Weighing scales – Self-positioning – Spring
Patent
1991-06-26
1992-12-08
Fuller, Benjamin R.
Weighing scales
Self-positioning
Spring
177255, G01G 300
Patent
active
051689456
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to force measuring apparatus in particular weighing machines of the platform type in which the magnitude of the imposed load is determined from the deflection of resiliently elastic elements such as coil or leaf springs.
Present weighing machines in general use employ complicated mechanisms to ensure the parallel descent of the weighing platform for the purposes of obtaining an accurate reading of weight.
By virtue of their complicated design they restrict efforts to cheapen their cost of manufacture and in some cases lack sufficient accuracy.
A lesser known domestic weighing machine employs three coiled springs of equal spring rate arranged at the corners of an equilateral triangle.
The coiled springs support the weighing platform and the measurement point for an imposed load at any position on the platform is taken from a central point of the equilateral array whereat the deflection of downward displacement of the platform will always correspond to the magnitude of the imposed load.
This known weighing machine has proved of some utility in domestic situations but it lacks the required accuracy for wider applications.
Moreover the tilting of the platform which necessarily occurs by virtue of its design is not a desirable feature and should for example the tilting be sufficient to take the platform out of contact with one or more of the coiled springs the effect on accuracy may be catastrophic.
However, the desirability of having a central take-off point as a measurement point using coiled springs more or less is a determinant of the known design since it is predicated on the knowledge that to realise a central take-off point required the coiled springs to be symmetrically and equiangularly disposed.
SUMMARY OF THE INVENTION
It is an object of the present invention to obviate the disadvantages of the prior art and to provide a weighing machine which provides a measurement of weight with high accuracy and without recourse to the procrustean devices of varying degrees of complexity which are employed at the present time to ensure the parallel descent of the weighing platform.
According to the present invention there is provided a weighing machine comprising one or more elongate elastic elements which provide for restorable deflection under load, the or each elastic element being mounted between spaced support means therefor, a weighing platform resting on the or each elastic element such that an imposed load at any position on the platform produces a resultant displacement thereof occurring at an invariant position and corresponding to the magnitude of the imposed load, and means for responding to said resultant displacement at said fixed position whereby to provide a measure of the magnitude of the imposed load on the platform.
Preferably the elastic elements are two leaf springs which are suspended between rigid supports forming the corners of a rectangle of which the leaf springs form parallel sides. With this arrangement the invariant position lies at the geometrical centre of the rectangle.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention will now be described by way of example with reference to the accompanying drawings wherein;
FIG. 1 side schematic, partially-sectional, view a beam under load supported at its ends by coiled springs of differing spring rates as an illustration of the production of an invariant off-centre measurement point to explain the theory behind the invention;
FIG. 2a is a plan and side view of an arrangement of coiled springs of differing spring rate supporting a stiff plate further to illustrate the production of an off-centre invariant measurement point according to the theory behind the invention;
FIG. 2b is a side, schematic, partially-sectional view of the structure of FIG. 2a;
FIG. 3 shows a side schematic, partially sectional view a leaf spring supported at its end and under asymmetric load to produce a longitudiual off-centre invariant measurement point;
FIG. 4 shows is a side, schematic, partially
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Fuller Benjamin R.
Gibson Randy W.
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