HIGH FREQUENCY OSCILLATOR, HIGH FREQUENCY WELDING SYSTEM AND METHOD FOR CONTROLLING THE FREQUENCY USING SAID TYPE OF HIGH FREQUENCY OSCILLATOR

Abstract

A high-frequency oscillator includes an electric resonant circuit, and a high-frequency welding system and a method for controlling the frequency uses a high-frequency oscillator, in particular in a high-frequency welding system. The electric resonant circuit includes at least one electronic component having an inductance and at least one capacitor having a capacitance. At least one additional magnetic coil is associated with the electronic component and can electronically influence the inductance of the electronic component.

Claims

1. A method for controlling a frequency, the method comprising: providing a high frequency oscillator having an electric resonant circuit comprising at least one electronic component having an inductance and at least one capacitor, wherein at least one magnetic coil is associated with the electronic component and with which the inductance of the electronic component is electronically influenceable; and controlling the frequency of the high frequency oscillator wear free by electronically adjusting the inductance.

2. The method according to claim 1, wherein the inductance is adapted by applying a direct current to at least one magnetic coil (5), which is associated with the electronic component providing the inductance in the electric resonant circuit.

3. The method according to claim 1, wherein an impedance of the electric resonant circuit is adjusted by adapting the inductance.

4. The method according to claim 1, wherein the inductance is gradually or continuously varied in an automatic search run until an optimal frequency is achieved in a load circuit of a high frequency welding system.

5. The method according to claim 1, wherein in high frequency welding systems with high frequency oscillators and/or in high frequency welding systems with solid state amplifiers, the tuning of the magnetic resonant circuit is used as resonance or impedance tuning in the load circuit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In the following, the invention will be described in more detailed based on an exemplary embodiment with reference to the drawings. In the drawings:

[0023] FIG. 1 shows a schematic diagram of the high frequency oscillator and

[0024] FIG. 2 shows a schematic diagram of a high frequency welding system.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0025] FIG. 1 shows a schematic diagram of a high frequency oscillator 1 comprising an electric resonant circuit 2. In the electric resonant circuit 2, the electronic component 3 that provides an inductance L is a coil. In addition, the resonant circuit comprises a capacitor 4 having a capacitance C. In its structural principle, the resonant circuit is a conventional LC resonant circuit. In this example, the electronic component 3 is designed as a coil with at least one copper tube. However, it is also possible to provide several coils as well as several capacitors.

[0026] The electronic component 3 is passed through a ring 5 made of a ferromagnetic material, around which a magnetic coil 6 is wound. The magnetic coil 6 is integrated in a control circuit 8 that comprises a controllable direct current source 7.

[0027] Through appropriate actuation of the direct current source 7, the magnetic coil 6 generates a magnetic field, which is superimposed on the field of the electronic component 3 and thus influences the inductance of the electronic component 3. When no current flows through the control circuit 8, there is no interference by the magnetic coil 6, so that the inductance of the electronic component 3 is at its maximum. The frequency of the electric resonant circuit 2 is thus minimal. When the control circuit 8 is operated in such a manner that the ring made of a ferromagnetic material is brought to saturation, a correspondingly strong magnetic field is generated by the magnetic coil 6 and the inductance of the electronic component 3 is reduced as far as possible. A frequency of the electric resonant circuit 2 is thus very high. Between these two extremes, the inductance of the electronic component 3 and thus the resonance frequency of the resonant circuit 2 can be adjusted sensitively and very quickly through appropriate actuation of the direct current source 7.

[0028] FIG. 2 shows a schematic representation of a high frequency welding system 9 for high frequency welding of plastic films, wherein a high frequency output oscillation is provided in a high frequency circuit 21 by means of a first high frequency oscillator according to the invention in a high frequency generator 20 and transmitted via a coaxial connection 10 to a load circuit 11.

[0029] In the load circuit 11, there is provided a magnetic resonant circuit 12, via which an electrode 13 and a counter electrode 14 are supplied with an appropriate high frequency voltage. The material to be welded is passed between the electrode 13 and the counter electrode 14. In the process, it is necessary to tune the system to the pending load, which is influenced for example by the thickness of the material to be welded. To this end, a second magnetically tuneable resonant circuit according to the invention is provided in 12, which comprises a means for electronically influencing its inductance such as the high frequency oscillator.

[0030] A higher-level controller 15 is provided for tuning the frequency in the high frequency circuit 21 by means of the first high frequency oscillator according to the invention and for adjusting a resonance frequency in the load circuit 11 by means of the second magnetic resonant circuit. Control signals of the higher-level controller are transmitted via suitable driver elements 16, 17 and amplifiers 18, 19 to the control circuit 8 for frequency control of the first high frequency oscillator in the high frequency circuit 21, respectively to a corresponding control circuit 22 of the second magnetic resonant circuit disposed in the load circuit 11. Thereby a complete control of the high frequency welding system is possible, thus allowing an optimal adjustment of the operating point.

[0031] The design according to the invention allows for a good frequency correction in the high frequency oscillator even in case of rapid load changes. It is not subject to mechanical wear and has no tendency to overshoot, since it does not have any mechanically movable components. Rather, the frequency of the resonant circuit of the oscillator is changed purely electronically by appropriately influencing its inductance. This is done by applying a direct voltage to at least one additional magnetic coil, which correspondingly influences the inductance of the electronic component provided in the resonant circuit.

[0032] Thus the inductance and therefore the frequency in the resonant circuit change depending on the actuation of the additional magnetic coil. The high frequency oscillator according to the invention can be used similarly for impedance control, respectively control of the resonance frequency in the load circuit of a high frequency welding system. Very high control accuracy and high control speed are also achievable there. A potentially higher power consumption can lead to a temperature increase, which can be contained by additional cooling for example by means of air or water. As a whole, this results in very high frequency stability and a good tuning of the load circuit, an automatic search run for the optimal operation frequency of the load circuit being also possible. The correction of the resonant circuit frequency is carried out without wear and electronically. An adjustment of the impedance can also be carried out electronically. In the process, the respective frequency of the oscillator is electronically adjusted by magnetic coils.

[0033] The invention is not limited to the shown exemplary embodiments and can be modified in numerous ways. For example, it is possible to use several magnetic coils with respectively one ring of ferromagnetic material. It is also possible to use the high frequency oscillator according to the invention not only as a high frequency generator for generating high frequency voltages or currents, but also for example as sensitive high pass or low pass filters.