Double resonating beam force transducer with reduced longitudinal pumping

• US 4,724,351 A
• Filed: 11/14/1984
• Issued: 02/09/1988
• Est. Priority Date: 04/01/1983
• Status: Expired due to Term

• Current Assignee: Weigh-Tronix, Inc. (Illinois Tool Works Inc.)
• Original Assignee: Quartex Incorporated
• Inventors: Kistler, Walter P., EerNisse, Errol P.
• Primary Examiner(s): Salce, Patrick R.
• Assistant Examiner(s): Voeltz, Emanuel Todd
• Application Number:
  US06/692,569
• Time in Patent Office: 1,182 Days
• Field of Search: 310/328, 310/338, 310/348, 310/367, 310/368, 310/312, 73/862.59
• US Class Current: 310/328
• CPC Class Codes: G01L 1/162 using piezoelectric resonators
• CPC Class Codes: G01P 15/097 by vibratory elements

Abstract

A double resonator beam force transducer configured to minimize longitudinal pumping by making the beams vibrate symmetrically. This can be accomplished by making the boundary conditions of the beams symmetrical or, if the boundary conditions are nonsymmetric, then by biasing the beams inwardly or outwardly to compensate for the nonsymmetrical boundary conditions of the beams. In the nonsymmetrical case where the beams would bow outwardly at their fundamental resonant frequency or an odd overtone thereof, an inward bias is provided to minimize longitudinal pumping. In the nonsymmetrical case where the beams would bow inwardly at an even overtone of the fundamental resonant frequency, an outward bias is provided to minimize longitudinal pumping. The inward or outward bias is provided in various embodiments by bowing the beams inwardly or outwardly, placing masses on the inner or outer edges of the beams, or tapering the inner or outer edges of the beams so that the width of the beams increase toward their midpoints.

Claims

1. A double-beam resonator having reduced longitudinal pumping, comprising a pair of generally parallel, spaced-apart beams of substantially equal length extending between a pair of supports and including means for causing said beams to resonate in opposite lateral directions, said supports having a lateral dimension that is greater than the distance between the outer edges of said beams so that at least a portion of said supports extend laterally beyond the outer edges of said beams, said supports extending from respective mounting pads having a lateral dimension that is greater than the lateral dimension of said supports such that said mounting pads extend laterally beyond the outer edges of said supports, said supports providing inward restoring forces to said beams to cause said beams to resonate inwardly and outwardly in substantially equal amounts about mean positions that are substantially straight, thereby minimizing the lateral deviation of said beams from said mean position in order to minimize the longitudinal pumping of said beams.

17. The resonator of claim 1, further including a pair of support structures on which respective mounting pads are mounted, said support structures being adapted to apply an externally generated force to said beams acting along the longitudinal axes of said beams so that said external force alters the resonant frequency of said beams.

29. The resonator of claim 1 wherein the side edges of said supports taper inwardly from said mounting pads to the outer edges of said beams.

30. The resonator of claim 1 wherein said supports are rectangularly shaped.

31. The resonator of claim 30 wherein the lateral dimensions of said rectangularly shaped supports are substantially equal to the sum of the distance between the outer edges of said beams and the distance between the inner edges of said beams so that said supports extend laterally beyond said beams by a distance of one-half the distance between the inner edges of said beams.

2. A double-beam resonator having reduced longitudinal pumping, comprising a pair of generally parallel beams of substantially equal length extending between a pair of mounting pads and including means for causing said beams to resonate in opposite lateral directions, said beams bowing inwardly toward each other at their midpoints to cause said beams to resonate inwardly and outwardly in substantially equal amounts about mean positions that are substantially straight, thereby minmizing the lateral deviation of said beams from said mean position in order to minimize the longitudinal pumping of said beams.

3. The resonator of claim 2 wherein the spacing between said beams at their midpoints is less than the spacing between said beams at their ends by about 2 percent to 3 percent of the width of each beam.

4. The resonator of claim 3 wherein the spacing between said beams at their midpoints is less than the spacing between said beams at their ends by about 2.5 percent of the width of each beam.

5. A double-beam resonator having reduced longitudinal pumping, comprising a pair of generally parallel beams of substantially equal length extending between a pair of mounting pads and including means for causing said beams to resonate in opposite lateral directions, said beams bowing outwardly away from each other at their midpoints to cause said beams to resonate inwardly and outwardly in substantially equal amounts about mean positions that are substantially straight, thereby minimizing the lateral deviation of said beams from said mean position in order to minimize the longitudinal pumping of said beams.

6. The resonator of claim 5 wherein the spacing between said beams at their midpoints is greater than the spacing between said beams at their ends by about 11 percent to 15 percent of the width of each beam.

7. The resonator of claim 6 wherein the spacing between said beams at their midpoints is greater than the spacing between said beams at their ends by about 13 percent of the width of each beam.

8. A double-beam resonator having reduced longitudinal pumping, comprising a pair of generally parallel beams of substantially equal length extending between a pair of mounting pads and including means for causing said beams to resonate in opposite lateral directions, said beams each carrying a mass at its midpoint along one lateral edge thereof to cause said beams to resonate inwardly and outwardly in substantially equal amounts about mean positions that are substantially straight, thereby minimizing the lateral deviation of said beams from said mean position in order to minimize the longitudinal pumping of said beams.

9. The resonator of claim 8 wherein said masses are carried on the inside edges of respective beams, thereby minimizing longitudinal pumping when said resonators operate at the fundamental resonant frequency of said beams or an odd overtone thereof.

10. The resonator of claim 8 wherein said masses are carried on the outside edges of said respective beams, thereby minimizing longitudinal pumping when said resonators are operated at even overtones of the fundamental resonant frequency of said beams.

11. A double-beam resonator having reduced longitudinal pumping, comprising a pair of generally parallel beams of substantially equal length extending between a pair of mounting pads and including means for causing said beams to resonate in opposite lateral directions, the width of each beam becoming greater toward the midpoint thereof to cause said beams to resonate inwardly and outwardly in substantially equal amounts about mean positions that are substantially straight, thereby minimizing the lateral deviation of said beams from said mean position in order to minimize the longitudinal pumping of said beams.

12. The resonator of claim 11 wherein each of said beams has an inside edge that tapers inwardly at its midpoint toward the other beam in order to minimize longitudinal pumping when said resonator is operating at the fundamental resonant frequency of said beams or odd overtones thereof.

13. The resonator of claim 11 wherein each of said beams has an outside edge that tapers outwardly at its midpoint away from the other beam in order to minimize longitudinal pumping when said resonator is operating at an even overtone of the fundamental resonant frequency of said beams.

14. A double-beam resonator having reduced longitudinal pumping, comprising a pair of generally parallel beams of substantially equal length extending between a pair of mounting pads and including means for causing said beams to resonate in opposite lateral directions, each of said mounting pads extending laterally beyond the outer edges of said beams a distance approximately equal to half the lateral distance between said beams to increase the inward restoring force exerted on said beams by said mounting pads to offset the outward restoring force exerted on said beams by said mounting pads, thereby causing said beams to resonate inwardly and outwardly in substantially equal amounts about mean positions that are substantially straight in order to minimize the longitudinal pumping of said beams.

15. A double-beam resonator having reduced longitudinal pumping, comprising a pair of generally parallel beams of substantially equal length extending between a pair of mounting pads and including means for causing said beams to resonate in opposite lateral directions, the outer edges of said beams tapering outwardly as they join said mounting pads to provide inward restoring forces to said beams to offset the outward restoring forces applied to said beams by said mounting pads, thereby causing said beams to resonate inwardly and outwardly in substantially equal amounts about mean positions that are substantially straight in order to minimize the longitudinal pumping of said beams.

16. A double-beam resonator having reduced longitudinal pumping, comprising a pair of generally parallel beams of substantially equal length extending between a pair of mounting pads and including means for causing said beams to resonate in opposite lateral directions, the inside edge of each of said beams having formed therein a notch at each end thereof to reduce the outward restoring force exerted on said beams by said mounting pads, thereby causing said beams to resonate inwardly and outwardly in substantially equal amounts about mean positions that are substantially straight in order to minimize the longitudinal pumping of said beams.

18. A force transducer, comprising:

a pair of spaced-apart mounting pads;

a pair of supports extending from respective mounting pads, said supports having lateral dimensions that are smaller than the lateral dimensions of said mounting pads such that said mounting pads extend laterally beyond the edges of said supports;

a pair of substantially parallel, spaced-apart beams of substantially equal length extending between said supports, said supports having a lateral dimension that is greater than the distance between the outer edges of said beams so that said supports extend laterally beyond the outer edges of said beams, said supports providing inward restoring forces to said beams, thereby causing said beams to resonate inwardly and outwardly in substantially equal amounts so that they have mean positions that are substantially parallel to each other, thereby minimizing the lateral deflection of said beams from said mean position for a given magnitude of peak-to-peak lateral deflection;

force-transmitting means for coupling an external force to said mounting pads acting along the longitudinal axes of said beams; and

drive means for causing said beams to resonate in opposite directions at a frequency determined by the magnitude of the longitudinal force applied to said beams.

24. The force transducer of claim 18 wherein the mounting characteristics of said beams from said mounting pads are laterally symmetrical so that the inward restoring force applied to said beams by said mounting pads is equal to the outward restoring force applied to said beams by said mounting pads.

32. The resonator of claim 18 wherein the side edges of said supports taper inwardly from said mounting pads to the outer edges of said beams.

33. The resonator of claim 18 wherein said supports are rectangularly shaped.

34. The resonator of claim 33 wherein the lateral dimensions of said rectangularly shaped supports are substantially equal to the sum of the distance between the outer edges of said beams and the distance between the inner edges of said beams so that said supports extend laterally beyond said beams by a distance of one-half the distance between the inner edges of said beams.

19. A force transducer, comprising:

a pair of spaced-apart mounting pads;

a pair of substantially parallel beams of substantially equal length extending between said mounting pads, said beams bowing inwardly at their midpoints, thereby causing said beams to resonate inwardly and outwardly in substantially equal amounts when said beams are resonating at their fundamental resonant frequency or an odd overtone thereof;

force-transmitting means for coupling an external force to said mounting pads acting along the longitudinal axes of said beams; and

drive means for causing said beams to resonate in opposite directions at a frequency determined by the magnitude of the longitudinal force applied to said beams.

20. The force transducer of claim 19 wherein the spacing between said beams at their midpoints is less than the spacing between said beams at their ends by about two percent to three percent of the width of each base.

21. A force transducer, comprising:

a pair of spaced-apart mounting pads;

a pair of substantially parallel beams of substantially equal length extending between said mounting pads, said beams bowing outwardly away from each other at their midpoints, thereby causing said beams to resonate inwardly and outwardly in substantially equal amounts when said beams are resonating at even overtones of the fundamental resonant frequency of said beams;

force-transmitting means for coupling an external force to said mounting pads acting along the longitudinal axes of said beams; and

drive means for causing said beams to resonate in opposite directions at a frequency determined by the magnitude of the longitudinal force applied to said beams.

22. The force transducer of claim 21 wherein the spacing between said beams at their midpoints is greater than the spacing between said beams at their ends by about 11 percent to 15 percent of the width of each beam.

23. A force transducer, comprising:

a pair of spaced-apart mounting pads;

a pair of substantially parallel beams of substantially equal length extending between said mounting pads, a mass mounted or each of said beams, said mass being symmetrically positioned at the midpoints of corresponding edges of said beams, said masses being mounted on the inside edges of said beams for operation of said beams at the fundamental resonant frequency thereof or an odd overtone thereof, and on the outer edges of said beams for operation at an even overtone of the fundamental resonant frequency of said beams;

force-transmitting means for coupling an external force to said mounting pads acting along the longitudinal axes of said beams; and

drive means for causing said beams to resonate in opposite directions at a frequency determined by the magnitude of the longitudinal force applied to said beams.

25. In a double resonating beam force transducer having a pair of beams connected between a pair of mounting pads, a method of minimizing the longitudinal pumping produced by said beams, comprising biasing said beams in directions opposite to the mean positions that said beams would otherwise assume when resonating at the fundamental resonant frequency of said beams or an overtone thereof.

26. The method of claim 25 wherein said beams are biased inwardly to minimize longitudinal pumping of said beams when said beams are resonating at the fundamental resonant frequency of said beams or an odd overtone thereof.

27. The method of claim 25 wherein said beams are biased outwardly to minimize longitudinal pumping of said beams when said beams are operating at an even overtone of the fundamental resonant frequency of said beams.

28. In a quartz crystal microresonator of the type including first and second stem portions, a pair of integral tines extending between said stem portions, a slot between said tines, said slot having opposed crotches where said tines join said stem portions, and a plurality of electrodes mounted on each so said tines, spaced along the length thereof, said electrodes being adapted for receipt of an AC voltage for causing said tines to oscillate, the improvement wherein each of said tines has a pair of opposed shoulders where said tines join said stem portions and wherein the widths of said shoulders at said opposite ends of said tines are approximately equal and approximately equal to one-half of the width of said crotches.

35. A double-beam resonator having reduced longitudinal pumping, comprising a pair of generally parallel, spaced-apart beams of substantially equal length extending between a pair of mounting pads and including means for causing said beams to resonate in opposite lateral directions, said mounting pads having lateral dimensions substantially equal to the sum of the lateral distance between the outer edges of said beams and the lateral distance between the inner edges of said beams such that said mounting pads extend laterally beyond the edges of said beams by a distance of approximately one-half the lateral distance between the inner edges of said beams.

36. A double-beam resonator having reduced longitudinal pumping, comprising a pair of generally parallel, spacedapart beams of substantially equal length extending between a pair of mounting pads and including means for causing said beams to resonate in opposite lateral directions, said mounting pads having lateral dimensions that are greater than the lateral distance between the outer edges of said beams so that at least a portion of said mounting pads extends laterally beyond the outer edges of said beams, the side edges of said mounting pads tapering inwardly to the outer edges of said beams.