U.S. patent number RE43,955 [Application Number 13/230,270] was granted by the patent office on 2013-02-05 for process for the production of a three-dimensional object with resolution improvement by pixel-shift.
This patent grant is currently assigned to Envisiontec GmbH. The grantee listed for this patent is Ali El-Sibiani, Hendrik John, Alexandr Shkolnik. Invention is credited to Ali El-Sibiani, Hendrik John, Alexandr Shkolnik.
United States Patent |
RE43,955 |
Shkolnik , et al. |
February 5, 2013 |
**Please see images for:
( Certificate of Correction ) ** |
Process for the production of a three-dimensional object with
resolution improvement by pixel-shift
Abstract
The invention relates to a process or a device for the
production of a three-dimensional object by layer-wise
solidification of a material which is solidifiable under the
application of electromagnetic irradiation by means of mask
illumination, wherein the mask is produced using an image forming
unit having a prescribed resolution, which is formed from a
constant number of image forming elements (pixels) being discrete
and being arranged in a spatially mutually fixed manner. For the
improvement of the resolution along the outer and inner contours of
the sectional areas of the object to be generated layer-wise in the
sub-pixel range, a multiple illumination per layer is performed,
which consists of a series of multiple images that are mutually
shifted in the sub-pixel range in the image/construction plane,
wherein a separate mask/bitmap is produced for each shifted
image.
Inventors: |
Shkolnik; Alexandr (Los
Angeles, CA), John; Hendrik (Hunxe, DE),
El-Sibiani; Ali (Dearborn Heights, MI) |
Applicant: |
Name |
City |
State |
Country |
Type |
Shkolnik; Alexandr
John; Hendrik
El-Sibiani; Ali |
Los Angeles
Hunxe
Dearborn Heights |
CA
N/A
MI |
US
DE
US |
|
|
Assignee: |
Envisiontec GmbH (Gladbeck,
DE)
|
Family
ID: |
34967004 |
Appl.
No.: |
13/230,270 |
Filed: |
September 12, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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60569893 |
May 10, 2004 |
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Reissue of: |
11126068 |
May 9, 2005 |
7790093 |
Sep 7, 2010 |
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Foreign Application Priority Data
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May 10, 2004 [DE] |
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10 2004 022 961 |
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Current U.S.
Class: |
264/401; 700/120;
264/497 |
Current CPC
Class: |
B33Y
30/00 (20141201); B33Y 50/02 (20141201); B29C
64/129 (20170801) |
Current International
Class: |
G02F
1/00 (20060101) |
Field of
Search: |
;264/401,497
;700/120 |
References Cited
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Primary Examiner: Del Sole; Joseph
Assistant Examiner: Stewart; Kimberly A
Attorney, Agent or Firm: Hansen IP Law PLLC
Parent Case Text
.Iadd.CROSS-REFERENCE TO RELATED APPLICATIONS.Iaddend.
.Iadd.This application claims the benefit of U.S. Provisional
Patent Application No. 60/569,893, filed on May 10, 2004..Iaddend.
Claims
The invention claimed is:
1. A process for the production of a three-dimensional object by
layer-wise solidification of a material solidifiable by the action
of electromagnetic irradiation by means of mask illumination,
comprising: providing a projection unit for producing a mask having
an image forming optic directed at a solidifiable material;
producing a mask, wherein the mask is produced by an image forming
unit having a prescribed resolution, which mask is formed from a
constant number of image forming elements (pixel) being discrete
and spatially arranged in a fixed manner to each other,
characterized in that, for improving the resolution in the
sub-pixel range along the outer and inner contours of the sectional
areas of the object to be generated layer-wise, a multiple
illumination is carried out for each layer which consists of a
sequence of a multitude of images mutually shifted in the sub-pixel
range in the image/construction plane, wherein a separate
mask/bitmap is produced for each shifted image.
2. The process according to claim 1, characterized in that said
image forming unit is formed of a constant number of image forming
elements (pixel) being discrete and spatially arranged to each
other in a two-dimensional matrix.
3. The process according to claim 1, characterized in that a
sequence of at least 2 images mutually shifted in the sub-pixel
range is carried out in the image/construction plane, corresponding
to the resolution of the image forming unit and under consideration
of the corresponding sub-pixel shift.
4. The process according to claim 1 for the generation of the
bitmap from a sectional area of a three-dimensional object,
characterized in that the sectional area, i.e. outer and inner
contours, are defined by vector paths which are superimposed by
technical image processing by a rastered area (bitmap), the
resolution of which exactly corresponds to the resolution of the
discrete elements (pixels) in the image forming unit and thus in
the image in the construction plane, wherein the superimposition of
vector paths and bitmap takes place in a superior-ordered
XY-coordinate system, and wherein the active pixels are calculated
by a specific algorithm in order to define the sectional area in
the form of a rastered mask.
5. The process according to claim 1, characterized in that the mask
generation (bitmapping) of each sectional area of a
three-dimensional object is carried out in the starting position
and in various states displaced (shifted) in the sub-pixel range in
XY, and that a total image having an enhanced resolution in the
contour portion corresponding to the pixel shift is obtained by the
superimposition of these bitmaps per sectional area.
6. The process according to claim 1, characterized in that a bitmap
is produced which is shifted relative to the sectional area by
delta X, which results in a new distribution of active pixels.
7. The process according to claim 1, characterized in that a bitmap
is produced which is shifted by delta Y in the sub-pixel range
relatively to the sectional area, which results in a new
distribution of active pixels.
8. The process according to claim 1, characterized in that a bitmap
is produced which is shifted along the pixel diagonal by delta X
and delta Y relatively to the sectional area, which results in a
new distribution of active pixels.
9. The process according to claim 1, characterized in that the
total illumination of an individual layer results from the sum of
the partial illuminations of the masks/bitmaps shifted in the
sub-pixel range.
10. The process according to claim 1, wherein, for each layer of
the object, a multitude of masks or bitmaps having different
sub-pixel shifts in XY can be generated and can be illuminated
serially for each layer to be hardened.
11. The process according to claim 1, characterized in that a
simplified process for resolution improvement is achieved in such a
manner that only the bitmap of the starting position and the bitmap
of the diagonal-shift by a half pixel-diagonal are produced and are
subsequently illuminated for each layer to be hardened.
12. The process according to claim 1, characterized in that, for
the shifted imaging of the rastered masks/bitmaps in the
construction plane which are produced in a shifted manner in the
sub-pixel range for the purpose of selectively hardening the
material layer, the image forming unit is tilted for each shifted
bitmap such that the desired shift of the image in the sub-pixel
range in the image/construction plane is achieved.
13. The process according to claim 1, characterized in that, for
the shifted imaging of the rastered masks/bitmaps in the
construction plane which are produced in a shifted manner in the
sub-pixel range for the purpose of selectively hardening the
material layer, the image forming unit for each shifted bitmap is
shifted by the corresponding sub-pixel range in X and Y, that is
parallel in plane to the image/construction plane.
14. The process according to claim 1, characterized in that, for
the shifted imaging of the rastered masks/bitmaps in the
construction plane which are produced in a shifted manner in the
sub-pixel range for the purpose of selectively hardening the
material layer, the image forming projection unit is maintained
fixed in its position, and the imaging optic of the projection unit
is tilted for each shifted bitmap such that the desired shift of
the image in the image/construction plane in the sub-pixel range is
achieved.
15. The process according to claim 1, characterized in that, for
the shifted imaging of the rastered masks/bitmaps in the
construction plane which are produced in a shifted manner in the
sub-pixel range for the purpose of selectively hardening the
material layer, the image forming projection unit is maintained
fixed in its position, and the imaging optic of the projection unit
is shifted for each shifted bitmap in XY such that the desired
shift of the image in the image/construction plane in the sub-pixel
range is achieved.
16. The process according to claim 1, characterized in that, for
the shifted imaging of the rastered masks/bitmaps in the
construction plane which are produced in a shifted manner in the
sub-pixel range for the purpose of selectively hardening the
material layer, the projection unit is tilted for each bitmap via
actuators such that the projected image in the construction plane
is shifted in the corresponding sub-pixel range in X and Y.
17. The process according to claim 1, characterized in that, for
the shifted imaging of the rastered masks/bitmaps in the
construction plane which are produced in a shifted manner in the
sub-pixel range for the purpose of selectively hardening of the
material layer, a cardanic mounted transparent, plane-parallel
plate is arranged between the projection unit and the
image/construction plane, which plate shifts, by rotation around
two axis (XY) which are present in-plane parallel to the
image/construction plane, the projection beam path and thus the
image in the image/construction plane in the sub-pixel range in X
and Y.
18. The process according to claim 1, characterized in that, for
the shifted imaging of the rastered masks/bitmaps in the
construction plane which are produced in a shifted manner in the
sub-pixel range for the purpose of selectively hardening of the
material layer, a transparent plane-parallel plate is arranged
between the projection unit and the image/construction plane, which
plate shifts, by rotation around an axis parallel to a
pixel-diagonal, the projection beam path and thus the image in the
image/construction plane in the sub-pixel range along the pixel
diagonal which is orthogonal thereto.
19. The process according to claim 1, characterized in that, for
the shifted imaging of the rastered masks/bitmaps in the
construction plane which are produced in a shifted manner in the
sub-pixel range for the purpose of selectively hardening of the
material layer, the projection unit is maintained fixed in its
position, and the projection beam is deflected via a mirror into
the image/construction plane, wherein the deflecting mirror is
provided with an adjustment possibility (cardanic support) by which
the projection beam for each shifted bitmap can be deflected such
that a shift of the image in the sub-pixel range is achieved in the
image-/construction plane.
20. The process according to claim 1, characterized in that the
projected light output for each pixel is varied by "grey scaling"
within a projection mask, in order to selectively influence the
hardening level in a layer thereby and thus to raise the light
output of the contour-pixel relative to the light output of the
area-pixel, in order to compensate the partial illumination due to
partial superimposition of a contour-pixel by the sub-pixel shift
of the individual bitmap in the contour portion.
21. The process of claim 1, wherein each image that is mutually
shifted in the subpixel range defines a degree of overlap between
the object and each pixel and the multiple illumination step
comprises projecting the electromagnetic radiation onto the
solidifiable material based on each degree of overlap for each
pixel and each mutually shifted image.
22. The process of claim 1, wherein each image in the multitude of
images corresponds to a different bitmap location relative to a
fixed coordinate system.
23. The process of claim 1, wherein the image forming unit includes
an image forming matrix, and the multiple illumination of each
object layer comprises: providing an image of the object layer;
defining a bitmap, wherein the bitmap has a plurality of grid
elements and each grid element corresponds to a location in the
image forming unit; superimposing the layer image on the bitmap to
define a first relative orientation between the layer image and the
bitmap; calculating a first degree of overlap between each grid
element and the layer image when the bitmap is in the first
relative orientation; shifting the bitmap relative to the layer
image to define a second relative orientation between the layer
image and the bitmap; calculating a second degree of overlap
between each grid element and the layer image when the layer image
is in the second relative orientation; and projecting
electromagnetic radiation onto the curable resin based on the first
degree of overlap and the second degree of overlap for each grid
element.
24. The process of claim 23, wherein the step of projecting
electromagnetic radiation onto the curable resin comprises first
projecting electromagnetic radiation onto the curable resin such
that each location in the image forming unit matrix projects
electromagnetic radiation having an intensity that corresponds to
the first degree of overlap for the bitmap grid element that
corresponds to the image forming unit matrix location and second
projecting electromagnetic radiation onto the curable resin such
that each location in the image forming unit matrix projects
electromagnetic radiation having an intensity that corresponds to
the second degree of overlap for the bitmap grid element that
corresponds to the image forming unit matrix location.
Description
TECHNICAL FIELD
The invention related to a process and a device for the production
of a three-dimensional object by layer-wise solidification of a
photohardening material by mask illumination by means of a rastered
image forming unit having constant resolution, wherein the
resolution within the image/construction plane shall be improved in
the sub-pixel range.
BACKGROUND ART
For the layer-wise construction of three-dimensional objects from
"light hardening" materials, various processes are mentioned in
literature, see in this respect "Automated Fabrication-Improving
Productivity in Manufacturing" of Marshall Burns, 1993 (ISBN
0-13-119462-3).
This invention relates to processes wherein the layer to be
generated is based on illumination by means of a rastered mask,
wherein the smallest physical resolution within the mask is
provided by the size of a pixel.
Known possibilities presently are, inter alia, illumination by a)
Projection unit (on the basis of DLP.RTM./DMD.RTM., LCD, ILA.RTM.,
etc.) b) LD-display (reflective, transmissive) c) LED-, or
laser-diode-line/-matrix (which is moved in XY-plane over the
layer) d) Line or matrix (which is moved in XY-plane over the
layer) based on MEM-technology (light-valve).
Some of these methods are described in the following patents:
IPC: B29C67/00 "Rapid Prototyping apparatus and method of Rapid
Prototyping" of Dicon AS (DK), (application)
US patent US005247180 A "Stereolithographic Apparatus and Method of
use" of Texas Instruments Inc., September 1993.
US patent US005980813 A "Rapid Prototyping using multiple
materials" of SRI International, November 1999;
Utility Model DE G 93 19 405.6 "Device for the production of a
three-dimensional object (model) according to the principle of
photosolidification" of Research Center Informatik at the
University Karlsruhe, Dez. 1993;
An application for the generation of micro-technical,
three-dimensional construction parts according to a similar process
is described in the Utility Model DE 299 11 122 U1 "Device for the
production of a three-dimensional object" DeltaMed et al., June
1999. PCT Application 02 008 019.8 "Device for the production of a
three-dimensional object" of Envision Technologies GmbH, April
2002.
U.S. Pat. No. 6,180,050 describes a linear scan technique for
layer-wise solidification in the production of three-dimensional
objects. The resolution is enhanced by scanning, in X-direction, an
illumination head having an array of optical fibers, which are
displaced in the Y-direction.
DRAWBACKS OF THE PRIOR ART
With all of the above described processes, the resolution of the
material layer to be hardened is in direct dependency from the
resolution of an image forming process.
With the projection processes, an intermediary positioned optic
additionally determines the scale of the projected or solidifiable
layer.
The resolution per area unit in the image/construction plane thus
is dependent on a) the resolution of the image forming unit or the
smallest element, called pixel, and their relative mutual
distances, called pixel-pitch, and b) the projection scale.
The surface roughness of the construction part thus is determined
by the smallest volume unit of one voxel (volume-pixel), the size
of which is composed of the projected pixel area in XY and the
layer thickness in Z. The resolution of the layer thickness is
prescribed by the smallest resolution (step level) of the actuator
in Z, in order to move the support platform. Resolutions already
down to the one-figure .mu.m range is achievable hereby. If an even
lower surface roughness of the construction part shall be realized,
the projection field and concurrently the width of the pixel area
must be down-sized.
As an example, the projection m.H. of a multi-media projector shall
be mentioned here; with a resolution of XGA (1024.times.768 image
dots), a pixel of 17 .mu.m and pixel-pitch of 17.9 .mu.m, one
realizes, at a projection to 275 mm.times.206 mm with an
enhancement factor of the projection optic of 15, a resolution in
the image/construction plane and thus in the layer to be solidified
of approximately 100 dpi, which corresponds to a pixel size in the
projection plane of about 0.254 mm.times.0.254 mm.
In order to e.g. double the resolution in the image-/construction
plane, while maintaining the same construction area, it is proposed
in the projection processes to half the projection/enhancement
factor (which means to quarter the area) and, for the illumination
of the four partial planes, to shift either the whole projection
unit or the construction space mutually in parallel.
This process has the significant drawback that relatively high
masses have to be moved towards each other very precisely in order
to ensure an exact abutment and a close connection of the partial
planes, which means a considerable expenditure of costs and
additional need of space in the whole arrangement for the mechanics
required therefore.
With the selective direct illumination by scanning m.H. of a LED-
or laser-diode-line/-matrix or direct illumination by a mask, which
is formed by a transmissive LCD, the resolution in the construction
plane is equivalent to the resolution in the image forming
unit.
OBJECT OF THE INVENTION
It is an object of the invention to provide a process or a device
which can enhance the resolution in the construction plane, while
maintaining the same large construction area, many times in the
sub-pixel range, i.e. to refine the rastering of the outer and
inner contours in the sectional planes of the object, a) without
having to carry out an illumination in partial areas to be composed
together, and b) without enhancing the resolution of the rastered
image-forming unit itself.
SOLUTION OF THE OBJECT
The present invention provides a process for the production of a
three-dimensional object by layer-wise solidification of a material
solidifiable by the action of electromagnetic irradiation by means
of mask illumination, wherein the mask is produced by an image
forming unit having a prescribed resolution, which mask is formed
from a constant number of image forming elements (pixel) being
discrete and spatially arranged in a fixed manner to each other,
characterized in that, for improving the resolution in the
sub-pixel range along the outer and inner contours of the sectional
areas of the object to be generated layer-wise, a multiple
illumination is carried out for each layer which consists of a
sequence of a multitude of images mutually shifted in the sub-pixel
range in the image/construction plane, wherein a separate
mask/bitmap is produced for each shifted image.
The invention also provides a device for the production of a
three-dimensional object by layer-wise solidification of a material
which is solidifiable under the application of electromagnetic
irradiation by means of mask illumination, whereby the irradiation
necessary for hardening is imaged into the image/construction
plane, wherein the device comprises a rastered, image forming unit
for the selective illumination, which is embodied either by line or
by matrix, characterized in that the image forming unit composes
the image from individual image dots (pixels) and thus forms a
rastered mask (bitmap), wherein the pixels are arranged within the
plane in a manner mutually fixed to each other, and that the image
forming unit and/or an imaging optic which is provided between the
image forming unit and the image/construction plane is/are designed
such that a sequence of a multitude of images, which are mutually
shifted in a sub-pixel range, can be created, wherein a separate
mask/bitmap can be produced for each shifted image.
Preferred embodiments of the process of the present invention
include one or more of the following features: (a) said image
forming unit is formed of a constant number of image forming
elements (pixel) being discrete and spatially arranged to each
other in a two-dimensional matrix; (b) a sequence of at least 2
images mutually shifted in the sub-pixel range is carried out in
the image/construction plane, corresponding to the resolution of
the image forming unit and under consideration of the corresponding
sub-pixel shift; (c) the sectional area, i.e. outer and inner
contours, are defined by vectorial trails which are superimposed by
technical image processing by a rastered area (bitmap), the
resolution of which exactly corresponds to the resolution of the
discrete elements (pixels) in the image forming unit and thus in
the image in the construction plane, wherein the superimposition of
vectorial trails and bitmap takes place in a superior-ordered
XY-coordinate system, and wherein the active pixels are calculated
by a specific algorithm in order to define the sectional area in
the form of a rastered mask; (d) the mask generation (bitmapping)
of each sectional area of a three-dimensional object is carried out
in the starting position and in various states displaced (shifted)
in the sub-pixel range in XY, and that a total image having an
enhanced resolution in the contour portion corresponding to the
pixel shift is obtained by the superimposition of these bitmaps per
sectional area; (e) a bitmap is produced which is shifted relative
to the sectional area by delta X, which results in a new
distribution of active pixels; (f) a bitmap is produced which is
shifted by delta Y in the sub-pixel range relatively to the
sectional area, which results in a new distribution of active
pixels; (g) a bitmap is produced which is shifted along the pixel
diagonal by delta X and delta Y relatively to the sectional area,
which results in a new distribution of active pixels; (h) the total
illumination of an individual layer results from the sum of the
partial illuminations of the masks/bitmaps shifted in the sub-pixel
range; (i) for each layer of the object, a multitude of masks or
bitmaps having different sub-pixel shifts in XY can be generated
and can be illuminated serially for each layer to be hardened; (j)
a simplified process for resolution improvement is achieved in such
a manner that only the bitmap of the starting position and the
bitmap of the diagonal-shift by a half pixel-diagonal are produced
and are subsequently illuminated for each layer to be hardened; (k)
for the shifted imaging of the rastered masks/bitmaps in the
construction plane which are produced in a shifted manner in the
sub-pixel range for the purpose of selectively hardening the
material layer, the image forming unit is tilted for each shifted
bitmap such that the desired shift of the image in the sub-pixel
range in the image/construction plane is achieved; (l) for the
shifted imaging of the rastered masks/bitmaps in the construction
plane which are produced in a shifted manner in the sub-pixel range
for the purpose of selectively hardening the material layer, the
image forming unit for each shifted bitmap is shifted by the
corresponding sub-pixel range in X and Y, that is parallel in plane
to the image/construction plane; (m) for the shifted imaging of the
rastered masks/bitmaps in the construction plane which are produced
in a shifted manner in the sub-pixel range for the purpose of
selectively hardening the material layer, the image forming
projection unit is maintained fixed in its position, and the
imaging optic of the projection unit is tilted for each shifted
bitmap such that the desired shift of the image in the
image/construction plane in the sub-pixel range is achieved; (n)
for the shifted imaging of the rastered masks/bitmaps in the
construction plane which are produced in a shifted mariner in the
sub-pixel range for the purpose of selectively hardening the
material layer, the image forming projection unit is maintained
fixed in its position, and the imaging optic of the projection unit
is shifted for each shifted bitmap in XY such that the desired
shift of the image in the image/construction plane in the sub-pixel
range is achieved; (o) for the shifted imaging of the rastered
masks/bitmaps in the construction plane which are produced in a
shifted manner in the sub-pixel range for the purpose of
selectively hardening the material layer, the projection unit is
tilted for each bitmap via actuators such that the projected image
in the construction plane is shifted in the corresponding sub-pixel
range in X and Y; (p) for the shifted imaging of the rastered
masks/bitmaps in the construction plane which are produced in a
shifted manner in the sub-pixel range for the purpose of
selectively hardening of the material layer, a cardanic mounted
transparent, plane-parallel plate is arranged between the
projection unit and the image/construction plane, which plate
shifts, by rotation around two axis (XY) which are present in-plane
parallel to the image/construction plane, the projection beam path
and thus the image in the image/construction plane in the sub-pixel
range in X and Y; (q) for the shifted imaging of the rastered
masks/bitmaps in the construction plane which are produced in a
shifted mariner in the sub-pixel range for the purpose of
selectively hardening of the material layer, a transparent
plane-parallel plate is arranged between the projection unit and
the image/construction plane, which plate shifts, by rotation
around an axis parallel to a pixel-diagonal, the projection beam
path and thus the image in the image/construction plane in the
sub-pixel range along the pixel diagonal which is orthogonal
thereto; (r) for the shifted imaging of the rastered masks/bitmaps
in the construction plane which are produced in a shifted manner in
the sub-pixel range for the purpose of selectively hardening of the
material layer, the projection unit is maintained fixed in its
position, and the projection beam is deflected via a mirror into
the image/construction plane, wherein the deflecting mirror is
provided with an adjustment possibility (cardanic support) by which
the projection beam for each shifted bitmap can be deflected such
that a shift of the image in the sub-pixel range is achieved in the
image-/construction plane; and (s) the projected light output for
each pixel is varied by "grey scaling" within a projection mask, in
order to selectively influence the hardening level in a layer
thereby and thus to raise the light output of the contour-pixel
relative to the light output of the area-pixel, in order to
compensate the partial illumination due to partial superimposition
of a contour-pixel by the sub-pixel shift of the individual bitmap
in the contour portion.
Preferred embodiments of the device of the present invention
include one or more of the following features: (1) said image
forming unit for the selective illumination is embodied by a
matrix; (2) a series of at least 2 images, which are mutually
shifted in a sub-pixel range, can be created in the
image/construction plane (3) said image forming unit is a
projection unit; (4) said image forming unit is a line,
particularly a matrix having discretely emitting elements for image
formation; (5) the device is provided with actuators in order to
shift the whole image forming unit per partial image in a
plane-parallel manner towards the image/construction plane in XY in
the sub-pixel range; (6) the device is provided with actuators
which can tilt the image forming unit per shift-generated bitmap
such that the individual, shift-generated bitmaps in the
image/construction plane are imaged in a manner shifted in the
sub-pixel range; (7) between the image forming unit and the
image/construction plane, a mirror is arranged as an imaging optic
and is cardanically mounted and is rotatable via actuators such
that the beam path is deflected into the image plane and that the
individual, shift-generated bitmaps in the image-/construction
plane can be imaged in a correspondingly shifted manner in the
sub-pixel range; (8) between the image forming unit and the
image/construction plane, a transparent plate having mutual
plane-parallel surfaces is arranged as an imaging optic and can be
tilted by means of one or more actuators such that the beam path is
shifted and that the individual, shift-generated bitmaps in the
image-/construction plane are imaged in a manner shifted in the
sub-pixel range; (9) the image forming projection unit is
maintained fixed in its position and that the imaging optic can be
shifted in XY in a sub-pixel range of the image forming unit via
actuators such that the desired shift of the image in the
image-/construction plane in a sub-pixel range is achieved; and
(10) the image forming projection unit is maintained fixed in its
position and that the imaging optic can be tilted via actuators
such that the desired shift of the image in the image/construction
plane in the sub-pixel range is achieved.
DESCRIPTION OF THE INVENTION AND ITS ADVANTAGES
By means of the process of the invention or the device of the
invention, the resolution in the image/construction plane is
improved in the sub-pixel range by means of "pixel-shift".
In particular, the present invention deals with the layer-wise
solidification for the production of three-dimensional objects or
construction elements by means of solidification of material
(specifically by means of photo-polymerization) through mask
projection, but not with a conventional layer-wise solidification
through (linear) scan technique. This can be carried out according
to the invention very efficiently and advantageously by using a
two-dimensionally set array as the image generating element,
wherein raster and/or resolution is(are) preset, e.g. by means of a
set micro mirror array.
Compared to the scan technique, which is called VAROS (Variable
Refraction Optical System) by Canon and "Double-CCD" by Epson, the
principle of reading and overlapping of images mutually shifted in
the sub-pixel range is used in this invention for rastered image
forming processes of rapid prototyping.
The resolution or the number of image dots of the rastered, image
forming unit itself does not have to be increased in order to
realize an improvement in the solution within the construction
plane.
For the enhancement of the resolution, the illumination does not
occur in correspondingly down-sized, adjacently disposed partial
areas, whereby the construction/illumination period for the whole
area would be increased by the number of partial areas; rather, the
projection/illumination occurs over the whole construction
area.
By the measure that an overlapping of images that are mutually
shifted in the sub-pixel range takes place, the
construction/illumination period of the whole area increases only
insubstantially.
The level of resolution improvement within the construction plane
can be chosen freely.
DESCRIPTION OF THE DRAWINGS AND THE PREFERRED EMBODIMENTS OF THE
INVENTION
The present invention will be explained in detail in the following
by way of examples and not in a limiting manner by means of
drawings.
FIG. 1 schematically shows a basic device for the generation of a
three-dimensional object 3 by layer-wise hardening of a
photohardening material 4 by means of mask projection 8, wherein
the projection unit 1 is present, with an image forming optic 2,
above the basin 6 which is filled with photohardening material 4,
and wherein the object 3 solidifies layer-wise on a support plate
5, which can be moved within the basin 6 in vertical direction. In
a process based on photohardening by means of mask illumination,
the irradiation necessary for hardening is projected into the
image/construction plane 7. The illumination is carried out by
means of a rastered image forming unit, which is formed in the form
of a matrix. The image thus is composed of single image dots
(pixels) and thus forms a rastered mask (bitmap), wherein the
pixels are arranged in a specially fixed manner to each other
within the plane.
By a simple example, FIG. 8-12 show the principle of a mask
generation (bitmapping) of a sectional area of a three-dimensional
object in the starting position (FIG. 8) and in various states of
the bitmap which are displaced (shifted) in the sub-pixel range
(FIG. 9-11), as well as the overlapping of all bitmaps (FIG.
12).
The sectional area, i.e. the outer and inner contours, are
prescribed by a sectorial trail 11, which is superimposed by a
rastered area (bitmap) 12, the solution of which exactly
corresponds to the resolution of the discrete elements (pixels)
within the projected image 8 which is formed by the image forming
matrix. Vectorial trail 11 and bitmap 12 thus exist within a
superior-ordered XY-coordinate system 10. FIG. 8 shows the bitmap
in its starting position. By means of a specific algorithm, the
active pixels 13 which describe the sectional area within the
bitmap 12 in its starting position are calculated.
In FIG. 9, the bitmap 14 is shifted within the sub-pixel range
relative to the sectional area by delta X, whereby a new
distribution of active pixels 15 is produced.
FIG. 10 shows a shift of bitmap 16 relative to the sectional area
by delta Y with active pixels 17.
FIG. 11 shows a diagonal shift of bitmap 18 relative to the
sectional area by delta X and delta Y with active pixels 19.
In FIG. 12, all bitmaps 12, 14, 16 and 18 with their active pixels
13, 15, 17 and 19 are shown superimposed, whereby a resolution
improvement in the (outer) contour portion of the sectional area is
clearly noticeable.
A simplified process for resolution improvement is achieved by the
measure that only bitmap 12 of the started position (FIG. 8) and
bitmap 18 of the diagonal shift (FIG. 11) are superimposed. In this
case, the bitmap or the image does only have to be shifted in one
direction along the diagonal of the pixels.
Depending on the resolution improvement desired for each object
layer, a multiple (at least twice) of masks or bitmaps having
different sub-pixel shifts can be generated and superimposed.
By means of a differently shifted and superimposed illumination of
each object/material layer (here by means of bitmaps 12, 14, 16,
18), a resolution improvement in XY in the portion of outer and
inner contours is achieved. In order to realize respective
sub-pixel shifts in the image within the construction plane, the
following various embodiments are described: 1) In FIG. 2, the
image forming unit 1 is tilted for each shifted bitmap such that
the desired shift of the image in the sub-pixel range within the
image/construction plane is achieved. 2) In FIG. 3, the image
forming unit 1 is shifted for each shifted bitmap by the
corresponding sub-pixel level in X and 7, that is parallel in plane
to the image/construction plane, by means of actuators. 3) In FIG.
4, the image forming projection unit is maintained fixed in its
position, The imaging optic 2 is tilted for each shifted bitmap
such that the desired shift of the image within the
image-/construction plane in the sub-pixel range is achieved. 4) In
FIG. 5, the image forming projection unit is maintained fixed in
its position. The imaging optic 2 is moved for each shifted bitmap
in XY such that the desired shift of the image within the
image-/construction plane in the sub-pixel range is achieved. 5)
Particular cases for imaging by image-ward telecentric irradiation
path, by an image-ward approximately telecentric irradiation path,
and by teleobjectives having long focal length, in order to keep
optical errors (angle errors, distortion) small: a) In FIG. 5, the
projection unit 1 is tilted for each shifted bitmap via actuators
such that the projection image 8 within the image/construction
plane 7 is shifted in the corresponding sub-pixel range in X and Y.
b) In FIG. 6, a cardanically mounted transparent, plane-parallel
plate 9 (glass plate) is disposed between the protection unit 1 and
the image/construction plane 7, which plate shifts the protection
irradiation path 8 and thus the image within the image/construction
plane 7 in the sub-pixel range in X and 7 by means of rotation
around two axis (XY), which are located parallel in plane to the
image/construction plane. c) In FIG. 7, the projection unit 1 is
maintained fixed in its position. The projection beam 8 is
deflected via a mirror 10 into the image/construction plane 7. The
deflecting mirror 10 is provided with an adjustment possibility
(cardanic support), by which the protection beam can be deflected
for each shifted bitmap such that a shift of the image within the
image/construction plane 7 in the sub-pixel range is achieved.
The embodiments 1) to 5) or a) to c) described above can be
realized individually or combined with each other.
The bitmaps of each individual layer necessary for mask projection
are generated from layer data, in which the outer and inner
contours of the respective object section is represented in
vectorial trails (as e.g. defined in the data format CLI).
For this, a specific SW is used which carries out the
transformation of the vectorial trails into the bitmap format
(bitmapping).
For each sub-pixel shift in XY, a separate bitmap is generated by
transforming the XY coordinates of the vectors (for the outer and
the inner contours) of the layer data by the respective
shift-offset in XY (in the sub-pixel range), and by superposing
them over the bitmap-raster, and thus by calculating a new
distribution of active pixels for each shift.
The projected light output per pixel can be varied by "grey
scaling" within a projection mask, in order to selectively
influence the hardening level in one layer thereby. This is
particularly meaningful in order to raise the light output of the
pixels of the contour because only partial superimposition of the
respective pixels of the contour are produced here due to the
sub-pixel shift over individual bitmaps (in the areas within the
contours a complete superimposition of the pixels of each
individual bitmap is ensured).
When projecting/superimposing the section images shifted by
sub-pixels, an almost homogeneous distribution of the light output
or the illumination intensity can be achieved by means of the
superimposition of grey scalings, particularly along the contours
of the projected area structure, through the sum of the grey
scaling masks.
* * * * *
References