Optical flow navigation system

• US 8,155,802 B1
• Filed: 07/11/2008
• Issued: 04/10/2012
• Est. Priority Date: 07/11/2008
• Status: Expired due to Fees

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Inventors: Rosenfeld, Jerome P.
• Primary Examiner(s): Nguyen, John
• Assistant Examiner(s): NG, MICHAEL L
• Application Number:
  US12/171,796
• Time in Patent Office: 1,369 Days
• Field of Search: 701/1, 701/3, 701/14, 356/139.04, 356/139.05, 348/148, 348/169, 348/36, 340/435
• US Class Current: 701/4
• CPC Class Codes: G05D 1/0858 specially adapted for vertical take-off of aircraft

Abstract

An optical navigation sensor includes four two-dimensional imagers, each aligned with an x or y axis of an orthogonal xyz coordinate system, and each defining mutually parallel vertical image directions and the same horizontal directions about a yaw axis. Translation or roll, pitch, and yaw cause image flow or movement, which can be determined by cross-correlation of successive images. Translation in the x or y direction is determined by differencing image motion in the horizontal direction, and translation in the z direction is determined by summing the image motion in the vertical direction. Pitch about x and roll about y are determined by differencing image motion in the vertical direction, and yaw about z is determined by summing the image flow in the horizontal direction.

Claims

1. A method for determining the state of a vehicle in terms of location and attitude relative to an external coordinate system defining first, second, and third mutually orthogonal coordinate axes, said method comprising the steps of:

providing first and second two-dimensional imagers having their field of view (a) mutually aligned with said first external coordinate axis, and (b) oppositely directed relative to said first external coordinate axis, said first and second imagers each defining a positive first imager direction parallel with said third external coordinate axis, and a positive second imager direction mutually pointing in the same direction about said third coordinate axis;

providing third and fourth two-dimensional imagers having their fields of view (a) mutually aligned with said second external coordinate axis, and (b) oppositely directed relative to said second external coordinate axis, said third and fourth imagers each defining a positive first imager direction parallel with said third external coordinate axis, and a positive second imager direction mutually pointing in the same direction about said third coordinate axis;

operating said first, second, third and fourth imagers during flight of said vehicle, to thereby produce a time sequence of images from said first, second, third and fourth imagers;

for each imager direction of each or said first, second, third and fourth imagers, cross-correlating a time-sequence of the images to thereby generate average angular change of features in the images for each of said first and second imager directions;

summing the angular change of said first imager in said second imager direction with the angular change of said second imager in said second imager direction to thereby determine angular change relative to a point on said second coordinate axis of said coordinate system;

summing the angular change of said third imager in said second imager direction with the angular change of said fourth imager in said second imager direction to thereby determine angular change relative to a point on said first coordinate axis of said coordinate system;

summing the angular changes of said first, second, third and fourth imagers in said first imager direction, to thereby determine angular change along relative to a point on said third coordinate axis of said coordinate system;

summing said angular change of said first imager in said first imager direction with said angular change of said second imager in said first imager direction to thereby determine pitch change about said second coordinate axis;

summing said angular change of said third imager in said first imager direction with said angular change of said fourth imager in said first imager direction to thereby determine roll change about a first coordinate axis; and

summing said angular change of said first, second, third and fourth imagers in said second imager direction to thereby determine yaw change about said third coordinate axis; and

operating an automatic control device using at least one of said angular change, said pitch change, said roll change and said yaw change, to maintain a desired state of said vehicle.

2. A method according to claim 1, wherein, in said steps of (a) summing to thereby determine angular change relative to a point on said second coordinate axis of said coordinate system and (b) summing to thereby determine angular change relative to a point on said first coordinate axis of said coordinate system each include the step of taking a difference.

3. A method according to claim 1, wherein said step of (a) summing said angular change to thereby determine pitch change and (b) summing said angular change to thereby determine roll change each include a subtraction.

4. A method for controlling the state of a vehicle in terms of location and attitude relative to a coordinate system defining first, second and third mutually orthogonal coordinate axes, said method comprising the steps of:

providing a vehicle body including propulsion system actuators and an automatic control device for receiving changes in the position and attitude of the vehicle body;

providing first and second two-dimensional imagers having their fields of view (a) mutually aligned with said first external coordinate axis, and (b) oppositely directed relative to said first external coordinate axis, said first and second imagers each defining a positive first imager direction parallel with said third external coordinate axis, and a positive second imager direction mutually pointing in the same direction about said third coordinate axis;

providing third and fourth two-dimensional imagers having their fields of view (a) mutually aligned with said second external coordinate axis, and (b) oppositely directed relative to said second external coordinate axis, said third and fourth imagers each defining a positive first imager direction parallel with said third external coordinate axis, and a positive second imager direction mutually pointing in the same direction about said third coordinate axis;

operating said first, second, third and fourth imagers during flight of said vehicle, to thereby produce a time sequence of images from said first, second, third and fourth imagers;

for each imager direction of each of said first, second, third and fourth imagers, correlating a time-sequence of the images to thereby generate average angular change of features in the images for each of said first and second imager directions;

summing the angular change of said first imager in said second imager direction with the angular change of said second imager in said second imager direction to thereby determine angular change relative to a point on said second coordinate axis of said coordinate system;

summing the angular change of said third imager in said second imager direction with the angular change of said fourth imager in said second imager direction to thereby determine angular change relative to a point on said first coordinate axis of said coordinate system;

summing the angular changes of said first, second, third and fourth imagers in said first imager direction, to thereby determine angular change relative to a point on a said third coordinate axis of said coordinate system;

summing said angular change of said first imager in said first imager direction with said angular change of said second imager is said first imager direction to thereby determine pitch change about said second coordinate axis;

summing said angular change of said third imager in said first imager direction with said angular change of said fourth imager in said first imager direction to thereby determine roll change about said first coordinate axis; and

summing said angular change of said first, second, third and fourth imagers in said second imager direction to thereby determine yaw change about said third coordinate axis; and

coupling to said automatic control device said angular change along said second coordinate axis of said coordinate system, angular change along said first coordinate axis of said coordinate system;

angular change along said third coordinate axis of said coordinate system;

pitch change about said second coordinate axis;

roll change about said first coordinate axis; and

yaw change about said third coordinate axis; and

operating said automatic control device to maintain a given state.

5. A method for determining the state of a vehicle, said method comprising the steps of:

defining a coordinate system having mutually orthogonal first, a second and a third coordinate axes;

providing first, second, third and fourth imagers, each of said imagers having a view of view aligned relative to a corresponding coordinate axis;

operating said first, second, third and fourth imagers during flight of said vehicle to produce a time sequence of images from said first, second, third and fourth imagers;

for each of said first, second, third and fourth imagers, cross-correlating the time-sequence of the images to generate an angular change of features in images;

summing said angular change of said first imager in one of said imager directions with said angular change of said second imager in said one of said imager directions to determine angular change relative to a point on said first coordinate axis of said coordinate system;

summing an angular change of said third imager in said one of said imager directions with an angular change of said fourth imager in said one of said imager directions to determine angular change relative to a point on said second coordinate axis of said coordinate system;

summing said angular changes of said first, second, third and fourth imagers in another of said imager directions, to determine an angular change relative to a point on said third coordinate axis of said coordinate system;

summing said angular change of said first imager in said another imager direction with said angular change of said second imager in said another imager direction to determine a pitch change about said second coordinate axis;

summing said angular change of said third imager in said one of said imager directions with said angular change of said fourth imager in said one of said imager directions to thereby determine roll change about said first coordinate axis;

summing said angular change of said first, second, third and fourth imagers in said another imager direction to determine yaw change about a third coordinate axis; and

operating an automatic control device using at least one of said angular change, said pitch change, said roll change and said yaw change to control propulsion system actuators associated with said vehicle.

6. A method for determining the state of a vehicle according to claim 5, wherein the coordinate system has an x-axis, a y-axis, and a z-axis,

wherein the first coordinate axis is parallel with the x-axis, the second coordinate axis is parallel with the y-axis, and the third coordinate axis is parallel with the z-axis;

wherein each of the first, second, third and fourth imagers has an image plane, each of the image planes comprising a vertical image plane direction (V-direction) and a horizontal image plane direction (H-direction);

wherein the V-directions of the first, second, third and fourth imagers are oriented in the +z-axis direction; and

wherein the H-direction of the first imager is oriented in the −

x-axis direction, the H-direction of the second imager is oriented in the +x-axis direction, the H-direction of the third imager is oriented in the +y-axis direction, and the H-direction of the fourth imager is oriented in the −

y-axis direction.

7. A method for determining the state of a vehicle according to claim 6, wherein the step of summing an angular change of said first imagers in one of said imager directions with an angular change of said second imager in another of said imager directions comprises summing the H-direction angular change from the first imager with an inverse of the H-direction angular change from the second imager.

8. A method for determining the state of a vehicle according to claim 6, wherein the step of summing an angular change of said third imager in said one of said imager directions with an angular change of said fourth imager in said one of said imager directions comprises summing the H-direction angular change from the third imager with an inverse of the H-direction angular change from the fourth imager.

9. A method for determining the state of a vehicle according to claim 6, wherein the step of summing said angular changes of said first, second, third and fourth imagers in another of said imager directions comprises summing the inverses of the V-direction angular changes from the first, second, third and fourth imagers.

10. A method for determining the state of a vehicle according to claim 6, wherein the step of summing said angular change of said first imager in said another imager direction with said angular change of said second imager in said another imager direction comprises summing the V-direction angular change from the first imager with an inverse of the V-direction angular change from the second imager.

11. A method for determining the state of a vehicle according to claim 6, wherein the step of summing said angular change of said third imager in said one of said imager directions with said angular change of said fourth imager in said one of said imager directions comprises summing the V-direction angular change from the fourth imager with an inverse of the V-direction angular change from the third imager.

12. A method for determining the state of a vehicle according to claim 6, wherein the step of summing the angular change of said first, second, third and fourth imagers in said another imager direction comprises summing the H-direction angular changes from the first, second, third and fourth imagers.

13. A system for determining the state of a vehicle, said system comprising

first, second, third and fourth imagers, each of said imagers having a field of view, and each of said imagers having an imager direction;

a processor executing instructions for performing the steps of;

operating said first, second, third and fourth imagers during flight of said vehicle to produce a time sequence of images from said first, second, third and fourth imagers;

for each imager direction of each of said first, second, third and fourth imagers, cross-correlating the time-sequence of the images to generate an angular change of features in images;

defining a coordinate system having mutually orthogonal first, a second and a third axes;

summing said angular change of said first imager in one of said imager directions with said angular change of said second imager in said one of said imager directions to determine angular change relative to a point on said first coordinate axis of said coordinate system;

summing an angular change of said third imager in said one of said imager directions with an angular change of said fourth imager in said one of said imager directions to determine angular change relative to a point on said second coordinate axis of said coordinate system;

summing said angular changes of said first, second, third and fourth imagers in another of said imager directions, to determine an angular change relative to a point on said third coordinate axis of said coordinate system;

summing said angular change of said first imager in said another imager direction with said angular change of said second imager in said another imager direction to determine a pitch change about said second coordinate axis;

summing said angular change of said third imager in said one of said imager directions with said angular change of said fourth imager in said one of said imager directions to thereby determine roll change about said first coordinate axis;

summing said angular change of said first, second, third and fourth imagers in said another imager direction to determine yaw change about a third coordinate axis; and

operating an automatic control device using at least one of said angular change, said pitch change, said roll change and said yaw change to control propulsion system actuators associated with said vehicle.

14. A system for determining the state of a vehicle according to claim 13, wherein the coordinate system has an x-axis, a y-axis and a z-axis,

wherein the first coordinate axis is parallel with the x-axis, the second coordinate axis is parallel with the y-axis, and the third coordinate axis is parallel with the z-axis;

wherein each of the first, second, third and fourth imagers has an image plane, each of the image planes comprising a vertical image plane direction (V-direction) and a horizontal image plane direction (H-direction);

wherein the V-directions of the first, second, third and fourth imagers are oriented in the +z-axis direction; and

wherein the H-direction of the first imager is oriented in the −

x-axis direction, the H-direction of the second imager is oriented in the +x-axis direction, the H-direction of the third imager is oriented in the +y-axis direction, and the H-direction of the fourth imager is oriented in the −

y-axis direction.

15. A system for determining the state of a vehicle according to claim 14, wherein the step of summing an angular change of said first imagers in one of said imager directions with an angular change of said second imager in another of said imager directions comprises summing the H-direction angular change from the first imager with an inverse of the H-direction angular change from the second imager.

16. A system for determining the state of a vehicle according to claim 14, wherein the step of summing an angular change of said third imager in said one of said imager directions with an angular change of said fourth imager in said one of said imager directions comprises summing the H-direction angular change from the third imager with an inverse of the H-direction angular change from the fourth imager.

17. A system for determining the state of a vehicle according to claim 14, wherein the step of summing said angular changes of said first, second, third and fourth imagers in another of said imager directions comprises summing the inverses of the V-direction angular changes from the first, second, third and fourth imagers.

18. A system for determining the state of a vehicle according to claim 14, wherein the step of summing said angular change of said first imager in said another imager direction with said angular change of said second imager in said another imager direction comprises summing the V-direction angular change from the first imager with an inverse of the V-direction angular change from the second imager.

19. A system for determining the state of a vehicle according to claim 14, wherein the step of summing said angular change of said third imager in said one of said imager directions with said angular change of said fourth imager in said one of said imager directions comprises summing the V-direction angular change from the fourth imager with an inverse of the V-direction angular change from the third imager.

20. A system for determining the state of a vehicle according to claim 14, wherein the step of summing the angular change of said first, second, third and fourth imagers in said another imager direction comprises summing the H-direction angular changes from the first, second, third and fourth imagers.