High-frequency heating device

In fabricating a door switch for a microwave oven, two switches are incorporated in a single switch case to allow a reduction in the size and to allow common use of switch components, thereby achieving a cost reduction through a reduction in the number of components. Further, a contact switching structure tilted in conjunction with opening and closing of a door is provided to achieve high accuracy in switching the switches. There is provided a first switch whose contact portions are switched by elastically displacing a conductive contact piece in the switch case when a first tilting lever is tilted, a second switch whose contact portions are switched by elastically displacing another conductive contact piece in the switch case at timing that is slightly different from the timing for switching the contact portions of the first switch, and a third switch which is switched when a second tilting lever is tilted.

TECHNICAL FIELD

The present invention relates to a high frequency heating apparatus in which a plurality of switches is efficiently incorporated to reduce the size of the apparatus and to improve the switching performance of the switches, the switches being switched in conjunction with opening and closing of a door of the high frequency heating apparatus.

BACKGROUND ART

A door switch mechanism of a microwave oven, which is a high frequency heating apparatus, will now be described by way of example. Three types of switches, i.e., a latch switch, a door switch, and a monitor switch are incorporated in the door switch mechanism of the microwave oven in consideration to safety in using the microwave oven, and those switches are switched with on and off signals which are obtained with time differences in conjunction with opening and closing of a door.

For example, a door key mounted on an inner surface of the door that exposes and closes an opening on a front side of the microwave oven is provided opposite to switches such as a micro-switch mounted on the main body of the microwave oven, and a switching operation is performed with the door key directly associated with the switches on the main body when the door is closed.

In this case, however, the operation of each switch may be mistimed as a result of a variation of the mounting position of the switch, and an excessively great force may be applied to the switches by an impact that occurs when the door is closed forcefully. For this reason, there has been a possibility of inducing factors causing variation of switching characteristics to disable normal operations of the switches.

A door switch mechanism is also known (JP-A-11-214147), in which two operation pins mounted on an inner surface of a door of a microwave oven are disposed opposite to two respective levers provided on the main body in a face-to-face relationship and in which micro-switches in internal positions are switched through the operation pins and levers in accordance with opening and closing of the door.

In this case, however, since long levers are required, the door switch mechanism as a whole has been large-sized, and a cost increase has resulted because of a great number of components involved. Further, the use micro-switches has involved complicated wiring operations because terminals of three micro-switches are oriented in different respective directions depending on the mounting directions thereof.

Under the circumstance, the invention makes it possible to achieve compactness by incorporating two switches in a single switch case and to achieve a cost reduction through a reduction in the number of components that is achieved by common use of switch components. Further, it is an object of the invention to provide a door switch for a microwave oven having a contact switching structure that is tilted in conjunction with opening and closing of a door to achieve highly accurate performance in switching a switch.

DISCLOSURE OF THE INVENTION

The invention provides a door switch for a microwave oven in which a plurality of switches are switched with time differences by movements of a plurality of tilting levers that are tilted in accordance with opening and closing operations of a door that exposes and closes an opening on a front side of the microwave oven, the includes a first switch whose contact portions are switched by elastically displacing a conductive contact piece in a switch case through a first cam formed at an inner end of a first tilting lever when said lever is tilted, a second switch whose contact portions are switched by elastically displacing another conductive contact piece in said switch case through a second cam formed at the inner end of said first tilting lever at timing different from the timing for switching the contact portions of said first switch, and a third switch switched through a third cam formed at the inner end of a second tilting lever when said lever is tilted.

According to the invention, since the two switches can be incorporated in the single switch case and a switching operation for turning the two switches on and off can be performed in conjunction with, in particular, a movement of the first tilting lever, the first tilting lever can be effectively used as a component common to the two switches to fabricate the device compact. In particular, since the first cam and the second cam formed at the inner end of the first tilting lever can be also used as switching operation members, the first tilting lever has the functions of a lever and a cam although it is a single component, which allows the number of components of the switch to be reduced. Further, the size and cost of the switch can be reduced as a result of the reduction in the number of components.

When the switching between the plurality of contact portions is performed with time differences in association with the position to which the first tilting lever is tilted, the timing of switching can be set as desired. Therefore, the contact portions of each switch can be switched at highly accurate timing in accordance with the tilting operation.

Conductive pieces in the form of plate springs may be used as said conductive contact pieces, and said conductive contact pieces themselves can be provided with an elastic returning force by forming the conductive contact pieces in any curved or bent shape that is suitable for putting them in contact with each other and moving them away from each other. The contact portions can be reliably made to contact and move away from each other by elastically displacing each of the conductive contact pieces in the direction of expanding the gap between the contact portions thereof and in the direction of narrowing the same in conjunction with the tilting force of the first tilting lever. A contact switching structure which is reliable and stable in that it has a capability of eliminating seizure between the contact portions can be obtained by employing a configuration in which the conductive contact portions are in slidable contact with each other.

As another mode of the invention, a door switch for a microwave oven may be provided, in which a switch base is mounted inside a main body frame associated with a door that exposes and closes an opening on a front side of a microwave oven; a first tilting lever and a second tilting lever tilting at different timing in accordance with opening and closing operations of said door are mounted on the switch base; and three switches mounted on said switch base are switched with time differences by movements of said two tilting levers. The door switch having a configuration in which a first pivot portion tiltably pivoted on a switch case and a first cam and a second cam for switching operations are provided at an inner end of said first tilting lever; a first lever pressure-receiving portion associated with a door key mounted on said door is provided at an outer end of said lever; and the switch case incorporates a first switch which includes a plurality of conductive contact pieces side by side so as to face said first cam and whose contact portions are switched when a first conductive contact piece contacts a second conductive contact piece by being urged and elastically displaced by said first cam as said first tilting lever is tilted and a second switch which includes a plurality of conductive contact pieces provided side by side so as to face said second cam and whose contact portions are switched when said second cam urges a fourth conductive contact piece which has been in contact with a third conductive contact piece to move it away from the same and to thereafter put said fourth conductive contact piece in contact with a fifth conductive contact piece at timing different from the timing for switching the contact portions of said first switch, and in which a second pivot portion tiltably pivoted on the switch base and a third cam associated with a push button of a third switch mounted on said switch base to push the same are provided at an inner end of said second tilting lever; and a second lever pressure-receiving portion associated with said door key is provided at an outer end of said second tilting lever.

In this case again, since the two switches are incorporated in the single switch case, the switch case and the first tilting lever can be used as components common to the two switches. Further, the operation timing of the switching operation for turning the first switch on and off and the switching operation for turning the second switch on and off can be accurately associated with each position of the first tilting lever when the lever is tilted. For example, a setting may be made such that the contact portions of the first switch are first switched when the first tilting lever is tilted and such that the contact portions of the second switch are thereafter switched at a slight time lag.

Referring to the direction in which the conductive contact pieces are disposed, since the contact pieces are disposed radially about the first pivot portion of the first tilting lever, the first can and the second cam of the first tilting lever tilting about the first pivot portion can be efficiently associated with the conductive contact pieces.

As another mode of the invention, a configuration may be employed, in which an outer end of each of the conductive contact pieces of said first switch and second switch are aligned with an outer end of a terminal protruding from an outer surface of said third switch so as to protrude in the same direction.

In this case, since the outer ends of the conductive contact pieces of and terminals of all switches can be protruded in the same direction, wiring operations can be facilitated to reduce the man-hour for wiring. In particular, when the outer ends of the terminals are all protruded to the same height in the same direction, wiring operations are further facilitated.

As another mode of the invention, a configuration may be employed, in which the distances from the pivot portions where said first tilting lever and second tilting lever are pivoted to the outer ends of the levers are longer than the distances from the pivot portions to the inner ends to set the leverage of the lever outer end of each of said tilting levers that is tilted about the pivot portion greater than the leverage of the inner end of the lever.

In this case, since a great leverage is set for the outer ends of the levers, a tilting force from the outer ends of the levers tilting about the pivot portions may be small according to the principles of the lever, and the tilting force can be efficiently transferred to the inner ends of the levers. Therefore, the first tilting lever and the second tilting lever have a small load resistance when tilted and can move smoothly.

As another mode of the invention, a configuration may be employed, in which a switch unit is formed by integrally incorporating said first tilting lever in said switch case.

The switch unit can be treated as a single unit although it comprises two components, i.e., the switch case and the first tilting lever, and the unit can therefore be easily assembled on the switch base. Since the two components can be assembled in advance as a single unit, they can be easily handled and managed.

As another mode of the invention, said switch case may be formed by combining a case main body and a case cover, and a recess having the same shape as that of said case main body may be formed on a switch case mounting surface of said switch base.

In this case, since the recess having the same shape as that of the case main body is formed in advance on the switch base as a switch housing portion in which the two switches are to be incorporated, the components constituting the switches can be directly incorporated in the recess, and a part of the switch base can therefore be used instead of the case main body. It is therefore possible to omit the case main body and to thereby reduce the number of components.

As another mode of the invention, said switch case may be formed by combining a case main body and a case cover, and a cover portion having the same shape as that of said case cover may be formed on a switch case mounting surface of said switch base.

In this case, since the cover portion having the same shape as that of the case cover is formed in advance on the switch base, the switch case can be formed only by mounting the case main body on the same. In this case again, since a part of the switch base can therefore be used instead of the case cover. It is therefore possible to omit the case cover and to thereby reduce the number of components.

Another configuration according to the invention is characterized in that there is provided a heating chamber for containing and heating foods, a high frequency generating device for supplying a high frequency to said heating chamber, an openable and closable door facing an open side of said heating chamber and having an operation pin, and a plurality of switches each of which is switched to establish conduction to a power supply circuit for heating at said heating chamber, and in that there is provided a signal switch operated through a first lever mounted on a switch mounting plate located on a side of said heating chamber in conjunction with the operation of said operation pin and a main switch operated through a second lever in conjunction with opening and closing operations of said door, said signal switch incorporating a short switch operated through said first lever.

According to the invention, since the signal switch incorporates the short switch, there is no need for providing a micro-switch to be used as a signal switch and a micro-switch to be used as a short switch independently. It is therefore possible to employ a simple structure and to achieve an advantage from the viewpoint of space in that space saving can be achieved.

Another configuration according to the invention is characterized in that there is provided a heating chamber for containing and heating foods, a high frequency generating device for supplying a high frequency to said heating chamber, an openable and closable door facing an open side of said heating chamber and having a first operation pin and a second operation pin, and a plurality of switches each of which is switched to establish conduction to a power supply circuit for heating at said heating chamber, and in that there is provided a signal switch operated through a first lever mounted on a switch mounting plate located on a side of said heating chamber in conjunction with the operation of said first operation pin and a main switch operated through a pin guide mounted on a front panel of said heating chamber and a second lever mounted on said switch mounting plate in conjunction with the operation of said second operation pin, said signal switch incorporating a short switch operated through said first lever.

According to the invention, the signal switch operates in conjunction with the operation of the first operation pin, and the switch is operated by the first lever mounted on the switch mounting plate located on a side of the heating chamber. The main switch operates in conjunction with the operation of the second operation pin, and the switch is operated by the pin guide mounted on the front panel of the heating chamber and the second lever mounted on the switch mounting plate. The signal switch incorporates the short switch which is operated through the first lever. Therefore, the signal switch and the short switch can be easily set to operate with time differences using the first lever.

Another configuration according to the invention is characterized in that said signal switch operated through said first lever and a switch unit incorporating said short switch are configured such that a contact of said signal switch is off and a contact of said short switch is in an on-state when the door of said heating chamber is open and such that, when the door of said heating chamber is closed, a first operating portion of said first lever urges a movable contact portion of said signal switch to turn on the same after a second operating portion of said first lever urges a movable contact portion of said short switch to turn said short switch from off to on.

According to the invention, when the door of the heating chamber is closed, the first operating portion of the first lever urges the movable contact portion of the signal switch to turn on the same after the second operating portion of the first lever urges a movable contact portion of the short switch to turn the short switch from off to on. It is therefore possible to allow the heating chamber to operate only after making sure that the door is in the closed state by setting a predetermined time as the interval that passes after the short switch is turned off until the signal switch is turned on.

Another configuration according to the invention is characterized in that said switch unit comprises said switch mounting plate and a switch cover covering the contact portion of said signal switch and the contact portion of said short switch and in that it has a configuration in which said main switch is mounted on said switch mounting plate; a rotary shaft of said first lever is provided on said switch mounting plate; and said first lever is inserted in said rotary shaft to hold it with said switch cover.

In this case, when the switch cover is attached to the switch mounting plate, the switch unit is covered, and the first lever is inserted in the rotary shaft. The support for the first lever is thus provided simply by an operation of mounting the same to the switch mounting plate, which simplifies a structure for automatic mounting.

Another configuration according to the invention is characterized in that a flange is extended forward of said rotary shaft of said first lever to prevent a liquid which has flowed along said first lever from entering.

In this case, the flange extended forward of the rotary shaft discharges any liquid such as meat juice or water which has flowed along the first lever to the outside to prevent it from entering the switch unit, which makes it possible to prevent any liquid from entering the switch unit and to thereby avoid erroneous operations attributable to corrosion of the contacts and the like.

Another configuration according to the invention is characterized in that the contact portions in said switch unit are provided behind said rotary shaft of said first lever to keep them less vulnerable to the invasion of a liquid which has flowed along said first lever.

In this case, since the contact portions in the switch unit are disposed behind the rotary shaft, any liquid such as meat juice or water which as flowed along the first lever will not enter the switch unit. It is therefore possible to avoid erroneous operations attributable to corrosion of the contacts and the like.

Another configuration according to the invention is characterized in that the contact portion of the short switch is provided lower to keep it less vulnerable to the invasion of a liquid which has flowed along the first lever.

In this case, the contact portion of the short switch is disposed lower, it is apart from the path of a liquid such as meat juice or water which has flowed along the first lever, and they can be kept less vulnerable to the invasion of a liquid.

Another configuration according to the invention is characterized in that there is provided an indicator indicating the operating position of said switch unit incorporating said signal switch and said short switch by a difference between the colors of the exteriors of said first lever and said switch unit.

In this case, the on and off states of a contact can be checked from the difference between the colors of the exteriors of the first lever and the switch unit differently.

Another configuration according to the invention is characterized in that there is provided an indicator indicating the operating position of said switch unit incorporating said signal switch and said short switch by marks provided on the exteriors of said first lever and said switch unit.

In this case, the on and off states of a contact can be checked from the marks provided on the exteriors of the first lever and the switch unit.

Another configuration according to the invention is characterized in that a protrusion is provided on the top side or bottom side of the exterior of said switch unit to prevent miss-wiring of a connection of said switch unit incorporating said signal switch and said short switch.

In this case, the protrusion provided on the top side or bottom side of the switch unit prevents miss-mounting of a connector connected to the signal switch and the short switch in the switch unit, and the connector can be reliably mounted.

Another configuration according to the invention is characterized in that a contact among contacts formed in said short switch which forms a short circuit between said short switch and said main switch is formed in a substantially R-like shape on one side thereof.

In this case, when contacts constituting the short circuit are shorted, since one of the contact is formed in a substantially R-like shape, an arc current generated between the contacts flows uniformly, which prevents the contact from scattering and allows the short circuit to be formed reliably.

Another configuration according to the invention is characterized in that a contact operating portion of said switch mounting plate is formed in a substantially comb-like shape to prevent dust from entering a gap between said switch mounting plate and said switch cover that is formed when said first lever is moved.

In this case, since the contact operating portion of the switch mounting plate is formed in a substantially comb-like shape, the switch mounting plate and the switch cover are in the form a maze. It is therefore possible to prevent dust from entering a gap between the switch mounting plate and the switch cover.

Another configuration according to the invention is characterized in that a grease reservoir is formed at a contact operating portion of said switch mounting plate and said first lever to prevent dust from entering a gap between said switch mounting plate and said switch cover that is formed when the first lever is moved.

In this case, the grease reservoir formed at the contact operating portion of the first lever prevents dust from entering a gap between the switch mounting plate and the switch cover which is formed when the lever is moved.

Another configuration according to the invention is characterized in that said switch cover is transparent.

In this case, the states of the internal contacts can be directly checked through the transparent switch cover.

Another configuration according to the invention is characterized in that the contacts of said signal switch and said short switch incorporated in said switch unit are offset from each other and wiped after they contact.

In this case, the contact portions of the signal switch and the contact portions of the short switch are offset from each other and wiped when they contact. Each contact portion is thus always cleaned to prevent arcing, whereby seizure of the contact due to an electric current can be prevented.

Another configuration according to the invention is characterized in that said first lever is returned by an elastic force of a contact piece of said short switch incorporated in said switch unit.

In this case, since the first lever is returned using an elastic repulsion of the contact piece of the short switch, there is no need for incorporating a returning member such as a return spring in the first lever, and a reduction in the number of components can be achieved.

Another configuration according to the invention is characterized in that said main switch is disposed opposite to said second lever and on the side of the second operation pin or a second operation key for operating said second lever with reference to a rotary shaft of said second lever.

In this case, since the main switch is disposed tangentially to the second lever, an operation of returning the second lever can be directly performed using a switch returning mechanism incorporated in the main switch. As a result, it is possible to omit a return spring or the like which is otherwise incorporated in the second lever, and the number of components can be thus reduced.

Another configuration according to the invention is characterized in that a protrusion is provided on said second lever to urge said first lever when said second lever is urged for turning said main switch on after said short switch is turned off.

In this case, as the second lever rotates, the first lever is rotated by the protrusion to turn the short switch off and to turn the main switch on thereafter. Thus, even if the second lever is pushed forcibly (pushed intentionally) when the door is open, it is possible to prevent a fuse in the short circuit from being blown.

In the drawings, reference numerals11,141,151, and200represent a microwave oven door switch;13and144represent a switch unit;15represents a switch case;16,146, and155represent a first tilting lever;24represents a second tilting lever;143represents a switch housing portion;153represents a cover portion;201represents a switch mounting plate;202represents a switch unit;203represents a first lever;204represents a second lever;205represents a main switch (switch);207and208represent a rotary shaft;216represents a switch cover;237represents a flange;238represents a grease reservoir;240represents a protrusion;250represents a signal switch (switch);253represents a short switch (switch); C1and C2represent a cam; SW1represents a latch switch; SW2represents a monitor switch; and SW3represents a door switch.

BEST MODE FOR CARRYING OUT THE INVENTION

A plurality of preferred embodiments of a high frequency heating apparatus according to the invention will now be described based on the drawings.

First Embodiment

As shown inFIGS. 1 and 2, a microwave oven door switch11used for a high frequency heating apparatus that is a first embodiment of the invention is formed by mounting a switch unit13and a micro-switch (hereinafter referred to as a latch switch) SW1on a wall of a switch base12provided by erecting a longitudinal substrate and mounting a latch switch mechanism14on another wall.

Referring to the above-mentioned switch unit13, as shown inFIG. 3, a lower end of an inverted-L-shaped first tilting lever16is incorporated a switch case15to integrate them, and two switches, i.e., a monitor switch SW2to serve as a third switch and a door switch SW3to serve as a first switch as will be described later are incorporated side by side in the switch case15. The switch case15is mounted to an upper part of a wall of the switch base12such that the first tilting lever16which is provided for operating the two switches protrudes from the switch case15.

First to third cylindrical shafts17ato16cprotrude from the upper part of the wall of the switch base12, and a fourth cylindrical shaft17dprotrudes from a lower part of the wall of the switch base12. The periphery of the switch unit13is anchored to prevent the unit from coming off using several anchoring nails18protruding from the upper part of the wall of the switch base12with the first cylindrical shaft17ainserted through the switch unit13, whereby the switch unit13is mounted to the switch base12integrally therewith.

The above-mentioned first cylindrical shaft17ais inserted through an insertion hole19provided so as to extend through the switch case15in the mounting direction of the same, whereby the switch case15is positioned, secured, and mounted on the switch base12.

The second cylindrical shaft17bis inserted through a slot20formed in the first tilting lever16to keep the first tilting lever free of interference in moving, the third cylindrical shaft17cis protruded in a position out of the range over which the first tilting lever16is tilted for the same reason. Further, holes in the second to fourth cylindrical shafts17bto17dare used for mounting the switch base12to a housing of a microwave oven which is not shown.

Further, a tilt-permitting nail21is protruded from the upper part of the wall of the switch base12, and an arcuate guide groove22formed in the first tilting lever16in a position in the middle of the height of the same so as to extend in the tilting direction thereof is engaged with the tilt-permitting nail21to guide the tilt of the lever.

The above-described first tilting lever16is tiltably pivoted by incorporating a lower end thereof in the switch case15which will be described later and is tilted about the internal pivot portion serving as a fulcrum of tilting under an external force from a door key when the door, which will be described later, is closed by a pressure-receiving protrusion23protruding as a first pressure-receiving portion from an upper end of the lever. When the lever16is tilted about the pivot portion serving as a fulcrum of tilting, a first cam and a second cam to be described later formed at the lower end of the lever operate to switch the switches SW2and SW3, respectively, to be described later.

The latch switch mechanism14is formed by combining the latch switch SW1that is the second switch and a second tilting lever24. The latch switch SW1is pivoted by inserting a pair of mounting shafts25protruding from another wall of the switch base12through a pair of through holes26horizontally extending through the latch switch SW1, and the latch switch SW1is integrally engaged with and secured to the switch base12with a pair of upper and lower engaging nails27.

The above-mentioned second tilting lever24is L-shaped and is pivoted by tiltably inserting a fulcrum shaft29protruding from the other wall of the switch base12through a pivot hole28provided in the bent position of the L-shape as shown inFIG. 4, and a tilt-permitting nail30protruding from an upper part of the other wall of the switch base12engages a tilt guide groove31on the lever24to support the second tilting lever24on the switch base12such that the lever will not come off.

Further, a third cam32protruding from the lower end of the second tilting lever24formed in the L-shape is inserted through a horizontal through hole33in the switch base12and is disposed so as to face a top surface of a push button34on the latch switch SW1mounted on the first wall, the second tilting lever24is tilted about the pivot hole28serving as a fulcrum of tilting when a pressure-receiving piece35serving as a second lever pressure-receiving portion protruding at an upper end of the lever receives an external force from the door key to be described later (a closing force to close the door) exerted on. At this time, a third cam32for a switching operation protruding at the lower end of said lever24urges the push button34on the latch switch SW1to perform a switching operation. When released from the press, the tilting lever24is tilted back to the initial position under a returning action of the push button34, and the latch switch SW1is also switched back to the initial state.

The tilt of a tilt guide piece36protruding from the second tilting lever24in the form of a semi-circle concentric with the pivot hole28is guided by a tilt guide nail37protruding from the lower part of the other wall of the switch base12to guide the tilt of the lever24.

FIG. 5is an external view of the switch unit13which is provided by incorporating the lower end of the first tilting lever16in the switch case15to integrate them.

In this case, the switch unit13can be treated as a single unit although it comprises two components, i.e., the switch case15and the first tilting lever16, and the switch unit13can be fabricated separately in advance. Therefore, said switch unit13and the door switch for a microwave oven can be easily assembled, fabricated, and managed, and freedom in selecting the quality of the materials will be increased. The components may be fabricated using different resin materials, e.g., using a thermosetting resin having high heat resistance for a case main body and a case cover and using an inexpensive thermoplastic resin for the switch base12.

Referring to the internal configuration of the switch case15, as shown inFIG. 6, it includes the first tilting lever16, a return spring38, first to fifth terminals T1to T5, a case main body39incorporating those components, and a case cover40in the form of a flat plate covering an open side of the main body.

The above-mentioned first tilting lever16has a pivot hole41at a lower end thereof that is incorporated in the case main body39to be described later for tiltably pivoting the lever, a spring mount42for mounting an annular return spring38for urging said lever16to support it in a standby position, and a first cam C1and a second cam C2for switching operations.

Referring to the case main body39, a side of a recess, which is an opening on one side of the body, is partially opened for mounting the lever. A tilting fulcrum shaft44is protruded on an inner surface of the recess facing the opening43. The shaft is inserted through the pivot hole41of the first tilting lever16to mount the lever in a tiltable manner. The first tilting lever16is tilted about the tilting fulcrum shaft44serving as a fulcrum of tilting in a range in which a switching operation can be performed.

Next, an internal structure of the switch unit13will now be specifically described.FIGS. 7 and 8show how the unit is incorporated in the case main body39. The case main body39is partitioned in the middle thereof by a partition plate45extending in the vertical direction to provide left and right cavities46and47, and a door switch SW3and a monitor switch SW2are disposed side by side in the order listed in the cavities46and47. The second cam C2and the first cam C1of the first tilting lever16are located above the cavities in association therewith.

First, the door switch SW3is constituted by the first terminal T1, the second terminal T2, and the second cam C2. Lower parts of the first and second terminals T1and T2, which are conductive plate spring pieces in the form of elongate rectangular plates, are press-fit into press-fit grooves39aand39bformed on one side of a lower part of the case main body39(the left side in the figure). The two terminals T1and T2are mounted such that outer ends thereof protrude in alignment with each other from a bottom surface of the case main body39to allow wiring and such that inner ends thereof face each other substantially in parallel with each other in the cavity46inside the case main body39to serve as a contact. Said second cam C2faces the inner end of he first terminal T1, and a contact switching structure is thereby provided, which is turned on/off when the inner end (free end) of the first terminal T1is put in contact with the inner end (free end) of the second cam C2or moved away from the same in accordance with a movement of said second cam C2.

The monitor switch SW2is constituted by the third terminal T3, the fourth terminal T4, the fifth terminal T5, and the first cam C1. The third to fifth terminals T3to T5, which are conductive plate spring pieces in the form of elongate rectangular plates, are press-fit into press-fit grooves39cto39eformed on the other side of the lower part of the case main body39(the right side in the figure). Outer ends of the three terminals T3to T5are protruded in alignment with each other from the bottom surface of the case main body39to allow wiring, and inner ends thereof face each other substantially in parallel with each other in the cavity47inside the case main body39to serve as contacts.

Further, a terminal holding piece48extends from the partition plate45into the cavity47on the side of the monitor switch SW2, and the inner end of the third terminal T3is press-fit and secured in a press-fit groove39fon the terminal holding piece48. A bent part T41of the fourth terminal T4whose inner end is formed in a step-like configuration is put in contact with the inner end of the third terminal T3. The first cam C1is associated with the free end beyond the bent part T41to provide a contact switching structure in which the free end of the fourth terminal T4is moved away from the third terminal T3and is thereafter put in contact with the free end of the fifth terminal T5according to movements of the first cam C1to switch the contacts.

As thus described, the first terminal T1and the fourth terminal T4are equivalent to movable terminals for switching contact portions and are elastically displaced under an urging force of the first cam C1and the second cam C2formed on a bottom surface of the first tilting lever16which will be described later. The first to fifth terminals T1to T5are identical in configuration except the fourth terminal T4and are interchangeable because they are identical components except that they are press-fit and mounted to the case main body39in different directions.

Further, the first tilting lever16between the first cam C1and the second cam C2is cut to form a stopper groove49thereon, and the stopper groove49is anchored at an apical part45aof the partition plate45located below the same, the apical part45aserving as a stopper portion. The amounts of operation of the cams caused by a tilt of the first tilting lever16are set by the length of the stopper groove49.

After the first tilting lever16, the return spring38, and the terminals T1to T5are incorporated in the recess of the case main body39, anchoring nails40aon the case cover40are engaged and connected with anchoring protrusions39gprotruding from both sides and top of the case main body39to couple those elements such that the open side of the case main body39is closed.

An operation of switching the contact portions of the microwave oven door switch11will now be described with reference toFIG. 9.

Normally, when the pressure-receiving protrusion23of the first tilting lever16is not pressed down as shown inFIG. 9(A), the first tilting lever16is urged by the return spring38, and the pressure-receiving protrusion23is in a standby state in which it can be pressed down. At this time, in the monitoring switch SW2, the fourth terminal T4contacts the fifth terminal T5to establish a normally closed contact or a conductive state, and the terminal does not contact the fifth terminal T5to establish a normally open contact or a non-conductive state.

In the door switch SW3, the first terminal T1and the second terminal T2do not contact to establish a normally open contact or a non-conductive state.

When the pressure-receiving protrusion23begins to receive an external force to cause an initial tilt of the first tilting lever16as shown inFIG. 9(B), the first cam C1integral with the first tilting lever16pushes the free end of the fourth terminal T4to elastically displace it in the direction of moving away from the contact portion of the third terminal T3. As a result, the contact portions of the third terminal T3and the fourth terminal T4are moved away from each other to become non-conductive. Thereafter, the fourth terminal T4is pressed against the contact portion of the fifth terminal T5located in face-to-face relationship therewith in the direction of displacement to become conductive.

When the first tilting lever16is further tilted, as shown inFIG. 9(C), the second cam C2presses the free end of the first terminal T1to elastically displace the same. As a result of the elastic displacement, the first terminal T1is pressed against the contact portion of the second terminal T2to become conductive, and the door switch SW3is switched to a closed position.

The pressure-receiving piece35of the latch switch mechanism14in a standby position that is set back from said pressure-receiving protrusion23is pushed by the first tilting lever16at a time lag. Thus, the first tilting lever16and the second tilting lever24are pushed in the order listed, and the third cam32pushes down the push button34of the latch switch SW1when the second tilting lever24is tilted.

When the external force on the first tilting lever16is removed, the first tilting lever16receives the returning force of the return spring38to return to the initial depressed standby position, and the terminals T1and T4on both sides of the same which have been elastically displaced also elastically return to the initial positions to return the contact portions to the initial standby state shown inFIG. 9(A).

Similarly, the external force on the second tilting lever24is removed substantially at the same time, and the second tilting lever24receives a returning force of the push button34to return to the initial depressed standby position, and the contact portions are switched from on to off and are returned to the initial standby state.

Since the monitor switch SW2and the door switch SW3provided side by side are disposed in fixed positions on both sides of the interior of the unit case15as thus described, there will be no variation in their mounting positions. Further, the switches SW2and SW3on both sides can be easily provided with an arbitrary contact switching configuration in which the contact switching timing of one of the switches, i.e., the monitor switch SW2according to the movement of the first tilting lever16is different from the contact switching timing of the other switch, i.e., the door switch SW3,

Therefore, the contact portions of each switch can be switched at accurate timing according to the tilting operation.

Since the two switches SW2and SW3can be incorporated in the single switch case15, common components can be effectively used, and the device can be fabricated compactly. In particular, the first tilting lever16has both of lever function and cam function in spite of the fact that it is a single component, and it is a common component that allows both of the switches SW2and SW3to be switched through one tilting operation. It is therefore possible to reduce the number of components of the switches.

Further, as shown inFIG. 10, the outer ends of the terminals T1to T5of the monitor switch SW2and the door switch SW3respectively are protruded in the same direction as outer ends of terminals T6and T7protruding from the bottom surface of the latch switch SW3. As a result, an arrangement can be chosen, in which the terminals are disposed in directions and positions that facilitate wiring operations, and the man-hour for wiring can therefore be reduced.

Further, referring to the first tilting lever16and the second tilting lever24, the distances from the pivot portions where the levers are pivoted to the outer ends of the levers are longer than the distances from the pivot portions to the inner ends to set the leverage of the lever outer end of each of the tilting levers16and24that is tilted about the respective pivot portion greater than the leverage of the inner end of the lever.

Thus, a tilting force from the outer end of the lever tilting about the pivot portion may be small according to the principles of the lever, and the tilting force can be efficiently transferred to the inner end of the lever. Therefore, the first tilting lever16and the second tilting lever24have a small load resistance when tilted and can move smoothly.

FIG. 11shows how a state of installation of the door switch11for a microwave oven having the switch unit13. The microwave oven door switch11is mounted such that the pressure-receiving protrusion23of the first tilting lever16faces an upper window52formed in an upper part of a main body frame51facing a door key50on a vertically opening door of a microwave oven and such that the pressure-receiving protrusion35of the second tilting lever24faces a lower window53formed under the same.

An upper nail54and a lower nail55are protruded from an upper part of the side of the door key50facing the windows, and the pressure-receiving protrusion23and the pressure-receiving protrusion35are urged as the door is opened and closed to move back and forth, whereby switching operations are performed.

In this case, the first tilting lever16is mounted such that the tilting direction of the same agrees with the direction (the horizontal direction in the figure) of the external force applied during a switching operation (when the door is closed). Thus, the first tilting lever16is obliquely pushed down and tilted when it receives the external force, and the contacts of the switches SW2and SW3on both sides thereof are accurately switched in conjunction with the tilting motion of the first tilting lever16.

FIG. 12shows an electrical circuit diagram of the door switch for a microwave oven. The terminals of each of the switches SW1, SW2, and SW3constituting the door switch11for a microwave oven are connected to a circuit in the microwave oven as illustrated.

FIG. 13shows a time chart for each of the switches SW1, SW2, and SW3constituting the door switch11for a microwave oven. The latch switch SW1and the door switch SW3are kept open in the depressed standby state in which the door of the microwave oven is open, and a close signal is output when they are pushed down as the door is closed. On the contrary, the monitor switch SW2is kept closed (the third terminal T3and the fourth terminal T4are in conduction) in the depressed standby state (in a free position) in which the door of the microwave oven is open and is opened when it is pushed down as the door is closed (the fourth terminal T4and the fifth terminal T5are in conduction). At this time, a cooking lamp of the microwave oven will be turned on, for example, by a signal output from the same.

The microwave oven is energized and enabled for cooking when the latch switch SW1and the door switch SW3are closed, and the operation is stopped when the switches are opened. However, in case that there is a problem at the contact portions of the switches SW1and SW3such as seizure of the contacts, the contact portions of the switches SW1and SW3may not be opened even when the door is opened. Since electromagnetic waves can be output from the microwave oven to cause a danger in such a case, a circuit configuration in employed, in which the normally closed contact of the monitor switch SW2finally closes to short-circuit the power supply circuit and in which a fuse is thereby blown to disconnect the power supply. Safety is thus maintained.

FIG. 14shows another embodiment of the door switch for a microwave oven. In the door switch141for a microwave oven, a switch housing portion143in the form of a recess similar to a case main body is formed on one wall of a switch base142. A return spring145, first to fifth terminals T11to T15, and a first tilting lever146constituting a switch unit144are incorporated in the switch housing portion143. The open side of the housing is closed with a case cover147to assemble the components integrally.

In this case, since a configuration can be employed in which the components constituting the switch are directly incorporated in the switch housing portion143formed on the switch base142in advance, a part of the switch base142can be used instead of a case main body. It is therefore possible to reduce the number of components.

FIG. 15shows another embodiment of the door switch for a microwave oven. In the door switch151for a microwave oven, a cover portion153having the same shape as that of a case cover is formed on one wall of a switch base152. A case main body156incorporating a return spring154, first to fifth terminals T21to T25, and a first tilting lever155is mounted to the cover portion153.

In this case again, a part of the switch base152can be used instead of a case cover because the switch base152is formed with the cover portion153having the same shape as that of a case cover in advance. A switch unit can be formed only by mounting the case main body156to the same. It is therefore possible to omit a case cover and to reduce the number of components.

As described above, since it is possible not only to house two switches, i.e., a monitor switch and a door switch in a single switch case but also to switch both of the switches though a first tiling lever, the switch case and the first tilting lever can be used as common components. As a result, a cost reduction, space saving, and compactness can be achieved through a reduction in the number of components. Since the two switches are disposed in fixed positions in the switch case, there will be no variation of the mounting positions. Since a switching operation takes place in conjunction with a tilting operation, the switches can be operated at accurate timing, and reliable and stable switching operations can be achieved.

Second Embodiment

A second embodiment of a high frequency heating apparatus according to the invention will now be described with reference toFIGS. 16 to 23.FIG. 16is an external perspective view of a door switch for a microwave oven used in the high frequency heating apparatus of the second embodiment taken from one side of the same.FIG. 17is an external perspective view of the door switch for a microwave oven inFIG. 16taken from another side of the same.FIG. 18is an exploded perspective view of the door switch for a microwave oven shown inFIG. 16.FIG. 19is an exploded perspective view of the door switch for a microwave oven shown inFIG. 17.FIG. 20is a sectional view of a switch unit of the door switch for a microwave oven shown inFIG. 16.FIG. 21shows an example of a problem in a circuit configuration.FIG. 22is a circuit configuration diagram according to the invention.FIGS. 23(a)-(c),24(a)-(c), and25(a)-(c) are illustrations of operations. The description will be omitted or simplified for parts identical or equivalent to those in the first embodiment.

As shown inFIG. 16, a door switch200for a microwave oven used in a high frequency heating apparatus is constituted by a switch mounting plate201, a switch unit202incorporating a first lever203, a second lever204, and a main switch205which is a second switch.

A protrusion207for mounting the first lever203and a rotary shaft208for rotatably supporting the first lever203are erected on an upper part of one surface206of the switch mounting plate201. The switch unit202having the first lever203, which is inserted in the rotary shaft208, is mounted to a switch unit securing portion209disposed so as to surround the rotary shaft208. The main switch205is mounted to a main switch securing portion210disposed behind the protrusion207.

As shown inFIG. 17, a rotary shaft212for rotatably supporting the second lever204is erected in a central part of another surface211of the switch mounting plate201, and a cam213formed on the second lever204extends through a horizontal hole214formed in the central part to protrude above the surface206.

As shown inFIG. 18, the switch unit securing portion209of the switch mounting plate201has three anchoring nails215protruding above the surface206and a rib217which is formed to protrude such that it will surround the switch cover216. The switch unit202is integrally mounted to the switch unit securing plate209by engaging three tabs220formed to protrude from the periphery of the switch cover216with anchoring nails215with the protrusion207inserted through a slot218in the first lever203and the rotary shaft208inserted through a pivot hole219of the first lever203. At this time, the first lever203is prevented from coming off the switch mounting plate201and is guided in tilting by the same by engaging an arcuate guide hole221the lever with a tilt-permitting nail222formed to protrude from one surface206of the plate. A pressure-receiving protrusion223is formed to protrude from the first lever203. The pressure-receiving lever223rotates the first lever203with an external force applied thereto form a door key when the door is closed. When the switch cover216is attached to the switch mounting plate201, the switch unit202is covered, and the first lever203is inserted in the protrusion207. The support for the first lever203is thus provided simply by an operation of mounting the same to the switch mounting plate201, which simplifies a structure for automatic mounting.

A main switch securing portion210of the switch mounting plate201has a pair of mounting shafts224protruding from the surface206and a pair of upper and lower engaging nails225. The main switch205is integrally mounted to the main switch securing portion210with the pair of engaging nails225, with the pair of mounting shafts224penetrating through a pair of through holes226horizontally extending through the main switch205to pivotally support the same. The main switch205is disposed tangentially to the second lever204. Since an operation of returning the second lever204can therefore be directly performed using a repulsion that occurs when a push button227provided on the main switch205returns, there is no need for incorporating a return spring or the like, and the number of components can be thus reduced.

As shown inFIG. 19, a pivot hole228of the second lever204is rotatably mounted around a rotary shaft212on another surface211of the switch mounting plate201. The second lever204is formed with a V-shaped outline, and it is formed with a pressure-receiving piece229on one end thereof and formed with a cam213on another end thereof. Since the pressure-receiving piece229rotates the second lever204based on an external force received from a door key, the cam213turns the push button227of the main switch205on. The second lever204is prevented from coming off the switch mounting plate201and is guided in tilting by the same by engaging an arcuate guide hole230and an arcuate guide protrusion231with tilt-permitting pieces232and233formed to protrude from the other surface211.

A base portion234of the first lever203of the switch unit202is rotatably housed in the switch cover216, and first and second operating portions235and236are formed to protrude from the periphery of the base portion234in the radial direction thereof. A normally open movable contact terminal251and a fixed contact terminal252which constitute a signal switch250serving as a first switch and a first fixed contact terminal254, a normally closed movable contact terminal255, and a second fixed contact terminal256which constitute a short switch253serving as a third switch are mounted in the switch cover216. The detailed description of the movement of the signal switch250and the short switch253is omitted because the description of the first embodiment applies. The switch cover216may be transparently formed. The state of internal contacts can be thus checked directly.

A protrusion240is provided on the second lever204. When the pressure-receiving piece229is urged by an external force from a door key, the protrusion240urges the first lever203to rotate the same, which allows the main switch205to be turned on after the short switch253is turned off.

Since the switch unit202incorporates the signal switch250and the short switch253, there is no need for providing a micro-switch to be used as a signal switch and a micro-switch to be used as a short switch independently. It is therefore possible to employ a simple structure and to achieve an advantage from the viewpoint of space in that space saving can be achieved. The signal switch250operates in conjunction with the operation of a first operation pin, and the switch is operated by the first lever203mounted on the switch mounting plate201which is located on a side of a heating chamber. The main switch205operates in conjunction with the operation of a second operation pin, and the switch is operated by a pin guide mounted on a front panel of the heating chamber and the second lever204mounted on the switch mounting plate201. The signal switch250incorporates the short switch250which is operated through the first lever203. Therefore, the signal switch250and the short switch253can be easily set to operate at different times using the first lever203. When a door of the heating chamber is closed, the first operating portion235of the first lever203urges the movable contact portion of the short switch253to turn it from off to on, and the second operating portion236of the first lever203thereafter urges the movable contact portion of the short switch253to turn it on. It is therefore possible to allow the heating chamber to operate only after making sure that the door is in the closed state by setting a predetermined time as the interval that passes after the short switch253is turned off until the signal switch250is turned on.

In the switch unit202, contact portions of the normally open movable contact terminal251and the fixed contact terminal252constituting the signal switch250and contact portions of the first fixed contact terminal254, the normally closed movable contact terminal255, and the second fixed contact terminal256constituting the short switch253are disposed behind the protrusions207and208. As a result, since a liquid such as meat juice or water which has flowed along the first lever203cannot enter the switch unit202, erroneous operations attributable to corrosion of the contact portions or the like can be avoided. Since the contact portions of the first fixed contact terminal254, the normally closed movable contact terminal255, and the second fixed contact terminal256constituting the short switch253are disposed lower, they are apart from the path of a liquid such as meat juice or water which flows along the first lever203, and they can be kept less vulnerable to the invasion of a liquid. One of contact portions forming a short circuit between the short switch253and the main switch205is formed in a substantially R-like shape. As a result, when the contact portions will not scatter when shorted because one of the contact portions is formed in a substantially R-like shape, which makes it possible to form a short circuit reliably. The contact portions of the signal switch250and the contact portions of the short switch253are offset from each other and wiped when they contact. Each contact portion is thus always cleaned to prevent arcing, whereby a leakage current is prevented. The first lever203is returned by an elastic force of a contact piece on the short switch253. Thus, there is no need for incorporating a returning member such as a return spring in the first lever203, and it is therefore possible to reduce the number of components.

The first lever203is formed with a flange237extending forward of the rotary shaft above the base portion234. A grease reservoir238is formed under the base portion234so as to protrude in the form of the character L toward the periphery. The flange237discharges any liquid such as meat juice or water which has flowed along the first lever203to the outside to prevent it from entering the switch unit202, which makes it possible to prevent any liquid from entering the switch unit202and to thereby avoid erroneous operations attributable to corrosion of the contacts and the like. The grease reservoir238prevents dust from entering through a gap between the switch mounting plate201and the switch cover216that is formed to allow the first lever203to move and prevents grease applied to the base portion234from flowing toward the contacts.

It is preferable to provide an indicator utilizing a difference between the colors of the exteriors of the first lever203and the switch unit202. As a result, it is possible to check the operating position of the switch unit202incorporating the signal switch250and the short switch253, in particular, the on and off states of the contacts. An indicator utilizing marks provided on the exteriors of the first lever203and the switch unit202may alternatively be provided. Thus, the on and off states of the contacts can be checked. A protrusion may be provided on the top side or bottom side of the exterior of the switch unit202. Thus, connectors to be connected to the signal switch250and the short switch253in the switch unit will not be erroneously mounted, and the connectors can therefore be reliably mounted.

As shown inFIG. 20, a rib217on the switch mounting plate201and an edge of the switch cover216are formed in a substantially comb-like shape. Since the switch mounting plate201and the edge of the switch cover24are therefore in the form a maze, it is possible to prevent dust from entering a gap between the switch mounting plate201and the switch cover216.

According to the prior art, when the second lever204is forcibly urged, for example, using a thin wire, the short switch253is in the on state because the door is open, and a fuse is therefore blown. One possible solution to this is to parallel—connect the normally close short switch253downstream of the main switch205and a relay contact RL-1as shown inFIG. 21. In such an arrangement, however, when seizure of the main switch205occurs, the first lever203is depressed to turn the signal switch250on after turning the short switch253off, and the relay contact RL-1is closed to form a power supply circuit. When the cook button is pushed in this state, the magnetron operates although the door is open, and electromagnetic waves thus leak.

On the contrary, according to the invention, the short switch253is parallel-connected downstream of the main switch205and a fuse F, and a relay contact RL-1is series-connected downstream of the connection between the short switch253and the fuse F. In such a circuit configuration, the fuse F is blown only when the main switch205seizes, and the first lever203is depressed to turn the short switch253off when the relay contact RL-1seizes. However, since the second lever204, which is concealed, is not depressed, the main switch205remains in the off state, and no electrical circuit is formed. Even if a cooking start button is pushed in this state, the magnetron does not operate, and the leakage of electrical waves can be prevented. As a result, even when the second lever204is pushed forcibly with the door kept open, the first lever203can be operated in conjunction with the second lever204to turn the short switch253off.

Operations will now be described with reference toFIGS. 23(a)-(c),24(a)-(c), and25(a)-(c).

Normal operations will be first described with reference toFIGS. 23(a)-(c) andFIGS. 24(a)-(c).

As shown inFIG. 23(a), when a door500is open, the first lever203and the second lever204are in the return position, and the short switch253, the signal switch250, and the main switch205are on, off, and on, respectively. When the door500begins to close, the first lever203starts rotating because the pressure-receiving protrusion223of the first lever203is urged.

As shown inFIG. 23(b), since the second lever204is not urged even when the door500begins to close, only the first lever203is rotated, and the normally closed movable contact terminal255is urged by the first operating portion235is made to leave the first fixed contact terminal255, which turns the short switch253off.

As shown inFIG. 23(c), since only the first lever203is urged with the second lever204kept unurged, the normally closed movable contact terminal255is urged by the first operating portion235and is electrically connected to the second fixed contact terminal256to turn the short switch253on. Then, the second operating portion236starts urging the normally open movable contact terminal251.

As shown inFIG. 24(a), as a result of the rotation of the first lever203, the normally open movable contact terminal251is urged by the second operating portion236into electrical contact with the fixed contact terminal252to turn the signal switch250on. Then, the door500starts urging the second lever204.

As shown inFIG. 24(b), as the closure of the door500proceeds, the short switch253is turned off, and the signal switch250is thereafter turned on. Thereafter, the second lever204is rotated independently of the first lever203to turn the main switch205on.

As shown inFIG. 24(c), the door500is closed when the short switch253, the signal switch250, and the main switch205are off, on, and on, respectively.

Next, as shown inFIG. 25(a), when the door500is open, the second lever204is in a return position A0, and the short switch253, the signal switch250, and the main switch205are on, off, and off, respectively.

As shown inFIG. 25(b), when the pressure-receiving piece229receives an external force to urge and rotate the second lever204from the return position A0to a position A1forcibly, the protrusion240urges and rotates the first lever203. As a result of the rotation of the first lever203, the first operating portion235urges and moves the normally closed movable contact255of the short switch253, and the short switch253is thereby turned off.

As shown inFIG. 25(c), when the second lever204is further urged to rotate from the position A1to a position A2, the main switch205is turned on.

As shown inFIG. 25(d), when the second lever204is further urged to rotate from the position A2to a position A3, the rotation of the second lever204stops. At this time, the main switch205is on, and the signal switch250remains off. Therefore, as the second lever204rotates, the first lever203is rotated by the protrusion240to turn the short switch253off and to turn the main switch205on thereafter. Thus, even if the second lever204is pushed forcibly (pushed intentionally) when the door is open, it is possible to prevent the fuse in the short circuit from being blown.

Referring to correspondence between the configuration of the invention and configurations of the above-described embodiments, the first switch in the first mode for carrying out the invention corresponds to the monitor switch of the embodiment. Similarly, the second switch corresponds to the door switch SW3; the third switch corresponds to the latch switch SW1; the first pivot portion corresponds to the pivot hole41and the tilting fulcrum shaft44; the second pivot portion corresponds to the pivot hole28and the fulcrum shaft29; the first lever pressure-receiving portion corresponds to the pressure-receiving protrusion23; the second lever pressure-receiving portion corresponds to the pressure-receiving piece35; and the first to fifth conductive contact pieces correspond to the first to fifth terminals T1to T5, T11to T15, and T21to T25.

The invention may be applied based on the technical ideas disclosed in the claims and is not limited to the configurations of the above-described embodiments.

While the invention has been described in detail with reference to particular embodiments, it will be apparent for those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention.

The present application is based on a Japanese patent application (JP-A-2003-136683) dated May 15, 2003 the contents of which are incorporated herein for reference.

INDUSTRIAL APPLICABILITY

According to the invention, two switches can be incorporated in a single switch case, and a first tilting lever can be provided a common component that allows the contact portions of both switches to be switched in conjunction with the movement of the lever. It is therefore possible to achieve reductions in the number of components, cost, and size of a device. Since both switches can be operated at arbitrary timing in conjunction with the movement of the first tilting lever, the switch can be provided with reliable and stable switching performance, and the switch can therefore be incorporated in a microwave oven as a switch of high safety.