JPH0238382B2 - SHASHUTSUSEIKEIKYUATSUSOCHINOSEIGYOHOHO - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a method of controlling a hydraulic system of an injection molding machine.

(b) Prior Art In controlling injection molding machines, a method of controlling the injection speed in multiple stages is generally used. In this case, a pressure responsive hydraulic circuit using an electromagnetic proportional valve and a pressure compensation valve is used to control the amount of oil supplied to the injection cylinder. A predetermined amount of oil is supplied to this electromagnetic proportional valve from a plurality of fixed pumps connected together. The plurality of pumps are selectively loaded in a predetermined combination so that the minimum amount of oil required for a predetermined injection speed can be supplied. For example, if three pumps with different oil discharge volumes are connected, seven levels of oil supply can be obtained (by putting each pump in a load state independently,
three stages can be obtained by combining any two pumps, and one stage can be obtained by loading all three pumps). The combination of pumps under load is switched at the same time as the opening of the electromagnetic proportional valve is switched based on a signal from a position sensor that detects when the screw has moved to a predetermined position.

(C) Problems to be Solved by the Invention However, in this conventional control method for the injection molding machine hydraulic system, there is a temporary shortage of supplied oil at the time of speed switching, and it is difficult to control the injection speed as specified. The problem is that there are cases where this is not possible. That is, for example, when a predetermined pump is switched from a no-load state to a loaded state, it takes a predetermined time, albeit a relatively short time, for the pressure oil of this pump to reach the electromagnetic proportional valve. This is caused by a delay in the rise of the oil pressure of the pump itself, expansion of the pipeline, compression of the hydraulic oil, etc. On the other hand, when the pump is switched from a loaded state to an unloaded state, on the other hand, the flow rate decreases with almost no time delay. As a result, for example, three pumps (pump 10 (discharge oil volume 10/
Despite the intention of setting the oil amount as shown in FIG. The amount of oil actually obtained will be as shown in FIG. In other words, immediately after switching all the pumps, the amount of oil supplied temporarily becomes almost 0, and if there is a pump that is newly loaded, the amount of oil increases in a stepwise manner, and in any case, the amount of oil supplied becomes almost zero. An oil shortage condition occurs. For this reason,
Problems such as this occur when the injection speed decreases or the rise of the injection speed is delayed. The present invention aims to solve the above problems.

(d) Means for Solving the Problems The present invention solves the above problems by switching the pump to the loaded state when the screw comes to a position a predetermined distance before the injection speed switching position. That is, in the method of the present invention, the injection speed of the injection molding machine is controlled by the opening degree of the electromagnetic proportional valve provided between the plurality of pumps and the injection cylinder, and each pump is controlled according to the set value of the injection speed. This is applied to injection molding machine hydraulic systems that can selectively switch between a loaded state and a no-load state to ensure the required flow rate, and can switch from a no-load state to a loaded state according to the injection speed setting. When the screw reaches the position before the injection speed switching position by a distance equal to the current injection speed setting multiplied by a predetermined constant, the pump to be loaded will switch to the loaded state, and the pump will switch to the loaded state according to the injection speed setting. A pump that is to be switched from a loaded state to a no-load state is designed to ensure the required amount of oil by switching to the no-load state at the same time as the opening of the electromagnetic proportional valve is changed when the screw reaches the injection speed switching position. be.

(e) Effect When the screw reaches a position a predetermined distance before the injection speed switching position, a predetermined pump is switched from a no-load state to a loaded state. The predetermined distance is the set value of the injection speed at that time multiplied by a predetermined constant. The predetermined constant is a constant determined depending on the characteristics of the pump, the pipe line, the hydraulic oil, and the like. As a result, the higher the set value of the injection speed at that time is, the more the pump is switched from the no-load state to the loaded state at a position before the injection speed switching position. As a result, the pump is in a state to discharge the required amount of oil at a position immediately before the screw reaches the injection speed switching position (the above-mentioned predetermined constant is set so as to achieve this). This ensures that the necessary amount of oil is always secured even immediately after switching the injection speed.

(F) Embodiments Hereinafter, embodiments of the present invention will be described with reference to Nos. 1 and 2 of the attached drawings.
This will be explained based on the diagram.

Three pumps 10, 12 and 14 with different discharge oil volumes (for example, the discharge oil volumes are 10/min and 20/min, respectively)
/min and 40/min) are respectively check valve 1.
6, 18 and 20 to conduit 22. Pumps 10, 12 and 14 can be switched between loaded and unloaded conditions by solenoid valves 24, 26 and 28, respectively. Conduit 22
A relief valve 30 is provided. Further, the pipe line 22 is connected to a pipe line 34 via an electromagnetic proportional valve 32. The conduit 34 is connected to an injection cylinder 36 . In addition, the pipe line 22 includes the pipe line 22 and the pipe line 3.
A pressure compensation valve 3 that controls the differential pressure between 4 and 4 to a predetermined value.
8 is provided. A piston 40 of the injection cylinder 36 is connected to a screw 42. The axial position of the screw 42 can be detected by a position sensor 44. The signal from position sensor 44 is input to comparator 46 . A signal from the speed switching position setter 48 and a signal from the corrected position memory 50 are also input to the comparator 46 . The speed switching position setter 48 has three speed switching positions between the screw backward position _S0 and the screw forward position _S4 .
S ₁ , S ₂ and S ₃ are set. Correction position memory 50
, predetermined correction positions (S ₁ ′, S ₂ ′ and S ₃ ′) is memorized. A speed setter 56 that operates based on the signal from the comparator 46 is provided, and this _speed setter ₅₆
Set speed between F ₁ , S ₁ → S ₂ Set speed between F ₂ , S ₂ →
Set speed F ₃ between S ₃ and set speed F ₄ between S ₃ → S ₄
is set. The opening degree of the electromagnetic proportional valve 32 is controlled by the signal from the speed setter 56 via the amplifier 58. Further, a pump selection device 60 controls the operation of the solenoid valves 24, 26, and 28 based on a signal from the speed setting device 56.
The pump selection device 60 is given in advance data on pumps to be put into a loaded state in accordance with the set value of the injection speed.

Next, the operation of this embodiment will be explained. First, when the screw 42 starts moving forward from the screw backward position S ₀ , the speed setter 56 outputs the set speed F ₁ to the amplifier 58 and the pump selection device 60 . As a result, the amplifier 58
2 is operated so that its opening degree is in a predetermined state corresponding to the set speed. Also, the pump selection device 60
turns on the solenoid valves 24 and 26 to place the pumps 10 and 12 in a loaded state. As a result, the pipe line 22 is supplied with an oil amount of 30/min. At this time, the opening degree of the electromagnetic proportional valve 32 is relatively close to the oil amount within the range of not exceeding 30/min (for example, 25/min).
The opening is set to allow the flow of water (minutes). The piston 40 and the screw 42 move forward due to the amount of oil supplied from the electromagnetic proportional valve 32 to the injection cylinder 36 via the conduit 34. The position of the screw 42 is detected by a position sensor 44, and this signal is input to a comparator 46, and is input to the speed switching position _S1 set by the speed switching position setter 48 and the correction position memory 50. The stored correction position S ₁ ′ (this S ₁ ′ is a larger value than S ₁ , that is, it is on the front side with respect to the forward direction of the screw 42. The coordinate values indicating the position are from S ₀ to S ₄ ), which is assumed to gradually decrease to .).

The comparator 4 indicates that the screw 42 has reached the corrected position S ₁ ' set by the corrected position memory 50.
6, comparator 46 outputs a signal to speed setter 56. Based on this signal, the speed setter 56 outputs a signal indicating the next set speed F ₂ to the pump selection device 60. Pump selection device 6
0 turns on the solenoid valve 28 based on this signal and switches the pump 14 to the loaded state (note that the loaded state of the pumps 10 and 12 is maintained as is at this point). When the pump 14 is switched to the loaded state, the amount of oil discharged from the pump 14 starts to rise, and immediately before the screw 42 reaches the speed switching position _S1 , the amount of oil discharged from the pump 14 (40/ minute) is supplied to the electromagnetic proportional valve 32. As a result, when the screw 42 reaches the speed switching position _S1 ,
There will be an oil amount of 70/min.

Next, when the comparator 46 confirms that the screw 42 has reached the speed switching position _S1 ,
Comparator 46 outputs a signal to speed setter 56 .
The speed setter 56 uses the amplifier 58 based on this signal.
and outputs a signal to the pump selection device 60. This causes the amplifier 58 to move the electromagnetic proportional valve 32 to the set speed.
At the same time, the pump selection device 60 turns off the solenoid valve 24 and the solenoid valve 26, and switches the opening degree corresponding to _F2 .
2 is in a no-load state. As a result, the solenoid proportional valve 3
The amount of oil supplied to 2 is 40 from the pump 14.
/minute. In this state, the solenoid proportional valve 32 is 40
The opening degree is set so that the oil amount is close to this (for example, 35/min) within a range that does not exceed 1/min.

Correction position stored in the correction position storage device 50
S ₁ ' is calculated by the calculator 54 as follows.
That is, the calculator 54 calculates the product of the predetermined constant k set by the constant setter 52 and the set speed _F1 , and adds it to the speed switching position _S1 , and stores this in the corrected position memory. It is stored in the device 50 as S ₁ ' (that is, S ₁ '=S ₁ +k·F ₁ ). The calculation constant k in this calculator 54 is determined by any solenoid valve, for example, the solenoid valve 2.
This corresponds to the delay time Δt from when the signal to turn it on is issued at 8 until the pressure oil from the pump 14 actually reaches the electromagnetic proportional valve 32. Therefore, it is sufficient to turn on the solenoid valve 28 △t time before reaching the speed switching position S ₁ , but it is necessary to turn on the solenoid valve 28 in advance at a position △t time before a certain position (for example, point S ₁ ). cannot be predicted. However, within this Δt time, the screw 42
The distance traveled by will vary depending on the actual moving speed of the screw 42 from S ₀ to S ₁ , and since the set speed at that point is F ₁ , S ₁ '−S ₁ = △t・
As F ₁ , it is possible to find a point S' at a time Δt before the S ₁ point. The value of the delay time Δt can be determined by conducting a test. Delay time △t
This occurs due to a delay in pump start-up, expansion of the pipe line, compression of hydraulic oil, etc., so there will be some differences in the delay time △t depending on the pump discharge capacity, pipe volume, etc. . Considering this difference, △
If you add some margin to the value of t and use this value as the constant k, the pump 14 will always be at the speed switching position _S1 .
This means that the amount of oil reached the electromagnetic proportional valve 32 (see Fig. 2).

The same operation as described above is performed when the screw 42 advances further and reaches the correction position S ₂ ' and the speed switching position S ₂ . That is, the corrected position memory 50
When the screw 42 reaches the correction position S ₂ ' set by the same calculation as above (S ₂ '=S ₂ +k・F ₂ ), the solenoid valve 26 is turned on and the screw 42 returns to the speed switching position. When _S2 is reached, the pressure oil of the pump 12 reaches the electromagnetic proportional valve 32. Further, a similar operation is performed when the screw 42 reaches the correction position S ₃ ' and the speed switching position S ₃ . That is, when the screw 42 reaches the correction position S ₃ ' set by the same calculation (S ₃ '=S ₃ +k·F ₃ ) in the calculator 54, the solenoid valve 24 and the solenoid valve 28 are turned on. When the screw 42 reaches the speed switching position S ₃ , the oil amount of the pump 10 and the pump 14 is in a state where it is supplied to the electromagnetic proportional valve 32. The amount of supplied oil thus obtained is as shown in FIG. Therefore, the necessary amount of oil is always ensured when switching speeds, and problems such as temporary oil shortage will not occur.
Further, the amount of oil in the pipe line 34 is always controlled by the electromagnetic proportional valve 32 and the pressure compensation valve 38.

(g) Effects of the Invention As explained above, according to the present invention, when the screw reaches a position before the injection speed switching position by a distance equal to the current injection speed multiplied by a predetermined constant, the pump Since the injection speed is switched to the loaded state, it is possible to prevent a decrease in the injection speed and a delay in the rise of the injection speed due to a delay in the rise of the pressure oil of the pump when changing the speed. Furthermore, since the injection speed is always under the control of the electromagnetic proportional valve, molding conditions can be easily adjusted and precise injection control can be performed.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an apparatus for carrying out the method of the present invention;
FIG. 2 is a diagram showing the characteristics of the oil amount obtained by the method of the present invention, FIG. 3 is a diagram showing the characteristics of the oil amount obtained by the conventional method for controlling the hydraulic system of an injection molding machine,
FIG. 4 is a diagram showing the characteristics of the required oil amount. 10, 12, 14...pump, 24, 26, 28
...Solenoid valve, 32...Solenoid proportional valve, 36...
Injection cylinder, 38...Pressure compensation valve, 42...Screw, 44...Position sensor, 46...Comparator, 48
...Speed switching position setter, 50...Correction position memory device,
52... Constant setter, 54... Arithmetic unit, 56... Speed setter, 60... Pump selection device.

Claims (1)

[Claims] 1. The injection speed of the injection molding machine is controlled by the opening degree of a solenoid proportional valve provided between a plurality of pumps and the injection cylinder, and each pump is controlled according to the set value of the injection speed. In a control method for an injection molding machine hydraulic system that can selectively switch between a loaded state and a no-load state so as to ensure the required flow rate, a pump that is to be switched from a no-load state to a loaded state according to a set value of injection speed is provided. is switched to the loaded state when the screw reaches the position before the injection speed switching position by a distance equal to the injection speed setting value at that time multiplied by a predetermined constant, and the loading state is changed according to the injection speed setting value. A method for controlling a hydraulic system of an injection molding machine, characterized in that a pump to be switched from a state to a no-load state is switched to a no-load state at the same time as the opening of an electromagnetic proportional valve is changed when the screw reaches an injection speed switching position.