JPH0752210A - Injection control device of injection molding machine - Google Patents

Abstract

PURPOSE:To prevent a mold from generating a damage or flashes by injecting by the optimum pressure, by a method wherein when present injection pressure acting upon a screw exceeds a control value set up beforehand by corresponding to a present position of the screw, a servomotor is controlled by a current command value obtained by deducting a fixed quantity from the current com mand value obtained by a speed loop control. CONSTITUTION:Screw positions Si, Si+1 are read into a servo CPU 20 from a control value memory file of a nonvolatile memory 24 based on a value of an address reference index i. While a present value P of injection pressure is read through a bus 22 and pressure monitoring CPU 17, a speed loop processing is performed based on a speed command VC calculated through processing of a position loop and a measured speed Vf and a current command (torque command) I is obtained. Then a control value Pk corresponding to a value of a register k is read through the control value memory file, when the present value P exceeds the control value Pk, corrective operation wherein a fixed value is deducted from the current command value I is performed and the value is taken as the current command value I of the current loop.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of an injection control device for an injection molding machine.

[0002]

2. Description of the Related Art In an electric injection molding machine that drives a servomotor to perform an injection operation, the position of a screw and its moving speed are feedback-controlled, and speed loop control is performed as a minor loop of position loop control. ing. The movement amount for each predetermined cycle corresponding to the injection movement speed is input as the position command to the control means of the position loop for each predetermined cycle until the command position is reached.
A position deviation is obtained by subtracting the actual movement amount from the commanded movement amount, the position deviation is multiplied by a position loop gain to obtain a speed command, and this speed command is used as a command to the speed loop. In the speed loop, PI (proportional / integral) control or the like is performed based on the speed command and the actual speed fed back, the torque command (current command) is obtained, the servo motor is driven to move the screw, and the position / speed is controlled. While performing the injection operation.

[0003]

The load applied to the injection servomotor that moves the screw in the axial direction varies depending on various circumstances. However, when the load is large and the screw follows the command, the load may be delayed. Since the position deviation increases, the speed command and the torque command (current command) increase. As a result, the servo motor generates a large force to drive the screw, but if an excessively strong injection pressure acts directly on the mold, the mold may be damaged or molding defects such as burrs may occur. is there.

An electric injection molding machine in which a maximum output of the injection servomotor is regulated by setting a constant torque limit in advance in a control circuit of the injection servomotor is already known. As for the problems related to the damage of burrs and the occurrence of burrs, the situation changes variously depending on the degree of resin filling in the mold, so the above-mentioned problems can be solved simply by limiting the maximum output of the injection servo motor. It is not possible.

For example, in order to prevent problems such as core breakage due to the strong pressure of the resin ejected into the mold at the initial stage of injection, it is necessary to set a low torque limit to protect the mold. However, at the same time, since the injection pressure is low, the circumference of the resin becomes poor, which may cause problems such as defective filling.

Therefore, an object of the present invention is to provide an injection control device for an injection molding machine, which can always perform an injection operation under the most suitable pressure condition in accordance with the characteristics of the resin or the mold, the filling condition of the resin, and the like. To do.

[0007]

The injection pressure control device of the present invention sequentially detects the current injection pressure acting on the screw and the current screw position, and the current injection pressure acting on the screw corresponds to the current screw position in advance. When the regulation value set by the above is exceeded, the above-mentioned object is achieved by a configuration characterized in that the servo motor is controlled by using a current command obtained by subtracting a predetermined amount from the current command obtained by the speed loop control as a current command.

Further, since the injection speed in the injection process is controlled according to the screw position, the injection speed with respect to the screw position is set to control the speed of the servo motor.

[0009]

In consideration of the characteristics of the resin and the mold and the relationship between the screw position and the filling condition of the resin, the regulation value of the injection pressure suitable for each screw position is set in advance. The injection control device of the injection molding machine controls the speed of the servo motor based on the injection speed set for the screw position,
The present injection pressure acting on the screw and the present screw position are sequentially detected, and it is determined whether or not the present injection pressure exceeds a regulation value set in advance corresponding to the present screw position. And if the current injection pressure exceeds the regulation value,
The injection control device of the injection molding machine subtracts a predetermined amount from the current command obtained by the speed loop control, and controls the servo motor using this amount as a current command to regulate the magnitude of the injection pressure.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a main part of an injection molding machine of an embodiment to which an injection control device of the present invention is applied. Reference numeral 1 is an injection cylinder of the injection molding machine, and reference numeral 2 is a screw. The screw 2 is driven in the injection axis direction by the injection servomotor M1 via a drive converter 5 for converting the axial rotation of the drive source into a linear motion in the injection axis direction, and also the screw 2 via the gear mechanism 3. It is adapted to be metered by a rotation servomotor M2. A pressure detector 4 is provided at the base of the screw 2, and the resin pressure acting in the axial direction of the screw 2, that is, the injection holding pressure in the injection holding process and the screw back pressure in the metering and kneading process are A / D.
It is detected via the converter 16. Injection servo motor M
1 is provided with a pulse coder P1 for detecting the position and movement speed of the screw 2, and the screw rotation servomotor M2 is provided with a pulse coder P2 for detecting the rotation speed of the screw 2.

The control unit 10 of the injection molding machine, which is the injection control unit, is a CNC which is a microprocessor for numerical control.
CPU 25, a PMC CPU 18 which is a microprocessor for a programmable machine controller, a servo CPU 20 which is a microprocessor for servo control, and a pressure monitoring CPU 17 which performs sampling processing of injection holding pressure and screw back pressure, Bus 22
Information can be transmitted between the microprocessors by selecting mutual input / output via the.

The PMC CPU 18 is connected to a ROM 13 which stores a sequence program for controlling the sequence operation of the injection molding machine and a RAM 14 which is used for temporary storage of operation data. On the other hand, CP for CNC
Connected to the U25 are a ROM 27 storing a program for controlling the injection molding machine as a whole and a RAM 28 used for temporary storage of operation data.

Each of the servo CPU 20 and the pressure monitor CPU 17 stores a ROM 21 storing a control program dedicated to servo control, a RAM 19 used for temporary storage of data, and a control program relating to sampling processing of various data. The ROM 11 and the RAM 12 used for temporary storage of data are connected. Further, the servo CPU 20 is connected with a servo amplifier 15 for driving a servo motor of each axis for clamping, ejector (not shown) and injection, screw rotation, etc., based on a command from the CPU 20. Pulse coder P1 provided in the servo motor M1 for driving and pulse coder P2 provided in the servo motor M2 for screw rotation
Each of the outputs from the etc. is fed back to the servo CPU 20.

The non-volatile memory 24 is a memory for storing molding data for storing molding conditions (injection speed, regulation value of injection pressure, etc.) and various set values, parameters, macro variables and the like relating to injection molding work. The interface 23 is an input / output interface for receiving signals from limit switches and operation panels provided in various parts of the injection molding machine and transmitting various commands to peripheral equipment of the injection molding machine. Further, the manual data input device 29 with a display is C
It is connected to the bus 22 via the RT display circuit 26 so that a monitor display screen, a function menu can be selected and various data input operations can be performed. A numeric keypad for inputting numerical data and various function keys are provided. Has been.

Then, the CNC CPU 25 is replaced by the ROM 27.
The servo CPU 20 distributes pulses to the servo motors of the respective axes based on the control program, and the servo CPU 20 outputs the movement commands distributed to the respective axes and the feedback signals of the positions detected by the detectors such as the pulse coders P1 and P2. Based on the velocity feedback signal and the velocity feedback signal, servo control such as position loop control, velocity loop control and current loop control is performed as in the conventional case, and so-called digital servo processing is executed.

FIG. 2 is a functional block diagram showing an outline of the digital servo function of the servo CPU 20 which executes each control of the position loop, the velocity loop and the current loop, taking the drive control of the injection servomotor M1 as an example.
C is based on various data set as molding conditions in the non-volatile memory 24, for example, data such as screw position corresponding to switching of injection speed and injection speed set for each injection stage.
Upon receiving a movement command per predetermined time output from the NC CPU 25, that is, a distribution pulse serving as a position command, software processing of a position loop, a velocity loop, and a current loop is performed at every predetermined cycle to operate the injection servomotor M1. Drive control. That is, in the position loop processing, similarly to the conventional case, the distributed pulses of the position command input from the CPU 25 for CNC are sequentially integrated and stored, and the position deviation signal is subtracted from the feedback signal of the position fed back from the pulse coder P1. Then, the position deviation is multiplied by the position loop gain to obtain the speed command Vc, which is passed to the processing of the speed loop. Further, in the processing of the speed loop, PI (proportionality / proportionality) based on the speed command Vc and the speed feedback signal Vf fed back from the pulse coder P1.
The current command (torque command) I is obtained by performing processing such as integration control, and this value I is further corrected if necessary (details will be described later), and then the current command I is passed to the processing of the current loop. In the current loop processing, as in the conventional case, PI control or the like is performed based on the current feedback corresponding to the actual current flowing in the injection servomotor M1 and the current command I from the speed loop to obtain each phase drive current, and the servo is performed. The drive torque of the injection servomotor M1 is controlled via the amplifier 15.

FIG. 4 is a diagram conceptually showing the structure of a regulation value storage file provided in the non-volatile memory 24 for storing the regulation value of the injection pressure corresponding to the screw position. FIG. 3 shows more specifically the correspondence relationship between the screw position and the regulation value, where the horizontal axis is the screw position and the vertical axis is the injection pressure. In the example of the figure, the screw start position is determined by the screw position S1, The injection position is indicated by the screw position S5. In this example, the most advanced position of the screw in the injection molding machine is defined as the coordinate origin, so in FIGS. 3 and 4, S1>S2>S3>S4> S5 (Sn)
And the screw movement direction at the time of injection is from left to right in FIG. The correspondence between the screw position and the regulation value as shown in FIG. 3 depends on the characteristics of the resin and the mold, particularly the correspondence between the screw position and the filling state of the resin, for example, in the initial stage of injection. It is determined in advance on the basis of conditions such as lowering the pressure of the resin sprayed inside. The regulation value of the injection pressure is determined for each screw movement section by arbitrarily dividing the movement stroke of the screw 2 from the injection start position to the injection completion position. When this relation is set and stored in the regulation value storage file, The regulation value of the injection pressure is input corresponding to the screw position dividing each section. For example,
The screw position S1 represents the screw movement section S1-S2, and the regulation value P1 of the injection pressure corresponding to the screw movement section S1-S2 is stored corresponding to the screw position S1 in the regulation value storage file of FIG. Will be done.

The operator sets a predetermined correspondence between the screw position and the regulation value using a ten-key pad or the like of the manual data input device 29 with a display and stores it in the regulation value storage file in advance. Needless to say, the screw position for setting the regulation value is not restricted by the set screw position for switching the injection speed.

FIG. 5 is a flow chart showing the outline of the pressure regulation processing executed by the servo CPU 20 for each processing cycle of the speed loop processing. The regulation of the injection pressure in this embodiment will be described below with reference to this flow chart. To do. It should be noted that this process is a process corresponding to the block of the velocity loop shown in FIG.

Based on data such as the injection speed switching position set in the non-volatile memory 24 as a molding condition and the set injection speed of each injection stage, the injection control of the injection command is performed according to the distribution pulse of the movement command output from the CNC CPU 25. The servo CPU 20 that has started the speed loop process for
After the current screw position S is read from the current position storage register and temporarily stored (step T1), the value of the address search index i is initialized to 1 (step T2). Next, the servo CPU 20 reads the screw positions Si and Si + 1 from the regulation value storage file of the non-volatile memory 24 based on the value of the address search index i, and the current screw position S is within the screw movement section Si to Si + 1. (Step T3). If not included, the servo CPU 20 sets the value of the index i to 1
It is incremented (step T4), and it is determined whether or not the current value of the index i exceeds the number [n-1] of screw moving sections set by division (step T).
5). If the current value of the index i does not exceed [n-1], the servo CPU 20 determines the screw current position S
In the same manner as described above, until the screw movement section Si to Si + 1 including is detected or the current value of the index i exceeds [n-1], steps T3 to T5 are performed in the same manner as described above.
The process of will be repeatedly executed.

If the screw movement section Si to Si + 1 including the current screw position S is detected and the result of the determination in step T3 is true, the servo CPU 2
0 stores the current value of the index i, that is, the address of the regulation value storage file that stores the regulation value of the injection pressure corresponding to the current screw position S in the register k (step T7),
Further, the current value of the index i is the number of screw moving sections [n
-1], it means that the screw 2 has moved forward beyond the setting section of the injection pressure regulation value, and in this case, the last screw moving section Sn-1 to S-1.
Address value [n-1] that stores the regulation value corresponding to n
Is stored in the register k (step T6), and the regulation value set for the screw movement sections Sn-1 to Sn is applied as the regulation value of the injection pressure corresponding to the current screw position S of the screw.

Next, the servo CPU 20 sends the present value P of the injection pressure via the bus 22 and the CPU 17 for pressure monitoring.
On the other hand, based on the speed command Vc calculated based on the position deviation in the position loop processing and the actual speed Vf calculated based on the feedback signal of the speed loop, the speed loop processing is performed in the same manner as in the conventional method. A current command (torque command) I is obtained (step T8). Since the process itself for obtaining the current command I is already known,
No particular explanation is given here.

Then, the servo CPU 20 uses the register k.
The value of the regulation value Pk corresponding to the value is read from the regulation value storage file and the magnitude relationship with the current value P of the injection pressure is compared (step T9). If the current value P exceeds the regulation value Pk, the step is performed. By performing a correction operation of subtracting a predetermined value β (where β> 0) from the value I of the current command calculated in the process of T8,
This value is used as the current command value I to be passed to the process of the current loop (step T10). If the current value P does not exceed the regulation value Pk, the current command value I calculated in the process of step T8 is directly used as the current command value. The value is I (correction operation is not performed). Next, the servo CPU 20 delivers the current command I to the processing of the current loop (step T11), and ends the speed loop control in this processing cycle. In the processing of the current loop, the current loop control is performed in the same manner as the conventional one by the current feedback corresponding to the actual current flowing in the injection servomotor M1 and the current command I from the speed loop.
The drive torque of the injection servomotor M1, that is, the injection pressure is controlled.

Hereinafter, the servo CPU 20 is the CP for CNC.
Until the pulse distribution process of U25 is completed, the digital servo control for each loop of position, velocity and current is repeatedly executed in the same manner as described above.

Therefore, the rotation of the injection servomotor M1 for driving the screw 2 is hindered for some reason, the position deviation of the position loop increases, and the speed command Vc from the position loop increases. However, the injection servomotor M1 is drive-controlled so as to maintain the resin pressure P acting on the screw 2 within a preset injection pressure regulation value Pk range, and damage to the mold or burrs due to excessive resin pressure. Are prevented from occurring.

[0026]

The injection control device of the present invention compares the current injection pressure acting on the screw with the regulation value of the injection pressure set corresponding to the present position of the screw, and the current injection pressure is determined to be the regulation value. If it exceeds, a predetermined amount is subtracted from the current command obtained by the speed loop control, and the servo motor is driven and controlled using this value as the current command, so even if the position deviation of the position loop increases. ,
A sudden increase in injection pressure is prevented, and accidents such as damage to the mold and occurrence of burrs can be prevented. In addition, the regulation value that regulates the injection pressure can be freely set by selecting an arbitrary screw position, so that the maximum injection pressure can be regulated according to the filling status of resin into the mold. Therefore, it is possible to always perform an injection operation at an optimum injection pressure for a mold having a complicated cavity shape or a mold that needs to perform an injection operation with a constant pressure characteristic.

[Brief description of drawings]

FIG. 1 is a block diagram showing a main part of an injection molding machine of an embodiment to which an injection control device of the present invention is applied.

FIG. 2 is a servo C provided in the injection control device of the embodiment.
It is a functional block diagram which shows the outline of the digital servo function of PU.

FIG. 3 is a diagram showing an example of setting a pressure regulation value in the injection control device of the embodiment.

FIG. 4 is a conceptual diagram showing a configuration of a regulation value storage file provided in the injection control device of the embodiment.

FIG. 5 is a flowchart showing a main part of pressure regulation processing by the injection control device of the embodiment.

[Explanation of symbols]

 1 Injection Cylinder 2 Screw 4 Pressure Detector 15 Servo Amplifier 19 RAM 20 Servo CPU 21 ROM 22 Bus 24 Nonvolatile Memory M1 Injection Servo Motor P1 Pulse Coder

Claims (2)

[Claims] 1. An electric injection molding machine for driving a screw in the axial direction by a servomotor to perform injection, and the current injection pressure acting on the screw and the current screw position are sequentially detected to detect the current injection pressure acting on the screw. When the value exceeds the regulation value set in advance corresponding to the screw current position, the injection molding is characterized in that the servo motor is controlled with the current command obtained by subtracting a predetermined amount from the current command obtained by the speed loop control. Machine injection control device. 2. The injection control device for an injection molding machine according to claim 1, wherein an injection speed with respect to a screw position is set, and the servomotor speed is controlled so as to match the set injection speed.