LOAD CELL

Abstract

A load cell includes an annular base unit where an axial height of the annular base unit is smaller than a diameter of the annular base unit. The annular base unit has a plurality of mounting portions. A plurality of strain gages are located in the plurality of mounting portions. The annular base unit includes a plurality of sections having a Young's modulus different from the Young's modulus of the material of the base unit.

Claims

1. A load cell, comprising an annular base unit, an axial height of said annular base unit being smaller than a diameter of said annular base unit, said annular base unit having a plurality of mounting portions, and a plurality of strain gages, said plurality of strain gages being located in the plurality of mounting portions, wherein said annular base unit comprises a plurality of sections having a Young's modulus different from the Young's modulus of the material of the base unit.

2. The load cell according to claim 1, wherein at least some sections of said plurality of sections are formed by holes provided in said annular base unit.

3. The load cell according to claim 2, wherein at least some of said holes extend in an axial direction of said annular base unit.

4. The load cell according to claim 2, wherein at least some of said holes are through holes opening into both axial surfaces of the base unit.

5. The load cell according to claim 2, wherein said holes are evenly distributed along a circumferential direction of said annular base unit.

6. The load cell according to claim 2, wherein at least some of said holes have a circular cross-section.

7. The load cell according to claim 2, wherein said annular base unit has a circumferential groove formed in at least one of an outer circumferential wall and an inner circumferential wall thereof, and said plurality of mounting portions and, hence, said plurality of strain gages is located in said circumferential groove.

8. The load cell according to claim 1, wherein a center point of at least some of said holes is located on a line extending in the middle between an inner circumferential surface and an outer circumferential surface of the base unit.

9. The load cell according to claim 1, wherein said annular base unit is made of a corrosion-resisting and/or corrosion-protected material and/or has a corrosion protective coating applied to it.

10. The load cell according to claim 1, wherein said strain gages are mounted to be sensitive to strain exerted in an axial direction of said annular base unit.

11. The load cell according to claim 1, wherein said strain gages are connected in a Wheatstone bridge configuration.

12. The load cell according to claim 1, wherein additional strain gages are provided and mounted to be insensitive to strain exerted in an axial direction of said annular base unit.

13. The load cell according to claim 1, wherein at least some of said strain gages are thin film strain gages.

14. The load cell according to claim 1, wherein the load cell includes a transducer connected to said strain gages and a transmitter for transmitting data received from said transducer via a wireless network.

15. The load cell according to claim 1, wherein the strain gages are located on the load cell such that they are accessible and replaceable while load is still applied to the load cell from an attached structure.

Description

[0036] FIG. 1 shows a perspective view of an embodiment of a base unit of a load cell according to the present invention;

[0037] FIG. 2 shows a side view of the base unit of FIG. 1;

[0038] FIG. 3 shows a possible arrangement of strain gages on a schematic perspective view of a load cell;

[0039] FIG. 4 shows a possible scheme of connection of the strain gages of FIG. 3;

[0040] FIG. 5 shows an exploded view of a possible arrangement of the load cell according to the present invention at an anchor of a structure; and

[0041] FIGS. 6a and 6b show possible variations of the arrangement of FIG. 5.

[0042] In FIG. 1, a base unit of a load cell according to the present invention is generally denoted by the reference numeral 10. The base unit 10 is of an annular shape with an inner diameter (the diameter of the center bore 12) and an outer diameter of the outer circumferential wall 14. The base unit 10 has a first axial end surface 16 and a second axial end surface 18 opposite to the first axial end surface 16 (see FIG. 2). In the shown embodiment, both axial end surfaces 16 and 18 extend perpendicular to the axial direction X of the base unit 10. A distance between the first axial end surface 16 and the second axial end surface 18 defines the axial length of the base unit 10.

[0043] The base unit 10 comprises a plurality of through holes 20 that extend from the first axial end surface 16 to the second axial end surface 18. Here, the through holes 20 open to the environment surrounding the base unit 10 and are filled with air at ambient pressure. In the embodiment shown in FIG. 1, eight through holes 20 are evenly distributed in a circumferential direction of the base unit 10 around the center axis X.

[0044] By increasing or decreasing the number and/or size of the holes 20, the stiffness and thus the Young's modulus of the base unit 10 can be adjusted. For example, by increasing the number and/or size of the hole 20 in the base unit 10, the stiffness of the base unit 10 is reduced such that a load cell comprising a respective base unit 10 is sensitive to lower forces, compared to a base unit having less or smaller holes 20.

[0045] Here, on the outer circumferential wall 14, eight mounting portions 22 are evenly distributed in the circumferential direction of the base unit 10. Each of the mounting portions 22 is adapted to receive a strain gage (see FIG. 3) that is adapted to measure forces that are introduced into the base unit 10, in particular to measure a change of a dimension of the base unit 10. It is to be understood that any convenient number of mounting portions 22 and of strain gages, respectively, is possible.

[0046] As can be seen in FIGS. 1 and 2, a circumferential groove 24 is extending in the outer circumferential wall 14 of the base unit 10 along the circumferential direction of the base unit 10 such that the mounting portions 22 or a strain gage attached thereto, respectively, bridges the circumferential groove 24 in the axial direction of the base unit 10. This may improve the sensitivity of the strain gages with respect to a change of dimension of the base unit 10.

[0047] In the shown embodiment, the number and size of the mounting portions 22 is selected such that an angle of 45? extends from one mounting portion 22 to an adjacent one in the circumferential direction of the base unit 10.

[0048] In an exemplary embodiment, the diameter of the center bore 12 may be 100 mm, the outer diameter of the base unit 10 may be 170 mm, and the length of the base unit 10 in the axial direction may be 30 mm. The width of mounting portion 22 in the circumferential direction of the base unit 10 may be approximately 20 mm. The depth of the circumferential groove 24 in the radial direction of the base unit 10 may be 5 mm and its width in the axial direction of the base unit 10 may be 10 mm. In an embodiment of the base unit 10 that is adapted for a specific use case, the diameter of each through hole 20 may be 6 mm.

[0049] As can be further seen in FIGS. 1 and 2, the first axial end wall 16 and the second axial end wall 18 have a reduced diameter or radius compared to the diameter or radius of the outer circumferential wall 14. This may reduce a beam effect.

[0050] Now, with reference to FIG. 3, a possible arrangement of strain gages 26-1 to 26-8 is shown that may be attached to the eight mounting portions 22 of the base unit 10 of FIGS. 1 and 2. In FIG. 3, the base unit 10 is only shown schematically as a cylinder 10.

[0051] It can be seen in FIG. 3 that the strain gages 26-1, 26-3, 26-5 and 26-7 are attached to the base unit 10 in a manner rotated by 90? with respect to the strain gages 26-2, 26-4, 26-6 and 26-8. As a result, only the strain gages 26-1, 26-3, 26-5 and 26-7 are sensitive to axial forces that are introduced into the base unit 10 in a direction that is substantially parallel to the arrow L. The remaining strain gages 26-2, 26-4, 26-6 and 26-8 that are sensitive with respect to a change of a diameter of the base unit 10, for example, may be used to provide data for a temperature compensation of the measurement results of the strain gages 26-1, 26-3, 26-5 and 26-7, since the material of the base unit 10 is increasing/decreasing in any direction due to a change of temperature.

[0052] With reference now to FIG. 4, it is to be understood that the strain gages 26-1 to 26-8 do not have to be connected from one strain gage to a neighboring strain gage directly, but may be connected arbitrarily, in particular as it is shown in FIG. 4. Starting at the top of FIG. 4, the +-side of an excitation of the arrangement of strain gages is indicated by P+ in between strain gage 26-8 and strain gage 26-1. The strain gage 26-1 is connected to the strain gage 26-5. The strain gages 26-5 and 26-2 are both connected to a +-side of a signal pathway. The strain gage 26-2 is then connected to the strain gage 26-6. The strain gages 26-6 and 26-3 are connected to a ?-side of the excitation described above. The strain gage 26-3 is also connected to the strain gage 26-7. Both of the strain gages 26-7 and 26-4 are connected to a ?-side of the signal pathway. Finally, the strain gage 26-4 is connected to the strain gage 26-8.

[0053] In FIG. 5, an exploded view of a possible arrangement of the load cell according to the present invention at an anchor of a structure is shown. In FIG. 5, a load cell 28 that comprises the base unit 10 described above is arranged between an anchor plate 30 and a bearing plate 32. On the opposite side of the anchor plate 30, an anchor strand tube 34 is disposed. The load cell 28 may be provided with a gasket at least on one of the first axial end surface 16 and the second axial end surface 18. Cables 36 that extend centrally through the anchor strand tube 34, the bearing plate 32, the load cell 28, the anchor plate 30, and a wedge plate 38 that is arranged on a side of the bearing plate 32 opposite to the load cell 28 (at least in the arrangement shown in FIG. 5) are connected to wedges 40 such that a fixation for the cables 36 is provided by an interaction of the cables 36, the wedges 40, and the wedge plate 38.

[0054] The cable ends located in the wedge plate 38 are then covered by a steel cap 42 that surrounds the wedge plate 38 and that is connected to the anchor plate 30. In the shown embodiment, a wireless transmitter module 44 is attached to the steel cap 42 that is adapted to receive data from the strain gages 26-1 to 26-8 and to transmit the received data to an external device, such as a server and/or a user terminal, e.g. a cell phone.

[0055] The arrangement of FIG. 5 is also shown in FIG. 6a in a sectional side view. Here, the anchor strand tube 34 and the cables 36 extend through a structure 46, such as a bridge pole.

[0056] In the following, an alternative arrangement to the arrangement in FIGS. 5 and 6a is described, wherein only the components are described, the arrangement of which is changed with respect to the arrangement of FIGS. 5 and 6a. For all other components of FIG. 6b, the description given with respect to FIGS. 5 and 6a may still be applicable.

[0057] In FIG. 6b, the load cell 28 is arranged in between the wedge plate 38 and the anchor plate 30 directly. Therefore, the bearing plate 32 may be omitted.

[0058] In both of the above-shown examples of FIGS. 6a and 6b, the load cell 28 may be provided as a separate element or may be provided as an integrated part of the wedge plate 38, of the anchor plate 30 or of the bearing plate 32.