JPH0426724B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a computer-based automatic control method for a proportional control valve in a low-pressure casting machine, and more specifically,
Various proportional control valves are installed in the circuit that supplies compressed gas to the holding furnace when pressurizing the inside of the molten metal holding furnace of a low-pressure casting machine according to a predetermined time-pressure curve (hereinafter referred to as target pattern). The present invention relates to a method suitable for automatically controlling a computer using a computer.

(Prior Art) The present applicant previously proposed, in the invention of Japanese Patent Application No. 60-95726 (Japanese Unexamined Patent Publication No. 61-253158), that the pressure of a gas that pressurizes the molten metal in the molten metal holding furnace of a low-pressure casting machine is , proposes to provide a proportional control valve in the gas supply circuit in order to control it according to a predetermined target pattern. That is, as shown in FIG. 6, the air supply hole 22 of the holding furnace 21 is connected to a compressed air source 26 via two electromagnetic on-off valves 23 and 24 arranged in parallel and a power pressure reducing valve 25, and the electromagnetic Open/close valve 23
A pressure sensor 27 is disposed between the holding furnace 21 and the holding furnace 21,
The electromagnetic on-off valves 23 and 24 are electrically connected to a microcomputer 28 that stores an optimal pressurizing pattern for optimally pressurizing the upper surface of the molten metal in the holding furnace 21, and the microcomputer 28 is connected to the proportional control valve 29 and the A pressure sensor 27 is electrically connected, and this proportional control valve 29 is connected to the power pressure reducing valve 25.
The structure is connected to the pilot part of the holding furnace 2.
Pressure sensor 27 measures the pressure in the space above the hot water level in 1.
This pressure signal is input to the microcomputer 28, and the microcomputer 28 calculates the required pressurizing pressure to the upper surface of the molten metal based on the set pressurizing pattern, and according to this calculation result, the electromagnetic While opening and closing the on-off valves 23 and 24 as appropriate, the operation of the power pressure reducing valve 25 is adjusted via the proportional control valve 29, and compressed air with a controlled pressure is supplied to the holding furnace 21 for a required period of time. The upper surface of the molten metal in 21 is pressurized according to a target pattern.

(Problem to be Solved by the Invention) However, the proportional control valve 29
When the upper surface of the molten metal in the holding furnace 21 was pressurized by operating the holding furnace 21, the following problem occurred. That is, when various analog values (V ₁ , V _{2 . .} .) are input as control signals to the proportional control valve 29, the proportional control valve 29 enters a state in which it can output a predetermined pressure, as shown in FIG. It took a long time to complete the process, and there was a type lag in the pressure output compared to the analog value input. Therefore,
When trying to change the pressure of compressed air supplied to the holding furnace 21 via the power pressure reducing valve 25 in a predetermined target pattern over time, the holding furnace 21
There was a problem in which the internal pressure changes deviated significantly from the target pattern. Furthermore, there was a problem in that the proportional control valve had a size limit, and when the holding furnace became large and required a large amount of gas, the proportional control valve could not cope with the capacity.

(Object of the Invention) The present invention has been made to solve the above problems, and eliminates the adverse effects caused by the time lag of a proportional control valve disposed between a compressed air source as a compressed gas source and a holding furnace. The proportional control valve can change the pressure of compressed air from the compressed air source to a pressure that corresponds to a predetermined target pattern and send it out. The purpose is to provide a control method.

(Means for Solving the Problems) In order to achieve the above objects, the present invention provides a first valve equipped with an electromagnetic on-off valve and a large-capacity proportional flow control valve.
The molten metal holding furnace is communicatively connected to a compressed gas source via a gas supply circuit and a second gas supply circuit provided in parallel with the first gas supply circuit and equipped with a small capacity proportional pressure control valve, and further, The electromagnetic on-off valve, the proportional flow control valve, and the proportional pressure control valve are electrically connected to a computer, and the electromagnetic on-off valve, the proportional flow control valve, and the proportional pressure control valve are controlled by the computer, In the computer-based automatic control method of a compressed gas supply circuit in a low-pressure casting machine for changing the pressure in the holding furnace along a target pattern of a preset time-pressure curve, the first gas supply circuit includes: Calculate the pressure increase rate between a certain inflection point (J) and the next inflection point (J+1) in the target pattern of the time-pressure curve preset in the calculator, based on the target pattern, and When the calculation result is larger than a certain value, a signal is sent to the electromagnetic on-off valve to open it, and this signal is sent to the electromagnetic on-off valve so that the opening of the proportional flow control valve corresponds to a value slightly smaller than the calculation result. transmitting a signal to the proportional flow control valve, and when the calculation result changes to become smaller than a certain value, transmitting a signal to the electromagnetic on-off valve so that the electromagnetic valve closes, and simultaneously stopping the signal to the proportional flow control valve; In parallel with the operation regarding the first gas supply circuit, the second gas supply circuit is operated at a time (ti+1) that is a unit time ahead of a certain moment (ti).
Calculating the target pressure (Pi+1) at based on the target pattern stored in advance in the computer,
The steady analog value (Vo) of the proportional pressure control valve corresponding to this calculated target pressure (Pi+1) is
It is calculated based on steady analog value data of the proportional pressure control valve stored in advance in the computer, the pressure (Pm) in the holding furnace at the time (ti) is measured, and this pressure (Pm) and the target pressure are calculated. (Pi+
1) Calculate the pressure deviation (△P) from The command analog value (V) is obtained by adding the steady analog value (Vo) to the analog value (Vd).
It is characterized by calculating the command analog value (V) and transmitting this command analog value (V) to the proportional pressure control valve.

(Function) In the present invention, the electromagnetic on-off valve and the proportional flow rate control are interlocked with each other under computer control to increase the pressure increase rate between the inflection point (J) and the next inflection point (J+1). When is larger than the certain value, the electromagnetic on-off valve is opened and a large volume of compressed gas is supplied to the holding furnace. In parallel with this, the corrected analog value (Vd) calculated based on the target pressure (Pi + 1) at the time (ti + 1) a unit time ahead of the instant (ti) is changed to the steady analog value ( Vo)
This added analog value is input to the proportional pressure control valve as a command analog value (V), and a small volume of compressed gas whose flow rate is controlled is supplied to the holding furnace.

In this way, the holding furnace is simultaneously supplied with a large volume of main compressed gas and a small volume of regulating compressed gas, so that the upper surface of the molten metal in the holding furnace has a pressure very close to that of the target pattern. It will be pressed by.

(Example) Next, regarding an example of the present invention, FIGS.
This will be explained in detail based on FIGS. 4 and 5. As shown in FIG. 1, which is a block diagram of an embodiment to which the present invention is applied, a compressed air source 1 as a compressed gas source includes a conduit 2, a mist separator 3, a primary pressure reducing valve 4, an electromagnetic on-off valve 5, a proportional It is connected to a molten metal holding furnace 8 via a flow rate control valve 6 and a filter 7 . Note that the proportional flow control valve 6 is adapted to send out compressed air at a flow rate proportional to the magnitude of the input current. In addition, the compressed air source 1 includes a branch pipe 9, a mist separator 10, a primary pressure reducing valve 11,
It is connected to the holding furnace 8 via a proportional pressure control valve 12 and a filter 13 . Note that the proportional pressure control valve 12 is configured to send out compressed gas having a pressure proportional to the magnitude of the input current. The proportional flow control valve 6 and the proportional pressure control valve 12 are electrically connected to a computer 18 via amplifiers 14 and 15 and D/A converters 16 and 17. The computer 18 stores various target patterns of time-pressure curves as shown in FIG.

Further, a pressure sensor 19 is attached to the holding furnace 8, and the pressure sensor 18 is connected to an A/D converter 20.
It is electrically connected to the computer 18 via.
Further, an electromagnetic on-off valve 22 is provided between the proportional flow rate control valve 6 and the filter 7 via a branch pipe 21. Note that 23 is a stalk and 24 is a mold.

In the device configured as described above, compressed air generated from a compressed air source 1 has its mist removed by a mist separator 3, is brought to an appropriate pressure by a primary pressure reducing valve 4, and then reaches an electromagnetic on-off valve 5. Under this condition, as shown in FIGS. 4 and 5, which are flowcharts of an embodiment of the present invention, when the apparatus is started, the computer first calculates the time-pressure characteristic curve of the proportional control valve. Check whether there is an inflection point shown in Figure 2. For example, if there is an inflection point (J), the pressure increase rate up to the next inflection point (J+1) is set in advance. C. If the calculated pressure increase rate is larger than a certain value (C) determined by the scale of the proportional flow rate control valve 6, the holding furnace 8, etc., the electromagnetic on-off valve 5 An open signal is input to , and the electromagnetic on-off valve 5 is opened. Next, the opening degree of the proportional flow rate control valve 6 necessary to obtain a pressure increase rate slightly smaller than this pressure increase rate is calculated, and the result is transferred to the proportional flow control valve 6 via the D/A converter 17 and the amplifier amplifier 15. The signal sent to the flow rate control valve 6. As a result, the proportional flow rate control valve 6 is activated, and accordingly, the holding furnace 8
Compressed air is supplied while being controlled so that the pressure inside the holding furnace 8 is slightly lower than the target pattern. Then, as shown in step 2, when the pressure increase rate changes to become smaller than the constant value (C), for example, the electromagnetic on-off valve 5 is closed by a signal from the computer 18, and at the same time the proportional flow control valve 6 is stopped (NO step in step 2). The compressed air entering the branch pipe 9 in parallel with the above operation is controlled as follows. That is, the compressed air generated from the compressed air source 1 has its mist removed by the mist separator 10 , is brought to an appropriate pressure by the primary pressure reducing valve 11 , and then reaches the proportional pressure control valve 12 . Then, in the calculator 18, first, the target pressure (Pi+1) at a time (ti+1) a unit time ahead of a certain moment (ti) is calculated based on the target pattern. Then,
The steady analog value (Vo) of the proportional pressure control valve 12 corresponding to this calculated target pressure (Pi+1) is
Proportional pressure control valve 12 stored in computer 18
is calculated based on the steady-state analog value of on the other hand,
The pressure signal in the holding furnace 8 at the time (ti) is detected by the pressure sensor 19 and inputted to the computer 18 via the A/D converter 20. When the pressure signal of this pressure (Pm) is input to this calculator 18, the pressure deviation (△P) is calculated from the target pressure (Pi+1) and the pressure in the holding furnace 8 (Pm), and then, This pressure deviation (ΔP) is multiplied by a preset gain (G) to calculate a corrected analog value (Vd). Next, the steady analog value (Vo) and the corrected analog value (Vd) are added to calculate a command analog value (V).
6 and transmitted to the proportional pressure control valve 12 via the amplifier firer 14. The above operations are performed from time to time. As a result, the main compressed air that has flowed through the conduit 2 and the regulating compressed air that has flowed through the branch pipe 9 are simultaneously supplied to the holding furnace 8, and the molten metal surface is kept at a pressure that is very close to the target pattern pressure. Molten metal is poured into the mold 24 by being pressed.
In this way, after pouring into the mold 24 is completed, the electromagnetic on-off valve 22 is opened for a predetermined period of time, and the holding furnace 8
Discharge the compressed air inside.

(Effects of the Invention) As is clear from the above description, according to the present invention, a small volume of compressed gas for adjustment is supplied to the holding furnace at the same time as a large volume of the main compressed gas.
Even if the holding furnace is large, the proportional pressure control 12 is controlled by an analog value (V) obtained by adding the auxiliary analog value (Vd) to the normal analog value (Vo) of the proportional pressure control 12. Because of this control, the adjustment accuracy of the adjustment fluid becomes very accurate, and the pressure of the controlled compressed gas comes very close to the pressure of the target pattern, providing excellent effects.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an apparatus according to an embodiment of the present invention, FIGS. 2 and 3 are time-pressure characteristic diagrams of a proportional control valve, and FIGS. 4 and 5 are an embodiment of the present invention. An exemplary flowchart, FIG. 6, is a block diagram of a conventional low-pressure casting machine.

Claims (1)

[Claims] 1. A first gas supply circuit equipped with an electromagnetic on-off valve and a proportional flow control valve for large capacity, and a second gas supply circuit provided in parallel with this first gas supply circuit and equipped with a proportional pressure control valve for small capacity. The molten metal holding furnace is communicatively connected to a compressed gas source through a computer, and the electromagnetic on-off valve, the proportional flow rate control valve, and the proportional pressure control valve are electrically connected to a computer to control the electromagnetic on-off valve, the proportional flow rate control valve, and the proportional flow rate control valve. A compressed gas supply circuit in a low pressure casting machine for controlling a control valve and the proportional pressure control valve by the computer and changing the pressure in the holding furnace along a target pattern of a preset time-pressure curve. An automatic control method using a computer, in which, for the first gas supply circuit, a certain inflection point (J) and a next inflection point (J+1) in a target pattern of a time-pressure curve preset in the computer are provided. The rate of pressure rise between the proportional flow control valve and A signal is sent to the proportional flow control valve so that the opening becomes a size corresponding to a value slightly smaller than the calculated result, and when the calculated result changes to become smaller than a certain value, the electromagnetic on-off valve closes. Simultaneously with the transmission to the electromagnetic on-off valve, the transmission to the proportional flow rate control valve is stopped, and in parallel with the operation regarding the first gas supply circuit, the second gas supply circuit is controlled from a certain instant of time (ti). Target pressure (Pi+1) at the time ahead (ti+1)
is calculated based on the target pattern stored in advance in the computer, and this calculated target pressure (Pi
The steady analog value (Vo) of the proportional pressure control valve corresponding to +1) is calculated based on the steady analog value data of the proportional pressure control valve stored in advance in the computer, and Measure the pressure (Pm), calculate the pressure deviation (△P) between this pressure (Pm) and the target pressure (Pi + 1), and apply a preset gain to this calculated pressure deviation (△P). (G) to calculate a corrected analog value (Vd), then add the steady analog value (Vo) to the corrected analog value (Vd) to calculate a command analog value (V), and then calculate the command analog value (V). (V) to the proportional pressure control valve, an automatic control method using a computer for a pressure gas supply circuit in a low pressure casting machine.