WO2014139487A1

WO2014139487A1 - A method and an apparatus for the redundant optical measurement and/or calibration of a position of an object in space

Info

Publication number: WO2014139487A1
Application number: PCT/CZ2014/000026
Authority: WO
Inventors: Michael VALÁŠEK; Martin NEČAS; Jlří ŠVÉDA
Original assignee: CVUT v Praze, Fakulta strojní
Priority date: 2013-03-11
Filing date: 2014-03-10
Publication date: 2014-09-18
Also published as: EP3004794A1; CZ2013179A3; CZ308920B6

Abstract

The invention concerns a method and an apparatus for the redundant optical measurement and/or optical calibration of a position of an object in space by means of at least one laser tracker placed on the measured or calibrated object and/or on a frame of the object and at least one reflector of a laser beam placed on the measured or calibrated object and/or on a frame of the object, whereas this method lies in that the laser tracker is set to at least one position on the frame in which it measures a position of at least three laser reflectors of laser beams on the frame, subsequently a calibration of the position of these laser reflectors of laser beams on the frame is performed, then the laser tracker is set to at least one position on the frame in which it measures the position of these at least three calibrated laser reflectors of laser beams on the frame and measures the position of at least three laser reflectors on the measured object and following these measurements the position of the measured object is determined, and/or the measured object on which the laser tracker is arranged is set to at least one position in space in which the laser tracker measures a position of at least three laser reflectors on a frame, on the base of these measurements a calibration of positions of laser reflectors on the frame is performed and, at the same time, the position of the measured object is determined. An apparatus for performing this method lies in comprising at least one laser tracker and at least three laser reflectors, whereas the laser reflectors are arranged in a triangle or a polygon. At least one laser tracker (4) is arranged on the linear guide (8₁) and/or at least one laser reflector (5) is arranged on the linear guide (8₂).

Description

A Method and an Apparatus for the Redundant Optical Measurement and/or Calibration of a Position of an Object in Space

Technical Field of the Invention

The invention concerns a method for the redundant optical measurement and/or the optical calibration of a position of an object in space by means of at least one laser tracker placed on a measured or calibrated object and/or on a frame of the object and at least one reflector of a laser beam placed on a measured or calibrated object and/or on a frame of the object and an apparatus for the redundant optical measurement and/or the optical calibration of a position of an object in space comprising at least one laser tracker placed on a measured or calibrated object and/or on a frame and at least one reflector of a laser beam placed on a frame and/or on a measured or calibrated object.

Technical Field of the Invention

An apparatus for a measurement and/or calibration of a position of an object in space including a method for the measurement and/or calibration are known e.g. from the EP 1968773B1 documents and from the PV 2010-178 patent application. A new method of the measurement and calibration of an object in space has been described using redundant measurements, which means that the number of sensors is larger than the number of degrees of freedom of the measured and/or the calibrated object in space. In these applications mechanical apparatuses for performing redundant measurements have been described.

Their disadvantage is a limited range and thus applicability in smaller working areas. They are difficult to be used in larger working areas and for larger machines and are quite expensive. Another disadvantage is that mechanical devices, especially if they are larger, can be influenced by outer acting forces, especially by the gravity force, by which the mechanical devices are deformed and thus measurement errors are caused.

This has been removed by PV 2012-897 application, however, at least three laser trackers have been used here. This is very costly. Further, such an apparatus would be voluminous and heavy. In this application, the laser tracker is a laser interferometer with a subsidiary reflector of a laser beam, where the laser interferometer is attached on a spherical joint (with two degrees of freedom) with feedback controlled drives. Each laser tracker arranged on a platform and/or on a frame transmits a laser beam, which is reflected from the reflector of the laser beam positioned on the frame and/or the platform and impinges back on the laser tracker, where it is processed by the laser interferometer and using a known, but sophisticated feedback control for the movement of the laser tracker in the spherical joint the laser interferometer is rotated so that the laser tracker can still track the laser beam transmitted by the reflector of the laser beam using the laser interferometer. From the knowledge of two angles of rotation of the laser beam measured in the spherical joint and from the knowledge of a length of the laser beam between the laser interferometer and the reflector of the laser beam measured using the laser interferometer, which represent spherical coordinates, the relative Cartesian position given by the Cartesian coordinates x, y, z of the laser tracker and the reflector of a laser beam is determined using a conversion of spherical coordinates to the Cartesian coordinates.

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.

The aim of this invention is to remove the above mentioned imperfections, above all to reduce the needed number of laser trackers to only one.

Subject Matter of the Invention

A subject matter of the method for the redundant optical measurement and/or optical calibration of a position of an object in space by means of at least one laser tracker placed on the measured or calibrated object and/or on a frame of the object and at least one reflector of a laser beam placed on the measured or calibrated object and/or on a frame of the object lies in a fact that the laser tracker is set to at least one position on the frame in which it measures a position of at least three laser reflectors of laser beams on the frame, subsequently a calibration of the position of these laser reflectors of laser beams on the frame is performed, then the laser tracker is set to at least one position on the frame in which it measures the position of these at least three calibrated laser reflectors of laser beams on the frame and measures the position of at least three laser reflectors on the measured object and following these measurements the position of the measured object is determined, and/or the measured object on which the laser tracker is arranged is set to at least one position in space in which the laser tracker measures a position of at least three laser reflectors on a frame, on the base of these measurements a calibration of positions of laser reflectors on the frame is performed and, at the same time, the position of the measured object is determined.

In some case, a laser tracker is re-set to at least one next position and in every new position a position of all the laser reflectors on the frame is measured, on the basis of the measurement in these positions the calibration of the positions of the laser reflectors on the frame is performed, subsequently the laser tracker arranged on the frame or on the measured object is re-set to at least one next position in which it measures positions of all the laser reflectors on the frame or on the measured object and on the base of these measured positions the position of the measured object is determined.

Or, in some case, laser reflectors and/or laser trackers are re-set to repeatable positions and a distance of these repeatable positions is measured.

Laser trackers use an absolute method for the measurement of positions of laser reflectors or an incremental method for the measurement of positions of laser reflectors in a case of resetting the laser reflectors and/or laser trackers to repeatable positions.

A subject matter of the apparatus for the redundant optical measurement and/or the optical calibration of a position of an object in space comprising at least one laser tracker placed on the measured or calibrated object and/or on a frame and at least one laser beam reflector placed on a frame and/or on the measured or calibrated object lies in that it comprises at least one laser tracker and at least three laser reflectors.

Preferably the laser reflectors are arranged in a triangle or a polygon, whereas it is further advantageous if at least one laser tracker is arranged on a linear guide and/or at least one laser reflector is arranged on another linear guide.

An advantage of the method and the apparatus as described in this invention is a possibility to use only one laser tracker for the redundant optical measurement and/or calibration of a position of an object in space. Review of the Figures in the Drawings

In the attached Figures there are depictions of the apparatus for the redundant optical measurement and/or calibration of a position of an object in space, where:

Fig. 1 - the apparatus with a laser tracker arranged on a frame,

Fig. 2 - an apparatus as depicted in Fig. 1 with linear guides for a laser tracker and a laser reflector,

Fig. 3 - an apparatus with a laser tracker on a machine - a measured object,

Fig. 4 - a schematic depiction of positions of laser reflectors and laser trackers as depicted in

Fig. 1

for the first phase of the measurement,

Fig. 5 - a schematic depiction as depicted in Fig. 4 for the second phase of the measurement, Fig. 6 - a schematic depiction of an arrangement of laser reflectors and a laser tracker on

a machine - a measured object as depicted in Fig. 3.

Examples of the Embodiments of the Invention

In Fig. 1 there is a basic embodiment of the apparatus for the redundant optical measurement and/or calibration of a position of an object in space depicted. This is a spatial view on the apparatus for the optical measurement and/or optical calibration of a position of an object 3 in space with one laser tracker 4 placed on a frame 1 and three reflectors 5b of a laser beam 6b located on a platform 2 attached on the measured object 3. Further, aside from the platform 2 attached on the measured object 3 an additional platform 1_ attached on the frame 1 is used on which three reflectors 5\ of the laser beam 6a are arranged and an additional platform ¾ attached on the frame i is used on which four reflectors 5_2 of the laser beam 6a are arranged in this embodiment. During the measurement the laser tracker 4 is being replaced to various positions, in the figure the positions {a}, (b), (c), {d) on the frame I are depicted.

The method of the measurement and/or calibration of a position of an object in space is such that it proceeds in two phases. In the first phase the calibration of the apparatus for the measurement and/or calibration of a position of an object in space is performed. In the second phase the very measurement and/or calibration of a position of the object 3 in space is performed. Typically this object 3 in space is an end effector 9, e.g. of a machine-tool, which is often represented by a chuck into which a tool or a measuring platform 2 is clamped.

Then the very measurement and/or calibration of a position of an object in space typically means a determination of a position of an end effector 9 of a machine within a sequence of positions in the machine working area or even a calculation of parameters of a machine kinematic model used for the control of its position in the working area. The laser beam marked 6a is used in the first phase and the laser beam marked 6b is used in the second phase.

The measurement method in the first phase is such that the laser tracker 4 in a position {a} by means of the absolute measurement method gradually measures positions of three points in which the reflectors 5i of the laser beam 6a located on the platform 7 attached on the frame I are placed and positions of next four points in which the reflectors 5 of the laser beam 6a located on the platform 7_₂ attached on the frame i are placed. Then the laser tracker 4 is moved to a position (c) on the frame 1 and similarly, by means of the absolute measurement method, performs the measurement of positions of all points in which the reflectors 5 and 5 of the laser beam 6a arranged on the platforms

and 72 attached on the frame1 are placed. There may be more laser reflectors 51, 5g on more platforms T_ and 7₂ and the laser tracker 4 may be placed to more positions, e.g. (a), {cj, (cf^ which is advantageous for increasing the measurement redundancy. In this phase of the measurement the minimal quantity are three reflectors 5 and one position of the laser tracker 4. Results of these measurements are used for making up an overdetermined system of equations describing coupling conditions given by a relative position of the measuring apparatus elements (the laser reflectors 5 and the laser tracker 4) from which the relative position of the measuring apparatus elements is determined. The measuring apparatus elements comprise a system of laser reflectors 5_l5 5_¾ in case of need others, placed on the frame i and the laser tracker 4 in particular positions {a}, (c), or possibly in other positions. Based on the made-up overdetermined system of equations, above all the positions of the points are determined in which the laser reflectors 5 \ and 5¾ attached on the frame i are placed, but also the positions {a}, (c) of the laser tracker 4 towards the frame i representing six coordinates for each position (for example a reference point (three coordinates) and orientation (three turnings)).

Also, in the first phase the calibration of the relative position of the laser reflectors 5b placed on the platform 2 on the object 3 can be performed. The method of this calibration is similar to the calibration of the relative position of the laser reflectors 5JL and 5_₂ attached on the frame L By means of the absolute measurement method the laser tracker 4 in a position (a) gradually measures positions of three points in which the reflectors 5b of the laser beam 6b arranged on the platform 2 attached on the object 3 are placed. Then the laser tracker 4 is moved from the position (a) to the position (c) on the frame 1 and similarly, by means of the absolute measurement method, performs again the measurement of positions of all points in which the reflectors 5b of the laser beam 6b arranged on the platform 2 attached on the object 3 are placed. Preferably there are more than three laser reflectors 5b placed on the platform 2 on the object 3 and preferably the laser tracker 4 is located to more than two positions (a), (c) from which the described measurements are carried out. Again three reflectors 5b and one position of the laser tracker 4 are the minimal quantity. The results of these measurements are used for making up an overdetermined system of equations describing coupling conditions given by a relative position of the measuring apparatus elements from which the relative position of the measuring apparatus elements is determined. In this case this is the relative position of the points in which the laser reflectors 5b are placed. Based on the made-up overdetermined system of equations, above all the relative positions of the points are determined in which the laser reflectors 5b attached on the object 3 are placed.

The measurement method in the second phase is such that the laser tracker 4 is placed to a position £b) which is generally different from e.g. positions (a) and {cj, because repeatability of placing to a congruent position is not assumed and first of all by means of the absolute measurement method the laser tracker 4 measures positions of three points in which the reflectors 5b of the laser beam 6b arranged on the platform 2 attached on the measured and/or calibrated object 3 are placed and then by means of the absolute measurement method gradually measures positions of three points in which the reflectors 5_j_ of the laser beam 6b arranged on the platform 1__\ attached on the frame \ are placed and positions of other four points in which the reflectors 5_2 of the laser beam 6b arranged on the platform Tg attached on the frame 1 are placed. Then the laser tracker 4 is moved from the position {b} to a position (d) on the frame 1 and by means of the absolute measurement method performs the measurement of positions of all the points in which the reflectors 5b of the laser beam 6b arranged on the platform 2 attached on the measured and/or calibrated object 3 are placed and in them the reflectors 5^ and 52 of the laser beam 6b arranged on the platforms 7i and 2a attached on the frame 1 are placed. The results of these measurements are used for making up an overdetermined system of equations describing coupling conditions given by a relative position of the measuring apparatus elements and the laser reflectors 5b placed on the object 3 (representing for example a machine-tool) from which the position (b), (d) of the laser tracker and above all the position of the laser reflectors 5b placed on the object 3 (representing for example a machine-tool) is determined, which is used for the measurement and/or calibration of the object 3 (representing for example a machine-tool).

If in the first phase a number of the laser reflectors 5_l5 5_2 on the frame 1 is R and a number of the positions (a), (c) of the laser tracker 4 is N, then one can make up 3*R*N equations for the calibration of the measuring apparatus represented by 3*R-6+6*N unknown values. The unknown values are e.g. three Cartesian coordinates XLO, YLO, ZLO for each laser reflector LO, free Cartesian coordinates XLS, yLS, ZLS of the centre of the laser tracker in the LS position and three Cardan angles φ^, ⁽PyLS, 9_ZLS of the orientation of the coordinate system fixed to the laser tracker towards the coordinate system of the frame in the LS position. The laser reflector position defined by the Cartesian coordinates x, y, z in the laser tracker coordinate system is measured. The made up equations - coupling conditions determine the laser reflector position in the laser tracker coordinate system. For each laser reflector and each laser tracker position three equations are made up based on this matrix equation

[XLO, YLO, ZLO,

T_z2(y_Ls) T_z3(z_Ls) TZ4(⁽|>XLS) T_Z5(⁽p_yLs) Τ_Ζ6(φ_Λδ)[^χ, y, z, 1]^T pursuant to designation from a book by Stejskal, V.-Valasek, M.: Kinematics and Dynamics of Machinery, Marcel Dekker, New York 1996.

Preferably the redundancy rate increases with the increased number of R and N. In the measurement described above R=7 and N=2, thus there are 27 unknowns and 42 equations. If a number of the laser reflectors 5_l5 5g on the frame 1 is R and a number of the laser reflectors 5b on the object 3 is S and a number of positions (b), (d) of the laser tracker 4 is M in the second phase, then we can make up 3*(R+S)*M equations for the measurement of a position of the object 3 and of positions (b), (d) of the laser tracker 4 represented by 6+6*M unknown values. Preferably the redundancy rate increases with the increased number of R, S and M. In the measurement described above R=7, S=3 and M=2, thus there are 18 unknowns and 60 equations.

By this procedure a position of the object 3 in space is determined, thus the position of the object 3 towards the frame l^ and more precisely the position of the object 3 towards the coordinate system in which the laser tracker 4 placed on the frame 1 performs the measurements. A necessary condition is that the reflectors 5 of the laser beam 6 placed on the platform 7 attached on the frame I create a triangle, thus they are not positioned in one straight line, and the reflectors 5b of the laser beam 6b placed on the platform 2 attached on the measured object 3 create a triangle as well, thus they are not positioned in one straight line. If they were positioned in one straight line, the made up equations would be singular ones or would be ill-conditioned.

Preferably more than only three reflectors 5b of a laser beam placed on the platform 2 attached on the measured object 3 can be used and more than only three reflectors 5^ and 5_2 of the laser beam placed on the platform

and Ί attached on the frame L Being their number n, preferably they should create n-polygon and not degenerate to (n-k)-polygon by positioning some three reflectors 5 in a number 3k in one straight line, thus reducing conditionality of the made up equations again.

In Fig. 2 there is another embodiment of the apparatus for the redundant optical measurement and/or calibration of a position of an object in space depicted. This is a spatial view on the apparatus for the optical measurement and/or optical calibration of a position of an object 3 in space with one laser tracker 4 placed on a frame I and three reflectors 5b of a laser beam 6b located on a platform 2 attached on the measured object 3. Further, aside from the platform 2 attached on the measured object 3 an additional platform

attached on the frame 1 is used on which three reflectors 5^ of the laser beam 6a are arranged and an additional platform attached on the frame I is used on which four reflectors 5_₂ of the laser beam 6a are arranged. Further, on the frame I a linear guide 8_i for a repeatable relocation of the laser tracker 4 between positions {a} a £e) is placed and a linear guide 8₂ for a repeatable relocation of the platform i with the laser reflector _3 between positions {fj a (g) on the frame I is placed. The measurement method is similar as described for the apparatus in Fig. 1. The measurement is performed in two phases. In the first phase the calibration of the apparatus for the measurement and/or calibration of a position of an object in space is performed. In the second phase the very measurement and/or calibration of a position of an object in space is performed.

Improvement of the measurement compared to the measurement with the apparatus described in Fig. 1 lies in that instead of the measurement of the laser reflectors 5_3 on the platform 7j in a position (f) and the follow-up measurement of other laser reflectors in a position (g) only one type of laser reflectors 5₃ on the platform 7^ is used, but the platform ¾ moves with them on the linear guide 8₂ between positions (f) and (g). An essential presupposition is repeatability of reaching the positions {0 and (g). An advantage is adding another overdetermination of made-up equations owing to the congruent distance p of the positions (fj and (g), which may be measured in case of need. A similar improvement of the measurement compared to the measurement with the apparatus described in Fig. 1 lies in that instead of positioning the laser tracker 4 on the frame I to generally unrepeatable positions (b), (c), (d) the laser tracker 4 is placed to a repeatable position (a) from which it is moved on the linear guide ¾ to a position (e) which is repeatedly reachable and its distance d from the position (a) can be measurable, too. An essential presupposition is repeatability of reaching the positions {a} and (e).

During the measurement of the laser reflectors 5 on the platform 7 in a position (f) and the follow-up measurement of laser reflectors in a next position (g) only one type of laser reflectors 5 on the platform 7 is used, but the platform 7¾ moves with them between positions (f) and (g). An essential presupposition is repeatability of reaching the positions (f) and (g). An advantage is adding another overdetermination of made up equations owing to the congruent distance p of the positions {0 and (g), which may be measured in case of need. An advantage is adding a further overdetermination of made-up equations owing to the congruent distance d of the positions {a} and (e), which may be measured in case of need.

A key characteristic is that the position { and (g) of the platform Ί is repeatable with an accuracy lower enough not to influence adversely a result of the made-up system of equations. The repeatability of the positions £fj and (g) and thus their invariability results in increasing overdetermination of the measurement when making-up coupling conditions. If the linear guide is equipped with admeasurement and the distance p of the positions (f) and (g) can be determined, this information can be used to make up coupling conditions and the measurement overdetermination can be enhanced by this information. Similarly the linear guide 8i can be used and the repeatability of the positions (a) and (e) and thus their invariability results in increasing overdetermination of the measurement when making up coupling conditions. If the linear guide is equipped with admeasurement and the distance d of the positions (a) and (e) can be determined, this information can be used to make up coupling conditions and the measurement overdetermination can be enhanced by this information.

The measurement method in the first phase is such that the laser tracker 4 in a position (a) by means of the absolute measurement method gradually measures positions of three points in which the reflectors 51 of the laser beam 6a arranged on the platform 7i attached on the frame I are placed and positions of next four points in which the reflectors 5 of the laser beam 6a arranged on the platform attached on the frame 1 are placed. Then, by means of the absolute measurement method a position of three points is measured in which the reflectors 5_3 of the laser beam 6a arranged on the platform 7¾ attached in a position (fj on the linear guide 82 on the frame I are placed and after moving the platform 73 with the laser reflectors 5_3_ on the linear guide 82 to a position (g) again the position of three points is measured in which the reflectors 53 of the laser beam 6a arranged on the platform 73 attached on the linear guide 82 on the frame i are placed. In some case the distance p of the positions (fj and (g) can be measured as well.

Then the laser tracker 4 is moved on the linear guide 81 to a position (e) on the frame whereas the distance d of positions {a) and (e) is possibly measured, and by means of the absolute measurement method performs the measurement of positions of all the points in which the reflectors 5_l5 5¾ and 53 of the laser beam 6a arranged on the platform 7_\, T and 7½ attached on the frame1 are placed.

Then the laser tracker 4 is moved to a position (c) on the frame 1 and by means of the absolute measurement method performs the measurement of positions of all the points in which the reflectors 51, 5_ and 5_3 of the laser beam 6a arranged on the platform 7_1? ¾ and 73 attached on the frame 1 are placed. The results of these measurements are used for making up an overdetermined system of equations describing coupling conditions given by a relative position of the measuring apparatus elements from which the relative position of the measuring apparatus elements is determined. The measuring apparatus elements comprise a system of laser reflectors 5_1? 52 and 5_3 placed on the frame 1 and particular positions (a), (e), (c) of the laser tracker. Based on the made-up overdetermined system of equations, above all the positions of the points are determined in which the laser reflectors 5i, 5_2 and 5^ attached on the frame I are placed, but also the positions {a}, (e), (c) of the laser tracker 4 towards the frame I representing six coordinates for each position (for example a reference point - 3 coordinates and orientation - 3 turnings).

Also, in the first phase the calibration of the relative position of the laser reflectors 5b placed on the platform 2 on the object 3 can be performed similarly as described in Fig. 1 with a possible improvement consisting in using the measurements from the repeatable positions (a) and (e) between which the laser tracker 4 is moved on the linear guide %

In the second phase the measurement method is such that the laser tracker 4 is placed to a position (a) on the linear guide 8₁ and at first the laser tracker 4 by means of the absolute measurement method measures a position of three points on which the reflectors 5b of the laser beam 6b arranged on the platform 2 attached on the measured and/or calibrated object 3 are placed and then by means of the absolute measurement method gradually measures positions of three points in which reflectors 5₁ of the laser beam 6b arranged on the platform 1__\ attached on the frame 1 are placed and positions of next four points in which reflectors 5₂ of the laser beam 6b arranged on the platform 7_₂ attached on the frame 1 are placed, then positions of three points in which reflectors 5_3 of the laser beam 6b arranged on the platform 73 attached in a position (f) on the linear guide 82 on the frame 1 are placed and after moving the platform ¾ with the laser reflectors 53 on the linear guide 82 to a position (g) the positions of three points are measured again in which the reflectors 5 of the laser beam 6b arranged on the platform ¾ attached on the linear guide 8₂ on the frame I are placed. In some case the distance p of the positions {fj and (g) can be measured as well.

Then the laser tracker 4 is moved on the linear guide 8_i to a position (e) on the frame 1, whereas the distance d of the positions (a) and (e is possibly measured, and by means of the absolute measurement method performs the measurement of positions of all the points in which the reflectors 5b of the laser beam 6b arranged on the platform 2 attached on the measured and/or calibrated object 3 are placed and the reflectors 5 \, _5 and of the laser beam 6b arranged on the platform 7 , 72 and 73_attached on the frame l_are placed. Then the laser tracker 4 is moved to a position (b), which is generally different from positions £a) and (e) because repeatability of positioning to a congruent position is not assumed, and by means of the absolute measurement method performs the measurement of positions of all the points in which the reflectors 5b of the laser beam 6b arranged on the platform 2 attached on the measured and/or calibrated object 3 are placed and the reflectors 5_l5 5₂_and 53 of the laser beam 6b arranged on the platforms 7i, 72 and 7¾ attached on the frame 1 are placed.

Then the laser tracker 4 is moved from the position {b} to a position (d) on the frame 1 and by means of the absolute measurement method performs the measurement of positions of all the points in which the reflectors 5b of the laser beam 6b arranged on the platform 2 attached on the measured and/or calibrated object 3 are placed and the reflectors 5_l5 5^ and 53 of the laser beam 6b arranged on the platform 7 and 73 attached on the frame I are placed. The results of these measurements are used for making up an overdetermined system of equations describing coupling conditions given by a relative position of the measuring apparatus elements and the laser reflectors 5b placed on the object 3, from which the positions (a), (e), (b), (d) of the laser tracker 4 and above all the position of the laser reflectors 5b placed on the object 3 is determined, which is used for the measurement and/or calibration of the object 3.

In Fig. 3 there is an alternative embodiment of the apparatus for the redundant optical measurement and/or calibration of a position of an object in space depicted. This is a spatial view on the apparatus for the optical measurement and/or optical calibration of a position of an object 3 in space with one laser tracker 4 placed on a platform 2 attached on the measured object 3. Further, aside from the platform 2 attached on the measured object 3 an additional platform 7i attached on the frame1 is used on which three reflectors 51 of the laser beam 6 are arranged and an additional platform 72 attached on the frame 1 is used on which four reflectors 5¾ of the laser beam 6 are arranged and an additional platform 7 attached within the working area of the machine 3 on the floor on the frame 1 is used on which three reflectors 5_3 of the laser beam 6 are arranged. During the measurement the laser tracker 4 is being relocated by the object 3 between more positions, e.g. (a) and (b).

Here the measurement method proceeds in one phase and combines the calibration of the apparatus for the measurement and/or calibration of a position of an object in space along with the very measurement and/or calibration of a position of an object in space.

The measurement method is such that the laser tracker 4 in a position (a) by means of the absolute measurement method gradually measures a position of three points in which the reflectors 5j_ of the laser beam 6 arranged on the platform 7i attached on the frame 1 are placed and positions of next four points in which reflectors 5_2 of the laser beam 6 arranged on the platform 72 attached on the frame1 are placed and positions of next three points in which reflectors 5_3 of the laser beam 6 arranged on the platform 7¾ attached on the frame I are placed.

Then the laser tracker 4 is moved with the machine 3 to a position (b) and by means of the absolute measurement method performs the measurement of positions of all the points in which the reflectors 5_l5 5_2 and 5j of the laser beam 6 arranged on the platform T_ Ί₂ and Ίι attached on the frame 1 are placed. There may be more laser reflectors 5_l5 5_2 and 5^ on more platforms 7_l5 7g and Τ with an advantage for increasing the measurement redundancy and the laser tracker 4 may be placed to many measured positions {a}, (b). Three reflectors 5 are a minimal number. The results of these measurements are used for making up an overdetermined system of equations describing coupling conditions given by a relative position of the measuring apparatus elements and all positions (a), (b) of the object 3 from which the relative position of the measuring apparatus elements and positions {a}, (b) of an end effector 9 of the machine-object 3 within its working area is determined. The measuring apparatus elements comprise a system of the laser reflectors 5j_, 5_¾ and 5₃ placed on the frame i and particular positions (a), (b) of the laser tracker 4 on the platform 2 in the end effector 9 of the machine-object 3. Based on the made-up overdeterniined system of equations, above all the positions (a), (b) of the laser tracker 4 on the platform 2 in the end effector 9 of the machine-object 3 towards the frame 1 are determined representing six coordinates for each position (for example a reference point - 3 coordinates and orientation - 3 taniings), but also positions of the points in which the laser reflectors 5_l5 5_ and 5j attached on the frame 1 are placed. In this case the calibration of the measuring apparatus and the measurement and/or calibration of a position of an object in space comprising positions of the end effector 9 of the machine-object 3 in space are performed at the same time.

In Fig. 4 there is a schematic vertical view on the apparatus for the redundant optical measurement and/or calibration of a position of an object in space as depicted in Fig. 1 in the first phase of the measurement. On the frame I of the machine-object 3 the platforms 7i (i=l, 2, n, n>l natural number) are attached, each of them with three laser reflectors 5. The laser tracker 4 is gradually moved to positions £bj) (j=l, 2, m, m>l natural number). In Fig. 4 the laser tracker 4 is depicted in a position (a) where, by means of the laser beam 6^ it measures positions of points in which the laser reflectors 5 are placed on the platform 7i. This way it gradually measures positions of all points in which the laser reflectors 5 are placed on all the platforms 7i. The results of these measurements are used for making up an overdetermined system of equations describing coupling conditions given by a relative position of the measuring apparatus elements from which the relative position of the measuring apparatus elements is determined. In this case this is the relative position of the points in which the laser reflectors 5 placed on the platforms 7i are placed. This way the calibration of the measuring apparatus is performed.

In Fig. 5 there is a schematic vertical view on the apparatus for the redundant optical measurement and/or calibration of a position of an object in space as depicted in Fig. 1 in the second phase of the measurement. On the frame \ of the machine-object 3 the platforms 7i (i=l, 2, n, n>l natural number) are attached, each of them with three laser reflectors 5. On the object 3 in the given position within its working area the platform 2 with three laser reflectors 5b (shown in the figures above) is attached in the end effector 9 (not shown). The laser tracker 4 is gradually moved to positions (b), {d), (e) and in each of these positions a position of points in which the laser reflectors 5b are placed on the platform 2 and a position of all points in which the laser reflectors 5 are placed on the platforms 7i is measured. The results of these measurements in each of the positions of the object 3 are used for making up an overdetermined system of equations describing coupling conditions given by a relative position of the measuring apparatus elements and the laser reflectors 5b placed on the object 3, from which the positions (b), (d), (e), of the laser tracker 4 and above all the position of the laser reflectors 5b placed on the object 3 are determined, which is used for the measurement and/or calibration of the machine 3 in the given position.

In Fig. 6 there is a schematic vertical view on the apparatus for the redundant optical measurement and/or calibration of a position of an object in space as depicted in Fig. 3. On the frame I of the machine-object 3 the platforms 7i (i=l, 2, n, n>l natural number) are attached, each of them with three laser reflectors 5. The laser tracker 4 is attached on the platform 2 of the object 3. The object 3 is gradually moved to positions (bj) (j=T, 2, m, m>l natural number). In Fig. 6 it is depicted in a position (a) where the laser tracker 4 attached on the platform 2 in the end effector 9 (not shown) of the object 3 measures by means of the laser beam 6 positions of the points in which the laser reflectors 5 are placed on the platform 7i. This way, in the given position of the object 3 it gradually measures positions of all the points in which the laser reflectors 5 are placed on all the platforms 7i. The results of these measurements in all the positions of the machine-object 3 are used for making up an overdetermined system of equations describing coupling conditions given by a relative position of the measuring apparatus elements from which the relative position of the measuring apparatus elements is determined and at the same time the measurement and/or calibration of a position of the object 3 (for example representing an end effector 9 of the machine) in space in all positions (bj) is performed. In this case this is a relative position of points in which the laser reflectors 5 on the platforms 7i are placed and the relative position of the object 3 in space, in which the platform 2 with the laser tracker 4 is attached, in all positions (b ).

Instead of the absolute measurement by means of the laser tracker 4 the incremental measurement may be used. This is possible in a way that instead of the laser reflectors 5 on the platforms 7 and 2 there are attaching points where the laser reflector 5 can be attached repeatably. The measurement proceeds in such a way that one laser reflector 5 is being continually gradually moved between positions on the platforms 7 and 2, where it is always attached repeatably and the appropriate measurement is performed.

The measurement according to Fig. 1 would proceed at the position (a) of the laser tracker 4 by gradually moving the laser reflector 5 from the position (a) to the positions 5ι, 5¾ then moving the laser tracker 4 to the position (c) and the laser reflector 5 from the position 5_2 to the positions 5_1? 5_2, and further on, then subsequently moving the laser tracker 4 to the position (b) and the laser reflector 5 from the position 5 to the positions 5_1; 5_2, 5b, then moving the laser tracker 4 to the position (d) and the laser reflector 5 from the position 5b to the positions 5_l5 5_2, 5b, and in case of need further on.

The measurement according to Fig. 3 would proceed by gradually moving the laser reflector 5 from the position (a) to the positions 5_l5 5_2, 5^ while the laser tracker 4 being in the position (a), then moving the laser tracker 4 to the position (b) and the laser reflector 5 from the position 5_,3 to the positions 5₁₅ 5¾ 5¾, and in case of need further on.

An advantage is the use of one laser reflector and higher accuracy of the incremental measurement. A disadvantage is a tardiness of moving the laser reflector 5.

Laser trackers can be replaced by optical video-cameras with a reference element and/or a laser beam source for a photosensitive element similarly as in the patent application PV 2012- 897.

The above described apparatus and measurement methods can be combined in various ways. For example, there may be only one laser reflector 5 on the platforms 7, while there are at least three laser reflectors 5 in total on the frame L There may be different number of laser reflectors on the platforms 7. On the measured object 3 there may be more platforms 2 with less or more than three laser reflectors 5, while on the measured object 3 there are at least three laser reflectors 5 in total. More than one laser tracker 4 can be used. More laser trackers 4 can perform measurements for the first phase of the measurement, and then subsequently more laser trackers 4 can perform measurements for the second phase of the measurement.

Measurement and its evaluation is carried out by a computer.

Claims

Patent Claims

1. A method for the redundant optical measurement and/or optical calibration of a position of an object in space by means of at least one laser tracker placed on the measured or calibrated object and/or on a frame of the object and at least one reflector of a laser beam placed on the measured or calibrated object and/or on a frame of the object, characterized in that the laser tracker is set to at least one position on the frame in which it measures a position of at least three laser reflectors of the laser beam on the frame, subsequently a calibration of the position of these laser reflectors of laser beams on the frame is performed, then the laser tracker is set to at least one position on the frame in which it measures the position of these at least three calibrated laser reflectors of laser beams on the frame and measures the position of at least three laser reflectors on the measured object and following these measurements the position of the measured object is determined, and/or the measured object on which the laser tracker is arranged is set to at least one position in space in which the laser tracker measures a position of at least three laser reflectors on the frame, on the base of these measurements a calibration of positions of laser reflectors on the frame is performed and, at the same time, the position of the measured object is determined.

2. The method for the redundant optical measurement and/or optical calibration of a position of an object in space as described in Claim 1, characterized in that the laser tracker is re-set to at least one next position and in each new position a position of all the laser reflectors on the frame is measured, on the basis of the measurements in these positions the calibration of the positions of the laser reflectors on the frame is performed, subsequently the laser tracker arranged on the frame or on the measured object is re-set to at least one next position in which it measures positions of all the laser reflectors on the frame or on the measured object and on the base of these measured positions the position of the measured object is determined.

3. The method for the redundant optical measurement and/or optical calibration of a position of an object in space as described in some of the Claims mentioned above, characterized in that the laser reflectors and/or laser trackers are re-set to repeatable positions.

4. The method for the redundant optical measurement and/or optical calibration of a position of an object in space as described in Claim 3, characterized in that distances of repeatable positions are measured.

5. The method for the redundant optical measurement and or optical calibration of a position of an object in space as described in some of the Claims mentioned above, characterized in that the laser trackers use the absolute method for the measurement of positions of laser reflectors.

6. The method for the redundant optical measurement and/or optical calibration of a position of an object in space as described in some of the Claims mentioned above, characterized in that the laser trackers use the incremental method for the measurement of positions of laser reflectors, when relocating laser reflectors and/or laser trackers to repeatable positions.

7. The apparatus for the redundant optical measurement and/or the optical calibration of a position of an object in space comprising at least one laser tracker placed on the measured or calibrated object and/or on a frame and at least one laser beam reflector placed on a frame and/or on the measured or calibrated object, characterized in that it comprises at least one laser tracker (4) and at least three laser reflectors (5).

8. The apparatus for the redundant optical measurement and/or optical calibration of a position of an object in space as described in Claim Ί, characterized in that the laser reflectors (5) are arranged in a triangle or a polygon.

9. The apparatus for the redundant optical measurement and/or optical calibration of a position of an object in space as described in some of the aforementioned Claims 7, 8, characterized in that at least one laser tracker (4) is arranged on the linear guide (8^ and/or at least one laser reflector (5) is arranged on the linear guide (8₂).