Method for measuring workpieces in machine tools

Abstract

To provide a method for measuring a position of workpiece which satisfactorily assists selection of a point to be probed as much as possible by requiring no or little special preliminary knowledge for an operator of a machine tool, and reduces labor necessary for measurement compared to a prior art.SOLUTION: There is provided a method for measuring workpiece in a machine tool. In the method, an operator (B) of a machine tool (WM) assists to measure workpiece (WS) and / or clamp means in a work area (A) of a machine tool by a probe (T) so that a model of the work area displayed on a screen (BS) of a numerical control device (NC) sufficiently coincides with reality. Therefore, the operator (B) can freely move the probe (T) around the workpiece (WS), and an automatically selected probe point (AP) is displayed together with quality information. If the quality is sufficient, the operator (B) can start a probing step by pressing a key, and progress of a measurement step is quickly fed back.SELECTED DRAWING: Figure 1

Description

[[TECHNICAL FIELD]]

[0001] The present invention relates to a method for measuring a workpiece and / or clamping means thereof in a machine tool, wherein the position of the coordinate system of the workpiece relative to the coordinate system of the machine tool is determined, so that program-controlled machining of the workpiece can be started. [[BACKGROUND ART]]

[0002] In CNC-controlled workpiece machining, position alignment between the coordinate system of the workpiece and the coordinate system of the machine tool is becoming increasingly important. Detection of position alignment is particularly important especially for raw materials close to the final shape, which are for example manufactured by precision casting or additive processes, or machined in another clamping device from previous processing steps and / or machined on other machines. In this case, it is usually sufficient to know the actual position of the workpiece relative to the machine tool (in the sense of deviation from the ideal position according to the expected values in the NC program), and the deviation from the ideal position can be taken into account by coordinate transformation during machining by the NC program in subsequent processing.

[0003] If clamping means that function to fix a workpiece in the machining area of a machine tool are to be considered, for example for collision monitoring during a machining process, the clamping means also need to be detected in the same way as the workpiece. Geometric models of both the workpiece and the clamping means are required, and their coordinate systems need to be positionally aligned relative to the coordinate system of the machine tool. In the following discussion, it is not necessary to distinguish between clamping means and a workpiece, therefore, in the following description, clamping means for a workpiece are also included in the term "workpiece", and the method according to the present invention can also be used for measuring clamping means (not including a clamped workpiece). In the flow of the method, it does not matter whether the clamping means, the workpiece to be machined, or both are measured together.

[0004] Currently, the latest numerical control systems have a graphical user interface (GUI) that allows users to view the virtual work area of ​​the machine tool. On the screen, for example, a workpiece is simulated and displayed on a table, and the machine axes (e.g., linear and rotary axes of a 5-axis machine) are displayed according to their current state. When clamping a workpiece, the operator can compare the virtual display with the actual clamping to make the position of the workpiece (and sometimes its clamping means) in the work area nearly match the assumptions of the NC program. Small deviations in individual degrees of freedom can then be measured and taken into account by coordinate transformations during NC program operation. In many cases, the degrees of freedom are already precisely known by the clamping, for example, by the flat surface of the workpiece on which it is placed on the machine table. The position of the workpiece is perpendicular to the table and precisely defined in terms of rotation around a direction on the table plane, and does not need to be determined by probing.

[0005] The position of a workpiece is typically measured or confirmed by probing it with a replaceable probe, for example, attached to a tool holder mounted on the axis of a machine tool. The probe is moved to a predetermined point on the workpiece by the machine tool's moving axis, and the probe point is registered. Here, the coordinates of the probe point in the Cartesian coordinate system can be calculated from the machine tool's motion, the axis position at the moment of probing, and the shape of the probe.

[0006] For example, the position of a workpiece's surface can be determined by probing three points. The displacement of the workpiece along this surface is not yet known. The position of the workpiece can be determined in all six degrees of freedom by probing various oriented and curved surfaces of the workpiece, or general areas. These can be thought of as three linear and mutually perpendicular spatial directions, often denoted as X, Y, and Z, and their respective rotations A, B, and C around these spatial directions. Various mathematical methods for determining the position based on measurement points on the body are described, for example, in the paper "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] DE102008045678A1 discloses a numerical control device (NPC) for a machine tool, configured to predictively monitor whether collisions are imminent between machine tool components that are movable relative to each other. This monitoring is based on a geometric and motion description of the machine tool. The NPC stores descriptions of clamping means, and the monitoring also includes clamping means for securing workpieces on the worktable, by describing the clamping means that are actually present in the machining area of ​​the machine tool so as to be components of the geometric and motion descriptions of the machine tool. Furthermore, for each clamping means, a probe cycle is stored that sets probe points to confirm the position of the clamping means. However, preparing descriptions of clamping means that include such probe cycles requires a certain amount of effort and is not justified in all cases. Regarding workpiece measurement, it is very laborious to generate such data for each individual workpiece and provide it to the NPC. Furthermore, if localized damage makes it impossible to use the probe points in the configured probe cycle, the measurement will fail.

[0008] U.S. Patent No. 5,208,763 discloses not only automatic measurement of the workpiece's position where the model is supposed to exist, but also a bidirectional mode in which the user selects the surface to probe first on the model and then moves the probe to the corresponding point on the tool. Once a sufficient number of measurement points are identified in this way, the actual position of all measurement points is determined by minimizing the square of the deviation between the assumed position of the workpiece and the measured position. However, this requires considerable experience and knowledge from the operator to initially select appropriate points that will allow the workpiece's position to be determined sufficiently accurately for all degrees of freedom after measurement. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] DE102008045678A1 [Patent Document 2] U.S. Patent No. 5208763 [Non-patent literature]

[0010] [Non-Patent Document 1] "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) [Overview of the Initiative] [Problems that the invention aims to solve]

[0011] Therefore, the object of the present invention is to provide an improved method for measuring the position of a workpiece that assists the operator of a machine tool as well as possible in selecting the point to be probed, requires the operator to have little or no special prior knowledge, and reduces the effort required for measurement compared to the prior art. [Means for solving the problem]

[0012] This problem is solved by the method described in claim 1. Advantageous details of this method also arise from claims dependent on claim 1. A method for measuring a workpiece in a machine tool is disclosed. In this method, the machine tool operator assists in measuring the workpiece and / or clamping means in the machine tool's work area using a probe, so that the model of the work area displayed on the screen of the numerical control device closely matches reality. For this purpose, the operator can move the probe freely around the workpiece, and automatically selected probe points are displayed along with quality information. If the quality is sufficient, the operator can start the probing process by pressing a key, and the progress of the measurement process is immediately fed back.

[0013] More specifically, a method for measuring a workpiece using a probe in the working area of ​​a machine tool equipped with a numerical control device, 1: Providing 3D models of the work area, probe, and workpiece, and displaying these models on the screen of the numerical control device as a virtual workpiece and virtual probe in a virtual work area; 2: A step of positioning the workpiece in the work area of ​​the machine tool and the virtual workpiece in the virtual work area so that the position of the workpiece in the work area and the position of the virtual workpiece in the virtual work area initially coincide, 3: The steps include manually positioning the probe relative to the workpiece, automatically selecting a planned probe point and probe direction based on the minimum distance of the virtual probe to the virtual workpiece, and displaying the planned probe point and probe direction in the virtual work area, 4: Determine the quality of the planned probe points, and if the quality is sufficient, approve the probing. The quality is determined, for example, based on the local curvature of the workpiece at the probe points. 5. If probing is approved, the steps include starting the probing and determining the coordinates of the probe point, 6: The steps include recalculating the workpiece position based on the probe point coordinates and updating the virtual workpiece position in the virtual work area, A method is disclosed that includes step 7: repeating steps 3 to 6 until the position of a virtual workpiece in a virtual work area finally coincides with the position of a workpiece in a work area.

[0014] Step 1 requires providing an appropriate model of the clamping situation within the machine tool's work area. Models of immutable components of the machine tool, such as the table, tool axis, and work area boundary, are usually provided, and this is consistent for all machining operations performed by the machine tool. For the workpiece (and its clamping means), such models are often obtained from CAD data or by machining a 3D scan and provided in common formats such as STL or STEP. This means the workpiece is described as a polyhedron, composed of linearly limited face elements (usually triangles). Face elements of a polyhedron have face normals, and vertices have vertex normals, which approximate the normal direction of the entity at this point. Vertex normals are usually components of the CAD data, but can alternatively be approximated as the average direction of adjacent faces.

[0015] The surface of a polyhedron can be described as a polygon mesh (also called a mesh). In this way, an arbitrarily shaped surface of an object can be described in a way that allows for the efficient calculation of matters such as face normals, vertex normals, local curvature of the surface, and distances to other objects. At this time, the mesh must be a closed surface, or "watertight," just like a real-world volume.

[0016] Furthermore, the model of the probe to be used must also be provided. The probe is typically a calibrated switching probe that, after probing the workpiece, emits a signal from a small (known) displacement of the probe sphere, followed by the reading of the positions of all machine axes. From this, the coordinates of the probe point can be calculated based on the known machine motion state and, for example, the probe shape stored in the tool table. It is also possible to output the displacement amount using a measuring probe, with a slight increase in computational load. Other probe bodies, such as disks or cylinders, can be used instead of the probe sphere.

[0017] The provided model, along with the relevant components of the machine tool, is displayed as a simulation graphic on the numerical control unit's screen, allowing a virtual view of the machine tool's work area. Such displays are common in modern control units, as they allow for visualization of the machining process even when, for example, the view of the actual machining area is obstructed by cooling lubricant or the control unit is positioned in a way that prevents viewing the machining area.

[0018] In Step 2, the position of the workpiece in the work area (e.g., center position and workpiece axis orientation) needs to initially match the position of the virtual workpiece in the virtual work area to a degree that it can be usefully probed in further ways. To this end, the operator can, on the one hand, attempt to clamp the workpiece in the work area as set in the virtual work area displayed on the numerical control device screen. Conversely, it is also possible to insert the workpiece into the work area and match the virtual workpiece to the actual clamp. The virtual workpiece can be moved and rotated on the screen to match the reality as closely as possible using directional keys or other input devices. It is also possible to guide the target in a two-stage or multi-stage process using both methods. For spatial orientation, for example, a T-slot on the machine tool table can be used to roughly position the workpiece in reality or virtually. Tests have demonstrated that positioning the work area probe opposite a prominent location on the workpiece as an orientation aid and adjusting the virtual workpiece to the virtual probe using the control device's directional keys is effective.

[0019] For example, an initial match or accuracy should be achieved such that no point on the workpiece is defined as being more than a few centimeters away from a virtual corresponding part. As a rough guideline, an initial match should be achieved that is half the dimension of the smallest element of the workpiece being measured, for example, half the diameter of the hole probed for workpiece measurement.

[0020] When probing is performed in the process of working on a workpiece, a probe event should be registered within a certain allowable range or expected range. If, in the subsequent process of the method, a probe event occurs too early or is not recognized within the allowable range, this indicates that there is a large deviation between the actual clamp and its virtual image. Thereafter, the situation can be addressed with a corresponding error message, and the initial alignment can be further improved in the sense of returning to step 2.

[0021] In step 3, the operator positions the probe in the work area. For this purpose, the probe can be moved within the work area via direction keys, a handwheel or other input devices, and this movement is also tracked within the virtual work area and displayed on the screen of the control device. To reach areas of the workpiece that cannot be directly accessed, the angular axes of the machine can also be further moved to tilt the workpiece or the probe. At this time, the function of maintaining a constant distance between the tool (the probe herein) and the workpiece is very beneficial. In addition, collision monitoring can provide assistance even when the position of the workpiece is not grasped with optimal accuracy. Moreover, even if the probe collides with other machine elements, the position thereof is always grasped, so the collision can be reliably detected.

[0022] Finally, the operator moves the probe to the vicinity of the area of the workpiece considered suitable for probing. Here, the control device continuously calculates the probe vector from the probe sphere to the workpiece. Thereby, the probing direction and the (planned) probing point on the workpiece are set. This calculation is performed by determining the shortest distance between the mesh of the probe sphere and the mesh of the workpiece, that is, the distance between the probe sphere and the virtual image of the workpiece. Since very high-speed numerical methods exist for this calculation (e.g., bounding volume hierarchy), the probe vector can be calculated and displayed at small time intervals, for example 20 milliseconds. Therefore, the operator can always check on the screen which probing point is currently targeted, and adjust the positioning of the probe.

[0023] In step 4, the quality of the probe points is continuously calculated, and probing is approved only if this quality is sufficient. Quality takes into account, for example, measurement accuracy, incorrect probe direction, and coding errors during modeling. The probe points have known inclusion planes, their neighboring planes, their vertex normals, and their face normals.

[0024] For high measurement accuracy, the workpiece must be probed as perpendicularly as possible. Edges and excessively curved surfaces should be avoided. To achieve this, the angle between the surface normal and the probe vector near the probe point should be considered, which should be at least less than 30 degrees, preferably less than 20 degrees, and even more preferably less than 10 degrees. In this context, the term "nearby" should be understood to mean that all surface elements around the probe point are considered, for example, those corresponding to the diameter of the probe body, including any existing uncertainty in the workpiece orientation. Alternatively, only the surface element immediately adjacent to the probed surface element may be considered. A large deviation between the surface normal and the probe vector indicates that the workpiece surface is strongly curved or has an edge. The local radius of curvature can be approximated from the surface containing the probe point and its vertex normal, which should be considerably larger than the radius of the probe sphere. Probing is impossible in areas with high curvature (i.e., small radius of curvature) or at edges.

[0025] Even slight discrepancies between reality and the modeling introduce significant uncertainty into the calculated coordinates. Therefore, probe points must be placed in areas of the modeled workpiece that are as accurately represented as possible. Since meshing straightens freeform surfaces, strong curvature results in modeling errors (code errors), and flat surfaces are desirable. For this reason, probe points should not be approved in such areas.

[0026] A further criterion for probe point quality is that the virtual probe sphere must be outside the virtual workpiece. If the virtual probe sphere intersects with the virtual workpiece or is completely inside it, the probe direction cannot be determined, and no suitable probe point exists.

[0027] When the probe vector is determined with sufficient quality from the probe point and probe direction relative to the probe's current position, the operator is notified. A good practice is to display the probe vector in red if the quality is insufficient, and in green if the quality is sufficient and the probing is approved. Other methods include displaying the probe vector only after the quality is sufficient, or deleting the probe vector or displaying a warning next to the probe vector if the quality is insufficient. Additionally, a check mark next to the probe vector indicating sufficient quality or approval of the probing should be intuitively understandable to the operator.

[0028] Steps 3 and 4 are performed sequentially and alternately in a loop, simultaneously, or in parallel, and the displayed probe vector may change several times between good quality and poor quality depending on the result of step 4 while the probe is moving in step 3. At this point, the probing process has not yet been performed.

[0029] This process ends when the operator begins probing in step 5, provided that probing is approved at this moment. The operator can then start the probing process along the current probe vector by pressing a key or via other input means. Each numerical control unit of a machine tool has a start key for initiating specific processes depending on the situation. This start key is appropriate in this case as well.

[0030] Through probing, the control device can determine the coordinates of the probe point in a conventional manner and provide them for subsequent processing. If the probe point is not within the expected range, or if the probe point is not registered even after passing a certain distance, the method is interrupted with an error message. In this case, the accuracy of the agreement between the actual clamp and the virtual clamp is insufficient, and therefore the quality calculation of the (planned) probe point becomes uncertain. In this case, the method must be restarted from the beginning or from step 2.

[0031] If probing begins in step 5 and the coordinates of the probe points are successfully determined, the additional information obtained in step 6 is processed. For this purpose, the position of the virtual workpiece is recalculated to take into account the positional information additionally obtained from the obtained coordinates of the probe points. A simple example is a probe point on a face probed in the X direction of a workpiece that extends in the Y and Z directions. By using the X coordinate of the probe point, the position of the virtual workpiece can be determined much more accurately than initially positioning the workpiece "by eye" in step 2. Even with this single probe point, the agreement between the virtual clamp and the actual clamp is better than the initial agreement. By probing another point on this face, shifted in the Y direction from the first probe point, the rotation of the workpiece around the Z axis can also be determined. Thus, adding probe points further improves the agreement. In general, it is recommended to distribute the probe points as much as possible across the entire workpiece to provide the best possible thrust for rotation.

[0032] In Step 6, additional support information can be provided to the operator, visually communicating the progress and quality of the entire process. In the virtual workspace, each probe point is continuously displayed. The workpiece should fit all of these visualized probe points. This allows the operator to recognize, for example, the deviation between the model and reality. The distance of all probe points to the model can be statistically evaluated, with the mean squared deviation representing quality. A deviation of approximately 0.5 mm is used as a guideline here, because this level of uncertainty allows for very effective collision monitoring, for example.

[0033] Furthermore, like traffic lights, colors could be used to indicate whether sufficient information has been obtained to determine the direction of each spatial axis. For example, if an object is only probed in the X direction, the Z component cannot be represented. This can be visualized by color-coding the axis display, for instance, using green for X and red for Z. This makes it very easy to recognize which probe direction will lead to improvements in the measurement process.

[0034] Directions already set by the clamping status are automatically or manually blocked and displayed in green or grayed out on the progress indicator, the latter indicating that this axial direction is not involved in the measurement process.

[0035] Furthermore, the progress of a specific workpiece position can be displayed graphically, either overall or coordinate-wise. Plotting the position change reached by the last probe point allows for an intuitive understanding of whether the measurement process is converging. The first probe point will still cause relatively large changes or corrections, while subsequent probe points should cause only small changes.

[0036] These indicators (matching virtual probe points, color-coded spatial directions, and correction progress acquired for each probe point) indicate to the operator, individually or in combination, whether the probing process is complete or whether further probing is needed elsewhere. Automatic evaluation of these criteria is also possible, allowing the system to detect the achievement of final agreement and terminate the method without operator intervention.

[0037] In the final step 7, a determination is made as to whether the match between the achieved virtual position and the actual position of the workpiece is sufficiently accurate, i.e., whether a final match has been achieved. If so, the workpiece measurement method is finished; otherwise, the process branches back to step 3 to find another probe point.

[0038] Here again, the term "workpiece" refers to the workpiece that is actually machined and / or the clamping means for it. The case where the clamping means is measured without a workpiece to be machined is also clearly included in the description and claims of this method.

[0039] The method described here has been shown to assist operators in a very intuitive way when measuring the clamping condition of machine tools with a probe. Compared to known methods, it requires no effort in programming fixed probe cycles. Workpiece abnormalities such as damage or markings can be simply avoided during probing. If there is only one workpiece model, measurement of workpieces of arbitrary shapes can be easily performed. By repeatedly feeding back the information acquired at each probe point, the operator can obtain indications for other probe points, and this method allows for very rapid gain of experience.

[0040] Through highly simplified yet precise, integrated steps that are automatically executed in the background of the process, the machine tool operator can complete the inherently complex process of measuring a workpiece by moving the probe around the workpiece and then, once probing is approved, executing the probing process with a start key. The information thus obtained is immediately fed back.

[0041] This method allows for easy measurement of irregularly shaped workpieces with free-form surfaces or inclined surfaces (such as pyramids). By using the machine's rotation axis, measurement points that are difficult to access can be included without increasing the operator's calculation effort.

[0042] Further advantages and details of the present invention will become apparent from the following description of various embodiments with reference to the figures. [Brief explanation of the drawing]

[0043] [Figure 1] Figure 1 shows a machine tool equipped with a numerical control device. [Figure 2] Figure 2 shows the position adjustment of the virtual workpiece in two directions. [Figure 3] Figure 3 shows the position adjustment of the virtual workpiece in two directions. [Figure 4] Figure 4 shows various acceptable and unacceptable probe points. [Figure 5]Figure 5 shows various acceptable and unacceptable probe points. [Figure 6] Figure 6 is a flowchart of the workpiece measurement method. [Modes for carrying out the invention]

[0044] Figure 1 shows a view of the work area A of a machine tool WM. A workpiece WS is placed on the worktable WT. The position of the workpiece WS is determined by probe T using a probe sphere TK. A numerical control unit (NC) is available for this purpose, and the virtual work area vA can be viewed on the screen BS.

[0045] The elements of the work area A that are important to operator B are also displayed in the virtual work area vA. The virtual work table vWT is equipped with a virtual workpiece vWS and a virtual probe vT having a virtual probe sphere vTK. Furthermore, the necessary 3D model is provided to the control unit NC by step 1 described above. In addition, a start key S is shown as the central operating element for the measurement method of workpiece WS, and this key starts the probing process in step 5.

[0046] Figures 2 and 3 show the directional keys RT of the numerical control device (NC), which enable the positioning of the virtual workpiece vWS required in step 2 of the method. By operating the directional keys for the desired axial directions X, Y, and Z, the virtual workpiece vWS can be moved on the virtual worktable vWT and its position can be aligned with the actual workpiece WS. In Figure 2, the virtual workpiece vWS is moved in the positive X direction, and in Figure 3, it is moved in the positive Z direction to initially align the virtual workpiece vWS with the actual workpiece WS.

[0047] Figures 4 and 5 show the display of screen BS between steps 3 and 4, where the virtual probe vT and virtual work vWS display the (planned) probe point AP and probe direction AR determined in step 3, respectively, and the quality of the probe point or the approval of the probe process is indicated by, for example, a check mark, a flash symbol, a deleted or not deleted arrow, a red or green arrow, or any other method. Figure 4 shows the acceptable probe point AP on the surface of the virtual work vWS and the unacceptable probe point AP corresponding to the edge of the virtual work vWS. The probe positions shown in Figure 5 are all unacceptable because the virtual probe sphere vTK is inside or intersecting the virtual work vWS.

[0048] Figure 6 shows the flowchart of the important steps 1-7 of the method described in the general section. 1: Provide 3D models of the work area A, probe T, and workpiece WS, and display these models on the screen BS of the numerical control device NC as a virtual workpiece vWS and virtual probe vT in a virtual work area vA. 2: A step of positioning the workpiece WS in the work area A of the machine tool WM and the virtual workpiece vWS in the virtual work area vA so that the position of the workpiece WS in the work area A and the position of the virtual workpiece vWS in the virtual work area vA initially coincide. 3: Manually position the probe T relative to the workpiece WS, automatically select the planned probe point AP and probe direction AR based on the minimum distance of the virtual probe vT to the virtual workpiece vWS, and display the planned probe point AP and probe direction AR in the virtual work area vA. 4. Determine the quality of the planned probe point AP, and if the quality is sufficient, approve the probing. The quality is determined, for example, based on the local curvature of the workpiece WS at the probe point AP. 5. If probing is approved, the probing is initiated (by operator B) and the coordinates of probe point AP are determined. If approval is not yet given, probe T is moved further instead, and from here the method branches back to step 3. 6. Recalculate the position of the workpiece WS using the coordinates of the probe point AP, and update the position of the virtual workpiece vWS in the virtual work area vA. 7. Repeat steps 3-6 until the position vWS of the virtual work in virtual workspace vA finally matches the position WS of the work in workspace A.

[0049] The numerical control (NC) system is configured to perform this method in steps 1-7, thereby providing operator B with optimal assistance in the task of measuring the workpiece WS. In the actual measurement of the workpiece, the desired objective can be achieved with only step 3 and very simple and intuitive operation by the operator. [Explanation of Symbols]

[0050] WM machine tools A work area WT Work Table WS Work T probe TK probe bulb NC Numerical Control System BS screen vA Virtual Workspace B Operator vWT Virtual Worktable vWS Virtual Workstation vTK virtual probe sphere S Start key RT Directional keys vT virtual probe AP probe point AR probe direction

Claims

1. A method for measuring a workpiece (WS) using a probe (T) in the working area (A) of a machine tool (WM) equipped with a numerical control device (NC), (1) Providing 3D models of the work area (A), probe (T), and workpiece (WS), and displaying these models on the screen (BS) of a numerical control device (NC) as a virtual workpiece (vWS) and virtual probe (vT) in a virtual work area (vA), (2) A step of positioning the workpiece (WS) in the work area (A) of the machine tool (WM) and the virtual workpiece (vWS) in the virtual work area (vA) such that the position of the workpiece (WS) in the work area (A) and the position of the virtual workpiece (vWS) in the virtual work area (vA) initially coincide. (3) The steps of manually positioning the probe (T) relative to the workpiece (WS), automatically selecting a planned probe point (AP) and probe direction (AR) based on the distance of the virtual probe (vT) to the virtual workpiece (vWS), and displaying the planned probe point (AP) and probe direction (AR) in the virtual work area (vA), (4) Determine the quality of the planned probe point (AP), approve the probing if the quality is sufficient, and return to step (3) if the probing is not approved. (5) If probing is approved, the steps include starting the probing and determining the coordinates of the probe point (AP), (6) The steps of recalculating the position of the workpiece (WS) based on the coordinates of the probe point (AP) and updating the position of the virtual workpiece (vWS) in the virtual work area (vA), (7) Repeat steps (3) to (6) until the position of the virtual workpiece (vWS) in the virtual work area (vA) and the position of the workpiece (WS) in the work area (A) finally coincide, A method of having.

2. The method according to claim 1, wherein in step (4), the quality is determined based on the local curvature of the virtual workpiece (vWS) at least the planned probe point (AP).

3. The method according to claim 1, wherein in step (4), the deviation between the probe direction (AR) and the surface normal of the workpiece (WS) near the probe point (AP) is referenced in order to determine the quality, and this deviation is at most 30 degrees in order to determine a probe point having sufficient quality.

4. The method according to claim 1, wherein in step (4), a probe point (AP) on the edge of the workpiece (WS) is excluded from probing and is determined not to have sufficient quality.

5. The method according to claim 1, wherein in step (4), the approval or disapproval indication is displayed in a diagram on the screen (BS).

6. The method according to claim 1, wherein in step (6), information regarding the match already achieved between the position of the virtual workpiece (vWS) and the position of the workpiece (WS) is additionally displayed on the screen (BS).

7. The method according to claim 6, wherein the progress of position correction of the virtual workpiece (vWS) performed by each probe point (AP) is displayed for a plurality of probe points (AP) that have already been processed.

8. The method according to claim 6, wherein each probe point (AP) is continuously displayed in the virtual work area (vA).

9. Numerical control device (NC) for a machine tool (WM), configured to perform the method according to any one of claims 1 to 8.

10. The method according to claim 3, wherein the deviation is a maximum of 10 degrees.

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