Food warmer cabinet control

Control means and method for controlling the characteristics of the operation of a food processing device by selective adjustment of temperature and vapor pressure including a chamber to hold food in process, a reservoir to hold water to be evaporated to the air in the chamber where a first heater is located in the reservoir to selectively provide heat of vaporization to the water to be evaporated, and second heater is supplied to heat air supplied to the chamber to increase the temperature of the air to a second temperature where the control means are provided to regulate time periods for which energy is supplied to the first and second heaters to control the humidity and temperature in the chamber.

BACKGROUND OF THE INVENTION 
The present invention relates to control means and methods for food 
processing devices useful for cooking, storing or modifying food at 
selected conditions of temperature and humidity until the food is to be 
served. Devices within the scope of the present invention have been found 
useful where food is to be processed, cooked, proofed (as described 
hereinafter) or held under controlled conditions or and combination 
thereof. 
With the increasing popularity of "fast food" establishments where food is 
precooked for later sale, there is a demand for food holding devices to 
maintain food at substantially uniform temperature for selected periods of 
time while preserving the taste, moisture content, texture and quality of 
the food. Further in other applications it is desirable to be able to 
restore food, particularly baked goods, to acceptable quality after long 
storage periods. 
In many instances storage of "fast foods" is particularly difficult because 
heat loss, bacteria growth and moisture loss experience by the food at 
storage conditions provided by prior art devices, particularly where the 
food is to be stored warm, contribute to rapid deterioration of the food. 
More particularly, it has been found that air circulation characteristics 
and improper storage temperature contribute significantly to bacteria 
growth and excessive loss of moisture which leads to food shrinkage, so 
that in improper storage atmosphere the food deteriorates after only a 
short period of time and loses its tenderness, appetizing taste and 
appearance. 
In accordance with another feature of the present invention it has been 
found that even where food is stored under favorable conditions in an 
enclosure, the food deteriorates at a rate dependent on the time the door 
to the enclosure is opened so the storage chamber is exposed to the 
ambient atmosphere. 
Additionally, it is known that in storage of some foods such as fried 
chicken or fish where a crust is provided, it is particularly desirable to 
maintain the crispness of the crust while minimizing the moisture loss 
from the underlying meat. Storage of such foods tends to require the 
satisfaction of seemingly mutually exclusive conditions, to hold the 
crispness of the crust by maintaining low moisture content in the crust 
while minimizing moisture loss from the food. In such foods excessive 
moisture loss results in shrinkage and loss of tenderness and adversely 
affects the texture of the meat. This can be prevented by controlling the 
temperature and humidity of the storage atmosphere. The problem is to 
prevent moisture flow from the underlying food to the crust while holding 
the crust in low moisture content. 
The prior art demonstrates various means for storing food such as shown in 
U.S. Pat. No. 4,038,968, U.S. Pat. No. 3,955,077, but neither provides for 
selective humidification and temperature control of warm moist air passed 
around a food by regulating the application of energy to a heater in a 
water reservoir or to an air heater to maintain the food at a uniform 
temperature while attempting to maintain moisture in the food. 
Additionally, U.S. Pat. No. 3,955,007 utilizes a moisture container 
assembly mounted in a heat holding compartment located above a gas burner 
assembly where the amount of moisture added to the circulating air bears 
no relationship to the temperature of the air so the moisture content is 
subject to change with the rate of the heat supplied to the humidifier. 
One arrangement for maintaining the moisture content and temperature of 
food products and for slowly cooking foods in some applications is shown 
in copending U.S. Application Ser. No. 521,344 filed Aug. 8, 1983. 
It is further recognized that prior art devices which provide only 
saturated air to a storage compartment do not recognize the dynamics of 
food storage and can lead to situations where breading crust, or other 
materials on the surface of a food product become soggy so the food looses 
its appeal even though the underlying meat may not loose its moisture. Or 
in some instances the food product loses its moisture to the crust so the 
worst possible situation arises. Such problems are further compounded when 
the food is frequently exposed to the atmosphere as by the door to the 
storage compartment. 
One known prior art reference U.S. Pat. No. 2,318,027 Sykes teaches a 
dehydration device where temperature and humidity are controlled in an 
enclosure by sensing wet bulb and dry bulb temperatures and spraying steam 
into a water reservoir to increase humidity. The use of heaters to 
maintain selected water reservoir temperature is not taught. 
Another prior art reference, U.S. Pat. No. 3,245,461 Allington, teaches a 
control arrangement to maintain humidity by monitoring wet bulb and dry 
bulb temperatures where cooling or heat is supplied to a water reservoir 
in response to change in wet bulb and dry bulb temperature. Nowhere does 
the reference recognize the value of the use of the reservoir temperature 
as a means of controlling the treatment of food. 
U.S. Pat. No. 3,518,949 Stock teaches an arrangement for conditioning dough 
etc. where a first control is provided to control air temperature in an 
enclosure by operation of a heater, second temperature control means are 
provided to limit the maximum temperature adjacent the heater and a 
humidity responsive switch is provided to energize a heater in a water 
reservoir to vaporize water to adjust humidity. Stock, like Allington and 
Sykes, does not teach control of the water temperature. Additionally, Luce 
U.S. Pat. No. 2,939,423 controls humidity by controlling temperature of 
the air and water but does not independently control air and water 
temperature. U.S. Pat. No. 3,424,231 Truhan, teaches controlling air and 
water temperatures but sprays water into the air, saturating the air at 
the water temperature rather than relying upon the exposed surface of the 
water in the reservoir to emit vapor into the air. 
No prior art device is known which recognizes the advantages of 
simultaneous control of humidity and temperature of the air in a food 
storage compartment to maintain control of the quality of the food and 
even permit cooking of the food by periodic alternate and/or cycled 
variations in the application of energy to heating devices which control 
the temperature and vapor pressure of the atmosphere to which the food is 
exposed. 
SUMMARY OF THE INVENTION 
The present invention provide a new and useful method and apparatus for 
food processing including cooking, storage, or reconditioning where 
provision is made to control the rate of moisture evaporation from a 
reservoir located within a food holding chamber and the temperature of the 
air within the chamber to adjust the food processing condition and 
periodically adjusting the time of supply of energy to the heaters to 
adjust the condition to achieve heretofore unabtainable food 
characteristics. 
Within the scope of the present invention, it is recognized that in the 
dynamics of food processing, processing time alone does not determine the 
quality of the food product, but rather the rate of change of conditions 
such as temperature and humidity do affect the characteristics. 
The present invention recognizes the importance of control of temperature 
and humidity within well defined limits and the importance of selected 
variation of these parameters in determining the quality of the food 
product. Additionally it has been unexpectedly found that by proper 
cycling of heat supplied to a water reservoir which supplies water for 
evaporation to a food holding chamber and by controlling the ambient 
temperature in the chamber and by proper cycling of the heat supplied to 
the chamber and the reservoir, food products particularly, bakery products 
can be reconstituted. 
Additionally, it has in some instances, been found particularly helpful to 
control the application of heat to the ambient air as well as to the 
heater in the water reservoir in response to the temperature of the food 
itself. 
More particularly, the present invention provides control means and method 
for controlling the operating characteristics of a food processing device 
by selective adjustment of temperature and vapor pressure including a 
chamber to hold food, a reservoir to hold water to be evaporated to the 
air in the chamber where a first heater is located in the reservoir to 
selectively provide heat of vaporization to the water to be evaporated, 
and second heater is supplied to heat air supplied to the chamber to 
increase the temperature of the air to a second temperature where the 
control means are provided to regulate time periods for which energy is 
supplied to the first and second heaters to control the humidity and 
temperature in the chamber. 
One example within the scope of the present invention is shown in the 
accompanying drawings and described hereinafter, it being understood that 
the arrangement shown is by way of illustration only and not by way of 
limitation.

DETAILED DESCRIPTION OF THE DRAWINGS 
Referring first to FIG. 1 which presents a block diagram illustration of 
one example of a device within the scope of the present invention, a food 
chamber 1 which is adapted to hold food to be processed as described 
hereinafter is indicated by dotted lines showing at least one thermocouple 
food probe 2, a water heater arrangement 10 and an air heater arrangement 
20 which are provided within the cabinet. 
The water heater includes a thermocouple 11 which is located within the 
water reservoir 12 where a water heater 13 is located also within the 
water reservoir 12. Reservoir 12 holds water to be evaporated into the 
atmosphere of the cabinet 1 by heater 13. A power input 14 is supplied to 
the water heater. A thermocouple output 16 is provided from thermocouple 
11 to an amplifier system 30 described hereinafter to supply a signal 
indicative of the temperature of the water in the reservoir. 
The thermocouple food probe 2 can be inserted into the food or other 
material to be processed, not shown, to directly reflect the temperature 
of the material. An output 3 from the thermocouple 2 is supplied to the 
thermocouple amplifier 30. 
Likewise, within cabinet 1 an air heater assembly 20 is provided having a 
thermocouple 21 to measure the temperatrue of the air in the cabinet where 
air represented by the arrows A passes through an air heater 25 and over 
the thermocouple 21. A signal 22 is provided from thermocouple 21 to the 
amplifier 30. 
Typically, the temperatures supplied from the thermocouple food probe 2, 
the water thermocouple 11 and the air temperature thermocouple 21 are used 
to monitor and modify the conditions of the atmosphere in cabinet, as 
described hereinafter. The signals are typically analog signals 
represented by the arrows 3A, 16A, and 22A and can be supplied to an 
analog-to-digital converter 40 where digital signals 3B corresponding to 
the signal 3A, 16B corresponding to signal 16A and 22B corresponding to 
signal 22A are supplied to a microprocessor 50 which interprets the 
temperatures received, compares the temperatures with a program in the 
microprocessor and supplies output signals 51-52 through an isolation unit 
53 to relays, for example solid state AC switches 54 provided within a 
power control system 55 to selectively operate air heater 13 and water 
heater 22 as required by the microprocessor in response to changes in 
temperature and to time as measured by a clock C which is carried onboard 
the microprocessor 50. 
Thus within the scope of the invention, the controller can, by switching 
the power supply to heaters 13 and 22, regulate the on and off time of the 
heaters to control the temperature and humidity in the enclosure thus 
providing heretofore unavailable food processes. A display 45 can be 
provided to indicate the status of the various features of the unit either 
continuously or on demand. 
In respect to the general outline of the processes shown in FIG. 1, FIG. 2 
is a more detailed schematic of one arrangement which can be utilized in 
accordance with the present invention, but it will be understood the 
example is not presented by way of limitation. 
In this regard, FIG. 2 illustrates signal inputs 3, 16, and 22 from the 
food thermocouple 3, the thermocouple 11 in the water, and the 
thermocouple 21 in the air, respectively, provided through the amplifier 
bank 30 which as illustrated in FIG. 2 can include three amplifiers, 
31-33. 
The outputs 3A, 16A, 22A, are fed to the analog-to-digital converter 40 
where a clock signal 42 and data signals 45 are output from the converter 
40. Signal 43 is provided likewise from the A/D converter 40 to 
microprocessor 50 as described hereinafter. 
The data signals 45 and clock signal 42 are likewise supplied to 
microprocessor 50 and to a memory device 55, for example, a read only 
memory device part number NMC9345N which is provided to retain the data. 
The data and the clock signal are likewise provided to a visual display 77 
which displays the instantaneous data, information input from a data pad 
78 (described hereinafter), and other data where the display can default 
to a selected variable, for example, the cabinet temperature in the 
abstence of requested data. 
Status outputs 61-64 are provided from microprocessor 50 to indicate 
various occurrences or conditions in the unit such as when the food in 
process is ready to be removed, when a door is open, when the water in the 
reservoir 12 is low or when food within enclosure must be removed. 
As described hereinafter, the control unit 50 can be programmed to operate 
on a selected number of programs which are selected by entry to the data 
pad 78. A usual indication can be provided to indicate which of the 
programs is selected, where for example the device can be adapted to 
select anyone of six programs. Data from the microprocessor is provided on 
lines 65-67 to a flip-flop device 76, for example part 74HC137 to provide 
six outputs 68-73 to a visual readout 74 to indicate which of the programs 
is in operation. 
The data pad 78 is provided for entry of signals to initiate various of the 
functions performed by the control device or to program the microprocessor 
and in this connection, as is known in the art, includes four columns 
C1-C4 and four rows R1-R4 so that the eight inputs are supplied to the 
microprocessor 50 and operated as binary combination to instruct the 
microprocessor for example to select a program to be operated by the 
device and to provide other instructions such as which overall function is 
to be conducted by the unit. 
A clock C can be provided to microprocessor 50 for timing as known in the 
art and inputs 10P are provided to IOP (input/output ports) of the 
microprocessor 50, first of all to flip-flop 81, for example a part number 
74C374 and where outputs 82, 83, 84 which are operated by IOP from the 
microprocessor 50 operate the power supply to the water heater and the air 
heater in the unit. Three of the outputs 86, 87, 88 can be supplied along 
with outputs B from a second flow-through latch 91, for example a part 
number 74C373 to the addresses to a memory device 89, for example a 
eraseable programable read-only memory where the programs to be conducted 
by the device have been stored. The data outputs D from the EPROM 89 are 
then supplied to the IOP ports of the microprocessor to permit the 
microprocessor to step through its functions and provide outputs to, for 
example, operate the heater 13 to adjust the vapor pressure in the 
atmosphere in which the food is placed so that the rate of evaporation of 
moisture from the food is controlled. 
Each program can be adapted to provide a number of stages of humidity 
during a single cooking cycle so that, for example in the case of meat, 
the humidity in the cabinet can be adjusted in accordance with either the 
time during which the cooking has been in effect or the temperature sensed 
by the temperature probe 2. The processor controller can also 
independently adjust the temperature in the cabinet and maintain the 
proper balance between the humidity and the cabinet temperature to provide 
numerous cooking or food processing combinations. 
FIG. 3 illustrates schematically an arrangement within the scope of the 
present invention. Enclosure 1 is shown which includes a inner cabinet 101 
having shelves 102 on which in the example shown, food 103 rests for 
cooking. Air stream B which has been treated as described hereinafter as 
to temperature and humidity is passed into enclosure 101 over shelves 102 
for emission as gas C to be treated. 
The air temperature thermocouple 21 is shown connected by means of lead 22 
to a controller 25 which includes the processes illustrated in FIG. 1 and 
2. 
The food probe 2 is likewise illustrated as is the lead 3 which supplies 
the signal from the probe 2 to the control system 25. Additionally, the 
water thermocouple 11 is shown connected by means of a lead 16 to the 
control 25. Heater 13 is shown located in a reservoir 106 which contains 
water 107. Air heater 22 is shown in the arrangement and is provided to 
heat the air stream D which flows over the reservoir 106 and can be 
impelled either by a fan 108 or within the scope of the present invention 
it has been found that natural convective currents provide sufficient air 
movement in most instances for satisfactory operation of the device. 
Accordingly, the cabinet air is circulated, either by air moving means 108 
or by convective forces, over reservoir 106 where vapor from the reservoir 
is mixed with the air stream which is then heated additionally by the 
heater 22 for passage into the enclosure 101. 
Further, while the foregoing description is presented with reference to 
electronic control, generally equivalent operating sequences could be 
accomplished by mechanical, pneumatic or other means. 
It will further be understood that the foregoing are a few examples of 
arrangements within the scope of the present invention and that other 
arrangements, also within the scope of the present invention, will occur 
to those skilled in the art upon reading the disclosure set forth 
hereinafter.