Arrangement for measuring angular velocity

• US 6,467,349 B1
• Filed: 09/12/2000
• Issued: 10/22/2002
• Est. Priority Date: 01/23/1998
• Status: Expired due to Term

• Current Assignee: Inergetic AB
• Original Assignee: Autoliv Development AB (Autoliv Incorporated)
• Inventors: Andersson, Gert, Hedenstierna, Nils, Svensson, Per
• Primary Examiner(s): MOLLER, RICHARD ALAN
• Application Number:
  US09/600,919
• Time in Patent Office: 770 Days
• Field of Search: 735/041.2, 735/041.3, 735/041.4, 735/041.5, 735/041.6, 735/142.1, 735/142.3
• US Class Current: 73/504.14
• CPC Class Codes: G01C 19/5656 the devices involving a micromechanical structure
• CPC Class Codes: G01C 19/574 the devices having two sensing masses in anti-phase motion

Abstract

In a sensor for measuring angular velocity a body is formed from a planer substrate The body defines a beam, the opposed ends of which are adapted to be fixed in position, the beam having a preferential bending direction which makes an acute angle with the plane of the planar substrate. The beam carries an inertia mass comprising two arms interconnected by a connecting bar, the central part of the connecting bar being formed integrally with part of the beam. Capacitative plates located adjacent a conductive layer on the arms are provided with potentials which cause the inertia mass to rotate about the axis of the connecting bar with a “see-saw” action which, because of the configuration of the beam leads to a rotational oscillation of the inertia mass in the plane of the substrate. If the arrangement is rotated about an axis coincident with the connecting bar, the inertia mass rotates about an axis coincident with the beam with an oscillating rotation. This is detected by capacitative plates to determine angular velocity.

Claims

1. A sensor adapted to respond to a rotation, said sensor comprising a body formed from a substantially planar substrate, said body incorporating a beam having a longitudinal axis, the beam having two opposed ends, each end being adapted to be fixed in position, the beam being provided with at least one inertia mass connected to the beam at a predetermined position, the body being associated with means for exciting a first oscillation of said at least one inertia mass substantially about an axis perpendicular to the plane of the substrate, there being means for detecting a second oscillation of said at least one inertial mass, substantially around an axis coincident with the longitudinal axis of the beam, which second oscillation is caused by the Coriolis force that arises when the body is subjected to rotation around an axis angularly displaced from perpendicular to said plane, but perpendicular to the said axis of the beam, the beam being configured so that the beam bends most easily in one predetermined direction, that direction making an acute angle with said plane, so that the direction is neither parallel with, nor perpendicular to said plane, so that the first oscillation may be initiated by an excitation force which is not parallel with said plane.

2. A sensor according to claim 1 wherein the beam is such that the first oscillation may be caused by an excitation force which is substantially perpendicular with said plane.

3. A sensor according to claim 1 wherein the predetermined direction in which the beam bends most easily is at approximately 55°

to the plane of the substrate.

4. A sensor according to claim 1 wherein said at least one inertia mass comprises two elements, located respectively on either side of the beam, within the plan of the substrate, the two elements being interconnected by a connecting bar, the central portion of the connecting bar being unitary with a portion of the beam.

5. A sensor according to claim 1 wherein the means for exciting the first oscillation said at least one inertia mass comprise at least one capacitative plate located adjacent a selected portion of said at least one inertia mass, and means to apply selected potentials to the capacitative plate, said at least one inertia mass being provided with a conductive portion, the arrangement being such that the potentials applied to the capacitative plate causes part of said at least one inertia mass to tend to be deflected out of the plane of the substrate.

6. A sensor according to claim 5 wherein there is a plurality of said capacitative plates.

7. A sensor according to claim 5 wherein the capacitative plate is on a substrate of glass or semi-insulating silicon.

8. A sensor according to claim 5 wherein the means for applying potentials to said capacitative plate are adapted to supply signals which generate a “

see-saw”

motion of said at least one inertia mass about a connecting bar connecting said at least one inertia mass to said beam, the effect of the configuration of the beam being such that said seesaw motion generates the said first oscillation about the axis perpendicular to the plane of the substrate.

9. A sensor according to claim 1 wherein the means for detecting the second oscillation comprise a capacitative plate located adjacent a selected portion of said at least one inertia mass, and means to measure the capacitance between said capacitative plate and the said body to detect said second oscillation.

10. A sensor according to claim 9 wherein there is a plurality of said capacitative plates.

11. A sensor according to claim 1 wherein there is only a single inertia mass, that inertia mass being located substantially centrally of the beam, half-way between the means provided at the opposed ends of the beam for mounting the beam in position.

12. A sensor according to claim 11 wherein the single inertia mass is symmetrical about the axis of the beam.

13. A sensor according to claim 1 wherein there are two inertia masses, the inertia masses being symmetrically disposed on the beam, each inertia mass being located at a position between the centre part of the beam and a respective end of the beam.

14. A sensor according to claim 13 wherein the two inertia masses are identical and symmetrical about the axis of the beam.

15. A sensor according to claim 13 wherein each inertia mass is provided with means for exciting an oscillation of the mass around an axis perpendicular to the plane of the substrate, the arrangement being such that the masses oscillate in anti-phase.

16. A sensor according to claim 1 wherein the body is formed from a mono-crystalline substrate.

17. A sensor according to claim 1 wherein the body is formed from silicon.

18. A sensor according to claim 1 adapted to provide an output signal representative of angular velocity.

19. A sensor according to claim 1 mounted on a motor vehicle to control deployment of a safety device.

20. A sensor adapted to respond to a rotation, said sensor comprising a body formed from a substantially planar substrate, said body incorporating a beam having a longitudinal axis, the beam having two opposed ends, each end being adapted to be fixed in position, the beam being provided with inertia mass means connected to the beam, the body being associated with means for exciting a first oscillation of the inertia mass means, that first oscillation being an oscillation about an oscillation axis, there being means for detecting a second oscillation of the inertia mass means, substantially around an axis perpendicular to said oscillation axis, which second oscillation is caused by the Coriolis force which arises when the body is subjected to a rotation about an axis angularly displaced from perpendicular to the plane of said planar substrate, but perpendicular to the said axis of the beam, wherein the inertia mass means comprises at least two discrete inertia masses, located at different positions spaced from each other along the length of the beam, the said two masses being excited to oscillate in anti-phase.

21. A sensor according to claim 20 wherein the oscillation axis is within the plane of the substrate and the perpendicular axis is coincident with the longitudinal axis of the beam.

22. A sensor according to claim 20 wherein there are two inertia masses, the two inertia masses are symmetrically disposed on the beam, each inertia mass being located at a position between the centre part of the beam and a respective end of the beam.

23. A sensor according to claim 22 wherein the two inertia masses are identical and symmetrical about the axis of the beam.

24. A sensor according to claim 20 wherein said inertia mass means comprises two elements, located respectively on either side of the beam, within the plane of the substrate, the two elements being interconnected by a connecting bar, the central portion of the connecting bar being unitary with a portion of the beam.

25. A sensor according to claim 20 wherein the first oscillation may be caused by an excitation force which is substantially perpendicular with said plane.

26. A sensor according to claim 20 wherein the means for exciting the first oscillation of the inertia mass means comprises a plurality of capacitative plates, at least one capacitative plate being located adjacent a selected portion of each inertia mass of said inertia mass means, and means to apply selected potentials to the capacitative plates, the inertia masses each being provided with a conductive portion, there being means to apply a predetermined potential to the conductive portion provided on each inertia mass, the arrangement being such that the potentials applied to the capacitative plates cause part of each inertia mass to tend to be deflected out of the plane of the substrate.

27. A sensor according to claim 26 wherein each capacitative plate is on a substrate of glass or semi-insulating silicon.

28. A sensor according to claim 26 wherein the means for applying potentials to said capacitative plates are adapted to supply signals which generate a “

see-saw”

motion of each inertia mass about a connecting bar connecting such inertia mass to said beam, the beam being configured so that the beam bends most easily in one predetermined direction, that direction making an acute angle with the plane of the substrate, so that the direction is neither parallel with, nor perpendicular to the plane, so that this “

see-saw”

motion generates an oscillation of each inertia mass about an axis perpendicular to the plane of the substrate.

29. A sensor according to claim 26 wherein the means for detecting the second oscillation comprise further capacitative plates, at least one further capacitative plate being located adjacent a selected portion of each inertia mass, there being means to measure a capacitance between each of said further capacitative plates, and the said body to detect said second oscillation.

30. A sensor according to claim 20 wherein the body is formed from a mono-crystalline substrate.

31. A sensor according to claim 20 wherein the body is formed from silicon.

32. A sensor according to claim 28 wherein the sensor is adapted to provide an output signal representative of angular velocity.

33. A sensor according to claim 20 mounted on a motor vehicle to control deployment of a safety device.