Magnetic heading reference

• US 4,418,480 A
• Filed: 04/09/1982
• Issued: 12/06/1983
• Est. Priority Date: 04/09/1982
• Status: Expired due to Fees

• Current Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Original Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Inventors: Garner, H. Douglas
• Primary Examiner(s): Stearns, Richard R.
• Application Number:
  US06/367,187
• Time in Patent Office: 606 Days
• Field of Search: 33/349, 33/356, 33/361, 33/DIG. 3, 318/647
• US Class Current: 33/349
• CPC Class Codes: G01C 17/30 Earth-inductor compasses
• CPC Class Codes: G01R 33/0206 Three-component magnetometers
• CPC Class Codes: Y10S 33/03 Photoelectric

Abstract

Devices for vectorially summing two signals. In a first embodiment (FIG. 3) the vectorial summation is implemented by a mechanical sin/cos mechanism in which a crank 22 drives two linear potentiometers 27 and 29, 90° out of phase. In a second embodiment (FIG. 6) a polarized light resolver generates the sin and cos functions. In a third embodiment (FIG. 8) a printed circuit resolver generates the sin and cos functions.

Claims

1. A device for generating a signal indicative of the difference between the actual heading and the selected heading of a vehicle comprising:

first and second magnetometers mounted on the vehicle in a horizontal plane during normal movement of the vehicle and with the sensing elements of the magnetometers at an angle with each other;

first demodulating means for demodulating the output of said first magnetometer;

first inverter means for inverting the output of said first demodulating means;

second demodulating means for demodulating the output of said second magnetometer;

second inverter means for inverting the output of said second demodulating means;

a dial calibrated in the points of a compass for selecting the heading of the vehicle;

means receiving the outputs of said first demodulating means and said first inverter means and under the control of said dial for generating a sin signal proportional to the output of said first demodulating means times the sin of the angle through which said dial is rotated;

means receiving the outputs of said second demodulating means and said second inverter means and under the control of said dial for generating a cos signal proportional to the output of said second demodulating means times the cos of the angle through which said dial is rotated; and

means for summing said sin signal and said cos signal to produce said signal indicative of the difference between the actual heading and the selected heading of the vehicle.

2. A device according to claim 1 wherein the sensing element of said first magnetometer is mounted perpendicular to the roll axis of said vehicle and the sensing of said second magnetometer element is mounted perpendicular to the sensing element of the first magnetometer.

3. A device according to claim 1 wherein a northerly turning error compensation signal is added to the output of said first demodulating means.

4. A device according to claim 1 wherein said means for generating said sin signal comprises:

a first linear potentiometer with one end of the potentiometer connected to receive the output from said first demodulating means and with its other end connected to receive the output from said first inverter means;

a first shaft attached to be rotated with said dial;

a second shaft;

a crank means attached to said first and second shafts such that the second shaft is parallel to, offset from and revolves around the centerline extended of said first shaft as the first shaft rotates; and

means for attaching the slider arm of said first linear potentiometer to said second shaft to be controlled by the movement of said second shaft whereby the potential at the slider of said first linear potentiometer is said sin signal.

5. A device according to claim 4 wherein said means for generating said cos signal comprises:

a second linear potentiometer with one end of the potentiometer connected to receive the output from said second demodulating means and with its other end connected to receive the output from said second inverter means; and

means for attaching the slider arm of said second linear potentiometer to said second shaft to be controlled by the movement of said second shaft wherein the slider arms of the first and second potentiometers are perpendicular to each other whereby the potential at the slider of said second linear potentiometer is said cos signal.

6. A device according to claim 1 wherein said means for generating said sin signal comprises:

first and second photocells connected in series with one side of the resulting series circuit connected to the output of said first demodulating means and with the other side of the series circuit connected to the output of said first inverter means;

a first sheet of linearly polarized material covering said first photocell;

a second sheet of linearly polarized material covering said second photocell such that its axis of polarization is perpendicular to the axis of polarization of said first sheet;

a light source for illuminating said first and second sheets;

a third sheet of linearly polarized material located between said light source and said first and second sheets; and

means for rotating said third sheet through an angle proportional to the angle through which said dial is rotated whereby the signal at the junction of said first and second photocells is said sin signal.

7. A device according to claim 6 wherein said means for generating said cos signal comprises:

third and fourth photocells connected in series with one side of the resulting series circuit connected to the output of said second demodulating means and with the other side of the series circuit connected to the output of said second inverter means;

said third and fourth photocells being in the path of said light source with said third sheet being between said light source and said third and fourth photocells;

a fourth sheet of linearly polarized material covering said third photocell such that its axis of polarization makes a 45°

angle with the axes of polarization of said first and second sheets; and

a fifth sheet of linearly polarized material covering said fourth photocell such that its axis of polarization is perpendicular to the axis of polarization of said fourth sheet whereby the signal at the junction of said third and fourth photocells is said cos signal.

8. A device according to claim 1 wherein said means for generating said sin signal comprises:

means for modulating the outputs of said first and second demodulating means before the outputs of the demodulating means are utilized;

a first printed circuit board with first and second elongated condenser plates etched thereon end to end in a straight line and electrically isolated from each other;

said first condenser plate connected to receive the output of said first demodulating means after it has been modulated and said second condenser plate connected to receive the output of said first inverter means;

a second printed circuit board with a condenser plate etched thereon;

a first sheet of dielectric material, a grounded metallic shield and a second sheet of dielectric material sandwiched between said first and second printed circuit boards;

shaft means attached to said dial and to said metallic shield for rotating the shield about a non-center point on the shield as said dial is rotated whereby the signal on said condenser plate on said second printed circuit board is said sin signal.

9. A device according to claim 8 wherein said means for generating said cos signal and for summing said sin signal and said cos signal comprises:

third and fourth elongated condenser plates etched on said first printed circuit board end to end in a straight line perpendicular to and crossing the line of said first and second condenser plates and electrically isolated from each other and from said first and second condenser plates;

said third condenser plate connected to receive the output of said second demodulating means after it has been modulated and said fourth condenser plate connected to receive the output of said second inverter means whereby the signal on said condenser plate on said second printed circuit board is the sum of said sin signal and said cos signal.

10. A device according to claim 9 wherein said condenser plate on said second printed circuit board is in the shape of a cruciform to correspond to the combined shape of the first, second, third and fourth condenser plates on said first printed circuit board.

11. In a device for generating a signal indicative of the difference between the actual heading and the selected heading of a vehicle in which two magnetometers are mounted on the vehicle in a horizontal plane during normal movement of the vehicle with the sensing elements of the magnetometers at an angle with each other and means for demodulating the outputs of the two magnetometers, a device for vectorially summing the two demodulated signals to produce a resultant signal that is a function of the error in the heading of the vehicle comprising:

inverter means for inverting the two signals from said demodulating means;

a first linear potentiometer with one end of the potentiometer connected to receive a demodulated signal and with its other end connected to receive the corresponding inverted signal;

a second linear potentiometer with one end of the potentiometer connected to receive the other demodulated signal and with its other end connected to receive the corresponding inverted signal;

a dial;

a first shaft attached to be rotated with said dial;

a second shaft;

a crank means attached to said first and second shafts such that the second shaft is parallel to, offset from and revolves around the centerline extended of said first shaft as the first shaft rotates;

means for attaching the slider arm of said first linear potentiometer to said second shaft to be controlled by the movement of said second shaft;

means for attaching the slider arm of said second linear potentiometer to said second shaft to be controlled by the movement of said second shaft wherein the slider arms of said first and second potentiometers are perpendicular to each other; and

means for summing the signals at the sliders of said first and said second potentiometers.

12. A device for generating a signal indicative of the difference between the actual heading and the selected heading of a vehicle comprising:

first and second magnetometers mounted on the vehicle in a horizontal plane during normal movement of the vehicle and with the sensing elements of the magnetometers at an angle with each other;

first inverter means for inverting the output of said first magnetometer;

second inverter means for inverting the output of said second magnetometer;

a dial calibrated in the points of a compass for selecting the heading of the vehicle;

means receiving the outputs of said first magnetometer and said first inverter means and under the control of said dial for generating a sin signal proportional to the output of said first magnetometer times the sin of the angle through which said dial is rotated;

wherein said means for generating a sin signal comprises;

a first printed circuit board with first and second elongated condenser plates etched thereon end to end in a straight line and electrically isolated from each other;

said first condenser plate connected to receive the output of said first magnetometer and said second condenser plate connected to receive the output of said first inverter means, a second printed circuit board wth a condenser plate etched thereon, a first sheet of dielectric material, a grounded metallic shield and a second sheet of dielectric material sandwiched between said first and second printed circuit boards, and shaft means attached to said dial and to said metallic shield for rotating the shield about a non-center point on the shield as said dial is rotated whereby the signal on said condenser plate on said second printed circuit board is said sin signal;

means receiving the outputs of said second magnetometer and said second inverter means and under the control of said dial for generating a cos signal proportional to the outpt of said second magnetometer times the cos of the angle through which said dial is rotated; and

means for summing said sin signal and said cos signal to produce said signal indicative of the difference between the actual heading and the selected heading of the vehicle.

13. In a device for generating a signal indicative of the difference between the actual heading and the selected heading of a vehicle in which two magnetometers are mounted on the vehicle in a horizontal plane during normal movement of the vehicle with the sensing elements of the magnetometers at an angle with each other and means for demodulating the outputs of the two magnetometers, means including a polarized light resolver with a dial for vectorally summing the two demodulated signals to produce a resultant signal that is a function of the error in heading of the vehicle comprising:

a first polarized light resolver means including said polarized light resolver receiving one of said demodulated signals for generating a sin function signal proportional to said one of said demodulated signals times the sin of the angle through which said dial is rotated;

a second polarized light resolver means including said polarized light resolver receiving the other of said demodulated signals for generating a cos function signal proportional to said other of said demodulated signals times the cos of the angle through which said dial is rotated; and

means for summing said sin and cos function signals to produce said resultant signal.

14. In a device as in claim 13 wherein one of said sensing elements is mounted perpendicular to the roll axis of said vehicle and the other of said sensing elements is mounted perpendicular to said one of said sensing elements.

15. In a device as in claim 13 wherein each of said first and second polarized resolver means comprises:

first and second photoresistive elements connected in series with the corresponding demodulated signal connected to an end of the resulting series circuit;

means for inverting the corresponding demodulated signal and connecting it to the other end of said series circuit;

a light source for illuminating said first and second photoresistive elements;

a first sheet of linearly polarized filter material covering said first photoresistive element;

a second sheet of linearly polarized filter material, with an axis of polarization perpendicular to the axis of polarization of said first sheet, covering said second photoresistive element;

a third sheet of linearly polarized filter material located between and light source and said first and second sheets of linearly polarized filter material; and

means for rotating said third sheet of linearly polarized material to select the heading of said vehicle.

16. In a device as in claim 15 wherein the first and second sheets of linearly polarized filter material in said first polarized light resolver have axes of polarization that make 45°

angles with the axes of polarization of said first and second sheets in said second polarized light resolver.

17. In a device as in claim 16 wherein said third sheet of linearly polarized filter material for said first and second polarized light resolver means is a single sheet which serves as the said third sheet for both resolver means.

18. In a device as in claim 17 including means for rotating said single sheet to select the heading of said vehicle comprising a dial calibrated in the points of a compass, and shaft means including a 2:

1 gear ratio connected between said dial and said single sheet for rotating said single sheet.

19. In a device as in claim 17 including means for summing the two voltage at the junctions of said first and second photoresistive elements for both said first and second polarized light resolver means.

20. In a device for generating a signal indicative of the difference between the actual heading and the selected heading of a vehicle in which two magnetometers are mounted on the vehicle in a horizontal plane during normal movement of the vehicle with the sensing elements of the magnetometers at an angle with each other, a device for vectorially summing the two magnetometer signals to produce a resultant signal that is a function of the error in heading of the vehicle comprising:

a first printed circuit board with four elongated condenser plates etched thereon in the shape of a cruciform and electrically isolated from each other;

a second printed circuit board with a condenser plate etched thereon in the shape of a cruciform;

a first sheet of dielectric material, a grounded metallic shield and a second sheet of dielectric material sandwiched between said first and second printed circuit boards;

a dial; and

shaft means attached to said dial and to said metallic shield for rotating the shield about a non-center point on said shield as said dial is rotated whereby the signal on the condenser plate on said second printed circuit board is said resultant signal.