JPH0113635B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to an induction heating device, and particularly to a device for heating a thin plate using crossed magnetic fields.

"Prior Art" Conventional induction heating devices heat by eddy current loss and hysteresis loss caused by electromagnetic induction in an alternating magnetic field. An induced current (eddy current) due to electromagnetic induction flows through a metal conductor in an alternating magnetic field, producing so-called eddy current loss.Furthermore, if the metal conductor is a ferromagnetic material, hysteresis loss is also added to the metal conductor. is heated.

For example, a conventional induction heating device connected to a single-phase power source has a configuration as shown in FIGS. 4A and 4B.

That is, the inductors 2a 1 _{to 2} are placed on the front and back sides of the heated body 1, facing each other with an optimal gap G.
f ₁ , 2a ₂ to 2f ₂ are arranged. These inductors are coils that are formed parallel to the feeding direction (direction of arrow X) of the heated object 1.
Each inductor facing each other via , that is, 2a ₁ ~
Each induction coil is connected in series and connected to a single-phase power supply so that the directions of the magnetic fields generated at 2f ₁ and 2a ₂ to _{2f 2} are in the same direction, and a magnetic circuit is formed by the upper and lower cores. It is configured to Then, magnetic flux φ due to an alternating magnetic field generated by these inductors in a direction perpendicular to the object to be heated 1 intersects the object to be heated, and as a result, the object to be heated 1 is heated by induction.

Further, the heated object 1 is transported at a constant speed in the direction of arrow X by a heated object moving means, for example, a feed roller R.

"Problems to be Solved by the Invention" By the way, the heating device described above has the following problems.

In other words, the magnetic field generated by the inductors 2a ₁ to 2f ₁ and 2a ₂ to 2f ₂ is an alternating magnetic field, not a moving magnetic field, and the magnetic flux density generated in the gap G by each inductor is Therefore, as shown in FIG.
Variations occur depending on the In addition, when three-phase alternating current is applied, a thrust force in the width direction acts on the object to be heated 1 due to the moving magnetic field, causing a positional shift in the object to be heated.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a thin plate heating device using crossed magnetic fields, which can uniformly heat an object to be heated.

"Means for Solving the Problems" The present invention provides a cross-magnetic field type heating device that heats an object by changing the magnetic flux that crosses the object. A plurality of induction coils are arranged in the width direction of the heating body to face the heated body with an optimum gap, and each of the coils is excited at a preset frequency, and each of the above-mentioned The above-mentioned problem is solved by a thin plate heating device using crossed magnetic fields, which is equipped with an excitation switching means that changes the order of excitation of the excitation coils at a predetermined period.

"Operation" According to the present invention, a plurality of induction coils are arranged in the width direction of the heated object with an optimum gap for the heated object, and each induction coil is operated at a predetermined frequency. Each induction coil is excited by an exciting current, and the order of excitation of each induction coil is switched at a predetermined period. Therefore,
The object to be heated by induction is not limited to the transfer direction.
It is heated evenly in the width direction perpendicular to the transport direction.

"Embodiments" Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is an electrical circuit diagram showing the configuration of an embodiment of the present invention. In this figure, 100,10
1 and 102 are connection terminals connected to each phase R, S, and T of the three-phase power supply. 103 is 3 connected in series
This is a well-known three-phase bridge composed of a pair of diode circuits, and converts input three-phase alternating current into direct current.

104 is a smoothing capacitor, which performs full-wave rectification of the three-phase alternating current and eliminates ripples contained in the converted direct current.

105 is an inverter. This inverter 1
05 is equipped with a transistor bridge 105a consisting of six transistor switches Tr ₁ to Tr ₆ . Each of the transistor switches Tr ₁ to _{Tr 6} constituting the bridge 105a is connected to the control circuit 1.
PWM control is performed by 05b.

This control circuit 105b operates based on the phase sequence command signal SS output from the phase sequence command circuit described below.
Each transistor switch Tr ₁ above in corresponding order
~ Tr ₆ is turned on/off to output an AC signal of a predetermined frequency and a phase order corresponding to the signal SS to the output terminals 105r, 105s, and 105t.

Reference numeral 106 designates the above-mentioned phase sequence command circuit, which outputs a phase sequence command signal SScw or SSccw corresponding to the phase sequence CW or CCW selected by the phase sequence selection switch contact 107 to the control circuit 105b.

The phase sequence selection switch contact 107 is constituted by a solid state relay or the like. This phase order selection switch contact 107 is switched by the pulse signal SP output from the selection switch control circuit 108. When the pulse signal SP is at the H level, the CW contact of the switch contact 107 is turned on, and when it is at the L level, the CW contact is turned on. CCW contact turns on.

The selection switch control circuit 108 is the oscillator 10
The oscillator 108a outputs a pulse signal SP with a repetition frequency f and a duty ratio of 50% to the solid state relay (not shown), which receives the pulse signal SP. repetition period T
to turn on/off the switch contact 107.

Induction coils 109, 110, and 111 are connected to the r, s, and t phases, and are star-connected. Induction coil 109 is connected to coil 2 in series.
00a and 200A, 200d and 200D are connected in parallel, and similarly the induction coil 11
0 is the coil 200b and 200 connected in series.
B, 200e and 200E are connected in series, and the induction coil 111 is connected in series with the coils 200c and 200.
C. The coil 200f and the coil 200F are connected in parallel. And coil 200
a and 200A, 200b and 200B, 200c and 200C, 200d and 200D, 200e and 20
0E, 200f and 200F are arranged on the heated body 1 and are opposed to each other with an optimum gap.

Next, the operation of this embodiment will be described.

First, a power switch (not shown) is turned on. Therefore, the oscillator 108a starts oscillation and outputs a pulse signal SP with a repetition frequency T and a duty ratio of 50%. Therefore, the phase order selection switch 107 is switched between CW and CCW, and the phase order command circuit 106 is switched between CW and CCW.
Direction command signals SScw and SSccw are output alternately.

The control circuit 105b controls each transistor Tr ₁ , Tr ₂ , Tr ₃ , Tr ₄ , Tr ₅ , Tr ₆ configuring the transistor bridge 105a based on the direction command signal SScw.
Three-phase alternating current with phase rotation in the CW direction is supplied to induction coils 108, 109, and 110 under PWM control. Therefore, phase currents as shown in FIG. 2A flow in the r, s, and t phases, and a magnetic field proportional to this phase current is generated. This magnetic field is a traveling magnetic field that travels in the CW direction as shown in FIG. 3A. Also, direction command signal
When SSccw is output, the control circuit 105b
Based on this signal, transistors Tr ₁ , Tr ₂ ,
By PWM controlling Tr ₃ , Tr ₄ , Tr ₅ , and Tr ₆ , the three-phase alternating current, which was previously a CW phase rotation, is now changed to
Switching to phase rotation in the CCW direction, this three-phase AC in the CCW direction is applied to the induction coils 108, 109, 110.
supply to. Therefore, the r, s, and t phases have the second
A phase current as shown in Figure B flows, and a magnetic field proportional to this phase current is generated. This magnetic field is a traveling magnetic field that travels in the direction of the arrow CCW shown in FIG. 3A.

The frequency of the three-phase alternating current described above is determined by the control circuit 105.
b is determined by the frequency of the control signal output to the transistor bridge 105a.

As an example, if the value is increased, inverter 105
Conversion frequency is 300Hz, oscillator 108a
Repetition frequency of pulse signal SP output by 25Hz
(repetition period 0.04 sec), and the duty ratio of the pulse signal SP is 50%, the phase rotation of 300 Hz three-phase AC changes from CW to CCW every 6 Hz, and then
It will switch from CCW to CW. Therefore, by induction heating by the moving magnetic field moving in the width direction of the thin plate, heating is performed uniformly in the width direction of the thin plate, and the thrust force acting in the width direction of the thin plate, which is the object to be heated, due to the moving magnetic field is instantaneous. Although it is oriented in the CW or CCW direction at the moment, the average value of the thrust is "0", and the misalignment of the thin plate in the width direction is not a problem.

"Effects of the Invention" As explained above, according to the present invention, the object to be heated can be heated uniformly, and the positional deviation of the object to be heated due to the thrust acting on the object to be heated can be eliminated. can get.

[Brief explanation of drawings]

Fig. 1 is an electric circuit diagram showing the configuration of an embodiment of the present invention, Fig. 2 A and B are diagrams showing three-phase alternating current waveforms of phase rotation CW and CCW, and Fig. 3 A is an induction coil and an electrical current waveform. Figure 4A shows the relationship between the induction coil and the heated body as seen from above, Figure 4A shows the relationship between the induction coil and the heated body in a conventional induction heating device, seen from above. Figures 1 and 2 are views from the side.
FIG. 3C is a diagram showing the temperature distribution of a thin plate when the thin plate is heated by a conventional induction heating device. 103...Diode bridge, 105...Inverter, 105b...Control circuit, 105a...
Transistor bridge, 106...Phase order command circuit, 107...Switch contact, 108...Selection switch control circuit, 108a...Oscillator.

Claims (1)

[Claims] 1. In a cross-magnetic-field type heating device that heats a heated object by changing the magnetic flux that crosses the heated object, the most suitable for the heated object is A plurality of induction coils are arranged facing each other with a gap, and each of the coils is excited at a preset frequency, and the order in which the excitation coils are excited is set at a predetermined period. 1. A heating device for a thin plate using crossed magnetic fields, characterized in that it is equipped with excitation switching means that can be changed.