JPH07102595B2 - Screw drive of injection molding machine - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a screw driving device for an injection molding machine having a pressure feedback control system having a PID pressure compensator.

[0002]

2. Description of the Related Art Conventionally, a screw (injection ram) is moved to the most advanced position in an empty purging process in a molding preparatory step carried out by an injection molding machine or in push-cut molding in which resin is not left in front of a screw. To move
At this most advanced position, a so-called metal contact in which the target of pressure control is metal is generated. In order to prevent the screw from colliding with the inner wall of the heating cylinder by the metal contact, the retaining ring 17h of the screw 2 is attached to the rear end portion 13b of the heating cylinder 13 at the most advanced position of the screw 2 as shown in FIG. Positioning is performed by abutting the front end face of the.

However, in the conventional screw driving device having the pressure feedback control system having the PID pressure compensating section, the control system is constituted by a single PID pressure compensating section, and the PID constant is mainly focused at the time of resin filling. Since the setting is small, there is a problem that when a metal contact (a rigid body) whose pressure is to be controlled has a control characteristic that causes hunting, the operability at the time of empty purging also deteriorates. In this case, a constant that can be compromised may be set for both resin filling and metal contact, but in the end, control characteristics such as stability and responsiveness are ambiguous and insufficient for both, and cannot be adopted.

The present invention solves the problems existing in the prior art as described above, and sets optimum control characteristics both at the time of resin filling and at the time of metal contact to improve stability, responsiveness, An object of the present invention is to provide a screw drive device of an injection molding machine capable of dramatically improving accuracy and operability.

[0005]

According to the present invention, the detected pressure value D
The screw drive device 1 of the injection molding machine is provided with the pressure control system 4 having the PID pressure compensating section (first pressure compensating section) 3 while performing the feedback control of the pressure so that the d matches the preset set value Ds. In particular, the second PID pressure compensator (second pressure compensator) 5 having a PID constant different from that of the first pressure compensator 3 and the forward position of the screw 2 are detected, and the screw 2 is When the preset switching position Ps is reached, the compensation unit switching unit 6 is provided for switching from the first pressure compensation unit 3 to the second pressure compensation unit 5.

In this case, the PID constant of the second pressure compensator 5 is set to have a larger gain than the PID constant of the first pressure compensator 3, and the switching position Ps is substantially 0 from the most advanced position Pm of the screw 2. It is desirable to set it in the range of 0.1 to 0.7 mm.

[0007]

Operation: The screw driving device 1 of the injection molding machine according to the present invention
According to the above, for example, when press-cut molding is performed, since the target of pressure control is resin (elastic body) during resin filling, feedback control using the first pressure compensating unit 3 having an optimum PID constant during resin filling can be performed. Done. In this case, the pressure detection value Dd is compared with the preset setting value Ds, and the movement of the screw 2 is feedback-controlled so that the detection value Dd matches the setting value Ds.

On the other hand, the screw 2 advances, and the most advanced position P
When the switching position Ps set to about 0.1 to 0.7 mm before m is reached, the function of the compensating unit switching unit 6 switches from the first pressure compensating unit 3 to the second pressure compensating unit 5. Therefore, when the screw 2 reaches the most advanced position Pm and makes metal contact, the second pressure having a PID constant that is optimal at the time of push-off, that is, a PID constant in which the gain is set to be larger than the PID constant of the first pressure compensating unit 3. Feedback control using the compensator 5 is performed.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, preferred embodiments according to the present invention will be described in detail with reference to the drawings.

First, the screw drive device 1 according to the present embodiment.
The configuration of the entire injection molding machine including the above will be described with reference to FIGS. 1 and 2.

The injection molding machine comprises an injection device 11 shown in FIG. 1 and a mold device 12 shown in phantom in FIG. Injection device 11
Is equipped with a heating cylinder 13 in the front part, the screw drive device 1 in the rear part, the heating cylinder 13 is equipped with an injection nozzle 14 in the front end, and a hopper 15 for supplying the molding material to the upper end in the rear part. It is equipped with a slidable screw 2. On the other hand, the screw drive device 1 is composed of an injection drive section and a metering drive section, and FIG. 1 shows only the injection drive section 1x. The injection drive unit 1x includes a fixed ball nut 16n and a ball screw 16 screwed into the ball nut 16n.
a ball screw mechanism 16 having a ball screw 16
The front end of s is coupled to the rear end of the screw 2 via, for example, a rotatable coupling 17, a retaining ring 17h of the screw 2, and a pressure sensor (load cell) 18 that detects the back pressure of the screw 2. In this case, the front end surface of the holding ring 17h abuts the rear end portion 13b of the heating cylinder 13 at the most advanced position (metal contact position) of the screw 2 (see FIG. 2). Furthermore, 19 is an AC servomotor, and the drive gear 20 provided on this output shaft 19s is a ball screw 16
It engages with a driven gear 21 provided at the rear end of s. The servo motor 19 is provided with a rotary encoder 22 that detects a rotation angle (rotation speed).

On the other hand, 4 is a pressure control system for performing feedback control. Reference numeral 31 is a subtracting unit, and the subtracting unit 31 is provided with a set value Ds of the filling pressure and a detection value Dd obtained from the pressure sensor 18. The subtraction unit 31 has a function of obtaining a deviation value Ap between the set value Ds and the detection value Dd, and its output side is connected to both input sides of the first pressure compensation unit 3 and the second pressure compensation unit 5. The output side of the first pressure compensation section 3 is connected to the input section of the addition section 33 via the switch section 32, and the output side of the second pressure compensation section 5 is connected via the switch section 34 to the addition section 33.
Connect to the other input of the.

In this case, the first pressure compensating section 3 and the second pressure compensating section 5 are both configured as PID pressure compensating sections, and the PID constant of the first pressure compensating section 3 is an optimum constant when the resin (elastic body) is filled. In addition, the PID constant of the second pressure compensation unit 5 is set so as to be different from the optimum constant at the time of metal contact in which the control target is a metal (rigid body). In this case, at least the PID constant of the second pressure compensator 5 is equal to the first pressure compensator 3
It is desirable to set the gain to be larger than the PID constant of, and to set the constants for I operation and D operation as necessary.

On the other hand, the output section of the addition section 33 is connected to the input side of the motor driver 35, and the motor driver 3
The output side of 5 is connected to the servomotor 19. In addition, 36
Is a switching control unit, a rotary encoder 22 is connected to the input side of the switching control unit, and a switching position reference value S
c inputs. In this case, the switching position reference value Sc is set to a position that is a distance Ls before the most advanced position Pm of the screw 2 (holding ring 17h). The distance Ls is preferably set to about 0.1 to 0.7 mm. On the other hand, the output side of the switching control unit 36 is connected to the switch units 32 and 34. The switching control unit 36 is the switch unit 3
A switching signal is given to 2 and 34, and the switch unit 32 or 3
4 has a function of selectively turning on and off. The switching control unit 36 and the switch units 32 and 34 constitute the compensation unit switching unit 6.

Next, the screw drive device 1 according to the present embodiment.
The operation will be described with reference to FIGS. 1 and 2.

The example illustrates push-cut forming. First, when the resin is filled, the target of pressure control is the resin having elasticity, and therefore, the filling pressure is feedback-controlled using the first pressure compensating unit 3 having the optimum PID constant at the time of filling the resin. In this case, since the screw 2 (holding ring 17h) does not reach the switching position Ps (see FIG. 2), the switching control unit 3
6, the switch unit 32 is switched on and the switch unit 34 is switched off. Pressure sensor 18 during control
Thus, the filling pressure of the resin (back pressure of the screw 2) is detected, and the detected value Dd is given to the subtractor 31. As a result, the subtractor 31 compares the set value Ds with the detected value Dd and outputs the deviation value Ap, and the deviation value Ap is pressure-compensated by the first pressure compensating unit 3, and the switch unit 32 and the adder 33 are operated. Is given to the motor driver 35 via the servo motor 19 so that the detected value Dd matches the set value Ds.
Is rotated, that is, the movement of the screw 2 is feedback-controlled.

On the other hand, as shown in FIG. 2, the screw 2 moves forward, that is, the holding ring 17h moves forward and the most advanced position Pm.
When the switch position Ps set to approximately 0.1 to 0.7 mm is reached before, the switch control unit 36 detects it and switches the switch unit 32 off and the switch unit 34 on. As a result, the first pressure compensator 3 is switched to the second pressure compensator 5. The holding ring located at the switching position Ps is indicated by 17hs in FIG. And screw 2
When the (holding ring 17h) reaches the most advanced position (metal contact position) Pm, the PID constant optimal for the metal contact, that is, the PID constant in which the gain is set larger than the PID constant of the first pressure compensation unit 3 Feedback control using the second pressure compensator 5 having
Therefore, the optimum control characteristics are set for both the resin filling and the metal contact, and the stability, responsiveness, accuracy and operability of the entire control are improved.

The embodiment has been described in detail above.
The present invention is not limited to such an embodiment,
The detailed configuration, method, numerical values, etc. can be arbitrarily changed without departing from the scope of the present invention.

[0019]

As described above, according to the present invention, the pressure feedback control is performed so that the detected pressure value matches the preset value, and the pressure having the PID pressure compensating portion (first pressure compensating portion) is provided. In a screw driving device of an injection molding machine including a control system, a PI different from the first pressure compensating unit
A second PID pressure compensating section (second pressure compensating section) having a D constant and a forward position of the screw are detected, and when the screw reaches a preset switching position, the first pressure compensating section receives the second pressure compensation. Since the compensator switching unit that switches to the control unit is provided, optimum control characteristics can be set both for resin filling and metal contact, and stability, responsiveness, accuracy and operability of the entire control are dramatically improved. There is a remarkable effect that it can be done.

[Brief description of drawings]

FIG. 1 is a block diagram of an injection molding machine including a screw drive device according to the present invention,

FIG. 2 is an operation explanatory view of the screw driving device,

[Explanation of symbols]

 1 Screw Driving Device 2 Screw 3 PID Pressure Compensation Section (First Pressure Compensation Section) 4 Pressure Control System 5 Second PID Pressure Compensation Section (Second Pressure Compensation Section) 6 Compensation Section Switching Section Dd Detected Value Ds Set Value

Claims (3)

[Claims] 1. An injection molding machine which performs pressure feedback control so that a detected pressure value matches a preset value and which includes a pressure control system having a PID pressure compensation section (first pressure compensation section). In the screw driving device, the second PID pressure compensating portion (second pressure compensating portion) having a PID constant different from that of the first pressure compensating portion, the forward position of the screw, and the switching position preset by the screw are detected. A screw driving device for an injection molding machine, comprising a compensating part switching part for switching from the first pressure compensating part to the second pressure compensating part. 2. The screw driving device of an injection molding machine according to claim 1, wherein the PID constant of the second pressure compensating unit is set to have a larger gain than the PID constant of the first pressure compensating unit. 3. The screw drive device for an injection molding machine according to claim 1, wherein the switching position is set to be approximately 0.1 to 0.7 mm before the most advanced position of the screw.