EP2146549A1 - Safety device for a cooker with high power microwave function - Google Patents

Abstract

The device (10) has changeover switches (S1, S2) connected with each other such that the switches provide a closure signal to a closure switch (14) e.g. relay, when the switches are in a switching position. The switches do not provide the closure signal to the closure switch when one of the changeover switches is in another switching position. The closure switch disconnects a power supply of a microwave source (12) i.e. magnetron, when the closure switch is closed according to a cycle of preset time lag after switching of one of the changeover switches into the latter position. An independent claim is also included for a method for securely switching off a microwave source in a cooking device with microwave function.

Description

The present invention relates to a safety device for a cooking appliance with microwave function. In the case of such cooking appliances, in the usage of the present invention, both pure microwave appliances and cooking appliances can be used 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 locks operated when the door is opened, and at least one of them must be a supervised door lock. 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, the failure of any single electrical or mechanical part that can affect the response of a door lock shall not allow any other door lock or interlock Disable supervision of a monitored door lock unless the unit 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. 7 displayed.

As in Fig. 7 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. 7 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. 7 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 be closed 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 is common that they have three with the door coupled switches, namely two closing switches for interrupting the power supply of the microwave source when opening the door and another switch for monitoring the function of one of the door switch.

In the interlock circuit of Fig. 7 In the open state, the door switches e3 and e5 directly interrupt the power supply to the microwave source, namely the current flow through the primary winding of the transformer m10. With higher power microwave sources, however, a direct connection of the power supply is no longer possible. In addition, the interlock circuit of Fig. 7 relatively complicated. In particular, the mechanical realization of the "third" door switch, that is, the monitoring switch e4, consuming.

The invention has for its object to provide a safety device for a cooking appliance with microwave function, which is also used in microwave sources higher power and ensures a safe shutdown of the microwave source with the door open.

This object is achieved by a safety device according to claim 1. Furthermore, it is achieved by the use of a safety device according to claim 14 and a method for safe shutdown of a microwave source with the door open according to claim 15. Advantageous developments are defined in the independent claims.

The safety device according to the invention comprises at least one electrically actuable closing switch, which interrupts the power supply of a microwave source in an open position and can be switched to a closed position by a closing signal. This closing switch is preferably a contactor or a relay acting as a circuit breaker.

Furthermore, the safety device comprises a first and a second changeover switch, which are coupled to a door of the cooking appliance in such a way that they are normally in a first switching position with the door open and in a second switching position when the door is closed. The limitation "normally" indicates that in exceptional cases it may happen that one of the changeover switches is not switched according to the position of the door, for example because its contact is stuck or stuck in a switching position. Exactly such accidents should be considered by the safety device.

The first and second changeover switches are connected so as to pass the closing signal to the closing switch when they are in the second switching position, and the closing signal is not transmitted to the closing switch when the second changeover switch is in the first switching position. Finally, the safety device comprises means which are suitable for suppressing the power supply of the microwave source when the closing switch is still closed at least after a predetermined delay time has elapsed after the first switch has been switched to the first position.

1. 1. Der Schließschalter ist aufgrund eines Fehlers in der geschlossenen Stellung hängengeblieben, beispielsweise festgeschweißt, so dass er auch ohne Schließsignal in der geschlossenen Stellung verbleibt, oder
2. 2. Der zweite Wechslerschalter ist abweichend vom Normalfall in der zweiten Schaltstellung hängengeblieben, in der er das Schließsignal nicht blockiert.

Normally, a state in which the first switch is in the first switching position and the closing switch is closed is unlikely to occur: Under normal circumstances, the first changeover switch is only in the first switching position when the door is open. When the door is open but should also be the second changeover switch in the first switching position, thereby preventing the closing signal is passed to the closing switch. If, in this case, the closing switch is still closed, there are only two possible explanations, namely:

1. 1. The closing switch is stuck due to a fault in the closed position, for example, welded, so that it remains in the closed position even without a closing signal, or
2. 2. The second change-over switch is deviated from the normal case in the second switching position stuck in which he does not block the closing signal.

In both of these cases, the power supply of the microwave source is interrupted, at least if this state still exists after a predetermined delay time has elapsed after the first changeover switch has been switched to the first switching position. The delay time is used to distinguish between abnormal switching states, which are based on disturbances, and transient switching states that result when the door is opened and closed, because the two changeover switches can not be switched exactly at the same time, or a specific switching order due to the special coupling the change-over switch is specified with the door. The delay time should thus last at least as long as the time difference when switching the door-operated changeover circuit, which is typically only a fraction of a second. Note that the reference to the delay time is not restrictive, since the delay time may well be "zero", namely, if further means are provided which allow transient switching states to be distinguished from switching states which are based on interference.

The very unlikely case that both sources of error exist simultaneously is disregarded in the context of the one-error theory used here. The safety device according to the invention thus ensures that the power supply of the microwave source is interrupted when the closing switch erroneously gets stuck in the closed position or the second changeover switch erroneously gets stuck in the second position. If the closing switch hangs in the open position in the complementary error case, the power supply of the microwave source is also permanently interrupted. Therefore, the closing switch is completely monitored. The same applies to the second changeover switch: if the second changeover switch should remain stuck in the first switching position, it permanently prevents a closing signal from being transmitted to the closing switch. This will also ensure that the closing switch is not closed until this error is corrected, thus preventing the microwave source from being powered. Therefore, the second changeover switch is completely monitored.

The safety device of the invention is suitable for high power microwave sources because the changeover switches are not the power supply itself, but only the power supply Close signal for the closing switch, ie a circuit breaker, switch. Further, despite a structure with only two switches coupled to the door, both the second changeover switch and the closing switch are completely monitored, so that the reliability of the shutdown of the microwave is ensured with the door open.

Preferably, the means for interrupting the power supply of the microwave source by a disturbance signal can be controlled such that it interrupts the power supply of the microwave source. As mentioned above, this fault signal must be generated at least when the first changeover switch is in the first switching position and the closing switch is still closed (at least after the specified delay time). The generation of the fault signal thus requires that the position of the closing switch is monitored.

In an advantageous embodiment, for this purpose, the closing switch in addition to at least one normally open contact for interrupting and closing the power supply of the microwave source an auxiliary contact, which is mechanically coupled to the at least one normally open contact such that it is switched together with the normally open contact. In this case, the auxiliary contact is arranged so that the fault signal is generated when the auxiliary contact is closed and the first changeover switch in the first switching position. Then, in fact, the trouble signal is generated when, as required above, the closing switch is closed and the first changeover switch is in the first switching position. Preferably, the fault signal is generated even when the auxiliary contact is closed and the second changeover switch is in the first switching position.

In an advantageous development of the auxiliary contact is connected in parallel to the first changeover switch so that the closing signal can be passed to the second changeover switch with the auxiliary contact closed, bypassing the first changeover switch. If the second changeover switch erroneously gets stuck in the second switching position when opening the door, a self-holding effect of the closing switch results, because the closing signal is independent of the fact that the first Changeover switch is switched when opening the door in the first switching position is continuously transmitted through the closed auxiliary contact to the second change-over switch and through this to the closing switch. The closing switch thus remains closed, so that the power supply of the microwave source is further ensured. Since the monitoring circuit also recognizes this condition and generates a fault signal, this fault signal can be used in a development of the invention to short-circuit at least two phases of the power supply of the microwave source, as explained in more detail below. However, such a short circuit will only be noticeable if the closing switch is closed, so that in fact current flows in the supply lines of the microwave source, which in turn is ensured by the self-holding function of the auxiliary switch. In this way, it can be achieved that the error of a second changeover switch which is suspended in the second switch position is actually noticed and the power supply of the microwave source is permanently interrupted.

The safety device may, for example, comprise a short-circuiting switch which is suitable for generating a short circuit between at least two phases of the power supply of the microwave source in response to the disturbance signal and at least one fuse which is designed and arranged to be under such a short circuit when the current flows triggers and interrupts the power supply of the microwave source.

In an advantageous development, the fault signal is also generated when the first changeover switch is in the second shift position and the second changeover switch is in the first shift position. This in turn is a switch combination that should never occur during normal operation. The cause of this switch combination could be that the first switch erroneously gets stuck in the second switching position when the door is opened.

This fault signal, which is due to an error of the first changeover switch, can be detected in an advantageous development in that the means for interrupting the power supply of the microwave source such self-holding is that the short-circuit switch can still be kept closed even if the cause for the generation of the interference signal, so for example, the aforementioned positions of the changeover switch was canceled. Namely, when the door is closed again and the second changeover switch is switched to the second switching position, the closing signal is passed to the closing switch, the closing switch is closed and the fuse triggered by the resulting short-circuit current. Therefore, in this development, the first changeover switch is monitored.

In a preferred embodiment, the shorting switch is a normally closed switch held in its open position by an operating signal, and the fault signal is simultaneously applied to at least two electrically operable normally closed switches which are opened in response to the fault signal and thereby interrupt the ready signal. This construction makes it possible, in a simple and reliable manner, to generate said short circuit between at least two phases of the power supply of the microwave source in response to the disturbance signal. This structure is safe in the one-fault theory because even if one of the normally closed switches should be stuck in the closed position, a safe short circuit is ensured by the other normally closed switch. A short circuit will also be switched if one of the normally closed switches malfunctions in the open position, or if the ready signal should fail for any reason.

Preferably, the normally closed switch is formed by a relay or contactor and the fault signal is formed by a current flowing through the electromagnet of the relay or contactor.

Furthermore, a delay element is preferably provided which delays the interference signal with respect to the switching operations of the changeover switches which generate the interference signal. The meaning of the delay element will be explained below with reference to an embodiment.

Preferably, the electromagnet is at least one contactor or relay, which forms one of the normally closed switch, suitable to operate a bypass switch, and the bypass switch is arranged in a conductor loop, via which the solenoid irrespective of the switching states of the first and second changeover switch with operated bypass switch with Power is supplied. This is a simple and robust way to make the monitoring circuit self-holding so that the short-circuit can be kept closed when the cause for the generation of the disturbance signal, ie the corresponding switching states of the changeover switch has been canceled.

Preferably, the first and the second changeover switch are coupled to the cooking appliance door such that upon closing the door first the second changeover switch and then the first changeover switch are switched to the second switching position, and when opening the door first the first changeover switch and then the second changeover switch be switched to the first switching position.

• Fig. 1 eine Sicherheitseinrichtung für ein Gargerät nach einer Weiterbildung der Erfindung;
• Fig. 2 die Sicherheitseinrichtung von Fig. 1, bei der der Schließschalter in der geschlossenen Stellung festhängt;
• Fig. 3 die Sicherheitseinrichtung von Fig. 1, bei der der zweite Wechslerschalter in der ersten Schaltstellung festhängt;
• Fig. 4 die Sicherheitseinrichtung von Fig. 1, bei der der zweite Wechslerschalter in der zweiten Schaltstellung festhängt;
• Fig. 5 die Sicherheitseinrichtung von Fig. 1, bei der der erste Wechslerschalter in der ersten Schaltstellung festhängt;
• Fig. 6 die Sicherheitseinrichtung von Fig. 1, bei der der erste Wechslerschalter in der zweiten Schaltstellung festhängt,
• Fig. 7 eine Sicherheitseinrichtung nach dem Stand der Technik, und
• Fig. 8 eine alternative Ausführungsform einer Sicherheitseinrichtung, in der ein weiterer Türschalter vorgesehen ist.

Further advantages and features of the present 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 a safety device for a cooking appliance according to a development of the invention;
• Fig. 2 the safety device of Fig. 1 in which the closing switch is stuck in the closed position;
• Fig. 3 the safety device of Fig. 1 in which the second changeover switch is stuck in the first switching position;
• Fig. 4 the safety device of Fig. 1 in which the second changeover switch is stuck in the second switching position;
• Fig. 5 the safety device of Fig. 1 in which the first changeover switch is stuck in the first switching position;
• Fig. 6 the safety device of Fig. 1 in which the first changeover switch is stuck in the second switching position,
• Fig. 7 a safety device according to the prior art, and
• Fig. 8 an alternative embodiment of a safety device in which a further door switch is provided.

Fig. 1 shows a safety device 10 for a cooking appliance with microwave function according to a development of the invention. Such a safety device is also referred to in the art as an "interlock circuit". The safety device 10 serves to ensure that the power supply to a microwave source 12 is interrupted when a door (not shown) of a cooking appliance is opened. In the exemplary embodiment shown, the microwave source 12 is a relatively high power magnetron whose power supply is switched indirectly via a contactor 14. The contactor 14 comprises three mechanical contacts 14b, 14c, 14d, which serve as a closing switch for the three phases L1, L2, L3 of the power supply of the magnetron 12. However, the invention is also applicable to microwave sources operated with only two phases. The mechanical contacts 14b, 14c and 14d are normally open and are pulled to the closed position by the magnetic field of a solenoid coil 14a as a control current flows therethrough. This control current will be referred to as "closing signal" in the following description. Furthermore, the contactor 14 comprises a fourth mechanical contact 14e, which is referred to below as "auxiliary contact" and whose function will be explained in more detail below. The auxiliary contact 14e is mechanically coupled to the remaining contacts 14b to 14d and is connected together with them.

The safety device further comprises a short circuit switch 16, which is also a contactor in the embodiment shown. The short circuit switch 16 comprises three mechanical contacts 16b, 16, c, 16d with which the phases L1, L2, and L3 can be short-circuited in pairs. The contacts 16b, 16c and 16d are normally closed, ie in the short-circuited position, and are pulled by a solenoid 16a into the opened switching position, when a control current flows through them.

In the lines of the three phases L1, L2, L3 of the power supply of the magnetron 12, a fuse 18 is provided in each case, which triggers when the phases are shorted when the closing switch 14, that is current flow, by the short-circuit switch 16. When the fuse 18 triggers, the microwave source 12 is permanent, namely put out of service until the fuse 18 is replaced. The fuse 18 may be formed for example by a fuse.

The safety device 10 further comprises a first changeover switch S1 and a second changeover switch S2. Both changeover switch S1, S2 are mechanically coupled to the door of the cooking device, in such a way that they are normally with the door open in a first switching position, the in Fig. 1 is shown, in which therefore the root 1 of the respective changeover switch S1, S2 is connected to the contact 2. When the door is closed, the changeover switch S1, S2 are each in a second switching position, that of Fig. 1 is opposite and in which the roots 1 of the changeover switch S1, S2 are each connected to the contact 3.

The safety circuit 10 further comprises a first terminal 20 and a second terminal 22, between which a voltage is applied when the microwave source 12 is in standby. The contacts 2 of the changeover switches S1, S2 are connected to a conductor 24, hereinafter referred to as "fault signal conductor", for reasons which will be explained in more detail below.

Between the fault signal conductor 24 and the second terminal 22, the magnetic coils 26a and 28a of a further contactor 26 and 28 are connected, which cooperate with a mechanical contact 26b and 28b. The contacts 26b, 28b are hereinafter referred to as Öffnerkontakte because they are normally closed and are switched by the magnetic field of the magnetic coils 26a and 28a in the open position when they are traversed by a current. The current through the coils 26a, 28a is a current between the perturbation signal conductor 24 and the second terminal 22 and will be referred to as a "perturbation signal" hereinafter.

The normally closed contacts 26b and 28b of the contactors 26 and 28, respectively, are connected in series with each other and with the solenoid coil 16a of the short-circuiting switch 16 between the first terminal 20 and the second terminal 22. Accordingly, when no current flows through the solenoids 26a, 28a, the normally closed contacts 26b and 28b are closed and current flows through the solenoid 16a of the shorting switch 16. This in turn causes the contacts 16b, 16c, 16d of the shorting switch 16 to open are kept so phases L1, L2 and L3 so not be shorted. The current through the solenoid 16a is also referred to as a "ready signal" in the present disclosure.

The contactors 26 and 28 comprise, in addition to the NC contacts 26b, 28b normally open contacts 26c and 28c, which are normally open and are pulled into the closed position, when the magnetic coils 26a, 28a are traversed by a disturbance signal. The make contacts 26c, 28c are connected in parallel between the first terminal 20 and the disturbance signal conductor 24 and cause the disturbance signal to be self-sustaining in the sense that it is maintained even when its original cause, namely certain switch combinations of the changeover switches S1, S2 and the auxiliary switch 14e are canceled. Therefore, the make contacts 26c, 28c in the present disclosure are also referred to as "bypass contacts."

The function of the safety device 10 will be explained below. For this purpose, the functionality is briefly explained in outline. After that then are based on the FIGS. 2 to 6 discusses the possible incidents, and explains how the safety circuit 10 responds to these incidents.

When the door is open, the changeover switch S1 and S2 are in their first switching position, the in Fig. 1 is shown. In this case, no current flows through the coil 14a of the closing switch 14, that is, there is no closing signal, and the contacts 14b, 14c and 14d of the closing switch 14 are opened. This causes the magnetron 12, ie the microwave source, to be disconnected from the power supply. With the door open of the cooking appliance is therefore ensured by the operated by the door changeover switch S1, S2 that no microwave radiation can be generated.

When the door is closed, the changeover switch S1 and S2, however, each switched to its second switching position, that of Fig. 1 is opposite. In this case, a current flows between the first contact 20 and the second contact 22 via the first changeover switch S1, the second changeover switch S2 and the solenoid 14a of the closing switch. This current serves as a closing signal for the closing switch 14, so that the contacts 14b, 14c and 14d are closed. Therefore, the magnetron 12, as it should be with the cooking appliance door closed, be powered. In addition, the auxiliary contact 14e of the closing switch 14 is closed, which is connected in parallel with the first changeover switch S1. This means that the closing current is maintained even when the changeover switch S1 is switched back to its first switching position.

Note that the fault signal conductor 24 is not connected to the first terminal 20 when the switches S1 and S2 are scheduled in their second switching position with the door closed. It is therefore also generated in this switching state of the changeover switch S1 and S2 no interference signal.

• Der erste Wechslerschalter S1 befindet sich in der zweiten und der zweite Wechslerschalter S2 in der ersten Schaltstellung, unabhängig von der Stellung des Hilfsschalters 14e,
• der Hilfsschalter K1 ist geschlossen und der erste Wechslerschalter ist in der ersten Schaltstellung, unabhängig von der Schaltstellung des zweiten Wechslerschalters S2, oder
• der Hilfsschalter 14e ist geschlossen und der zweite Wechslerschalter S2 ist in der ersten Schaltstellung, unabhängig von der Schaltstellung des ersten Wechslerschalters.

A fault signal, on the other hand, is generated when combinations of the positions of the changeover switches S1, S2 and the auxiliary switch 14e occur which are not provided during operation, for example, because one of the changeover switches S1, S2 gets stuck in one of its switching positions, or because the closing switch 14 is defective, for example, welded in the closed position. Specifically, in the illustrated embodiment, a disturbance signal is generated when one of the following combinations occurs:

• The first changeover switch S1 is located in the second and the second changeover switch S2 in the first switching position, regardless of the position of the auxiliary switch 14e,
• the auxiliary switch K1 is closed and the first changeover switch is in the first switching position, regardless of the switching position of the second changeover switch S2, or
• the auxiliary switch 14e is closed and the second changeover switch S2 is in the first switching position, regardless of the switching position of the first changeover switch.

The fault signal activates the solenoid coils 26a, 28a of the contactors 26, 28, thereby opening the associated normally closed contacts 26b, 28b, breaking the current through the coil 16a of the shorting switch 16, and the contacts 16b, 16c, 16d of the shorting switch 16 interrupting the phases of the power supply short of the magnetron 12. If the closing switch 14 is also closed when the short-circuiting switch 16 is closed, current flows under short-circuit conditions and the fuses 18 are triggered. That is, the error that generated the disturbance signal is detected immediately and causes the microwave source to become inoperative.

However, if the closing switch 14 is open when the trouble signal occurs, the phase short circuit will not be noticed at first because there is still no current flowing in the associated conductors. However, the make contacts 26c, 28c of the contactors 26, 28 cause the disturbance signal, that is, the current flowing through the solenoids 26a, 28a, to be maintained even when the combination of the positions of the switches S1, S2 and 14e which caused the disturbance signal is canceled has been. As soon as the closing switch 14 is closed the next time, current flows through the short-circuited conductors of the power supply of the magnetron 12, and the fuses 18 trip. Due to the self-sustaining property of the disturbance signal is thus achieved that even those errors are monitored, which do not lead directly to a triggering of the fuses 18. In other words, the safety device 10 has a "memory" for faulty switch position combinations that are due to defective switches.

In the previous discussion, only switch position combinations in the closed or in the open state of the cooking appliance door were discussed. Since the changeover switch S1, S2 operated by the door can not be actuated exactly at the same time, occur when opening and closing the door transient switch position combinations, which in itself lead to the generation of the interference signal. In the concrete exemplary embodiment, the changeover switches S1 and S2 are coupled to the cooking appliance door such that, when the door is closed, first the second changeover switch S2 and then the first changeover switch S1 are switched to the second switching position, and the first changeover switch is first reversed when the door is opened S1 and then the second changeover switch S2 switched to the respective first switching position. During normal opening and closing of the door, there is therefore a very short period of time in which the changeover switches S1, S2 are in "unscheduled" combinations, and in which a fault signal would actually have to be generated. In fact, however, the inertia of the magnetic coils 26a, 28a is sufficiently large that only such a short-term disturbance signal is insufficient to switch the contactors 26, 28. If the inertia of the coils 26a, 28a is insufficient, an additional delay element could be provided. It should be noted, however, that in the worst case, a transient combination of switches can result in a short-circuit and thus triggering of the fuse 18 when the door is opened or closed, so that this in no way affects the safety of the safety device. In practice, however, such inadvertent release of the fuse 18 can readily be prevented by suitable switch geometries and the natural delay in the coils 26a, 28a.

An alternative solution to the problem of transient switching states is in Fig. 8 shown in a modification of the safety device 10 of Fig. 1 is shown. The safety device of Fig. 8 includes another door-operated switch 30, which is connected between the second contact of the first changeover switch S1 and the interference signal conductor 24. The switch 30 is coupled to the appliance door (not shown) so that it is open when the door is closed and closed when the door is open. Further, it is coupled to the door so that it is closed when opening the door at the same time or later, when the second changeover switch S2 is switched to the first switching position.

If when opening the door, the first changeover switch has already been switched to the first switching position, the second changeover switch S2 but not yet, can not Fault signal to the fault signal conductor 24 are applied, since the switch 30 is still open at this time. The fault signal can not be applied to the fault signal conductor 24 until the switch 30 is closed. At this time, the second changeover switch S2 should normally already be switched to the first switching position, and therefore the auxiliary contact 14e of the closing switch should be open, so that in this normal case also no fault signal is generated. However, if the second changeover switch S2 in the second switching position or the closing switch 14 should hang in the closed position, a fault signal and a short circuit is generated after closing the switch 30.

The additional door switch 30 thus makes it possible to prevent a fault signal being generated due to transient switching combinations.

In the following, the possible incidents of the components of the safety device 10 are examined in detail. The analysis is based on the so-called "one-fault theory", in which it is assumed that only one component is defective at a time. The unlikely event that two components fail at the same time is not considered in this analysis.

Fault of the closing switch 14

In Fig. 2 is the case that the closing switch 14 gets stuck in the closed position, shown schematically. This can be done, for example, by welding one or more of its contacts 14b to 14e. As long as the cooking appliance door is closed, the closed closing switch 14 corresponds to the normal state, so that this case is not critical. However, when the door is opened, first the first changeover switch S1 and then the second changeover switch S2 switches to the first switching position. Although the solenoid 14a is no longer traversed by the closing signal current after switching the second changeover switch S2 in the first switching position, the contacts 14b to 14e remain closed due to the error, that is, the magnetron 12 is further supplied with power. However, since the first changeover switch S1 switches to the first switching position when opening, the fault signal conductor 24 is above the closed auxiliary contact 14e and the first changeover switch S1 connected to the first terminal 20, and it flows a current as a fault signal through the magnetic coils 26a, 28a. Another connection between the first terminal 20 and the fault signal conductor 14 results from the closed auxiliary contact 14e and the second changeover switch S2 in the first switching position. The current-carrying solenoid coils 26a, 28a open the associated Öffnerkontakte 26b, 28b, the current through the coil 16a of the short-circuit switch 16 is interrupted and the contacts 16b, 16c, 16d of the short-circuit switch 16 are closed. There is a short-circuit current between the phases L1, L2 and L3, through which the fuses 18 are triggered. Thereafter, the microwave source 12 is no longer operational.

If the closing switch 14 gets stuck due to a defect in the open position, the power supply of the magnetron 12 is also interrupted for the duration of the defect. The closing switch 14 or its contacts 14b to 14e are therefore completely monitored.

Error of the second changeover switch

Fig. 3 shows the case in which the second changeover switch S2 gets stuck in the first switching position. In this error, regardless of the switching position of the first changeover switch S1 no closing signal to the solenoid 14a of the closing switch 14 can be applied. Even after closing the door, in which the first changeover switch S1 is switched to the second switching position, the magnetron 12 can not be supplied with power. In other words, the microwave source is automatically disabled by this error.

Fig. 4 shows the case in which the second changeover switch S2 gets stuck in the second switching position. The second switching position corresponds to the normal case with the door closed. Since with the door closed and the first changeover switch S1 is in the second switching position, a current flows as a closing signal through the first changeover switch S1, the second changeover switch S2 and the solenoid 14a of the closing switch 14, the contacts 14b to 14e are closed. Note, the closed auxiliary contact 14e of the closing switch 14 provides a second connection, parallel to the first changeover switch S1, between the second changeover switch S2 and the first connection 20.

When the first changeover switch S1 is switched to the first switching position when the appliance door is opened, the closing signal current can continue to flow via the closed auxiliary contact 14e to the second changeover switch S2. At the same time, however, the first terminal 20 is connected to the disturbance conductor 24 via the auxiliary closed contact 14e and the first changeover switch S1, i. a current flows as a fault signal through the magnetic coils 26a, 28a, which in turn causes in the manner described above, that the short-circuit switch 16 is closed. It comes to a short-circuit current and the fuses 18 trigger. Thus, the second changeover switch S2 is completely monitored.

Disruptions of the first changeover switch S1

In Fig. 5 the case is shown that the first changeover switch stuck in the first switching position. If in this disorder, the door is closed, only the second changeover switch S2 is switched to the second switching position. There is no closing signal current flow, that is, the microwave source 12 can not be put into operation. Therefore, this error is monitored. Note that in this case no interference signal is generated.

Finally shows Fig. 6 the case in which the first changeover switch S1 gets stuck in the second switching position. The second switching position corresponds to the case of a closed door and initially remains undetected when the door is closed. However, this is safe, since a microwave function is provided anyway with the door closed. However, when the door is opened, only the second changeover switch S2 switches to the first switching position, while the first changeover switch S1 gets stuck in the second switching position. The magnetron 12 is safely disconnected from the power supply by switching the second switch S2 to the first switching position. Furthermore, the disturbance conductor 24 is now in the second switching position via the first changeover switch S1 and the second changeover switch S2 is connected to the first terminal 20 in the first switching position, so that a disturbance signal flows through the solenoid coils 26a, 28a. Again, this fault signal causes the shorting switch 16 to short circuit the conductors of the magnetron 12 power supply, but there is no short circuit current because the closing switch 14 is open. In other words, the error of the first changeover switch S1 is not yet apparent at this time.

A short-circuit current can only occur when the second changeover switch S2 is switched to the second switching position again when the door is closed again. However, then the cause for the generation of the disturbance signal (switch S1 in the second and switch S2 in the first switching position) is eliminated. Nevertheless, the disturbance signal is maintained by the make contacts 26c, 28c which were closed by the magnetic field of the solenoids 26a, 28a at the first occurrence of the disturbance signal. Therefore, when the appliance door is closed again, a short-circuit current is generated which triggers the fuses 18, so that this fault is also monitored and the appliance is put out of action.

Error of other components

Also errors in other components of the safety device 10 do not question the safety. If the solenoid coil 14a of the closing switch 14 should be defective, the contacts 14b to 14c of the closing switch 14 remain open, that is, the microwave source 12 is disabled.

If the solenoid 16a of the short-circuit switch 16 should fail, it closes the phases of the power supply of the microwave source 12 short, so that they can not be put into operation either.

Finally, the contactors 26 and 28 are completely redundant: even if one of the contactors fails in any way, the desired function is filled by the other contactor. Thus, even if one of the magnetic coils 26a, 28a, one of the normally closed contacts 26b, 28b or one of the make contacts 26c, 28c should be defective, the short-circuit switch 16 is still safely switched by the fault signal.

In the Fig. 1 shown and based on the FIGS. 2 to 6 So discussed embodiment of the invention thus provides a safety device 10 for a cooking appliance with microwave function, which can also be used at high microwave power, in which the power supply of the microwave source via circuit breaker as the contactor 14 is to be switched. The safety device, as part of the one-fault theory, ensures that microwave radiation can never be generated when the appliance door is open, and it complies with the relevant standards. Finally, despite these benefits, the safety device 10 is simple in construction and also allows complete monitoring of the two switches S1 and S2 coupled to the appliance door without the need for a third switch operated by the door for this monitoring, thereby saving considerable costs.

The features described above may be of importance in various combinations.

LIST OF REFERENCE NUMBERS

10

safety device

12

magnetron

14

closing switch

14a

Magnetic coil of the closing switch 14

14b to 14d

Working contacts of the closing switch 14

14e

Auxiliary contact of the closing switch 14th

16

Short-circuit switch

16a

Electromagnet of the short-circuit switch 16

16b to 16d

Contacts of the short-circuit switch 16

18

fuse

20

first connection

22

second connection

24

Störsignalleiter

26

contactor

26a

Magnetic coil of the contactor 26

26b

Normally closed contact of the contactor 26

26c

Closing contact of the contactor 26th

28

contactor

28a

Magnetic coil of contactor 28

28b

Normally closed contact of the contactor 28

28c

Close contact of the contactor 28

30

door switch

Claims (15)

Safety device (10) for a cooking appliance with microwave function, with at least one electrically actuable closing switch (14) which interrupts the power supply of a microwave source (12) in an open position, and is switchable by a closing signal into a closed position, with a first and a second change-over switch (S1, S2), which can be coupled to a door of the cooking appliance in such a way that they are normally in a first switching position with the door open and in a second switching position with the door closed,
wherein the first and second changeover switches (S1, S2) are connected so as to pass the closing signal to the closing switch (14) when in the second switching position, and the closing signal is not transmitted to the closing switch (14) when the second one Changeover switch (S2) is in the first switching position, and
with means which are suitable for interrupting the power supply of the microwave source (12) when the closing switch (14) is still closed after a predetermined delay time has elapsed after the first switch (S1) has been switched to the first position. Safety device (10) according to claim 1, wherein the closing switch (14) is formed by a contactor or a relay and the closing signal is constituted by a current to be passed through the electromagnet (14a) of the contactor or relay. Safety device (10) according to claim 1 or 2, wherein the means for interrupting the power supply of the microwave source by a disturbance signal are controllable such that they interrupt the power supply of the microwave source. Safety device (10) according to claim 3, wherein the closing switch (14) at least one working contact (14b, 14c, 14d) for interrupting and closing the power supply of the microwave source (12) and an auxiliary contact (14e), which is mechanically coupled to the at least one make contact (14b, 14c, 14d) such that it is switched together with the at least one make contact (14b, 14c, 14d) .
wherein the auxiliary contact (14e) is arranged so that the fault signal is generated when the first auxiliary contact (14e) is closed and the first and / or the second changeover switch (S1, S2) in the first switching position. Safety device (10) according to claim 4, wherein the auxiliary contact (14e) is connected in parallel to the first changeover switch (S1), that the closing signal with closed auxiliary contact (14e), bypassing the first changeover switch (S1) to the second changeover switch (S2) passed can be. A safety device (10) according to any one of claims 3 to 5, wherein the means for interrupting the power supply of the microwave source (12) comprises a shorting switch (16) adapted to short circuit between at least two phases of the power supply in response to the disturbance signal To generate microwave source (12), and at least one fuse (18) which is formed and arranged so that it triggers in a current flow under such a short circuit and the power supply of the microwave source (12) interrupts. Safety device (10) according to one of claims 3 to 6, wherein the fault signal is generated when the first changeover switch (S1) in the second switching position and the second changeover switch (S2) is in the first switching position. A safety device (10) according to any one of claims 6 or 7, wherein the means for interrupting the power supply of the microwave source (12) are self-holding such that the shorting switch (16) can be kept closed when the cause for the generation of the disturbance signal has been removed , A safety device (10) according to any one of claims 6 to 8, wherein the shorting switch (16) is a normally closed switch held in its open position by a standby signal, and the fault signal is simultaneously applied to at least two electrically actuable normally closed switches (26, 28 ) can be applied, which are opened in response to the fault signal and thereby interrupt the ready signal. A safety device (10) according to claim 9, wherein at least one of the normally closed switches (26, 28) is constituted by a relay or contactor and the fault signal is constituted by a current passing through the electromagnet (26a, 28a) of the relay or contactor (26). 26, 28) flows. A safety device (10) according to claim 10, wherein the electromagnet (26a, 28a) is adapted to actuate a bypass switch (26c, 28c) in at least one contactor or relay (26, 28) forming one of the normally closed switches, and the Bypass switch (26c, 28c) is arranged in a conductor loop, via which the electromagnet (26a, 28a), regardless of the switching states of the first and second changeover switch (S1, S2) when the bypass switch (26c, 28c) is energized. Safety device (10) according to one of claims 3 to 11, wherein a delay element is provided which delays the interference signal with respect to the switching operations of the changeover switches (S1, S2) which generate the interference signal, and / or a switch (30) is provided , which is coupled to the door so that it prevents the generation of a fault signal in a state in which in normal operation when closing or opening the door first one of the changeover switch (S1, S2) has been actuated. Safety device (10) according to any one of the preceding claims, wherein the first and the second changeover switch (S1, S2) are coupled to the cooking appliance door such that when closing the door first, the second changeover switch (S2) and then the first changeover switch (S1) are each switched to the second switching position, and when opening the door first, the first changeover switch (S1) and then the second changeover switch (S2) are each switched to the first switching position. Use of a safety device (10) according to one of claims 1 to 13 for a cooking appliance with microwave function. Method for safely switching off a microwave source (12) in a cooking appliance with microwave function, in which at least one electrically actuable closing switch (14) interrupts the power supply of the microwave source (12) in an open position and is switched to a closed position by a closing signal,
in which a first and a second changeover switch (S1, S2) are actuated by a door of the cooking appliance in such a way that they are normally in a first switching position with the door open and in a second switching position with the door closed,
wherein the first and second changeover switches (S1, S2) pass the closing signal to the closing switch (14) when in the second switching position, and the closing signal is not transmitted to the closing switch (14) when the second changeover switch (S2) is turned on is in the first switching position,
and wherein the power supply of the microwave source is interrupted when the closing switch (14) after a predetermined delay time after switching the first switch (S1) is still closed in the first switching position.

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