Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Mechanical measurement system
Reexamination Certificate
2003-01-11
2004-07-13
Barlow, John (Department: 2863)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Mechanical measurement system
C073S660000
Reexamination Certificate
active
06763312
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to multiple discriminant analysis (MDA) and data integration of vibration in rotating machinery. As used herein “discriminant” is defined as “A linear set of variables that will classify events or items for which the variables are measured with the smallest possible amount of misclassification”—
Dictionary of Scientific and Technical Terms
, McGraw & Hill, Fifth Edition.
BACKGROUND OF THE INVENTION
Vibration analysis of rotating machinery to monitor life expectancy evolved following World War II, and has now been accepted as the most effective condition assessment and failure detection technique for rotating machinery. It is based on the principle that all rotating machines exhibit distinct operational and defect related vibration patterns that occur at rotational frequencies caused by forces, discontinuities, geometry placement and the physical condition of various machine elements. These vibration patterns change in energy and frequency content as the physical condition of the machine deteriorates. Measuring and interpreting the cause of the change enables those skilled in the art to detect problems early in the degradation process and initiate action to prevent machine failure, prevent production shutdown and potentially catastrophic failures. This technology has become the mainstay of modern predictive (PDM) and reliability centered maintenance (RCM) programs throughout the world. Various measurement techniques are hereinafter described, and the determinants derived are hereinafter described and discussed.
In spite of its technical effectiveness, the nature and complexity of vibration data and the process of extracting predictive failure data has added to the cost of its implementation and impeded its widespread commercial use. Highly skilled engineering level specialists, with extensive training, are often required for routine reviews and interpretations of data. The loss of one or two highly trained personnel can disrupt or cripple a major maintenance program.
Two of the most common techniques in general use for detection, measurement and analysis of vibrations in rotating machinery are Overall Measurement and Spectral Band Analysis. The overall measurement technique utilizes a piezoelectric crystal accelerometer to convert the mechanical vibration motion to a voltage proportional to the instantaneous acceleration mode vibration and monitors the root mean square (RMS) value of the broad frequency band displacement, acceleration or velocity signal. When the overall vibration level exceeds a predetermined threshold, a warning is initiated and inspection, repair, or machine shutdown action ensues.
This technique has the advantage of providing a single number, expressed in acceleration g units, in/sec velocity units or mil-inch displacement units, to indicate the machine condition. However, this technique has a weakness in that it often fails to detect subtle high frequency, low level bearing defects. High level energy from shaft imbalance and misalignment often dominates the overall signal causing it to be insensitive to low energy bearing problems. For this reason machinery bearing component failures often occur without warning, because this technique failed to provide adequate warning. The spectral band analysis technique, a more recent and improved technique employs a spectrum band analysis, where the vibration signal of defined bandwidth (upper and lower frequency content) is time sampled and converted into digital form. A Fast-Fourier Transform procedure is performed on the acquired data transforming it from the sampled time domain to the frequency domain in the form of frequency bands of varying amplitude. The level of each band indicates the frequency of the particular forcing function revealing its identity and its severity.
This format allows highly experienced maintenance personnel to directly observe the contributions of each problem source to the overall level at its own characteristic frequency. The individual frequencies, or spectral windows (placed around critical frequency bands) allow highly trained personnel to identify the source of a problem. For example, imbalance occurs at primary rotational frequency, misalignment at two or three times rotational frequency and the level of each component will identify the condition. Alarm levels are often preset for specific frequency bands. Levels above some predetermined levels indicate degradation. When the bands of interest include several selected narrow fast Fourier transfer bands, this technique is sometimes referred to as spectral windowing or enveloping.
This technique has the advantage of allowing the highly skilled maintenance practitioner (as used herein “practitioner” refers to a person experienced in rotating machine maintenance) to observe both high and low level signals at high and low frequencies to detect both imbalance and bearing signals. This spectrum analysis technique is very effective when used by an experienced maintenance practitioner, but not very effective in the hands of most untrained maintenance personnel. The spectrum analyzers and other analysis devices required are complex and require highly specialized training. The spectral data generated by such techniques is voluminous and cumbersome to store track and interpret. For these reasons, use of spectral analysis has been limited to the use of large organizations, able to maintain highly skilled maintenance teams trained in vibration analysis, or to contract with outside consulting firms.
The nature of the data produced in spectral analysis technique poses technical problems as well. The data ranges in frequency from a few Hz to 30 kHz and signal levels ranging from microvolts to volts. This data presents special problems in terms of analog or digital data transmission and storage. More importantly, the raw data generated is not easily understood and useful to management personnel.
Accordingly the present invention provides a new and improved multiple discriminant vibration detection, analysis and data integration system and method that reduces an entire highly sophisticated vibration analysis process to a few uniquely derived discrete numbers in a predetermined range. These numbers quickly convey the useful information required by a non-technical user, or a skilled practitioner, in order to judge the reliability, dynamic condition, the expected life and/or the degradation state of a machine bearing or group of machines bearings. The derived numbers may be displayed in a variety of ways, but generally in a fashion where a first twenty percent of the range would indicate a normal or acceptable level, the middle forty percent of the range would indicate cautionary alert and the other forty percent would indicate alarm/action.
The invention further provides a new and improved system and method for providing a signal indicative of and visual indication of the life expectancy of the bearing based on the dynamic forces exerted on the bearing. This is provided as a “stand alone” signal exclusive of the present bearing degradation condition.
An object of this invention is to provide a new, improved and simplified method and system for determining the vibratory condition of a rotating machine with rolling element bearings.
Another object of this invention is to provide a new, improved and simplified method and system that utilizes detected vibration of a machine to assess the conditions in a rotating machine, both as to the present state of bearing degradation and as due to the composite dynamic forces acting on bearings that lead to a shortened life expectancy.
Another object of this invention is to provide a multiple discriminant analysis method and apparatus that may be easily used by non-technical management and unskilled or moderately skilled personnel.
A further object of this invention is to provide a method and system that uses system operational discriminants combined in a unique fashion to accurately signify present bearing condition and life expectancy.
Still further objects of this invent
Barlow John
Curcio Robert
DeLio & Peterson
Dynamic Measurement Consultants, LLC
Sun Xiuqin
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