Measuring and testing – Dynamometers – Responsive to force
Patent
1986-03-24
1987-11-03
Ruehl, Charles A.
Measuring and testing
Dynamometers
Responsive to force
7386263, 338 47, 338 99, G01L 118, H01C 1010
Patent
active
047036630
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a force sensor for the electric measurement of forces, torques, accelerations, pressures and mechanical stresses which are converted within the force sensor into a mechanical normal stress field and in turn into an electrical resistance change using a flat piezo-resistive measuring element the resistive material thereof being provided on an electrically insulated carrier body in the shape of at least one filament having joints at the filament ends and being connected in material contact with said body; the measuring element being arranged transverse to the normal stress field which is transmitted to the measuring element from at least one transmission body (DE-A No. 1932899).
Such force sensors, which advantageously eliminate the elastic element necessary for the types of force sensors using strain gauges may be used with advantage in particular for measuring purposes where only a very small insertion height is available, for instance, when screw forces are to be measured. In this case, the force sensor should have the form and size of a washer. Similar requirements exist when measuring bearing forces, machining forces, forming forces, joining forces and impact forces. Force sensors in material testing equipment should be of minimal height in order to reduce the length of the equipment frame and therefore to increase the total stiffness of the testing equipment. Very low force sensor height is further required for measuring the stress in concrete, for measuring pressure in systems with extreme pressures and when measuring high pressure shock waves in the soil and when measuring explosion and detonation pressures in various media. Furthermore, low force sensor height is of great advantage for all dynamic measuring purposes, since thereby the stiffness and the resonance frequency of the force sensor are increased.
For a long time now measuring methods for determining high static pressures using piezo-resistive measuring elements consisting, for instance, of manganin wire located in liquids or solids have been known (VDI-Berichte Nr. 93, VDI-Verlag 1966, pages 21 to 24 and Journal "The Review of Scientific Instruments", volume 35 (1964), pages 989 to 992). The change in the electric resistance of the measuring element is, in this case, a measure for the pressure. For measuring high pressure shock waves measuring elements with resistance filaments of manganin are used which are located within or between solid bodies. The direction of the mechanical stresses to be measured is, in this case, normal to the plane of the measuring element (Journal "ISA Transactions", volume 7 (1968), pages 223 to 230). In order to investigate tribological slide and roll contact zones in components used in building machines, for instance, gears, roller and sliding bearings and camtappet pairs, measuring elements are directly applied to these components by means of modern coating processes such as electric beam vapor deposition. Such measuring elements are used for measuring the pressure response in a lubricating gap and for measuring the Hertzian stress distribution at direct contact (Journal "Konstruktion", volume 32 (1980), No. 6, pages 241 to 246).
When measuring high static pressures from 30 kbar upwards a solid with a low shear module, such as, pyrophyllite or silver chloride is used as pressure transmission medium. Nevertheless, there are often large measuring errors since the solid does not act like a frictionless liquid and, therefore, in the measuring element a quasi-hydrostatic stress is caused which may be differ from one measurement application to the other.
Regarding sensors for measuring forces and mechanical stresses according to DE-A No. 1932899 it is of great disadvantage with those of low height that the lateral strains occuring in the measuring element transverse to the direction of the normal stress field cause large measuring errors. The magnitude of these lateral strains depends on the lateral strain field of the input surfaces of the sensor. This strain field influences the piezo-resi
REFERENCES:
patent: 2090188 (1937-08-01), Dahlstrom
patent: 3314034 (1967-04-01), Caris
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