Method for controlling an ultrasonic generator and ultrasonic generator - Patents.com

Abstract

The present invention relates to an ultrasonic generator and a method for controlling an oscillator unit (13) of an ultrasonic generator (10) in a machine tool for generating ultrasonic waves for exciting a tool (26). A control variable for controlling the frequency f of an electric control signal HFS generated by the oscillator unit (13) is determined depending on an analysis of the size of the input and / or output current I or the input and / or output power P of the ultrasonic generator (10).

Description

[Technical field]

[0001] The present invention relates to a method for controlling an oscillator unit of an ultrasonic generator in a machine tool for the generation of ultrasonic waves for exciting a tool for machining a workpiece, wherein a control variable is determined for controlling the frequency f of an electrical control signal generated by the oscillator unit.

[0002] The invention further relates to an ultrasonic generator in a machine tool for the generation of ultrasonic waves for exciting a tool for machining a workpiece, comprising an oscillator unit designed to emit an electric control signal for the generation of ultrasonic waves and a control unit designed to determine a control variable for controlling the frequency f of the electric control signal generated by the oscillator unit. [Background technology]

[0003] Corresponding methods and systems for controlling an ultrasonic generator of a machine tool for machining a workpiece are known from DE 10 2020 201 540 A1. In this method, electric signals with different frequencies are generated for machining the workpiece, which frequencies are in the frequency range of ultrasonic waves. Ultrasonic waves are generated by the electric signals, which are transmitted to the tool. A phase shift of the electric signal as a function of the frequency is then determined as a regulation variable, said phase shift being analyzed as a function of the frequency. Finally, a regulation algorithm for controlling the frequency of the ultrasonic waves generated by the ultrasonic generator is determined as a function of the analysis of the phase shift. The determination and analysis of the phase shift as a regulation variable is complex. The voltage and current curves of the electric signal have to be evaluated simultaneously with each other.

[0004] A further method for controlling an ultrasonic generator is known from DE 10 2016 214 699 A1, in which a ceramic sensor is additionally required on the tool.

[0005] On this basis, the object underlying the present invention is to develop 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 set in a simple manner, in particular such that a precise and reproducible amplitude deflection of the tool can be set. Summary of the Invention

[0006] This object is solved according to the invention in part in that the control variables are determined depending on the analysis of the size / amplitude of the ultrasonic generator's input and / or output current I or input and / or output power P. The invention is based on the idea of ​​using, preferably exclusively, the currents recorded continuously during operation, in particular the input current Iein or the resultant power Pzu, to readjust the vibration of the system.

[0007] Preferably, the electrical control signal HFS generated by the oscillator unit is amplified by an amplifier unit of the ultrasonic generator, and the analysis of the size / amplitude of the input and / or output current I comprises a comparison of the size / amplitude of the input and / or output current Iein of the amplifier circuit with a set point current value Isoll.

[0008] In a particularly preferred procedure, it is provided that the set point current value Isoll is determined by scanning the tool prior to machining with an ultrasonic generator and by the oscillator unit vibrating the tool during a frequency sweep in a definable frequency band with different frequencies f, the amplifier unit input current Iein or input power Pein is recorded during the frequency sweep across frequencies f, and based on the current curve, a maximum current Imax or maximum power Pmax is determined and stored as the set point value at the resonance point RS and the associated resonance frequency fres.

[0009] Machining of the workpiece at the stored resonant frequency fres can then commence.

[0010] Furthermore, according to the invention, it is proposed that the input current Iein or the input power Pein of the amplifier unit is measured during machining of the workpiece, the magnitude of the input current Iein as an actual current value is continuously compared with the maximum current Imax as a setpoint current value (reference variable), a control variable for the oscillator unit (setting device) is determined depending on the difference (adjustment difference) between the actual current value and the maximum current Imax, and the frequency f as a setting variable for the oscillator unit (setting device) is changed by the control variable in such a way that the input current Iein reaches or approaches the maximum current Imax. This method offers the advantage that it is only the input current Iein that has to be measured and the current curve is obtained in a simple manner. Also, the control variable can be determined using simple means as the difference between the input current and the maximum current at resonance.

[0011] It should be particularly emphasized that, when there is a change in the frequency f of the oscillator unit, the reaction of the input current Iein is analyzed, and whenever there is a rise in the input current Iein when there is a change in the frequency f, the frequency f is changed in the same direction as the change until the input current I reaches a maximum current Imax, and whenever there is a fall in the input current I when there is a change in the frequency f, the frequency f is changed in the opposite direction to the change until the input current Iein reaches a maximum current Imax. Rapid control is achieved by the method.

[0012] The inventive idea is characterized in that the amplitude deflection AMP of the tool is set using the size of the input current Iein, which is here set using the setting of the frequency f of the oscillator unit, the frequency being higher or lower than the resonant frequency fres.

[0013] The invention further relates to an ultrasonic generator in a machine tool for the generation of ultrasonic waves for exciting a tool for machining a workpiece, the ultrasonic generator comprising an oscillator unit designed to emit an electric control signal HFS having a frequency f for the generation of ultrasonic waves, and a control unit designed to determine a control variable for controlling the frequency f of the electric control signal HFS generated by the oscillator unit.

[0014] According to the invention it is provided that the control unit is preferably designed to determine the control variables solely in response to an analysis of the size / amplitude of the input and / or output current I or the size / amplitude of the input and / or output power P of the ultrasonic generator (10).

[0015] The ultrasonic generator preferably comprises an amplifier unit designed to amplify the electrical control signal HFS generated by the oscillator unit, the ultrasonic generator having a current sensor designed to measure an input current Iein of the amplifier unit, the control unit having a comparator unit designed to compare the input current Iein with a set point current value Isoll, preferably a resonant current Ires, and provide it as a regulated difference, and the control unit has a regulator unit designed to determine a control variable depending on the regulated difference between the input current Iein and the set point current value Isoll.

[0016] Particularly preferably, an energy transmitter, e.g. an inductive transmitter, cable connection or slip ring transmitter, is connected to the output of the amplifier unit, the energy transmitter being connected to a piezoelectric system which converts the high frequency electrical output signal HF present at the output of the amplifier unit into ultrasonic vibrations, the piezoelectric system being coupled to the tool for transmitting the ultrasonic vibrations to the tool.

[0017] Further details, advantages and features of the present invention can be gathered, individually and / or in combination, from the claims and the features found therein, but also from the following description of preferred examples which can be found in the description of the drawings. [Brief description of the drawings]

[0018] [Figure 1] FIG. 2 is a block diagram of an ultrasonic generator for generating ultrasonic waves for vibrating a tool. [Diagram 2] FIG. 2 is a block diagram of the generator unit and the control unit. [Diagram 3] 1 is a curve of the input current of an amplifier unit of an ultrasonic generator as a tuning variable against the frequency as a setting variable for setting the optimum operating point. [Figure 4] 1 is a curve of the input current of an amplifier unit of an ultrasonic generator as a tuning variable against the frequency as a setting variable for setting an operating point with a given vibration amplitude. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] 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 connected on the input side to a grid voltage 20.

[0020] An energy transmitter 22, for example an inductive transmitter or alternatively a cable connection or slip ring transmitter, is connected to the output of the amplifier unit 14, where a high frequency electrical output signal HF is present for operating a piezoelectric system 24. The piezoelectric system 24, which generates ultrasonic vibrations from the high frequency electrical output signal HF, is coupled to a tool 26 or to a tool holder (not shown) receiving the tool 26, and couples the ultrasonic vibrations to the tool 26, such that said tool performs the required ultrasonic vibrations. The frequency and amplitude of the ultrasonic vibrations are settable by the frequency f and the amplitude of the high frequency electrical output signal HF.

[0021] It is known from the literature that machining processes such as grinding or metal cutting machining can be assisted by coupling ultrasonic vibrations into a tool 26, since they generate oscillations of the tool which generate motion amplitudes in the range of a few micrometers at the contact between the tool and the workpiece, which result in a reduction of the process forces. Ultrasonic waves can be introduced into the tool longitudinally and / or transversely.

[0022] The idea behind the invention is to adjust the frequency and / or amplitude of the ultrasonic vibrations of the tool 26 based on the size of the input current Iein or the input power Pein of the amplifier unit 14. In particular, an improved amplitude adjustment should be provided, regardless of the damping of the system. The adjustment of the input current I is performed using the control unit 12.

[0023] 2 shows a block diagram of the control unit 12 designed in the form of a microcontroller. The control unit 12 comprises a comparator unit 28, a regulator unit 30 and a calculation and storage unit 32. The input current Iein of the amplifier unit 14 is measured by the current sensor 16 and is supplied to the comparator unit 28 and to the calculation and storage unit 32 as an actual current value Iist. A set point current value Isoll is provided by the calculation and storage unit 32 and is supplied to the comparator unit 28. The output of the comparator unit 28 is connected to the input of the regulator unit 30. The regulator unit 30 generates a control variable with which the frequency f of the high frequency electrical control signal HFS of the oscillator unit 13 can be set. The control variable, present at the output of the regulator unit 30 and proportional to the frequency f of the high frequency control signal HFS, is provided to the storage unit 32. The amplitude of the high frequency control signal HFS can also be set, which is substantially proportional to the amplitude deflection of the tool 26, regardless of the frequency f.

[0024] The high frequency electrical control signal HFS is connected to an input of an amplifier circuit 14 and is amplified by the amplifier circuit 14. An amplified high frequency electrical output signal HF is present at an output of the amplifier circuit 14 for exciting a piezoelectric system 24.

[0025] According to the present invention, the following steps are performed:

[0026] Since the efficiency of the workpiece machining due to the superposition of ultrasonic vibrations depends in particular on the geometry of the tool used and its clamping length, the tool 26 is scanned in a first step by a frequency sweep of the ultrasonic generator 10. The frequency sweep, i.e. the scan, is carried out in a selected and defined frequency band defined by a minimum frequency of the control signal HFS, for example fmin=1 kHz, and a maximum frequency, for example fmax=100 kHz. The oscillator unit 13 is designed to generate a high-frequency control signal HFS in a further frequency band, for example fmin=1 kHz to fmax=100 kHz. During the frequency sweep, the input current Iein of the amplifier circuit 14 and the control variable present at the output of the regulator unit 30 and proportional to the frequency f of the oscillator unit 13 are recorded and stored in the calculation and storage unit 32, allowing the recording of a curve of the input current Iein against the frequency f.

[0027] 3 shows a curve of the input current Iein recorded during a frequency sweep over the frequency f of the high-frequency control signal HFS, which corresponds to the frequency f of the ultrasonic vibrations. Based on the recorded input current Iein, in a second step, a resonance point RS for the system composed of the energy transmitter 22, the piezoelectric system 24 and the tool 26 is determined in the calculation and storage unit 32. At the resonance point RS, the input current Iein shows its maximum value Imax (max). The maximum value Imax is stored. The point of the maximum value Imax, i.e. the frequency f at the resonance point RS, is stored in the calculation and storage unit 32 as the resonance frequency fres.

[0028] After determining the resonant frequency fres, machining of the workpiece using the tool 26 can begin in a third step.

[0029] During operation of the tool 26, the input current Iein is continuously measured using the current sensor 16. Using the input current Iein continuously recorded during operation, the frequency f of the oscillator unit 13 and thus the frequency f of the amplified high frequency output signal HF is readjusted in a fourth step.

[0030] The input current Iein measured as an actual current value and the maximum value Imax of the input current are supplied as input variables to a comparator unit 28. In the comparator unit 28, the input current Iein measured as an actual current value is compared with the maximum value Imax as a setpoint current value. If the measured input current Iein is below the setpoint current value Imax from the frequency sweep, for example 10% below Imax, a regulation difference is present at the output of the comparator unit 28, which regulation difference is supplied to a regulator unit 30. Depending on the regulation difference, a control variable is generated at the output of the regulator unit 30, and by means of the control variable the oscillator unit 13 is operated to set the frequency f of the high frequency control signal HFS. The frequency f of the high frequency control signal HFS is the setpoint variable for the regulation section formed by the amplifier unit 14, the energy transmitter 22, the piezoelectric system 24 and the workpiece 26.

[0031] Therefore, controlling the frequency f of the oscillator unit 13 also sets the frequency of the high frequency output signal HF for operating the energy transmitter 22 having the piezoelectric system 24 and the tool 26 as a tuning section, so that the input current Iein reaches its maximum value Imax.

[0032] Figure 3 shows that when the measured input current Iein is smaller than the maximum value Ima, the system can be located at either the operating point AP1 where f1 < fres or the operating point AP2 where f2 > fres. To determine the operating point AP1 or AP2, the oscillator unit 13 is operated by a setting variable such that the frequency of the oscillator unit 13 is increased or decreased in increments of, for example, 1 Hz, 10 Hz, or 100 Hz. At the same time, the behavior of the input current Iist is analyzed. If the input current Iist increases when the frequency f is increased, the system is at the operating point AP1, and the frequency f is increased until the input current Iist reaches the maximum value Imax. However, if the input current Iist drops when the frequency f is increased, the system is at the operating point AP2, and thus the frequency f is decreased until the input current Iist reaches the maximum value Imax.

[0033] Therefore, the idea underlying this method is to readjust the system using the input current Iist continuously recorded during operation, and when the current value Imax from the frequency sweep (+ / - tolerance) is not achieved, the system is returned to its maximum current Imax by analyzing a slight change (+ / -) in the frequency f and the resulting behavior (response) of the input current Iist.

[0034] In other words, the amplifier circuit 14 having the current sensor 16 as a measuring device, the comparator unit 28 as a comparator, the regulator unit 30 as a regulator, the oscillator unit 13 as a setting device, and the energy transmitter 22, the piezoelectric system 24, and the tool 26 forms an adjustment circuit as an adjustment section, and the input current Iist as an adjustment variable is readjusted during operation such that the input current Iist reaches its maximum value Imax and the system is effectively operated at the resonance point RS.

[0035] In the method according to the invention, it is also possible to control the amplitude deflection Amp of the tool 26 using the supplied input current Iist.

[0036] FIG. 4 shows the input current Iist versus the frequency f of the high-frequency signal HF. By varying the frequency f, for example to a frequency value famp, the input current Iist can be set to a current value Iamp such that the system is at the required operating point AP with the required amplitude Amp of the tool 26. By varying the frequency f, the operating point AP can be shifted on the curve of the input current Iist in the direction of the indicated arrow, i.e. rising or falling on the curve. The shift of the operating point AP on the current curve corresponds to a change in the amplitude deflection or vibration amplitude of the tool 26. By moving the operating point AP of the system on an approximately linear partial section of the current curve with a constant slope, the vibration amplitude can be set between a maximum amplitude maxAmp and a minimum amplitude minAmp. In other words, an amplitude adjustment is achieved based on the input current Iist.

Claims

1. A method for controlling an oscillator unit (13) of an ultrasonic generator (10) in a machine tool for generating ultrasonic waves for exciting a tool (26) for machining a workpiece, the method comprising: determining a control variable for controlling a frequency f of an electrical control signal generated by said oscillator unit (13), the control variable being determined for controlling a frequency f of an electrical control signal generated by said oscillator unit (13), the method comprising:

4. The method of claim 3, wherein the control variables are determined in response to an analysis of the size of the input and / or output current I or the input and / or output power P of the ultrasonic generator (10).

2. The control variables are determined solely in response to an analysis of the input and / or output currents I or the input and / or output powers P.

2. The method according to claim 1 .

3. The electrical control signal HFS is amplified by an amplifier unit (14) of the ultrasonic generator (10), and the analysis of the size of the input and / or output current I comprises a comparison of the size / amplitude of the input and / or output current Iein of the amplifier unit (14) with a set point current value Isoll.

3. The method according to claim 1 or 2.

4. The set point current value Isoll is determined by scanning the tool (26) before performing the machining by the ultrasonic generator (10) and by the oscillator unit (13) exciting the tool (26) during a frequency sweep in a definable frequency band having different frequencies f, the input current Iein or the input power Pein of the amplifier unit (14) is recorded during the frequency sweep across the frequencies f, and based on the current curve a maximum current Imax is determined and stored as the set point current value at a resonance point RS and the associated resonance frequency fres. The method according to any one of claims 1 to 3, characterized in that

5. Machining of the workpiece (26) at the stored resonant frequency fres is commenced. The method according to any one of claims 1 to 4, characterized in that

6. The input current Iein or the input power Pein of the amplifier unit (14) is measured during machining of the workpiece (26), the size / amplitude of the input current Iein as an actual current value Iist is continuously compared with the maximum current Imax as the set point current value Isoll, and depending on the difference between the actual current value Iist and the maximum current Imax, the control variable is determined, whereby the frequency f of the oscillator unit (13) is changed in such a way that the actual current value Iist reaches or approaches the maximum current Imax. The method according to any one of claims 1 to 5, characterized in that

7. In the event of a change in the frequency f of the oscillator unit (13), the reaction of the input current Iein is analyzed, and whenever the input current Iein rises in the event of a change in the frequency f, the frequency f is further changed in the same direction as the change until the input current Iein reaches the maximum current Imax, and whenever the input current Iein falls in the event of a change in the frequency f, the frequency f is changed in the opposite direction to the change until the input current Iein reaches the maximum current Imax. The method according to any one of claims 1 to 6, characterized in that

8. The amplitude deflection AMP of the tool (26) is set using the size of the input current Iein. The method according to any one of claims 1 to 7, characterized in that

9. The size of the input current Iein is set using the setting of the frequency f of the oscillator unit (13), said frequency being higher or lower than the resonant frequency fres. The method according to any one of claims 1 to 8, characterized in that

10. An ultrasonic generator (10) in a machine tool for generating ultrasonic waves for exciting a tool (26) for machining a workpiece, comprising: an oscillator unit (13) designed to emit an electrical control signal HFS having a frequency f for generating said ultrasonic waves; a control unit (12) designed to determine a control variable for controlling the frequency f of the electrical control signal HFS generated by the oscillator unit (13); 1. An ultrasonic generator comprising: an ultrasonic transducer configured to determine a control variable in response to an analysis of the size / amplitude of an input and / or output current I or the size / amplitude of an input and / or output power P of the ultrasonic generator;

11. The ultrasonic generator (10) comprises an amplifier unit (14) designed to amplify the electrical control signal HFS generated by the oscillator unit (13), The ultrasonic generator (10) comprises a current sensor (16) designed to measure the input current Iein of the amplifier unit (14), said control unit (12) having a comparator unit (28) designed to compare said input current Iein with a set point current value Isoll, preferably a resonant current Ires, and to provide it as a regulated difference; The control unit (12) comprises a regulator unit (30) designed to determine the control variable depending on the regulation difference between the input current Iein and a setpoint current value Isoll.

11. The ultrasonic generator according to claim 10.

12. An energy transmitter (22), e.g. an inductive transmitter, cable connection or slip ring transmitter, is connected to the output of the amplifier unit (14), the energy transmitter (22) being connected to a piezoelectric system (24) which converts a high frequency electrical output signal (HF) present at the output of the amplifier unit (14) into ultrasonic vibrations, the piezoelectric system (24) being coupled to the tool (26) for transmitting the ultrasonic vibrations to the tool.

12. An ultrasonic generator according to claim 10 or 11.

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