U.S. patent number 3,742,178 [Application Number 05/213,335] was granted by the patent office on 1973-06-26 for induction cooking appliance including cooking vessel having means for wireless transmission of temperature data.
This patent grant is currently assigned to General Electric Company. Invention is credited to John D. Harnden, Jr..
United States Patent |
3,742,178 |
Harnden, Jr. |
June 26, 1973 |
INDUCTION COOKING APPLIANCE INCLUDING COOKING VESSEL HAVING MEANS
FOR WIRELESS TRANSMISSION OF TEMPERATURE DATA
Abstract
Herein disclosed is an induction cooking range having a counter
which supports a food-containing vessel. The vessel is heated by
the range's induction coil which operates at high frequency. The
invention includes a temperature sensing unit comprising a
temperature detection unit and a temperature receiving unit. The
former unit is incorporated in the cooking vessel while the latter
unit is remotely located therefrom in the induction range. The
aforesaid temperature receiving unit receives radio frequency
transmissions of temperature data from the temperature detection
unit in the vessel. The temperature detection unit in the vessel is
powered by the main field produced by the induction coil.
Inventors: |
Harnden, Jr.; John D.
(Schenectady, NY) |
Assignee: |
General Electric Company
(Schenectady, NY)
|
Family
ID: |
22794703 |
Appl.
No.: |
05/213,335 |
Filed: |
December 29, 1971 |
Current U.S.
Class: |
219/627;
220/592.22; 219/621; 219/667; 220/573.1; 219/385; 219/501;
340/870.17; 340/870.31; 340/870.39; 374/141 |
Current CPC
Class: |
A47J
27/002 (20130101); A47J 36/321 (20180801); H05B
6/062 (20130101); H05B 2213/07 (20130101); H05B
2213/06 (20130101) |
Current International
Class: |
A47J
27/62 (20060101); A47J 27/00 (20060101); A47J
27/56 (20060101); H05B 6/06 (20060101); H05B
6/12 (20060101); H05b 005/04 () |
Field of
Search: |
;219/10.49,10.75,10.77,450,501 ;340/210 ;220/9R ;73/362,343R
;307/117 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Truhe; J. V.
Assistant Examiner: Reynolds; B. A.
Parent Case Text
CROSS-REFERENCES TO RELATED APPLICATIONS
A fuller appreciation of induction cooking appliances, generally,
as well as some of the sophistications which may be embodied
therein is to be had by referring to the following U.S. Patent
applications: Ser. No. 200,526, filed Nov. 19, 1971, in behalf of
David L. Bowers et al., titled SOLID STATE INDUCTION COOKING
APPLIANCE; Ser. No. 200,424, filed Nov. 19, 1971, in behalf of J.D.
Harnden, Jr. et al., titled SOLID STATE INDUCTION COOKING
APPLIANCES AND CIRCUITS. The entire right, title and interest in
and to the inventions described in the aforesaid patent
applications, as well as in and to the aforesaid applications, and
the entire right, title and interest in and to the invention
hereinafter described, as well as in and to the patent application
of which this specification is a part, are assigned to the same
assignee.
Claims
What is claimed is:
1. In combination, an induction heating appliance and a vessel said
appliance comprising vessel supporting means for supporting said
vessel, said supporting means being of a non-magnetic material in
which no substantial heating current is induced when subjected to a
changing magnetic field, an induction coil proximate said
supporting means but separated from the vessel by the supporting
means which is situated between said coil and said vessel, said
coil being energizable for producing a main changing magnetic
field, means for energizing said coil with electric power, and a
temperature receiving unit included in said appliance; said vessel
comprising a portion in which heating current is induced by said
main changing magnetic field when said vessel is supported by said
supporting means, and a temperature detection unit supported by
said vessel, said temperature detection unit including a
temperature sensor unit for sensing the temperature of said vessel,
said temperature detection unit being energizable by said main
changing magnetic field to produce an auxiliary changing magnetic
field which contains temperature data corresponding to the
temperature sensed by said temperature sensor unit, said
temperature receiving unit including means responsive to said
auxiliary changing magnetic field for producing a signal
representative of the temperature sensed by said temperature sensor
unit, said temperature detection unit supported by said vessel
being further comprised of a pick-up coil for developing a first
voltage when subjected to said main changing magnetic field, a
rectifier for converting said first voltage to a rectified second
voltage, a voltage controlled oscillator energized by said second
voltage for producing a variable frequency output signal, said
temperature sensor unit providing an impedance corresponding to a
temperature sensed by said sensor unit, said temperature sensor
unit being electrically coupled with said voltage controlled
oscillator whereby said oscillator produces an output signal of a
frequency corresponding to the temperature sensed by said sensor
unit, and a transmitting coil electrically coupled with said
voltage controlled oscillator for producing said auxiliary changing
magnetic field corresponding to the output signal produced by said
oscillator.
2. An inductively heatable vessel comprising: a first metallic wall
member and a second non-metallic wall member having portions
thereof sealed together to form a sealed double-walled vessel
having an enclosed space between said wall members, said first wall
member forming an inside wall surface of said vessel, said first
wall member having heating current induced therein when said first
wall member is subjected to a changing magnetic field, said second
non-metallic wall member having no substantial heating current
induced therein when subjected to a changing magnetic field, said
second wall member serving as a supportable outside wall of said
vessel, a temperature detection unit located within said space
between said wall members, said temperature detection unit
including a temperature sensor unit for sensing the temperature of
at least said first wall member, said temperature detection unit
being further comprised of a pick-up coil, a rectifier, an
oscillator and a transmit coil, said pick-up coil producing a first
voltage in response to the changing magnetic field to which said
first wall member is subjected, said rectifier producing from said
first voltage a rectified voltage, said oscillator being driven by
said rectified voltage and producing a variable frequency output
signal corresponding to a temperature sensed by said temperature
sensor unit, said transmit coil in response to the output signal
produced by said oscillator producing an auxiliary changing
magnetic field, said auxiliary changing magnetic field containing
temperature data corresponding to the temperature sensed by said
sensor unit.
3. In combination, an inductively heatable vessel and a temperature
receiving unit located remotely from said vessel, said vessel
comprising a first metallic wall member and a second non-metallic
wall member, said wall members having portions thereof sealed
together to form a double-walled vessel having an enclosed space
between said walled members, said first metallic wall member
forming the inside surface of said vessel, said first wall member
being adapted for having heating current induced therein when
subjected to a changing magnetic field, said second non-metallic
wall member having no substantial heating current induced therein
when subjected to a changing magnetic field, a temperature
detection unit located within said space between said wall members,
said temperature detection unit including a temperature sensor unit
for sensing the temperature of at least said first wall member,
said temperatue detection unit including means for transmitting an
auxiliary changing magnetic field containing data representative of
the temperature sensed by said temperature sensor unit to said
remotely located temperature receiving unit, said remotely located
temperature receiving unit comprising a receiving coil adapted for
being magnetically coupled with said auxiliary changing magnetic
field and for producing an electrical signal therefrom
representative of the temperature sensed by said temperature sensor
unit of said temperature detection unit and a temperature signal
processing circuit for processing the signal from said receiving
coil to produce another signal representative of said temperature
sensed by said temperature sensor unit, and display means coupled
with said temperature signal processing circuit for indicating the
temperature sensed by said temperature sensor unit, said
temperature detection unit further comprising a pick-up coil, a
rectifier, an oscillator and a transmit coil, said pick-up coil
producing a first voltage in response to the changing magnetic
field to which said first wall member is subjected, said rectifier
producing from said first voltage a rectified voltage, said
oscillator being driven by said rectified voltage and producing a
variable frequency output signal corresponding to a temperature
sensed by said temperature sensor unit, said transmit coil in
response to the output signal produced by said oscillator producing
the auxiliary changing magnetic field, said auxiliary changing
magnetic field containing temperature data corresponding to the
temperature sensed by said sensor unit.
4. In combination, an induction cooking appliance and a cooking
vessel, said appliance comprising vessel supporting means in which
no substantial heating current is induced when subjected to a
changing magnetic field, an induction coil proximate said
supporting means but separated from the vessel by the supporting
means which is located between the vessel and the coil, said coil
being energizable for producing a main changing magnetic field,
means for energizing said induction coil with electric power, and a
temperature receiving unit supported by said appliance, said vessel
comprising a first metallic wall member and a second non-metallic
wall member, said wall members having portions thereof sealed
together to form a double-walled vessel with an enclosed space
between said wall members, said first metallic wall member forming
the inside surface of said vessel and being adapted for containing
foodstuff to be cooked, said first wall member and also being
adapted for having heating current induced therein when said vessel
is supported by said vessel supporting means such that said first
wall member of said vessel is subjected to said main changing
magnetic field, a temperature detection unit located within said
space between said wall members, said temperature detection unit
including a temperature sensor unit for sensing the temperature of
at least said first metallic wall member, said temperature
detection unit being energizable by said main changing magnetic
field to produce an auxiliary changing magnetic field containing
temperature data corresponding to the temperature sensed by said
temperature sensor unit, said temperature detection unit further
comprising a pick-up coil for developing a first voltage when
subjected to said main changing magnetic field, a rectifier for
converting said first voltage to a rectified second voltage, a
voltage controlled oscillator energized by said second voltage for
producing a variable frequency output signal, said temperature
sensor unit providing an impedance corresponding to a temperature
sensed by said sensor unit, said temperature sensor unit being
electrically coupled with said voltage controlled oscillator
whereby said oscillator produces an output signal of a frequency
corresponding to the temperature sensed by said sensor unit, and a
transmitting coil electrically coupled with said voltage controlled
oscillator for producing an auxiliary changing metallic field
corresponding to output signal produced by said oscillator, said
auxiliary magnetic field containing temperature data corresponding
to the temperature sensed by said temperature sensor unit, said
temperature receiving unit including means responsive to said
auxiliary changing magnetic field for producing a signal
representative of the temperature sensed by said temperature sensor
unit.
Description
BACKGROUND OF THE INVENTION
This invention pertains to induction cooking, or warming,
appliances, generally; and, in particular to an induction cooking,
or warming, appliance including an induction coil for heating a
food-containing vessel and for energizing a temperature detection
unit incorporated in the vessel whereby said temperature detection
unit initiates wireless transmission of temperature data from the
vessel to a receiving unit which may be remotely located on the
appliance.
Prior art electric ranges (i.e., those employing resistance heater
surface elements) and gas ranges present a number of problems with
respect to temperature sensing. With such prior art ranges the
approach most often employed is to directly sense the temperature
of the vessel. For this purpose a contact-type temperature sensor
unit is usually employed; i.e., the temperature sensor unit is
placed so that it is in direct contact with the cooking vessel
being heated. The vessels involved are usually fabricated from cast
iron, stainless steel, copper, or copper-clad stainless steel, etc.
These vessels are considered conventional and are abundantly
available. Temperature sensing as done in the prior art has not
proved entirely satisfactory for, among others, the following
reasons:
First, with prior art electric and gas ranges the primary heating
source (e.g., the surface mounted electrical resistance coils or
the gas fed flames) spuriously heats the temperature sensing unit
and, moreover, other heated parts of the range thermally perturb
the temperature sensing unit as well.
Second, in prior art electric and gas ranges because of the
relatively high temperatures involved, principally because of the
nature of the primary heating source and its proximity to the
vessel-contacting temperature sensor, the materials from which the
temperature sensing units and their associated components may be
fabricated are rather restricted.
Third, in prior art electric and gas ranges, principally because of
the high temperatures occasioned by the nature of the primary
heating source and its proximity to the contract-type temperature
sensing unit extensive thermal shielding, or insulation, is
required.
Fourth, in prior art electric and gas ranges because of the severe
thermal stresses created in the vessel-contacting temperature
sensing unit, as a consequence of the high tenperatures occasioned
by the nature of the primary heating source and its proximity to
the temperature sensing unit, relatively massive and sophisticated
as well as somewhat mechanically complex spring arrangements and
structures were required for the purpose of maintaining adequate
contact between the temperature sensing unit and the cooking
vessel.
The four problems, hereinbefore mentioned, are discussed in greater
detail hereinafter.
In prior art electric and gas ranges the temperature sensing means
and its associated components are directly heated, spuriously, in
some measure by a high temperature primary heating source. For
example, in the conventional electric range a temperature sensing
unit is located at the center of a spirally wound resistance
heating coil. This heating coil and the temperature sensing unit
are both mounted on the top or the working surface of the range
counter. A cooking vessel rests on and contacts the heating coil as
well as the temperature sensing unit. Although the temperature
sensing unit directly contacts the heated cooking vessel, it is
also subjected to direct spurious heating by the range's heating
coil; e.g., by radiation and convection. In addition, the
temperature of the temperature sensing unit is influenced by, among
other things, the metallic counter of the electric range. Similarly
in a gas range, the flames directly heat the temperature sensing
unit. Moreover, heated metallic gridirons as well as the heated
metallic counter top thermally influence the temperature sensing
unit.
Also, in prior art electric and gas ranges, because of the nature
of the primary heating source and its proximity to the temperature
sensing unit, various component parts of the temperature sensing
unit have to be fabricated with materials which are capable of
withstanding relatively high temperatures; e.g., approximately
1,400.degree.F-1,600.degree.F. For example, in the conventional
prior art electric range wherein the temperature sensing unit is
located at the center of the spiral resistance heating coil which
is, in turn, mounted on the metallic counter top of the range, the
temperature sensing unit and its associated components are
subjected to the elevated temperatures hereinbefore set forth.
Significant thermal stresses are, as a result, induced in the
temperature sensing unit as well as in its associated components.
Similar conditions occur in gas ranges.
In prior art electric and gas ranges, principally because of the
nature of the primary heating source and its proximity to the
temperature sensing unit contacting the cooking vessel, the
temperature sensing unit as well as its associated components are
required to have extensive thermal shielding, or insulation, for
the purpose of minimizing the influences of spurious heating by the
high temperature heating source as well as by the metallic range
counter and metallic gridirons. Without some effective thermal
shielding or insulation, the temperature sensing unit will provide
a false indication of temperature unless temperature compensation
is appropriately applied. However, such compensation is not
feasible because of the wide range of cooking conditions. For
example, it is very difficult to achieve a system in which both
steady-state and transient, or dynamic, compensation is easily
achieved. In any event, cooking performance is compromised.
Moreover, without effective thermal shielding severe thermal
stresses induced in the various component parts of the temperature
sensing unit will cause a disabling, or sometimes destruction of
the temperature sensing unit.
The prior art temperature sensing units, especially those which are
employed with the prior art electric ranges for the purpose of
contacting the cooking vessel, are generally massive and are of a
rather sophisticated and somewhat mechanically complex structure
and arrangement. The high temperature environment within which the
temperature sensing unit is located permits severe thermal stresses
to be induced in the various components of the temperature sensing
unit. These stresses tend to promote warping of the various
components. For example, because of the aforesaid thermal stresses,
a relatively massive double-spring arrangement is usually employed
in combination with a temperature responsive device. The
temperature responsive device, acting against spring restraint,
contacts the bottom surface of the cooking vessel. The vessel rests
on a flat spiral heating coil disposed on the top surface of the
range counter. The massive double-spring arrangement is rather
stiff and this is due in large part to the need to make the
arrangement structurally resistant to thermal deformation. Such a
spring arrangement generally functions satisfactorily to enable the
temperature sensing unit to contact a relatively smooth flat-bottom
surface of a relatively heavy cooking vessel such as a cast iron
pot containing foodstuff to be cooked. Being in contact with the
surface of the vessel, it is conceptually possible for the
temperature sensing unit to detect the temperature of the vessel.
However, in the event that a relatively light weight pot is used or
if a pot having a rather irregularly contoured bottom surface is
used, such prior art contact type temperature sensing units
employing the aforesaid stiff spring arrangement proved
unsatisfactory. For example, if a cooking vessel is used which is
not sufficiently heavy, there will be an insufficient weight to
adequately compress the spring arrangement. One consequence will be
that the vessel will not rest on the resistance heating coil in the
most intimate contact possible therewith. The cooking vessel will,
as a result, be raised or tilted and thereby allow inefficient heat
transfer between the resistance heating coil and the vessel. In
addition, a prior art contact-type sensor unit could not,
obviously, be applied to a double-walled cooking vessel where no
relationship exists between inner and outer wall temperatures;
i.e., no relationship between the cook surface temperature and the
outer wall temperature. Secondly, physical space or clearance
resulting with vessels having feet which rest on counter tops in
prior art ranges would require sensors having springs to make
conventional temperature sensing heads travel rather large
distances.
SUMMARY OF THE INVENTION
Although the invention is hereinafter described, and illustrated in
the accompanying drawings, as being employed in combination with an
induction range it is, nevertheless, to be understood that the
invention's applicability is not limited to induction cooking
ranges but may be embodied in, for example, portable counter top
warming or cooking appliances, such as warming trivets, as well as
in other types of induction heating apparatus which need not,
necessarily, be used for cooking or warming food.
One object of the invention is the provision of an induction
cooking/warming appliance including a cooking/warming vessel, said
appliance including a temperature sensing unit for sensing or
detecting the temperature of cooking/warming vessel or utensil
being heated.
Another object of the invention is the provision of an induction
cooking/warming appliance including the aforesaid temperature
sensing unit wherein said sensing unit is free from spurious
heating.
Another object of the invention is the provision of an induction
cooking/warming appliance including the aforesaid temperature
sensing unit, the materials of fabrication of said temperature
sensing unit not being restricted by the elevated temperatures
heretofore encountered in prior art electric and gas ranges.
Another object of the invention is the provision of an induction
cooking/warming appliance including the aforesaid sensing unit,
said temperature sensing unit not requiring the thermal insulation
or shielding in the ways or to the extent heretofore employed in
prior art electric and gas ranges.
Another object of the invention is the provision of an induction
cooking/warming appliance including the aforesaid temperature
sensing unit, said temperature sensing unit being capable of
accurately sensing the temperature of the vessel regardless of the
weight of the vessel and/or the weight of the food therein and/or
regardless of whether the vessel has or has not an irregular outer
surface or contour; said temperature sensing unit not requiring the
prior art spring construction or arrangement.
Another object of the invention is the provision of an induction
cooking/warming appliance including a temperature sensing unit
which can accurately detect the temperature of the vessel
regardless of the fact that the vessel may have an outer wall which
is thermally non-conductive.
Another object of the invention is the provision of an induction
cooking/warming appliance including the aforesaid temperature
sensing unit for sensing the temperature of a vessel being heated;
said vessel being supported by a vessel supporting means having an
uninterrupted working surface.
Another object of the invention is the provision of an induction
cooking/warming appliance including wireless means for transmitting
temperature data from the vessel to a location which is relatively
remote from the vessel.
Another object of the invention is the provision of an induction
cooking/warming appliance including wireless means for transmitting
temperature data from a vessel being heated to a location remote
therefrom; said wireless means being powered by a portion of the
main induction field which is employed for heating the vessel.
Another object of the invention is the provision of a novel
cooking/warming vessel which is adapted for being inductively
heated as well as for initiating the wireless transmission of
temperature data from the vessel to a relatively remote
location.
The invention, hereinafter described and illustrated in the
accompanying drawings, enables the achievement of the
aforementioned objectives, as well as others, in that there is
provided an induction cooking or warming appliance and a vessel
adapted for being inductively heated. The vessel includes a portion
in which heating current may be induced for the purpose of heating
said portion as well as food contained within said vessel. The
cooking appliance is comprised of a vessel supporting means in
which no substantial heating current is induced when the supporting
means is subjected to a changing magnetic field. The vessel
supporting means includes a surface which is adapted for supporting
the vessel. Advantageously, the aforementioned surface of the
vessel supporting means may be an uninterrupted surface which may
also serve as a working surface for the preparation of food, among
other things. The cooking appliance is provided with an induction
coil which is energizable from a suitable power source so as to
provide a changing magnetic field of at least ultrasonic frequency.
The changing magnetic field causes heating current to be induced in
the aforementioned inductively heatable portion of the cooking
vessel. As a result, food contained within the vessel may be
heated. Also provided is a temperature sensing unit which is
comprised of a temperature detecting unit and a temperature
receiving unit. Briefly, the temperature detecting unit is
incorporated in the vessel and said unit derives power from the
aforementioned changing magnetic field produced by the remote
induction coil. With the power thus derived, the temperature
detecting unit is enabled to transmit temperature data acquired by
a temperature sensor unit located in the vessel to a temperature
receiving unit which may be remotely located elsewhere on the
cooking appliance. The temperature receiving unit includes a
receiving coil which is coupled with a temperature signal
processing circuit. Temperature data received by the receiving coil
is processed in the temperature signal processing circuit and a
signal is developed which is representative of the temperature of
interest.
One feature of the invention resides in the transmission of
temperature data from a temperature detection unit to a remotely
located temperature receiving unit. Such transmission is made at
sufficiently high frequency so that the energy contained in the
harmonic distortion of the main field produced by the induction
coil is far less than the transmitted frequency which contains the
temperature data.
Another feature of the invention resides in the provision of a
novel cooking/warming vessel in which there is incorporated various
electrical and electronic components; i.e., those components of
which the temperature detection unit is comprised.
Other objects and features, as well as a fuller understanding of
the invention, will appear by referring to the following detailed
description, claims and drawings.
DESCRIPTION OF THE DRAWING FIGURES
FIG. 1 is an enlarged cross section view of a cooking vessel
supported on the counter of an induction cooking range, the vessel
having incorporated therein a temperature detection unit which is
part of the present invention.
FIG. 2 is a block diagram showing the electrical system for heating
the vessel and for transmitting temperature data from the vessel by
wireless means.
FIG. 3 is a cross section view similar to that shown in FIG. 1; the
vessel and its various component parts exemplifying a modification
of the vessel shown at FIG. 1.
FIG. 4 is a perspective view of an induction cooking range showing
the top or working surface of the range on which there is supported
a cooking vessel like that shown in either FIGS. 1 or 3.
DESCRIPTION OF PREFERRED EMBODIMENTS
Referring first to FIG. 4, there is illustrated an induction
cooking range designated generally by the reference number 20. The
range 20 is provided with a counter 22 which is suitably supported
by a range substructure 24. Located at the rear of counter 22 and
fastened to substructure 24 is an instrument and control panel 26.
On panel 26 there is mounted a number of controls 28 and a like
number of temperature indicators, which may be dial-type
thermometers 30. On the top or working surface of counter 22 there
is illustrated four dotted line circles. These circles suggest
locations where four cooking vessels such as pots, pans, etc. may
be located during the cooking process. As shown, a cooking vessel
34 is rested on the working or top surface of counter 22, covering
one of the dotted line circles. Below each of the dotted line
circles under counter 22 is an induction coil 36. Induction coil 36
is separated from the bottom surface of counter 22 by air gap;
induction coil 36 being a relatively flat spirally-wound coil. The
induction coil 36 has formed at the center thereof a central
aperture designated generally by the reference number 38. The
induction coil 36 is electrically connected as shown in FIGS. 1 and
2 to the output of a solid state inverter 44 which, in turn, has an
input which is electrically connected to the output of the
rectifier 46. The inverter 44 is a solid state inverter and as
combined with rectifier 46 forms a static power conversion circuit
designated generally by the reference number 43. The rectifier 46
includes an input which is electrically connected to a conventional
A.C. source 48 which may be a 60 Hz, single phase, 110 or 220 volt
source. More specific details of the static power conversion
circuit 43 including rectifier 46 and inverter 44 may be had by
referring to the patent applications hereinbefore noted. Also shown
in FIGS. 1 and 2 is one of the controls 28 which may, for example,
be a switch which is electrically coupled with inverter 44 for the
purpose of controlling the flow of power therefrom to the induction
coil 36. The control 28 is marked in degree F settings to enable a
housewife to "call for" a particular temperature or temperature
range performance. However, a temperature indicator 30 associated
with a particular control 28 provides a visible indication of the
actual temperature of vessel 34. The temperature indicator 30
provides, in addition, an indication of the rate of temperature
rise and fall. These rates of temperature change are considered to
be an important aspect of the cooking process.
While a dial-type thermometer 30 is illustrated and disclosed
herein, it is to be understood that a digital display of
temperature or temperature range or rate may be employed.
The rectifier 46 may be a regulated full-wave bridge rectifier
employing solid state devices and operating to convert A.C. input
power to D.C. output power. Also, inverter 44 employs SCR's which,
in the performance of their control switching function, enable the
inverter 44 to deliver relatively high frequency power (ultrasonic
or above) to drive, or power, the induction coil 36.
As discussed in more detail hereinafter, the vessel 34 has
incorporated therein a temperature detection unit which radiates a
high frequency signal representative of the sensed temperature of
the cooking vessel. This radiated signal is received by a
temperature receiving unit designated generally by the reference
number 50. The temperature receiving unit being located, as shown
in FIGS. 1 and 3, below the range counter 22. From the temperature
receiving unit 50 the aforementioned radiated electromagnetic
signal is converted to an electrical signal and delivered to an
input of a temperature signal processing circuit 45 (FIGS. 1 and 2.
). The temperature signal processing circuit 45 then develops an
output signal representative of the temperature of cooking vessel
34 and this output signal is ultimately delivered to the electrical
temperature indicator 30.
As indicated at FIGS. 1 and 2 the temperature signal processing
circuit 45 includes: a first input coupled to the rectifier 46 for
deriving therefrom a D.C. voltage; a second input in the form of a
pair of electrical conductors which extend from a receiving coil 54
of temperature receiving unit 50, and, an output comprising a pair
of conductors directly connected to the thermometer 30.
In the cross section view of FIG. 1 one embodiment of cooking
vessel 34 is illustrated. As shown, vessel 34 is comprised of an
outer cup, or cup-like, member 70. Nested within the outer cup 70
is an inner cup 71. At the top rim of vessel 34 where the inner and
outer cups 71 and 70 contact each other they are bonded and sealed
so as to provide a hermetically sealed double wall vessel 34. The
space between the inner wall surfaces of the cups 70 and 71 may, as
shown, be filled with thermal insulation material 72. In the
alternative, the space between the inner wall surfaces of the cups
70 and 71 may be air filled or they may be evacuated. The inner cup
71 may be formed from a relatively thin sheet of magnetic stainless
steel. Generally, the inner cup 71 is preferably formed from a
material which: is magnetically permeable, is electrically
conductive; has a relatively high electrical resistivity; and, is
thermally conductive. Materials other than stainless steel may be
used. The outer cup 70 may, as indicated, be formed from plastic
materials, epoxies, or polyimides. Since no substantial heating
current is induced in either counter 22 or in the outer cup 70 of
vessel 34 the material from which the outer cup 70 is formed is not
subjected to elevated temperatures. For example, in the embodiment
of the vessel 34 shown in FIG. 1 the outer cup 70 will be subjected
to temperatures significantly below 550.degree.F. As an alternative
material, the outer cup 70 may be formed from any of a number of
ceramic materials.
As shown in FIG. 1 there is bonded to the bottom surface of the
inner cup 71 a copper disk or plate 73. Circulating heating
currents are induced in the copper disk or plate 73 as well as in
the stainless steel inner cup 71; the rapidly changing magnetic
field, produced by induction coil 36 being coupled beyond an air
gap and counter 22 so as to ultimately intercept the disk 73 and
cup 71 to induce heating currents in these latter members.
Advantageously, the copper disk, or plate, 73 provides a relatively
large thermal mass which is effective for the retension of a
significant amount of heat in the vessel 34 over a relatively long
period of time. Because induction heating is employed the cup 71
and the disk 73 thereof are not heated to a temperature higher than
about 550.degree.F. In specifying 550.degree.F herein some margin
for safety is included. Moreover, since no substantial amount of
heating current is induced in counter 22, it may be fabricated from
materials which are not usable in conventional prior art electric
or gas ranges. For example, counter 22 may be fabricated from
epoxies, plastics, polyimides, or glass treated to withstand
temperatures of about 550.degree.F, etc. If required for purposes
of electrostatic shielding and/or structural enhancement and/or
decoration, the counter 22 may include some metallic content.
However, the inclusion of metallic material in counter 22 is
necessarily limited to a small amount or so distributed so as to
prevent formation of ohmic electrical circuits, in order to permit
substantial quantities of the power developed by induction coil 36
to be coupled with the disk 73 and inner cup 71 of cooking vessel
34, for the purpose of heating them.
Referring now to FIGS. 1 and 2, a temperature sensing unit in
accordance with the present invention is comprised of a temperature
detection unit, which is incorporated in the vessel 34, and a
temperature receiving unit 50. While the induction coil 36 produces
electromagnetic radiations in the ultrasonic or higher ranges for
the purpose of inducing heating currents in disk 73 and inner cup
71 of vessel 34, it also provides the energy for driving or
powering the temperature detection unit incorporated in the vessel
34. This is described in more detail hereinafter.
The various components of the temperature detection unit which are
incorporated in vessel 34 are diagrammatically shown as being
contained within the dotted line box which is appropriately labeled
in FIG. 2. Similarly, the various components of the temperature
receiving unit 50 are located within a separate dotted line box
which is also appropriately labeled in FIG. 2.
Operationally, electromagnetic energy produced by induction coil 36
is coupled through an air gap and beyond counter 22 into the
receptor disk 73 and inner cup 71 of vessel 34. The major portion
of this coupled energy is used for inducing heating currents in the
members 73 and 71 as described hereinbefore. However, as suggested
in FIG. 2, a small portion of this radiant energy is coupled to a
pick-up coil 60. As shown in FIG. 1 the pick-up coil 60 is
concentrically disposed around the copper disk 73 in vessel 34. The
voltage developed across the pick-up coil 60 is delivered to the
input of a rectifier 61. As shown in FIG. 1 rectifier unit 61 is
packaged in a small space and located in vessel 34 between the cups
70 and 71 at a location which is relatively remote from the copper
disk or plate 73. Advantageously, the rectifier 61 being so located
is not subjected to elevated temperatures. The rectifier 61
develops a regulated D.C. output which is delivered to an input of
a voltage control oscillator 62 (hereinafter referred to as VCO
62). The VCO 62 includes an additional input from a temperature
sensor unit 63 which may be a thermistor unit. As suggested in FIG.
1 the thermistor unit 63 is also situated in the space between the
nested cups 70 and 71 and is in direct contact with the inner
stainless steel cup 71. Thermistor unit 63 is in contact with that
wall surface of the cup 71 which is disposed opposite the inner
wall surface of the cup 70; the thermistor 63 being located within
the double wall structure of the vessel 34. A transmit coil 64 is
coupled to the output of VCO 62. As shown in FIG. 1, the transmit
coil 64 is located in the space between the nested cup 70 and 71
above the rectifier package 61 and the oscillator package 62 toward
the upper rim of vessel 34. VCO 62 is also located directly below
the transmit coil 64 in the space between the nested cups 70 and
71. The output frequency of the VCO 62 is very much greater than
the frequency output of induction coil 36. For example, VCO 62 in
the embodiment shown develops an output signal voltage at a
frequency of at least a megahertz or multiple thereof. The coil 36,
on the other hand, operates at about 18 kilohertz. In brief, the
temperature sensor, or thermistor, unit 63 which is in contact with
the metallic inner cup 71 changes its resistance, or impedance, in
response to the temperature of the cup 71. The change in the
resistance or impedance of thermistor unit 63 changes the operating
voltage of VCO 62 and thereby causes the VCO 62 to alter its
frequency of oscillation in response to the voltage change
introduced thereto by thermistor unit 63. Thus, there is developed
across the transmit coil 64 a signal voltage of a frequency which
varies as a function of the resistance or impedance of thermistor
unit 63. The thermistor unit 63 varies its impedance or resistance
as a function of the temperature of the member 71. The high
frequency developed across transmit coil 64 is coupled with the
receiving coil 54 which is a part of the temperature receiving unit
50. As indicated, receiving coil 54 may conveniently be secured to
a lower surface of the counter 22 as suggested in FIG. 1 so as to
be able to receive radiated electromagnetic energy from the
transmit coil 64 in vessel 34. The receiving coil 54 is preferably
embedded, or potted, within a suitable matrix of polyimide
material. Also embedded in the same matrix with the coil 54 is
shielding means 66 which advantageously may be ferrite which serves
the purpose of shielding the coil 54 from the field radiated by
induction coil 36. The ferrite shielding means 66 are, as suggested
in FIG. 1, located within the matrix on opposite sides of coil 54;
i.e., between the coil 54 and the induction coils 36. However, the
coil 54 remains relatively unshielded at other locations which
allow the transmit coil radiations to be received by coil 54,
unimpeded by the shielding means 66. The shielding means 66 are
also diagrammatically illustrated in FIG. 2.
Electromagnetic energy coupled to the receiving coil 54 from
transmit coil 64 develops a voltage across the coil 54 which is
delivered to an input of the temperature signal processing circuit
45. The signal processing circuit 45, which derives its power from
rectifier 46 as indicated in FIG. 2, develops an output signal
representative of the temperature of the vessel 34 as detected by
thermistor unit 63. This output signal is delivered directly to a
temperature indicator 30. Thus, for a particular temperature
developed in vessel 34, thermistor unit 63 has a particular
resistance or impedance corresponding to this temperature. The
resistance of thermistor unit 63 causes a voltage change within VCO
62. The output frequency of VCO 62 is a function of the voltage
change occasioned by the resistance change of thermistor unit 63.
The output frequency developed by VCO 62 is impressed across
transmit coil 64 which, in turn, electromagnetically drives the
receiving coil 54. The coil 54 has a signal of a particular
frequency and voltage developed thereat and this signal is fed to
the temperature signal processing circuit 45 which, in turn,
develops an output signal corresponding to the temperature of
vessel 34. This output signal may be converted and the temperature
displayed by indicator 30.
As an alternative mode of operation, VCA 62 may operate in a pulsed
mode so as to cause transmit coil 64 to be energized in a clocked
type fashion with the result that interference from the main field
produced by induction coil 36 is avoided.
In FIG. 1 for purposes of clarity, the cross sectional dimension of
the outer cup 70 is shown as being larger than that of the inner
cup 71. However, it is to be understood that the cross section of
the outer cup 70 may be smaller than shown in FIG. 1. The cross
section dimension may, for example, be the same size as the cross
section dimension of the inner cup 71, or it may be smaller. Also
in FIG. 1 the vessel 34 is shown as having feet such as feet 75
molded in the outer cup 70. It may be that an alternative form of
vessel construction is desirable such as that shown in FIG. 3 where
a modified vessel 34A is shown. The modified vessel 34A does not
include feet.
The rectifier 61 and VCO 62 as shown in FIG. 1 may be fabricated
and packaged as separate or combined integrated circuits. In one
form these separate integrated circuits may have the general forms
or configurations illustrated in FIG. 1. Suffice it to say that:
rectifier 61 and VCO 62 are preferably in the form of integrated
circuits which have been miniaturized and packaged accordingly. Not
shown in FIG. 1 or in FIG. 3 are the various electrical connections
for the pick-up coil 60, rectifier 61, oscillator 62 and transmit
coil 64. The conductors interconnecting these various elements may
be embedded in the insulation 72.
In FIG. 3 there is shown a modified form of cooking vessel 34A. As
indicated the vessel 34A is of a double wall construction which
includes inner and outer nested cups 71 and 70, respectively. These
cups are formed from the same materials as hereinbefore indicated.
The space between these nested cups may be filled with insulation
72, as shown, or the space may be filled with air or evacuated. The
outer cup 70 does not have feet (such as the feet 75 employed in
the embodiment of the vessel 34 shown in FIG. 1). In vessel 34A
there is bonded to the bottom surface of the inner cup 71 an
annular copper disk or plate 73A. The disk 73A performs the same
function as the disk 73 in vessel 34 of FIG. 1. Also, as shown in
FIG. 3, the vessel 34A has incorporated therein a pick up coil 60,
rectifier 61, oscillator 62 and transmit coil 64. Also located in
the central aperture of the copper disk 73A and bonded to cup 71 is
a temperature sensor unit 63, which may be a thermistor unit.
Operationally, the system shown in FIG. 3 functions in the same way
as hereinbefore discussed with reference to FIGS. 1 and 2.
Accordingly, the invention hereinbefore described and illustrated
in the accompanying drawings provides an induction cooking or
warming appliance which includes, together with a vessel, a
temperature sensing unit which is free from the spurious heating
encountered in prior art electric and gas ranges. In this regard
the nature of the heating source does not produce the same elevated
temperatures at the same locations or within the same components.
For example, the induction coil 36 induces heating currents in the
cup 71 and disks 73 and 73A in the vessel 34 or 34A rather than in
the counter 22. The temperature detection unit which is located
within the vessel and the temperature receiving unit 50 are located
in a region of relatively low magnetic field intensity. Also, the
thermistor unit 63 has a resistance of the order of 10.sup.6 ohms
so that, at best, only insignificant heating current is induced
therein. Also the thermistor leads may be twisted to cancel induced
voltages. The various electronic components incorporated within the
vessel and under the counter are not subjected to a temperature as
high as the specification temperature of 550.degree.F. Certainly
these components are not subjected to the elevated temperatures of
1,600.degree.F which occur at certain regions in prior art electric
and gas ranges. In this regard, the present invention discloses
that the electronic components 60, 61, 62 and 64 are surrounded by
thermal insulation 72 and some, or all, components may be remotely
located from heated elements such as 73 and those parts of cup 71
which are at the more elevated temperatures. Also, in addition to
locating the aforesaid components remotely from higher temperature
parts of the vessel, they may be thermally connected to the outer
cup member 70 and, hence, to a lower temperature environment.
Beneficially, with the present invention the materials of
fabrication of the temperature sensing unit (temperature detection
unit and components as well as the temperature receiving unit and
components) are not restricted by the elevated temperatures
encountered with prior art electric and gas ranges. Hence, many
materials such as plastics, epoxies, polyimides are usable in the
practice of the present invention.
Moreover, because there is no heat source as in prior art ranges,
hereinbefore described, and because of the location of the various
components of the temperature detection and temperature receiving
unit, the various components herein used need not be thermally
shielded or insulated in the ways or to the extent employed in
prior art electric and gas ranges.
With the temperature sensing unit employed in the present invention
an accurate sensing of the temperature of the vessel may be
achieved. This may be done regardless of the weight of the vessel
and, further, without regard to whether the outside surface of the
vessel has an irregular surface or contour. Moreover, with the
temperature sensing unit provided herein, the prior art spring
construction or arrangement is not required. Nor, would springs be
of any use in connection with temperature sensing as done with
present inventions.
Another advantageous aspect of the subject invention is that the
counter 22 or vessel supporting means may have an uninterrupted
working surface on the top thereof. An important advantage of the
present invention is that temperature data may be transmitted by
wireless means to a location which may be relatively remote from
the cooking or warming area.
Although the invention has been described and illustrated by means
of specific embodiments thereof, it is nevertheless to be
understood that many changes in materials, details of construction
and in the combination and arrangement of parts or components may
be made without departing from the spirit and the scope of the
invention, which is defined by the claims hereinafter
appearing.
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