JPS5947438B2 - high frequency heating coil - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a high frequency heating coil device, particularly a high frequency heating coil device having a high frequency heating coil in close proximity to an object to be heated.

The induction heating phenomenon in which a good conductor or magnetic material placed in a magnetic field is heated by electromagnetic induction is well known, and several high-frequency induction heating devices using this heating phenomenon have been put into practical use.

A heat sealing process for sealing a storage container filled with q of cooked foods is known as a preferred example of the use of a high-frequency induction heating device. A typical storage container is made of a triple-layered sheet made of aluminum or other metal foil laminated with a resin film on both sides, and after this sheet is shaped into a bag or other container shape, the joint is heat-sealed, leaving a portion behind. .

The storage container thus produced is filled with cooked food, and the filling opening is immediately heat-sealed. Conventional heat sealing means is known to press a heating element against the sealing part and melt and bond the resin film at the joint part by heat conduction, but in order to prevent the resin film on the outside of the metal foil from melting Since the temperature of the heating element cannot be raised above a certain level, it takes a long time for the inner resin film that forms the joint to melt. In particular, when high-temperature, short-time sterilization is performed in order not to impair the flavor of food and to increase the efficiency of heat sterilization work, the melting temperature of the inner resin film must withstand high temperatures, and the outer resin film must withstand high temperatures. Since it is disadvantageous in terms of cost to make the resin film have a high melting temperature, the difference in melting temperature between the inner and outer parts becomes smaller, and it takes a considerably longer time to melt the inner part. In addition, it is preferable to use strong nylon as the inner resin film to prevent damage to the storage container, but nylon easily absorbs water due to its characteristics, so when melting and bonding the inner resin film, nylon absorbs moisture. The moisture in the nylon will evaporate and the inner resin film will foam, so the temperature at the joint must be lowered to a temperature at which the evaporated moisture will be absorbed by the nylon again while the pressure remains in place. If high-frequency induction heating is used in such a heat-sealing process, the metal foil of the sheet will be directly heated, and the inner resin film will be effectively melted and bonded, dramatically improving work efficiency. If the supply of high-frequency power to the coil is stopped, the heat of the heated sheet is transferred to the heating coil, which has a lower temperature, and the above-mentioned foaming can be suppressed.

When heat-sealing, the heating coil is pressed against the sheet, so the heating coil and the metal foil that is the object to be heated come very close to each other, and the mutual induction coefficient between the heating coil and the metal foil is large, resulting in a high power factor of the heating coil. used in the state.

In order to supply power to such a load with a high power factor, the most suitable high frequency power source is a switching type inverter using power transistors or thyristors. That is, this type of high-frequency power supply does not require a large tank circuit like the vacuum tube oscillator type described above, and is small, inexpensive, and highly efficient. As the power supply circuit for this high-frequency induction heating, a power supply circuit using a power transistor that is small and inexpensive and has high heating efficiency is preferable.

When power is supplied using such a transistor type power supply circuit, the maximum power that can be extracted increases as the power factor of the load increases. In other words, the power supplied to the load is proportional to the product of the collector voltage and current, which is regulated by the breakdown limit of the drive transistor, but if the power factor of the load is low, the energy stored in the inductance of the load increases,
This stored energy only goes back and forth between the power supply and the inductance every time the drive transistor switches, and cannot be converted into active power. Therefore, a high-frequency induction heating device using a transistor power supply circuit requires a heating coil with a high power factor.

In order to increase the power factor of the heating coil, it is preferable to make the mutual induction coefficient between the heating coil and the heated object as close to 1 as possible. As is well known, as the gap between the heating coil and the heated object increases, the power factor of the heating coil decreases rapidly. Therefore, it is desirable that induction heating be performed with the heating coil and the object to be heated in close contact with each other. In such contact-type induction heating, a large heat conduction effect occurs from the heated object to the heating coil, and the temperature of the seal part is lower than the temperature of the periphery of the seal part that does not come into contact with the heating coil. The peripheral portion was melted before the other portion was melted, making it virtually impossible to seal. However, with conventional high-frequency heating coils, the heating coil device itself removes heat from the storage container, making it impossible to perform efficient induction heating. The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a heating coil with good thermal efficiency suitable for a contact-type high-frequency heating device. The heating coil according to the present invention will be explained in detail below based on the drawings.

FIG. 1 shows the basic flat spiral coil shape of an ordinary heating coil.

This heating coil 10 is pressed against the object to be heated in an insulated state, and a portion corresponding to the shape of the coil is heated. FIG. 2 shows an intermediate stage of manufacturing a bag-like storage container, in which two triple-layered laminated sheets 11 are stacked, and the heating coil 10 moves over them in the direction of the arrow, as indicated by diagonal lines. Joint portion 12 is heat sealed. Then, by cutting the joint portion 12 as shown by the chain line, a package-shaped storage container with three sides joined can be obtained. At the time of this manufacture, the flat spiral coil 10 shown in FIG. 1 cannot be used because it is heat-sealed up to the part indicated by the broken line, as is clear from the slightly exaggerated view of FIG. 2. For this reason, in actual use, it is probably necessary to separate the heating coil 10 from the laminated sheet 11, which is the object to be heated, so that one side 10A of the heating coil 10 becomes an ineffective side. FIG. 3 shows a state in which the storage container manufactured as described in FIG. 2 is filled with cooked food and then the opening 13 is heated and sealed by the heating coil 10. Even in this case, the ineffective side 1 of the heating coil 10
It is easily understood that 0A is not close to the object to be heated.
In a heating coil having such an ineffective side, the ineffective side does not electromagnetically couple with the object to be heated, so the mutual induction coefficient decreases, and it is not a good idea to obtain a heating coil with a high power factor. In FIG. 1, it appears that by bringing the ineffective side 10A of the heating coil 10 close to the heating side 10B, one narrow band-shaped heating seal is achieved.

However, more realistically, this idea would be rejected because the mutual induction coefficient itself would decrease as a result. FIG. 4 shows a conventional improved heating coil for airtightly sealing the opening of a storage container, in which a ferrite magnetic core 14 is fixed to a flat spiral coil 10. In this conventional example, most of the magnetic flux generated from the heating coil 10 passes through the magnetic core 14 as shown by arrow P, contributing to an increase in the mutual induction coefficient.
However, even in this case, the mutual induction coefficient of the entire heating coil is suppressed due to the presence of the magnetic flux Q that does not interlink with the heated body due to the ineffective side 10A. FIG. 5 shows a schematic configuration diagram of the high-frequency heating coil according to the present invention, and the ineffective side 10
A short circuit coil 15 is provided to reduce leakage magnetic flux Q that interlinks only with A. The shorting coil 15 is arranged so that one side thereof is close to the inactive side IOA of the heating coil 10, and forms a shorting current path surrounding the magnetic circuit of the magnetic core 14. When the short-circuit coil 15 is provided as shown in the figure, the leakage magnetic flux Q interlinks with the short-circuit coil 15, so that a current flows in the short-circuit coil 15 in a direction that cancels out the leakage magnetic flux Q as shown in the figure. As a result, it is understood that the leakage magnetic flux Q is canceled out by the short circuit coil 15, and the electromagnetic mutual induction coefficient as a whole of the heating coil increases. In the embodiment of FIG. 5, the shorting coil 15 consists of a wound coil of copper wire, but it is also possible to form the shorting coil with a conductive metal plate.

An embodiment in which a metal mount for fixing a heating coil also serves as a shorting coil is shown in FIGS. 6 and 7. In this embodiment, the mount 16 is made of brass that has high electrical conductivity and mechanical strength and is easy to process, and serves as a short circuit coil. The mounting base 16 is made of a rod having a substantially U-shaped cross section, and is firmly fixed to the moving arm IT of the storage container heat sealing machine with screws 18 and 19, as shown in FIG. A magnetic core 14 made of ferrite and having a U-shaped cross section is fixed in the longitudinal direction of the mounting base 16. A heater 20 forming a heat generating device is further embedded in the magnetic core 14, and when the storage container and the heating coil device come into contact during the heating sealing process of the storage container, the heating coil device itself absorbs the heat of the storage container. prevent theft. This heater 20 is extremely suitable for a contact-type high-frequency induction heating device, and if this heater 20 is not provided, a situation will occur in which only the peripheral area of the desired seal portion is heated unnecessarily. Probably. Heating side IO of heating coil 10
B is fixed to the front surface of the heater 20 and its ineffective side IOA is fixed to the mounting base 16, so that the heating coil 10 is arranged so as to surround the magnetic core 14.

In this state, the mounting base 16 is attached to the side 1 that is close to the invalid side IOA.
6A and the opposite end 16B form a short-circuit current path surrounding the magnetic circuit of the magnetic core 14 to absorb leakage magnetic flux due to the ineffective side IOA. Copper protection plates 21 and 22 are fixed to the front surfaces of the heating side IOB and the ineffective side IOA of the heating coil 10 to prevent the heating coil 10 from being damaged. A temperature detection device 23 such as a thermistor is fixed near the heating side IOB of the heating coil 10, and the temperature of the heating side IOB is constantly detected.

It is desirable that the temperature of the heating side IOB is set near the melting temperature of the inner resin film of the laminated sheet forming the storage container.
For this purpose, the output signal of the temperature detection device 23 is supplied to the heater 20 via a well-known temperature control circuit (not shown). As is clear from the above configuration, according to the high-frequency heating coil device according to the present invention, the high-frequency heating coil is always maintained at an appropriately selected temperature. Highly efficient induction heating is performed without taking away heat.

According to the present invention, by bringing the heating coil 10, which has been heated to a predetermined temperature by the heater 20, into contact with the object to be heated, the temperature of only the desired seal portion is rapidly raised to near the melting temperature, and the temperature of the other portion of the object to be heated is rapidly increased. A large temperature gradient is formed between the two parts. This temperature gradient, together with high-frequency induction heating, is very effective in heating and sealing only the desired sealing portion in a short time. By providing the heater 20, the heating coil device itself is prevented from absorbing heat from the storage container, which may cause foaming of the resin film. It is low enough to suppress it.

FIG. 8 shows another embodiment of the present invention, in which the ineffective side IOA of the heating coil is located on the opposite side of the heating side IOB with the heater 20 in between.

An opening 16aJ is formed in a part of the mounting base 16,
The invalid side IOA is inserted into this opening 16a. According to this embodiment, the heating coil device can be miniaturized, and the mutual induction coefficient between the ineffective side IOA of the heating coil 10 and the object to be heated is extremely small, so that when performing a band sealer during bag making as shown in FIG. It is also preferable. FIG. 9 shows an example of the characteristics of the heating coil, with the heating time plotted on the horizontal axis and the temperature of the heated object on the vertical axis.

Characteristic A shows a state where the heating coil temperature is set to 25°C, which is close to room temperature, and characteristic B shows a state where it is set to 160°C, and in both cases, the high frequency input is regulated to 500 watts. As is clear from this characteristic diagram, it is understood that an extreme difference occurs in the temperature rise of the heated object. For example, it takes less than 0.2 seconds to heat up to the melting temperature of 175°C when heater heating is included, but it takes as much as 0.5 seconds without heating, and during this time an adjacent storage container that does not come into contact with the heating coil is heated. There is a drawback that other parts of the material are melted by induction heating. 10th
Another embodiment of the present invention is shown in the figure, in which a metal foil molded container 3
0 and its lid 31 are heat sealed. After the container 30 is filled with cooked food, the lid 31 is fitted onto the flange portion 33 to which the resin film is attached. Next, the container 30 is attached to the mounting base 1
The flange portion 32 of the heating coil 10 is placed on a ring-shaped heating coil 10 fixed to the heating coil 6, and is pressurized from above with a pressure ring 33. Although not shown, the mount 16 has a built-in heating device such as a heater and a temperature detection device.
When the mounting base 16 is made of a good electrical conductor, a portion 34 thereof is cut off to prevent a short circuit phenomenon. When sealing is performed by high-frequency induction heating with the heating coil according to the present invention, substantially the same heating coil 2 as described above is used.
A method of pressing the sealing part with the heating side of a heating coil using a single heating coil, and a method of pressing the heating side of one heating coil against the sealing part,
There is a method of arranging the magnetic core of the heating coil and the magnetic core that forms the magnetic circuit on opposing sides, but there is not much difference in heating characteristics between the two.

As explained above, according to the high frequency induction heating coil device according to the present invention, an extremely high power factor can be obtained.

The power factor of the coil according to the present invention can be set to a value of 0.9 or more, and the power factor value of the conventional general induction coil is 0.
．． It is clear that the improvement has an extremely large effect compared to the case where the value is 1 or less. A high power factor heating coil can dramatically improve its heating efficiency.

That is, since the electric power supplied to the object to be heated is proportional to the power factor of the heating coil, when the same electric power is supplied to the object to be heated, the current value can be reduced in a heating coil with a high power factor.
Reducing the current value of the heating coil offers various advantages in the fabrication of high frequency induction heating devices.

This can be understood from the fact that the heating coil according to the present invention has a power factor that is 10 times or more and a current value that is 1/10 or less compared to the conventional heating coil. These values mean that the diameter of the heating coil wire for supplying the same electric power can be reduced to 1/10 or less, and this point is extremely important. Reducing the diameter of the heating coil wire makes it easier to form the heating coil into any desired shape. Further, the reduction in the current value has the advantage that the structure of the conducting wire portion can be simplified, and furthermore, the conducting wire can be made thinner and no cooling device is required.
This has the advantage that a flexible conducting wire with a small diameter can be used especially in a device in which the heating coil must be movable. As a power supply circuit suitable for the high-frequency heating coil device according to the present invention, a small and inexpensive power supply circuit for the high-frequency heating device that can obtain high-efficiency, large-output high-frequency power using a power transistor or thyristor is suitable.

FIG. 11 shows the basic configuration of a power supply circuit used in the present invention.

The output transformer 210 has a primary winding 211 and a secondary winding 212.
The primary winding 211 has an intermediate tap 213 connected to a power supply circuit 220. The secondary winding 212 of the output transformer 210 is connected to a high frequency heating coil according to the invention. The power supply circuit 220 includes a commercial power supply 221, a full-wave rectifier circuit 222, and a high-frequency bypass capacitor 223,
Intermediate tap 213 of transformer 210 outputting full-wave rectified power
to be applied. Output transistor circuits 230 and 240 are connected to both ends of the primary winding 211 of the output transformer 210, and both output transistor circuits 230 and 240 include output transistors 231 and 241, and a current limiting resistor 232, respectively.
, 242, and reactive power return diodes 233, 243. The collectors of the output transistors 231 and 241 are connected to both ends of the primary winding 211, respectively, and the signals from the oscillation circuit 250 are connected to the bases of the drive circuits 234 and 2.
The signal is amplified and applied at step 44. Note that the transistors 235, 236, 245, and 246 of the drive circuit are used in a saturated state. The collector of the output transistor 231 is connected to the feedback circuit 2.
71, output transistor 241 via drive circuit 244
Similarly, the collector of the output transistor 241 is connected to the base of the output transistor 231 via a feedback circuit 272 and a drive circuit 234. In this embodiment, the drive circuits 234, 244 receive feedback signals 371
, 372 are provided to reduce the power loss that occurs because they are applied from points A and b, which have fairly high voltages, and the transistors in this circuit are used in a saturated state. That is, since the base voltages of the output transistors 231 and 241 need only be low, drive circuits 234 and 244 with low power supply voltages +E and -E are provided, and the feedback signals 371 and 3T are
By amplifying the current of No. 2 in the drive circuits 234 and 244, the current value of the feedback signal 372 can be reduced, and the power loss in the feedback resistors 111 and 112 can be reduced. The drive circuits 234 and 244 include NPN transistors 235 and 245 to which a positive voltage +E is applied to the collector, and a PNP transistor 236 to which a negative voltage -E is applied to the collector.
, 246. Control transistors 1, 277 and 2T8 are connected to the drive circuits 234 and 244, and although these control transistors 2T7 and 278 are normally kept in an off state, they are turned on during power control or overcurrent protection.

A power control signal C, an overcurrent protection signal d, and a zero volt start signal e are applied to the bases of the control transistors 277 and 278, respectively. The zero volt start signal e is turned off, and the pulsating voltage of the intermediate tap 213 is sufficient to turn on the output transistors 231 and 241, and one of the output transistors 231 and 241 is undefined, but for example, a rectangular shape forming the oscillation circuit 250 is activated. Assume that the output J of the wave generator is positive and the output transistor 231 is turned on.

Then, the voltage at the collector a of the output transistor 231 becomes zero, and the voltage at the collector b of the output transistor 2240 becomes twice the voltage at the intermediate tap 213 due to the transformer action of the output transformer. Therefore, output transistor 231 is kept on and output transistor 241 is kept off.
Eventually, the output J of the square wave generator becomes negative, and the output K becomes positive S.
Then, the drive signal for the output transistor 231 turns off, but there is a slight delay in turning off the output transistor 231 due to the accumulated charge, and eventually the output transistor 231 turns off.
31 turns off, the collector a of the output transistor 231 becomes positive, the feedback signal 372 is amplified by the drive circuit 244, and the output transistor 241 is turned on. As described above, after confirming the off operation of one output transistor, the other output transistor is turned on, so
Both output transistor circuits cannot operate at the same time.
Generation of current spikes etc. that adversely affect the circuit is prevented, and destruction of the drive transistor etc. is prevented.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing the basic flat spiral coil shape of a normal heating coil, Fig. 2 is a plan view showing the process of manufacturing a bag-shaped storage container using the heating coil shown in Fig. FIG. 1 is a plan view showing the process of airtightly sealing the opening of a bag-like storage container using a heating coil, FIG. 4 is a schematic diagram showing a conventional heating coil, and FIG. 5 is a schematic configuration of a high-frequency heating coil according to the present invention. 6 is a perspective view showing a preferred embodiment of the high-frequency heating coil according to the present invention, FIG. T is a sectional view of FIG. 6, and FIG. 8 is a sectional view showing another embodiment of the present invention. FIG. 9 is a characteristic diagram of a heating coil according to the present invention, FIG. 10 is a sectional view showing still another embodiment of the present invention, and FIG. 11 is a power supply circuit diagram suitable for the present invention. 10... Heating coil, 10A... Ineffective side, 10B... Heating side, 14... Magnetic core, 15... Short circuit coil, 20... Heat generating device, 23... Temperature detection device.

Claims (1)

[Claims] 1. A high-frequency heating device comprising a high-frequency heating coil that presses a sheet locally having a phase bonding area in the bonding area, and each sheet has a conductive foil that generates heat due to eddy current generation in at least one of the sheets. The sheet is made of a resin material that is laminated to extend over a wider area than the bonding area, and is melted enough to bond by the heat generated by the conductor foil, and the high-frequency heating coil presses the sheet. 1. A high-frequency heating device comprising: a heat generating device that generates enough heat to suppress conduction of heat generated by the sheet to the high-frequency heating coil in a state in which the sheet is heated.