Image analysis – Applications – Motion or velocity measuring
Reexamination Certificate
1999-04-15
2001-11-13
Johns, Andrew W. (Department: 2621)
Image analysis
Applications
Motion or velocity measuring
Reexamination Certificate
active
06317506
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is directed to apparatus and method to measure the characteristics of the motion of objects undergoing substantially periodic motion using image analysis. Though developed to characterize the motions of microelectromechanical systems (“MEMS”), and, in particular, to test MEMS resonators, the present invention can be applied to any oscillating system.
MEMS resonators represent a fundamental type within a class of relatively new technologies developed by micromachining silicon and other materials. MEMS devices are expected to become part of future generations of communication, navigation, and information handling systems because of their simplicity, small size, and low power requirements. Methods of fabricating standard integrated circuits are compatible with making MEMS.
MEMS resonators show special promise as oscillators, filters, and mixers at radio frequencies. They can also function as accelerometers and gyroscopes in location-finding devices. Unlike conventional microelectronic devices, MEMS resonators have moving parts. Thus characterizing their operation requires analyzing images recorded while they operate.
Designing, fabricating, and testing MEMS devices require tools to verify that their dimensions, motions, and electrical signals substantially meet the designer's intent. Tools that accomplish these tasks automatically at the wafer level are especially desirable.
Tools that characterize electrical behavior are readily available from VLSI technology. The challenge is to combine both electrical and optical testing to simultaneously examine the motions that are the distinguishing characteristic of MEMS (and other periodic) devices. Further, a MEMS resonator may or may not have sensing means built in to enable electrical measurements that characterize the operation of the DUT. Even if a MEMS resonator has such means, the electrical measurement may require sophisticated equipment or circuits. Optical measurements are therefore preferred.
The most common optical measurements of DUT motion in the prior art require manually controlled test equipment, measuring the magnitude of DUT motion from visual observations under a microscope. There have been reports of more sophisticated techniques: measurements with a laser vibrometer or analysis of a series of time-resolved images produced by strobed illumination. But these techniques have limitations. Laser vibrometry is a spot method applicable mostly to measurements in the Z-plane (that is, perpendicular to the DUT's surface). Stroboscopy, and a derivative that combines interferometry with a strobed illumination source, measure motions in three dimensions using registration algorithms with six degrees of freedom. However, these stroboscopic techniques are limited to DUT motions that fall below an upper frequency limit set by how fast the source of illumination can be strobed, i.e., turned on and off.
Thus there exists a need for apparatus and methods of measuring DUT motions that is precise, sophisticated, and not subject to the limitations of the prior art.
SUMMARY OF THE INVENTION
The present invention makes measurements in the X-Y plane (i.e., the plane of the DUT surface). Measurement can be extended to the third dimension with interferometry. The upper limit on the frequency of DUT motions analyzed by the present invention is limited only by the device that provides the stimulus or by the DUT itself. Because the present invention uses standard video images, recorded while the DUT is illuminated continuously, the technique imposes no frequency limits. The present invention is also significantly faster and less expensive to implement than the prior art. There is no known commercially available test equipment with the capabilities of the present invention, and MEMS resonators currently in production have motional frequencies above the limit of the testing techniques of the prior art.
The primary advantage of the present invention is that it quickly characterizes devices that have very high motional frequencies, e.g., on the order of megahertz. Motion estimates are derived from standard video images analyzed with a novel blur synthesismatching algorithm, rather than from images made with strobed illumination and analyzed with sophisticated image-registration algorithms.
The present invention uses inexpensive equipment that is commercially available. For example, it uses continuous (rather than strobed) illumination. It does not require an expensive laser vibrometer ($85,000) or an external spectrum analyzer ($25,000), because the analysis is performed in software. And the present invention uses an inexpensive video camera based on a charge-coupled device (“CCD”) ($300) instead of a high-resolution digital camera ($15,000).
Still another new feature is that the present invention offers a self-contained test that provides for DUT stimulus and electrical and optical measurements, together with on-line data analysis and reporting during testing.
Therefore one object of the present invention is to provide apparatus and method for measuring DUT motions of objects in periodic motion (such as MEMS resonators) that overcomes the drawbacks of the prior art.
Another object of the present invention is to provide apparatus and method for measuring DUT motions of objects such as MEMS resonators that have no frequency limitations.
Briefly stated, the present invention provides apparatus and method to measure the characteristics of the substantially periodic motion of a mechanical system. A nonintrusive technique measures such motion by analysing images of a movable component of the system without requiring a motion sensor built into the system. If the system includes a motion sensor, the present invention can calibrate it. The present invention applies to an object of any length scale if it can be imaged. The displacement of a component is obtained from a single, time-exposed image while the system is in periodic motion and a reference image made with the component at rest. The technique, implemented as one component of an automated test-bed apparatus, is significantly faster than the prior art. The present invention is especially efficient in characterizing the mechanical performance of MEMS. Speed facilitates both hands-on testing of prototypes and testing in production environments. Results from the present invention applied to a microfabricated resonator are compared with electrical measurements derived from an integrated comb-drive. Benchmark comparisons demonstrate that the present invention delivers comparable results in shorter times with simpler, less expensive apparatus than the prior art. The present invention removes any upper limit on the frequency of motions that can be analyzed.
According to an embodiment of the invention, apparatus to measure parameters of a substantially periodic motion of an object, comprises: a device to capture a first image of the object at rest and at least one second image of the object in motion; a digitizer to digitize the first and the at least one second images; a computer to synthesize from the digitized first image a series of artificial images of the object in motion; and an analyzer to compare the series to the at least one digitized second image, thereby measuring the amplitude.
According to a feature of the invention, a method of measuring parameters of a substantially periodic motion of an object, comprises the steps of: illuminating the object at rest and in motion; capturing a first image of the object at rest and at least one second image of the object in motion when the object is illuminated; digitizing the first and the at least one second images; synthesizing from the digitized first image a series of artificial images of the object in motion; and comparing the series to the at least one digitized second image, thereby measuring the amplitude.
According to another feature of the invention, apparatus to measure parameters of a substantially periodic motion of an object, comprises: means for illuminating the object at rest and in m
Burns Daniel J.
Helbig Herbert F.
Burstyn Harold L.
Johns Andrew W.
Mancini Joseph A.
Nakhjavan Shervin
The United States of America as represented by the Secretary of
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