JP2000150126A - Induction heating apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To give an alarm by detecting whether or no there is a material to be heated in a heating coil when starting an induction heating apparatus. SOLUTION: This induction heating apparatus is equipped with a heating coil 2 to inductively heat a material 4 and continuously carried, up to a designated high temperature from a room temperature, a matching capacitor 3 to compose a resonance circuit by being connected to the heating coil 2, a high frequency inverter device 1 to supply high frequency power to the resonance circuit, a voltage detector 21 to detect an output voltage of the high frequency inverter device 1, a current detector 22 to detect an output current from the high frequency inverter device 1, and a judgment circuit 25 to judge whether or not there is the material 4 to be heated in the heating coil 2 by the size of a ratio of the output voltage to the output current when starting induction heating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction heating device having a function of automatically detecting that an unnecessary material remains in a heating coil at the time of starting the induction heating device and issuing a warning.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram of an induction heating device disclosed in Japanese Patent Application Laid-Open No. 61-185885. In the figure, 1 is a high-frequency inverter device that generates a high-frequency AC voltage, 2 is a heating coil wound in a solenoid shape that generates a high-frequency magnetic field when a high-frequency voltage is applied by the high-frequency inverter device 1, and 3 is a power factor improving device. 4 is a steel material heated by an eddy current generated by a high-frequency magnetic field generated in the heating coil 2, 5 is a voltage detector that detects an output voltage of the high-frequency inverter device 1,
Reference numeral 6 denotes starting voltage command means for giving a starting command to the high-frequency inverter device 1, reference numeral 7 denotes a starting voltage reference signal generator for generating a reference signal for determining a starting output voltage of the high-frequency inverter device 1, and reference numeral 8 denotes high-frequency inverter device 1. Is an output voltage reference setter that generates a reference signal for keeping the output voltage constant after the start of operation, 10 is an auxiliary AC power supply connected in parallel with the heating coil 2, and 11 is an auxiliary AC power supply 10
An opening and closing circuit for opening and closing the electrical connection between the heating coil 2 and
12 is a current detecting means for detecting the output of the auxiliary AC power supply 10, 13 is a rectifying circuit for converting the AC signal detected by the detecting means 12 to DC, and 14 is rectifying the starting voltage reference signal generator 7 from the starting reference signal. Arithmetic means 19 for subtracting the output signal of the circuit 13 to give a starting voltage signal to the starting voltage commanding means 6; 19 compares the magnitude of the output signal from the voltage detector 5 with the output signal of the output voltage reference setting device 8 And an output means for outputting an output signal.

The operation of the induction heating device will be described below. During continuous operation of the induction heating device, the material to be heated 4
Is continuously conveyed to the heating coil 2 at a constant speed by a heated material conveying mechanism (not shown), heated to a predetermined temperature (usually around 1200 ° C.) and discharged from the heating device, and a post-process not shown (Usually a forging press).

[0004] The heating coil 2 and the capacitor 3 constitute a resonance circuit, and energy for maintaining the resonance circuit is continuously supplied from the high-frequency inverter device 1. Therefore, the frequency of the AC voltage generated by the high-frequency inverter device 1 is substantially equal to the resonance frequency of the heating coil 2 and the capacitor 3, which are loads.

Here, a description will be given of when the induction heating device is started, that is, when the high-frequency inverter device 1 is started to generate an AC voltage. When the induction heating device is started, there is a state in which the material 4 to be heated is present in the heating coil 2 and a state in which the material 4 is not present. Varies from case to case.

Here, the higher the ratio of the material to be heated 4 in the heating coil 2, the higher the frequency of the high-frequency inverter device 1.
, The load seen from the high-frequency inverter device 1 becomes lighter (the load impedance is higher) as the ratio of the material to be heated 4 entering the heating coil 2 is smaller. Status).

The high-frequency inverter device 1 generates a voltage called a start-up voltage at the time of start-up and applies it to a load, thereby giving the load voltage an initial resonance energy. If no special modification is made to the voltage of the high-frequency inverter device 1 at the time of starting, that is, the starting voltage, the resonance voltage waveform generated in the load after the start is generally as shown in FIG. 5 depending on the state of the load, that is, the degree of the load. .

That is, when the load is heavy, the heating coil 2
When the ratio of the material 4 to be heated is large, the resonance voltage waveform may be attenuated sequentially and the start may fail.
On the other hand, when the load is light, the material to be heated 4
When the degree of the input is small, the resonance voltage waveform sequentially increases, the voltage becomes excessively high, an overvoltage protection function (not shown) operates, and the operation of the high-frequency inverter device 1 may be stopped.

Here, before the induction heating device is started and before the high-frequency inverter device 1 is started, the switching circuit 11 is first closed, and the auxiliary AC power supply device 10 is supplied to the circuit including the heating coil 2 and the capacitor 13. . The frequency generated by the auxiliary AC power supply 10 is selected to be substantially close to the resonance frequency of the heating coil 2 and the capacitor 3, and the magnitude of the generated voltage V is constant.

The current I detected by the current detector 12
Depends on the degree of the load, and the current I is large when the load is heavy, and the current I is small when the load is light.
Since this detection current I is AC, it is rectified by the rectifier circuit 13 and converted into DC, and is compared with the signal of the starting voltage reference signal generator 7 by the calculating means 14.

The value thus compared, that is, the calculating means 14
The output value of the high-frequency inverter device 1 changes through the starting voltage command means 6 such that the starting voltage is increased when the load is heavy and the starting voltage is decreased when the load is light. Commanded.

According to the above-described method, the starting voltage of the high-frequency inverter device 1 is commanded to an appropriate value depending on the weight of the load, that is, the degree of the material 4 to be heated contained in the heating coil 2, and after starting the induction heating device, The resonance voltage of the load circuit is maintained at a constant value as shown in FIG.

Here, when the high-frequency inverter device 1 starts, the switching circuit 11 opens. High frequency inverter device 1
After a certain period of time has elapsed after the start of the control, control is performed so as to match the set value of the output voltage instead of the start voltage. In this case, the output voltage detected by the output voltage detector 5 and the output voltage reference value output from the output voltage reference setter 8 are calculated by the arithmetic means 1.
9, the output voltage is commanded to the high-frequency inverter device 1, and the output voltage is controlled so that the output voltage becomes the reference value of the output voltage reference setter 8.

[0014]

As described above, in the conventional induction heating apparatus, the weight of the load is determined before the start by adding the auxiliary AC power supply, and the start voltage of the high-frequency inverter is appropriately set. It is possible.

However, there are the following problems. Generally, induction heating devices installed on forging lines tend to increase in size and capacity with the times, and the length of the heating coil also tends to increase, and the heating coil and high-frequency inverter device also consist of multiple sections. There are many.

For this reason, the following problem has arisen. In an induction heating device, a material to be heated is continuously heated and discharged to a subsequent process. However, the induction heating device is frequently stopped due to a trouble in a post-process (press device) or a trouble in the induction heating device itself. In this case, the heating coil is stopped in a state where the material to be heated remains.

In the induction heating device for heating a relatively long material to be heated, which is called a bar material, of about 5 m to 6 m, the material to be heated is placed in front of the induction heating device due to a trouble in a post-process (pressing device) or the induction heating device. It may return to the process (heated material supply device). Thereafter, when the trouble is cleared and the induction heating device is restarted, if the material to be heated remains in the heating coil, the following problems occur.

(1) Normally, the material to be heated is continuously heated and heated from the inlet to the outlet of the heating coil, but the material to be heated remaining in the heating coil at the time of startup is heated from an intermediate step. And does not rise to a predetermined forging temperature (about 1250 ° C.). (2) When restarting the induction heating device, the type (size, material, etc.) of the material to be heated may be changed, but the type of material to be heated remaining in the heating coil at the time of startup is different.
This leads to the mixing of different materials into the final product.

Therefore, in the induction heating apparatus, it is desirable that there is no material to be heated in the heating coil regardless of whether the apparatus is started or restarted. However, in the conventional induction heating apparatus, although the starting voltage can be appropriately set, it is not possible to detect that the material to be heated is in the heating coil, and thus the above-described problem may occur.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and detects an object to be heated in a heating coil when the induction heating apparatus is started, and issues an alarm. Is provided.

[0021]

According to a first aspect of the present invention, there is provided an induction heating apparatus which heats a material to be continuously conveyed to a predetermined temperature higher than a normal temperature, and is connected to the heating coil. A matching capacitor that forms a resonance circuit, a high-frequency inverter device that supplies high-frequency power to the resonance circuit, and a heating device that detects the presence of a material to be heated in the heating coil and starts an alarm when starting induction heating. It has material detection means.

In the induction heating apparatus according to the second aspect of the present invention, the heating target detecting means is provided with a plurality of sections each including a high-frequency inverter device and a heating coil. It detects whether there is a material to be heated in the heating coil and issues an alarm, and displays a section in which the material to be heated is detected.

According to a third aspect of the present invention, there is provided a heating material detecting means for an induction heating device, comprising: a voltage detector for detecting an output voltage of the high frequency inverter; and a current detector for detecting an output current of the high frequency inverter. Also, the apparatus has a judgment circuit for judging the presence or absence of the material in the heating coil based on the ratio of the output voltage and the output current at the time of starting the induction heating.

According to a fourth aspect of the present invention, there is provided a heating target detecting means for an induction heating device, comprising: a voltage detector for detecting an output voltage of the high-frequency inverter; and a current detector for detecting an input current of the high-frequency inverter. Also, the apparatus has a judgment circuit for judging the presence or absence of a material in the heating coil based on the magnitude of the ratio of the output voltage and the input current when starting the induction heating.

The heating target detecting means of the induction heating apparatus according to the present invention is a frequency detector for detecting an output frequency of the high-frequency inverter, and a heating coil based on the magnitude of the output frequency when starting the induction heating. It has a judgment circuit for judging the presence or absence of the material in the inside.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 Hereinafter, embodiments of the present invention will be described with reference to the drawings. In FIG.
Is an output voltage detector for detecting the output voltage of the high-frequency inverter device 1, 22 is an output current detector for detecting the output current of the high-frequency inverter device 1, 23 is a rectifier circuit for rectifying the detected output voltage, and 24 is a detected circuit. A rectifier circuit for rectifying the output current, and 25 is a judgment circuit.
Indicates the presence or absence of a material to be heated in the heating coil from the output voltage detection result and the output current detection result. If it is determined that there is, a stop command is issued to the high-frequency inverter device 1 and a warning is given to a worker. The lamp 26 is turned on. The other configuration is the same as the configuration shown in FIG.

Next, the operation of the apparatus according to this embodiment will be described with reference to the time chart of FIG. When starting the induction heating device according to the present embodiment, the following operation is performed. First, a start command is issued from the determination circuit 25 to the high-frequency inverter device 1, and the high-frequency inverter device 1 starts supplying a high-frequency voltage to the resonance circuit of the heating coil 2 and the capacitor 3, which are loads.

At that time, the output voltage of the high-frequency inverter device 1 reaches the set value almost in the first few cycles, and the output current is the same. Here, the output voltage detected from the output voltage detector 21 is converted to DC through the rectifier circuit 23, and the output current detected from the output current detector 22 is
4 and converted into a direct current, and input to the determination circuit 25, respectively.

Here, when the material 4 to be heated is present in the heating coil 2, the impedance of the load viewed from the high-frequency inverter device 1 becomes small, and the ratio KT between the output voltage detection value VT and the output current detection value IT becomes small. . On the other hand, if the material to be heated 4 is not in the heating coil 2, the impedance of the load viewed from the high-frequency inverter device 1 increases, and the ratio KT between the output voltage detection value VT and the output current detection value IT increases.

The determination circuit 25 determines the ratio KT between the output voltage detection value VT and the output current detection value IT input T seconds after startup.
And the following determination is made. (1) If KT> K1, the material to be heated is not in the heating coil. (2) If KT ≦ K1, the material to be heated is in the heating coil.

The determination boundary K1 of the above-mentioned ratio KT for determining the presence or absence of the material to be heated in the heating coil can be obtained in advance by calculation. Since KT changes depending on the ratio of the material 4 to be heated in the heating coil 2, it is desirable to obtain KT based on experimental data.

If the condition (1) is determined, the high-frequency inverter 1 continues to supply the voltage to the heating coil 2 as it is, and a new material 4 to be heated is supplied into the heating coil 2 from the inlet. The temperature is raised by heating.

If the condition (2) is judged, the judgment circuit 25 issues a stop command to the high-frequency inverter device 1 and issues an alarm on the display 26 so that the material to be heated remains in the heating coil 2. To show that

That is, the determination circuit 25 determines the presence or absence of the material 4 to be heated in the heating coil 2 based on the detected output voltage value and output current value a certain time after the start of the induction heating device. If the material to be heated 4 is in the heating coil 2, the activation of the high frequency inverter device 1 is stopped, and the display 2 indicates that the material to be heated 4 remains in the heating coil 2.
Display and warn by 6

Embodiment 2 In the first embodiment, the output current of the high-frequency inverter device 1 is detected to detect the impedance of the load of the high-frequency inverter device 1. However, the same effect can be obtained by detecting the input current of the high-frequency inverter device 1. Can be In this case, the current detector is placed on the input side of the high-frequency inverter device 1 and detects the input current of the high-frequency inverter device 1.

Since the input current is a value proportional to the output current,
The ratio between the output voltage and the input current becomes a value proportional to the load impedance, and the presence or absence of the material to be heated 4 in the heating coil 2 can be determined in the same manner as the method described in the first embodiment.

That is, the determination circuit 25 determines the presence or absence of the material 4 to be heated in the heating coil 2 based on the output voltage value and the input current value detected after a certain time from the start of the induction heating device. If the material to be heated 4 is in the heating coil 2, the activation of the high frequency inverter device 1 is stopped, and the display 2 indicates that the material to be heated 4 remains in the heating coil 2.
Display and warn by 6

Embodiment 3 Embodiments 1 and 2 above
Although the output voltage and the output current are used as detection information for judging the presence or absence of the material to be heated in the heating coil, the output frequency of the high-frequency inverter device 1 may be used. FIG. 3 shows the embodiment.

In FIG. 3, reference numeral 27 denotes an output frequency detector for detecting the output frequency of the high-frequency inverter device 1, and other components are the same as those shown in the first embodiment. Here, the output frequency detector 27 detects the above output frequency and converts it into a voltage value proportional to the output frequency. The determination circuit 25 can determine the output frequency value based on the magnitude of the input voltage value.

Here, when the material 4 to be heated is inside the heating coil 2, the impedance at both ends of the heating coil 2 increases, so that the resonance frequency of the load circuit of the high-frequency inverter device 1 decreases, and the detected output frequency also increases. Become smaller. Therefore, the determination circuit 25 determines the presence of the material to be heated 4 based on the output frequency of the voltage conversion output from the output frequency detector 27.

On the other hand, if the material to be heated 4 is not in the heating coil 2, the impedance at both ends of the heating coil 2 becomes small, so that the resonance frequency of the load circuit of the high-frequency inverter device 1 becomes high and the detected output frequency becomes high. Become. Similarly, the determination circuit 25 determines the absence of the material to be heated from the output frequency value of the voltage conversion output from the output frequency detector 27.

Therefore, from the voltage-converted output frequency value FT a certain time after the start of the induction heating device, the determination circuit 25 determines whether or not the heated material 4 is in the heating coil 2. If is located in the heating coil 2, the activation of the induction heating device 1 is stopped, and a warning is displayed on the display 26 that the material to be heated 4 remains in the heating coil 2.

As in the first embodiment, the judgment circuit 25 makes the following judgment based on the detected value FT of the output frequency. (1) If FT> K2, the material to be heated is not in the heating coil. (2) If FT ≦ K2, the material to be heated is in the heating coil. As in the first embodiment, the determination boundary K2 of the output frequency value FT for determining the presence or absence of the material to be heated in the heating coil can be obtained in advance by calculation. Also, this K
Since the value 2 varies depending on the ratio of the material 4 to be heated in the heating coil 2, it is desirable to obtain the value 2 based on experimental data.

Embodiment 4 FIG. In the first to third embodiments, the high-frequency inverter device 1 and the heating coil 2 are each one.
These may be three or more each.

In the case of three or more units, the first to third embodiments are used.
This is the same as the operation method described above. That is, the detection means according to any one of the first to third embodiments is provided for each section constituted by the high-frequency inverter device and the heating coil, and the detection is performed after a certain time from when the induction heating device is started. From the values, the determination circuit 25 determines which section of the heating coil 2 has the material 4 to be heated.

The determination circuit 25 determines that the material 4 to be heated 4
Is determined to be in the heating coil 2, the high-frequency inverter device 1 is stopped from starting, and
Displays the section number remaining in the heating coil 2 on the display 26 to warn the user.

In this embodiment, only one determination circuit 25 is required for all the sections, and it is possible to determine the presence or absence of the material to be heated in any section from the information of the detection value input from each section. If there is a section where the material to be heated remains, the corresponding section number is displayed on the display 26 so that the operator of the induction heating apparatus can easily find the material to be heated remaining. it can.

[0048]

According to the first aspect of the present invention, a heating coil for inductively heating a material to be continuously conveyed from room temperature to a predetermined high temperature, and a matching circuit connected to the heating coil to form a resonance circuit A capacitor, N high-frequency inverters for supplying high-frequency power to the resonance circuit, and a heated-material detecting means for detecting the presence of the material to be heated in the heating coil at the start of induction heating and issuing an alarm. With this configuration, there is an effect that it is possible to prevent uneven heating of the material to be heated remaining in the heating coil when the induction heating device is started, thereby causing a variation in quality.

According to the second aspect, the means for detecting a material to be heated is
A plurality of sections consisting of a high-frequency inverter device and a heating coil are provided, and these sections are monitored in an integrated manner to detect which section of the heating coil contains the material to be heated and to issue an alarm. By displaying the number of the section where the material is detected, there is an effect that the heating coil in which the material to be heated remains can be easily specified even though the heating coil is divided into a plurality of sections.

According to the third aspect of the present invention, the material-to-be-heated detecting means includes a voltage detector for detecting the output voltage of the high-frequency inverter, a current detector for detecting the output current of the high-frequency inverter, Since the heating circuit has a judgment circuit for judging the presence or absence of a material in the heating coil based on the ratio of the output voltage and the output current at the time of starting heating, the material to be heated remaining in the heating coil when the induction heating device is started up Can be easily detected.

According to the fourth aspect of the present invention, the heating target detecting means includes a voltage detector for detecting an output voltage of the high frequency inverter, a current detector for detecting an input current of the high frequency inverter, and an induction device. Since the heating circuit has a judgment circuit for judging the presence or absence of the material in the heating coil based on the ratio of the output voltage and the input current at the time of starting the heating, the material to be heated remaining in the heating coil when the induction heating device is started Can be easily detected.

According to the fifth aspect of the present invention, the material to be heated detecting means is a frequency detector for detecting the output frequency of the high-frequency inverter device, and the heated material in the heating coil is detected when the induction heating is started. Since the determination circuit for determining the presence or absence of the heating material is provided, there is an effect that the presence or absence of the material to be heated in the heating coil can be determined with a simple configuration.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing an operation chart of the embodiment.

FIG. 3 is a circuit configuration diagram showing a third embodiment of the present invention.

FIG. 4 is a circuit configuration diagram showing a conventional invention.

FIG. 5 is a diagram showing an operation chart of the conventional invention.

[Explanation of symbols]

1 high frequency inverter device, 2 heating coil, 3 matching capacitor, 4 material to be heated, 21 output voltage detector,
22 output current detector, 23, 24, 28 rectifier circuit,
25 judgment circuit, 26 display, 27 output frequency detector.

Claims (5)

[Claims] 1. A heating coil for inductively heating a material to be continuously conveyed to a predetermined temperature higher than room temperature, a matching capacitor connected to the heating coil to form a resonance circuit, and a high-frequency An induction heating device having a high-frequency inverter device for supplying electric power, wherein the induction heating device includes a heated material detection unit that detects the presence of the heated material in the heating coil and issues an alarm when starting the induction heating. Heating equipment. 2. A heating target detecting means is provided with a plurality of sections each including a high frequency inverter device and a heating coil, and these sections are collectively monitored, and the heating target material is present in any one of the heating coils. 2. The induction heating apparatus according to claim 1, wherein a warning is issued by detecting the state, and a section in which the material to be heated is detected is displayed. 3. The heating target detecting means includes a voltage detector for detecting an output voltage of the high-frequency inverter device, a current detector for detecting an output current of the high-frequency inverter device,
3. The induction heating apparatus according to claim 1, further comprising a judgment circuit for judging the presence or absence of a material in the heating coil based on the magnitude of the ratio between the output voltage and the output current when starting the induction heating. 4. A heated material detecting means includes: a voltage detector for detecting an output voltage of the high-frequency inverter device; a current detector for detecting an input current of the high-frequency inverter device;
3. The induction heating apparatus according to claim 1, further comprising a judgment circuit for judging the presence or absence of a material in the heating coil based on the magnitude of the ratio between the output voltage and the input current when starting the induction heating. 5. A heating material detecting means includes: a frequency detector for detecting an output frequency of the high-frequency inverter device; and a determination for judging the presence or absence of a material in the heating coil based on the magnitude of the output frequency when starting the induction heating. The induction heating device according to claim 1, further comprising a circuit.