CA2065007A1 - Food service cart with individually activatable heaters - Google Patents

Abstract

A heating system for use in a food service cart includes a plurality of vertically spaced tray supports attached to the cart (10) and a plurality of heaters attached to the cart at a plurality of vertically spaced locations in alingment with shelf locations for heating foods carried on service trays (30) and supported by the tray supports. A device associated with the service trays (30) activitates individual heaters. A thermostatic control controls the power supplied by each respective heater during a predetermined time period and includes a sensing mechanism for sensing temperature and a power adjusting mechanism for adjusting the power supplied by the heater. The sensing mechanism senses temperature over a predetermined range having upper and lower temperature limits, and the power adjusting mechanism reduces the power at which the heater operates to a lower power level when the sensing mechanism senses the upper temperature limit and increases the power at which the heater operates to a higher power level above the lower power level when the sensing mechanism senses temperature at or below the lower temperature limit. Food is rethermalized by a method that continuously applies power through a heater over the predetermined time period, alternately at the high and low power levels.

Description

` WO 91/02478 2 ~ 6 ~ O ~ 7 Pcr/US9O/o4312 :`
FOOD SERVICE CART WITH
INDMDUALLY ACTIVATABLE HEATERS
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TECHNICAL ~LD
The present invention relates to tood service systems wherein individual portions ot precooked food are supported on trays within moveable carts. The carts are placed in a chilled environment to store the (ood in a chilled state. Selected tood(s on the trays are . . .
rethermalized in the cart, i.e., heated to a hot serving temperature, while other portions ot tood on the trays remain in the chllled state.
The rethermalization method o~ the present invention is directed to conductlvely applying heat to the selected rood portions through a heating plate which is heated by a thermostatically controlled electri-cal heater.
~i B~CKGROUND OF THE INVENllON
Varlou~s types o~ tood service systems and conductive heating rethermalization methods are known in the prior art. A mn~t basic tood service system is one in which tood ls served immedia~ely, or only a short time period, arter the ood is cooked or prepared. Typi-cally in better restaurants, tood is served immediately a~ter it is cooked or preipared. Such immediate service o- the tood generally results in the best quality of ood. ln other environments such as tast ~; iood restaurants and ca~eterias, tood is not served immediately atter preparaaon, but rather kept warm and served in the warm state. In fast tood r~#taurants~ ood such as hambur~ers is kept hot in dlspos-able plastic containers. In cateterias, tood can be kept warm in the bulk state and served to individuals on a request basis, or tood can be prepared in bulk and, thereatter, divided into individual portions and kept warm in a pellet system. A pellet system can also be used in non-ca~eteria environments, such as hospitals wherein the food is i .
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placed on serving dishes and covered wlth insulated domes to keep the food warm until service.
:~ A significant drawback of systems which keep food warm for a- short period ot time before service is that the time period during which the food can be kept safe and warm is relatlvely limited, and the quality of the food deteriorates over time.
A rethermalization system is another prior art type of food service system. In a retherOmalizatio~nF~stem, ~ood is coo~ed or pre-pared and then chi ed in bulk t~o~4~ tor less. Eventually the food is ~ divided into individual portions and stored in a chilIed state until it is ; reheated. The United States Food and Drug Administration (FDA) guidelines specify that the chilled and stored temperature must be 4 44 C
(40F)or less. A short time before the food is to be served, the tood which is to ~e served hot is brought to a safe serving temperature, i.e.
. it is ~eæhermalized. FDA g~idelines specify that a safe serving tem-perature is(l65F)or greater. The present invention is directed to certain improvements iQ structural and tunctional aspects ot a rethermalization system which uses conductive heating.
One manner ot classifying prior art conductive heating rethermalization systems is by the location ot the heating elements is within the system. That is, prior art rethermalization systems have ;' located the heating element in either a tood serving dish, a dish sup-; s;, porting tray, or a shelf attached within a service cart.
;~ U.S. Patent No. 3,908,749 to Williams discloses a food service ;i4~' system wherein precooked foods are held on trays within a chilled environment cart. Food tO be rethermalized is held within a dish ~ which has an electrical resistance heating element embedded in itS;~ base. Contact buttons to connect the heating element to an electrical .~i power source extend from the bottom of the base of the dish. The dish extends through a hole in a tood service tray, and when the tray is supported in the service cart, the contact buttons rest on exposed leaf contacts which extend from a rear wall ot the service cart.
Embedding the electrical heating element within the dish sig-nificantly increases the cost and complexity ot the dish. A dish within a food service system undergoes severe handling since it must ~3 r~
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wo 91/02478 2 ~ 6 5 Q 0 7 Pcr/US9O/o~312 carry ~ood, is subjected to heat for rethermalizing the rood~ and therearter is subjected to heat, chemicals and handling impact in washing and drytng processes. Thus, the dtsh is the component of this system which must be replaced most frequently. A system which incorporates the heating element into the dish thus has a relatively high long-term operating expense. Another disadvantage of this type ot ~ood service system is that relatively large electrical contacts must remain exposed in the cart to provide the electrical connection to the contacts or the dish. Such exposed contacts are thus subject to corro-slon and water damage during operation and cleaning.
Food service rethermalization systems which incorporate heat-ing elements into the service tray have disadvantages similar to dish heating element systems. That is, the cost ot the trays is relatively high and the trays are subject to breakage because ot trequent han-dling during tood service and cleaning. E~posed contacts are also required to provide electrical connection to the heating elements embedded in the trays. Another disadvantage or tray heating element systems is that the trays become warped arter a period Or time due to the rrequent heating and coollng cycles to which the trays are sub-jected and their relatively large planar conriguration. Once the trays become warped, good surrace contact between the heating element portion ot the tray and the dlshes to be heated is lost. As a conse-quence, accurate, and possibly adequate, heat is not applied to the iood during rethermalizatlon. Examples ot rood service rethermalization systems which utilize trays incorporating heating elements are tound in U.S. Patent Nos. 4,068,115 to Mack et al.;
~,167,983 to Selder et al. and 4,235,282 to deFilippis et al.
Food ærvice rethermalization systems which incorporate the heathe elements Into shelves supported in the ærllice cart alleviate the problem ot the hlgh cost ot the more replaceable portions or the system, i.e. expensive dishes and trays. Furthermore, since the heat-ing elements are tormed as a portion ot the cart, i.e. a shelt within the cart, the connection or the electrical heating elements to a power source is incorporated within enclosed portions or the sheli and cart, alleviatlng the problem ot expoæd contacts. However, , .
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WO 91/02478 2 ~ 6 ~ O 0 7 PCr/USs0/043~2 rethermalization carts with she~ located heating elements do have certain limitations or disadvantages. Such systems generaLly incorpo-rate a plurality ot heating elements in a ~ixed manner into a single shelf. Thus, when one of the heating elements on a shelf becomes inoperative, the entire shelf must be replaced, rather than replacing the single inoperative heating element. Examples of food service rethermalization systems wherein the heating elements are incorpo rated into shelves within the service cart are found in U.S. Patent No.
4,346,756 to Dodd et al.; 4,323,110 to Rubbright et al. and 4,285,391 to Bourner.
Prior art rethermalization food service carts have one or more columns of vertically spaced storage shelves on which trays carrying dishes ol ~ood are held. Dependent upon whether the tray at a fiven shelf location is carrying food to be heated, the heating elements at the respective shel~ locations have to be activated at aD appropriate time. Power to all Or the heating elements is generally turned on manuaUy or via an automatic timer program. However, separate activation of the individual heating elements at the shelf locations is . . .
dependent on whether or not rood to be heated ls present at the shelf locathn. One technique is to have the food service personnel acti-vate a manual switch as the ~ood tray is loaded on the shelt, it the tray contains food to be heated. Howevér, such a technique is labor lntensive and requires that the rood service operator inspect the food "t,' on the tray or otherwise have an indication ot whether tood to be heated ls present on a tray belng placed onto the shel~.
Rubbright et al. '110 discloses a programmable system for acti-vating heating elements at various shelt locations. In this system, a transport modular pack is programmed to have each heater element ~j rollow a particular and independent tlme/temperature curve depen-dent upon the rood to be heated at the particular shelt location. ThiS
technique is very complicated and labor intensive, and requires spe clal care and attentiveness by a sl~ed operator, since a specific time/temperature curve must be programmed by the operator into the modular pack ror each indlvib~al me~.

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Another prior art technique tor activating the inc~vidual heat-ing elements at the shelf locations relies upon tray positioning. In Seider et al. ~983, electrical heater contacts on the dishes mate with projecting electrical power contacts at the shelf locations when the tray is positioned in one direction, but do not make electrical contact when the tray is positioned in the 180 opposite direction. In Bourner ~391, a mechanical switch is placed at each shelt location and is acti-vated by a tray cover when the tray is positioned in one direction, but is not activated when the tray is positioned in the 180 opposite direction, because of a cùt out formed in the cover. Again, care must be taken by the tood service operator in positioning the trays within the shelves. Frequently the loading of the shelves with the trays occurs at a separate location, or is attended to by a ditferent person, trom the loading or the food onto the tray. Thus, miscommunication or misunderstanding as to the tood located on the tray can result in incorrect positioning or the tray.
Electrical conductive heaters in prior art rethermalization systems and rethermalization methods using such heaters have exhib-ited certain limitations or drawbacks in the manner in which the food is rethermalized. Most typically, a rethermalization system utilizes a resistance heater, which operates intermittent~y at a single power level during rethermalization, i.e. during the time when the food is initially brought trom the chilled state to a serving temperature. The resistance heater is controlled by an on~ott thermostat which oper-ates between upper ana lower temperature ot limits. Typically, the reslstance heater applies heat over a predetermined tlme period.
Wblle such a heating method has worked satlstactory"it is subject to ~rtatn limttatlons. For e~ample, the system must he designed to work withln a practical time period. Wh~e it would be desirable trom a labor/cost standpoint to rethermalize chilled tood as quiclcly as pas-sible, lt is dit-tcult to achieve high quality tood when rethermalization occurs too quickly. For example, certain portions ot food may hecome soorched while others remain cold, or the tood may become dehydrated or dbcolored when rethermalizanon occurs too rapldly.

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: WO 91/02478 2 0 6 5 0 ~ 7 PCr/l~lS90/04312 -- 6 -- :
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One commercial rethermalizaffon system accomplishes rethermalization ot food in approximately one quarter of an hour.
However, the range or variety of rood which can be rethermalized is limited and special plating techniques are required for many of the lighter or more fragile oods. The term "plating techniques~ refers to the special way or manner in which certain foods, which are to be rethermalized, are placed on dishware to assure that the foods retain their quality af ter rethermalization. Plating techniques are mo6t frequently used with llght and fragile foods. Examples of plating techniques include supporting food on a dlsh within a dish or on toast, adding gravy or water to the food, or spraying the dishes with a non-stick coating. Thus, while the time dunng which rethermalization takes place is less, any operating e~pense savings is very likely lost by the added expense is reguired in the special plating techniques.
Conversely, when the time tor rethermalization is signiticantly increased, ror example, to one hour as suggested in Williams ~749 for an entree ot a meat and one or two vegetables, the need for special plating techniques is reduced and a wider variety Or food can be rethermalized. However, a one hour rethermalization time period can be too long when three meals per day must be prepared in typical institutional environments such as hospltals, prisons or nursing homes since scheduling options rOr handling and recyling the carts ror the next meal are limited.
The system disclQsed in Bourner ~391 rethermalizes chilled food in approximately a one-half hour time period. Such a rethermalization time period has proven to be a satistactory compro-mlse. That is, a relatively wide variety o~ tood can be rethermalized without the requirement ot using special plating techniques. Furthe~
more, the one-halt hour time period has wt proven to be too restric-tive on service personnel, allowing sutficient time rOr preparation and service Or three meals per day in an institutional environment.
Nevertheless, even the system disclosed in Bourner ~391 has certain limitations. For example, an unr~tricted range Or ~oods can-not be rethermalized without special plating or guality degradation.
It is dirricult to rethermalize small portions of low density, fragile ' :

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~WO 91/024~8 2 ~ 6 ~ O ~ 7 PCr/~lS90/04312 ~oods, while retaining high quality Or the foods and at the same time rethermalize large portions Or high density, dyrficult to heat foods ; wtthin the same time period. It is believed that one of the causes of this limitation is that the thermostat which controls the heater must operate at a relatively high temperature range in order to su ficiently heat the more difficult to rethermalize food, and that at such higher temperature ranges, the easier to heat foods become overcooked.
. A system which utilizes a resistance heater at a single power rating also hæ proven unforgiving when certain set parameters are varied. For example, ir portion sizes are varied too much from speci-fled portlons, qualtty Or the reheated food deteriorates. This ~s par-ticularly true i~ too much o- a dense food is placed in combination rith too llttle o a ~ragile, low density food. Such a system is also very voltage dependent. Thus, if the voltage supplied to the heating , elements drops significantly below the rm, ~or example more than 5%, insu~ficient power may be supplied by the heating elements to heat the higher density, more difricult to heat foods. Similarly, if the ~;voltage supplied to the heating elements increases excessively, for ,~e~ample lO9~, excessive heat may be supplied to the more fragile foods causing deterioraaon in the quallty o these ~oods.
The system tn Dodd et al. '756 uses a separate low power hold-ing circuit for keeping food warm after it has been rethermalized. A
higher power primary heating circuit is thermostatically controlled ~iand used to rethermalize the tood over a predetermined time period.
:iThus, while thls system uses separate heaters having different power , ra~n~, only the higher power heater is used for rethermalization, while the lower power heater is used primarily to keep the already rethermaltzed food warm. A switch is used to select between the two heating optlons.
The system in Mack et al. 'll5 uses PTC power heaters as the preterred type of heater embedded in the dish. The use o~ a resis-tance heater controlled by a thermostat is mennoned as an alterna-nve to the PTC heater. The PTC heaters operate basically as multi-modal reststance heaters so that below their critical temperature they have a low electrlcal reslstance, whtle above tt the resistance is very .

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--WO 91/02478 2 ~ ~ ~ ~ ~ - 8 - PCr/US90tO4312 high. Near the critical temperature, the resistance varies between the extremes. There~ore, depending upon temperature a PTC heater will deliver d~terent wattages. During the development of the present system, it was found that PTC heaters had both structural and ~unctional disadvantages. The heaters initially draw very high cu~
rent, requiring more expensive high power capability electrical ser-- vice. AlSo, it the initial input temperature ot the food varied from ~ preset standards, the heaters would not adequately heat the food to proper serving temperature.
- The Rubbright et al. ~110 system programs an individual time/temperature curve for each heater element. A predetermined time period is not used lor a~l ot the types of foods to be rethermalized. Rather, a particular time/temperature curve is used to control heater temperature and time Independently for each heat-ing element depending upon the type ot tood being rethermalized. A
certain number ot programs are available lor use and are coordinated with various types or combinations of foods. The tood service opera-tor thus must coordinate the particular lood or combination of toods with the appropriate program. The ~ood service handling process ~s thus complicated, requiring extra care and attention during meal preparation and special training for the operators of the system.
The lood service system and method ol rethermalization of the present invention was developed to overcome the structural and f unc-tional limitaaons ot the prior art systems and methods discussed ' above.
SII~ARY O~ ~ INVENTION
The present invention is directed to a heating system tor use in a tood service cart tor storing and heating toods. The system includes a plurality ot vertically spaced tray supports attached to the cart for supportlng tood service trays at a plurallty ot verticaLly spaced shelf locations, and a plurality ot heaters attached to the cart at a plurality of verticaUy spaced locations in alignment with the shel~ locations for heating toods carried on service trays and supported by the tray sup-ports. A mechanism initiates the supply ot power to the heaters and a timer turns the power ott to the heaters atter a predetermined time -,,~ .. . ..

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WO 91/02478 2 0 6 ~ O ~ 7 Pcr/US9O/o4312 _ 9 period has elapsed. A thermostatic control controls the power sup-plied by each respective heater during the predetermined time period.
The control includes a sensing device for sensing temperature and a power adjusting device for adjusting the power supplied by the heater.
The sensing device senses temperature over a predetermined range having upper and lower temperature limits, and the power adjusting device reduces the power at which the heater operates to a lower power level when the sensing device senses the upper temperature ~mit and increases the power at which the heater operates to a higher power level above the lower power level when the sensing device senses temperature at or below the lower temperature limit.
The present invention is also directed to a heater module per se which incorporates the heater and thermcstatic control.
In a preferred embodiment, each heater includes an electrical heating element, and the power adjusting device includes a switch which shorts a portion ot the heating element out oi' the operative heater circuit to operate the heater at the increased power level, and which places the portion ot the heating element into the operative heater circuit to operate the heater at the reduced power level.
Another aspect of the present invention is directed to a method ol heating precooked food stored at a plurality o~ locations within a food service cart. ~ccording to the method, a preselected amount of tood to be heated is supported adJacent an individual heater, and heat Is supplied to the lood trom the heater over a prede-termined time period in a thermostatically controlled manner as fol-lows: Heat is initlally supplied at a high power level from the begin-ning of the predetermined time period; and thereafter reduced to a low power level lower than the high power level when an upper tem-perature of a temperature range of the thermo6tatic control is reached. The heater operates at the low power level until a lower temperature of the temperature range is reached and then increases to a higher power level above the low power level. The heat is again reduced to a low power level lower than the higher power level when the upper temperature d the temperature range is reached; and the steps oi' reducing and increasing the power are continuously wo 91/02478 2 0 6 ~ O 1) 7 Pcr/US90/o4312 performed over the predetermined time period to continuously supply heat from the heater to the food during the predetermined time period.
Another aspect of the present method relates to selecting a range of foods with various heat energy requirements to be rethermalized; and to selecting oi an appropriate rethermalization time period and low and high power levels which wiLls satisfactorily rethermalize the range ot roods.
The terms two-stage heater and two-stage method of rethermalization will be used herein as shorthand terminology for the heater and thermo6tatic control which supplies power continuously during the rethermalization time either at a high ,oower level or at a low power level, and to the method of rethermalization using the application of heat at the high and low power levels. The two stage heater and method of rethermaltzation overcomes, to a degree, cer-tain ~ood processing limitations ot a single-stage rethermalization heater (the on-oft operation of a single-power heater). For example, foods with a broader range of heat energy requirements can be rethermalized with the two-stage heater without degrading food qual-lty. As a corollary, less special plating techniques are required for the lower density, fragile toods. ~Iso, a mixture of high energy requirement and low energy requirement roods can be more readily rethermalized simultaneously ufing the two-stage heater. Such mixed rethermallzatlon with the two-stage heater works particularly well wtth round dishes which both are aesthetically pleasing and allow freedom to vary portion sizes ot one, two, or three foods.
The two-stage heater sg~stem and method is also more forgiving in va~ious respects over a stngle-stage rethermalization heater system and method. That is, accurate portion sizes are not as critical when the two-stage heater and method is used. Simllarly, vartations in the voltage applled to the heaters does not as readily af~ect the quality of the rethermalized food.
Another advantage of the two-stage heater and method is that a lower and narrower thermostat range can be used wtthin the prede-termined rethermaiizanon time ,oerioo. When a lower and more ;~

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~ ~ WO 91102478 2 0 6 ~ O Q 7 PCI/US90/04312 , ' ' - 11-accurate thermo6tat range is used, there 3s leas chance that the food will bec~me scorched, or that the more fragile foods will have their quality degraded. AlSo, excess power is not used when meals consist-ing primarily of light, rragile foods reach the desired serving temperature.
Another aspect o~ the present invention is directed to a system for selectively activating lndividual heaters in a food service carn An individual switch mechanism is connected to each of the heaters ror turning power on and o~t separately to each one Or the heaters. A
switch activator mechanism activates the switch mechanism, and is associated with covers ~or hot food to be carried on the service trays i~i whereby one or the switch mechanisms turns power on to a respective one ot the heaters when one o~ the covers is carried by a tray and supported in the cart above the last-mentioned switch mechanism. In one embo~ment, the switch mechanism includes a pivotable housing, a magnet supported at one end ot the housing and a mercury switch activated and carried by the pivotable houslng. A preferred rorm of switch actlvator mechanism is a ring or magnetlc material supported in the base o- the rood cover.
j~, The system which uses an individual switch mechanism con-nected to each heater in combination with a switch activator mecha-nism carried In the covers rOr hot rood simplities the process Or acti-vating the indlvidual heaters, as well as reduces the lL~celihocd ot error in activating the heaters. As i~ood is placed on dishware, it is common practice to place a cover over tood which is intended to be hot. The present system accomplishes individual heater activation by this sim-ple one-step process. The step Or manually, and individually, activat-y a S~itCQ ror each shelt location, programmine a control module for each meal, or properly orientating trays within a service cart is thereby eliminated.
A rurther aspect Or the present invention is directed to a heater module rOr use in a rood serv~ cart wherein a heating ele-ment houslnl~ is removably attached to ~ne cart at a shelr location. A
heater plate sized to contact one rood carrying member, and at least one electrical heating element are carried in the heat~ element , . .

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~ WO 91/02478 2 0 6 5 0 ~ 7 PCI/US90/04312 ~'., ' .
houslng with the heating element in thermal contact with the heater plate. The heating element housing includes a mechanism for remov-ably attaching the housing to the cart whereby the heating element for a respective heater plate is individually removable trom the cart by removing the heating element housing. ~he heating element hous-ing preferably has a pair of openings for receiving a pair of support pins extending from a support beam in the cart. P~epair, replacement and cleaning of heating elements and heaters is simplified by the present heater module since each individual heater can be removed separately. In prior art shel~-mounted heaters, a plurality of heaters was rixedly attached to each shelr location so that individual replace-ment and repair of the heaters could not be accomplished.
Various advantages and features of novelty which characterize the invention are pointed ouS with particularity in the claims annexed hereto and rormlng a part hereor. However, rOr a better understand-ing of the ~nvention, its advantages, and ob~ects obtained by its use, reference should be made to the drawin~s which rorm a turther part hereof and to the accompanying descriptive matter, in which there is iLlustrated and described pre~erred embodiments ot the invention.
BREF DEsca~ oN OP THE DRAWINGS
Figure 1 is a perspective view of a ~ood service system includ-ing a mob~e ~ood service cart and a re~rigeration cabinet:
Figure 2 is a partial rear view of the tood service cart;
Figure 3 is a horizontal sectional view or the rood service cart, illustrating one food tray supported at a shelt location and another food tray in the process or being inserted into a shelf;
Figure ~ is a partlal front elevational view illustrating trays, dlshware, and covers supported at shel~ locanons with one overall cover partlally broken away;
Figure S is a partial sectional view illustrating dishware sup-ported on a heater;
Figure 6 is a partial side elevational view with the side wall of the service cart removed and illustrating rood trays and coveris sup-ported at horizontally spaced shelt locations;

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Wo 91/02478 2 0 ~ ~ ~ o 7 PCr/US90/043~2 s Figure 7 is a top plan view of a heater module with selected internal details shown in dash line Figure 8 is a cross sectional view taken generally along line 8-8 ;, Or Figure 7 with a portion of a tray and cover lllustrated above the heater module;
Figure 9 is a top plan view of a generally T-shaped heater ele-ment support bar;
Figure 10 ~s a ~ront view of the support bar;
. Figure 11 is a cross-sectional view taken generally along line ll-ll o~ Figure 9;
Figure 12 is a plan view of a cover plate ror the support bar;
Figure 13 is a lront elevational view of a heater module;
A` Figure 14 is a rear elevational view o~ the heater module;
Figure 15 is a cross-sectional view taken along line ~5-15 of Figure 7;
Figure 16 is a partial esploded perspective view o~ a heater ', module, tray and cover, illustrating a pivoting switch;
. Figure 17 is a plan view o~ a smaller heater module;
Figure 18 is a plan view or an attachment plate of the module ot Figure 17;
. Figure 19 is a parnal exploded perspective view o~ a heater . module, illustrating an alternate switch mechanism;
~ Figure 20 is a diagrammatic view ot the resistance pattern of ,~ one embodiment ot a heater element;
ji Flgure 21 is a diagrammatic view o the resistance patte. ~ of another heater element;
j~; Figure 22 is circuit diagram o~ one embodiment of a two-stage heater and heater control;
Figure 23 is a circuit diagram o~ another embodiment ol a two-stage heater and heater control;
Figure 24 is a circuit diagram Or a rurther embodiment Or a .. two-stage heater and heater control; and s Figure 25 is a graph illustrating a theoretical comparison . between a two-stage heater in accordance with the present invention and a single-stage heater.

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- ~ WO sI/02478 2 0 6 ~ O ~ 7 Pcr/US90/04312 D~TA~ED DESCRlPTlON
^ Food Service Svstem J ' Relerring to the drawings, wherein ~ke numerals indicate like elements, there is illustrated a food service system indicated gener-ally as 10 Food service system 10 includes a mobile food service cart 12~ which functions as a rethermalization and service cart, and a re~rigeration cabinet 14 Cart 12 is ~ormed generaLly o- sheet meta~ and includes a su~
port base 16 A ~irst pair or wheels 18 depend ~rom one of the sides of base 16 and a second pair o~ steerable and lockable wheels 20 i- depend from its other side. A first side wall 22 extends upwardly from a ~irst side of base 16 and a second side wall 24 extends upwardly ~rom a second side ot base 16. A top wall 26 is connected to and extends between the upper ends ot tirst and second side walls 22 and 24 Tubular members 25 (one Or which is shown along the rront edge ot cart 12 in Flgure 1) are attached to the ~ront and back edges ot each side wall 22 and 24; and generallg U-shaped tubular members 2 are attached to and connected between top wall 26 and side walls 22 and 24, and base 16 and side wal~s 22 and 24, along the tront and back edges o~ cart 12 Tub~ar members 25, 27 provide additional rigidity to cart 12. A handle 28 is attached to the exterior ot side waLI 24, and ` is used to move and steer cart 12. The Iront and back ot cart 12 are open to allow ~ree acce~s tor the insertion and removal ot ~ood ser-~A, vice trays 30. Male electrical connector contacts 32, which connect ~; cart 12 to an electrical power source, extend trom base 16 immedi-ately below side waLt 22 In use cart 12 is loaded with trags 30, which in turn support precooked or otherwise prepared tood. Therea~ter, cart 12 is wheeled into retrigeration cabinet 14 where it wlU be stored in a chllled state until rethermalization Reirigeration cabinet 1~ includes a ~ront access door 34 to allow entry and removal Or cart 12, and wh~ch seals the retrlgeration cabinet. A emale electrical receptacle 36 is attached to the interior back wall o cabinet 14. When cart 12 is backed compbtely Into cabinet 14, contacts 32 engage receptacle 36 to thereby connect cart 12 to a main electrical power supply in a .

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Wo 91/02478 2 0 ~ ~ O ~ 7 PCr/~IS90/04312 conventional manner. Electrical power to receptacle 36, and, hence, ;~ cart 12 can be initiated manually through switch 31, or switch 31 can be programmed to turn power on at a preselected time. A conven-tional timer 33 is also provided to control the amount of time that power is supplied to the cart.
Ir cart 12 is to be used in a centralized rethermalization sys-tem, cabinet 14 can be replaced by a refrigerator room wherein a .~ plurality of spaces and electrical receptacles are provided for a plu-rality of carts 12, and the entire room is refrigerated.
~, Food Service Tra~r and Dishware , As seen ln Figure 3, a pair or support bars 38 are attached to the inside surfaces ot side walls 22 and 24 at both the rront and back of cart 12. At a g1ven hofizontal location, support bars 38 define a front and a back shelf location to support a pair or trays 30.
^ Support bars 38 are preferably formed of a rigid plastic. As .
seen in Figure 4, support bars 38 have a generally T-shaped cross~ection with pins 40 Iormed integral with the top section of the T. Pins 40 extend through apertures in side walls 22 and 24 to thereby , secure support bars 38 to side walls 22 and 24. An alignment and ,-locking projection 39 extends trom the top surrace ot support bars 38.
Projection 39 mates with a slot 41 along the bottom edge ot tray 30 to ~`, hold tray 30 in position.
, ,, Tray 30 has a generally rectangular conriguration with an upstanding peripheral rim 42, which e~tends upward rrom a support surrace 44. A dlvider 46 also e~ctends upward rrOm the sup,oort sur-taoe 44 and divides surrace 44 intc a tood holding area and a utensil/napkin holding area. In the tood holding area a round large entroe opening 48, and a round small soup opening 50, are tormed. A
rim 49 e~tends upward trom surtace 44 and around the periphery of opening 48. A rlm 51 e~tends upward trom surta~e 44 and around opening 50. AS seen in Figure 4, an entree dish 52 tits within entree opening 48 and a soup bowl 54 tits within soup opening 50. Entree dish 52 and soup bowl 54 both have a conventional round shape. As seen in Figure S, the diameter Or dish 52 increases slightly trom its smallest dlameter along lts bottom sur~ace, and is correlated to the !

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.iad~in Syner~' ~ics, Inc . 3 1?~43 PCT

diameter ot opening 48 such that the bottom surface ot dish 52 e.Ytends down slightly below the lower surface of tray 30, and the side and upper rim of dish 52 are out ot contact with rim 49 of tray 30.
The diameter of soup bowl 54 is likewise correlated to the diameter of o opening 50.
Entree dish 52 and soup bowl 54 are designed to i}e capable of s~ holding hot toods. An insulated entree cover 56 is therefore provided to cover dish s2 and tood held on the dish; and an insulated soup cover 58 is provided to extend over and cover soup bowl 54. A disposable lid is also placed directly on top of soup bowl S4. The diameter of cover . 56 iS greater than the diameter of dish 52 and slightly greater than the outside diameter of rim 48. In this manner, cover 48 is aligned over dish 52 and opening 48 so that the base of cover 56 rests on sup-port surface 44. In a similar manner, the diameter of soup cover 48 is greater than the diameter of soup bowl 54 and rim Sl.
;~ An overall food cover 60 is provided to cover the entire food carrying area o( support surface 44. Cover 60 provides protection for toods, other than hot food covered by covers 56 and 58 which are sup-ported in the tood service area 4~ o~ tray 30. The utensil/napkin sup-port area remains open so that utensils, napkins, menu and patient identi~ication can i~e placed on the tray after all the food has i~een placed on tray 30 and covered. Covers 56 and 58 are Insulated covers preferably formed ot an outer hard plastic shell fiLled with an insula-. tion material as seen in Figures 8 and 16. Cover 60 is preferably tormed Or a rigid injection molded plastic.
~r. Heatin~ SYstem ~i As seen in Flgure 3, a pair of large entree heater assemblies or modules 64 and a pair ot small soup heater semblies or modules 66 are located at each horizontal shelt location. Figures 9, 10, 11 and 12 illustrate the support structure tor supporting heater modules 64 and ~` 66 at the horizontal shelf locations. Heaters 6~ and 66 are collecti~elv referred to as heatir,g meanS 6~, 66 which is comprised ot heating pads 64 and 56. As seen therein, a generally T-shaped bar 68 extends between opposite side walls 22 and 24. T-bar 68 is preferably tormed of a high strength aluminum material and includes a central rib 70, a cross member 72 whlch extends perpendic-ularly trom oppasite sides o( rib 70, and a pair ot wa~ members 74.

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- Wan members 74 extend perpendicularly away from opposite distal ends o~ cro~s member 72 so that a hollow open-ended rectangular area s is defined between cro~s member 72 and wall members 74. A base cover 76 fits within the hollow area and covers the open end between walls ?4. Wiring, shown diagrammatically as 73, extends through the hollow area to connect the heater modules to a main power source through contacts 32. A plurality of notches 80 are formed in the int~
rior ot wall member 74, and projections or clips 82 extend rrom an upper surface ot cover 76 and it within notches 80 to secure base cover 76 in place.
A plastic end piece 84 is located at each end ot bar 68 and dis-posed between a respective end of bar 68 and one Or the walls 22, 24.
Each end piece 84 has a smaLl cross section portion 86 whlch friction-aLly fits into the hollow interior of bar 68, and an e~terior portion 88 which tits between the interior surface ot the wall members 22 and 24 and the distal ends or bar 68. Exterior portion 88 has a curved exte-rior surIace.
Bar 68, base cover 76 and end pie~es 84 are secured to walls 22 and 24, preferably by screws, one of which 81 is shown in dash-line in Figure 9, ev ~nding through the walls and into end pieces 84. Four support pin 0 e~ctend from each longitudinal edge ol bars 68. Each pin 90 is attached to bar 68 ln a conventional manner, preferably by screw threads. Pins 90 have a large diameter base portion 92 and a small diameter dlstal pornon 94. A frlction member, such as an rlng 96, is secured to the distal end of base portion 92. Pins 90 tunctlon to support heater modules 64 and 66 in a cantiliever manner trom bar 68. ~s seen in Figure ~, a cylindrical bore 98 is formed through the housllu of heater module 64 ad~acent each ot .ts sides.
Similar bores are lormed In heater module 66. Palrs o pins 90 fit within bores 98 to support the heater modules. In thls manner, heater modules 64 and 66 are supported at a plurality ot vertica~y spaced shelt locations. The pin 90 and bore 98 connection and support tech-nique aLlows each individual heater module, which is sized to heat a singla dish or bowl, to be individually removed for service or rephoemenl.

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~ ?lurality of ~,ertical!~ spaced hea~i"g ~.eans 64. 66. are oositior.ed ad,acc~..t tra~ suppor;s 33. Each heating means 6~. 66. comprises a plurali;~- of heatin~ pads 6~
and 66 which are each individuall~ and separately controlla~le and removable. S~vitch rr.eans 116 are wsi;ioned adjacent .he tray support le~el and allow ror indi~iidual acti-vation of each hearing pad 6~ and 66 separatei- in an ON/OFF condition. ~hus. positi~,e assurance tha t food positioned on tray 30 is o~:er the proper indi~ idual hea;ing pad 5~ or - 66 ~hich is in the correc~ O.~/OFF condition. B; correct ON/OF.- condir.on. i. is mean~ tl~a; food .-hicn .equires heatinz will ~e placed o~:er one of the hea;lng pa~ 5~.
or 66 ~hich will ~e actuated ;o ~egin ~ea.ir:, a; a p~eset ti.-.e. rood hnicA ~oes ?.or req ~i.e hea;lng can ~e ?laced 3n ~ e o;~er .^-at, pads ô' or 66 a..d t~is hea;ing ,ad Will not ~e actuated: ~hus. m~intaining tho co~d .ood in the ch,.!~ s~a;e. Accordir~, ~o ;he present invention. foods hrich ~equ..o heatlr.~ ~d those w,h,ch rs~ul.~ coo!in~ can be pLaced on rhe same ~ray over se?ara~ hoating pads 6~ and 6rJ. The food ~ ich requires heating ~ e heated to tAe ?roper ternpe.a;ure while ~he food which mustrem~.ain chil:ed ~ill ~e chiiled. .~11 of this is acco~,plisned :vit~out ~e~uiring a subs~a;l-tial amo~:nt of skil! on the pa, t of t~.e ~ocd ser;ice :;orks.s. .~ll t,~a~ is rsqui.ed for the wor.~:era to place a cover ~ver ~ho~e i~ems to ~e hsa;sd. ~ i;h .he chii~ed i~e.~s ra~ain-ing uncovered.
~ ach heating pad 64, 66 is provided ~i;h t~o ~ores 98 and elsct.ica! connectors L~. At each tra~ support loca;ion in carr 1~ ~he~e is provided a bar 58 having four pins g0 on opposite ~ides and e!ectncal rece?~acles lS0 in ~ar 68 on the same si~es of bar 68 as pins 90 and Which correspor.d to the ~osition of pirs ~0. There~ore. each heat.ng pad 5~ and 66 can ~e remo~a~l~; a;.ached to bar 6~ and cart 12 ~ .,~zrtir.g pins .

gO ;vithin bores g8 ~vith electrical connectors ~ ~4 being inserted in;o recoptacles 1~0.
Thus, if one of heating pads 6~ or 66 ar a i~,en tray loca;ion is ~amag~d or ~us; ~e repaired. only the damaged heating pad need be removed. Further. repaih are simpli-fied in that heating pads 64 and 66 plu~ into car. 12 and only need to be unplugged for removal. ~epair can thus be effected without hig~y sJcilled personne~ and in a mini-mum of time.
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- Details of heater module 64 are best seen in Figures 7, 8 and 13-15. Heater module 66, except where noted otherwise particularly - ~ with reference to Figures 17 and 18, is constructed similar to heater ~ module 64. The exterior of heater module 64 is de~ined by a plastic . housing 100, a metal heater plate 102, a plastic switch attachment plate 104 and a rubber or plasric gasket 106. The components which are held within the interior of heater module 64 include a res~stive electrical heating element 108, an insulation plate 110, a thermostat 112, a (use 114, a pivot switch mechanism 116, and an indicator llght 118.
Housing 100 is formed o~ a relatively rigid, high temperature resistant, injection molded thermoplastic. Housing 100 includes a i~ bottom or base 120 and a per.pheral waLI 122 extending upward from bottom 120 about the periphery ot housing 100. Peripheral wall 122 ' has a tapered or slanted top and bottom exterior surface along the ,; front and sides of housing 100. The slanted top surface, along the front of housing 100, assists in guiding a dish into position on top of ;~ the heater. A round opening 124 is formed in peripheral wall 122 and ,; includes a support ledge 126.
Heater plate 102 is pre~erably formed or a nickel plated alumi-num plate having a thickness o~ approximately o~ (1/8~), Plate 102 iS
~;, genera1~y round and has a circular perimeter generally mating w~th the conriguration o~ round opening 124. A plurality or support legs 128 extend downward at a plurality or locations about the perimeter . of heater plate 102. A resistive heating e~ement 108, such as shown in Flgure 20, is secured to the bottom Or heater plate 102.
' i Element 108 is preferably rormed or a resistance rOil in thepattern iLlustrated in Flgure 20. The rOil is encased in a s~icon rubber and is attached to plate 102 during vulcanization o~ the rubber by the s application Or heat and pressure. Plate 110, tormed o~ an insulative material, such as a ceramic riber or the IL~ce, is therearter secured in pa6ition below heating element 108 by resting on top of ledge 126.
Thermostat 112 is secured with an adhesiYe directly to the bottom of heater plate 102 within a centrally located opening in heating ele-ment lOB. Heater plate 102 and the components secured to it are . I

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WO 91/02478 PCr/US90/04312 attached to housing 100 by securing legs 128 within holes 130 formed within housing 100 adjacent peripheral wall 122. The border between heater plate 100 and opening 124 is sealed with a room temperature vulcanized silicon rubber to prevent entry of liquid into the interior of the housing.
Switch attachment plate 104 has a generaLly triangular config-uration as seen in Figure 7. A mating support ledge, which follows the peripheral contour of plate 104, is formed in the bottom of hous-ing 100 and, as seen parffally in Figure 14, plate 104 fits on the sup-port ledge. Plate 14 is permanently secured to the support ledge by either an adhesive or welding, preferably by sonic welding. The Inte-rior of housing 100 is thus hermetically sealed, allowing hea~er 64 to be cleaned in a pressure washing process. Plate 104 supports pivot switch mechanism 116, which functions to individually activate heat-ing element 108 in each respective heater assembly. Pivot switch mechanism 116 includes an L-shaped housing 130 with a magnet 132 carried in one open end ot housing 130, and a mercury switch received within an opening in the other end or housing 130. A pair of support rlanges 136 extend upward from the interior or plate 104 to pivotally support housing 130 via a support pin 138 passing through holes in rlanges 136 and housing 130.
In the deactivated state or switch 116, the end of housing 130 which carries magnet 132 is pivoted downward and the opposite end carrying mercury switch 134 is pivoted upward. In thls position me~
cury switch 134 Is in its open state and power is not supplied to heat-ing element 1û8. Switch 116 is activated by placing an ir~ated .~, cover 56 over a d~sh ot food to be rethermalized. As seen in Figures 8 i.~ and 16, an annular rlng 140 of a magnettc metallic matertal is heldwithin the perimeter of cover 56 ad~acent lts hqeP. As seen in Figure 8, with tray 30 and cover 56 tn position, magnet 132 is drawn upward toward meta~tc ring 140 and mercury switch 134 pivots downward to be placed in its closed state. Activation of an appropriate heater module is thus readily assured, since whenever an insulated cover is placed over food to ~e heated, the heater module is automatically acttvated. A cylindrical propction 142 ts formed integral with the . . .

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upper surface of housing 100 to receive magnet 132 and allow suffi-cient upward pivoting to activate mercury switch 134. A pair of ele~
trical connector pins 144 are supported by a pair of spaced rlanges 148 formed on plate 140 in a hermetically sealed manner. Pins 144 connect to a main power supply bypassing through holes 150 in the side T-bar 68 and connecting to electrical wiring ~4 supported within the hollow interior Or T-bar 68.
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Figures 17 and 18 iUustrate details of small heater mod~e 66.
As seen therein, attachment plate 108~ ditfers in configuration from attachment plate 108 used in module 64. Attachment plate 108~
extends across the entire back of module 66 and has the configuration of two triangles connected by a central strip. Switch 116 is supported on tlanges 136~ on one Pt the triangles, and connector pins 144 extend from flanges 148~ the other triangle. Otherwlse, module 66 is con-structed similar to module 64.
Figure 19 illustrates an alternate embodiment of a switch mechanism 116A tn which pivotable housing 130, magnet 132 and mercury switch 134 is replaced by a reed switch 134A. Magnetic ring 140 in cover 56 is replaced by a magnet 140A located in a small area along the base Or cover 56. In order to properly align magnet 140A
with reed switch 134A, a projection 49A is formed adjacent rim 49 on ....
tray 30 and cooperates with a mating recess 57 formed in the interior surtace ot cover 56. This embodlment ot switch mechanism and acti-vating mechanism Is a secondary embo~ment and should be used only in environments where persons or patients with heart pacemakers are not present, since magnet 140~ within cover 56 could interfere with the operation Or the pacemakers.
Ftgure 20 illustrates the resistance pattern ot heating element 108 Or heater assembly 64, and Flgure 22 is a circuit diagram illiustrat-ing the manner in which power is supplled through heating element 108 to accomplish two-stage heating. Two-stage heating refers to the fact that h one stage the heater operates at a high power level and in another stage operates at a lower power level. The resistance pattern shown in Figure 20 has a generally circular perimeter and is sized and ., .

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~ :' , -: ' PCT/US9ù/G4312 ;'. Aladdin Syner~etics, Inc - 21- - B 1.~3 P~r arrangcd to cover substantially all Or thc bottom suriace of heater plate 102. Ihermosr~t 112 ir.cludessers,ng mea;~s for sensir.g ~he ~empera~ure and po~er an~ adjusting or s~itch rnoans for adjusting the po~ver supolied by the heatcrs 6~. 66 by s-xitching ~e;~een high resis;-~nce he~tir,a and Io~ resis~ar.co hoating. as illl~;,a;ed i.~ Figures 22-25.
As seen in Flgure 22, powcr is supplied to resistive elements A, ;~ B and C ot heatlng elcment 108 when mercury switch 116 is clr~sed.When ~hermostat 112 is open, current passcs through all 3 resistive elements A, B and C and provides heat at a rirst power level. How-ever, when thermostat 112 is closed, current is shunted past resistive element A and only passes through resistivc elcments B and C; C
being a low voltage indicator light circuit. In this state, heat is sup-plied at a highcr power Icvcl since the currcnt passcs through a lower resistance (B ~ C). Thus, during a re~hermali?.ation time period (~he ~ime period during which timer 33 supplies elcctrical powcr), power is always supplied to the tood bcing rethcrmalizcd.
~; Detaiis of the rethermalization will he discusscd in gr~ater ~, dctail in the dlccussion ot the rcthcrmalization method. Howcvcr brletly, when tood to be rethermallzed is in its cold state and power is initial~y suppllcd to heatcr element 108, thermostat 112 is In Its closed state so that heat Is Initially supplleci at high power through resistive elemcnts B and C. When the thermostat rcaches its uppcr limit, it .j~ opens, so that current tlows through all thrcc rcsistive elemcnts A, 8 and C at lower power. Thereatter, when thc thcrmostat reaches its lower temp~rature limlt It again closcs to short current trom resistive element A, and again supply heat at the high power Icvel. Thus, throughout tlle rethermallzatlon period hcat is actlvcly supplicd to :~, the tood belng rethermalized, but at varying powcr levels.
s sccn In Figure 20, thc higher resistancc ot rcsistivc elcmcnt A Is accomplished by a plurality of parallcl rcsistancc elcmcnts con-nected at connect~on points I and 2, which arc aiso shown in Figure ~;~ 22. In Flgure 21, whlch illustrates an altcrnate heating elcmcnt 108tor use In the smaller Soup heater moaiule 66, the higher resistance ot rcsistivc element A is accomplished by using a smaller rcsistancc elc-ment connected at connectlon points 1 and 2.
Flgure 23 illustrates an alternate emboaiiment of heater ele-mcnt and control circuit arrangement which atso accomplishes two-stage heating. In this embodiment, a flrst rcsistive hc~ting element :, :

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Aladdin Synero~tics~ Inc. B 12943PCT

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A~ is connected in parallel to a second resistive heating element B~.Thermostat 112~ controls the passage ot current through elements A' and B~ so that current passes through both elements in the high power mode of operation and through only element A~ in the low power mode Or operation. The resistance of element Br is preferably higher than the resistance of element A~ so that in the low power mode of opera-tion, the power is proportional relatively low, e.g. 25% of the total power when current passes through both elements A' and B~. Element C~ can also be included for an ind~icator light.
Figure 24 illustrates another embodiment of heater element and control circuit arrangement which also accomplishes two~tage heating. in this embodiment, a first resistive heating element A~ is also connected in parallel to a second resistive heating element B~.
However, thermostat 112~ alternately supplies current to elemen~s A~
and B~. The resistance ot elements A" and B~' is selected so that when current passes through element A~ the heater operates at a high power level, and when current passes through element B~ the heater operates at a lower power level. Element C~ can also be included for an indicator light.
Rethermalization Method Food service system 10, and in particular the two stage heating elements 108, 108~ are particularly useful in a method of rethermalizing chilled, precooked ~ood. The food is stored at the plu-rality Or shelt locations within ~ood service cart 12. Within cart 12, a preselected amount of tood to be heated is supported adjacent each ind~vid~u9al hxeater,k64, 66. Generally, the total food portion ~or an entree can vary rrom(3-14 ounces),with the entree including one, two or three dirfe~rent ~oods. ~milarly, the food to be heated by the soup 0 )~ 1 0~
heater element can vary from~ to 6 ounces)of soup, cereal, hot des-serts, rolls or other liquids. The use of the tw~stage heater in accor-dance with the present invention i~s particu~arly advantageous for rethermalizing entrees, and more particularly entrees which vary in their range of heat requirements. Entree foods generally include meat, fish, poultry, casseroles, starches and vegetables.

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. ~ ' WO 91/02478 2 Q ~ 7 Pcr/~S9O/04312 The tw~stage heater applies heat to the food over a predeter-mined time period as set by timer 33. For example, the predeter-;~ mined time period can range from 30-45 minutes, with 36 minutes being the preferred time. The heat is supplied by the heater in a thermostatically controlled manner as follows:
j 1) Heat is initia~ly supplied from the heater at a high - power level from the beginning of the predetermined time period;
2) The heat from the heater is reduced to a lower power level, lower than the higher power level, when an upper temperature of a temperature range of the thermostatic control is reached;

3) The heater operates at the low power level until a lower temperature ot the temperature range is reached, and then increased to a higher power level above a low power level;
; 4) The heat from the heater is reduced to a low power level, lower than the higher power level, when the upper temperature ot the temperature range is reached; and steps 3 and 4 are cyclically pertormed over the predetermined time period to continuously supply ,heat from the heater to the ~ood during the predetermined time ,~ period.
; Turning to Figure 25, the two-stage application of heat in a rethermalization method in accordance with the present invention is compared to the application ot heat in a prior art one-stage rethermalization method. ln this prior art method heat is supplied by a single power heater which is cyclically turned on and or~ over the predetermined rethermaiization time period. The graph is a theoreti-cal graph and assumes that: (1) the total power or the prior art ~!heater is the same as the high power level o~ the heater used in the present method; (2) all heaters operate between the same thermostat llmlts; and (3) the same tood portion, an average entree portion, is being heated. The graph illustrates the temperature sensed by a the~
mostat coupled to the bottom ot the heater plate.
,As seen in the graph, both systems initially supply heat to the system at the same rate. Atter the upper temperature ot the therm~
static temperature range is reached, the prior art system completely shuts oft its single power heater, while the present system continues .
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to apply heat through a low power heater. Thus, as seen in the graph, the temperature sensed by the thermostat decreases more rapidly in the prior art system than the temperature sensed in the present sys-tem. As a result, over a typical rethermalization time period, the prior art system must cycle its heater on more frequently than the high power heater of the present system is cycled on. The chances of scorching of food being rethermalized occurs during the tempera-ture peaks, so that there are more opportunities to scorch the food in the prior art system. This scorching danger is actually grèatèr in typ-ical prior art syStems which operate at higher temperature ranges than illustrated in the theoretical graph shown in Figure 25. For example, as will be discussed hereinafter, the method of the present ilvention operates the heaters within a thermostatic temperature range between,~220F and 235F + 5F) whereas a typical prior art heater operating over the same predetermined time period would operate between ~45F and 270F~. Prior art systems, which rether~m7alize~in2even shorter time periods, operate at even higher thermostat c ranges, e.g(350F to 400F) .
The present heating method also is directed to the manner of refining or adapting the two-stage heating method to a broad range of food types to be rethermalized. In order to accomplish this objective, the qualities or the toods, which determine the degree of heating the :.
foods require, had to be classified or organized. The following chart A, liSts the various tood qualities or parameters which render the foods difrlcult or easy to heat, i.e. foods having either a high heat 7, energy requirement or a low heat energy requirement.
: As seen in Chart A, the food qualities which would determine . whether a particular food is ditficult or easy to heat include tood den-sity, portion size, configuration, moisture content, specific heat, and fragility. The variance af the supply voltage also affects the ability of the heater to heat the tood.
Food density refers to mass per unit volume ot the tood, with the higher density tood being more W~icult to heat than the lower density roods. Larger portions Or tood, for exampl~e (Six ounces)or ? more, are more dif~icult to heat than smaller portions ot ~ood, for .
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Aladdin Sy:ler5~ ~ics, Inc . B ~1294~1~C~n 4~, ~`o ~ l o ~
example(1-1/2 to 3 ounces) .The configuration of the food, in particu-lar, the amount of surface area of the food which contacts the heat-ing plate determines the ease with which a food can be heated. Flat rood with relatively large surface area in contact with the heating plate is much easier to heat than unnat food which has very low sur-face contact with the heating plate. Moisture content also afrects the ease with which the food can be heated, wirh the higher moisture content rood~ e.g. 70-75 percent liquid being easier to heat due to steaming than the foods with less mo~sture content, e.g. 3a-7s per-cent liquid content. Specific heat also is a contributing factor to whether the food is difficult or easy to heat with loods of high spe cific heat, e.g. 0.85 to O.9j, being generally more difficult to heat than foods with low speciric heat, e.g. 0.65 to 0.80. Fragility of ~ood relers to whether a particular food can sustain its integrity and qual-ity, e.g. not dry out or lose its color or texture, when it undergoes heating. Foods such as meatloar, casseroles, lasagna and salisbury steaks are relatively sturdy and thus can undergo high energy heating, whlle such toods as poached eggs, omelets, rice, baked fish, pancakes and rare steaks are (ragile and cannot undergo high Intensity heating.
To arrive at the power settings and thermostat operating range to be used in the two-stage heating rethermalization method, extremes of toods with high energy heating requirements and foods with low energy heating requirements were rirst tested. Test exam-ples are shown ln the last column ot Chart A. A preferred technique for arriving at the low power and high power settings was first to determine an amount ot low power which could rethermalize low energy requirement toods, e.~,. 2 ounces ot peas or 2 stack6ed ~acncakes by raising their temperature~rom~elow(40F)to approximately,~(140F) The low heat energy re~uirement tood was not brought to the typical rethermalization temperature range ot,~l75F to 2~0F)with only the i lower power heater, since the final heater would utilize the two~tage -' heater and, thererore, would result in an additional baosting of power over and above the use ol only the low power~ lh~ea~ter~ O-~
Foods with high energy heat requirement for exa~ple, a(4 to 6 , ounce)salisbury s3ak with(4 ounces~ol mashed potatoes an~p ounces) $u~ r~
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PCT/ US~O/ ~4312 Aladdin SynerseLics~ Inc. B 129~3~C~

of broccoli spears were thereafter tested in the following manner:
The selected low power heater was run continuously and additional , power was supplied by a secondary heater at progressively higherpower until the high energy heat requirement food was adequately - rethermalized rrom below~(~0 F) to ~above,~65 F) . The intermittent application or the additional power was controlled between predeter-mined thermostatic settings. Once a high power or additional power setting was determined, the combinations ot Iow power and high power settings was tested on low heat energy requirement foad to determine if the rood could be adequately heated or if its quality was ; destroyed. Adjustments were made up and down the power sca~e on ;' both the low power heater and high power heater with the power to the high power heater being decreased when the power to the low power heater was ~ncreased. Through this process, it was eventually determined that optimum power settings for the high and low power ; heaters was a low power setting slightly lower than the initial setting ot the low power heater for low energy requirement roods and a s~ghtly increased power settlng tor the high power heater over the initial power supplied to the high heat energy requirement toods.
This test procedure was used at progressively lower thermostat range settings. That is, inctial testing,occurred at a typical higher prior art thermostatic range, e.g. between(245F to 280F).However, it was eventually determined that a thermostatic temperature range d 1l~-C lo~ C ~ C
between(215F and 240F)Jpreferably between,~220F and 2~,.1.. r~ S.
power supplied at 41 watts at the low power setting and 15 (watts~at the hlgh power setting accompli~shed the objectives of satisfactory retherma~zing entree ~ood of both high and 1OW energy requirements, as well as rethermalizing mixtures ot low and high energy require-ment o~ food such as shown in Chart A. Suitable power ranges ror the J..,l,. ~ . .
e~ trlee heater should be approximately 35 to 45 watts)for low power and 150 to 160(watts)~or high power.
';!, In order to establish the thermostat and power settings for small heater module 66, a similar procedure was followed. As a result, it was determined that a thermo~at range between(240 and sc~
275lworked satisfactorily with power supplied at 10(watts)at the low ., .
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r J~ S ~c -power setting and 46(watts)at the high power setting. With these power and thermostat settings, it was found that a variety of difficult to heat liquids, as well as delicate, llght weight rolls could be heated.
When rolls are to be heated, they can be supported on small dishes or a disposable plate or lid rather than on bowls.
--~ In order to establish the above parameters of this method of rethermalization, i.e. the range of foods to be rethermalized and the thermostat and power settings, other system constants had to be set.
For e.Yample, the thickness and size of the heater plate had to be held constant throughout the testing. It was determined that the system worked well with a nickel plated aluminum heatin~ plate having a thickness o~(l/8 of an inch)and a diameter of approximately(7 inches), The size, shape and configuration of the dish also had to be held constant. It was found that a highly conductive ceramic dish with an alumina additive to increase its convectiveness was suitable ;~ lor the rethermalization process. The preferred dish has a diameter of approximately(7 3/4~)and a thickness of appro~c~mately(~ of an i inch). In order to ensure proper heat conduction trom the aluminum heater plate to the dish, the dish should be extremely flat with very .~ Iittle concavity and no convex points.
The size, shape and configuration of the bowl for the small heater also was held constant during testing. A round four inch bowl, with an eight fluid ounce capacity, and made of a high heat resistant ; injection molded plastic was flound to be suitable. A bowl with a bot-tom thickness ot approximately a(orty-thousandths ot an inch)had the appropriate thermal conductivity. The bottom of the bowl also was kept very nat and a thin high heat resistant plastic lid was placed on top ol the bowls.
Numerous characteristics and advantages of the invention have ,~ been described in detail in the ~oregoing description with reference to ; the accompanying drawings. However, the disclosure is illustrative only and the lnvention is not limited to the precise illustrated embodi-ments. Various changes and modifications may be alfected therein by persons skilled in the art without departing trom the scope or spirit of the invention.

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Claims

PCT/US90/04312 August 20, 1991 Aladdin Synergetics, Inc. B 12943 PCT

N e w C l a i m s 32. A rethermalization cart (12) comprising a plurality of vertically and hori-zontally spaced individual heaters (64,66) for heating foods carried on service trays (30) supported on a plurality of vertically spaced tray supports (38) characterized in that said trays supports (38) are independent of heaters (64. 66). individual switch means (116) connected to each of said heaters (64, 66) for turning power on and off separately to each one of the heaters (64. 66). covers (56. 58) for hot food including switch activa-tor means (140) for activating said switch means (116), and operable for activating said switch means (116), when positioned on said tray (30), with said covers (56. 58) posi-tioned over hot food. with said switch activator means (14) being operable when said cover is in first and second different orientations on and relative to said tray (30).
above said switch means (116).
33. The rethermalization cart as recited in claim 32 wherein said cover (56.
58) is symmetrical about a vertical axis.
34. The rethermalization cart as recited in claim 33 wherein said cover (56.
58) is circular in cross-section.
35. The rethermalization cart as recited in claim 32 wherein said covers (56, 58) only cover hot food areas (48. 30) of said tray (30) while leaving the remainder of said tray (30) open.
36. A food storing and rethermalizing system comprising: a food service cart (12) having a cart interior; a food tray (30) having a hot food location (48. 50) thereon; a tray cover (36. 58) positionable in a covering position for covering the hot food location (48. 50): a tray supporter (38) for removably supporting said food tray (30) in said cart interior in a cart location; a heater (64, 66) for heating, with said food tray in the cart location. food at the hot food location (48, 50); a switch (116) for turning power on and off to said heater (64, 66); and an activator (140), associated with said tray cover (56, 58), for activating said switch (116) with said tray cover (56, 58) in the covering posi-tion and said food tray (30) in the cart location; characterized in that the improvement comprises:
mating alignment means (49) for aligning said activator (140) with said switch (116), said alignment means (49) including an inner peripheral base surface on said cover (56, 58) and an upward rim (49) on said food tray (30) and configured to mate with said base surface.
37. The rethermalization system as recited in claim 36 wherein said rim (49, 51) is round.
38. The rethermalization system as recited in claim 36 wherein at least two heaters (64, 56) are positioned at each shelf location and each said heater (64, 66) has a different overall power rating.
39. The rethermalization system as recited in claim 36 wherein one of said switch (116) and said switch activator (140) is a magnet and the other is made of mag-netic material.
40. The rethermalization system as recited in claim 39 wherein said switch (116) includes a pivotable housing (130), said magnet (132) being supported at one end of said housing (130), and a switch activated by the pivoting motion of said pivotable hous-ing (130).
41. The rethermalization system as recited in claim 40 wherein said switch (116) is a mercury switch carried by said pivotable housing (130).

Aladdin Synergetics, Inc. B 12943 PCT

42. The rethermalization system as recited in claim 39 wherein said switch (116) includes a reed switch (134A) and said switch activator (140) includes a magnet (140A) for activating said reed switch (134A).
43. The rethermalization system as recited in claim 36 further comprising a plurality of vertically spaced support bars (68) within said cart interior, including sup-porting pins (90) extending from said support bars (68). and attaching means (90, 98. 144 and 150) for removably attaching said heaters (64, 56) to said cart (12) including open-ings (98) for receiving said supporting pins (90).
44. A method of activating a rethermalization cart (12) having a plurality of vertically spaced tray supports (38) and a plurality of horizontally and vertically spaced heaters (64. 66) positioned adjacent said tray supports (38). a plurality of trays (30) hav-ing at least one hot food area (48, 50) and covers (56, 58) which are positionable over said hot food areas (48. 50). the method characterized by the steps of:
placing food to be heated on said tray (30) within said hot food area (48, 50) or placing food that is to remain cold in said hot food area (48. 50):
aligning at least one cover (56. 58) with one hot food area (48. 50) and placing said at least one cover (56. 58) over a hot food area (48. 50) while leaving a cover (56. 58) having a switch activator off of cold food in said hot food area (48. 50):
inserting said tray (30) within said cart (12) such that said hot food areas (48. 50) are positioned over said heaters (64. 66): and activating individual switch means (116) contained within said heaters (64, 66) by individual switch activators (140) carried by said covers (56. 58) that are over said hot food areas when hot food is carried in said tray (30).

Aladdin Synergetics B 12943 PCT

45. The method as recited in claim 44 further comprising the step of ensuring that cold food contained in said hot food area (48, 50) remains cold by leaving said hot food area (48. 50) uncovered.
16. The method as recited in claim 44 further comprising the step of ensuring that said switch means (116) is activated by said cover (56.58) switch activator when said cover (56. 58) is in a plurality of different orientations on said tray.
47. The method as recited in claim 44 further comprising the step of aligning said covers (56. 58) with said hot food area (48. 50) by a rim (49, 51) formed around the periphery of said hot food area (48, 50) which cooperates with an inner peripheral sur-face of said covers (56. 58) to ensure that said switch activator will activate said switch means (116) when said tray (30) is inserted with said car; (12).
48. A food storing and rethermalizing system said system comprising: a food service cart (12) having a car interior: a food tray, (30) having first; (43) and second (50) spaced hot food locations: a food tray, supporter (33) for removably supporting said food tray (30) in said cart interior and thereby in a cart location: a first heater (54) for heat-ing, with said tray (30) in the cart location. food at the first hot food location (48): a second heater (66) for heating, with said tray (30) in the cart location, food at the sec-ond hot food location (50): a first cover (56) positionable in a covering position to cover the first hot food location (48): and a second cover (58) positionable in a covering posi-tion. and generally independent of whether said first cover (56) is in its covering posi-tion to cover the second hot food location (50): characterized in that the improvement comprises:
first switch activator means (140), operatively associated with said first cover (56) being in its covering position. for activating said first heater (164) Aladdin Synergetics B 12943 PCT

generally only with said first cover (56) in the covering position and said food tray (30) in the cart location: and second switch activator means (140). operatively associated with said second cover (66) being in its covering position and operable generally separately of said first switch activator means (140). for activating said second heater (56) gener-ally only with said second cover (58) in the covering position and said food tray (30) in the cart location.
49. The system as recited in claim 48 wherein said first and second heaters (64, 68) include switches (116) which are activated by said switch activator means (140).
and wherein one of said switches (116) or said switch activator means (140) is made of a magnetic material. and the other includes a magnet.
50. The system as recited in claim 49 wherein said switch (116) includes a pivotable housing (130). said magnet (132) supported at one end of said housing (130) and a switch activated by the pivoting motion of said pivotable housing (130).
51. The system as recited in claim 50 wherein said switch (116) a mercury switch carried by said pivotable housing(130).
52. The system as recited in claim 49 wherein said switch (116) includes a reed switch (134A) and said switch activator (140) includes a magnet (140A) For activat-ing said reed switch (134A).
53. The system as recited in claim 48 wherein said tray (30) and covers (56.
58) include mating alignment means (49. 50) for aligning said switch activators (140) with said switches (116) when said tray (30) is inserted in the cart location.
54. The system as recited in claim 53 wherein said mating alignment means comprises rims (49. 50) which mate with an inner surface portion of the base of said covers (56. 58).

Aladdin Synergetics B 12943 PCT

55. A food storing and rethermalizing system, said system comprising: a food service cart (12) having a cart interior: a food tray (30) having a hot food location (48.
50) thereon: a tray cover (56. 58) positionable in a covering position for covering the hot food location (48. 50); a tray supporter (38) for removably supporting said food tray (30) in said cart interior in a cart location: and a heater (64. 66) for heating. with said food tray (30) in the cart location. food at the hot food location (48. 50) characterized in that the improvement comprises:
magnetic switch activating means (116, 140) for activating said heater (64, 60), said activating means (116. 140) including a first magnet element (140) carried by said cover and a second magnet element (115) supported by said cart and operatively interacting with said first element (140) to activate said heater (64. 66). with said tray, cover (56, 58) in the covering position and said food tray (30) in the cart location.
56. The system as recited in claim 55 wherein said tray, (30) includes mating alignment means for activating switches (116) connected to said heater (64. 65). said alignment means including rims (49.50) on said tray (30) and a corresponding inner sur-face on said covers (56.58).
57. The system as recited in claim 55 wherein said heater (64. 65) is remov-able from said cart which has a support bar (68) with outwardly extending supporting pins (90) extending from the support bar (68). and said heater (64.66) has openings (98) for receiving said supporting pins (90).
58. A food storing and rethermalizing system comprising: a food service cart (12) having a cart interior; a fool tray (30) having a hot food location (48) and another food location (50) thereon: an insulated cover (56) positionable in a covering position and supported by said food tray (30) for covering the hot food location (48): a tray sup-porter (38) for removably supporting said food tray (30) in said cart interior in a cart Aladdin Synergetics B 12943 PCT

location: and a heater (64) for heating, with said food tray (30) in the cart location. food at the hot food location (48):characterized in that the improvement comprises:
switch activator means (140) for activating said heater (64) with said insu-lated cover (36) in the covering position and said food tray (30) in the cart location. said switch activator means (140) including a first switching element (140) carried by said insulated cover (56) and a second switching element cooperable with said first switch-ing element and connected to said heater:and a protective cover (60) supportable by said food tray (30) and with said food tray (30) in the cart location. and protectively over both said insulated cover (56) when in the covering position and said another food location (30).
59. The system as recited in claim 58 wherein said tray (30) includes mating alignment means for aligning said activator (140) and a switch (116) connected to said heater (64). said alignment means including a rim (49) on said tray (30) and a corre-sponding inner surface on said insulated cover (56).
60. The system as recited in claim 59 wherein said rim (49) is round.
61. The system as recited in claim 58 wherein at least two heaters (64. 66) arepositioned at each cart location and each heater(64.66) has a different overall power rating.
62. The system as recited in claim 58 wherein one of said heater (64) includes a switch (116). and one of said switch (116) and said switch activator means (140) is a magnet and the other is made of magnetic material.
63. The system as recited in claim 62 wherein said switch (116) includes a pivotable housing (130). said magnet (132) being supported at one end of said housing (130). and a switch activated by the pivoting motion of said pivotable housing (130).

64. The system as recited in claim 53 wherein said switch (116) is a mercury switch carried by said pivotable housing (130).
65. The system as recited in claim 62 wherein said switch (115) includes a reed switch (134A) and said switch activator (110) includes a magnet (140A) for activat-ing said reed switch (134A).
66. The system as recited in claim 58 wherein said switch activator (140) is capable of activating said switch (116) in first and second different orientations on and relative to said tray (30).
67. the system as recited in claim 58 wherein said cart includes a pluraity of vertically spaced heaters (64.66) and a plurality of vertically spaced support bars (68) positioned adjacent said heaters (64. 66), said supoort bars (68) having outwardly extending support pins (90). and attaching means (90, 98. 144 and 150) for removably attaching said heaters (64, 66) to said cart (12) including openings for receiving said support pins (90).
68. A food thermalizing process. said process comprising the steps of: provid-ing a food service tray (30) with first and second food locations (48.50): providing a food service cart (12) defining a tray location and having first and second heaters (64.
66) associated with the tray location. each having respective first and second switch members (116) connected thereto: and placing food to be heated generally at the first food location;characterized in that the improvement comprises the steps of:
placing a cover (56) supporting a first switch element (140) over the food at the first food location (48) and thereby supported by said tray (30). and:
positioning the tray (30) with the cover (56) thereon in the tray location and thereby adjacent to the first and second heaters (64.66) such that the first heater (64) is actuated by the cooperation of the now proximate first switch member (116) and first switch element (140) and thereby heating the food at the first food location (48) and leaving the second heater (66) unactuated.
69. The process of claim 68 further comprising, before said tray (30) position-ing step, placing food which is nor to be heated at the second food location (50).
70. The process of claim 69 wherein said positioning step includes leaving the second heater (66) unactuated and thereby not heating, with the tray (30), at the tray location, the food at the second location (50).
71. The process of claim 69 wherein said positioning step including the food at the second location (50) being uncovered by an individual insulated cover With the tray (30) in the tray location.
72. The process of claim 69 further comprising, after said heating the food at the first location (48) by the first heater (64) step, removing the tray (30) from the cart (12). removing the cover (56) off of the food at the first location (48), serving the unheated food of the second location (50), and serving the uncovered and heated food of the first location (48).

73. The process of claim 68 further comprising, after said heating the food at the first location (48) by the first heater (64) step, removing the tray (30) from the cart (12).
74. The process of claim 68 further comprising, after said placing step and before said positioning step, positioning a protective cover (60) over both the positioned cover (56) and the second food area (50).
75. The process of claim 68 wherein said positioning step includes aligning the first switch element (140) and the first switch member (116).

76. The process of claim 75 wherein said aligning step includes mating an inner peripheral surface of said positioned cover (56) with a rim (49) formed on said tray adjacent the first food location (48).
77. The process of claim 68 further comprising the step of individually removing said heaters (64, 66) from said cart (12).
78. The process of claim 77 wherein said removing step includes unplugging each said heater separately, and further comprising the step of separately plugging new heaters (64, 66) into the car: (12) to replace the removed heaters (64, 66).
79. The process of claim 67 wherein said heating step includes cycling the temperature between an upper and a lower temperature.