Load cell

• US 5,313,023 A
• Filed: 04/03/1992
• Issued: 05/17/1994
• Est. Priority Date: 04/03/1992
• Status: Expired due to Term

• Current Assignee: Avery Weigh-Tronix LLC (Illinois Tool Works Inc.)
• Original Assignee: Weigh-Tronix, Inc. (Illinois Tool Works Inc.)
• Inventors: Johnson, Thomas H.
• Primary Examiner(s): MILLER JR, GEORGE
• Application Number:
  US07/863,162
• Time in Patent Office: 774 Days
• Field of Search: 177/229, 177/210 FP, 73/862.59, 73/862.627
• US Class Current: 177/229
• CPC Class Codes: G01L 1/14 by measuring variations in capacitance or inductance of electrical elements, e.g. by measuring variations of frequency of electrical oscillators
• CPC Class Codes: G01L 1/162 using piezoelectric resonators
• CPC Class Codes: G01L 1/2206 Special supports with preselected places to mount the resistance strain gauges; Mounting of supports
• CPC Class Codes: G01L 9/0005 using variations in capacitance G01L9/0072 takes precedence
• CPC Class Codes: G01L 9/0022 of a piezoelectric element
• CPC Class Codes: G01P 15/097 by vibratory elements

Abstract

The invention is a load cell for the measurement of force, independent of displacement, created by means such as weight, acceleration, pressure, and the like. The load cell has a beam structure with beams positioned parallel to each other in at least one plane. Generally, these parallel beams are attached to a stationary substrate and have sensing means attached between the two beams. In operation, deflection of one beam creates a response in the sensing means due to the relative action or deflection in the second beam.

Claims

1. A force sensing load cell comprising:

(a) a block comprising an interior wall defining an aperture therein, said interior wall comprising a base;

(b) a load bearing element having first and second ends, said load bearing element affixed to said base at said first end, said load bearing element being affixed at said second end to said interior wall and spanning across said aperture, said load bearing element comprising a cantilever beam;

(c) a capacity supporting cantilever beam, said cantilever beam spaced apart from, and parallel in at least one plane to, said load bearing element; and

(d) means for sensing force, said force sensing means affixed between said load bearing element and said capacity supporting cantilever beam in a manner which rejects frictional movement whereby, when stressed, the parallel deflection of said load bearing element and said capacity supporting cantilever beam of said load cell compensates for changes in modulus and allows for variation in deflection created by environment stresses.

2. The load cell of claim 1 wherein said load bearing element and said capacity supporting cantilever beam have central openings within their structure.

3. The load cell of claim 1 wherein said base and said force sensing means are joined through said load bearing element and said capacity supporting cantilever beam to form a square central opening, wherein at least said base and said force sensing means lie opposite and parallel to each other.

4. The load cell of claim 1 wherein said sensing means comprises a piezoelectric resonator secured to said load bearing element and said capacity supporting cantilever beam by an adhesive.

5. The load cell of claim 1 wherein said sensing means comprises a piezoelectric quartz resonator comprising a first tine and a second tine lying parallel to each other and attached at their ends.

6. The load cell of claim 1, wherein said load bearing element is arranged to span across said aperture in an axis generally parallel to an axis of deflection of said load cell due to applied force.

7. The load cell of claim 1, wherein said load cell base extends into said aperture from said interior wall.

8. A force sensing load cell comprising:

(a) a three-dimensional structure having an interior opening defined by an upper wall, a lower wall, and first and second side walls;

(b) a base affixed to at least one wall within the interior opening of said three-dimensional structure;

(c) a load bearing element having first and second ends, wherein said load bearing element is affixed to said base at said first end and to at least one wall of said three-dimensional structure interior opening at said load bearing element second end such that said load bearing element spans across said interior opening;

(d) a capacity supporting cantilever beam, said cantilever beam affixed to said base, and spaced apart from, and parallel in at least one plane to, said load bearing element; and

(e) means for sensing force, said force sensing means affixed between said load bearing element and said capacity supporting means.

9. The load cell of claim 8 wherein said base is attached within said interior opening through a flexure to said interior opening lower wall.

10. The load cell of claim 8 wherein said load bearing element and said capacity supporting cantilever beam have central openings within their structure.

11. The load cell of claim 8 wherein said base and said sensing means are joined through said load bearing element and said capacity supporting cantilever beam to form a square central opening, wherein at least said base and said sensing means lie opposite and parallel to each other.

12. The load cell of claim 8 wherein said sensing means comprises a piezoelectric resonator secured to said load bearing element and said cantilever beam by an adhesive.

13. The load cell of claim 8 wherein said sensing means comprises a piezoelectric quartz resonator comprising a first tine and a second tine, said first and second tines lying parallel to each other, and connected at either end.

14. The load cell of claim 8 wherein said base is affixed to said interior opening lower wall, and wherein said load bearing element comprises a beam attached to said base and spanning from said base to said upper wall generally parallel to said first and second side walls.

15. A force sensing load cell comprising:

(a) a three-dimensional structure having an interior opening defined by an upper wall and a lower wall joined by first and second side walls;

(b) a base positioned within said interior opening and affixed to at least one of said interior opening walls;

(c) a first capacity supporting cantilever beam, said first capacity supporting cantilever beam affixed to said base and extending within the plane of said three-dimensional structure interior opening;

(d) a second capacity supporting cantilever beam, affixed to said base and spaced apart from, and parallel in at least one plane to, said first capacity supporting cantilever beam, said second capacity supporting cantilever beam also extending within said three-dimensional structure interior opening;

(e) a load beam having first and second ends, said load beam affixed to said base at said load beam first end and parallel, in at least one plane to, said first capacity supporting cantilever beam and said second capacity supporting cantilever beam, said load beam spaced apart from and positioned intermediate between both of said first and second capacity supporting cantilever beams, and wherein said load beam spans across said interior opening and is affixed at said second end to at least one of said interior opening walls;

(f) a first means for sensing displacement, said displacement sensing means affixed between said first capacity supporting cantilever beam and said load beam; and

(g) a second means for sensing displacement, said second displacement sensing means affixed between said load beam and said second capacity supporting cantilever beam, whereby stressing said load cell through the incidence of a force provides independent signal processing of said first and second sensor means producing a common mode signal separate from a differential mode signal.

16. The load cell of claim 15 additionally comprising circuit means for receipt and processing of said common mode and said differential mode signals.

17. The load cell of claim 15 wherein said base is affixed to said interior opening lower wall by a flexure.

18. The load cell of claim 17 wherein said load beam is affixed at said second end to said interior opening upper wall by a flexure.

19. The load cell of claim 15 wherein said three-dimensional structure upper and lower walls each comprise flexures at the joining points of said first and second side walls.

20. A force sensing load cell, comprising:

(a) a block having an interior opening defined by an upper wall and a lower wall joined by first and second side walls, wherein said block comprises;

(i) a base attached to said block interior opening lower wall;

(ii) a load beam spanning across said interior opening and having first and second ends, wherein said load beam first end is attached to said base and said load beam second end is attached to said block interior opening upper wall; and

(iii) a capacity supporting cantilever beam attached to said base and oriented generally parallel to said load beam, wherein said capacity supporting cantilever beam is spaced apart from said load beam; and

(b) a quartz resonator, affixed between said load beam and said capacity supporting cantilever beam wherein said base and said quartz resonator are joined through said load beam and said capacity supporting cantilever beam to form an opening, and wherein said base and said quartz resonator lie opposite and parallel to each other.

21. The load cell of claim 20, wherein said block is formed as a monolithic structure.

22. The load cell of claim 20, wherein said quartz resonator is affixed to said load bearing beam and said capacity supporting beam by an epoxy adhesive.

23. The load cell of claim 20, wherein said quartz resonator is a crystal quartz double-ended tuning fork.

24. A force sensing load cell, comprising:

(a) a block having an interior opening defined by an upper wall and a lower wall joined by first and second side walls, wherein said block comprises;

(i) a base attached to said block interior opening lower wall;

(ii) a load beam spanning across said interior opening and having first and second ends, wherein said load beam first end is attached to said base and said load beam second end is attached to said block interior opening upper wall;

(iii) a first capacity supporting cantilever beam attached to said base and oriented generally parallel to said load beam, wherein said first capacity supporting cantilever beam is spaced apart from said load beam; and

(iv) a second capacity supporting cantilever beam attached to said base and oriented generally parallel to said load beam such that said load beam is intermediate said first and second capacity supporting cantilever beams, wherein said second capacity supporting cantilever beam is spaced apart from said load bearing beam;

(b) a first quartz resonator affixed between said load bearing beam and said first capacity supporting cantilever beam wherein said base and said first quartz resonator are joined through said load beam and said capacity supporting cantilever beam to form an opening, and wherein said base and said first quartz resonator lie opposite and parallel to each other; and

(c) a second quartz resonator affixed between said load bearing beam and said second capacity supporting cantilever beam wherein said base and said second quartz resonator are joined through said load beam and said second capacity supporting cantilever beam to form an opening, and wherein said base and said second quartz resonator lie opposite to and parallel to each other.

25. The load cell of claim 24, wherein said block is formed as a monolithic structure.

26. The load cell of claim 24, wherein said first and second quartz resonators are affixed to said load bearing beam and said first and second capacity supporting beams, respectively, by epoxy adhesive.

27. The load cell of claim 24, wherein said first and second quartz resonators are crystal quartz double-ended tuning forks.

28. A force sensing load cell comprising:

(a) a block having an aperture therein;

(b) a load bearing spring, said load bearing spring spanning said block aperture;

(c) a capacity supporting spring, said capacity supporting spring positioned parallel to said load bearing spring within said block aperture; and

(d) means for sensing force, said force sensing means affixed between said load bearing spring and said capacity movement whereby, when stressed, the parallel deflection of said load bearing spring and said capacity supporting spring of said load cell compensate for changes in modulus and allows for variation in deflection created by environmental stresses.