Passive optical velocity measurement device and method

• US 5,745,226 A
• Filed: 11/04/1996
• Issued: 04/28/1998
• Est. Priority Date: 11/04/1996
• Status: Expired due to Term

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: Litton Systems Incorporated
• Inventors: Gigioli, George W. Jr.
• Primary Examiner(s): Buczinski, Stephen C.
• Application Number:
  US08/743,523
• Time in Patent Office: 540 Days
• Field of Search: 356/4.06, 356/28
• US Class Current: 356/28
• CPC Class Codes: G01P 3/36 Devices characterised by the use of optical means, e.g. using infrared, visible, or ultraviolet light G01P3/68 takes precedence; gyrometers using the Sagnac effect, i.e. rotation-induced shifts between counter-rotating electromagnetic beams G01C19/64
• CPC Class Codes: G01S 11/12 using electromagnetic waves other than radio waves

Abstract

An optical velocity measuring device includes a pair of V/H sensors effectively located at two different distances from a moving object. Each sensor is used to determine an image velocity and a corresponding angular velocity of the object. The angular velocity measurements and the difference in distance or optical path length of the individual sensors are used to determine the absolute linear tangential speed of the object without determining the absolute distance to the object.

Claims

1. A velocity sensing apparatus for sensing the velocity of a wheeled vehicle comprising:

a first sensor receiving light from the vehicle along a first optical path having a first optical path length, the light having a predetermined intensity spatial frequency component associated with a selected feature of the vehicle, the first sensor comprising;

a first grating having a line frequency selected such that the first grating passes light from the vehicle at the spatial frequency associated with the selected feature of the vehicle,

a first detector receiving light passed by the first grating and generating a first signal indicative of motion of the vehicle;

a second sensor receiving the light from the vehicle along a second optical path having a second optical path length, a differential optical path length being defined by a difference between the first and second optical path lengths, the second sensor comprising;

a second grating having the line frequency selected such that the second grating passes light from the vehicle at the spatial frequency associated with the selected feature of the vehicle,

a second detector receiving light passed by the second grating and generating a second signal indicative of motion of the vehicle; and

a processor coupled to the first sensor and the second sensor, the processor receiving the first signal and generating therefrom a first angular velocity measurement for the vehicle, and receiving the second signal and generating therefrom a second angular velocity measurement for the vehicle, wherein the processor computes an absolute velocity of the vehicle using the differential optical path length and the first and second angular velocity measurements.

2. The velocity sensing apparatus of claim 1 wherein the intensity spatial frequency component associated with the selected feature of the vehicle is about 0.04 cycles per inch.

3. The velocity sensing apparatus of claim 1 wherein the selected feature of the vehicle is a wheel well of the vehicle.

4. The velocity sensing apparatus of claim 1 wherein the first and second sensors comprise velocity/distance quotient (V/H) sensors.

5. A method for sensing the velocity of a wheeled vehicle comprising:

predetermining an intensity spatial frequency component of light associated with a selected feature of the vehicle;

with a first sensor, receiving light from the vehicle along a first optical path having a first optical path length;

providing a first grating having a line frequency selected such that the first grating passes light from the vehicle at the spatial frequency associated with the selected feature of the vehicle;

with a first detector, receiving light passed by the first grating and generating a first signal indicative of motion of the vehicle;

in a processor, receiving the first signal and generating a first angular velocity measurement for the vehicle;

with a second sensor, receiving the light from the vehicle along a second optical path having a second optical path length;

computing a differential optical path length, said differential optical path length being defined by a difference between the first and second optical path lengths;

providing a second grating having the line frequency selected such that the second grating passes light from the vehicle at the spatial frequency associated with the selected feature of the vehicle;

with a second detector, receiving light passed by the second grating and generating a second signal indicative of motion of the vehicle;

in the processor, receiving the second signal and generating a second angular velocity measurement for the vehicle; and

in the processor, computing an absolute velocity of the vehicle using the differential optical path length and the first and second angular velocity measurements.

6. A velocity sensing apparatus for sensing the velocity of a wheeled vehicle comprising:

a first sensor receiving light from the vehicle along a first optical path having a first optical path length, the light having an intensity spatial frequency component of about 0.04 cycles per inch associated with a selected feature of the vehicle, the first sensor comprising;

a first grating having a line frequency selected such that the first grating passes light from the vehicle at the spatial frequency associated with the selected feature of the vehicle,

a first detector receiving light passed by the first grating and generating a first signal indicative of motion of the vehicle, and

a second sensor receiving the light from the vehicle along a second optical path having a second optical path length, a differential optical path length being defined by a difference between the first and second optical path lengths, the second sensor comprising;

a second grating having the line frequency selected such that the second grating passes light from the vehicle at the spatial frequency associated with the selected feature of the vehicle,

a second detector receiving light passed by the second grating and generating a second signal indicative of motion of the vehicle; and

a processor coupled to the first sensor and the second sensor, the processor receiving the first signal and generating a first angular velocity measurement for the vehicle, and receiving the second signal and generating a second angular velocity measurement for the vehicle, wherein the processor computes an absolute velocity of the vehicle using the differential optical path length and the first and second angular velocity measurements.

7. The velocity sensing apparatus of claim 6 wherein the selected feature of the vehicle is a wheel well of the vehicle.

8. The velocity sensing apparatus of claim 6 wherein the first and second sensors comprise velocity/distance quotient (V/H) sensors.

9. A method for sensing the velocity of a wheeled vehicle comprising:

selecting an intensity spatial frequency component of light at about 0.04 cycles per inch and associated with a selected feature of the vehicle;

with a first sensor, receiving light from the vehicle along a first optical path having a first optical path length;

providing a first grating having a line frequency selected such that the first grating passes light from the vehicle at the spatial frequency associated with the selected feature of the vehicle;

with a first detector, receiving light passed by the first grating and generating a first signal indicative of motion of the vehicle;

in a processor, receiving the first signal and generating a first angular velocity measurement for the vehicle;

with a second sensor, receiving the light from the vehicle along a second optical path having a second optical path length;

computing a differential optical path length, said differential optical path length being defined by a difference between the first and second optical path lengths;

providing a second grating having the line frequency selected such that the second grating passes light from the vehicle at the spatial frequency associated with the selected feature of the vehicle;

with a second detector, receiving light passed by the second grating and generating a second signal indicative of motion of the vehicle;

in the processor, receiving the second signal and generating a second angular velocity measurement for the vehicle; and

in the processor, computing an absolute velocity of the vehicle using the differential optical path length and the first and second angular velocity measurements.

10. A velocity sensing apparatus for sensing the velocity of a wheeled vehicle comprising:

a first sensor receiving light from the vehicle along a first optical path having a first optical path length, the light having an intensity spatial frequency component associated with a wheel well of the vehicle, the first sensor comprising;

a first grating having a line frequency selected such that the first grating passes light from the vehicle at the spatial frequency associated with the wheel well of the vehicle,

a first detector receiving light passed by the first grating and generating a first signal indicative of motion of the vehicle, and

a second sensor receiving the light from the vehicle along a second optical path having a second optical path length, a differential optical path length being defined by a difference between the first and second optical path lengths, the second sensor comprising;

a second grating having the line frequency selected such that the second grating passes light from the vehicle at the spatial frequency associated with wheel well of the vehicle,

a second detector receiving light passed by the second grating and generating a second signal indicative of motion of the vehicle; and

a processor coupled to the first sensor and the second sensor, the processor receiving the first signal and generates a first angular velocity measurement for the vehicle, and receiving the second signal and generating a second angular velocity measurement for the vehicle, wherein the processor computes an absolute velocity of the vehicle using the differential optical path length and the first and second angular velocity measurements.

11. The velocity sensing apparatus of claim 10 wherein the intensity spatial frequency component associated with the selected feature of the vehicle is about 0.04 cycles per inch.

12. The velocity sensing apparatus of claim 10 wherein the first and second sensors comprise velocity/distance quotient (V/H) sensors.

13. A method for sensing the velocity of a wheeled vehicle comprising:

with a first sensor, receiving light from the vehicle along a first optical path having a first optical path length, the light having an intensity spatial frequency component associated with a wheel well of the vehicle;

providing a first grating having a line frequency selected such that the first grating passes light from the vehicle at the spatial frequency associated with the wheel well of the vehicle;

with a first detector, receiving light passed by the first grating and generating a first signal indicative of motion of the vehicle;

in a processor, receiving the first signal and generating a first angular velocity measurement for the vehicle;

with a second sensor, receiving the light from the vehicle along a second optical path having a second optical path length;

computing a differential optical path length, said differential optical path length being defined by a difference between the first and second optical path lengths;

providing a second grating having the line frequency selected such that the second grating passes light from the vehicle at the spatial frequency associated with the wheel well of the vehicle;

with a second detector, receiving light passed by the second grating and generating a second signal indicative of motion of the vehicle;

in the processor, receiving the second signal and generating a second angular velocity measurement for the vehicle; and

in the processor, computing an absolute velocity of the vehicle using the differential optical path length and the first and second angular velocity measurements.