Measuring and testing – Vibration – Sensing apparatus
Reexamination Certificate
1999-02-16
2001-04-03
Chapman, John E. (Department: 2856)
Measuring and testing
Vibration
Sensing apparatus
C356S329000
Reexamination Certificate
active
06209396
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method for contact-free, optical displacement- and/or vibration measurement of an object by means of at least one interferometer with at least one laser, at least one control unit which guides the laser beam to a plurality of points of the object to be measured, so that the object is scanned by the laser beam, and at least one output unit for the high-resolution display of the measurement results. The invention further relates to an apparatus for the implementation of the method.
Such a method and apparatus are known from DE 31 13 090 A1 in which the following procedure is performed: a video image of the structure to be investigated is recorded, and a rectangular grid of measurement points is inserted into this video image using a computer. In this way, a rectangular grid of measurement points is superimposed upon the object to be measured. The object to be measured is set in vibration, and the laser beam of an interferometer is directed toward the predefined grid points under the control of the computer. At each of these points the vibration spectrum is recorded in a contact-free manner by this interferometer. Following the measurement, the individual vibration spectra are analyzed in the computer, and the vibration image of the object is reconstructed for individual frequencies selected from the vibration spectrum. These vibration images are output by an output unit (image screen).
Optionally, individual measurement points can also be erased from the measurement grid.
This method and the associated apparatus are disadvantageous inasmuch as the arrangement of the measurement points in a predetermined grid is unsatisfactory for the analysis of vibrations with complicated geometric configurations. These can be recorded only by means of an extremely large number of measurement points, with the result that the measurement can no longer be performed in a reasonable period of time.
Additionally, for the analysis of vibration modes, in particular of car doors or the like, it is known to arrange individual sensors at different points of the workpiece to be measured. The sensors are accelerometers which, on the one hand, falsify the measurement result by virtue of their own bulk and, on the other hand, cannot be attached in the desired amount or at all the desired locations. Particularly in the case of small workpieces, the use of such bulky accelerometers rapidly becomes subject to insuperable limitations.
SUMMARY OF THE INVENTION
Proceeding from this, an object of the invention is to provide a method and apparatus which enable vibration analysis to be performed even in the case of workpieces which have a complicated geometric configuration or are very small.
This object is achieved in accordance with the invention in that, for a scanning process, the measurement points are freely positioned on the object to be measured, individually and/or in at least one grid adaptable in its contour, wherein different measurement point sub-quantities to be analyzed in correlation with one another are classified in different categories and are analyzed as a function of the category to which they are assigned.
Whereas previously in scanning processes, a surface or an object to be measured (also referred to herein as “measured object”) was covered with a rectangular and right-angled grid and measured point by point, wherein it was possible to vary the size of the grid, density of points and number of points at which measurement was to take place, the method according to the invention facilitates a substantially more adapted procedure.
In this procedure one generally simply defines the surface on which scanning is to take place, for example by marking its outline on the screen with the mouse, and then fills this freely defined surface with measurement points using the computer. For this purpose, for example, the number of measurement points or their density and other parameters are input into the computer.
Thus, for example, in the case of a circular measured object, a circular grid pattern is defined, the contour of which is thus adapted to the measured object. On the other hand, in the case of an obliquely extending, rod-shaped measured object, a grid of the same configuration is created. In this way, the measurement points can be positioned precisely on the measured object, whereas in the conventional procedure surface-covering and precise positioning of the measurement points on the measured object is not possible in the case of complicated geometric configurations.
If the vibration characteristic of a measured object is to be investigated, it is generally insufficient to define a number of measurement points in an arbitrarily selected geometric shape on the two-dimensional image of the measured object. Rather, an interpolating correlation must be established between the individual measurement points of a measured object or a part of the measured object to permit analysis of the vibration characteristic. Here, it is particularly advantageous to define different categories in which different sub-quantities of the measurement points to be analyzed in correlation with one another are classified.
Thus, for example, it is possible for a three-dimensional measured object to be covered with a two-dimensional measurement point grid which also takes into consideration the third dimension in the analysis: for example, a cable could extend at some distance in front of a planar measured object in the beam path of the laser beam. From the imaging on a two-dimensional grid, the analysis unit does not initially recognize that the measurement points situated on the cable have nothing to do with the planar measured object and must not be correlated in the analysis, so as not to falsify the measured vibration characteristic of the planar measured object. However, it is necessary for the measurement points situated on the planar measured object on both sides of the cable to be correlated respectively with one another and to be interpolated in order to permit a complete analysis of the vibration characteristic of the planar measured object.
The method according to the invention now offers the possibility, for example, of defining a rectangular grid on the planar measured object considered in the present example, and at the same time of placing a polygon of measurement points over the cable considered in the present example, wherein the measurement points situated on the cable are classified in a first category, and the remaining measurement points of the grid are classified in a second category and are respectively separately analyzed.
To simplify handling, category types assigned to different geometric objects, such as circles, ellipses, lines, etc., can be pre-defined. The individual category types can be provided with grid types, such as rectangular, hexagonal, polar, etc., and with standardized features for the data acquisition, such as the number of averaging operations, the measurement duration, and the number of measured values.
The measurement points can also be classified in different categories in accordance with the expected vibration characteristic, or can also be classified subsequently in accordance with the measured vibration characteristic, and the measurement points can be individually measured, displayed and/or analyzed in accordance with the category to which they are assigned. It is thus possible to separately record and display different regions of the measured object which vibrate with a common phase in themselves, albeit not with one another. For example, in the case of the measurement of a disc brake of a motor vehicle, the brake disc can be covered with measurement points of a circular category type filled with a polar grid. In the same operating step, the calliper is then measured with a polygonal category type filled with a dense, hexagonal grid and also having additional measurement points at the edge.
As already shown by the described examples, within the scope of the invention it is possible to define a plurality of grids for a scan
Schüssler Matthias
Wörtge Michael
Akin Gump Strauss Hauer & Feld L.L.P.
Chapman John E.
Polytec GmbH
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