Load cell

• US 6,898,989 B2
• Filed: 12/01/2000
• Issued: 05/31/2005
• Est. Priority Date: 12/03/1999
• Status: Expired due to Fees

• Current Assignee: ABB AB (ABB Limited)
• Original Assignee: ABB AB (ABB Limited)
• Inventors: Persson, Åke, Norling, Fredrik
• Primary Examiner(s): Lefkowitz, Edward
• Assistant Examiner(s): Martir, Lilybett
• Application Number:
  US10/169,364
• Publication Number:
  US 20030131672A1
• Time in Patent Office: 1,642 Days
• Field of Search: 738/626.37, 738/626.36, 738/626.38, 738/626.21, 738/626.25, 738/626.26, 738/626.27, 738/626.29, 738/626.32, 738/626.33
• US Class Current: 73/862.637
• CPC Class Codes: G01L 1/125 by using magnetostrictive means magnetostrictive sensors H10N35/101
• CPC Class Codes: G01L 1/127 by using inductive means G01L1/122, G01L1/125 take precedence

Abstract

A load cell comprising a load carrying structural framework is arranged with at least one measuring zone (15, 16) arranged with a measuring means. A load F applied in the x-direction parallel to two outer beams (1, 4) of the framework is transferred to two inner beams (2, 3) by two side beams (5, 6). The load on the measuring zones (15, 16) is greater than the load applied parallel to outer beams (1, 4) in a ratio of the distance h between the joints of the two outer beams divided by the distance d between the joints of the two inner beams. When a load is applied in the y-direction parallel to the two side beams (5, 6), the load on the measuring zones is also greater than the load applied at the side beams, in this case by a ratio of the distance l between the joints (7 and 11), (10 and 14) divided by distance d. In a load cell according to the preferred embodiment of the invention measuring zones (315, 316) are defined by recesses 330-337 and planar gaps 317-319 running from one side of the load cell to the other in the z-direction. The load cell according to the invention is accurate even with small loads and is insensitive to the effects of temperature gradients across the load cell in the x, y, or z-direction.

Claims

1. A load cell comprising a load-carrying structural framework of two essentially parallel rigid beams, arranged essentially parallel to an applied load (f) and at least one measuring zone equipped with means for strain measurement arranged between the two beams, wherein the structural framework comprises two outer beams (1, 4, 301, 304) which are connected by means of joints (7-10, 307-310) to two inner beams (2, 3, 302, 303) by at least two side beams (5, 6, 305, 306) which each extend between said two outer beams and connect to said two outer beams and to said two inner beams, and at least one measuring zone (15, 16, 315, 316) equipped with means for strain measurement is arranged between the two inner beams, and upon an application of a load in an x-direction parallel to the two outer beams, the amount of load applied to said at least one measuring zone (15, 16) is in proportion to a ratio of a distance h between the joints (7 and 10, 11 and 14, 307 and 310, 311 and 314) connecting outer beams (1, 4, 301, 304) to side beams (5, 6, 305, 306) divided by a distance d between the joints (8 and 9, 12 and 13, 308 and 309, 312 and 313) connecting the inner beams (2, 3, 302, 303) to the side beams (5, 6, 305, 306) and said means for strain measurement are suitably adapted such that an output signal representative of the applied load or detected load change is generated.

2. A load cell according to claim 1, wherein at least one joint (7-10, 11-14, 307-310, 311-314) is formed by at least one recess (330-332, 335-337).

3. A load cell according to claim 2, wherein at least one inner beam comprises at least one recess (331, 333, 334, 336).

4. A load cell according to claim 2, wherein at least one recess includes a material with a lower elastic modulus than an adjacent beam.

5. A load cell according to claim 1, wherein the inner beams are joined to each other by said at least one measuring zone.

6. A load cell according to claim 1, wherein the two inner beams are separated from one another along part of their inner length by at least one planar gap (318, 618).

7. A load cell according to claim 1, wherein at least one joint (7-10, 307-310) is formed by at least one planar gap (618, 619).

8. A load cell according to claim 1, wherein at least one said measuring zone further comprises an area of reduced thickness relative to the thickness of any of the beams (1-6, 301-306).

9. A load cell according claim 1, wherein at least one said measuring zone further comprises an area of the same thickness relative to the thickness of any of the beams (1-6, 301-306).

10. A load cell according to claim 9, wherein at least one planar gap includes a material with a lower elastic modulus that an adjacent beam.

11. A load cell according to claim 1, wherein at least one said measuring zone further comprises an area of increased thickness relative to the thickness of any of the beams.

12. A load cell according to claim 1, wherein said measuring means arranged on said measuring zone (15, 16, 315, 316) consists of one or more magnetoelastic sensors.

13. A load cell according to claim 1, wherein said measuring means arranged on said measuring zone (15, 16, 315, 316) consists of one or more magnetoelastic sensors.

14. A load cell according to claim 1, wherein said measuring means consists of one or more piezo-electric devices.

15. The use of a load cell according to claim 1 for measurement of an x-direction component of a load F or the total load when applied in the x-direction.

16. A load cell comprising a load-carrying structural framework of two essentially parallel rigid beams, arranged essentially perpendicular to an applied load (f) and at least one measuring zone equipped with means for strain measurement arranged between the two beams, wherein the structural framework comprises two outer beams (1, 4, 301, 304) which are connected by means of joints (7-10, 307-310) to two inner beams (2, 3, 302, 303) by at least two side beams (5, 6, 305, 306) which each extend between said two outer beams and connect to said two outer beams and to said two inner beams, and at least one measuring zone (15, 16, 315, 316) equipped with means for strain measurement is arranged between the two inner beams, and upon an application of a load in a y-direction parallel to the two side beams, the amount of load applied to said at least one measuring zone (15, 16) is in proportion to a ratio of a distance l between the joints (7 and 11, 10 and 14, 307 and 311, 310 and 314) connecting outer beams (1, 4, 301, 304) to side beams (5, 6, 305, 306) divided by a distance d between the joints (8, and 9, 12 and 13, 308 and 309, 312 and 313) connecting the inner beams (2, 3, 302, 303) to the side beams (5, 6, 305, 306) and said means for strain measurement are suitably adapted such that an output signal representative of the applied load or detected load change is generated.

17. The use of a load cell according to claim 16, for measurement of a y-direction component of a load F or the total load when applied in the y-direction.