Load cell

• US 5,391,844 A
• Filed: 05/19/1993
• Issued: 02/21/1995
• 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: Wyatt, Michael R., Johnson, Thomas H.
• Primary Examiner(s): MILLER JR, GEORGE
• Application Number:
  US08/064,834
• Time in Patent Office: 643 Days
• Field of Search: 177/229, 177/210 FP, 73/862.59, 73/862.627
• US Class Current: 177/229
• CPC Class Codes: G01G 19/42 for counting by weighing G01G19/387 takes precedence
• CPC Class Codes: G01G 21/24 Guides or linkages for ensuring parallel motion of the weigh-pans
• CPC Class Codes: G01G 3/1412 the supports being parallelogram shaped
• 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 1/165 with acoustic surface waves
• CPC Class Codes: G01L 1/2206 Special supports with preselected places to mount the resistance strain gauges; Mounting of supports
• CPC Class Codes: G01L 1/2243 the supports being parallelogram-shaped
• 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 base 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 load cell body 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 opening and affixed to at least one of said opening walls;

(c) a first cantilever beam affixed to said base;

(d) a second cantilever beam affixed to said base;

(e) a first transducer comprising two parallel tines joined together at their ends, said first transducer affixed between said first cantilever beam and said base;

(f) a second transducer comprising two parallel tines joined together at their ends, said second transducer affixed between said second cantilever beam and said base; and

(g) means for sealing said load cell body interior opening.

2. The load cell of claim 1 wherein said first and second transducers comprise quartz crystal double-ended tuning fork resonators.

3. The load cell of claim 1 wherein said sealing means comprises silicon.

4. The load cell of claim 1 wherein said load cell interior opening comprises a front side and a back side and said sealing means comprises first and second silicon sealing windows, said first sealing window positioned over said load cell interior opening front side and said second sealing window is positioned over said interior opening back side.

5. The load cell of claim 4 wherein said first and second cantilever beams are positioned parallel to each other within the plane of the load cell interior opening and parallel to said base.

6. The load cell of claim 4 wherein said second sealing window comprises a plate.

7. The load cell of claim 1 wherein said first and second transducers are connected by electrical leads, said leads inserted through said sealing means.

8. The load cell of claim 7 wherein said electrical leads comprise a dampening coating.

9. A force sensing load cell comprising:

(a) a load cell body having an interior opening defined by an upper wall and a lower wall joined by first and second side walls said interior opening having a back end and a front end;

(b) a base positioned within said load cell interior opening and affixed to said opening lower wall said base comprising a load beam adjoining said opening upper wall;

(c) a first cantilever beam, said first cantilever beam affixed to said base;

(d) a second cantilever beam, said second cantilever beam affixed to said base;

(e) a first piezoelectric quartz crystal transducer comprising two parallel tines joined together at their ends, said first transducer affixed between said first cantilever beam and said load beam;

(f) a second piezoelectric quartz crystal transducer comprising two parallel tines joined together at their ends, said second transducer affixed between said second cantilever beam and said load beam; and

(g) means for sealing said load cell body interior opening.

10. The load cell of claim 9 wherein said load cell interior opening comprises a front side and a back side and said sealing means comprises first and second silicon sealing windows, said first sealing window position over said load cell interior opening front side and said second sealing window is positioned over said interior opening back side.

11. The load cell of claim 10 wherein said second sealing window comprises a stop plate.

12. The load cell of claim 9 wherein said first and second cantilever beams are positioned parallel to each other within the plane of the load cell interior opening and parallel to said load beam.

13. The load cell of claim 9 wherein said first and second transducers are connected by electrical leads, said leads inserted through said sealing means.

14. The load cell of claim 13 wherein said electrical leads comprise a dampening coating.

15. The load cell of claim 9 wherein said first and second transducers are encapsulated and said sealing means comprises silicon gel inserted into said load cell body interior opening.

16. A force sensing load cell comprising:

(a) a monolithic load cell body having an interior opening defined by an upper wall and a lower wall joined by first and second side walls said interior opening having a back end and a front end;

(b) a base positioned within said opening and affixed to said opening lower wall said base comprising a load beam adjoining said opening upper wall;

(c) a first cantilever beam, said first cantilever beam affixed to said base;

(d) a second cantilever beam, said second cantilever beam affixed to said base;

(e) a first piezoelectric quartz crystal transducer comprising two parallel tines joined together at their ends, said first transducer affixed between said first cantilever beam and said load beam;

(f) a second piezoelectric quartz crystal transducer comprising two parallel tines joined together at their ends, said second transducer affixed between said second cantilever beam and said load beam;

(g) a first sealing window affixed to said interior opening front end, said first sealing window shaped to conform to the opening; and

(h) a second sealing window affixed to said interior opening back end, said second sealing window shaped to conform to the walls defining the interior opening.

17. The load cell of claim 16 wherein said first and second cantilever beams are positioned parallel to each other within the plane of the load cell interior opening and parallel to said base.

18. The load cell of claim 16 wherein said first and second transducers are connected by electrical leads, said leads inserted through said second seal.

19. The load cell of claim 18 wherein said electrical leads comprise a dampening coating.

20. The load cell of claim 16 wherein said second sealing window comprises a plate.