CA2065030A1 - Food service cart with individually removable heaters - Google Patents

Abstract

A heating system for use in a food service cart (12) includes a plurality of vertically spaced tray supports (30) attached to the cart (12) and a plurality of heaters attached to the cart at a plurality of vertically spaced locations in alignment with shelf locations for heating foods carried on service trays and supported by the tray supports. The heaters are individually removable from the cart. 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

W O 91/02480 PC~r/US90/04314 2(~65030 :,..
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:-, ., FOOD SERVICE CART WITH INDnlDUALLY
REMOVABLE HEATERS
~i TECHNICAL F'IELD
The present invention relates to food service systems wherein individual portions of precooked food are supported on trays within moveable carts. The carts are placed in a chilled environment to store the food in a chiLied state. Selected foods on the trays are rethermalized in the cart, i.e., heated to a hot serving temperature, while other portions of food on the trays remain in the chilled state.
The rethermalization method of the present invention is directed to conductively applying heat to the selected food portions through a heating plate which is heated by a thermostatically controlled electri-cal heater.
BACKGROUND OP THE INVENTION
Various types ol food service systems and conductive heating rethermalization methods are known in the prior art. A most basic lood service system is one in which food is served immediately, or only a short time period, after the food is cooked or prepared. Typi-cally in better restaurants, food is served immediately after it is cooked or prepared. Such immediate service of the food generally results in the best quality o~ food. In other environments such as fast ~ood restaurants and cafeterias, food is not served immediately after preparation, but rather kept warm and served in the warm state. In fast food restaurants, food such as hamburgers is kept hot in dispos-able plastic containers. In cafeterias, food can be kept warm in the bulk state and served to individuals on a request basis, or food can be prepared in b~l~k and, thereafter, divided into individual portions and kept wdrm in a peJIet system. A peLlet system can also be used in n~n-cafeter'a em/ilonm~nts, SuC~l as hospitaJs wherein the food is ... ..

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placed on serving dishes and covered with insulated domes to keep the ;: food warm until service.
A significant drawback of systems which keep food warm for a short period of time before service is that the time period during which the food can be kepe safe and warm is relatively limited, and ~; the quality of the food deteriorates over time.
A rethermalization system is another prior art type of food Y ~-44~c qo-F) pared and then chilled in bulk to,~t(for less. Eventually the food is divided into individual portions and stored in a chilled state until it is reheated. The United States Food and Drug Administration (FDA) ~; guidelines specify that the chi~ed and stored temperature must be ~-4~ C
~40F)or less. A short time before the food is to be served, the food which is to be served hot is bro~lght to a safe serving temperature, i.e.
it is rethermalized. FDA guidelines specify that a safe serving tem-perature21s (165~F)or greater. The present invention is directed to certain improvements in structural and functional aspects of a .~ rethermalization system which uses conductive heating.
One manner of classifying prior art conductive heating rethermalization systems iS by the location of the heating elements ~ wi~hin the system. That is, prior art rethermalization systems have ;? located the heating element in either a food serving dish, a diSh sup-porting tray, or a shelf attached within a service cart.
U.S. Patent No. 3,908,~9 to Williams discloses a food service 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 power source extend ~rom the bottom of the base of the dish. The dish extends through a hole in a food service tray, and when the tray ~, iS supported in the service cart, the contact buttons rest on expased lea,f contactS which extend from a rear wall of the service cart.
Embedding the electrical heating element within the dish sig-nificantly increases the cost and complexity of the dish. A dlSh ~ within a ~ood service system undergoes severe handling sinCe it must :~ .
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WO 91/02480 Pcr/uS9~)/04314 ~ 3 ~ 20~o3 ' carry food, is subjected to heat for rethermalizing the food, and thereafter is subjected to heat, chemicals and handling impact in washing and drying processes. Thus, the dish is the component of this system which must be replaced most f requently. A system which ' incorporates the heating element into the dish thus has a relatively ., high long-term operating expense. Another disadvantage of this type of food service system is that relatively large electrical contacts must remain exposed in the cart to provide the electrical connection to the contacts of the dish. Such exposed contacts are thus subject to corro-sion 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 of the trays is relatively high and the trays are subject to breakage because of frequent han-dling during food service and cleaning. Exposed contacts are also required to provide electrical connection to the heating elements embedded in the trays. Another disadvantage of tray heating element systems is that the trays become warped after a period of time due to the frequent heating and cooling cycles to which the trays are su~
jected and their relatively large planar configuration. Once the trays become warped, good surface contact between the heating element portion of the tray and the dishes to be heated is lost. As a conse-quence, accurate, and possibly adequate, heat is not applied to the food during rethermalization. Examples of food service rethermalization systems which utilize trays incorporating heating elements are found in U.S. Patent Nos. 4,068,115 to Mack et al.;
4,167,983 to Seider et al. and 4,235,282 to deFilippis et al.
Food service rethermalization systems which incorporate the heating elements into shelves supported in the service cart alleviate the problem of the high cost of the more replaceable portions of the system, i.e. expensive dishes and trays. Furthermore, since the heat-ing elements are formed as a portion of the cart, i.e. a shelf within the cart, the connection of the electrical heating elements to a power source is incorporated within enclosed portions of the shelf and cart, alleviating the problem of exposed contacts. However, ., .
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rethermalization carts with shelf located heating elements do have certain limitations or disadvantages. Such systernsi generally incorpo-rate a plurality of heating elements in a fixed manner into a single shelf. Thus, when one of the heating elements on a shelf kecomes . .
inoperative, the entire shelf must be replaced, rather than repla~ing the single inoperative heating element. Examples of food service rethermali~ation 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 of food are held. Dependent upon whether the tray at a given shelf location is carrying food to be heated, the heating elements at the respective shelf locations have to ~e activated at an appropriate time. Power to all of the heating elements is generaLly turned on manually or via an automatic timer program. However, separate activation of the individual heating elements at the shelf locations is dependent on whether or not food to be heated is present at the shelf location. One technique is to have the food service personnel acti-vate a manual switch as the food tray is loaded on the shelf, if the tray contains food to be heated. However, such a technique is labor intensive and requires that the food service operator inspect the food on the tray or otherwise have an indication of whether food to be heated is present on a tray being placed onto the shelf.
Rubbright et al. '110 discloses a programmable system for acti-vating heating elements at various shelf locations. In this system, a transport modular pack is programmed to have each heater element follow a particular and independent time/temperature curve depen-dent upon the food to be heated at the particular shelf location. This technique is very complicated and labor intensive, and requires spe-cial care and attentiveness by a skilled operator, since a specific time/temperature curve must be programmed by the operator into the modular pack for each individual meal.

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Another prior art technique for activating the individual 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 shelf 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 cut out formed in the cover. Again, care must be taken by the food 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 attenW to by a different person, from the loading of the food onto the tray. Thus, miscommunication or misunderstanding as to the food located on the tray can result in incorrect positioning of 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 intermittently at a single power level during rethermalization, i.e. during the time when the food is initially brought from the chilled state to a serving temperature. The resistance heater is controlled by an on-off thermostat which oper-ates between upper and lower temperature of limits. Typically, the resistance heater applies heat over a predetermined time period.
While such a heating method has worked satWactory, it is subject to certain limitations. For example, the system must be designed to work within a practical time period. Whlle it would be desirable from a labor/cost standpoint to rethermalize chilled food as quiclcly as pos-sible, it is difficult to achieve high quality food when rethermalization occurs too quickly. For example, certain portions of food may become scorched while others remain cold, or the food may become dehydrated or discolored when rethermalization occurs too rapidly.

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One commercial rethermalization system accomplishes rethermalization of food in approximately one quarter of an hour.
However, the range or variety of food which can be rethermalized is limited and special plating techniques are required for many of the lighter or more fragile foods. 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 f~ods re~ain their quality after rethermalization. Plating techniques are most frequently used with light and fragile foods. Examples of plating techniques include supporting food on a dish 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 during which rethermalization takes place is less, any operating expense savings is very likely lost by the added expense is required in the special plating techniques.
Conversely, when the time for rethermalization is significantly increased, for example, to one hour as suggested in Williams '749 for an entree of a meat and one or two vegetables, the need for special plating techniques is reduced and a wider variety of 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 æ hospitals, prisons or nursing homes since scheduling options for handling and recyling the carts for the next meal are limlted.
The system disclosed in Bourner ~391 rethermalizes chilled food in approximately a one-half hour time period. Such a rethermalization time period has proven to be a satisfactory compro-mise. That is, a relatively wide variety of food can be rethermalized without the requirement of using special plating techniques. Further-more, the one-half hour time period hæ not proven to be too restric-tive on service personnel, allowing sufficient time for preparation and service of three meals per day in an institutional environment.
Nevertheless, even the system disclosed in Bourner '391 has certain limitations. For example, an unrestficted range of foods can-not be rethermalized without special plating or quality degradation.
It is di~ficult to rethermalize small portions of low density, fragile J

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foods, while retaining high quality of the foods and at the same time rethermalize large portions of high density, difficult to heat foods within 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 sufficiently 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 has proven unforgiving when certain set parameters are varied. For example, if portion sizes are varied too much from speci-fied portions, quality of the reheated food deteriorates. This is par-ticularly true if too much of a dense food is placed in combination with too little of a fragile, low density food. Such a system is also very voltage dependent. Thus, if the voltage supplied to the heating elements drops significantly below the norm, for example more than 5%, insufficient power may be supplied by the heating elements to heat the higher density, more difficult to heat foods. Similarly, if the voltage supplied to the heating elements increases excessively, for example 10%, excessive heat may be supplied to the more fragile foods causing deterioration in the quality of these foods.
The system in Dodd et al. '~56 uses a separate low power hold-ing circuit for keeping food warm arter it hæ been rethermalized. A
higher power primary heating circuit is thermostatically controlled and used to rethermalize the food over a predetermined time period.
Thus, whlle this system uses separate heaters having different power ratings, only the higher power heater is used for rethermalization, while the lower power heater is used primarily to keep the already rethermalized food warm. A switch is used to select between the two heating options.
The system in Mack et al. ~115 uses PTC power heaters æ the preferred type of heater embedded in the dish. The use of a resis-tance heater controlled by a thermostat is mentioned æ an alterna-tive to the PTC heater. The PTC heaters operate bæically æ multi-modal resistance heaters so that below their critical temperature they have a low electrical resistance, while above it the resistance is very ~ Wo 91/02480 PCr/~iS90/04314 high. Near the critical temperature, the resistance varies between the extremes. Thereore, depending upon temperature a PTC heater will deliver different wattages. During the development of the present system, it was found that PTC heaters had both structural and functional disadvantages. The heaters initially draw very high cur-rent, requiring more expensive high power capability electrical ser-vice. Also, if the initial input temperature of 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 for all of 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 of food being rethermalized. A
certain number of programs are available for use and are coordinated with various types or combinations of foods. The food servlce opera-tor thus must coordinate the particular food or combination of foods with the appropriate program. The food service handling process is thus complicated, requiring extra care and attention during meal preparation and special training for the operators of the system.
The food service system and method of rethermalization of the present invention was developed to overcome the structural and func-tional limitations of the prior art systems and methods discussed above.
SUMMARY OF THE INVENlION
The present invention is directed to a heating system for use in a food service cart for storing and heating foods. The system includes a plurality of vertically spaced tray supports attached to the cart for supporting food service trays at a plurality of vertically spaced shelf locations, and a plurality of heaters attached to the cart at a plurality of vertically spaced locations in alignment with the shelf locations for heating foods carried on service trays and supported by the tray sup-ports. A mechanism initiates the supply of power to the heaters and a timer turns the power off to the heaters after a predetermined time , WO 91/02480 Pcr/US9O/04314 - 9 ~ 5 ~ 3 ~

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 limit 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 thermostatic control.
ln a preferred embodiment, each heater includes an electrical heating eiement, and the power adjusting device includes a switch which shorts a portion of the heating element out of the operative heater circuit to operate the heater at the increased power level, and which places the portion of 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 of heating precooked food stored at a plurality of locations within a food service cart. According to the method, a preselected amount of food to be heated is supported adjacent an individual heater, and heat is supplied to the food from the heater over a prede-termined time period in a thermostatically controlled manner as fol-lows: Heat is inltially 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 o the thermostatic 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 of the temperature range is reached; and the steps of reducing and increasing the power are continuously .
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` W O 91/02480 PC~r/~'S90/04314 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 of an appropriate rethermalization time period and low and high power levels which will satisfactorily rethermalize the range of foods.
The terms two-stage heater and two-stage method of rethermalization will ~e used herein as shorthand terminology for the heater and thermostatic control which supplies power continuously dùring the rethermalization time either at a high power 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 rethermalization overcomes, to a degree, cer-tain ~ood processing limitations of a single-stage rethermalization heater (the on-off operation of a single-power heater). For example, foods with a broader range Or heat energy requirements can be rethermalized with the two-stage heater without degrading food qual-ity. AS a corollary, less special plating techniques are required for the lower density, fragile foods. Also, a mixture of high energy requirement and low energy requirernent foods can be more readily rethermalized simultaneously using the two-stage heater. Such mixed rethermalization wlth the tw~stage heater works particularly well with round dishes which both are aesthetically pleasing and allow freedom to vary portion sizes of one, two, or three foods.
The two-stage heater system and method is also more forgiving in various respects over a single-stage rethermalization heater system and method. That is, accurate portion sizes are not as critical when the two-stage heater and method is used. Similarly, variations in the voltage applied to the heaters does not as readily affect 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 within the prede-termined rethermalization time period. When a lower and more . .

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, accurate thermostat range is used, there is less chance that the food will become 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, fragile foods reach the desired serving temperature.
Another aspect of the present invention is directed to a system for selectively activating individual heaters in a food service cart.
An individual switch mechanism is connected to each of the heaters for turning power on and off separately to each one of the heaters. A
switch activator mechanism activates the switch mechanism, and is associated with covers for hot food to be carried on the service trays whereby one of the switch mechanisms turns power on to a respective one of the heaters when one of the covers is carried by a tray and supported in the cart above the last-mentioned switch mechanism. In one embodiment, the switch mechanism includes a pivotable housing, a magnet supported at one end of the housing and a mercury switch activated and carried by the pivotable housing. A preferred form of switch activator mechanism is a ring of magnetic material supported in the base of the food cover.
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 for hot food simplifies the process of acti-vating the individual heaters, as well as reduces the ~ce~ihood of error in activating the heaters. As food is placed on dishware, it is common practice to place a cover over food which is intended to be hot. The present system accomplishes individual heater activation by this sim-ple one-step process. The step of manually, and individually, activat-ing a switch for each shel~ location, programming a control module for each meal, or properly orientating trays within a service cart is thereby eliminated.
A further aspect of the present invention is directed to a heater module for use in a food service cart wherein a heating ele-ment housing is removably attached to the cart at a shelf location. A
heater plate sized to contact one food carrying member, and at least one electrical heating element are carried in the heating element , .
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housing with the heating element in thermal contact with the heater plate. The heating eiement 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 from the ca~t by removing the heating element housing. The heating element hous-ing prelerably has a pair of openings for receiving a pair of support pins extending from a support beam in the cart. Repair, replacement and cleaoing Or heatlng elements and heaters iS simplified by the present heater mod~e since each individual heater can be removed separately. In prior art shelf-mounted heaters, a plurality of heaters was fixedly attached to each shelt location 50 that individual replac~
ment and repair of the heaters could not be accompl~shed.
'~ Other aspects of this invention are as follows:
A heater module for use in a food service cart for storing and heating foods wherein a plurality of vertically spaced tray supports are attached to the cart for supporting food service trays at a plurality of vertically spaced shelf locations, said module being characterized , by:
i a heating element housing generally separate from the food service trays and the , tray supports, to be removably attached to the cart at a shelf location;
;~ a heatcr platc sized to contact one food carrying member; and at least one electrical heating element carried in said heating element housing in thermal contact with said heater plate;
, wherein said heating element housing includes attaching means for removably attaching said housing to the cart such that said at least one electrical heating element for a ~' respective heater platc is individually removable from the cart, indepcndently of the food service trays and the tray supports, by rcmoving said heating element housing.

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~ A heating system including: a food service cart for storing and heating foods; and i at least one tray support attached to said cart tor supporting a food service tray, said heating system characterized by:
at least one heating elemeut housing removably attached to said cart;
a heater plate sized to contact one food carrying member;
,~at least one heating element cani~d in said heating element housing in thermal ,contact with said heater plate; and : ,..;
i~attaching means for removably attaching said housing to said cart such that said at least one heating element for a respective said lleater plate is individually removable from said , .....
~'cart by removing said heating element housing independently from said tray support and the food ,service tray.
:.A rethermalization cart comprising: a bottom; a top; at least two sides connecting said bottom and top together; and a plur?lity of tray supports positioned at vertically spaced intervals for supporting a plurality of tc~od service trays, sai-i rethermalization cart characterized ,~a plurality of heating pads positioned adjacent said tray supports, and separable from said tray supports and food service trays;
attaching means for individually removably attaching each said heating pad to said cart so as to extend in said cart in a cantilevered fashion; and thermostatic control means attached to each said heating pad for controlling the temperature of said heating pads.
,j A rethermalization cart hlcluding: a cart frame; and at least one tray support ,!attached to said cart frame for supporting, in a tray support position, a food service tray having first and second hot food areas, characterized in that said rethermalization cart comprises:

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12b -,, ' first and second heater modules securable relative to said cart frame so that food ^' at the first and second hot food areas of the food service tray, when in the tray support position, .~. can be heated by said first and second heater modules, respecti~ely, and so that said first and . .
second heater modules are mdividually and separately removable relative to said cart frame.

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:, A relhermalization cart including: a cart frame including side walls, said cart frame defining at least in part a cart interior and a cart opening; and tray support means mounted /~ to said side walls for supporting in a tray support position in said cart interior a food service tray ~. having first and secon~ hot food areas, wherein the food service tray is moved to and from the ,~. tray support position through said cart opelling; characterized in that said rethermalization cart ,I comprises:
said cart frame including a cross-bar member extending horizontally between said~, side walls; and J first and second conductive heater pads secured directly to said cross-bar member, extending in a cantilever fashion towalds said cart opening, and positioned so that food at the first and second hot food areas ot the food service tray, when in thc support position, can be conductively heated by said first and second conductive heater pads, respectively.
A rethermalization cart inchlding (a) a cart frarne having side walls and (b) at least $ one tray support attached to said side w211s for supportmg in a tray support position a food ; .' service tray having at least one hot food area, characterized in that said rethermalization cart comprises:
a cross-bar mcmber attached to and extending between said side walls; and ,.j l a heater module removably securable to said cross-bar member so that when said heater module is secured and activated food at the hot food area of the food service tray, when in the support position, can be heated by said heater module, and so that said heater module is . removable from said cross-bar member.

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- 12c -A rethermalizatiorl calt for supporting a plurality of trays having a plurality of food compartments and tray openings toi- supporting therein one vf a plurality of serving containers containing food items, com?rising: a plurality of cart shelves, each said shelf having ~; supporting means for supporting at least one of the pluralily of trays thereon and having heating means capable of conforming to the tray openings for heating the serving containers positioned thereon, each said heating mearls including a plurality of heater pads; characterized in that said rethermalization cart comprises:
- a box chaMel ru~ning generally the widlh of said cart at each said shelf;
wherein each said heater pad has mountin~ means which mates with said box channel for releasably and individually securing each said heater pad to said shelf; and . electrical connection assemblies com~ectable to each said heater pad and running ; inside said box channel.
,.; A rethermali~ation cart system cvmprising:
a car~ having a frame defining at least in part a cart irtterior including an open front area, side areas and an open rear area;
first tray support means for supporting in said cart interior and in a first support `~ position a first tray having a first lhroughopenin~ such that the first tray passes through the open ', front area when being inserted into anJ removed from lhe cart fiist support position;
second tray support means for supporting in said cart interior and in a second support position a second tray having a second through-opening such that the second tray passes through the open rear area when being inserted into and removed from the cart second support position;
a first conductive heatin~ element extendhlg in cantilevered fashion from a position spaced inwardly from said front area ard out towards said froM area, said first tray support means and said first conductive heating element being arranged such that a first food dish positioned in the first through-openillg of the first tray is in direct thermal contact with said - first conductive heating element when the first tray is in the first support position; and .~ .
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- 12d -a second conductive heating element extending in cantilevered fashion from a position spaced inwardly from said rear area and out towards said rear area, said second tray -, suppon means and said second conductive heating element being arranged such that a second ~f ' food dish positioned in the second through-opening of the second tray is in direcmhermal contact with said second conductive heating element when the second tray is in the second support r position.
'r A rethermalization cart system COnlpriSin~:
a cart ha~ing a bottom, a top and two side walls joined together to define open front and rear areas;
at least one tray having a tray top surface and at least one through-opening in said tray top surface;
at least one food dish removably pcsiticnable generally in said through-opening in an operative pOsitioll;
first tray support means for supporting a ~ray in said cart interior inserted through said open front area;
at least one first heating element positioned spaced inwardly from said open front area and closely adjacent said first tray support means such that said food dish is adapted ~o be in direct thermal contact, through said through-opening, with said second heating element when said tray is supported by said second tray support means;
second tray support means for supporting a tray in said cart interior inserted through said open re~r area; and at least one second heating element positionsd spaced inwardly from said open rear area and closely adjacent said second tray support means such that said food dish is adapted to be in direct thermal contact, through said through-opening, with said second heating element when said tray is supported by said second tray support means.
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- 12e -A rethennalization cart including (a) a cart wall assembly defining at least in part a can interior having a plurality of tray assembly locations and a cart opening through which tray assemblies can pass relative to the tray assembly locations, (b) supporting means for supporting, at one of the tray assembly loca~ions and in an insert position, a tray assembly inserted in through said cart openhlg, the tray assembly having at least one hot food location.
and (c) at least one conduc~ive heater pad positioned such that food at the hot food location of - the tray assembly in the insert position can be heated thereon, characterized in that the . ~ improvement comprises:
;~ cantilever sea~ring means for securing said conductive heater pad to said cart wall assembly in a cantilcver rnanner such that said conductive heater pad extends from a position in said cart interior and outwardly towards said cart opening.
A rethermalization cart heater module, comprising:
a heater module housing having a top surface opening;
a conductive heater plate mounted at said top surface opening;
, a resistive heating assembly protectively enclosed in said housing and in thermal contact with said heater plate for heating same;
a temperature sensor in said housing and positioned for measuring the temperature of said heater plate and thereby for controlling at least in part the food retherrnalizing operation of said resistive heating assembly; and individual switch means protectively enclosed in said housing for turning power on and off to said resistive heating assembly, said switch means being activated by means outside , of said housing.

A rethermalization cart heater modulc, comprising:
a heater module housing having a top surface opening;
a conductive heater plate mounted at said top surface opening;

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a temperature sensor in said housing and positioned for measuring the temperature .
; ~ of said heater plate and thereby for controlling at least in part the food rethermalizing operation of said resistive heating assembly;
mounting means for mounting said housing in and to a rethermalization cart such .. that a food carrying tray can be inserted into the rethermalization cart and operatively positioned relative to said conductive heater plate; and a plurality of heater plate support legs extending downwardly from said heater ., plate and supported at lower ends thereof by said housing.
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A rethermalization cart heater module, comprising:

; a heater module housing having a top surface opening and an attachrnent end which is operatively and removably attachable to and in a rethermalization cart;

., a conductive heater plate mounted at said top surface opening;

, a resistive heating assembly protectively enclosed in said housing and in thermal ., contact with said heater plate for heating same;
a temperature sensor in said housing and positioned for measuring the temperature , of said heater plate and thereby for controlling at least in part the food rethermalizing operation of said resistiv~ heating assembly;
mounting members which mount said housing via said attachrnent end in and to a rethermalization cart such that a food carrying tray can be inserted into the rethermalization cart and operatively positioned relative to said conductive heater plate;

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-- 12g --a pair of spaced flanges secured to said housing in a herrnetically sealed fashion;
and electrical connector pins supported by said spaced flanges and extending out from attachment end for operatively connecting said resistive heating assembly to a power supply , ;, ~ associated with the retherrnalization cart.
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, A rethermalization cart heater module, comprising:
a heater module housing having a top surface opening, said housing including a base and a peripheral wall extending upwards from said base, said peripheral wall having tapered top and bottom exterior surfaces along front and sides of said housing, and said top surface opening being formed in said peripheral wall;
a conductive heater plate mounted at said top surface opening;
a resistive heating assembly protectively enclosed in said housing and in thermal contact with said heater plate for heating same; and a temperature sensor protectively enclosed in said housing and positioned for measuring the temperature of said heater plate and thereby for controlling at least in part the tood rethermalizing operation of said resistive heating assembly.
i Various advanta~es and features ot novelty which characterize the lnvention are pointed out ~ith prtlcularity In the claims annexed hereto and tormin~ a part hereot. However, tor a better understand-~ ot th inventlon, Its advant~es, and obpcts obtained by lts use, reterence should be ~de to th drawin~s whlch form a turther part hereot and to t~ a~ompan~ d scrtpave matter, in which there is illustrated and d~rlbed preterred embodlmen~ of the invention.

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- 12h -:, BRn~F DESCRlPTION OF T~E DR~WINGS
Figure 1 is a perspective view ot a tood service system includ-. i ing a mob~e tood service cart and a retri~eration cabinet;
~ Fi~re 2 is a partlal rear vlew o~ the tood service cart;
, ., F~ure 3 Is a horlzontal sectional vlew ot the tood service cart, ,~ ~llustratin~ one tood tray supported at a shelt ~ocation and another tood tray 11l th proc~s ot bein~ irtserted lnto a sheLf;
Fl~ure ~ ls a partlal tront elevatlonal view illustratin~ trays, dishware, and covers supported at shel~ locadons wlth one overall cover partlally broken away:
-~ Flgure 5 is a partlal sectional view illustrating dlshware sup-. ported on a heater:
Fl~ure 6 tS a partial side elevational view w1th the stde wan of the service cart removed and illustratin~ food trays and covers sup-. ported at horizontally spaced shelt locations;

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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 : of Figure 7 with a portion of a tray and cover illustrated above the heater module;
, Figure 9 is a top plan view of a generally T-shaped heater ele-ment suppart bar;
Figure 10 is a front view of the support bar;
~ . Figure 11 is a cross-sectional view taken generally along line ; ll-11 of Figure 9;
. Figure 12 is a plan view of a cover plate for the support bar;
,, Figure 13 is a front elevational view of a heater module;
Figure 14 is a rear elevational view of the heater module;
Figure 15 is a cross-sectional view taken along line 15-15 of Figure 7;
Figure 16 is a partial exploded perspective view of a heater ., module, tray and cover, illustrating a pivoting switch;
; Figure 17 is a plan view of a smaller heater module;
Figure 18 is a plan view of an attachment plate of the module , of Figure 17;
Figure 19 is a partial exploded perspective view of a heater '. module, illustrating an alternate switch mechanism;
Figure 20 is a diagrammatic view of the resistance pattern of one embodiment of a heater element;
Figure 21 is a diagrammatic view of the resistance pattern of another heater element;
Figure 22 is circuit diagram of one embodiment of a two-stage J heater and heater control;
; Figure 23 is a circuit diagram of another embooiment of a two-stage heater and heater control;
Figure 24 is a circuit diagram of a further embodiment of a two~tage heater and heater control; and 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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- PC T/ US 90/ 0~314 Aladdin Syner~getic s, Inc . ~ R12~44p~'r . .
. DETAILED DESCRIPTION
Food Service Svstem Referring to the drawings, wherein like 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 refrigeration cabinet 14. b o ~ o~
; Cart 12 is formed generally of sheet metal and includes a~;up-port base 16. A first pair of wheels 18 depend from one of the sides of base 16 and a second pair of steerable and lockable wheels 20 depend from its other side. A first side wall 22 extends upwardly from a rirst side of base 16 and a second side wa~ 24 extends upwardly rrom a second side Or base 16. A top wall 26 is connected to and extends between the upper ends of first and second side walls 22 and 24. Tubular members 25 (one of which is shown along the front edge Or cart 12 in Figure 1) are attached to the rrOnt and back edges of each side wall 22 and 24; and generally 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 walls 22 and 24, along the front and back edges of cart 12. Tubular members 2s, 27 provide additional rigidity to cart 12. A handle 28 is attached to the e~terior Or side wall 24, and ~; is used to move and steer cart 12. The front and back ol cart 12 are open to allow free access for the insertion and removal of tood ser-vice trays 30. Male electrical connector contacts 32, which connect cart 12 to an electrical power source, extend from base 16 immedi-ately below side wall 22.
In use cart 12 is loaded with trays 30, which in turn support precooked or otherwise prepared food. Thereafter, cart 12 is whee~ed into reIrigeration cabinet 14 where it will be stored in a chilled state ;~1 until rethermalization. Refrigeration cabinet 14 includes a front :, access door 34 to allow entry and removal ol cart 12, and which seals ~ the refrigeration cabinet. A female electrical receptacle 36 is 'I attached to the interior back wail of cabinet 14. When cart 12 is j backed completely into cabinet 14, contacts 32 engage receptacle 36 to thereby connect cart 12 tO a main electrical power supply in a ., .

:~.,.. " , , ^ . , wo 91/02480 pcr/us9o/o43l4 2 ~ ? 0 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 ~s also provided to control the amount of time that power is supplied to the cart.
If 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~l and Dishware As seen in Figure 3, a pair of support bars 38 are attached to the inside surfaces of side walls 22 and 24 at both the front and back of cart 12. At a given horizontal location, support bars 38 define a front and a back shelf location to support a pair of trays 3~.
- Support bars 38 are preferably formed of a rigid plastic. As seen in Figure 4, support bars 38 have a generally T~haped . cross-section with pins 40 formed 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 from the top surface of support bars 38.
Projection 39 mates with a slot 41 along the bottom edge of tray 30 to hold tray 30 in position.
Tray 30 has a generally rectangular configuration with an upstanding pefipheral fim 42, which extends upward from a support surrace 44. A divider 46 also extends upward from the support su~
, face 44 and divides surface 44 into a food holding area and a utensil/napkin holding area. In the food holdlng area a round large entree opening 48, and a round small soup opening 50, are formed. A
rim 49 extends upward from surface 44 and around the periphery of opening 48. A rim 51 extends upward from surface 44 and around opening 50. As seen in Figure 4, an entree dish 52 fits within entree opening 48 and a soup bowl 54 fits within soup opening 50. Entree dish 52 and soup bowl 54 both have a conventional round shape. As seen in Figure 5, the diameter of dish 52 increases slightly from its smallest diameter along its bottom surface, and is correlated to the $

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' diameter of opening 48 such that the bottom surface of dish 52 ~ e~tends down slightly below the lower surface of tray 30, and the side - and upper rim of dish 52 are out of contact with rim 49 of tray 30.
The diameter of soup bowl 54 is likewise correlated to the diameter of opening 50.
Entree dish 52 and soup bowl 54 are designed to be capable of ; c. ~c~ X~ c ts holding hot foods~' An insulated entree cover 56 is therefore provided to cover dish 52 and food held on the dish; and an insulated soup cover 58 is provided to extend over and cover soup bowl 54. A disp~sable lid is aLso placed directly on top of soup bowl 54. 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 ~8 is greater than the diameter of soup bowl j4 and rim 51.
An overall food cover 60 is provided to cover the entire food carrying area of support surface 44. Cover 60 provides protection for foods, other than hot food covered by covers 56 and 58 which are sup-ported in the food service area 44 of tray 30. The utensil/napkin sup-port area remains open so that utensils, napkins, menu and patient identification can be placed on the tray after al! the rood has been placed on tray 30 and covered. Covers 56 and 58 are insulated covers preferably formed of an outer hard plastic shell filled with an insula-tion material as seen in Figures 8 and 16. Cover 60 is preferably formed of a rigid injection molded plastic.
Heatine SYstem As seen in Figure 3, a pair of large entree heater asselmbliesjeF p~ o~
modules 6~ and a pair of small soup heater assemblies~ modules 66 are located at each horizontal shelf location. Figures 9, 10, 11 and 12 illustrate the support structure for supporting heater modules 6~ and 66 at the hor~izontal shelf locations. As seen therein, a generally T-shape~lP~ 68 e~ctends between oppasite side walls 22 and 24. T-bar 68 is preferably formed of a high strength aluminum material and includes a central rib 70, a cross member ~2 which extends perpendic-ularly from oppasite sides of rib 70, and a pair of wall members 74.

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- l7 Wall members ?4 extend perpendicularly away from oppasite distal 0 ~
ends of crosslmember 72 so that a hollow open-ended rec~angular area is defined between CfOSS 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 inte-rior of wall member 74, and projections or clips 82 extend from an upper surface of cover 76 and fit within notches 80 to secure base cover 76 in place.
A plastic end piece 84 is located at each end of bar 68 and dis-posed between a respective end of bar 68 and one of the walls 22, 24.
Each end piece 84 has a small cross section portion 86 which friction-ally fits into the hollow interior of bar 68, and an ex;erior p~rtion 88 which fits between the interior surface of the wall members 22 and 24 and the distal ends of bar 68. Exterior portion 88 has a curved e~te-rior surface.
Bar 6a, base cover 76 and end pieces 84 are secured to walls 22 and 24, preferably by screws, one of which 81 is shown in dash-line in Figure 9, e.Ytending through the walls and into end pieces 84. Four support pins 90 e~tend from each longitudinal edge of bars 68. Each pin 90 is attached to bar 68 in a conventional manner, preferably by screw threads. Pins 90 have a large diameter base portion 92 and a smau diameter distal portion 94. A friction member, such as an O-ring 96, is secured to the distal end of base portion 92. Pins 90 function to support heater modules 64 and 66 in a cantileve;r manner from bar 68. As seen in Figure ?, a cylindrical bore~,98 is ~ormed through the housing of heater module 64 adjacent each of its sides.
Slmilar bores are formed in heater module 66. Pairs of pins 90 fit within bores 98 to support the heater modu~es. In this manner, heater modules 64 and 66 are supported at a plurality of vertically spaced shelf locations. The pin 90 and bore 98 connection and support tech-nique allows each individual heater module, which is sized to heat a single dish or bowl, to be individually removed for service or replacement.

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Details of heater module 64 are best seen in Fig~lres 7, 8 and ; 13-15. Heater module 66, except where noted otherwise particularlywith reference to Figures 17 and 18, is constructed similar to heater module 64. The e~terior of heater module 64 is defined by a plastic housing 100, a metal heater plate 102, a plastic switch attachment plate 104 and a rubber or plastic gasket 106. The components which are held within the interior of heater module 64 include a res~siive electrical heating element 108, an insulation plate 11Q, a thermostat 112, a fuse 114, a pivot switch mechanism 116, and an indicator light 118.
Housing 100 is formed of a relatively rigid, high temperature ~ resistant, injection molded thermoplastic. Housing 100 includes a ; ~ bottom or base 120 and a peripheral wall 122 e~ctending upward ~rombot;om 120 about the periphery o~ 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 preferably formed of a nickel plated alumi-num plate having a thickness of approximately of,~/8"). Plate 102 is generally round and has a circular perimeter generally mating with the configuration of round opening 124. A plurality of support legs ;~ 128 extend downward at a plurality of locations about the perimeterof heater plate 102. A resistive heating element 108, such as shown ~, in Figure 2a, is secured to the bottom of heater plate 102.
~ Element 108 is preferably formed of a resistance foil in the -~ pattern illustrated in Figure 20. The foil is encased in a silicon rubber ~, and is attached to plate 102 during vulcanization of the rubber by the application of heat and pressure. Plate 110, formed of an insulative material, such as a ceramic ri~er or the ~<e, is thereafter secured in position below heating element 108 bg resting on top or ledge 126.
Thermostat 112 is secured with an adhesive directly to the bottom of heater plate 102 within a centrally located opening ln heating ele-ment 108. Heater plate 102 and the components secured to It are PC ~ i ~ a ~O, 0431~
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attached to housing 100 by securing legs 128 within holes 1~0 formed within housing 100 adjacent peripheral wall 122. The border between heater plate ~,~and opening 124 is sealed with a room temperature vulcanized silicon rubber to prevent entry Or 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 partially 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 heater 64 to i be cleaned in a pressure washing process. Plate 104 supparts pivot , o.~ --~c~s 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 rnag4et 132 carried in one open end of housing 130, and a mercury switch"received within an opening in the other end of housing 130. A pair o~ support rlanges 136 e.Ytend upward from the interior of plate 104 to pivotally support housing 130 via a support pin 138 passing through holes in ~langes 136 and housing 130.
In the deactivated state o~ switch 116, the end of housing 130 which carries magnet 132 is pivoted downward and the opposite end carrying mercury switch 13~ iS pivoted upward. In this position mer-cury switch 134 iS in its open state and power is not supplied to heat-ing element 108. Switch 116 is activated by placing an insulated cover 56 over a dish c~ food to be rethermalized. As seen in Figures 8 o~ s~;tc~ ac~ O~ ~ c ~s and 16, an annular ring~l40 of a magnetic metallic material is held within the perimeter of cover 56 adjacent its base. As seen in Figure 8, with tray 30 and cover 56 in position, magnet 132 is drawn upward toward metallic ring 140 and mercury switch 134 pivots downward to be placed in Its closed state. Activation or an appropriate heater module is thus readily assured, since whenever an insulated cover is placed over ~ood to be heated, the heater module is automatically act~vated. A cylindrical projection 142 is rormed 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 elec-trical connector pins 144 are supported by a pair of spaced ~langes 148 formed on plate~ in a hermetically sealed mann(e~r. Pi~ 44 connect to a main power supply bypassing through holes 150Ain the side T-bar 68 and connecting to electrical wiring 74 supported within the hollow interior of T-bar 68.
Figures 17 and 18 illustrate details of small heater module 66.
As seen therein, attachment plate 108~ differs in configuration from j~ attachment plate 108 used in module 64. Attachment plate 108' extends acros~ the entire back of module 66 and has the configuration of two triangles connected by a central strip. Switch 116 is supported on f1anges 136~ on one of the triangles, and connector pins 144 e:ctend from flanges 148~ the other triangle. Otherwise, module 66 is con-f structed similar to module 64.
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~: Flgure 19 illustrates an alternate em~odiment of a switch ;' mechanism 116A in 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 i~ along the base of cover 56. In order to properly align magnet 140A
'~ with reed switch 134A, a projection 49A is formed adjacent rim ~9 on tray 30 and cooperates with a mating recess 57 formed In the interior surface of cover 56. This embodiment of switch mechanism and acti-vating mechanism is a secondary embodiment and should be used only in environments where persons or patients with heart pacemakers are not present, since magnet 140A within cover 56 could interfere with ~j the operation of the pacemakers.
Figure 20 illustrates the resistance pattern Or heating element ~' 108 Or heater assembly 64, and Figure 22 is a circuit diagram illustrat-ing the manner In whlch power is supplied through heating element 108 to accomplish two-stage heating. Two-stage heating refers to the fact that in 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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arranged to cover substantially all of the bottom surface of heater ;~ plate 102. F`~v~ ,5~r~ prc~c~r~ ak~ a~ ~oL~r~l C ~; `r C I-~ ~ r ~_ oc, l~ a l; ~ o \ ~ ~ a ~ s) ~ ~a ~ L, .
As seen in Figure 22, power is supplied to resistive elernents A, B and C of heating element 108 when mçrcury switch 116 is closed.
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When thermostat 1~2~is open, current passes through all 3 resistive elements A, B and C and provides heat at a first power level. Kow-ever, when thermostat 112 is closed, current is shunted past resis~ive element A and only passes through resistive elements B and C, C
being a low voltage indicator light circuit. In this state, heat is sup-plied at a higher power level since the current passes through a lower resistance (B I C). Thus, during a rethermalization time peri~o (the time period during which timer 33 supplies electrical power), power is always supplied to the food being rethermalized.
Details of the rethermalization will ~e discussed in grea~er detail in the discussion of the rethermalization method. However briefly, when rood to be rethermalized is in its cold state and power is initially supplied to heater element 108, thermostat 112 is in its clcsed state so that heat is initially supplied at high power through resistive elements B and C. When the thermostat reaches its upper limit, it opens, so that current flows through all three resistive elements A, B
and C at lower power. Thereafter, when the thermostat reaches its lower temperature Limit it again closes to short current trom resistive element A, and again supply heat at the high power level~ Thus, ", throughout the rethermalization period heat is actively supplied to the food being rethermalized, but at varying power levels.
As seen iQ Figure 20, the higher resistance of resistive element l A is accomplished by a plurality of parallel resistance elements con-nected at connection points 1 and 2, which are also shown in Figure 22. In Flgùre 21, whlch illustrates an alternate heating element 108 for use in the smaller soup heater module 66, the higher resissance of resistive element A is accomplished by using a smaller resistance ele-ment connected at connection points 1 and 2.
Flgure 23 illustrates an alternate embodiment o~ heater ele-ment and control circuit arrangement which also accomplishes two-stage heating. In this embodiment, a first resistive heating element ~o>~ a~ I I Z ~ C
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A' is connected in parallel to a second resistive heating element B~.
Thermostat 112~ controls the passage of 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 of operation. The resistance of element B~ is preferably higher than the resistance of element A~ so that in the low power mode of opera-tisn, the power ls proportional relatively low, e.g. 2596 o~ the total power when current passes through both elements A~ and Bb Element Cr can also ~e included for an indicator light.
Figure 24 Ulustrates another embodiment of heater element and control circuit arrangement which also accomplishes two-stage heating. In this embodiment, a first resistive heating element A~ is a~o connected in parallel ;o a second resistive heating element B~.
However, thermostat 112~ alternately supplies current to elements A~
and B~. The resistance of 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 food. The food is stored at the plu-rallty of shelf locations within food service cart 12. Within cart 12, a preselected amount of food to be heated is supported adjacent each individual heater 64, 66. Generally, the total food portion for an s ~. ~q~ ~ ~o~
entree can vary from~ ounces) with the entree including one, two or three different foods. Similarly, the food to be heated by the soup '8S ~o l~o ~ lo~k~
heater element can vary rrom(3 to 6 ounces~of soup, cereal, hot des-serts, rolls or other liquids. The use oI the two-stage heater in accor-dance with the present invention is particularly advantageous for rethermalizing entrees, and more particularly entrees which vary in thelr range of heat requirements. Entree foods generally include meat, fish, poultry, casseroles, starches and vegetables.

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The two-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:
1) Heat is initially 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 of 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 of the temperature range is reached; and steps 3 and 4 are cyclically performed over the predetermined time period to continuously supply heat from the heater to the food during the predetermined time period.
Turning to Figure 2S, the two-stage application of heat in a rethermalization method in accordance with the present invention is compared to the application of heat in a prior art one-stage rethermalization method. In this prior art method heat is supplied by a single power heater which is cyclically turned on and off over the predetermined rethermalization time period. The graph is a theoreti-cal graph and assumes that: (1) the total power of the prior art heater is the same as the high power level of the heater used in the present method; (2) all heaters operate between the same thermostat limits; and (3) the same food portion, an average entree portion, is being heated. The graph illustrates the temperature sensed by a ther-mostat coupled to the bottom of the heater plate.
As seen in the graph, both systems initially supply heat to the system at the same rate. After the upper temperature of the thermo-static temperature range is reached, the prior art system completely shuts orf 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 or the present system is cycled on. The chances ot scorching of food being rethermallzed 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 greater in typ-ical prior art systems which operate at higher temperature ranges than illustrated In the theoretical graph shown in Figure 25. For ~,~ example, ~ will be discussed hereinafter, the method of the present ~ invention operates the heaters within a thermostatic temperature ; range between (220 F) and~(235 F + 5 F~ ,whereas a typical prior art heater op~rating over the same predetermined time period would s operate between~(245F and 270F~, Prior art systerns, which ,~ rethermali,ze in even shorter time periods, operate at even higher thermostatic ranges, e.g.,~S0F to 400F), '; The present heating method also is directed to the manner of refining or adapting the two~tage heating method to a broad range of ~ tood types to be rethermallzed. ~n order to accomplish this objective, ,i the qualities Or the roods, which determine the degree Or heating the foods require, had to be classified or organized. The rollowing chart A, lists the various lood qualities or parameters which render the foods difficult or easy to heat, i.e. foods having either a high heat energy requirement or a low heat energy requirement.
As seen in Chart A, the rood quallties which would determine whether a partlcular rood is difficult or easy to heat include foQd den-sity, port~on size, configuration, moisture content, specific heat, and ~, fragility. The variance of the supply voltage also affects the ability of the heater to heat the food.
Food density refers to mass per unit volume of the food, with the higher density ~ood being more difricult to he~a~t than the lower density ro~ds. Larger portions Or rood, rOr example(six ounces~or more, are more difficult to heat than smaller portions of food, for ,;
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:.' PcT/lia~c'/~- '31 ' Aladdin Syn-r~etics, Inc. , B12944PCT

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e~ample(1-1/2 to 3 ounces), The configuration of the food, in particu-lar, the amount of surface area of the foad which contacts the heat-ing plate determioes the ease with which a food can be heated. Flat food with relatively large surface area in contact with the heating plate is much easier to heat than unflat food which has very low sur-face contact with the heating plate. Moisture content also affects the ease with which the food can be heated, with the higher moisture content food, e.g. 70-75 percent liquid being easier to heat due to steaming than the toods with less moisture content, e.g. 38-75 per-cent liquid content. Specific heat also is a contributing factor to whether the food is difficult or easy to heat with foods of high spe-.~cific heat, e.g. 0.85 to 0.95, being generally more difficult to heat than foods with low specific heat, e.g. 0.65 to 0.80. Fragility of food ,~re~ers 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 meatloaf, ca~;seroles, lasagna and salisbury steaks are relatively sturdy and thus can undergo high energy heating, while such foods as poached eggs, ome!ets, 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 roods with high energy heating requirements and ~oods ;,with low energy heating requirements were first tested. Test e~am-~, ples are shown in the last column of Chart A. A preferred technique for arriving at the low power and high power settings was rirst to determine an amount of~l,ow power which could rethermalize low energy requirement loods, e.g.(2 ounces~of peas or 2 stacked pancakes by raising their temperature from below~(40F)to approximately(l40F.) The low heat energy re~uirement food was not brought to the typical rethermallzation temperaC~ure range o~(l75F to 210F)with only the . lower power heater, since the rinal heater would utilize the two-stage ~i heater and, there~ore, would result in an additional boosting of power over and above the use o~ only the low powe~r ge~ate,r~ o'~ k j Foods t~ith hligh~eknergy heat re~uirement folr exam~le, a~ to 6 ,' ounce)salisbury steak with(4 ounces)of mashed pota~oes an~4 ounces) ~ '; ? ~ "1 rU ~ E S ~' t'~ ~ ' ~'; ' ' ' ' 't' . ~ ' .' ` .
.:

PCT/~iS90/04314 Alad~in Syrle~ge~ics, Inc. ~.12,44PC~

- 26 ~
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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 higher power until the high energy heat requirement food was adequately rethermalized from below,~40F)to ~ove~65F). The intermittent application of the additional power was controlled between predeter-mined thermostatic settings. Once a high power or additional power setting was determined, the combinations of low power and high power settings was tested on low heat energy requirement food to determine if the tood could be adequately heated or if its quality was destroyed. Adjustments were made up and down the power scale 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 increased. Through this process, it was evenn;ally determined that optimum power settings for the high and low power heaters was a low power setting slightly lower than the initial setting of the low power heater for low energy requirement foods and a slightly increased power setting for the high power heater over ~he .,.
' initial power supplled to the high heat energy requirement foods.
This test procedure was used at progressively lower thermostat ,r range settings. That is, initial testing occurred at a typical higher prior art thermostatic rangè, e.g.6et~w8eeCn,$245F to 280~F),However, it was eventually determined that a thermostatic temperature range ~o 2 C ~ 'C
between~l5F and 240F),preferably between(220F and 235F),and , power supplied at 41 watts at the low power setting and 156 watts at the high power setting accomplished the objectives ol satisfactory rethermalizing entree ~ood of both high and low energy requirements, as well as rethermalizing mixtures of low and high energy require-ment of tood such as shown in Char$ A; Suitable pow"er ranges for the entree heater should be approximately 35 to 45(watts)for low power rO~l.. y~
and 150 to 160~(watts)for 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 thermostat ran~e between 240 and 2?5 worked satisfactorily with power supplied at 10~atts)at the low ., J . ~ 7, ' ~

.

PCT/US90/0431~
Aladdl~ Syne~ l ics, Inc. ~1~94aF~`'T, :

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, light 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.
~n 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 example, the thickness and size of the heater plate had to be held ' constant throughout the testing. It was determined that the system worked wen with a nickel plated aluminum heating plate llaving a ,` thic~ness of,~/8 o~ an inch)and a diameter of app~oximately(7 inches).
~he size, shape and con~iguration of the di~sh also had to be - held constant. It was round that a highly cdnductive ceramic dish ; with an alumina additive to increase its convectiveness was suitable for the rethermalization process. The preferred dish has a diameter of approximately(7 3/4~3and a thickness of approximately(~ of an . inch) . In order to enlsure proper heat conduc~ion from the aluminum heater plate to the dish, the dish should be e.Ytremely flat with very little concavity and no convex points.
./ The slze, shape and configuration of the bowl for the small `, 2 ~ hea~ter also was held constant during testing. A round(four inch)bowl, with an,~ight ~luid ounce)capacity, and made of a high heat resistant injection molded plastic was foupd to be suitable. A bowl with a bot-tom thickness of approximately a~orty-thousandths of an inch)had the appropriate thermal conductivity. The bottom of the bowl also was kept very flat and a thin high heat resistant plastic lid was placed on top o~ the bowls.
Numerous characteristics and advantages of the invention have been described In detail In the foregolng description with refecence to the accompanying drawings. However, the disclosure is illustrative only and the invention is not limited to the precise illustrated embodi-ments. Various changes and modifications may be af~ected therein by - persons skilled in the art without departing from the scope or spirit of the lnvention.

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Claims (119)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A heater module for use in a food service cart for storing and heating foods wherein a plurality of vertically spaced tray supports are attached to the cart for supporting food service trays at a plurality of vertically spaced shelf locations, said module being characterized by:
a heating element housing generally separate from the food service trays and the tray supports, to be removably attached to the cart at a shelf location;
a heater plate sized to contact one food carrying member; and at least one electrical heating element carried in said heating element housing in thermal contact with said heater plate;
wherein said heating element housing includes attaching means for removably attaching said housing to the cart such that said at least one electrical heating element for a respective heater plate is individually removable from the cart, independently of the food service trays and the tray supports, by removing said heating element housing.

2. The heater module as recited in claim 1 wherein said heating element housing has a pair of openings for receiving a pair of support pins extending from a support beam in the cart.

3. The heater module as recited in claim 1 or 2 including individual switch means connected to said at least one electrical heating element for turning power on and off to said heating element, said switch means being supported within said heating element housing and being activatable by switch activator means associated with covers for hot food to be carried on service trays to be supported in the cart such that one of said switch means turns power on to a respective one of said heater modules when one of the covers is carried by a tray and supported in the cart above said last-mentioned switch means.

4. The heater module as recited in claim 3 wherein said heating element housing includes a switch attachment plate forming a portion of the major bottom surface of said heating element housing, said switch means being supported on an interior surface of said attachment plate.

5. The heater module as recited in claim 4 including support flanges extending upward from said interior surface of said attachment plate, and said switch means including a pivotable housing pivotably carried by said support flanges, a magnet supported at one end of said pivotable housing, and a switch activated by the pivoting motion of said pivotable housing.

6. The heater module as recited in claim 5 wherein said switch is a mercury switch carried by said pivotable housing.

7. The heater module as recited in claim 4 wherein said switch means includes a reed switch.

8. The heater module as recited in claim 1 or 2 further comprising switch means for shorting a portion of said at least one heating element out of an operative heater circuit to operate at an increased power level and for placing said portion of said heating element into the operative heater circuit to operate at a reduced power level.

9. The heater module as recited in claim 8 wherein said heating element is arranged to cover substantially all of the surface area of said heater plate.

10. The heater module as recited in claim 9 wherein said heater plate is generally circular.

11. The heater module as recited in claim 1 or 2 wherein said at least one heating element includes first and second electrical heating elements, switch means for supplying power to both said heating elements in an increased power mode of operation and for supplying power to one of said heating elements in a reduced power mode of operation.

12. The heater module as recited in claim 11 wherein said second heating element is a higher power heater than said first heating element, and said switch means supplies power to said first heating element in the reduced power mode of operation.

13. The heater module as recited in claim 11 wherein said first and second heating elements are arranged to both cover substantially all of the surface area of said heater plate.

14. The heater module as recited in claim 13 wherein said heater plate is generally circular.

15. The heater module as recited in claim 1 or 2 wherein said heater plate is round and said housing includes a round opening in its upper surface for receiving said heater plate.

16. The heater module as recited in claim 15 further comprising a plurality of support legs extending downward from said heater plate and received within apertures formed in the interior surface of the bottom of said heating element housing.

17. The heater module as recited in claim 15 wherein said at least one heating element is attached to, and covers substantially all of the bottom surface of, said heater plate.

18. The heater module as recited in claim 17 further comprising a thermostat attached to the center of the bottom surface of said heater plate.

19. A heating system including: a food service cart for storing and heating foods; and at least one tray support attached to said cart for supporting a food service tray, said heating system characterized by:
at least one heating element housing removably attached to said cart;
a heater plate sized to contact one food carrying member;
at least one healing element carried in said heating element housing in thermal contact with said heater plate; and attaching means for removably attaching said housing to said cart such that said at least one heating element for a respective said heater plate is individually removable from said cart by removing said heating element housing independently from said tray support and the food service tray.

20. The heating system as recited in claim 19 further comprising a plurality of said tray supports attached to said cart at a plurality of vertically spaced shelf locations.

21. The heating system as recited in claim 19 or 20 wherein said heating element housing is attached to said cart in a cantilever manner.

22. The heating system as recited in claim 20 further comprising a support bar extending between and attached to opposite sides of said cart at each of said shelf location and a pair of support pins extending from each of said support bars for supporting one of said heating element housings, and said heating element housings each having a pair of openings for receiving one pair of said supporting pins.

23. The heating system as recited in claim 22 further comprising one of a male or female electrical connector carried by said support bars between said pins, and the other of said male or female connectors carried by said heating element housing in an area between said pair of openings.

24. The heating system as recited in claim 23 wherein said female electrical connector is carried by said support bars and said male electrical connector is carried by said heating element housing.

25. The heating system as recited in claim 22 wherein said support bars each have a generally T-shaped configuration with the cross portion of the T being hollow and carrying electrical wiring for connecting said heating elements to a source of electrical power.

26. The heating system as recited in claim 19 or 20 further comprising individual switch means connected to each of said at least one electrical heating element for turning power on and off separately to each one of said at least one healing element in thermal contact with a respective said heater plate, and switch activator means associated with covers for hot food to be carried on service trays to be supported in said cart such that one of said switch means turns power on to a respective one of said at least one heating element when one of the covers is carried by a tray and supported in said cart above said last-mentioned switch means.

27. The heating system as recited in claim 19 or 20 wherein said cart includes a base, a top and a pair of spaced side walls extending between said base and said top and between the front and the back of said cart, and tubular members adjacent both the front and the back of said cart.

28. A rethermalization cart comprising: a bottom; a top; at least two sides connecting said bottom and top together; and a plurality of tray supports positioned at vertically spaced intervals for supporting a plurality of food service trays, said rethermalization cart characterized by:
a plurality of heating pads positioned adjacent said tray supports, and separable from said tray supports and food service trays;
attaching means for individually removably attaching each said heating pad to said cart so as to extend in said cart in a cantilevered fashion; and thermostatic control means attached to each said heating pad for controlling the temperature of said heating pads.

29. The rethermalization cart as recited in claim 28 wherein said thermostatic control means controls the power supplied by each respective said heating pad during a predetermined rethermalization time period, said control means including sensing means for sensing temperature and power adjusting means for adjusting the power supplied by said heating pad, said sensing means sensing temperature over a predetermined range having upper and lower temperature limits, and said power adjusting means reducing the power at which said heating pad operates to a lower power level when said sensing means senses the upper temperature limit and increasing the power at which said heating pad operates to a higher power level above the lower power level when said sensing means senses temperature at or below the lower temperature limit.

30. The rethermalization cart as recited in claim 28 wherein said attaching means includes a plurality of support pins spaced a fixed distance apart and attached at each said tray support location and said heating pads each having a plurality of openings spaced a distance apart so as to correspond to said support pin spacing, said support pins being insertable into said heating pads to allow said heating pads to be individually removable and to support said heating pads in a cantilevered fashion.

31. The rethermalization cart as recited in claim 29 wherein said heating pad includes an electrical heating element, said power adjusting means includes switch means for shorting a portion of said heating element out of an operative heater circuit to operate said heating element at the increased power level and for placing said portion of said heating element into the operative heater circuit to operate said heating element at the reduced power level.

32. The rethermalization can as recited in claim 31 further comprising a heating plate forming the contact surface of said heating pad for contact with a food carrying member, and said heating element being arranged in said heating pad to cover substantially all of the surface area of said heating plate.

33. The rethermalization cart as recited in claim 32 wherein said heating pad is generally circular.

34. The rethermalization cart as recited in claim 32 wherein said sensing means is located to sense the temperature of said heating plate.

35. The rethermalization cart as recited in claim 28 further comprising individual switch means connected to each of said heating pads for turning power on and off separately to each one of said heating pads and switch activator means for activating said switch means associated with covers for hot food lo be carried on service trays supported on said tray supports such that one of said switch means turns power on a respective one of said heating pads when one of the covers is carried by a trays and supported in the cart above said last-mentioned switch means.

36. The rethermalization cart as recited in claim 28 wherein said attaching means comprises a plug-in assembly.

37. A rethermalization cart including: a cart frame; and at least one tray support attached to said cart frame for supporting, in a tray support position, a food service tray having first and second hot food areas, characterized in that said rethermalization cart comprises:
first and second heater modules securable relative to said cart frame so that food at the first and second hot food areas of the food service tray, when in the tray support position, can be heated by said first and second heater modules, respectively, and so that said first and second heater modules are individually and separately removable relative to said cart frame.

38. The rethermalizationa cart as recited in calim 37 wherein said cart frame defines at least in part a cart opening through which the food service tray passes to and from the tray support position, and said first and second heater modules when secured to said cart frame extend cantilevered outwardly towards said cart opening.

39. The rethermalization cart as recited in claim 37 wherein said cart frame includes spaced side walls and a cross member extending between said side walls, and further comprising attaching means for removably attaching said first and second heater modules to said cross member.

40. The rethermalization cart as recited in claim 39 wherein said attaching means includes a plurality of mechanical attachment members.

41. The rethermalization cart as recited in claim 39 wherein said cross member comprises a bar member defining an enclosed channel through which wiring for said first and second heater modules passes.

42. The rethermalization cart as recited in claim 37 wherein said first and second heater modules each comprise thermostatically-controlled conductive heater pads having respective temperature sensors mounted directly thereto.

43. The rethermalization cart as recited in claim 37 wherein said first heater module includes a housing, a heater plate supported by said housing, and at least one electrical heating element carried in said housing and in thermal contact with said heater plate.

44. The rethermalization cart as recited in claim 43 wherein said at least one electrical heating element is arranged to cover substantially all of the surface area of said heater plate, and said heater plate is generally circular.

45. The rethermalization cart as recited in claim 43 wherein said first heater module includes a plurality of support legs extending downward from said heater plate and received in apertures formed in an interior bottom surface of said housing.

46. The rethermalization cart as recited in claim 43 wherein said first heater module includes a temperature sensor mounted to the center of a bottom surface of said heater plate.

47. The rethermalization cart as recited in claim 37 wherein said first healer module includes a first electrical heating assembly and first individual switch means for turning power on and off to said first electrical heating assembly, and said second heater module includes a second electrical heating assembly and second individual switch means for turning power on and off to said second electrical heating assembly.

48. The rethermalization cart as recited in claim 37 wherein said cart frame includes a wheeled base and first and second side walls extending up from said base, and said tray support includes a first tray support member mounted to said first side wall and a second tray support member mounted to said second side wall and aligned with said first tray support member.

49. The rethermalization cart as recited in claim 37 wherein the food service tray includes first and second through-openings, a first food dish disposed in the first through-opening and thereby at the first hot food area and a second food dish disposed in the second through-opening and thereby at the second hot food area, and wherein said first and second heater modules are positioned relative to said cart frame such that with the food service tray in the tray support position the bottom of the first food dish can be conductively heated by said first heater module to thereby heat food in the first food dish and the bottom of the second food dish can be conductively heated by said second heater module to thereby heat food in the second food dish.

50. The rethermalization cart as recited in claim 37 wherein said at least one tray support comprises a plurality of tray supports attached to said cart frame at a plurality of vertically spaced shelf locations for simultaneously supporting a plurality of food service trays in said cart frame in respective food heating positions.

51. The rethermalization cart as recited in claim 37 wherein said cart frame includes a support bar to which said first heater module is removably and operably securable, said support bar includes a first electrical connector and said first heater module includes a second electrical connector mateable with said first electrical connector.

52. The rethermalization cart as recited in claim 51 wherein said support bar has a generally T-shaped configuration with the cross portion of the T being hollow and carrying electrical wiring for connecting said first heater module to a source of electrical power.

53. The rethermalization cart as recited in claim 51 wherein said second heater module is removably and operably securable to said support bar, and said cart frame includes a pair of side walls and said support bar extends between said side walls.

54. The rethermalization cart as recited in claim 53 wherein said cart frame defines open front and back areas on opposite sides of said support bar and said first and second heater modules extend from said support bar in a cantilever man?er out towards said open front area, and further comprising third and fourth heater modules operatively securable to said support bar so as to extend in a cantilever manner towards said open back area, said third and fourth heater modules being positioned to heat foods carried by a food service tray supportable in said cart frame on the back side of said support bar and inserted in through said open back area.

55. The rethermalization cart as recited in claim 37 wherein said cart frame includes support structure, and further comprising mechanical support attaching means for individually, separately and removably attaching said first and second heater modules to said support structure, electrical wiring protectively enclosed in said support structure and electrical connecting means for electrically connecting said first and second heater modules to said wiring.

56. The rethermalization cart as recited in claim 37 further comprising refrigeration means for receiving said cart frame therein and refrigerating food items carried on the food service tray in the tray support position.

57. The rethermalization cart as recited in claim 37 wherein said cart frame includes a pair of side walls, and a pair of heater module support bars extending between said side walls, said support bars being disposed parallel and one above the other, and the area defined between said support bars being substantially open from the front to the back of said cart frame.

58. The rethermalization cart as recited in claim 57 wherein said support bars each define an enclosed horizontal passageway, and further comprising heater module electrical wiring passing through said passageways and protectively enclosed therein.

59. The rethermalization cart as recited in claim 37 wherein the food service tray includes a first cover for the first hot food area and a separate second cover for the second hot food area, and further comprising actuating means for actuating said first heater module only when the first cover is over the first hot food area and said second heater module only when the second cover is over the second hot food area.

60. The rethermalization cart as recited in claim 37 wherein the food service tray is generally rectangularly shaped having a pair of long sides and a pair of short sides and the first and second hot food areas are generally side-by-side along the same long side, said cart frame includes a pair of side walls, and when in the support position, the long sides of the food service tray extend generally between said side walls and the short sides are generally parallel to said side walls.

61. The rethermalization cart as recited in claim 60 wherein said side walls define therebetween an open front area and an opposite open rear area, the food service tray being inserted into the tray support position through said open front area, said at least one tray support defining a front tray support, and the tray support position defining a front tray support position, and further comprising a rear tray support attached to said cart frame for supporting in a rear tray support position another food service tray having hot food areas and inserted in through said open rear area, and heater modules for heating the foods at the hot food areas with the another food service tray in the rear tray support position.

62. The rethermalization cart as recited in claim 61 wherein the front and rear tray support positions are generally in the same horizontal plane.

63. A rethermalization cart including: a cart frame including side walls, said cart frame defining at least in part a cart interior and a cart opening; and tray support means mounted to said side walls for supporting in a tray support position in said cart interior a food service tray having first and second hot food areas. wherein the food service tray is moved to and from the tray support position through said cart opening; characterized in that said rethermalization cart comprises:
said cart frame including a cross-bar member extending horizontally between said side walls; and first and second conductive heater pads secured directly to said cross-bar member, extending in a cantilever fashion towards said cart opening, and positioned so that food at the first and second hot food areas of the food service tray, when in the support position, can be conductively heated by said first and second conductive heater pads, respectively.

64. The rethermalization cart as recited in claim 63 further comprising attaching means for removably attaching said first and second conductive heater pads to said cross-bar member such that said heater pads are individually, independently and separately attachable to said cross-bar member.

65. A rethermalization cart including (a) a cart frame having side walls and (b) at least one tray support attached to said side walls for supporting in a tray support position a food service tray having at least one hot food area, characterized in that said rethermalization cart comprises:

a cross-bar member attached to and extending between said side walls; and a heater module removably securable to said cross-bar member so that when said heater module is secured and activated food at the hot food area of the food service tray, when in the support position, can be heated by said heater module, and so that said heater module is removable from said cross-bar member.

66. A rethermalization cart for supporting a plurality of trays having a plurality of food compartments and tray openings for supporting therein one of a plurality of serving containers containing food items, comprising: a plurality of cart shelves, each said shelf having supporting means for supporting at least one of the plurality of trays thereon and having heating means capable of conforming to the tray openings for heating the serving containers positioned thereon, each said heating Means including a plurality of heater pads; characterized in that said rethermalization cart comprises:
a box channel running generally the width of said cart at each said shelf;
wherein each said heater pad has mounting means which mates with said box channel for releasably and individually securing each said heater pad to said shelf; and electrical connection assemblies connectable to each said heater pad and running inside said box channel.

67. The rethermalization cart as recited in claim 66 further comprising a wheeled cart frame to which said shelves are mounted, and refrigeration means for receiving said wheeled cart frame therein and for refrigerating food items carried by trays supported by said supporting means.

68. The rethermalization cart as recited in claim 66 wherein said heater pads are cantilever mounted to said box channel and extend outwardly towards a cart front opening.

69. The rethermalization cart as recited in claim 66 wherein said electrical connection assemblies are operatively connectable to an electrical power source for energizing said heater pads.

70. The rethermalization cart as reacted in claim 66 wherein said box channel is enclosed thereby protectively housing said d electrical connection assembles.

71. A rethermalization cart system comprising:
a cart having a frame defining at least in part a cart interior including an open front area, side areas and an open rear area;
first tray support means for supporting in said cart interior and in a first support position a first tray having a first through-opening such that the first tray passes through the open front area when being inserted into and removed from the cart first support position;
second tray support means for supporting in said cart interior and in a second support position a second tray having a second through-opening such that the second tray passes through the open rear area when being inserted into and removed from the cart second support position;
a first conductive heating element extending in cantilevered fashion from a position spaced inwardly from said front area and out towards said front area, said first tray support means and said first conductive heating element being arranged such that a first food dish positioned in the first through-opening of the first tray is in direct thermal contact with said first conductive heating element when the first tray is in the first support position; and a second conductive heating element extending in cantilevered fashion from a position spaced inwardly from said rear area and out towards said rear area, said second tray support means and said second conductive heating element being arranged such that a second food dish positioned in the second through-opening of the second tray is in direct thermal contact with said second conductive heating element when the second tray is in the second support position.

72. The rethermalization cart system as recited in claim 71 further comprising a hollow tubular bar supported by said cart and wherein said first and second conductive heating elements are attached to said hollow tubular bar, and linking means contained within said hollow tubular bar operatively linking said first and second conductive hearing elements to a source of energy for providing the heat to warm food placed on said food dish in said cart.

73. The rethermalization cart system as recited in claim 72 wherein said tray is supported by said tray support bars and said hollow tubular bar.

74. A rethermalization cart system comprising:
a cart having a bottom, a top and two side walls joined together to define open front and rear areas;
at least one tray having a tray top surface and at least one through-opening in said tray top surface;
at least one food dish removably positionable generally in said through-opening in an operative position;
first tray support means for supporting a tray in said cart interior inserted through said open front area;

at least one first heating element positioned spaced inwardly from said open front area and closely adjacent said first tray support means such that said food dish is adapted to be in direct thermal contact, through said through-opening, with said second heating element when said tray is supported by said second tray support means;
second tray support means for supporting a tray in said cart interior inserted through said open rear area; and at least one second heating element positioned spaced inwardly from said open rear area and closely adjacent said second tray support means such that said food dish is adapted to be in direct thermal contact, through said through-opening, with said second heating element when said tray is supported by said second tray support means.

75. The rethermalization cart system as recited in claim 74 wherein said cart includes a frame assembly with two side wall tubular members in each side wall, one adjacent the front area of said cart and the other adjacent the rear area, said bottom and said top each having one U-shaped tubular member positioned at the front area for joining the tops and bottoms of the front side wall tubular members and one U-shaped tubular member positioned at the rear area for joining the tops and bottoms of the rear side wall tubular members.

76. The rethermalization cart system as recited in claim 75 wherein a hollow tubular T-shaped bar extends from one side wall of said cart interior to the other, with the leg of said T-shaped bar extending upwardly to prevent trays from sliding from the open front to the open rear areas.

77. The rethermalization cart system as recited in claim 76 wherein said first and second heating elements are connected to said T-shaped bar and to a source of power through said T-shaped bar.

78. The rethermalization cart system as recited in claim 77 further comprising a plurality of first tray support means positioned in vertically spaced alignment at said open front area and a plurality of second tray support means positioned in vertically spaced alignment at said open rear area, at least one first or second heating element is positioned adjacent a respective one of each of said first or second tray support means.

79. A rethermalization cart including (a) a cart wall assembly defining at least in part a cart interior having a plurality of tray assembly locations and a cart opening through which tray assemblies can pass relative to the tray assembly locations, (b) supporting means for supporting, at one of the tray assembly locations and in an insert position, a tray assembly inserted in through said cart opening, the tray assembly having at least one hot food location, and (c) at least one conductive heater pad positioned such that food at the hot food location of the tray assembly in the insert position can be heated thereon, characterized in that the improvement comprises:
cantilever securing means for securing said conductive heater pad to said cart wall assembly in a cantilever manner such that said conductive heater pad extends from a position in said cart interior and outwardly towards said cart opening.

80. The rethermalization cart as recited in claim 79 wherein said conductive heater pad defines a first heater pad, the hot food location defines a first hot food location, and the tray assembly has a second hot food location, and further comprising a second heater pad positioned such that food at the second hot food location of the tray assembly when in the insert position can be heated thereon.

81. The rethermalization cart as recited in claim 80 wherein said cantilever securing means defines first cantilever securing means, and further comprising second cantilever securing means for securing said second heater pad to said cart wall assembly in a cantilever manner such that said second heater pad extends from a position in said cart interior and outwardly towards said cart opening.

82. The rethermalization cart as recited in claim 81 wherein said cart wall assembly includes a cross member to which said first and second cantilever securing means secure said first and second heater pads, respectively.

83. The rethermalization cart as recited in claim 82 wherein said cart wall assembly includes a base and a pair of side walls extending up from said base and generally on opposite sides of said cart opening, and said cross bar extends between said side walls.

84. The rethermalization cart as recited in claim 82 wherein said cross member defines an enclosed channel through which wiring for said first and second heater pads passes.

85. The rethermalization cart as recited in claim 82 wherein said cross member includes first electrical connectors and said first and second heater pads include second electrical connectors operatively mateable with respective ones of said first electrical connectors.

86. The rethermalization cart as recited in claim 82 wherein said cross member has a generally T-shaped configuration with the cross portion of the T being hollow and carrying electrical wiring for connecting said first and second heater pads to a source of electrical power.

87. The rethermalization cart as recited in claim 81 wherein said first and second cantilever securing means both include a plurality of mechanical attachment members.

88. The rethermalization cart as recited in claim 81 wherein said first and second cantilever securing means allow said first and second heater pads to be individually and separately removable relative to said cart wall assembly.

89. The rethermalization cart as recited in claim 81 wherein the tray assembly includes first and second through-openings, a first food dish disposed in the first through-opening and thereby at the first hot food location and a second food dish disposed in the second through-opening and thereby at the second hot food location, and wherein said first and second cantilever securing means position said first and second heater pads, respectively, such that with the tray assembly in the tray insert position the bottom of the first food dish can be conductively heated by said first heater pad and the bottom of the second food dish can be conductively heated by said second heater pad.

90. The rethermalization cart as recited in claim 79 wherein said cart wall assembly includes a pair of cart walls and a cross bar extending between said cart walls, and said cantilever securing means secures said conductive heater pad to said cross bar.

91. The rethermalization cart as recited in claim 90 wherein said cross bar defines an enclosed channel through which wiring for said conductive heater pad passes.

92. The rethermalization cart as recited in claim 90 wherein said supporting means includes aligned tray support members mounted to said cart walls.

93. The rethermalization cart as recited in claim 90 wherein said cantilever securing means allows the tray assembly to be moved from the insert position out of said cart opening with said heater pad remaining secured to said cross bar.

94. The rethermalization cart as recited in claim 90 wherein said at least one conductive heater pad includes first and second heater pads both securable by said cantilever securing means to said cross bar and thereby both extending out towards said cart opening.

95. The rethermalization cart as recited in claim 94 wherein said cantilever securing means allows said first and second heater pads to be individually, independently and separately removable from said cross bar.

96. The rethermalization cart as recited in claim 90 wherein said cart opening defines a front cart opening, said cart wall assembly defines a back cart opening on the opposite side of said cross bar as said front cart opening, and further comprising another conductive heater pad secured to said cross bar so as to extend cantilevered towards said back cart opening and positioned to heat food carried by a tray assembly inserted into said cart interior through said back cart opening and to an insert position on the back side of said cross bar.

97. The rethermalization cart as recited in claim 90 wherein said cantilever securing means secures said conductive heater pad to said cross bar such that said heater pad is spaced a distance inward from both of said side walls.

98. A rethermalization cart heater module, comprising:
a heater module housing having a top surface opening;
a conductive heater plate mounted at said top surface opening;
a resistive heating assembly protectively enclosed in said housing and in thermal contact with said heater plate for heating same;
a temperature sensor in said housing and positioned for measuring the temperature of said heater plate and thereby for controlling at least in part the food rethermalizing operation of said resistive heating assembly; and individual switch means protectively enclosed in said housing for turning power on and off to said resistive heating assembly, said switch means being activated by means outside of said housing.

99. The heater module of claim 98 wherein said housing includes a switch attachment plate to which said switch means is secured.

100. The heater module of claim 98 wherein said switch means has on and off positions and said housing includes an upward projection in which at least a portion of said switch means is received when in at least one of the on and off positions.

101. The heater module of claim 98 wherein said housing includes a base and a peripheral wall extending upwards from said base, said peripheral wall having tapered top and bottom exterior surfaces along the front and sides of said of said housing, and said top surface opening being formed in said peripheral wall.

102. The heater module of claim 98 wherein said housing has an attachment end which is operatively and removably attachable to and in a rethermalization cart, and further comprising electrical connector pins extending out from said attachment end for operatively connecting said resistive heating assembly to a power supply associated with the rethermalization cart.

103. The heater module of claim 98 further comprising a plurality of support legs extending downwardly from said heater plate and supported at lower ends thereof by said housing.

104. The heater module of claim 98 wherein said temperature sensor is secured directly to the bottom of said heater plate.

105. The heater module of claim 98 wherein said switch means comprises a mercury switch.

106. The heater module of claim 98 wherein said switch means comprises a reed switch.

107. The heater module of claim 98 wherein said switch means is magnetically actuated.

108. A rethermalization cart heater module, comprising:
a heater module housing having a top surface opening;
a conductive heater plate mounted at said top surface opening;
a resistive heating assembly protectively enclosed in said housing and in thermal contact with said heater plate for heating same;

a temperature sensor in said housing and positioned for measuring the temperature of said heater plate and thereby for controlling at least in part the food rethermalizing operation of said resistive heating assembly;
mounting means for mounting said housing in and to a rethermalization cart such that a food carrying tray can be inserted into the rethermalization cart and operatively positioned relative to said conductive heater plate; and a plurality of heater plate support legs extending downwardly from said heater plate and supported at lower ends thereof by said housing.

109. The heater module of claim 108 wherein said housing includes a plurality of interior openings in which lower ends of said support legs are received.

110. The heater module of claim 108 wherein said support legs are secured at upper ends thereof directly to said heater plate.

111. The heater module of claim 108 wherein said support legs extend downwardly at a plurality of spaced locations about the perimeter of said heater plate.

112. The heater module of claim 108 further comprising an insulation plate secured in position below said heating assembly by resting on a ledge of said housing.

113. The heater module of claim 108 further comprising individual switch means protectively enclosed in said housing for turning power on and off to said resistive heating assembly.

114. The heater module of claim 108 wherein said housing includes a base and a peripheral wall extending upwards from said base, said peripheral wall having tapered top and bottom exterior surfaces along the front and sides of said housing, and said top surface opening being formed in said peripheral wall.

115. A rethermalization cart heater module, comprising:
a heater module housing having a top surface opening and an attachment end which is operatively and removably attachable to and in a rethermalization cart;
a conductive heater plate mounted at said top surface opening;
a resistive heating assembly protectively enclosed in said housing and in thermal contact with said heater plate for heating same;
a temperature sensor in said housing and positioned for measuring the temperature of said heater plate and thereby for controlling at least in part the food rethermalizing operation of said resistive heating assembly;
mounting members which mount said housing via said attachment end in and to a rethermalization cart such that a food carrying tray can be inserted into the rethermalization cart and operatively positioned relative to said conductive heater plate;
a pair of spaced flanges secured to said housing in a hermetically sealed fashion;
and electrical connector pins supported by said spaced flanges and extending out from attachment end for operatively connecting said resistive heating assembly to a power supply associated with the rethermalization cart.

116. The heater module of claim 115 wherein said housing includes a base and a peripheral wall extending upwards from said base, said peripheral wall having tapered top and bottom exterior surfaces along the front and sides of said housing, and said top surface opening being formed in said peripheral wall.

117. The heater module of claim 115 further comprising a plurality of heater plate support legs extending downwardly from said heater plate and supported at lower ends thereof by said housing.

118. A rethermalization cart heater module, comprising:
a heater module housing having a top surface opening, said housing including a base and a peripheral wall extending upwards from said base, said peripheral wall having tapered top and bottom exterior surfaces along front and sides of said housing, and said top surface opening being formed in said peripheral wall;
a conductive heater plate mounted at said top surface opening;
a resistive heating assembly protectively enclosed in said housing and in thermal contact with said heater plate for heating same; and a temperature sensor protectively enclosed in said housing and positioned for measuring the temperature of said heater plate and thereby for controlling at least in part the food rethermalizing operation of said resistive heating assembly.

119. The heater module of claim 118 further comprising electrical connector pins extending out from said housing for operatively and removably connecting said resistive heating assembly to a power supply associated with a rethermalization cart.