JP2793901B2 - In-line screw injection molding machine - Google Patents

Description

The present invention relates to an in-line screw type injection molding machine.

(Prior art) Conventionally, an injection molding machine that melts a resin by a screw, accumulates the molten resin in a front portion of a heating cylinder, and then injects the molten resin from a nozzle by advancing the screw is a method that melts and injects a material. Performed on the same axis, it is called an in-line screw type injection molding machine.

In this type of inline screw injection molding machine, the resin is transferred to the front of the heating cylinder while being melted by rotating the screw, and the screw is pushed back by the pressure of the resin during that time.

The molten resin is measured by the retreat distance of the screw that has been pushed back, and the rotation of the screw is stopped when the screw reaches a specified position.

Here, a suck back process is provided before the injection process. In the suckback step, the screw is retracted to a predetermined position to reduce the resin pressure, so that the resin accumulated in front of the screw does not leak from the nozzle.

In this case, the position of the screw is detected by a position detector, a proximity switch, and the like, and the injection cylinder is retracted until the screw reaches the set position. The control for this is performed by speed control with the screw speed as the control object.

(Problems to be Solved by the Invention) However, in the above-described conventional inline screw-type injection molding machine, when the screw is retracted to the suck-back position, the resistance changes depending on the type of resin and the resin melting temperature, so that an overrun occurs. Such as the suck back position varies.

As a result, not only does the injection start position vary and the molding stability is impaired, but if the overrun amount is too large, air is sucked in from the nozzle tip and is caught in the molten resin, resulting in poor molding. Cause.

The present invention solves the above-mentioned problems of the conventional in-line screw injection molding machine, and provides an in-line screw injection molding machine capable of improving the accuracy of screw position and improving molding stability. Aim.

(Means for Solving the Problems) For this purpose, in the in-line screw type injection molding machine of the present invention, a screw position detector for detecting a screw position during a suck back process and outputting a screw position actual value, and controlling A screw position setting device that outputs a screw position command value set based on the screw position actual value at the time of starting, and means for calculating a deviation between the screw position instruction value and the actual screw position value after control is started And means for receiving the deviation signal and controlled to move the screw.

In another in-line screw injection molding machine of the present invention, the means for moving the screw is a variable displacement pump for controlling a discharge pressure and a discharge flow rate.

(Operation) According to the present invention, in the in-line screw-type injection molding machine as described above, a screw position detector that detects a screw position during a suckback process and outputs a screw position actual value, and starts control. A screw position setting device that outputs a screw position command value set based on the screw position actual value at the time, and a means for calculating a deviation between the screw position instruction value and the screw position actual value after starting the control, Means for receiving the deviation signal and controlled to move the screw.

In this case, the actual screw position value at the start of the control is set as the screw position command value, and the actual screw position command value after the control is started is compared with the actual screw position command value. Can be

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

FIG. 1 is a schematic diagram of an in-line screw injection molding machine of the present invention.

In the figure, 1 is a heating cylinder, 2 is a heating cylinder 1
The screw 3, which is rotatably supported in the front and rear, is a space in front of the heating cylinder. When the screw 2 retreats, the resin is stored in the space in front of the heating cylinder. Reference numeral 4 denotes a resin supply port, and the resin naturally falls into the heating cylinder 1 via the resin supply port 4 in the measuring step.

Reference numeral 5 denotes an injection cylinder for moving the screw 2 back and forth, and has oil chambers 5b and 5c before and after the piston 5a. 6
Is a screw position detector for detecting the position of the screw 2 moved by the injection cylinder 5, 7 is an oil motor for rotating the screw 2, and 8 is a rotation speed detection for detecting the rotation speed of the oil motor 7. The container 9 is a nozzle for injecting resin.

Numeral 11 denotes an electromagnetic directional control valve connected to the oil chamber 5b of the injection cylinder 5, which drains oil in the oil chamber 5b to the tank 12 at the position I, and a variable displacement pump at the position II.
The oil from 14 is supplied to the oil chamber 5b. The variable displacement pump 14
Is capable of controlling pressure and flow rate, and has a flow rate controller 15.

Reference numeral 17 denotes an electromagnetic directional control valve which supplies oil from the variable displacement pump 14 to the oil chamber 5c of the injection cylinder 5 at an I position, drains the oil in the oil chamber 5c at a II position, and II
At the position I, the oil from the variable displacement pump 14 is supplied to the oil motor 7 and the oil in the oil chamber 5c is drained.

 Reference numeral 20 denotes a relief valve, and reference numeral 21 denotes a proportional electromagnetic relief valve.

In the in-line screw type injection molding machine having the above configuration, the resin supplied from the resin supply port 4 to the rear end of the heating cylinder 1 is sent forward by the rotation of the screw 2 and the heat from the heating cylinder 1 and is also heated and compressed. The molten resin is stored in the front space 3 of the screw 2.

At this time, the screw 2 is rotated by the oil motor 7, and the rotation speed detector 8 detects the rotation of the screw 2. Meanwhile, the injection cylinder 5 allows the screw 2 to rotate and moves in the axial direction.

The proportional electromagnetic relief valve 21 is for generating a back pressure when the screw 2 moves backward. After the completion of the measuring process, the electromagnetic directional control valve 11 forcibly retracts the screw 2 to perform suckback in order to lower the resin pressure in the front space 3 so that the resin does not leak from the nozzle 9.

FIG. 2 is a control block diagram of the in-line screw injection molding machine of the present invention.

In the figure, reference numeral 6 denotes a screw position detector, and a signal detected by the screw position detector 6 is sent to the control device 30. The control device 30 is configured by a device having an arithmetic function such as a microcomputer.

In the control device 30, the screw position detected by the screw position detector 6 is converted into a signal by the signal converter 32, and sent to the subtractor 34 as the actual screw position value x (t) and fed back.

On the other hand, the screw position setting device 31 calculates and sets the screw position command value as a function of time x _REF = f (t) based on x (t = 0) at the start of suckback control.

In the subtractor 34, the screw position command value x
A deviation symbol between _REF and the actual screw position value x (t) is calculated. Then, the deviation symbol is sent to the control compensation computing unit 35, and its output value is converted into a driving signal by the signal converter 37, and is input to the flow controller 15.

In the inline screw type injection molding machine having the above configuration, when the variable displacement pump 14, the flow rate controller 15, and the solenoid b of the electromagnetic directional switching valve 17 are driven, the variable displacement pump 14
Is discharged to the oil motor 7 via the electromagnetic direction switching valve 17 at the position III, and the oil motor 7 rotates.

When the oil motor 7 rotates, the screw 2
Is rotated, and the resin that has entered through the resin supply port 4 is subjected to mechanical shear while being sent forward, and is heated from the outside by a heater wound around the heating cylinder 2. As a result, the resin is plasticized and melted, and the heating cylinder 1
And the screw 2 is retracted.

When the screw 2 moves back to the preset weighing position,
Variable displacement pump 14, flow controller 15, solenoid directional control valve 17
Is released, and the flow rate process is completed.

Here, a suck-back process is started so that the resin stored in the front space 3 of the heating cylinder 1 does not leak from the nozzle 9.

That is, by driving the variable displacement pump 14, the flow rate controller 15, and the solenoid b of the electromagnetic directional control valve 11, the oil discharged by the variable displacement pump 14 is injected through the electromagnetic directional control valve 11 at the II position. The oil is supplied to the oil chamber 5b of the cylinder 5.
As a result, the screw 2 is forcibly retracted (suck back) to a preset suck back position, and the pressure of the resin in the front space 3 is reduced by controlling as follows.

Variable displacement pump 14, flow controller 15, solenoid directional control valve
When the b solenoid of No. 11 is driven and the suckback process starts, the actual screw position value x (t) sent from the screw position detector 6 is taken into the control device 30 via the signal converter 32. Then, the actual screw value x at the start of the control
Screw position command value x _REF = f (t) calculated and set based on (t = 0) and actual screw position value x (t)
Is calculated as the difference signal [x _REF −x (t)].

This deviation signal is input to the control compensation calculator 35, which performs a plurality of calculations including gain adjustment.

The control signal output via the control compensation calculator 35 and the signal converter 37 is input to the flow controller 15, and the discharge oil amount of the variable displacement pump 14 is controlled according to the control signal. Then, oil is sent to the oil chamber 5b of the injection cylinder 5, and the screw 2 fastened to the piston 5a of the injection cylinder 5 is retracted.

Here, the screw position setting device 31 calculates and sets a continuous signal from the current position of the screw 2 to a position where the suckback process is completed. When the screw 2 arrives at or near the suckback completion position, the deviation signal [ _xREF- x (t)] becomes equal to or less than a preset settling reference value.

| x _REF −x (t) | ≦ U U: Setting reference value At the same time, the control signal sent from the control device 30 becomes 0 output, and at the same time, the excitation of the solenoid b of the electromagnetic directional control valve 11 is released, and the suck back process is performed. Is completed.

The present invention can also be applied to the control of the suck-back step performed before the measurement.

Therefore, it is possible to improve the accuracy of the screw position and prevent the screw position during the suck back process from being varied even when the resistance of the resin changes according to the type and melting temperature of the resin, thereby improving the molding stability. Can be improved.

Then, while the screw moves from the position where the suck-back starts to the position where the suck-back ends, the retreat speed can be gradually reduced, so that the stability of the suck-back process can be improved.

Although the above embodiment describes the case where a proportional electromagnetic variable displacement pump that performs pressure / flow control is used, a constant displacement pump or a load sensing type variable displacement pump is used as a hydraulic drive source. The case can also be applied.

FIG. 3 is a hydraulic circuit diagram in an in-line screw type injection molding machine showing a second embodiment of the present invention.

In the drawing, reference numeral 5 denotes an injection cylinder provided for moving the screw 2 forward and backward, and is connected to a proportional electromagnetic flow control valve or servo valve 39 for suck back. The servo valve 39 is supplied with oil from a constant displacement pump or a load sensing type variable displacement pump 40.

Also in this case, a control device similar to the control device shown in FIG. 2 is provided, and the control device calculates a position command value x _REF which is a function of time, and detects the signal by the screw position detector 6 to perform signal conversion. The actual screw position value x (t) converted by the device 32 is fed back, and a deviation signal is calculated.

Then, the deviation signal is sent to the control compensation calculator 35, and the output value is input to the proportional electromagnetic flow control valve or the servo valve 39 via the signal converter 37, and the screw position control in the suck back process is performed. It has become.

Note that the present invention is not limited to the above embodiment,
Various modifications are possible based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

(Effects of the Invention) As described in detail above, according to the present invention, in an in-line screw type injection molding machine, a screw position detector that detects a screw position during a suck-back process and outputs a screw position actual value. A screw position setting device that outputs a screw position command value set based on the screw position actual value at the time of starting the control, and a screw position actual value after the screw position command value and the control are started. It has means for determining the deviation, and means for receiving the signal of the deviation and controlled to move the screw.

In this case, the actual screw position value at the start of the control is set as the screw position command value, and the actual screw position command value after the control is started is compared with the actual screw position command value. Can be

Therefore, it is possible to improve the accuracy of the screw position and prevent the screw position during the suck back process from being varied even when the resistance of the resin changes according to the type and melting temperature of the resin, thereby improving the molding stability. Can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an inline screw injection molding machine of the present invention, FIG. 2 is a control block diagram of the inline screw injection molding machine of the present invention, and FIG. 3 is an inline showing a second embodiment of the present invention. It is a hydraulic circuit diagram in a screw type injection molding machine. 1 ... heating cylinder, 2 ... screw 5 ... injection cylinder, 6 ... screw position detector, 7 ... oil motor, 11, 17 ... electromagnetic directional control valve, 14 ... variable displacement pump, 15 …… Flow controller, 31 …… Screw position setting device,
39 ... Servo valve.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B29C 45/46-45/50 B29C 45/76-45/82

Claims (2)

(57) [Claims] 1. A screw position detector for detecting a screw position during a suck-back process and outputting a screw position actual value, and (b) setting based on the screw position actual value at the time of starting control. A screw position setting device for outputting the set screw position command value; (c) means for calculating a deviation between the screw position command value and the actual screw position value after control is started; and (d) a signal for the deviation. Means for receiving and controlling the screw to move the screw. 2. The in-line screw injection molding machine according to claim 1, wherein the means for moving the screw is a variable displacement pump for controlling a discharge pressure and a discharge flow rate.