JP7808119B2 - Vibration gyroscope and angular velocity sensor equipped with the same - Google Patents

Description

This disclosure relates to a vibratory gyroscope and an angular velocity sensor equipped with the same.

Conventionally, vibratory gyroscopes have been known as gyroscopes used in angular velocity sensors. For example, electromagnetic gyroscopes and piezoelectric gyroscopes equipped with a gyro element having multiple electrodes on the surface of a ring-shaped vibrator are well known (see, for example, Patent Documents 1 and 2).

In angular velocity sensors that use such a vibratory gyroscope, a bias component may be superimposed on the output signal of the vibratory gyroscope. The bias component, also known as the zero-point output or offset, becomes a noise component when detecting angular velocity.

Patent document 3 discloses a vibrator comprising a circular first annular portion, a square second annular portion, and a connecting portion connecting the first and second annular portions. It also discloses a vibratory gyroscope comprising this vibrator. In this vibrator, the four corners of the second annular portion serve as vibration nodes in both the primary and secondary vibrations of the vibrator. Supporting the vibrator at these four corners prevents vibration leakage from the vibrator and the propagation of unwanted vibrations from outside. This suppresses drift in the detection voltage of the angular velocity sensor, improving angular velocity detection sensitivity.

Patent No. 5410518 Japanese Patent Application Laid-Open No. 2019-032302 International Publication No. 2013/005625

The bias component mentioned above is generated due to the angular misalignment between the multiple electrodes provided in the vibratory gyroscope and the difference in frequency of the vibrator's natural vibration mode. The bias component is also generated due to the angular misalignment between the vibration axis of the vibration mode in the vibratory gyroscope and the arrangement of the electrodes.

The former angular deviation can be improved to some extent by improving the processing accuracy during gyroscope manufacturing. Furthermore, the difference in frequency between the vibrator's natural vibration modes can be improved to some extent by appropriately setting the vibrator's symmetry, including the relative positions of the primary and secondary drive electrodes.

On the other hand, the latter angular deviation relative to the bias component is difficult to improve by taking measures to improve the first two, and therefore limits the performance of vibratory gyroscopes. However, until now, this has not been much of a problem in terms of the performance required of vibratory gyroscopes. However, in recent years, there has been a demand for highly accurate angular velocity measurement, and cases have arisen in which this angular deviation becomes a problem.

The present disclosure has been made in consideration of these points, and its purpose is to provide a vibration-type gyroscope capable of reducing the bias component contained in the output signal, and an angular velocity sensor equipped with the same.

To achieve the above object, the vibratory gyroscope according to the present disclosure comprises at least an external structure and an internal structure disposed inside the external structure in a planar view. The external structure includes at least a frame-shaped fixed portion having a center point in a planar view. The internal structure comprises at least a vibrator having a common center point with the fixed portion in a planar view, and a plurality of support portions that connect the vibrator to the fixed portion and support the vibrator so that it can vibrate. When the vibrator has a vibration mode of cos Nθ (N is an integer of 2 or greater), electrodes are arranged in 4N directions at equal angular intervals around the center point in the circumferential direction of the vibrator. The internal structure has (4N x S1)-fold rotational symmetry (S1 is an integer of 1 or greater) with respect to an axis that passes through the center point of the vibrator and intersects the surface of the vibrator. The external structure has (2N x S2)-fold rotational symmetry with respect to the axis. The outer structure has (2N×S3) (S3 is an integer of 1 or more) corners on the outer periphery or inner periphery and (2N×S3) side surfaces.

An imaginary plane having the axis as one side and passing through one of the midlines of the multiple corners and/or multiple side surfaces of the external structure is defined as a first imaginary plane, and an imaginary plane located at a position obtained by rotating the first imaginary plane by (360/4N) degrees around the axis is defined as a second imaginary plane. The external structure has a first cross-section cut by the first imaginary plane and a second cross-section cut by the second imaginary plane. Among the pairs of the first cross-section and the second cross-section, there is at least one specific pair of the first cross-section and the second cross-section. The cross-sectional area of the first cross-section included in the specific pair is different from the cross-sectional area of the second cross-section.

The plurality of electrodes includes at least a primary drive electrode that excites a primary vibration in the vibrator. The primary drive electrode is positioned so as to intersect with either the first imaginary plane or the second imaginary plane that cuts the first cross section and the second cross section of the specific pair.

The angular velocity sensor according to the present disclosure comprises at least the vibrating gyroscope, a primary AC power supply that applies AC power of a predetermined frequency to the primary drive electrode, a primary detection unit that detects a voltage signal generated in the primary detection electrode, a secondary AC power supply that applies AC power to the secondary drive electrode, a secondary detection unit that detects a voltage signal generated in the secondary detection electrode, and a calculation unit that calculates angular velocity based on the output signal of the secondary AC power supply.

The vibration gyroscope disclosed herein can reduce the bias component contained in the output signal.The angular velocity sensor disclosed herein can reduce the bias component contained in the output signal of the vibration gyroscope, thereby improving the accuracy of angular velocity detection.

FIG. 1 is an exploded perspective view of a vibration gyroscope according to a first embodiment. FIG. 1 is a plan view of a vibratory gyroscope. FIG. 3 is a cross-sectional view taken along line III-III in FIG. 2. FIG. 3 is an enlarged view of a portion surrounded by a dashed line in FIG. 2. FIG. 2 is a schematic diagram of a circuit block of the angular velocity sensor. FIG. 2 is a schematic diagram showing a primary vibration state of a vibrator. FIG. 2 is a schematic diagram showing a secondary vibration state of a vibrator. FIG. 1 is a plan view of a vibration gyroscope according to a first comparative example. 9 is a schematic diagram showing a primary vibration state of the vibrator shown in FIG. 8 . 9 is a schematic diagram showing a secondary vibration state of the vibrator shown in FIG. 8 . FIG. 10 is a plan view of a vibration gyroscope according to a second comparative example. FIG. 2 is a schematic plan view of an external structure. FIG. 10 is a schematic diagram showing a deformation state of the external structure when vibrating on the first vibration axis. FIG. 10 is a schematic diagram showing the deformation state of the external structure when vibrating on the second vibration axis. FIG. 10 is a schematic plan view of an external structure according to a third comparative example. FIG. 15 is a schematic diagram showing a deformation state of the external structure shown in FIG. 14 during vibration in the first cos 2θ mode. FIG. 15 is a schematic diagram showing a deformation state of the external structure shown in FIG. 14 during vibration in the second cos 2θ mode. FIG. 15 is a schematic diagram showing another deformation state of the external structure shown in FIG. 14 during vibration in the first cos 2θ mode. FIG. 15 is a schematic diagram showing another deformation state of the external structure shown in FIG. 14 during vibration in the second cos 2θ mode. FIG. 10 is a plan view of a vibration gyroscope according to a first modified example. FIG. 17 is an enlarged view of the portion surrounded by the dashed line in FIG. 16. FIG. 10 is a schematic plan view of an external structure according to a second embodiment. FIG. 10 is a schematic plan view of another external structure. FIG. 10 is a schematic plan view of a further external structure. FIG. 11 is a schematic plan view of a first external structure according to Modification 2. FIG. 10 is a schematic plan view of a second external structure. FIG. 10 is a schematic plan view of a third external structure. FIG. 10 is a schematic plan view of a fourth external structure. FIG. 10 is a schematic plan view of a fifth external structure. FIG. 10 is a schematic plan view of a sixth external structure. FIG. 10 is a schematic plan view of the seventh external structure. FIG. 10 is a plan view of a vibration type gyroscope according to a third embodiment. FIG. 2 is a schematic diagram showing a primary vibration state of a vibrator. FIG. 2 is a schematic diagram showing a secondary vibration state of a vibrator.

Embodiments of the present disclosure will now be described with reference to the drawings. Note that the following description of the preferred embodiments is merely exemplary in nature and is not intended to limit the present disclosure, its applications, or its uses.

(Embodiment 1)
[Configuration of Vibration Gyroscope]
FIG. 1 shows an exploded perspective view of a vibratory gyroscope according to this embodiment, FIG. 2 shows a plan view, FIG. 3 shows a cross-sectional view taken along line III-III in FIG. 2, and FIG. 4 shows an enlarged view of a portion surrounded by a dashed line in FIG. 2.

For ease of explanation, only the fixed portion 10 of the gyro element 110 is shown in Figure 1. Furthermore, the magnetic field application portion 80 is not shown in Figures 1 and 2. It should also be noted that Figures 1 to 4 are schematic illustrations of the structure of the vibratory gyroscope 100 and do not accurately represent the actual dimensional relationships between the various components.

In the following description, the radial direction of the vibrator 20 will be referred to as the radial direction, the outer circumferential direction of the vibrator 20 as the circumferential direction, and the direction perpendicular to the radial direction and perpendicular to a plane containing the radial and circumferential directions as the axial direction. Furthermore, in the radial direction, the center side of the vibrator 20 will be referred to as the inner side, and the outer circumferential side will be referred to as the outer side. In the axial direction, the side on which the upper yoke 81 (see Figure 3) is provided will be referred to as the upper side, and the side on which the lower yoke 83 (see Figure 3) is provided will be referred to as the lower side. Furthermore, the vibratory gyroscope 100 viewed from the axial direction will be referred to as a planar view. The upper surface of each component shown below will be referred to as the front surface, and the lower surface will be referred to as the back surface. Furthermore, the direction passing through the center point O of the vibrator 20 and intersecting the surface of the fixed part 10, in this case a virtual line extending in the axial direction, will be referred to as the axis O1 (see Figure 3).

Furthermore, one or more primary drive electrodes may be collectively referred to as primary drive electrodes PD, and one or more secondary drive electrodes may be collectively referred to as secondary drive electrodes SD. One or more primary detection electrodes may be collectively referred to as primary detection electrodes PPO, and one or more secondary detection electrodes may be collectively referred to as secondary detection electrodes SPO.

As shown in Figure 1, the vibratory gyroscope 100 has a gyro element 110, a spacer 120, a base 130, and a magnetic field application unit 80 (see Figure 3). The vibratory gyroscope 100 is an electromagnetic gyroscope. The structure and function of the gyro element 110 will be described in detail later. In this specification, "parallel," "same," or "matching" means being parallel, the same, or matching, including the processing tolerances and assembly tolerances of the vibratory gyroscope 100 and each of its constituent parts, and does not mean that the two objects being compared are parallel, the same, or matching in the strict sense.

The spacer 120 is a frame-shaped member with a central through-hole and is made of ceramic such as glass. In a plan view, the spacer 120 has 4xn (n is an integer greater than or equal to 1) rotational symmetry with respect to the axis O1. The fixed portion 10 and the spacer 120 have inner and outer peripheries. The spacer 120 is disposed in contact with the back surface of the fixed portion 10. The spacer 120 is provided to adjust the distance between the upper yoke 81 (described later) and the vibrator 20. The pedestal 130 is a cylindrical member with a flange on its upper portion. Note that the lower portion of the pedestal 130 may be a regular octagonal prism with the same rotational symmetry as the inner periphery 10a of the fixed portion 10. The pedestal 130, like the spacer 120, is made of ceramic such as glass. The pedestal 130 is disposed in contact with the back surface of the spacer 120. The pedestal 130 is provided to hold the magnetic field application unit 80. When the spacer 120 is omitted, the base 130 is disposed in contact with the rear surface of the fixed part 10. The fixed part 10 and the spacer 120 are bonded together, for example, with an adhesive. The spacer 120 and the base 130 are bonded together, for example, with an adhesive.

The structure consisting of the fixed part 10, spacer 120, and base part 130 is sometimes referred to as the external structure 60. If the spacer 120 is omitted, it goes without saying that the external structure 60 is composed of the fixed part 10 and base part 130. Furthermore, the spacer 120 and base part 130 may be integrated into one component.

Furthermore, the external structure 60 has (2N x S2)-fold rotational symmetry with respect to the axis O1. Here, N is an integer greater than or equal to 2, and S2 is an odd number greater than or equal to 1. In this embodiment, N = 2 and S2 = 1. In other words, the external structure 60 has four-fold rotational symmetry with respect to the axis O1. Note that the shapes of the parts constituting the external structure 60, that is, the shapes of the fixing part 10, the spacer 120, and the base part 130, do not have to be the same in plan view.

As shown in FIG. 2 , the outer periphery of the external structure 60 has (2N×S3) corners (corresponding to the corners of the fixed part 10) and side midlines (corresponding to the side midlines of the fixed part 10). Here, S3 is an integer greater than or equal to 1, and in this embodiment, S3 = 1. That is, the outer periphery of the external structure 60 has four corners and four side midlines. Note that, although the "corners" of the external structure 60 are "points" in plan view, they actually correspond to intersections along the axial direction of adjacent side surfaces of the external structure 60. In this specification, the "side midline" refers to an imaginary line in the axial direction passing through the midpoint of the relevant side surface. Furthermore, the term "side surface" collectively refers to one or more side surfaces provided on the inner periphery of the external structure 60 (corresponding to the inner periphery 10a of the fixed part 10) and one or more side surfaces provided on the outer periphery (corresponding to the outer periphery 10b of the fixed part 10). Furthermore, the "side surface" may be a flat surface or a curved surface.

As shown in Figure 2, the gyro element 110 has a fixed portion 10, a vibrator 20, multiple support portions 30, multiple electrodes 40a to 40h, and a magnetic field application portion 80. The structure consisting of the vibrator 20, multiple support portions 30, and multiple electrodes 40a to 40h is sometimes referred to as the internal structure 70. As is clear from Figure 2, the internal structure 70 is disposed inside the external structure 60 in a planar view.

As shown in FIG. 2, the fixed portion 10 is a frame-shaped member having an opening 11 in the center. When viewed from the axial direction (a direction perpendicular to the paper surface in FIG. 2), in other words, in a plan view, its inner periphery 10a is a regular octagon, while its outer periphery 10b is a regular rectangle. The fixed portion 10 is formed so that the midline of one side of the inner periphery 10a is located on the diagonal of the outer periphery 10b. Note that, in a plan view, the center point O of the fixed portion 10 coincides with the center point O of the vibrator 20. Also, in a plan view, the center point O of the external structure 60 coincides with the center point O of the vibrator 20. Note that the center points O of the fixed portion 10, vibrator 20, and external structure 60 may be simply referred to as center points O. The corners of the external structure 60 may be obtuse, right, or acute angles in a plan view. The corners of the external structure 60 are not limited to polygonal corners, and include C-chamfered and R-chamfered corners. The C-chamfered corners and the R-chamfered corners correspond to the intersection lines of the virtual extensions of adjacent side surfaces of the outer structure 60 .

As shown in FIG. 2 , imaginary planes having the axis O1 (see FIG. 3 ) as one side and passing through each of the four corners of the outer periphery of the external structure 60 in a planar view are defined as imaginary planes OA1, OA3, OA5, and OA7, respectively. Furthermore, imaginary planes having the axis O1 as one side and passing through each of the midlines of the four side surfaces of the outer periphery of the external structure 60 in a planar view are defined as imaginary planes OA2, OA4, OA6, and OA8, respectively. Here, an imaginary plane OA _j+1 , where j is an integer greater than or equal to 1 and less than or equal to 7, is located at a position obtained by rotating the imaginary plane OA _j by 45 degrees clockwise around the axis O1 as the central axis. Note that in the following description, when the first imaginary plane is defined as an imaginary plane having the axis O1 as one side and passing through any of a plurality of corners on the outer or inner periphery of the external structure 60 in a planar view, the second imaginary plane is defined as an imaginary plane obtained by rotating the first imaginary plane by (360/4N) degrees around the axis O1 as the central axis. Furthermore, even when the first imaginary plane is defined as a virtual plane having the axis O1 as one side and passing through any of the midlines of a plurality of side surfaces on the outer periphery or inner periphery of the external structure 60 in a plan view, the second imaginary plane is defined as a virtual plane obtained by rotating the first imaginary plane by (360/4N) degrees around the axis O1 as the central axis. In the example shown in Fig. 2, when the imaginary planes OA1, OA3, OA5, and OA7 are respectively defined as first imaginary planes, the imaginary planes OA2, OA4, OA6, and OA8 correspond to second imaginary planes, respectively.

Also, assume cross sections of the external structure 60 cut at imaginary planes OA1 to OA8. The radial length L1 of the cross section cut at imaginary plane OA1 is longer than the radial length L2 of the cross section cut at imaginary plane OA8. In other words, the cross-sectional area of the cross section cut at imaginary plane OA1 is larger than the cross-sectional area of the cross section cut at imaginary plane OA8. A similar relationship applies to the cross sections cut at imaginary plane OA1 and the cross sections cut at imaginary plane OA2. Furthermore, a similar relationship applies to the cross sections of the external structure 60 cut at imaginary plane OA3 and the cross sections cut at imaginary planes OA2 and OA4, respectively. This also applies to the cross section cut at imaginary plane OA5 and the cross sections cut at imaginary planes OA4 and OA6, respectively. This also applies to the cross section cut at imaginary plane OA7 and the cross sections cut at imaginary planes OA6 and OA8, respectively. Therefore, as described above, the imaginary planes OA1, OA3, OA5, and OA7 are each defined as the first imaginary plane, and the imaginary planes OA2, OA4, OA6, and OA8 are each defined as the second imaginary plane. In this case, the cross section of the external construct 60 cut by the first imaginary plane is defined as the first cross section 12, and the cross section of the external construct 60 cut by the second imaginary plane is defined as the second cross section 13. The second cross section 13 is located at a position obtained by rotating the first cross section 12 by (360/4N) degrees around the axis O1 as the central axis. Furthermore, the cross-sectional area of the first cross section 12 is different from the cross-sectional area of the second cross section 13. Specifically, the cross-sectional area of the former is larger than the cross-sectional area of the latter.

In this specification, "cutting" refers to a virtual cut on an object, and does not mean actually cutting the object.

2, even if one of the multiple first cross sections 12 and one of the second cross sections 13 are arbitrarily selected from each of the multiple first cross sections 12 and the multiple second cross sections 13, the cross-sectional area of the first cross section 12 will always be different from the cross-sectional area of the second cross section 13. However, among the pairs selected from the multiple first cross sections 12 and the multiple second cross sections 13, there may be a pair in which the cross-sectional area of the first cross section 12 is the same as the cross-sectional area of the second cross section 13. However, even in this case, as will be described later, the first imaginary plane or the second imaginary plane intersecting the primary drive electrode PD in a planar view passes through the first cross section 12 or the second cross section 13 in which the cross-sectional area of the cross section cut by the first imaginary plane and the cross-sectional area of the cross section cut by the second imaginary plane are different from each other.

Also, inside the opening 11, the vibrator 20, multiple support members 30, multiple electrodes 40a-40h, and magnetic field application unit 80 are arranged. As shown in FIG. 3, the fixed portion 10 is a member having a layered structure in which a first silicon layer 51, a silicon oxide layer (insulating layer) 52, and a second silicon layer 53 are layered in this order. A silicon oxide film 54 is formed on the surface of the second silicon layer 53. The structure of the fixed portion 10 is not particularly limited to this.

The vibrator 20 is a circular ring-shaped member obtained by processing the second silicon layer 53, and is configured so that when subjected to an external force, the internal structure 70 including the vibrator 20 and the external structure 60 vibrate in a cos Nθ mechanical vibration mode (hereinafter sometimes simply referred to as the vibration mode).

The support portion 30 is a member obtained by processing the second silicon layer 53, and is formed integrally with the vibrator 20. The support portion 30 connects the vibrator 20 to the fixed portion 10, supporting the vibrator 20 in a cantilevered manner, or, from another perspective, supporting the vibrator 20 so that it can vibrate. As is clear from Figure 3, the surfaces of the fixed portion 10, vibrator 20, and support portion 30 are parallel to each other. The back surfaces of the fixed portion 10, vibrator 20, and support portion 30 are parallel to each other.

As shown in FIG. 4, each of the multiple support parts 30 has a first leg part 31 and a second leg part 32. The first leg part 31 and the second leg part 32 each have a first end part 30a and a second end part 30b. The first end part 30a is connected to a corner of the inner periphery 10a of the fixed part 10. The second end part 30b is connected to the vibrator 20.

Each of the imaginary planes OA1 to OA8 is positioned so as to pass between the first leg 31 and the second leg 32 that support each of the eight electrodes 40. Furthermore, the first leg 31 and the second leg 32 that support the same electrode 40 are positioned symmetrically with respect to one of the eight imaginary planes OA1 to OA8.

The first leg 31 also has first to fifth portions 31a, 31b, 31c, 31d, and 31e. The first portion 31a extends radially from the first end 30a toward the center point O of the vibrator 20. The second portion 31b is bent at one end of the first portion 31a and extends circumferentially. The third portion 31c is bent at one end of the fifth portion 31e and extends radially toward the center point O of the vibrator 20, reaching the second end 30b. The fourth portion 31d extends radially from one end of the second portion 31b toward the center point O of the vibrator 20. The fifth portion 31e is folded back at one end of the fourth portion 31d in the opposite direction to the folding back direction of the second portion 31b and extends circumferentially. Note that an imaginary line (not shown) extending from the first portion 31a, the third portion 31c, and the fourth portion 31d does not necessarily pass through the center point O.

Similarly, the second leg 32 has first to fifth portions 32a, 32b, 32c, 32d, and 32e. The first portion 32a extends radially from the first end 30a toward the center point O of the vibrator 20. The second portion 32b is bent at one end of the first portion 32a and extends circumferentially. The third portion 32c is bent at one end of the fifth portion 32e and extends radially toward the center point O of the vibrator 20, reaching the second end 30b. The fourth portion 32d extends radially from one end of the second portion 32b toward the center point O of the vibrator 20. The fifth portion 32e extends circumferentially, folding back at one end of the fourth portion 32d in the opposite direction to the folding back direction of the second portion 32b. It should be noted that the virtual line (not shown) extending from the first portion 32a, the third portion 32c, and the fourth portion 32d does not necessarily pass through the center point O.

Each of the electrodes 40a to 40h is a conductive member formed in a loop shape within the surface of the vibrator 20. Furthermore, each of the electrodes 40a to 40h is provided continuously from the surface of the support portion 30 to the surface of the vibrator 20. In the following description, unless particular attention is paid to the orientation or function of the electrodes 40a to 40h, the electrodes 40a to 40h may be collectively referred to as electrodes 40.

2 and 4, the electrode 40 extends from the first end 30a of the first leg 31, via the second end 30b of the first leg 31, the vibrator 20, and the second end 30b of the second leg 32, to the first end 30a of the second leg 32. One end of the electrode 40 is connected to an electrode pad 42 via a lead-out wiring 41 formed on the surface of the fixed part 10. Similarly, the other end of the electrode 40 is connected to an electrode pad 42 via a lead-out wiring 41 formed on the surface of the fixed part 10. The electrode 40, lead-out wiring 41, and electrode pad 42 are integrally formed on the surface of the silicon oxide film 54.

Some or all of the electrodes 40 with the same function that are arranged in different orientations are connected by wiring (not shown). The wiring may be provided on the fixed part 10. Alternatively, it may be a metal wire that connects the electrode pads 42 together.

As shown in FIG. 2, two sets of electrodes 40 with four different functions are arranged circumferentially on the surface of the vibrator 20. Each set of electrodes 40 includes a primary drive electrode PD, a secondary drive electrode SD, a primary detection electrode PPO, and a secondary detection electrode SPO, arranged in this order clockwise along the circumferential direction. The multiple electrodes 40a-40h are all the same size. Furthermore, the multiple electrodes 40a-40h are arranged 45 degrees apart in the circumferential direction, with the center point O as their apex. Therefore, electrodes 40 with the same function included in the gyro element 110 are arranged 180 degrees apart in the circumferential direction, with the center point O as their apex. For example, the two primary drive electrodes PD (electrodes 40a, 40e) are arranged 180 degrees apart in the circumferential direction, with the center point O as their apex.

As described above, eight electrodes 40a-40h are arranged at equal angular intervals around the circumference of the annular vibrator 20. Furthermore, as shown in FIG. 2, eight sets of support members 30, each corresponding to one of the electrodes 40a-40h, are also arranged at equal angular intervals around the circumference of the vibrator 20. In other words, the internal structure 70 has (4N x S1)-fold rotational symmetry about the axis O1. Here, S1 is an integer greater than or equal to 1, and in this embodiment, S1 = 1. In other words, the internal structure 70 has eight-fold rotational symmetry about the axis O1.

As shown in FIG. 3, the magnetic field application unit 80 has an upper yoke 81, a magnet 82, and a lower yoke 83. The upper yoke 81 and the lower yoke 83 are each a cylindrical member with a bottom made of a magnetic material such as iron. The upper yoke 81 and the lower yoke 83 are arranged so that the cylindrical portion of the upper yoke 81 and the cylindrical portion of the lower yoke 83 face each other with an axial gap between them. In addition, the vibrator 20 is arranged between the cylindrical portion of the upper yoke 81 and the cylindrical portion of the lower yoke 83. The vibrator 20 is arranged between the edge of the upper yoke 81 and the edge of the lower yoke 83 with an axial gap between them.

The magnet 82 has a north pole on one of its upper and lower sides and a south pole on the other. The magnet 82 is held by the upper yoke 81 or the lower yoke 83, or both, and is fixedly positioned inside the vibrator 20.

Magnetic flux flowing from one magnetic pole of magnet 82 passes through one of upper yoke 81 and lower yoke 83 and reaches vibrator 20 and electrodes 40a-40h formed on its surface. Furthermore, the magnetic flux passes through vibrator 20 and electrodes 40a-40h, and flows into the other magnetic pole of magnet 82 via the other of upper yoke 81 and lower yoke 83.

In this way, the magnetic field application unit 80 applies a magnetic field to the multiple electrodes 40a to 40h in a direction that intersects with the surface of the vibrator 20, in this case the axial direction. The magnetic field application unit 80 is supported by the base 130, thereby maintaining its radial and axial position relative to the vibrator 20.

The gyro element 110 is a MEMS (Micro Electro Mechanical Systems) element obtained by processing a well-known SOI (Silicon On Insulator) substrate using, for example, micromachining technology that applies semiconductor microfabrication technology.

This MEMS element is manufactured, for example, as follows: An SOI substrate having a first silicon layer 51, a silicon oxide layer 52, and a second silicon layer 53 is thermally oxidized to form a silicon oxide film 54 on the surface of the second silicon layer 53.

Next, a mask pattern (not shown) is used to form multiple electrodes 40a-40h, lead-out wiring 41, and electrode pads 42 on the surface of the silicon oxide film 54. For example, a metal film is deposited on the surface of the silicon oxide film 54 through the mask pattern to form multiple electrodes 40a-40h, lead-out wiring 41, and electrode pads 42.

Using another mask pattern (not shown), the silicon oxide film 54 and second silicon layer 53 are etched and removed down to the silicon oxide layer 52. Through this process, the original shapes of the support portion 30 and vibrator 20 are formed.

Next, the surfaces of the electrodes 40a-40h, the lead-out wiring 41, the electrode pads 42, the support portion 30, and the vibrator 20 are protected with wax or the like. Next, a mask pattern (not shown) corresponding to the opening 11 in the fixed portion 10 is used to etch and remove the first silicon layer 51 located below the support portion 30 and the vibrator 20. Furthermore, the same mask pattern is used to etch and remove the silicon oxide layer 52, thereby obtaining the aforementioned MEMS element.

The etching of the first silicon layer 51 and the silicon oxide layer 52 may be dry etching or wet etching. In either case, however, it is preferable to use an etchant that has high etching selectivity with respect to the layer underlying the etching layer.

[Configuration and Operation of Angular Velocity Sensor]
Fig. 5 is a schematic diagram of a circuit block of the angular velocity sensor. For ease of explanation, Fig. 5 shows only the primary drive electrodes PD, primary detection electrodes PPO, secondary drive electrodes SD, and secondary detection electrodes SPO of the vibratory gyroscope 100 in a simplified manner.

As shown in Figure 5, the angular velocity sensor 1000 has a vibration type gyroscope 100, a primary AC power supply 200, a primary detection unit 210, a secondary AC power supply 220, a secondary detection unit 230, and a calculation unit 240.

A primary AC power supply 200 is connected to two primary drive electrodes PD included in the vibratory gyroscope 100. A primary detection unit 210 is connected to two primary detection electrodes PPO connected in series. A secondary AC power supply 220 is connected to two secondary drive electrodes SD. A secondary detection unit 230 is connected to two secondary detection electrodes SPO connected in series. A calculation unit 240 is connected to the secondary AC power supply 220. The two primary detection electrodes PPO may be connected in series inside the gyro element 110, or may be connected in series inside a circuit (not shown) provided external to the gyro element 110. Similarly, the two secondary detection electrodes SPO may be connected in series inside the gyro element 110, or may be connected in series inside a circuit (not shown) provided external to the gyro element 110.

The operation of the angular velocity sensor 1000 is described below.

When AC current Ip is supplied to primary drive electrode PD from primary AC power supply 200, a Lorentz force is applied to primary drive electrode PD in a direction that intersects the direction of the magnetic field applied from magnetic field application unit 80 and the direction of AC current Ip. In other words, the Lorentz force acts in a direction parallel to the surface of vibrator 20. Vibrator 20, which is provided with primary drive electrode PD, is deformed by this Lorentz force. Furthermore, since the direction of the Lorentz force periodically reverses depending on the frequency of AC current Ip, vibrator 20 vibrates at the same frequency. In this case, vibrator 20 vibrates in a direction parallel to its surface.

By setting the frequency of the AC current Ip to match the natural vibration frequency of the vibration gyroscope 100, a primary vibration is excited in the vibrator 20.

Also, to generate such primary vibration in the vibrator 20, an AC current Ip must be passed through each of the two primary drive electrodes PD. Specifically, the AC current Ip is set to flow in the same direction between the two primary drive electrodes PD located 180 degrees apart in the circumferential direction, in this case, clockwise when viewed from above. The connection relationship between the two primary drive electrodes PD and the primary AC power supply 200 only needs to satisfy the above-mentioned settings, and the two primary drive electrodes PD may be connected in series or in parallel to the primary AC power supply 200.

The primary detection electrode PPO detects the primary vibration and generates a voltage signal whose magnitude corresponds to the amplitude. This voltage signal is fed back to the primary detection unit 210. Based on the voltage signal generated at the primary detection electrode PPO, the primary detection unit 210 outputs an output signal to the primary AC power supply 200. Based on the output signal from the primary detection unit 210, the primary AC power supply 200 controls the amplitude and frequency of the AC current Ip so that the vibration frequency and amplitude of the vibrator 20 remain constant.

Figure 6 shows a schematic representation of the primary vibration state of the vibrator, and Figure 7 shows a schematic representation of the secondary vibration state of the vibrator.

The annular vibrator 20 undergoes primary vibration to form an ellipse shown by the dashed line in Figure 6. Specifically, the vibrator 20 undergoes primary vibration to form two ellipses periodically with their major axes perpendicular to each other. The major axes of each ellipse are sometimes referred to as the vibration axis of the primary vibration. The vibration axis PM is the vibration axis of the cos Nθ mode of the vibrator 20. In the vibratory gyroscope 100 of this embodiment, the vibration axis PM is determined to coincide with the first vibration axis of the external structure 60. The first vibration axis of the external structure 60 refers to the vibration axis of a vibration mode in which the influence on the vibration of the cos Nθ mode of the vibrator 20 cannot be ignored. The direction of the vibration axis PM is determined as a result of the mechanical coupling between the external structure 60 and the internal structure 70. The same applies to the second vibration axis of the external structure 60, which will be described later. In the vibratory gyroscope 100 of this embodiment, the vibration axis of the primary vibration coincides with the vibration axis PM. One vibration axis PM is determined to coincide with the imaginary planes OA1 and OA5 in plan view, and the other vibration axis PM is determined to coincide with the imaginary planes OA3 and OA7 in plan view.

On the other hand, when a Coriolis force is applied to the vibrator 20 and an angular velocity is generated around the axis, the direction of the major axis of the ellipse changes. In the case of the vibratory gyroscope 100 of this embodiment shown in Figure 1, as shown in Figure 7, the major axis of the ellipse rotates 45 degrees relative to the primary vibration, and the vibrator 20 enters a secondary vibration state. Hereinafter, the major axis of each ellipse in the secondary vibration state may be referred to as the vibration axis of the secondary vibration. Furthermore, the vibration axis SM is the vibration axis of the cos Nθ mode of the vibrator 20. In the vibratory gyroscope 100 of this embodiment, the vibration axis SM is determined to coincide with the second vibration axis of the external structure 60. The second vibration axis of the external structure 60 refers to the vibration axis of a vibration mode whose influence on the cos Nθ mode vibration of the vibrator 20 cannot be ignored, and the direction of the vibration axis SM is determined as a result of the mechanical coupling between the external structure 60 and the internal structure 70. The second vibration axis of the external structure 60 will be described later. One vibration axis SM is determined to coincide with the imaginary planes OA2 and OA6 in plan view, and the other vibration axis SM is determined to coincide with the imaginary planes OA4 and OA8 in plan view.

A magnetic field is also applied to the secondary detection electrode SPO in a direction that intersects with its surface. Furthermore, in response to the vibration of the vibrator 20, the secondary detection electrode SPO also vibrates in a direction parallel to its surface. As a result, a sinusoidal AC voltage is generated in the secondary detection electrode SPO according to the strength of the magnetic field and the movement speed during vibration. Furthermore, because the movement speed of the secondary detection electrode SPO differs when the vibrator 20 is in the primary vibration state and the secondary vibration state, the voltage generated in each state also differs.

The secondary detection unit 230 detects the voltage generated at the secondary detection electrode SPO and outputs a signal corresponding to the magnitude of the voltage to the secondary AC power supply 220.

The output signal of the secondary detection unit 230 is input to the secondary AC power supply 220. Based on this output signal, the secondary AC power supply 220 supplies current to the secondary drive electrode SD to drive the vibrator 20 so as to cancel out the secondary vibration generated in the vibrator 20. The secondary AC power supply 220 also outputs an output signal based on the output current to the calculation unit 240.

As explained above, a force acts on each electrode 40 during operation of the angular velocity sensor 1000, and a corresponding mechanical axis of motion is hypothetically assumed. In light of this, the orientation of the electrodes 40 can also be said to be such that the assumed axis of motion (hereinafter sometimes referred to as the axis of the electrode 40) for each electrode is arranged at equal angular intervals around the circumference of the vibrator 20. In this embodiment, each of the electrodes 40a-40h has the same shape and size. Therefore, the axis of the electrode 40 passes through the midpoint of each electrode 40 in a planar view. However, if the size or shape of each of the electrodes 40a-40h differs from that shown in Figures 2 and 4, the position of the axis of the electrode 40 will also move accordingly. For example, it may not pass through the midpoint of each electrode 40. When focusing on the function of the electrode 40, the axis of the electrode 40 may be referred to more specifically as, for example, the axis of the primary drive electrode PD.

As is clear from Figures 6 and 7, in the vibratory gyroscope 100 of this embodiment, the axis of the primary drive electrode PD overlaps with the vibration axis PM. Furthermore, the axis of the secondary drive electrode SD overlaps with the vibration axis SM. However, this relationship is not essential, and the shapes of each part of the vibratory gyroscope 100 and the arrangement of the electrodes 40a to 40h may be set so that any one of the axes of the primary drive electrode PD, secondary drive electrode SD, primary detection electrode PPO, and secondary detection electrode SPO overlaps with the vibration axis PM. This will be described in more detail later.

The calculation unit 240 calculates the angular velocity based on the output signal of the secondary AC power supply 220. The output signal of the secondary AC power supply 220 varies depending on whether the vibrator 20 is in a primary vibration state or a secondary vibration state. Furthermore, when the vibrator 20 is in a secondary vibration state, the output signal of the secondary AC power supply 220 varies depending on the magnitude of the applied angular velocity. The calculation unit 240 calculates the angular velocity based on the output signal of the secondary AC power supply 220.

The vibratory gyroscope 100, primary AC power supply 200, primary detection unit 210, secondary AC power supply 220, secondary detection unit 230, and calculation unit 240 may be mounted on separate boards, or may be mounted on the same board. The vibratory gyroscope 100, primary AC power supply 200, primary detection unit 210, secondary AC power supply 220, secondary detection unit 230, and calculation unit 240 may be housed in separate packages (not shown). The vibratory gyroscope 100 and other components may be mounted on separate boards or housed in separate packages. In that case, the primary AC power supply 200 and the secondary AC power supply 220 may be mounted on yet another board or housed in another package.

[Effects, etc.]
As described above, the vibratory gyroscope 100 according to this embodiment includes at least the external structure 60 and the internal structure 70 arranged inside the external structure 60 in a planar view. The external structure 60 includes at least the frame-shaped fixed portion 10 having a center point O in a planar view. More specifically, the external structure 60 includes at least one of the spacer 120 and the pedestal portion 130. The spacer 120 is arranged in contact with the back surface of the fixed portion 10. The pedestal portion 130 is arranged in contact with the back surface of the fixed portion 10 or the spacer 120.

The internal structure 70 includes at least an annular vibrator 20 that has a common center point O with the fixed part 10 in a plan view, a support part 30 that connects the vibrator 20 to the fixed part 10 and supports the vibrator 20 so that it can vibrate, and electrodes 40a to 40h that are each formed in a loop shape within the plane of the vibrator 20. When the vibrator 20 has a vibration mode of cos Nθ (N is an integer of 2 or greater), the electrodes 40a to 40h are arranged in 4N directions at equal angular intervals around the center point O of the vibrator 20 in the circumferential direction of the vibrator 20.

The internal structure 70 has (4N x S1) (S1 is an integer greater than or equal to 1) rotational symmetry about an axis O1 that passes through the center point O of the vibrator 20 and intersects the surface of the vibrator 20. The external structure 60 has (2N x S2) (S2 is an odd number greater than or equal to 1) rotational symmetry about the axis O1.

The first imaginary plane is an imaginary plane with the axis O1 as one side and passing through one of the midlines of the multiple corners and/or multiple side surfaces of the external structure 60. The second imaginary plane is an imaginary plane rotated (360/4N) degrees from the first imaginary plane with the axis O1 as its central axis.

The first cross section 12 is a cross section cut by a first imaginary plane in the external structure 60. The second cross section 13 is a cross section located at a position obtained by rotating the first cross section 12 by (360/4N) degrees around the axis O1 as the central axis. One or more first cross sections 12 and second cross sections 13 exist in the external structure 60. Furthermore, among the pairs of first cross sections 12 and second cross sections 13, there is at least one pair of first cross sections 12 and second cross sections 13 that are a specific pair. The cross-sectional area of the first cross section 12 included in the specific pair is different from the cross-sectional area of the second cross section 13 included in the specific pair. In this embodiment, the cross-sectional area of the former cross section is larger than the cross-sectional area of the latter cross section.

The plurality of electrodes 40a-40h includes at least a primary drive electrode PD that excites a primary vibration in the vibrator 20. The primary drive electrode PD is arranged so as to intersect with a first imaginary plane that cuts the first cross section 12 included in the specific set described above. The primary drive electrode PD may also be arranged so as to intersect with a second imaginary plane that cuts the second cross section 13 included in the specific set described above.

The vibratory gyroscope 100 further includes a magnetic field application unit 80 that applies a magnetic field to the eight electrodes 40a to 40h in a direction that intersects the surface of the vibrator 20, in this case the axial direction.

By configuring the vibratory gyroscope 100 in this manner, the bias component mentioned above can be reduced. This will be explained further below.

Even when no Coriolis force is acting on the vibration gyroscope 100, a signal of a certain magnitude may be output from the angular velocity sensor 1000. This signal is the bias component mentioned above. Of the bias components, a component called the quadrature bias (Quad Bias) Ωquad becomes a noise component in the output signal of the vibration gyroscope 100 and, ultimately, the angular velocity sensor 1000, and therefore needs to be reduced. The quadrature bias Ωquad is expressed by the following equation (1):

Ωquad=(360sin4α/ _2KB )×Δf...(1)
where:
K _B : Constant Δf: Difference (Hz) between the vibration frequency fp of the vibration axis PM of the vibrator 20 in the cos Nθ mode and the vibration frequency fs of the vibration axis SM in the cos Nθ mode
α: Angle deviation (°) between the axis of the primary drive electrode PD or the axis of the secondary drive electrode SD and the vibration axis PM or the vibration axis SM of the vibrator 20 in the cos Nθ mode
is.

As is clear from equation (1), the quadrature bias Ωquad can be reduced by reducing the vibration frequency difference Δf and the angular deviation α. Of these, the vibration frequency difference Δf can be reduced by bringing the vibration frequencies fp and fs closer together. To achieve this, as described above, the symmetry of the arrangement of the secondary drive electrodes SD on the surface of the vibrator 20 can be made the same as the symmetry of the arrangement of the primary drive electrodes PD, thereby improving the symmetry of the vibrator. Alternatively, the vibrator 20 can be processed using a laser or the like to bring the vibration frequencies fp and fs closer together.

In the vibratory gyroscope 100 of this embodiment, as shown in FIG. 2, two primary drive electrodes PD are arranged 180 degrees apart in the circumferential direction on the surface of the vibrator 20. Similarly, two secondary drive electrodes SD are arranged 180 degrees apart in the circumferential direction on the surface of the vibrator 20. The secondary drive electrodes SD are also arranged in a direction adjacent to the arrangement direction of the primary drive electrodes PD. Furthermore, as mentioned above, the sizes of the multiple electrodes 40 are all the same. In addition, micromachining technology is applied when manufacturing the gyro element 110, and processing errors in the electrodes 40, including the spacing between adjacent electrodes 40, are minimized. As a result, the symmetry of the arrangement of the secondary drive electrodes SD on the surface of the vibrator 20 can be made to approach the symmetry of the arrangement of the primary drive electrodes PD.

On the other hand, the directions of the vibration axes PM and SM are affected by the shape of the external structure 60, particularly its rotational symmetry and mass distribution about the axis O1, as will be described later. Furthermore, the directions of the axes of the electrodes 40a to 40h are determined by the orientation of the electrodes 40a to 40h relative to the center point O. If an angular deviation α occurs between the directions of the vibration axes PM and SM and the direction of the axis of the primary drive electrode PD, the aforementioned bias component may become non-negligible depending on the magnitude of α.

Figure 8 shows a plan view of a vibration gyroscope according to a first comparative example. Figure 9 schematically shows the primary vibration state of the vibrator shown in Figure 8, and Figure 10 schematically shows the secondary vibration state of the vibrator shown in Figure 8. The vibration gyroscope 100 shown in Figure 8 corresponds to the conventional configuration disclosed in Patent Document 2.

The vibratory gyroscope 100 shown in Figure 8 has the primary drive electrode PD, secondary drive electrode SD, primary detection electrode PPO, secondary detection electrode SPO, and support portion 30 rotated 22.5 degrees counterclockwise around center point O compared to the vibratory gyroscope 100 shown in Figure 2. Furthermore, because the orientation of the support portion 30 and electrodes 40 has been changed, the shape of the electrodes 40 and the shape and arrangement of the lead-out wiring 41 of the vibratory gyroscope 100 shown in Figure 8 are different from those of the vibratory gyroscope 100 shown in Figure 2.

As shown in Figures 8 and 9, the directions of the vibration axes PM and SM in the vibratory gyroscope 100 shown in Figure 8 are the same as those of the vibratory gyroscope 100 shown in Figure 2. That is, in a planar view, one vibration axis PM is determined to coincide with imaginary planes OA1 and OA5 that pass through opposing corners of the external structure 60. The other vibration axis PM is determined to coincide with imaginary planes OA3 and OA7 that pass through other opposing corners of the external structure 60. Furthermore, in a planar view, one vibration axis SM is determined to coincide with imaginary planes OA2 and OA6 that pass through the midlines of opposing side surfaces of the external structure 60. The other vibration axis SM is determined to coincide with imaginary planes OA4 and OA8 that pass through the midlines of other opposing side surfaces of the external structure 60.

On the other hand, in the vibratory gyroscope 100 shown in Figure 8, the orientation of the electrodes 40 has changed compared to the example shown in Figure 2. As a result, the axis of the primary drive electrode PD does not coincide with the vibration axis PM, and the angular deviation α between them is 22.5 degrees. Similarly, the axis of the secondary drive electrode SD does not coincide with the vibration axis SM, and the angular deviation α between them is 22.5 degrees. In other words, the sine term sin4α in equation (1) is 1. Therefore, as is clear from equation (1), the quadrature bias Ωquad cannot be made zero unless the vibration frequency difference Δf is made zero. However, to make the vibration frequency difference Δf zero, the processing error of the vibratory gyroscope 100 needs to be brought as close to zero as possible, which is difficult in practice.

Furthermore, when the angular misalignment α is non-zero, the force generated in the primary drive electrode PD acts to excite both the natural vibration having the vibration axis PM and the natural vibration having the vibration axis SM in the vibrator 20. However, in reality, the secondary detection electrode SPO and secondary drive electrode SD, described below, are used to cancel out vibrations other than the primary vibration. Therefore, even when the angular misalignment α is non-zero, only the primary vibration actually occurs in the axial direction of the primary drive electrode PD. However, compared to when only the natural vibration having the vibration axis PM is excited, a voltage is also applied to the secondary drive electrode SD, which is the source of the angular velocity detection signal, and this becomes a bias component. In light of this, to reduce the bias component, the vibration axes PM and SM of the natural vibration generated in the vibrator 20 must be spatially and mechanically separated. Furthermore, the vibration axis PM must coincide with the axial direction of the primary drive electrode PD, which is the axial direction of the primary vibration; that is, the angular misalignment α must be zero. The rotational symmetry of the internal structure 70 and the rotational symmetry of the external structure 60 about the axis O1 affect this. These will be explained later.

Figure 11 shows a partial plan view of a vibratory gyroscope according to a second comparative example. The vibratory gyroscope 100 shown in Figure 11 corresponds to the conventional configuration disclosed in Patent Document 1. For ease of explanation, the drawing wiring 41 and electrode pads 42 are omitted from Figure 11.

The vibratory gyroscope 100 shown in Figure 11 differs from the vibratory gyroscope 100 shown in Figures 2 and 3 in the shape of the support portion 30. Specifically, eight support portions 30 are arranged at equal angular intervals in the circumferential direction, corresponding to the eight electrodes 40. Furthermore, one end of each support portion 30 is connected to a corner of the inner circumference 10a of the fixed portion 10, and is bent in a zigzag shape to extend to the vibrator 20.

The shape of the primary drive electrode PD shown in Figure 11 is asymmetric with respect to the imaginary plane OA8. The shape of the primary drive electrode PD at a position not shown is asymmetric with respect to the imaginary plane OA4. Therefore, the axis of the primary drive electrode PD also has an angular offset with respect to the imaginary planes OA4 and OA8. Similar relationships regarding the shape and axis of electrode 40 also apply to the secondary drive electrode SD, primary detection electrode PPO, and secondary detection electrode SPO, respectively.

Furthermore, the shapes of the eight support members 30 are asymmetric with respect to the imaginary planes OA1 to OA8 in a planar view. In the vibratory gyroscope 100 shown in Figures 1 and 2, the vibration axis PM coincides with the first imaginary plane (imaginary planes OA1, OA3, OA5, and OA7) in a planar view (see Figure 6). The direction of the vibration axis PM is determined to coincide with the direction of the first vibration axis of the external structure 60. However, in the vibratory gyroscope 100 shown in Figure 11, due to the asymmetry in the shapes of the support members 30 and electrodes 40 described above, the vibration axis PM does not overlap with any of the imaginary planes OA1 to OA8. Therefore, the direction of the vibration axis PM does not coincide with the direction of the first vibration axis of the external structure 60. Similarly, the vibration axis SM does not overlap with any of the imaginary planes OA1 to OA8. Therefore, the direction of the vibration axis SM does not coincide with the direction of the second vibration axis of the external structure 60, which will be described later.

In this embodiment, the support portion 30 has a first leg 31 and a second leg 32. Each of the imaginary planes OA1 to OA8 is arranged to pass between the first leg 31 and the second leg 32 supporting each of the eight electrodes 40. Furthermore, the first leg 31 and the second leg 32 supporting the same electrode 40 are arranged symmetrically with respect to one of the eight imaginary planes OA1 to OA8. That is, the first leg 31 and the second leg 32 are arranged symmetrically with respect to the first imaginary plane cutting the first cross section 12 included in the specific set described above or the second imaginary plane cutting the second cross section 13 included in the specific set. The electrode 40 extends from the first end 30a of the first leg 31, via the second end 30b of the first leg 31, the vibrator 20, and the second end 30b of the second leg 32, to the first end 30a of the second leg 32.

According to this embodiment, the vibration axis PM can be aligned with the first imaginary plane, in this case, the imaginary planes OA1 and OA5. As a result, the angle deviation α between the direction of the vibration axis PM and the direction of the axis of the primary drive electrode PD can be reduced, thereby reducing the bias component. This will be explained further below.

The vibration axes PM and SM of the natural vibrations generated in the vibrator 20 and the rotational symmetries of the internal structure 70 and the external structure 60 relative to the axis O1 affect the operation of the vibratory gyroscope 100.

As shown in Figures 6 and 7, the vibrator 20 vibrates in primary and secondary vibration states. At this time, the vibration axes of the two vibration states are offset by 45 degrees spatially and 90 degrees mechanically, and are independent vibration axes. Furthermore, the vibration axes of the primary and secondary vibrations are aligned with the vibration axis PM and vibration axis SM, respectively.

Generalizing the reference direction of the vibration axis as φ, the spatial vibration axis angles of the two cos Nθ modes are expressed by equations (2) and (3), respectively.

θp=φ+i×(360/2N)...(2)
θs=φ+Δφ+i×(360/2N)...(3)
where:
θp: Angle (degrees) of the spatial vibration axis PM of the first-order cos Nθ mode
θs: Angle (degrees) of the spatial vibration axis SM of the second-order cos Nθ mode
i: an integer satisfying the relationship 0≦i<2N−1; Δφ: an angular difference between the spatial vibration axes of the first and second cos Nθ modes;
Δφ=360/4N (degrees)
is.

As mentioned above, vibrator 20 has (4N x S1) rotational symmetry with respect to axis O1. Therefore, the mass distribution and stiffness distribution of vibrator 20 are also symmetrical with respect to vibrations in the first-order cos Nθ mode and the second-order cos Nθ mode. Therefore, the vibration frequency of the first-order cos Nθ mode and the vibration frequency of the second-order cos Nθ mode are roughly equal (however, due to the influence of processing errors, these vibration frequencies do not strictly match in actual vibrators). Typically, the spatial vibration axis of the cos Nθ mode is determined by the direction in which the natural vibration frequency of vibrator 20 is minimized and maximized. In this regard, the spatial vibration axis of vibrator 20's cos Nθ mode is determined by minute asymmetries due to the influence of processing errors, etc., and variations in the direction of the vibration axis are a cause of the angular deviation α.

On the other hand, the vibrator 20 is connected to the fixed part 10 of the external structure 60 via the support part 30. Therefore, when the vibrator 20 vibrates, the external structure 60 also vibrates, and the vibration state of the external structure 60 affects the vibration state of the vibrator 20. Because the external structure 60 has a complex three-dimensional structure, many natural vibration modes exist. Here, the vibration axis that influences the vibration state of the vibrator 20 and leads to a direction that becomes the vibration axis of the first-order cos Nθ mode is called the first vibration axis of the external structure 60, and the direction spatially shifted by (360/4N) degrees from the first vibration axis is called the second vibration axis of the external structure 60.

As described above, the external structure 60 has (2N x S2) rotational symmetry with respect to the axis O1. Furthermore, portions of the external structure 60 with the same mass and rigidity appear at a period of (360/2N) degrees in the circumferential direction. Therefore, the first vibration axis of the external structure 60 is spatially separated from the second vibration axis. Furthermore, due to these factors, the vibration frequency of the first vibration mode of the external structure 60 differs from the vibration frequency of the second vibration mode. In this embodiment, since the outer periphery 10b of the external structure 60 has (2N x S2) rotational symmetry with respect to the axis O1 in a planar view, the entire external structure 60 also has (2N x S2) rotational symmetry. However, this is not limited thereto, and for example, the inner periphery 10a of the external structure 60 may have (2N x S2) rotational symmetry with respect to the axis O1. Both the outer periphery 10b and the inner periphery 10a may have (2N x S2) rotational symmetry. Furthermore, the external structure 60 may have (2N×S2) rotational symmetry due to the structure of the front and/or back surface, or an internal structure that cannot be seen from the front and/or back surface.

The first and second vibration modes of the external structure 60 affect the vibration state of the vibrator 20, so that the vibration frequency of the first cos Nθ mode of the vibrator 20 differs from the vibration frequency of the second cos Nθ mode.

The direction of the vibration axis PM is determined to coincide with the direction of the first vibration axis of the external structure 60. In the external structure 60 of this embodiment, the direction of the first vibration axis overlaps with imaginary planes OA1, OA3, OA5, and OA7, which have the axis O1 as one side and pass through each of the four corners of the external structure 60. This is because this portion, i.e., the first cross section 12, has the largest cross-sectional area in the external structure 60 and is a characteristic vibration axis that affects the direction of the vibration axis of the first-order cos Nθ mode of the vibrator 20. In this case, the vibration axis PM overlaps with the first imaginary plane (imaginary planes OA1, OA3, OA5, and OA7) in a planar view. The direction 45 degrees circumferentially away from the direction of the vibration axis PM coincides with the direction of the vibration axis SM. 2 , the vibration axis SM overlaps with second imaginary planes (imaginary planes OA2, OA4, OA6, and OA8) that have the axis O1 as one side and pass through the midlines of the four side surfaces of the outer periphery 10b of the external structure 60. In addition, in the external structure 60, the cross-sectional area of this portion, that is, the second cross section 13, is smaller than the cross-sectional area of the first cross section 12.

The vibration state of the external structure 60 defined in this manner will be explained in comparison with a third comparative example. Figure 12 shows a schematic plan view of the external structure of this embodiment. Figure 13A is a schematic diagram showing the deformation state of the external structure when vibrating on the first vibration axis. Figure 13B is a schematic diagram showing the deformation state of the external structure when vibrating on the second vibration axis. Here, the first vibration axis refers to the vibration axis of the external structure having a vibration mode in which the influence on the vibration of the cos Nθ mode of the vibrator 20 cannot be ignored, and the same applies to the second vibration axis.

14 shows a plan view of an external structure according to a third comparative example. FIG. 15A is a schematic diagram showing the deformation state of the external structure shown in FIG. 15 when vibrating in the first cos 2θ mode. FIG. 15B is a schematic diagram showing the deformation state of the external structure shown in FIG. 14 when vibrating in the second cos 2θ mode. FIG. 15C is a schematic diagram showing another deformation state of the external structure shown in FIG. 14 when vibrating in the first cos 2θ mode. FIG. 15D is a schematic diagram showing another deformation state of the external structure shown in FIG. 14 when vibrating in the second cos 2θ mode. For ease of explanation, although not shown, the internal structure 70 shown in FIG. 2 is disposed inside the external structure 60 shown in FIG. 12. The internal structure 70 shown in FIG. 2 is disposed inside the external structure 60 shown in FIG. 14. In this case, the connection position of the support portion 30 relative to the inner periphery 10a of the fixed portion 10 is the same as that shown in FIG. 2.

The external structure 60 shown in FIG. 14 differs from the external structure 60 of this embodiment shown in FIG. 12 in that the outer periphery of the external structure 60 is a regular octagon. In other words, both the inner and outer peripheries of the external structure 60 shown in FIG. 14 are regular octagons. Therefore, the external structure 60 shown in FIG. 14 has the same rotational symmetry as the internal structure 70, i.e., eight-fold rotational symmetry, with respect to the axis O1. Furthermore, an imaginary plane with the axis O1 as one side and passing through one of the corners of the outer periphery of the external structure 60 is defined as imaginary plane OA1. Furthermore, imaginary planes located at positions obtained by rotating the imaginary plane OA1 clockwise by 22.5 degrees around the axis O1 as the central axis are defined as imaginary planes OA2 to OA16, respectively.

Therefore, just as when the vibration modes of the vibrator 20 were considered, the mass distribution and stiffness distribution of the external structure 60 are also symmetrical for the vibrations of the first cos 2θ mode and the second cos 2θ mode. As a result, the vibration axis PM can take two forms: passing through opposing corners of the external structure 60 as shown in FIG. 15A , or passing through the midlines of opposing sides of the outer periphery 10b of the external structure 60 as shown in FIG. 15C . Furthermore, when the vibration axis PM passes through opposing corners of the external structure 60, the vibration axis SM passes through opposing corners of the outer periphery 10b of the external structure 60 as shown in FIG. 15B . When the vibration axis PM passes through the midlines of opposing sides of the external structure 60, the vibration axis SM passes through the midlines of opposing sides of the external structure 60 as shown in FIG. 15D .

Furthermore, due to the symmetry of the external structure 60, the vibration frequency of the first cos 2θ mode and the vibration frequency of the second cos 2θ mode are approximately equal. Therefore, when the orientation of the vibration axis of the first cos Nθ mode of the vibrator 20 is determined as a result of the mechanical coupling between the external structure 60 and the internal structure 70, the external structure 60 can be in either of the deformed states shown in Figures 15A and 15C. Furthermore, when the external structure 60 is in the deformed state shown in Figure 15A in the first cos Nθ mode of the vibrator 20, the external structure 60 is in the deformed state shown in Figure 15B in the second cos Nθ mode of the vibrator 20. When the external structure 60 is in the deformed state shown in Figure 15C in the first cos Nθ mode of the vibrator 20, the external structure 60 is in the deformed state shown in Figure 15D in the second cos Nθ mode of the vibrator 20. That is, there are cases where the direction of the vibration axis of the first cos Nθ mode of the external structure 60 coincides with the direction of the vibration axis PM, and cases where the direction of the vibration axis of the first cos Nθ mode in a different deformation state coincides with the direction of the vibration axis PM. In either case, the frequencies of the first and second cos Nθ modes are approximately equal, so in the actual vibrator 20, the spatial vibration axis of the first cos Nθ mode is determined by a slight asymmetry due to the influence of processing errors and the like, and variations in the direction of the vibration axis become a cause of the angle deviation α.

On the other hand, by applying the external structure 60 shown in FIG. 12, the direction of the first vibration axis of the external vibrator 60 is determined to be a direction passing through opposing corners of the external structure 60. Furthermore, the direction of the second vibration axis of the external vibrator 60 is determined to be a direction passing through the midlines of opposing side surfaces of the external structure 60. Furthermore, the vibration frequency of the second cos 2θ mode of the external structure 60 is higher than the vibration frequency of the first cos 2θ mode. As a result, when the vibrator 20 excites the first cos 2θ mode, the external structure 60, as a result of the mechanical coupling with the internal structure 70, repeats the deformation state shown in FIG. 13A in accordance with the vibration axis of the first cos 2θ mode. When the vibrator enters the second cos 2θ mode state, the external structure 60 repeats the deformation state shown in FIG. 13B in accordance with the vibration axis of the second cos 2θ mode.

As described above, according to this embodiment, by defining the rotational symmetry of the vibratory gyroscope 100 with respect to the axis O1, the direction of the first vibration axis of the external structure 60 is uniquely determined, and accordingly, the direction of the second vibration axis of the external structure 60 is also determined to be spatially shifted by (360/4N) degrees, in this case, 45 degrees, from the direction of the first vibration axis. As a result, the vibration axis of the first cos 2θ mode of the vibrator 20, which is mechanically coupled to the external structure 60 via the support 30, is determined to be in the direction of the first vibration axis of the external structure 60. Furthermore, the vibration axis of the second cos 2θ mode of the vibrator 20 is determined to be in the direction of the second vibration axis of the external structure 60. Furthermore, by arranging the primary drive electrode PD so that the direction of the first vibration axis of the external structure 60 coincides with the direction of the axis of the primary drive electrode PD, the vibration axis of the primary vibration of the vibrator 20 can be made to coincide with the direction of the vibration axis of the primary cos 2θ mode, and therefore the angle deviation α, and therefore the quadrature bias Ωquad, can be made close to zero. This allows the bias component included in the output signal of the vibrating gyroscope 100 to be significantly reduced, making it possible to detect angular velocity with high accuracy.

Furthermore, it is preferable that the support portion 30 on which the electrode 40 is disposed is composed of a first leg portion 31 having the first to fifth portions 31a to 31e and a second leg portion 32 having the first to fifth portions 32a to 32e. It is more preferable that the first leg portion 31 and the second leg portion 32 are disposed symmetrically with respect to the aforementioned imaginary planes OA1 to OA8.

By configuring the support portion 30 in this manner, when the vibrator 20 is subjected to primary vibration, it can be supported without significantly affecting the vibration. Furthermore, by providing the support portions 30 at equal angular intervals around the circumference and by providing the first leg portions 31 and second leg portions 32 symmetrically with respect to the imaginary planes OA1 to OA8, the vibrator 20 can be connected to the fixed portion 10 with equal balance. This allows the vibrator 20 to stably undergo primary vibration.

The angular velocity sensor 1000 of this embodiment comprises at least a vibrating gyroscope 100, a primary AC power supply 200 for passing an AC current of a predetermined frequency through the primary drive electrode PD, a primary detection unit 210 for detecting a voltage signal generated in the primary detection electrode PPO, a secondary AC power supply 220 for passing an AC current through the secondary drive electrode SD, a secondary detection unit 230 for detecting a voltage signal generated in the secondary detection electrode SPO, and a calculation unit 240 for calculating the angular velocity based on the output signal of the secondary AC power supply 220.

On the surface of the vibrator 20, a primary drive electrode PD, a secondary drive electrode SD, a primary detection electrode PPO, and a secondary detection electrode SPO are arranged in this order clockwise along the circumferential direction. The vibratory gyroscope 100 has two sets of these electrodes 40. The primary drive electrode PD excites a primary vibration in the vibrator 20. The primary detection electrode PPO detects the primary vibration of the vibrator 20. The secondary detection electrode SPO detects the secondary vibration generated in the vibrator 20. The secondary drive electrode SD drives the vibrator 20 to cancel out the secondary vibration generated in the vibrator 20. However, if the angular deviation α is not zero, the force generated in the primary drive electrode PD acts to excite both the natural vibration having the vibration axis PM and the natural vibration having the vibration axis SM in the vibrator 20. However, in reality, the secondary detection electrode SPO and the secondary drive electrode SD act to cancel out vibrations other than the primary vibration, so even if the angular deviation α is not zero, only the primary vibration actually occurs. At this time, a voltage is also applied to the secondary drive electrodes SD, which are the source of the angular velocity detection signal, and this serves as a bias component.

The angular velocity sensor 1000 of this embodiment can reduce the bias component contained in the output signal of the vibration type gyroscope 100, thereby improving the accuracy of angular velocity detection.

In addition, according to this embodiment, the voltage generated at the primary detection electrode PPO is detected by the primary detection unit 210, and the output signal of the primary detection unit 210 is fed back to the primary AC power supply 200, thereby stabilizing the primary vibration generated by the vibrator 20.

The voltage generated at the secondary detection electrode SPO is detected by the secondary detection unit 230, and the output of the secondary AC power supply 220 is controlled based on the output signal of the secondary detection unit 230, thereby canceling out the secondary vibration generated by the vibrator 20. In this way, the vibration state of the vibrator 20 can be stabilized. This also reduces the noise components contained in the output signal of the secondary AC power supply 220, improving the accuracy of angular velocity detection.

<Modification 1>
Fig. 16 shows a plan view of a vibrating gyroscope according to this modification, and Fig. 17 shows an enlarged view of the portion surrounded by the dashed line in Fig. 16. In Figs. 16 and 17 and the subsequent drawings, the same parts as those in the first embodiment are designated by the same reference numerals, and detailed description thereof will be omitted.

The vibration type gyroscope 100 of this modified example shown in Figure 16 differs from the vibration type gyroscope 100 shown in Figure 1 in the following ways.

First, the corners of the inner circumference 10a of the fixed part 10 shown in Figure 16 are rotated 22.5 times counterclockwise relative to the example shown in Figure 2. On the other hand, the arrangement of the electrodes 40a to 40h is the same as the example shown in Figure 2.

In this modified example, the first leg 31 and second leg 32 of the support part 30 are also arranged symmetrically with respect to one of the imaginary planes OA1 to OA8. However, as shown in FIG. 17, the first leg 31 consists of first to third parts 31a to 31c. The first part 31a is connected to one end of the second part 31b, and the third part 31c is connected to the other end. Similarly, the second leg 32 consists of first to third parts 32a to 32c. The first part 32a is connected to one end of the second part 32b, and the third part 32c is connected to the other end.

In this modified example, the imaginary plane OA1 also passes through a corner of the outer periphery 10b of the external structure 60. Furthermore, the imaginary planes OA2 and OA8 are located at positions obtained by rotating the imaginary plane OA1 by 45 degrees with the axis O1 as one side. However, whereas in the example shown in FIG. 2, the imaginary planes OA1, OA2, and OA8 each pass through the midlines of the side surfaces of the inner periphery 10a of the external structure 60, in this modified example, they each pass through a corner of the inner periphery 10a of the external structure 60. Furthermore, when viewed from the corner of the outer periphery 10b of the external structure 60, the positions of the first cross section 12 and the second cross section 13 are the same as those shown in FIG. 2.

The vibratory gyroscope 100 may be configured in this manner. In this modified example, the cross-sectional area of the first cross section 12 of the external structure 60 is also larger than the cross-sectional area of the second cross section 13.

Therefore, the vibratory gyroscope 100 shown in this modified example also achieves the same effects as the configuration shown in embodiment 1. That is, the direction of the first vibration axis of the external structure 60 is uniquely determined, and accordingly, the direction of the second vibration axis of the external structure 60 is determined to be spatially shifted 45 degrees from the direction of the first vibration axis. The primary drive electrode PD is arranged so that the direction of the first vibration axis of the external structure 60 coincides with the direction of the axis of the primary drive electrode PD. This allows the vibration axis of the primary vibration of the vibrator 20 to coincide with the direction of the vibration axis of the primary cos 2θ mode, thereby bringing the angle deviation α close to zero and significantly reducing the bias component included in the output signal of the vibratory gyroscope 100, enabling angular velocity to be detected with high accuracy.

(Embodiment 2)
Fig. 18A shows a schematic plan view of an external structure according to this embodiment, Fig. 18B shows a schematic plan view of another external structure, and Fig. 18C shows a schematic plan view of a further external structure. Note that for ease of explanation, Fig. 18C shows a simplified view of the vibrating body 20 and the support portion 30.

In the vibratory gyroscope 100 shown in embodiment 1 and variant 1, the rotational symmetry of the external structure 60 is set to four times about the axis O1 by changing the shape of the outer periphery of the external structure 60 from the shape of the inner periphery. However, the method of setting the rotational symmetry of the external structure 60 to (2N x S2) times about the axis O1 is not particularly limited to this. As shown in Figure 14, even when both the inner and outer peripheries of the external structure 60 are regular octagons, the rotational symmetry of the external structure 60 can be set to four times about the axis O1.

The shape of the external structure 60 shown in Figures 18A and 18B is the same as the shape of the external structure 60 shown in Figure 14. That is, both the inner and outer peripheries of the external structure 60 shown in Figures 18A and 18B are regular octagons. The positions of the imaginary planes OA1 to OA16 are also the same as those shown in Figure 14. For example, as shown in Figure 18A, one or more holes 61 are provided on the front and/or back surface of the external structure 60 at positions spaced 90 degrees apart from each other in the circumferential direction. Note that the holes 61 may be through holes that pass through the external structure 60, or may be blind holes that do not pass through.

In this case, assuming N = 2, for example, imaginary plane OA4 is located at a position obtained by rotating imaginary plane OA2 clockwise by (360/4N) = 45 degrees around axis O1. Furthermore, in external structure 60, holes 61 are provided in the portion through which imaginary plane OA4 passes, whereas holes 61 are not provided in the portion through which imaginary plane OA2 passes. Therefore, the cross-sectional area of the portion through which imaginary plane OA2 passes is larger than the cross-sectional area of the portion through which imaginary plane OA4 passes. In other words, in external structure 60, the portion through which imaginary plane OA2 passes corresponds to the aforementioned first cross-section 12, and the portion through which imaginary plane OA4 passes corresponds to the second cross-section 13. A similar relationship applies to the portions through which imaginary planes OA6, OA8, OA10, OA12, OA14, and OA16 pass. The portions through which the imaginary planes OA6, OA10, and OA14 pass correspond to the first cross section 12, and the portions through which the imaginary planes OA8, OA12, and OA16 pass correspond to the first cross section 12.

18A also achieves the same effect as the configuration shown in embodiment 1. That is, the direction of the first vibration axis of the external structure 60 is uniquely determined, and accordingly, the direction of the second vibration axis of the external structure 60 is determined to be spatially offset by 45 degrees from the direction of the first vibration axis. In this case, in a planar view, the first vibration axis coincides with the imaginary planes OA2, OA6, OA10, and OA14, and the second vibration axis coincides with the imaginary planes OA4, OA8, OA12, and OA16. By arranging the primary drive electrode PD so that the axis of the primary drive electrode PD coincides with one of the imaginary planes OA2, OA6, OA10, and OA14, the angular deviation α can be brought close to zero, significantly reducing the bias component included in the output signal of the vibratory gyroscope 100, and enabling highly accurate detection of angular velocity.

Also, as shown in Figure 18B, one or more grooves 62 may be provided on the front and/or back surface of the external structure 60 at positions spaced 90 degrees apart in the circumferential direction. In this case, the same effect as that achieved by the configuration shown in Figure 18A can be achieved. Note that the grooves 62 may be through grooves that pass through the external structure 60, or may be non-through grooves that do not pass through.

Instead of providing grooves 62, membranes 63 may be provided. The material of membrane 63 may be metal or insulator. In this case, the same effect as that achieved by the configuration shown in Figure 18A can be achieved. However, when membrane 63 is provided, the cross-sectional areas of the portions of external structure 60 through which imaginary planes OA4, OA8, OA12, and OA16 pass will be larger than the cross-sectional areas of the portions through which imaginary planes OA2, OA6, OA10, and OA14 pass.

Also, as shown in Figure 18C, the inner periphery of the external structure 60 may be a regular square and the outer periphery a regular octagon. In this case, the rotational symmetry of the external structure 60 is also four-fold with respect to the axis O1. Note that in the example shown in Figure 18C, an imaginary plane that has the axis O1 as one side and passes through one of the corners of the outer periphery of the external structure 60 is defined as imaginary plane OA1. Furthermore, imaginary planes at positions obtained by rotating imaginary plane OA1 clockwise by 22.5 degrees around the axis O1 as the central axis are defined as imaginary planes OA2 to OA16, respectively.

18C, in a planar view, the first vibration axis coincides with imaginary planes OA4, OA8, OA12, and OA16, and the second vibration axis coincides with imaginary planes OA2, OA6, OA10, and OA14. By positioning the primary drive electrode PD so that its axis coincides with one of imaginary planes OA4, OA8, OA12, and OA16, the angular deviation α can be brought close to zero, significantly reducing the bias component contained in the output signal of the vibratory gyroscope 100, and enabling angular velocity to be detected with high accuracy.

<Modification 2>
19A to 19C are schematic plan views of first to third external structures according to this modification, respectively, and FIGS. 20A to 20D are schematic plan views of fourth to seventh external structures, respectively.

The external structure 60 shown in Figures 19A to 19C corresponds to the external structure 60 shown in Figures 18A to 18C, respectively. Therefore, the rotational symmetry of the external structure 60 shown in Figures 19A to 19C is also (2N x S2) times, or in this case, four times, about the axis O1.

On the other hand, the positions at which the holes 61, grooves 62, or membranes 63 are provided in the external structure 60 shown in Figures 19A and 19B are shifted by 22.5 degrees in the circumferential direction compared to the external structure 60 shown in Figures 18A and 18B. For example, in the example shown in Figures 19A and 19B, the holes 61 and grooves 62 are provided in four locations on the surface located between the inner corner and the outer corner of the external structure 60. Note that the holes 61 and grooves 62 are located at positions 90 degrees apart in the circumferential direction, similar to those shown in Figures 18A and 18B.

In the example shown in Figure 19C, the inner periphery and inner structure of the outer structure 60 are rotated by 22.5 degrees relative to the outer structure 60 and inner structure shown in Figure 18C. Therefore, imaginary planes OA3, OA7, OA11, and OA15 have the axis O1 as one side and pass through the four corners of the inner periphery of the outer structure 60. In addition, imaginary planes OA1, OA5, OA9, and OA13 have the axis O1 as one side and pass through the midlines of the four side surfaces of the inner periphery of the outer structure 60. In this case as well, for example, imaginary plane OA3 is located 45 degrees circumferentially away from imaginary plane OA1, with the axis O1 as the rotation axis.

19C, the cross-sectional areas of the portions through which the imaginary planes OA1, OA5, OA9, and OA13 pass are larger than the cross-sectional areas of the portions through which the imaginary planes OA3, OA7, OA11, and OA15 pass. In the external structure 60, the portions through which the imaginary planes OA1, OA5, OA9, and OA13 pass correspond to the first cross section 12 described above, and the portions through which the imaginary planes OA3, OA7, OA11, and OA15 pass correspond to the second cross section 13. In a planar view, the first vibration axis and vibration axis PM of the external structure 60 overlap one of the first imaginary plane (imaginary planes OA1, OA5, OA9, and OA13) and the second imaginary plane (imaginary planes OA3, OA7, OA11, and OA15), and the second vibration axis and vibration axis SM of the external structure 60 overlap the other.

The external structure 60 may be configured as shown in Figures 19A to 19C, and in this case, similar effects to those achieved by the configuration shown in embodiment 1 can be achieved. Furthermore, without being limited to this, the external structure 60 may also be configured as shown in Figures 20A to 20D. The external structure 60 shown in Figure 20A has the inner periphery of the external structure 60 rotated by a predetermined angle relative to the outer periphery, with the axis O1 as the central axis, compared to the example shown in Figure 2. The external structure 60 shown in Figures 20B and 20C has the positions of the holes 61, grooves 62, or membranes 63 shifted by a predetermined angle circumferentially, with the axis O1 as the center, compared to the example shown in Figures 18A and 18B. The external structure 60 shown in Figure 20D has the inner periphery of the external structure 60 rotated by a predetermined angle relative to the outer periphery, with the axis O1 as the central axis, compared to the example shown in Figure 18C. In these cases, similar effects to those achieved by the configuration shown in embodiment 1 can be achieved.

(Embodiment 3)
Fig. 21 shows a plan view of the vibratory gyroscope according to this embodiment, Fig. 22 shows a schematic diagram of the primary vibration state of the vibrator, and Fig. 23 shows a schematic diagram of the secondary vibration state of the vibrator.

The vibratory gyroscope 100 of this embodiment shown in Figure 21 has 12 electrodes 40 arranged in the circumferential direction, and the vibrator 20 has a vibration mode of cos3θ. In other words, this corresponds to the case where N = 3 mentioned above.

When viewed in the axial direction, the outer periphery of the external structure 60 is a regular hexagon, while the inner periphery is a regular dodecagon. As with variant 1, the outer structure 60 is formed so that the corners of the inner periphery are positioned diagonally across from the outer periphery when viewed in the axial direction. The shape of the support part 30 is similar to that shown in Figure 16. Furthermore, the connection positional relationship of the first end part 30a to the corners of the inner periphery 10a of the fixed part 10 is also the same as that shown in Figure 16.

As shown in Figure 16, when viewed from the axial direction, the primary drive electrode PD, secondary drive electrode SD, primary detection electrode PPO, and secondary detection electrode SPO are arranged in this order on the surface of the vibrator 20 at equal angular intervals in a clockwise direction. However, the vibratory gyroscope 100 has three sets of electrodes 40 with different functions.

As shown in FIG. 21 , imaginary planes OB1, OB3, OB5, OB7, OB9, and OB11 have the axis O1 as one side and pass through a corner on the inner periphery and a corner on the outer periphery of the external structure 60, respectively. Meanwhile, imaginary planes OB2, OB4, OB6, OB8, OB10, and OB12 have the axis O1 as one side and pass through a corner on the inner periphery and the midline of the side surface of the outer periphery of the external structure 60, respectively. Furthermore, in a planar view, a second imaginary plane OBk+1 (k is an odd number from 1 to 11) is located at a position rotated (360/4N) degrees, in this case, 30 degrees, from the first imaginary plane OBk around the axis O1 as its central axis. Furthermore, in a planar view, the distance between the corner on the inner periphery and the corner on the outer periphery of the external structure 60 through which the imaginary plane OBk (k is an odd number from 1 to 11) passes is defined as L3. The distance between a corner of the inner circumference of the external structure 60, through which the imaginary plane OBk+1 passes, and the midline of the side surface of the outer circumference is defined as L4. As shown in FIG. 21 , L3>L4. In other words, in the external structure 60, the cross-sectional area of the portion cut by the first imaginary plane OBk, i.e., the first cross section 12, is larger than the cross-sectional area of the portion cut by the second imaginary plane OBk+1, i.e., the second cross section 13. Furthermore, in a plan view, the second cross section 13 is located at a position obtained by rotating the first cross section 12 by (360/4N)=30 degrees around the axis O1.

As shown in this embodiment, when 12 electrodes 40 are arranged, the support portions 30 are also arranged in 12 directions at equal angular intervals in the circumferential direction. In other words, the internal structure 70 has 12 rotational symmetries (4N x S1) times, or in this case, if N = 3 and S1 = 1, then 12 rotational symmetries. On the other hand, in the vibratory gyroscope 100 shown in Figure 21, by making the outer periphery of the external structure 60 a regular hexagon, the rotational symmetry can be (2N x S2) times, or in this case, if N = 3 and S2 = 1, then 6 rotations can be achieved.

In the vibratory gyroscope 100 configured in this manner, when the vibrator 20 vibrates with the primary vibration, three antinodes and three nodes of the primary vibration are generated, as shown in FIG. 22. Furthermore, the positions of the antinodes and the nodes alternate at the vibration frequency of the primary vibration. In this embodiment, as shown in FIG. 22, the vibration axis of the primary vibration coincides with the first imaginary plane OBk in a planar view, and therefore the vibration axis of the primary vibration coincides with the vibration axis PM of the cos3θ mode.

Furthermore, when the vibrator 20 vibrates with secondary vibration, three antinodes and three nodes of the secondary vibration are generated, as shown in Figure 23. Furthermore, the positions of the antinodes and the nodes alternate at the vibration frequency of the secondary vibration. In this embodiment, as shown in Figure 23, the vibration axis SM and the second imaginary plane OBk+1 coincide in a planar view. In other words, in a planar view, the vibration axis SM is located at a position rotated 30 degrees from the vibration axis PM, with the axis O1 as the vertex.

Therefore, in the configuration shown in this embodiment, as in Embodiments 1 and 2, the direction of the vibration axis PM is determined to overlap the first vibration axis of the external structure 60, and accordingly, the direction of the vibration axis SM is determined to overlap the second vibration axis of the external structure 60. In this embodiment, the direction of the vibration axis SM is determined at a position obtained by rotating the vibration axis PM by (360/4N) degrees, in this case 30 degrees, around the axis O1 as the central axis. By arranging the primary drive electrode PD so that the axis of the primary drive electrode PD coincides with either the first imaginary plane OBk or the second imaginary plane OBk+1, the angular deviation α can be brought close to zero, significantly reducing the bias component included in the output signal of the vibratory gyroscope 100, enabling highly accurate detection of angular velocity.

(Other embodiments)
New embodiments can also be created by appropriately combining the components shown in Embodiments 1 to 3 and Modifications 1 and 2. For example, the shape of the external structure 60 shown in Modification 2 may be applied to the vibratory gyroscope 100 shown in Embodiment 1.

In addition, while the present specification has shown an example in which the vibratory gyroscope 100 is an electromagnetic gyroscope, this is not particularly limited and may also be a piezoelectric gyroscope. In the case of a piezoelectric gyroscope, the configuration and relative positions of the fixed portion 10, vibrator 20, and support portion 30 are the same as those shown in, for example, Figures 2, 16, and 21. The relative positions of the primary drive electrode PD, primary detection electrode PPO, secondary drive electrode SD, and secondary detection electrode SPO are also the same as those shown in Figures 2, 16, and 21.

However, the magnetic field application unit 80 is omitted. Also, each of the multiple electrodes 40 is changed to a piezoelectric structure in which a lower electrode layer (not shown), a piezoelectric layer (not shown), and an upper electrode layer (not shown) are stacked in this order. In this case, an AC voltage is supplied from the primary AC power supply 200 shown in Figure 5. That is, the primary AC power supply 200 of the present disclosure applies AC power of a predetermined frequency to the primary drive electrode PD. When an AC voltage is applied between the upper electrode layer and the lower electrode layer, the piezoelectric layer expands and contracts periodically. The vibrator 20 vibrates in response to this expansion and contraction. By matching the frequency of the AC voltage to the resonant frequency of the vibrator 20, primary vibration is excited in the vibrator 20.

Furthermore, since the magnetic field application unit 80 is omitted, the spacer 120 may also be omitted. The shape of the base unit 130 may also be changed. The structure of the present disclosure is also applicable when the vibratory gyroscope 100 is an electrostatic gyroscope.

The vibrator 20 described in this specification is not limited to a circular shape, as long as it has a shape that changes the vibration state when primary vibration is excited and angular velocity is generated. For example, it may have a regular polygonal ring shape or a disk shape. It may also have a hemispherical shape. When the vibrator 20 is hemispherical, the direction perpendicular to the flat surface of either the front or back surface of the vibrator 20 is the axial direction of the gyro element 110.

Furthermore, the support portion 30 only needs to be able to connect the vibrator 20 to the fixed portion 10 without interfering with the vibration of the vibrator 20, and its shape is not limited to the shapes shown in Figures 2, 16, and 21. For example, a dummy support portion 30 without electrodes 40 formed on its surface may be provided.

Furthermore, the side surfaces of the fixing part 10 and the external structure 60 do not have to be linear in plan view. For example, they may be part of an arc or an elliptical arc. Furthermore, the outer or inner periphery of the external structure 60 may be circular in plan view. Or, it may be a polygon other than a regular polygon. It is sufficient that the external structure 60 has (2N x S2) rotational symmetry with respect to the axis O1.

In addition, instead of connecting multiple secondary detection electrodes SPO in series, the voltages generated by each may be input to the calculation unit 240 and addition processing may be performed within the calculation unit 240. Similarly, instead of connecting multiple primary detection electrodes PPO in series, the voltages generated by each may be input to the calculation unit 240 (not shown), addition processing may be performed within the calculation unit 240, and the voltages may be input to the primary AC power supply 200.

The vibratory gyroscope disclosed herein can reduce the bias component contained in the output signal, making it useful for application to high-precision angular velocity sensors.

10 Fixed portion 12 First cross section 13 Second cross section 20 Vibrator 30 Support portions 40a to 40l Electrode 51 First silicon layer 52 Silicon oxide layer 53 Second silicon layer 54 Silicon oxide film 60 External structure 70 Internal structure 80 Magnetic field application portion 81 Upper yoke 82 Magnet 83 Lower yoke 100 Vibratory gyroscope 110 Gyro element 120 Spacer 130 Base portion 200 Primary AC power supply 210 Primary detection portion 220 Secondary AC power supply 230 Secondary detection portion 240 Calculation portion 1000 Angular velocity sensor O Center point O1 Axes OA1 to OA16 Imaginary planes OB1 to OB12 Imaginary planes

Claims (8)

An external structure;
An internal structure disposed inside the external structure in a plan view,
The external structure includes:
The fixing portion includes at least a frame-shaped fixing portion having a center point in a plan view,
The internal structure includes:
a vibrator having a common center point with the fixed portion in a plan view;
a plurality of support parts that connect the vibrator to the fixed part and support the vibrator so that the vibrator can vibrate;
At least
When the vibrator has a vibration mode of cosNθ (N is an integer of 2 or more),
Electrodes are arranged in 4N directions at equal angular intervals around the center point in the outer circumferential direction of the vibrator,
the internal structure has (4N×S1)-fold rotational symmetry (S1 is an integer equal to or greater than 1) with respect to an axis that passes through the center point and intersects with a surface of the vibrator,
The external structure has (2N×S2) rotational symmetry (S2 is an odd number greater than or equal to 1) with respect to the axis,
The external structure has (2N×S3) (S3 is an integer of 1 or more) corners on an outer periphery or an inner periphery and (2N×S3) side surfaces,
a virtual plane having the axis as one side and passing through one of the midlines of the plurality of corners and/or the plurality of side surfaces of the external structure as a first virtual plane;
When a virtual plane located at a position obtained by rotating the first virtual plane by (360/4N) degrees around the axis line as a central axis is defined as a second virtual plane,
The external structure includes:
a first cross section cut by the first virtual plane;
a second cross section cut by the second imaginary plane,
Among the pairs of the first cross section and the second cross section, there is at least one pair of the first cross section and the second cross section that is a specific pair,
The cross-sectional area of the first cross section included in the specific set is different from the cross-sectional area of the second cross section;
the plurality of electrodes includes at least a primary drive electrode that excites a primary vibration in the vibrator;
a first imaginary plane that cuts the first cross section included in the specific set, and a second imaginary plane that cuts the second cross section, the first drive electrode being arranged to intersect with either one of the first imaginary plane that cuts the first cross section included in the specific set and the second imaginary plane that cuts the second cross section. The support portion has a first leg portion and a second leg portion,
Among the pairs of the first leg portion and the second leg portion, there are one or more pairs that are symmetrically arranged with respect to the first virtual plane that cuts the first cross section included in the specific pair or the second virtual plane that cuts the second cross section included in the specific pair,
For the first leg portion and the second leg portion of some pairs of the one or more pairs,
2. The vibratory gyroscope according to claim 1, wherein the electrodes are provided continuously on a surface of the first legs of the partial set, a surface of the vibrator located between the first legs of the partial set and the second legs of the partial set, and a surface of the second legs of the partial set. the external structure includes at least one of a spacer and a base portion,
the spacer is disposed in contact with a rear surface of the fixing portion,
2. The vibratory gyroscope according to claim 1 , wherein the base portion is disposed in contact with a rear surface of the fixed portion or the spacer. the external structure includes at least one of a spacer and a base portion,
the spacer is disposed in contact with a rear surface of the fixing portion,
3. The vibratory gyroscope according to claim 2, wherein the base portion is disposed in contact with a rear surface of the fixed portion or the spacer. The vibratory gyroscope of claim 3, wherein, in a plan view, at least one of the inner and outer peripheries of the external structure has (2N x S2) rotational symmetry about the axis. 5. The vibratory gyroscope according to claim 4, wherein at least one of the inner periphery and the outer periphery of the external structure has (2N×S2) rotational symmetry about the axis in a plan view. 7. An angular velocity sensor comprising the vibration type gyroscope according to claim 1,
The plurality of electrodes include:
a primary detection electrode for detecting a primary vibration generated in the vibrator;
a secondary drive electrode that drives the vibrator so as to cancel out secondary vibrations generated in the vibrator;
a secondary detection electrode for detecting the secondary vibration;
The angular velocity sensor
a primary AC power source that applies AC power of a predetermined frequency to the primary drive electrode;
a primary detection unit that detects a voltage signal generated in the primary detection electrode;
a secondary AC power source that applies AC power to the secondary drive electrode;
a secondary detection unit that detects a voltage signal generated in the secondary detection electrode;
The angular velocity sensor further includes a calculation unit that calculates an angular velocity based on the output signal of the secondary AC power supply. an output signal of the primary detection unit is fed back to the primary AC power supply to stabilize the primary vibration generated by the vibrator;
controlling the output of the secondary AC power supply based on the output signal of the secondary detection unit so as to cancel the secondary vibration generated in the vibrator;
The angular velocity sensor according to claim 7 , wherein the calculation unit calculates the angular velocity based on the output signal of the secondary AC power supply.