Electronic scale

Details Electronic scale Electronic scale

1983-03-07

1984-09-18

Moose, Jr., Harry E.

Weighing scales

Self-positioning

Electrical current generating or modifying

177256, G01G 314, G01G 2108

Patent

active

044718470

DESCRIPTION:

BRIEF SUMMARY
This invention relates to an electronic scale.
Generally, exact measuring of a force in one direction is comparatively simple. Thus, for instance by weighing in a suspended scale, pan exact weight information can be obtained by using one measuring sensor. However, in most cases a swinging and unstable scale pan cannot be accepted but a substantially rigid pan or platform for the load is needed.
In order to achieve a stable scale pan the pan could for instance be suspended on three arms extending from a base and being connected to the pan by means of strain gauges. Alternatively, a load cell could be placed under each corner of a platform. Both these solutions require several sensors which have to be trimmed to exactly the same sensitivity in order to indicate the same weight independently of the position of the load on the pan or the platform. Such constructions are technically relatively complex and expensive.
If, instead, a central load cell below the middle of the platform is used, large moments are produced when the load is moved to a corner. These moments must be taken up by the load cell without any registration error, which is hardly possible to achieve not even with specially designed load cells, particularly when the platform is large or the demand for accuracy is great.
To eliminate such side forces and undesired moments, known mechanical scale constructions having means for parallel guiding of the platform have been used. The electronic sensor is in these cases so disposed that the force is taken up solely in one direction. In some cases, such sensors have been substituted for a weighing spring or a system of balancing weights. When the original mechanical scale construction has been of an expensive precision type and the integration of the sensor has been made with great exactness, a good result has been achieved, although at a very high cost.
It is also previously known (U.S. Pat. Nos. 4,274,501 and 4,276,949), to use scales having intermediate measuring units which are supported at six points and which are provided with sensor means. However, the supporting joints are so arranged that the levers are very short, and consequently the accuracy is also very low. Another drawback when using this type of scales is that the supporting points are formed as knives which can easily be damaged and subject to wear affecting the exactness of the scale.
The failure of many attempts to modify existing mechanical scales for electronic weighing depends on the fact that sometimes such short balancing arms have been used in the mechanical construction that the demand for accuracy with respect to the length of the arm has been of the magnitude of 1/1000 mm. This is difficult both to achieve and to maintain, i.a. due to wear.
The basis of this invention is the desire to provide an electronic scale which is simple and cheap from a manufacturing point of view and comprises a sensor which, as far as possible, eliminates all undesirable forces and moments caused by the positioning of the load on a platform or the like, and which only needs one sensor. The construction should also be such that short moment arms, which demand great manufacturing precision, and also knives and sockets which can result in friction or wear are avoided. The length of the moment arms should be optimized to be as long as mechanically possible. Further, no mechanical adjustment on assembly should normally be necessary.
The above object is achieved according to the invention by using a so-called double three-point support, meaning that the scale pan or corresponding part is supported at three points in a sensor device which in turn is supported at three other points in a base. By using two three-point supports the construction is statically fully determined.
The invention will now be described by way of example with reference to the accompanying drawings.
FIG. 1 is a partly broken perspective view of an embodiment of a scale according to the invention.
FIG. 2 is a plan view, partly in section, of an embodiment of a sensor device according to t

REFERENCES:
patent: 3938603 (1976-02-01), Shoberg et al.
patent: 4274501 (1981-06-01), Gallo et al.
patent: 4382479 (1983-05-01), Lee et al.

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