Posted 20 Dec 2010 22:14
Introduction The advent of PID control has been 60 years of history, the use of PID (proportional - integral - derivative) control design can eliminate the inertia of the temperature controller the temperature error, PID control is the introduction to PID control according to the system come out has been 60 years of history, by PID (proportional - integral - derivative) control the temperature controller can be designed to eliminate the temperature error of inertia, PID control is the proportional error according to the system - integral - derivative to calculate the control volume, due to the traditional PID control algorithm, the computation is simple, easy to adjust, robust, have a very wide range of applications; mathematical model for a certain purpose, according to Yuan Xing internal pattern and nature of the property, through the necessary simplifying assumptions, the use of appropriate mathematical tools, which makes the abstract, simplified mathematical structures. Mathematical model can be used to predict the future development of law of things, or to control the development of a phenomenon of optimal strategies under a sense or good policy. Plastic extrusion machine is mainly is the use of plastic plasticity, the plastic in the machine barrel and screw through the heating effect, after crushing, melting, plastic, exhaust, compaction process, the final shaping and cooling, plastic extrusion machine is shaped plastic composite pipe extrusion and production of key equipment. Extrusion temperature is too low, poor extrusion the material, resulting in front-end load is too large extrusion bodies; extrusion temperature is too high, you may change the characteristics of raw materials lead to product obsolescence, so out of temperature control determines the performance of plastic extrusion machine . Extruder heating device used in the electrical heating, resistance heating and induction heating is divided into. Cooling unit is divided into two kinds of wind cooling and water cooling, air cooling is to control the cooling fan away the heat, but use more water discharge pipe in the water cycle take control of the heat, melt pressure measurement device with sensors. Figure 1 shows the temperature control of plastic extrusion machine plastic extrusion schematic diagram of Figure 1 Schematic diagram of temperature control unit 1. Heating and cooling water temperature control during the modeling and analysis of nonlinear mathematical model is an abstract simulation, it uses symbols, formulas, procedures, graphics and other mathematical language characterize the nature of objective things, properties and internal relations, is the real world but the nature of the simplified description. Mathematical model of the three main functions: to explain, to determine and forecast, which is the mathematical model can be used to explain the phenomenon and the occurrence of certain objective reasons. To Extruder heating and water cooling process modeling and analysis of nonlinear temperature control, the first object will be charged with the process control applications from the specific stripping out of the controlled object is simplified as shown in Figure 2, the heating closed containers and water cooling model, the use of mathematical language of the actual object simplification and assumptions necessary for its creation of a suitable mathematical model. Figure 2 Simplified airtight container for heating and water cooling model (1) system control object wall heat transfer is negligible. (2) system control object penetration of wind is negligible. If we do not take into account the inertia of the actuator and temperature control is passed behind the object, according to the conservation of energy, per unit time into the energy of the object per unit time minus the outflow of energy from the object within the object is equal to the rate of change of energy storage stocks, and its differential equation: Q = Chrr * (dT / dt) = Qe-Qc where: Q - the heat change airtight container (KJ / h); Chrr - room temperature heat capacity (KJ / ?; T - air temperature ; Qe - heat into electric heating (KJ / h); Qc - water cooling away the heat (KJ / h); If we do not take into account the inertia of the actuator and temperature control is passed behind the object, according to the principle of heat balance, thermal components heat balance differential equation: q2 = C2 * (dT2/dt) = 2 * S2 * (T1-T2) where: C2 - thermal resistance of the heat capacity (KJ / ?; T2 - Heat resistance temperature ( ?; q2 - unit of time to pass the air thermal resistance of heat (KJ / h); 2 - air and heat resistance of the surface heat transfer coefficient between the (KJ/m2 h ?; S2 - thermal resistance of the surface area (m2) ; T1 - indoor air temperature, return air temperature ( ?. Actual Extruder heating and water cooling process, we must take into account the inertia of the actuator and the temperature control object transfer delay, heating and water cooling inertia for containing energy storage component, so the mutation can not immediately reproduce the input signal, and its differential equation for the dc (t) T --- + c (t) = r (t) dt where: the input signal r (t) the output signal c (t) temperature control object transfer lags (also known as delayed link), the differential is c (t) = r (t - t) where: t for the lag time input signal r (t) the output signal c (t) for plastic extruder heating control is a linear process, heating only affects the size of the input signal amplitude of the response, but does not change the shape of response curve. Extruder temperature control as will normally be about 200 ? when the water cooling, liquid water was instantly vaporizes away large amounts of heat, water cooling of the input signal with different size, and shape of the amplitude response curve will have significant change, so that the output has a variety of different forms. Therefore, the traditional PID temperature controller is difficult to ensure the host temperature fluctuations in the stability control system to achieve a variety of plastic extrusion temperature requirements, as shown in Figure 3 Extruder heating and water cooling temperature of the conventional PID control curve. Figure 3 Extruder traditional heating and water cooling process PID temperature control curve 2. Controller P8160 nonlinear heating and cooling water temperature control design WEST is the world's top 500 enterprises DANAHER Group, a subsidiary of the United States, WEST's thermostat up to a thousandth of accuracy, compared with most foreign Thermostat better price, in the textile setting machine, furnace, plastic, wire and cable industry wide application range. WEST company designed specifically for plastic extruder temperature controller P8160, drawing on the traditional PID control, the introduction of fuzzy rules of the algorithm and implementation, including the parameters of fuzzification, fuzzy rule inference, parameter ambiguity, PID controller, and several other important part of the fuzzy PID controller P8160 temperature control block diagram shown in Figure 4. Computer according to the reference input and feedback signals, calculate the actual temperature and the temperature deviation between theory and the current rate of change bias in the fuzzy inference device experience in the use of fuzzy reasoning, fuzzy reasoning output PID controller, the proportional coefficient, integral coefficient and the differential coefficient, use them as reference for the current controller PID control, the control each time the controller parameters are controlled according to the specific conditions in real-time correction, and therefore the optimal control action can achieve results. Figure 4 Fuzzy PID Controller P8160 temperature control block diagram of control principle with the temperature controller P8160, plastic extruder by heating and water cooling process is called fuzzy rules can effectively control the cooling process of cooling the water vapor produced nonlinear effect, as shown in Figure 5 Extruder heating and water cooling process P8160 traditional fuzzy PID temperature control curve, you can see P8160 stable during the heating process to solve the problem of integral saturation, to achieve control of temperature, but red ; When you change the set point temperature, cooling process is quick, small overshoot, and in a short time once again reaches the set point, control the temperature fluctuation is small, so that the whole host to the extrusion temperature temperature control requirements, increase transfer rates of solid materials, stable plastic out of production while improving product quality. Figure 5 Plastic Extruder heating and water cooling process P8160 Fuzzy PID temperature control curve 3. Extruder temperature controller-specific features of other applications P8160