JPH0911287A - Injection control method for injection molding machine - Google Patents

Abstract

PURPOSE: To correctly control injecting operation over the whole process by controlling injection speed based on a set injection speed until a resin reaches a pressure sensor and performing feedback control of injection pressure based on a set pressure and a current pressure after the resin has reached the pressure sensor. CONSTITUTION: A pressure sensor 7 for detecting pressure in an injection molding die 1 is provided. Change of the pressure in the injection molding die 1 is set in a control device 10. Until a resin reaches the pressure sensor 7, injection speed is controlled based on a set injection speed. On the other hand, after the resin has reached the pressure sensor 7, feedback control of injection pressure is performed based on the set pressure in the injection molding die 1 and a current pressure to be detected by the pressure sensor 7. Thus, switching of injection speed control to pressure control can be done by accurately determining charge of the resin into a cavity. By feedback control based on a correct detected pressure, the set pressure in the mold 1 can be reproduced correctly.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art A resin reaction force is detected by a load cell or the like attached to the base of a screw, and feedback control of the injection pressure is performed over the entire injection process including holding pressure so that the resin reaction force reaches a set pressure. The injection control method of the injection molding machine to be performed is already known. However, with such a configuration, if the resin begins to solidify in the pressure-holding stage in the latter half of the injection process, the resin pressure in the injection molding die cannot be accurately transmitted to the cylinder, so the resin reaction force in the cylinder is reduced. There is a case where feedback control of the holding pressure cannot be normally performed in the load cell that is detected by considering it as the resin pressure inside the mold. An injection control method has also been proposed in which a pressure sensor is installed in the injection molding die and the resin pressure in the die cavity is directly detected by this pressure sensor to perform feedback control of the injection pressure. In the configuration where the pressure sensor is provided in the molding die, the resin pressure cannot be detected by the pressure sensor from the start of injection until the resin is filled in the injection molding die. There is a problem that the control of is completely left to the limit.

Generally, in the injection molding operation, the difference in the injection speed has a great influence on the quality of the product at the stage of filling the resin into the cavity (particularly, the flow mark).
In addition, it is said that the difference in injection pressure (holding pressure) has a great influence on the quality of the product after the completion of filling (especially sink marks, burrs, etc.). It is necessary to switch appropriately between the control and. Therefore, injection control is also performed in which the screw position in the injection process is specified to switch from speed control to pressure control.However, by measuring the weight of a sample shot and determining the screw position, the injection control is maintained. Even if the switching position to the pressure is obtained, the screw position corresponding to the completion point of filling the cavity is not necessarily uniform due to the difference in the metering and kneading state, etc., and the control switching timing is specified by the screw position. However, the speed control is not always switched to the pressure control according to the filling state of the resin into the cavity.

Further, since the load cell attached to the base of the screw detects a resin reaction force above a certain level, it is considered that the filling of the resin into the cavity is completed, and the speed control is switched to the pressure control. A control method has also been proposed, but because the viscosity of the resin (resin reaction force acting on the screw) changes variously depending on the cylinder temperature, etc., the load cell detects the constant resin reaction force to check the resin filling status in the cavity. There is no guarantee that it will be detected properly.

[0005]

SUMMARY OF THE INVENTION The object of the present invention is to solve the above-mentioned drawbacks of the prior art, to accurately judge the filling state of the resin in the cavity, and to switch from the injection speed control to the pressure control. An object of the present invention is to provide an injection control method of an injection molding machine capable of performing

[0006]

According to the present invention, a pressure sensor for detecting the pressure inside an injection molding die is provided, and a change in the pressure inside the injection molding die is set in a control device. While the injection speed is controlled based on the set injection speed until it reaches the sensor, after the resin reaches the pressure sensor, it is detected by the set pressure inside the injection mold and the pressure sensor. The above-mentioned object is achieved by a configuration characterized in that the injection pressure is feedback-controlled based on the present pressure.

Further, the optimum injection condition suitable for the injection molding die can be stably reproduced by using the sampling data at the time of molding the good product as the pressure inside the injection molding die which becomes the target value.

Further, the value detected by the pressure sensor or the pressure inside the injection molding die set in advance in the control device is read for each sampling cycle in the injection process, and the resin is determined depending on whether the value exceeds a predetermined value or not. By determining whether or not the pressure sensor is reached, the speed control and the pressure control can be appropriately switched by the pressure sensor.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a main part of a configuration of an electric injection molding machine according to an embodiment to which an injection control method of the present invention is applied. The structure of the cylinder 2, the screw 3, the load cell 8, the power transmission mechanism 4, and the injection servomotor 5 is exactly the same as that of the conventional electric injection molding machine. The injection servomotor 5 and the rotary motion of the motor 5 are converted into linear motions. The power transmission mechanism 4 for converting drives the screw 3 in the cylinder 2 in the injection axis direction.

The load cell 8 is a pressure sensor provided between the output shaft of the power transmission mechanism 4 and the screw 3 in order to detect the resin reaction force acting on the screw 3. It is not a pressure sensor for detecting resin pressure. Therefore, it is possible to substitute the pressure sensor mounted inside the tip of the cylinder 2, that is, the pressure sensor for detecting the pressure in the cylinder. Its use will be described later.

A pressure sensor 7 for detecting the resin pressure inside the injection molding die 1 is a suitable position in the injection molding die 1, for example, a cold slug well (generally Z
It is provided at the pin position), the runner part, the product part, and other pools. The design and manufacture of the injection mold 1 is a user side problem, and the injection mold 1
When performing the injection molding operation by using, the user is allowed to arbitrarily determine depending on what kind of filling stage the injection speed control is switched to the injection pressure control.

Incidentally, it is common to provide a gas vent or the like in the injection molding die 1 in order to prevent the resin in the injection molding die 1 from being burnt due to the generation of high heat due to the gas compression. Even without a special gas vent,
It is necessary to be able to discharge the gas from the parting line or the seam of the core. As a result, even if injection is started, the pressure sensor 7 is completely filled with the resin, or at least until the resin reaches the position where the pressure sensor 7 is disposed. No pressure is detected by.

A control device 10 for driving and controlling the injection molding machine.
Is a C for CNC which is a microprocessor for numerical control
A PU 25, a PMC CPU 18 which is a programmable machine controller microprocessor, a servo CPU 20 which is a servo control microprocessor, and A
CP for pressure monitoring for detecting resin reaction force and resin pressure in the injection molding die 1 from the load cell 8 and the pressure sensor 7 via the / D converter 16 and performing sampling processing.
U17, and information can be transmitted between the microprocessors by selecting mutual input / output via the bus 22.

The PMC CPU 18 is connected to the ROM 13 which stores a sequence program for controlling the sequence operation of the injection molding machine and the RAM 14 which is used for temporary storage of operation data. The CNC CPU 25 is connected to the entire injection molding machine. A ROM 27 that stores a control program that controls the image and a RAM 28 that is used for temporary storage of calculation data are connected.

Each of the servo CPU 20 and the pressure monitoring CPU 17 has a ROM 21 storing a control program dedicated to servo control, a RAM 19 used for temporary storage of data, a resin reaction force acting on the screw 3 and injection molding. A ROM 11 storing a control program relating to a sampling process of resin pressure in the mold 1 and a RAM 12 used for temporary storage of data are connected. Further, the servo CPU 20 is connected to a servo amplifier for driving a servo motor for each axis such as mold clamping, screw rotation, ejector (not shown above) and injection based on a command from the CPU 20, The output from the pulse coder attached to the servo motor of each axis is the servo C
It will be returned to PU20. Then, the current position of each axis, its moving speed, etc. are calculated by the servo CPU 20 based on the feedback pulse from the pulse coder. In FIG. 1, a servo amplifier 1 for the injection axis
5, only the injection servo motor 5 and the pulse coder 6 of the motor 5 are shown, but the configuration of each axis for mold clamping, ejector, etc. is the same as this. However, it is not necessary to detect the current position for the screw rotation type, but only the speed.

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 body and for transmitting various commands to peripheral equipment of the injection molding machine. .

The manual data input device 29 with a display is connected to the bus 22 via the CRT display circuit 26, and is capable of displaying a graph screen, selecting a function menu and inputting various data. A numeric keypad for inputting and various function keys are provided.

The non-volatile memory 24 is a memory for storing molding data for storing molding conditions and various set values, parameters, macro variables and the like relating to injection molding work. Further, in this embodiment, in addition to these data, the set value of the change in the pressure inside the injection molding die 1 is set and stored in a predetermined data format (see FIG. 6). The setting of the pressure change inside the injection molding die 1 as the target value will be described in detail in the description of the "target value setting process" described later.

With the above configuration, the PMC CPU 18 controls the sequence operation of the entire injection molding machine, and the CNC C
The PU 25 outputs a movement command or a speed command to the servo motor of each axis based on the control program of the ROM 27, the molding conditions of the non-volatile memory 24, etc., and the servo CPU 2
0 is a servo command such as position loop control, speed loop control or current loop control based on the movement command or speed command for each axis and the position and speed feedback signals detected by a detector such as a pulse coder. Control is performed and so-called digital servo processing is executed.

Needless to say, in the injection process, the injection speed / pressure switching control mode is performed by setting the injection / holding pressure switching position with reference to the screw position to perform priority control of the injection speed and then switching to control of the injection pressure. It is also possible to carry out, and at the stage of injection molding work such as condition setting,
According to the injection speed / pressure switching control mode, the number of injection stages and the number of pressure-holding stages are set to be plural, and the injection speed and the injection pressure (holding pressure) are variously changed for each stage. Optimum molding conditions suitable for the injection molding die 1 can be obtained. In addition, the output of the load cell 8 is detected while performing the priority control of the injection speed, and when the value reaches a predetermined value, the priority control of the injection speed is terminated and the injection pressure (holding pressure) is maintained at a predetermined pressure. The present applicants have also proposed an injection control method in which the control of (1) is started, but it is also possible to perform injection molding work such as condition setting by utilizing such a method. The above-mentioned load cell 8 is used in such condition setting work when the injection pressure is detected and speed control / pressure control is switched.

FIG. 3 is a diagram for detecting a change in the pressure inside the injection molding die 1 in the injection speed / pressure switching control mode and setting and storing the change in the control device 10 as a set value which is a target value of the pressure control. It is a flow chart which shows an outline of "target value setting processing." This process is performed by the pressure monitoring CPU 17 and the servo CPU 20 during the operation of the injection molding machine.
It is repeatedly executed at predetermined intervals in synchronization with the processing of the speed loop in.

The pressure monitoring CPU 17 which has started the "target value setting process" first determines whether or not the function menu of the "reference registration mode" is selected (step a).
1), only when this function menu is selected
The processing after step a2 is continuously performed. Therefore, the substantial "target value setting process" is executed only when the function menu of "reference registration mode" is selected. The "target value setting process" is to sample the change of the pressure in the injection molding die 1 in the injection process at the time of molding a good product,
Since this is for setting in the non-volatile memory 24 as a target value for pressure control, the operator must select the function menu of "reference registration mode" after completing the injection molding work for condition setting. There is. The operator selects the "reference registration mode" by operating the function key 9 of the manual data input device 29 with a display during the continuous molding operation.

When the function menu of "reference registration mode" is selected, that is, when the determination result of step a1 is true, the pressure monitoring CPU 17 then determines whether the sampling execution flag F'is set. It is determined whether or not (step a2). At the stage immediately after selecting the function menu of "reference registration mode", the sampling execution flag F'is not set, so the pressure monitoring CP
U17 further determines whether or not the injection start detection flag F ″ is set (step a3). The injection start detection flag F ″ is not set at the stage immediately after selecting the function menu of “reference registration mode”. In this state, the CPU 17 for pressure monitoring is further connected to the RAM 1 of the CPU 18 for PMC.
4 and determines whether or not the injection execution flag F is set (step a4). Injection execution flag F
Is a PMC CPU1 for controlling the entire sequence operation
Since the flag is set when the injection process start command is output by 8, the injection execution flag F may or may not be set at this point. That is, if the injection process of a certain molding cycle has already started at the time when the operator selects the function menu of "reference registration mode", the injection execution flag F is set, and the operator selects "reference registration mode". If the process of the injection process is not performed at the time when the function menu is selected, the injection execution flag F is not set. The injection process mentioned here is an injection process in the injection speed / pressure switching control mode, that is, by setting the injection / holding pressure switching position based on the screw position, the injection speed priority control and the injection pressure priority control are performed. In the same injection process as the conventional one in which the switching is performed, or by detecting the output of the load cell 8 while performing the priority control of the injection speed, when the value reaches a predetermined value, the priority control of the injection speed is performed. Injecting pressure (holding pressure) is started with a predetermined pressure after it is cut off, and the same injection process as the conventional one (in short, it is necessary to extract sampling data when molding good products after completion of condition setting). Injection control which is performed only), and does not include feedback control of injection pressure performed according to the gist of the present invention.

When the injection execution flag F is already set, if the sampling data extraction is started at this point, the data from immediately after the start of injection until this point will not be extracted, so the pressure monitoring CPU 17 ,
At this point, the sampling data extraction is not started, the sampling process in this molding cycle is postponed, the processing of the processing cycle is ended, and the start of the injection process in the next molding cycle is awaited. . Further, if the injection execution flag F is not set, it means that the process of the injection process is not being performed at the time when the operator selects the function menu of the “reference registration mode”. CPU 17 for pressure monitoring cannot be processed.
Sets the injection start detection flag F ″ (step a
5) It waits for the start of the injection process in the next molding cycle. That is, if the setting of the injection execution flag F ″ is detected in the subsequent processing cycle after the setting of the injection start detection flag F ″ is completed in this way, the point at which the injection execution flag F changes from OFF to ON The rise of the injection process can be detected.

As a result, if the injection process has already been started when the operator selects the "reference registration mode" function menu, the determination process of steps a1 to a4 is completed until the injection process is completed. Only is repeatedly executed, and when this injection process is completed, step a
After the injection start detection flag F ″ is set in the process of No. 5, only the determination process of steps a1 to a3 and step a6 is repeatedly executed until the process of the next injection process is started. Further, if the process of the injection process has not been performed at the time when the operator selects the function menu of the “reference registration mode”, as described above, the process of step a5 causes the injection start detection flag at that time. F ″ is set, and thereafter, only the determination process of steps a1 to a3 and step a6 is repeatedly executed in the same manner as described above. The content of the process of step a6 is substantially the same as the process of step a4. It is the same.

When the next injection step is started while the pressure monitoring CPU 17 repeatedly executes the determination processing of steps a1 to a3 and step a6, P
The injection execution flag F is set by the MC CPU 18, and the pressure monitoring CPU 17 detects this in the determination processing of step a6. That is, it is the detection of the rise of the injection process described above. Therefore, the CPU 17 for pressure monitoring resets the injection start detection flag F ″, sets the sampling execution flag F ′, and initializes the address index i that determines the sampling data storage area to zero (step a).
7) Then, the sampling process of the current value MPR of the pressure inside the injection molding die 1 is started. Note that an example of the table provided in the RAM 12 for storing the sampling data is shown in FIG. 6 for reference.

The pressure monitoring CPU 17 which has started the sampling process first increments the value of the address index i by 1 (step a8), reads the pressure data from the pressure sensor 7, and corresponds the value to the value of the address index i. Then, the data is stored in the storage area MPi of the table in the RAM 12 (step a9). Next, the pressure monitoring CPU 17
Determines whether or not the injection execution flag F has been reset, that is, whether or not one injection process of a certain molding cycle has been completed (step a10), but if not completed, in this processing cycle The "target value setting process" is ended as it is. The reset operation of the injection execution flag F is performed by the PMC CPU 18 similarly to the operation at the time of setting, and the pressure monitor CPU 17
Is not directly related to the behavior of.

In the subsequent processing cycle, the above-mentioned step a
Since the sampling execution flag F'is already set by the process of 7, the steps a1 and a2
And the processing of steps a8 to a10 are repeatedly executed, and based on the value of the address index i that is sequentially incremented, the value of the current pressure value MPR inside the injection molding die 1 for each sampling cycle is RAM12
The data will be sequentially stored in the storage area MPi of the internal table.

Then, when the injection execution flag F is reset by the PMC CPU 18 and the completion of the injection and pressure holding control in the one injection step is detected by the determination processing in step a10, the pressure monitoring CPU 17 returns to the "reference. After canceling the selection of the function menu of "registration mode" and resetting the sampling execution flag F ', after shifting the final value of the address index i, that is, the total number of sampling data to the register n, the value of the address index i is initialized. Then, the value of the total number n of sampling data and all the stored contents of the table are transferred to and stored in the nonvolatile memory 24, and the data in the RAM 12 is erased (step a1).
1). Incidentally, the time required for this one injection step (including the holding pressure) is equal to the time obtained by multiplying the processing cycle of the "reference registration mode" (the processing cycle of the speed loop) by n.

As an example, each of the sampling data MP1 to MPn of the internal pressure of the injection molding die 1 obtained in the injection process at the time of molding a good product is directly controlled as the target value of the change of the internal pressure of the injection molding die 1 as an example. Although the device which is configured and stored in the device 10 has been described, the data such as the correction and the editing is further added to the data, and the data after the correction or the editing is newly stored in the nonvolatile memory 24 of the control device 10.
You may make it memorize | store in. As a method of working such as correction and editing, the table data transferred to the non-volatile memory 24 can be rewritten by a direct numeric input operation using a numeric keypad, or a diagram showing sampling data can be displayed manually with a display. There is a method of displaying the data on the data input device 29 and changing the shape of the diagram by an operation using a graphic cursor, digitizing this again, and automatically writing it as data in the corresponding position of the table.
In both cases, the data editing method itself belongs to the related art, and a detailed description thereof will be omitted.

FIG. 2 is a functional block diagram showing an outline of speed / pressure switching control executed in the injection pressure feedback control mode after the completion of condition setting. Vi is C
It is a movement command given from the NC CPU 25 to the servo CPU 20, that is, a distribution pulse for each predetermined cycle output from the CNC CPU 25 according to the injection speed for each injection stage set with the screw position as a reference. Until the pressure sensor 7 detects the resin pressure ε which is a preset comparison value for detecting the completion of resin filling or the arrival at a predetermined position, the switch S conceptually shown in FIG. The speed control based on the above-mentioned movement command is executed in exactly the same manner as the conventional one. In other words, C for CNC
The PU 25 outputs the movement command Vi to the servo CPU 20,
The servo CPU 20 performs a position loop process based on the movement command Vi and the position feedback signal from the pulse coder 6 of the injection servo motor 5 to obtain a speed command corresponding to the position deviation, and further, this speed command and the pulse coder 6 Based on the velocity feedback signal from the motor, a torque command (current command) corresponding to the speed deviation is obtained, and the current loop process is performed in the same manner as in the conventional case, and the injection servomotor 5 is operated via the servo amplifier 15. Is driven to perform feedback control of the injection speed.

When the pressure sensor 7 detects the preset resin pressure ε, the switch S is switched to the B side, and the CNC CPU 25 causes the inside of the injection molding die 1 set as described above. Pressure sampling data MP
i (however, i = 1 to n) is sequentially read in correspondence with the sampling cycle, the value of the in-mold pressure MPR at that point is subtracted from the value of the sampling data MPi which is the target value of the pressure control, and this pressure deviation is set to a predetermined value. The pressure command value Pvi for obtaining the in-mold pressure comparable to the target value MPi is obtained by multiplying the gain, and the injection pressure feedback control is performed by inputting the pressure command value Pvi into the speed loop process instead of the above speed command. Will be done. If an appropriate gain is selected, the above-mentioned switch function S is provided between the speed loop and the current loop, and the pressure command value Pvi is input to the processing of the current loop to control the injection pressure feed. It is also possible.

FIG. 4 shows an outline of processing for realizing the function shown in FIG. This processing is processing that is repeatedly executed by the CPU 25 for CNC in the injection pressure feedback control mode at predetermined intervals in synchronization with the processing of the speed loop in the CPU 20 for servo.

The CNC CPU 25 first determines whether or not the injection execution flag F is set (step b1). If the flag F is not set, it means that the process of the injection process is not performed at this point, and therefore the processes after step b2 are not executed, and the process of the cycle ends.

In the case of the injection process, the CNC CPU
25 increments the value of the address index i for retrieving the sampling data (same configuration as in FIG. 6) stored in the non-volatile memory 24 by 1 (step b
2) Prepare to read the sampling data corresponding to the processing cycle. Since the initial value of the address index i is set to zero by the initial setting, in the process executed immediately after the injection execution flag F is set, that is, immediately after the start of the injection process, the value of i in the process of step b2. Will be set to 1.

Next, the CNC CPU 25 determines whether or not the pressure control switching flag MF is set (step b3). This flag MF is a flag set by the CPU 25 when the pressure sensor 7 detects the arrival of the resin. Therefore, if this flag is not set, it is necessary to perform feedback control of the injection speed based on the set injection speed, and if the pressure control switching flag MF is set, the sampling data MPi of the mold internal pressure and the sampling data MPi This means that it is necessary to perform pressure feedback control based on the current value MPR of the mold internal pressure.

Therefore, if the pressure control switching flag MF is not set, the CNC CPU 25 reads the current value MPR of the mold internal pressure via the pressure monitoring CPU 17 (step b4), and the current mold internal pressure is read. Value MP
It is determined whether or not R is equal to or less than the set value ε, that is, whether or not the resin has reached the position where the pressure sensor 7 is provided (step b5).

If the current value MPR of the mold internal pressure is less than or equal to the set value ε and the resin has not reached the position where the pressure sensor 7 is disposed, the CNC CPU 25 sets the injection speed set to the screw position as a reference. A corresponding movement command Vi is obtained and output to the servo CPU 20, and feedback control of the injection speed similar to the conventional one is performed (step b6). This is the process when the switch S in FIG. 2 is on the A side.

Next, the CPU 25 for CNC determines whether or not the value of the address index i has reached the total number n of sampling data, that is, whether or not the processing of the injection step including the holding pressure may be terminated ( If it has not reached step b7), the process of this cycle is ended as it is.

Thereafter, as long as the current value MPR of the mold internal pressure, which is not more than ε, is continuously detected, the CPU 25 for CNC 25
Repeats the processing from step b1 to step b7 in the same manner as described above to cause the servo CPU 20 to perform the feedback control of the injection speed similar to the conventional one, while the resin reaches the position where the pressure sensor 7 is arranged. Then, when the pressure sensor 7 detects the pressure, the determination result of step b5 becomes false, and the CNC CPU 25 sets the pressure control switching flag MF (step b8), and the sampling data MPi of the mold internal pressure and the mold internal Current pressure value MP
The feedback control of pressure based on R and will be started.

Sampling data MPi of mold internal pressure
In the pressure feedback control based on the current value MPR of the mold internal pressure, the CNC CPU 25 reads the sampling data MPi of the mold internal pressure from the nonvolatile memory 24 based on the value of the address index i, and A deviation between the current value MPR of the pressure and the sampling data MPi of the mold internal pressure which is the target value at that time is obtained, and the deviation is multiplied by a predetermined gain to obtain a pressure command P instead of the speed command.
The process of obtaining vi is performed, and the value is determined by the servo CPU 20.
Will be input to the speed loop processing of (step b
10). This is the process when the switch S is on the B side in FIG.

As a result of the pressure control switching flag MF being set, steps b1 to b in the following processing cycle.
3. Step b9 (reading process of MPR in place of step b4) to step b10 and step b7 are repeatedly executed every predetermined period, and the current value MPR of the mold internal pressure and the target value of the mold at that time are obtained. Feedback control of the pressure is performed based on the sampling data MPi of the internal pressure.

Finally, in the discrimination processing of step b7, the value of the address index i is the total number n of sampling data.
When it is confirmed that the
The pressure control switching flag MF is reset to initialize the address index i to zero (step b11), and the PMC CPU
An injection completion command is output to 18 (step b12), and the processing of that cycle is ended.

The PMC CPU 18 receiving this resets the injection execution flag F, and as a result, the injection step of the new molding cycle is started and the injection execution flag F is set again until the injection speed is set to the above-mentioned speed and pressure. The feedback control goes into a practical dormant state. Then, when the injection step of the next molding cycle is started again, the same process as described above is repeatedly executed with the initialized value of the address index i as the initial value.

As described above, the injection speed feedback control based on the set injection speed is performed from immediately after the start of injection until the resin reaches the position where the pressure sensor 7 is disposed, while the resin is pressure sensor 7 The pressure sensor 7 directly detects the resin pressure in the injection molding die 1 to perform feedback control of the pressure inside the die from the time when the injection pressure holding step is completed until the injection pressure holding step is completed. Therefore, the switching from injection to holding pressure can be accurately detected, and the mold internal pressure can be surely controlled over the entire holding pressure process.

FIG. 7 is a conceptual diagram showing the relationship between the screw driving force and the mold internal pressure in the injection pressure feedback control mode. The change in the actual measured value of the mold internal pressure shown by the solid line in the figure results in , The target mold internal pressure MP
It roughly matches the time series data of i. In the process of the injection pressure feedback control mode described above, the injection pressure feedback control is not executed in the section until the current value MPR of the mold internal pressure reaches the set value ε, and the speed control before that is continued. However, as long as the feedback control of the speed based on the set injection speed is normally performed, P is the time when the speed control is switched to the pressure control.
There is no significant deviation in the pressure waveform inside the mold in the section. Further, since the mold internal pressure MPi, which is the target value, gradually increases in the section Q, the screw driving force (output of the servomotor 5) for realizing this also gradually increases. Further, after passing the section of Q, the mold internal pressure MPi which is the target value exceeds the peak and gradually decreases, but at the same time, the driving force of the screw 3 is transmitted to the inside of the injection molding mold 1 due to the gate seal and the like due to cooling. The driving force of the screw 3 required to eliminate the pressure deviation in the injection mold 1 does not decrease so much, and as a result, the driving force of the screw 3 is considerably large. The resin pressure inside the injection molding die 1 is maintained at the target value MPi which is a relatively low value.

In the conventional injection control method in which the holding pressure is feedback-controlled by the load cell 8 and the pressure sensor in the injection cylinder 2, the driving force of the screw 3 is determined by detecting the resin pressure in the injection cylinder 2. However, no consideration is given to the fact that the driving force of the screw 3 is not transmitted to the inside of the injection molding die 1 due to the gate seal or the like, and the substantial in-mold pressure is reduced. However, with the injection control method of the present embodiment, the resin pressure in the injection molding die 1 can be appropriately maintained at the set pressure MPi regardless of the conditions such as the gate seal.
In the conventional injection control method of performing the feedback control of the holding pressure by the load cell 8 and the pressure sensor in the injection cylinder 2, the sampling data itself, which is the target value, is the resin pressure in the injection cylinder 2, so at first glance,
It is likely that the in-mold pressure at the time of sampling will be reproduced simply by feeding back the resin pressure in the injection cylinder 2 and maintaining it at the set pressure. However, in reality, changes in the mold, cylinder temperature (resin temperature), etc. Since the sealing condition of the gate changes variously depending on the situation, even if the resin pressure in the injection cylinder 2 is held in the sampling data, it is impossible to reproduce the same in-mold pressure as at the time of sampling. On the other hand, in the injection control method of the present embodiment, the pressure change inside the injection molding die 1 at the time of molding a good product is sampled, and the pressure change inside the injection molding die 1 is directly detected to determine the holding pressure. Since feedback control is performed,
Reproduction of the holding pressure is rarely alienated due to the influence of disturbances such as gate seals.

In addition, since injection control is performed by applying feedback control of the injection speed based on the set injection speed from immediately after the start of injection until the resin reaches the position where the pressure sensor 7 is disposed, injection molding is performed. Even though the pressure sensor 7 is provided inside the mold 1, the injection control can be effectively performed immediately after the start of injection and at the resin filling stage.

As described above, by actually detecting the current value MPR of the internal pressure of the injection molding die 1, it is determined whether or not the resin has reached the position where the pressure sensor 7 is arranged, and the pressure control is switched. However, it is also possible to judge this by referring to the sampling data stored in the non-volatile memory 24.

FIG. 5 shows a process in which the arrival of the resin at the pressure sensor 7 is determined by referring to the sampling data. Note that steps c1 to c shown in FIG.
3, step c6 to step c8, step c10 to step c12 are performed in step b already described in FIG.
Since the processing is exactly the same as the processing of 1 to step b3, step b6 to step b8, and step b10 to step b12, description thereof will be omitted.

The example shown in FIG. 5 differs from the example described with reference to FIG. 4 in that, first, in the example of FIG. 4, the current value MPR of the internal pressure of the injection mold 1 is actually read and the value is ε or less. While it is determined whether or not the resin reaches the pressure sensor 7 by determining whether or not (FIG. 4: step b4 to step b5), in the example of FIG. The sampling data MPi + 1 of the internal pressure of the injection molding die 1 one cycle ahead is read from the sampling data of the internal pressure of the injection molding die 1 stored in 24, and it is determined whether or not the value is within the set value ε. The point is that it is predicted whether or not the resin reaches the pressure sensor 7 in the processing cycle of the next speed loop (FIG. 5: step c5).

Here, if the sampling data MPi + 1 is within the set value ε, naturally, the value of the sampling data MPi of the internal pressure of the injection mold 1 in the processing cycle, which is one cycle before that, is also within ε. is there. Therefore, it means that the resin has not reached the pressure sensor 7 at this point, and the processing for performing the feedback control of the injection speed based on the set injection speed is applied in the processing cycle (FIG. 5: step). c6).

Even if the sampling data MPi + 1 is not within the set value ε, as long as the pressure control switching flag MF is not set, the internal pressure of the injection molding die 1 in the processing cycle one cycle before is set. Since the value of the sampling data MPi is within the set value ε (for the reason described later), it is necessary to apply the process for performing the feedback control of the injection speed based on the set injection speed in the processing cycle. However, in this case, since it is clear that the resin reaches the pressure sensor 7 in the next processing cycle, the pressure control switching flag MF is set at this time (FIG. 5: step c8), and the same as above. Feedback control of the injection speed based on the set injection speed is performed (FIG. 5: step c6). That is, even at the time of sampling during molding of a good product, the pressure sensor 7 always detects a value within the set value ε until the resin first arrives, and after the resin once arrives, the pressure sensor 7 always exceeds the set value ε. Since the value is continuously detected, the sampling data MPi + 1 of the internal pressure one cycle ahead is always prefetched based on the sampling cycle during the pressure feedback control after the sampling is completed as shown in step c5 of FIG. , Ε or more, the flag MF in the first processing cycle in which the sampling data MPi + 1 is detected, that is, in the i-th processing cycle.
Is set, feedback control of the final speed based on the set injection speed is performed in the processing cycle, and the current value MPR of the mold internal pressure from the next processing cycle i + 1th and the target value at that time MPR are set. It suffices to start the pressure feedback control based on the sampling data MPi + 1 of the mold internal pressure. This is the reason why the branch destination after executing step b8 in FIG. 4 is different from the branch destination after executing step c8 in FIG.

Others are exactly the same as the example shown in FIG.

[0055]

According to the injection control method of the present invention, after confirming the filling of resin with the pressure sensor in the injection mold, the pressure inside the injection mold set in advance and the current detected by the pressure sensor are detected. Since the injection pressure feedback control is started based on the pressure, the conventional injection control method that switches from speed control to pressure control by specifying the screw position and detecting the load of the load cell attached to the base of the screw Unlike the above, the injection speed control can be switched to the pressure control by appropriately determining the resin filling into the cavity. In addition, the pressure sensor inside the injection molding die directly detects the resin pressure inside the injection molding die to perform feedback control of the injection pressure, so the load cell and the injection cylinder inside the screw are installed at the base of the screw. Unlike the conventional injection control method in which the resin reaction force is detected by the pressure sensor attached to the resin and the feedback control of the pressure is performed, the resin inside the injection mold is vulnerable to solidification of the resin or disturbance such as the gate seal. There is no difference between the pressure and the detected resin pressure, and the set pressure inside the injection mold can be accurately reproduced by the feedback control of the pressure based on the accurate detected pressure. In addition, since the injection speed is controlled by the injection speed until the injection mold is filled with resin, a pressure sensor is provided inside the injection mold to control the injection pressure throughout the injection process. Unlike the conventional injection control method in which feedback control is performed, the injection operation immediately after the start of injection does not become unstable, and accurate injection control can be performed over the entire injection process.

Further, the sampling data at the time of molding the non-defective product is used as the pressure inside the injection mold, which is the target value, and whether or not the resin has reached the pressure sensor is detected by the pressure sensor at each sampling cycle in the injection process. Since the value or the pressure inside the injection mold set in advance in the controller is read and it is judged whether or not the value is above a predetermined value, the pressure change in the same state as when molding a good product is accurately measured. It can be reproduced.

[Brief description of the drawings]

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

FIG. 2 is a functional block diagram showing an outline of pressure feedback control in the same embodiment.

FIG. 3 is a flowchart showing an outline of target value setting processing by a control device of the injection molding machine of the embodiment.

FIG. 4 is a flowchart showing an example of a speed loop process for performing pressure control by the control device of the injection molding machine of the same embodiment.

FIG. 5 is a flowchart showing another example of a speed loop process for carrying out pressure control.

FIG. 6 is a diagram conceptually showing an example of a table storing sampling data.

FIG. 7 is a conceptual diagram showing an example of the relationship between the screw driving force and the mold internal pressure in the injection pressure feedback control mode.

[Explanation of symbols]

F Injection execution flag F ′ Sampling execution flag F ″ Injection start detection flag MF Pressure control switching flag i Address index MPR Current value of internal pressure of injection mold MPi Sampling data of internal pressure of injection mold (target of internal pressure) Value) n Total number of sampling data Vi Position command 1 Injection mold 2 Cylinder 3 Screw 4 Power transmission mechanism 5 Servo motor for injection 6 Pulse coder 7 Pressure sensor 8 Load cell 10 Controller 16 A / D converter 17 CPU for pressure monitor 24 Non-volatile memory 25 CNC CPU 29 Manual data input device with display

Claims (4)

[Claims] 1. A pressure sensor for detecting the pressure inside the injection molding die is provided, a change in the pressure inside the injection molding die is set in a control device, and set until the resin reaches the pressure sensor. While controlling the injection speed based on the injection speed,
After the resin reaches the pressure sensor, feedback control of the injection pressure is performed based on the set pressure inside the injection molding die and the current pressure detected by the pressure sensor. Injection control method for injection molding machine. 2. The injection control method for an injection molding machine according to claim 1, wherein the set pressure inside the injection molding die is sampling data at the time of molding a good product. 3. The method according to claim 1, wherein the detection value of the pressure sensor is read at each sampling cycle in the injection process, and when the value exceeds a predetermined value, it is considered that the resin has reached the pressure sensor. An injection control method for the injection molding machine described. 4. The pressure inside the set injection molding die is read at each sampling cycle in the injection step, and when the value exceeds a predetermined value, it is considered that the resin has reached the pressure sensor. Item 3. An injection pressure control method for an injection molding machine according to Item 1 or 2.