Three-dimensional coordinate measuring device

Abstract

A coordinate measurement device and method of operating is provided. The coordinate measurement device launches and collimates visible light through a launch-collimator assembly that is exchangeable in the coordinate measuring device without realignment of any elements within the coordinate measuring device. The coordinate measurement device includes a Fabry-Perot laser, a lensing system, a first optical fiber, and a thermoelectric cooler. A fiber network receives the light from the optical fiber and passes a first portion of the light to a launch-collimator assembly. The launch-collimator assembly launches the first portion of the light into space and collimates the launched light into a first beam. A distance meter measures a first distance to a target illuminated by the first beam. A processor determines 3D coordinates of the target based at least in part on a measured first angle of rotation, a measured second angle of rotation, and the measured first distance.

What is claimed is: 
     
         1 . A coordinate measuring device comprising:
 a light source operable to emit a first light, the light source including a Fabry-Perot laser, a lensing system, a first optical fiber, and a thermoelectric cooler, the Fabry-Perot laser operable to produce visible light at a first wavelength, the lensing system operable to couple the produced first light into the first optical fiber, the first optical fiber being a single-mode optical fiber, the thermoelectric cooler operable to hold the Fabry-Perot laser at a constant temperature;   a fiber network operable to receive the first light from the output optical fiber and to pass a first portion of the first light to a launch-collimator assembly, the launch-collimator assembly operable to launch the first portion of the first light into free space and to collimate the launched first light into a first beam of light;   a first motor and a second motor operable to direct the first beam of light to a first direction, the first direction determined by a first angle of rotation about a first axis and a second angle of rotation about a second axis, the first angle of rotation produced by the first motor and the second angle of rotation produced by the second motor;   a first angle measuring device operable to measure the first angle of rotation and a second angle measuring device operable to measure the second angle of rotation;   a distance meter operable to measure a first distance to a target illuminated by the first beam of light; and   a processor operable to determine three-dimensional (3D) coordinates of the target based at least in part on the measured first angle of rotation, the measured second angle of rotation, and the measured first distance.   
     
     
         2 . The coordinate measuring device of  claim 1 , further comprising:
 a Faraday isolator operable to pass the first light traveling in a forward direction away from the light source but to block the first light traveling in a reverse direction toward the light source, the Faraday isolator including an input optical fiber coupled to the first optical fiber, the Faraday isolator further including an output optical fiber, the output optical fiber being a single-mode optical fiber.   
     
     
         3 . The coordinate measuring device of  claim 1 , wherein a bias current sent to the Fabry-Perot laser is adjusted to emit light at a constant average optical power. 
     
     
         4 . The coordinate measuring device of  claim 1 , wherein optical power losses from the Fabry-Perot laser to the target and back to the Fabry-Perot laser are large enough are large enough to prevent destabilization of the Fabry-Perot laser over a range of rated operating temperatures of the coordinate measuring device. 
     
     
         5 . The coordinate measuring device of  claim 2 , wherein a combination of isolation from the Faraday isolator and optical power losses from the Fabry-Perot laser to the target and back to the Fabry-Perot laser is large enough to prevent destabilization of the Fabry-Perot laser over a range of rated operating temperatures of the coordinate measuring device. 
     
     
         6 . The coordinate measuring device of  claim 5 , wherein a temperature control device is brought into contact with the Faraday isolator, the temperature control device operable to control the temperature of the Faraday isolator, thereby increasing the isolation of the Faraday isolator over the range of rated operating temperatures. 
     
     
         7 . The coordinate measuring device of  claim 2 , wherein the Faraday isolator includes a Faraday rotator having a Faraday-rotator crystal and a magnet, the magnet positioned to immerse the Faraday-rotator crystal in a magnetic field. 
     
     
         8 . The coordinate measuring device of  claim 7 , wherein the Faraday isolator is a polarization-independent Faraday isolator including a first birefringent beam displacer, the Faraday rotator, a half-wave plate, and a second birefringent beam displacer. 
     
     
         9 . The coordinate measuring device of  claim 8 , wherein the first optical fiber is not a polarization-maintaining optical fiber and the input optical fiber is not a polarization-maintaining optical fiber. 
     
     
         10 . The coordinate measuring device of  claim 1 , wherein the target is a retroreflector. 
     
     
         11 . The coordinate measuring device of  claim 1 , wherein the distance meter is an absolute distance meter (ADM). 
     
     
         12 . The coordinate measuring device of  claim 11 , wherein a first portion of the first returned light from the target passes through the launch-collimator assembly to the ADM. 
     
     
         13 . The coordinate measuring device of  claim 1 , further including an ADM module, the ADM module being an integrated unit that includes the first light source, the Faraday isolator, the fiber network, and radio-frequency (RF) electronics, the RF electronics used to modulate the Fabry-Perot laser and to process electrically-detected optical signals passing through the fiber network, the ADM module further including an optical-fiber adapter for coupling the fiber network to the launch-collimator assembly. 
     
     
         14 . A method of determining three dimensional coordinates of a target, the method comprising:
 providing a light source operable to emit a first light, the light source including a Fabry-Perot laser, a lensing system, a first optical fiber, and a thermoelectric cooler;   producing a visible light at a first wavelength and coupling the first light into the first optical fiber;   maintaining the Fabry-perot laser at a constant temperature with the thermoelectric cooler;   receiving the first light with a fiber network operable from an output optical fiber;   transmitting a first portion of the first light to a launch-collimator assembly;   launching with the launch-collimator assembly the first portion of the first light into free space and to collimate the launched first light into a first beam of light;   directing the first beam of light to a first direction with a first motor and a second motor, the first direction determined by a first angle of rotation about a first axis and a second angle of rotation about a second axis, the first angle of rotation produced by the first motor and the second angle of rotation produced by the second motor;   measuring the first angle of rotation with a first angle measuring device and the second angle of rotation with a second angle measuring device;   measuring a first distance to a target illuminated by the first beam of light with a distance meter; and   determining three-dimensional (3D) coordinates of the target based at least in part on the measured first angle of rotation, the measured second angle of rotation, and the measured first distance.   
     
     
         15 . The method of  claim 14 , further comprising passing the first light traveling in a forward direction away from the light source through a Faraday isolator, and preventing the first light traveling in a reverse direction through the a Faraday isolator toward the light source, wherein the Faraday isolator includes an input optical fiber coupled to the first optical fiber, the Faraday isolator further including an output optical fiber, the output optical fiber being a single-mode optical fiber. 
     
     
         16 . The method of  claim 14 , further comprising transmitting a bias current to the Fabry-Perot laser and adjusting the emitted light to be at a constant average optical power. 
     
     
         17 . The method of  claim 14 , further comprising providing optical power losses from the Fabry-Perot laser to the target and back to the Fabry-Perot laser that are large enough are large enough to prevent destabilization of the Fabry-Perot laser over a range of rated operating temperatures of the coordinate measuring device. 
     
     
         18 . The method of  claim 17 , further comprising:
 contacting a temperature control device with the Faraday isolator; and   controlling the temperature of the Faraday isolator with the temperature control device to increase the isolation of the Faraday isolator over the range of rated operating temperatures.   
     
     
         19 . The method of  claim 15 , wherein the Faraday isolator includes a Faraday rotator having a Faraday-rotator crystal and a magnet, the magnet positioned to immerse the Faraday-rotator crystal in a magnetic field.