JPH0815750B2 - Injection molding machine pressure control method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric injection molding machine that performs injection with a servomotor, and more particularly to a pressure control method such as injection pressure (holding pressure) and back pressure.

2. Description of the Related Art In an electric injection molding machine, a screw is driven in the axial direction by a servo motor to cause injection, and the pressure applied to the resin during injection is detected by a pressure sensor such as a load cell, and the detected injection pressure (maintenance) is maintained. There is known an injection pressure control method in which feedback control is performed so that the pressure becomes a set value. In addition, during measurement, the output torque of the injection servomotor is controlled with respect to the resin pressure generated by the rotation of the screw and melting of the resin, and the resin is given a predetermined back pressure to perform back pressure control. Are also known (for example, JP-A-62-97818).

Further, so-called digital servo control in which the above-mentioned control of the servo motor is digitally controlled by a processor is also known in Japanese Patent Laid-Open No. 64-18619.

SUMMARY OF THE INVENTION The present invention relates to a pressure control method for controlling pressure such as injection pressure and back pressure by the digital servo control described above. However, in the conventional pressure control, the position control during pressure control is performed. However, there is a drawback that the control, that is, the screw position cannot be controlled. Only the pressure is monitored during the pressure control, and only the feedback control is performed so that the detected pressure becomes the set pressure, the position of the screw is not monitored, and the position control of the screw is not performed.

For example, in the pressure-holding process, only pressure control is performed,
If the screw position is not controlled, the screw position will not be controlled even if the screw position exceeds the target position due to insufficient amount of resin, etc., so try to output the set injection pressure. As a result, the screw may be further advanced (toward the nozzle), and the screw may collide with the nozzle or the like to damage the screw, the nozzle, or the heating cylinder.

Therefore, it is an object of the present invention to provide a pressure control method capable of controlling the screw position even during pressure control.

Means for Solving the Problems The present invention controls driving a screw with a servomotor,
It has a digital servo controller that controls the pressure applied to the resin such as injection pressure and back pressure with a processor.
In the pressure control method of the injection molding machine that detects the pressure applied to the resin during measurement and controls the pressure, in the pressure control section of the injection process, the measurement process, etc., the position deviation or speed deviation is less than or equal to the set value Then, the position control is switched to, and when the position deviation or the speed deviation exceeds the set value, the control is switched to the pressure control so that the screw position is controlled even during the pressure control.

Operation FIG. 1 is a block diagram of the injection servo motor control system for explaining the operation principle of the present invention. Block B1 is a position loop transfer function block, Kx is a position gain, and block B2 is a speed loop transfer function. In the block, the example shown in FIG. 1 shows an example of performing PI (proportional, integral) control, where K1 is an integral gain and K2 is a proportional gain. The block B4 is a block of the current loop controller. Reference numeral 2 is an injection servo motor, 4 is a pressure sensor such as a load cell for detecting the pressure applied to a screw driven by the servo motor 2, and 3 is a pulse coder and block for detecting the rotational position of the servo motor 2 to detect the screw position. B3 is an F / V converter that converts the output of the pulse coder 3 into an actual speed voltage, block B5 is a block of a transfer function of pressure control, K3 is an integral gain, and K4 is a proportional gain. SW is a switch for switching between position control and pressure control.

The position deviation ex is obtained by subtracting the rotational position Xr of the servomotor 2 detected by the pulse coder 3 from the command position Xs, and the position command ex is multiplied by the position gain ex to obtain the speed command Vs. The actual speed Vr of the servomotor 2 output from the F / V converter B3 is subtracted from the speed command Vs to obtain the speed deviation ev, and integral and proportional control is performed to obtain the current command Is as a torque command. In the case of position control, the switch SW is turned on to the speed control block B2 side, and the current command Is obtained in the speed control block B2 is input to the current control unit B4 to drive and control the servo motor 2. The switch SW is switched according to the amount of the position deviation ex or the speed deviation ev during the pressure control. If the position deviation ex or the speed deviation ev is less than or equal to the set value, the position control side (speed control block side)
Switch to the pressure control block side when the set value is exceeded. In the pressure control block B5, the resin pressure Pr applied to the screw detected by the pressure sensor 4 is set to the set pressure Ps.
Then, the pressure deviation ep is obtained by subtracting from it, the PI command is performed to obtain the current command Is as the torque command, and the current command Is is output to the current control unit B4 via the switch SW.

Switch SW in the injection speed control section of the injection process
Is switched to the position control side, position and injection speed control is performed, and if the value of the position deviation ex or speed deviation er is less than or equal to the set value when in the pressure control section such as the pressure holding process, the position remains unchanged. The speed control is performed, but when the set value is exceeded, the switch SW is switched, and the pressure control is performed so that the detected pressure Pr becomes the set pressure Ps. Further, the position deviation ex and the speed deviation ev are obtained even during the pressure control, and when the position deviation ex and the speed deviation ev become equal to or less than the set values, the position control is switched to the position control side. As a result, the screw does not exceed the target position, and the screw, nozzle, and heating cylinder are not damaged.

The same applies to back pressure control and other pressure control, and pressure control or position control is switched depending on whether the position deviation ex and the speed deviation ev are greater than or equal to the set values. Will be controlled.

Embodiment FIG. 2 is a block diagram of an essential part of an injection molding machine for carrying out the present invention, showing only an injection shaft related to pressure control,
Other mold clamping shafts, screw rotating shafts, etc. are not shown.

Reference numeral 1 is a screw, 2 is an injection servomotor for moving the screw 1 in the axial direction to inject resin, 3 is a pulse coder attached to the injection servomotor 2, and 4 is pressure of a load cell or the like for detecting pressure applied to the resin. Sensor, 5
Is a heating cylinder.

Further, 10 is a numerical control device (hereinafter, referred to as NC device) for controlling the injection molding machine, and the NC device 10 is an NC processor (hereinafter, referred to as CPU) 11, a programmable machine,
Has a controller (hereinafter referred to as PMC) 12 and NC CPU 11
A ROM 17, which stores a control program, and a RAM 18, which is used for temporary storage of data and the like, are connected to each other via a bus 25. A ROM 19 storing a sequence program and a RAM 20 used for temporary storage of data are bus-connected to the PMC CPU 12. Reference numeral 14 is a bus arbiter controller (hereinafter referred to as BAC), which is a non-volatile shared RAM 15 for storing NC programs and various setting values, the NC CPU 11 and PMC.
The CPU 12 is connected to the bus 25, and the bus used by the BAC 14 is controlled. A CRT / MDI (manual data input device with display device) 22 is connected to the BAC 14 via an operator panel controller 21.

Reference numeral 13 is a CPU for controlling output torque, speed, and position of the injection servomotor 2, that is, a servo control CPU. The CPU has a bus 25 for storing control programs and data. The input / output circuit 24 and the NC CUP 11 are also connected to the servo shared RAM 16 that can be accessed by both the NC CPU 11 and the servo control CPU 13.

Driver (including D / A converter) in the input / output circuit 24
The power amplifier 6 is connected via 7 and the injection servomotor 2 is driven by the output of the power amplifier 6. Further, the input / output circuit 24 outputs the output of the power amplifier 6, that is, the drive current data obtained by converting the drive current of the injection servomotor 2 by the A / D converter 9 and the output of the pressure sensor 4 into the A / D converter 8. The pressure data converted into a digital signal by and the output of the pulse coder 3 are input.

In the above configuration, first CR parameters
Input from T / MDI22 and set and store in shared RAM15. Position loop gain in servo control in relation to the present invention
Kx, integral gain K1 of speed control loop, proportional gain K2, integral gain K3 in pressure control, proportional gain K4, and constant Δx1 for position deviation in pressure-holding process and metering process, which is the criterion for switching between position control and pressure control. , Δx2
(Or constants Δv1, Δv2 for speed deviation) Furthermore,
Set pressure, back pressure, etc. are set and stored.

Then, when the drive command of the injection molding machine is input, for NC
The CPU 11 reads the above parameters from the shared RAM 15 and writes them in the servo shared RAM 16, and the servo CPU 13 reads this data and executes the servo control processing described later.

FIG. 3 is a servo CP in one embodiment of the present invention in which either position control or pressure control is switched depending on the position deviation ex.
It is a flow chart of processing which U13 performs for every position and speed control processing cycle.

In the injection process, the servo CPU 13 reads the movement command Xs written in the servo shared RAM 16 from the NC CPU 11 for each cycle, adds this movement command Xs to the register that stores the position deviation ev, and the previous cycle During the period, the actual movement amount Xr fed back from the pulse coder 3 is subtracted to obtain the position deviation ex (step S1). Next, it is judged whether or not the pressure is being maintained (step S2). In the injection process, when the injection speed control is completed and the pressure holding process is started, the PMC CPU 12 writes a switching command to the pressure holding control in the shared RAM 15, and the NC CPU 11 reads this command and the servo CPU 13 via the servo shared RAM 16 Let us know. During the injection speed control, since the command to switch to the holding pressure is not issued, the servo CPU 13 shifts from step S2 to step S3, and if it is not under measurement, shifts to step S4 and the position obtained in step S1. The deviation ex is multiplied by the position gain Kx to obtain the speed command Vs, the actual speed Vr is subtracted from the speed command Vs to obtain the speed deviation ev (step S-5), and the above speed is stored in the register A as integral control of the speed loop. A value obtained by multiplying the deviation ev by the integral gain K1 is added, and further, a value obtained by multiplying the speed deviation ev by the proportional gain K2 is added to the value of the register to obtain a current command Is as a torque command (step S
6, S7). Then, this current command Is is passed to the current loop processing (step S8), and the processing of the cycle of the position / speed control loop processing cycle ends. Hereinafter, this processing will be repeated for each processing cycle.

The injection speed control is completed, and the command to switch to the holding pressure control is PM.
When input from the CPU 12 for C through the CPU 11 for NC and the shared RAM 16 for servo, the CPU 13 for servo operates from step S2 to step S2.
The process proceeds to 9 and it is determined whether the absolute value of the position deviation ex calculated in step S1 is equal to or less than the set value Δx1 for the pressure holding process.
Normally, at the end of the injection speed control, since the resin is filled in the mold, a large force is required for the screw 1 to move forward, and the positional deviation ex is large and larger than the set value Δx1. Therefore, the process proceeds from step S9 to step S10, and the actual pressure Pr applied to the resin detected by the pressure sensor 4 is subtracted from the set pressure (holding pressure) Ps to obtain the pressure deviation ep, which is used as the integral control of the pressure control. A value obtained by multiplying the pressure deviation ep by the integral gain K3 of pressure control is added to the register B, and the value of the register B is proportional to the pressure deviation ep.
Calculate the current command Is by adding the value multiplied by K4 (step S1
0, S11, S12), and delivers this current command Is to the current loop processing (step S8). That is, when the absolute value of the position deviation ex is larger than the set value Δx1 in step S9, steps S10 to S
Twelve pressure controls will be performed in each cycle. Then, if the screw advances too much and the positional deviation ex becomes equal to or less than the set value Δx1, even in the pressure control section, the process proceeds from step S9 to step S4, and steps S4 to
The position and speed control of S7 is executed. Position deviation like this
When ex becomes equal to or less than the set value Δx1, the pressure control is switched to the position control, so the screw does not go beyond the target position and it is possible to prevent the screw tip from colliding with the nozzle and damaging the screw and nozzle. .

Further, the servo CPU 13 also performs the same processing in controlling the back pressure, and in the weighing process, the command position Xs is set so as to retract the screw at a slow speed (direction opposite to the injection direction).
give. On the other hand, as the screw rotates, the resin melts and a pressure is generated, which causes the screw to forcibly retreat, causing the actual position Xr to exceed the commanded position Xs, and the sign of the position deviation ex is reversed. Servo motor 2
Will be driven in the ejection direction. When the absolute value of the position deviation ex is smaller than the set value Δx2, steps S1 and S
The positions and speeds of 2, S3, S13, S4 to S8 are controlled, and the servomotor 2 is in a state of applying a brake when the screw 1 moves backward. Then, when the absolute value of the position deviation ex becomes larger than the set value Δx2, the pressure control of steps S14 to S16 is performed and the set pressure (set back pressure) Ps2 becomes the actual pressure Pr.
Feedback control is performed so that Then, when the position of the screw 1 detected by the pulse coder 3 reaches the measuring position, the rotation of the screw 1 is stopped and the measuring process is completed. It should be noted that the position loop gain Kx, the velocity loop, and the integral gains K1, K3, and the proportional gains K2, K4 of the pressure control may be changed in the injection process and the measurement process.

FIG. 4 shows a second embodiment of the present invention, which is different from the first embodiment in that the position / speed control or pressure control is switched depending on the magnitude of the speed deviation ex. Only.

The larger the position deviation ex is, the larger the speed deviation ev is. Therefore, substantially the same control can be obtained by using the speed deviation ex instead of the position deviation ex and switching between position control and pressure control.

Comparing the flowchart of FIG. 3 and the flowchart of FIG. 4, the processing for obtaining the speed command Vs and the speed deviation ev is performed before determining whether or not the pressure control is performed, and is related to the pressure control and the position control. The same as the first embodiment shown in FIG. 3, except that the speed deviation ev is always obtained for each cycle, and the position control or pressure control is determined by the speed deviation ev. Is. That is, the position deviation ex is calculated from the command position Xs and the actual Xr, and the position gain Kx
Calculate the speed command Vs by multiplying by and the actual speed from this speed command Vs
Vr is subtracted to obtain the speed deviation ev (steps S101 to S103),
When pressure control is not performed, that is, when neither pressure-holding nor metering is in progress, and the absolute value of speed deviation ev is less than or equal to set values Δv1, Δv2 even during pressure control, PI control of speed control is performed to obtain current command Is (step S106, S107), in the pressure control section, if the absolute value of the speed deviation ev is larger than the set value Δv1 or Δv2, PI control of pressure control is performed and the actual pressure is
The Pr (holding pressure, back pressure) is controlled so as to become the set pressure Ps1 or Ps2, and the current command Is is obtained and passed to the current loop processing.

In the above embodiment, the pressure control was only holding pressure and back pressure, but even during injection speed control, for example, when the pressure exceeds a set pressure, the pressure control is performed by position deviation or speed deviation as described above. You may make it switch to position control.

Advantageous Effects of the Invention The present invention controls the position even during pressure control such as holding pressure and back pressure, so that the screw advances beyond the target position during injection and holding pressure control, and the screw, nozzle, and heating cylinder are There is no possibility of damage, and even during back pressure control, it is possible to easily shift to back pressure control, and it is possible to carry out the same processing method including holding pressure and back pressure control, which simplifies control.

[Brief description of drawings]

FIG. 1 is a block diagram of a servomotor control system for explaining the principle of operation of the present invention, FIG. 2 is a block diagram of an electric injection molding machine for carrying out the present invention, and FIG. 3 is a first block diagram of the present invention. 4 is a flow chart of the second embodiment of the present invention. 1 ... screw, 2 ... injection servo motor, 3 ...
Pulse coder, 4 ... Pressure sensor, 5 ... Heating cylinder, 6-electrode amplifier, 7 ... Driver, 8,9 ... A / D converter, 10 ... Numerical control device (NC device).

Claims (8)

[Claims] 1. A screw is driven and controlled by a servo motor,
In a pressure control method of an injection molding machine which has a digital servo control device for performing pressure control by a processor, detects pressure applied to resin, and controls the pressure, a position deviation is set for each molding process during pressure control. A pressure control method for an injection molding machine, comprising: switching to position control when the value falls below a preset value, and switching to pressure control when the positional deviation exceeds the preset value. 2. A screw is driven and controlled by a servo motor,
It has a digital servo controller that controls injection pressure with a processor, and detects the pressure applied to the resin during the pressure holding process.
In a pressure control method of an injection molding machine for controlling the pressure,
A pressure control method for an injection molding machine, comprising: switching to position control when the position deviation becomes equal to or less than a set value during the pressure holding step, and switching to pressure control when the position deviation exceeds the set value. 3. A screw is driven and controlled by a servo motor,
In a pressure control method of an injection molding machine, which has a digital servo control device for performing back pressure control by a processor, detects pressure applied to resin during measurement, and controls the pressure, during measurement,
A pressure control method for an injection molding machine, comprising: switching to position control when the position deviation is below a set value, and switching to pressure control when the position deviation exceeds the set value. 4. A screw is driven and controlled by a servo motor,
A pressure control method for an injection molding machine, which has a digital servo control device for controlling injection pressure and back pressure by a processor, detects the pressure applied to the resin during the pressure holding process and during measurement, and controls the pressure. When the position deviation becomes less than or equal to the set value set for each process during and during measurement,
If you switch to position control and the position deviation exceeds the set value above,
A pressure control method for an injection molding machine, characterized by switching to pressure control. 5. A screw is driven and controlled by a servo motor,
In a pressure control method for an injection molding machine, which has a digital servo control device for performing pressure control by a processor, detects pressure applied to resin, and controls the pressure, a velocity deviation is set for each molding process during pressure control. A pressure control method for an injection molding machine, comprising: switching to position control when the value falls below a preset value, and switching to pressure control when the speed deviation exceeds the preset value. 6. A screw is driven and controlled by a servo motor,
It has a digital servo controller that controls injection pressure with a processor, and detects the pressure applied to the resin during the pressure holding process.
In a pressure control method of an injection molding machine for controlling the pressure,
A pressure control method for an injection molding machine, comprising: switching to position control when the speed deviation becomes equal to or less than a set value during the pressure holding step, and switching to pressure control when the speed deviation exceeds the set value. 7. A screw is driven and controlled by a servo motor,
In a pressure control method of an injection molding machine, which has a digital servo control device for performing back pressure control by a processor, detects pressure applied to resin during measurement, and controls the pressure, during measurement,
A pressure control method for an injection molding machine, comprising: switching to position control when the speed deviation is below a set value, and switching to pressure control when the speed deviation exceeds the set value. 8. A screw is driven and controlled by a servo motor,
A pressure control method for an injection molding machine, which has a digital servo control device for controlling injection pressure and back pressure by a processor, detects the pressure applied to the resin during the pressure holding process and during measurement, and controls the pressure. When the speed deviation becomes less than or equal to the set value set for each process during and during measurement,
When switching to position control and the speed deviation exceeds the above set value,
A pressure control method for an injection molding machine, characterized by switching to pressure control.