Weighing scales – Self-positioning – Electrical current generating or modifying
Patent
1996-02-27
1998-07-28
Gellner, Michael L.
Weighing scales
Self-positioning
Electrical current generating or modifying
177229, G01G 3147
Patent
active
057865493
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates generally to a load sensor for use with a weighing scale and, more particularly, to a low profile load sensor of unitary construction.
BACKGROUND ART
A low profile weighing scale having one load sensor has such tendency that may produce a different weight value depending upon the position to which a load is applied due to the fact that the load sensor can not have sufficient thickness. Such phenomenon is referred to as "positional error". Therefore it is a common practice that, in a flat-type weighing scale, a platform is mounted on four load sensors and the output of such load sensors are summed. However, such flat-type scale has deficiencies in that it adds the production cost because a plurality of load sensors must be used and they must have the uniform output levels.
A simple type scale, such as a weighing scale for measuring the weight of persons, having a weighing range of 100 kg to 200 kg is generally designed in such manner that load-applied-points and fulcrums are provided on four corners of the scale to receive the load in distributed condition, and levers (load transmission beams) are provided to collectively transmit the load to a point at which one sensing device is positioned.
Such simple low profile scale (or lever type scale) commonly uses a knife edge member for an arrangement of load-applied-point and fulcrum. However, such knife edge member is unstable in construction, requires several components, and accordingly, increases the number of steps of assembling. In order to solve such problems, that is, for the purpose of eliminating the unstable construction and of reducing in number of the components and the steps of assembling, various kinds of low profile scales including integrated load sensors have been proposed wherein a flexible hinge coupling or so called "an elastic coupling" is formed in a portion of the lever member for the arrangement of fulcrum and load-applied-point.
Prior art integrated load sensors using such elastic couplings are disclosed in, for example, Japanese Utility Model Publication No. 61-36891; Japanese Patent Laid-Open No. 64-43729; Japanese Utility Model Publication No. 62-3697; and Japanese Patent Laid-Open No. 63-205524.
A load sensor as disclosed in said Japanese Utility Model Publication No. 61-36891 uses the flexure of a leaf spring for the hinge coupling. Such load sensor has, however, deficiencies in that, for a scale of smaller weighing range, a stress of flexure of the leaf spring would be added to a load to be measured, which prevents the precise transmission of the load, and therefore, adversely affects the reliablility of measurement.
Another load sensor for a weighing scale in which the hinge coupling is formed by making the material thinner with a press machining to give an elasticity, as disclosed in said Japanese Patent Laid-Open No. 64-43729, can not handle the change in length (or horizontal distance) due to the flexure, thereby increasing the burden on the flexible portion. Furthermore, a load sensor in which upper and lower parallel slots are provided and vertical leaf springs are positioned, as disclosed in said Japanese Utility Model Publication No. 61-36891, requires a thicker member for giving an effective length of the spring, which limits the realization of low profile scale. In this case, a special machining process for making the vertical leaf spring is additionally required. A load sensor as disclosed in said Japanese Utility Model Publication No. 62-3697 also has the same problems.
DISCLOSURE OF INVENTION
In view of the above, it is an object of the present invention to solve the above-mentioned problems of hinge couplings of the prior art lever type weighing scale by providing a new and improved low profile load sensor having features of high precision and low cost.
According to the present invention, a low profile load sensor for use with a weighing scale having a base and a platform, which comprises: and said platform mounting members for receiving a load applied to said platf
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Gellner Michael L.
Gibson Randy W.
Tanita Corporation
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