Shear beam load cell

Details Shear beam load cell Shear beam load cell

1999-04-20

2001-05-01

Gibson, Randy W. (Department: 2859)

Weighing scales

Self-positioning

Electrical current generating or modifying

C177S229000, C073S862474

Reexamination Certificate

active

06225576

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates generally to a mechanoelectric converter, and more particularly, to a weighing device designed to convert mechanical loads into electric signals using a ceramic shear beam load cell.
2. Related Art
Heretofore, strain gage load cells used in scales for weighing applications consisted of a complex detection circuit made of resistors, which were mounted on the surface of a solid metal substrate. Referring to
FIG. 1
, a prior art strain gage load cell
10
is shown. In this device, a complex thin film or metal foil strain gage circuit
14
is mounted, typically by a glueing process, to a metal substrate
12
, such as stainless steel or aluminum. Load cell
10
is mounted to a base (not shown) via through-holes
16
.
FIG. 2
depicts another type of prior art strain gage load cell used in the industry. In this version, substrate
12
is hollowed out at midsection
18
in order to focus the stress in the area where the strain gage circuit
14
is mounted, thereby increasing the sensitivity accuracy of the device.
However, the machining associated with constructing strain gage load cells in either manner is quite costly. This may be partially attributed to the inherent cost of machining a substrate made of stainless steel.
Another costly disadvantage to the current methods used in the industry is the attachment process. Although gluing the strain gages to the surface of the substrate has recently become a reliable means of attachment, the expense remains high.
Based on the above, there exists a need to provide an accurate weighing device that is easier and less costly to produce.
SUMMARY OF THE INVENTION
The present invention provides a device that overcomes the above-identified problems of the related art through the use of, in general, a weighing device utilizing a strain gage load cell. The load cell is constructed of two substrates mounted in parallel, each having a pair of resistors embedded on opposing faces of the substrate pair. In the alternative, the resistors may be embedded on opposing faces of a single substrate. The substrates are preferably ceramic.
The first general aspect of the present invention provides for a weighing apparatus, comprising: a) a substrate pair including a first and a second substrate positioned substantially parallel to each other; b) a first and a second strain sensor mounted on opposing faces of the substrate pair; and c) a first and a second spacer, coupled to the first and second substrates at opposite ends thereof, for maintaining the first and second substrates in a spaced apart parallel position. This aspect allows for an accurate weighing apparatus that is cheaper and easier to construct than prior art weighing devices because of the two substrate configuration, having resistors mounted thereon. This aspect also allows for a weighing apparatus that does not deform or “creep” in response to cyclic loading.
The second general aspect of the present invention provides for a weighing apparatus, comprising: a) a first and a second substrate positioned substantially parallel to each other; b) a first and a second strain sensor mounted on opposite surfaces of the first substrate; and c) a first and a second spacer, coupled to the first and second substrates at opposite ends thereof, for maintaining the first and second substrates in a spaced apart parallel position. This allows for similar advantages as those mentioned in the first aspect.
The third general aspect of the present invention provides for a weighing apparatus comprising: a first spacer mounted to a base and a second spacer mounted to a weighing substrate; a first substrate fastened to the first and second spacers, the first substrate having a pair of resistors and a pair of trimming resistors mounted on a first side of the first substrate; a second substrate fastened to the first and second spacers and spaced from and in parallel with the first substrate, the second substrate having a pair of resistors mounted to a second side of the second substrate; and a set of traces connecting the first and second pair of resistors and the pair of trimming resistors to a microprocessing unit which is connected to an output unit. This aspect provides similar advantages as those associated with the first aspect. It also provides for a trimming device that is easier to manufacture, has better thermal tracking, eliminates the need for additional wiring, and allows for easier balancing via a laser trimming process.
The foregoing and other features and advantages of the present invention will be apparent from the following more particular description of preferred embodiments of the invention.


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