Measuring and testing – Specimen stress or strain – or testing by stress or strain... – Specified electrical sensor or system
Patent
1992-02-13
1994-03-29
Myracle, Jerry W.
Measuring and testing
Specimen stress or strain, or testing by stress or strain...
Specified electrical sensor or system
7386269, 324209, 34087032, G01B 716
Patent
active
052974391
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a sensor far detecting mechanical stress, deformation or similar magnitudes of an object of measurement.
STATE OF THE ART
When measuring mechanical stress, strain or force it is known to make use of measuring sensors based on magneto-elastic material. Magneto-elastic material has the advantage that it enables contactless signal transmission from a magneto-elastic sensor element to an electronic unit for evaluation of the signal from the sensor element.
The relative permeability of a magneto-elastic element depends on the mechanical stress to which the element is subjected, e.g. by a strain within the surface on which it is mounted. During this process, signal scanning can be achieved with the aid of a coil system, the inductance of which is influenced by the permeability of the magneto-elastic element.
An important application area for magneto-elastic sensors is torque measurement on rotating shafts, for instance as described in patent specification WO 88/00690. In this case the magneto-elastic element is mounted in two axial zones mutually beside one another on a rotating shaft, with the element oriented in the two main directions of stress. A coil system consisting, on the one hand, of two sensor solenoids and, on the other hand, an excitation solenoid extending axially over both sensor solenoids is mounted with the shaft extending axially within and through the solenoids.
This embodiment has the advantage that the sensor solenoids permit moderate axial displacements of the rotating shaft in relation to the solenoids without significant effect on the output signal. They have the disadvantage that the solenoids entirely enclose the rotating shaft with attendant requirements as regards accessibility during assembly and use.
In view of this disadvantage there are also sensor coils which do not surround but instead face the rotating shaft with the coil's axis of symmetry oriented in the radial direction of the rotating shaft. However, this arrangement of the sensor coils has the important disadvantage that the output signal does not only depend on the permeability of the magneto-elastic element but also to a great extent on the displacement of the rotating shaft relative to the sensor coils. A method of reducing this disadvantage is described in patent specification DE 3620412 A1, but this invention can only deal with relatively small displacements. None of the known sensor coil arrangements are particularly suitable for a more detailed analysis of complex stress situations.
So as to enable high accuracy of the measuring result it is desirable for the sensor not to be subject to any significant relationship of dependence as regards the distance between the coil and the magneto-elastic element, as is the case with known embodiments.
Arrangements for contactless signal transmission are as such known in many contexts. Within an entirely different sphere of technology, i.e. with anti-theft systems, it is known to make use of so-called anti-theft labels. Such systems consist of a detection system capable of identifying by electromagnetic means the proximity of an anti-theft label within a detection zone, thereby the detection is in principle based on some resonance phenomenon.
Patent specification U.S. Pat. No. 4,578,654 describes such an anti-theft label with an LC circuit produced by thick-film technology and enclosed in the label. The signal transmission is effected with the aid of a detection system comprising also aerials and a transmitter. High-frequency energy from the transmitter excites the LC circuit causing it to oscillate at a predetermined resonance frequency, which in its turn is detected by a receiver in the detection system. The resonance of the LC circuit can be detected without difficulty within a large detection zone about the aerials and irrespective of the LC circuit's position in relation to the aerial.
However, the anti-theft label serves only to detect whether an object is within a certain zone or not. The signal from the label does not, accordingly, con
REFERENCES:
patent: 3636437 (1972-01-01), Soulant, Jr. et al.
patent: 3827291 (1974-08-01), McCalvey
patent: 4312001 (1982-01-01), Marzolf
Lord Donald G.
Tyren Carl H.
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