U.S. patent application number 09/187915 was filed with the patent office on 2001-11-15 for controller and method for administering and providing on-line handling of deviations in a hydrostatic sterilization process.
Invention is credited to WENG, ZHIJUN.
Application Number | 20010041150 09/187915 |
Document ID | / |
Family ID | 22691013 |
Filed Date | 2001-11-15 |
United States Patent
Application |
20010041150 |
Kind Code |
A1 |
WENG, ZHIJUN |
November 15, 2001 |
CONTROLLER AND METHOD FOR ADMINISTERING AND PROVIDING ON-LINE
HANDLING OF DEVIATIONS IN A HYDROSTATIC STERILIZATION PROCESS
Abstract
A hydrostatic sterilization system, a controller for use in the
hydrostatic 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
carriers and to provide on-line handling of a deviation in a
scheduled parameter during the process. The carriers carry
containers of a shelf stable food product that is to be sterilized
in the sterilization process. In addition to the controller, the
hydrostatic sterilization system includes a hydrostatic sterilizer.
The controller controls the hydrostatic 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 carriers 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
SUITE 3400
FOUR EMBARCADERO CENTER
SAN FRANCISCO
CA
941114187
|
Family ID: |
22691013 |
Appl. No.: |
09/187915 |
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;
426/392 |
Current CPC
Class: |
A23L 3/027 20130101;
A23L 3/003 20130101 |
Class at
Publication: |
422/3 ; 422/26;
422/40; 422/105; 422/108; 422/109; 422/110; 426/231; 426/232;
426/392 |
International
Class: |
G05B 001/00; A61L
002/08 |
Claims
What is claimed is:
1. A method of administering a sterilization process being
performed by a hydrostatic sterilizer on a continues line of
carriers of containers, the method comprising the steps of:
controlling the hydrostatic sterilizer to perform the hydrostatic
sterilization process according to scheduled parameters; and when a
deviation in a specific one of the scheduled parameters occurs,
identifying those of the carriers 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 chamber of the hydrostatic sterilizer through
which the line of carriers is conveyed, (2) a scheduled water level
in a sterilization chamber of the hydrostatic sterilizer through
which the line of carriers is conveyed, (3) a scheduled initial
product temperature for the line of carriers, and (4) a scheduled
conveyor speed for conveying the line of carriers through the
hydrostatic sterilizer.
3. The method of claim 1 further comprising the step of: compiling
an actual retort time temperature profile for a chamber of the
hydrostatic sterilizer; and wherein the identifying step comprises
the steps of: selecting at least some of the carriers that are
effected by the deviation; for each of the selected carriers that
has been conveyed into the chamber during the deviation, simulating
a product cold spot time-temperature profile for the carrier based
on the actual retort temperature profile; computing the total
lethality predicted to be delivered to the carrier 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 carrier 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 carrier is loaded into the hydrostatic 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 carrier is unloaded from the hydrostatic
sterilizer.
6. The method of claim 5 wherein: the lethality actually delivered
over the first time interval is based on the portion of the 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 carrier 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 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 hydrostatic sterilizer on a continues line of carriers of
containers, the controller comprising: control circuitry configured
to control the hydrostatic 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 hydrostatic 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 carriers 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 chamber of the hydrostatic
sterilizer through which the line of carriers is conveyed, (2) a
scheduled water level in a sterilization chamber of the hydrostatic
sterilizer through which the line of carriers is conveyed, (3) a
scheduled initial product temperature for the line of carriers, and
(4) a scheduled conveyor speed for conveying the line of carriers
through the hydrostatic sterilizer.
10. The controller of claim 8 wherein: the process control program
is fuirther programmed to compile an actual retort time temperature
profile for a chamber of the hydrostatic sterilizer; and the
deviation program is programmed to identify the identified carriers
by: selecting at least some of the carriers that are effected by
the deviation; for each of the selected carriers that has been
conveyed into the chamber during the deviation, simulating a
product cold spot time-temperature profile for the carrier based on
the actual retort temperature profile; computing the total
lethality predicted to be delivered to the carrier 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 carrier 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 carrier is loaded into the hydrostatic
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 carrier is unloaded from the
hydrostatic sterilizer.
13. The controller of claim 12 wherein: the lethality actually
delivered over the first time interval is based on the portion of
the 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 carrier 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 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 hydrostatic sterilization system comprising: a hydrostatic
sterilizer configured to perform a sterilization process on a
continues line of carriers; a controller configured to: control the
hydrostatic sterilizer in performing the hydrostatic sterilization
process according to scheduled parameters; when a deviation in a
specific one of the scheduled parameters occurs, identify those of
the carriers 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 hydrostatic 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 chamber of
the hydrostatic sterilizer through which the line of carriers is
conveyed, (2) a scheduled water level in a sterilization chamber of
the hydrostatic sterilizer through which the line of carriers is
conveyed, (3) a scheduled initial product temperature for the line
of carriers, and (4) a scheduled conveyor speed for conveying the
line of carriers through the hydrostatic sterilizer.
17. The hydrostatic sterilization system of claim 15 further
comprising: a sensor to sense actual retort temperatures in a
chamber of the hydrostatic sterilizer; the controller is further
configured to: compile an actual retort time temperature profile
from the sensed actual retort temperatures; and identify the
identified carriers by: selecting at least some of the carriers
that are effected by the deviation; for each of the selected
carriers that have been conveyed into the chamber during the
deviation, simulating a product cold spot time-temperature profile
for the carrier based on the actual retort temperature profile;
computing the total lethality predicted to be delivered to the
carrier 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 carrier satisfies the
target lethality.
18. The hydrostatic 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 hydrostatic 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 carrier is loaded into the
hydrostatic 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 carrier is unloaded
from the hydrostatic sterilizer.
20. The hydrostatic sterilization system of claim 19 wherein: the
lethality actually delivered over the first time interval is based
on the portion of the 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 carrier is first affected by the
deviation to the current sample real time.
21. The hydrostatic sterilization system of claim 26 wherein: the
lethality predicted to be delivered over the second time interval
is based on the portion of the 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 hydrostatic sterilization process being performed
on line of carriers that each carry a set 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 carriers with under processed containers
as a result of the deviation.
BACKGROUND OF THE INVENTION
[0002] A hydrostatic sterilization system is a continuous source
processing system. It 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 does not
benefit from mechanical agitation of containers, as is performed in
a rotary sterilization system.
[0003] A hydrostatic sterilization system comprises a hydrostatic
sterilizer that has a conveyor (or chain) and a line of carriers
{1, . . . , i, . . . , I}.sub.line conveyed by the conveyor. Each
carrier i carries a set of containers and is conveyed through the
hydrostatic sterilizer by the conveyor. The conveyor has a
scheduled conveyor speed for conveying the carriers through the
hydrostatic sterilizer. Moreover, the containers carried by each
carrier are treated with scheduled retort temperatures in the
hydrostatic sterilizer.
[0004] In order for the food product in the containers of each
carrier 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 hydrostatic sterilization process to the product cold
spot of each container of the carrier. Here, t.sub.f,i and
t.sub.d,i are the loading and unloading times when the carrier is
loaded into and unloaded from the hydrostatic 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 conveyor speed and the retort temperatures are
then scheduled so that the containers of each carrier will receive
a scheduled time-temperature treatment that delivers a total
lethality to the containers which satisfies the target total
lethality.
[0005] As is well known, the lethality F.sub.i delivered to each
container in a carrier i over a particular time interval [t.sub.m,
t.sub.k] is given by the lethality equation: 1 F i = t m t k 10 ( T
cs ( t ) s - T REF ) / z t
[0006] 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 time-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 container over the total time
interval [t.sub.f,i, t.sub.d,i] due to the scheduled retort
temperatures is given by this lethality equation, where
t.sub.m=t.sub.f,i and t.sub.k=t.sub.d,i.
[0007] The total time interval [t.sub.f,i, t.sub.d,i9 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-temperature 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 Corporations LOG-TEC controller.
[0008] However, if any of the actual retort temperatures in the
hydrostatic sterilizer drops below a corresponding scheduled retort
temperature, a temperature deviation occurs. Traditionally, when
such a deviation occurs, the controller stops the conveyor and
prevents any of the carriers {1, . . . , i, . . . , I}.sub.line
from being loaded into or unloaded from the hydrostatic sterilizer
until the deviation is cleared. But, this approach causes numerous
problems. For example, significant production down time will
result. And, many carriers { . . . , i . . . }.sub.ovpr will have
over processed containers since the total lethalities { . . . ,
F.sub.i over [t.sub.f,i, t.sub.d,i], . . . }.sub.over actually
delivered to these containers 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 hydrostatic
sterilization system.
[0009] 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 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. patent 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.
[0010] In contrast, each carrier i in a hydrostatic 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] actually
delivered to each carrier's containers is different. This makes it
difficult to identify, while on-line and in real time, each carrier
that will have a total lethality predicted to be delivered to its
carriers 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 hydrostatic sterilization
process without stopping the conveyor has been inhibited.
[0011] However, in Weng, Z., Park, D. K., and Heyliger, T. L.,
Process Deviation Analysis of Conduction Heating Canned Foods
Processed in a Hydrostatic Sterilizer Using a Mathematical Model,
Food Processing Automation Conference IV, FPEI, ASAE, pp. 368-379,
1995, the distribution of the total lethalities F.sub.1 over
[t.sub.f,1, t.sub.d,1], . . . , F.sub.i over [t.sub.f,i,
t.sub.d,i], . . . , F.sub.I over [t.sub.f,i, t.sub.d,I] actually
delivered for carriers {1, . . . , i, . . . ,I}.sub.line was
studied when a temperature deviation occurred. From this, an
off-line approach was proposed to identify each carrier i with a
total lethality F.sub.i over [t.sub.f,i, t.sub.d,i] that was
actually delivered which is less than the target total lethality
F.sub.targ, But, this approach is not performed in real time and
limited to the conditions of a single temperature deviation and a
well controlled water level in the sterilization chamber of the
hydrostatic sterilizer.
SUMMARY OF THE INVENTION
[0012] In summary, the present invention comprises a hydrostatic
sterilization system, a controller for use in the hydrostatic
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 carriers and provide
on-line handling of a deviation from a scheduled parameter during
the process. The carriers carry containers of a shelf stable food
product that is to be sterilized in the sterilization process. In
addition to the controller, the hydrostatic sterilization system
includes a hydrostatic sterilizer.
[0013] The controller controls the hydrostatic sterilizer to
perform the hydrostatic sterilization process according to
scheduled parameters. When a deviation in a specific one of the
scheduled parameters occurs, the controller identifies those of the
carriers 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. This specific scheduled
parameter may be a scheduled retort temperature in a chamber of the
hydrostatic sterilizer through which the line of carriers is
conveyed. This specific scheduled parameter may also be a scheduled
water level in a sterilization chamber of the hydrostatic
sterilizer through which the line of carriers is conveyed. Or, it
may be a scheduled initial product temperature for the containers
in the camers or a scheduled conveyor speed for conveying the
carriers in line through the hydrostatic sterilizer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a block diagram of a hydrostatic sterilization
system in accordance with the present invention.
[0015] FIG. 2 is a block diagram of a controller of the hydrostatic
sterilization system of FIG. 1.
[0016] FIG. 3 is an overall process flow diagram for the controller
of FIG. 2 in controlling a hydrostatic sterilization process
performed by the hydrostatic 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 carriers 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 hydrostatic
sterilization system 100 for performing a hydrostatic sterilization
process on containers of a food product. The system 100 comprises a
hydrostatic sterilizer 102, a programmed controller 104, and a host
computer 105. The hydrostatic sterilizer includes a continuous line
of carriers {1, . . . i, . . . ,I}.sub.line and a conveyor 108 that
conveys the carriers through the hydrostatic sterilizer. Each
carrier i carries a set of the containers and is conveyed by the
conveyor through the hydrostatic sterilizer so that process is
performed on these containers. The controller and host computer are
used to administer the process.
1. Exemplary Embodiment
[0021] In an exemplary embodiment, the hydrostatic sterilizer 102
includes a feed (or pre-cooking) chamber 115-1, a sterilization
chamber (or steam dome) 115-2, a discharge (or pre-cooling) chamber
115-3, and a cooling chamber (or cooling tower) 115-4 through which
the carriers {1, . . . i, . . . , I}.sub.line are conveyed in line
by the conveyor 108. The containers are loaded into the carriers by
a loading device 110 and unloaded from the carriers by an unloading
device 114.
[0022] The feed chamber 115-1 contains a column of water and serves
as a hydrostatic valve to prevent the loss of pressure and
temperature in the sterilization chamber 115-2. The conveyor 108
has a vertical leg (or pass) 111-1 in the feed chamber for
conveying the carriers {1,. . . , i, . . . , I}.sub.line through
the column of water. The column of water is heated so as to
pre-cook the containers carried by the carriers to minimize the
thermal shock they will experience when entering the sterilization
chamber. In order to do so, the heated water is attempted to be
kept at a corresponding scheduled pre-cooking retort temperature
T.sub.sRT1.sup.0 for the feed chamber.
[0023] The carriers {1, . . . i, . . . ,I}.sub.line are then
conveyed through the sterilization chamber 115-2 by the conveyor
108. The conveyor has multiple vertical legs (or passes) 111-2 in
the sterilization chamber for conveying the carriers through steam
in the sterilization chamber. The steam is used to cook the
containers carried by the carriers and is attempted to be kept at a
corresponding scheduled cooking retort temperature T.sub.sRT2.sup.0
for the sterilization chamber. Temperature deviations, however, may
occur in the sterilization chamber. If the hydrostatic sterilizer
is of the type where the water level in the sterilization chamber
is not controlled and rises during a temperature deviation, a
portion of each of the legs in the sterilization chamber may be
immersed in the water during the temperature deviation. As a
result, some of the carriers will also be cooked with water. But,
if the hydrostatic sterilizer 102 is of the type in which the water
level is kept substantially constant, then the carriers will only
be cooked by steam.
[0024] Like the feed chamber 115-1, the discharge chamber 115-3
contains a column of water and serves as a hydrostatic valve to
prevent the loss of pressure and temperature in the sterilization
chamber 115-2. In this case, another vertical leg (or pass) 111-3
of the conveyor 108 in the discharge chamber conveys the carriers
{1, . . . i, . . . . . ,I}.sub.line through this column of water
after they have been conveyed through the sterilization chamber.
And, this column of water is cooled so as to pre-cool the
containers carried by the carriers. This is done to minimize the
thermal shock these containers will experience when entering the
cooling chamber. Here, the cooled water is kept at a corresponding
scheduled pre-cooling retort temperature T.sub.sRT3.sup.0 for the
feed chamber.
[0025] After the carriers {1, . . . i, . . . ,I}.sub.line exit the
discharge chamber 115-3, they are conveyed through the cooling
chamber 115-4 by the conveyor 108. As in the sterilization chamber,
the conveyor has multiple vertical legs 111-4 in the cooling
chamber for conveying the carriers through cooled water in the
cooling chamber. The cooled water cools the containers carried by
the carriers. It is kept at a corresponding scheduled cooling
retort temperature T.sub.sRT4.sup.0 for the sterilization
chamber.
[0026] At each sample real time t.sub.T (e.g., every 0.1 to 1
seconds) of the hydrostatic 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.aRT4(t.sub.r) in the corresponding chambers 115-1, . . . , 4.
The hydrostatic sterilizer also has sensors 112 and 113 that
respectively sense the actual water level WL.sub.a(t.sub.r) and
actual water temperature T.sub.aWT(t.sub.r) in the sterilization
chamber 115-2 at each sample real time t.sub.r. Similarly, the
hydrostatic sterilizers sensor 107 senses the actual conveyor speed
v.sub.a(t.sub.r) of the conveyor 108 at each sample real time t.
Finally, the loading device 110 periodically (e.g., every 20 to 30
minutes) removes a container being fed into the hydrostatic
sterilizer and a sensor 117 of the hydrostatic sterilizer senses
its actual initial product temperature T.sub.aIP(t.sub.r) at that
time t.sub.r.
[0027] The controller 104 administers the hydrostatic sterilization
process by controlling the hydrostatic 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.aRT4(t.sub.r) sensed by the sensors 117 and 116-1, . . . , 4,
the water level WL.sub.a(t.sub.r) and actual water temperature
T.sub.aWT(t.sub.r) sensed by the sensors 112 and 113, the actual
conveyor 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.
[0028] The host computer 105 is used to provide input information,
namely input parameters and software, used by the controller 104 in
administering the hydrostatic sterilization process. The host
computer is also used to receive, process, and display output
information about the process which is generated by the
controller.
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 hydrostatic sterilization process by
generating control signals that control the sequential operation of
the hydrostatic 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
hydrostatic sterilization process, the control circuitry 129
receives sensor signals from the sensors 107, 112, 113, 117, and
116-1, . . . , 4 that represent the actual conveyor speed
v.sub.a(t.sub.r), the actual water level WL.sub.a(t.sub.r), the
actual water temperature T.sub.aWT(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.aRT4(t.sub.r). The control
circuitry generates the control signals for controlling the
hydrostatic sterilizer 102 in response to these temperatures. These
temperatures 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 conveyor time-speed profile v.sub.a(t), a water
level-time profile WL.sub.a(t), an actual water time-temperature
profile T.sub.aWT(t), an actual initial product time-temperature
profile T.sub.aIp(t), and actual retort time-temperature profiles
T.sub.aRT1(t), . . . , T.sub.aRT4(t) for the corresponding chambers
115-1, . . . , 4. These profiles are used in the manner described
later for providing on-line handling of temperature deviations
during the hydrostatic sterilization process.
[0033] The sensors 116-1, . . . , 4 are preferably located in the
slowest heating regions of the chambers 115-1, . . . , 4 to provide
conservative estimates of the actual retort temperatures
T.sub.aRT1(t.sub.r), . . . , T.sub.aRT4(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 chambers.
[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
hydrostatic 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 hydrostatic 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 carriers {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
carriers { . . . , 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 hydrostatic
sterilization process according to the overall process flow of FIG.
3, the input parameters for the hydrostatic 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 carriers 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.sRT4.sup.0. Finally, the input
parameters include a scheduled water level WL.sub.s in the
sterilization chamber 115-2, the minimum and maximum conveyor
speeds v.sub.min and v.sub.max, and length and location information
L.sub.1, . . . , L.sub.4 for the legs 114-1, . . . , 4 in the
corresponding chambers 115-1, . . . , 4.
[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.sRT4.sup.0, WL.sub.s, v.sub.min, v.sub.max, and L.sub.1, . .
. , L.sub.4 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 hydrostatic sterilization process to be
administered to a carrier i to define an initially scheduled
conveyor speed v.sub.s.sup.0 for the conveyor 108. This also
results in an initially scheduled time-temperature treatment
T.sub.sRT(t).sub.i.sup.0 that is to be given to the containers in
each carrier i. This treatment includes pre-cooking, cooking,
pre-cooling, and cooling portions at the corresponding scheduled
pre-cooking, cooking, pre-cooling, and cooling retort temperatures
T.sub.sRT1.sup.0, . . . , T.sub.sRT4.sup.0 over corresponding
initially scheduled time durations .DELTA.hd 1.sup.0, . . . ,
.DELTA.t.sub.4.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 conveyor 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 spots of the containers of each carrier i during the
hydrostatic 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.sRT4.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
spots of the containers of each carrier i during the hydrostatic
sterilization process. In doing so, the program iteratively and
incrementally computes a predicted total lethality F.sub.i that
satisfies the target total lethality F.sub.targ and is predicted to
be delivered to these product cold spots over a simulated total
time interval [0, .DELTA.t.sub.1.sup.0+ . . .
+.DELTA.t.sub.4.sup.0]. This computation is made based on the
product cold spot time-temperature profile T.sub.CS(t).sub.1.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.4.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.4.sup.0] is
iteratively and incrementally computed until the initially
scheduled conveyor 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.4.sup.0 are determined
from the conveyor speed v.sub.s.sup.0 and the length and location
information L.sub.1, . . . , L.sub.4 for the legs 111-1, . . . , 4
ofthe conveyor 108. Thus, definition of the conveyor speed
v.sub.s.sup.0 also includes definition of the pre-cooking, cooking,
pre-cooling, 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.4.sup.0 are based.
[0042] The process control program 123 controls the administration
of the hydrostatic sterilization process in steps 136 to 149. In
doing so, it first sets a counter j to zero in step 136. This
counter is used to count each time that the currently scheduled
conveyor speed v.sub.s.sup.j is adjusted during the hydrostatic
sterilization process.
[0043] Then, at the current sample real time t.sub.T, the process
control program 123 causes the control circuitry 129 in step 137 to
administer the hydrostatic sterilization process at the currently
scheduled conveyor speed v.sub.s.sup.j and at the scheduled retort
temperatures T.sub.sRT1.sup.0, . . . , T.sub.sRT4.sup.0 in the
corresponding chambers 115-1, . . . , 4. In doing so, the control
circuitry appropriately controls the hydrostatic sterilizer 102 and
monitors the actual retort temperatures T.sub.aRT1(t.sub.r), . . .
, T.sub.aRT4(t.sub.T) in the corresponding chambers 115-1, . . . ,
4 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.sRT4.sup.0. In this embodiment of the controller 104, the
scheduled retort temperatures will remain the same throughout the
hydrostatic sterilization process regardless if temperature
deviations occur in the chambers. Thus, if such a temperature
deviation does occur in a particular chamber 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
chamber 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.aRT4(t.sub.r) in the chambers
115-1, . . . , 4 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.aRT4(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 conveyor speed v.sub.s.sup.j at each time t.sub.r. This
is done to compile a conveyor time-speed profile v(t) for the
hydrostatic sterilization process to provide a record of the
changes in the conveyor 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 chambers 115-1, . . . , 4. 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
carriers { . . .i, . . . } .sub.underpr that were identified in
step 148 for segregation and are being unloaded by the unloading
device 114 at the current sample real time t.sub.r will then have
their under processed containers segregated in step 141. The
process control program causes the control circuitry 129 to control
the unloading device 114 in performing this segregation in the
manner discussed later. In step 149, the process control program
sets the currently scheduled conveyor speed va to the initially
scheduled conveyor speed v.sub.s.sup.0 if all of the carriers { . .
. , i, . . . }.sub.aff affected by a temperature deviation have
been unloaded. Both steps 141 and 149 are discussed later in more
detail. The process control program then administers the
hydrostatic 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 chamber
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 sterilization chamber 115-2. In step 142, the program 125
identifies the carrier i that at the time t.sub.r has the minimum
total lethality F.sub.i.sup.j predicted to be delivered to the
product cold spots of the containers it carries over the currently
scheduled total time interval [t.sub.f,i, t.sub.d,i.sup.j] for the
carrier. This minimum lethality carrier i is identified from among
the carriers { . . . , i, . . . }.sub.aff that are currently
affected by the temperature deviation. These affected carriers are
those of the carriers {1, . . . , . . . , I}.sub.line that are at
the time tr currently in the chamber 115-n in which the temperature
deviation is occurring. This is determined using the conveyor
time-speed profile v(t) compiled in step 139 and the length and
location information L.sub.1, . . . , L.sub.4 for the legs 111-1, .
. . , 4.
[0048] In one approach for identifying the minimum lethality
carrier i from among the affected carriers { . . . , 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 carriers { . . . , i, . . . }.sub.sel selected to be evaluated.
Based on these lethalities, the program iteratively bisects the
list of affected carriers to select the selected carriers from
among the affected carriers until the minimum lethality carrier i
is identified.
[0049] The approach just described is useful for handling a
temperature deviation in the sterilization chamber 115-2 if the
hydrostatic sterilizer 102 is of the type in which the water level
WL.sub.a(t.sub.r) in the sterilization chamber is kept
substantially constant. However, if the hydrostatic sterilizer is
of the type where the water level is not controlled and rises
during a temperature deviation, a portion of each of the legs 111-2
will be immersed in the water during a temperature deviation. As a
result, some of the affecetd carriers { . . . i, . . . }.sub.aff
will be immersed in this water as well. Moreover, if the
temperature deviation is long enough, these carriers may be
immersed several times because of the multiple legs in the
sterilization chamber. Each of these carriers will therefore be
treated with the portion(s) of the actual water time-temperature
profile T.sub.aWT(t) over the time interval(s) that it is immersed
in the water and with the portions of the actual retort
temperatures T.sub.aRT2(t) over the time intervals that it is not
immersed. Here, k identifies each time interval for which the
carrier is immersed.
[0050] As a result, there will be pockets of affected containers {
. . . , i, . . . }.sub.aff that have very low predicted total
lethalities { . . . , F.sub.i.sup.j over [t.sub.f,i,
t.sub.d,i.sup.j], . . . }.sub.aff, as shown in FIG. 5. Thus, in a
variation of the first approach just described, the temperature
deviation program 125 may initially use predefined intervals to
initially select carriers { . . . , i, . . . }.sub.int at the
intervals for evaluation. Then, around those of the initially
selected carriers 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. This ensures that each of the pockets of carriers with very
low predicted total lethalities is evaluated.
[0051] In still another approach for identifying the minimum
lethality carrier i, the temperature deviation program 125 may
select all of the affected carriers { . . . , i, . . . }.sub.aff as
the selected carriers { . . . , 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 carrier 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 carriers, the minimum lethality carrier
i is identified.
[0052] 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 carrier 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 product cold spots
of the carrier's contianers over the actual time interval
[t.sub.f,i, t.sub.r] that the carrier has been in the hydrostatic
sterilizer 102. This is done by simulating the portion of the
hydrostatic 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
carrier 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 containers
of the carrier i, 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
carrier was in the chambers 115-1, . . . , n. Here, n identifies
the chamber 115-n in which the temperature deviation is occurring.
And, if the temperature deviation occurs in the sterilization
chamber 115-2, as shown in the example of FIG. 4, and the
hydrostatic sterilizer 102 is of the type where the water level in
the sterilization chamber is not controlled, then this simulation
is also done based on each portion of the actual water
time-temperature profile T.sub.awT(t) over any corresponding
portion of the time interval (t.sub.1,i.sup.j, t.sub.r] that the
carrier was immersed in the water.
[0053] The actual initial product temperature T.sub.aIP(t.sub.f,i)
for the carrier 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,i.sup.j, t.sub.r] for the selected carrier i are
determined by the temperature deviation program 125 from the
conveyor time-speed profile v(t) and the length and location
information L.sub.1, . . . , L.sub.n for the legs 111-1, . . . , n.
If the temperature deviation occurs in the sterilization chamber
115-2 and the water level in it is not controlled, then any
portion(s) of the time interval (t.sub.1,i.sup.j, t.sub.r] that the
carrier was immersed in the water are determined from the conveyor
time-speed profile and the length and location information for the
legs and the water level-time profile WL.sub.a(t).
[0054] In the example of FIG. 4, the temperature deviation occurs
in the sterilization chamber 115-2. 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,r] is
based in this case on the portion of the actual retort
time-temperature profile T.sub.aRT1(t) over the actual time
interval [t.sub.f,i, t.sub.1,i.sup.j], the portion(s) of the retort
time-temperature profile T.sub.aRT2(t) over the actual time
interval (t.sub.1,i.sup.j, t.sub.r] that the carrier was not
immersed in the water in the sterilization chamber, and any
portion(s) of the actual water time-temperature profile
T.sub.aWT(t) over any corresponding portion(s) of the time interval
(t.sub.1,i.sup.j, t.sub.r] that the carrier was immersed in the
water. The time interval [t.sub.f,i, t.sub.1,i.sup.j] has the
initially scheduled time duration .DELTA.t.sub.1.sup.0 since the
temperature deviation began at the deviation begin time t.sub.e
while the carrier i was in the sterilization chamber. If, however,
this carrier was in the chamber 115-1 when the deviation began,
then the time interval [t.sub.f,i, t.sub.1,i.sup.j] would have a
different time duration .DELTA.t.sub.1.sup.j because the conveyor
speed v.sub.s.sup.j would have been changed while the carrier was
in that chamber.
[0055] 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 cold spot of the selected carrier 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.
[0056] Then, the temperature deviation program 125 simulates the
remaining portion of the hydrostatic sterilization process that is
predicted to be administered to the containers of the selected
carrier i over the scheduled remaining time interval (t, tdi]
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.sRT4.sup.0 over the currently
scheduled remaining time intervals (t.sub.r, t.sub.n,i.sup.j], . .
. , (t.sub.3,i.sup.j, t.sub.d,i.sup.j].
[0057] The actual product cold spot temperature
T.sub.CS(t.sub.r).sub.i.su- p.j for the product cold spots of the
containers of the selected carrier 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.3,i.sup.j,t.sub.d,i.-
sup.j] for the carrier i are determined by the temperature
deviation program 125 from the conveyor time-speed profile v(t),
and the chamber length and location information L.sub.1, . . . ,
L.sub.4.
[0058] In the example of FIG. 4, the temperature deviation occurs
in the sterilization chamber 115-2. 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.sRT2.sup.0, T.sub.sRT3.sup.0, and
T.sub.sRT4.sup.0 respectively over the currently scheduled
remaining time intervals (t.sub.r, t.sub.2,i.sup.j],
(t.sub.2,i.sup.j,t.sub.3,i.sup.j], and (t.sub.3,i.sup.j,
t.sub.d,i.sup.j]. In this example, the time intervals and
(t.sub.1,i.sup.j,t.sub.2,i.sup.j], (t.sub.2,i.sup.j,
t.sub.3,i.sup.j], and (t.sub.3,i.sup.j,t.sub.d,i.sup.j]
respectively have re-scheduled time durations .DELTA.t.sub.2.sup.j,
.DELTA.t.sub.3.sup.j, and .DELTA.t.sub.4.sup.j that are different
than the initially scheduled time durations .DELTA.t.sub.2.sup.0,
.DELTA.t.sub.3.sup.0, and .DELTA.t.sub.4.sup.0 since the currently
scheduled conveyor speed v.sub.s.sup.j at the current sample real
time t.sub.r has been re-scheduled from the initially scheduled
conveyor speed v.sub.s.sup.0.
[0059] 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 spots of the containers of the
selected carrier 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.sup.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 product cold spots 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.
[0060] Then, in step 143, the temperature deviation program 125
determines at the current sample real time t.sub.r if the carrier 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 carriers { . . . , 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 carriers { . . . , i, . . .
}.sub.underpr that are being unloaded at the time t.sub.r to be
segregated. Then, in the manner discussed earlier, the process
control program 123 administers the hydrostatic 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.
[0061] 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 conveyor speed v.sub.s.sup.j
is set to the minimum conveyor 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) conveyor speed v.sub.s.sup.j in step
146.
[0062] In step 146, the re-scheduled conveyor speed v.sub.s.sup.j
is defined in a similar manner to the way in which the initially
scheduled conveyor 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 carrier i are used in simulating the remaining
portion of the hydrostatic 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
carrier in step 142. Similar to step 135, this is done iteratively
and incrementally until the conveyor speed is determined for which
the predicted total lethality satisfies the total target lethality
F.sub.targ or the conveyor speed equals the minimum conveyor 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.
[0063] The definition of the re-scheduled conveyor 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 pre-cooling and cooling portions at the scheduled retort
temperatures T.sub.sRT4.sup.0 and T.sub.sRT4.sup.0 over
corresponding re-scheduled time durations .DELTA.t.sub.4.sup.j and
.DELTA.t.sub.4.sup.j.
[0064] 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 carrier i will satisfy the target total lethality
F.sub.targ. But, as just mentioned, the re-scheduled conveyor speed
v.sub.s.sup.j may be limited to the minimum conveyor 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 carriers { . . . ,
i, . . . }.sub.underpr from among the affected carriers { . . . ,
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 carrier i is of course one of the under processed
carriers. The under processed carriers are to be segregated and are
identified at the current real sample time t in step 148 by the
program.
[0065] FIG. 5 shows the distribution of the affected carriers {. .
. , i, . . . }.sub.aff and the under processed carriers {. . . , i,
. . . }.sub.underpr to be segregated at the time t.sub.r. In
identifying the under processed carriers in step 148, the program
125 uses a similar approach as that used in step 142 to identify
the minimum lethality carrier i. But, in this case, the additional
criteria of the target total lethality F.sub.targ is used to expand
the search.
[0066] Once the under processed carriers { . . . , 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 unloading device 114 in segregating the containers
of any of the under processed carriers that are being unloaded at
the current sample real time t.sub.r. In order to properly
segregate these containers, the process control program tracks the
under processed carriers to determine when they will be unloaded.
This is done using the conveyor time-speed profile v(t) and the
length and location information L.sub.1, . . . , L.sub.4 for the
legs 111-1, . . . , 4.
[0067] 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 carriers { . . .
, 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 carriers is dynamically updated and
maintained. Since the containets of these under processed carriers
are segregated when unloaded in step 141, this will ensure that the
containers in only those of the carriers {1, . . . , i, . . .
I}.sub.line that are adequately processed are released for
distribution.
[0068] The list of affected carriers { . . . 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 carriers in
this list until they have all been unloaded. This tracking is done
in the same manner in which the under processed carriers are
tracked. The process control program 123 will then set the
currently scheduled conveyor speed v.sub.s.sup.j back to the
initially scheduled conveyor speed v.sub.s.sup.0 in step 149.
[0069] 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 carrier 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.aRT4(t) that it has been treated with
over the hydrostatic sterilization process. Moreover, this results
in the list of under processed carriers { . . . , i, . . .
}.sub.underpr being further updated and expanded.
[0070] 1.c. Detailed Process Flow for Step 135 of FIG. 3
[0071] 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 conveyor speed v.sub.s.sup.0. In doing so, this
program iteratively performs a simulation of the hydrostatic
sterilization process that is predicted to be administered to each
carrier i in sub-steps 150 to 160 of step 135.
[0072] In step 150, the process scheduling program 124 first
defines the initially scheduled conveyor speed v.sub.s.sup.0 as the
maximum conveyor speed v.sub.max. Then, in step 151, the program
defines the time durations .DELTA.t.sub.1.sup.0, . . . ,
.DELTA.t.sub.4.sup.0 for how long each carrier i is scheduled to be
in the respective chambers 115-1, . . . , 4. This is done based on
the initially scheduled conveyor speed and the length and location
information L.sub.1, . . . , L.sub.4 for the chambers.
[0073] 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 hydrostatic sterilization
process for the carrier i. The program also initially sets the
predicted product cold spot temperature
T.sub.CS(t.sub.s).sub.i.sup.0 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 these product cold spots
over the current simulation time interval [0, t.sub.s] initially
set by the program to zero.
[0074] 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.
[0075] 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 spots of the containers in the carrier 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 these product cold
spots 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.T,
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.sRT4.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.3.sup.0, .DELTA.t.sub.4.sup.0]. These time intervals
indicate how long the carrier i is scheduled to be in the
respective chambers 115-1, . . . , 4.
[0076] The lethality F.sub.1.sup.0 that is predicted to be
delivered to the product cold spots of the containers in the
carrier i over the current simulation time increment
[t.sub.s-.DELTA.t.sub.r, t.sub.s9 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.
[0077] In step 156 of each iteration, the process scheduling
program 124 computes the lethality F.sub.1.sup.0 predicted to be
delivered to the product cold spots of the containers in the
carrier 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 spots 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.
[0078] Then, in step 157 of each iteration, the process scheduling
program 124 determines whether the current simulation time ts has
reached the end time [.DELTA.t.sub.1.sup.0+ . . .
+.DELTA.t.sub.4.sup.0] of the simulated hydrostatic sterilization
process for the carrier 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 hydrostatic 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 product cold spots
of the carriers containers over the total simulation time interval
[0, .DELTA..sub.1.sup.0+ . . . +.DELTA.t.sub.4.sup.0].
[0079] When this finally occurs, the process scheduling program 124
determines in step 159 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 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 conveyor speed v.sub.s.sup.0 by a
predefined conveyor speed offset .DELTA.v. This results in the
re-definition of this conveyor speed. Steps 151 to 160 are then
repeated until step 159 is satisfied. The conveyor speed for which
step 159 is satisfied is then used in steps 136 to 148 of FIG. 3 in
the manner discussed earlier.
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 spots of the containers in the carrier i over the
actual time interval [t.sub.f,i, t.sub.r] that the carrier has been
in the hydrostatic 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 hydrostatic sterilization process that
has been administered to the product cold spots 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 carrier i has actually been
in the respective chambers 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 conveyor time-speed
profile v(t). In addition, if the temperature deviation is
occurring in the sterilization chamber 115-2 and the sterilization
chamber is of the type in which its water level is not controlled,
the program also defines the portion(s) of the time interval
(t.sub.n-1,i.sup.j, t.sub.r] that the carrier was immersed in the
water. The definition of these time intervals is based on the
accumulated conveyor time-speed profile v(t), the length and
location information L.sub.1 and L.sub.2 for the legs 111-1 and 2,
and the water level-time profile WL.sub.a(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 spots of the
containers in the carrier 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 spots 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 spots of the containers in the carrier
i over the current simulation time increment
[t.sub.s-.DELTA.t.sub.r, t.sub.s]. With one exception, 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.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). The exception is in the case where the temperature
deviation is occurring in the sterilization chamber 115-2 and the
sterilization chamber is of the type in which its water level is
not controlled. In this case, the portions of the actual water
time-temperature profile T.sub.aWT(t) over the portion(s) of the
time interval (t.sub.n-1,i.sup.j, t.sub.r] that the carrier was
immersed in the water are used instead of the corresponding
portion(s) of the actual retort time-temperature profile
T.sub.aRT2(t).
[0084] The actual lethality F.sub.i.sup.j that was delivered to the
product cold spots of the containers carried by the carrier 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 cold spots of the containers in the carrier 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 fmally 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 carrier 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 spots of the containers in a selected carrier over
the total time interval [t.sub.f,i, t.sub.d,i.sup.j] that the
carrier is in the hydrostatic sterilizer 102. In this case, the
program iteratively performs a simulation of the predicted
remaining portion of the hydrostatic sterilization process to be
administered to this carrier 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,i.sup.j], . . . ,
(t.sub.3,i.sup.j, t.sub.d,i.sup.j] that the carrier i is predicted
to be in the respective chambers 115-n, . . . , 4 after the current
sample real time t.sub.r. The definition of these time intervals in
step 169 is based on the currently scheduled conveyor 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 spots of the
containers carried by the carrier 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 spots 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 spots of the containers in the carrier
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.sRT4.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.3,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 spots of the containers in the
carrier 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 unloading time
t.sub.d,i.sup.j for the carrier 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 unloading 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.sup.j]
1.f. Detailed Process Flow for Step 146 of FIG. 3
[0095] 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 conveyor 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 hydrostatic sterilization process
predicted to be administered to the minimum lethality carrier 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.
[0096] In step 178, the temperature deviation program 125 first
decrements the currently scheduled conveyor speed v.sub.s.sup.j by
the predefined conveyor speed offset .DELTA.v. If the decremented
conveyor speed is greater than the minimum conveyor speed
v.sub.min, the re-scheduled conveyor speed is defined as the
decremented conveyor speed. However, if the decremented conveyor
speed is less than or equal to the minimum conveyor speed, then the
re-scheduled conveyor speed is defined as the minumum conveyor
speed.
[0097] Since a re-scheduled conveyor speed v.sub.s.sup.j is defined
in step 178, the re-scheduled remaining time intervals (t.sub.r,
t.sub.n,i.sup.j], . . . , (t.sub.3,i.sup.j, t.sub.d,i.sup.j] that
the minimum lethality container i is predicted to be in the
respective chambers 115-n, . . . , 4 after the current sample real
time t.sub.r need to be defined. This is done in step 179.
[0098] Step 180 to 186 are the same as steps 170 to 176 of FIG. 8
and discussed in section i.e. Thus, these steps are used to compute
a total lethality F.sub.i.sup.j predicted to be delivered to the
product cold spots of the containers in the minimum lethality
carrier 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 cold spot temperature
T.sub.CS(t.sub.r).sup.j for the minimum lethality carrier i
computed in steps 161 to 168 of FIG. 7.
[0099] 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 conveyor speed v.sub.s.sup.j equals the
minimum conveyor 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 conveyor speed has been reached. In this way, the
conveyor speed is re-scheduled.
[0100] 2. Alternative Embodiments
[0101] 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.
[0102] 2.a. Scheduling and Re-Scheduling Variations
[0103] The operator of the hydrostatic sterilization process 100
may want to keep the initially scheduled conveyor speed
v.sub.s.sup.0 and retort temperatures T.sub.sRT1.sup.0, . . . ,
T.sub.sRT4.sup.0 constant throughout the entire hydrostatic
sterilization process. Thus, in this embodiment, the temperature
deviation program 125 is simply used to identify the under
processed carriers { . . . , 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.
[0104] In another embodiment, the initially scheduled retort
temperatures T.sub.sRT1.sup.0, . . . , T.sub.sRT4.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.sRT4.sup.j in
a similar manner to which it defined a re-scheduled conveyor 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 conveyor speed
v.sub.s.sup.0 may be kept constant or a re-scheduled conveyor speed
v.sub.s.sup.j may be defined in conjunction with the re-scheduled
retort temperature.
2.b. Identifying and Segregating Over Processed Carriers
[0105] Since re-scheduled conveyor speed v.sub.s.sup.j may be
defined when a temperature deviation occurs, it is possible that
some of the carriers {1, . . . , i, . . . , I} may be over
processed due to the slower re-scheduled conveyor 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
carriers { . . . , 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 carriers { . . . , i, . . . }.sub.underpr
are identified in step 148 of FIG. 3 and discussed in section 1.b.
The containers in these carriers would be segregated in the same
way that the conatiners of under processed carriers are segregated
in step 141 of FIG. 3. As a result, the conatiners in the remaining
carriers that are not under or over processed would have a uniform
quality food product using this technique.
2.c. More Conservative Approaches
[0106] 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 carrier i has been in the hydrostatic
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] and, if required, the actual water
time-temperature profile T.sub.aWT(t) over the portion(s) of the
time interval (t.sub.1,i.sup.j, t.sub.r] that the carrier is
immersed in the water of the sterilization chamber 115-2.
[0107] However, a more conservative embodiment could be employed
which uses only the the actual retort time-temperature profile
T.sub.aRTn(t) for the chamber 115-n in which the temperature
deviation occurs. For example, only the portion of this actual
retort time-temperature profile over the time interval from the
time when the carrier is first affected by the temperature
deviation to the current sample real time t.sub.r would be used.
However, there is an exception in the case where the temperature
deviation is occurring in the sterilization chamber 115-2 and the
sterilization chamber is of the type in which its water level is
not controlled. In this case, the actual water time-temperature
profile T.sub.aWT(t) over the portion(s) of this time interval
(t.sub.1,i.sup.j, t.sub.r] that the carrier is immersed in the
water of the sterilization chamber 115-2 would be used instead of
the corresponding portion(s) of the actual retort time-temperature
profile T.sub.aRT2(t). Then, 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 chambers 115-1, . . . , n-1 in which the temperature
deviation is not occurring.
[0108] Thus, if the carrier enters the chamber 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
corresponding portion(s) of the actual retort time-temperature
profile T.sub.aRTn(t) and, if required, actual water
time-temperature profile T.sub.awr(t) over this time interval. But,
if the temperature deviation begins at the deviation begin time
t.sub.d while the carrier is in this chamber, then the portion of
the product cold spot time-temperature profile over the time
interval (t.sub.n-1,i.sup.j, t.sub.d] 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
corresponding portion(s) of the actual retort and water
time-temperature profiles 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.
[0109] Similarly, the actual initial product temperature
T.sub.aIP(t.sub.f,i) for a carrier 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.
2.d. More Aggressive Approaches
[0110] A more aggressive approach than that described earlier in
section 1.c. can be taken for defining the initially scheduled
conveyor 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 conveyor speed
obtained in step 160 in the last iteration is used as the initially
scheduled conveyor speed. However, if this is not the case, then
the conveyor speed from the last iteration is overly conservative.
As a result, a second additional step may be added to increase this
conveyor 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
conveyor speed is further refined in an aggressive manner.
[0111] Similarly, a more aggressive approach can also be taken for
defining the re-scheduled conveyor 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.
2.e. Deviations in Scheduled Initial Product Temperature, Water
Level, and/or Conveyor Speed
[0112] 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,
the scheduled water level WL.sub.s, and/or the currently scheduled
conveyor speed v.sub.s.sup.j. These deviations would be detected by
monitoring the actual initial product time-temparature profile
T.sub.aIP(t), the actual water level-time profile WL.sub.a(t), and
the actual conveyor 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 any under and/or over processed carriers { . .
. , i, . . . }.sub.underpr and/or { . . . , i, . . . }.sub.overpr
resulting from the deviation and then segregate their containers.
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.
2.f. Different Combinations of Chambers
[0113] The hydrostatic sterilizer 102 of FIG. 1 was described as
having a feed chamber 115-1, a sterilization chamber 115-2, a
discharge chamber 115-3, and a cooling chamber 115-4.
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 hydrostatic sterilizer may have less or
more chambers. For example, the hydrostatic sterilizer may have a
pressure pre-cooking chamber and/or a pressure pre-cooling chamber.
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 chambers used.
2.g. Other Continuous Source Sterilization Systems
[0114] The present invention has been decribed in the context of a
hydrostatic 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 systems sterilizer. For example, the invention may be used in a
rotary sterilizer, as described in concurrently filed and
co-pending U.S. patent application Ser. No. 09/______, entitled
Controller and Method for Administering and Providing On-Line
Handling of Deviations in a Rotary Sterilization Process, filed on
Nov. 6, 1998, with Weng, Z. as named inventor. This patent
application is hereby explicitly incorporated by reference.
3. Conclusion
[0115] 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.
* * * * *