JPH0236801B2 - SHASHUTSUSEIKEIKYORYUTAISEIGYOSOCHI - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a fluid control device for an injection molding machine that allows an injection actuator to start up quickly.

<Prior Art> Conventionally, a so-called power match type fluid control device in which the discharge pressure and flow rate of a variable pump are made to correspond to the pressure and flow rate required by the load of an actuator using a pilot valve is shown in FIG. (Hydraulic and Pneumatic Design, Vol. 14, No. 1, January 1976, Nikkan Kogyo Shimbun, p. 64). This fluid control device includes a variable pump 1
01, a pilot valve 102, and a normally closed throttle switching valve 105 having a vent passage 105a that communicates with the tank 103 via the pilot line 104 when the spring chamber 102a of the pilot valve 102 is in neutral state. When the throttle switching valve 105 is in the normal position, that is, the neutral position, when the throttle valve 105 is not operated, the spring chamber 102a of the pilot valve 102 is communicated with the tank 103 to unload the variable pump 101 using a vent unloading method. Therefore, in the conventional power match type fluid control device, the throttle switching valve 10
5 from the neutral position to the switching position, the time required to completely fill the main line 107 and pilot line 104 with fluid and compress it before the actuator 106 responds, and the position at which it is unloaded. Since it takes time to bring the pilot valve 102, which is stationary, into the operating state, there is a disadvantage that dead time inevitably occurs and the responsiveness of the actuator 106 is poor. In this way, the actuator 10
If the responsiveness of No. 6 is poor, the following serious problems will occur in the injection molding machine. In other words, in order to perform good molding, it is necessary to push the molten resin into every corner of the mold, but if the actuator's response is poor, the molten resin cannot be pushed into the mold quickly, and the molten resin Partially cools and hardens during the process, causing the problem that the molten resin cannot be pushed into every corner of the mold. This means that the injection cycle is on the order of seconds, so the responsiveness is small.
Even a difference of 0.1 seconds will have a significant impact on the quality of the molded product.

In view of the above-mentioned conventional circumstances, it is an object of the present invention to provide a fluid control device for an injection molding machine in which the start-up response of an injection actuator is good.

<Means for Solving the Problems> In order to achieve the above object, the fluid control device for an injection molding machine of the present invention has the following features as illustrated in FIG.
A throttle valve 7 is installed in the main line 6 that connects the variable pump 1 and the pump port normally closed type switching valve 3 that controls only the operating direction of the injection actuator 5, and a pilot line branches from before and after the throttle valve 7. 8 and 9 are respectively connected to the pilot chamber and spring chamber of the pilot valve 2a for flow rate control, and further, the front part of the throttle valve 7 is connected to the pilot chamber of the pilot valve 2b for pressure control via a pilot line 8. On the other hand, the front part of the throttle valve 7 is placed in the spring chamber of the pressure control pilot valve 2b.
A pilot relief valve 1 connected to the main line 6 by a pilot line 56 having a throttle 55 and for setting a set pressure in multiple stages to the main line 6.
8 is connected to the spring chamber of the pressure control pilot valve 2b, and by switching the pressure control pilot valve 2b and the flow rate control pilot valve 2a, the discharge amount control section 16 of the variable pump 1 is connected to the main line. 6 and tank line 12.

<Function> When the pump port of the switching valve 5 that does not operate the injection actuator 5 is closed, the fluid in the main line and the pilot line is brought to a pressure corresponding to a predetermined low pressure set by the pilot relief valve 18 in advance. As the pressure is compressed, the pressure control pilot valve 2b is placed not in a position corresponding to unloading, but in a position corresponding to the low pressure, that is, in a transient position, and the flow rate control pilot valve 2a is placed on the maximum discharge side. Since there,
When the switching valve 3 is switched, the pressure control pilot valve 2b and the flow rate control pilot valve 2
a immediately operates, and the injection actuator 5 is quickly raised. Further, since the pilot relief valve 18 for setting the set pressure in multiple stages is connected to the spring chamber of the pressure control pilot valve 2b, multi-stage control of the pressure can be performed.

<Examples> The present invention will be described in detail below with reference to illustrated examples.

This fluid control device for an injection molding machine includes a variable discharge amount pump 1, a pilot valve 2 that controls the discharge amount and discharge pressure of the variable pump 1, closed center type switching valves 3 and 4, and the switching valve 3. It is equipped with a double-rod type hydraulic cylinder 5 which is an injection actuator whose direction is controlled by the injection actuator.

A normally open throttle valve 7 is installed in the main line 6 between the variable pump 1 and the pump ports P, P of the switching valves 3, 4.

The pilot valve 2 is constituted by a combination of a flow rate control pilot valve 2a and a pressure control pilot valve 2b, each of which is a three-port throttle switching valve, in order to accurately control the flow rate and pressure.

The pressure before and after the throttle valve 7 is transmitted to the pilot chamber and spring chamber at both ends of the flow control pilot valve 2a through pilot lines 8 and 9, respectively. Further, the pressure in front of the throttle valve 7 is transmitted via the pilot line 8 to the pilot chamber and port 1 of the flow rate control pilot valve 2a and the pilot chamber and port 1 of the pressure control pilot valve 2b. . The spring chamber of the pressure control pilot valve 2b is connected to the pilot line 8 via a line 56 having a throttle 55 installed in the middle. Further, port n of the pressure control pilot valve 2b is connected to the pilot line 17.
The pressure control pilot valve 2b is connected to the discharge amount control section 16 of the variable pump 1 via the
In addition, the port m of the pilot valve 2a for flow rate control and the tank 13 are connected to the pilot line 12.
are connected via.

On the other hand, a pilot relief valve 18 is connected to the spring chamber of the pressure control pilot valve 2b. The pilot relief valve 18 consists of a low-pressure relief valve 18a, a high-pressure relief valve 18b, and a normally open two-position electromagnetic switching valve 18c.

The primary ports of the relief valves 18a and 18b are connected to each other via a pilot line 61. Further, the secondary port of the relief valve 18a is connected to the tank 63 via a line 62 in which the switching valve 18c is installed in the middle. Further, the line 61 is connected to the spring chamber of the pressure control pilot valve 2b via a pilot line 66.

Therefore, this pilot relief valve 18
In the state shown in FIG. 1, the relief valve 18
The secondary port of a is connected to the tank 6 via the switching valve 18c.
3, the pressure is set to the low pressure side set by the relief valve 18a, and when current is applied to the solenoid 70 of the switching valve 18c to switch it, the secondary port of the relief valve 18a and Since the communication with the tank 63 is cut off, the relief valve 18
The pressure is set to the high pressure side set in b. That is, the pilot relief valve 18 can set its set pressure in multiple stages, that is, at high pressure or low pressure.

On the other hand, when controlling the speed of the hydraulic cylinder 5, that is, controlling the flow rate, the pilot relief valve 18 is not at the set pressure, so the pressure control pilot valve 2b is operated so that both the pilot chamber and spring chamber have the same pressure. and is located at symbol position _V2 . And the pilot valve 2 for flow control
a is located at the symbol position V ₁ or at the symbol position V ₂ , and controls the fluid to the discharge amount control unit 16 of the variable pump 1 to keep the differential pressure before and after the throttle valve 7 constant. do. Furthermore, during pressure control when the filling of the resin 34 is completed and the hydraulic cylinder 5 is stopped, no fluid flows through the throttle valve 7 and the pressures before and after the throttle valve 7 are the same, so the pilot valve for flow control is 2a is located at symbol position _V2 . The pressure control pilot valve 2b is located at the symbol position _V1 or _V2 , and the variable pump 1
The pressure in the main line 6 is maintained at a constant pressure by controlling the discharge amount.

On the other hand, the load ports A and B of the switching valve 3 are connected to ports 27 and 28 of the double rod type hydraulic cylinder 5 via lines 25 and 26, respectively.

On the other hand, in the injection machine 30, a screw shaft 33 is fitted into a heating cylinder 32 having a hopper 31 on the upper part thereof so as to be freely movable forward and backward and rotatable. Then, by rotating the screw shaft 33 by means not shown, the resin 34 in the hopper 31 can be sucked into the heating cylinder 32. The rod 29 of the hydraulic cylinder 5 is connected to one end of the screw shaft 33, while a mold 35 is placed at the tip of the heating cylinder 32.

The fluid control device for an injection molding machine having the above configuration operates as follows.

Now, this fluid control device is in the state shown in FIG. 1, in which the resin 34 has been sucked into the heating cylinder 32 from the hopper 31, and the pilot relief valve 18a is in the state shown in FIG. Therefore, it is assumed that the pressure is set to a low pressure.

At this time, a part of the fluid discharged from the variable pump 1 passes through the main line 6, the throttle valve 7, the pilot line 8, the throttle 55, and the pilot line 66, and is delivered to the tank 6 from the pilot relief valve 18a.
It is discharged in 3. Therefore, the pressures in the main line 6 and the pilot lines 8, 9, and 66 correspond to the low pressure that is the set pressure of the pilot relief valve 18a. That is, main line 6 and pilot lines 8, 9, 6
6 is compressed in advance to a predetermined low pressure even in the normal state of the switching valve 3 in which the hydraulic cylinder 5 is not driven.

On the other hand, the pressure control pilot valve 2b controls the discharge amount control section 16 of the variable pump 1, and controls the throttle valve 5.
The difference between the pressure at the front of the throttle valve 55 and the pressure at the rear of the throttle 55 is determined by the spring 3 in the spring chamber of the pressure control pilot valve 2b.
Set it to a constant value corresponding to the spring force of 8. That is,
For example, when the difference in pressure between the pilot chamber and spring chamber of the pressure control pilot valve 2b exceeds the spring force of the spring 38, the pressure control pilot valve 2b is located at the symbol position V ₁ on the left side of the figure, and the main fluid from line 6 through its ports l, n;
While supplying it to the discharge amount control unit 16 to reduce the discharge amount of the variable pump 1 and lower the pressure in front of the throttle 55,
For example, when the difference in pressure between the pilot chamber and spring chamber of the pressure control pilot valve 2b becomes less than the spring force of the spring 38, the pressure control pilot valve 2b is located at the symbol position _V2 on the right side of the figure, and the discharge is stopped. The fluid from the volume control unit 16 is discharged into the tank 13 via ports n, m and the flow rate control pilot valve 2a to increase the discharge volume of the variable pump 1, and the flow rate of the variable pump 1 is increased.
The pressure in front of the throttle 55 is increased to keep the differential pressure before and after the throttle 55 constant.

Therefore, in the normal position of the switching valve 3, the pressure control pilot valve 2b is at the symbol position in order to keep the differential pressure across the throttle 55 constant.
In a transient state between V ₁ and V ₂ , that is, in a state where port l and port n are constricted and communicated, a part of the fluid discharged from variable pump 1 is passed through ports l and n. is supplied to the discharge amount control unit 16 to incline a swash plate (not shown) by a predetermined angle,
The variable pump 1 is made to discharge a predetermined amount of fluid.
In other words, the pressure control pilot valve 2b is connected to ports l and n where the variable pump 1 is unloaded.
As mentioned above, instead of being located at the symbol position V ₁ that fully opens the gap between the symbol position V ₁ and
During the transition from V2 to _V2 , a constant amount of fluid is being discharged.

At this time, the fluid discharged from the variable pump 1 is divided into two parts, the low-pressure side pilot relief valve 18a and the discharge amount control section 16, and is discharged to the tanks 63 and 41, respectively. The discharged fluid is a small amount, and its discharge pressure is a low pressure set by the pilot relief valve 18a. Therefore, the power loss determined by the product of pressure and flow rate at this time is relatively small compared to a fixed pump control method or a variable pump that discharges high-pressure fluid.

In this state, the switching valve 18c is switched to close the secondary side of the low-pressure side pilot relief valve 18a, and at the same time, the pilot relief valve 18b is set to a high pressure corresponding to the first set pressure, and at the same time, the switching valve 3 is switched to the symbol on the left side. Switch to position.

Then, the fluid discharged from the variable pump 1 is supplied to the port 27 of the hydraulic cylinder 5 via the throttle valve 7 and the switching valve 3, and the rod 29 and screw shaft 33 are moved to the right in FIG. It will be done. Then, the resin 34 is supplied into the mold 35.

The rising response of the hydraulic cylinder 5 at this time is the main line 6, the pilot lines 8, 9,
Because the fluids 17, 66, and 61 have been compressed to a low pressure in advance as described above, and the pressure control pilot valve 2b is in a transient state between the symbol positions _V1 and _V2 , it is possible to quickly symbol position
Since there is no fluid flowing through the throttle valve ₇ , the pressures in the pilot chamber and spring chamber of the flow rate control pilot valve 2a become equal, and the flow rate control pilot valve 2a is positioned at the symbol position _V2 . The combination of this and the fact that the throttle valve 7 is open from the beginning are good. That is, the hydraulic cylinder 5 of this fluid control device for an injection molding machine quickly starts up at the same time as the signal is applied to the switching valve 3 and the switching valve 18c. In contrast, conventional fluid control devices start up after a dead time has elapsed after applying a signal to switch. This is because, as mentioned above, in order to operate the hydraulic cylinder, the main line and pilot line must be filled with fluid and compressed, and the pilot valve corresponds to the maximum discharge amount from the position corresponding to the unloaded state. Due to the fact that you have to move to the side where you want to do it.

Furthermore, even when the switching valve 3 is in the neutral position, this fluid control device does not perform vent unloading as in the conventional example, so the actuator 4 can be connected to the downstream side of the throttle valve 7 and operated.

As the resin is supplied into the mold 35 as described above, the resistance to the advancement of the screw shaft 33 increases, and the filling pressure applied to the piston of the hydraulic cylinder 5, that is, the pressure behind the throttle valve 7 increases. The fluid pressure gradually increases as shown by the curve before time _T1 in FIG.

At this time, the flow rate control pilot valve 2a is in operation and maintains the differential pressure across the throttle valve 7 constant regardless of the increase in the filling pressure, thereby controlling the fluid flow, that is, accurate speed control of the hydraulic cylinder 5. I'm going. That is, when the filling pressure increases and the differential pressure across the throttle valve 7 becomes less than a predetermined pressure, the pressure difference between the pilot chamber and the spring chamber of the flow control pilot valve 2a to which the pressure before and after the throttle valve 7 is transmitted, respectively, increases. The spring force of the spring 39 in the spring chamber becomes lower, and the flow rate control pilot valve 2a is located at the symbol position _V2 .
Then, the discharge amount control section 16 of the variable pump 1 is communicated with the tank 13 via the pilot line 17 and the pilot valves 2a and 2b, and the swash plate (not shown) of the variable pump 1 is tilted toward the maximum discharge side to control the discharge. The pressure difference across the throttle valve 7 is increased. On the other hand, if the pressure downstream of the throttle valve 7 decreases and the pressure difference before and after the throttle valve 7 exceeds a predetermined pressure, the pressure difference between the pilot chamber and spring chamber of the flow control pilot valve 2a will become Spring 3 in the spring chamber
9, the flow control pilot valve 2a is located at the symbol position _V1 . and,
The discharge amount control section 16 of the variable pump 1 is controlled by a pilot line 17, a pressure control pilot valve 2b located at symbol position _V2 , and a pilot line 8.
The swash plate of the variable pump 1 is inclined toward the non-discharge side to reduce the discharge amount and the differential pressure across the throttle valve 7. To summarize, the flow control pilot valve 2a is the throttle valve 7.
Depending on the differential pressure before and after the throttle valve 7, the variable pump 1 is positioned at the symbol position _V1 or the symbol position _V2 , and the discharge amount of the variable pump 1 is controlled to adjust the differential pressure before and after the throttle valve 7. Hold constant.

At the time of this fluid control, the discharge of the variable pump 1 At the time of this fluid control, in order to control the discharge amount of the variable pump 1, fluid is not flowing to any other place other than the discharge amount control section 16, that is, it is returned directly to the tank. Since there is no fluid, power match control is performed and power loss is further reduced.

Next, by advancing the screw shaft 33, the mold 3
When the filling of the resin 34 into the inside of the injection machine 3 is completed, the injection machine 3
0 is a transition from an injection state to a settling state in which the hydraulic cylinder 5 does not operate. Then, the filling pressure rapidly increases as shown by the curve on the right side from time T ₁ in FIG. 2, and reaches the first settling pressure P ₁ shown by the curve on the right side from time T ₂ . In other words, this fluid control device
The flow rate control state shifts to a pressure control state in which the discharge amount of the variable pump 1 is extremely small. During the transition to this pressure control state, the flow rate control pilot valve 2a operates to control the flow rate, so as shown by the solid line in Figure 3, the pressure override characteristic is better than that shown by the broken line, and the corner The horsepower at point 51b increases, and the cycle of the injection machine can be completed quickly even under high load, improving efficiency.

The first set pressure _P1 is determined by the set pressure of the pressure control pilot relief valve 18b. That is, since the pressure control pilot relief valve 18b maintains the fluid pressure on its primary port side at its set pressure, the spring chamber of the pressure control pilot valve 2b also maintains its set pressure. Therefore, under this pressure control state, the pressure control pilot valve 2b sets the filling pressure to the first setting so that the differential pressure between the pilot chamber and the spring chamber corresponds to the spring pressure of the spring chamber. Position the symbol position V ₁ to keep the pressure P ₁ or symbol position V ₂
It controls the discharge amount control section 16 of the variable pump 1. In steady state, the pressure control pilot valve 2b is located at the symbol position _V1 ,
The discharge amount of the variable pump 1 is controlled to be extremely small. At this time, the drain from the discharge amount control section 16 is transferred to the tank 4 via the drain line 40.
I am guided by 1. The pressure difference between the pilot chamber and the spring chamber occurs because the fluid flowing from the variable pump 1 to the pilot relief valve 18 passes through the throttle 55.

The curve between time T ₁ and T ₂ in FIG. 2 shows a transition period from the flow rate control state to the pressure control state, and 44 in the curve shows surge pressure, that is, pressure overshoot.

When a predetermined period of time has elapsed under the first set pressure _P1 and the point T2 in FIG. ₂ is reached, the switching valve 18c is switched and the low pressure side pilot relief valve 18a
The set pressure is lowered by the operation of , and the filling pressure is brought to the second set pressure _P2 , that is, the holding pressure. in this way,
To lower the set pressure to the second set pressure,
This is because if the resin is pressurized at high pressure, burrs will occur.

When maintaining this pressure, the pilot valve 2a,
2b is a small valve that controls only the fluid for the discharge amount control section 16, and the pilot relief valves 18a and 18b also control a small amount of pilot fluid. No significant pressure undershoot will occur. Therefore, the molded product will not have any negative effects such as sinking or chipping.

Pressure control for the second set pressure _P2 is performed by the pressure control pilot valve 2b in the same manner as for the first set pressure. That is, the pressure control pilot valve 2b is operated so that the difference between the pressure in its pilot chamber and the pressure in the spring chamber, which is the set pressure of the pilot relief valve 18a, corresponds to the spring force of the spring 38, thereby controlling the filling pressure to the second level. Settling pressure P ₂
Keep it.

In the above embodiment, the pilot relief valve 18 is constructed by combining two pilot relief valves 18a and 18b, but a single electromagnetic pilot relief valve (not shown) may be used.

<Effects of the Invention> As is clear from the above, according to this invention,
When the pump port of the switching valve is closed, the fluid in the main line and the pilot line is compressed to a pressure corresponding to a predetermined low pressure set by the pilot relief valve, and the pressure control pilot valve is moved to a position corresponding to the unload position. Since the injection actuator is placed in a transitional position, the response is quick and the injection actuator can be started up quickly.Therefore, the resin does not cool down and harden during the process, and the resin can reach every corner of the mold. You can press the resin. Furthermore, since a pilot relief valve for setting the set pressure in multiple stages is connected to the spring chamber of the pilot valve for pressure control, the pressure can be controlled in multiple stages. In addition, since the pump port normally closed type switching valve and throttle valve are separated, multiple actuators can be connected downstream of the throttle valve, and even if the pump port of the switching valve for one actuator is closed, other actuator. Further, according to the present invention, since the pilot valve for pressure control and the pilot valve for flow rate control are used,
It has good pressure override characteristics and can further improve the efficiency of power-saving control, and the pilot valve can be configured with a small valve, reducing pressure undershoot, thereby eliminating sinks and chips in the molded resin. can.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of one embodiment of the present invention, Fig. 2 is a time-filling pressure characteristic diagram of the above embodiment, Fig. 3 is a pressure overwrite characteristic diagram of the above embodiment, and Fig. 4 is a diagram of the conventional example. It is a circuit diagram. 1... Variable pump, 2... Pilot valve, 2a
...Pilot valve for flow rate control, 2b...Pilot valve for pressure control, 5...Actuator, 6...
Main line, 7...throttle valve, 18...pilot relief valve.

Claims (1)

[Claims] 1 A throttle valve 7 is installed in the main line 6 that connects the pump port normally closed type switching valve 3 that controls only the operating direction of the injection actuator 5 and the variable pump 1, and a pilot valve branching from before and after the throttle valve 7 is installed. Lines 8 and 9 are connected to the pilot chamber and spring chamber of the pilot valve 2a for flow rate control, respectively, and the front part of the throttle valve 7 is connected via the pilot line 8 to the pilot chamber of the pilot valve 2b for pressure control. On the other hand, the front end of the throttle valve 7 is connected to the spring chamber of the pressure control pilot valve 2b by a pilot line 56 having a throttle 55, and the set pressure of the main line 6 is set in multiple stages. The pilot relief valve 18 is connected to the spring chamber of the pressure control pilot valve 2b.
Fluid control for an injection molding machine, characterized in that the discharge amount control section 16 of the variable pump 1 is switched and connected to the main line 6 and the tank line 12 by switching the flow rate control pilot valve 2a. Device.