Abstract:
An industrial control system uses a number of autonomous control units, each associated with one piece of equipment in an industrial process. The autonomous control units include data indicating not only their constraints of operation but also reflecting the constraints of operation of machines to which they are attached and with which they share common operating parameters. An autonomous controller associated with a machine having operating parameters in common with another machine adopts the intersection of the ranges of the machine constraint of the two machines. Machine constraints are preserved to the extent possible as ranges so as to permit flexibility in selecting and seeking goals by the individual autonomous control units.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. application Ser. No. 09/164,204 filed Sep. 30, 1998, now U.S. Pat. No. 6,091,998 filed Jul. 18, 2000 and entitled: Self-Organizing Industrial Control System Using Bidding Process. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     BACKGROUND OF THE INVENTION 
     The present invention relates to industrial controllers for the real-time control of equipment used in manufacturing and in particular to an industrial controller that automatically organizes equipment for the manufacture of a products based on the capabilities of the equipment. 
     Industrial controllers are special purpose computers used in controlling industrial processes. Under the direction of a stored control program, an industrial controller examines a series of inputs reflecting the status of the controlled process and changes a series of outputs controlling the industrial process. The inputs and outputs may be binary, that is, on or off, or analog, providing a value within a continuous range. The inputs may be obtained from sensors attached to the controlled equipment and the outputs may be signals to actuators on the controlled equipment. 
     Unlike the standardized software normally executed on conventional computers, the control program executed on an industrial controller is normally unique to each controlled process. The writing and troubleshooting of the control program is thus a significant cost in the creation of an industrial control system. After the controlled program is complete, it must often be modified as the product to be manufactured changes or as equipment is exchanged, replaced or repaired. 
     The above referenced parent to this application describes a self-configuring industrial control system employing a number of autonomous control units, each associated with a particular piece of manufacturing equipment. The autonomous control units are programmed with data describing the capabilities of their equipment and the equipment&#39;s ability to interact with other equipment. A desired product is described in a “job description language” and broadcast to the autonomous control units, each which identifies portions of the job that they can complete. The autonomous control units then exchange bids and counterbids with the other autonomous control units to allocate the job among units and to select the desired operating parameters of the associated equipment. The autonomous control units are programmed with generalized goals so that the allocation may be further optimized for high productivity, low cost or some other objective measure. 
     The bidding process accommodates competing goals of the different pieces of equipment. Nevertheless, this bidding process can be quite time consuming and in certain instances, can disproportionately allocate resources to downstream equipment whose counterbids drive the ultimate job plan produced. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention simplifies the bidding process through the use of an initial exchange of operational constraints between each autonomous controller. In this exchange step, the autonomous controllers compare the ranges of their machines&#39; inputs and outputs to the corresponding ranges of connected input and outputs of predecessor and successor machines. By internalizing these ranges, the bidding process is substantially simplified. Further, to the extent possible, inconsistencies in the ranges are remedied by producing new ranges rather than individual values. In this way, local choices in the optimization provided by the bidding process is preserved. 
     Specifically, the present invention provides an industrial control system for controlling an industrial process of interconnected machines operating to produce a manufactured product according to a job plan. The industrial control includes a plurality of interconnected autonomous control units, one associated with each machine, each having an electronic memory. The electronic memory holds data representing machine constraints indicating constraints on the operation of a given machine resulting from limitations of the machine and inter-machine relationships indicating physical operating parameters of the given machine linked to the physical operating parameters of another machine. An electronic computer executes a stored program to modify the machine constraints associated with the given machine by the machine constraints of a machine related by the inter-machine relationships and evaluates the feasibility of executing a portion of a job plan for the manufacture of a product by the given machine based on the modified machine constraints. 
     Thus, it is one object of the invention to provide each autonomous control unit with information about constraints that may be imposed on the job plan by other machines to which the given machine may be related, for example, by shared inputs or outputs. By bringing this information into each autonomous control unit, inefficient communication between the autonomous control units is minimized and a solution to the allocation of the job plan among machines is more rapidly obtained. 
     The memory may hold multiple machine constraints and multiple inter-machine relationships identified to different material paths between machines. The machine constraints associated with a given material path are modified by the machine constraints of only machines related by the inter-machine relationship associated with the given material path. 
     Thus, it is another object of the invention to address constraints imposed by adjacent machines without unduly limiting the solution sought by the autonomous control units. By segregating constraints according to machine paths, constraints applicable to one machine path are not necessarily imputed to other machine paths. 
     The electronic computer may respond to a job plan and bids by other autonomous control units to create a bid for the job plan describing performance of a portion of the job plan that may be performed by the given machine according to the modified machine constraints. In the alternative, the computer may create a counterbid proposing further modification of the machine constraints. Further in response to counterbids by other autonomous control units, the electronic computer may create a modified bid for the job plan according to the modified machine constraints adjusted by the received counterbid. 
     Thus, it is another object of the invention to provide a method of coordinating autonomous control units to exchange machine constraint ranges that may be used in conjunction with a bid and counterbid system for producing a particular value within those constraint ranges. 
     The inter-machine relationships may match identical operating parameters that are inputs or outputs of interconnected machines. 
     Thus it is yet another object of the invention to allow upstream machines to impose their constraints on downstream machines as well as downstream machines being able to impose their input constraints on upstream machines thereby improving knowledge of each machine as to the restraints of the overall process. 
     The machine constraints may be ranges of operating parameters for the given machine and the modification of the machine constraints may produce a multivalue range of operating parameters that is a subset of the range of operating parameters. 
     Thus it is another object of the invention to preserve the machine constraints as ranges of values rather than individual values to allow greatest freedom within an individual autonomous control unit for local optimization. 
     The foregoing and other objects and advantages of the invention will appear from the following description. In the description, reference is made to the accompanying drawings which form a part hereof and in which there is shown by way of illustration a preferred embodiment of the invention. Such embodiment does not necessary represent the full scope of the invention, however, and reference must be made to the claims herein for interpreting the scope of the invention. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     FIG. 1 is a perspective view of a simplified rolling mill composed of a sequential set of machines each associated with an autonomous control unit per the present invention; 
     FIG. 2 is a schematic block diagram of the autonomous control units of FIG. 1 showing the inter connection of the autonomous control units through interfaces on a common link and a processors and memories of the autonomous control units; 
     FIG. 3 is a detailed block diagram of the memory of one autonomous control unit of FIG. 2 showing the contained bid program, constraint data, goal data, self assessment data, and a model of the equipment associated with the autonomous control unit; 
     FIG. 4 is a expanded block diagram of the constraint data, goal data, self assessment data, and model of FIG. 3; 
     FIG. 5 is a graphical representation of the equipment of the rolling mill of FIG. 1 as defined by various inputs and constraints; 
     FIG. 6 is a flow chart of the bid program of FIG. 3 such as may be used to generate a control strategy for the machines of FIGS. 1 and 5; and 
     FIG. 7 is a flow chart of the operation of the model of FIG. 3 and 4 in the responding to a counter-bid per the flow chart of FIG.  6 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Components of the Control System 
     Referring now to FIG. 1, an industrial process  10  may provide for the processing of metal billets  12  through a series of machines  14 . Each machine  14  may have an associated autonomous control unit  16  being either discrete devices as shown in FIG. 1 or portions of a centralized machine. The autonomous control units  16  may be separate computers interconnected by a common communication link  18  and also connected by the communication link  18  to a controller  20  and a human/machine interface such as a computer terminal  22  of conventional design. Alternatively, the autonomous control units  16  may be partitions of controller  20  communicating with the machines  14  via sensors and actuators on the machines  14 . 
     In an example process  10 , suitable for control by the present invention, machines  14  may include a reheat furnace  14   a  for heating precast billets  12  to a predetermined temperature, a rolling mill  14   b  for rolling the billets  12  to a predetermined diameter, a water bath  14   c  for cooling the billets  12  with water and a Stelmor conveyor  12   d  cooling the billets  12  with air. The billets  12  may alternatively come directly from a continuous casting machine  14   e  at casting temperature without the need for reheating by reheat furnace  14   a.  In this case the billets pass directly from the continuous caster  14   e  to the rolling mill  14   b.    
     Referring now to FIGS. 2 and 3, each autonomous control unit  16  includes an interface circuit  24  connected with the common communication link  18  and handling communication protocols so that the autonomous control units  16  may communicate bids and counter-bids among themselves and may receive a job description as will be discussed below. The interface circuits  24  of each autonomous control unit  16  are connected by an internal bus  26  to a processor  28  and memory  30 . 
     Data Structures 
     Referring now to FIG. 3, the memory  30  holds a bid program  32  that will be used to generate bids and counter-bids to be exchanged among the autonomous control units  16  in developing a control strategy for the machines  14 . The bid program  32  communicates with the other autonomous control units  16  according to a communications protocol program  35  which also serves to store and sort bids and counter-bids and job descriptions and direct bids and counter-bids to the correct device as will be described. 
     The bid program  32  has access to stored data tables representing constraint data  34 , which generally quantifies the limitations of performance of the associated machine  14 , goal data  36 , which describes preferences among modes of operation of the associated machine  14  within the constraints  34 , self assessment data  38  generally describing the dynamic state of the associated machine, and a model  40  modeling operation of the associated machine by mathematical means. 
     Referring to FIG. 4, the constraints  34  are of a number of different kinds. Task constraints  42  describe generally the kind of operation that the associated machine  14  is intended to perform. Thus, for example, the reheat furnace  14   a  may perform heating tasks (GOTO TEMP), the rolling mill  14   b  (as shown) may perform a diameter reduction task (GOTO DIA.). The task constraints  42  allow the autonomous control units  16  to make a threshold determination as to whether their associated machines  14  will make a bid for a particular task of a plan to produce a product. Continuing with the example of the rolling mill  14   b,  the autonomous control unit  16   a  of the rolling mill  14   b  will only bid for tasks requiring diameter reductions. 
     The constraint data also includes input constraints  44  describe the limits of the inputs to the associated machine  14 . The inputs (as opposed to the outputs of the machines  14 ) are well defined and their ranges are set by the physical design of the machine. For example, for the rolling mill  14   b  the input will be amount of gas valve opening and the range of the input will be from zero to one hundred percent. For the rolling mill  14   b  the inputs will be rolling diameter from 0 to 1. For the water bath  14   c  the input will be water flow rate and for the Stelmor conveyor  14   d  the inputs will be air flow rate. As used herein, input constraints are only those constraints independent of the operation of other machines  14 . 
     The constraints  34  also include path constraints  46  which generally reflect limitations on the possible paths of the product, the billet  12 , between machines  14  as dictated by their physical layout. In this example, two paths are available, the first in which the billet  12  passes from reheat furnace  14   a  to rolling mill  14   b,  then to water bath  14   c  and finally to Stelmor conveyor  14   d  and the second where the billet  12  passes from continuous caster  14   e  to rolling mill  14   b  then to water bath  14   c  and finally to Stelmor conveyor  14   d.  These path topologies are reflected in the path constraints  46  listing the path in a first column and a set of intermediate constraints  48  (as will be described) in a second column. From this table all possible paths between machines  14  may be determined. The task constraints  42 , the path constraints  46  and the input constraints  44  will be termed generally “operational” constraints as they constrain the operation of the machine  14  in contrast to the inter-machine constraints to be described below. 
     Referring also to FIG. 5, deriving from the path constraints  46  and possibly including other inputs of the machines  14  are the “inter-machine” or “intermediate” constraints  48  representing operating parameters shared between machines  14  based on the path of the material between machines  14 . Generally these intermediate constraints  48  connect identical operating parameters of the machines  14  forming outputs of upstream machines in the material path with inputs of downstream machines in the material flow path. Thus the input temperature of the rolling mill  14   b  will be constrained to be equal to output temperature of the reheat furnace  14   a  or the output temperature of the continuous caster  14   e  depending on the particular path. The continuous caster  14   e  has an output speed and hence this is an inter-machine constraint for that path only. Generally, the rolling mill  14   b  and water box  14   c  also share output and input temperatures respectively, and also billet speed i.e., the speed of exit of the billet  12  from the rolling mill  14   b  equaling the speed of entry of the billet into the water box  14   c.    
     As a result of the coiling of the billet product in the Stelmor conveyor  14   d  the water box  14   c  and Stelmor conveyor  14   d  do not share the parameter of conveyor speed but do share the parameter of temperature as the temperature of the billet output from the water box  14   b  will equal the temperature of the billet  12  entering to the Stelmor conveyor. 
     Referring again to FIGS. 3 and 4, the memory may also hold goal data  36  implemented as a utility function  50  having as input arguments one or more of the characterizing parameters of the machine  14  either inputs or outputs, and as a value an arbitrarily defined utility which reflects a preprogrammed goal of the autonomous control unit  16 . In the case of the rolling mill  14   b,  the utility function  50  may be a function of speed reflecting a desire for high production, but also a particular speed for metallurgical reasons. A more complex utility function  50  might consider other metallurgical properties and wear on the equipment. Generally the autonomous control unit  16  strives to maximize utility within the operational and intermediate constraints. 
     Other machines will have other goals as selected and programmed by the user or manufacturer. The goals for the reheat furnace  14   a,  the water box  14   c  and Stelmor conveyor  14   d  are generally reduction of gas, water and air volume respectively. 
     Referring still to FIGS. 3 and 4, the self assessment data  38  will typically include various sensed parameters  52  of the associated machine  14 . As shown in FIG. 4 for the rolling mill  14   b,  the self assessment data includes current rolling diameter and the rolling speed (sensed outputs). A general operational status for the rolling mill  14   b  may also be provided as generated from other inputs and outputs and possibly a heuristic program evaluating the fitness of the machine  14 . Generally the self assessment data  38  is used to modify the operation constraints  34  if the operational status of the machine  14  is somehow impaired. 
     The model  40  provides a mathematical description  54  relating inputs to the machine  14  to its outputs. In the example of the rolling mill  14   b,  a simple linear equation of three variables is shown relating output temperature of the rolling mill  14   b  to the input temperature the rolling speed and the diameter reduction. This model reflects generally the fact that the rolling process can increase the temperature of the stock. Generally far more complex models may be created relating one or more inputs to particular outputs of the machine. In most cases, the inverse of the model function is not also a function and thus an iterative process must be used to deduce an input from an output such as a binary search using successive input values until the desired output is arrived at. 
     For the reheat furnace  14   a,  the model  40  will take into account the time integral of the gas valve opening as reflects the heating of the furnace. The model for the water box  14   c  may relate cooling water flow and process speed to surface and internal temperatures. The model  40  for Stelmor conveyor  14   d  will provide a time and air flow relationship to temperature of the output billet  12 . The construction of such models is generally understood in the art and will depend on the particular machine  14 . 
     Job Description Language 
     Referring now to FIGS. 1 and 5, a “product” autonomous control unit  16  may be implemented by an arbitrary controller  20  to represent the desired product to be manufactured from the billet  12 . This product autonomous control unit provides a convenient unit for implementing the functions of describing the product to the autonomous control units  16  of the machines  14  and of evaluating the plans produced by the autonomous control units  16  against the product definition. For this first task, the product autonomous control unit, accepts input from a user through computer terminal  22  describing the product characteristics and produces a machine independent description of desired tasks for producing that product in a job description language. In the preferred embodiment the job description language is an ASCII text file providing a number of steps defining desired machine outputs. For example, to produce a rolled billet, the job description is as follows: 
     
       
         
               
               
             
           
               
                   
               
             
             
               
                 STEP 1= 
                 GOTO TEMP(ALL)&lt;1300.0 
               
               
                 STEP 2= 
                 GOTO DIAMETER=5.5 TOL(−0.2, 0.2) 
               
               
                   
                 CONSTRAIN TEMP(ALL)&lt;1300.0 
               
               
                   
                 CONSTRAIN TEMP(ALL)&gt;825.0 AT TIME=END 
               
               
                   
                 DEPENDS ON (1) 
               
               
                 STEP 3= 
                 GOTO TEMP(SURF)=850 TOL(−5.0, 5.0) 
               
               
                   
                 CONSTRAIN TEMP(ALL)&gt;825.0 AT TIME=0.0 
               
               
                   
                 CONSTRAIN TEMP(SURF)&gt;450.0 AND&lt;1300.0 
               
               
                   
                 WITH DIAMETER=5.5 
               
               
                   
                 DEPENDS ON (2) 
               
               
                 STEP 4= 
                 GOTO TEMP(AVG)=650.0 TOL(−5.0, 5.0) IN TIME&lt;15.0 
               
               
                   
                 CONSTRAIN TEMP(SURF)&gt;500 AT TIME&gt;=0.0 AND 
               
               
                 &lt;=2.0 
               
               
                   
                 WITH DIAMETER=5.5 
               
               
                   
                 DEPENDS ON (3) 
               
               
                 STEP 5= 
                 GOTO TEMP(AVG)=600.0 TOL(−5.0,5.0) IN TIME &gt;40.0 
               
               
                   
                 WITH DIAMETER = 5.5 
               
               
                   
                 DEPENDS ON (4) 
               
               
                   
               
             
          
         
       
     
     Each step defines temperatures (TEMP), diameters (DIAMETER) and tolerances (TOL) of the billet and the sequence (DEPENDS ON) and timing (AT TIME) of the steps. In this example both surface temperature (SURF) and overall temperature (ALL) is considered and so the models  40  must provide outputs for both. 
     Operation of the Control System 
     The operation of the autonomous control units  16  (and the controller  20 ) will now be described with reference to the flow chart of FIG.  6 . The flow chart of FIG. 6 is executed in part by different autonomous control unit  16   a  and the controller  20  as will be apparent from context. 
     At a first step, the job description language (JDL) is generated by the autonomous control unit implemented in controller  20  for the product is represented by process block  60 . At succeeding process block  62  the JDL is broadcast over the communication link  18 . 
     As indicated by decision block  64 , each autonomous control unit receiving the broadcast JDL evaluates the tasks of the JDL generally in light of its own task constraints  42  and submits to the most upstream autonomous control unit  16  in the path (indicated by the path constraints  46 ), and in this case the reheat furnace  14   a,  an indication of which tasks represented by steps in the JDL, it can perform. 
     The most upstream autonomous control unit  16   a,  based on the received indications about task capability from the other autonomous control units  16 , next tries to create one or more “template job plans” representing a possible allocations of tasks to machines  14 . In the event that there is not at least one autonomous control unit  16  indicating an ability to perform at least each step the JDL, the most upstream autonomous control units  16   a  proceeds to a fail state  66  indicating that the desired product cannot be produced by the machines  14 . 
     More typically, at process block  68 , one or more job templates will be created as described. A number of different job templates may address different allocation of machines  14  to different steps of the JDL or different material flow paths in the case where the topology is not as simple as the example used herein. Or different job templates may address different products. 
     The job plans are then broadcast to the autonomous control units  16  which extract the path constraints  46  from the material paths contained in the job plans and establish a set of machine relationships manifest in the inter-machine constraints  48 . A different set of machine relationships will be prepared for each job plan reflecting possibly different material paths and hence different machine interactions. Each autonomous control unit  16  initially is programmed with a set of ranges for the intermediate constraints  48 , the ranges based on the known characteristics of the machine associated with the autonomous control unit  16 , for example, a speed or temperature range which may be determined by the design of the machine  14 . As indicated by process block  69 , these initial ranges are then exchanged with the upstream and downstream machines sharing the same operational parameters as indicated by the inter-machine constraints  48 . For example, for a first path where rolling mill  14   b  receives billets  12  from the reheat furnace  14 ( a ), the oven output temperature range may be 0 to 2000 degrees substantially larger than the rolling mill  14   b  input temperature range of 1000 to 1200 degrees. In this case, the intersection of these two ranges 1000-1200 is adopted by the reheat oven  14   a  and the rolling mill  14   b  for this shared parameter. In contrast, for a second path where the rolling mill  14   b  receives billets  12  from the continuous caster  14 ( e ), the casting process may require a narrow temperature range about 800 degrees so as to preserve pliability of the billets  12  and to prevent eruption of the cooling liquid interior. In this case, the intersection of the ranges for the continuous caster  14   e  and the rolling mill  14   b  is the single value 800. Note that if the rolling mill  14   b  had a smaller range in input temperature than the output of the continuous caster  14   e,  the smaller range of the rolling mill  14   b  would be adopted by the continuous caster. 
     The purpose of this exchange of ranges is to simplify the bidding process which is described below by enabling the autonomous control units to eliminate bids, and hence avoid the bidding process, for values outside the combined solutions space of these ranges. 
     After this exchange, the most upstream machine  14 , either the reheat furnace  14   a  or the continuous caster  14   e,  then reads the first step of the JDL, which in this case that indicates that the temperature of the product should be raised to a value of less than 1300 degrees, and evaluates whether it can create a bid for that task as indicated by process block  70 . Specifically, the autonomous control unit  16  evaluates its current temperature in its self assessment  52  and its goals  36  and the requirements of the JDL to creates a bid indicating a specific temperature to which the reheat furnace will raise the billet  12 . In this case the intermediate constraints  48  are those associated with the reheat furnace  14   a  and material path I. Simultaneously, a similar process is performed by the continuous caster  14   e  for material path II. 
     Assuming that the autonomous control unit  16   a  of the reheat furnace  14   a  (and/or the continuous caster  14   e ) may make a bid within the above constraints, the program proceeds to decision block  72  to test if this is the last autonomous control unit on the job path (i.e., in either case, the Stelmor conveyor  14   d ). At this time it is not, and so the program proceeds to process block  74  where the bids are perfected by transmitting them to the succeeding rolling mill  14   b  and more generally to the autonomous control unit(s) immediately downstream from the autonomous control unit  16  making the bid. The autonomous control unit  16   a  also updates an internal bid storage table(not shown). 
     The process then proceeds to the next autonomous control unit  16   b  as generally shown by process block  76 . The next autonomous control unit  16   b,  associated with the rolling mill  14   b,  receives the template plans and the bids proposed by the reheat furnace  14   a  and the continuous caster  14   e.  At process block  70  autonomous control unit  16   b  determines whether it can make a bid based on the information from the JDL and on the constraints  34 , including this time, constraints from the intermediate constraint table  48  which links the input temperature or the rolling mill  14   b  to the output temperature of the reheat furnace  14   b  or continuous caster  14   e  depending on the bid. The modification of the intermediate constraint table  48  to reflect the restraints of adjacent machines makes this generation of the bids more robust against constraints of the other machines and thus less likely to trigger time consuming counter bids. Nevertheless, because the counterbid process strives to preserve the range of the intermediate constraint table  48 , the autonomous control unit making the bid can exercise some influence on the job plan from its unique goals. 
     In the example given, the JDL requires that the temperature of the billet  12  be greater than 825 degrees at the end of the rolling. Assuming for the moment that the temperature selected by the reheat furnace  14   a  is insufficient for the rolling mill  14   b  to reach the required output temperature (as may be determined by model  40  for the rolling mill  14   b ) then at process block  70  the autonomous control unit  16   b  proceeds to process block  104  to generate a counter-bid because no bid could be generated meeting the then existent constraints. 
     For the counter-bid, the autonomous control unit  16   b  must first determine a acceptable input temperature to the rolling mill  14   b.  Generally this cannot be done by consulting stored input constraints for temperature because the relevant constraints will dynamically depend on the particular output temperature required. Accordingly the program  32  of the autonomous control unit  16   b  must refer to the model  40 . 
     Referring now to FIG. 7, the process of determining the necessary input temperature (or an arbitrary input value from a defined output) begins at a process block  82  in which the new defined output condition is established. In this example the output condition is a temperature of greater than 825 degrees as required by the JDL. 
     At decision block  84 , a unconstrained input is identified, in this case an input temperature from the reheat furnace  14   a  within temperature range permitted by the rolling mill  14   b.  By unconstrained it is meant that the input may be varied in a desired direction without violating the inputs constraints  44 . 
     At process block  86 , the identified input is modified, in a direction to reduce the difference between the desired output value (per the JDL and process block  82 ) and the modeled output value produced by evaluating the model  40  with the unmodified input. The modified input is then evaluated by executing the model  40  as indicated at process block  88  to produce a new output. 
     At decision block  90 , the current output from the model  40  is matched to the desired new output from process block  82  and if the outputs match within a tolerance the modified input established at process block  86  is used for the counter-bid as indicated by process block  92 . The counterbid incorporates a new range for the input rather than a single input value so as to preserve the flexibility of the autonomous control units accepting the counter bid as much as possible. If the modification of the input was downward, then the input becomes the new upper boundary of the input range, whereas if the modification of the input was upward, the input becomes the new lower boundary of the range. The new range is forwarded to autonomous control units for the corresponding upstream machine as part of the counterbid. 
     More typically, at least initially, the outputs will not match and the program loops back to process block  84  for a second or subsequent iteration. If prior to a matching of the outputs, the input becomes constrained and there are no further inputs that can be modified the program proceeds to a fail block  94  indicating the process cannot be completed. 
     Referring again to FIG. 6, assuming that a suitable counter-bid can be obtained at process block  92  of FIG. 7, the counter-bid is perfected by forwarding it to the proceeding autonomous control unit  16  in this case autonomous control unit  16   a  for the reheat furnace  14   a.    
     Autonomous control unit  16   a  receiving the counter-bid at decision  96 , adopts the new range of operational parameters contained therein for its intermediate constraints associated with the particular path of the relevant job plan and then determines whether it can accept the counter-bid&#39;s new proposed output temperature range by modifying its original bid. The model  40  for the reheat furnace  14   a  (not shown) may be invoked to determine whether with practical inputs (per input constraints  44 ) the desired output temperature value can be obtained. Often a range of possible modified bids are available and one bid is selected by use of the goal  50 . The counter-bid may be accepted if the autonomous control unit  16   a  can create a bid within the new range as indicated by process block  74 . This new bid is sent to the next succeeding autonomous control unit  16   b  as part of the job template as before and received by autonomous control unit  16   b  at process block  70  as has been described. Note that because the modified intermediate constraints are always a subset of the original intermediate constraints, the new bid will also satisfy the original intermediate constraints. 
     Referring again to decision block  96 , if the counter-bid cannot be accepted then at decision block  100  a test is performed to see it the autonomous control units  16  receiving the counter-bid is the first autonomous control unit  16 . If it is, then the program proceeds to process block  102  and a failure condition is indicated as would be the case were the reheat furnace  14   a  receiving the counter-bid. 
     More typically, however, the autonomous control unit  16  receiving a counter-bid will not be the first autonomous control unit  16  and thus it is possible to make yet another counter-bid indicated by process block  104  to yet an earlier autonomous control unit  16  so as to possibly relax an earlier intermediate constraint. 
     Bids and counter-bids may thus ripple up and down the chain of autonomous control units  16   a,    16   b,    16   c,  and  16   d  and the chain of autonomous control units  16   e,    16   b,    16   c,  and  16   d  until at process block  72  the last autonomous control unit in the material path is successfully bids for each chain and the program proceeds to process block  104  and the completed plans are forwarded to the product autonomous control unit in the controller  20  to be evaluated. 
     The product autonomous control unit in controller  20  may then accept one of the plans or may change the job description in a process analogous to the counter-bidding proposal and the process may be repeated. As a result of the possibility of unresolvable bidding outcomes, the product autonomous control unit  16  normally produces a time limit on the process which if exceeded causes the process to indicate a failure. 
     The above description has been that of a preferred embodiment of the present invention, it will occur to those that practice the art that many modifications may be made without departing from the spirit and scope of the invention. In order to apprise the public of the various embodiments that may fall within the scope of the invention, the following claims are made.