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BACKGROUND OF THE INVENTION
This invention relates generally to electrical appliances and specifically
to microwave ovens which have a frame defining a cooking chamber, and a
door hingedly mounted to the frame. More particularly, this invention
relates to such appliances which utilize an interlock switch, mounted in
the door jamb, actuated by probe means extending from the door in
alignment with the door jamb. The interlock switch permits the oven to be
operated only when the oven door is fully closed and latched, thereby
providing a highly desirable safety feature.
Interlock switches used for this purpose typically comprise two
electrically coupled switches, both of which must be actuated in order for
operating power to be passed to the oven. The value of such an interlock
switch is, of course, reduced if one of the two electrically coupled
switches becomes welded closed due to tampering, equipment malfunction or
some spurious condition. If this occurs, actuation of the unaffected
switch will be the only action necessary to allow operating power to be
passed to the oven. This, of course, would defeat many of the safety
benefits associated with a conventional interlock switch.
SUMMARY OF THE INVENTION
The subject invention is characterized by an interlock switch comprising a
housing having an inside front wall and three groups of conductive switch
elements, most of which are mounted along that wall in cantilever
arrangement. Mounted inside the housing is a stationary barrier located
between a first group and a second group of conductive switch elements and
a movable barrier located between the second group and the third group of
conductive elements. The stationary barrier has a portion displaced from
the front wall defining a first gap therewith, and the movable barrier has
a portion displaced from the front wall defining a second gap therewith
disposed within the first gap and the second gap interconnects one of the
conductive switch elements in the first group with one of the conductive
switch elements in the third group. Because the buss is substantially
captivated within the gaps defined by the front wall and the stationary
and movable barriers, the likelihood of it interfering with the operation
of the switch elements even if it becomes broken off is greatly minimized.
BRIEF DESCRIPTION OF THE DRAWINGS
The preferred embodiment of the invention summarized above is shown in the
accompanying drawings wherein:
FIG. 1 is a schematic, perspective view of an electrical appliance
incorporating the invention;
FIG. 2 is a schematic, plan view of the interlock switch used with the
appliance shown in FIG. 1;
FIG. 3 is a schematic, plan view of the interlock switch shown in FIG. 2 in
a partially actuated condition;
FIG. 4 is a schematic, plan view of the interlock switch shown in FIG. 2 in
a fully actuated condition;
FIG. 5 is an enlarged, schematic, perspective of a portion of the appliance
and the interlock switch shown in FIG. 1; and
FIG. 6 is an enlarged, schematic, perspective view of the portion of the
interlock switch shown in FIG. 5, but in an actuated condition.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION
Referring now to FIG. 1 there is illustrated a preferred embodiment of the
invention. In particular, there is illustrated an electrical appliance,
such as a microwave oven 10, having a frame 12 defining a chamber 11 into
which food to be heated by oven 10 is placed. Frame 12 further includes a
door jamb 13 into which is mounted an interlock switch 20.
Oven 10 further includes an oven door 15 which is typically hingebly
mounted to frame 12. Near the free end of oven door 15 there is mounted
probe means 16, preferably in the form of a rigid pin member 17 and a
movable latch pawl 18. Pin member 17 and latch pawl 18 are preferably
aligned with door jamb 13, and in particular are aligned, respectively,
with a first actuator 40 and a second actuator 50 associated with
interlock switch 20. As explained in greater detail hereinafter, pin
member 17 operates first actuator 40 as oven door 15 becomes partially
closed, and latch pawl 18 operates second actuator 50, when oven door 15
is fully closed and latched.
The operation of probe means 16 in the form of pin member 17 and latch pawl
18 are shown best by referring to FIGS. 5 and 6. As oven door 15 closes,
rigid pin member 17 abuts a contact face 42 of first actuator 40, thereby
moving a slider 44 horizontally (see horizontal arrow in FIG. 6) against a
coil spring 46. The movement of slider 44 causes actuation of several
switch elements associated with interlock switch 20 in a manner explained
in greater detail hereinafter.
Similarly, latch pawl 18 operates second actuator 50 when oven door 15 is
fully closed and latched. Thus, still referring to FIGS. 5 and 6,
interlock switch 20 comprises a housing 22 having a rear wall 24. Rear
wall 24 defines a notch 36 and a latch 39 extending therein. Latch 39 has
an angled face 37 and a horizontal face 38 adapted to be sequentially
contacted by a latch surface 19 of latch pawl 18. When latch pawl 18
begins to advance into notch 36 in side wall 24, during the closure of
oven door 15, latch surface 19 is urged downwardly by angled face 37 of
latch 39. As latch pawl 18 advances further into notch 36, latch surface
19 slides along horizontal face 38 of latch 39 until face 38 is aligned
with a cutout 31 defined in latch pawl 18. When this occurs, latch pawl 18
springs upwardly (see vertical arrow in FIG. 6), whereby oven door 15 is
fully closed and latch pawl 18 becomes latched with latch 39.
As shown in FIGS. 5 and 6, in this preferred embodiment, probes 16,17
operate actuators 40,50 without actually entering the interior of housing
22 of interlock switch 20. Indeed, throughout the entire operation of
switch 20, actuators 40,50 isolate the outside environment of switch 20
from the interior of housing 22. As a result, door probe wear particles
and other spurious material cannot readily enter housing 22 and perhaps
interfere with the operation of the various components therein. Further,
this arrangement greatly minimizes the likelihood that access to the
interior of housing 22 can be gained via an external implement (such as a
knife or screwdriver) through tampering, carelessness or accident.
Operation of actuator 50 by the latching of latch pawl 18 to latch 39
causes actuator 50 to move from the position shown in FIG. 5, to the
position shown in FIG. 6. This, in turn, causes actuation of several
switch elements associated with interlock switch 20 in a manner explained
in greater detail hereinafter. From the foregoing description, however, it
should be clear that the sequence of movement of actuators 40 and 50 is
such that first actuator 40 is operated by rigid pin member 17 before oven
door 15 is fully closed, but second actuator 50 is not operated by latch
pawl 18 until oven door 15 is fully closed and latched.
The specific components of interlock switch 20 and their operational
sequence in response to the movement of actuators 40 and 50 is illustrated
in FIGS. 2-4. In particular, FIG. 2 illustrates the position of the switch
elements comprising interlock switch 20 when oven door 15 is open, FIG. 3
illustrates the position of those switch elements when oven door 15 is
partially closed, and FIG. 4 illustrates the position of those switch
elements when oven door 15 is fully closed and latched.
Referring now to FIG. 2, housing 22 of interlock switch 20 is shown to
include, in addition to rear wall 24, a pair of side walls 26, 28 a bottom
wall 25, and a plurality of anchoring fixtures 32 defining an interior
front wall 34. Extending outwardly from side walls 26, 28 are a pair of
mounting ears 29 which are used to facilitate the mounting of interlock
switch 20 in door jamb 13 of oven 10.
Interlock switch 20 further includes a stationary barrier 70 which
preferably comprises a rigid member extending upwardly from base 25 near
the center of housing 22. Pivotally mounted to base 25 of housing 22 is a
platform 54 having a movable barrier 60 extending upwardly therefrom along
substantially the same line defined by stationary barrier 70 when oven
door 15 is in the fully closed position of FIG. 4. A pair of substantially
parallel flange members 67, 68 also extend upwardly from platform 54
intersecting, respectively, the opposite ends of movable barrier 60. Also
extending upwardly from platform 54 are three rigid pins 61, 62 and 63
whose function will be explained hereinafter.
An additional moveable barrier 64, extending substantially parallel to
stationary barrier 70 when oven door 15 is in the fully closed position of
FIG. 4 also extends upwardly from platform 54. Additional barrier 64
terminates in a hub 66 which is mounted over a post 65 extending upwardly
from base 25. Actuator 50 is preferably integrally formed with platform 54
near the end thereof opposite hub 66. Thus, movement of actuator 50, in
response to movement of latch pawl 18, causes platform 54 to pivot about
post 65. This movement of platform 54 causes a corresponding movement of
pins 61, 62 and 63, movable barrier 60, and additional barrier 64.
Housing 22 further incorporates a slider guide 45 through which slider 44
can be moved back and forth in response to the operation of actuator 40 by
rigid pin member 17. Extending upwardly from slider 44 is a pair of
actuator pins 47, 48, and extending transversely from slider 44 is an
actuator arm 49. The functions of actuator pins 47, 48 and actuator arm 49
will be explained hereinafter.
Mounted inside housing 22 of interlock switch 20 are a plurality of
electrically conductive switch elements 100-109. Switch elements 100.106
and switch elements 108-109 have, respectively, fixed ends 110-116 and
118-119, substantially captivated between adjacent ones of anchoring
fixtures 32, and (except for switch element 108) free ends 120-126 and
128-129.
Interlock switch 22 also includes an electrically conductive switch element
107 which is preferably integrally formed with switch element 108. Thus,
in this embodiment, switch element 107 has a free end 127 and an
interconnected end 117 which connects with an interconnected end 128 of
switch element 108. Each of switch elements 100-109 is preferably mounted
edgewise within housing 22 of interlock switch 20, so that they sometimes
function as leaf springs, and are formed of electrically conductive
material such as copper or the like.
In this preferred embodiment switch elements 100 and 101 form part of a
circuit for an auxiliary device such as a lamp (not shown), and are
normally closed, i.e., in the "make" condition, when oven door 15 is in
the open position of FIG. 2. Thus, the lamp in the circuit comprising
switch elements 100 and 101 will be illuminated when oven door 15 is open.
Switch elements 101 and 102 preferably form part of a primary interlock
circuit for microwave oven 10, and are normally open, i.e., in the "break"
condition when oven door 15 is in the open position of FIG. 2. Thus,
switch elements 101 and 102 prevent operating power from being supplied to
microwave oven 10 as long as oven door 15 is open, converting to the
"make" condition only when the door is fully closed and latched.
Switch elements 103 and 104 preferably form part of a logic circuit (not
shown) which, in accordance with well known microwave oven operation,
controls many of the oven's operating parameters and sequences. As shown
in FIG. 2, switch elements 103 and 104 are normally in the "break"
condition when oven door 15 is open, thereby rendering the logic circuitry
inoperative at that time.
Switch elements 105 and 106 comprise the secondary interlock for microwave
oven 10. As with the primary interlock defined by switch elements 101 and
102, switch elements 105 and 106 are normally in the "break" condition
when oven door 15 is open, changing to the "make" condition only when oven
door 15 is fully closed and latched.
Switch elements 106 and 107 form part of a monitoring circuit which
includes a fuse (not shown), and are normally in the "make" condition when
the oven door is open. In accordance with conventional interlock switch
operation, if switch elements 106 and 107, and switch elements 105 and
106, are ever simultaneously closed, such as if a malfunction causes
switch elements 105 and 106 to be welded together, the fuse will blow,
thereby preventing operating power from being supplied to oven 10 even if
all other conditions for proper oven operation have been satisfied. Switch
element 106, sometimes referred to herein as a common switch element, has
a monitor side 106a and an interlock side 106b. A part 138 of switch
element 106 on the monitor side 106a is adapted to contact a portion 136
of switch element 107 near the free end 127 thereof when oven door 15 is
open. On the other hand, a part 132 on the interlock side 106b of switch
element 106 is adapted to contact a portion 134 of switch element 105 when
oven door 15 is fully closed and latched.
Finally, switch elements 108 and 109, which are normally in the "break"
condition when oven door 15 is open, form part of a second auxillary
circuit which may also include a lamp (not shown). In this preferred
embodiment switch elements 108 and 109 are disposed lower in housing 22
than any of the other switch elements 100 through 107. In particular,
switch elements 108 and 109 are located in a plane slightly above base 25
of housing 22, while switch elements 100 through 107 are located in a
plane closer to the top of housing 22.
A buss 90, preferably comprised of an integrally formed segment 94 of
switch element 102 and an integrally formed segment 92 of switch element
106 serves to electrically interconnect those two switch elements. For
safety purposes, buss 90 is mounted edgewise in gaps 75 and 77, thereby
being substantially captivated between interior front wall 34 on the one
hand, and the forward end 72 of stationary barrier 70 and the forward end
of movable barrier 64, i.e., hub 66 on the other hand. The segments 92, 94
comprising buss 90 are preferably formed by bending portions of switch
elements 102 and 106 until the ends of the bent portions are in facing
relationship. These ends of segments 92, 94 are then electrically
interconnected in any conventional manner.
Stationary barrier 70 and movable barrier 60, along with portions of rear
wall 24, side wall 26 and interior front wall 34, define a first
compartment 80 within housing 22 of interlock switch 20. First compartment
80 serves to confine, within that compartment, any pieces of interlock
switch 20 which, due to part failure, abuse, or manufacturing error,
become broken off and loose inside housing 22. By isolating such broken
off pieces in this manner, they cannot accidentally fall into a portion of
housing 22 outside the boundaries of first compartment 80 and accidentally
short circuit or interfere with other switch elements or components. For
the same purpose, stationary barrier 70, movable barrier 60 and additional
barrier 64, along with portions of rear wall 24 and interior front wall 34
define a second compartment 85, isolated from other portions of housing
22. Similarly, additional barrier 64, along with portions of rear wall 24,
side wall 28 and interior front wall 34 define a third compartment 88,
isolated from other portions of housing 22.
The operation of interlock switch 20 can now be explained. When oven door
15 is open, the switch elements of interlock switch 20 take the
configuration shown in FIG. 2. In this configuration, pin 61 provides a
force on switch element 101 substantially in the direction of arrow 140.
Similarly, pin 63 provides a force on switch element 105 substantially in
the same direction as arrow 140. On the other hand, pin 62 provides a
force on switch element 103 in the direction opposite arrow 140. Thus,
when actuator 50 is operated by latch pawl 18 (FIG. 6) the force opposing
the movement of actuator 50 is substantially reduced. In particular, if
the magnitude of the force at each of pins 61, 62 and 63 is substantially
equal, the combined force of pins 61, 62 and 63 opposing movement of
actuator 50 is approximately one third that which it would be if the
forces applied by all three pins 61, 62 and 63 were in the same direction
as arrow 140.
As oven door 15 begins to close, the operation of rigid pin member 17 and
actuator 40 takes effect. This, in turn, causes slider 44, and hence
actuator pins 47, 48 and actuator arm 49, to move from the positions shown
in FIG. 2 to the position shown in FIG. 3. Thus, switch elements 108 and
109 move from the "break" to the "make" position, while switch elements
107 and 106 move from the "make" to the "break" position. Further, switch
element 106 moves closer to (but still does not contact) switch element
105.
When oven door 15 is fully closed, and latch pawl 18 is latched to latch 39
(FIG. 6), the switch elements change from the positions shown in FIG. 3 to
the positions shown in FIG. 4. More particularly, switch elements 105 and
106 contact one another. Switch elements 103 and 104 move from the "break"
to the "make" position, switch elements 101 and 102 move from the "break"
to the "make" position, and switch elements 100 and 101 move from the
"make" to the "break" position.
The interlock switch described herein, when used in connection with an
electrical appliance such as microwave oven 10, provides many
efficiencies, economies, and safety features. For example, the use of
switch element 106 as a cantilevered common switch element adapted to
contact switch element 107 on one side of switch element 106 and to
contact switch element 105 on the other side of switch element 106,
combines the advantages of reliability, efficiency, economy, and
compactness in a single switch. Further, the use of stationary and movable
barriers of the type described isolates any pieces of interlock switch 20
which, due to part failure, abuse, or manufacturing error, become broken
off or loose inside housing 22. As such, these broken off pieces cannot
accidentally fall into portions of housing 22 outside the boundaries of
the compartments in which they are confined, and accidentally short
circuit or interfere with other switch elements or components.
Additionally, by captivating buss 90 in gaps 75 and 77, and forming it
integrally from portions of switch elements 102 and 106, the chances of
buss 90 breaking away and causing electrical or mechanical damage to the
other components of interlock switch 20 is greatly reduced.
In view of the foregoing, the above described interlock switch, adapted for
use with an electrical appliance such as a microwave oven, has numerous
benefits and advantages not available heretofore. However, several
modifications and embodiments of this switch, and its operating
environment, which do not part from the true scope of the invention, will
become apparent to those skilled in the art. Accordingly, all such
modifications and embodiments are intended to be covered by the appended
claims.
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