DE102020208567B4 - Calibration of a reference body for determining the guidance error of a machine axis - Google Patents

Abstract

Method for calibrating a reference body (14), which is a reference body (14) for a guide error determination of a machine axis (X, Y, Z), comprising: - providing a coordinate measuring device (100) that has at least one linear machine axis (X) for moving along has a coordinate axis (x) and at least one sensor arrangement (12) which can be moved by this machine axis (X) and has at least two distance sensors (S0, S1);- providing the reference body (14), the reference body (14) being located two along the machine axis X) has extending areas (B0, B1);- arranging the sensor arrangement (12) with a first relative orientation to the reference body (14) at a first position (x0) and at least one second position (x1) along the coordinate axis (x) and acquiring distance measurement 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 array (12) with a second relative orientation to the reference body (14) at a first position (x0) and at at least one second position (x1) and detecting 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);- determining an angular error quantity (Δβ) of the reference body (14) using 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).

Description

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

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 specified movements. These can be, for example, translation or rotation axes. The movements can be generated by a drive which is preferably assigned individually to the machine axis and which can comprise an electric motor, for example. This can be controlled in a manner known per se in order to carry out desired movements, for example by means of an electronically and/or digitally operable control device. The control signals used for activation can cause the axis to perform a desired movement and, for example, indicate the drive power to be applied by the drive for this purpose.

A coordinate measuring machine, with which object coordinates, for example of an industrially manufactured workpiece, can be detected in a known manner, 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 desired 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 enable a movement along one of these axes (ie each machine axis can be assigned to each coordinate axis). Consequently, a coordinate measuring machine typically has two machine axes (typically referred to as the X and Y axes) extending horizontally and at right angles to one another. 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, for example, in the one explained below 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, for example, 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 about coordinate axes that deviate from the machine axis (i.e., in a direction that differs from a desired direction of movement of the machine axis). In addition, when moving along a machine axis, torsional errors can also occur, which relate to a twisting 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 can result, for example, from manufacturing inaccuracies in the guides, the scales and/or the bearings of a machine axis. The possible guidance errors when moving a machine axis marked X are listed below. The X machine axis (or its movement axis) extends along (or parallel to) the x axis of a Cartesian coordinate system, which also includes a y axis and a z axis. The possible lead errors that occur when moving the X machine axis along the X coordinate axis are as follows:

• - A position error xTx(xi) concerns the displacement of the machine axis X in the direction of the x-axis at location xi;
• - A translational error xTy(xi) concerns the displacement of the machine axis X in the direction of the y-axis at location xi;
• - A translational error xTz(xi) concerns the displacement of the machine axis X in the direction of the z-axis at location xi;
• - A torsional error xRx(xi) relates to the torsion of the machine axis X around the x-axis at location xi;
• - A rotation error xRy(xi) relates to the rotation of the machine axis X around the y-axis at location xi;
• - A rotation error xRz(xi) affects the rotation of the machine axis X around 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 in an analogous manner 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 torsional error then relates to a rotation of the Y, Z machine axis around the coordinate axes parallel thereto or, in other words, around itself. Rotational errors are present around 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 around all three X, Y, Z machine axes is omitted at this point.

It is also known to detect such guidance errors in the form of concrete 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(ies) in the sense of calibration values. If, for example, position values of the machine axis(s) are used to derive measured values, as is usual 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 calibrating 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 from the prior art are known for determining guidance errors. In the DE 10 2008 024 444 A1 a solution is disclosed, for example, in which a scanning device is moved along a reference body in order to determine guide 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, guide error values that have been corrected for imperfections in the reference body can be determined.

However, it is disadvantageous in this connection that a calibrated coordinate measuring machine has to be used to calibrate the reference body. If it was not calibrated immediately before measuring the reference object, this coordinate measuring machine may have changed due to changing environmental influences or aging effects. For this reason, coordinate measuring machines are regularly recalibrated. However, there can 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. So-called inclination scales are also often used when calibrating the high-precision coordinate measuring machines. Their measurements are often characterized by low reproducibility, especially when measuring the xRx torsional error described above, so that residual errors remain, which can negatively influence the calibration result of the reference body.

From the DE 198 30 646 A1 the following is also known: A method for correcting geometric process errors of at least one axis of a coordinate measuring machine, in which the process errors of at least one axis are recorded with a measuring device over the entire measurement volume with a support point grid, and in which the process errors of at least one axis are also recorded is carried out in at least one partial volume of the entire measurement volume with an increased support point density, the measurement device being arranged at least approximately at a virtual zero mark of at least one axis of the partial volume and the recording of the process errors in the partial volume then being carried out.

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, a high calibration accuracy should be achievable with limited effort.

This object is solved by the subject matter of the appended independent claims. Advantageous developments are specified in the dependent claims. The above explanations and features of the prior art can also be provided for or apply to the present solution, unless otherwise stated or apparent.

According to a general idea for a solution, the calibration is performed 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 measured distance values. The measured distance values can be recorded with distance sensors, which do not necessarily have to be calibrated or can at least be calibrated with little effort. However, coordinate measurement values, which are determined in a conventional manner by a measurement system of the coordinate measuring machine, can 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 impact on accuracy than before. It is therefore not necessary to use a high-precision coordinate measuring machine.

Instead, it is proposed to arrange a sensor arrangement in different defined relative orientations to the reference body and to detect distance values there with the distance sensors. An angular error variable of the reference body is determined on the basis of the measured distance values obtained. This angle error quantity can be stored as a calibration value. Future measured values for determining the guidance error, which are recorded using the reference body, 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 axis positions of the machine axis.

The angular error variable of the reference body preferably relates to an angle that arises when a surface of the reference body facing a measuring sensor of the coordinate measuring machine and/or a plane parallel thereto 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 guidance error determination (in particular torsional error determination) of a machine axis (of a coordinate measuring machine), having:

• - Providing 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 by this machine axis and has at least two distance sensors;
• - Providing the reference body, wherein the reference body has two areas 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 detecting 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 measured distance values with one of the distance sensors at each of the positions;
• - Determination of an angle error variable of the reference body based on 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 the coordinate measuring machine and/or moved by it in the same way as a measuring sensor (e.g. a tactile probe or an optical coordinate measuring sensor). The machine axis can in particular be a horizontal axis and in particular a machine axis usually denoted by X. In principle, however, the method can be applied to any machine axis or reference body provided for this purpose.

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

In the first relative alignment, the distance sensors can each lie directly opposite one of the regions of the reference body. In the case of the second relative alignment, on the other hand, preferably only one of the distance sensors can be opposite one of the areas. These are preferred around the area that this distance sensor was not directly opposite in the first relative alignment. In other words, at least one of the distance sensors can measure a first area, which is preferably opposite this distance sensor, during the first relative alignment. In the case of the second relative orientation, however, the distance sensor can be arranged in such a way that another area is opposite it. In contrast, the further distance sensor that then remains cannot carry out any distance measurements in the second relative alignment and/or cannot be opposite any of the areas.

The machine axes of the coordinate measuring machine can be moved accordingly in order to arrange the sensor arrangement with the first or second relative alignment. As will be explained, this movement is preferably at an angle and in particular orthogonal (i.e. at right angles) to the coordinate axis. For example, this movement can be performed by a generally different machine axis and preferably a different horizontal machine axis of the coordinate measuring machine.

Instead of a relative orientation, one could also speak of a relative setting, 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 quantity 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 measured values obtained in the future when measuring the reference body and in particular total angle values explained below.

Advantageously, the solution presented allows the same structure, i.e. the same reference body and in particular also the same sensor arrangement, to be used for calibrating the reference body and determining the guidance error of the coordinate measuring machine.

A development of the solution presented (i.e. the method and/or the device) provides that during 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, in particular vertically opposite when the reference body is in a horizontal position.

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. However, this preferably only applies to one of the distance sensors, whereas the other distance sensor is not assigned to any of the areas or misses any of the areas.

These variants of the first and second relative alignment enable the required measured distance values to be recorded with 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 in the second relative alignment only one of the distance sensors carries out distance measurements and/or only measures one of the named areas.

According to a development of the solution presented, a total angle value is determined at each of the positions in the first relative alignment using at least some of the measured distance values. In particular, the measured distance values of the sensors can be used when they measure an area opposite them in each of the positions. The total angle value can be an angle 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 be aligned generally parallel to a measuring table surface of the coordinate measuring machine.

Alternatively or additionally, it can be provided that a torsional error quantity 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 measured distance 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 torsional error, reference is made to the list of possible guide error variables above.

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

In particular, it can also be provided in this connection that the angle error quantity of the reference body is determined using a difference between the total angle values and the torsional error quantity. For example, the torsional error quantity, in particular a torsional error difference explained above, can be subtracted from the difference in the total angle values in order in this way to obtain an angular error difference of the angular error in the second position from the angular 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 angle error variable 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 determine a position of, for example, a quill and/or a measuring sensor of the coordinate measuring machine from the axis positions of the machine axes. From this, in turn, the coordinates of a currently measured object can be inferred. 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 above-mentioned advantage 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 method includes:

• - Saving values of the angular error magnitude of the reference body in a calibration file that is associated with the reference body.

This calibration file can be referred to at later stages, particularly during future calibrations of the coordinate measuring machine. It is particularly advantageous that other coordinate measuring devices that are to be calibrated using the same reference body can also use this calibration file. So you don't have to determine the angle error size again yourself.

• - 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 machine, with at least one linear machine axis for moving along a coordinate axis and with at least one sensor arrangement that can be moved by this machine axis and has at least two distance sensors,
and with a control device that 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 measured distance 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 measurement values with at least one of the distance sensors at each of the positions;
• - Determination of an angle error variable of the reference body based on 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 measuring is approached by the sensor arrangement, i.e. the sensor arrangement in the manner described here in several positions, for example a third or fourth position along the coordinate axis and with the first and second relative alignment is positioned. Accordingly, the distance measurement values described here can be determined in a large number of positions and values of the angular error variable of the reference body can be determined on this basis. If this is carried out for a large number of positions along the coordinate axis under consideration, a course of the angular error and/or the angular error magnitude (eg the angular error difference) of the reference body along the coordinate axis can be determined. For example, a value of the angle error size 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 angle size were determined as part 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, the profile of the angular error value described can then be determined, for example, and/or angular error values 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 alignments, can match. Even with a large number of positions, as many of them as possible preferably match. But this is not mandatory. In the event of position deviations, the relevant measured values and/or error sizes can instead be interpolated (i.e. calculated for a common position using measured values and/or error sizes recorded at other positions).

In general, the device can be set up to carry out a method according to any of the aspects described herein. All of the above explanations of and developments of features of the method can also apply to the device features or be provided for them. In general, the device (ie the coordinate measuring machine) can include any other feature in order to carry out all of the method steps outlined 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.

Exemplary embodiments of the invention are explained below with reference to the accompanying schematic figures.

• 1 shows a perspective view of a coordinate measuring machine with a reference body, wherein the coordinate measuring machine corresponds to a device according to an embodiment of the invention and executes 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 in a first relative alignment in a first position ( 2 ) and a second position ( 3 ).
• 4 , 5 show the measurement of the reference body with the sensor arrangement in a second relative alignment in the first ( 4 ) and second ( 5 ) position.

In 1 a coordinate measuring machine 100 is shown, which is an example of a device 10 according to the invention. The coordinate measuring machine 100 is constructed in a conventional manner. It comprises three mutually orthogonal machine axes X, Y, Z, which each define 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). Since 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, paths along which the machine axes denoted by X, Y, Z can execute movements are shown in dashed lines.

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

When moving along the X machine axis, the other machine axes Y, Z are also moved accordingly along this axis or the x coordinate axis running parallel thereto. A sensor arrangement 12 is arranged on the Z machine axis, which is a quill. This includes two distance sensors S0, S1. These are spaced apart by a distance d along the Y machine axis. The sensor arrangement 12 lies opposite a reference body 14 which is elongated along the X-machine axis (or x-coordinate axis). This has two areas B0, B1, which are also correspondingly elongated along the X machine axis. How from the below 2 until 5 As can be seen, these areas B0, B1 are designed as protruding elongated tracks, for example, but this is not mandatory.

In the manner described below, the sensor arrangement 12 with the 1 positioned at a starting position x0 along the x-coordinate axis as shown in the first relative orientation. Then distance values to the areas B0 and B1 are determined with each of the distance sensors S0, S1. Subsequently, the sensor arrangement 12 is 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. Distance measurements are also carried out there with both of the sensors S0, S1. This corresponds to the procedure explained below from the 2 and 3 . Subsequently, in the same positions, taking another second relative orientation from the 4 and 5 again made a distance measurement, 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 14 with an opposite sensor arrangement 12. The cross-sectional plane lies in the yz plane 1 , so that the x-coordinate axis is perpendicular to the sheet plane. Also for the following others 3 until 5 an analogous cross-sectional plane is chosen.

Shown are the regions B0, B1 and, in the first relative alignment, the distance sensors S0, S1 lying opposite them. The arrangement is such that the distance sensors S0, S1 each measure a directly opposite area B0, B1, with the opposite relating to a corresponding orientation along the z-coordinate axis.

It is also shown that the reference body 14 has an angle error β(x0). In this case, x0 designates the shown first observed position along the x-coordinate axis (starting position). The angular error β(x0) describes a tilting of a plane E1 comprising the areas B0, B1 and/or running parallel thereto relative to the horizontal (i.e. to the X-Y plane). The torsional 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 named error xRx(x0) is determined for a horizontal plane analogous to the angle error β(x0) mentioned above.

The distance values a(x0)S0-B0 and a(x0)S1-B1 recorded by the distance sensors S0, S1 in the shown position x0 are also entered.

In the case of the previous calibration of the reference body 14, a high-precision coordinate measuring machine discussed above is completely calibrated in advance. For the detection of the torsional errors of this coordinate measuring machine, a tilt scale is used, which is disadvantageous for the reasons mentioned in the introduction. The torsional errors are then known, for example, at each x-position of the coordinate measuring device and can be stored in a calibration file (CAA file) of this coordinate measuring device. The reference body 14 is then calibrated with this coordinate measuring machine at a later point in time. 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 angular error β of the reference body.

From the representation of 2 it follows that a generally measured total angle γ(xi) at any position xi along the x-coordinate axis corresponds to a sum of the torsional error xRx and the angular error β of the reference body 14: $$g\left(xi\right)=xRx\left(xi\right)+\beta \left(xi\right)$$

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 area distance d. For small angles, the simplified equation applies: $$g\left(x_i\right)=\frac{\left(a\left(x_i\right)\mathrm{<figure-callout\; id="1"\; label="S"\; filenames="DE102020208567B4\_0008.png,DE102020208567B4\_0009.png"\; state="\{\{state\}\}">S</figure-callout>}1-B1\right)-\left(a\left(x_i\right)S0-B0\right)}{\mathrm{i.e}}$$

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

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

However, it is also provided that a second relative orientation between the sensor arrangement 12 and the reference body 14 can also be generated by moving the sensor arrangement 12 with the Y machine axis. This relative orientation is in the 4 and 5 shown. In this case, only one of the distance sensors S0, S1 is opposite one of the areas B0, B1 along the z-coordinate axis or can measure one of the areas B0, B1. The relative arrangement takes place in such a way that the distance sensor S0 then the formerly in the first relative alignment 2 and 3 area B1 not measured by him. Alternatively, it could also be provided that the distance sensor S1 measures the area B0, which is correspondingly not measured during the first relative alignment, or lies opposite it.

At preferably the same positions x0, x1, distance values to the area B1 are then determined with the appropriately selected distance sensor S0 (see a(xO)SO-B1 in 4 and a(x1)SO-B1 5 ). It is also possible to acquire distance values at other x-positions. Then, for common x-positions with the first and second relative alignment, measured distance values can be determined by calculation (eg by interpolation).

A basic idea of measuring with two relative orientations is that both the first relative orientation of the 2 and 3 and the second relative orientation of the 4 and 5 the sensor arrangement 12 or the quill of the coordinate measuring device 100 coupled thereto tilts in the same way when moving between the positions or measurement locations x0, x1. However, since the area B1 is detected with different sensors S0, S1 in the first and second relative alignment, the distance measurement values determined accordingly in total in relation to this area B1 provide information about the extent of the tilting. More precisely, the angular and torsional errors can be determined separately from this effect in the manner described below.

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

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

Finally, taking into account the effect described above, a torsional error difference for small angles can also be determined as a torsional error quantity ΔxRx(x1,x0) according to Equation 4 below: $$\mathrm{\Delta }xRx\left(\mathrm{<figure-callout\; id="1"\; label="x"\; filenames="DE102020208567B4\_0008.png,DE102020208567B4\_0009.png"\; state="\{\{state\}\}">x</figure-callout>}\mathrm{1,}x0\right)=\frac{a{\left(x1\right)}_{S0-\mathrm{<figure-callout\; id="1"\; label="B"\; filenames="DE102020208567B4\_0008.png,DE102020208567B4\_0009.png"\; state="\{\{state\}\}">B</figure-callout>}1}-a{\left(x0\right)}_{S0-\mathrm{<figure-callout\; id="1"\; label="B"\; filenames="DE102020208567B4\_0008.png,DE102020208567B4\_0009.png"\; state="\{\{state\}\}">B</figure-callout>}1}-\left(a{\left(x1\right)}_{\mathrm{<figure-callout\; id="1"\; label="S"\; filenames="DE102020208567B4\_0008.png,DE102020208567B4\_0009.png"\; state="\{\{state\}\}">S</figure-callout>}1-\mathrm{<figure-callout\; id="1"\; label="B"\; filenames="DE102020208567B4\_0008.png,DE102020208567B4\_0009.png"\; state="\{\{state\}\}">B</figure-callout>}1}-a{\left(x0\right)}_{\mathrm{<figure-callout\; id="1"\; label="S"\; filenames="DE102020208567B4\_0008.png,DE102020208567B4\_0009.png"\; state="\{\{state\}\}">S</figure-callout>}1-B1}\right)}{\mathrm{i.e}}$$

Based on the above equation (1), all variables are therefore available to determine the angle error variable of reference body 14 that is actually of interest and, in the example shown, the angle error difference Δβ: $$\mathrm{\Delta }\beta \left(x\mathrm{1,}x0\right)=\mathrm{\Delta }g\left(x\mathrm{1,}x0\right)-\mathrm{\Delta }xRx\left(\mathrm{<figure-callout\; id="1"\; label="x"\; filenames="DE102020208567B4\_0008.png,DE102020208567B4\_0009.png"\; state="\{\{state\}\}">x</figure-callout>}\mathrm{1,}x0\right)$$

Taking into account all of the above variables and in particular Equation 4, it becomes clear that only measured distance values from the distance sensors S0, S1 are required to determine this angular error variable of the reference body 14 and no calibration values of the coordinate tens measuring device 100. It is also understood that the position x1 is chosen arbitrarily and that general position xi and in particular a plurality of different positions x1 . . . xn can also be taken into account. In each of these positions x1...xn, for example, 3 and 5 analog measurements are carried out, whereas the 2 and 4 can define general surveys in a starting position x0. A profile of the angular error β (in particular of Δβ) over all measurement positions x1 .

In the calibration mode of the coordinate measuring machine 100, it can initially assume any starting position that serves as a reference. Then distance measurements at the first relative alignment can be analogous to 2 and 3 be made. Equation (5) can be rearranged according to ΔxRx to determine the torsional error compared to the starting position or reference. The influence of the faulty reference body 14 can be taken into account by the determined course of β and in particular Δβ. The torsional error of the coordinate measuring machine 100 can thus be determined precisely, which improves the calibration quality

In other words, for each calibration of a coordinate measuring machine 100, the reference body 14 can be measured in the two different relative alignments. From this, the angular error quantity β of the reference body 14 and ultimately the torsional error xRx of the coordinate measuring device 100 can be calculated.

In order to reduce the measurement effort, however, it can be assumed that once an angular error quantity β of the reference body 14 has been determined, it remains constant. The determined angle error variable of the reference body 14 can consequently be stored in a (digital) calibration file assigned to the reference body 14 . For calibration processes with further coordinate measuring devices 100 one can fall back on values of the angular error size from this calibration file of the reference body 14 . The reference body 14 therefore does not necessarily have to be measured with these additional coordinate measuring devices 100 in the second relative orientation. However, the measurement of the reference body 14 to determine the magnitude of the angle error is preferably repeated at certain time intervals, for example once a year.

Reference List

10

contraption

12

sensor arrangement

14

reference body

100

coordinate measuring machine

S0, S1

distance sensors

B0, B1

areas

γ(xi)

total angle measured at any position xi along the x-coordinate axis

i.e

range spacing

xRx(xi)

Torsion error (rotation of the machine axis X around the x-axis at location xi)

β(xi)

Angular error of the reference body at position xi

Δβ

angle error size

a(xi)

Measured distance value of a distance sensor S0, S1 at location xi (usually specified for one of the areas B0, B1)

Claims (11)

Method for calibrating a reference body (14), which is a reference body (14) for a guide error determination of a machine axis (X, Y, Z), comprising: - providing a coordinate measuring device (100) that has at least one linear machine axis (X) for moving along has a coordinate axis (x) and at least one sensor arrangement (12) which can be moved by this machine axis (X) and has 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 least one second position (x1) along the coordinate axis (x) and detecting 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 relative orientation to the reference body (14) at a first position (x0) and at at least one second position (x1) and detecting 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 angle error quantity (Δβ) of the reference body (14) using the determined measured distance 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 after 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 after 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 only one of the distance sensors (S0, S1) carries out distance measurements during the second relative alignment. Method according to one of the preceding claims, characterized in that on the basis of at least some 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 measurement 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) about the coordinate axis (x) is determined. procedure after claim 6 and 7 , characterized in that the angular error quantity (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 quantity. Method according to one of the preceding claims, characterized in that no coordinate measurement values and/or calibration values generated by a measuring system of the coordinate measuring machine are used to determine the angle error quantity (Δβ) of the reference body (14). Method according to one of the preceding claims, further characterized by : - storing values of the angular error variable (Δβ) of the reference body (14) in a calibration file which is associated with 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 of this machine axis (X) movable sensor arrangement 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 acquiring distance measurements (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 relative orientation to the reference body (14) at a first position (x0) and at a second position (x1) along the coordinate axis (x) and detecting distance measurement 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 angle error quantity (Δβ) of the reference body (14) using the determined measured distance 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).

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