JPH0698670B2 - Extruder temperature control method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a temperature control method for an extruder.

[Prior Art] There are several devices and methods for determining an appropriate PID constant of a temperature controller in a temperature control system of an extruder. Conventional methods include the transient response method by Ziegler-Nichols and the limit sensitivity method.Recently, an expert method that uses the response waveform of the measured temperature, or a device that obtains a fixed signal on the operation output from the temperature controller And there are ways.

The plastic material put into the extruder is heated from the outside of the cylinder while being transferred forward by the screw,
It is melted by the internal heat generated by the shearing action of the screw. At this time, the calorific value that cannot be completely cooled by natural cooling is forcibly cooled by gas or liquid.When controlling the temperature with a PID controller, a dual type that has heating output and cooling output Is used.

The conventional control method by the PID controller compares the set temperature and the control point temperature by the temperature sensor at the butt point, and the PID controller calculates the operation output y (t)% as shown in the following formula,
It outputs it to the process and controls it.

(However, PB (℃); proportional band, Ti (seconds); integration time, Td
(Seconds); differential time, e (t); indicates temperature deviation) The above-mentioned PB, Ti, and Td are called PID constants, and are appropriately determined by the user according to the operating conditions. Therefore PI
If the D constant was set improperly, good control could not be performed.

In addition, the cylinder of the extruder has heating control and cooling control as described above, and a heater is used for heating control.
D The influence of the operation output from the controller on the process becomes linear and the proper PID constant can be determined. However, the cooling control causes the operation output to change due to the phase change of water (liquid → gas). However, the effect on PID was non-linear and it was not possible to determine an appropriate PID constant.

For example, when using an aluminum casting heater with a water-cooled pipe as shown in FIG.
The static cooling characteristics that show the relationship between the ON time of the solenoid valve that allows cooling water to pass through and the cooling capacity are explained below. Generally, at a temperature of 100 ° C to 300 ° C at which the extruder is operated, the cooling pipe is used when the amount of cooling water is small. Almost all of the water inside is vaporized, but the amount of heat taken up increases as the amount of cooling water increases, and new cooling water is injected before the temperature of the inner wall of the cooling pipe recovers sufficiently. The temperature difference between
It will be understood that the rate of vaporization decreases due to the decrease in the heat quantity of the heater applied to the cooling water, and the cooling effect decreases.

More specifically, when the screw speed is low, that is, when the amount of heat generated is low and the ON rate of the solenoid valve is low, the amount of cooling water sent to the cooling pipe in the heater is small, and the cooling water is easily vaporized and The amount of cooling heat per valve ON time, that is, the cooling gain becomes large (region I).

On the other hand, when the screw rotation speed is high, the solenoid valve ON rate is high and the amount of water supplied increases, resulting in a decrease in the cooling effect and a decrease in the cooling gain (region III).

Therefore, there is an inflection point between the regions I and III, and the cooling gain in the vicinity of this is an intermediate value between the regions I and II (region I
I).

As described above, the cooling characteristics are slightly different depending on the size of the extruder and the design of the cooling system, but the inclination of the characteristics itself is considerably different depending on the valve opening, the set temperature, and the cooling cycle. Naturally, the PID constant also changes depending on each area.

With the conventional device, it was not possible to determine the optimum PID constant in each region because this very strong nonlinearity could not be measured.

[Object of the Invention] The present invention has been made from such a viewpoint, and its object is to perform heating control with a PID controller before starting a molding operation and to turn on a cooling solenoid valve at a constant level by a command from a sequencer. -Providing an extruder temperature control method with precise temperature control by optimizing the PID constant by controlling the static cooling characteristics of the extruder itself by controlling with the OFF pattern. is there.

[Points of the Invention] An extruder temperature control method according to the present invention includes a temperature detection sensor, a heating heater, and a cooling device operated by a cooling solenoid valve, and has a dual output type with a communication function for heating and cooling. In the extruder temperature control method in which the PID controller and the circuit that connects the cooling solenoid valve to the sequence that can automatically control the cooling solenoid valve with an arbitrary constant ON-OFF pattern are switchably provided and controlled, the normal molding operation is performed. Before entering, control the heating with the PID controller and control the cooling solenoid valve with a constant ON-OFF pattern according to the command from the sequence to measure and calculate the static cooling characteristics and optimize the PID constant of the PID controller. The feature of the present invention is that the extruder is controlled so that the PID controller is switched during the normal molding operation.

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to FIG. The computer 11 is provided with a setting keyboard 12 for setting various conditions, and the computer 11 and the dual output type PID controller 13 with a communication function can communicate with each other by RS232C, and the screw 14 is internally provided. The temperature of the barrel 15 of the extruder provided is PID by the temperature sensor 16.
It is sent to the controller 13. As a result, the temperature of the barrel 15 can be transmitted to the computer 11, and the temperature set in the computer 11 can be transmitted to the PID controller 13 in both directions.

The sequencer 17 generates a fixed signal of a constant ON / OFF pattern for heating / cooling in response to a command from the computer 11, and outputs the heating / cooling output to the cylinder 15 by the changeover switch 18.
Whether to perform the command from the PID controller 13 or the command from the computer 11 can be selected for each heating and cooling. The operation of the changeover switch 18 can also be performed by a command from the computer 11, and even if the changeover switch 18 is on the PID controller 13 side, the measured temperature can be transmitted to the computer 11. Although FIG. 1 shows one channel, it is possible to control a plurality of barrels 15 at the same time. In addition, the changeover switch 18
When the D controller 13 side is set, normal temperature control is performed. An example of obtaining the static cooling characteristics by using the above temperature control will be described below. When the temperature of the barrel 15 is set to the set temperature by the PID controller 13 and it is forcibly cooled by the ON time of the cooling solenoid valve 19 which is set in the cooling cycle to be controlled, the temperature will drop, but the output on the heating side by the heater 20 will be PID adjusted. If it is controlled by the total 13, the temperature is maintained near the set temperature. At that time, if the difference between the measured temperature and the set temperature is, for example, continuously within ± 1 ° C for a certain period of time, if the average heating operation output from the PID controller 13 is obtained, the arbitrary cooling solenoid valve 19 turns ON. The static cooling capacity over time can be determined. This is shown in the flow chart of FIG.

The flowchart will be described here. The sequencer 17 is instructed to generate a cooling fixed signal with a preset constant ON-OFF pattern at 31, and the heater is switched to the heater 18 at 32.
The PID controller 13 controls 20 to control the cooling solenoid valve 19 on the cooling fixed signal generation side. At 33, the measured temperature from the PID controller 13 and the data of the heating operation output are sampled,
Calculate the deviation between the measured temperature and the set temperature sampled in 34 and judge whether the deviation is within ± 1 ° C,
If it is within the range, the temperature continuous equilibrium time is calculated at 35, and it is judged at 36 whether or not the temperature continuous equilibrium time is the preset equilibrium time, and steps 33 to 36 are repeated until YES. Calculate an average heating maneuver output at 37 using all sampled heating maneuver outputs that are within the temperature continuous equilibrium time when YES.

Since heating is required to maintain the set temperature in the uncooled state, the average heating operation output in the uncooled state is obtained in advance to determine the cooling capacity for the ON time of any solenoid valve 19 for cooling. As shown in the following formula.

Cooling capacity = (Average heating operation output for any cooling solenoid valve ON time)-(Average heating operation output without cooling) Generally, the heating operation output from the PID controller 13 is output in%. Since the capacity of 20 is available, the cooling capacity can be converted to KW.

In this way, by changing the ON time of the solenoid valve for cooling 19 and repeating the above (enabled by the computer 11), the static cooling characteristics at the set temperature to be controlled and the cooling cycle can be obtained. Will be possible.

[Effect of the Invention] As described above, the method for controlling the temperature of an extruder according to the present invention makes it possible to correctly measure the static cooling characteristics in which the influence of the operation output on the process becomes nonlinear, and thus the PID constant is obtained. The temperature controllability of the extruder can be refined.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention, FIG. 1 is a mechanism diagram, FIG. 2 is a flow chart diagram, and FIG. 3 is a diagram showing static characteristics. 11 …… Computer, 13 …… Dual output type PID controller with communication function, 17 …… Sequencer, 18 …… Changeover switch.

Continuation of the front page (56) References JP-A-62-37122 (JP, A) Actually developed Shou-54-31066 (JP, U)

Claims (1)

[Claims] 1. A temperature detecting sensor, a heating heater,
A dual output type PID controller with a communication function for heating and cooling equipped with a cooling device operated by a cooling solenoid valve and a sequencer that can automatically control the cooling solenoid valve with an arbitrary constant ON-OFF pattern In the temperature control method of the extruder, which is switchably provided with a circuit to control, the heating is controlled by the PID controller and the cooling solenoid valve is constantly turned on by the command from the sequencer before starting the normal molding operation. -Extruder temperature control method in which static cooling characteristics are measured and calculated by controlling with an OFF pattern to optimize the PID constant of the PID controller, and the PID controller is switched to during normal molding operation.