Method for controlling an ultrasonic generator, and ultrasonic generator

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 generating 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 present invention further relates to an ultrasonic generator in a machine tool for generating ultrasonic waves for exciting a tool for machining a workpiece, comprising an oscillator unit designed to emit an electrical control signal for generating ultrasonic waves and a control unit designed to determine a control variable for controlling the frequency f of the electrical control signal generated by the oscillator unit.

Background Art

[0003] A corresponding method and system 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, for machining a workpiece, electrical signals having different frequencies are generated, the frequencies being within the ultrasonic frequency range. The ultrasonic waves transmitted to the tool are generated by the electrical signals. A phase shift of the electrical signal depending on the frequency is then determined as an adjustment variable, and the phase shift is analyzed depending on the frequency. Finally, an adjustment algorithm for controlling the frequency of the ultrasonic waves generated by the ultrasonic generator is determined depending on the analysis of the phase shift. The determination and analysis of the phase shift as an adjustment variable are complex. The voltage and current curves of the electrical signal have to be evaluated simultaneously with each other.

[0004] A further method for controlling an ultrasonic generator is known from DE 10 ******** A1. In this method, a ceramic sensor is additionally required on the tool.

[0005] Based on this, the fundamental objective of the present invention is to develop a method for controlling an ultrasonic generator of the type of machine tool described above, such that the vibration of the tool can be set in an easy manner, and in particular, that the amplitude deflection of the tool can be set accurately and reproducibly. [Overview of the project]

[0006] This objective is partially addressed by the present invention in which the control variable is determined in accordance with an analysis of the size / amplitude of the input and / or output current I of the ultrasonic generator, or the input and / or output power P. The present invention is preferably based solely on the idea of ​​readjusting the system's vibrations using a current continuously recorded during operation, particularly the input current Iein or the combined power Pzu.

[0007] Preferably, the electrical control signal HFS generated by the oscillator unit is amplified by the amplifier unit of the ultrasonic generator, and the size / amplitude analysis 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 the setpoint current value Isoll.

[0008] In a particularly preferred procedure, the setpoint current value Isoll is determined by scanning the tool before machining with the ultrasonic generator and by the oscillator unit exciting the tool during a frequency sweep in a definable frequency band having different frequencies f; the amplifier unit input current Iein or input power Pein is recorded during the frequency sweep over frequency f; and based on the current curve, the maximum current Imax or maximum power Pmax is determined and stored as the setpoint value at the resonance point RS and the associated resonance frequency fres.

[0009] Machining of the workpiece at the preserved resonant frequency fres can then be initiated.

[0010] Furthermore, according to the present invention, the input current Iein or input power Pein of the amplifier unit is measured during the machining of the workpiece, the size of the input current Iein as the actual current value is continuously compared with the maximum current Imax as the setpoint current value (reference variable), the control variable for the oscillator unit (setting device) is determined according to the difference (adjustment difference) between the actual current value and the maximum current Imax, and the frequency f as the setpoint variable for the oscillator unit (setting device) is changed by the control variable so that the input current Iein reaches or approaches the maximum current Imax. This method offers the advantage that only the input current Iein needs to be measured, and the current curve can be obtained in a simple manner. In addition, the control variable can be determined by simple means as the difference between the input current and the maximum current at the resonance point.

[0011] It must be particularly emphasized that when the oscillator unit's frequency f changes, the response of the input current Iein is analyzed, and when the input current Iein rises in response to the change in frequency f, the frequency f is changed in the same direction as the change until the input current reaches its maximum current Imax, and whenever the input current I falls in response to the change in frequency f, the frequency f is changed in the opposite direction to the change until the input current Iein reaches its maximum current Imax. Rapid control is achieved in this manner.

[0012] The original idea is characterized by the tool's amplitude deflection amplifier being set using the size of the input current Iein. Here, the size of the input current Iein is set using the setting of the oscillator unit's frequency f, which is higher or lower than the resonant frequency fres.

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

[0014] According to the present invention, the control unit is preferably designed to determine control variables in accordance with an analysis of the size / amplitude of the input and / or output current I of the ultrasonic generator (10), or the size / amplitude of the input and / or output power P.

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

[0016] Particularly preferably, an energy transmitter, such as an inductive transmitter, cable connection, or slip ring transmitter, is connected to the output of an amplifier unit, and the energy transmitter is connected to a piezoelectric system that converts a high-frequency electrical output signal HF present at the output of the amplifier unit into ultrasonic vibrations, and the piezoelectric system is coupled to a tool to transmit the ultrasonic vibrations to the tool.

[0017] Further details, advantages, and features of the present invention can be gathered not only from the claims and features found herein, individually and / or in combination, but also from the following description of preferred examples found in the description of the drawings. [Brief explanation of the drawing]

[0018] [Figure 1] This is a block diagram of an ultrasonic generator for generating ultrasonic waves to vibrate tools. [Figure 2] This is a block diagram of the generator unit and control unit. [Figure 3] This is a curve of the input current of the ultrasonic generator's amplifier unit as an adjustment variable, with respect to frequency as a setting variable for determining the optimal operating point. [Figure 4] The curve of the input current of the ultrasonic generator's amplifier unit is used as an adjustment variable with respect to frequency, which is a setting variable for setting an operating point with a predetermined vibration amplitude. [Modes for carrying out the invention]

[0019] Figure 1 shows a block diagram of an ultrasonic generator 10, which includes a control unit 12, an oscillator unit 13, an amplifier unit 14, sensor units such as a current sensor 16, and a voltage supply unit 18 connected to the grid voltage 20 on the input side.

[0020] An energy transmitter 22, such as an inductive transmitter or alternatively a cable connection or slip ring transmitter, is connected to the output of an amplifier unit 14, where a high-frequency electrical output signal HF is present to operate 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) that receives the tool 26, and couples the ultrasonic vibrations to the tool 26 so that the tool performs the required ultrasonic vibrations. The frequency and amplitude of the ultrasonic vibrations can be set 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 are assisted by coupling ultrasonic vibrations to the tool 26, because the ultrasonic vibrations generate the oscillation of the tool, which generates a movement amplitude within the range of a few micrometers at the contact between the tool and the workpiece, and the reduction of the process force results from that amplitude. The ultrasonic waves can be introduced longitudinally and / or transversely into the tool.

[0022] The idea underlying the present 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, improved amplitude adjustment should be provided regardless of the attenuation of the system. The adjustment of the input current I is carried out using the control unit 12.

[0023] Figure 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 memory unit 32. The input current Iein of the amplifier unit 14 is measured by the current sensor 16 and supplied as the actual current value Iist to the comparator unit 28 and the calculation and memory unit 32. The setpoint current value Isoll is provided by the calculation and memory unit 32 and 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 that can set the frequency f of the high-frequency electrical control signal HFS of the oscillator unit 13. 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 memory unit 32. Regardless of the frequency f, the amplitude of the high-frequency control signal HFS, which is substantially proportional to the amplitude deflection of the tool 26, can also be set.

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

[0025] According to the present invention, the following procedure is executed.

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

[0027] FIG. 3 shows the curve of the input current Iein recorded during frequency sweeping over the frequency f of the high-frequency control signal HFS, and the frequency f of the high-frequency control signal HFS corresponds to the frequency f of the ultrasonic vibration. Based on the recorded input current Iein, in the second step, the 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 (maximum). The maximum value Imax is stored. The frequency f at the point of the maximum value Imax, i.e., the resonance point RS, is stored in the calculation and storage unit 32 as the resonance frequency fres.

[0028] After determining the resonance frequency fres, the machining of the workpiece using the tool 26 can be started in the third step.

[0029] During the operation of 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 therefore the frequency f of the amplified high-frequency output signal HF, is readjusted in the fourth step.

[0030] The input current Iein, measured as an actual current value, and the maximum value of the input current Imax are supplied to the comparator unit 28 as input variables. 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 lower than the setpoint current value Imax from the frequency sweep, for example, 10% below Imax, a tuning difference exists at the output of the comparator unit 28, and this tuning difference is supplied to the tuner unit 30. Depending on the tuning difference, a control variable is generated at the output of the tuner unit 30, and using 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 a set variable for the tuning 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, which has a piezoelectric system 24 and tool 26 as adjustment sections, so that the input current Iein reaches its maximum value Imax.

[0032] Figure 3 shows that when the measured input current Iein is less 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 set 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 therefore 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 measurement 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] Figure 4 shows the input current Iist with respect to the frequency f of a high-frequency signal HF. By changing the frequency f, for example, to the frequency value famp, the input current Iist can be set to the current value Iamp such that the system is at the required operating point AP with the required amplitude Amp of the tool 26. By changing the frequency f, the operating point AP can be shifted on the curve of the input current Iist in the direction of the arrow shown, 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 a substantially straight subsection 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, amplitude adjustment is achieved based on the input current Iist. The invention described in the original claims of this application is listed below. [1] A method for controlling an oscillator unit (13) of an ultrasonic generator (10) in a machine tool for generating ultrasonic waves to vibrate a tool (26) for machining a workpiece, wherein a control variable is determined to control the frequency f of an electrical control signal generated by the oscillator unit (13), The method is characterized in that the control variable is determined according to an analysis of the size of the input and / or output current I or input and / or output power P of the ultrasonic generator (10). [2] The control variables are determined solely by an analysis of the input and / or output current I, or the input and / or output power P. The method according to [1], characterized in that [3] The electrical control signal HFS is amplified by the 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 the setpoint current value Isoll. The method according to [1] or [2], characterized by the following: [4] The setpoint current value Isoll is determined by scanning the tool (26) before machining is performed by the ultrasonic generator (10), and by the oscillator unit (13) vibrating the tool (26) during a frequency sweep in a definable frequency band having different frequencies f, the input current Iein or input power Pein of the amplifier unit (14) is recorded during the frequency sweep over the frequency f, and based on the current curve, the maximum current Imax is determined and stored as the setpoint current value at the resonance point RS, and the associated resonance frequency fres. The method according to any one of [1] to [3], characterized by the following: [5] Machining of the workpiece (26) is started at the stored resonant frequency fres. The method according to any one of [1] to [4], characterized by the following: [6] The input current Iein or input power Pein of the amplifier unit (14) is measured during machining of the workpiece (26), and the size / amplitude of the input current Iein as the actual current value Iist is continuously compared with the maximum current Imax as the setpoint current value Isoll, and the control variable is determined according to the difference between the actual current value Iist and the maximum current Imax, thereby changing the frequency f of the oscillator unit (13) so that the actual current value Iist reaches or approaches the maximum current Imax. The method according to any one of [1] to [5], characterized by the following: [7] When the frequency f of the oscillator unit (13) changes, the response of the input current Iein is analyzed, and when the input current Iein rises in response to the change in 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 response to the change in 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 [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 [1] to [7], characterized by the following: [9] The size of the input current Iein is set using the frequency f setting of the oscillator unit (13), the frequency being higher or lower than the resonant frequency fres. The method according to any one of [1] to [8], characterized by the following:

[10] An ultrasonic generator (10) in a machine tool for generating ultrasonic waves to vibrate a tool (26) for machining a workpiece, An oscillator unit (13) designed to emit an electrical control signal HFS having a frequency f for generating the aforementioned ultrasonic waves, An ultrasonic generator comprising: 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), wherein the control unit (12) is designed to determine the control variable in accordance with an analysis of the size / amplitude of the input and / or output current I of the ultrasonic generator (10), or the size / amplitude of the input and / or output power P.

[11] The ultrasonic generator (10) has an amplifier unit (14) designed to amplify the electrical control signal HFS generated by the oscillator unit (13), and the ultrasonic generator (10) has a current sensor (16) designed to measure the input current Iein of the amplifier unit (14), The control unit (12) has a comparator unit (28) designed to compare the input current Iein with a setpoint current value Isoll, preferably a resonant current Ires, and provide it as an adjustment difference. The control unit (12) has a regulator unit (30) designed to determine the control variable according to the adjustment difference between the input current Iein and the setpoint current value Isoll. The ultrasonic generator according to

[10] , characterized in that it is a device.

[12] An energy transmitter (22), for example, an inductive transmitter, a cable connection or a slip ring transmitter, is connected to the output of the amplifier unit (14), the energy transmitter (22) is connected to a piezoelectric system (24) that converts a high-frequency electrical output signal (HF) present at the output of the amplifier unit (14) into ultrasonic vibrations, the piezoelectric system (24) is coupled to the tool (26) to transmit the ultrasonic vibrations to the tool. An ultrasonic generator as described in

[10] or

[11] , characterized by the above.

Claims

1. A method for controlling an oscillator unit (13) of an ultrasonic generator (10) in a machine tool for generating ultrasonic waves to vibrate a tool (26) for machining a workpiece, wherein a control variable is determined to control the frequency f of an electrical control signal generated by the oscillator unit (13), The method is characterized in that the control variable is determined solely by analyzing 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 electrical control signal HFS is amplified by the 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 the setpoint current value Isol. The method according to claim 1, characterized in that

3. The setpoint current value Isol is determined by scanning the tool (26) before machining is performed by the ultrasonic generator (10), and by the oscillator unit (13) vibrating the tool (26) during a frequency sweep in a definable frequency band having different frequencies f; the input current Iein or input power Pein of the amplifier unit (14) is recorded during the frequency sweep over the frequency f; and based on the current curve, the maximum current Imax is determined and stored as the setpoint current value at the resonance point RS and the associated resonance frequency fres. The method according to claim 2, characterized in that

4. Machining of the workpiece (26) is started at the stored resonant frequency fres. The method according to claim 3, characterized in that

5. The input current Iein or input power Pein of the amplifier unit (14) is measured during machining of the workpiece (26), and the size / amplitude of the input current Iein as the actual current value Iist is continuously compared with the maximum current Imax as the setpoint current value Isol. Depending on the difference between the actual current value Iist and the maximum current Imax, the control variable is determined, thereby changing the frequency f of the oscillator unit (13) so that the actual current value Iist reaches or approaches the maximum current Imax. The method according to claim 3, characterized in that

6. When the frequency f of the oscillator unit (13) changes, the response of the input current Iein is analyzed. If the input current Iein rises when the frequency f changes, the frequency f is further changed in the same direction as the rise until the input current Iein reaches the maximum current Imax. Whenever the input current Iein falls when the frequency f changes, the frequency f is changed in the opposite direction to the rise until the input current Iein reaches the maximum current Imax. The method according to claim 3, characterized in that

7. 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 6, characterized in that

8. The size of the input current Iein is set using the frequency f setting of the oscillator unit (13), where the frequency is higher or lower than the resonant frequency fres. The method according to any one of claims 1 to 7, characterized in that

9. An ultrasonic generator (10) in a machine tool for generating ultrasonic waves to vibrate a tool (26) for machining a workpiece, An oscillator unit (13) designed to emit an electrical control signal HFS having a frequency f for generating the aforementioned ultrasonic waves, A control unit (12) is designed to determine a control variable for controlling the frequency f of the electrical control signal HFS generated by the oscillator unit (13), and An ultrasonic generator comprising the above, wherein the control unit (12) is designed to determine the control variables exclusively in accordance with the analysis of the size / amplitude of the input and / or output current I of the ultrasonic generator (10), or the size / amplitude of the input and / or output power P.

10. The ultrasonic generator (10) has an amplifier unit (14) designed to amplify the electrical control signal HFS generated by the oscillator unit (13), and the ultrasonic generator (10) has a current sensor (16) designed to measure the input current Iein of the amplifier unit (14). The control unit (12) has a comparator unit (28) designed to compare the input current Iein with the setpoint current value Isol and provide it as an adjustment difference. The control unit (12) has a regulator unit (30) designed to determine the control variable according to the adjustment difference between the input current Iein and the setpoint current value Isol. The ultrasonic generator according to claim 9, characterized in that...

11. An energy transmitter (22) is connected to the output of the amplifier unit (14), the energy transmitter (22) is connected to a piezoelectric system (24) that converts a high-frequency electrical output signal (HF) present at the output of the amplifier unit (14) into ultrasonic vibrations, and the piezoelectric system (24) is coupled to the tool (26) to transmit the ultrasonic vibrations to the tool. The ultrasonic generator according to claim 10, characterized in that...

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