Patent Application
20140368500
The invention generally relates to metrology and, more particularly, the invention relates to metrology using imaging devices.
Coordinate measuring machines (CMMs) are widely used for the geometric inspection and measurement of manufactured objects having a multitude of features. These features are often dispersed throughout the object at different locations and in different orientations. To improve industrial processes using CMMs, many such machines should quickly direct a measurement sensor toward relevant features in a manner that minimizes the measurement cycle time. This has been especially true of tactile probing systems where a single point stylus must make many moves to collect sufficient data about each feature of an object. In some applications, this tactile inspection method is too slow. The art has responded to this problem by developing more advanced probing systems, such as laser point or line scanners, which collect more data with a smaller range of motion.
Computed tomography inspection systems also have been used for inspection and measurement. Undesirably, such systems known to the inventors require the acquisition of an object's entire volume. Accordingly, industrial computed tomography systems scan the entire object volume through a complete rotation of 360 degrees with a plurality of either 2D x-ray projection images (cone beam/flat panel scanners) or 1D X-ray scan lines (helical/line scanners). Software later reconstructs these images into planar slices or complete volumes for analysis.
One problem with this scanning approach is that it often collects a high volume of information. This high volume of data then must be processed, which takes a long time (e.g., 30-45 minutes, which is unacceptably long for many industrial inspection systems), and takes up extra space for data storage. Use of the prior art computed tomography approach for geometric inspection therefore often is quite impractical.
In accordance with one embodiment of the invention, a method of measuring an object registers the object with a model of the object, and determines at least one feature of the object to scan. Next, the method controls an X-ray scanning device to scan less than the entirety of the object to produce visual data representing at least one scanned portion. The at least one scanned portion has the at least one feature, while the X-ray scanning device is controlled as a function of registering the object and model.
The method further may reconstruct the at least one scanned portion of the object from the visual data to produce a reconstruction. Next, the method may measure the at least one feature from the reconstruction. Sometimes, the method may determining a plurality of features of the object to scan, and control the X-ray scanning device to scan less than the entirety of the object to produce visual data representing at least one scanned portion—where the at least one scanned portion includes the plurality of features. In a similar manner, the X-ray scanning device may be controlled to produce visual indicia representing a plurality of scanned portions. The at least one scanned portion also may at least a portion of the at least one feature.
Some embodiments may load the object into a CT machine that contains the X-ray scanning device, and sometimes has a fixture that does not obstruct the X-ray scanning device. The fixture may be movable in a variety of manners, such as in a translational direction and in a rotational direction. Moreover, the model may include a 3D CAD model. Indeed, among other things, the feature may include an internal feature or an external feature of the object. The X-ray scanning device may have a source that moves less than 360 degrees around the object when scanning the object. Among other ways, the X-ray scanning device may scan a plurality of intersecting planes of the object.
In accordance with another embodiment of the invention, an apparatus for measuring an object has a registration module configured to register the object with a model of the object, and a fixture for supporting the object. The apparatus also has a controller, operatively coupled with the registration module, configured to control an X-ray scanning device to scan less than the entirety of the object to produce visual data representing at least one scanned portion. The at least one scanned portion includes at least one feature, and the scanner is controlled as a function of the registration of the object and model.
Illustrative embodiments of the invention are implemented as a computer program product having a computer usable medium with computer readable program code thereon. The computer readable code may be read and utilized by a computer system in accordance with conventional processes.
Accordingly, prior art computed tomography inspection systems have been used mainly for non-destructive testing purposes so that their design requires the complete acquisition of an object's entire volume since the exact location of internal features may be unknown. In today's industrial computed tomography systems, the entire object volume is scanned through a complete rotation of 360 degrees with a plurality of either 2D x-ray projection images (cone beam/flat panel scanners) or 1D X-ray scan lines (helical/line scanners). These images are later reconstructed by software into planar slices or complete volumes for analysis. One problem with this approach, when considering geometric measurement, is that often too much unwanted information is collected. Since features being measured for geometric analysis usually have known nominal locations and orientations within the object being inspected, a complete acquisition that includes all the volume between those features is unnecessary. The current computed tomography inspection systems known to the inventors act blindly to collect all of the data contiguously through the object. The collection of this superfluous data bogs down processing time, takes up extra space for data storage, and makes the application for geometric inspection of larger objects using computed tomography highly impractical.
Thus, as noted, illustrative embodiments position an object within a computed tomography system to collect data only in the relevant regions where features of interest lie. This may be accomplished by selectively scanning cross-sectional plans that are orthogonal to those features of interest and at a minimum spacing between scan plans necessary to preserve geometry accuracy.
A nominal definition of the object or CAD model may also be used to fully automate the process of determining where the features of interest lie within the object to be measured—a CAD model contains all of the geometric information about the features of interest, such as their orientation and position within an object. This information may be used to strategically plan the scanning trajectories and number of projections required to effectively measure all the features of interest within an object without acquiring superfluous data and slowing down the reconstruction process. The prerequisite to using the nominal definition is that it is in-sync, i.e., registered with the object so that the position and orientations can be known. This may be accomplished by knowing only a few reference data points on the surface of the part relative to how it is being held in the positioning system's fixture. These reference points can be determined in advance by having measurements of the fixture data and stored for later reference.
Those skilled in the art should more fully appreciate advantages of various embodiments of the invention from the following “Description of Illustrative Embodiments,” discussed with reference to the drawings summarized immediately below.
In illustrative embodiments, a metrology x-ray scanning device cooperates with a computer system to scan only relevant portions of a known object. To that end, the system registers the object with a model of that same object to provide system awareness of the object itself, and the feature(s) of interest. After completing the registration process, the system uses the model information to scan appropriate regions relevant to the feature(s) of interest. Details of illustrative embodiments are discussed below.
More specifically, like others in the art, the CT machine 18 in this figure has a housing that both forms an internal chamber for containing various components, and acts as a shield to x-rays. The chamber of the CT machine 18 contains an x-ray source 22 that transmits x-rays (typically) in a generally cone-shaped pattern (a/k/a “cone beam”), toward and through an object 10 within its interior region. This interior region, which contains the object 10 being imaged as it is receiving x-rays, is referred to herein as an “active region 24.” As known by those skilled in the art, the object 10 attenuates the x-rays to some degree, changing the pattern of x-rays on the opposite side of the object 10. A detector 26 on the opposite side of the object 10 detects this pattern, producing a two-dimensional representation/image of the object 10.
To obtain a three-dimensional representation/image, however, the system 16 moves the position of the object 10 relative to the x-ray source 22 and detector 26. Some CT machines 18 rotate the x-ray source 22 and detector 26 (referred to as “source/detector pair 22/26”) while leaving the object 10 stationary. Other CT machines 18, such as that shown in
Illustrative embodiments may use any of a variety of different types of systems. For example, some embodiments may use linear detectors, while other embodiments may use flat panel detectors. Depending on the system type (e.g., linear or flat panel), projections may be in the form of line images (e.g., linear system) or plane images (e.g., flat panel system) ultimately used to reconstruct cross-sectional slices or volumes, respectively.
Conventional software techniques convert this plurality of two-dimensional images/projections into a detailed, comprehensive three-dimensional representation of the object 10. For example, the computer system 20, which has a display device 32, a CPU/memory/logic within a chassis 34 (i.e., a computer), input device 36 (e.g., a keyboard and/or mouse), and other conventional components, may execute these conventional software routines to generate a three-dimensional representation of the object 10. The computer system 20, however, also may execute other routines that improve scanning throughput.
More specifically, as noted above, various embodiments do not scan the entire object 10. Instead, the system 16 scans only relevant portions of the object 10.
In this example, the object 10 is a rectangular box having a boss 38 extending from a front face (i.e., an external feature of the object 10), and a through-hole 40 in extending through an upper portion of its width (i.e., an internal feature of the object 10). To illustrate this more clearly,
The front view shows the boss 38 extending from the face and the through-hole 40 extending through the width in phantom/dashed lines. In a similar manner, the side view shows the opening to the through-hole 40, and the boss 38 extending from the front face. One thing of note is that the two features of interest, the boss 38 and the through-hole 40, diverge from one another and thus, do not have generally parallel longitudinal axes. It also should be noted that while the features of interests have longitudinal axes, some futures of other objects may be irregularly shaped, without well-defined axes, and still be capable of analysis by various embodiments of invention.
More specifically, both figures show the object 10 on the rotary table 28 of
In addition to rotating, the rotary table 28 also may move translationally relative to the source/detector pair 22/26 within the scanning machine 18. For example, some embodiments translationally move the rotary table 28 without moving the source/detector pair 22/26. Other embodiments, however, translationally move the source/detector pair 22/26 without translationally moving the rotary table 28. Yet other embodiments may translate both the rotary table 28 and the source/detector pair 22/26. In a manner similar to conventional techniques, this relative movement is used to scan along the longitudinal axis of the feature being imaged.
While remaining stationary relative to one another (i.e., the detector and source 22), the source/detector pair 22/26 may move or orbit the object 10 along an arc identified in the drawings by the angle identified by the Greek letter theta “θ.” Moreover, between scans, this arc may be rotated relative to its center by some angle to scan along other trajectories. For example, the arc may scan directly over the top of the object 10 during one set of scans, and then rotate ninety degrees relative to its center to scan over the sides (e.g., the front) during another set of scans.
As shown in
A specially configured logic apparatus 44 performs some of the requisite steps (discussed below with regard to
In particular, the logic apparatus 44 includes a plurality of modules or sub-systems that communicate by means of a conventional communication mechanism, such as a bus 46. Indeed, those skilled in the art can use other communication mechanisms, such as a wireless medium, direction connections, etc. and thus, a bus is discussed by example only. Accordingly, those skilled in the art may select any of a number of different mechanisms for operatively coupling the modules.
The modules cooperate to perform the desired functions discussed below, ultimately measure a feature or portion of the object 10. To that end, the logic apparatus 44 includes a registration module 48 configured to register the object 10 with a model of the object 10. As discussed below, among other things, the model may include a computer aided design (CAD) model or other relevant type of model known in the art. As known by those in the art, a CAD model typically has all the geometric information about the features of interest, such as their orientation and relative positions within the object 10. It is this specific information that drives various embodiments.
The logic apparatus 44 also includes a reconstruction module 50 configured to reconstruct scanned portions of the object 10 from visual data generated by the source 22 and detector 26, and a measuring module 52 configured to measure the feature/portions of the object 10 from the reconstructed object portions. A controller 54 uses the information from the other modules to control the system 16 to scan an appropriate amount of the object 10. For example, using information and instructions from the other modules, the controller 54 can direct the source 22 and detector 26 to obtain visual data of prescribed portions of the object 10.
As discussed in greater detail below, each module may be implemented by hardware, software, or a combination of hardware and software. For example, some or all of the modules may be implemented as integrated circuits on a printed circuit board, as software components executing on the computer system 20, or both.
The process begins by configuring the system 16 to measure one or a plurality of like objects 10, such as that shown in
The process thus continues to step 502, in which an operator loads the object 10 into an imaging machine 18 (e.g., a fixture in the machine 18), such as the CT scanning machine 18 shown in
The process then continues to step 504, which performs a number of configuration and calibration steps that permits the system to repeatedly measure the same type of object 10 multiple times. To that end, using the registration module 48, the process registers the object 10 (via the fixture) with a model of the object 10. Specifically, unlike clinical use of a CT scanner, it is expected that the technician/operator should know the nominal features of the object 10 through the CAD model. Using the object 10 of
1) a rectangular shape,
2) the short boss 38 extending from its front face, and
3) the through-hole 40 extending through its width.
In fact, the operator and system 16 also should know the general dimensions of the object 10, the inner dimension of the through-hole 40, the diameter of the boss 38, as well as the general contours of the object surfaces (i.e., the planarity of its surfaces). Accordingly, using the registration information of the object 10 and the rotary table 28 (discussed below), the system 16 registers the object 10 with the CAD model. In other words, using the CAD model, the system 16 already has informational knowledge of the object 10 as it is positioned on the rotary table 28 (even if the object 10 is not yet loaded) and thus, uses the CAD model to identify nominal portions of the object 10.
This step continues by calculating efficient trajectories for the source/detector pair 22/26 to scan the object. In so doing, this step searches the nominal model for the features of interest, determines approximately where those features are located on the actual object 10, and then generates scanning trajectories to acquire visual indicia/data of the features of interest. In illustrative embodiments, step 504 loads the CAD model into a simulation program that calculates trajectories that will capture the features of interest while scanning a minimal amount of unnecessary portions of the object 10. In other words, this step calculates trajectories for minimizing the amount of data that is gathered and ultimately processed in later steps. Accordingly, this step should further reduce the time to process the object 10. After calculating the trajectories, this step loads the desired trajectories into the controller 54, which controls the movement of the source/detector pair 22/26.
At this step, the process may begin processing many different objects 10 that nominally have the characteristics of the object in the CAD model. Stated another way, the process now may measure many objects 10 intended to have the features of the CAD model. Although only one scan is discussed in the subsequent steps, those skilled in the art should understand that various steps (discussed below) can be repeated multiple times after registration is completed.
It also should be reiterated that although a CAD model is described and discussed, those skilled in the art can use other types of models. Accordingly, discussion of a CAD model is for illustrative purposes only and not intended to limit all embodiments.
The process continues to step 506, which scans the desired portions of the object 10 to produce visual indicia/data representing the object 10. Among other ways, the features to be scanned may be pre-programmed as noted above, or selected at the time of scanning using the CAD model. Accordingly, illustrative embodiments image/scan less than the entirety of an object as a function of the registration of the object 10 with the model.
To those ends, with reference to
Continuing with step 506, the process then rotates the rotary table 28 ninety 90 degrees, and then scans a first prescribed portion of the through-hole 40 and stops scanning. This is shown in the lower picture of
It should be noted that the source/detector pair 22/26 does not necessarily complete a full orbit around the object 10. Some embodiments rotate less than 360 degrees around the object 10 since the entire 360 degrees of information may be unnecessary (in some uses). The operator and/or system 16 may determine an appropriate amount of rotation. Moreover, the source/detector pair 22/26 may make multiple scans that are either parallel to each other, or intersecting each other. This was suggested above when discussing how the source/detector pair 22/26 may rotate its arc between scans. It thus is not necessary that all scans be parallel.
After scanning the appropriate portion or portions of the object 10, the reconstruction module 50 reconstructs the object 10 using conventional reconstruction processes known in the CT art (step 508). The system 16 may display the reconstructed object 10 on the display device 32, store it in memory, or both. The process concludes at step 510, in which the measuring module 52 measures the desired features of interest of the reconstructed object 10.
Accordingly, illustrative embodiments image or scan only portions of the object 10 that are necessary to obtain an accurate measure of the feature of interest, significantly reducing measurement times. This advance should enable a more facile, effective industrial inspection process.
Various embodiments of the invention may be implemented at least in part in any conventional computer programming language. For example, some embodiments may be implemented in a procedural programming language (e.g., “C”), or in an object oriented programming language (e.g., “C++”). Other embodiments of the invention may be implemented as preprogrammed hardware elements (e.g., application specific integrated circuits, FPGAs, and digital signal processors), or other related components.
In an alternative embodiment, the disclosed apparatus and methods (e.g., see the various flow charts described above) may be implemented at least in part as a computer program product for use with a computer system. Such implementation may include a series of computer instructions fixed either on a tangible medium, such as a computer readable medium (e.g., a diskette, CD-ROM, ROM, or fixed disk). The series of computer instructions can embody all or part of the functionality previously described herein with respect to the system.
Those skilled in the art should appreciate that such computer instructions can be written in a number of programming languages for use with many computer architectures or operating systems. Furthermore, such instructions may be stored in any memory device, such as semiconductor, magnetic, optical or other memory devices, and may be transmitted using any communications technology, such as optical, infrared, microwave, or other transmission technologies.
Among other ways, such a computer program product may be distributed as a removable medium with accompanying printed or electronic documentation (e.g., shrink wrapped software), preloaded with a computer system (e.g., on system ROM or fixed disk), or distributed from a server or other remove device over the network (e.g., the Internet or World Wide Web). Of course, some embodiments of the invention may be implemented as a combination of both software (e.g., a computer program product) and hardware. Still other embodiments of the invention are implemented as entirely hardware, or entirely software.
Although the above discussion discloses various exemplary embodiments of the invention, it should be apparent that those skilled in the art can make various modifications that will achieve some of the advantages of the invention without departing from the true scope of the invention.
This patent application claims priority from provisional U.S. patent application No. 61/835,952, filed Jun. 17, 2013 entitled, “METHOD AND APPARATUS OF MEASURING OBJECTS USING SELECTIVE IMAGING,” and naming Jonathan O'Hare and Stephen Darrouzet as inventors, the disclosure of which is incorporated herein, in its entirety, by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61835952 | Jun 2013 | US |
