Customising to improve CADCAMperformanceby Roger BillsdonADE Analysis & Design Engineering Ltd.

A little customised software can substantially increase the benefits tobe gained from a general-purpose CADCAM system. Often onlyrelatively modest costs are involved. This article considers sometypical applications for customising, the need for data links withother systems and some design and development issues.

Introduction

Customising general-purpose com-puter-aided design and manufacturing(CADCAM) software can enable theuser to enhance the functionality of astandard system and tailor or fine tune itto particular requirements without lossof flexibility.

The better CADCAM systems nowprovide good macro and interfacingfacilities. Thus they provide a goodbasis for developing customised sol-utions which were previously only pos-sible with bespoke systems. It is nowalso feasible to establish data links withother systems and thus move towards alinked engineering business system. Inthis way the benefits of CADCAM canbe spread more widely within acompany.

Applications for customisation

The better applications for customisingare usually those which are relativelywell constrained and involve repetitivedesign procedures — for example thedesign and drafting of large electricmotors which are to a 'standard' designbut which are tailored to each individual.customer order. Another commonexample is where standard componentsor items of equipment are employed inmany different designs, such as in elec-trical distribution systems and petro-chemical plant.

Well constrained applications areoften rather specialist and may be speci-fic to a single company. Even where anumber of companies share the sameapplication, different design pro-

56

cedures may be employed by each com-pany. Thus the market is likely to bemuch too small for a CADCAM systemvendor to contemplate developing andmarketing a module to meet individualrequirements.

If a vendor did develop a module for aparticular customer, he would thenobviously try to sell the same module tothe buyer's competitors, and this couldbe detrimental to the company's com-petitive position. In designing suchmodules vendors are obliged to gener-alise the specification so as to appeal toas broad a market as possible. A jack-of-all-trades, master-of-none can be theunfortunate result. The advantage of acustomised solution is that it is mucheasier to produce a system capable ofvery high performance in respect of asingle client's specific requirementsthan it is to address many diverserequirements in a market and achieveeven a modest performance.

Some of the more common areas forcustomisation are:

parts listinglinks to other systemsdesign calculation routinesdrawing management and controlmenus for special symbol librariesparametric design calculation and

analysis• connectivity reporting for wiringand piping applications• geometric data selection and extrac-tion for numerical control or stressanalysis.

The first two of these examples are con-sidered in the following sections.

Parts listing

Parts listing can be a very productiveapplication area for CADCAM systemsin terms of time savings and reducederrors. In some situations draftsmenactually spend more time on parts list-ing than on drawing activities. Overallaverage proportions of a draftsman'stime are 10% spent on parts listing and30% on drawing. Therefore, by addingparts listing to a general-purpose CAD-CAM drafting system, the proportion ofthe draftsman's work addressed by thesystem can be significantly increased.Furthermore, parts listing is usuallyconsidered to be tedious work, and soany CADCAM aids are likely to be popu-lar with the users.

While parts listing is a very wide-spread requirement, and one fromwhich substantial benefits can bederived, it is an area wilfully ignored bymost vendors. One reason appears tobe that parts listing is a mundane appli-cation which lacks the sales appeal ofgraphics. CADCAM system vendorsgenerally claim to offer parts listing, butmost only provide basic facilities. Typi-cal limitations are as follows:

• All parts listing data is held in thedrawing. This can represent a substan-tial volume of data in some cases. In oneelectrical schematic drawing appli-cation ADE found that parts listing dataexceeded the geometry data by an aver-age ratio of 2:1 and that the drawing filesize was causing significant degradationin interactive response times. Draftingproductivity rates were suffering.• All parts list data has to be entered atthe CADCAM workstation. For signifi-cant volumes of data this represents avery ineffective use of a high-cost work-station primarily intended for interac-tive graphics work. Alphanumeric datashould be manipulated on low-cost

Computer-Aided Engineering Journal April 1986

VDUs on the grounds of cost and easeof use.

• No facilities are provided for hand-ling design modifications in a reliableand consistent manner. With most sys-tems a completely new parts list has tobe generated after each design modi-fication, and the previous version issimply discarded. In many situations,particularly where quality assuranceprocedures are stringent, as in thedefence and nuclear industries, thismethod of handling design modifica-tions is unacceptable.• Input of parts list data is entirely bythe keyboard. Most CADCAM users arenot proficient typists, and so the work isgenerally slow and inaccurate. Menuscontaining commonly used words andphrases, automatic numbering for itemnumbers, and standard componentparts list data files are three simple aidswhich can be provided for the user.

These limitations can often be over-come with a little customisation in addi-tion to the normal requirement forsetting up company formats for partslisting sheets.

Linking data to other systems

Unfortunately most CADCAM systemsare currently used as general-purposedrawing machines operating in isola-tion. The benefits are limited to the*drawing office and are of limited con-sequence to the overall company oper-ation. Linking data between systemsshould be considered by all those withCADCAM systems.

The ultimate goal should be a linkedengineering business system (LEBS)designed to speed the flow of infor-mation and to minimise clerical effortand errors throughout the company.Commercial data processing systemshave already made significant progresstowards this style of operation withcommunications and sharing of databetween previously separate appli-cations and systems. CADCAM, with afew notable exceptions, has mademuch less progress. In large part this isbecause CADCAM is a newer technol-ogy, and there seems no reason todoubt that CADCAM will evolve alongsimilar lines.

The difficulties involved in this areashould not be underestimated. Therisks are high, as is the investment inhardware, software, training and datafile creation. The potential benefits aresubstantial but essentially medium tolong term. Therefore a gradual phaseddevelopment should be carefully plan-ned. An LEBS specification should bedrawn up at the outset to act as a goal.Without such a focus it is easy to fall into

such pitfalls and short-term expedientsas:• the installation of a number of dis-parate systems which must always oper-ate in isolation because of fundamentalincompatibilities• the introduction of low-cost draft-ing systems because of the superficiallyattractive and quick financial returns.

While the overall project is difficult andcomplex, many elements are relativelysimple. In the following section a com-mon example is discussed, that of link-ing CADCAM parts list data to anothersystem such as:

production controlbill of materialsgeneral-purpose database packagesplanning and estimating or costingPERT (program evaluation and

review technique) or critical pathnetworking• quality assurance.

Linking CADCAM parts list data

Generally, a data link is best establishedusing an intermediate text file, pro-duced by the CADCAM system and readin by the other system (see Fig. 1). Thefile can be held on disk if both systemsare implemented on the samecomputer network, or, if differentcomputers are involved, magnetic tapeis a popular option.

The chief advantage of the intermedi-ate file approach is that it forms a clearlydefined interface between the two sys-tems. The necessary customised soft-ware on either side of the file can

therefore be developed and maintainedalmost independently — essential whenmore than one supplier is involved.Also at the system design stage the datato be included in the intermediate filegives a clear indication of the func-tionality of the data link which is equallyunderstandable by the users and thesoftware writers.

The most common problem is thehandling of design modifications so thatconsistent and accurate transfer of partslist data is assured. A system able toautomatically process all design modi-fications is generally difficult to con-ceive. One possible solution is toinclude an identifier against each itemin the intermediate file to indicate new,deleted and changed data arising fromthe design modification. At least thenthe attention of the receiver of the infor-mation is directed to those areas ofchange, as in the interests of flexibility itis usually best to include unaffecteddata as well. When a complete parts listfile is generated at each design modi-fication with such identifiers included, auseful design modification audit trail isprovided.

Design and development issues

Traditionally the development basis fortailor-made or bespoke systems waslimited to basic software tools such asgraphics, database and command lan-guage packages. Software houses likeADE would use these basic tools todevelop tailored systems, each onebeing built virtually from scratch. Withthis approach, provided that the specifi-cation was well conceived and that the

extract andformat required

data

re-formatfor input to

other system

Fig. 1 Example parts list data link

Computer-Aided Engineering Journal April 1986 57

\» ' C FNC/NFFR/NC LTD F ( G U P g 9 ,

Fig. 2 Simple plant design example

software was of good quality, the resultwas a finely tuned, high-performancesystem. However, in the interests ofminimising software developmentcosts, the flexibility provided was usu-ally limited. Thus changes of productdesign or production method couldnecessitate fundamental changes oreven complete re-writes of thesoftware.

Over the past few years standard gen-eral-purpose CADCAM systems haveincreasingly provided better interfacesto their databases and high-level lan-guage facilities. Added to this is thegreater computer power provided by32bit computers and virtual-memoryoperating systems. Previously, even ifgood CADCAM system interfaces hadbeen available, there was so little com-puting power remaining once the stan-dard CADCAM software was loadedthat little could be accomplished by anyother software.

The two key factors to be consideredin assessing a CADCAM system's suit-ability for customising are:

• the programming environment• database and command languageinterfaces.

Most CADCAM software is written inFortran or Basic. It is important that thecomputer has a good, reliable compileror interpreter. Standard software toolssuch as scientific sub-routine libraries,database packages and statistical analy-sis packages can also be useful in someapplications. This requirement is mosteasily satisfied by those CADCAM sys-tems which are implemented on stan-dard, general-purpose computers suchas Prime, DEC or IBM.

Interfaces to CADCAM systems areusually provided either by a high-levellanguage or by a collection of Fortransub-routines. Examples of the formerapproach include GRIP from McDon-nell Douglas Information Systems (for-merly McAuto), NEWVAR fromComputervision and DAL from GECalma. Such languages tend to bebased on a programming language suchas Basic with extensions, which are usu-ally a sub-set of the CADCAM interac-tive command language, for geometrydefinition and other operations. TheDARS module of Medusa and theCADCD and CADET modules ofCADAM are examples of the latterapproach. These modules provide col-lections of sub-routines which can beused in Fortran programs as a means ofinserting and extracting data from theCADCAM drawing files.

There are many issues which must beconsidered when designing acustomised extension to a CADCAMsystem. Many will be specific to the par-ticular application or system, but onecommon issue is whether to aid or toautomate.

There are often several alternativesystem design solutions which providevarying degrees of automation. Fullyautomatic solutions, if successful, maybe expensive and the development timescales can be endless! A more pragma-tic approach is usually preferable wherethe aim is to aid the user rather than toreplace him. The role of the computershould be limited to the more mundaneand repetitive aspects of the job, while

the more intuitive aspects are best leftto the user, who will welcome the chal-lenge and job interest. Hours ofcomputer processing time can berequired to reach some conclusionswhich seem obvious to the user. A com-mon example is the positioning ofdimensions or annotation in a drawing.Generally it is difficult to devise a sys-tem which will always select the bestposition, and it is better to allow theuser some scope for interactively modi-fying the positions of those which thesystem got 'wrong'.

Staffing

Other than the very large organisationswhich can justify employing their ownfull-time CADCAM analysts and pro-grammers, the design and developmentof customisation software is usuallysubcontracted out to specialists. TheCADCAM system vendor will some-times undertake customisation work,but usually only where significant mar-ket opportunities exist. More often it isindependent software houses like ADEthat undertake customisation work. Agood software house will produce a bet-ter designed system in a shorter timethan the non-specialist. The choice ofsoftware house is obviously a key deci-sion and should be made with care. Inparticular the client should:

• interview the members of the teamwho will work on the project — it isobviously important that they should beable to communicate effectively withthe client's engineers• obtain references from two or threeprevious clients with applications invol-ving similar techniques and systems• study system and user documenta-tion — if a user wants to have the oppor-tunity of taking over the support andfurther development of the software,adequate system documentation is avital factor, and good user documenta-tion is always essential.

Conclusions

Customised software can substantiallyincrease the benefits to be gained froma general-purpose CADCAM system.Customising can transform the pro-ductivity of a system by adding func-tionality to meet specific requirementswhile retaining the flexibility of the gen-eral-purpose system. Linking databetween systems should be consideredby all those with CADCAM systems as ameans of broadening the impact ofCADCAM and the benefits to be gained.

R. Billsdon is a Director of ADE Analysis & Design Engineering Ltd., 20 Hall Lane, Burwell,Cambridge CB5 OHB, England.

58 Computer-Aided Engineering Journal April 1986

"The leading product in Low-CostSupermicro Technology since 1981"

Since the introduction of the Sage II 68000, the STRIDEproduct range has expanded in power, performance andcapacity, whilst retaining possibly the best price/perfor-mance ratio in the industry — making it, we believe, theleading product in low-cost 68000 Supermicro technologysince 1981!

From floppies to 450MB hard disk the STRIDE has manystandard features and options that are not found on othersuper micros:

68000 CPU - 12 MHzVMEbus interface1MB - 12MB RAM4 - 22 serial portsCentronics parallel port20MB - 450MB hard disk60MB streaming tapeBattery backed-up real time clock4KB CMOS RAMFloating point unitMemory management unitLocal area networkOperating systems : Unix V, BOS/LAN,Mirage, P-System, RM COS, Occam,Mosys, CP/M-68k, PDos and others.Languages : Pascal, Basic, C, Fortran 77,APL, Cobol, Modula 2, Lisp, Occam,Forth, Tripos

With these features, STRIDE is able to exploitthe full range of 68000 applications. With anadvanced multi-user, multi-tasking BIOS anda built-in local area network, no othermicrocomputer offers the same flexibility within itsprice range...

...Inmos have chosen the STRIDE as theirdevelopment tool for their fifth generationTRANSPUTER....Oxford University, Smiths Industries, BritishLeyland, Courtaulds, Tarmac and other majorshave included STRIDE in their computingstrategy.

The STRIDE product range can benefit YOU! Contact usTODAY for more information and the location of yournearest STRIDE dealer.

FQUINOXThe British specialists in multi-user computer systems

Equinox Computer Systems Ltd. 114-116 Curtain Road, London EC2A 3AH. Telephone: 01-739 3450. Telex: 27341.

Computer-Aided Engineering Journal April 1986 59