JPH0127563B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a demagnetizing device that generates a demagnetizing magnetic field by passing a gradually decreasing alternating current through a coil by controlling the phase of a thyristor connected to an alternating voltage, especially a commercial power source. be.

Conventional devices of this type include those that automatically switch the charging time constant of the capacitor in the ignition circuit using mechanical contacts such as rotary relays to vary the ignition angle, or semiconductor devices such as UJT and PUT. There was one using a relaxation oscillator circuit. However, with these circuits, it was not possible to stably set the firing angle, and it was also difficult to precisely adjust the alternating current magnetic field.

In view of this point, an object of the present invention is to provide a demagnetizing device equipped with a thyristor phase control circuit capable of generating a gradually decreasing demagnetizing magnetic field with good stability.

In order to achieve this object, the present invention provides a thyristor firing phase control circuit that includes a clock generator that generates clock pulses with a pulse interval that subdivides a half cycle of an AC power supply, and a clock generator that counts input clock pulses and calculates the clock pulses. A preset counter section generates an ignition signal when the number reaches a presettable predetermined number, and a preset counter section that counts the number of half cycles of the input AC power supply and demagnetizes the predetermined number according to the counted value. A counter unit that sequentially sets the number of increments, a control unit that causes the preset counter unit to perform a counting operation every half cycle and presets a predetermined number corresponding to the number of increments, and a control unit that performs input after the demagnetization operation starts. The demagnetizing device is configured to include a control section that stops the demagnetizing operation when the number of half cycles reached a predetermined number.

Next, the present invention will be explained based on the illustrated embodiments.

In FIG. 1, 1 is a clock generation section;
The oscillation frequency is, for example, a half period of the commercial power supply.
It is set to subdivide 10 mS into 256 (2 ⁸ ) intervals (if the clock pulse interval is sufficiently short for 10 mS, it is not necessarily necessary to divide exactly).

2 is preset with the complement of the predetermined number of the calculated value of the 8-bit binary counter 7, and counts the input clock pulses C based on the preset value, until the count value reaches the maximum count value (predetermined number).
"255", that is, it is a preset counter that sets all 8-bit output lines to "1" when the counted number of clock pulses c reaches a preset predetermined number. 3 is a NAND gate which receives this 8-bit output signal as an input, and its output becomes the ignition signal d. 4 is a monostable multivibrator which is triggered by a half-cycle pulse a generated every 1/2 cycle of the power supply, which stops the oscillation of the clock generator 1 for the time set by RV1, and which stops the oscillation of the clock generator 1 for the time set by RV1. A preset pulse b is generated to preset the binary counter 2 at the trailing edge of the rectangular wave.
6 is an AND gate into which the clock pulse c and the firing signal d are input. Note that the circuit parts 4 to 6 described above constitute a control section according to the present invention. The ignition signal d is supplied to a half-wave rectifier thyristor circuit (not shown), which causes current to alternately flow in both directions through the demagnetizing coil depending on the voltage polarity of the AC power source.

7 is a binary counter which inputs the half-period number pulse a, whose count value sets the predetermined increment of the preset counter 2 after the start of operation, and an inverter 8 is connected to each of its 8-bit output lines. With this connection, the complement of the maximum count value can be preset in the preset counter 2. 9 is a NAND gate which receives the 8-bit output signal of the binary counter 7, and the output signal is all "1", that is, the count value is
255, its output becomes "0" and the half-cycle pulse a supplied to the binary counter 7 via the AND gate 10 is cut off. That is, these circuit sections 9 and 10 constitute another control section of the present invention that starts and stops the demagnetizing operation.

The operation of such a circuit configuration will be explained with reference to FIG. In addition, the time axis of the waveforms b to d and the amplitude changes of e in FIG. 2 are shown enlarged.

When a reset pulse is applied to the binary counter 7 at the start of operation, the output becomes all "0". For example, if the ignition start phase angle is set to 10° using the variable resistor RV1, the clock pulse c in the phase angle range of 10° from the zero crossing point of the power supply voltage waveform (0°, 180°, ...) is 14. (256×10/180) blanking is performed, and a preset pulse b is supplied to the preset counter 2 at a phase angle of 10°. During this period, the first half-cycle pulse a is detected by the binary counter 7.
This output becomes “10000000”, and the preset counter 2 receives the complement “01111111” from the preset pulse b.
(“254”). As a result, when the 15th clock pulse c is input to the preset counter 2 via the AND gate 6, the count value reaches "255", the output signal becomes all "1", and the NAND gate 3 receives the firing signal d. Occur. The trailing edge of this ignition pulse d becomes the ignition pulse. Incidentally, when the ignition signal d is generated, the AND gate 6 is closed and the subsequent clock pulse c is immediately cut off.

With the next half-cycle pulse a, the count value of the binary counter 7 becomes "2", and the preset counter 2 is preset to "253" by the preset pulse b. Therefore, at the 16th clock pulse c, the output signal becomes all "1", and at this point, the ignition pulse d is generated. Therefore, the coil current e decreases by a change in the flow angle corresponding to the pulse interval of the clock pulse c.

In this way, in response to an increase in the number of half cycles of the input AC power supply after the start of operation, a half cycle pulse a is input to the binary counter 7, and every time the count up, an ignition signal d is generated in the preset counter 2.
The coil current e gradually decreases as the predetermined number of clock pulses c necessary to generate the ignition signal d increases, and each time the preset counter 2 repeats the count to generate the ignition signal d. When the count value of the binary counter 7 reaches "242", the 242nd clock pulse c enters the next blanking period and is no longer supplied to the preset counter 2, and the coil current e no longer flows. Furthermore, when the count value of the binary counter 7 reaches "255", the output signal becomes all "1", and in order to close the ant gate 10 via the NAND gate 9, the demagnetization operation is performed unless a reset signal is applied to the binary counter 7 again. stops.

As is clear from the above description, it is possible to generate an AC demagnetizing magnetic field in which the AC magnetic field at the commercial power frequency decreases stepwise in response to the pulse interval of the clock pulse c. At this time, the initial value of the magnetic field can be adjusted by the variable resistor RV1 according to the coercive force of the object to be treated, etc., and current consumption can be saved. Furthermore, by making the generation interval of the clock pulse c adjustable, the rate of change of the coil current, that is, the slope of the envelope, can be adjusted. However, in the above-described embodiment, if the frequency of the clock pulse c is made higher, the maximum counts of the preset counter 2 and the binary counter 7 must be correspondingly increased. However, if the frequency is to be lowered, it can be varied arbitrarily using the same circuit. Therefore, for example, for a magnetic material with a large coercive force such as ferrite, the initial value should be large and the slope should be made gentle, and for alnico, iron, etc. with a small coercive force, the initial value should be small and the slope should be steep. Adjustments can be made to suit the object.

Incidentally, in the embodiment shown in FIG. 1, the preset counter 2 and the binary counter 7 can be replaced with a circuit using a shift register.

As is clear from the above description, by digitally controlling the phase of the thyristor, a stable gradually decreasing alternating current magnetic field can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the circuit configuration of a demagnetizing device according to the present invention, and FIG. 2 shows waveforms of various parts thereof. 1: Clock generator, 5: Pulse forming circuit,
2: Preset counter, 7: Binary counter, 4: Monostable multivibrator.

Claims (1)

[Claims] 1. A demagnetizing device in which a gradually decreasing alternating current is passed through a coil that generates a magnetic field for demagnetizing by controlling the phase of the firing point of a thyristor connected to an alternating current power source. , a phase control circuit includes a clock generator 1 that generates clock pulses at pulse intervals that subdivide a half period of the AC power supply, and a clock pulse generator that counts the input clock pulses and, when the number of pulses reaches a presettable predetermined number, generates an ignition signal. a counter that counts the number of half cycles of the input AC power supply and sequentially sets an increase number from the start of the demagnetization operation to the predetermined number according to the counted value. making the units 7 and 8 and the preset counter unit perform the counting operation every half cycle;
and a control section 4 to 6 that presets the predetermined number corresponding to the increase number, and a control section 9 that stops the demagnetizing operation when the half cycle input from the start of the demagnetizing operation reaches a predetermined number. 10. A demagnetizing device comprising: