EP0597181B1 - Method and device for demagnetizing of magnetic materials - Google Patents

Abstract

The invention assumes that the envelope of a decreasing alternating magnetic field for demagnetizing magnetic materials must be larger than can be achieved by conventional oscillating circuits. Accordingly, a gradually decreasing alternating magnetic field having a large decay factor is generated in an oscillating circuit (C1, L1, L2) in whose air-core coil (L1) the material is held. By specifically recharging the capacitor (C1) from a recharging capacitor (C2) by means of a power supply (LS2), the capacitor voltage (U1) is increased and the energy which is reduced by damping is resupplied synchronously with the oscillation process, so that the envelope E(t) of the alternating field is specifically enlarged and the duration of the decaying alternating magnetic field in the air-core coil (C1) is prolonged. <IMAGE>

Description

The invention relates to a method and an apparatus for Demagnetize or calibrate magnetic materials in a decaying alternating magnetic field according to the generic term of the main claim. Demagnetization processes are based insist that magnets have an alternating magnetic field with decreasing Amplitude are exposed. The demagnetization will repeated several times, in between the magnetization of the Magnet or its working point is measured.

For workpieces that are to be demagnetized, in usually resonant circuit circuits used, the alternating field reproducibly decreases. An example of such a circuit can be found in DE 25 12 753 A1.

DE 3005927 C2 proposes a method in which the magnetic flux density in the air gap of the demagnetized Magnet is measured and the enveloping amplitude of the AC field is lowered when the desired value is reached is. The method is based on the fact that the amplitude of the magnetic Alternating field of a resonant circuit by changing the Supply voltage with automatically set resonance frequency is forcibly reduced.

It has also been suggested that the energy content of the Resonant circuit at the beginning of the decaying alternating field to control for a short period of time. For this, a DC voltage source is used connected to the capacitor of the resonant circuit (EP 0021274 Al). The purpose of this circuit is especially to increase the maximum value of the first amplitude, so that complete demagnetization can be achieved can.

The disadvantages of known demagnetization processes are that the value of demagnetization, especially with shape anisotropic Materials (e.g. AlNiCo), not hit precisely enough becomes. With a not inconsiderable part of permanent magnets there is no stable operating point, although the setpoint is set correctly nominally. The known methods are associated with instabilities that have so far not been sufficiently eliminated could become.

Another disadvantage is that the air coil for Holds the magnet or the device containing the magnet must have a special shape and low ohmic resistance. The last requirement could be limited by the use of silver wire or even superconducting coils, but this is not an economical alternative.

The invention has for its object a method and specify a device with which magnetic materials can be demagnetized more reliably.

The task comes with the characteristic features of the main claim solved. An apparatus for performing the method is specified in secondary claims. Beneficial Refinements can be found in the subclaims. Farther the use of the device for magnetizing is proposed.

The invention assumes that the duration of the falling magnetic alternating field for demagnetization particularly long must be, or that the ratio of successive amplitudes must be larger than with an alternating field generating resonant circuits can be reached. The larger the envelope of the alternating field, or the slower the alternating field subsides and the more often the magnet switches between positive and negative half-wave of the decreasing magnetic field experiences, the better the magnetic areas of the adjusting magnet set and stabilized. The relationship the amplitudes of successive equipolar Half periods (or the decay constant) should therefore be close to 1 be.

Amplitude ratios close to 1 naturally lead to long ones Adjustment times. The ratio can advantageously also be as constant value between 0.9 and 1.0 can be set. A the upper limit lies on the one hand in the technically achievable, to but others must adjust the magnets to an economical one Duration can be limited.

The underlying principle can be described in that synchronous to the magnetic alternating field in the resonant circuit Energy is fed. The energy is preferably fed in in cycle times with shorter units than one half period of the alternating field.

It is also proposed to feed the energy in such a way that the decay constant of the envelope of the alternating field is as large as possible, i.e. between 0.9 and 1.0.

Without special measures or intervention in a resonant circuit is the duration and the amplitude ratio of the alternating field limited due to the existing damping.

By the measures according to the invention it is with air coils less important, what shape and what quality (L / R) this to have. Air coils can be used, which are under conventional Conditions very bad as inductance in Parallel resonant circuits would work. When using the invention don't particularly need the volume and internal resistance, or the resulting quality to be observed.

In a resonant circuit, the frequency f = [1 / (LC) - R ² / (4L ² )] ^1/2 results in an alternating magnetic field with an exponentially decaying amplitude A in the air coil. The envelope E (t) of the alternating field is described by: E (t) = A O exp (-αt).

The sizes mean: L = inductance; C = capacity; R = effective resistance of the resonant circuit; t = time; A _o = initial amplitude; α = R / (2L) = decay constant.

A resonant circuit that is used for magnetization or demagnetization contains, besides the magnet, its magnetization should be changed, usually more conductive and magnetic Materials. Losses due to magnetic reversal occur in them and eddy currents, this creates the resonant circuit damped and the oscillation frequency fl can no longer describe solely by the formula given above, which only treated the ohmic damping. The following is intended as the amplitude ratio the ratio of two successive ones positive amplitudes of the alternating field A2 (t + T) / A1 (t) be understood. The period is T. The amplitude ratio (or the decay constant α) in resonant circuits with magnetic materials is even less favorable than in resonant circuits only with ohmic losses.

In one embodiment of the invention, it is proposed that by recharging at least one capacitor of the resonant circuit the duration of the evenly decaying alternating field extend to the energy lost through damping to deliver later. One can for certain performance areas, one another capacitor the first capacitor in the resonant circuit connect in parallel, so that several capacitors for recording of the make-up energy are available.

1. Messung und Steuerung der primären Ladespannung des Kondensators und Messung der Ladespannung des Nachladekondensators,

2. Messung der Amplitude (und Frequenz) des Wechselfeldes oder solcher Größen, die ihnen proportional sind,

3. Dosierung und Synchronisierung der Energieeinspeisung anhand der Messung nach 1., so daß das Wechselfeld einen zeitlich vorgebbaren Verlauf mit besonders großer Abklingkonstante annimmt.

There are various possibilities for recharging the capacitor in the resonant circuit to compensate for the energy lost through damping, which results in several further embodiments. The following measures must be taken to control the recharging of the capacitor:

1. measurement and control of the primary charging voltage of the capacitor and measurement of the charging voltage of the recharging capacitor,

2. measurement of the amplitude (and frequency) of the alternating field or of quantities which are proportional to them,

3. Dosage and synchronization of the energy supply based on the measurement according to 1., so that the alternating field assumes a time-definable course with a particularly large decay constant.

The invention is described in more detail in the single figure. she shows a circuit arrangement with energy feed for extension of the alternating field.

In the air coil L1 of a resonant circuit is in one Bracket a magnet that is to be demagnetized. As far as it is the geometrical or electrical dimensions of the arrangement Allow the entire magnet in the holder included device attached. The parallel resonant circuit consists of two inductors L1 and L2 and the capacitor C1. The primary energy for the resonant circuit (for the time 0 of the alternating field) is from a high voltage power supply LS1 provided once by charging the capacitor C1.

To influence the even decay of the alternating field with a certain decay constant α are provided: a Measuring tap U1 on the capacitor Cl for measuring the vibration profile, a power supply for recharging the capacitor C1 via a second high-voltage power supply LS2 and an electronic one Control unit SM, with the shape or duration of the magnetic Alternating field can be controlled synchronously with the oscillation of the resonant circuit is. The control unit SM consists essentially of a microprocessor MP, associated program or data memories (e.g. EPROM), an analog-digital converter ADW and one Interface unit IOP. The control unit SM can overall can also be realized by a personal computer.

During the charging phase of capacitor C1 through the high-voltage power supply LS1 are the electronic switches S1, S4, S5 and S6 in the open state. The switch S3 is in Position "b". The function of switch S6 and diode D1 is described below.

The charging current flows into capacitor C1 when from the control unit SM activates the power supply LS1, or the switch S2 is closed. The voltage measurement on capacitor C1 is carried out via an analog-digital converter ADW, via which the voltage U1 of the control unit SM is supplied. The measured Voltage is proportional to the amplitude of the alternating magnetic field. When a certain predetermined charging voltage is reached U1 the power supply LS1 is switched off, or the switch S2 opened. With the also from the control unit SM When the switch S1 is closed, the resonant circuit begins L1, L2, C1 to swing.

Frequencies f1 in demagnetizing resonant circuits for larger ones Magnets are in the range of 50 to 250 Hz; a typical value is around f1 = 100 Hz. Without additional intervention in the The resonant circuit or without energy feed is after about 10 to 12 periods the amplitude of the alternating field under 1 percent of the Output amplitude decreased and then no longer effective.

To compensate for all ohmic and magnetic damping losses in the resonant circuit and to generate a predetermined decay constant the capacitor C1 becomes from the energy of the charging capacitor C2 reloaded. The voltage U2 at the charging capacitor C2 is tapped and the control unit SM via the analog-digital converter ADW fed. A sine / square wave converter SR1 detects only positive voltages U1 and controls a switchable square wave generator G1. This creates during the positive half wave of the voltage across capacitor C1 an in-phase square wave voltage with a frequency f2, the is significantly greater than the frequency f1 of the AC voltage on capacitor C1. In the present case, the frequency becomes f2 Selected 30 times larger (f2 = 3 kHz). The frequency of the square wave voltage f2 can also range from 10 to 100 times the frequency fl vary. The rectangular generator G1 triggers a monoflop M1. The sine / square wave converter SR1 generates one in-phase square wave voltage to the voltage across capacitor C1. In the positive half-wave of the square wave voltage, the Rectangular generator G1 a high-frequency square wave voltage. During the negative half wave of the capacitor voltage is the Output of the rectangular generator G1 "low"; there will be no control signal submitted.

The output of the monoflop M1 controls via the switch S3 in position "b" is the duty cycle of switch S5. With everyone positive edge of the square wave voltage of the square wave generator G1 the closing of switch S5 is triggered (via monoflop M1). The cycle time Tt is at the selected frequency f2 about 300 microseconds. The duty cycle of the switch S5 is frequency preset manually using potentiometer TR1; thus the effective recharge current for the capacitor C1 determinable.

With the three units sine / square wave converter SR1, square wave generator G1 and monoflop M1 becomes the frequency and duty cycle of the switch S5 determined by hardware.

Before the demagnetization process is started, by the control unit SM charges the capacitor C2 Closes switch S4. There is a second one High voltage power supply LS2 available. The capacity of the Charging capacitor C2 is about twice the size of the Capacitor C1 selected. The charging voltage U2 of the capacitor C2 must be larger than that by a certain factor (K1) Start voltage of capacitor C1. The typical value is a Factor K1 = 2 suggested. Now with a certain one Duty cycle of the switches S5 in the positive half-wave of AC voltage on and off, so a certain flows Amount of charge from the charging capacitor C2 via the diode D2 Switch S5 and inductor L2 to capacitor C1 and charges it in small steps in sync with the vibration process, which makes the envelope of the alternating magnetic field slower decays as without reloading. Reloading is preferred repeated for all subsequent positive half-waves.

The inductance L2 is for the operation of the resonant circuit Cl, L1, L2 only of minor importance because of their ohmic Resistance even contributes somewhat to damping. she will however used to large when closing switch S5 Compensating currents between charging capacitor C2 and capacitor C1 to avoid, which would otherwise destroy the switch S5. There the frequency f2 of the recharge (determined by the duty cycle of the switch S5) is significantly greater than the oscillation frequency f1 of the resonant circuit C1, L1, L2, the inductance L2 be smaller in this ratio to their inductive Limit resistance.

By optimally dimensioning the components and the right ones Choice of reload frequency, it is possible to reload energy almost lossless to transmit.

The diode D2 between the high-voltage power supply LS2 and the resonant circuit C1, L1, L2 is used so that the resonant circuit during the negative half-wave remains separated from the capacitor C2. The Demagnetization stops when the amplitude of the alternating field has dropped below 1 percent of the initial value.

The circuit arrangement described dispenses with during the negative half-wave of the alternating magnetic field to recharge capacitor C1. However, it is also possible to expand the circuit arrangement in such a way that during the negative half-wave of the alternating magnetic field the capacitor C1 is recharged in the correct phase. With the symmetrical operation a direct current component of the Alternating field avoided, so that no zero line shift at complete demagnetization occurs.

When switch S4 is open, capacitor C2 is not recharged. Reduced by the charge transfer to capacitor C1 the amount of charge in the charging capacitor C2 over time about exponential. The gradual decrease in the tension of the Charging capacitor C2 is quite desirable because the duration of the Alternating field should be finite. Raising the envelope and extension of the alternating field is due to the amount of charge in capacitor C2, the charging voltage U2 of capacitor C2 (Factor K1) and the duty cycle of the switch S5. The duration of the process is defined by the duty cycle. In this simple embodiment, the control unit SM only controls the charging voltage U2 of the capacitor C2.

The additional effort by using two power supplies is not Disadvantage because the power supplies are each for the performance very different charging voltages U1 and U2 can be. In further refinements, it can be provided that only one high voltage power supply instead of two power supplies to use. Here, the one power supply must be on the larger one Charging power can be designed.

In another possibility, the power supplies can also be switched in this way be that the power supply LS1 charges the capacitor C2 and / or the power supply LS2 recharges the capacitor C1. In the figure is the waiver of a power supply, or the simultaneous Use of both power supplies for recharging each capacitor with a dashed connection between the power supply LS1 and switch S4 indicated. In one of these modes - as already described - switches S2 and S4 controlled accordingly by the control unit SM, so that at simultaneous monitoring of voltages U1 or U2 synchronously for the oscillation of the resonant circuit in phase from the power supply LS1 charge to capacitor C2 and / or from power supply LS2 charge flows to capacitor C1.

In a further embodiment of a demagnetizing resonant circuit becomes the extensive capabilities of the microprocessor used. It is with different magnetic materials namely advantageous, as many parameters of the magnetic Manipulate alternating field. The alternating field can be regarding change the following sizes: Skip the first half-wave from influencing the alternating field or beginning of the influencing with an even later half-wave; Raising the decay constant to a fixed value and keeping it constant the value or generation of a time-varying decay constant. The switch S3 is therefore used for this type of manipulation brought into position "a" and thus from monoflop M1 uncoupled.

The pulse duty factor is no longer via the three modules SR1, G1, M1 fixed. The synchronization via the control unit SM takes place via the tap GG behind the sine / square converter SR1. The duty cycle of the switch S5 is therefore programmed controllable and all parameters for changing the alternating field the resonant circuit (in particular duty cycle, charging voltages the capacitors C1 and C2) are free within limits variable.

The program control can be done in a tabular manner amplitude values are specified in the permanent memory of the microprocessor MP are, each of the prevailing initial conditions (e.g. the charging voltage). By comparing the amplitude-proportional measurement voltage U1 with that in the read-only memory stored target values of the envelope E (t) of the alternating field the duty cycle of switch S5 is controlled so that the envelope E (t) determines predetermined amplitude values, or with a decay constant (e.g. α = 0.92) follows.

The influencing of the decaying alternating field by energy feed can also be done by comparing the amplitude proportional Measuring voltage U1 with a high-performance microprocessor the control unit SM calculated in real time, likewise setpoints dependent on the initial conditions Envelope E (t) of the alternating field can be made.

In an alternative method, the control unit SM in operating in pulse width modulation mode. For this, a Microprocessor with integrated pulse width modulation used, so that the microprocessor does the job of the rectangle generator G1 and the monoflop M1 takes over. This will result in This mode of operation has the advantages of manipulating the duty cycle fully used over time.

In an alternative embodiment it can be provided that closed during demagnetization of switch S4 remains. The capacitor C2 is continuously from the High voltage power supply LS2 recharged and the alternating magnetic field can be influenced even longer.

The oscillation cycle ends when the amplitude A (measured value U1) less than 1 percent of the initial amplitude (initial measured value) is. The value of the magnetization of the magnet will finally measured.

Usually after the first demagnetization cycle Target value of the magnetization, which is within a certain target bandwidth lies (for example ± 10 percent), not yet reached, so that further demagnetization cycles follow have to. These cycles are based on the principle of successive approximation. The principle is like this implemented that the charging voltage of capacitor C1 in the next Cycle by half the difference of the previous two Values with a certain sign are changed. A new Demagnetization cycle follows the first cycle with a new one Charging voltage U1.

The circuit arrangement can also be used for magnets to magnetize. To operate the circuit arrangement as Magnetizing device are those with the reference symbol AM summarized parts (switch S6, control line for switch S6, diode D1 against ground) added to the resonant circuit. The Switches S1 and S4 are set to the "off" position. Of the Switch S6 is turned on by the control unit SM. Of the Capacitor C1 is closed when switch S2 is closed Power supply LS1 charged until a certain high charging voltage in the capacitor C1. To generate the switch S1 is closed. The resulting vibration is without negative half-wave, because the Diode D1 shorts the voltage of the negative half wave.

Claims (18)

1. A method for demagnetizing magnetic materials in a decaying alternating magnetic field of an electrical resonant circuit with an amplitude which may be influenced, wherein the energy content of the resonant circuit (C1,L1,L2) is controllable by the supplying of energy, characterised in that the supplying of energy into the resonant circuit (C1,L1,L2) takes place in synchronism with the influence of the periodic magnetic field.
2. A method for demagnetizing according to claim 1, characterised in that the supplying of energy takes place in shorter time units than a half period (T/2) of the alternating field.
3. A method for demagnetizing according to claim 1 or 2, characterised in that energy is supplied in such a way that the decay constant (α) of the envelope E(t) = A₀ exp(-αt) of the alternating field is close to 1.0.
4. A method for demagnetizing according to one of the preceding claims, characterised in that at least one capacitor (C1) of the resonant circuit (C1,L1,L2) is recharged.
5. A method for demagnetizing magnetic materials according to one of the preceding claims, characterised in that the recharging takes place only during homopolar half-waves of the alternating field.
6. A method for demagnetizing according to one of the preceding claims, characterised in that the recharging starts only at the beginning of the second or a later half-wave.
7. A method for demagnetizing according to one of claims 4 to 6, characterised in that the primary charging and the recharging of the capacitor (C1) is effected from a single power supply unit (LS1).
8. A method for demagnetizing according to one of claims 4 to 6, characterised in that the recharging is effected as a charge transfer from a capacitor (C2).
9. A method for demagnetizing according to one of claims 1 to 8, characterised in that the energy for the primary charging of the capacitor of the resonant circuit (C1) and the supply to the recharging capacitor (C2) is delivered from one power supply unit (LS1, LS2) respectively.
10. A method for demagnetizing according to one of claims 1 to 8, characterised in that the energy for the primary charging of the capacitor (C1) of the resonant circuit (C1,L1,L2) and the supply to the recharging capacitor (C2) is delivered selectively from one of two power supply units (LS1, LS2).
11. A method for demagnetizing according to one of the preceding claims, characterised in that the influencing of the decaying alternating field by supplying energy is effected by a control unit (SM) by comparing an amplitude-proportional measurement voltage (U1) with desired values of the envelope E(t) of the alternating field which are stored in a read-only memory (MP) and are dependent on the initial conditions.
12. A method for demagnetizing according to one of claims 1 to 10, characterised in that the influencing of the decaying alternating field by supplying energy is effected by a control unit (SM) by comparing an amplitude-proportional measurement voltage (U1) with desired values of the envelope E(t) of the alternating field which are calculated in real time by a microprocessor (MP) and are dependent on the initial conditions.
13. A method for demagnetizing according to one of the preceding claims, characterised in that the influencing of the decaying alternating field by supplying energy is effected by a control unit (SM) in the pulse-width modulation operating mode.
14. A method for demagnetizing according to one of claims 1 to 10, characterised in that the influencing of the decaying alternating field is effected by controlling a switch (S5) between the recharging capacitor (C2) or the recharging power supply unit (LS1,LS2) and the capacitor (C1) of the resonant circuit, the said switch being controlled by the voltage (U1) at the resonant circuit capacitor.
15. A device for demagnetizing according to the method specified in claims 1 to 14, consisting of a holder for the magnetic material in an air-cored coil of a resonant circuit (C1,L1,L2), comprising electrical components, inserted in the resonant circuit (C1,L1,L2), with which the configuration of the alternating field may be varied, and a device for delivering energy into the resonant circuit (C1,L1,L2), characterised in that the resonant circuit (C1,L1,L2) has a measuring take off point (U1) by which the capacitor voltage (U1) may be supplied to a control unit (MP,SM) to control the alternating field, in that the frequency and phase of the voltage (U1) is supplied by the measuring take off point (U1) to the control unit (SM) via a sine/square wave converter (SR1), in that the control unit (MP,SM) compares the capacitor voltage (U1) with values for a predetermined decay constant (a) close to 1.0 in cycle times (Tt) which are small in relation to the period (T) of the alternating field, and in that the control unit (SM) controls a switch (S5) between the recharging capacitor (C2) or the recharging power supply unit (LS1,LS2) and the capacitor (C1) of the resonant circuit and thus impresses a change on the alternating field which corresponds to a predeterminable configuration of the envelope E(t) of the decaying alternating field.
16. A device for demagnetizing according to the method specified in claims 1 to 14, consisting of a holder for the magnetic material in an air-cored coil of a resonant circuit (C1,L1,L2), comprising electrical components, inserted in the resonant circuit, with which the configuration of the alternating field may be varied, and a device for delivering energy into the resonant circuit, characterised in that the resonant circuit capacitor voltage (U1) is supplied to a sine/square wave converter (SR1), in that the output signal of the sine/square wave converter (SR1) acts on a square wave generator (G1) and a monostable flip-flop (M1) which is connected in series and is adjustable by a potentiometer (TR1), and in that the output signal of the monostable flip-flop (M1) determines the pulse duty cycle of a switch (S5) between the recharging capacitor (C2) or the recharging power supply unit (LS1,LS2) and the capacitor (C1) of the resonant circuit.
17. A device for demagnetizing according to one of claims 15 or 16, characterised in that the control of the switch (S5) between the recharging capacitor (C2) or the recharging power supply unit (LS1,LS2) and the capacitor (C1) of the resonant circuit may be switched over by a switch (S3), so that the device can be operated either in the microprocessor control operating mode according to claim 15 or in the set value control operating mode according to claim 16.
18. Use of the device according to one of claims 15 to 17 for magnetizing magnetizable materials, characterised in that a switchable earth connection (AM) is connected in parallel with the resonant circuit (C1,L1,L2) to limit the alternating magnetic field to a half-wave.

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