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Int J Adv Manuf Technol (1998) 14:269-279 1998 Springer-Verlag
London Limited
The hlterrtationa~ 3o.rnal of
Advanced fflanufacturing Technologu
Creating Machinable Textures for CAD/CAM Systems
Chow Kin Yean,* Chua Chee Kai,t Terry Ong* and Lin Fengt *Delcam
International PLC, Birmingham, UK; and +Nanyang Technological
University, Singapore
Texture is app,!ied on three-dimensionally modelled surfaces in
computer graphics to enhance visual effect. This research focuses
on the development of three-dimensional textured sur- faces which
are suitable for manufacturing. Three approaches for creating the
three-dimensional texture are presented.
The first approach is to process a design from either an
artist's sketch or an image from a two-dimensional scan. The second
approach uses a three-dimensional scanned texture. Both these
approaches depend on the quality of the scanned image and are more
tedious than the third approach, which is to convert texture using
parameters and is a more direct approach. In the user interface
design, two custom-made forms are developed to cater for both
regular and irregular textures.
The case studies have shown that the textures created are not
only good for a visual effect, but are also machinable. The
development work is incorporated into the ArtCAM system which is a
specialised CAD~CAM system that is capable of generating
three-dimensional shapes from two-dimensional art- work.
Keywords: ArtCAM; Artwork; Computer-aided design and
computer-aided manufacturing (CAD/CAM); Three-dimen- sional
texture
1. Introduction
The use of the computer has greatly improved the speed of
computing complex and complicated numerical problems. With the
integration of the computer in manufacturing systems, production
time has been reduced significantly. The evolu- tion of CAD/CAM
(computer-aided design/computer-aided manufacturing) systems has
enabled more complex parts to be modelled and manufactured.
CmTently, most of the parts mod- elled are of a complex shape and
the representation of the complex shape is mainly by
three-dimensional complex sur-
Correspondence and offprint requests to: Dr Chua Chee Kai,
School of Mechanical and Production Engineering, Nanyang
Technological University, Nanyang Avenue, Singapore 639798.
faces e.g. Bezier surfaces Ill, NURB surfaces [2] and G ~
surfaces [3].
In computer graphics, texture is added to the complex surface to
make the part appear more realistic. The incorporation of texture
on the modelled surface enhances the visual effect of the modelled
part. This improves the graphics simulation of the part as a real
object. Currently, most texturing techniques are similar to either
solid texturing [4] or bump mapping [5]. These texturing techniques
do not provide a three-dimensional representation of the textured
surface. This implies that the textured surface modelled cannot be
manufactured, that is, the texture itself cannot be machined.
Therefore, there is a need to create a "real" three-dimensional
texture which can be machined.
There are two main categories of texture - "macrotexture" and
"microtexture" [6]. "Macrotexture" refers to surface primi- tives
that are governed by specific placement rules, whereas
"microtexture" refers to surfaces that are just beyond our
perceptual resolving power. "Microtexture" is a texture that is
most likely to be formed from machining or finishing processes. The
range of surface texture specified by ANSI B46.1 is 0- 50 txm. This
surface texture is called "microtexture". The range of surface
finish obtained by a milling process is 1-200 ~m according to
British Standard BS 1134 Part 1. Using a rigid NC (numerical
control) mill machine [7], a surface tolerance of 10 Ixm can be
easily achieved [8]. The texture under research and development in
this work falls in the "macrotexture" group.
2. Approaches to Create 3D Textured Surface
There are three approaches to create surface texture. The
texture created from any of these approaches is mapped onto a
three-dimensional surface to form a textured surface within the
software ArtCAM. The three approaches differ primarily in the
source of the texture. The source of the texture refers to the
initial form of the texture representation. The first source is
from a two-dimensional image. The second source is from a sample
textured surface, which is three-dimensional, e.g. produced by
finishing processes such as sand blasting. The third source is
derived from a custom-made form defined with
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270 K. Y. Chow et al.
several texture parameters. Figure 1 shows the flowchart of the
three approaches for creating the textured surface.
2.1 From Two-Dimensional Image to Texture
The two-dimensional textured image is obtained either by
scanning an existing textured surface or from the creation of a
computer graphics artist. The two-dimensional textured image must
be a grey-scaled image. This is because the development of the
image to the three-dimensional relief surface in ArtCAM is made in
relation to the colour intensity of the image. This approach
requires two steps for transforming the source to the texture. The
first step is to obtain a textured image that involves the scanning
process or the drawing process. The second step is to create a
relief image which is derived from the colour intensity of the
image.
2.2 From Sample Three-Dimensional Scanned Surface to Texture
The sample textured surface is obtained from finishing pro-
cesses like sand blasting and chemical etching. The three-
dimensional information of this textured surface is acquired by a
three-dimensional laser digitiser. The laser digitiser outputs the
surface information as a point cloud data. This point data is then
converted to the data format of ArtCAM which forms the texture.
This approach requires three steps. The first step is to create the
textured surface. The second step is to digitise the textured
surface. The final step is to convert the point data obtained from
laser digitiser to the data format of the texture.
2.3 Using Custom-Made Forms to Create Texture
The custom-made form is a map that contains several para- meters
used to define the characteristics of the texture. The parameters
of texture are next transformed into the data format
Sample Textured Surface Custom Form with Texture Parameters
-A~CAM
E 3D Scanner
i 3D Point Data I I
A~Read +
I 3D Relief Sutthce [
ArtCAM
Texture
Mapping
Textured Surface
2D Scanner PaintBrush
2D Textured Image t 1
ArtCAM
1 3D Relief Surface I
ArICAM I
I 3D Surface ]
Fig. 1. Approaches to creating 3D texture surfaces.
of the texture in ArtCAM. This approach requires only one step
in transforming the source to the texture.
2.4 Evaluation of the Three Approaches
The first approach - from a 2D texture image - involves two
steps in obtaining the textured surface. The entire process of
creating the texture is purely software-based. The design of the
textured image is dependent on the skill of the artist.
Alternatively, the textured image can be extracted from the sample
images found in an application software such as Corel Draw.
However, not all textured images can be converted into texture.
This is because the conversion of the image to textnre is made on
the basis of the colour intensity. Some textured images might not
be suitable.
The second approach - from a sample textured surface - involves
three steps. This approach is more cumbersome than the first one.
As the creation of the sample textured surface is time consuming,
the time taken for the conversion from the sample surface to the
texture is longer than for the first approach. The second approach
can obtain good textural infor- mation from a laser digitiser.
Thus, the texture created from the source is more reliable than for
the first approach, but the accuracy of the textural information is
dependent on the accu- racy of the laser digitiser.
The third approach - from custom-made forms - involves only one
step. In terms of conversion time, this approach is the fastest. It
provides a more direct way for obtaining texture in comparison to
the other two approaches.
3. Relief Generation Process by ArtCAM
The generation of a textured surface on a 3D shape can be
achieved using the software ArtCAM developed by Delcam
International. The textured surface developed is based on the
software library of ArtCAM. The textured surface can be wrapped
onto the three-dimensional relief generated from 2D artwork. Figure
2 shows the flow process of converting 2D artwork into a 3D
relief.
The development of 3D relief by ArtCAM starts from 2D artwork.
The artwork data can be either in vector format or bitmap format.
The supported vector formats are "eps", "dxf' and "pcx". The
supported bitmap formats are "bmp", "gif', "jpg" and "tif'. The
next step is to assign colour to the artwork; this is generally
done with the artwork in vector format. With the bitmap, some
manipulation such as colour reduction and colour linking is carried
in the ArtCAM software. The reduction of colour is to ensure the
generation of smooth 3D surfaces.
The next step is to associate a unique shape profile to each
colour. There are three types of shape profile: flat profile; slope
profile; and curve profile [9]. Several parameters are associated
with these profiles such as the sloping angle for the slope angle
and the profile height for the flat profile. After the profile is
assigned to each colour, the 3D relief is then gener- ated.
From the generated 3D relief, a cutter tool path can next be
generated. The generated cutter tool path can be displayed
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Artwork in vector data Artwork in bitmap format
~ Colour assigned to the artwork
Bitmap manipulation
Associate shape to each cotour
Generate 3D relief from artwork
i, Toopath Generation
Toopath Simulation
[ - -~> Final Product
Fig, 2. Relief generation by ArtCAM.
and rendered. This can be simulated as the actual machined
relief. ArtCAM is ideal for making both the male and female mould
for mould production and 3D engraving shape.
Figure 3 shows the artwork and the generated relief for the logo
of the Jaguar car. The relief is generated from the profiles
associated with the colour. There several advantages in using
ArtCAM for logo production. First, the logo design can be
reproduced exactly. ArtCAM is useful for repeated work or the
maintenance of moulds. Secondly, the 3D surface finish can be
visualised before proceeding with the cutting of the material. This
will save production time, cost and material and,
Creating Machinable Textures ./'or CAD~CAM Systems 27]
therefore, it is able to gain early customer acceptance of
design. Lastly, ArtCAM can quickly create a 3D product from 2D
artwork.
4. Application of Texture from Textured Image
Of the three approaches for creating 3D textured surfaces, the
second approach, where a sample textured surface is used, simply
involves converting the 3D scanned data to ArtCAM data for texture
mapping. As the texture is created from computer graphics, creating
a textured surface from a textured image is a more general
approach. The general process of converting a textured image into a
3D texture is shown in Fig. 4.
From the textured image, the colour paiette of the image is
checked, if the image is not in the grey scale, the image is
converted into the grey scale format. Next, the user will be
prompted for the maximum height of the texture to be gener- ated.
Using the maximum height, the height scale is evaluated from
subdividing the maximum height by the number of colours of the
image.
The next step is to assign the computed height scale to colours.
Then, the texture relief is generated from the colour. Finally, the
texture relief is mapped onto the base relief to form the textured
relief.
Figure 5 shows 2D artwork and the generated base relief. The
artwork is created by typing in English letters and Chinese
characters. The letters and characters are in vector format. By
filling the outline of the letters and characters with different
colours, the bitmap artwork is created (as shown in Fig. 5). A
different profile shape is assigned to a different colour. With
Fig. 3. Artwork and generated relief of the Jaguar logo.
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272 K. Y. Chow et at.
I Textured image [
I Check for image colour palette type I
o
Convert Mmage ~o grey sca e Yes
Sub-divide maximum height
I Assign height scale to each colour I
I Generate texture relief I
,L I Map texture relief to base relief I
Fig. 4. Converting textured image to texture relief.
the shape associated to each colour, the base relief is
generated as shown in Fig. 5. With the bitmap textured image as
shown in Fig. 6, a texture relief is generated.
The final part is created by mapping the generated texture
relief onto the base relief. Figure 7 shows the relief of the
final product. The texture is excluded from the lettering of the
relief, as intended.
With this final relief, the tool path can be generated with a
specified cutter type and size. Figure 8 shows the machined part of
the final relief. The texture on the machined part (Fig. 8) is
exactly the same as the computer-generated relief (Fig. 7).
5. Design Considerations for Custom- Made Forms
The custom-made form for textured surfaces is designed for two
types of texture: regular and irregular. Several factors need to be
considered in the design of the custom form for the texture. These
factors will govern the internal representation and the external
interface of the texture custom form and concentrate mainly on
practicality and feasibility.
5.1 Simplicity
The texture form should contain the optimal number of para-
meters to represent the texture efficiently. The number of
parameters must be as small as possible so as not to confuse the
user. Parameters must not be inter-dependent, that is, the value of
one parameter must not be dependent on the value of another. If
this is not possible, the interrelationship between the parameters
must be kept to the minimum. This is to ensure that the user can
easily understand the custom-design form and thus be able to apply
the form to create the texture.
Fig. 5. Two-dimensional artwork and generated relief. Fig. 6.
Textured image.
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Crea~ing Machinable Textures .liar CAD~CAM Systems 273
Fig. 7. Computer-generated relief.
5.2 Easy Computation
The computation of the textm'e information must not be too time
consuming. The longer the time taken to compute the texture, the
slower would be the design of the part. Conse- quently, the
time-to-production would be prolonged, and ulti- mately this wo~ald
reduce the competitiveness of the product. Therefore, the
computation of the texture should be as fast as
possible, However, the calculation must be complex enough for
the representation of texture. This implies that the calculation of
the texture representation must be optimised.
5.3 Flexibility
The texture custom-design form must be able to create different
shapes for the texture pattern. However, this must be carried
Fig. 8. Machined part.
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274 K. E Chow et aL
out without compromising the time or complexity of the design.
This is to ensure that the design time for the texture would not
unacceptably increase the overall design time of-the pro- duct. The
custom-design form must also permit ease of modifi- cation of the
shape of the texture pattern. With the above two features, the form
will be flexible in both the design and modification aspects.
5.4 Fine Representation of Texture
The custom form must be able to reveal the fine details of the
texture on a surface, and allow them to be displayed on the
computer screen. In addition, this fine detail must be machinable
on a CNC (computer numerical control) machine, so that it can be
machined into a tangible product.
6. Regular Texture
The result of the regular texture designed is illustrated on the
base relief generated from the artwork as shown in Fig. 9. With the
artwork, the base relief is generated as shown in Fig. 10. This
relief is a smooth dome-like surface with some lettering on it. The
base relief is not textured.
The custom-made form of a regular texture is designed based on
the four design factors. The form is internally a 2D 10 x 10 grid
map which is analogous to a 2D textured image. Each value in the
grid represents the height of the textured surface. There are two
additional parameters associated with this texture map. These two
parameters are the spacing and the height scale. The spacing
defines the distance between each grid point in the texture map.
The height scale shows the height. The user interface for the form
is shown in a dialogue
box in Fig. 11. This user interface is in the form of a dialogue
within a developed software programme. The programme developed is
part of the development framework of the software (ArtCAM TM)
developed by Delcam International PLC.
The shape of the textured pattern can be changed by assigning
numerical values to the grid of the texture map. Inputting of
numerical values to the texture map and changing of the numerical
values are done frequently during the design stage of the texture
pattern. Thus, a set of templates is created to assist the user to
create pattern, which can speed up the design and creation of the
pattern. In addition, these templates provide some guidance to the
user on how to use the form. The created templates include the
round, sphere, null, square, triangle, diamond and the prism
blocks. The round block template creates cylindrically shaped
texture patterns. The square block template produces rectangular
shaped texture pat- terns. The diamond block template creates
diamond-shaped base block texture patterns. The sphere block
template creates semi-spherical shaped texture patterns. Figure 11
shows the relief mapped by the generated texture pattern created by
the sphere block template, The prism block template creates a
square based pyramid texture pattern. All the shapes designed for
the texture patterns are tile-mapped onto the surface.
By combining the generated relief (Fig. 10) and the textured
mapped relief (Fig. 11), the final relief is created as shown in
Fig. 12. The creation of the final relief is achieved by merging
the higher height value of the two reliefs. Figure 13 shows the
machined part of the relief. The machined regular texture is
similar to the modelled relief. Thus, the regular texture created
is machinable.
Fig. 9. Artwork for final relief,
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Creating Machinable Textures for CAD~CAM Systems 275
Fig. 10. Generated relief.
Fig. 11. Dome-like relief mapped with regular texture.
7. Irregular Texture
Apart from regular textures, the other form of texture is the
irregular texture. For natural objects, most of the textures appear
in irregular forms. Some examples of irregular texture are animal
skin, marble, stone and wood surfaces. Irregular texture does not
exhibit pattern properties like placement rules and texture element
shapes.
Figure 14 shows the artwork of a dinosaur. The ~xue shape of the
dinosaur is not generated from the artwork. The artwork can only
generate a relief which has a 3D image of the dinosaur. Figure 15
shows the generated relief of the dinosaur. The skin of the
dinosaur is smooth, but generally, the skin of a dinosaur is not
smooth. Therefore, creating a texture for the skin of the dinosaur
is essential to make the relief model as realistic as possible.
The design factors for the custom-made form of irregular
textures are similar to those of regular textures. The dialogue
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276 K. Y. Chow et al.
Fig. 12. Final relief mapped with regular texture.
Fig. 13. Machined model of the final relief.
box, as shown in Fig. 15, is the user interface for custom- made
forms of irregular textures. The form consists of four parameters,
namely, the map size, the height range, the random seed value and
the texture-generating method. The generated texture is basically a
square relief with height values. The map size is the dimension of
the square relief in real units. The height variation of the
texture relief is very fine. The height range value is between zero
height and the maximum allowable
height of the relief. The height range parameter of the form is
the maximum allowable height of the texture relief.
The generation of irregular textures requires random fields. The
random seed value parameter of the form is the initial value for
the random field. The value of the seed parameter can be a number
or a character. Currently, two types of texture have been
developed. These are the lime stone and wood grain texturing, more
will be added in future.
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Creating Machinable Textures for CAD~CAM Systems 277
Fig. 14. Artwork of a dinosaur.
Fig. 15. Generated relief of the dinosaur.
With the map size value set to 10 mm and the height range value
set to 0.5 ram, a texture relief is generated. The random seed
value for the generated texture relief is "monster". The texturing
selected is the wood grain, The generated texture relief is to
simulate the skin of the dinosaur. Figure 16 shows the generated
texture relief for the dinosaur.
Using the texture relief as shown in Fig. 16 as the skin
texture, the texture is mapped onto the generated relief of the
dinosaur. Figure 17 shows the final relief of the dinosaur with
skin texture mapped on. The skin texture is mapped around the
dinosaur model except for the belly portion.
As compared with the relief without texture (shown in Fig. 15),
the relief with texture (Fig. t7) looks more realistic. Fig. 18
shows the machined model of the dinosaur, which looks very much
like the computer displayed model, Thus, the irregular texture
created fulfils both requirements - good visual display and
machinability.
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278 K. E Chow et al.
Fig. 16. Textured relief for the dinosaur.
Fig. 17. Dinosaur relief mapped with texture.
8. Conclusion
Texturing is very popular in computer graphics for the realistic
display of 3D surfaces. There is a need to produce textured surface
with 3D information for manufacturing purposes. Three approaches
for creating 3D textured surfaces have been presented. The last
approach, using custom-designed forms with texture parameters, is
the fastest and most direct.
Acknowledgements
This report is part of the documentation on the development
project of the software ArtCAM TM. This development project is a
joint project of Delcam International, the School of Mechanical and
Production Engineering of Nanyang Techno- logical University and
the GINITIC Institute of Manufacturing Technology. This S$2 M
development project is partly spon-
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Creating Machinable Textures for CAD~CAM Systems 279
Fig. 18. Machined model of the dinosaur.
sored by the National Science and Technology Board, Singa- pore.
The authors would like to express their appreciation to Delcam
International for approving the use of the library and development
framework of ArtCAM TM software.
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