Weighing system having a weighing cell

Abstract

The invention relates to a weighing system (10) having a weighing cell (1) which extends in the longitudinal direction (L) and at least parts of which are elastically deformable, wherein the weighing cell (1) has, at a first end (2), means (3) for fastening the cell (1) and, at a second end (4) which is opposite in the longitudinal direction (L), means (5) for receiving a test object (6). According to the invention, the weighing cell (1) has a group of first bending elements (A, B, C, D), at least one second bending element (E) arranged in the region of the second end (2), and at least one third bending element (F) arranged between one of the first bending elements (A, B, C, D) and the second bending element (E), for flexurally elastic deformation of the portions of the weighing cell (1) that adjoin the particular bending element (A, B, C, D, E, F), wherein the first bending element (D) is arranged at the second end (4) of the weighing cell (1) and the respective distances (AB, AD, BC, CD) between the bending elements (A) and (B), between the bending elements (B) and (C), between the bending elements (A) and (D) and between the bending elements (C) and (D) are substantially of equal length, wherein the second bending element (E) is flexurally elastically coupled to each of the bending elements (A) and (C) and the respective distances (EA, EC) between the second bending element (E) and the bending elements (A) and (C) are substantially equal, and wherein the third bending element (F) is flexurally elastically coupled to the second bending element (E) and also to the first bending element (B).

Description

[0001] Description: Weighing system with load cell

[0002] The invention relates to a weighing system with a longitudinally extending load cell according to the preamble of claim 1. In particular, the invention relates to extensometry, i.e., the field of mechanical engineering that focuses on solving problems related to the measurement of forces via the extension of mechanical structures based on the theory of elasticity.

[0003] Such measurement systems with load cells have long been used to measure forces and loads. Such load cells generally employ an elastic structure that is tensioned, compressed, or bent by a force applied to the structure. Strain sensors such as wire or semiconductor strain gauges are used to measure the force-induced tension, compression, or bending.

[0004] Some common load cells feature visible or hidden shapes, such as "S-shaped," "plate-shaped," or "Roberval balance (hollow bar)" geometries. These geometries are designed to compensate for off-axis loads and provide a high-deformation area where, for example, strain gauges can be mounted.

[0005] The Robervals balance uses a parallelogram mechanism to eliminate the horizontal deviation of loads that would affect the measurement when using a simple lever.

[0006] US 4454770A discloses a load cell with a parallelogram configuration consisting of a pair of spaced, generally parallel force-absorbing elements connected by a cantilever beam and a parallel spacer beam. The cantilever beam projects vertically from one of the force-absorbing elements, and its end is attached to the other beam by a flexure joint.

[0007] DE 2917169 A1 relates to a load cell using strain gauges for determining weight and force and, in particular, concerns a load cell with a parallelogram design in which any axial loading of the probe arm is avoided and a common surface of the probe arm is subjected to equal tensile and compressive loads by means of a bending element that transmits the load.

[0008] US 6324918 B1 discloses a sensor comprising a flexible beam with a rectangular cross-section and rigid, solid end blocks at both ends for attaching the sensor in a tester. The beam has two symmetrically shaped through slots cut in mutually perpendicular directions so that they partially intersect within a beam body. Each slot has notches at its opposite ends that are wider than the slots, so that the distance from the inner wall of the notch to the outer side surface of the beam is shorter than the distance of this surface from the inner wall of the slot. Strain gauges are attached to mutually perpendicular surfaces at the ends of the beam, which are flexible in the direction of the force to be measured and rigid in the vertical direction.

[0009] US 4128001 A relates to a parallel-beam load cell in which the sensitivity to changes in the transverse load position is reduced by changing the shape of one of the beams near a strain gauge element, thereby changing the neutral axis of the beam with respect to the strain gauge element. The sensitivity of the load position in the longitudinal direction is reduced by changing the cross-sectional area of ​​one of the beams adjacent to a strain gauge element. US 4718287 A discloses a force measuring device comprising a parallelepiped block whose height is greater than its width and which is provided with an opening along its width to form a parallelogram.

[0010] US 2003097887 A1 relates to a load cell with overload protection, in which a central cantilever is provided between the load beams in the load cell structure and is defined by narrow-width slots. When an excessive load is applied, the load cell structure deforms and contacts the cantilever, transferring the load to it.

[0011] US 4655305 A relates to a device for detecting the load on a platform with an integrated sensor block consisting of a double cantilever beam, one end of which is attached to a fixed support and the opposite end of which supports the platform. The beam is divided into an upper and a lower section, each section having two flexures spaced apart along the length of the beam section. The flexures on the lower beam section are spaced apart by a distance greater than the distance between the flexures in the upper beam section. Strain gauge resistance elements are connected to the outer surface of the upper section at the flexure point.

[0012] Common extensometry measurement solutions often use strain gauges as force sensors, which estimate the magnitude of the force but not its direction. To overcome this shortcoming, mechanical structures specifically designed for force measurement using extensometry, so-called load cells or load cells, generally have specific geometries to ensure a known direction of the measured force. Therefore, when using load cells, the direction of the force is considered given and does not need to be measured. Nevertheless, assuming a direction in high-precision measurement systems introduces an unacceptable error. It is therefore the object of the present invention to provide a measurement system with an optimized load cell geometry.

[0013] This object is achieved by a weighing system with a load cell according to claim 1. Advantageous embodiments of the invention are the subject of subclaims.

[0014] The invention relates to a weighing system with a load cell extending in the longitudinal direction, which is elastically deformable at least in sections, wherein the load cell has means for fixing the cell at a first end and means for receiving a test object at a second end opposite in the longitudinal direction.

[0015] According to the invention, the load cell has a group of first bending elements (A, B, C, D), at least one second bending element (E) arranged in the region of the second end and at least one third bending element (F) arranged between one of the first bending elements (A, B, C, D) and the second bending element (E) for a flexurally elastic deformation of the partial regions of the load cell adjacent to the respective bending element (A, B, C, D, E, F).

[0016] The first flexure (D) is arranged at the second end of the load cell and the respective distance (AB, AD, BC, CD) between the flexures (A) and (B), the flexures (B) and (C), the flexures (A) and (D) and the flexures (C) and (D) is substantially equal.

[0017] The second bending element (E) is elastically coupled to the bending elements (A) and (C) and the respective distance (EA, EC) between the second bending element (E) and the bending elements (A) and (C) is essentially the same.

[0018] The third bending element (F) is elastically coupled to the second bending element (E) and to the first bending element (B).

[0019] The invention therefore relates to the detection of forces and weights of test objects and in particular to a torque-insensitive load cell with bending elements.

[0020] According to the invention, this novel geometry only allows a vertical displacement or movement of the bending elements and the load cell as a whole.

[0021] The load cell therefore consists of a series of flexures that connect different sections of the load cell. The geometric dimensions of the sections, e.g., their length, are determined by the distance between the corresponding flexures arranged in these sections. The flexures are arranged in the advantageous formation specified above, for example, in a parallelogram configuration of the sections.

[0022] The means for fixing the load cell at its first end serve to fasten the bending element (E) or the partial area of ​​the load cell between the bending elements (E) and (F), for example to a holder which supports the load cell.

[0023] The means for receiving the test object at the second end opposite the load cell in the longitudinal direction serve to receive the test object, in particular to connect the test object to the load cell via the bending element (D). Furthermore, this structure contributes to the fixation of the portion of the load cell that is to be moved in a straight line.

[0024] This load cell measurement system measures forces and loads on the test object by tensioning, compressing, or bending the elastic structure of the load cell through a force applied to it. The force is induced in the load cell by the test object. Strain sensors can be used to measure the force-induced tension, compression, or bending.

[0025] According to a first advantageous embodiment of the invention, the first bending elements (A, B, C, D) are arranged to one another in the unloaded basic position of the load cell of the weighing system essentially in the form of a parallelogram.

[0026] In particular, it is advantageous for the body to have sub-regions that are connected to one another by a respective bending element (A, B, C, D, E, F) for flexible movement, particularly with at least one recess provided between at least two sub-regions. This allows for a particularly lightweight and flexible construction. It is also possible to manufacture the body in one piece, thus eliminating the need for complex assembly of individual parts.

[0027] According to an advantageous embodiment of the invention, the bending elements (A, B, C, D, E, F) are designed as flexible, thin-walled sections between two partial areas to be connected in the body, in particular as film hinges or joints.

[0028] This design makes it very easy to achieve the desired flexibility of the load cell. This is because the thin-walled sections that form the flexural elements between the sub-areas can be taken into account during manufacturing. These thin-walled sections, i.e., the flexural elements, are elastically deformable, whereas the sub-areas connected by the flexural elements are not (significantly) deformable because they have greater wall thicknesses than the flexural elements. This achieves the desired movement or bending of the load cell.

[0029] According to a variant of the invention, the load cell is designed to be substantially axially symmetrical with respect to the longitudinal axis (L), thereby simplifying the overall structure, which also has an advantageous effect on the manufacturing costs.

[0030] In particular, it can be provided that the first bending elements

[0031] (B) and (D) each approximately on the longitudinal axis (L) of the load cell and / or wherein the first bending elements (A) and (C) are each arranged at approximately the same distance from the longitudinal axis.

[0032] According to a further development of the invention, the respective distance (EA, EC) between the second bending element (E) and the bending elements (A) and

[0033] (C) greater than the distance (AB, AD, BC, CD) between the first bending elements (A, B, C and D) to each other.

[0034] It is also conceivable that the distance (EF) between the second bending element (E) and the third bending element (F) is approximately equal to the distance (BF) between the bending element (B) of the first group and the third bending element (F). Overall, a load cell can be manufactured in a particularly space-saving manner that is essentially axially symmetrical with respect to the longitudinal axis (L) and also implements a Peaucelier-Lipkin connection as described below.

[0035] The two bending elements (A) and (D) and / or the two bending elements

[0036] (C) and (D) and / or the two bending elements (B) and (F) and / or the two bending elements (F) and (E) and / or the two bending elements (C) and (E) and / or the two bending elements (A) and (E) can each be connected by substantially diamond-shaped partial regions of the body (1), which has an optimal effect on the distribution or transmission of the force induced by the test object.

[0037] In particular, the load cell can have at least three recesses arranged between the essentially diamond-shaped sections of the body. This allows for a particularly lightweight and flexible design.

[0038] A particularly advantageous embodiment of the invention is one in which an additional fastening means (8) for securing the body is arranged between the first end (2) of the body (1) and the third bending element (F). This increases the stability of the load cell and the measurement accuracy.

[0039] For attaching at least one strain gauge for measuring the force-induced stress, compression, or bending, at least one flat section can be formed on at least the third bending element (F). A flat section is understood to be an area within which a strain gauge can be arranged. In particular, strain sensors such as foil, wire, or semiconductor strain gauges can be used.

[0040] It is also conceivable that flat sections for accommodating strain gauges are provided on other bending elements.

[0041] A particularly advantageous embodiment of the invention is one in which the load cell is essentially plate-shaped and / or formed in one piece. This further optimizes the production of the load cell. According to an advantageous variant of the invention, the load cell with the flexural elements (A, B, C, D, E, F) is designed in the manner of a Peaucelier-Lipkin connection. In this case, the flexural element (D) describes a vertical, straight displacement, while the flexural element (B) rotates.

[0042] Peaucellier's inversor is a coupling mechanism for converting circular motion into linear motion and vice versa. Peaucellier's inversor is based on inversion on a circle, which has the property of transforming circles into straight lines through the center of inversion. Due to this property, Peaucellier's inversor can also be used to construct an image point under the inversion. Lipman Lipkin discovered the same mechanism independently of Peaucellier (see Wikipedia.org).

[0043] In a particularly advantageous manner, the means for receiving a test object can comprise clamps, screw connections and / or adhesive / welded and / or magnetic connections.

[0044] The test object can be a brake pad or a back plate of a friction pad.

[0045] Further objects, advantages, features, and possible applications of the present invention will become apparent from the following description of an exemplary embodiment with reference to the drawing. All described and / or illustrated features, individually or in any meaningful combination, constitute the subject matter of the present invention, regardless of their summary in the claims or their reference back to them. These show, partly schematically:

[0046] Figure 1 is a side view of a weighing system with a load cell,

[0047] Figure 2 is a perspective view of the weighing system according to Figure 1,

[0048] Figure 3 is a further perspective view of the weighing system according to Figure 1 with a strain gauge and

[0049] Figure 4 shows a side view of the weighing system according to Figure 1 with a test object.

[0050] In the following figures of the drawing, identical or equivalent components are provided with reference numerals based on an embodiment in order to improve readability.

[0051] The invention relates to the detection of forces and weights of test objects, and in particular to a torque-insensitive weighing system 10 comprising a load cell 1 having bending elements (A, B, C, D, E, F) arranged in a special geometry. This allows only a vertical displacement of partial areas of the load cell 1, thus significantly improving measurement accuracy.

[0052] The load cell 1 consists of a series of bending elements (A, B, C, D, E, F) which connect different parts of the load cell 1.

[0053] Figure 1 shows the weighing system 10 with the load cell 1 extending in the longitudinal direction (L), which is elastically deformable at least in sections. The load cell 1 has means 3 for securing the cell 1 at a first end 2 and means 5 for receiving a test object 6 at a second end 4 opposite in the longitudinal direction (L).

[0054] Figures 1 and 2 show the weighing system 10 with the load cell 1 in a side view and in perspective.

[0055] Figure 3 shows the weighing system 10 with a strain gauge 11 and Figure 4 shows the weighing system 10 with a test object 6 arranged thereon.

[0056] Figures 1 to 4 further show that the load cell 1 is essentially plate-shaped and in this case formed in one piece.

[0057] As can be seen from Figures 1 to 4, the load cell 1 has a group of first bending elements (A, B, C, D), at least one second bending element (E) arranged in the region of the second end 2 and at least one third bending element (F) arranged between one of the first bending elements (A, B, C, D) and the second bending element (E) for a flexurally elastic deformation of the partial regions of the load cell 1 adjacent to the respective bending element (A, B, C, D, E, F).

[0058] The first bending element (D) is arranged at the second end 4 of the load cell 1.

[0059] The respective distance (AB, AD, BC, CD) between the bending elements (A) and (B), the bending elements (B) and (C), the bending elements (A) and (D) and the bending elements (C) and (D) is essentially the same length in the present case, as Figures 1 to 4 also illustrate.

[0060] The second bending element (E) is elastically coupled to the bending elements (A) and (C) and the respective distance (EA, EC) between the second bending element (E) and the bending elements (A) and (C) is essentially the same size (cf. Figures 1 to 4).

[0061] The third bending element (F) is elastically coupled to the second bending element (E) and to the first bending element (B) (see Figures 1 to 4).

[0062] As the figures further show, the first bending elements (A, B, C, D) are arranged to one another essentially in the form of a parallelogram in the unloaded basic position of the load cell 1 of the weighing system 10.

[0063] The load cell 1 has sub-regions that are connected to each other by a bending element (A, B, C, D, E, F) for flexible movement. In this case, at least one recess 7 is provided between at least two sub-regions.

[0064] As Figures 1 to 4 further show, the bending elements (A, B, C, D, E, F) are designed as flexible, thin-walled sections between two sub-areas to be connected in the load cell 1, in this case as film hinges or joints. Due to the comparatively small wall thickness compared to the wall thickness of the sub-areas of the load cell 1 that are connected by the bending elements, the measuring cell 1 is bent at the predetermined - thin-walled - points, so that the force introduced by the test object is transmitted to specific areas or points due to the predetermined geometry of the measuring cell.

[0065] It is also evident that the load cell 1 is designed to be substantially axially symmetrical with respect to the longitudinal axis (L) of the load cell 1. In the present exemplary embodiment, the first bending elements (B) and (D) as well as the first bending elements (A) and (C) are each arranged at approximately the same distance from the longitudinal axis (L).

[0066] The respective distance (EA, EC) between the second bending element (E) and the bending elements (A) and (C) is in this case greater than the distance (AB, AD, BC, CD) between the first bending elements (A, B, C and D) to each other.

[0067] The distance (EF) between the second bending element (E) and the third bending element (F) is approximately the same as the distance (BF) between the bending element (B) of the first group and the third bending element (F).

[0068] In the present embodiment, the two bending elements (A) and (D) and the two bending elements (C) and (D) and the two bending elements (B) and (F) and the two bending elements (F) and (E) and the two bending elements (C) and (E) and the two bending elements (A) and (E) are each connected by substantially diamond-shaped partial regions of the body (1) (cf. Figures 1 to 4).

[0069] As the figures also show, the load cell 1 has at least three recesses 7 arranged between the essentially diamond-shaped sections of the load cell 1. The sections between the bending elements are diamond-shaped so that they are as rigid as possible and do not deform.

[0070] Figures 3 and 4 show an embodiment of the weighing system 10 in which a flat section 9 is formed on the third bending element (F), on which a strain gauge 11 is arranged.

[0071] The means 5 for receiving a test object 6 can have holes for, for example, clamps, screw connections, and / or adhesive / welded and / or magnetic connections. Figure 4 shows an embodiment in which a test object 6 is schematically illustrated. The test object 6 can be a brake pad or a backing plate of a friction lining.

[0072] The arrow with the reference number 12 in Figure 4 also indicates the direction in which the load acts on the measuring cell 1 in the case of a measurement, or the direction in which the force is introduced into the measuring cell 1.

[0073] As Figures 1 to 4 further show, in the present case, a further fastening means 8 for fixing the load cell 1 is arranged between the first end 2 of the load cell 1 and the third bending element (F). In this way, the load cell 1 can be fastened not only with the means 3 to the end 2 of the load cell 1, but also to the further fastening means 8 for additional stabilization. For example, the load cell 1 can be fixed by means of a screw connection; other fastening means 3, 8 are also conceivable.

[0074] After applying a load 12 to the measuring cell 1, ie, after attaching the test object 6 to the load cell 1 and thus inducing the force, a movement, in particular a deformation of the load cell 1, takes place. Due to the structure of the load cell 1, this movement occurs almost exclusively in the vertical direction, ie, downwards.

[0075] In other words, this measuring system 10 with the load cell 1 measures forces and loads of the test object 6 by tensioning, compressing, or bending the elastic structure of the load cell 1 through a force exerted on this structure. The force is induced in the load cell 1 by the arranged test object 6. Strain sensors, in particular strain gauges 11, can be used to measure the force-induced tension, compression, or bending (see Figures 3 and 4). In particular, the partial regions of the load cell 1 connected to the bending element (B) describe a rotation or bending around the bending element (F), since this is the region with the greatest deformation of the load cell 1. For this reason, in the embodiment shown here, the flat section 9, on which the strain gauge 11 is arranged (see Figures 3 and 4), is provided in the region of the bending element (F).

[0076] The distances (AB), (BC), (CD), (DA) have the same linear dimensions, and the distances (CG), (AG) are equal to each other. Due to these geometric dimensions, the flexure (D) moves vertically in a nearly perfect straight line.

[0077] The design shown is for production by wire EDM, a common technology that allows for very small radii between the edges to be created, depending on the part's requirements. It is known to see parts manufactured by spark erosion with a radius of approximately 0.025 mm. The plate-shaped load cell 1 in the present case can have a length of approximately 114 mm, a width of approximately 50 mm, and a height of approximately 6 mm. In this example, the holes for fastening the test object 6 or the load cell 1 have a diameter of 3 mm for the use of M3 screws, and the radius between the edges is 0.025 mm.

[0078] The load cell 1 can be made of aluminum. List of reference symbols

[0079] 1 load cell

[0080] 2 first end load cell

[0081] 3 remedies

[0082] 4 second end load cell

[0083] 5 remedies

[0084] 6 Test object

[0085] 7 Recess

[0086] 8 additional fasteners

[0087] 9 flat section

[0088] 10 Weighing system

[0089] 1 1 strain gauge

[0090] 12 Last

[0091] Longitudinal direction

[0092] A, B, C, D first bending elements

[0093] E second bending element

[0094] F third bending element

[0095] AB, AD distance

[0096] BC, CD distance

[0097] EA, EC distance

[0098] EF, FB distance

Claims

Patent claims 1 . Weighing system (10) with a load cell (1) extending in the longitudinal direction (L) which is elastically deformable at least in sections, wherein the load cell (1) has means (3) for fixing the cell (1) at a first end (2) and means (5) for receiving a test object (6) at a second end (4) opposite in the longitudinal direction (L), characterized in that the load cell (1) has a group of first bending elements (A, B, C, D), at least one second bending element (E) arranged in the region of the second end (2) and at least one third bending element (F) arranged between one of the first bending elements (A, B, C, D) and the second bending element (E) for a flexurally elastic deformation of the partial regions of the load cell (1) adjacent to the respective bending element (A, B, C, D, E, F), wherein the first bending element (D) at the second end (4) of the load cell (1 ) and the respective distance (AB, AD, BC, CD) between the bending elements (A) and (B),the bending elements (B) and (C), the bending elements (A) and (D) and the bending elements (C) and (D) are substantially the same length, wherein the second bending element (E) is coupled in a bending-elastic manner to the bending elements (A) and (C) and the respective distance (EA, EC) between the second bending element (E) and the bending elements (A) and (C) is substantially the same size, wherein the third bending element (F) is connected on the one hand to the second, Bending element (E) and on the other hand is elastically coupled to the first bending element (B).

2. Weighing system (10) according to claim 1, characterized in that the first bending elements (A, B, C, D) are arranged to one another substantially in the form of a parallelogram in the unloaded basic position of the load cell (1) of the weighing system (10).

3. Weighing system (10) according to claim 1 or 2, characterized in that the load cell (1) has partial regions which are connected to one another for flexible movement by a respective bending element (A, B, C, D, E, F), in particular wherein at least one recess (7) is provided between at least two partial regions.

4. Weighing system (10) according to one of claims 1 to 3, characterized in that the bending elements (A, B, C, D, E, F) are designed as flexible, thin-walled sections between two partial areas to be connected in the load cell (1), in particular as film hinges or joints.

5. Weighing system (10) according to one of claims 1 to 4, characterized in that the load cell (1) is designed to be substantially axially symmetrical with respect to the longitudinal axis (L).

6. Weighing system (10) according to one of claims 1 to 5, characterized in that the first bending elements (B) and (D) are each arranged approximately on the longitudinal axis (L) of the load cell (1) and / or wherein the first bending elements (A) and (C) are each arranged at approximately the same distance from the longitudinal axis (L).

7. Weighing system (10) according to one of the preceding claims, characterized in that the respective distance (EA, EC) between the second bending element (E) and the bending elements (A) and (C) is greater than the distance (AB, AD, BC, CD) between the first bending elements (A, B, C and D) to one another.

8. Weighing system (10) according to one of the preceding claims, characterized in that the distance (EF) between the second bending element (E) and the third bending element (F) is approximately the same as the distance (BF) between the bending element (B) of the first group and the third bending element (F).

9. Weighing system (10) according to one of the preceding claims, characterized in that the two bending elements (A) and (D) and / or the two bending elements (C) and (D) and / or the two bending elements (B) and (F) and / or the two bending elements (F) and (E) and / or the two bending elements (C) and (E) and / or the both bending elements (A) and (E) are each connected by substantially diamond-shaped portions of the body (1).

10. Weighing system (10) according to one of the preceding claims, characterized in that the load cell (1) has at least three recesses (7) which are arranged between the substantially diamond-shaped partial regions of the load cell (1). 1 1. Weighing system (10) according to one of the preceding claims, characterized in that a further fastening means (8) for fixing the load cell (1) is arranged between the first end (2) of the load cell (1) and the third bending element (F).

12. Weighing system (10) according to one of the preceding claims, characterized in that at least one flat section (9) is formed on at least the third bending element (F).

13. Weighing system (10) according to claim 12, characterized in that at least one strain gauge (11) for measuring the force-induced tension, compression or bending is arranged on the at least one planar section (9).

14. Weighing system (10) according to one of the preceding claims, characterized in that the load cell (1) is substantially plate-shaped.

15. Weighing system (10) according to one of the preceding claims, characterized in that the load cell (1) is formed in one piece.

16. Weighing system (10) according to one of the preceding claims, characterized in that the load cell (1) with the bending elements (A, B, C, D, E, F) is formed in the manner of a Peaucelier-Lipkin connection.

17. Weighing system (10) according to one of the preceding claims, characterized in that the means (5) for receiving a test object (6) comprise clamps, screw connections and / or adhesive / welded and / or magnetic connections.

18. Weighing system (10) according to one of the preceding claims, characterized in that the test object (6) is a brake pad or a back plate of a friction pad.

19. Use of a weighing system, in particular according to one of the Claims 1 to 18, for determining the weight of a brake pad or a backing plate of a friction pad.

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