Integrated capacitive bridge and integrated flexure functions inertial measurement unit

• US 7,310,577 B2
• Filed: 09/29/2004
• Issued: 12/18/2007
• Est. Priority Date: 09/29/2004
• Status: Expired due to Fees

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Campbell, Ray F., Wada, Joan D., Raab, John P.
• Primary Examiner(s): Nguyen, Tan Q.
• Application Number:
  US10/953,726
• Publication Number:
  US 20060069469A1
• Time in Patent Office: 1,175 Days
• Field of Search: 701/4, 701/220, 701/116, 701/221, 702/150, 702/153, 73/17.5, 73/17.7, 73/17.8, 735/143.2, 342/358, 280/5.507
• US Class Current: 701/220
• CPC Class Codes: G01C 21/166 Mechanical, construction or arrangement details of inertial navigation systems
• CPC Class Codes: G01C 21/183 Compensation of inertial measurements, e.g. for temperature effects
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 15/18 in two or more dimensions

Abstract

An inertia control system includes an integrated inertial measurement unit coupled to an inertial platform. The integrated inertial measurement unit includes three accelerometer gimbals/axes (first, second, and third) respectively, each including a pair of flexure plate accelerometers. First and second accelerometers are coupled to the first gimbal, third and fourth accelerometers are coupled to the second gimbal, and fifth and sixth accelerometers are coupled to the third gimbal. The system further includes a processor utilizing outputs from the inertial measurement unit in three processor modes, including a leveling mode, a compass mode, and an operational mode.

Claims

1. A system for controlling inertia of an object comprising:

an inertial platform;

an inertial measurement unit coupled to said inertial platform, said inertial measurement unit comprising a z-axis gimbal, an x-axis gimbal, and a y-axis gimbal, whereby a first flexure accelerometer and a second flexure accelerometer are coupled to said z-axis gimbal, a third flexure accelerometer and a fourth flexure accelerometer are coupled to said x-axis gimbal, and a fifth flexure accelerometer and a sixth flexure accelerometer are coupled to said y-axis gimbal;

a processor leveling said platform perpendicular to a local gravity vector, said processor computing a spatial gravity vector with respect to said platform as a function of first gimbal angles whereby said x-, y-, and z-axis gimbals experience maximum forces, said processor controlling said gimbals such that an xz-plane, formed as a function of an intersection of axes of rotation of said x- and z-axis gimbals, is perpendicular to said local gravity vector, said processor further rotating said platform about a z-axis and recording a second gimbal angle wherein a maximum positive force vector is generated, thereby establishing an east-west vector, and said processor recording said first gimbal angles and said second gimbal angle.

2. The system of claim 1, wherein said processor further comprises logic holding gimbal angles of said x-axis gimbal and said y-axis gimbal constant and rotating said z-axis gimbal through 360°

and thereby generating one of said first gimbal angles.

3. The system of claim 1, wherein said processor comprises logic leveling said platform perpendicular to said local gravity vector through holding gimbal angles of said z-axis gimbal and said y-axis gimbal constant and rotating said x-axis gimbal through 360°

thereby generating one of said first gimbal angles.

4. The system of claim 1, wherein said processor comprises logic leveling said platform perpendicular to a local gravity vector through holding gimbal angles of said x-axis gimbal and said z-axis gimbal constant and rotating said y-axis gimbal through 360°

thereby generating one of said first gimbal angles.

5. The system of claim 1, wherein said processor comprises logic recording said second gimbal angle wherein said maximum positive force vector is generated through reading said second gimbal angle on a gyrocompass coupled to said platform.

6. The system of claim 1, wherein said processor further comprises logic maintaining an inertial position of said platform as a function of said first gimbal angles and said second gimbal angle.

7. The system of claim 1, wherein said processor further comprises logic generating velocity, distance, or platform orientation data as a function of said first gimbal angles and said second gimbal angle.

8. The system of claim 1, further comprising a z-axis angular readout device, an x-axis angular readout device, and a y-axis angular readout device, said x-, y-, and z-axis angular readout devices detecting current angular position of said x-axis gimbal, said y-axis gimbal, and said z-axis gimbal respectively relative to said platform.

9. The system of claim 8, wherein said z-axis angular readout device comprises at least one of an electrical resolver, an optical encoder, or a mechanical interface.

10. The system of claim 1 further comprising an actuator activating an object control device in response to a platform control signal from said processor.

11. The system of claim 10, wherein said object control device comprises at least one of a thruster, an attitude control device, a missile steering nozzle, or a vane actuator.

12. The system of claim 1, wherein said first flexure plate accelerometer comprises at least one of a dual capacitance accelerometer or a dual bridge accelerometer.

13. A method for controlling an inertial measurement unit having a z-axis gimbal with a first flexure accelerometer and a second flexure accelerometer positioned thereon, an x-axis gimbal with a third flexure accelerometer and a fourth flexure accelerometer positioned thereon, and y-axis gimbal with a fifth flexure accelerometer and a sixth flexure accelerometer positioned thereon, said z-, x-, and y-axis gimbals mounted on a platform, said method comprising:

leveling the platform perpendicular to a local gravity vector;

computing a spatial gravity vector with respect to the platform as a function of first angles whereby the x-, y-, and z-axis gimbals experience maximum forces;

controlling the gimbals such that an xz-plane, formed as a function of an intersection of axes of rotation of the x- and z-axis gimbals, is perpendicular to said local gravity vector;

rotating the platform about a z-axis and recording a second gimbal angle wherein a maximum positive force vector is generated, thereby establishing an east-west vector; and

recording said first gimbal angles and said second gimbal angle.

14. The method of claim 13, wherein leveling the platform perpendicular to said local gravity vector further comprises holding gimbal angles of the x-axis gimbal and the y-axis gimbal constant and rotating the 2-axis gimbal through 360°

thereby generating one of said first angles.

15. The method of claim 13, wherein leveling the platform perpendicular to said local gravity vector further comprises holding gimbal angles of the z-axis gimbal and the y-axis gimbal constant and rotating the x-axis gimbal through 360°

thereby generating one of said first angles.

16. The method of claim 13, wherein leveling the platform perpendicular to a local gravity vector further comprises holding gimbal angles of to x-axis gimbal and the z-axis gimbal constant and rotating the y-axis gimbal through 360°

thereby generating one of said first angles.

17. The method of claim 13, wherein recording said second gimbal angle wherein said maximum positive force vector is generated further comprises reading said second gimbal angle on a gyrocompass coupled to the platform.

18. The method of claim 13 further comprising maintaining an inertial position of the platform as a function of said first gimbal angles and said second gimbal angle.

19. The method of claim 13 further comprising generating velocity distance, or platform orientation data as a function of said first gimbal angles and said second gimbal angle.

20. A method for controlling an inertial measurement unit having a z-axis gimbal with a first flexure accelerometer and a second flexure accelerometer positioned thereon, an x-axis gimbal with a third flexure accelerometer and a fourth flexure accelerometer positioned thereon, and y-axis gimbal with a fifth flexure accelerometer and a sixth flexure accelerometer positioned thereon, said z-, x-, and y-axis gimbals mounted on a platform, said method comprising:

leveling the integrated inertial measurement unit with respect to a local vertical;

establishing a directional reference for the integrated inertial measurement unit;

positioning the platform perpendicular to a local gravity vector;

reading present gimbal positions for the z-axis gimbal, the x-axis gimbal, and the y-axis gimbal;

holding gimbal angles of the fifth flexure accelerometer and the sixth flexure accelerometer and the third flexure accelerometer and the fourth flexure accelerometer constant;

rotating the first flexure accelerometer and second flexure accelerometer gimbal through 360°

;

while rotating the first and second flexure accelerometer gimbal, recording first and second flexure accelerometer gimbal angles where a first maximum force is detected;

rotating the third and fourth flexure accelerometer gimbal through 360°

;

while rotating the third and fourth flexure accelerometer gimbal, recording third and fourth flexure accelerometer gimbal angles where a second maximum force is detected;

rotating the fifth and sixth flexure accelerometer gimbal through 360°

;

while rotating the fifth and sixth flexure accelerometer gimbal, recording fifth and sixth flexure accelerometer gimbal angles where a third maximum force is detected;

computing a spatial gravity vector with respect to the platform as a function of said first, second, and third maximum force data;

computing and commanding gimbal angles that will result in an xz-plane being perpendicular to said spatial gravity vector;

checking whether a signal from the first flexure accelerometer is equal to a signal from the second flexure accelerometer;

recording a value of said first flexure accelerometer signal and said second flexure accelerometer signal;

rotating the x-axis gimbal 90°

such that a z-axis is up and the third and fourth flexure accelerometers are perpendicular to said local vertical;

checking whether a signal from the third flexure accelerometer is equal to a signal from the fourth flexure accelerometer;

verifying vertical orientation by rotating the platform 90°

so that said z-axis is vertical and the third and fourth flexure accelerometers are generating equal signals also equal to a value measured by the first and second flexure accelerometers;

restoring said xz-plane to a predetermined position;

recording a value of said third and fourth flexure accelerometer signals;

checking whether a value of said first and second flexure accelerometer signals equal said value of said third and fourth flexure accelerometer signals;

rotating the platform back to said xz-plane perpendicular to said vertical;

computing a level of the platform;

leveling the platform;

rotating the leveled platform about said z-axis;

recording a gimbal angle where a force vector is maximum and positive establishing an east-west direction as a function of said gimbal angle;

using said gimbal angle as a compass reference base of an operational mode;

rotating said xz-plane 360°

clockwise while recording an output of a gyrocompass;

rotating said xz-plane counterclockwise for 360°

;

selecting maximum points of said xz-plane as a function signals from said gyrocompass;

recording a defined angular position as an east-west earth rotation factor;

rotating the inertial measurement unit to said target vector;

activating said operation mode;

recording said gimbal angles for maintenance of inertial position and guidance utility in said operation mode;

maintain said inertial position as a function of said angular outputs;

reading a present position of all the gimbals;

redefining a current access position as a local level pointing at a predetermined target for computational usage;

controlling a gimbal drive for maintaining current inertial position of the gimbals;

checking whether platform angular acceleration at the x-, y-, and z-axes are equal to zero; and

driving either the x-, y-, or z-axis gimbal in response to a signal that platform angular acceleration of the x-, y-, and z-axes gimbals are not equal to zero.