Optical: systems and elements – Single channel simultaneously to or from plural channels – By partial reflection at beam splitting or combining surface
Reexamination Certificate
2001-07-25
2003-09-02
Sikder, Mohammad (Department: 2872)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By partial reflection at beam splitting or combining surface
C359S631000, C359S633000, C359S640000
Reexamination Certificate
active
06614596
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention is directed to increasing the illumination density color within a field of view of an imaging system.
2. Description of Related Art
Uniform, diffuse illumination of a workpiece is often necessary in commercial vision systems to accentuate an edge of the workpiece within a designated field of view. Since most workpieces are not transparent, diffuse illumination of the workpiece is also necessary so that light which is reflected from the workpiece can be collected by an imaging system. Furthermore, an adjustable diffuse illumination source accommodates the observation and inspection of workpieces having a wide variety of shapes.
The adjustable illumination provides the ability to illuminate workpieces having different characteristics, such as, for example, shape, composition, and surface finish. In some systems, the intensity of light emitted by a light source is adjustable when the magnification of the imaging system is adjustable.
Also, conventional lighting systems project light onto the workpiece at an adjustable angle relative to an axis which is normal to the imaging plane. This angle is referred to as the angle of incidence. In many conventional vision systems, the axis normal to the imaging plane is parallel to, or coincides with, the optical axis of the vision system. Light projected at an angle of incidence which is between 0° and 90° may improve the surface contrast of the image and may also more clearly illuminate textured surfaces. Typically, such light sources have a prescribed range for the angle of incidence varying between 10° and 70°. Such a range is relatively broad and, therefore, provides adequate contrast in a variety of workpiece images.
Furthermore, conventional vision systems can also adjust or select the circumferential position of the source of diffuse lighting about an optical axis. Typically, the position of the diffuse lighting source is adjustable or selectable in, for example, addressable sectors or quadrants. As such, the field of view of the camera can be illuminated by any combination of sectors and quadrants of such a circular lighting system. Additionally, the intensity level of the light source can be coordinated with the circumferential position of the light source to optimize the illumination of a workpiece edge.
For example, some conventional vision systems include an annular light system that emits rectangular or toroidal patterns. The light system is an annulus which is divided into four quadrants. Other conventional vision systems include a ring light having an annulus which is subdivided into eight or more sectors. Additionally, some conventional vision systems have hemispherically-shaped light systems to direct light from a multitude of positions relative to an optical axis. The center of the hemisphere serves as a focal point for the light sources. Furthermore, any combination of sectors or quadrants can simultaneously be illuminated with varying illumination levels.
In other conventional programmable ring lighting systems, a very large number of fiber optic cables are arranged such that first ends of the fiber optical cables receive light from a high-intensity light source, such as a halogen lamp. The second ends of the fiber optic cables are arranged in a ring around the optical axis. The fiber optic cables, or sets of the fiber optic cables, can be individually controlled to project the light from the light source onto the field of view of the camera using an annular mirror and a parabolic annular mirror.
Recently, manufacturers of conventional vision systems have started offering a solid-state replacement for the traditional halogen lamps that have been used in conventional diffuse light sources. These manufacturers now offer light emitting diodes (LEDs) that offer high reliability, a longer service life, lower cost, good intensity modulation capabilities and a wide variety of frequency ranges.
One exemplary solid-state lighting system is disclosed in U.S. Pat. No. 5,580,163 to Johnson, II. As shown in
FIG. 13
, the 163 patent discloses a focusing light source with a flexible mount
502
for multiple light-emitting elements
504
. Each light-emitting element
504
emits a beam of light onto a work piece
506
at a predetermined azimuthal angle &agr;
n
to form a predetermined pattern of light. To adjust or focus the multiple light-emitting elements
504
, the flexible mount
502
is rotated in one direction toward the center of the mount
502
or a second direction away from the center of the mount
502
. In various other embodiments, the light-emitting elements
504
can be separately colored light-emitting elements. To achieve multi-colored illumination, illumination from a plurality of the light-emitting elements
504
is combined at the workpiece.
The total azimuthal angle range corresponding to the sources used to achieve a particular multi-colored illumination is approximately x&agr;
n
, where x is the number of different colored light-emitting elements
504
used. Thus, the multi-colored illumination provided by such a system cannot be controlled in azimuthal angle increments which are as narrow as the light emitting elements
504
. Furthermore, any shadows in the field of view will exhibit zones of various colors, since each color component in the illumination is projected form a slightly different direction. Additionally, the illumination density, that is the illumination intensity projected onto the field of view on the workpiece from a given azimuthal angle range, is significantly limited by the characteristics of the individual conventional light-emitting elements
504
.
Another exemplary lighting system is identified as prior art in the 163 patent itself. As a shown in FIG. 14 of the 163 patent, a beam of light is emitted from a light-emitting element
504
towards a work piece
506
at an angle of incidence &bgr; determined by the angle of the pivoting member
503
. This exemplary lighting system generally suffers the previously discussed limitations of the lighting system of the 163 patent if solid-state sources are used for the light-emitting elements
504
.
Furthermore,
FIG. 14
illustrates another characteristic of conventional adjustable lighting systems. Conventional lighting systems emit a beam of approximately circular cross-section from each light-emitting element. The beams may also be collimated or focused. However, when a beam of light is emitted at an angle of incidence &bgr;
1
which is not normal to the illuminated workpiece surface, an approximately oval-shaped or elliptical pattern is created on a planar work piece
506
with an illumination field
512
having edges at a given x
1
and y
1
distance from the center of the illumination field
512
, where x
1
is greater than y
1
.
Moreover, as the angle of incidence increases as shown by &bgr;
2
, when the beam intersects with a plane positioned along the optical axis
508
the distance y
1
of the illumination field
514
is approximately the same as y
1
of the illumination field
512
, while the distance x
2
of the illumination field
514
becomes longer than x
1
. Since the field of view along an optical system axis
508
is generally a circle centered about the optical axis, such elliptical illumination fields are not desirable for achieving the maximum illumination density for a given type of light-emitting element. For example, if the distance y
1
is set approximately at the edge of a circular field of view, the distance x
1
will extend beyond the edge of the field of view and a significant amount of available illumination energy will be wasted outside of the field of view.
Another exemplary solid-state lighting system is disclosed in U.S. Pat. No. 5,897,195 to Choate. The 195 patent discloses an oblique LED illuminator device with a cylindrical or truncated-conical array of LEDs. The array of LEDs produces collimated light beams that are directed onto axially-spaced, inclined surfaces formed on the outer periphery of a hollow, similarly-shaped Fresnel-like diffuser. The a
Mitutoyo Corporation
Sikder Mohammad
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