Weighing scales – Self-positioning – Electrical current generating or modifying
Reexamination Certificate
1999-05-07
2001-02-27
Gibson, Randy W. (Department: 2859)
Weighing scales
Self-positioning
Electrical current generating or modifying
C177S229000, C073S001130
Reexamination Certificate
active
06194672
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns a balance in which the weight force of a load to be weighed is introduced through a load receiver that is constrained in parallel-guided motion by two guide links extending in parallel at a distance from each other, each of the guide links being connected at one end to the load receiver and at the opposite end to a stationary part of the balance. The load receiver is guided in relation to the stationary part of the balance in a parallel-displacement mode within the plane of the parallelogram that is defined by the four ends of the guide links. The balance has a force transducer to convert the weight force into an electrical signal and a lever mechanism for transmitting the weight force from the load receiver to the force transducer with a first and a second lever as well as a mechanical coupling area for the releasable connection with a calibration weight., The first lever has an input arm extending from a coupling that introduces the force from the load receiver and is formed on a load receiver portion facing the stationary part to a first support that serves as lever fulcrum and is formed on a portion of the stationary part facing the load receiver; and the first lever also has an output arm extending from the support in the direction towards the stationary part. Receiving the force through a coupling from the output arm of the first lever, the second lever is held by a second support serving as lever fulcrum formed on a portion of the stationary part facing the load receiver; and the second lever also has a portion that extends in the direction towards the load receiver and serves to further transmit the weight force to the force transducer.
2. Description of the Related Art
In a known balance of this kind (DE 196 05 087 A1) whose lever mechanism has a total of three levers for the successive reduction of the weight force introduced into the load receiver, the coupling area that serves for the connection of the calibration weight is arranged on an arm of the third lever that is coupled to the second lever (the third lever following the second lever in the force reduction chain). A small calibration force introduced to this coupling area thus corresponds to a weight force on the load receiver of a multiple amount that is determined by the reduction ratio of the lever mechanism. Therefore, by using this arrangement of the coupling area, the application of a relatively large weight force to the load receiver may be simulated by a calibration weight of desirable small size. In particular, with a calibration weight corresponding only to a small fraction of the capacity load of the balance, it is possible to perform a calibration as if a full load were placed on the balance.
However, with this simulated application of the full capacity load it is not possible in the calibration process to cancel errors in the lever ratio occurring in those levers of the mechanism that precede the lever that is equipped with the coupling area. Over the course of the lifetime of a balance, lever ratio errors of this kind can easily develop because the levers that follow the first lever are supported and coupled to each other by very delicate, thin flexure pivots that can suffer deformations when the balance is subjected to shocks.
SUMMARY OF THE INVENTION
The object of the present invention is to develop a balance of the kind described at the beginning in such a manner that, with a calibration weight corresponding to only a fraction of the full load of the balance, it is possible to perform a full-load calibration unimpaired by ratio errors of the lever mechanism where the risk that the calibration is affected by lever ratio errors from extraneous causes is largely avoided.
According to the invention, the solution of this problem is to provide the input arm of the first lever with an extension that extends beyond the coupling into the space adjoining the side of the load receiver facing away from the stationary part, at which location the extension is equipped with a coupling area for the calibration weight.
With the inventive solution, the calibration weight by way of the extension acts immediately on the input arm of the first lever. Possible ratio errors occurring in the parts of the lever mechanism after the input arm of the first lever, e.g., as a result of shock-induced deformations of the couplings and fulcrums of the levers, are cancelled in the calibration process. By giving an appropriate length to the extension beyond the point where the coupling connects the load receiver with the input lever arm in proportion to the length of the input lever arm between the coupling and the first support, the calibration force that correlates with the full-capacity load of the balance is reduced correspondingly, e.g., to an amount of {fraction (1/10)} to {fraction (1/40)} of the full-capacity load. Thus, the full-load calibration can be performed with a relatively small calibration weight resulting in design economies in the size and weight of the balance.
In an advantageous embodiment of the invention, the coupling area for the calibration weight contains a guide for positioning the calibration weight on the extension, guiding the calibration weight to take its defined working position under the influence of gravity. In this, the location where the calibration weight is transferred to the guide does not have to be defined with any particular accuracy. As the calibration weight passes along the guide under the influence of gravity, it automatically reaches its precisely defined working position, so that its distance from the first support of the first lever is maintained very accurately in the calibration process.
A practical configuration of the inventive balance has the characteristic feature that the extension of the input arm of the first lever is formed by two legs located at a distance from each other on opposite sides of the plane of the parallelogram. The ends of the legs that are nearer to the stationary part are firmly attached to the first lever, the coupling area for the calibration weight is formed at the opposite ends of the legs, and the load receiver extends between the legs with lateral clearance. This allows the two legs to be dimensioned in a manner that is appropriate for the desired full-capacity load and the desired weight amount of the calibration weight, independent of the interior space of the parallelogram enclosed by the load receiver, the stationary part and the two guide links. In particular, the legs may be configured as separate from the first lever and attached to the latter with screws.
In a further useful embodiment within this context, the ends of the two legs that form the coupling area are designed in the shape of receiving forks oriented against the direction of gravity for the calibration weight to be deposited in the direction of gravity. When the calibration weight is set down, it will seat itself in the receiving fork to a depth where it is positioned without any horizontal play in its precisely defined location relative to the first support of the first lever, thereby allowing the calibration process to be performed with a high degree of accuracy.
For reasons of structural rigidity, it is practical to connect the two legs by a brace extending transverse to the plane of the parallelogram in the area of the ends that form the coupling area.
In accordance with a further thought of the present invention, the force transducer is located in a space delimited on the one hand by the side of the load receiver facing away from the stationary part and on the other hand by the coupling area for the calibration weight; and the portion of the second lever that runs in the direction towards the load receiver has an extension that reaches to the force transducer. In this embodiment, the space required for the force transducer is at the same time available for the extension of the input lever arm that extends through this space in the direction of the plane of the parallelogram, whereby a des
Burkhard Hans-Rudolf
Schneider Ferdinand
Gibson Randy W.
Kueffner Friedrich
Mettler-Toledo GmbH
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