JPH0448341B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a plastic injection molding machine, and more particularly to a temperature control device in a heating cylinder thereof.

[Background of the invention]

A typical plastic injection molding machine has an injection screw arranged in a heating cylinder so that it can rotate and move forward and backward. The rotation of this screw feeds the molten synthetic resin into the storage chamber at the tip of the heating cylinder, and then the screw is moved forward to inject and fill the cavity with the synthetic resin.

In order to mold plastics with high precision and quality, the heating cylinder is
It is divided into a plurality of heating zones of ~6 or so, and temperature control is performed for each heating zone.

This temperature control is based on proportional control (P control), with the addition of differential control (D control) to compensate for delays in the temperature control process, and integral control (I control) to reduce the offset value. A so-called PID control method is used.

By appropriately combining each set value of this PID control, the temperature of the heating cylinder is controlled so that the frequency of turning the heater on and off and the deviation from the set temperature are kept to a minimum for a certain set temperature. It can be performed.

Regarding the optimal values of P, I, and D settings in this PID temperature control method, the method of Ziegler & Nichols is known.
In a state where the control is stable, the control operation is set to P control only, the proportional band is gradually narrowed, and the proportional band in which cycling occurs is determined. At this time, it is given by the following formula from the proportional band Kp (%) and the vibration period Tc (minutes). Note that the set values of 1.6, 0.5, and 0.125 in each formula are award values.

P=1.6Kp I=0.5Tc D=0.125Tc The tendency of each characteristic when changing the setting values of P, I, and D control is as follows.

(b) When the setting value of P is increased, ・Overshoot is small.

・Response becomes gradual.

(b) When the set value of P is decreased, ・Overshoot becomes large.

・Response becomes faster.

(c) If you increase the setting value of D, ・Overshoot is small.

・Response becomes gradual.

(d) When the setting value of D is decreased, ・Overshoot becomes large.

・Response becomes faster.

(E) When the setting value of I is increased, ・The offset value will be small.

・Response becomes gradual.

(f) If the setting value of I is decreased, ・The offset value becomes large.

・Response becomes faster.

However, in an injection molding machine, the heat capacity of the heating cylinder (the heat capacity of the heating cylinder is determined by the model), the set temperature of the heating cylinder (the set temperature of the heating cylinder is determined by the type of raw resin), and the formation P, depending on the cycle time, especially the molten resin filling time, pressure holding time, and cooling time (these are determined by the type of raw resin, the wall thickness, weight, and flow path length of the molded product), etc. Since the optimal setting values for I and D control are mutually related in a complicated manner, they cannot be easily set using only the above-mentioned empirical formula or the above-mentioned tendency.

Furthermore, something unique to injection molding machines is that even if the same molding machine is used, each time the mold or materials used are replaced,
Due to the above-mentioned factors, it is complicated to frequently reset the PID control setting values once determined.

In addition, external disturbances such as air temperature, water temperature, and applied voltage, as well as temporary stoppage of the molding cycle due to factors such as clogging of the injection nozzle or malfunction of the mold that prevents the molded product from falling automatically, are added to the PID. Modification of control values cannot be done manually.

For this reason, it is usually common experience to
We set the PID control value, constantly checked the actual status of the heater on/off switching frequency and the deviation value from the set temperature, and corrected the set value little by little based on past experience, which took a very long time. They were pursuing better temperature control.

On the other hand, the defective rate of molded products largely depends on the stability of the temperature of the heating cylinder, especially its nozzle, and is more dependent on the appropriateness of other setting conditions such as injection output, injection speed, holding pressure and cooling time. It has a big impact. In other words, it is an empirical fact that if PID control of the heating cylinder temperature is optimally performed, the defective rate of molded products will be drastically reduced.

As mentioned above, it is important to perfectly manage the temperature of the heating cylinder using optimal PID control.

[Purpose of the invention]

The purpose of the present invention is to solve the problems of the prior art described above, and to provide PID setting values so that general users who do not have special knowledge about PID control can easily obtain the optimal PID control setting state. An object of the present invention is to provide a heating cylinder temperature control device for an injection molding machine that can automatically correct the temperature of the injection molding machine, thereby reducing formation defects.

[Summary of the invention]

In order to achieve the above-mentioned object, the present invention divides a heating cylinder into a plurality of heating zones along its axial direction, and each heating zone is equipped with a heating means such as a band heater and a thermocouple. The present invention is directed to a heating cylinder temperature control device for an injection molding machine, which is equipped with a temperature measuring means and controls the temperature in each heating zone.

In the present invention, the proportional control temporary set value, the integral control temporary set value, and the differential control temporary set value are set for each heating zone based on the molding conditions such as the resin material used and the molding cycle time, respectively, using a keyboard switch or the like. temporary setting means for setting by input; actual temperature sampling means for sampling the actual temperature of each heating zone at a constant cycle; The data calculated based on the input signal is compared with a preset reference value, and the deviation value between the actual temperature of each heating zone and its set temperature is calculated based on the comparison result. and a correction calculation unit that corrects each of the temporary set values so that they fall within the allowable limits, and the provisional settings for proportional control, integral control, and differential control are adjusted according to command signals from the correction calculation unit. This feature is characterized by a configuration in which each value is automatically corrected.

[Embodiments of the invention]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a functional block diagram of a heating cylinder temperature control device in an injection molding machine according to this embodiment, and FIGS. 2, 3, and 4 are flowcharts of PID automatic correction control.

First, the schematic structure and operation of the heating cylinder temperature control device will be explained using FIG.

There is a hopper 2 at the top of the injection machine body 1 for feeding raw materials.
Further, a heating cylinder 3 is provided in front of the injection machine main body 1. Although not shown, an injection screw is disposed in the hollow portion of the heating cylinder 3 so as to be rotatable and movable back and forth.
A mold 4 composed of a fixed mold 4a and a movable mold 4b is arranged in front of the heating cylinder 3.

In this embodiment, the heating cylinder 3 is divided into four heating zones from the tip: a nozzle heating zone, a front heating zone, a central heating zone, and a rear heating zone. Hn5, a front heater Hf6, a central heater Hc7, and a rear heater Hr7 are wrapped around each other, and each of the heaters 5 to 8 is composed of a band heater. In addition, in the vicinity of each heater 5 to 8, there is a nozzle heater temperature sensor TCn9 consisting of a thermocouple, a front heater temperature sensor TCf10,
A temperature sensor Tc11 for the central heater and a temperature sensor TCr12 for the rear heater are respectively attached so that the actual temperature of each heating zone can be measured.

Inside the heating cylinder 3 are the aforementioned heaters 5 to 8.
The pellet-shaped resin material 13 is heated to a predetermined temperature by
is supplied into the heating cylinder 3. The supplied resin material 13 is sequentially kneaded, plasticized, and melted by the rotation of the screw and the heating of the heaters 5 to 8, and is fed into the storage chamber in the nozzle section. After that, injecting the molten resin into the mold 4,
It is filled, cooled, and solidified to obtain a molded product of a desired shape.

Temperature control of the heating cylinder 3 will be explained.
The actual temperature of each heating zone heated by each of the heaters 5 to 8 described above is determined by the temperature sensors 9 to 12.
The detection signal is input to the central processing unit (CPU) 16 via the A/D converter 15 of the heater temperature control device 14. this
The CPU 16 stores a read-only memory (ROM) 17 that stores programs for the heater temperature control device 14, etc., and stores temporary set values for PID control, sampled actual temperatures of the heating cylinders 3, etc., which will be described later, at predetermined addresses. A random access memory (RAM) 18, a clock generating means 19 for generating a clock signal, and an output interface 20 are connected, respectively. In addition, the output interface 20 includes a non-contact relay SSRn21 for the nozzle heater and a non-contact relay SSRf2 for the front heater.
2. Connected to a non-contact relay SSRc23 for the central heater and a non-contact relay SSRr24 for the rear heater.

As shown in the figure, the nozzle heater non-contact relay SSRn21 is connected to the front heater non-contact relay SSRn26 of the nozzle heater circuit 25.
SSRf22 is the contact point 28 of the front heater circuit 27
, the non-contact relay SSRc23 for the central heater
is connected to the contact point 30 of the center heater circuit 29, and the non-contact point SSRr24 for the rear heater is connected to the contact point 32 of the rear heater circuit 31, respectively.

In the figure, 33 is the coil of the nozzle heater intermediate relay Rn, 34 is the contact of the intermediate relay Rn, and 35
is the coil of the front heater intermediate relay Rf, 36 is the contact of the intermediate relay Rf, 37 is the coil of the center heater relay Rc, and 38 is the intermediate relay Rc.
39 is a coil of the intermediate relay Rr for rear heater, and 40 is a contact of the intermediate relay Rr.

41 is a control device for the entire injection molding machine, 42 is a display device, and 43 is a keyboard for inputting temporary setting values, which will be described later.

Next, the automatic correction flow for PID setting values will be explained for each item using FIGS. 2 to 7.
These figures are a flow chart and an explanatory diagram of PID automatic correction control of the nozzle heater section.

(A) Automatic correction of P (proportional control) set value As shown in Figure 2, in step (hereinafter abbreviated as S) 1, the desired set temperature Ts and PID control provisional value are set for each heating zone of the heating cylinder. A keyboard 43 whose setting values are shown in FIG.
is input to the heater temperature adjustment device 14 using the . This provisional setting value is provisionally set based on, for example, the above-mentioned Ziegler and Nicholas method. For example, in the case of a nozzle heater, P=30℃, I=300
Temporarily set D = 30 seconds.

Next, in S2, the tentative setting value of P (P=30℃)
is called from RAM 18 to CPU 16. At this time, the number of elapsed times N is 0.

After calling the provisional setting value of P to the CPU 16 as described above, in S3, the actual temperature T of the heating cylinder is measured by the temperature sensor 9 at a fixed period (for example,
A sampling operation is performed in which T ₁ , T ₂ , T ₃ .

The measured actual temperatures T ₁ , T ₂ , T ₃ ... are the set value Ts
At the same time, a constant processing cycle tc (for example, 10 minutes) is determined, and the actual temperature within that processing cycle tc is A deviation value ΔTp is calculated (S4). FIG. 5 illustrates this deviation value ΔTp.

ΔTp=|Tmax−Tmin| It is determined in S5 whether the deviation value ΔTp calculated in this way is larger than a stability limit value (for example, 3° C.). If the deviation value ΔTp is larger than the stability limit value, the process proceeds to S6, where the set value of P is increased by 1° C., and the steps from S3 to S6 described above are repeated. While doing this, the deviation value ΔTp falls within the desired stability limit, and this is confirmed twice (Number of elapsed times N = 2, see S7 and S8), and S9
In this step, the final value of P is input to a predetermined address in the RAM 18.

(B) Automatic correction of the D (differential control) setting value.
In S11, the actual temperature T of the heating cylinder is measured by the temperature sensor 9, and read as T ₁ , T ₂ , T ₃ . Perform sampling operations to input data to RAM18).

Next, in S12, the temporary setting value of D (30 seconds in this example) is set as the processing cycle tc, and the processing cycle tc
The deviation difference ΔTd between the first actual temperature t ₁ and the final actual temperature t _o of the processing cycle tc is calculated. FIG. 6 shows this deviation value ΔTd.

ΔTd=|T _o −T ₁ | Then, it is determined in S13 whether the calculated deviation value ΔTd is larger than the stability limit value (for example, 2°C), and if the deviation value ΔTd is smaller than the stability limit value,
Proceed to S14 and increase the value of D by, for example, 1 second,
The steps from S11 to S14 described above are repeated several times. In the meantime, the deviation value ΔTd falls within the desired stability limit value, and after confirming this twice (see S15 and S16), the final value of D is input to a predetermined address in the RAM 18 in S17. .

(C) Automatic correction of I (integral control) set value Temporary set value of I input in advance (I = 300 seconds)
is called to the CPU 16 in S18. Next, in S19, the actual temperature of the heating cylinder is measured by the temperature sensor 9 at regular intervals (for example, every 10 seconds) at T ₁ , T ₂ ,
A sampling operation is performed to read T ₃ .

In S20, the temporary setting value of I (300 seconds in this example) is directly used as the processing cycle Tc, and the average value of the actual temperatures T ₁ , T ₂ , T ₃ , . . . T _o measured during that period is calculated. Next, in S21, the average value and the set value
Calculate the deviation value ΔTi from Ts.

ΔTi=|−Ts| FIG. 7 shows these average values and set value Ts.

It is determined in S22 whether the deviation value ΔTi calculated in this manner is larger than a stability limit value (for example, 1° C.). If the deviation value ΔTi is larger than the stability limit value, the process proceeds to S23, where the set value of I is increased by 10 seconds, and the steps from S19 to S23 described above are repeated. While doing this, the deviation value ΔTi falls within the desired stability limit and confirms this twice (Number of elapsed times N = 2, see S24 and S25)
Then, in S26, the final value of I is input to a predetermined address in the RAM 18, and the PID automatic correction control is ended.

Similar automatic corrections are also performed in parallel in other heater sections.

In this embodiment, in order to shorten the control time,
Although the present invention is a program that first automatically corrects the P setting value, then automatically corrects the D setting value, and finally automatically corrects the I setting value, the present invention is not limited to this, and for example, the P setting value is automatically corrected. , I, and D may be automatically corrected in this order.

In addition, PID automatic correction is completed once the flow steps shown in Figures 2 to 4 are completed, but in order to cope with subsequent disturbances, S2 and S3 are changed as shown in Figure 2. It is a good idea to go back and perform the same process as above. In this way, the difference between the actual temperature of the heating cylinder and the desired temperature can always be kept within 1° C. until the molding operation is completed.

〔Effect of the invention〕

The present invention has the above-mentioned configuration, and since the initially provisionally set P, I, and D setting values can be automatically corrected, the troublesome manual correction can be reduced to a minimum, for example, in about 30 minutes. The difference between the actual temperature of the heating cylinder and the desired set temperature can be reduced to within 1°C within a short period of time, which improves the quality of injection molded products, which are particularly sensitive to temperature, and reduces the defective rate. , an injection molding machine with good handling properties can be provided.

[Brief explanation of drawings]

The drawings are all for explaining embodiments of the present invention, and FIG. 1 is a functional block diagram of a heating cylinder temperature control device in an injection molding machine, and FIGS.
4 and 4 are flowcharts of PID automatic correction control, and FIGS. 5, 6, and 7 are explanatory diagrams showing the calculated deviation value ΔT. 3... Heating cylinder, 5... Nozzle heater, 6
...Front heater, 7...Central heater, 8...Rear heater, 9...Temperature sensor for nozzle heater, 1
0... Temperature sensor for front heater, 11... Temperature sensor for central heater, 12... Temperature sensor for rear heater, 14... Heater temperature adjustment device, 17...
ROM, 18...RAM, 19...Clock generating means, 25...Nozzle heater circuit, 27...Front heater circuit, 29...Central heater circuit,
31... Rear heater circuit, 43... Keyboard.

Claims (1)

[Claims] 1. An injection molding machine in which a heating cylinder is divided into a plurality of heating zones along the axial direction, each heating zone is provided with a heating means and a temperature measuring means, and the temperature is controlled in each heating zone. In the heating cylinder temperature control device, provisional settings are used to set provisional proportional control settings, provisional integral control settings, and provisional differential control settings for each heating zone based on molding conditions such as the resin material used and molding cycle time. means, an actual temperature sampling means for sampling the actual temperature of each heating zone at a fixed period, and data and a reference value calculated based on a signal inputted by the sampling means within a fixed processing period. and a correction calculation unit that compares and corrects each provisional setting value based on the comparison result so that the deviation value between the actual temperature of each heating zone and its set temperature falls within an allowable limit. A heating cylinder temperature control device for an injection molding machine. 2. In claim 1, the correction calculation unit is configured to correct the temporary set values in the order of a proportional control temporary set value, a differential control temporary set value, and an integral control temporary set value. A heating cylinder temperature control device for an injection molding machine.