Moving platform orientation tracking system

Patent metadata

Field	Value
Publication number	US-9341697-B2
Application number	US-201213531918-A
Country	US
Kind code	B2
Filing date	Jun 25, 2012
Priority date	Jun 25, 2012
Publication date	May 17, 2016
Grant date	May 17, 2016

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.

First claim

We claim:

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 D 1 of said first detector is proportional to cos 2 θ and the output D 2 of said second detector is proportional to sin 2 θ, where θ is the rotational orientation of said moving platform with respect to a predefined coordinate system, with θ approximately given by:

θ
=

cos

-
1

⁢

D
⁢

⁢
1

D
⁢

⁢
1

+

D
⁢

⁢
2

,

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

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 D 1 is proportional to cos 2 θ and said second output D 2 is proportional to sin 2 θ, where θ is the rotational orientation of said moving platform with respect to a predefined coordinate system, with θ approximately given by:

θ
=

cos

-
1

⁢

D
⁢

⁢
1

D
⁢

⁢
1

Assignees

• Mahajan Milind
• Winker Bruce K
• Teledyne Scient & Imaging Llc

Inventors

• Mahajan Milind
• Winker Bruce K

Classifications

• G01S17/74

  Systems using reradiation of electromagnetic waves other than radio waves, e.g. IFF, i.e. identification of friend or foe · CPC title

• G01S3/783

  using amplitude comparison of signals derived from static detectors or detector systems · CPC title

• G01S17/42 Primary

  Simultaneous measurement of distance and other co-ordinates (indirect measurement G01S17/46) · CPC title

• G01S7/499 Primary

  using polarisation effects · CPC title

• G01S1/70 Primary

  using electromagnetic waves other than radio waves · CPC title