AU662174B2 - A food storing and rethermalizing system - Google Patents

Description

r 662174

AUJSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE

SPECIFICATION

STANDARD

PATENT

P/00/01.1 Regulation 3.2 Inventioni Title: A food storijg nid rotlierlizitg systern The following statement Is a full description of this Invention, method of performing It kcno:wn to us: including the best

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1P61850/IP 211/10/92

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A FOOD STORING ANT) RETITERMALIZING SYSTEM TECHNICAL FIELD The present invention relates to food storing and rethermalizing 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 chilled state. Selected foods on the trays are rethermalized in the carl, healed 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 S' is heated by a thermostatically controlled electrical heater.

I BACKGROUND OF THE INVENTION Various types of food service systems and conductive heating rethermalization methods are known in the prior art. A most basic food service system is one in which food is served immediately, or only a short time period, after the food is cooked or prepared. Typically 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 of food. In other environments such as fast food restaurants and cafeterias, food is not served immediately anfer preparation, but rather kept warm and served in the warm state. In fast food restaurants, food such as hamburgers is kept hot in disposable 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 bulk and, thereafter, divided into individual portions and kept warm in a pellet system. A pellet system can also be used in non-cafeteria environments, such as hospitals wherein the food is MPS0139/PS oh mmo-.

-2placed 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 kept safe and warm is relatively limited, and the quality of the food deteriorates over time.

A rethermallzatlon system is another prior art type of food service system. In a rethermalization system, food is cooked or pre- F or pared and then chilled in bulk to 40 ^4e 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 chilled and stored temperature must be or less. A short time before the food is to be served, the food which is to be served hot is brought to a safe serving temperature, i.e.

it is rethermalized. FDA guidelines specify that a safe serving temperature is 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 within the system. That is, prior art rethermalization systems have located the heating element in either a food serving dish, a dish supporting tray, or a shelf attached within a service cart.

U.S. Patent No. 3,908,749 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 from 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 exposed leaf contacts which extend from a rear wall of the service cart.

Embedding the electrical heating element within the dish significantly increases the cost and complexity of the dish. A dish within a food service system undergoes severe handling since it must L -r a I -3carry 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 frequently. A system which incorporates the heating element into the dish thus has a relatively high long-term operating expense. Another disadvantage of this type 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 corrosion and water damage during operation and cleaning.

Food service rethermalization systems which incorporate heating 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 handling during food service and cleaning. Exposed contacts are also i 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 subjected and their relatively large planar configuration. Once the trays S- become warped, good surface contact between the heating element portion of the tray and the dishes to be heated is lost. As a consequence, 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 heating 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 Ssource is incorporated within enclosed portions of the shelf and cart, alleviating the problem of exposed contacts. However, 1 -4rethermalization carts with shelf located heating elements do have certain limitations or disadvantages. Such systems generally incorporate a plurality of heating elements in a fixed manner into a single shelf. Thus, when one of the heating elements on a shelf becomes inoperative, the entire shelf must be replaced, rather than replacing the single inoperative heating element. Examples of food service rethermallzation systems wherein .the heating elements are incorporated 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 be 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 activate 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 iood 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 activating 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 dependent upon the food to be heated at the particular shelf location. This technique is very complicated and labor intensive, and requires special 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.

al 1 iW s ti i Another prior art technique for'activating the individual heating elements at the shelf locations relies upon tray positioning. In Selder 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 1800 opposite direction. In Bourner '391, a mechanical switch is placed.at each shelf location and is activated by a tray cover when the tray is positioned in one direction, but is not activated when the tray is positioned in the 1800 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 attended 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 exhibited 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 operates between upper ana lower temperature of limits. Typically, the i resistance heater applies heat over a predetermined time period.

While such a heating method has worked satisfactory,,it is subject to certain limitations. For example, the system must be designed to work within a practical time period. While it would be desirable from a labor/cost standpoint to rethermalize chilled food as quickly as possible, 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.

i C 1 I ;1 -6- One commercial rethermalliation 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 foods retain 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 nonstick coating. Thus, while the time during which rethermalization takes place is less, any operating expense savings is very likely lost by S' the added expense is required in the special plating techniques.

Conversely, when the time for rethermallzation is significantly Si 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 S" 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 as hospitals, prisons or nursing homes since scheduling options for handling and recyling the carts for the next meal are limited.

The system disclosed in Bourner '391 rethermalizes chilled food in approximately a one-half hour time period. Such a rethermallzation 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. Furthermore, the one-half hour time period has not proven to be too restrictive 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 unrestricted range of foods can- 'not be rethermalized without special plating or quality degradation.

It is difficult to rethermalize small portions of low density, fragile r 7- 1i 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 specified portions, quality of the reheated food deteriorates. This is particular!y true if too much of a dense food is placed in combination 4ith 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 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 Dotd et al. '756 uses a separate low power holding circuit for keeping food warm after it has been rethermalized. A higher power primary heating circuit is thermostatically controlled and used to rethermalize the food over a predetermined time period.

Thus, while 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 as the preferred type of heater embedded in the dish. The use of a resistance heater controlled by a thermostat is mentioned as an alternative to the PTC heater. The PTC heaters operate basically as multimodal resistance heaters so that below their critical temperature they have a low electrical resistance, while above it the resistance is very Drawing number recommended to accompany the abstract V A 04? 2 2 11092 l.2 c.to.e (Signature) (D Wayne McMaster (Date) Registered Patent Attorney for Aladdin Synergetics, Inc.

-8it high. Near the critical temperature, the resistance varies between the extremes. Therefore, 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 current, requiring more expensive high power capability electrical service. 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 Rubbrigh et al. '110 system programs an individual time/temperature curve for each heater element. A predetermined Stime 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 heating element depending upon the type of food being rethermalizfd. A certain number of programs are available for use and are coordinated 'with various types or combinations of foods. The food service operator thus must coordinate the particular food or combination of foods with the appropriate program. The food service handling process is 20 thus complicated, requiring extra care and attention during meal preparation and specie -aining 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 funetional limitations of the prior art systems and methods discussed above.

s o a e Ia-s cnuuement rrom the applicant(s) of the basic application(s) listed on the patent request torm I (eg by assignment, by mesne assignment, by consent, etc) (Continued over) E I 8a.

SUiimARY OF THE INVENTION The present invention is directed to food storing and rethermalizing system for use in a food service cart for storing and heating foods.

According to a first embodiment of this invention there is provided a food storing and rethermalizing system comprising; a food service cart having a cart interior; a food tray having a hot food location thereon; a tray cover positionable in a covering position for covering the hot food location; a tray support for removeably supporting said food tray in said cart interior in a cart location; a heater for heating, with said food tray in the cart location, food at the hot food location; a switch for turning power on and off to Ssaid heater; and an activator, associated with said tray cover, for activating said switch with said tray cover in the covering position and said food tray in the cart location; characterised in that the improvement comprises; mating alignment means for aligning said activator with said switch, said alignment means including an inner peripheral base surface on said cover and an upward rim on said food tray and configured to mate with said base surface.

The upward rim on the food tray is preferably round.

Preferably, at least two heaters are positioned at each shelf location and each of the heaters has a different overall power rating.

One of said switch and said switch activator is, desirably, a magnet and the other is made of magnetic material.

MPS0137/PS 8b.

The switch may include a pivotable housing with the magnet being supported at one end of the housing. The switch may, thereby, be activated by the pivoting motion of said pivotable housing.

Preferably, the switch is a mercury switch carried by said pivotable housing.

Alternatively, the switch may include a reed switch and said switch activator may include a magnet for activating said reed switch.

The above rethermalization system may further comprise a plurality of vertically spaced support bars within said cart interior, including supporting pins extending from said support bars and attaching means for removeably attaching said heaters to said cart including openings for receiving said support pins.

According to a second embodiment of this invention there is provided a food storing and rethermalizing system said system comprising; a food 15 service cart having a cart interior; a food tray having first and second spaced Lot food locations; a food tray supporter for removeably supporting .said food tray in said cart interior and thereby in a cart location; a first heater for heating, with said tray in the cart location, food at the first hot food location; a second heater for heating, with said tray in the cart location, food at the second hot food location; a first cover positionable in a covering position to cover the first hot food location; and a second cover positionable in a covering position, and generally independent of whether said first cover is in its covering positioning to cover the second hot food location; characterised in that the improvement comprises; first switch activator means, operatively associated with said first cover being in its covering position, for activating said first heater generally only with said first cover in the covering position and said food tray in the cart location; and second switch activator means, operatively associated with said second cover being in its covering position and operable generally f MPS0137/PS L Note: This MUST be signed FOR ALL APPLICATIONS Omit/Delete if not appropriate S8c.

separately of said First switch activator means, for activating said second heater generally only with said second cover in the covering position and said food tray in the cart location.

The first and second heaters preferably include switches which are activated by said switch activator means. One of the switches or the switch activator means is, desirably, made of a magnetic material, and the other includes a magnet. The switch may include a pivotable housing having the magnet supported at one each thereof. The switch may be activated by the pivoting motion of said pivotable housing.

Preferably, the switch is a mercury switch carried by the pivotable housing.

Alternatively, the switch may include a reed switch and the switch activator may include a magnetic for activating the reed switch.

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In the above system, the tray and the covers preferably include mating 15 alignment means for aligning said switch activators with said switches when said tray is inserted in the cart location. The mating alignment means may comprise rims which mate with an inner surface portion of the base of the covers.

According to a third embodiment of this invention there is provided a food S 20 storing and rethermalizing system, said system comprising: a food service car' having a cart interior; a food tray having a hot food location thereon; a tray cover positionable in a covering position for covering the hot food location; a tray support for removably supporting said food tray in said cart interior in a cart location; and a heater for heating, with said food tray in the cart location, food at the hot food location; characterised in that the improvement comprises; Smagnetic switch activating means for activating said heater, said Sactivating means including a first magnet element carried by said cover and a second magnet element supported by said cart and operatively interacting with said first element to activate said MPS0137/PS 24. A food rethermalizing process, said process comprising the steps of: providing a food service tray with -sai- first and second food locations; providing a food service cart /2 8d.

heater, with said tray cover in the covering position and said food tray in the cart location.

Preferably, the tray includes mating alignment means for activating switcl es connected to said heater, said alignment means including rims on said tray and a corresponding inner surface on said covers.

It is desired that the heater be removable from the cart which has a support bar with outwardly extending supporting pins extending from the support bar, and the heater has openings for receiving said supporting pins.

According to a fifth embodiment of this invention there is provided a food storing and rethermalizing system comprising: a food service cart having a cart interior; a food tray having a hot food location and another food location thereon; an insulated cover positionable in a covering position and supported by said food tray for covering the hot food location; a tray 15 support for removeably supporting said food tray in said cart interior in a cart location; and a heater for heating with said food tray in the cart location, food at the hot focd location; characterised in that the improvement comprises: switch activator means for activating said heater with said insulated 20 cover in the covering position and said food tray' in the cart location, said switch activator means including a first switching element carried by said insulated cover and a second switching element cooperable with said first switching element and connected to i said heater; and 25 a protective cover supportable by said food tray and with said food tray in the cart location, and protectively over both said insulated cover when in the covering position and said another food location.

Preferably, the tray includes mating alignment means for aligning the activator and a switch connected to tho heater, said alignment means including a rim on the tray and a corresponding inner surface on said insulated cover. The rim is preferably round.

MPS0137/PS :4 The above system preferably comprises at least two heaters positioned at each cart location, each heater having a different overall power rating.

One of the heaters may include a switch. One of the switch and the switch activator means is preferably a magnet and the other is made of magnetic material. The switch may include a pivotable housing, the magnet being supported at one end of the housing. The switch may be activated by the pivoting motion of said pivotable housing. Preferably, the switch is a mercury switch carried by the pivotable housing.

Alternatively, the switch may include a reed switch, in which case the switch activator includes a magnet for activating the reed switch.

Preferably, the switch activator is capable of activating said switch in first and second different nrientations on and relative to the tray.

In the above system, the cart preferably includes a plurality of vertically spaced heaters and plurality of vertically spaced support bars positioned 15 adjacent said heaters said support bars having outwardly extending support pins and attaching means for removably attaching said heaters to said cart including openings for receiving said support pins.

According to a fifth embodiment of this invention there is provided a food rethermalizing process, said process comprising the steps of: providing a Sswitch members connected thereto; and placing food to be heated generally at the first food location; characterised in that the improvement comprises the steps of: placing a cover supporting a first switch element over the food at the first food location and thereby supported by said tray; and positioning the tray with the cover thereon in the tray location and thereby adjacent to the first and second heaters such that the first heater is actuated by the cooperation of the now proximate first MPS0137/PS IP61850/IP 21/10/92 I i 8f.

switch member and first switch element and thereby heating the food at the first food location and leaving the second heater unactuated.

The process may further comprise, before said tray positioning step, placing food which is not to be heated at the second food location. The positioning step may include leaving the second heater unactuated and thereby not heating, with the tray, at the tray location, the food at the second location.

The positioning step may include the food at the second location being uncovered by individual insulated cover with the tray in the tray location.

After the step of heating the food at the first location by the first heater, the process may further comprise the step of removing the tray from the cart.

The above process may further comprise, after the step of heating the food at the first location by the first heater, removing the tray from the cart, removing the cover off the food at the first location, serving the unheated food of the second location, and serviig the uncovered and heated food of the first location.

The above process may further comprise, after the placing step and before the positioning step, the step of positioning a protective cover over both the positioned cover and the second food location. The positiuning step may include aligning the first switch element and the first switch member. This aligning stop may include mating an inner peripheral surface of said positioned cover with a rim formed on said tray adjacent 25 the first food location.

The above process may further comprise the step of individually removing the heaters from the cart. This removing step may include unplugging each of the heaters separately, and further comprise the step of separately plugging new heaters into the cart to replace the removed heaters.

MPS0137/PS L i. I MPS0139/PS :f:riSI:"

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1 The heating step may include cycling the temperature between an upper and a lower temperature.

The food storing and rethermalizing system of this invention 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 supports. A mechanism initiates the supply of power to the heaters and a time turns the power off to the heaters after a predetermined time I r rr r i c r r MPS0137/PS Y ii AAAL L&AAA SAOIL U6 IL UIUME r -9period has elapsed. A thermostatic control controls the power supplied 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.

In a preferred embodiment, each heater includes an electrical heating element, 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 S. 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- 25 termined time period in a thermostatically controlled manner as follows: Heat is initially suppnea at a high power level from the begin- S. ning of the predetermined time period; and thereafter reduced to a Slow power level lower than the high power level when an upper temperature of a temperature range of 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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I7 S- 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 be used herein as shorthand terminology for the heater and thermostatic control which supplies power continuously Sduring 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, certain food processing limitations of a single-stage rethermalization heater (the on-off operation of a single-power heater). For example, foods with a broader range of heat energy requirements can be rethermalized with the two-stage heater without degrading food quality. 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 requirement foods can be more readily rethermalized simultaneously using the two-stage heater. Such mixed rethermalization with the two-stage heater works particularly well 25 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 30 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 predetermined rethermalization time period. When a lower and more 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 consisting 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 f or turning power on and of f 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 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 cono nec ted to each heater in combination with a switch activator mechanism carried in the covers for hot food simplifies the process of activating the Individual heaters, as well as reduces the likelihood 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 simpie one-step process. The step of manually, and individually, activating a switch for each shelf 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 servitp- cart wherein a heating ele-I ment housing is removably attached to ie 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 1, I III I f 12 housing with the heating element in thermal contact with the heater plate. The heating element housing includes a mechanism for removably attaching the housing to the cart whereby the heating element for a respective heater plate Is individually removable from the cart by removing the heating element housing. The heating element housing preferably has a pair of openings for receiving a pair of support pins extending from a support beam in the cart. Repair, replacement and cleaning of heating elements and heaters is simplified by the present heater module since each individual heater can be removed separately. In prior art shelf-mounted heaters, a plurality of heaters was fixedly attached to each shelf location so that Individual replacement and repair of the heaters could not be accomplished.

Various advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the Invention, its advantages, and objects obtained by its use, reference should be made to the drawings which form a further part hereof and to the accompanying descriptive matter, in which there is illustrated and described preferred embodiments of the Invention.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective view of a food service system including a mobile food service cart and a refrigeration cabinet; Figure 2 is a partial rear view of the food service cart; Figure 3 Is a horizontal sectional view of the food service cart, illustrating one food tray supported at a shelf location and another food tray in the process of being Inserted into a shell; Figure 4 is a partial front elevational view i.1lustrating trays, dlshware, and covers supported at shelf locations with one overall cover partially broken away; Figure 5 is a partial sectional view illustrating dishware supported on a heater; Figure 6 is a partial side elevational. view with the side wall of the service cart removed and illustrating food trays and covers supported at horizontally spaced shelf locations; 1, L_ j_ UA1 .lAUJ IIJ S r ~1 S, 13 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 element support bar; SFigure 10 is a front view of the support bar; Figure 11 is a cross-sectional view taken generally along line 11-11 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; 25 Figure 21 is a diagrammatic view of the resistance patter of another heater element; Figure 22 is circuit diagram of one embodiment of a two-stage heater and heater control; Figure 23 is a circuit diagram of another embodiment of a S 30 two-stage heater and heater control; ,Figure 24 is a circuit diagram of a further embodiment of a two-stage 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.

have a low electrical resistance, while above it the resistance is very 71

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i:l: ii;i 14

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ti Li Vi 'ii ki~ Lj DETAILED DESCRIPTION Food Service System Referring to the drawings, wherein like numerals indicate like elements, there is illustrated a food service system indicated generally 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.

Cart 12 is formed generally of sheet metal and includes a support 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 depend from its other side. A first side wall 22 extends upwardly from a first side of base 16 and a second side wall 24 extends upwardly fLom a second side of base 16. A top wall 26 is connected to and extends between the upper ends of first and second side walls 22 and 15 24. Tubular members 25 (one of which is shown along the front edge of cart 12 in Figure 1) are attached to the front and back edges of each side wall 22 and 24; and generally U-shaped tubular members 27 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 20 edges of cart 12. Tubular members 25, 27 provide additional rigidity to cart 12. A handle 28 is attached to the exterior of side wall 24, and is used to move and steer cart 12. The front and back of cart 12 are open to allow free access for the insertion and removal of food service trays 30. Male electrical connector contacts 32, which connect cart 12 to an electrical power source, extend from base 16 immediately 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 wheeled into refrigeration cabinet 14 where it will be stored in a chilled state until rethermalization. Refrigeration cabinet 14 includes a front access door 34 to allow entry and removal of cart 12, and which seals the refrigeration cabinet. A female electrical receptacle 36 is attached to the interior back wall of cabinet 14. When cart 12 is backed completely into cabinet 14, contacts 32 engage receptacle 36 to thereby connect cart 12 to a main electrical power supply in a I I

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15 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 conventional timer 33 is 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 system, cabinet 14 can be replaced by. a refrigerator room wherein a plurality of spaces and electrical receptacles are provided f or a plurality of carts 12, and the entire room is refrigerated.

Food Service Tray and Dlshware 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 15 Support bars 38 are preferably formed ol a rigid plastic. As seen in Figure 4, support bars 38 have a generally T-shaped crass-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 20 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 peripheral rim 42, which extends upward from a support surface 44. A divider 46 also extends upward from the support surf ace 44 and divides surf ace 44 into a f ood hc~ldlng area and a utensil/napkin holding area. In the food holding 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 f Its within entree opening 48 and a soup bowl 54 fits within soup opening 50. Entree dish 52 and soup bowl 54 both have a convenional 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 -16diameter of opening 48 such that the bottom surface of dish 52 extends 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 The diameter of soup bowl 54 is likewise correlated to the diameter of opening Entree dish 52 and soup bowl 54 are designed to be capable of 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 disposable 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 support surface 44. In a similar manner, the diameter of soup cover 48 is greater than the diameter of soup bowl 54 and rim 51.

An overall f-jad 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 supported in the food service area 44 of tray 30. The utensil/napkin support area remains open so that utensils, napkins, menu and patient identification can be placed on the tray after all the food 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 insulation material as seen in Figures 8 and 16. Cover 60 is preferably .:25 formed of a rigid injection molded plastic.

Head= se As seen in Figure 3, a pair o~f large entree heater assemblies or modules 64 and a pair of small soup heater assemblies or modules 66 are located at each horizontal shelf location. Figures 9, 10, 11 and 12 illustrate the support structure for supporting heater modules 64 and 66 at the horizontal shelf locations. As seen therein, a generally T -shaped bar 68 extends between opposite side walls 22 and 24. T-barI 68 is preferably formed of a high strength aluminum material and includes a central rib 70, a cross member 72 which extends perpendicularly from opposite sides of rib 70, and a pair of wall members 74.

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o '-4 4 17 Wall members 74 extend perpendicularly away from opposite distal ends of cross member 72 so that a hollow open-ended rectangular area is defined between cross member 72 and wall members 74. A base cover 76 fits within the hollow area and covers the open end between walls 74. 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 interior 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 disposed 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 frictionally fits into the hollow interior of bar 68, and an exterior portion 88 which fits between the interior surface of the wall members 22 and 24 and the distal ends of bar 68. Exte.'or portion 88 has a curved exterior surface.

Bar 68, 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, eR-'ending through the walls and into end pieces 84. Four support pins 30 extend 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 small diameter distal portion 94. A friction member, such as an 0-ring 96, is secured to the distal end of base portion 92. Pins function to support heater modules 64 and 66 in a cantilever manner from bar 68. As seen in Figure 7, a cylindrical bore 98 is formed through the housing of heater module 64 adjacent each of its sides.

Similar bores are formed in heater module 66. Pairs of pins 90 fit within bores 98 to support the heater modules. 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 technique allows each Individual heater module, which is sized to heat a single dish or bowl, to be individually removed for service or replacement.

I 1 30 operatively interacting with said first element to activate said MPS0137/PS 18 Details of heater module 64 are best seen in Figures 7, 8 and 13-15. Heater module 66, except where noted otherwise particularly with reference to Figures 17 and 18, is constructed similar to heater module 64. The exterior of heater module 64 is 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 resistive electrical heating element 108, an insulation plate 110, 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 extending upward from bottom 120 about the periphery of 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.

20 Heater plate 102 is preferably formed of a nickel plated aluminum plate having a thickness of approximately of Plate 102 is generally round and has a circular perimeter generally mating with the configuration of round opening 124. A plurality of suppF.rt legs 128 extend downward at a plurality of locations about the perimeter 25 of heater plate 102. A resistive heating element 108, such as shown in Figure 20, 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 S- 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 fiber or the like, is thereafter secured in position below heating element 108 by resting on top of ledge 126.

Thermostat 112 is secured with an adhesive directly to the bottom of ,heater plate 102 within a centrally located opening in heating element 108. Heater plate 102 and the components secured to it are including a rim on the tray and a corresponding inner surface on said insulated cover. The rim Is preferably round.

MPSO137/ PS -19 attached to housing 100 by securing legs 128 within holes 130 formed within housing 100 adjacent peripheral wall 122. The border between heater plate 100 and opening 124 Is sealed with a room temperature vulcanized silicon rubber to prevent entry of liquid into the interior of the housing.

Switch attachment plate 104 has a genera.Uy triangular configuration as seen in Figure 7. A mating support ledge, which follows the peripheral contour of plate 104, Is formed in the bottom of housing 100 and, as seen partially in Figure 14, plate 104 fits on the support ledge. Plate 14 is permanently secured to the support ledge by either an adhesive or welding, pireferably by sonic welding. The interior of housing 100 is thus hermetically sealed, allowing heater 64 to be cleaned in a pressure washing process. Plate 104 supports pivot switch mechanism 116, which functions to individually activate heating element 108 in each* respective heater assembly. Pivot switch mechanism 116 includes an L-shaped housing 130 with a magnet 132 carried in one open end of housing 130, and a mercury switch received within an opening in the other end of housing 130. A pair of support flanges 136 extend upward from the interior of plate 104 to pivotally support housing 130 via a support phn 138 passing through holes in flanges 136 and housing 130.

In the deactivated state of switch 116, the end of housing 130 which carries magnet 132 Is pivoted downward and the opposite end carrying mercury switch 134 is pivoted upward. In this position mercury switch 134 Is in its open state and power is not supplied to heating element 108. Switch 116 is activated by placing an insulated cover 56 over a dish of food to be rethermalized. AS seen in Figures 8 and 16, an annular ring 140 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 covbr 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 of an appropriate heater module Is thus readily assured, since whenever an insulated cover Is placed over food to be heated, the heater module is automatically activated. A cylindrical projection 142 Is formed integral with the

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20 :Ii upper surface of housing 100 to receive magnet 132 and allow sufficient upward pivoting to activate mercury switch 134. A pair of electrical connector pins 144 are supported by a pair of spaced flanges 148 formed on plate 140 in a hermetically sealed manner. Pins 144 connect to a main power supply bypassing through holes 150 in the side T-bar 68 and connecting to electrical wiring 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 attachment plate 108 used in module 64. Attachment plate 108' extends across the entire back of module 66 and has the configuration of two triangles connected by a central strip. Switch 116 is supported on flanges 136' on one of the triangles, and connector pins 144 extend from flanges 148' the other triangle. Otherwise, module 66 is constructed similar to module 64.

Figure 19 illustrates an alternate embodiment 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 along the base of cover 56. In order to properly align magnet 140A S; with reed switch 134A, a projection 49A is formed adjacent rim 49 on tray 30 and cooperates with a mating recess 57 formed in the interior surface of cover 56. This embodiment of switch mechanism and activating mechanism is a secondary embodiment and should be used only S" 25 in environments where persons or patients with heart pacemakers are not present, since magnet 140A within cover 56 could interfere with the operation of the pacemakers.

Figure 20 illustrates the resistance pattern of heating element 108 of heater assembly 64, and Figure 22 is a circuit diagram illustrating the manner in which 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 heaters.

MPS0137/PS ::Pa- -21arranged to cover substantially all of the bottom surface of heater plate 102.

As seen in Figure 22, power is supplied to resistive elements A, B and C of heating element 108 when mercury switch 116 is closed.

When thermostat 112 is open, current passes through all 3 resistive elements A, B and C and provides heat at a first power level. However, when thermostat 112 is closed, current is shunted pait resistive element A and only passes through resistive elements B and C, C being a low voltage indicator light circuit. In this state, heat is supplied at a higher power level since the current passes through a lower resistance (B Thus, during a rethermalization time period (the time period during which timer 33 supplies electrical power), power is always supplied to the food being rethermalized.

Details of the rethermalization will be discussed in greater detail in the discussion of the rethermalization method. However briefly, when food to be rethermallzed is in its cold state and power is initially supplied to heater element 108, thermostat 112 is in its closed 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 from 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 in Figure 20, the higher resistance of resistive element A is accomplished by a plurality of parallel resistance elements connected at connection points I and 2, which are also shown in Figure 22. In Figure 21, which illustrates an alternate heating element 108 for use in the smaller soup heater module 66, the higher resistance of resistive element A is accomplished by using a smaller resistance element connected at connection yoints 1 and 2.

Figure 23 illustrates ar. dternate embodiment of heater element and control circuit arrangement which also accomplishes twostage heating. In this embodiment, a first resistive heating element

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L -I MPS0137/PS -22 1 4 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 operation, the power is proportional relatively low, e.g. 25% of the total power when current passes through both elements A' and Element C' can also be included for an indicator light.

Figure 24 illustrates 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 also connected in parallel to a second resistive heating element B".

However, thermostat 112" alternately supplies current to elements A" and 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 rethermallzing chilled, precooked food. The food is stored at the plurality 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 entree can vary from 3-14 ounces, with the entree including one, two or three different foods. Similarly, the food to be heated by the soup I heater element can vary from 3 to 6 ounces of soup, cereal, hot desserts, rolls or other liquids. The use of the two-stage heater in accordance with the present invention is particularly advantageous for rethermalizing entrees, and more particularly entrees which vary in their range of heat requirements. Entree foods generally include meat, fish, poultry, casseroles, starches and vegetables.

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23 The two-stage heater applies heat to the food over a predetermined time period as set by timer 33. For example, the predetermined 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 l heat from the heater to the food during the predetermined time .period.

Turning to Figure 25, the two-stage application of heat in a rethermalization method in accordance with the present invention is compared to the application 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 c.i and off over the predetermined rethermalization time period. The graph is a theoretical graph and assumes that: the total power of the prior art heater is the same as the high power level of the heater used in the i present method; all heaters operate between the same thermostat limits; and the same food portion, an average entree portion, is being heated. The graph illustrates the temperature sensed by a thermostat 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 thermostatic temperature range is reached, the prior art system completely shuts off Its single power heater, while the present system continues 1 'y 24 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 system. As a result, over a typical rethermalization time period, the prior art system must cycle its heater on more frequently than the high power heater of the present system is cycled on. The chances of scorching of food being retherma_.zed occurs during the temperature peaks, so that there are more opportunities to scorch the food in the prior art system. This scorching danger is actually greater in typical prior art systems which operate at higher temperature ranges than illustrated in the theoretical graph shown in Figure 25. For example, as will be discussed hereinafter, the method of the present invention operates the heaters within a thermostatic temperature range between 220°F and 235°F 5 0 F, whereas a typical prior art 15 heater operating over the same predetermined time period would operate between 245 0 F and 270°F. Prior art systems, which rethermalize in even shorter time periods, operate at even higher thermostatic ranges, e.g. 350 0 F to 400 0

F.

The present heating method also is directed to the manner of refining or adapting the two-stage heating method to a broad range of food types to be rethermallzed. In order to accomplish this objective, the qualities of the foods, which determine the degree of heating the foods require, had to be classified or organized. The following chart A, lists the various food qualities or parameters which render the .I 25 foods difficult or easy to heat, i.e. foods having either a high heat S' energy requirement or a low heat energy requirement.

As seen in Chart A, the food qualities which would determine whether a particular food is difficult or easy to heat include food density, portion size, configuration, moisture content, specifV, 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 food being more difficult to heat than the lower density foods. Larger portions of food, for example six ounces or more, are more difficult to heat than smaller portions of food, for j example 1-1/2 to 3 ounces. The configuration of the food, in particular, the amount of surface area of the food which contacts the heating plate determines the ease with which a .ood 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 surface 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 foods with less moisture content, e.g. 38-75 percent liquid content. Specific heat also is a contributing factor to whether the food is difficult or easy to heat with foods of high specific 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 refers to whether a particular food can sustain its integrity and quality, e.g. not dry out or lose its color or texture, when it undergoes heating. Foods such as meatloaf, casseroles, lasagna and salisbury steaks are relatively sturdy and thus can undergo high energy heating, while such foods as poached eggs, omelets, rice, baked fish, pancakes and rare steaks are fragile 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 foods with high energy heating requirements and foods with low energy heating requirements were first tested. Test exampies are shown in the last column of Chart A. A preferred technique I 25 for arriving at the low power and high power settings was first to determine an amount of low power which could rethermalize low energy requirement foods, e.g. 2 ounces of peas or 2 stacked pancakes by raising their temperature from below 40OF to approximately 140".

The low heat energy requirement food was not brought to the typical rethermalization temperature range of I5 0 F to 210 0 F with only the lower power heater, since the final heater would utilize the two-stage heater and, therefore, would result in an additional boosting power over and above the use of only the low power heater.

Foods with high energy heat requirement for example, a 4 to 6 ounce salisbury steak with 4 ounces of mashed potatoes and 4 ounces r -26of 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 rethermallzed from below 40 F to above 165 F. The intermittent application of the additional power was controlled between predetermined 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 food 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 Sthe high power heater being decreased when the power to the low power heater was increased. Through this process, it was eventually determined that optimum power settings for the high and low power heaters was a low power setting slightly lower than the initial setting of the low power heater for low energy requirement foods and a slightly increased power setting for the high power heater over the initial power supplied to the high heat energy requirement foods.

This test procedure was used at progressively lower thermostat range settings. That is, initial testing occurred at a typical higher prior art thermostatic range, e.g. between 245 0 F to 280 0 F. However, it was eventually determined that a thermostatic temperature range between 215 0 F and 240"F, preferably between 220°F and 235°F, and 25 power supplied at 41 watts at the !ow power setting and 156 watts at the high power setting accomplished the objectives of satisfactory rethermalizing entree food of both high and low energy requirements, as well as rethermalizing mixtures of low and high energy requirement of food such as shown in Chart A. Suitable power ranges for the entree heater should be approximately 35 to 45 watts for low power 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 range between 240° and 2750 worked satisfactorily with power supplied at 10 watts at the low 3 1! I r 'r I I C- LC 1 i: ii i

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11%^ i; I -ii-: 27 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 rois are to be heated, they can be supported on small dishes or a disposable plate or lid rather than on bowls.

In order to establish the above parameters of this method of rethermalization, i.e. the range of foods to be rethermalized and the thermostat and power settings, other system constants had to be set.

For example, the thickness and size of the heater plate had to be held constant throughout the testing. It was determined that the system worked well with a nickel plated aluminum heating plate having a thickness of 1/8 of an inch and a diameter of approximately 7 inches.

The size, shape and configuration of the dish also had to be held constant. It was found that a highly conductive ceramic dish with an alumina additive to increase its convectiveness was suitable for the rethermalization process. The preferred dish has a diameter of approximately 7 3/4" and a thickness of approximately i of an inch. In order to ensure proper heat conduction from the aluminum heater plate to the dish, the dish should be extremely flat with very little concavity and no convex points.

The size, shape and configuration of the bowl for the small heater also was held constant during testing. A round four inch bowl, with an eight fluid ounce capacity, and made of a high heat resistant injection molded plastic was found to be suitable. A bowl with a bottom thickness of approximately a forty-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 of the bowls.

Numerous characteristics and advantages of the Invention have been described in detail in the foregoing description with reference 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 affected therein by persons skilled in the art without departing from the scope or spirit of the invention.

Chart A Heat Requirement High Food Density (High) meat loaf lasagna potatoes sac S choese chicken oatmeal Size of Portion Large! (6 oz or more) total plate weight 10-12 01.

bone-in chkn.

lasagna (thick) small (1.5-3 0z.') total plate weight 3-4 01.

Configuration Unflat/low Surface Area broccoli brussel spts bk. potato mac. S chs.

Flat/Large Surface Area sliced meats casseroles steaks mash. pot.

Moisture Content Low (3i-75%) ham bk. chkn.

High (75-95%)~ spinach casseroles gravies beef broth Specif ic Heat High (.85-.95) apples potatoes Low (.65-.80) ham chicken sausage beef Sturdy ,eatloaf casseroles lasagna sals. stk.

Fragile poached eggs omelette rice rst. beef baked fish pancakes stk (rare) Low 108 High 125 4-6 oz salisbury steaks, 4 oz mashed potato, 4 oz. broc sprs.

0chicken thigh, 4 oz (bone-in), 3 oz brussel sprouts, 4-5 oz baked potato oz~0 sal. stk.

6 oz mashed pot.

2 o1 carrots 04-6 oz oatmeal o 4-6 oz brot~h a .ched egg, ast 0one chs. omlte 2 oz. peas or corn or rice 2 pancakes 0(stacked) (stacked) *rolls Tes ted Fragility Voltage Examples Heat Requirement

(LOW)

rice omelette Low pancakes bread, rolls peas corn Heat Requirement Mixed 8 oz. Lasagna (tall) 1.5 oz.

green peas whole baked pot.

2 oz. sliced roast beet 6 oz. meat loaf, 2 oz. rice 4oz. rice, 6 oz glazed chicken (Oriental) 8 oz. mac ch.

oz. broc.

6 oz. stuffed baked flounder 2 oz. green peas

Claims (14)

1. A food storing and rethermalizing system, including a food service cart having a cart interior; a food tray having a hot food location thereon; a tray cover positionable in a covering position for covering the hot food location; a tray support 1or removably supporting said food tray in said cart interior in a cart location; a heater for heating food at the hot food location when said food tray is in the cart location; a switch for turning power on and off to said heater; an activator associated with said tray cover, for activating said switch with said tray cover when said tray cover is in the covering position and said food tray is in the cart location; and a mating alignment means for aligning said activator with said switch, said mating alignment means including an inner peripheral base surface on said cover and an upward rim on said food tray configured to mate with said base surface.

2. A food storing and rethermalization system according to claim 1, wherein saio. rim is round.

3. A food storing and rethermalization system according to claim 1 or claim 2, wherein said food service cart has a plurality of shelf locations, at least two heaters being positioned at each shelf location with each heater having a different overall power rating.

4. A food storing and rethermalization system according to any one of claims 1 to 3, wherein one of said switch and said switch activator is a magnet and the other is made of magnetic material.

A food storing rethermalization system according to claim 4, wherein said switch includes a pivotable housing, said magnet being supported at one end of said pivotable housing, and a switch activated by the pivoting motion of said pivotable housing.

6. A food storing and rethermalization system according to claim 5, wherein said switch is a a mercury switch carried by said pivotable housing.

7. A food storing and rethermalization system according to claim 4, wherein said switch includes a reed switch, and said switch activator includes a magnet for activating said Sreed switch.

116002.6- 11 April 1995 (11:51) L I k. P i 31

8. A food storing and rethermalization system according to any one of claims 1 to 7, further including a plurality of vertically spaced support bars within said cart interior, including support pins extending from said support bars, and attaching means for removably attaching said heaters to said cart including openings for receiving said supporting pins.

9. A food storing and rethermalizing system as claimed in any one of claims 1 to 9, wherein there is further included a second heater for heating food at a second hot food location when said tray is in the cart location; and a second cover positionable in a covering position, to cover the second hot food location independently of whether said tray cover is in its covering position.

10. A food storing and rethermalizing system as claimed in claim 9, wherein there is further included a second switch activator means, operatively associated with said second cover when said second cover is in its covering position and operable generally independently of said activator for activating said second heater generally only with said second cover in the covering position and said food tray in the cart location; and a second switch for turning power on and off to said second heater.

11. A food storing and rethermalizing system according to claim 10, wherein said switch and o said second switch are activated by said activator said said switch activator means Irespectively, and wherein one of said switch or said switch activator means, are made of 0 0 a magnetic material, and the other includes a magnet.

12. A food storing and rethermalizing system according to claim 11, wherein said switch and said second switch each include a pivotable housing, said magnet being supported at one end of said housing, and an included switch activated by the pivoting motion of said i :i pivotable housing and being supported at the other end of said housing.

13. A food storing and rethermalizing system according to any one of claims 10 to 12, wherein said switch and said second switch are mercury switches.

14. A food storing and rethermalizing system according to any one of claims 10 to 13, Swherein said switch and said second switch each include reed switches, and said activator T and said switch activator each include magnets for activating each said reed switch. PMELCD\9516002.6 11 April 1995 (11:51) ~I -i ;1 ,l-r;l I (/S C ii; r MiB- L 32 A food storing and rethermali7ing system according to any one of claims 10 to 14, wherein said tray and said second cover includes second mating alignment means for aligning said second switch activator means with said switch when said tray is inserted in the cart location. 16. A food storing and rethermalizing system according to claim 15, wherein said second alignment means comprises a rim which mates with an inner surface portion of the base of said second cover. 'io i I. o °olrl a i 17. A food storing and rethermalizing system according to any one of claims 1 to 16, wherein said heater is removable from said food service cart, said food service cart having a support bar with a plurality of outwardly extending supporting pins extending from said support bar, said heater having at least one opening for receiving at least one of said supporting pins. 18. A food storing and rethermalizing system as claimed in claim 17, wherein said second heater is removable from said food service cart, said second heater having at least one second heater opening for receiving at least one of said supporting pins. 19. A food storing and rethermalizing system as claimed in any one of claims 9 to 18, further including a protective cover supportable by said food tray and with said food tray in the cart location, and protectively over both said tray cover and said second cover when in the covering position and said another food location. A food storing and rethermalizing system according to any one of claims 1 to 19, wherein said tray cover is of an insulating material. 21. A food storing and rethermalizing system according to any one of claims 9 to 20, wherein said second cover is of an insulating material. 22. A food storing and rethermalizing system according to any one of claims 1 to 21, wherein said activator is capable of activating said switch in first and second different orientations on and relative to said food tray. 11 April 1995 (11:51) 33 23. A food storing a 1 ad rethermalizing system as claimed in any one of claims 1 to 22, wherein said second switch activator means is capable of activating said second switch in first and second different orientations on and relative to said food tray. 24. A food rethermalizing process, said process comprising the steps of: providing a food service tray with -said- first and second food locations; providing a food service cart defining a tray location and having first and second heaters associated with the tray location, each having respective first and second switch members connected thereto; and placing food to be heated generally at the first food location; placing a cover supporting a first switch element over the food at the first food location and thereby supported by said tray; and positioning the tray with the cover thereon in the tray location and thereby adjacent to the first and second heaters such that the first heater is actuated by the cooperation of the now proximate first switch member and first switch element and thereby heating the food at the first food location and leaving the second heater unactuated. 25. A food storing and rethermalizing process according to claim 24, further including, before said tray positioning step, placing food which is not to be heated at the second food location. 26. A food storing and rethermalizing process according to claim 25, wherein said positioning step includes leaving the second heater unactuated and thereby not heating the .20 food at the second location when the tray is at tie tray location. I 27. A food storing and rethermalizing process according to claim 25, wherein said positioning step includes the food at the second location being uncovered by an individual insulated cover when the tray is in the tray location. 28. A food storing and rethermalizing process according to any one of claims 24 to 27, 2 further including, after said heating the food at the first location by the first heater step, removing the tray from the cart, removing the cover off the food at the first location, serving the unheated food of the second location, and serving the uncovered and heated r- o food of the first location. FHPMELCD\95016002.6- 11 April 1995(11:51) 34 29. A food storing and rethermalizing process according to any one of claims 24 to 28, further including, after said heating the food at the first location by the first heater step, removing the tray from the cart. A food storing and rethermalizing process according to any one of claims 24 to 29, further including, after said placing step and before said positioning step, positioning a protective cover over both the positioned cover and the second food location. 31. A food storing and rethermalizing process according to any one of claims 24 to wherein said positioning step includes aligning the first switch element and the first switch member. 32. A food storing and rethermalizing process according to claim 31, wherein said aligning step includes mating an inner peripheral surface of said positioned cover with a rim formed on said tray adjacent the first food location. 33. A food storing and rethermalizing process according to any one of claims 24 to 32, further including the step of individually removing said heaters from said cart. 34. A food storing and rethermalizing process according to claim 33, wherein said removing step includes unplugging each said heater separately, and further including the step of separately plugging new heaters into the cart to replace the removed heaters. 1 35. A food storing and rethermalizing process according to any one of claims 24 to 34, wherein said heating step includes cycling the temperature between an upper and a lower temperature. S ALADDIN SYNERGETICS INC. April 1995 6 I FHPMELCD\95016002.6 11 April 1995 (11:51) i ~i- t ABSI'IRACT A food storing and rethermalizing system comprising a food service cart (12) having a cart interior, a food tray (30) having a hot food location thereon, a tray cover (56, 58) positionable in a covering position for covering the hot food location, a tray support (38) for removably supporting said food tray (30) in said cart interior in a cart location, a heater (64, 66) for heating, with said food tray (30) in the cart location, food at the hot food location, a switch (116) for turning power on and off to said hoater (64, 66), and an activator (140), associated with said tray covor (56, 58), for activating said switch with said tray cover in the covering position and said food tray (30) in the cart location, the improvement comprising mating alignment means for aligning said activator (140) with said switch (116), said alignment means including an inner peripheral base surface on said cover (56, 58) and an upward rim on said food tray and configured to mate with said base surface. C I rC ii I ii ii I I I oil, 1 crr eiriit i orrrrr sc r r i or IP61852/IP 21/10/92