U.S. patent application number 10/126582 was filed with the patent office on 2003-06-12 for 3d shape-measuring apparatus using biaxial anamorphic magnification.
This patent application is currently assigned to Industrial Technology Research Institute. Invention is credited to Lin, Ming-Hui, Liou, Tung-Fa.
Application Number | 20030107819 10/126582 |
Document ID | / |
Family ID | 21679872 |
Filed Date | 2003-06-12 |
United States Patent
Application |
20030107819 |
Kind Code |
A1 |
Lin, Ming-Hui ; et
al. |
June 12, 2003 |
3D SHAPE-MEASURING APPARATUS USING BIAXIAL ANAMORPHIC
MAGNIFICATION
Abstract
A 3D shape-measuring apparatus using biaxial anamorphic
magnification comprises a light source that projects a light onto
an object surface to be sensed. Via an electrical image-grabbing
device, such as CCD camera, the light reflected from the object is
grabbed to determine the coordinate locations sensed on the object.
Before the electrical image-grabbing device, the light reflected
from the object passes respectively through a curved reflecting
mirror or an assembly of telecentric cylindrical lenses to adjust
an image magnification along the light projection direction, and an
assembly of cylindrical lenses to adjust an image magnification
along a direction perpendicular to the light projection direction.
Thereby, resolution nonuniformity with respect to near and far
distance is resolved while the observable range of the CCD camera
can further be efficiently changed into a measurable field.
Inventors: |
Lin, Ming-Hui; (Hsin-Chu,
TW) ; Liou, Tung-Fa; (Hsin-Chu, TW) |
Correspondence
Address: |
BACON & THOMAS, PLLC
625 SLATERS LANE
FOURTH FLOOR
ALEXANDRIA
VA
22314
|
Assignee: |
Industrial Technology Research
Institute
Hsin-Chu Hsien
TW
|
Family ID: |
21679872 |
Appl. No.: |
10/126582 |
Filed: |
April 22, 2002 |
Current U.S.
Class: |
359/668 |
Current CPC
Class: |
G02B 13/10 20130101 |
Class at
Publication: |
359/668 |
International
Class: |
G02B 013/08 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 7, 2001 |
TW |
090130271 |
Claims
What is claimed is:
1. A 3D shape-measuring apparatus using biaxial anamorphic
magnification comprising: a light source projecting a light plane
or a light ray onto a surface of an object to be sensed, the light
intersection onto the surface of the object being a curved light
intersection or a punctual light intersection; a curved reflecting
mirror having a concave surface of continuous curvature to reflect
the light projected from the light source and reflected from the
surface of the object, and change an angle of view in the direction
of the light projection; an assembly of cylindrical lenses through
which passes the light reflected from the curved reflecting mirror,
the assembly of cylindrical lenses adjusting an image magnification
along a direction paralleled to the light intersection; and an
electrical image-grabbing device comprising a driver circuit, an
assembly of objective lenses, and an image sensor, the light after
passing through the assembly of cylindrical lenses traveling
through the objective lenses to form an image on the image sensor;
wherein the light after being projected from the light source onto
the surface of the object, generates a reflected light that further
reflects via the curved reflecting mirror, and travels through the
assembly of cylindrical lenses into the image-grabbing device to
form an image on the image sensor.
2. The 3D shape-measuring apparatus using biaxial anamorphic
magnification of claim 1, wherein the curved reflecting mirror has
a monotonously cylindrical reflecting surface.
3. The 3D shape-measuring apparatus using biaxial anamorphic
magnification of claim 1, wherein the assembly of cylindrical
lenses at least comprises a concave cylindrical lens and a convex
cylindrical lens, an image magnification of either increase or
decrease respectively depending on the respective focal length and
the placement order of the concave and convex cylindrical lenses
with respect to the light path.
4. The 3D shape-measuring apparatus using biaxial anamorphic
magnification of claim 1, wherein the axis of each cylindrical lens
of the assembly of cylindrical lenses is not perpendicular to the
axis of the light path to the objective lenses, and forms an
adequate included angle therewith to obtain an optimal image
formation.
5. The 3D shape-measuring apparatus using biaxial anamorphic
magnification of claim 1, wherein an image plane of the image
sensor within the electrical image-grabbing device is not
perpendicular to the axis of the light path from the objective
lenses in order to obtain optimal measuring precision and
resolution.
6. The 3D shape-measuring apparatus using biaxial anamorphic
magnification of claim 1, further comprising an optical filter
placed before the objective lenses within the electrical
image-grabbing device to filter at least a specific wavelength of
light.
7. A 3D shape-measuring apparatus using biaxial anamorphic
magnification comprising: a light source projecting a light
projecting plane or onto a surface of an object to be sensed, the
light intersection onto the surface of the object being a curved
light intersection or a punctual light intersection; an assembly of
telecentric cylindrical lenses comprising an assembly of second
cylindrical lenses and a planar reflecting mirror, wherein the axis
of the second cylindrical lenses is perpendicular to the light
projection direction and parallel with the light projection plane,
an angle of view along the light projection direction being reduced
after the light has passed through the assembly of telecentric
cylindrical lenses; an assembly of first cylindrical lenses through
which passes a light path from the assembly of telecentric
cylindrical lenses, the first cylindrical lenses changing an image
magnification along a direction parallel to the light intersection;
and an electrical image-grabbing device comprising a driver
circuit, an assembly of objective lenses, and an image sensor,
wherein the focal point of the second cylindrical lenses approaches
the location of the objective lenses, and the light path after the
first cylindrical lenses travels through the objective lenses to
form an image on the image sensor; wherein the light after being
projected from the light source into an incident light on the
surface of the object, generates a reflected light that further
travels through the assembly of telecentric cylindrical lenses and
the assembly of first cylindrical lenses into the image-grabbing
device to form an image on the image sensor.
8. The 3D shape-measuring apparatus using biaxial anamorphic
magnification of claim 7, wherein the assembly of first cylindrical
lenses at least comprises a concave cylindrical lens and a convex
cylindrical lens, an image magnification of either increase or
decrease respectively depending on the respective focal length and
the placement order of the concave and convex cylindrical lenses
with respect to the light path.
9. The 3D shape-measuring apparatus using biaxial anamorphic
magnification of claim 7, the axis of each cylindrical lens of the
assembly of first cylindrical lenses is not perpendicular to the
axis of the light path to the objective lenses, and forms an
adequate included angle therewith to obtain an optimal image
formation.
10. The 3D shape-measuring apparatus using biaxial anamorphic
magnification of claim 7, an image plane of the image sensor within
the electrical image-grabbing device is not perpendicular to the
axis of the light path from the objective lenses to obtain optimal
measuring precision and resolution.
11. The 3D shape-measuring apparatus using biaxial anamorphic
magnification of claim 7, further comprising an optical filter
placed before the objective lenses within the electrical
image-grabbing device to filter at least a specific wavelength of
light.
Description
FIELD OF THE INVENTION
[0001] The invention relates to a 3D shape-measuring apparatus
using biaxial anamorphic magnification that, more particularly,
uses telecentric property to uniformize resolution ranging from
near distance to far distance.
BACKGROUND OF THE INVENTION
[0002] An image-grabbing device for 3D shape-measuring apparatus
conventionally comprises a camera lens with fixed focal length
associated with a charge coupled device (CCD) camera having fixed
resolutions and a fixed size, the CCD camera having fixed viewing
angle along the vertical direction and the horizontal direction.
Thus, if the object distance is increasingly decreased, the
observable field is increasingly reduced while the resolution is
increased. On the contrary, if the object distance is increased,
the observable field is increased while the resolution is
decreased. When the optical axis of CCD camera is oblique with the
light projection direction, the resolution along the light
projection direction is adversely decreased. This resolution is all
the more decreased as the light source distance is increased.
[0003] To increase the resolution along the light projection
direction, the U.S. Pat. No. 6,046,812 uses an anisotropic
magnification cylindrical lens to magnify the image along the light
projection direction, which thereby increases the resolution there
along. Meanwhile, the image magnification along the perpendicular
direction is not changed. To achieve the same results as disclosed
above, an assembly of prisms may be also used to obtain anisotropic
magnification, as disclosed in the U.S. Pat. No. 4,872,747.
[0004] Therefore, the conventionally known methods can increase the
resolution along the light projection direction. However, those
methods fail to remedy a decrease of the resolution along the light
projection direction as the light source distance is increased.
This resolution nonuniformity occurs when a near distance
resolution is sufficient while a far distance resolution is not
sufficient. In the conventional technology, the parameters of the
CCD camera further usually determine the resolution along a
direction perpendicular to the light projection direction.
Therefore, the choice of focal length and object distance has
already decided the resolution along the perpendicular direction.
If one desires to change the resolution along the perpendicular
direction, either the focal length or object distance only can be
changed. However, conventional 3D shape-measuring apparatus have
their preferable object distance of operation, and the adjustment
range of the object distance is therefore relatively limited. As a
result, changing the focal length is thus usually implemented.
Regardless a change of either the object distance or focal length,
the resolution along the light projection direction would
accordingly change, therefore, the parameters of an assembly of
anisotropic or anamorphic lenses should be modified. Generally, the
focal length of an objective lens directly determines the
resolution in either direction. For cost considerations, most
objective lenses are standard with fixed focal length such as CCTV
lenses. Therefore from a design consideration, simultaneously
fulfilling the requirements of biaxial resolutions is a difficult
task.
[0005] FIG. 1 is a schematic view that illustrates the resolution
of a conventional method without anamorphic magnification. In FIG.
1, a light projection plane 11 is projected onto a surface of an
object 20 to be sensed, meanwhile the configuration of the light 7
reflected from the object 20 toward the CCD camera to be grabbed
via equally spaced CCD pixels thereof is also shown. As shown in
FIG. 1, without anamorphic magnification, the CCD camera has a
substantially large angle of view of the light projection
direction. However, a far distance resolution dramatically drops.
Moreover, because the depth of field of conventional objective
lenses is substantially limited, the measuring precision in the
area of far distance is therefore substantially affected.
[0006] FIG. 2 is a schematic view that illustrates the use of a
cylindrical lens for a resolution improvement as disclosed in the
U.S. Pat. No. 6,046,812. In FIG. 2, a light projection plane 11 is
projected onto a surface of an object 20 to be sensed, meanwhile
the configuration of the light 7 reflected from the object 20
toward the CCD camera to be grabbed via equally spaced CCD pixels
thereof is also shown. As shown in FIG. 2, the use of a cylindrical
lens reduces the angle of view of the light projection direction,
which increases its resolution. However, far distance resolution is
still adversely lower than near distance resolution.
SUMMARY OF THE INVENTION
[0007] It is therefore a principal object of the invention to
provide a 3D shape-measuring apparatus using biaxial anamorphic
magnification that can anamorphically magnify an image whatever
perpendicular to or parallel with a light projection direction. As
a result, uniform resolutions along parallel and perpendicular
directions with respect to the light projection direction are
obtained for 3D measurement while the resolutions further do not
decrease as the distance of the light source increases.
[0008] To accomplish the above and other objectives, the invention
provides a 3D shape-measuring apparatus using biaxial anamorphic
magnification that comprises the following elements. A light source
projects a light plane or a light ray on a surface of an object to
be sensed. The projected light intersects the surface of the object
into a light intersection that can be a curve or a point that is
reflected toward a curved reflecting mirror (an assembly of
telecentric cylindrical lenses is also suitable). After reflecting
on the curved reflecting mirror, the reflected light travels
through an assembly of first cylindrical lenses into an electrical
image-grabbing device (CCD camera) to form an image onto an image
sensor, such as a charge coupled device, therein. Thereby, the
coordinates of the points hit by the light from the light source,
which can be a laser, are calculated. In the invention, either the
curved reflecting mirror or the assembly of telecentric cylindrical
lenses can adjust the magnification of an image along the light
projection direction. The curved reflecting mirror can be a concave
mirror with a continuous curvature that reflects the light
reflected from the object. The assembly of telecentric cylindrical
lenses comprises an assembly of second cylindrical lenses and a
planar reflecting mirror that reduce the angle of view of the light
projection direction. The focal location of the assembly of
telecentric cylindrical lenses further approaches the principal
plane of objective lenses. The assembly of first cylindrical lenses
adjusts an image magnification along a direction perpendicular to
the light projection. Finally, the image is formed on the image
sensor (such as a charge coupled device) of the electrical
image-grabbing device.
[0009] With the invention as described above, under an optical
design of anamorphic magnification, a certain level of quality of
image formation can be maintained while increasing the resolutions.
The observable range of the CCD camera thus can be efficiently
changed into a measurable field.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The drawings included herein provide a further understanding
of the invention and, incorporated herein, constitute a part of the
invention disclosure. A brief introduction of the drawings is as
follows:
[0011] FIG. 1 illustrates a resolution conventionally obtained
without anamorphic magnification.
[0012] FIG. 2 illustrates a conventional use of a cylindrical lens
to improve the resolution.
[0013] FIG. 3 illustrates the resolution principle of the
invention.
[0014] FIG. 4 and FIG. 5 illustrate a 3D shape-measuring apparatus
according to a first embodiment of the invention.
[0015] FIG. 6 illustrates a 3D shape-measuring apparatus according
to a second embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0016] Wherever possible in the following description, similar
reference numerals and symbols will refer to similar elements
unless otherwise illustrated.
[0017] The invention provides a 3D shape-measuring apparatus using
biaxial anamorphic magnification that is an image-grabbing device
arranged in a manner to sense the location of a light intersection
on a surface of an object caused by a light projected thereon from
a light source. According to one specific feature of the invention,
the image-grabbing device of the invention specifically has high
and uniform resolutions. FIG. 3 illustrates the resolution
principle of the invention in which one element is the use of a
curved reflecting mirror to reduce the angle of view of the light
projection direction and, furthermore, uniformize near and far
distance resolutions. In comparison with the conventional structure
as shown in FIG. 1 and FIG. 2, the invention enables the resolution
of the reflected light 7 grabbed by the electrical image-grabbing
device 60 to be uniform. As a result, resolution nonuniformity with
respect to near and far distances is therefore resolved in the
invention. A detailed description of embodiments and examples of
the invention now is made with reference to FIG. 4 through FIG.
6.
[0018] [First Embodiment]
[0019] To resolve the problem of directional resolution
nonuniformity with respect to a light projection in near and far
distance, the invention provides a 3D shape-measuring apparatus
using biaxial anamorphic magnification that uses telecentric
property to uniformize near and far distance resolutions.
[0020] Referring to FIG. 4, a schematic view illustrates a
shape-measuring apparatus according to a first embodiment of the
invention. As shown in FIG. 4, the shape-measuring apparatus
comprises a light source 10 that projects an incident light plane
(or light ray) onto a surface of an object 20. The 3D coordinates
of a light intersection 21 of the incident light on the surface of
the object (which can be a curve or a point) can be calculated via
a triangulation method. The light intersection 21, reflected from
the object 20, then is reflected through a curved reflecting mirror
40A, travels through an assembly of cylindrical lenses 50, to be
finally inputted into an electrical image-grabbing device 60 for
image formation. The electrical image-grabbing device 60 (CCD
camera) principally comprises an objective lenses 61 with fixed
focal length, an image sensor (for example, a charge coupled device
62) and the driver circuit thereof. An optical filter may be
additionally mounted before the objective lenses 61 to filter
specific wavelength of the light ray. According to the size of the
charge coupled device 62 and the focal length of the objective
lenses 61, the horizontal and vertical angles of view of the
electrical image-grabbing device 60 can be determined. The
directions included in the horizontal angle of view in the light
plane are perpendicular to the direction of light projection, and
the directions included in the vertical angle of view in the light
plane are the directions of light projection. Hence, the horizontal
angle of view is changed through the cylindrical lenses 50 while
the vertical angle of view is changed through the curved reflecting
mirror 40A. An upper limit plane 31 and a lower limit plane 32
represent the upper and lower limits of the vertical angle of
view.
[0021] As shown in FIG. 5, according to the geometrical
relationship between the location of the curved reflecting mirror
40A and the electrical image-grabbing device 60, the curvature of
the surface of the curved reflecting mirror 40A is continuous to
approximately form a telecentric structure. In other words, each
portion of the curved surface of the reflecting mirror 40A has a
focal length that is close to the distance between the said portion
of the curved surface and the electrical image-grabbing device 60.
The purpose is to obtain reflection planes between the upper and
lower limit planes 31, 32 of the vertical angle of view that are
approximately parallel and, furthermore, vis-a-vis each pixel along
a vertical direction arrayed by the charge coupled device 62, can
maintain an equal spacing distance along the direction of light
projection in the light projection plane 11. Hence, in comparison
with conventional structures without reflecting mirror or with only
a planar reflecting mirror, the angle of view along the direction
of light projection can be compressed, and the resolution there
along is thereby enhanced. Moreover, because the continuous
curvature of the curved reflecting mirror 40A enables to obtain a
telecentric property, the resolution along the direction of light
projection does not decrease along with increasing the light source
distance. As a result, the resolution obtained is favorably
uniform. In order to improve the quality of image formation, the
image formation plane (charge coupled device 62, CCD) of the
electrical image-grabbing device 60 must be adequately adjusted.
The adjustment angle of the image formation plane should vary in
accordance with various factors including the included angle
between the light projection and the optical axis of the
image-grabbing device 60, the curvature and the location of the
curved reflecting mirror 40A.
[0022] As shown in FIG. 5, the assembly of cylindrical lenses 50
comprises at least a concave cylindrical lens 51 and a convex
cylindrical lens 52. The axis of the concave cylindrical lenses 51
and convex cylindrical lenses 52 need not be necessarily
perpendicular to the optical axis to the electrical image-grabbing
device 60. To obtain a better image formation, an appropriate axis
inclination of the concave and convex cylindrical lenses 51, 52 may
be accomplished. When the concave cylindrical lens 51 is placed
proximate to the object 20 side while the convex cylindrical lens
52 is placed proximate to the electrical image-grabbing device 60
side, the horizontal angle of view obtained is larger and the image
is consequently zoomed more. Oppositely, if the placement of both
lenses (concave cylindrical lenses 51 and convex cylindrical lenses
52) is interchanged, the horizontal angle of view obtained is
decreased and the image is consequently zoomed less. Furthermore,
the image magnification can be changed via adjusting the position
or parameter variation of the cylindrical lenses.
[0023] [Second Embodiment]
[0024] FIG. 6 is a schematic view that illustrates a second
embodiment of the invention. As shown in FIG. 6, the curved
reflecting mirror 40A is replaced with an assembly of telecentric
cylindrical lenses 40B, comprised of a cylindrical lens 401B and a
planar reflecting mirror 402B, in the second embodiment. Similar to
the first embodiment, the light source 10 projects light in the
light projection plane 11 onto the object 20. The light projected
intersects a surface of the object 20 into a punctual or curved
light intersection. The light intersection, reflected from the
object 20 into a light path 30, travels through the cylindrical
lens 401B, reflects onto the planar reflecting mirror 402B, and
passes through the assembly of cylindrical lenses 50 (concave
cylindrical lens 51 and convex cylindrical lens 52) and through the
objective lenses 61 (camera lens) to form an image on the charge
coupled device 62. To uniformize near and far distance resolutions,
the focal length of the cylindrical lens 401B approaches the light
distance between the cylindrical lens 401B and the objective lenses
61 and, moreover, the aperture is located on the objective lenses
61. Thereby, a telecentric structure is achieved, and the light
paths 30, between the object 20 and the cylindrical lens 401B, to
which correspond equal spacing images on the charge coupled device
62, are approximately equally spaced parallel light paths. As
illustrated in FIG. 6, the light paths 30 are approximately equally
spaced and parallel with one another. As a result, the problem of
nonuniformity of near and far distance resolutions is resolved.
Compared with the invention, the conventional technology may use an
assembly of cylindrical lenses that, however, are located proximate
to the camera lens to maintain a measurable range. The result
conventionally obtained is therefore only an increase of the
resolution without using telecentric property. As a result, the
problem of resolution nonuniformity with respect to near and far
distances still remains. Via mounting of cylindrical lens 401B and
planar reflecting mirror 402B to obtain a telecentric property, the
invention favorably improves the problem of resolution
nonuniformity with respect to near and far distances. In the
invention, the placement of cylindrical lens 401B and planar
reflecting mirror 402B may be also advantageously interchanged, and
the cylindrical lens 401B may also be an assembly of cylindrical
lenses. However, if the cylindrical lens 401B is replaced with an
assembly of cylindrical lenses, the assembly of cylindrical lenses
must be suitably distant from the objective lenses 61. Furthermore,
both assemblies of cylindrical and objective lenses should have
sufficient spaces to use telecentric property while maintaining a
sufficient observable field.
[0025] It should be apparent to those skilled in the art that the
above description is only illustrative of specific embodiments and
examples of the invention. The invention should therefore cover
various modifications and variations made to the herein-described
structure and operations of the invention, provided they fall
within the scope of the invention as defined in the following
appended claims.
* * * * *