Self-calibrating laser tracker and self-calibration method

Patent metadata

Field	Value
Publication number	US-9869757-B2
Application number	US-201314653815-A
Country	US
Kind code	B2
Filing date	Dec 19, 2013
Priority date	Dec 20, 2012
Publication date	Jan 16, 2018
Grant date	Jan 16, 2018

Abstract

Some embodiments of the invention relate to a laser tracker for determining the position of a target and in particularly for the continuous tracking of the target. In some embodiments, the laser tracker includes a beam source for generating measurement radiation, an angle measuring function for determining a horizontal pivot angle and a vertical pivot angle, a distance measuring function and a position sensitive surface detector for determining a point of impact of the reflected measurement radiation on the surface detector and for generating an output signal in order to control a target tracking function. The laser tracker may include a self-calibrating function for calibrating a beam offset using a reflecting calibration device.

First claim

What is claimed is:

1. A laser tracker for determining the position of a target, the laser tracker comprising:
a beam source for generating measurement radiation,
a base defining a vertical axis,
a support defining a tilting axis, which is orthogonal to the vertical axis, wherein the support is pivotable in a motorized fashion about the vertical axis relative to the base and a horizontal pivoting angle is defined by an orientation of the support relative to the base,
a beam directing unit, which is pivotable in a motorized fashion about the tilting axis relative to the support, wherein a vertical pivoting angle is defined by an orientation of the beam directing unit relative to the support, for emission and orientation of the measurement radiation and for reception of at least part of the measurement radiation reflected at the target,
angle measuring functionality for determining the horizontal pivoting angle and the vertical pivoting angle,
distance measuring functionality, and
a position-sensitive surface detector, for determining an impingement point of the reflected measurement radiation on the surface detector and for generating an output signal for controlling a target tracking functionality,
wherein the laser tracker, for determining calibration parameters with regard to a position and/or direction of the measurement radiation additionally comprises a retroreflective calibration device for use with a self-calibration functionality, in the context of which an impingement point of the measurement radiation reflected by the calibration device on the position-sensitive surface detector is determinable, wherein:
the calibration device has a retroreflector, which retroreflector, in a two-dimensional region, independently of the impingement point of the measurement radiation within the two-dimensional region, is designed for generating an offset-free, coaxial retroreflection of measurement radiation impinging on it.

2. The laser tracker as claimed in claim 1 , wherein:
the determinable calibration parameters comprise a servocontrol point.

3. The laser tracker as claimed in claim 1 , wherein:
in the context of the self-calibration functionality with the measurement radiation a path on the retroreflector is traversable, such that measurement radiation reflected in each case at a multiplicity of different points of the two-dimensional region is generatable, and
the laser tracker is designed to ascertain an average value in the context of the self-calibration functionality for a multiplicity of measurement data generated by the measurement radiation reflected at the multiplicity of different points.

4. The laser tracker as claimed in claim 1 , wherein:
the retroreflector has a multiplicity of individual reflectors.

5. The laser tracker as claimed in claim 4 , wherein:
the retroreflector is embodied as a retroreflective film or a rigid microprism array.

6. The laser tracker as claimed in claim 4 , wherein:
the individual reflectors comprise reflective spheres or prisms.

7. The laser tracker as claimed in claim 1 , wherein:
the retroreflector comprises either or both plastic and glass.

8. The laser tracker as claimed in claim 1 , wherein:
the retroreflector is arranged on the base or on the support, and
the beam directing unit is designed to traverse with the measurement radiation a circular or meandering or linear path on the retroreflector.

9. The laser tracker as claimed in claim 1 , wherein:
the retroreflector is integrated into the base or into the support or fixedly connected to the base or the support.

10. The laser tracker as claimed in claim 1 , wherein:
the retroreflector is arranged in the beam directing unit or between the beam source and the beam directing unit in combination with a device for light shading in a beam path to the position-sensitive surface detector.

11. The laser tracker as claimed in claim 1 , wherein:
the retroreflector is arranged in the beam directing unit or between the beam source and the beam directing unit in a manner movable into a beam path of the measurement radiation.

12. The laser tracker as claimed in claim 1 , wherein:
the retroreflector is arranged in a plane situated non-orthogonally with respect to the direction of the measurement radiation.

13. The laser tracker as claimed in claim 1 , wherein:
the retroreflector is movable in the context of the self-calibration functionality into a plane situated non-orthogonally with respect to the direction of the measurement radiation.

14. The laser tracker as claimed in claim 1 , wherein:
the retroreflector is embodied as a part of a plate, which is pivotable or rotatable about a rotation spindle, such that measurement radiation reflected in each case at a multiplicity of individual reflectors of the retroreflector is generatable, wherein the plate is arranged in a manner rotatable between two predefined rotation angles or in a manner rotatable continuously in at least one rotation direction.

15. The laser tracker as claimed in claim 14 , wherein:
the plate is embodied with:
a first surface portion formed by the retroreflector,
a second surface portion, which is substantially nontransmissive to the measurement radiation and has a light absorbing and/or in reflection diffusely scattering dark surface, and
a third surface portion which is substantially transmissive to the measurement radiation.

16. The laser tracker as claimed in claim 14 , wherein:
the retroreflector is arranged non-perpendicularly to the rotation spindle, such that a wobble movement of the retroreflector is implementable upon a rotation of the retroreflector about the rotation spindle.

17. The laser tracker as claimed in claim 1 , wherein:
a first camera for capturing the spatial orientation of the target, and
a second camera for coarsely localizing the target.

18. The laser tracker as claimed in claim 1 , wherein:
the measurement radiation is a laser beam, and the laser tracker comprises an absolute distance measuring device and/or an interferometer.

19. The laser tracker as claimed in claim 1 , wherein:
the two-dimensional region of the retroreflector is larger than a beam diameter of the impinging measurement radiation.

20. The laser tracker as claimed in claim 1 , wherein:
the two-dimensional region is large enough to be impinged on by the measurement radiation if:
a midpoint of the two-dimensional region is targeted with the measurement radiation, and
the measurement radiation strays within expectable bounds.

21. A self-calibration method for a laser tracker, the method comprising:
emitting measurement radiation onto a calibration device,
generating a retroreflection of measurement radiation impinging on the calibration device as reflected measurement radiation,
determining an impingement point of the measurement radiation reflected by the calibration device on a position-sensitive surface detector, and
determining calibration parameters with regard to a position and/or direction of the measurement radiation, wherein:
the calibration device has a retroreflector integrated into the laser tracker or fixed to the laser tracker, wherein
the measurement radiation is emitted onto a two-dimensional region of the retroreflector, and
independently of the impingement point of the measurement radiation within the two-dimensional region, an offset-free, coaxial retroreflection of the measurement radiation is generated as reflected measurement radiation.

22. T

Assignees

• Leica Geosystems Ag

Inventors

• Markendorf Albert

Classifications

• G01S17/42

  Simultaneous measurement of distance and other co-ordinates (indirect measurement G01S17/46) · CPC title

• G01S17/06 Primary

  Systems determining position data of a target · CPC title

• G01S17/66

  Tracking systems using electromagnetic waves other than radio waves · CPC title

• G01S7/497 Primary

  Means for monitoring or calibrating · CPC title

• G01S7/4972

  Alignment of sensor · CPC title