Measuring and testing – Dynamometers – Responsive to force
Patent
1997-02-11
1998-10-27
Dougherty, Elizabeth L.
Measuring and testing
Dynamometers
Responsive to force
7386268, G01L 112
Patent
active
058279806
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
European reference EP-B-0 354 386 discloses a measuring pickup for changes in length or distance with mechanical/electrical conversion of measured variables, in which pickup a measuring capacitor with two electrode structures which can be adjusted in parallel with one another is provided as an adjustable capacitor. The comb-like, interlocking electrode structures each comprise a plurality of planar electrodes which are arranged in parallel at a distance from one another and are assigned to one another in pairs. A highly asymmetrical arrangement of the electrode structures permits capacitive isolation to be achieved so that the entire capacitance of the measuring capacitor results from a parallel circuit comprising pairs of electrodes which are each formed by mutually assigned electrodes. The change in capacitance caused by the variable electrode spacing of the pairs of electrodes is used as measured variable. The measuring pickups are used in particular for the contactless measurement of torques on rotating shafts. With electrode structures constructed as microstructures, torsions of several micrometers can be detected, for example. For general measurement of a linear force or extension, the measuring pickups described in European reference EP-B-0 354 386 are suitable only to a limited degree since the temperature-related extension directly changes the distances between the electrodes and thus falsifies the measurement result.
For measuring static or dynamic forces and/or extensions, use is usually made of strain gauges which comprise a plurality of loops of thin resistance wire which are embedded into a carrier made of paper and artificial resin. This carrier is bonded onto the measurement point and, as a result, also experiences the change in length of the measured object. The lengthening or shortening of the wire loops which occurs in this process yields a change in resistance which is proportional to the extension of the measured object. In addition to applications in which the measurement of an extension is the primary purpose of the measurement, a strain gauge can also be used to measure a force by way of the extension. However, limited ability to cope with load changes and overloading, as well as complex application methods, restrict the use of these strain gauges, in particular in terms of use in the field in the construction of plant and machinery.
SUMMARY OF THE INVENTION
The invention is based on the problem of substantially improving the industrial measurement of forces or extension and is to be significantly extended in its range of application in comparison with known strain gauges.
In general terms the present invention is a force or extension sensor with capacitive transducer, having comb-like, interlocking electrode structures, which are electrically insulated from one another, in a measuring capacitor. The structures are adjustable in parallel with one another by two attachment points as a function of the force or extension to be measured. The total capacitance of the measuring capacitor is determined by the parallel circuit comprising individual electrode pairs which are each formed by an electrode of one of the electrode structures, and an associated, adjacent electrode of the second electrode structure. The electrode spacing, which can vary in accordance with the force or the extension to be measured, of the electrode pairs is, within the entire measuring range, small in comparison with the distance between adjacent electrodes, which are not associated with one another, of the two electrode structures. The attachment points of the electrode structures lie on a junction line which runs parallel to the direction of the electrodes and which is oriented at an angle of 40.degree. to 50.degree. with respect to the direction of the force or the extension to be measured.
In an advantageous development of the present invention the junction line is oriented at an angle of 45.degree. with respect to the direction of the force or the extension to be measured. Furthe
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Experimental Mechanics, vol. 15, No. 8, Aug. 1975, Measurement of Static Strain at 2,000.degree. F., by O. Larry Gillette, pp. 316-322.
Doemens Gunter
Gilch Markus
Dougherty Elizabeth L.
Siemens Aktiengesellschaft
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