WO2014131379A2 - A method to increase accuracy of the optical measurement of a position of a point in space by means of a redundant measurement - Google Patents

A method to increase accuracy of the optical measurement of a position of a point in space by means of a redundant measurement Download PDF

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Publication number
WO2014131379A2
WO2014131379A2 PCT/CZ2014/000019 CZ2014000019W WO2014131379A2 WO 2014131379 A2 WO2014131379 A2 WO 2014131379A2 CZ 2014000019 W CZ2014000019 W CZ 2014000019W WO 2014131379 A2 WO2014131379 A2 WO 2014131379A2
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WO
WIPO (PCT)
Prior art keywords
measurement
point
laser tracker
measured
space
Prior art date
Application number
PCT/CZ2014/000019
Other languages
French (fr)
Other versions
WO2014131379A3 (en
Inventor
Michael VALÁŠEK
Martin NEČAS
Original Assignee
Čvut V Praze, Fakulta Strojní
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 Čvut V Praze, Fakulta Strojní filed Critical Čvut V Praze, Fakulta Strojní
Priority to EP14710789.0A priority Critical patent/EP2962126A2/en
Publication of WO2014131379A2 publication Critical patent/WO2014131379A2/en
Publication of WO2014131379A3 publication Critical patent/WO2014131379A3/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/66—Tracking systems using electromagnetic waves other than radio waves
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
    • G01B11/03—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness by measuring coordinates of points
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/002—Measuring arrangements characterised by the use of optical techniques for measuring two or more coordinates

Definitions

  • the invention concerns a method to increase accuracy of the optical measurement of a position of a point in space by means of a redundant measurement through at least one laser tracker for the absolute method of a position measurement comprising at least one laser tracker and at least one measured point in space in which a reflector of a laser beam is placed.
  • Today's laser trackers coming-out from US4714339 offer two methods measuring a position of a point in space.
  • One of them is called incremental and is based on an incremental method of measuring by a laser tracker, wherein the reflector is tracked by an optical laser beam gradually during its movement from a known position to an unknown position to be measured.
  • the other of them is called absolute and is based on a discontinuous method of measuring by a laser tracker, wherein the reflector is found by an optical laser beam by a jump from a known position to an unknown position to be measured.
  • Accuracy of the absolute measurement method by means of a laser tracker is substantially lower than of the incremental method.
  • the aim of this invention is to increase the absolute measurement method accuracy.
  • Subject matter of the invention is to increase the absolute measurement method accuracy.
  • the subject matter of the method to increase accuracy of the optical measurement of a position of a point in space by means of a redundant measurement through at least one laser tracker for the absolute method of a position measurement comprising at least one laser tracker and at least one measured point in space in which a reflector of a laser beam is placed lies in the fact that the measurement is performed in more steps, wherein in the first step the laser tracker is set to a position for fransmitting an optical laser beam to a measured point and its position is measured using the absolute measurement method, in the follow-up step the laser tracker is set to a different position and then the laser tracker is re-set back to the original position for transmitting the optical beam to the measured point for the second measuring of its position by means of the absolute measurement method and this procedure is repeated at least three times, whereas before every next measurement of the position of this point in space the laser tracker is set to a different position and the resulting value of the position of the measured point in space is determined by the statistical processing of the measured values of the position of the measured point.
  • An advantage of the method and the apparatus described in this invention is a possibility to increase considerably the absolute measurement method accuracy by the laser tracker.
  • Fig. 2 the apparatus with a laser tracker arranged on a machine
  • Fig. 1 there is a schematic depiction of the basic arrangement of the apparatus for the optical measurement of a position of a point in space by means of a redundant measurement.
  • This is the basic arrangement spatial projection, wherein for the optical measurement of a position of a point 2 in space placed on a machine 7 using the absolute measurement by the laser tracker I located on a frame 6, whereas a reflector 4 of a laser beam 5 attached on the machine 7 is located in the point 2.
  • the laser tracker 1 measures the position of the measured point 2 which is placed in the centre of the reflector 4 of the laser beam 5.
  • the position of the measured point 2 is measured by means of the absolute measurement, thus by means of measuring two angles of the laser tracker 1_ which are equivalent to angles of the azimuth and elevation of the laser beam 5 between the laser tracker 1 and the measured point 2 ⁇ and by means of measuring a distance between the laser tracker 1 and the measured point 2.
  • the key is a measurement of a distance by the absolute method (ADM - Absolute Distance Meter), wherein the measured object can be a random object and it does not need to go through the tracked route from a known position to a measured position as for the traditional measurement by means of the laser interferometer.
  • the measurement proceeds in more steps and the measurement procedure is as follows: in the first step the laser tracker I is set to a position for transmitting the optical laser beam 5 to the measured point 2 and its position is measured by means of the absolute measurement method, in the follow-up step the laser tracker 1 is set to a different position, for example the optical laser beam 5 impinges on a point 3a on the frame 6 or on a point 3b on the machine 7 or on a point 3c on the frame 6, in which the reflector 4 of the laser beam 5 is placed, or on a point 3d on the machine 7 in which the reflector 4 of the laser beam 5 is placed. Then the laser tracker 1 is reset back to the original position for transmitting the optical laser beam 5 to the measured point
  • the laser tracker 1 is set to a different position, wherein the optical laser beam impinges on the point 3a or the point 3b or the point 3c or the point 3d or on another point except the point 2.
  • the resulting value of the position of the measured point in space is determined by the statistical processing of the measured values of the position of the measured point 2.
  • these points 3 are placed on the left side, on the right side, above and under the measured point 2 when viewing from the laser tracker 1.
  • the measurement proceeds as follows: in the first step the laser tracker I is set to a position for transmitting the optical laser beam 5 to the measured point 2 and its position is measured by means of the absolute measurement method, follow-up the laser tracker I is set to a different position, for example the optical laser beam 5 impinges on some of the points 3 on the frame 6, then the laser tracker I is re-set back to its original position for transmitting the optical laser beam 5 to the measured point 2 for the second measurement of its position by means of the absolute measurement method, then, alternately, the laser tracker I focuses the optical laser beam 5 on the points 3, for example 3 ls 3_3, 3 4 , 3 , , h, 2 4 , 3_2, and so on and further the repeated measurement of the position of the point 2 proceeds.
  • the laser tracker focuses on the measured point 2 alternately from the left side, from the right side, from the top and from the bottom, so that mechanical problems of the measurement given by tolerances and friction occur in the measured values symmetrically, equally.
  • This enables a less bias of the calculated arithmetical average in comparison with the accurate value of the position of the measured point 2.
  • Ways of changeover between the changing-over points 3 can be varied, both deterministic sequences and purposely completely random sequences.
  • more measured points on more laser reflectors can be used within the framework of this invention, in case of need more laser trackers can be used etc.
  • the measurement of the measured point position and its evaluation is carried out by a computer, whereas it is advantageous to increase the redundancy rate.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Length Measuring Devices By Optical Means (AREA)
  • Optical Radar Systems And Details Thereof (AREA)

Abstract

The invention concerns a method to increase accuracy of the optical measurement of a position of a point in space by means of a redundant measurement through at least one laser tracker for the absolute method of a position measurement comprising at least one laser tracker and at least one measured point in space in which a reflector of a laser beam is placed and its subject matter lies in the fact that the measurement is performed in more steps, wherein in the first step the laser tracker is set to a position for transmitting an optical laser beam to a measured point and its position is measured using the absolute measurement method, in the follow-up step the laser tracker is set to a different position and then the laser tracker is re-set back to the original position for transmitting the optical beam to the measured point for the second measuring of its position by means of the absolute measurement method and this procedure is repeated at least three times, whereas before every next measurement of the position of this point in space the laser tracker is set to a different position and the resulting value of the position of the measured point in space is determined by the statistical processing of the measured values of the position of the measured point. Further, it is advantageous to set the laser tracker after each measurement alternately on a different side from the position for transmitting the optical beam to the measured point.

Description

A method to increase accuracy of the optical measurement of a position of a point in space by means of a redundant measurement
Technical field of the invention
The invention concerns a method to increase accuracy of the optical measurement of a position of a point in space by means of a redundant measurement through at least one laser tracker for the absolute method of a position measurement comprising at least one laser tracker and at least one measured point in space in which a reflector of a laser beam is placed.
State-of-the-art
Today's laser trackers coming-out from US4714339 offer two methods measuring a position of a point in space. One of them is called incremental and is based on an incremental method of measuring by a laser tracker, wherein the reflector is tracked by an optical laser beam gradually during its movement from a known position to an unknown position to be measured. The other of them is called absolute and is based on a discontinuous method of measuring by a laser tracker, wherein the reflector is found by an optical laser beam by a jump from a known position to an unknown position to be measured. Accuracy of the absolute measurement method by means of a laser tracker is substantially lower than of the incremental method.
The aim of this invention is to increase the absolute measurement method accuracy. Subject matter of the invention
The subject matter of the method to increase accuracy of the optical measurement of a position of a point in space by means of a redundant measurement through at least one laser tracker for the absolute method of a position measurement comprising at least one laser tracker and at least one measured point in space in which a reflector of a laser beam is placed lies in the fact that the measurement is performed in more steps, wherein in the first step the laser tracker is set to a position for fransmitting an optical laser beam to a measured point and its position is measured using the absolute measurement method, in the follow-up step the laser tracker is set to a different position and then the laser tracker is re-set back to the original position for transmitting the optical beam to the measured point for the second measuring of its position by means of the absolute measurement method and this procedure is repeated at least three times, whereas before every next measurement of the position of this point in space the laser tracker is set to a different position and the resulting value of the position of the measured point in space is determined by the statistical processing of the measured values of the position of the measured point.
Further, it is advantageous to set the laser tracker after each measurement alternately on a different side from the position for transmitting the optical beam to a measured point.
An advantage of the method and the apparatus described in this invention is a possibility to increase considerably the absolute measurement method accuracy by the laser tracker.
Review of the figures in the drawings
In the attached Figures there is a depiction of the apparatus for the optical measurement of a position of a point in space by means of a redundant measurement, where
Fig. 1 - the apparatus with a laser tracker arranged on a frame and
Fig. 2 - the apparatus with a laser tracker arranged on a machine
Examples of the embodiments of the invention
In Fig. 1 there is a schematic depiction of the basic arrangement of the apparatus for the optical measurement of a position of a point in space by means of a redundant measurement. This is the basic arrangement spatial projection, wherein for the optical measurement of a position of a point 2 in space placed on a machine 7 using the absolute measurement by the laser tracker I located on a frame 6, whereas a reflector 4 of a laser beam 5 attached on the machine 7 is located in the point 2. Through the laser beam 5 the laser tracker 1 measures the position of the measured point 2 which is placed in the centre of the reflector 4 of the laser beam 5. The position of the measured point 2 is measured by means of the absolute measurement, thus by means of measuring two angles of the laser tracker 1_ which are equivalent to angles of the azimuth and elevation of the laser beam 5 between the laser tracker 1 and the measured point 2^ and by means of measuring a distance between the laser tracker 1 and the measured point 2. The key is a measurement of a distance by the absolute method (ADM - Absolute Distance Meter), wherein the measured object can be a random object and it does not need to go through the tracked route from a known position to a measured position as for the traditional measurement by means of the laser interferometer. The measurement proceeds in more steps and the measurement procedure is as follows: in the first step the laser tracker I is set to a position for transmitting the optical laser beam 5 to the measured point 2 and its position is measured by means of the absolute measurement method, in the follow-up step the laser tracker 1 is set to a different position, for example the optical laser beam 5 impinges on a point 3a on the frame 6 or on a point 3b on the machine 7 or on a point 3c on the frame 6, in which the reflector 4 of the laser beam 5 is placed, or on a point 3d on the machine 7 in which the reflector 4 of the laser beam 5 is placed. Then the laser tracker 1 is reset back to the original position for transmitting the optical laser beam 5 to the measured point
2 for the second measurement of its position by means of the absolute measurement method and this procedure is repeated more times, at least three times, whereas before every next measurement of the position of this point 2 in space the laser tracker 1 is set to a different position, wherein the optical laser beam impinges on the point 3a or the point 3b or the point 3c or the point 3d or on another point except the point 2. The resulting value of the position of the measured point in space is determined by the statistical processing of the measured values of the position of the measured point 2. The statistical processing of these measured values of the position of the measured point 2 in space can be carried out in a way that an arithmetic average of the measured values of the position of the measured point 2 in space is calculated and this average is the resulting value of the position of the measured point 2 in space. More complicated methods for the statistical processing of the measured values can be used as well, for example the particular measurements can be considered with a different significance according to a predetermined measurement uncertainty or a regression to a predetermined measurement error probability distribution can be carried out first in histograms of the performed measurements. This method of the measurement assessment represents the statistical processing of redundant measurements of the position of the measured point 2. Calculation of the average or other statistical processing is carried out by a computer.
The basic method of processing based on the calculation of the average of the measured point 2 position measured values comes out from the knowledge that the measurement error probability is subject to the normal distribution. The calculation of the average reduces the uncertainty of the measurement results substantially. Re-setting the laser tracker 1 prior to each new measurement of the position of the point 2 and its re-setting back to the position for the measurement of the position of the point 2 ensures that unpredictable phenomena, e.g. an influence of tolerances, friction, current fluctuation in drives and others, show themselves randomly, create a statistically determinable probability distribution of influence of these errors and this will allow improving the measurements through statistical methods. Further, focusing on the measured point 2 alternately from the left side, from the right side, from the top and from the bottom is advantageous, thus a nonbiased probability distribution of measurement deviations from the accurate value occurs as described in the embodiment in Fig. 2.
In Fig. 2 there is a schematic depiction of a spatial projection of an arrangement of the apparatus for the optical measurement of a position of a point in space by means of a redundant measurement similar to the arrangement in Fig. 1, wherein the laser tracker i is placed on the machine 7 and the measured point 2, in which the reflector 4 of the laser beam 5 is located, is arranged on the frame 6 and there are more points 3 on which the optical laser beam impinges when the laser tracker i is set to a different position. In Fig. 2. there have been points 31, 3_2, 3^, 34, created in which the laser beam 4 reflectors have been located and these points 31, 3_2, 3j, 34 are arranged on various sides from the measured point 2. Essentially these points 3 are placed on the left side, on the right side, above and under the measured point 2 when viewing from the laser tracker 1. The measurement proceeds as follows: in the first step the laser tracker I is set to a position for transmitting the optical laser beam 5 to the measured point 2 and its position is measured by means of the absolute measurement method, follow-up the laser tracker I is set to a different position, for example the optical laser beam 5 impinges on some of the points 3 on the frame 6, then the laser tracker I is re-set back to its original position for transmitting the optical laser beam 5 to the measured point 2 for the second measurement of its position by means of the absolute measurement method, then, alternately, the laser tracker I focuses the optical laser beam 5 on the points 3, for example 3 ls 3_3, 34, 3 , , h, 24, 3_2, and so on and further the repeated measurement of the position of the point 2 proceeds. This way the laser tracker focuses on the measured point 2 alternately from the left side, from the right side, from the top and from the bottom, so that mechanical problems of the measurement given by tolerances and friction occur in the measured values symmetrically, equally. This enables a less bias of the calculated arithmetical average in comparison with the accurate value of the position of the measured point 2. Ways of changeover between the changing-over points 3 can be varied, both deterministic sequences and purposely completely random sequences.
For determination of a position of an object, e.g. a machine, more measured points on more laser reflectors can be used within the framework of this invention, in case of need more laser trackers can be used etc.
The measurement of the measured point position and its evaluation is carried out by a computer, whereas it is advantageous to increase the redundancy rate.
Laser trackers can be replaced by optical video-cameras with a reference element and/or a laser beam source for a photosensitive element.
An optical video-camera is set to a position for a measurement with the aid of two angles equivalent to angles of the azimuth and elevation performed by two actuators which ensure that the video-camera always tracks a reference element and by assessing the reference element image both the reference element distance is determined from its known dimensions and a correction of the set angles equivalent to the angles of the azimuth and elevation is determined. Subsequently the reference element position towards the video-camera is calculated. By the above described method of the redundant measurement, the measurement of a position of a point in space in which a reference element is placed can be made more accurate.
Similarly, a laser beam source can be set to a position for a measurement with the aid of two angles equivalent to angles of the azimuth and elevation performed by two actuators which ensure that the laser beams transmitted from the laser beam source in a number of at least 3 always impinge on a photosensitive element and by assessing the laser beams impingement position on the photosensitive element both the photosensitive element distance is determined from the known angles of the laser beams and a correction of the set angles equivalent to the angles of the azimuth and elevation is determined. Subsequently the photosensitive element position towards the laser beam source is calculated. By the above described method of the redundant measurement, the measurement of a position of a point in space in which a photosensitive element is placed can be made more accurate.

Claims

Patent Claims
1. A method to increase accuracy of the optical measurement of a position of a point in space by means of a redundant measurement through at least one laser tracker for the absolute method of a position measurement comprising at least one laser tracker and at least one measured point in space in which a reflector of a laser beam is placed, characterized by the fact that the measurement is performed in more steps, wherein in the first step the laser tracker is set to a position for transmitting an optical laser beam to a measured point and its position is measured using the absolute measurement method, in the follow-up step the laser tracker is set to a different position and then the laser tracker is re-set back to the original position for transmitting the optical beam to the measured point for the second measuring of its position by means of the absolute measurement method and this procedure is repeated at least three times, whereas before every next measurement of the position of this point in space the laser tracker is set to a different position and the resulting value of the position of the measured point in space is determined by the statistical processing of the measured values of the position of the measured point.
2. The method to increase accuracy of the optical measurement of a position of a point in space by means of a redundant measurement as described in claim 1, characterized by the fact that after each measurement the laser tracker is set alternately to a different side from the position for transmitting the optical beam to the measured point.
PCT/CZ2014/000019 2013-02-27 2014-02-25 A method to increase accuracy of the optical measurement of a position of a point in space by means of a redundant measurement WO2014131379A2 (en)

Priority Applications (1)

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EP14710789.0A EP2962126A2 (en) 2013-02-27 2014-02-25 A method to increase accuracy of the optical measurement of a position of a point in space by means of a redundant measurement

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CZPV2013-150 2013-02-27
CZ2013-150A CZ310064B6 (en) 2013-02-27 2013-02-27 A method of increasing an accuracy of optical measurement of position of a point in space using redundant measurement

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WO2014131379A2 true WO2014131379A2 (en) 2014-09-04
WO2014131379A3 WO2014131379A3 (en) 2014-10-23

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Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4714339A (en) 1986-02-28 1987-12-22 The United States Of America As Represented By The Secretary Of Commerce Three and five axis laser tracking systems

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4939678A (en) * 1987-11-19 1990-07-03 Brown & Sharpe Manufacturing Company Method for calibration of coordinate measuring machine
US4884889A (en) * 1987-11-19 1989-12-05 Brown & Sharpe Manufacturing Company Calibration system for coordinate measuring machine
US5216236A (en) * 1991-02-19 1993-06-01 National Research Council Of Canada Optical tracking system
US5671053A (en) * 1995-11-16 1997-09-23 Virtek Vision Corp. Method of calibrating laser projector using moving reflector
US6810597B2 (en) * 1999-04-08 2004-11-02 Renishaw Plc Use of surface measuring probes
US8619265B2 (en) * 2011-03-14 2013-12-31 Faro Technologies, Inc. Automatic measurement of dimensional data with a laser tracker

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4714339A (en) 1986-02-28 1987-12-22 The United States Of America As Represented By The Secretary Of Commerce Three and five axis laser tracking systems
US4714339B1 (en) 1986-02-28 1997-03-18 Us Army Three and five axis laser tracking systems
US4714339B2 (en) 1986-02-28 2000-05-23 Us Commerce Three and five axis laser tracking systems

Also Published As

Publication number Publication date
WO2014131379A3 (en) 2014-10-23
EP2962126A2 (en) 2016-01-06
CZ310064B6 (en) 2024-07-10
CZ2013150A3 (en) 2014-09-03

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