Laser radar projection with object feature detection and ranging

• US 20080246943A1
• Filed: 12/11/2007
• Published: 10/09/2008
• Est. Priority Date: 02/01/2005
• Status: Active Grant

• Current Assignee: Faro Technologies Incorporated
• Original Assignee: Laser Projection Technologies, Inc. (Faro Technologies Incorporated)
• Inventors: Kaufman, Steven P., Savikovsky, Arkady, Stave, Joel, Chagaris, Christopher C.
• Granted Patent: US 8,085,388 B2
• Time in Patent Office: Days
• US Class Current: 356/5.01
• CPC Class Codes: G01B 11/2518 Projection by scanning of the object
• CPC Class Codes: G01N 2021/8411 Application to online plant, process monitoring
• CPC Class Codes: G01N 2021/8472 Investigation of composite materials
• CPC Class Codes: G01N 21/4738 Diffuse reflection precedence is given to G01N21/55 - G01N21/57 if specular component is taken into consideration, e.g. also for testing fluids, fibrous materials
• CPC Class Codes: G01N 21/9515 Objects of complex shape, e.g. examined with use of a surface follower device measuring contours and curvatures G01B11/24
• CPC Class Codes: G01N 21/95623 using a spatial filtering method per se G02B
• CPC Class Codes: G01N 2201/0642 Light traps; baffles
• CPC Class Codes: G02B 26/101 with both horizontal and vertical deflecting means, e.g. raster or XY scanners colour television using laser beams scanning a display screen H04N9/3129
• CPC Class Codes: G02B 30/56 by projecting aerial or floating images
• CPC Class Codes: G03B 21/005 Projectors using an electronic spatial light modulator but not peculiar thereto
• CPC Class Codes: G03B 21/28 Reflectors in projection beam in illumination beam G03B21/2066
• CPC Class Codes: G03B 35/18 by simultaneous viewing
• CPC Class Codes: G06T 7/521 from laser ranging, e.g. using interferometry; from the projection of structured light
• CPC Class Codes: H04N 9/3129 scanning a light beam on the display screen scanning a light beam on a screen in displays other than projection devices G09G3/02; scanning systems in general G02B26/10; projectors using laser light sources in general H04N9/3161
• CPC Class Codes: H04N 9/3185 Geometric adjustment, e.g. keystone or convergence optical or mechanical adjustment of convergence H04N9/317; using scanning means H04N3/22; optical or mechanical adjustments of projectors not peculiar to the presence of an electronic spatial light modulator G03B21/14
• CPC Class Codes: H04N 9/3194 including sensor feedback

Abstract

A 3D pulsed laser projection system scans an object to produce a dense 3D point cloud and projects a laser light beam onto an object as a glowing template. A high-sensitivity optical feedback system receives and detects a feedback beam of the output beam light diffusely reflected from the object. The feedback light and projected beam share the same beam path between steering mirrors and the object. A light suppression component controls stray scattered light, including ambient light, from being detected. A time-of-flight measurement subsystem provides a distance-to-object measurement for projected pulses. An acousto-optical modulator, variable gain detected signal amplification and variable photo-detector power together produce a dynamic range for detected reflected feedback signals of at least 100,000, and up to 500,000. Optical fiber cables spatially filter scattered light and isolate the photo-detectors thermally. The laser is preferably pulsed at least 50 kHz, with sampling of the projected and feedback reflected optical pulse signals at a sampling rate of up to 10 gigasamples per second.

Claims

1. A 3D laser scanner and projection system that can detect features detection on and range distance to points on the surface of an object, comprising:

a laser projector that projects a pulsed laser light beam on the surface and scans the pulsed output beam along a beam path over the surface where a portion of said output light is diffusely reflected from the surface back to said projector as a feedback signal light beam,

a first optical signal detector at said laser projector that receives said feedback signal light beam and converts it into a digital image signal that corresponds to the detected feedback signal light, and

a suppression system that controls stray light against reaching said optical detector that would prevent the detection of said feedback signal light,

said projected light beam and said feedback signal light beam associated with a given point on the surface propagating in opposite directions along said beam path; and

a time-of-flight measuring system that calculates the elapsed time of flight and distance traveled of pulses from said laser, to points on the object surface, and back via said signal light feedback beam to said detector.

2. The 3D laser scanner and projection system of claim 1 wherein said time of flight measurement system includes a beam splitter located in said beam path that divides said projected pulsed laser light beam into a reference beam portion and a signal beam portion, and a second reference optical detector that converts said reference beam portion into a corresponding electrical reference signal.

3. The 3D laser scanner and projection system of claim 2 wherein said time of flight measurement system further includes a lens that focuses said reference beam portion onto said second reference optical detector.

4. The 3D laser scanner and projection system of claim 2 wherein said time of flight measuring system further comprises a computer that compares said digital image signals with the corresponding electrical reference signal to produce a measurement of the distance from said laser projector to the object surface that produces said feedback signal light beam.

5. The 3D laser scanner and projection system of claim 4 wherein said time of fight measurement system further comprises an electronic circuit that samples said reference beam signal, and said digital image signal at a rate sufficient to provide accurate values for said elapsed time of flight and the intensity of said feedback signal light beam.

6. The 3D laser scanner and projection system of claim 5 wherein said pulsed laser beam is pulsed at least 50 kHz and sampling occurs at least 5 gigasamples per second.

7. The 3D laser scanner and projection system of claim 5 further comprising a clock that synchronizes the operation of said laser, said sampling circuit, said computer, and said scanning.

8. The 3D laser scanner and projection system of any of claims 1-7 further comprising a dynamic range modulator that adjusts the operation of said 3D laser scanner and projection system in response to the light reflective characteristics of the object being scanned and projected upon.

9. The 3D laser scanner and projection system of claim 8 wherein said dynamic range variation is on the order of at least 100,000.

10. The 3D laser scanner and projection system of claim 9 wherein said dynamic variation range is near 500,000.

11. The 3D laser scanner and projection system of claim 8 wherein said dynamic range modulator includes an acousto-optical modulator located in said pulsed output beam and operable to vary the intensity of said pulsed output beam over a range from 1 to 300 to 500.

12. The 3D laser scanner and projection system of claim 11 wherein said acousto-optical modulator splits said pulsed output beam into a first order beam and a zero order beam, where said first order beam is scanned on said object and said zero order beam is suppressed.

13. The 3D laser scanner and projection system of claim 12 wherein said dynamic range modulator further includes a variable gain amplifier of said digital image signal output by said first optical signal detector.

14. The 3D laser scanner and projection system of claim 13 wherein said dynamic range modulator further includes a variable power supply for said first optical signal detector that varies its dynamic response to said received feedback signal light beam.

15. The 3D laser scanner and projection system of any of claims 4-7 wherein said first optical signal detector and said second reference signal detector are optically coupled to said system by optical fibers that thermally isolate said detectors from heat produced by said computer.

16. The 3D laser scanner and projection system of claim 8 wherein said light suppression system comprises a spatial light filter that admits said feedback light beam to said photodetector while substantially blocking stray light, and said spatial filter comprises an optical fiber with a central light-conducting core aligned with said optical detector and a converging lens that brings said feedback light beam to a focus at one end of said central light receiving core.

17. The laser light projection system of claim 1 wherein said light suppression system comprises a beam splitter located in said beam path that decouples said output light beam from said feedback light beam.

18. The laser light projection system of claim 1 wherein said light suppression system further comprises a light dump that eliminates the split portion of said output light beam that is not projected onto the surface.

19. The laser projection system of claim 1 wherein said computer controls said scanning and processes said digital image.

20. The laser projection system of claim 19 wherein said computer directs said scanning to produce a scan box glowing template

21. The laser projection system of claim 20 wherein said computer controls said scanning as an iterated raster scanning over all or a selected portion of said object to obtain valid 3D and related light information for substantially all scan pixels.

22. A method for assembling component parts with precision placement, and fabrication processing and/or verification in space, onto and/or supported by an object, comprising,

projecting a scanned pulsed laser light beam onto the object,

forming a signal channel portion of said pulsed laser light beam that is projected onto the object and a reference channel portion that is not projected,

selecting features on the object before assembly, said selecting including creating a scan box around a selected feature,

scanning said projected light beam within the scan box,

detecting light diffusely reflected back from said object along said scanned laser light beam signal portion,

substantially suppressing light from entering the detector so as to adversely affect its detection of said feedback light,

creating a digital image of said features from said detected feedback light, said creating including coupling the time of flight of a pulse of said signal channel portion light beam to the corresponding pulse in the reference channel portion to provide projection-to-object range information for scanned object points, and

projecting a glowing template on the object that guides the assembly of the parts or fabrication processing or verification on or to the object.

23. The method of claim 22 further comprising:

calculating fiducial points from said features, and

calculating from plural fiducial points on the object the relative position and orientation of the source of said projecting and said object.

24. The method of claim 22 wherein the intensity of said feedback light beam from said surface is in the range of 50 to 500 picowatts.