JP2628753B2 - Screw retreat speed control device for injection molding machine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a screw retreat speed control device for an injection molding machine.

(Prior art) Conventionally, a molding material heated and fluidized in a heating cylinder is injected into a mold by high pressure, cooled and solidified or hardened therein, and then the mold is opened to take out a molded product. There is a screw-type machine that performs injection molding by moving a screw in the heating cylinder back and forth.

FIG. 5 is a diagram showing a control device of the conventional injection molding machine.

In the figure, a screw 2 is supported inside a heating cylinder 1 of an injection molding machine so as to be freely rotatable and forward and backward.
It is connected to a drive system composed of a hydraulic cylinder 3 and a hydraulic motor 4, and is rotated and moved forward and backward by the drive system.

The screw 2 in FIG. 5 is in a state where the injection molding shot has been completed. Here, prior to the next shot, the operation of melting and plasticizing the molding material 5 and storing it at the tip of the head, that is, weighing is performed. In the measuring step, the screw 2 is driven and rotated by the hydraulic motor 4, and at this time,
The molding material 5 dropped and supplied from the material supply port 10 is melt-plasticized in the heating cylinder 1 while moving forward in the groove 6 by the rotation of the screw 2, and is stored at the front end of the screw 2. The pressure of the molding material 5 in the heating cylinder 1 generated by the melt plasticization becomes a reaction force against the screw 2, and the screw 2 retreats to a preset position by the reaction force.

The molding material 5 stored at the front end of the screw 2 is injected into the cavity 9 of the mold 8 from the nozzle 7 by pushing the screw 2 forward by the hydraulic cylinder 3.

Further, after the injection step is completed, to compensate for the cooling and shrinkage of the molding material 5 in the cavity 9,
A fixed injection oil pressure is applied, but when this pressure-holding step is completed, the screw 2 is rotated again and the metering is performed.

Here, in the conventional injection molding machine, the injection speed of the screw 2 is used during the injection process, the switching pressure is set when the injection process is shifted to the pressure-holding process, and the hydraulic cylinder 3 is held during the pressure-holding process. The screw speed and screw back pressure, ie the hydraulic cylinder 3
A method is employed in which feedback control is performed in accordance with the screw position and time set in advance by the hydraulic pressure in the inside. The switching from the injection step to the pressure holding step includes a method of setting the hydraulic pressure in the cylinder in advance as described above and a method of setting the screw position in advance.

For this purpose, the control device of the injection molding machine is provided with a screw speed controller 12 and an injection speed controller 13,
A pressure holding regulator 14 and a screw back pressure regulator 15 are provided to be switchable by a switch 16. Then, these adjusters 12, 13, 14, 15 actuate the servo valves 17, 18 to drive the hydraulic motor 4 and the hydraulic cylinder 3. Further, a screw tachometer 19, a speed detector 20, and a pressure detector 21 are provided for feedback control, and the screw rotation speed, screw speed, and oil pressure in the injection cylinder 3 detected by the screw tachometer 19 are adjusted by the respective regulators 12. , 13,14,15. These controls are performed in accordance with the program set by the program setting unit 22.

It should be noted that a digital displacement detector 23 is provided to control the oil pressure and the number of revolutions according to the set value of the screw position.

(Problems to be Solved by the Invention) However, in the screw retreating degree control device of the injection molding machine having the above configuration, the screw speed and the hydraulic pressure in the injection cylinder 3 are adjusted by the regulators 12, 14, 15 during the measuring process. Is fed back to and control is performed,
The screw retreat speed is not constant in each cycle, and the screw retreat time, that is, the measuring time varies.

As a result, each cycle becomes unstable, and it becomes difficult to operate the injection molding machine stably and continuously.

The present invention solves the problem of the above-described conventional screw retreat speed control device of an injection molding machine, and in the metering process, the screw retreat speed is kept constant in each cycle even when the screw back pressure is feedback-controlled. Can be
An object of the present invention is to provide a screw retreat speed control device for an injection molding machine, which can prevent variations in a screw retreat time and a measuring time.

(Means for Solving the Problems) For this purpose, in the screw retreat speed control device for an injection molding machine according to the present invention, a screw is provided on one side of a piston, and a rod is formed on the other side. An injection cylinder having an oil chamber formed on each side of the injection cylinder, a first servo valve for supplying pressure oil to an oil chamber on the screw side of the injection cylinder, and a hydraulic oil in the oil chamber on the rod side of the injection cylinder. A second servo valve for supplying a reference screw, a program setting device for storing a reference screw retreat speed pattern, a speed detector for detecting the screw retreat speed,
A screw retreat speed adjuster that controls the first servo valve based on the reference screw retreat speed pattern and the detected retreat speed to adjust the screw retreat speed;
It has a pressure detector for detecting the pressure of the oil chamber on the rod side, and a screw back pressure regulator for controlling the second servo valve based on the detected pressure to adjust the screw back pressure.

(Operation) According to the present invention, in the screw retreat speed control device for an injection molding machine as described above, a screw is provided on one side of a piston, and a rod is formed on the other side. An injection cylinder having an oil chamber formed on the rod side, a first servo valve for supplying pressure oil to the oil chamber on the screw side of the injection cylinder, and a supply of pressure oil to the oil chamber on the rod side of the injection cylinder. A second servo valve, a program setting device for storing a reference screw retreat speed pattern, a speed detector for detecting the screw retreat speed, and a reference screw retreat speed pattern and the detected retreat speed. A screw retreat speed adjuster for controlling the first servo valve to adjust the screw retreat speed, a pressure detector for detecting the pressure of the oil chamber on the rod side, A screw back pressure adjuster that controls the second servo valve based on the obtained pressure and adjusts the screw back pressure.

In this case, in the metering step, when the screw is retracted, the screw back pressure regulator controls the second servo valve based on the pressure in the rod-side oil chamber detected by the pressure detector, and controls the screw. Adjust back pressure.

Further, the screw retreat speed adjuster controls the first servo valve based on the reference screw retreat speed pattern and the screw retreat speed detected by the speed detector to adjust the screw retreat speed.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

A screw retreat speed control device of an injection molding machine according to the present invention will be described with reference to FIGS.

FIG. 1 is a control block diagram of a screw retreat speed control device for an injection molding machine of the present invention, FIG. 2 is a diagram showing a relationship between a screw stroke and a screw rotation speed, FIG. 3 is a diagram showing a relationship between a screw stroke and a screw retreat speed, and FIG. FIG. 5 is a diagram showing the relationship between time and screw retreat speed.

In the drawing, the screw 2 is moved forward and backward by an injection cylinder 3 and rotated by a hydraulic motor 4 in the same manner as the control method implemented in the conventional injection molding machine. The injection cylinder 3 has a screw 2 disposed in front of a piston 3c and a rod 3d formed rearward. Oil chambers 3a and 3b are formed before and after the piston 3c, and the oil chamber 3a is connected to the oil chamber 3a via a first servo valve 31.
Is supplied with pressure oil via a second servo valve 18.

The injection cylinder 3 is operated by an injection speed adjuster 13, a holding pressure adjuster 14, a screw back pressure adjuster 15, and a screw retreat speed adjuster 32, and the hydraulic motor 4 is operated by a screw speed adjuster 12. .

The injection speed controller 13 has the screw speed detected by the speed detector 20, and the screw rotation speed controller 12 has the screw rotation speed detected by the screw tachometer 19, and the pressure holding regulator 14. And the screw back pressure regulator 15 has a pressure detector 21
The feedback of the injection pressure detected by the above is fed back to the screw retreat speed adjuster 32 with the retreat speed of the screw 2 detected by the speed detector 20.

Here, in the screw retreat speed control device of the injection molding machine of the present invention, the servo valve 31 is controlled by the screw retreat speed adjuster 32, and the pressure oil adjusted by the servo valve 31 is supplied to the oil chamber 3a. Is done. As described above, the injection cylinder 3 is a double-acting type having oil chambers 3a and 3b on both sides of a piston 3c.

Then, the pressure oil adjusted by the screw retreat speed adjustment supply 32 is supplied to the oil chamber 3a on the side where the screw 2 is provided, and the injection cylinder 3 is operated by the pressure oil to retreat the screw 2.

In the injection molding machine, the screw speed is adjusted by the injection speed adjuster 13 in the injection step in the same manner as in the conventional control method. Further, during the transition from the injection step to the pressure holding step, nozzle pressure control is performed by the pressure detector 26, and in the pressure holding step, the pressure detector 26
Is fed back to the pressure keeping regulator 14 and the screw back pressure regulator 15 for control. Further, in the weighing process, the retreat speed of the screw 2 detected by the speed detector 20 is fed back to the screw retreat speed adjuster 32 so that the screw is set to the reference screw retreat speed pattern set in the program setting unit 22. Adjust the retreat speed.

Next, a control method of the screw retreat speed control device of the injection molding machine according to the present invention will be described.

In the program setting unit 22, the screw rotation speed corresponding to the screw stroke is set by a weighing program set by the operator. That is, between the strokes S ₀ and S ₁ , the screw rotation speed of N ₁ is set to S ₁ , S ₂
A screw speed of N ₂ in between, in between S _2, S ₃ N
The screw speed is set to ₃ . Incidentally, the stroke S ₀ metering start position, the stroke S ₃ shows the measurement ending position.

In the case of performing weighing by the weighing program, a screw retreat speed pattern is first obtained at the time of purging for trial hitting of the resin, and if this operation is performed until purging is stabilized, a reference screw retreat speed pattern is obtained.

The reference screw retreat speed pattern is shown by the working line in FIG. FIG. 3 shows the screw retreat speed (V _B ′) in each stroke.

FIG. 4 shows the reference screw retreat speed pattern created by the screw retreat speed at each time. The reference screw retreat speed pattern is made into a table by comparing the screw retreat speed V _B ′ for a number of sampling times, and the table is stored in the RAM area of the program setting device.

On the other hand, the current screw retreat speed is detected at each sampling time (indicated by a broken line in FIG. 4), and is compared with the screw retreat speed stored in the table to obtain a deviation e.

The screw evacuation speed adjuster 32 is actuated by the deviation e, the operation amount u of the servo valve 31 is determined, a command is sent to the servo valve 31, and the screw evacuation speed pattern shown by the dashed line is replaced by the solid screw evacuation speed pattern. Will be modified to

It should be noted that the present invention is not limited to the above embodiments, and various modifications are possible based on the gist of the present invention, and they are not excluded from the scope of the present invention.

(Effects of the Invention) As described above in detail, according to the present invention, in a screw retreat speed control device of an injection molding machine, a screw is provided on one side of a piston, and a rod is formed on the other side, An injection cylinder in which an oil chamber is formed on the screw side and the rod side of the piston, and a first servo valve for supplying pressure oil to the oil chamber on the screw side of the injection cylinder;
A second servo valve for supplying pressure oil to the oil chamber on the rod side of the injection cylinder, a program setting device for storing a reference screw retreat speed pattern, a speed detector for detecting the screw retreat speed, A screw retreat adjusting device that controls the first servo valve based on the screw retreat speed pattern and the detected retreat speed to adjust the screw retreat speed, and a pressure detector that detects a pressure in the rod-side oil chamber. And the second based on the detected pressure.
And a screw back pressure regulator for controlling the back pressure of the screw.

In this case, in the metering step, when the screw is retracted, the screw back pressure regulator controls the second servo valve based on the pressure in the rod-side oil chamber detected by the pressure detector, and controls the screw. Adjust back pressure.

Further, the screw retreat speed adjuster controls the first servo valve based on the reference screw retreat speed pattern and the screw retreat speed detected by the speed detector to adjust the screw retreat speed.

In this case, while adjusting the screw back pressure based on the pressure of the oil chamber on the rod side of the injection cylinder, it is possible to adjust the retreat speed of the screw based on the pressure of the oil chamber on the screw side of the injection cylinder. The screw retraction speed does not fluctuate due to the fluctuation of the back pressure.

Therefore, the screw retreat speed can be made constant in each cycle, and it is possible to prevent variations in the screw retreat time and the metering time.

[Brief description of the drawings]

1 is a control block diagram of a screw retreat speed control device for an injection molding machine according to the present invention, FIG. 2 is a diagram showing a relationship between a screw stroke and a screw rotation speed, FIG. 3 is a diagram showing a relationship between a screw stroke and a screw retreat speed, and FIG. FIG. 5 is a diagram showing a relationship between time and screw retreat speed, and FIG. 5 is a diagram showing a control device of a conventional injection molding machine. 1 ... heating cylinder, 2 ... screw, 3 ... hydraulic cylinder, 3a, 3b ... oil chamber, 3c ... piston, 3d ... rod, 4 ... hydraulic motor, 5 ... molding material, 6 ... Groove, 7
… Nozzle, 8… Mold, 9… Cavity, 12… Screw speed regulator, 13… Injection speed regulator, 14… Holding pressure regulator, 15… Screw back pressure regulator, 17 , 18,31 …… Servo valve, 19 …… Screw tachometer, 20 …… Speed detector, 21
…… Pressure detector, 22 …… Program setting device, 32 …… Screw retreat speed controller.

Claims (1)

(57) [Claims] 1. An injection cylinder in which a screw is disposed on one side of a piston, a rod is formed on the other side, and oil chambers are formed on the screw side and the rod side of the piston, respectively. A first servo valve for supplying pressure oil to a screw-side oil chamber of the injection cylinder; (c) a second servo valve for supplying pressure oil to a rod-side oil chamber of the injection cylinder; A program setting unit for storing a reference screw retreat speed pattern; (e) a speed detector for detecting the screw retreat speed; and (f) a speed detector based on the reference screw retreat speed pattern and the detected retreat speed. (G) a pressure detector for detecting the pressure in the oil chamber on the rod side, and (h) a pressure detector for detecting the pressure in the oil chamber on the rod side. Based A screw back pressure regulator for controlling the second servo valve to adjust the back pressure of the screw.