JPH0238384B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an injection process control method for an electric injection molding machine used for molding synthetic resin.

[Prior art] In molding machines that use an electric motor as a drive source, which has already been developed, the holding pressure in the holding pressure process is controlled by controlling the torque value of a servo motor. The injection process is completed by changing the holding pressure all at once to zero or the set value of the back pressure.

[Problems to be solved by the invention] The injection process of a general molding machine includes a filling process from the start of injection until the mold is almost filled with resin, and a compression process to compress the resin filled in the mold. It can be considered to be divided into pressure holding processes, such as to compensate for shrinkage of compressed and filled molten resin due to cooling, to recompress it, or to stop backflow of resin to the nozzle side of the machine.

The holding pressure during the holding pressure process just before the end of the injection process is
The injection is performed using the hydraulic pressure of the injection cylinder, and the set pressure is not zero in order to obtain a high-quality product.The molten resin in the heating cylinder and nozzle is in a pressurized state, and from this state the holding pressure is reduced. The set value is dropped all at once to zero or a back pressure value to complete the injection process.

For injection molding machines that use conventional hydraulics,
Depending on the flow resistance when the hydraulic oil in the injection cylinder flows out of the cylinder or the operating characteristics of the hydraulic valve, the screw at the end of the injection process may be It does not recede too much, and no problems with molding have been found.

However, the control of the holding pressure in the holding pressure process is
In the case of the electric type, which controls the trick value of the servo motor as described above, the pressure energy accumulated by the molten resin remaining in the compressed state inside the heating cylinder and the nozzle section is used to reduce the pressure after the injection process is completed. Even though the force of the driving source was removed,
Sukuriyu's retreating force is generated, and Sukuriyu continues to move backward. The force that controls this screw retraction force is the control force due to the frictional force of the screw mechanism, etc., and it is smaller than in the case of hydraulic drive, so the screw does not move backward against such braking force. I end up doing too much.

If the screw moves back too much, the resin pressure in front of the screw in the heating cylinder tends to become negative.
Sometimes a cavity forms in the heating cylinder in front of the screw, which must be filled with molten resin. In extreme cases, the screw moves backward beyond the measuring position. If this causes the resin pressure in front of the screw in the heating cylinder to become negative or create a cavity, bubbles may occur in the molten resin, measurement may vary, and resin plasticization may become unstable. etc., resulting in a decrease in the quality of the molded product. Furthermore, if the screw moves backward beyond the measuring position, measuring becomes impossible and molding cannot be performed.

[Means for Solving the Problems] This invention solves the problems of injection process control using accumulated pressure energy, and provides a new method that does not cause any adverse effects even if the injection process is controlled by controlling the torque value. The purpose of this invention is to provide a method for controlling the injection process.

A feature of the present invention for the above-mentioned purpose is that a servo motor is used as a drive source, and when injecting molten resin by converting the rotational force of the servo motor into thrust force of an injection screw using a screw mechanism, immediately before the end of the injection process, The purpose of the present invention is to reduce the torque value of the servo motor over time to attenuate and control the injection force until the end of the injection process, and then end the injection process.

[Function] As mentioned above, when the torque value of the servo motor is decreased over time from just before the end of the injection process to the end of the injection process, the pressure accumulated by the molten resin in the heating cylinder is reduced. The energy also attenuates as time passes, and the backward movement of the screw is slowed down, making it difficult for negative pressure to occur in the heating cylinder, and the screw can be stopped at the set position.

Further, the present invention will be explained in detail with reference to illustrated embodiments.

[Example] In FIG. 1 and FIG. 2, the injection process is performed by using a heating cylinder 2 containing an injection member by means of a screw 1, and a housing 4 on a machine base 3 which also serves to hold the injection heating cylinder.
and has. Inside the housing 4, there is a screw movable member 6 connected via a rotation shaft 5 connected to the rear end of the screw 1, and housing front and rear walls 4a parallel to the rotation shaft 5 as shown in FIG. , 4b on both sides, and the screw movable member 6 is attached to the support shafts 7, 7 by penetrating both ends thereof so as to be slidable in the front and rear direction.

A small-diameter extension shaft 5a having a gear 8 for rotating the screw is protruded from the rear end of the rotation shaft 5.
The screw movable member 6 is connected to the end of the extension shaft 5a via a thrust bearing 9. The central part of the screw movable member 6 is cylindrical, and a screw receiving member 10 having a screw threaded on the inner peripheral surface is fitted into the rear end of the central part. , is screwed in concentrically with the screw 1.

The rear end of this screw shaft 11 is a shaft portion 11a rotatably held on the housing rear wall 4b with a thrust bearing 12, and a gear 13 is attached to the shaft portion 11a.

The gears 8 and 13 are respectively meshed with gears 17 and 18 which are attached to a transmission shaft 14 on the lower side inside the housing 4 with clutches 15 and 16,
The drive shaft of a DC electric servo motor 19 equipped with a transmission shaft 14 and a coccometer generator 21 connected to the lower surface of the housing 4 is connected through a drive belt 20, and the servo motor 19 is used as a drive source to perform the above-mentioned operation. The screw 1 is rotatably and axially movable.

Screw 1 in the electric injection device with the above structure
The rotational backward movement (material metering) of the screw 1 is carried out by the gears 17 and 8, and the injection forward movement of the screw 1 is carried out by the gear 1.
8 and 13. That is, the rotation of the gear 13 also rotates the screw shaft 11, and this rotational force is applied to the screw receiving member 1 on the side of the screw movable member that is prevented from rotating.
0 is converted into thrust. Then, the screw 1 moves forward together with the screw movable member 6, and the molten resin in the heating cylinder 2 charged in front of the screw is injected from the nozzle into the clamped molds 23 and 24.

25 is a metering stop position detector, 26 is an injection speed switching position detector, and 27 is an injection secondary pressure switching position detector, each of which includes a proximity switch, a limit switch, etc.

28 is an actuator of the position detector that moves together with the screw movable member 6.

FIG. 3 is a block diagram illustrating a control device, in which a central control device 29 for machine control equipped with a microprocessor and a memory device, and a DC electric servo motor 1 are shown.
9 and the servo motor control amplifier 30 connected to the tachometer generator 21, a speed command D-A converter 31 for converting the digital signal from the central control device 39 into an analog electric signal, and a torque command D -A converter 32 and servo motor 19
A forward/reverse rotation command circuit 33 is connected thereto.

The servo motor control amplifier 30 has a function of controlling forward/reverse rotation of the servo motor 19 as well as the upper limit values of rotation speed (speed), torque (current), etc. according to commands from the central control device 29, and controls the tachometer generator 21. The signal is fed back to perform constant speed control of the rotational speed (speed).

The central control device 29 also includes the position detector 2.
5 to 27, clutch coils 15 and 16, time setting devices T ₁ to T ₄ , △T, speed setting devices V ₁ , V ₂ , torque setting devices P ₁ , P ₂ , P ₃ , and pressure reduction value setting device △P Although not shown, an operating switch, a control amplifier for the screw back pressure control device 22, a speed setting device for screw rotation (metering), a torque setting device, etc. are also connected.

Next, a method of controlling the injection process will be explained. FIG. 4 is a control relationship diagram of injection speed and injection torque for explaining control of the injection process, and the horizontal axis indicates time.

When the measurement (material charge) is performed, the measurement stop position detector 25 is activated, and the conditions for transitioning to the injection process, such as the conditions for the completion of the measurement process and the conditions for the completion of mold clamping, are met,
The injection process begins by energizing the injection clutch 16.

When the time setter T ₁ is selected and the set time t ₁ has elapsed and the injection clutch is connected, the injection time starts to be counted, and the normal rotation command circuit of the motor rotation command circuit 33 is activated and the speed is set. vessel V ₁ ,
Torque setting device P ₁ is selected, and the digital signal corresponding to the set value is sent to the speed command DA converter 31 and the torque command DA converter 32 as command signals for the speed value and torque value, respectively. , the servo motor control amplifier 30 is commanded using analog values, and the motor rotates forward at injection speed command value υ ₁ and torque command value (torque upper limit value) P ₁ to start the filling process. The line between a and b in FIG. 4 is the injection clutch connecting process at the start of the injection process.

The filling process starts, and the injection speed switching position detector 2
When the screw reaches the operating position 6, the injection speed setting device _V2 is selected and the speed command value of the servo motor is changed to _υ2 . The period between b and c in FIG. 4 is the filling process.

The screw reaches the set value of υ ₂ and the injection advances further to continue the compression process. When the injection pressure secondary pressure switching position detector 27 is activated, it starts measuring the injection secondary pressure time and the torque setting device P ₂ is activated. selected, and the servo motor is controlled by the torque command value of _p2 . Between c and d in FIG. 4, the screw forms part of the compression process in the speed control region.

At point d in Fig. 4, in the balance between the servo motor trick command value P ₂ and the resin load in the mold that is being filled, the compression process continues and the load due to resin pressure increases. The speed control area switches to the torque control area and moves to the pressure holding process. The holding pressure becomes the value corresponding to the command of P ₂ , and the process moves to the holding pressure process. When the set time t ₃ of the time setting device T ₃ has elapsed, the servo motor for which the torque setting device P ₃ has been selected changes to the value of P ₃ . Controlled by the command value, the holding pressure becomes a value corresponding to the command _P3 , which becomes the tertiary pressure. The area between d and e in FIG. 4 includes a pressure holding process that includes a part of the compression process in the torque control area, and is also a secondary pressure control area.

When the set time t ₂ of the time setting device T ₂ has elapsed, the pressure holding process ends and the injection pressure decay control, that is, the injection pressure releasing process begins. The area between e and f in FIG. 4 is the tertiary pressure control area of the pressure holding process.

When the injection pressure release process starts, the calculation function of the microprocessor inside the central control device 29 sets the holding pressure command value _P3 to the setting set by the time setting device △T and the pressure reduction value setting device △P. Values △t and △p
will be gradually reduced by

In other words, when entering the injection pressure release process, the servo motor torque command value becomes p ₃ -△p, and then △t
As time elapses, the torque command value is further decreased by the value Δp from the previous torque setting value, and the torque command value is switched stepwise to 0, thereby controlling the injection pressure release process.

When the torque command value becomes 0, the speed command and forward rotation command of the servo motor are stopped, the injection clutch 16 is de-energized, and the set time t ₄ of the time setting device T ₄ is set.
The injection process ends after . Time setter T ₄
is used to set the time until the injection clutch 16 is released from demagnetization, and is a timing setting device necessary for moving to the next step, the metering step, etc.

In the above example, the speed command, normal rotation command, and torque command value are turned OFF when they reach 0, but the speed command may be turned OFF at point f, and depending on the size of the load, the servo It is also possible to release the pressure by using the regeneration control function of the motor control amplifier, and in this case, the speed command and forward rotation command may be turned off at point f. The period between f and g in FIG. 4 is an injection pressure release process, and the period between f and h is an injection clutch release process.

The above control explanation is for automatic operation and normal control conditions, but if a gate jam in the mold occurs during the injection process, the injection time will elapse and the injection process will be terminated. There may be times when the injection process is not normally transferred to the pressure holding process, and the central control device 29 is programmed to terminate the injection process after injection pressure release control even in such abnormal cases. . That is, when even one of the various vector lock conditions necessary for the injection process operation disappears during the injection process, stepwise pressure relief control is performed in the same way as the injection pressure relief control described above, based on the torque setting value at that time. Do. The microprocessor is programmed to terminate the injection process after the pressure relief process of the injection process.

As another example, in the servo motor control amplifier 30, a capacitor and a resistor are inserted into the torque command circuit only during the pressure release process, so that the torque command value immediately returns to 0 even if there is no external torque command. Injection pressure relief control may be performed using a control circuit with a time constant to prevent this from occurring. In this case, confirmation that the motor control torque has become 0 can be made by checking the time using a timer.

[Effects of the Invention] Since the present invention controls the injection process as described above, it has the following effects.

(1) Since the injection force is attenuated, even if the holding pressure is removed all at once, the injection screw will not move rapidly backwards, and the inside of the heating cylinder in front of the injection screw will not become negative pressure.

(2) Retraction control of the injection screw becomes easy, and measurement failure does not occur.

(3) Since the torque value of the servo motor can be electrically controlled to control the attenuation of the injection force, control can always be performed reliably.

(4) Since the entire process from the start of the injection process to the pressure holding process can be automatically and continuously controlled, operability is improved and the pressure in the final pressure holding process can be freely set.

[Brief explanation of drawings]

The drawings show an embodiment of the injection process control method for an electric injection molding machine according to the present invention, and FIG. 1 is a partially longitudinal front view of the electric injection molding machine, and FIG. 2 is a cross-sectional plan view of the injection device. , FIG. 3 is a block diagram of the control circuit, and FIG. 4 is a control relationship diagram for speed/torque setting. 1... Screw, 2... Heating cylinder, 5... Rotating shaft, 6...
Screw movable member, 14... Transmission shaft, 15, 16
...Clutch, 19...Servo motor, 21...Tachometer generator, 25...Measuring position detector, 26
... Injection speed switching position detector, 27... Injection pressure secondary pressure switching position detector, 28... Actuator, 29
...central control device, 30...servo motor control amplifier.

Claims (1)

[Claims] 1. When using a servo motor as a drive source and injecting molten resin by converting the rotational force of the servo motor into the thrust force of the injection screw using a screw mechanism, just before the end of the injection process, the torque value of the servo motor is changed over time. 1. An injection process control method for an electric injection molding machine, characterized in that the injection force is attenuated and controlled until the end of the injection process, and then the injection process is ended.