Weighing scales – Means holding load-driven element against motion
Reexamination Certificate
2001-03-29
2003-07-29
Gibson, Randy (Department: 2841)
Weighing scales
Means holding load-driven element against motion
C177S156000
Reexamination Certificate
active
06600112
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a weighing scale (hereinafter called a scale, for short) in the general sense of a weighing device with a housing. Inside the housing is a force transducer, and connected to the latter is a load-transmitting member that passes through an opening in the housing and serves to transmit the weighing load to the force transducer. With scales of this type, the following two concerns need to be addressed: First, when the scale is not in use, it may be desirable to immobilize the movable parts inside the scale with an arrestment device for protection against random forces that could be detrimental to the accuracy of the scale. Second, it is a known fact that scales are often used in a dirty environment and that, furthermore, the materials themselves that are being weighed can contaminate a scale and thereby cause its accuracy to deteriorate. Many applications require that the process of applying and releasing the arrestment can be performed in rapidly alternating succession.
OBJECT OF THE INVENTION
It is therefore the objective of the present invention to further develop a scale of the type described above by providing arrestment and sealing means that can be alternated rapidly between the applied and released state and are effective in preserving the accuracy of the scale in the presence of the aforementioned conditions.
SUMMARY OF THE INVENTION
According to the invention, the objective just stated is met by an arrangement where a controllably expandable and contractible elastic device is interposed between a first, spatially fixed part and a second, movable part of the scale. The fixed part is connected to the scale housing, while the movable part is connected to the load-transmitting member. Thus, when a load is applied to the load-transmitting member, the movable part will be displaced in relation to the fixed part. In the expanded state, the elastic device closes a gap between the fixed and movable part, whereby the gap is sealed and the movable part is immobilized, i.e., arrested in relation to the fixed part. The elastic device can be configured so that its deactivated rest mode corresponds to the expanded state of the device, where the movable part of the scale is arrested. In this case, the device will contract when activated, whereby the arrestment of the movable part is released. As an alternative possibility, the device can be configured so that its deactivated rest mode corresponds to the contracted state of the device, where the movable part is in a released condition, while activating the device will cause the latter to expand, whereby the movable part is arrested. In addition to immobilizing the second part, the arrestment in either case will to a certain extent have the effect of a seal between the movable part and the spatially fixed part that is connected to the scale housing.
A solution of this kind is of twofold benefit: On the one hand, the concept of expanding and contracting an elastic device, which could be a spring, allows the movable part to be arrested against the fixed part either by a form-fitting engagement (where the elastic device expands into a counterpart of a matching concave shape) or by a friction-based engagement. On the other hand, when the elastic device is in its expanded state, it can also form a seal.
The ability to function as a seal is realized in particular with an arrangement where the elastic device forms a hollow space for a fluid and the expansion and contraction is effected by increasing or decreasing the amount of fluid contained in the hollow space. In practice, this can be achieved by providing a device for selectively moving fluid into and out of the hollow space. This also represents a simple way of activating and deactivating the device.
The sealing function is achieved most efficiently by arranging the elastic device at the place where the load-transmitting member passes through an opening in the scale housing. This has the advantage, that the seal is provided in the immediate area where the functionally required opening in the scale housing is located. It would of course be conceivable to arrange the seal somewhere more in the interior of the scale and to provide a dirt-collecting chamber, but the arrangement of the seal at the periphery of the housing proves to be more advantageous.
Although it would be possible within the scope of the present invention to attach the elastic device to the movable part and to let it expand against the spatially fixed part, the favored arrangement is to connect the elastic device to the spatially fixed part and let it expand against and make contact with the movable part. Preferably also attached to the fixed part is a conduit system for injecting and removing fluid.
Within the context of the invention, it is readily conceivable to configure an elastic arrestment device, e.g., in the form of individual cushions that could be mechanically expandable, for example by pressurizing the cushions. However, the preferred form of the elastic device is a ring-shaped cushion that is interposed between the fixed part and the movable part and in its non-expanded state has a cylindrical surface of predetermined diameter with an axial orientation in the travel direction of the movable part. The ring-shaped cushion can be seated on a support body (represented by a ring-shaped support in the preferred embodiment described below) that fills the inside of the ring-shaped cushion and is preferably connected to a conduit for letting fluid in and out of the cushion.
In order to achieve the largest possible area of pressurized contact between the fixed part and the movable part, it is advantageous if the ring-shaped support has a convex-curved contour shape facing towards the movable part, with a contour radius about equal to the ring diameter of the cushion. The convex surface shape of the cushion produces a particularly effective sealing interface compared, e.g., to a mere line contact between the fixed part and the movable part.
If the expansion of the cushion is based on hydraulic or (preferably) pneumatic pressure, a uniform pressure distribution can be achieved if the ring-shaped support has a ring channel in the shape of a groove facing the interior surface of the ring cushion.
The contact engagement of the elastic device between the fixed part and the movable part creates the danger that the movable part will be exposed to non-symmetric forces that could be harmful or even destructive to the weighing cell. It is therefore advantageous to use a design feature that will allow a certain amount of play in the horizontal directions.
Further details of the invention will be discussed in the following description of a preferred embodiment and a variant version of the preferred embodiment that are schematically represented in the drawings.
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patent: 3587760 (1971-06-01), Linz et al.
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patent: 5703334 (1997-12-01), Hansson et al.
patent: 5789714 (1998-08-01), Doerksen
patent: 0197982 (1986-10-01), None
patent: 0572181 (1993-12-01), None
Gibson Randy
Kueffner Friedrich
Mettler-Toledo GmbH
LandOfFree
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