JP3398854B2 - Method of adjusting characteristics of energy trap type piezoelectric vibratory gyroscope - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gyroscope for detecting a rotational angular velocity, and more particularly to a method for adjusting a characteristic of a piezoelectric vibrating gyroscope using an energy trapping vibration mode of a piezoelectric vibrator.

[0002]

2. Description of the Related Art A piezoelectric vibrating gyroscope (hereinafter referred to as a piezoelectric vibrating gyro for the sake of simplicity) is a state in which a piezoelectric vibrator is excited in a certain direction and then the piezoelectric vibrator vibrates in a direction perpendicular to the exciting direction. It detects the Coriolis force generated in the direction of excitation and the direction perpendicular to the rotation axis when it is rotated around the axis of, and detects the angular velocity of rotation. Recently, there are various applications. Are being used for such as a navigation system and a camera shake correction mechanism of a VTR camera.

As a piezoelectric vibrating gyro, for example, a piezoelectric vibrating gyro utilizing an energy trapping vibration mode using a piezoelectric vibrator that vibrates in an energy trapping vibration mode in which vibration energy is concentrated in the vicinity of a drive electrode is disclosed in, for example, Japanese Patent Laid-Open No. 2004-242242 62-162915 and JP-A-5-3225.
No. 80 is proposed.

In the piezoelectric vibrating gyro using the energy trapping vibration mode, since the vibration energy is concentrated on the local portion of the piezoelectric vibrator, it is easy and easy to support the piezoelectric vibrator, and a free lead wire is unnecessary. There are advantages.

In Japanese Patent Laid-Open No. 62-162915, in order to confine vibration energy locally, the thickness of the vibrator is locally thickened, and that portion is polarized in the thickness direction, and drive electrodes are provided on the opposite end faces of the thick local area. It is disclosed that a detection electrode is provided on the opposite side surface. Further, as another example, a drive electrode and a detection electrode are provided on one surface of a piezoelectric plate, and an interdigital electrode is provided between the drive electrodes as a detection electrode.

Japanese Unexamined Patent Publication (Kokai) No. 5-322580 discloses that a partial region of a piezoelectric plate is polarized in the thickness direction, and 2 is formed on the main surface of the polarized region.
Disclosed is a piezoelectric vibrating gyro in which a pair of counter electrodes are provided with their facing directions at right angles, one counter electrode serving as a drive electrode, and the other counter electrode serving as a detection electrode.

[0007]

Problems to be Solved by the Invention JP-A-62-1629
The piezoelectric vibrating gyro utilizing the energy trapping vibration mode disclosed in No. 15 has manufacturing difficulties such that the thickness of the piezoelectric plate must be locally increased or the interdigital electrodes must be formed. Further, since the pair of drive electrodes and the pair of detection electrodes are provided in the vicinity of each other, the drive electric field applied from the drive electrodes into the piezoelectric plate is influenced by the detection electrodes, and the drive electric field direction changes to obtain accuracy. There is a defect that it does not exist.

The piezoelectric vibrating gyro using the energy trapping vibration mode disclosed in JP-A-5-322580 has a simple structure and is easy to manufacture, but a pair of drive electrodes and a pair of detection electrodes are provided in the vicinity of each other. Because
The drive electric field applied from the drive electrode to the piezoelectric plate is affected by the detection electrode, the direction of the drive electric field is changed, and it is difficult to obtain an accurate detection output.

Further, since the structure of the conventional piezoelectric vibration gyro is complicated, it is difficult to adjust the resonance frequency and the detection output.

Therefore, the present invention proposes a piezoelectric vibrating gyro that utilizes a high precision energy trapping vibration mode that is small in size, simple in structure and manufacturing, and provides a characteristic adjusting method capable of easily adjusting the characteristic. With the goal.

According to the present invention, by sharing the output electrode with a part of the driving electrode in a limited area of the main surface of the piezoelectric plate,
An object of the present invention is to provide a method capable of easily adjusting characteristics by finely adjusting an electrode area in a piezoelectric vibration gyro utilizing an energy trapping vibration mode in which an output electrode does not adversely affect a driving electric field. And

[0012]

According to the present invention, one of two positions, which are separated from each other by a predetermined distance in the first direction, on the main surface of the portion having polarization in the thickness direction of the piezoelectric plate. A strip-shaped first electrode is provided at a position in a direction perpendicular to the first direction, and a strip-shaped second electrode extending in a position substantially perpendicular to the first direction at another position. And a third electrode is formed, a driving voltage for excitation is applied between the first electrode and the second and third electrodes, and the Coriolis force generated in the second and third electrodes is applied. The electromotive force corresponding to the vibration is detected, and the first
In the piezoelectric vibrating gyroscope, the energy trapping vibration mode of the thickness shear vibration generated between the electrode and the second and third electrodes is utilized.
A characteristic adjusting method of an energy trap type piezoelectric vibrating gyroscope, characterized in that characteristics including a resonance frequency and a detection output are adjusted by trimming at least one electrode of the first, second and third electrodes. To be

In the piezoelectric vibrating gyroscope, the entire surface of the piezoelectric plate including the piezoelectric plate and the first, second and third electrodes is covered with a thin layer of a light-transparent insulating material. It is also possible to adjust the characteristics by performing the trimming by irradiating a laser beam on the coating.

[0014]

FIG. 1 is a perspective view showing the structure of a vibrator of an energy-confinement type vibration gyro having a small structure and a simple structure to which the present invention is applied. As shown in FIG. 1, for the piezoelectric vibrator, for example, a piezoelectric plate 10 having a polarization axis in the thickness direction at the central portion, which is made of a piezoelectric ceramic plate such as PZT or barium titanate, is used. A strip-shaped first electrode 11 is provided on the main surface of the central portion of the piezoelectric plate 10. The second electrode 12 and the third electrode 11 are arranged at a position separated from the first electrode 11 by a predetermined distance in parallel with the first electrode 11.
Electrodes 13 are formed so as to be separated from each other. These electrodes 11, 12 and 13 have terminal portions 1 for leading them to the outside.
4, 15, 16 are connected. It should be noted that these electrodes and terminals may be made of silver paste or gold sputter. Of course, other conductive films can be adopted. A lead wire may be used without providing the terminal portion for leading to the outside on the vibrator.

As shown in the figure, three-dimensional coordinates are determined with the Z direction as the thickness direction, the X axis as the facing direction of the electrodes, and the Y axis as the direction orthogonal to these.

When a drive voltage (AC) is applied between the first electrode 11 and the second and third electrodes, vibration in the X direction is excited. In this state, when the piezoelectric plate 10 rotates around the Z axis, vibration due to the Coriolis force is generated in the Y direction, which causes electromotive force between the second and third electrodes. By detecting this electromotive force, the magnitude of vibration due to the Coriolis force, and thus the rotational angular velocity, can be detected.

Since the vibration energy is confined in the central portion of the piezoelectric plate and does not reach the periphery, it is easy to support the peripheral portion of the piezoelectric plate.

FIG. 2 is a block diagram showing a circuit configuration connected to the piezoelectric vibrator 1 of FIG. Referring to FIG.
In the second and third electrodes 12 and 13 of the piezoelectric vibrator 1,
The current detection circuits 18 and 19 are respectively connected. A differential circuit 22 is connected to the output sides of the current detection circuits 18 and 19, and a detection output of the piezoelectric vibration gyro is obtained via the synchronous detection circuit 23 and the rectification circuit 24. On the other hand, the current detection circuits 18 and 19 are connected to the oscillation circuit 25 for satisfying the self-excited oscillation condition, and the drive circuit 2 for giving the X-direction vibration.
It is connected to the first electrode 11 via 6 and constitutes a self-oscillation circuit. By this self-excited oscillation circuit, an AC voltage having a frequency substantially equal to the resonance frequency of the thickness shear vibration of the piezoelectric vibrator is applied to the electrode 11.

FIG. 3 is a diagram showing a configuration example of the current detection circuit of FIG. 2, which has a function of virtually grounding the second and third electrodes. In this circuit, the non-inverting input terminal (+) of the operational amplifier 31 is grounded to the reference voltage, and the resistor R is connected from the output terminal of the operational amplifier 31 to the inverting input terminal. The inverting input terminal (-) is always kept at the ground reference potential by the virtual ground function of the operational amplifier. When a current flows into this inverting terminal, it is converted into a voltage by the resistor R. That is, an output of Vout = -iR is obtained. That is, this current detection circuit is a circuit that functionally has an input impedance of almost zero and can obtain an output voltage proportional to the input current.

This current detection circuit is replaced with the current detection circuit 1 shown in FIG.
Used for 8 and 19. At that time, the inverting input terminal (−) is connected to the second and third electrodes 12 and 13. As a result, the driving voltage is applied to the first electrode 11 and the second and third electrodes 11.
Between the electrodes 12 and 13 of the
And the electromotive force between the third electrodes 12 and 13 can be detected as a potential difference between the outputs of the current detection circuits 18 and 19.

Next, the driving principle of the piezoelectric vibrator of FIG. 1 will be specifically described with reference to the drawings.

FIGS. 4A and 4B show FIGS.
FIG. 3 is a plan view showing a basic structure of the energy trap type vibrator shown in FIG. 4 and a sectional view showing only an electrode portion.
Referring to FIGS. 4A and 4B, X is formed on the same plane of the central portion of the piezoelectric plate 10 polarized in the thickness direction (Z-axis direction).
Slit-shaped electrodes D1 and D2 are formed facing each other with a gap in the axial direction. Note that T1 and T2 are terminal portions. When a voltage is applied between the terminals T1 and T2, an electric field in a direction substantially parallel to the plane of the plate (X direction) is applied to the region (inter-electrode region) of the piezoelectric plate 10 between the opposing electrodes D1 and D2. Therefore, the interaction between the electric field and the polarization in the thickness direction (Z-axis direction) orthogonal to the electric field causes strain in the inter-electrode region in the X direction. Electrode D1,
If the dimension of D2 is designed according to the characteristics of the piezoelectric plate 10 and the applied voltage is an AC voltage having a frequency matching the resonance frequency of the inter-electrode region, thickness shear vibration can be excited in the inter-electrode region. The vibration is attenuated around the inter-electrode region and is trapped without propagating. That is, an energy trap oscillator can be configured. Also, this vibration is
Since it is a thickness shear vibration caused by an electric field parallel to the surface of the piezoelectric plate, it is called a parallel electric field excitation type thickness shear vibration. The thickness shear vibration is vibration in which the displacement direction of the piezoelectric plate is parallel to the plate surface and the wave propagation direction is in the plate thickness direction. In order to illustrate the state of this vibration, FIG. 5 shows a displacement distribution in the thickness direction (Z-axis direction) when resonating at a half wavelength.

The vibrator of FIGS. 1 and 2 utilizes the above basic structure. That is, the first electrode 11 is D
The second electrode 12 and the third electrode 13 which are one electrode and are opposed thereto are the D2 electrode. The D2 electrode is divided into two to form a detection electrode to form a second electrode 12 and a third electrode 13, which are connected to current detection circuits 18 and 19 having a virtual ground function, respectively. As a result, the second electrode 12 and the third electrode 13 are virtually maintained at the reference potential, and thus can be regarded as potential ground terminals. Therefore, when a drive voltage for excitation having a frequency substantially equal to the resonance frequency of the thickness shear vibration mode of the piezoelectric plate is applied to the first electrode 11, the first, second, and In the area (inter-electrode area) surrounded by the third electrodes 11, 12 and 13, the center of the first electrode 11 and the second and third electrodes 12 and 1 are formed.
Direction of the line connecting the midpoints of the lines connecting the centers of 3 (X direction)
Thickness shear vibration of the energy trapping vibration mode of is generated.

In this state, when the piezoelectric plate 10 is rotated around an axis orthogonal to its main surface, due to the action of the Coriolis force, the direction (Y) orthogonal to the direction of the thickness shear vibration being excited. Direction) thickness-shear vibration occurs. Due to the thickness shear vibration generated by this Coriolis force, the first
Between the electrode 11 and the second electrode 12 of the first electrode 1
The impedance between 1 and the third electrode 13 changes,
As a result, the current value flowing into the current detection circuits 18 and 19 changes. Second electrode 12 and third electrode 1
As described above, since 3 is arranged symmetrically with respect to the direction of the thickness-shear vibration being excited (X direction), the current that changes due to the vibration due to the Coriolis force flowing into the current detection circuits 18 and 19 is , Have the same amplitude, 180
The currents have different degrees of phase. Therefore, the current detection circuit 1
The output voltages of 8 and 19 are also different in phase by 180 degrees from each other, and the difference between these output voltages is calculated by the differential circuit 22.
Is detected as a differential voltage by the synchronous detection circuit 23, and this voltage is synchronously detected by the synchronous detection circuit 23 at a predetermined timing.
By rectifying at 4, a DC output voltage proportional to the applied rotational angular velocity can be obtained as a detection output.

On the other hand, the current detection circuits 18 and 19 include an oscillation circuit 25 and a vibrator drive circuit 2 for satisfying the self-excited oscillation condition.
It is connected to the electrode 11 via 6 and constitutes a self-excited oscillation loop. As a result, the resonance frequency of the vibrator is automatically detected and the vibrator can be efficiently driven, so that a highly sensitive gyro can be obtained.

FIG. 6 shows another circuit configuration.
Electrode 11 is grounded and resistance R is placed between the second and third electrodes.
A voltage dividing circuit composed of a series circuit of 1 and R2 is connected, and the oscillation driving circuit 27 is controlled by the divided voltage. This oscillation drive circuit is grounded, so that a drive voltage is applied between the first electrode 11 and the second and third electrodes. The oscillation drive circuit 27 comprises the oscillation circuit 25 and the drive circuit 26 shown in FIG. Both ends of the voltage dividing circuit are connected to the differential amplifier circuit 22. The differential amplifier circuit 22, the detection circuit 23, and the rectifier circuit 24 are the same as those in FIG.

In the description of the present invention, the phrase "the piezoelectric plate has polarization in the thickness direction" is not limited to being polarized only in the thickness direction, but also includes having a polarization component in the thickness direction. . Of course, the larger the polarization component in the thickness direction, the better. Therefore, the one polarized in the thickness direction is the most advantageous.

When piezoelectric ceramics is used as the piezoelectric plate 10, polarization treatment is required as is well known, but the polarization region may be the entire piezoelectric plate or only the region for confining vibration. May be.

As the piezoelectric plate 10, a piezoelectric crystal plate (for example, crystal, LiNbO3, LiTO3, etc.) can be used. In that case, in order to have a polarization axis in the thickness direction, Z
A cut plate is most preferred, but a rotating Y-cut plate can also be used.

Next, a method for adjusting the characteristics of the above-mentioned piezoelectric vibrating gyro will be described with reference to FIGS. 7 and 8.

FIG. 7A is a plan view of the vibrator 1 shown in FIG. 1 in which the inter-electrode distances d1, d2 and d3 are written. Referring to the figure, these electrodes 11, 12 and 13
When at least one of these is trimmed and the distance between these electrodes is changed, the resonance frequency changes as shown in FIG. That is, the distance d1 between the first electrode 11 and the second electrode 12 and the distance d2 between the first electrode 11 and the third electrode 13 are the same distance D in terms of design. For the time being, D = d1 = d2.

When D is changed by trimming the first electrode 11 by using a laser beam, as shown in FIG.
As shown in (a), although the resonance frequency frx in the excitation direction (X direction) changes according to the change in the distance D, the resonance frequency frx in the excitation direction (X direction) and the thickness direction (Z direction) are perpendicular to each other ( The resonance frequency fry in the Y direction) hardly changes and is kept constant. At this time, if the inter-electrode distances d1 and d2 are slightly deviated on the actually manufactured vibrator, the electrodes 12 or 13 are trimmed to finely adjust the distances. be able to.

Also, the second and third electrodes 12 and 1
When the distance d3 between the two electrodes 3 is changed by trimming at least one of both electrodes, the resonance frequency frx is kept constant as shown in FIG. Changes.

Therefore, it is possible to finely adjust the resonance frequency by trimming any one of the electrodes 11, 12 and 13, and it is possible to adjust the characteristics of the piezoelectric vibration gyro.

Also, the second and third electrodes 12 and 1
The magnitude of the detection output can be finely adjusted by changing the length of the opposite side of 3.

Fine adjustment can be achieved by trimming with a sand trimmer or a laser beam in a state before the surface of the piezoelectric plate including the electrode surface is covered with an insulating coating.

Even after the surface of the piezoelectric plate including the electrode surface is insulation-coated, if a light-transmissive material is used for the insulation coating layer, laser trimming can be performed using a laser beam.

This state is shown in FIG. 7 (b). In the figure, 17 is a light-transmissive insulating coating layer, and 40
Is the laser beam.

[0039]

According to the present invention, driving is performed using only a pair of slit-shaped electrodes arranged in parallel on the main surface of a piezoelectric plate, and one of the pair of electrodes is divided into two. Since the detection electric field is detected by the detection electrode, the driving electric field is not adversely affected by the existence of the detection electrode, and the energy in the Y direction can be detected while keeping the electric field for exciting the X direction vibration. About the confinement type vibration gyro,
Since the characteristics of the piezoelectric gyro can be finely adjusted by a simple method of changing the electrode area by trimming any one of the three electrodes, a highly accurate and highly reliable gyro can be obtained.

[Brief description of drawings]

FIG. 1 is a perspective view showing a configuration of a piezoelectric vibrator according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a circuit configuration of a gyro using a piezoelectric vibrator.

3 is a circuit diagram showing an example of a current detection circuit used in the circuit of FIG.

4A and 4B are views showing a basic structure of a vibrator adopted in the piezoelectric vibrator of FIGS. 1 and 2, in which FIG. 4A is a plan view and FIG. 4B is a side view excluding a terminal portion of an electrode.

5 is a diagram showing a displacement distribution in a thickness direction in a thickness shear vibration of a vibrator having the basic structure of FIG.

FIG. 6 is a block diagram showing another circuit configuration of a gyro using a piezoelectric vibrator.

7A and 7B are diagrams for explaining fine adjustment of characteristics of the piezoelectric vibrator of FIG. 1, FIG. 7A is a plan view in which a distance between electrodes is written, and FIG.
The figure is a side view.

8 is a graph showing a change in the resonance frequency with respect to a change in the distance between the electrodes in FIG. 7, FIG. 8 (a) is a graph when the distances d1 and d2 in FIG. 7 are changed, and FIG. d
It is a graph when 3 is changed.

[Explanation of symbols]

1 Piezoelectric vibrator 10 Piezoelectric plate 11 First electrode 12 Second electrode 13 Third electrode 14, 15, 16 Terminal part 17 Insulation coating layer 18 Current detection circuit 19 Current detection circuit 22 Differential circuit 23 Synchronous detection circuit 24 Rectifier circuit 25 oscillator circuits 26 Drive circuit 27 Oscillation drive circuit 31 operational amplifier 40 laser beam

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-10-148526 (JP, A) JP-A-10-148525 (JP, A) JP-A-10-68625 (JP, A) JP-A-10- 47967 (JP, A) JP-A-5-322580 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01C 19/56 G01C 25/00 G01P 9/04 G01P 21/02

Claims (2)

(57) [Claims] 1. A piezoelectric plate having, on a main surface of a portion having a polarization in a thickness direction, at a position perpendicular to the first direction in one of two positions separated from each other by a predetermined distance in the first direction. A strip-shaped first electrode is provided in the same direction, and strip-shaped second and third electrodes extending in a direction substantially perpendicular to the first direction and spaced apart from each other are formed at the other position,
A drive voltage for excitation is applied between the first electrode and the second and third electrodes to detect an electromotive force corresponding to vibration due to Coriolis force generated in the second and third electrodes. In the piezoelectric vibrating gyroscope, the energy trapping mode of the thickness shear vibration that occurs between the first electrode and the second and third electrodes is utilized. A characteristic adjusting method for an energy trapping type piezoelectric vibrating gyroscope, which comprises adjusting a characteristic including a resonance frequency and a detection output by trimming at least one of the electrodes. 2. The characteristic adjusting method according to claim 1, wherein the piezoelectric vibrating gyroscope has a light-transparent insulating surface over the entire surface of the piezoelectric plate including the piezoelectric plate and the first, second and third electrodes. A characteristic adjusting method for an energy trapping type piezoelectric vibrating gyroscope, which is characterized in that it is covered with a thin layer of a material, and the trimming is performed by irradiating a laser beam on the covering.