Television – Special applications – With endoscope
Reexamination Certificate
2002-08-21
2004-10-19
Kelley, Chris (Department: 2613)
Television
Special applications
With endoscope
Reexamination Certificate
active
06806899
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT
(Not Applicable)
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to optical metrology, and particularly to the problem of making accurate non-contact dimensional measurements of objects that are viewed through an endoscope.
2. Description of Related Art
2a. Perspective dimensional measurements with endoscopes
In the past several decades, the use of optical endoscopes has become common for the visual inspection of inaccessible objects, such as the internal organs of the human body or the internal parts of machinery. These visual inspections are performed in order to assess the need for surgery or equipment tear down and repair; thus the results of the inspections are accorded a great deal of importance. Accordingly, there has been much effort to improve the art in the field of endoscopes.
Endoscopes are long and narrow optical systems, typically circular in cross-section, which can be inserted through a small opening in an enclosure to give a view of the interior. They almost always include a source of illumination that is conducted along the interior of the scope from the outside (proximal) end to the inside (distal) end, so that the interior of a chamber can be viewed even if it contains no illumination. Endoscopes come in two basic types; these are the flexible endoscopes (fiberscopes and videoscopes) and the rigid borescopes. Flexible scopes are more versatile, but borescopes can provide higher image quality, are less expensive, are easier to manipulate, and are thus generally preferred in those applications for which they are suited.
While endoscopes (both flexible and rigid) can give the user a relatively clear view of an inaccessible region, there is no inherent ability for the user to make a quantitative measurement of the size of the objects he or she is viewing. There are many applications for which the size of an object, such as a tumor in a human body, or a crack in a machine part, is a critically important piece of information. Making a truly accurate measurement under these circumstances is a long-standing problem that has not been adequately solved until recently.
In a first co-pending application, now U.S. Pat. No. 6,009,189, entitled “Apparatus And Method For Making Accurate Three-Dimensional Size Measurements Of Inaccessible Objects”, filed Aug. 16, 1996, and which is incorporated herein by reference, I taught a new and complete system for making measurements of objects with an imaging optical system, with particular emphasis on endoscopic applications. In a second co-pending application, now U.S. Pat. No. 6,121,999, entitled “Eliminating Routine Alignment Calibrations in Perspective Dimensional Measurements”, filed Jun. 9, 1997, I taught certain improvements to the measurement system as applied to the endoscopic application. I will hereinafter refer to the first co-pending application as “Application 1” and the second as “Application 2”.
My previous invention makes possible a new class of endoscopic measurement instruments of unprecedented measurement accuracy. This measurement system is a version of a technique I call “perspective dimensional measurement”. By “perspective” I am referring to the use of two or more views of an object, obtained from different viewing positions, for dimensional measurement of the object. By “dimensional measurement”, I mean the determination of the true three-dimensional (height, width, and depth) distance(s) between two or more selected points on the object.
As a necessary and integral part of my complete measurement system, I taught how to calibrate it in the referenced applications. I taught the use of a complete set of robust calibration procedures, which removes the need for the measurement system to be built accurately to a specific geometry, and also removes any need for the imaging optical system(s) to be built accurately to specific optical characteristics. Instead, I taught how to calibrate the geometry and characteristics of the opto-mechanical hardware, and how to take that actual geometry into account in the measurement process. The complete set of calibration procedures I taught includes three different types of calibration. In optical calibration, the detailed characteristics of each imaging optical system (i.e., camera), when used as a precision image forming device, are determined. In alignment calibration, the orientations of each camera's measurement coordinate axes with respect to the motion of the camera are determined. Finally, in motion calibration, any errors in the actual motion of the camera(s), as compared to the ideal motion, are determined. In Application 2, improvements to the system were made that eliminated the necessity of repeating the alignment calibration in certain important circumstances.
In some embodiments, my previous invention enables one to make accurate measurements using a standard, substantially side-looking, rigid borescope. Since the person who needs the measurement will often already own such a borescope, the new method offers a significant cost advantage over earlier measurement techniques.
In other embodiments, my previous invention provides for new types of self-contained endoscopic measurement instruments, both rigid and flexible, which offer significantly improved measurement accuracy as compared with those previously available. I call these new instruments the electronic measurement borescope and the electronic measurement endoscope.
While my system, as previously disclosed, does produce accurate dimensional measurements, there is room for improvement. The problem is that a new optical calibration may have to be performed each time the focus of the instrument is adjusted. One of the parameters determined during optical calibration is proportional to the magnification of the image. Without making special provisions for it, the magnification will most likely not be constant with focus, and thus every time the instrument is refocused, there is the logical requirement for a new optical calibration. Additional parameters that are determined during optical calibration are the location of the optical axis on the image sensor and the distortion of the image. These parameters may also vary as the focal state (that is, the object plane that is in focus) of the instrument is changed, which would be additional reasons to require a new calibration. Of course, whether a new calibration would actually be required in any specific instance depends on the accuracy required of the dimensional measurement, and on the characteristics of the camera being used in that instance.
When a standard borescope is used with my previous invention, there is the further difficulty that when an image sensor is mounted to the borescope to perform perspective measurements and the assembly is then calibrated, this calibration is lost if the image sensor is subsequently removed from the borescope. One may wish to remove the image sensor temporarily either to use the borescope for visual inspection, or to use the image sensor with another borescope that has different characteristics. What is needed here is a way to allow the removal and replacement of the measurement image sensor while maintaining calibration of the measurement system.
2b. Magnification and focus in optical metrology and machine vision
It is known that the magnification of an image formed by an optical system depends on the range of the object; that is, the magnification depends on the distance between the object and the optical system. It is also known that there is a well defined relationship between the position of a focusing component in an optical system and the range of an object that is in focus. These known relationships have been used in a class of endoscopic measurement instruments that implement a technique that I call measurement by focus. U.S. Pat. Nos. 4,078,864 to Howell (1978) and 5,573,492 to Dianna and Costello (1996) are examples of this approach. In these instruments, a focusing component is instrumented to produce a datum that i
Bugg George A
Kelley Chris
Tavella Michael J.
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