Method and system for controlling an ultrasonic generator of a machine tool for machining a workpiece

Abstract

The present invention relates to a system and method for controlling an ultrasonic generator of a machine tool to generate ultrasound for machining a workpiece. According to the invention, a determined ultrasonic phase shift as a function of frequency is analyzed, and based on this analysis, a regulation algorithm for controlling the ultrasonic frequency generated by the ultrasonic generator is determined.

Description

Technical Field

[0001] A method and system for controlling an ultrasonic generator of a machine tool to generate ultrasound for machining a workpiece. Background Art

[0002] Machine tools allow for flexible, mostly chip-removing machining of workpieces. Therefore, they include a variety of different tools, depending on the component size and the material being machined. Typically, chip-removing machining of metallic materials is performed using milling or lathe machining with geometrically defined edges. However, brittle and hard workpieces such as ceramics may only be adequately machined with geometrically defined edges due to their material-specific properties. In such applications, ultrasonic machining is often more suitable for cost-effective machining of the workpieces.

[0003] For this purpose, there are some machine tools known in the art in which the tool kinematics of conventional machining processes, such as grinding or chip removal, are supported by the addition of high-frequency vibrations. These oscillations generate motion amplitudes in the range of a few micrometers at the contact point between the tool and the workpiece, thereby reducing the machining forces.

[0004] Ultrasonic machine tools include an ultrasonic generator that generates ultrasonic vibrations. These vibrations are transmitted primarily via a piezoelectric system to a tool holder that is replaceably inserted into, for example, a milling spindle. The efficiency of ultrasonically processed workpieces depends on, for example, the geometry of the tool used and its clamping length. Summary of the Invention

[0005] An object of the present invention is to provide a method and a system, respectively, for controlling an ultrasonic generator of a machine tool to generate ultrasound for machining a workpiece, which enable optimized ultrasonic machining by the machine tool.

[0006] This object is solved by the features according to independent claims 1 and 8. The dependent claims thus relate to special embodiments of the invention.

[0007] The method for controlling an ultrasonic generator of a machine tool for generating ultrasonic waves for machining a workpiece according to the present invention includes the following steps: generating electrical signals having different frequencies within the ultrasonic frequency range. This allows for optimal utilization of the natural frequency of the vibration system used for machining the workpiece. In some embodiments, the electrical signals having different frequencies can be generated continuously. In some embodiments, the generated electrical signals can include multiple superimposed electrical signals having different frequencies.

[0008] Preferably, all frequency points of the generated different frequencies are part of a predetermined frequency band that determines the possible operating range with respect to the frequency. This can have the advantage of ensuring that the frequency adjustment also meets the requirements of the workpiece processing with respect to the frequency.

[0009] In a particularly advantageous embodiment, generating the electrical signals with different frequencies may comprise sweeping a predetermined frequency spectrum (frequency passing). In some embodiments, the frequency spectrum of the different frequencies, in particular the frequency spectrum of the sweeping frequency passing, may depend on the tool (mass, temperature), machining parameters (feed, rotation speed, cross feed) and / or one or more workpiece characteristics such as material, geometry, size, mass, etc.

[0010] Another step of the method is to apply ultrasonic waves to the tool via an electrical signal. When applying ultrasonic waves, for example, the generated electrical signal can be converted into a mechanical signal (ultrasonic wave) by, for example, a motor such as a piezoelectric motor.

[0011] The method further comprises the steps of determining a phase shift (phase shift angle) of the ultrasonic wave as a function of frequency, analyzing the phase shift as a function of frequency, and determining a regulation algorithm for controlling the ultrasonic frequency generated by the ultrasonic generator based on the analysis of the phase shift.

[0012] Determining the phase shift of the ultrasonic wave may, for example, include determining a phase shift angle (phase shift) between the voltage of the generated electrical signal and the current of the generated electrical signal.

[0013] Analysis of the phase shift may include a quantitative comparison of the phase shift as a function of frequency with a phase reference value.

[0014] The advantage of this approach is that, when a machine tool uses ultrasound to process different workpieces, the frequency of the ultrasound can be easily and effectively adjusted to ensure that the vibrating tool resonates with the ultrasound as closely as possible. Consequently, energy consumption (in the form of ultrasound) can be reduced to deflect the tool's operating range by a predetermined amount.

[0015] The use of different control algorithms based on the analysis of the phase shift as a function of frequency has the advantage that the controller (control algorithm) can be designed particularly efficiently and stably. In addition, errors caused by noise, for example, when determining the phase shift as a control amplitude can be ignored.

[0016] In a particularly advantageous configuration of the method, for example, when phase shift analysis indicates that, at a frequency point, the first phase reference value is relatively low, the method can include the step of specifying a phase shift adjustment target, adjusting the frequency generated by the ultrasonic generator to achieve the phase shift adjustment target, and machining the workpiece while adjusting the ultrasonic frequency. Under the condition that the first phase reference value is relatively low, it can be determined whether the predetermined adjustment target can be (approximately) achieved. Based on this, the adjustment algorithm can be optimized. This has the advantage of enabling a particularly efficient and robust controller design.

[0017] The phase shift adjustment target can be, for example, a phase shift of 0° or within a range close to 0°, which means that at the corresponding frequency, the body to which the ultrasound waves are applied is in a resonant state. This has the advantage of amplifying overlapping ultrasound waves, thereby reducing the energy consumption required to achieve the desired amplitude of the ultrasound waves.

[0018] The first phase reference value can advantageously have a value that is in particular 3° above the phase control target. This can have the advantage that overshoots during regulation / control, for example at the phase control target when regulating to a phase value of 0°, do not lead to a modification of the regulation algorithm.

[0019] In a particularly effective embodiment, when the phase shift adjustment target can be achieved using two different frequencies, the frequency generated by the ultrasonic generator for achieving the phase shift adjustment target can be adjusted to the higher of the two frequencies. This has the advantage of reducing the energy consumption required to generate the predetermined deflection.

[0020] In a particularly advantageous configuration, when, for example, a phase shift adjustment target can be achieved using two or more different frequencies, the frequency generated by the ultrasonic generator to achieve the phase shift adjustment target can be adjusted to a frequency at which the impedance (resistance) for generating ultrasonic waves is lower than the impedance values at the two or more different frequencies. This has the advantage that, when, for example, ultrasonic waves are generated using a piezoelectric motor, a lower voltage is required to generate the desired ultrasonic excitation.

[0021] In a particularly optimized embodiment, for example, when the analysis of the phase shift shows that the first phase reference value is exceeded at all frequency points and / or the second phase reference value is relatively low at at least one frequency point, the method may include the following steps: adjusting the frequency generated by the ultrasonic generator so that the phase shift is minimized, and processing the workpiece while adjusting the frequency of the ultrasonic wave.

[0022] This can have the advantage of using a minimum controller that is particularly effective at finding the minimum, for example, when it is expected that a phase adjustment target of 0° may not be achieved. Thus, the control of the ultrasonic generator and, therefore, the control of the machine tool for improved workpiece machining with respect to energy savings and workpiece machining speed can be optimized.

[0023] In a particularly general embodiment, for example, when the analysis of the phase shift shows that a second phase reference value is exceeded at all frequency points, the method may include the steps of determining a frequency of different frequencies at which the determined phase shift is minimum, machining the workpiece while adjusting the frequency of the ultrasonic wave, and varying the frequency in a predetermined machining frequency band around the determined frequency during machining of the workpiece.

[0024] This can have the advantage that, in particular in cases where phase noise and minimal phase shift are of low significance, the tool can be excited as well as possible so that it resonates with the excitation. As a result, the energy consumption required to vibrate the tool to a predetermined degree can be reduced.

[0025] In a preferred embodiment, the processing frequency band may be a frequency band of ±600 Hz around a center frequency. In some embodiments, varying the frequency of the frequency sweep may specifically comprise a frequency pass. For example, this may occur linearly via a voltage controlled oscillator (VCO).

[0026] In a particularly advantageous embodiment, in particular when changing the frequency by discrete values, the step size at the edge of the frequency band can be larger than the step size in the center of the processing frequency band.

[0027] In a particularly advantageous embodiment, the method may comprise the following steps: determining the phase shift between the generated ultrasonic wave and the reflected ultrasonic wave as a function of frequency while varying the frequency; analyzing the phase shift as a function of frequency; determining a new frequency from a processing frequency band around the determined frequency with the minimum phase shift; and varying the frequency in the processing frequency band around the newly determined frequency.

[0028] This has the advantage that, in particular when it is difficult to identify the minimum phase shift, the frequency control can be improved by iterative adjustment to a more resonant frequency range of the tool. As a result, the energy consumption for workpiece machining can be minimized.

[0029] In a particularly flexible embodiment, the method may comprise the steps of determining a phase shift between the generated ultrasonic waves and the reflected ultrasonic waves as a function of frequency during machining of the workpiece, analyzing the phase shift as a function of frequency during machining of the workpiece, and varying a regulation algorithm for controlling the ultrasonic frequency generated by the ultrasonic generator based on the analysis of the phase shift.

[0030] This has the advantage that the control of the ultrasonic generator, in particular the control algorithm, is instantly adapted (in particular during workpiece processing, according to the embodiment and optimally) to changes in system parameters that occur, for example, due to heat sources, tool properties, workpiece properties, processing characteristics, etc. As a result, workpiece processing can be improved in terms of quality, speed and energy consumption.

[0031] A system for controlling an ultrasonic generator of a machine tool for generating ultrasonic waves for machining a workpiece according to the present invention includes an ultrasonic generator for generating ultrasonic waves for machining a workpiece, a phase shift determination unit for determining a phase shift of the ultrasonic waves, an evaluation unit for analyzing the phase shift as a function of frequency and determining a regulation algorithm based on the analysis of the phase shift, and a control unit for regulating the frequency based on the phase shift between the generated and reflected ultrasonic waves and based on the determined regulation algorithm.

[0032] For example, the ultrasonic generator may include a piezoelectric motor for converting electric current into mechanical motion, and / or a frequency generator for generating electric current and voltage at predetermined frequencies, respectively.

[0033] In some embodiments, the ultrasonic generator can generate electrical signals having different frequencies. In some embodiments, the electrical signals having different frequencies can be generated continuously. In some embodiments, the generated electrical signal can include multiple superimposed electrical signals having different frequencies. For example, one electrical signal can be converted into an ultrasonic wave by one or more piezoelectric motors.

[0034] An example of an ultrasonic phase shift is the phase shift between the current and voltage of an electrical signal converted to ultrasound.

[0035] The phase shift determination unit may be an analog and / or digital circuit for determining the phase shift.Thus, in some embodiments, the phase shift determination unit may comprise one or more analog-to-digital converters (ADCs).

[0036] For analyzing the phase shift, the evaluation unit may comprise analog and / or digital circuits.Thus, in some embodiments, the evaluation unit may comprise one or more analog-to-digital converters.

[0037] In some embodiments, the control unit may include analog regulation circuits and / or digital regulation. In some embodiments, the control may occur in discrete time or continuous time. In some embodiments, the control parameter regulated may be output as a quantized or continuous value. The control unit may be configured to regulate / control the frequency of the ultrasound generated by the ultrasonic generator.

[0038] In some embodiments, the ultrasound generator, the phase shift determination unit, the evaluation unit and / or the control unit, or parts of the aforementioned units, may each be fused into one unit.

[0039] In a particularly advantageous embodiment of the invention, the evaluation unit can be configured to analyze the phase shift and to determine a control algorithm during workpiece machining.

[0040] Thus, the quality of workpiece machining can be monitored. In some embodiments, the machine tool can control the machining speed based on the analysis of the phase shift. As a result, the lifespan can be improved due to lower wear.

[0041] In a particularly flexible embodiment of the invention, the control unit can be configured to change the control algorithm during workpiece processing. This has the advantage that the workpiece processing is adapted to the system parameters during processing. As a result, workpiece processing can be improved in terms of energy consumption and workpiece processing quality.

[0042] In a particularly preferred embodiment of the present invention, the system can be configured to perform the method according to one of claims 1 to 7. The system can thereby optimize system parameters for workpiece machining, such that energy consumption, machining speed, and tool wear can be optimized.

[0043] The method for controlling an ultrasonic generator of a machine tool for generating ultrasonic waves for machining a workpiece according to the present invention comprises the following steps: generating electric signals having different frequencies for machining a workpiece; applying ultrasonic waves to a tool by means of the electric signals, in particular with the aid of a piezoelectric motor; determining a phase shift (phase shift angle) of the ultrasonic waves as a function of frequency; determining a frequency at which the phase shift has a minimum value; changing the frequency in a predetermined machining frequency band near the determined frequency; and machining the workpiece.

[0044] Thus, in particular in the case of resonances of the tool which are difficult to detect or in the case of noise superimposed on the signal, the tool can be excited ultrasonically so that ultrasonic amplitudes can be generated with low energy consumption.

[0045] In a particularly advantageous embodiment, the method may comprise the further steps of determining the ultrasonic phase shift as a function of frequency during machining of the workpiece; determining a new frequency at which the phase shift has a minimum value after the frequencies in a predetermined machining frequency band around the determined frequency have been changed; and changing the frequencies in the predetermined machining frequency band around the newly determined frequency.

[0046] This has the advantage that the method reacts particularly effectively to modified system parameters, such as temperature, workpiece quality, workpiece shape, tool, etc.

[0047] A system for controlling an ultrasonic generator of a machine tool for generating ultrasonic waves for machining a workpiece according to the present invention includes an ultrasonic generator for generating ultrasonic waves for machining a workpiece, a phase shift determining unit for determining a phase shift of the ultrasonic waves, an evaluation unit for analyzing the phase shift of the ultrasonic waves and determining a frequency at which the phase shift has a minimum value based on the analysis of the phase shift; and a control unit for changing the frequency in a predetermined machining frequency band around the determined frequency.

[0048] In some embodiments, the ultrasonic generator can generate electrical signals having different frequencies. In some embodiments, the electrical signals having different frequencies can be generated continuously. In some embodiments, the generated electrical signal can include multiple superimposed electrical signals having different frequencies. For example, one electrical signal can be converted into an ultrasonic wave by one or more piezoelectric motors.

[0049] An example of an ultrasonic phase shift is the phase shift between the current and voltage of an electrical signal converted to ultrasound. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Further details and advantages of the present invention and various embodiments will be based on the following Figures 1 to 6 becomes clear through the description.

[0051] Figure 1 A method for controlling an ultrasonic generator of a machine tool according to an embodiment of the present invention is schematically shown.

[0052] Figure 2 The phase response of the phase shift of ultrasound determined according to the present invention is shown as a function of frequency.

[0053] Figure 3 The phase response of the phase shift of ultrasound determined according to the present invention is shown as a function of frequency.

[0054] Figure 4 The phase response of the phase shift determined according to the present invention is shown as a function of frequency.

[0055] Figure 5 The phase response 21 of the phase shift determined according to the invention is shown as a function of frequency.

[0056] Figure 6 A system for controlling an ultrasonic generator of a machine tool according to an embodiment of the present invention is schematically shown.

[0057] Figure 7 An ultrasonic generator according to one embodiment of the present invention is schematically shown.

[0058] Figure 8 An evaluation unit according to an embodiment of the present invention is schematically shown.

[0059] Figure 9 A control unit according to an embodiment of the present invention is schematically shown. DETAILED DESCRIPTION

[0060] Figure 1A method for controlling an ultrasonic generator for a machine tool according to one embodiment of the present invention is schematically illustrated. Within this method, steps may be added, separated, combined, and / or performed in parallel without departing from the present invention. Furthermore, the order of the steps may be modified without thereby compromising the present invention.

[0061] In the first step S11, electrical signals with different frequencies are generated. Thus, in some embodiments, electrical signals with multiple frequencies (wide spectrum) can be generated. Thus, in some embodiments, electrical signals with different frequencies can be generated sequentially.

[0062] In another step S12, ultrasonic waves are applied to the tool via an electrical signal. This means that the tool or a portion of the tool is vibrated by applying ultrasonic waves. For example, the ultrasonic waves can be applied by converting the electrical signal into ultrasonic waves, particularly by one or more piezoelectric motors. In some embodiments, the ultrasonic waves can be generated directly at or on the tool by a corresponding motor at or on the tool.

[0063] Step S13 comprises determining the phase shift of the ultrasonic wave as a function of frequency. This can be performed, for example, by an algorithm, in particular for determining the phase shift between the current and voltage of the electrical signal converted into ultrasound. In some embodiments, the phase shift can also be determined approximately.

[0064] In another step S14, the phase shift is analyzed as a function of frequency. This may include comparing the phase shift as a function of frequency with one or more phase reference values. In some embodiments, analyzing the phase shift may include a qualitative evaluation of the phase shift as a function of frequency.

[0065] In some embodiments, the predetermined frequency band may not be given but may be determined by analyzing the phase shift.

[0066] Based on the analysis in step S14, a control algorithm for controlling the ultrasonic frequency is determined in step S15. Preferred examples of the control algorithm used in the present invention are changing the frequency within a predetermined frequency band (frequency pass), in particular sweeping, wherein the frequency band is redefined after the pass based on the minimum value of the phase shift; a minimum algorithm configured to minimize the control amplitude by adjusting the control parameter (manipulated variable), in particular by convex optimization, and a control algorithm configured to adjust the control amplitude to a predetermined value (e.g., zero crossing) by the manipulated variable (control parameter).

[0067] For example, the minimum algorithm may be a step of detecting a minimum value at a first frequency, increasing the first frequency to a second frequency; comparing the phase shift of the first frequency with the phase shift of the second frequency; when the phase shift of the second frequency is less than the phase shift of the first frequency, using the second frequency as the first frequency; when the phase shift of the second frequency is greater than the phase shift of the first frequency, reducing the first frequency to the second frequency, comparing the phase shift of the second frequency with the phase shift of the first frequency; and when the phase shift of the second frequency is less than the phase shift of the first frequency, using the second frequency as the first frequency.

[0068] Depending on the number of switches between increasing and decreasing the first frequency, the step sizes for increasing and decreasing the frequency, respectively, may be enlarged and reduced, respectively.

[0069] In a further step S16 , the workpiece is machined. During the workpiece machining S16 , it is possible, depending on the embodiment, to return to step S14 . Thus, the frequency of the ultrasound can be adapted to system modifications (modifications that affect the resonant frequency of the tool).

[0070] In some embodiments, step S11 is preceded by step S10 in which a frequency band is specified. Preferably, the different frequencies generated in step S11 are included in the frequency band specified in step S10. Thus, it is possible to ensure that the frequency of the ultrasound is adjusted to a predetermined resonance rather than a higher or lower order resonance.

[0071] Figure 2 The phase response of the phase shift of ultrasound determined according to the present invention is shown as a function of frequency. Along the X-axis, the frequency is given in kilohertz. On the Y-axis, the phase shift Phi is given in degrees. Figure 2 The phase response 21 shown in FIG as a function of frequency is lower than the first phase reference value 23 at its minimum value 30. The first phase reference value may be, for example, a value of 3°. Since the minimum value of the phase response is lower than the first phase reference value 23, the frequency of the ultrasonic wave will be adjusted to the phase shift adjustment target 31. Figure 2 In the example shown, the adjustment target is 0°.

[0072] If the minimum value 30 of the phase response 21 is within the range between the first phase reference value 23 and the second phase reference value 24 , the frequency of the ultrasound will be adjusted to the frequency with the minimum phase shift 30 .

[0073] If the minimum value 30 of the phase response 21 does not fall below the phase reference value 24, or if the minimum value 30 of the phase response 21 exceeds the phase reference value 24, respectively, it is advantageous according to the invention to use a sweep algorithm (through a predetermined frequency band). This has the advantage that, in particular, in the case of a phase response superimposed by noise, an optimal result can still be obtained. Figure 2In the illustrated diagram, the second phase reference value 24 is approximately 58°, and the first phase reference value 23 is approximately 5°. Here, the adjustment target 31 is set to 0°. However, the values of the first and second phase reference values and the adjustment target can vary. Ideally, the qualitative ratio of these magnitudes should remain constant.

[0074] In some embodiments, the first phase reference value 23 can match the second phase reference value 24, there can be only one of the first or second phase reference value, and there can be other phase reference values respectively, so that the regulation algorithm for controlling the ultrasonic frequency generated by the ultrasonic generator is determined from two or more regulation algorithms for controlling the frequency of the ultrasonic generator based solely on the analysis of the phase shift.

[0075] Figure 3 The phase response of the phase shift determined according to the invention is shown as a function of frequency by way of example. Figure 3 In, similar to Figure 2 , shows a phase response 21 including a minimum 30. Figure 3 Along the Y-axis, the phase scale is shown on the right and the impedance scale is shown on the left. On the X-axis, the frequency is shown in Hertz.

[0076] Apart from Figure 2 In addition to the phase response shown in 21, Figure 3 Also shown is the impedance response 22. Thus, the impedance response 22 as a function of frequency can be determined to exhibit a maximum at the first zero crossing point 28 of the phase response, and the impedance 22 to exhibit a minimum at approximately the second zero crossing point 29 of the phase response. Therefore, in an ultrasonic generator controlled according to current, it is advantageous to control the frequency to a frequency having a low impedance value.

[0077] exist Figure 3 As can also be seen in Figure 3 , the phase response can include a plurality of minima 30, 30a. Therefore, it is advisable to limit the operating range associated with the spectrum to a predetermined frequency band, for example by means of a lower limit 25 and an upper limit 26. This ensures that the frequency generated by the ultrasonic generator is adjusted to the predetermined resonance of the tool.

[0078] Figure 4 The phase response of the phase shift determined according to the present invention is shown as a function of frequency. Figure 3 similar, Figure 4 Phase is also shown on the right side of the graph along the Y-axis, and impedance is shown on the left side of the graph along the Y-axis. Along the X-axis, frequency is shown in Hertz. Figure 4The phase response shown in FIG includes a minimum value 30 that exceeds a first phase reference value 23 while being below a second phase reference value 24. The first phase reference value in this embodiment is 3° and the second phase reference value in this embodiment is 67°. However, these values are not binding and are merely exemplary.

[0079] and Figure 2 similar, Figure 4 It is also shown that it may be advisable to specify the operating range with respect to frequency (predetermined frequency band), for example by means of limits 25 and 26, so that the frequency generated by the ultrasonic generator is specifically adjusted to the predetermined resonance position of the tool. In some embodiments, after a first frequency pass, it may be additionally helpful to limit the operating range with respect to frequency (predetermined frequency band) to a smaller frequency range 27, thereby speeding up the frequency pass and improving the frequency pass in terms of accuracy.

[0080] Since the minimum value 30 is lower than the second phase reference value 24 and exceeds the first phase reference value 23, according to the present invention, it is necessary to use a minimum algorithm for adjusting the ultrasonic frequency generated by the ultrasonic generator so that the phase shift is minimized.

[0081] Figure 5 The phase response of the phase shift determined according to the invention is shown as a function of frequency by way of example. Figure 5 In the , the Y axis shows the phase and the X axis shows the frequency. Figure 5 , it is apparent that the phase response 21 as a function of frequency has a minimum value 30 that is neither below the first phase reference value 23 nor below the second phase reference value 24. Therefore, advantageously, the controller is configured to adjust the frequency of the generated ultrasonic wave by varying the frequency of the generated ultrasonic wave within a processing frequency band 35 centered around the minimum phase shift 30. Advantageously, the minimum values for varying the frequency and phase shift, respectively, can occur more quickly and at greater frequency intervals at the edges of the processing frequency band 35 than at the center of the processing frequency band 35. This has the advantage of preventing rapid adjustments in determining the phase shift due to signal noise.

[0082] Advantageously, after each pass through the frequency band, the minimum value of the phase shift can be determined anew and the frequency band of the changing frequency can be adapted accordingly.

[0083] Figure 6 A system 50 for controlling an ultrasonic generator of a machine tool according to an embodiment of the present invention is schematically shown. Within the system of the present invention, multiple functional units can be added, separated, merged and / or modified with respect to their division.

[0084] The system 50 includes an ultrasonic generator 51, a phase determination unit 52, an evaluation unit 53, and a control unit 54. The ultrasonic generator 51 is configured to vibrate a tool 55 or a portion of the tool 55, in particular at a frequency between 20 and 40 kHz (ultrasonic) for machining a workpiece. Therefore, the ultrasonic generator 51 is configured to vary the frequency. In some embodiments, the ultrasonic generator 51 can be configured to continuously generate ultrasonic waves having different frequencies. In some embodiments, the ultrasonic generator 51 can be configured to generate ultrasonic waves comprising a plurality of superimposed ultrasonic waves having different frequencies.

[0085] Preferably, all frequency points of the different frequencies generated by the ultrasonic generator 51 are part of a predetermined frequency band that determines the possible operating range of the frequency. This can have the advantage of ensuring that the frequency adjustment also meets the frequency requirements of the workpiece processing.

[0086] In a particularly advantageous embodiment, the ultrasonic generator 51 can be configured to generate ultrasonic waves having different frequencies by sweeping a predetermined frequency spectrum (passing frequencies). In some embodiments, the frequency spectrum of different frequencies, in particular the frequency spectrum of the sweep (passing frequencies), can depend on the tool (mass, temperature, geometry), machining characteristics (feed, crossfeed, rotation speed), and / or one or more workpiece characteristics, such as material, geometry, size, and mass. Therefore, in some embodiments, the ultrasonic generator 51 can include a voltage-controlled oscillator (VCO).

[0087] In an advantageous embodiment, the ultrasonic generator 51 may include a piezoelectric motor for applying ultrasonic waves to the tool 55 .

[0088] In some embodiments, the ultrasonic generator may include a digital-analog-converter (DAC) for generating an electrical signal of a predetermined frequency, which may be converted into ultrasound having a predetermined frequency by, for example, a piezoelectric motor.

[0089] The phase determination unit for determining the phase shift of the ultrasonic wave may be configured to include a phase shift between a current and a voltage of an electrical signal having a frequency for generating the ultrasonic wave, in particular by a piezoelectric motor.

[0090] This can occur, for example, via analog or digital circuitry. Thus, in some embodiments, the phase determination unit 52 can include one or more analog-to-digital converters (ADCs). Thus, the phase determination unit 52 can advantageously be connected to the ultrasonic generator 51 via analog or digital signal transmission. In some embodiments, the phase determination unit 52 can be configured to determine a phase shift for executing an algorithm or program code, respectively.

[0091] The phase determination unit may for example comprise a unit for subtracting two phase values and / or for executing an algorithm for determining a phase shift of the two signals.In some embodiments, for determining the phase shift, the phase determination unit may comprise an analog circuit for determining the phase shift.

[0092] In some embodiments, the phase determination unit may be connected to the tool 55 .

[0093] The evaluation unit 53 can be configured to analyze the determined phase shift and determine the adjustment algorithm based on the analysis of the phase shift. Thus, the analysis can include a quantitative comparison of the phase shift determined as a function of frequency with one or more phase reference values. In some embodiments, the analysis can include a quantitative analysis of the phase shift determined as a function of frequency, in particular a comparison of the phase shift determined as a function of frequency with a reference phase response.

[0094] Preferred examples of control algorithms that can be used in the present invention are changing the frequency around a minimum value (frequency passing) in a predetermined frequency band, in particular sweeping the frequency band, wherein the frequency band shift is redefined after the passing according to the minimum value of the phase shift; a minimization algorithm that is configured to minimize the control amplitude by means of a control parameter (manipulated variable), in particular by means of a convex optimization; and a control algorithm that is configured to adjust the control amplitude to a predetermined value (e.g. zero crossing) by means of a manipulated variable (control parameter).

[0095] For example, the minimum algorithm may be a step of detecting a minimum value at a first frequency, increasing the first frequency to a second frequency; comparing the phase shift of the first frequency with the phase shift of the second frequency; when the phase shift of the second frequency is less than the phase shift of the first frequency, taking the second frequency as the first frequency; when the phase shift of the second frequency is greater than the phase shift of the first frequency, reducing the first frequency to the second frequency, comparing the phase shift of the second frequency with the phase shift of the first frequency; and when the phase shift of the second frequency is less than the phase shift of the first frequency, taking the second frequency as the first frequency.

[0096] Depending on the number of switches between increasing and decreasing the first frequency, the step sizes for increasing and decreasing the frequency, respectively, may be enlarged and reduced, respectively.

[0097] The control unit 54 is configured to control the frequency-specific ultrasonic waves generated by the ultrasonic generator 51 according to the determined regulation algorithm and the determined phase shift. Therefore, the control unit 54 can be connected to the ultrasonic generator 51 by means of analog or digital signal transmission.

[0098] The advantage of this approach is that, for machine tools using ultrasound to process different workpieces, the frequency of the ultrasound can be easily and effectively adjusted to ensure that the vibrating tool resonates with the ultrasound as closely as possible. Consequently, energy consumption (in the form of ultrasound) can be reduced to deflect the tool's operating range by a predetermined amount.

[0099] The use of different control algorithms based on the analysis of the phase shift as a function of frequency has the advantage that the controller (control algorithm) can be designed particularly efficiently and stably. In addition, errors in the determination of the phase shift as a control amplitude, for example due to noise, can be ignored.

[0100] In a preferred embodiment, the evaluation unit 53 may be configured to analyze phase shifts during machining of the workpiece and to determine a regulating algorithm based on the analysis.

[0101] In a preferred embodiment, the control unit may be configured to change the regulating algorithm during machining of the workpiece.

[0102] This has the advantage that, in particular, when system parameters are modified, for example due to changes in workpiece characteristics (e.g., size, mass), machining characteristics, and / or tool characteristics (mass, temperature), the ultrasonic frequency can be immediately adjusted. This protects the tool and improves workpiece quality.

[0103] Figure 7 An ultrasonic generator according to an embodiment of the present invention is schematically shown. The ultrasonic generator 51 may include an ultrasonic wave generating unit 71, in particular in the form of a piezoelectric motor. In addition, the ultrasonic generator 51 may include a unit for changing the frequency 72, in particular in the form of a voltage-controlled oscillator (VCO).

[0104] In some embodiments, the ultrasonic generator 51 may comprise a unit for performing a frequency pass, in particular a frequency sweep 73. In some embodiments, the unit for performing a frequency pass 73 may comprise a unit for changing the ultrasonic frequency 72 and / or an ultrasonic generating unit.

[0105] Figure 8 The schematic diagram shows an evaluation unit 53 according to one embodiment of the present invention. In some embodiments, the evaluation unit 53 may include a digital-to-analog converter (DAC) 92 for converting a digital signal into an analog signal, in particular for controlling a voltage-controlled oscillator or for controlling a piezoelectric motor. Furthermore, the evaluation unit 53 may include an analog-to-digital converter (ADC) 93 for converting an analog signal, in particular an analog signal usable including a phase shift as information, into a digital signal.

[0106] The evaluation unit 53 may comprise a unit 94 for analyzing the phase shift as a function of the frequency. Furthermore, the evaluation unit may comprise a unit 95 for determining a control algorithm, in particular dependent on the analysis of the phase shift.

[0107] Figure 9 A control unit 54 according to an embodiment of the invention is schematically shown. The control unit may comprise a unit 96 for executing a regulation algorithm, in particular for regulating the frequency as a function of the phase shift and / or the impedance.

[0108] Furthermore, the control unit 54 can comprise a unit 97 for changing the regulating algorithm, in particular during machining of a workpiece.

[0109] In some embodiments, the control unit 54 may be directly connected to the phase determination unit in a digital or analog manner.

Claims

1. A method for controlling an ultrasonic generator of a machine tool for generating ultrasonic waves for machining a workpiece, comprising the following steps: generating electrical signals of different frequencies for machining a workpiece, wherein the frequencies are within an ultrasonic frequency range; applying ultrasonic waves to the tool by means of the electrical signal; determining the phase shift of the ultrasonic wave as a function of frequency; Analyze phase shift as a function of frequency; determining a regulation algorithm for controlling the frequency of ultrasonic waves generated by the ultrasonic generator based on the phase shift analysis; and The frequency of the ultrasonic wave generated by the ultrasonic generator is adjusted according to the phase shift of the ultrasonic wave and the determined adjustment algorithm.

2. The method according to claim 1, wherein When the phase shift analysis shows that, at a frequency point, the first phase reference value is relatively lower, the method comprises the following steps: Specify the phase shift adjustment target; Adjusting the frequency generated by the ultrasonic generator to achieve a phase shift adjustment target; and The workpiece is processed while adjusting the ultrasonic frequency.

3. The method according to claim 2, wherein When the phase shift adjustment target can be achieved by two different frequencies, The frequency generated by the ultrasonic generator for achieving the phase shift adjustment target will be adjusted to the higher frequency of the two different frequencies.

4. The method according to any one of claims 1 to 3, wherein When the analysis of the phase shift shows that the first phase reference value is exceeded at all frequency points and the second phase reference value is relatively lower at at least one frequency point, the method comprises the following steps: Adjusting the frequency generated by the ultrasonic generator to minimize the phase shift; and The workpiece is processed while adjusting the ultrasonic frequency.

5. The method according to any one of claims 1 to 3, wherein When the phase shift analysis indicates that the second phase reference value is exceeded at all frequency points, the method comprises the following steps: determining a frequency among a plurality of different frequencies at which a phase shift determined is minimized; machining a workpiece while adjusting the ultrasonic frequency; and The frequency in a predetermined frequency band is changed around the determined one frequency during workpiece machining.

6. The method according to claim 5, comprising the steps of: determining the phase shift between a generated ultrasonic wave and a reflected ultrasonic wave as a function of frequency when the frequency is varied; Analyze phase shift as a function of frequency; determining a new frequency from a frequency band around the determined frequency having a minimum phase shift; and The frequency in a predetermined frequency band is changed around the determined new frequency.

7. The method according to any one of claims 1 to 3, comprising the steps of: Determining the phase shift between an ultrasonic wave generated during machining of a workpiece and a reflected ultrasonic wave as a function of frequency; Analyze the phase shift as a function of frequency during workpiece machining; and A control algorithm for controlling the frequency of the ultrasonic waves generated by the ultrasonic generator is changed as a function of the analysis of the phase shift.

8. A system for controlling an ultrasonic generator of a machine tool to generate ultrasound for machining a workpiece, comprising: an ultrasonic generator for generating ultrasonic waves for processing a workpiece; a phase determination unit, configured to determine a phase shift of the ultrasonic wave; an evaluation unit for analyzing the phase shift as a function of frequency and determining a control algorithm based on the analysis of the phase shift; and a control unit configured to adjust the frequency according to the phase shift of the ultrasonic wave and the determined adjustment algorithm; The system is configured to perform the method according to any one of claims 1 to 7.

9. The system according to claim 8, characterized in that The evaluation unit is configured to analyze phase shifts during machining of the workpiece and to determine a control algorithm, and / or The control unit is configured to change the adjustment algorithm during machining of the workpiece.

10. A system for controlling an ultrasonic generator of a machine tool to generate ultrasound for machining a workpiece, comprising: an ultrasonic generator for generating ultrasonic waves for processing a workpiece; a phase determination unit, configured to determine a phase shift of the ultrasonic wave; an evaluation unit for analyzing the phase shift as a function of frequency and determining a control algorithm based on the analysis of the phase shift; and The control unit is configured to adjust the frequency according to the phase shift of the ultrasonic wave and the determined adjustment algorithm.

11. The system according to claim 10, The evaluation unit is configured to analyze phase shifts during machining of the workpiece and to determine a control algorithm, and / or The control unit is configured to change the adjustment algorithm during machining of the workpiece.

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