CA1161124A - Induction heating apparatus with a breakage-proof thermister - Google Patents
Induction heating apparatus with a breakage-proof thermisterInfo
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- CA1161124A CA1161124A CA000369411A CA369411A CA1161124A CA 1161124 A CA1161124 A CA 1161124A CA 000369411 A CA000369411 A CA 000369411A CA 369411 A CA369411 A CA 369411A CA 1161124 A CA1161124 A CA 1161124A
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- induction heating
- magnet
- magnet member
- top plate
- heating apparatus
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Abstract
INDUCTION HEATING APPARATUS
Abstract of the Disclosure The present invention relates to an improved induction heating apparatus as applied, for example, to a cooking oven. The apparatus includes a magnet having a bore formed in it, with a thermistor being installed on the top plate of the apparatus in a position corresponding to the bore so as to eliminate possible breakage of the thermistor. The curie temperature of the magnet member can be set at a predetermined level for a further improvement in safety.
Abstract of the Disclosure The present invention relates to an improved induction heating apparatus as applied, for example, to a cooking oven. The apparatus includes a magnet having a bore formed in it, with a thermistor being installed on the top plate of the apparatus in a position corresponding to the bore so as to eliminate possible breakage of the thermistor. The curie temperature of the magnet member can be set at a predetermined level for a further improvement in safety.
Description
The present invention generally relates to an induction heating apparatus and ~lore particularly, to an induction heating apparatus as applied, for example, to a cooking oven which is arranged to detect, by the use of a magnet, whether a container for heating is of magnetizable material or not. In addition, a thermister is used to control the temperature oE the container and consequently that of an object to be heated to an optimum level.
Commonly, in an induction heating apparatus, for example, in an induction heating cooking oven, if a container made of non-magnetizable material is used for heating, various problems such as the abnormal oscillation of the inverter used in the supply, the impression of an extremely large current to the heating coil, commutation failure of control elements, etc. tend to take place due to rapid variations of coil impedance. As a result, a magnet member is provided so that the cooking oven can only be started when a container of magnetizable material is placed on a top plate of the oven. A thermistor is also provided for detecting abnormally high temperatures which give rise to a deterioration of the coil insulation. The thermistor also controls energization of the coil so as to maintain the object to be heated at an optimum temperature.
An object of the present invention is to provide an improved induction heating apparatus as applied, for example, to a cooking oven in which there is employed a magnet member having a bore formed therein, with a thermistor being provided on the top plate of the apparatus in a position corresponding to said bore, Additionally, the curie temperature of the magnet member ` ' can be set at a predetermined level for a further improvement in safety.
Another important object of the present invention is to provide an improved induction heating apparatus in which there is provided a magnet receptacle for setting or restricting the vertical travel of the magnet member through attraction thereo~ toward the container. The thermistor is disposed in a recess of the magnet receptacle so as to be pressed against the top plate thereby protecting the thermistor from possible breakage and also for simplifying assembly during manufacture.
~ still further object of the present invention is to provide an improved induction heating apparatus of which is simple in construction and stable in operation, and which can be manufactured on a large scale at low cost.
In accordance with an aspect of the invention there is provided an induction heating apparatus having an induction heating coil provided below a top plate for supporting a container of magnetizable material, said induction heating apparatus comprising a thermistor element provided on the undersurface of the top plate for controlling energization of said induction heating coil, a magnet member movably provided below said top plate so as to be raised through attraction thereof to said container, and a switching member provided below said magnet member for selective energization and de-energization of said induction heating coil in association with the movement of the magnet member, said magnet mernber being formed therein with a bore in a predetermined position corresponding to said thermistor element so as to accommodate said thermistor element into said bore upon rising of said
Commonly, in an induction heating apparatus, for example, in an induction heating cooking oven, if a container made of non-magnetizable material is used for heating, various problems such as the abnormal oscillation of the inverter used in the supply, the impression of an extremely large current to the heating coil, commutation failure of control elements, etc. tend to take place due to rapid variations of coil impedance. As a result, a magnet member is provided so that the cooking oven can only be started when a container of magnetizable material is placed on a top plate of the oven. A thermistor is also provided for detecting abnormally high temperatures which give rise to a deterioration of the coil insulation. The thermistor also controls energization of the coil so as to maintain the object to be heated at an optimum temperature.
An object of the present invention is to provide an improved induction heating apparatus as applied, for example, to a cooking oven in which there is employed a magnet member having a bore formed therein, with a thermistor being provided on the top plate of the apparatus in a position corresponding to said bore, Additionally, the curie temperature of the magnet member ` ' can be set at a predetermined level for a further improvement in safety.
Another important object of the present invention is to provide an improved induction heating apparatus in which there is provided a magnet receptacle for setting or restricting the vertical travel of the magnet member through attraction thereo~ toward the container. The thermistor is disposed in a recess of the magnet receptacle so as to be pressed against the top plate thereby protecting the thermistor from possible breakage and also for simplifying assembly during manufacture.
~ still further object of the present invention is to provide an improved induction heating apparatus of which is simple in construction and stable in operation, and which can be manufactured on a large scale at low cost.
In accordance with an aspect of the invention there is provided an induction heating apparatus having an induction heating coil provided below a top plate for supporting a container of magnetizable material, said induction heating apparatus comprising a thermistor element provided on the undersurface of the top plate for controlling energization of said induction heating coil, a magnet member movably provided below said top plate so as to be raised through attraction thereof to said container, and a switching member provided below said magnet member for selective energization and de-energization of said induction heating coil in association with the movement of the magnet member, said magnet mernber being formed therein with a bore in a predetermined position corresponding to said thermistor element so as to accommodate said thermistor element into said bore upon rising of said
- 2 -;
magnet member for preventing collislon therebetween.
In accomplishing these and other objects, according to one preferred embodiment of the present invention, there is provided an induction heating apparatus having an induction heating coil disposed below a top plate for supporting a container of magnetizable materialr and comprising a thermistor element provided on the undersurface of the top plate for controlling energization of the induction heating coil. A magnet member is movably provided below the top plate so as to be raised through attraction thereof to the container. A switching member is provided below the magnet member for selective energization and de-energization of the induction heating coil in association with the movement of the magnet member. The magnet member has a bore located in a predetermined position corresponding to the thermistor element so as to accommodate the thermistor element into the bore upon the rising of the magnet member.
In drawings which illustrate embodiments of the invention:
Fig. 1 is a fragmentary side sectional view of a main portion of a conventional induction heating apparatus;
Fig. 2 is a fragmentary side sectional view of a main.
portion of an improved induction heating apparatus according to one preferred embodiment of the present invention;
Fig. 3 is a fragmentary side sectional view of a modification of the embodiment of Fig. 2;
Fig. 4 is an electrical block diagram showing the circuit of the heating apparatuses o~ Figs. 2 and 3;
Fig. 5 is a fragmentary side sectional view of another ,, L -~
modification; and Fig. 6 is a fragmentary side sectional view of a further modification of the embodiment of Fig. 5.
Before the description of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout the figures.
Fig. 1 shows the construction of a conventional induction heating cooking oven. A thermistor Tm is affixed at the central portion on the undersurface of a top plate P of the cooking oven for more accurately detecting the temperature of a container V. A magnet member M is movably accommodated for movement only in the vertical direction, within a magnet support tube Ms, which is surrounded by an induction heating coil C supported by a coil support Cs. A microswitch SW secured to a base plate B of the oven through a fixing plate L in a position below the magnet member M so as to be switched by the vertical movement of the magnet member M. The magnet member M is further accommodated in a cover member Mc to be spaced from the thermistor Tm by a predetermined amount, upon contact of the upper edge of the case member Mc with the undersurface of the top plate P which prevents the magnet member M from directly contacting the thermistor Tm when the magnet member M is raised through attraction thereof to the container V.
In the above conventional arrangement, however, there is the disadvantages that the assembly of the oven is extremely inefficient. The thermistor Tm must be affixed to the undersurface of the top plate P and wiring for the thermistor Tm has to be carried out by applying current collecting paste, or the like, onto the top plate P. In .1 ~
addition, there is a possibility that the cover member Mc can strike against the undersurface of the top plate P and breaks. This would result in the breakage of the - thermistor Tm.
Fig. 2 shows a main portion of an improved induction heating apparatus HA according to one preferred embodiment of the present invention~ The heating apparatus HA
generally includes a top plate 1 for holding a container or vessel V, a heat sensing element or thermistor 2 attached to the central portion on the undersurface of the top plate 1, a magnet support tube 4 provided between the central portion of the undersurface of the top plate 1 and a bottom plate 6 of the apparatus housing and a magnet member 3, for example, of a cylindrical shape. The ma~net member 3 has a bore 3a formed therein and is movably supported in the support tube 4 for movement in the vertical direction. A microswitch 5 is provided in the support tube 4 in a position below the magnet member 3 at a predetermined height from the bottom plate 6 and is secured to the bottom plate through a support plate 5Q so as to be selectively turned ON or OFF by the vertical movement of the magnet member 3. An induction coil or heating coil 8 is supported by a coil support 7 and surrounds the support tube 4 in a position adjacent to the top plate 1. The thermistor 2 is supported and pressed against the undersurface of the top plate 1 by one end of a support rod R which extends through the bore 3a is secured at its other end to the base plate 6. Thermistor 2 is arranged to be accommodated into the bore 3a of the cylindrical magnet member 3 when the magnet member 3 is raised towards the top plate 1. The curie temperature of ~ T `
the magnet member 3 is set to be lower than the temperature at the undersurface of-the top plate 1 when the temperature of the induction heating coil 8 has reached its allowable limit.
In Fig. 3, there is shown a modification of the induction heating apparatus HA of Fig. 2. In the modified induction heating apparatus HB of Fig. 3, the support rod R is replaced by a support rod RB which supports the thermistor 2 at its one end, and is movably received at its other end in a cylindrical bore 9a of a support tube 9 suitably secured to the base plate 6. A spring member Sp is disposed around the support rod RB in a position between the upper end of the rod RB and the upper edge of the support tube 9 for normally urging the rod RB upwardly in Fig. 3 so as to achieve a close contact of the thermistor 2 to the undersurface of the top plate 1.
Since other constructions and functions of the modified heating apparatus HB of Fig. 3 are generally similar to those of the arrangement of Fig. 2, a detailed description thereof is omitted here for brevity.
Fig. 4 shows an electrical block diagram for the induction heating apparatus according to the present invention. A first rectification and smoothing circuit 12 and the primary winding of a transformer 13 are connected across the terminals of an AC power source E. The induction heating coil ~ and the emitter and collector of an output transistor 16 are connected in series between the positive and negative terminals of the first rectification and smoothing circuit 12. A protecting diode 17 is connected in the reverse direction between the collector and emitter of the output transistor 16. A
eapacitor 18 is eonneeted in parallel to the protecting diode 17. A second rectification and smoothing circuit 14 is coupled to the secondary winding of the transformer 13. The positive terminal of the seeond reetifieation and smoothing eireuit 14 is eonneeted to the positive terminal of a monostable multi~vibrator 19 through the microswitch S, and the negative terminal of the circuit 14 is coupled to the ground terminals of the monostable multi-vibrator 19 and an astable multi-vibrator 20 which is coupled to the monostable multi-vibrator 19. The output terminal of the monostable multi-vibrator 19 is connected to the base o~ the output transistor 16. The thermistor 2 is eoupled to a temperature detecting eircuit 21 so as to control, for example, the base input signal ~or the output transistor 16 or output signal of the transistor 16 by the output signal of the temperature deteeting eureuit 21.
By the above arrangement, the heating operation is started by turning ON a starting switch (not shown), with the eontainer V placed on the top plate 1.
If the eontainer V is of magnetizable material, the magnet member 3 is raised through the attraetion thereof towards the eontainer V, and thus, the mieroswitch 5, whieh is normally open through depression by the magnet member 3, is elosed to apply positive voltage to the positive terminal of the monostable multi-vibrator 19.
The monostab].e multi-vibrator 19 produces pulses of a width of predetermined time, rising at the timing of the pulse periodieally developed from the astable multi-vibrator 20, and by rendering the output transistor 16 eonductive with the output pulse of the monostab].e multi-vibrator 19, the induction heating eoil 8 is energized for the induction heating operation.
As the induction heating is continued, the teMperature of the container V is raised, with a consequent increase of the resistance value of the thermistor 2, and when the temperature of the container V has reached the predetermined level, and the resistance of the thermistor 2 has been decreased down to a predetermined value, the temperature detecting circuit 21 functions to cut off the input signal or output signal, etc. of the output transistor 16.
Therefore, not only is the object to be cooked, which is accommodated in the container V, maintained at an optimum heating temperature, but also the abnormal heating of the container V is positively prevented. Moreover, in the case where there are some problems with the thermistor 2 or in the temperature detection circuit 21 the further rising of the temperature of the container V causes the temperature of the magnet member 3 to reach the curie temperature. The magnet member 3 then loses its magnetism and fall5 downward to open the microswitch 5. The monostable multi~vibrator 19 stops producing pulses and energization of the induction heating coil 8 is cut off.
Therefore, a further improvement is acheived for the safe operation of the heating apparatus. On the other hand, if the container V is of non-magnetizable material, the magnet member 3 does not ascend and the microswitch 5 remains open and no heat is generated.
Since a bore 3a for accommodating the thermistor 2 is provided in the magnet member 3, the magnet member never strikes against the thermistor 2, thereby eliminating the possibility of the magnet breaking the thermistor.
Furthermore, since the curie ternperature of the magnet member is set to be lower than the al~owable temperature limit at the undersurface of the top plate 1, an abnormal temperature rise due to heating, especially heating without objects, may be positively prevented even if the thermistor is inoperative.
Referring to Fig. 5, there is shown a further modification of the arrangement of Fig. 2. In this modified induction heating apparatus ~C of Fig. 5, the magnet support tube 4 and thermistor support rod R are dispensed with and the magnet member 3 is movably accommodated in a magnet receptacle or casing D which is supported by a plate 5~-1 laterally extending from the upper edge of the support plate 5~ which also supports a microswitch 5. This arrangement restricts the lateral movement of the magnet member 3. The magnet receptacle D
has a configuration which conforms with the external shape of the magnet member 3 and has a recess Do at its center corresponding to the bore 3a of the magnet member 3. In the recess Do, there is disposed a resilient thermistor support material 2f, for example, of expanded silicon rubber or the like on which the thermistor 2 is mounted.
A heat collecting plate 2h is disposed on the thermistor 2 for effectively conducting the heat of the top plate 1 to the thermistor 2. Moreover, since the height from the upper surface of the magnet receptable D to the upper surface of the heat collecting plate 2h is arranged to be higher than the height from the upper surface of the receptable D to the undersurface of the top plate 1, the resilient thermistor support material 2f is normally compressed between the undersurface of the top plate 1 and 1 9 ~
the bottom wall of the recess Do, and thus, the heat collecting plate 2h and the thermistor 2 are pressed against the undersurface of the top plate 1. The microswitch ~ is disposed below the magne-t member 3 by the support plate 5Q and is activated by the movement of the magnet member 3 in a similar manner as in the arranyement of Fig. 2.
In the arrangement of Fig. 5, when the container V of magnetizable material is placed at a predetermined position on the top plate 1, the magnet member 3 is attracted by the container V and attached to the inner face of the upper portion of the magnet receptacle D. The microswitch contacts are closed to start the heating.
If, however, a container V of non-magnetizable material is placed on the top plate 1, the magnet member 3 is not attracted, and the microswitch 5 is kept open, and the heating coil 8 is not energized.
Since the magnet receptacle D remains stationary, with only the magnet member 3 moving vertically within the receptacle D, neither the magnet member 3 nor the magnet receptacle D is brought into contact with the top plate 1 and the heat sensing element or thermistor 2, and thus, not only are the impact noises reduced to a large extent, but the top plate, magnet receptacle, thermistor, etc. are completely free from the danger of breakage.
Furthermore, troublesome assembly procedures for installing the heat sensing element, such as bonding, application of electrically conductive paste, etc. are eliminated by virtue of elastically supporting the thermistor.
Referring to Fig.~6, there is shown another modification of the arrangement of Fig. 5. In the modified heating apparatus HD of Fig. 6, the magnet receptacle D of Fig. 5 is arranged -to be integrally formed with the coil suppor~ 7D. The thermistor 2 is disposed in the central recess Do in a sirnilar manner as in the arrangement of Fig. 5. This configuration simplifies construction and facilitates manufacture.
It should be noted here that, in the foregoing embodiments, althouyh the present invention has been mainly described with reference to an induction heating apparatus as applied to cooking ovens, the concept of the present invention is not limited in its application to the cooking ovens alone, but may readily be applied to induction heating apparatuses for industrial purposes in general.
As is clear from the foregoing description, in the induction heating apparatuses HC and HD according to the present invention, since the magnet member and magnet casing or the like are arranged not to be brought into contact with the top plate, possible breakage of the top plate, magnet receptable, heat sensing element, etc. i5 positively prevented. Moreover, owing to the arrangement in which the heat sensing element is adapted to be pressed against the top plate through the elastic supporting of the heat sensing element by the magnet receptable, it becomes unnecessary to bond the heat sensing element to the top plate or to apply electrically conductive paste.
magnet member for preventing collislon therebetween.
In accomplishing these and other objects, according to one preferred embodiment of the present invention, there is provided an induction heating apparatus having an induction heating coil disposed below a top plate for supporting a container of magnetizable materialr and comprising a thermistor element provided on the undersurface of the top plate for controlling energization of the induction heating coil. A magnet member is movably provided below the top plate so as to be raised through attraction thereof to the container. A switching member is provided below the magnet member for selective energization and de-energization of the induction heating coil in association with the movement of the magnet member. The magnet member has a bore located in a predetermined position corresponding to the thermistor element so as to accommodate the thermistor element into the bore upon the rising of the magnet member.
In drawings which illustrate embodiments of the invention:
Fig. 1 is a fragmentary side sectional view of a main portion of a conventional induction heating apparatus;
Fig. 2 is a fragmentary side sectional view of a main.
portion of an improved induction heating apparatus according to one preferred embodiment of the present invention;
Fig. 3 is a fragmentary side sectional view of a modification of the embodiment of Fig. 2;
Fig. 4 is an electrical block diagram showing the circuit of the heating apparatuses o~ Figs. 2 and 3;
Fig. 5 is a fragmentary side sectional view of another ,, L -~
modification; and Fig. 6 is a fragmentary side sectional view of a further modification of the embodiment of Fig. 5.
Before the description of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout the figures.
Fig. 1 shows the construction of a conventional induction heating cooking oven. A thermistor Tm is affixed at the central portion on the undersurface of a top plate P of the cooking oven for more accurately detecting the temperature of a container V. A magnet member M is movably accommodated for movement only in the vertical direction, within a magnet support tube Ms, which is surrounded by an induction heating coil C supported by a coil support Cs. A microswitch SW secured to a base plate B of the oven through a fixing plate L in a position below the magnet member M so as to be switched by the vertical movement of the magnet member M. The magnet member M is further accommodated in a cover member Mc to be spaced from the thermistor Tm by a predetermined amount, upon contact of the upper edge of the case member Mc with the undersurface of the top plate P which prevents the magnet member M from directly contacting the thermistor Tm when the magnet member M is raised through attraction thereof to the container V.
In the above conventional arrangement, however, there is the disadvantages that the assembly of the oven is extremely inefficient. The thermistor Tm must be affixed to the undersurface of the top plate P and wiring for the thermistor Tm has to be carried out by applying current collecting paste, or the like, onto the top plate P. In .1 ~
addition, there is a possibility that the cover member Mc can strike against the undersurface of the top plate P and breaks. This would result in the breakage of the - thermistor Tm.
Fig. 2 shows a main portion of an improved induction heating apparatus HA according to one preferred embodiment of the present invention~ The heating apparatus HA
generally includes a top plate 1 for holding a container or vessel V, a heat sensing element or thermistor 2 attached to the central portion on the undersurface of the top plate 1, a magnet support tube 4 provided between the central portion of the undersurface of the top plate 1 and a bottom plate 6 of the apparatus housing and a magnet member 3, for example, of a cylindrical shape. The ma~net member 3 has a bore 3a formed therein and is movably supported in the support tube 4 for movement in the vertical direction. A microswitch 5 is provided in the support tube 4 in a position below the magnet member 3 at a predetermined height from the bottom plate 6 and is secured to the bottom plate through a support plate 5Q so as to be selectively turned ON or OFF by the vertical movement of the magnet member 3. An induction coil or heating coil 8 is supported by a coil support 7 and surrounds the support tube 4 in a position adjacent to the top plate 1. The thermistor 2 is supported and pressed against the undersurface of the top plate 1 by one end of a support rod R which extends through the bore 3a is secured at its other end to the base plate 6. Thermistor 2 is arranged to be accommodated into the bore 3a of the cylindrical magnet member 3 when the magnet member 3 is raised towards the top plate 1. The curie temperature of ~ T `
the magnet member 3 is set to be lower than the temperature at the undersurface of-the top plate 1 when the temperature of the induction heating coil 8 has reached its allowable limit.
In Fig. 3, there is shown a modification of the induction heating apparatus HA of Fig. 2. In the modified induction heating apparatus HB of Fig. 3, the support rod R is replaced by a support rod RB which supports the thermistor 2 at its one end, and is movably received at its other end in a cylindrical bore 9a of a support tube 9 suitably secured to the base plate 6. A spring member Sp is disposed around the support rod RB in a position between the upper end of the rod RB and the upper edge of the support tube 9 for normally urging the rod RB upwardly in Fig. 3 so as to achieve a close contact of the thermistor 2 to the undersurface of the top plate 1.
Since other constructions and functions of the modified heating apparatus HB of Fig. 3 are generally similar to those of the arrangement of Fig. 2, a detailed description thereof is omitted here for brevity.
Fig. 4 shows an electrical block diagram for the induction heating apparatus according to the present invention. A first rectification and smoothing circuit 12 and the primary winding of a transformer 13 are connected across the terminals of an AC power source E. The induction heating coil ~ and the emitter and collector of an output transistor 16 are connected in series between the positive and negative terminals of the first rectification and smoothing circuit 12. A protecting diode 17 is connected in the reverse direction between the collector and emitter of the output transistor 16. A
eapacitor 18 is eonneeted in parallel to the protecting diode 17. A second rectification and smoothing circuit 14 is coupled to the secondary winding of the transformer 13. The positive terminal of the seeond reetifieation and smoothing eireuit 14 is eonneeted to the positive terminal of a monostable multi~vibrator 19 through the microswitch S, and the negative terminal of the circuit 14 is coupled to the ground terminals of the monostable multi-vibrator 19 and an astable multi-vibrator 20 which is coupled to the monostable multi-vibrator 19. The output terminal of the monostable multi-vibrator 19 is connected to the base o~ the output transistor 16. The thermistor 2 is eoupled to a temperature detecting eircuit 21 so as to control, for example, the base input signal ~or the output transistor 16 or output signal of the transistor 16 by the output signal of the temperature deteeting eureuit 21.
By the above arrangement, the heating operation is started by turning ON a starting switch (not shown), with the eontainer V placed on the top plate 1.
If the eontainer V is of magnetizable material, the magnet member 3 is raised through the attraetion thereof towards the eontainer V, and thus, the mieroswitch 5, whieh is normally open through depression by the magnet member 3, is elosed to apply positive voltage to the positive terminal of the monostable multi-vibrator 19.
The monostab].e multi-vibrator 19 produces pulses of a width of predetermined time, rising at the timing of the pulse periodieally developed from the astable multi-vibrator 20, and by rendering the output transistor 16 eonductive with the output pulse of the monostab].e multi-vibrator 19, the induction heating eoil 8 is energized for the induction heating operation.
As the induction heating is continued, the teMperature of the container V is raised, with a consequent increase of the resistance value of the thermistor 2, and when the temperature of the container V has reached the predetermined level, and the resistance of the thermistor 2 has been decreased down to a predetermined value, the temperature detecting circuit 21 functions to cut off the input signal or output signal, etc. of the output transistor 16.
Therefore, not only is the object to be cooked, which is accommodated in the container V, maintained at an optimum heating temperature, but also the abnormal heating of the container V is positively prevented. Moreover, in the case where there are some problems with the thermistor 2 or in the temperature detection circuit 21 the further rising of the temperature of the container V causes the temperature of the magnet member 3 to reach the curie temperature. The magnet member 3 then loses its magnetism and fall5 downward to open the microswitch 5. The monostable multi~vibrator 19 stops producing pulses and energization of the induction heating coil 8 is cut off.
Therefore, a further improvement is acheived for the safe operation of the heating apparatus. On the other hand, if the container V is of non-magnetizable material, the magnet member 3 does not ascend and the microswitch 5 remains open and no heat is generated.
Since a bore 3a for accommodating the thermistor 2 is provided in the magnet member 3, the magnet member never strikes against the thermistor 2, thereby eliminating the possibility of the magnet breaking the thermistor.
Furthermore, since the curie ternperature of the magnet member is set to be lower than the al~owable temperature limit at the undersurface of the top plate 1, an abnormal temperature rise due to heating, especially heating without objects, may be positively prevented even if the thermistor is inoperative.
Referring to Fig. 5, there is shown a further modification of the arrangement of Fig. 2. In this modified induction heating apparatus ~C of Fig. 5, the magnet support tube 4 and thermistor support rod R are dispensed with and the magnet member 3 is movably accommodated in a magnet receptacle or casing D which is supported by a plate 5~-1 laterally extending from the upper edge of the support plate 5~ which also supports a microswitch 5. This arrangement restricts the lateral movement of the magnet member 3. The magnet receptacle D
has a configuration which conforms with the external shape of the magnet member 3 and has a recess Do at its center corresponding to the bore 3a of the magnet member 3. In the recess Do, there is disposed a resilient thermistor support material 2f, for example, of expanded silicon rubber or the like on which the thermistor 2 is mounted.
A heat collecting plate 2h is disposed on the thermistor 2 for effectively conducting the heat of the top plate 1 to the thermistor 2. Moreover, since the height from the upper surface of the magnet receptable D to the upper surface of the heat collecting plate 2h is arranged to be higher than the height from the upper surface of the receptable D to the undersurface of the top plate 1, the resilient thermistor support material 2f is normally compressed between the undersurface of the top plate 1 and 1 9 ~
the bottom wall of the recess Do, and thus, the heat collecting plate 2h and the thermistor 2 are pressed against the undersurface of the top plate 1. The microswitch ~ is disposed below the magne-t member 3 by the support plate 5Q and is activated by the movement of the magnet member 3 in a similar manner as in the arranyement of Fig. 2.
In the arrangement of Fig. 5, when the container V of magnetizable material is placed at a predetermined position on the top plate 1, the magnet member 3 is attracted by the container V and attached to the inner face of the upper portion of the magnet receptacle D. The microswitch contacts are closed to start the heating.
If, however, a container V of non-magnetizable material is placed on the top plate 1, the magnet member 3 is not attracted, and the microswitch 5 is kept open, and the heating coil 8 is not energized.
Since the magnet receptacle D remains stationary, with only the magnet member 3 moving vertically within the receptacle D, neither the magnet member 3 nor the magnet receptacle D is brought into contact with the top plate 1 and the heat sensing element or thermistor 2, and thus, not only are the impact noises reduced to a large extent, but the top plate, magnet receptacle, thermistor, etc. are completely free from the danger of breakage.
Furthermore, troublesome assembly procedures for installing the heat sensing element, such as bonding, application of electrically conductive paste, etc. are eliminated by virtue of elastically supporting the thermistor.
Referring to Fig.~6, there is shown another modification of the arrangement of Fig. 5. In the modified heating apparatus HD of Fig. 6, the magnet receptacle D of Fig. 5 is arranged -to be integrally formed with the coil suppor~ 7D. The thermistor 2 is disposed in the central recess Do in a sirnilar manner as in the arrangement of Fig. 5. This configuration simplifies construction and facilitates manufacture.
It should be noted here that, in the foregoing embodiments, althouyh the present invention has been mainly described with reference to an induction heating apparatus as applied to cooking ovens, the concept of the present invention is not limited in its application to the cooking ovens alone, but may readily be applied to induction heating apparatuses for industrial purposes in general.
As is clear from the foregoing description, in the induction heating apparatuses HC and HD according to the present invention, since the magnet member and magnet casing or the like are arranged not to be brought into contact with the top plate, possible breakage of the top plate, magnet receptable, heat sensing element, etc. i5 positively prevented. Moreover, owing to the arrangement in which the heat sensing element is adapted to be pressed against the top plate through the elastic supporting of the heat sensing element by the magnet receptable, it becomes unnecessary to bond the heat sensing element to the top plate or to apply electrically conductive paste.
Claims (7)
1. An induction heating apparatus having an induction heating coil provided below a top plate for supporting a container of magnetizable material, said induction heating apparatus comprising a thermistor element provided on the undersurface of the top plate for controlling energization of said induction heating coil, a magnet member movably provided below said top plate so as to be raised through attraction thereof to said container, and a switching member provided below said magnet member for selective energization and de-energization of said induction heating coil in association with the movement of the magnet member, said magnet member being formed therein with a bore in a predetermined position corresponding to said thermistor element so as to accommodate said thermistor element into said bore upon rising of said magnet member for preventing collision therebetween.
2. An induction heating apparatus as claimed in claim 1, wherein said thermistor element is supported at one end of a support rod extending through said bore of the magnet member and secured, at the other end thereof, to a base plate of the induction heating apparatus so as to be pressed against the undersurface of said top plate for close contact therewith.
3. An induction heating apparatus as claimed in claim 1, wherein said thermistor element is supported at one end of a support rod extending through said bore of the magnet member and movably received, at the other end thereof, in a support tube secured to a base plate of the induction heating apparatus, with a spring member being disposed between said one end of said support rod and a corresponding end of said support rod for pressing the thermistor element against the undersurface of said top plate for close contact therebetween.
4. An induction heating apparatus as claimed in claim 1, wherein said magnet member is movably accommodated in a magnet support tube provided between said top plate and a base plate of the induction heating apparatus, with said switching member being disposed below said magnet member in said magnet support tube at a predetermined height from said base plate.
5. An induction heating apparatus as claimed in claim 1, wherein said magnet member is movably accommodated in a magnet receptacle provided below and adjacent to said top plate and having a recess conforming in shape with said bore of the magnet member, said thermistor element being disposed on a resilient support member received in said recess, with a heat collecting plate being further applied on said thermistor element for pressing said thermistor element against the under surface of said top plate through said heating collecting plate for close contact therebetween.
6. An induction heating apparatus as claimed in claim 5, wherein said magnet receptable is integrally formed with a coil support member for said induction heating coil
7. An induction heating apparatus having, below a top plate thereof for supporting a container of magnetizable material thereon, an induction heating coil, a hollow magnet member to be raised through attraction thereof with respect to the container, and a switching member arranged to be selectively opened and closed at its contacts in association with the movement of said magnet member, said magnet member being movably accommodated in a magnet receptable which restricts the amount of rising of said magnet member, said magnet receptacle having a thermistor element provided thereon so as to be pressed against said top plate for controlling energization of said induction heating coil and maintaining temperature of load constant.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP1073580A JPS6057666B2 (en) | 1980-01-30 | 1980-01-30 | induction heating cooker |
| JP10735/1980 | 1980-01-30 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1161124A true CA1161124A (en) | 1984-01-24 |
Family
ID=11758543
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000369411A Expired CA1161124A (en) | 1980-01-30 | 1981-01-27 | Induction heating apparatus with a breakage-proof thermister |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JPS6057666B2 (en) |
| CA (1) | CA1161124A (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS61171189U (en) * | 1985-04-15 | 1986-10-23 | ||
| US7989986B2 (en) * | 2006-03-23 | 2011-08-02 | Access Business Group International Llc | Inductive power supply with device identification |
-
1980
- 1980-01-30 JP JP1073580A patent/JPS6057666B2/en not_active Expired
-
1981
- 1981-01-27 CA CA000369411A patent/CA1161124A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| JPS6057666B2 (en) | 1985-12-16 |
| JPS56107491A (en) | 1981-08-26 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |