JPS58198890A - Induction heater - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an induction heating device that heats a material using an alternating magnetic field generated in an output coil.

The induction heating device is equipped with an induction power generator that outputs an alternating current according to an output command signal and an output coil that generates an alternating magnetic field according to the supplied alternating current. It generates an electric current to heat the material, and in recent years it has rapidly become widely used in the fields of processing, melting, and welding steel materials because it keeps the working environment clean and the temperature rises quickly. It has become.

However, due to fluctuations in the commercial power supply supplied to the induction power generator, deterioration of circuit components, or aging, a discrepancy between the actually output induction power and the power setting value may occur, resulting in variations in the products produced. Sometimes it happened.

The temperature of the heated material is directly measured and the power setting value for the induction power generator is corrected based on the measured signal. When moving, it is necessary to detect the temperature of the material in a non-contact manner, and a photodetector such as a radiation thermometer is generally used. However, the photodetector requires a circuit for converting light into electricity as well as a compensation circuit for dealing with variations in emissivity of smoke and materials, making the circuit complex and expensive. Furthermore, since the photodetecting element is sensitive to heat, consideration must be given to cooling it with water.

On the other hand, it is known that in induction heating, the power supplied to the material is proportional to the eddy current, which varies in magnitude depending on the rate of change of the magnetic field generated by the output coil. Also, as a matter of course, the temperature of the material has a correlation with the power supplied to the material.

The present invention focuses on the above points, and includes a detection coil that generates an output voltage according to the rate of change of the magnetic field in the magnetic field generated by the output coil, and the induction power generation device The present invention aims to construct a simple and high-performance induction power feedback circuit by modifying the output command signal to the inductive power, thereby improving the accuracy of material temperature control in induction heating.

The present invention will be explained below with reference to illustrated embodiments.

In the figure, a commercial power source Vm is supplied to the induction power generation device 1, and an output coil/I/2 is connected to the power generation device 1 so as to flow an alternating current 1 which is outputted from this device in large quantities. In the magnetic field F generated around the output coil 2 by this alternating current 1, there is provided a detection coil /L/3 which induces a voltage V(1) at both ends of the magnetic field F in accordance with the rate of change of the magnetic field F. is connected to the power control circuit 4.The power control circuit 4 includes a rectifying and smoothing circuit 41 that converts the output voltage Vd of the detection coil/l/3 into DC, an amplifier circuit 42 that amplifies the output of this smoothing circuit 41, and a power setting signal. A differential voltage calculation circuit 43 that subtracts the output voltage of the amplifier circuit 42 from the voltage of Vs and outputs the difference voltage Δ■, and adds the difference voltage Δ■ and the voltage of the power setting signal Vs to output an output command signal Vc. The output of the output command circuit 44 is connected to the induction power generator 1.The amplifier circuit 42 is provided with a resistor R for gain adjustment.

The operation of the induction heating device configured as described above will be described below.

The induced power generator 1 receives an output command signal Vc output from the power control circuit 4 and outputs an alternating current 1 proportional to the voltage of the command signal Vo.

The alternating current 1 flows through the output coil L'2 connected to the power generating device 1, and generates an alternating magnetic field F having a strength proportional to the current 1 around the output coil. A voltage α proportional to the rate of change of the magnetic field F is induced at both ends of the detection coil 30 placed in the alternating magnetic field F.

In the power control circuit number, the input voltage Vd is rectified and smoothed by the smoothing circuit 41 and converted into DC, and then the amplifier circuit 42
Amplify with. The differential voltage calculation circuit 43 calculates a differential voltage Δ obtained by subtracting the output voltage of the amplifier circuit 42 from the voltage of the power setting signal Vs.
Outputs V. This difference voltage Δ■ takes a positive value when the voltage of the power setting signal Vs is higher than the output voltage of the amplifier circuit 42, and takes a negative value in the opposite case.

The output command circuit 44 adds the difference voltage Δ■ and the voltage of the power setting signal Vs by -4, but adjusts the resistor R of the amplifier circuit 42 to add the voltage exclusively to the power set by the power setting signal Vs. If the output voltage of the amplifier circuit 42 is set to be equal to the voltage of the power setting signal VB when power is applied to the material, in this case Δ■ will reach OV, so the output command circuit 44 will The power setting signal yB is output as is as the output command signal Vc. If the commercial power supply Vm of the induction power generation device 1 decreases, the stain force generation device 1
When the output current 1 becomes smaller and only a small amount of power is supplied to the material compared to the set power, the output voltage of the amplifier circuit 42 becomes smaller than the voltage of the power setting signal S, and the difference voltage Δ
When (2) is a positive value, the voltage of the output command signal Vc to which this differential voltage Δ■ is added increases, and the output current 1 of the induced power generator 1 increases.

On the other hand, if power larger than the set power is supplied to the material, the voltage difference Δ■ becomes a negative value, so the voltage of the output command signal Vc to which this voltage difference Δ■ is added becomes small. The output current 1 of the power generation device 1 becomes smaller, and the power supplied to the material becomes smaller. In this way, the material is always supplied with a power equal to the set power.

As described above, according to the induction heating device of the present invention, the electric power actually supplied to the material by the induction power generating device is constantly monitored by the detection coil, and the output command signal to the electric power generating device is corrected. The set power is always supplied to the material regardless of fluctuations in the commercial power supplied to the generator or deterioration of the circuit components of the power generator.

Furthermore, since the detection coil is a simple one made by winding an insulated wire around an iron pipe, it is inexpensive and easy to maintain, and it can be used even in environments where welding debris and active gases are present for many years. Furthermore, if the number of turns of the coil is increased to increase the sensitivity, it is possible to detect the power applied to the material even at a location away from the heating section.

[Brief explanation of drawings]

The figure shows one embodiment of the present invention and is a configuration diagram of an induction heating device. −7− ], ... Induction power generator 2 ... Output coil 3 ... Detection coil 4 ... Power control circuit 43 ... Difference Voltage calculation circuit 44... Output command circuit V S... Power setting signal Vc... Output command signal Agent Patent Attorney Motomuma Ito --8--

Claims (1)

[Claims] In an induction heating device comprising an output coil and an induction power generator that supplies an alternating current to the output coil according to an output command signal, a detection coil is provided in a magnetic field generated by the output coil, and the output command signal is output. A power control circuit is provided, and the power control circuit includes a difference voltage calculation circuit that calculates a difference voltage obtained by subtracting the voltage of the detection signal generated in the detection coil from the voltage of the power setting signal, and a difference voltage calculation circuit that calculates the difference voltage obtained by subtracting the voltage of the detection signal generated in the detection coil from the voltage of the power setting signal, and An induction heating device comprising: an output command circuit that uses a voltage to which the differential voltage is added as the voltage of the output command signal.