Measuring and testing – Dynamometers – Responsive to force
Patent
1997-02-11
1998-05-12
Dombroske, George M.
Measuring and testing
Dynamometers
Responsive to force
73862626, G01L 104
Patent
active
057509042
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
European reference EP-B-0,354,386 discloses a measuring pick-up for length or distance variations with mechanical to electrical conversion of the measured quantities in which, as a variable capacitor, a measuring capacitor with two electrode structures which can be moved parallel to one another is provided. The electrode structures, of comb-like design and interengaging, each consist of a plurality of planar electrodes, arranged parallel with a mutual separation, which are assigned to one another in pairs. Capacitive decoupling is achieved by a highly asymmetric arrangement of the electrode structures, so that the total capacitance of the measuring capacitor is given by connecting in parallel electrode pairs which are each formed by electrodes assigned to one another. The capacitance variation caused by the variable electrode separation of the electrode pairs is used as the measured quantity. The measuring pick-ups are, in particular, used in the contactless measurement of torques on rotating shafts. Using electrode structures designed as micro-structures, torsions of a few micrometers can, for example, be detected. The measuring pick-ups described in European reference EP-B-0,354,386 are only partially suitable for general measurement of the linear force or extension (displacement) since the thermally induced extension directly varies the electrode separations and thereby vitiates the measurement result.
For static or dynamic force or extension measurements, use is generally made of strain gauges which consist of a plurality of loops of thin resistive wire which are embedded in a support made of paper and synthetic resin. This support is adhesively bonded to the measuring point and consequently also undergoes the length variation of the object to be measured at this point. The lengthening or shortening of the wire loops which then occurs produces a resistance change which is proportional to the extension of the object to be measured. Further to applications in which measuring an extension is the primary purpose of the measurement, a force may also be measured, by means of the extension, using a strain gauge. However, limited resistance to cyclic loading and overloads, and elaborate application processes, limit the use of these strain gauges, in particular in plant and machine construction use under rugged conditions.
SUMMARY OF THE INVENTION
The object of the invention is substantially to improve industrial force and extension measurement and considerably to widen its field of application compared to known strain gauges.
In general terms the present invention is a force or extension sensor with a capacitive transducer. Electrode structures of a measuring capacitor are electrically insulated from one another, have a comb-like design and interengage. They can be moved parallel to one another via two securing points as a function of the force to be measured or of the extension to be measured. The total capacitance of the measuring capacitor is determined by parallel connection of individual electrode pairs which are in each case formed by one electrode of one electrode structure and an associated adjacent electrode of the second electrode structure. Within the total measuring range, the electrode separation of the electrode pairs, which can vary according to the force to be measured or the extension to be measured, is small compared to the distance between adjacent electrodes, not assigned to each other, of the two electrode structures. The force to be measured, or the extension to be measured, is determined from t he change in the resulting capacitance of an electrical series circuit comprising a measuring capacitor and an identically designed compensating capacitor arranged orthogonally to the measuring capacitor. The securing points of the compensating capacitor are selected such that the thermally induced variations in the electrode separation of the measuring capacitor and of the compensating capacitor have opposite signs.
Advantageous developments of the present inventio
REFERENCES:
patent: 4289035 (1981-09-01), Lee
patent: 4941363 (1990-07-01), Doemens et al.
patent: 5000048 (1991-03-01), Kordts
patent: 5397911 (1995-03-01), Hiyama et al.
patent: 5447067 (1995-09-01), Biebl et al.
patent: 5447068 (1995-09-01), Tang
Doemens Gunter
Gilch Markus
Dombroske George M.
Noori Max H.
Siemens Aktiengesellschaft
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