EP4298459A1 - Dispositif de poursuite laser à deux fonctionnalités de mesure et mesure de distance fmcw - Google Patents

Dispositif de poursuite laser à deux fonctionnalités de mesure et mesure de distance fmcw

Info

Publication number
EP4298459A1
EP4298459A1 EP21708593.5A EP21708593A EP4298459A1 EP 4298459 A1 EP4298459 A1 EP 4298459A1 EP 21708593 A EP21708593 A EP 21708593A EP 4298459 A1 EP4298459 A1 EP 4298459A1
Authority
EP
European Patent Office
Prior art keywords
radiation
transmission
axis
measurement
laser tracker
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP21708593.5A
Other languages
German (de)
English (en)
Inventor
Marcel Rohner
Alexandre PADUCH
Thomas LÜTHI
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Leica Geosystems AG
Original Assignee
Leica Geosystems AG
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Leica Geosystems AG filed Critical Leica Geosystems AG
Publication of EP4298459A1 publication Critical patent/EP4298459A1/fr
Pending legal-status Critical Current

Links

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
    • G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
    • G01S17/06—Systems determining position data of a target
    • G01S17/42—Simultaneous measurement of distance and other co-ordinates
    • 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
    • G01B21/22—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 angles or tapers; for testing the alignment of axes
    • 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
    • G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
    • G01S17/06—Systems determining position data of a target
    • G01S17/08—Systems determining position data of a target for measuring distance only
    • G01S17/32—Systems determining position data of a target for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
    • G01S17/34—Systems determining position data of a target for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated using transmission of continuous, frequency-modulated waves while heterodyning the received signal, or a signal derived therefrom, with a locally-generated signal related to the contemporaneously transmitted signal
    • 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
    • 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
    • G01S17/88—Lidar systems specially adapted for specific applications
    • G01S17/89—Lidar systems specially adapted for specific applications for mapping or imaging
    • 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
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/481—Constructional features, e.g. arrangements of optical elements
    • G01S7/4817—Constructional features, e.g. arrangements of optical elements relating to scanning
    • 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
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/481—Constructional features, e.g. arrangements of optical elements
    • G01S7/4818—Constructional features, e.g. arrangements of optical elements using optical fibres
    • 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
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/491—Details of non-pulse systems
    • G01S7/4911—Transmitters
    • 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
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/497—Means for monitoring or calibrating

Definitions

  • the invention relates to a coordinate measuring machine, in particular designed as a laser tracker, for the industrial coordinate determination of the position of a target with an optical distance measuring unit.
  • Laser trackers are used, for example, in industrial surveying, e.g. for the coordinative determination of the position of points on a component such as a vehicle body, for example as part of an inspection, or for continuous position monitoring (e.g. also determining the speed) of a moving machine part.
  • Such laser trackers are typically designed for a coordinative determination of the position of a retro-reflecting target point and for a continuous tracking of this target point by means of a tracking unit.
  • a target point can be replaced by a retro-reflective unit (e.g.
  • Cube corner prism which is targeted with an optical measuring beam, typically a laser beam, generated by a beam source of the tracking unit or by a distance meter of the laser tracker.
  • the laser beam is reflected parallel back to the laser tracker, with the reflected beam being detected using detection means of the tracking unit or distance meter.
  • Direction of reception of the beam determined for example by means of angle measurement sensors associated with a deflection mirror or a sighting unit of the system.
  • a distance from the laser tracker to the target point is determined, e.g. using a transit time or phase difference measurement, using an optical interferometer or using the Fizeau principle.
  • the position coordinates of the target point are determined based on the emission or reception direction and the distance.
  • a generic laser tracker has, for example, a beam steering unit with a base, a support and a beam emitting component, the support being mounted on the base such that it can rotate about a first axis of rotation, and the beam emitting component being mounted on the support such that it can rotate about a second axis of rotation that is essentially orthogonal to the first axis of rotation .
  • the beam transmission component has, for example, common exit and entry optics for a distance measuring beam and a sighting beam, which is used, for example, for precise angular position determination of the cooperative target and for tracking the target object.
  • the beam transmission component can also have separate lenses for different beam components or separate entry optics and separate exit optics.
  • both the support and the beam transmission component are moved in a motorized manner.
  • laser trackers have a tracking area sensor in the form of a position-sensitive detector (PSD) for continuous target tracking, measuring laser radiation reflected at the target being able to be detected thereon.
  • PSD position-sensitive detector
  • a PSD is to be understood as a locally analogous working area sensor, with which a focal point of a light distribution on the sensor area can be determined very quickly and with a high resolution.
  • the sensor's output signal is generated by means of one or more photosensitive surfaces.
  • the laser tracker usually has a separate ATR light source and a special one for the Wavelength of the ATR light source sensitive ATR detector (eg CCD area sensor) integrated.
  • ATR Automatic Target Recognition
  • the user can manually, roughly aim at the target object, for example by using an aiming and/or overview camera arranged on the laser tracker to image the target object on a user display of the laser tracker or on the display of a separate peripheral device (e.g. data logger as a remote control) and is targeted.
  • an aiming and/or overview camera arranged on the laser tracker to image the target object on a user display of the laser tracker or on the display of a separate peripheral device (e.g. data logger as a remote control) and is targeted.
  • another camera can, for example, take pictures of the target and use image processing to detect movements of the target (or movements of objects moving along with the target), thereby facilitating retrieval of the retroreflector and re-coupling of the laser beam to the retroreflector in the event the target loses its "locked” state.
  • a deviation of the received measuring beam from a zero position is determined on a fine targeting sensor, by means of which a position difference between the center of the retroreflector and the point of impact of the laser beam on the reflector is determined and the alignment of the laser beam is corrected or tracked depending on this deviation be that the offset on the fine pointing sensor is reduced, in particular is "zero" so that the beam is aligned towards the center of the reflector.
  • laser trackers of the prior art have at least one distance meter, which can be designed, for example, as an interferometer (IFM). Since such distance measuring units can only measure relative changes in distance, so-called absolute distance meters (ADM) are installed in today's laser trackers in addition to interferometers. For example, such a combination of measuring devices for Distance determination by the product AT901 from Leica Geosystems AG. A combination of an absolute distance meter and an interferometer for distance determination with a HeNe laser is known, for example, from WO 2007/079600 A1.
  • US 2014/0226145 A1 discloses a laser tracker that can measure both a retroreflective target and a natural (ie non-retroreflective) surface.
  • the laser tracker has a first absolute distance meter, which, as is known, is designed for measuring to a retroreflector.
  • the laser tracker has a second absolute distance meter, which is designed to measure to an object surface.
  • the respective absolute distance meters send their measurement radiation through a single exit optic, they are separate, independent units. The need to provide two completely independent, separate absolute distance meters is complex in terms of production technology and is therefore expensive.
  • a special task is in particular to provide a simplified and more compact construction of the distance measuring unit, the measuring functionalities of the laser tracker being expanded at the same time, but the measuring accuracy of the previous measuring functionalities being maintained or increased.
  • a first aspect of the invention relates to a laser tracker for the industrial, coordinative determination of the position of a target object.
  • the laser tracker has a transmission unit with a transmission component that can be rotated about two axes of rotation on, wherein the transmission component is configured to emit a sighting beam defining a sighting axis and a distance measuring beam defining a distance measuring axis.
  • the laser tracker also has an angle detector configured to acquire angle data relating to a rotation of the transmitting component about the two axes of rotation.
  • the transmission unit has a control direction and the laser tracker is configured to automatically keep the transmission component aligned with the target object by means of the control device by rotating it about the two axes of rotation, the control device using the aiming beam emitted in the direction of a cooperative target of the target object to align the Send component determined relative to the cooperative target.
  • control data for adjusting the orientation of the transmission component with respect to the two axes of rotation can thus be generated based on returning parts of the sighting beam.
  • the control data can then be used to automatically adjust the alignment of the transmission component with respect to the two axes of rotation, and the target axis can thus be aligned to the measuring point defined by the cooperative target of the target object.
  • the laser tracker has a distance measuring unit, configured to carry out a distance measurement to the target object, during which the distance measuring beam is emitted by the transmission component in the direction of the target object and returning parts of the distance measuring beam are received.
  • the laser tracker can be used to determine an orientation of the transmission component relative to a cooperative target of the target object - e.g. by means of the sighting beam and the angle data - in order to derive coordinates of the target object in combination with the distance measurement to the target object.
  • a passive reflection unit with defined reflection properties can serve as a cooperative target, for example a steel ball with known Dimensions or a retroreflector like a cubic prism.
  • the term "cooperative target” refers to a target specifically intended for use in connection with a fine targeting process and, for example, target tracking.
  • the cooperative target "cooperates" with the laser tracker, e.g. a fine pointing unit and/or tracking unit, by having clearly defined attributes such as special reflection properties, a known shape, or known dimensions, which are used by the laser tracker for the purpose of the fine pointing process and/or the tracking process are exploited.
  • the laser tracker is also configured to perform a calibration functionality for referencing the distance measurement axis and the target axis, comprising: a target axis reference measurement, wherein a first target point is assigned target axis angle data for an alignment of the transmission component by means of the angle detector when the target axis is rotated by the transmission component around the two axes of rotation is aligned with the first target point, a distance measuring beam scanning, with a reference object being scanned, with a large number of different orientations of the transmission component being set with respect to the two axes of rotation and the different orientations by means of the distance measuring beam respectively associated scanning distances to the reference object and by means of the angle detector associated scanning angle data for the respective orientation of the transmission component are assigned to the two axes of rotation, generating a geometric model, such as a ceremoniwo lke or a lattice model (often also referred to as a mesh model, wireframe model, surface representation or polygonal network model), the reference object using the sampling distances and the sampling
  • referencing is understood to mean a determination of a relative geometric alignment of the distance measurement axis with respect to the sighting axis, which makes it possible, for example, for a point aimed at with the distance measurement beam to be unequivocally assigned to a point aimed at with the sighting beam. Furthermore, this makes it possible, for example, that any point in space can be deliberately targeted with both the distance measuring beam and the targeting beam.
  • the referencing can be used in order to coordinate the distance measuring axis and the target axis with one another by means of an adjustable beam steering element.
  • the calibration functionality according to the invention makes it possible to provide a laser tracker with two measurement functionalities, namely the so-called "classic" measurement (and tracking) of a cooperative, e.g. retro-reflective, target and a, e.g. scanning, measurement of a diffusely scattering target, the both measurement functionalities can be carried out using the same optoelectronic distance meter and can be referenced to one another.
  • the space required in the beam steering unit and the calibration and production costs can be reduced.
  • the laser tracker is configured such that the referencing data is derived based on the assumption that the spatial arrangement of the first and second target points is fixed, in particular that the positions of the first and second target points in space are identical.
  • the laser tracker has an automatic target search functionality for automatically finding the first target point and/or the reference object. Consequently, the laser tracker according to this embodiment is able, within the framework of the calibration functionality, to carry out the target axis reference measurement and the distance measurement beam scanning automatically with the aid of the automatic target search functionality.
  • the laser tracker is configured such that the second target point is identified based on the assumption that the reference object is at least partially spherical and the second target point corresponds to the center point of a sphere defined by the at least partially spherical shape of the reference object.
  • a further aspect of the invention relates to a laser tracker for the industrial, coordinative determination of the position of a target object.
  • the laser tracker has a transmission unit with a transmission component that can be rotated about two axes of rotation, the transmission component being configured to emit an aiming beam that defines a target axis and a distance measurement beam that defines a distance measurement axis.
  • the laser tracker has an angle detector configured to detect angle data relating to a rotation of the transmission component about the two axes of rotation and a distance measuring unit configured to carry out a distance measurement to the target object, in the context of which the distance measuring beam is transmitted by the transmitting component in the direction of the target object and the returning parts of the distance measuring beam are received will.
  • the laser tracker can be used to determine an orientation of the transmission component relative to a cooperative target of the target object, for example by means of the sighting beam and the angle data.
  • the laser tracker is configured to carry out a calibration functionality for referencing the distance measurement axis and the target axis, having: a target axis reference measurement, wherein a first target point is assigned target axis angle data for an alignment of the transmission component by means of the angle detector when the target axis is aligned to the first target point by rotating the transmission component about the two axes of rotation, an intensity scan, wherein a scanning of a reference object takes place, wherein a large number of different alignments of the transmission component with respect to the two rotational axes are set and the different alignments are assigned to the different alignments by means of the distance measurement beam, in each case associated reception intensities of returning parts of the distance measurement beam and by means of the angle detector associated scanning angle data for the respective alignment of the transmission component about the two rotational axes, a Identifying a predefined second target point provided by the reference object based on an intensity distribution of the received intensities on the reference object, in in particular by identifying a highlight of the
  • the laser tracker is configured to identify the second target point based on the assumption that the reference object is at least partially spherical and the second target point is a point on the surface of the sphere or the center of a sphere defined by the at least partially spherical shape of the reference object is assigned (in particular corresponds to this point).
  • the radius of the sphere defined by the at least partially spherical shape of the reference object is stored on the laser tracker, so that the referencing takes place taking into account this previously known radius, the identification of the predefined second target point being able to take place, for example, by identifying a highlight in the reception intensities.
  • a target with an excellent feature visible in the reception intensities can be used, e.g. a high-contrast target, where a predefined point can be clearly determined by means of intensity measurement.
  • a further aspect of the invention relates to a laser tracker for the industrial, coordinative determination of the position of a target object.
  • the laser tracker has a transmission unit with a transmission component that can be rotated about two axes of rotation, the transmission component being configured to emit an aiming beam that defines a target axis and a distance measurement beam that defines a distance measurement axis.
  • the laser tracker has an angle detector configured to detect angle data relating to a rotation of the transmission component about the two axes of rotation and a distance measuring unit configured to carry out a distance measurement to the target object, in the context of which the distance measuring beam is transmitted by the transmitting component in the direction of the target object and the returning parts of the distance measuring beam are received will.
  • the laser tracker has an optical coupling element configured to generate a common transmission path for the sighting beam and the distance measuring beam. Furthermore, a first beam steering element is arranged in the transmission path of the sighting beam upstream from the optical coupling element, configured for setting a transmission direction of the sighting beam relative to the transmission component. Additionally or alternatively, a second beam steering element is arranged in the transmission path of the distance measuring unit, upstream from the optical coupling element, configured for setting a transmission direction of the distance measuring beam relative to the transmission component.
  • the laser tracker is now configured here as part of the distance measurement, depending on a set distance to the target object, in particular depending on a set focus parameter with regard to focusing of the Distance measuring beam on the target object to make an adjustment of the first and / or the second beam steering element, eg based on referencing data for referencing the distance measuring axis and the target axis, which were determined by a calibration functionality as explained above.
  • the laser tracker is configured such that the first and/or the second beam steering element is adjusted in such a way that the distance measuring axis is coaxial or parallel to the target axis.
  • MEMS Micro-Electro-Mechanical System
  • Other possibilities are accumulator-optical elements, liquid lens elements, crystals which generate refractive index gradients through an electric field, etc.
  • the distance measuring unit has an adjustable focus unit configured to set a variable focus parameter for focusing the distance measuring beam onto the target object, in particular wherein the adjustable focus unit is configured and arranged such that the optical path of the sighting beam is free from the effect of the focus unit.
  • the focus unit is arranged outside of the optical path of the sighting beam, ie only in the optical path of the distance measuring beam.
  • the laser tracker is configured to carry out a distance measuring beam scan or an intensity scan of the reference object from a first distance and a further distance measuring beam scan or a further intensity scan of a further reference object or the same reference object from a second distance different from the first distance, with the distance measuring unit having an adjustable distance, for example Focus unit to adjust a variable focus parameter with regard to the focussing of the distance measuring beam and a first value of the focus parameter is set for the first distance and a second value of the focus parameter that is different from the first distance is set for the second distance, deriving first referencing data for the distance measuring beam scan or the intensity scan from the first distance and deriving second referencing data for the further distance measuring beam scanning or the further intensity scanning from the second distance, and a compensation parameter or a parameter set of compensation parameters, e.g. at least three compensation parameters, for referencing the distance measuring axis and the target axis as a function of the distance, in particular the focus parameter, by taking into account the first and the second referencing data.
  • the distance measuring unit
  • Another aspect of the invention relates to a laser tracker for the industrial coordinative position determination of a target object, having a support, a transmission component that can be rotated with respect to the support and has a beam exit, and a distance measuring unit with a laser beam source arranged in the support and a light guide arrangement configured for the fiber-guided supply of radiation from the laser beam source into the sending component.
  • the distance measuring unit is configured to carry out a distance measurement to the target object, during which at least part of the radiation is emitted via the beam exit and parts of the radiation returning from the target object are detected, with the distance measurement being based on the principle of a modulated continuous wave radar.
  • the laser beam source is configured to generate a first and a second laser radiation, with at least one of the two laser radiations being frequency-modulated, with a Frequency gradient of the first laser radiation is different from a frequency gradient of the second laser radiation.
  • the laser tracker has an optics arrangement arranged in the support, which is configured to split the first laser radiation into a first measurement radiation and a first reference radiation and to feed the first reference radiation into a reference interferometer arrangement. Furthermore, the optics arrangement is configured to divide the second laser radiation into a second measurement radiation and a second reference radiation and to feed the second reference radiation into the reference interferometer arrangement.
  • the reference interferometer arrangement is used, for example, to ensure characterization of the, for example, linear tuning of the respective laser radiation.
  • the reference interferometer arrangement has at least two arms for separately guiding parts of the first and/or second reference radiation, one of the two arms being designed as a temperature-controllable and/or temperature-stabilizable fiber-guided reference section and the at least two arms in a superimposition section for generating a reference output radiation be merged again.
  • the reference section can be temperature-controlled, for example, in the sense that the temperature can be measured and taken into account as part of the distance measurement. Alternatively or additionally, the temperature for the distance measurement is actively stabilized in order to keep the length of the reference section constant.
  • the first reference output radiation is then fed to the transmission component via a single-mode fiber, for example.
  • the laser tracker also has a frequency shifter, e.g. based on an acousto-optical modulator, the frequency shifter being configured to split the first measurement radiation into a first transmission radiation and a first local oscillator radiation that is frequency-shifted with respect to the first transmission radiation, and to split the second measurement radiation into a second transmission radiation and one second local oscillator radiation frequency-shifted with respect to the second transmission radiation.
  • a frequency shifter e.g. based on an acousto-optical modulator, the frequency shifter being configured to split the first measurement radiation into a first transmission radiation and a first local oscillator radiation that is frequency-shifted with respect to the first transmission radiation, and to split the second measurement radiation into a second transmission radiation and one second local oscillator radiation frequency-shifted with respect to the second transmission radiation.
  • the optical fiber arrangement is configured for fiber-guided feeding of the first and second transmission radiation and the first and second local oscillator radiation, and for example the reference output radiation, into the transmission component, with part of the first and second transmission radiation being transmitted to the target object via the beam exit of the transmission component for the distance measurement and parts of the first and second transmission radiation returning from the target object are detected and, furthermore, the parts of the first and second transmission radiation returning from the target object, e.g. in the transmission component, are superimposed with the first and second local oscillator radiation, respectively, in order to, based on Distance measurement to derive the distance to the target object according to the principle of a modulated continuous wave radar.
  • the reference radiation could also be detected outside the transmission component and thus only corresponding electrical or digitized signals could be provided for consideration in the distance measurement, e.g. by feeding the signals to the transmission component.
  • the received signals recorded in the transmission component or generated from transmission and local oscillator radiation could also be transmitted to the support by electrical or digital means.
  • the optics arrangement is designed as a free-beam optics. This is advantageous for a compact design, for example.
  • the frequency shifter is located in the strut, with the optics assembly and the reference interferometer assembly configured to output the reference radiation by means of heterodyne radiation mixing using the frequency shifter or another frequency shifter arranged in the support.
  • the optics arrangement and the light guide system are configured such that the first and second transmission radiation together and the first and second local oscillator radiation are fed together via a common fiber to the transmission component, in particular with the two fibers each being designed as polarization-maintaining fibers.
  • the transmission component has an internal control channel with a separate receiver, shielded from returning parts of the first or second transmission radiation, for a separate distance measurement based on the principle of a modulated continuous-wave radar.
  • part of the first or second transmission radiation and part of the first or second local oscillator radiation are decoupled into the internal control channel, and based on this, a separate distance measurement based on the internal control channel is carried out according to the principle of a modulated continuous wave radar in order to thermally and/or or mechanically caused changes in the fibers of the light guide arrangement when deriving the distance to the target object.
  • the frequency shifter is located in the transmitter component, with the laser tracker having another frequency shifter located in the support.
  • the optics arrangement and the reference interferometer arrangement are configured such that the reference output radiation is subdivided by means of heterodyne radiation mixing Use of the further, arranged in the support, frequency shifter is generated.
  • the optics arrangement and the light guide arrangement are configured such that the first and the second measurement radiation are fed to the transmission component via a common fiber, eg a polarization-maintaining fiber. For example, downstream from the further frequency shifter arranged in the support, the division of the first and second laser radiation as well as the supply of the first and second reference radiation to the reference interferometer arrangement in the free beam takes place.
  • the first and the second laser radiation are guided through the further frequency shifter arranged in the support, the first and the second measurement radiation corresponding to radiation of the same order of the further frequency shifter arranged in the support.
  • the first and second measurement radiation is based on a part of the first and second laser radiation that is free from a frequency shift caused by the additional frequency shifter arranged in the support.
  • the first and second measurement beams are decoupled upstream from the further frequency shifter arranged in the support and guided past the further frequency shifter arranged in the support into the transmission component.
  • the frequency shifter is arranged in the transmission component, the optics arrangement and the reference interferometer arrangement being configured in such a way that the reference output radiation is generated by means of homodyne radiation mixing.
  • the optics arrangement and the light guide arrangement are then configured such that the first and the second measurement radiation are fed to the transmission component via a common fiber, e.g. a polarization-maintaining fiber.
  • the optics arrangement and the reference interferometer arrangement are arranged together in a module housing that can be separated from the laser tracker in one piece.
  • the arrangement of the module housing in the support, in particular with corresponding plug connections of the fibers of the light guide arrangement being arranged in the vicinity of the module housing in the support, for example, has the advantage that the sensitive optics arrangement and the reference interferometer arrangement together with the support fibers are easily replaceable, which, for example, the maintenance and repair costs can be reduced.
  • the reference interferometer arrangement comprises a first and a second reference interferometer which are configured to provide a first and a second partial radiation, respectively, of the reference output radiation.
  • the first reference interferometer has two arms for separately guiding parts of the first reference radiation, one of the two arms of the first reference interferometer being guided over the (temperature-controllable and/or temperature-stabilizable, fiber-guided) reference section and the two arms of the first reference interferometer in the superimposition section for generating the first partial radiation are recombined.
  • the second reference interferometer has two arms for separately guiding parts of the second reference radiation, one of the two arms of the second reference interferometer being guided over a further temperature-controllable and/or temperature-stabilizable fiber-guided reference section and the two arms of the second reference interferometer in the superimposition section for generating the second partial radiation be merged again.
  • the two arms of the first reference interferometer are separated from the two arms of the second reference interferometer.
  • the first and the second partial radiation are then fed to the transmission component via a single-mode fiber, for example.
  • the reference section and the further reference section are arranged in a common temperature-controllable and/or temperature-stabilizable box.
  • the laser tracker can alternatively also be configured to algorithmically separate the interferometer output signal of a common interferometer with regard to components of the first and second reference radiation.
  • the reference interferometer arrangement has a (e.g. single) reference interferometer, which has two arms for separately guiding parts of the first and second reference radiation, one of the two arms being guided over the reference path and the two arms being brought together again in the superimposition section.
  • the optics arrangement is further configured such that the first and the second reference radiation are combined upstream of the reference interferometer and fed to the reference interferometer together as parts of the same interferometer input radiation.
  • the interferometer output radiation is then fed to the transmission component, for example via a single-mode fiber, with the laser tracker being configured to algorithmically separate an interferometer output signal generated by the reference interferometer with regard to portions of the first and second reference radiation.
  • the light guide arrangement has a fiber that is only partially protected by a tube, the fiber that is partially protected by a tube having a tube in a region of the passage between the support and the transmission component.
  • the partial use of tube has the advantage, for example, that the mechanical stress on the fiber through the tube can be reduced due to different thermal expansion coefficients.
  • the fiber that is only partially protected with a tube is only attached Places with - due to the operation of the laser tracker - mechanical stress protected with tube.
  • the transmission component has an objective, two fiber collimators, a receiver and two, e.g. polarizing, beam splitters arranged in series on an arrangement axis parallel or coaxial to the optical axis of the objective.
  • the first and the second transmission radiation are emitted via one of the two fiber collimators onto the beam splitter which is arranged axially closer to the objective and is configured to deflect at least part of the first and the second transmission radiation axially in the direction of the objective.
  • the first and second local oscillator radiation are emitted via the other of the two fiber collimators onto the beamsplitter located axially further from the objective, which is configured to deflect at least a portion of the first and second local oscillator radiation axially towards the receiver.
  • the two beam splitters are configured to allow at least parts of the parts of the first or second transmission radiation returning from the target to pass through to the receiver.
  • the transmission component also has a 1/4 retardation plate, which is arranged, for example, on the arrangement axis between the objective and the two beam splitters.
  • the transmission component can have an adjustable aperture in the optical path of the first and second transmission radiation.
  • the transmission component has an attenuator configured to adjustably attenuate the first and second transmission radiation emitted from one of the two fiber collimators, the attenuator being arranged, for example, between the one of the two fiber collimators and the beam splitter arranged axially closer to the objective.
  • the attenuator can be pivoted in and out of the optical path of the first and the second transmission radiation or configured for the selectable setting of different attenuation factors (mitigation strengths).
  • the attenuator is based on a fiber-coupled variable optical attenuator.
  • the transmission component has a beam steering element between each of the two fiber collimators and the respective associated beam splitter, configured for adjusting the beam directions of the first and second transmission radiation or the first and second local oscillator radiation.
  • the transmission component has an at least partially reflecting reference component and is configured to transmit at least part of the first and second transmission radiation in a free beam to the reference component and to take into account parts of the first and second transmission radiation returning from the reference component as part of the distance measurement.
  • a single constantly operated laser could be used as the laser beam source in combination with an electro-optical modulator arranged in the support (with RF generation).
  • an electro-optical modulator arranged in the support (with RF generation).
  • Such a beam generation structure is described, for example, in European Patent Application No. 18 190343.6.
  • the frequency shifter is arranged in the transmission component, for example, in order to transmit the first or second transmission radiation and the first or second local oscillator radiation generate.
  • the interferometrically measurable distance has its origin in the frequency shifter, which means that the fiber used to pass through the axis is not included in the measurement distance.
  • the fiber problems mentioned above continue to apply to the output fibers of the frequency shifter arranged in the transmission component, but are essentially reduced to thermal effects, since the mechanically changing axis bushing is no longer required.
  • Another aspect of the invention relates to a laser tracker for the industrial coordinative position determination of a target object, having a support, a transmission component that can be rotated with respect to the support and has a beam exit and a distance measuring unit with a laser beam source arranged in the support and an optical fiber arrangement configured for the fiber-guided supply of radiation from the laser beam source in the sending component.
  • the distance measuring unit is configured to carry out a distance measurement to the target object, during which at least part of the radiation is emitted via the beam exit and parts of the radiation returning from the target object are detected.
  • the laser beam source is configured to generate a frequency-modulated laser radiation and the laser tracker further has a frequency shifter, e.g. Furthermore, the laser tracker is configured to emit at least part of the transmission radiation via the beam exit of the transmission component to the target object and to superimpose parts of the transmission radiation returning from the target object and at least part of the local oscillator radiation in order to calculate the distance to the target object based on the distance measurement according to the principle of a modulated continuous wave radar.
  • the transmission component also has an at least partially reflecting reference component and is configured to transmit at least part of the transmission radiation in a free beam to the reference component and parts of the transmission radiation returning from the reference component record and to take into account these parts of the transmission radiation coming back from the reference component for the distance measurement to the target object.
  • the laser tracker is configured to take into account the parts of the transmission radiation returning from the reference component by superimposing the parts of the transmission radiation returning from the reference component with at least part of the local oscillator radiation.
  • the reference component is designed as a partially reflecting lens, in particular as a meniscus lens.
  • a disc or plane plate, or a back reflex on a beam splitter would also be conceivable.
  • beam components that are not deflected in the direction of the target object could be detected and measured in a separate channel in the transmission component.
  • the reflection enables the detection and compensation of remaining thermally or mechanically caused changes in fiber lengths, which can thus be detected in real time and compensated for in the distance measurement.
  • the laser tracker is configured to compensate for fluctuations in a fiber length of a fiber used for the beam guidance of the transmission radiation and/or local oscillator radiation, based on the assumption that the optical path of the transmission radiation containing the fiber for the transmission radiation should be constant towards the reference component.
  • the reflection at the reference component could be used directly as local oscillator radiation, with the position of the reflection corresponding to the zero point, for example.
  • the reflection at the reference component is used more as an additional calibration.
  • the transmission component has a lens and a beam splitter, with the lens and the beam splitter being arranged on an axis parallel or coaxial to the optical axis of the lens Arranged in a row, so that at least part of the transmission radiation is deflected axially towards the lens via the beam splitter.
  • the reference component is arranged in a static area between the lens and the beam splitter along the arrangement axis, wherein the static area is free from axially moving components of the transmission component and is delimited on the beam splitter side by the beam splitter, and wherein the beam splitter is configured at least parts of the Let pass reference component returning parts of the transmission radiation.
  • the area between the outermost optical component and the beam splitter further comprises a movable area with axially moving components, e.g.
  • At least part of the transmission radiation is deflected axially in the direction of the lens via the beam splitter, and the beam splitter is configured to let through at least parts of the parts of the transmission radiation returning from the target object.
  • the transmission component is designed as a transmission component that can be rotated about two axes of rotation
  • the laser tracker has a control device by means of which the transmission component can be aligned to the target object in a motorized manner by rotation about the two axes of rotation.
  • a coordinate measuring machine e.g. a laser tracker according to one of the embodiments described above, thanks to the occurrence of speckle patterns (often simply referred to as speckle) can be further expanded, for example, to measure a Rate of rotation of a rotating target object, e.g. a target object that is in self-rotation.
  • speckle patterns can occur a Doppler shift in the frequency of the distance measuring beam caused by the axial component of the rotational speed of the target object at the point of impact of the distance measuring axis on the target object can be observed. As discussed below, this can be exploited to derive the (instantaneous) rate of rotation of the target object about the axis of rotation.
  • the two-axis arrangement of the transmission component enables simplified determinations of the axis of rotation and the speed of the rotating target object compared to the prior art, for example by means of automatic measurement of the target object to determine the orientation of a front face of the rotating object through which the axis of rotation passes in relation to the axis of rotation.
  • a further aspect of the invention relates to a coordinate measuring machine for the industrial coordinate determination of the position of a point in space, e.g. designed as a laser tracker, having a transmitter unit configured to adjust the alignment of a measuring axis with respect to two axes of rotation.
  • the coordinate measuring machine has a distance measuring unit with a laser beam source, wherein the distance measuring unit is configured to carry out a distance measurement, in the context of which at least part of the radiation generated with the laser beam source is emitted via the transmitting unit along the measuring axis into space and the returned parts of the radiation, referred to as received radiation are recorded.
  • the distance measuring unit has an optical arrangement for carrying out the distance measurement according to the principle of a modulated continuous wave radar (see, for example, the coordinate measuring devices described above). Furthermore, the coordinate measuring machine has an angle detector, configured to acquire angle data with regard to the orientation of the measurement axis about the two axes of rotation.
  • the coordinate measuring machine also has a rotation rate measurement functionality for determining a rotation rate of a target object rotating about a rotation axis, wherein the coordinate measuring machine is configured, with respect to a measurement direction along the measurement axis, for a Receive frequency of the received radiation to determine a Doppler shift and, taking into account a 6DoF position (6 degrees of freedom, the six degrees of freedom) of the rotation axis of the target object relative to the coordinate measuring device, to derive the rotation rate of the target object.
  • a rotation rate measurement functionality for determining a rotation rate of a target object rotating about a rotation axis
  • the coordinate measuring machine is configured, with respect to a measurement direction along the measurement axis, for a Receive frequency of the received radiation to determine a Doppler shift and, taking into account a 6DoF position (6 degrees of freedom, the six degrees of freedom) of the rotation axis of the target object relative to the coordinate measuring device, to derive the rotation rate of the target object.
  • the yaw rate measurement functionality has two stages, with an automatic Doppler measurement of the target object being carried out as part of a first stage, having different orientations of the measurement axis with respect to the two axes of rotation and a determination of the Doppler shift for each of the different orientations.
  • the 6DoF position of the rotation axis of the target object relative to the coordinate measuring machine is automatically determined, for example assuming a constant rotation rate of the target object during the first stage.
  • the (instantaneous) rotation rate can then be determined by aligning the measuring axis with a measuring point on the target object, with the measuring point being offset away from the axis of rotation, e.g. with the coordinate measuring machine measuring a radial distance of the axis of rotation due to the 6DoF position of the axis of rotation Measuring point to the axis of rotation is derived and taken into account when determining the rate of rotation.
  • the coordinate measuring machine is configured to take into account geometry data in the context of the first and/or second stage, which provide information regarding the external shape of the target object.
  • the coordinate measuring machine has, for example, a further stage configured for automatic coordinate scanning of the target object and for determining geometric information regarding an external shape of the target object, which is taken into account in the first and/or second stage.
  • the coordinate scanning is carried out using the distance measuring unit and several different alignments of the measuring axis with respect to the two axes of rotation and/or using a camera-based scanning by a camera of the coordinate measuring machine, eg based on the principle of stereophotogrammetry or fringe projection.
  • a 3D model of the target object for example a point cloud or a grid model, can thus be generated by the coordinative scanning and taken into account in the context of the first and/or second stage.
  • movement components in the direction of the measurement axis which result from non-planarity of the target object, can be taken into account or compensated for.
  • the coordinate measuring machine is configured to carry out the distance measurement according to the principle of dual-chirp frequency modulation and thereby derive the distance as an absolute distance between the coordinate measuring machine and the target object.
  • the distance measuring unit is configured to generate laser radiation and to divide the laser radiation into a transmission radiation and a local oscillator radiation, e.g. wherein the distance measuring unit is configured to generate a frequency-modulated laser radiation and has a frequency shifter for dividing the laser radiation into the transmission radiation and the local oscillator radiation, the local oscillator radiation is frequency-shifted to the transmission radiation.
  • the distance measuring unit is designed to emit at least part of the transmitted radiation via the transmitting unit along the measuring axis and to superimpose the local oscillator radiation on parts of the transmitted radiation returning from the target object.
  • the laser beam source is configured to generate a further, typically frequency-modulated, laser radiation, a frequency gradient of the laser radiation being different from a frequency gradient of the further laser radiation, for example, at least at times.
  • the Doppler shift can thus be determined taking into account the further laser radiation.
  • the coordinate measuring machine has a segmented receiver for performing a speckle measurement functionality. The segmented receiver is configured to detect at least part of the received radiation, the receiver having a plurality of, in particular at least three, receiving surfaces that can be read out separately from one another.
  • a typical segmented receiver of this type is a quadrant detector, for example, with the segments forming four quadrants of a receiving surface and the receiving surfaces being close together, so that there is only a narrow gap between adjacent quadrants.
  • the speckle measurement functionality of the coordinate measuring machine is configured to determine a speckle pattern of the received radiation detected by the receiver at a point in time.
  • the receiver is thus designed, for example, to at least partially resolve a speckle field.
  • a course of speckle patterns of the received radiation determined at different points in time is determined, with the rate of rotation being derived taking into account the course of the speckle patterns determined at the different points in time.
  • the rotation rate is determined by finding a repeating feature of the speckle pattern, specifically a periodicity of the repeating feature.
  • a direction of movement could also be determined from the course of the speckle pattern.
  • the speckle measurement functionality is configured to determine a speckle centroid of the speckle pattern detected by the receiver at a point in time and to determine a profile of speckle centroids of the speckle pattern generated at the different points in time, determined at different points in time.
  • the yaw rate can thus be derived, taking into account the course of the speckle centroids determined at the different points in time, for example by determining a repeating pattern, in particular a periodicity, of the speckle centroids.
  • EP 2513595 B1 also describes, for example, a possibility known in the prior art for using a segmented receiver, e.g. a quadrant detector, to determine a speckle centroid.
  • a segmented receiver e.g. a quadrant detector
  • a further aspect of the invention relates to a coordinate measuring machine for the industrial coordinate determination of the position of a point in space, e.g. designed as a laser tracker, having a transmitter unit configured to adjust the alignment of a measuring axis with respect to two axes of rotation.
  • the coordinate measuring machine has a distance measuring unit with a laser beam source, wherein the distance measuring unit is configured to carry out a distance measurement, in the context of which at least part of the radiation generated with the laser beam source is emitted via the transmitting unit along the measuring axis into space and the returned parts of the radiation, referred to as received radiation are recorded.
  • the coordinate measuring machine has an angle detector, configured to acquire angle data with regard to the orientation of the measurement axis about the two axes of rotation.
  • the coordinate measuring machine also has a segmented receiver and a speckle measurement functionality, the segmented receiver being configured to detect at least part of the received radiation and having a plurality of receiving surfaces that can be read separately from one another, and the speckle measurement functionality being configured to determine a a point in time of the speckle pattern of the received radiation detected by the receiver and for determining a course of speckle patterns of the received radiation determined at different points in time.
  • the distance measuring unit has an optical arrangement for carrying out the distance measurement according to the principle of a modulated continuous wave radar (see, for example, the coordinate measuring devices described at the outset).
  • the coordinate measuring machine has a yaw rate measurement functionality for determining a yaw rate of a target object rotating about an axis of rotation, the yaw rate being derived taking into account the course of the speckle pattern determined at the different points in time, e.g. by determining a recurring feature of the speckle pattern, in particular a periodicity of the repeating feature.
  • the speckle measurement functionality is configured to determine a speckle centroid of the speckle pattern detected by the receiver at a point in time and to determine a course of speckle centroids of the speckle pattern generated at the different points in time, determined at different points in time, taking the rotation rate into account of the course of the speckle centroids determined at the different points in time is derived, e.g. by determining a repeating pattern, in particular a periodicity, of the speckle centroids.
  • Fig. 1 Schematic of a measurement system according to the prior art
  • inventive laser tracker during a measurement in the first measurement functionality for determining sighting axis angle data within the framework of the calibration functionality
  • inventive laser tracker during a measurement in the second measurement functionality for determining scanning distances and scanning angle data within the framework of the calibration functionality
  • FIG. 6 shows a first embodiment of an optical arrangement for an inventive laser tracker based on the principle of a modulated continuous-wave radar
  • FIG. 7 shows a second embodiment of an optical arrangement for an inventive laser tracker based on the principle of a modulated continuous-wave radar
  • 8 shows a third embodiment of an optical arrangement for an inventive laser tracker based on the principle of a modulated continuous-wave radar
  • FIGS. 6 and 8 shows an optical transmission and reception arrangement in the transmission component, as could be used, for example, in the embodiments illustrated in FIGS. 6 and 8;
  • FIG. 10 shows an exemplary arrangement for measuring the yaw rate of a target object in its own rotation using a coordinate measuring device having a yaw rate measurement functionality.
  • FIG. 1 schematically shows a measurement system according to the prior art for determining 3D coordinates of an object 100.
  • the measurement system has a laser tracker 101 and a mobile scanning unit 2 up.
  • a retroreflector 3 is attached to the scanning unit 2, which can be targeted by the laser tracker 101 using a laser beam 4 as a tracking or measuring beam, as a result of which the position of the scanning unit 2 relative to the laser tracker 101 can be determined.
  • state-of-the-art laser trackers 101 now have a camera (not shown) in an increasingly standardized manner, so that the orientation of the scanning unit 2 can be determined by means of markings (not shown) applied to it and image processing of a camera recording.
  • a scanning beam 5 is also emitted at the mobile scanning unit 2, with which the object surface is scanned and local measurement coordinates of the respective position of the surface are determined.
  • the measurement points measured in this way on the object 100 can be referenced in an object coordinate system by means of the laser tracker 101 and global 3D coordinates of the object 100 can be generated.
  • Such measuring systems are used, for example, in industrial production when measuring aircraft or automobiles, for example, and can enable quality control of workpieces during production.
  • the mobile scanning unit 2 is typically designed as a hand-held scanner or is mounted on an articulated arm that can be moved by a motor or on a robot, for example a UAV (“Unmanned Aerial Vehicle”).
  • UAV Unmanned Aerial Vehicle
  • the scanning unit 2 typically has to be brought close to the object surface for a measurement, for example less than one meter.
  • this is not always possible or involves a great deal of effort, for example in the case of large overhanging objects, for example aircraft components in a production hall, in compliance with the necessary safety precautions for the safety of the worker, a ladder for a worker guiding the mobile scanner 2 having to be continuously repositioned or by the position of the measuring object having to be continuously adjusted to the measuring task using sometimes heavy equipment.
  • a laser tracker 1 for example having a first and a second measuring functionality, the first measuring functionality being designed for the coordinate determination of the position of a cooperative, for example retroreflective, target 3 and the second measuring functionality being designed for the coordinate determination of the position of a ( essentially) diffusely scattering target, ie for scanning a natural surface of a target object 100, here for example an airplane wing, and for generating a point cloud of the surface based on a number of scanning positions of the surface.
  • the laser tracker 1 is configured, for example, such that a target-tracking movement or a movement of the laser beam 4 following a predefined scan pattern 6 is made possible.
  • the laser tracker is configured in the second measurement functionality to carry out a large number of distance measurements to a large number of diffusely scattering targets or target points on the surface of a target object to be measured.
  • the laser tracker is configured, e.g. by means of a correspondingly designed control and evaluation unit, so that for the large number of distance measurements, angles of rotation recorded with angle measuring devices are linked to the measured distances, so that point positions of the respective target points are defined by the linking, and a number the point cloud having point positions can be generated. For example, this occurs at a rate of at least 100 spot positions per second. For example, at least 1000 or at least 10,000 point positions are determined per second.
  • the first measurement functionality can therefore be used, for example, for generic tracking of a movable workpiece 100 equipped with retroreflectors 3 or for measuring individual, specially marked reference points on the surface of object 100, which are equipped with retroreflectors 3.
  • a mobile scanning unit 2 see Fig 1
  • the second measurement functionality instead of using a mobile scanning unit 2 (see Fig 1) be switched to the second measurement functionality in order to measure the surface of the target object 100, for example referenced to a reference point measured in the first measurement functionality and marked with a retroreflector 3 .
  • the laser tracker 1 according to the invention can be used to scan the object surface in the second measurement functionality over comparatively large distances, e.g. over a few meters up to a few tens of meters, in order to generate a three-dimensional point cloud of the object surface .
  • the laser tracker according to the invention is configured to carry out the distance measurement in both measurement functionalities using the same opto-electronic distance meter, which means that the space requirement in the beam steering unit and the calibration and production costs can be reduced, for example.
  • One approach is to emit pulsed electromagnetic radiation, such as laser light, onto a target to be measured and then to receive an echo from this target as a backscattering object, with the distance to the target to be measured being determined, for example, based on the transit time, the shape, and/or the phase of the pulse can be determined.
  • pulsed electromagnetic radiation such as laser light
  • Such laser distance meters have meanwhile established themselves as standard solutions in many areas.
  • the opto-electronic distance meter of the laser tracker is designed for a distance measurement according to the pulse propagation time principle, with the entire signal form being recorded, for example, by scanning and sampling the entire backscattered (and possibly emitted) pulse form (so-called “waveform digitizing”, WFD).
  • An emitted pulse signal is detected by scanning the radiation detected by a detector, identifying a signal within the scanned area and finally determining a position of the signal over time.
  • the opto-electronic distance meter of the laser tracker according to the invention is designed, for example, for distance measurement according to the principle of a modulated continuous wave radar, also called FMCW distance measurement (FMCW: “Frequency Modulated Continuous Wave”).
  • FMCW FMCW: “Frequency Modulated Continuous Wave”.
  • a tunable laser source is used in an FMCW arrangement.
  • the optical frequency of the laser source is tuned linearly and at a known tuning rate, although the absolute wavelength of the signal generated in this way is only known to a certain extent.
  • the radiation sent to the target is often called the transmit radiation or transmit signal, with the return portions of the transmit radiation being called the receive radiation or receive signal.
  • the received radiation is superimposed with a second radiation which is not emitted to the target but is derived from the laser radiation on which the emitted transmission radiation is based.
  • the second radiation is often called local oscillator radiation or local oscillator radiation.
  • the resulting beat frequency of the mixed product, the interferogram is a measure of the distance to the target.
  • the distance measuring devices used to implement these methods usually use a signal generator, by means of which a signal, for example a rising or falling frequency ramp, is impressed on a radiation source that can be modulated.
  • a signal for example a rising or falling frequency ramp
  • modulatable lasers are used as radiation sources.
  • transmission and reception optics are used in the optical area, which are followed, for example, by a detector for heterodyne mixing, A/D converters and a digital signal processor.
  • the change in the frequency of the emitted transmission signal represents the scale of the measurement. Depending on the accuracy required of the distance measurement, this scale can be verified or determined more precisely by means of an additional measurement. Sufficiently linear tuning of the laser source, for example, often requires additional effort.
  • part of the emitted radiation is guided over a reference interferometer with a defined reference length. Based on the known reference length, the resulting beat product can be used to deduce the temporal change in frequency of the emitted transmission signal. If the reference length is not known or is unstable, for example due to temperature influences, it can be determined using an additional calibration unit, for example a gas cell or a Fabry-Perot element.
  • the target is a target that is stationary relative to the range finder, i.e. a target that has a distance from the range finder that does not change over time.
  • suitable compensation measures however, absolute distance measurements to moving or vibrating targets can also be carried out.
  • a radial movement of the target relative to the distance meter leads to a Doppler shift in the reception frequency due to the Doppler effect.
  • the Doppler shift can be compensated for, for example, by a combined measurement using successively increasing and decreasing frequency ramps, since in the case of a constant radial target velocity of the target, the Doppler shift is the same for both ramps, but the beat frequencies generated by the two ramps are different.
  • two simultaneous and opposing frequency ramps are used, i.e. emitting radiation with two radiation components, with the frequency of a first radiation component moving “up”, i.e. to higher frequencies, and at the same time the frequency of a second radiation component moving “down”, i.e. to lower frequencies , is tuned.
  • the laser tracker is configured, for example, for polarization-based, spectral-based, or algorithmic separations.
  • Such a measurement principle for a modulated continuous-wave radar with two laser beams to compensate for the Doppler effect, with at least one of the two laser beams being frequency-modulated, is called the dual-chirp frequency modulation principle or dual-laser frequency modulation principle.
  • the laser tracker has a base 7, a support 8 and a transmitter component 9, the support 8 being rotatably mounted on the base 7 about a first axis of rotation and the transmitter component 9 about an axis substantially orthogonal to the first axis of rotation second axis of rotation is rotatably attached to the support 8.
  • the transmission component 9 has, for example, common exit and entry optics for a distance measuring beam and a sighting beam (often also used, for example, as a tracking beam).
  • the base 7, support 8 and the transmission component 9, which can thus be rotated about two axes of rotation and defines a target axis 10, are also often referred to jointly as the beam steering unit 11.
  • the laser tracker is configured to emit a targeting or tracking beam along the sighting axis 10 and to receive returning portions of the targeting or tracking beam.
  • the laser tracker is configured, for example, to derive an angular position change of a cooperative target of the target object relative to the laser tracker based on the tracking beam, and to generate control data for adjusting the orientation of the beam steering unit 11 .
  • the laser tracker has a distance measuring unit configured to determine a distance to the target object by emitting a distance measuring beam defining a distance measuring axis 12 via a beam exit of the transmitting component 9 and detecting returning parts of the distance measuring beam.
  • the orientation or a change in orientation of the beam steering unit 11 is determined, for example, by means of an angle detector, which is configured to acquire angle data relating to a rotation of the beam steering unit 11 about its two axes of rotation, i.e. to acquire a rotation of the support 8 relative to the base 7 and a rotation of the Transmitter component 9 relative to support 8.
  • the transmission component 9 and thus the target axis 10 are aligned for target tracking in such a way that a cooperative target, for example a retroreflector 3 (see Fig. 1) or a so-called tooling ball, is projected by means of a beam from the transmission component 9 along the target axis 10 emitted tracking beam is targeted.
  • a cooperative target for example a retroreflector 3 (see Fig. 1) or a so-called tooling ball
  • the tracking beam is reflected parallel to the target axis 10 back to the transmission component 9, with the reflected beam being detected using detection means of the beam steering unit 11.
  • an emission or reception direction of the tracking beam ie a direction of the sighting axis 10
  • the receiver of the beam steering unit is designed as a position-sensitive detector (PSD) with which a focal point of a light distribution on the sensor surface can be determined very quickly and with high resolution.
  • PSD position-sensitive detector
  • a deviation of the received tracking beam from a zero position is determined and the alignment of the beam steering unit 11, i.e. the alignment of the sighting axis 10, is continuously adjusted depending on this deviation so that the sighting axis 10 is aligned with the center of the retroreflector 3.
  • a distance measuring beam defining a distance measuring axis 12 is emitted from the transmitting component 9 by means of the optical distance measuring unit in order to determine a distance to the target object.
  • the distance measuring unit and the beam steering unit 11 are preferably configured and coordinated with one another in such a way that the target directions defined by the sighting axis 10 and by the distance measuring axis 12 are precise match, ie emerge coaxially from the transmission component 9.
  • This enables, for example, a simplified, at best direct (no computational effort) referencing of position data from a measurement to a retroreflector (sighting beam or tracking beam defines target direction) with position data from a measurement to a diffusely scattering target (distance measuring beam defines target direction).
  • the relative orientation of the two target directions to one another can vary, for example due to aging and temperature influences and mechanical effects.
  • Variable optical components such as a focus unit or swiveling filters can also cause the measuring axis to be deflected.
  • the focus setting of the distance measuring beam changes from a focus set essentially to infinity for measuring retroreflectors to a distance-dependent focus setting for essentially sharp imaging of the diffusely scattering target object .
  • the distance-dependent focus adjustment can take place, for example, by means of a focus unit that can be set for different distances or by means of a focus unit designed as a fixed focus unit, which provides a nominal focus.
  • the focus unit is preferably part of the distance measuring unit and is arranged in the laser tracker in such a way that the focus unit does not affect the targeting or tracking radiation, i.e. that the targeting or tracking radiation does not pass through the focus unit.
  • this change in focus can lead to different offsets of the distance measurement axis 12 to the sighting axis 10 for different measurement distances.
  • adjustable attenuation filters are used in the transmission channel of the distance measurement unit in order to adapt the transmitted signal amplitude to the electronic reception unit depending on the set measurement functionality, so that intensity differences of the returning radiation be compensated for measurements on retroreflective targets compared to measurements on natural, diffusely scattering targets.
  • the laser tracker according to the invention is configured, for example, to carry out a calibration functionality, shown schematically in Figures 4 and 5, for referencing the distance measuring axis 12 to the target axis 10.
  • the sighting beam i.e. the sighting axis 10
  • a first target point 13A represented e.g. by a retroreflector 3
  • sighting axis angle data are determined using the angle measuring means for the alignment of the Target axis 10 defined by the alignment of beam steering unit 11 to first target point 13A.
  • the laser tracker scans a reference object 14, e.g. a so-called tooling ball, with reference object 14 being scanned with the distance measuring beam by moving support 8 and/or beam steering unit 9, with associated scanning distances to the target object and associated scanning angle data for the movement of the beam steering unit are recorded.
  • a reference object 14 e.g. a so-called tooling ball
  • the laser tracker is now configured to identify a predefined second target point 13B on the reference object 14 based on the scanning angle data and the associated scanning distances. Based on this, the laser tracker derives referencing data for referencing the distance measurement axis 12 and the sighting axis 10, based on the sighting axis angle data and the scanning angle data and a previously known spatial relationship between the first target point 13A and the second target point 13B.
  • the angle data when measuring on the retroreflector 3 are defined by the target axis 10
  • the angle information is based on the scanning of the reference object 14 by the distance measuring axis 12 is defined, whereby a referencing of the distance measurement axis 12 to the target axis 10 is made possible.
  • a retroreflector 3 and then a tooling ball 14 are placed in such a way that the first target point 13A and the second target point 13B coincide.
  • the first target point 13A and/or the second target point 13B can be targeted or identified, for example, based on known geometric information which provides a form of information of a cooperative target or of the reference object 14 .
  • the highlight point for transmission radiation impinging on the sphere of the tooling ball 14 can also be determined and used, for example, to derive angle information with regard to the center of the sphere.
  • the laser tracker is configured such that the shape information and/or the known spatial relationship between the first target point and the second target point is stored as reference information on the laser tracker, or the laser tracker is configured to query and/or receive this reference information.
  • a measuring sphere with a known dimension is used as a reference object, which is placed in such a way that the center of the sphere coincides with the second target point 13B or assumes a known relative position with respect to the second target point.
  • a specially configured hollow calibration hemisphere could be used, which accommodates a retroreflector in the center of the sphere, so that as part of the calibration functionality of the laser tracker, the sighting axis reference measurement is carried out using the retroreflector arranged in the calibration hemisphere and only for distance measuring beam scanning or intensity scanning the calibration hemisphere must be rotated 180 degrees so that the back of the calibration hemisphere serves as a reference object.
  • the sighting beam and/or the distance measuring beam are often emitted in wavelength ranges that are invisible to the human eye, for example in the infrared wavelength range.
  • Generic laser trackers therefore often have another pointing beam in the visible wavelength range, for example as an orientation aid for a user.
  • such a pointing beam is also used, for example, for reasons of eye safety when using laser beams that are invisible to the human eye.
  • a further aspect of the invention relates to the aiming or tracking transmitter of a laser tracker described above having a laser diode emitting in the visible wavelength range and the aiming or tracking radiation being provided in the visible wavelength range.
  • the pointing beam is thus provided by a dual use of the aiming or tracking radiation, so that, for example, further orientation or calibration of the pointing beam to the aiming or distance measuring beam is omitted.
  • FIGS. 6 to 8 schematically show different embodiments of the optical arrangement of an inventive laser tracker based on the principle of a modulated continuous-wave radar.
  • an FMCW rangefinder is suitable both for measuring cooperative targets and for measuring (essentially) diffusely scattering targets.
  • the distance measurement is based on two simultaneous opposing frequency ramps, whereby, for example, the frequency of a first part of the radiation is tuned “up”, i.e. to higher frequencies, and at the same time the frequency of a second part of the radiation is tuned “down”, i.e. to lower frequencies.
  • the laser tracker has a laser beam source (not shown), configured to generate the first and the second frequency-modulated radiation, which can be emitted, for example, in a free beam or, as shown in FIGS. 6 to 8, by means of two separate fibers 15A, 15B via respective fiber collimators 16A, 16B to a free-beam optics arrangement 17 arranged in the support 8.
  • a laser beam source not shown
  • the first and the second frequency-modulated radiation which can be emitted, for example, in a free beam or, as shown in FIGS. 6 to 8, by means of two separate fibers 15A, 15B via respective fiber collimators 16A, 16B to a free-beam optics arrangement 17 arranged in the support 8.
  • the laser tracker has a reference interferometer 18A, 18B arranged in the support for each of the two frequency ramps, each with a defined reference length.
  • the various radiations or radiation components are then guided from the support 8 into the transmission component 9 via optical fibers.
  • the laser tracker has a frequency shifter 19 arranged in the support 8, for example an accousto-optical modulator.
  • the frequency shifter 19 the laser radiation coming from the laser beam source and coupled via two fiber collimators 16A, 16B is converted into a part without a frequency shift (unshifted part, dotted line) and divided into a part with frequency shift (frequency-shifted part, dashed line).
  • the free-beam optical arrangement 17 then further separates these radiation components into measurement radiation and reference radiation, the measurement radiation without frequency shift being used as transmission radiation 20A, 20B and the measurement radiation with frequency shift being used as local oscillator radiation 21A, 21B.
  • the two reference interferometers 18A, 18B are each constructed as heterodyne interferometers, with the frequency-shifted reference radiation 22A, 22B, for example, covering a longer path than the unshifted frequency radiation 23A, 23B, with one arm each, here e.g. for the frequency-shifted reference radiation 22A, 22B, 5m.
  • the two arms of the reference interferometer are then superimposed and the superimposed signal is transferred to optical fibers 25A, 25B, e.g. single-mode fibers.
  • These fibers 25A, 25B therefore already contain the radiation superimposed in the respective interferometer, which is why the exact fiber lengths essentially have no influence on the measurement result. As a result, these fibers 25A, 25B do not have to remain stable either.
  • the superimposed reference radiations of the two reference interferometers are directed to corresponding reference receivers 26A, 26B arranged in the transmission component 9 .
  • the two transmission beams 20A, 20B which are subjected to opposite frequency ramps, for example, are fed to the transmission component 9 via a common fiber 27, e.g. a polarization-maintaining fiber.
  • a common fiber 27 e.g. a polarization-maintaining fiber.
  • the two local oscillator radiations 21A, 21B are fed to the transmission component 9 in a common fiber 28 .
  • the transmission radiation 20A, 20B and the local oscillator radiation 21 A, 21 B are brought to interference only in the transmission component, with the local oscillator radiation 21 A, 21 B being sent directly to the receiver and the transmission radiation 20A, 20B first to the target and running back.
  • the two fibers 27, 28 are part of the measurement section. If the length of one to the other changes by dl, the distance to the target appears changed by dl/2. It must therefore be ensured that the lengths of the fibers 27, 28 do not change relative to one another, or that the lengths change equally.
  • the arrangement of the laser beam source, free-radiation optics arrangement 17 and the two reference interferometers 18A, 18B in the support 8 enables, for example, a more compact and simpler construction of the transmission component 9.
  • the various radiations or radiation components have to go from the support 8 to the transmission component via optical fibers 9 are performed.
  • the individual optical fibers (waveguides) used for this feed still belong to the measurement section. It must therefore be ensured that the fibers belonging to the measurement section do not change in relation to one another or that the fibers at least change to the same extent.
  • both fibers are typically of the same length and are laid as parallel as possible. Ideally, both fibers are exposed to the same thermal (temperature) and mechanical (bending, pressure, torsion) conditions.
  • an identical fiber routing is associated with a high level of control and stabilization effort and, for example, electrical cables in the axle bushing between the support and the transmitting component can press differently on the fibers, which can cause so-called microbends and local stress.
  • the "loose tubes" used to protect the fibers can also pull and hit the fiber due to different thermal expansion coefficients, with rolled-up fibers for example a so-called "stick-slip effect" occurring.
  • the laser tracker in a further embodiment shown in Fig. 7 has two frequency shifters 19, 19', one of the two frequency shifters for generating the transmission radiation 20A, 20B and the local oscillator radiation 21 A, 21 B in the transmission component 9 and the other for providing the heterodyne reference interferometer 18A , 18B is further arranged in the support 8.
  • FIG. 7 shows one of the two frequency shifters for generating the transmission radiation 20A, 20B and the local oscillator radiation 21 A, 21 B in the transmission component 9 and the other for providing the heterodyne reference interferometer 18A , 18B is further arranged in the support 8.
  • the free-beam optics arrangement 17 and the light guide arrangement are adapted in such a way that only the non-frequency-shifted parts of the measurement radiation, for example subjected to opposing frequency ramps, are fed through a common fiber 27 to the transmission component 9 .
  • the second frequency shifter can be dispensed with if the reference interferometers 18A, 18B' are designed as homodyne interferometers.
  • FIG. 9 shows an optical transmission and reception arrangement in the transmission component, as could be used, for example, in the embodiments illustrated in FIGS. 6 to 8.
  • FIG. 9 shows an optical transmission and reception arrangement in the transmission component, as could be used, for example, in the embodiments illustrated in FIGS. 6 to 8.
  • the transmission component has an objective 29, two fiber collimators 30A, 30B, a receiver 31, a focus arrangement 32, two beam splitters 34A, 34B arranged on an arrangement axis 33, here coaxial to the optical axis of the objective, and a laser source 35 for generating a sighting or .tracking beam on.
  • Other components typically used for beam steering or shaping are also conceivable, such as, for example, partially transparent or polarizing mirrors and delay components, for example lambda/4 plates.
  • the laser tracker has an adjustable attenuation filter 36, for example in the transmission channel of the transmission radiation, in order to adapt the transmitted signal amplitude to the receiver 31 depending on the set measurement functionality. For example, differences in the intensity of the returning radiation can be compensated for when measurements are made on retroreflective targets compared to measurements on natural, diffusely scattering targets.
  • the transmission radiation is emitted via the beam splitter 34A arranged closer to the objective 29 in the direction of the target, whereas the local oscillator radiation is deflected directly onto the receiver 31 by the beam splitter 34B further away from the objective.
  • the laser tracker is configured so that the sighting beam is coupled into the transmission or reception path of the distance measuring beam by means of an optical coupling element 37, so that the distance measuring beam and the sighting beam are essentially parallel or coaxial from the transmission component 9 exit.
  • the laser tracker can have a calibration functionality as described above for referencing the distance measuring axis 12 and the target axis 10.
  • the laser tracker can be configured for active compensation of changes in orientation of the two target directions 10, 12 relative to one another, for example in the case where the focus arrangement 32 is configured to set a variable focus parameter with regard to focusing the distance measuring beam on the target object .
  • the laser tracker has, for example, in the transmission path of the sighting beam upstream of the optical coupling element 37 a first beam steering element, eg one or more adjusting wedges, configured to set a transmission direction of the sighting beam relative to the beam steering unit (not shown), and/or has the laser tracker in the transmission path of the transmission radiation upstream of the optical coupling element 37 a second beam steering element, for example one or more adjusting wedges 38, configured to adjust a transmission direction of the transmission beam relative to the beam steering unit.
  • a first beam steering element eg one or more adjusting wedges
  • the laser tracker then adjusts the first and/or the second beam steering element as a function of the focus parameter, for example based on a compensation parameter determined according to the above calibration functionality for a focus- or distance-dependent referencing of the distance measurement axis 12 and the sighting axis 10 .
  • the laser tracker has access to a predefined lookup table with a list of focus-dependent compensation parameters, for example.
  • the transmission component also has an at least partially reflecting reference component 39, which reflects at least part of the transmission radiation before it exits the transmission component, so that any remaining thermally induced fluctuations in the beam guidance of the transmission radiation can be compensated for, for example by analyzing a superimposition of the reference component 39 returning parts of the transmission radiation with a part of the local oscillator radiation and a comparison with a superimposition of the parts of the transmission radiation returning from the target object with a part of the local oscillator radiation.
  • the reference component 39 is designed as a partially reflecting lens, e.g. as a meniscus lens, and is arranged between the focus arrangement 32 and the beam splitter 34A for the transmission radiation, so that, e.g. between the reference component 39 and the beam splitter 34A, no axially movable parts act on the transmission radiation.
  • a partially reflecting lens e.g. as a meniscus lens
  • FIG. 10 shows an exemplary arrangement for measuring the yaw rate of a target object 101 in its own rotation using a coordinate measuring device having a yaw rate measurement functionality.
  • a rotating machine part 101 is targeted as part of an inspection or for continuous position and speed monitoring. If the distance measuring axis 12 is aligned with a measuring point on the machine part 101, the measuring point having a point distance (offset) 40 from the axis of rotation 41 of the machine part 101 (and the distance measuring axis 12 is not parallel to the axis of rotation 41), the occurrence of speckles a Doppler shift along the distance measuring axis 12 caused by the axial component, with respect to the distance measuring axis 12, of the rotational speed of the machine part at the impact point 42. As a result, the rotational speed 43 at the impact point 42 of the machine part 101 about the rotational axis 41 can be derived.
  • a segmented detector e.g. a quadrant detector
  • the direction of movement and the rate of rotation can be determined without precise knowledge of the geometry (position of the axis, plane of rotation), since the centroid in the different segments periodically moves with regard to the rotation cycle of the Workpiece 101 moves.
  • the scanning functionality provided by the two-axis arrangement of the transmission component 9 enables one of the initially described functions Laser tracker 11 automatically determines the geometry of the machine part 101. This enables a simplified, in particular automatic, determination of the axis of rotation 41 and thus the speed of the rotating machine part 101 without prior knowledge of the relative alignment of the distance measuring axis 12 with respect to the frontal plane of rotation 44 and the axis of rotation 41 .
  • the adjoining end face 44 can be scanned in a coordinated manner and a 3D model can thus be created, for example while the machine part is in rest.
  • a 3D model can thus be created, for example while the machine part is in rest.
  • information about the orientation of the end face 44 in relation to the distance measurement axis 12 and the geometry of the end face 44 is derived.
  • the end face 44 is then scanned during the rotation of the machine part 101 and the Doppler shift is determined for different orientations of the distance measuring axis 12, whereby a speed map with respect to the rotation of the end face 44 about the axis of rotation 41 is generated, for example.
  • the point of intersection of the rotation axis 41 with the target object can then be determined via the zero speed (no Doppler shift) and, taking into account the distance measurement axis 12 and the geometry of the end face 44, the alignment of the rotation axis 41 and the rotation speed 43 be determined at the impact point 42, for example by realigning the distance measurement axis 12 to the impact point 42 with a known radius 40. It is understood that these figures shown are only possible

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  • General Physics & Mathematics (AREA)
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Abstract

L'invention se rapporte à un dispositif de poursuite laser pour la détermination de position coordinative industrielle d'une cible, le dispositif de suivi laser fournissant deux fonctionnalités de mesure, à savoir une fonctionnalité de mesure permettant de mesurer et de suivre une cible coopérative, par exemple rétro-réfléchissante, et une fonctionnalité de mesure permettant une mesure, par exemple de balayage, d'une cible à diffusion diffuse, les deux fonctionnalités de mesure pouvant être effectuées et référencées l'une par rapport à l'autre au moyen du même dispositif de mesure de distance optoélectronique.
EP21708593.5A 2021-02-24 2021-02-24 Dispositif de poursuite laser à deux fonctionnalités de mesure et mesure de distance fmcw Pending EP4298459A1 (fr)

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PCT/EP2021/054595 WO2022179683A1 (fr) 2021-02-24 2021-02-24 Dispositif de poursuite laser à deux fonctionnalités de mesure et mesure de distance fmcw

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CN117907982B (zh) * 2024-03-19 2024-05-31 深圳市速腾聚创科技有限公司 激光雷达测距测速的方法以及激光雷达

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CN101553707B (zh) 2006-01-13 2013-08-07 莱卡地球系统公开股份有限公司 坐标测量设备
US8896843B2 (en) 2009-12-14 2014-11-25 Leica Geosystems Ag Method for speckle mitigation in an interferometric distance meter by determining a pointing direction
US9036134B2 (en) 2013-02-12 2015-05-19 Faro Technologies, Inc. Multi-mode optical measurement device and method of operation
EP2801841B1 (fr) * 2013-05-10 2018-07-04 Leica Geosystems AG Appareil de suivi laser comprenant une unité d'enregistrement d'une cible pour le pistage d'une cible et une détection d'orientation

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