JP2512519B2 - Extruder cylinder temperature control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Field of Industrial Application) The present invention relates to a cylinder temperature control method for an extruder, which controls the cylinder temperature of the extruder by heating control and cooling control.

(Prior Art) A plastic material charged into an extruder is melted by a screw while being transferred to the front by heating from the outside of the cylinder and internal heat generated by the shearing action of the screw. At this time, the amount of heat that cannot be completely cooled by natural cooling is adopted by a temperature control method in which the gas or liquid is forcibly cooled. In order to perform heating control and cooling control in this way, a dual type PI with heating output and cooling output
D controller is used.

A conventional cylinder temperature control method for an extruder will be described with reference to FIG. Set temperature from temperature setting unit 1 and process 5
The deviation temperature e (t) (° C.) from the control point temperature at is obtained by the comparator 3 and input to the PID controller 4. PID controller 4
Calculates an operation output m (t) as expressed by the following equation (1) and outputs the operation output m (t) to the process 5, which is a control target, for heating control or cooling control. If m (t) is positive, heating control is performed, and if m (t) is negative, cooling control is performed.

(However, PB: proportional band (℃), Ti: integration time (sec), T
d: Derivative time (sec)) These PB, Ti, and Td are called PID constants, and are set appropriately according to operating conditions. If this PID constant is set inappropriately, good control will not be possible. Generally, the larger the constant PB is, the smaller m (t) is, and the stability in the steady state is increased, but it takes time to reach the set temperature with respect to the change of e (t) with respect to the set temperature and disturbance. It tends to take a lot of money.

Also, the cylinder of the extruder has heating control and cooling control as described above, and in the heating control, the heater is used and the influence of the operation output from the PID controller on the process becomes almost linear and the appropriate PID constant is determined. However, in the cooling control, the influence of the operation output on the process became non-linear because of the phase change between the liquid water and the gas, which was the cooling medium, and the proper PID constant could not be determined.

In the temperature control system of the extruder, the so-called time proportional concept is adopted as the operation output method from the PID controller. For example, in the case of cooling, the amount of cooling water is controlled by the ON / OFF time of the solenoid valve according to a certain cooling control period T as shown in FIG. The relationship between m (t) in equation (1) and the ON time of the solenoid valve is shown by equation (2).

ON time = Tm (t) / 100 (2) For example, an electromagnetic wave that passes cooling water when the cooling control cycle T is 30 seconds by using an aluminum casting heater with a water cooling pipe to keep the heater temperature at 150 ° C. FIG. 9 shows the static cooling characteristics, which is the relationship between the valve ON rate (operation output m (t)) and the static cooling capacity. As shown in FIG. 9, at a temperature of 100 to 300 ° C. at which the extruder is usually operated, when the amount of cooling water is small, almost all the water in the cooling pipe is vaporized, so that the cooling effect is good. However, as the amount of cooling water increases, the amount of heat taken increases and new cooling water is injected before the temperature of the inner wall of the cooling pipe recovers sufficiently, so the temperature difference between the water temperature and the inner wall of the cooling pipe becomes small, and the cooling water The rate of vaporization decreases due to the decrease in the heat quantity of the heater given to the element, and the cooling effect decreases.
Furthermore, when the amount of cooling water increases, it hardly vaporizes,
Further, the cooling effect is reduced.

More specifically, when the screw speed is low,
That is, when the heat generation amount is low and the ON rate of the solenoid valve is low, the amount of cooling water in the cooling pipe in the heater is small and the cooling water is easily vaporized, and the cooling heat amount per solenoid valve ON time, that is, the cooling gain becomes large. On the other hand, when the screw rotates at a high speed, a large amount of heat is generated, the ON rate of the solenoid valve is high, and the supply amount is large.

(Problems to be Solved by the Invention) As described above, the non-linear static cooling characteristics differ depending on the size of the extruder and the cooling system, and also differ depending on the set temperature. Further, the calorific value varies depending on the screw rotation speed and the location of the cylinder, which affects the static cooling performance. Therefore, it is extremely difficult to determine the PID constant in consideration of such many factors.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a cylinder temperature control method for an extruder that can perform control with an optimum control constant even when the set temperature or the amount of heat generation changes.

[Structure of Invention]

(Means for Solving the Problem) The above-mentioned object is to perform cooling control or heating control by a controller that performs at least proportional operation and integral operation to calculate an operation output so as to eliminate the deviation temperature between the cylinder set temperature and the measured temperature. In the method of controlling the cylinder temperature of the extruder, the constant of proportional operation of the controller is changed based on the deviation temperature and the state of the operation output. .

(Operation) According to the method for controlling the cylinder temperature of the extruder of the present invention, the proportional constant is changed according to the deviation temperature between the set temperature and the measured temperature and the change in the operation output state of the controller to change the nonlinear cooling characteristic. The optimum control is made according to the above.

(Example) Hereinafter, the present invention will be described based on an illustrated example.

A cylinder temperature control method for an extruder according to an embodiment of the present invention will be described with reference to FIG. Similar to the conventional cylinder temperature control method for an extruder, the deviation temperature e (t) between the set temperature from the temperature setting unit 1 and the control point temperature in the process 5
(° C) is calculated by the comparator 3 and input to the PD controller 4.
The PID controller 4 calculates an operation output m (t) as expressed by the above-mentioned equation (1) and outputs it to the process 5 which is a control target to control heating or cooling.

The feature of this embodiment is that a storage arithmetic unit 6 is further provided. The memory computing unit 6 includes the maximum and minimum cooling proportional bands previously determined by the amount of cooling water, and the expansion proportional cooling bands PB1, PB2, ..., PBn (PB1 <PB2 <... <PBn)
Remember. The memory calculator 6 calculates the deviation temperature e (t) from the comparator 3 and the operation output m (t) from the PID controller 4, and the measured temperature is not too large from the set temperature from the deviation temperature e (t). Whether the operation output is stable or not is determined, and the optimum cooling proportional band PB is determined based on this determination result.
Command the PID controller 4.

The basic PID constant in this control is the heating control PID.
A constant, for example, the transient response method by Ziegler-Nichols, the limit limit method, the expert method that uses the response waveform of the measured temperature, or the method for obtaining the identification signal on the operation output from the PID controller, etc. Keep it.

Next, a method of determining the maximum and minimum cooling proportional bands from the amount of cooling water will be described with reference to FIG. The second characteristic is an approximation of the static cooling characteristic of FIG. It is divided into three regions I to III according to the cooling ON rate. Almost all the cooling water is vaporized in the region I, a part of the cooling water is vaporized in the region II, and the cooling water is hardly vaporized in the region III. If the cooling water amount F (kg / hour) at any valve opening is measured in advance, the cooling water flow rate can be known from the cooling ON rate. Therefore, the cooling ON rate A on the horizontal axis in Fig. 2 can be calculated as The amount of cooling water F1 (kg / hour) can be converted by the formula 3).

F1 = 0.01 · F · A (3) If all the cooling water is vaporized in the region I, the cooling capacity H1 (kw) at the flow rate F1 can be calculated by the following equation (4).

H1 = (F1 / 860) x (540 + T2-T1) (4) where 540 is the heat of vaporization, T1 (° C) is the inlet temperature of the cooling water, and T
2 (℃) is the outlet temperature of the cooling water, and 860 is a constant for converting kcal / hour to kw. Since T2 (° C) evaporates cooling water, it may be considered as 100 ° C. The outlet temperature of the cooling water is 100 ℃
However, the cooling capacity H2 (kw) when it is not vaporized at all can be obtained by the following equation (5).

H2 = (F1 / 860) x (100-T1) (5) When the cooling valve opening is determined in this way, the cooling capacity of the cooling water in a specific state is theoretically obtained from the cooling ON rate. be able to.

The cooling capacity (kw) on the vertical axis in FIG. 2 can be set to the heating ON rate (%) if the maximum heater output of the extruder is known.

Therefore, FIG. 2 shows the relationship between the heating capacity of the heater and the cooling capacity of the cooling water at any ON rate. The ratio of the largest heating capacity and cooling capacity is shown by the slope of the straight line 11 from the formula (4) and the maximum output, and the ratio of the next largest heating capacity and cooling capacity is the formula (5) and the maximum output. It is shown by the slope of line 12. The product of this straight line 11 and the heating proportional band is the maximum cooling proportional band, and the product of the slope of the straight line 12 and the heating proportional band is the minimum cooling proportional band.

Next, the cylinder temperature control method of the extruder according to this embodiment will be described with reference to the flowchart of FIG. FIG. 3 shows the operation of the storage arithmetic unit 6, and is a part of the overall control flow. The operation of FIG. 3 is performed at regular intervals. Further, first, the cooling proportional band is set to the minimum cooling proportional band PB1.

In the control flow of the memory computing unit 6, it is first determined in step 21 whether the cooling proportional band currently set is the minimum cooling proportional band PB1. If it is also the minimum cooling proportional band PB1, no processing is performed and the process proceeds to step 23 and subsequent steps. If the current cooling proportional band is not the minimum cooling proportional band PB1, it is determined in step 22 whether the deviation temperature e (t) is smaller than -TT ° C. If the deviation temperature e (t) is less than -TT ° C, that is, the measured temperature is higher than the set temperature by a predetermined temperature TT ° C, the step
28, for example, set the minimum cooling proportional band PB1 to PID controller 4
Command. In step 28, the PID controller 4 may be instructed to use a cooling proportional band one step lower than the present. That is, if the current cooling proportional band is PBi, the cooling proportional band PBi is one step lower.
Set to -1. When the deviation temperature e (t) is larger than -TT ° C, that is, the measured temperature is not higher than the preset temperature TT ° C, the process proceeds to step 23 and subsequent steps.

In step 23, the current cooling proportional band is the maximum cooling proportional band.
Whether it is PBn or not is determined, and if it is the maximum, nothing is processed and the process returns to the return, and the process of the storage operation unit 6 is ended. If it is not the maximum, go to step 24.

Next, it is determined whether or not the operation output is being repeatedly heated and cooled alternately and is unstable (step 2).
4, 25). It is considered unstable if heating and cooling are repeated in a short cycle. For example, as shown in FIG. 4 (a), the interval TH between the heating control periods T1H and T2H and the interval TC between the cooling control periods T1C and T2C are determined within a certain period T, and the intervals TH and TC
The ratio TH / TC of is calculated. If this ratio TH / TC satisfies, for example, the following expression (6), it is judged to be "unstable".

0.7 <TH / TC <1.3 (6) If it is judged to be unstable in step 25, step
At 29, the PID controller 4 is instructed to provide a larger cooling proportional band.
That is, if the current cooling proportional band is PBi, PBi + 1 is commanded. Then, the process returns to the end and the processing of the memory computing unit 6 is completed.

If the operation output is only cooling, the process proceeds to steps 26 and 27 to calculate and judge whether or not the operation is unstable. If the cooling ON rate repeatedly changes significantly, it is considered to be unstable. For example, as shown in FIG. 4 (b), the minimum MIN (i) and the maximum MAX (i) of the cooling ON rate alternately occur, and the maximum cooling ON rate MAX (i) is 3% or more in succession three times. And the ratio MIN (i) / MAX (i)
Is 2 or more, it is considered to be unstable. If it is judged to be unstable in step 27, in step 30, the PID controller 4 sets the cooling proportional band larger than the current cooling proportional band PBi by, for example, 20%.
Command. This is because the "unstable" when the cooling control is continued is eliminated by slightly increasing the cooling proportional band as compared with the case where the cooling and the heating are alternately repeated.

FIG. 5 shows the experimental results of the temperature control according to this embodiment,
FIG. 6 shows the experimental results of conventional temperature control. The upper graph is the temperature control result, and the lower graph is the operation output at that time. The experiment is the third of the 90φmm single screw extruder.
A step-like disturbance (internal heat generation) was intentionally put in the zone. As you can see from the comparison. The maximum deviation temperature is about 1/2 of that of the conventional example, and the time required to reach the set temperature is about 10 minutes shorter than that of the conventional example.

The present invention is not limited to the above embodiment, and various modifications can be made. For example, in the above embodiment, the controller is a PID controller that performs proportional operation, integral operation, and derivative operation, but it may be a PI controller that performs proportional operation and integral operation.

〔The invention's effect〕

As described above, according to the present invention, even if the set temperature or the calorific value inside the extruder changes, even if there is strong nonlinearity in the static cooling characteristics, the optimum control constant is commanded according to the change. be able to. Therefore, the control temperature is stable in the shortest time, and safe continuous operation can be performed.

[Brief description of drawings]

FIG. 1 is a block diagram of an apparatus for carrying out a method for controlling a cylinder temperature of an extruder according to an embodiment of the present invention, FIG. 2 is a graph approximately representing static cooling characteristics of a cylinder of an extruder, and FIG. FIG. 4 is a flow chart showing a cylinder temperature control method of the extruder, FIG. 4 is a time chart for explaining control stability in the cylinder temperature control method of the extruder, and FIG.
FIG. 6 is a graph showing a control result by a cylinder temperature control method of an extruder according to the present invention, FIG. 6 is a graph showing a control result by a cylinder temperature control method of a conventional extruder, and FIG. 7 is a cylinder temperature of a conventional extruder. FIG. 8 is a block diagram of an apparatus for carrying out the control method, FIG. 8 is a time chart for explaining time proportional control in temperature control, and FIG. 9 is a graph showing static cooling characteristics of a cylinder of an extruder. 1 ... Temperature setting section, 3 ... Comparison section, 4 ... PID controller,
5 ... Process, 6 ... Memory calculator.

Claims (1)

(57) [Claims] 1. A cylinder temperature of an extruder in which cooling control or heating control is performed by a controller that calculates an operation output by performing at least a proportional operation and an integral operation so as to eliminate a deviation temperature between a set temperature of a cylinder and a measured temperature. In the control method, the constant of proportional operation of the controller is changed based on the deviation temperature and the state of the operation output.