JPH0525869Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to an injection control device for an injection molding machine that controls injection using a variable discharge rate pump and an electromagnetic pressure control valve.

(Prior Art) In the injection process, the injection speed is controlled by controlling the discharge rate of a variable discharge rate pump, and the injection pressure is controlled by an electromagnetic pressure control valve. These control signals for the discharge amount and pressure were issued at the same time as the start of injection.

(Problem to be solved by the invention) However, in the case of a control device in which such an injection control signal is issued at the same time as the start of injection, the rising speed at the start of injection depends on the response speed of the variable displacement pump and the electromagnetic pressure control valve. Regulated.

For this reason, when molding requires a quick injection start-up, such as for thin-walled molded products, problems such as solidification of the molten resin and formation of short shots occur. For this reason, an accumulator is used to support high-speed injection, but it is costly and
The hydraulic circuit also had to be complicated.

(Means for Solving the Problem) In order to solve the problem, in the present invention, a screw is inserted into the heating cylinder, an injection cylinder is provided that allows the screw to move forward and backward, and a variable The discharge volume pump is connected to the oil passage, and an electromagnetic switching valve is provided in the middle of the oil passage, which cuts off the oil passage at a neutral position and opens the oil passage when the solenoid is energized, and connects the variable discharge volume pump and the electromagnetic switching valve. In an injection molding machine having an electromagnetic pressure control valve branched from the middle of an oil path, there is provided a pre-injection start signal output circuit that outputs a pre-injection start signal prior to the start of injection, and a circuit that outputs a pre-injection start signal simultaneously with the output of the pre-injection start signal. A timer for starting time measurement, and a discharge amount control signal for controlling the discharge amount of the discharging amount pump and the pressure of the electromagnetic pressure control valve to a predetermined state based on respective set values based on the pre-injection start signal. An injection control device characterized by having an output circuit, a pressure control signal output circuit, and a solenoid excitation output output circuit for energizing a solenoid of the electromagnetic switching valve to start injection based on a timing end signal of the timer. It is prepared.

(Function) Prior to the start of injection, a pre-injection start signal is generated, a timer is clocked by the pre-injection start signal, and during that time the discharge amount of the variable discharge amount pump and the pressure of the electromagnetic pressure control valve are maintained at a predetermined state. Since the injection process starts at the same time as the timer ends, the injection process starts instantly.

(Example) In order to clarify the present invention more specifically, the present invention will be described below with reference to the drawings showing an example.

In FIG. 1, 1 is a heating cylinder of an injection molding machine, and 2 is a screw fitted into the heating cylinder 1 so as to be rotatable and reciprocating.

3 is a hopper for storing raw materials to be supplied to the screw 2.

4 is an injection cylinder for moving the screw 2 forward and backward, and 4A is a piston of the injection cylinder 4. 4B is a forward oil chamber of the injection cylinder 4 defined by the piston 4A;
4C is a retreat side oil chamber.

5 is an oil motor for rotating the screw 2.

10 is a variable discharge amount pump as a hydraulic power source.

In this embodiment, it is in sliding contact with the heads of a plurality of pistons,
An axial piston variable displacement pump is used in which the displacement increases or decreases depending on the inclination of the swash plate that causes the piston to reciprocate.

Reference numeral 10A denotes a proportional solenoid valve of the variable discharge amount pump, which basically increases or decreases the discharge amount of the variable discharge amount pump 10 in proportion to its electromagnetic force. Although not shown in detail, the proportional solenoid valve 10
When a predetermined electrical input based on a set value is applied to A, the plunger of the proportional solenoid valve 10A strokes, and the pilot oil is supplied to the tank on the back side of the control piston opposing the spring across the swash plate. The amount of escape is changing. The greater the output of the proportional solenoid valve 10A, the greater the amount of pilot oil escaping into the tank, the control piston being defeated by the spring force, the amount of inclination of the swash plate increases, and the amount of discharge increases. Then, the swash plate is balanced at a position where there is no deviation between the feedback signal from the tilt amount detection sensor and the setting signal, and the discharge amount is determined.

11 is a sequence valve provided at the discharge port of the variable discharge amount pump 10.

Reference numeral 12 denotes a three-position, four-way electromagnetic switching valve provided in the middle of an oil passage connecting the secondary side of the sequence valve 11 and the forward-side oil chamber 4B of the injection cylinder 4. 12a and 12b are solenoids of the three-position, four-way electromagnetic switching valve, respectively. In the neutral position of the 3-position 4-way electromagnetic switching valve, the P port on the variable discharge amount pump 10 side is disconnected, and the A port on the forward side oil chamber 4B side of the injection cylinder 4 is disconnected.
The port and the T port on the tank side are in communication, and the remaining B port on the oil motor 5 side is disconnected. When the solenoid 12a is energized, the P port and the A port are connected, the B port and the T port are disconnected, and when the solenoid 12b is energized,
The P port and B port communicate with each other, and the A port and T port communicate with each other.

13 is a logic valve that can disconnect or adjust the opening between the inlet port and the outlet port depending on whether the pilot oil pressure is high or low;
It is installed in the middle of the oil path connecting the port and tank.

Reference numeral 14 denotes a pilot oil passage, to which pilot oil at an appropriate pressure is supplied as necessary from a pilot oil pressure source (not shown).

Reference numeral 15 denotes a two-position, four-way electromagnetic switching valve provided in the middle of an oil passage connecting the secondary side of the sequence valve 11 and the retreating side oil chamber 4C of the injection cylinder 4. 15a is a solenoid of the two-position four-way electromagnetic switching valve 15. The 2-position 4-way electromagnetic switching valve 15 has a neutral position in which the port on the variable discharge amount pump 10 side is disconnected, the port on the retreat side oil chamber 4C side of the injection cylinder 4 and the T port on the tank side are in communication, and the remaining 3 positions 4 The connection port between the A port of the directional electromagnetic switching valve 12 and the oil passage that joins the oil passage connecting the forward oil chamber 4B is disconnected. When the solenoid 15a is excited, the discharge side oil passage of the variable discharge amount pump 10 communicates with the retreat side oil chamber 4C of the injection cylinder 4, and the forward side oil chamber 4B communicates with the tank.

16 is a relief valve, and the sequence valve 11
The oil passage connecting the three-position four-way electromagnetic switching valve 12 is branched from the middle and is provided in a bleed-off state.

17 is a vent oil passage of the relief valve 16.

And 18 is an electromagnetic pressure control valve for venting the relief valve 16.

Reference numeral 19 denotes a two-position, four-way electromagnetic switching valve for appropriately switching between a vent oil passage and a pilot oil passage to the electromagnetic pressure control valve 18. 19a is a solenoid of the two-position four-way electromagnetic switching valve 19. In its neutral position, the two-position, four-way electromagnetic switching valve 19 communicates a vent oil passage between the relief valve 16 and the electromagnetic pressure control valve 18, and communicates the pilot oil passage 14 with the tank side. When the solenoid 19a is energized, the vent oil passage of the relief valve 16 is shut off, and the pilot oil passage 14 is connected to the electromagnetic pressure control valve 18.

In this embodiment, a logic valve 13 and a 2-position 4-way electromagnetic switching valve 19 are provided in order to enable particularly precise control of the screw back pressure during plasticization. The pressure is controlled by the relief valve 16 at the time of injection.
is configured to be vent-controlled by the electromagnetic pressure control valve 18.

Of course, as is generally done, the relief valve 16 itself may be an electromagnetic pressure control valve to control the injection pressure and the back pressure during plasticization. In this case, the logic valve 13 and the 2-position 4-way electromagnetic switching valve 19 can be omitted.

20 is a main control section of the control device, 21 is a sequence control section, 22 is a process control section, and 23 is an output section. The input section, memory section, setting section, etc. are omitted from illustration.

The sequence control section 21 has a pre-injection start signal output circuit that outputs a pre-injection start signal prior to injection, and a timer that starts timing at the same time as the output of the pre-injection start signal. Of course, it has a start signal output circuit for the plasticization metering process and all other sequence circuits necessary to carry out a normal molding cycle.

The process control section 22 includes an output of the proportional solenoid valve 10A and an electromagnetic pressure control valve for controlling the discharge amount of the variable discharge amount pump 10 based on the respective set values based on the instruction signal from the sequence control section 21. It has a discharge amount control signal output circuit and a pressure control signal output circuit for controlling the pressure of 18 to a predetermined state.

The output unit 23 excites the solenoid 12a of the 3-position, 4-way electromagnetic switching valve 12 to start injection based on the timing end signal of a timer that starts timing at the same time as the output of the pre-injection start signal of the sequence control unit 21. It has a solenoid excitation output output circuit. Further, the output section 23 outputs the solenoid 12 according to the instruction signal from the sequence control section 21.
Each of the solenoid excitation output output circuits and the like is provided for outputting a solenoid excitation output to each of the solenoid excitation output circuits b, 15a, and 19a.

The main control section 20 coordinates calculations and controls among the sequence control section 21, the process control section 22, the output section 23, and the like.

Next, the operation will be explained.

In the state shown in FIG. 1, the screw is at its forward limit and the control system is in a neutral state. First, the plasticizing and measuring process will be explained.

In response to the plasticization metering process start signal from the sequence control unit 21, the solenoid 1 is activated from the output unit 23.
A solenoid excitation output is output to each of 2b and 19a, and the proportional solenoid valve 10A of the variable discharge rate pump 10 is output from the discharge rate control signal output circuit of the process control unit 22, and the electromagnetic pressure control valve 18 is output from the pressure control signal output circuit. A control signal based on the set value is output to each of them.

In this case, the set value is the rotation speed of the oil motor 5 determined by the discharge amount of the variable discharge amount pump 10, that is, the rotation speed of the screw 2, and the electromagnetic pressure control valve 18.
This is the set value of the back pressure of the screw 2 determined by the pressure of .

Control oil discharged from the variable discharge amount pump 10 passes through a Siemens valve 11 and reaches a three-position, four-way electromagnetic switching valve 12. The 3-position 4-way electromagnetic switching valve 12
Since the solenoid 12b is energized, the control oil is introduced into the oil motor 5, and the oil motor 5 and thus the screw 2 rotate at a predetermined number of rotations.

The raw resin supplied from the hopper 3 is transferred to the front of the heating cylinder 1 by the rotating screw 2,
On the way, it is plasticized and melted by heat transfer from the heating cylinder 1 and its own shear heat generation, and is stored at the tip of the screw 2.

As the plasticized and molten raw material resin is stored at the tip of the screw 2, the screw 2 moves back, but at this time, an appropriate oil pressure (usually about 5 to 10 kg/cm ^{2 )} is applied to the forward side oil chamber 4B of the injection cylinder 4. ) to apply back pressure to the screw 2.

In this embodiment, the opening degree of the logic valve 13 is controlled by controlling the pressure in the pilot oil passage 14 to a predetermined pressure using the electromagnetic pressure control valve 18, and the oil in the forward side oil chamber of the injection cylinder 4 is transferred to the tank. By controlling the amount of escape, the pressure in the forward oil chamber 4B is controlled.

When the plasticization, melting, and storage of the raw resin progresses in this way, and a predetermined amount of molten resin is stored at the tip of the screw 2, a detection device such as an encoder or limit switch confirms the position of the screw 2 at that time. By stopping the rotation of the screw 2, the plasticizing and measuring process is completed.

Next, the injection process will be described.

Although not shown, on the mold clamping device side, the movable mold attached to the movable platen is closed against the fixed mold attached to the fixed platen, and the pressure is further increased to a predetermined mold clamping pressure to complete mold clamping. .

Then, the injection process begins and injection, that is, the advancement of the screw 2, is started, but in the present invention, a pre-injection start signal is output from the pre-injection start signal output circuit of the sequence control section 21 prior to the start of injection. It's becoming like that.

Simultaneously with the output of the pre-injection start signal, the timer in the sequence control section 21 starts measuring time. In this embodiment, the timer is provided in the sequence control section 21 as a variable timer whose set time can be adjusted.
The main control unit 20 may be provided with a fixed timer of approximately 0.1 to 0.2 seconds.

In response to the pre-injection start signal, a set value is sent to each of the proportional solenoid valve 10A of the variable discharge rate pump 10 from the discharge rate control unit signal output circuit of the process control unit 22 and the electromagnetic pressure control valve 18 from the pressure control signal output circuit. A control signal based on this is output.

The set value in this case is the piston 4 of the injection cylinder 4 determined by the discharge amount of the variable discharge amount pump 10.
This is the set value of the injection pressure determined by the forward speed of A, that is, the injection speed of the screw 2 and the pressure of the electromagnetic pressure control valve 18. The first outputs from the discharge amount control signal output circuit and the pressure control signal output circuit are the settings for the initial (in the case of multi-stage program control, the first stage) injection speed and initial injection pressure. It is a value-based control signal.

The variable discharge amount pump 10 is neutral and discharges a very small amount, but the discharged oil is 20Kg/cm ²
The flow to the secondary side is blocked by the sequence valve 11 set at a certain level, and the water escapes from the case drain to the tank inside the pump.

Now, from the discharge amount control signal output circuit of the process control unit 22 to the proportional solenoid valve 1 of the variable discharge amount pump 10.
When a control signal based on the initial injection speed is input to 0A, the proportional solenoid valve 10
The plunger A strokes, the amount of inclination of the swash plate changes accordingly, and the discharge amount is determined.

The discharged oil then passes through the sequence valve 11 to the 3-position, 4-way electromagnetic switching valve 12, and is blocked on the primary side of the 3-position, 4-way electromagnetic switching valve 12, which is in a neutral state.

The 2-position 4-way electromagnetic switching valve 19 is also in a neutral state, and the oil discharged between the variable discharge amount pump 10 and the 3-position 4-way electromagnetic switching valve 12 is controlled by the electromagnetic pressure control valve 18.
The pressure rises to the initial injection pressure by the relief valve 16 which is vent-controlled.

In the sequence control unit 21, the timer that had started timing at the same time as the output of the pre-injection start signal ends its timing. That is, during the timing of the timer, the delay in the startup response of the variable displacement pump 10, the electromagnetic pressure control valve 18, etc. is eliminated, and the oil path from the variable displacement pump 10 to the 3-position, 4-way electromagnetic switching valve 12 is The control state corresponding to the initial injection speed and injection pressure is completed.

In response to the timing end signal of the timer in the sequence control section 21, an output for exciting the solenoid 12a of the 3-position 4-way electromagnetic switching valve 12 is output from the solenoid excitation output output circuit of the output section 23.

At the P port of the 3-position 4-way electromagnetic switching valve 12,
In a predetermined control state, the discharged oil of the variable discharge amount pump, which has been blocked, is instantaneously introduced into the forward oil chamber 4B of the injection cylinder 4, and injection starts with virtually no response delay.

Since the response delay of the variable discharge amount pump 10 is eliminated, the cavity filling speed of molten resin can be made sufficiently high from the beginning, and thin-wall molding can be performed without the need for an accumulator. be.

When the injection process is completed, the plasticizing and metering process begins again in preparation for the next cycle of injection.

In addition, when it is necessary to move the screw 2 backward for back-back or other reasons, the solenoid 15a of the 2-position 4-way electromagnetic switching valve 15 is energized from the output section 23 in response to an instruction signal from the sequence control section 21, although detailed explanation will be omitted. By outputting the output, the oil discharged from the variable discharge amount pump 10 is introduced into the retreat side oil chamber 4C of the injection cylinder 4, and the forward side oil chamber 4B is made to communicate with the tank.

(Effects) Since the delay in the rise response of the variable discharge amount pump and the electromagnetic pressure control valve is eliminated prior to injection, the cavity filling speed of the molten resin can be made sufficiently high from the beginning.

Therefore, it is possible to handle molding that requires a quick injection start-up, such as thin-wall molding, for example, without the need for an accumulator.

[Brief explanation of drawings]

FIG. 1 is a block diagram of essential parts for explaining one embodiment of the present invention. 1...Heating tube, 2...Screw, 4...Injection cylinder, 10...Variable discharge amount pump, 10A...
Proportional solenoid valve, 12...3 position 4-way solenoid switching valve,
16... Relief valve, 17... Vent oil path, 18
... Solenoid pressure control valve, 20 ... Main control section, 21
... sequence control section, 22 ... process control section, 23 ... output section.

Claims (1)

[Scope of utility model registration request] A screw is inserted into the heating cylinder, an injection cylinder is provided that allows the screw to move forward and backward, the injection cylinder and a variable displacement pump are connected through an oil path, and the oil path is connected at a neutral position in the middle of the oil path. In an injection molding machine equipped with an electromagnetic switching valve that opens when the solenoid is energized and an electromagnetic switching valve that opens when the solenoid is energized, and an electromagnetic pressure control valve that branches off from the middle of the oil path connecting the variable discharge amount pump and the electromagnetic switching valve, injection starts. a pre-injection start signal output circuit that outputs a pre-injection start signal prior to the pre-injection start signal; a timer that starts timing at the same time as the output of the pre-injection start signal;
A discharge rate control signal output circuit and a pressure control signal output circuit for controlling the discharge rate of the variable discharge rate pump and the pressure of the electromagnetic pressure control valve to predetermined states based on respective set values by the pre-injection start signal. An injection control device comprising a solenoid excitation output circuit for energizing a solenoid of the electromagnetic switching valve to start injection based on a timing end signal of the timer.