U.S. patent application number 17/420136 was filed with the patent office on 2022-03-03 for multiplexed image acquisition device for optical system.
The applicant listed for this patent is Orbotech Ltd.. Invention is credited to Yigal Katzir, Ilia Lutsker, Elie Meimoun.
Application Number | 20220070343 17/420136 |
Document ID | / |
Family ID | 1000006003803 |
Filed Date | 2022-03-03 |
United States Patent
Application |
20220070343 |
Kind Code |
A1 |
Katzir; Yigal ; et
al. |
March 3, 2022 |
Multiplexed Image Acquisition Device for Optical System
Abstract
An image acquisition device including a first plurality of
cameras arranged in a mutually spaced configuration, each having a
field of view, each field of view lying in a plane and a second
plurality of photon emitters arranged in a multiplicity of
generally circumferential arrangements about each camera of the
first plurality of cameras, at least one photon emitter within the
generally circumferential arrangement directing light to a field of
view of one of the first plurality of cameras that is not the
closest field of view thereto.
Inventors: |
Katzir; Yigal; (Rishon
Lezion, IL) ; Lutsker; Ilia; (Kfar Saba, IL) ;
Meimoun; Elie; (Jerusalem, IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Orbotech Ltd. |
Yavne |
|
IL |
|
|
Family ID: |
1000006003803 |
Appl. No.: |
17/420136 |
Filed: |
January 9, 2020 |
PCT Filed: |
January 9, 2020 |
PCT NO: |
PCT/IL2020/050037 |
371 Date: |
June 30, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62791897 |
Jan 14, 2019 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04N 5/247 20130101;
G02B 5/001 20130101; G02B 27/30 20130101; G02B 5/04 20130101; H04N
5/2256 20130101; H04N 5/2254 20130101 |
International
Class: |
H04N 5/225 20060101
H04N005/225; H04N 5/247 20060101 H04N005/247; G02B 27/30 20060101
G02B027/30; G02B 5/04 20060101 G02B005/04; G02B 5/00 20060101
G02B005/00 |
Claims
1. An image acquisition device comprising: a first plurality of
cameras arranged in a mutually spaced configuration, each of said
cameras having a field of view, each of said fields of view lying
in a plane; and a second plurality of photon emitters arranged in a
multiplicity of arrangements about each camera of said first
plurality of cameras, at least one of said photon emitters within
said arrangements directing light to one of said fields of view of
one of said first plurality of cameras that is not a closest of
said field of views thereto.
2. The image acquisition device according to claim 1, wherein said
mutually spaced configuration of said first plurality of cameras
comprises a staggered array of rows of cameras, said fields of view
of said first plurality of cameras being at least partially
overlapping when viewed in a direction generally perpendicular to a
direction of said rows.
3. The image acquisition device according to claim 1, wherein said
plane is a common plane occupied by each of said fields of
view.
4. The image acquisition device according to claim 3, wherein said
plane coincides with a surface of a substrate to be imaged by said
image acquisition device.
5. The image acquisition device according to claim 1, wherein each
of said cameras defines a camera axis, each of said arrangements
being centrally intersected by said camera axis.
6. The image acquisition device according to claim 1, wherein each
of said photon emitters comprises an LED.
7. The image acquisition device according to claim 1, wherein each
said arrangement comprises at least one ring of photon
emitters.
8. The image acquisition device according to claim 7, wherein said
at least one ring of photon emitters comprises an inner ring of
photon emitters and an outer ring of photon emitters, said inner
and said outer rings being generally concentric.
9. The image acquisition device according to claim 8, wherein said
inner ring emits light of a first wavelength and said outer ring
emits light of a second wavelength, said first and said second
wavelengths being mutually different.
10. The image acquisition device according to claim 9, wherein said
inner ring includes IR LEDs and said outer ring are includes amber
LEDs.
11. The image acquisition device according to claim 1, wherein said
field of view to which light is directed by one of said photon
emitters is entirely illuminated by said one of said photon
emitters.
12. The image acquisition device according to claim 1, further
comprising an illumination platform having an upper surface and a
lower surface, said upper surface being proximal to said first
plurality of cameras, said lower surface being distal from said
first plurality of cameras, said second plurality of photon
emitters being mounted on said lower surface.
13. The image acquisition device according to claim 12, wherein a
multiplicity of apertures is formed in said illumination platform,
each of said apertures allowing viewing therethrough of said field
of view by one of said cameras.
14. The image acquisition device according to claim 13, wherein
each of said arrangements of photon emitters circumferentially
surrounds each of said apertures.
15. The image acquisition device according to claim 14, wherein
each of said cameras comprises a telecentric lens.
16. The image acquisition device according to claim 15, wherein
each of said apertures is generally rectangular.
17. The image acquisition device according to claim 12, further
comprising at least one collimator for collimating said light.
18. The image acquisition device according to claim 17, wherein
said at least one collimator is mounted on a collimator board.
19. The image acquisition device according to claim 18, wherein
said collimator board is located adjacent to said illumination
platform, between said illumination platform and said plane.
20. The image acquisition device according to claim 19, further
comprising at least one deflecting element for directing said light
output by said at least one collimator.
21. The image acquisition device according to claim 20, wherein
said at least one deflecting element is mounted on a deflector
board.
22. The image acquisition device according to claim 21, wherein
said deflector board is located abutting said collimator board.
23. The image acquisition device according to claim 20, wherein
said deflector board is formed monolithically with said collimator
board.
24. The image acquisition device according to claim 20, wherein
said at least one deflecting element directs said light output
towards a single field of view.
25. The image acquisition device according to claim 20, wherein
said at least one deflecting element directs said light output
towards more than one field of view.
26-43. (canceled)
44. The image acquisition device according to claim 17, further
comprising at least one deflecting element coupled to said at least
one collimator.
45-47. (canceled)
48. The image acquisition device according to claim 44, wherein
said at least one collimator is coupled to said at least one photon
emitter of said arrangement directing light to at least one other
field of view in addition to said field of view illuminated by said
arrangement, said at least one deflecting element directing said
light to said at least one other field of view in addition to said
field of view illuminated by said arrangement.
49. The image acquisition device according to claim 48, wherein
said at least one deflecting element comprises at least one prism
having a plurality of exit facets angled to direct said light
towards said at least one other field of view in addition to said
field of view illuminated by said arrangement.
50-57. (canceled)
58. The image acquisition device according to claim 13, wherein
each of said arrangements of photon emitters surrounds each of said
apertures.
59-64. (canceled)
65. The image acquisition device according to claim 20, wherein
said at least one deflecting element comprises a third plurality of
axicons.
66. The image acquisition device according to claim 65, wherein
said third plurality of axicons comprises an array of axicons
having a density of between 4-10000 axicons/cm.sup.2.
67. The image acquisition device according to claim 65, wherein
said third plurality of axicons comprises axicons having mutually
similar optical properties.
68. The image acquisition device according to claim 65, wherein
said third plurality of axicons comprises axicons having mutually
different optical properties.
69. The image acquisition device according to claim 1, wherein each
of said arrangements illuminates one of said fields of view,
wherein each of said arrangements, when projected on said plane of
said field of view illuminated thereby, circumferentially surrounds
said field of view.
70. The image acquisition device according to claim 1, wherein said
multiplicity of arrangements are generally circumferential.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to optical systems
and more particularly to image acquisition devices for use in
optical systems.
BACKGROUND OF THE INVENTION
[0002] Various types of optical systems including image acquisition
devices are known in the art.
SUMMARY OF THE INVENTION
[0003] The present invention seeks to provide a multiplexed, high
resolution, high throughput, highly compact, easily manufacturable
image acquisition device for use in optical systems, in particular
optical scanning systems. The invention seeks to achieve these
goals while at the same time providing a relatively intense and
both spatially and angularly substantially uniform illumination.
The invention is particularly useful for fast and high accuracy
reading of registration fiducial marks in production systems for
manufacturing electronic substrates such as printed circuit boards,
semiconductor wafers, chip packaging substrates and solar
panels.
[0004] There is thus provided in accordance with a preferred
embodiment of the present invention an image acquisition device
including a first plurality of cameras arranged in a mutually
spaced configuration, each having a field of view, each field of
view lying in a plane and a second plurality of photon emitters
arranged in a multiplicity of generally circumferential
arrangements about each camera of the first plurality of cameras,
at least one photon emitter within the generally circumferential
arrangement directing light to a field of view of one of the first
plurality of cameras that is not the closest field of view
thereto.
[0005] Preferably, the mutually spaced configuration of the first
plurality of cameras includes a staggered array of rows of cameras,
fields of view of the first plurality of cameras being at least
partially overlapping when viewed in a direction generally
perpendicular to a direction of the rows.
[0006] Preferably, the plane is a common plane occupied by each
field of view.
[0007] Preferably, the plane coincides with a surface of a
substrate to be imaged by the image acquisition device.
[0008] Preferably, each camera defines a camera axis, each
generally circumferential arrangement being centrally intersected
by the camera axis.
[0009] Preferably, the photon emitter includes an LED.
[0010] Preferably, each generally circumferential arrangement
includes at least one ring of photon emitters.
[0011] Preferably, the at least one ring of photon emitters
includes an inner ring of photon emitters and an outer ring of
photon emitters, the inner and outer rings being generally
concentric.
[0012] Preferably, photon emitters including the inner ring emit
light of a first wavelength and photon emitters including the outer
ring emit light of a second wavelength, the first and second
wavelengths being mutually different.
[0013] Preferably, the photon emitters including the inner ring are
IR LEDs and the photon emitters including the outer ring are amber
LEDs.
[0014] In accordance with a preferred embodiment of the present
invention, the field of view to which light is directed by the
photon emitter is entirely illuminated by the photon emitter.
[0015] Preferably, the image acquisition device also includes an
illumination platform having an upper surface and a lower surface,
the upper surface being proximal to the first plurality of cameras,
the lower surface being distal from the plurality of cameras, the
second plurality of photon emitters being mounted on the lower
surface.
[0016] Preferably, a multiplicity of apertures is formed in the
illumination platform, each aperture allowing viewing therethrough
of the field of view by the camera.
[0017] Preferably, each generally circumferential arrangement of
photon emitters circumferentially surrounds each aperture.
[0018] Preferably, each camera includes a telecentric lens.
[0019] Preferably, each aperture is generally rectangular.
[0020] Preferably, the image acquisition device also includes at
least one collimator, for collimating the light.
[0021] Preferably, the at least one collimator is mounted on a
collimator board.
[0022] Preferably, the collimator board is located adjacent to the
illumination platform, between the illumination platform and the
plane.
[0023] Preferably, the image acquisition device also includes at
least one deflecting element for directing the light output by the
at least one collimator.
[0024] Preferably, the at least one deflecting element is mounted
on a deflector board.
[0025] Preferably, the deflector board is located abutting the
collimator board.
[0026] Additionally or alternatively, the deflector board is formed
monolithically with the collimator board.
[0027] In accordance with a preferred embodiment of the present
invention, the at least one deflecting element directs the light
output towards a single field of view.
[0028] In accordance with another preferred embodiment of the
present invention, the at least one deflecting element directs the
light output towards more than one field of view.
[0029] There is additionally provided in accordance with another
preferred embodiment of the present invention an image acquisition
device including a first plurality of cameras arranged in a
mutually spaced configuration, each having a field of view, each
field of view lying in a plane, a second plurality of photon
emitters arranged in a multiplicity of generally circumferential
arrangements, each generally circumferential arrangement
illuminating a field of view, each generally circumferential
arrangement, when projected on the plane of the field of view
illuminated thereby, circumferentially surrounding the field of
view and at least one photon emitter of at least one generally
circumferential arrangement directing light to at least one other
field of view in addition to the field of view illuminated by the
at least one generally circumferential arrangement.
[0030] Preferably, the mutually spaced configuration of the first
plurality of cameras includes a staggered array of rows of cameras,
fields of view of the first plurality of cameras being at least
partially overlapping when viewed in a direction generally
perpendicular to a direction of the rows.
[0031] Preferably, the plane is a common plane occupied by each
field of view.
[0032] Preferably, the plane coincides with a surface of a
substrate to be imaged by the image acquisition device.
[0033] Preferably, each camera defines a camera axis, each
generally circumferential arrangement being centrally intersected
by the camera axis.
[0034] Preferably, the photon emitter includes an LED.
[0035] Preferably, each generally circumferential arrangement
includes at least one ring of photon emitters.
[0036] Preferably, the at least one ring of photon emitters
includes an inner ring of photon emitters and an outer ring of
photon emitters, the inner and outer rings being generally
concentric.
[0037] Preferably, photon emitters including the inner ring emit
light of a first wavelength and photon emitters including the outer
ring emit light of a second wavelength, the first and second
wavelengths being mutually different.
[0038] Preferably, the photon emitters including the inner ring are
IR LEDs and the photon emitters including the outer ring are amber
LEDs.
[0039] Preferably, the image acquisition device also includes an
illumination platform having an upper surface and a lower surface,
the upper surface being proximal to the first plurality of cameras,
the lower surface being distal from the plurality of cameras, the
second plurality of photon emitters being mounted on the lower
surface.
[0040] Preferably, a multiplicity of apertures is formed in the
illumination platform, each aperture allowing viewing therethrough
of the field of view by the camera.
[0041] Preferably, each generally circumferential arrangement of
photon emitters circumferentially surrounds each aperture.
[0042] Preferably, each camera includes a telecentric lens.
[0043] Preferably, each aperture is generally rectangular.
[0044] Preferably, the image acquisition device also includes at
least one collimator coupled to at least one photon emitter.
[0045] Preferably, the at least one collimator is mounted on a
collimator board.
[0046] Preferably, the collimator board is located adjacent to the
illumination platform, between the illumination platform and the
plane.
[0047] Preferably, the image acquisition device also includes at
least one deflecting element coupled to the at least one
collimator.
[0048] Preferably, the at least one deflecting element is mounted
on a deflector board.
[0049] Preferably, the deflector board is located abutting the
collimator board.
[0050] Additionally or alternatively, the deflector board is formed
monolithically with the collimator board.
[0051] In accordance with a preferred embodiment of the present
invention, the at least one collimator is coupled to the at least
one photon emitter of the generally circumferential arrangement
directing light to at least one other field of view in addition to
the field of view illuminated by the generally circumferential
arrangement, the at least one deflecting element directing the
light to the at least one other field of view in addition to the
field of view illuminated by the generally circumferential
arrangement.
[0052] Preferably, the at least one deflecting element includes at
least one prism having a plurality of exit facets angled to direct
the light towards the at least one other field of view in addition
to the field of view illuminated by the generally circumferential
arrangement.
[0053] There is also provided in accordance with yet another
preferred embodiment of the present invention an image acquisition
device including a first plurality of cameras arranged in a
mutually spaced configuration, each having a field of view, each
field of view lying in a plane and a second plurality of photon
emitters arranged in a multiplicity of arrangements about each
camera of the first plurality of cameras, at least one photon
emitter of the second plurality of photon emitters directing light
to a field of view of at least one of the first plurality of
cameras that is not the closest field of view thereto.
[0054] Preferably, the mutually spaced configuration of the first
plurality of cameras includes a staggered array of rows of cameras,
fields of view of the first plurality of cameras being at least
partially overlapping when viewed in a direction generally
perpendicular to a direction of the rows.
[0055] Preferably, the plane is a common plane occupied by each
field of view.
[0056] Preferably, the plane coincides with a surface of a
substrate to be imaged by the image acquisition device.
[0057] Preferably, each camera defines a camera axis, each
arrangement being intersected by the camera axis.
[0058] Preferably, the photon emitter includes an LED.
[0059] Preferably, the image acquisition device also includes an
illumination platform having an upper surface and a lower surface,
the upper surface being proximal to the first plurality of cameras,
the lower surface being distal from the plurality of cameras, the
second plurality of photon emitters being mounted on the lower
surface.
[0060] Preferably, a multiplicity of apertures is formed in the
illumination platform, each aperture allowing viewing therethrough
of the field of view by the camera.
[0061] Preferably, each arrangement of photon emitters surrounds
each aperture.
[0062] Preferably, each camera includes a telecentric lens.
[0063] Preferably, each aperture is generally rectangular.
[0064] Preferably, the image acquisition device also includes at
least one collimator, for collimating the light.
[0065] Preferably, the at least one collimator is mounted on a
collimator board.
[0066] Preferably, the collimator board is located adjacent to the
illumination platform, between the illumination platform and the
plane.
[0067] Preferably, the image acquisition device also includes at
least one deflecting element for directing the light output by the
at least one collimator.
[0068] Preferably, the at least one deflecting element includes a
third plurality of axicons.
[0069] Preferably, the third plurality of axicons includes an array
of axicons having a density of between 4-10000
axicons/cm.sup.2.
[0070] In accordance with a preferred embodiment of the present
invention, the third plurality of axicons includes axicons having
mutually similar optical properties.
[0071] In accordance with another preferred embodiment of the
present invention, the third plurality of axicons includes axicons
having mutually different optical properties.
BRIEF DESCRIPTION OF THE DRAWINGS
[0072] The present invention will be understood and appreciated
more fully from the following detailed description, taken in
conjunction with the drawings in which:
[0073] FIG. 1 is a simplified illustration of an optical system
including an image acquisition device forming a part thereof,
constructed and operative in accordance with a preferred embodiment
of the present invention;
[0074] FIGS. 2A, 2B and 2C are simplified respective perspective,
side and front view illustrations of a portion of an image
acquisition device of the type shown in FIG. 1;
[0075] FIG. 3 is a simplified illustration of an arrangement of
photon emitter assemblies on an illumination platform in an image
acquisition device of the type shown in FIGS. 1-2C;
[0076] FIG. 4 is a simplified conceptual illustration of a
projection of photon emitters onto a plane of fields of view of
cameras in an image acquisition device of the type shown in FIGS.
1-2C;
[0077] FIGS. 5A, 5B and 5C are simplified respective illustrations
of an illumination assembly and components thereof, forming part of
an image acquisition device of the type shown in FIGS. 1-4,
constructed and operative in accordance with a preferred embodiment
of the present invention;
[0078] FIG. 6 is a simplified illustration of an optical
illumination module of an illumination assembly of the type shown
in FIGS. 5A-5C;
[0079] FIG. 7 is a simplified illustration of light output from an
optical illumination module of the type shown in FIG. 6;
[0080] FIG. 8 is a simplified illustration of an optical
illumination module of an illumination assembly constructed and
operative in accordance with another preferred embodiment of the
present invention;
[0081] FIG. 9 is a simplified illustration of light output from an
optical illumination module of the type shown in FIG. 8;
[0082] FIG. 10 is a simplified illustration of an optical
illumination module of an illumination assembly constructed and
operative in accordance with yet another preferred embodiment of
the present invention;
[0083] FIG. 11 is a simplified illustration of light output from an
optical illumination module of the type shown in FIG. 10;
[0084] FIG. 12 is a simplified illustration of an optical
illumination module of an illumination assembly constructed and
operative in accordance with still another preferred embodiment of
the present invention;
[0085] FIG. 13 is a simplified illustration of an optical system
including an image acquisition device forming a part thereof,
constructed and operative in accordance with another preferred
embodiment of the present invention;
[0086] FIGS. 14A, 14B and 14C are simplified respective
perspective, side and front view illustrations of a portion of an
image acquisition device of the type shown in FIG. 13;
[0087] FIGS. 15A, 15B and 15C are simplified respective
illustrations of an illumination assembly and components thereof,
forming part of an image acquisition device of the type shown in
FIGS. 13-14C, constructed and operative in accordance with a
preferred embodiment of the present invention;
[0088] FIG. 16 is a simplified illustration of an optical
illumination module of an illumination assembly of the type shown
in FIGS. 15A-15C;
[0089] FIG. 17 is a simplified pictorial illustration of light
output from an optical illumination module of the type shown in
FIG. 16; and
[0090] FIG. 18 is a simplified plot of simulated light output from
an optical illumination module of the type shown in FIG. 16.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0091] Reference is now made to FIG. 1, which is a simplified
illustration of an optical system including an image acquisition
device forming a part thereof, constructed and operative in
accordance with a preferred embodiment of the present
invention.
[0092] As seen in FIG. 1, there is provided an optical system 100
including an image acquisition device 102. Optical system 100 may
be any type of system employing optical elements and benefitting
from the inclusion of an image acquisition device therein, such as,
by way of example only, an optical scanning system, optical
inspection system, optical processing system or optical
manufacturing system. Here, by way of example, optical system 100
is shown to be embodied in a form typical of an optical scanning
system and image acquisition device 102 to be mounted thereon. It
is appreciated, however, that this representation of optical system
100 and the location of image acquisition device 102 therein is
illustrative only and may readily be varied in accordance with the
design requirements of optical system 100.
[0093] Image acquisition device 102 preferably includes optical
elements operative to illuminate a substrate handled by optical
system 100 and to subsequently acquire an image thereof. Image
acquisition device 102 may therefore be termed an optical head 102.
As seen most clearly at an enlargement 110 showing an enlarged view
of optical head 102, optical head 102 preferably includes a first
plurality of cameras 120 arranged in a mutually spaced
configuration, each camera having an associated field of view 122,
each field of view 122 lying in a plane such as a plane 124. Plane
124 preferably coincides with a surface of the substrate to be
imaged, such that fields of view 122 of cameras 120 lie on the
substrate surface. In the case of a planar target, plane 124
occupied by the fields of view 122 may be a common plane, within
which plane 124 all of fields of view 122 of cameras 120 lie.
Alternatively, in the case of a non-planar substrate to be imaged,
fields of view 122 of cameras 120 may lie in more than one
plane.
[0094] Optical head 102 further preferably includes a second
plurality of photon emitters 130 arranged in a multiplicity of
generally circumferential arrangements 132 about each camera of
first plurality of cameras 120, which photon emitters 130
preferably illuminate fields of view 122. It is a particular
feature of a preferred embodiment of the present invention that at
least one photon emitter within the generally circumferential
arrangement 132 of photon emitters directs light to a field of view
122 of one of the first plurality of cameras 120 which is not the
closest field of view to that photon emitter. Such an arrangement
of plurality of photon emitters 130 with respect to plurality of
cameras 120 allows plurality of photon emitters 130 to provide
wide-angle generally uniform illumination of field of views 122 in
a highly compact form factor, as is explained in greater detail
henceforth with respect to FIGS. 3 and 4.
[0095] Second plurality of photon emitters 130 is preferably
mounted on an underside 138 of an illumination platform 140.
Illumination platform 140 is preferably located beneath entrance
facets 142 of lenses of cameras 120, interfacing cameras 120 and
fields of view 122, with underside 138 of illumination platform 140
distal from entrance facets 142. A multiplicity of apertures 144 is
preferably formed in illumination platform 140, wherethrough light
emanating from illuminated fields of view 122 arrives at cameras
120. Second plurality of photon emitters 130 is preferably
circumferentially arranged with respect to apertures 144 in a
non-overlapping configuration, so as to illuminate fields of view
122 without obscuring light emanating therefrom, as is detailed
henceforth with reference to FIG. 4.
[0096] Light emitted by plurality of photon emitters 130 may be
directed towards fields of view 122 in the manner described above
by means of various beam shaping optical elements 150, which
optical elements 150 may have collimating and/or deflecting
functionalities. Such optical elements 150 may be mounted on one or
more boards, such as a collimator board 152 and a deflector board
154, shown in FIG. 1 to be located adjacent to each other and to
illumination platform 140. It is appreciated that collimator and
deflector boards 152, 154 may be provided separate from
illumination platform 140 or may be integrally formed therewith,
such that plurality of photon emitters 130 and beam shaping optical
elements 150 occupy a monolithic, multi-tiered platform. Further
details concerning the preferable structure and function of the
illuminator assemblies formed by photon emitters 130 in conjunction
with beam shaping optical elements 150 are provided henceforth,
with reference to FIGS. 5A-7.
[0097] First plurality of cameras 120 is preferably organized in a
staggered array, comprising a series of generally parallel mutually
offset rows forming a series of staggered columns. During scanning
of a substrate by optical head 102, the substrate and optical head
102 are preferably in relative motion along a scan direction
generally indicated by an arrow 156. Such motion may be by way of
movement of the substrate in scan direction 156 as optical head 102
remains stationary, by way of movement of optical head 102 in scan
direction 156 as the substrate remains stationary or by way of
movement of both optical head 102 and the substrate.
[0098] As appreciated from consideration of FIG. 1, the scan
direction 156 is preferably generally perpendicular to the
direction of the rows of cameras 120, such that the direction of
the rows defines a cross-scan direction. Plurality of cameras 120
are preferably mutually spaced apart in both a scan and cross-scan
direction so as to allow single-pass scanning of a substrate, when
the substrate and optical head 102 are in relative motion along
scan direction 156.
[0099] Here, by way of example, first plurality of cameras 120 is
seen to comprise 32 individual cameras 160 arranged in three
staggered rows and capable of providing single-pass scanning of a
target. It is appreciated, however, that first plurality of cameras
120 may comprise a greater or fewer number of individual cameras
160 arranged in a variety of array architectures, depending on the
imaging requirements of optical system 100. In particular, a fewer
number of cameras 120 than that illustrated may be employed, such
that single-pass scanning of the entire substrate is not enabled.
In such a case, movement along scan direction 156 may be
complemented by a stepwise movement in the cross-scan direction,
perpendicular to scan direction 156.
[0100] The arrangement and structure of plurality of cameras 120
may be best understood with reference to FIGS. 2A-2C, showing a
representative portion of first plurality of cameras 120. As seen
in FIGS. 2A-2C, first plurality of cameras 120 is preferably
distributed over a first 162, a second 164 and a third 166 row in a
partially overlapping arrangement as viewed in scan direction 156.
As best appreciated from consideration of FIG. 2C, such a
staggered, partially overlapping arrangement of cameras 160
provides a continuous lateral field of view 168 as viewed in scan
direction 156, thereby allowing single-pass scanning of a target.
By way of example, the 32 camera arrangement shown herein may
provide single-pass scanning of a substrate having a width of
approximately 600 mm in a cross-scan direction.
[0101] As seen most clearly in FIGS. 2B and 2C, each camera 160
defines a camera axis 170 and the field of view 122 of each camera
160 is that field of view lying directly beneath the camera 160 and
intersected by the camera axis 170. Thus, by way of example, a
first camera 172 has a first corresponding field of view 174, a
second camera 176 has a second corresponding field of view 178 and
so forth. Circumferential arrangements 132 of second plurality of
photon emitters 130 are preferably generally centered about and
intersected by camera axis 170 of each camera 160.
[0102] Each camera 160 preferably comprises a lens portion 180 and
an associated camera board 182 connected thereto. Camera board 182
may be a printed circuit board (PCB) hosting an integrated-circuit
sensor chip and electronics for camera driving and control. Camera
boards 182 may be formed individually or, for manufacturing
convenience, may be formed as a common element. The operation of
plurality of cameras 120 may be additionally controlled by
electronic circuitry formed on a set of control boards 186. By way
of example, a group of eight individual cameras 160 may be
connected to and controlled by a single control board 186 located
posterior to the cameras 160. Control boards 186 may also house
electronics for the control and driving of plurality of photon
emitters 130. Control boards 186 may be cooperatively coupled to
camera boards 182 so as to coordinate the operation of first
plurality of cameras 120 and second plurality of photon emitters
130.
[0103] Lens portion 180 is particularly preferably embodied as a
telecentric lens. A telecentric lens suitable for use in cameras
160 may be of the type commercially available from Schneider Optics
of Bad Kreuznach, Germany; Edmund Optics of New Jersey, US; NET New
Electronic Technology GMBH of Finning, Germany; and
Opto-Engineering of Mantua, Italy.
[0104] As is known in the art, in telecentric lenses the image of
the field of view is formed by light rays propagating substantially
parallel to the lens axis 170, due to the manner in which light is
captured by the telecentric lens. It is therefore understood by one
skilled in the art that it is the telecentric nature of lens
portions 180 in combination with the generally rectangular shape of
the light sensitive region of the image sensor of camera board 182
that give rise to the generally rectangularly shaped fields of view
122 and the corresponding rectangularly shaped apertures 144 shown
herein. It is appreciated, however, that lenses of types other than
telecentric lenses may be incorporated in the first plurality of
cameras 120 of the present invention, in which case modifications
may be made as required in order to accommodate the shapes of the
fields of view associated therewith.
[0105] As best appreciated from consideration of FIG. 2B, a width
of fields of view 122 is considerably smaller than a diameter of
the corresponding camera lens 180, consistent with the telecentric
nature of camera lens 180. It is a particularly advantageous
feature of the present invention that first plurality of cameras
120 is capable of providing single-pass scanning of a target
despite the camera fields of view being considerably smaller than
the camera lens diameter. By way of example, in the optical head
102 of the present invention, single pass scanning may be achieved
despite fields of view 122 having a width of the order of
approximately 20 mm less than a diameter of corresponding lenses
180.
[0106] This is in contrast to conventional single-pass optical
imaging systems, in which single-pass scanning is typically enabled
by the use of cameras having fields of view at least as large as
the camera lens itself.
[0107] Reference is now made to FIG. 3, which is a simplified
illustration of an arrangement of photon emitter assemblies on a
portion of an illumination platform in an image acquisition device
of the type shown in FIGS. 1-2C.
[0108] As seen in FIG. 3, second plurality of photon emitters 130
is arranged in generally circumferential arrangements 132 about
apertures 144 on underside 138 of illumination board 140. Each
circumferential arrangement 132 of photon emitters 130 is
preferably embodied as at least one ring of photon emitters here
comprising, by way of example, a pair of mutually concentric rings
of photon emitters comprising an outer ring 300 and an inner ring
302. Each pair of mutually concentric outer and inner rings 300 and
302 of photon emitters 130 preferably circumferentially surrounds a
corresponding aperture 144. It is appreciated, however, that
circumferential arrangements 132 of photon emitters may
alternatively comprise a greater or fewer number of rings of photon
emitters surrounding each of apertures 144.
[0109] Photon emitters 130 are preferably embodied as LEDs.
Preferably, LED members 304 of outer ring 300 provide light of a
different wavelength than LED members 306 of inner ring 302. By way
of example, LEDs 304 in outer ring 300 may be IR LEDs and LEDs 306
in inner ring 302 may be amber LEDs. It is appreciated, however,
that LEDs 304, 306 respectively comprising inner and outer rings
300 and 302 may provide light of a variety of wavelengths and are
not limited to providing light of mutually different wavelengths.
Furthermore, it is appreciated that photon emitters 130 are not
limited to being LEDs and may comprise any other suitable source of
photons, such as diode lasers, vertical-cavity surface-emitting
lasers (VCSEL), vertical-external-cavity surface-emitting-lasers
(VECSEL), super-luminescent diodes or output ends of light emitting
optical fibers.
[0110] It is a particular feature of a preferred embodiment of the
present invention that second plurality of photon emitters 130 is
arranged such that at least one of outer rings 300, here indicated
by a ring of striped hatched LEDs 310, is overlapping with another
one of outer rings 300, here indicated by a ring of crosshatched
LEDs 312. As a result of the mutually overlapping arrangement of
neighboring outer rings 300, at least one photon emitter member 304
of one of outer rings 300 lies within the generally circular
boundary circumscribed by photon emitter members 304 of another one
of outer rings 300. In the case of the two exemplary overlapping
rings of photon emitters indicated by hatching in FIG. 3, it is
seen that four crosshatched LEDs 312 lie within the boundary
circumscribed by striped hatched LEDs 310 and four striped hatched
LEDs 310 lie within the boundary circumscribed by crosshatched LEDs
312. As also depicted in FIG. 3, outer rings 300 may also overlap
with inner rings 302 of a neighboring field of view 144.
Additionally or alternatively, neighboring ones of inner rings 302
may mutually overlap, depending on the radius thereof.
[0111] Such a multiplexed overlapping arrangement of photon
emitters may occupy substantially less volume than the volume that
would be occupied by a non-multiplexed, non-overlapping arrangement
of photon emitters, thereby leading to a significant reduction in
the size of optical head 102. By way of example, optical head 120
of the type illustrated in FIG. 1 including 3 rows of cameras 160,
may occupy a mechanical depth of 180-220 mm in scan direction 156.
Notwithstanding the compactness of the arrangement of the present
invention, the optical head 102 of the present invention is
preferably capable of carrying out single-pass scanning of a
substrate, due to the unique multiplexed arrangement of photon
emitters 130 and partially overlapping cameras 120 employed
therein. The total depth of optical head 102 constitutes an extra
substrate scanning length. As would be appreciated by persons
skilled in the art, the compact construction made possible by the
present invention may translate into shorter scan travel, higher
speed operation and lower cost scan stage.
[0112] Furthermore, since outer rings 300 and in certain
embodiments also inner rings 302 are overlapping, the radius of
each ring is less strictly limited by space constraints on
illumination board 140. Outer ring 300 may have both a relatively
large radius and substantially dense, azimuthally evenly spaced
photon emitter placement. By way of example, each of rings 300 may
have an effective optical radius in the range of 80-100 mm Further
by way of example, inner ring 302 may provide illumination
subtending 20.degree.-30.degree. and outer ring 300 provide
illumination subtending 30.degree.-50.degree. relative to the lens
optical axis 170 at the center of field of view 144. Overlapping
outer ring 300 and inner ring 302 thus functionally substitute for
far bulkier distinct physical ring light assemblies, providing
generally uniform, wide angle illumination of fields of view 144
for a given separation between cameras 120 and plane 124.
[0113] This is in contrast to conventional imaging systems, in
which provision of uniform wide angle illumination typically
necessitates either a large camera-substrate separation or an
extremely expansive arrangement of illumination sources.
[0114] By way of example, entrance facets 142 of lenses 180 of
cameras 120 may be separated from the fields of view 122 associated
therewith, and hence from the substrate, by a distance in the range
of approximately 50-100 mm, taken along camera axis 170.
Particularly preferably, the substrate being imaged by cameras 120
may be separated from entrance facets 142 of lenses 180 of cameras
120 by a distance in the range of 70-90 mm This distance may
correspond to approximately double to quadruple the length of a
diagonal of each field of view 122. Were rings 300 not to be
overlapping, such a separation between the cameras and fields of
view would either necessitate an extremely large inter-camera
spacing to give wide-angle illumination, or would result in very
narrow or uneven angle illumination of the fields of view, both of
which features would be undesirable and are avoided in the present
invention.
[0115] Additionally, due at least to the close substrate-camera
spacing facilitated by the multiplexed partially overlapping
arrangement of photon emitters in the present invention, the system
of the present invention preferably provides high resolution
images. By way of example, an optical head of the present invention
may acquire images with a spatial resolution in the range of 6-30
.mu.m (lens object-side numerical aperture in the range 0.01-0.05)
and particularly preferably in the range of 8-16 .mu.m in the green
part of the visible spectrum (lens object-side numerical aperture
in the range 0.02-0.04). The provision of high resolution images is
a highly advantageous feature of the present invention and is in
contrast to conventional imaging systems, in which much lower
resolution images are typically acquired.
[0116] It is understood that the generally circumferential
arrangements 132 of plurality of photon emitters 130, here depicted
as comprising inner and outer rings 302 and 300, are not limited to
being strictly circular. In actuality, circumferential arrangements
132 of photon emitters 130 may diverge from true circles within a
tolerance of approximately .+-.20%. Furthermore, circumferential
arrangements 132 of photon emitters 130 are not limited to being
planar. Rather, circumferential arrangements 132 may be composed of
photon emitters 304, 306 located at variety of azimuthal angles
with respect to fields of view 144, within a tolerance of
approximately .+-.15.degree..
[0117] The illumination of fields of view 122 by plurality of
photon emitters 130 may be best understood with reference to FIG.
4, showing a simplified conceptual illustration of a projection of
photon emitters onto a plane of fields of view 122 of plurality of
cameras 120 in optical head 102. It is appreciated that for the
sake of simplicity and clarity, beam shaping elements 150 are
omitted from FIG. 4 and only photon emitters 130 are depicted in
relation to fields of view 122.
[0118] As seen in FIG. 4, when second plurality of photon emitters
130 is projected onto plane 124 occupied by fields of view 122,
plurality of photon emitters 130 circumferentially surrounds fields
of view 122 and neighboring outer rings 300 of photon emitters 130,
such as outer rings 300 formed by LEDs 310 and 312, mutually
overlap.
[0119] By way of example, LEDs 310 of one of outer rings 300 direct
light to a first field of view 400 surrounded thereby, as indicated
by a first set of arrows 402. LEDs 312 of another one of outer
rings 300 direct light to a second field of view 404 surrounded
thereby, as indicated by a second set of arrows 406. Due to the
overlap between neighboring rings 300 of LEDs 310 and 312, those of
LEDs 310 lying within the boundary circumscribed by LEDs 312 are
closer to second field of view 404 surrounded and illuminated by
ring of LEDs 312, yet direct illumination to the more distant first
field of view 400. Similarly, those of LEDs 312 lying within the
boundary circumscribed by LEDs 310 are closer to the first field of
view 400 surrounded and illuminated by ring of LEDs 310, yet direct
illumination to the more distant second field of view 404.
[0120] It is appreciated that although the architecture and
operation of photon emitters 130 with respect to fields of view 122
has been described hereinabove with respect to two particular
individual fields of view 400 and 404, the description hereinabove
is generally applicable to other photon emitters and fields of view
constructed and operative in accordance with preferred embodiments
of the present invention.
[0121] Reference is now made to FIGS. 5A, 5B and 5C, which are
simplified respective illustrations of an illumination assembly and
components thereof, forming part of an image acquisition device of
the type shown in FIGS. 1-4, constructed and operative in
accordance with a preferred embodiment of the present
invention;
[0122] As seen in FIGS. 5A-5C, each circumferential arrangement 132
of plurality of photon emitters 130, here, by way of example,
composed of outer ring 300 and inner ring 302 of LEDs, lies about
camera axis 170 of camera 160. Here, by way of example, beam
shaping optical elements 150 are shown to be housed by a collimator
plate 500 and a deflector plate 502 stacked thereon. Each
circumferential arrangement 132 of photon emitters 130, in
combination with corresponding beam shaping optical elements 150
associated therewith, may be termed an illumination assembly
504.
[0123] It is appreciated that although a single annular
illumination assembly 504 is illustrated in FIG. 5A, for the sake
of simplicity and clarity of description, in actuality, multiple
ones of illumination assembly 504 are preferably incorporated in
optical head 102 in a multiplexed, mutually overlapping
arrangement, as described hereinabove. Particularly preferably,
illumination platform 140, collimator plate 500 and deflector plate
502 are formed as continuous, expansive elements having multiple,
mutually overlapping arrangements of illumination assemblies 504
formed thereon, as illustrated in FIGS. 1-4.
[0124] Outer ring 300 and inner ring 302 of plurality of photon
emitters 130 are preferably mounted on an LED mounting plate 510,
as seen most clearly in FIG. 5B showing an enlarged view thereof.
Mounting plate 510 preferably includes a plurality of capacitors
(not shown) connected to electrical circuitry, for controlling
operation of photon emitters 130. In a preferred operational mode,
photon emitters 130 are driven by short pulses of electrical
current. This allows image acquisition during continuous relative
motion between the optical head 102 and the scanned target, while
minimizing image blur. Capacitors and the circuitry associated
therewith enabling such short pulse driving may be of the type
described in Chinese Patent Application No. 201510828406.3,
assigned to the same assignee as the present invention and
incorporated herein by reference.
[0125] It is understood that mounting plate 510 preferably
constitutes a segment of illumination platform 140. Thus, although
mounting plate 510 is shown herein as holding only inner and outer
rings 302, 300 of photon emitters thereon, a portion of
illumination platform 140 corresponding to mounting plate 510 may
in actuality also host additional photon emitters, which additional
photon emitters are members of other rings of photon emitters,
encroaching on outer ring 300 and optionally also on inner ring
302.
[0126] Collimator plate 500 is preferably located immediately
beneath LED mounting plate 510 and preferably includes an array of
light collimators 520, each light collimator 522 of array of light
collimators 520 preferably cooperating with and being axially
aligned with respect to a corresponding photon emitter on mounting
plate 510. Here, by way of example, array of light collimators 520
comprises a dual-ring array, corresponding to inner and outer rings
302, 300 of photon emitters. It is understood, however, that
collimators 522 may be arranged in any suitable configuration
capable of providing the required collimation of light emitted by
plurality of photon emitters 130. It is further understood that
collimator plate 500 preferably constitutes a segment of a larger
preferably planar sheet of light collimators, forming a part of
collimator board 152.
[0127] In accordance with the specific type of photon emitter
employed, collimators 522 may comprise one or more of spherical,
circularly symmetric aspherical, cylindrical or free-form lenses or
reflectors including Fresnel counterparts of those optical
elements. By way of example, collimators 522 illustrated in FIG. 6
are single-element aspheric lenses.
[0128] Deflector plate 502 is preferably located immediately
beneath collimator plate 500 and preferably includes an array of
light deflectors 530, as seen most clearly in FIG. 5C showing an
enlarged view thereof. Each light deflector 532 of array of light
deflectors 530 preferably cooperates with and is located
longitudinally beneath a corresponding photon emitter 130 and
collimator 522.
[0129] Each light deflector 532 preferably comprises one or more
free-form optical elements. By way of example, as seen most clearly
in FIGS. 5C and 6, light deflector 532 may be a prism having an
irregularly chamfered entry facet 542 and exit facet 546. Persons
skilled in the art will recognize that facets 542 and 546
collectively function in a manner resembling a free-form prism for
deflecting light impinging thereon. Free-form facets 542 and 546 of
the particular design shown in FIG. 6 additionally exhibit partial
light collimation functionality, complementing the collimating
function of aspheric collimators 522, in order to achieve improved
illumination uniformity and efficiency at the respective field of
view 122. The high deflection efficiency of deflector 532 in
combination with collimator 522 preferably also minimizes the
escape of stray light from each photon emitter to fields of view
other than those intended to be illuminated by each given photon
emitter. It is understood that deflector plate 502 preferably
constitutes a segment of a larger planar sheet of light deflectors,
forming a part of deflector board 154.
[0130] It is understood that collimator and deflector plates 500,
502 preferably each constitute only a segment of collimator and
deflector boards 152, 154 respectively. Thus, although collimator
and deflector plates 500, 502 are shown herein as holding only two
rings of collimating and deflecting elements respectively thereon,
a portion of collimator and deflector boards 152, 154 corresponding
to collimator and deflector plates 500, 502 may in actuality also
host additional collimator and deflector elements respectively,
which additional collimator and deflector elements preferably
correspond to and cooperate with photon emitters encroaching on
rings of photon emitters on a corresponding portion of illumination
platform 140.
[0131] LED mounting plate 510 is preferably fabricated as a printed
circuit board (PCB) on which are additionally preferably mounted
some or all of the LED driving electronic circuitry. Alternatively,
LED mounting plate 510 as well as collimator plate 500 and
deflector plate 502, including the various optical elements housed
thereby, may be manufactured by three-dimensional printing
techniques (e.g. by Luximprint V.O.F of the Netherlands). Other
known manufacturing techniques that may be employed for producing
collimator elements 522 and deflecting elements 532 include
injection molded plastic, Computer Numerical Control (CNC)
machining and glass molding. It is appreciated that illumination
assemblies 504 thus are constructed of generally planar, readily
manufacturable elements, which may be produced at low cost and be
easily assembled
[0132] Each vertical stack of photon emitter 130, collimator 522
and light deflector 532 may be collectively termed an illumination
module 550. An exemplary illumination module 550 is illustrated in
FIG. 6, light output from which illumination module 550 is shown in
a highly simplified manner in FIG. 7. As appreciated from
consideration of FIGS. 6 and 7, illumination module 550 preferably
directs collimated light emitted by the photon emitter, such as an
LED, forming a part thereof towards the associated field of view
122. Preferably, collimators 522 and deflectors 532 are functional
to direct light from photon emitter 130 in a manner such that each
illumination module 550 illuminates the entirety of a single field
of view 122, as seen in FIG. 7.
[0133] It is understood that the inclusion of deflectors 532 in
illumination module 550 and illumination assembly 504 in order to
direct collimated light from collimators 522 towards fields of view
122 is exemplary only and that deflectors 532 may be replaced by
other light directing mechanisms. By way of example, deflectors 532
may be obviated and light angled towards fields of view 122 by
other mechanisms as are known in the art. These mechanisms include
but are not limited to planar refractive beam deflectors and
diffraction gratings, the latter being particularly effective in
combination with laser type photon emitters.
[0134] It is appreciated that, in some embodiments of the present
invention, it may be advantageous for at least one illumination
module of at least one illumination assembly 504 to illuminate more
than one field of view 122, rather than only a single field of view
as illustrated in the case of illumination module 550.
[0135] The illumination of more than one field of view by an
illumination module of the present invention may be desirable
since, due to the highly dense arrangement of photon emitters 130,
individual photon emitters 130 respectively belonging to
neighboring circumferential arrangements 132 may be designated to
be located at physically intersecting locations on illumination
platform 140. As only one photon emitter may occupy a given
location on illumination platform 140, this creates a region of
conflict between two or more photon emitters 130 competing to
occupy at least part of the same region on illumination platform
140.
[0136] A conflict may arise between two or more photon emitters 130
of neighboring inner rings 302, between two or more photon emitters
130 of neighboring outer rings 300, or between two or more photon
emitters 130 of neighboring inner and outer rings 302 and 300.
[0137] Such a conflict may be resolved by shifting the location of
one or more of the photon emitters 130 competing to occupy the same
position. However, this solution may not be viable in the case that
the at least one competing photon emitter requires shifting to an
unacceptably distant position from the circumferential arrangement
132 to which the photon emitter belongs, preventing the at least
one photon emitter 130 from providing the required illumination to
the associated field of view 122.
[0138] Such a conflict may alternatively be resolved, in accordance
with one preferred embodiment of the present invention, by placing
a single photon emitter 130 at the position of conflict on
illumination platform 140, the single photon emitter 130 forming
part of a light-splitting illumination module directing light
towards more than one field of view 122. The single photon emitter
130 occupying the position of conflict effectively replaces the
multiple photon emitters that were designated to occupy that
position, by outputting light towards the fields of view that were
designated to be illuminated by additional photon emitters
occupying that position. The single photon emitter 130 occupying
the position of conflict thus directs light to at least one other
field of view in addition to the field of view illuminated by the
generally circumferential arrangement 132 to which the photon
emitter belongs.
[0139] The illumination of more than one field of view by an
illumination module of the present invention may be advantageous
even if the above-described conflict is not present, in order to
reduce the number of illumination modules and hence the number of
photon emitters required on illumination platform 140. This may
reduce manufacturing costs, power dissipation and complexity in
certain embodiments of the present invention.
[0140] Illumination module 550 may be modified so as to illuminate
more than one field of view, by replacement of single deflecting
element 532 by a plurality of deflecting elements. By way of
example, deflecting element 532 may be replaced by a plurality of
prisms having a number and orientation of facets corresponding to
the number and orientation of required light output beams.
[0141] Various examples of illumination modules of the present
invention configured to direct light towards more than one field of
view, and the corresponding light outputs therefrom, are
illustrated in a highly simplified form in FIGS. 8-12.
[0142] Turning now to FIG. 8, an illumination module 850 preferably
includes photon emitter 130, a collimating element such as
collimator 522 and a deflecting element 852. It is appreciated that
the collimating element included in illumination module 850 is not
necessarily of the same structure as collimator 522 and may be
optimized in accordance with the desired performance
characteristics of illumination module 850. Deflecting element 852
is preferably embodied as a split prism having a first output facet
854 and a second output facet 856. First and second output facets
854, 856 are preferably of mutually different orientations, and are
preferably each oriented so as to direct light to a different field
of view. For example, as seen in FIG. 9, first output facet 854 may
project an output beam towards a first field of view 860 and second
output facet 856 may project an output beam towards a second field
of view 862. A third field of view 864 is preferably not
illuminated by illumination module 850.
[0143] Output facets 854 and 856 of deflector element 852 are
illustrated as comprising concave surfaces in FIGS. 8 and 9. It is
understood, however, that these facets may alternatively be formed
as convex, outward pointing or protruding surfaces rather than
inward pointing or recessed surfaces.
[0144] It is understood that illumination module 850 thus
effectively at least partially replaces the functionality of two
individual illumination modules 550 that would have illuminated
first and second fields of view 860 and 862 respectively.
[0145] Turning now to FIG. 10, an illumination module 1050
preferably includes photon emitter 130, a collimator element such
as collimator 522 and a deflecting element 1052. Deflecting element
1052 is preferably embodied as a split prim having first, second
and third output facets 1054, 1056 and 1058. First--third output
facets 1054-1058 are preferably each orientated so as to direct
light to a different field of view. Output facets 1054-1058 are
illustrated as convex surfaces in FIG. 10. It is understood,
however, that these facets may also be designed as concave
surfaces, as illustrated in FIG. 11. For example, as seen in FIG.
11, first output facet 1054 may direct light to first field of view
860, second output facet 1056 may direct light to second field of
view 862 and third output facet 1058 may direct light to third
field of view 864.
[0146] It is understood that illumination module 1050 thus
effectively at least partially replaces the functionality of three
individual illumination modules 550 that would have illuminated
first, second and third fields of view 860, 862 and 864,
respectively.
[0147] It will be appreciated by persons skilled in the art that
the split illumination modules such as illumination modules 850 and
1050 differ somewhat in performance in comparison to a non-split
illumination module, such as illumination module 550. This is
because each split illumination module only projects light from a
portion of the exit aperture thereof, with respect to each field of
view. Additionally, the light power of the split illumination
module is distributed over more than one field of view, resulting
in the delivery of less light power to each individual field of
view illuminated thereby.
[0148] In the case of substantially diffusely reflecting substrates
loss of light power tends to be the more significant of these
effects. The relative loss of light power may be compensated for by
providing a physically larger and/or higher power photon emitter
130 within the split illumination module. Additionally or
alternatively, the relative power loss may be compensated for by
equalizing the illumination of each field of view by providing
additional illumination from other light-splitting illumination
modules.
[0149] In the case of at least partially specularly reflecting
substrates, the angle subtended by the illumination module may also
be significant. In such cases, a split illumination module of the
type illustrated in FIG. 12 may be advantageous, in order to
preserve the angular extent of the illumination.
[0150] Turning now to FIG. 12, an illumination module 1250
preferably includes photon emitter 130, a collimating element such
as collimator 522 and a deflecting element 1252. Deflecting element
1252 is preferably embodied as multi-faceted, convex or concave,
prism, directing light to multiple fields of view. The multi-prism
design of deflecting element 1252 serves to evenly distribute
illumination across the exit facet thereof as a multitude of small
illumination gaps, which illumination gaps are scrambled by the
substrate reflection properties and imaging lens acceptance
angle.
[0151] It is understood that a given illumination assembly may
include any combination of illumination modules of the present
invention, including illumination modules illuminating only a
single field of view and light-splitting illumination modules
illuminating multiple fields of view, depending on the requirements
of the optical inspection system in which the illumination assembly
is incorporated.
[0152] Reference is now made to FIG. 13, which is a simplified
illustration of an optical system including an image acquisition
device forming a part thereof, constructed and operative in
accordance with another preferred embodiment of the present
invention.
[0153] As seen in FIG. 13, there is provided an optical system 1300
including an image acquisition device 1302. Optical system 1300 may
be any type of system employing optical elements and benefitting
from the inclusion of an image acquisition device therein, such as,
by way of example only, an optical scanning system, optical
inspection system, optical processing system or optical
manufacturing system. Here, by way of example, optical system 1300
is shown to be embodied in a form typical of an optical scanning
system and image acquisition device 1302 to be mounted thereon. It
is appreciated, however, that this representation of optical system
1300 and the location of image acquisition device 1302 therein is
illustrative only and may readily be varied in accordance with the
design requirements of optical system 1300.
[0154] Image acquisition device 1302 preferably includes optical
elements operative to illuminate a substrate handled by optical
system 1300 and to subsequently acquire an image thereof. Image
acquisition device 1302 may therefore be termed an optical head
1302. As seen most clearly at an enlargement 1310 showing an
enlarged view of optical head 1302, optical head 1302 preferably
includes a first plurality of cameras 1320 arranged in a mutually
spaced configuration, each camera having an associated field of
view 1322, each field of view 1322 lying in a plane such as a plane
1324. Plane 1324 preferably coincides with a surface of the
substrate to be imaged, such that fields of view 1322 of cameras
1320 lie on the substrate surface. In the case of a planar target,
plane 1324 occupied by the fields of view 1322 may be a common
plane, within which plane 1324 all of fields of view 1322 of
cameras 1320 lie. Alternatively, in the case of a non-planar
substrate to be imaged, fields of view 1322 of cameras 1320 may lie
in more than one plane.
[0155] Optical head 1302 further preferably includes a second
plurality of photon emitters 1330 arranged in a multiplicity of
arrangements 1332 about each camera of first plurality of cameras
1320, which photon emitters 1330 preferably illuminate fields of
view 1322. Particularly preferably, multiplicity of arrangements
1332 of photon emitters 1330 are arranged about an axis 1326 of
each camera of first plurality of cameras 1320.
[0156] It is a particular feature of a preferred embodiment of the
present invention that at least one photon emitter in at least one
of arrangements 1332 directs light to a field of view 1322 of one
of the first plurality of cameras 1320 which is not the closest
field of view to that photon emitter. Such an arrangement of
plurality of photon emitters 1330 with respect to plurality of
cameras 1320 allows plurality of photon emitters 1330 to provide
wide-angle generally uniform illumination of fields of view 1322 in
a highly compact form factor, as is explained in greater detail
henceforth.
[0157] Second plurality of photon emitters 1330 is preferably
mounted on an underside 1338 of an illumination platform 1340.
Illumination platform 1340 is preferably located beneath entrance
facets 1342 of lenses of cameras 1320, interfacing cameras 1320 and
fields of view 1322, with underside 1338 of illumination platform
1340 distal from entrance facets 1342. A multiplicity of apertures
1344 is preferably formed in illumination platform 1340,
wherethrough light emanating from illuminated fields of view 1322
arrives at cameras 1320. Second plurality of photon emitters 1330
is preferably arranged with respect to apertures 1344 in a
non-overlapping configuration, so as to illuminate fields of view
1322 without obscuring light emanating therefrom. In certain
embodiments photon emitters 1330 may be distributed over the entire
area of illumination platform 1340 so as to maximize the
illumination intensity and uniformity whilst retaining a compact
form factor.
[0158] Light emitted by plurality of photon emitters 1330 may be
directed towards fields of view 1322 in the manner described above
by means of various beam shaping optical elements 1350, which
optical elements 1350 may have collimating and/or deflecting
functionalities. Such optical elements 1350 may be mounted on one
or more boards, such as a collimator board 1352 upon which are
preferably mounted collimating elements and a deflector board 1354
upon which are preferably mounted deflecting elements. Collimator
board 1352 and deflector board 1354 are shown in FIG. 13 to be
located adjacent to each other and to illumination platform 1340.
It is appreciated that collimator and deflector boards 1352, 1354
may be provided separate from illumination platform 1340 or may be
integrally formed therewith, such that plurality of photon emitters
1330 and beam shaping optical elements 1350 occupy a monolithic,
multi-tiered platform.
[0159] It is a particular feature of a preferred embodiment of the
present invention illustrated in FIG. 13 that deflector board 1354
is embodied as an array of a third plurality of axicons 1355 having
light deflecting functionality. Array of axicons 1355 is preferably
formed as a tightly packed array of conical optical elements,
typically comprising plastic or glass. As is well known in the art,
axicons 1355 deflect light substantially equally in all directions
relative the vertical direction along which light is incident
thereon, such that no light is transmitted along the vertical axis
and a ring of deflected light is generated. In the embodiment of
the present invention shown in FIG. 13, axicons 1355 receive light
from second plurality of photon emitters 1330, by way of
collimating elements on collimator board 1352, and in turn generate
rings of light illuminating fields of view 1322. The collective
effect of the tightly packed array of axicons 1355 is thus to
project a ring-shaped radiance distributed with respect to the
fields of view 1322. A virtual ring illumination is thereby created
with respect to each field of view 1322, without requiring a
physical circumferential arrangement of light sources. Further
details concerning the preferable structure and function of the
illuminator assemblies formed by photon emitters 1330 in
conjunction with array of axicons 1355 and additional beam shaping
optical elements 1350 are provided henceforth, with reference to
FIGS. 15A-17.
[0160] First plurality of cameras 1320 is preferably organized in a
staggered array, comprising a series of generally parallel mutually
offset rows forming a series of staggered columns. During scanning
of a substrate by optical head 1302, the substrate and optical head
1302 are preferably in relative motion along a scan direction
generally indicated by an arrow 1356. Such motion may be by way of
movement of the substrate in scan direction 1356 as optical head
1302 remains stationary, by way of movement of optical head 1302 in
scan direction 1356 as the substrate remains stationary or by way
of movement of both optical head 1302 and the substrate.
[0161] As appreciated from consideration of FIG. 13, the scan
direction 1356 is preferably generally perpendicular to the
direction of the rows of cameras 1320, such that the direction of
the rows defines a cross-scan direction. Cameras 1320 are
preferably mutually spaced apart in both a scan and cross-scan
direction so as to allow single-pass scanning of a substrate, when
the substrate and optical head 1302 are in relative motion along
scan direction 1356.
[0162] Here, by way of example, first plurality of cameras 1320 is
seen to comprise 32 individual cameras 1360 arranged in three
staggered rows and capable of providing single-pass scanning of a
target. It is appreciated, however, that first plurality of cameras
1320 may comprise a greater or fewer number of individual cameras
1360 arranged in a variety of array architectures, depending on the
imaging requirements of optical system 1300. In particular, a fewer
number of cameras 1320 than that illustrated may be employed, such
that single-pass scanning of the entire substrate is not enabled.
In such a case, movement along scan direction 1356 may be
complemented by a stepwise movement in the cross-scan direction,
perpendicular to scan direction 1356.
[0163] The arrangement and structure of plurality of cameras 1320
may be best understood with reference to FIGS. 14A-14C, showing a
representative portion of first plurality of cameras 1320. As seen
in FIGS. 14A-14C, first plurality of cameras 1320 is preferably
distributed over a first 1362 a second 1364 and a third 1366 row in
a partially overlapping arrangement as viewed in scan direction
1356. As best appreciated from consideration of FIG. 14C, such a
staggered, partially overlapping arrangement of cameras provides a
continuous lateral field of view 1368 as viewed in scan direction
1356, thereby allowing single-pass scanning of a target. By way of
example, the 32 camera arrangement shown herein may provide
single-pass scanning of a substrate having a width of approximately
600 mm in a cross-scan direction.
[0164] As seen most clearly in FIGS. 14B and 14C, each camera 1360
defines camera axis 1326 and the field of view 1322 of each camera
1360 is that field of view lying directly beneath the camera 1360
and intersected by the camera axis 1326. Thus, by way of example, a
first camera 1372 has a first corresponding field of view 1374, a
second camera 1376 has a second corresponding field of view 1378
and so forth, as seen in FIG. 14B. Arrangements 1332 of second
plurality of photon emitters 1330 are preferably generally centered
about and intersected by camera axis 1326 of each camera 1360.
[0165] Each camera 1360 preferably comprises a lens portion 1380
and an associated camera board 1382 connected thereto. Camera board
1382 may be a printed circuit board (PCB) hosting an
integrated-circuit sensor chip and electronics for camera driving
and control. Camera boards 1382 may be formed individually or, for
manufacturing convenience, may be formed as a common element. The
operation of plurality of cameras 1320 may be additionally
controlled by electronic circuitry formed on a set of control
boards 1386. By way of example, a group of eight individual cameras
1360 may be connected to and controlled by a single control board
1386 located posterior to the cameras 1360. Control boards 1386 may
also house electronics for the control and driving of plurality of
photon emitters 1330. Control boards 1386 may be cooperatively
coupled to camera boards 1382 so as to coordinate the operation of
first plurality of cameras 1320 and second plurality of photon
emitters 1330.
[0166] Lens portion 1380 is particularly preferably embodied as a
telecentric lens. A telecentric lens suitable for use in cameras
1360 may be of the type commercially available from Schneider
Optics of Bad Kreuznach, Germany; Edmund Optics of New Jersey, US;
NET New Electronic Technology GMBH of Finning, Germany; and
Opto-Engineering of Mantua, Italy.
[0167] As is known in the art, in telecentric lenses the image of
the field of view is formed by light rays propagating substantially
parallel to the lens axis 1326, due to the manner in which light is
captured by the telecentric lens. It is therefore understood by one
skilled in the art that it is the telecentric nature of lens
portions 1380 in combination with the generally rectangular shape
of the light sensitive region of the image sensor of camera board
1382 that give rise to the generally rectangularly shaped of fields
of view 1322 and the corresponding rectangularly shaped apertures
1344 shown herein. It is appreciated, however, that lenses of types
other than telecentric lenses may be incorporated in the first
plurality of cameras 1320 of the present invention, in which case
modifications may be made as required in order to accommodate the
shapes of the fields of view associated therewith.
[0168] As best appreciated from consideration of FIG. 14B, a width
of fields of view 1322 is considerably smaller than a diameter of
the corresponding camera lens 1380, in keeping with the telecentric
nature of camera lens 1380. It is a particularly advantageous
feature of the present invention that first plurality of cameras
1320 is capable of providing single-pass scanning of a substrate
despite the camera fields of view being considerably smaller than
the camera lens diameter. By way of example, in the optical head
1302 of the present invention, single pass scanning may be achieved
despite fields of view 1322 having a width of the order of
approximately 20 mm less than a diameter of corresponding lenses
1380.
[0169] This is in contrast to conventional single-pass optical
imaging systems, in which single-pass scanning is typically enabled
by the use of cameras having fields of view at least as large as
the camera lens itself.
[0170] Reference is now made to FIGS. 15A, 15B and 15C, which are
simplified respective illustrations of an illumination assembly and
components thereof, forming part of an image acquisition device of
the type shown in FIGS. 13-14C, constructed and operative in
accordance with a preferred embodiment of the present
invention;
[0171] As seen in FIGS. 15A-15C, plurality of photon emitters 1330
on a portion of illumination platform 1340 preferably surround
camera axis 1326 of camera 1360. A collimator plate 1500 is
preferably positioned beneath photon emitters 1330 and array of
axicons 1355 preferably located therebeneath. Photon emitters 1330
surrounding camera 1360, in combination with corresponding beam
shaping optical elements 1350 associated therewith including
axicons 1355, may be termed an illumination assembly 1504.
[0172] It is appreciated that although a single illumination
assembly 1504 is illustrated in FIG. 15A, for the sake of
simplicity and clarity of description, in actuality, multiple ones
of illumination assembly 1504 are preferably incorporated in
optical head 1302 in a multiplexed, mutually overlapping
arrangement, as described hereinabove. Particularly preferably,
illumination platform 1340, collimator plate 1500 and axicon array
1355 are preferably formed as continuous, expansive elements having
multiple, mutually overlapping arrangements of illumination
assemblies 1504 formed thereon, as illustrated in FIGS. 13-14C.
[0173] Photon emitters 1330 are preferably mounted on an LED
mounting plate 1510, as seen most clearly in FIG. 15B showing an
enlarged view thereof. Mounting plate 1510 preferably includes a
plurality of capacitors (not shown) connected to electrical
circuitry, for controlling operation of photon emitters 1330. In a
preferred operational mode, photon emitters 1330 are driven by
short pulses of electrical current. This allows image acquisition
during continuous relative motion between the optical head 1302 and
the scanned target, while minimizing image blur. Capacitors and the
circuitry associated therewith enabling such short pulse driving
may be of the type described in Chinese Patent Application No.
201510828406.3, assigned to the same assignee as the present
invention and incorporated herein by reference.
[0174] It is understood that mounting plate 1510 preferably
constitutes a segment of illumination platform 1340. It is
understood that the particular geometric arrangement of photon
emitters 1330 on mounting plate 1510 illustrated in FIG. 15B is
exemplary only, and that photon emitters 1330 may be arranged in
any suitable repeating or non-repeating arrangement on mounting
plate 1510, at least partially surrounding aperture 1344 formed
therein.
[0175] Collimator plate 1500 is preferably located immediately
beneath LED mounting plate 1510 and preferably includes an array of
light collimators 1520, each light collimator 1522 of array of
light collimators 1520 preferably cooperating with and being
located longitudinally beneath a corresponding photon emitter on
mounting plate 1510. In actuality, when constructing illumination
assembly 1504, the density and arrangement of photon emitters 1330
is typically set in accordance with the practicable density with
which array of light collimators 1520 may be constructed.
[0176] Here, by way of example, array of light collimators 1520
comprises a rectangular array, corresponding to the arrangement of
photon emitters 1330. It is understood, however, that collimators
1522 may be arranged in any suitable configuration capable of
providing the required collimation of light emitted by plurality of
photon emitters 1330. By way of example, photon emitters 1330 on
plate 1510 and collimators 1522 on plate 1500 may be arranged in
hexagonal grids, alternative tightly packed formations or
non-regular arrays, in accordance with system requirements and
engineering considerations. It is further understood that
collimator plate 1500 preferably constitutes a segment of a larger
preferably planar sheet of light collimators, forming a part of
collimator board 1352.
[0177] In accordance with the specific type of photon emitter
employed, collimators 1522 may comprise one or more of spherical,
circularly symmetric aspherical, cylindrical or free-form lenses or
reflectors including Fresnel type counterparts of those optical
elements. By way of example, collimator 1522 illustrated in FIGS.
15A and 16 is a single-element aspheric lens.
[0178] Array of axicons 1355 is preferably located immediately
beneath collimator plate 1500 and preferably includes an array of
light deflecting axicons, as seen most clearly in FIG. 15C showing
an enlarged view thereof. Axicons 1355 may have a hexagonal, square
or other shaped border, in order to allow tight packing thereof
into an array. Array of axicons 1355 is preferably but not
necessarily symmetrical with respect to aperture 1344. In the
embodiment of array of axicons 1355 illustrated in FIG. 15C, all of
axicons 1355 are shown to be mutually identical, with the same
dimensions and cone angle. It is appreciated, however, that this is
exemplary only and that axicons comprising array of axicons 1355
may be mutually different. For example, axicons 1355 may be of
various dimensions and cone angles so as to generate light rings of
more than one angle. Axicons suitable for use in the present
invention may be of the type commercially available on a custom
basis from Jungbecker Karl GmbH & Co., of Olpe, Germany; ALP
Lighting Components Inc. of Niles, Ill., USA; Bright View
Technologies Corporation of Durham, N.C., USA; Gaggione SAS of
Montreal La Cluse, France; PowerPhotonic Ltd. of Fife, United
Kingdom; and CDA GmbH of Suhl, Germany
[0179] LED mounting plate 1510 is preferably fabricated as a
printed circuit board (PCB) on which are additionally preferably
mounted some or all of the LED driving electronic circuitry.
Alternatively, LED mounting plate 1510 as well as collimator plate
1500, including the various optical elements mounted thereon, may
be manufactured by three-dimensional printing techniques (e.g. by
Luximprint V.O.F. of the Netherlands). Other known manufacturing
techniques that may be employed for producing collimator elements
1522 include injection molded plastic, Computer Numerical Control
(CNC) machining and glass molding. It is appreciated that
illumination assemblies 1504 thus are preferably constructed of
generally planar, readily manufacturable elements, which may be
produced at low cost and be easily assembled.
[0180] Each vertical stack of photon emitter 1330, collimator 1522
and a corresponding portion 1530 of axicon array 1355 may be
collectively termed an illumination module 1550. An exemplary
illumination module 1550 is illustrated in FIG. 16, light output
from which illumination module 1550 is shown in a highly simplified
manner in FIG. 17. As appreciated from consideration of FIGS.
15A-17, light emitted by each photon emitter 1330 preferably
propagates towards the corresponding collimator element 1522, which
collimator element 1522 preferably collimates the light received
thereat and produces a collimated light output. The collimated
light output from collimator element 1522 preferably propagates
towards the corresponding portion 1530 of array of axicons
1355.
[0181] Each axicon element in array of axicons 1355 is preferably
functional to generate light output in the form of a conical
surface 1700, as illustrated in FIG. 17. Due to the highly dense
arrangement of array of axicons 1355, array of axicons 1355
preferably generates multiple, overlapping conical surfaces or
rings of light. Axicon array 1355 is preferably structured and
arranged such that the light rings generated thereby overlap and
aggregate upon fields of view 1322, thereby illuminating fields of
view 1322 and minimizing the amount of stray light falling on
regions between fields of view 1322.
[0182] In accordance with a particularly preferred embodiment of
the present invention, array of axicons 1355 comprises an array of
axicons formed of molded transparent plastic material. The plastic
material may comprise one or more of acrylic, polycarbonate, cyclic
olefin polymer or any other optical grade plastic material that may
be molded or shaped into a desirable optical design. Particularly,
the use of polycarbonate is advantageous due to the relatively high
refractive index thereof, enabling the achievement of large
deflection angles. Axicons may be convex, as illustrated in FIGS.
15A-17. Additionally or alternatively, axicons may be concave.
[0183] Array of axicons 1355 may have a density in the range of
4-10000 axicon/cm.sup.2. Axicons 1355 preferably have an apex angle
in the range of 80.degree. to 130.degree. and a corresponding
deflection angle in the range of 29.degree.-12.5.degree. in the
case that array of axicons 1355 comprises acrylic plastic, and in
the range of 35.degree.-15.degree. in the case that array of
axicons 1355 comprises polycarbonate. It is appreciated, however,
that these values are illustrative only and may be readily varied
by one skilled in the art depending on the light output
requirements of illumination module 1550. In particular, it is
appreciated that there is a trade-off between the number of axicons
included in array of axicons 1355 and the size of each axicon and
that the design of array of axicons 1355 may be optimized in
accordance with the functional requirements thereof.
[0184] As described hereinabove, each axicon conical prism in array
1355 projects a light beam propagating generally equally in all
azimuthal directions with a narrow angle relative to an axicon axis
1702. This light beam preferably intersects the substrate surface
with ring shaped light distribution 1700, as shown in FIG. 17. In
contrast to other preferred embodiments of the present invention
described hereinabove, the light output of array of axicons 1355 is
not associated with any particular one of fields of view 1322.
Rather, the light output of array of axicons 1355 is spread
substantially evenly throughout the substrate area 1324 occupied by
fields of view 1322. Light incident on regions between fields of
view 1322 is thus wasted. However, due to the tightly packed
arrangement of plurality of cameras 1320, the proportion of light
so wasted is minimized
[0185] It is appreciated that, for the sake of clarity, the light
output of only a single axicon of the array 1355 is shown in FIG.
17. However, it is readily understood that generally similar
although not necessarily identical light outputs are preferably
projected by each axicon in array 1355. The collective effect of
the light output of the entirety of array of axicons 1355, as
observed from the viewpoint of each field of view 1322, is that of
a ring-shaped angular spread of light having a well-defined angle
relative to the axis 1326 of the telecentric lens 1380.
[0186] It is a particular advantage of this embodiment of the
present invention that the irradiance provided by array of axicons
1355 is highly uniform and substantially spatially invariant,
exhibiting minimal variation in intensity at different locations
within each field of view 1322 illuminated thereby. The spatial
invariance of the irradiance provided by array of axicons 1355 may
be appreciated from consideration of FIG. 18, illustrating
simulation results of the angular radiance projected by an
illumination arrangement of the type illustrated in FIG. 17.
[0187] As seen in FIG. 18, the simulated angular radiance as seen
at the center and corner of each of two fields of view 1322A and
1322B is plotted. Field of view 1322A is selected to lie in the
middle row 1364 of the plurality of cameras 1320, whereas field of
view 1322B is selected to lie in an edge row such as row 1362. As
clear from a comparison of the angular radiance plots, the angular
radiance as observed at various locations within and between each
field of view 1322 is substantially uniform.
[0188] It is understood that the angular radiance plotted in FIG.
18 is a simulation of the radiance provided by an ideal array of
axicons 1355, constructed and operative in accordance with a
preferred embodiment of the present invention. As is appreciated by
those skilled in the art, in actual practice the axicon array may
comprise manufacturing variations and tolerances. By way of
example, the actual axicon apex would be of finite radius of
curvature rather than infinitely sharp as simulated and adjacent
axicons would typically be separated by finite transition areas
rather than being immediately abutting as simulated. These
manufacturing tolerances may result in the formation of gaps within
the ring-shaped radiance distributions shown in FIG. 18, thus
degrading the uniformity and shift invariance of the
illumination.
[0189] In order to minimize the formation of gaps within the
ring-shaped radiance distributions projected by array of axicons
1355 in embodiments of the present invention, each axicon in array
of axicons 1355 is preferably of very small dimensions relative to
the separation between array of axicons 1355 and the corresponding
fields of view 1322. By way of example, the separation between
array of axicons 1355 and fields of view 1322 is preferably between
about 10-100 times greater than a dimension of the base of each
axicon. As a result, angular gaps in the radiance patterns
projected by array of axicons 1355 are generally insignificant in
relation to the light scattering properties of the substrate and
the acceptance angle of imaging lens 1380.
[0190] In accordance with certain embodiments of the present
invention, array of axicons 1355 may comprise axicons having
generally the same optical properties. Alternatively, array of
axicons 1355 may be formed of axicons having mutually different
geometries, such as mutually different apex angles, and hence
mutually different optical properties. By way of example, array of
axicons 1355 may comprise interleaved axicons of two or more
mutually different geometries, projecting two or more generally
concentric angular radiance rings of mutually different deflection
angles.
[0191] Interleaving may comprise alternating placing of a first
type of axicon and a second type of axicon in accordance with a
regularly or non-regularly repeating pattern. In certain
embodiments, the interleaving may be differently structured
depending on the location in relation to camera axes 1326.
[0192] Simultaneous provision of light rings of more than one
deflection angle may be advantageous in applications where the
features to be observed on the scanned substrate comprise a number
of different reflection properties. In such a case, light having a
small incidence angle with respect to camera axis 1326 may have the
property of enhancing the edges of generally specularly reflecting
surfaces such as metals. Light incident at relatively large angles
may have the property of enhancing point defects such as scratches
and dust particles. However, light incident at excessively broad
angles may be undesirable due to reduced overall contrast.
[0193] It is understood that in the case that array of axicons 1355
comprises axicons of two or more geometries and hence deflection
angles, each axicon of a first geometry presents a radiance gap
within the angular ring of light generated by each axicon of a
second geometry, as observed from field of view 1322. By way of
example, an array of axicons 1355 may comprise a first type of
axicon projecting light rings with a 15.degree. deflection angle,
interleaved with a second type of axicon projecting light rings
with a 35.degree. deflection angle. As viewed from field of view
1322 in the direction of the 35.degree. radiance ring, each bright
spot is observed as emanating from the second type of axicon of
35.degree. deflection angle, located at the direction of
observation. The first type of 15.degree. deflection angle axicon,
located adjacent to the 35.degree. deflection angle axicon, would
be perceived as a dark spot in the 35.degree. deflection angle
projected light ring, since the 15.degree. deflection angle axicon
contributes to the 15.degree. radiance ring.
[0194] Similarly, as viewed from field of view 1322 in the
direction of the 15.degree. radiance ring, each bright spot is
observed as emanating from the first type of axicon of 15.degree.
deflection angle, located at the direction of observation. The
second type of 35.degree. deflection angle axicon, located adjacent
to the 15.degree. deflection angle axicon, would be perceived as a
dark spot in the 15.degree. deflection angle projected light ring,
since the 35.degree. deflection angle axicon contributes to the
35.degree. radiance ring.
[0195] However, provided a relatively dense array of axicons is
employed, the above-described radiance gaps may be made to be small
enough to be of negligible significance for a given
application.
[0196] It will be appreciated by persons skilled in the art that
the present invention is not limited by what has been particularly
claimed hereinbelow. Rather, the scope of the invention includes
various combinations and subcombinations of the features described
hereinabove as well as modifications and variations thereof as
would occur to persons skilled in the art upon reading the forgoing
description with reference to the drawings and which are not in the
prior art.
* * * * *