Method for controlling an ultrasonic generator, and ultrasonic generator

Abstract

The invention relates to an ultrasonic generator and to a method for controlling an oscillator unit (13) of the ultrasonic generator (10) in a machine tool for producing ultrasound in order to excite a tool (26). A manipulated variable for controlling the frequency f of an electric control signal HFS generated by the oscillator unit (13) is determined on the basis of an analysis of the magnitude of an input and / or output current I or an input and / or output power P of the ultrasonic generator (10).

Description

[0001] Description

[0002] Method for controlling an ultrasonic generator and ultrasonic generator

[0003] The invention relates to a method for controlling an oscillator unit of an ultrasonic generator in a machine tool for generating ultrasound to excite a tool for machining a workpiece, wherein a control variable for controlling a frequency f of an electrical control signal generated by the oscillator unit is determined.

[0004] Furthermore, the invention relates to an ultrasonic generator in a machine tool for generating ultrasound for exciting a tool for machining a workpiece, comprising an oscillator unit designed to output an electrical control signal for generating the ultrasound, a control unit designed to determine a control variable for controlling a frequency f of the electrical control signal generated by the oscillator unit.

[0005] A corresponding method and system for controlling an ultrasonic generator of a machine tool for machining a workpiece is known from DE 10 2020 201 540 A1. In this method, electrical signals with different frequencies are generated for machining a workpiece, with the frequencies being in the ultrasound frequency range. Ultrasonic waves are generated using the electrical signals, which are transmitted to a tool. A phase shift of the electrical signals is then determined as a controlled variable depending on the frequency, and the phase shift is analyzed as a function of the frequency. Finally, a control algorithm for controlling the frequency of the ultrasound generated by the ultrasonic generator is determined based on the analysis of the phase shift. Determining and analyzing the phase shift as a controlled variable is complex. This requires the voltage and current curves of the electrical signals to be evaluated simultaneously.

[0006] Another method for controlling an ultrasonic generator is known from DE 10 2016 214 699 A1. This method also requires a ceramic sensor on the tool.

[0007] Based on this, the present invention is based on the object of developing a method for controlling an ultrasonic generator of a machine tool of the type mentioned at the outset in such a way that the vibration of the tool can be easily adjusted and, in particular, a precise and reproducible amplitude deflection of the tool can be adjusted.

[0008] The object is achieved according to the invention, among other things, by determining the control variable as a function of an analysis of the magnitude or amplitude of an input and / or output current I or an input and / or output power P of the ultrasonic generator. The invention is based on the idea of ​​readjusting the oscillation of the system, preferably exclusively via the current continuously recorded during operation, in particular the input current lein or the resulting power Pzu.

[0009] Preferably, the electrical control signal HFS generated by the oscillator unit is amplified by an amplifier unit of the ultrasonic generator, wherein the analysis of the magnitude or amplitude of the input and / or output current I comprises a comparison of the magnitude or amplitude of an input and / or output current lein the amplifier circuit with a current setpoint Isoll.

[0010] In a particularly preferred method, the current setpoint Isoll is determined by scanning the tool before machining using the ultrasonic generator, by the oscillator unit exciting the tool during a frequency sweep in a definable frequency band with different frequencies f, wherein the input current lein or the input power Pein of the amplifier unit is recorded during the frequency sweep over the frequency f and based on the current curve, a current maximum Imax or a power maximum Pmax is determined and stored as a setpoint at a resonance point RS and an associated resonance frequency fres.

[0011] The machining of the workpiece can then be started with the stored resonance frequency fres.

[0012] Furthermore, according to the invention, it is proposed that the input current lein or the input power Pein of the amplifier unit is measured during machining of the workpiece, that the magnitude of the input current lein as the actual current value is continuously compared with the maximum current Imax as the desired current value (reference variable), and that the control variable for the oscillator unit (actuating device) is determined as a function of a deviation (control difference) between the actual current value and the maximum current Imax, wherein the frequency f as the manipulated variable for the oscillator unit (actuating device) is changed by means of the control variable such that the input current lein reaches or approaches the maximum current Imax. The method offers the advantage that only the input current lein needs to be measured and that the current curve can be created in a simple manner.In addition, the control variable can be determined as the deviation between the input current and the current maximum at the resonance point using simple means.

[0013] It is particularly noteworthy that when the frequency f of the oscillator unit changes, the response of the input current lein is analyzed. If the input current lein increases with a change in the frequency f, the frequency f is changed in the same direction of the change until the input current reaches the maximum current Imax. If the input current I decreases with a change in the frequency f, the frequency f is changed in the opposite direction of the change until the input current lein reaches the maximum current Imax. This method achieves fast control.

[0014] An independent inventive concept is characterized in that an amplitude deflection AMP of the tool is adjusted via the magnitude of the input current lein. The magnitude of the input current lein is adjusted by setting the frequency f of the oscillator, wherein the frequency is greater or less than the resonance frequency fres. Furthermore, the invention relates to an ultrasonic generator in a machine tool for generating ultrasound to excite a tool for machining a workpiece. The ultrasonic generator comprises an oscillator unit configured to output an electrical control signal HFS at a frequency f for generating the ultrasound, and a control unit configured to determine a control variable for controlling the frequency f of the electrical control signal HFS generated by the oscillator unit.

[0015] According to the invention, it is provided that the control unit is designed to determine the control variable preferably exclusively as a function of an analysis of the size or amplitude of the input and / or output current I or the size or amplitude of the input and / or output power P of the ultrasonic generator (10).

[0016] Preferably, the ultrasonic generator comprises an amplifier unit which is designed to amplify the electrical control signal HFS generated by the oscillator unit, wherein the ultrasonic generator has a current sensor which is designed to measure the input current lein of the amplifier unit, and wherein the control unit has a comparator unit which is designed to compare the input current lein with a current setpoint Isoll, preferably a resonance current Ires, and to provide it as a control difference, and wherein the control unit has a controller unit which is designed to determine the control variable as a function of the control difference between input current lein and current setpoint Isoll.

[0017] Particularly preferably, an energy transformer, such as an induction transformer, a cable connection or a slip ring transformer, is connected to an output of the amplifier unit, wherein the energy transformer is connected to a piezo system which converts a high-frequency electrical output signal HF present at an output of the amplifier unit into the ultrasonic vibration, and wherein the piezo system is coupled to the tool for transmitting the ultrasonic vibration to the tool.

[0018] Further details, advantages and features of the invention emerge not only from the claims, the features to be derived from them - individually and / or in combination, but also from the following description of preferred embodiments to be derived from the drawings.

[0019] They show:

[0020] Fig. 1 is a block diagram of an ultrasonic generator for generating ultrasound to excite a tool,

[0021] Fig. 2 is a block diagram of a generator and control unit,

[0022] Fig. 3 shows a curve of an input current of an amplifier unit of the ultrasonic generator as a control variable over the frequency as a control variable for setting an optimal operating point and

[0023] Fig. 4 shows a curve of an input current of an amplifier unit of the ultrasonic generator as a controlled variable over the frequency as a manipulated variable for setting an operating point with a predetermined oscillation amplitude.

[0024] Fig. 1 shows a block diagram of an ultrasonic generator 10, comprising a control unit 12, an oscillator unit 13, an amplifier unit 14, a sensor unit, such as a current sensor 16, and a voltage supply 18, which is connected on the input side to the mains voltage 20.

[0025] An energy transformer 22, such as an induction transformer or, alternatively, a cable connection or a slip-ring transformer, is connected to an output of the amplifier unit 14, to which a high-frequency electrical output signal HF is applied, for controlling a piezo system 24. The piezo system 24, which generates an ultrasonic vibration from the high-frequency electrical output signal HF, is coupled to a tool 26 or a tool holder (not shown) receiving the tool 26 in order to couple the ultrasonic vibration into the tool 26 so that it executes the desired ultrasonic vibration. A frequency and an amplitude of the ultrasonic vibration can be adjusted by a frequency f and an amplitude of the high-frequency electrical output signal HF.It is known from the literature that coupling ultrasonic vibration into the tool 12 supports a machining process, such as grinding or cutting. This is because the ultrasonic vibration generates an oscillation of the tool, which generates movement amplitudes in the range of a few micrometers at the contact point between the tool and the workpiece, resulting in a reduction in the process forces. The ultrasound can be introduced into the tool longitudinally and / or transversely.

[0026] The invention is based on the idea of ​​regulating the frequency and / or amplitude of the ultrasonic vibration of the tool 26 based on the magnitude of an input current lein or an input power Pin of the amplifier unit 14. In particular, improved amplitude control is to be provided independent of the system's damping. The control of the input current I is carried out by the control unit 12.

[0027] Fig. 2 shows a block diagram of the control unit 12, which is designed in the form of a microcontroller. The control unit 12 comprises a comparator unit 28, a controller unit 30, and a computing and storage unit 32. The input current lein of the amplifier unit 14 is measured by the current sensor 16 and fed to the comparator unit 28 and the computing and storage unit 32 as the actual current value liste. The computing and storage unit 32 provides a desired current value Isoll, which is fed to the comparator unit 28. An output of the comparator unit 28 is connected to an input of the controller unit 30. The controller unit 30 generates a control variable with which the frequency f of a high-frequency electrical control signal HFS of the oscillator unit 13 can be adjusted. The control variable present at the output of the controller unit 30, which is proportional to the frequency f of the high-frequency control signal HFS, is provided to the memory unit 32.Independently of the frequency f, an amplitude of the high-frequency control signal HFS can also be set, which is essentially proportional to the amplitude deflection of the tool 26.

[0028] The high-frequency electrical control signal HFS is connected to an input of the amplifier circuit 14 and is amplified by it. The amplified high-frequency electrical output signal HF is available at the output of the amplifier circuit 14 to excite the piezo system 24. According to the invention, the following procedure is carried out.

[0029] Since the efficiency of workpiece machining by superimposing an ultrasonic vibration depends in particular on the geometry of the tool used and its clamping length, the tool 26 is scanned in a first step by means of a frequency sweep of the ultrasonic generator 10. The frequency sweep, i.e., scanning, also called sweeping, is performed in a selected, defined frequency band, which is defined by a minimum frequency of the control signal HFS of, for example, fmin - 1 kHz and a maximum frequency of, for example, fmax = 100 kHz. The oscillator unit 13 is designed to generate the high-frequency control signal HFS in a further frequency band of, for example, fmin = 1 kHz to fmax = 100 kHz.During the frequency sweep, the input current lein of the amplifier circuit 14 and the control variable present at the output of the controller unit 30, which is proportional to the frequency f of the oscillator unit 13, are recorded and stored in the computing and storage unit 32 in order to be able to record a curve of the input current lein over the frequency f.

[0030] Fig. 3 shows the curve of the input current lein recorded during the frequency sweep against the frequency f of the high-frequency control signal HFS, where the frequency f of the high-frequency control signal HFS corresponds to the frequency f of the ultrasonic oscillation. Based on the recorded input current lein, a resonance point RS for the system comprising energy exchanger 22, piezo system 24, and tool 26 is determined in a second step in the computing and storage unit 32. At the resonance point RS, the input current lein exhibits its maximum value Imax (Maximun). The maximum value Imax is stored. The frequency f at the point of the maximum value Imax, i.e. at the resonance point RS, is stored as the resonance frequency fres in the computing and storage unit 32.

[0031] After determining the resonance frequency fres, the machining of the workpiece with the tool 26 can start in a third step.

[0032] During operation of the tool 26, the input current lein is continuously measured by the current sensor 16. In a fourth step, the frequency f of the oscillator unit 13, and thus the frequency f of the amplified high-frequency output signal HF, is adjusted using the input current lein, which is continuously recorded during operation.

[0033] The measured input current Iein as the actual current value and the maximum value Imax of the input current are fed to the comparator unit 28 as input variables. In the comparator unit 28, the measured input current lein as the actual current value is compared with the maximum value Imax as the current setpoint. If the measured input current lein falls below the current setpoint Imax from the frequency sweep, e.g., 10% below Imax, a control deviation is present at the output of the comparator 28, which is fed to the controller unit 30. Depending on the control deviation, a control variable is generated at the output of the controller unit 30, which control variable is used to control the oscillator unit 13 to adjust the frequency f of the high-frequency control signal HFS. The frequency f of the high-frequency control signal HFS is a manipulated variable for a controlled system formed by the amplifier unit 14, energy exchanger 22, piezo system 24, and workpiece 26.

[0034] Consequently, by controlling the frequency f of the oscillator unit 13, the frequency of the high-frequency output signal HF for controlling the energy transmitter 22 with piezo system 24 and tool 26 as a control system is also adjusted so that the input current lein reaches its maximum value Imax.

[0035] Fig. 3 shows that for a measured input current lein that is smaller than the maximum value Imax, the system can be either at an operating point AP1 with f1 < fres or at an operating point AP2 with f2 > fres. To determine the operating point AP1 or AP2, the oscillator unit 13 is controlled by the manipulated variable such that the frequency of the oscillator unit 13 is increased or decreased in steps of, for example, 1 Hz, 10 Hz or 100 Hz. At the same time, the behavior of the input current lst is analyzed. If the input current lst increases when the frequency f is increased, the system is at the operating point AP1 and the frequency f is increased further until the input current lst reaches the maximum value Imax. However, if the input current lst decreases when the frequency f is increased, the system is at the operating point AP2, so the frequency f is decreased until the input current lst reaches the maximum value Imax.Consequently, the method according to the invention is based on the idea of ​​readjusting the system via the input current list which is permanently recorded during operation, whereby when the current value Imax from the frequency sweep (+ / - tolerance) is undershot, the system is driven back to its current maximum Imax by slightly changing (+ / -) the frequency f and analyzing the resulting behavior (reaction) of the input current list.

[0036] In other words, current sensor 16 as measuring device, comparator unit 28 as comparator, controller unit 30 as controller, oscillator unit 13 as actuating device and amplifier circuit 14 with energy transformer 24, piezo system 15 and tool 26 as controlled system form a control loop, wherein the input current I as controlled variable is adjusted during operation in such a way that it reaches its maximum value Imax and the system is effectively operated at the resonance point RS.

[0037] The method according to the invention also makes it possible to control an amplitude deflection Amp of the tool 26 via the supplied input current l.

[0038] Fig. 4 shows the input current l versus the frequency f of the high-frequency signal HF. By changing the frequency f, e.g. to a frequency value famp, the input current l can be set to a current value l such that the system is at a desired operating point AP with the desired amplitude Amp of the tool 26. By changing the frequency f, the operating point AP on the curve of the input current l can be shifted in the direction of the arrows shown, i.e. rising or falling on the curve. A shift of the operating point AP on the current curve corresponds to a change in the amplitude deflection or oscillation amplitude of the tool 26. By moving the operating point AP of the system on the approximately straight section of the current curve with a constant gradient, the oscillation amplitude can be set between a maximum amplitude maxAmp and a minimum amplitude minAmp.In other words, amplitude control is carried out based on the input current list.

Claims

Patent claims Method for controlling an ultrasonic generator and ultrasonic generator. Method for controlling an oscillator unit (13) of an ultrasonic generator (10) in a machine tool for generating ultrasound to excite a tool (26) for machining a workpiece, wherein a control variable for controlling a frequency f of an electrical control signal HFS generated by the oscillator unit (13) is determined, characterized in that the control variable is determined as a function of an analysis of the magnitude of an input and / or output current I or an input and / or output power P of the ultrasonic generator (10).

2. A method according to claim 1, characterized in that the control variable is determined exclusively as a function of the analysis of the input and / or output current I or the input and / or output power P. A method according to claim 1 or 2, characterized in that the electrical control signal HFS is amplified by an amplifier unit (14) of the ultrasonic generator (10) and that the analysis of the magnitude of the input and / or output current I comprises a comparison of the magnitude or amplitude of an input and / or output current in the amplifier unit (14) with a current setpoint Isoll.

4. Method according to at least one of the preceding claims, characterized in that the current setpoint Isoll is determined by scanning the tool (26) before processing using the ultrasonic generator (10). The process is carried out by the oscillator unit (13) exciting the tool (26) during a frequency sweep in a definable frequency band with different frequencies f, wherein the input current lein or the input power Pein of the amplifier unit (14) is recorded during the frequency sweep over the frequency f, and based on the current waveform, a current maximum Imax as the target current Isoll at a resonance point RS and an associated resonance frequency fres are determined and stored. A method according to at least one of the preceding claims, characterized in that the machining of the workpiece (26) is started with the stored resonance frequency fres. A method according to at least one of the preceding claims, characterized in that the input current lein or the input power Pein of the amplifier unit (14) is measured during the machining of the workpiece (26), and that the magnitude or...The amplitude of the input current lein as the actual current value list is continuously compared with the current maximum Imax as the current setpoint Isoll, and depending on a deviation between the actual current value list and the current maximum Imax, the control variable is determined by means of which the frequency f of the oscillator unit (13) is changed such that the actual current value list reaches or approaches the current maximum Imax.A method according to at least one of the preceding claims characterized in that, when the frequency f of the oscillator unit (13) is changed, a reaction of the input current lein is analyzed, wherein, if the input current lein increases when the frequency f changes, the frequency f is further changed in the direction of the change until the input current lein reaches the maximum current Imax, and wherein, if the input current lein decreases when the frequency f changes, the frequency f is changed in the opposite direction of the change until the input current lein reaches the maximum current Imax. A method according to at least one of the preceding claims, characterized in that the amplitude displacement AMP of the tool (26) is set via the magnitude of the input current lein. A method according to at least one of the preceding claims, characterized in that the magnitude of the input current lein is set via the setting of the frequency f of the oscillator unit (13), wherein the frequency is greater or less than the resonant frequency fres.Ultrasound generator (10) in a machine tool for generating ultrasound to excite a tool (26) for machining a workpiece, comprising: an oscillator unit (13) configured to output an electrical control signal HFS with a frequency f for generating the ultrasound, a control unit (12) configured to determine a control variable for controlling the frequency f of the electrical control signal HFS generated by the oscillator unit (13), characterized in that the control unit (12) is configured to determine the control variable as a function of an analysis of the magnitude or amplitude of the input and / or output current I or of the magnitude or amplitude of the input and / or output power P of the ultrasound generator (10).Ultrasound generator according to claim 10, characterized in that the ultrasound generator (10) has an amplifier unit (14) configured to amplify the electrical control signal HFS generated by the oscillator unit (13), and that the ultrasound generator (10) has a current sensor (16) configured to measure the input current to the amplifier unit (14). that the control unit (12) has a comparator unit (28) configured to compare the input current lein with a current setpoint Isoll, preferably a resonant current Ires, and to provide it as a control error, and that the control unit (12) has a controller unit (30) configured to adjust the control variable as a function of the control error between the input current lein and To determine the current setpoint (Isoll). Ultrasound generator according to claim 10 or 11, characterized in that an energy transformer (22), such as an induction transformer, a cable connection or a slip ring transformer, is connected to an output of the amplifier unit (14), that the energy transformer (22) is connected to a piezoelectric system (24) which converts a high-frequency electrical output signal (HF) applied to an output of the amplifier unit (14) into the ultrasonic vibration, and that the piezoelectric system (24) is used for The transmission of the ultrasonic vibration to the tool (26) is coupled to it.

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