MOVING PLATFORM ORIENTATION TRACKING SYSTEM

• US 20130342841A1
• Filed: 06/25/2012
• Published: 12/26/2013
• Est. Priority Date: 06/25/2012
• Status: Active Grant

• Current Assignee: Teledyne Scientific & Imaging, LLC (Teledyne Technologies Incorporated)
• Original Assignee: Teledyne Scientific & Imaging, LLC (Teledyne Technologies Incorporated)
• Inventors: Winker, Bruce K., MAHAJAN, MILIND
• Granted Patent: US 9,341,697 B2
• Time in Patent Office: Days
• US Class Current: 356/369
• CPC Class Codes: G01S 17/42 Simultaneous measurement of distance and other co-ordinates indirect measurement G01S17/46
• CPC Class Codes: G01S 17/74 Systems using reradiation of electromagnetic waves other than radio waves, e.g. IFF, i.e. identification of friend or foe
• CPC Class Codes: G01S 3/783 using amplitude comparison of signals derived from static detectors or detector systems
• CPC Class Codes: G01S 7/499 using polarisation effects

Abstract

An orientation tracking system for a moving platform includes a transmitter which generates an beam having a known polarization with respect to a predefined coordinate system. The moving platform includes an ellipsometric detector capable of detecting the polarized beam when within the line-of-sight of the transmitter, and measuring its polarization state. The polarization state indicates the rotational orientation of the moving platform with respect to the predefined coordinate system. The beam could also be used to convey guidance commands to the platform.

Claims

1. A moving platform orientation measurement system, comprising:

a transmitter which generates a beam of electromagnetic radiation having a known polarization with respect to a predefined coordinate system; and

a moving platform, said platform comprising an ellipsometric detector capable of detecting said polarized beam when within the line-of-sight of said transmitter and measuring its polarization state;

such that said polarization state indicates the rotational orientation of said moving platform with respect to said predefined coordinate system.

2. The system of claim 1, wherein said beam of electromagnetic radiation is a linearly polarized laser beam.

3. The system of claim 1, wherein said polarized beam has a polarization extinction ratio of >

2;

1.

4. The system of claim 1, wherein said ellipsometric detector comprises:

a polarizing beamsplitter which splits a detected polarized beam into first and second components having orthogonal polarizations, the amplitudes of which vary with the polarization state of said detected beam; and

first and second detectors arranged to receive said first and second components having orthogonal polarizations, respectively, and to generate respective outputs that vary with the intensities of their received components.

5. The system of claim 4, wherein the output D1 of said first detector is proportional to cos²θ

and the output D2 of said second detector is proportional to sin²θ

, where θ

is the rotational orientation of said moving platform with respect to said predefined coordinate system, with θ

given by;

6. The system of claim 4, further comprising a collecting lens located between said polarizing beamsplitter and said transmitter and arranged to concentrate said detected beam onto said detectors.

7. The system of claim 1, wherein a free space link is established between said transmitter and said ellipsometric detector when said ellipsometric detector is within the line-of-sight of said polarized beam,

further comprising a phase-locked-loop (PLL) circuit coupled to said ellipsometric detector and arranged to track said rotational orientation and thereby mitigate the degradation in the accuracy of said rotational orientation determination that might otherwise occur when said optical link is disrupted.

8. The system of claim 1, wherein said moving platform further comprises a reflector arranged to reflect said polarized beam, said system further comprising a detector, an array of detectors, and/or a camera arranged to receive said reflected beam.

9. The system of claim 8, wherein said reflector is a retroreflector.

10. The system of claim 8, further comprising a beamsplitter located between said transmitter and said detector, said array of detectors, and/or said camera and arranged to allow the transmitter and said detector, said array of detectors, and/or said camera detector to share the same optical aperture.

11. The system of claim 10, wherein said beamsplitter located between said transmitter and said detector, said array of detectors, and/or said camera is a spatial beamsplitter.

12. The system of claim 8, further comprising a rangefinding detector, said system arranged such that data from said rangefinding detector is used to determine the range (z coordinate) of said moving platform.

13. The system of claim 8, further comprising an array of detectors or a camera, said system arranged such that data from said array of detectors or said camera is used to determine the x and y coordinates of said moving platform.

14. The system of claim 8, wherein said beam is pulsed, further comprising a means of timing the transit time of said pulses from said transmitter to said moving platform and back to said detector such that the range of said moving platform with respect to said transmitter can be determined based on said transit time.

15. The system of claim 1, wherein said transmitter comprises:

a laser which produces a laser beam; and

a polarizer which linearly polarizes said laser beam.

16. The system of claim 1, wherein said transmitter is arranged to encode guidance commands into said beam by pulsing said beam, said moving platform arranged to detect and decode said pulses and thereby detect said guidance commands.

17. The system of claim 1, wherein said moving platform is arranged to receive guidance commands via said polarized beam and to vary its trajectory in response to said guidance commands.

18. A moving platform orientation measurement system, comprising:

a transmitter which generates a beam of electromagnetic radiation having a known polarization with respect to a predefined coordinate system;

a moving platform which includes a reflector arranged to reflect said polarized beam;

an ellipsometric detector capable of detecting said reflected polarized beam when within the line-of-sight of said platform and measuring its polarization state;

such that said polarization state indicates the rotational orientation of said moving platform with respect to said predefined coordinate system.

19. The system of claim 18, wherein a free space link is established between said transmitter, said optical reflector and said ellipsometric detector when said ellipsometric detector is within the line-of-sight of said reflected polarized beam,

further comprising a phase-locked-loop (PLL) circuit coupled to said ellipsometric detector and arranged to track said rotational orientation and thereby mitigate the degradation in the accuracy of said rotational orientation determination that might otherwise occur when said link is disrupted.

20. The system of claim 18, wherein said reflector is a retroreflector.

21. The system of claim 18, wherein said transmitter is arranged to encode guidance commands into said beam by pulsing said beam, said moving platform arranged to detect and decode said pulses and thereby detect said guidance commands.

22. A method of guiding a moving platform, comprising:

transmitting a beam of electromagnetic radiation;

polarizing said beam with a known polarization with respect to a predefined coordinate system;

detecting the polarization state of said polarized beam at said platform when said platform is within the line-of-sight of said transmitted beam; and

determining the rotational orientation of said moving platform with respect to said predefined coordinate system based on said detected polarization state.

23. The method of claim 22, further comprising:

reflecting said polarized beam from moving platform;

receiving said reflected beam; and

determining the range of said moving platform based on the transit time of said transmitted and reflected beam.

24. The method of claim 23, further comprising imaging said reflected beam and determining the x and y coordinates of said moving platform based on said imaging.

25. The method of claim 22, further comprising:

pulsing said transmitted beam;

determining the range of said moving platform by measuring the transit time of said pulses to and from said moving platform

26. The method of claim 25, further comprising:

encoding guidance commands into said beam by pulsing said beam; and

detecting and decoding said pulses at said moving platform and thereby detect said guidance commands.

27. A method of guiding a moving platform, comprising:

transmitting a beam of electromagnetic radiation;

polarizing said beam with a known polarization with respect to a predefined coordinate system;

reflecting said polarized beam from a moving platform;

detecting the polarization state of said reflected polarized beam; and

determining the rotational orientation of said moving platform with respect to said predefined coordinate system based on said detected polarization state.

28. A moving platform guidance system, comprising:

a transmitter which generates a pulsed beam of electromagnetic radiation having a known polarization with respect to a predefined coordinate system;

a moving platform, said platform comprising an ellipsometric detector capable of detecting said polarized pulsed beam when within the line-of-sight of said transmitter and measuring its polarization state;

such that said polarization state indicates the rotational orientation of said moving platform with respect to said predefined coordinate system;

a reflector on said moving platform arranged to reflect said polarized pulsed beam;

a detector arranged to receive said reflected beam; and

a means of timing the transit time of said pulses from said transmitter to said moving platform and back to said detector such that the range of said moving platform with respect to said transmitter can be determined based on said transit time;

a camera arranged to receive the reflected beam to determine the x, y coordinates of said moving platform;

said system arranged to encode guidance commands into said polarized pulsed beam,

said moving platform arranged to detect and decode said pulses and thereby detect said guidance commands and to vary its trajectory in response to said guidance commands.

29. The system of claim 28, wherein said reflector is a retroreflector.