Weighing scales – Self-positioning – Electrical current generating or modifying
Patent
1985-12-10
1988-04-26
Miller, Jr., George H.
Weighing scales
Self-positioning
Electrical current generating or modifying
7386265, G01G 314, G01L 122
Patent
active
047398485
DESCRIPTION:
BRIEF SUMMARY
The invention relates to scales and particularly but not exclusively to scales for weighing people of the kind that are used in the home and are usually referred to as bathroom scales.
Bathroom scales with a mechanical linkage operating against a spring and rotating a dial are well known and are widely used. Scales with a digital readout have also been proposed but such scales normally incorporate a single transducer acted on by a mechanical linkage of the kind used in conventional bathroom scales and are consequently no more acurate than such previous designs.
According to the invention, scales are provided including a load receiving platform and display means characterised in that weight on the platform is transferred to at least one force plate supported on support members, a plurality of strain gauges are mounted on the force plate or plates adjacent the positions at which the force plate or plates is or are supported on th support members and are effective, upon deformation of the force plate or plates as a result of weight on the platform, to produce electrical signals, means are provided for summing the electrical signals to form a composite load signal and the display means display the composite load signal as a weight reading.
By summing the electrical signals from the strain gauges electrically, many of the disadvantages and errors associated with scales which utilise a mechanical linkage to sum weight components can be obviated.
Preferably the force plate or plates includes at least three and preferably four strain gauges and preferably each strain gauge comprises a pair of piezo electric resistors. Advantageously, the portion of the or each force plate against which each of the respective support members bears is formed as a double encastred beam, that is to say having both ends in the force plate, and the piezo electric resistors are provided one at or adjacent the centre of the beam and the other at or adjacent one of the ends of the beam such that when the beam is loaded one resistor is placed in tension and the other is placed in compression.
Preferably the resistors and connections therefore are provided on the force plate or plates by thick film screen printing.
Advantageously, the force plate is formed of stainless steel coated with a dielectric material and has all the resistors forming the strain gauges and connection therefore screen printed and fired on the dielectric material.
Each beam is preferably of substantially diamond shape and is formed by stamping out portions of the stainless steel plate to leave the beam of narrow width adjacent its ends and with a wide middle portion, the transitions between the ends and the middle portion being rounded off from a strict diamond shape. Preferably the force plate is generally U-shaped so that, in the interests of economic use of material, a sheet of material can be cut up with very little wastage by interlocking three U-shapes together, that is to say with the limbs of two of the shapes nested between the two limbs of the third U-shape.
Advantageously each beam has its longitudinal extent at right angles to the longitudinal extent of the arm of the U-shaped force plate in which it is provided.
Preferably each support member bears against the underside of the middle portion of a respective one of the beams by means of a transverse knife edge type mounting. Each knife edge type mounting preferably has upstanding spigots to locate the mounting by bearing against side edges of the respective beam. Preferably the actual knife edge that bears against the beam is of a length considerably less than the width of the beam, for example half the width of the beam, and is slightly convex to reduce errors due to sensitivity of the strain gauges to transverse strain. The support members are preferably vertically movable in a base member to which the force plate is secured. Preferably the base member is formed of a plastics material, such as polypropylene, and has in its upper face recesses which receive downwardly extending flanges provided on the force
REFERENCES:
patent: 3611797 (1971-10-01), Pugnaire
patent: 4355692 (1982-10-01), Ostrelich
patent: 4574899 (1986-03-01), Griffin
Esselte Meto International GmbH
Miller Jr. George H.
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