U.S. patent application number 09/188531 was filed with the patent office on 2002-01-03 for controller and method for administering and providing on-line handling of deviations in a rotary sterilization process.
Invention is credited to WENG, ZHIJUN.
Application Number | 20020001535 09/188531 |
Document ID | / |
Family ID | 22693553 |
Filed Date | 2002-01-03 |
United States Patent
Application |
20020001535 |
Kind Code |
A1 |
WENG, ZHIJUN |
January 3, 2002 |
CONTROLLER AND METHOD FOR ADMINISTERING AND PROVIDING ON-LINE
HANDLING OF DEVIATIONS IN A ROTARY STERILIZATION PROCESS
Abstract
A rotary sterilization system, a controller for use in the
rotary sterilization system, and a method performed by the
controller are disclosed. The system, controller, and method are
used to administer a sterilization process performed on a line of
containers and provide on-line handling of a deviation in a
scheduled parameter during the process. The containers contain a
shelf stable food product that is to be sterilized in the
sterilization process. In addition to the controller, the rotary
sterilization system includes a rotary sterilizer. The controller
controls the rotary sterilizer in performing the sterilization
process according to scheduled parameters. When a deviation in a
specific one of the scheduled parameters occurs, the controller
identifies those of the containers that will in response have a
total lethality predicted to be delivered to them during the
sterilization process that is less than a predefined target
lethality.
Inventors: |
WENG, ZHIJUN; (FRESNO,
CA) |
Correspondence
Address: |
FLEHR HOHBACH TEST ALBRITTON & HERBERT
FOUR EMBARCADERO CENTER
SUITE 3400
SAN FRANCISCO
CA
941114187
|
Family ID: |
22693553 |
Appl. No.: |
09/188531 |
Filed: |
November 6, 1998 |
Current U.S.
Class: |
422/3 ; 422/105;
422/108; 422/109; 422/110; 422/26; 422/40; 426/231; 426/232;
99/467; 99/483 |
Current CPC
Class: |
A23L 3/003 20130101;
A23L 3/06 20130101 |
Class at
Publication: |
422/3 ; 422/26;
422/40; 422/105; 422/108; 422/109; 422/110; 426/231; 426/232;
99/483; 99/467 |
International
Class: |
G05B 001/00; B01J
019/00 |
Claims
What is claimed is:
1. A method of administering a sterilization process being
performed by a rotary sterilizer on a continuous line of
containers, the method comprising the steps of: controlling the
rotary sterilizer to perform the rotary sterilization process
according to scheduled parameters; and when a deviation in a
specific one of the scheduled parameters occurs, identifying those
of the containers that will in response have a total lethality
predicted to be delivered to them during the sterilization process
that is less than a predefined target lethality.
2. The method of claim 1 wherein the specific one of the scheduled
parameters is one of the group consisting of (1) a scheduled retort
temperature in a temperature zone of the rotary sterilizer through
which the line of containers is conveyed, (2) a scheduled initial
product temperature for the containers, and (3) a scheduled reel
speed for conveying the containers in line through the rotary
sterilizer.
3. The method of claim 1 further comprising the step of: compiling
an actual retort time temperature profile for a temperature zone of
the rotary sterilizer; and wherein the identifying step comprises
the steps of: selecting at least some of the containers that are
effected by the deviation; for each of the selected containers that
has been conveyed into the temperature zone during the deviation,
simulating a product cold spot time-temperature profile for the
container based on the actual retort temperature profile; computing
the total lethality predicted to be delivered to the container
during the sterilization process based on the product cold spot
time-temperature profile; and determining whether the total
lethality predicted to be delivered to the container satisfies the
target lethality.
4. The method of claim 3 wherein the simulating step uses a finite
difference simulation model to simulate the product cold spot
time-temperature profile.
5. The method of claim 4 wherein the total lethality is the sum of
(1) a lethality actually delivered over a first time interval from
when the container is loaded into the rotary sterilizer to a
current sample real time, and (2) a lethality predicted to be
delivered over a second time interval from the current sample real
time to when the container is unloaded from the rotary
sterilizer.
6. The method of claim 5 wherein: the lethality actually delivered
over the first time interval is based on the portion of the product
cold spot time-temperature profile over the first time interval;
the portion of the product cold spot time-temperature profile over
the first time interval is based on at least a portion of the
actual retort temperature profile over a time interval from a time
when the container is first affected by the deviation to the
current sample real time.
7. The method of claim 6 wherein: the lethality predicted to be
delivered over the second time interval is based on the portion of
the product cold spot time-temperature profile over the second time
interval; the scheduled parameters include one or more scheduled
retort temperatures that are scheduled for the sterilization
process in the second time interval; and the portion of the product
cold spot time-temperature profile over the second time interval is
based on the one or more scheduled retort temperatures.
8. A controller for administering a sterilization process performed
by a rotary sterilizer on a continuous line of containers of
containers, the controller comprising: control circuitry configured
to control the rotary sterilizer; a memory configured to store a
process control program and a deviation program, the process
control program being programmed to cause the control circuitry to
control the rotary sterilizer in performing the sterilization
process according to scheduled parameters, the deviation programmed
being programmed to identify, when a deviation in a specific one of
the scheduled parameters occurs, those of the containers that will
in response have a total lethality predicted to be delivered to
them during the sterilization process that is less than a
predefined target lethality; and a microprocessor coupled to the
memory and the control circuitry and configured to execute the
process control and temperature deviation programs.
9. The controller of claim 8 wherein the specific one of the
scheduled parameters is one of the group consisting of (1) a
scheduled retort temperature in a temperature zone of the rotary
sterilizer through which the line of containers is conveyed, (2) a
scheduled initial product temperature for the containers, and (3) a
scheduled reel speed for conveying the containers in line through
the rotary sterilizer.
10. The controller of claim 8 wherein: the process control program
is further programmed to compile an actual retort time temperature
profile for a temperature zone of the rotary sterilizer; and the
deviation program is programmed to identify the identified
containers by: selecting at least some of the containers that are
effected by the deviation; for each of the selected containers that
has been conveyed into the temperature zone during the deviation,
simulating a product cold spot time-temperature profile for the
container based on the actual retort temperature profile; computing
the total lethality predicted to be delivered to the container
during the sterilization process based on the product cold spot
time-temperature profile; and determining whether the total
lethality predicted to be delivered to the container satisfies the
target lethality.
11. The controller of claim 10 wherein the deviation program is
programmed to use a finite difference simulation model to simulate
the product cold spot time-temperature profile.
12. The controller of claim 10 wherein the total lethality is the
sum of (1) a lethality actually delivered over a first time
interval from when the container is loaded into the rotary
sterilizer to a current sample real time, and (2) a lethality
predicted to be delivered over a second time interval from the
current sample real time to when the container is unloaded from the
rotary sterilizer.
13. The controller of claim 12 wherein: the lethality actually
delivered over the first time interval is based on the portion of
the product cold spot time-temperature profile over the first time
interval; the portion of the product cold spot time-temperature
profile over the first time interval is based on at least a portion
of the actual retort temperature profile over a time interval from
a time when the container is first affected by the deviation to the
current sample real time.
14. The controller of claim 13 wherein: the lethality predicted to
be delivered over the second time interval is based on the portion
of the product cold spot time-temperature profile over the second
time interval; the scheduled parameters include one or more
scheduled retort temperatures that are scheduled for the
sterilization process in the second time interval; and the portion
of the product cold spot time-temperature profile over the second
time interval is based on the one or more scheduled retort
temperatures.
15. A rotary sterilization system comprising: a rotary sterilizer
configured to perform a sterilization process on a continuous line
of containers; a controller configured to: control the rotary
sterilizer in performing the rotary sterilization process according
to scheduled parameters; when a deviation in a specific one of the
scheduled parameters occurs, identify those of the containers that
will in response have a total lethality predicted to be delivered
to them during the sterilization process that is less than a
predefined target lethality.
16. The rotary sterilization system of claim 15 wherein the
specific one of the scheduled parameters is one of the group
consisting of (1) a scheduled retort temperature in a temperature
zone of the rotary sterilizer through which the line of containers
is conveyed, (2) a scheduled initial product temperature for the
containers, and (3) a scheduled reel speed for conveying the
containers in line through the rotary sterilizer.
17. The rotary sterilization system of claim 15 further comprising:
a sensor to sense actual retort temperatures in a temperature zone
of the rotary sterilizer; the controller is further configured to:
compile an actual retort time temperature profile from the sensed
actual retort temperatures; and identify the identified containers
by: selecting at least some of the containers that are effected by
the deviation; for each of the selected containers that have been
conveyed into the temperature zone during the deviation, simulating
a product cold spot time-temperature profile for the container
based on the actual retort temperature profile; computing the total
lethality predicted to be delivered to the container during the
sterilization process based on the product cold spot
time-temperature profile; and determining whether the total
lethality predicted to be delivered to the container satisfies the
target lethality.
18. The rotary sterilization system of claim 17 wherein the
controller is still further configured to use a finite difference
simulation model to simulate the product cold spot time-temperature
profile.
19. The rotary sterilization system of claim 17 wherein the total
lethality is the sum of (1) a lethality actually delivered over a
first time interval from when the container is loaded into the
rotary sterilizer to a current sample real time, and (2) a
lethality predicted to be delivered over a second time interval
from the current sample real time to when the container is unloaded
from the rotary sterilizer.
20. The rotary sterilization system of claim 19 wherein: the
lethality actually delivered over the first time interval is based
on the portion of the product cold spot time-temperature profile
over the first time interval; the portion of the product cold spot
time-temperature profile over the first time interval is based on
at least a portion of the actual retort temperature profile over a
time interval from a time when the container is first affected by
the deviation to the current sample real time.
21. The rotary sterilization system of claim 26 wherein: the
lethality predicted to be delivered over the second time interval
is based on the portion of the product cold spot time-temperature
profile over the second time interval; the scheduled parameters
include one or more scheduled retort temperatures that are
scheduled for the sterilization process in the second time
interval; and the portion of the product cold spot time-temperature
profile over the second time interval is based on the one or more
scheduled retort temperatures.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention relates generally to a controller for
administering a rotary sterilization process being performed on
line of containers. In particular, it pertains to such a controller
that also provides on-line handling of a deviation in a scheduled
parameter during the process by identifying any containers that
will be under processed as a result of the deviation.
BACKGROUND OF THE INVENTION
[0002] A rotary sterilization system is a continuous source
processing system with intermittent product agitation. This system
is widely used in the canning industry to sterilize a shelf stable
food product packaged in containers. It is used most often for
sterilizing a food product that benefits from mechanical agitation
of the containers.
[0003] A rotary sterilization system includes a rotary sterilizer
that has one or more cooking shells through which a line of
containers {1, . . . , i, . . . , I}.sub.line are conveyed. The
containers are cooked in the cooking shell(s) at one or more
scheduled cooking retort temperatures. The containers are then
conveyed in line through one or more cooling shells of the rotary
sterilizer. Similar to the cooking shell(s), the containers are
cooled in the cooling shell(s) at one or more scheduled cooling
retort temperatures.
[0004] The containers {1, . . . , i, . . . , I}.sub.line are
conveyed through each cooking and cooling shell by spiral tracks
and a reel. The reel has a scheduled reel speed and imparts
movement while the spiral tracks provide the direction for the
containers to be conveyed through the shell. This also provides
mechanical agitation of the food product within the containers.
[0005] In order for the food product in each container i to be
commercially sterilized, a total lethality F.sub.i over a total
time interval [t.sub.f,i, t.sub.d,i] that satisfies a predefined
target total lethality F.sub.targ must be delivered during the
rotary sterilization process to the product cold spot of the
container. Here, t.sub.f,i and t.sub.d,i are the feed and discharge
times when the container is fed into and discharged from the rotary
sterilizer. The target total lethality is set by the USDA (U.S.
Department of Agriculture), the FDA (Food and Drug Administration),
and/or a suitable food processing authority for destroying certain
microorganisms. The reel speed and the cooking and cooling retort
temperatures are then scheduled so that each container i will
receive a scheduled time-temperature treatment that delivers a
total lethality to the container which satisfies the target total
lethality.
[0006] As is well known, the lethality F.sub.i delivered to the
product cold spot of a container i over a particular time interval
[t.sub.m, t.sub.k] is given by the lethality equation: 1 F 1 = t m
t k 10 ( T cs ( t ) s - T REF ) / z t
[0007] where t.sub.m and t.sub.k are respectively the begin and end
times of the time interval [t.sub.m, t.sub.k], T.sub.CS(t).sub.i is
the product cold spot timne-temperature profile for the container,
z is the thermal characteristic of a particular microorganism to be
destroyed in the sterilization process, and T.sub.REF is a
reference temperature for destroying the organism. Thus, the total
lethality F.sub.i delivered to the product cold spot over the total
time interval [t.sub.f,i, t.sub.d,i] due to the scheduled cooking
and cooling retort temperatures is given by this lethality
equation, where t.sub.m=t.sub.f,i and t.sub.k=t.sub.d,i.
[0008] The total time interval [t.sub.f,i, t.sub.d,i] and the
product cold spot time-time-temperature profile T.sub.CS(t).sub.i
must be such that the total lethality F.sub.i over [t.sub.f,i,
t.sub.d,i] satisfies the target total lethality F.sub.targ. In
order to ensure that this occurs, various mathematical simulation
models have been developed for simulating the product cold spot
time-temnperature profile based on the scheduled retort
temperatures. These models include those described in Ball, C. O.
and Olson, F. C. W., Sterilization in Food Technology: Theory,
Practice and Calculations, McGraw-Hill Book Company, Inc., 1957;
Hayakawa, K., Experimental Formulas for Accurate Estimation of
Transient Temperature of Food and Their Application to thermal
Process Evaluation, Food Technology, vol. 24, no. 12, pp. 89 to 99,
1970; Thermobacteriology in Food Processing, Academic Press, New
York, 1965; Teixeira, A. A., Innovative Heat Transfer Models: From
Research Lab to On-Line Implementation in Food Processing
Automation II, ASAE, p. 177-184, 1992; Lanoiselle, J. L., Candau,
Y., and Debray E., Predicting Internal Temperatures of Canned Foods
During Thermal Processing Using a Linear Recursive Model, J. Food
Sci., Vol. 60, No. 4, 1995; Teixeira, A. A., Dixon, J. R.,
Zahradnik, J. W., and Zinsmeister, G. E., Computer Optimization of
Nutrient Retention in Thermal Processing of Conduction Heated
Foods, Food Technology, 23:137-142, 1969; Kan-Ichi Hayakawa,
Estimating Food Temperatures During Various Processing or Handling
Treatments, J. of Food Science, 36:378-385, 1971; Manson, J. E.,
Zahradnik, J. W., and Stumbo, C. R., Evaluation of Lethality and
Nutrient Retentions of Conduction-Heating Foods in Rectangular
Containers, Food Technology, 24(11):109-113, 1970; Noronha, J.,
Hendrickx, M., Van Loeg, A., and Tobback, P., New Semi-empirical
Approach to Handle Time-Variable Boundary Conditions During
Sterilization of Non-Conductive Heating Foods, J. Food Eng.,
24:249-268, 1995; and the NumeriCAL model developed by Dr. John
Manson of CALWEST Technologies, licensed to FMC Corporation, and
used in FMC Corporation's LOG-TEC controller.
[0009] However, if any of the actual retort temperatures in the
cooking and cooling shells drops below a corresponding scheduled
cooking or cooling retort temperature, a temperature deviation
occurs. Traditionally, when such a deviation occurs, the controller
stops the shells' reels and prevents any of the containers {1, . .
. , i, . . . , I}.sub.line from being fed into or discharged from
the rotary sterilizer until the deviation is cleared. But, this
approach causes numerous problems. For example, significant
production down time will result. And, many containers { . . . , i,
. . . }.sub.overpr will be over processed since the total
lethalities { . . . , F.sub.i over [t.sub.f,i, t.sub.d,i], . . .
}.sub.overpr actually delivered to their product cold spots will
significantly exceed the target total lethality F.sub.targ. All of
these problems may result in severe economic loss to the operator
of the rotary sterilization system.
[0010] In order to prevent such loss, a number of approaches have
been discussed and proposed for on-line control of sterilization
processes. However, all of these approaches concern control of
batch sterilization processes performed on a batch of containers
{1, . . . , i, . . . , I}.sub.batch. In a batch sterilization
process, all of the containers generally receive the same
time-temperature treatment whether or not a temperature deviation
occurs. Thus, when a deviation does occur, a correction to the
process can be made which simultaneously effects all of the
containers so that a minimum total lethality F.sub.i over [t.sub.b,
t.sub.e] will be delivered to the product cold spot of each
container i, where t.sub.b and t.sub.e are the begin and end times
of the batch sterilization process. An example of such an approach
is described in concurrently filed and co-pending U.S. Pat.
application Ser. No. 09/______, entitled Controller and Method for
Administering and Providing On-Line Correction of a Batch
Sterilization Process, filed on Nov. 6, 1998, with Weng, Z. as
named inventor. This patent application is hereby explicitly
incorporated by reference.
[0011] In contrast, each container i in a rotary sterilization
process will receive a unique time-temperature treatment. Thus, the
total lethality F.sub.i over [t.sub.f,i, t.sub.d,i] that is
actually delivered to each container is different. This makes it
difficult to identify, while on-line and in real time, each
container that will have a predicted total lethality delivered to
it that is below the target total lethality F.sub.targ. As a
result, the development of a controller that provides on-line
handling of a temperature deviation in a rotary sterilization
process without stopping the reels of the cooking and cooling
shells has been inhibited.
SUMMARY OF THE INVENTION
[0012] In summary, the present invention comprises a rotary
sterilization system, a controller for use in the rotary
sterilization system, and a method performed by the controller. The
system, controller, and method are used to administer a
sterilization process performed on a line of containers and provide
on-line handling of a deviation in a scheduled parameter during the
process. The containers contain a shelf stable food product that is
to be sterilized in the sterilization process. In addition to the
controller, the rotary sterilization system includes a rotary
sterilizer.
[0013] The controller controls the rotary sterilizer in performing
the rotary sterilization process according to scheduled parameters.
When a temperature deviation below a specific scheduled temperature
occurs, the controller identifies those of the containers that will
in response have a total lethality predicted to be delivered to
them during the rotary sterilization process that is less than a
predefined target lethality. This specific scheduled parameter may
be a scheduled retort temperature in a temperature zone of the
rotary sterilizer through which the line of containers is conveyed.
It also may be a scheduled initial product temperature for the
containers or a scheduled reel speed for conveying the containers
in line through the rotary sterilizer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a block diagram of a rotary sterilization system
in accordance with the present invention.
[0015] FIG. 2 is a block diagram of a controller of the rotary
sterilization system of FIG. 1.
[0016] FIG. 3 is an overall process flow diagram for the controller
of FIG. 2 in controlling a rotary sterilization process performed
by the rotary sterilization system of FIG. 1.
[0017] FIG. 4 is a timing diagram for handling a temperature
deviation according to the overall process flow diagram of FIG.
3.
[0018] FIG. 5 is a lethality distribution diagram showing the
distribution of lethalities for containers affected by the
temperature deviation shown in FIG. 4.
[0019] FIGS. 6 to 9 are detailed process flow diagrams for various
steps of the overall process flow diagram of FIG. 3.
DETAILED DESCRIPTION OF THE INVENTION
[0020] Referring to FIG. 1, there is shown a rotary sterilization
system 100 for performing a rotary sterilization process on a
continuous line of containers {1, . . . , i, . . . , I}.sub.line.
Each container i contains a food product that is to be sterilized
during the process. The system 100 comprises a rotary sterilizer
102, a programmed controller 104, and a host computer 105.
[0021] 1. Exemplary Embodiment
[0022] In an exemplary embodiment, the rotary sterilizer 102
includes a cooking shell 106-1 and a cooling shell 106-2 through
which the containers {1, . . . , i, . . . ,I}.sub.line are conveyed
in line. The containers are cooked in the cooking shell 106-1 and
cooled in the cooling shell 106-2. Each of these shells has spiral
tracks 108 and a reel 109 to convey the containers through the
shell. The reel 109 imparts movement while the spiral tracks 108
provide the direction for the containers to be conveyed through the
shell 106-1 or 2.
[0023] Furthermore, a feed device 110 of the rotary sterilizer 102
feeds the containers {1, . . . , i, . . . , I}.sub.line in line to
the cooking shell 106-1. The feed device is designed to prevent the
escape of steam while loading the containers onto the reel of the
cooking shell 106-1. The containers are transferred from the reel
109 of the cooking shell 106-1 to the reel 109 of the cooling shell
106-2 by a transfer device 112. Like the feed device, the transfer
device is designed to prevent the escape of steam from the cooking
shell while the containers are transferred between the reels of the
cooking and cooling shells. The containers are finally off-loaded
from the cooling shell's reel by a discharge device 114.
[0024] In this exemplary embodiment, the cooking shell 106-1 has
multiple temperature zones 115-1, 2, and 3. The containers {1, . .
. , i, . . . I}.sub.line are pre-cooked in the temperature zones
115-1 and 2 at corresponding scheduled retort temperatures
T.sub.sRT1.sup.0 and T.sub.sRT2.sup.0. The zone 115-3 is used to
cook the containers at a corresponding scheduled retort temperature
T.sub.sRT3.sup.0. Similarly, the cooling shell 106-3 has
temperature zones 115-4 and 5 in which the containers are cooled at
corresponding scheduled retort temperatures T.sub.sRT4.sup.0 and
T.sub.sRT5.sup.0. However, as those skilled in the art will
recognize and as will be explained later in section 2, other
embodiments do exist where fewer or more cooking and/or cooling
shells with fewer and/or more temperature zones are used.
[0025] At each sample real time t.sub.r (e.g., every 0.1 to 1
seconds) of the rotary sterilization process, the sensors 116-1, .
. . , 4 of the hydrostatic sterilizer 102 respectively sense the
actual retort temperatures T.sub.aRT1(t.sub.r), . . . ,
T.sub.aRT5(t.sub.r) in the corresponding temperature zones 115-1, .
. . , 5 of the cooking and cooling shells 106-1 and 2. Similarly,
the rotary sterilizer's sensor 107 senses the actual reel speed
v.sub.a(t.sub.r) of the reels of the cooking and cooling shells at
each each sample real time t.sub.r. Finally, the feed device 110
periodically (e.g., every 20 to 30 minutes) removes a container
being fed into the rotary sterilizer and a sensor 117 of the rotary
sterilizer senses its actual initial product temperature
T.sub.aIP(t.sub.r) at that time t.sub.r.
[0026] The controller 104 administers the rotary sterilization
process by controlling the rotary sterilizer 102 and providing
on-line handling of any temperature deviations during the process.
This is done in response to the actual initial product and retort
temperatures T.sub.aIP(t.sub.r) and T.sub.aRT1(t.sub.r), . . . ,
T.sub.aRT5(t.sub.r) sensed by the sensors 117 and 116-1, . . . , 5
at each sample real time t.sub.r, the actual reel speed
v.sub.a(t.sub.r) sensed by the sensor 107, and the actual initial
product temperature T.sub.aIP(t.sub.r) sensed by the sensor
117.
[0027] The host computer 105 is used to provide input information,
namely input parameters and software, used by the controller 104 in
administering the rotary sterilization process. The host computer
is also used to receive, process, and display output information
about the process which is generated by the controller.
[0028] 1.a. Hardware and Software Configuration of Controller
104
[0029] Turning to FIG. 2, the controller 104 comprises a main
control computer 118 that includes a microprocessor (i.e., CPU)
119, a primary memory 120, and a secondary memory 121. The
microprocessor executes an operating system 122, a process control
program 123, a process scheduling program 124, and a temperature
deviation program 125 of the controller. The operating system and
programs are loaded from the secondary memory into the primary
memory during execution.
[0030] The operating system 122 and the programs 123 to 125 are
executed by the microprocessor 119 in response to commands issued
by the operator. These commands may be issued with a user interface
126 of the main control computer 118 and/or the host computer 105
via a host computer interface 127 of the controller 104. The
operating system controls and coordinates the execution of the
other programs. Data 128 generated by the operating system and
programs during execution and data 128 inputted by the operator is
stored in the primary memory. This data includes input information
provided by the operator with the user interface and/or the host
computer via the host computer interface. It also includes output
information provided to the user interface or the host computer via
the host computer interface that is to be displayed to the
operator.
[0031] The controller 104 also comprises control circuitry 129. The
control circuitry includes circuits, microprocessors, memories, and
software to administer the rotary sterilization process by
generating control signals that control the sequential operation of
the rotary sterilizer 102. As alluded to earlier, the software may
be downloaded from the host computer 105 and provided to the
control circuitry by the process control program 123. The control
signals are generated in response to commands generated by this
program and issued to the control circuitry from the microprocessor
119 via a control circuitry interface 130 of the main control
computer 118.
[0032] Furthermore, at each sample real time t.sub.r of the rotary
sterilization process, the control circuitry 129 receives sensor
signals from the sensors 107, 117, and 116-1, . . . , 5 that
represent the actual reel speed v.sub.a(t.sub.r) and the actual
initial product and retort temperatures T.sub.aIP(t.sub.r) and
T.sub.aRT1(t.sub.r), . . . , T.sub.aRT5(t.sub.r). The control
circuitry generates the control signals for controlling the rotary
sterilizer 102 in response to these sensed parameters. These sensed
parameters are also provided to the microprocessor 119 via the
control circuitry interface 130 and recorded by the process control
program 123 as data 128 in the primary memory 120. In this way, the
process control program compiles and records in the primary memory
120 an actual reel time-speed profile v.sub.a(t), an actual initial
product time-temperature profile T.sub.aIP(t), and actual retort
time-temperature profiles T.sub.aRT1(t), . . . , T.sub.aRT5(t) for
the corresponding temperature zones 115-1, . . . , 5. These
profiles are used in the manner described later for providing
on-line handling of temperature deviations during the rotary
sterilization process.
[0033] The sensors 116-1, . . . , 5 are preferably located in the
slowest heating regions of the temperature zones 115-1, . . . , 5
to provide conservative estimates of the actual retort temperatures
T.sub.aRT1(t.sub.r), . . . , T.sub.aRT5(t.sub.r). However, if this
is not possible, the process control program 123 may adjust the
temperatures provided by the sensors to estimate the actual retort
temperatures at the slowest heating regions. This adjustment would
be done according to temperature distribution data 128 in the
primary memory 120 generated from heating and cooling temperature
distribution tests conducted on the temperature zones.
[0034] As mentioned earlier, the operating system 122 and the other
programs 123 to 125 are normally stored in the secondary memory 121
and then loaded into the primary memory 120 during execution. The
secondary memory comprises one (or multiple) computer readable
memory(ies) 132 that is(are) readable by the main control computer
118 of the controller 104. The computer readable memory(ies)
is(are) therefore used to direct the controller in controlling the
rotary sterilization process. The computer readable memory(ies) may
comprise a PROM (programmable read only memory) that stores the
operating system and/or the other programs. Alternatively or
additionally, the computer readable memory(ies) may comprise a
magnetic or CD ROM storage disc that stores the operating system
and/or the other programs. The computer readable memory(ies) in
this case is(are) readable by the main control computer with a
magnetic or CD ROM storage disk drive of the secondary memory.
Moreover, the operating system and/or the other programs could also
be downloaded to the computer readable memory(ies) or the primary
memory from the host computer 105 via the host computer interface
127.
[0035] The controller 104 controls the rotary sterilization process
according to the flow and timing diagrams of FIGS. 3 to 9. In doing
so, a finite difference simulation model is used by the process
scheduling program 124 to simulate a scheduled product cold spot
time-temperature profile T.sub.CS(t).sub.i.sup.0 that applies to
all of the containers {1, . . . i, . . . , I}.sub.line. Similarly,
the temperature deviation program 125 uses the model to simulate
corresponding product cold spot time-temperature profiles { . . . ,
T.sub.CS(t).sub.i.sup.j, . . . } for corresponding selected
containers { . . . , i, . . . }.sub.sel at each sample real time
t.sub.r during a temperature deviation. This model may be the
earlier mentioned NumeriCAL model and used for both conduction
heated food products and convection heated food products. Or, it
may be one of the models described in the Teixeira et al., 1969 and
Manson et al., 1970 references and used for conduction heated food
products. As will be evident from the foregoing discussion, the
novelty of the invention described herein is not in which model is
used, but in the manner in which it is used according to the flow
and timing diagrams in FIGS. 3 to 9.
1.b. Overall Process Flow
[0036] In the first step 134 for controlling the rotary
sterilization process according to the overall process flow of FIG.
3, the input parameters for the rotary sterilization process are
defined and provided to the controller 104. The input parameters
include a predefined sampling time period .DELTA.t.sub.r for each
real time increment [t.sub.r-.DELTA.t, t.sub.r] from the previous
sample real time t.sub.r-.DELTA.t.sub.r to the current sample real
time t.sub.r during the process. The input parameters also include
a initially scheduled product temperature T.sub.sIP for the food
product in the containers being processed. The input parameters
further include the traditional heating and cooling factors
j.sub.h, f.sub.h, x.sub.bh, f.sub.2, j.sub.c, and f.sub.c to be
used in the simulation model. The heating factors j.sub.h, f.sub.h,
x.sub.bh, and f.sub.2 are respectively the heating time lag factor,
the heating curve slope factor, the broken heating time factor, and
the broken heating curve slope factor that are pre-defined for the
food product. Similarly, the cooling factors j.sub.c and f.sub.c
are respectively the cooling time lag factor and the cooling curve
slope factor that are also pre-defined for the food product. The
input parameters additionally include the earlier discussed thermal
characteristic z for destroying a particular microorganism in the
food product and the associated reference temperature T.sub.REF.
Also included in the input parameters is the earlier discussed
target total lethality F.sub.targ and earlier discussed scheduled
retort temperatures T.sub.sRT1.sup.0, . . . , T.sub.sRT5.sup.0.
Finally, the input parameters include the minimum and maximum reel
speeds v.sub.min and v.sub.max and reel step information S for the
reels 109 and spiral tracks 108 of the cooking and cooling shells
106-1 and 2 and length and location information L.sub.1, . . . ,
L.sub.5 for the corresponding temperature zones 115-1, . . . , 5 in
the shells.
[0037] In order to perform step 134, the operator issues commands
with the user interface 126 and/or the host computer 105 to invoke
the process control program 123. Then, the operator enters the
input parameters T.sub.IP, j.sub.h, f.sub.h, x.sub.bh, f.sub.2,
j.sub.c, f.sub.c, F.sub.targ, T.sub.sRT1.sup.0, . . . ,
T.sub.sRT5.sup.0, v.sub.min, v.sub.max, S, and L.sub.1, . . . ,
L.sub.5 with the user interface 126 and/or the host computer 105.
The process control program 123 loads the entered input parameters
into the primary memory 120 for use by the programs 123 to 125. The
execution of these programs is controlled and coordinated by the
process control program in the manner discussed next.
[0038] The process control program 123 first invokes the process
scheduling program 124. In step 135, the process scheduling program
simulates the entire rotary sterilization process to be
administered to a container i to define an initially scheduled reel
speed v.sub.s.sup.0 for the reels of the cooking and cooling shells
106-1 and 2. This also results in an initially scheduled
time-temperature treatment T.sub.sRT(t).sub.i.sup.0 that is to be
given to each container i. This treatment includes pre-cooking
portions at the scheduled retort temperatures T.sub.sRT1.sup.0 and
T.sub.sRT2.sup.0 over corresponding initially scheduled time
durations .DELTA.t.sub.1.sup.0 and .DELTA.t.sub.2.sup.0. The
treatment also includes a cooking portion at the scheduled retort
temperature T.sub.sRT3.sup.0 over a corresponding initially
scheduled time duration .DELTA.t.sub.3.sup.0. Finally, the
treatment includes cooling portions at the scheduled retort
temperatures T.sub.sRT4.sup.0 and T.sub.sRT5.sup.0 over
corresponding initially scheduled time durations
.DELTA.t.sub.4.sup.0 and .DELTA.t.sub.5.sup.0. The precise manner
in which step 135 is performed is discussed in greater detail in
section 1.c., but will be briefly discussed next.
[0039] The initially scheduled reel speed v.sub.s.sup.0 and the
initially scheduled total time-temperature treatment
T.sub.sRT(t).sub.i.sup.0 are defined by using the simulation model
mentioned earlier. Specifically, the process scheduling program 124
uses the simulation model to iteratively and incrementally simulate
an initially predicted product cold spot time-temperature profile
T.sub.CS(t).sub.i.sup.0 that is predicted to occur at the product
cold spot of each container i during the rotary sterilization
process. This simulation is based on the input parameters
T.sub.sIP, j.sub.h, f.sub.h, x.sub.bh, f.sub.2, j.sub.c, f.sub.c,
and T.sub.sRT1.sup.0, . . . , T.sub.sRT5.sup.0.
[0040] The process scheduling program 124 also iteratively and
incrementally computes an initially predicted lethality
F.sub.i.sup.0 that is predicted to be delivered to the product cold
spot of each container i during the rotary sterilization process.
In doing so, the program iteratively and incrementally computes a
predicted total lethality F.sub.i.sup.0 that satisfies the target
total lethality F.sub.targ and is predicted to be delivered to the
product cold spot over a simulated total time interval [0,
.DELTA.t.sub.1.sup.0+ . . . +.DELTA.t.sub.5.sup.0]. This
computation is made based on the product cold spot time-temperature
profile T.sub.CS(t).sub.i.sup.0 over this total time duration and
the input parameters z and T.sub.REF. Furthermore, the lethality
equation described earlier is used to make this computation, where
t.sub.m=0, t.sub.k=.DELTA.t.sub.1.sup.0+ . . .
+.DELTA.t.sub.5.sup.0, T.sub.CS(t)=T.sub.CS(t).sub.i.sup.0, and
F.sub.i=F.sub.i.sup.0.
[0041] The initially predicted total lethality F.sub.i.sup.0 over
[0, .DELTA.t.sub.1.sup.0+ . . . +.DELTA.t.sub.5.sup.0] is
iteratively and incrementally computed until the initially
scheduled reel speed v.sub.s.sup.0 is determined for which this
lethality satisfies the target total lethality F.sub.targ.
Moreover, the initially scheduled time durations
.DELTA.t.sub.1.sup.0, . . . , .DELTA.t.sub.5.sup.0 are determined
from the reel speed v.sub.s.sup.0, the reel step information S, and
the temperature zone length and location information L.sub.1, . . .
, L.sub.5. Thus, definition of the reel speed v.sub.s.sup.0 also
includes definition of the pre-cooking, cooking, and cooling
portions of the initially scheduled total time-temperature
treatment T.sub.sRT(t).sup.0 on which the portions of the profile
T.sub.CS(t).sup.0 over the time durations .DELTA.t.sub.1.sup.0, . .
. , .DELTA.t.sub.5.sup.0 are based.
[0042] The process control program 123 controls the administration
of the rotary sterilization process in steps 136 to 149. In doing
so, it first sets a counterj to zero in step 136. This counter is
used to count each time that the currently scheduled reel speed
v.sub.s.sup.j is adjusted during the rotary sterilization
process.
[0043] Then, at the current sample real time t.sub.r, the process
control program 123 causes the control circuitry 129 in step 137 to
administer the rotary sterilization process at the currently
scheduled reel speed v.sub.s.sup.j and at the scheduled retort
temperatures T.sub.sRT1.sup.0, . . . , T.sub.sRT5.sup.0 in the
corresponding temperature zones 115-1, . . . , 5. In doing so, the
control circuitry appropriately controls the rotary sterilizer 102
and monitors the actual retort temperatures T.sub.aRT1(t.sub.r), .
. . , T.sub.aRT5(t.sub.r) in the corresponding temperature zones
115-1, . . . , 5 at the time t.sub.r to verify that they are at
least equal to the corresponding scheduled retort temperatures
T.sub.sRT1.sup.0, . . . , T.sub.sRT5.sup.0. In this embodiment of
the controller 104, the scheduled retort temperatures will remain
the same throughout the rotary sterilization process regardless if
temperature deviations occur in the temperature zones. Thus, if
such a temperature deviation does occur in a particular temperature
zone 115-n, then the control circuitry administers corrections at
the time t.sub.r so that the actual retort temperature
T.sub.aRTn(t.sub.r) in the temperature zone 115-n will eventually
be brought up to at least the corresponding temperature
T.sub.sRTn.sup.0.
[0044] Then the process control program 123 waits for the next
sample real time t.sub.r=t.sub.r+.DELTA.t.sub.r in step 138. In
step 139, this program records the actual retort temperatures
T.sub.aRT1(t.sub.r), . . . , T.sub.aRT5(t.sub.r) in the temperature
zones 115-1, . . . , 5 at each sample real time t.sub.r. By doing
so, the program 123 compiles the corresponding actual retort
time-temperature treatments T.sub.aRT1(t), . . . , T.sub.aRT5(t).
Similarly, the program records the actual initial product
temperature T.sub.aIP(t.sub.r) periodically sensed by the sensor
117 to compile the actual initial product time-temperature profile
T.sub.aIP(t). Furthermore, the program also records the currently
scheduled reel speed v.sub.s.sup.j at each time t.sub.r. This is
done to compile a time-reel speed profile v(t) for the rotary
sterilization process to provide a record of the changes in the
reel speed v.sub.s.sup.j.
[0045] Then, in step 140, the process control program 123
determines whether any temperature deviations are occurring at the
time t.sub.r in the temperature zones 115-1, . . . , 5. In doing
so, the program 123 monitors each temperature T.sub.aRTn(t.sub.r)
to determine if it is less than the corresponding scheduled cooking
or cooling retort temperature T.sub.sRTn.sup.0.
[0046] If no deviation is occurring, then the process control
program 123 proceeds to step 141. Any of the under processed
containers { . . . , i, . . . }.sub.underpr that were identified in
step 148 for segregation and are being discharged by the discharge
device 114 at the current sample real time t.sub.r are then
segregated in step 141 by the discharge device. The process control
program causes the control circuitry 129 to control the discharge
device 114 in performing this segregation in the manner discussed
later. In step 149, the process control program sets the currently
scheduled reel speed v.sub.s.sup.j to the initially scheduled reel
speed v.sub.s.sup.0 if all of the containers { . . . , i, . . .
}.sub.aff affected by a temperature deviation have been discharged.
Both steps 141 and 149 are discussed later in more detail. The
process control program then administers the rotary sterilization
process in step 137 and waits for the next sample real time
t.sub.r=t.sub.r+.DELTA.t.sub.r in step 138 to repeat the steps 139
to 149.
[0047] However, if the process control program 123 does determine
in step 140 that a temperature deviation is occurring in a
temperature zone 115-n at the current sample real time t.sub.r,
then the process control program invokes the temperature deviation
program 125. In the example shown in FIG. 4, the temperature
deviation occurs in the temperature zone 115-3. In step 142, the
program 125 identifies the container i that currently at the time
t.sub.r has the minimum total lethality F.sub.i.sup.j predicted to
be delivered to its product cold spot over its currently scheduled
total time interval [t.sub.f,i, t.sub.d,i.sup.j]. This minimum
lethality container i is identified from among the containers { . .
. , i, . . . }.sub.aff that are currently affected by the
temperature deviation. These affected containers are those of the
containers {1, . . . , i, . . . , I}.sub.line that are at the time
t.sub.r currently in the temperature zone 115-n in which the
temperature deviation is occurring. This is determined using the
reel step information S, the reel time-speed profile v(t) compiled
in step 139, and the length and location information L.sub.1, . . .
, L.sub.5 for the temperature zones 115-1, . . . , 5.
[0048] In one approach for identifying the minimum lethality
container i from among the affected containers { . . . , i, . . .
}.sub.aff, the temperature deviation program 125 may use an
optimization search technique, such as the Brendt method disclosed
in Press, W. H., Teukolsky, S. A., Vettering, W. T., and Flannery,
B. P., Numerical Recipes in Fortran: The Art of Scientific
Computing, Cambridge University Press, 1992. In this case, the
program iteratively computes predicted total lethalities { . . . ,
F.sub.i.sup.j over [t.sub.f,i, t.sub.d,i.sup.j], . . . }.sub.sel
for containers { . . . , i, . . . }.sub.sel selected to be
evaluated. Based on these lethalities, the program iteratively
bisects the list of affected containers to select the selected
containers from among the affected containers until the minimum
lethality container i is identified.
[0049] In a variation of the approach just described, the
temperature deviation program 125 may initially use predefined
intervals to initially select containers { . . . , i, . . .
}.sub.int at the intervals for evaluation. Then, around those of
the initially selected containers that have the lowest predicted
total lethalities {. . . , F.sub.i.sup.j over [t.sub.f,i,
t.sub.d,i.sup.j], . . . }.sub.int, the optimization search
technique just described is used.
[0050] In still another approach for identifying the minimum
lethality container i, the temperature deviation program 125 may
select all of the affected containers { . . . , i, . . . }.sub.aff
as the selected containers { . . . , i, . . . }.sub.sel for
evaluation. In doing so, the program computes at each sample real
time t.sub.r the predicted total lethality F.sub.i.sup.j over
[t.sub.f,i, t.sub.d,i.sup.j] for each container i. From the
computed lethalities {. . . , F.sub.i.sup.j over [t.sub.f,i,
t.sub.d,i.sup.j], . . . }.sub.sel for the selected containers, the
minimum lethality container i is identified.
[0051] In each of the approaches just described, the predicted
total lethality F.sub.i.sup.j over [t.sub.f,i, t.sub.d,i.sup.j] for
each selected container i is computed in the same way.
Specifically, the temperature deviation program 125 first computes
an actual current lethality F.sub.i.sup.j delivered to the
container's product cold spot over the actual time interval
[t.sub.f,i, t.sub.r] that the container has been in the rotary
sterilizer 102. This is done by simulating the portion of the
rotary sterilization process that was actually administered over
this time interval. In doing so, the simulation model mentioned
earlier is used to iteratively and incrementally simulate the
actual portion of the product cold spot time-temperature profile
T.sub.CS(t).sub.i.sup.j over this time interval for the container
i. This is done based on the input parameters j.sub.h, f.sub.h,
x.sub.bh, f.sub.2, j.sub.c, and f.sub.c, the actual initial product
temperature T.sub.aIP(t.sub.f,i) for the container i, and the
portions of the actual retort time-temperature profiles
T.sub.aRT1(t), . . . , T.sub.aRTn(t) respectively over the actual
time intervals [t.sub.f,i, t.sub.1,i.sup.j], . . . ,
(t.sub.n-1,i.sup.j, t.sub.r] that the container was in the
temperature zones 115-1, . . . , n. Here, n identifies the
temperature zone 115-n in which the temperature deviation is
occurring. As mentioned earlier, in the example of FIG. 4, this is
the temperature zone 115-3.
[0052] The actual initial product temperature T.sub.aIP(t.sub.f,i)
for the container i is obtained from the actual initial product
time-temperature profile T.sub.aIP(t) compiled in step 139. The
actual time intervals [t.sub.f,i, t.sub.1,i.sup.j], . . . ,
(t.sub.n-1,.sup.j, t.sub.r] for the selected container i are
determined by the temperature deviation program 125 from the reel
time-speed profile v(t), the reel step information S, and the
temperature zone length and location information L.sub.l, . . . ,
L.sub.n.
[0053] In the example of FIG. 4, the temperature deviation occurs
in the temperature zone 115-3. Thus, the portion of the product
cold spot temperature profile T.sub.CS(t).sub.i.sup.j that actually
occurred over the actual time interval [t.sub.f,i, .sub.r] is based
in this case on the portions of the actual retort time-temperature
profiles T.sub.aRT1(t), T.sub.aRT2(t), and T.sub.aRT3(t)
respectively over the actual time intervals [t.sub.f,i,
t.sub.1,i.sup.j], (t.sub.1,i.sup.j, t.sub.2,i.sup.j,], and
(t.sub.2,i.sup.j, t.sub.r]. The time intervals [t.sub.f,i,
t.sub.1,i.sup.j] and (t.sub.1,i.sup.j, t.sub.2,i.sup.j,] have the
initially scheduled time durations .DELTA.t.sub.1.sup.0 and
.DELTA.t.sub.2.sup.0 since the temperature deviation began at the
deviation begin time t.sub.e while the container i was in the
temperature zone 115-3. If, however, this container was in another
temperature zone 115-1 or 2 when the deviation began, then the time
intervals [t.sub.f,i, t.sub.1,i.sup.j] and/or (t.sub.1,i.sup.j,
t.sub.2,i.sup.j,] would have different time durations
.DELTA.t.sub.1.sup.j and/or .DELTA.t.sub.2.sup.j because the reel
speed v.sub.s.sup.j would have been changed while the container was
in that temperature zone.
[0054] From the actual portion of the product cold spot
time-temperature profile T.sub.CS(t).sub.i.sup.j over [t.sub.f,i,
t.sub.r] and the input parameters z and T.sub.REF, the temperature
deviation program 125 iteratively and incrementally computes the
actual current lethality F.sub.i.sup.j that has been delivered to
the product cold spot of the selected container i over the actual
time interval [t.sub.f,i, t.sub.r]. This is done using the
lethality equation described earlier, where t.sub.m=t.sub.f,i,
t.sub.k=t.sub.r, T.sub.CS(t)=T.sub.CS(t).sub.i.sup.j, and
F.sub.i=F.sub.i.sup.j. The precise manner in which the actual
current lethality is computed in step 142 is discussed in greater
detail in section 1.d.
[0055] Then, the temperature deviation program 125 simulates the
remaining portion of the rotary sterilization process that is
predicted to be administered to the selected container i over the
scheduled remaining time interval (t.sub.r, t.sub.d,i.sup.j]
assuming that the temperature deviation ends after the time
t.sub.r. In performing this simulation, the simulation model
mentioned earlier is used to iteratively simulate the predicted
remaining portion of the product cold spot time-temperature profile
T.sub.CS(t).sub.i.sup.j based on the input parameters j.sub.h,
f.sub.h, X.sub.bh, f.sub.2, j.sub.c, and f.sub.c, the actual
product cold spot temperature T.sub.CS(t.sub.r).sub.i.sup.j at the
time t.sub.r, and the scheduled retort temperatures
T.sub.sRTn.sup.0, . . . , T.sub.sRT5.sup.0 over the currently
scheduled remaining time intervals (t.sub.r, t.sub.n,i.sup.j], . .
. , t.sub.4,i.sup.j,t.sub.d,i.sup.j].
[0056] The actual product cold spot temperature
T.sub.CS(t.sub.r).sub.i.su- p.j for the selected container i is
obtained from the actual portion of the product cold spot
time-temperature profile T.sub.CS(t).sub.i.sup.j over [t.sub.f,i,
t.sub.r] that was just described. Moreover, the currently scheduled
time intervals (t.sub.r, t.sub.n,i.sup.j], . . . ,
(t.sub.4,i.sup.j,t.sub.d,i.sup.j] for the container i are
determined by the temperature deviation program 125 from the reel
time-speed profile v(t), the reel step information S, and the
temperature zone length and location information L.sub.1, . . . ,
L.sub.5.
[0057] In the example of FIG. 4, the temperature deviation occurs
in the temperature zone 115-3. Thus, the predicted remaining
portion of the product cold spot temperature profile
T.sub.CS(t).sub.i.sup.j is based on the scheduled retort
temperatures T.sub.sRT3.sup.0, T.sub.sRT4.sup.0, and
T.sub.sRT5.sup.0 respectively over the currently scheduled
remaining time intervals (t.sub.r, t.sub.3,i.sup.j],
(t.sub.3,i.sup.j,t.sub.4,i.sup.j], and
(t.sub.4,i.sup.j,t.sub.d,i.sup.j]. In this example, the time
intervals (t.sub.2,i.sup.j, t.sub.3,i.sup.j],
(t.sub.3,i.sup.j,t.sub.4,i.- sup.j] and
(t.sub.4,i.sup.j,t.sub.d,i.sup.j] respectively have re-scheduled
time durations .DELTA.t.sub.3.sup.j, .DELTA.t.sub.4.sup.j, and
.DELTA.t.sub.5.sup.j that are different than the initially
scheduled time durations .DELTA.t.sub.3.sup.0,
.DELTA.t.sub.4.sup.0, and .DELTA.t.sub.5.sup.0 since the currently
scheduled reel speed v.sub.s.sup.j at the current sample real time
t.sub.r has been re-scheduled from the initially scheduled reel
speed v.sub.s.sup.0.
[0058] The temperature deviation program 125 iteratively and
incrementally computes the total lethality F.sub.i.sup.j predicted
to be delivered to the product cold spot of the selected container
i over the scheduled total time interval [t.sub.f,i,
t.sub.d,i.sup.j]. This is done based on the predicted remaining
portion of the product cold spot time-temperature profile
T.sub.CS(t).sub.i.sup.j over (t.sub.r, t.sub.d,i.sup.j], the actual
current lethality F.sub.i.sup.j over [t.sub.f,i, t.sub.r] that was
just described, and the input parameters z and T.sub.REF. This is
also done using the lethality equation described earlier, where
t.sub.m=t.sub.r, t.sub.k=t.sub.d,i.sup.j,
T.sub.CS(t)=T.sub.CS(t).sub.i.s- up.j, and F.sub.i=F.sub.i.sup.j.
The predicted total lethality is the sum of the actual current
lethality and a predicted remaining lethality F.sub.i.sup.j that is
predicted to be delivered to the container's product cold spot over
the time interval [t.sub.r, t.sub.d,i.sup.j]. The precise manner in
which the predicted total lethality is computed in step 142 is
discussed in greater detail in section 1.e.
[0059] Then, in step 143, the temperature deviation program 125
determines at the current sample real time t.sub.r if the container
i with the minimum predicted total lethality F.sub.i.sup.j over
[t.sub.f,i, t.sub.d,i.sup.j] is less than the target total
lethality F.sub.targ. If it is not, then this means that all of the
affected containers { . . . , i, . . . }.sub.aff also have
predicted total lethalities { . . . , F.sub.i.sup.j over
[t.sub.f,i, t.sub.d,i.sup.j], . . . }.sub.aff that are at least
equal to the target total lethality. In this case, the process
control program 123 proceeds to step 141 and causes any of the
previously identified under processed containers { . . . , i, . . .
}.sub.underpr that are being discharged at the time t.sub.r to be
segregated. Then, in the manner discussed earlier, the process
control program 123 administers the rotary sterilization process in
step 137 and waits for the next sample real time
t.sub.r=t.sub.r+.DELTA.t.sub.r in step 138 to repeat the steps 139
to 148.
[0060] In this embodiment, if it is determined in step 143 that the
minimum total lethality F.sub.i.sup.j over [t.sub.f,i,
t.sub.d,i.sup.j] is less than the target total lethality
F.sub.targ, then the temperature deviation program 125 determines
in step 144 if the currently scheduled reel speed v.sub.s.sup.j is
set to the minimum reel speed v.sub.min. If it is not, then the
program increments the counter j in step 145 and defines a
re-scheduled (or adjusted) reel speed v.sub.s.sup.j in step
146.
[0061] In step 146, the re-scheduled reel speed v.sub.s.sup.j is
defined in a similar manner to the way in which the initially
scheduled reel speed v.sub.s.sup.0 is defined in step 135. But, in
this case the actual product cold spot temperature
T.sub.CS(t.sub.r).sub.i.sup.j at the time t.sub.r and the actual
current lethality F.sub.i.sup.j over [t.sub.f,i, t.sub.r] for the
minimum lethality container i are used in simulating the remaining
portion of the rotary sterilization process in order to compute a
predicted total lethality F.sub.i.sup.j over [t.sub.f,i,
t.sub.d,i.sup.j]. This is done in a similar manner to that
described earlier for computing the predicted total lethality for a
container in step 142. But, similar to step 135, this is done
iteratively and incrementally until the reel speed is determined
for which the predicted total lethality satisfies the total target
lethality F.sub.targ or the reel speed equals the minimum reel
speed v.sub.min. The precise manner in which step 146 is performed
is discussed in greater detail in section 1.f, but will be briefly
discussed next.
[0062] The definition of the re-scheduled reel speed therefore also
results in the definition of a re-scheduled remaining
time-temperature treatment T.sub.sRT(t).sub.i.sup.j. The treatment
includes a remaining cooking portion at the scheduled retort
temperature T.sub.sRT3.sup.0 over a corresponding re-scheduled time
duration .DELTA.t.sub.3.sup.j. Similarly, the treatment also
includes cooling portions at the scheduled retort temperatures
T.sub.sRT4.sup.0 and T.sub.sRT5.sup.0 over corresponding
re-scheduled time durations .DELTA.t.sub.4.sup.j and
.DELTA.t.sub.5.sup.j.
[0063] Ideally, it is desired that the minimum predicted total
lethality F.sub.i.sup.j over [t.sub.f,i, t.sub.d,i.sup.j] for the
minimum lethality container i will satisfy the target total
lethality F.sub.targ. But, as just mentioned, the re-scheduled reel
speed v.sub.s.sup.j may be limited to the minimum reel speed
v.sub.min. In this case, the minimum predicted total lethality will
not satisfy the target total lethality F.sub.targ. If the
temperature deviation program 125 determines this to be the case in
step 147, then this means that under processed containers { . . . ,
i, . . . }.sub.underpr from among the affected containers { . . . ,
i, . . . }.sub.aff will have predicted total lethalities { . . . ,
F.sub.i.sup.j over [t.sub.f,i, t.sub.d,i.sup.j], . . .
}.sub.underpr that are less than the target total lethality. The
minimum lethality container i is of course one of the under
processed containers. The under processed containers are to be
segregated and are identified at the current real sample time
t.sub.r in step 148 by the program.
[0064] FIG. 5 shows the distribution of the affected containers { .
. . , i, . . . }.sub.aff and the under processed containers { . . .
, i, . . . }.sub.underpr to be segregated at the time t.sub.r. In
identifying the under processed containers in step 148, the program
125 uses a similar approach as that used in step 142 to identify
the minimum lethality container i. But, in this case, the
additional criteria of the target total lethality F.sub.targ is
used to expand the search.
[0065] Once the under processed containers { . . . , i, . . .
}.sub.underpr have been identified at the current real sample time
t.sub.r, the process control program 123 then proceeds to step 141.
As discussed earlier, this program causes the control circuitry 129
to control the discharge device 114 in segregating any of the under
processed containers that are being discharged at the current
sample real time t.sub.r. In order to segregate the under processed
containers, the process control program tracks these containers to
determine when they will be discharged. This is done using the reel
time-speed profile v(t), the reel step information S, and the
temperature zone length and location information L.sub.1, . . . ,
L.sub.5.
[0066] The steps 137 to 149 are repeated until the temperature
deviation is cleared. In this way, at each sample real time t.sub.r
during the deviation, the list of under processed containers { . .
. , i, . . . }.sub.underpr at the time t.sub.r is combined with the
list from the previous sample real time t.sub.r. As a result, the
list of under processed containers is dynamically updated and
maintained. Since these under processed containers are segregated
when discharged in step 141, this will ensure that only those of
the containers {1, . . . , i, . . . I}.sub.line that are adequately
processed are released for distribution.
[0067] The list of affected containers { . . . , i, . . . }.sub.aff
is also dynamically updated and maintained in the same manner as
the list of under processed containers { . . . , i, . . .
}.sub.underpr. When the temperature deviation is cleared, this list
will remain the same and the process control program 123 tracks the
containers in this list until they have all been discharged. This
tracking is done in the same manner in which the under processed
containers are tracked. The process control program 123 will then
set the currently scheduled reel speed v.sub.s.sup.j back to the
initially scheduled reel speed v.sub.s.sup.0 in step 149.
[0068] Furthermore, the controller 104 has the unique feature of
being able to handle multiple temperature deviations. For example,
if another temperature deviation does occur, then the steps 137 to
149 are repeated during this deviation. Therefore, even if a
selected container i is exposed to multiple temperature deviations,
the predicted total lethality F.sub.i.sup.j over [t.sub.f,i,
t.sub.d,i.sup.j] that will be delivered to it can be accurately
determined based on those of the actual retort temperature profiles
T.sub.aRT1(t), . . . , T.sub.aRT5(t) that it has been treated with
over the rotary sterilization process. Moreover, this results in
the list of under processed containers { . . . , i, . . .
}.sub.underpr being further updated and expanded.
[0069] 1.c. Detailed Process Flow for Step 135 of FIG. 3
[0070] FIG. 6 shows the detailed process flow that the process
scheduling program 124 uses in step 135 of FIG. 3 to define the
initially scheduled reel speed v.sub.s.sup.0. In doing so, this
program iteratively performs a simulation of the rotary
sterilization process that is predicted to be administered to each
container i in sub-steps 150 to 160 of step 135.
[0071] In step 150, the process scheduling program 124 first
defines the initially scheduled reel speed v.sub.s.sup.0 as the
maximum reel speed v.sub.max. Then, in step 151, the program
defines the time durations .DELTA.t.sub.1.sup.0, . . . ,
.DELTA.t.sub.5.sup.0 for how long each container i is scheduled to
be in the respective temperature zones 115-1, . . . , 5. This is
done based on the initially scheduled reel speed, the reel step
information S for the reels 109 and spiral tracks 108 of the
cooking and cooling shells 106-1 and 2, and the length and location
information L.sub.1, . . . , L.sub.5 for the temperature zones.
[0072] In step 152, the current sample simulation time t.sub.s is
initially set to zero by the process scheduling program 124. This
is the begin time of the simulated rotary sterilization process for
the container i. The program also initially sets the predicted
product cold spot temperature T.sub.CS(t.sub.s).sub.i.sup.0 of the
container's product cold spot at this time to the scheduled initial
product temperature T.sub.sIP. Similarly, the lethality
F.sub.i.sup.0 predicted to be delivered to the product cold spot
over the current simulation time interval [0, t.sub.s] is initially
set by the program to zero.
[0073] Steps 153 to 157 are then performed by the process
scheduling program 124 in each iteration of the simulation. In step
153 of each iteration, the program increments the current sample
simulation time t.sub.s by the amount of the sampling period
.DELTA.t.sub.r. This results in a new current sample simulation
time t.sub.s.
[0074] Then, in step 154 of each iteration, the process scheduling
program 124 simulates the portion of the product cold spot
time-temperature profile T.sub.CS(t).sub.i.sup.0 predicted to occur
at the product cold spot of the container i over the current
simulation time increment [t.sub.s-.DELTA.t.sub.r, t.sub.s]. This
is done using the simulation model discussed earlier and is based
on the predicted product cold spot temperature
T.sub.CS(t.sub.s-.DELTA.t.sub.r).sub.i.sup.0 for the product cold
spot at the previous sample simulation time t.sub.s-.DELTA.t.sub.r
and the heating and cooling factors j.sub.h, f.sub.h, x.sub.bh,
f.sub.2, j.sub.c, and f.sub.c. In the first iteration, this product
cold spot temperature will be the scheduled initial product
temperature T.sub.sIP from step 152. However, in each subsequent
iteration, the product cold spot temperature is obtained from the
portion of the product cold spot temperature profile predicted over
the previous simulation time increment [t.sub.s-2.DELTA.t.sub.r,
t.sub.s-.DELTA.t.sub.r] that was simulated in step 154 of the
previous iteration. Moreover, the simulation is also based on the
respective scheduled retort temperatures T.sub.sRT1.sup.0, . . . ,
T.sub.sRT5.sup.0 when the current sample simulation time t.sub.s is
within the corresponding simulation time intervals [0,
.DELTA.t.sub.1.sup.0], . . . , [.DELTA.t.sub.1.sup.0+. . .
+.DELTA.t.sub.4.sup.0, .DELTA.t.sub.5.sup.0]. These time intervals
indicate how long the container i is scheduled to be in the
respective temperature zones 115-1, . . . , 5.
[0075] The lethality F.sub.i.sup.0 that is predicted to be
delivered to the product cold spot of the container i over the
current simulation time increment [t.sub.s-.DELTA.t.sub.r, t.sub.s]
is then computed by the process scheduling program 124 in step 155
of each iteration. This is done based on the portion of the product
cold spot time-temperature profile T.sub.CS(t).sub.i.sup.0
predicted over this time increment and the input parameters z and
T.sub.REF. This is also done in accordance with the lethality
equation described earlier, where t.sub.m=t.sub.s-.DELTA.t.sub.r,
t.sub.k=t.sub.s, T.sub.CS(t)=T.sub.CS(t).- sub.i.sup.0, and
F.sub.i=F.sub.i.sup.0.
[0076] In step 156 of each iteration, the process scheduling
program 124 computes the lethality F.sub.i.sup.0 predicted to be
delivered to the product cold spot of the container i over the
current simulation time interval [0, t.sub.s]. This is done by
adding the predicted lethality F.sub.i.sup.0 over the current
simulation time increment [t.sub.s-.DELTA.t.sub.r, t.sub.s] in step
154 to the lethality F.sub.i.sup.0 predicted to be delivered to the
product cold spot over the previous simulation time interval [0,
t.sub.s-.DELTA.t.sub.r]. In the first iteration, the predicted
lethality over the previous simulation time interval is zero from
step 152. In each subsequent iteration, this lethality is computed
in step 156 of the previous iteration.
[0077] Then, in step 157 of each iteration, the process scheduling
program 124 determines whether the current simulation time t.sub.s
has reached the end time [.DELTA.t.sub.1.sup.0+ . . .
+.DELTA.t.sub.5.sup.0] of the simulated rotary sterilization
process for the container i. If it is not, then the program returns
to step 153 for the next iteration. In this way, steps 153 to 157
are repeated in each subsequent iteration until it is determined
that the end time for the simulated rotary sterilization process
has been reached. When this finally occurs, the program sets in
step 158 the lethality F.sub.i.sup.j over the current simulation
time interval [0, t.sub.s] to the total lethality F.sub.i.sup.j
predicted to be delivered to the container's product cold spot over
the total simulation time interval [0, .DELTA.t.sub.1.sup.0+ . . .
+.DELTA.t.sub.5.sup.0].
[0078] When this finally occurs, the process scheduling program 124
determines in step 158 whether the predicted total lethality
F.sub.i.sup.0 over [0, .DELTA.t.sub.1.sup.0+ . . .
+.DELTA.t.sub.5.sup.0] is at least equal to the target total
lethality F.sub.targ. If it is not, then the program decrements in
step 160 the initially scheduled reel speed v.sub.s.sup.0 by a
predefined reel speed offset .DELTA.v. This results in the
re-definition of this reel speed. Steps 151 to 160 are then
repeated until step 159 is satisfied. The reel speed for which step
159 is satisfied is then used in steps 136 to 148 of FIG. 3 in the
manner discussed earlier.
[0079] 1.d. Detailed Process Flow for Computing Lethality
F.sub.i.sup.j over [t.sub.f,i, t.sub.r) in Steps 142 and 148 of
FIG. 3
[0080] FIG. 7 shows the detailed process flow that the temperature
deviation program 125 uses in steps 142 and 148 of FIG. 3 to
compute the actual current lethality F.sub.i.sup.j delivered to the
product cold spot of the container i over the actual time interval
[t.sub.f,i, t.sub.r] that the container has been in the rotary
sterilizer 102. This is done by iteratively performing sub-steps
161 to 168 of steps 142 and 148 to simulate the actual portion of
the rotary sterilization process that has been administered to the
container's product cold spot over this time interval. Here, steps
161 to 168 are respectively similar to steps 151 to 158 of FIG. 6
and discussed in section 1.c., except for the differences discussed
next.
[0081] In step 161, the temperature deviation program 125 defines
the actual time intervals [t.sub.f,i, t.sub.1,i.sup.j], . . . ,
(t.sub.n-1,i.sup.j, t.sub.r] that the container i has actually been
in the respective temperature zones 115-1, . . . , n up to the
current sample real time t.sub.r. In this step, the definition of
these time intervals is based on the accumulated reel time-speed
profile v(t).
[0082] In step 162, the temperature deviation program 125 initially
sets the product cold spot temperature
T.sub.CS(t.sub.s).sub.i.sup.j for the product cold spot of the
container i at the initial sample simulation time t.sub.s to the
actual initial product temperature T.sub.aIP(t.sub.f,i). This
temperature is obtained from the actual initial product
time-temperature profile T.sub.aIP(t). Moreover, the program
initially sets the actual lethality F.sub.i.sup.j delivered to the
product cold spot over the current simulation time interval
[t.sub.f,i, t.sub.s] to zero.
[0083] In step 164 of each iteration, the process scheduling
program 124 simulates the portion of the product cold spot
time-temperature profile T.sub.CS(t).sub.i.sup.j that actually
occurred at the product cold spot of the container i over the
current simulation time increment [t.sub.s-.DELTA.t.sub.r,
t.sub.s]. This simulation is based on the respective actual retort
temperatures T.sub.aRT1(t.sub.s), . . . , T.sub.aRTn(t.sub.s) when
the current simulation time t.sub.s is within the corresponding
simulation time intervals [t.sub.f,i, t.sub.1,i.sup.j], . . . ,
(t.sub.n-1,i.sup.j, t.sub.r]. These actual retort temperatures are
obtained from the corresponding actual retort time-temperature
profiles T.sub.aRT1(t), . . . , T.sub.aRTn(t).
[0084] The actual lethality F.sub.i.sup.j that was delivered to the
product cold spot of the container i over the current simulation
time increment [t.sub.s-.DELTA.t.sub.r, t.sub.s] is then computed
by the temperature deviation program 125 in step 165 of each
iteration. This is done based on the actual portion of the product
cold spot time-temperature profile T.sub.CS(t).sub.i.sup.j that was
simulated over this time increment. In this case,
T.sub.CS(t)=T.sub.CS(t).sub.i.sup.j and F.sub.i=F.sub.i.sup.j in
the lethality equation described earlier.
[0085] In step 166 of each iteration, the temperature deviation
program 125 computes the actual lethality F.sub.i.sup.j delivered
to the product cold spot of the container i over the current
simulation time interval [t.sub.f,i, t.sub.s]. This is done by
adding the actual lethality F.sub.i.sup.j over the current
simulation time increment [t.sub.s-.DELTA.t.sub.r, t.sub.s] in step
164 to the actual lethality F.sub.i.sup.j over the previous
simulation time interval [t.sub.f,i, t.sub.s-.DELTA.t.sub.r].
[0086] Then, in step 167 of each iteration, the temperature
deviation program 125 determines whether the current simulation
time t.sub.s has reached the current sample real time t.sub.r. If
it is not, then the program returns to step 163 for the next
iteration. In this way, steps 163 to 167 are repeated in each
subsequent iteration until it is determined that the current sample
real time has been reached. When this finally occurs, the
temperature deviation program 125 sets in step 168 the lethality
F.sub.i.sup.j over the current simulation time interval [t.sub.f,i,
t.sub.s] to the actual current lethality F.sub.i.sup.j over the
actual time interval [t.sub.f,i, t.sub.r] and the product cold spot
temperature T.sub.CS(t.sub.s).sub.i.sup.j for the container at the
current sample simulation time to the actual product cold spot
temperature T.sub.CS(t.sub.r).sub.i.sup.j at the current sample
real time.
[0087] 1.e. Detailed Process Flow for Computing Lethality
F.sub.i.sup.j over [t.sub.f,i, t.sub.d,i.sup.j] in Steps 142 and
148 of FIG. 3
[0088] FIG. 8 shows the detailed process flow that the temperature
deviation program 125 uses in steps 142 and 148 of FIG. 3 to
compute the lethality F.sub.i.sup.j predicted to be delivered to
the product cold spot of a selected container over the total time
interval [t.sub.f,i, t.sub.d,i.sup.j] that the container is in the
rotary sterilizer 102. In this case, the program iteratively
performs a simulation of the predicted remaining portion of the
rotary sterilization process to be administered to this container
using sub-steps 169 to 176 of steps 142 and 148. Like steps 161 to
168, steps 169 to 176 are respectively similar to steps 151 to 158
of FIG. 6 and discussed in section 1.c., except for the differences
discussed next.
[0089] In step 169, the temperature deviation program 125 defines
the remaining time intervals (t.sub.r, t.sub.n,1.sup.j], . . . ,
(t.sub.4,i.sup.j, t.sub.d,i.sup.j] that the container i is
predicted to be in the respective temperature zones 115-n, . . . ,
5 after the current sample real time t.sub.r. The definition of
these time intervals in step 169 is based on the currently
scheduled reel speed v.sub.s.sup.j.
[0090] In step 170, the temperature deviation program 125 initially
sets the initial sample simulation time t.sub.s to the current
sample real time t.sub.r. The program also initially sets the
predicted product cold spot temperature
T.sub.CS(t.sub.s).sub.i.sup.j for the product cold spot of the
container i at this sample simulation time to the actual product
cold spot temperature T.sub.CS(t.sub.r).sub.i.sup.j obtained from
step 168 of FIG. 7. Moreover, the program initially sets the
predicted lethality F.sub.i.sup.j to be delivered to the product
cold spot over the current simulation time interval [t.sub.f,i,
t.sub.s] to the actual lethality F.sub.i.sup.j over the actual time
interval [t.sub.f,i, t.sub.r] also obtained from step 168.
[0091] In step 172 of each iteration, the temperature deviation
program 125 simulates the portion of the product cold spot
time-temperature profile T.sub.CS(t).sub.i.sup.j that is predicted
to occur at the product cold spot of the container i over the
current simulation time increment [t.sub.s-.DELTA.t.sub.r,
t.sub.s]. The simulation is based on the respective scheduled
retort temperatures T.sub.sRTn.sup.0, . . . , T.sub.sRT5.sup.0 when
the current simulation time t.sub.s is within the corresponding
simulation time intervals (t.sub.r, t.sub.n,i.sup.j], . . . ,
(t.sub.4,i.sup.j, t.sub.d,i.sup.j].
[0092] The lethality F.sub.i.sup.j that is predicted to be
delivered over the current simulation time increment
[t.sub.s-.DELTA.t.sub.r, t.sub.s] is then computed by the
temperature deviation program 125 in step 173 of each iteration.
This is done based on the predicted portion of the product cold
spot time-temperature profile T.sub.CS(t).sub.i.sup.j that was
simulated over this time increment in step 172.
[0093] In step 174 of each iteration, the temperature deviation
program 125 computes the lethality F.sub.i.sup.j predicted to be
delivered to the product cold spot of the container i over the
current simulation time interval [t.sub.f,i, t.sub.s]. This is done
by adding the predicted lethality F.sub.i.sup.j over the current
simulation time increment [t.sub.s-.DELTA.t.sub.r, t.sub.s] from
step 173 to the predicted lethality F.sub.i.sup.j over the previous
simulation time interval [t.sub.f,i, t.sub.s-.DELTA.t.sub.r].
[0094] Then, in step 175 of each iteration, the temperature
deviation program 125 determines whether the current sample
simulation time t.sub.s has reached the predicted discharge time
t.sub.d,i.sup.j for the container i. If it has not, then the
program returns to step 171 for the next iteration. In this way,
steps 171 to 175 are repeated in each subsequent iteration until it
is determined that the predicted discharge time has been reached.
When this finally occurs, the program sets in step 176 the
lethality F.sub.i.sup.j over the current simulation time interval
[t.sub.f,i, t.sub.s] to the predicted lethality. F.sub.i.sup.j over
the currently scheduled total time interval [t.sub.f,i,
t.sub.d,i].
[0095] 1.f. Detailed Process Flow for Step 146 of FIG. 3
[0096] FIG. 9 shows the detailed process flow that the temperature
deviation program 125 uses in step 146 of FIG. 3 to define the
re-scheduled reel speed v.sub.s.sup.j. This program uses sub-steps
178 to 187 to iteratively perform a simulation of the remaining
portion of the rotary sterilization process predicted to be
administered to the minimum lethality container i identified in
step 142 of FIG. 3 and discussed in section 1.b. Steps 178 to 187
are respectively similar to steps 159 and 151 to 159 of FIG. 6 and
discussed in section 1.c., except for the differences discussed
next.
[0097] In step 178, the temperature deviation program 125 first
decrements the currently scheduled reel speed v.sub.s.sup.j by the
predefined reel speed offset .DELTA.v. If the decremented reel
speed is greater than the minimum reel speed v.sub.min, the
re-scheduled reel speed is defined as the decremented reel speed.
However, if the decremented reel speed is less than or equal to the
minimum reel speed, then the re-scheduled reel speed is defined as
the minimum reel speed.
[0098] Since a re-scheduled reel speed v.sub.i.sup.j is defined in
step 178, the re-scheduled remaining time intervals (t.sub.r,
t.sub.n,i.sup.j], . . . , (t.sub.4,i.sup.j, t.sub.d,i.sup.j] that
the minimum lethality container i is predicted to be in the
respective temperature zones 115-n, . . . , 5 after the current
sample real time t.sub.r need to be defined. This is done in step
179.
[0099] Step 180 to 186 are the same as steps 170 to 176 of FIG. 8
and discussed in section 1.e. Thus, these steps are used to compute
a total lethality F.sub.i.sup.j predicted to be delivered to the
product cold spot of the minimum lethality container i over the
re-scheduled total time interval [t.sub.f,i, t.sub.d,i.sup.j]. It
should be noted here that this is done using the actual current
lethality F.sub.i.sup.j over [t.sub.f,i, t.sub.r] and the actual
product cold spot temperature T.sub.CS(t.sub.r).sup.j for the
minimum lethality container i computed in steps 161 to 168 of FIG.
7.
[0100] Then, in step 187, the temperature deviation program 125
determines if the predicted total lethality F.sub.i.sup.j over
[t.sub.f,i, t.sub.d,i.sup.j] satisfies the target total lethality
F.sub.targ. If it does not, then the program determines in step 188
whether the re-scheduled reel speed v.sub.s.sup.j equals the
minimum reel speed v.sub.min. If it does not, then steps 181 to 188
are repeated until it is determined in step 187 that the target
lethality has been satisfied or it is determined in step 188 that
the minimum reel speed has been reached. In this way, the reel
speed is re-scheduled.
[0101] 2. Alternative Embodiments
[0102] As indicated earlier, the embodiment of controller 104
associated with FIGS. 3 to 9 and described in section 1. is an
exemplary embodiment. Alternative embodiments that utilize the
principles and concepts developed in FIGS. 3 to 9 and section 1. do
exist. Some of these embodiments are discussed next.
[0103] 2.a. Scheduling and Re-Scheduling Variations
[0104] The operator of the rotary sterilization process 100 may
want to keep the initially scheduled reel speed v.sub.s.sup.0 and
retort temperatures T.sub.sRT1.sup.0, . . . , T.sub.sRT5.sup.0
constant throughout the entire rotary sterilization process. Thus,
in this embodiment, the temperature deviation program 125 is simply
used to identify the under processed containers { . . . , i, . . .
}.sub.underpr in the manner discussed earlier in section 1.b. when
a temperature deviation occurs. More specifically, the steps 145 to
147 would be eliminated from the flow diagram of FIG. 3.
[0105] In another embodiment, the initially scheduled retort
temperatures T.sub.sRT1.sup.0, . . . , T.sub.sRT5.sup.0 may be
re-scheduled when a temperature deviation occurs. In this case, the
temperature deviation program 125 would define a re-scheduled
retort temperature T.sub.sRT1.sup.j, . . . , or T.sub.sRT5.sup.j in
a similar manner to which it defined a re-scheduled reel speed
v.sub.s.sup.j in step 146 of FIG. 3 and steps 178 to 188 of FIG. 9.
In this embodiment, the initially scheduled reel speed
v.sub.s.sup.0 may be kept constant or a re-scheduled reel speed
v.sub.s.sup.j may be defined in conjunction with the re-scheduled
retort temperature.
[0106] 2.b. Identifying and Segregating Over Processed
Containers
[0107] Since re-scheduled reel speed v.sub.s.sup.j may be defined
when a temperature deviation occurs, it is possible that some of
the containers {1, . . . , i, . . . , I} may be over processed due
to the slower re-scheduled reel speed. In this case, a maximum
total lethality F.sub.max may be pre-defined and included as one of
the input parameters. Then, the over processed containers { . . . ,
i, . . . }.sub.overpr with predicted total lethalities { . . . ,
F.sub.i.sup.j over [t.sub.f,i, t.sub.d,i.sup.j], . . . }.sub.overpr
over this maximum total lethality would be identified in a similar
manner to that way in which the under processed containers { . . .
, i, . . . }.sub.underpr are identified in step 148 of FIG. 3 and
discussed in section 1.b. These containers would be segregated in
the same way that the under processed containers are segregated in
step 141 of FIG. 3. As a result, the remaining containers that are
not under or over processed would have a uniform quality food
product using this technique.
[0108] 2.c. More Conservative Approaches
[0109] In steps 142 and 148 of FIG. 3 discussed in section 1.b. and
in steps 161 to 168 of FIG. 7 discussed in section 1.d., an
aggressive approach was discussed for simulating the actual portion
of the product cold spot time-temperature profile
T.sub.CS(t).sub.i.sup.j that occurs over the actual time interval
[t.sub.f,i, t.sub.r] that a container i has been in the rotary
sterilizer 102. Specifically, this portion of the product cold spot
time-temperature profile is based on the actual retort
time-temperature profiles T.sub.aRT1(t), . . . , T.sub.aRTn(t) over
the corresponding time intervals [t.sub.f,i, t.sub.1,i.sup.j], . .
. , (t.sub.n-1,i.sup.j, t.sub.r].
[0110] However, a more conservative embodiment could be employed
which uses only the portion of the actual retort time-temperature
profile T.sub.aRTn(t) over the time interval from the time when the
container is first affected by the temperature deviation to the
current sample real time t.sub.r. Specifically, the portion of the
product cold spot time-temperature profile T.sub.CS(t).sub.i.sup.j
over the time intervals [t.sub.f,i, t.sub.1,i.sup.j], . . . ,
(t.sub.n-2,i.sup.j, t.sub.n-1,i.sup.j] would be based on the
corresponding scheduled retort temperatures T.sub.sRT1.sup.0, . . .
, T.sub.sRTn-1.sup.0 for the temperature zones 115-1, . . . , n-1
in which the temperature deviation is not occurring.
[0111] Thus, if the container enters the temperature zone 115-n
while the temperature deviation is occurring, the portion of the
product cold spot time-temperature profile T.sub.CS(t).sub.i.sup.j
over the time interval (t.sub.n-1,i.sup.j, t.sub.r] would still be
based on the portion of the actual retort time-temperature profile
T.sub.aRTn(t) over this time interval. But, if the temperature
deviation begins at the deviation begin time t.sub.d while the
container is in this temperature zone, then the portion of the
product cold spot time-temperature profile over the time interval
(t.sub.n-1,i.sup.j, t.sub.e] would be based on the scheduled
temperature T.sub.sRTn.sup.0. In this case, only the portion of the
product cold spot time-temperature profile over the time interval
(t.sub.d, t.sub.r] would be based on the portion of the actual
retort time-temperature profile T.sub.aRTn(t) over this time
interval. In either case, this results in the actual lethality
F.sub.i.sup.j delivered over the time interval [t.sub.f,i, t.sub.r]
being computed more conservatively in steps 142 and 148 of FIG. 3
and in sub-steps 161 to 168 of FIG. 7.
[0112] Similarly, the actual initial product temperature
T.sub.aIP(t.sub.f,i) for a container i was used in steps 142 and
148 of FIG. 3 and in sub-steps 161 to 168 of FIG. 7 of FIG. 7 for
computing the actual lethality F.sub.i.sup.j over [t.sub.f,i,
t.sub.r]. However, rather than using this actual initial product
temperature, the scheduled initial product temperature T.sub.sIP
may be used. This also results in the actual lethality being more
conservative.
[0113] 2.d. More Aggressive Approaches
[0114] A more aggressive approach than that described earlier in
section 1.c. can be taken for defining the initially scheduled reel
speed v.sub.s.sup.0. In this approach, a first additional step
could be added after step 159 of FIG. 6 to determine whether the
predicted total lethality F.sub.i.sup.0 over [0,
.DELTA.t.sub.1.sup.0+ . . . +.DELTA.t.sub.4.sup.0] is within the
target total lethality F.sub.targ by a predefined lethality
tolerance .DELTA.F. If this is the case, the reel speed obtained in
step 160 in the last iteration is used as the initially scheduled
reel speed. However, if this is not the case, then the reel speed
from the last iteration is overly conservative. As a result, a
second additional step may be added to increase this reel speed by,
for example, 0.5.DELTA.v. Steps 151 to 159 and the two additional
steps are then repeated until the first additional step is
satisfied. In this way, the initially scheduled reel speed is
further refined in an aggressive manner.
[0115] Similarly, a more aggressive approach can also be taken for
defining the re-scheduled reel speed v.sub.s.sup.j. In this case,
the steps 178 to 188 of FIG. 9 discussed in section 1.f. would also
include the two additional steps just described.
[0116] 2.e. Deviations in Scheduled Initial Product Temperature
and/or Reel Speed
[0117] In addition to temperature deviations in the scheduled
retort temperatures T.sub.sRT1.sup.0, . . . , T.sub.sRT5.sup.0,
there may be deviations in other scheduled parameters of the rotary
sterilization process. For example, there may be deviations in the
scheduled initial product temperature T.sub.sIP and/or the
currently scheduled reel speed v.sub.s.sup.j. Thus, the controller
104 may be configured to handle these deviations as well in order
to identify any under and/or over processed containers { . . . , i,
. . . }.sub.underpr and/or { . . . , i, . . . }.sub.overpr
resulting from the deviation. This is done in a similar manner to
that described earlier in sections 1.b. to 1.e. for temperature
deviations in the scheduled retort temperatures.
[0118] 2.d. More Aggressive Approaches
[0119] A more aggressive approach than that described earlier in
section 1.c. can be taken for defining the initially scheduled reel
speed v.sub.s.sup.0. In this approach, a first additional step
could be added after step 159 of FIG. 6 to determine whether the
predicted total lethality F.sub.i.sup.0 over [0,
.DELTA.t.sub.1.sup.0+ . . . +.DELTA.t.sub.4.sup.0] is within the
target total lethality F.sub.targ by a predefined lethality
tolerance .DELTA.F. If this is the case, the reel speed obtained in
step 160 in the last iteration is used as the initially scheduled
reel speed. However, if this is not the case, then the reel speed
from the last iteration is overly conservative. As a result, a
second additional step may be added to increase this reel speed by
0.5.DELTA.v. Steps 151 to 159 and the two additional steps are then
repeated until the first additional step is satisfied. In this way,
the initially scheduled reel speed is further refined in an
aggressive manner.
[0120] Similarly, a more aggressive approach can also be taken for
defining the re-scheduled reel speed v.sub.s.sup.j. In this case,
the steps 178 to 188 of FIG. 9 discussed in section 1.f would also
include the two additional steps just described. However, another
additional step would also have to be added.
[0121] 2.e. Deviations in Scheduled Initial Product Temperature
and/or Reel Speed
[0122] In addition to temperature deviations in the scheduled
retort temperatures T.sub.sRT1.sup.0, . . . , T.sub.sRT4.sup.0,
there may be deviations in other scheduled parameters of the
hydrostatic sterilization process. For example, there may be
deviations in the scheduled initial product temperature T.sub.sIP
and/or the currently scheduled reel speed v.sub.s.sup.j. These
deviations would be detected by monitoring the actual initial
product time-temperature profile T.sub.aIP(t) and the actual reel
time-speed profile v.sub.a(t).sup.j. Thus, the controller 104 may
be configured to handle these deviations as well in order to
identify and segregate any under and/or over processed containers {
. . . , i, . . . }.sub.underpr and/or { . . . , i, . . .
}.sub.overpr resulting from the deviation. This is done in a
similar manner to that described earlier in sections 1.b. to 1.e.
for temperature deviations in the scheduled retort
temperatures.
[0123] 2.f. Different Combinations of Cooling and Cooking Shells
and Temperature Zones
[0124] The rotary sterilizer 102 of FIG. 1 was described as having
one cooking shell 106-1 with three temperature zones 115-1, . . . ,
3 and one cooling shell 106-2 with two temperature zones 115-4 and
5. Correspondingly, the flow and timing diagrams of FIGS. 3 to 9
were described in this context as well. However, those skilled in
the art will recognize that the rotary sterilizer may have more
than one cooking shell and more than one cooling shell with more or
less temperature zones. For example, in a simple case, the cooking
and cooling shells may each have just one uniform temperature zone.
As those skilled in the art will recognize, the flow and timing
diagrams of FIGS. 3 to 9 would have to be correspondingly adjusted
for the specific combination of cooking and cooling shells and
temperature zones used.
[0125] 2.g. Other Continuous Source Sterilization Systems
[0126] The present invention has been described in the context of a
rotary sterilization system 100. However, as those skilled in the
art will recognize, the invention can be similarly practiced in any
other continuous source sterilization system in which containers or
carriers of containers are conveyed in line through the system's
sterilizer. For example, the invention may be used in a hydrostatic
sterilizer, as described in concurrently filed and co-pending U.S.
Pat. application Ser. No. 09/______, entitled Controller and Method
for Administering and Providing On-Line Handling of Deviations in a
Hydrostatic Sterilization Process, filed on Nov. 6, 1998, with
Weng, Z. as named inventor. This patent application is hereby
explicitly incorporated by reference.
[0127] 3. Conclusion
[0128] While the present invention has been described with
reference to a few specific embodiments, the description is
illustrative of the invention and is not to be construed as
limiting the invention. Various modifications may occur to those
skilled in the art without departing from the true spirit and scope
of the invention as defined by the appended claims.
* * * * *