Measuring and testing – Dynamometers – Responsive to multiple loads or load components
Reexamination Certificate
1999-09-02
2001-07-03
Noori, Max (Department: 2855)
Measuring and testing
Dynamometers
Responsive to multiple loads or load components
C073S775000, C073S795000
Reexamination Certificate
active
06253626
ABSTRACT:
FIELD OF THE INVENTION
The present invention is in the field of transducer bodies used for mounting strain gages.
BACKGROUND OF THE INVENTION
Strain gage based transducers for translating an input of mechanical energy into equivalent electrical signals are well-known in the art. Force-measuring transducers, referred to as “load cells”, typically comprise a “spring element” or “flexure element” of metal with strain gages bonded to its surface to measure bending, direct stress, or shear. For purposes of this application the physical structure incorporating the spring or flexure element will generally be referred to as a “transducer body”.
In terms of force-measuring capacity there are generally two classes of transducer body: low capacity bodies of the “bending element” type, for example rings and cantilever beams; and, high capacity bodies of the shear-web and column types.
Cantilever-beam and ring-shaped transducer bodies are relatively flexible, low force transducer bodies, being useful for measuring only up to about 1,000 pounds of force.
In the high capacity category, I-beam and column shapes excel for axial loading above 1,000 pounds, but present unique problems in terms of accurate measurement, for example “cross-talk” errors from off-axis load and bending components. For these and other reasons, column-type load cells have been noted by at least one well-known authority as waning in popularity.
FIG. 1
illustrates a prior art column type transducer body in solid lines, with an alternate I-beam style illustrated in phantom lines. The transducer body of
FIG. 1
includes ends designed to be threaded into axial connection with two objects between which a force is generated, for example a hydraulic cylinder and tool operated by the cylinder. Transducer bodies of the type illustrated in
FIG. 1
are sometimes referred to as “single-axis envelopes” because they are designed for single-axis load measurements.
As noted above, single-axis column or I-beam type transducer bodies such as those illustrated in
FIG. 1
are typically preferred for higher force-measuring applications, i.e. over 1,000 pounds. Below that range the column and I-beam shapes do not deform sufficiently, or have to be made too small in diameter to be usefully stable.
SUMMARY OF THE INVENTION
In its broadest aspect, the present invention is a ring-type flexure element formed into a single-axis envelope of the type illustrated in
FIG. 1
, replacing the typical column or I-beam.
The ring-type flexure element in a single-axis envelope (axis-1) allows the transducer body to be used for truly accurate multi-axis force measurements when strain gages are arranged according to the first aspect.
In another aspect of the present invention, the ring element incorporated into the single-axis envelope is provided with a novel interior stiffening web. The web provides rigidity to the ring, reducing the deflection of the relatively soft ring and helping to localize strain under strain gages mounted on the ring element. In the preferred, illustrated form the web is perforated in a symmetrical pattern, which for single axis loading localizes (concentrates) strains immediately under the strain gages.
Sets of strain gages are mounted directly on the flat surfaces of the web inside the ring to measure single-axis compression/tension loading. Used only with these web-mounted gages, the inventive transducer body is capable of more accurate high capacity single-axis measurements than a traditional column element or “H” section. Bending and shear measurements on the inventive transducer body with strain gages located at 45° and 90° around the outside of the ring provide the means to measure axis-2 and axis-3 forces. This combination of web-mounted and ring-mounted strain gaging provides true three-axis measurement not previously available.
The 45° strain gaging on the outside of the ring measures axis-2 forces proportional to side-bending strains, something not possible with single-axis envelopes of the type shown in FIG.
1
. The web with holes as located enhances the performance for axis-2 measurements over what could be obtained by gaging a simple proving ring structure on its own. Additionally, the 90° strain gaging on the outside of the ring to measure shear is an improvement over the old style proving ring
REFERENCES:
patent: 4628745 (1986-12-01), Hatamura
patent: 4640138 (1987-02-01), Meyer et al.
patent: 4695963 (1987-09-01), Sagisawa et al.
patent: 4823618 (1989-04-01), Ramming
patent: 5315882 (1994-05-01), Meyer et al.
C.C. Perry & H.R. Lissner, “The Strain Gage Primer” 2nd Edition, McGraw-Hill Book Company (1955).
Sketch of M.C. Shaw Ring Transducer Body, 1956.
“Strain Gage Based Transducers” 2nd Ed. The Technical Staff of Measurements Group, Inc. (1988) Chapter 2: “Load Cells”.
Barrett Gary L.
Shoberg Ralph S.
Noori Max
RS Technologies, Ltd.
Young & Basile P.C.
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