Vibration gyro

• US 6,281,619 B1
• Filed: 05/08/1998
• Issued: 08/28/2001
• Est. Priority Date: 05/09/1997
• Status: Expired due to Fees

• Current Assignee: Citizen Holdings Co., Ltd. (Citizen Electronics Company Limited)
• Original Assignee: Citizen Watch Co Limited (Citizen Electronics Company Limited)
• Inventors: Yamamoto, Izumi, Yanagisawa, Tohru
• Primary Examiner(s): Dougherty, Thomas M.
• Application Number:
  US09/074,691
• Time in Patent Office: 1,208 Days
• Field of Search: 310/318, 310/370, 310/328, 310/311, 310/360, 310/365-367
• US Class Current: 310/370
• CPC Class Codes: G01C 19/56 Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces

Abstract

A four-beam tuning fork is provided in which the base part thereof is stationary regardless of the vibration of the resonator, the same vibration mode being used for both excitation and detection, and the outputs from a plurality of beams are used to cancel the noise output caused by externally applied vibration

Claims

1. A vibrating gyro comprising four beams, electrodes, and a base part, wherein said beams are made of an anisotropic crystal that exhibits elasticity and piezo-electric characteristics, said beams being oriented in a X, Y, Z space having an X-axis, a Y-axis, and a Z-axis, respectively forming an X-Y plane, an X-Z plane and a Y-Z plane therebetween, said Z-axis passing through a vertex of said anisotropic crystal,

said beams having a width set along said X-axis, each of said beams extending in an upright direction from a surface of said base part, said beams having a length being parallel to a Y′

axis that is formed by rotating the Y axis within the Y-Z plane with a certain angle, said beams also having a thickness being parallel to a Z′

axis that is formed by rotating the Z axis within the Y-Z plane with a certain angle,

said beams having electrodes that are formed on a side surface thereof,

said base being made of an anisotropic crystal that exhibits elasticity,

said base having a configuration of a square prism and being provided with said four beams formed integrally with said base part, said four beams being disposed in mutually parallel fashion on said base and arranged equiangularly and equidistantly with respect to a center of said base part,

a bottom surface of said base being used for the support thereof,

wherein self-excited oscillation is caused using said electrodes of first and second beams of said four beams, resulting in a first bending vibration and simultaneously a second bending vibration, a vibration frequency of said second bending vibration coinciding with said first bending vibration in a direction that is perpendicular to said first bending vibration,

a third bending vibration being generated as a vibration that is synthesized from said first bending vibration and second bending vibration as well as, a fourth bending vibration being generated from said third bending vibration by Coriolis force caused by rotation of said vibration gyro, in a direction perpendicular to the direction of said third bending vibration, and further wherein,

a voltage, resulting from a fifth bending vibration that is a component of a certain vibrating direction of said fourth bending vibration, which coincides with a vibrating direction of said first bending vibration and that is detected via said electrodes of third and fourth beams of said four beams,

and a voltage, resulting from a sixth bending vibration that is a component of a certain vibrating direction of said fourth bending vibration, which coincides with a vibrating direction of said second bending vibration, that is detected by said electrodes of said third and fourth beams.

2. A vibrating gyro according to claim 1,

wherein said anisotropic crystal is quartz, and wherein a rotation angle within the Y-Z plane of said crystal is − 17±

2 degrees, said rotation angle being rotated −

17±

2 degrees from the Z axis in the Y-axis direction, and

wherein said four parallel beams, which are arranged equiangularly and equidistantly by with respect to a center of said base, and said base of said vibrating gyro are arranged so that a resonant frequency of a first bending vibration almost coincides with a resonant frequency of a second bending vibration by making the ratio of the width in the Z′

direction to the width in the X direction 0.9946±

0.02.

3. A vibrating gyro according to claim 1, wherein said anisotropic crystal is lithium niobate, and wherein a rotation angle within the Y-Z plane of said crystal is −

15±

2 degrees, said rotation angle being rotated 15±

2 degrees from the Z axis in the Y-axis direction, and

wherein said four parallel beams, which are arranged equiangularly and equidistantly with respect to a center of said base, and said base of said vibrating gyro are arranged so that a resonant frequency of said first bending vibration almost coincides with a resonant frequency of said second bending vibration by making the ratio of the width in the Z′

direction to the width in the X direction being 0.9965±

0.02.

4. A vibrating gyro according to claim 1, further comprising an oscillator circuit for generating a signal to induce said first bending vibration and to induce said second bending vibration.

5. A vibrating gyro according to claim 1, wherein said third beam and the fourth beams each exhibit said third bending vibration and are provided with an electrode for detecting said third bending vibration, and wherein said detecting electrode of said third beam and said detecting electrode of said fourth beam can detect the respective signals, each one of displacement directions of said signals being opposite to each other at some given instant in time, wherein said gyro further has a configuration in that both third and fourth detecting electrodes are connected to each other so as to electrically add said detected signals to each other.

6. A vibrating gyro according to claim 4, further comprising:

a first extraction electrode on a third one of said four beams that extracts a signal thereon resulting from said third bending vibration and said fourth bending vibration;

a phase-shift circuit that shifts the phase of said signal from said first extraction electrode by 90 degrees;

a binary quantizing circuit that binarizes an output of said phase-shift circuit;

a second extraction electrode on a fourth one of said four beams that extracts a signal thereon resulting from said third bending vibration and said fourth bending vibration; and

a lock-in amplifier which detects said signal from said second extraction electrode by using the output of said binary quantizing circuit.

7. A vibrating gyro according to claim 4, further comprising:

first extraction electrode on a third one of said four beams that extracts a voltage thereon resulting from said second bending vibration and said fifth bending vibration;

a second extraction electrode on a fourth one of said four electrodes which extracts a voltage thereon resulting from said second bending vibration and the sixth bending vibration;

an adding circuit that adds outputs from said first and second extraction electrodes;

a phase-shift circuit that shifts the output from said adding circuit by 90 degrees;

a binary quantizing circuit that binarizes the output of said phase-shift circuit;

a third extraction electrode that extracts a voltage thereon resulting from said first bending vibration and said fifth bending vibration;

a fourth extraction electrode that extracts a voltage thereon resulting from said second bending vibration and said sixth bending vibration;

a subtraction circuit which subtracts outputs from said third and fourth extraction electrodes; and

;

a lock-in amplifier which detects the output of said subtraction circuit by using the output of said binary quantizing circuit.

8. A vibrating gyro according to claim 4, further comprising a lowpass filter for adjusting the output signal of said oscillator circuit so that the amplitude and phase of said first bending vibration coincide with the amplitude and phase of said second bending vibration.

9. A vibrating gyro according to claim 1, wherein positions of said four beams are disposed on said base in a square arrangement.

10. A vibrating gyro according to claim 1, wherein said beams have a cross-sectional shape which is rectangular or circular.

11. A vibrating gyro according to claim 1, wherein said electrodes are formed by metal deposition which is applied to a side surface thereof.

12. A vibrating gyro according to claim 1, wherein the shape of said base is a rectangular prism.

13. A vibrating gyro according to claim 1, wherein said anisotropic crystal is lithium tantalate, and wherein a rotation angle within the Y-Z plane of said crystal is −

12±

2 degrees, said rotation angle being rotated 12±

2 degrees from the Z axis in the Y-axis direction, and

wherein said four parallel beams, which are arranged equiangularly and equidistantly with respect to a center of said base, and said base of said vibrating gyro are arranged so that a resonant frequency of said first bending vibration almost coincides with a resonant frequency of said second bending vibration by making the ratio of the width in the Z′

direction to the width in the X direction be 0.9952±

0.02.

14. A vibrating gyro according to claim 1, wherein attachment positions of said four beams are arranged equidistantly, parallely and equiangularly with respect to a center of said base, and each beam is configured so that thereof as viewed from the X direction is of a different length than a second side thereof as viewed from the Z′

direction, so that a resonant frequency of a first bending vibration substantially coincides with a resonant frequency of a second bending vibration.

15. A vibrating gyro made of an anisotropic crystal, said gyro comprising:

a base; and

four substantially parallel beams extending substantially normally from a same side of said base and being disposed substantially symmetrically about said base;

wherein each beam has attached thereto a plurality of electrodes, and at least one of said plurality of electrodes is a non-planar electrode attached to the beam so as to assume a non-planar conformation, and

said beams being oriented in a X, Y, Z space having an X-axis, a Y-axis, and a Z-axis, respectively forming an X-Y plane, an X-Z plane and a Y-Z plane therebetween, said Z-axis passing through a vertex of said anisotropic crystal.

16. A vibrating gyro according to claim 15, wherein said beams have a cross-sectional shape which is rectangular or circular.

17. A vibrating gyro according to claim 16, wherein, if said thickness is set along the X-axis, then said width is parallel to the Z′

-axis.

18. A vibrating gyro according to claim 15, wherein said electrodes are formed by metal deposition which is applied to a side surface thereof.

19. A vibrating gyro according to claim 15, wherein the shape of said base is a rectangular prism.

20. A vibrating gyro according to claim 17, wherein said anisotropic crystal is lithium tantalate, and wherein a rotation angle within the Y-Z plane of said crystal is −

12±

2 degrees, said rotation angle being rotated 12±

2 degrees from the Z axis in the Y-axis direction, and

wherein said four parallel beams, which are arranged equiangulary and equidistantly with respect to a center of said base, and said base of said vibrating gyro are arranged so that a resonant frequency of said first bending vibration almost coincides with a resonant frequency of said second bending vibration by making the ratio of the width in the Z′

direction to the width in the X direction be 0.9952±

0.02.

21. A vibrating gyro according to claim 15, wherein attachment positions of said four beams are arranged equidistantly, parallely and equiangulary with respect to a center of said base, and each beam is configured so that thereof as viewed from the X direction is of a different length than a second side thereof as viewed from the Z′

direction, so that a resonant frequency of a first bending vibration substantially coincides with a resonant frequency of a second bending vibration.

22. A vibrating gyro according to claim 15, wherein said beams are substantially rectangular in cross-section and said non-planar conformation results from said non-planar electrodes being attached to two sides of said beams.

23. A vibrating gyro according to claim 22, wherein each beam has attached there two non-planar electrodes and two planar electrodes.

24. A vibrating gyro according to claim 15, wherein said beams are formed of an anisotropic crystal.

25. A vibrating gyro according to claim 24, wherein said anisotropic crystal exhibits elasticity and piezo-electric characteristics.

26. A vibrating gyro according to claim 24, wherein said anisotropic crystal is one of quartz, lithium niobate and lithium tantalate.

27. A vibrating gyro according to claim 15, wherein said beams have a cross-sectional shape which is rectangular or circular.

28. A vibrating gyro according to claim 15, wherein said electrodes are formed by metal deposition which is applied to a side surface thereof.

29. A vibrating gyro according to claim 15, wherein the shape of said base is a rectangular prism.

30. A vibrating gyro according to claim 15, wherein said anisotropic crystal is lithium tantalate, and wherein a rotation angle within the Y-Z plane of said crystal is −

12±

2 degrees, said rotation angle being rotated 12±

2 degrees from the Z axis in the Y-axis direction, and

wherein said four parallel beams, which are arranged equiangularly and equidistantly with respect to a center of said base, and said base of said vibrating gyro are arranged so that a resonant frequency of said first bending vibration almost coincides with a resonant frequency of said second bending vibration by making the ratio of the width in the Z′

direction to the width in the X direction be 0.9952±

0.02.

31. A vibrating gyro according to claim 15, wherein attachment positions of said four beams are arranged equidistantly, parallely and equiangularly with respect to a center of said base, and each beam is configured so that thereof as viewed from the X direction is of a different length than a second side thereof as viewed from the Z′

direction, so that a resonant frequency of a first bending vibration substantially coincides with a resonant frequency of a second bending vibration.

32. A vibrating gyro comprising four beams, electrodes, and a base part, wherein said beams are made of an anisotropic crystal that exhibits elasticity and piezo-electric characteristics, said beams being oriented in a X, Y, Z space having an X-axis, a Y-axis, and a Z-axis, respectively forming an X-Y plane, an X-Z plane and a Y-Z plane therebetween, said Z-axis passing through a vertex of said anisotropic crystal,

in a case of a beam having a rectangular prism shape, said beams having a width along which each of said beams extending in an upright direction from a surface of said base part, said beams having a length being parallel to a Y′

axis that is formed by rotating the Y axis within the Y-Z plane with a certain angle, said beams also having a thickness being parallel to a Z′

axis that is formed by rotating the Z the axis within the Y-Z plane with a certain angle,

said beams having at least one electrode that is formed by metal deposition which is applied to at least one selected side surface thereof,

said base being made of an anisotropic crystal that exhibits elasticity and piezo-electric characteristics,

the shape of said base being that of a rectangular prism,

said base and said four beams being formed together as one, said four beams being disposed in mutually parallel fashion in said base in a pattern having two rows of two beams each,

the bottom surface of said base being used for the support thereof,

wherein self-excited oscillation is caused using said electrodes of said first and second beams, a first bending vibration being caused to occur,

a second bending vibration being generated which has a vibration frequency that coincides with said first bending vibration in a direction that is perpendicular to said first bending vibration,

a third bending vibration being generated as a vibration that is synthesized from said first bending vibration and said second bending vibration,

a voltage that results from a fifth bending vibration that is a component of a fourth bending vibration in the direction of said first bending vibration and in a direction that is perpendicular to said third bending vibration that is excited by a Coriolis force caused by rotation being detected via said electrodes of said third and fourth beams,

and a voltage that results from a sixth bending vibration that is a component of said fourth bending vibration in the direction of said second bending vibration is detected by said electrodes of said third and fourth beams.