US20020001535A1 - Controller and method for administering and providing on-line handling of deviations in a rotary sterilization process - Google Patents

Abstract

A rotary sterilization system, a controller for use in the rotary sterilization system, and a method performed by the controller are disclosed. The system, controller, and method are used to administer a sterilization process performed on a line of containers and provide on-line handling of a deviation in a scheduled parameter during the process. The containers contain a shelf stable food product that is to be sterilized in the sterilization process. In addition to the controller, the rotary sterilization system includes a rotary sterilizer. The controller controls the rotary sterilizer in performing the sterilization process according to scheduled parameters. When a deviation in a specific one of the scheduled parameters occurs, the controller identifies those of the containers that will in response have a total lethality predicted to be delivered to them during the sterilization process that is less than a predefined target lethality.

Description

TECHNICAL FIELD OF THE INVENTION
• The present invention relates generally to a controller for administering a rotary sterilization process being performed on line of containers. In particular, it pertains to such a controller that also provides on-line handling of a deviation in a scheduled parameter during the process by identifying any containers that will be under processed as a result of the deviation.[0001]
BACKGROUND OF THE INVENTION
• A rotary sterilization system is a continuous source processing system with intermittent product agitation. This system is widely used in the canning industry to sterilize a shelf stable food product packaged in containers. It is used most often for sterilizing a food product that benefits from mechanical agitation of the containers.[0002]
• A rotary sterilization system includes a rotary sterilizer that has one or more cooking shells through which a line of containers {1, . . . , i, . . . , I}[0003]_lineare conveyed. The containers are cooked in the cooking shell(s) at one or more scheduled cooking retort temperatures. The containers are then conveyed in line through one or more cooling shells of the rotary sterilizer. Similar to the cooking shell(s), the containers are cooled in the cooling shell(s) at one or more scheduled cooling retort temperatures.
• The containers {1, . . . , i, . . . , I}[0004]_lineare conveyed through each cooking and cooling shell by spiral tracks and a reel. The reel has a scheduled reel speed and imparts movement while the spiral tracks provide the direction for the containers to be conveyed through the shell. This also provides mechanical agitation of the food product within the containers.
• In order for the food product in each container i to be commercially sterilized, a total lethality F[0005]_iover a total time interval [t_f,i, t_d,i] that satisfies a predefined target total lethality F_targmust be delivered during the rotary sterilization process to the product cold spot of the container. Here, t_f,iand t_d,iare the feed and discharge times when the container is fed into and discharged from the rotary sterilizer. The target total lethality is set by the USDA (U.S. Department of Agriculture), the FDA (Food and Drug Administration), and/or a suitable food processing authority for destroying certain microorganisms. The reel speed and the cooking and cooling retort temperatures are then scheduled so that each container i will receive a scheduled time-temperature treatment that delivers a total lethality to the container which satisfies the target total lethality.
• As is well known, the lethality F[0006]_idelivered to the product cold spot of a container i over a particular time interval [t_m, t_k] is given by the lethality equation:${\mathrm{<figure-callout\; label="F"\; filenames="US20020001535A1-drawings-page-2.png,US20020001535A1-drawings-page-4.png"\; state="\{\{state\}\}">F</figure-callout>}}_1={\int }_{t_m}^{t_k}{10}^{\left({T_{\mathrm{cs}}\left(t\right)}_s-T_{\mathrm{REF}}\right)/z}t$

  
• where t[0007]_mand t_kare respectively the begin and end times of the time interval [t_m, t_k], T_CS(t)_iis the product cold spot timne-temperature profile for the container, z is the thermal characteristic of a particular microorganism to be destroyed in the sterilization process, and T_REFis a reference temperature for destroying the organism. Thus, the total lethality F_idelivered to the product cold spot over the total time interval [t_f,i, t_d,i] due to the scheduled cooking and cooling retort temperatures is given by this lethality equation, where t_m=t_f,iand t_k=t_d,i.
• The total time interval [t[0008]_f,i, t_d,i] and the product cold spot time-time-temperature profile T_CS(t)_imust be such that the total lethality F_iover [t_f,i, t_d,i] satisfies the target total lethality F_targ. In order to ensure that this occurs, various mathematical simulation models have been developed for simulating the product cold spot time-temnperature profile based on the scheduled retort temperatures. These models include those described in Ball, C. O. and Olson, F. C. W.,Sterilization in Food Technology: Theory, Practice and Calculations,McGraw-Hill Book Company, Inc., 1957; Hayakawa, K.,Experimental Formulas for Accurate Estimation of Transient Temperature of Food and Their Application to thermal Process Evaluation,Food Technology, vol. 24, no. 12, pp. 89 to 99, 1970;Thermobacteriology in Food Processing,Academic Press, New York, 1965; Teixeira, A. A.,Innovative Heat Transfer Models: From Research Lab to On-Line Implementationin Food Processing Automation II, ASAE, p. 177-184, 1992; Lanoiselle, J. L., Candau, Y., and Debray E.,Predicting Internal Temperatures of Canned Foods During Thermal Processing Using a Linear Recursive Model,J. Food Sci., Vol. 60, No. 4, 1995; Teixeira, A. A., Dixon, J. R., Zahradnik, J. W., and Zinsmeister, G. E.,Computer Optimization of Nutrient Retention in Thermal Processing of Conduction Heated Foods,Food Technology, 23:137-142, 1969; Kan-Ichi Hayakawa,Estimating Food Temperatures During Various Processing or Handling Treatments,J. of Food Science, 36:378-385, 1971; Manson, J. E., Zahradnik, J. W., and Stumbo, C. R.,Evaluation of Lethality and Nutrient Retentions of Conduction-Heating Foods in Rectangular Containers,Food Technology, 24(11):109-113, 1970; Noronha, J., Hendrickx, M., Van Loeg, A., and Tobback, P.,New Semi-empirical Approach to Handle Time-Variable Boundary Conditions During Sterilization of Non-Conductive Heating Foods,J. Food Eng., 24:249-268, 1995; and the NumeriCAL model developed by Dr. John Manson of CALWEST Technologies, licensed to FMC Corporation, and used in FMC Corporation's LOG-TEC controller.
• However, if any of the actual retort temperatures in the cooking and cooling shells drops below a corresponding scheduled cooking or cooling retort temperature, a temperature deviation occurs. Traditionally, when such a deviation occurs, the controller stops the shells' reels and prevents any of the containers {1, . . . , i, . . . , I}[0009]_linefrom being fed into or discharged from the rotary sterilizer until the deviation is cleared. But, this approach causes numerous problems. For example, significant production down time will result. And, many containers { . . . , i, . . . }_overprwill be over processed since the total lethalities { . . . , F_iover [t_f,i, t_d,i], . . . }_overpractually delivered to their product cold spots will significantly exceed the target total lethality F_targ. All of these problems may result in severe economic loss to the operator of the rotary sterilization system.
• 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}[0010]_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_iover [t_b, t_e] will be delivered to the product cold spot of each container i, where t_band t_eare the begin and end times of the batch sterilization process. An example of such an approach is described in concurrently filed and co-pending U.S. Pat. application Ser. No.09/______,entitledController 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.
• In contrast, each container i in a rotary sterilization process will receive a unique time-temperature treatment. Thus, the total lethality F[0011]_iover [t_f,i, t_d,i] that is actually delivered to each container is different. This makes it difficult to identify, while on-line and in real time, each container that will have a predicted total lethality delivered to it that is below the target total lethality F_targ. As a result, the development of a controller that provides on-line handling of a temperature deviation in a rotary sterilization process without stopping the reels of the cooking and cooling shells has been inhibited.
SUMMARY OF THE INVENTION
• In summary, the present invention comprises a rotary sterilization system, a controller for use in the rotary sterilization system, and a method performed by the controller. The system, controller, and method are used to administer a sterilization process performed on a line of containers and provide on-line handling of a deviation in a scheduled parameter during the process. The containers contain a shelf stable food product that is to be sterilized in the sterilization process. In addition to the controller, the rotary sterilization system includes a rotary sterilizer.[0012]
• The controller controls the rotary sterilizer in performing the rotary sterilization process according to scheduled parameters. When a temperature deviation below a specific scheduled temperature occurs, the controller identifies those of the containers that will in response have a total lethality predicted to be delivered to them during the rotary sterilization process that is less than a predefined target lethality. This specific scheduled parameter may be a scheduled retort temperature in a temperature zone of the rotary sterilizer through which the line of containers is conveyed. It also may be a scheduled initial product temperature for the containers or a scheduled reel speed for conveying the containers in line through the rotary sterilizer.[0013]
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a block diagram of a rotary sterilization system in accordance with the present invention.[0014]
• FIG. 2 is a block diagram of a controller of the rotary sterilization system of FIG. 1.[0015]
• FIG. 3 is an overall process flow diagram for the controller of FIG. 2 in controlling a rotary sterilization process performed by the rotary sterilization system of FIG. 1.[0016]
• FIG. 4 is a timing diagram for handling a temperature deviation according to the overall process flow diagram of FIG. 3.[0017]
• FIG. 5 is a lethality distribution diagram showing the distribution of lethalities for containers affected by the temperature deviation shown in FIG. 4.[0018]
• FIGS.[0019]6 to9 are detailed process flow diagrams for various steps of the overall process flow diagram of FIG. 3.
DETAILED DESCRIPTION OF THE INVENTION
• Referring to FIG. 1, there is shown a[0020]rotary sterilization system100 for performing a rotary sterilization process on a continuous line of containers {1, . . . , i, . . . , I}_line. Each container i contains a food product that is to be sterilized during the process. Thesystem100 comprises arotary sterilizer102, aprogrammed controller104, and ahost computer105.
• 1. Exemplary Embodiment[0021]
• In an exemplary embodiment, the[0022]rotary sterilizer102 includes a cooking shell106-1 and a cooling shell106-2 through which the containers {1, . . . , i, . . . ,I}_lineare conveyed in line. The containers are cooked in the cooking shell106-1 and cooled in the cooling shell106-2. Each of these shells hasspiral tracks108 and areel109 to convey the containers through the shell. Thereel109 imparts movement while the spiral tracks108 provide the direction for the containers to be conveyed through the shell106-1 or2.
• Furthermore, a[0023]feed device110 of therotary sterilizer102 feeds the containers {1, . . . , i, . . . , I}_linein line to the cooking shell106-1. The feed device is designed to prevent the escape of steam while loading the containers onto the reel of the cooking shell106-1. The containers are transferred from thereel109 of the cooking shell106-1 to thereel109 of the cooling shell106-2 by atransfer device112. Like the feed device, the transfer device is designed to prevent the escape of steam from the cooking shell while the containers are transferred between the reels of the cooking and cooling shells. The containers are finally off-loaded from the cooling shell's reel by adischarge device114.
• In this exemplary embodiment, the cooking shell[0024]106-1 has multiple temperature zones115-1,2, and3. The containers {1, . . . , i, . . . I}_lineare pre-cooked in the temperature zones115-1 and2 at corresponding scheduled retort temperatures T_sRT1⁰and T_sRT2⁰. The zone115-3 is used to cook the containers at a corresponding scheduled retort temperature T_sRT3⁰. Similarly, the cooling shell106-3 has temperature zones115-4 and5 in which the containers are cooled at corresponding scheduled retort temperatures T_sRT4⁰and T_sRT5⁰. However, as those skilled in the art will recognize and as will be explained later in section2, other embodiments do exist where fewer or more cooking and/or cooling shells with fewer and/or more temperature zones are used.
• At each sample real time t[0025]_r(e.g., every 0.1 to 1 seconds) of the rotary sterilization process, the sensors116-1, . . . , 4 of thehydrostatic sterilizer102 respectively sense the actual retort temperatures T_aRT1(t_r), . . . , T_aRT5(t_r) in the corresponding temperature zones115-1, . . . , 5 of the cooking and cooling shells106-1 and2. Similarly, the rotary sterilizer'ssensor107 senses the actual reel speed v_a(t_r) of the reels of the cooking and cooling shells at each each sample real time t_r. Finally, thefeed device110 periodically (e.g., every 20 to 30 minutes) removes a container being fed into the rotary sterilizer and asensor117 of the rotary sterilizer senses its actual initial product temperature T_aIP(t_r) at that time t_r.
• The[0026]controller104 administers the rotary sterilization process by controlling therotary sterilizer102 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_aIP(t_r) and T_aRT1(t_r), . . . , T_aRT5(t_r) sensed by thesensors117 and116-1, . . . ,5 at each sample real time t_r, the actual reel speed v_a(t_r) sensed by thesensor107, and the actual initial product temperature T_aIP(t_r) sensed by thesensor117.
• The[0027]host computer105 is used to provide input information, namely input parameters and software, used by thecontroller104 in administering the rotary sterilization process. The host computer is also used to receive, process, and display output information about the process which is generated by the controller.
• 1.a. Hardware and Software Configuration of[0028]Controller104
• Turning to FIG. 2, the[0029]controller104 comprises amain control computer118 that includes a microprocessor (i.e., CPU)119, aprimary memory120, and asecondary memory121. The microprocessor executes anoperating system122, aprocess control program123, aprocess scheduling program124, and atemperature deviation program125 of the controller. The operating system and programs are loaded from the secondary memory into the primary memory during execution.
• The[0030]operating system122 and theprograms123 to125 are executed by themicroprocessor119 in response to commands issued by the operator. These commands may be issued with auser interface126 of themain control computer118 and/or thehost computer105 via ahost computer interface127 of thecontroller104. The operating system controls and coordinates the execution of the other programs.Data128 generated by the operating system and programs during execution anddata128 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.
• The[0031]controller104 also comprisescontrol circuitry129. The control circuitry includes circuits, microprocessors, memories, and software to administer the rotary sterilization process by generating control signals that control the sequential operation of therotary sterilizer102. As alluded to earlier, the software may be downloaded from thehost computer105 and provided to the control circuitry by theprocess control program123. The control signals are generated in response to commands generated by this program and issued to the control circuitry from themicroprocessor119 via a control circuitry interface130 of themain control computer118.
• Furthermore, at each sample real time t[0032]_rof the rotary sterilization process, thecontrol circuitry129 receives sensor signals from thesensors107,117, and116-1, . . . ,5 that represent the actual reel speed v_a(t_r) and the actual initial product and retort temperatures T_aIP(t_r) and T_aRT1(t_r), . . . , T_aRT5(t_r). The control circuitry generates the control signals for controlling therotary sterilizer102 in response to these sensed parameters. These sensed parameters are also provided to themicroprocessor119 via the control circuitry interface130 and recorded by theprocess control program123 asdata128 in theprimary memory120. In this way, the process control program compiles and records in theprimary memory120 an actual reel time-speed profile v_a(t), an actual initial product time-temperature profile T_aIP(t), and actual retort time-temperature profiles T_aRT1(t), . . . , T_aRT5(t) for the corresponding temperature zones115-1, . . . ,5. These profiles are used in the manner described later for providing on-line handling of temperature deviations during the rotary sterilization process.
• The sensors[0033]116-1, . . . ,5 are preferably located in the slowest heating regions of the temperature zones115-1, . . . ,5 to provide conservative estimates of the actual retort temperatures T_aRT1(t_r), . . . , T_aRT5(t_r). However, if this is not possible, theprocess control program123 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 totemperature distribution data128 in theprimary memory120 generated from heating and cooling temperature distribution tests conducted on the temperature zones.
• As mentioned earlier, the[0034]operating system122 and theother programs123 to125 are normally stored in thesecondary memory121 and then loaded into theprimary memory120 during execution. The secondary memory comprises one (or multiple) computer readable memory(ies)132 that is(are) readable by themain control computer118 of thecontroller104. The computer readable memory(ies) is(are) therefore used to direct the controller in controlling the rotary sterilization process. The computer readable memory(ies) may comprise a PROM (programmable read only memory) that stores the operating system and/or the other programs. Alternatively or additionally, the computer readable memory(ies) may comprise a magnetic or CD ROM storage disc that stores the operating system and/or the other programs. The computer readable memory(ies) in this case is(are) readable by the main control computer with a magnetic or CD ROM storage disk drive of the secondary memory. Moreover, the operating system and/or the other programs could also be downloaded to the computer readable memory(ies) or the primary memory from thehost computer105 via thehost computer interface127.
• The[0035]controller104 controls the rotary sterilization process according to the flow and timing diagrams of FIGS.3 to9. In doing so, a finite difference simulation model is used by theprocess scheduling program124 to simulate a scheduled product cold spot time-temperature profile T_CS(t)_i⁰that applies to all of the containers {1, . . . i, . . . , I}_line. Similarly, thetemperature deviation program125 uses the model to simulate corresponding product cold spot time-temperature profiles { . . . , T_CS(t)_i^j, . . . } for corresponding selected containers { . . . , i, . . . }_selat each sample real time t_rduring 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 to9.
1.b. Overall Process Flow
• In the[0036]first step134 for controlling the rotary sterilization process according to the overall process flow of FIG. 3, the input parameters for the rotary sterilization process are defined and provided to thecontroller104. The input parameters include a predefined sampling time period Δt_rfor each real time increment [t_r-Δt, t_r] from the previous sample real time t_r-Δt_rto the current sample real time t_rduring the process. The input parameters also include a initially scheduled product temperature T_sIPfor the food product in the containers being processed. The input parameters further include the traditional heating and cooling factors j_h, f_h, x_bh, f₂, j_c, and f_cto be used in the simulation model. The heating factors j_h, f_h, x_bh, and f₂are 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_cand f_care 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_REF. Also included in the input parameters is the earlier discussed target total lethality F_targand earlier discussed scheduled retort temperatures T_sRT1⁰, . . . , T_sRT5⁰. Finally, the input parameters include the minimum and maximum reel speeds v_minand v_maxand reel step information S for thereels109 andspiral tracks108 of the cooking and cooling shells106-1 and2 and length and location information L₁, . . . , L₅for the corresponding temperature zones115-1, . . . ,5 in the shells.
• In order to perform[0037]step134, the operator issues commands with theuser interface126 and/or thehost computer105 to invoke theprocess control program123. Then, the operator enters the input parameters T_IP, j_h, f_h, x_bh, f₂, j_c, f_c, F_targ, T_sRT1⁰, . . . , T_sRT5⁰, v_min, v_max, S, and L₁, . . . , L₅with theuser interface126 and/or thehost computer105. Theprocess control program123 loads the entered input parameters into theprimary memory120 for use by theprograms123 to125. The execution of these programs is controlled and coordinated by the process control program in the manner discussed next.
• The[0038]process control program123 first invokes theprocess scheduling program124. Instep135, the process scheduling program simulates the entire rotary sterilization process to be administered to a container i to define an initially scheduled reel speed v_s⁰for the reels of the cooking and cooling shells106-1 and2. This also results in an initially scheduled time-temperature treatment T_sRT(t)_i⁰that is to be given to each container i. This treatment includes pre-cooking portions at the scheduled retort temperatures T_sRT1⁰and T_sRT2⁰over corresponding initially scheduled time durations Δt₁⁰and Δt₂⁰. The treatment also includes a cooking portion at the scheduled retort temperature T_sRT3⁰over a corresponding initially scheduled time duration Δt₃⁰. Finally, the treatment includes cooling portions at the scheduled retort temperatures T_sRT4⁰and T_sRT5⁰over corresponding initially scheduled time durations Δt₄⁰and Δt₅⁰. The precise manner in which step135 is performed is discussed in greater detail in section 1.c., but will be briefly discussed next.
• The initially scheduled reel speed v[0039]_s⁰and the initially scheduled total time-temperature treatment T_sRT(t)_i⁰are defined by using the simulation model mentioned earlier. Specifically, theprocess scheduling program124 uses the simulation model to iteratively and incrementally simulate an initially predicted product cold spot time-temperature profile T_CS(t)_i⁰that is predicted to occur at the product cold spot of each container i during the rotary sterilization process. This simulation is based on the input parameters T_sIP, j_h, f_h, x_bh, f₂, j_c, f_c, and T_sRT1⁰, . . . , T_sRT5⁰.
• The[0040]process scheduling program124 also iteratively and incrementally computes an initially predicted lethality F_i⁰that is predicted to be delivered to the product cold spot of each container i during the rotary sterilization process. In doing so, the program iteratively and incrementally computes a predicted total lethality F_i⁰that satisfies the target total lethality F_targand is predicted to be delivered to the product cold spot over a simulated total time interval [0, Δt₁⁰+ . . . +Δt₅⁰]. This computation is made based on the product cold spot time-temperature profile T_CS(t)_i⁰over this total time duration and the input parameters z and T_REF. Furthermore, the lethality equation described earlier is used to make this computation, where t_m=0, t_k=Δt₁⁰+ . . . +Δt₅⁰, T_CS(t)=T_CS(t)_i⁰, and F_i=F_i⁰.
• The initially predicted total lethality F[0041]_i⁰over [0, Δt₁⁰+ . . . +Δt₅⁰] is iteratively and incrementally computed until the initially scheduled reel speed v_s⁰is determined for which this lethality satisfies the target total lethality F_targ. Moreover, the initially scheduled time durations Δt₁⁰, . . . , Δt₅⁰are determined from the reel speed v_s⁰, the reel step information S, and the temperature zone length and location information L₁, . . . , L₅. Thus, definition of the reel speed v_s⁰also includes definition of the pre-cooking, cooking, and cooling portions of the initially scheduled total time-temperature treatment T_sRT(t)⁰on which the portions of the profile T_CS(t)⁰over the time durations Δt₁⁰, . . . , Δt₅⁰are based.
• The[0042]process control program123 controls the administration of the rotary sterilization process insteps136 to149. In doing so, it first sets a counterj to zero instep136. This counter is used to count each time that the currently scheduled reel speed v_s^jis adjusted during the rotary sterilization process.
• Then, at the current sample real time t[0043]_r, theprocess control program123 causes thecontrol circuitry129 instep137 to administer the rotary sterilization process at the currently scheduled reel speed v_s^jand at the scheduled retort temperatures T_sRT1⁰, . . . , T_sRT5⁰in the corresponding temperature zones115-1, . . . ,5. In doing so, the control circuitry appropriately controls therotary sterilizer102 and monitors the actual retort temperatures T_aRT1(t_r), . . . , T_aRT5(t_r) in the corresponding temperature zones115-1, . . . ,5 at the time t_rto verify that they are at least equal to the corresponding scheduled retort temperatures T_sRT1⁰, . . . , T_sRT5⁰. In this embodiment of thecontroller104, the scheduled retort temperatures will remain the same throughout the rotary sterilization process regardless if temperature deviations occur in the temperature zones. Thus, if such a temperature deviation does occur in a particular temperature zone115-n, then the control circuitry administers corrections at the time t_rso that the actual retort temperature T_aRTn(t_r) in the temperature zone115-n will eventually be brought up to at least the corresponding temperature T_sRTn⁰.
• Then the[0044]process control program123 waits for the next sample real time t_r=t_r+Δt_rinstep138. Instep139, this program records the actual retort temperatures T_aRT1(t_r), . . . , T_aRT5(t_r) in the temperature zones115-1, . . . ,5 at each sample real time t_r. By doing so, theprogram123 compiles the corresponding actual retort time-temperature treatments T_aRT1(t), . . . , T_aRT5(t). Similarly, the program records the actual initial product temperature T_aIP(t_r) periodically sensed by thesensor117 to compile the actual initial product time-temperature profile T_aIP(t). Furthermore, the program also records the currently scheduled reel speed v_s^jat each time t_r. This is done to compile a time-reel speed profile v(t) for the rotary sterilization process to provide a record of the changes in the reel speed v_s^j.
• Then, in[0045]step140, theprocess control program123 determines whether any temperature deviations are occurring at the time t_rin the temperature zones115-1, . . . ,5. In doing so, theprogram123 monitors each temperature T_aRTn(t_r) to determine if it is less than the corresponding scheduled cooking or cooling retort temperature T_sRTn⁰.
• If no deviation is occurring, then the[0046]process control program123 proceeds to step141. Any of the under processed containers { . . . , i, . . . }_underprthat were identified instep148 for segregation and are being discharged by thedischarge device114 at the current sample real time t_rare then segregated instep141 by the discharge device. The process control program causes thecontrol circuitry129 to control thedischarge device114 in performing this segregation in the manner discussed later. Instep149, the process control program sets the currently scheduled reel speed v_s^jto the initially scheduled reel speed v_s⁰if all of the containers { . . . , i, . . . }_affaffected by a temperature deviation have been discharged. Bothsteps141 and149 are discussed later in more detail. The process control program then administers the rotary sterilization process instep137 and waits for the next sample real time t_r=t_r+Δt_rinstep138 to repeat thesteps139 to149.
• However, if the[0047]process control program123 does determine instep140 that a temperature deviation is occurring in a temperature zone115-n at the current sample real time t_r, then the process control program invokes thetemperature deviation program125. In the example shown in FIG. 4, the temperature deviation occurs in the temperature zone115-3. Instep142, theprogram125 identifies the container i that currently at the time t_rhas the minimum total lethality F_i^jpredicted to be delivered to its product cold spot over its currently scheduled total time interval [t_f,i, t_d,i^j]. This minimum lethality container i is identified from among the containers { . . . , i, . . . }_affthat are currently affected by the temperature deviation. These affected containers are those of the containers {1, . . . , i, . . . , I}_linethat are at the time t_rcurrently in the temperature zone115-n in which the temperature deviation is occurring. This is determined using the reel step information S, the reel time-speed profile v(t) compiled instep139, and the length and location information L₁, . . . , L₅for the temperature zones115-1, . . . ,5.
• In one approach for identifying the minimum lethality container i from among the affected containers { . . . , i, . . . }[0048]_aff, thetemperature deviation program125 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_i^jover [t_f,i, t_d,i^j], . . . }_selfor containers { . . . , i, . . . }_selselected to be evaluated. Based on these lethalities, the program iteratively bisects the list of affected containers to select the selected containers from among the affected containers until the minimum lethality container i is identified.
• In a variation of the approach just described, the[0049]temperature deviation program125 may initially use predefined intervals to initially select containers { . . . , i, . . . }_intat the intervals for evaluation. Then, around those of the initially selected containers that have the lowest predicted total lethalities {. . . , F_i^jover [t_f,i, t_d,i^j], . . . }_int, the optimization search technique just described is used.
• In still another approach for identifying the minimum lethality container i, the[0050]temperature deviation program125 may select all of the affected containers { . . . , i, . . . }_affas the selected containers { . . . , i, . . . }_selfor evaluation. In doing so, the program computes at each sample real time t_rthe predicted total lethality F_i^jover [t_f,i, t_d,i^j] for each container i. From the computed lethalities {. . . , F_i^jover [t_f,i, t_d,i^j], . . . }_selfor the selected containers, the minimum lethality container i is identified.
• In each of the approaches just described, the predicted total lethality F[0051]_i^jover [t_f,i, t_d,i^j] for each selected container i is computed in the same way. Specifically, thetemperature deviation program125 first computes an actual current lethality F_i^jdelivered to the container's product cold spot over the actual time interval [t_f,i, t_r] that the container has been in therotary sterilizer102. This is done by simulating the portion of the rotary sterilization process that was actually administered over this time interval. In doing so, the simulation model mentioned earlier is used to iteratively and incrementally simulate the actual portion of the product cold spot time-temperature profile T_CS(t)_i^jover this time interval for the container i. This is done based on the input parameters j_h, f_h, x_bh, f₂, j_c, and f_c, the actual initial product temperature T_aIP(t_f,i) for the container i, and the portions of the actual retort time-temperature profiles T_aRT1(t), . . . , T_aRTn(t) respectively over the actual time intervals [t_f,i, t_1,i^j], . . . , (t_n-1,i^j, t_r] that the container was in the temperature zones115-1, . . . , n. Here, n identifies the temperature zone115-n in which the temperature deviation is occurring. As mentioned earlier, in the example of FIG. 4, this is the temperature zone115-3.
• The actual initial product temperature T[0052]_aIP(t_f,i) for the container i is obtained from the actual initial product time-temperature profile T_aIP(t) compiled instep139. The actual time intervals [t_f,i, t_1,i^j], . . . , (t_n-1,^j, t_r] for the selected container i are determined by thetemperature deviation program125 from the reel time-speed profile v(t), the reel step information S, and the temperature zone length and location information L_l, . . . , L_n.
• In the example of FIG. 4, the temperature deviation occurs in the temperature zone[0053]115-3. Thus, the portion of the product cold spot temperature profile T_CS(t)_i^jthat actually occurred over the actual time interval [t_f,i,_r] is based in this case on the portions of the actual retort time-temperature profiles T_aRT1(t), T_aRT2(t), and T_aRT3(t) respectively over the actual time intervals [t_f,i, t_1,i^j], (t_1,i^j, t_2,i^j,], and (t_2,i^j, t_r]. The time intervals [t_f,i, t_1,i^j] and (t_1,i^j, t_2,i^j,] have the initially scheduled time durations Δt₁⁰and Δt₂⁰since the temperature deviation began at the deviation begin time t_ewhile the container i was in the temperature zone115-3. If, however, this container was in another temperature zone115-1 or2 when the deviation began, then the time intervals [t_f,i, t_1,i^j] and/or (t_1,i^j, t_2,i^j,] would have different time durations Δt₁^jand/or Δt₂^jbecause the reel speed v_s^jwould have been changed while the container was in that temperature zone.
• From the actual portion of the product cold spot time-temperature profile T[0054]_CS(t)_i^jover [t_f,i, t_r] and the input parameters z and T_REF, thetemperature deviation program125 iteratively and incrementally computes the actual current lethality F_i^jthat has been delivered to the product cold spot of the selected container i over the actual time interval [t_f,i, t_r]. This is done using the lethality equation described earlier, where t_m=t_f,i, t_k=t_r, T_CS(t)=T_CS(t)_i^j, and F_i=F_i^j. The precise manner in which the actual current lethality is computed instep142 is discussed in greater detail in section 1.d.
• Then, the[0055]temperature deviation program125 simulates the remaining portion of the rotary sterilization process that is predicted to be administered to the selected container i over the scheduled remaining time interval (t_r, t_d,i^j] assuming that the temperature deviation ends after the time t_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_CS(t)_i^jbased on the input parameters j_h, f_h, X_bh, f₂, j_c, and f_c, the actual product cold spot temperature T_CS(t_r)_i^jat the time t_r, and the scheduled retort temperatures T_sRTn⁰, . . . , T_sRT5⁰over the currently scheduled remaining time intervals (t_r, t_n,i^j], . . . , t_4,i^j,t_d,i^j].
• The actual product cold spot temperature T[0056]_CS(t_r)_i^jfor the selected container i is obtained from the actual portion of the product cold spot time-temperature profile T_CS(t)_i^jover [t_f,i, t_r] that was just described. Moreover, the currently scheduled time intervals (t_r, t_n,i^j], . . . , (t_4,i^j,t_d,i^j] for the container i are determined by thetemperature deviation program125 from the reel time-speed profile v(t), the reel step information S, and the temperature zone length and location information L₁, . . . , L₅.
• In the example of FIG. 4, the temperature deviation occurs in the temperature zone[0057]115-3. Thus, the predicted remaining portion of the product cold spot temperature profile T_CS(t)_i^jis based on the scheduled retort temperatures T_sRT3⁰, T_sRT4⁰, and T_sRT5⁰respectively over the currently scheduled remaining time intervals (t_r, t_3,i^j], (t_3,i^j,t_4,i^j], and (t_4,i^j,t_d,i^j]. In this example, the time intervals (t_2,i^j, t_3,i^j], (t_3,i^j,t_4,i^j] and (t_4,i^j,t_d,i^j] respectively have re-scheduled time durations Δt₃^j, Δt₄^j, and Δt₅^jthat are different than the initially scheduled time durations Δt₃⁰, Δt₄⁰, and Δt₅⁰since the currently scheduled reel speed v_s^jat the current sample real time t_rhas been re-scheduled from the initially scheduled reel speed v_s⁰.
• The[0058]temperature deviation program125 iteratively and incrementally computes the total lethality F_i^jpredicted to be delivered to the product cold spot of the selected container i over the scheduled total time interval [t_f,i, t_d,i^j]. This is done based on the predicted remaining portion of the product cold spot time-temperature profile T_CS(t)_i^jover (t_r, t_d,i^j], the actual current lethality F_i^jover [t_f,i, t_r] that was just described, and the input parameters z and T_REF. This is also done using the lethality equation described earlier, where t_m=t_r, t_k=t_d,i^j, T_CS(t)=T_CS(t)_i^j, and F_i=F_i^j. The predicted total lethality is the sum of the actual current lethality and a predicted remaining lethality F_i^jthat is predicted to be delivered to the container's product cold spot over the time interval [t_r, t_d,i^j]. The precise manner in which the predicted total lethality is computed instep142 is discussed in greater detail in section 1.e.
• Then, in[0059]step143, thetemperature deviation program125 determines at the current sample real time t_rif the container i with the minimum predicted total lethality F_i^jover [t_f,i, t_d,i^j] is less than the target total lethality F_targ. If it is not, then this means that all of the affected containers { . . . , i, . . . }_affalso have predicted total lethalities { . . . , F_i^jover [t_f,i, t_d,i^j], . . . }_affthat are at least equal to the target total lethality. In this case, theprocess control program123 proceeds to step141 and causes any of the previously identified under processed containers { . . . , i, . . . }_underprthat are being discharged at the time t_rto be segregated. Then, in the manner discussed earlier, theprocess control program123 administers the rotary sterilization process instep137 and waits for the next sample real time t_r=t_r+Δt_rinstep138 to repeat thesteps139 to148.
• In this embodiment, if it is determined in[0060]step143 that the minimum total lethality F_i^jover [t_f,i, t_d,i^j] is less than the target total lethality F_targ, then thetemperature deviation program125 determines instep144 if the currently scheduled reel speed v_s^jis set to the minimum reel speed v_min. If it is not, then the program increments the counter j instep145 and defines a re-scheduled (or adjusted) reel speed v_s^jinstep146.
• In[0061]step146, the re-scheduled reel speed v_s^jis defined in a similar manner to the way in which the initially scheduled reel speed v_s⁰is defined instep135. But, in this case the actual product cold spot temperature T_CS(t_r)_i^jat the time t_rand the actual current lethality F_i^jover [t_f,i, t_r] for the minimum lethality container i are used in simulating the remaining portion of the rotary sterilization process in order to compute a predicted total lethality F_i^jover [t_f,i, t_d,i^j]. This is done in a similar manner to that described earlier for computing the predicted total lethality for a container instep142. But, similar to step135, this is done iteratively and incrementally until the reel speed is determined for which the predicted total lethality satisfies the total target lethality F_targor the reel speed equals the minimum reel speed v_min. The precise manner in which step146 is performed is discussed in greater detail in section 1.f, but will be briefly discussed next.
• The definition of the re-scheduled reel speed therefore also results in the definition of a re-scheduled remaining time-temperature treatment T[0062]_sRT(t)_i^j. The treatment includes a remaining cooking portion at the scheduled retort temperature T_sRT3⁰over a corresponding re-scheduled time duration Δt₃^j. Similarly, the treatment also includes cooling portions at the scheduled retort temperatures T_sRT4⁰and T_sRT5⁰over corresponding re-scheduled time durations Δt₄^jand Δt₅^j.
• Ideally, it is desired that the minimum predicted total lethality F[0063]_i^jover [t_f,i, t_d,i^j] for the minimum lethality container i will satisfy the target total lethality F_targ. But, as just mentioned, the re-scheduled reel speed v_s^jmay be limited to the minimum reel speed v_min. In this case, the minimum predicted total lethality will not satisfy the target total lethality F_targ. If thetemperature deviation program125 determines this to be the case instep147, then this means that under processed containers { . . . , i, . . . }_underprfrom among the affected containers { . . . , i, . . . }_affwill have predicted total lethalities { . . . , F_i^jover [t_f,i, t_d,i^j], . . . }_underprthat are less than the target total lethality. The minimum lethality container i is of course one of the under processed containers. The under processed containers are to be segregated and are identified at the current real sample time t_rinstep148 by the program.
• FIG. 5 shows the distribution of the affected containers { . . . , i, . . . }[0064]_affand the under processed containers { . . . , i, . . . }_underprto be segregated at the time t_r. In identifying the under processed containers instep148, theprogram125 uses a similar approach as that used instep142 to identify the minimum lethality container i. But, in this case, the additional criteria of the target total lethality F_targis used to expand the search.
• Once the under processed containers { . . . , i, . . . }[0065]_underprhave been identified at the current real sample time t_r, theprocess control program123 then proceeds to step141. As discussed earlier, this program causes thecontrol circuitry129 to control thedischarge device114 in segregating any of the under processed containers that are being discharged at the current sample real time t_r. In order to segregate the under processed containers, the process control program tracks these containers to determine when they will be discharged. This is done using the reel time-speed profile v(t), the reel step information S, and the temperature zone length and location information L₁, . . . , L₅.
• The[0066]steps137 to149 are repeated until the temperature deviation is cleared. In this way, at each sample real time t_rduring the deviation, the list of under processed containers { . . . , i, . . . }_underprat the time t_ris combined with the list from the previous sample real time t_r. As a result, the list of under processed containers is dynamically updated and maintained. Since these under processed containers are segregated when discharged instep141, this will ensure that only those of the containers {1, . . . , i, . . . I}_linethat are adequately processed are released for distribution.
• The list of affected containers { . . . , i, . . . }[0067]_affis also dynamically updated and maintained in the same manner as the list of under processed containers { . . . , i, . . . }_underpr. When the temperature deviation is cleared, this list will remain the same and theprocess control program123 tracks the containers in this list until they have all been discharged. This tracking is done in the same manner in which the under processed containers are tracked. Theprocess control program123 will then set the currently scheduled reel speed v_s^jback to the initially scheduled reel speed v_s⁰instep149.
• Furthermore, the[0068]controller104 has the unique feature of being able to handle multiple temperature deviations. For example, if another temperature deviation does occur, then thesteps137 to149 are repeated during this deviation. Therefore, even if a selected container i is exposed to multiple temperature deviations, the predicted total lethality F_i^jover [t_f,i, t_d,i^j] that will be delivered to it can be accurately determined based on those of the actual retort temperature profiles T_aRT1(t), . . . , T_aRT5(t) that it has been treated with over the rotary sterilization process. Moreover, this results in the list of under processed containers { . . . , i, . . . }_underprbeing further updated and expanded.
• 1.c. Detailed Process Flow for[0069]Step135 of FIG. 3
• FIG. 6 shows the detailed process flow that the[0070]process scheduling program124 uses instep135 of FIG. 3 to define the initially scheduled reel speed v_s⁰. In doing so, this program iteratively performs a simulation of the rotary sterilization process that is predicted to be administered to each container i in sub-steps150 to160 ofstep135.
• In[0071]step150, theprocess scheduling program124 first defines the initially scheduled reel speed v_s⁰as the maximum reel speed v_max. Then, instep151, the program defines the time durations Δt₁⁰, . . . , Δt₅⁰for how long each container i is scheduled to be in the respective temperature zones115-1, . . . ,5. This is done based on the initially scheduled reel speed, the reel step information S for thereels109 andspiral tracks108 of the cooking and cooling shells106-1 and2, and the length and location information L₁, . . . , L₅for the temperature zones.
• In[0072]step152, the current sample simulation time t_sis initially set to zero by theprocess scheduling program124. This is the begin time of the simulated rotary sterilization process for the container i. The program also initially sets the predicted product cold spot temperature T_CS(t_s)_i⁰of the container's product cold spot at this time to the scheduled initial product temperature T_sIP. Similarly, the lethality F_i⁰predicted to be delivered to the product cold spot over the current simulation time interval [0, t_s] is initially set by the program to zero.
• [0073]Steps153 to157 are then performed by theprocess scheduling program124 in each iteration of the simulation. Instep153 of each iteration, the program increments the current sample simulation time t_sby the amount of the sampling period Δt_r. This results in a new current sample simulation time t_s.
• Then, in[0074]step154 of each iteration, theprocess scheduling program124 simulates the portion of the product cold spot time-temperature profile T_CS(t)_i⁰predicted to occur at the product cold spot of the container i over the current simulation time increment [t_s-Δt_r, t_s]. This is done using the simulation model discussed earlier and is based on the predicted product cold spot temperature T_CS(t_s-Δt_r)_i⁰for the product cold spot at the previous sample simulation time t_s-Δt_rand the heating and cooling factors j_h, f_h, x_bh, f₂, j_c, and f_c. In the first iteration, this product cold spot temperature will be the scheduled initial product temperature T_sIPfromstep152. 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_s-2Δt_r, t_s-Δt_r] that was simulated instep154 of the previous iteration. Moreover, the simulation is also based on the respective scheduled retort temperatures T_sRT1⁰, . . . , T_sRT5⁰when the current sample simulation time t_sis within the corresponding simulation time intervals [0, Δt₁⁰], . . . , [Δt₁⁰+. . . +Δt₄⁰, Δt₅⁰]. These time intervals indicate how long the container i is scheduled to be in the respective temperature zones115-1, . . . ,5.
• The lethality F[0075]_i⁰that is predicted to be delivered to the product cold spot of the container i over the current simulation time increment [t_s-Δt_r, t_s] is then computed by theprocess scheduling program124 instep155 of each iteration. This is done based on the portion of the product cold spot time-temperature profile T_CS(t)_i⁰predicted over this time increment and the input parameters z and T_REF. This is also done in accordance with the lethality equation described earlier, where t_m=t_s-Δt_r, t_k=t_s, T_CS(t)=T_CS(t)_i⁰, and F_i=F_i⁰.
• In[0076]step156 of each iteration, theprocess scheduling program124 computes the lethality F_i⁰predicted to be delivered to the product cold spot of the container i over the current simulation time interval [0, t_s]. This is done by adding the predicted lethality F_i⁰over the current simulation time increment [t_s-Δt_r, t_s] instep154 to the lethality F_i⁰predicted to be delivered to the product cold spot over the previous simulation time interval [0, t_s-Δt_r]. In the first iteration, the predicted lethality over the previous simulation time interval is zero fromstep152. In each subsequent iteration, this lethality is computed instep156 of the previous iteration.
• Then, in[0077]step157 of each iteration, theprocess scheduling program124 determines whether the current simulation time t_shas reached the end time [Δt₁⁰+ . . . +Δt₅⁰] of the simulated rotary sterilization process for the container i. If it is not, then the program returns to step153 for the next iteration. In this way, steps153 to157 are repeated in each subsequent iteration until it is determined that the end time for the simulated rotary sterilization process has been reached. When this finally occurs, the program sets instep158 the lethality F_i^jover the current simulation time interval [0, t_s] to the total lethality F_i^jpredicted to be delivered to the container's product cold spot over the total simulation time interval [0, Δt₁⁰+ . . . +Δt₅⁰].
• When this finally occurs, the[0078]process scheduling program124 determines instep158 whether the predicted total lethality F_i⁰over [0, Δt₁⁰+ . . . +Δt₅⁰] is at least equal to the target total lethality F_targ. If it is not, then the program decrements instep160 the initially scheduled reel speed v_s⁰by a predefined reel speed offset Δv. This results in the re-definition of this reel speed.Steps151 to160 are then repeated untilstep159 is satisfied. The reel speed for which step159 is satisfied is then used insteps136 to148 of FIG. 3 in the manner discussed earlier.
• 1.d. Detailed Process Flow for Computing Lethality F[0079]_i^jover [t_f,i, t_r) inSteps142 and148 of FIG. 3
• FIG. 7 shows the detailed process flow that the[0080]temperature deviation program125 uses insteps142 and148 of FIG. 3 to compute the actual current lethality F_i^jdelivered to the product cold spot of the container i over the actual time interval [t_f,i, t_r] that the container has been in therotary sterilizer102. This is done by iteratively performingsub-steps161 to168 ofsteps142 and148 to simulate the actual portion of the rotary sterilization process that has been administered to the container's product cold spot over this time interval. Here, steps161 to168 are respectively similar tosteps151 to158 of FIG. 6 and discussed in section 1.c., except for the differences discussed next.
• In[0081]step161, thetemperature deviation program125 defines the actual time intervals [t_f,i, t_1,i^j], . . . , (t_n−1,i^j, t_r] that the container i has actually been in the respective temperature zones115-1, . . . , n up to the current sample real time t_r. In this step, the definition of these time intervals is based on the accumulated reel time-speed profile v(t).
• In[0082]step162, thetemperature deviation program125 initially sets the product cold spot temperature T_CS(t_s)_i^jfor the product cold spot of the container i at the initial sample simulation time t_sto the actual initial product temperature T_aIP(t_f,i). This temperature is obtained from the actual initial product time-temperature profile T_aIP(t). Moreover, the program initially sets the actual lethality F_i^jdelivered to the product cold spot over the current simulation time interval [t_f,i, t_s] to zero.
• In[0083]step164 of each iteration, theprocess scheduling program124 simulates the portion of the product cold spot time-temperature profile T_CS(t)_i^jthat actually occurred at the product cold spot of the container i over the current simulation time increment [t_s-Δt_r, t_s]. This simulation is based on the respective actual retort temperatures T_aRT1(t_s), . . . , T_aRTn(t_s) when the current simulation time t_sis within the corresponding simulation time intervals [t_f,i, t_1,i^j], . . . , (t_n−1,i^j, t_r]. These actual retort temperatures are obtained from the corresponding actual retort time-temperature profiles T_aRT1(t), . . . , T_aRTn(t).
• The actual lethality F[0084]_i^jthat was delivered to the product cold spot of the container i over the current simulation time increment [t_s-Δt_r, t_s] is then computed by thetemperature deviation program125 instep165 of each iteration. This is done based on the actual portion of the product cold spot time-temperature profile T_CS(t)_i^jthat was simulated over this time increment. In this case, T_CS(t)=T_CS(t)_i^jand F_i=F_i^jin the lethality equation described earlier.
• In[0085]step166 of each iteration, thetemperature deviation program125 computes the actual lethality F_i^jdelivered to the product cold spot of the container i over the current simulation time interval [t_f,i, t_s]. This is done by adding the actual lethality F_i^jover the current simulation time increment [t_s-Δt_r, t_s] instep164 to the actual lethality F_i^jover the previous simulation time interval [t_f,i, t_s-Δt_r].
• Then, in[0086]step167 of each iteration, thetemperature deviation program125 determines whether the current simulation time t_shas reached the current sample real time t_r. If it is not, then the program returns to step163 for the next iteration. In this way, steps163 to167 are repeated in each subsequent iteration until it is determined that the current sample real time has been reached. When this finally occurs, thetemperature deviation program125 sets instep168 the lethality F_i^jover the current simulation time interval [t_f,i, t_s] to the actual current lethality F_i^jover the actual time interval [t_f,i, t_r] and the product cold spot temperature T_CS(t_s)_i^jfor the container at the current sample simulation time to the actual product cold spot temperature T_CS(t_r)_i^jat the current sample real time.
• 1.e. Detailed Process Flow for Computing Lethality F[0087]_i^jover [t_f,i, t_d,i^j] inSteps142 and148 of FIG. 3
• FIG. 8 shows the detailed process flow that the[0088]temperature deviation program125 uses insteps142 and148 of FIG. 3 to compute the lethality F_i^jpredicted to be delivered to the product cold spot of a selected container over the total time interval [t_f,i, t_d,i^j] that the container is in therotary sterilizer102. In this case, the program iteratively performs a simulation of the predicted remaining portion of the rotary sterilization process to be administered to this container using sub-steps169 to176 ofsteps142 and148. Likesteps161 to168,steps169 to176 are respectively similar tosteps151 to158 of FIG. 6 and discussed in section 1.c., except for the differences discussed next.
• In[0089]step169, thetemperature deviation program125 defines the remaining time intervals (t_r, t_n,1^j], . . . , (t_4,i^j, t_d,i^j] that the container i is predicted to be in the respective temperature zones115-n, . . . ,5 after the current sample real time t_r. The definition of these time intervals instep169 is based on the currently scheduled reel speed v_s^j.
• In[0090]step170, thetemperature deviation program125 initially sets the initial sample simulation time t_sto the current sample real time t_r. The program also initially sets the predicted product cold spot temperature T_CS(t_s)_i^jfor the product cold spot of the container i at this sample simulation time to the actual product cold spot temperature T_CS(t_r)_i^jobtained fromstep168 of FIG. 7. Moreover, the program initially sets the predicted lethality F_i^jto be delivered to the product cold spot over the current simulation time interval [t_f,i, t_s] to the actual lethality F_i^jover the actual time interval [t_f,i, t_r] also obtained fromstep168.
• In[0091]step172 of each iteration, thetemperature deviation program125 simulates the portion of the product cold spot time-temperature profile T_CS(t)_i^jthat is predicted to occur at the product cold spot of the container i over the current simulation time increment [t_s-Δt_r, t_s]. The simulation is based on the respective scheduled retort temperatures T_sRTn⁰, . . . , T_sRT5⁰when the current simulation time t_sis within the corresponding simulation time intervals (t_r, t_n,i^j], . . . , (t_4,i^j, t_d,i^j].
• The lethality F[0092]_i^jthat is predicted to be delivered over the current simulation time increment [t_s-Δt_r, t_s] is then computed by thetemperature deviation program125 instep173 of each iteration. This is done based on the predicted portion of the product cold spot time-temperature profile T_CS(t)_i^jthat was simulated over this time increment instep172.
• In[0093]step174 of each iteration, thetemperature deviation program125 computes the lethality F_i^jpredicted to be delivered to the product cold spot of the container i over the current simulation time interval [t_f,i, t_s]. This is done by adding the predicted lethality F_i^jover the current simulation time increment [t_s-Δt_r, t_s] fromstep173 to the predicted lethality F_i^jover the previous simulation time interval [t_f,i, t_s-Δt_r].
• Then, in[0094]step175 of each iteration, thetemperature deviation program125 determines whether the current sample simulation time t_shas reached the predicted discharge time t_d,i^jfor the container i. If it has not, then the program returns to step171 for the next iteration. In this way, steps171 to175 are repeated in each subsequent iteration until it is determined that the predicted discharge time has been reached. When this finally occurs, the program sets instep176 the lethality F_i^jover the current simulation time interval [t_f,i, t_s] to the predicted lethality. F_i^jover the currently scheduled total time interval [t_f,i, t_d,i].
• 1.f. Detailed Process Flow for[0095]Step146 of FIG. 3
• FIG. 9 shows the detailed process flow that the[0096]temperature deviation program125 uses instep146 of FIG. 3 to define the re-scheduled reel speed v_s^j. This program uses sub-steps178 to187 to iteratively perform a simulation of the remaining portion of the rotary sterilization process predicted to be administered to the minimum lethality container i identified instep142 of FIG. 3 and discussed in section 1.b.Steps178 to187 are respectively similar tosteps159 and151 to159 of FIG. 6 and discussed in section 1.c., except for the differences discussed next.
• In[0097]step178, thetemperature deviation program125 first decrements the currently scheduled reel speed v_s^jby the predefined reel speed offset Δv. If the decremented reel speed is greater than the minimum reel speed v_min, the re-scheduled reel speed is defined as the decremented reel speed. However, if the decremented reel speed is less than or equal to the minimum reel speed, then the re-scheduled reel speed is defined as the minimum reel speed.
• Since a re-scheduled reel speed v[0098]_i^jis defined instep178, the re-scheduled remaining time intervals (t_r, t_n,i^j], . . . , (t_4,i^j, t_d,i^j] that the minimum lethality container i is predicted to be in the respective temperature zones115-n, . . . ,5 after the current sample real time t_rneed to be defined. This is done instep179.
• [0099]Step180 to186 are the same assteps170 to176 of FIG. 8 and discussed in section 1.e. Thus, these steps are used to compute a total lethality F_i^jpredicted to be delivered to the product cold spot of the minimum lethality container i over the re-scheduled total time interval [t_f,i, t_d,i^j]. It should be noted here that this is done using the actual current lethality F_i^jover [t_f,i, t_r] and the actual product cold spot temperature T_CS(t_r)^jfor the minimum lethality container i computed insteps161 to168 of FIG. 7.
• Then, in[0100]step187, thetemperature deviation program125 determines if the predicted total lethality F_i^jover [t_f,i, t_d,i^j] satisfies the target total lethality F_targ. If it does not, then the program determines instep188 whether the re-scheduled reel speed v_s^jequals the minimum reel speed v_min. If it does not, then steps181 to188 are repeated until it is determined instep187 that the target lethality has been satisfied or it is determined instep188 that the minimum reel speed has been reached. In this way, the reel speed is re-scheduled.
• 2. Alternative Embodiments[0101]
• As indicated earlier, the embodiment of[0102]controller104 associated with FIGS.3 to9 and described insection 1. is an exemplary embodiment. Alternative embodiments that utilize the principles and concepts developed in FIGS.3 to9 andsection 1. do exist. Some of these embodiments are discussed next.
• 2.a. Scheduling and Re-Scheduling Variations[0103]
• The operator of the[0104]rotary sterilization process100 may want to keep the initially scheduled reel speed v_s⁰and retort temperatures T_sRT1⁰, . . . , T_sRT5⁰constant throughout the entire rotary sterilization process. Thus, in this embodiment, thetemperature deviation program125 is simply used to identify the under processed containers { . . . , i, . . . }_underprin the manner discussed earlier in section 1.b. when a temperature deviation occurs. More specifically, thesteps145 to147 would be eliminated from the flow diagram of FIG. 3.
• In another embodiment, the initially scheduled retort temperatures T[0105]_sRT1⁰, . . . , T_sRT5⁰may be re-scheduled when a temperature deviation occurs. In this case, thetemperature deviation program125 would define a re-scheduled retort temperature T_sRT1^j, . . . , or T_sRT5^jin a similar manner to which it defined a re-scheduled reel speed v_s^jinstep146 of FIG. 3 andsteps178 to188 of FIG. 9. In this embodiment, the initially scheduled reel speed v_s⁰may be kept constant or a re-scheduled reel speed v_s^jmay be defined in conjunction with the re-scheduled retort temperature.
• 2.b. Identifying and Segregating Over Processed Containers[0106]
• Since re-scheduled reel speed v[0107]_s^jmay be defined when a temperature deviation occurs, it is possible that some of the containers {1, . . . , i, . . . , I} may be over processed due to the slower re-scheduled reel speed. In this case, a maximum total lethality F_maxmay be pre-defined and included as one of the input parameters. Then, the over processed containers { . . . , i, . . . }_overprwith predicted total lethalities { . . . , F_i^jover [t_f,i, t_d,i^j], . . . }_overprover this maximum total lethality would be identified in a similar manner to that way in which the under processed containers { . . . , i, . . . }_underprare identified instep148 of FIG. 3 and discussed in section 1.b. These containers would be segregated in the same way that the under processed containers are segregated instep141 of FIG. 3. As a result, the remaining containers that are not under or over processed would have a uniform quality food product using this technique.
• 2.c. More Conservative Approaches[0108]
• In[0109]steps142 and148 of FIG. 3 discussed in section 1.b. and insteps161 to168 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_CS(t)_i^jthat occurs over the actual time interval [t_f,i, t_r] that a container i has been in therotary sterilizer102. Specifically, this portion of the product cold spot time-temperature profile is based on the actual retort time-temperature profiles T_aRT1(t), . . . , T_aRTn(t) over the corresponding time intervals [t_f,i, t_1,i^j], . . . , (t_n−1,i^j, t_r].
• However, a more conservative embodiment could be employed which uses only the portion of the actual retort time-temperature profile T[0110]_aRTn(t) over the time interval from the time when the container is first affected by the temperature deviation to the current sample real time t_r. Specifically, the portion of the product cold spot time-temperature profile T_CS(t)_i^jover the time intervals [t_f,i, t_1,i^j], . . . , (t_n−2,i^j, t_n−1,i^j] would be based on the corresponding scheduled retort temperatures T_sRT1⁰, . . . , T_sRTn−1⁰for the temperature zones115-1, . . . , n-1 in which the temperature deviation is not occurring.
• Thus, if the container enters the temperature zone[0111]115-n while the temperature deviation is occurring, the portion of the product cold spot time-temperature profile T_CS(t)_i^jover the time interval (t_n−1,i^j, t_r] would still be based on the portion of the actual retort time-temperature profile T_aRTn(t) over this time interval. But, if the temperature deviation begins at the deviation begin time t_dwhile the container is in this temperature zone, then the portion of the product cold spot time-temperature profile over the time interval (t_n−1,i^j, t_e] would be based on the scheduled temperature T_sRTn⁰. In this case, only the portion of the product cold spot time-temperature profile over the time interval (t_d, t_r] would be based on the portion of the actual retort time-temperature profile T_aRTn(t) over this time interval. In either case, this results in the actual lethality F_i^jdelivered over the time interval [t_f,i, t_r] being computed more conservatively insteps142 and148 of FIG. 3 and insub-steps161 to168 of FIG. 7.
• Similarly, the actual initial product temperature T[0112]_aIP(t_f,i) for a container i was used insteps142 and148 of FIG. 3 and insub-steps161 to168 of FIG. 7 of FIG. 7 for computing the actual lethality F_i^jover [t_f,i, t_r]. However, rather than using this actual initial product temperature, the scheduled initial product temperature T_sIPmay be used. This also results in the actual lethality being more conservative.
• 2.d. More Aggressive Approaches[0113]
• A more aggressive approach than that described earlier in section 1.c. can be taken for defining the initially scheduled reel speed v[0114]_s⁰. In this approach, a first additional step could be added afterstep159 of FIG. 6 to determine whether the predicted total lethality F_i⁰over [0, Δt₁⁰+ . . . +Δt₄⁰] is within the target total lethality F_targby a predefined lethality tolerance ΔF. If this is the case, the reel speed obtained instep160 in the last iteration is used as the initially scheduled reel speed. However, if this is not the case, then the reel speed from the last iteration is overly conservative. As a result, a second additional step may be added to increase this reel speed by, for example, 0.5Δv.Steps151 to159 and the two additional steps are then repeated until the first additional step is satisfied. In this way, the initially scheduled reel speed is further refined in an aggressive manner.
• Similarly, a more aggressive approach can also be taken for defining the re-scheduled reel speed v[0115]_s^j. In this case, thesteps178 to188 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 and/or Reel Speed[0116]
• In addition to temperature deviations in the scheduled retort temperatures T[0117]_sRT1⁰, . . . , T_sRT5⁰, there may be deviations in other scheduled parameters of the rotary sterilization process. For example, there may be deviations in the scheduled initial product temperature T_sIPand/or the currently scheduled reel speed v_s^j. Thus, thecontroller104 may be configured to handle these deviations as well in order to identify any under and/or over processed containers { . . . , i, . . . }_underprand/or { . . . , i, . . . }_overprresulting from the deviation. This is done in a similar manner to that described earlier in sections 1.b. to 1.e. for temperature deviations in the scheduled retort temperatures.
• 2.d. More Aggressive Approaches[0118]
• A more aggressive approach than that described earlier in section 1.c. can be taken for defining the initially scheduled reel speed v[0119]_s⁰. In this approach, a first additional step could be added afterstep159 of FIG. 6 to determine whether the predicted total lethality F_i⁰over [0, Δt₁⁰+ . . . +Δt₄⁰] is within the target total lethality F_targby a predefined lethality tolerance ΔF. If this is the case, the reel speed obtained instep160 in the last iteration is used as the initially scheduled reel speed. However, if this is not the case, then the reel speed from the last iteration is overly conservative. As a result, a second additional step may be added to increase this reel speed by 0.5Δv.Steps151 to159 and the two additional steps are then repeated until the first additional step is satisfied. In this way, the initially scheduled reel speed is further refined in an aggressive manner.
• Similarly, a more aggressive approach can also be taken for defining the re-scheduled reel speed v[0120]_s^j. In this case, thesteps178 to188 of FIG. 9 discussed in section 1.f would also include the two additional steps just described. However, another additional step would also have to be added.
• 2.e. Deviations in Scheduled Initial Product Temperature and/or Reel Speed[0121]
• In addition to temperature deviations in the scheduled retort temperatures T[0122]_sRT1⁰, . . . , T_sRT4⁰, 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_sIPand/or the currently scheduled reel speed v_s^j. These deviations would be detected by monitoring the actual initial product time-temperature profile T_aIP(t) and the actual reel time-speed profile v_a(t)^j. Thus, thecontroller104 may be configured to handle these deviations as well in order to identify and segregate any under and/or over processed containers { . . . , i, . . . }_underprand/or { . . . , i, . . . }_overprresulting from the deviation. This is done in a similar manner to that described earlier in sections 1.b. to 1.e. for temperature deviations in the scheduled retort temperatures.
• 2.f. Different Combinations of Cooling and Cooking Shells and Temperature Zones[0123]
• The[0124]rotary sterilizer102 of FIG. 1 was described as having one cooking shell106-1 with three temperature zones115-1, . . . ,3 and one cooling shell106-2 with two temperature zones115-4 and5. Correspondingly, the flow and timing diagrams of FIGS.3 to9 were described in this context as well. However, those skilled in the art will recognize that the rotary sterilizer may have more than one cooking shell and more than one cooling shell with more or less temperature zones. For example, in a simple case, the cooking and cooling shells may each have just one uniform temperature zone. As those skilled in the art will recognize, the flow and timing diagrams of FIGS.3 to9 would have to be correspondingly adjusted for the specific combination of cooking and cooling shells and temperature zones used.
• 2.g. Other Continuous Source Sterilization Systems[0125]
• The present invention has been described in the context of a[0126]rotary sterilization system100. However, as those skilled in the art will recognize, the invention can be similarly practiced in any other continuous source sterilization system in which containers or carriers of containers are conveyed in line through the system's sterilizer. For example, the invention may be used in a hydrostatic sterilizer, as described in concurrently filed and co-pending U.S. Pat. application Ser. No.09/______,entitled Controller and Method for Administering and Providing On-Line Handling of Deviations in a Hydrostatic Sterilization Process, filed on Nov. 6, 1998, with Weng, Z. as named inventor. This patent application is hereby explicitly incorporated by reference.
• 3. Conclusion[0127]
• 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.[0128]

Claims (21)

What is claimed is:

1. A method of administering a sterilization process being performed by a rotary sterilizer on a continuous line of containers, the method comprising the steps of:

controlling the rotary sterilizer to perform the rotary sterilization process according to scheduled parameters; and

when a deviation in a specific one of the scheduled parameters occurs, identifying those of the containers that will in response have a total lethality predicted to be delivered to them during the sterilization process that is less than a predefined target lethality.

2. The method ofclaim 1 wherein the specific one of the scheduled parameters is one of the group consisting of (1) a scheduled retort temperature in a temperature zone of the rotary sterilizer through which the line of containers is conveyed, (2) a scheduled initial product temperature for the containers, and (3) a scheduled reel speed for conveying the containers in line through the rotary sterilizer.

3. The method ofclaim 1 further comprising the step of:

compiling an actual retort time temperature profile for a temperature zone of the rotary sterilizer; and

wherein the identifying step comprises the steps of:

selecting at least some of the containers that are effected by the deviation;

for each of the selected containers that has been conveyed into the temperature zone during the deviation,

simulating a product cold spot time-temperature profile for the container based on the actual retort temperature profile;

computing the total lethality predicted to be delivered to the container during the sterilization process based on the product cold spot time-temperature profile; and

determining whether the total lethality predicted to be delivered to the container satisfies the target lethality.

4. The method ofclaim 3 wherein the simulating step uses a finite difference simulation model to simulate the product cold spot time-temperature profile.

5. The method ofclaim 4 wherein the total lethality is the sum of (1) a lethality actually delivered over a first time interval from when the container is loaded into the rotary sterilizer to a current sample real time, and (2) a lethality predicted to be delivered over a second time interval from the current sample real time to when the container is unloaded from the rotary sterilizer.

6. The method ofclaim 5 wherein:

the lethality actually delivered over the first time interval is based on the portion of the product cold spot time-temperature profile over the first time interval;

the portion of the product cold spot time-temperature profile over the first time interval is based on at least a portion of the actual retort temperature profile over a time interval from a time when the container is first affected by the deviation to the current sample real time.

7. The method ofclaim 6 wherein:

the lethality predicted to be delivered over the second time interval is based on the portion of the product cold spot time-temperature profile over the second time interval;

the scheduled parameters include one or more scheduled retort temperatures that are scheduled for the sterilization process in the second time interval; and

the portion of the product cold spot time-temperature profile over the second time interval is based on the one or more scheduled retort temperatures.

8. A controller for administering a sterilization process performed by a rotary sterilizer on a continuous line of containers of containers, the controller comprising:

control circuitry configured to control the rotary sterilizer;

a memory configured to store a process control program and a deviation program, the process control program being programmed to cause the control circuitry to control the rotary sterilizer in performing the sterilization process according to scheduled parameters, the deviation programmed being programmed to identify, when a deviation in a specific one of the scheduled parameters occurs, those of the containers that will in response have a total lethality predicted to be delivered to them during the sterilization process that is less than a predefined target lethality; and

a microprocessor coupled to the memory and the control circuitry and configured to execute the process control and temperature deviation programs.

9. The controller ofclaim 8 wherein the specific one of the scheduled parameters is one of the group consisting of (1) a scheduled retort temperature in a temperature zone of the rotary sterilizer through which the line of containers is conveyed, (2) a scheduled initial product temperature for the containers, and (3) a scheduled reel speed for conveying the containers in line through the rotary sterilizer.

10. The controller ofclaim 8 wherein:

the process control program is further programmed to compile an actual retort time temperature profile for a temperature zone of the rotary sterilizer; and

the deviation program is programmed to identify the identified containers by:

selecting at least some of the containers that are effected by the deviation;

for each of the selected containers that has been conveyed into the temperature zone during the deviation,

simulating a product cold spot time-temperature profile for the container based on the actual retort temperature profile;

computing the total lethality predicted to be delivered to the container during the sterilization process based on the product cold spot time-temperature profile; and

determining whether the total lethality predicted to be delivered to the container satisfies the target lethality.

11. The controller ofclaim 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 ofclaim 10 wherein the total lethality is the sum of (1) a lethality actually delivered over a first time interval from when the container is loaded into the rotary sterilizer to a current sample real time, and (2) a lethality predicted to be delivered over a second time interval from the current sample real time to when the container is unloaded from the rotary sterilizer.

13. The controller ofclaim 12 wherein:

the lethality actually delivered over the first time interval is based on the portion of the product cold spot time-temperature profile over the first time interval;

the portion of the product cold spot time-temperature profile over the first time interval is based on at least a portion of the actual retort temperature profile over a time interval from a time when the container is first affected by the deviation to the current sample real time.

14. The controller ofclaim 13 wherein:

the lethality predicted to be delivered over the second time interval is based on the portion of the product cold spot time-temperature profile over the second time interval;

the scheduled parameters include one or more scheduled retort temperatures that are scheduled for the sterilization process in the second time interval; and

the portion of the product cold spot time-temperature profile over the second time interval is based on the one or more scheduled retort temperatures.

15. A rotary sterilization system comprising:

a rotary sterilizer configured to perform a sterilization process on a continuous line of containers;

a controller configured to:

control the rotary sterilizer in performing the rotary sterilization process according to scheduled parameters;

when a deviation in a specific one of the scheduled parameters occurs, identify those of the containers that will in response have a total lethality predicted to be delivered to them during the sterilization process that is less than a predefined target lethality.

16. The rotary sterilization system ofclaim 15 wherein the specific one of the scheduled parameters is one of the group consisting of (1) a scheduled retort temperature in a temperature zone of the rotary sterilizer through which the line of containers is conveyed, (2) a scheduled initial product temperature for the containers, and (3) a scheduled reel speed for conveying the containers in line through the rotary sterilizer.

17. The rotary sterilization system ofclaim 15 further comprising:

a sensor to sense actual retort temperatures in a temperature zone of the rotary sterilizer;

the controller is further configured to:

compile an actual retort time temperature profile from the sensed actual retort temperatures; and

identify the identified containers by:

selecting at least some of the containers that are effected by the deviation;

for each of the selected containers that have been conveyed into the temperature zone during the deviation,

simulating a product cold spot time-temperature profile for the container based on the actual retort temperature profile;

computing the total lethality predicted to be delivered to the container during the sterilization process based on the product cold spot time-temperature profile; and

determining whether the total lethality predicted to be delivered to the container satisfies the target lethality.

18. The rotary sterilization system ofclaim 17 wherein the controller is still further configured to use a finite difference simulation model to simulate the product cold spot time-temperature profile.

19. The rotary sterilization system ofclaim 17 wherein the total lethality is the sum of (1) a lethality actually delivered over a first time interval from when the container is loaded into the rotary sterilizer to a current sample real time, and (2) a lethality predicted to be delivered over a second time interval from the current sample real time to when the container is unloaded from the rotary sterilizer.

20. The rotary sterilization system ofclaim 19 wherein:

the lethality actually delivered over the first time interval is based on the portion of the product cold spot time-temperature profile over the first time interval;

the portion of the product cold spot time-temperature profile over the first time interval is based on at least a portion of the actual retort temperature profile over a time interval from a time when the container is first affected by the deviation to the current sample real time.

21. The rotary sterilization system of claim26 wherein:

the lethality predicted to be delivered over the second time interval is based on the portion of the product cold spot time-temperature profile over the second time interval;

the scheduled parameters include one or more scheduled retort temperatures that are scheduled for the sterilization process in the second time interval; and

the portion of the product cold spot time-temperature profile over the second time interval is based on the one or more scheduled retort temperatures.

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