Weighing scales – Self-positioning – Electrical current generating or modifying
Patent
1990-07-11
1993-02-02
Miller, Jr., George H.
Weighing scales
Self-positioning
Electrical current generating or modifying
177229, 73862627, G01G 314, G01G 308, G01L 122
Patent
active
051831252
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a load-sensing element for a balance, and in particular to a load-sensing element for a balance embodied by a beam that receives a load on one end. The balance has a horizontal recess with substantially reduced, identical cross sections of material on the top and bottom of the recess which form bending points, in such a manner as to make two guide bars of a parallel guide between the bending points, and in which a measurement signal is derived by wire strain gauges on the bending points.
2. Prior Art
A load-sensing element of this type is known from European Patent Document 0 227 850. It is disadvantageous that the bending points of one guide bar are unequally strained, because the bending moment of the entire beam is superimposed on the bending moments of the individual guide bars. To compensate for this, it is known to embody the material cross sections at the bending points differently (European Patent Document 0 207 240). It is also known to improve the linearity of such a load-sensing element by the special disposition of a connecting rod between one guide bar and a measurement cell (German Published, Unexamined Patent Application DE-OS 32 39 002).
A disadvantage of the known load-sensing elements is that when there is a large new load, the resultant measurement signal varies sharply if the engagement point of the load longitudinally of the beam changes even slightly--in a range of as little as 1/10 of a millimeter--as can happen from wear, for example.
SUMMARY OF THE INVENTION
It is the object of the present invention to improve a load-sensing element of the above-described type such that its sensitivity to variations in the load engagement point is decreased or eliminated.
According to the present invention, this object is attained by disposing wire strain gauges on the bending points of one guide bar; the other guide bar has a shoulder between the bending points, at which shoulder the outer cross section of the beam increases, and the center lines in the material cross section of the bending points forming this guide bar are offset from one another by a predetermined amount.
As a consequence of the shoulder, the offset in the center lines of the material cross section at the bending points increases the outer cross section of the beam or beams, which increases the outer cross section of the beam, on the precondition that at the bending points, the distances between the outer faces of the beams and the opening must be equal. When a load is imposed, the offset creates an additional torque, which strains the bending points with an additional bending moment. This can be determined, by suitable dimensioning, such that a certain deflection of the engagement point of the load on the beam no longer leads to any perceptible change in the derived measurement signal.
A further provision of the present invention is that the load-sensing element is embodied by three beams which are joined together in the shape of an E by a transverse beam, and that the fastening of the load-sensing element on a bracket is effected at the free ends of the two outer beams, and the load is received on the free end of the middle beam. This has the advantage, when each of the beams is embodied by two guide bars, forming a parallel guide, that the force plane of an exerted load always remains the same, even if the loaded middle beam deflects. Linearity is improved considerably thereby.
BRIEF DESCRIPTION OF THE DRAWINGS
An exemplary embodiment of the invention and its advantageous further features will now be described in detail, referring to the accompanying drawings. Shown are:
FIG. 1, which is a schematic layout of a balance with a load-sensing cell according to the present invention;
FIG. 2, which is a perspective view of the load-sensing cell;
FIG. 3, which is a section taken along the line III--III in FIG. 2;
FIG. 4, which is a view of the bending of two beams of the load-sensing element under load;
FIG. 5, which is a view of the exemplary emb
REFERENCES:
patent: 4022288 (1977-05-01), Canevari
patent: 4505345 (1985-03-01), Jetter
patent: 4593778 (1986-06-01), Konishi et al.
patent: 4678050 (1987-07-01), Wirth et al.
patent: 4718287 (1988-01-01), Mishliborsky
patent: 4892163 (1990-01-01), Aumard
Miller Jr. George H.
Soehnle-Waagen GmbH & Co.
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