JPS6237711Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a control device for an injection molding machine that can be applied to robots, machine tools, etc.

When the injection and pressure holding of an injection molding machine are controlled by the hydraulic system diagram shown in Fig. 1, the injection speed in the injection process is controlled by the servo valve 2, and the hydraulic pressure of the cylinder 5 at that time is Control valve 3 performs preset adjustment. Next, when switching to the pressure holding process, the pressure control valve 3 is blocked, and when pressure holding control is performed by controlling the servo valve 2, the cylinder oil pressure fluctuates when switching from speed control to pressure control.

A conventional control block diagram for controlling the hydraulic system diagram of FIG. 1 is shown in FIG. FIG. 4 shows an example of fluctuations in the oil pressure of the hydraulic cylinder 5 in this case. Now, in Figure 2, during the injection process, the first-order delay circuit 1
The command value set by the injection speed setter 11 through the speed sensor 3 and the injection speed of the ram 7, which is advanced by the hydraulic cylinder 5 shown in FIG. A calculation amplifier 15 compares and calculates the feedback amount.

The output of the operational amplifier 15 is sent to the analog switch 2.
8, the voltage is transmitted to the control coil 2a of the servo valve 2 via the voltage amplifier 16 and the power amplifier 17, and the servo valve 2
The injection speed of the ram 7 is controlled by controlling. During this injection speed control, the oil pressure of the cylinder 5 is controlled in an open loop by the proportional electromagnetic pressure control valve 3 connected to this system.

The injection high pressure setting device 22 that sets the hydraulic pressure of the hydraulic cylinder during injection speed control is connected to the multiplexer 2.
3, the set value of the injection high pressure is transmitted to the linear compensation circuit 24. Power amplifier 25 is analog switch 3
0, the output signal of the linear compensation circuit 24 is input, and the output signal is output to the power amplifier 26. The output signal of the power amplifier 26 is transmitted to the control coil 3 of the pressure control valve 3.
transmitted to a.

That is, during the speed control period of the injection process, the analog switches 28 and 30 are conductive, and the analog switch 29 is closed.
is in a non-conducting state, and the oil pressure of the hydraulic cylinder 5 is regulated by the proportional electromagnetic control valve 3, which is preset according to the injection high pressure setting value of the setting device 22.

Next, when the injection process is switched to the pressure holding process, the analog switch 28 becomes non-conductive and the analog switches 29 and 30 become conductive. At this time, the pressure control valve 3 is blocked by the signal from the pressure valve block setter 33 whose control coil 3a is selected by the multiplexer 23.

When entering the pressure holding process, the setting value set by the holding pressure setting device 19 via the first-order delay circuit 20 and the hydraulic pressure of the hydraulic cylinder detected by the pressure sensor 18 via the pressure sensor amplifier 18a. The arithmetic amplifier 21 performs a comparison operation with the feedback value of . The output signal of the operational amplifier 21 passes through the analog switch 29, the voltage amplifier 16, and the power amplifier 17, which are in a conductive state, and controls the control coil 2a of the servo valve 2, thereby maintaining the ram 7. Control pressure pressure.

The holding pressure setting device 19 normally has a multi-stage setting, and the first-order delay circuit 20 allows the command value to be continuously set when changing the setting value of the holding pressure. It has a smooth switching function.

In the injection process, the injection speed needs to be precisely controlled, but a rough pressure is fine, so a pressure control valve with open loop control is used for pressure, and a high precision servo valve is used in closed loop for speed. ing. In addition, in the pressure holding process, only pressure accuracy is required, regardless of speed.

Therefore, the pressure accuracy of the pressure control valve 3 used in the injection process was insufficient, and consideration was given to using the servo valve 2 used in the injection process and using the pressure sensor 18 to achieve highly accurate pressure control. has been done. In this way, the servo valve 2 controls the speed,
The reason why it is also used for pressure control is mainly a cost issue.

Although this control circuit has good accuracy in both the injection process and the pressure holding process, and is satisfactory in terms of cost, it is suitable as a control circuit for use in an injection molding machine, but it has the following drawbacks.

That is, when switching from speed control in the injection process to pressure control in the pressure holding process, the setting value of the holding pressure setting device rises later than the feedback signal coming from the pressure sensor due to the first-order delay circuit 20, so the servo valve Once the cylinder oil pressure is lowered and the output of the primary delay circuit 20 rises, it is again controlled by the set value of the holding pressure setting device.

Therefore, a sudden drop in cylinder oil pressure causes a momentary drop in the pressure of the resin being injected into the mold, which has the disadvantage of adversely affecting the quality of precision molded products that require specific dimensions, weight, and surface finish. Ta.

The present invention was proposed to eliminate the above-mentioned conventional drawbacks, and is intended to eliminate the instantaneous pressure drop in cylinder oil pressure that occurs when switching from speed control in the injection process to pressure control in the holding process in an injection molding machine. To,
The feedback signal from the pressure sensor during the speed control period before switching to pressure control is applied to the output side of the primary lag circuit to which the setting value of the holding pressure setting device is applied, and when switching to pressure control. To provide a control device for an injection molding machine that allows continuous and smooth transition from the cylinder hydraulic pressure at that time to the holding pressure preset by the holding pressure setting value without sudden changes. That is.

An embodiment of the present invention will be described below with reference to the drawings. As an example of the case where the present invention is applied, a hydraulic system diagram is shown in FIG. 1, and a control block diagram is shown in FIG. 3. In FIG. 1, a hydraulic pump 1 has a servo valve 2 that controls the oil flow rate by a control coil 2a.
It is connected to the hydraulic cylinder 5 via hydraulic piping or the like. A proportional electromagnetic pressure control valve 3 is connected to an intermediate portion of the connection circuit between the output side of the servo valve 2 and the hydraulic cylinder 5. The proportional electromagnetic pressure control valve 3 controls the pressure in the inlet system of the hydraulic cylinder 5 in an open loop by a control coil 3a during the speed control period of the injection process.

In addition, the ram 7 injects the molten resin at the tip of the ram inside the barrel (not shown) into the mold, and during the pressure holding process after injection is completed, the resin in the mold is held at a predetermined pressure and molded. It is connected to the rod 6 of the hydraulic cylinder and moves forward and backward. Pressure sensor 18
is a sensor that detects the hydraulic pressure of the hydraulic cylinder 5, and the speed sensor 12 is a sensor that detects the speed at which the ram 7 moves in the injection direction (arrow direction). Further, the mechanism for detecting the injection speed of the ram 7 using a speed sensor may be any method such as a rack and pinion or a lever, and is not shown in the drawings.

In the control block diagram (Fig. 3) showing an embodiment of the present invention for controlling the hydraulic system shown in Fig. 1, an injection speed setting device 11 is used to set the injection speed of the ram 7. A plurality of values can be set, and it is switched by a signal from a sequence circuit (not shown), and is connected to an operational amplifier 15 via a first-order delay circuit 13. 12 is a speed sensor,
As described above, the injection speed of the ram 7 is detected, and after the speed sensor amplifier 14 converts the amplification level, it is applied to the operational amplifier 15 as a feedback value. The injection speed setting value and the ram speed feedback value are compared and calculated by the arithmetic amplifier 15 and applied to the voltage amplifier 16 via the analog switch 28.

The power amplifier 17 inputs the output of the voltage amplifier 16 and controls the control coil 2a of the servo valve 2 that controls the flow rate of oil sent to the hydraulic cylinder 5. The holding pressure setting device 19 is used to set the holding pressure of the ram 7, and can normally set a plurality of values.It is switched by a signal from a sequence circuit (not shown), and is sent to the first-order delay circuit 20 by an analog switch. 32.

This first-order delay circuit 20 has a function that, when switching from a predetermined pressure setting value to another setting value, the switching transition of the same setting value is performed continuously and smoothly using a sequence circuit (not shown). , the output is applied to the operational amplifier 21. Also, a pressure sensor 1 that detects the hydraulic pressure of the hydraulic cylinder 5
8 is level-converted by the pressure sensor amplifier 18a and then applied to the operational amplifier 21 as a pressure feedback value. The pressure sensor amplifier 18
The output terminal of a and the output terminal of the first-order lag circuit 20 are:
It is connected via an analog switch 31. The pressure feedback signal of the hydraulic cylinder 5 and the holding pressure set value are compared and calculated by the arithmetic amplifier 21, and the power amplifier 16 which operates the control coil of the servo valve 2 during the pressure holding process via the analog switch 29 is operated. Connected to input.

The multiplexer 23 includes an injection high pressure setting device 22,
The pressure control valve block setting device 33 and the screw back pressure setting device, which is omitted in the other figure in the actual injection machine, are switched in accordance with a sequence signal, and a predetermined setting value is applied to the linear compensation circuit 24. The linear compensation circuit 24 converts the set value-pressure characteristic of the pressure control valve 3 into a linear relationship, and is not necessarily required. The output of this linear compensation circuit 24 is applied to a voltage amplifier 25 via an analog switch 30 which is turned on in response to a predetermined sequence signal. On the other hand, the power amplifier 26 inputs the output of the voltage amplifier 25 and controls the control coil 3a of the pressure control valve 3 that controls the hydraulic pressure of the hydraulic cylinder 5.

Next, the operation will be explained. During the speed control period of the injection process, a gate signal is applied to the gate terminal _S1 , and the analog switches 28, 30, and 31 become conductive. During this time, no gate signal is applied to the gate terminal _S2 , and the analog switches 29 and 32 are in a non-conducting state. The analog switch 32 opens and closes the input side of the first-order lag circuit 20, and is used to prevent leakage to the primary side of the first-order lag circuit during the injection process.

Next, when entering the pressure control period of the pressure holding process, terminal S ₁
The gate signal is turned off, the gate signal is applied to the terminal _S2 , the analog switches 28, 30, and 31 are rendered nonconductive, and the analog switches 29 and 32 are rendered conductive. The gate terminals S ₃ and S ₄ are terminals that apply a gate signal to operate the pressure control valve 3 according to its function when the ram 7 is rotating or in a stationary state.

Now, the hydraulic pressure of the hydraulic cylinder 5 is adjusted in an open loop by the pressure control valve 3 to the value set by the injection high pressure setting device 22, and the injection speed of the ram 7 is adjusted to the value set by the injection speed setting device 11. It is assumed that the injection process is being controlled in a closed loop by the servo valve 2. At this time, the two comparison input terminals of the operational amplifier 21 are
Since the analog switch 31 is conductive, a feedback signal proportional to the output of the pressure sensor 18 is applied, and the first-order delay circuit is charged to a value corresponding to the pressure at that time.

Next, when the pressure holding process begins, the gate signal S ₁ is
When OFF and _S2 are turned ON, the analog switches 28, 30, and 31 are disconnected and the analog switches 29 and 32 are conductive. It operates depending on the deviation of the feedback value from 18.
In this case, the primary delay circuit 20 is charged to a value corresponding to the pressure before switching, and the pressure shifts from this value to the value set by the holding pressure setting device.

The present invention is configured as explained in detail above, and when switching from the injection process to the pressure holding process, the primary lag circuit is charged with the feedback signal from the pressure sensor to a value corresponding to the pressure before switching. , the charging value is continuously shifted to the setting value of the holding pressure setting device, and as a result, it is possible to switch from the injection high pressure to the holding pressure without causing a sudden pressure drop in the hydraulic pressure of the hydraulic cylinder of the ram.

FIG. 5 shows changes in the hydraulic pressure of the hydraulic cylinder from the injection process to the pressure holding process. In Fig. 5, the curve o'-a'-b'-c'-d'-e'-f' shows the change in the load hydraulic pressure during the injection process, and the curve f'-g'-
For r′−s′, the holding pressure setting value is the load pressure during injection.
The curve f'-g''-r'' is the packing pressure during the packing process when it is higher than f', and the curve f'-g''-r'' is lower than f'.

In addition, the curves of f'-g' and f'-g'' at the switching point A'-B' change continuously, and the switching point shown in Fig. 4 when the present invention is not used. f in A-B
- It is possible to prevent the oil pressure of a hydraulic cylinder such as pg from dropping suddenly for a moment. This has an effect on the size, weight, and surface finish of a molded product whose temperature is lowered and cooled during injection by an injection molding machine, especially when precision molding is performed.

[Brief explanation of the drawing]

Fig. 1 is a hydraulic system diagram of a general injection molding machine, Fig. 2 is a control block diagram of a conventional injection molding machine, Fig. 3 is a control block diagram of an injection molding machine showing an embodiment of the present invention, and Fig. 4 is a control block diagram of an injection molding machine showing an embodiment of the present invention. The figure is a diagram showing the relationship between time and oil pressure in the conventional injection and pressure holding process, and FIG. 5 is a diagram showing the relationship between time and oil pressure in the injection and pressure holding process of the present invention. Explanation of the main parts of the diagram, 1... Hydraulic pump, 2...
... Servo valve, 3 ... Solenoid pressure control valve, 5 ... Hydraulic cylinder, 7 ... Ram, 11 ... Injection speed setting device, 12 ... Speed sensor, 13 ... Primary delay circuit, 15 ... Calculation increase Wiper, 18...pressure sensor,
19... Holding pressure setting device, 20... Primary delay circuit, 21... Arithmetic amplifier, 28, 29, 30, 3
1, 32...Analog switch.

Claims (1)

[Scope of utility model registration request] The holding pressure setter, which is connected to the input side of the arithmetic amplifier through the first-order delay circuit, and the signal processing circuit of the pressure sensor that detects the cylinder oil pressure or the resin pressure in the mold are input, and the comparison calculation is performed in the same circuit. An analog switch is provided between the signal processing output circuit of the pressure sensor and the first-order delay circuit, and between the holding pressure setting device and the first-order delay circuit. By making the circuit conductive, the first-order delay circuit is charged in advance to a value proportional to the feedback signal of the pressure sensor during the injection process, and when the injection process is switched to the holding pressure process, the holding pressure is continuously maintained at the predetermined holding pressure setting. A control device for an injection molding machine characterized by being able to transfer.