Weighing scales – Self-positioning – Electrical current generating or modifying
Patent
1995-03-21
1997-01-28
Gellner, Michael L.
Weighing scales
Self-positioning
Electrical current generating or modifying
73862626, 3612834, 361291, G01G 314, G01G 706, G01G 1902
Patent
active
055979840
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to the field of weigh scales and, in particular, to dynamic or static weigh scales using a capacitance transducer.
BACKGROUND ART
U.S. Pat. No. 3,782,486 discloses a device for sensing and measuring a transient load such as one imposed by at least one wheel on an axle of a passing vehicle. The device comprises a low profile pad or mat comprising three electrode plates separated by a dielectric, elastomeric material. Capacitance is established between the central electrode and each of the outside electrodes. The electrodes are connected to a device for detecting variations in the electrode spacing owing to transient loads. Void areas are located in the body of the mat to provide for mat deformation proportional to the magnitude of the applied load. The patent describes the need for a portable weight sensing device having the characteristics of (a) portability, (b) simplicity, (c) ruggedness and reliability, (d) insensitivity to location of load and (e) cheapness. Disclosure of other capacitance weighing transducers is found in British patent specification 1,453,934 and Canadian patents 1,069,945; 1,013,779 and 901,028. All of these transducers have different types of elastomeric dielectric materials. All measure a load using the change in the capacitance of the transducer caused by compression of the dialectic.
Despite some claims to the contrary, capacitance transducers using elastomeric dielectric materials may not have a linear response and may have significant hysteresis under a variety of conditions and loads. Tests on such mats suggest that the cause is that diametric properties of the combination of expansion gaps (or air holes) and elastomeric material between the electrodes may vary in a non-linear manner under compression, that elasticity of the material may be temperature dependant and that there may be memory effects in elastomeric material when loads are applied in rapid succession.
It is an object of this invention to construct an improved capacitance transducer which does not rely upon compression of elastomeric dielectric materials to change the capacitance. Instead, the present invention employs a novel principle of bending adjacent electrode plates in synchronous opposition over a plurality of substantially rigid dielectric separators to create a plurality of areas of closer proximity between the plates to effect capacitance changes.
DISLCOSURE OF THE INVENTION
In this description and in the claims the words "horizontal" and "vertical" and the like are used to describe the respective orientation of parts of the invention to each other without necessarily requiring that the parts have that orientation in an absolute sense during operation. Nevertheless, it is anticipated that ordinarily the parts will have such orientation in normal use.
The present invention is a transducer for a weigh scale or the like. Each transducer comprises a capacitance mat having a plurality of electrode plates lying over one another. Each of the electrode plates is spaced apart from the others by a dielectric layer comprising a plurality of dielectric separators. The dialectic separators may be dots, squares, strips or other shapes which allow a uniform spacing across the layer to permit the electrode plates to bend over the separators into the spaces between the separators when a load is applied to the mat. The separators are sufficiently thick and are spaced sufficiently close together to allow plate bending without electrode contact under expected loads (although overload stops may be an alternative or additional feature). The surface of the separators is securely attached between adjacent electrode plates to resist shear forces generated dining use of the mat. The separators preferably extend across the plates to permit plate bending at any area of load application. The spacing of the separators, and their dimensions may be optimized empirically or otherwise without further invention by persons skilled in the art for specific load ranges and desired sensitivity.
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REFERENCES:
patent: 3565195 (1971-02-01), Miller et al.
patent: 3678378 (1972-07-01), Trott et al.
patent: 3875481 (1975-04-01), Miller et al.
patent: 4266263 (1981-05-01), Haberl et al.
patent: 4793429 (1988-12-01), Bratton et al.
RESEARCH DISCLOSURE May 1987, Havant GB pp. 318-319, disclosed anonymously, "The Captive Pad Sensor".
Gellner Michael L.
Gibson Randy W.
Sowal Technologies International Inc.
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