Method and apparatus for manufacturing a workpiece from a workpiece blank, as well as a computer program

Abstract

A device for manufacturing a workpiece has a workpiece holder (22) for a workpiece blank (26) and a machining tool (28, 34). A machine control (14) generates a motor current (40, 44) that drives the machining tool (28, 34) relative to the workpiece holder (22). A vibration sensor (36) detects a time-resolved signal (38) that represents a vibration profile during the machining of the workpiece blank (26) at a first nominal machining position with respect to a vibration axis (x1). Based on the vibration profile, a partial signal profile is determined that represents a directional component of the motor current (40, 44) along the vibration axis (x1). Using the partial signal profile, an actual first machining position is determined.Subsequently, the workpiece blank (26) is machined at at least one second machining position, depending on the actual first machining position.

Description

[0001] The present invention relates to a method and a device for producing a workpiece from a workpiece blank using an automatically controlled workpiece processing machine, in particular a machine tool with machining capabilities.

[0002] Many industries make intensive efforts to increase production output and product quality. Product quality is often defined by whether the manufactured workpieces conform to predefined workpiece specifications, particularly regarding the shape, position, and dimensions of defined workpiece features, surface roughness, structure, and / or gloss level. Workpieces that do not meet the predefined specifications must either be reworked or rejected, which impacts production output and efficiency. To monitor product quality, it is common practice to integrate one or more measuring devices into the production plant and sometimes even directly into a workpiece processing machine, especially a machine tool.However, adjusting a manufacturing process in real time when product quality declines is difficult because acquiring and evaluating measurement results on workpieces during or shortly after production takes time, and the time lag is often too great to efficiently use the measurement results for production control. For many measurement methods, the time until a result is available is often significantly longer than the production cycle times or the period of fluctuations in the production process.

[0003] Particular challenges arise when a complex workpiece is manufactured in a process chain with multiple machining steps that require reclamping the workpiece blank. Reclamping in this case means that the workpiece blank, or the partially manufactured workpiece, must be transferred from one fixture to a second and, if necessary, secured. This is especially true when a workpiece blank is to be machined on six sides ("all around") with tight tolerances. Reclamping typically results in the loss of a clear reference between the workpiece surfaces machined in different setups.

[0004] In some cases, it is possible to integrate quality inspections into the manufacturing process by, for example, measuring a machined surface on a workpiece blank in the machining area and in the fixture used for machining, before the partially machined workpiece blank is further processed. Measuring probes, such as those offered by companies like Renishaw or Blum-Novotest, can be used in the machining area for this purpose. However, the machining process must be interrupted for such in-process measurements, which impacts the machine's production output.

[0005] Nevertheless, quality control in industrial manufacturing processes has been of great interest for years in order to achieve cost-efficient production and high product acceptance among customers. Many concepts and approaches exist for establishing quality assurance processes in the industrial manufacturing of workpieces.

[0006] US 10 180 667 B2, for example, discloses a measurement technology integrated into a manufacturing machine for measuring a manufactured workpiece, in which the measurement results are interpreted by a trained artificial intelligence (AI). Based on the measurement results, the AI ​​determines new target control data.

[0007] The publication “Process Force Measurement with Spindle-Integrated Sensors” by Christian Brecher, Hans-Martin Eckel, Marcel Fey, and Felix Butz, DOI 10.3139 / 104.111982, ZWF 113 (2018) 10; pages 660–663 © Carl Hanser Verlag GmbH & Co. KG, ISSN 0032-678X, describes how knowing the process force with which a workpiece blank is machined allows for detailed insights into the manufacturing process and the manufacturing system. The process force forms the basis for process optimization and monitoring of the manufacturing system. Process forces can be calculated indirectly via a relative displacement between the spindle shaft and the spindle housing. For this reason, a main spindle was equipped with non-contact displacement sensors in the form of eddy current sensors to determine the force at the tool in the main machine axes.

[0008] Integrating such displacement sensors into the spindle of a workpiece machining machine is quite expensive, and existing workpiece machining machines cannot easily be retrofitted.

[0009] When a machining center has to exert a greater force during the machining of a workpiece blank, a higher motor power and, consequently, a higher motor current are generally required. Motor power and motor current therefore correlate with the process force, but on their own do not provide sufficient information density to determine the forces occurring during machining with the resolution and accuracy desirable for efficient and error-correcting machining.

[0010] DE 44 05 660 A1 discloses a method for operating a machine tool for removing material, in particular a circular saw, milling machine, grinding machine or the like, based on a model state program implemented in a host computer.

[0011] A machine tool is used, whereby the host computer receives current state signals from the machine tool and, based on these state signals and, if applicable, the model state, uses numerical analysis to determine operating behavior that impairs the machining performance, or predictively calculates such operating behavior. Adaptive control of selected operating parameters of the machine tool is performed with the aim of dynamically changing the operating parameters to values ​​within a range calculated using the model state program or predefined, in order to achieve a predetermined machining behavior.

[0012] Against this background, it is an object of the present invention to provide a method and a device that enable the efficient production of high-quality workpieces, particularly with regard to the shape, position, and dimensions of defined workpiece features. It is especially an object of the invention to provide a method and a device that enable the efficient production of workpieces with tight tolerances on spaced-apart and, in particular, mutually opposite workpiece faces.

[0013] These problems are solved by a method for producing a workpiece from a workpiece blank with the features of claim 1 and by a device for producing a workpiece with the features of claim 10. The problems are further solved by a computer program with the features of claim 11.

[0014] According to one aspect of the invention, a method for producing a workpiece from a workpiece blank is provided, comprising the following steps: - Providing a workpiece machining machine with a workpiece holder configured to hold the workpiece blank, with a machining tool movable relative to the workpiece holder, with a drive motor configured to move the machining tool relative to the workpiece holder depending on an supplied motor current, with a machine control configured to generate the motor current, and with at least one vibration sensor configured to detect a time-resolved signal representing a vibration profile during the machining of the workpiece blank, - Obtaining a data set representing nominal workpiece properties of the workpiece, - Machining the workpiece blank with the machining tool at a first nominal machining position, whereby the machine control generates the motor current depending on the data set, - Capturing an initial signal waveform that exhibits a multitude of successive instantaneous values ​​during the machining of the workpiece blank at the first nominal machining position, where the instantaneous values ​​represent an instantaneous motor current, - Recording an initial current vibration profile along a first defined vibration axis during the machining of the workpiece blank at the first nominal machining position using at least one vibration sensor, - Determining a partial second signal waveform comprising a multitude of successive partial instantaneous values ​​of the motor current during machining of the workpiece blank at the first nominal machining position, wherein the partial instantaneous values ​​represent a directional component of the motor current along the first defined vibration axis, - Determining an actual first processing position using the partial second signal waveform, and - Machining the workpiece blank at at least one second machining position depending on the data set and depending on the actual first machining position.

[0015] According to another aspect, a device for producing a workpiece from a workpiece blank is provided, with - a workpiece fixture designed to hold the workpiece blank, - a machining tool that is movable relative to the first workpiece holder, - a drive motor designed to move the machining tool relative to the workpiece holder depending on an supplied motor current, - a machine control system designed to generate the motor current, and - at least one vibration sensor configured to capture a time-resolved signal representing a vibration profile during the machining of the workpiece blank, the machine control further being configured to execute the following process steps: - Obtaining a data set representing nominal workpiece properties of the workpiece, - Generating the motor current depending on the data set for machining the workpiece blank with the machining tool at a first nominal machining position, - Capturing an initial signal waveform that exhibits a multitude of successive instantaneous values ​​during the machining of the workpiece blank at the first nominal machining position, where the instantaneous values ​​represent an instantaneous motor current, - Recording an initial current vibration profile along a first defined vibration axis during the machining of the workpiece blank at the first nominal machining position using at least one vibration sensor, - Determining a partial second signal waveform comprising a multitude of successive partial instantaneous values ​​during the machining of the workpiece blank at the first nominal machining position, wherein the partial instantaneous values ​​represent an effective directional component of the motor current along the first defined vibration axis, - Determining an actual first processing position using the partial second signal waveform, and - Machining the workpiece blank at at least one second machining position depending on the data set and depending on the actual first machining position.

[0016] Furthermore, a computer program with program code is provided that is designed to execute a procedure of the aforementioned type when the program code is executed on a machine control of a corresponding device.

[0017] The data set can be a CAD data set, a CAM data set, and / or a set of control commands for machine control. It defines and / or represents nominal workpiece data, in particular dimensional properties relating to the shape, size, and location of features that the workpiece to be manufactured should possess. Features can include, for example, the diameter, depth, and location of a hole, radii, distances, and / or lengths of edges, among others. The industrial production of workpieces based on or dependent upon such a data set is common practice today.

[0018] The machine control system can include a numerical control (NC control), as is familiar to experts in machine tools. Alternatively or additionally, the machine control system can include a programmable logic controller (PLC) and / or other programmable components or logic circuits, including standard PCs, industrial PCs, microcontrollers, ASICs, FPGAs, and / or processors and memory connected via communication networks. Advantageously, the machine control system can include one or more drive control units that provide individual motor currents for driving electric motors, depending on control commands from a control program running on the machine control system.

[0019] The new method and device acquire, on the one hand, successive instantaneous values ​​of one or more individual motor currents or of signal values ​​that correlate with the motor currents. In some embodiments, the successive instantaneous values ​​of the respective current control loops can be provided in the machine control system. The successive instantaneous values ​​represent a motor current profile and thus also correlate with the respective motor power.

[0020] Furthermore, the new method and the new device capture at least one vibration signal with temporal resolution during the machining of a workpiece; that is, a signal representative of vibration along a vibration axis during the machining of the workpiece blank. The vibration axis is a spatial axis. It therefore represents a defined spatial direction. The temporally resolved vibration signal represents a vibration profile during the machining of a workpiece along this spatial direction.

[0021] Based on the signal and vibration profiles, at least a partial signal profile is determined such that the directional information of the vibration profile is assigned to a portion of the signal profile. In other words, the signal profile is quantitatively divided into a partial signal profile that can be attributed to the vibration along the vibration axis and another portion that cannot. A spatial directional information corresponding to the spatial direction of the vibration is thus imprinted on the partial signal profile and, consequently, on the motor current. This makes it possible to analyze and / or model the machining of the workpiece in the defined spatial direction, taking into account the instantaneous motor current that is responsible for the movement of the machining tool relative to the workpiece and / or a corresponding motor power output.Based on this, a process force with which the machining tool acts on the workpiece blank can be determined. Alternatively or additionally, the actual feed rate of the machining tool relative to the workpiece blank can be determined. Both methods make it possible to determine, at least approximately, the actual machining position on the workpiece.

[0022] The new method and device implement virtual measurement technology in that actual workpiece properties after machining are determined during machining using the signal profile and at least one vibration profile – in other words, they are "virtually measured." This virtual measurement makes it possible to measure a partially machined workpiece in situ and concurrently during the manufacturing process, utilizing workpiece properties known from previous machining operations. The machining tool effectively becomes a virtual measuring tool, and the new method and device use the measured values ​​obtained in this way during the ongoing manufacturing process to optimize further machining of the workpiece blank.Advantageously, a second machining position can be selected depending on the actual first machining position obtained in the described manner, for example by moving the machining tool to the second machining position with a modified control command.

[0023] The new process and device enable the production of a workpiece with very precisely arranged features. Advantageously, it eliminates the need for the interruption of the manufacturing process that was required in previous methods to measure a partially machined workpiece within the machine's work area. The new process and device thus enable higher production output when manufacturing workpieces with tightly toleranced features. The aforementioned problem is therefore completely solved.

[0024] In a preferred embodiment of the invention, a second current vibration profile along a second defined vibration axis, which lies transversely to the first defined vibration axis, is recorded during the machining of the workpiece blank at the first nominal machining position, wherein a partial further signal profile with a plurality of partial further instantaneous values ​​is determined, wherein the partial further instantaneous values ​​represent a directional component of the motor current along the second defined vibration axis, and wherein the actual first machining position is further determined using the partial further signal profile.

[0025] Preferably, a third current vibration profile is also recorded along a third defined vibration axis, wherein the third vibration axis is transverse and, in particular, orthogonal to the first and second vibration axes. Furthermore, a third partial signal profile is preferably determined, and the actual first machining position is further determined using the partial third signal profile.

[0026] The designs enable a more precise determination of the actual first machining position in several dimensions and thus an even more precise manufacturing of a workpiece with regard to dimensions, shape and position.

[0027] In a further embodiment, at least one vibration sensor is a multi-axis sensor that detects a multitude of current vibration profiles along a multitude of vibration axes that lie transversely to each other.

[0028] Alternatively, the at least one vibration sensor can incorporate a multitude of single-axis sensors. This design allows for very simple integration of the sensors for multi-axis process monitoring into a workpiece machining center. Advantageously, existing machines can also be easily retrofitted with this design. Another advantageous embodiment includes at least one vibration sensor on the machining tool and at least one further vibration sensor on the workpiece blank and / or the workpiece holder. This embodiment has the advantage that a difference between the respective vibration signal profiles can be calculated, preferably a difference with respect to each detected spatial axis. If the workpiece blank vibrates almost identically to the machining tool, this can indicate that no machining of the workpiece blank is taking place at that particular moment, and in particular, that no material is being removed.If, on the other hand, the workpiece did not vibrate at all, the entire vibration energy could be attributed to the machining process, in particular a cutting process.

[0029] In another embodiment, it includes at least one vibration sensor and at least one acceleration sensor.

[0030] This design enables a very cost-effective implementation, especially for multi-axis process monitoring.

[0031] In a further embodiment, the first signal waveform is captured with a first sampling rate, while the first actual vibration waveform is captured with a second sampling rate that is higher than the first sampling rate.

[0032] This design enables cost-effective information enrichment for process monitoring, while advantageously utilizing the capabilities of the machine control system for recording the motor current.

[0033] In a further embodiment, the partial second signal profile is determined with a multitude of interpolation values ​​between temporally successive partial instantaneous values, wherein at least one interpolation value from the multitude of interpolation values ​​interpolates two successive partial instantaneous values ​​depending on the first current vibration profile.

[0034] In this configuration, upsampling takes place, i.e., a computational increase in the sampling rate at which the signal is captured. This configuration enables higher resolution and thus an even more precise determination of the actual first machining position. In particular, the effects of individual cutting edges of a machining tool can be determined especially well with this configuration.

[0035] In a further embodiment, the workpiece machining machine has a spindle that rotates the machining tool relative to the workpiece blank, with the motor current driving the spindle.

[0036] Alternatively or additionally, the motor current, or another motor current, can cause a translational movement of the machining tool relative to the workpiece blank. Detecting vibrations in the area of ​​a motor spindle that rotates the machining tool relative to the workpiece blank enables particularly efficient quality control and production process optimization, since rotary movements occur very frequently during machining of workpieces and vibrations during rotary movements have a significant impact.

[0037] In a further embodiment, the machining tool has several cutting edges that engage with the workpiece blank during machining, whereby a characteristic value is determined depending on the partial second signal curve, which represents a potential discrepancy between the cutting edges, and where an error signal is generated depending on the characteristic value.

[0038] This design enables early detection of wear and / or damage to the machining tool, thus allowing for a determined decision to replace it early. Unnecessary tool changes based solely on qualitative criteria, such as the number of operating hours, can be advantageously avoided.

[0039] In a further embodiment, the determination of the partial second signal progression and / or the determination of the actual first processing position is carried out using a pre-trained AI model.

[0040] In this configuration, data is advantageously available that was acquired using one or preferably several production runs, whereby both vibration data and representative data on the respective motor currents were recorded. Preferably, the data also include measurement results and / or derived parameters that are representative of the product properties of the workpieces produced in the production runs. In particular, the measurement results and / or derived parameters can represent actual differences between a nominal machining position and an actual machining position.Using such data, an AI model (Artificial Intelligence model), such as a neural network, can be trained and then efficiently used to determine the actual initial machining position based on a current signal profile and at least one current vibration profile. In this way, the actual initial machining position can be determined very quickly during the course of an ongoing manufacturing process.

[0041] It is understood that the aforementioned features and those to be explained below can be used not only in the combination specified, but also in other combinations or alone, without leaving the scope of the present invention.

[0042] Exemplary embodiments of the invention are shown in the drawing and are explained in more detail in the following description, wherein Fig. 1 shows a schematic representation of an embodiment of the device, Fig. 2 a schematic representation with an exemplary course of a motor current, three simultaneous vibration courses and two partial motor current courses determined from them shows, Fig. Figure 3a shows, by way of example, a displacement in the Y direction (in µm) as a function of a cutting edge position of a tool with four cutting edges, which was detected using eddy current sensors. Fig. 3b the Fig. 3a shows the corresponding data from a vibration sensor, and Fig. 4. A flowchart showing an exemplary embodiment of a method for manufacturing a workpiece.

[0043] In Fig. Figure 1 is an embodiment of the new device, designated in its entirety by reference numeral 10. In this embodiment, the device 10 comprises a workpiece machining machine 12 with three motor-driven spindles in a work area, as well as a machine control 14, which in this case controls all three spindles. In other embodiments, the device 10 may comprise one or more separate workpiece machining machines, which are controlled individually or in combination by one or more machine control systems. Preferably, embodiments of the device 10 include at least one machining operation on workpieces.

[0044] The workpiece machining center 12 is depicted here as a multi-axis machine tool capable of performing various machining operations, such as cutting, milling, drilling, turning, grinding, and others. Examples of such machine tools are commercially available from a variety of suppliers, including Nakamura, DMG Mori Seiki, Chiron, Heller, and many others. In other embodiments, the workpiece machining center may have only one spindle, configured, for example, solely for turning or solely for milling and / or drilling workpieces.

[0045] Workpiece processing machines have at least one movable machine element, the movement of which is controlled by the machine control 14. In Fig. In Figure 1, the workpiece machining machine 12 has, for example, a first turning spindle 16, a second turning spindle 18 opposite the first turning spindle 16, and a drilling and milling spindle 20. The first turning spindle 16 has a first workpiece holder 22, typically in the form of a chuck. The second turning spindle 18 has a second workpiece holder 24. A bar-shaped workpiece blank 26 is clamped in the first workpiece holder 22. The turning spindle 16 incorporates a drive motor in a known manner and rotates the bar 26 about its longitudinal axis in a known manner. In this way, it enables turning operations with a turning tool 28, which can be moved along a path 30 relative to the workpiece holder 22 and the workpiece blank held therein. In principle, the turning tool 28 can be manually engaged with the workpiece blank 26 to machine the material.In preferred embodiments, however, the turning tool 28 is controlled by the machine control 14 along the path 30 via one or more additional drive motors (not shown here). The workpiece blank 26 can also be machined with several different turning tools, for example, with different cutting angles. In some embodiments, the workpiece machining machine 12 can have a tool turret equipped with a plurality of tools (not shown here).

[0046] The second turning spindle 18 enables turning of the workpiece blank 26 with a further turning tool 32, particularly after the workpiece blank 26 has been reclamped from the first workpiece holder 22 to the second workpiece holder 24. The milling spindle 20 carries a drilling or milling tool 34 in a known manner and enables further machining of the workpiece blank 26. This further machining can, in particular, include separating the partially machined workpiece blank 26 from the remaining bar and / or drilling and / or milling operations with the workpiece blank stationary. Alternatively or additionally, in further embodiments, a workpiece blank can be held in a fixed clamping on a workpiece table (not shown here) while it is machined with a machining tool.

[0047] In the embodiment according to Fig. In the 1, sensors 36 are arranged in the area of ​​each spindle. The sensors can also be arranged at other locations in the working area of ​​the workpiece machining machine 12, for example, in the area of ​​the tools 28, 32, 34. Here, the sensors each provide a time-resolved signal 38 that represents a vibration profile during the machining of the workpiece blank 26. The sensor signals 38 are supplied to the machine control 14. In some preferred embodiments, the sensors 36 include one or more acceleration sensors, each of which measures acceleration along a defined sensor axis x. iIn particularly preferred embodiments, the sensors 36 each include a triaxial accelerometer that provides corresponding acceleration signals with respect to three mutually orthogonal signal axes x1, x2, x3. The acceleration signals represent, in particular, a vibration during the machining of the workpiece blank along the respective signal axis (vibration axis) x1, x2, x3.

[0048] The machine control 14 generates one or more currents for machining the workpiece blank 26 in a manner known per se. In this embodiment, these currents are supplied as motor currents 40, 42, 44 to the drive motors in the spindles 16, 18, 20 and, if applicable, to other drive motors (not shown). The higher the respective motor current, the higher the torque and / or (depending on the load) the rotational speed or linear velocity that the drive motor transmits to the workpiece blank 26 and / or to the machining tool 28, 32, 34. As is known to those skilled in the art, the machine control 14 can have one or more control loops with which the respective instantaneous value of the respective drive current is individually adjusted depending on a control program.Advantageously, each control loop includes at least one sensor 46, 48, 50, with which current instantaneous values ​​of the respective motor current 40, 42, 46 can be recorded with temporal resolution in order to obtain a current motor current profile.

[0049] Fig. Figure 2 shows a schematic representation of an exemplary motor current waveform 52, thus a first signal waveform. The abscissa represents time t and the ordinate the motor current I. In preferred embodiments, instantaneous values ​​of the motor current I(t) are acquired at a sampling rate (represented here by a schematically indicated sampling interval ΔT) that corresponds to the sampling rate at which the control loops of the machine control 14 operate. In other words, the signal waveform 52 can be acquired in preferred embodiments using the control loops themselves and advantageously without additional current meters.

[0050] In some preferred embodiments, the respective machining position is set and controlled by stepper motors. Each stepper motor includes a discrete counter that allows for high-resolution acquisition and adjustment of the instantaneous motor position. The position control causes the motor to rotate to a specific position. The motor current required for this is measured. However, positional uncertainty results from bending and / or dynamics of the motor shaft and the tool. Therefore, the actual machining position on the workpiece blank 26 can only be estimated with a relatively large uncertainty based solely on the signal waveform 52. This is particularly true if the machining tool has multiple cutting edges, which is often the case with milling heads, for example.

[0051] Below signal waveform 52 are in Fig. Figure 2 schematically depicts three exemplary vibration profiles 54, 56, and 58, which were recorded simultaneously with the signal profile 52 during the machining of the workpiece blank and with respect to three vibration axes x1, x2, and x3 arranged transversely and, in particular, orthogonally to each other. Vibration profile 54, for example, shows a relatively strong vibration along the first vibration axis x1 with clearly measurable periodic fluctuations. These fluctuations could, for example, result from an interaction between the feed rate and the engagement of a cutting edge. Vibration profile 56 shows, for example, a slight but still measurable vibration along the second vibration axis x2. Vibration profile 58 shows, for example, a barely measurable or even non-measurable vibration along the third vibration axis x3.

[0052] According to one aspect of the new method, partial signal profiles 60, 62 are determined based on the signal profile 52 and the vibration profiles 54, 56, 58. The respective instantaneous values ​​of the partial signal profiles 60, 62 sum at each time t to the respective instantaneous value of the signal profile 52. ‖(P1(t),P2(t),P3(t))‖=PTotal(t)

[0053] Mathematically speaking, this represents a total power P Gesamt (t) is divided into several partial power curves, whereby the law of conservation of energy is observed (amplitude equation). Since the power correlates with the respective motor current drawn, the amplitude equation is given here in terms of the motor power.

[0054] Since the vibration with respect to the third vibration axis x3 is practically zero in this exemplary case, only two partial signal waveforms 60, 62 with respective non-zero instantaneous values ​​result. The same applies, of course, if the vibrations are determined with respect to only two vibration axes. In some embodiments, vibrations with respect to a plurality of axes, including one or more translational axes and / or one or more rotational axes, can be detected. Advantageously, in these embodiments, the signal waveform 52 can be divided into a corresponding plurality of partial motor current waveforms or corresponding partial power waveforms.

[0055] The partial signal waveforms advantageously represent a respective effective directional component of the total motor current or total power with respect to the respective vibration axes. In other words, the signal waveform 52 is thus divided here into partially direction-dependent signal waveforms 60, 62 using the vibration waveforms 54, 56, 58. This advantageously makes it possible to determine a process force occurring during the machining of the workpiece blank as a function of direction, even if the movement of the machining tool relative to the workpiece blank is generated with a total motor current that does not carry any directional information with respect to the machining of the workpiece blank.

[0056] The distribution of the total motor current can advantageously be based on the following relationship: ∬aiT1T2dt∼Pi(T2)−Pi(T1)

[0057] A double integration of the acceleration a iThe amplitude in an axial direction i between a first time T1 and a second time T2 is largely proportional to the difference in the direction-related power P at times T1 and T2 (directional relation). The amplitude equation primarily ensures the long-wavelength accuracy of the approximation, while the direction equation enables subsampling (dt). In other words, the direction relation provides support points for high-frequency interpolation of the enriched signals. In some preferred embodiments, the vibration profiles with respect to the vibration axes can be acquired at a higher sampling rate than the signal profile. This provides more support points for determining the partial signal profiles than the overall signal profile offers.The partial signal profiles can therefore be advantageously determined with a higher number of respective instantaneous values ​​than the number of instantaneous values ​​recorded for the overall signal profile.

[0058] If the underlying mathematical problem cannot be uniquely solved, Occam's razor (the principle of parsimony) can be used to find a solution. This involves, for example, searching for sparse (and therefore simple) solutions.

[0059] Fig. Figure 3a shows an example of a displacement 64 in the Y-direction as a function of the cutting edge position of a rotating tool with four cutting edges. In this case, the displacement 64 was detected using eddy current sensors. Fig. Figure 3b shows corresponding data 66, which were recorded using a vibration sensor. The acceleration values ​​were integrated twice. Fig. 3b can the relocation 64 from Fig. 3a. Measurement errors are also integrated. Therefore, it is advantageous to consider the motor power P. The motor power, and thus the motor current, correlates with the machining force, which in turn correlates with the magnitude of the displacement (deviation from the center of rotation). Advantageously, the instantaneous amplitude of the displacement can be determined from the instantaneous power, and the instantaneous direction of the displacement can be determined from the vibration data. Thus, there is a direction relationship and an amplitude equation.

[0060] Fig.Figure 4 shows an embodiment of the method for manufacturing a workpiece. According to step 70, a data set 72 is first obtained, representing the desired workpiece properties of a new workpiece to be manufactured. This can be a CAD data set, a CAM data set, or a data set with control commands for the machine control 14, for example, a data set with control commands in the form of M-codes and / or G-codes. Based on the data set, a first nominal machining position on a workpiece blank is selected according to step 74. In preferred embodiments, the first machining position has a very tight tolerance with respect to a further machining position on the workpiece blank. Subsequently, the workpiece blank is machined at the first machining position with a tool according to step 76.Simultaneously, vibration signals relating to one or more vibration axes are acquired with temporal resolution according to step 78, and the motor current with which the machining tool is moved relative to the workpiece blank is acquired according to step 80. Advantageously, the motor current is acquired with a first sampling rate that corresponds to the sampling rate in the control loop of the machine control system. Preferably, the vibration signals are acquired with a second sampling rate that is higher than the first sampling rate in the control loop of the machine control system.

[0061] Based on the vibration signals acquired in step 78 and the motor current acquired in step 80, partial motor current waveforms are determined in the manner described above, according to step 82. In some embodiments, a corresponding partial signal waveform is determined for each vibration axis for which a vibration signal was acquired.

[0062] Advantageously, in some embodiments, a process force acting in the respective vibration direction can be determined based on the partial motor current profiles, as indicated in the aforementioned publication by Brecher, Eckel, Fey, and Butz. According to step 84, in some embodiments where the machining tool has multiple cutting edges, a characteristic value can be determined using the partial motor current profiles and / or the direction-related process forces. This value is representative of any discrepancy in the machining of the workpiece blank with the different cutting edges. If the discrepancy is too large, which may be the result of a damaged cutting edge, for example, a fault signal is generated in the preferred embodiments. This signal prompts a machine operator to check and, if necessary, replace the machining tool.

[0063] In step 86, an actual first machining position is determined based on the partial motor current profiles and, if applicable, on the process forces determined in the respective vibration direction. The actual first machining position may differ from the previously selected nominal machining position, for example, due to wear of the machining tool, environmental influences, and / or individual material properties of the workpiece blank.

[0064] In step 88, a modified path and / or a modified second machining position are determined based on the actual first machining position. The modified path and / or modified second machining position may differ from a nominal path and / or nominal second machining position. The nominal path and / or nominal second machining position are typically derived from data set 72. The modified path and / or modified second machining position are advantageously adapted to the actual first machining position. This is particularly beneficial when the nominal first and nominal second machining positions are defined with tight tolerances relative to each other. The modified path and / or modified second machining position advantageously contribute to ensuring that the tolerances with respect to the actual first machining position can be maintained.According to step 90, the workpiece blank is then machined at the modified second machining position and / or with the modified path curve at the second machining position.

[0065] In preferred embodiments, the method and the device enable upsampling of the sampling rate at which instantaneous motor current values ​​are available in a conventional machine control system, in order to better resolve the effects of individual cutting edges, and furthermore, dimensional enrichment with respect to individual spatial directions. For example, a 1D (unidirectional) motor current time series is transformed into a 3D displacement time series using a triaxial accelerometer. This dimensionality is only an example here and can be further increased with appropriate hardware, in particular to three rotational and / or three translational degrees of freedom.

[0066] It is understood that the described process can be extended to a large number of first and second machining positions on a workpiece blank, so that the workpiece ultimately produced largely meets the desired specifications.

Claims

[1] Method for producing a workpiece from a workpiece blank (26), comprising the steps: - Providing a workpiece machining machine (12) with a workpiece holder (22) configured to hold the workpiece blank (26), with a machining tool (28, 34) movable relative to the workpiece holder (22), with a drive motor (16) configured to move the machining tool (28) relative to the workpiece holder (22) depending on an supplied motor current, with a machine control (14) configured to generate the motor current, and with at least one vibration sensor (36) configured to detect a time-resolved signal (38) representing a vibration profile during the machining of the workpiece blank (26), - Obtaining (70) a data set representing nominal workpiece properties of the workpiece, - Machining (76) the workpiece blank (26) with the machining tool (28) at a first nominal machining position, wherein the machine control (14) controls the motor current depending on the data set, - Acquiring (80) a first signal waveform (52) which exhibits a plurality of temporally successive instantaneous values ​​during the machining of the workpiece blank (26) at the first nominal machining position, wherein the instantaneous values ​​represent an instantaneous motor current, - Recording (78) a first current vibration profile (54) along a first defined vibration axis (x1) during the machining of the workpiece blank (26) at the first nominal machining position using the at least one vibration sensor (36), - Determining (82) a partial second signal waveform (60) comprising a plurality of temporally successive partial instantaneous values ​​during the machining of the workpiece blank (26) at the first nominal machining position, wherein the partial instantaneous values ​​represent an effective directional component of the instantaneous motor current along the first defined vibration axis (x1), - Determining (86) an actual first processing position using the partial second signal waveform (60), and - Machining (90) of the workpiece blank (26) at at least a second machining position depending on the data set and depending on the actual first machining position. [2] Method according to claim 1, wherein a second current vibration profile (56) is detected along a second defined vibration axis (x2) which lies transversely to the first defined vibration axis (x1) during the machining of the workpiece blank (26) at the first nominal machining position, wherein a partial further signal profile (62) is determined with a plurality of partial further instantaneous values, wherein the partial further instantaneous values ​​represent an effective directional component of the motor current along the second defined vibration axis (x2), and wherein the actual first machining position is further determined using the partial further signal profile (62). [3] Method according to claim 1 or 2, wherein the at least one vibration sensor (36) is a multi-axis sensor that detects a plurality of current vibration profiles (54, 56, 58) along a plurality of vibration axes (x1, x2, x3) that are transverse to each other. [4] Method according to any one of claims 1 to 3, wherein the at least one vibration sensor (36) includes at least one acceleration sensor. [5] Method according to any one of claims 1 to 4, wherein the first signal waveform (52) is captured with a first sampling rate, and wherein the first actual vibration waveform (54) is captured with a second sampling rate which is higher than the first sampling rate. [6] Method according to any one of claims 1 to 5, wherein the partial second signal profile (60) is determined with a plurality of interpolation values ​​between successive partial instantaneous values, wherein at least one interpolation value from the plurality of interpolation values ​​interpolates two successive partial instantaneous values ​​depending on the first current vibration profile (54). [7] Method according to any one of claims 1 to 6, wherein the workpiece machining machine (12) has a spindle (16, 18, 20) which rotates the machining tool (28, 32, 34) relative to the workpiece blank (26), and wherein the motor current drives the spindle (16, 18, 20). [8] Method according to any one of claims 1 to 7, wherein the machining tool (34) has several cutting edges which engage with the workpiece blank (26) during machining, wherein a characteristic value is determined as a function of the partial second signal curve (60) which represents a potential discrepancy between the cutting edges, and wherein an error signal (84) is generated as a function of the characteristic value. [9] Method according to any one of claims 1 to 8, wherein the determination of the partial second signal profile (60) and / or the determination (86) of the actual first processing position is carried out using a pre-trained AI model. [10] Device for producing a workpiece from a workpiece blank (26), with - a workpiece holder (22) designed to hold the workpiece blank (26), - a machining tool (28) that is movable relative to the first workpiece holder (22), - a drive motor (16) which is designed to move the machining tool (28) relative to the workpiece holder (22) depending on a supplied motor current (40), - a machine control (14) which is configured to generate the motor current (40), and - at least one vibration sensor (36) configured to detect a time-resolved signal (38) representing a vibration profile during the machining of the workpiece blank (26), wherein the machine control (14) is further configured to perform the following process steps: - Obtaining (70) a data set representing nominal workpiece properties of the workpiece, - Generating the motor current (40) depending on the data set for machining (76) the workpiece blank (26) with the machining tool (28) at a first nominal machining position, - Acquiring (80) a first signal waveform (52) which exhibits a plurality of temporally successive instantaneous values ​​during the machining of the workpiece blank (26) at the first nominal machining position, wherein the instantaneous values ​​represent an instantaneous motor current, - Recording (78) a first current vibration profile (54) along a first defined vibration axis (x1) during the machining of the workpiece blank (26) at the first nominal machining position using the at least one vibration sensor (36), - Determining (82) a partial second signal waveform (60) comprising a plurality of temporally successive partial instantaneous values ​​during the machining of the workpiece blank (26) at the first nominal machining position, wherein the partial instantaneous values ​​represent an effective directional component of the motor current (40) along the first defined vibration axis (x1), - Determining (86) an actual first processing position using the partial second signal waveform (60), and - Machining (90) of the workpiece blank (26) at at least a second machining position depending on the data set and depending on the actual first machining position. [11] Computer program with program code configured to execute a method according to any one of claims 1 to 9 when the program code is executed on a machine control (14) of a device (12) according to claim 10.

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