Micromachined device with rotationally vibrated masses

• US 5,869,760 A
• Filed: 06/02/1997
• Issued: 02/09/1999
• Est. Priority Date: 06/06/1995
• Status: Expired due to Term

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Geen, John A.
• Primary Examiner(s): Oda, Christine K.
• Application Number:
  US08/867,602
• Time in Patent Office: 617 Days
• Field of Search: 73/504.12, 73/504.04, 73/504.03, 73/514.29, 73/514.37, 73/514.38, 73/514.32, 73/362.59, 73/DIG. 1, 73/DIG. 4, 73/510, 310/308, 310/309
• US Class Current: 73/504.12
• CPC Class Codes: G01C 19/5712 the devices involving a micromechanical structure
• CPC Class Codes: G01P 15/18 in two or more dimensions
• CPC Class Codes: H02N 1/008 Laterally driven motors, e.g. of the comb-drive type

Abstract

A micromachined device has a plurality of rotationally dithered masses that are used to sense acceleration. To eliminate common modes, the masses are dithered in an equal and opposite manner. To help maintain this relationship between the movement of the masses, a coupling fork provides minimal resistance to anti-phase movement and substantial resistance to in-phase movement. Electrodes are used to detect changes in capacitance between the masses and the substrate resulting from rotation of the device about a radial axis of a mass. These electrodes are electrically connected to eliminate gradients that are caused by external forces and manufacturing differences. Four masses or more can be provided, arranged in a two-dimensional array, such as a square or hexagon with a coupling fork provided between each pair of masses, and with electrodes connected to eliminate gradients.

Claims

1. A micromachined device formed in a substrate comprising:

a first mass suspended over the substrate;

a second mass suspended over the substrate;

a third mass suspended over the substrate;

a fourth mass suspended over the substrate;

the four masses arranged so that each mass is adjacent to two other masses; and

means for rotationally dithering each of the first, second, third, and fourth masses so that each mass moves in an equal and opposite manner relative to an adjacent mass.

2. The device of claim 1, wherein the four masses are arranged in a square.

3. The device of claim 2, further comprising four couplings, each coupling coupled to a pair of adjacent masses, each coupling minimally resisting relative anti-phase movement between the corresponding pair of adjacent masses, and providing substantial resistance to relative in-phase movement between the corresponding pair of adjacent masses.

4. The device of claim 1, further comprising a first electrode and a second electrode for each mass, wherein the first electrode of each mass is electrically coupled to the second electrode of another mass so as to cancel gradients.

5. The device of claim 4, wherein the first and second electrodes are used to sense a Coriolis acceleration.

6. The device of claim 4, wherein the masses are arranged in a square.

7. The device of claim 1, wherein the four masses are rotationally dithered such that there is no local momentum relative to the substrate.

8. The device of claim 1, further including fifth and sixth masses suspended over the substrate, the first through sixth masses being arranged in a hexagon.

9. A micromachined device formed in a substrate comprising:

a first mass suspended over the substrate and including a circular portion and a sector;

means for rotationally dithering the first mass; and

a suspension beam having one end coupled to the sector and extending radially outwardly from the first mass and doubling-back to extend radially inwardly to an anchor at the other end of the suspension beam, the suspension beam resisting gravitational force between the first mass and the substrate and allowing the first mass to be dithered.

10. The device of claim 9, wherein the beam has a dog-leg portion.

11. A micromachined device formed in a substrate comprising:

a first mass suspended over and dithered relative to the substrate and having first and second movable electrodes that are movable relative to the substrate;

a first set of first and second fixed electrodes that are fixed relative to the substrate and spaced from the respective first and second movable electrodes of the first mass for sensing capacitance therebetween;

a second mass suspended over and dithered relative to the substrate, the second mass being dithered in a manner equal and opposite to the dithering of the first mass, the second mass having first and second movable electrodes that are movable relative to the substrate, wherein the first electrodes and second electrodes for each mass are located in similar corresponding positions;

a second set of first and second fixed electrodes that are fixed relative to the substrate and spaced from the respective first and second movable electrodes of the second mass for sensing capacitance therebetween;

wherein the first fixed electrode of the first set is electrically coupled to the second fixed electrode of the second set and the second fixed electrode of the first set is electrically coupled to the first fixed electrode of the second set, the electrical couplings being such that the couplings cancel gradients in the device.

12. The micromachined device of claim 11, further comprising third and fourth masses, each of the third and fourth masses with respective first and second movable electrodes and first and second fixed electrodes.

13. The micromachined device of claim 11, wherein the first and second sets of fixed electrodes are formed on the surface of the substrate.

14. The micromachined device of claim 13, wherein the masses are each dithered rotationally about a central axis.

15. The micromachined device of claim 11, wherein the masses are each dithered rotationally about a central axis.