Measuring and testing – Specimen stress or strain – or testing by stress or strain... – Specified electrical sensor or system
Patent
1990-03-01
1991-06-04
Ruehl, Charles A.
Measuring and testing
Specimen stress or strain, or testing by stress or strain...
Specified electrical sensor or system
7386204, 73DIG2, 324209, G01B 724, G01L 516
Patent
active
050203789
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a device for non-contact measuring of stresses in a bar-shaped body, e.g. a cylindrical bar, shaft or the like.
In many different technical areas it is desired to be able to measure during operation without contact the stresses to which a structural element, e.g. a shaft, a tool or the like, is exposed during the use thereof in order to be able to control in dependence on the measuring values obtained, e.g. feed rate, drive power supplied etc, in order to prevent that the structural element or an element cooperating therewith or a workpiece actuated by the structural element is damaged or exposed to non-desirable stresses.
According to one prior art device for non-contact measuring of torsion stresses in shafts, drills or other bar-shaped bodies, the bar is provided in two axially spaced zones with a number of thin strips of an amorphous magnetoelastic material, uniformly distributed in the circumferential direction in the related zone. The strips are affixed to the circumferential surface of the related zone at a pitch of substantially 45.degree., the pitch direction in one zone being opposite to the pitch direction in the other zone. The bar is encircled by stationary pick-up coils having equal numbers of winding turns, which are provided for each zone, each pick-up coil extending in a plane which is perpendicular to the axis of the bar, as well as an outer stationary excitation coil encircling the zones with strips and also the pick-up coils and extending axially in relation to the axis of the bar. The excitation coil can be connected to a drive unit for generating a magnetic field over the strip zones and the pick-up coils, and the pick-up coils are connected to a measuring unit for indicating signals generated in the pick-up coils. The device is based on the known condition that the magnetic properties of amorphous magnetoelastic materials are changed in dependence on the stress condition of the material. Thus, the strips affixed to the bar are exposed to stresses when the bar is exposed to stresses. When a magnetic field is applied over the pick-up coils and the zones with strips a current will be induced in the pick-up coils which are actuated by the strips of amorphous magnetoelastic material located inwardly of the coils. The output signal from the pick-up coils accordingly depends on the magnetic properties of the strips and sinCe these properties will be changed in dependence on the mechanical stress condition of the strips, the output signals from the pick-up coils will represent the stresses existing in the bar. The pick-up coils for the two zones with strips are connected in series in opposition. When the bar is not exposed to load there will thus be obtained a resulting zero output signal. If the bar is exposed to torsion stress there will be obtained an output signal which depends on the magnitude of the torsion stress as well as the direction of the torque.
A drawback of the prior art device described above is that it can be utilized only for measuring torsion stresses but does not allow e.g. bending stresses or axial stresses, for which the bar may be exposed, to be measured. Bending stresses to which the bar is exposed thus will generate no resulting output signal in the pick-up coils. If the bar is exposed to axial stress also the zero output signal will be obtained.
Another drawback of the prior art device is that the strength of the signals obtained from the pick-up coils is relatively low due to the fact that the strips of amorphous magnetoelastic material do not extend perpendicularly to the planes of the pick-up coils; they include an angle with these planes. As a consequence thereof the prior art device is relatively sensitive to axial displacement of the bar in relation to the coils.
According to another prior art torque meter which in a corresponding manner as has been described above comprises two zones having strips of a thin amorphous magnetoelastic material the two pick-up coils encircling the bar are replaced by two pick-up heads each consis
REFERENCES:
patent: 4414855 (1983-11-01), Iwasaki
Hesthamer Tore
Tyren Carl
AB SKF
Renz Jr. Eugene E.
Ruehl Charles A.
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