This patent application claims a benefit to the filing date of U.S. Provisional Patent Application Ser. No. 62/113,709 that was filed on Feb. 9, 2015 and is titled, “Automated Stent Inspection System.” The disclosure of U.S. 62/113,709 is incorporated by reference herein in its entirely.
(1) Field of the Disclosure
Disclosed herein is an optical inspection system utilizing a borescope effective to image the inner bore (or inside diameter) of a part under inspection. More particularly, various embodiments disclose systems to provide uniform lighting and fixed magnification to facilitate use of a computer-based vision system.
(2) Description of Related Art
A borescope is an optical device having a rigid or flexible tube with an eyepiece or video screen at one end and objective lens at the other end. An optical relay, that may be a series of lenses for a rigid tube and optical fibers for a flexible tube, conducts an image viewed at the objective lens to the eyepiece. Representative borescopes are disclosed in U.S. Pat. No. 6,333,812, “Borescope” by Rose et al. and in U.S. Pat. No. 9,074,868, “Automated Borescope Measurement Tip Accuracy Test,” by Bendall et al. Both U.S. Pat. No. 6,333,812 and U.S. Pat. No. 9,074,868 are incorporated by reference herein in their entirties.
Borescopes are commonly used to assess the quality of inner surfaces of a wide variety of industrial components. Such an inner surface may be the inside diameter of a through-hole structure, such as a pipe or a stent, or a blind bore structure, such as a cartridge case. Whether an eyepiece or a video screen is used to view the image, a person is typically required to perform an analysis and determine the surface quality of a component under inspection. One particularly important class of parts that require such inspections are small precision cylindrical components. Medical stents and rifle barrels are two exemplary members of this class. When the cylindrical component has a relatively large inner diameter, it is easier and more practical to insert a traditional camera and lens fully within the cylinder. When the cylindrical component has a relatively small inside diameter, nominally 12 millimeters or less, a borescope is preferred.
Rather than rely on an inspector's judgment, manufacturers of dimension critical components prefer to rely on the more consistent and reliable performance of a computer-based vision system to assure quality. However, current borescope inspection systems generally lack a means to automatically acquire and analyze a set of borescope generated images. Further, the lighting available with current borescopes generally creates too much glare and uneven illumination for machine vision algorithms to make measurements and find defects robustly.
Disclosed herein are borescopes and inspection systems useful with computer-based vision systems that do not suffer the shortcomings of previous devices and systems.
In accordance with a first embodiment, there is provided a borescope having an image conducting tube with a beamsplitter cube adjacent a distal end of the image conducting tube. This borescope is configured to view an inner surface of an object disposed adjacent a first side of the beamsplitter cube. The borescope has a light source effective to provide light illuminating the inner surface from an opposing second side of the beamsplitter cube.
In accordance with a second embodiment, there is provided a borescope configured to view an inner surface of an object under inspection. This borescope includes an image conducting tube with a reflector adjacent a distal end thereof and an outer tube circumscribing the image conducting tube. This outer tube is capable of independent rotation around the image conducting tube. The borescope further has a plurality of optical fibers forming a light conduit mounted to optics effective to transmit light from a proximal end of the image conducting tube to the distal end thereof, whereby the light exits through an annulus at the distal end. An input window of the light conduit is responsive in shape to collect light from the optical fibers and a motor is effective to rotate the outer tube, reflector and light conduit so as to acquire image data anywhere along 360 degrees of the inner diameter of the object.
The boroscopes may be used in an inspection system for imaging an inner surface of an object where at least a portion of the object has general rotational symmetry. The inspection system includes a source of illumination, a fixture configured to support the object, a rotary stage configured to support the fixture such that rotation of the rotary stage rotates the object about a central cylindrical axis of that portion of the object that is generally rotationally symmetric. A first digital camera and lens are capable of imaging an exterior surface of the object. A borescope has a reflector at its distal end. This reflector redirects a field of view of the borescope to capture a view of the inner surface of the object by a second digital camera located at a proximal end of the borescope. A motion controller collects encoder signals from the rotary stage and using those encoder signals calculates a set of rotary positions at which to trigger the first and second digital cameras to acquire image data. A computer is programmed to receive and process the image data and is also capable of one or more of displaying and performing quality analysis of the processed image data.
With reference to
The object under inspection is held in a fixture and rotated about its central cylindrical axis by a motorized rotary stage. A borescope is inserted into the object and images are captured sequentially by a digital camera as the object is rotated. A ninety degree (“right angle”) turning prism is affixed to an end of the borescope so that it images the inner wall surface of the generally cylindrical object. An encoder on the rotary stage may be used to trigger the digital camera at appropriate intervals. Each 360 degrees of rotation will create a strip of “unrolled” image. To then capture additional images along the length of the cylinder, a linear motion stage can be used to move the rotary stage holding the fixture and object under inspection iteratively with respect to the borescope until it is fully imaged.
In one preferred embodiment, the digital camera is a line scan camera and is aligned with the right angle prism enabling the camera to build up a line-by-line image of the inner surface. By choosing a line scan camera that acquires a thin line of part image parallel to the central axis of the cylinder, problems with imaging a curved object with a flat area camera sensor can be avoided. If a telecentric stop is placed between the set of relay lenses that comprise the main body of the borescope, the magnification of the taken image will be fixed. A fixed magnification supports better image-to-image strip alignment; especially important when the individual images taken at iterative steps along the x-axis need to be joined together to form a larger whole image that represents a full scan of the inner surface across 360 degrees. Slight rotational mechanical eccentricities of the holding fixture and the inherent lack of perfect cylindricality of typical real-world parts under inspection results in variable working distances of the part to the borescope. The telecentric stop avoids distortion artifacts that might otherwise be caused by changes in magnification. Furthermore machine vision analysis is most effective if the pixels being analyzed are all based on the same magnification.
A uniform illumination approach is achieved by using a beamsplitter cube in place of a simple mirror arrangement and bringing light to the object under inspection from the opposite side of the beamsplitter cube. In embodiments where the cylindrical component under inspection is not fully opaque, such as a medical stent, placing the light source outside the part under inspection and shining light towards the surface being imaged through the beamsplitter cube can create a uniformly illuminated image.
For a more common inspection requirement, where the object being inspected is a generally opaque cylindrical component, bright field illumination may be obtained by bringing light through fiber optics to the beamsplitter cube and driving that light into a light guide placed behind the beamsplitter cube. If the backside of the beamsplitter cube is rounded to conform to the shape of the borescope, a wider angle of bright field illumination coverage can be introduced. A configuration that brings light up and around the rounded beamsplitter cube as well as through the beamsplitter cube using either fiber optics or a clear silvered specially shaped optical manifold can achieve both bright field and dark field illumination in the same borescope. If a color camera is used and different colors of illumination are used for the bright field opposed to the dark field, then both types of image can be obtained and analyzed separately and simultaneously.
For situations where it is preferable to maintain the part being inspected stationary and instead rotate the borescope's field-of-view to create the image strips, the fiber optics can be cleaved right before the prism or beamsplitter cube and light can be transmitted across a precision annular slip ring. If the prism is mounted also on the slip ring it can rotate. A tubular member that transmits torque can be slidably positioned over the entire borescope and used to rotate the reflecting optics and the remaining end of the fiber optics on the other side of the slip ring as a unit. This tubular member that rotates can be rigid or flexible depending on the type of borescope it surrounds.
Application software running on the computer 80 allows a user to interact with the inspection system via a user interface 97 and specify, axially and rotationally, what areas of the object to image. The software is further configured to stitch together multiple image data of an inner surface or an outer surface enabling the computer to display a single unrolled view of the inner bore of the object.
Although the disclosed subject matter has been described and illustrated with respect to embodiments thereof, it should be understood by those skilled in the art that features of the disclosed embodiments can be combined, rearranged, etc., to produce additional embodiments within the scope of the invention, and that various other changes, omissions, and additions may be made therein and thereto, without parting from the spirit and scope of the present invention.
Number | Date | Country | |
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62113709 | Feb 2015 | US |