Laser tracker

Abstract

Some embodiments of the invention include a coordinate measuring machine for detecting the position and alignment of a spatially movable measuring aid. The coordinate measuring meaching may include a retroreflector: a base; a support, which is fixed on the base rotatably about a first rotation axis; a beam directing unit, which is fixed to the support rotatably about a second rotation axis, substantially orthogonal to the first rotation axis; means for detecting a rotation angle of the support relative to the base; and means for detecting a rotation angle of the beam directing unit relative to the support. In some embodiments, in the beam directing unit comprises a laser emission and reception optical unit and a first optical distance measuring unit having at least one first distance measuring device for measuring the distance to a retroreflector of the measuring aid by means of a first measurement radiation.

What is claimed is: 
     
         1 . A laser tracker comprising:
 a base,   a support, which is fixed on the base rotatably about a first rotation axis,   a beam directing unit, which is fixed to the support rotatably about a second rotation axis, which is substantially orthogonal to the first rotation axis,   means for detecting a rotation angle of the support relative to the base, and   means for detecting a rotation angle of the beam directing unit relative to the support,   wherein the beam directing unit comprises:
 a laser emission and reception optical unit for emitting measurement radiation and for receiving measurement radiation reflections, 
 a first optical distance measuring unit having at least one first distance measuring device for measuring the distance to the retroreflector by means of a first measurement radiation, and 
 a second optical distance measuring unit comprising a second beam source for emitting a second measurement radiation, a detector and a control and processing unit for measuring a distance to a diffusely scattering surface of a target object by means of the second measurement radiation, wherein:
 the second beam source comprises drive means and is designed to generate a frequency-modulated laser beam having a continuously varying frequency as second measurement radiation, 
 a part of the second measurement radiation can be split off as reference beam, 
 a portion of the second measurement radiation that is reflected from the surface of the target object is forwardable to the detector, and 
 the second optical distance measuring unit is designed to ascertain a distance to the surface of the target object on the basis of a frequency evaluation of the reference beam and the measurement radiation reflection, a distance to the surface of the target object. 
 
   
     
     
         2 . The laser tracker according to  claim 1 , wherein:
 the second measurement radiation can be split off as reference beam by means of a first beam splitter provided in the beam path of the second measurement radiation in the beam directing unit.   
     
     
         3 . The laser tracker according to  claim 1 , wherein:
 the second optical distance measuring unit is designed to ascertain a distance to the surface of the target object on the basis of the principle of the evaluation of a phase difference between the frequency modulation of the reference signal and the frequency modulation of the reflected measurement radiation signal   
     
     
         4 . The laser tracker according to  claim 1 , wherein the second optical distance measuring unit comprises:
 an optical reference system having a first optical fiber, a second optical fiber and a reference beam detector, wherein the first and second optical fibers in each case have a known, mutually different length, wherein the two lengths differ from one another in a ratio of at least 2:1, and the reference beam is forwardable to the optical reference system; or   a mixer, wherein the reference beam and the reflected measurement radiation reflection are forwardable to the mixer, and the mixer is designed for carrying out a homodyne or heterodyne mixing method, wherein the second optical distance measuring unit comprises a low-pass filter disposed downstream of the mixer.   
     
     
         5 . A laser tracker comprising:
 a base,   a support, which is fixed on the base rotatably about a first rotation axis,   a beam directing unit, which is fixed to the support rotatably about a second rotation axis, which is substantially orthogonal to the first rotation axis,   means for detecting a rotation angle of the support relative to the base, and   means for detecting a rotation angle of the beam directing unit relative to the support,   wherein the beam directing unit comprises:
 a laser emission and reception optical unit for emitting measurement radiation and for receiving measurement radiation reflections, 
 a first optical distance measuring unit having at least one first distance measuring device for measuring the distance to the retroreflector by means of a first measurement radiation, and 
 a second optical distance measuring unit comprising a second beam source for emitting a second measurement radiation, a detector and a control and processing unit for measuring a distance to a diffusely scattering surface of a target object by means of the second measurement radiation, wherein:
 the first optical distance measuring unit and/or the second optical distance measuring unit are/is designed for a frequency-comb-based or frequency-comb-supported distance measurement. 
 
   
     
     
         6 . The laser tracker according to  claim 5 , wherein:
 a scanning functionality, in the context of which the laser tracker is designed to carry out, by means of the second measurement radiation, a multiplicity of distance measurements with respect to a multiplicity of measurement points on the surface of the measurement object,   the control and processing unit is designed in such a way that for the multiplicity of the distance measurements, the rotation angles respectively detected are linked with the measured distance, such that a point position is in each case defined by the linking, and   a point cloud comprising a number of the point positions is generatable.   
     
     
         7 . The laser tracker according to  claim 5 , further comprising:
 a calibration functionality for calibrating the first optical distance measuring unit and/or the second optical distance measuring unit, wherein:
 the control and processing unit is designed in such a way that the first measurement radiation and the second measurement radiation are emittable in a temporal relationship onto a retroreflector, and 
 the first optical distance measuring unit and/or the second optical distance measuring unit are/is calibratable on the basis of a first distance to the retroreflector as measured by the first optical distance measuring unit and a second distance to the retroreflector as measured by the second optical distance measuring unit. 
   
     
     
         8 . The laser tracker according to  claim 5 , wherein:
 the beam directing unit comprises a position-sensitive detector for detecting the first measurement radiation or second measurement radiation reflected by a target, such that depending on a position of the reflected measurement radiation on the detector the alignment of the measurement radiation is readjustable for a continuous target tracking, wherein the beam directing unit additionally comprises a localization camera for the coarse localization of the measuring aid and/or an overview camera for providing images for a user;   the first optical distance measuring unit comprises an interferometer and/or an absolute distance measuring device;   the beam directing unit comprises deflection means for generating a common beam path of the first measurement radiation and the second measurement radiation in the beam directing unit, such that the first measurement radiation and the second measurement radiation are emittable through the same laser emission and reception optical unit;   the laser emission and reception optical unit is designed as a laser emission optical unit and a laser reception optical unit separate from the latter; and/or
 the beam directing unit comprises two laser emission and reception optical units, the first measurement radiation is emittable through the first laser emission and reception optical unit, and the second measurement radiation is emittable through the second laser emission and reception optical unit. 
   
     
     
         9 . A method for using an FMCW module in a laser tracker for providing additional measurement functionality, wherein the laser tracker comprises a beam directing unit having:
 a laser emission and reception optical unit for emitting measurement radiation and for receiving measurement radiation reflections, and   an optical distance measuring apparatus having at least one first distance measuring device for measuring the distance to a measuring aid by means of a first measurement radiation,   wherein the method comprises:
 generating a frequency-modulated laser beam having a continuously variable frequency as second measurement radiation by means of a beam source of the FMCW module, 
 emitting the second measurement radiation onto a target to be measured, wherein one part of the second measurement radiation is split off as reference beam, and another part of the second measurement radiation is emitted through the laser emission and reception optical unit, 
 a portion of the second measurement radiation that is reflected from the target and received through the laser emission and reception optical unit is forwarded to a detector of the FMCW module, and 
 a distance to the target is ascertained on the basis of a frequency evaluation of the reference beam and the reflected portion of the second measurement radiation. 
   
     
     
         10 . The method according to  claim 9 , wherein:
 the distance to the target is ascertained on the basis of the principle of the evaluation of a phase difference between the frequency modulation of the reference signal and the frequency modulation of the reflected measurement radiation signal.   
     
     
         11 . The method according to  claim 9 , wherein:
 the target to be measured is a diffusely scattering surface of a measurement object, wherein:
 the second measurement radiation is emitted onto the diffusely scattering surface, 
 a portion of the second measurement radiation is reflected from the surface, and 
 the distance to the surface is ascertained, 
 wherein:
 a multiplicity of distance measurements with respect to a multiplicity of measurement points on the surface are carried out by means of the second measurement radiation, 
 for the multiplicity of the distance measurements a present alignment of the beam directing unit is linked with the respectively measured distance, such that a point position is in each case defined by the linking, and 
 a point cloud comprising a number of the point positions is generated. 
 
   
     
     
         12 . The method according to  claim 9 , wherein:
 the target to be measured is a retroreflector   the second measurement radiation is emitted onto the retroreflector,   the second measurement radiation is reflected as measurement radiation reflection from the retroreflector, and   the distance to the retroreflector is ascertained,   wherein the first measurement radiation and the second measurement radiation are emitted onto the retroreflector, wherein a distance measured by means of the first measurement radiation and a distance measured by means of the second measurement radiation are used for calibrating the first optical distance measuring device and/or the WFD module or the FMCW module, wherein the first measurement radiation and the second measurement radiation are emitted simultaneously.   
     
     
         13 . A non-transitory computer program product having program code, stored on a machine-readable carrier, for controlling or carrying out the method of  claim 9 . 
     
     
         14 . A laser tracker comprising:
 a base,   a beam directing unit for directing or deflecting measurement radiation, wherein it is arranged rotatably about a first and about a second rotation axis relative to the base,   means for detecting a first and second rotation angle of the beam directing unit, and   an optical distance measuring unit having at least one first distance measuring device for measuring the distance to the retroreflector by means of a first measurement radiation, and wherein:
 the distance measuring unit is designed for frequency-comb-based or frequency-comb-supported distance measurement.