JPH0432403B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a relief pressure control circuit which is particularly effective when used, for example, for pressure control of an injection cylinder of an injection molding machine.

<Prior Art> Conventionally, there is a pressure control circuit for relief as shown in FIG. (Hydraulic pneumatic design, No. 17
See Figure 4, Volume 10, Page 71. ) This relief pressure control circuit connects an electromagnetic relief valve 5 to a main line 3 that connects a pressure source 1 and an injection cylinder 2, and also connects a pressure detector 7 that detects the pressure of the main line 3 to an operational amplifier 6. detection pressure signal
Id and the target pressure signal Io are input, and the electromagnetic relief valve 5 is controlled based on the comparison value between the detected pressure signal Id and the target pressure signal Io, that is, the main pressure is controlled by pressure feedback control via the main line 3. The pressure in line 3 is controlled. Further, this relief pressure control circuit connects a safety valve 7 for regulating the maximum pressure to the main line 2.

<Problems to be Solved by the Invention> By the way, in the conventional relief pressure control circuit described above, during the transition from the flow rate control state (means not shown) to the pressure control state, as shown by curve A in FIG. The problem is that large and long-lasting pressure overshoots occur.

The reason why such pressure overshoot occurs is as follows. In FIG. 3, Po is the target pressure to be controlled by the electromagnetic relief valve 5, Pm is the set pressure of the safety valve 7, and E is the time when the injection cylinder 2 reaches the stroke end and shifts from the flow rate control state to the pressure control state. . In the flow rate control state before the above time E, the pressure in the main line 3 detected by the pressure detector 7 is extremely lower than the target pressure Po, so the operational amplifier 6 is outputting the maximum output, and the electromagnetic relief valve 5 is completely closed. It is in a closed state. In this state, the control elements of the feedback system, such as the operational amplifier 6 and the electromagnetic relief valve 5, are in a saturated state with respect to the signal magnitude. Next, after time E, when the fluid pressure in the main line 3 exceeds the target pressure Po, the operational amplifier 6 is reversed from the saturation state with a certain time constant unique to this feedback system. Due to the delay in the output of the electromagnetic relief valve 5 by this time constant, a large pressure overshoot exceeding the target pressure Po continues for a long time, as shown by curve A in FIG. This pressure overshoot is larger than the pressure overshoot determined by the inherent characteristics of the electromagnetic relief valve 5 itself and lasts for a long time.

In order to solve this problem, it is conceivable to shorten the time constant of the feedback system including the operational amplifier 6 to reduce the overshoot and shorten the time, but this causes the problem of oscillation.

In addition, in order to eliminate the drawback of pressure overshoot caused by pressure feedback control, it is possible to control the electromagnetic relief valve 5 in an open loop, but in this case, it is possible to control the electromagnetic relief valve 5 in an open loop. Drift occurs and pressure control accuracy deteriorates.

Therefore, the purpose of this invention is to maintain static pressure control accuracy equivalent to pressure feedback control while suppressing pressure overshoot to a small and short-term pressure overshoot similar to conventional open loop control during the transition period when entering the pressure control state. be.

<Means for Solving the Problems> In order to achieve the above object, the relief pressure control circuit of the present invention includes a relief main valve 13 that controls the pressure of the main line 11, as shown in FIG.
A pilot relief valve 26 is connected to the spring chamber 16 that is not in communication with the main line 11, and the pilot relief valve 26 is controlled in accordance with a comparison value between the fluid pressure in the spring chamber 16 and the target pilot pressure. It is characterized in that a feedback system 27 is provided for inputting signals to control the fluid pressure in the spring chamber 16 to the target pilot pressure, and a pressure source 31 is connected to the spring chamber 16.

<Function> With the above configuration, fluid flows into the upstream side of the pilot relief valve 26 from the pressure source 31 that can generate the target pilot pressure. The pilot relief valve 26 operates constantly to discharge the fluid, and is connected to the main line 11 of the main relief valve 13.
The fluid pressure in the spring chamber 16, which is not in communication with the spring chamber 16, is precisely controlled to the target pilot pressure by a control signal from the feedback system 27. in this way,
The relief main valve 13 is configured to control the pressure in the spring chamber 16 by the operating pilot relief valve 26 regardless of whether the main line 11 is under flow control, pressure control, or in a transition state from flow control to pressure control. The pressure is always controlled to be constant, and the pressure in the main line 11 corresponding to the fluid pressure in the spring chamber 16 is controlled.

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

In FIG. 1, 11 is a main line connected to a pressure source 12, and 13 is a relief main valve connected to the main line 12.

The relief main valve 13 has a piston 15 slidably fitted into the valve chamber 14. A spring 17 is compressed in the spring chamber 16 at one end of the piston 15, and the spring 17 pushes the piston 15 toward the valve seat 1.
8 to open and close the gap between the inlet 21 and the outlet 22.

A pilot relief valve 26 is connected to the spring chamber 16 of the main relief valve 13 via a throttle 25, and the pilot relief valve 26 and the spring chamber 16 are further connected by a feedback system 27. The internal pressure is controlled by feedback. The feedback system 27 includes a pressure detector 28 and an operational amplifier 29. The pressure detector 28 is connected to the spring chamber 16 of the relief main valve 13.
A signal representing this fluid pressure is input to an operational amplifier 29. A target pilot pressure signal Ip corresponding to the specified fluid pressure of the main line 11 to be controlled is further input to the operational amplifier 29. The operational amplifier 29 compares the signal representing the fluid pressure in the spring chamber 16 detected by the pressure detector 28 with the target pilot pressure signal Ip,
A control signal obtained by amplifying this comparison value is output to the pilot relief valve 26. Therefore, the pilot relief valve 26 converts the fluid pressure in the spring chamber 16 of the main relief valve 13 into the target pilot pressure signal Ip.
Feedback control is performed to the target pilot pressure corresponding to the

On the other hand, a pressure source 31 which is not directly related to the pressure source 12 having a pressure higher than the target pilot pressure is connected between the spring chamber 16 and the throttle 26 of the main relief valve 13. It is connected via 32. Therefore, a constant flow of fluid always flows between the spring chamber 16 and the throttle 25.
As a result, the pilot relief valve 26 is always in operation at a certain opening degree.

With the above configuration, the pilot relief valve 26 is always in operation at a certain opening degree as described above, and the fluid pressure in the spring chamber 16 of the main relief valve 13 is controlled by the pilot relief valve 26. The target pilot pressure is accurately controlled regardless of the operating state of the main line 11, that is, regardless of the flow rate control state, pressure control state, or transient state from flow control to pressure control of the main line 11.

Suppose now that the main line 11 shifts from the flow rate control state to the pressure control state, and the pressure of the main line 11 rises rapidly.

Then, the piston 1 of the relief main valve 13
When the fluid pressure in the main line 11 becomes higher than the sum of the fluid pressure in the spring chamber 16, which is accurately controlled to the target pilot pressure, and the spring force of the spring 17, the main line 5 immediately retreats to the spring chamber 16 side. 11 pressure is controlled. When the piston 15 retreats, the fluid pressure in the spring chamber 16 tends to rise, but the fluid in the spring chamber 16 is quickly discharged from the pilot relief valve 26, which always operates at a certain opening. 16 does not rise excessively, the piston 15 quickly retreats, and the pressure overshoot in the main line 11 is small and lasts only for a short period of time, as shown by curve B in FIG. From a different perspective, since fluid is flowing into the pilot relief valve 26 from the pressure source 31 having a pressure higher than the target pilot pressure through the pressure compensated flow rate adjustment valve 32, the operational amplifier 29
The pilot relief valves 26 and 26 are not saturated and are in a balanced state, so they operate with good responsiveness, and as a result, the pressure overshoot in the main line 11 is reduced. In other words, the pressure overshoot inherent in pressure feedback control due to the saturation of the operational amplifier, etc. in conventional pressure feedback control does not occur, and only a pressure overshoot equivalent to the pressure overshoot occurs due to the pressure overshoot by the relief main valve 13 itself, that is, the open control. That's why.

In addition, statically, the pressure in the spring chamber 16 of the main relief valve 13 is accurately controlled to the target pilot pressure by the pilot relief valve 26, so the fluid pressure in the main line 11 is controlled by conventional pressure feedback control. The static characteristics of pressure control with the same high precision can be obtained.

In the above embodiment, a pressure-compensated flow regulating valve is used as the flow regulating valve, but a throttle may be used instead.

<Effects of the Invention> As is clear from the above explanation, according to the relief pressure control circuit of the present invention, it is possible to enter a pressure control state while maintaining static characteristics (pressure control accuracy) equivalent to conventional pressure feedback control. During the transition period, pressure overshoot can be suppressed to the same level as conventional open control.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, FIG. 2 is a circuit diagram of a conventional example, and FIG. 3 is a graph illustrating pressure overshoot in the above embodiment and the conventional example. 11... Main line, 12, 31... Pressure source, 1
3...Main valve for relief, 26...Pilot relief valve, 27...Feedback system, 32...Flow rate adjustment valve with pressure compensation.

Claims (1)

[Claims] 1. A pilot relief valve 26 is connected to the spring chamber 16 of the relief main valve 13 that controls the pressure of the main line 11, which is not in communication with the main line 11, and the pilot relief valve 26 is
inputting a control signal corresponding to a comparison value between the fluid pressure in the spring chamber 16 and the target pilot pressure to
A relief pressure control circuit characterized in that a feedback system 27 for controlling the fluid pressure in the spring chamber 16 to the target pilot pressure is provided, and a pressure source 31 is connected to the spring chamber 16.