Self-compensating laser tracker

• US 7,466,401 B2
• Filed: 01/04/2008
• Issued: 12/16/2008
• Est. Priority Date: 09/05/2003
• Status: Active Grant

• Current Assignee: Faro Technologies Incorporated
• Original Assignee: Faro Technologies Incorporated
• Inventors: West, James K., Bridges, Robert E., Cramer, Peter G.
• Primary Examiner(s): Punnoose; Roy M
• Application Number:
  US11/969,566
• Publication Number:
  US 20080100824A1
• Time in Patent Office: 347 Days
• Field of Search: 356/154
• US Class Current: 356/154
• CPC Class Codes: G01B 11/002 for measuring two or more coordinates
• CPC Class Codes: G01C 15/002 Active optical surveying means optical plumbing G01C15/105
• CPC Class Codes: G01S 17/42 Simultaneous measurement of distance and other co-ordinates indirect measurement G01S17/46
• CPC Class Codes: G01S 17/66 Tracking systems using electromagnetic waves other than radio waves
• CPC Class Codes: G01S 7/4811 common to transmitter and receiver
• CPC Class Codes: G01S 7/4813 Housing arrangements
• CPC Class Codes: G01S 7/497 Means for monitoring or calibrating
• CPC Class Codes: G02B 5/122 cube corner, trihedral or triple reflector type

Abstract

An apparatus and method for compensating a coordinate measurement machine is provided, which may be a laser-based coordinate measurement machine, laser tracker, or other coordinate measurement device. In one exemplary method, such compensation comprises self-compensation of payload parameters by means of embedded tracker targets. In another exemplary embodiment, such compensation comprises self-compensation of payload, azimuth-post, axis, or R0 parameters by means of embedded temperature sensors.

Claims

1. A self compensating laser tracker, comprising:

a laser source;

a support on which the laser source is positioned, at least a portion of the support or laser source configured to permit redirection of a laser beam emitted from the source; and

at least one temperature sensor provided within or on said laser source or support.

2. A self compensating laser tracker in accordance with claim 1, wherein the support comprises an adjustable payload, and wherein one of said at least one temperature sensor is provided on or within said payload.

3. A self compensating laser tracker in accordance with claim 1, wherein at least a portion of the support comprises an azimuth post, and wherein one of said at least one temperature sensor is provided on or within a portion of said azimuth post.

4. A self compensating laser tracker in accordance with claim 3, wherein at least two temperature sensors are provided on or within different portions of said azimuth post.

5. A self compensating laser tracker in accordance with claim 4, wherein said at least two temperature sensors are provided at opposing sides of said azimuth post.

6. A self-compensating laser tracker in accordance with claim 1, wherein the support comprises a yoke, and wherein one of said at least one temperature sensor is provided on or within said yoke.

7. A self-compensating laser tracker in accordance with claim 6, wherein at least two temperature sensors are provided on or within different portions of said yoke.

8. A self-compensating laser tracker in accordance with claim 7, wherein said at least two temperature sensors are provided at opposing end portions of said yoke.

9. A self-compensating laser tracker, comprising:

a laser source;

a support on which the laser source is positioned, at least a portion of the support or laser source configured to permit redirection of a laser beam emitted from the source;

at least two reflecting members provided on the support, wherein the support or laser source is configured to permit direction of the laser beam to said at least two reflecting members; and

at least one temperature sensor provided within or on said laser source or support.

10. A self-compensating laser tracker in accordance with claim 9, wherein one of said at least two reflecting members comprises a retroreflector and a second of said at least two reflecting members comprises a mirror.

11. A method of self-compensation of a laser tracker, comprising:

calculating or recording an angular departure or offset parameter within a first time period;

calculating or recording temperature data from at least one temperature sensor provided within or on a portion of said laser tracker within said first time period;

calculating or recording temperature data from said at least one temperature sensor provided within or on a portion of said laser tracker within a second time period; and

calculating a temperature corrected value of said at least one parameter based on a comparison of temperature data from said first time period and said second time period.

12. A method of self-compensation of a laser tracker in accordance with claim 11, comprising calculating a proportionality constant for said temperature correction by varying temperature of the portion of the temperature sampled laser tracker while simultaneously measuring said at least one parameter.

13. A method of self-compensation of a laser tracker in accordance with claim 11, wherein said at least one parameter is calculated according to one of the following:

RX=RX₀+k_RX·

Δ

T;

RY=RY₀+k_RY·

Δ

T;

TX=TX₀+k_TX·

Δ

T;

TY=TY₀+k_TY·

Δ

T, wherein

k is said proportionality constant.

14. A method of self-compensation of a laser tracker in accordance with claim 11, wherein said at least one temperature sensor is provided within or on a portion of a laser tracker payload.

15. A method of self-compensation of a laser tracker, comprising:

calculating or recording an azimuth post parameter within a first time period;

calculating or recording temperature data from at least one temperature sensor provided within or on said azimuth post within said first time period;

calculating or recording temperature data from said at least one temperature sensor provided within or on said azimuth post within a second time period; and

calculating a temperature corrected value of said at least one parameter based on a comparison of temperature data from said first time period and said second time period.

16. A method of self-compensation of a laser tracker in accordance with claim 15, comprising calculating a proportionality constant for said temperature correction by varying temperature of the portion of the temperature sampled azimuth post while simultaneously measuring said at least one parameter.

17. A method of self-compensation of a laser tracker in accordance with claim 16, wherein said temperature corrected parameter indicates the temperature induced change of height of the gimbal point of said laser tracker according to the following:

Δ

Z_GIMBAL=k<sub>AZ—

POST</sub>·

Δ

T<sub>AZ—

POST</sub>, wherein k is the proportionality constant.

18. A method of self-compensation of a laser tracker in accordance with claim 15, wherein at least two temperature sensors are provided on different sides of said azimuth post.

19. A method of self-compensation of a laser tracker in accordance with claim 15, wherein said temperature corrected azimuth parameter indicates temperature induced movement of the gimbal point in the plane perpendicular to the azimuth axis, calculated by Δ

X_GIMBAL=k<sub>AZ—

POST—

X—

GIMBAL</sub>·

Δ

T<sub>AZ—

POST—

X</sub> and Δ

Y_GIMBAL=k<sub>AZ—

POST—

Y—

GIMBAL</sub>·

Δ

T<sub>AZ—

POST—

Y</sub>, wherein the representative temperature differences between the two sides of the azimuth post in the X and Y directions are Δ

T<sub>AZ—

POST—

X</sub> and Δ

T<sub>AZ—

POST—

Y</sub>, and wherein k is a proportionality constant.

20. A method of self-compensation of a laser tracker in accordance with claim 19, wherein the proportionality constant is calculated by varying the temperature of the environment incident to said temperature sensors while said tracker makes repeated measurements of four retroreflective targets, wherein said targets are located in approximately the same horizontal plane, wherein two of said four retroreflective targets have an angular separation of approximately 90degrees, and wherein two of said retroreflective targets are further from the laser tracker and have an angular separation of approximately 90 degrees.

21. A method of self-compensation of a laser tracker in accordance with claim 15, wherein said temperature corrected azimuth parameter indicates temperature induced change in the direction of the azimuth post, calculated by Δ

AngX<sub>AZ—

POST</sub>=k<sub>AZ—

POST—

X—

ANGLE</sub>·

Δ

T<sub>AZ—

POST—

Y</sub> and Δ

AngY<sub>AZ—

POST</sub>=k<sub>AZ—

POST—

Y—

ANGLE</sub>·

Δ

T<sub>AZ—

POST—

X</sub>, wherein the representative temperature differences between the two sides of the azimuth post in the X and Y directions are Δ

T<sub>AZ—

POST—

X</sub> and Δ

T<sub>AZ—

POST—

Y</sub>, and wherein k is a proportionality constant.

22. A method of self-compensation of a laser tracker, comprising:

calculating or recording an axis non-squareness parameter within a first time period;

calculating or recording temperature data from at least two temperature sensors provided within or on separate portion of yoke within said laser tracker within said first time period;

calculating or recording temperature data from said at least two temperature sensors within a second time period; and

calculating a temperature corrected value of said axis non-squareness parameter based on a comparison of temperature data from said first time period and said second time period.

23. A method of self-compensation of a laser tracker in accordance with claim 22, wherein said temperature sensors are located on opposite ends of the laser tracker yoke.

24. A method of self-compensation of a laser tracker in accordance with claim 22, comprising calculating a proportionality constant for said temperature correction by varying the temperature across that portion of the yoke that contains the temperature sensors while simultaneously measuring said axis non-squareness parameter.

25. A method of self-compensation of a laser tracker in accordance with claim 24, wherein the axis non-squareness parameter is determined by making frontsight and backsight measurements of azimuth angle, zenith angle and distance of at least two retroreflectors at different zenith angles or of at least two mirrors at different zenith angles.

26. A method of self-compensation of a laser tracker in accordance with claim 24, wherein said temperature corrected parameter indicates the temperature induced deviation from perpendicularity of the zenith and azimuth axes according to the following:

Δ

AXNS=h_AXNS·

Δ

T<sub>ZE—

AXIS·

,</sub> wherein k is the proportionality constant.

27. A method of self-compensation of a laser tracker, comprising:

calculating or recording an R0 parameter within a first time period;

calculating or recording temperature data from at least one temperature sensor provided within or on a portion of said laser tracker such that the measured temperature is representative of the temperature of the path between the gimbal point of the laser tracker and at least one home point within said first time period;

calculating or recording temperature data from said at least one temperature sensor within a second time period; and

calculating a temperature corrected value of said R0 parameter based on a comparison of temperature data from said first time period and said second time period.

28. A method of self-compensation of a laser tracker in accordance with claim 27, wherein the change in the R0 parameter is calculated according to Δ

R0=k_R0·

Δ

T_R0 and wherein k is a proportionality constant.

29. A method of self-compensation of a laser tracker in accordance with claim 27, wherein the proportionality constant is calculated by placing said laser tracking in said home position and monitoring the change in distance to the home point as a function of temperature.

30. A self-compensating laser tracker that emits a laser beam, comprising:

a rotatable payload from which the laser beam is emitted;

at least two embedded, non-moveable, reflecting members provided on a support for the payload;

wherein one of said at least two reflecting members is a cube corner retroreflector and a second of said at least two reflecting members is a mirror;

at least one temperature sensor provided within or on said laser source or support and;

wherein the cube corner retroreflector and the mirror are fixed in position on the support relative to the rotatable payload and relative to each other and are structured to reflect the laser beam in a frontsight mode and a backsight mode when the payload is rotated accordingly in order to determine and then self-compensate for deviations in desired payload parameters where the payload parameters describe position and orientation of the laser beam.

31. A self-compensating laser tracker in accordance with claim 30, wherein said support comprises a gimbaled mechanism.

32. A self-compensating laser tracker in accordance with claim 30, wherein said gimbaled mechanism produces motion in the azimuth and zenith directions.