JPH04334428A - Purging method for injection molding machine - Google Patents

Abstract

PURPOSE:To prevent effectively the damage to a screw head generated by a residual material by carrying out the given purging and then moving back a screw to the given standby position when no material is sensed in a heating cylinder and completing purging. CONSTITUTION:The given purging is carried out, and then whether a material is in a heating cylinder 2 or not is sensed, and when no material is sensed therein, a screw 3 is moved back to the given standby position Po and the process of completing purging is carried out. At that time, the standby position Po is the position which separates an inner face 2i of the heating cylinder 2 from a screw head 3s at least by the distance Lb in the axial direction and forms a given space S. Or else, the standby position Po is set as the utmost backward position of the screw 3. As a result, if a residual material W is solidified, the fixed area to the screw head 3s is almost eliminated, and the breakage of screw head 3s is prevented even when the screw 3 is rotated in the state that the material W is not sufficiently melted.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purging an injection molding machine by discharging material from a heating cylinder when molding is finished or when changing materials.

0002

[Prior Art] Generally, when injection molding machines finish molding or change materials, a purge process is performed to empty the heating cylinder by discharging all the remaining material. The molding machine performs automatic purge processing. When performing an automatic purge process, the purge process itself can be performed automatically by repeating the rotation of the screw and blank firing a predetermined number of times, but when the purge is automatically completed, it is necessary to check that the material in the heating cylinder is completely gone. It is necessary to terminate the purge after detecting this.

[0003] Conventionally, as a method for terminating purge,
A method disclosed in Japanese Unexamined Patent Publication No. 2-169225 is known. In this method, the screw is advanced from the retracted position to the tip of the cylinder, a purge process is performed to discharge the residual resin (material), the screw is rotated for a predetermined period of time, and the melting pressure of the resin is detected. This operation is repeated until the detected melt pressure falls below a predetermined value, and the purge is completed when the detected melt pressure becomes below a predetermined value.

0004

However, in the conventional method described above, the screw is generally set at the most advanced position at the end of the purge. The reason for this is that in the final stage of the purge process, by advancing the screw to its most advanced position, the resin (material) inside the heating cylinder is
At the same time, as disclosed in the above publication,
This is because the presence or absence of residual resin is detected by rotating the screw, and if there is no residual resin, the purge is completed and the screw is set to the most advanced position.

However, even after the purge is completed, the inner surface 71i of the heating cylinder 71 and the screw 7 actually
A small amount of material W remains between the two screw heads 72s. Therefore, when the screw 72 is set to the most advanced position, the remaining material W is cooled and solidified as it is,
It is fixed to the inner surface 71i and the screw head 72s. As a result, the injection molding machine is operated during the next molding, and the screw 7
2, there was a problem that the screw head 72s would be fixed and the screw head 72s would be damaged. That is, since the temperature near the tip of the heating cylinder 2 is relatively low, the melting rate of the solidified material W is slower than in other parts, and the screw head 72s is usually provided with a backflow prevention ring. Since the screw head 72s is the part of the screw 72 having the weakest mechanical strength, the screw head 72s is particularly susceptible to damage.

The present invention solves the problems existing in the conventional technology, and effectively prevents damage to the screw head due to residual material, increases the melting rate of the residual material, and improves work efficiency. The purpose of the present invention is to provide a method for purging an injection molding machine that allows the purging of an injection molding machine.

[0007]

[Means for Solving the Problems] A purging method for an injection molding machine according to the present invention detects the presence or absence of material W in the heating cylinder 2 after executing a predetermined purge process, and detects the absence of material W. Then, the purge termination process is performed in which the screw 3 is retreated to a predetermined standby position Po to terminate the purge. In this case, standby position P
o is at least the inner surface 2i of the heating cylinder 2 and the screw head 3
A predetermined setting position or the most retracted position of the screw 3 can be selected to provide a predetermined gap S between the screws 3 and s. Note that the following method can be used to detect the presence or absence of the material W. First, the screw 3 is rotated for a preset time Ts.
The retracted position Pd of the screw 3 is detected, and when the retracted position Pd is below a preset setting position Ps, the absence of the material W is detected. Also, the magnitude of the load current of the drive motor 4 that rotates the screw 3 is detected, and the current detection value Id becomes less than or equal to a preset current setting value Is, and the time during which the current detection value Id is less than or equal to the current setting value Is is a preset setting time Tt. When the above continues, the absence of material W is detected.

[0008]

[Operation] According to the method of purging an injection molding machine according to the present invention, the presence or absence of material W in the heating cylinder 2 is detected after a predetermined purge process is executed.

[0009] Detection of the material W is performed as follows, for example. First, the screw 3 is rotated for a preset time Ts.
Rotate only. At this time, if there is material in the heating cylinder 2, the screw 3 will move backward due to the back pressure of the material accumulated in the front, whereas if there is no material, the screw 3 will idle without moving back. Therefore, after the set time Ts has elapsed, the retracted position Pd of the screw 3 is detected, the retracted position Pd is compared with a preset setting position Ps, and the retracted position Pd is detected.
If d is below the set position Ps, it is determined that the material has run out. In addition, the set time Ts is selected to be a time sufficient for the rotation speed to stabilize from the start of rotation of the screw 3, and the set position Ps is set to be longer than the most advanced position of the screw 3.
You can select a slightly rearward position.

[0010] When it is detected that there is no material W, the screw 3 is retreated to a predetermined standby position Po. As a result, as shown in FIG. 4, the inner surface 2 of the heating cylinder 2
i and the screw head 3s are separated by a distance Lb in the axial direction, and a predetermined gap S is provided. As a result, even if the remaining material W solidifies, there is almost no adhesion area to the screw head 3s, and even if the screw 3 is rotated when the material W is not sufficiently melted, damage to the screw head 3s is prevented. Ru. Moreover, since the screw 3 is located at the high temperature portion of the heating cylinder 2 at the start of the next operation, the melting rate of the solidified material W is accelerated.

On the other hand, when the most retracted position of the screw 3 is set as the standby position Po, in addition to the space S being provided, the rotation of the screw 3 is locked by the interlock function. Therefore, when starting the next operation, it is necessary to move the screw 3 forward in order to release the lock, and by moving the screw 3 forward, it becomes possible to scrape off the solidified material W, making it possible to move the screw head 3s more effectively. damage is prevented.

0012

Embodiments Next, preferred embodiments of the present invention will be described in detail with reference to the drawings.

First, the general structure of an injection molding machine capable of carrying out the purge method according to the present invention will be explained with reference to FIG.

In FIG. 3, M indicates an injection molding machine, and 1
1 is an injection device attached to a machine base 10. Injection device 11
is equipped with a heating cylinder 2, has an injection nozzle 12 at the tip, and has a hopper 13 at the rear for supplying material into the heating cylinder 2. A screw 3 is inserted into the heating cylinder 2, and the rear end of the screw 3 is rotatably connected to the front end of a slider 15 that is horizontally movable along a guide bar 14. Further, a metering servo motor 16 (drive motor 4) equipped with a pulse encoder 17 is attached to the slider 15, and a transmission mechanism 18 for transmitting the rotation of the motor 16 to the screw 3 is disposed. Configure. Furthermore, the machine base 10 includes a pulse encoder 21.
Attaching the injection servo motor 20 equipped with
The output shaft 20s is connected to the rear end of the slider 15 via a ball screw mechanism 22, thereby forming a drive unit 23 for forward and backward movement of the screw.

On the other hand, the metering servo motor 16 and pulse encoder 17 are connected to a servo motor control section 31, and the injection servo motor 20 and pulse encoder 21 are connected to a servo motor control section 32. Further, each of the servo motor control units 31 and 32 is connected to a molding machine control device 33 having a built-in computer function that controls the entire injection molding machine.

In this case, the pulse encoder 17 detects the speed or rotation amount of the metering servo motor 16, and the pulse encoder 21 detects the speed or rotation amount of the injection servo motor 20. Further, the control device 33 gives a control command to the servo motor control section 31 and controls the weighing servo motor 1.
6 to rotate the screw 3, and also give a control command to the servo motor control unit 32 to control the rotation speed and rotation torque of the injection servo motor 20.
The position of the screw 3 is detected by controlling the back pressure when the screw 3 advances and rotates, and further by processing the output signal of the pulse encoder 21 of the injection servo motor 20.

Next, a method of purging an injection molding machine according to the present invention will be explained with reference to FIGS. 1 and 3.

FIG. 1 shows a flowchart of the purge method according to the present invention, particularly the automatic purge termination process when the purge process is completed.

First, the automatic purge program is called in the control device 33, and automatic purge processing is executed. The purge process itself is executed by repeating rotation of the screw 3 and blank firing a predetermined number of times. After the purge process, an automatic purge end process is executed. Note that the screw 3 is set to the most advanced position by the purge process.

First, the metering servo motor 16 is activated at the same time as the timer function section of the control device 33 starts measuring time.
The screw 3 starts rotating (steps 51, 52). The timer function unit times out after counting a preset time Ts (step 53). When the time is up, the operation of the metering servo motor 16 is stopped, thereby stopping the rotation of the screw 3 (step 54
). Then, the stop position at this time, that is, the retreat position Pd
is detected by processing the output signal of the pulse encoder 21 (step 55). The obtained retreat position Pd is then given to the control device 33, where it is compared with a preset setting position Ps.

At this time, if the retreat position Pd exceeds the set position Ps, that is, if Pd>Ps, the screw 3
is advanced to the most advanced position, the material is discharged based on purge processing, and the processing from step 51 is executed again (steps 56, 57, 58, 59). In this state, material still exists, and the purge process will continue.

On the other hand, if the retreat position Pd is below the set position Ps,
That is, if the condition of Pd≦Ps is satisfied, it is determined that there is no material in the heating cylinder 2, and the screw 3 is retracted (
Step 60). The retreat position is up to a preset standby position Po, and the amount of retreat at this time is set by the timer function section. That is, the timer function section starts timing at the same time as the screw 3 starts retracting, and reaches the preset time T.
After measuring t, the time is up (steps 61 and 6
2). When the time is up, the operation of the metering servo motor 16 is stopped, and the backward movement of the screw 3 is stopped (step 63). In this case, the standby position Po is set by the set time Tt and the backward speed of the screw 3. Of course, the standby position Po may be set as an absolute position and the retraction of the screw 3 may be controlled by position information obtained by processing the output signal of the pulse encoder 21. Then, the screw 3 is placed in the standby position Po, and a purge end command is output to completely end the purge. This state is shown in FIG.

On the other hand, in step 60, the screw 3
may be moved back to the most retracted position. In this case, the most retracted position becomes the standby position Po, and the process is executed according to the flowchart shown in FIG. In addition, in FIG. 2,
Steps that are the same as those shown in FIG. 1 are given the same reference numerals, and illustrations of other steps that are the same as those in FIG. 1 are omitted. Therefore, in this example, when retracting the screw 3 to the most retracted position, the metering servo motor 16 is operated to retract the screw 3, and when the most retracted position is reached, the operation of the motor 16 is stopped. Then, the screw 3 is stopped from retreating (steps 64 and 65). Then, the screw 3 is set to the most retracted position, a purge end command is output, and the purge is completely ended.

[0024] As a method of detecting the presence or absence of the material W, the magnitude of the load current of the weighing servo motor 16 that rotates the screw 3 is detected using, for example, a current transformer attached to the power supply line, and the detected current value is The absence of the material W may be detected when Id becomes less than or equal to a preset current value Is and the time at which the current is less than or equal to the current value Is continues for a preset time period Tt or more. In addition, any other detection method can be applied.

The embodiments have been described in detail above, but
The invention is not limited to such embodiments. For example, the processing of each part may be performed by a hardware configuration or may be executed by software. Further, the servo motor may be replaced with a general-purpose motor or a hydraulic drive mechanism. Furthermore, the position of the screw may be detected by a position detector attached to the screw. In addition, the detailed structure, method, etc. may be arbitrarily changed without departing from the gist of the present invention.

[0026]

As described above, the method for purging an injection molding machine according to the present invention detects the presence or absence of material in the heating cylinder after executing a predetermined purge process, and if it is detected that there is no material, The purge termination process involves retracting the screw to a predetermined standby position to complete the purge, which effectively prevents damage to the screw head due to residual material, increases the melting rate of residual material, and improves work efficiency. It has the remarkable effect of being able to achieve

[Brief explanation of drawings]

FIG. 1 is a flowchart showing a method of purging an injection molding machine according to the present invention;

FIG. 2 is a flowchart in which some steps of another embodiment of the same purge method are omitted;

FIG. 3 is a schematic configuration diagram of an injection molding machine that can implement the purge method according to the present invention;

FIG. 4 is a vertical cross-sectional view showing the screw position according to the purge method according to the present invention;

FIG. 5 is a longitudinal cross-sectional view showing the screw position according to the conventional purge method;

[Explanation of symbols]

2 Heating cylinder 2i Inner surface 3 Screw 3s screw head 4 Drive motor Po Standby position S Gap W Material

Claims (5)

[Claims] Claim 1: In a purge method for an injection molding machine that discharges material in a heating cylinder, after performing a predetermined purge process, the presence or absence of material in the heating cylinder is detected, and if it is detected that there is no material; A method for purging an injection molding machine, comprising performing a purge termination process in which the screw is retreated to a predetermined standby position to terminate the purge. 2. The method of purging an injection molding machine according to claim 1, wherein the standby position is a preset position for creating a predetermined gap between at least the inner surface of the heating cylinder and the screw head. 3. The method of purging an injection molding machine according to claim 1, wherein the standby position is the most retracted position of the screw. [Claim 4] When detecting the presence or absence of material, the screw is rotated for a preset time, the retracted position of the screw is detected, and when the retracted position is below the preset position, it is determined that there is no material. 2. The method of purging an injection molding machine according to claim 1, further comprising detecting. 5. When detecting the presence or absence of material, the magnitude of the load current of the drive motor that rotates the screw is detected, and the current detection value is equal to or less than a preset current value, and the time during which the current value is equal to or less than the current value is determined. 2. The method of purging an injection molding machine according to claim 1, further comprising detecting the absence of material when the purge continues for a preset time or more.