Moving platform orientation tracking system

• US 9,341,697 B2
• Filed: 06/25/2012
• Issued: 05/17/2016
• 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: Mahajan, Milind, Winker, Bruce K.
• Primary Examiner(s): Ton, Tri T
• Application Number:
  US13/531,918
• Publication Number:
  US 20130342841A1
• Time in Patent Office: 1,422 Days
• Field of Search: 356/364, 356/369, 356/138, 35613903-13908, 356/614, 356/623, 250/203.1, 250/203.6, 702150-154
• US Class Current: 1/1
• 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 which is unpolarized or which has a circular polarization;

a moving platform;

a reflector mounted on said platform and arranged to reflect said beam;

a polarizer mounted in front of said reflector; and

an ellipsometric detector proximate to said transmitter, capable of detecting said reflected beam when within said reflected beam'"'"'s line-of-sight and measuring its polarization state, the polarization of said reflected beam varying with the platform'"'"'s rotational orientation;

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;

first and second detectors arranged to receive said first and second components having orthogonal polarizations from said polarizing beamsplitter, respectively, and to generate respective outputs,

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 a predefined coordinate system, with θ

approximately given by;

2. The system of claim 1, further comprising a collecting lens located between said polarizing beamsplitter and said reflected beam and arranged to concentrate said detected beam onto said detectors.

3. The system of claim 1, wherein a free space link is established between said transmitter, said moving platform, and said ellipsometric detector when said ellipsometric detector is within the line-of-sight of said reflected 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.

4. The system of claim 1, said system further comprising a detector, an array of detectors, and/or a camera arranged to receive said reflected beam.

5. The system of claim 1, wherein said reflector is a retroreflector.

6. The system of claim 4, further comprising a beamsplitter located between said transmitter and said detector, said array of detectors, and/or said camera, said system arranged with no additional optical elements between said beamsplitter and said moving platform such that said transmitted beam is directly conveyed from said beamsplitter to said moving platform and said reflected beam is directly conveyed from said beamsplitter to said detector, said array of detectors, and/or said camera detector.

7. The system of claim 6, wherein said beamsplitter located between said transmitter and said detector, said array of detectors, and/or said camera is a spatial beamsplitter.

8. The system of claim 4, 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.

9. The system of claim 4, wherein said detector, said array of detectors, and/or said camera comprise 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.

10. The system of claim 4, 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, said array of detectors, and/or said camera such that the range of said moving platform with respect to said transmitter can be determined based on said transit time.

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

a laser which produces a laser beam; and

a polarizer which circularly polarizes said laser beam.

12. 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.

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

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

transmitting a beam of electromagnetic radiation;

receiving said beam at said moving platform and encrypting the rotational orientation of said moving platform on said beam in the form of beam polarization;

reflecting said encrypted beam from said moving platform;

providing a polarizing beamsplitter;

detecting said reflected beam by using said polarizing beamsplitter to split said polarized beam into first and second components having orthogonal polarizations, the amplitudes of which vary with the polarization state of said detected beam;

generating first and second outputs,

wherein said first output D1 is proportional to cos²θ and

said second output D2 is proportional to sin²θ

, where θ

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

approximately given by;

15. The method of claim 14, further comprising:

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

16. The method of claim 15, further comprising imaging said reflected beam and determining the x and y coordinates of said moving platform based on said imaging.

17. The method of claim 14, 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.

18. The method of claim 17, 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.

21. The method of claim 14, wherein said transmitted beam is unpolarized or circularly polarized, said moving platform comprising:

a reflector; and

a polarizer mounted in front of said reflector;

said polarizer arranged to encrypt the rotational orientation of said moving platform on said beam prior to its being reflected.

22. The method of claim 14, wherein said transmitted beam is linearly polarized, said moving platform comprising:

a reflector; and

a quarter wave plate mounted in front of said reflector which rotates said linear polarized beam by 2θ

, where θ

is the rotational orientation of said moving platform with respect to a predefined coordinate system;

said quarter wave plate arranged to encrypt the rotational orientation of said moving platform on said beam prior to its being reflected.

19. A moving platform guidance system, comprising:

a transmitter which generates a pulsed beam of electromagnetic radiation which is unpolarized or which has a circular polarization;

a moving platform;

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

a polarizer mounted in front of said reflector;

a detector arranged to receive said reflected beam;

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;

an ellipsometric detector proximate to said transmitter, capable of detecting said reflected beam when within said detector'"'"'s line-of-sight and measuring its polarization state, the polarization of said reflected beam varying with the platform'"'"'s rotational orientation;

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 from said polarizing beamsplitter, respectively, and to generate respective outputs,

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 a predefined coordinate system, with 0 approximately given by;

20. The system of claim 19, wherein said reflector is a retroreflector.

23. A moving platform orientation measurement system, comprising:

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

a moving platform;

a reflector mounted on said platform and arranged to reflect said beam;

a quarter wave plate mounted in front of said reflector which rotates said linear polarized beam by 2θ

, where θ

is the rotational orientation of said moving platform with respect to a predefined coordinate system; and

an ellipsometric detector proximate to said transmitter, capable of detecting said reflected beam when within said detector'"'"'s line-of-sight and measuring its polarization state, the polarization of said reflected beam varying with the platform'"'"'s rotational orientation;

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;

first and second detectors arranged to receive said first and second components having orthogonal polarizations, respectively, and to generate respective outputs; and

circuitry which receives said detector outputs and determines said platform'"'"'s rotational orientation based on said detector outputs.

24. The system of claim 23, wherein a free space link is established between said transmitter, said 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.

25. A moving platform orientation measurement system, comprising:

a transmitter which generates a beam of electromagnetic radiation which is unpolarized or which has a circular polarization;

a moving platform;

a reflector mounted on said platform and arranged to reflect said beam;

a polarizer mounted in front of said reflector;

an ellipsometric detector proximate to said transmitter, capable of detecting said reflected beam when within said reflected beam'"'"'s line-of-sight and measuring its polarization state, the polarization of said reflected beam varying with the platform'"'"'s rotational orientation, 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;

first and second detectors arranged to receive said first and second components having orthogonal polarizations from said polarizing beamsplitter, respectively, and to generate respective outputs,

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 a predefined coordinate system, with θ

approximately given by;

26. A moving platform orientation measurement system, comprising:

a transmitter which generates a beam of electromagnetic radiation which is unpolarized or which has a circular polarization;

a moving platform;

a reflector mounted on said platform and arranged to reflect said beam;

a polarizer mounted in front of said reflector;

an ellipsometric detector proximate to said transmitter, capable of detecting said reflected beam when within said reflected beam'"'"'s line-of-sight and measuring its polarization state, the polarization of said reflected beam varying with the platform'"'"'s rotational orientation;

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, said detector outputs used to determine said platform'"'"'s rotational orientation;

a detector, an array of detectors, and/or a camera arranged to receive said reflected beam; and

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;

wherein said rangefinding detector and said detector, said array of detectors, and/or said camera are located immediately adjacent to said transmitter, said system arranged such that said transmitted beam is conveyed to said moving platform via a ‘

transmit’

aperture and said reflected beam is conveyed to said rangefinding detector and to said detector, said array of detectors, and/or said camera via first and second ‘

receive’

apertures, respectively, said transmit aperture and said first and second receive apertures being spatially distinct from each other.