Torsional sensing load cell

• US 5,925,832 A
• Filed: 10/01/1997
• Issued: 07/20/1999
• Est. Priority Date: 10/01/1997
• Status: Expired due to Fees

• Current Assignee: GAGETEK, LLC
• Original Assignee: Gagetek Company
• Inventors: Bruns, Robert W.
• Primary Examiner(s): Dougherty, Elizabeth L.
• Application Number:
  US08/942,314
• Time in Patent Office: 657 Days
• Field of Search: 73/862.632, 73/862.635, 73/862.641, 177/225
• US Class Current: 73/862.635
• CPC Class Codes: G01L 1/042 of helical springs
• CPC Class Codes: G01L 1/048 of torsionally deformable elements

Abstract

A torsional sensing load cell comprises a load sensing member having first and second deflecting portions. Force-receiving areas are defined on upper and lower surfaces of the deflecting portions for bearing a load and its corresponding reactive force. This imposes a torque on the load sensing member which is detected by transducers positioned to detect torsional stress. The transducers are coupled in a bridge circuit and are placed such that the output signal of the circuit is insensitive to the location of an applied load.

Claims

1. A load cell comprising:

a load sensing member having first and second ends;

first means for receiving an applied load and for directing the force of the applied load to a first portion of the sensing member;

second means for receiving a reactive force opposing the force of the applied load and for directing the reactive force a second portion of the sensing member, the first and second means located so that the force of the applied load in combination with the reactive force torsionally stress the sensing member; and

first and second transducers mounted on the sensing member between the first and second portions;

the transducers responsive to torsional stresses and coupled to form a bridge circuit for producing output signals in response to the torsional stresses;

the transducers positioned such that the combined output of the transducers for a given applied load is proportional to the product of the distance between the transducers and a force component of the applied load that is perpendicular to a plane passing through the sensing member at portions where the transducers are mounted.

2. The load cell of claim 1 wherein the transducers further are positioned so that a tangent to the sensing member at each transducer is perpendicular to a line between the transducers.

3. The load cell of claim 1 wherein the transducers are surface-mounted.

4. The load cell of claim 1 wherein the first means is an upper loading platform spaced apart from and coupled to the sensing member at the first portion, and the second means is a lower loading platform spaced apart from and coupled to the sensing member at the second portion.

5. The load cell of claim 4 wherein the loading platforms are solid members.

6. The load cell of claim 4 wherein the loading platforms each have an opening therethrough.

7. The load cell of claim 1 wherein the sensing member is an annular member having a gap formed therethrough to define the first and second ends, the first and second transducers being mounted on diametrically opposite sides of the annular member.

8. The load cell of claim 7 wherein the transducers are located on diametrically opposed sides along the outside diameter of the annular member.

9. The load cell of claim 1 wherein the sensing member is a solid member having a slot formed thereinto, the slot extending the full extent of the solid member along a longitudinal axis thereof, the ends being portions of the solid member on each side of the slot.

10. The load cell of claim 9 wherein the solid member is rectangularly shaped and the transducers are mounted on opposing outside surfaces of the solid member.

11. The load cell of claim 9 wherein the solid member is cylindrical and the transducers are mounted on diametrically opposing locations upon the exterior surface of the cylindrical solid member.

12. A torsional sensing load cell comprising:

a load-sensing member having upper and lower surfaces, the load sensing member having a gap extending between the upper and lower surfaces and through a width of the body thereof, the load sensing member having first and second force-bearing sections located thereon;

means for suspending the load sensing member at the force-bearing sections so that a loading force and a reactive force are directed only to the force-bearing sections, the force-bearing sections positioned so as to subject the load sensing member to a torsional stress; and

first and second transducers mounted to first and second portions of the load sensing member between the force-bearing sections, the first and second portions containing a plane passing therethrough, the loading force having a force component perpendicular to the plane;

the transducers positioned such that the sum of the torsional stress experienced by the first transducer and the torsional stress experienced by the second transducer is proportional to the distance between the transducers times the magnitude of the perpendicular force component;

whereby the transducers produce signals in response to the torsional stress which can be combined to produce a signal that is independent of the location of the loading and reactive forces.

13. The load cell of claim 12 wherein the transducers are mounted so that a tangent to the load sensing member at each transducer is perpendicular to a line therebetween.

14. The load cell of claim 12 wherein the transducers each includes two sets of strain gage elements arranged in a chevron pattern, the strain gage elements being electrically coupled in a bridge circuit arrangement.

15. The load cell of claim 12 wherein the transducers each includes one set of strain gage elements coupled in a voltage divider circuit.

16. The load cell of claim 12 wherein the transducers are surface mounted.

17. The load cell of claim 12 wherein the load sensing member is an annular member, and the transducers are mounted at diametrically opposed positions along either the outer perimeter of the annular member or the inner perimeter of the annular member.

18. The load cell of claim 12 wherein the load sensing member is a rectangularly shaped member and the transducers are mounted on opposing sides upon the exterior surface of the rectangularly shaped member.

19. The load cell of claim 18 wherein the rectangularly shaped member has a cylindrically shaped interior.

20. A torsional sensing load cell comprising:

a central body having a slotted opening thereinto, the slotted opening defining a first deflectable member and a second deflectable member, each deflectable member having a force-receiving portion;

first and second transducers respectively mounted to first and second areas of the central body; and

upper and lower load bearing members, each spaced apart from the central body and coupled thereto at the force-receiving portions of the deflectable members so that the force of an applied load and the corresponding reactive force are directed only to the force-receiving portions of the central body;

the transducers mounted so that a tangent to the central body at each transducer is perpendicular to a line between the transducers;

the transducers being coupled in a Wheatstone bridge arrangement to produce an output signal which is independent of the location of the applied load.

21. The load cell of claim 20 wherein the transducers are mounted upon the surface of the central body.

22. The load cell of claim 20 wherein the central body is an annular-shaped member.

23. The load cell of claim 22 wherein the transducers are mounted on the exterior surface of the annular member in a diametrically opposed manner.

24. The load cell of claim 22 wherein the transducers are mounted on the interior surface of the annular member in a diametrically opposed manner.

25. The load cell of claim 20 wherein the central body is generally rectilinear and the transducers are mounted to the surface thereof.

26. The load cell of claim 25 wherein the central body is substantially a solid member.

27. The load cell of claim 25 wherein the central body is hollow.

28. The load cell of claim 27 wherein the hollow portion defines a cylindrical shape.

29. In a load sensing member that is split to form two ends, a method of measuring a load comprising the steps of:

selecting first and second force receiving locations on the load sensing member;

applying the force of a load to the first force receiving location;

applying an opposing reactive force to the second force receiving location, the first and second force receiving locations being selected so that the applied forces produce a torsional stress through the load sensing member;

selecting first and second measuring locations between the first and second force receiving locations so that the torsional stress at the first measuring location summed with the torsional stress at the second measuring location is proportional to the distance between the two measuring locations times a force component of the load which is perpendicular to a plane passing through both measuring locations;

measuring the torsional stress at the first and second measuring locations; and

combining the measured torsional stresses to determine the load.

30. The method of claim 29 wherein the first and second force receiving locations are in opposed relation so that the forces applied thereto are oppositely directed.

31. The method of claim 30 wherein the first force receiving location is located on a first of the two ends of the load sensing member and the second force receiving location is located on a second of the two ends of the load sensing member.

32. A load cell comprising:

a load sensing member having first and second deflecting arms, the first deflecting arm having a first portion thereof to which a loading force is applied, the second deflecting arm having a second portion thereof to which a reactive force is applied, the first and second portions positioned so that the applied force in combination with the reactive force torsionally stress the load sensing member; and

first and second transducers mounted to the load sensing member and positioned so as to be respectively subjected to first and second torsional stresses, the sum of the first and second torsional stresses being proportional to the magnitude of a perpendicular force multiplied by the distance between the transducers, the perpendicular force being a component of the applied force that is perpendicular to a plane passing through portions of the load sensing member at locations where the transducers are mounted.

33. The load cell of claim 32 wherein the transducers are positioned so that lines tangent to the sensing member at each transducer are perpendicular to a line between the transducers.

34. The load cell of claim 32 wherein the transducers are surface mounted.

35. The load cell of claim 32 further including an upper loading platform spaced apart and coupled to the load sensing member at the first portion of the first deflecting arm, and a lower loading platform spaced apart and coupled to the load sensing member at the second portion of the second deflecting arm.

36. The load cell of claim 32 wherein the load sensing member is an annular member having a gap formed therethrough to define the first and second deflecting arms, the first and second transducers being mounted on diametrically opposed sides of the annular member.

37. The load cell of claim 36 wherein the transducers are located along the outside diameter of the annular member.

38. The load cell of claim 32 wherein the sensing member is a solid member having a slot formed thereinto, the slot extending the full extent of the solid member along a longitudinal axis thereof, the deflecting arms being portions of the solid member on each side of the slot.

39. The load cell of claim 32 wherein the load sensing member is rectangularly shaped and the transducers are mounted on opposing outside surfaces thereof.

40. The load cell of claim 38 wherein the solid member is cylindrical and the transducers are mounted on diametrically opposed locations on the exterior surface of the solid member.