JP4077174B2 - Injection molding machine and injection molding method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to injection molding, and more particularly, to an injection molding method and an injection molding machine in which a screw is driven using an injection motor and a molded product is molded through material injection and pressure holding processes.
[0002]
[Prior art]
6 and 7 are a time chart and a flowchart showing the operation of a conventional example of this type of injection molding machine. When the injection stroke is started at time t50, the control cycle time is waited (step S51), and a speed command is generated (step S52). The speed command is changed from time t50 to DV51, DV52, DV53, and it is determined whether or not the screw of the injection molding machine has reached the switching position at which the injection stroke should be switched to the pressure holding stroke (step S53). If the switching position has not been reached, the speed command continues to be executed by repeatedly returning to steps S51 and S52. As a result, the detected pressure with respect to a material such as molten plastic gradually increases as indicated by a one-dot chain line (FIG. 6).
[0003]
In step S53 described above, when it is determined that the switching position has been reached at time t60, the control cycle time is waited (step S54), and the speed command is switched to the pressure command to perform the pressure holding stroke (step S55). It is determined whether the pressure holding time has expired (step S56). Until the pressure holding time expires, the pressure command is lowered from q52 to q51 at time t62. When the pressure holding time expires at time t63, the process proceeds to the next molding cycle. In this series of strokes, at time t60, at time t61 immediately after switching to the pressure holding stroke, a peak occurs in the detected pressure (injection pressure) due to the inertial force of the screw drive system.
[0004]
[Problems to be solved by the invention]
In the conventional injection molding machine described above, a peak occurs in the detected pressure (injection pressure) due to the influence of the inertia force of the screw drive system immediately after switching from the speed control of the injection stroke to the holding pressure control. This is because in an injection molding machine using a plasticizing motor or an injection motor for driving a screw, the inertial force of the injection screw drive system including the motor described above is considerably larger than that of a hydraulic injection molding machine. This is because when switching from the speed control to the holding pressure control, the braking by the pressure control is not in time, and a sudden peak is generated. In such an extreme case, it may be considered that the screw crashes into the tip of the heating cylinder. Even if a screw crash does not occur, if a peak in the injection pressure occurs in this way, protrusions, so-called “burrs”, occur in the molded product, reducing the quality and, depending on the case, additional correction work may be required. There are problems that can occur.
[0005]
The present invention has been made to solve the above problems, and in an injection molding machine using a motor for driving a screw, the inertial force of the screw driving system is changed when switching from screw speed control to holding pressure control. An object of the present invention is to provide an injection molding apparatus and an injection molding method capable of automatically decelerating a screw and switching to holding pressure control so that no peak occurs in the injection pressure due to the influence.
[0006]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention is an injection molding machine that drives a screw (13) using a motor (20) and molds a product through a material injection and pressure holding process. A deceleration control means (30) for reducing the injection speed of the screw (13) is provided immediately before the pressure stroke.
[0007]
In the present invention, the deceleration control means (30) includes a predicted deceleration position calculation means for calculating a predicted deceleration position (Pa), a predicted deceleration position (Pa) calculated by the predicted deceleration position calculation means, and a predetermined hold. Comparing means for comparing the pressure switching setting position (Ph), and when the predicted deceleration position (Pa) exceeds the holding pressure switching setting position (Ph), deceleration is started. is there.
[0008]
Further, in the present invention, the predicted deceleration position calculating means calculates the predicted deceleration position (p) based on the current detection position (p) of the screw (13), the current speed (v), and the predicted deceleration time (t). Pa) is calculated.
[0009]
The predicted deceleration position calculation means includes a current detection position (p) of the screw (13), a current speed (v), a predicted deceleration time (t), a control delay time (d), and a pressure holding speed (Vh). ) To calculate a predicted deceleration position (Pa).
[0010]
In the present invention, the predicted deceleration time (t) is obtained by dividing the current speed (v) by the deceleration acceleration (α), and the deceleration acceleration (α) is a predetermined maximum deceleration time (Tm). ) Divided by a predetermined control period (θ) and divided by a predetermined maximum speed (Vm).
[0011]
In the present invention, the deceleration control means shifts to the pressure holding step when the detected current position (p) of the screw (13) exceeds the pressure holding switching setting position (Ph). It is what.
[0012]
According to such an injection molding machine, the screw speed is reduced immediately before the pressure-holding stroke, so that the injection pressure is affected by the inertial force of the screw drive mechanism immediately after the pressure-holding stroke. There is no peak, and there is no “burr” in the molded product.
[0013]
The present invention also relates to an injection molding method in which a screw (13) is driven using a motor (20) and a product is molded through material injection and a pressure holding process. 13) is provided with a deceleration stroke that decelerates the injection speed.
[0014]
According to such an injection molding method, the screw speed is decelerated immediately before the pressure-holding stroke, so that the back pressure is affected by the inertial force of the screw drive mechanism immediately after the pressure-holding stroke is started. There is no peak, and there is no “burr” in the molded product.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings.
Embodiment 1 FIG.
1 is a diagram for explaining the configuration of a screw-type injection molding machine according to Embodiment 1 of the present invention, FIG. 2 is a time chart showing the operation of the injection molding machine of FIG. 1, and FIG. It is a flowchart which shows operation | movement of this injection molding machine. FIG. 1 shows a screw-type injection molding machine 100 in which a movable mold (not shown) and a fixed mold (not shown) have been clamped and a nozzle touch to the fixed mold is performed. This shows a state in which the injection of the molten material from the nozzle (not shown) in the previous cycle is completed and the next cycle is about to be started.
[0016]
In the injection molding machine 100 of FIG. 1, a material such as plastic stored in the hopper 12 is dropped onto the screw 13 in the heating cylinder 11. The screw 13 is rotatably supported in the heating cylinder 11 and one end thereof is supported by a bearing 17. The control unit 30 gives a rotation command DR to the servo motor amplifier 31 so that an appropriate amount of plastic material or the like dropped on the screw 13 is measured and plasticized. The servo motor amplifier 31 rotates the plasticizing motor 14 by a predetermined number of rotations while referring to the output value of the encoder 15 according to the rotation command DR, and rotates the screw 13 in the heating cylinder 11 via the belt 16. Let The plastic material or the like dropped on the screw 13 is melted by the heat of the heating cylinder 11, measured by the rotating screw 13, and fed in the direction of the nozzle (left direction in FIG. 1).
[0017]
Thus, the screw 13 receives pressure in the direction of the arrow DD opposite to the feeding direction by the molten plastic material or the like fed in the heating cylinder 11 in the nozzle direction. This pressure is detected by the load cell 18 and supplied to the control unit 30 through the load cell amplifier 32 as a detected pressure q. The control unit 30 receives the detection speed v from the encoder 23 of the injection motor 20 and the detection position p from the counter 34 that receives the data of the encoder 23, and the detection pressure (back pressure) q is set to a predetermined set pressure. Thus, the torque command DT and the speed command DV are given to the servo motor amplifier 33.
[0018]
Upon receiving the torque command DT and the speed command DV, the servo motor amplifier 33 rotates the injection motor 20 based on the commands DT and DV while referring to the output value of the encoder 23, via the belt 21 and the ball screw 22. The moving plate 19 is moved backward (rightward in FIG. 1). Accordingly, the screw 13 moves back in the heating cylinder 11 as the moving plate 19 is retracted by the ball screw 22 while feeding a molten plastic material or the like in the nozzle direction and receiving a set pressure.
[0019]
That is, the RR portion in FIG. 1 does not move, and the FF portion (excluding the heating cylinder 11) moves backward. When it is confirmed from the output value of the encoder 23 that the molten plastic material or the like has been appropriately measured, the control unit 30 stops the rotation of the plasticizing motor 14 and detects the detected pressure of the load cell 18 and the detected speed of the encoder 23. v. Referring to the detection position p of the counter 34, the injection motor 20 is rotated, and the moving plate 19 is moved in the nozzle direction (left direction in FIG. 1) to shift to the execution of the injection stroke and the pressure holding stroke.
[0020]
Execution of the above-described injection stroke and pressure holding stroke will be described with reference to FIGS. 2 and 3. In this case, it is assumed that the injection condition ECN and the pressure holding condition HCN are given to the control unit 30 in advance as shown in FIG. When the injection stroke is started at time t0 shown in FIG. 2, the control unit 30 waits for a control cycle time (step S31) and generates a speed command DV and a torque command DT (torque limit value) ( Step S32). The speed command DV is gradually increased from time t0, and it is determined whether or not the predicted deceleration position of the screw 13 has reached a predetermined holding pressure switching position (step S33).
[0021]
When the predicted deceleration position has not reached the holding pressure switching position, the control unit 30 repeatedly returns to steps S31 and S32, for example, according to the injection condition ECN, to send the speed command DV to DV2 at times t1 to t2, and to time t3. It is set to DV4 at .about.t4 and set to DV3 slightly lower than DV4 at times t5 to t6, and the detected pressure q detected by the load cell 18 gradually increases as shown by a one-dot chain line (FIG. 2).
[0022]
In the above-described determination in step S33, when the predicted deceleration position reaches the holding pressure switching position, for example, the control unit 30 waits for the control cycle time to execute the deceleration stroke (step S34), and time t6 to t6. A deceleration speed command is generated during the period t7 (step S35), the speed command DV is decreased from DV3 to DV1, and the time command DV is maintained at DV1 from time t7 to t8, and the screw 13 is kept at the holding pressure switching position. Is determined (step S36). Therefore, the detected pressure q received by the control unit 30 from the load cell 18 via the load cell amplifier 32 immediately reaches the maximum value q3 and stops rising. If it is determined in step S36 that the screw 13 has not reached the holding pressure switching position, the control unit 30 repeatedly returns to steps S34 and S35 to set, for example, the speed command DV to DV1 in accordance with the injection condition ECN. To do.
[0023]
In step S36, when it is determined that the screw 13 has reached the holding pressure switching position at time t8, the control unit 30 waits for a control cycle time (step S37) and performs a speed command to perform the holding pressure process. The injection motor 20 is controlled so that the detected pressure q from the load cell 18 indicates the pressure q2. In this way, when the pressure holding process is switched, the detected pressure q from the load cell amplifier 32 rapidly decreases and becomes the detected pressure q2 at time t9. That is, in this case, since the screw 13 is rapidly decelerated from time t6 to t7, the peak of the detected pressure q is generated in the pressure holding stroke without being affected by the inertial force of the screw drive system. There is no.
[0024]
At time t10, the control unit 30 issues a pressure command so that the detected pressure q of the load cell 18 becomes q1, and after maintaining the specified time, completes the pressure holding stroke at time t11 and performs the next cycle injection. Move to the molding process. In the deceleration stroke at the above-described times t6 to t8, the control unit 30 changes the speed command linearly so as to be substantially proportional to the passage of time, so it can be set very simply, but according to other appropriate curves It is also possible to change.
In FIG. 3, it goes without saying that the processing order of control cycle time waiting (S31, S34, S37) and control command generation (S32, S35, S38) may be reversed.
[0025]
In the control stroke by the control unit 30 described above, in order to shift from the injection stroke to the pressure holding stroke, the control portion 30 detects the predicted deceleration position before the switching position to be switched from the injection stroke to the pressure holding stroke, The speed of the screw 13 is rapidly decelerated from when the predicted deceleration position is detected. Therefore, as already described, when the screw 13 reaches the switching position, the speed of the screw 13 is sufficiently low, so even if the speed command is switched to the pressure command at the switching position, Thus, an abnormal peak does not occur in the detected pressure q due to the influence of the inertial force of the screw drive system, and as a result, defects such as so-called “flash” of the molded product associated with the peak do not occur. The control unit 30 is preferably composed of a CPU that executes control according to a control program stored in the storage unit, or a semiconductor integrated circuit such as an LSI in which control contents are incorporated as logic.
[0026]
During the injection stroke in the above-described control, the predicted deceleration position Pa is compared with the holding pressure switching setting position Ph, and when the predicted deceleration position Pa exceeds the holding pressure switching setting position Ph, the process proceeds to the deceleration stroke. Here, a calculation example regarding the calculation algorithm of the predicted deceleration position Pa will be described. When the maximum deceleration time Tm, maximum speed Vm (known by design value), control cycle θ (known by design value), position conversion factor k (known by design value), current speed v, current position p,
[0027]
Deceleration acceleration: α = Vm / (Tm / θ)
Deceleration expected time; t = v / α
Deceleration predicted position; Pa = p + k (t × v / 2)
[0028]
Can be obtained. In the deceleration stroke, the speed command can be generated by subtracting the speed command by the deceleration acceleration α to the pressure holding speed setting Vh every control cycle. During the deceleration stroke, the current position is compared with the holding pressure switching setting position Ph, and when the current position exceeds the holding pressure switching position Ph, the process proceeds to the holding pressure stroke. As mentioned above, although embodiment of this invention was described taking the example to the plastic molding machine, it cannot be overemphasized that it is applicable to a metal injection molding machine.
[0029]
As described above, according to the first embodiment, the peak pressure is not generated in the detected pressure of the screw reaction force at the start of the pressure-holding stroke, and as a result, the “flash” caused by the peak pressure is applied to the molded product. It does not occur and can improve product quality.
[0030]
Embodiment 2.
In the first embodiment, the predicted deceleration position Pa is calculated based on the detected current position p of the screw 13, the current speed v, and the predicted deceleration time t. In the first embodiment, the pressure is reduced to the holding pressure speed Vh, and when it has been decelerated, the holding pressure switching position Ph is passed. However, before the pressure is sufficiently reduced to the holding pressure speed Vh, the holding pressure is switched. The position Ph may be passed. This is because the actual motor movement does not respond immediately after outputting the speed command, but there is a slight control delay time, and after the speed command is output, the actual screw speed is reduced. Is based on the occurrence of a delay. If this control delay is not taken into account in the prediction calculation, there will be a delay if deceleration is started from the predicted deceleration position. Therefore, even if the final injection speed setting value or the holding pressure setting value is changed, deceleration will occur. There is also a risk that the condition will change. For this reason, in the case where the holding pressure is switched before sufficiently decelerating, due to the influence of the inertia force of the screw drive system, braking by pressure control is not in time when switching from speed control to holding pressure control, A sudden peak may occur. In such an extreme case, it may be considered that the screw crashes into the tip of the heating cylinder.
[0031]
Therefore, in the second embodiment, the predicted deceleration position Pa is calculated based on the current detection position p of the screw 13, the current speed v, the predicted deceleration time t, the control delay time d, and the pressure holding speed Vh. By predicting even the control delay time in the calculation prediction of the predicted deceleration position calculation, the predicted deceleration position calculation can be made more strict and the prediction closer to the actual machine motion can be made. Optimal automatic deceleration immediately before the pressure switching position makes it possible to switch the holding pressure, thereby suppressing the influence of inertia and obtaining a safer and more stable molded product. The time chart for calculating the predicted deceleration position in the first and second embodiments is shown in comparison with FIGS.
[0032]
In the second embodiment, during the injection process, the predicted deceleration position Pa is compared with the holding pressure switching setting position Ph, and when the predicted deceleration position Pa exceeds the holding pressure switching setting position Ph, the process proceeds to the deceleration process.
A calculation algorithm example of the predicted deceleration position Pa will be described. Maximum deceleration time Tm, maximum speed Vm (known by design value), control cycle θ (known by design value), position conversion coefficient k (known by design value), current speed When v, current position p, control delay time d, and pressure holding set speed Vh are set,
[0033]
Deceleration acceleration: α = Vm / (Tm / θ)
Deceleration prediction time; t = (v−Vh) / α
Deceleration predicted position; Pa = p + k × [(V + Vh) × t / 2 + v × d]
Here, Tm, d, and Vh use values set by the setting means, p uses a detection position, and v uses a detection speed or a speed command value.
[0034]
In the deceleration process, as in the first embodiment, a deceleration command can be generated by decelerating the speed command by the deceleration acceleration α to the pressure holding speed Vh for each control cycle. During the deceleration process, the current position is compared with the holding pressure switching setting position Ph, and when the current position exceeds the holding pressure switching position Ph, the process proceeds to the holding pressure process. Note that the control delay time d may be calculated from the relationship between the command speed and the detected speed.
[0035]
【The invention's effect】
As described in detail above, the injection molding method and injection molding machine according to the present invention is an injection process in the case of injection molding in which a screw is driven using a motor and a product is molded through material injection and pressure holding processes. By providing a deceleration stroke that decelerates the screw injection speed immediately before the pressure holding stroke, no peak pressure is generated in the detected pressure of the screw reaction force at the start of the pressure holding stroke, and as a result There is no occurrence of “burrs” caused by the peak pressure, and the product quality can be improved.
[Brief description of the drawings]
FIG. 1 is a view for explaining the configuration of a screw-type injection molding machine according to an embodiment of the present invention.
2 is a time chart showing an operation after an injection stroke of the injection molding machine of FIG. 1; FIG.
FIG. 3 is a flowchart showing an operation after an injection stroke of the injection molding machine of FIG. 1;
FIG. 4 is a time chart for calculating a predicted deceleration position in the first embodiment.
FIG. 5 is a time chart for calculating a predicted deceleration position in the second embodiment.
FIG. 6 is a time chart showing an operation after an injection stroke of a conventional injection molding machine.
FIG. 7 is a flowchart showing an operation after an injection stroke of a conventional injection molding machine.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 Heating cylinder, 12 Hopper, 13 Screw, 14 Plasticizing motor, 15, 23 Encoder, 16, 21 Belt, 17 Bearing, 18 Load cell, 19 Moving plate, 20 Injection motor, 22 Ball screw, 30 Control part, 31, 33 servo motor amplifier, 32 load cell amplifier, 34 counter, 100 injection molding machine.

Claims (5)

In an injection molding machine that drives a screw (13) using a motor (20) and molds a product through a material injection and pressure holding process,
A deceleration control means (30) for reducing the injection speed of the screw (13) is provided immediately before the pressure holding process in the injection process,
The deceleration control means (30) includes a predicted deceleration position calculation means for calculating a predicted deceleration position (Pa), a predicted deceleration position (Pa) calculated by the predicted deceleration position calculation means, and a predetermined holding pressure switching setting value (Ph). And a comparison means for comparing)
When the predicted deceleration position (Pa) exceeds the holding pressure switching setting position (Ph), deceleration is started.
The deceleration predicted position calculating means calculates the predicted deceleration position (Pa) based on the detected current position (p), current speed (v), and predicted deceleration time (t) of the screw (13). Machine.   The predicted deceleration position calculation means includes a current detection position (p) of the screw (13), a current speed (v), a predicted deceleration time (t), a control delay time (d), and a pressure holding speed (Vh). ) To calculate a predicted deceleration position (Pa). 2. The injection molding machine according to claim 1, wherein the predicted deceleration position (Pa) is calculated.   The predicted deceleration time (t) is obtained by dividing the current speed (v) by the acceleration during deceleration (α), and the acceleration during deceleration (α) is calculated using a predetermined maximum deceleration time (Tm) for a predetermined control cycle. The injection molding machine according to claim 2, wherein the injection molding machine is obtained by dividing a predetermined maximum speed (Vm) by a value divided by (θ).   The said deceleration control means transfers to the said pressure-holding process, when the detection present position (p) of the said screw (13) exceeds the said pressure-holding switch setting position (Ph). The injection molding machine according to claim 3. In an injection molding method of an injection molding machine that drives a screw (13) using a motor (20) and molds a product through material injection and pressure holding steps,
When the injection speed of the screw (13) is decelerated immediately before the pressure holding process in the injection process, a predicted deceleration position (Pa) is calculated, and the calculated predicted deceleration position (Pa) and a predetermined holding pressure switching setting value ( Ph) are compared, and when the predicted deceleration position (Pa) exceeds the holding pressure switching setting position (Ph), deceleration is started.
The predicted deceleration position calculation is an injection molding machine that calculates the predicted deceleration position (Pa) based on the detected current position (p), current speed (v), and predicted deceleration time (t) of the screw (13). Injection molding method.

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