JPS645431B2 - - Google Patents

Description

[Detailed description of the invention] Industrial application field The present invention performs a heating operation when a pot is placed;
This invention relates to an induction heating cooker featuring a magnetic pot detection means that prevents wasteful power consumption when a pot is not placed.

Conventional configurations and their problems In principle, induction heating cookers generate heat through eddy currents generated by alternating magnetic fields in the pot itself, so they have an extremely rapid thermal response compared to electric heaters or gas. Therefore, even if the excitation of the heating coil is temporarily interrupted when the pot to be heated is not placed, and the excitation is resumed after the pot is placed again, the same effect as a conventional heat source is exhibited. Therefore, if the equipment heats up and stops in response to the raising and lowering of the pot during cooking, the usage efficiency will be high and it will be economical. For this reason, magnetic pot detection means for detecting the presence or absence of a pot have been employed for some time, and the most typical example thereof is shown in FIG. A permanent magnet 2 is housed in a pair of resin cases 3a and 3b at the center of the disc-shaped heating coil 1, and when there is no pot 5, the permanent magnet 2 is lowered by its own weight, and the resin The tip of the case 3b presses down the lever of the microswitch 4 and closes the contact of the microswitch 4b. Here, when the pot 5 is placed on the ceramic pot mounting plate 6, the magnet 2 is attracted to the pot 5 and moves upward, and at that time, the cases 3a and 3b
will also be raised together. As a result, the lever of the microswitch 4 is brought into a state where there is no external force, and the contact is reversed and closed. If the excitation of the heating coil 1 is controlled by reversing the contacts of the micro switch 4,
It becomes possible to drive only when the magnetic pot 5 is placed. However, the problem with this embodiment is that the microswitch is a mechanical opening/closing mechanism, and the current flowing through the contacts is a minute signal current that controls the excitation operation of the frequency converter. It may become non-conductive due to the oxide film,
It is mechanically or electrically unreliable.

FIG. 2 shows another conventional example. This compensates for the drawbacks of the example shown in FIG. 1, and a cylindrical resin case 3 is placed in the center of the heating coil 1. A pair of permanent magnets 2a and 2b are housed in the magnet with the same magnetic poles facing each other and spaced apart from each other.
The lower magnet 2b is fixed, and the upper magnet 2a is movable up and down. A reed switch 7 is fixed to the middle part of the two magnets 2a and 2b, and when the pot 5 is not present, the magnet 2a hangs downward.
In this state, the reed switch 7 is positioned so that the two magnets 2a and 2b cancel each other's magnetic fields and the magnetic field strength becomes zero. In this configuration, when the pot 5 is placed on the mounting plate 6, only the magnet 2a attracts and moves upward, so the position of the reed switch 7 is set relative to the magnet 2a.
b, the balance of the magnetic field is lost, and the reed switch 7 senses the magnetic field due to the influence of the magnetic field of the lower magnet 2b, the contact point is reversed, and a control signal is sent to the frequency converter. The problem with this conventional example is that although the drawbacks due to the reliability of the contacts have been solved by using the reed switch 7, the alternating magnetic field of the heating coil 1 gathers around the reed switch 7 as shown by the broken line, and The direction of the magnetic field is the reed switch 7
Since it coincides with the high-sensitivity axis of , there is a problem that the reed switch 7 malfunctions during induction heating. For this purpose, it is necessary to separately provide a shield pipe 8 made of non-magnetic metal around the outer periphery of the reed switch 7 as shown in the figure. Further, since there are variations in magnetization strength between the upper and lower magnets, the mounting position of the reed switch 7 is extremely delicate, and there is a problem that position adjustment is required.

OBJECTS OF THE INVENTION The present invention solves the above-mentioned conventional problems and provides an induction heating cooker equipped with a magnetic pot detecting means with high operational reliability.

Structure of the Invention The induction cooking device of the present invention includes a frequency conversion device that converts a commercial power frequency to an ultra-audible frequency, a disc-shaped heating coil excited by the frequency conversion device, and a magnetic pot placed above the heating coil. a first magnet that attracts and moves along the central axis of the heating coil when placed; a second magnet that operates in conjunction with the first magnet and generates a DC bias magnetic field orthogonal to the central axis of the heating coil; a magnetic field detection element that detects a magnetic field in the direction of the DC bias magnetic field generated by a second magnet, the magnetic field detection element being disposed opposite to the position of the second magnet when the first magnet is attracted. ,
The structure is such that the DC bias magnetic field generated by the second magnet is detected to drive and control the frequency converter.

DESCRIPTION OF THE EMBODIMENTS An embodiment of the present invention is shown in FIG. Commercial power supply 1
A frequency conversion device 12 connected to the heating coil 1 is connected to cause a high frequency current of an ultraaudible frequency whose frequency has been converted to flow through the heating coil 1 . On the central axis of the disc-shaped heating coil 1, there is a magnetic pot 5 that attracts and attracts the magnetic pot 5.
A movable first magnet 2 is internally integrated into a pair of heat-resistant resin cases 3a and 3b, and is provided so as to be movable up and down along a central axis. The lower part of the case 3b branches to form a branch part 3c, and a pair of second magnets 1 are provided at the bottom of the branch part 3c for biasing a DC magnetic field perpendicular to the central axis.
0a and 10b are fixed. Further, in order to detect a magnetic field orthogonal to the central axis, a magnetic field detection element 9 such as a Hall element or a ferromagnetic thin film resistance element is installed in the case 3.
It is fixed in the space of the branch part 3c of b, and its position changes when the first magnet 2 and the second magnets 10a, 10b are attracted and moved toward the pot mounting plate 6 by the pot 5. The DC bias magnetic field generated by the second magnets 10a and 10b is fixed so as to match the position of the magnetic field detection element 9.

As is clear from FIG. 4, when the pot 5 is not placed, the first magnet and the second magnet 10a, 10b
is located below, the magnetic field strength at the fixed position of the magnetic field detection element 9 is zero, and the magnetic field detection element 9
The frequency conversion device 12 is not excited by the output of . When the pot 5 is placed on the mounting plate 6, the first and second magnets 2, 10a, 10b move upward, and as a result, the DC bias magnetic field also moves upward as shown by the broken line in FIG. A magnetic field sufficient for reversal is applied to the sensing element 9, and excitation of the frequency converter 12 is started. Here, the alternating magnetic field by the heating coil 1 is
As shown in the figure, since there is only a component parallel to the axis on the central axis, there is no effect of malfunction on the magnetic field detection element 9 that operates with orthogonal magnetic fields as in the embodiment of the present invention.

FIG. 5 shows a second embodiment of the invention. The pair of cases 3a and 3b have the same structure in which the first magnet 2 is housed, but case 3b is molded by mixing ferrite powder and resin, and its shape is the same as that shown in Fig. 3. . However, the branch part 3c of the case 3b has a structure contained in the case 3b so that a DC bias magnetic field in the opposite direction is applied to the part facing the magnetic field sensing element 9 when the pot 5 is in the "present" or "absent" state. Ferrite particles are magnetized, and two sets of second
The magnets 10c, 10d and 10a, 10b are formed. That is, when the magnet 2 is descending as shown in FIG. 6, the magnetic field sensing element 9 is biased with a magnetic field of -B by one set of magnets 10c and 10d among the second magnets, and vice versa. When the magnet 2 is attracting and moving upward, a +B magnetic field is biased by the other pair of magnets 10a and 10b. Therefore, the magnetic field detection element 9 only needs to detect the polarity of the DC magnetic field sufficiently deeply biased by the four magnets 10a to 10d, resulting in extremely stable operation. Furthermore, since the molded product of ferrite and resin is magnetized at any location, the positional accuracy of the magnetized magnet is high, and it is highly effective for mass production.

Effects of the Invention As explained above, the induction heating cooker of the present invention (1) uses a magnetic field detection element and is non-contact, so there is no risk of malfunction due to oxidation/corrosion of the contacts or dust, etc. Does not occur.

(2) It is easy to use a strong magnet to create a large DC bias magnetic field, and the magnetic field detection element operates digitally by turning on or off, so there is no malfunction due to noise.

(3) Since there is a one-to-one correspondence between the moving distance of the magnet and the moving distance of the magnetic field, the change in the DC bias magnetic field is sharp, and there is no need to adjust the position of the magnetic field sensing element.

(4) There is no need to take measures against malfunctions caused by high-frequency magnetic fields from the heating coil.

It has great effects such as

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a schematic configuration showing a conventional induction heating cooker, FIG. 2 is a cross-sectional view of a schematic configuration of another conventional example, and FIG. 3 is an induction heating cooking example showing an embodiment of the present invention. 4 is an explanatory diagram of the operation of FIG. 3, FIG. 5 is a sectional diagram of another embodiment of the present invention, and FIG. 6 is an explanatory diagram of the operation of FIG. 5. . 1... Heating coil, 2... First magnet, 9...
Magnetic field detection element, 10... second magnet, 12... frequency conversion device.

Claims (1)

[Claims] 1. A frequency conversion device that converts a commercial power frequency to an ultra-audible frequency, a disc-shaped heating coil excited by the frequency conversion device, and a magnetic pot that heats when placed above the heating coil. A first magnet that attracts and moves along the central axis of the heating coil, a second magnet that operates in conjunction with the first magnet and generates a DC bias magnetic field perpendicular to the central axis of the heating coil; a magnetic field detection element that detects a magnetic field in the direction of the DC bias magnetic field, the magnetic field detection element is disposed opposite to the position of the second magnet when the first magnet is attracted, and the second magnet An induction heating cooker configured to detect a direct current bias magnetic field generated by a magnetic field and drive and control a frequency converter. 2. The induction heating cooker according to claim 1, wherein the second magnet is constituted by two sets of magnets so that DC bias magnetic fields in opposite directions are applied in the presence or absence of a pot.