SYSTEM AND METHOD FOR DETERMINING RANGE IN 3D IMAGING SYSTEMS

• US 20090076758A1
• Filed: 11/17/2008
• Published: 03/19/2009
• 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
• Granted Patent: US 8,547,532 B2
• Time in Patent Office: Days
• US Class Current: 702/97
• 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 for calibrating a device having a laser, two or more detectors, timing electronics connected to the detectors and a processor, wherein the processor determines transit time for output pulses transmitted from the laser to a remote target and back to the detector, the method comprising:

providing a means for selectively coupling a variable portion of the output pulses into one or more resonators;

periodically injecting output pulses from the laser in one end of the resonator such that a pulse train exits the other end of the resonator;

monitoring pulses exiting the fiber with the detectors and generating a signal when a pulse is detected at each detector;

passing the signal through the timing electronics to be calibrated;

monitoring variations in delay between pulses in the pulse train exiting the fiber; and

calibrating the timing electronics as a function of the variations.

2. The method of claim 1, wherein the resonators are optical fibers having an optical path length whose variation with temperature can be accurately characterized.

3. The method of claim 1, wherein the resonators are optical fibers having a optical path length that does not vary with temperature

4. The method of claim 1, wherein the means of generating multiple pulses is a fiber coupler.

5. The method of claim 1, wherein the means of generating multiple pulses is a fiber bundle.

6. The method of claim 1, wherein monitoring pulses exiting the fiber includes determining a transit time for pulses transmitted through the resonator/attenuator.

7. A method of correcting measurements of a three dimensional object comprising the steps of:

taking a set of spatial measurements of the three dimensional object;

determining an approximation to the surface normals of said object;

estimating a range correction based on the surface normal; and

applying the range correction to the set of measurements.

8. A method of increasing the spatial resolution of the measurements of a three dimensional object comprising the steps of:

estimating a blur function of the range measurements;

taking a set of spatial measurements of the three dimensional object; and

making a new set of spatial estimates based on the estimated blur function and the spatial measurements.

9. A resonator/attenuator for calibrating an imaging system, comprising:

an attenuator;

a fiber coupler connected to the attenuator, wherein the fiber coupler includes a first and a second output port and wherein the fiber coupler receives an optical pulse from the attenuator and distributes a portion of the optical pulse to the first and second output ports;

a fiber resonator connected to the first output port of the fiber coupler, wherein the fiber resonator receives the optical pulse transmitted by the first output port and generates a pulse train; and

means for directing the pulse train on one or more detectors of an imaging system.

10. The resonator/attenuator of claim 9, wherein the attenuator is a variable attenuator, wherein the variable attenuator can be set to prevent optical pulses from reaching the imaging system through the resonator/attenuator.

11. A resonator/attenuator for calibrating an imaging system, comprising:

an attenuator;

a fiber resonator connected to the attenuator, wherein the fiber resonator includes a fiber bundle having a plurality of optical fibers, wherein each optical fiber provides a different delay, wherein the fiber bundle receives an optical pulse transmitted by the attenuator and transmits the pulse through the fiber bundle to an output; and

means for directing the output of the fiber bundle on one or more detectors of an imaging system.

12. The resonator/attenuator of claim 11, wherein the attenuator is a variable attenuator, wherein the variable attenuator can be set to prevent optical pulses from reaching the imaging system through the resonator/attenuator.