Doppler rotational velocity sensor

• US 6,621,561 B2
• Filed: 09/20/2001
• Issued: 09/16/2003
• Est. Priority Date: 09/22/2000
• Status: Active Grant

• Current Assignee: Virginia Tech Intellectual Properties, Inc.
• Original Assignee: Virginia Tech Intellectual Properties, Inc.
• Inventors: Holton, Carvel E.
• Primary Examiner(s): Buczinski, Stephen C.
• Application Number:
  US09/957,381
• Publication Number:
  US 20020075475A1
• Time in Patent Office: 726 Days
• Field of Search: 356/28, 356/28.5
• US Class Current: 356/28.5
• CPC Class Codes: G01P 3/366 by using diffraction of light for measuring speed of fluids G01P5/26
• CPC Class Codes: G01P 3/44 for measuring angular speed G01P3/56 takes precedence
• CPC Class Codes: G01S 17/58 Velocity or trajectory determination systems; Sense-of-movement determination systems
• CPC Class Codes: G01S 17/88 Lidar systems specially adapted for specific applications
• CPC Class Codes: G01S 7/4818 using optical fibres

Abstract

The disclosed invention concept utilizes a homodyne/heterodyne interferometer technique in a modified lidar in such a manner as to sense the rotational velocity magnitude and sense of a rotating (or “spinning”) object. Sensing is accomplished in assessing either the Doppler bandwidth of a single axis system or in sensing the frequency separation of Doppler spectrums in a “two” axis system. The technique is unique in that the Doppler bandwidth is linearly proportional to rotational velocity and independent of intercept position in the rotation plane. The technique as disclosed is based on optical fiber lidar techniques, but can be implemented in free-space optics as well. The disclosed invention therefore comprises both a technique for utilization of an optical fiber lidar and a new arrangement of lidar elements. Compact and cost effective, standoff rotation velocity sensors and systems can be fabricated with this technique.

Claims

1. A method of determining a rotational velocity of an object, the method comprising:

directing at least one beam of light at the object creating thereby an illumination area on a surface of the object;

sensing at least one beam of light reflected or backscattered from the object;

determining a Doppler spectral bandwidth of the sensed beam of light reflected or backscattered from the object;

determining a width of the illumination area;

determining an angle at which the at least one beam of light directed at the object intercepts the rotating object; and

calculating the rotational velocity of the object based upon the equation;

2. The method as set forth in claim 1 wherein the Doppler bandwidth or separation frequencies are rotationally and positionally invariant after the angle at which the beam of light directed at the object intercepts the surface of the rotating object is fixed.

3. A Doppler rotational velocity sensor system comprising:

a light source generating an optical signal at a prescribed wavelength;

a signal multiplexing device receptive of the optical signal from the light source and operative thereby to provide as output a beam of light directed to a diffusely reflecting target at a prescribed angular orientation and further operative thereby to accept as input thereto Doppler shifted radiation reflected or backscattered from the target;

wherein the beam of light subtends a prescribed width of an intersecting illumination area on the surface of the target; and

a detector receptive of the Doppler shifted radiation and a Fresnel reflection of the beam of light and operative thereby to provide as output a signal indicative of the rotational velocity of the target.

4. The sensor system as set forth in claim 3 further comprising:

a signal amplifier receptive of the signal indicative of the rotational velocity of the target and operative thereby to provide as output an amplified rotational velocity signal; and

a spectral processor receptive of the amplified rotational velocity signal and operative thereby to provide as output a signal indicative of the Doppler velocity spectrum.

5. The sensor system as set forth in claim 3 further comprising a telescope for launching the beam of light to the target and receiving the Doppler shifted radiation.

6. The sensor system as set forth in claim 5 further comprising an optical fiber system interconnecting the light source, the signal multiplexing device, the detector, the signal amplifier, the spectral processor and the telescope and operative to convey the optical signal, the output beam of light, the Doppler shifted radiation, the Fresnel reflection, the rotational velocity signal, the amplified rotational velocity signal and the signal indicative of the Doppler velocity spectrum therealong.

7. A Doppler rotational velocity sensor system comprising:

a light source generating an optical signal at a prescribed wavelength;

a coupling device receptive of the optical signal from the light source and operative thereby to divide the optical signal and provide as output a local oscillator signal and a transmitted beam of light;

a circulator receptive of the transmitted beam of light from the coupling device and operative thereby to direct the transmitted beam of light to a diffusely reflecting target at a prescribed angular orientation and further operative thereby to accept as input thereto Doppler shifted radiation reflected or backscattered from the target;

wherein the transmitted beam of light subtends a prescribed width of an intersecting illumination area on the surface of the target;

a frequency modulator receptive of the local oscillator signal from the coupling device and operative thereby to provide as output a frequency offset local oscillator signal;

a signal combiner receptive of the frequency offset local oscillator signal from the frequency modulator and the Doppler shifted radiation from the circulator providing thereby a Doppler optical signal; and

a detector receptive of the Doppler optical signal from the signal combiner providing thereby as output an in phase signal indicative of the rotational velocity of the target.

8. The sensor system as set forth in claim 7 further comprising:

a signal amplifier receptive of the signal indicative of the rotational velocity of the target and operative thereby to provide as output an amplified rotational velocity signal; and

a spectral processor receptive of the amplified rotational velocity signal and operative thereby to provide as output a signal indicative of the Doppler velocity spectrum.

9. The sensor system as set forth in claim 7 further comprising a telescope for launching the beam of light to the target and receiving the Doppler shifted radiation.

10. The sensor system as set forth in claim 9 further comprising an optical fiber system interconnecting the light source, the coupling device, the circulator, the detector, the frequency modulator, the signal combiner, the signal amplifier, the spectral processor and the telescope and operative to convey the optical signal, the output beam of light, the local oscillator signal, the frequency offset local oscillator signal, the Doppler shifted radiation, the Doppler optical signal, the rotational velocity signal, the amplified rotational velocity signal and the signal indicative of the Doppler velocity spectrum therealong.

11. A method of determining a rotational velocity of an object having a diffusely reflecting surface, the method comprising:

directing at least one beam of light at the object creating thereby an illumination area on a surface of the object;

sensing at least one beam of light reflected or backscattered from the object;

determining a Doppler spectral bandwidth of the sensed beam of light reflected or backscattered from the object;

determining a width of the illumination area;

determining an angle at which the at least one beam of light directed at the object intercepts the rotating object; and

calculating the rotational velocity of the object based upon the equation;