Absolute distance meter that measures a moving retroreflector

• US 7,352,446 B2
• Filed: 09/30/2005
• Issued: 04/01/2008
• Est. Priority Date: 09/30/2004
• Status: Active Grant

• Current Assignee: Faro Technologies Incorporated
• Original Assignee: Faro Technologies Incorporated
• Inventors: Bridges, Robert E., Hoffer, John M.
• Primary Examiner(s): Tarcza; Thomas H.
• Assistant Examiner(s): Ratcliffe; Luke D.
• Application Number:
  US11/239,854
• Publication Number:
  US 20060066836A1
• Time in Patent Office: 914 Days
• Field of Search: 356/5.13
• US Class Current: 356/5.13
• CPC Class Codes: G01B 11/024 by means of diode-array scanning
• 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 17/36 with phase comparison between the received signal and the contemporaneously transmitted signal
• CPC Class Codes: G01S 17/42 Simultaneous measurement of distance and other co-ordinates indirect measurement G01S17/46
• CPC Class Codes: G01S 17/50 Systems of measurement based on relative movement of target
• CPC Class Codes: G01S 17/58 Velocity or trajectory determination systems; Sense-of-movement determination systems
• CPC Class Codes: G01S 17/66 Tracking systems using electromagnetic waves other than radio waves

Abstract

A laser device and method capable of one or more dimensional absolute distance measurements and/or surface scanning and/or coordinate measurements of a moving external retroreflector or other moving target surfaces without using an incremental interferometer.

Claims

1. A laser tracker device capable of absolute distance measurement without using an incremental interferometer and capable of scanning three dimensional coordinate positions of a moving external retroreflector or other moving target surfaces comprising:

a source of laser light that is amplitude or intensity modulated and sent to and returned from the moving external retroreflector or other moving target surfaces to the laser tracker device along a measurement path;

an opto-electronic component to convert the laser light returned from the retroreflector or target surfaces along the measurement path into a first electrical signal;

conditioning electronics for conditioning the first electrical signal to create a second electrical signal;

digitizing electronics to produce digitized values of the second electrical signal;

a digital signal processor for receiving the digitized values of the second electrical signal wherein the digital signal processor comprises at least a phase extractor module structured to execute a velocity dependant phase extractor function upon the digitized values and wherein the digital signal processor calculates an absolute distance d to the moving retroreflector or other target moving at a velocity v; and

at least two angular encoders for determining coordinate angles to the retroreflector or other target surface wherein the data processor computes three dimensional coordinate positions of the retroreflector or other target based on at least the absolute distance d and the coordinate angles.

2. The laser tracker of claim 1 further comprising:

a position detector for assisting in aiming the laser tracker by measuring the position of the returned laser light from the moving external retroreflector or other moving target surfaces.

3. The laser tracker of claim 1 further comprising:

reference beam optical components for directing part of the laser light to the measurement path containing the moving external retroreflector or other moving target surfaces and part of the laser light to a separate reference path.

4. The laser tracker of claim 3 further comprising opto-electronic components to convert said laser light in said measurement path into an RF measurement signal and to convert said laser light in said reference path into an RF reference signal, where said RF measurement signal and said RF reference signal are electrical signals that retain modulation at a first frequency f_RF, and further comprising additional conditioning electronics for conditioning the RF measurement signal to create an IF measurement signal and for conditioning the RF reference signal to create an IF reference signal.

5. The laser tracker of claim 4 further comprising additional and digitizing electronics to produce digitized values of said IF measurement signal and said IF reference signal at a third frequency f_SAMP, which is a multiple of a second frequency f_IF and

wherein the data signal processor calculates the absolute distance d to the retroreflector or other moving target surface moving at velocity v in air having index of refraction n, speed in vacuum c, and integer ratio V=f_SAMP/f_IF from said digitized values x_k of said IF measurement signal and said digitized values y_k of said IF reference signal using the following formulas,

$R_{\mathrm{MOD}}=c/(2$

nf RF ) , ⁢

a = ∑

k = 0 V - 1 ⁢

x k ⁢

sin ⁡

( 2 ⁢

π

⁢

⁢

k ⁢

⁢

f IF - v / R MOD f SAMP ) , ⁢

b = ∑

k = 0 V - 1 ⁢

x k ⁢

cos ⁡

( 2 ⁢

π

⁢

⁢

k ⁢

⁢

f IF - v / R MOD f SAMP ) , ⁢

p M = tan - 1 ⁡

( a / b ) , ⁢

g = ∑

k = 0 V - 1 ⁢

y k ⁢

sin ⁡

( 2 ⁢

π

⁢

⁢

k ⁢

⁢

f IF - v / R MOD f SAMP ) , ⁢

h = ∑

k = 0 V - 1 ⁢

y k ⁢

cos ⁡

( 2 ⁢

π

⁢

⁢

k ⁢

⁢

f IF - v / R MOD f SAMP ) , ⁢

p R = tan - 1 ⁡

( g / h ) , ⁢

d = d 0 + R MOD ⁡

[ W + ( p M - p R ) / 2 ⁢

π

] ,

where d₀ is a constant and W is an integer that accounts for the number of whole modulation lengths R_MOD to said retroreflector.

6. The laser tracker of claim 1 further comprising:

a beam-steering mechanism that directs the laser light sent out of the laser tracker; and

a position detector that monitors the position of the laser light relative to a retrace point on the position detector and wherein the beam-steering mechanism adjusts the direction of the laser light according to position data from the position detector.

7. The laser tracker of claim 1 further comprising synchronization electronics which determine a timing of absolute distance measurements relative to an electrical synchronization signal.

8. The laser tracker of claim 7 wherein the digital signal processor processes a Kalman filter to synchronize the absolute distance measurements with position detector measurements from a position detector and angle measurements from the angular encoders and to provide an estimation of distance and speed of the moving external retroreflector or other moving target surfaces as a function of time and in the presence of noise.

9. The laser tracker of claim 1 wherein the angular encoder, on each of two mechanical axes, measures an angle to the moving external retroreflector or other moving target surfaces.

10. A laser device capable of one dimensional absolute distance measurement of a moving external retroreflector or other moving target surfaces without using an incremental interferometer comprising:

a source of laser light that is amplitude or intensity modulated and sent to and returned from the moving external retroreflector or other moving target surfaces to the laser device along a measurement path;

an opto-electronic component to convert the laser light returned from the retroreflector or target surfaces along the measurement path into an electrical signal;

digitizing electronics to produce digitized values of the electrical signal;

a digital signal processor for receiving the digitized values of the electrical signal wherein the digital signal processor comprises at least a phase extractor module structured to execute a velocity dependant phase extractor function upon the digitized values and wherein the digital signal processor calculates an absolute distance d to the moving retroreflector or other target moving at a velocity v.

11. The laser device of claim 10 further comprising:

a position detector for assisting in aiming the laser tracker by measuring the position of the returned laser light from the moving external retroreflector or other moving target surfaces.

12. The laser device of claim 11 further comprising:

reference beam optical components for directing part of the laser light to the measurement path containing the moving external retroreflector or other moving target surfaces and part of the laser light to a separate reference path.

13. The laser device of claim 12 further comprising opto-electronic components to convert said laser light in said measurement path into an RF measurement signal and to convert said laser light in said reference path into an RF reference signal, where said RF measurement signal and said RF reference signal are electrical signals that retain modulation at a first frequency f_RF;

and further comprising additional conditioning electronics for conditioning the RF measurement signal to create an IF measurement signal and for conditioning the RF reference signal to create an IF reference signal.

14. The laser device of claim 13 further comprising additional digitizing electronics to produce digitized values of said IF measurement signal and IF reference signal at a third frequency f_SAMP, which is a multiple of second frequency f_IF and

wherein the data processor calculates the absolute distance d to the retroreflector or other moving target surface moving at velocity v in air having index of refraction n, speed in vacuum c, and integer ratio V=f_SAMP/f_IF from said digitized values x_k of said IF measurement signal and said digitized values y_k said IF reference signal using the following formulas,

$R_{\mathrm{MOD}}=c/(2$

nf RF ) , ⁢

a = ∑

k = 0 V - 1 ⁢

x k ⁢

sin ⁡

( 2 ⁢

π

⁢

⁢

k ⁢

⁢

f IF - v / R MOD f SAMP ) , ⁢

b = ∑

k = 0 V - 1 ⁢

x k ⁢

cos ⁡

( 2 ⁢

π

⁢

⁢

k ⁢

⁢

f IF - v / R MOD f SAMP ) , ⁢

p M = tan - 1 ⁡

( a / b ) , ⁢

g = ∑

k = 0 V - 1 ⁢

y k ⁢

sin ⁡

( 2 ⁢

π

⁢

⁢

k ⁢

⁢

f IF - v / R MOD f SAMP ) , ⁢

h = ∑

k = 0 V - 1 ⁢

y k ⁢

cos ⁡

( 2 ⁢

π

⁢

⁢

k ⁢

⁢

f IF - v / R MOD f SAMP ) , ⁢

p R = tan - 1 ⁡

( g / h ) , ⁢

d = d 0 + R MOD ⁡

[ W + ( p M - p R ) / 2 ⁢

π

] ,

where d₀ is a constant and W is an integer that accounts for the number of whole modulation lengths R_MOD to said retroreflector.

15. The laser device of claim 10 further comprising:

a beam-steering mechanism that directs the laser light sent out of the laser tracker; and

a position detector that monitors the position of the laser light relative to a retrace point on the position detector and wherein the beam-steering mechanism adjusts the direction of the laser light according to position data from the position detector.

16. The laser device of claim 10 further comprising synchronization electronics which determine a timing of absolute distance measurements relative to an electrical synchronization signal.

17. The laser device of claim 16 wherein the digital signal processor processes a Kalman filter to synchronize the absolute distance measurements with position detector measurements from a position detector and to provide an estimation of distance and speed of the moving external retroreflector or other moving target surfaces as a function of time and in the presence of noise.

18. A laser tracker device capable of absolute distance measurement without using an incremental interferometer and capable of scanning three dimensional coordinate positions of a moving external retroreflector or other moving target surfaces comprising:

a source of laser light that is amplitude or intensity modulated and sent to and returned from the moving external retroreflector or other moving target surfaces to the laser tracker device along a measurement path;

an opto-electronic component to convert the laser light returned from the retroreflector or target surfaces along the measurement path into a first electrical signal;

conditioning electronics for conditioning the first electrical signal to create a second electrical signal;

digitizing electronics to produce digitized values of the second electrical signal;

a digital signal processor for receiving the digitized values of the second electrical signal wherein the digital signal processor calculates an absolute distance d to the moving retroreflector or other target moving at a velocity v and executes a velocity dependant phase extractor function upon the digitized values;

at least two angular encoders for determining coordinate angles to the retroreflector or other target surface wherein the data processor computes three dimensional coordinate positions of the retroreflector or other target based on at least the absolute distance d and the coordinate angles;

a position detector; and

wherein the digital signal processor processes a Kalman filter to synchronize the absolute distance d measurements with position detector measurements from the position detector and to provide an estimation of distance and speed of the moving external retroreflector or other moving target surfaces as a function of time and in the presence of noise.

19. A laser device capable of one dimensional absolute distance measurement of a moving external retroreflector or other moving target surfaces without using an incremental interferometer comprising:

a source of laser light that is amplitude or intensity modulated and sent to and returned from the moving external retroreflector or other moving target surfaces to the laser device along a measurement path;

an opto-electronic component to convert the laser light returned from the retroreflector or target surfaces along the measurement path into an electrical signal;

digitizing electronics to produce digitized values of the electrical signal;

a position detector;

a digital signal processor for receiving the digitized values of the electrical signal wherein the digital signal processor calculates an absolute distance d to the moving retroreflector or other target moving at a velocity v and wherein the digital signal processor during the calculation also processes a Kalman filter to synchronize the absolute distance d measurements with position detector measurements from the position detector and to provide an estimation of distance and speed of the moving external retroreflector or other moving target surfaces as a function of time and in the presence of noise.

20. A method capable of one dimensional absolute distance measurement of a moving external retroreflector or other moving target surfaces without using an incremental interferometer comprising:

sending and returning a source of laser light that is amplitude or intensity modulated and sent to and returned from the moving external retroreflector or other moving target surfaces to the laser device along a measurement path;

converting the laser light returned from the retroreflector or target surfaces along the measurement path into an electrical signal;

digitizing values of the electrical signal;

receiving the digitized values of the electrical signal;

executing a velocity dependant phase extractor function upon the digitized values; and

calculating an absolute distance d to the moving retroreflector or other target moving at a velocity v.

21. A laser tracker method capable of absolute distance measurement without using an incremental interferometer and capable of scanning three dimensional coordinate positions of a moving external retroreflector or other moving target surfaces comprising:

sending and returning a source of laser light that is amplitude or intensity modulated and sent to and returned from the moving external retroreflector or other moving target surfaces to the laser tracker device along a measurement path;

converting the laser light returned from the retroreflector or target surfaces along the measurement path into a first electrical signal;

conditioning the first electrical signal to create a second electrical signal;

producing digitized values of the second electrical signal;

receiving the digitized values of the second electrical signal and

executing a velocity dependant phase extractor function upon the digitized values;

calculating an absolute distance d to the moving retroreflector or other target moving at a velocity v; and

determining coordinate angles to the retroreflector or other target surface; and

computing three dimensional coordinate positions of the retroreflector or other target based on at least the absolute distance d and the coordinate angles.