JPH11121154A - Induction heating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an induction heating device that controls output voltage of an inverter device by detecting the temperature of a heated material by means of a resonance frequency. SOLUTION: In an induction heating device that heats multiple heated materials 23 continuously transferred by a transferring means 22 at a predetermined speed in a normal operation by means of heating coils 9, 10 by supplying high frequency power from an inverter devices 15, 16 to which the heating coils 9, 10 and capacitors 11,12 are connected, after the transferring means 22 is stopped and the transfer of frequency power is also stopped, when the transfer of the heated materials 23 is started by the transferring means 22 and the high frequency power from the inverter devices 15, 16 is supplied again, resonant frequencies of the heating coils 9, 10 and the capacitors 11, 12 are detected by frequency detection means 13, 14 and the temperatures of the heated materials 23 are detected from the resonance frequencies by means of a control means 17 and hence, the output voltages of the inverter devices 15, 16 are controlled according to the temperatures of the heated materials 23.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction heating apparatus in which a material to be heated is continuously conveyed by conveying means.

[0002]

2. Description of the Related Art FIG. 5 is a block diagram of a conventional induction heating apparatus described in Japanese Patent Publication No. Hei 6-93379. In FIG. 5, the case of the steady operation will be described. The material to be heated 1 is continuously conveyed through a low-temperature heating coil 4 and a high-temperature heating coil 5 at a predetermined speed during a steady operation by a conveying means 3 driven by a motor 2. Then, the material 1 to be heated is gradually heated, heated to a predetermined temperature, for example, about 1200 ° C. at the outlet of the heating coil 5 at the subsequent stage, discharged, and sent to a pressing device (not shown) in a subsequent process. . At the time of steady operation, each material 1 to be heated in the heating coils 4 and 5 is
As shown in a curve A in FIG. 6, the temperature gradually rises from the normal temperature to a predetermined temperature (for example, 1200 ° C.) as the paper is transported. This means that each of the inverter devices 6, 7 for supplying high-frequency power to each of the heating coils 4, 5
Is controlled by the control means 8 so that the temperature of the material to be heated 1 matches the temperature rising pattern of the curve A in FIG.

Next, a description will be given of a restart operation. In FIG. 5, when the pressing device (not shown) in the post-process is stopped due to a failure or the like, it is necessary to stop the feeding of the material to be heated 1 to the post-process. Is done. Accordingly, the inverter devices 6 and 7 are stopped,
The supply of the high-frequency power to the heating coils 4 and 5 is stopped.
As a result, when the press device (not shown) resumes operation, the temperature of each of the materials 1 to be heated in the heating coils 4 and 5 is decreased as shown by a curve B in FIG. When the operation restart signal is input, only the heating coil 5 at the subsequent stage is supplied with high-frequency power from the inverter device 7 and stationary heating is performed in a state where the material to be heated 1 is not conveyed. The temperature of the material 1 to be heated at the time of starting the stationary heating is calculated based on the stop time of the heating coils 4 and 5, the heat radiation loss of the material 1 to be heated, and the heat transfer to the air. Then, the heating value is estimated by calculation or a preliminary experiment, and the stationary heating period is ended by judging the time when the temperature approaches the steady temperature.

[0004] When the stationary heating period ends, a low-speed feeding period in which the material 1 to be heated is conveyed at a speed SL lower than the steady speed SO starts. At this time, the output power PL of the inverter device 6 for the low-temperature range is a value obtained by multiplying the output power PO during the steady operation by SL / SO. As a result, the output voltage VL of the inverter device 6 is proportional to the square root of the output power, and is a value obtained by multiplying the output voltage VLO during steady operation by the square root of SL / SO. The electric power supplied from the high-temperature inverter 7 to the heating coil 5 is equal to the difference (TS-TL) between the predetermined heating temperature TS and the temperature TL of the material 1 to be heated at the start of the low-speed feeding.
), Assuming that the weight of the material 1 to be passed through the heating coil 5 per time is M, it is calculated by (TS-TL) · (specific heat of the material 1 to be heated) · M / (heating efficiency).

[0005] The temperature of the material to be heated 1 in the heating coil 5 in the subsequent stage gradually rises, and when the material to be heated 1 at the entrance of the heating coil 5 in the subsequent stage is discharged at the start of the low-speed feeding period. Becomes a temperature rise curve, and the temperature of the material to be heated 1 becomes a predetermined temperature (for example, 1200 ° C.).

[0006]

Since the conventional induction heating apparatus is configured as described above, the temperature of the material 1 to be heated at the time of starting the stationary heating is determined by the time during which the heating coils 4 and 5 are stopped, and Since the heat radiation loss of the material to be heated 1 and the heat transfer of the air are calculated and determined, the material 1 to be heated in the heating coils 4 and 5 is calculated.
However, there is a problem that it is difficult to accurately grasp the temperature of the heating target 1 at the outlet of the heating coil 5 to a predetermined temperature.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an induction heating apparatus in which the temperature of a material to be heated is detected based on a resonance frequency and the output voltage of an inverter device is controlled. The purpose is to provide.

It is still another object of the present invention to provide an induction heating device that controls the output voltage of the inverter device and controls the conveying speed of the material to be heated so as to be lower than a predetermined speed during steady operation.

[0009]

An induction heating apparatus according to the first aspect of the present invention connects a heating coil and a capacitor to supply high-frequency power from an inverter apparatus, and continuously supplies the high-frequency power at a predetermined speed in a steady operation by a conveying means. In an induction heating device in which a plurality of materials to be conveyed are heated by a heating coil, the conveying means is stopped, and the conveyance of the material to be heated is stopped in the heating coil, and an inverter device is provided. After the supply of the high-frequency power is stopped, the transfer of the material to be heated by the transfer unit is started again, and when the high-frequency power is supplied from the inverter device, the resonance frequency of the heating coil and the capacitor is detected by the frequency detection unit. Then, the control means detects the temperature of the material to be heated from the resonance frequency, and controls the output voltage of the inverter device according to the temperature of the material to be heated. It is obtained by the.

[0010] An induction heating apparatus according to a second aspect of the present invention comprises:
The control is performed so that the transfer speed at the time of the restart operation of the transfer means is lower than the steady operation.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. FIG. 1 is a configuration diagram of the first embodiment. In FIG. 1, reference numeral 9 denotes a heating coil for a low temperature region, 10 denotes a heating coil for a high temperature region, 11 denotes a matching capacitor connected to the heating coil 9, 12 denotes a matching capacitor connected to the heating coil 10, and 13 denotes a matching capacitor. The resonance frequency of the heating coil 9 and the capacitor 11 is detected by the resonance frequency detection means. 14
Is a resonance frequency detecting means for detecting a resonance frequency of the heating coil 10 and the capacitor 12. Inverter devices 15 and 16 supply high-frequency power to the heating coil 9 and the heating coil 10, respectively.

Reference numeral 17 denotes control means for detecting the temperature of the material to be heated 22 described later from the resonance frequencies detected by the resonance frequency detection means 13 and 14, and controlling the voltage of each of the inverter devices 15 and 16 by a built-in program. Heated material 2 described later
Optimum values such as a resonance frequency value and a voltage value at the time of low-speed operation are stored for three types. Reference numeral 18 denotes an operation condition input means for inputting the type of the material to be heated 23, the heating temperature and the like to be described later to the control means 17. Reference numeral 19 denotes a motor whose rotation is controlled by a speed control means 20. Reference numeral 20 denotes a speed control unit which controls the motor 19 according to a command from the control unit 17. Reference numeral 21 denotes a pinch roller driven by a motor 19, which continuously conveys a material 23 to be described later into the heating coils 9, 10. The transfer means 22 is constituted by 19 to 21. Reference numeral 23 denotes a material to be heated, which is conveyed into the heating coils 9 and 10 by the conveying means 22.

Next, the operation will be described. 1 to 3
, The material 23 to be heated
Is heated by the heating coils 9 and 10. In this case, the temperature rising pattern is, for example, about 1,000 at the outlet of the heating coil 9 for the low temperature region as shown by the curve A in FIG.
1,200 ° C. at the outlet of the heating coil 10 for high temperature range
The condition C is input from the operating condition input means 18 to the control means 17 (step S ₁ ). Then, the control means 17 instructs the inverter devices 15 for the low-temperature region and the inverter device 16 for the high-temperature region to output the output voltages VLO and VHO during the steady operation, respectively.

When the material to be heated 23 is heated in accordance with the temperature rising pattern shown by the curve A in FIG. 2 and the pressing device (not shown) in the subsequent process is stopped, the conveying means 22 is stopped and the inverter is stopped. The devices 15, 16 are also shut down. As a result, the temperature of the material 23 to be heated in the heating coils 9 and 10 decreases, and the temperature pattern becomes a curve B or a curve C shown in FIG. growing.

A description will now be given of a restart of operation in which a press device (not shown) in a post-process returns to return to a normal operation. First reads the command output voltage VL1, VH1 low speed S1, and the inverter device 15, 16 as a condition of the driver at the time of restarting operation (step S _2). Then, an operation restart instruction is issued from the control means 17 (step S ₃ ), and the speed control means 20 receives, for example, one of the steady speeds during the steady operation.
A low speed operation command of a low speed S1 of / 2 is issued. At the same time, for each of the inverter devices 15 and 16, equation (1)
And the voltages VL1 and VH1 at the time of the low-speed operation shown in the equation (2).

[0016]

(Equation 1)

VL0 and VH0 are steady voltages output from the inverters 15 and 16 during steady operation, and S0 is a steady speed. The material 23 to be heated is heated by the heating coils 9 and 10 to which the output voltages VL1 and VH1 are supplied during the low-speed operation of the inverter devices 15 and 16 while being conveyed at low speed S1 by the conveying means 22.

FIG. 4 shows the inductance of the heating coils 9 and 10 and the heating coils 9 and 10 with respect to the temperature of the material 23 to be heated.
FIG. 3 is an explanatory diagram showing a relationship between resonance frequencies of the capacitors 11 and 12. The heating coils 9 and 10 have, for example, a structure in which a copper tube is wound a plurality of times in a cylindrical shape, and have a constant inductance. However, the inductance L of the heating coil 23 has the following relationship in a state where the material 23 to be heated exists inside. (1) The inductance L is large when the material to be heated 23 has magnetism close to room temperature. (2) When the temperature of the material to be heated 23 rises, the temperature increases to a transformation point (about 770 ° C.) at which the magnetism disappears. However, when the magnetism disappears beyond the transformation point, the inductance L decreases.

The condensers 11 and 12 include heating coils 9 and 1
For zero matching, the capacitance C is kept constant. In the induction heating device, the frequency F of the induced current is determined by Expression (3) by the resonance between the inductance L and the capacitance C. Therefore, the inverter devices 15 and 16 supply high-frequency power having a frequency following the resonance frequency to the heating coils 9 and 10. In addition, since the material 23 to be heated from a low temperature to a high temperature is mixed in the heating coil 9, the inductance L and the resonance frequency F are total values. However, as shown in FIG. 4, when the temperature of the heated material 23 is low, the resonance frequency F is small,
When the temperature is high, the resonance frequency F increases.

[0020]

(Equation 2)

When high-frequency power is supplied to the heating coils 9 and 10, the resonance frequencies of the heating coil 9 and the capacitor 11 in the low temperature range and the heating coil 10 and the capacitor 12 in the high temperature range are detected by the resonance frequency detecting means 13 and 14. Are detected (steps S ₄ and S ₆ ). Next, the control means 17 detects the temperature of the material to be heated 23 in the low temperature range and the high temperature range from each resonance frequency, and controls the output voltages of the inverter devices 15 and 16 according to the temperatures (steps S ₅ and S ₅₎ . ₇ ). That is, the stop time becomes longer and the material to be heated 2
When the temperature of the inverter 3 is low as shown by the curve B in FIG. 2, the output voltages of the inverter devices 15 and 16 are increased. FIG.
In the case where the stop time is short and the temperature does not decrease much as indicated by the curve C, the output voltages of the inverter devices 15 and 16 are reduced.

As described above, as shown in FIG.
In the case where the temperature is low as shown by the curve B in FIG.
By increasing the output voltage of the heating target materials 5 and 16,
Since the temperature of No. 3 rises rapidly, the return to the steady state can be promoted. When the temperature of the material to be heated 23 is high as shown by the curve C in FIG.
By lowering the output voltage of 16, the temperature of the material to be heated 23 gradually increases, so that an excessive rise in temperature can be prevented.

For example, when the temperature of a steel material to be heated having a diameter of 50 mm is increased to 1,200 ° C., the following judgment is made from the relationship between the resonance frequency and the temperature of the material to be heated. (1) When the resonance frequency is 2.6 kHz or less (below the transformation point shown in FIG. 4), the temperature of the material 23 to be heated at the outlet of the heating coil 9 is about 700 ° C. or less. Therefore, the temperature difference up to 1,000 ° C. in the steady state is large. (2) When the resonance frequency is 2.9 kHz or more (the transformation point shown in FIG. 4 or more), the temperature of the material 23 to be heated at the outlet of the heating coil 9 is about 900 ° C. or more. Therefore, the temperature difference up to the steady state is small. The temperature of the material 23 to be heated at the outlet of the high-temperature region heating coil 10 is detected by a thermometer (not shown) as in the conventional case.

Next, the determination of the timing for returning from low-speed operation to steady-state operation will be described. The resonance frequencies of the low-temperature section (heating coil 9 and capacitor 11) and the high-temperature section (heating coil 10 and capacitor 12) are constantly detected by the respective frequency detecting means 13 and 14. For example, when the resonance frequency detecting means 13 of the low-temperature section detects the resonance frequency in the steady state shown at point A in FIG. 4, the control means 17 sets the temperature of the material 23 to be heated at the outlet of the heating coil 9 to the steady state. it is detected that approached (step S _8), an instruction to return to normal operation with to end the low-speed operation command (step S _9).

In the steady operation, a steady voltage VLO is supplied to the heating coil 9 in the low temperature section, and a steady voltage VHO is supplied to the heating coil 10 in the high temperature section. In the above, the case where the return to the steady operation is commanded by the resonance frequency detected by the resonance frequency detecting means 13 of the low temperature section has been described, but the resonance frequency detected by the resonance frequency detecting means 14 of the high temperature section has been described. The same effect can be expected even if the return to the steady operation is commanded by the frequency.

In addition, while the temperature of the material 23 to be heated is detected when the operation is resumed, the output voltages of the inverters 15 and 16 are controlled, and the speed at which the material 23 is transported is reduced. When the temperature of the material to be heated 23 is small and the temperature of the material to be heated 23 is small, the same effect can be expected only by controlling the output voltages of the inverter devices 15 and 16.

Also, when the operation is resumed, the material to be heated 23 in the subsequent heating coil 10 is heated so as to approach a predetermined temperature by stationary heating without feeding the material to be heated 23, and then the operation is started at a low speed. By switching, waste materials that do not reach the predetermined temperature can be reduced.

As described above, when the operation is resumed,
Is started, and the inverter devices 15, 16
When the high-frequency power from is supplied to the material 23 to be heated, the resonance frequencies are detected by the resonance frequency detecting means 13 and 14 and the temperature of the material 23 to be heated is detected.
By controlling the output voltage, the material to be heated 23 can be heated to a predetermined temperature.

Further, the heating temperature of the material 23 to be heated can be heated to a predetermined temperature by setting the conveying speed of the material 23 to be heated at the time of resuming the operation to a lower speed than the steady speed in the steady operation.

In the first embodiment, the description has been given of the structure composed of the two sections of the low-temperature section and the high-temperature section. Provided with a resonance frequency detecting means for detecting the temperature of the material to be heated in each section, it is possible to determine the output voltage of the inverter device when the operation is resumed. Then, it is possible to detect that the temperature of the material to be heated in any of the sections approaches the steady state, and to return to the steady operation.

[0031]

According to the first aspect of the present invention, the transfer of the material to be heated is started when the operation is resumed, and when the high frequency power of the material to be heated is supplied from the inverter device, the resonance frequency is detected by the resonance frequency detecting means. By detecting the temperature of the material to be heated and controlling the output voltage of the inverter device according to the temperature of the material to be heated, it is possible to prevent the temperature of the material to be heated from excessively increasing. The time required to raise the temperature to a predetermined temperature can be shortened.

According to the second aspect of the present invention, the material to be heated can be heated to a predetermined temperature by setting the transport speed of the material to be heated at the time of restart of operation to be lower than the steady speed in the steady operation. Thus, it is possible to appropriately instruct the return to the steady operation.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention.

FIG. 2 is an explanatory diagram illustrating a relationship between a transport direction and a temperature of a material to be heated in FIG.

FIG. 3 is a flowchart showing the operation of FIG.

FIG. 4 is an explanatory diagram showing a relationship between a temperature of a material to be heated and an inductance and a resonance frequency of a heating coil in FIG. 1;

FIG. 5 is a configuration diagram showing a conventional induction heating device.

FIG. 6 is an explanatory diagram showing a relationship between a transport direction and a temperature of a material to be heated in FIG. 5;

[Explanation of symbols]

9,10 heating coil, 11,12 condenser, 1
3, 14 resonance frequency detecting means, 15, 16 inverter device, 17 control means, 22 conveying means, 23 material to be heated.

Claims (2)

[Claims] 1. A heating coil is connected to a condenser to supply high-frequency power from an inverter device, and a plurality of materials to be continuously conveyed by a conveying means at a predetermined speed in a steady operation are controlled by the heating coil. In the induction heating device configured to heat, while the conveyance means is stopped and the conveyance of the material to be heated is stopped in the heating coil, and the supply of the high-frequency power from the inverter device is stopped, The transfer of the material to be heated by the transfer means is started, and when high-frequency power is supplied from the inverter device, the resonance frequency of the heating coil and the capacitor is detected by frequency detection means, and the control means The temperature of the material to be heated is detected from the resonance frequency, and the output voltage of the inverter device is controlled according to the temperature of the material to be heated. An induction heating device characterized in that: 2. The induction heating apparatus according to claim 1, wherein the control unit controls the transport speed of the transport unit to be lower than the normal operation.