JPH07290549A - Hydraulic circuit of injection molding machine - Google Patents

Abstract

PURPOSE:To obtain an arbitrary flow rate characteristic by providing a control unit controlling the operation pressure of a pressure reducing valve on the basis of the output signal of a pressure sensor detecting the load pressure of an actuator. CONSTITUTION:When the detection pressure of a pressure sensor 27 is inputted to a control unit 34, the control unit 34 operates the sum of the detection pressure of the pressure sensor 27 and the pressure difference set to a valve differential pressure setting device 32. It is judged whether the pressure is larger than the upper limit pressure value set to a command pressure upper limit setting device 33 and, in the case of YES, the pressure lowered to the upper limit value is outputted to an electromagnetic proportional relief valve 11 and, in the case of NO, the pressure is outputted to the valve 11 as it is. As a result, a pressure reducing valve 5 functions as a pressure reducing type pressure compensation valve so that the pressure on the downstream side of the valve 5 becomes load pressure + set pressure difference and an arbitrary flow rate characteristic can be obtained with respect to load pressure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic circuit of an injection molding machine.

[0002]

2. Description of the Related Art The applicant of the present invention has developed a hydraulic circuit for an injection molding machine shown in FIG. 5 (Japanese Utility Model Publication No. 5-25870). A hydraulic circuit of this injection molding machine includes a pressure reducing valve 5 in a main pipe line 3 between an accumulator 4 as a hydraulic pressure source and an actuator 2 such as a cylinder which receives a supply of hydraulic oil from the accumulator 4 and operates a screw or the like. , The pressure compensating valve 6, and the electromagnetic flow rate adjusting valve 7, and the pressure conduit 8 is connected to the pressure conduit 8 connecting the vent port of the pressure compensating valve 6 to the secondary side (downstream side) of the flow adjusting valve 7. An electromagnetic switching valve 9 that opens and closes is provided. Reference numeral 1 is a hydraulic pump.

In the hydraulic circuit of this injection molding machine, when the pressure line 8 is opened by the electromagnetic switching valve 9, the pressure on the secondary side of the flow rate adjusting valve 7, that is, the load pressure of the actuator 2 is the spool of the pressure compensating valve 6. Since it is applied to the side of the spring 6a, the pressure difference before and after the flow rate adjusting valve 7 is kept constant (a value corresponding to the force of the spring 6a) by the pressure compensating valve 6. Therefore, the actuator 2 advances the screw at a constant speed and injects the resin regardless of the change in the load. Controlling the injection process in this way forces the resin into the mold,
Problems such as warpage are likely to occur in the molded product.

When the pressure pipe 8 is closed by the switching valve 9,
The pressure compensating function of the pressure compensating valve 6 is lost, and the pressure on the primary side (upstream side) of the flow rate adjusting valve 7 is the vent line 10 of the pressure reducing valve 5.
It is fixed to the set pressure of the pressure reducing valve 5 which is remotely operated by the electromagnetic proportional relief valve 11 provided in the. Therefore, even if the opening degree of the flow rate adjusting valve 7 is constant, the pressure difference before and after the flow rate adjusting valve 7 changes due to the change in the load pressure of the actuator 2, and the flow rate of the hydraulic oil supplied to the actuator 2 increases or decreases. For example, the forward speed of the screw changes.
As a result, an injection operation in which the speed is low during filling in a portion having a high resistance in the mold and becomes high in the opposite case is automatically obtained, and problems such as warpage are eliminated.

[0005]

According to the hydraulic circuit of the above-mentioned injection molding machine, two kinds of control methods can be freely selected by switching the electromagnetic switching valve 9, but an arbitrary flow rate characteristic can be obtained. I can't. Further, when the switching valve 9 shuts off the pressure conduit 8 and the function of the pressure compensating valve 6 is lost, the flow rate adjusting valve 7 becomes a mere throttle valve, so that it is vulnerable to disturbance such as being easily influenced by the oil temperature. , The repeatability is poor and there are complaints.

One object of the present invention is to provide a hydraulic circuit of an injection molding machine which can obtain an arbitrary flow rate characteristic.

Another object of the present invention is to provide a hydraulic circuit of an injection molding machine which is resistant to disturbance and has good repeatability.

[0008]

In order to achieve the above object, the present invention provides a main pipe between an accumulator as a hydraulic pressure source and an actuator which receives a supply of hydraulic oil from the accumulator and operates a screw or the like. The load pressure of the actuator is detected in the hydraulic circuit of the injection molding machine in which a pressure reducing valve for reducing the pressure of the hydraulic oil and a flow rate adjusting valve for adjusting the flow rate of the hydraulic oil passing through the pressure reducing valve are provided in the passage. A pressure sensor and a control device for controlling the operating pressure of the pressure reducing valve based on the output signal of the pressure sensor are provided. The hydraulic source may be a hydraulic pump.

In the hydraulic circuit of the injection molding machine, an electromagnetic proportional relief valve for controlling the operating pressure of the pressure reducing valve controlled by the control device may be provided in the vent line of the pressure reducing valve. In addition, a pressure compensating valve is provided in a branch pipe branched from the vent pipe between the pressure reducing valve and the electromagnetic proportional relief valve, a pilot line thereof is provided on the secondary side of the pressure reducing valve, and a vent port is provided as a first pressure line. 2 of the flow control valve by
It is also possible to adopt a configuration in which they are connected to the secondary side, respectively, and the vent port of the pressure compensating valve is cut off from the primary side of the pressure reducing valve by blocking the first pressure pipeline at the first position in the first pressure pipeline. It is also possible to provide a switching valve that connects to the branched second pressure line and opens the first pressure line at the second position to shut off the second pressure line.

[0010]

The pressure sensor detects the load pressure of the actuator and outputs it to the control device. The control device controls the operating pressure of the pressure reducing valve based on the output signal of the pressure sensor. Therefore, an arbitrary flow rate characteristic can be obtained by changing the control content of the control device. In the case where the vent line of the pressure reducing valve is provided with an electromagnetic proportional relief valve that changes the operating pressure of the pressure reducing valve under the control of a control device, the operating pressure of the pressure reducing valve can be indirectly controlled by remote control. become.

When the pressure compensating valve is provided, the pressure difference before and after the flow rate adjusting valve can be kept constant without using a control device. Further, if a switching valve is provided in the pressure conduit of the pressure compensating valve, the operation of the pressure compensating valve can be easily switched by the switching valve.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a hydraulic circuit of an injection molding machine according to the present invention will be described with reference to FIG. The same members as those in FIG. 5 are designated by the same reference numerals, and detailed description thereof will be omitted.

The pressure compensating valve 21 is provided in a branch pipe 22 which is branched from the vent pipe line 10 between the pressure reducing valve 5 and the electromagnetic proportional relief valve 11, and the pilot pipe line 23 is connected to the pressure reducing valve 5 of the pressure reducing valve 5. The main flow path 3 on the next side and the vent port 21b are connected to the electromagnetic flow control valve 7 by the pressure line 24.
Each is connected to the main pipe 3 on the next side. An electromagnetic switching valve 25 is provided on the pressure line 24. When the solenoid is excited, the solenoid operated directional control valve 25 has a pressure line 24.
And the vent port 21b of the pressure compensating valve 21 is connected to another pressure line 2 which is branched from the main line 3 on the primary side of the pressure reducing valve 5.
6 and when the solenoid is demagnetized, the pressure line 24 is opened and the other pressure lines 26 are shut off as shown in FIG.

A pressure sensor 27 is provided in the main pipe line 3 on the secondary side of the flow rate adjusting valve 7. Pressure sensor 27
Is for detecting the pressure of the hydraulic oil on the secondary side of the flow rate adjusting valve 7 (the load pressure of the actuators 2, 28), and the detection signal thereof is transmitted via the pressure sensor input circuit 29 to the arithmetic circuit 30.
Output to.

The arithmetic circuit 30 includes a pressure sensor input circuit 2
9, a proportional valve output circuit 31, a valve differential pressure setting device 32,
Also, the command pressure upper limit setter 33 is connected, and the proportional valve output circuit 31 is connected to the solenoid of the electromagnetic proportional relief valve 11. The valve differential pressure setting device 32 sets the pressure difference between the primary side and the secondary side of the flow rate adjusting valve 7, and the arithmetic circuit 30.
Outputs a control signal to the proportional valve output circuit 31 in accordance with the detection signal of the pressure sensor 27 so that the pressure difference set by the valve differential pressure setting device 32 is obtained, and the electromagnetic proportional relief valve 11
To control.

The command pressure upper limit setter 33 includes an arithmetic circuit 30.
The maximum pressure value output from the solenoid to the electromagnetic proportional relief valve 11 is set, and it is possible to regulate the maximum pressure corresponding to a molded product, a mold or the like. The arithmetic circuit 30, the pressure sensor input circuit 29, the proportional valve output circuit 31, and the valve differential pressure setting device 32 constitute a control device 34. The actuator 2 is used, for example, for forward and backward movement of a screw, and the other actuator 28 is used, for example, for mold clamping, and a hydraulic device (not shown) such as a direction switching valve is provided in each of these pipelines. ing.
The actuators 2 and 28 operate alternatively.

Next, the operation of the hydraulic circuit of the injection molding machine according to the present invention will be described. Control device 3 for electromagnetic proportional relief valve 11
When controlling with 4, the flow rate adjusting valve 7 is added to the valve differential pressure setting device 32.
The pressure difference _{ΔP SV} required on the primary side and the secondary side of the solenoid valve is set, and the upper limit value P _{INMAX of the} pressure is set in the command pressure upper limit setter 33. The vent port 21b of the compensation valve 21 is connected to the primary side of the pressure reducing valve 5 via the pressure line 26 to operate the injection molding machine.

When the pressure P _L detected by the pressure sensor 27 is input to the control unit 34 (step S1 in FIG. 2), the control unit 34 detects the pressure P _L detected by the pressure sensor 27 and the valve differential pressure setting unit 3.
The sum P _IN with the pressure difference ΔP _SV set to 2 is calculated (step S2). Then, in step S3, it is judged whether or not the pressure P _IN is larger than the upper limit pressure value P _INMAX set in the command pressure upper limit setter 33, and if YES, it is lowered to the upper limit value P _INMAX in step S4. pressure P _iN is also the case of NO the pressure P _iN is output to the electromagnetic proportional relief valve 11 as it is (step S5). As a result, the pressure reducing valve 5 functions as a pressure reducing type pressure compensating valve so that the pressure on the downstream side becomes the load pressure P _L + the set pressure difference ΔP _SV, and an arbitrary flow rate characteristic with respect to the load pressure is obtained. By obtaining it, when the resin is injected by the operation of the actuator 2 in the injection step, it is possible to solve the problem such as warping of the molded product.

In FIG. 3, the pressure difference before and after the flow control valve 7 is 7
The load pressure-flow rate characteristic of the conventional hydraulic circuit (the pressure line 8 is open in FIG. 5) and the set pressure difference are ΔP for kg / cm ² .
It is a comparison diagram of the load pressure-flow rate characteristic of the hydraulic circuit of the present invention when _SV (however, ΔP _SV > 7 kg / cm ² ). See also FIG.
FIG. 4 is a comparison diagram of a performance range of a conventional hydraulic circuit and a performance range of a hydraulic circuit according to the present invention.

As described above, in the present invention, the flow rate adjusting valve 7
Since the pressure difference between before and after can be set arbitrarily, the maximum flow rate of the hydraulic oil (maximum speed of the actuator 2) and the load pressure-flow rate characteristic can be optimally set according to the molded product or the like. When the pressure difference of the flow rate adjusting valve 7 is set to a large value (usually 7 to 10 kg / cm ² ), the maximum flow rate of the hydraulic oil increases and the load pressure-flow rate characteristic override increases. By properly using these characteristics depending on the molded product,
It is possible to improve warpage, burrs, short shots and the like of the molded product. Further, by appropriately setting the flow rate characteristics, the filling speed can be smoothly decelerated (according to the load pressure) as the resin filling progresses, and high-speed low-pressure molding becomes possible.

In the above description, since the pressure on the primary side of the pressure reducing valve 5 and the force of the spring 21a are applied to the vent port 21b side of the spool of the pressure compensating valve 21, the pressure compensating valve 21 will not open. None, vent port 21b
Even if the hydraulic oil leaks from the side, the above state is maintained.

When the actuator 28 is operated to move the movable platen in a mold clamping process or a mold opening process other than the injection filling process, the solenoid of the electromagnetic switching valve 25 is demagnetized to open the pressure line 24, and the control device is opened. 34 is stopped and the actuator 28 is operated. At this time, the pressure compensating valve 21 functions normally to maintain the pressure difference across the flow rate adjusting valve 7 at a constant value corresponding to the force of the spring 21a. When the solenoid of the electromagnetic switching valve 25 is excited to connect the vent port 21b of the pressure compensation valve 21 to the primary side of the pressure reducing valve 5,
The pressure compensation valve 21 does not work. Such control can also be applied to the injection process. A fixed pump or a variable discharge pump can be used as the hydraulic pump.

[0023]

As described above, in the hydraulic circuit of the injection molding machine according to the present invention, the hydraulic circuit between the accumulator as a hydraulic pressure source and the actuator for actuating the screw or the like by receiving the hydraulic oil from the accumulator. Detecting the load pressure of the actuator in a hydraulic circuit of an injection molding machine in which a pressure reducing valve that reduces the pressure of hydraulic oil and a flow rate adjusting valve that adjusts the flow rate of the hydraulic oil that has passed through the pressure reducing valve are provided in the main pipeline. Since a pressure sensor for controlling the operating pressure of the pressure reducing valve is provided based on the output signal of the pressure sensor, an arbitrary flow rate characteristic can be obtained. Therefore, when used for controlling the injection process, it is possible to eliminate defects such as warpage, burrs, and short shots of the molded product. It is also resistant to disturbance and has good repeatability.

If a vent valve of the pressure reducing valve is provided with an electromagnetic proportional relief valve which is controlled by a control unit and changes the operating pressure of the pressure reducing valve, the operating pressure of the pressure reducing valve can be easily controlled by remote control or the like. You can Further, when the pressure compensating valve is provided, the pressure difference before and after the flow rate adjusting valve can be kept constant without using the control device. Furthermore, if a switching valve is provided in the pressure conduit of the pressure compensation valve,
The operation of the pressure compensation valve can be easily switched by the switching valve.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a hydraulic circuit of an injection molding machine according to the present invention.

FIG. 2 is a flow chart of the present invention.

FIG. 3 is a diagram showing a relationship between load pressure and flow rate.

FIG. 4 is a diagram showing a performance range.

FIG. 5 is a hydraulic circuit of a conventional injection molding machine.

[Explanation of symbols]

 1 Hydraulic Pump 2 Actuator 3 Main Pipeline 4 Accumulator 5 Pressure Reduction Valve 7 Electromagnetic Flow Control Valve 10 Vent Pipeline 11 Electromagnetic Proportional Relief Valve 21 Pressure Compensation Valve 21a Spring 21b Vent Port 22 Branch Pipe 23 Pilot Pipeline 24 Pressure Pipeline 25 Electromagnetic Switching Valve 26 Pressure pipe 27 Pressure sensor 28 Actuator 29 Pressure sensor input circuit 30 Calculation circuit 31 Proportional valve output circuit 32 Valve differential pressure setting device 33 Command pressure upper limit setting device 34 Control device

Continuation of front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location F15B 11/05 A 8512-3H (72) Inventor Junichiro Hirasawa 2-5-1, Shirooka, Nagaoka, Niigata Stock Association Niigata Iron Works Nagaoka Factory

Claims (5)

[Claims] 1. A pressure reducing valve for reducing the pressure of hydraulic oil, and a pressure reducing valve in a main pipe line between an accumulator as a hydraulic pressure source and an actuator which receives a supply of hydraulic oil from the accumulator and operates a screw or the like. In the hydraulic circuit of the injection molding machine provided with a flow rate adjusting valve for adjusting the flow rate of the hydraulic oil passing through the pressure sensor for detecting the load pressure of the actuator, and the pressure reducing valve for the pressure reducing valve based on the output signal of the pressure sensor. A hydraulic circuit for an injection molding machine, comprising a control device for controlling an operating pressure. 2. The hydraulic circuit for an injection molding machine according to claim 1, wherein the hydraulic source is a hydraulic pump. 3. An injection molding machine according to claim 1, wherein an electromagnetic proportional relief valve for controlling the operating pressure of the pressure reducing valve is provided in the vent pipe line of the pressure reducing valve and controlled by a controller. Hydraulic circuit. 4. A branch pipe branched from a vent pipe between the pressure reducing valve and the electromagnetic proportional relief valve, a pressure compensating valve having its pilot pipe on the secondary side of the pressure reducing valve, and a vent port having a first pressure. The hydraulic circuit of the injection molding machine according to claim 1, wherein the hydraulic circuit is provided by being connected to the secondary side of the flow rate control valve by a pipe line. 5. A first pressure line in the first position at the first position.
The pressure line is shut off to connect the vent port of the pressure compensating valve to the second pressure line branched from the primary side of the pressure reducing valve, and at the second position, the first pressure line is opened to open the second pressure line. The hydraulic circuit of the injection molding machine according to claim 4, further comprising a switching valve that shuts off the passage.