CN111243825A

CN111243825A - Device for demagnetizing ferromagnetic material

Info

Publication number: CN111243825A
Application number: CN201811443160.8A
Authority: CN
Inventors: 乌尔斯·迈耶
Original assignee: Individual
Current assignee: Moire Magnetic Materials Co.,Ltd.
Priority date: 2018-11-29
Filing date: 2018-11-29
Publication date: 2020-06-05
Anticipated expiration: 2038-11-29
Also published as: CN111243825B

Abstract

The invention relates to a device for demagnetizing ferromagnetic materials by means of a magnetic field with alternating polarity generated by a coil through which a current flows, which is particularly advantageous, stable in terms of process technology, simple in construction and energy-saving. The device includes: an inductor and a capacitor in the form of a magnetic coil, which together form an electrical resonant circuit; and a circuit for supplying electrical energy, characterized in that oscillations of the voltage and current present in the resonant circuit are automatically and exclusively established and maintained in the resonant frequency.

Description

Device for demagnetizing ferromagnetic material

Technical Field

The present invention relates to a device for demagnetizing ferromagnetic materials.

Background

To demagnetize the ferromagnetic material, a magnetic field with a polarity that varies with decreasing amplitude is used. These magnetic fields are generated by conductor coils, hereinafter referred to simply as coils, through which an electric current flows in accordance with the desired magnetic field strength. This decreasing amplitude of the magnetic field is formed by appropriately controlling the current strength. A time-varying magnetic field is thereby formed, to which the object to be demagnetized is exposed. Alternatively, a time-invariant (zeitlich konnstans) magnetic field of continuously changing polarity is used, in which the object to be demagnetized is moved out of the region of maximum field strength into a field-free environment.

Disclosure of Invention

The invention relates to a device for generating a magnetic field by means of a current-carrying coil (Stromdurchfloren coil), which is particularly advantageous, technically stable, structurally simple and energy-saving.

Drawings

Figure 1 schematically shows a system of known type for feeding a magnetic coil at a fixed frequency and a variable voltage.

Figure 2 shows schematically the feeding of a magnetic coil with a voltage source in a series resonant circuit.

Fig. 3 shows schematically the feeding of the magnetic coil with a pulsed on-capacitor in a parallel resonant circuit.

Figure 4 shows a circuit for feeding the magnetic coil at resonant frequency by means of a bipolar feed.

Fig. 5 shows a circuit for automatic control at a resonance frequency.

Figure 6 shows a circuit for feeding a magnetic coil at a resonant frequency with a single pole feed, the magnetic coil having a center tap.

Fig. 7 shows a circuit for feeding a magnetic coil with a monopole feed at a resonance frequency through a bridge circuit for a switching element.

Wherein the reference numerals are as follows:

1 supply voltage

2 rectifier

3 D.C. intermediate circuit

4 power amplifier

5 envelope generator

6 amplitude rating

7 oscillating circuit

8 rated value signal

9 coil voltage

10 degaussing coil

11 oscillating capacitor

12 voltage source

13 coil current

14 current source

15 coil voltage

16 switch

20 control circuit

21 flow divider

22 current actual value signal

23N-power switch

24P-power switch

25 control signal for N-power switch

26 control signal for P-power switch

27 actual value voltage of the feed side of the resonant circuit

28 actual value voltage of switch side of resonant circuit

30 differential amplifier

31 actual value signal of resonance circuit voltage

32 threshold switch zero voltage

33 polarity signal voltage

34 threshold switch zero current

35 polarity signal current

36 switch logic

37 voltage regulator

38 clock adjustment signal

40 bipolar DC voltage source

41 feed voltage midpoint

42 negative supply voltage

43 positive feed voltage

44 unipolar DC voltage source

45 supply voltage, positive pole

46 supply voltage, negative pole

50 control circuit

51 coil with center tap

52 NPN power switch

53 control signal for power switch

60 control circuit

Voltage tap on coil 61

62, 63, 64, 65 bridge power components in a circuit

66, 67, 68, 69 control signals for power components

Detailed Description

Fig. 1 schematically shows a known device for generating a magnetic field, for example for demagnetizing ferromagnetic materials, a supply voltage 1 supplies a rectifier 2, which feeds a dc intermediate circuit 3, a power amplifier 4 generates a voltage 9 for feeding a coil 10, the power amplifier is supplied with a setpoint signal 8, which originates from an oscillator circuit 7, which generates a sinusoidal signal with a fixed frequency and an adjustable amplitude, the envelope (H ü llkurve) of the adjustable system being identical to a frequency converter according to the prior art, which already has the function of demagnetization with a temporally constant magnetic field of a predetermined frequency and amplitude, in order to demagnetize with a temporally variable magnetic field, the sinusoidal setpoint signal 8 for the voltage 9 is supplied to the power amplifier 4, the setpoint signal 8 is generated in the oscillator circuit 7, the amplitude of the setpoint signal 8 is generated in the form of pulses over the time course of an envelope, which is generated in the controller 5 as an amplitude setpoint value 6.

Such a system can be implemented for drives with induction motors by means of an industrial frequency converter or inverter by adding a controller suitable for the purpose.

A disadvantage of this solution is, on the one hand, the lack of process-engineering control, which is given by the different inductances resulting from the charging of the coil. The current flowing through the coil and the magnetic field generated thereby are determined only inaccurately as a function of the applied frequency and voltage. But more importantly the reactive current requirements of such circuits. The power element must provide this reactive current and is therefore designed in dependence on the apparent power of the coil. This is indicated by the corresponding large losses in the circuit. Finally, commercially available frequency converters are in principle designed to provide three-phase voltages as required by industrial motors. However, only one of the phases is used for feeding the degaussing coil. For this purpose, commercially available frequency converters are equipped in a redundant manner and the construction is unnecessarily complicated. They are used for degaussing purposes, as in the publication "Entmagnetisieren von Von" published by Magnetic AG for degaussing large-area objects as a process preparation before the welding process

Objekten alsProzessvorbereiling vor Schweissverfahren ") as known on

pages

3 and 9.

By generating this reactive current by means of a capacitor, the disadvantages of the underutilized circuit in relation to the reactive current requirement of the coil can be eliminated. The corresponding basic configuration is shown in fig. 2. A capacitor 11 is arranged in series with the coil 10, thereby forming a series resonant circuit. A voltage source 12 (usually a frequency converter), fed by the direct current intermediate circuit 3, supplies an operating voltage to the series resonant circuit. The voltage source itself is also added to the series connection of the coil 10 and the capacitor 11. The resulting current 13 depends in a known manner on the feed frequency of the resonant circuit and the tuning of the resonant frequency (abstimung). This must be considered as a disadvantage, since the resonance frequency depends on the charging of the coil 10 with ferromagnetic material. This effect is applied to the method described in patent document CH 698521. By adjusting the feed frequency with respect to the tooth shape of the resonant circuit, the working point can be moved in the direction of the resonance point in a targeted manner depending on the amount of ferromagnetic material. This increases the efficiency of the overall device as the amount of ferromagnetic material increases.

This solution presupposes that the feed frequency deviates specifically from the resonant frequency of the resonant circuit, and leads to a loss of efficiency of the overall circuit.

In principle, it is also possible to operate the resonant circuit formed by the coil 10 and the capacitor 11 as a parallel resonant circuit. This is illustrated in fig. 3. A current source 14 fed by the direct current intermediate circuit 3 charges the capacitor when the switch 16 is open. If the voltage 15 reaches its target value, the current source 14 is opened and the switch 16 is closed. The resonant circuit formed by the coil 10 and the capacitor 11 now oscillates at its resonant frequency. A typical application of this circuit is the demagnetization of a color picture tube for a television set, as described in patent document US 4599673. This circuit design is also described in patent document EP0021274, which is applied in various ways. However, their properties are not sufficient to demagnetize industrial components and products made of modern steel. In a free-decaying resonant circuit, the drop in current amplitude occurs too fast for qualitatively satisfactory demagnetization results. In patent document EP0282290 a circuit for degaussing a television picture tube is described which slows down the attenuation by periodically switching in a second capacitor. As can be seen from the patent, this is related to the asymmetry of the amplitude course (Amplitudenverlauf) of the degaussing current. However, this asymmetry hinders process reliability during degaussing.

The device described in the following has the idea that the resonant circuit is not fed by an alternating voltage or alternating current source, but its energy loss is compensated by a circuit acting as a negative resistance. Such a resonant circuit operates substantially at the resonance point. The resonance frequency therefore continuously and directly follows the coil inductance which is present. The effect of the amount of ferromagnetic material in the coil is directly compensated by adjusting the frequency. The circuit always operates with optimum efficiency. This also means that the components required for the circuit are best utilized and are optimal in terms of the effect of the degaussing process.

The structure of such a circuit is shown in fig. 4. The supply voltage 1 is converted in a bipolar supply circuit 40 into a positive dc voltage 42 and a negative dc voltage 43 having a common intermediate point 41. The intermediate point is connected to one pole of a resonant circuit formed by the coil 10 and the capacitor 11. The other pole of the resonant circuit is connected to two

power switches

23 and 24, which are shown here with transistor symbols. The voltage of the resonant circuit is tapped off at both poles as measured value 27 (actual value of the resonant circuit voltage on the supply side) or 28 (actual value of the resonant circuit voltage on the switch side). The current flowing in the resonant circuit is tapped off by a shunt 21 as a current actual value signal 22. The N-power switch 23 connects the resonant circuit to a negative supply voltage 42 and the P-power switch 24 also connects it to a positive supply voltage 43. The semiconductor elements used in the two power switches may be bipolar transistors, Darlington-transiston, insulated gate bipolar transistors or field effect transistors. The control in the sense of switching on and off is performed by means of the

signal

25 or 26. The control circuit 20 generates these two

signals

25 and 26 on the basis of an indication of the resonant circuit voltage from the measured

values

27 or 28 and an indication of the resonant circuit current from the measured value 22 and the nominal value 6 of the amplitude of the resonant circuit voltage.

The function of the control circuit 20 shown in fig. 4 is shown in fig. 5. The differential amplifier 30 determines the actual value signal 31 for the resonant circuit voltage from the measured

values

27 and 28. The threshold switch 32 thus forms a digital signal 33 comprising two values, respectively 1 corresponding to the positive resonant circuit voltage and 0 corresponding to the negative resonant circuit voltage. The threshold switch 34 forms from the current actual value signal 22 a digital signal 35 comprising two values, 1 for a positive current and 0 for a negative current. The voltage regulator 37 forms a digital clock adjustment signal 38 from the amplitude setpoint value 6 and the actual value signal 31. The switching logic 36 determines the control signals 25 and 26 for the two power switches based on the state of the

signals

33, 35 and 38. This will be achieved as follows: when the resonant circuit voltage exceeds a zero value in the positive direction (digital signal 33 goes from 0 to 1), P-power switch 24 turns on. It then follows the clock given by signal 38 until it turns off (digital signal 35 changes from 1 to 0) when the current crosses zero in the negative direction (Nulldurchgang). When the resonant circuit voltage exceeds a zero value in the negative direction (digital signal 33 goes from 1 to 0), N-power switch 23 turns on. It then follows the clock given by signal 38 until it turns off (digital signal 35 changes from 0 to 1) when the current crosses zero in the positive direction. In this way, losses in the resonant circuit are compensated by the phase-dependent, regulated metered supply. The circuit acts as a negative resistance, which is placed in parallel with the resonant circuit. The resulting oscillation frequency corresponds to the natural resonance frequency, which is given by the inductance value of the coil and the capacitance value of the capacitor. The amplitude of the resonant circuit voltage can be controlled using the amplitude rating 6.

Figure 6 shows a circuit for feeding a magnetic coil at a resonant frequency with a single pole feed, the magnetic coil having a center tap. The supply voltage 1 is converted in the supply circuit 44 into a direct voltage having a positive pole 45 and a negative pole 46. The positive electrode 45 is connected to an intermediate point of a coil 51 which forms a resonant circuit with the capacitor 11. The two poles of the resonant circuit are each connected to a power switch 52 of the same type, which is illustrated here by a transistor symbol. The voltage across the resonant circuit is tapped off at both poles as a measured value 27 or as an actual value 28.

The current flowing in the resonant circuit is tapped off via a shunt 21 as a current actual value signal 22. Two power switches 52 connect the resonant circuit to the negative pole 46 of the supply voltage. The semiconductor elements used in the two power switches may be bipolar transistors, darlington transistors, insulated gate bipolar transistors or field effect transistors. The switching on and off is effected by means of signals 53, which are generated by the control circuit 50 in a manner similar to the operation shown in fig. 5. The same type of monopole feed and two power switches represents a particular advantage of this embodiment.

Figure 7 shows a circuit for feeding a magnetic coil with a monopole feed at a resonant frequency and by manipulation of a bridge circuit. The supply voltage 1 is converted in the supply circuit 44 into a direct voltage having a positive pole 45 and a negative pole 46. The feed voltage reaches a bridge circuit known from frequency converters and servo amplifiers, which bridge circuit comprises power switches 62, 63, 64 and 65. The coil 10 and the capacitor 11 form a resonant circuit. The two poles of the resonant circuit are located on the diagonal of the bridge circuit. The resonant circuit voltage is transmitted to the control circuit via two voltage taps 61. The current flowing in the resonant circuit is tapped off via a shunt 21 as a current actual value signal 22. The entire bridge circuit is preferably designed as an integrated module. The control in the sense of switching the individual legs on and off takes place via

signals

66, 67, 68, 69, which are generated by control circuit 60 in a manner similar to the operation shown in fig. 5. A particular advantage of this embodiment is the use of power components configured as integrated modules.

Claims

1. An apparatus for demagnetizing a ferromagnetic material, comprising: an inductor and a capacitor in the form of a magnetic coil, which together form an electrical resonant circuit; and a circuit for supplying electrical energy, characterized in that oscillations of the voltage and current present in the resonant circuit are automatically and exclusively established and maintained in the resonant frequency.

2. The apparatus of claim 1, wherein the circuit for providing electrical energy is clocked by the magnitude of the voltage and current present in the resonant circuit.

3. The apparatus of claim 2, wherein the circuit for providing electrical energy is regulated for the resonant circuit to a preset nominal value of an alternating voltage in the resonant circuit.

4. The apparatus of claim 2, wherein the circuit for providing electrical energy is regulated for the resonant circuit to a preset nominal value of an alternating current in the resonant circuit.

5. The device according to claim 1 or 2, characterized in that the energy supply to the resonance circuit is realized by clock-pulsing an external voltage source on.

6. The device according to claim 1 or 2, characterized in that the energy supply to the resonance circuit is realized by clock-pulsing an external current source.

7. A device according to claim 5 or 6, characterized in that the voltage source supplying energy is switched on in an alternating manner of two polarities.

8. A device according to claim 5 or 6, characterized in that the circuit for supplying energy operates with a bipolar voltage source, wherein both polarities are alternately switched on by means of two switching elements.

9. A device according to claim 5 or 6, characterized in that the coil forming the oscillating circuit is provided with a center tap, wherein the circuit supplying energy works with a unipolar voltage source and alternately supplies power to the two end terminals of the coil.

10. The device according to claim 5 or 6, in case a unipolar voltage source is used, characterized in that the circuit providing energy is designed as a bridge circuit, so that the supplied current is fed alternately in both directions into the resonance circuit.