Planar mechanical resonator sensitive along an axis perpendicular to its plane

• US 20040112134A1
• Filed: 01/15/2004
• Published: 06/17/2004
• Est. Priority Date: 02/23/2001
• Status: Active Grant

• Current Assignee: Sagem SA (Safran SA)
• Original Assignee: Sagem SA (Safran SA)
• Inventors: Beitia, Jose
• Granted Patent: US 6,889,550 B2
• Time in Patent Office: Days
• US Class Current: 73/504.12
• CPC Class Codes: G01C 19/5684 the devices involving a micromechanical structure

Abstract

The invention concerns a mechanical resonator with a planar monolithic vibrating structure extending along a closed contour whereof the axis of sensitivity is substantially perpendicular to the plane of said structure. The invention is characterised in that the planar structure (1) is a regular convex polygon with 4 k vertices (3) (k being the order of the vibrational mode implemented when the resonator is vibrated) and is suspended to a fixed base (4, 5) via n suspension arms (2) with substantially radial extension arranged substantially symmetrically.

Claims

1. A mechanical resonator with plane monolithic vibrating structure extending along a closed contour whose sensitivity axis is substantially perpendicular to the plane of said structure,

characterized in that the plane structure (1) is convex regular polygonal with 4 k vertices (3) (k being the order of the vibratory mode implemented when the resonator is set vibrating) and is suspended from a fixed mount (4, 5) by way of n suspension arms (2) of substantially radial extension which are arranged substantially symmetrically.

2. The mechanical resonator as claimed in claim 1, characterized in that the convex regular polygonal vibrating structure with 4 k vertices possesses identical patterns which repeat with angular intervals of π

/2 k,

by virtue of which said polygonal vibrating structure exhibits an isotropy of geometry (Δ

ƒ

_g=0, Δ

α

_g=0).

3. The mechanical resonator as claimed in claim 1 or 2, characterized in that, for a vibratory mode of order 2 (k=2), the plane vibrating structure (1) is of octagonal shape and is made of a crystalline material with trigonal structure, with a cut made in the X, Y plane,

by virtue of which the vibrating structure exhibits an isotropy of material (Δ

ƒ

_m=0, Δ

α

_m=0) for order 2.

4. The mechanical resonator as claimed in claim 3, characterized in that the octagonal vibrating structure is made of quartz.

5. The mechanical resonator as claimed in claim 1 or 2, characterized in that, for a vibratory mode of order 3 (k=3), the plane vibrating structure (1) is of dodecagonal shape and is made of a crystalline material with cubic structure, with a cut made in a plane containing the X axis, or the Y axis, or the Z axis, by virtue of which the vibrating structure exhibits an isotropy of material (Δ

ƒ

_m=0, Δ

α

_m=0) for order 3.

6. The mechanical resonator as claimed in claim 5, characterized in that the dodecagonal vibrating structure is made of silicon.

7. The mechanical resonator as claimed in one of claims 1 to 6, characterized in that the suspension arms (2) are n=4 k in number and are angularly spaced by an angular interval of π

/2 k,

by virtue of which the vibrating structure exhibits an isotropy of suspension (Δ

ƒ

_s=0, Δ

α

_s=0).

8. The mechanical resonator as claimed in claim 2 and as claimed in any one of claims 3 to 6 and as claimed in claim 7, characterized in that the polygonal vibrating structure (1) simultaneously exhibits isotropies of geometry (Δ

ƒ

_g=0, Δ

α

_g=0) and of material (Δ

ƒ

_m=0, Δ

α

=0) and of suspension (Δ

ƒ

_s=0, Δ

α

_s=0), in terms of frequency and coupling, by virtue of which it is able to operate in gyrometric mode or in gyroscopic mode.

9. The mechanical resonator as claimed in claim 1, characterized in that the polygonal vibrating structure with 4 k vertices (1) is made of a crystalline material with non trigonal structure for k=2 or non cubic structure for k=3, and therefore exhibits basically an anisotropy of material (Δ

ƒ

_m≠

0, Δ

α

_m≠

0), and in that said polygonal vibrating structure (1) is then devised so as furthermore to exhibit at least one localized modification of geometry and/or that the suspension exhibits at least one localized modification, so that said polygonal vibrating structure exhibits an anisotropy of geometry (Δ

ƒ

_g≠

0, Δ

α

_g≠

0) and/or an anisotropy of suspension (Δ

α

_s≠

0, Δ

α

_s≠

0), respectively, able to compensate for the anisotropy of material,

by virtue of which said polygonal vibrating structure exhibits an isotropy in terms of frequency (Δ

f=0) and coupling (Δ

α

=0) and the resonator is able to operate in gyrometric mode or in gyroscopic mode.

10. The mechanical resonator as claimed in claim 1, characterized in that the suspension arms (2) are n<

4 k in number and are angularly spaced by an angular interval of 2π

/n, with n chosen such that n≦

k−

2 or n≧

k+2 with n≠

pk (p integer), the polygonal vibrating structure therefore exhibiting basically an anisotropy of suspension (Δ

ƒ

_s≠

0, Δ

α

_s≠

0) and in that said polygonal vibrating structure (1) is then devised so as to furthermore exhibit localized defects of geometry which are angularly offset by an angular value of π

/k and are able to cause a defect of mass of order 2 k which engenders an anisotropy in terms of geometry (Δ

ƒ

_g≠

0, Δ

α

_g≠

0) able to compensate for the anisotropy of suspension due to the insufficient number of suspension arms,

by virtue of which said polygonal vibrating structure exhibits an isotropy in terms of frequency (Δ

f=0) and coupling (Δ

α

=0) and the resonator is able to operate in gyrometric mode or in gyroscopic mode.

11. The mechanical resonator as claimed in claim 10, characterized in that the localized defects of geometry are situated at least in the vicinity of where the suspension arms (2) are linked to the vibrating structure (1).

12. The mechanical resonator as claimed in any one of claims 2 to 8, characterized in that the vibrating structure (1) exhibits at least one anisotropy of geometry (Δ

ƒ

_g≠

0, Δ

α

_g≠

0), or of material (Δ

ƒ

_m≠

0, Δ

α

_m≠

0), or of suspension (Δ

ƒ

_s≠

0, Δ

α

_s≠

0), by virtue of which it is able to operate only in gyrometric mode.

13. The mechanical resonator as claimed in any one of the preceding claims, characterized in that the mount (5) surrounds the plane vibrating structure (1) and in that the suspension arms (2) are outside the vibrating stricture (1).

14. The mechanical resonator as claimed in any one of claims 1 to 11, characterized in that the mount is a central hub (4) substantially concentric with the vibrating structure (1) and in that the suspension arms (2) are inside the vibrating structure (1).

15. The mechanical resonator as claimed in claim 13 or 14, characterized in that it furthermore comprises resonating beams (7) which are carried by a central hub (8) substantially concentric with the vibrating structure (1) with closed contour and which radiate around said central hub (8) substantially in the plane of the vibrating structure with closed contour (1),

by virtue of which the mechanical resonator has all its vibrating elements (1, 7) situated substantially in one and the same plane and is able to detect the three components Ω

x, Ω

y and Ω

z of a rate of rotation Ω

imparted to the mount, the components Ω

x and Ω

y being detected by the resonating beams and the component Ω

z being detected by the vibrating structure with closed contour and by virtue of which the mechanical resonator is able to operate in gyrometric mode or in gyroscopic mode on the three axes.

16. The use of a plane mechanical resonator sensitive along the transverse axis to operation in gyroscopic mode as claimed in any one of claims 11 to 14, within a plane monolithic gyro-accelerometric inertial sensor able to provide the information Ω

x, Ω

y, Ω

z and γ

_x, γ

_y, γ

_z.