JPH0541863Y2 - - Google Patents

Description

[Detailed description of the invention] (Industrial application field) This invention relates to an injection speed control circuit for an injection molding machine, and in particular enables highly accurate injection speed control over the entire range from low speed to high speed. This relates to control circuits.

(Prior art) Injection speed control of recent injection molding machines divides the speed control section into multiple (N) sections (generally N = 3 to 5) and sets injection speed switching positions, and sets between each switching position. The injection speed is controlled using the speed for each section.

This will be explained in detail according to Figs. 3 and 4. In Fig. 3, 1 is an injection ram with hydraulic pressure acting on the rear, and a screw 5 integrated at the front end that moves back and forth. I'm starting to do that. Reference numeral 2 denotes a hydraulic cylinder for injection, which is integrated with a screw cylinder 6, and is provided with a hopper 4 at the upper part thereof. 3 is a hydraulic motor for rotating the screw 5, 7 is a mold, 8 is a fixed platen, and 9 is a movable platen.

Reference numeral 14 indicates an injection ram position sensor that detects the position of the injection ram and emits a signal thereof, and 15 indicates an injection condition setting panel. This injection condition setting panel 1
5 includes a filling and holding pressure setting device 10, an injection speed setting device 11, an injection speed switching position setting device 12, etc., so that values can be set respectively. In the conventional example shown in the figure, the injection speed is divided into four, V ₁ to V ₄ , and each injection speed is set to injection switching positions S1 to S2, S2.
This is the set injection speed within each section of ~S3, S3~S4, and S4~.

Reference numeral 16 denotes an injection ram position comparator, which compares the measured value from the injection ram position sensor 14 with the injection speed switching positions S1 to S4 set by the injection speed switching position setting device 12.
The results are sent to the filling/holding pressure setting device 10 and the injection speed setting device 11.

Reference numeral 17 indicates a flow rate valve control amplifier, which controls the flow rate of the proportional flow valve 25 according to each set injection speed V ₁ to _{V 4} from the injection speed setting device 11 . Also,
21, the poppet 18 is normally pushed up by the spring 19 to block the flow, and when the solenoid a of the solenoid valve 22 is activated, the poppet 18 is pushed up by the spring 19.
9 is a normally closed logic valve that allows pressure oil to flow downwards, and one port of the logic valve 21 is connected to the proportional flow valve 25 via the switching valve 24, and the other port is connected to the injection valve 25. It is connected to the hydraulic cylinder 2. Note that 23 indicates an accumulator.

In order to control the injection speed with the conventional control circuit configured as described above, the solenoid a of the solenoid valve 22 is energized throughout the entire injection period as shown in FIG. By pushing down the spring 19, the pressure oil from the switching valve 24 can be supplied to the injection hydraulic cylinder 2. The pressure oil supplied from the accumulator 23 is transferred to the proportional flow valve 25.
The injection speed is controlled via the flow valve control amplifier 17 by
The flow rate is controlled to correspond to V ₁ to _{V 4} and is supplied to the injection hydraulic cylinder 2 via the logic valve 21 . The injection speeds V ₁ to _{V 4} are digitally set prior to operation of the injection molding machine. The usage range of injection speed can be set in the range of 0 to 99%, and each setting speed of the injection speed setting device 11
V ₁ to _{V 4} are the _maximum values of speed that can be set _, respectively.
It is set in %. In the illustrated example, these values are n ₁ =20, n ₂ =80, n ₃ =35, and n=10, respectively.

By the way, in recent injection speed control, the control range has become particularly wide, and it is now common knowledge that the ratio of the minimum injection speed to the maximum injection speed is about 1:500. However, the above control circuit has the problem that if the machine capacity is designed for the maximum injection speed, the accuracy of control at the low speed portion deteriorates, and in the opposite case, high speed injection becomes impossible.

(Problems to be Solved by the Invention) The present invention solves the problems that conventional control circuits of this type have, namely, that the conventional circuit causes wide fluctuations in injection speed during one injection molding process. We aim to provide a control circuit that can smoothly control from a high injection speed to a low injection speed and vice versa, by solving the problem that the injection speed cannot be followed in some cases, resulting in poor control accuracy or inability to mold. It is something to do.

(Means for Solving the Problems) Therefore, the present invention provides a control circuit that supplies hydraulic pressure from a hydraulic pressure supply source to the injection hydraulic cylinder of an injection molding machine and controls the injection speed from the same hydraulic pressure supply source. Facing the hydraulic cylinder, a large-flow proportional flow valve for high speed and a small-flow proportional flow valve for low speed are connected in series, and a logic valve that opens only at high-speed injection is installed. It is connected in parallel with the proportional flow valve for small flow rate, and is used as a means to solve the problem.

(Function) Both the small flow rate and large flow rate proportional flow valves are kept in operation at all times while the machine is operating. When a low injection speed command is given, the logic valve is closed.
Pressure oil flows into the injection hydraulic cylinder from a proportional flow valve with a small flow rate to operate the injection ram at a low speed. When a command for a high injection speed is input, the logic valve opens, and a large amount of pressure oil flows through the logic valve through the large proportional flow valve, enters the injection hydraulic cylinder, and operates the injection ram at high speed.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

1 and 2 show this embodiment, FIG. 1 shows a control circuit according to this embodiment, and FIG. 2 shows the relationship between injection speeds in each section.

In FIG. 1, the parts having the same symbols as those of the conventional example shown in FIG. The explanation will focus on the parts that will be done.

In the figure, numeral 31 is a small flow proportional flow valve that controls a low injection speed, and forms a circuit with a large flow proportional flow valve 25 via a solenoid valve 32. are connected in parallel. The flow rate of this small flow proportional flow valve 31 is controlled by a flow valve control amplifier 33 that controls the low speed portion according to the injection speed V ₁ to _{V 4} from the injection speed setting device 11. ing. On the other hand, in order to control the flow rate of the large-flow proportional flow valve 25, a high-speed flow valve control amplifier 17 is installed in parallel with the low-speed flow valve control amplifier 33, as in the past.

34 is a calculation unit that calculates the set injection speed (Vmax x n
%) is larger or smaller than the low upper limit injection speed (Vmax x ns%) that can be controlled by the small flow rate proportional flow valve 31, that is, the ratio n of the set injection speed is the lower upper limit injection speed. The relay 35 is operated only when n>ns, and the solenoid a of the solenoid valve 22 for opening the logic valve 21 is energized.

Next, the operation of the control circuit according to this embodiment with such a configuration will be explained with reference to FIG. The injection speed switching positions S1 to S4 set in are compared by the injection ram position comparator 16, and the results are sent to the filling and holding pressure setting device 10 and the injection speed setting device 11. During each section of injection, in proportion to the command voltage from the injection speed setter 11, the proportional flow valve 25 for large flow rate or the proportional flow valve for small flow rate is The opening degree of the proportional flow valve 31 is controlled.

Here, if the above setting injection speed (Vmax×n
%) is smaller than the low-speed upper limit injection speed (Vmax×ns), low-speed controls V ₁ , V ₃ , and V ₄ are performed. To explain this specifically, the solenoid a of the solenoid valve 22 is de-energized via the relay 35 through logical processing by the arithmetic unit 34 .
On the other hand, solenoid b of the solenoid valve 32 is constantly energized. The voltage of the speed setter 11 is applied to both the two flow rate valve control amplifiers 17 and 33, causing both the large flow rate and small flow rate proportional flow valves 25 and 31 to operate. However, at this point, since the solenoid a is not energized, the logic valve 21 is closed. Therefore, the pressure oil from the accumulator 23 is
The large flow rate flows in the order of proportional flow valve 25 → switching valve 24 → solenoid valve 32 → proportional flow valve 31, and pressure oil accurately controlled only by proportional flow valve 31 is supplied to injection hydraulic cylinder 2.

Further, when the set injection speed (Vmax×n) is higher than the low-speed upper limit injection speed (Vmax×ns), high-speed control _V2 is performed as follows. The relay 35 is activated by the signal from the calculator 34, and the solenoid a
is excited. At this time, the two proportional flow valves 25 and 31 are both operating as in the case of low speed control, but since solenoid a is energized, the poppet 18 of the logic valve 21 presses the spring 19 downward. A large flow rate of pressure oil controlled by the proportional flow valve 25 is supplied directly to the injection hydraulic cylinder 2 through the logic valve 21.

In addition to the illustrated embodiment, the excitation and
The selection of de-energization, that is, the selection of high-speed control or low-speed control, can also be performed by a manual changeover switch instead of the calculator 34.

When operating the changeover switch manually, if low speed control is selected with the changeover switch (not shown), solenoid a is always de-energized during injection, and is controlled by the proportional flow valve 31 with a small flow rate throughout the entire range. Although the maximum speed will be lower, accurate injection speed control can be achieved over the entire range. On the other hand, when high-speed control is selected, solenoid a is constantly energized and controlled by the large flow rate proportional flow valve 25 throughout the entire range.

Furthermore, since the set injection speed value is determined and the system is configured to automatically switch to each proportional flow valve, the device is easy to use and can perform a wide range of speed control from high speed to accurate low speed control.

Furthermore, in injection molding, it is often necessary to choose between placing emphasis on high-speed injection or high-precision injection speed control, and in such cases, it is necessary to adopt a configuration that allows manual switch selection. In other words, it is possible to perform suitable control that adapts to the requirements.
The device can also be simplified.

(Effects of the invention) As explained above in detail, the present invention is a machine that can obtain high injection speed by adding a small flow rate valve for low speed control to the large flow rate proportional flow valve in the circuit. Despite this, it is possible to control the low injection speed with high precision. Furthermore, by adopting the circuit configuration of the present invention, it becomes unnecessary to turn on and off each proportional flow valve, making it possible to eliminate unstable operation during speed switching.

[Brief explanation of the drawing]

Fig. 1 is an injection speed control circuit diagram of an injection molding machine showing an embodiment of the present invention, Fig. 2 is a diagram showing switching states of injection speed during molding according to this embodiment, and Fig. 3 is a conventional injection speed control circuit. The circuit diagram and FIG. 4 are also diagrams showing switching states of injection speed during conventional molding. Explanation of the main parts of the diagram, 21...Logic valve, 2
5, 31...Proportional flow valve, 22, 32...Solenoid valve.

Claims (1)

[Scope of utility model registration request] In a control circuit that supplies hydraulic pressure from a hydraulic supply source to an injection hydraulic cylinder of an injection molding machine and controls the injection speed, a proportional flow valve with a large flow rate for high speed is connected from the hydraulic pressure supply source to the hydraulic cylinder. and a proportional flow valve with a small flow rate for low speed are connected in series, and a logic valve that opens only at high injection rate is connected in parallel with the proportional flow valve with a small flow rate. Features an injection speed control circuit.