computer aided decoration of ceramic tableware. part i: 3-d decoration

Comput. & Graphics, Vol. 21, No. 5, pp. 641-653, 1997 XC 1997 Elsevier Science Ltd. All rights reserved

Printed in Great Britain

PII: s0097-8493(97)00041-1

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Technical Section

COMPUTER AIDED DECORATION OF CERAMIC TABLEWARE. PART I: 3-D DECORATION

CHEE KAI CHUA’I, ROBERT GAY’ and WOLFGANG HOHEISEL’

‘School of Mechanical and Production Engineering, Nanyar.g Technological University, Nanyang Avenue, Singapore 639798, Republic of Singapore

e-mail: [email protected] ‘Gintic Institute of Manufacturing Technology, 71, Nanyang Drive, Singapore 638075,

Republic of Singapore ‘Karlsruhe CIM Transfer Centre, Steinbeis Foundation for Economic

Promotion, Bismarckstrasse 45, 7500 Karlsruhe Germany

Abstract-Computer usage in the ceramic tableware industry has largely been confined to word processing, spreadsheets, database, payroll, inventory and statistical process control. Computer Aided Design and Computer Aided Manufacturing (CAD/CAM)is slowly Iraining ground in this industry. The relatively high speed of generating physical designs from conceptuali:sation using CAD/CAM and Rapid Prototyping have suggested their use for the decoration of ceramic tableware. A CAD/CAM system, or more specifically, Computer Aided Decoration Of Ceramic Tableware (CADOCT), is developed for the design and Inanufacture of patterns to be decorated on ceramic tableware. Numerous industrial case studies featuring ceramic tableware prototypes are carried out and presented to illustrate the various advantages of using the prototype CADOCT system. These advantages include significant time and cost savings. It also avoids the heavy reliance on traditional practices. and the experience and skills of craftsmen. The major contribution of the research is an innovative iapproach from art to part or, from conceptualisation to realization, for the decoration of ceramic table&are. Part I, a study of the problems and the proposed prototype system are described. as well as the solutions of 3-D decoration. In Part II, the application of rapid tooling is described. lt 1997 Elsevier Science Ltd. All rights reserved

1. INTRODUCTION

The ceramic tableware industry has been traditionally regarded as one which is heavily craft-based. Computer usage in the ceramic tableware industry has largely been confined to word processing, spreadsheets, database, payroll, inventory and statistical process control. Computer Aided Design and Computer Aided Manufacturing (CAD/CAM) is slowly gaining ground in this industry only recently, despite having been around for about 30 y. The relatively high speed of generating physical designs from conceptualisation using CAD/CAM and Rapid Prototyping (RP) have suggested their use for the decoration of ceramic tableware.

In recent years. the use of computers and other forms of automation in the ceramic tableware industry has increased [l-3]. In particular, the application of CAD/CAM to ceramic production is feasible for manufacturing sanitary ware, tableware and technical ceramics [4-61. The Pfalzgraff Com- pany of the United States of America [7] has for instance used CAD/CAM for the 3-D modelling and NC programming of its rectangular baker. It has reported that the CAD/CAM method involves eight steps while the manual method involves IO steps. Also the formal method requires approximately

’ Author for correspondence.

28 worker-h and the latter approximately 62 worker-h. Therefore, the obvious savings in using CAD/ CAM amounts to 34 worker-h and two fewer steps. The less-obvious savings lie within the increased accuracy and the ability to predict and archive with CAD/CAM.

Edwards [8] developed a CAD/CAM system which automates the cutting of decorative patterns on crystal glassware. The use of CAD for pattern design has been implemented in the pottery industry 191. Siikamaki [lo] describes DeskArtes, a Finnish CAD system for ceramic design which is used by Hackman Companies Arabia (ceramics), Iittala (glass) and various design companies. Aesthedes system of Barco Graphics [l l] is another CAD system for design and production of tableware patterns. It reports a significant time saving of 50-60% in producing a set of tableware fittings and colour separation.

In recent years, a group of manufacturing methods based on a layer-to-layer building principle, or collectively ltnown as RP Methodologies. has emerged [12, 131. Two such methods, SLA [ 141 and Solid Ground Curing (SGC) [15] are being re- searched for I:ableware production.

With the new developments in technology ad- vancements in CAD, CAM and RP, there is thus a need for an extensive study on the computerisation, automation and integration of the design and manufacture of decoration for ceramic tableware.

641

642 C. K. Chua, R. Gay and W. Hoheisel

Fig. 1. A Typical handcrafted block mould of an incised decorated plate.

Computer-Aided Decoration of Ceramic Tableware (CADOt :-T)

/ References

Scanner

\ c Production

, \

Designer’s Toolbox 1. Placement Routines ‘u:

2. Adaptation Routines (I 3. Geometric Libraries U, 4 Relief Generation Routines # 5. Mapping Routine #

6. Output Interfaces ;t

f@ CA1 IA Platform

t! ArtCAM Platft~m

Fig. 2. The CADOCT system.

Computer aided decoration of tableware. Part I 643

2. PRACTICES AND PROBLEMS ASSOCIATED WITH PRINTED TRANSFER OR DECAL DECORATION

The work done on printed transfer which is basically 2-D has been extensively published in [16, 171. This paper will however focus on the problems associated with moulded or incised decoration (which is basically 3-D) which is described in the next section.

3. PRACTICES AND PROBLEMS ASSOCIATED WITH MOULDED OR INCISED DECORATION

Moulded or incised decorations were one of the earliest types of clayware ornaments. They are still used today for tableware decorations. Low moulded relief is achieved by cutting the design right into the plaster of Paris mould used to shape the ware. When this type of technique is used, the moulded design is sometimes tilled in afterwards with coloured decals or hand-painted. In practice. incised designs are cut into the ware with a sharp tool. The following steps describe briefly the design and production of moulded or incised decorations [14]:

( 1) Model the tableware in plaster based on concept design, including moulded or incised design.

(2) Cast the block mould, which is essentially the negative form of the model.

(3) Produce a number of trial pieces of ware from the block mould for testing of quality such as shape, function, appearance and closeness to concept design.

(4) Produce a case mould for each part of the block once the trial has been approved.

(5) Obtain the working moulds using the case moulds. These moulds are produced in plaster and have an expected life of between 70 to 100 casts.

(6) Begin the main production process called casting. This will continue to other processes such as glazing and firing.

Ceramic tableware design and development techniques have remained unchanged for many decades and still rely heavily on craft techniques. Thus, the quality of the plaster mode1 in step one above is dependent largely on the skills and experience of the modeller. Th#- closeness with which the final product matches the designer’s original concept is strongly correlated to the skills of the modeller.

Incised or moulded decorations are still manually cut in practice. Decorations in tableware are usually reliefs cut into the block mould of the tableware. made usually of plaster of Paris. Figure 1 shows as a typical block mould. It takes weeks of painstaking hand crafting by a master craftsman of decades of experience to achieve the fine. intricate details.

A second major problem arising from the traditional industry is that the lead time for new products has not varied and is currently too long for today’s competitive market place. This alone suggests the use of CAD and RP to address the issues of long lead time and slow response to competitors. Furthermore, the model, block and trial processes are repeated several times until t.he tableware proves satisfactory. Such iterative processes work best in CAD where modifica-

Fig. 3. A basic pattern.


tions and corrections are easy and fast. Also, RP allows the modified model to be created quickly.

1. COMPUTER AIDED DECORATION OF CERAMIC TABLEWARE (CADOCT)

As mentioned before, many efforts in the compu- terization and automation of the ceramic tableware are piecewise. A comprehensive, integrated and computerised CAD/CAM system dedicated to the design and manufacture of decoration on ceramic tableware is found lacking. The overall goal of this project is, therefore, to research and develop a system to meet these requirements. The prototype system is called Computer Aided Decoration Of Ceramic Tableware (CADOCT).

4.1. CADOCT architecture At the centre of the CADOCT system is a graphics

workstation running a 3-D CAD/CAM system. The CADOCT system has three modules namely, the input module, the designer’s toolbox and the output module. The interaction between these modules are depicted in Fig. 2.

4.2. .Input module Besides the standard input devices like a keyboard,

graphics tablet and mouse. the CADOCT system is connected by an image-acquisition subsystem com- prising of a high-resolution, colour flatbed scanner and supporting software. With this combination of inpu,: devices. a variety of incoming data can be accommodated by the system. For example, pre- liminary hand sketches can be carried out on the graphics tablet by a tableware designer. Subse- quently, engineering designs can be modelled using the CAD facilities. On the other hand, existing designs from references such as competitors’ catalo- gues, companies’ previous designs and others can be captured through the flatbed scanner.

4.3. Designer’s toolbox Analogous to a worksman’s toolbox of spanners,

screwdriver, etc., the tableware designer is provided with a useful set of tools in the Designer’s Toolbox. These tools include:

(1) Placement Routines. These placement routines are simply a combination of two types of

Fig. 4. Circularly adaptecl patterns.

Computer aided decoration of tableware. Part I 645

transformation routines-translation and rotation. They allow the designer to automatically place motifs around a tableware, with ease and choice such as the number of duplications.

(3) Adaptation Routines. Unlike placement routines, adaptation routines are more powerful and combine scaling and distortion (both stretching and compression) in addition to translation and rotation. While they are generally slower in computation, they are more common and complement the placement routines. The designer can again automatically adapt motifs around a tableware with similar choices,

(3) Geometric Libraries. Geometric libraries are databases of designs aimed at boosting the designer’s productivity. In effect, it is an electro- nic catalogue of designs. Libraries can be organised according to the types of designs such as award-winning designs. or classified by the clients they are designed for. Libraries promote reuse and are a good productivity tool.

(4) Relief Generation Routines. These are applicable to the moulded or incised decorations. Working from 2-D patterns, relief generation routines

facilitate the definition of the third dimension through parameters such as whether the decoration is convex or concave, and the size and shape of the decoration.

(5) Mapping Routines. These are true mapping routines which allow the reliefs to be mapped onto 3-D tableware items such as the coffee pots and plates. Visualization and inspection can take place on the computer monitor. I f unsatisfac- tory, redesign can be take place at the relief definition stage and the process repeated.

(6) Output Interfaces. An interface to output devices is necessary to convert computer model files into a file suitable for RP building. The acceptable & &to file format for RP is STL or Stereolitho- graphy File Format. Other output interfaces are more standard and these include output to printers, plotters and CNC machines.

4.4. OtLtpllt nloclLllc Two types of output are necessary: a plot file for

the silk-screen printing process for the type of decoration using decals or transfers, and a STL file for the Stere’slithography or other RP methods for

Fig. 5. General adaptation of an octagonally shaped dinner plate

C. K. Chua. R. Gay and W. Hoheisel

Fig. 6. 2-D artwork

building rapid models for subsequent tooling and It is important to remember that the colour manufacture. In plotting, the prepress procedure of reproduction processes required for ceramics are

colour separation is undertaken. This requires very different to those in the graphic/publishing knowledge of ceramic print colours and the identi- sector. As many as 12 or more colour separations fication of the number of ceramic coour separations may be needed in order to provide the colour match needed to reproduce the colours in the original. and to accommodate ceramic colour behaviour

Fig. 7. Touched-up image.

Computer aided decoration of tableware. Part I

Fig. 8. Shape of a tableware plate model

under the rigours of the ceramic production process. Once the fits are ganged together to form cost- effective print plates, the required number of colour separations are extracted in register.

Regardless of the RP methods used. the STL file format is used for the building of parts to take place. A STL file is basically a triangular mesh file with ,I’, Y, Z coordinates of its three vertices and outward normal for each triangle.

software for product design for a particular range of industries which include ceramic tableware [ 161, glassware, bottle making, both plastic and glass, jewellery [ 181. packaging, food processing, for moulded products and products produced from forming rolls. coins and badges. and embossing rollers [19]. 411 of these industries share a common

5. ADAPTATION AND PLACEMENT ROUTINES FOR GENERATING 2D DECORATIONS I Selected colour I

The work related to the adaptation and placement routines has been published in two journal papers [16. 171. Reference [16] describes the special computer programmes which have been developed to adapt decorative patterns into different variations of size and shape of tableware. Reference [17] focuses on a method of generating motifs along a circular arc and describes the solution in detailed mathematics. Hence, these routines for solving 2-D decoration problems will not be elaborated in this paper as they have already been published. As an example of a circular adaptation, Figs 3 and 4 illustrate the basic pattern and circularly adapted patterns respectively. Typical tableware includes dinner plates. coffee saucers, conical cups, bowls and teapots. For more general shapes, a generic algorithm is used. Figure 5 illustrates a generic shape such as an octagonally- shaped plate with adapted floral patterns.

0 Plane 0 Round Cl Square

•I Ccnvex Cl Concave

Max. height: I 0.0 I

Base. height: 0.0

Angle: 45.0

Scale: I.0 1

Height Array

6.3-D DECORATION GENERATION METHODOLOGY

6. I. Introduction There are presently several commercially-available Fig. 51. Control panel for the shape profile

648 C. K. Chua. R. Gay and VJ. Hoheisel

A--L.- __ll__.I // A‘\\e ._. ” -_ -_.-A \

Flat pmtilc: square prolilc Round profile

-A----\.-- Flat proftlr: with base hcigbt Squwc profile with hssc height and maximum height :md maximum haght

~~~i~~~ we

Fig. 10. Various shapes of the 3-D relief.

problem: most of their products have elements of complex engraving or low relief on them [20], Traditionally, such work is carried out by skilled engravers either in-house, or more often by a third- party sub-contractor, working from 2-D artwork. This procrss is costly. open to unwanted misinter- pretation of the design by the engraver and most importantly, lengthens the time of the design cycle.

The CAD/CAM revolution has boosted the production and the performance of many industries everywhere for the past 15 y [21]. However. its applications in the above industries are still at their infancy stage. Prototyping is still very much a manual process which relies largely on the skills of an experienced craftsman who uses handtools such as a small chisel to carve and shape the mode1 out of a plaster block [5]. Little attention has been focused on the use of quick and accurate RP equipment for building prototypes in this industry.

The use of CAD/CAM and RP technologies such as SLA and Laminated Object Manufacturing (LOM) reduces the time required for design mod- ifications and improvement of prototypes. The steps

Cross section of the region. x=.iOmm Cr,xs wction of the region. x=.iOmm

Angle=60 deg. Angle=60 deg.

Scale= I .o Scllr=l.O

Angle=20 deg.

Scale= I .o

involved in the art to part process include the following:

(1) Scanning of artwork; (2) Generation of surfaces; (3) Generation of 3-D decoration reliefs: (4) Wrapping of reliefs on surfaces: (5) Converting triangular mesh files to STL file; (6) Building of mode1 by the SLA and LOM.

The flow of this series of stages is illustrated using floral design as a case study.

The function of scanning software is to automatically or semi-automatically create a 2-D image from 2-D artwork. It would normally be applied in cases where it would be too complicated and time consuming to model the part from a drawing using existing CAD techniques.

The 2-D artwork is first read into ArtCAM, the CAD/CAM system used for the project, using a Sharp JX A4 scanner. Figure 6 shows the 2-D artwork of a

-I\ Angle=20 deg.

Sc.tle= I .o

Angle=20 deg. Scale=0.6

Angle=20 deg.

Sc:tle=0.6

Fig. 11. An illustration of’ the overall profile height

Computer aided decoration of tableware, Part I 649

:

i ,’ I ‘ I

! “._

) /‘-

%pre rofk with angle 45 degrees and basehe tlxnm. b

Rand p-of& with angle 30 degrees, base height 1 mm and max. height 2 mm.

Fig. 12. An illustration of the definition of shape profiles on different regions.

Fig. 13. 3-D decoration reliefs of an artwork.


Fig. 14. 3-D reliefs wrapped onto the dinner plate surface.

floral design which has been generated using the In i he ArtCAM environment, the scanned image is circular adaptation routine. -This combination of first reduced from a colour image to a monochrome hardware and software allows for the direct produc- image with the fully automatic ‘Gray Scale’ function. tion of a standard image from the artwork, which Alternatively, the number of colours in the image can can be read directly into ArtCAM. The 2-D artwork be reduced using the ‘Reduce Colour’ function. A in such instances represent the designs to be used on colour palette is provided for colour selection and the the face of a tableware item such as a dinner plate. various areas of the images are coloured. either using

Fig. 15. Wrapped decoration reliefs converted into triangular mesh files

diff flOC

ima

6.3. T

reqi buil

Computer aided decoration of tableware. Part I

Fig. 16. Two sets of triangular mesh files-decoration reliefs and tableware plate shape-are automatically combined.

erent sizes and types of brushes or the automatic generated. A triangular mesh file is p )d fill function. Figure 7 illustrates the touched-up automaticalLy from the 3-D model. This is se. a base onto which the relief data is wrapped a

combined with the relief model to form the Gmercrtion oj surj2m.5 part.

‘he shape of a tableware is modelled to the uired dimensions in the CAD system for model 6.4. Gerwration oj’3-D dworution reli<fs

Iding. Figure 8 shows a tableware plate model The next stage in creating the 3-D decoratic

reduced used as nd later finished

on relief

Fig. 17. Colonr-shaded remIran model file

652 C. K. Chua, R. Gay and \Y. Hoheisel

DUCT 5.2 TRIANGLE BLOCK P 18 AUG ‘I 993 21.43.28 0

A 1 GREEN Paint Duct @l

1 0 4 2 0 0.00000 10.00000 0.00000 20.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 1 .ooooo 1 .ooooo 0.00000 1.00000 0.00000 1 .ooooo

0 0 0 0 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 1 .ooooo 0.00000 0.00000 10.00000 0.00000 0.00000 0.00000 0.00000 1 .ooooo 0.00000 0.00000 0.00000 20.00000 0.00000 0.00000 0.00000 1 .ooooo 0.00000 0.00000 10.00000 20.00000 0.00000 0.00000 0.00000 1 .ooooo 0.00000 0.00000

3 1 4 4 I 2

Fig. 18. The original triangulx file format

is to assign each colour in the image a shape profile. There are various fields which control the shape profile of the selected coloured region, namely, the overall general shape for the region, the curvatures of the profile (convex or concave), the maximum height, base height, angle and scale. Figure 9 shows the control panel for the shape profile.

There are three possibilities for the overall general shape: a plane shape profile will appear completely

flat, ,lyhereas a round shape profile will have a rouna.ed cross section and lastly, the square shape profile will have straight angled sides. Figure 10 illustrates the various shapes of the 3-D reliefs. For each of these shapes, there is an option to define the profile as either convex or concave.

The square and round profiles can be given a maximum height. If the specified shape reaches this height:, it will ‘plateau’ out at this height giving in effect

solid print facet normal -0.00000e+00 2.00000e+02 -0.00000e+00

outer loop vertex 0.00000e+00 0.00000e+00 2.OOOOOe+O1 vertex 0.00000e+O0 0.00000e+00 O.OOOOOe+OO vertex 1.00D00eHll O.OOOOOe+OO 2.OOOOCk+Ol

endloop endfacet facet normal 0.00000e+00 2.00000e+02 O.OOC~OOe+OO outer loop vertex 1 .OOOOOe+01 0.00000e+00 2.00000e+Ol vertex 0.00000e+00 0.00000e+00 O.O0000e+OO vertex 1 .OOOOOe+Ol 0.00000e+00 0.0000Oe+00

endloop endfacet

Fig. 19. The converted triangular file to follow the STL formal.

Computer aided decoration of tablewape. Part I 653

a flat region with rounded or angled corners, depend- ing on whether a round or square shape was selected for the overall profile respectively (see Fig. 10).

The overall profile height which covers the respective region can be controlled by specifying the required angle of the profile which represents the tangent angle of the curve at the edge of the region. Figure 11 further illustrates the concept of the overall profile height. An alternative to control the overall profile height is to use the ‘scale’ function to flatten out or elevate the height of the shape profile. The relief detail can be examined in a dynamic Graphic Window within the ArtCAM environment itself. Figure 12 shows an illustration of the definition of shape profiles on different regions. Figure 13 illustrates the 3-D decoration relief of an artwork.

6.5. Wrapping qf reliefs on surfaces

The 3-D decoration relief is next wrapped onto the triangular mesh lile generated from the tableware plate surfaces using the command Wrap (see Fig. 14). This is a true surface wrap and not a simple projection. The wrapped relief is also converted into triangular mesh files (see Fig. 1.5). The triangular mesh files can be used to produce 3D model suitable for colour shading and machining. The two sets of triangular mesh files, of the relief and the coin shape, are automatically combined (see Fig. 16). The resultant model hle can be colour-shaded and used by the SLA to build the prototype (see Fig. 17).

6.6. Corlverting triangular mesh files to STL .file The STL format is originated by 3D System Inc. as

the input format to the SLA, and has since been accepted as the de facto standard of input for RP systems [22-241. Upon conversion to STL, the object’s

surfaces are triangulated. which means that the STL format essentially consists of a description of inter- joining triangles that enclose the object’s volume. The triangular mesh files are also triangulated surfaces, however, of a slightly different format (see Fig. 18). Therefore, an interface programme written in Turbo-C language is developed for the purpose of conversion. The converted triangular file adheres to the standard STL format as in Fig. 19. It has the capability of handling triangular files of huge memory size.

7. CONCLUSION

The problems in the traditional ceramic tableware manufacturing industry are discussed. A comprehensive CAD/CAM system, or more specifically, CA- DOCT is proposed and developed as a prototype system. The 3D decoration methodology is intro- duced. In Part II of the paper. the application of RP technologies will be demonstrated for several tableware items.

REFERENCES

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computer aided decoration of ceramic tableware. part i: 3-d decoration

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