Double-integrating silicon acceleration sensing device

• US 5,044,201 A
• Filed: 08/13/1990
• Issued: 09/03/1991
• Est. Priority Date: 06/05/1989
• Status: Expired due to Fees

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Titus, John D., Farace, Louis P.
• Primary Examiner(s): CHAPMAN JR, JOHN E
• Application Number:
  US07/566,789
• Time in Patent Office: 386 Days
• Field of Search: 73/490, 73/503, 73/515, 73/516 R, 73/516 LM, 361/280, 361/283
• US Class Current: 73/503
• CPC Class Codes: G01P 15/0802 Details
• CPC Class Codes: G01P 15/125 by capacitive pick-up

Abstract

A double integrating silicon acceleration sensing device which is solid state and micromachined measures the acceleration of an object and determines the distance travelled by that object through its trajectory. The device comprises a hermetically sealed container. The cavity within the container is divided by a flexible silicon diaphragm into two separate cavities, one shallow and the other deep. The two cavities are filled with a fluid which is relatively incompressible over the range of operating pressure. The fluid can only transfer between the two cavities through an orifice. Two capacitor plates form a capacitor within the shallow cavity. One of the plates is secured to a central portion of the diaphragm, and the other plate is secured adjacent to and opposite of the first plate within the shallow cavity. When the accelerometer is at rest, the two plates are separated by a given distance X_g. When the accelerometer experiences an acceleration, the diaphragm deflects into the deep cavity forcing fluid from the deep cavity into the shallow cavity. The gap between the two capacitor plates X_g increases causing a change in the total capacitance. This capacitance value is exactly proportional to the distance travelled by the object for constant acceleration, and is approximately proportional to the distance travelled for other acceleration pulses. When capacitor plates are coupled adjacent and opposite each other in the deep cavity, in addition to capacitor plates in the shallow cavity, a differential capacitance results.

Claims

1. An acceleration sensing device comprising:

device housing including a sealed cavity;

flexible diaphragm dividing said sealed cavity into a plurality of small cavities;

said plurality of small cavities filled with a generally incompressible fluid;

conduit means connecting said plurality of small cavities;

said conduit means allowing flow of said fluid between said plurality of small cavities;

a plurality of capacitor plates ;

a first of said plurality of capacitor plates coupled to said flexible diaphragm and a second of said plurality of capacitor plates coupled to said housing and adjacent to said first of said plurality of capacitor plates; and

orifice means for controlling the rate of flow of said generally incompressible fluid between said plurality of small cavities.

2. An acceleration sensing device according to claim 1 wherein said flexible diaphragm comprises:

a plurality of semi-spherical cavity means for increasing the flexibility of said diaphragm ; and

said plurality of semi-spherical cavity means blemishing at least one face of said diaphragm.

3. An acceleration sensing device according to claim 2 wherein said plurality of semi-spherical cavity means are arranged in a hexagonal close pack pattern on said at least one face.

4. An acceleration sensing device according to claim 1 wherein said flexible diaphragm comprises a silicon material.

5. An acceleration sensing device according to claim 1 wherein said acceleration sensing device further comprises:

a third of said plurality of capacitor plates coupled to said flexible diaphragm; and

a fourth of said plurality of capacitor plates coupled to said housing adjacent to said third of said plurality of capacitor plates.

6. In a vehicle system, an acceleration sensing device comprising:

silicon diaphragm;

first means for increasing the flexibility of said silicon diaphragm, said first means coupled to said silicon diaphragm;

said first means including;

a plurality of semi-spherical cavity means for increasing the flexibility of said silicon diaphragm;

said plurality of semi-sperical cavity means blemishing at least one face of said silicon diaphragm;

said silicon diaphragm coupled across and dissecting a sealed chamber containing a fluid;

second means for allowing said fluid to flow between the dissected portions of said sealed chamber at a predetermined rate; and

said second means connected between the dissected portions of said sealed chamber.

7. An acceleration sensing device according to claim 6 wherein said second means comprises an orifice for controlling the rate of flow of said fluid.

8. In a vehicle system, an acceleration sensing device comprising:

device housing including a sealed cavity;

flexible diaphragm dividing said sealed cavity into a plurality of small cavities;

said plurality of small cavities filled with a generally incompressible fluid;

a plurality of semi-spherical cavity means for increasing the flexibility of said diaphragm;

said plurality of semi-spherical cavity means blemishing at least one face of said diaphragm;

conduit means connecting said plurality of small cavities;

said conduit allowing flow of said fluid between said plurality of small cavities;

a plurality of capacitor plates;

a first of said plurality of capacitor plates coupled to said flexible diaphragm;

a second of said plurality of capacitor plates coupled to said housing and adjacent to said first of said plurality of capacitor plates; and

orifice means for controlling the rate of flow of said generally incompressible fluid between said plurality of small cavities.

9. An acceleration sensing device according to claim 8 wherein said plurality of semi-spherical cavity means are arranged in a hexagonal close pack pattern on said at least one face.

10. An acceleration sensing device according to claim 8 wherein said flexible diaphragm comprises a silicon material.

11. An acceleration sensing device according to claim 8 wherein the device further comprises:

a third of said plurality of capacitor plates coupled to said flexible diaphragm; and

a fourth of said plurality of capacitor plates coupled to said housing adjacent to said third of said plurality of capacitor plates.

12. In a projectile system, an acceleration sensing device comprising:

silicon diaphragm;

a plurality of semi-spherical cavity means for increasing the flexibility of said silicon diaphragm;

said plurality of semi-spherical cavity means blemishing at least one face of said silicon diaphragm;

said silicon diaphragm coupled across and dissecting a sealed chamber containing a fluid;

means for allowing said fluid to flow between the dissected portions of said sealed chamber at a predetermined rate; and

said means for allowing connected between the dissected portions of said sealed chamber.

13. An acceleration sensing device according to claim 12 wherein said second means comprises an orifice for controlling the rate of flow of said fluid.