Control system for and method of combining materials

Abstract

An apparatus and method for combining multiple materials. The multiple materials may include both a major material and one or more minor materials. The major and minor materials are added at transient or steady state flow rates, depending upon a command from a control signal. The actual flow rates track the commanded flow rates, but deviate by an error. The claimed arrangement provides an instantaneous and time-based error believed to be unobtainable in the prior art.

1 . A method for combining materials comprising at least one major material and at least one minor material, said at least one major material and at least one minor material combining to make a total, said method comprising the steps of: 
 providing a confluence region;    supplying at least one major material into said confluence region;    adding at least one minor material to said confluence region in the vicinity of said major material, whereby said major material and said at least one minor material come into contacting relationship in a first proportion and are maintained within said confluence region; and    changing the amount of said at least one major material and said at least one minor material added to said confluence region throughout a first period of time, while maintaining said first proportion of said at least one major material to a respective setpoint and said first proportion of said at least one minor material to a respective setpoint within an instantaneous error of not more than ± about five percent of full scale flow rate, said first period of time being less than one second.    
   
   
       2 . A method according to  claim 1 , wherein said instantaneous error is not more than about ±3 percent.  
   
   
       3 . A method according to  claim 2 , wherein said first period of time is not more than about one-half second.  
   
   
       4 . A method according to  claim 1  wherein said step of adding at least one minor material to said confluence region comprises of the step of continuously adding the at least one minor material.  
   
   
       5 . An apparatus for combining at least two materials together, said apparatus being able to undergo a transient whereby the amount of said materials blended per unit time is varied either to be greater than or less than a prior rate of blending said materials, whereby said transient produces an instantaneous error and a cumulative error between a command signal having a setpoint which is changed at time T=0 and a measured flow rate, said instantaneous error being not more than:  
         IE<A*M *exp(− t /τ)  where IE is the instantaneous error in volume per unit time, and    A is the magnitude of the setpoint change at time zero, normalized to unity,    M is a scale factor ranging from about 0.1 to about 0.5,    t is the instantaneous time in seconds, not to exceed about 1.5 *τ,    τ is a time constant ranging from about 0.1 to about 1.0 seconds.    
   
   
       6 . An apparatus according to  claim 5 , wherein τ is 1 and t ranges from 0 to about 0.5*.  
   
   
       7 . An apparatus according to  claim 5 , wherein τ is 0.5 and t ranges from 0 to about 3*τ.  
   
   
       8 . An apparatus according to  claim 5  wherein M is 0.5, τ is 1 and t ranges from 0 to about 2.0*τ.  
   
   
       9 . An apparatus according to  claim 5  wherein M is 0.5, τ is 0.5 and t ranges from 0 to about 2*τ.  
   
   
       10 . An apparatus according to  claim 5  wherein M is 0.25, τ is 1 and t ranges from 0 to about 1.5*τ.  
   
   
       11 . A control system for blending at least two fluids materials together, said control system being able to undergo a transient lasting not more than one second, whereby the amount of materials added per unit time is varied either to be greater than or less than a rate of adding said materials prior to said transient, whereby said transient produces an cumulative error over a period of time given by the formula:  
         IE   k =[Command Signal for Flow Rate] k −[Actual Flow Rate] k    wherein Command Signal for Flow Rate is the desired flow rate,    Actual Flow Rate is the resulting flow rate in the system, and    a transition between a continuous time t, and a discrete time is given by the formula        t=k*ΔT,      wherein k is an index for a discrete time period ΔT, and    t and ΔT are measured in seconds; and    wherein for a transient command signal of normalized magnitude equal to one said cumulative error for the period from t=0 to t=T final , for T final  up to about 5 seconds or less is given by the formula:      CE Tfinal <0.50.    
   
   
       12 . An apparatus according to  claim 11 , wherein said cumulative error is given by the formula  
       CE Tfinal <0.37.  
   
   
       13 . An apparatus according to  claim 11 , wherein T final  is up to about 4 seconds.  
   
   
       14 . An apparatus according to  claim 11 , wherein T final  is up to about 3 seconds.  
   
   
       15 . An apparatus according to  claim 12 , wherein T final  is up to about 4 seconds.  
   
   
       16 . An apparatus according to  claim 12 , wherein T final  is up to about 3 seconds.