CA2413343A1 - Method and apparatus for testing optical components - Google Patents
Method and apparatus for testing optical components Download PDFInfo
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- CA2413343A1 CA2413343A1 CA002413343A CA2413343A CA2413343A1 CA 2413343 A1 CA2413343 A1 CA 2413343A1 CA 002413343 A CA002413343 A CA 002413343A CA 2413343 A CA2413343 A CA 2413343A CA 2413343 A1 CA2413343 A1 CA 2413343A1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/84—Systems specially adapted for particular applications
- G01N21/88—Investigating the presence of flaws or contamination
- G01N21/95—Investigating the presence of flaws or contamination characterised by the material or shape of the object to be examined
- G01N21/958—Inspecting transparent materials or objects, e.g. windscreens
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
- G01M11/02—Testing optical properties
- G01M11/0242—Testing optical properties by measuring geometrical properties or aberrations
- G01M11/0278—Detecting defects of the object to be tested, e.g. scratches or dust
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- Life Sciences & Earth Sciences (AREA)
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- Investigating Materials By The Use Of Optical Means Adapted For Particular Applications (AREA)
- Testing Of Optical Devices Or Fibers (AREA)
Description
METHOD AND APPARATUS FOR TESTING OPTICAL COMPONENTS
FIELD OF THE INVENTION
The present invention refers to the optical inspection and, particularly, to a method and apparatus for the automatic optical inspection of optical objects for cosmetic defects consisting of surface flaws and occlusions, which cause variations of their local optical properties.
BACKGROUND OF THE INVENTION
Optical components must be tested far defects prior to their utilization, particularly to for surfaces flaws such as scratches, smears, cracks, chips, stains, and for occlusions such as bubbles or streaks. Conventionally, the testing optical components is carried out by trained personnel by visual inspection. This approach is not quantitative in principle, and cannot be carried out objectively and reliably. The performance varies with different inspectors and with the same inspector from time to time.
I5 Efforts are being made to develop methods and devices for the automatic and objective testing of optical components. The following patents deal with subject matter: DE
3620146 {LTS 4,841,139); DE 3620108 (US 4,822,165); DE 3620129 (US 4,815,844);
DD
241120 (US 3,988,068); and UK 34851172 (US 3,892,494).
These have significant drawbacks. The proposed solutions in these patents are not 2o cost effective in the sense that they are too complex and slow for use in mass production lines.
Systems that utilize complex scanning means are too slow to inspect thousands of lenses per hour, as required in such lines.
Another group of patents dealing with the subject matter (US 6,075,591; US
5,627,638; US 5,438,405) is more cost effective and rapid, but they axe either less sensitive or 25 have non-sufficient resolution and/or defect orientation dependent sensitivity.
Significant problem for both groups of patents arises from sensitivity to various lens parameters. The lenses may be positive or negative, spherical, cylindrical or both, aspheric and progressive. Most solutions have difficulties in adapting to different batches of lenses that have different geometrical properties, using different illumination geometries for each batch, thus 3o consuming time in arranging the set up between batches.
Yet, a serious problem arises from illumination methodology itself, patents using light sources with characteristics that different in nature from the recommendation in the various optical standards, lead to differences in the defects appearance, thus causing a serious reliability
FIELD OF THE INVENTION
The present invention refers to the optical inspection and, particularly, to a method and apparatus for the automatic optical inspection of optical objects for cosmetic defects consisting of surface flaws and occlusions, which cause variations of their local optical properties.
BACKGROUND OF THE INVENTION
Optical components must be tested far defects prior to their utilization, particularly to for surfaces flaws such as scratches, smears, cracks, chips, stains, and for occlusions such as bubbles or streaks. Conventionally, the testing optical components is carried out by trained personnel by visual inspection. This approach is not quantitative in principle, and cannot be carried out objectively and reliably. The performance varies with different inspectors and with the same inspector from time to time.
I5 Efforts are being made to develop methods and devices for the automatic and objective testing of optical components. The following patents deal with subject matter: DE
3620146 {LTS 4,841,139); DE 3620108 (US 4,822,165); DE 3620129 (US 4,815,844);
DD
241120 (US 3,988,068); and UK 34851172 (US 3,892,494).
These have significant drawbacks. The proposed solutions in these patents are not 2o cost effective in the sense that they are too complex and slow for use in mass production lines.
Systems that utilize complex scanning means are too slow to inspect thousands of lenses per hour, as required in such lines.
Another group of patents dealing with the subject matter (US 6,075,591; US
5,627,638; US 5,438,405) is more cost effective and rapid, but they axe either less sensitive or 25 have non-sufficient resolution and/or defect orientation dependent sensitivity.
Significant problem for both groups of patents arises from sensitivity to various lens parameters. The lenses may be positive or negative, spherical, cylindrical or both, aspheric and progressive. Most solutions have difficulties in adapting to different batches of lenses that have different geometrical properties, using different illumination geometries for each batch, thus 3o consuming time in arranging the set up between batches.
Yet, a serious problem arises from illumination methodology itself, patents using light sources with characteristics that different in nature from the recommendation in the various optical standards, lead to differences in the defects appearance, thus causing a serious reliability
-2-problem by producing artifacts that are not detectable in the standard procedures. The main problem of the existing patents dealing with automated inspection in mass production lines is a lack of reliable detection of light scattered by defects at small angles, as required by recommendation in the various optical standards. Furthermore some of the illumination methods s are sensitive to different defect locations and orientations causing difficulties in simultaneously detecting defects in both surfaces and inside the lens and therefore resulting in non-homogeneous yield.
The present invention overcomes these difficulties and shortcomings of the said previous patents.
1o SUMMARY OF THE INVENTION
It is the object of the present invention to provide a new method and apparatus for the inspection of optical objects for cosmetic defects consisting of surface flaws and occlusions, in which the disadvantages of the above prior art are substantially reduced or overcome. The 15 system can be used in mass production and gives rapid and reliable results.
Means are advantageously provided for the automatic evaluation of the test results and for grading of the optical components.
Other purposes and advantages of the invention will become apparent; as the description proceeds.
2o In accordance with one aspect of the present invention, there is provided a method for the inspection of an optical object for the existence therein of cosmetic defects, said method comprising:
providing diverging beams of inspection radiation and directing said beams on said optical object so that each point thereof is illuminated by set of rays at a variety of angles having 25 nearly axial symmetry;
projecting said beams through said optical object on a retro reflecting screen and obtaining thereby a retro reflected rays traveling back along the same optical paths to said optical object, illuminating, if any, said cosmetic defects being distinguishable owing to the light scattering by said cosmetic defects, and emerging from said optical object;
3o blocking non-scattered part of said retro reflected radiation to prevent its detection;
monitoring a radiation scattered at small tangential angles by said defects and obtaining thereby a dark field image of said optical object; and detecting and analyzing said dark field image of said optical object..
In accordance with another aspect of the present invention, there is provided an ~. a " . . ~ . . _. ..M~,~... ~. ,.. ~~~r~p~. ~ . .~..,,.~.M .,w t . :
~~.a,~.~~.:. . ~. :.a,~,AF ~r _.".m. .,
The present invention overcomes these difficulties and shortcomings of the said previous patents.
1o SUMMARY OF THE INVENTION
It is the object of the present invention to provide a new method and apparatus for the inspection of optical objects for cosmetic defects consisting of surface flaws and occlusions, in which the disadvantages of the above prior art are substantially reduced or overcome. The 15 system can be used in mass production and gives rapid and reliable results.
Means are advantageously provided for the automatic evaluation of the test results and for grading of the optical components.
Other purposes and advantages of the invention will become apparent; as the description proceeds.
2o In accordance with one aspect of the present invention, there is provided a method for the inspection of an optical object for the existence therein of cosmetic defects, said method comprising:
providing diverging beams of inspection radiation and directing said beams on said optical object so that each point thereof is illuminated by set of rays at a variety of angles having 25 nearly axial symmetry;
projecting said beams through said optical object on a retro reflecting screen and obtaining thereby a retro reflected rays traveling back along the same optical paths to said optical object, illuminating, if any, said cosmetic defects being distinguishable owing to the light scattering by said cosmetic defects, and emerging from said optical object;
3o blocking non-scattered part of said retro reflected radiation to prevent its detection;
monitoring a radiation scattered at small tangential angles by said defects and obtaining thereby a dark field image of said optical object; and detecting and analyzing said dark field image of said optical object..
In accordance with another aspect of the present invention, there is provided an ~. a " . . ~ . . _. ..M~,~... ~. ,.. ~~~r~p~. ~ . .~..,,.~.M .,w t . :
~~.a,~.~~.:. . ~. :.a,~,AF ~r _.".m. .,
-3-apparatus for the inspection of optical objects for the existence of cosmetic defects comprising:
ring illumination means for providing diverging beams of inspection radiation and for the illumination of said optical object thereby so that each point thereof is illuminated by set of rays at a variety of angles having nearly axial symmetry, and projecting said beams through s said optical object onto a retro reflecting screen and obtaining thereby a retro refle<;ted rays traveling back along the same optical paths doing said optical cosmetic defects being distinguishable owing to the light scattering by said cosmetic defects at small angles;
imaging means for forming dark field image of said optical object in such a manner that the rays scattered by said defects at small tangential angles form said image ; and 1 o image detecting means and image processing means for analyzing said dark field image of said optical object for said cosmetic defects.
Preferably, the illumination means is a ring or annular source of radiation.
Preferably, the diameter of the central non-radiating area of said ring illumination means exceeds an entrance pupil of said imaging means.
1 s Preferably, the image detecting means is in the form of a scanning photodetector or rather in the form of a mufti-element detector capable of measuring the brightness distribution in the dark field image. Preferably, it is a high resolution TV camera.
Preferably, the retro-reflecting screen is in the form of an array of micro lenses or micro spheres followed by reflective surface, or rather micro corner cube array.
2o The present invention ensures that the retro reflected rays of illuminating radiation propagate back to illuminating means along the same optical path as the incident rays illuminating the optical object, providing an illumination of each point of the optical object with a plurality of rays with angles close to an observation angle without any dependence on the optical power of the optical object. 'The consequence of such an arrangement is the possibility to 2s image and detect, in a power-independent manner, radiation scattered back and forward at small angles without risk of detecting non-scattered radiation by the imaging branch of the inspection system. Thereby, dark field image of different objects may be captured by one pre-set imaging device, which renders the method and the apparatus of the present invention particularly suitable for automated quality control.
3o Depending on the type of the inspected optical object, the apparatus according to the present invention may comprise means for collimating illumination radiation and means allowing bringing illuminating and imaging branches of the system in optical coincidence.
In an alternative embodiment, the illuminating means and imaging and detecting
ring illumination means for providing diverging beams of inspection radiation and for the illumination of said optical object thereby so that each point thereof is illuminated by set of rays at a variety of angles having nearly axial symmetry, and projecting said beams through s said optical object onto a retro reflecting screen and obtaining thereby a retro refle<;ted rays traveling back along the same optical paths doing said optical cosmetic defects being distinguishable owing to the light scattering by said cosmetic defects at small angles;
imaging means for forming dark field image of said optical object in such a manner that the rays scattered by said defects at small tangential angles form said image ; and 1 o image detecting means and image processing means for analyzing said dark field image of said optical object for said cosmetic defects.
Preferably, the illumination means is a ring or annular source of radiation.
Preferably, the diameter of the central non-radiating area of said ring illumination means exceeds an entrance pupil of said imaging means.
1 s Preferably, the image detecting means is in the form of a scanning photodetector or rather in the form of a mufti-element detector capable of measuring the brightness distribution in the dark field image. Preferably, it is a high resolution TV camera.
Preferably, the retro-reflecting screen is in the form of an array of micro lenses or micro spheres followed by reflective surface, or rather micro corner cube array.
2o The present invention ensures that the retro reflected rays of illuminating radiation propagate back to illuminating means along the same optical path as the incident rays illuminating the optical object, providing an illumination of each point of the optical object with a plurality of rays with angles close to an observation angle without any dependence on the optical power of the optical object. 'The consequence of such an arrangement is the possibility to 2s image and detect, in a power-independent manner, radiation scattered back and forward at small angles without risk of detecting non-scattered radiation by the imaging branch of the inspection system. Thereby, dark field image of different objects may be captured by one pre-set imaging device, which renders the method and the apparatus of the present invention particularly suitable for automated quality control.
3o Depending on the type of the inspected optical object, the apparatus according to the present invention may comprise means for collimating illumination radiation and means allowing bringing illuminating and imaging branches of the system in optical coincidence.
In an alternative embodiment, the illuminating means and imaging and detecting
-4-means may be interchanged such. that the illuminating means is in the form of a small size source of radiation, and the imaging and detecting means has an annular aperture of the imaging lens.
The apparatus also comprises a straight light stop for preventing detection of non-scattered radiation, a retro reflecting screen, a beam-deflecting element, which couples illuminating and imaging branches of the apparatus and image processing means.
Preferably, the illuminating means is in the form of a small size source of radiation of any design providing a suitable illumination of the optical object along an optical axis. It is desirable that the source of radiation has dimensions less than diameter of the straight light stop, 1 o whereby only radiation scattered to small tangential angles radiation may be imaged.
Preferably, the beam-deflating element is a beam-splitter of any suitable type, the imaging and detecting means is in the form of a CCD or CMOS camera with an imaging lens having a large annular aperture.
Preferably, the straight light stop is in the form of a black or mirrored target placed is on the optical axis of the camera. lens. The light stop and exit pupil of the source of radiation are spaced from the beam-deflecting element at the same distances. Thereby, the straight light stop is brought into the optical coincidence with the point source of radiation.
That is all the rays of non-scattered retro reflected radiation arrive at the light stop and are blocked by it. Thus only rays of the radiation scattered at small tangential angles by defects and occlusions arrive to the 20 aperture of the imaging lens and may be detected.
The method and apparatus according to the present invention may be used for the inspection of both transparent phase objects and specular objects having at least one reflecting surface. Both the transparent and the specular objects may have curved and flat shapes and may be in the form of optical elements or in the foxrn of a sheet material translated linearly and 25 transversely to the direction of the radiation propagation. The method and the apparatus of the present invention may be used not only for the detection and analysis of cosmetic defects of optical objects, but also for detection of bifocal segments and engraving marks, made by lens manufacturers and determining an orientation of ophthalmic lenses.
BRIEF DESCRIPTION OF THE DRAWINGS
3o Embodiments of the invention will now be described by way of example only, with reference to the following drawings in which:
Fig. 1 is a schematic illustration of a principal embodiment of an apparatus according to .. . .,~ ,.~,. .f~ ~ .. . ~..~..v ~. ,,,... N. . $ r , . ,a .~,~. ~ r. aT =
The apparatus also comprises a straight light stop for preventing detection of non-scattered radiation, a retro reflecting screen, a beam-deflecting element, which couples illuminating and imaging branches of the apparatus and image processing means.
Preferably, the illuminating means is in the form of a small size source of radiation of any design providing a suitable illumination of the optical object along an optical axis. It is desirable that the source of radiation has dimensions less than diameter of the straight light stop, 1 o whereby only radiation scattered to small tangential angles radiation may be imaged.
Preferably, the beam-deflating element is a beam-splitter of any suitable type, the imaging and detecting means is in the form of a CCD or CMOS camera with an imaging lens having a large annular aperture.
Preferably, the straight light stop is in the form of a black or mirrored target placed is on the optical axis of the camera. lens. The light stop and exit pupil of the source of radiation are spaced from the beam-deflecting element at the same distances. Thereby, the straight light stop is brought into the optical coincidence with the point source of radiation.
That is all the rays of non-scattered retro reflected radiation arrive at the light stop and are blocked by it. Thus only rays of the radiation scattered at small tangential angles by defects and occlusions arrive to the 20 aperture of the imaging lens and may be detected.
The method and apparatus according to the present invention may be used for the inspection of both transparent phase objects and specular objects having at least one reflecting surface. Both the transparent and the specular objects may have curved and flat shapes and may be in the form of optical elements or in the foxrn of a sheet material translated linearly and 25 transversely to the direction of the radiation propagation. The method and the apparatus of the present invention may be used not only for the detection and analysis of cosmetic defects of optical objects, but also for detection of bifocal segments and engraving marks, made by lens manufacturers and determining an orientation of ophthalmic lenses.
BRIEF DESCRIPTION OF THE DRAWINGS
3o Embodiments of the invention will now be described by way of example only, with reference to the following drawings in which:
Fig. 1 is a schematic illustration of a principal embodiment of an apparatus according to .. . .,~ ,.~,. .f~ ~ .. . ~..~..v ~. ,,,... N. . $ r , . ,a .~,~. ~ r. aT =
-5-the present invention;
Figs. 2, 3 and 4 illustrate different embodiments of the apparatus shown in Fig. 1;
Figs. 5 illustrates a principle of defect detection by means of an optical setup according to the present invention;
Fig. 6 illustrates dark field image obtained in accordance with the present invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
In the further description the term "tangential angle" means an angle between the optical axis and a ray in the plane in which the optical axis lies, the term "azimuth angle" means an angle in a plane perpendicular to the optical axis. The term "cosmetic defects" means surface to flaws and occlusions, such as scratch, crack, dig, chip, inclusion, bubble, etc., which cause light scattering and/or variations of local optical properties of the component.
Fig. 1 schematically illustrates a principal embodiment of an apparatus for optical inspection of an optical object A1 for the existence of cosmetic defects andlor occlusions in its bulk or on its surfaces, such as for example defects D l and D2.
As seen, the apparatus comprises illumination means 1 in the form of a ring source of radiation for the illumination of the optical object A1 with a plurality of diverging incident radiation beams, a retro reflecting screen 2 on which the optical object A1 projects the incident radiation beams, imaging and detecting means 3 for the observation of the optical object A1 and the det~tion of the scattered by the optical object A1 illuminating and retro reflected radiation, 2o and image processing means 7 for tile analysis of the image. .
The imaging and detecting means 3 of the apparatus is in the form a scanning photodetector or rather in the form of a TV camera 8, such as, for example, CCD or CMOS
camera, with an imaging lens 9 having a large aperture. The camera 8 is disposed on the optical axis of the apparatus. It is desirable that the TV camera has a high resolution.
The illumination means 1 may be in the form of a fiber optic ring light guide connected to a light source of any suitable type, a fluorescent ring lamp or ring illuminator comprising multiple miniature light sources such as LED's or filament lamps.
The ring illumination means is mounted coaxially with imaging and detecting means 3 and providing nearly coaxial illumination of the optical object Al. The ring light source 1 may be mounted 3o close to the plane of entrance pupil of camera. Pens 9 or at some distance from it along the apparatus optical axis. In the last case the ring light source is to be mounted without screening
Figs. 2, 3 and 4 illustrate different embodiments of the apparatus shown in Fig. 1;
Figs. 5 illustrates a principle of defect detection by means of an optical setup according to the present invention;
Fig. 6 illustrates dark field image obtained in accordance with the present invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
In the further description the term "tangential angle" means an angle between the optical axis and a ray in the plane in which the optical axis lies, the term "azimuth angle" means an angle in a plane perpendicular to the optical axis. The term "cosmetic defects" means surface to flaws and occlusions, such as scratch, crack, dig, chip, inclusion, bubble, etc., which cause light scattering and/or variations of local optical properties of the component.
Fig. 1 schematically illustrates a principal embodiment of an apparatus for optical inspection of an optical object A1 for the existence of cosmetic defects andlor occlusions in its bulk or on its surfaces, such as for example defects D l and D2.
As seen, the apparatus comprises illumination means 1 in the form of a ring source of radiation for the illumination of the optical object A1 with a plurality of diverging incident radiation beams, a retro reflecting screen 2 on which the optical object A1 projects the incident radiation beams, imaging and detecting means 3 for the observation of the optical object A1 and the det~tion of the scattered by the optical object A1 illuminating and retro reflected radiation, 2o and image processing means 7 for tile analysis of the image. .
The imaging and detecting means 3 of the apparatus is in the form a scanning photodetector or rather in the form of a TV camera 8, such as, for example, CCD or CMOS
camera, with an imaging lens 9 having a large aperture. The camera 8 is disposed on the optical axis of the apparatus. It is desirable that the TV camera has a high resolution.
The illumination means 1 may be in the form of a fiber optic ring light guide connected to a light source of any suitable type, a fluorescent ring lamp or ring illuminator comprising multiple miniature light sources such as LED's or filament lamps.
The ring illumination means is mounted coaxially with imaging and detecting means 3 and providing nearly coaxial illumination of the optical object Al. The ring light source 1 may be mounted 3o close to the plane of entrance pupil of camera. Pens 9 or at some distance from it along the apparatus optical axis. In the last case the ring light source is to be mounted without screening
-6-the optical object Al i.e. to be out of a field of view of the imaging means 3.
The retro reflecting screen 2 may be in the form of a micro lens array followed by mirrored/diffusive reflector or micro sphere array on a white background or rather corner cube microstructure such as, for example, described in G. W. Neudeck et al, Precision crystal corner cube arrays for optical grating formed by (100) silicon planes with selective epitaxial growth, App. Opt. 35, 3466-3470, 1996.
The image processing means 7 comprises a computer to which the image is transferred via a frame grabber 10 and which is provided with dedicated software for the analysis of the defects, including the determination of their location, dimensions and types.
1o Monitoring and analyzing systems associated with the computer may be of any suitable type.
In operation, the illuminating radiation from the illuminating means 1 is directed to the optical object A1 travels through said element to the retro-reflecting screen 2, is retro-reflected by the screen 2 toward the optical abject providing each point of the optical object with nearly coaxial wide azimuth angle illumination, and travels through it, so that the reflected rays propagate back to the ring light source 1 along the same optical paths as the incident rays illuminating the optical object as shown in FIG. 5. Thus the illuminating radiation being retro reflected provides illumination of each point of the optical object at angles close to observation angle and the non-scattered part of the retro reflected radiation can't reach entrance aperture of the imaging and detecting means 3.
2o Whenever illuminating radiation meets any single defect or occlusion DI in the component A1, it will be scattered by the defect forward and back to form rays, which emerge from the optical object at any angles to undisturbed rays. Part of the rays of the scattered radiation pass to the aperture of camera lens 9, such as the ones schematically indicated as S 1 and S2 in Fig. 1. 'Thus only rays of the light scattered by defects and occlusions at small. angles to initial propagation directions arrive to camera lens aperture and may be detected by TV
camera. 8. This is illustrated in FIG. 5, which shows bundle of original rays a, b and retro reflected rays a', b' providing an illumination of small part of the optical object A1 containing cosmetic defect D, bundle of rays c, which is part of radiation from a, a', b and b' scattered by D
toward the aperture of the camera lens 9 and bundle of rays c' scattered by D
and being detected 3o after retro reflection by screen 2.
The TV camera 8 images the optical object A1 providing its dark field image.
The image is transferred in digital form to the image processing means including computer 7, where it is processed by means of dedicated software for detection of optical object cosmetic defects,
The retro reflecting screen 2 may be in the form of a micro lens array followed by mirrored/diffusive reflector or micro sphere array on a white background or rather corner cube microstructure such as, for example, described in G. W. Neudeck et al, Precision crystal corner cube arrays for optical grating formed by (100) silicon planes with selective epitaxial growth, App. Opt. 35, 3466-3470, 1996.
The image processing means 7 comprises a computer to which the image is transferred via a frame grabber 10 and which is provided with dedicated software for the analysis of the defects, including the determination of their location, dimensions and types.
1o Monitoring and analyzing systems associated with the computer may be of any suitable type.
In operation, the illuminating radiation from the illuminating means 1 is directed to the optical object A1 travels through said element to the retro-reflecting screen 2, is retro-reflected by the screen 2 toward the optical abject providing each point of the optical object with nearly coaxial wide azimuth angle illumination, and travels through it, so that the reflected rays propagate back to the ring light source 1 along the same optical paths as the incident rays illuminating the optical object as shown in FIG. 5. Thus the illuminating radiation being retro reflected provides illumination of each point of the optical object at angles close to observation angle and the non-scattered part of the retro reflected radiation can't reach entrance aperture of the imaging and detecting means 3.
2o Whenever illuminating radiation meets any single defect or occlusion DI in the component A1, it will be scattered by the defect forward and back to form rays, which emerge from the optical object at any angles to undisturbed rays. Part of the rays of the scattered radiation pass to the aperture of camera lens 9, such as the ones schematically indicated as S 1 and S2 in Fig. 1. 'Thus only rays of the light scattered by defects and occlusions at small. angles to initial propagation directions arrive to camera lens aperture and may be detected by TV
camera. 8. This is illustrated in FIG. 5, which shows bundle of original rays a, b and retro reflected rays a', b' providing an illumination of small part of the optical object A1 containing cosmetic defect D, bundle of rays c, which is part of radiation from a, a', b and b' scattered by D
toward the aperture of the camera lens 9 and bundle of rays c' scattered by D
and being detected 3o after retro reflection by screen 2.
The TV camera 8 images the optical object A1 providing its dark field image.
The image is transferred in digital form to the image processing means including computer 7, where it is processed by means of dedicated software for detection of optical object cosmetic defects,
-7-their classification and measurement.
Fig. 2 to 4 illustrate different embodiments of the apparatus of the present invention.
An apparatus according to the embodiment of Fig. 2 has the illumination means in the form of a small size source of radiation 21 for the illumination of the optical object A2 with s a diverging incident radiation beam, a retro reflecting screen 22 on which the optical object A2 projects the incident radiation beam, imaging and detecting means 23 with a straight light stop 24 for the observation of the optical object A2 and the detection of the scattered by defects of the optical object A2 retro reflected radiation, and image processing means 27 for the analysis of the image. The apparatus also comprises a beam-deflecting element 25, which directs the incident 1o beam towards the inspected object A1, and which passes the retro reflected and the imaging rays towards the imaging means 23.
The apparatus also may include a positive lens 26, which decreases divergence of the incident illuminating beam and which projects the retro reflected beam while focusing it onto light stop element 24 and forms in combination with the camera lens 29 a telecentric lens 15 for imaging the inspected optical object A2.
The illumination means 21 is in the form of a small size source of radiation of any design providing suitable, preferably wide, divergence of radiation illuminating the optical object A2 along an optical axis. It is desirable that the source of radiation has dimensions less than diameter of the straight light stop 24, whereby only radiation scattered to small tangential 2o angles may be imaged. Fig. 2 illushates possible design of the illumination means 21 in the form of a unit consisting of a source of radiation 11 which may be an arc or filament lamp, a focusing optics 12, a concave mirror 13 and a pinhole 14, which in fact represents a point-like exit of the source of radiation 21. An alternative design of the illuminating means 21 may comprise a laser followed by a focusing or defocusing optics of any design.
2s The beam-deflecting element 25 is, preferably, a bean-splitter of any suitable type.
Thus, the beam-deflecting element .25 may be in the form of an ordinary semi transparent mirror or it may rather be designed as a polarizing beam-splitter followed by a ~/4 retarding plate.
The imaging and detecting means 23 of the apparatus is in the form of a CCD
camera 28 with an imaging lens 29 having a large annular aperture. The strait light stop 24 in the 3o form of a black or mirrored target is placed on the optical axis of the camera lens. The camera 28 is disposed on the apparatus optical axis so that the light stop 24 in the pupil of the lens 29 is spaced from the beam-deflecting element 25 at the same distance as the point source of radiation 21. Thereby, the straight light stop 24 is brought into the optical coincidence with the point _g-source of radiation, i.e. all the rays of non-scattered retro reflected illuminating radiation arrive to the light stop 24 and are blocked by it. Thus, similarly to the embodiment of Fig. 1, only rays of the light scattered at small tangential angles by defects and occlusions arrive to the annular aperture of the camera lens 29 and may be detected by TV camera 28.
Fig. 3 illustrates an apparatus according to the present invention, designed for the inspection of specular objects. The illumination means of the apparatus of Fig. 3, comprise a point source of radiation 31 and a positive lens 36 providing a collimated beam for the illumination of an inspected optical object A3 having a reflective surface and projecting the illuminating radiation on a retro-reflecting screen 32. T'he imaging and detecting means 33 of the 1o apparatus include an imaging lens 39 having an annular aperture and a straight light stop 34.
Fig. 4 illustrates an apparatus according to the present invention with an alternative optical setup. In this case, an apparatus has an illumination means in the form of a ring source of radiation 41 with a diameter of the central non-radiating area more than lens aperture of an imaging means 43. The apparatus also comprises a beam-deflecting element 45, which directs the incident beam towards the inspects object A4, and which passes the retro reflected and the imaging rays towards the imaging means 43. Fig. 4 also illustrates the configuration in which an element 40 is used in the imaging branch of the apparatus, to bring the image 48' of a camera 48 into the optical coincidence with the unit 41. if required, a similar element may be used in the illumination branch of the apparatus.
2o Fig. 6 illustrates dark field image obtained at small scattering angles in accordance with the present invention. As seen, in the image the lens defects have a high contrast and may be easily detectable as well as the shapes and the disposition of the defects therein may be found.
The method of the present invention and the apparatus may have features, which may differ, within the scope of the invention, from the features described above and shown in the drawings.
Fig. 2 to 4 illustrate different embodiments of the apparatus of the present invention.
An apparatus according to the embodiment of Fig. 2 has the illumination means in the form of a small size source of radiation 21 for the illumination of the optical object A2 with s a diverging incident radiation beam, a retro reflecting screen 22 on which the optical object A2 projects the incident radiation beam, imaging and detecting means 23 with a straight light stop 24 for the observation of the optical object A2 and the detection of the scattered by defects of the optical object A2 retro reflected radiation, and image processing means 27 for the analysis of the image. The apparatus also comprises a beam-deflecting element 25, which directs the incident 1o beam towards the inspected object A1, and which passes the retro reflected and the imaging rays towards the imaging means 23.
The apparatus also may include a positive lens 26, which decreases divergence of the incident illuminating beam and which projects the retro reflected beam while focusing it onto light stop element 24 and forms in combination with the camera lens 29 a telecentric lens 15 for imaging the inspected optical object A2.
The illumination means 21 is in the form of a small size source of radiation of any design providing suitable, preferably wide, divergence of radiation illuminating the optical object A2 along an optical axis. It is desirable that the source of radiation has dimensions less than diameter of the straight light stop 24, whereby only radiation scattered to small tangential 2o angles may be imaged. Fig. 2 illushates possible design of the illumination means 21 in the form of a unit consisting of a source of radiation 11 which may be an arc or filament lamp, a focusing optics 12, a concave mirror 13 and a pinhole 14, which in fact represents a point-like exit of the source of radiation 21. An alternative design of the illuminating means 21 may comprise a laser followed by a focusing or defocusing optics of any design.
2s The beam-deflecting element 25 is, preferably, a bean-splitter of any suitable type.
Thus, the beam-deflecting element .25 may be in the form of an ordinary semi transparent mirror or it may rather be designed as a polarizing beam-splitter followed by a ~/4 retarding plate.
The imaging and detecting means 23 of the apparatus is in the form of a CCD
camera 28 with an imaging lens 29 having a large annular aperture. The strait light stop 24 in the 3o form of a black or mirrored target is placed on the optical axis of the camera lens. The camera 28 is disposed on the apparatus optical axis so that the light stop 24 in the pupil of the lens 29 is spaced from the beam-deflecting element 25 at the same distance as the point source of radiation 21. Thereby, the straight light stop 24 is brought into the optical coincidence with the point _g-source of radiation, i.e. all the rays of non-scattered retro reflected illuminating radiation arrive to the light stop 24 and are blocked by it. Thus, similarly to the embodiment of Fig. 1, only rays of the light scattered at small tangential angles by defects and occlusions arrive to the annular aperture of the camera lens 29 and may be detected by TV camera 28.
Fig. 3 illustrates an apparatus according to the present invention, designed for the inspection of specular objects. The illumination means of the apparatus of Fig. 3, comprise a point source of radiation 31 and a positive lens 36 providing a collimated beam for the illumination of an inspected optical object A3 having a reflective surface and projecting the illuminating radiation on a retro-reflecting screen 32. T'he imaging and detecting means 33 of the 1o apparatus include an imaging lens 39 having an annular aperture and a straight light stop 34.
Fig. 4 illustrates an apparatus according to the present invention with an alternative optical setup. In this case, an apparatus has an illumination means in the form of a ring source of radiation 41 with a diameter of the central non-radiating area more than lens aperture of an imaging means 43. The apparatus also comprises a beam-deflecting element 45, which directs the incident beam towards the inspects object A4, and which passes the retro reflected and the imaging rays towards the imaging means 43. Fig. 4 also illustrates the configuration in which an element 40 is used in the imaging branch of the apparatus, to bring the image 48' of a camera 48 into the optical coincidence with the unit 41. if required, a similar element may be used in the illumination branch of the apparatus.
2o Fig. 6 illustrates dark field image obtained at small scattering angles in accordance with the present invention. As seen, in the image the lens defects have a high contrast and may be easily detectable as well as the shapes and the disposition of the defects therein may be found.
The method of the present invention and the apparatus may have features, which may differ, within the scope of the invention, from the features described above and shown in the drawings.
Claims
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002413343A CA2413343A1 (en) | 2002-12-02 | 2002-12-02 | Method and apparatus for testing optical components |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002413343A CA2413343A1 (en) | 2002-12-02 | 2002-12-02 | Method and apparatus for testing optical components |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2413343A1 true CA2413343A1 (en) | 2004-06-02 |
Family
ID=32476989
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002413343A Abandoned CA2413343A1 (en) | 2002-12-02 | 2002-12-02 | Method and apparatus for testing optical components |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2413343A1 (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2239552A4 (en) * | 2007-12-26 | 2015-07-08 | Hoya Corp | Image picking-up device for lens |
| WO2017046340A1 (en) * | 2015-09-17 | 2017-03-23 | Carl Zeiss Vision International Gmbh | Device and method for visualizing a mark on a spectacle lens |
| CN114136440A (en) * | 2021-10-29 | 2022-03-04 | 交通运输部公路科学研究所 | Portable retroreflection luminosity and chromaticity combined measurement method and device |
| WO2022162532A1 (en) * | 2021-01-26 | 2022-08-04 | Alcon Inc. | Method for the inspection of an ophthalmic lens for semi-opaque defects |
-
2002
- 2002-12-02 CA CA002413343A patent/CA2413343A1/en not_active Abandoned
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2239552A4 (en) * | 2007-12-26 | 2015-07-08 | Hoya Corp | Image picking-up device for lens |
| WO2017046340A1 (en) * | 2015-09-17 | 2017-03-23 | Carl Zeiss Vision International Gmbh | Device and method for visualizing a mark on a spectacle lens |
| WO2022162532A1 (en) * | 2021-01-26 | 2022-08-04 | Alcon Inc. | Method for the inspection of an ophthalmic lens for semi-opaque defects |
| CN114136440A (en) * | 2021-10-29 | 2022-03-04 | 交通运输部公路科学研究所 | Portable retroreflection luminosity and chromaticity combined measurement method and device |
| CN114136440B (en) * | 2021-10-29 | 2023-09-08 | 交通运输部公路科学研究所 | Portable retroreflection luminosity and chromaticity combined measurement method and device |
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Legal Events
| Date | Code | Title | Description |
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| FZDE | Discontinued | ||
| FZDE | Discontinued |
Effective date: 20050630 |