HOUSEHOLD APPLIANCE WITH DOOR MONITORING DEVICE

Description

[0001] The invention relates to a household appliance comprising a compartment that can be closed by a door and at least one door monitoring device. The invention is particularly advantageously applicable to PEF ("Pulsed Electric Field") cooking appliances and microwave ovens.

[0002] For certain household appliances, the operation of which involves certain risks, the opening of the door must be reliably detected for reasons of operational safety. Examples of this include microwave ovens, where the magnetron must not be switched on when the door is open because otherwise the microwave energy density occurring in the area in front of the open door can cause burns. In PEF cooking appliances, which are also safety-critical, high voltages exist between the contact plates and between the contact plates. Contact with these contacts or with the food or liquid placed between them during operation will result in intense electric shocks. It is irrelevant whether the contact is made directly or via cutlery (e.g., a knife, fork, or wet toothpick).

[0003] The doors of such household appliances are often monitored by micro-pressure switches. These switch off the appliance when the door is open or prevent the activation of certain operating states and function according to the same principle: The closed door mechanically actuates the micro-pressure switch, which is mounted inside the household appliance. In the actuated state (door closed), the switch contact is typically closed. When the door is opened, the switch is returned to its original position by spring force or gravity and thus opened again. The switching state of the micro-pressure switch is queried by an electric current via its internal switching contacts. The use of micro-pressure switches is quite safe because, for example, in the event of a cable break, an open state is detected, and a short circuit in the connecting wires, which could simulate a closed switch, can be prevented by design measures (e.g.a suitable wire guide in the device) can be reliably prevented.

[0004] However, the contacts of the micro-pressure switch can become "sticky" over time, meaning they don't open when the door is opened. This "sticky contact" can have various causes, sometimes in combination: 1) When the contacts open, an arc forms. This arc is particularly likely to occur when the current required to detect a closed contact is high (for example, because the power consumption in the device increases sharply due to component failure) and / or flows through an inductance which briefly generates high electrical voltages through self-induction. The arc causes corrosion on the contact surface and (depending on the polarity of the contact voltage) to material being transported between the contacts. Intense arcs can weld the two contacts together. 2) If the contact surfaces have become rough over time due to corrosion, the unevenness can cause the two contacts to jam together. This jamming occurs particularly when the two contacts roll against each other during the closing process. 3) The force of the spring which is supposed to separate the contacts when the contact is not actuated can decrease over time, e.g.The contact strength may decrease due to fatigue, overuse, etc. Therefore, the contacts are not always separated immediately and reliably.

[0005] To reduce the danger of micro-pressure switches, two micro-pressure switches are often used, connected in series and actuated together. It then makes no difference which of the two switches opens. The safety function is fulfilled very reliably. However, if one contact sticks, the promised operational safety again depends on only one switch, namely the remaining one. This situation can only be monitored by suitable additional electrical or electronic measures, e.g., by an additional, separate logical connection of the individual switches. However, even these additional measures can fail and must therefore be monitored separately.

[0006] DE 10 2012 222 152 A1 discloses a household appliance having a door and a door detection device for detecting a door state of the door, wherein the door detection device has a capacitive sensor whose moving electrode is the door.

[0007] EP 0 456 846 A1 discloses an electronic door safety device for microwave ovens which is based on the principle of influencing coils subjected to high frequency, the magnetic circuit of which is interrupted by the movement of the door.

[0008] DE 38 170 75 A1 discloses a door safety switch for a household appliance, in particular a microwave oven with a microwave-tightly closable cooking chamber, with an electrical switching element which can be actuated by a switching plunger arranged on the door of the appliance in the closed position of the door, wherein the switching element is arranged on a carrier element and the switching element is automatically adjusted during assembly by closing the cooking chamber door.

[0009] US 2014197161 A discloses a door switch device for a microwave oven that deactivates the microwave system without requiring separate "fingers" or pliers on the door face to reach into the main body of the oven to activate a switch. The switch uses stackable switches activated by a single switch lever. The switch lever is preferably made of a solid piece of ultra-high molecular weight (UHMW) polyethylene to maintain the precision of the angular dimensions between the surfaces contacting the door hinge arm and the switch arm.

[0010] AU 595 424 B2 discloses a household appliance having the features of the preamble of claim 1.

[0011] It is the TaskThe present invention aims to at least partially overcome the disadvantages of the prior art and, in particular, to provide a simple and inexpensive way of implementing particularly reliable door monitoring.

[0012] This object is achieved according to the features of the independent claims. Advantageous embodiments are the subject of the dependent claims, the description, and the drawings.

[0013] The object is achieved by a household appliance having a chamber that can be closed by means of a door and at least one door monitoring device with at least one contact pair comprising two contact parts, one of which is arranged on the door and the other contact part is arranged on a stationary part of the household appliance.

[0014] This provides the advantage of providing a self-locking door contact monitoring system for household appliances that reliably detects an open door even if the contact parts of the contact pair are stuck together, and / or reliably enables the household appliance or its components to be safely switched off or deactivated even if the contact parts are stuck together. This household appliance thus uses a door monitoring device or "door lock" that uses the mechanical connection between the mutually movable contact parts as a safety device.

[0015] For this purpose, the two contact parts of at least one contact pair do not represent components of a structural unit (e.g. a switch), but rather separate parts. The two contact parts of a contact pair only touch when the door is closed and then form an electrical connection.

[0016] The following applies: a) When a previously opened door is closed, the two contact parts of the contact pair touch each other properly and the closing of the door is correctly detected. b) If the contact parts do not touch when the door is closed - e.g. in the event of a fault - this may be annoying for the user as they cannot operate the household appliance, but it is not safety-relevant in the sense of door monitoring. In such a case, the user can, for example, call customer service. c) When a previously closed door is opened, the two contacts separate from each other as required or as required under normal circumstances, and the opening of the door can be correctly detected. d) If the two contact parts stick together so tightly that they do not separate when the door is opened, they prevent the door from opening. The safety of the appliance is thus maintained. The user notices that the door cannot be opened and can switch off the appliance via the control panel and / or call customer service.e) If a user opens a door that initially cannot be opened due to sticky contacts, using force and / or tools (e.g., using a wooden spoon as a lever to open the door), the contact parts are torn apart and thus separated, and the switching function is restored. In this case, it is not a problem from a safety perspective if the device is subsequently defective, as its safety is maintained.

[0017] Consequently, a door opening can always be reliably detected even with adhesive contact parts, and a lack of contact between the contact parts when the door is closed does not lead to a safety-critical condition.

[0018] The contact part arranged on the immovable part of the household appliance may also be referred to below as the "immovably arranged" contact part, and the contact part arranged on the door may also be referred to as the "door contact part".

[0019] The chamber that can be closed by means of the door can be a chamber for treating items such as food to be cooked and can also be referred to as a cooking chamber, oven chamber, etc.

[0020] In a further development, the at least one door monitoring device is connected to a circuit ("evaluation circuit"), wherein the evaluation circuit is configured to monitor the contact state of the two contact parts of the at least one contact pair and, in a generally known manner, to prevent operation of at least one safety-critical device component (e.g., a magnetron or a PEF signal generator) if the at least one contact pair of the at least one door monitoring device is separated from one another. In a further development, this can be implemented such that, to determine the contact state, an electrical current flowing through the contact parts of a contact pair is interrogated in a generally known manner.This provides the advantage that a typically higher operating current for a device component does not need to be conducted via the at least one contact pair, which ensures particularly high operational reliability and prevents wear of the contact parts, e.g., due to arcing. However, in another development, the at least one contact pair can also be inserted directly into a circuit for supplying at least one - e.g., safety-critical - device component. In one variant, the door monitoring device can have only the at least one contact pair and, if necessary, one or more electrical lines. When the contact parts are separated, the circuit of the safety-critical device component is also interrupted.

[0021] If several contact pairs are present (in one or more door monitoring devices), operational reliability is increased even further. For this purpose, in particular at least two contact pairs can be electrically connected in series. In general, several door monitoring devices can be present, each with one or more contact pairs, which advantageously increases redundancy. The contact pairs can be arranged in different areas of the door in a particularly advantageous manner in order to be able to detect, for example, the door being forced open at just one corner of the door or the opening state (open or closed) of a warped or loose door particularly reliably. If there are several door monitoring devices, these can be connected separately to an evaluation circuit and / or connected or interconnected in any way, e.g. electrically in series.

[0022] One embodiment of the door monitoring device is that it has exactly one contact pair. This allows for a particularly simple and cost-effective design.

[0023] In one embodiment, each of the two contact parts of a contact pair is connected to at least one electrical line, e.g., for conducting a current (the measuring current or operating current), e.g., to an evaluation circuit of the household appliance, wherein the at least one electrical line of the door contact part runs through the door. This electrical line can be designed as a dedicated flexible line (e.g., a cable) or formed by metallic parts of the door itself; in the latter case, the door hinge can provide the electrical transition to the rest of the household appliance.

[0024] At least the immovable contact part has a plurality of (e.g. two) electrically separated contact surfaces and the electrical lines are connected to the plurality of contact surfaces. The door contact part is designed such that, when the door is closed, it electrically connects at least two of these contact surfaces of the immovable contact part. This has the advantage that the door monitoring device can be electrically connected exclusively via the immovable contact part, e.g. to an evaluation circuit. This in turn advantageously avoids conducting current through the door to the door contact part located therein. Conducting current through the door can have the following disadvantages: If the current is conducted directly through a door hinge, this can lead to unreliable contact detection due to a possibly fluctuating electrical resistance of the door hinge, especially in the case of a mechanically worn door hinge.However, the operational reliability of the system is maintained because in the event of a faulty failure to detect the closed door, the device will not function - and this condition is safe.

[0025] If the current is fed into the door using a dedicated flexible electrical cable, such as a cable, etc., the advantage is that the frequent mechanical bending of the cable when opening and closing the door will cause it to break.

[0026] Another advantage is that if an electrical consumer present in the door (e.g. a control panel) is to be supplied, an unfavourable current supply to the door contact part via a dedicated cable in the area of ​​the door hinge can be avoided due to, for example, a lack of space.

[0027] In a further development, the door contact part has corresponding contact surfaces that are electrically connected to each other for contacting the contact surfaces of the stationary contact part. In a further development, the door contact part has an electrically conductive part, e.g., a metal part, whose surface has the contact surfaces. This is particularly simple and inexpensive to implement.

[0028] One embodiment of the door monitoring device is that it has two pairs of contacts whose door contact parts are electrically connected to each other. The two pairs of door contacts are electrically connected in series with respect to the current flowing through them. This embodiment enables further increased operational reliability. Here, too, the door monitoring device can be electrically connected exclusively via the stationary contact parts, e.g., to an evaluation circuit. This, in turn, advantageously prevents current from flowing through the door to the contact parts located therein.

[0029] In one embodiment, the immovable part of the household appliance is a door flange. This achieves the advantage that the immovable contact parts arranged there are particularly easy to form and install. In the case of a pivoting door, an advantageous development for an advantageously reliable solution for the contact of the contact pairs even at small opening angles of the door and an advantageous variety of their design is that the contact part(s) located in the door and thus the contact pair(s) are located on a side of the door opposite a door hinge; in the case of a horizontally pivoting door with bottom-mounted door hinge(s), for example, on an upper edge of the door when closed.

[0030] In general, the door can also be a door that slides sideways or can be opened in another way.

[0031] The contact elements of a contact pair are designed as complementary plug-in elements of a plug-in connection, or the contact pair forms a plug-in connection. This enables even more reliable contact between the contact elements when the door is closed than when designed as flat contact surfaces. This is advantageous, for example, if the door or frame has warped, or if the door has shifted relative to the frame.

[0032] At least one of the contact parts of at least one contact pair that contacts when the door is closed has an annular groove. This advantageously provides a particularly cost-effective, robust, and reliable way of connecting the contact parts of a contact pair.

[0033] One embodiment provides at least one of the contact parts with a predetermined breaking point. This advantageously allows, if the contact pair can no longer be opened properly and the user therefore opens the door with force, this contact part can be destroyed in a defined manner (e.g., broken), thus interrupting its electrical connection to the evaluation circuit or the safety-relevant device component.

[0034] The contact pairs can be used to supply electrical power to loads located in the door (e.g., operating elements, displays, etc.). For example, the loads can be connected to at least one electrical line connected to a door contact pair and supplied via the current flowing through it. In a further development, if the door is opened, the power supply to the load is interrupted.

[0035] By appropriately interconnecting several contact parts or by appropriately designing individual contact surfaces of a fixed contact part, any number of poles can be protected. For example, a two-pole fuse can be provided for simple power supplies and a three- or four-pole fuse for three-phase devices. This is especially true if the contact pair(s) are directly integrated into a circuit for these device components.

[0036] It is therefore a further development that the contact parts or contact pairs are single-pole or single-pole protecting contact parts or contact pairs. It is a further development that the contact parts or contact pairs are multi-pole or multi-pole protecting contact parts or contact pairs.

[0037] One embodiment is that the household appliance is a PEF ("Pulsed Electric Field") cooking appliance. However, the household appliance can also be a microwave oven, e.g., a standalone microwave oven or a microwave / oven combination. In general, however, any household appliance equipped with a door can be equipped with the door monitoring device described above. For example, service hatches, etc., can also be equipped with it.

[0038] The above-described properties, features and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more clearly understood in connection with the following schematic description of an embodiment, which is explained in more detail in connection with the drawings. Fig.1 shows a simplified sketch of a household appliance with a compartment that can be closed by a door and a door monitoring device according to a first embodiment with the door closed; Fig.2 shows a sectional side view of the household appliance from Fig.1with the door open; Fig. 3 shows a front view of a section of a household appliance in the area of ​​a door monitoring device according to a second embodiment with the door closed; Fig. 4 shows a front view of a section of a household appliance in the area of ​​a door monitoring device according to a third embodiment with the door closed; Fig. 5 shows an oblique view of a possible structural design of one of the two contact parts of the door monitoring device according to the second embodiment; and Fig. 6 shows a sectional side view of a sketch of contact parts hidden inside one another when the door is closed, with one of the contact parts in a design according to Fig.5 .

[0039] Fig.1shows a simplified sectional side view of a household appliance 1, e.g., a PEF cooking appliance or a microwave oven, with a treatment chamber for food ("chamber" 2) that can be closed by means of a door 4 pivotable about a door hinge 3. The household appliance 1 further comprises a door monitoring device with a contact pair 6, 7, comprising a first ("door") contact part 6 arranged on the door 4, and a second ("immobile") contact part 7 arranged on a stationary part of the household appliance 1 in the region of a flange 8.

[0040] The two contact parts 6, 7 are each connected to an electrical line 9 and 10, respectively, with the electrical line 9 of the door contact part 6 leading through the door 4 and further into the body of the household appliance 1 in the area of ​​the door hinge 4. The two electrical lines 9, 10 are connected to an evaluation circuit 11 of the door monitoring device.

[0041] The evaluation circuit 11 is designed to detect whether the two contact parts 6, 7 are connected to each other or not. For this purpose, for example, a voltage can be applied via the electrical lines 9, 10 and a corresponding current I can be detected: if the current I flows, it can be concluded that the two contact parts 6, 7 are connected to each other. If no current I flows, it can be concluded that the two contact parts 6, 7 - as in Fig. 2shown - are separated from each other. Based on the detection of the contact state of the two contact parts 6, 7, the household appliance 1 can, e.g., by means of the evaluation circuit 11 or a control device connected thereto (not shown), switch off or leave switched off safety-critical components of the household appliance 1, such as a magnetron, a PEF pulse generator, etc.

[0042] The door monitoring device here comprises the two contact parts 6 and 7, the evaluation circuit 11 and the associated connecting cables 9 and 10.

[0043] Fig.2 shows the household appliance 1 with the door 4 open, with the two contact parts 6, 7 separated from each other. In this case, no current I flows through the contact parts 6, 7 and thus also not through the electrical lines 9, 10.

[0044] For example, household appliance 1 can be operated safely under the following scenarios: a) When the previously opened door 4 is closed, the two contact parts 6, 7 touch each other if the condition is correct, and the closed state of the door 4 can be correctly detected by the evaluation circuit 11. b) If the contact parts 6, 7 do not touch each other when the door 4 is closed - e.g. in the event of a fault - the evaluation circuit 11 will falsely detect an open state, but this is not safety-relevant in the sense of monitoring the door 4. In such a case, the user can, for example, call customer service. c) When the previously closed door 4 is opened, the two contact parts 6, 7 always separate from each other, and the open state of the door is correctly detected. d) If the two contact parts are stuck together so tightly (e.g. are welded together) that they do not separate when an attempt is made to open the door 4, they will prevent the door 4 from opening.The safety of the household appliance 1 is thus maintained. The user notices that the door 4 cannot be opened and can then, for example, switch the household appliance 1 off and / or call customer service. e) If a user opens the door 4 by using force and / or with the help of tools (for example using a wooden spoon as a lever to open the door) if the door 4 initially cannot be opened due to sticky contact parts 6, 7, the contact parts 6, 7 are torn apart and thus separated, and the switching function is restored. In this case, it is not a problem from a safety perspective if the household appliance 1 is subsequently defective, as its safety is maintained. If at least one of the contact parts 6, 7 is designed with a predetermined breaking point, current I will no longer flow even if the door 4 is subsequently closed.

[0045] Fig.3shows a front view of a section of a household appliance 12 with the door 15 closed. The household appliance 12 is designed analogously to the household appliance 1, but has two contact pairs 6, 7 and 13, 14. The contact pair 6, 7 is designed as in the household appliance 1, with its stationary contact part 7 also connected to the evaluation circuit 11 via the electrical line 10. The second contact pair 13, 14, similarly, has a "third" door contact part 13 and a "fourth" stationary contact part 14, which is arranged in the region of the flange 8. Analogously to the first contact pair 6, 7, the door contact part 14 is connected to the evaluation circuit 11 via an electrical line 16. The first contact part 6 and the third contact part 13 are electrically connected to one another, for example, via metallic components of the door 15 or, as shown, via a dedicated electrical line 17.Whether the door 15 is closed is detected by the evaluation circuit 11 by the fact that a current I flows through both (electrically connected in series) contact pairs 6, 7 and 13, 14. If even just one of the contact pairs 6, 7 or 13, 14 is open, no current I flows. This exemplary embodiment has the advantage of increasing operational reliability: if the contact pairs 6, 7 and 13, 14 are located, for example, at different corners of the door 15, this can take into account the case in which a user forcibly bends the door open at a corner and then at least there the associated contact parts 6, 7 or 13, 14 are separated from one another. The door monitoring device has further advantages over the door monitoring device . Fig.1 and Fig.2The evaluation circuit 11 is connected exclusively to the immovable contact parts 7, 14, so that an electrical line 9 through the door 15 or through metallic components of the door 15 is unnecessary. Such a current conduction only in the household appliance 1 outside the door 15, in turn, results in the following advantages, among others: It prevents the current I from being conducted directly through the door hinge 3 with its possibly fluctuating electrical resistance, which in turn prevents unreliable contact detection, particularly in the case of a mechanically worn door hinge 3.

[0046] Another advantage is that, when an electrical load present in the door 15 (e.g., a control panel, not shown) is to be supplied, an unfavorable current flow to the door contact parts 6 and 13 via the door hinge 3 or via a cable 9 in the area of ​​the door hinge 3, which is due to, for example, lack of space, is avoided. Furthermore, a break in the electrical cable 9 due to frequent mechanical stress when opening and closing the door 15 can be ruled out.

[0047] The door monitoring device here comprises the contact parts 6, 7, 13 and 14, the evaluation circuit 11 and the lines 10, 16 and 17.

[0048] Fig.4 shows a front view of a section of a household appliance 18 with the door 21 closed. The door monitoring device has a contact pair 19, 20 with a first door contact part 19 and a stationary contact part 20 which is arranged in the region of the flange 8.

[0049] In contrast to the household appliance 1, the immovable contact part 20 has several (here: two) electrically separated contact surfaces 22a, 22b, to which electrical lines 10 and 16 leading to the evaluation device 11 are connected.

[0050] When the door 21 is closed, the door contact part 19 acts as an electrical (short-circuit) bridge between the two contact surfaces 22a, 22b, allowing a current I to flow between the contact surfaces 22a, 22b via the door contact part 19. This allows the same advantages as in the household appliance 12 to be achieved even when using only one contact pair 19, 20.

[0051] The function as an electrical bridge can be implemented, for example, by having the contact surfaces 24a, 24b of the door contact part 20, which can be contacted with the contact surfaces 22a, 22b, be surface areas of an electrically conductive component, e.g., a metallic piece. Alternatively, the contact surfaces 24a, 24b can be electrically separated from one another as shown and connected to one another via an electrical line 25.

[0052] The door monitoring device here comprises the contact parts 19 and 20, the evaluation circuit 11 and the connecting cables 10 and 16.

[0053] Fig.5shows in an oblique view a structural design of one of the two contact parts 19, 20, here the immovable contact part 20, as a plug-in element of a plug-in connection or coupling of the two complementarily shaped contact parts 19, 20. The immovable contact part 20 has an annular groove 26 and a central hole 27. In the area of ​​the annular groove 26, the two contact surfaces 22a and 22b are present.

[0054] Fig.6shows a sectional side view of the two contact parts 19 and 20, which are hidden inside each other when the door is closed. The door contact part 19 has a circular rib that can be inserted into the annular groove 26 and a pin-shaped projection that can be inserted into the central hole 27. The contact surfaces 22a and 22b are contacted by the contact mating surfaces 24a and 24b, respectively, whereby the contact mating surfaces 24a and 24b are electrically connected to one another, as indicated by the line 25. This plug-in connection or coupling is mechanically particularly stable and enables reliable contact between the contact surfaces 22a and 22b and the contact mating surfaces 24a and 24b, respectively.

[0055] Alternatively, the contact surfaces 22a, 22b can be provided as annular contact surfaces in the annular groove 26, e.g., on opposite side walls. One of the contact surfaces 22a, 22b can also be provided in the annular groove 26, and the other of the contact surfaces 22b, 22a in the region of the hole 27. It is also possible to form the door contact part 19 as a one-piece metal part, so that a dedicated line 25 can be omitted or is formed by the metal part itself. In this case, the contact mating surfaces 24a and 24b correspond to the surface area of ​​the door contact part 19 that actually comes into contact with the contact surfaces 22a, 22b.

[0056] In general, the shape of the contact parts 19 and 20 can also be exchanged, ie the door contact part 19 has the annular groove 26 and the hole 27 and the door contact part 20 has the circular rib and the pin-shaped projection that can be inserted therein.

[0057] Furthermore, the contact pairs can also be used to supply electrical energy to loads located in the door (e.g., operating elements, displays, etc.). For example, the loads can be connected to electrical lines 9 or 25 and powered by the current flowing therein.

[0058] Of course, the present invention is not limited to the embodiment shown.

[0059] Thus, the exemplary embodiments depict a single-pole fuse. However, by appropriately interconnecting several contact parts or by appropriately designing individual contact surfaces of a fixed contact part, any number of poles can be protected. For example, a two-pole fuse can be provided for simple power supplies and a three- or four-pole fuse for three-phase devices. This applies in particular if the contact pair(s) are directly integrated into an electrical circuit for these device components.

[0060] In general, "a", "an", etc., can be understood as a singular or a plural, in particular in the sense of "at least one" or "one or more", etc., unless this is explicitly excluded, e.g. by the expression "exactly one", etc. List of reference symbols

[0061] 1Household appliance 2Chamber 3Door hinge 4Door 6Door contact part 7Fixed contact part 8Flange 9Electrical cable 10Electrical cable 11Evaluation circuit 12Household appliance 13Door contact part 14Fixed contact part 15Door 16Electrical cable 17Electrical cable 18Household appliance 19Door contact part 20Fixed contact part 21Door 22aContact surface 22bContact surface 24aContact counter surface 24bContact counter surface 25Electrical cable 26Annular groove 27Central hole ICurrent

Claims

1. Pulsed electric field "PEF" household appliance (18), having a compartment (2), which can be closed by means of a door (21), and at least one door monitoring apparatus (11,19, 20) having at least one contact pair (19, 20) comprising two contact parts (19, 20), of which one of the contact parts (19) is arranged on the door (21) and the other contact part (20) is arranged on a non-movable part (8) of the household appliance (15), wherein - at least the contact part (20) that is arranged on the non-movable part (8) has multiple contact surfaces (22a, 22b) that are electrically separated from one another and the electrical lines (10, 16) are connected to the multiple contact surfaces (22a, 22b), - the contact parts (19, 20) that contact one another when the door (21) is in the closed state form a respective pair of plug-in contacts (22a, 24a, 22b, 24b) and - a first contact part (19) of these contact parts (19, 20) is formed in a complementary manner with respect to the second contact part (20) and has contact mating surfaces (24a, 24b) which make contact with the respective contact surface (22a, 22b) of the second contact part (20) when the door is in the closed state, characterised in that at least one second contact part (20) of these contact parts (19, 20) has an annular groove (26), in the area of which at least one of the contact surfaces (22a, 22b) is present.

2. Household appliance (18) according to claim 1, wherein the two contact surfaces (22a, 22b) of the second contact part (20) are arranged on opposite segments of an identical side wall of the annular groove (26).

3. Household appliance (18) according to claim 1, wherein the two contact surfaces (22a, 22b) of the second contact part (20) are present as annular contact surfaces arranged on opposite side walls in the annular groove (26).

4. Household appliance (18) according to one of the preceding claims, wherein the one contact part (20) has a central hole (27) in addition to the annular groove (26).

5. Household appliance (18) according to claim 4, wherein the first contact part (19) has a circular rib which can be inserted into the annular groove (26) and a pin-shaped projection which can be inserted into the central hole (27).

6. Household appliance (18) according to claim 1, wherein the one contact part (20) has a central hole (27) in addition to the annular groove (26), and wherein one of the contact surfaces (22a, 22b) of the second contact part (20) is present in the annular groove (26) and the other of the contact surfaces (22b, 22a) of the second contact part (20) is present in the region of the hole (27).

7. Household appliance (18) according to one of the preceding claims, wherein the contact mating surfaces (24a, 24b) of the first contact part (19) are connected electrically with one another.

8. Household appliance (18) according to one of the preceding claims, wherein the first contact part (19) is embodied as an integral metal part.

9. Household appliance (1) according to one of claims 1 to 6, wherein the two contact parts (6, 7) of the contact pair (6, 7) is connected in each case to at least one electrical line (9, 10), wherein the at least one electrical line (9) of the contact part (6) arranged on the door (4) leads through the door (4).

10. Household appliance (1; 18) according to one of the preceding claims, wherein the at least one door monitoring apparatus (11, 19, 20) has precisely one contact pair (19, 20).

11. Household appliance (18) according to one of the preceding claims, wherein the non-movable part (8) is a door flange.

12. Household appliance (18) according to one of the preceding claims, wherein at least one of the contact parts (19, 20) has a predetermined fracture point.

13. Household appliance (18) according to one of the preceding claims, wherein the door monitoring apparatus (11, 19, 20) has an evaluation circuit (11), which is electrically connected to at least one of the contact parts (19, 20), so as to monitor an open state of the associated contact pairs (19, 20).