JP2641057B2 - Holding pressure switching method of injection molding machine - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a holding pressure switching system for an injection molding machine.

2. Description of the Related Art When switching from an injection process to a pressure-holding process in an injection molding machine, it is necessary to confirm that the resin is completely filled in a mold cavity.

Conventionally, as a method for detecting whether or not the resin in the mold cavity is completely filled, roughly, it is considered that the filling of the resin is completed by detecting that the screw has reached the pressure holding switching position. Others detect the actual pressure of the resin in the mold cavity or the reaction force of the resin acting on the screw to confirm the completion of the resin filling. In the case where the holding pressure is switched by the screw position, the timer is used in combination to continue the molding operation even when the screw cannot be pushed down to the holding pressure switching position due to poor measurement or the like, In some cases, when the screw does not reach the pressure holding switching position even after the set time of the timer has elapsed, the pressure is forcibly shifted to the pressure holding step. Also,
In the case of detecting the injection reaction force and confirming the completion of resin filling, insufficient filling occurs due to insufficient measurement, etc., even if the screw is pushed to the most advanced position, the injection pressure does not increase and switching to holding pressure is not performed Therefore, continuous molding may not be possible, and a timer is used in the same manner as above, and if the injection pressure does not reach the holding pressure switching pressure even after the timer set time has elapsed, the forcible pressure holding process is performed. Some have been migrated.

However, to ensure that the resin has been completely filled,
Needless to say, it is desirable to use a closed-loop type pressure detection system in which the completion of filling is confirmed by directly detecting the actual pressure of the resin in the mold cavity and the reaction force of the resin acting on the screw.

Problems to be Solved by the Invention However, in the case of a method of detecting pressure and switching to the pressure holding step according to the detected pressure, even if the actual pressure of the resin in the mold cavity is detected, the resin acting on the screw Even if the reaction force is detected, in the conventional system, it is essential to provide a pressure detector, and the cost is inevitably higher than other systems.

Therefore, an object of the present invention is to provide a pressure-holding switching method for an injection molding machine that can reliably check the filling state of resin in a mold cavity, similarly to the conventional pressure-holding switching method using pressure detection without providing a pressure detector. To provide.

Means for Solving the Problems The present invention detects the position deviation between the current position of the screw and the command position given to the screw in the injection step, and when the detected position deviation exceeds a set predetermined value, the injection is performed. It was configured to start the pressure-holding step as completion.

In the injection process, when the resin is not filled in the mold cavity, the reaction force of the resin acting on the screw, that is, the resin pressure is small, so the screw operates according to the command position and the set injection speed. However, when the reaction force of the resin acting on the screw increases as the resin in the mold cavity is filled, it becomes difficult for the screw to operate following the command position and the set injection speed.

Therefore, the position deviation between the current position of the screw and the command position given to the screw gradually increases, and when the position deviation exceeds a predetermined value, the resin in the mold cavity is completely charged. This means that after confirming that, the pressure-holding step is started.

Examples Hereinafter, examples of the present invention will be described.

FIG. 1 is a diagram showing a main part of an electric injection molding machine for implementing an embodiment of the present invention and a main part of a control system of the injection molding machine, wherein reference numeral 1 denotes a screw, and reference numeral 2 denotes an injection servo. Reference numeral 3 denotes a pulse coder mounted on the servomotor 2 for injection, and reference numeral 4 denotes a cylinder.

Numeral 100 denotes a numerical controller (hereinafter referred to as an NC device) as a control device for controlling the injection molding machine.
0 is the microprocessor for NC (hereinafter referred to as CPU) 108
And a CPU 110 for a programmable machine controller (hereinafter referred to as a PMC). The CPU 110 for the PMC is used for a ROM 113 storing a sequence program for controlling a sequence operation of the injection molding machine and a temporary storage of data.
The RAM 106 is connected. The CPU 111 for the NC includes a ROM 111 storing a management program for controlling the entire injection molding machine, and a servo circuit 10 for driving and controlling servomotors for each axis for injection, clamping, screw rotation, ejector, and the like.
1 is connected via the servo interface 107. In FIG. 1, only the servomotor 2 for injection and the servo circuit 101 of the servomotor 2 are shown. Also, 1
03 is a non-volatile shared RAM composed of a bubble memory and a CMOS memory, which stores an NC program for controlling each operation of the injection molding machine, and various setting values, parameters and macro variables relating to molding conditions. And a setting memory unit. 109 is a bus arbiter control (hereinafter BAC
The BAC 109 includes an NC CPU 108 and a PMC CPU 110,
The buses of the shared RAM 103, the input circuit 104, and the output circuit 105 are connected, and the bus used is controlled by the BAC 109. 114 is an operator panel controller 1
This is a manual data input device with a CRT display device (hereinafter referred to as CRT / MDI) connected to the BAC109 via the C12, and displays various setting screens and work menus on the CRT display screen, and various operation keys (soft keys And ten keys, etc.) to input various setting data and select a setting screen. Reference numeral 102 denotes a RAM connected to the NC CPU 108 via a bus, which is used for temporary storage of data and the like.

In FIG. 1, an injection shaft of an injection molding machine, that is, an injection servomotor 2 for driving and injecting a screw 1 is attached to the injection servomotor 2, and the rotation of the servomotor is detected and the screw position is detected. Is shown, and other mold clamping shafts, screw rotation shafts, ejector shafts and the like are omitted. Therefore, NC equipment
Only the servo circuit 101 in the injection motor 100 for injection is shown, and the servo circuits for the other axes are omitted. The servo circuit 101 is connected to the injection servomotor 2, and the output of the pulse coder 3 is also input to the servo circuit 101. Further, a torque limit value for controlling the output torque of the injection servomotor 2 is output from the output circuit 105 to the servo circuit 101.

In the configuration as described above, the NC device 100
The PMC CPU 110 performs sequence control with the NC program for controlling each operation of the injection molding machine stored in 3 and the parameters of various molding conditions stored in the setting memory unit and the sequence program stored in the ROM 113. The NC CPU 108 distributes pulses to the servo circuits 101 of the respective axes of the injection molding machine via the servo interface 107 to control the injection molding machine.

Then, the servo circuit 101 of each axis subtracts the pulse from the pulse coder 3 from the distribution pulse received via the servo interface 107, and outputs an error register for outputting the current error amount for the command position and an output of the error register to D / A is converted and output as a speed command, the speed command is compared with the current speed obtained by F / V conversion of the output of the pulse coder 3, and a current command to flow to the servomotor, that is, a torque command is output. The current flowing through the servomotor 2 is compared with the current command output from the speed controller, the current flowing through the servomotor 2 is controlled, and the output torque is controlled. Further, a servo circuit for controlling the injection pressure, the holding pressure, the back pressure, etc., like the injection shaft, is provided with a torque limiter for limiting the command value of the torque command in order to control the output torque of the servomotor 2. Output circuit 105
The torque limit value is controlled by the output from the controller.

Hereinafter, the holding pressure switching operation in the first embodiment will be described together with a flowchart (see FIG. 2) of the holding pressure switching process executed by the PMC CPU 110 in the task processing at predetermined intervals.

Note that the shared RAM 103 includes a command position storage register Ps that stores the amount of pulse distribution performed by the NC CPU 108 to the servo circuit 101 of the injection servomotor 2 via the save interface 107, that is, a command position of the screw 1. A current position storage register Pa for integrating and storing the pulses input from the pulse coder 3 to the servo circuit 101, that is, a current position storage register Pa for storing the current position of the screw, is provided in the setting memory section of the RAM 103. In the process, a positional deviation between the current position of the screw used for determining the shift to the pressure holding step and the command position given to the screw (hereinafter, referred to as a pressure holding switching position deviation) is set and stored.

The PMC CPU 110 executes the process shown in FIG. 2 at predetermined intervals. First, it is determined whether or not the injection start flag F set when the injection is started has been set (step S1). If the injection start flag F has not been set,
It is determined whether injection is currently being performed. This is determined by whether or not an injection axis forward command is output from the NC CPU 108 and whether the injection molding machine is currently set to the manual mode or the automatic mode, and the injection axis forward command is output. If the automatic mode is set, it is determined that the injection is being performed (step S2). If the injection is not being performed, the pressure holding switching process in this processing cycle is ended.

Hereinafter, the discriminating process of step S1 and step S2 is repeatedly executed at predetermined intervals, but if it is determined in step S2 that the injection is being performed, the injection start flag F is set and the fact that the injection process is started is stored. Then, the injection timer Ts is set to a predetermined time and started (Step S3) to start monitoring the injection time (Step S4).

After the start of injection, the NC CPU 108 starts pulse distribution processing for each predetermined cycle based on the injection conditions set and stored in the setting memory section of the shared RAM 103, and sends the servo interface 107 to the servo circuit 101 of the injection servomotor 2. , And the injection operation by the screw 1 is started. Further, the distribution pulses output at predetermined intervals are accumulated and stored in the command position storage register Ps, and the pulses input from the pulse coder 3 to the servo circuit 101 with the rotation of the injection servomotor 2 are stored in the current position storage register Pa. The command position of the screw 1 and the actual current position are stored in registers Ps and Pa, respectively.

On the other hand, the PMC CPU 110, which stores the start of the injection process and starts the injection timer Ts, then stores the current position storage register P
The value of the command position storage register Ps is subtracted from the value of a to calculate the position deviation between the current position of the screw 1 and the command position, and whether the position deviation exceeds the set pressure-holding switching position deviation Pt. (Step S5), but immediately after the start of injection, the resin is not filled in the mold cavity, and the reaction force of the resin acting on the screw 1 is small, so that the screw 1 follows the distributed pulse. The position deviation does not exceed the pressure-holding switching position deviation Pt. (Note that in this embodiment, since the coordinate system having the origin of the screw most advanced position in the screw axis direction is used. , The forward direction of the screw is a minus direction, and the value of Pa (current position) -Ps (command position) is positive or 0). Therefore, next, the process proceeds to step S6 to determine whether or not the set time of the injection timer Ts has expired. At the time immediately after the start of injection, the set time of the injection timer Ts has not been completed. CPU 110 ends the pressure holding switching process in this processing cycle.

Since the injection start flag F has already been set in the processing cycle after the next cycle, the PMC CPU 110
The determination processing of steps S5 and S6 is repeatedly executed.

In this way, while the PMC CPU 110 repeats the determination processing, the resin acting on the screw 1 as the resin is filled into the mold cavity by the screw 1 driven to be injected based on the pulse distribution processing of the NC CPU 108 The injection servomotor 2 cannot drive the screw 1 following the distributed pulse, and the pulse output from the pulse coder 3 by the actual rotation of the injection servomotor 2 is increased. The difference between the current position storage register Pa for cumulative storage and the command position storage register Ps for cumulative storage of the distribution pulses related to the injection servomotor 2, that is, the position deviation gradually increases.

When the PMC CPU 110 determines that the value of the position deviation is larger than the pressure-holding switching position deviation Pt while repeatedly executing the determination processing of step S1, step S5, and step S6 (step S5), the PMC The CPU 110 for NC considers that the filling of the resin into the mold cavity is complete, and
Output signal to U108 to shift to pressure-holding process (Step S
7) The flag F for storing the injection process is reset (step S8), and the pressure-holding switching process ends. Note that the NC CPU 108 that has shifted to the pressure holding switching starts the pressure holding based on the pressure holding conditions set and stored in the setting memory unit of the shared RAM 103, that is, the torque limit value of the injection servomotor 2.

If the set time of the injection timer Ts has expired before the position deviation value (Pa-Ps) does not exceed the pressure-holding switching position deviation Pt (step S6), it is considered that the injection process has ended, The process is shifted to the pressure-holding step.

In the present embodiment, a position deviation between the current position of the screw 1 and the command position given to the screw is detected using the current position storage register Pa and the command position storage register Ps provided in the shared RAM 103. However, the value of the error register in the injection servo circuit 101 may be read and used as the position deviation.

Next, a second embodiment in which the pressure-holding step is started when the speed deviation between the current speed of the screw 1 and the injection speed set for the screw 1 exceeds a set value will be briefly described.

In the present embodiment, a screw current speed storage register Va that stores an A / D converted value of the current speed obtained by F / V converting the output of the pulse coder 3 in the servo circuit 101 of the injection servomotor 2. Is provided in the shared RAM 103, and the current speed of the screw 1 is written in the screw current speed storage register Va for each processing cycle of the NC CPU 108. The first point is that a speed deviation Vt between the current speed of the screw used for the determination of the shift to the pressure holding process and the injection speed set for the screw (hereinafter referred to as a pressure holding switching speed deviation) Vt is set and stored. Different from the embodiment.

Hereinafter, the holding pressure switching operation in the present embodiment will be described together with a flowchart (see FIG. 3) of the holding pressure switching process executed by the PMC CPU 110 in the task processing at predetermined intervals.

In addition, in step S11 in the pressure holding switching process of the present embodiment.
The processing from step S14 to step S14 is the same as the processing from step S1 to step S4 in the above-described pressure holding switching processing of the first embodiment, and a description thereof will not be repeated.

The PMC CPU 110 that has stored the start of the injection process and started the injection timer Ts in the same manner as in the first embodiment, then starts from the injection speed setting value Vs stored in the setting memory unit of the shared RAM 103. The current speed Va of the screw 1 stored in the screw current speed storage register is subtracted, a speed deviation between the current speed of the screw 1 and the set injection speed is calculated, and the speed deviation is stored in the register Vt. It is determined whether or not the speed deviation is exceeded (step S15). At the time immediately after the start of the injection, the resin is not filled in the mold cavity, and the reaction force of the resin acting on the screw 1 is small. Are driven following the pulse to be distributed, and the speed deviation does not exceed the pressure holding switching speed deviation. Therefore, next, the process proceeds to step S16 to determine whether or not the set time of the injection timer Ts has expired. At the time immediately after the start of the injection, the set time of the injection timer Ts has not been completed. CPU 110 ends the pressure holding switching process in this processing cycle.

Since the injection start flag F has already been set in the processing cycle after the next cycle, the PMC CPU 110 proceeds to step S1.
The determination processing of step 1, step S15, and step S16 is repeatedly executed.

In this way, while the PMC CPU 110 repeats the determination processing, the resin acting on the screw 1 as the resin in the mold cavity is filled by the screw 1 driven to be injected based on the pulse distribution processing of the NC CPU 108. The injection servomotor 2 cannot drive the screw 1 following the distributed pulse, and the moving speed of the screw 1 gradually decreases, so that the current speed of the screw 1 is stored. The difference between the current screw speed storage register Va and the injection speed setting value Vs stored in the setting memory section of the shared RAM 103, that is, the speed deviation (Vs-Va) gradually increases.

Then, while the PMC CPU 110 repeatedly performs the determination processing of step S11, step S15, and step S16, when it is determined that the pressure holding pressure switching speed deviation Vt is exceeded (step S1).
5), the PMC CPU 110 considers that the filling of the resin into the mold cavity is completely completed, and outputs a signal for shifting to the pressure holding process to the NC CPU 108 (step S17). Is reset (step S18).
The pressure holding switching process ends.

If the injection timer Ts times out (step S16) before the difference (Vs−Va) between the set speed Vs and the actual speed Va exceeds the pressure-holding switching speed deviation Vt (step S16), the above-described first embodiment will be described. Switch to the pressure-holding step as in the case.

In the second embodiment, in order to detect the current speed of the screw 1, the current speed obtained by F / V converting the output of the pulse coder 3 is A / D converted, and this value is stored in a screw current speed storage register. Va is stored in Va, but the increment of the pulse output from pulse coder 3 is
The current speed of the screw 1 may be calculated by calculating the value for each processing cycle of the 110 and dividing this value by the processing cycle of the CPU 110 for PMC. Further, a tacho generator may be provided in the injection servomotor 2 and the output of the tacho generator may be A / D converted. When the servo circuit is a software servo, it is not necessary to provide an A / D converter or the like because the current speed also has a digital value in the software servo.

In the two embodiments described above, the screw 1
Since the position deviation and the speed deviation caused by the reaction force of the resin acting on the pressure are values proportional to the resin pressure, the pressure-change switching position deviation and the pressure-change switching speed deviation are made to correspond to the set pressure-holding pressure at the start of the pressure-holding. By setting, not only the completion of filling the mold cavity with the resin can be confirmed, but also the holding pressure switching corresponding to the set holding pressure can be performed.

Advantageous Effects of the Invention The present invention detects the reaction force of the resin acting on the screw by increasing the control deviation regarding the position of the screw in the injection step, and checks the filling state of the resin in the mold cavity, so that special It is not necessary to provide a simple pressure detector, and it is possible to reliably check the filling state of the resin and switch from the injection process to the pressure-holding process as in the conventional pressure-holding switching method with a pressure detector. it can.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an electric injection molding machine according to an embodiment for implementing the method of the present invention and a main part of a control system of the injection molding machine. FIG. 2 shows a holding pressure switching process in the first embodiment. FIG. 3 is a flowchart showing the pressure-holding switching process in the second embodiment. 1 ... screw, 2 ... servomotor for injection, 3 ...
Pulse coder, 4 ... Cylinder, 100 ... Numeric controller, 101 ... Servo circuit, 102,106 ... RAM, 103 ... Shared
RAM, 104 ... input circuit, 105 ... output circuit, 107 ... servo interface, 108 ... microprocessor for numerical control, 109 ... bus arbiter controller, 110 ...
Programmable machine controller microprocessor, 111, 113 ROM, 112 operator panel controller, 114 Manual data input device with CRT display.

Claims (1)

(57) [Claims] In an electric injection molding machine, after starting injection,
A pressure-holding switching method for an injection molding machine, wherein a position deviation of a difference between a current position of a screw and a movement command position to the screw is detected, and when the position deviation exceeds a predetermined value, the process shifts to a pressure-holding step.