Optical six-degree of freedom tracking apparatus and method

• US 8,487,837 B2
• Filed: 11/06/2008
• Issued: 07/16/2013
• Est. Priority Date: 11/06/2008
• Status: Active Grant

• Current Assignee: BAE Systems Information and Electronic Systems Integration Incorporated (BAE Systems Plc)
• Original Assignee: BAE Systems Information and Electronic Systems Integration Incorporated (BAE Systems Plc)
• Inventors: Alexander, William C., Gilbert, Daniel
• Primary Examiner(s): Sharifi-Tafreshi, Koosha
• Application Number:
  US12/266,347
• Publication Number:
  US 20100109976A1
• Time in Patent Office: 1,713 Days
• Field of Search: 345/156, 345/158, 345 7- 9, 359/630, 359/632, 356/138, 356/152, 356/147, 701 1- 18
• US Class Current: 345/8
• CPC Class Codes: F41G 3/225 Helmet sighting systems
• CPC Class Codes: G01S 3/784 using a mosaic of detectors
• CPC Class Codes: G01S 5/163 Determination of attitude using inertial means G01C9/00; control of attitude G05D1/49
• CPC Class Codes: G02B 2027/0187 slaved to motion of at least a part of the body of the user, e.g. head, eye
• CPC Class Codes: G02B 27/017 Head mounted

Abstract

An optical tracking system, and method therefor, tracks the movement of an object, such as a pilot'"'"'s helmet, within an enclosed area, such as a cockpit. The system/method comprises a plurality of light sources fixedly mounted in predefined locations within the enclosed area and a light sensor mounted on the object. Each light source is modulated using a different frequency from the other light sources to make that light source uniquely identifiable. Modulated light from the various light sources is converted by the sensor into an electrical signal. This composite signal is subsequently separated into individual signals based on their unique modulations, and the light source for each signal is identified. The signals are thereafter processed to determine an azimuth and an elevation for the line-of-sight to each light source. The azimuth and elevation information may then be used to determine the position and orientation of the object.

Claims

1. An optical sensor system for tracking movement of an object within an enclosed area, the optical sensor system comprising:

an optical sensor fixedly mounted on the object, the optical sensor configured to transform impinging light into an electrical signal;

an analog-to-digital converter connected to the optical sensor and configured to digitize the electrical signal from the optical sensor; and

a signal processor connected to the analog-to-digital converter and configured to determine an azimuth and an elevation of a line-of-sight from the optical sensor to a light source within the enclosed area based on the digitized signal from the analog to digital converter;

wherein the optical sensor includes a plurality of light detectors, one or more of the light detectors being oriented at an angle relative to at least one adjacent light detector; and

wherein the signal processor determines the azimuth and the elevation of the line-of-sight to the light source by separating the digitized signal into a plurality of individual signals, each one of the plurality of individual signals being identifiable according to its modulation frequency, each modulation frequency corresponding to a different light source, and normalizing all signal amplitudes corresponding to each light source.

2. The system according to claim 1, wherein the enclosed area is a fighter jet cockpit and the object is a fighter pilot'"'"'s helmet.

3. The system according to claim 1, further comprising one or more of the following:

an optical filter for preventing certain types of light from impinging the optical sensor;

a transimpedance amplifier for converting the electrical signal from the optical sensor from a current to a voltage; and

an operational amplifier for boosting a signal strength of the electrical signal from the optical sensor.

4. The system according to claim 1, wherein the optical sensor includes a plurality of light detectors, one or more of the light detectors being oriented at an angle relative to at least one adjacent light detector.

5. The system according to claim 4, wherein the plurality of light detectors includes a sufficient number of light detectors to provide the optical sensor with a substantially hemispherical overall field of view.

6. The system according to claim 4, wherein the plurality of light detectors includes from three to five light detectors.

7. A method of tracking movement of an object within an enclosed area in six degrees of freedom, the method comprising:

receiving light at an optical sensor system fixedly mounted on the object, the light being emitted from a plurality of light sources fixedly mounted at predefined locations along an interior of the enclosed area, each light source emitting light having a uniquely identifiable modulation frequency;

determining an azimuth and an elevation of a line-of-sight from the optical sensor system to each light source based on the uniquely identifiable modulation frequency of each light source,

separating the electrical signal into a plurality of individual signals, each one of the plurality of individual signals being identifiable according to its modulation frequency, each modulation frequency corresponding to a different one of the plurality of light sources; and

determining which light detector produced the largest amplitude signal for each light source and normalizing all signal amplitudes corresponding to each light source using the largest amplitude signal.

8. The method according to claim 7, wherein the enclosed area is an airplane cockpit and the object is a pilot'"'"'s helmet.

9. The method according to claim 7, wherein the optical sensor system includes a plurality of light detectors placed in close proximity to one another, each light detector converting the light from the plurality of light sources into an electrical signal.

10. The method according to claim 9, further comprising separating the electrical signal into a plurality of individual signals, each one of the plurality of individual signals being identifiable according to its modulation frequency, each modulation frequency corresponding to a different one of the plurality of light sources.

11. The method according to claim 7, further comprising translating the azimuth and the elevation of the line-of-sight for the plurality of light sources into X-axis, Y-axis, Z-axis, roll, yaw, and pitch information for the object.