Method and device for controlling an ultrasonic tool unit for machining on a machine tool

Abstract

Device for controlling an ultrasonic tool unit for machining a workpiece (WS) on a machine tool (1000), comprising: a control device (1120) for controlling an ultrasonic transducer (20) of the ultrasonic tool unit mounted on a work spindle (1040) of the machine tool for machining a workpiece (WS) on the basis of a sensor signal input into a controller (1123) by means of a generator (1124) operated by the controller (1123), on the basis of a first parameter set assigned to the ultrasonic tool unit and setting the operation of the controller (1123), characterized in that the control device comprises a memory device (1121) for storing a plurality of parameter sets adjusting the operation of the controller (1123), and the control device is configured such that an operating setting of the controller (1123) can be switched by changing the first parameter set setting the operation of the controller (1123) on the basis of a second parameter set assigned to the ultrasonic tool unit from the plurality of parameter sets stored in the storage device (1121).

Description

[0001] The present invention relates to a method and a device for controlling an ultrasonic tool unit for machining a workpiece on a machine tool. BACKGROUND OF THE INVENTION

[0002] In the state of the art, machine tools are known in which, during machining of a workpiece by a tool, an ultrasonic vibration of the tool can be superimposed on the rotational movement of the tool.

[0003] For example, DE 10 2016 214 699 A1 discloses a method for machining a workpiece on a numerically controlled machine tool using a tool. Using a sensor signal emitted by an ultrasonic generator, a material change on the workpiece can be detected during a relative movement between the tool and the workpiece.

[0004] DE 10 2012 219 254 A1 relates to a method for machining a workpiece, wherein a cutting tool is guided relative to the workpiece and a vibration is superimposed with an amplitude of at least 5 µm. A supply circuit for a piezo actuator of a vibrating tool generates a voltage at the voltage output with a DC component and an AC component.

[0005] DE 10 2011077 568 A1 discloses another method for machining a workpiece with a tool, in which the tool engages the workpiece, creating a cutting motion between the two. A relative first vibration motion superimposed on the cutting motion is created between the workpiece and the tool in such a way that one or more characteristic values ​​of the first vibration motion and one or more characteristic values ​​of the cutting motion are adjusted relative to one another. The superimposed vibration motion can also be created in such a way that distinguishable surface areas of the workpiece are created.

[0006] DE 10 2007 013 055 A1 discloses a method for determining a frequency characteristic of an electrically controllable ultrasonic tool, comprising the steps of applying an electrical noise signal as a control signal to the tool, measuring the temporal course of an electrical variable on the ultrasonic tool as a measurement signal, carrying out a frequency analysis in the measured course, and determining the frequency characteristic based on the analysis result.

[0007] In this context, EP 1 763 416 B1 describes a tool with a tool holder which has a tool holder receptacle for adaptation to a rotatable spindle nose at a first end and a tool receptacle at a second end opposite the first end, and with a tool head which can be inserted into the tool receptacle, wherein the tool holder comprises a vibration motor.

[0008] In such a machine tool, an ultrasonic transducer in the tool holder, which generates the ultrasonic vibration of the tool, a vibrating body and the tool inserted in the tool holder form an oscillating system that is excited to mechanical vibrations by an electrical signal, whereby the largest possible mechanical vibration amplitude is obtained when the oscillating system is excited at its resonance frequency.

[0009] The problem here is that the resonance frequency can change during a machining process. There are essentially three reasons for this. Firstly, the vibrating system or parts of it can heat up during machining, causing the material properties to change. This leads to a temperature drift of the resonance frequency. Secondly, the vibration is dampened by the machining forces when the tool comes into contact with the workpiece, whereby the resonance frequency of the system in the case of a damped vibration is lower than the free resonance frequency of the system. In addition, the coupling of the vibration system to the workpiece creates a new, coupled vibration system whose resonance frequency is usually higher than the free resonance frequency. In practice, these three effects occur in combination, although the dominant effect depends on the specific machining situation.

[0010] It should also be noted that in addition to the shift in the resonance frequency, a change in power also plays a role, since the interaction of the tool with the workpiece may require a higher output voltage to achieve the same power.

[0011] If the free resonance frequency is used for excitation, but the actual resonance frequency of the system differs from this during machining, the tool will oscillate with a smaller amplitude, which will reduce the efficiency of the machining process.

[0012] For this reason, it is important to detect a change in the resonance frequency of the oscillating system in order to be able to adjust the oscillation parameters accordingly so that the largest possible oscillation amplitude is achieved again.

[0013] From ultrasonic welding applications, it is known that for this purpose both the free resonance frequency and a change in the resonance frequency of the system can be determined from output values ​​of the generator, which supplies the electrical signal for the mechanical vibration to the piezo drive in the tool holder. The generator receives an electrical impedance from the vibrating system connected via an inductive transmitter path. This electrical impedance is frequency-dependent and has a minimum at the mechanical resonance frequency. Accordingly, if the resonance frequency shifts, the generator adjusts its frequency until it reaches the impedance minimum again. In addition to the frequency of the impedance minimum, the processing also changes the impedance value itself, i.e. to drive the same power, a higher output voltage is necessary.

[0014] However, this method is not suitable for machining because, unlike with ultrasonic welding, the impedance curves of the sonotrodes used and the tools employed are much more complex: On the one hand, there are significantly more impedance minima due to the many different vibration modes of the complexly shaped tools. On the other hand, the influencing factors that cause a shift in the resonance frequency are more extreme in their effect, i.e. the frequency shift can be so large that further impedance minima are skipped. During welding, a sonotrode exerts approximately the same pressure on the workpiece throughout the entire process. This leads to a one-off frequency shift that remains the same for recurring processes and for which the impedance minimum can always be clearly identified.In contrast, the frequency shift during machining changes continuously due to changing engagement conditions of the tool in the material and, as described above, the assignment is often no longer possible solely on the basis of an impedance measurement.

[0015] This is due to the fact that a large number of differently shaped tools are used, for example, drills and milling cutters of different dimensions and cutting tools with different cutting edge geometries, which leads to a greater variance in the shape of the impedance curve compared to ultrasonic welding. Furthermore, during machining, the force acting on the vibrating system is generally significantly greater, so the change in the impedance curve is much more pronounced.

[0016] In addition, due to the repetitive processing steps involved in welding, the dominant frequency shift effect can be easily predicted, which limits the system's possible responses. In contrast, in machining, all effects must be considered, which is why the prediction options or the options for restricting the control parameters are insufficient.

[0017] Furthermore, it is not possible to distinguish bending vibrations or similar from axial vibration modes based solely on impedance measurements. Likewise, there are purely electrical resonances that do not generate any vibrations at all. These parasitic effects cannot be detected using current methods.

[0018] Another problem with monitoring vibration based on generator power is that it is unknown what proportion of the power actually goes into generating vibration and what proportion goes into other processes, such as heating the components involved. Therefore, it is possible that changes in vibration may not be detected because the proportion of the power supplied by the generator that goes into generating vibration changes, but not the total power output by the generator.

[0019] In light of the above considerations, a generic method for controlling an oscillatory system was described in DE 10 2015 212 809 A1, in particular by controlling the generator by determining the resonance frequency and controlling on the basis of the determined resonance frequency.

[0020] Based on the above prior art and in view of the above considerations, it is an object of the present invention to further develop the generic method in order to provide improved control of the oscillatory system, which can be better adapted to different processing conditions.

[0021] In particular, it is an object of the present invention to provide a method which makes it possible to achieve a higher machining accuracy in the ultrasonic machining of a workpiece under different or changing machining conditions. SUMMARY OF THE INVENTION

[0022] To achieve the above objects, the subject matter of the independent claims is proposed. The dependent claims relate to advantageous embodiments of the method according to the invention and the devices according to the invention.

[0023] According to embodiments, a device for controlling an ultrasonic tool unit for machining a workpiece on a machine tool is proposed, comprising a control device for controlling an ultrasonic transducer of the ultrasonic tool unit mounted on a work spindle of the machine tool for machining a workpiece on the basis of a sensor signal input into a controller by means of a generator operated by the controller, on the basis of a first parameter set assigned to the ultrasonic tool unit and setting the operation of the controller.

[0024] The control device preferably comprises a memory device for storing a plurality of parameter sets. The control device is preferably configured to switch an operating setting of the controller by changing the first parameter set that sets the operation of the controller based on a second parameter set assigned to the ultrasonic tool unit from the plurality of parameter sets stored in the memory device.

[0025] According to a preferred embodiment, the control device is configured to switch the operating setting of the controller during machining of the workpiece.

[0026] According to a preferred embodiment, the control device is configured to switch the operating setting of the controller when the type of machining of the workpiece changes.

[0027] According to a preferred embodiment, the first parameter set is assigned to a first processing type of a plurality of processing types and preferably the second parameter set is assigned to a second processing type of the plurality of processing types.

[0028] Preferably, the majority of machining operations include milling and drilling.

[0029] According to a preferred embodiment, the control device is configured to switch an operating setting of the controller by changing a parameter set assigned to the ultrasonic tool unit on the machine tool with another ultrasonic tool unit on the basis of a parameter set assigned to the other ultrasonic tool unit from the plurality of parameter sets stored in the memory device.

[0030] According to a preferred embodiment, the control device is configured to switch an operating setting of the controller by changing a parameter set assigned to the tool on the basis of a parameter set assigned to the other tool from the plurality of parameter sets stored in the memory device when a tool on the ultrasonic tool unit on the machine tool is replaced with another tool.

[0031] According to a further exemplary embodiment, a machine tool with a work spindle for receiving an ultrasonic tool unit and a device for controlling the ultrasonic tool unit for machining a workpiece on the machine tool according to one of the above aspects is proposed.

[0032] According to embodiments, a method for controlling an ultrasonic tool unit for machining a workpiece on a machine tool is also proposed, comprising controlling an ultrasonic transducer of the ultrasonic tool unit mounted on a work spindle of the machine tool for machining a workpiece on the basis of a sensor signal input into a controller by means of a generator operated by the controller, on the basis of a first parameter set assigned to the ultrasonic tool unit and setting the operation of the controller.

[0033] Preferably, the method comprises storing or saving a plurality of parameter sets in a storage device of a control device of the machine tool.

[0034] Preferably, the method comprises switching an operating setting of the controller by changing the first parameter set that sets the operation of the controller on the basis of a second parameter set assigned to the ultrasonic tool unit from the plurality of parameter sets stored in the memory device.

[0035] According to a preferred embodiment, the switching of the operating setting of the controller is carried out during machining of the workpiece.

[0036] According to a preferred embodiment, the switching of the operating setting of the controller is carried out when the machining type of the workpiece is changed.

[0037] According to a preferred embodiment, the first parameter set is assigned to a first processing type of a plurality of processing types and preferably the second parameter set is assigned to a second processing type of the plurality of processing types.

[0038] According to a preferred embodiment, the plurality of machining types may include milling and drilling.

[0039] According to a preferred embodiment, the method comprises exchanging the ultrasonic tool unit on the machine tool with another ultrasonic tool unit and switching an operating setting of the controller by changing a parameter set assigned to the ultrasonic tool unit on the basis of a parameter set assigned to the other ultrasonic tool unit of the plurality of parameter sets stored in the memory device.

[0040] According to a preferred embodiment, the method comprises exchanging a tool on the ultrasonic tool unit on the machine tool with another tool and switching an operating setting of the controller by changing a parameter set assigned to the tool on the basis of a parameter set assigned to the other tool from the plurality of parameter sets stored in the memory device.

[0041] Further aspects and their advantages as well as advantages and more specific embodiments of the aspects and features described above are described in the following, but in no way limiting, descriptions and explanations of the attached figures. BRIEF DESCRIPTION OF THE CHARACTERS Fig. 1 shows an example of a tool holder in sectional view which can be used in the method according to the invention. Fig. 2 shows an example of a part of a machine tool with which the method according to the invention can be carried out. Fig. 3 shows an example electrical impedance curve. Fig. 4 shows schematically an exemplary embodiment of a device according to the invention. Fig. 5 shows an example frequency spectrum. Fig. 6 shows an embodiment of a device according to the invention. Fig. 7 shows, by way of example, a schematic representation of a machine tool with a tool holder (tool head), which can be used in the method according to the invention according to embodiments. Fig. Figure 8 shows examples of different impedance and phase curves depending on the frequency. Fig. 9A and Fig. 9B shows examples of different impedance and phase curves depending on the frequency. DETAILED DESCRIPTION OF THE FIGURES AND PREFERRED EMBODIMENTS OF THE PRESENT INVENTION

[0042] Examples and embodiments of the present invention are described in detail below with reference to the accompanying figures. Identical or similar elements in the figures may be designated by the same reference numerals, although sometimes different reference numerals may be used.

[0043] It should be emphasized, however, that the present invention is in no way limited or restricted to the exemplary embodiments and their embodiment features described below, but further comprises modifications of the exemplary embodiments, in particular those which are encompassed by modifications of the features of the described examples or by combination of one or more of the features of the described examples within the scope of protection of the independent claims.

[0044] Fig. 1 shows an exemplary structure of a tool holder 10 that can be used in the method according to the invention. At one end of the tool holder 10, there is, for example, a tool receiving section 11 for receiving a tool 90 (not shown).

[0045] In the tool holder 10, several, for example six, perforated disk-shaped first piezo elements 21 are stacked, which are connected, for example, via a transmission section 12 to the tool receiving section 11 and form an ultrasonic transducer 20 for converting an electrical voltage into a mechanical vibration.

[0046] The mechanical vibration of the first piezo elements 21 is transmitted, for example, to the tool 90 via the transmission section 12. The first piezo elements 21 can be designed, for example, as piezoceramic discs with electrodes arranged between them. The energy supply to the ultrasonic transducer 20 is provided, for example, via a transformer (first transformer) which, on the machine side, comprises a first pot core 31 and a primary winding 32 (not shown) and, on the tool side, comprises a second pot core 33 and a secondary coil 34, which are arranged, for example, as ring elements on the outside of the tool holder 10.

[0047] On a side of the stack of first piezo elements 21 facing away from the tool holding section 11, a perforated disk-shaped piezoelectric sensor element 40 is arranged, for example, which is mechanically coupled to the first piezo elements 21 but is electrically insulated from the first piezo elements 21 by an insulating element 43, which can be designed as a ceramic perforated disk. The piezoelectric sensor element 40 is electrically insulated, for example, from a fastening element 13, e.g., a fastening nut, by a further insulating element 43. The fastening element 13 serves, for example, to fasten the piezoelectric sensor element 40 to the ultrasonic transducer 20 and to prestress the first piezo elements 21 due to the dynamic load.

[0048] The first piezo elements 21 and the piezoelectric sensor element 40 are, for example, oriented in the same way, which on the one hand enables the generation and detection of the vibration in the same direction and on the other hand achieves a space-saving arrangement of the elements in the tool holder 10.

[0049] The piezoelectric sensor element 40 converts the mechanical vibrations of the vibratory system, which comprises the tool 90, the transmission section 12, the ultrasonic transducer 20 and the piezoelectric sensor element 40, into a sensor signal S2, which can be transmitted as an electrical voltage via a wire connection 50 from the piezoelectric sensor element 40 through the tool holder 10 to a transmitter element 60 on the outside of the tool holder 10.

[0050] From the transmitter element 60, the sensor signal S2 is transmitted contactlessly to a machine-side receiver element 80 (not shown). The transmitter element 60 is part of another transformer (second transformer) and comprises a first ferrite core 61 and a primary winding 62; the receiver element 80 is also part of the second transformer and comprises a second ferrite core 81 and a secondary winding 82. Thus, the sensor signal S2 can be transmitted inductively from the tool holder 10 to a machine-side sensor signal evaluation device 110 (not shown). Alternatively, optical transmission is also possible, with the transmitter element 60 being designed as an LED and the receiver element 80 as a photodiode. The transmitter element 60 can be dimensioned and positioned such that it fits into a bore 70 for a data chip for tool data according to the DIN 69893 standard.The tool holder 10 can be rotatable relative to a stationary part of the machine tool (not shown).

[0051] In Fig. 2 shows an example of an arrangement of the energy transmission device 30 for transmitting the energy for the ultrasonic transducer 20 into the tool holder 10 in the form of a working signal S1 and the arrangement of the transmitter element 60 and the receiver element 80 for transmitting the sensor signal S2 from the tool holder 10 as a sectional view.

[0052] The energy transmission device 30 is designed, for example, as a transformer (first transformer) with a first pot core 31, a primary winding 32, a second pot core 33 and a secondary winding 34, wherein the openings of the pot cores 31, 33 face one another, for example, and the windings 32, 34 are arranged, for example, in the respective pot cores 31, 33. The second pot core 33 is arranged, for example, in a ring shape on the tool holder circumference; the first pot core 31 is positioned, for example, at a distance in the axial direction from the second pot core 33 in a machine-side housing 100 and is arranged, for example, as a ring segment or as a full ring around the tool holder 10. The working signal S1 is thus, for example, in the axial direction (in Fig. 2 from top to bottom) is transmitted inductively from the primary winding 32 to the secondary winding 34.

[0053] The receiver element 80 is also located in the housing 100, for example. The transmitter element 60 is arranged at a distance from the receiver element 80, for example in a bore 70 on the tool holder 10. The sensor signal S2 is thus transmitted, for example, in the radial direction (in Fig. 2 from left to right) is transmitted contactlessly from the transmitter element 60 to the receiver element 80. Multiple transmitter elements 60 can also be arranged circumferentially on the tool holder 10 in order to reduce signal losses during the transmission of the sensor signal S2 during rotation of the tool holder 10. Likewise, multiple receiver elements 80 can be arranged opposite the transmitter element 60 or the transmitter elements 60.

[0054] During the rotation of the tool holder 10, the second pot core 33 and the secondary winding 34 of the energy transmission device 30 as well as the transmitter element 60 rotate with the tool holder 10, while the housing 100 with the first pot core 31 and the primary winding 32 of the energy transmission device 30 as well as with the receiver element 80 is mounted, for example, on the tool spindle (not shown) and does not rotate.

[0055] In the following, the behavior of the oscillatory system during a machining process is illustrated using the example of Fig. 3. The oscillatory system, which in one embodiment of the invention comprises the ultrasonic transducer 20 as a piezo drive, the transmission section 12, the tool 90 inserted into the tool receiving section 11, the piezoelectric sensor element 40 for generating a sensor signal S2, and the fastening element 13 for the piezoelectric sensor element 40, is excited to a mechanical oscillation by an operating signal S1 generated by a generator 120, which is transmitted to the ultrasonic transducer 20 via the energy transmission device 30. The operating frequency f1 of the operating signal S1 determines the frequency of the mechanical oscillation; the power P1 output by the generator 120 determines the oscillation amplitude.For a given power P1, the vibration amplitude is maximum at the resonance frequency f2 of the oscillating system, where the resonance frequency f21 of the free vibration of the system usually differs from the resonance frequency f22 of the system during machining.

[0056] Fig. Figure 3 shows exemplary electrical impedance curves that generator 120 sees from the oscillating system connected via the first transformer 31-34 as an inductive transmitter path. The impedance curve of the free oscillation exhibits an impedance maximum (series resonance) at a lower frequency and an impedance minimum (parallel resonance) at a higher frequency. The position of the impedance minimum corresponds to the resonant frequency f21 of the free oscillation.

[0057] During machining, the generator 120 sees a changed impedance curve with less pronounced extremes. In addition, the minimum is shifted compared to the minimum during free vibration. Fig. 3, the minimum is shifted toward higher frequencies during machining, i.e., in the example shown, the resonance frequency f22 during machining is higher than the resonance frequency f21 of the free vibration. However, it is also possible that the resonance frequency f22 becomes lower than the resonance frequency f21 of the free vibration during machining. Which case occurs and how much the resonance frequency changes depends on the influence of the damping caused by the machining forces, the heating of the system during machining, and the resonance behavior of the coupled vibration systems involved.

[0058] The free resonance frequency f21 can be determined from output values ​​of the generator 120, which supplies the working signal S1 for the piezo drive, or with the aid of the method according to the invention, which is described below with reference to Fig. 4, before the tool 90 enters the workpiece, and is used as an estimate for a working frequency f1 with which the largest possible vibration amplitude is achieved. The method according to the invention is used to detect a change in the resonance frequency f2 during machining, the value of which can then be used to bring the working frequency f1 closer to the actual resonance frequency f2 or to increase the power of the working signal S1 so that the original amplitude is again achieved.

[0059] Fig. Figure 4 schematically shows an embodiment of a device according to the invention with which the method according to the invention can be carried out. The device can be part of a machine tool. Shown is a tool holder 10 with a sensor element 40, the structure of which corresponds to that shown in Fig. 1. A tool 90 for ultrasonic machining of workpieces is mounted on the tool holder 10.

[0060] A generator 120 outputs an operating signal S1 as a drive signal for the piezo drive in the tool holder 10. The operating signal S1 has the operating frequency f1 and is transmitted contactlessly into the rotating tool holder 10 with the power P1 via the energy transmission device 30, which is designed as a transformer comprising the primary winding 32 including the first pot core 31 and the secondary winding 34 including the second pot core 33. In addition, the generator 120 outputs, for example, a test signal St with a power Pt. <P1 aus, das dem Arbeitssignal S1 überlagert wird und dessen Frequenz in einem Bereich um f1 variiert.

[0061] Due to the signals S1 and St, the oscillating system in the tool holder 10 is excited to oscillate, the frequency spectrum of which essentially has two frequencies. An example frequency spectrum is shown in Fig. 5. The larger peak in the frequency spectrum results from the forced oscillation of the system, which is excited at the operating frequency f1 at a relatively high power P1. The smaller peak results from the forced oscillation of the system, which is excited at a frequency varying around f1, but with such low power Pt that this oscillation decays very quickly at all frequencies except the instantaneous resonant frequency f2 of the system due to damping.

[0062] Due to the vibration of the oscillatory system, the piezoelectric sensor element 40 also vibrates in the same way, thus generating an electrical sensor signal S2 containing information about the frequency spectrum of the vibration. The sensor signal S2 is read out of the rotating tool holder 10 via a further transformer, which includes the primary winding 62 including the first ferrite core 61 and the secondary winding 82 including the second ferrite core 81, without contact by a readout device 130 and transmitted to an analysis device 140a.

[0063] The analysis device 140a determines, for example, the frequencies contained in the frequency spectrum of S2, so that in a device for determining the resonant frequency 140b, which can be implemented as part of the analysis device 140a, the frequency of the largest peak in the spectrum (main frequency) can be assigned to the operating frequency f1, and the frequency of the smaller peak in the spectrum (secondary frequency) can be assigned to the resonant frequency f2. The readout device 130, the analysis device 140a, and the device for determining the resonant frequency 140b can also be combined into two devices or implemented as a single device.

[0064] The value of the determined resonance frequency f2 is transmitted to a first control device 150, which controls the generator 120 such that the frequency f1 of the working signal S1 is adjusted to the value of the resonance frequency f2.

[0065] Alternatively or additionally, the value of the determined resonance frequency f2 can be transmitted to a second control device 160, which controls the generator 120 such that the power P1, with which the working signal S1 is radiated into the tool holder 10, is increased to a power P1', so that even with an excitation with f1≠f2, the mechanical vibration amplitude is reached which would be reached as the maximum amplitude with an excitation with the resonance frequency f2.

[0066] In this way, the mechanical vibration amplitude of the tool tip can be stabilized at a specific value, which has a positive effect on the precision of machining with the tool 90. Stabilizing the vibration amplitude at the maximum possible value for a given power also increases the efficiency of workpiece machining.

[0067] Via a user interface 170, a user of the device can control the first control device 150 and / or the second control device 160 so that the operating signal S1 is adjusted only upon user command or upon the occurrence of a specified condition. The user can also specify that the operating signal S1 be adjusted automatically at regular or irregular intervals based on the most recently determined resonance frequency f2.

[0068] The generator 120, the readout device (or detection device) 130, the analysis device 140a and the first control device 150 can be combined to form a device 200 for outputting output signals and receiving input signals, wherein a first output signal of this device 200 corresponds to the working signal S1, a second output signal to the test signal St, and an input signal to the sensor signal S2.

[0069] Fig. Figure 6 shows a circuit diagram of the previously described components with an exemplary compensation circuit. It shows the equivalent circuit of the piezo drive in the tool holder 10, the first transformer 31-34 with the primary winding 32 on the left and the secondary winding 34 on the right, and the ultrasonic generator 120. On the machine side, a capacitor 180 is connected in parallel with the transformer 31-34, the value of which can be changed via a relay 190 (not shown).

[0070] Depending on the phase shift between voltage and current, reactive power flows back and forth between generator 120 and tool holder 10. This reactive power performs no mechanical work and only contributes to system heating. The reactive power can be compensated by capacitance 180. However, since the compensated electrical impedance also has a frequency response, compensation only works sufficiently well for small changes in the operating frequency f1 while maintaining a constant value of capacitance 180. In the event of a large change or a large deviation of the resonant frequency f2 from the operating frequency f1, the value of capacitance 180 is switched accordingly by a relay 190.

[0071] The compensation circuit can be designed as a parallel circuit, a series circuit or a combination circuit of capacitances and / or inductances and can be switched by a relay 190.

[0072] Fig. 7 shows, by way of example, a schematic representation of a machine tool 1000 according to an embodiment of the invention, with a tool holder 10 (tool head), which can be used in the method according to the invention according to embodiments.

[0073] The machine tool 1000 can be configured, for example, as a numerically controlled milling machine, a numerically controlled universal milling machine, or a numerically controlled machining center. To control a relative movement between the tool and the workpiece, the machine tool can have a plurality of controllable linear axes (usually referred to as the X-axis, Y-axis, and / or Z-axis, for example) and / or one or more circular or rotary axes (usually referred to as the A-axis, B-axis, and / or C-axis, for example).

[0074] For example, the machine tool 1000 in Fig. 7 a machine bed 1010, a machine stand 1020 and a spindle head 1030, wherein the machine bed 1010 carries, for example, a workpiece table 1050 and the spindle head 1030 carries, for example, a work spindle 1040.

[0075] The tool table 1050 is mounted, for example, on horizontal linear guides 1051 arranged in a horizontal direction on the machine bed 1010, and is movable in a horizontal direction, and is movably controllable via a linear drive 1052 of a first linear axis of the machine tool 1000. A workpiece WS is clamped, for example, on the tool table in a workpiece clamping device 1053.

[0076] The spindle head 1030 is mounted, for example, on vertical linear guides 1031, which are arranged on the machine stand 1020 in a vertical direction, so as to be linearly movable in the vertical direction, and is movable and controllable via a linear drive 1032 of a second linear axis of the machine tool 1000, so that the work spindle 1040, on which a tool head 10 (tool holder) holding a tool 90 is received, is also vertically movable.

[0077] In further embodiments, one or more further linear axes can be provided, e.g. to additionally enable a linear movement of the workpiece relative to the tool in a direction perpendicular to the drawing plane of the Fig. 7 to enable.

[0078] Furthermore, one or more rotary or rotary axes can be provided, such as a rotary axis with a rotary axis drive for rotating the tool table 1050 (so-called rotary table). A relative movement of the tool 90 relative to the workpiece WS can be controlled by means of the above-described linear and, if applicable, rotary or rotary axes or their drives.

[0079] For this purpose, a control device 1100 of the machine tool 1000 has a machine control device 1110, which, for example, comprises a CNC or NC control device 1112, which is configured to control the functions or machining processes on the machine tool 1000, for example based on NC data stored in a storage device 1111. In addition, the machine control device 1110 has, for example, a PLC or SPS device 1113 ("PLC" for Programmable Logic Controller or "SPS" for Programmable Logic Controller).

[0080] The PLC or SPS device 1113 is particularly preferably configured to transmit control signals to actuators of the machine tool based on control commands of the NC control device 1112 or, if appropriate, independently of the NC control device 1112, for example to the linear drives 1052 or 1032 of the linear axes or generally to drives of the machine axes or also to the spindle drive 1042 of the work spindle 1040.

[0081] In addition, the PLC or SPS device 1113 is configured to receive or read out sensor signals from position measuring sensors (not shown) of the machine tool 1000, which indicate actual positions of the drives and / or machine axes measured in real time during machining, and optionally forward them to the NC control device 1112. The PLC or SPS device 1113 can also be configured to enable other machine-internal or external devices or apparatuses to read out position data from the PLC or SPS device 1113 that indicate the actual positions of the drives and / or machine axes.

[0082] In addition to the spindle drive 1042 already mentioned above, the work spindle 1040 further comprises a tool holder 1041 (tool holder section) on which the tool head 10 is received and can be driven in rotation by means of the spindle drive 1042 (in particular for generating the cutting movement).

[0083] The tool head 10 is shown only schematically and has, for example, a tool interface body 14 (e.g. a tool taper, or steep or hollow shank taper, or also a Morse taper or other tool interfaces), with which the tool head 10 is received on the tool holder 1041 of the work spindle 1040. For example, the tool head 10 can be analogous to Fig. 1 be constructed.

[0084] The tool head 10 has, for example, an inductive receiver unit 32 (e.g. analogous to the secondary coil or winding 34 of the Fig. 1) for contactless or inductive reception of a control signal from the transmitter unit 32 (primary coil or winding) which is attached to the spindle head (or to the spindle).

[0085] For example, the tool head 10 in Fig. 7 further comprises an actuator 20 (e.g. ultrasonic transducer or ultrasonic generator, possibly comprising one or more piezo elements by way of example) and a sensor 40 for controlling the actuator 20. The actuator 20 is configured to cause the tool head 10 or the tool 90 accommodated in the tool head 10 to oscillate (in particular in the direction of the tool axis 92) on the basis of the control signal, preferably in particular in the ultrasonic range, ie in particular at ultrasonic frequencies or at frequencies above 10 kHz or in particular, for example, above 15 kHz, for example up to 60 kHz.

[0086] The tool head 10 also has the tool receiving section 11, on which the milling tool 90 is received or held. The tool 90 has a tool axis 92, about which the tool is driven in rotation via the spindle drive 1042.

[0087] To drive the actuator 20 or to control or regulate the vibration of the tool 90, the control device 1100 of the machine tool 1000 has a further control device 1120 (ultrasonic transducer control), which generates the control signal based on the sensor signal of the sensor 40 (vibration control) and outputs it via the transmitter unit 32 to the tool head 10 for transmission to the receiver device 34 for the actuator 20. In further embodiments, the control device 1120 can also be integrated into the machine control device 1110 and / or comprise an external data processing device, e.g., a computer, or be formed by an externally connected data processing device, e.g., a computer.

[0088] The control device 1120 comprises, for example, a generator 1124 (e.g., analogous to the generator 120 above) for generating the high-frequency control signal that is output to the actuator 20. The frequency of the control signal is high-frequency (i.e., in particular, with a frequency greater than 10 kHz, preferably greater than 15 kHz) and is preferably in the ultrasonic range.

[0089] The generator 1124 is connected, for example, to a controller unit 1123, which is configured to control the operation of the generator 1124 on the basis of the sensor signal of the sensor 40 output to the controller unit. The control can be carried out, for example, analogously to the aspects described above.

[0090] The control device 1120 further comprises, for example, a storage device 1121 for storing parameter data, in particular comprising control parameters that are used by the control device 1120 as a basis for controlling the actuator 20 (ultrasonic transducer).

[0091] The control device 1120 further comprises, for example, a data processing device 1122 configured to read and process the data from the storage device 1121. In particular, the data processing device 1122 is configured to read parameter data from the storage device 1121 and to determine control parameters that are input to the controller 1123 as a basis for controlling the operation of the generator 124.

[0092] According to embodiments of the invention, it is provided to store a plurality of parameter sets as parameter data in the storage device 1121, wherein the respective parameter sets are assigned to different tools, different ultrasonic transducers, different tool holders and different machining types or machining conditions.

[0093] The data processing device 1122 is preferably configured, in particular, to read out a suitable parameter set from the memory device 1121 on the basis of a currently used tool, tool holder, ultrasonic transducer and, in particular, on the basis of a current machining type or on the basis of the current machining conditions and to output corresponding control parameters to the controller 1123.

[0094] For this purpose, it is preferably possible to carry out a parameter set change before or during processing in order to adjust the controller 1123 on the basis of a changed parameter set in a processing-dependent manner.

[0095] For example, during machining, a parameter set change can be carried out during a tool change on the machine tool 1000, in which a changed parameter set corresponding to the tool to be changed, tool holder and / or its ultrasonic transducer is read out in the storage device 1121 and set on the controller 1123.

[0096] For example, a parameter set change can also be carried out during machining on the machine tool 1000, in which a changed parameter set is read out in the memory device 1121 according to changed machining conditions or a changed machining type and set on the controller 1123.

[0097] For background information, please refer to the Fig. 8, Fig. 9A and Fig. 9B, which shows different impedance and phase curves depending on the frequency.

[0098] Fig. 8 shows, in particular, examples of different impedance and associated phase curves as a function of frequency over a wide frequency range from approximately 15 kHz to approximately 60 kHz for different tools (A: open-end milling cutter, B: closed-end milling cutter or C: closed-end milling cutter).

[0099] It can be seen that different tools can exhibit very different impedance and corresponding phase responses, with sometimes very different impedance and phase deflections at the respective minima and maxima, and also with shifted resonance frequencies. It is particularly important to note that multiple maxima and minima, i.e., multiple resonances, occur across the frequency range.

[0100] Basically, the phase profile has a minimum at resonance points, so that the phase is suitable as a control variable for controlling the generator 120 or 1124 to a resonance point. The respective impedance profile has a maximum (parallel resonance) first and then a minimum (series resonance) at each resonance point. The order of maximum and minimum is due to our inductive energy transfer. In the case of a direct connection without a transformer, the order is always exactly reversed (minimum - maximum).

[0101] According to exemplary embodiments, the control of the generator is designed such that the controller 1123 attempts to adjust the frequency so that the ultrasonic transducer or actuator 20 is operated at a frequency at the impedance maximum of the resonance point.

[0102] However, it should be noted that in Fig. 8 different curves can be seen, which, for example, always come from the same actuator 20 with the same transmitter. In general, the following factors can influence the exact characteristics of the curves: • the size of the air gap between transmitter and receiver, • mechanical tolerances in the production of actuators and transmitters, • electrical tolerances in the manufacture of actuators and transmitters, and • any malfunctions within the machine

[0103] Due to the fact that (a) differences between the individual impedance curves can arise due to tolerances and aging effects and (b) due to the use of many different tools, the following measures are proposed according to exemplary embodiments: To determine a resonance point, a frequency scan can be performed over a larger frequency range using the 120 / 1224 generator to search for the minima in the phase curve. These minima in the phase curve are usually well defined (see Fig. 8) and can therefore be determined in a frequency scan.

[0104] As a rule, there are several minima within a larger preset frequency range, e.g. 15 kHz and 60 kHz (see Fig. 8), so that if several minima are found in the frequency scan, a distinction can be made and a suitable resonance point can be selected.

[0105] Regarding frequency determination through the frequency scan, the generator can be given a specification as to which phase differences should be classified as resonance points. For example, a maximum depth and / or a minimum depth of the minimum can be specified or predefined. In particular, minima below the minimum depth can be ignored as "noise."

[0106] However, different actuators 20 (e.g. with different tools 90) can in turn produce minima of different depths.

[0107] During operation, controller 1123 should now drive or control generator 1124 such that the frequency is set during operation such that the frequency is at resonance (frequency control). For this purpose, the phase of the sensor signal from sensor 40 can be used as the control variable.

[0108] On the other hand, the controller 1123 can be set such that the generator delivers a constant current amplitude to the actuator at resonance, since a constant current amplitude is physically linked to a constant oscillation amplitude (current control).

[0109] However, due to Ohm's law, the generator can only drive a maximum current I = U / R for a given maximum output voltage U. If the desired output current (e.g., specified by the operator) exceeds this value, the controller may become unstable, since there is no state in which the specified value can be reached.

[0110] Conversely, the maximum output voltage can only be specified up to a certain limit, since otherwise the resolution of the controller would be unnecessarily reduced for a given number of steps between 0V and a maximum voltage.

[0111] In addition to the pure impedance / phase parameters, parameters of the PID controllers used and potentially further parameters for setting the frequency and / or current controllers also play a role: With PID controllers, the parameters underlying the control are preferably designed to be optimal or adapted to the system to be controlled in order to enable precise processing.

[0112] Due to the different actuators and tools that can be used, as well as due to different machining scenarios, machining conditions or machining types, no universal parameter set is suitable.

[0113] Preferably, a function is enabled on the control device 1120 that allows an operator to set up a tool holder with a specific actuator or, if applicable, with a specific tool. During the setup, suitable parameters can be determined, selected, and set as a basis for the subsequent control of the drive of the actuator, if applicable in conjunction with a specific tool, or stored in the memory device 1121.

[0114] For example, a frequency scan can be performed over a very wide frequency range (possibly in predefined frequency ranges over a wide range and, if necessary, up to the entire technical bandwidth of the generator). All resonance points found can then be individually tested, particularly to determine which resonance points are suitable for machine operation with the tool holder or actuator to be configured, possibly in conjunction with a specific tool. There are various options for this: (1) When dampened, e.g., by moving the tool onto a test workpiece, only suitable resonances react (these are damped). A possible setup procedure would examine or scan all resonances under damping and eliminate unsuitable resonances by comparing curves. (2) The actual mechanical vibration can be measured in the machine using optical (or other) methods to select suitable resonances based on the vibration amplitudes realized. Unsuitable resonance points can be eliminated, for example, based on the vibration shape. (3) Over a defined time, an oscillation can be generated at the respective resonance points and the behavior of the oscillation at each resonance point as a function of time can be observed: If the temporal behavior corresponds to a conventional temperature drift, the corresponding resonance point can be selected as suitable. (4) Additional sensors (e.g. temperature sensor on the transformer) can detect deviations when the oscillation is switched on (e.g. excessive power loss due to heat development on the transformer) in order to eliminate unsuitable resonance points.

[0115] It is further possible to apply one or more of the above selection methods to select a suitable resonance point among a plurality of resonance points.

[0116] After selecting a suitable resonance point, the frequency range of the generator during operation can then be restricted to a suitable range around the selected resonance point, in particular in such a way that no further resonances are present in the suitable range.

[0117] An example of this is Fig. 9A and Fig. 9B. Fig. Figure 9A shows an impedance curve and a corresponding phase curve over a wide frequency range, for example from approximately 17 kHz to approximately 35 kHz, with two larger phase minima (resonance points) being detected in the frequency scan. Here, for example, a resonance point is selected, and a frequency range around the selected resonance point can be set using a lower limit UG and an upper limit OG, which does not include any further resonance points. See Fig. 9B (a smaller resonance point at approximately 21.9 kHz can be ignored as noise, since it has a minimum depth below an adjustable minimum depth).

[0118] Consequently, the generator can react to actual changes in the resonance frequency (e.g. due to damping, heating) only within the selected frequency range through optimized control, but does not accidentally run into a wrong resonance point.

[0119] Additionally, an impedance / phase measurement can be performed. Based on this, the maximum impedance is determined, and the maximum output voltage of the generator is selected (via a switch) as needed. The measurement is performed either through a dedicated measuring circuit or by activating the oscillation and measuring all relevant quantities during operation.

[0120] The controller 1123 may include a frequency controller and a current controller (e.g., based on PID controllers).

[0121] The response of the controller 1123 to changes in the input variable (e.g. phase for frequency control and / or current for current control) can be adjusted by a plurality of controller constants (e.g. BPID controller constants), e.g. determined by three constants (depending on the source, e.g. designated Kp, Ti or Td)

[0122] Furthermore, you can define a deadband for the input variable, for example. This means that a change is only considered as such if it is greater than the deadband width. For smaller changes within the deadband width, controller 1123 can remain inactive (essentially switched off).

[0123] Such a setup operation is preferably performed to determine a suitable parameter set for a specific combination of tool holders (with transmitter and actuator), preferably in conjunction with a specific tool. In exemplary embodiments of the invention, respective setup operations are particularly preferably performed for a plurality of specific combinations of tool holders with transmitter and actuator, preferably in conjunction with a specific tool, and respective parameter sets are stored in the storage device 1121.

[0124] This can also be performed by the machine tool manufacturer, and such parameter sets can be pre-stored as parameter data on the machine tool or read in later. Furthermore, this can also be performed by an operator on the machine tool to store new parameter sets in the storage device 1121. Depending on the system used, these parameter sets can then be called up, e.g., during a corresponding tool change during machining or by an operator when setting up a tool on the machine tool.

[0125] Furthermore, different parameter sets can be stored for specific tools, specific tool holders with ultrasonic transducers (actuators) or specific combinations of tools with tool holders for different machining conditions or machining types, e.g. for drilling (drilling usually generates rapid load changes when entering / exiting the workpiece material, to which the controller must react quickly) or for milling (milling usually generates more uniform and slower load changes. If the controller is too dynamic here, it can oscillate and become unstable).

[0126] In particular, it is possible for the respective machining-dependent parameter sets to be changed during machining on the machine tool, or for switching between respective machining-dependent parameter sets during machining on the machine tool depending on the machining type or machining conditions. This can also be carried out automatically via the data processing device 1122, which, for example, depending on the specifications of the current NC data (e.g., based on a currently executing NC program), reads the corresponding parameter set from the storage device 1121 when the machining type changes and adjusts or switches the controller 1123 accordingly.

[0127] Examples and embodiments of the present invention and their advantages have been described in detail above with reference to the accompanying figures. It should be emphasized again that the present invention is in no way limited or restricted to the above-described embodiments and their design features, but rather further encompasses modifications of the embodiments, in particular those encompassed by modifications of the features of the described examples or by combining one or more of the features of the described examples within the scope of the independent claims.

Claims

[1] Device for controlling an ultrasonic tool unit for machining a workpiece (WS) on a machine tool (1000), comprising: a control device (1120) for controlling an ultrasonic transducer (20) of the ultrasonic tool unit mounted on a work spindle (1040) of the machine tool for machining a workpiece (WS) on the basis of a sensor signal input into a controller (1123) by means of a generator (1124) operated by the controller (1123), on the basis of a first parameter set assigned to the ultrasonic tool unit and setting the operation of the controller (1123), characterized by , that the control device comprises a memory device (1121) for storing a plurality of parameter sets adjusting the operation of the controller (1123), and the control device is configured such that an operating setting of the controller (1123) can be switched by changing the first parameter set setting the operation of the controller (1123) on the basis of a second parameter set assigned to the ultrasonic tool unit from the plurality of parameter sets stored in the storage device (1121). [2] Device according to claim 1, characterized by that the control device (1120) is designed to switch the operating setting of the controller (1123) during the machining of the workpiece (WS). [3] Device according to claim 1 or 2, characterized by that the control device (1120) is designed to switch the operating setting of the controller when the type of machining of the workpiece (WS) changes. [4] Device according to one of the preceding claims, characterized bythat the first parameter set is assigned to a first processing type of a plurality of processing types and the second parameter set is assigned to a second processing type of the plurality of processing types. [5] Device according to claim 4, characterized by that the majority of machining operations include milling and drilling. [6] Device according to one of the preceding claims, characterized by that the control device (1120) is configured, when the ultrasonic tool unit on the machine tool is replaced with another ultrasonic tool unit, to switch an operating setting of the controller (1123) by changing a parameter set assigned to the ultrasonic tool unit on the basis of a parameter set assigned to the other ultrasonic tool unit from the plurality of parameter sets stored in the memory device (1121). [7] Device according to one of the preceding claims, characterized by that the control device (1120) is configured, when a tool on the ultrasonic tool unit on the machine tool is replaced with another tool, to switch an operating setting of the controller (1123) by changing a parameter set assigned to the tool on the basis of a parameter set assigned to the other tool from the plurality of parameter sets stored in the memory device (1121). [8] Machine tool with a work spindle (1040) for receiving an ultrasonic tool unit, and a device for controlling the ultrasonic tool unit for machining a workpiece on the machine tool according to one of the preceding claims. [9] Method for controlling an ultrasonic tool unit for machining a workpiece (WS) on a machine tool, comprising: Controlling an ultrasonic transducer (20) of the ultrasonic tool unit mounted on a work spindle (1040) of the machine tool for machining a workpiece on the basis of a sensor signal input into a controller (1123) by means of a generator (1124) operated by the controller (1123), on the basis of a first parameter set assigned to the ultrasonic tool unit and setting the operation of the controller (1123), characterized by Storing a plurality of parameter sets that adjust the operation of the controller (1123) in a memory device (1121) of a control device of the machine tool, and Switching an operating setting of the controller (1123) by changing the first parameter set setting the operation of the controller (1123) on the basis of a second parameter set assigned to the ultrasonic tool unit from the plurality of parameter sets stored in the storage device (1121). [10] Method according to claim 9, characterized by that the switching of the operating setting of the controller (1123) is carried out during machining of the workpiece (WS). [11] Method according to claim 9 or 10, characterized by that the switching of the operating setting of the controller (1123) is carried out when the machining type of the workpiece (WS) is changed. [12] Method according to one of the preceding claims, characterized by that the first parameter set is assigned to a first processing type of a plurality of processing types and the second parameter set is assigned to a second processing type of the plurality of processing types. [13] Method according to claim 12, characterized by that the majority of machining operations include milling and drilling. [14] Method according to one of the preceding claims, characterized byReplacing the ultrasonic tool unit on the machine tool with another ultrasonic tool unit, and switching an operating setting of the controller (1123) by changing a parameter set assigned to the ultrasonic tool unit on the basis of a parameter set assigned to the other ultrasonic tool unit of the plurality of parameter sets stored in the storage device (1121). [15] Method according to one of the preceding claims, characterized by Replacing a tool on the ultrasonic tool unit on the machine tool with another tool, and switching an operating setting of the controller by changing a parameter set assigned to the tool on the basis of a parameter set assigned to the other tool from the plurality of parameter sets stored in the storage device (1121).

Images