On-line multi-force adaptation during processing

Abstract

A method for operating a numerically controlled machine is proposed, comprising: receiving a sequence of control commands which, when executed by the numerically controlled machine, cause the numerically controlled machine to machine a workpiece to obtain a predetermined workpiece geometry, wherein the sequence of control commands comprises information about a discretized tool path defined by a sequence of support points, information about a simulated value of a first interaction parameter describing an interaction of a tool of the numerically controlled machine with the workpiece for each support point, information about a simulated value of at least a second interaction parameter describing an interaction of the tool of the numerically controlled machine with the workpiece for each support point, measuring a value of the first interaction parameter for a first position of the tool when machining the workpiece based on the received sequence of control commands, comparing the measured value of the first interaction parameter for the first position of the tool with the simulated value of the first interaction parameter for the first position of the tool, determining an adapted value of the second interaction parameter for a subsequent position of the tool based on a result of the comparison.

Description

[0001] This disclosure relates to a computer-aided optimization method for CNC machining of workpieces. In particular, this disclosure relates to a method for operating a CNC machine, a control unit for the CNC machine, and a computer program for performing the method.

[0002] WO 2018 / 041476 A1 relates to a computer-aided optimization method for a CNC machining process of a workpiece using a machining module. The method is characterized in that, in a first step, the machining process is simulated using a specified workpiece geometry and a sequence of control commands for controlling the machining module. Using the obtained simulation results, at least one characteristic variable of the machining process is then determined. This at least one characteristic variable is checked with respect to at least one specified optimization variable of the machining process of the workpiece using the machining module. If a deviation from the at least one optimization variable is determined during the check, the determined deviation between the at least one characteristic variable and the at least one optimization variable is used to adapt the control command sequence, and the simulation, determination, and check steps are performed again using the adapted control command sequence. If all optimization criteria are met, the resulting control command sequence is provided for using the machining module to produce the workpiece. The above method extends the digital toolchain for manufacturing workpieces on a CNC machine tool using a sequence of control commands, thereby simplifying and improving the generation of the control command sequence, i.e., NC code. During the machining of a workpiece using a CNC machine tool, the tool will typically be subjected to forces and torques. If the CNC machine is not rigid enough, force and / or torque may cause the tool to deflect.

[0003] Before actually modifying the workpiece, the process of machining the workpiece using a CNC machine can be simulated. As a result of this simulation, the forces experienced by the tool at a certain location can be obtained. The CNC machine can then use the information obtained through this simulation process to, for example, counteract the deflection caused by the forces acting on the tool by modifying the actual trajectory of the tool.

[0004] The workpiece blank, which will be machined to obtain a workpiece with a predetermined workpiece geometry, may have properties different from those assumed for the simulation. For example, the size of the workpiece blank or its ductility may deviate. Consequently, the actual forces experienced by the tool may differ from the simulated forces. Therefore, correctly counteracting tool deflection may become more difficult.

[0005] Therefore, a method for operating CNC machines may be needed that allows for more precise machining of workpieces to obtain workpieces with a geometry that is closer to the predetermined workpiece geometry.

[0006] The aforementioned need has been addressed by the subject matter of the independent claims. Advantageous embodiments are described in the dependent claims.

[0007] A method for operating a CNC machine is proposed, comprising: receiving a sequence of control commands, which, when executed by the CNC machine, cause the CNC machine to machine a workpiece to obtain a predetermined workpiece geometry, wherein the sequence of control commands includes information about a discretized toolpath defined by a sequence of support points, information about simulated values ​​of a first interaction parameter describing the interaction between the CNC machine's tool and the workpiece at each support point, and information about simulated values ​​of at least a second interaction parameter describing the interaction between the CNC machine's tool and the workpiece at each support point; measuring the value of the first interaction parameter for a first position of the tool when machining the workpiece based on the received sequence of control commands; comparing the measured value of the first interaction parameter for the first position of the tool with the simulated value of the first interaction parameter for the first position of the tool; and determining an adapted value of a second interaction parameter for a following position of the tool based on the result of the comparison.

[0008] The first and / or subsequent positions of the tool can correspond to support points of the discretization tool path. Alternatively, the first and / or subsequent positions of the tool can be positions between two support points of the discretization tool path.

[0009] In embodiments of the method, each support point indicates a movement trajectory to the next support point executed by the machine's tool. The movement trajectory from each support point to the next can correspond to linear movement. For example, it could indicate direct travel from the current positions x1, y1, and z1 to positions x2, y2, and z2. Alternatively, it could indicate movement via following a path with a center x... c y c z c The trajectory of an arc of a circle with radius r travels to positions x2, y2, and z2. The entire discretization tool path can consist of basic movement trajectories such as linear motion and arcs. The positions to be traveled can also be indicated using circular or spherical coordinates.

[0010] Simulating the machining process before actual machining of the workpiece to obtain the values ​​of the interaction parameters can prevent the production of workpieces with geometries that do not conform to the predetermined workpiece geometry. These values ​​can also be referred to as simulated values.

[0011] In one embodiment, measuring the value of a first interaction parameter for a first position of the tool includes measuring the current. Measuring the current is possible even if the environment of the tool / workpiece interaction is affected by coolant or metal debris.

[0012] In another embodiment, the first interaction parameter is the torque experienced by the tool of the CNC machine. The tool of the CNC machine can be held in the spindle, and the torque experienced by the tool can correspond to the torque experienced by the spindle. This torque can be related to the current used to rotate the spindle.

[0013] In another embodiment, the second interaction parameter is the force experienced by the tool of the CNC machine. This force can correspond to a force expressed in three dimensions. The value of the force can correspond to a vector or scalar. The force experienced by the tool can correspond to a cutting force. A tool rotated by a CNC machine may experience a cutting force or torque. The feed rate or the workpiece and tool material may also experience forces and torques. The cutting force may have a direct impact on the tool deflection during workpiece machining and the achievable tolerances. Information about the cutting force can help keep tolerances within specified limits. Furthermore, the cutting force and torque may have a direct impact on the surface quality of the final workpiece. This also applies to the workpiece temperature at the machining point. Additionally, force, torque, and temperature also affect tool wear. Therefore, the CNC machine can determine when the tool needs to be replaced due to excessive wear. Conversely, tool wear may also affect the torque and / or force experienced by the tool, which can lead to deviations between simulated and actual values. Therefore, the proposed method can also help obtain a predetermined geometry using the tool used.

[0014] According to an additional embodiment, determining the adaptation value of the second interaction parameter for a subsequent position of the tool based on the result of the comparison includes: determining the adaptation value of the second interaction parameter for a subsequent position of the tool based on the result of the comparison and the value of the first interaction parameter for the subsequent position.

[0015] Another embodiment specifies that the control command sequence includes information for determining the adaptation value of the second interaction parameter. This information may correspond to mathematical formulas, constants, and / or algorithms. The mathematical formulas, constants, and / or algorithms may have already been determined during simulation of the processing procedure.

[0016] In another embodiment, the CNC machine is one of a lathe, milling machine, drilling machine, or grinding machine.

[0017] According to an additional embodiment, the method includes: measuring the values ​​of a first interaction parameter for a plurality of subsequent positions of the tool; comparing the measured values ​​of the first interaction parameter for the subsequent positions of the tool with simulated values ​​of the first interaction parameter for the subsequent positions of the tool; filtering the result of the comparison; and determining an adapted value of a second interaction parameter for the subsequent positions of the tool based on the filtered result of the comparison.

[0018] Another embodiment specifies that the method includes: measuring the values ​​of a first interaction parameter for a plurality of subsequent positions of the tool, filtering the measured values ​​of the first interaction parameter, comparing the filtered values ​​of the first interaction parameter for the subsequent positions of the tool with simulated values ​​of the first interaction parameter for the subsequent positions of the tool, and determining, based on the comparison result, an adapted value of a second interaction parameter for the subsequent positions of the tool.

[0019] In another embodiment, filtering includes using a low-pass filter.

[0020] According to an additional embodiment, filtering includes using a filter that is adapted to features of a predetermined workpiece geometry.

[0021] In addition, a control unit for a numerically controlled machine is proposed, wherein the control unit is configured to perform any of the methods described above.

[0022] Furthermore, this disclosure relates to a computer program comprising instructions that, when executed by a computer, cause the computer to perform any of the methods described above.

[0023] The accompanying drawings included in this application are incorporated in and form a part of this specification. They illustrate embodiments of the present disclosure and, together with the description, serve to explain the principles of the disclosure. The drawings illustrate only certain embodiments and do not limit the scope of the disclosure. In the drawings:

[0024] Figure 1 The diagram illustrates the toolpath used to process the workpiece;

[0025] Figure 2 The diagram illustrates the path of the first discretization tool;

[0026] Figure 3 The diagram illustrates the simulated and measured values ​​of the first interaction parameter;

[0027] Figure 4 The diagram illustrates the simulated and measured values ​​of the second interaction parameter;

[0028] Figure 5 The diagram illustrates a method for operating a CNC machine;

[0029] Figure 6 The diagram illustrates the adapted and measured values ​​of the second interaction parameter; and

[0030] Figure 7 The diagram illustrates the adapted and measured values ​​of the second interaction parameter.

[0031] Figure 1A CNC machine 110 in the form of a milling machine is shown, which operates a tool 111 in the form of a milling cutter. The tool 111 can rotate about an axis R to remove material from a workpiece 120 in contact with the tool 111. In this example, the axis R is parallel to the axis z.

[0032] Workpiece 120 includes a first part 121 made of a first material and a second part 122 made of a second material. The first material and the second material may have different properties. For example, machining the first material may be more difficult than machining the second material.

[0033] The rotary tool 111 can move along the tool path 130 to machine the workpiece 120, thereby obtaining a predetermined workpiece geometry indicated by dashed lines. Figure 1 In the example shown, tool path 130 lies in a single plane defined by axes x and y. Furthermore, the rotation axis of the rotating tool 111 remains unchanged. Typically, tool path 130 can describe any trajectory in three-dimensional space and includes information about the orientation of the rotation axis R in three-dimensional space.

[0034] During the machining of workpiece 120 using tool 111, tool 111 will be subjected to forces and torques. If machine 110 is not sufficiently rigid, the forces and / or torques may cause deflection of tool 111. In particular, larger forces or torques will increase this deflection, and the robot may have lower stiffness than the machining center. This deflection may cause the workpiece geometry to not correspond to the intended predetermined workpiece geometry. Specifically, the deviation between the actual workpiece geometry and the intended predetermined workpiece geometry may exceed the predetermined tolerance.

[0035] To generate a sequence of control commands for controlling the CNC machine 110 to process the workpiece 120, the toolpath 130 can be discretized into smaller parts, and this can be achieved. Figure 2 The first discretization tool path 230 is shown. The first discretization tool path 230 can be defined by a first sequence of support points 231 to 262. Each support point 231 to 262 can define a movement to the next support point performed by tool 111.

[0036] Before actually modifying workpiece 120, the process of machining workpiece 120 using CNC machine 110 can be simulated. Until then, a first discretized toolpath 230 can be used. For each support point in the first sequence of support points 231 to 262, at least one interaction parameter 265 to 296 can be obtained. This simulation can take into account the materials of workpiece 120 and tool 111 to modify the geometry of the workpiece. For example, the interaction parameters can correspond to the torque experienced by tool 111, or the temperature of tool 111, or the temperature of workpiece 120, or the force experienced by tool 111 at the corresponding support point 231 to 262. If the values ​​of interaction parameters 265 to 296 exceed a critical threshold, CNC machine 110 can use information about at least one interaction parameter to counteract undesirable consequences. For example, if the temperature determined for the corresponding support point 231 to 262 is too high, CNC machine 110 can provide additional cooling at the interface between tool 111 and workpiece 120. Furthermore, the CNC machine 110 can counteract the deflection caused by the force acting on the tool 111 by modifying the actual trajectory of the tool 111. Figure 2 The diagram illustrates simulated forces 265 to 296 acting on tool 111 during processing.

[0037] Figure 3 The illustration shows simulated and measured values ​​of a first interactive parameter obtained for an exemplary machining process. In this example, the first interactive parameter is torque. Simulated value 301 and measured value 302 of torque are plotted over time. Torque values ​​and time are expressed in arbitrary units. The curve of measured value 302 substantially follows the curve of the simulated value. However, differences can be observed when the torque value changes. Differences in the torque value can indicate that the force experienced by the tool of the CNC machine has also changed.

[0038] Figure 4 The diagram illustrates the simulated and measured values ​​of the second interaction parameter. In this example, the second interaction parameter is the force in the x-direction (411, 412), y-direction (421, 422), and z-direction (431, 432) during the machining time. Curves 411, 421, and 431 correspond to the simulated values ​​of the force in the x-direction, y-direction, and z-direction, respectively. Correspondingly, curves 412, 422, and 432 correspond to the measured values ​​in the x-direction, y-direction, and z-direction, respectively.

[0039] For higher forces, the difference between the simulated and measured values ​​of the second interaction parameter increases. Furthermore, the difference between the simulated and measured values ​​of the second interaction parameter becomes more pronounced.

[0040] The value of the first interaction parameter can be obtained from the simulation. Furthermore, during the processing, the value of the first interaction parameter may be easier to measure than the value of the second interaction parameter.

[0041] For example, the torque experienced by the tool 111 of the CNC machine 110 during machining can correspond to the current required to rotate the spindle of the CNC machine 110.

[0042] Variations in the process parameters used to machine the workpiece—for example, the selection of tool 111 different from the tool assumed for the simulation, different feed rates selected by the CNC machine operator, workpiece material different from the initially planned workpiece material, and different geometry of the blank workpiece—may cause the measured value of the second interaction parameter to differ from its simulated value. During workpiece machining, the second interaction parameter may be difficult to measure. For example, measuring the forces experienced by the tool during machining can be very challenging. The second interaction parameter can be linked to the first interaction parameter.

[0043] The proposed approach is to use measured and simulated values ​​of a first interaction parameter to obtain an adapted value for a second interaction parameter. This adapted value of the second interaction parameter can then be used by a CNC machine to counteract undesirable machine behavior, such as deflection of tool 111 during machining. Torque deviations can be used to derive the adapted force value from the simulated force value.

[0044] Specifically, it is proposed to use the following formula to calculate the appropriate force:

[0045]

[0046] in, ΔM =( M measured - M simulated )

[0047] Variable F is related to force, and variable M is related to torque. Parameter k describes the effect of torque difference on force. In the example formula depicted above, parameter k can be a constant describing the linear dependence of force on torque difference. For example, this linear relationship could correspond to the linear relationship between spindle torque and feed rate. However, it is also possible for a second interaction parameter to show a quadratic or cubic dependence on the first interaction parameter. Typically, this dependence can be determined using a neural network or a model of the processing environment.

[0048] Figure 5 The illustration depicts a method for operating a CNC machine. The machining process is simulated using a simulation module 511 of a manufacturing system 510 with an added computer. The simulation module 511 provides simulated values ​​for a first interactive parameter (here, simulated spindle torque M). simulated The simulated value of the second interaction parameter (here: simulated force F) Xsimulated F Ysimulated F Zsimulated ).

[0049] The computer-aided manufacturing process provides a sequence of control commands to the control unit 520 of the CNC machine used for machining the workpiece. This sequence of control commands includes analog values ​​as mentioned above. During workpiece machining, the sensor unit 521 continuously receives measurements of a first interactive parameter from the machine (here: the measured spindle torque M). measured The comparison unit 622 will compare the measured value of the first interaction parameter (here: M) with the measured value of the first interaction parameter. measured The simulated value of the first interaction parameter (here: M) and the simulated value of the first interaction parameter. simulated The algorithm compares the results (ΔM) with the parameters (k) and provides the result to the algorithm unit 523, which then derives the parameters (k). X k Y k Z This is used to adapt the force for subsequent positions of the tool. The second interactive parameter adaptation unit 524 receives the parameter (here: k) MX k MY k MZ ), and calculate the adaptation value of the second interaction parameter (here: F) from it. Xadapted F Yadapted F Zadapted Then, the control unit 520 uses the adaptation value F of the second interaction parameter. Xadapted F Yadapted F Zadapted To control the machine. Specifically, the machine or control unit 620 can use a force adaptation value F. Xadapted F Yadapted F Zadapted This is used to counteract the deflection caused by the force acting on the tool by modifying the actual trajectory of the tool.

[0050] Figure 6 The diagram illustrates the adapted and measured values ​​of the second interaction parameter. Adapted value F Xadapted 613, F Yadapted 623, F Zadapted The value 633 is very close to the corresponding measured values ​​612, 622, and 632. This indicates that adapting the measurement based on the first interaction parameter to the value of the second interaction parameter yielded good results.

[0051] In particular, Figure 4 and Figure 6 The comparison shows that adaptation allows for better reference of the workpiece using a better understanding of the forces actually acting on the tool, and thus allows for better modification of the machining process to avoid the consequences of tool deflection. This can be particularly useful if higher forces are expected, especially during the roughing pass.

[0052] Figure 7 Another example is shown of the simulated value 711, the measured value 712, and the adapted value 713 of the second interaction parameter. In this example, these values ​​are shown as force (expressed in Newtons) over time (in arbitrary units). The adapted value 713 has been derived based on the deviation between the measured value and the simulated value of the first interaction parameter. Figure 7 In the example, the first interaction parameter is the principal axis. Specifically, curve 720 shows the adaptation coefficient, expressed as a percentage (%), which is derived from the deviation between the measured and simulated values ​​of the first interaction, and which has been used to adapt the value of the second interaction parameter.

[0053] Any functional dependency between the fit coefficient, or generally the simulated value of the first interaction parameter, the measured value of the first interaction parameter, and the fitted value of the second interaction parameter, can vary depending on the tool's position on the toolpath, tool wear, and / or the material properties of the workpiece. Of course, any other influence on tool operation may also alter this functional dependency. Furthermore, the rate of change of this functional dependency can vary depending on the tool's position or other operating conditions.

[0054] In this way, the responsiveness to deviations from the simulated behavior can be adapted to various operating conditions. For example, to make the initial cut smoother, the responsiveness can be reduced at the beginning of the toolpath. Furthermore, the force applied in response to such deviations can be limited to a safe amount.

[0055] Furthermore, the comparison between the measured value of the first interaction parameter for the first position of the tool and the simulated value of the first interaction parameter for the first position of the tool can be performed by the controller of the CNC machine. This comparison can typically be implemented as the quantization of the difference (ΔM in the above embodiment) between the measured value of the first interaction parameter for the first position of the tool and the simulated value of the first interaction parameter for the first position of the tool. Preferably, this difference can be quantized as a floating-point value.

[0056] Therefore, the adaptation value of the second interaction parameter can be continuously determined based on this difference. Specifically, the adaptation value of the second interaction parameter can be calculated as a continuous function of this difference. The adaptation value of the second interaction parameter can then be used to control a CNC machine. Changes in the adaptation value typically cause a change in the measured value of the first interaction parameter (M in the above embodiment). measuredThe changes in the first interactive parameter are then fed back to the controller of the CNC machine, thereby establishing a closed control loop. The measured value of the first interactive parameter serves as the process variable, the simulated value of the first interactive parameter serves as the reference variable, and the difference serves as the control error. This closed-loop control allows for continuous control of the tool operation and continuous correction of deviations from the simulation.

[0057] The countermeasure used to correct the deviation from the simulation (i.e., the application of the fit value) has a quantitative and continuous relationship with the actual measured deviation from the simulation (i.e., the measured difference). In particular, a lower difference can lead to a lower countermeasure, and a higher difference can lead to a higher countermeasure, with a continuous and smooth transition between the two cases. As mentioned above, the corresponding offset can depend on the corresponding difference in a linear, quadratic, or cubic manner.

Claims

1. A method for operating a numerically controlled machine, comprising: A sequence of control commands is received, which, when executed by a CNC machine, causes the CNC machine to process a workpiece to obtain a predetermined workpiece geometry. The control command sequence includes: Information about the discretization toolpath defined by the sequence of support points. Information regarding the simulated values ​​of the first interaction parameter, which describes the interaction between the tool and the workpiece of the CNC machine at each support point. Information regarding simulated values ​​of at least a second interaction parameter that describes the interaction between the tool and workpiece of a CNC machine at each support point. When processing a workpiece based on a received sequence of control commands. Measure the value of the first interaction parameter for the first position of the tool. The measured value of the first interaction parameter for the first position of the tool is compared with the simulated value of the first interaction parameter for the first position of the tool. Based on the results of the comparison, an adaptation value for the second interaction parameter for the subsequent position of the tool is determined. The CNC machine is controlled by a controller; Quantify the difference between the measured value of the first interaction parameter for the first position of the tool and the simulated value of the first interaction parameter for the first position of the tool; The adaptation value of the second interaction parameter is continuously determined based on the difference. The CNC machine is controlled by using the adaptation value of the second interaction parameter; The measured value of the first interactive parameter is fed back to the controller to establish a closed control loop, wherein the measured value of the first interactive parameter is used as a process variable, the simulated value of the first interactive parameter is used as a reference variable, and the difference is used as a control error.

2. The method according to claim 1, Each support point indicates the movement trajectory to the next support point executed by the CNC machine's tool.

3. The method according to claim 1 or 2, The measurement of the value of the first interactive parameter for the first position of the tool includes the measurement of the current.

4. The method according to claim 1 or 2, The first interaction parameter is the torque experienced by the tool of the CNC machine.

5. The method according to claim 1 or 2, The second interaction parameter is the force exerted on the tool of the CNC machine.

6. The method according to claim 1 or 2, The adaptation values ​​for the second interaction parameter for subsequent positions of the tool, determined based on the results of the comparison, include: The adapted value of the second interaction parameter for the subsequent position of the tool is determined based on the result of the comparison and the simulated value of the second interaction parameter for the subsequent position.

7. The method according to claim 1 or 2, The control command sequence includes information for determining the adaptation value of the second interaction parameter.

8. The method according to claim 7, The information described therein is at least one of a mathematical formula, a constant, or an algorithm.

9. The method according to claim 1 or 2, Numerical control machines are robots.

10. The method of claim 1, wherein the method comprises: Measure the values ​​of the first interaction parameter for several subsequent positions of the tool; The measured value of the first interaction parameter for the subsequent position of the tool is compared with the simulated value of the first interaction parameter for the subsequent position of the tool; The comparison results are then filtered. The filtered results of the comparison are used to determine the appropriate values ​​for the second interaction parameters for the subsequent positions of the tool.

11. The method according to claim 1, wherein the method comprises: Measure the values ​​of the first interaction parameter for several subsequent positions of the tool; The measured value of the first interaction parameter is filtered; The filtered value of the first interaction parameter for the subsequent position of the tool is compared with the simulated value of the first interaction parameter for the subsequent position of the tool. as well as Based on the results of the comparison, an adaptation value for the second interaction parameter for the subsequent position of the tool is determined.

12. The method according to claim 10 or 11, The filtering mentioned therein includes the use of a low-pass filter.

13. The method according to claim 10 or 11, The filtering includes using a filter that is adapted to the features of the predetermined workpiece geometry.

14. The method according to claim 1 or 2, The functional dependence between the simulated value of the first interaction parameter, the measured value of the first interaction parameter, and the adapted value of the second interaction parameter varies depending on the tool position, tool wear, and / or the material properties of the workpiece.

15. The method according to claim 14, The rate of change of the functional dependency depends on the location of the tool.

16. A control unit for a numerically controlled machine, wherein the control unit is configured to perform the method according to any one of claims 1 to 15.

17. A computer program product comprising instructions that, when executed by a computer, cause the computer to perform the method according to any one of claims 1 to 15.

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