JP2002052582A - Injection molding machine and method for injection molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an injection molding machine capable of avoiding an influence of an inertial force of a screw drive system by automatically decelerating a screw before switching from a speed control to a dwelling control. SOLUTION: A controller 30 of this injection molding machine 100 provides a decelerating step of decelerating an injection speed of the screw at a finishing time of an injecting step immediately before a dwelling step in the case of injection molding for molding a plastic product by driving the screw 13 by using a plasticizing motor 14 and an injection motor 20, and intermediating plasticizing, injecting and dwelling steps of a plastic material supplied from a hoper 12 onto the screw 13. Thus, at a starting time of the dwelling step, a peak pressure is not generated at a detected pressure of a screw reaction, and hence a 'wflash' for causing the peak pressure is not generated for the molding, and a product quality can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to injection molding, and more particularly to an injection molding method and an injection molding machine for driving a screw using an injection motor to form a molded article through a material injection and pressure-holding process. .

[0002]

2. Description of the Related Art FIGS. 6 and 7 are a time chart and a flow chart showing the operation of a conventional example of this type of injection molding machine. When the injection stroke starts at time t50, the control waits for a control cycle time (step S51), and generates a speed command (step S52). Speed command at time t5
From 0, it is changed to DV51, DV52, DV53, and it is determined whether or not the screw of the injection molding machine has reached a switching position to switch from the injection stroke to the pressure-holding stroke (step S53). If the switching position has not been reached, the speed command is continuously executed by repeatedly returning to steps S51 and S52. As a result, the detected pressure on the material such as the molten plastic gradually increases as shown by the dashed line (FIG. 6).

In step S53, at time t6
If it is determined that the switching position has been reached to 0, 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 S5).
5) It is determined whether the dwell time has expired (step S56). Until the dwell time expires, the pressure command is reduced from q52 to q51 at time t62. When the dwell time expires at time t63, the process proceeds to the next molding cycle. During this series of steps, at time t60
At time t61 immediately after switching to the pressure-holding stroke, the detected pressure (injection pressure) has a peak due to the inertial force of the screw drive system.

[0004]

In the above-described conventional injection molding machine, the detection pressure (injection pressure) is affected by the inertia force of the screw drive system immediately after switching from the speed control of the injection stroke to the holding pressure control. A peak occurs. This is because in an injection molding machine that uses a plasticizing motor or an injection motor to drive the screw, the inertial force of the injection screw drive system including the above-mentioned motor is considerably larger than that of a hydraulic injection molding machine. This is because when switching from speed control to pressure holding control, braking by pressure control is not in time, and a sudden peak is generated. In such an extreme case, it is conceivable that the screw collides with the tip of the heating cylinder. Even if no screw collision occurs,
When a peak occurs in the injection pressure in this way, a projection, a so-called "burr", is formed on the molded product, deteriorating the quality, and in some cases, causing additional correction work.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem. In an injection molding machine using a motor for driving a screw, when switching from screw speed control to pressure holding control, a screw drive system is provided. 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 a peak does not occur in an injection pressure due to an inertial force.

[0006]

In order to solve the above-mentioned problems, the present invention drives a screw (13) by using a motor (20) to form a product through a material injection and pressure-holding process. The injection molding machine is characterized in that deceleration control means (30) for reducing the injection speed of the screw (13) is provided immediately before the pressure-holding stroke in the injection step.

In the present invention, the deceleration control means (30) includes a deceleration predicted position calculation means for calculating a deceleration predicted position (Pa), and a deceleration predicted position (Pa) calculated by the deceleration predicted position calculation means. Comparing means for comparing a predetermined holding pressure switching set position (Ph), wherein deceleration is started when the predicted deceleration position (Pa) exceeds the holding pressure switching set position (Ph). Is what you do.

In the present invention, the deceleration predicted position calculating means may calculate the deceleration based on a detected current position (p) of the screw (13), a current speed (v) and a predicted deceleration time (t). It is characterized in that a predicted position (Pa) is calculated.

The deceleration predicted position calculating means includes a detected current position (p) of the screw (13) and a current speed (v).
The deceleration predicted position (Pa) is calculated based on the deceleration predicted time (t), the control delay time (d), and the dwell speed (Vh).

In the present invention, the deceleration predicted time (t) is obtained by dividing the current speed (v) by the deceleration (α), and the deceleration (α) is obtained.
Is obtained by dividing a predetermined maximum speed (Vm) by a value obtained by dividing a predetermined maximum deceleration time (Tm) by a predetermined control cycle (θ).

In the present invention, the deceleration control means shifts to the pressure holding step when the current detection position (p) of the screw (13) exceeds the pressure holding switching set position (Ph). It is characterized by the following.

According to such an injection molding machine, the speed of the screw is reduced immediately before the pressure-holding stroke. Therefore, immediately after shifting to the pressure-holding stroke, the screw is affected by the inertia of the screw driving mechanism. There is no peak in the injection pressure, and there is no "burr" in the molded product.

The present invention also relates to an injection molding method for driving a screw (13) using a motor (20) to form a product through a material injection and a pressure-holding process. A deceleration stroke for reducing the injection speed of the screw (13).

According to such an injection molding method, the screw speed is reduced immediately before the pressure-holding stroke, so that the screw is affected by the inertia of the screw driving mechanism immediately after the shift to the pressure-holding stroke. There is no peak in the back pressure, and no burrs occur in the molded product.

[0015]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Embodiment 1 FIG. FIG. 1 is a diagram for explaining a 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. 3 is a flowchart showing the operation of the injection molding machine of FIG. FIG. 1 shows a movable mold (not shown) and a fixed mold (not shown) in a screw-type injection molding machine 100.
Is completed, the nozzle is touched to the fixed mold, the injection of the molten material from the nozzle (not shown) in the previous cycle of injection molding is completed, and the state is about to shift to the next cycle Is shown.

In the injection molding machine 100 shown in FIG. 1, a material such as plastic stored in a hopper 12 is dropped onto a screw 13 in a heating cylinder 11. The screw 13 is rotatably supported in the heating cylinder 11, and one end of the screw 13 is supported by a bearing 17. The control unit 30 gives the rotation command DR to the servo motor amplifier 31 so that the plastic material or the like dropped on the screw 13 is measured in an appropriate amount and plasticized. The servo motor amplifier 31 rotates the plasticizing motor 14 by a predetermined number of rotations with reference 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 it. The plastic material or the like that has fallen on the screw 13 is melted by the heat of the heating cylinder 11, is measured by the rotating screw 13, and is sent in the direction of the nozzle (to the left in FIG. 1).

As described above, the molten plastic material or the like fed into the heating cylinder 11 in the nozzle direction causes
The screw 13 receives pressure in the direction of arrow DD opposite to the feeding direction. This pressure is detected by the load cell 18 and given to the control unit 30 via the load cell amplifier 32 as a detected pressure q. The control unit 30 determines 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.
, The torque command DT and the speed command DV are given to the servo motor amplifier 33 so that the detected pressure (back pressure) q becomes a predetermined set pressure.

The servo motor amplifier 33, which has received the torque command DT and the speed command DV, rotates the injection motor 20 based on the commands DT and DV while referring to the output value of the encoder 23, and the belt 21 and the ball screw 22
The moving plate 19 is retracted (to the right in FIG. 1) via Accordingly, the screw 13 feeds the molten plastic material or the like in the nozzle direction, and retreats in the heating cylinder 11 according to the retreat of the moving plate 19 by the ball screw 22 while receiving the set pressure.

That is, the RR portion in FIG. 1 does not move,
The FF portion (except for the heating cylinder 11) is retracted. When the control unit 30 confirms that the appropriate measurement of the molten plastic material or the like has been performed from the output value of the encoder 23, the control unit 30 stops the rotation of the plasticizing motor 14, detects the pressure of the load cell 18, and detects the speed of the encoder 23. v, the injection motor 20 while referring to the detection position p of the counter 34.
Is rotated to move the moving plate 19 in the nozzle direction (left direction in FIG. 1), and shift to execution of the injection stroke and the pressure-holding stroke.

The execution of the above-described injection stroke and pressure-holding stroke will be described with reference to FIGS. In this case, as shown in FIG.
It is assumed that N and the holding pressure condition HCN are given.
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 S31). Step S32). The speed command DV is gradually increased from the time t0, and it is determined whether or not the predicted deceleration position of the screw 13 has reached a predetermined pressure-holding switching position (step S33).

When the predicted deceleration position has not reached the pressure-holding switching position, the control unit 30 repeatedly returns to steps S31 and S32, for example, according to the injection condition ECN, to change the speed command DV to DV2 at times t1 to t2. ,
DV4 is set between times t3 and t4, and DV3 is set slightly lower than DV4 between times t5 and t6, and the detected pressure q detected by the load cell 18 gradually increases as shown by the dashed line (FIG. 2).

If it is determined in step S33 that the deceleration predicted position has reached the pressure-holding switching position, for example, the control unit 30 waits for a control cycle time to execute a deceleration stroke (step S34). During the period from time t6 to t7, a deceleration speed command is generated (step S35), and the speed command DV is reduced from DV3 to DV1, and from time t7 to t8.
Then, while trying to maintain the speed command DV at DV1, it is determined whether or not the screw 13 has reached the pressure-holding switching position (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 increasing. If it is determined in step S36 that the screw 13 has not reached the pressure-holding switching position, the control unit 30 repeatedly returns to steps S34 and S35 to set the speed command DV to DV1, for example, according to the injection condition ECN. I do.

If it is determined in step S36 that the screw 13 has reached the pressure-holding switching position at time t8, the control unit 30 waits for a control cycle time (step S37) to perform the pressure-holding process. Then, the speed command is switched to the pressure command, and the injection motor 20 is controlled so that the detected pressure q from the load cell 18 indicates the pressure q2. As described above, when the pressure is switched to the pressure-holding process, the detected pressure q from the load cell amplifier 32 rapidly decreases and reaches the detected pressure q2 at time t9. That is, in this case, at time t6
From t7 to t7, the screw 13 is rapidly decelerated, so that no peak is generated in the detected pressure q during the pressure-holding stroke without being affected by the inertial force of the screw drive system.

At time t10, the control unit 30 issues a pressure command so that the detected pressure q of the load cell 18 becomes q1,
After maintaining the prescribed time, the pressure-holding process is completed at time t11, and the process shifts to the injection molding process of the next cycle. In the deceleration stroke from time t6 to time t8, the control unit 30
Can be set very simply because the speed command is changed linearly so as to be approximately proportional to the passage of time, but it can also be changed according to another appropriate curve. or,
In FIG. 3, the control cycle time wait (S31, S34, S3
It goes without saying that the processing order of 7) and the control command generation (S32, S35, S38) may be reversed.

In the control process by the control unit 30, the control unit 3 shifts from the injection process to the pressure-holding process.
0 indicates that a predicted deceleration position before the switching position at which the injection stroke should be switched to the pressure-holding stroke is detected, and the speed of the screw 13 is rapidly reduced from the detection of the predicted deceleration position. Therefore, as described above, screw 1
When 3 reaches the switching position, the speed of the screw 13 is sufficiently low.
Even if the speed command is switched to the pressure command, an abnormal peak is not generated in the detected pressure q due to the influence of the inertia force of the screw drive system as in the related art. No defects such as "" occur. It is preferable that the control unit 30 be configured by 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 the control content is incorporated as logic.

During the injection stroke in the above 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 shifts to the deceleration stroke. However, an example of the calculation regarding the calculation algorithm of the deceleration predicted position Pa will be described here. 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 v, current position p,

Acceleration at deceleration; α = Vm / (Tm / θ) Predicted deceleration time; t = v / α Predicted deceleration position; Pa = p + k (t × v / 2)

Can be obtained by In the deceleration stroke, a deceleration command can be generated by subtracting the speed command by the deceleration α to the dwell speed setting Vh for each control cycle. During the deceleration stroke, the current position is compared with the pressure holding switching setting position Ph, and when the current position exceeds the pressure holding switching position Ph, the process shifts to the pressure holding stroke. As described above, the embodiment of the present invention has been described by taking a plastic molding machine as an example, but it goes without saying that the present invention can be applied to a metal injection molding machine.

As described above, according to the first embodiment, a peak pressure is not generated in the detection pressure of the screw reaction force at the start of the pressure-holding stroke, so that the molded product is caused by the peak pressure. No burrs are generated, and the product quality can be improved.

Embodiment 2 In Embodiment 1,
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 pressure-holding speed Vh, and passes the pressure-holding switching position Ph when the deceleration is completed. However, the pressure-holding switching is performed before the pressure is sufficiently reduced to the pressure-holding speed Vh. It may pass through the position Ph. This is because the actual motor movement does not respond immediately after outputting the speed command, but has some control delay time.After outputting the speed command, the actual screw speed decreases. By the time a delay occurs. If this control delay is not taken into account in the prediction calculation, a delay will occur if deceleration is started from the deceleration predicted position, and therefore, even when the set value of the final injection speed or the set value of the holding pressure speed is changed, There is a possibility that a problem that the condition changes may occur. For this reason, in the case where the holding pressure is switched before sufficiently decelerating, the inertia force of the screw drive system causes the braking from the speed control to the holding pressure control. A sudden peak may occur. In such an extreme case, it is conceivable that the screw collides with the tip of the heating cylinder.

Therefore, in the second embodiment, the screw 13
Current position p, current speed v, and estimated deceleration time t
, The control delay time d, and the pressure-holding speed Vh to calculate the predicted deceleration position Pa. By making the calculation more rigorous and performing a prediction closer to the actual machine movement, it becomes possible to optimally automatically decelerate immediately before the holding pressure switching position and switch the holding pressure, thereby reducing the influence of inertia. In order to obtain a safer and more stable molded product. It should be noted that time charts for calculating the predicted deceleration position in the first and second embodiments are shown in comparison with FIGS.

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 shifts to the deceleration process. I do. The calculation algorithm example of the deceleration predicted position Pa will be described. The maximum deceleration time Tm, the maximum speed Vm (known by design value), the control cycle θ (known by design value), the position conversion coefficient k (known by design value), the current speed v,
When the current position p, the control delay time d, and the holding pressure setting speed Vh,

Acceleration at deceleration; α = Vm / (Tm / θ) Predicted deceleration time; t = (v−Vh) / α Predicted deceleration position; Pa = p + k × [(V + Vh) × t / 2 +
v × d] Here, Tm, d, and Vh use the values set by the setting means, p uses the detection position, and v uses the detection speed or the speed command value.

In the deceleration step, as in the first embodiment, a deceleration command can be generated by decelerating the speed command to the dwell speed Vh by the deceleration α at each control cycle. During the deceleration process, the current position is compared with the pressure holding switching setting position Ph, and when the current position exceeds the pressure holding switching position Ph, the process proceeds to the pressure holding process. The control delay time d may be calculated from the relationship between the command speed and the detected speed.

[0035]

As described in detail above, the injection molding method and the injection molding machine of the present invention use a motor to drive a screw to form a product through a material injection and pressure-holding process. In such a case, by providing a deceleration stroke for reducing the injection speed of the screw immediately before the pressure-holding stroke in the injection step, a peak pressure is not generated in the detected pressure of the screw reaction force at the start of the pressure-holding stroke, As a result, it is possible to improve the product quality without generating "burrs" in the molded product due to the peak pressure.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a configuration of a screw-type injection molding machine according to an embodiment of the present invention.

FIG. 2 is a time chart showing an operation of the injection molding machine of FIG. 1 after an injection stroke.

FIG. 3 is a flowchart showing an operation of the injection molding machine of FIG. 1 after an injection stroke.

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 according to 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 of the conventional injection molding machine after an injection stroke.

[Explanation of symbols]

11 heating cylinder, 12 hopper, 13 screw,
14 Plasticizing motor, 15, 23 Encoder, 1
6,21 belt, 17 bearing, 18 load cell, 1
9 moving plate, 20 injection motor, 22 ball screw,
30 control unit, 31, 33 servo motor amplifier, 32
Load cell amplifier, 34 counter, 100 injection molding machine.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4F206 AP062 AP072 AP092 AP10 AR082 AR11 JA07 JD03 JL02 JM04 JM13 JN13 JP13 JP18 JQ88

Claims (7)

[Claims] 1. A screw (1) using a motor (20).
3) In the injection molding machine for molding the product through the material injection and the pressure-holding process by driving 3), the deceleration control means (30) for reducing the injection speed of the screw (13) immediately before the pressure-holding process in the injection step. An injection molding machine characterized by being provided. 2. The deceleration control means (30) calculates a deceleration predicted position (Pa), and a deceleration predicted position (P) calculated by the deceleration predicted position calculation means.
a) and a comparison means for comparing a predetermined pressure-holding switching set position (Ph), and when the predicted deceleration position (Pa) exceeds the pressure-holding switching set position (Ph), deceleration is started. The injection molding machine according to claim 1, wherein: 3. The predicted deceleration position calculating means includes a detected current position (p) of the screw (13) and a current speed (v).
The injection molding machine according to claim 2, wherein the deceleration predicted position (Pa) is calculated based on the deceleration predicted time (t). 4. The deceleration predicted position calculating means includes a detected current position (p) of the screw (13) and a current speed (v).
The injection molding machine according to claim 2, wherein a predicted deceleration position (Pa) is calculated based on the predicted deceleration time (t), the control delay time (d), and the dwell speed (Vh). . 5. The deceleration predicted time (t) is obtained by dividing a current speed (v) by a deceleration (α), and the deceleration (α) is a predetermined maximum deceleration time (Tm). The injection molding machine according to any one of claims 2 to 4, wherein the injection molding machine is obtained by dividing a predetermined maximum speed (Vm) by a value obtained by dividing a predetermined control cycle (θ). 6. The screw (1)
The detection current position (p) of 3) is set at the holding pressure switching set position (P
The injection molding machine according to any one of claims 1 to 5, wherein the process shifts to the pressure holding step when h) is exceeded. 7. A screw (1) using a motor (20).
(3) In the injection molding method for molding a product through the material injection and the pressure-holding process by driving the material, a deceleration process for reducing the injection speed of the screw (13) is provided immediately before the pressure-holding process in the injection process. Characteristic injection molding method.