METHOD FOR MEASURING A WORKPIECE

Description

[0001] The present invention relates to a method for measuring a workpiece, comprising the following steps: providing a workpiece, wherein the workpiece has a surface with a surface structure; specifying a geometric measurement of the workpiece, wherein the geometric measurement is a diameter of the workpiece and wherein the geometric measurement and a target-actual deviation of the geometric measurement are defined in a reference plane; specifying a measuring path; tactile acquisition of measured values ​​on the workpiece by bringing a measuring probe into contact with the surface of the workpiece and scanning the workpiece in contact with the surface along the specified measuring path; computationally determining the geometric measurement and the target-actual deviation of the geometric measurement from the measured values ​​within the reference plane.

[0002] Workpieces are measured to meet specified quality requirements. The aforementioned procedure serves to determine the deviation between the target and actual diameter of a workpiece. The measured deviation can then be compared to ensure compliance with a specified tolerance.

[0003] When measuring diameter, the surface structure of the workpiece can distort the measurement result. If the surface structure has grooves, scratches, furrows, or similar features, the measuring probe may be guided in the valleys or depressions of these grooves, scratches, furrows, or similar features as it traverses the measuring path, resulting in an inaccurate diameter measurement.

[0004] For example, the surface structure of a circular cylindrical shaft shoulder may, due to prior turning, describe a helical groove that winds around the central axis of the shoulder. During measurement of the outer diameter of this cylindrical shaft shoulder, the probe, with its stylus ball or tip, may run within this groove, so that only the "valley" of the surface structure—that is, only the minimum outer diameter—is measured, not the actual outer diameter. In other words, if one compares such a helical groove of the surface structure, in a highly magnified form, to an external thread, in the worst case only the core diameter of such a thread would be measured, not the nominal diameter, since the probe is guided between the thread flanks during the measurement.

[0005] Document US 2011 / 0184695 A1 describes the measurement of internal diameters using a spiral measuring path.

[0006] Against this background, the invention is based on the technical problem of providing a method that enables a reliable measurement of the diameter of a workpiece whose surface has a surface structure.

[0007] The technical problem described above is solved by a method according to claim 1. Further embodiments of the invention will become apparent from the dependent claims and the description below.

[0008] According to the invention, a method is provided comprising the following steps: providing a workpiece, wherein the workpiece has a surface with a surface structure; specifying a geometric measurement of the workpiece, wherein the geometric measurement is a diameter of the workpiece and wherein the geometric measurement and a target-actual deviation of the geometric measurement are defined in a reference plane; specifying a measuring path; tactile acquisition of measured values ​​on the workpiece by bringing a measuring probe into contact with the surface of the workpiece and scanning the workpiece along the specified measuring path; computationally determining the geometric measurement and the target-actual deviation of the geometric measurement from the measured values ​​within the reference plane. The invention is characterized in that the specified measuring path lies at least partially outside the reference plane.

[0009] Contrary to previously known conventions, the measuring path is therefore deliberately defined, at least in sections, outside the reference plane in which the measured quantity "diameter" is defined. This allows for the acquisition of not only diameter measurements but also measurements of the surface structure, which may distort the measurement. In this way, the influence of the surface structure on the measurement result can be identified and factored out. For example, it can be specified that the measuring path intersects the reference plane at a single point and / or that the measuring path and the reference plane have at most one point in common.

[0010] The measuring probe can be a measuring probe with a stylus ball, whereby the stylus ball is intended to be placed against the workpiece.

[0011] The stylus ball can, for example, have a diameter of 0.1 mm or more. The stylus ball can, for example, have a diameter of 1 mm or more. The stylus ball can, for example, have a diameter of 2 mm or more. The stylus ball can, for example, have a diameter of 10 mm or less. The stylus ball can, for example, have a diameter of 6 mm or less. The stylus ball can, for example, have a diameter of 4 mm or less.

[0012] The stylus ball can, for example, be made of one of the following materials: ruby, silicon nitride, zirconium oxide, ceramic or hard metal.

[0013] The measuring probe can have a rod to which the stylus ball is attached at one end. The rod can be made of, for example, one of the following materials: steel, hard metal, ceramic, composite material (e.g., carbon fiber), aluminum, or titanium.

[0014] The measuring probe can be a scanning measuring probe and / or a switching measuring probe.

[0015] When it is stated that the geometric measurement is a diameter of the workpiece, i.e., when it is stated that a diameter is being measured, this can refer to measuring an outer diameter or an inner diameter of the workpiece.

[0016] Such an outer diameter can be measured, for example, on the outer surface of a circular cylindrical or conical shaft shoulder. An inner diameter can be measured, for example, on the inner surface of a circular cylindrical recess, such as a bore or the like, or a conical recess.

[0017] When the geometric measurement is described as being the diameter of the workpiece, i.e., when the measurement of a diameter is mentioned, this can refer to the measurement of a constant diameter, such as the measurement of a circular cross-section of a cylindrical workpiece section, or the like. Alternatively, the measurement of a diameter can refer to the measurement of a non-constant diameter, such as the measurement of an elliptical cross-section of an elliptical workpiece section, or the like. It is understood that the measurement of a diameter in this context can also include the measurement of a radius, and vice versa.

[0018] The reference plane can be a plane that is oriented orthogonally to an axis of symmetry of a workpiece section, i.e., it forms a 90-degree angle with the axis of symmetry at which the diameter is measured. For example, the reference plane can be oriented orthogonally to a central axis of a circular cylindrical section of a workpiece with respect to which the circular cylindrical section is rotationally symmetric. Similarly, the reference plane can be oriented orthogonally to a central axis of an elliptical section of a workpiece with respect to which the elliptical section of the workpiece is rotationally symmetric.

[0019] The reference plane can be a plane that is not orthogonal to an axis of symmetry of a workpiece section, i.e., it forms an angle other than 90 degrees with the axis of symmetry.

[0020] The reference plane can be a planar plane. For example, such a planar plane can be oriented parallel to a coordinate plane of a Cartesian coordinate system of a measuring machine with which the procedure in question is carried out. Alternatively, such a planar plane can be oriented at a distance from a coordinate plane of a Cartesian coordinate system of a measuring machine with which the procedure in question is carried out.

[0021] The workpiece surface features grooves. The terms grooves, furrows, and ridges are used synonymously here. The grooves may have a width greater than 10 µm and less than 500 µm. They may have a width greater than 10 µm and less than 100 µm. They may have a width greater than 10 µm and less than 100 µm. They may have a width greater than 10 µm and less than 50 µm. They may have a depth greater than 3 µm and less than 50 µm. They may have a depth greater than 3 µm and less than 20 µm. It may be provided that the grooves have a depth of more than 5 µm and less than 15 µm, in particular a depth of 10 µm or less.

[0022] The grooves are at least partially helical. In particular, the grooves can be completely helical. The grooves exhibit an inclination and a direction of rotation with respect to the reference plane.

[0023] According to the invention, the inclination and / or direction of rotation of the grooves are determined based on manufacturing parameters of a workpiece machining operation that preceded the workpiece preparation. For example, these parameters may be from a previous turning operation, such as the workpiece rotational speed, cutting speed, depth of cut, and feed rate. For example, the turning operation may have been performed as external longitudinal turning with a turning tool.

[0024] Alternatively or additionally, the inclination and / or the direction of rotation or orientation of the grooves are detected according to the invention before and / or during the tactile measurement.

[0025] The terms orientation, direction of rotation and sense of rotation are used synonymously here.

[0026] It may be provided that the measuring path is specified or defined taking into account the inclination and / or the direction of rotation of the grooves.

[0027] The measuring path crosses the grooves and exhibits, at least in sections, an inclination and / or direction of rotation that differs from the grooves. The measuring path can therefore be deliberately run perpendicular and / or in the opposite direction to the inclination and / or direction of rotation of the grooves in order to measure a profile of the grooves. In particular, the width and / or depth of grooves in the surface structure can be measured along the measuring path.

[0028] The measuring path is at least partially helical. In particular, it may be provided that the measuring path is entirely helical. For example, the measuring path may be at least partially or entirely helical, e.g., when measuring a diameter on a circular cylindrical workpiece section.

[0029] In particular, the measuring path may be designed to be at least partially spiral. It may also be designed to be entirely spiral. For example, the measuring path may be designed at least partially or entirely as a conical spiral, for instance, when a diameter is measured on a conical section of the workpiece.

[0030] To improve the measurement result, it can be provided that two or more measuring paths are scanned during tactile measurement and that the measuring paths differ with respect to one or more of the following parameters: starting point of the measuring path, end point of the measuring path, length of the measuring path, direction of rotation or orientation of the measuring path, inclination of the measuring path. In this way, a surface profile or surface structure can be reliably recorded.

[0031] Measuring with two or more measuring paths can be used to tactilely detect the inclination and / or direction of rotation of the grooves. In particular, measuring with two or more measuring paths can serve as a preparatory measurement for a series of subsequent measurements, in order to define a single measuring path that intersects the grooves for these subsequent measurements. Thus, for a series of components, the inclination and / or direction of rotation of the grooves can first be determined on one component using two or more measuring paths, in order to then perform the measurement of all subsequent components more quickly using a derived single measuring path.

[0032] In particular, the slope and / or the direction of rotation of the grooves can be automatically detected.

[0033] It can be provided that a first measuring path and a second measuring path are defined, wherein a starting point of the first measuring path and a starting point of the second measuring path lie in a common starting plane, wherein the starting plane is oriented particularly parallel to the reference plane, and / or wherein an endpoint of the first measuring path and an endpoint of the second measuring path lie in a common end plane, wherein the end plane is oriented particularly parallel to the reference plane, and / or the first measuring path and the second measuring path have an angular offset from each other. This approach also enables improved acquisition of the surface structure or a surface profile in order to determine the influence of the surface structure on the diameter measurement result.

[0034] It may be stipulated that the acquired measurements are projected onto the reference plane. In this way, for example, when measuring an outer diameter, a circumscribed circle (or maximum measured outer diameter) and a confined circle (or minimum measured outer diameter) are obtained within the reference plane. Alternatively or additionally, to determine a measured actual diameter, it may be specified that a best-fit diameter is determined from the measured values ​​using least squares (LSD) and defined as the measured actual diameter.

[0035] The workpiece can be rotated around a longitudinal axis during measurement. The measuring probe can be moved radially towards the workpiece. For example, a longitudinal axis of the workpiece, which could be a previously described axis of symmetry, can be oriented collinearly with a rotational axis around which the workpiece rotates during measurement. Such a rotational axis could be, for example, the spindle axis of a rotary table of a measuring machine, with the workpiece clamped to the rotary table. Therefore, it can be provided that the workpiece is rotated around its own axis during measurement, i.e., while traversing the measuring path.

[0036] It can be provided that the measuring probe is freely movable in any spatial direction during the tactile acquisition of measured values ​​on the workpiece and is not locked in any spatial direction. Any distortion of a diameter measurement caused by the surface structure of the workpiece is therefore not compensated for in this case by locking the measuring probe in one or more coordinate directions, but rather by deliberately defining the measuring path outside the reference plane of the diameter to be measured, or at least partially outside the reference plane of the diameter to be measured.

[0037] The invention is described in more detail below with reference to an exemplary embodiment shown in a drawing. The drawing schematically depicts: FIG. 1A A workpiece to be measured in a front view along its longitudinal axis; FIG. 1B The workpiece made of Fig. 1A in a longitudinal section IB-IB according to Fig. 1A ; FIG. 1C An enlarged view of a measuring situation; Fig. 2A The workpiece made of Fig. 1B with a measuring path according to the invention; Fig. 2B the workpiece made of Fig. 1A with a measuring path according to the invention; Fig. 3A a workpiece to be measured in a longitudinal section with three measuring paths according to the invention; Fig. 3B the workpiece made of Fig. 1A in a front view along its longitudinal axis; Fig. 3C measured values ​​of the measuring paths projected onto the reference plane; Fig. 4 a flowchart of the method according to the invention.

[0038] First, with reference to the Figuren 1A, 1B und 1C explains the problem underlying the invention.

[0039] In Figur 1A A workpiece 2 is shown. The workpiece 2 is a hollow cylinder 2 with a circular cylindrical outer surface 4 and with a circular cylindrical inner surface 6, which defines a through-opening 8.

[0040] The diameter of the inner surface 6 is to be measured using a measuring probe 10. Line 12 represents, in a highly schematic and exaggerated representation, the actual diameter of the inner surface 6 to be measured. Circle 14 represents the specified target diameter 14 of the inner surface 6, which should be achieved during the manufacturing of the through-hole 8.

[0041] Such a diameter is usually measured within a predefined reference plane M1, which is shown in the sectional view according to Fig. 1B The reference plane M1 is parallel to the coordinate plane yz. Therefore, the x-value according to the Cartesian coordinate system x, y, z is the same for every point in the plane M.

[0042] In other words, the measuring probe 10 should be held in a constant position in the x-direction throughout the entire diameter measurement, so that the measuring probe 10 remains within the reference plane M1 throughout the entire diameter measurement, or rather, records only measured values ​​within the reference plane M. Typically, in such a measurement task, the workpiece 2 is rotated about its longitudinal axis A, which is collinear with the x-axis, so that the measuring probe 10 experiences and records only deflections in the y-direction.

[0043] Depending on how the through-opening 8 was manufactured on the workpiece 2, the workpiece 2 has a surface structure 16 in the area of ​​the inner surface 6, which is shown here in Fig. 1B is represented by the grooves 18 which run inclined to the yz-plane.

[0044] These grooves 18 of the surface structure 16 may, for example, have been created by internal turning of the through-hole 8 using a turning tool. The grooves 18, which can also be referred to here as turning grooves 18, are essentially helically wound around the x-axis and can lead to unintended guidance and a consequent deflection of the measuring probe in the x-direction during measurement, as shown in Fig. 1B hinted at.

[0045] This guidance and deflection of the measuring probe 10 from the reference plane M1 can occur because the measuring probe 10 is guided within the grooves 18 during the measurement as a result of the rotation of the workpiece 2 around the axis A and is moved through the grooves in the positive or negative x-direction, depending on the direction of rotation of the workpiece 2, in the manner of a worm or ball screw drive.

[0046] The challenge here is not initially the displacement of the measuring probe in the x-direction, which can easily be eliminated from the measurement result computationally, but rather the fact that the measuring probe 10 runs exclusively in the valleys 20 of the grooves 18 during the measurement and does not scan the peaks 22 of the grooves 18, as shown in Fig. 1C illustrated.

[0047] Thus, the measuring probe 10 only detects the maximum inner diameter I-max of the through-hole 8, but not the minimum diameter I-min of the through-hole 8. Because the measuring probe 10 is guided through the essentially helical surface structure 18, the measurement result is therefore distorted. Consequently, the measurement yields an actual value that is too large for the measured inner diameter of the through-hole 8. If an outer diameter were being measured, such guidance of the measuring probe in the grooves would result in an actual value that is too small for the measured outer diameter.

[0048] For workpiece 2, this problem is solved according to the invention by specifying or defining a measuring path 100 which lies at least partially outside the reference plane M1 within which the diameter to be measured lies ( Fig. 2A, Fig. 2B ).

[0049] The predefined measuring path 100 starts at a starting point in a starting plane S1, which has a distance from the reference plane M1. The predefined measuring path 100 ends at an endpoint in an end plane E1, which has a distance from the reference plane M1 ( Fig. 2A, Fig. 2B The measuring path 100 intersects the reference plane M1 at a single point. The starting point is marked by a circle, the point of intersection by a square, and the endpoint by a triangle.

[0050] The reference plane M1, the starting plane S1, and the ending plane E1 are oriented parallel to the yz coordinate plane. The starting plane S1 lies at height x1 in the x-direction, the reference plane M at height x2, and the ending plane E1 at height x3, where x1 < x2 < x3.

[0051] The essentially helical grooves 18 have a negative direction of rotation with respect to the x-axis, while the measuring path 100 has a positive direction of rotation in the opposite direction. In other words, the helical grooves 18 are clockwise while the measuring path 100 is counterclockwise.

[0052] The measuring path 100 therefore crosses the grooves 18 during the measurement, so that the measuring probe 10 traverses both the valleys 20 of the grooves 18 and scans the peaks 22 of the grooves 18 in the x-direction. Thus, the profile of the grooves 18 can be captured along the measuring path 100 during the diameter measurement.

[0053] Therefore, a first method according to the invention is described, comprising the process steps ( Fig. 4 ): (A) Providing a workpiece 2, wherein the workpiece 2 has a surface 6 with a surface structure 16, wherein the surface structure 16 of the workpiece 2 has grooves 18, the grooves 18 are helical and the grooves 18 have an inclination and a direction of rotation with respect to the reference plane M1; (B) Specifying a geometric measurement of the workpiece 2, wherein the geometric measurement is a diameter of the workpiece 2 and wherein the geometric measurement and a target-actual deviation of the geometric measurement are defined in a reference plane M1; (C) Specifying a measuring path 100, wherein the specified measuring path 100 lies at least partially outside the reference plane M1, the measuring path 100 crosses the grooves 18 and has a direction of rotation different from that of the grooves 18 and the measuring path 100 is helical;(D) Tactile acquisition of measured values ​​on the workpiece, in which a measuring probe 10 is brought into contact with the surface 6 of the workpiece 2 and the measuring probe 10 scans the workpiece 2 in contact with the surface 6 along the predetermined measuring path 100; (E) Computational determination of the geometric measured quantity and the target-actual deviation of the geometric measured quantity from the measured values ​​within the reference plane M1, wherein the acquired measured values ​​are projected onto the reference plane.

[0054] The following describes a further elaboration of the procedure with reference to the Figuren 3A, 3B , 3C described, whereby only the differences to the embodiment described above are discussed and essentially identical features are assigned the same reference numerals.

[0055] Figur 3A shows a workpiece 2, which differs from the example described above in that it has a surface structure 16 grooves 18, which corresponds to the previously described example. Figuren 1 and 2 The described grooves 18 run in opposite directions.

[0056] For better clarity, only two grooves 18 in Figur 3A As shown. In order to better capture the profile of the surface structure 16, not only one, but three measurement paths are specified for the method variant described here. Therefore, a first measurement path 200, a second measurement path 300, and a third measurement path 400 are defined.

[0057] The starting points of the respective measurement paths 200, 300, and 400 all lie in the same starting plane S1 and are each marked by circles. The endpoints of the respective measurement paths 200, 300, and 400 are marked by triangles and all lie in the same end plane E1. Each of the measurement paths 200, 300, and 400 intersects the reference plane M1 at only one point.

[0058] Each of the measuring paths 200, 300, 400 has a direction of rotation that differs from or is opposite to that of the grooves 18, is essentially helical and crosses the grooves 18.

[0059] The measuring paths 200, 300, and 400 differ from each other in that their starting points within the starting plane S1 each have an angular offset from one another. Similarly, the endpoints of the respective measuring paths 200, 300, and 400 also each have an angular offset from one another in the end plane E2. These nested measuring spirals 200, 300, and 400 allow different areas of the surface structure 16 to be captured and taken into account in the calculation of the diameter.

[0060] The results of the measurements are, in particular, profile drawings of the grooves 18 (not shown), which can be superimposed to determine the groove profile, the inclination and the direction of rotation of the grooves.

[0061] In the representation according to Figur 3B The measuring paths are shown radially indented at a distance from each other. However, this is only done to clarify the respective starting and ending points of measuring paths 200, 300, 400 in the top view, whereby it is clear that each of the measuring paths 200, 300, 400 has the same diameter as its geometric measurement.

[0062] In Figur 3CThe measurement points projected onto the reference plane from the measurements corresponding to measuring paths 200, 300, and 400 are shown. From this, a circumscribed circle or a maximum measured diameter I-max and a confined circle or a minimum measured diameter I-min can be determined. As a measurement result, a best-fit diameter can be determined from the measured values ​​using least squares and defined as the measured actual diameter. This measured actual diameter can then be compared with the specified target diameter to check whether a specified tolerance for the through-hole 8 has been maintained.

[0063] Therefore, a second method according to the invention is specified, comprising the following process steps: (A) Providing a workpiece 2, wherein the workpiece 2 has a surface 6 with a surface structure 16, wherein the surface structure 16 of the workpiece 2 has grooves 18, the grooves 18 being at least helical and the grooves 18 having an inclination and a direction of rotation with respect to the reference plane M1; (B) Specifying a geometric measurement of the workpiece 2, wherein the geometric measurement is a diameter of the workpiece 2 and wherein the geometric measurement and a target-actual deviation of the geometric measurement in a reference plane M1 are defined;(C) Specifying three measuring paths 200, 300, 400, wherein the specified measuring paths 200, 300, 400 lie at least partially outside the reference plane M1, the measuring paths 200, 300, 400 cross the grooves 18 and have a direction of rotation different from the grooves 18, and the measuring paths 200, 300, 400 are helical, wherein the starting points of the measuring paths 200, 300, 400 lie in a common starting plane S1, wherein the starting plane S1 is oriented parallel to the reference plane M1, wherein the end points of the measuring paths 200, 300, 400 lie in a common end plane E1, wherein the end plane E1 is oriented in particular parallel to the reference plane M1, and the measuring paths 200, 300, 400 have an angular offset from each other; (D) Tactile acquisition of measured values ​​on the workpiece. 2, in which a measuring probe 10 is brought into contact with the surface 6 of the workpiece 2 and the measuring probe 10 scans the workpiece 2 in contact with the surface 6 along the specified measuring paths 200, 300, 400;(E) Calculating the geometric measurement and the target-actual deviation of the geometric measurement from the measured values ​​within the reference plane M1, whereby the acquired measured values ​​are projected onto the reference plane M1.

[0064] Measuring with three measuring paths 200, 300, 400 can be used to tactually determine the inclination and / or direction of rotation of the grooves 18. In particular, measuring with these three paths can serve as a preparatory measurement for a series of subsequent measurements, in order to define a single measuring path that intersects the grooves 18. This single measuring path can be one of the measuring paths 200, 300, 400 or a different, additional measuring path that intersects the grooves 18 (not shown). Thus, for a series of components, the inclination and / or direction of rotation of the grooves 18 can first be determined on one component using three measuring paths, in order to then perform the measurements of all subsequent components more efficiently using a derived, single measuring path. The individual measuring path can have a different inclination and / or orientation and / or starting plane and / or ending plane than measuring paths 200, 300, 400. Reference sign

[0065] 2Workpiece / Hollow cylinder 4Outer surface 6Inner surface 8Through opening 10Measuring probe 12Actual diameter 14Target diameter 16Surface structure 18Grooves 20Valley 22Tip 100Measuring path 200Measuring path 300Measuring path 400Measuring path M1Reference plane S1Start plane E1End plane I-max diameter I-min diameter (A)Process step (B)Process step (C)Process step (D)Process step (E)Process step

Claims

1. Method for measuring a workpiece, comprising the method steps of: - providing a workpiece (2), wherein the workpiece (2) has a surface (6) with a surface structure (16); - predefining a geometric measured variable of the workpiece (2), - wherein the geometric measured variable is a diameter of the workpiece (2) and - wherein the geometric measured variable and a nominal-actual deviation of the geometric measured variable are defined in a reference plane (M1); - predefining a measuring path (100, 200, 300, 400); - tactile sensing of measured values on the workpiece (2), - by bringing a measuring probe (10) into contact with the surface (6) of the workpiece (2) and - the measuring probe (10) scans the workpiece (2) in contact with the surface (6) along the predetermined measuring path (100, 200, 300, 400); - computational determination of the geometric measured variable and the nominal-actual deviation of the geometric measured variable from the measured values within the reference plane (M1); - wherein the predefined measuring path (100, 200, 300, 400) lies at least partially outside the reference plane (M1) and - wherein the measuring path (100, 200, 300, 400) is helical at least in sections, characterized in that the surface structure (16) of the workpiece comprises grooves (18), the grooves (18) are helical at least in sections, the grooves (18) have an inclination and a direction of rotation with respect to the reference plane (M1) and the measuring path (100, 200, 300, 400) crosses the grooves (18) and, at least in sections, has an inclination and / or direction of rotation which deviates from the inclination and / or direction of rotation of the grooves (18), the inclination and / or the direction of rotation of the grooves (18) are determined on the basis of manufacturing parameters of a workpiece machining operation which has preceded the provision of the workpiece, and / or that the inclination and / or direction of rotation of the grooves (18) is detected before and / or during tactile measurement.

2. Method according to one of the preceding claims, characterized - in that two or more measuring paths (200, 300, 400) are scanned during tactile measurement, and - in that these measuring paths (200, 300, 400) differ with respect to one or more of the following parameters: starting point of the measuring path, end point of the measuring path, length of the measuring path, direction of rotation of the measuring path, inclination of the measuring path.

3. Method according to claim 7, characterized - in that a first measuring path (200, 300, 400) and a second measuring path (200, 300, 400) are predefined, - wherein a starting point of the first measuring path (200, 300, 400) and a starting point of the second measuring path (200, 300, 400) lie in a common starting plane, wherein the starting plane is oriented in particular parallel to the reference plane, and / or - wherein an end point of the first measuring path (200, 300, 400) and an end point of the second measuring path lie in a common end plane, wherein the end plane is oriented in particular parallel to the reference plane, and / or - the first measuring path (200, 300, 400) and the second measuring path (200, 300, 400) have an angular offset relative to one another.

4. Method according to one of the preceding claims, characterized - in that the acquired measured values are projected onto the reference plane (M1).

5. Method according to one of the preceding claims, characterized - in that the workpiece (2) rotates about a longitudinal workpiece axis (A) during measurement and / or - wherein the measuring probe (10) is freely movable in any spatial direction during the tactile sensing of measured values on the workpiece and is not blocked in any spatial direction.