Extruder temperature controller

Abstract

A plastic extruder system having a barrel and a shell with heat exchange elements surrounding the barrel is disclosed. Two thermocouples are provided, one for sensing the temperature of the inner surface of the barrel and the other for sensing the temperature of the shell. A system controller, into which a desired barrel setpoint temperature can be set and stored, receives and stores the independent temperature signals from the thermocouples and controls the heat exchange elements to automatically maintain the temperature of the extruder barrel close to the desired barrel setpoint temperature.

What is claimed is: 
     
       1. An extruder system having a barrel .Iadd.having an axis and a plurality of zones at different positions along said axis, .Iaddend. a shell surrounding said barrel .Iadd.and having a plurality of zones corresponding to said zones of said barrel .Iaddend.and having heat exchange elements .Iadd.for exchanging heat with said zones of said barrel, .Iaddend.   heat exchange element power means,   at least one pair of temperature sensitive elements .Iadd.in each of said plurality of zones.Iaddend., one of said pair being placed to sense the temperature adjacent the inner surface of said barrel, the other of said pair being placed to sense the temperature of said shell, and   a controller having   temperature signal input means for receiving an independent temperature signal from .[.each.]. .Iadd.said one temperature sensitive element and for receiving an independent temperature signal from said other temperature sensitive element .Iaddend.of said pair of temperature sensitive elements,   setpoint signal input means for inputting a setpoint signal representative of a desired barrel temperature setpoint .Iadd.for each one of said plurality of zones of said barrel.Iaddend.,   storage means for independently storing .[.each of said input independent temperature signals and.]. .Iadd.said independent temperature signal from said one temperature sensitive element, said independent temperature signal from said other temperature sensitive element, and .Iaddend.said input setpoint signal, and   control means responsive to said stored input setpoint signal and each of said stored input independent temperature signals .Iadd.for each of said zones .Iaddend.to derive output signals .Iadd.for each of said zones, said control means including means responsive to said stored input setpoint signal for providing a control signal for each of said zones, and means responsive to the deviation between said stored input setpoint signal and said stored input temperature signal from said one temperature sensitive element of said pair, for varying said control signal for each of said zones, said control means further including means responsive to said control signals, as varied by said means for varying a control signal, and said stored input temperature signal from said other temperature sensitive element of said pair, for providing said output signals for each of said zones.Iaddend.,   said heat exchange element power means being responsive to said output signals automatically to maintain the temperature of .Iadd.each of .Iaddend.said .Iadd.zones of said .Iaddend.barrel close to said input setpoint temperature .Iadd.for each of said zones of said barrel..Iaddend.   
     
     
       2. An extruder system as claimed in claim 1, wherein said heat exchange elements include both heating and cooling elements and said output signals selectively operate said heating and cooling elements.   
     
     
       3. The extruder of claim 1, wherein said controller further provides heating limit storage providing a limit temperature signal,   disable signal means responsive to said stored heating limit temperature signal and said stored temperature signal corresponding to said shell temperature for generating a power disable signal for output to said heat exchange element power means.   
     
     
       4. In an extruder system having a barrel and heat exchange apparatus for said barrel, said apparatus comprising a shell surrounding said barrel, said shell providing heat exchange elements, and   heat exchange element power control means,   said system further having at least one pair of temperature sensitive elements, one of said pair being placed to sense the temperature adjacent the inner surface of said barrel, the other of said pair being placed to sense the temperature of said shell,   that improvement comprising a controller having temperature signal input means for receiving an independent temperature signal from each of said pair of temperature sensitive elements,   setpoint signal input means for inputting a setpoint signal representative of a barrel temperature setpoint,   storage means for independently storing each of said input independent temperature signals and said input setpoint signal,   heat exchange element cycle storage means providing a set of signals representative of a plurality of heat exchange element on and off times,   signal deriving means responsive to said stored input setpoint signal and each of said stored input independent temperature signals to derive indexing signals,   indexing means responsive to said indexing signals for applying said indexing signals to said heat exchange element cycle storage means to select certain of said stored heat exchange element on and off time signals, and   output means for outputting said selected signals to control said heat exchange element power control means, whereby the temperature of said extruder barrel is maintained close to said input setpoint temperature.     
     
     
       5. The controller of claim 4, further having gain signal storage means, said signal deriving means being further responsive to said stored gain signal.   
     
     
       6. In an extruder system having a barrel and apparatus for heating and cooling said barrel, said apparatus comprising a shell surrounding said barrel, said shell providing heater elements and cooling elements, and   heater element power control means and cooling element control means,   said system further having at least one pair of temperature sensitive elements, one of said pair being placed to sense the temperature adjacent the inner surface of said barrel, the other of said pair being placed to sense the temperature of said shell,   that improvement comprising a controller having temperature signal input means for receiving an independent temperature signal from each of said pair of temperature sensitive elements,   setpoint signal input means for inputting a setpoint signal representative of a barrel temperature setpoint.   storage means for independently storing each of said input independent temperature signals and said input setpoint signal,   heater and cooler cycle storage means providing a set of signals representative of a plurality of heater and cooler on and off times.   signal deriving means responsive to said stored input setpoint signal and each of said stored input independent temperature signals to derive indexing signals,   indexing means responsive to said indexing signals for applying said indexing signals to said heater and cooler cycle storage means to select certain of said stored heater and cooler on and off time signals, and   output means for outputting said selected signals to control said heater element power control means and said cooling element control means, whereby the temperature of said extruder barrel is maintained close to said input setpoint temperature.     
     
     
       7. The improvement of claim 6, wherein said controller further provides heater element limit temperature storage providing a limit temperature signal,   disable signal means responsive to said stored heater element limit temperature signal and said stored temperature signal corresponding to said shell temperature for generating a disable signal for output to said heater element control means.   
     
     
       8. In an extruder system having a barrel and heat exchange apparatus for said barrel, said apparatus comprising a shell surrounding said barrel, said shell providing heat exchange elements, and   heat exchange element power control means,   said system further having at least one pair of temperature sensitive elements, one of said pair being placed to sense the temperature adjacent the inner surface of said barrel, the other of said pair being placed to sense the temperature of said shell,   that improvement comprising a controller having temperature signal input means for receiving an independent temperature signal from each of said pair of temperature sensitive elements,   setpoint signal input means for inputting a setpoint signal representative of a barrel temperature setpoint,   storage means for independently storing each of said input independent temperature signals and said input setpoint signal,   heat exchange element cycle storage means further providing a set of signals representative of a plurality of heat exchange element on and off times and a reset signal,   a comparator for comparing each of said stored input independent temperature signals with said stored input setpoint signal for deriving a pair of actual error signals each representative of the difference beween one said input independent signal and said input setpoint signal,   reset signal means including a multiplier for deriving a product signal representative of the product of a said actual error signal corresponding to said barrel inner surface temperature, and said stored reset signal, and an adder for deriving a replacement reset signal representative of the sum of said stored reset signal and said product signal,   control setpoint signal means including an adder for summing said stored input setpoint signal and said replacement reset signal to derive a control setpoint signal,   control error signal means including a comparator for comparing each of said stored input independent temperature signals with said control setpoint signal to derive a pair of control error signals,   control sum error means for deriving a control sum error signal representative of a weighted average of said pair of control error signals,   indexing means for applying said control sum error signal to select certain of said stored duty cycle time signals and on-time signals, and   output means for outputting said selected signals for control of said heat exchange element power control means, whereby the temperature of said extruder barrel is maintained close to said input setpoint temperature.     
     
     
       9. In an extruder system having a barrel and apparatus for heating and cooling said barrel, said apparatus comprising a shell surrounding said barrel, said shell providing heater elements and cooling elements, and   heater element power control means and cooling element control means,   said system further having at least one pair of temperature sensitive elements, one of said pair being placed to sense the temperature adjacent the inner surface of said barrel, the other of said pair being placed to sense the temperature of said shell,   that improvement comprising a controller having temperature signal input means for receiving an independent temperature signal from each of said pair of temperature sensitive elements,   setpoint signal input means for inputting a setpoint signal representative of a barrel temperature setpoint,   storage means for independently storing each of said input independent temperature signals and said input setpoint signal,   heater and cooler cycle storage means further providing a set of signals representative of a plurality of heater and cooler operating cycles on and off times, a reset signal and a reset gain signal,   a comparator for comparing each of said stored input independent temperature signals with said stored input setpoint signal for deriving a pair of actual error signals each representative of the difference between one said input independent signal and said input setpoint signal,   reset signal means including a multiplier for deriving a product signal representative of the product of a said actual error signal corresponding to said barrel inner surface temperature, and said stored reset signal, and an adder for deriving a replacement reset signal representative of the sum of said stored reset signal and said product signal,   control setpoint signal means including an adder for summing said stored input setpoint signal and said replacement reset signal to derive a control setpoint signal,   control error signal means including a comparator for comparing each of said stored input independent temperature signals with said control setpoint signal to derive a pair of control error signals,   control sum error means for deriving a control sum error signal representative of a weighted average of said pair of control error signals,   indexing means for applying said control sum error signal to select certain of said stored operating cycle signals, and   output means for outputting said selected operating cycle signals for control of said heater element power control means and said cooling element control means, whereby the temperature of said extruder barrel is maintained close to said input setpoint temperature.     
     
     
       10. The improvement of claim 9, wherein said cooling elements comprise coolant circulation elements, and said cooling element control means comprises coolant circulation control means, said controller further providing flash point storage means for storing a signal representative of the flash point temperature of said coolant,   modifying value storage means for storing at least two modifying value signals,   a comparator for comparing said stored input temperature signal corresponding to said shell temperature with said stored coolant flash point temperature signal and deriving therefrom a difference signal, and   cycle modifying means responsive to said difference signal to select one of said modifying value signals and responsive to said selected modifying value signal to modify said selected cooler operating cycle signal to derive a modified signal for output to said coolant circulation control means.     
     
     
       11. In an extruder system having a barrel and apparatus for cooling said barrel by circulation of a coolant, said apparatus comprising a shell surrounding said barrel, said shell providing coolant circulation elements, and   coolant circulation control means,   said system further having at least one pair of temperature sensitive elements, one of said pair being placed to sense the temperature adjacent the inner surface of said barrel, the other of said pair being placed to sense the temperature of said shell,   that improvement comprising a controller having temperature signal input means for receiving an independent temperature signal from each of said pair of temperature sensitive elements,   setpoint signal input means for inputting a setpoint signal representative of a barrel temperature setpoint,   storage means for independently storing each of said input independent temperature signals and said input setpoint signal,   coolant cycle storage means further providing a set of signals representative of a plurality of coolant circulation control operating cycles,   signals deriving means responsive to said stored input setpoint signal and each of said stored input independent temperature signals to derive an indexing signal,   indexing means responsive to said indexing signal for applying said indexing signal to said coolant cycle storage means to select a particular said stored operating cycle,   output means for outputting said selected signals to said coolant circulation control means,   flash point storage means for storing a signal representative of the flash point temperature of said coolant,   modifying value storage means for storing at least two modifying value signals,   a comparator for comparing said stored input temperature signal corresponding to said shell temperature with said stored coolant flash point temperature signal and deriving therefrom a difference signal, and   cycle modifying means responsive to said difference signal to select one of said modifying value signals and responsive to said selected modifying value signal to modify said selected operating cycle signal to derive a modified signal for output to said coolant circulation control means.     
     
     
       12. In an extruder system having a barrel and apparatus for cooling said barrel by circulation of a coolant, said apparatus comprising a shell surrounding said barrel, said shell providing coolant circulation elements, and   coolant circulation control means,   said system further having at least one pair of temperature sensitive elements, one of said pair being placed to sense the temperature adjacent the inner surface of said barrel, the other of said pair being placed to sense the temperature of said shell,   that improvement comprising a controller having temperature signal input means for receiving an independent temperature signal from each of said pair of temperature sensitive elements,   setpoint signal input means for inputting a setpoint signal representative of a barrel temperature setpoint.   storage means for independently storing each of said input independent temperature signals and said input setpoint signal,   coolant cycle storage means providing a set of signals representative of at least two coolant circulation control operating cycles,   flash point storage means for storing a signal representative of the flash point temperature of said coolant,   a comparator for comparing said stored input temperature signal corresponding to said shell temperature with said stored coolant flash point temperature signal and deriving therefrom a difference signal, and   cycle selecting means responsive to said stored input setpoint signal, each of said stored independent temperature signals, and said difference signal to select one of said operating cycle signals for output to said coolant circulation control means. .Iadd.     
     
     
       13.  An extruder system having a barrel having an axis and a plurality of zones at different positions along said axis,   a shell surrounding said barrel and having a plurality of zones corresponding to said zones of said barrel, and heat exchange elements for exchanging heat with said zones of said barrel,   a heat exchange element power source means,   at least one pair of temperature sensitive elements in each of said plurality of zones,   a first element of each said pair being placed to sense the temperature adjacent the inner surface of its said barrel zone,   the second element of each said pair being placed to sense the temperature of said shell in said zone, and   a controller having   temperature signal circuit elements for receiving a temperature signal from each of said temperature sensitive elements of said pairs,   reference signal circuit elements for providing reference signals each representative of a desired barrel temperature for one of said plurality of zones, and   control circuit elements responsive to said reference signals and each of said input temperature signals to derive a separate output signal for each said zone, and to supply said output signals to said heat exchange element power source means to automatically maintain the temperature of said barrel close to said reference signal temperature for each said zone,   characterized in that   said temperature signal circuit elements receive independently said temperature signals from each of said temperature sensitive elements,   storage circuit elements are provided for storing independently each of said temperature signals and each of said reference signals, before supplying them to said control circuit elements, and   said control circuit elements are arranged to separately receive at least three control signals for each of said zone comprising   a first control signal based on said stored temperature signal from said first element of said pair in said zone,   a second control signal based on said stored reference signal for said zone, and   a third control signal based on said stored temperature signal from said second element of said pair in said zone,   said controller being further characterized in that said control circuit elements include means for varying said second control signal on the basis of the deviation of said stored reference signal compared with said stored temperature signal from said first element of said pair,   said controller being still further characterized by having output signal generating means for providing said output signal at least on the basis of the deviation between said second control signal, as varied by said means for varying, and said third control signal. .Iaddend. .Iadd.   
     
     
       14.  The extruder system of claim 13 further characterized in that said output signal generating means provides said output signal for said zone on the basis of a comparison between an algebraic combination of said stored temperature signals from said pair of elements, and   said second control signal as varied by said means for varying. .Iaddend. .Iadd.15. The extruder system of claim 13 further characterized in that said control circuit elements are arranged to disable said heat exchange element power source means in accordance with a comparison of said stored temperature signal from said second element with a predetermined limit   
     
     
        temperature signal. .Iaddend. .Iadd.16.  The extruder system of claim 13 further comprising means for circulating a coolant in said heat exchange elements, and further characterized in that said control circuit elements are arranged to regulate the circulation of said coolant by said circulating means in accordance with a comparison of said stored temperature signal from said second element with a predetermined signal representative of the flashpoint of said coolant. .Iaddend. .Iadd.17. The extruder system of claim 13 further characterized in that said means for varying is arranged to effect a variation of said second control signal only upon the occurrence of predetermined conditions. .Iaddend. .Iadd.18. The extruder system of claim 17 further characterized in that said control circuit elements are arranged to determine as the occurrence of one said condition when a predetermined algebraic combination of said stored temperature signals from said pair of elements has remained within a predetermined band for at least a predetermined period of time. .Iaddend. .Iadd.19. The extruder system of claim 17 further characterized in that said control circuit elements are arranged to determine as the occurrence of one said condition when the difference between the stored temperature signal from said first element of said pair and said reference signal, as unvaried by said means for varying, is greater than a predetermined amount..Iaddend. .Iadd.20. The extruder system of claim 19 further characterized in that said control circuit elements are arranged to determine as the occurrence of another said condition when a predetermined algebraic combination of said stored temperature signals from said pair of elements has remained within a predetermined band for at least a predetermined period of time, and said variation of said second control signal is effected only upon the simultaneous occurrence of both said conditions. .Iaddend. .Iadd.21. The extruder system of claim 17 further characterized in that said control circuit elements are arranged to determine as the occurrence of one said condition when the difference between a predetermined algebraic combination of said stored temperature signals from said pair of elements, and   said second control signal as varied by said means for varying, is not smaller than a predetermined amount. .Iaddend. .Iadd.22. The extruder system of claim 13   wherein said control circuit elements are further arranged to receive a fourth control signal based on said stored temperature signal from said first element in said pair in said zone, and   wherein said output signal generating means is arranged for providing said output signal on the further basis of the deviation between said second control signal, as varied by said means for varying, and said fourth control signal..Iaddend.