JPH0643086B2 - Plasticization control device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasticization control device for an injection molding machine, and more particularly to a plasticization control device for keeping a molten resin temperature constant. .

(Prior Art) FIG. 2 shows an example of the configuration of a control system for controlling the screw rotational speed and screw back pressure during plasticization of an injection molding machine, which the applicant previously proposed in Japanese Patent Laid-Open No. 61-7455. It is a block diagram.

In FIG. 2, when a solid particle resin material 1 is fed from a hopper 2, the screw 3 rotates to melt and plasticize the resin material 1, and at the time of injection, the plasticized resin is extruded. Play a role. The hydraulic motor 4 rotates the screw 3, and the plasticized resin is sent by the screw 3 and stored in the tip of the cylinder 5. The heater 6 plays a role of heating the cylinder 5. Further, the injection hydraulic cylinder 7 applies a back pressure to the screw 3 during plasticization of the resin, and generates a force for pushing out the screw 3 at the injection speed during injection.

Reference numeral 8 is a proportional flow valve for adjusting the amount of oil to the hydraulic motor 4 or the injection hydraulic cylinder 7, and the switching valve 9 serves to switch the destination of the oil from the proportional flow valve 8. The proportional pressure valve 10 plays a role of adjusting the pressure in the injection hydraulic cylinder 7, and the screw position detector 11 functions as the screw 3
The moved position of is detected. The injection pressure controller 12
It outputs the upper limit value in the injection hydraulic cylinder 7 at the time of injection and the holding pressure set value in the holding pressure process.
Outputs the valve opening degree command of the proportional flow valve 8 necessary to obtain the screw injection speed during injection. The hydraulic pump 14 plays a role of delivering high-pressure oil, and the electric motor 15 drives the hydraulic pump 14. The tank 16 stores oil, and the mold 17 solidifies the injected molten resin inside.

The thermocouples 21 are arranged at a plurality of points along the screw groove and are attached near the surface of the screw groove. 22 is a lead wire of the thermocouple 21, 23 is a signal transmitter for outputting the detection signal of the thermocouple 21 to the outside, 24 is a rotation detector for detecting the screw rotation speed, 26
Is a resin temperature setting device that gives a setting pattern of the molten resin temperature along the screw groove. 27 is a subtracter for outputting the difference between the two input quantities, and there is only the number of resin temperatures detected along the screw groove. Reference numeral 29 denotes a plasticizing controller, which inputs a deviation between the resin temperature pattern along the screw groove and the set pattern, and outputs a valve opening command for the proportional flow valve 8 and a pressure set value for the proportional pressure valve 10. Reference numeral 30 denotes a switching device, which responds to the signals input from the injection start command A and the plasticization start command B by the signal from the injection speed setting device 13 and the plasticization controller 29.
Output any of the signals from. A switching device 31 outputs either a signal from the injection pressure controller 12 or a signal from the plasticizing controller 29 according to the signals A and B.

Now, in FIG. 2, the injection start command A is the injection speed setter 13
Is input to the injection speed setting device 13, the injection speed setting device 13 outputs to the switching device 30 a valve opening command of the proportional flow valve 8 according to the screw position.
When the injection start command A is input, the switch 30 outputs the valve opening command from the injection speed setting device 13. Switching device 30
Is input to the proportional flow valve 8, and the proportional flow valve 8 takes a predetermined valve opening. Further, the proportional flow valve 8 sends the required oil amount to the switching valve 9, and when the injection start command A is input, the switching valve 9 sends the oil amount from the proportional flow valve 8 to the injection hydraulic cylinder 7.

On the other hand, when the injection start command A is input to the injection pressure controller 12, the injection pressure controller 12 switches the pressure upper limit value in the injection hydraulic cylinder 7 and the pressure holding setting value in the pressure holding process according to the screw position. Output to the device 31. When the injection start command is input, the switch 31 outputs the output of the injection pressure controller 12, that is, the pressure setting value of the proportional pressure valve 10 to the pressure valve 10. The proportional pressure valve 10 releases oil so that the pressure in the injection hydraulic cylinder 7 becomes a predetermined pressure.

The injection cylinder 7 moves the screw 3 at a predetermined injection speed. The resin injected into the mold 17 begins to cool, while the next plasticizing step of the resin begins. Further, in order to control the temperature of the molten resin during plasticization, a plurality of thermocouples 21 buried along the screw groove detect the molten resin temperature along the screw groove, and the resin detected by this thermocouple 21. The temperature is the lead wire 22 that is wired in the screw 3.
Is sent to the signal transmitter 23. The signal transmitter 23 outputs a plurality of resin temperatures to the outside.
26 outputs each set value of the resin temperature at the position corresponding to the screw position where each thermocouple is buried to the subtractor 27, and each of the subtractors 27 outputs the resin output by the signal transmitter 23. Calculate the difference between the actual temperature value and the set value, and
Output to.

The outputs ΔT ₁ , ΔT ₂ , ΔT ₃ , and ΔT ₄ of the subtracter 27 can be expressed by the following equations.

Here, T _{S1 to} T _S4 are outputs of the resin temperature setting device 26 and are set values of the molten resin temperature at each position along the screw groove.

T _{1 to} T ₄ : Outputs of the signal transmitter 23, which are actual values of the resin temperature at each position along the screw groove.

Further, the plasticization controller 29 calculates the screw rotation speed by the following equation,
The request signals N _d and P _d for the screw back pressure are calculated.

N _d = K _N1 ΔT ₁ + K _N2 ΔT ₂ + K _N3 ΔT ₃ + K _N4 ΔT ₄ (2) P _d = K _P1 ΔT ₁ + K _P2 ΔT ₂ + K _P3 ΔT ₃ + K _P4 ΔT ₄ (3) where K _{N1 to} K _N4 are proportional gains of the screw rotation speed request signal with respect to the temperature deviation ΔT ₁ to ΔT ₄ of the molten resin, and K _N1
˜K _N4 > 0.

K _{P1 to} K _P4 : Proportional gain of the screw back pressure request signal with respect to the temperature deviation ΔT ₁ to ΔT ₄ of the molten resin, K _P1 to
K _P4 > 0.

Assuming that the actual value of the screw rotation speed from the rotation speed detector 24 is Na, the plasticization controller 29 calculates the valve opening degree command V _d for the proportional flow valve 8 from the following equation.

Here, K _V is a proportional gain of the valve opening request signal of the proportional flow valve 8 with respect to the deviation of the screw rotational speed.

K _I : Integral gain of the valve opening request signal of the proportional flow valve 8 with respect to the deviation of the screw rotational speed.

At the same time, the plasticizing controller 29 sends the screw back pressure request signal P
Output _d .

The resin temperature T _i (i = 1 to 4) is equal to the set temperature T _Si (i = 1
When it is lower than ˜4), ΔT _i (i = 1 to 4)> 0, and the screw rotation speed request signal increases from the expression (2). As the screw speed increases, the internal frictional heat and plasticizing capacity increase.

On the other hand, according to the equation (3), the screw back pressure request signal also increases, but if the screw back pressure increases, the plasticizing ability decreases. Therefore, it is considered that the effects of both the increase in screw speed and the increase in screw back pressure cancel each other out, and the plasticizing ability hardly changes. However, since the internal frictional heat increases as the screw rotation speed increases, the resin temperature rises and approaches the set temperature.

On the contrary, when the resin temperature is higher than the set temperature, ΔT _i (i =
1 to 4)> 0, and the screw rotation speed request signal is reduced from the expression (2). As the screw speed decreases, the internal frictional heat and plasticizing capacity decrease.

On the other hand, although the screw back pressure request signal also decreases from the equation (3), if the screw back pressure decreases, the plasticizing capacity increases. Therefore, it is considered that the effects of both the reduction of the screw rotational speed and the reduction of the screw back pressure cancel each other out and the plasticizing ability hardly changes. However, internal frictional heat decreases as the screw speed decreases,
The resin temperature decreases and approaches the set temperature.

Further, the plasticization controller 29 outputs the valve opening command V _d for the proportional flow valve 8 to the switch 30 at the same time when the plasticization start command B is input. At the same time, the pressure set value for the proportional pressure valve 10 is output to the switch 31. When the plasticizing start command B is input, the switching devices 30 and 31 output the output from the plasticizing controller 29 to the proportional flow valve 8 and the proportional pressure valve 10, respectively. The proportional flow valve 8 sends the amount of oil to the switching valve 9 so that the screw rotation speed matches the screw rotation speed request signal of the plasticization controller 29. Proportional pressure valve 10, screw back pressure is released to the oil amount of the injection hydraulic cylinder to match the screw back pressure request signal P _d plasticizing controller 29. When the plasticization start command B is input to the switching valve 9, the amount of oil from the proportional flow valve 8 is changed to the hydraulic motor 4.
Then, the screw rotation speed becomes equal to the screw rotation speed request signal of the plasticizing controller 29.

(Problems to be Solved by the Invention) In order to stabilize the quality of molded products of conventional injection molding machines, it is necessary to keep the plasticizing resin temperature constant. For this reason, as shown in FIG. The detection signal of the plasticized resin temperature is obtained from a plurality of thermocouples mounted nearby. However, this resin temperature detection signal has a problem as a feedback signal for controlling the resin temperature for the following reason.

(1) In order to detect the resin temperature accurately and without time delay, it is desirable to embed a thermocouple near the screw groove surface. However, in the injection molding machine, the resin pressure was 1500 kg / cm ² or more in the pressure-holding step, so it was not possible to embed the thermocouple sufficiently close to the screw groove surface for reasons of strength. Therefore, the resin temperature detection signal used for controlling the resin temperature has problems in accuracy and responsiveness.

(2) Since the plasticized resin has a very large viscosity coefficient as compared with water or the like, it is difficult to uniformly mix the molten resin. Therefore, the spatial variation of the plasticized resin temperature also increases, and there is a problem that the resin temperature measured when the plasticized resin flows out from the vicinity of the screw tip varies with time.

(Means for Solving Problems) The present invention has been proposed in order to solve the above-mentioned conventional problems. A hydraulic motor for rotating a screw of an injection molding machine and an oil amount to be sent to the hydraulic motor are provided. Valves that adjust the oil flow rate with electrical signals such as proportional flow rate valves and servo valves to adjust, injection hydraulic cylinders that apply back pressure to the screw, and electrical signals such as proportional pressure valves and servo valves that release oil volume from the injection hydraulic cylinders. In a plasticizing control device consisting of a valve that adjusts the hydraulic pressure with a screw position detector and a screw position detector that detects the screw position, a torque detector that detects the screw torque and a screw torque setting as a function of time or a function of the screw position. A screw torque setting device that outputs a value, and a subtractor that inputs the output of the torque detector and the output of the screw torque setting device and outputs the difference between them And a configuration consisting of a first controller and a second controller that perform (proportional + integral) calculation by inputting the output of the subtractor, and this is a means for solving the problem. is there.

(Operation) In the present invention, the plasticization process is expressed using a mathematical model, and a simulation mathematical model including the control system shown in FIG. 2 is created. Using this simulation mathematical model, the plasticization process is simulated by a computer. The resin temperature in the mathematical model is accurate and there is no time delay,
Since the uniformed resin temperature can be obtained, the ideal resin temperature control can be performed in the simulation calculation.

By the way, most of the heat required to plasticize resin is
This is due to internal friction caused by screw rotation. The internal friction changes when the screw back pressure is changed even if the screw rotation speed is the same. When the screw back pressure is changed, since the surface pressure between the solid resin and the output inner surface and the pressure gradient of the plasticized molten resin are different, the traveling speed of the solid resin is different and the internal friction heat is changed. This internal frictional heat is an amount represented by screw torque or screw horsepower. Fortunately, these quantities can be detected accurately without any time delay. Therefore, the screw rotation speed and screw back pressure can be changed without detecting the plasticized resin temperature, which is the time change of the ideal screw torque or screw horsepower required to perform the ideal resin temperature control in the simulation calculation. Can be realized.

(Embodiment) The present invention will be described below with reference to the embodiments of the drawings. FIG. 1 is a block diagram of a plasticization control device showing an embodiment of the present invention. Since the parts denoted by the reference numerals 1 to 17, 30, and 31 in FIG. 1 are the same as the parts having the same reference numerals shown in FIG. 2, detailed description thereof will be omitted here. Only the differences from FIG. 2 will be described.

In FIG. 1, reference numeral 41 denotes a screw torque setter determined by computer simulation using a mathematical model including a plasticizing process and a plasticizing control system, which is a function generator for giving a temporal change of the screw torque set value. 42 is a screw torque detector, 43 is a subtracter that outputs the difference between the output from the screw torque setting device 41 and the output of the torque detector 42, and 44 and 45 perform (proportional + integral) calculation on the output of the subtractor 43. The output of the controller 44 is output to the switching device 30, and the output of the controller 45 is output to the switching device 31.

Next, the operation of the embodiment of the present invention configured as described above will be described. After the injection start command A is input to the injection speed setting device 13, the molten resin is injected into the mold 17 to start cooling. On the other hand, the process until the plasticizing step of the next resin is the same as the conventional configuration example, so the description thereof will be omitted here, and description will be given from the time when the plasticizing step of the next resin starts. I will do it.

When the plasticization start command B is input to the screw torque setting device 41, a request signal for the screw torque is automatically output to the subtractor 43 with the passage of time from that point. On the other hand, the actual value of the screw torque is output from the torque detector 24 and input to the subtractor 43. Subtractor 43 outputs to the control unit 44 calculates the difference between the actual screw torque Q _a and screw torque setpoint Q _d.

The controller 44 calculates the valve opening command V _d for the proportional flow valve 8 from the following equation.

Here, K _VP is a proportional gain of the valve opening request signal of the proportional flow valve 8 with respect to the screw torque deviation.

K _VI : Integral gain of the valve opening request signal of the proportional flow valve 8 with respect to the screw torque deviation.

Further, the controller 45 controls the pressure setting value P _d for the proportional pressure valve 10.
Is calculated from the following formula.

Here, K _PP is a proportional gain of the pressure set value of the proportional pressure valve 10 with respect to the screw torque deviation.

K _PI : An integral gain of the pressure set value of the proportional pressure valve 10 with respect to the screw torque deviation.

Incidentally, (5) (6) the screw torque deviation by the formula _(Q d -Q
_The reason for including the integral term for _a ) is to make the screw torque deviation zero.

The controller 44 outputs the valve opening degree command V _d for the proportional flow valve 8 to the switch 30. The controller 45 also outputs the pressure set value for the proportional pressure valve 10 to the switch 31. When the plasticizing start command B is input, the changers 30 and 31 output the request commands V _d and P _d from the controllers 44 and 45 to the proportional flow valve 8 and the proportional pressure valve 10, respectively. The proportional flow valve 8 sends the amount of oil to the switching valve 9 in order to change the screw rotation speed so that the screw torque matches the set value. The proportional pressure valve 10 releases the oil amount in the injection hydraulic cylinder 7 in order to change the screw back pressure so that the screw torque matches the set value. When the plasticization start command B is input, the switching valve 9 sends the amount of oil from the proportional flow valve 8 to the hydraulic motor 4 to change the screw rotation speed.

In the above description, when the plasticization start command B is input to the torque setter 41, the screw torque request signal is automatically output according to the elapse of time. However, in FIG. The output of the device 11 is input to the screw torque setting device 41 as shown by the dotted line. This indicates that a configuration in which the plasticization start command B is input to the setter 41 and then the screw torque set value corresponding to the screw position is output can also exhibit the same effect. However, at this time, it is necessary to obtain the screw torque required to keep the molten resin temperature constant by computer simulation as a value corresponding to the screw position.

(Effects of the Invention) Since the present invention is configured as described in detail above,
In the plasticizing process of the injection molding machine, the temporal change of the screw torque required to keep the molten resin temperature constant is obtained in advance by computer simulation, and the obtained temporal change of the screw torque is By repeating each injection, it is possible to easily obtain the plasticization control device capable of keeping the molten resin temperature constant.

[Brief description of drawings]

FIG. 1 is a block diagram of a plasticization control device of an injection molding machine as one embodiment of the present invention, and FIG. 2 is a block diagram of a plasticization control device of a conventional injection molding machine. Description of main parts of the figure 3 …… Screw 4 …… Hydraulic motor 7 …… Injection hydraulic cylinder 8 …… Proportional flow valve 10 …… Proportional pressure valve 11 …… Screw position detector 41 …… Screw torque setter 42 …… Screw torque detector 43 …… Subtractor 44 …… First controller 45 …… Second controller

Claims (1)

[Claims] 1. A hydraulic motor for rotating a screw of an injection molding machine, a valve for adjusting an oil flow rate by an electric signal such as a proportional flow valve or a servo valve for adjusting the amount of oil sent to the hydraulic motor, and a back pressure for the screw. A plasticizing control device consisting of an injection hydraulic cylinder that applies a pressure, a valve that adjusts the hydraulic pressure with electric signals such as a proportional pressure valve or a servo valve that releases the amount of oil from the injection hydraulic cylinder, and a screw position detector that detects the screw position. At, a torque detector for detecting the screw torque,
A screw torque setting device that outputs a screw torque setting value as a function of time or as a function of screw position,
A subtracter that inputs the output of the torque detector and the output of the screw torque setting device and outputs the difference between the two, and a first controller that inputs the output of the subtractor and performs (proportional + integral) calculation. And a second controller, which is a plasticizing control device.