JPH072356B2 - Injection pressure control system of electric injection molding machine - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection pressure control system in an electric injection molding machine in which a screw is axially moved by a servomotor to perform injection.

Conventional technology In a hydraulic injection molding machine that uses a conventional hydraulic pressure to move a screw in the axial direction for injection, the injection pressure is detected in the injection process, and when a certain set pressure is reached, the holding pressure of the next process is maintained. Although the process is shifted to the process, if an excessive injection pressure is applied at the time of injection, a molded product may be defective or the mold itself may be damaged. Therefore, a limiter is set with respect to the maximum pressure at the time of injection, and when the injection pressure exceeds the limiter, an alarm is issued and a pressure holding process is started.

On the other hand, an electric injection molding machine that drives injection by driving the screw in the axial direction with a servo motor has also been developed. As described above, the injection pressure control in this electric injection molding machine is excessive. In order to prevent injection pressure, a torque limit is applied to a servomotor that drives a screw in the axial direction so that a torque larger than a predetermined value is not generated and the maximum injection pressure is limited.

Problems to be Solved by the Invention As described above, when injection is performed by hydraulic pressure in the control of injection pressure, the hydraulic pressure and the pressure applied to the molten resin at the time of injection are the same in terms of action and reaction. ,
This injection pressure control is relatively simple.

However, in an electric injection molding machine in which a screw is moved by a servo motor in the axial direction for injection, the pressure applied to the resin and the pressure output from the servo motor, that is, the torque, do not always match. Since the injection speed is controlled, the pressure in the mold cavity may be rapidly increased during injection and the mold may be damaged. Therefore, it is necessary to limit the maximum injection pressure, that is, the output torque of the servomotor. By the way, if the maximum injection pressure is limited, there is a drawback that the rise of the injection speed at the start of injection becomes slow. That is, when the torque limit is applied to the servo motor by limiting the maximum injection pressure, the output torque is limited, resulting in insufficient force, which does not reach the set speed at a fast start-up, but slowly rises until the set speed is reached. Therefore, there is a drawback that the injection speed control becomes difficult.

Therefore, an object of the present invention is to provide an electric injection molding machine,
An object of the present invention is to provide an injection control method that facilitates injection speed control, prevents excessive injection pressure from occurring, and prevents damage to a mold.

Means for Solving the Problems The present invention, in an injection pressure control system in an electric injection molding machine, is provided with an injection pressure detecting means for detecting an injection pressure during an injection process, and the injection pressure detected by the injection pressure detecting means. The above-mentioned problem was solved by arranging such that when the pressure becomes equal to or higher than the set mold protection pressure, the pressure-holding step is not started and the measuring step is started.

Action Even if the maximum injection pressure during injection is large, the injection pressure detection means detects the injection pressure, and if the detected injection pressure becomes equal to or higher than the set mold protection pressure, the pressure holding step does not proceed,
Since the pressure shifts to the measuring step and the pressure becomes low, a large pressure is not applied to the mold, so that the mold is not damaged.
On the other hand, because the maximum injection pressure is set to a large value, a large force is generated at the start of injection, the injection speed rises faster, the injection speed is easier to control, and the molded product is of good quality. be able to.

Embodiment FIG. 1 is a block diagram of an essential part of an injection molding machine for carrying out an embodiment of the present invention, in which 1 is a screw of the injection molding machine and 2 is a screw.
Is a pressure detector for detecting the pressure applied to the screw 1, that is, the injection pressure applied from the molten resin via the screw 1. The pressure detector is provided on the thrust bearing portion of the pusher plate (not shown) that thrust-supports the screw 1. The load cell sensor and the like are provided to detect the pressure applied to the screw 1. Reference numeral 3 is a servo motor as a drive source for moving the screw 1 in the axial direction of the screw via the pusher plate or the like for injection. Further, 4 is a position detector attached to the motor shaft of the servo motor 3, which detects the position of the screw from the rotational position of the servo motor 3 and inputs the detection signal to the servo interface 16 of the numerical controller 10 described later. is doing.

10 is a numerical control system (hereinafter referred to as NC device)
10 is a microprocessor for NC (hereinafter referred to as CPU) 11
And a programmable machine controller (hereinafter referred to as PMC) CPU12. The PMC CPU12 is connected to a ROM15 that stores various sequence programs and the like.
The C CPU 11 is used for the ROM 14 that stores the management program that controls the injection molding machine as a whole, for temporary storage of data, etc.
A RAM 21 and a servo circuit 17 for driving and controlling a servo motor for each axis for injection, mold clamping, screw rotation, ejector, etc. are connected via a servo interface 16. In FIG. 1, only the injection servo motor 3 and the servo circuit 17 are shown. Reference numeral 18 denotes a non-volatile shared RAM having a backup power source, which stores a program for controlling each operation of the injection molding machine, various set values, parameters and the like. 13 is a bus arbiter controller (hereinafter referred to as BAC), and the BAC 13 has an NC CPU 11 and a PMC CP.
The U12, the shared RAM 18, the input circuit 19, and the output circuit 20 are connected to each other, and the bus used is controlled by the BAC 13. Further, a manual data input device with a CRT display device (hereinafter referred to as CRT / MDI) 23 is connected to the BAC 13 via an operator panel controller 22, and further, the above P
An A / D converter 24 that converts the output of the pressure detector 2 from an analog signal to a digital signal is connected to the MC CPU 12.

In the above configuration, the NC program that controls the operation of the injection molding machine is stored in the shared RAM 18, and the CRT / MDI
Various parameters related to the injection molding operation are set from 23 and stored in the shared RAM 18. For example, as the parameters related to the present embodiment, the torque limit value of the maximum injection pressure at the time of injection, the mold protection pressure, the torque limit value corresponding to the safety pressure, the injection speed, the torque limit value at the time of holding pressure,
CRT / MDI23 for torque limit values for back pressure during weighing
Set more.

As described above, when the injection molding machine is operated after setting various parameters, the NC device 10 performs the operations shown in FIG. 2 for each process of injection, pressure holding, and weighing. Note that FIG. 2 shows a flowchart of the operation processing performed by the PMC CPU 12, and the NC CPU 11 reads the NC program and performs the same processing such as pulse distribution on each axis as in the conventional case.

When entering the injection process, the PMC CPU 12 reads the torque limit value corresponding to the maximum injection pressure set in the shared RAM 18,
It outputs to the servo circuit 17 via the output circuit 20, and limits the output torque of the servo motor 3 to the torque corresponding to the maximum injection pressure (step S1). Then, injection is started (step S2), the CPU 11 for NC distributes the pulse to the injection position of each stage at the injection speed of each stage set in the shared RAM 18, and the servo motor 3 via the servo interface 16 and the servo circuit 17. Is driven to move the screw 1 to cause injection. On the other hand, the PMC CPU 12 monitors the injection pressure detected by the pressure detector 2 converted into a digital signal by the A / D converter 24, and reaches the mold protection pressure lower than the maximum injection pressure set in the shared RAM 18. It is monitored whether or not the injection is completed and whether or not the injection is completed (steps S3 and S4). The end of injection can be judged by the position of the screw, the time from the start of injection, and the fact that the injection pressure has reached the holding pressure switching pressure. The injection is terminated when the switching position is reached. If the operation is normal, the injection is normally completed before the injection pressure detected by the pressure detector 2 reaches the mold protection pressure, and the screw position is maintained from the NC CPU 11 via the BAC 13 and the shared RAM 18. A signal indicating that the pressure switch position has been reached is output, and when this signal is detected by the PMC CPU 12,
The CPU 12 for C outputs the torque limit set in the shared RAM 18 to the servo circuit 17 via the BAC 13 and the output circuit 20 to limit the output torque of the servo motor 3 to a torque equal to or less than the holding pressure, and to set the timer T1. Start (Step S
Five). When the holding pressure is divided into several stages, the torque limit value of the holding pressure of each stage and the timer of the holding time are set respectively to perform the holding control. However, since it is not the gist of the present invention, a case of performing one-step pressure holding control is described. Then, the PMC CPU 12 determines whether or not the timer T1 has timed out (step S6),
When the time is up, the pressure-holding process is terminated, and the torque limit for back pressure is output to the injection servo motor 3 via the output circuit 20 (step S7) to output the set back pressure. Meanwhile, the motor for screw rotation (not shown) is driven to start the measurement (step S8). Then, when the screw 1 retreats with the melting pressure of the resin (on the right side in FIG. 1) and reaches the measuring point, the CPU 11 for NC,
When it is detected via the BAC 13 (step S9), the rotation of the screw 1 is stopped, and the processes of this injection, pressure holding, and measuring process are completed.

On the other hand, during the injection process, when it is detected by the pressure detector 2 via the A / D converter 24 that the injection pressure becomes equal to or higher than the set mold protection pressure for some reason in step S3, the PMC for C
The PU 12 limits the output torque of the servo motor 3 to the torque limit value corresponding to the low safety pressure set in the shared RAM 18 and starts the timer T2 (step S1.
0). Then, when the timer T2 times out, the processing of steps S5 and S6 of the pressure-holding process is not performed, and the process proceeds to step S7 and subsequent steps of the weighing process. That is, when the injection pressure exceeds the mold protection pressure for some reason at the time of injection and there is a risk of damaging the mold, the output torque of the servo motor 3 is immediately limited to a low torque and the mold pressure is set to a safe pressure. Prevent damage. This step S10,
If the injection pressure reaches the mold protection pressure during injection without performing the process of S11, the process may immediately proceed to step S7 and limit the output torque of the servomotor 3 of the injection shaft to a torque with a low back pressure.

As described above, in the present invention, the detection means for detecting the injection pressure at the time of injection is provided, and when the injection pressure reaches the set mold protection pressure or higher, the injection operation is stopped and the pressure is reduced,
Since the process shifts to the metering process without performing the pressure-holding process, the maximum injection pressure during injection can be made large, so the set injection speed during injection rises faster, and injection speed control becomes easier. Moreover, the mold is not damaged.

[Brief description of drawings]

FIG. 1 is a block diagram of an essential part of an injection molding machine for carrying out an embodiment of the present invention, and FIG. 2 is an operation processing flowchart in the embodiment. 1 ... screw, 2 ... pressure detector, 3 ... servo motor,
4 ... Position detector, 10 ... Numerical control device.

Claims (2)

[Claims] 1. An electric system in which a servomotor for moving a screw in an axial direction to perform injection applies a torque limit corresponding to a set maximum injection pressure to perform injection process control, and then sequentially shifts to a pressure holding process and a metering process. In the injection pressure control system of the injection molding machine, an injection pressure detection means for detecting the injection pressure during the injection process is provided, and when the injection pressure detected by the injection pressure detection means is equal to or higher than the set mold protection pressure, the holding pressure is maintained. An injection pressure control system for an electric injection molding machine that does not shift to the process but shifts to the measuring process. 2. When the injection pressure detected by the injection pressure detecting means exceeds a set mold protection pressure, a torque limit corresponding to a low safety pressure is applied to the servo motor, and the servo is performed in the injection direction for a predetermined time. The injection pressure control system for an electric injection molding machine according to claim 1, wherein after the motor is driven, the measuring process is started.