Micromachined accelerometer

• US 5,668,319 A
• Filed: 03/21/1996
• Issued: 09/16/1997
• Est. Priority Date: 02/07/1994
• Status: Expired due to Fees

• Current Assignee: Regents of the University of California (University of California)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Garabedian, Raffi
• Primary Examiner(s): Williams, Hezron E.
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US08/621,202
• Time in Patent Office: 544 Days
• Field of Search: 73/514.09, 73/514.06, 73/514.07, 73/654, 73/754, 73/715, 73/716, 73/717, 73/718, 73/719
• US Class Current: 73/514.09
• CPC Class Codes: G01P 15/0802 Details
• CPC Class Codes: G01P 15/123 by piezo-resistive elements, e.g. semiconductor strain gauges

Abstract

A fluid proof mass accelerometer fabricated from bonded substrate layers. The device includes a plurality of micromachined fluid cavities which are joined by micromachined fluid channels. The fluid cavities extend from the bonded inner surfaces of the substrate layers to thin resilient membranes which are generally coplanar with the surface. In one embodiment, each substrate layer is thinned toward its outer surface thereby forming integral resilient membranes. In another embodiment, the cavities extend entirely through base substrate layers and thin substrate layers are bonded to the base substrate layers to form a resilient membranes over the cavities. The cavities and channels are sealed and filled with a high density fluid and, when subjected to acceleration, force exerted on the fluid contained within the cavities will cause the cavities to deflect. Signals from pressure sensors positioned on the membranes are algebraically combined to determine translational and rotational acceleration.

Claims

1. A multi-axis hydrostatic accelerometer, comprising:

(a) a substrate having first and second substantially planar outer surfaces;

(b) first, second, third, and fourth spaced-apart fluid coupled cavities positioned within said substrate between said first and second outer surfaces;

(c) first, second, third, fourth, fifth, sixth, seventh and eighth resilient membranes integrally formed in said substrate, said first, second, third and fourth membranes respectively positioned between said first, second, third and fourth cavities and said first outer surface of said substrate, said third, fourth, fifth and sixth membranes respectively positioned between said first, second, third and fourth cavities and said second outer surface of said substrate; and

(d) first, second, third, fourth, fifth, sixth, seventh and eighth pressure sensing means for respectively sensing pressure exerted on said first, second, third, fourth, fifth, sixth, seventh and eighth membranes by displacement of a fluid sealed within said cavities during acceleration of said substrate;

(e) wherein said membranes are deflected due to pressure exerted on said membranes by displacement of said fluid during axial acceleration of said substrate, said axial acceleration including translational acceleration and rotational acceleration;

(f) wherein said pressure sensing means provide electronic output signals for determining acceleration along at least three independent translational axes and at least two rotational axes.

2. A multi-axis hydrostatic accelerometer as recited in claim 1, wherein acceleration is determined according to

3. A multi-axis hydrostatic accelerometer as recited in claim 1, further comprising pressure relief means for absorbing thermal expansion of said fluid, said pressure relief means integrally formed in said substrate and coupled to said cavities by said fluid.

4. A multi-axis hydrostatic accelerometer, comprising:

(a) a substrate having substantially planar first and second outer surfaces;

(b) first, second, third, and fourth spaced-apart cavities positioned within said substrate between said first and second outer surfaces;

(c) first, second, third, fourth, fifth, sixth, seventh and eighth resilient membranes integrally formed in said substrate, said first, second, third and fourth membranes respectively positioned between said first, second, third and fourth cavities and said first outer surface of said substrate, said third, fourth, fifth and sixth membranes respectively positioned between said first, second, third and fourth cavities and said second outer surface of said substrate; and

(d) a first channel connecting said first and second cavities;

(e) a second channel connecting said third and fourth cavities;

(f) a fluid sealed within said channels and said cavities wherein said channels and said cavities are coupled by said fluid; and

(g) first, second, third, fourth, fifth, sixth, seventh and eighth pressure sensing means for respectively sensing pressure exerted on said first, second, third, fourth, fifth, sixth, seventh and eighth membranes by displacement of said fluid during acceleration of said substrate;

(h) wherein said membranes are deflected due to pressure exerted on said membranes by displacement of said fluid during axial acceleration of said substrate, said axial acceleration including translational acceleration and rotational acceleration;

(I) wherein said pressure sensing means provide electronic output signals for determining acceleration along at least three independent translational axes and at least two rotational axes.

5. A multi-axis hydrostatic accelerometer as recited in claim 4, wherein acceleration is determined according to

6. A multi-axis hydrostatic accelerometer as recited in claim 4, further comprising pressure relief means for absorbing thermal expansion of said fluid, said pressure relief means integrally formed in said substrate and coupled to said cavities and said channels by said fluid.

7. A multi-axis hydrostatic accelerometer as recited in claim 4, further comprising:

(a) a third channel connecting said second and third cavities; and

(b) a fourth channel connecting said first and fourth cavities.

8. A multi-axis hydrostatic accelerometer as recited in claim 4, wherein said first and second channels are elongated, wherein said first and second channels have midpoints at which said first and second channels intersect, and wherein said first channel is substantially perpendicular to said second channel.

9. A multi-axis hydrostatic accelerometer, comprising:

(a) a first substantially planar substrate layer;

(b) a second substantially planar substrate layer;

(c) said first and second substrate layers having opposing bonded inner surfaces, said first and second substrate layers having outer surfaces;

(d) first, second, third, and fourth spaced apart cavities extending from the bonded inner surface of the first substrate layer toward the outer surface of said first substrate layer;

(e) fifth, sixth, seventh, and eighth spaced apart cavities extending from the bonded inner surface of the second substrate layer toward the outer surface of said second substrate layer;

(f) first, second, third and fourth resilient membranes integrally formed in said first substrate layer, said first, second, third and fourth membranes respectively positioned between said first, second, third and fourth cavities and said outer surface of said first substrate layer;

(g) fifth, sixth, seventh and eighth resilient membranes integrally formed in said second substrate layer, said fifth, sixth, seventh and eighth membranes respectively positioned between said fifth, sixth, seventh and eighth cavities and said outer surface of said second substrate layer; and

(h) a first channel connecting said first, second, fifth and sixth cavities;

(i) a second channel connecting said third, fourth, seventh and eighth cavities;

(j) a fluid sealed within said first channel and said first, second, fifth and sixth cavities wherein said first channel and said first, second, fifth and sixth cavities are coupled by said fluid;

(k) said fluid sealed within said second channel and said third, fourth, seventh and eighth cavities wherein said second channel and said third, fourth, seventh and eighth cavities are fluidly coupled; and

(l) first, second, third, fourth, fifth, sixth, seventh and eighth pressure sensing means for respectively sensing pressure exerted on said first, second, third, fourth, fifth, sixth, seventh and eighth membranes by displacement of said fluid during acceleration;

(m) wherein said membranes are deflected due to pressure exerted on said membranes by displacement of said fluid during axial acceleration of said substrate, said axial acceleration including translational acceleration and rotational acceleration;

(n) wherein said pressure sensing means provide electronic output signals for determining acceleration along at least three independent translational axes and at least two rotational axes.

10. A multi-axis hydrostatic accelerometer as recited in claim 9, wherein acceleration is determined according to

11. A multi-axis hydrostatic accelerometer as recited in claim 9, further comprising pressure relief means for absorbing thermal expansion of said fluid, said pressure relief means integrally formed in said substrate and coupled to said cavities and said channels by said fluid.

12. A multi-axis hydrostatic accelerometer as recited in claim 9, further comprising:

(a) a third channel connecting said second, third, sixth and seventh cavities; and

(b) a fourth channel connecting said first, fourth, fifth and eighth cavities.

13. A multi-axis hydrostatic accelerometer as recited in claim 9, wherein said first and second channels are elongated, wherein said first and second channels have midpoints at which said first and second channels intersect, and wherein said first channel is substantially perpendicular to said second channel.