JPH033892B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a weighing machine having a structure in which a weighing stage is directly supported by a load cell.

Conventionally, a weighing machine in which a weighing platform is directly supported by a load detection part has a configuration in which a weighing platform 4 is fixed to a weighing unit 3 directly connected to the end of an arm 2 of a roberval mechanism 1, as shown in FIG. Are known. With this configuration, it is possible to manufacture a weighing machine with good characteristics unique to the Roberval mechanism, which allows accurate weighing even when the load moves to any position shown by arrows A, B, and C in the figure on the top surface of the platform 4. . When using this feature to make it into a load cell type, the second
It will look like the figure. The illustrated type of load cell has a structure in which the parts corresponding to the hinge parts 5, 6, 7, and 8 of the Roberval mechanism shown in Fig. 1 are made into elastic hinges 9, 10, 11, and 12, and each of the elastic hinge parts has strain. A gauge 13 is attached to detect the stress proportional to the load. In general, a load cell with this shape is called a parallel gram type load cell, and this structure does not change the measured value even if the load position on the platform 18 changes and has good linearity, so it is used as a parallel gram type load cell. A scale that is directly connected to a weighing platform is often used as the general basic structure of a scale. However, in this type of weighing machine, if the platform 18 is made larger to a certain extent as shown in FIGS. When tension occurs in the upper arm 14 and elastic hinges 11, 12 of the load cell, compression occurs in the lower arm 15 and elastic hinges 9, 10, and a load is applied as shown by arrow E, the arm 14 and elastic hinges 11, 12 compression occurs in the arm 15 and the elastic hinges 9, 10, and FIG. 2b is a side view of FIG. 2a.
When a load is applied as shown by arrows F or G, the arms 14, 15 and the hinges 9, 10, 11, 12 are twisted. Therefore, if a load is applied near the periphery of the platform 18, even if the load is the same, the stress state at the elastic hinge will differ depending on the position, and the linearity of the load cell will deteriorate, causing hysteresis and other load characteristics. becomes significantly worse.

To solve this problem, conventional weighing machines that require a relatively large platform are equipped with two load cells 16, 1, as shown in FIG.
7 is disposed on the lower surface of the platform to support one platform 15. At first glance, it seems that this configuration can be easily manufactured by simply arranging parallel gram type load cells side by side, but in reality, when two parallel gram type load cells 16 and 17 are mounted on one mounting base, two The load cells interfere with each other, and the force generated by this interference mixes into the load bearing section of the load cell and acts as a disturbance force, resulting in poor accuracy. Also, in some cases, interference forces that are too large can damage the load cell. In order to eliminate this phenomenon, it is best to make the mutual dimensions of the two load cells and the mutual dimensions of the load cell mounting part of the platform as similar as possible, but the load cell has an extremely small amount of displacement due to the load. Therefore, the precision of the work must be improved. For example, the dimensions h ₁ and h ₂ in the figure need to be manufactured accurately to about 0.01 mm in practice, which makes the product extremely expensive.

Another conventional configuration is shown in FIG. This is the rotation around the X axis and the Y
As a structure that allows rotation around the axis and rotation around the Z axis, it is intended to eliminate the interference of forces due to mutual attachment of the load cells 24 and 25, but this also does not cause interference of forces. Since the rotation around each axis must be fixed after ascertaining the above, skill is required for the fixing work. Mutual interference cannot be completely eliminated. Moreover, since the connection part between the load cell and the mounting table is complicated, the product cannot be manufactured at a low cost.

This invention aims to solve the above-mentioned problems such as limitations on the size of the platform, interference of forces, and simplification of the structure in a weighing machine configured to support one platform with two load cells for weighing. It is.

The present invention will be explained below based on the illustrated embodiments. In FIG. 5, 27 is the first load cell;
28 is a second load cell, 29 is a mounting table, 30 is a shaft, and 38 is a hanging ring.

The first and second load cells 27 and 28 are both of the same parallelogram type, and their fixed sides are attached to the base 31 at a predetermined distance from each other. A midway portion of the shaft 30 is fixed to the load loading position of the first load cell 27 via a metal fitting 35. A protrusion 33 that supports a hanging ring 38 is protrudingly provided at the load loading position of the second load cell 28 . The axis 30 is horizontal, and the protrusion 33
protrudes in a direction parallel to .

The platform 30 is a highly rigid flat plate having a rectangular upper surface, and is arranged such that one longitudinal end thereof is located above the shaft 30 and the other end is located above the protrusion 33. It is located in

The shaft 30 has a length corresponding to the width of the platform, and bearings 40 and 41 are fitted to both ends of the shaft 30, and the bearings are fixed to the lower surface of the platform 29. This allows the platform 29 to rotate only around the horizontal axis 30. That is, the mounting table 29 is
-X' direction, Y-Y' direction, Z-Z' direction is restricted, rotation around the virtual axis E is also restricted, and axis 3
It is positioned in all directions except rotation around 0.

The hanging ring 38 supports one side of the platform 29 by engaging the upper portion with the projection 33 and the lower portion thereof with the projection 32 . The protrusion 32 is formed by fixing a member 42 to the lower surface of the platform 29 and protruding horizontally from the side surface thereof in parallel with the protrusion 33. By being supported by the hanging ring 38, the platform 29 is in a horizontal state with only its rotational direction restricted by its own weight around the shaft 30 or the load on the platform. That is, the second load cell 28 side of the mounting table 29 is supported at one point.
This also restricts the movement of the platform 29 around the axis 30.

The first and second depending on the load placed on the platform 29.
The load states on the load cells 27 and 28 are such that, on the one hand, the load transmitted to the shaft 30 is applied to the load portion of the load cell 27 via the metal fitting 35, and on the other hand, a constant load is applied to the protrusion 33 via the hanging ring 38. . That is, on the first load cell 27 side, even if the load position moves on the platform 29, it will actually move on the shaft 30 due to the relative rotation of the fitting portion between the shaft 30 and the bearings 40, 41. The first load cell 27 is not subjected to twisting, and since the second load cell 28 is supported at one point, the second load cell 28 is also not subjected to twisting. In addition, when manufacturing a weighing machine, the dimensional difference between h ₁ and h ₂ in Fig. 3 is determined by the shaft 30 and bearing 40,
41, the load cell 27,
28 can be assembled without interfering with each other. Furthermore, even in the completed weighing machine, even if the platform 29, base 31, etc. expand or contract due to temperature changes,
In addition, even if the platform 29 is distorted, the fifth
The inclination angle θ shown in FIGS. b and c changes only slightly, and no interference occurs between the load cells 27 and 28.

Therefore, compared to conventional weighing machines of this type, this weighing machine is less susceptible to changes in the load position on the platform, and is less subject to dimensional restrictions during manufacturing, making it easier to achieve high precision. Even after manufacturing, high precision can be maintained without force interference between the load cells. In addition, with this weighing machine, the adjustment at the time of assembly was conventionally done by adjusting the four corner sensitivities of the two load cells respectively, but the adjustment in the axial direction of G-G' in the diagram of the first load cell 27 was changed. It is only necessary to match the sensitivity of the adjustment and the second load cell 28, and the adjustment time is significantly shortened. In a weighing machine with such a configuration, the degree of torsion applied to the load cell does not increase even if the platform is extended in the horizontal direction perpendicular to the axis 30. Together, they can be used as a large platform.

FIG. 6 shows a modification of the above embodiment, in which the first load cell 27 is used to reduce the height of the weighing machine.
The center of the load cell 28 and the axis of the shaft 30 are offset horizontally by a dimension m, so that the load on the second load cell 28 is applied via a freely rotating spherical body 39.

FIG. 7 shows yet another modification of the above embodiment, and is an example of a structure in which overhang of the platform does not occur when a load is applied in the direction of H-H' in the figure. That is, the axis of the shaft 30 and the protrusion 33 are each positioned slightly outward from the lower end positions of the platform 29.

These modified examples also have the same effects as the above embodiments.

As described above, according to the present invention, it is possible to provide a weighing machine that can solve the problem of force interference between load cells, ease restrictions on mounting platform dimensions, and simplify the structure.

[Brief explanation of the drawing]

Figure 1 is a schematic side view showing an example of a basic weighing machine using a conventional Roberval mechanism, and Figure 2 is a 1
Fig. 3 shows an example of a conventional weighing machine using two parallel gram type load cells, a is a schematic side view, b is a schematic front view, and Fig. 3 is an example of a conventional weighing machine using two parallel gram type load cells. An example is shown in which a is a schematic side view, b is a schematic front view, c is a partial perspective view, Fig. 4 is a schematic perspective view showing another conventional weighing machine using two parallel gram type load cells, and Fig. 5 6 shows an embodiment of the invention, a is a schematic perspective view, b is a side view of the hanging ring, c is a partially sectional front view of the hanging ring, FIG. 6 is a partially cutaway schematic perspective view of a modification of the above embodiment, and FIG.
The figure is a partially cutaway schematic perspective view of another modification of the above embodiment. 27...First load cell, 28...Second load cell, 29...Table, 30...Axle, 32,3
3...Protrusion, 38...Hanging ring, 39...Sphere, 4
0,41...Bearing.

Claims (1)

[Scope of Claims] 1. In a weighing machine in which a platform is supported by two load cells, a first and a second load cell, a shaft horizontal to the load portion of the first load cell is fixed, and the above-described shaft is attached to the shaft. The load section of the second load cell is configured such that one side of the table is supported via a bearing section, and the rotation of the table around the axis due to the load acting on the table is restricted only in the direction of rotation. A weighing machine characterized by a structure in which the other side of the above-mentioned stand is supported. 2. The weighing machine according to claim 1, wherein the center line of the shaft is located outward from a vertical plane including the outer edge of the upper surface of the table. 3. A patent characterized in that the supported position on the side of the table supported by the load section of the second load cell is located outward from a vertical plane including the outer edge of the top surface of the table. A weighing machine according to claim 1.