SYSTEM FOR GENERATING ACOUSTIC ULTRASONIC VIBRATION WITH IMPROVED AMPLITUDE CONTROL

Abstract

A system for generating acoustic ultrasonic vibration, with a generator for generating an alternating voltage (U) with a frequency f and converter for converting the alternating voltage into acoustic ultrasonic vibration, with a control device, which captures the vibration amplitude (A.sub.ist) of the ultrasonic vibration and compares said vibration amplitude with a desired vibration amplitude (A.sub.soil) and changes a manipulated variable with the goal of bringing the captured vibration amplitude (A.sub.ist) closer to the desired vibration amplitude (A.sub.soil). The generator has a frequency control module with a frequency control input. The frequency control module defines, in accordance with a signal present at the frequency control input, the frequency (f) of the alternating voltage (U) to be generated. A system which at least mitigates the mentioned disadvantages, allows higher processing speeds and associated abrupt load changes. A control apparatus converts an input signal into a manipulated signal, the desired vibration amplitude (A.sub.soil) being provided as the input signal, and the manipulated signal being connected to the frequency control input.

Claims

1. A system for generating an ultrasonic acoustic vibration with a generator for generating an alternating electrical voltage U with a frequency f and a converter for converting the alternating electrical voltage into an ultrasonic acoustic vibration with a regulation device which detects the vibration amplitude A.sub.ist of the ultrasonic vibration and compares it with a desired vibration amplitude A.sub.soil and changes a manipulated variable with the aim of approximating the detected vibration amplitude A.sub.ist to the desired vibration amplitude A.sub.soil, wherein the generator has a frequency control module with a frequency control input which determines the frequency f of the alternating voltage U to be generated as a function of a signal present at the frequency control input, wherein a drive control unit is provided which converts an input signal into a manipulated variable signal, the desired vibration amplitude A.sub.soil being provided as the input signal, and the manipulated variable signal being connected to the frequency control input, wherein the frequency of the electrical alternating voltage is used as the manipulated variable, and wherein the regulation device outputs a control variable signal which is connected to the frequency control input.

2-4. (canceled)

5. The system according to claim 1, wherein the manipulated variable signal and the manipulated variable signal are added or the manipulated variable signal is subtracted from the manipulated variable signal, and the sum or the difference is connected to the frequency control input.

6. The system according to claim 1, wherein the generator has two operating modes, in which in a first operating mode only the regulation device is used and in a second operating mode both the regulation device and the drive control unit are used.

7. The system according to claim 6, wherein if the desired vibration amplitude A.sub.soil remains constant or does not change by more than a predetermined amount during a predetermined time interval, the first operating mode is used and if the desired vibration amplitude A.sub.soil changes by more than the predetermined amount during the predetermined time interval, the second operating mode is used.

8. The system according to claim 5, wherein the generator has two operating modes, in which in a first operating mode only the regulation device is used and in a second operating mode both the regulation device and the drive control unit are used.

9. The system according to claim 8, wherein if the desired vibration amplitude A.sub.soil remains constant or does not change by more than a predetermined amount during a predetermined time interval, the first operating mode is used and if the desired vibration amplitude A.sub.soil changes by more than the predetermined amount during the predetermined time interval, the second operating mode is used.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Further advantages, features and possible applications of the present invention will become clear from the following description of a preferred embodiment and the associated figures. The following show:

[0032] FIG. 1 a schematic representation of a device that can be equipped with the system according to the invention,

[0033] FIG. 2 a schematic representation of the time dependence of the vibration amplitude and force, and

[0034] FIG. 3 shows a schematic block diagram of the regulation device according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0035] FIG. 1 shows a schematic representation of a device for the intermittent ultrasonic processing of a material web. The material web 1 is moved in the direction of the arrow between a sonotrode 2 and a counter tool 3. Both the sonotrode 2 and the counter-tool 3 are roller-shaped in this embodiment. The sonotrode 2 is pressed with a force F in the direction of the counter-tool 3, so that the material web 1 is pressed together between the sonotrode 2 and the counter-tool 3.

[0036] To set the sonotrode in motion, it is coupled to a converter (not shown), which converts an alternating electrical voltage into an acoustic ultrasonic vibration. For this purpose, an alternating electrical voltage is transmitted from a generator (not shown) to the converter, which transmits the generated acoustic ultrasonic vibration to the sonotrode 2.

[0037] The material web 1 is processed when the sonotrode 2 is pressed onto the material web with the appropriate welding force F.sub.A and the sonotrode oscillates with an appropriate oscillation amplitude A.

[0038] However, there are applications in which not the entire material web 1 is to be processed, but only sections of it.

[0039] In these cases, the amplitude of the ultrasonic oscillation of the sonotrode is always reduced in the design shown when no processing is to take place. The material web is also passed between the sonotrode and the counter tool, but due to the reduced amplitude of the ultrasonic oscillation, no processing takes place.

[0040] This is shown schematically in FIG. 2. The diagram shows both the vibration amplitude (solid line) and the welding force (dotted line) with which the sonotrode is pressed in the direction of the counter tool, in arbitrary units. It can be seen that in an interval I, the vibration amplitude assumes the value A and the force with which the sonotrode is moved in the direction of the counter tool assumes the value F.sub.A. The actual processing takes place in interval I.

[0041] Before and after processing in interval I, both the vibration amplitude in interval II and the force with which the sonotrode is pressed in the direction of the counter tool are reduced to the values B and FB. No processing takes place during movement interval II. Between the movement interval II and the processing interval I, a ramp interval III is shown here, in which the vibration amplitude is continuously increased or decreased.

[0042] In this ramp interval III, it is not possible for conventional regulation devices to adjust the vibration amplitude quickly enough at very high path speeds, with the result that machining may occur in movement interval II, which is not desired, or that insufficient machining takes place at the beginning of machining interval I.

[0043] Therefore, the invention provides for the additional intervention of a drive control unit at least in ramp interval III, which converts the desired vibration amplitude A.sub.soil into a manipulated variable signal, the manipulated variable signal being connected to the frequency control input of the frequency control module.

[0044] FIG. 3 shows an example block diagram of an embodiment of the system according to the invention. The actual regulated system 6 is usually exposed to a disturbance variable 9. Disturbance variables can, for example, be changes in length in the system, e.g. due to changes in temperature.

[0045] In this example, a setpoint generator 4 specifies the desired vibration amplitude 4. This is compared with the actual vibration amplitude, i.e. the ACTUAL-signal 8, which is provided via the feedback signal, and the result of the comparison, e.g. as a difference, is made available to a regulating element 5.

[0046] If the regulating element 5 detects a deviation between the setpoint and actual values, the manipulated variable signal 11, which is provided to a frequency control input of the controlled system 6, is changed.

[0047] So far, the block diagram describes a known control method. However, a process-related abrupt change in the setpoint vibration amplitude would also result in an abrupt signal change at the input of the regulating element.

[0048] According to the invention, the setpoint amplitude is now transmitted in parallel to a drive unit 10, which calculates a manipulated variable signal from it, which is then added to the output of the regulating element 5, so that the sum of the manipulated variable signal generated by the drive unit and the manipulated variable signal generated by the regulating element is present at the frequency control input of the control path 6.

[0049] The process-related change in the target amplitude, which is known in advance, is therefore no longer regulated as a disturbance, but driven out via the drive control unit. To prevent abrupt intervention by regulating element 5, either i) the regulating parameter set of regulating element 5 can ensure relatively sluggish regulation (e.g. in the case of a PID controller, the D component is reduced and the I component increased), or ii) regulating element 5 can be deactivated for a short time in the event of an abrupt change in the setpoint amplitude, or iii) the setpoint signal can be made available to regulating element 5 at a slightly later point in time than to control unit 10, whereby the magnitude of the signal delay at the regulating element can correlate with the dead time of the control path. As a result, the control quality of the system can be significantly improved and the system can be used at significantly higher web speeds.

LIST OF REFERENCE SIGNS

[0050] 1 Material web [0051] 2 Sonotrode [0052] 3 Counter tool [0053] 4 Setpoint generator [0054] 5 Regulating element [0055] 6 Controlled system [0056] 7 Feedback signal [0057] 8 Actual signal [0058] 9 Disturbance variable [0059] 10 Control unit [0060] 11 Manipulated variable signal [0061] F Force [0062] F.sub.A Welding force [0063] A Oscillation amplitude [0064] I Interval [0065] II Movement interval [0066] III Ramp interval