Weighing scales – Self-positioning – Electrical current generating or modifying
Reexamination Certificate
2001-05-25
2003-05-13
Gibson, Randy (Department: 2841)
Weighing scales
Self-positioning
Electrical current generating or modifying
C177S212000, C177S229000, C073S862639
Reexamination Certificate
active
06563060
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electronic balance provided with a Roberval mechanism. The present invention can be applied to the so-called electronic balance provided with a balance mechanism and also to the so-called electronic scale provided with various load sensors without having a balance mechanism.
2. Description of the Prior Art
In the case of many electronic balances and electronic scales, a weighing dish for mounting a load to be measured is supported by a Roberval mechanism (also referred to as a parallel guide) in order to control the movement of the weighing dish. The Roberval mechanism has a structure in which a movable pillar is supported by an upper and a lower beams parallel with each other for a fixed pillar fixed to or integrated with the frame of a balance mechanism or scale mechanism. Both ends of each beam are respectively connected to the fixed pillar or movable pillar through an elastic fulcrum. A weighing dish is supported by the movable pillar. Then, a load working on the weighing dish is transmitted to an electrical load detecting section through a movable pillar or, moreover, through a lever. The electrical load detecting section includes a shift sensor and an electromagnetic-force generator feedback-controlled by using an output of the sensor as a detected value in the case of an electromagnetic-force-equalizing electronic balance. Further, the section includes a vibration chord and its exciting section in the case of a chord-vibrating scale.
As the above Roberval mechanism, the following Roberval mechanisms are known which have a structure obtained by assembling a fixed pillar, a movable pillar, and an upper and a lower beam as members independent of each other as disclosed in the official gazette of Japanese Unexamined Utility Model Publication No. Sho 63-35924 (1988) and moreover, an integral structure obtained by boring one flat base material as disclosed in the official gazette of Japanese Unexamined Patent Publication No. Sho 63-277936 (1988).
The above Roberval mechanisms respectively prevent a weighing dish from overturning or tilting and moreover, have a function for eliminating an error due to a one-sided load on the weighing dish, that is, a four-corner error (one-sided error).
The four-corner-error eliminating function of the Roberval mechanism is not effectuated before the parallelism of an upper and a lower beam is strictly adjusted. In other words, before elastic fulcrum portions provided for both ends of an upper and a lower beam are adjusted so that vertical intervals of the fulcrum portions coincide with each other. Generally, the accuracy of the parallelism ranges between 0.1 and 10 &mgr;m though it depends on an allowable four-corner error (balance accuracy). Therefore, it is difficult to meet the accuracy of parallelism in accordance with the machining accuracy of a part and adjustment while actually changing load mounting positions on a weighing dish after assembling, that is, the so-called four-corner-error adjustment is necessary.
The four-corner-error adjustment is performed by adjusting a one-sided error in the longitudinal direction of each beam of the Roberval mechanism, that is, the axial direction (hereafter referred to as longitudinal direction) and the direction orthogonal to the longitudinal direction (hereafter referred to as crosswise direction) while changing load mounting positions on a weighing dish. Therefore, in the case of a Roberval mechanism of an integral structure, portions corresponding to front, rear, right, and left are removed from a part of elastic fulcrum portions at both ends of an upper and a lower beam respectively or as disclosed in the official gazette of Japanese Unexamined Utility Model Publication No. Sho-35924 (1988), the adjustment mechanism of a corresponding portion is operated in the case of a Roberval mechanism provided with an adjustment mechanism for inching the position of a fixed portion to a fixed pillar of each elastic fulcrum portion.
Among the above Roberval mechanisms, the rigidity in the crosswise direction is lower than that in the longitudinal direction and thereby, a one-sided error easily occurs in the crosswise direction because the integral-structure Roberval mechanism obtained by boring a flat base material has a small crosswise-directional dimension. Therefore, the above integral-structure Roberval mechanism has a problem that it is difficult to correspond to a large weight or large dish.
On the other hand, an assembling-type Roberval mechanism has a problem that the adjustment result of a one-sided error in the longitudinal direction influences that of a one-sided error in the crosswise directions and vice versa and thus, adjustment of the errors is difficult.
The present inventor has proposed an electronic balance capable of solving the above problems and preventing a one-sided error from occurring in the crosswise direction even when using a Roberval mechanism having a small rigidity in the crosswise direction and simplifying the adjustment of a four-corner error of the mechanism compared to the conventional case (refer to the official gazette of Japanese Unexamined Patent Publication No. 2000-162026). In the case of the electronic balance, a second Roberval mechanism orthogonal to a Roberval mechanism (first Roberval mechanism) in which a weighing dish is supported by a movable pillar when viewed from above is used and the movable pillar of the second Roberval mechanism is integrated with that of the first Roberval mechanism. Then, an axial-directional (longitudinal-directional) one-sided load of the first Roberval mechanism is shouldered by the first Roberval mechanism and a one-sided load in the crosswise direction of the first Roberval mechanism (torsional direction about the axis of the first Roberval mechanism) is mainly shouldered by the second Roberval mechanism. Thereby, the adjustment operability is improved by separating the adjustment of a one-sided load in the crosswise direction from that in the longitudinal direction and simultaneously, weakness of the first Roberval mechanism in crosswise-directional rigidity can be covered.
Furthermore, it is preferable to provide a flexible portion soft in a tilted direction of the movable pillar of the first Roberval mechanism, in which a tilt is caused by a one-sided load in the axial direction of the first Roberval mechanism, in other words, a flexible portion for providing flexibility in the longitudinal direction of a beam of the first Roberval mechanism for the second Roberval mechanism. In this case, when a one-sided load in the axial direction of the first Roberval mechanism works and thereby, a force for tilting the movable pillar in the axial direction works, it is possible to absorb the force by the flexible portion and prevent the second Roberval mechanism substantially sharing the movable pillar from being influenced.
Moreover, in the case of the above proposed configuration, by housing the first Roberval mechanism in a square pipe so that the axial direction is parallel with the axis-center direction of the square pipe and setting the second Roberval mechanism to an end face of the square pipe, the positional relation between fixed pillars of two Roberval mechanism is not fluctuated due to a load to be measured and a compact and high-performance electronic balance having a high rigidity is obtained by utilizing the high torsional rigidity of the square pipe.
According to the above proposal of the present inventor, it is possible to substantially adjust one-sided errors independently in the longitudinal and crosswise directions to a weighing dish in the first and second Roberval mechanisms and realize a high-rigidity and compact electronic balance by combining these first and second Roberval mechanism with square pipes. However, according to further detailed examination by the present inventor, the following problems have been clarified.
In other words, when a one-sided load works in the crosswise direction, that is, when a torsional-directi
Gibson Randy
Rader & Fishman & Grauer, PLLC
Shimadzu Corporation
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