JP2005313409A - Injection molding machine and hold pressure changeover control method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the hold pressure changeover control device of an electromotive injection molding machine capable of performing hold pressure changeover by optimumly performing automatic deceleration on this side of a hold pressure changeover position by always operating and forming a deceleration control order and capable of obtaining a stable molded product. <P>SOLUTION: A control device which sets the deceleration and acceleration of a screw, a hold pressure setting speed and a control delay time to detect the present position of the screw during an injection process and operates the deceleration control order on the basis of the detected present position and the set control delay time and the hold pressure setting speed and the deceleration so that the dwelling setting speed is obtained immediately before the hold pressure changeover position is provided. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an injection molding machine that drives a screw using an injection motor and obtains a molded product through material injection and a pressure holding process, and a pressure holding switching control method for the injection molding machine.

  In the injection holding pressure control of the conventional electric injection molding machine, the motor speed control is performed to keep the moving speed of the screw constant during the injection process, and the process proceeds to the pressure holding process when the holding pressure switching setting position is passed. In the pressure-holding step, force control is performed by motor torque control that controls the injection pressure constant until the injection pressure-hold timer expires or pressure control that constitutes a pressure feedback system.

  Further, there is known a control that shifts to a deceleration process after decelerating to a target speed and then shifts to a pressure holding process by detecting passage of a predicted calculated switching position or a set position before the pressure holding switching position. (For example, refer to Patent Document 1).

4 is a configuration diagram of a screw type injection molding machine, FIG. 5 is a time chart showing the operation of the injection molding machine, and FIG. 6 is a flowchart showing the operation of the injection molding machine.
In the injection molding machine 100, 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 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 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. 4).

  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.

  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. 4). 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.

  That is, the RR portion in FIG. 4 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. 4) to shift to the execution of the injection stroke and the pressure holding stroke.

  Execution of the above-described injection stroke and pressure holding stroke will be described with reference to FIGS. 5 and 6. In this case, it is assumed that the control unit 30 is given the injection condition ECN and the pressure holding condition HCN in advance as shown in FIG. When the injection stroke is started at time t0 shown in FIG. 5, the control unit 30 waits for the control cycle time (step S61) and generates a speed command DV and a torque command DT (torque control value) ( Step S62). 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 S63).

  When the predicted deceleration position has not reached the holding pressure switching position, the control unit 30 repeatedly returns to steps S61 and S62, 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 that is slightly lower than DV4 at times t5 to t6, and the detected pressure q detected by the load cell 18 gradually rises as shown by a one-dot chain line (FIG. 5).

  In the determination of step S63 described above, 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 S64), and from time t6 to time t6. A deceleration speed command is generated during the period t7 (step S65), 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 S66). 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 S66 that the screw 13 has not reached the holding pressure switching position, the control unit 30 repeatedly returns to steps S64 and S65 to set, for example, the speed command DV to DV1 in accordance with the injection condition ECN. To do.

  If it is determined in step S66 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 S67) 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.

  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 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.

  During the injection stroke in the above-described control, the deceleration predicted position is compared with the holding pressure switching position, and when the predicted deceleration position exceeds the holding pressure switching position, the process proceeds to the deceleration stroke. In the deceleration process, a deceleration command can be generated by subtracting the speed command from the pressure holding speed setting value by the deceleration acceleration every control cycle. During the deceleration stroke, the current position is compared with the holding pressure switching position, and when the current position exceeds the holding pressure switching position, the process proceeds to the holding pressure stroke.

Japanese Patent Laid-Open No. 2002-055822

  In the technique disclosed in the above-mentioned patent document, a predicted deceleration position before the holding pressure switching position is calculated from the current screw position during injection and the current detection speed, and by passing through the predicted deceleration position, a deceleration process is started, and deceleration is performed. The speed instruction is generated, the speed is reduced to the target speed, and the holding pressure is switched. Such a control method is based on the speed command generated when the predicted decrease position before the holding pressure switching position is not accurate, or when the load such as cylinder pressure is too large after the deceleration process and the motor torque is limited. If the vehicle is not decelerated following this, there is a disadvantage that the vehicle is decelerated considerably before the holding pressure switching position, or enters the holding pressure switching position at a speed that is too fast.

  As described above, if the vehicle is decelerated considerably before the holding pressure switching position, it takes a long time until the holding pressure is switched, and if the injection time is not stable or the injection pressure is too early at the holding pressure switching position. Then, a sudden peak pressure may occur, and there is a problem that molding quality is not stable. Further, when an error occurs in the prediction, there is a problem that the same deceleration is not performed when the final injection speed or the holding pressure setting is changed.

  The present invention has been made in order to solve the above-described problems, and by always calculating and generating a deceleration control command before the holding pressure switching position, the pressure is automatically reduced optimally before the holding pressure switching position. An object of the present invention is to provide an injection molding machine that can be switched, and thus can obtain a stable molded product, and a holding pressure switching control method for the injection molding machine.

  In order to solve the above-described problems, the electric injection molding machine and the holding pressure switching control method for the electric injection molding machine according to the present invention are set to a deceleration acceleration (α) set in advance for deceleration control before holding pressure switching, By providing means for calculating the current speed command value (v) from the control delay time (d), the set value of the pressure holding speed (Vh), and the current detection position (p) of the screw, immediately before the pressure holding switching position. It is possible to decelerate optimally.

  That is, the electric injection molding machine according to the present invention includes a transmission mechanism that converts the forward / backward movement of the screw into a rotational motion, an electric motor that moves the screw forward / backward through the transmission mechanism, deceleration acceleration and pressure holding of the screw. Setting means for setting the set speed and control delay time, current position detecting means for detecting the current position of the screw during the injection stroke, the current position detected by the current position detecting means, and the control set in the setting unit And a calculation means for calculating a deceleration speed command so as to be the pressure holding setting speed immediately before the pressure holding switching position based on the delay time, the pressure holding setting speed, and the deceleration acceleration.

  Further, the holding pressure switching control method for the electric injection molding machine according to the present invention sets the screw deceleration acceleration, the holding pressure setting speed, and the control delay time in advance, and detects the current position of the screw during the injection stroke. Based on the detected current position, the control delay time set in the setting unit, the holding pressure setting speed, and the deceleration acceleration, the screw deceleration speed is set to the holding pressure setting speed immediately before the holding pressure switching position. The screw is automatically decelerated immediately before the holding pressure switching position by an electric motor through a transmission mechanism that calculates a command and converts the forward / backward movement of the screw into a rotational motion.

  According to such a configuration, the optimum deceleration speed command value is always calculated and calculated from the current detection position of the screw even during the deceleration process. The flow is reduced and stabilized.

  As described above in detail, according to the present invention, since the automatic deceleration is optimally performed before the holding pressure switching position, the flow of the screw after holding pressure switching due to the inertia force is small, the conditions can be set intuitively, and the quality can be improved. There is an effect that a stable molded product can be obtained. Even when the setting of the pressure holding speed and the injection speed is changed, the optimum automatic deceleration can be obtained.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a time chart of injection holding pressure control in the embodiment of the present invention, FIG. 2 is a flowchart of injection holding pressure control in the embodiment of the present invention, and FIG. 3 shows an example of calculation algorithm of deceleration speed command of the present invention. It is explanatory drawing. The overall configuration of the electric injection molding machine in the embodiment of the present invention is the same as that shown in FIG.

  However, in the configuration shown in FIG. 4, in the present embodiment, in the control unit 30, a setting device (memory) as setting means for setting the screw deceleration acceleration, the pressure holding setting speed, and the control delay time, and the injection stroke Based on the current position detected by the counter (34 in FIG. 4) as the current position detecting means for detecting the current position of the screw, the control delay time set in the setting means, the pressure holding set speed, and the deceleration acceleration, Computation means for computing a deceleration speed command is provided so as to obtain a pressure keeping setting speed immediately before the pressure keeping switching position.

  Hereinafter, the operation of the injection molding machine in the embodiment will be described with respect to the injection holding pressure control operation. During the injection process, the set speed command value that has been set is output (steps S31 and S32), and the deceleration speed command v calculated and calculated from the current screw detection position (counter output value) p as described later is the set speed command. When the value is smaller than the value Vs (step S34: v <Vs), a deceleration speed command v is output (step S35). When the screw detection position p passes the holding pressure switching position Ph (step S37, Y), the process proceeds to the holding pressure process (steps S38 to S40). On the other hand, when the deceleration speed command v is not smaller than the set speed command value Vs (step S34: v ≧ Vs), the set speed command value Vs is output.

  Here, a calculation example of the calculation algorithm of the deceleration speed command v of the present invention will be described. In actual motor control, there is a response delay after the speed command is issued. Therefore, considering the control delay time and considering the distance traveled after deceleration with reference to FIG. 3, the deceleration acceleration α, the control delay time d, When the pressure holding pressure setting speed Vh, the deceleration speed command v, the current detection position p, and the pressure holding switching position Ph are assumed to be a position Pa from the current position to the pressure holding switching position, the area P corresponding to the hatched line in FIG.

P = Pa−d · Vh = d · β + (2 · Vh + β) β / 2α (1)
It becomes. Here, Pa is an area surrounded by a time axis, a speed axis, a dotted line, and a time at which the dotted line intersects with v = Vh, and is represented by Pa = p−Ph. Β = v−Vh, α, d, Vh, and Ph are values set by the setting means, and p is a detection position.

  The value of P in the equation (1) will be further described. P is obtained by adding the area of A and the area of B in FIG. Here, the area of the parallelogram of A is d × β, the area of the trapezoid of B is (Vh + v) × t / 2, and there is a relationship of t = β / α and v = Vh + β. As a sum of the areas of B and B, the right side of equation (1) is obtained.

Therefore, the deceleration speed command v is
When P ≦ 0, v = Vh,
When P> 0, the solution β of the above quadratic equation is obtained and v = β + Vh.
For reference, when V is obtained when P> 0,
v = α [√ {(d + Vh / α) ² + 2P / α} −d].

  During the injection process, a set speed command value Vs is generated for each control cycle, a deceleration speed command v is calculated from the current detection position p, and when v <Vs, the deceleration speed command v is output. The pressure is automatically reduced to the target pressure holding speed Vh from the front of the pressure switching position. When the current position exceeds the holding pressure switching position Ph, the pressure holding process is started. Note that the control delay time d may be automatically calculated from the relationship between the command speed and the detected speed. As the deceleration acceleration α, a value calculated from set value information of the maximum speed and the maximum deceleration time may be used.

  According to the embodiment of the present invention, since the automatic deceleration is optimally performed before the holding pressure switching position, the flow of the screw after the holding pressure switching by the inertia force is small, and the deceleration is performed considerably before the holding pressure switching position as in the prior art. There is no end to it. Therefore, it takes no long time until the holding pressure is switched, the injection time is stable, and there is no premature entry at the holding pressure switching position, so as shown by the one-dot chain line in FIG. In addition, there is no sudden peak pressure that often occurs in the past, and the molding quality is stable. In addition, when changing the setting of the final injection speed and the pressure holding speed, it is easy to intuitively set conditions, and an optimum automatic deceleration can be obtained.

It is a time chart which shows the operation | movement of the injection pressure control in embodiment. It is a flowchart which shows operation | movement of embodiment. It is a figure which shows the example of the calculation algorithm of the deceleration speed instruction | command of this invention. It is a whole block diagram of an electric injection molding machine. It is a time chart which shows the operation | movement of the conventional injection holding pressure control. It is a flowchart which shows the operation | movement of the conventional injection pressure control.

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 (2)

A transmission mechanism that converts the forward / backward movement of the screw into rotational movement;
An electric motor for moving the screw forward / backward through the transmission mechanism;
Setting means for setting the deceleration acceleration and holding pressure setting speed and control delay time of the screw;
Current position detecting means for detecting the current position of the screw during the injection stroke;
Based on the current position detected by the current position detecting means, the control delay time set in the setting unit, the pressure setting speed, and the deceleration acceleration, the pressure holding setting speed is set immediately before the pressure holding switching position. An injection molding machine comprising: a calculation means for calculating a deceleration speed command. Set the screw deceleration acceleration, pressure holding set speed and control delay time in advance.
While detecting the current position of the screw during the injection stroke, based on the detected current position, the control delay time set in the setting unit, the pressure setting speed, and the deceleration acceleration, the holding position is set immediately before the holding pressure switching position. Calculate the screw deceleration speed command to achieve the pressure setting speed,
A holding pressure switching control method for an injection molding machine, wherein the screw is automatically decelerated immediately before a holding pressure switching position by an electric motor through a transmission mechanism that converts a forward / backward movement of the screw into a rotational motion.

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