EP2148552B1 - Safety device for a cooking device with microwave function - Google Patents

Description

The present invention relates to a safety device for a cooking appliance with microwave function. In the case of cooking appliances of this type, it can be both pure microwave appliances and cooking appliances which, in addition to a microwave cooking function, provide further cooking functions, such as frying, steaming, etc.

Safety devices of the type mentioned have the purpose to ensure that no microwaves can escape when the door of the cooking appliance is open. Requirements for such safety devices are laid down in the EU standards EN 60335-2-90 ("Special requirements for industrial microwave ovens") and EN 60335-2-25 ("Special requirements for microwave ovens and combined microwave ovens"). According to these standards, the cooking appliances must have at least two door interlocks that are actuated when the door is opened, and at least one of these must be a supervised door interlock. Further, at least one door latch must include a switch that shuts off the microwave generator or its power circuit when the door is opened. In particular, the monitoring device of the monitored door lock must disable the device if its switching part controlling the microwave generator fails. Finally, failure of any single electrical or mechanical part that can affect the response of a door lock shall not disable any other door lock or monitoring of a supervised door lock, unless the device becomes inoperative.

A safety device for a cooking appliance, in this case for a pure microwave oven, is in the DE 33 37 141 A1 shown. The associated electrical circuit, which is also referred to as "interlock circuit" is in Fig. 1 displayed.

As in Fig. 1 is shown, is a working circuit 1 for the microwave source, namely the magnetron K6 and its associated components, between two network phases I and II of the power grid.

The interlock circuit of Fig. 1 includes two door switches e3 and e5, which can be actuated directly by the appliance door. Furthermore, it comprises a monitoring switch e4 whose switching contact can be actuated by a switch which is articulated on the appliance door of the microwave oven. The circuit arrangement of Fig. 1 shows the circuit status with the door closed. In this position, the door switches e3 and e5 are closed, and the monitoring switch e4 is in the open position. When the door is opened, normally the two door switches e3 and e5 should open and the monitor switch e4 should close without load. However, if the door switch e3 due to frequent, under load use or hang sticking, that is, when opening the door does not open, it is independently of the monitoring switch e4 closed by said switching arm, and a monitoring circuit 2 is to the full mains voltage of 220V. This has the consequence that a fuse e9 blows, whereby a starter circuit 3 is interrupted, so that after closing the door a restart is no longer possible.

Further interlock circuits are known from the patents DE 28 49 803 . DE 34 15 271 and DE 100 00 569 A1 known. All of these prior art interlock circuits have in common that they have three switches coupled to the appliance door, namely two closing switches for interrupting the power supply of the microwave source when the door is opened and another switch for monitoring the function of one of the door switches.

The EP 0 450 846 A2 discloses a power supply circuit for a microwave oven comprising first and second bus bars connected to a power source. A high voltage transformer has a primary winding having first and second ends connected to the first and second bus bars, respectively. A first door switch is connected between the first bus bar and the first end of the primary winding, the first door switch being opened by opening the door of the microwave oven. A second door switch is connected between the second bus bar and the second end of the primary winding, the second switch being opened by opening the door of the microwave oven. The circuit further includes a third switch having a movable contact and first and second fixed contacts, the movable contact contacting the first fixed contact in response to closing the door and the second fixed contact in response to opening the door. The movable contact and the first fixed contact are connected between the first switch and the first end when the door is closed. The movable contact and the second fixed contact are connected between the first switch and the second bus bar when the door is opened.

The DE 32 44 675 A1 discloses a monitoring device for a safety device for safety shutdown of microwave ovens. A microwave device is connected via circuit breaker and two-phase relay contacts to a power supply. The circuit breakers are used to monitor within the microwave oven, and they interrupt current paths to the microwave oven when the door is opened to a cooking chamber of the microwave oven. A first circuit breaker must be monitored. For this purpose, the second circuit breaker is designed as a changeover switch. Opens the first switch due to functional failure when opening the cooking chamber is no longer, then the switched second circuit breaker voltage is applied to a monitoring circuit. If, in the event of a fault, the first circuit breaker remains closed even though the second circuit breaker is switched, a base current for a transistor is no longer current limited by a resistor. Through this

Overcurrent, the transistor is destroyed, a relay drops, so that the two relay contacts open and the electronics control is disabled.

The US 4,345,144 refers to an arrangement for monitoring locking and unlocking of an oven door. The assembly includes a latch member for locking a hand-operated latch. A lock member verification switch for detecting a part of the lock member which engages with the pawl member is provided. The invention has for its object to provide a safety device for a cooking appliance with microwave function, which can be implemented easily and inexpensively and still meets the above-cited safety standards.

This object is achieved by a safety device according to claim 1. Further, it is achieved by a cooking appliance according to claim 11, the use of a safety device according to claim 12 and a method for safe shutdown of a microwave source with the door open according to claim 13. Advantageous developments are defined in the independent claims.

The safety device according to the invention comprises a closing switch which is coupled to a door of the cooking appliance in such a way that it is normally opened when the door is open and closed when the door is closed, and in the open position prevents the microwave source of the cooking appliance from being supplied with power. The restriction "normally" indicates that in exceptional cases it may happen that the closing switch is not switched according to the position of the door, for example because its contact will stick or stick. Exactly such accidents should be considered by the safety device.

Furthermore, the safety device comprises a changeover switch which is coupled to the appliance door in such a way that it is normally in a first switching position when the door is open and in a second switching position when the door is closed. In this case, the changeover switch prevents in its first switching position that the microwave source is supplied with power.

Finally, the safety device comprises a fuse which interrupts the supply of the microwave source with power when the closing switch is closed and the changeover switch is in the first switching position.

As will be explained in more detail below with reference to an exemplary embodiment, even this very simple safety device with only two door switches already offers the safety required by the relevant standards. As a result, the safety device can be realized much simpler and cheaper than those of the prior art, which always use at least three door switches.

According to section 19.1 ("Improper Operation") of the EN 60335-1 standard, it is regularly assumed that only one improper condition at a time is to be reproduced. Specifically, it is therefore assumed in the following considerations that only one of the two switches is faulty at the same time. This approach is also referred to below as "one-error theory". In the safety circuit of the invention, the closing switch is the monitored switch: if the closing switch namely deviated from the normal case should remain closed despite the door open, because he gets stuck, for example, in the closed position, the fuse blows, because the change-over switch with the door open in the first shift position is located. The second fact can be assumed in the context of the one-error theory, because not both switches are assumed to be faulty at the same time.

However, if the closing switch, in deviation from the normal case, gets stuck in the open position when the door is closed, the microwave source is not supplied with power, ie this error is also detected immediately. The closing switch is therefore completely monitored. Incidentally, however, the changeover switch is partially monitored: namely, if the changeover switch, deviating from the normal case, with the door closed in the first switching position gets stuck, it is assumed by the one-fault theory that the closing switch is closed, so that in turn Blown fuse and the microwave operation is overridden.

As will be explained in more detail below, further incidents are either harmless or not taken into account in the context of the one-fault theory, because they require the simultaneous failure of both switches.

Preferably, a resistor is provided in series with the fuse when the closing switch is closed and the changeover switch is in the first position.

Furthermore, the closing switch and the changeover switch are coupled to the appliance door in such a way that, when the door is closed, first the changeover switch is switched to the second switching position and then the closing switch is closed. Conversely, when the door is opened, the closing switch is first opened and then the changeover switch is switched to the first position. The switching sequence can be specified by suitable mechanical coupling of the switch with the door. This ensures that the fuse can blow only if the corresponding switch combination occurs due to a switch failure, and not only temporarily due to an inappropriate switching sequence when opening or closing the door.

Preferably, the changeover switch in the first position connects a first node to a second node and in the second position the first node to a third node, wherein the first node and the closing switch are connected in series. In this case, preferably the current with which the microwave source is supplied with power flows through the third node. This ensures, as required above, that the power supply to the microwave source is interrupted when the closing switch is open and / or the changeover switch is in the first switching position.

In an alternative embodiment, however, the supply current for the microwave source itself does not have to be passed through the third node, but a signal with which the microwave source is driven or switched could also be passed through the third node. For example, the signal could be a current to which a relay is switched. Also in such an embodiment, the close switch in the open and / or changeover switches in the first position would prevent the microwave source from being powered.

The resistor is preferably connected in series with the second node. The fuse may be connected in series with the first or second node.

Finally, the fuse is preferably a fuse which, if the current flow is too high, interrupts the current and is thereby destroyed, for example by a fuse. This permanently puts the microwave source out of operation in the event of a fault until the error has been detected and corrected.

Fig. 1

eine Interlock-Schaltung nach dem Stand der Technik;

Fig. 2

eine Interlock-Schaltung nach einer Weiterbildung der Erfindung;

Fig. 3A

die Interlock-Schaltung von Fig. 2 bei geöffneter Tür und defektem Schließschalter;

Fig. 3B

die Interlock-Schaltung von Fig. 2 bei geöffneter Tür und defektem Wechslerschalter;

Fig. 3C

die Interlock-Schaltung von Fig. 2 bei geschlossener Tür und defektem Schließschalter; und

Fig.3D

die Interlock-Schaltung von Fig. 2 bei geschlossener Tür und defektem Wechslerschalter.

Further advantages and features of the invention will become apparent from the following description in which the invention with reference to an embodiment will be explained with reference to the accompanying drawings. Show:

Fig. 1

an interlock circuit according to the prior art;

Fig. 2

an interlock circuit according to a development of the invention;

Fig. 3A

the interlock circuit of Fig. 2 with open door and defective closing switch;

Fig. 3B

the interlock circuit of Fig. 2 with the door open and defective changeover switch;

Fig. 3C

the interlock circuit of Fig. 2 with closed door and defective closing switch; and

figure 3D

the interlock circuit of Fig. 2 with closed door and defective changeover switch.

Fig. 2 shows an interlock circuit 10 according to a development of the invention, which is a safety device for a cooking appliance with microwave function. The interlock circuit 10 comprises a first terminal 12 and a second terminal 14, between which a voltage is applied or can be applied, which is suitable for generating a working current through a microwave source 18. The microwave source 18 is typically a magnetron.

Between the first terminal 12 and a first node 1, a fuse 16 and a closing switch S _{1 are connected} in series. A changeover switch S ₂ is provided, which in a first switching position, the in Fig. 2 is shown by the solid line connecting the first node 1 with a second node 2. In this switching position, a current flows between the terminals 12 and 14 through a resistor 20. When the changeover switch S ₂ in a second switching position (dashed line) connects the nodes 1 and 3, a current flows between the terminals 12 and 14 through the microwave source 18th and can provide them with power.

The switches S ₁ and S ₂ are coupled to the door of a cooking appliance with microwave function (not shown) such that when the door is open (solid switching position in Fig. 2 ) of the closing switch S _{1 is} opened and the changeover switch S ₂ in the first switching position, and with the door closed, the closing switch S ₁ closed and the changeover switch S ₂ in the second switching position (dashed switching position in Fig. 2 ). Furthermore, the switches S ₁ and S ₂ are coupled to the appliance door such that when the door is closed, the changeover switch S _{2 is} first switched to the second switching position and then the closing switch S _{1 is} closed. Conversely, when opening the door, the closing switch S _{1 is first} opened and then the changeover switch is switched to the first switching position.

As Fig. 2 can be seen, both the closing switch S ₁ must be closed and the changeover switch S ₂ in the second switching position, so that the microwave source 18 is supplied with power. Therefore, both switches S ₁ , S _{2 are} independently suitable to turn off the microwave source 18 and their power supply when the door is opened. Further, the closing switch S _{1 is} a monitored switch that disables the microwave source 18 when it fails. Here, the failure is that the switch S ₁ gets stuck in a position that differs from the door position, that is, for example, when the door is closed or closed when the door is open. This is by reference to Fig. 3 explained in more detail.

The interlock circuit 10 should also ensure safe operation if one of the switches S ₁ , S _{2 is} defective, namely stuck in a switching position. Basically, there are two door positions (open and closed) and two switch positions of the two switches S ₁ and S ₂ 2 ³ = 8 possible circuit and door state combination that can occur. Of these eight combinations, there are two combinations in which the switch positions of the switches S ₁ and S ₂ coincide with the current door position. Even if one of the switches S ₁ , S ₂ would be stuck in its switching position in this case, make these errors no problems, as they correspond to the intended operation anyway. These two cases can therefore be disregarded.

Furthermore, there are two cases in which both switch positions deviate from the current door position, namely S ₁ closed and S ₂ open in the second switching position with the door open or S ₁ and S ₂ in the first switch position with the door closed. However, these cases assume that both switches, S ₁ and S ₁ , are defective at the same time. This unlikely case need not be taken into account in the one-error theory.

This leaves four combinations of door and switch positions to be considered. These combinations are in Fig. 3A to D shown.

Fig. 3A shows the case that the door is open and the closing switch S _{1 is} defective, namely deviating from the current door position is closed. In this case, a current flows between the terminals 12 and 14 through the fuse 16 and the resistor 20. Der Resistor 20 is so small that the resulting current flow causes the fuse 16 to blow. It can not be generated microwave radiation, since the changeover switch S _{2 is} in the first switching position. In addition, the microwave source 18 can not be put into operation later, since the fuse 16 is permanently burned. This case is still detected in any case, and the closing switch S ₁ is thus monitored in this regard.

Fig. 3B shows the case in which the changeover switch S _{2 is} defective with the door open and is different from the current door position in the second switching position. Also in this case, no microwave radiation can be generated since the power supply of the microwave source 18 is interrupted by the closing switch S ₁ . In this case, even with the door open, microwave radiation can not escape from the device despite failure of the changeover switch S ₂ .

Fig. 3C shows the case in which the door is closed and the closing switch S _{1 is} defective, namely deviating from the current door position is open. Also in this case, the microwave source 18 is cut off from the power supply, although in this case, ie with the door closed, the generation of microwaves would be harmless anyway. However, the failure of the microwave function directs the user to the fault of the closing switch S ₁ . Out FIGS. 3A and 3C So it follows that the closing switch S ₁ is monitored in the sense that any deviation of the switching position of door position leads directly to a failure of the microwave function, so that the error is readily detected. More specifically, the combination of the closing switch S ₁ and the fuse 16 constitutes a monitoring device of the monitored door lock which disables the device according to the directive EN 60335-2-90, paragraph 22, 106, if the switching part (here the closing switch S ₁ ), the the microwave source 18 controls failed.

Finally shows Fig. 3D the case that when the door is closed, the changeover switch S ₂ is different from the current door position in the first switching position. Also in this case, the microwave source 18 is not powered, and as in the case of Fig. 3A the fuse 16 will blow. This means that this failure of the changeover switch S _{2 is} detected.

From the above description it is clear that in all of the cases possible in the one-fault theory it is ensured that no microwave radiation can be generated with the door open. Further, the closing switch S _{1 is} completely monitored, and the microwave source 18 is rendered inoperative when the closing switch S ₁ fails. In particular, the interlock circuit 10 complies with the above-mentioned European Union safety guidelines, and this with an extremely simple and inexpensive construction which requires only two door switches.

The in the Fig. 2 and 3 Of course, shown interlock circuit 10 is just one embodiment of the invention, and numerous modifications are possible. For example, the switches S ₁ and S ₂ directly switch the current for the microwave source 18 in the exemplary embodiment shown. However, instead of the microwave source 18, it would be possible to provide a switching element, for example a relay, which in turn switches a microwave source. Essential to the invention is only that the interlock circuit is used so that the power supply to the microwave source is prevented when the closing switch S _{1 is} opened and / or the changeover switch S ₂ in the first position, regardless of which other components are switched in between.

The fuse 16 could of course also be connected between the resistor 20 and the second node 2.

Although a preferred embodiment has been recorded and described in detail in the drawings and foregoing description, this should be considered as illustrative and not restrictive of the invention. The features described may be of importance in any combination.

LIST OF REFERENCE NUMBERS

1-3

node

10

Interlock circuit

12

first connection

14

second connection

16

fuse

18

magnetron

20

resistance

S ₁

closing switch

S ₂

changeover switch

Claims (13)

1. A safety device (10) for a cooking device with microwave function,
   with a NO (normally open) switch (S1) which is coupled with a door of the cooking device in such a manner that as a standard it is opened when the door is opened and closed when the door is closed, and which in its opened position prevents a microwave source (18) from being supplied with current, with an alteration switch (S2) which is coupled with the device door in such a manner that as a standard it is in a first switch position when the door is opened and in a second switch position when the door is closed, and which in the first switch position prevents the microwave source from being supplied with current, and
   with a fuse (16) which interrupts the supply of the microwave source (18) with current when the NO switch (S1) is closed and the alteration switch (S2) is in the first switch position, characterized in that the NO switch (S1) and the alteration switch (S2) are coupled with the door in such a manner that during a closing of the door, the alteration switch is first switched to the second switch position and then the NO switch (S1) is closed.
2. A safety device (10) according to claim 1, in which a resistance (20) is provided which is connected in series with the fuse (16) when the NO switch (S1) is closed and the alteration switch (S2) is in the first switch position.
3. A safety device according to any one of the preceding claims, in which the NO switch (S1) and the alteration switch (S2) are coupled with the device door in such a manner that during an opening of the door, the NO switch (S1) is first opened and then the alteration switch (S2) is switched to the first switch position.
4. A safety device (10) according to any one of the preceding claims, in which the alteration switch (S2) in the first position connects a first node (1) with a second node (2) and in the second position connects the first node (1) with a third node (3), and in which the first node (1) and the NO switch (S1) are connected in series.
5. A safety device (10) according to claim 4, in which the current by means of which the microwave source (18) is supplied with power flows through the third node (3).
6. A safety device (10) according to claim 4, in which a signal by means of which the microwave source (18) is triggered or switched flows through the third node (3).
7. A safety device (10) according to claim 6, in which the signal is generated by a current by means of which a relay is switched.
8. A safety device (10) according to any one of claims 4 to 7, in which the resistance (20) is connected in series with the second node (2).
9. A safety device (10) according to any one of claims 4 to 8, in which the fuse (16) is connected in series with the first or the second node (1, 2).
10. A safety device (10) according to any one of the preceding claims, in which the fuse (16) is designed in such a manner that when the current flow is too high, it interrupts the current and is destroyed as a result.
11. A cooking device with microwave function which comprises a safety device according to any one of claims 1 to 10.
12. The use of a safety device (10) according to any one of claims 1 to 10 for a cooking device with microwave function.
13. A method for the secure shutdown of a microwave source in a cooking device with microwave function, in which
    a NO (normally open) switch (S1) is actuated by a door of the cooking device in such a manner that as a standard it is opened when the door is opened and closed when the door is closed, wherein the NO switch (S1) in the opened position prevents the microwave source (18) from being supplied with current,
    an alteration switch (S2) is actuated by the device door in such a manner that as a standard it is in a first switch position when the door is opened and in a second switch position when the door is closed, wherein the alteration switch (S2) in the first switch position prevents the microwave source (18) from being supplied with current, and in which a fuse interrupts the supply of the microwave source (18) with current when the NO switch (S1) is closed and the alteration switch (S2) is in the first switch position, characterized in that the NO switch (S1) and the alteration switch (S2) are actuated by the door in such a manner that during the closing of the door, the alteration switch is first switched to the second switch position and the NO switch (S1) is then closed.

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