Chopper-stabilized absolute distance meter

• US 6,847,436 B2
• Filed: 04/10/2002
• Issued: 01/25/2005
• Est. Priority Date: 04/10/2001
• Status: Expired due to Fees

• Current Assignee: Faro Technologies Incorporated
• Original Assignee: Faro Laser Trackers, LLC (Faro Technologies Incorporated)
• Inventors: Bridges, Robert E.
• Primary Examiner(s): Gregory, Bernarr E.
• Assistant Examiner(s): ANDREA, BRIAN K
• Application Number:
  US10/119,664
• Publication Number:
  US 20030020895A1
• Time in Patent Office: 1,021 Days
• Field of Search: 356/4.01, 356 501- 515
• US Class Current: 356/4.02
• CPC Class Codes: G01S 17/32 using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
• CPC Class Codes: G01S 17/36 with phase comparison between the received signal and the contemporaneously transmitted signal
• CPC Class Codes: G01S 7/4811 common to transmitter and receiver
• CPC Class Codes: G01S 7/4812 transmitted and received beams following a coaxial path
• CPC Class Codes: G01S 7/4818 using optical fibres

Abstract

An absolute distance measurement device is provided, including reference and measurement laser signal paths, comprising a laser source providing a laser signal and a chopper assembly, comprising a rotatable surface defining at least one aperture provided through a portion of the rotatable surface; wherein the laser signal is directed to different points on the rotatable surface of the chopper assembly such that as the rotatable surface is rotated, the aperture selectively permits transmission and selectively prevents transmission of each of said at least two laser signal paths.

Claims

1. An absolute distance measurement device including reference and measurement laser signal paths, comprising:

a laser source providing a laser signal;

a chopper assembly, comprising a rotatable surface defining at least one aperture provided through a portion of the rotatable surface;

wherein the laser signal is directed to different points on the rotatable surface of the chopper assembly such that as the rotatable surface is rotated, the aperture selectively permits transmission and selectively prevents transmission of each of said at least two laser signal paths;

a reference retroreflector, provided on said reference laser signal path; and

an absolute distance meter, which determines the distance from said reference retroreflector positioned on a reference path to a target positioned on a measurement path.

2. The absolute distance measurement device of claim 1, wherein the laser signal is directed to different points on the rotatable surface by one or more of an optical fiber, mirror, lens, beam splitter and prism.

3. The absolute distance measurement device of claim 1, further comprising at least one optical fiber, which is configured to transmit a laser signal derived from said laser source.

4. The absolute distance measurement device of claim 3, wherein at least one optical flber is positioned between the laser source and the rotatable surface.

5. The absolute distance measurement device of claim 4, wherein said at least one optical fiber is coupled to a fiber optic coupler at a first end thereof, and wherein said fiber optic coupler is coupled to two optical fibers at a second end thereof, the said two optical fibers directing a laser signal to different points on said rotatable surface.

6. The absolute distance measurement device of claim 5, wherein said two optical fibers coupled to said fiber optic coupler at a second end thereof are of substantially the same overall lengths.

7. The absolute distance measurement device of claim 4, wherein said at least one optical fiber outputs a laser signal, and wherein said laser signal is directed to different points on said rotatable surface by a beam splitter and by a mirror.

8. The absolute distance measurement device of claim 2, wherein said rotatable surface is reflective.

9. The absolute distance measurement device of claim 8, wherein said rotatable surface reflects laser light to at least one beam block.

10. The absolute distance measurement device or claim 2, wherein said laser signal is passed through a collimating lens prior to being directed to different points on said rotatable surface.

11. The absolute distance measurement device of claim 3, wherein at least one optical fiber is positioned between the rotatable surface and at least one of a reference retroreflector and a target provided on a measurement path.

12. The absolute distance measurement device of claim 11, wherein said at least one optical fiber is provided at least partially along a reference path terminated by a reference retroreflector, wherein said reference retroreflector is one of a fiber retroreflector or a corner cube retroreflector.

13. The absolute distance measurement device claim 11, wherein at least one optical fiber is provided at least partially along a reference path terminated by a retroreflector, and wherein at least one optical fiber is provided at least partially along a measurement path directed towards a target;

and further wherein said at least one optical fiber provided along said reference path and said at least one optical fiber provided along said measurement path are of substantially the same overall lengths.

14. The absolute distance measurement device of claim 1, wherein said chopper assembly further comprises a chopper motor operatively associated with said rotatable surface.

15. The absolute distance measurement device of claim 14, wherein said chopper assembly further comprises an angle sensor operatively associated with said chopper motor.

16. The absolute distance measurement device of claim 1, wherein said aperture selectively permits transmission of at least one of said at least two laser signal paths to a reference retroreflector.

17. The absolute distance measurement device of claim 1, wherein said aperture selectively permits transmission of at least one of said at least two laser signal paths to a target provided along a measurement path.

18. The absolute distance measurement device of claim 17, wherein a diochroic beam splitter is provided between said aperature and said target.

19. The absolute distance measurement device of claim 18, further comprising an optoelectronic assembly providing an optoelectronic laser signal to said dichroic beam splitter, such that the dichroic beam splitter combines the outgoing optoelectronic laser signal and the outgoing laser signal passing through the aperture of the rotatable surface and along the measurement path.

20. The absolute distance measurement device of claim 19, wherein the optoelectronic laser signal has a wavelength in the visible range.

21. The absolute distance measurement device of claim 1, wherein the laser source provides a laser signal having a wavelength in the near infrared range.

22. The absolute distance measurement device of claim 19, wherein the optoelectronic assembly further includes an interferometric distance-measuring device.

23. The absolute distance measurement device of claim 1, wherein said laser source is provided within auxiliary assembly remote relative to said chopper assembly.

24. The absolute distance measurement device of claim 1, wherein a reflected laser signal is directed to an optical detector by a coupler.

25. The absolute distance measurement device of claim 24, wherein said reflected laser signal is prevented from destabilizing said laser source by an isolator positioned between said coupler and said laser source.

26. The absolute distance measurement device of claim 24, wherein said optical detector provides an electrical output signal, which is applied to a radio frequency port of a mixer.

27. The absolute distance measurement device of claim 26, wherein an electrical signal generator applies a signal to a local oscillator port of said mixer.

28. The absolute distance measurement device of claim 27, wherein said mixer produces an intermediate frequency signal, which is passed to a phase meter.

29. The absolute distance measurement device of claim 28, wherein a reference oscillator provides a reference signal to said electrical signal generator and to said phase meter.

30. The absolute distance measurement device of claim 28, wherein said phase meter provides a succession of phase values to a microprocessor, which determines the distance from a reference retroreflector positioned on a reference path to a target positioned on a measurement path.

31. An absolute distance measurement device including reference and measurement laser signal paths, comprising:

a laser source providing a laser signal;

a chopper assembly, comprising a rotatable surface defining at least one aperture provided through a portion of the rotatable surface;

wherein the laser signal is directed to different points on the rotatable surface of the chopper assembly such that as the rotatable surface is rotated, the aperture selectively permits transmission and selectively prevents transmission of each of said at least two laser signal paths; and

a phase meter providing a succession of phase values to a microprocessor, which determines the distance from a reference retroreflector positioned on a reference path to a target positioned on a measurement path.