Laser tracker having target-seeking functionality

Patent metadata

Field	Value
Publication number	US-10048379-B2
Application number	US-201414905755-A
Country	US
Kind code	B2
Filing date	Jul 16, 2014
Priority date	Jul 16, 2013
Publication date	Aug 14, 2018
Grant date	Aug 14, 2018

Abstract

Some embodiments of the invention relate to a laser tracker for continuously tracking a reflective target and for determining the position of the target, comprising a base that defines a vertical axis and a beam-deflecting unit for emitting measurement radiation. The beam-deflecting unit can be pivoted about the vertical axis and a tilt axis in relation to the base in a motorized manner and a measurement axis is defined by an emission direction of the measurement radiation. The laser tracker may have a fine distance measurement unit for precisely determining a distance to the target, an angle measurement functionality for determining an orientation of the beam-deflecting unit in relation to the base, and a target-seeking unit. The target-seeking unit has illuminating means, a camera having a position-sensitive detector for detecting illumination radiation reflected by the target, and a control and evaluating unit having seeking functionality for finding the target.

First claim

What is claimed is:

1. A laser tracker for continuously tracking a reflective target and for determining the position of the target, the laser tracker comprising:
a base defining a vertical axis,
a beam deflecting unit for emitting a measurement radiation and for receiving at least a part of the measurement radiation reflected by the target, with the beam deflecting unit pivoting around the vertical axis and a tilt axis relative to the base in a motorized manner and a measurement axis being defined by an emission direction of the measurement radiation,
a position-sensitive fine targeting detector defining a fine targeting field of view for fine targeting and tracking the target with the help of detecting the measurement radiation reflected by the target,
a fine distance measurement unit for precisely determining the distance to the target with the help of the measurement radiation,
an angle measuring functionality for determining an orientation of the beam deflecting unit relative to the base and
a target-seeking unit comprising:
at least a first and a second illumination light with a fixed distance to one another defining a first basic length for illuminating the target with electromagnetic illumination radiation,
a camera defining a field of view with a position-sensitive detector, wherein
the camera, regarding its optical axis, is offset regarding the measurement axis,
the camera can be used to acquire a picture,
in the picture, at least a part of the illumination radiation of the first and the second illumination lights reflected by the target can be acquired as a first and a second light spot, and

a control and evaluating unit with seeking functionality for finding the target depending on the light spots so that the measurement radiation can be directed towards the target based on finding the target,

wherein when executing the seeking functionality,
at least one picture position is determined depending on the first and/or the second light spot on the detector,
a piece of parallax correction information is determined by picture processing the picture taken, the information taking into account a separation of the light spots and depending on a distance of the two light spots to one another, and
the process of finding the target is performed using the at least one picture position and depending on the parallax correction information, so that a parallax defined by the measurement axis and the optical axis of the camera is taken into account.

2. The laser tracker according to claim 1 , wherein:
the first and second illumination lights are designed in such a way that the electromagnetic illumination radiation can be emitted divergently with a wavelength in the infrared range, with
the first and second illumination lights being designed as light-emitting diodes for emitting light with a wavelength in the infrared range,
the intensity of the illumination radiation being dynamically variable, and/or
the camera being designed in such a way that essentially only infrared illumination radiation can be acquired, specifically with the camera being equipped with a filter, especially for the essentially exclusive transmission of the infrared radiation to the position-sensitive detector.

3. The laser tracker according to claim 1 , wherein:
the target-seeking unit is equipped with at least a third and a fourth illumination light with a basic length differing from the first basic length, used instead of the first and the second illumination lights or in addition to these for illuminating the target, with the illumination lights to be used being selected depending on the known nature of the target when the seeking functionality is executed.

4. The laser tracker according to claim 1 , wherein:
an overlap of the illumination radiation cross-sectional forms of the first and the second illumination lights, acquired in a picture of a camera, impairing a separate picture position determination depending on the respective light spot, is avoided or resolved by
the process of illuminating the target by the first and the second illumination lights and the process of acquiring a single light spot position created by the above being performed at different times when executing the seeking functionality,
the first and the second illumination lights each being capable of emitting illumination radiation of different wavelengths and/or polarization, separable by the camera, with the help of filters,
the individual cross-sectional forms being segmented by picture processing the picture, using edge detection, segmenting circular shapes, circular shapes with a defined diameter or diameter interval, specifically using Circular Hough Transformation (CHT) or scale-invariant kernel operators, and/or
matching the light spot form acquired in the picture from the overlapping individual illumination radiation cross-sectional forms with a stored sample based on a best-fit method, with sub-pixel accuracy, with the respective individual light spot position of the illumination radiation of the respective illumination light acquired in the picture being determined on the basis of the harmonized position of the sample in the picture, with sub-pixel accuracy, with at least one, especially, two pieces of information being co-stored for the stored sample that permits to derive sample-internally defined sample positions to be used for finally determining the respective light spot position within the sample, specifically with the information being the sample-internally defined sample position or a defined sample position determination algorithm.

5. The laser tracker according to claim 1 , wherein:
the laser tracker includes a calibration functionality, during the execution of which a referenced assignment of picture positions and parallax correction information to roughly approximated positions of the target is developed and stored and/or the known position of the first and second illumination lights relative to the optical axis and/or measurement axis and/or the fixed basic length of the first and second illumination lights and/or the known position of the optical axis relative to the measurement axis are determined, with, when executing the calibration functionality,
the fine distance measurement unit targeting and measuring a target provided in different positions with the help of the measurement radiation,
for every position of the target the at least one picture position being determined, and
the measurement of the target and the at least one picture position and parallax correction information determined in this regard being used to derive the relative positions of the first and second illumination lights regarding the measurement axis and the basic length.

6. The laser tracker according to claim 1 , wherein:
the control and evaluating unit includes a picture position determination functionality, during the execution of which a picture position is determined with the help of picture processing in a picture acquired by the camera in such a way that the picture position represents the position in the picture of an illumination radiation cross-sectional form acquired in the picture, with the help of center of gravity calculation on the basis of the light spot form acquired in the picture, with the help of a brightness and/or contrast analysis, and/or
by matching the illumination radiation cross-sectional form acquired in the picture with a stored sample based on a best-fit method, with sub-pixel accuracy, with at least one picture position of the illumination radiation acquired in the picture being determined on the basis of the harmonized position of the sample in the picture, with sub-pixel accuracy, with one piece of information being co-stored for the stored sample that permits to derive sample-interna

Assignees

• Leica Geosystems Ag

Inventors

• Markendorf Albert
• Böckem Burkhard

Classifications

• G01S17/86

  Combinations of lidar systems with systems other than lidar, radar or sonar, e.g. with direction finders · CPC title

• G01C1/04

  combined with cameras · CPC title

• G01S17/08

  for measuring distance only (indirect measurement G01S17/46; active triangulation systems G01S17/48) · CPC title

• G01S17/48

  Active triangulation systems, i.e. using the transmission and reflection of electromagnetic waves other than radio waves · CPC title

• G01C3/08

  Use of electric radiation detectors · CPC title