Patent Application
20100295939
The present invention relates to the fields of inspection, imaging and image analysis. More specifically, the present invention relates to an optical imaging system for material inspection and methods for using it.
Imaging apparatus comprising cameras, light sources and data analysis instruments are used in a variety of industries and applications, for both off-line and inline inspections. Current imaging systems typically have a downward looking camera and lighting to view an object positioned on a surface below the image sensor. Such systems have degraded performance for a variety of reasons and suffer from problems such as magnification variance, variant optical distortion and poor, uneven illumination.
Additionally, current systems incorporate cameras, optics, and lighting configured for specific objects and object sizes which generally require careful and repeatable placement and restraint of the object. Objects must be carefully arranged or held in a specific orientation and at a specific distance from the image sensor in order to obtain a clear, repeatable image with optimal illumination for accurate processing. Otherwise magnification changes, distortion variances across the field-of-view, and variant illumination will reduce measurement accuracies. Furthermore, many standard imaging systems are only capable of accommodating objects, and sample sets, having specific overall dimensions, thus requiring great care in sample preparation and requiring recalibration of the system for each object should optical magnification change. Consequently, current imaging systems are typically difficult to use and may be limited in their capability to capture consistent multiple views of an object or image multiple objects each having different dimensions or characteristics.
Some systems, such as those described in U.S. Patent Publication no. 2005/0278126 A1 (Rosakis), U.S. Pat. No. 5,361,308 (Lee) and U.S. Pat. No. 4,947,666 (Hametner et al.), do not provide for any means of minimizing optical variances and distortion inherent with reflected light vision systems, nor do these devices enable the unconstrained orientation of an object to be imaged.
Therefore there exists a need for a high resolution imaging and/or measurement and inspection system capable of mitigating and optimizing the effects of reflected and/or ambient light that does not constrain the orientation of an object to be imaged.
There is also a need for imaging and/or inspection systems that are easy to use, and are flexible for use in a variety of different ways.
The present invention relates to an imaging or inspection system that provides a high resolution image with minimal distortion that allows very accurate image reproduction and measurements of various aspects of an object imaged or inspected by the system. In one aspect, the invention comprises an imaging apparatus, a processor and housing. The imaging apparatus includes a camera, an object inspection site located substantially at the focus plane of the camera lens, a light source for lighting the object inspection site and means for controlling light.
In another aspect, the invention comprises an imaging apparatus having a resolution of about 0.1 mil to about 1 mil. The imaging apparatus comprises an object inspection site, a camera, a light source and means for controlling light.
In a third aspect, the invention comprises a method for using an imaging or inspection system comprising an imaging apparatus including an object inspection site, a camera, a light source, a processor and a means for controlling light. The method involves the steps of placing an object at the object inspection site, controlling light, imaging the object, transmitting the image to a processor and analyzing the image.
For illustrative purposes, the principles of the present invention are described by referencing various exemplary embodiments thereof. Although certain embodiments of the invention are specifically described herein, one of ordinary skill in the art will readily recognize that the same principles are equally applicable to, and can be employed in other apparatus and methods within the scope of the present invention. Before explaining the disclosed embodiments of the present invention in detail, it is to be understood that the invention is not limited in its application to the details of any particular embodiment shown. The terminology used herein is for the purpose of description and not of limitation. Further, although certain methods are described with reference to certain steps that are presented herein in certain order, in many instances, these steps may be performed in any order as may be appreciated by one skilled in the art, and the methods are not limited to the particular arrangement of steps disclosed herein.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are now described.
The present invention relates to an imaging system and to methods for its use. The system may be used, for example, to optically inspect an object, provide an enlarged image of an object, enable precise measurement of a feature of an object and/or analyze the geometry or curvature of an object surface or profile. The imaging system of the present invention is able to correct for optical distortion from reflected light and produce high contrast images with very uniform lighting. Furthermore, the imaging system is easy to use and does not require any special arrangement or handling of an object to be imaged.
As shown in
In an exemplary embodiment, to enhance the imaging capability of imaging apparatus 1, at least the interior surface of housing 4 is preferably fabricated from a substantially non-specular reflective material, and, more preferably, a completely diffuse reflective material. The interior surface of housing 4 is employed in the present invention to control a significant portion of the lighting that is employed to light the object to be imaged. This is accomplished by selecting an appropriate light reflective ability for the interior surface of housing 4 for a particular imaging task.
For example, in some embodiments, interior surface of housing 4 could be a white, reflective material to maximize light reflection from interior surface of housing 4. In other embodiments, interior surface of housing 4 can facilitate the provision of diffuse, even lighting to the object to be inspected. The ideal interior surface of housing 4 may depend on issues such as the need to minimize interference from object surface imperfections and to provide edge contrast, for example.
Shroud 3 may be used to cover an object to be imaged and object inspection site 5 in order to deflect or absorb ambient light that would otherwise illuminate object inspection site 5. Preferably, the edges of shroud 3 may extend over the sides of lower housing 4 completely covering object inspection site 5 and the object to be imaged. Shroud 3 blocks ambient light from reaching objection inspection site 5 and the object being imaged, which might otherwise degrade and reduce contrast of the resultant image. In an exemplary embodiment, an interior surface of shroud 3 may be fabricated from any substantially non-reflecting material, preferably a completely non-reflecting material. The use of a substantially or completely non-reflecting material for the interior surface of shroud 3 maximizes the contrast, particularly the edge contrast, of the object to be imaged with the background against which the object is imaged since the interior surface of shroud 3 forms the background against which the object is imaged. This provides a significant advantage of the present invention since the resolution and accuracy of image processing software is noticeably enhanced when the image initially provided to the software for processing is a high contrast image.
Suitable materials and/or coatings for housing 3, 4 are known to skilled persons. In the embodiment shown, housing 3, 4 is formed from a lower housing 4 and a shroud 3 which may be removed from, or adjusted relative to, lower housing 4 for placement of an object on the object inspection site 5. For imaging or inspection, shroud 3 may be located atop lower housing 4 to form a functional housing 3, 4 as described above.
Object inspection site 5 is located within housing 3, 4, preferably substantially at the location of a focus plane of camera 6. Object inspection site 5 may include any suitable object inspection site. In the embodiment of
The transparent surface of object inspection site 5 may have any suitable dimension that accommodates the object being imaged. Typically, the transparent surface is larger than the object area which is illuminated by the light source. Optionally, object inspection site 5 may also include a contoured surface area for cradling an object to be imaged or retention structures for retaining an object during imaging, such as fasteners, belts or clamps if it is desired to fix the object in a particular position for imaging or inspection.
In other embodiments, such as that shown in
A camera 6 is located within housing 4 and is oriented and placed so as to be focused on object inspection site 5. Preferably, camera 6 is rotationally aligned with object inspection site 5 to minimize reflection and to image the entire surface area. Camera 6 includes a lens 7 that is preferably pre-focused and locked on object inspection site 5 to eliminate the need to focus lens 7 each time a new object is placed on object inspection site 5. Mirrors or other optical devices may also be used to adjust the distance from lens 7 to the focus plane, if desired. This step of orienting and focus lens 7 relative to object inspection site 5 pre-calibrates imaging apparatus 1 so that high resolution images may be obtained regardless of the orientation of an object on object inspection site 5. Any camera, including digital cameras, analog cameras, color cameras and black and white cameras, and line scan cameras may be used in imaging apparatus 1. For purposes of this invention, a camera is defined as any device capable of capturing an image including any video recording device, such as camcorders.
Preferably, camera 6 is capable of achieving a minimum pixel resolution of about 1600 by 1200. Measurement accuracy is determined by camera resolution and the area of inspection site 5. For area scan cameras/sensors pixel resolutions from 640×480 to 4992×6668 are currently available, and line scan cameras/sensors from 512 to 12,000. The size of the image inspection site 5 is significant since smaller areas allow greater resolution with the same camera since more pixels can be devoted per unit area if a smaller area is viewed.
In addition, since the device of the present invention is able to provide one or more of a high contrast image and consistent edge fidelity, this enables the use of software to implement sub-pixel interpolation techniques which allow even greater image resolutions by imaging at a sub-pixel level. Without being bound by theory, it is believed that resolutions of as small as 1/25th of a pixel dimension may be possible using sub-pixel interpolation to process the image. Sub-pixel interpolation is a known method of image processing which interpolates information from the gray scale variant across an edge of the object image to provide sub-pixel accuracy for the image.
The device of the present invention provides consistent illumination and optical performance over the entire image inspection site thereby enabling use of sub-pixel interpolation with the object to be inspected located anywhere on the object inspection site 5. This makes the device easy to use since the operator merely needs to place the object at any location on object inspection site 5 without having to worry about locating the object at a very specific location to enhance the image.
As shown in
Imaging apparatus 1 of
In an exemplary embodiment, imaging apparatus 1 comprises a first polarizer 9 and a second polarizer 10 is located between lens 7 of camera 6 and object inspection site 5 to further minimize/remove reflection. In a preferred embodiment, each polarizer is a polymeric or glass material, more preferably, a polyimide or glass material. One adjustable polarizer may cover lens 7. One or both polarizers 9, 10 are oriented to minimize or eliminate reflection from the lower surface of object inspection area 5. Imaging apparatus 1 also includes at least one light source 8 capable of enabling imaging of an object placed at object inspection site 5. Light source 8 may be located anywhere within housing 4. In an exemplary embodiment, light source 8 surrounds lens 7, and the light is transmitted through a primary polarizer 10 to the transparent surface of the object inspection site 5. Any lighting, including visible, infrared, and ultraviolet lighting and dark field illumination, capable of providing a sufficient amount of light to the object inspection site 5 may be used. Preferably light source 8 produces highly diffuse light generated from LED and/or fluorescent bulbs. More preferably, light source 8 produces a diffuse light that is substantially uniform and minimizes localized reflections. Most preferably, the light source 8 is an LED array covered with a polymeric material, preferably frosted acrylic plexiglass that enhances the provision of uniform diffuse lighting.
In alternative embodiments, one of which is depicted in
In an exemplary embodiment, light source 8 has the same relative shape and size as inspection site 5 to enhance light intensity and evenness. Preferably, light source 8 may be customized to provide a uniform diffuse light over a desired portion of object inspection site 5, more preferably over the entire surface of object inspection site 5. Light source 8 may, in some embodiments, be located between lens 7 and object inspection site 5. In such a case, opening 15 is provided to allow light from object inspection site 5 to pass through light source 8 to lens 7, as shown in
If light source 8 is located below or behind lens 7, relative to the position of object inspection site 5, again an opening 15 may be provided in light source 8 such that light source 8 surrounds lens 7 since back-lighting of lens 7 would be of no value. Location of light source 8 between lens 7 and object inspection site 5 is preferred since camera 6 and/or lens 7 may interfere with light transmission from light source 8 to object inspection site 5 if light source 8 is located below or behind camera 6, relative to object inspection site 5. Preferably, light source 8 is located a sufficient distance from object inspection site 5 to ensure that the diffuse light fills in the void created by opening 15 in light source 8. Camera 6 may also include a shading correction to compensate for non-ideal light sources and lighting non-uniformity, if necessary.
Means for controlling light may include any one or more of the following options: the provision of a specific type of lighting, the positioning of one or more light sources, the shape(s) of the one or more light sources, the provision of multiple light sources, the provision of one or more polarizers, the adjustment of one or more polarizers, the light absorbance/reflective properties of an interior surface or portion of housing 4 and/or shroud 3, and the use of housing 3, 4 to minimize or prevent ambient light from reaching the interior of the housing. Also, means for controlling light may include software compensation by processor 2, for example, by calibration of the device prior to use. In one embodiment, a white surface or object may be located at object inspection site 5 and image processing may be done to compensate for any unevenness in the light observed on the white surface or object. This is possible since the lighting provided for imaging is a fixed quantity because this lighting is provided by consistent devices located within housing 3, 4 and not influenced by ambient lighting from outside housing 3, 4.
Camera 6 is enabled for transmission of data to processor 2, by suitable cabling or wireless connection. Processor 2 of the imaging system may be used to analyze and/or manipulate an image captured by camera 6. As required, processor 2 may also be capable of correcting distortions created by wide-angle camera lenses, correcting uneven lighting, displaying varying degrees of magnification of an imaged object, detecting defects on an imaged object, and/or precisely measuring one or more features of an imaged object.
The imaging system of the present invention may produce high field depth images and high resolution images of and has the capability to measure features to accuracies of from about 0.1 mil to about 5 mil, more preferably, about 0.5 mil to about 2.5 mil and most preferably, about 0.5 mil to about 1 mil. The imaging system of the present invention significantly improves on prior imaging technologies by producing consistent high fidelity and high contrast images. This is accomplished through providing a diffuse, even illumination while minimizing the amount of reflected and ambient light which permits a very high image resolution and precise measurement of features of an object. Without wishing to be bound by theory, the housing, alignment of the camera with respect to the object inspection site, the optional use of one or more polarizers, the provision of uniform diffuse lighting and substantially non-reflective shroud substantially reduces the amount of reflected and ambient light that causes optical distortions and degradations. These measures enable high-resolution imaging and accurate measurement of imaged objects.
In another aspect of the invention, the imaging system may be used to image an object. First an appropriate camera 6, lens 7 and light source 8 may be selected for each imaging application. Camera 6 may then be oriented and positioned with respect to object inspection site 5 to focus on an object. The distance from lens 7 of camera 6 to the object is controlled by inspection site 5. The optional polarizers may then be adjusted to minimize the amount of reflected light from object inspection site 5. This calibration of camera 6 enables high resolution imaging regardless of the placement or orientation of an object located on object inspection site 5. An object may then be randomly placed or dropped anywhere on or at object inspection site 5 in any orientation. Optionally, the object may be secured to object inspection site 5 using a retaining mechanism. Shroud 2 is preferably placed over the object and object inspection site 5 so that the sides of shroud 2 extend completely over the object and object inspection site 5 to minimize exposure to ambient light. Camera 6 may then be used to capture an image of the object, which may be transmitted to processor 2. The images may be remotely transmitted and subsequently analyzed. Alternatively, the images may be transmitted after camera 6 is connected to processor 2 with a cable, USB cord, wirelessly or any suitable connection. Processor 2 may be used to correct an optical distortion, correct for uneven lighting, enlarge the transmitted images, measure a feature of the transmitted images, compare a transmitted image with another image, determine the geometry or curvature of an imaged object from the transmitted image, and/or measure and identify any defects of an imaged object from the transmitted image. Additionally, the enclosure and shroud design inhibit dirt and dust contamination of optical surfaces greatly reducing the need for cleaning, while also minimizing physical contact with camera 6 and lens 7 thus reducing the need for recalibration. Positive air pressure may be applied internally to housing 3, 4 to further reduce optical contamination.
It is envisioned that the imaging system of the present invention may be useful for a number of applications that require magnification of an optical image or the precise measurement of a feature of an object with an accuracy equivalent to the resolution and image fidelity of the resultant image. In particular, the imaging system may be especially beneficial for determining the geometry of the surface of an object, enabling microscopic and enlarged analysis of an object, facilitating quality control inspection in manufacturing, inspecting construction materials and extruded products such as PVC piping, soft products (i.e. fabrics, papers, leathers), measuring particles, detecting counterfeit objects and analyzing fingerprints or assisting individuals who are visually impaired. Additionally, the imaging system may be configured as a table gauge for making measurements, configured to assist individuals who are vision impaired, or provide a high magnification image for visual assessment of objects such as gem stones for example.
In an alternative embodiment of the present invention, continuous measurement can be undertaken by moving objects across the object inspection site. Thus, for example, a suitable conveying apparatus can be associated with the device of the present invention to move objects across the object inspection site for continuous inspection. Also, one or more encoders could be employed for accurate positioning of an object on said object inspection site. This would permit, for example, comparison of the object to a database of objects or object parts. In this manner, objects could be identified, and additional information about objects could be obtained from a database based on identification of the object or a component part thereof, or edges of an object could be inspected or imaged.
Referring to
Thus, the embodiment of
Referring to
In a more preferred embodiment of
Referring to
In one embodiment, a line scan camera could be used to create an image of the entire surface as the device is moved relative to the object. In this instance, an encoder attached to rollers 40 or wheels may be used to control the readout of the line scan camera. In this embodiment, the entire object inspection site 5 can be covered by the object to be inspected in order to prevent ambient light from reaching lens 7.
The embodiment of
The device of the present invention may be employed for off-line measurement of objects, for example, to inspect parts or manufactured objects for quality control purposes or to identify defects. Alternatively, the device of the present invention may be used as part of a feedback control loop wherein measurements taken by the device are used to provide information used for feedback control of a device or process for manufacturing, machining or altering a part or object.
A device in accordance with
As a result, the device of the present invention was able to accurately measure the coating thicknesses of coatings applied to the PVC pipe to ensure that such coatings had been properly applied. Coating thickness measurement accuracies to within a few mils were easily achieved.
The device in accordance with
The device of the present invention, by virtue of its use of highly diffuse illumination, substantially eliminates the effects of surface textures and patterns on the leather from the image. It was found that certain types of defects in the leather could also be exposed by use of dark field illumination. Thus, the present device was demonstrated to be useful for leather inspection.
The device should be similarly useful for inspection of soft, flexible materials such as fabrics since distortion of the image is minimized by the fact that the object can be laid flat on the object inspection site 5. Characters and barcodes weaved within the material can efficiently be decoded via processor 2 due to the image consistency, evenness of illumination, and mitigation of distortion.
Additionally, the invention will be useful for particle sizing since particulates may be oriented and illuminated in an optimal manner for this purpose. Particle stacking is mitigated to a significant degree by the action of gravity at object inspection site 5 while sample preparation for measurement is easy to implement since the particles can be randomly placed within inspection area 5.
It is to be understood that although numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US09/31398 | 1/19/2009 | WO | 00 | 7/23/2010 |
| Number | Date | Country | |
|---|---|---|---|
| 61023929 | Jan 2008 | US |
