Patent Publication Number: US-11656344-B2

Title: Light-based position measurement device with atmospheric correction

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority to U.S. provisional patent application No. 63/016,964, filed on Apr. 28, 2020; the entirety of which is hereby incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates a position measurement device that uses a beam of light with the ability to correct for atmospheric distortions. 
     Background 
     A beam of light, such as a laser beam is often used as means of performing dimensional measurements of objects and for positioning objects. Often, light is transmitted by a device to a reflective target that directs the light back to be processed by one or more sensors to determine position and orientation in up to six degrees of freedom, which includes 3-D position with respect to a defined coordinate system and rotation about the three axes of the coordinate system. The reflective targets are coupled to the object being measured in some way that the target information can be translated to a measurement of the object or its position. 
     In other systems, there is a device that transmits a laser beam to the target, and rather than reflecting the beam back to the source, is capable of performing a position measurement with respect to the laser beam. 
     Some systems may have both where the target reflects a portion of the light back to the source for position measurement while the target performs additional processing often combining the results to create a six degree of freedom measurement. 
     The accuracy of these devices is impacted by atmospheric distortions that are created when the medium though which the light is traveling, such as air is not homogenous with respect to parameters such as temperature, pressure, or humidity. An everyday example of this is the shimmer that is observed when viewing an asphalt road that is has been sitting in the sun, which heats the air near the surface and then rises up and swirls through the cooler air. Different parts of the beam traveling though these variances will travel at slightly different speeds, which will create changes in direction as well as causing the beam to arrive at a sensor at slightly different times creating wavefront distortion. A distorted beam can introduce measurement errors in sensors that measure beam position, so measurements devices that use these sensors generally require air to be homogenous and will further use filtering methods such as averaging to reduce the impact of any distortions. Because these disturbances occur at low frequency, samples have to be taken over a long period of time to ensure that their corresponding errors can be minimized. 
     An example of one of these systems for performing 3-D measurements is defined in U.S. Pat. No. 4,790,651 Tracking Laser Interferometer, Brown et al. This device follows a reflective target using an interferometer to provide the distance to the target and angular encoders in combination with a position-sensing device to provide the transverse measurements. In this system, rotation of the target about the axes of the coordinate system is not available. Often, the reflector is mounted in a sphere that has a known radius from the center of the target to the surface of the sphere such that the target measurements can be projected to the location where the surface of the sphere touches the object being measured. 
     An alternate method of measuring more degrees of freedom is disclosed in U.S. Pat. No. 4,714,339 Three and Five Axis Laser Tracking Systems, Lau et al. Described is a target with a beam splitter and a position-sensing device, which can provide two rotation angles and two linear displacements. The shortcoming of this invention is the field of view for determining the pitch and yaw angles is limited to the field of view of the position sensing device. In addition, there is no measurement of rotation about the axis of the beam. 
     U.S. Pat. No. 9,976,947 Position Measurement Device. Hoffer discloses a method for performing a six degree of freedom measurement using a combination of moving optics and the polarization property of light. 
     Each of these demonstrate methods to measure one or more degrees of freedom, but do not address the challenge of atmospheric disturbances that occur during measurement. 
     A wavefront sensor has the ability to measure the distortions and correct them either mathematically or to adjust an optic to correct the distortion and minimize the error in real-time thus allowing for faster measurements while maintaining accuracy in environments that are more prone to atmospheric distortions. 
     SUMMARY OF THE INVENTION 
     The invention is directed to a device with the ability to measure its position in one or more degrees of freedom with respect to a beam of light while addressing errors caused by atmospheric distortions. Atmospheric distortions can be measured using a wavefront sensor. Data from such a sensor can be used in combination with a beam position sensing device, such that wavefront data can determine if beam position device data should be discarded or can be used to correct the beam position device mathematically. Alternately, the wavefront sensor data can be used to control an adaptive optic that has the ability to receive a distorted beam and then transmit an undistorted beam to the beam position sensing device, eliminating the need to mathematically correct the data from the beam position sensing device. Finally, the wavefront sensor itself can be used to both measure wavefront distortions as well as determine beam position. 
     These corrected beam position measurements can be done in systems where a beam reflected from a target is measured by a light source as well as targets that process the beam position directly. These corrected measurements can be combined with measurements of the length of the beam and beam steering assemblies to produce large volume measurements in up to six degrees of freedom. 
     An exemplary embodiment of the measurement system has a measurement light transmitter and measurement light receiver. The measurement light transmitter comprises a mechanical assembly that couples a laser with collimating optics to create a collimated, Gaussian light beam with a diameter of approximately 10 mm. The collimated laser beam is directed from the aperture in the measurement light transmitter toward a measurement light receiver comprising a mechanical assembly with an aperture leading to a wavefront sensor. The working area of the sensor is large enough to accommodate the center of the laser beam impinging 2 mm off-center without clipping off the edges of the beam. The wavefront sensor has integrated electronics that convert sensor outputs to a stream of digital values through a serial interface that represent the position of the beam, on the sensor, the intensity profile of the beam, and the wavefront, which is target input wavefront data. The target input wavefront data is processed by a transverse measurement and control algorithm executed on a processor to produce a positional measurement of the beam position on the sensor and output the value through a communication interface. 
     An exemplary embodiment of the wavefront sensor is a Shack-Hartman sensor where a lenslet array is mounted one focal length from a photodiode array. An exemplary lenslet array would be a two dimensional grid of 501×501 lenses covering an exemplary photodiode array of 1503×1503 pixels with a size of 15 m×15 mm. Each lens in the lenslet array would be represented by 9 pixels. The exemplary target input wavefront data would then consist of 2,259,000 values ranging from 0 to 255, which would be subdivided into 3×3 arrays of pixels that represent data related to each lenslet. 
     An exemplary target transverse measurement and control algorithm, which is a transverse measurement algorithm, the target input wavefront data is first processed to find the boundary of the beam on the sensor, which allows calculation of a beam position. We then evaluate the data within the boundary to determine the amount of distortion of the beam. If the beam is not distorted, the algorithm emits the calculated beam position. Otherwise, it discards the data and waits for the new wavefront data from the sensor. This is accomplished by first creating a coarse image, which all of the pixels for a single lens in the lenslet array are added together to create lenslet pixel value. The lenslet pixels are organized in a 2D array corresponding to their physical position. The coarse image is then evaluated to find the edges of the beam using a first order derivative, which establishes the working area for sensor. In addition, the M 2  value for the beam is calculated within the working area from the target input wavefront data and compared to an expected M 2  value. If the calculated value deviates from the expected value by less than a predetermined percentage, the centroid of the beam is calculated, and that position of that centroid is reported with respect to the location of the pixel at the center of the sensor. If the calculated M 2  value exceeds the predetermined percentage, all of the data is discarded and new data is retrieved from the sensor. This filtering process ensures that only undistorted data is used for position calculations. 
     An exemplary embodiment, the measurement light transmitter measures the position of a reflective target. The measurement light transmitter comprises a mechanical structure that couples the laser, collimating optics, two 50/50 non-polarizing beam splitters, a beam position sensing device and a wavefront sensor. The mechanical assembly also provides a mechanical mount allowing it to be held in a fixed position. The laser is coupled with collimating optics to create a collimated, Gaussian light beam with a diameter of approximately 10 mm. The laser beam impinges on a first 50/50 non-polarizing beam splitter such that a portion of the beam is reflected and absorbed and the reaming portion is transmitted toward a retro reflector with 80% reflectance whose apex is within 1 mm of the center of the laser beam and located at an arbitrary distance along the axis. The retro reflector reflects a light beam back toward the device that is parallel to the outgoing beam. The reflected beam impinges on the first beam splitter such that a portion is reflected toward the second beam splitter. The second beam splitter is mounted so that its center aligns with the center of the first beam splitter. The second splitter transmits a portion of the beam to the beam position sensing device and reflects a portion of the beam toward a wavefront sensor. Both the beam position sensing device and wavefront sensor centers are aligned with the center of the second beam splitter. The beam position sensing device produces electrical signals that correspond to both the beam power and beam position impinging on the sensor. The wavefront sensor has integrated electronics that convert sensor outputs to a stream of digital values through a serial interface. The measurement device further comprises electronics to condition the signals from the beam position sensing device and convert them to numeric values. The electronics also comprise a processor and a communication system. The processor reads the values from both the beam position sensing device and the wavefront sensor. The wavefront sensor data is used to calculate the amount of distortion. The beam position is then calculated using data from the beam position sensor and adjusting it for the distortion as measured by the wavefront sensor. 
     An exemplary target transverse measurement and control algorithm, which is a transverse measurement algorithm, the data from a beam position sensing device such as a lateral photo diode is processed to calculate an initial beam position. Data from the wavefront sensor is then processed by calculating the center of gravity of the light for each lenslet and comparing that to the ideal center of gravity. An average error in the center of gravity in two dimensions can then be calculated, and that error is then applied to the PSD beam position data output to correct the position reading to produce the transverse measurement of the light beam. 
     In an exemplary embodiment, the beam position sensing device is a lateral photodiode that generates four current signals that correspond to both the intensity of the beam and the beam position impinging on the cell. These signals are labeled A, B, C, and D and the beam position sensing device is oriented such that the A and C signals correspond to the horizontal position of the beam and the B and D signals correspond to the vertical position of the beam. Transimpedance amplifiers convert the individual currents to voltages and are scaled such that signals from the device will not exceed the voltage limits of an analog to digital converter when the beam is 2 mm off center. The four voltages are digitized with the A/D and those values used to calculate the position are a target beam position data output; 
     A and C represent the horizontal position of the beam on the sensor, so the horizontal position calculated by the beam position calculation algorithm as follows: 
     
       
         
           
             
               
                 
                   Hz 
                   = 
                   
                     
                       ( 
                       
                         
                           A 
                           - 
                           C 
                         
                         
                           A 
                           + 
                           C 
                         
                       
                       ) 
                     
                     ⁢ 
                     scale 
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     B and D represent the vertical position of the beam on the sensor, so the vertical position calculated by the beam position calculation algorithm as follows: 
     
       
         
           
             
               
                 
                   Vt 
                   = 
                   
                     
                       ( 
                       
                         
                           B 
                           - 
                           D 
                         
                         
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                           + 
                           D 
                         
                       
                       ) 
                     
                     ⁢ 
                     scale 
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     An exemplary embodiment further includes adaptive optics, driving electronics for the adaptive optics, and an algorithm to calculate the configuration of the adaptive optics that inserted into the beam path before the beam position sensing device such that the beam exiting the beam splitter will first impinge the adaptive optics and then be relayed to the beam position sensing device. The processor reads data from the wavefront sensor and calculates the wavefront distortion, which in turn is used to configure the adaptive optics, which will reshape the light beam which will create a corrected light beam that impinges on the beam position sensing device. The beam position can then be calculated from the beam position sensing device without performing any additional mathematical adjustments for wavefront distortion. 
     In an exemplary embodiment, the measurement light transmitter comprises a distance measurement device. The distance measurement is combined with the beam positions measurements to produce a three-dimensional location of a target. 
     In an exemplary embodiment, the measurement light transmitter further comprises a two axis beam steering assembly. The beam steering assembly provides a larger field of view for the device. 
     An exemplary phase comparison algorithm uses 10 sample from a first radial measurement input, and calculates the phase first calculating the real and imaginary portions as follows (note sine and cosine angles are in radians): 
     
       
         
           
             
               
                 
                   
                     X 
                     1 
                   
                   = 
                   
                     
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                       10 
                     
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                         ⁢ 
                         
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                           ( 
                           
                             
                               2 
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                             10 
                           
                           ) 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   3 
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                     Y 
                     1 
                   
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                           n 
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                         9 
                       
                         
                       
                         
                           I 
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                           sin 
                           ( 
                           
                             
                               2 
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                             10 
                           
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                   ( 
                   4 
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     The phase angle is then calculated as follows:
 
θ= a  tan( X   1   /Y   1 )  (5)
 
     A distance can then be calculated as follows:
 
Distance=(θ/2π)*scale  (6)
 
     Definitions 
     Motor, as used herein, is a device capable of changing the physical position of an object. 
     An encoder, as used herein, is a device capable of measuring the physical displacement of an object. 
     The term optic, as used herein, is an item that is able to modify one or more properties of light such as intensity, direction, polarization, or wavelength. 
     Steering Optic, as used herein is any item that can change the direction of a beam of light either through reflection or refraction. 
     Aperture as used herein, is defined as a boundary. In other words, a beam splitter has a physical size and only light can enter the optical system there. 
     Intensity sensor, as used herein, is a photo sensor, photo diode, lateral photo diode, quadcell, image sensor (photodiode array, CCD, CMOS). We classify all of these together since each one provides at its basic level an intensity reading. Everything other than the photo sensor (photo diode), can provide additional information such as position. 
     Beam position sensing device, as used herein is a lateral photo diode, quadcell or image sensor (photodiode array, CCD, CMOS), capable of providing information that can determine the position of a beam of light with respect to some defined location on the sensor. 
     Beam steering assembly, as used herein defines a device capable of redirecting an input light beam in a different direction as providing data as to the orientation of its optics that can be related to the direction of the outgoing beam. 
     Distance measurement device, as used herein as capable of measuring the length of a laser beam through techniques such as interferometry or intensity modulation. 
     Beam splitter as used herein is any device that that is able to receive a single beam and split it into two or more beams. Beam splitters have types that include cube, plate, or fiber. Beams may be split by intensity (non-polarizing beam splitter), by polarization (polarizing beam splitter), or wavelength (dichroic beam splitter). A beam splitter may also combine two or more beam inputs back into a single beam output. 
    
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention, and together with the description serve to explain the principles of the invention. 
         FIG.  1    show an exemplary measurement system showing a source with a probe as the target. 
         FIG.  2    shows an exemplary measurement source light aperture. 
         FIG.  3    shows an exemplary measurement system showing a measurement system with a simple reflective target. 
         FIG.  4    shows an exemplary target platform capable of providing multiple degrees of freedom measurement and projected to a measurement probe tip. 
         FIG.  5    shows an exemplary measurement source platform with indicators, beam steering, distance measurement with measurement and reference sensors, wavefront measurement, wavefront correction, and a PSD. Can measure 3D position of a reflective target and correct for distortions from moving air. An intelligent target can determine roll, pitch and yaw using a polarized beam from the source and the indicators. 
         FIG.  6    shows an exemplary measurement source schematic with a light source including polarization modulation, transverse measurement beam splitter and PSD, wavefront beam splitter, wavefront measurement sensor, distance measurement beam splitter, distance measurement sensor, distance reference sensor, beam steering, reflective target, source device interface, processor, and communication system. 
         FIG.  7    shows an exemplary measurement source schematic with a light source including polarization modulation, transverse measurement beam splitter and PSD, wavefront beam splitter, wavefront measurement sensor, wavefront correction, distance measurement beam splitter, distance measurement sensor, distance reference sensor, beam steering, reflective target, source device interface, processor, and communication system. 
         FIG.  8    shows an exemplary target schematic with beam steering, target reflector beam splitter, reflective target, wavefront beam splitter, wavefront measurement sensor, a position sensor, target device interface, and a target communication system. 
         FIG.  9    shows an exemplary target schematic with beam steering, target reflector beam splitter, reflective target, wavefront beam splitter, wavefront measurement sensor, wavefront correction, a position sensor, target device interface, and a target communication system. 
         FIG.  10    shows an exemplary reflective target that is a flat mirror. Light can be reflected back toward the source, but the mirror must be nominally perpendicular to the measurement beam. 
         FIG.  11    shows an exemplary reflective target that is a retro reflector. The light beam reflected back is parallel to the emitted beam regardless of the orientation of the reflector. 
         FIG.  12    shows an exemplary reflective target is a retro sphere. 
         FIG.  13    shows an exemplary reflective target that is an intelligent probe. 
         FIG.  14    shows an exemplary light source that is a laser or an LED with collimating optics. The collimating optics allow the projection of a narrow beam over a long range. 
         FIG.  15    shows an exemplary light source with a laser and an optical isolator such that light from the reflective target does not enter back into the laser. 
         FIG.  16    shows an exemplary intensity sensor that is a lateral photo diode. The sum of the four output signals from the sensor represent the overall intensity of the beam impinging on the sensor. The difference between the output signals represents the position of the beam. The lateral photo diode is typically a single piece of silicon with a resistive layer to derive position information. 
         FIG.  17    shows an exemplary intensity sensor that is quadcell, which is four photo diodes. The sum of the four output signals from the sensor represent the overall intensity of the beam impinging on the sensor. The difference between the output signals represent the position the beam. The position is determined the amount of the beam impinging on each of the photo diodes. 
         FIG.  18    shows an exemplary intensity sensor that is an image sensor such as a photo diode array of a CCD. These are typically used in digital cameras and consist of millions of photo diodes. Beam position and intensity can be determined using standard image processing techniques. 
         FIG.  19    is an exemplary intensity sensor, which detects intensity levels of light. 
         FIG.  20    is an exemplary beam position sensing device. 
         FIG.  21    is an exemplary wavefront detection sensor. 
         FIG.  22    Exemplary wavefront detection sensor, also referred to as a Shack-Hartman sensor. Beam passes through the micro lenses that focus the beam on the photo diode array. Micro lenses can either be glass lenses or small apertures. In this figure, the ideal wavefront is shown. 
         FIG.  23    is an exemplary ideal wavefront pattern projected onto the sensor. 
         FIG.  24    is an exemplary wavefront detection sensor with a distorted wavefront pattern. 
         FIG.  25    is an exemplary distorted wavefront pattern projected onto the sensor. 
         FIG.  26    is an exemplary target beam steering assembly and source beam steering assembly. 
         FIG.  27    is an exemplary target beam steering assembly and source beam steering assembly. 
         FIG.  28    is an exemplary target beam steering assembly and source beam steering assembly. 
         FIG.  29    is an exemplary target beam steering assembly and source beam steering assembly. 
         FIG.  30    is an exemplary target beam steering assembly and source beam steering assembly. 
         FIG.  31    shows an exemplary wavefront corrector that is a deformable mirror. 
         FIG.  32    shows an exemplary wavefront corrector that is a liquid crystal array. 
         FIG.  33    shows an exemplary target device interface circuit. 
         FIG.  34    shows an exemplary source device interface circuit. 
         FIG.  35    is an exemplary target processor with algorithms to process transverse measurement and control. 
         FIG.  36    shows an exemplary source processor. 
         FIG.  37    shows an exemplary communication system, where communication is with a person where the display is an output to the user and the buttons are input from the user. 
         FIG.  38    shows an exemplary wired communication system such as serial, Ethernet, and USB. 
         FIG.  39    shows an exemplary wireless communication system such as Bluetooth or WiFi. 
         FIG.  40    shows an exemplary Cartesian coordinate system. 
         FIG.  41    is an exemplary source beam steering assembly. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views of the figures. The figures represent an illustration of some of the embodiments of the present invention and are not to be construed as limiting the scope of the invention in any manner. Further, the figures are not necessarily to scale, some features may be exaggerated to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. 
     DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS 
     As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having” or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Also, use of “a” or “an” are employed to describe elements and components described herein. This is done merely for convenience and to give a general sense of the scope of the invention. This description should be read to include one or at least one and the singular also includes the plural unless it is obvious that it is meant otherwise. 
     Certain exemplary embodiments of the present invention are described herein and are illustrated in the accompanying figures. The embodiments described are only for purposes of illustrating the present invention and should not be interpreted as limiting the scope of the invention. Other embodiments of the invention, and certain modifications, combinations and improvements of the described embodiments, will occur to those skilled in the art and all such alternate embodiments, combinations, modifications, improvements are within the scope of the present invention. 
       FIG.  1    is an exemplary measurement system comprising of a measurement source  101 , which is a measurement light transmitter, with an emitted a measurement beam  102  transmitted toward a light receiving target  106 , which is a measurement light receiver, and received through the target light aperture  111  impinging on a sensor and the data produced by said sensor may be processed to produce one or more position measurements with respect to the light receiving target coordinate system  107 . Said light receiving target may calculate a position of a target extension tip  109  at the end of a target extension  108  allowing for measurements out of the line of sight of the said measurement beam. Said light receiving target may comprise a reflective target  105  reflecting a portion of said emitted measurement beam as a reflected measurement beam  103  back toward said measurement source and received by said measurement source impinging upon one or more sensors. Data produced by these sensors will be processed to produce position measurements within a measure coordinate system  104 . 
       FIG.  2    is an exemplary measurement source  101  with a measurement source light aperture  112  capable of both transmitting an emitted measurement beam  102  and receiving a reflected measurement beam  103 . Also shown is a source orientation indicator assembly  115  that when used in combination with an image sensor can be used to address 180-degree ambiguity of the roll measurement or can be used to determine additional degrees of freedom. The source indicators can be a light source or a reflective target. 
       FIG.  3    is an exemplary measurement system where only a reflective target  105  is used and position measurements are produced with respect to coordinate system  104 . 
       FIG.  4    is an exemplary target electro-optical assembly  201  that is found in a light receiving target  106 . Said target electro-optical assembly comprises a target electro-optical mounting structure  202  to which all optics and sensors are mounted in a fixed relationship to each other. Measurement beam  102  enters through the target light aperture  111  and impinges on a target beam steering assembly  203  capable of redirecting said measurement beam toward target reflector beam splitter  204  thus allowing for a wide range of angles said measurement beam can enter said target light aperture. Said target reflector beam splitter sends a portion of said measurement beam toward reflective target  105 , which will reflect light back through said target reflector beam splitter, which will reflect a portion of light back toward said target beam steering assembly which in turn transmits a reflected measurement beam  103  back a path parallel to said measurement beam. A portion of light is transmitted through said target reflector beam splitter towards a target wavefront beam splitter  205 . A portion of light is reflected toward and impinges on target wavefront sensor  206 . A portion of light is transmitted toward target reference beam splitter  207 , which reflects a portion of light toward a target wavefront corrector  208  which in turn reflects the beam to a target beam position sensing device  214 . Rigidly attached to said target-electro optical assembly is a target extension  108  such that target extension tip  109  is in a known and fixed positional relationship to said target electro-optical assembly. A portion of the light transmitted through said target reference beam splitter passes through a variable polarizing filter platform  209  to a first beam intensity sensor  210  that is a first beam position device  211 . Said first beam position device is at a different distance than said target beam position sensing device allowing for the combination of the two sensor readings to determine angular and transverse positions with respect to said measurement beam. Said variable polarizing filter platform allows the determination of rotation around the beam axis if said measurement beam is polarized. One or more target orientation indicators  110  can be used in combination with an image sensor to determine the coarse orientation of the probe, which overcomes a limitation of polarization having a 180-degree ambiguity for the roll measurement or can be used to determine additional degrees of freedom. 
       FIG.  5    is an exemplary source electro-optical assembly  301  that is found in a measurement source  101 . Said source electro-optical assembly comprises a source electro-optical mounting structure  302  to which all light sources optics and sensors are mounted in a fixed relationship to each other. A light source assembly  312  is mounted to said source electro-optical mounting structure such that it emits a beam of light toward a transverse measurement beam splitter  307  which transmits a portion of the beam toward a distance measurement beam splitter  304 , which reflects a portion of the beam toward first radial reference sensor  305  and transmits a portion of light toward a source beam steering assembly  303 , which can direct the beam in two dimensions through measurement source light aperture  112  as emitted measurement beam  102 . Reflected measurement beam  103  passes back though said measurement source light aperture reflected by said source beam steering assembly back to said distance measurement beam splitter. A portion of the beam is reflected toward first radial measurement sensor  306 , and a portion of the beam transmitted through said distance measurement beam splitter back to said transverse measurement beam splitter. A portion of this light is reflected by said transverse measurement beam splitter toward source transverse beam splitter  308 , which transmits a portion of the beam to a source wavefront sensor  309 , and reflect the remaining portion toward a source wavefront corrector  310 . Said wavefront corrector then reflect the beam toward source beam position sensing device  311 . 
       FIG.  6    is an exemplary schematic of a measurement source  101 . A light source assembly  312  is a measurement light source  401  that emits a light beam  404 , which is an intensity modulated light beam  402  and a linear polarized light beam  403 . Reflected measurement beam  103  passes through distance measurement beam splitter  304  and transverse measurement beam splitter  307  and reflected to source transverse beam splitter  308 . Said source transverse beam splitter reflect a portion of the beam as a wavefront distortion measurement beam  407 . Said wavefront distortion measurement beam impinges on a source wavefront sensor  309 , which measures any atmospheric distortions. Said source transverse beam splitter transmits a source position measurement beam  410  that represents the displacement of the apex of the reflective target  105  from the center of emitted measurement beam  102 . Said source wavefront sensor and said source beam position sensing device are connected to source device interface circuit  416 , which condition signals from the device and digitize them. Source processor  417  is then able to combine the digitized values to produce a position measurement that is communicated through a source communication system  418 . Also shown is a polarization modulation system  405  that produces a polarization modulated light beam  406 , which is a polarized light beam  419 , which can be used by a light receiver to determine rotation around the axis of said light beam. Also shown is first radial reference measurement beam  414  that is reflected from said distance measurement beam splitter on the outgoing beam. Also shown is a first radial measurement beam  412 , which is reflected from said distance measurement beam splitter from the beam returning from the target. Said first radial measurement beam and first radial reference measurement beam are used to calculate a distance to the target. 
       FIG.  7    is an exemplary schematic of a measurement source  101  that has an additional source wavefront corrector  310  inserted between the source transverse beam splitter  308  and the source beam position sensing device  311 , which allows to said source wavefront corrector to reshape the beam and reflect a wavefront corrected measurement beam  408 . Said wavefront corrector is also connected to the source device interface circuit such that the processor can read the digitized data for source wavefront sensor  309  and then send data to said source wavefront corrector to correct the wavefront distortions. 
       FIG.  8    is an exemplary schematic of a light receiving target  106 . Emitted measurement beam  102  is reflected by target reflector beam splitter  204  to target wavefront beam splitter  205 . Said target wavefront beam splitter reflect a target wavefront measurement beam  509  toward target wavefront sensor  206 . Said target wavefront beam splitter transmits a beam to a target position measure beam  501  sensing device  214 . Said target wavefront sensor and said target beam position sensing device are connected to target device interface circuit  503 , which condition signals from the device and digitize them. Target processor  504  is then able to combine the digitized values to produce a position measurement that is communicated through a target communication system  505 . A portion of said emitted measurement beam is transmitted through said target reflector beam splitter as a target measurement beam  511  and impinges on reflective target  105  and is reflected back as reflected measurement beam  103 . 
       FIG.  9    is an exemplary schematic of a light receiving target  106  that has an additional target wavefront corrector  208  inserted between the target wavefront beam splitter  205  and the target beam position sensing device  214 , which allows said target wavefront corrector to reshape the beam and reflect a target wavefront corrected measurement beam  510 . Said target wavefront corrector is also connected to the target device interface circuit  503  such that the target processor  504  can read the digitized data for target wavefront sensor  206  and then send data to said target wavefront corrector to correct the wavefront distortions. 
       FIG.  10    is an exemplary reflective target  105 , which is a flat mirror  1101 . 
       FIG.  11    is an exemplary reflective target  105 , which is a retroreflector  1102 . 
       FIG.  12    is an exemplary reflective target  105 , which is a retrosphere  1103 . 
       FIG.  13    is an exemplary reflective target  105 , which is a light receiving target  106 . 
       FIG.  14    is an exemplary measurement light source  401  which comprises either a light emitting diode  1201  or a laser  1202  with collimating optics  1203 . 
       FIG.  15    is an exemplary measurement light source  401  with the addition of optical isolator  1205 . 
       FIG.  16    is an exemplary source beam position sensing device  311  and an exemplary target beam position sensing device  214 , which is a beam position sensing device  1302 , which is a lateral photo diode  1301 . 
       FIG.  17    is an exemplary source beam position sensing device  311  and an exemplary target beam position sensing device  214 , which is a beam position sensing device  1302 , which is a quadcell  1305 . 
       FIG.  18    is an exemplary source beam position sensing device  311  and an exemplary target beam position sensing device  214 , which is a beam position sensing device  1302 , which is an image sensor  1306 . 
       FIG.  19    is an exemplary intensity sensor  1309 , which is a photo sensor  1307 . 
       FIG.  20    is an exemplary beam position sensing device with a light beam  404  with a position that is measured with respect to sensor reference position  1316 , which is a target beam position input  1308  or a source beam position input  1315 . 
       FIG.  21    is an exemplary target wavefront sensor  206  and source wavefront sensor  309  with a light beam  404  with a position that is measured with respect to sensor reference position  1316 , which is a target beam position input  1308  or a source beam position input  1315 . 
       FIG.  22    is an exemplary target wavefront sensor  206  and source wavefront sensor  309  which is a Shack-Hartmann sensor  1402 . Said Shack-Hartmann sensor comprises a lenslet array  1403  positioned in front of a photodiode array  1404 . A wavefront distortion measurement beam  407  or a target wavefront measurement beam  509  with an ideal wavefront  1401  passes through said lenslet array projecting an image onto said photodiode array as a target wavefront sensor input  1405  or a source wavefront sensor input  1409 , which includes positional information and distortion information. The light beam  404  produces beam spot #### on the sensor having a boundary 
       FIG.  23    shows an exemplary ideal wavefront pattern  1406  related to the ideal wavefront  1401 . 
       FIG.  24    is Shack-Hartman sensor  1402  with a distorted wavefront  1407 . 
       FIG.  25    is a distorted wavefront pattern  1408  representing distortion information of the wavefront data. 
       FIG.  26    is an exemplary dual-axis mirror assembly  1501 , which is a beam steering assembly  1529 , comprising a first rotating mirror  1502 , one or more optic positioners  1512 , one or more optic position sensors  1514 , a first axis of rotation  1503 , and a second axis of rotation  1505 . Said first rotating mirror is one or more beam steering optics  1516 . Said one or more optic positioners are comprised of first axis mirror rotator  1507 , that rotates said one or more beam steering optics in a first axis direction of rotation  1504  about said first axis of rotation. Said one or more optic positioners further comprises second axis mirror rotator  1509 , that rotates said one or more beam steering optics in a second axis direction of rotation  1506  about said second axis of rotation. Said one or more optic position sensors comprises a first axis angle sensor  1508  that measures said first axis direction of rotation and a second axis angle sensor  1510  that measures said second axis direction of rotation. Said beam steering assembly may be either a target beam steering assembly  203  or a source beam steering assembly  303 . Said one or more optic positioners is either a target beam steering motor system  1511  or a source beam steering motor system  1530 . Said one or more optic position sensors is either a target beam steering position measurement system  1513  or a source beam steering position measurement system  1531 . Said one or more beam steering optics is either a target beam steering optic system  1515 , or a source beam steering optic system  1532 . 
       FIG.  27    is an exemplary dual axis mirror assembly  1501  where the first angle sensor  1508  second axis angle sensor  1510  comprises a mirror position laser  1517 , a mirror position laser output beam  1518 , and a mirror position reflected beam  1519  that impinges on a mirror position sensing device  1520  that uses the beam position to determine first axis direction of rotation  1504  and second axis direction of rotation  1506 . 
       FIG.  28    is an exemplary beam steering assembly  1529  that is a gimbal mirror assembly  1521 . 
       FIG.  29    is an exemplary beam steering assembly  1529  that is a dual mirror assembly  1522  where one or more beam steering optics  1516  comprises a first rotating mirror  1502  and a second rotating mirror  1523 . 
       FIG.  30    is an exemplary beam steering assembly  1529  is a dual refracting optic assembly  1524  comprising a first rotating refracting optic assembly  1525  and a second rotating refracting optic assembly  1527  wherein one or more beam steering optics  1516  comprises a first refracting optic  1526  and a second refracting optic  1528  capable of directing a light beam at different angles determined by the rotation of the optic around the axis of the beam. An example would be a wedge prism. 
       FIG.  31    is an exemplary target wavefront corrector  208 , which is also a target wavefront correcting optic  1803  and exemplary source wavefront corrector  310  which is also a source wavefront correcting optic  1804 , all of which is a deformable mirror  1801  where an emitted measurement beam  102  or a reflected measurement beam  103  with a distorted wavefront is reflected with an ideal wavefront. 
       FIG.  32    is an exemplary target wavefront corrector  208 , which is also a target wavefront correcting optic  1803  and exemplary source wavefront corrector  310  which is also a source wavefront correcting optic, all of which is a liquid crystal array  1802  where an emitted measurement beam  102  or a reflected measurement beam  103  with a distorted wavefront and transmitted with an ideal wavefront. 
       FIG.  33    is an exemplary target device interface circuit. A wavefront corrector interface circuit  1909  has a target input wavefront correction data  1914  that is converted to target wavefront correction signal output  1913  that connects to the target wavefront correcting signal input  1912  used to control the configuration of the target wavefront corrector  208 . Target beam position sensing device  214  has a one or more target beam intensity signal outputs  1915  connected to a target beam position signal input  1916  to exemplary target beam position sensing device interface  1908  whose output is target beam position output data  1917  representing the position of a light beam on the sensor. A target wavefront sensor  206  has a target wavefront signal output  1931  connected to target wavefront signal input  1932  of target wavefront sensor conditioning circuit  1904  with a target output wavefront data  1933  representing a wavefront of the measurement. A target beam steering assembly  203  has target beam steering position signal output  1948  connected target beam steering position input  1934  for the target beam steering interface circuit  1906  to generate target output beam steering position data  1936  representing the orientation of the assembly. The target beam steering interface circuit  1906  also has a target input beam steering motor data  1937  that is used to generate a target beam steering motor signal output  1935  connected to a target beam steering motors signal input  1949  which causes the target beam steering assembly  203  to change its orientation. First beam intensity sensor  210  has one or more first intensity signal outputs  1922  connected to a first intensity signal input  1923  of target first intensity interface  1901  with a first intensity data output  1924 . 
       FIG.  34    is an exemplary source device interface circuit  416 . A modulation data input  2025  is connected to a modulation data modulation circuit  2019  with modulation output  2020  that connects to modulation input  2011  of light source assembly  312 , which is used to change the output intensity as directed. A first radial reference sensor  305  with a first radial reference signal output  2012  and a first radial measurement sensor  306  with a first radial measurement signal output  2013  are connected to first radial reference signal input  2016  first radial measurement signal  2017  respectively of a first phase comparison circuit  2014  which outputs an output first phase difference data  2018  representing a distance to a target. Source beam position sensing device  311  has a one or more source beam intensity signal outputs  2042  connected to a source beam position signal input  2044  to source beam position sensing device interface  2043  whose output is source beam position data output  2045  representing the position of a light beam on the sensor. A source wavefront sensor  309  has a source wavefront signal output  2007  connected to source wavefront signal input  2009  of source wavefront sensor conditioning circuit  2008  with a source output wavefront data  2010  representing a wavefront of the measurement. A source wavefront corrector interface circuit  2047  has a source input wavefront correction data  2048  that is converted to source wavefront correction signal output  2049  that connects to the source wavefront correcting signal input  2046  use to control the configuration of the source wavefront corrector  310 . A source beam steering assembly  303  has source beam steering position signal output  2060  connected to source beam steering position input  2038  for the source beam steering interface circuit  2037  to generate source output beam steering position data  2039  representing the orientation of the assembly. The source beam steering interface circuit  2037  also has a source input beam steering motor data  2040  that is used to generate a source beam steering motor signal output  2041  connected to a source beam steering motors signal input  2059  which causes the source beam steering assembly  303  to change its orientation. 
       FIG.  35    is an exemplary target processor  504  with one or more measurement data outputs  2127 . A target input wavefront data  2109 , a first beam position data input  2114 , target input beam steering position data  2115 , and a target beam position data input  2117  are inputs to a target transverse measurement and control algorithm  2108  produces a target output transverse measurement  2110 , a target output beam steering motor data  2116 , and target output wavefront correction data  2130 . 
       FIG.  36    is an exemplary source processor  417  with one or more source measurement data outputs  2221 . A source transverse measurement and control algorithm  2204  with a source input wavefront data  2205 , a source beam position data input  2216 , and a source input beam steering position data  2214  produce a source output transverse measurement  2206 , a source output beam steering motor data  2215 , and a source output wavefront correction data  2217 . A source radial measurement and control algorithm  2207  with an input first phase difference data  2208  calculates a source radial measurement  2209 . 
       FIG.  37    is an exemplary communication system that is a user interface  3301  comprising a display  3302  to show measurement data and buttons  3303  to process user input. 
       FIG.  38    is an exemplary wired communication system  3304  comprising serial communications such as RS232 or SPI  3306 , Ethernet  3307 , and USB  3308  capable of communicating with a wired receiving device  3309 . 
       FIG.  39    is an exemplary wireless communication system  3310  comprising Bluetooth communications  3312  and WiFi Communications  3313  communicating with a wireless receiving device  3314 . 
       FIG.  40    shows an exemplary cartesian coordinate system  3701  with a x-axis  3703 , y-axis  3706 , and a z-axis  3709 . All 3 axes are mutually perpendicular and intersect at the measurement origin  3702 . Measurements in this coordinate system consist of a distance from the measurement origin along x-axis (DX)  3704 , distance from measurement origin along y-axis (DY)  3707 , distance from measurement origin along z-axis (DZ)  3710 , rotation around x-axis (RX)  3705 , rotation around y-axis (RY)  3708 , and around z-axis (RZ)  3711 . 
       FIG.  41    shows an exemplary target beam steering assembly  203  and an exemplary source beam steering assembly  303 . Here, the source electro-optical assembly  301  is mounted such that the entire platform can be rotated about two axes. 
     Throughout the description of the invention, we place adjectives in front of the term measurement beam in an effort to show how a light beam propagates through the various optics. Those skilled in the art will recognize that all of the optics have a known behavior and therefore all sensor readings can be equated back to a single light beam emitted from the measurement source, so we may also for simplicity refer a light beam impinging on a sensor as the measurement beam. A measurement beam may be a reflected measurement beam, a split measurement beam, a corrected measurement beam, and a refocused measurement beam. 
     It will be apparent to those skilled in the art that various modifications, combinations and variations can be made in the present invention without departing from the scope of the invention. Specific embodiments, features and elements described herein may be modified, and/or combined in any suitable manner. Thus, it is intended that the present invention cover the modifications, combinations and variations of this invention provided they come within the scope of the appended claims and their equivalents. 
     REFERENCES 
     The reference listed below are herein incorporated by reference in their entirety:
     U.S. Pat. No. 4,790,651 Tracking Laser Interferometer, Brown et al.;   U.S. Pat. No. 4,714,339 Three and Five Axis Laser Tracking Systems, Lau, et al.;   U.S. Pat. No. 5,305,091 Optical Coordinate Measuring System for Large Objects, Gelbart et al.;   U.S. Pat. No. 5,530,549 Probing Retroreflectors and Methods of Measuring Surfaces Therewith, Brown;   U.S. Pat. No. 6,049,377 Five-Axis/Six-Axis Laser Measuring System, Lau, et al.;   U.S. Pat. No. 6,675,122 Indirect Position Determination with the Aid of A Tracker,   U.S. Pat. No. 7,230,689 Multi-Dimensional Measuring System, Lau;   U.S. Pat. No. 7,312,862 Measurement System for Determining Six Degrees of Freedom of an Object;   U.S. Pat. No. 7,576,836 Camera Based Six Degree-of-Freedom Target Measuring and Target Tracking Device, Bridges;   U.S. Pat. No. 8,670,114 Device and Method for Measuring Six Degrees of Freedom, Bridges, et al.;   U.S. Pat. No. 8,773,667 Sphere Bar Probe, Edmonds, et al.   European Patent 0880674 A System for Point-By-Point Measuring of Spatial Coordinates. Pettersen;   U.S. Pat. No. 9,976,947, Position Measurement Device, John M Hoffer Jr.;   U.S. provisional patent application No. 63/016,964 to John M. Hoffer, Jr., filed on Apr. 28, 2020 and entitled Light Receiving Measurement Device with the Ability to Measure One or More Degrees of Freedom.   

     OTHER PUBLICATIONS 
     
         
         R. Paschotta, article on ‘Shack-Hartmann wavefront sensors’ in the Encyclopedia of Laser Physics and Technology, 1. edition October 2008, Wiley-VCH, ISBN 978-3-527-40828-3. 
         Sheldakova, Julia &amp; Kudryashov, A. &amp; Zavalova, Valentina &amp; Cherezova, T. (2007). Beam quality measurements with Shack-Hartmann wavefront sensor and M2-sensor: Comparison of two methods. Proceedings of SPIE—The International Society for Optical Engineering. 6452.10.1117/12.720045. 
         Gonzlez, Rafael C. and Woods, Richard C. Digital Image Processing Second Edition, 2002 Prentice Hall, Inc. ISBN: 0-201-18075-8.