinds of memory：short term memory(STM)and long term memory(LTM) External to the designer，there are many‘‘design storage locations”including graphical representation media such as pieces of paper and CAD tools，as well as other media such as textual notes，handbooks，and colleagues Each location has certain properties that affect how it can beused in designDetail on the charac Leris【ics of the STM and the LTM ls based on Newell and Simon‟smodel[20 J Extensions have been made to it for visual imagery【1 l，12，13 J and effortshave been made to codil~~it【21 it must be realized that the contents of the model given here are not folly agreed to in the cognitive psychology community，but the),are cer tainly secure enough to provide a basis for discussing the role of CAD in mechanical design2．1Short-term memory Short tern：memorg ls verv fast and powerful The contents of the STM are the information we are aware of,that is，our conscious mind All design operations(。