JPS6011432B2 - induction heating device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an induction heating apparatus equipped with a control device for predicting and controlling the output of a heating power source according to the temperature of a workpiece and heating a material to be heated to a predetermined temperature.

As an induction heating apparatus, the one shown in FIG. 1 is known as an induction heating apparatus equipped with a control device that heats a workpiece to a predetermined temperature even if variations in load conditions, feed rate, etc. occur.

In Figure 1, la and lb are the power supplies for the induction heating device, and 2
is a heating coil, 3 is a material feed rate detector, 4 is a temperature detector, 5 is a voltage setting device for power supplies la and ib, 6 is a function generator that outputs a signal proportional to the square root of the feed rate, and 7 is an increaser 8 is a temperature setting device, and 9 is a workpiece.

Next, the operation of the conventional device will be explained.

The device shown in Fig. 1 supplies power from four power supplies la and lb to dedicated heating coils 2, and attempts to heat the workpiece to a predetermined temperature while it passes through the heating coils 2. .

Now, if the shape of the workpiece 9 and the feed speed are known, ``Once the final heating temperature is determined, the required power is calculated.

The coil voltage for supplying the necessary power to the workpiece 9 is determined from the relationship between the coil shape and the workpiece shape. Therefore, if the conditions do not change, by setting the coil voltage first, the workpiece can always be heated to the required temperature.

Recently, it has become increasingly common for metal pipes to be heated using feeding heating devices, but the feeding speed for long pipes is much higher than that for conventional hollow materials, and fluctuations in pipe wall thickness are also a problem. As a result, fluctuations in the weight per unit length of the workpiece being heated and fluctuations in the feed rate due to slips, etc., cannot be ignored.

Therefore, in the past, the coil voltage was constant, but
By making it variable according to fluctuations in the conditions, it is possible to obtain uniform heating.

In FIG. 1, first, if the work size, processing amount, and heating temperature are determined, the output voltages of the power supplies la to lb are determined.

The voltage is set by the voltage setting device 5. The heating temperature is also set using the temperature setting device 8.

Now, let us consider a case where the feed speed of the workpiece 9 fluctuates. When the output voltage of each power source la to lb is constant, the temperature decreases in inverse proportion to the feed speed. Further, the power consumption of the work 9 is proportional to the square of the output voltage. Therefore, if the feed speed increases now, the temperature of the workpiece can be kept constant by increasing the output voltage of the power supply by the square root of the increased rate. A feed rate detector 3 detects the feed rate of the workpiece.

The feeding speed detector 3 was installed on the output and input sides of the coil.
This is because when the joint of the workpiece is fixed in the coil, the output voltage is set according to the faster feed speed.
The function generator 6 is a device that generates a signal of the square root of the speed change, and compares the value set by the voltage setting device 6 with the value of the function generator 6, and depending on which one is larger, the output of the power supplies la to lb is determined. It is determined. By doing this, it became possible to correct temperature changes due to speed changes.

In addition, in order to correct temperature changes due to changes in the shape of the workpiece (for example, changes in the shape of the workpiece or changes in wall thickness for pipes), the final temperature of the workpiece is detected by the temperature detector 4, and the final temperature of the workpiece is detected by the function generator 6. By comparing with the output, correction is performed by feeding back to the final stage power supply lb. However, in such conventional devices, a person has to set the output voltage every time the workpiece changes or the throughput changes.

Recently, heating of metal pipes has been actively carried out, but in the case of metal pipes, there are many types of wall thickness even if the outer diameter is the same.
Furthermore, when the number of electric wires increases, the possibility of setting errors increases if the settings are made manually, requiring a great deal of human labor, which has become a bottleneck in system automation. In addition, although induction heating equipment has a large energy-saving effect, the heating mechanism is electromagnetic and acts directly on the material, rather than relying on radiation or heat conduction like a furnace, so it is a process with a very slow response. ing. Therefore, temperature control is generally very difficult in such processes, and conventional analog control still has the following problems.

'1} Reliability of temperature data [21 Discrepancy between the temperature detection point and the point heated by the coil (i.e. the effect of dead time on feedback) Therefore, with conventional analog control, temperature unevenness occurs due to changes in the pipe wall thickness. As a result, the control system is prone to hunting, and in practice it is almost impossible to correct temperature irregularities due to changes in wall thickness.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and includes a workpiece shape detection device, a workpiece feed speed detector, and an arithmetic device to detect the temperature for each data. By calculating and applying the necessary power to each stage, there is no need for people to individually set the electrical conditions in response to changes in the unit weight of the workpiece and changes in the throughput.
Furthermore, the present invention provides a novel induction heating device that can accurately correct the temperature of the fluctuating portion even when the temperature fluctuates during operation. 2a and 2b are induction heating coils, 3 is a pipe feed rate detection device, and 4 is a radiation thermometer with scanning or fixed thermometers facing each other, and the average temperature over the entire circumference of the pipe is measured by the method described later. It is for detection.

Reference numeral 5 denotes a sensor for detecting the wall thickness of a pipe, which is composed of, for example, several turns of a detection coil.

That is, when the power density supplied to the detection coil 5 is increased beyond a certain level, the magnetic permeability of the pipe inside the enemy detection coil 5 becomes close to 1, and the current penetration depth 6 becomes equal to the frequency of the power supply. It will be a fixed value. The impedance of the detection coil 5 is determined by the ratio of the outer dimension aw of the pipe to 6 and the wall thickness t of the pipe.
It is known that it is determined by two functions, each with the ratio of and dw as variables. Therefore, the wall thickness of the pipe can be detected by detecting the outer diameter w of the pipe and determining the impedance of the detection coil 5 from the voltage applied to the detection coil 5 and the current flowing through the detection coil 5. be. Reference numeral 6 denotes a sensor for detecting the external dimensions of a pipe, and is configured to, for example, install an electromagnet near the pipe, and determine the distance between the electromagnet and the pipe based on the magnitude of the current flowing through the electromagnet to determine the external dimensions of the pipe. ing.

Note that the wall thickness detection sensor 5 and the outer diameter dimension detection sensor 6 described above are just examples, and the wall thickness may be detected using other ultrasonic waves, or the outer diameter may be detected using a phototube or the like. Of course, dimensions may also be measured. 7 is a central processing unit; 8 is a power source 9 for the wall thickness detection sensor 5 and outer diameter size detection sensor 6; a power factor correction capacitor;
Reference numeral 10 indicates a switch for adjusting the capacitor capacity, and reference numeral 11 indicates an arithmetic portion of the arithmetic unit 7 for controlling the power supplies lb and lc.

Here, the thermometer side of the pipe using the radiation thermometer 4 will be explained.

It is known that metal pipes can have partial wall thickness deviations due to the manufacturing process.

Therefore, by detecting temperature at only one point, it is difficult to distinguish between local temperature unevenness due to uneven thickness and temperature unevenness over the entire longitudinal direction. Therefore, in the present invention, a method is adopted in which the pipe is processed while rotating, and the temperature at each point is averaged to eliminate the influence of temperature unevenness in the circumferential direction. There are two methods of measurement: one using fixed thermometers facing each other and the other using a scanning thermometer.Both methods measure the temperature over the entire circumference, reducing noise in temperature control, and The purpose is to make temperature data reliable for quality control. That is, Figures 5 and 6
As shown in the figure, by tilting the pipe conveying V roller 41 by 450 degrees with respect to the pipe, the pipe rotates once as it advances along the length D (D is the diameter of the pipe).

Therefore, the thermometer-side trajectory of the thermometer 4 becomes a trajectory as shown by T in FIG. 6, and when this is shown in a developed view with the pipe opened, it becomes as shown in FIG. 7.

Therefore, if the average is taken over the mD shown in FIG. 7, it means that the average is taken over the entire circumference of the pipe in this section.
That is, the feed rate detector 3 in FIG. 2 detects that the pipe is mD
By detecting that data has been taken while the pipe is moving (that is, during one rotation) and averaging the data up to that point, it is possible to continuously capture the temperature along the length of the pipe. In addition, in the case of Figures 5 and 6, there was one thermometer, but this may be replaced with two as shown in Figures 8a and b, so that the average temperature over the entire circumference is 9. The column shown in the figure shows that the data is collected only among the sheep.

In the same way, by placing n thermometers around the circumference and collecting data from only the crucian and cucumber spaces on the sides, the average temperature around the entire circumference can be calculated.

Next, the operation of the mysterious induction heating device according to the present invention configured as above will be explained.

In the induction heating device of this invention, the heating power sources la to l
c as an independent power supply for the preheating zone and control zone (
1) The control zone (0) is selected, and the following operations are performed within the allowable range of the heating temperature increase pattern given for operation regarding the selection of the power setting value for each zone.

[A] In the preheating zone, the power setting value is determined so that the outlet temperature reaches a sufficiently constant temperature level allowed by the heating pattern.

The 'o' control zone (1) is a control zone (1) in which the thermal and electrical properties of the material are constant within the control zone (0), and the relationship between heating power and temperature is close to linear.
) determine the power setting value of the heating power supply.

With this determination, the feedforward control to the control zone (0) using the temperature signal from the thermometer on the control zone (1) side functions extremely effectively.

Furthermore, variations in the outlet temperature of the control zone (1) are mainly caused by variations in the dimensions of the material (outer diameter, wall thickness, etc.).

For this reason, the control zone (1) not only has the function of heating the material to a certain temperature, but also has the function of a detector that detects dimensional changes in the material by temperature, and this detection function allows it to detect these temperature fluctuation disturbances. A major feature is that it can be kept to a minimum.

From the above, the control zone (1) does not require fine control of the milk furnace, and the heating power source may be configured with a plurality of heating coils connected to one power source.

In the control zone (B), the outlet temperature is controlled to be the target temperature, but as far as possible within the power setting range of the control zone (0), it is controlled to be the median value of the allowable range. Determine the outlet temperature of zone (1).

Here, the reason why the power supplies are made independent in the three areas is mainly due to the following reason.

'11 Magnetic metals have different properties below and above the magnetic state point, and the current penetration depth also differs.

Therefore, in order to achieve optimal heating, it is necessary to change the power supply frequency. [21] Since the properties of metal materials differ at the magnetic transformation point (hereinafter referred to as the Curie point), more effective control can be achieved by changing the power supply control method for each region.

(3) In the case of induction heating, since the heat generating portion is only on the surface of the material, temperature unevenness is likely to occur between the center of the surface.

It is also known that the temperature difference is proportional to the surface power density of the material. Therefore, in the final coil, it is necessary to reduce the surface power density to eliminate temperature unevenness at the center of the surface.

Next, the operation of each heating zone will be specifically explained.

First, the central processing unit 7 receives data such as the specific gravity y of the pipe, the specific heat C, the target temperature, the coil shape, the power supply frequency, and the coil constants in the magnetic region (coil efficiency, coil power factor co
Input the easy table for s and c) and coil impedance).

The reason for inputting a simple table of coil constants in the magnetic region is as follows. In induction heating in the magnetic region, the magnetic permeability changes with the surface power density of the pipe, so the coil efficiency, power factor cos◇c, and impedance Zc
will also change.

However, the surface power density of the pipe is ri, cos c,
Since it is determined by random calculation, trial and error calculations must be performed in order to obtain the accurate required applied power.

If such calculations are performed, the storage capacity of the calculation device will increase, and even if the calculations are performed faithfully, it is thought that there will be a considerable discrepancy between the theoretical value and the actual value. Therefore, input a table as shown in FIG. 3 as an example.

In other words, Fig. 3 shows that, for example, if the power supply capacity of the power supply la in Fig. 2 is 750Kw, the power is divided into five, and for each pipe outer diameter dw, the power is distributed over a certain range of pipe wall thickness (range that is expected to be heated). , Mu, cosJc, Zc for each power castle
It is calculated and tabulated.

It goes without saying that the number of divisions should be considered depending on the pipe size and power supply capacity.

Now, suppose that the pipe has passed through the wall thickness detection sensor 5, the outer dimension detection sensor 6, and the feed rate detector 3.

The central processing unit 7 receives new information such as the wall thickness t of the pipe,
The outer diameter dw and the feed rate VF are given.

Since the central processing unit 7 is given dw and t, it calls the coil constants (coil efficiency r, coil power factor cos?c, coil impedance Zc) in that case, and determines the output voltage E of the power source la using the following procedure. . If dw and t detected by sensors 5 and 6 are not shown in Figure 3, connect the closest values with a straight line and slide by the amount of deviation to obtain cos◇c. do.

The central processing unit 7 can determine the voltage to be applied to the coil 2a by performing the following calculation in order to heat the pipe to the Curie point (approximately 770 qo) in the power source la, that is, in the heating zone.

If the unit weight of the pipe is M, (k9'), MIni t(dW-t)y (1) If the feed speed is VF, the weight processed per unit time (kg/h) is =M.・VF (2) The energy Q (Kcal/h) to be supplied to the pipe is Q: Earth-C-△8 (3) However, △8' indicates the temperature difference between the Curie point temperature of the pipe and room temperature. .

Therefore, in order to apply the above Q to the heating coil 2a, 2
The applied voltage E (V) of a is E2F now.

-C Thought C (4) Above '1} in central processing unit 7
The calculations of formulas to {41} are performed, and the output of the power source la is controlled so that the output voltage of formula [4} can be applied.

In the case of FIG. 2, self-excited thyristor inverters are used as the power supplies la, lb, and lc in one embodiment.

Therefore, the output frequency of the power supplies la to lc is the heating coil 2a to
It is almost determined by the resonant frequency of the parallel resonant circuit composed of 2c and capacitor 9.

Now that we know the outer dimension Pw and wall thickness t of the pipe,
By controlling the output of la with the central processing unit 7 and at the same time turning on and off the switch 10 according to commands from the central processing unit 7, the total capacitance of the capacitor 9 is adjusted and the output frequency of the power supply la is also set to the optimum value. Fine tune.

When the pipe passes through the heating coil 2a, the temperature detector 4 detects the temperature of the pipe.

At the position of the temperature detector 4, the pipe is heated to approximately 77,000 ℃, but since the power source la only performs rough control as described above, it is thought that the values do not match exactly.

Therefore, subsequently the power supplies lb and lc, i.e. the control zone (1),
(0) performs high precision control.

When performing high-precision control using these power sources lb and lc, the temperature of the pipe is above the Curie point, and the pipe has a magnetic permeability of 1, just like non-magnetic metals, so it is very difficult to control. The capacity of the arithmetic unit does not particularly increase.The configuration of control zones (1) and (0) is as follows:
The operation will be explained.

Basic formula for control The amount of heat Q given to the pipe per unit time is Q, = C (
8) (ao-8i) Aw・VF where・C(a)...Specific heat of pipe 8o...

Outlet temperature 8i...Inlet temperature Aw...Pipe cross-sectional area Vp...Pipe processing speed Next, the amount of heat Q2 that the heating coil gives to the work per unit time is Q2PW,'' (5)
If we consider heat loss due to heat radiation in the heating coil to be included in Pw, then in steady state Q,:Q2;PW:C(a)(801ai)AwVF...
■This is the basic formula for control.

Next, when the coil power P is calculated from this Pw, taking into account the heat radiation loss PL, it becomes P: 〈PW+PL)... (7).

In this case, the control amount for the feedforward control is obtained from the coil't 7 formula from the target outlet temperature 0* of each zone and the actually measured temperature 0 on the inlet side.

Note that in order to actually control the output of the heating power source, the voltage or current of the heating coil must be controlled, and if the coil voltage is Vc, then VC=K;...■ If the coil current is lc, then ba ＊y
(9) lciK Z.

It can be expressed as COS◇CP...

Here, Zo is the coil impedance, cos is the coil power factor, and K is the correction coefficient.

Although Zo and cos0c vary depending on Pw or the temperature and material of the workpiece, the average values in the heating temperature range are approximately used.

Furthermore, the correction coefficient K of the feed forward formula (hereinafter abbreviated as ff) [81 or (9) is modified as follows depending on the heating outlet temperature (actual heating performance temperature).

KN=KN0. 10Q(ao*-8o)/(ao*-ai
*)…00 However, 8i*;
Set temperature on the inlet side of the workpiece 80*: Output side 60; Actual temperature on the exit side of the workpiece By modifying K in this way, the control formula is closer to the current situation, and more accurate temperature control is possible. .

This is the basic formula for feedback (hereinafter abbreviated as f.B). The control operation will be explained using FIG. 4 according to the following basic equations.

In addition, Fig. 4 shows 11 in Fig. 2, power supply lb, and heating coil 2b.
, that is, the control zone (1), but since the same applies to the control zone (0), only the control zone (1) will be explained here.

First, the target temperature of control zone (1) is set to 8*. Here, the target temperature 8* is the control zone (0) as described above.
The temperature increase value that can be raised with half of the power that can be applied is set as the temperature subtracted from the final target temperature. By setting the load distribution in this way, it is possible to increase the control allowance for the upper and lower limits of the control zone (b). If the control allowance percentage is determined in advance, the following determination method can be used. First, if the control cost at the final power source is x% of the final power source, then (100-x%)
The value obtained by subtracting the temperature increase value at the electric power from the target temperature becomes the final power supply inlet temperature. Even if there are a large number of power sources, the target outlet temperature of each power source can be determined sequentially using the same procedure. Now, the arithmetic device 11 takes in data from the inlet side thermometer 4a, and averages the pipe temperature in the averaging processing arithmetic unit 117 using the method described above.

As a result, the target temperature a* and the inlet temperature ai are compared, and the specific heat calculating section 118 and the processing weight calculating section 119 calculate the specific heat and the processing weight. Furthermore, from the same input, the heat radiation loss calculation unit 11 calculates the heat radiation loss of the pipe, and the required heat amount calculated up to the processing weight calculation unit 119,
The outputs of the heat radiation loss calculation section 110 are added.

Next, the modified gain of the modified gain calculation section 111 is given an appropriate initial value at the first stage, and the coil efficiency A calculated by the coil constant calculation section 113 taking this initial value into consideration.
, coil power factor cos? c, a control output according to the coil impedance Zc is output to the power source lb.

The calculation of the coil constant in the coil constant calculation section 113 is performed based on the coil diameter, coil length, and
Based on the pipe resistivity, power frequency, and number of coil turns,
The calculation is performed using the pipe wall thickness t and the pipe outer cover dimension dw detected by the detector.

At this time, if the pipe is in a magnetic region, the magnetic permeability of the pipe must be taken into consideration when calculating the above coil constant, making the calculation complicated. However, as mentioned above, in the control zone (1), French = 1 Since it is the area of buddha, cosgc,
Calculation of Zc is easily possible. The outlet temperature ao appearing as a result of the above is measured by the outlet thermometer 4b, and averaged with the inlet thermometer 4a according to the procedure of the same machine.

This outlet temperature ao is then compared with the target temperature 0*,
8. The static compensation coefficient calculation unit 1
12, the initial value of the modified gain calculation unit 111 is modified. As described above, the relationship between temperature and power output, which is comprised of the specific heat calculation section 118, the processing weight calculation section 119, the modified gain calculation section 111, and the coil constant calculation section 113, is corrected to a more correct one.

By the way, f・ is generally used as a control method in a control system.
Learning control, etc. as an extended concept of B, day, or fB is a well-known technique.

However, in an actual control system, these ff, f・
The major issue is how to configure the purpose and combination of B, and this will determine whether the control will be the most appropriate and stable for the actual process. In the control device according to the present invention, ff is a dynamic temperature disturbance, i.e.,
This is intended to perform comparative temperature control, and fB is intended to correct steady temperature deviations due to deviations in initial settings, changes in outside temperature, changes in temperature of conveyor rolls, etc.

Considering the actual control loop in a simplified manner, we now set the amount of f・f to H
q, fB amount is fBq, and the control amount finally set to the heating power source is Q. In this control system, Q = (10Q beats q)
...(11).

Here, it should also be called a distribution coefficient for controlling Q'ffq and fBq.

The method for determining Q is: Q=QRq+(1-Q)fBq...(12)0
<Q<1 can be considered, but in the actual process f
fq and f-equilibrium interact with each other, and it is extremely difficult to determine the optimal Q.

Therefore, in this method, equation (11) is adopted, and Q is the distance la for averaging the signals from the thermometer and the control length lb.
It has been found that there is an optimal value Qs determined by the ratio of .

By adopting the control method described above, extremely stable temperature control against various temperature disturbances has become possible for all types of materials and operating conditions.

Furthermore, from the results of actual operation, the following results were obtained regarding la and lb'. This average length is set to be equal to or less than the heating coil length regardless of the conveyance speed.

Further, the timing for controlling the output to the heating power source is set immediately before the portion of the heated material corresponding to the initial raw temperature data used to calculate the average value used for output calculation enters the heating coil.

It has been confirmed through experiments that by doing this, the optimum data can be obtained as the average temperature of the part affected by the setting change to the heating coil.

In the above explanation, the shape and dimensions of the material to be heated are detected also in the child heating zone, and based on this detection signal, the coil constant is selected by a calculation device to control the power output of the child heating zone. However, in some cases, it is also possible to apply a constant voltage in the preheating zone, and to correct the temperature due to dimensional fluctuations of the heated material only in the control zone using the control method described above. .

In this case, the configuration of the control device such as the arithmetic device can be made simpler.

Further, as an embodiment of the present invention, control in the control zone is
Although the explanation has been given regarding the control performed in the region where m>1, the same control may of course be performed in the region where m>1.

In that case, it would be more practical to provide a table as shown in FIG. 3 as information. As described above in detail using one embodiment, the following effects can be expected by the induction heating of the present invention.

1 Change in workpiece size (change in outer diameter if it is a round bar, etc.)
Even if the workpiece's feed speed changes, it can be automatically heated to the target temperature at all times.

2. When changing the work size or processing amount, there is no need to change the electrical condition settings each time.

3 Even in the case of sudden changes in load conditions, such as changes in wall thickness when the material is a pipe, etc., the output of the power source is determined based on the heating results, so heating always reaches the target set temperature. I can do it.

4 By dividing the power supply into each temperature range and selecting the control method that is most suitable for that range, the material can be heated optimally for each temperature range, and the computing equipment required for control can also be miniaturized. It becomes possible to do so.

5. Since control is performed above the magnetic transformation point, the control system can be simplified and the arithmetic unit can be downsized.

6 When detecting temperature, we use a circuit that calculates the average value, so we can avoid the influence of temperature unevenness in the vertical direction (which occurs when there is damage or uneven thickness in the pipe) and accurately detect temperature unevenness only in the longitudinal direction. be able to.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a control system showing a conventional induction heating device equipped with a control system for correcting fluctuations in load conditions;
FIG. 2 is a block diagram of a control system showing an embodiment of the present invention;
Fig. 3 is a table showing an example of input data, Fig. 4 is a block diagram showing the configuration of the control system of control zone (1) in Fig. 2, and Figs. FIG. 3 is a diagram for explaining the method. In the figure, la to lc are power supplies for induction heating, 2a to 2c are induction heating coils, 3 is a material feed rate detector, 4a to 4c are material temperature detectors, 5 is a sensor for detecting the wall thickness of a pipe, 6
7 is a central processing unit, 8 is a power supply, 9 is a power factor correction capacitor, and switches for a contactor and the like. Note that the same reference numerals in the drawings indicate the same or equivalent parts. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9

Claims (1)

[Scope of Claims] 1. In an apparatus in which a material to be heated is heated to a target temperature while being continuously conveyed by induction heating devices arranged in tandem,
A heating coil divided into a preheating zone and a control zone, a heating power source provided corresponding to each zone, a shape and dimension detection device for detecting the dimensions such as the thickness and outer diameter of the material to be heated, and a heated material in each zone. The preheating zone includes a temperature detection device that detects the temperature of the material, and a calculation device that calculates the required power of the control zone according to the dimensions of the material to be heated detected by the shape and dimension detection device and the target temperature. heating the material to be heated to around the temperature of its magnetic transformation point, and when the temperature of the material to be heated on the outlet side of the preheating zone detected by the temperature detection device does not reach the temperature of the magnetic transformation point, The temperature of the heated material is set to a temperature equal to or higher than the magnetic transformation point, and the heated material reaches its target heating temperature based on the required power from the calculation device according to the target heating temperature of the heated material. An induction heating device characterized in that the heating voltage of the control zone is controlled. 2 The material to be heated is conveyed while skewing, and the temperature of each zone is measured by the temperature detection device using a thermometer to calculate the average length of the heating coil of each zone or the length equivalent to 1/n of the heating zone length. When performing feedforward and feedback control of the heating temperature in the control zone using this measurement data, the distribution system of the feedforward amount and feedback amount is calculated based on the average value interval of the temperature measurement value and the heating coil length or By determining the heating zone length, mutual interference between feedback control and feedforward control can be minimized in response to changes in material type and operating conditions, and by using voltage as the heating power control set value, 2. The induction heating device according to claim 1, wherein temperature disturbance due to dimensional variation of the heating material is minimized. 3 The calculation device calculates a coil constant according to each temperature range and applied voltage in advance from the relationship between the dimensions of the heated material and the coil diameter, and selects a predetermined coil according to the detection signal of the heated material dimension detection device. The induction heating device according to claim 1 or 2, which is configured to read out a constant.