U.S. patent number 3,854,021 [Application Number 05/380,188] was granted by the patent office on 1974-12-10 for electromagnetic heating system which includes an automatic shielding mechanism and method for its operation.
This patent grant is currently assigned to Chemetron Corporation. Invention is credited to William E. Leyers, Donald G. Moore.
United States Patent |
3,854,021 |
Moore , et al. |
December 10, 1974 |
ELECTROMAGNETIC HEATING SYSTEM WHICH INCLUDES AN AUTOMATIC
SHIELDING MECHANISM AND METHOD FOR ITS OPERATION
Abstract
A tray inserted into an electromagnetic oven positions an energy
shield to interfit with elements on the tray to isolate selected
items upon the tray from the electromagnetic energy and operates
interlock devices to activate the microwave energy source.
Inventors: |
Moore; Donald G. (Glencoe,
IL), Leyers; William E. (Louisville, KY) |
Assignee: |
Chemetron Corporation (Chicago,
IL)
|
Family
ID: |
23500243 |
Appl.
No.: |
05/380,188 |
Filed: |
July 18, 1973 |
Current U.S.
Class: |
219/729; 426/234;
219/734; 219/736 |
Current CPC
Class: |
H05B
6/766 (20130101); H05B 6/6447 (20130101) |
Current International
Class: |
H05B
6/80 (20060101); H05B 6/76 (20060101); H05b
009/06 () |
Field of
Search: |
;219/10.55,85 ;99/447
;126/390 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Reynolds; Bruce A.
Attorney, Agent or Firm: Mason, Kolehmainen, Rathburn &
Wyss
Claims
What is claimed as new and desired to be secured by Letters Patent
of the United States is:
1. An electromagnetic oven system for heating materials carried on
a tray comprising an oven cavity having electrically conductive
walls and an open end for receiving trays inserted therein, a door
to open and close said open end, means for directing microwave
energy into said cavity, an electrically conductive shield mounted
for movement in said cavity between an open tray receiving position
and a closed position, means including said shield when in said
closed position and cooperating with the bottom wall of said cavity
to provide substantial shielding of a portion of a tray inserted in
said cavity from microwave energy therein, and actuator means for
moving said shield from said open to said closed position.
2. The oven system of claim 1 wherein said actuator means includes
linkage means interconnecting said door and said shield and switch
means responsive to said linkage whereby said switch assumes a
heating enabling position when a tray is properly shielded in said
oven.
3. The oven system of claim 1 including means for detachably and
pivotally interconnecting said shield and a rear wall of said
cavity, said actuator means including an element detachably
engaging said shield for operatively interconnecting the same with
said linkage means.
4. The oven system of claim 1 wherein said actuator means includes
a tongue extending into said cavity from said rear wall and having
a free outer end, said shield including attachment means for
receiving the free end of said tongue.
5. The combination of claim 1 wherein said shield includes opposed
side walls each having a lower edge, a strip in conductive relation
with the bottom wall of said cavity and adapted to interfit in side
by side shielding relation with a lower edge of at least one of
said side walls when said shield is in said closed position.
6. The combination of claim 5, which includes insulating means
positioned between said strip and said lower edge of said shield
when said shield is in said closed position, thereby to prevent
arcing between said strip and said lower edge of said shield.
7. The combination of claim 1 including on said tray conductive
means defining upstanding flanges adapted to interfit in side by
side shielding relation with lower edge portions of the side and
front walls of said shield when the latter is in said closed
position.
8. The combination of claim 7, which includes insulating means
positioned between said flanges and said lower edge portions when
said shield is in said closed position.
9. The oven system of claim 1 in combination with said tray, said
oven cavity having a conductive bottom wall for supporting said
tray and a rear wall adjacent one edge thereof, said tray including
a conductive strip on the upper surface thereof outlining at least
a part of said portion to be shielded, and said shield having at
least a front wall with a lower edge positioned adjacent said
conductive strip when the shield is in said closed position.
10. The oven of claim 1 wherein said actuator means includes a
depending spring within said shield for engaging the edge of a tray
as it is inserted in said oven cavity from said open end for moving
said shield from said open toward said closed position.
11. The oven of claim 10 wherein said spring is positioned to be
engaged by said tray before said tray is fully inserted in said
cavity whereby continued tray insertion and pivotal movement of
said shield toward said closed position proceed simultaneously.
12. The oven of claim 10 wherein said actuator means includes
second linkage means interconnecting said door and said shield for
biasing said shield forcefully against an inserted tray in response
to closing of said door.
13. The method of heating objects in a cavity adapted to receive
microwave energy comprising the steps of locating the objects in a
predetermined array on a tray, lowering a shield over the objects
in response to insertion of the tray in the cavity, and heating
those objects not within the shield.
14. The method of claim 13 including the step of securing said
shield in position over a tray in said cavity, and activating a
heating circuit in response to closing a door to the cavity.
15. An electromagnetic oven system for heating selected materials
on a tray comprising an oven cavity having an opening for receiving
trays, a door to open and close said opening, means defining a
horizontal conductive tray support in said cavity, means for
supplying microwave energy to said cavity, an electrically
conductive shield mounted for movement in said cavity between an
open tray receiving position and a closed position, means including
said shield when in said closed position and cooperating with said
tray support to provide substantial total shielding of a portion of
a tray inserted in said cavity from microwave energy therein, and
actuator means for moving said shield from said open to said closed
position.
16. The combination of claim 15, wherein said tray is made of
insulating material.
17. The combination of claim 16, wherein there is provided means
for preventing the bottom edge of said shield from producing
dielectric breakdown of the material of said tray in the vicinity
of said bottom edge when said shield is in said closed
position.
18. The combination of claim 15, wherein said tray is made of
plastic material, and conductive means on said tray and adapted to
cooperate with the bottom edge of said shield when in said closed
position to distribute the microwave field within the material of
said tray in the vicinity of said bottom edge.
19. The combination of claim 18, wherein said conductive means
includes a thin conductive strip secured to said tray and
positioned to be in the vicinity of the bottom edge of said shield
when said shield is in said closed position.
20. The combination of claim 19, wherein said conductive strip is
relatively wide as compared to said bottom edge of said shield,
thereby to reduce field concentration within the material of said
tray.
21. The combination of claim 15, wherein said tray is made of
insulating material and is provided with a relatively wide
conductive strip on the upper surface thereof in the vicinity of
the bottom edge of said shield when said shield is in said closed
position, thereby to prevent microwave energy from entering the
area of said tray covered by said shield.
22. The combination of claim 15, which includes means for moving
said shield from said open position to said closed position as said
tray is inserted into said cavity and in such manner that the
forward edge of said shield moves substantially vertically in
relation to said tray as it is inserted.
23. The combination of claim 15, which includes a member mounted on
said tray in a position somewhat ahead of the forward edge of said
shield when said shield is in said closed position, whereby said
member acts as a barrier to prevent food items from being
positioned in an area where they will be struck by said shield as
it is moved to said closed position.
24. The oven system of claim 15, wherein said actuator means is
responsive to insertion of a tray into said cavity for moving said
movable shield portion from said open to said closed position.
25. The combination of claim 15, which includes means for
preventing the application of microwave energy to said cavity in
the event said shield is not properly positioned relative to a tray
on said conductive tray support in said cavity.
26. The combination of claim 15, wherein said shield is detachably
mounted in said cavity, and means for preventing the application of
microwave energy to said cavity in the event a tray has been
inserted in said cavity and said door closed without said shield
also being mounted in said cavity.
27. An electromagnetic oven system for heating selected materials
on a tray comprising, an oven cavity having an opening for
receiving trays, means for supplying microwave energy to said
cavity, and shielding means at least a portion of which is attached
to and positioned within said cavity for substantially totally
shielding a portion of a tray positioned in said cavity from
microwave energy therein.
28. The combination of claim 27, which includes actuator means for
moving a portion of said shielding means from an open
tray-receiving position to a closed shielding position.
29. The combination of claim 28, wherein said movable shield
portion includes conductive side and front walls, the bottom edges
of which are positioned over said tray when said shield portion is
in said closed position, thereby to define said totally shielded
portion of said tray.
30. The combination of claim 28, wherein said shielding means
includes a rear wall of said cavity which cooperates with said
movable shield portion to define said totally shielded portion of
said tray.
31. The combination of claim 28, wherein said shielding means
includes a conductive tray support within said cavity which
cooperates with said movable shield portion to define said totally
shielded portion of said tray.
32. The combination of claim 28, wherein said movable shield
portion is pivotally mounted for movement within said cavity.
33. The combination of claim 32, wherein the tray is provided with
a rim portion, and means on said movable shield portion and adapted
to be engaged by said rim portion as the tray is removed from the
oven to facilitate pivotal movement of said shield portion to said
open position.
34. The combination of claim 28, which includes alarm means for
indicating when said movable shield portion is not properly
positioned relative to a tray which has been positioned in said
cavity.
35. The combination of claim 27, wherein said shield portion is
detachably mounted in said cavity, and alarm means for indicating
when a tray has been inserted into said cavity without said shield
portion being also positioned within said cavity.
36. An electromagnetic oven system for heating selected materials
on a tray comprising, an oven cavity having an opening for
receiving trays, means for supplying microwave energy to said
cavity, means for positioning a tray at a predetermined location
within said cavity, and shielding means at least a portion of which
remains in said cavity while a plurality of trays are successively
positioned within said cavity for substantially completely
shielding a portion of a tray positioned at said predetermined
location in said cavity from microwave energy therein.
37. The method of selectively heating objects in a cavity adapted
to receive microwave energy comprising the steps of, locating the
objects in a predetermined array on a tray with at least one of
said objects in a predetermined area of said tray which is
unshielded when outside said cavity, inserting said tray with said
objects located thereon into a predetermined area of said cavity,
substantially completely shielding said area of a tray when located
in said predetermined area of said cavity against microwave energy
therein, and supplying microwave energy to said cavity to heat
those objects outside said shielded portion of said tray.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
Applications Ser. No. 380,187 and 380,487 filed by Donald G. Moore
on the same day as the present application and assigned to the same
assignee as the present application disclose other aspects of the
preferred embodiment of the invention.
BACKGROUND OF THE INVENTION
The present invention relates to electromagnetic heating systems
and, more particularly, to systems which selectively heat various
elements of a load such as a complete meal or the like in a single
operation. In particular, the present invention provides a
combination for moving a shield over certain food items or the like
by inserting a tray conveying those items into an oven and to a
method for its operation.
In institutions, such as hospitals, it is desirable to provide a
means whereby a complete meal may be brought up to serving
temperature in a single, quick operation. If this can be done, the
meals may be prepared in an assembly-line fashion on weekdays and
during normal working hours, and then they may be kept refrigerated
until the time when they are to be served.
A typical meal normally includes some food items which require
heating before they may be served and other food items which are
preferably served cold. For example, the salad and dessert portions
of a meal are preferably served cold. The main entree of a meal is
preferably served hot. If a meal includes coffee or tea, the coffee
or tea is preferably served very hot.
A conventional oven ordinarily supplies heat energy to every
portion of the meal. In an electromagnetic oven, on the other hand,
any food item that is completely enclosed in an electrically
conductive wrapper or shield is not heated. It is therefore
possible to heat a complete meal in a microwave oven without
heating, for example, a dessert such as ice cream that is wrapped
in aluminum foil. However, wrapping all itmes such as desserts,
salads, and beverages such as milk in foil adds considerably to the
cost of preparing a meal. Difficulties may also arise any time a
shielded item is placed into an electromagnetic oven because the
shield distorts the electromagnetic field within the oven. Arcing
can also result, especially if the shielding has any sharp edges or
is positioned adjacent a conductive wall of the oven chamber.
Placing a protective box by hand on each tray over items to be kept
cool is effective but laborious and can result in errors of
misplacement or complete omission.
There is a need, therefore, for an improved apparatus and method to
provide shielding for selected items to be heated in a microwave
oven together with an interlock mechanism to operate the oven only
when the shield is properly in place.
BRIEF SUMMARY OF THE INVENTION
An object of this invention is the automatic shielding of some of
the objects in an oven from heating in the oven.
A primary object of the present invention is to provide a mechanism
which automatically shields some of the items on a tray from
electromagnetic energy when the tray is inserted into an
electromagnetic oven.
A further object of the invention is provision of a
position-sensing mechanism arranged to respond to the final
location of the shield and tray within the oven.
A still further object of the invention is provision of a mechanism
which gives forth an audible warning and disables the oven until
the problem is corrected when the shield is not properly seated
against the tray.
A further object of the invention is provision of a method for
heating objects to a non-uniform temperature in accord with a
controlled energy distribution and object placement in the
oven.
Other objects, features and advantages of the invention are
apparent in the detailed description which follows. The features of
novelty which characterize the invention are pointed out with
particularity in the claims annexed to and forming a part of this
specification.
These and other objects of the invention are achieved by provision
of an electromagnetic oven system for heating materials carried on
a tray comprising an oven cavity having conductive walls and an
open end for receiving trays inserted therein, a door to open and
close said open end, means for directing microwave energy into said
cavity, a conductive shield mounted for movement in said cavity
between an open tray-receiving position and a closed position
shielding a portion of a tray inserted in said cavity from
microwave energy therein, and actuator means responsive to the
insertion of a tray into said cavity for moving said shield from
said open to said shielding position.
The invention includes the method of heating objects in a cavity
adapted to receive heating amounts of microwave energy comprising
the steps of locating the objects in a predetermined array on a
tray, lowering a shield over the objects in response to the
insertion of the tray in the cavity and heating those objects not
within the shield.
In a preferred embodiment the method includes the steps of securing
the shield and activating a heating circuit in response to closing
of the door to the cavity.
The invention also includes the steps of grouping together items
which are to be heated in a first region called a heating zone, and
assembling items which are not to be heated in a second region
called a protected zone. In the preferred embodiment of the
invention, the items are arranged on a tray whereon the heating
zone is an L-shaped region which partially surrounds the protected
zone.
When a tray is inserted into the oven, the mechanism lowers a
shield within the oven to cover all items located in the protected
zone of the tray; closing the oven door secures the shield in place
and activates an enabling mechanism in the heating control
circuits. This shield may comprise a box-like structure that is
hingedly mounted within the oven and that is drawn down into
position either by the motion of the tray into the oven, by the
closure of the oven door, or by other equivalent means. Preferably,
the tray is supported by a conductive shelf or bottom wall of the
oven which also serves as a bottom wall for the box-like shield.
The back and side conductive walls of the oven may also cooperate
with the shield, if desired.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the invention, frequent references
will be made to the drawings wherein:
FIG. 1 is a front perspective view of a microwave oven constructed
in accordance with the teachings of the invention and showing the
shield in a raised position;
FIG. 2 is a perspective view of the shield which is shown hingedly
mounted within the oven of FIG. 1 and which is automatically
brought into position to shield certain food items resting upon the
tray shown in FIG. 3;
FIG. 2A is a front, elevational view of the shield shown in FIG.
2;
FIG. 3 is an isometric view of a tray for use in the oven shown in
FIG. 1, additionally adapted to cooperate with the shield shown in
FIG. 2, and also carrying a ferrite oven control element;
FIGS. 4 and 5 are sectional views of the oven shown in FIG. 1 taken
along the lines 4--4 in FIG. 1 to illustrate the manner whereby the
shield shown in FIG. 2 is brought down into place to protect items
upon a tray that is inserted into the oven;
FIG. 6 is a front sectional view taken along the lines 6--6 in FIG.
5 to illustrate engagement of the shield shown in FIG. 2 with
upstanding flanges upon a tray and the oven bottom to minimize the
amount of electromagnetic radiation which reaches the shielded
items placed upon the tray; and
FIG. 7 is a right-hand sectional view of the oven shown in FIG. 1
taken along the section lines 7--7 to show the mechanical mechanism
which is actuated when the oven door is closed and which secures
the shield into protecting position within the oven.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The preferred embodiment of the invention is a modified version of
a conventional microwave oven. A suitable oven is a system 70/80
MenuMaster oven sold by the Atherton Division of Litton Industries,
Inc., Minneapolis, Minnesota, but other conventional microwave
ovens may also be used in constructing the invention.
Referring now to the drawings, therein is illustrated an oven 100
having electrically conductive walls to accept food items
distributed over a tray as described below. The back wall 101 of
the oven has sockets 102 and 104 between which extends a movable
tongue 106. The floor 108 of the oven 100 is constructed from an
electrically conductive non-magnetic material. The oven floor and
back wall cooperate with the shield 200 to form a substantially
closed, electrically conductive enclosure.
An angle 109 secured to the floor and extending up and across the
back wall 101 acts as a guide for the tray and aids to seal the
shield 200 shown supported by the tongue 106 which is raised by
spring biasing means. Dotted lines 120 indicate elements of the
control mechanism which cooperate with a sensor on the tray to
control oven operation. Indicator lamps 116, 118, and 119 disclose
the condition of the oven operating sequence. Hook 402 assists in
supporting the door 112 and also operates elements of the interlock
mechanism as discussed further below.
FIG. 2 depicts the shield 200 which is shown pivotally mounted
within the oven 100 in FIG. 1. The shield 200 includes rearwardly
extending fingers 202 and 204 which engage corresponding sockets
102 and 104. Bracket 208 secures the shield to tongue 106. Leaf
spring 206 depends within the shield and, in part, lowers the
shield when a tray is in the oven.
The shield 200 has its lower edge 212 coated with an electrical
insulator 210, e.g., Teflon tape to prevent arcs from forming
between the shield 200 and the angle 109, upstanding flanges on the
tray 310 and 312 or the strip 318 (FIG. 3). The shield 200 is so
arranged within the oven 100 that when lowered into position over a
tray, it creates a region shielded from the electromagnetic
radiation that is developed within the oven 100.
Portions of the corners 214 and 216 are provided with contours
which complement the edges of the tray against which it is located
in the protecting position. In alternate embodiments, a plurality
of leaf springs of similar configuration to spring 206 may assist
in lowering the shield. The bracket 208 may be formed integrally
with the top of the shield.
The tray 300 shown in a preferred embodiment in FIG. 3, has an
upper side 301 and edges 301A. An L-shaped conductive strip 318 on
its upper side 301 supports a pair of conductive, upstanding
flanges 310 and 312 which in part define zones 302, 304, and 306
within which load items may be placed and provide coupling to the
cavity floor for microwave energy. Since the flanges 310 and 312
engage the shield 200 on opposite surfaces, it is necessary to have
the two flanges 310 and 312 separated from one another by a notch
322.
The flanges 310 and 312 in the L-shaped strip 318 have dimensions,
including radii, which are selected to reduce field concentrations
and to effect an electromagnetic energy seal with the floor of the
oven and with the front and side wall of the shield 200. The body
of the tray is constructed from polyester fiber glass which has
excellent mechanical strength but only fair dielectric properties.
Barrier 319 serves to direct load items to locations where they
will not interfere with the lowering of the shield. In a preferred
embodiment, a ferrite sensor 308 is cemented or otherwise attached
to each of the trays 300 and is part of the oven control system. A
cover 314 overlies the sensor 308 to provide mechanical protection
in addition to regulating the amount of microwave energy which
reaches the sensor.
As is illustrated in FIGS. 4-6, tongue 106 extends outwardly from
the oven back wall and engages bracket 208 upon the top of the
shield 200. The tongue is rigidly attached to a shaft 416 (FIGS. 4,
5 and 7) which runs the length of the back wall 101 of the oven 100
and which is mounted at its two ends by means not shown which
permit the shaft 416 to rotate. The shaft 416 is also rigidly
attached to a lever 412 (FIGS. 4, 5, and 7) which extends forwardly
along the right-hand wall of the oven 100 (see FIG. 4). A first
spring 414 normally biases the lever 412 to apply an angular torque
to the shaft 416 which tends to rotate the tongue 106 upwards
within the oven. A stop (not shown) limits the upward motion of the
tongue 106. When the rearwardly-extending fingers 202 and 204 of
the shield 200 are inserted into sockets 102 and 104 in the back of
the oven, the bracket 208 is slipped over the tongue 106 so that
the angular positioning of the shield 200 within the oven is
determined by the position of the tongue 106. The bias applied to
the lever 412 by the spring 414 causes the tongue 106 to hold the
shield 200 normally suspended in air when no tray is present.
Other features of the mechanism are illustrated in FIG. 7. A crank
406 mounted to rotate about its support 407 is connected by chain
408 to a hook 402 mounted on the door 112. Tension spring 420
opposes the action of the chain. The end 409 of the crank is
connected by spring 410 to the lever 412. A SPDT switch 418 is
mounted for actuation by the lever 412 and a normally open switch
422 is located for actuation by the end 409 of the crank 406. The
normally open contacts of the switch 418 are connected into the
oven control circuit and the normally closed contacts are in an
alarm circuit with contacts of the switch 422.
In operation of an embodiment of the invention, food itmes are
arranged on a tray so that items not to be heated are all placed
within the protected zone 303; food items to be heated are placed
within one of the heating zones 302, 304 and 306.
When the tray 300 is inserted into the oven 100, the leading edge
320 of the tray engages the leaf spring 206 and draws the sheild
200 down substantially over the region 303 on the tray.
The tension of the spring 414 is relatively weak and is easily
overcome when a tray 300 presses against the leaf spring 206 that
is attached to the shield 200. Since the tray is moving rearwardly
at the same time that the leading lower edge 212 of the shield 200
is moving through a rearwardly-directed arc, both the tray 300 and
the lower edge 212 are simultaneously moving in the same direction,
so that the edge 212 moves almost straight down relative to the
tray 300 and does not strike food items 326 positioned toward the
front of the tray. If the shield 200 were brought into position
only by closure of the oven door 112 and not by motion of the tray
300, then the rearwardly-directed arc through which the leading
edge 212 of the sheild 200 swings would sweep over the heating
region of the tray, possibly striking against taller food items
positioned in that region. The action of the leaf spring 206
eliminates this problem and allows larger items to be placed upon
the tray than would otherwise be possible. If the leaf spring 206
is omitted from the shield 200, then the shield 200 is brought
downwards over the tray 300 by the tongue 106 which is actuated by
the closure of the oven door 112.
If a food item does happen to get under the leading edge 212 of the
shield 200, the leaf spring 206 flexes and does not permit the
shield 200 or the food item to be damages. In a preferred
embodiment, the relatively weak leaf spring 206 need not completely
seat the shield 200 upon the tray 300 as a separate door-actuated
lever mechanism is provided for that purpose.
As shown in FIG. 7, while the door 112 of the oven is open, a hook
402 attached to the door 112 pulls on a chain 408 to stretch a
spring 420 and rotate the crank 406 so that the crank 406 applies
no tension to the spring 410. The spring 410 thus has no effect
upon the lever 412 when the oven door 112 is open.
When the oven door 112 is closed, the chain 408 goes limp and
permits the spring 420 to rotate the crank 406 in a clockwise
direction to the limit of its travel. The spring 410 then exerts a
strong effort upon the lever 412. This effort develops a torque
which is transmitted by the shaft 416 to the tongue 106 and thence
to the shield 200. This torque seats the sheild 200 firmly upon the
tray 300 within the oven 100.
The normally open contacts of a position-sensing SPDT electrical
switch 418, mounted adjacent the lever 412, are closed by the lever
412 only if the lever 412 is rotated into a position corresponding
to a properly-seated shield 200. If the shield 200 is prevented
from seating properly, then the lever 412 does not swing far enough
to actuate the switch 418. If the shield 200 is not in place when
the oven door is closed, then the lever 412 is free to rotate
beyond the position at which it actuates the switch 418 and again
the contacts do not close. Unless the lever 412 closes the contacts
of the switch 418, the heating circuits of the oven do not
function. If the switch 418 is not actuated when the oven door is
closed, the normally closed contacts enable switch 422 to give an
audible warning to the oven operator that something is amiss.
After the oven door 112 is closed, heating of the food items within
the zones 302, 304 and 306 commences. The interior of the oven is
flooded with microwave energy at a frequency of 2,450 megacycles
generated by a conventional magnetron microwave energy source.
During the heating process, HEATING lamps 116 on the front of the
oven are illuminated to signal that microwave energy is, in fact,
being supplied to the oven. When the heating process if finished, a
SERVE lamp 119 automatically comes on to signal that the tray may
be removed from the oven. At this time, the oven door 112 is opened
by grasping and pulling down on the handle 114 and the tray 300 is
removed from the oven 100. Engagement of the corner 216 of the
shield with the rear rim of the tray as the tray is withdrawn aids
in elevating the shield to its raised position. All items within
the protected zone 303 are still cold, since they were shielded by
the shield 200; other items upon the tray have been heated.
While the embodiment illustrated herein was described with
reference to the automatic ferrite control of application Ser. No.
380,187, it will be understood by those skilled in the art that the
shield and interlock mechanisms are equally adaptable to a timer
controlled oven.
The apparatus and method of this invention also are useful with
conventional oven having convection or radiant heat when the shield
200 is fabricated from material having low thermal conductivity and
preferably low heat capacity.
Although the present application has been described with reference
to an illustrative embodiment thereof, it should be understood that
numerous other modifications and embodiments may be devised by
those skilled in the art that will fall within the scope of the
present invention.
* * * * *