Measuring and testing – Vibration – Vibrator
Reexamination Certificate
2000-02-22
2002-04-23
Moller, Richard A. (Department: 2856)
Measuring and testing
Vibration
Vibrator
Reexamination Certificate
active
06374677
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the field of signal analysis, and more particularly to a micromechanical resonator that allows signal detection in multiple time and frequency domains.
BACKGROUND OF THE INVENTION
Future electro-mechanical machines and structures will increasingly participate in their own service and maintenance using embedded distributed self-diagnostics that are remotely accessible to monitor machine health, detect and isolate subtle performance degradation, and in some cases even reconfigure some machines to adapt to changing operating environments. Traditionally, corrective maintenance and preventative maintenance have been the only two service paradigms. More recently, predictive or condition-based maintenance using micromechanical resonators, enabled by Micro-Electro-Mechanical Systems (MEMS) technology is emerging as an alternative. Condition-based maintenance is just-in-time maintenance based on the actual health of the machine and its components. Since it avoids the cumulative cost of unnecessary service calls associated with preventative maintenance and the occurrence of machine failure and degradation associated with corrective maintenance, condition-based maintenance provides substantial cost savings.
Fault manifestation in electro-mechanical systems with multiple moving elements in complex operating regimes, however, is typically non-stationary in that the frequencies describing specific faults vary over time. The multiple actuating elements such as motors and solenoids produce rich mechanical excitation signals at multiple time and frequency domains. Traditional Fourier spectral analysis techniques, such as the Fourier transform, while useful for establishing the signal bandwidth, is unsuitable for analyzing the time-varying properties of the signal that are important for diagnosis purposes. Another problem is that failure modes of system components are difficult to identify and characterize using time-based or frequency-based analysis. Hence, signature analysis with a time-frequency representation, such as that provided by the short-time Fourier transform (STFT) is required for condition monitoring of these systems.
A conventional micromechanical resonator for signature analysis is an array of tuning forks. Each tuning fork of the array resonates at a particular frequency while being insensitive to other frequencies. Thus, the entire spectral content of a vibration signal can be covered using a large number of tuning forks with closely spaced resonant frequencies. As shown in
FIG. 1
, array
10
includes higher frequency tuning forks
12
, mid frequency tuning forks
14
, and lower frequency tuning forks
16
. Conventional arrays typically use a gas to damp out resonant vibration of the tuning forks.
Conventional micromechanical resonators provide frequency information, but do not provide the ability to separate this information into specific time intervals or windows of constant length. These tuning fork arrays, however, suffer from two problems. First, the duration of the time interval is limited by the viscous properties of the damping gas. Since elements that move faster will damp out sooner, the duration of time intervals is frequency dependent and varies for different frequency tuning forks. Thus, the amount of damping that may be employed will be limited by the sensitivity of the high frequency components. This affects the ability of the low frequency tuning forks to distinguish new events from old events in situations in which the new event occurs before the old event has been damped out. Second, some condition-based maintenance algorithms, such as short-time Fourier transform, require all the tuning forks to be damped simultaneously while others, such as wavelet transformation, require a hierarchy of time intervals between damping. Conventional tuning fork arrays, however, do not provide this capability.
In light of the foregoing, there is a need for a method and a micromechanical resonator for arresting the motion of micromechanical resonators to allow detection of rich electromechanical excitation signals at multiple time and frequency domains.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to an micromechanical resonator that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
In accordance with the purposes of the present invention, as embodied and broadly described, the invention provides a micromechanical resonator including at least one resonant mass having an equilibrium position, at least one anchor electrode that provides electrostatic damping of the resonant mass, and a substrate having a planar surface.
In another embodiment, the present invention provides a micromechanical resonator including at least one resonant mass having an equilibrium position, a clamp, wherein the clamp provides mechanical clamping of the resonant mass, and a actuator for applying the clamp.
In another embodiment, the present invention provides an array of micromechanical resonators including a plurality of resonant masses and a plurality of mechanisms to damp the resonant masses, wherein the damping mechanisms are simultaneously activated to allow the array to measure discrete time intervals.
In another embodiment, the invention provides an array of micromechanical resonators including a plurality of resonant masses and a plurality of mechanisms to clamp the resonant masses, wherein the clamping mechanisms are configured to allow the array to measure a hierarchy of time intervals.
In yet another embodiment, the invention provides a method of clamping and releasing a mechanical sensor including the steps of measuring the frequency of an event for an initial time interval using a resonant mass having an equilibrium position, clamping the resonant mass, and releasing the resonant mass in its equilibrium position to measure a second time interval.
The accompanying drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and together with the description serve to explain the principles of the invention.
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Berlin Andrew A.
Hung Elmer S.
Zhao Feng
Finnegan Henderson Farabow Garrett & Dunner LLP
Moller Richard A.
Xerox Corporation
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