Compensated composite structure

• US 20060111798A1
• Filed: 11/22/2004
• Published: 05/25/2006
• Est. Priority Date: 11/22/2004
• Status: Active Grant

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Campbell, Ray F., Khatiblou, Mohsen A., Costello, Michael J., Wada, Joan D.
• Granted Patent: US 7,360,425 B2
• Time in Patent Office: Days
• US Class Current: 700/60
• CPC Class Codes: G01P 15/125 by capacitive pick-up

Abstract

A method for constructing a compensated composite structure, including a support tube coupled to a flexure plate and enclosing a capacitor plate, includes selecting a material for the support tube whereby the coefficient of expansion is larger than that of the material of the capacitor plates. Further, the method includes selecting the lengths of the support tube and the capacitor plate such that the composite structure is insensitive to changes in temperature.

Claims

1. A compensated composite structure comprising:

a first support structure comprising a first material comprising a first coefficient of thermal expansion, said first support structure comprising a first end and a second end;

a first insulator coupled to said first end of said first support structure;

a first capacitor plate comprising a second material comprising a second coefficient of thermal expansion, said first capacitor plate coupled to said first insulator and surrounded by said first support structure; and

a flexure plate comprising said second material, said flexure plate disposed in a substantially parallel relation to said first capacitor plate, said flexure plate coupled to said second end of said first support structure, said flexure plate and said first capacitor plate defining a first distance,

wherein said first distance varies in response to acceleration forces acting upon said flexure plate thereby generating at least one capacitance signal.

2. The system of claim 1 further comprising a second support structure comprising said first material, said second support structure comprising a first end and a second end, wherein said flexure plate is coupled to said second end of said second support structure.

3. The system of claim 2 further comprising a second insulator coupled to said first end of said second support structure.

4. The system of claim 3 further comprising a second capacitor plate comprising said second material, said second capacitor plate coupled to said second insulator and surrounded by said second support structure.

5. The system of claim 4, wherein said second capacitor plate is spaced apart from and in parallel relation to said first capacitor plate.

6. The system of claim 1, wherein said flexure plate is coupled to said first support structure and said second support structure through support flexures.

7. The system of claim 1, wherein said first coefficient of thermal expansion is greater than said second coefficient of thermal expansion.

8. The system of claim 1, wherein a length of said first support structure extending from said first insulator is larger than a length of said first capacitor plate extending from said first insulator.

9. The system of claim 1 further comprising:

a second support structure comprising said first material, said second support structure comprising a first end and a second end, wherein said flexure plate is coupled to said second end of said second support structure;

a second insulator coupled to said first end of said second support structure; and

a second capacitor plate coupled to said second insulator and surrounded by said second support structure, wherein said flexure plate is disposed in substantially parallel relation to said second capacitor plate, said flexure plate coupled to said second end of said second support structure, said flexure plate and said second capacitor plate defining a second distance,

wherein said second distance varies in response to acceleration forces acting upon said flexure plate thereby generating a second capacitance signal.

10. The system of claim 9 further comprising a first oscillator receiving said at least one capacitance signal and generating a first frequency signal in response thereto.

11. The system of claim 10 further comprising a second oscillator receiving said second capacitance signal and generating a second frequency signal in response thereto;

and

a frequency subtraction device subtracting said second frequency signal from said first frequency signal and generating therefrom an overall frequency signal.

12. The system of claim 11 further comprising a linearizer receiving said overall frequency signal and generating therefrom a linearized acceleration signal.

13. The system of claim 12 further comprising an actuator adapted to activate a system component in response to said linearized acceleration signal, wherein said system component comprises a thruster or an attitude control device.

14. An accelerometer system comprising:

a housing;

a flexure plate section enclosed within said housing and comprising

a first support structure comprising a first material comprising a first coefficient of thermal expansion, said first support structure comprising a first end and a second end,

a first insulator coupled to said first end of said first support structure;

a first capacitor plate comprising a second material comprising a second coefficient of thermal expansion, said first capacitor plate coupled to said first insulator and surrounded by said first support structure,

a second support structure comprising said first material, said second support structure comprising a first end and a second end,

a second insulator coupled to said first end of said second support structure,

a second capacitor plate coupled to said second insulator and surrounded by said second support structure,

a flexure plate comprising said second material and disposed between and in substantially parallel relation to said first capacitor plate and said second capacitor plate, said flexure plate coupled to said second end of said first support structure and said second end of said second support structure, said flexure plate and said first capacitor plate defining a first distance wherein said first distance varies in response to acceleration forces acting upon said flexure plate thereby generating a first capacitance signal, said flexure plate and said second capacitor plate defining a second distance wherein said second distance varies in response to acceleration forces acting upon said flexure plate thereby generating a second capacitance signal; and

a rigid plate section enclosed within said housing and electrically isolated from said flexure plate section and comprising a third capacitor plate and a fourth capacitor plate spaced apart from and in parallel relation to said first capacitor plate, and a rigid plate disposed between and in substantially parallel relation to said third capacitor plate and said fourth capacitor plate,

said rigid plate electrically isolated from said housing, said rigid plate and said third capacitor plate defining a third distance and generating a third capacitor signal and said rigid plate and said fourth capacitor plate defining a fourth distance and generating a fourth capacitor signal, wherein a fifth distance is defined between said rigid plate and said flexure plate such that said fifth distance is a function of acceleration forces,

said first capacitor signal, said second capacitor signal, said third capacitor signal and said fourth capacitor signal connect to form a bridge adapted to generate a bridge voltage signal.

15. The system of claim 14 further comprising a differential amplifier adapted to adjust a gain of said bridge voltage signal.

16. The system of claim 15 further comprising a demodulator receiving said bridge voltage signal and rectifying said bridge voltage signal as a function of a reference excitation phase, thereby generating a rectified waveform.

17. The system of claim 16 further comprising an analog filter receiving said rectified waveform and generating a filtered analog signal therefrom.

18. The system of claim 17 further comprising an analog-to-digital converter receiving said filtered analog signal and generate a digital word therefrom;

a digital linearizer receiving said digital word and generating a linearized signal therefrom; and

a computer activating a system component in response to said linearized signal.

19. The system of claim 14, wherein said flexure plate is coupled to said first support structure and said second support structure through support flexures.

20. The system of claim 14, wherein said first coefficient of thermal expansion is greater than said second coefficient of thermal expansion.

21. The system of claim 14, wherein a length of said first support structure extending from said first insulator is larger than a length of said first capacitor plate extending from said first insulator.

22. An accelerometer system comprising:

a housing;

a first support structure enclosed within said housing and comprising a first material comprising a first coefficient of thermal expansion, said first support structure comprising a first end and a second end,

a first insulator coupled to said first end of said first support structure;

a first capacitor plate comprising a second material comprising a second coefficient of thermal expansion, said first capacitor plate coupled to said first insulator and surrounded by said first support structure,

a second support structure comprising said first material, said second support structure comprising a first end and a second end,

a second insulator coupled to said first end of said second support structure,

a second capacitor plate coupled to said second insulator and surrounded by said second support structure,

a flexure plate comprising said second material and disposed between and in substantially parallel relation to said first capacitor plate and said second capacitor plate, said flexure plate coupled to said second end of said first support structure and said second end of said second support structure, said flexure plate and said first capacitor plate defining a first distance wherein said first distance varies in response to acceleration forces acting upon said flexure plate thereby generating a first capacitance signal, said flexure plate and said second capacitor plate defining a second distance wherein said second distance varies in response to acceleration forces acting upon said flexure plate thereby generating a second capacitance signal.

23. The system of claim 22, wherein said flexure plate is coupled to said first support structure and said second support structure through support flexures.

24. The system of claim 22, wherein said first coefficient of thermal expansion is greater than said second coefficient of thermal expansion.

25. The system of claim 22, wherein a length of said first support structure extending from said first insulator is larger than a length of said first capacitor plate extending from said first insulator.

26. 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 first gimbal, whereby a first flexure accelerometer is coupled to said first gimbal,

said first flexure accelerometer comprising a first support structure comprising a first material comprising a first coefficient of thermal expansion, said first support structure comprising a first end and a second end,

a first insulator coupled to said first end of said first support structure;

a first capacitor plate comprising a second material comprising a second coefficient of thermal expansion, said first capacitor plate coupled to said first insulator and surrounded by said first support structure,

a second support structure comprising said first material, said second support structure comprising a first end and a second end,

a second insulator coupled to said first end of said second support structure,

a second capacitor plate coupled to said second insulator and surrounded by said second support structure,

a flexure plate comprising said second material and disposed between and in substantially parallel relation to said first capacitor plate and said second capacitor plate, said flexure plate coupled to said second end of said first support structure and said second end of said second support structure, said flexure plate and said first capacitor plate defining a first distance wherein said first distance varies in response to acceleration forces acting upon said flexure plate thereby generating a first capacitance signal, said flexure plate and said second capacitor plate defining a second distance wherein said second distance varies in response to acceleration forces acting upon said flexure plate thereby generating a second capacitance signal,

a processor leveling said platform perpendicular to a local gravity vector as a function of said first capacitance signal and said second capacitance signal.

27. The system of claim 26, wherein said flexure plate is coupled to said first support structure and said second support structure through support flexures.

28. The system of claim 26, wherein said first coefficient of thermal expansion is greater than said second coefficient of thermal expansion.

29. The system of claim 26, wherein a length of said first support structure extending from said first insulator is larger than a length of said first capacitor plate extending from said first insulator.

30. An accelerometer comprising:

a cylindrical support structure comprising a first material comprising a first coefficient of thermal expansion;

a first capacitor plate comprising a second material comprising a second coefficient of thermal expansion, wherein said first coefficient of thermal expansion is greater than said second coefficient of thermal expansion, said first capacitor plate surrounded by and thermally insulated from said support structure;

a second capacitor plate positioned a distance from and in parallel relation to said first capacitor plate, said second capacitor plate comprising said second material surrounded by and thermally isolated from said support structure;

a flexure plate comprising said second material and disposed between and in substantially parallel relation to said first capacitor plate and said second capacitor plate, said flexure plate coupled to said support structure through support flexures, said flexure plate and said first capacitor plate defining a first distance wherein said first distance varies in response to acceleration forces acting upon said flexure plate thereby generating a first capacitance signal, said flexure plate and said second capacitor plate defining a second distance wherein said second distance varies in response to acceleration forces acting upon said flexure plate thereby generating a second capacitance signal.

31. The system of claim 30 further comprising a first oscillator receiving said first capacitance signal and generating a first frequency signal in response thereto.

32. The system of claim 31 further comprising a second oscillator receiving said second capacitance signal and generating a second frequency signal in response thereto;

and

a frequency subtraction device subtracting said second frequency signal from said first frequency signal and generating therefrom an overall frequency signal.

33. The system of claim 32 further comprising a linearizer receiving said overall frequency signal and generating therefrom a linearized acceleration signal.

34. The system of claim 33 further comprising an actuator adapted to activate a system component in response to said linearized acceleration signal, wherein said system component comprises a thruster or an attitude control device.

35. The system of claim 30 further comprising a support ring fixedly attached to said support structure, whereby said support structures are coupled to said support structure through said support ring.

36. A method for constructing a compensated composite structure comprising:

selecting a first material for a capacitor plate and a flexure plate disposed in parallel relation to said capacitor plate, said material comprising a first coefficient of thermal expansion;

determining a length of said capacitor plate;

selecting a second material for a support structure for said capacitor plate and said flexure plate, said second material comprising a second coefficient of thermal expansion larger than said coefficient of thermal expansion;

determining a length for said support structure larger than said length of said capacitor plate;

insulating said capacitor plate from said support structure; and

coupling said support structure to said flexure plate.

37. The method of claim 36, wherein determining said length of said capacitor plate and determining said length for said support structure further comprise determining a length of said capacitor plate and a length of said support structure such that the composite structure is insensitive to changes in temperature.

38. The method of claim 36, wherein determining said length of said capacitor plate and determining said length for said support structure further comprise determining a length of said capacitor plate and a length of said support structure such that an effective coefficient of vertical expansion of the composite structure is twice as large as a horizontal coefficient of thermal expansion thereof.

39. A method for compensating for temperature effects on a composite structure, including a support tube coupled to a flexure plate through support flexures and enclosing two capacitor plates, which are disposed parallel to the flexure plate, comprising:

selecting a material for the support tube whereby a coefficient of expansion of the support tube is larger than that of a material of the capacitor plates and the flexure plate; and

selecting lengths of the support tube and the capacitor plates such that the composite structure is insensitive to changes in temperature.

40. The method of claim 39, wherein selecting said lengths further comprises selecting lengths of said capacitor plates such that an effective coefficient of vertical expansion of said capacitor plates is twice as large as a horizontal coefficient of thermal expansion thereof.