DE102020208567A1 - Calibration of a reference body for determining the guidance error of a machine axis - Google Patents

Abstract

The invention relates to a method for calibrating a reference body (14), which is a reference body (14) for determining guidance errors on a machine axis (X, Y, Z), comprising: - providing a coordinate measuring device (100) which has at least one linear machine axis (X) for moving along a coordinate axis (x) and at least one of this machine axis (X) movable sensor arrangement (12) with at least two distance sensors (S0, S1); - providing the reference body (14), the reference body (14) two along each other the machine axis (X) has regions (B0, B1) extending; - arranging the sensor arrangement (12) with a first relative orientation to the reference body (14) at a first position (x0) and at at least one second position (x1) along the coordinate axis (x) and acquisition of distance measured values (a (x0) S0-B0, a (x0) S1-B1; a (x1) S0-B0, a (x1) S1-B1) with the two distance sensors (S0, S1) each of the positions (x0, x1); - arrange the r sensor arrangement (12) with a second relative orientation to the reference body (14) at a first position (x0) and at the at least one second position (x1) and acquisition of measured distance values (a (x0) S0-B1; a (x1) S0-B1) with one of the distance sensors (S0, S1) at each of the positions (x0, x1); - Determination of an angular error size (Δβ) of the reference body (14) on the basis of the determined distance measurement values (a (x0) S0- B0, a (x0) S1-B1; a (x1) S0-B0, a (x1) S1-B1; a (x0) S0-B1; a (x1) S0-B1). The invention also relates to a coordinate measuring machine (100).

Description

The invention relates to a method and a device for calibrating a reference body for determining guidance errors of a machine axis of a coordinate measuring device.

Coordinate measuring devices, machine tools, machine kinematics or general technical systems can include controllable machine axes in a manner known per se in order to carry out predetermined movements. This can e.g. be translation or rotation axes. The movements can be generated by a drive, preferably individually assigned to the machine axis, which e.g. may include an electric motor. This can be controlled in a manner known per se to carry out desired movements, for example by means of an electronically and / or digitally operable control device. The control signals used for actuation can cause the axis to perform a desired movement and e.g. specify a drive power to be provided by the drive for this purpose.

A coordinate measuring machine, with which object coordinates can be recorded in a known manner, for example from an industrially manufactured workpiece, typically comprises at least three controllable machine axes. These are preferably arranged in such a way that a measuring device moved by them (for example a measuring sensor that detects the object in a tactile or non-contact manner) can be moved to any position in a Cartesian coordinate system. For this purpose, the machine axes can be aligned along the corresponding axes of the coordinate system and / or each enable a movement along one of these axes (ie one machine axis can be assigned to a coordinate axis). Consequently, a coordinate measuring machine typically has two machine axes extending horizontally and at right angles to one another (typically referred to as the X and Y axes). Furthermore, a vertically extending machine axis is often provided, which can also be referred to as the Z axis. A corresponding structure of a coordinate measuring machine is explained, for example, in the following DE 10 2008 024 444 A1 and in the DE 10 2018 208 189 A1 shown.

It is also known that such machine axes can have so-called guidance errors. These are e.g. about translation or rotation errors that overlay the actually desired movement when moving along the machine axis. In particular, they can result in movement components that are present along or around coordinate axes deviating from the machine axis (i.e. in a direction deviating from a target direction of movement of the machine axis). In addition, when moving along a machine axis, torsional errors can also occur, which relate to a rotation of the machine axis about itself or about its own longitudinal axis.

• - Ein Positionsfehler xTx(xi) betrifft die Verschiebung der Maschinenachse X in Richtung der x-Achse am Ort xi;
• - Ein Translationsfehler xTy(xi) betrifft die Verschiebung der Maschinenachse X in Richtung der y-Achse am Ort xi;
• - Ein Translationsfehler xTz(xi) betrifft die Verschiebung der Maschinenachse X in Richtung der z- Achse am Ort xi;
• - Ein Torsionsfehler xRx(xi) betrifft die Verdrehung der Maschinenachse X um die x-Achse am Ort xi;
• - Ein Rotationsfehler xRy(xi) betrifft die Verdrehung der Maschinenachse X um die y-Achse am Ort xi;
• - Ein Rotationsfehler xRz(xi) betrifft die Verdrehung der Maschinenachse X um die z-Achse am Ort xi.

Such guide errors can have various causes and result, for example, from manufacturing inaccuracies in the guides, the scales and / or the bearings of a machine axis. The following lists the possible guidance errors when moving a machine axis marked with an X. The X machine axis (or its axis of movement) extends along (or parallel to) the x axis of a Cartesian coordinate system which also includes a y and a z axis. The possible guidance errors that occur when moving the X machine axis along the x coordinate axis are as follows:

• - A position error xTx (xi) relates to the displacement of the machine axis X in the direction of the x-axis at location xi;
• A translation error xTy (xi) relates to the displacement of the machine axis X in the direction of the y-axis at location xi;
• - A translation error xTz (xi) relates to the displacement of the machine axis X in the direction of the z axis at location xi;
• - A torsion error xRx (xi) concerns the rotation of the machine axis X about the x-axis at location xi;
• - A rotation error xRy (xi) concerns the rotation of the machine axis X about the y-axis at the location xi;
• - A rotation error xRz (xi) concerns the rotation of the machine axis X about the z-axis at location xi.

The locations xi can be distributed over the entire movement path that can be traversed by the X machine axis.

It goes without saying that the nomenclature can also be transferred analogously to a Z machine axis extending along (or parallel to) the z axis and a Y machine axis extending along (or parallel to) the y axis . Instead of xi, a location zi or yi would then be considered. Furthermore, the torsion error then relates to a rotation of the Y, Z machine axis about the coordinate axes parallel to it or, in other words, about itself. Rotation errors exist about the remaining coordinate axes. The person skilled in the art is familiar with the corresponding nomenclature, which is why a complete reproduction of all 18 possible guide errors about all three X, Y, Z machine axes is not provided at this point.

It is also known to detect such guidance errors in the form of specific guidance error values at the individual xi, yi and zi positions and to store them in a machine control. The guidance errors can be used to mathematically correct position values and / or control signals of the machine axis (s) in the sense of calibration values. For example, if position values of the machine axis (s) are used to derive measured values from them, as is common with a coordinate measuring machine, for example, the previously determined guide error values can be used to correct the measured values accordingly (i.e. to calculate the guide errors from the determined values). Further background information on determining guide errors and the calibration of coordinate measuring machines based on them can be found in DE 10 2008 024 444 A1 and the DE 44 21 302 C1 .

Various approaches are known from the prior art for determining guidance errors. In the DE 10 2008 024 444 A1 For example, a solution is disclosed in which a scanning device is moved along a reference body in order to determine guidance error values based thereon (referred to there as axis error values). Since the reference body is measured in advance with a calibrated coordinate measuring machine and body error values are determined for this purpose, imperfections of the reference body can also be taken into account. In other words, guidance error values adjusted for imperfections of the reference body can be determined.

In this context, however, it is disadvantageous that a calibrated coordinate measuring machine must be used to calibrate the reference body. If it was not calibrated immediately before measuring the reference object, this coordinate measuring machine can have changed due to changing environmental influences or aging effects. For this reason, coordinate measuring machines are regularly recalibrated. However, there may be a period of time between the last calibration and the measurement of the reference body in which such changes have already had a disadvantageous effect.

Furthermore, a high-precision coordinate measuring machine is to be used for measuring the reference body, which is not available to every user and can generally be characterized by high costs. In addition, so-called inclination scales are often used when calibrating the high-precision coordinate measuring machines. Their measurements, especially when measuring the xRx torsion error described above, are often characterized by poor reproducibility, so that residual errors remain which can negatively influence the calibration result of the reference body.

There is therefore a need to improve the calibration of a reference body that is used to determine the guidance error of a machine axis, which is preferably part of a coordinate measuring machine. In particular, it should be possible to achieve high calibration accuracy with limited effort.

This object is achieved by the subject matter of the attached independent claims. Advantageous further developments are given in the dependent claims. The above explanations and features of the prior art can also be provided in the present solution or apply to it, unless otherwise stated or evident.

According to a general solution idea, the calibration takes place by determining an angular error variable (for example an absolute angular error, but preferably an angular error difference and / or a position-dependent angular error profile) of the reference body, preferably using only distance measurement values. The measured distance values can be recorded with distance sensors that do not necessarily have to be calibrated or at least can be calibrated with little effort. Coordinate measurement values that are conventionally determined by a measurement system of the coordinate measurement machine can, however, be partially or completely dispensed with for calibrating the reference body. This also means that the calibration quality of the coordinate measuring machine has less of an influence on the accuracy than before. Consequently, there is no need to use a high-precision coordinate measuring machine.

Instead, it is proposed to arrange a sensor arrangement in different defined relative alignments to the reference body and to detect distance values there with the distance sensors. An angle error magnitude of the reference body is determined on the basis of the distance measured values obtained. This angle error quantity can be stored as a calibration value. Future measured values acquired using the reference body for determining guidance errors can be corrected in a conventional manner using such calibration values. As explained below, angular error variables of the reference body and / or calibration values are preferably determined and stored as a function of the axis positions of the machine axis.

The angle error variable of the reference body preferably relates to an angle that occurs when a surface of the reference body facing a measuring sensor of the coordinate measuring machine and / or a plane parallel to it is tilted about or relative to the coordinate axis along which the machine axis is moved. In particular, it can be the angle between the horizontal and / or a plane parallel to a measuring table surface of the coordinate measuring machine and the aforementioned surface of the reference body.

• - Bereitstellen eines Koordinatenmessgeräts, das wenigstens eine lineare Maschinenachse zum Bewegen entlang einer Koordinatenachse aufweist und wenigstens eine von dieser Maschinenachse bewegbare Sensoranordnung mit wenigstens zwei Abstandssensoren;
• - Bereitstellen des Referenzkörpers, wobei der Referenzkörper zwei sich entlang der Maschinenachse erstreckende Bereiche aufweist;
• - Anordnen der Sensoranordnung mit (oder in) einer ersten Relativausrichtung zu dem Referenzkörper an einer ersten Position und an wenigstens einer zweiten Position entlang der Koordinatenachse und Erfassen von Abstandsmesswerten mit den beiden Abstandssensoren an jeder der Positionen;
• - Anordnen der Sensoranordnung mit einer zweiten Relativausrichtung zu dem Referenzkörper an einer ersten Position und an wenigstens einer zweiten Position und Erfassen von Abstandsmesswerten mit einem der Abstandssensoren an jeder der Positionen;
• - Bestimmen einer Winkelfehlergröße des Referenzkörpers anhand der ermittelten Abstandsmesswerte.

In particular, a method for calibrating a reference body is proposed, which is a reference body for a guide error determination (in particular torsion error determination) of a machine axis (a coordinate measuring device), having:

• Provision of a coordinate measuring device which has at least one linear machine axis for moving along a coordinate axis and at least one sensor arrangement which can be moved from this machine axis and has at least two distance sensors;
• Providing the reference body, the reference body having two regions extending along the machine axis;
• - Arranging the sensor arrangement with (or in) a first relative orientation to the reference body at a first position and at at least one second position along the coordinate axis and acquiring distance measurement values with the two distance sensors at each of the positions;
• Arranging the sensor arrangement with a second relative orientation to the reference body at a first position and at at least one second position and detecting distance measured values with one of the distance sensors at each of the positions;
• - Determination of an angular error size of the reference body on the basis of the determined distance measurement values.

The machine axis can, for example, move a quill on which the sensor arrangement is arranged. In general, the sensor arrangement can be arranged on and / or moved by the coordinate measuring device in a manner analogous to a measuring sensor (e.g. a tactile button or an optical coordinate measuring sensor). The machine axis can in particular be a horizontal axis and in particular a machine axis usually designated by X. In principle, however, the method can be applied to any machine axes or reference bodies provided for this purpose.

The reference body can generally be elongated. It can extend with a correspondingly pronounced longitudinal extension along the coordinate axis and / or the machine axis. The two areas of the reference body can be protruding and / or projection-like areas but also elongated recesses. In particular, these can also be elongated and e.g. be formed in the form of a web.

During the first relative alignment, the distance sensors can each be directly opposite one of the areas of the reference body. In the second relative alignment, on the other hand, only one of the distance sensors can preferably lie opposite one of the areas. This is preferably the area which this distance sensor was not directly opposite in the first relative alignment. In other words, in the first relative alignment, at least one of the distance sensors can measure a first area which is preferably opposite this distance sensor. In the second relative alignment, however, the distance sensor can be arranged in such a way that another area is opposite it. The further distance sensor then still remaining, on the other hand, cannot take any distance measurements during the second relative alignment and / or cannot face any of the areas.

To arrange the sensor arrangement with the first or second relative alignment, the machine axes of the coordinate measuring device can be moved accordingly. As will be explained, this movement is preferably carried out at an angle and in particular orthogonally (ie at a right angle) to the Coordinate axis. For example, this movement can be carried out by a generally different machine axis and preferably a different horizontal machine axis of the coordinate measuring device.

Instead of a relative alignment, one could also speak of a relative position, relative positioning or relative orientation. This is preferably present in a plane defined perpendicular to the machine axis and / or coordinate axis.

The angular error magnitude of the reference body can be an absolute value of the angular error. However, it is preferably a difference between the angular error measured in the second position and the angular error in the first position.

This angle error variable of the reference body can be stored in a manner known per se as a calibration value in order to be able to correct measurement values obtained in the future when measuring the reference body and in particular total angle values explained below.

Advantageously, the solution presented enables the same structure, i.e. the same structure, to be used for the calibration of the reference body and the determination of the guide errors of the coordinate measuring machine. the same reference body and in particular also the same sensor arrangement can be used.

A further development of the solution presented (i.e. the method and / or the device) provides that, in the first relative alignment, a first distance sensor detects the first area and a further distance sensor detects the second area. As mentioned, these areas can each be directly opposite the distance sensors, especially when the reference body is in a horizontal position, vertically opposite.

Additionally or alternatively, it can be provided that in the second relative alignment the first distance sensor detects the second area or the further distance sensor detects the first area. In other words, the distance sensors switch to the area that they did not previously detect. Preferably, however, this only applies to one of the distance sensors, whereas the other distance sensor is not assigned to any of the areas or does not measure any of the areas.

These variants of the first and second relative alignment enable the required distance measurement values to be recorded with a few axis movements and with a short measurement duration.

As mentioned, according to a further general embodiment of the solution presented, it can be provided that, during the second relative alignment, only one of the distance sensors takes distance measurements and / or measures only one of the areas mentioned.

According to a further development of the solution presented, a total angle value at each of the positions is determined in the first relative alignment based on at least some of the measured distance values. In particular, the measured distance values of the sensors can be used if they measure an area opposite them in each of the positions. The total angle value can be an angle that lies between a plane that runs parallel to the two measured areas and / or includes them (or includes the measuring points of these areas detected by the distance sensors) and a preferably horizontal plane. For example, this horizontal plane can have the coordinate axis and a further coordinate axis orthogonal thereto (in particular the Y axis) and / or can be oriented generally parallel to a measuring table surface of the coordinate measuring device.

Alternatively or additionally, it can be provided that a torsional error variable and in particular a torsional error difference of the machine axis about the coordinate axis is determined on the basis of at least some of the distance measured values. The torsional error difference can be the difference between the torsional errors in the first and in the second position. For the definition of the torsion error, reference is made to the list of possible control error variables above.

In this case, all distance measured values that were determined for one of the areas in both the first and the second relative alignment can be taken into account as distance measured values, this preferably being done for both of the positions under consideration. It can be provided in the manner described above that the corresponding area is measured by both of the distance sensors.

In particular, it can also be provided in this context that the angle error variable of the reference body is determined on the basis of a difference between the total angle values and the torsional error variable. For example, the torsional error magnitude, in particular a torsional error difference explained above, can be subtracted from the difference in the total angle values in order to obtain in this way an angle error difference between the angle error in the second position and the angle error in the first position.

As mentioned above, the solution presented here is advantageously characterized in that the distance values determined by the distance sensors are used to determine the angular error magnitude of the reference body. It is preferably generally provided that no other measured values are used, in particular no coordinate values determined by a measuring system of the coordinate measuring machine. Such a measuring system can be the known systems of a coordinate measuring machine, which from axis positions of the machine axes a position of e.g. a quill and / or a measuring sensor of the coordinate measuring machine. From this, in turn, conclusions can be drawn about the coordinates of a currently measured object. According to the invention, however, such measured values or the general coordinate measuring system of the coordinate measuring machine are not used and / or taken into account. Instead, measured values determined exclusively by the distance sensors and in particular distance measured values are preferably used. This is accompanied by the advantage mentioned above that the coordinate measuring machine itself does not have to be calibrated with high precision.

• - Abspeichern von Werten der Winkelfehlergröße des Referenzkörpers in einer Kalibrierdatei, die dem Referenzkörper zugeordnet ist.

A further development of the procedure includes:

• - Storage of values of the angular error size of the reference body in a calibration file that is assigned to the reference body.

This calibration file can be used in later stages, in particular during future calibrations of the coordinate measuring machine. It is particularly advantageous that other coordinate measuring machines that are to be calibrated using the same reference body can also use this calibration file. You do not have to determine the angle error size yourself again.

• - Anordnen der Sensoranordnung mit einer ersten Relativausrichtung zu einem Referenzkörper an einer ersten Position und an einer zweiten Position entlang der Koordinatenachse und Erfassen von Abstandsmesswerten mit den beiden Abstandssensoren an jeder der Positionen;
• - Anordnen der Sensoranordnung mit einer zweiten Relativausrichtung zu dem Referenzkörper an einer ersten Position und an einer zweiten Position entlang der Koordinatenachse und Erfassen von Abstandsmesswerten mit wenigstens einem der Abstandssensoren an jeder der Positionen;
• - Bestimmen einer Winkelfehlergröße des Referenzkörpers anhand der ermittelten Abstandsmesswerte.

The invention also relates to a coordinate measuring device with at least one linear machine axis for moving along a coordinate axis and with at least one sensor arrangement with at least two distance sensors that can be moved from this machine axis,
and with a control device which is set up to control the machine axis and sensor arrangement as follows:

• Arranging the sensor arrangement with a first relative orientation to a reference body at a first position and at a second position along the coordinate axis and detecting distance measured values with the two distance sensors at each of the positions;
• Arranging the sensor arrangement with a second relative orientation to the reference body at a first position and at a second position along the coordinate axis and detecting distance measured values with at least one of the distance sensors at each of the positions;
• - Determination of an angular error size of the reference body on the basis of the determined distance measurement values.

Both in the method and in the device it can be provided that an even larger number of positions for measurement is approached by the sensor arrangement, that is, that the sensor arrangement is in a number of positions, for example a third or fourth position, in the manner described here the coordinate axis and with the first and second relative alignment. Correspondingly, the distance measurement values described herein can be determined in a multiplicity of positions and values of the angular error magnitude of the reference body can be determined based thereon. If this is carried out for a large number of positions along the observed coordinate axis, a course of the angular error and / or the angular error magnitude (e.g. the angular error difference) of the reference body can be determined along the coordinate axis. For example, a value of the angle error magnitude of the reference body can then also be determined by interpolation for a position that lies between two positions in which distance values and in particular values of the angular magnitude were determined within the scope of the calibration.

In summary, one development provides that the detection of distance values described here takes place in a large number of positions along the coordinate axis and, for example, in at least 10 or also at least 50 positions. On the basis of the angular error values of the reference body determined for each of the positions, e.g. the described course of the angular error magnitude can be determined and / or angular error magnitudes for further positions can be determined by calculation.

In particular, the first and second positions in which measured distance values are recorded with both relative orientations can coincide. Even with a large number of positions, as many of them as possible preferably match. But this is not mandatory. In the case of position deviations, the relevant measured values and / or error variables can instead be interpolated (ie calculated for a common position using measured values and / or error variables recorded at other positions).

In general, the device can be configured to carry out a method in accordance with any of the aspects described herein. All of the above explanations on and developments of features of the method can also apply to the device features or be provided for them. In general, the device (that is to say the coordinate measuring machine) can comprise any further feature in order to carry out all of the method steps described herein and / or to provide functions.

• 1 zeigt eine perspektivische Ansicht eines Koordinatenmessgeräts mit einem Referenzkörper, wobei das Koordinatenmessgerät einer Vorrichtung gemäß einem Ausführungsbeispiel der Erfindung entspricht und ein Verfahren gemäß einem Ausführungsbeispiel ausführt.
• 2, 3 zeigen Detailansichten einer Sensoranordnung des Koordinatenmessgeräts aus 1 beim Vermessen des Referenzkörpers bei einer ersten Relativausrichtung in einer ersten Position (2) und einer zweiten Position (3).
• 4, 5 zeigen das Vermessen des Referenzkörpers mit der Sensoranordnung bei einer zweiten Relativausrichtung in der ersten (4) und zweiten (5) Position.

Embodiments of the invention are explained below with reference to the attached schematic figures.

• 1 shows a perspective view of a coordinate measuring machine with a reference body, the coordinate measuring machine corresponding to a device according to an embodiment of the invention and executing a method according to an embodiment.
• 2 , 3 show detailed views of a sensor arrangement of the coordinate measuring machine 1 when measuring the reference body with a first relative alignment in a first position ( 2 ) and a second position ( 3 ).
• 4th , 5 show the measurement of the reference body with the sensor arrangement with a second relative alignment in the first ( 4th ) and second ( 5 ) Position.

In 1 is a coordinate measuring machine 100 shown, which is an example of a device according to the invention 10 is. The coordinate measuring machine 100 is constructed in a conventional manner. It comprises three machine axes X, Y, Z running orthogonally to one another, each of which defines linear movement axes. These run along the machine coordinate system shown. The machine coordinate system is oriented in such a way that its x and y axes define a horizontal spatial plane, whereas the z axis runs vertically (i.e. defines an axis along which the gravitational force acts). As the coordinate measuring machine 100 corresponds to a conventional design, the individual machine axes X, Y, Z and their drives are not shown in detail. However, the lines shown in dashed lines are along which the machine axes labeled X, Y, Z can execute movements.

In the following, the X machine axis is considered as an example. The procedure described below can also be transferred to the other machine axes Y, Z.

When traversing along the X machine axis, the other machine axes Y, Z are also traversed accordingly along this axis or the x coordinate axis running parallel to it. A sensor arrangement is located on the Z machine axis, which is a quill 12 arranged. This includes two distance sensors S0 , S1 . These are spaced from one another by a distance d along the Y machine axis. The sensor arrangement 12 lies on a reference body which is elongated along the X machine axis (or x coordinate axis) 14th across from. This has two areas B0 , B1 which are also designed to be correspondingly elongated along the X machine axis. As from the following 2 to 5 these areas are evident B0 , B1 for example designed as protruding elongated tracks, but this is not mandatory.

In the manner described below, the sensor arrangement 12 with the in 1 The illustrated first relative alignment is positioned at a starting position x0 along the x coordinate axis. Then with each of the distance sensors S0 , S1 Distance values to the areas B0 and B1 determined. Then the sensor assembly 12 positioned by means of the X machine axis in at least one further and preferably in a plurality of further positions x1 ... xn along the x coordinate axis. There will also be both of the sensors S0 , S1 Distance measurements made. This corresponds to the procedure explained below from 2 and 3 . Then, in the same positions, taking another second relative orientation from the 4th and 5 another distance measurement was carried out, but then only with one of the distance sensors S0 , S1 . This then measures another of the areas B0 , B1 than in the in 1 as well as the 2 and 3 shown first relative orientation.

2 shows a schematic cross-sectional view through the reference body 14th with opposite sensor arrangement 12 . The cross-sectional plane lies in the yz plane 1 so that the x- The coordinate axis is perpendicular to the plane of the sheet. Also for the following others 3 to 5 an analogous cross-sectional plane is selected.

The areas are shown B0 , B1 as well as in the first relative alignment, these distance sensors each opposite S0 , S1 . The arrangement is such that the distance sensors S0 , S1 an area immediately opposite each other B0 , B1 measured, whereby the opposite refers to a corresponding alignment along the z-coordinate axis.

It is also shown that the reference body 14th has an angle error β (x0). Here, x0 denotes the shown first considered position along the x-coordinate axis (starting position). The angle error β (x0) describes a tilting of one of the areas B0 , B1 comprehensive and / or parallel to this level E1 relative to the horizontal (i.e. to the XY plane). The torsion error xRx (x0) is also shown as a further error potential. This is the position-dependent error that results from the rotation of the X machine axis when moving along the x coordinate axis. The mentioned error xRx (x0) is determined in relation to an analogous horizontal plane as the above-mentioned angle error β (x0).

The ones in the shown position x0 from the distance sensors S0 , S1 Distance values a (x0) S0-B0 and a (xO) S1-B1 recorded in each case are also entered.

With previous calibration of the reference body 14th a high-precision coordinate measuring machine discussed above is completely calibrated in advance. An inclination balance, which is disadvantageous for the reasons mentioned in the introduction, is used to detect the torsional errors of this coordinate measuring machine. The torsion errors are then known, for example, at every x position of the coordinate measuring machine and can be stored in a calibration file (CAA file) of this coordinate measuring machine. The reference body will then be used at a later point in time 14th calibrated with this coordinate measuring machine. A total angle γ (xi) can initially be calculated from measured distance values. The torsional errors of the high-precision coordinate measuring machine, which are read from the calibration file, are subtracted from this total angle γ (xi) at each x position. The difference is then the angle error β of the reference body.

From the representation of 2 it results that a generally measured total angle γ (xi) at any position xi along the x-coordinate axis is a sum of the torsion angle xRx and the angle error β of the reference body 14th corresponds to: $$\gamma \left(xi\right)=x\mathrm{R.}x\left(xi\right)+\beta \left(xi\right)$$

The angle γ can generally be determined from the difference between the measured distance values a (xi) S1-B1, a (xi) S0-B0 and the range distance d. The simplified equation applies to small angles: $$\gamma \left(x_i\right)=\frac{\left(a\left(x_i\right)\mathrm{S.}1-\mathrm{B.}1\right)-\left(a\left(x_i\right)\mathrm{S.}0-\mathrm{B.}0\right)}{d}$$

In 3 is to illustrate the problem, the measurement of the reference body 14th shown in a second position x1 along the x-coordinate axis. It can be seen that both the angle error β (x1) and the torsion error xRx (x1) are position-dependent. Correspondingly, the distance values a (x1) S0-B0 and a (x1) S1-B2 differ significantly from the first position x0 2 .

In principle, the method according to the invention nevertheless provides for the respective distance values from the positions x0, x1 shown 2 and 3 to investigate.

It is also provided, however, by moving the sensor arrangement 12 with the Y-machine axis also a second relative alignment between the sensor arrangement 12 and the reference body 14th to create. This relative alignment is in the 4th and 5 shown. Only one of the distance sensors is in each case S0 , S1 one of the areas B0 , B1 along the z coordinate axis opposite or can be one of the areas B0 , B1 measured. The relative arrangement takes place in such a way that the distance sensor S0 then the formerly in the first relative alignment of the 2 and 3 area not surveyed by him B1 missing. Alternatively, it could also be provided that the distance sensor S1 the area not measured in the first relative alignment B0 missing or facing it.

The correspondingly selected distance sensor is then used at preferably the same positions x0, x1 S0 Distance values to the area B1 determined (see a (x0) S0-B1 in 4th and a (x1) SO-B1 5 ). It is also possible to record distance values at other x positions. Then, for common x positions with the first and second relative alignment, measurable distance values can be determined computationally (for example by interpolation).

A basic idea of measuring with two relative shaving directions is that the first relative orientation of the 2 and 3 as well as the second relative orientation of the 4th and 5 the sensor arrangement 12 or the quill of the coordinate measuring machine coupled with it 100 tilted in the same way when moving between the positions or measuring locations x0, x1. By that but the area B1 with different sensors S0 , S1 is detected in the first and second relative alignment, give the correspondingly overall determined distance measurement values in relation to this area B1 information about the extent of the tilt. More precisely, the angle and torsion errors can be determined separately from this effect in the manner described below.

So based on the first relative alignment from the 2 and 3 First, the angle error differences in the measuring positions x1 and x0 are determined according to the following equation 2: $$\Delta \beta \left(x\mathrm{1,}x0\right)=\beta \left(x1\right)-\beta \left(x0\right)$$

Likewise, a total angle difference can also be obtained from the respective measurement result 2 and 3 can be determined as follows: $$\Delta \gamma \left(x\mathrm{1,}x0\right)=\gamma \left(x1\right)-\gamma \left(x0\right)$$

Finally, taking into account the effect described above, a torsional error difference for small angles can also be determined as the torsional error quantity ΔxRx (x1, x0) according to Equation 4 below: $$\Delta x\mathrm{R.}x\left(\mathrm{<figure-callout\; id="1"\; label="x"\; filenames="DE102020208567A1\_0008.png,DE102020208567A1\_0009.png"\; state="\{\{state\}\}">x</figure-callout>}\mathrm{1,}x0\right)=\frac{a{\left(x1\right)}_{\mathrm{S.}0-\mathrm{B.}1}-a{\left(x0\right)}_{\mathrm{S.}0-\mathrm{B.}1}-\left(a{\left(x1\right)}_{\mathrm{S.}1-\mathrm{B.}1}-a{\left(x0\right)}_{\mathrm{S.}1-\mathrm{B.}1}\right)}{d}$$

On the basis of the above equation (1), all variables are therefore available for the angle error variable of the reference body that is actually of interest 14th and in the example shown to determine the angle error difference Δβ: $$\Delta \beta \left(x\mathrm{1,}x0\right)=\Delta \gamma \left(x\mathrm{1,}x0\right)-\Delta x\mathrm{R.}x\left(\mathrm{<figure-callout\; id="1"\; label="x"\; filenames="DE102020208567A1\_0008.png,DE102020208567A1\_0009.png"\; state="\{\{state\}\}">x</figure-callout>}\mathrm{1,}x0\right)$$

Taking into account all of the above variables and in particular equation 4, it becomes clear that to determine this angular error variable of the reference body 14th only distance measured values of the distance sensors S0 , S1 are required and no calibration values of the coordinate measuring machine 100 . Furthermore, it goes without saying that the position x1 is arbitrarily selected and general position xi and in particular also a plurality of different positions x1... Xn can also be taken into account. In each of these positions x1 ... xn, for example, to 3 and 5 analog measurements are carried out, whereas the 2 and 4th Define general measurements in a starting position x0. A profile of the angle error β (in particular of Δβ) over all measurement positions x1... Xn can then also be calculated from the measured variables determined overall in this way.

In calibration mode of the coordinate measuring machine 100 this can initially take any starting position that serves as a reference. Distance measurements for the first relative alignment can then be carried out analogously to 2 and 3 be made. Equation (5) can be converted to ΔxRx in order to determine the torsional error in relation to the starting position or reference. Through the determined course of β and in particular Δβ, the influence of the faulty reference body can thereby 14th be taken into account. Thus, the torsional error of the coordinate measuring machine 100 precisely determined, which improves the calibration quality

In other words, for each calibration of a coordinate measuring machine 100 the reference body 14th can be measured in the two different relative orientations. From this, the angular error size β of the reference body can be determined 14th and finally the torsion error xRx of the coordinate measuring machine 100 be calculated.

In order to reduce the measurement effort, however, it can be assumed that an angular error variable β of the reference body, once determined 14th remains constant. The determined angular error size of the reference body 14th can consequently in one of the reference bodies 14th assigned (digital) calibration file. For calibration processes with other coordinate measuring machines 100 one can refer to values of the angular error size from this calibration file of the reference body 14th To fall back on. The reference body 14th does not necessarily have to be done with these additional coordinate measuring machines 100 are measured in the second relative alignment. The measurement of the reference body is preferred 14th to determine the size of the angular error, however, repeated at certain time intervals, for example once a year.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 102008024444 A1 [0003, 0008, 0009]
• DE 102018208189 A1 [0003]
• DE 4421302 C1 [0008]

Claims (11)

A method for calibrating a reference body (14), which is a reference body (14) for determining guidance errors of a machine axis (X, Y, Z), comprising: - Providing a coordinate measuring device (100) which has at least one linear machine axis (X) for moving along a coordinate axis (x) and at least one sensor arrangement (12) movable from this machine axis (X) with at least two distance sensors (S0, S1); - providing the reference body (14), the reference body (14) having two regions (B0, B1) extending along the machine axis (X); - Arranging the sensor arrangement (12) with a first relative orientation to the reference body (14) at a first position (x0) and at at least one second position (x1) along the coordinate axis (x) and acquisition of measured distance values (a (x0) S0- B0, a (x0) S1-B1; a (x1) S0-B0, a (x1) S1-B1) with the two distance sensors (S0, S1) at each of the positions (x0, x1); - Arranging the sensor arrangement (12) with a second orientation relative to the reference body (14) at a first position (x0) and at at least one second position (x1) and acquisition of measured distance values (a (x0) S0-B1; a (x1) S0-B1) with one of the distance sensors (S0, S1) at each of the positions (x0, x1); - Determination of an angular error size (Δβ) of the reference body (14) on the basis of the determined distance measured values (a (x0) S0-B0, a (x0) S1-B1; a (x1) S0-B0, a (x1) S1-B1; a (x0) S0-B1; a (x1) S0-B1). Procedure according to Claim 1 , characterized in that in the first relative alignment a first distance sensor (S0) detects the first area (B0) and a further distance sensor (S1) detects the second area (B1). Procedure according to Claim 1 or 2 , characterized in that in the second relative alignment the first distance sensor (S0) detects the second area (B1) or the further distance sensor (S1) detects the first area (B0). Method according to one of the preceding claims, characterized in that a change between the first relative orientation and the second relative orientation comprises a movement along an axis (y) which runs at a right angle to the coordinate axis (x). Method according to one of the preceding claims, characterized in that during the second relative alignment only one of the distance sensors (S0, S1) carries out distance measurements. Method according to one of the preceding claims, characterized in that on the basis of at least part of the measured distance values (a (x0) S0-B0, a (x0) S1-B1; a (x1) S0-B0, a ( x1) S1-B1) a total angle value (γ (xi)) is determined at each of the positions (x0, x1). Method according to one of the preceding claims, characterized in that on the basis of at least some of the distance measured values (a (x0) S0-B1, a (x1) S0-B1; a (x0) S0-B0, a (x1) S0-B0 ); a (x0) S1-B1, a (x1) S1-B1) a torsional error quantity (xRx (x1)) of the machine axis (X) around the coordinate axis (x) is determined. Procedure according to Claim 6 and 7th , characterized in that the angular error size (Δβ) of the reference body (14) is determined on the basis of a difference between the total angle values (y (xi)) and the torsional error size. Method according to one of the preceding claims, characterized in that no coordinate measurement values and / or calibration values generated by a measurement system of the coordinate measuring machine are used to determine the angular error magnitude (Δβ) of the reference body (14). Method according to one of the preceding claims, further characterized by : storing values of the angular error magnitude (Δβ) of the reference body (14) in a calibration file which is assigned to the reference body (14). Coordinate measuring machine (100) with at least one linear machine axis (X, Y, Z) for moving along a coordinate axis (x) and with at least one sensor arrangement movable from this machine axis (X) with at least two distance sensors (S0, S1), and with a control device which is set up to control the machine axis (X) and sensor arrangement (12) as follows: Arranging the sensor arrangement (12) with a first relative orientation to a reference body (14) at a first position (x0) and at a second position (x1) along the coordinate axis (x) and recording of distance measured values (a (x0) S0-B0, a (x0) S1-B1; a (x1) S0-B0, a (x1) S1-B1) with the two distance sensors (S0, S1) at each of the positions (x0, x1); - Arranging the sensor arrangement (12) with a second orientation relative to the reference body (14) at a first position (x0) and at a second position (x1) along the coordinate axis (x) and detecting distance measured values (a (x0) S0-B1 ; a (x1) S0-B1) with at least one of the distance sensors (S0, S1) at each of the positions (x0, x1); - Determination of an angular error size (Δβ) of the reference body (14) on the basis of the determined distance measurement values (a (x0) S0-B0, a (x0) S1-B1; a (x1) S0-B0, a (x1) S1-B1; a (x1) S0-B1; a (x2) S0-B1).

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