Reducing offset in accelerometers

• US 6,892,576 B2
• Filed: 07/18/2003
• Issued: 05/17/2005
• Est. Priority Date: 07/19/2002
• Status: Expired due to Term

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Juneau, Thor, Samuels, Howard R., Hollocher, David C., Judy, Michael
• Primary Examiner(s): CHAPMAN JR, JOHN E
• Application Number:
  US10/622,380
• Publication Number:
  US 20040055382A1
• Time in Patent Office: 669 Days
• Field of Search: 735/143.2, 735/141.8, 735/040.1, 735/040.2
• US Class Current: 73/514.32
• CPC Class Codes: B81B 2201/0235 Accelerometers
• CPC Class Codes: B81B 2203/051 Translation according to an axis parallel to the substrate
• CPC Class Codes: B81B 2203/055 Translation in a plane parallel to the substrate, i.e. enabling movement along any direction in the plane
• CPC Class Codes: B81B 3/0072 For controlling internal stress or strain in moving or flexible elements, e.g. stress compensating layers
• CPC Class Codes: G01P 15/0802 Details
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 15/18 in two or more dimensions
• CPC Class Codes: G01P 2015/0814 for translational movement of the mass, e.g. shuttle type
• CPC Class Codes: G01P 2015/082 for two degrees of freedom of movement of a single mass
• CPC Class Codes: Y10T 29/49007 Indicating transducer
• CPC Class Codes: Y10T 74/1293 Flexure hinges for gyros

Abstract

Accelerometer offset is reduced by forming mass support structures within an inner periphery of the mass, affixing the mass support structures to the substrate by at least one anchor positioned near the mass'"'"' center of mass, and affixing the sensing fingers proximate to the anchor. The mass support structures can be affixed to the substrate using a single anchor or multiple anchors that are positioned close together. The sensing fingers can be affixed to the substrate or to the mass support structures. The mass is typically suspended from within its periphery but toward its outer periphery.

Claims

1. An accelerometer comprising:

a substrate;

a mass having an outer periphery, a cavity defining an inner periphery, and a plurality of elongated fingers along a portion of the inner periphery;

mass support structures, positioned within the inner periphery and affixed to the substrate by at least one anchor positioned proximate to the mass'"'"' center of mass, for supporting the mass above the substrate and allowing movement of the mass relative to the substrate along at least one linear axis, and

a plurality of elongated sensing fingers for sensing movement of the mass fingers relative to the sensing fingers, the sensing fingers positioned substantially alongside the mass fingers within the inner periphery and affixed to the substrate proximate to the at least one anchor such that mechanical stresses cause the mass fingers and the sensing fingers to move in substantially equal ways.

2. An accelerometer according to claim 1, wherein the mass support structures comprise:

a plurality of suspension springs; and

a plurality of support arms, wherein the suspension springs are disposed between the mass and the support arms, and wherein the support arms are affixed to the substrate.

3. An accelerometer according to claim 2, wherein the support arms are configured substantially in one of:

a cruciform configuration; and

an “

H”

configuration.

4. An accelerometer according to claim 1, wherein the mass support structures are affixed to the substrate using a single anchor.

5. An accelerometer according to claim 4, wherein the single anchor is a substantially square anchor.

6. An accelerometer according to claim 1, wherein the mass support structures are affixed to the substrate using multiple anchors positioned substantially symmetrical about the mass'"'"' center of mass.

7. An accelerometer according to claim 1, wherein at least one elongated sensing finger is affixed to the substrate using a single elongated anchor in order to reduce rotation of the elongated sensing finger about the anchor.

8. An accelerometer according to claim 1, wherein at least one elongated sensing finger is affixed to the substrate using multiple anchors in order to reduce rotation of the elongated sensing finger about the anchors.

9. A method for reducing offset in an accelerometer, the method comprising:

forming a mass having an outer periphery, a cavity defining an inner periphery, and a plurality of elongated finger structures along a portion of the inner periphery;

forming a plurality of mass support structures within the inner periphery of the mass;

forming a plurality of elongated sensing fingers substantially alongside the mass fingers within the inner periphery of the mass for sensing movement of the mass fingers relative to the sensing fingers;

affixing the mass support structures to a substrate by at least one anchor positioned proximate to the mass'"'"' center of mass for supporting the mass above the substrate and allowing movement of the mass relative to the substrate along at least one linear axis; and

affixing the plurality of elongated sensing fingers to the substrate proximate to the at least one anchor such that mechanical stresses cause the mass fingers and the sensing fingers to move in substantially equal ways.

10. A method according to claim 9, wherein the mass support structures comprise:

a plurality of suspension springs; and

a plurality of support arms, wherein the suspension springs are disposed between the mass and the support arms, and wherein the support arms are affixed to the substrate.

11. A method according to claim 10, wherein the support arms are formed substantially in one of:

a cruciform configuration; and

an “

H”

configuration.

12. A method according to claim 9, wherein affixing the mass support structures to the substrate comprises:

affixing the mass support structures to the substrate using a single anchor.

13. A method according to claim 12, wherein the single anchor is a substantially square anchor.

14. A method according to claim 9, wherein affixing the mass support structures to the substrate comprises:

affixing the mass support structures to the substrate using multiple anchors positioned substantially symmetrical about the mass'"'"' center of mass.

15. A method according to claim 9, wherein affixing the plurality of elongated sensing fingers to the substrate comprises:

affixing at least one elongated sensing finger to the substrate using a single elongated anchor in order to reduce rotation of the elongated sensing finger about the anchor.

16. A method according to claim 9, wherein affixing the plurality of elongated sensing fingers to the substrate comprises:

affixing at least one elongated sensing finger to the substrate using multiple anchors in order to reduce rotation of the elongated sensing finger about the anchors.