Measuring and testing – Vibration – Resonance – frequency – or amplitude study
Patent
1997-04-14
1998-11-24
Oda, Christine K.
Measuring and testing
Vibration
Resonance, frequency, or amplitude study
73655, 73656, 364508, 356349, 356351, G01B 900, G01H 900
Patent
active
058410309
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND AND SUMMARY OF THE INVENTION
The invention relates to a process for determining the vibration characteristics of a body by modal analysis.
During a modal analysis, the dynamic structural response of the body to an external excitation is determined at defined points of the body. For this purpose, acceleration sensors are mounted at these points, whose output signal supplies information on the acceleration of the body at the respective points in at least one acceleration direction. Computing processes which follow permit the supplying of information on the vibration characteristics of the body for the respective excitation frequency and permit, for example, the determination of the modal parameters of the vibration system. The parameters are: the natural frequencies, natural shapes, generalized masses and modal dampings.
If the vibration characteristics of a complex body are to be determined, this requires a relatively large number of sensors at a correspondingly large number of measuring points. Since the sensors and the pertaining transmission elements for the measuring signal, as a rule electric lines, themselves have a mass and a stiffness, this results in a change of the vibration characteristics which becomes even larger as more measuring points are provided and as the body to be measured becomes lighter. The modal analysis therefore reaches the limits of its usage range.
It is an object of the invention to provide a process of the above-mentioned type by which it is possible to carry out modal analysis for a virtually unlimited number of measuring points of the body.
The invention achieves this object by a process for determining the vibration characteristics of a body by modal analysis, wherein the body is excited to carry out vibrations and, at one viewing angle, several optical interference images of the body are recorded. On the basis of a mathematical/physical model, the interference images are analyzed with respect to the vibration characteristics existing at predetermined points. The thus obtained information on the vibration characteristics of these points is subjected to the modal analysis.
The vibration characteristics are determined optically by means of interference images. This determination takes place without any impairment of the body itself, particularly without an application of any measured value sensors.
In contrast to obtaining only one optical interference image by which the vibration form and amplitude of the structure is determined for a defined excitation frequency, the interference images in this case are used as measuring data for adapting the parameters of a mathematical/physical model by which the characteristics of the object are described as a system. This model is derived from the known fundamental equation for the dynamic forces of a linear, time-invariant, elastomechanical multi-freedom degree system which can be affected by arbitrary external forces. It is assumed that this structure with N discrete degrees of freedom can be described by an oscillator chain with N modal, decoupled degrees of freedom.
From the transmission characteristics between the vibrations of the bodies at the different points determined from the interference images and the excitation power, the modal parameters of the body can then be at least partially determined by way of modal-analytic evaluations.
The invention can be practically developed in various ways. The (coherent) laser technique is preferred for obtaining the interference images. As a result, it is possible to detect vibrations if the vibration amplitude is larger than half the wave length of the laser. As an alternative, it is possible to obtain the interference image by means of a Moire process.
When coherent light is used, each interference image itself can be obtained in a different fashion. A hologram in the form of, for example, a double or multiple-pulse hologram is preferred which can be correspondingly reconstructed for the analysis.
Instead of a hologram, holographic interferometry or laser Doppler vibrometry ma
REFERENCES:
patent: 3604253 (1971-09-01), Kersch
patent: 3899921 (1975-08-01), Hockley
patent: 4913550 (1990-04-01), Montgomery et al.
"Schwingungsformanalyse Mit Holografischer Interferometric Und Modalanalyse" by. M. Week, H. ostendorp, and M. sellhorst Technisches messen JM 1982-1988, Bal 60, No. 6 Jun. 1993.
"Measurement of the Longitudinal and transverse Vibration frequencies of a Rod by speckle Interferometry" by A. Bayon, F. gascon, and A. Varade. (May, 1993) IEEE Transactions on Ultrasonics Feroelectrics and Frequency Control, No. 3, New York.
Freymann Raymond
Honsberg Wolfram
Steinbichler Hans
Winter Franz
Bayerische Motoren Werke Aktiengesellschaft
Miller Rose M.
Oda Christine K.
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