JP2003300236A - Method for controlling injecting of motor-operated injection molding machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To control injection pressure during injection not to exceed a limiting pressure even when abnormality occurs. <P>SOLUTION: A screw 3 is advanced at a set speed, and a molten material is injected into a mold cavity while an injection speed and the injection pressure P are always measured. In a comparison part 10c, the sum of the injection pressure P and a pressure increase ΔP during an inertial flow is compared with the limiting pressure PL. In the case of P+ΔP≥PL, an urgent braking signal is sent from a controller 10 to an injection servo-motor 8 to urgently brake the motor 8 to prevent the injection pressure from exceeding the limiting pressure PL. After that, the injection pressure P is controlled to keep an injection restriction pressure Pa. After that, by judging whether the screw 3 reaches a pressure change-over position or not, an injection molding machine is stopped while the injection restriction pressure Pa is kept, or control to transfer to a pressure keeping process is implemented. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric injection molding machine for forming a molded article by injecting a molten material in a cylinder into a cavity of a mold by advancing a screw by driving an electric motor. The present invention relates to an injection control method.

[0002]

Injection molding in an electric injection molding machine is generally performed by a mold closing process of closing a mold, a mold clamping process of clamping the mold, a nozzle touch process of pressing a nozzle against a sprue of the mold, and an electric motor. By rotating the ball screw connected to the screw, the screw in the cylinder is advanced to inject the molten material accumulated in the front of the screw into the mold cavity, and then the generation of bubbles and sink marks is suppressed. For the next cycle, the screw is rotated to melt the resin for the next cycle in the time between the pressure-holding process where a holding pressure is applied for a while and the molten material filled in the mold cavity is cooled and solidified. While opening the mold to remove the solidified molded product from the mold, the plasticizing process of accumulating in the front of the cylinder, and the molded product to the protruding pin provided on the mold. Consisting of a mold opening-molded article ejection process for pushing me.

FIG. 5 is a graph showing the relationship between the injection speed V and the injection pressure P with respect to the injection pressure holding time t from the conventional injection process to the pressure holding process.

Generally, in injection control in injection molding, the screw is advanced at a set speed, and the injection pressure P rises as the filling amount of the molten material into the mold cavity increases with the injection time. At the holding pressure switching position before the molten material filled in the mold cavity becomes a full pack, the speed control is switched to the pressure control, and then the holding pressure is applied for a while. In addition, the operator must ensure that the injection pressure P does not exceed the injection limit pressure Pa during the speed-controlled injection process.
It is common to set the injection speed and the injection limiting pressure.

However, in an abnormal state during injection, for example, when injection is performed under the wrong molding condition such that the holding pressure switching position is not reached even when the mold cavity is fully packed and the high speed is maintained, or during filling. When the melted material is clogged in the narrowed flow passage portion such as the nozzle or the mold gate, the pressure rapidly rises and the injection pressure P becomes the injection limit pressure Pa, as shown in FIG. Can be reached.

In such a case, in the conventional control method, when the injection pressure P reaches the injection limiting pressure Pa,
Pressure control is generally applied in which the injection speed V is braked to limit an increase in the injection pressure P and the injection limit pressure Pa is maintained.

[0007]

However, in the electric injection molding machine, when the pressure P during injection approaches the injection limiting pressure Pa, the above-mentioned abnormal state occurs and the injection pressure P rapidly rises. If a situation occurs in which the injection limit pressure Pa is reached by sudden braking of the electric motor by the above-mentioned control to suddenly reduce the injection speed V to stop the pressure increase, the rotor of the electric motor is stopped. , The bearing that rotatably supports the screw around its axis, the ball screw mechanism that is assembled to the bearing, the timing belt that conveys the power of the electric motor to the ball screw mechanism, the inertia of the drive system such as the screw, Therefore, a slight advance of the screw during deceleration, that is, the inertia flow cannot be avoided. The inertial flow rate of the screw is generally injection speed × deceleration time / 2, and at this time, for example, when nozzle clogging occurs, the molten material from the screw tip to the nozzle tip is compressed, causing a pressure increase and injection. The pressure P exceeds the injection limit pressure Pa, and further exceeds the limit pressure P _L which does not damage the injection device and the mold, and reaches the abnormal pressure Pb. In addition, the amount of pressure increase when decelerating from a certain speed to speed 0 is generally represented by the amount of pressure increase at the maximum injection speed × (injection speed / maximum injection speed) ² . That is, when the injection speed is low, the amount of pressure increase due to inertial flow is small, so there is no problem, but when the speed approaches the maximum injection speed, the amount of pressure increase becomes extremely large. There was a risk of damaging the mold. It should be noted that the injection limit pressure Pa, a limit pressure on the molding quality of such limitations do not damage the mold pressure or size of the molded article, is the pressure to repeatedly acting out of the allowable dimension, a threshold pressure P _L Is a single-shot limit pressure that does not damage the injection device or the mold during an abnormality.

Therefore, the present invention provides a safe injection control method for an electric injection molding machine in which the injection pressure does not exceed the limit pressure due to an abnormal molding condition or an abnormal pressure rise caused by clogging of molten material. The purpose is to provide.

[0009]

In order to achieve the above object, an injection control method for an electric injection molding machine of the present invention is based on a forward speed of a screw in a cylinder and an injection pressure.
In the injection control method of the electric injection molding machine, which controls the rotation speed of the injection servo motor that moves the screw via the ball screw to control the injection of the molten material into the cavity of the mold, the controller brakes the injection servo motor. The pressure increase ΔP during inertial flow, which is the pressure that rises during deceleration until the screw speed becomes 0 after the signal is transmitted, is obtained in advance, and the value and the limit pressure P _L are stored in the storage unit of the controller. Then, in the comparison section of the controller, the sum of the injection pressure of the molten material in the cylinder, which is constantly measured by the load cell during injection, and the pressure increase ΔP during inertial flow is compared with the limit pressure P _L, and P + ΔP ≧ P _In the case of _L , that is, when P ≧ P _L −ΔP is reached (the injection pressure at this time is P
m)), and a step of transmitting a sudden braking signal to the injection servomotor to reduce the forward speed of the screw to zero.

As described above, the injection control method for the electric injection molding machine according to the present invention uses the inertial flow when the vehicle is suddenly braked from the injection speed at the time when an abnormal state such that injection cannot be performed occurs during injection. The increase of injection pressure, that is, the pressure increase ΔP during inertial flow is obtained in advance, and the sum of the pressure increase ΔP during inertial flow and the injection pressure P of the molten material in the cylinder constantly measured by the load cell is the limit pressure P _L. Eject while comparing with. That is, in the injection control method for the electric injection molding machine of the present invention, even when an abnormal state occurs during injection, the amount of pressure increase during inertia flow of the screw that occurs when the injection servomotor is braked and braked. Since the speed control of the injection servo motor is performed in anticipation of the step-up ΔP during inertial flow, even if an abnormal condition occurs such that injection cannot be performed, a pressure exceeding the limit pressure P _L will be applied to the injection molding machine or the mold. It does not happen.

Further, in the injection control method of the electric injection molding machine according to the present invention, the maximum injection speed is set to Vmax by the controller.
When the pressure increase amount at the maximum injection speed is ΔPmax, the pressure increase amount ΔP at an arbitrary injection speed Vd is ΔP = ΔPmax ×
It may include a step of obtaining (Vd / Vmax) ² .

Further, the injection control method for the electric injection molding machine of the present invention may include a step of obtaining the limit pressure P _L as the injection limit pressure Pa + α which is the limit pressure during injection.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic configuration diagram of an injection device of an electric injection molding machine according to an embodiment of the present invention.

The injection device of the electric injection molding machine is a cylinder 1.
And is inserted into the cylinder 1 so that it can rotate and move forward and backward,
A screw 3 having a screw head 2 at its tip, a load cell 7 for measuring the distortion due to the reaction force of the screw 3 at the time of injection as an injection pressure at one end of the screw 3 on the side opposite to the screw head 2, and the screw 3 in the axial direction. The ball screw 6 to be moved to the
An injection servo motor 8 for rotating the injection servo motor 8 and a controller 10 for controlling the injection servo motor 8 based on a signal from the load cell 7 and a signal from an encoder 9 provided in the injection servo motor 8. Further, the injection device of the electric injection molding machine rotates the screw 3 while melting the resin supplied into the cylinder 1, and rotates the screw 3 toward the front (to the left in FIG. 1) to plasticize while rotating the screw 3. It has a rotary servomotor 4 equipped with.

The controller 10 includes a setting unit 10a for setting a speed setting value of the axial moving speed of the screw 3 which is the injection speed, a pressure limit value of the injection pressure, a holding pressure, etc. Storage unit 10b for storing ΔP, limit pressure P _L, etc. (pressure increase during inertial flow ΔP, limit pressure P _L will be described later), speed set value and detection speed or injection pressure limit value and detection pressure value are compared Comparing unit 10
c is provided. The injection pressure detected by the load cell 7 is amplified by an amplifier (not shown) and input to the controller 10. The rotation speed of the injection servomotor 8 is detected by the encoder 9, and the screw 3
Is input to the controller 10 as the detection speed of and is controlled based on this input value.

The storage unit 10b of the controller 10 has an erroneous state during injection, for example, when the mold cavity (not shown) is fully packed, the holding pressure switching position is not reached and a high speed is maintained. When an injection state under the molding conditions or a state in which the molten material is clogged in the narrowed flow path portion such as the nozzle 1a or the mold gate during filling, sudden braking is performed from the speed at that time. The boosting pressure ΔP during inertial flow of the injection pressure due to the inertial flow at time is stored. Further, the storage unit 10b also stores a limit pressure P _L (see FIG. 2) or α when the limit pressure P _L = the injection limit pressure Pa + α is set as a limit value that does not damage the injection device or the mold. .

In this embodiment, the injection pressure is detected by the load cell 7 and the speed of the screw 3 is detected by the encoder 9. However, the present invention is not limited to this, and the injection pressure is detected by the cylinder 1. A pressure sensor may be attached for detection, or the speed of the screw 3 may be directly measured.

Next, the injection control method when an abnormal state occurs during injection in the electric injection molding machine of the present embodiment having the above-mentioned configuration will be described.

First, a signal is transmitted from the controller 10 to the injection servomotor 8 so that the screw 3 advances at a set speed, and the molten material is injected into the mold cavity. At this time, injection is performed while constantly measuring the injection speed and the injection pressure P (step S1).

Further, at this time, the comparison unit 10c compares and calculates whether or not the sum of the injection pressure P and the pressure ΔP during inertial flow is larger than the limit pressure P _L (step S2). P + Δ
When P ≧ P _L (the injection pressure at this time is shown as Pm in FIG. 2), the controller 10 causes the injection servo motor 8 to
By sending a sudden braking signal multiplied by sudden braking in the injection servo motor 8, to prevent the injection pressure P is boosted beyond the limit pressure P _L (step S3). Then, the injection limiting pressure Pa
The pressure control is executed by (step S4). Further, thereafter, it is determined whether or not the screw position has advanced to the pressure maintaining switching position (step S5), and if the screw 3 has not advanced to the pressure maintaining switching position, the injection limiting pressure Pa is maintained (in FIG. 2). , Solid line) Stop the machine (step S)
6). When the screw 3 has advanced to the pressure holding switching position, the pressure holding process is started (broken line in FIG. 2) (step S7).
The relationship of the injection pressure P with respect to the injection pressure holding time t in each of the above steps is as shown in FIG.

On the other hand, in step S2, P + ΔP <P _L
In the case of, it is further determined whether or not P <Pa (step S8), and P <Pa is established, that is, in a normal state, predetermined speed control in the injection process is executed (step S9), and the screw position is maintained. After advancing to the pressure switching position, the pressure maintaining process is started (step S7). In this case, the relationship between the injection pressure P and the injection pressure P is the same as in the conventional case.
As shown in FIG.

Further, in step S8, P ≧ Pa holds,
That is, when P + ΔP <P _L and P ≧ Pa are satisfied, the process proceeds to step S4, and pressure control is executed at the injection limiting pressure Pa. When the injection limit pressure Pa has been filled, the screw 3 is moved forward, and it is determined whether the screw position has advanced to the holding pressure switching position (step S5).
If the screw 3 has not advanced to the holding pressure switching position,
The machine is stopped while maintaining the injection limiting pressure Pa (solid line in FIG. 2) (step S6). In this case, the relationship between the injection pressure P and the injection pressure holding time t is as shown in FIG.

In step S3, the injection servomotor 8
When decelerating with constant deceleration, the desired speed Vd during deceleration
The boosted amount ΔP at ΔP = ΔPmax × (Vd / Vma
x) ²Required by. Where Vmax is the maximum injection speed
And ΔPmax is the inertia flow at the maximum injection speed
Is the boosted amount.

[0025]

As described above, according to the present invention, the injection pressure P is constantly measured during injection, and P + ΔP
Injection is performed while determining whether or not ≧ P _L, and sudden braking control of the injection servo motor 8 is performed when an abnormal state occurs during injection and there is a risk of exceeding the limit pressure P _L. Therefore, even if an abnormal state occurs during injection, the injection molding machine or the mold is not subjected to pressure exceeding the limit pressure P _L, and damage to the injection molding machine or the mold is prevented in advance. You can

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of an electric injection molding machine according to an embodiment of the present invention.

FIG. 2 is a graph showing an example of a waveform of injection pressure according to the injection control method of the present invention when an abnormal state occurs during injection.

FIG. 3 is a flowchart for explaining an example of the injection control method of the present invention.

FIG. 4 is a graph showing an example of a waveform of an injection pressure by the injection control method of the present invention when P + ΔP ≦ P _L and P ≧ Pa are satisfied during injection.

FIG. 5 is a graph showing an example of a waveform of injection pressure by a conventional injection control method.

FIG. 6 is a graph showing an example of a waveform of injection pressure by an injection control method when an abnormal state occurs during injection in the related art.

[Explanation of symbols]

1 cylinder 1a nozzle 2 screw heads 3 screws 3 Timing belt 4 rotation servo motor 5 tachometer 6 ball screws 7 load cell 8 injection servo motor 9 encoder 10 controller 10a setting section 10b storage unit 10c Comparison section 11 Bearing part 12 Timing belt

Claims (3)

[Claims] 1. A molten material is injected into a cavity of a mold by controlling a rotation speed of an injection servomotor for moving a screw through a ball screw based on a forward moving speed of a screw in a cylinder and an injection pressure. In an injection control method of an electric injection molding machine for controlling, the injection servomotor (8) from the controller (10).
The pressure ΔP during inertial flow, which is the pressure that rises during deceleration until the speed of the screw (3) reaches 0 after the braking signal is transmitted to the engine, and the limit pressure P _L during injection molding are stored.
At the time of injection, the sum of the injection pressure P of the molten material in the cylinder (1), which is constantly measured, and the pressure increase ΔP during inertial flow,
Comparing with the limit pressure P _L , when P + ΔP ≧ P _L , a rapid braking signal is transmitted to the injection servomotor (8) to reduce the forward speed of the screw (3) to zero. An injection control method for an electric injection molding machine, comprising: 2. When the maximum injection speed is Vmax and the pressure increase amount at the maximum injection speed is ΔPmax, the pressure increase ΔP during inertia flow during deceleration from an arbitrary speed Vd of the screw (3) is ΔP = ΔPmax × The injection control method for an electric injection molding machine according to claim 1, including a step of obtaining (Vd / Vmax) ² . 3. A step of obtaining the limit pressure P _L as an injection limit pressure Pa + α which is a limit pressure during injection,
An injection control method for an electric injection molding machine according to claim 1.