162 Philips tech. Rev. 36,162-175,1976, No. 6

Computer-aided design

In designing mechanical parts a great deal of the design time is taken up in making thedrawings and updating them as required. Now that the cost of computer time is steadilydecreasing, it is worth while investigating whether automation of these activities is apossibility and an economic proposition. Work has been inprogress at the Philips Labora-tories in Hamburg since 1973, in cooperation with colleagues at Philips Data Systems,Eiserfeld, on an integrated computer system in which parts are completely detailed in adialogue between the designer and a computer via an 'interactive display'. The systemalso provides the programming of the numerically controlled manufacture of the partand delivers punched control tapes for these machines. For certain types of parts, such aspunched metal parts, the tools required for the production process can also be designedin this way. The geometry of a workpiece can be stored in a data bank; the system employsan existing method developed for commercial data processing.

P. Blume

Introduetion

Since the early sixties steadily increasing use hasbeen made of computers in the design of mechanicaldevices and in production-planning departments -'computer-aided design' and 'computer-aided manu-facture', abbreviated to CAD/CAM. The objective isto make the computer do the routine work that peoplefind so uninspiring. There is also the hope that the useof a computer will enable the design to be producedmore rapidly and less expensively.

Before taking a closer look at the problems, let usfirst give a definition of the term 'mechanical design'.This term includes the assembly ofa number ofsuitablecomponents to form a complete machine as well asthe separate geometrical specification of the individualparts. Both effectiveness and cost have to be taken intoaccount, by choosing appropriate materials, makingprovision for strength requirements, following stan-dards recommendations, and by keeping manufactur-ing as simple and inexpensive as possible [IJ. The resultof design is 'a large variety of technical data in formssuch as drawings of parts and sub-assemblies, partslists, adjustment instructions, manufacturing instruc-tions, etc., enabling other people to manufacture theproduct' [2J.

Stages in the design process

In engineering design the process of 'thinking out'a product - a process associated with the gradual tak-ing shape of an idea that is originally undefined - is

Dr P. BIl/me is with Philips GmbH Forschungslaboratorium Ham-burg, Hamburg, West Germany.

divided into several stages (seefig. 1) [3J. The first is theconcept stage in which the original assignment, usuallya list of requirements, is taken as the starting point in asearch for design ideas that might offer a solution tothe problem. The most suitable of these ideas is selectedand is sketched by hand, not necessarily to scale in itsoriginal version. In the ensuing design stage, this sketchis used as a basic for a design drawing, which alreadyshows all the parts to scale, with connecting dimen-sions. At the same time general calculations are made.to make sure that the design satisfies the main designcriteria relating to service life, strength and cost. In thelast, or detailing stage all the parts are finally specified,dimensioned and drawn in detail. Drawings are thenmade of sub-assemblies and the parts lists are compiled.For complicated designs it may be necessary to repeatone or more of these stages a number of times until theiterative process yields an optimum design.

The diagram in fig. 2 gives a general picture of thevarious activities encountered in design. We see thatdrawing accounts for most of the time, 33 %, and that15% of the time is devoted to the actual designing. It isparticularly interesting that only 3% of the total designtime is used for computing. This means that very littletime would be saved ifthe computer were only used forcalculations; to obtain any real rationalization of thedesign process it is necessary to pay particular atten-tion to the actual drawing and designing.

To find out where the computer could be used in thevarious design activities, it is necessary to separatethese into heuristic activities and algorithmic activ-

Philips tech. Rev. 36, No. 6

Fig.!. Diagram of the designprocess for a mechanical part.The three stages of the processare shown on the left, and thedetailed activities at the centre,while on the right the work issubdivided into heuristic orcreative work and algorithmicwork, i.e. work performed inaccordance with a certain set öfinstructions. A rough sketch ofthe device is produced in theconcept stage; a design drawingbased on that sketch is made inthe design stage. In the detailingstage the various parts aredetailed and drawn.

CAD/CAM SYSTEM

stages in theprocess

~

concept

ities [4l. Heuristic work may be defined as the creativework, i.e. 'invention', the work based on the designer'sability to think in terms of abstract ideas and to takedecisions in complex situations. Except in a few ele-mentary cases this work cannot be taken over by thecomputer in the present state of technology. Algorith-mic work may be defined as work for which an'algorithm' can be given, i.e, a series of instructions orprocedural steps for the solution of a specificproblem.Such activities can very readily be performed by acomputer. In design work the actual drawing (and

design

detailing

activities

check drawings

-.,IIIIIIIIII

-.,IIIIIIIIII

_..J

-.,III·II

163

type of work

mainlyheuristic

heuristic-algorithmic

algorithmic-heuristic

mainlyalgorithmic

calculations, of course) belong to this category.If we now apply this to the various stages of the

design process as represented in fig. 1, we see that the

[1] This definition is taken from the Brockhaus encyclopedia,17th edition, 1967.

[2] S. Hildebrand, Feinmechanische Bauelemente, Carl HanserVerlag, Munich 1968,p. 27.

[3] U. Baatz, Bildschirmunterstütztes Konstruieren, Funktiens-findung, Prinziperarbeitung, Gestaltung und Detaillierungmit Hilfe graphischer Datenverarbeitungsanlagen, thesis,Rheinisch- Westfälische Technische Hochschule Aachen,1971.

[4] See the thesis mentioned in note [3].

164

concept stage chiefly comprises heuristic work. A fewalgorithmic activities occur in the design stage whilethe detailing stage consists largely of algorithmic work.It follows that in the first instance computer-aided

Fig. 2. Diagram showing how the total design time for mechanicalparts is subdivided, according to a study made by the machine-tool laboratory of the Rheinisch-Westfälische Technische Hoch-schule Aachen [5J. The actual designing accounts for 15% of thetime, and calculation only 3%. The largest part of the time, 33 %,is devoted to drawing.

16 16 30

I---

~ -<.0

~----- ~- --- l-: - ._-- f-~

-2 22.5 20

CYL/25,22.5,X=0,Y=0,Z=0/CYBEOL/25,2/CYL/30,20/CYREO/30,1.6,28.6,X=-16/CYL/35,30,X=60CYL/30,20/CYREO/30, 1.6,28.6, X=16/CYL/25, 22.5/CYBEOR/25,2/

1punched cord

CAOsystem

Fig.3. Input of the shape of a workpiece to the computer. Thecode, taken from a workpiece-descriptive programming lan-guage 17J, consists of a mnemonic description of each element ofthe workpiece, followed by a number of digits indicating thedimensions of the element and its locations in space. ThusCYL(25, 22.5, X = 0, Y = 0, Z = 0 means a cylinder with adiameter of 25 cm and a length of 22.5 cm whose axis lies alongthe x-axis and with the centre of its left-hand side face at thepoint (0,0,0). CYBEOL means 'a cylinder with a bevel on theoutside, left' and CYR EO 'a cylinder with a recess on the outside'.

P. BLUME Philips tech. Rev. 36, No. 6

design can be usefully employed only in the detailingstage. To what extent parts of the design stage willlend themselves to 'computerization' depends largelyon the type of design.

Three main types of design may be distinguished:new designs, variants and adaptations. In the caseof new designs the result is a completely new product.In such cases, therefore, recourse cannot be had todesign data for earlier products; the work has to passthrough all the stages of the design process. In variantsthe principle and operation of the design are alreadyknown so that the concept stage can be omitted.Changes may however be made to certain parts of thedesign. In adaptations the design of the product isalready established in such detail that it may only benecessary to alter a number of dimensions.

In the following there will be a discussion of a CADsystem that can be used to develop designs of the firsttype, i.e. new designs. (This does not of course excludeits use for the other types of design.) New designs arevery often necessary in mechanical parts of electricaland electronic products; the rapid developments heremean that products and their mechanical parts areconstantly subject to change. Since a new design hasto pass through all the design stages, it follows fromwhat has been said above that at present the use of aCAD system for this type of construction has to berestricted to the detailing stage. The emphasis here ison the description of the geometrical shape of the vari-ous parts of the design, to provide a starting point formaking drawings and design changes with the aid ofthe computer.

Application of work piece-descriptive programming lan-guages

The geometry of the workpiece can be described withthe aid of workpiece-descriptive programrning lan-guages that have been developed, at various centres,from the APT language for prograrnming numericallycontrolled tools [6]. Using a shaft as our example it willbe shown how the description of a workpiece is effectedwith a language of this kind; the language used herewas developed by E. Schnelle at the Technische Uni-versität Berlin [7]; the drawing of the shaft and theresulting text are shown in jig. 3.

The shaft is first divided into basic shapes or bodiessuch as, in this case, cylinders, which in their turn canbe modified by 'form elements'. Each basic shape andeach form element is described by a term consisting ofa mnemonic description (up to six letters), followedbya number of digits describing the size of the body orelement or its location in space. In the example infig. 3 the left-hand part of the shaft is described first:CYL means cylinder; this designation is followed in

Philips tech. Rev. 36, No, 6

Fig. 4. The COC 1700 Digi-graphic computer system for thegraphic processing of data. Theinteractive display is connectedto the CD 1704central processorvia a control unit with a 'picturestore'; the computer itselfhas theusual mass stores and peripheralequipment. Information fromthe computer store can be dis-played on the screen of thepicture tube and can be alteredor added to by using a light penand keyboards connected to theinteractive display. This meansthat very fast input of bothalphanumeric and graphic in-formation is possible, while theinput can be verified immediatelyon the screen.

CAD/CAM SYSTEM 165

punched-tape tapereader punch

400 characters 120 charactersper s

disc memorieseach 3.2 x106words

turn by the diameter and length of the cylinder and theinitial coordinates required to indicate the cylinder'slocation in space. As in APT, abbreviations are usedto describe the elements; for instance, CYBEOL means'cylinder bevel outside, left' and CYREO stands for'cylinder recess outside'.The description of the workpiece data by a pro-

gramming language has the advantage that the user ofthe system can describe the workpiece at his own pacein advance without having to take computer times intoaccount. The text is punched on to cards and only thenfed to the CAD system. This method, however, has thegreat disadvantage that the designer, who generallyexpresses his ideas in a direct graphical way, has toexpress himself in a language with an extensive vocab-ulary. Moreover, this verbal system is sensitive toerrors. An input system in which the designer com-municates graphically is therefore preferable.In this article the development of such a CAD/CAM

system will be discussed. The system is not only usedfor designing workpieces, it also carries out produc-tion-planning activities right up to the generation ofthe perforated tapes for the manufacture of 'corn-ponents on numerically controlled machine tools [8J. •

tele-type

lineprinter

300 linesper min

punched-cardreader

300 cardsper minper s

CD 170432k

16bits/word1.1 ps cycl

r---'-------, magnetic-tape memories30kHz.800 bits/inch

control unit'--_-, __ -' display file

CO 1744Bk

CO 274odisplay

functionkeyboarq

light penalphanumerickeyboard

Input via an interactive display

The graphical communication with the computercan be realized in a very direct manner with the aid ofan interactive display. The term 'interactive' indicatesthat the display permits a dialogue between the designerand the computer [9J. Fig. 4 gives a general impressionof a computer system designed for this purpose; itconsists mainly of a central processor with the usualperipheral equipment (typewriter, card and tape pun-ches and readers, a high-speed printer, and magnetictape and disc stores) plus some other input and outputdevices for graphic information, such as a digitizer, adevice which can transfer a drawing in digital form,e.g. on to paper tape, and a data plotter. The heart of

[5] R. Simon, Rechnerunterstütztes Konstruieren, eine Mög-Iichkeit zur Rationalisierung im Konstruktionsbereich, thesis,Rheinisch- Westfälische Technische Hochschule Aachen,1968.

[6] J. Vlietstra, The APT programming language for the nu-merical control of machine tools, Philips tech. Rev. 28,329-335, 1967.

[7] E. Schnelle, Rechnerunterstütztes Konstruieren im Dialog,thesis, Technische Universität Berlin, 1972; see also: I. C.Braid, Designing with volumes, thesis, University of Cam-bridge, 1973.

[8] This research was carried out with support from the govern-ment of the Federal Republic of Germany.

[9] See the thesis mentioned in note [3]. ,

166

the system is the display unit, with either a circular ora rectangular picture tube, and a picture store in whichthe information to be reproduced on the screen isstored in a digital code. With the aid of this store thepicture is generated approximately 40 times persecond so that a stationary and flicker-free picture isobtained (a 'refreshed display').

The system is made interactive by the electronic lightpen, which identifies any picture element it is pointedat; seefig. 5. The tip of the light pen contains a photo-

P. BLUME Philips tech. Rev. 36, No. 6

passed on to the computer until the user has confirmedthat it is the element intended. This confirmation is alsoeffected with the light pen, which is pointed at a specialword, 'accept', on the picture tube.

The method of inputting a geometrical shape 'inter-actively' via the display will now be described, againusing the example of fig. 3. The drawing of the work-piece will appear within a rectangle. On a circularpicture tube four segments remain outside this area andthese are available for writing in lists of instructions

Fig. 5. The interactive display in operation. lf the light pen is pointed at a partjeular elementon the display, the position of that element is conveyed to the computer. The display can beused to input graphic information to a computer. It is also possible la intervene in the progressof a program by pointing at command words displayed on the picture tube. The user can thusengage in a dialogue with the computer via the display; hence the term 'interactive'.

cell that picks up a light pulse from the screen at theinstant when the indicated element is written by thecathode-ray beam of the picture tube. Identificationconsists in determining which picture element from thepicture store is read out when the light pulse appears.This information is then fed to the computer, whichthen acts on this information, e.g. by carrying out aparticular operation on the picture element, asindicated by the program. The light pen can also beused to start a program or branches of programs bypointing it at words written on the screen, e.g. instruc-tions. To ensure that it is in fact the desired word, pointor line segment that is fed in, the element pointed atalways flickers initially and the information is not

and comments. These lists represent choices of actionsthat the user can select with the light pen, and arecalled menus.

The dialogue between the computer and designerstarts with the presentation in one of the four segmentsof the picture tube of a menu of workpiece families:turned parts, sheet-metal parts, milled parts, etc. Selec-tion of one of these words with the light pen indicatesto the computer that the program for describing, say,turned parts has to be run. A menu of elements describ-ing such parts then immediately appears on the screen.Since there is not much room in the segments andresearch has shown that recognition of a word becomesdisproportionately more difficult with increasing length

Philips tech. Rev. 36, No. 6

»sbattrecessbevelled edge leftbevelled edge rightrun out leftrunout rightkeywaydrilled centre holeCRend

CAD/CAM SYSTEM

Fig. 6. Dialogue between the designer and the computer duringthe interactive input of the geometry of a shaft. The centralrectangular region of the circular screen contains a drawing ofthe part ofthe workpiece that has already been input. Lists ofthenames of elements descriptive of the kind of workpiece desiredcan be displayed in the four segments round this rectangle. Theselists are known as 'menus'. When one of these elements is in-dicated by pointing the light pen at it, this element is added to thedrawing ofthe workpiece. The dimensions are inserted via a key-board or by pointing at a 'number' menu that is also displayedon the screen. a) When a shaft is to be described the word 'shaft'is assigned from the menu on the left and the diameter and lengthare input. This part of the shaft then appears in the working fieldof the picture tube. The following are then added successively inthe same way; a bevelled edge (b), a recess for a retaining ring (c)and a machine-tool run out (d). The shaft is now extended to-wards the right by the addition of a second shaft section (e) towhich a keyway is added (f).

of the list, a menu usually contains no more than eightwords. If more than eight words are necessary, theyare divided between a number of hierarchically ar-ranged menus.The first menu for turned parts contains the most

important shapes and form elements that can occur,such as a shaft section, a bevel, a recess, a tool runout,etc. In describing a turned part of the type shown infig. 3 the workpiece is divided into separate shaft sec-tions of a certain thickness and then, after the startingpoint has been determined, the first section is input. Thedesigner therefore first points to the word 'shaft' on themenu (fig. 6a). Each time a particular element has beenselected the parameters required for its further defini-tion appear in the top segment of the picture tube,together with a drawing to clarify them. In the case ofthe shaft this drawing is a rectangle and the parametersare the diameter and the length. The values of theparameters are input either via a keyboard or with thelight pen by pointing at digits in a menu displayed onthe screen and consisting of the digits 0 to 9. Theadvantage of this .method is that the designer does nothave to put the light pen down to use the keyboard.When the dimensions have been input, a drawing ofthe desired section of the shaft appears at the indicatedposition in the rectangle, symmetrically in relation tothe axis (see fig. 6a).The end of this shaft section must now be bevelled.

The term 'bevel' is then pointed at and another diagramappears, this time with the angle and width ofthe bevel

shaft

«bevelled edge left

CRend

shaftHrecess

CRend

shaft

«runout right

CRend

«shatt

CRend

shaft

»keyway

CRend

167

Q=

304560

-8--------

-ffi3---- ----

-Et--------

-ffiE(3- ----

-Q3-----torque M=

t

168

as parameters, together with a small menu of the mostcommon values for the angle (fig. 6b). Displaying theseangle values has the advantage that it is only necessaryto point at the desired value instead of supplying eachdigit separately. From this rather trivial example wecan see how the system ensures that the decisions thatthe user has to take are prepared in such a way thatthey demand the least possible effort from him. Thisemerges still more clearly in the steps which follow:the introduetion of a recess for a retaining ring and arunout for grinding. After indicating the term 'recess'(fig. 6c), another diagram appears on the screen com-plete with parameters; the dimension 1 of th~ newelement where it connects with the part already formedis particularly important. Since there are standardthicknesses and widths for these retaining rings andrecesses, depending on the diameter of the shaft, thesedimensions are read directly from tables stored in thecomputer memory/ The designer therefore only has toindicate the parameter I.Four shapes A, B, C and D are laid down in the

standard DIN 509 for the tool runout (fig. 6d). Bypointing at these letters one by one the designer cannow make diagrams of these four possibilities vis-ible on the tube, enabling him to select the shape whichhe finds most suitable. Since the parameters of the fourshapes are specified for each shaft diameter in thestandard, the designer only has to indicate the shapehe has selected and confirm it.The following stages in the input of the shaft take

place in an analogous way (figs. 6e and f). We shallonly consider one more possible stage in more detail:the addition of a keyway. Like the tool runout, thiselement is covered by a DIN standard; in any par-ticular companya preselection is generally made fromthe standard versions and these are listed in a menu.The length of the keyway can still be chosen freely with-in certain limits; this dimension depends on the torqueto be transmitted. Thus if a program is included thatcalculates the length of the key from the maximumtorque required, all the user of the system has to in-dicate in addition to the torque is the connecting dimen-sion (l in fig. 6f) in relation to one of the end faces ofthe shaft.In the example given above we see that, despite the

use of the computer and the interactive ~isplay, aconsiderable amount of data still has to" be inputmanually, even for a simple workpiece. The examplealso shows clearly that by the start of the detailingprocess, i.e. at the point where the CAD system begins,the workpiece has already assumed a fairly definiteshape. At this point it might not really seem that theuse of this equipment is worth while in comparisonwith conventional drawing on a drawing-board. If the

P. BLUME . Philips tech. Rev. 36, No. 6

drawing alone is considered, then it is definitely notvery helpful. But the great advantage of using the com-puter, however, is that when the dialogue with thecomputer has been completed a full geometrical de-scription of the workpiece is available in the computermemory. This allows the information to be auto-matically processed, in whole or in part, from thispoint onwards for the production-planning or prep-aration processes that follow the detailing. Theseactivities can also be executed with the interactivedisplay: the workpiece data can be stored in an elec-tronie file (on magnetic tape or magnetic disc); imme-diate access is then available if updating is necessary;the parts of the workpiece can be called separatelyfrom the file and arranged on the screen to form sub-assemblies. Alternatively, the data can be used again ina dialogue, for generating the control information forproducing the parts on numerically controlled machinetools.

The geometrical structure of a workpiece

We shall now take a closer look at the geometricalmodel of a workpiece. The shape of the body can bedescribed unambiguously by giving the positions of allthe points on its bounding surfaces. If these surfaceshave a completely irregular shape, it can mean in theextreme case that an infinitely large number of pointsand hence an infinitely large amount of data is neces-sary for an exact description. Usually, the designer willlook for a more regular shape with more regular limit-ing surfaces, which gives a good approximation to thebody within the specification and can be described witha smaller amount of data.

Engineering workpieces are not usually irregularlyshaped bodies but objects made on machine tools andhence of a more regular shape. Turned parts, forinstance, are made on a lathe and have rotational sym-metry. An investigation carried out in the mechanicalengineering laboratory of the Rheinisch- WestfälischeTechnische Hochschule Aachen, on workpieces froma production run [10] shows that a large number of theworkpieces examined can be made up from a smallnumber of basic shapes such as blocks and cylinders.By way of example, fig. 7 shows a shaft and the basicshapes into which it can be divided. The workpiece-de-scriptive programming languages are based on thisprinciple. Since, as we shall show below, basic shapescan be described with only limited data, the descriptionof .objects composed from them, modified if necessaryby simple form elements, requires a minimum of in-formation.

A basic geometrical shape is determined by a hier-archy of descriptive ·elements; ..fig. 8 shows this hier-

Philips tech. Rev. 36, No. 6 CAD/CAM SYSTEM lJi9

archy for a cube. On the top step we have the bodyitself; on the second step are the surfaces bounding thebody; these in turn are bounded by the edges that formthe third step and these are in turn bounded by the

form element

L~ r ~-yt3-

basic shapesFig. 7. Example ofa composite body and the basic shapes, in thiscase cylinders, into which it can be divided. The basic shapes, inturn, can be further modified by the addition of form elementssuch as bevels, as shown here.

LlJ4 3

Fig. 8. Schematic representation of the geometrical structure ofa basic shape, in this case a cube. The structure can be describedwith a number of hierarchically arranged lists in which the vari-ous elements such as faces, edges and vertices are given, and withdescriptions of the relationships between these elements. Thedivision into elements and relationships is very convenient forthe storage of the structure in a computer memory.

points forming the fourth step. From this classificationthere emerges a hierarchy of lists for describing anobject, e.g. an 'edge list' comprising edges a to I andcontaining the description of these edges (straight,circular, 'etc.) and a 'point list' containing the coor-dinates of the various points. In addition to the ele-ments themselves; the relations between the elementscan be described. In the case of-the cube, for instance"

there is a relation between the surface A and the edgesa, b, c and d, since A is bounded by these edges; thereis also, for example, a relation between vertex 1 andedges a, d and g, because vertex 1 is the vertex commonto these edges.For basic shapes a complete description of the

geometry using these lists is in general highly redun-dant. A cube, for example, can be described adequatelyboth in size and its position in space ,by giving thelength of its side together with the direction cosines ofone of the surfaces and the coordinates of a singlevertex point. There is, however, considerably lessredundancy in the more complicated composite objectsgenerally encountered in practice. However, practiceshows that considerable loss of time in the dialogue viathe interactive display is incurred if all the coordinatesof the angular points and centres of the basic shapesand all the data on the edges have to be generatedbefore the workpiece can be displayed. It is thereforeadvisable to store a complete 'redundant' geometricaldescription of the workpiece together with its basicshapes and form elements in the computer memory.

Data storage in the computer

The geometric data is stored in a computer system inthe form of 'data structures', i.e. structured collectionsof data in which various objects and their interrelationsare recorded. In recent years a number of data-structuretypes have been developed; one of these is that of theCODASYL group [Ill. This design was developed onthe basis of experience with the storage of data forcommercial data processing. In our experience, how-ever, the CODASYL structure is also very useful forthe storage of geometrical structures.The elements of the CODASYL structure are the

record and the set. A record is a representation of anobject by its properties or attributes. Thus the recordofthe object 'point' consists ofthe serial number ofthepoint and its X-, y- and z-coordinates. A group ofobjects with the same characteristics constitute arecord type; the group of all point records thus formsthe 'points' record type. Conversely, each record in-dividually is called an 'occurrence' of a record type,which means to say that it is one of the class formingthe record type. A set defines a relation between recordtypes, e.g. between the record type of a body and therecord type of its bounding surfaces. The term 'occur-rence' is used in connection with a set, in the same wayas in connection with a record type, if a particular

[10] See the thesis mentioned in note [4]. ,[11] CODASYL Data Base Task Group, report, April 1971;

CODASYL is an acronym for COnference of DAta SYstemsLanguages.

170

relation between individual records is intended. Inpractice the set is realized by means of a reference con-tained in the record, for example to certain otherrecords or to a table that in its turn contains references.The following notation has been developed by C. W.Bachman [12) for representing data structures: recordtypes and records are shown as rectangles and a set isrepresented by an arrow connecting the rectangles(fig. 9a and b).

Brecord type 'occurrences'

Q

bodies

1:n

faces

set occurrence of set12

Fig. 9. Schematic representation of the basic elements in the. CODASYL structure for the storage of data in a data bank. a)A rectangle represents a record, a description of an object, or arecord type, i.e. the collection of all the records of a particulartype. Every record can be regarded as an occurrence of a recordtype. In the application described here the record is used todescribe an element in the geometrical description of a work-piece. b) An arrow between two rectangles represents a set, thedescription of a relationship between two record types. The setis defined such that there is always one record that is theOWNER of one or more MEMBERS (e.g. a single body consist-ing of two (curved) surfaces); only I :11 relationships can bedescribed by sets. The term occurrence is also employed in thecase of a set ifwhat is meant is the relation between an OWNERrecord and its MEMBER records.

In the CODASYL structure the set is organized insuch a way that a single record type is always shown asthe OWNER, one or more record types as MEMBERS.The 'occurrence' of a set always consists of oneOWNER record and zero, one or more MEMBERrecords (e.g. a body as the OWNER and two or morebounding surfaces as MEMBERS). This means that aset can only define 1: n relationships. The arrowrepresenting the set always points from the OWNERto the MEMBER. In the geometrical data for whichwe wish to use the CODASYL structure, m: n relation-ships occur regularly instead' of 1: n relation-ships,e.g. between edges and vertices: each edge has two

P. BLUME Philips tech. Rev. 36, No. 6

end points and each vertex can belong to two or moreedges. If, in an 'edge-vertex' set, we started from avertex as MEMBER, two edges would again occur asOWNERS of this vertex, which is not allowed in theCODASYL structure. This problem can be overcomeby introducing relation records, which are extrarecords used only as links between other records. Byway of examplefig. lOa and b show how the connectionbetween edges and vertices can be defined with the aidof relation records. In the 'edge-relation record' seteach OWNER record 'edge' has two 'occurrences' ofthe relation-record type as MEMBERS. Each of theserecords in turn is associated with another relationrecord as MEMBERS of a vertex as OWNER in the'vertex-relation record' set. To find the vertices as-sociated with a particular edge we must therefore lookfirst in the 'edge-relation record' set of MEMBERrelation records associated with the edge as OWNER;the vertices associated with these relation records canthen be found as OWNERS in the 'vertex-relationrecord' set.

With the aid of these elements of the CODASYLsystem the data structure of engineering workpiecescan be represented in the manner illustrated in fig. 11.

recordtype

1:n 1:m

m:n relationship Q

record 1

occurrences of an m:n relationship

f2Fig. 10. a) Representation of a data structure in which an /11 : 11

relation occurs. To enable the records and sets as defined in fig. 9to be employed in this case, a relation record forming the linkbetween the two records is inserted. b) The examples given hereare the occurrences of two sets that indicate, via a relationrecord, the connection between the edges of a cube and threevertices, one of which is the common vertex.

Philips tech. Rev. 36, No. 6 CAD/CAM SYSTEM 171

To distinguish them from ordinary records the recordrelation types in this figure are symbolized by circles.While data structures such as the CODASYL struc-

ture are adapted to the requirements of data processing,the form in which they are stored in a computer

Fig. 11. Representation ofthe data structure ofa workpiece in theCODASYL system. Relation records are shown here as circles.

memory has not yet been dealt with. This form, thestorage structure, is not only influenced by the datastructure but also by the organization of the memory,e.g. the addressing, the coding of information, etc.This point cannot however be discussed in this article.Knowledge of the storage structure is not in factrequired by the user; the data structures expressed bymeans of CODASYL data-structure elements de-scribed above can be stored in any data bank based onthe CODASYL system (e.g. the Philips PHOLAS (131)without further knowledge of the storage structure. Adata bank of this kind is used to store the geometricaldata for mechanical workpieces.

The integrated CAD/CAM system

For executing the various activities required in thedesigning and production planning of sheet-metalparts, we have developed an integrated CAD/CAMsystem, which is shown schematically in fig. 12 [141.The application of the system starts in the detailingstage of product design and covers tool design and theprogramming of numerically controlled wire spark-machining equipment used for making the productiontools.The geometrical data for sheet-metal parts is input

in the same interactive way as described above forturned parts. Our experience is that much less use canbe made of form elements here. Also, fewer designrules are available. Since sheet-metal parts are muchused in assemblies such as chassis, cabinets and frames,it is likely that design systems for these will be devel-oped in the future.Once the geometry of the workpiece has been de-

scribed, a digital representation is stored in the partsfile. The technological and organizational data are thenadded and the part is dimensioned (fig. 13). Thedimensioned part must of course be clearly readable,for example the dimension lines and the lines of thepart must not intersect. Producing such a drawing isusually so complicated (see figs. 14 and 15) that thisactivity cannot be performed by an algorithm butrequires human intervention: the light pen is pointed atthe line that has to be dimensioned. This line then startsto flicker as was explained above, and when it has beenconfirmed that it is the line intended, the coordinatesof its end points are read from the data structure, thedimension is calculated and then automatically dis-played on the screen together with the dimension andextension lines. If some of the dimensions thus gen-erated are inconveniently located, e.g. because theyinterseet other dimension lines or contour lines of theworkpiece, they can be moved to any other more suit-able place by the light pen. To enable the representa-tion of the dimensions to be called later, together withthe geometry of the workpiece, this information is alsostored in the parts file.Drawings of the workpiece design can be made auto-

matically with an x-y plotter; this data is supplied bythe parts file via a postprocessor that converts the datafrom the data structure into machine code for the plot-ter pen. It is possible to define a standard interface so

[12] C. w. Bachman, Data structure diagrams, Data Base 1,No.2,1969.

[13] Introduetion to PHOLAS, publication of Philips Electro-logica BY, Apeldoorn, July 1974.

[14] We should like to acknowledge the valuable help, relating tothe mechanical engineering of the system, that was given byDr Burmester of the Philips Data Systems Division,Eiserfeld, West Germany.

IIIIIIIIIIIII-. - ---: - - - --, - - -,- - - - --IIII

172

INPUT.·AND

DIALOGUE

o. DISPLAY

I DESIGN I

o

"0'0J • •

.. .... . "

.'

I·1II

IIII---------r-------IIIIIIIIIIIII

P. BLUME

detailingof

parts

parts file

tool design

tool fileIpRODucnON PLANNING II

IIIIII..1 programming for

numerical control

~>Fig.12. Integrated designv'and manufacturing system (CADICAlM) for punchéd metal.parts, The upper part shows how thedetailing stage: of designing: takes place.in a dialogue between thedesignér andthe cómputer via "the interactive display. The work-piece data generated in 'this way is stored in the parts file. This

.';

Philips tech. Rev. 36, No. 6

OUTPUT

drawings

tool drawings

parts 'lists

punched tape

data provides the starting point for designing the tools such assingle-stage blanking tools, again by means of the interactivedisplay. The resulting data is collected in the tool data bank.Finally, in the control-programming stage, information is addedin a dialogue for generating the numerical-control tapes.

Philips tech. Rev. 36, No. 6

Fig.13. Drawing of a punchedmetal part displayed on thescreen after input of the geom-etry. The description is nowcomplete but no dimensionshave so far been added.

Fig. 14. The same workpiece asin fig. 13 after dimensioning.

CAD/CAM SYSTEM

that the various makes of x-y plotter will operate with only oneprogram for converting the data structure to that code.

In the integrated system shown in fig. 12 the parts file formsthe interface between the activities of the design and production-planning offices. In the design of sheet-metal parts a typical activityin production-planning is the design of the punching tools required;this is also done with the aid of the interactive display. The part iscalled from the data bank, and then the outer contour and theinner contours are identified with the light pen. These contoursare nearly identical with the cutting contours of the main toolparts - the die and punch. A computer program now calculates

Fig. IS. Drawing of a bent sheet-metal part as displayed on the screen; threeviews are given, together with the dimensions.

173

174

the total length of these contours and then determinesthe cutting force, taking into account the shear strengthof the material. For parts that require bending, a'development' on a plane must first be made. This isalso done interactively, by showing the various viewsof the part on the screen to form the developed part.The corrections that have to be applied in determiningthe dimensions ofthe part on account of the distortionsoccurring along the bent edges can be carried out bythe computer, e.g. in accordance with the recommen-dations of the standard DIN 6935.

Once the cutting force has been determined, the sizeof the tools is deterrnined. Then the contour is posi-tioned in the die; where possible the point of applica-tion of the cutting force is made to lie at the centre ofthe tool; this positioning operation is carried out auto-matically by a computer program. After the angle atwhich the strip of material is fed to the press has beenselected, the contour can still be rotated round thispoint of application to a position in which the leastpossible loss of material occurs in the punching opera-tion.

When this has been done, the shape of the punch andthe various piercing tools (for the smaller holes) canalso be determined by using design algorithms. Inaddition, other tool parts are detailed, such as the'stripper' and the 'ejectors', which, after the punching,remove the material. The parts are then dimensionedinteractively and the data stored in the tool data bank(see fig. 12). Drawings are made in the same way as forthe parts. Fig. 16 shows an example of a punch tool asdisplayed on the screen.

P.BLUME Philips tech. Rev. 36, No. 6

Fig.16. Drawing of a punchingtool as described in a dialoguewith the computer.

The design of the tools is followed by the program-ming for producing these tools on numerically con-trolled machines. We assume that a numerically con-trolled wire-type spark-machining equipment - inwhich a wire electrode is moved through the materialin much the sarne way as a fretsaw - is available forcutting the contours. A machine of this kind can beprogramrned very efficiently in the sarne interactivemanner used for input of the geometrical data. Thetool is called from the tool file and displayed on thescreen. The contours to be cut are then identified withthe light pen and the machining movements and thenon-machining movements (the displacement of thewire to a new starting position) are indicated in relationto the initial hole for the insertion of the spark wire;see fig. 17. Since sharp corners cannot be cut with thewire spark machine, any corners have to be roundedoff. The numerical-control tape is then generated auto-matically by means of a postprocessor. J nformationabout the tool path can also be stored in a data file forany later processing necessary (this is not shown in thefigure).

The programs relating to part description were com-pleted in October 1975, and programs for designingsingle-stage blanking tools are approaching comple-tion. A postprocessor for programming the numericalcontrol has been made for the 'AGIE-Cut' sparkmachine type DEM 15, and the dialogue for thismachine is also ready. A number of tools have alreadybeen machined with the aid of a tape prepared in thisway. The first prototype of the complete system will beready by the end of 1976.

Philips tech. Rev. 36, No. 6

Fig. 17. The programming ofthenumerically controlled wire-spark machining equipment, forcutting a punch pin for the partshown in fig. 13. The shape ofthe punch is called from the tooldata bank; the designer thenuses the light pen to indicate thepath the wire must followthrough the material, startingfrom a new hole each time. Themovements between the variousstarting holes are indicated bydashed lines. The path to befollowed by the wire is recordedon punched tape.

CAD/CAM SYSTEM 175

The economic aspects

In conclusion, we should like to consider theeconomic aspects of the use of an interactive display.The system discussed here is based on the CDC 1700Digigraphic computer system; the heart of the systemis a minicomputer with a store for 32 k words, each of16 bits, and a cycle time of l.l fLs (fig. 4). At presentthe hourly rate for a system of this ki nd used 12 hoursper day is still about twice the cost of one man-hour.If, however, the continuing development towardscheaper hardware and increasing personnel costs is

Summary. Description of an integrated computer system fordesigning mechanical parts. The vital feature of the system isthe 'interactive display' that enables the user to feed graphicalinformation into the computer by means of a light pen. Theapplication of the system is as yet restricted to the detailing stageof the design process; the method consists of a dialogue betweenthe designer and the computer via the display, in the course ofwhich the designer can use the light pen to select from a numberof basic shapes and form elements presented on the picture tube,thus building up the workpiece step by step. All dimensions arefed in by keyboard or with the light pen, The article begins witha short survey of the conventional design process and then, asexample to illustrate the use of the CAD system, describes theinput of the data for a turned part via the interactive display.The descriptive method employed for this, consisting in the useof basic shapes and form elements, is taken from the workpiece-descriptive programming languages. The CODASYL structure

taken into account, the time can be seen to be rapidlyapproaching when an hour of computer time will nolonger be as expensive as a man-hour. When that timecomes, design work with the CAD/CAM system willonly have to be completed twice as quickly as in theconventional way for economic justification. If the fullpotentialof the system is considered, it will be foundthat this factor can already be attained. Economically,therefore, the system will probably not give rise to anyproblems in the next few years but the number of pro-grams available will have to be considerably enlarged.

developed for commercial data files is used for description of theworkpiece and for storage of the workpiece data in the computermemory. In this process the geometrical structure of the work-piece is described by a hierarchy of the geometrical elements(faces, edges, vertices) and their interrelationships. These can berepresented by the 'record' and 'set' structure elements of theCODASYL system. In the integrated CAD/CAM system forpunched metal parts, which is being developed at the PhilipsHamburg laboratories, the punching tools required are alsodesigned. First the cutting force required is computed and themost economical strip layout is determined, again via the display.The die plate and punch are then designed. This is followed by thenumerical-control programming for the manufacture of thesetools. This process, also carried out on the screen, yields thepunched tapes used in this case for the numerical controlof aspark-machining set. The article ends with a brief survey of theeconomic aspects of the system.

176 Philips tech. Rev ..36, No.o6

Recent scientific publicationsThese publications are contributed by staff of laboratories and plants which form part ofor cooperate with enterprises of the Philips group of companies, particularly by staff ofthe following research laboratories:

'" Philips Research Laboratories, Eindhoven, The Netherlands EMullard Research Laboratories, RedhilI, Surrey, England M·Laboratoires d'Electronique et de Physique Appliquée, 3 avenue Descartes,

94450 Limeil-Brévannes, France . LPhilips GmbH Forschungslaboratorium Aachen, WeiBhausstral3e, 51 Aachen,

~~ - APhilips GmbH Forschungslaboratorium Hamburg, Vogt-Kölln-Straûe 30,

2000 Hamburg 54, Germany HMBLE Laboratoire de Recherches, 2 avenue Van Becelaere, 1170 Brussels

(Boitsfort), Belgium BPhilips Laboratories, 345 Scarborough Road, Briarcliff Manor, N.Y. 10510,

U.S.A. (by contract with the North American Philips Corp.) N

Reprints of most of these publications will be available in the near future. Requests forreprints should be addressed to the respective laboratories (see the code letter) or to PhilipsResearch Laboratories, Eindhoven, The Netherlands.

E. Arnold & M. Poleshuk: Carrier generation at theSi-Si02 interface under pulsed conditions.J. appl. Phys. 46, 3016-3018, 1975 (No. 7). M, N

F. Bagdasarjanz: Quantisiert adaptive Entzerrung vonFernsprechleitungen zur Datenübertragung.Thesis, Zürich 1975. (Philips Res. Repts. Suppl. 1975,No.9.) E

D. Bois & D. Beaudet: Photoluminescence study oftheshallow acceptor states in n-type GaAs.J. appl. Phys. 46, 3882-3884, 1975 (No. 9). L

J. Bootsma: Liquid-lubricated spiral-groove bearings.Thesis, Delft 1975. (Philips Res. Repts. Suppl. 1975,No.7.) E

K. H. J. Buschow, M. Brouha & C. Langereis: Spon-taneous magnetostriction in ThCo5.Solid State Comm. 16, 789-790, 1975 (No. 6). E

K. Carl: Ferroelectric properties and fatiguing effectsof modified PbTiOa ceramics.Ferroelectrics 9, 23-32, 1975 (No. 1/2). A

D. den Engelsen & B. de Koning: Ellipsometry of blacklipid membranes of egg lecithin and chloroplast ex-tracts.Photochem. Photobiol. 21,77-80, 1975 (No. 2). E

J. Flinn: Piezoelectric ceramics and their applications.Physics Education 10, 274-280, 1975 (No. 4). M

G. Groh: Holographische Methoden in der medizini-schen Diagnostik.Radiologe 15, 236-244, 1975 (No. 6). H

w. K. Hofker (philips Research Labs., AmsterdamDivision): Implantation of boron in silicon.Thesis, Amsterdam 1975. (Philips Res. Repts. Suppl.1975,No. 8.)

J. G. Kloosterboer: Interaction of bivalent metal ionswith their chelates of ethylenedinitrilotetraacetic acid(EDTA) and 1,2-trans-cyclohexylenedinitrilotetraaceticacid (CDTA).Inorg. Chem. 14, 536-540, 1975 (No. 3). E

R. Koppe: Das Abbildungsproblem beim rechnerunter-stützten Entwurf von Layouts integrierter Schaltungen.Angew. Informatik 1975, 223-232 (No. 6). H

J. G. M. de Lau: Influence of chemical compositionand microstructure on high-frequency properties ofNi-Zn-Co ferrites.Thesis, Eindhoven 1975. (Philips Res. Repts. Suppl.1975,No. 6.) E

A. Mircea & A. Mitonneau: A study of electron trapsin vapour-phase epitaxial GaAs.Appl. Phys. 8, 15-21, 1975 (No. I). L

R. F. Mitchell & E. Read: Suppression of bulk waveradiation from surface acoustic wave devices.IEEE Trans. SU-22, 264-270, 1975 (No. 4). M

A. Pirotte & P. Wodon: A query language for a rela-tional data base.Lecture Notes in Computer Science 26, 524-531, 1975(Springer, Berlin). B

L. Verhoeven: CAL; a videophone colour system forlow bandwidth channels.Nachrichtentechn. Z. 28, 99-101, 1975(No. 3). E

Volume 36, 1976, No. 6 Published 29th November 1976pages 149-176

PH I LI PS TECHNICAL REVIEWVOLUME 36, 1976, No. 7

Optical communication by means of glass fibres

A new technique is gradually beginning to emergefor the transmission of informationby cable. This technique can offer a very wide bandwidth, yet the quantity of materialrequired per kilometre of cable is relatively small. The element carrying the informationflow is not a metal wire or a coaxial tube, but an extremely thin glass fibre of specialcomposition, inside which modulated light waves can propagate. The light is produced anddetected by solid-state elements, whose dimensions are well suited to those of the fibres.

In this issue of Philips Technical Review examples are presented of results that havebeen achieved by Philips Research in a number of sectors in this field. These relate tomethods for making glass fibres and assessing their suitability, the development of astable Ga.As]AlxGal-xAs laser, investigating the possibilities of detection with anavalanche photodiode, a modulation method in which the intensity of the laser pulseis independent of temperature, and a solution to the difficult problem of mechanicallycoupling the very thin fibres to the solid-state elements. The issue starts with a shortintroductory article that briefly outlines the potential and the difficulties of opticalcommunication with glass-jibre cables.

The title photograph shows part of a drum with two glass fibres wound on it; the one to the right is suitable, the other is not. Theleft-hand fibre loses a great deal of light sideways, whereas in the right-hand fibre (200 rn long) almost all the light emerges at the end.