JPH0757516B2 - Hydraulic circuit of injection molding machine - Google Patents

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 having a four port valve for controlling a hydraulic actuator.

[0002]

2. Description of the Related Art A conventional hydraulic circuit in an injection molding machine is shown in FIG. In the figure, 50 is an injection device of an injection molding machine, which has a heating cylinder 51 at the front and a screw drive 52 at the rear.
Equipped with. The heating cylinder 51 has an injection nozzle 53 at the front end, a hopper 54 at the rear part, and a screw 55 inside. Further, the screw driving unit 52 has a built-in ram 57.
An injection cylinder 56 for advancing or retracting the screw 55 is provided, and a hydraulic motor 58 for rotating the screw 55 via a ram 57.

On the other hand, the injection cylinder 56 constitutes a hydraulic circuit 60 together with the hydraulic circuit body 61. Hydraulic circuit body 6
1 includes a servo valve 62, which is a four-port valve attached to a piping block that is movable together with an injection device 50 provided in a machine base 59. The P port of the servo valve 62 is an accumulator 64 and a hydraulic pump 63, and the T port is an oil port. In the tank 65, the A port is connected to a supply / discharge port 66 communicating with the front cylinder chamber 56f of the injection cylinder 56, and the B port is connected to a supply / discharge port 67 communicating with the rear cylinder chamber 56r of the injection cylinder 56.

Therefore, the injection cylinder 56 is operated by the switching control of the servo valve 62, and the screw 55 is moved forward, backward, and stopped.

[0005]

By the way, in the conventional hydraulic circuit 60, the front cylinder chamber 56f and the rear cylinder chamber 56r of the injection cylinder 56 have the same cross-sectional area, and the inflow amount and the return amount of the pressure oil to the injection cylinder 56 are set. Constant, and by controlling the servo valve 62, the screw 5
Since the position, speed, and pressure of No. 5 are feedback-controlled, it is possible to perform forward / backward control, gear shift control, and position control with high accuracy and high responsiveness.

However, since the servo valve 62 is a four-port valve, the A port and the B port are connected to the cylinder chambers 56f and 56r of the injection cylinder 56, respectively. Therefore, for example, the path of the pressure oil during forward control of the screw 55 is supplied to the rear cylinder chamber 56r via the P port and B port of the servo valve 62, and the front cylinder chamber 56f to the A port of the servo valve 62. T
It is returned to the oil tank 65 via the port. As a result, the pressure oil in the hydraulic circuit 60 passes through the servo valve 62 twice, and the pressure loss is doubled as compared with the case where it passes once. After all, the conventional hydraulic circuit 60 requires a large servo valve in consideration of the pressure loss due to the pressure oil passing through the servo valve 62 twice, and there is a drawback that the entire hydraulic circuit 60 becomes large and the cost increases. It was

Further, the four-port valve is unsuitable for high-speed control when compared with, for example, a three-port valve, so it is necessary to select a servo valve having a large flow rate to realize high-speed control. , The frequency response decreases, the control accuracy decreases, and the system becomes unstable. In the end, when various controls including high speed and low speed are performed, there is a difficulty in that high-level and accurate control cannot be performed as a whole.

The present invention solves the problems existing in the prior art as described above. In particular, the pressure loss of the four-port valve is reduced by half to reduce the size and cost of the four-port valve used. The objective is to provide a hydraulic circuit for an injection molding machine that can achieve advanced and accurate control.

[0009]

According to the present invention, when a hydraulic circuit 1 of an injection molding machine equipped with a four-port valve for controlling an injection cylinder 2 which is a hydraulic actuator, for example, a four-port servo valve 3 is used, a servo is used. A relief valve 6a capable of opening / closing control is provided between one of the supply / discharge ports of the injection cylinder 2 of the valve 3, for example, between the A port connected to the supply / discharge port 4f of the front cylinder chamber 2f and the T port connected to the oil tank 5.
6 c, a directional control valve 6 b and other control valves 6 are connected to a bypass circuit 7.

[0010]

According to the hydraulic circuit 1 of the injection molding machine of the present invention, the servo valve 3 can be selectively operated as a four-port valve or a three-port valve by controlling the opening / closing of the control valve 6. That is, if the control valve 6 is controlled to the closing side,
Since the bypass circuit 7 is cut off, the servo valve 3 can function as an original four-port valve, and if the control valve 6 is controlled to the open side, the bypass circuit 7 for returning oil to the servo valve 3 is provided. Will be connected,
It can function as a substantial three-port valve.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, preferred embodiments according to the present invention will be described in detail with reference to the drawings.

First, the structure of the hydraulic circuit 1 of the injection molding machine according to the present invention will be described with reference to FIG.

Reference numeral 10 denotes an injection device in an injection molding machine, which includes a heating cylinder 11 in the front part and a screw driving part 12 in the rear part. The heating cylinder 11 has an injection nozzle 13 at the front end, a hopper 14 at the rear part, and a screw 15 inside. Further, the screw driving unit 12 is an injection cylinder 2 that advances or retracts the screw 15 by a built-in ram 16.
And a hydraulic motor 17 for rotating the screw 15 via the ram 16.

On the other hand, the injection cylinder 2 is a hydraulic circuit main body 1s.
Together with this, the hydraulic circuit 1 according to the present invention is configured. The hydraulic circuit main body 1s includes a servo valve 3 which is a four-port valve, the P port of the servo valve 3 is connected to the accumulator 21 and the hydraulic pump 22, and the T port is connected to the accumulator 23 and the oil tank 5, and the servo The port A of the valve 3 is connected to a supply / discharge port 4f communicating with the front cylinder chamber 2f of the injection cylinder 2, and the port B is connected with a supply / discharge port 4r communicating with the rear cylinder chamber 2r of the injection cylinder 2.
Connect to.

A relief valve 6a (control valve 6) is connected between the A port and the T port of the servo valve 3. This constitutes the bypass circuit 7. on the other hand,
The pilot circuit 31 of the relief valve 6a is connected to the P port via the choke 32, and the vent circuit 33 is connected to the oil tank 5 via the choke 34 and the direction control valve 35. By connecting the pilot circuit 31 to the P port, the responsiveness at the time of opening and closing the relief valve 6a can be enhanced, and by connecting the vent circuit 33 to the directional control valve 35, the responsiveness to the relief valve 6a can be improved. High smooth opening and closing control can be performed.
Further, by connecting the choke 34 to the vent circuit 33, it is possible to arbitrarily set the time constant and the back pressure with respect to the return oil, which characterize the response speed when the bypass circuit 7 is controlled to be opened and closed.

Accordingly, the opening / closing of the relief valve 6a can be controlled by opening / closing the directional control valve 35, and the timing of opening / closing can be set by the choke 34.

Next, an actual method of using the hydraulic circuit 1 will be described with reference to FIGS.

FIG. 2A is a timing chart showing the open / closed state of the relief valve 6a corresponding to the molding cycle in the injection molding machine. First, in the speed control section (injection) of the injection process, the directional control valve 35 is controlled to control the relief valve 6a to the open side. As a result, the bypass circuit 7 is brought into a flow state, and the servo valve 3 functions as a substantially three-port valve.

That is, in the speed control section, pressure oil is supplied from the hydraulic pump 22 to the rear cylinder chamber 2r of the injection cylinder 2 by the control of the servo valve 3, the ram 16 and the screw 15 advance, and the inside of the heating cylinder 11 moves. Screw 15
The molten resin measured in front of is injected and filled into a mold cavity (not shown) through the injection nozzle 13. On the other hand, oil is discharged from the front cylinder chamber 2f, and the discharged oil is returned to the oil tank 5 through both the bypass circuit 7 and the servo valve 3 in the flowing state. At this time, most of the oil passes through the bypass circuit 7 side where the flow rate increases. Therefore, the pressure loss is significantly reduced, and the state becomes suitable for speed control in which a relatively large flow rate is caused, such as during injection.

Incidentally, FIG. 3 shows the characteristics of the forward speed (injection speed) V of the injection cylinder, the forward pressure Pf, and the backward pressure Pr in the speed control section when the bypass circuit 7 is cut off to function as a four-port valve. FIG. 4 shows the characteristics of the forward speed (injection speed) V of the injection cylinder, the forward pressure Pf, and the backward pressure Pr in the speed control section when the bypass circuit 7 is in the flow state and functions as a three-port valve. As is clear from the comparison of the figures, in the case of FIG.
When the forward speed V is Vi (for example, 300 mm / sec),
The forward pressure Pf and the backward pressure Pr are both P1 (for example, 82
kg / cm ²⁾ is in equilibrium in the case of FIG. 4 may be a forward velocity V is the same Vi (300 mm / sec), the forward pressure Pf and backward pressure Pr is considerably lower than P1 P2 ( Equilibrate at, for example, 34 kg / cm ² . Therefore, when the servo valve 3 is made to function as a three-port valve, the forward pressure Pf can be suppressed to a low level, and a large pressure difference from the hydraulic pressure Pa supplied from the accumulator 21 can be obtained. That is, [Pa-P2]> [Pa-P1], and a large flow rate can be secured.

On the other hand, when the speed control section ends, the directional control valve 35 is controlled to control the relief valve 6a to the closing side. As a result, the bypass circuit 7 is shut off and the servo valve 3 functions as an original four-port valve. The closing period of the relief valve 6a is continued until the pressure control section (at the time of holding pressure), the measuring step and the mold opening / closing step are completed, and the opening side is controlled again at the start of the speed control section in the next molding cycle.

Next, a modified embodiment according to the present invention will be described with reference to FIGS. It should be noted that the modified examples all relate to modification of the form of the control valve 6. Therefore, in each drawing, the same parts as those in FIG. 1 are designated by the same reference numerals to clarify the configuration thereof, and detailed description thereof will be omitted.

First, the modified embodiment shown in FIG. 5 is different in that an electromagnetic relief valve 36 is used instead of the direction control valve 35 in the embodiment shown in FIG. That is, the relief valve 6a
The vent circuit 33 is connected to the oil tank 5 via the electromagnetic relief valve 36, and the back pressure of the return oil at the time of injection can be arbitrarily set by setting the pressure of the electromagnetic relief valve 36. For example, setting the back pressure to zero allows it to function as a complete three-port valve. If the back pressure is set to an appropriate value, the function of the 4-port valve can be added, the inertial force of the 3-port valve can be removed, and the superiority of the position control of the 4-port valve can be secured. it can.

On the other hand, FIG. 6 is different in that a directional control valve (logic valve) 6b is used as the control valve 6, and is provided with a second directional control valve 37 for switching and controlling the directional control valve 6b.
In this case, the overall function is the same as that of the embodiment shown in FIG. 1, but the modified embodiment shown in FIG. 6 has an advantage that the responsiveness can be enhanced. In FIG. 6, reference numerals 38 and 39 denote chokes. The control state of the directional control valve 37 in the molding cycle of the injection molding machine is as shown in FIG.
During non-molding and during injection (speed control section), the solenoid of the second directional control valve 37 is turned off, and all other steps are turned on.

Further, FIG. 7 is different in that a relief valve 6c of a logic valve type is used as the control valve 6, and an electromagnetic relief valve 40 for switching and controlling the relief valve 6c is provided. The modified embodiment shown in FIG. 7 has an advantage that the back pressure can be arbitrarily set, like the modified embodiment shown in FIG. Note that FIG.
Inside, 41 shows a choke.

The embodiment has been described in detail above.
The present invention is not limited to such an embodiment.
For example, although the injection cylinder is illustrated as the hydraulic actuator, the invention can be similarly applied to any other hydraulic actuator such as a mold opening / closing cylinder. Moreover, the four-port valve and the control valve do not prevent the use of valves other than those illustrated. In addition, the detailed configuration and the like can be arbitrarily changed without departing from the scope of the present invention.

[0027]

As described above, in the hydraulic circuit of the injection molding machine according to the present invention, the A port connected to one of the supply / discharge ports of the hydraulic actuator of the four-port valve and the T port connected to the oil tank.
Since the bypass circuit in which the control valve capable of opening / closing control is connected is provided between the ports, the following remarkable effects are achieved.

By halving the pressure loss of the four-port valve, the performance can be satisfied even with a four-port valve that is one rank lower. Therefore, it is possible to reduce the size and cost of the four-port valve used, especially the expensive servo valve. Can be planned.

Since the function of the four-port valve and the function of the three-port valve can be selectively used, various controls including high speed and low speed can be appropriately dealt with, and advanced and stable control can be realized.

Since the back pressure and responsiveness to the return oil of the bypass circuit can be arbitrarily set, the intermediate characteristics of the three-port valve and the four-port valve can be arbitrarily set, and high-precision control is possible.

[Brief description of drawings]

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

FIG. 2 is a timing chart showing a state of a bypass circuit in the hydraulic circuit,

FIG. 3 is a characteristic diagram of forward speed (injection speed), forward pressure and backward pressure in the injection cylinder when the bypass circuit in the hydraulic circuit is turned off.

FIG. 4 is a characteristic diagram of forward speed (injection speed), forward pressure and backward pressure in the injection cylinder when the bypass circuit in the hydraulic circuit is in a circulating state,

FIG. 5 is a circuit diagram of a hydraulic circuit according to a modified embodiment of the present invention,

FIG. 6 is a circuit diagram of a hydraulic circuit according to another modified embodiment of the present invention,

FIG. 7 is a circuit diagram of a hydraulic circuit according to another modified embodiment of the present invention,

FIG. 8 is a circuit diagram of a hydraulic circuit of an injection molding machine according to the related art,

[Explanation of symbols]

 1 Hydraulic Circuit 2 Injection Cylinder 3 Servo Valve 4f Supply / Discharge Port 5 Oil Tank 6 Control Valve 7 Bypass Circuit

Claims (6)

[Claims] 1. In a hydraulic circuit of an injection molding machine having a four-port valve for controlling a hydraulic actuator, between the A port connected to one of the supply / discharge ports of the hydraulic actuator and the T port connected to an oil tank in the four-port valve. A hydraulic circuit for an injection molding machine, comprising a bypass circuit connected to a control valve capable of controlling opening and closing. 2. The hydraulic circuit for an injection molding machine according to claim 1, wherein the hydraulic actuator is an injection cylinder. 3. The supply / discharge port on one side is a supply / discharge port communicating with the front cylinder chamber of the injection cylinder.
Alternatively, the hydraulic circuit of the injection molding machine described in 2. 4. The hydraulic circuit for an injection molding machine according to claim 1, wherein the four-port valve is a servo valve. 5. The hydraulic circuit for an injection molding machine according to claim 1, wherein the control valve is a relief valve. 6. The hydraulic circuit for an injection molding machine according to claim 1, wherein the control valve is a directional control valve.