Weighing scales – Self-positioning – Electrical current generating or modifying
Reexamination Certificate
2000-08-22
2003-04-29
Gibson, Randy W. (Department: 2841)
Weighing scales
Self-positioning
Electrical current generating or modifying
C177S229000, C073S862627, C073S862637, C029S593000
Reexamination Certificate
active
06555767
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to strain gage load cells for weighing, force measurement, and pressure measurement.
2. Description of the Related Art
A strain gage load cell is basically a metal structure subject to a load to be measured, with strain gages sensing strain in the loaded structure. The strain gages are connected in an electrical bridge circuit. Power is supplied acros one bridge diagonal, and an output signal across the other diagonal is used as an indication of the load on the metal structure. Strain gage load cells have been used extensively for weighing, force measurements, and pressure measurements since the middle of the 20
th
century.
The output signal from a strain gage load cell derives entirely from changes in the resistance of the strain gages. Accurate load measurements require that the strain gages sense the strain in the loaded structure accurately, and also that the strains in the loaded structure are true measures of the load on the metal structure. Only certain specially heat treated metal alloys, selected for low mechanical hysteresis and low creep are suitable for use in the loaded metal structure in high accuracy strain gage load cells for “legal for trade” weighing. It is also important to insure that the load is transferred to the metal structure without errors caused by slip or shifting of the point of load application.
Extensive efforts to make strain gage load cells more accurate have led to hundreds of different strain gage load cell designs now known in the art. Known strain gage load cells are all-metal designs. Most high accuracy strain gage load cells have both the loaded metal structure and the load application parts machined from one piece of load cell quality alloy. This provides ideal load introduction and measurement of applied strains, but the cost for material and machining are high.
Some planar gage type load cells for low load ratings have sensing structures machined from a flat sheet of metal, with fold-back arms and other load application and support parts of metal bolted to the sensing structure. This lowers the cost of material and machining, but the assembly cost is increased, and the repeatability is generally impaired.
SUMMARY OF THE INVENTION
A main object of the present invention is to provide strain gage load cells that are less expensive to make than prior art strain gage load cells, while maintaining high accuracy and repeatability.
This object is obtained by a strain gage load cell with a load sensing structure, comprising a load cell sensing element of load cell quality material and a non-sensing element of a plastic material joined to said sensing element.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and, in part, will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
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Gray Robert L.
Lockery Harry E.
Flintec Inc.
Gibson Randy W.
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