The Application Of Fuzzy Control Algorithms In Papermaking Process

Paper-making process is a very complex chemical process, whichinvolves equipment, both the quantitatively and types could not becompared with other industrial projects. And the production processesinvolves the numerous monitoring point, further more, a majority ofwhich takes on the characteristics of highly nonlinear,multi-interference, strong coupling, pure lag etc. Nevertheless, mostlyloops are controlled by the traditional or integrated PID algorithms(such as the Siemens' FB41, FB42). Siemens Step 7 FB42 is theintegrated non-continuous PID functional modules, primarily forrepresented electric devices figured control loop, which is a special onethat the implementing agencies only accept digital signals from thecontroller transmissions in the control loop. This kind of loop is widelyused in the present paper-making process, its remarkable characteristicis the digital implementing agency, and the characteristic brings newquestion to this kind of loop.The thesis discussed the handling characteristics of the digital loopin paper-making based on the brief introduction of paper-making flow,has studied Siemens PID function block FB42 and its internalconstitution, and its certain questions in the application process. Inview of these questions, fuzzy control theory related knowledge isproposed to the solution, and performs the simulation confirmation. Inthis foundation, the new control plan is invested the actualpaper-making process through programmed. According to this masterline, this article has launched the discussion from following severalaspects.First, the dissertation elaborated the research background of thistopic, introduced the typical process of pulp & paper-making, and hasdrawn out the application widespread and research significance of thedigital loop in pulp & paper-making. Meanwhile, the characteristic ofelectric valve is summarized, which is the most commonly usedimplementing agency in control loop, then the simulation model ofelectric valve has established, and several kind of typical digital loopapplying the electric valve is analyzed in paper-making industry.After simple introduction fuzzy control elementary knowledge, thethesis analyzed the interior each part of work flow of Siemens functionblock FB42, through experimental and read the source code discoveredits internal work process approximately may divide into the PIDoperation and the pulse outputs two bulks. Among them, the PIDoperation has mainly completed the proportion and the integral action.The integral parameter unfixed is one of FB42 characteristics, which isconnected with the operation cycle, the valve travel time and the error.This kind of parameter choice process considerate loop error is withoutdoubt advantageous to balance the contradiction of system stability andresponse fast. The control signal of PID operation is not directly inputfor the digital implementing agency, therefore, transforms the PIDcontrol output through a three-step component into one or more pulsesoutputs, which is an important characteristic of distinguishing fromother PID algorithms. In these analysis results foundations, thesimulation model of Siemens PID function block has established.Second, according to the model of the electric valve and functionblock, linking the actual project application, several main questions hassummarized.In the final analysis, the reason that the digital loop existed thequestions is its non-linearity and making little of the function blockstructure. Therefore, the thesis produced the idea of revisingdynamically FB42 parameters with the loop error. In order to avoid thenegative influence which the non-linearity brings, embarked from theactual project experience, proposed the new strategy that combiningfuzzy control theory and FB42 to solve the questions.The union of fuzzy control theory and FB42 bodies in theformulation of fuzzy rules. According the analysis achievement ofexisting controller and the adjustment experience, the rules table isframed and the simulation model is established. This model and thementioned that of electric valve and function block constitutes acomplete simulation loop through the mutual signal transmission.Finally, the response curves obtained from simulating loop contrastto the one under the PID function block, the loop speed of responsechanges quickly and the adjustment cycle reduce. At the same time, thechanges of valve open degree under the two algorithms indicated thatthe valve quick moving and accurate and the switch times decreaseender the new algorithm. This simulation result confirmed the newcontrol plan indeed to be able to make up the insufficiency of the digitalloop under the PID function block controlling.Performs the new algorithm through the PLC programming in thescene digital loop to apply, the loop control effect promotion isremarkable, which further explained this plan is practical and feasible,has the widespread promotion application value.