INERTIAL MEASUREMENT UNIT (IMU) MULTI-POINT THERMAL CONTROL

• US 20110127365A1
• Filed: 12/01/2009
• Published: 06/02/2011
• Est. Priority Date: 12/01/2009
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Chappell, Charles D.
• Granted Patent: US 8,558,150 B2
• Time in Patent Office: Days
• US Class Current: 244/3.2
• CPC Class Codes: F41G 7/36 using inertial references
• CPC Class Codes: F42B 15/01 Arrangements thereon for guidance or control steering arrangements F42B10/60; aircraft flight control B64C; guidance systems other than those installed aboard F41G7/00, F41G9/00; locating by use of radio or other waves G01S; flight control in general G05D1/00; computer aspects G06]
• CPC Class Codes: F42B 19/01 Steering control
• CPC Class Codes: G01C 21/183 Compensation of inertial measurements, e.g. for temperature effects
• CPC Class Codes: H05B 1/02 Automatic switching arrangements specially adapted to apparatus ; Control of heating devices thermally-actuated switches H01H37/00

Abstract

A thermally controlled gas bearing supported inertial measurement unit (IMU) system is provided. The system comprises a sensor assembly enclosing one or more sensors and a plurality of heating elements, wherein each of the plurality of heating elements is proximal to the sensor assembly. The system also comprises a plurality of temperature sensors configured to determine a temperature of a region of the sensor assembly and a control unit configured to adjust a temperature of at least one of the plurality of heating elements based on feedback from the at least one temperature sensor.

Claims

1. A thermally controlled gas bearing supported inertial measurement unit (IMU) system, comprising:

a sensor assembly enclosing one or more sensors;

a plurality of heating elements, wherein each of the plurality of heating elements is proximal to the sensor assembly;

a plurality of temperature sensors configured to determine a temperature of a region of the sensor assembly; and

a control unit configured to adjust a temperature of at least one of the plurality of heating elements based on feedback from the at least one temperature sensor.

2. The system of claim 1, wherein a control unit configured to adjust a temperature of at least one of the plurality of heating elements based on feedback further comprises adjusting the temperature of at least one of the plurality of heating elements to substantially maintain a thermal gradient across the sensor assembly within a predetermined temperature range.

3. The system of claim 1, wherein a control unit configured to adjust a temperature of the plurality of heating elements based on feedback is further configured to:

increase the temperature of a heating element proximate to a relatively cooler region; and

decrease the temperature of a heating element proximate to a relatively warmer region.

4. The system of claim 1, further comprising:

a plurality of gas pads that float the sensor assembly, each of the plurality of heating element is mounted on one of the plurality of gas pads.

5. The system of claim 4, further comprising:

wherein the plurality of gas pads are positioned substantially evenly around the sensor assembly;

wherein the plurality of heating elements comprises annular heating elements, wherein each annular heating element is affixed to one of the sixteen gas pads; and

wherein the temperature of the sensor assembly at any given point is substantially maintained within 5 degrees Fahrenheit.

6. The system of claim 4, wherein each of the plurality of heating elements is annular in shape and is affixed to a backside of one of the plurality of gas pads.

7. The system of claim 4, wherein at least one of the plurality of gas pads comprises a porous material.

8. The system of claim 1, further comprising:

wherein the control unit is further configured to rotate the sensor assembly based on maintaining an approximately stable temperature of the sensor assembly.

9. The system of claim 1, wherein the control unit controls each of the plurality of heating elements individually.

10. A method of reducing a thermal gradient of an assembly, the method comprising:

determining temperatures of a plurality of regions of the assembly; and

adjusting the temperature of a plurality of heating elements proximal to the assembly based on the temperatures of the plurality of regions, wherein the temperature output of the plurality of heating elements is adjusted to maintain a thermal gradient across the assembly within a predetermined temperature range.

11. The method of claim 10, wherein the plurality of heating elements warm pressurized gas outputted by a plurality of gas pads used to float the assembly.

12. The method of claim 10, wherein determining temperatures of a plurality of regions further comprises detecting relatively warmer and relatively cooler regions of the assembly.

13. The method of claim 12, wherein adjusting the temperature of a plurality of heating elements further comprises:

raising the temperature of a heating element proximate to a relatively cooler region of the assembly; and

lowering the temperature of a heating element proximate to a relatively warmer region of the assembly.

14. The method of claim 10, further comprising:

rotating the assembly to reposition a warmer region further away from the plurality of heating elements; and

rotating the assembly to reposition a cooler region closer to one of the plurality of heating elements.

15. The method of claim 10, further comprising:

determining the angular position of the assembly.

16. The method of claim 10, wherein adjusting the temperature of a plurality of heating elements is controlled by a control unit using feedback from a plurality of temperature sensors located within the assembly.

17. The method of claim 10, further comprising:

determining temperatures of the plurality of regions of the assembly whenever the assembly undergoes a rotation; and

adjusting the temperatures of the heating elements based on the temperatures of the regions now proximate to the heating elements.

18. An inertial navigation system (INS) onboard an aerial vehicle, comprising:

an inertial measurement unit (IMU) comprising;

a sensor assembly, wherein the sensor assembly is approximately spherical in shape;

at least one motion sensor; and

a plurality of temperature sensors;

a gas jet control assembly, comprising;

a plurality of gas pads that output pressurized gas to support the sensor assembly, wherein the sensor assembly is free to rotate; and

a plurality of heating elements, wherein each of the plurality of heating element is affixed to one of the plurality of gas pads, wherein the plurality of heating elements warm the pressurized gas; and

a control unit configured to adjust the temperature of each of the plurality of heating elements based on the relative temperature of the surface of the sensor assembly proximate to the plurality of heating elements, wherein the control unit comprises;

a processing unit configured to execute a thermal control routine to control the temperature of the sensor assembly.

19. The INS of claim 18, further comprising:

wherein the aerial vehicle is a missile;

wherein the at least one motion sensor comprises three accelerometers; and

wherein the gas pads are configured to rotate the sensor assembly.

20. The INS of claim 18, further comprising:

wherein the control unit that is configured to adjust the temperature of the heating elements is further configured to;

increase power provided to a heating element proximate to a relatively cooler region of the sensor assembly; and

decrease power provided to a heating element proximate to a relatively warmer region of the sensor assembly; and

wherein the thermal control routine controls the temperature of the sensor assembly by maintaining a thermal gradient across the sensor assembly substantially within a predetermined temperature range.