JP7604176B2 - High Frequency Induction Heating Equipment - Google Patents

Description

The present invention relates to a high-frequency induction heating device that uses the principle of electromagnetic induction to heat metals and other materials.

A high-frequency induction heating device generates a magnetic field by passing a high-frequency current through a heating coil, and generates an induced current in a metallic object to be heated that is placed inside or near the heating coil. This induced current generates Joule heat in the object to be heated, thereby heating the object to be heated (see Patent Document 1).

For example, when using a high-frequency induction heating device in a manufacturing process in which a metal object to be heated is pressed into a resin part, proper control of the temperature of the object to be heated is an important factor in producing a high-quality product, but it is not possible to attach a temperature sensor to each object to be heated, such as a nut or sleeve. Therefore, conventionally, temperature control has been performed using a radiation thermometer or the like.
However, temperature measurement using a radiation thermometer is easily affected by external disturbances, and there is a problem in that there is a large measurement error of, for example, 50° C. to 100° C.

JP 2020-87807 A

The present invention has been made to solve the above problems, and aims to provide a high-frequency induction heating device that can measure the temperature of a heated object, to which it is difficult to attach a temperature sensor, with a smaller error than conventional methods.

The high-frequency induction heating device of the present invention is characterized by comprising a heating coil configured to receive a high-frequency current and generate an induced current in an object to be heated by high-frequency induction, an oscillator configured to convert a DC voltage to an AC voltage and supply a high-frequency current to the heating coil, a current sensor configured to measure the current supplied to the primary side of the oscillator, and a temperature calculation unit configured to calculate an estimated value of the temperature of the object to be heated by inputting the integrated value of the current measured by the current sensor into a regression line equation showing the relationship between the integrated value and the temperature of the object to be heated.

Furthermore, one configuration example of the high-frequency induction heating device of the present invention is characterized in that it further includes a judgment unit configured to judge whether the estimated value of the temperature of the heated object exceeds a predetermined temperature threshold value.
Furthermore, one configuration example of the high-frequency induction heating device of the present invention is characterized in that it further includes a simple regression analysis unit configured to acquire data on the integrated current value for each heating test measured by the current sensor and data on the temperature of the heated object for each heating test measured by a temperature sensor attached to the heated object during multiple heating tests performed before calculating an estimated value of the temperature of the heated object, and to determine an equation for the regression line based on the acquired data.

The high-frequency induction heating device of the present invention is characterized by comprising a heating coil configured to generate an induced current in an object to be heated by high-frequency induction when supplied with a high-frequency current; an oscillator configured to convert a DC voltage into an AC voltage and supply the high-frequency current to the heating coil; a current sensor configured to measure the AC current supplied to the secondary side of the oscillator; a voltage sensor configured to measure the AC voltage supplied to the secondary side of the oscillator; and a temperature calculation unit configured to calculate an estimated value of the temperature of the object to be heated by inputting the integrated value of the product of the AC current measured by the current sensor and the AC voltage measured by the voltage sensor into a regression line equation showing the relationship between the integrated value and the temperature of the object to be heated.

Furthermore, one configuration example of the high-frequency induction heating device of the present invention is characterized in that it further includes a judgment unit configured to judge whether the estimated value of the temperature of the heated object exceeds a predetermined temperature threshold value.
Furthermore, one configuration example of the high-frequency induction heating device of the present invention is characterized in that it further includes a simple regression analysis unit configured to acquire data on the integrated value of the product of the AC current and the AC voltage for each heating test measured by the current sensor and the voltage sensor, and data on the temperature of the heated object for each heating test measured by a temperature sensor attached to the heated object, during multiple heating tests performed before calculating an estimated value of the temperature of the heated object, and to determine an equation for the regression line based on the acquired data.

According to the present invention, by providing a current sensor and a temperature calculation unit, or by providing a current sensor, a voltage sensor, and a temperature calculation unit, it is possible to measure the temperature of a heated object, for which it is difficult to attach a temperature sensor, with an error smaller than that of a conventional radiation thermometer in the process of heating the heated object using a high-frequency induction heating device.

FIG. 1 is a block diagram showing the configuration of a high-frequency induction heating device according to a first embodiment of the present invention. FIG. 2 is a flow chart for explaining the operation of the high-frequency induction heating device according to the first embodiment of the present invention. FIG. 3 is a flowchart illustrating a method for deriving a regression line according to the first embodiment of the present invention. FIG. 4 is a diagram showing an example of the change in current and temperature during one heating test. FIG. 5 is a diagram for explaining a method for deriving a regression line according to the first embodiment of the present invention. FIG. 6 is a block diagram showing the configuration of a high-frequency induction heating device according to a second embodiment of the present invention. FIG. 7 is a flow chart for explaining the operation of the high-frequency induction heating device according to the second embodiment of the present invention. FIG. 8 is a flowchart illustrating a method for deriving a regression line according to the second embodiment of the present invention. FIG. 9 is a diagram for explaining a method of deriving a regression line according to the second embodiment of the present invention. FIG. 10 is a block diagram showing an example of the configuration of a computer that realizes the high-frequency induction heating apparatus according to the first and second embodiments of the present invention.

[Principle of the Invention]
It has been experimentally found that the integrated value of the product of the primary side voltage V and the primary side current I during heating of a high frequency induction heating device has a linear relationship with the temperature of the heated object.
The inventors realized that when the primary side voltage V is constant during heating, only the primary side current I changes, and therefore the temperature of the heated object can be determined from the integrated value of the current I during heating.

[First embodiment]
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a block diagram showing the configuration of a high-frequency induction heating device according to a first embodiment of the present invention. The high-frequency induction heating device includes a heating coil 1 that receives a high-frequency current and generates an induced current in an object to be heated 11 by high-frequency induction, an oscillator 2 that converts a DC voltage V into an AC voltage and supplies a high-frequency current to the heating coil 1, a matching box 3 provided between the oscillator 2 and the heating coil 1, a control unit 4 that controls the oscillator 2, a current sensor 5 that measures a DC current I supplied to the primary side of the oscillator 2, a temperature calculation unit 6 that calculates an estimated value of the temperature of the object to be heated 11 by inputting an integrated value of the current I measured during heating into a regression line equation showing the relationship between the integrated value and the temperature of the object to be heated 11, a display unit 7 that displays the temperature, a judgment unit 8 that judges whether the estimated value of the temperature of the object to be heated 11 exceeds a predetermined temperature threshold value, a judgment result output unit 9 that outputs the judgment result, and a simple regression analysis unit 10 that determines the equation of the regression line based on data obtained during multiple heating tests performed before calculating the estimated value of the temperature of the object to be heated 11.

As shown in FIG. 1, the object to be heated 11 is placed inside the heating coil 1 (or in the vicinity of the heating coil 1). An example of the object to be heated 11 is a nut or sleeve that is pressed into a resin part in a heated state. The heating coil 1 and the object to be heated 11 need to be mechanically fixed.

Next, the operation of the high-frequency induction heating device of this embodiment will be described with reference to FIG. 2. The control unit 4 outputs a heating control signal to the oscillator 2 in response to, for example, a user's instruction to start heating (YES in step S100 in FIG. 2). When the heating control signal is input from the control unit 4, the oscillator 2 starts supplying a high-frequency current to the heating coil 1 via the matching box 3 (step S101 in FIG. 2). The matching box 3 matches the impedance of the oscillator 2 and the heating coil 1 to improve the efficiency of supplying the high-frequency current from the oscillator 2 to the heating coil 1. By supplying a high-frequency current to the heating coil 1, an induced current is generated in the metallic heated object 11 placed inside the heating coil 1, and this induced current generates Joule heat in the heated object 11.

The oscillator 2 converts an externally supplied DC voltage V into an AC voltage and supplies a high-frequency current to the heating coil 1. The current sensor 5 measures a current I supplied to the primary side of the oscillator 2.
The temperature calculation unit 6 acquires data on the current I measured by the current sensor 5 (step S102 in FIG. 2). The temperature calculation unit 6 acquires data on the current I at regular intervals until the heating time from the start of heating (start of oscillation) reaches a set value (YES in step S103 in FIG. 2). As a result, the temperature calculation unit 6 records time-series data on the current I.

When the heating time reaches the set value, the control unit 4 stops outputting the heating control signal. This causes the oscillator 2 to stop supplying high-frequency current to the heating coil 1 (step S104 in FIG. 2). This stops heating the object 11.

When the heating time reaches the set value and heating stops, the temperature calculation unit 6 inputs the integrated value of the time series data of the current I acquired from the start to the end of heating into a predetermined regression line equation showing the relationship between the integrated value and temperature to calculate an estimated value of the temperature of the heated object 11 (step S105 in FIG. 2). If the estimated value of the temperature T of the heated object 11 is T _E , the integrated value of the current I is I _INTEGRAL , the slope of the regression line showing the relationship between the integrated value I _INTEGRAL and the estimated value T _E of the temperature T is a, and the intercept of the regression line is b, the equation of the regression line is as follows. The method of deriving the regression line will be described later.
T _E = a × I _INTEGRAL + b ... (1)

The display unit 7 displays the estimated value T _E of the temperature T of the heated object 11 calculated by the temperature calculation unit 6 (step S106 in FIG. 2). In this embodiment, the estimated value T _E is displayed, but the data of the estimated value T _E may be transmitted to the outside.

The judgment unit 8 judges whether the estimated value T _E of the temperature T of the heated object 11 calculated by the temperature calculation unit 6 exceeds a predefined temperature threshold value (step S107 in FIG. 2). Specifically, the judgment unit 8 judges that there is an abnormality when the estimated value T _E is less than the lower temperature limit T _LOWER or exceeds the upper temperature limit T _UPPER , and judges that there is a normality when the estimated value T _E is equal to or greater than the lower temperature limit T _LOWER and equal to or less than the upper temperature limit T _UPPER .

The judgment result output unit 9 outputs the judgment result of the judgment unit 8 (step S108 in FIG. 2). The judgment result can be output, for example, by displaying information informing the judgment result or by transmitting information informing the judgment result to the outside.

In this embodiment, by utilizing the relationship between the integrated value I _INTEGRAL of the current I and the temperature T of the object 11, it is possible to measure the temperature of the object 11, which is difficult to attach a temperature sensor to, with an error smaller than that of a conventional radiation thermometer.

Next, a method for deriving a regression line showing the relationship between the integrated value I _INTEGRAL of the current I and the estimated value T _E of the temperature T of the heated object 11 will be described. In this embodiment, before actually heating the heated object 11 to manufacture a product, a preliminary heating test is performed multiple times using the same heating coil 1 and heated object 11 as used in manufacture, data on the integrated value I _INTEGRAL of the current I and data on the temperature of the heated object 11 are obtained, and the regression line is obtained.

Figure 3 is a flowchart explaining how to derive the regression line. First, a user of a high-frequency induction heating device attaches a temperature sensor such as a thermocouple to the heated object 11 placed inside the heating coil 1 (or in the vicinity of the heating coil 1).

The control unit 4 outputs a heating control signal to the oscillator 2 in response to, for example, a command from the user to start a test (YES in step S200 in FIG. 3). When the heating control signal is input from the control unit 4, the oscillator 2 starts supplying a high-frequency current to the heating coil 1 via the matching box 3 (step S201 in FIG. 3).

The simple regression analysis unit 10 acquires data on the current I measured by the current sensor 5 (step S202 in FIG. 3).
A temperature sensor attached to the object 11 measures the temperature T of the object 11. The simple regression analysis unit 10 acquires data on the temperature T measured by the temperature sensor (step S203 in FIG. 3). The simple regression analysis unit 10 acquires data on the current I and the temperature T at regular intervals until the heating time from the start of heating reaches a set value (YES in step S204 in FIG. 3). As a result, the simple regression analysis unit 10 records time series data on the current I and time series data on the temperature T.

When the heating time reaches the set value, the control unit 4 stops outputting the heating control signal. This causes the oscillator 2 to stop supplying high-frequency current to the heating coil 1 (step S205 in FIG. 3).

Next, the high-frequency induction heating device cools the object 11 to be heated (step S206 in FIG. 3). A cooling device (not shown) is used to forcibly cool the object 11 to be heated. Here, the device may wait for a predefined time, or may wait until the temperature T measured by the temperature sensor falls below a defined value.

The simple regression analysis unit 10 waits until the heated object 11 cools down, and then changes the heating conditions (step S207 in FIG. 3). The heating conditions include the set value of the heating time and the heating efficiency (the impedance of the matching box 3). The matching box 3 is equipped with a matching transformer (not shown), and the impedance can be changed by changing the tap of this matching transformer, thereby changing the heating efficiency.
The simple regression analysis unit 10 changes at least one of the set value of the heating time and the heating efficiency.

The control unit 4 determines whether the number of heating tests has reached a predetermined number (e.g., two) (step S208 in FIG. 3), and if the number of heating tests has not reached the predetermined number, returns to step S201 and outputs a heating control signal to the oscillator 2.
In this manner, the processes of steps S201 to S207 are repeated until the predetermined number of heating tests are completed. Fig. 4 is a diagram showing an example of changes in current I and temperature T during one heating test.

After a predetermined number of heating tests have been completed, the simple regression analysis unit 10 performs a simple regression analysis based on the recorded time series data of the current I and the time series data of the temperature T, and calculates the slope a and intercept b of the regression line (step S209 in FIG. 3).
Specifically, when the integrated value I _INTEGRAL of the current I for each heating test and the maximum value of the temperature T for each heating test are obtained as shown in Fig. 5, for example, the simple regression analysis unit 10 calculates the slope a and intercept b of the regression line L by the least squares method. In the example of Fig. 5, I1 is the integrated value of the current I in the first heating test, T1 is the maximum value of the temperature T in the first heating test, I2 is the integrated value of the current I in the second heating test, and T2 is the maximum value of the temperature T in the second heating test.

Then, the simple regression analysis unit 10 sets the calculated values of the slope a and the intercept b in the temperature calculation unit 6 (Step S210 in FIG. 3).
This completes the process in Fig. 3. The process in Fig. 3 is performed before the object 11 is actually heated to manufacture a product, but if the type of at least one of the heating coil 1 and the object 11 is changed, the process in Fig. 3 must be performed again.

According to this embodiment, the regression line can be derived from a preliminary heating test and the temperature calculation unit 6 can be automatically set, which can improve the efficiency of equipment startup.

[Second embodiment]
Next, a second embodiment of the present invention will be described. Fig. 6 is a block diagram showing the configuration of a high-frequency induction heating device according to the second embodiment of the present invention. The high-frequency induction heating device includes a heating coil 1, an oscillator 2, a matching box 3, a control unit 4, a current sensor 5a that measures an AC current Ia supplied to the secondary side of the oscillator 2, a temperature calculation unit 6a, a display unit 7, a determination unit 8, a determination result output unit 9, a simple regression analysis unit 10a, and a voltage sensor 12 that measures an AC voltage Va supplied to the secondary side of the oscillator 2.

Next, the operation of the high frequency induction heating apparatus of this embodiment will be described with reference to Fig. 7. Steps S300 and S301 in Fig. 7 are the same as steps S100 and S101 in Fig. 2.
The current sensor 5a measures an AC current Ia supplied to the secondary side of the oscillator 2. The voltage sensor 12 measures an AC voltage Va supplied to the secondary side of the oscillator 2.

The temperature calculation unit 6a acquires data on the AC current Ia measured by the current sensor 5a and data on the AC voltage Va measured by the voltage sensor 12 (step S302 in FIG. 7). The temperature calculation unit 6a acquires data on the AC current Ia and the AC voltage Va at regular intervals until the heating time from the start of heating (start of oscillation) reaches the set value (YES in step S303 in FIG. 7). As a result, the temperature calculation unit 6a records time-series data on the AC current Ia and the AC voltage Va.

When the heating time reaches the set value and heating is stopped (step S304 in FIG. 7), the temperature calculation unit 6a calculates an estimated value of the temperature of the heated object 11 by inputting the integrated value of the time series data of the product of the AC current Ia and the AC voltage Va acquired from the start to the end of heating into a predetermined regression line equation showing the relationship between the integrated value and temperature (step S305 in FIG. 7). If the estimated value of the temperature T of the heated object 11 is T _E , the integrated value of the product of the AC current Ia and the AC voltage Va is W _INTEGRAL , the slope of the regression line showing the relationship between the integrated value W _INTEGRAL and the estimated value T _E of the temperature T is a, and the intercept of the regression line is b, the equation of the regression line is as follows. The method of deriving the regression line will be described later.
T _E =a×W _INTEGRAL +b...(2)

Steps S306 to S208 in FIG. 7 are the same as steps S106 to S108 in FIG. 2.

Next, a method for deriving a regression line showing the relationship between the integrated value W _INTEGRAL and the estimated value T _E of the temperature T of the heated object 11 will be described. In this embodiment, before actually heating the heated object 11 to manufacture a product, preliminary heating tests are performed multiple times using the same heating coil 1 and heated object 11 as used in manufacture, data on the integrated value W _INTEGRAL and data on the temperature of the heated object 11 are obtained, and the regression line is calculated.

Figure 8 is a flowchart explaining how to derive the regression line. Steps S400 and S401 in Figure 8 are the same as steps S200 and S201 in Figure 3.

The simple regression analysis unit 10a acquires data on the AC current Ia measured by the current sensor 5a and data on the AC voltage Va measured by the voltage sensor 12 (step S402 in FIG. 8).
As in the first embodiment, a temperature sensor attached to the object 11 measures the temperature T of the object 11. The simple regression analysis unit 10a acquires data on the temperature T measured by the temperature sensor (step S403 in FIG. 8). The simple regression analysis unit 10a acquires data on the AC current Ia, the AC voltage Va, and the temperature T at regular intervals until the heating time from the start of heating reaches a set value (YES in step S404 in FIG. 8). As a result, the simple regression analysis unit 10a records time-series data on the AC current Ia, the AC voltage Va, and the temperature T.

When the heating time reaches the set value and heating is stopped (step S405 in FIG. 8), the high-frequency induction heating device cools the object 11 to be heated (step S406 in FIG. 8).
As in the first embodiment, the simple regression analysis unit 10a waits until the object 11 to be heated cools down, and then changes the heating conditions (step S407 in FIG. 8).

After a predetermined number of heating tests have been completed, the simple regression analysis unit 10a performs a simple regression analysis based on the time series data of the product of the AC current Ia and the AC voltage Va and the time series data of the temperature T, and calculates the slope a and intercept b of the regression line (Step S409 in FIG. 8).
Specifically, when the integrated value W _INTEGRAL of the product of the AC current Ia and the AC voltage Va for each heating test and the maximum value of the temperature T for each heating test are obtained as shown in Fig. 9, for example, the simple regression analysis unit 10a calculates the slope a and intercept b of the regression line L by the least squares method. In the example of Fig. 9, W1 is the integrated value of the product of the AC current Ia and the AC voltage Va in the first heating test, T1 is the maximum value of the temperature T in the first heating test, W2 is the integrated value of the product of the AC current Ia and the AC voltage Va in the second heating test, and T2 is the maximum value of the temperature T in the second heating test.

Then, the simple regression analysis unit 10a sets the calculated values of the slope a and the intercept b in the temperature calculation unit 6a (Step S410 in FIG. 8).
Thus, in this embodiment, it is possible to obtain the same effects as in the first embodiment. In this embodiment, the current sensor 5a and the voltage sensor 12 are provided between the oscillator 2 and the matching box 3, but they may be provided between the matching box 3 and the heating coil 1.

The control unit 4, temperature calculation unit 6, 6a, display unit 7, judgment unit 8, judgment result output unit 9, and simple regression analysis unit 10, 10a of the high-frequency induction heating device described in the first and second embodiments can be realized by a computer equipped with a CPU (Central Processing Unit), a storage device, and an interface, and a program that controls these hardware resources. An example of the configuration of this computer is shown in Figure 10.

The computer includes a CPU 100, a storage device 101, and an interface device (hereinafter abbreviated as I/F) 102. The I/F 102 is connected to an oscillator 2, current sensors 5, 5a, a voltage sensor 12, the hardware of a display unit 7, the hardware of a judgment result output unit 9, a temperature sensor, and the like. In such a computer, a program for implementing the method of the present invention is stored in the storage device 101. The CPU 100 executes the processing described in the first and second embodiments according to the program stored in the storage device 101.

The present invention can be applied to high-frequency induction heating devices.

1...heating coil, 2...oscillator, 3...matching box, 4...control unit, 5, 5a...current sensor, 6, 6a...temperature calculation unit, 7...display unit, 8...judgment unit, 9...judgment result output unit, 10, 10a...simple regression analysis unit, 11...heated object, 12...voltage sensor.

Claims (6)

A heating coil configured to receive a high-frequency current and generate an induced current in an object to be heated by high-frequency induction;
an oscillator configured to convert a DC voltage into an AC voltage and supply a high frequency current to the heating coil;
a current sensor configured to measure a current supplied to a primary side of the oscillator;
and a temperature calculation unit configured to calculate an estimated value of the temperature of the object to be heated by inputting an integrated value of the current measured by the current sensor into a regression line equation showing the relationship between the integrated value and the temperature of the object to be heated. 2. The high frequency induction heating device according to claim 1,
The high frequency induction heating device further comprises a determination unit configured to determine whether the estimated value of the temperature of the object to be heated exceeds a predefined temperature threshold value. The high frequency induction heating device according to claim 1 or 2,
A high-frequency induction heating device further comprising a simple regression analysis unit configured to acquire data on an integrated current value for each heating test measured by the current sensor and data on the temperature of the heated object for each heating test measured by a temperature sensor attached to the heated object during multiple heating tests performed before calculating an estimated value of the temperature of the heated object, and to determine an equation for the regression line based on the acquired data. A heating coil configured to receive a high-frequency current and generate an induced current in an object to be heated by high-frequency induction;
an oscillator configured to convert a DC voltage into an AC voltage and supply a high frequency current to the heating coil;
a current sensor configured to measure an alternating current supplied to a secondary side of the oscillator;
a voltage sensor configured to measure an AC voltage supplied to a secondary side of the oscillator;
and a temperature calculation unit configured to calculate an estimated value of the temperature of the object to be heated by inputting an integrated value of the product of the AC current measured by the current sensor and the AC voltage measured by the voltage sensor into a regression line equation showing the relationship between the integrated value and the temperature of the object to be heated. 5. The high frequency induction heating device according to claim 4,
The high frequency induction heating device further comprises a determination unit configured to determine whether the estimated value of the temperature of the object to be heated exceeds a predefined temperature threshold value. 6. The high frequency induction heating device according to claim 4,
a simple regression analysis unit configured to obtain data on an integrated value of the product of the AC current and the AC voltage for each heating test measured by the current sensor and the voltage sensor, and data on the temperature of the heated object for each heating test measured by a temperature sensor attached to the heated object, during multiple heating tests performed before calculating an estimated value of the temperature of the heated object, and to determine an equation for the regression line based on the obtained data.

Images