Method for measuring a workpiece in a machine tool

Abstract

The invention discloses a method for measuring a workpiece in a machine tool. With the method an operator (B) of the machine tool (WM) is supported in measuring a workpiece (WS) and / or a clamping member in the working space (A) of the machine tool by means of a probe (T) such that a model of the working space shown on a screen (B) of a numerical control device (NC) is sufficiently well in agreement with reality. For this, the operator (B) can freely move the probe (T) around the workpiece (WS) and gets an automatically selected touch point (AP) displayed together with quality information. If the quality is sufficient, the operator (B) can trigger the probing process by pressing a button and gets immediate feedback about the progress of the measuring process.

Description

Technical Field

[0001] This invention relates to a method for measuring a workpiece and / or its clamping components in a machine tool. Here, the position of the workpiece's coordinate system relative to the machine tool's coordinate system is determined, thereby enabling program-driven machining of the workpiece to commence. Background Technology

[0002] Alignment between the workpiece's coordinate system and the machine tool's coordinate system is becoming increasingly important in CNC-driven workpiece machining. This alignment is particularly crucial for near-net-shape parts manufactured, for example, through investment casting or additive manufacturing processes, or for near-net-shape parts that have already been machined in other fixtures and / or other machines through previous machining steps. Generally, it is sufficient to know the actual position of the workpiece (according to the NC program's expectations, in the sense of deviation from the ideal position) relative to the machine tool, so that deviations from the ideal position via coordinate system information can be considered during subsequent machining operations using the NC program.

[0003] If, during machining, for example for collision monitoring, a clamping member used to hold the workpiece in the machining space of the machine tool should be considered, then the clamping member must also be considered as part of the workpiece. The geometric model must be applicable to both the workpiece and the clamping member, with its coordinate system aligned with the machine tool's coordinate system. Because for the following considerations, it is not necessary to distinguish between the clamping member and the workpiece (the term "workpiece" hereinafter also includes the clamping member of the workpiece), and it is feasible to apply the method according to the invention for measuring the clamping member (the workpiece not being clamped). It is entirely irrelevant to the operation of this method whether the clamping member, the workpiece to be machined, or both should be measured.

[0004] Modern CNC machines feature a graphical user interface (GUI) that allows users to view the machine tool's virtual workspace. The screen displays, for example, a workpiece on a worktable in a simulation, showing the machine axes (e.g., linear and rotary axes of a 5-axis machine) according to their current state. With the workpiece already clamped, the operator can ensure, by comparing the virtual view with the actual clamping, that the workpiece's position (and, if necessary, its clamping components) in the workspace roughly corresponds to the assumptions of the NC program. Small deviations in each degree of freedom can then be measured and taken into account when processing the NC program using coordinate system information. Typically, the degrees of freedom are accurately known through clamping, i.e., by the flat surface of the workpiece on which it is placed on the machine's worktable. Therefore, the workpiece's position perpendicular to the worktable and its rotation relative to a direction located in the plane of the worktable are accurately defined without needing to be determined by touch.

[0005] Measuring or determining the position of a workpiece is typically achieved by using a detector that touches the workpiece, such as a tool post at the spindle of a machine tool. The detector travels along a movable axis of the machine tool to a predetermined point on the workpiece and records the point of contact. The coordinates of this point, in a Cartesian coordinate system, can be calculated from the machine tool's dynamics, the axis position at the time of contact, and the geometry of the detector.

[0006] Therefore, for example, the position of a workpiece's surface can be determined by touching three points. The movement of the workpiece along this surface remains unknown. The position of the workpiece in all six degrees of freedom can be determined by touching various aligned, curved, or general areas of the workpiece. This can be three linear and mutually perpendicular spatial directions, typically represented by X, Y, and Z, and corresponding rotations A, B, and C around these spatial directions. Different mathematical methods, such as determining the position based on measured points of the subject, can be described, for example, in the article "A Method for Registration of 3D-Shapes" by Paul J. Besl and Neil D. McKay (IEEE Transactions on Pattern Analysis and Machine Intelligence, Vol. 14, No. 2, February 1992).

[0007] DE 102008045678A1 discloses a CNC device for a machine tool, configured to predict and monitor threatening collisions between movable parts of the machine tool. This monitoring is based on the geometric and dynamic descriptions of the machine tool. Clamping members are also introduced to secure the workpiece to the workpiece table, and a description of the clamping members, describing the clamping members actually present in the machining space of the machine tool, is stored in the CNC device, making this description an integral part of the geometric and dynamic descriptions of the machine tool. Furthermore, a contact cycle is stored for each clamping member, which determines the contact point used to determine the position of the clamping member. However, providing such a description of the clamping members, including the contact cycle, is costly and not always reasonable. Generating and storing this data in the CNC device is particularly costly for a single workpiece, relative to workpiece measurement. Moreover, the measurement fails if the contact point cannot be applied within a predetermined contact cycle due to localized damage.

[0008] In addition to the automated measurement of the workpiece position (the model must be suitable for this measurement), US5208763A discloses an interactive module according to which the user first selects the surface to be touched in the model, thereby guiding the probe to the corresponding position of the tool and touching that position. If enough measurement points are obtained in this way, the actual position is determined for all measurement points by minimizing the square of the deviation between the assumed position and the measured position of the workpiece. However, for this, the operator must possess a variety of experiences and knowledge to first select suitable points that can achieve sufficiently accurate determination of the workpiece position for all degrees of freedom after measurement. Summary of the Invention

[0009] Therefore, the object of the present invention is to provide an improved method for measuring the position of a workpiece, which supports the machine tool operator as well as possible when selecting the contact point, requires little or no basic knowledge from the operator, and reduces the cost of measurement compared to the prior art.

[0010] A method for measuring a workpiece in a machine tool is disclosed. This method supports the machine tool operator in measuring the workpiece and / or clamping components in the machine tool's workspace using a probe, ensuring that the workspace model displayed on the CNC device screen closely matches reality. The operator can freely move the probe around the workpiece and obtain automatically selected contact points along with displayed mass information. If the mass is sufficient, the operator can trigger the probing process by pressing a button and immediately receive feedback on the progress of the measurement.

[0011] More precisely, a method for measuring a workpiece in the workspace of a machine tool using a CNC device and a detector is disclosed, the method comprising the following steps: 1. Provide 3D models of the workspace, detector, and workpiece, and display these models on the CNC device screen as virtual workpieces and virtual detectors in a virtual workspace. 2. Position the workpiece in the machine tool's workspace and the virtual workpiece in the virtual workspace, so that the positions of the workpiece in the workspace and the virtual workpiece in the virtual workspace are initially consistent. 3. In contrast to manual workpiece positioning detectors, this method automatically selects the planned contact point and contact direction based on the minimum distance between the virtual detector and the virtual workpiece, and displays the planned contact point and contact direction in the virtual workspace. 4. Determine the mass of the planned contact point and activate the detector when the mass is sufficient, wherein the mass at the contact point is determined, for example, based on the local bending of the workpiece. 5. Trigger detection and determine the coordinates of the touch point when the detector is started. 6. Recalculate the workpiece position using the coordinates of the touch points and update the position of the virtual workpiece in the virtual workspace. 7. Repeat steps 3 to 6 until the position of the virtual workpiece in the virtual workspace finally matches the position of the workpiece in the workspace.

[0012] In step 1, a matching model of the clamping condition must be provided within the machine tool's workspace. This model typically exists for unchanging components of the machine tool, such as the worktable, the machine spindle, and the boundaries of the workspace, and is identical for all machining operations performed using that machine tool. For the workpiece (and its clamping components), this model can be obtained from CAD data or via processed 3D scanning, typically in common formats such as STL or STEP. Therefore, the workpiece is described as a polyhedron composed of face elements (usually triangles) defined by straight lines. The face elements of this polyhedron have face normals, i.e., vertex normals, which approximate the normal direction of the actual body at that point. Vertex normals are typically components of the CAD data; alternatively, they can be approximated as the average direction of adjacent faces.

[0013] The faces of a polyhedron can be described as a polygonal mesh (also called a grid). Therefore, it is also possible to describe faces of arbitrary shapes in this way, enabling efficient calculation of things such as face normals, vertex normals, local curvature of faces, and distances to other bodies. Here, the mesh should (like every real, volume-dependent body) have closed faces, i.e., "water-sealed" faces.

[0014] The detector used must also be modeled. The detector is typically a calibrated switch detector that outputs a signal after contacting the workpiece and the probe ball, resulting in a small (known) deflection, thereby reading the state of all machine axes. The coordinates of the contact point can be calculated based on known machine dynamics and, for example, the detector geometry stored in the tool holder. A measuring detector (capable of outputting the value of its deflection) can also be applied with slightly increased effort. Besides the probe ball, other contact bodies are also feasible, such as disks or cylinders.

[0015] The provided model, along with the relevant components of the machine tool, is displayed as a simulated image on the screen of the CNC device, thus realizing a virtual view of the machine tool's workspace. Therefore, this display is now common on modern controllers and allows for viewing of the machining process, even when the view of the actual machining space is obscured by cooling lubricant, or when the controller is arranged so that the workspace is not visible.

[0016] In step 2, the current position of the workpiece in the workspace (i.e., the center position and alignment of the workpiece axis) must initially align with the position of the virtual workpiece in the virtual workspace to enable meaningful contact in subsequent steps. To this end, the operator can attempt to clamp the workpiece in the workspace as specified in the virtual workspace displayed on the CNC device screen. Alternatively, it is feasible to insert the workpiece into the workspace and then align the virtual workpiece with the actual clamping. Using directional buttons or other input devices, the virtual workpiece can be moved and rotated on the screen to match reality as closely as possible. Two-stage or multi-stage processes using both methods can also achieve the desired result. For spatial positioning, a T-slot is used, for example, on the machine tool table, which provides a rough positioning of the (real or virtual) workpiece. It has been demonstrated that positioning the detector in the workspace at a protruding position relative to the workpiece as an orientation aid is beneficial, and the virtual workpiece is then aligned with the virtual detector accordingly using the controller's directional buttons.

[0017] Initial consistency or accuracy should be achieved, for example, by defining initial consistency and accuracy such that the distance between any point on the workpiece and its virtual corresponding point does not exceed a few centimeters. Empirically, it is also applicable to seek half the size of the smallest element to be measured on the workpiece as the initial consistency, i.e., half the diameter of a hole, which should be touched for measuring the workpiece.

[0018] If the workpiece is touched in a further step of the method, a certain tolerance or expected range is derived, within which the detection result should be recorded. If the detection result is detected too early or not within the tolerance range in a further step of the method, this indicates an excessive deviation between the actual clamping and the virtual image. Subsequently, it can respond with the corresponding error message and initially improve the initial consistency by jumping back to step 2.

[0019] In step 3, the operator positions the detector within the workspace. This can be done using directional buttons, handwheels, or other input devices, with the movement also considered in a virtual workspace and displayed on the controller screen. To reach areas of the workpiece that cannot be directly accessed, the machine's angular axis can be moved, for example, to tilt the workpiece or detector. The ability to maintain a constant distance between the tool (in this case, the detector) and the workpiece is particularly useful here. Collision monitoring is supported even if the workpiece's position has not yet been identified with ideal accuracy. Collisions between the detector and other machine components can still be reliably identified because their positions are always known.

[0020] Finally, the operator moves the detector to an area close to the workpiece, an area meaningful for detection. Here, the controller continuously calculates the touch vector from the detector ball to the workpiece. Thus, the touch direction and the (planned) touch point on the workpiece are predetermined. This calculation is achieved by finding the shortest distance between the grid of the detector ball and the grid of the workpiece (i.e., between the virtual images of the detector ball and the workpiece). For this calculation, a very fast digitization method (bounded volume hierarchy) exists, enabling the calculation and display of the touch vector at small time intervals (e.g., 20 milliseconds). The operator can constantly view the screen to see which touch point is currently being targeted and can adjust the detector's positioning.

[0021] In step 4, the mass of the contact point is continuously calculated, and the contact is only allowed if the condition is met, i.e., the mass is sufficient. Mass must take into account factors such as measurement accuracy, incorrect probe orientation, and tendon errors in modeling. For the contact point, the enclosing face, its adjacent faces, and its point normal and face normal are known.

[0022] For high measurement accuracy, the contact must be made as perpendicular to the workpiece as possible; edges and overly curved surfaces must be avoided. To achieve this, the angle between the surface normal and the contact vector near the contact point can be considered, and this angle should always be less than 30 degrees, preferably less than 20 degrees, or better yet, less than 10 degrees. The expression "near" in this context should be understood, for example, as considering all surface elements located in the region surrounding the contact point, whose diameter corresponds to the diameter of the contact body plus any remaining uncertainty in the alignment of the workpiece. Alternatively, the directly adjacent surface elements of the contacted surface element can also be considered. A large deviation between the surface normal and the contact vector indicates an overly curved surface or even an edge in the workpiece. The local curvature can be approximated by the surface surrounding the contact point and its point normal, and should be significantly larger than the radius of the probe sphere. Contact should not be made in areas of high curvature (and thus small radius of curvature) or complete edges.

[0023] Even small discrepancies between reality and the model can lead to large uncertainties in the calculated coordinates. Therefore, the contact point should be located in the most accurate modeled area of ​​the workpiece possible. Because the mesh linearizes the freeform surface, strong curvature is subject to modeling errors (tendon errors) and is preferably planar. Therefore, contact points should not be allowed in such areas.

[0024] Another criterion for the quality of the contact point is that the virtual probe ball must be located outside the virtual workpiece. If the virtual probe ball cuts through the virtual workpiece, or is completely inside the virtual workpiece, the probe orientation cannot be determined and a suitable contact point does not exist.

[0025] If, for the current position of the detector, the touch vector, consisting of the touch point and the touch direction, is determined to have sufficient mass, a signal is issued to the operator. A good approach is to display the touch vector in red when the mass is insufficient, and in green when the mass is sufficient, thus permitting touch. The display of the touch vector can be altered only when the mass is sufficient, or the touch vector can be crossed out or a warning displayed next to it when the mass is insufficient. Furthermore, for the operator's visual understanding, a hook next to the touch vector serves as an indication that the mass is sufficient and touch is permitted.

[0026] Steps 3 and 4 are performed consecutively, simultaneously, or in parallel within a loop, wherein, based on the result in step 4, the touch vector shown in step 3 can be switched between sufficient and insufficient mass multiple times during detector movement. At this point, the detection process has not yet begun.

[0027] The process ends when the touch is triggered by the operator in step 5. This is conditional upon touch being permitted at that moment. Subsequently, the operator can trigger a probing process along the current touch vector by pressing a button or via other input means. A start button is located on each CNC unit of the machine tool so that the process determined by the context can begin. This start button is also provided under this interrelationship.

[0028] Using touch, the controller can determine the coordinates of the touch point in a conventional manner and make it available for further processing. If the touch point is not within the expected area, or if no touch point is recorded after a certain path, the method terminates with an error message. Therefore, the consistency between the actual clamping and the virtual clamping is not accurate enough, and consequently, the calculation of the quality of the (planned) touch point is no longer reliable. Therefore, the method should be restarted from the beginning or from step 2.

[0029] If a touch is triggered in step 5 and the coordinates of the touch point are successfully determined, the additional information obtained is processed in step 6. For this, the position of the virtual workpiece is recalculated so that the additional positional information is considered using the coordinates of the obtained touch point. A simple example is a touch point on a surface of the workpiece that extends along the Y and Z directions, touching along the X direction: compared to locating the workpiece by visual inspection at the beginning of step 2, the X coordinates of the touch point can now determine the position of the virtual workpiece much more accurately. Using the touch point, the consistency between the virtual clamping and the actual clamping is better than initially. If other points on the surface are probed, and those points move in the Y direction to the first touch point, the rotation of the workpiece around the Z-axis can also be determined. The additional touch points further improve consistency. It is generally recommended to distribute the touch points as much as possible across the entire workpiece to achieve the best possible leverage for rotation.

[0030] In step 6, the operator can also provide additional support information that clearly conveys the progress and quality of the entire process.

[0031] In the virtual workspace, each touch point is persistently displayed. The workpiece should then be placed flush against all virtual touch points. The operator can, for example, identify deviations between the model and reality. The distances from all touch points to the model can be statistically estimated, where the mean squared error provides an indication of quality. Here, the reference point is a deviation of approximately 0.5 mm; this uncertainty allows for very good collision monitoring, for example.

[0032] Using a traffic light analogy, color coding can also indicate whether there is sufficient information to determine the corresponding spatial axis orientation. If, for example, one only probes an object in the X direction, the z component cannot be described. This can be virtualized, for example, by storing axis markers in color with green X and red Z. Then, very simple identification of which direction of contact still leads to improvements in the measurement process.

[0033] The orientation, determined by the clamping condition, should be locked automatically or by the operator and displayed in green or gray in the progress indicator, the latter indicating that the axis orientation is not involved in the measurement process.

[0034] Furthermore, one can visualize changes in the position of a specific workpiece across the entire coordinate system or for each coordinate in a graph. If the positional changes are depicted using the nearest probe point, one can visually detect whether the measurement process has converged. While the first probe point may cause a relatively large change or correction, subsequent probe points should only cause small changes.

[0035] These indicators (closely aligned with the virtual touch point, the spatial orientation of the color indication, and the corrected distribution obtained for each touch point) show the operator, individually or in combination, whether the touching process is complete or further touching at other locations is still required. Automated evaluation of this standard is also feasible, enabling the identification of a final, consistent implementation and termination of the method without operator intervention.

[0036] In the final step 7, it is determined whether the agreed-upon virtual and actual positions of the workpiece are sufficiently accurate, i.e., whether a final agreement has been reached. If so, the method for measuring the workpiece ends; otherwise, it branches back to step 3 and attempts to find another contact point.

[0037] In this regard, it should be reiterated that the term "workpiece" refers to the actual workpiece to be processed and / or the clamping member. Specifically, the description and claims of this method also include the case where the clamping member is measured without a workpiece to be processed.

[0038] It has been demonstrated that the method described herein supports the operator in a very intuitive way by measuring the clamping condition in the machine tool using a probe. Unlike known methods, it is not necessary to program for fixed probe cycles. Anomalies in the workpiece, such as damage or markings, can be easily ignored during probes. Measurement of workpieces of arbitrary shapes can be achieved in a simple manner, provided only a model of the workpiece exists. Through iterative feedback on the information obtained using each contact point, the operator receives good indications about other contact points and gains experience very quickly in this way.

[0039] By moving the detector around the workpiece, the automated steps in the method's background can be very simply and precisely summarized, allowing the machine operator to complete the truly complex process of measuring the workpiece, so that the touch process can be implemented subsequently when touch is permitted via the start button. Feedback on the information obtained can be directly realized.

[0040] This method enables the simple measurement of workpieces with irregular shapes, such as free-form or inclined surfaces (e.g., pyramids). By applying the machine's circular shaft, even hard-to-reach measurement points can be accessed by the operator without additional computational costs. Attached Figure Description

[0041] Other advantages and aspects of the invention will become apparent from the following description of different embodiments according to the accompanying drawings.

[0042] This is shown here: Figure 1 A machine tool with a numerical control device is shown. Figure 2 and Figure 3 The alignment of the virtual workpiece in two directions is shown. Figure 4 and Figure 5 It shows various permitted and prohibited touch points. Figure 6 A flowchart of a method for measuring a workpiece is shown. Detailed Implementation

[0043] Figure 1 A view of the workspace A of machine tool WM is shown. There, the workpiece WS is arranged on the worktable WT. The position of workpiece WS is determined by probe T using a probe ball TK to detect workpiece WS. For this purpose, a numerical control unit NC is provided, which enables viewing of a virtual workspace vA on the screen BS.

[0044] The components of workspace A that are important to operator B are also shown in the virtual workspace vA: a virtual worktable vWT with a virtual workpiece vWS, and a virtual detector vT with a virtual probe ball vTK. The required 3D models are provided in the controller NC according to step 1 above. A start button S is also shown as the central operating element in the method for measuring workpiece WS, which triggers the probing process in step 5.

[0045] exist Figure 2 and Figure 3 The diagram shows the direction buttons RT of the CNC device, which achieve the desired positioning of the virtual workpiece vWS in step 2 of the method. By manipulating the corresponding desired axis directions X, Y, and Z, the virtual workpiece vWS can be moved onto the virtual workpiece stage vWT, making its position consistent with the actual workpiece WS. Figure 2 In the middle, the virtual workpiece vWS moves in the positive X direction, in Figure 3 The virtual workpiece vWS moves in the positive Z direction so that it is initially aligned with the actual workpiece WS.

[0046] Figure 4 and Figure 5 The diagrams shown on screen BS during steps 3 and 4 are illustrated. In the diagrams of the virtual detector vT and the virtual workpiece vWS, the (planned) touch point AP and touch direction AR determined in step 3 are displayed, along with indications of the quality of the touch point or successful initiation of the detection process, such as by means of hook and lightning symbols, crossed or uncrossed arrows, red or green arrows, or any other method. Figure 4 The diagram shows permitted touch points AP on the surface of the virtual workpiece vWS and prohibited touch points AP (which involve the edges of the virtual workpiece vWS). Figure 5 The detector positions shown are both prohibited because the virtual probe ball vTK would be located inside or cut into the virtual workpiece vWS.

[0047] Figure 6 The flow chart of the method described in the general section, which has its basic steps 1-7, is shown: 1. Provide a 3D model of workspace A, detector T and workpiece WS and display the model on the screen BS of the CNC device as a virtual workpiece vWS and a virtual detector vT in the virtual workspace vA.

[0048] 2. Position the workpiece WS in the workspace A of the machine tool WM and position the virtual workpiece vWS in the virtual workspace vA, so that the position of the workpiece WS in the workspace A and the position of the virtual workpiece vWS in the virtual workspace vA have initial consistency.

[0049] 3. Relative to the workpiece WS manual positioning detector T, here, based on the minimum distance of the virtual detector vT relative to the virtual workpiece vWS, the planned touch point AP and touch direction AR are automatically selected, and the planned touch point AP and touch direction AR in the virtual workspace vA are shown.

[0050] 4. Determine the quality of the planned contact point AP and initiate detection when the quality is sufficient, wherein the quality is determined, for example, based on the local curvature of the workpiece WS at the contact point AP.

[0051] 5. Trigger the probe (by operator B) and determine the coordinates of the touch point AP when the probe is initiated. If the trigger is not achieved, and instead of further movement of the probe T, the method branches back to step 3 from here.

[0052] 6. Recalculate the position of the workpiece WS using the coordinates of the touch point AP and update the position of the virtual workpiece vWS in the virtual workspace vA.

[0053] 7. Repeat steps 3 to 6 until the position of the virtual workpiece vWS in the virtual workspace vA finally matches the position of the workpiece WS in workspace A.

[0054] The numerical control (NC) device is configured to operate the method described in steps 1-7, thereby optimally supporting operator B in measuring workpiece WS during their task. In the actual measurement of the workpiece, only steps 3 and 5 require very simple and intuitive interaction from the operator to achieve the desired result.

Claims

1. A method for measuring a workpiece (WS) in the workspace (A) of a machine tool (WM) using a numerically controlled device (NC) with the aid of a detector (T), the method comprising the following steps: 1) Provide 3D models of the workspace (A), the detector (T), and the workpiece (WS), and represent the models as virtual workpiece (vWS) and virtual detector (vT) in a virtual workspace (vA) on the screen (BS) of the numerical control device (NC). 2) Position the workpiece (WS) in the workspace (A) of the machine tool (WM) and the virtual workpiece (vWS) in the virtual workspace (vA), such that the position of the workpiece (WS) in the workspace (A) and the position of the virtual workpiece (vWS) in the virtual workspace (vA) are initially aligned. 3) Manually position the detector (T) relative to the workpiece (WS). Here, the planned touch point (AP) and touch direction (AR) are automatically selected based on the distance of the virtual detector (vT) relative to the virtual workpiece (vWS), and the planned touch point (AP) and touch direction (AR) are displayed in the virtual workspace (vA). 4) Determine the quality of the planned touch point (AP) and allow touch when the quality is sufficient, wherein the quality is determined at least based on the local curvature of the virtual workpiece (vWS) at the planned touch point (AP). 5) Trigger a touch if touch is permitted and determine the coordinates of the touch point (AP). 6) Recalculate the position of the workpiece (WS) using the coordinates of the touch point (AP), and update the position of the virtual workpiece (vWS) in the virtual workspace (vA). 7) Repeat steps 3 to 6 until the position of the virtual workpiece (vWS) in the virtual workspace (vA) finally matches the position of the workpiece (WS) in the workspace (A).

2. The method according to claim 1, wherein, in step 4, in order to determine the mass, the deviation between the contact direction (AR) and the surface normal of the workpiece (WS) near the contact point (AP) is considered, wherein, The deviation is allowed to be up to 30° in order to assess the touch point with sufficient quality.

3. The method according to claim 2, wherein, The allowable deviation is a maximum of 20°.

4. The method according to claim 3, wherein, The allowable deviation is a maximum of 10°.

5. The method according to any one of claims 1 to 4, wherein in step 4, a contact point (AP) on the edge of the workpiece (WS) is excluded from the contact, and the contact point is determined to have insufficient mass.

6. The method according to any one of claims 1 to 4, wherein in step 4, an indication of permission or disallowment is displayed graphically on the screen (BS).

7. The method according to any one of claims 1 to 4, wherein in step 6, information regarding an agreement reached between the position of the virtual workpiece (vWS) and the position of the workpiece (WS) in the method is also displayed on the screen (BS).

8. The method of claim 7, wherein, according to the method, for a plurality of touch points (APs) that have been processed, a process is displayed to show the correction flow of the position of the virtual workpiece (vWS) caused by the corresponding touch point (AP).

9. The method of claim 7, wherein each touch point (AP) is persistently displayed in the virtual workspace (vA).

10. A numerical control (NC) device for a machine tool (WS), the NC device being configured to perform the method according to any one of the preceding claims.

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