System and method for determining range in 3D imaging systems

• US 7,236,235 B2
• Filed: 07/06/2004
• Issued: 06/26/2007
• Est. Priority Date: 07/06/2004
• Status: Active Grant

• Current Assignee: Topcon Positioning Systems Incorporated (Topcon Corporation)
• Original Assignee: Dimsdale Engineering, LLC
• Inventors: Dimsdale, Jerry
• Primary Examiner(s): Tarcza; Thomas H.
• Assistant Examiner(s): Ratcliffe; Luke D.
• Application Number:
  US10/886,073
• Publication Number:
  US 20060007422A1
• Time in Patent Office: 1,085 Days
• Field of Search: 356/5.01
• US Class Current: 356/5.01
• CPC Class Codes: G01S 17/10 using transmission of interrupted, pulse-modulated waves determination of distance by phase measurements G01S17/32
• CPC Class Codes: G01S 17/894 3D imaging with simultaneous measurement of time-of-flight at a 2D array of receiver pixels, e.g. time-of-flight cameras or flash lidar
• CPC Class Codes: G01S 7/4865 Time delay measurement, e.g. time-of-flight measurement, time of arrival measurement or determining the exact position of a peak peak detection in noise, signal conditioning G01S7/487
• CPC Class Codes: G01S 7/4868 Controlling received signal intensity or exposure of sensor
• CPC Class Codes: G01S 7/497 Means for monitoring or calibrating

Abstract

A system and method of imaging an object. An array of detectors is mounted in an image plane. Each detector in the array of detectors is connected to a timing circuit having an interpolator, wherein the interpolator includes a first circuit which charges a first capacitor at a different rate than it discharges. An optical pulse is transmitted toward an object so that a portion of the optical pulse is reflected from the object as a reflected pulse and a first value representative of when the optical pulse was transmitted toward the object is recorded. The reflected pulse is detected at one or more detectors and a pulse characteristic of the pulse and a second value representative of when the reflected pulse arrived at the detector are recorded. Range to the object is then calculated as a function of the first and second values and the reflected pulse characteristic.

Claims

1. A method of imaging an object, comprising:

mounting an array of detectors in an image plane;

connecting each detector to a timing circuit;

generating a correction table, wherein generating a correction table includes connecting a resonator/attenuator to the array of detectors, directing a calibrating optical pulse into the resonator/attenuator such that the resonator/attenuator transmits two or more optical pulses to the array of detectors, and correcting for nonlinearities at each detector;

transmitting a transmit optical pulse toward an object so that a portion of the transmit optical pulse is reflected from the object as a reflected pulse, wherein transmitting the transmit optical pulse includes recording a first value, wherein the first value is representative of when the transmit optical pulse was transmitted toward the object;

detecting arrival of the reflected pulse at one or more detectors within the array of detectors, wherein detecting arrival of the reflected pulse includes;

integrating the reflected pulse over a predetermined interval of time to determine a reflected pulse characteristic; and

recording a second value, wherein the second value is representative of when the reflected pulse arrived at the detector; and

measuring range to the object as a function of the first and second values, the reflected pulse characteristic and the correction table.

2. The method according to claim 1, wherein recording a second value includes storing a value representative of a capacitor voltage.

3. The method according to claim 1, wherein transmitting an optical pulse includes directing a portion of the optical pulse to a detector and wherein recording a first value includes storing a value representative of a capacitor voltage.

4. The method according to claim 1, wherein each timing circuit includes an interpolator, wherein each interpolator includes an interpolator circuit which charges a capacitor at a different rate than it discharges the capacitor, and wherein recording a second value includes triggering the interpolator circuit as a function of when the reflected pulse arrived at the detector.

5. The method according to claim 4, wherein triggering the interpolator circuit includes discharging the capacitor at a first rate until a subsequent transition of the master clock.

6. The method according to claim 4, wherein triggering the interpolator includes:

discharging the capacitor at a first rate until a subsequent transition of the master clock; and

capturing voltage across the capacitor.

7. The method according to claim 1, wherein the resonator attenuator includes a variable attenuator, a fiber coupler, a fiber resonator and a fiber collimator and wherein directing a calibrating optical pulse into the resonator/attenuator includes passing the calibrating optical pulse through the variable attenuator and the fiber coupler.

8. The method according to claim 7, wherein the variable attenuator can be set to prevent optical pulses from reaching the detector array through the resonator/attenuator.

9. The method according to claim 1, wherein the resonator attenuator includes a variable attenuator and a fiber bundle and wherein directing a calibrating optical pulse into the resonator/attenuator includes passing the calibrating optical pulse through the variable attenuator and the fiber bundle.

10. The method according to claim 1, wherein the resonator attenuator includes one or more optical fibers, wherein each end of each optical fiber is coated so that they are partially reflective and wherein directing a calibrating optical pulse into the resonator/attenuator includes passing the calibrating optical pulse through the one or more optical fibers.

11. A method of imaging an object, comprising:

mounting one or more detectors in an image plane;

connecting each detector to a timing circuit;

connecting a resonator/attenuator to the one or more detectors, wherein the resonator attenuator includes a variable attenuator, a fiber coupler, a fiber resonator and a fiber collimator;

generating a correction table, wherein generating a correction table includes directing a calibrating optical pulse into the resonator/attenuator such that two or more optical pulses are projected on the one or more detectors, and correcting for nonlinearities at each detector, wherein directing a calibrating optical pulse into the resonator/attenuator includes passing the calibrating optical pulse through the variable attenuator and the fiber coupler;

transmitting a transmit optical pulse toward an object so that a portion of the transmit optical pulse is reflected from the object as a reflected pulse, wherein transmitting the transmit optical pulse includes recording a first value, wherein the first value is representative of when the transmit optical pulse was transmitted toward the object;

detecting arrival of the reflected pulse at one or more detectors within the array of detectors, wherein detecting arrival of the reflected pulse includes;

integrating the reflected pulse over a predetermined interval of time to determine a reflected pulse characteristic; and

recording a second value, wherein the second value is representative of when the reflected pulse arrived at the detector; and

measuring range to the object as a function of the first and second values, the reflected pulse characteristic and the correction table.

12. The method according to claim 11, wherein the variable attenuator can be set to prevent optical pulses from reaching the detector array through the resonator/attenuator.

13. A method of imaging an object, comprising:

mounting one or more detectors in an image plane;

connecting each detector to a timing circuit;

connecting a resonator/attenuator to the one or more detectors, wherein the resonator/attenuator includes a variable attenuator and a fiber bundle;

generating a correction table, wherein generating a correction table includes directing a calibrating optical pulse into the resonator/attenuator such that two or more optical pulses are projected on the one or more detectors, and correcting for nonlinearities at each detector, wherein directing a calibrating optical pulse into the resonator/attenuator includes passing the calibrating optical pulse through the variable attenuator and the fiber bundle;

transmitting a transmit optical pulse toward an object so that a portion of the transmit optical pulse is reflected from the object as a reflected pulse, wherein transmitting the transmit optical pulse includes recording a first value, wherein the first value is representative of when the transmit optical pulse was transmitted toward the object;

detecting arrival of the reflected pulse at one or more detectors within the array of detectors, wherein detecting arrival of the reflected pulse includes;

integrating the reflected pulse over a predetermined interval of time to determine a reflected pulse characteristic; and

recording a second value, wherein the second value is representative of when the reflected pulse arrived at the detector; and

measuring range to the object as a function of the first and second values, the reflected pulse characteristic and the correction table.

14. The method according to claim 13, wherein the variable attenuator can be set to prevent optical pulses from reaching the detector array through the resonator/attenuator.