Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
  • G01S17/66—Tracking systems using electromagnetic waves other than radio waves
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B21/00—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant
  • G01B21/02—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant for measuring length, width, or thickness
  • G01B21/04—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant for measuring length, width, or thickness by measuring coordinates of points
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
  • G01D18/00—Testing or calibrating apparatus or arrangements provided for in groups G01D1/00 - G01D15/00
  • G01D18/002—Automatic recalibration
  • G01D18/004—Continuous recalibration
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
  • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
  • G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
  • G01D5/28—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with deflection of beams of light, e.g. for direct optical indication
  • G01D5/30—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with deflection of beams of light, e.g. for direct optical indication the beams of light being detected by photocells
  • G01D5/305—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with deflection of beams of light, e.g. for direct optical indication the beams of light being detected by photocells controlling the movement of a following part
• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
  • G05B2219/00—Program-control systems
  • G05B2219/30—Nc systems
  • G05B2219/33—Director till display
  • G05B2219/33263—Conversion, transformation of coordinates, cartesian or polar
• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
  • G05B2219/00—Program-control systems
  • G05B2219/30—Nc systems
  • G05B2219/37—Measurements
  • G05B2219/37193—Multicoordinate measuring system, machine, cmm
• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
  • G05B2219/00—Program-control systems
  • G05B2219/30—Nc systems
  • G05B2219/40—Robotics, robotics mapping to robotics vision
  • G05B2219/40233—Portable robot
• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
  • G05B2219/00—Program-control systems
  • G05B2219/30—Nc systems
  • G05B2219/45—Nc applications
  • G05B2219/45061—Measuring robot

Definitions

• the present disclosure relates to two coordinate measuring devices.
• One of these devices belongs to a class of instruments that measure the coordinates of a point by probing the point with an articulated mechanical structure.
• the probing may be performed with a mechanical probe tip or with a non-contact scanning device.
• the position of the probe tip is determined by the readings of angular encoders located at the mechanical joints that interconnect the articulating segments.
• This type of device whether it uses a mechanical probe tip or a scanner, is referred to as an articulated-arm coordinate measuring machine (CMM).
• CCMM articulated-arm coordinate measuring machine
• An exemplary system belonging to this class of devices is described by U.S. Patent No. 5,402,582 to Raab.
• the other of these devices is an instrument, referred to as a laser tracker, which measures the coordinates of a point by sending a laser beam to a retroreflector target that is in contact with the point.
• the laser tracker determines the coordinates of the point by measuring the distance and the two angles to the retroreflector.
• the distance is measured with a distance-measuring device such as an absolute distance meter or an interferometer.
• the angles are measured with an angle-measuring device such as an angular encoder.
• a gimbaled beam-steering mechanism within the instrument directs the laser beam to the point of interest.
• Exemplary systems belonging to this class of instruments are described by U.S. Patent No. 4,790,651 to Brown et al. and U. S. Patent No. 4,714,339 to Lau et al.
• the articulated-arm CMM is capable of being bent into a variety of orientations. Because of this, it is able to measure "hidden” points; that is, points that are hidden from the line-of-sight view of a measuring device such as a laser tracker.
• the laser tracker can measure over a much larger volume than the articulated-arm CMM. What is needed is a way to obtain the convenience of measuring hidden points with the articulated- arm CMM over the larger measurement volume of the laser tracker.
• An embodiment may comprise a system for coordinate measurement comprising: a laser tracker; a retroreflector; a moveable articulated-arm coordinate measuring machine (CMM) that may be relocated to different positions; an assembly for attaching the retroreflector to the articulated-arm coordinate measuring machine (CMM); wherein the system is structured so that a laser beam may be sent from the laser tracker in order to measure a position of the retroreflector relative to the laser tracker in a first coordinate system while the articulated-arm coordinate measuring machine (CMM) also measures the position of retroreflector relative to the articulated-arm coordinate measuring machine (CMM) in a second coordinate system and wherein the moveable articulated-arm coordinate measuring machine (CMM) may be relocated to different positions and the measurements may be performed again; and means for transforming the first coordinate system and/or the second coordinate system to a common coordinate frame of reference.
• CCMM articulated-arm coordinate measuring machine
• An embodiment may comprise a method for coordinate measurement comprising: placing a laser tracker at a fixed location; placing at another location a moveable articulated-arm coordinate measuring machine (CMM) to which a retroreflector has been attached thereto so that the retroreflector may be moved to different locations while the laser tracker remains in the fixed location; sending and reflecting a laser beam from the laser tracker to the retroreflector in order to measure a position of the retroreflector in a first coordinate system and also measuring the position of the retroreflector with the articulated- arm coordinate measuring machine (CMM) while the retroreflector is located in the same position in order to also measure the position of the retroreflector relative to the articulated- arm coordinate measuring machine (CMM) in a second coordinate system; and transforming the measurements of the position of the retroreflector taken in first coordinate system and/or the second coordinate system to a common coordinate frame of reference.
• CCMM articulated-arm coordinate measuring machine
• An embodiment may also comprise a retroreflector assembly for use with an articulated-arm coordinate measuring machine (CMM) comprising: a retroreflector; and a mount to attach the retroreflector on the articulated-arm coordinate measuring machine (CMM).
• CCM articulated-arm coordinate measuring machine
• An embodiment may also comprise a method of relocating an articulated-arm coordinate measuring machine (CMM) for measuring an object at different positions about the object comprising: measuring a first set of coordinates in a first coordinate system of a first position of a retroreflector located on an arm of an articulated-arm coordinate measuring machine (CMM) by using angular sensors located in the articulated-arm coordinate measuring machine (CMM); measuring also a first set of second coordinates in a second coordinate system of the retroreflector located on the arm by using a laser tracker and a laser beam sent from the laser tracker to reflect back from the retroreflector to the laser tracker; moving links of the articulated-arm coordinate measuring machine (CMM) to reposition the retroreflector to a second position and measuring a second set of coordinates in a first coordinate system of the second position of the retroreflector located on an arm of an articulated-arm coordinate measuring machine (CMM) by using angular sensors located in the articulated-arm coordinate measuring machine (CMM); measuring
• An embodiment may also comprise a laser measurement apparatus for measuring objects comprising: an articulated-arm coordinate measuring machine (CMM) having angular encoders; a laser tracker having a distance meter and angular encoders; and a retroreflector for use with the laser tracker located on the arm of the articulated-arm (CMM).
• CCM articulated-arm coordinate measuring machine
• a laser tracker having a distance meter and angular encoders
• a retroreflector for use with the laser tracker located on the arm of the articulated-arm (CMM).
• FIGURE 1 is a perspective view of an articulated-arm CMM used in conjunction with a laser tracker
• FIGURE 2 is an exploded, perspective view of a retroreflector clamp assembly
• FIGURE 3 is a perspective view of the articulated-arm CMM relocated to a second position through the use of the laser tracker;
• FIGURE 4 is a perspective view of a mounted sphere assembly
• FIGURES 5 A and 5B are perspective views of the retroreflector nest in contact with the mounted sphere.
• FIGURES 6A and 6B are perspective view of an articulated-arm CMM with reference made to the mathematical nomenclature.
• FIGURE 1 An example of a large-scale coordinate probing system 100 is shown in FIGURE 1.
• Probing system 100 comprises articulated-arm CMM 200, retroreflector clamp assembly 300, and laser tracker 400.
• Other orientations, arrangements, set-ups, and variations are possible and contemplated depending upon the specific application in the field for example. Thus, this example should not be considered to be limiting.
• FIGURE 2 shows an exploded view of retroreflector clamp assembly 300, which comprises spherically mounted retroreflector (SMR) 310, kinematic nest 320, and clamp 330.
• SMR 310 comprises cube-corner retroreflector 312 embedded within partial sphere 314.
• Cube-corner retroreflector 312 comprises three flat mirror segments (Ml, M2, M3) which are joined together in such a way that each glass segment makes a ninety degree angle with respect to the other two glass segments.
• the point of common intersection of the three glass segments is called the apex "A" of SMR 310.
• the apex "A" is located at the spherical center of partial sphere 314.
• Kinematic nest 320 attaches to the top of clamp 330, which in turn locks onto the final link 210 of articulated-arm CMM 200.
• clamp 330 allows the retroreflector clamp assembly 300 to be placed onto articulated-arm CMM 200.
• Kinematic nest 320 has three point-like contacts (not shown) onto which the spherical surface of SMR 310 rests. These point-like contacts ensure that the center of SMR 310 remains at the same point in space as SMR 310 is rotated.
• Kinematic nest 320 preferably contains a magnet in its base to ensure that SMR 310 is kept in constant contact with the three point-like contacts.
• Laser tracker 400 sends laser beam 410 to SMR 310.
• Cube-corner retroreflector 312 reflects the light from the laser tracker back to the laser tracker 400 along the same line 410 as the outgoing laser beam.
• the laser tracker 400 monitors the position of the returning laser beam and adjusts the position of the tracker head 402 to keep the laser beam centered on SMR 310, even as the SMR 310 is moved from point to point, hi this example, the operator moves the end of articulated-arm CMM 200 to three distinct positions, but may also move the articulated-arm CMM 200 to twelve or more positions or possibly one position only.
• Articulated-arm CMM 200 does this by using its built-in angular encoders (not shown) which typically are located in the joints of the articulated-arm CMM 200.
• Laser tracker 400 does this by using its distance meter and angular encoders (not shown). Other types of encoders and distance meters may also be used.
• a transformation matrix is determined for converting from the coordinate system of articulated-arm CMM 200 to the coordinate system of laser tracker 400 or vice versa.
• both sets of data can be converted into some other preferred coordinate system xyz.
• articulated-arm CMM 200 When measuring a large object with articulated-arm CMM 200, it is often necessary to move articulated-arm CMM 200 to a different position in order to measure other portions of the large object that are not accessible to measurement from the first position. This action of moving articulated-arm CMM 200 to a different position is referred to as "relocation.”
• the above procedure of simultaneously measuring the position of SMR 310 with articulated-arm CMM 200 and laser tracker 400 is performed whenever articulated-arm CMM 200 is relocated (see Figure 3 where articulated-arm CMM 200 is moved from position A to position B for example). This permits the data collected from the several locations of articulated-arm CMM 200 to be seamlessly stitched together in the same common coordinate system in the same frame of reference. With the method described above, articulated-arm CMM 200 can be quickly and accurately relocated to any position within the measurement volume of laser tracker 400.
• FIGURE 3 An example of articulated-arm CMM 200 moved from a first position (POSITION A) to a second position (POSITION B) to measure a large object 600 is shown in FIGURE 3.
• the laser tracker 400 provides fast and accurate relocation of the articulated-arm CMM 200.
• the following techniques may also be implemented to improve the accuracy of relocating an articulated-arm CMM: (1) measure many points (for example, more than three) with the articulated-arm CMM and laser tracker; (2) measure points separated as much as possible in three-dimensional space (that is, near the outer edges of the articulated-arm measurement envelope); and (3) measure points covering all three dimensions (that is, avoid collecting points that lie entirely on or near a plane).
• Mounted sphere 500 comprises metal sphere 510, magnetic nest 520, and base 530.
• Metal sphere 510 may have the same diameter as SMR 310, for example.
• Magnetic nest 520 has three point-like contacts (not shown) onto which the metal sphere 510 rests.
• a magnet (not shown) holds metal sphere 510 securely against the three point-like contacts.
• Magnetic nest 520 is attached to base 530, which in turn is attached to the floor on another stable surface.
• FIGURES 6A, 6B To clarify the meaning of these vectors, local coordinate systems (xA,yA, ZA) and (xF,yF, zp) for articulated-arm CMM 200 and final link 210, respectively, are shown in FIGURES 6A, 6B.
• the constraint of metal sphere 510 causes vectors r' and r to remain constant even as the links of articulated-arm CMM 200 are moved about.
• the equation that relates the two vectors is:
• T( ⁇ .) is a 4 x 4 transformation matrix that depends on the so- called Denavit-Hartenberg (DH) parameters for each link, as explained in the book by Manseur cited above.
• DH Denavit-Hartenberg
• the other DH parameters are characteristic of a particular articulated-arm CMM and will already have been determined by a factory compensation procedure carried out at the time the articulated-arm CMM is manufactured.
• the fixed parameters are determined by a separate factory compensation procedure.
• the vector notation O 1 indicates that T is a function of the angular encoder readings for all of the joints in the Arm, and i indicates the i"' measurement, where each measurement corresponds to a different position of articulated-arm CMM 200, two example positions of which are shown in FIGURES 5 A, 5B. If articulated-arm CMM 200 is moved to a large number of different positions, there will not be a unique solution to Equation (1). Instead, the best estimate of the vectors f' and r is made by minimizing the total residual error. For the /"' measurement, the residual error is defined as:
• f and r are selected to minimize the sum of the square of the ras,- values.
• f' and r are each represented by three coordinate values (for example, x, y, and z), so that there are six parameter values that need to be found.
• the procedure for selecting parameters to minimize a sum of squared values is well known in the art and is readily carried out using widely available software. This procedure will therefore not be discussed further.
• articulated-arm CMM 200 is conveniently relocated by simultaneously measuring by position of SMR 310 with articulated-arm CMM 200 and laser tracker 400 with SMR 310 moved to several different positions.
• the measurements collected by articulated-arm CMM 200 are related to the measurements of laser tracker 400 through the equation:
• s and s' are the coordinates of the SMR 310 in the frame of reference of laser tracker 400 and the frame of reference of articulated-arm CMM 200, respectively.
• the quantities rx, ry, rz are the Euler angles representing rotations about the X, Y and Z axes respectively, and tx,ty,tz are the displacements in X, Y and Z respectively.
• the matrix M(rx, ry, rz, tx, ty, tz) transforms the coordinates of SMR 310, as measured by the relocated articulated-arm CMM 200, into the frame of reference of laser tracker 400 which in this example is the common coordinate frame of reference.
• any suitable frame of reference is the entity determined by the relocation procedure, and it the matrix may be computed in any suitable means such as in a processor or in software (not shown) for example. Once it is known, it can equally be applied to a measurement of a probe tip 205 attached to the final link 210.
• the probe-tip 205 coordinate as measured by articulated-arm CMM 200, is transformed by matrix M ⁇ rx, ry, rz, tx, ty, tz) to give the coordinates of the probe tip 205 in the frame of reference of laser tracker 400.
• a standard least-squares fit calculation is performed to find the values of the 6 fit parameters rx, ry, rz, yx, ty, tz that minimize the sum of the squares of the residual errors.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Radar, Positioning & Navigation (AREA)
• Remote Sensing (AREA)
• Length Measuring Devices With Unspecified Measuring Means (AREA)
• A Measuring Device Byusing Mechanical Method (AREA)
• Length Measuring Devices By Optical Means (AREA)

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Cited By (39)

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• 2006
  • 2006-06-23 CN CN200680022308XA patent/CN101203730B/zh not_active Expired - Fee Related
  • 2006-06-23 DE DE602006013626T patent/DE602006013626D1/de not_active Expired - Lifetime
  • 2006-06-23 US US11/473,710 patent/US7804602B2/en active Active
  • 2006-06-23 EP EP06785365A patent/EP1893942B9/en not_active Expired - Lifetime
  • 2006-06-23 WO PCT/US2006/024353 patent/WO2007002319A1/en not_active Ceased
  • 2006-06-23 EP EP10159062A patent/EP2202482A1/en not_active Withdrawn
  • 2006-06-23 JP JP2008518398A patent/JP2008547026A/ja active Pending
• 2012
  • 2012-11-30 JP JP2012262714A patent/JP2013061349A/ja active Pending
  • 2012-11-30 JP JP2012262715A patent/JP2013068625A/ja active Pending

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