Micromachined rate and acceleration sensor having vibrating beams

• US 5,331,854 A
• Filed: 06/08/1993
• Issued: 07/26/1994
• Est. Priority Date: 02/08/1991
• Status: Expired due to Fees

• Current Assignee: L-3 Communications Corporation (L3Harris Technologies, Inc.)
• Original Assignee: Alliedsignal Inc. (Honeywell International Inc.)
• Inventors: Hulsing, Rand H. II
• Primary Examiner(s): CHAPMAN JR, JOHN E
• Application Number:
  US08/073,818
• Time in Patent Office: 413 Days
• Field of Search: 73/517 AV, 73/505, 73/510, 73/511, 73/517 R, 73/862.59, 73/DIG. 1
• US Class Current: 73/514.37
• CPC Class Codes: F02G 1/044 having at least two working members, e.g. pistons, delivering power output
• CPC Class Codes: F02G 1/0445 Engine plants with combined cycles, e.g. Vuilleumier
• CPC Class Codes: F02G 2250/18 Vuilleumier cycles
• CPC Class Codes: F02G 2253/03 Stem seals
• CPC Class Codes: F16F 2230/0052 Physically guiding or influencing
• CPC Class Codes: F16F 2230/34 Flexural hinges
• CPC Class Codes: F16L 37/24 in which the connection is made by inserting one member axially into the other and rotating it to a limited extent, e.g. with bayonet action
• CPC Class Codes: G01C 19/5719 using planar vibrating masses driven in a translation vibration along an axis
• CPC Class Codes: G01C 19/5747 each sensing mass being connected to a driving mass, e.g. driving frames
• CPC Class Codes: G01P 15/0802 Details
• CPC Class Codes: G01P 15/097 by vibratory elements
• CPC Class Codes: G01P 15/18 in two or more dimensions
• CPC Class Codes: G01P 2015/0828 the mass being of the paddle type being suspended at one of its longitudinal ends
• CPC Class Codes: Y10S 73/01 Vibration

Abstract

Apparatus is disclosed for measuring the specific force and angular rotation rate of a moving body. A silicon substrate has first and second substantially planar and substantially parallel surfaces. An accelerometer is formed of the substrate and has a force sensing axis. An output signal is provided which is indicative of the moving body along the force sensing axis. The accelerometer is mounted so as to be movable along a vibration axis perpendicular to the force sensing axis. The accelerometer is driven so as to impart a dithering motion thereto of a predetermined frequency along the vibration axis. The accelerometer includes a frame, a proof mass and a hinge interconnected between the frame and the proof mass for rotating the proof mass about a hinge axis when the moving body is subjected to a force along the force sensing axis. The accelerometer further includes at least one vibrating beam having first and second ends respectively coupled to the frame and the proof mass, a longitudinal axis disposed perpendicular to the force sensing axis and the vibration axis, and a conductive path disposed along the vibrating beam. The hinge axis is substantially parallel to the vibration axis. A signal generator applies a periodic drive signal to the conductive path. The periodic drive signal has a resonant frequency that is a function of the force applied along the force sensing axis to the moving body.

Claims

1. Apparatus for measuring the specific force and angular rotation rate of a moving body, comprising:

a) a silicon substrate having first and second substantially planar surface disposed substantially parallel to each other;

b) an accelerometer formed of said substrate and having a force sensing axis for producing an output signal indicative of the acceleration of the moving body along said force sensing axis;

c) mounting means formed of said substrate for mounting said accelerometer such that said accelerometer can be moved along a vibration axis perpendicular to said force sensing axis;

d) drive means coupled to said accelerometer for imparting a dithering motion thereto of a predetermined frequency along said vibration axis;

e) said accelerometer comprising an accelerometer frame, a proof mass, hinge means interconnected between said frame and said proof mass for rotating said proof mass about a hinge axis when the moving body is subjected to a force along said force sensing axis, at least one vibrating beam having first and second ends respectively coupled to said frame and said proof mass and a longitudinal axis disposed perpendicular to said force sensing axis and said vibration axis, and a conductive path disposed along said vibrating beam, said hinge axis disposed substantially parallel to said vibration axis; and

f) signal generator means for producing and applying to said conductive path a periodic drive signal having a resonant frequency that is a function of the force applied along said force sensing axis to the moving body.

2. The measuring apparatus as claimed in claim 1, wherein said proof mass has a first end interconnected by said hinge means to said frame and a free end permitted to rotate freely about said hinge axis with respect to said frame.

3. The measuring apparatus as claimed in claim 2, wherein said proof mass includes a center of gravity and a pendulous axis aligned to intersect said center of gravity and said hinge axis, and there is further included flexible means interconnected between said frame and said free end of said proof mass for flexibly restraining the pivoting of said proof mass about said pendulous axis.

4. The measuring apparatus as claimed in claim 3, wherein said hinge means is formed adjacent said first planar surface and said flexible means is formed adjacent said second planar surface and defining a reference plane passing through said hinge axis and a point of interconnection of said proof mass to said flexible means, said center gravity lying within said reference plane.

5. The measuring apparatus as claimed in claim 4, wherein said force sensing axis lies perpendicular to said reference plane and is disposed at an acute angle with respect to said first and second planar surfaces, and there is further included a housing adapted to be attached to the moving body and means for mounting said silicon substrate within said housing such that said force sensing axis is oriented with respect to the moving body.

6. The measuring apparatus as claimed in claim 5, wherein said housing has a base having a substantially planar mounting surface for orienting said accelerometer with respect to the moving body, and said mounting means for mounting said silicon substrate such that said first and second surfaces are disposed with respect to said mounting surface at an angle equal to the complement of said acute angle.

7. The measuring apparatus as claimed in claim 3, wherein said accelerometer frame has an inner peripheral edge of substantially rectangular configuration comprising first and third opposing edges and second and fourth opposing edges, said proof mass disposed within said inner peripheral edge of said frame and having an external peripheral edge of a corresponding rectangular configuration comprising first and third opposing edges and second and fourth opposing edges, said hinge means connecting said first edge of said proof mass to said first edge of said accelerometer frame.

8. The measuring apparatus as claimed in claim 7, wherein said flexible means comprises a strut having a first end connected to said fourth edge of said accelerometer frame and a second end connected to said proof mass, said strut extending along substantially the entire length of said third edge of said proof mass.

9. The measuring apparatus as claimed in claim 8, wherein said strut is of an L-shape comprising an extended portion extending along substantially the entire length of said third edge of said proof mass and a foot portion connected to said third edge of said proof mass adjacent to said second edge of said proof mass, whereby the length of said extended portion of said strut and its flexibility are increased.

10. The measuring apparatus as claimed in claim 1, wherein said accelerometer frame has an external periphery of substantially rectangular configuration including first and third opposing peripheral edges and second and fourth opposing peripheral edges, said mounting means comprising a mounting frame having an inner-periphery of substantially rectangular configuration including first and third opposing, inner peripheral edges and second and fourth opposing, inner peripheral edges, and at least one flexure having a first end affixed to said third inner peripheral edge of said mounting frame and a second end connected to said second external peripheral edge of said accelerometer frame, said flexure extending at rest along a path substantially parallel to said second and fourth inner peripheral edges of said mounting frame and being aligned with said second, external peripheral edge of said accelerometer frame, said accelerometer frame having a cut away portion such that the unrestricted length of said flexure is selected to impart an "S-bend" flexure thereto.

11. The measuring apparatus as claimed in claim 10, wherein said mounting means comprises a second flexure having a first end affixed to said third inner-peripheral edge of said mounting frame and a second end connected to said fourth external peripheral edge of said accelerometer frame, said second flexure extending at rest along a path substantially parallel to said second and fourth inner peripheral edge of said mounting frame, said accelerometer frame having a second cut away portion, such that the length of said second flexure is selected to impart an "S-bend" flexure thereto.

12. An accelerometer for measuring specific force of acceleration of a moving body, comprising:

a) a monolithic substrate having first and second substantially planar surface disposed substantially parallel to each other;

b) an accelerometer formed of said substrate and having a force sensing axis for producing an output signal indicative of the acceleration of the moving body along said force sensing axis;

c) said accelerometer comprising an accelerometer frame, a proof mass, hinge means interconnected between said frame and said proof mass for allowing said proof mass about a hinge axis when the moving body is subjected to a force long said force sensing axis, said proof mass having a first end interconnected by said hinge means to said frame and a free end permitted to rotate freely about said hinge axis with respect to said frame, said proof mass further having a center of gravity and a pendulous axis aligned to intersect said center of gravity and said hinge axis, flexible means interconnected between said frame and said free end of proof mass for flexibly restraining the pivoting of said proof mass about said pendulous axis, at least one vibrating beam having first and second ends respectively coupled to said frame and said proof mass and a longitudinal axis, and conductive path disposed long said vibrating beam; and

d) signal generator means for producing and applying to said conductive path a periodic drive signal having a resonant frequency that is a function of the force applied along said force sensing axis to the moving body.

13. The accelerometer as claimed in claim 12, wherein said hinge means is formed adjacent said first planar surface and said flexible means is formed adjacent-said second planar surface and defining a reference plane passing through said hinge axis and a point of interconnection of said proof mass to said flexible means, said center gravity lying within said reference plane.

14. The accelerometer as claimed in claim 13, wherein said force sensing axis lies perpendicular to said reference plane and is disposed at an acute angle with respect to said first and second planar surfaces, and there is further included a housing adapted to be attached to the moving body and means for mounting said silicon substrate within said housing such that said force sensing axis is oriented with respect to the moving body.

15. The accelerometer as claimed in claim 14, wherein said housing has a base having a substantially planar mounting surface for orienting said accelerometer with respect to the moving body, and said mounting means for mounting said silicon substrate such that said first and second surfaces are disposed with respect to said mounting surface at an angle equal to the complement of said acute angle.

16. The accelerometer as claimed in claim 12, wherein there is included a unitary magnet for emanating flux from first and second surfaces thereof, and magnetic circuit means for establishing a flux path between said second surface of said silicon substrate and said second surface of said unitary magnet.

17. The accelerometer as claimed in claim 16, wherein said magnetic circuit means comprises a portion disposed adjacent said second planar surface of said silicon substrate, said magnetic circuit portion concentrating said magnetic flux through said conductive path.