Geoffroy LAUVAUX Research Engineer (CIRTES) Orientation of artistic parts with Stratoconception ® Stratoconception ®, Part orientation, Art

Geoffroy LAUVAUXResearch Engineer (CIRTES)

Orientation of artistic parts with Stratoconception®

Stratoconception®, Part orientation, Art

http://www.afpr.asso.fr/aepr/AN/v_index.htm

Centre de Recherche Technologique

CIRTES29 bis, rue d ’Hellieule

88100 Saint-Dié-des-VosgesFRANCE

Tél (33) 03 29 55 11 71Fax (33) 03 29 55 10 45

e-mail : [email protected] : www.cirtes.fr

Antenne CIRTES - Carmaux :

ISTM 53bis, avenue Bouloc Torcatis81400 Carmaux

Tél : 33.(0)5.63.76.72.41Fax : 33.(0)5.63.36.30.64

E-mail : [email protected]

CIRTESEuropean Centre for Rapid Prototyping


Stratoconception® processPrinciple


Part orientation in RPGeneralities

• Z-axis deviation• « Staircase effect »• Part compaction• Specific characteristics of the

process

Influence of part orientation in RP:


Part orientation in RP Stratoconception®

• Cutting optimizations

• Assembly simplification

• Undercutting minimization

Specific objectives of Stratoconception® in part orientation:

In Stratoconception®, part orientation is determined by the direction of stratification


UndercuttingSolutions

Two-sidded cutting

Undercutting

Stratification repartition

Part orientation

Stratification direction

No undercutting

Undercutting

Stratification direction

90°


Art vs Mechanical partsShapes - Finding a direction of stratification

Artistic part: no elementary shape, no obvious direction.

Mechanical part: planes, holes, cylinders, cones…


Art vs Mechanical partsSubjective criteria


Art vs Mechanical partsSubjective criteria

Shadow volumes generated by a human choice of axis

Shadow volumes generated by an automatic choice of axis


Art vs Mechanical partsFinishing


Choosing a direction of stratification Surface orientation & reflection line

Green = upside facets

Red = downside facets

Yellow = reflection line


Choosing a direction of stratificationZ-buffer

Z-buffer principle

9

2

1

9 9 9 9 9 9

9 9 9

9

9

999999

9

9

9

9

1 1

1

2

2 2

2222

2 2

9

2

1

0

Direction of the view(orthogonal projection)

Z-buffer of the view

A pixel, in a Z-buffer, contains the distance to the element from the eye position in the 3D scene.If many elements are projected onto the same pixel, only the nearest value is preserved.

Eye position


Choosing a direction of stratification Shadow volumes quantification

• The sum of Z-buffer’s values gives the volume of the STL and its shadow

• As the volume of a STL is easy to calculate, shadow volume (or undercutting in our case) is known

Z-buffer plane

Shadow volumeSTL

Directional light(stratification direction)

Volumes in Z-buffer


Choosing a direction of stratification Shadow volumes quantification

Advantages

• Z-buffer can be quickly calculate by graphic accelerator (GPU)

• Shadow’s complexity doesn’t matter

Disadvantages

• Approximation due to the buffer (precision depends on the resolution)


Choosing a direction of stratification Shadow volumes visualisation

1

3

2

1 1

1

1

2

2

From a Z-buffer to a surface

Exemple: bunny’s leg


Choosing a direction of stratification Shadow volumes visualisation


The search for a direction of stratification Minimizing the shadow volumes

An iterative method to find the direction wich minimize shadow volumes

1. Choose a direction W

2. Calculate shadow volumes for a set of directions near W

3. The direction generating the smallest shadow volume becomes W

4. Go to step 2, directions of the new set must be closest to W than the previous ones


Examples Stanford bunny

Axis (human choice)Z-axisShadow volumes=0.236%

Axis (automatic search)X=0.351 Y=0.441 Z=0.826Shadow volumes=0.094%

• Automatic axis is better than human’s one

• Human choice is, in most cases, limited to X,Y or Z axis


Examples The bust of Jules Ferry

Axis (human choice)X-axisShadow volumes=2.384%

Axis (automatic search)X= -0.01 Y= 0.99 Z= 0.02Shadow volumes=0.931%

• Automatic axis is THEORICALLY better than human’s one

• The human choice is better, due to subjective criteria


Examples Océane

Axis (human choice)Y-axisShadow volumes=0.294%

Axis (automatic search)X= -0.11 Y=0.842 Z=0.528Shadow volumes=0.156%

• Automatic axis is better than human’s one

• The automatic axis doesn’t correspond to a specific component


Examples Mechanical parts

• Automatic axis is worst than human one’s due to an optimized stratification

• Human choice of axis is a surface’s normal


Examples Mechanical parts

• Automatic axis = human one’s

• X, Y or Z axis


Future works

• Use an optimized stratification when searching for the best axis (for mechanical parts)

• Possibility to add a subjective criterion when searching for the best axis (for artistic parts)


Thank you for your attention

Documents

Geoffroy LAUVAUX Research Engineer (CIRTES) Orientation of artistic parts with Stratoconception ® Stratoconception ®, Part orientation, Art