JP2820825B2 - Resin pressure control device for electric injection molding machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric injection molding machine for moving a screw in an axial direction by a servomotor to inject resin in a cylinder into a mold and to press the resin to a predetermined pressure. The present invention relates to a resin pressure control device.

[0002]

2. Description of the Related Art Conventionally, there has been known an electric injection molding machine in which a screw in a cylinder is axially moved by a servomotor to inject a resin in a cylinder into a mold and to press the resin to a predetermined pressure. This electric injection molding machine has a cylinder 10 for filling with resin, as shown in FIG. At the tip of the cylinder 10 is a nozzle 1 for injecting resin into a mold.
1 is provided, and the cylinder 10 is provided with a heater (not shown) for melting the resin. Cylinder 10
A screw 13 for pressing the resin toward the nozzle 11 is slidably and rotatably fitted in the axial direction, and a resin is inserted into the cylinder 10 at the rear end thereof.
A hopper 14 for feeding into the inside is provided. Further, a pulley 15 is fixed to the rear end of the screw 13, and a rod 16 extending in the radial direction is externally fitted only rotatably. Further, a timing belt 17 is wound around the pulley 15, and the timing belt 17 is also wound around a pulley 19 fixed to a shaft of a motor 18 for rotating the screw 13. Is transmitted to the screw 13 via the pulley 19, the timing belt 17 and the pulley 15. The timing belt 17, the motor 18, and the pulley 19 can move in the direction of the arrow AB integrally with the screw 13.

On the other hand, a ball nut 20 is provided at the tip of the rod 16, and a ball screw 21 that is rotatably supported by a support (not shown) is screwed to the ball nut 20. Ball screw 21
A pulley 22 is fixed to one end of the pulley 22.
, A timing belt 23 is wound, and the timing belt 23 is also wound around a pulley 25 fixed to a shaft of a motor 24 for rotating the ball screw 21. As a result, the torque of the motor 24 is
5, transmitted to the ball screw 21 via the timing belt 23 and the pulley 22,
The rod 16 and the screw 13 move in the direction of the arrow AB integrally with the ball nut 20 by the rotation of.

Next, the operation will be described. When the motor 18 rotates, the rotation of the motor 18 is transmitted to the screw 13 via the pulley 19, the timing belt 17 and the pulley 15, and the screw 13 rotates. Screw 13
The resin in the hopper 14 is supplied to the inside of the cylinder 10 by the rotation of, and the resin pressure inside the cylinder 10 increases. At the same time, the motor 23 generates a constant force for rotating in the direction of arrow D, and the force of the motor 23 is transmitted to the ball screw 21 via the pulley 25, the timing belt 23, and the pulley 22, and the ball screw 21, the rod 1
The resin inside the cylinder 10 is pressed with a predetermined pressing force by the screw 13 through 6. By supplying the resin into the cylinder 10 by the rotation of the screw 13, the resin pressure inside the cylinder 10 overcomes the pressing force of the screw 13 in the arrow A direction, and the screw 13 moves in the arrow B direction. When the screw 13 is pushed back to a predetermined position, the motor 18 stops and the cylinder 10 is stopped.
A predetermined amount of resin is supplied to the inside (a measuring step).

When the screw 13 is moved in the direction of arrow A after supplying a predetermined amount of resin, the resin in the cylinder 10 is injected from the nozzle 11 into the mold (injection step). Then, the screw 13 presses the resin in the direction of arrow A with a predetermined pressing force in order to maintain a predetermined resin pressure until the resin in the mold is hardened (pressure holding step). At this time, the cylinder 10 is heated by the heater, and the resin in the cylinder 10 is not cured. In the pressure-holding step, which greatly affects the accuracy of the molded product, the output current of the servo motor 24 is controlled to a value corresponding to the set pressure-holding pressure in order to control the actual resin pressure to be the set pressure. ing.

[0006]

Since the conventional electric injection molding machine is configured as described above, the friction of the mechanical movable part, the linearity of the output current of the servo motor with respect to the current, the influence of the temperature characteristic, etc. It is not possible to obtain the accurately set resin pressure, and the operator has to observe the molded product and reset the set resin pressure. There was a problem that required skill. Further, by controlling the output current of the servo motor 24 to a value corresponding to the set dwell pressure, the servo motor 24
However, there is a problem that the current required for starting and stopping of the resin is limited, so that the resin pressure cannot be quickly switched. SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and has high precision without being influenced by external factors such as friction of a mechanical moving portion, linearity of a servo motor current versus output torque, and temperature characteristics. It is another object of the present invention to provide a resin pressure control device which quickly sets a pressure and does not require control adjustments due to differences in molded product size, mold type, and resin.

[0007]

According to the present invention, there is provided a resin pressure control device, comprising: a pressure detector for detecting a resin pressure; a position detector for detecting a moving position of a screw; And a position / pressure change detection unit for calculating the screw movement amount per unit pressure from the screw movement amount, and the resin pressure becomes the set resin pressure from the difference between the resin pressure and the set pressure and the screw movement amount per unit pressure. And a control unit that controls the resin pressure by moving the screw position according to the screw movement amount calculated by the calculation unit.

[0008]

The resin pressure control device according to the present invention detects the resin pressure and the moving position of the screw. Further, the amount of screw movement per unit pressure is determined from the amount of change in resin pressure when the resin is pressed and the amount of screw movement, and the resin pressure is determined based on the difference between the resin pressure and the set pressure and the amount of screw movement per unit pressure. Therefore, the necessary screw movement amount is calculated by the calculation unit. Then, the resin position is controlled by the control unit by moving the screw position according to the screw movement amount calculated by the calculation unit. This allows
High-precision control can be performed without being affected by external factors such as the size of the molded product, the mold type, and the type of resin, and the output pressure of the servomotor is not limited, so that the resin pressure can be quickly controlled.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a resin pressure control device according to one embodiment of the present invention. This resin pressure control device has a resin pressure detector 1 for detecting a resin pressure and a position detector 2 for detecting a rotational position of a screw by detecting a rotational position of a servomotor. And the position detector 2 include a resin pressure change amount when the resin is detected by the resin pressure detector 1 and the position detector 2.
The position / pressure change detection unit 3 for obtaining the screw movement amount per unit pressure from the movement amount of the screw 13 detected by the above is connected. Further, the resin pressure detector 1 and the position /
The pressure change detection unit 3 includes a target position calculation unit 4 that calculates a screw movement amount necessary for the resin pressure to reach the set resin pressure from the difference between the detected resin pressure and the set pressure and the screw movement amount per unit pressure. Is connected. The target position calculation unit 4 includes a linear function interpolation unit 5 for instructing the target position calculation unit 4 to move by the movement amount per unit processing time in consideration of the set speed and the acceleration / deceleration amount in addition to the screw movement amount. Is connected. The linear function interpolation unit 5 includes:
The servo motor 24 according to the instruction from the linear function interpolation unit 5
Is connected, and the servo control unit 6 is connected to the servo motor 24 via the servo amplifier 7.

FIG. 2 is a schematic view showing an injection in an electric injection molding machine.
FIG. 4 is a diagram illustrating a relationship between a screw position and a resin pressure in a pressure holding step. Point A is the injection start point, point B is the point at which the resin is completely filled into the mold, and point B to point C is the section where the resin is compressed. Of the screw movement amount.

Next, the operation of this embodiment will be described with reference to the flowchart of FIG. A series of processes shown in the flowchart of FIG. 3 is a sampling control process that is repeatedly performed at predetermined time intervals. The position / pressure change detecting section 3 calculates a change amount Δs from the current position of the screw 13 and the previous position and integrates the change amount into s (step 1). Similarly, the resin pressure calculates the change amount Δp from the previous and current pressures. It is obtained and integrated with p (step 2). It is determined whether or not the integrated value of the pressure change amount is equal to or more than a predetermined value (step 3). If it is determined that the integrated value of the pressure change amount is equal to or more than the predetermined value, the integrated pressure change amount p and the movement are determined. The amount of screw movement k per unit pressure is calculated from the amount s (step 4), and the integrated values s and p are cleared for the next integration (step 5). The reason why the change amount of the pressure and the change amount of the position are integrated is to obtain the screw movement amount k per unit pressure with as small an error as possible by averaging. Then, when the mechanical operation enters the pressure-holding step (step 6), the target position calculating section 4 multiplies the difference between the set pressure pt and the currently detected pressure pa by the screw movement amount k per unit pressure to set the pressure. The target movement amount d of the screw 13 for achieving the pressure is calculated (step 7). Then, the movement amount per unit processing time is obtained by taking into account the speed and the acceleration / deceleration amount set for the target movement amount d (step 8), and the servo control unit 6 is instructed (step 9). By repeatedly performing the above-described processing, the position of the screw 13 is moved by the servomotor so that the resin pressure matches the set pressure. When a time sufficient for the resin in the mold to harden has elapsed, the pressure-holding step ends.

In step 6 described above, it is determined whether or not the injection operation has determined that the mechanical operation has not entered the pressure-holding step (step 10). If it is determined that the injection operation is performed, injection control is performed. If it is determined that it is not the injection process,
It is determined whether or not the process is a plasticizing process (step 11). If it is determined that the process is a plasticizing process, plasticizing control is performed. When it is determined that the process is not the plasticizing process, it is determined whether or not the process is the suckback process (step 12). When it is determined that the process is the suckback process, the suckback control is performed.

[0013]

As described above, according to the present invention,
Since the screw movement amount per proper unit pressure, the resin pressure is obtained, and the screw movement is calculated by calculating the necessary screw movement amount because the resin pressure becomes the set pressure from the difference between the set pressure and the resin pressure, Even when the mold type and the type of resin are changed, no control adjustment is required, a quick and accurate holding pressure can be obtained, and a precise and stable injection molding can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a resin pressure control device according to one embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a screw position and a resin pressure in an injection and pressure-holding step in the electric injection molding machine according to the present embodiment.

FIG. 3 is a flowchart illustrating the operation of the present embodiment.

FIG. 4 is a schematic configuration diagram showing a general electric injection molding machine.

[Explanation of symbols]

 Reference Signs List 1 resin pressure detector 2 position detector 3 position / pressure change detection unit 4 target position calculation unit 5 linear function interpolation unit 6 servo control unit 10 cylinder 11 nozzle 13 screw 18, 24 servo motor

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) B29C 45/76-45/82 B29C 45/17 B29C 45/50, 45/60

Claims (1)

(57) [Claims] 1. A motor-driven injection molding machine which moves a screw in an axial direction by a servomotor to inject resin in a cylinder into a mold and presses the resin to a predetermined pressure. A pressure detector, a position detector for detecting a screw movement position, and a position for calculating a screw movement amount per unit pressure from a resin pressure change amount at the time of resin pressing and a screw movement amount.
A pressure change detection unit, a calculation unit that calculates a screw movement amount necessary for the resin pressure to reach the set resin pressure from a difference between the resin pressure and the set pressure and a screw movement amount per unit pressure, and a screw calculated by the calculation unit A control unit for controlling a resin pressure by moving a screw position according to a moving amount.