JP3537541B2 - Hydraulic control of injection molding machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic control device for an injection molding machine, and more particularly to a screw which performs pressure control in accordance with a resin in a filling and pressure-holding process and retreats by a resin pressure in a measuring process. The present invention relates to a hydraulic control device for an injection molding machine that performs back pressure control to provide an appropriate movement resistance.

[0002]

2. Description of the Related Art In a weighing process performed by an injection molding machine, it is necessary to provide an appropriate movement resistance when the screw is retracted while rotating. This movement resistance is
Generally, this is performed by controlling the back pressure in a hydraulic circuit that drives the injection cylinder. In the injection molding machine,
This type of hydraulic circuit includes, for example, Japanese Utility Model 4-40990.
There is a hydraulic circuit as disclosed in Japanese Unexamined Patent Publication (Kokai) No. H10-26095.

In FIG. 4, reference numeral 1 denotes a heating cylinder, and 3 denotes a hopper for supplying a resin to the heating cylinder 1. A screw 2 is rotatably inserted inside the heating cylinder 1. The base end of the screw 2 is connected to the hydraulic motor 4 and the rod 5a of the hydraulic cylinder 5, and is configured to be able to move inside the heating cylinder 1 while rotating. Reference numeral 7 denotes a hydraulic pressure source, and pressure oil is supplied to the hydraulic motor 4 via a direction switching valve 8, and is supplied to the hydraulic cylinder 5 through a direction switching valve 9.

When the screw 2 is rotated, when the solenoid a of the direction switching valve 8 is excited, the pressure oil of the hydraulic source 7 is supplied to the hydraulic motor 4, so that the screw 2 rotates. At this time, the screw 2 receives the pressure of the resin accumulated in the front and tries to retreat to the base end side. For this reason,
The piston 5a of the hydraulic cylinder 5 is retracted, and the pressure oil in the cylinder chamber on the head side of the hydraulic cylinder 5 is discharged from the direction switching valve 8 through the pressure control valve 10 to the tank 11. Therefore, by setting the operating pressure of the pressure control valve 10 to an appropriate value, the back pressure generated in the return line 12 can be controlled to adjust the movement resistance applied when the screw 2 moves backward.

Next, in the hydraulic circuit shown in FIG.
Reference numeral 3 denotes a direction switching valve provided to increase the resolution of pressure control. When the solenoid is energized, the directional switching valve 13 supplies the pressure oil in the cylinder chamber on the head side to the pipes 12, 1
4 and the hydraulic cylinder 5 via the directional control valves 13 and 9
To form a differential circuit that is returned to the cylinder chamber on the rod side.

In this case, in the hydraulic cylinder 5, if the rod side and the head side have the same pressure P, the piston pressure receiving area on the head side is Ah, and the piston pressure receiving area on the rod side is Ar.
A force of T1 = (Ah-Ar) .times.P (1) is applied to the piston 5b, and this becomes a movement resistance acting on the screw 2. On the other hand, when the operation circuit is not used, the piston 5
Since the force acting on b is T2 = Ah · P (2), using the actuation circuit, even if the pressure set value at the pressure control valve 10 is the same, the screw 2 actually acts as a moving resistance. The acting force will be reduced by Ar · P.

Therefore, in order to apply the same moving resistance to the screw, it is necessary to increase the set pressure of the pressure control valve 10, which means that the pressure control valve 1
This means that the resolution of the pressure setting of 0 is increased and fine adjustment is possible.

Also, in the filling and pressure-holding step, the mounting position of the directional control valve 8 and its spool type are changed in accordance with the resin used for molding, and the directional control valve 13 is excited, whereby the rod of the hydraulic cylinder 5 is turned on. A differential circuit in which the pressure oil on the side flows through the pipes 147 and 12 and returns to the cylinder chamber on the head side of the hydraulic cylinder 5 can be formed. Again,
When the same filling resistance or dwelling resistance is to be applied to the screw 2 as when the differential circuit is not used, the same can be said for the measuring step.

[0009]

When the differential circuit is selected at the time of weighing as described above, there is an advantage that the resolution of the pressure setting is improved, but the pressure controlled by the pressure control valve 10 and the screw 2 The difference in the movement resistance, the filling pressure, and the force applied as the holding pressure may cause the back pressure to be incorrectly set. That is, the pressure control valve used to control the pressure is of a manually adjustable type or of a remotely adjustable electromagnetic relief valve. It has been pointed out that since the operation itself is the same in the case where the operating circuit is used and the case where it is not used, the back pressure is often set incorrectly, which causes molding failure. In addition, the erroneous setting of the pressure can similarly occur when setting the filling pressure and the holding pressure.

Therefore, an object of the present invention is to solve the above-mentioned problems of the prior art, and to make it clear that when a differential circuit is used, the apparent set pressure differs from the pressure actually acting on the screw. It is an object of the present invention to provide a hydraulic control device for an injection molding machine which can prevent such a problem.

[0011]

In order to achieve the above object, the present invention provides a heating barrel, a screw rotatably and axially removably inserted into the heating barrel, and a screw. A hydraulic motor that rotationally drives the bearing, a bearing unit that rotatably supports the screw at the rear end,
A second cylinder having an injection-side first cylinder chamber and a pressure-receiving area larger than the piston pressure-receiving area of the first cylinder chamber is connected to the screw via the bearing unit.
In an injection molding machine provided with a pair of injection cylinders in which a cylinder chamber is defined via a double-rod-shaped piston, a hydraulic circuit for driving the injection cylinder includes a normal circuit and a first circuit.
A direction switching valve capable of selectively switching one of a differential circuit in which the cylinder chamber and the second cylinder chamber communicate with each other; an electromagnetic pressure control valve for controlling the pressure of the first cylinder chamber to a pressure set value; Input means for inputting necessary data for the electromagnetic pressure and a ratio of a piston pressure receiving area of the first cylinder chamber to a piston pressure receiving area of the second cylinder chamber as a correction coefficient.
Correct the apparent pressure set value of the force control valve, and
When the circuit is selected, the force acting on the screw is selected
Calculating means for calculating a substantial set pressure of the electromagnetic pressure control valve so as to be maintained the same as when the pressure setting is not performed; and a pressure setting for outputting a pressure setting signal corresponding to the corrected set pressure to the electromagnetic pressure control valve. Means.

In the above configuration, when the differential circuit is not selected, the pressure setting means operates to set the pressure set value to the set pressure of the electromagnetic pressure control valve. An indicator for displaying the operating pressure is provided, and the indicator displays a set pressure value when the differential circuit is selected.

[0013]

According to the present invention, when the differential circuit is selected, the pressure set value of the electromagnetic pressure control valve corrects the ratio of the piston pressure receiving area of the first cylinder chamber to the piston pressure receiving area of the second cylinder chamber. A pressure setting signal corrected as a coefficient and corresponding to the corrected pressure set value is applied to the electromagnetic pressure control valve to set the operating pressure of the electromagnetic pressure control valve.

By this pressure setting, the screw has:
When the differential circuit is not selected, the same force acts as when pressure control is performed under the initial pressure set value of the electromagnetic pressure control valve.

[0015]

An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows an embodiment in a measuring step of the present invention, and reference numeral 30 denotes a screw inserted into a heating barrel of an injection molding machine (not shown). This screw 30
Is rotatably supported by a bearing unit 36 and is connected to the hydraulic motor 32. The screw 30 is connected to a pair of injection cylinders 34, 34 via a bearing unit 36, so that the injection cylinders 34, 34 can advance and retreat in the heating barrel in the axial direction while rotating. .

The injection cylinder 34 in this embodiment is a cylinder using a double rod-shaped piston 38, and a first cylinder chamber 39 and a second cylinder chamber 40 are formed inside the cylinder by the piston 38. ing. The first cylinder chamber 39 is a cylinder chamber on the side that advances the screw 30 when pressure oil is introduced, and the small-diameter rod 42 that is joined to the piston 38 on the first cylinder chamber 39 side is a bearing for the bearing. It is connected to the unit 36. On the other hand, the rod inserted into the second cylinder chamber 40 has
In order to set the pressure receiving area of the piston 38 smaller than that of the first cylinder chamber 39, a large diameter rod 44 having an outer diameter C larger than the outer diameter A of the small diameter rod 42 is used. The large-diameter rod 44 is joined to the piston 38 via a screw, and a distal end of the large-diameter rod projects from the cylinder cover, so that the large-diameter rod 44 can be replaced with a large-diameter rod 44 of various sizes.

Next, a hydraulic circuit for controlling the operation of the injection cylinders 34, 34 will be described. Numeral 50 is a hydraulic pump, and 52 is a direction switching valve for controlling the operation of the injection cylinder 34 by switching a pipeline for sending the pressure oil discharged from the hydraulic pump 50 to the injection cylinder 34.
Reference numeral 4 denotes a direction switching valve that forms a differential circuit during the metering step and the filling / holding step.

The directional control valve 52 is a three-position, four-port directional control valve. When the solenoid 52b is excited, the pressure port P and the B port communicate with each other.
B port is introduced into the first cylinder chamber 39. On the other hand, when the solenoid 52a is excited, the pressure port P and the A port communicate with each other, and the pressure oil is discharged from the injection cylinder 34.
Are connected by piping so as to be supplied to the second cylinder chamber 40 from the A port.

The directional control valve 54 is a two-position, three-port directional control valve.
When the drive hydraulic circuit of the injection cylinder 34 is formed and its solenoid is excited, in the metering process, the first cylinder chamber 39 of the injection cylinder 34 is set to indicate the flow of the pressurized oil by arrows.
The pipeline is switched so as to form a differential circuit that communicates with the second cylinder chamber 40.

Reference numeral 56 denotes an electromagnetic pressure control valve which is incorporated in a pipe returning to the tank 58 and controls the pressure generated in the differential circuit. A pilot-type electromagnetic relief valve is used.

The direction control valves 52 and 54 and the electromagnetic pressure control valve 56 are controlled by a controller 60. The controller 60 includes a central processing unit, a main storage device including a ROM in which a program is stored and a RAM in which input data is stored, and an input / output port. An input device 61 for inputting data such as an outer diameter B of 38 and data such as a pressure setting pressure, a display 62 for displaying a pressure set value of a pressure control valve 56 and the like, and an alarm 63 are connected. I have.

The controller 60 executes the processing of the flowchart shown in FIG. 2 according to a program stored in the ROM, and sends a pressure setting signal to the electromagnetic pressure control valve 56. When a voltage signal proportional to the set pressure is applied to the solenoid via a D / A converter and a drive circuit (not shown), the electromagnetic pressure control valve 56 sets the operating pressure to the set value. Has become.

Next, referring to the flowchart of FIG.
The operation of the controller 60 at the time of weighing will be described. First, data of the pressure set value D is input from the input device 61 (step S1). In this embodiment, data expressed as a ratio (%) to the settable maximum pressure is used. Next, when the differential circuit is selected (Yes in step S2), the process proceeds to step S3, where the outer diameter A of the small diameter rod 42, the inner diameter B of the injection cylinder 34, the outer diameter C of the large diameter rod 44, and the like. Then, the process proceeds to data input processing necessary for pressure control.

When the correction coefficient K and the set pressure E of the electromagnetic pressure control valve 56 are calculated from these data (steps S5 and S6), the value of E is checked in step S7 to check the calculation result. I do. If it is an abnormal value, an alarm signal is output to the alarm 63 (step S).
8) If the setting is to be continued, the process returns to the first step S1 (Yes in step S9), and if the setting is to be canceled, the process ends (no in step S9). Step S
15 is a process when the outer diameter A of the small-diameter rod 42 is equal to the outer diameter C of the large-diameter rod 43. In this case, since the differential pressure control cannot be performed, the process returns to the input process again, or The process ends.

On the other hand, if there is no problem with the value of E, the solenoid of the directional control valve 54 is turned on to switch to the differential circuit.
And the hydraulic circuit for driving the injection cylinder 34 is switched from a normal circuit to a differential circuit.

In step S11, a voltage signal corresponding to the set pressure E is applied to the solenoid of the electromagnetic pressure control valve 56 as a pressure setting signal, whereby the operating pressure of the electromagnetic pressure control valve 56 becomes E = K.・ D ... (3) is set.

Here, assuming that the moving resistance acting when the screw 30 actually retreats is F1, the pressure set value is D
Therefore, F1 = π / 4 × D {(B ² −A ² ) − (B ² −C ² )} = π / 4 × D (C ² −A ² ) (4)

On the other hand, the electromagnetic pressure control valve 5 is set to the same pressure set value.
6 and set the moving resistance to F when no operating circuit is selected.
Assuming that 2, F2 = π / 4 × D (B ² −A ² ) (5)

By substituting the corrected voltage set value of equation (3) set in step S6 into equation (4), F1 = π / 4 × KD (C ² −A ² ) = π / 4 × D ( B ² −A ² ) (6)

Therefore, by correcting the apparent pressure set value D by multiplying the correction coefficient K, F1 = F2, and the screw 30 has a difference between the pressure set value D of the same value before and after the selection. The same movement resistance acts regardless of whether or not a motion circuit is selected.

In step S12 of displaying the set pressure E of the electromagnetic pressure control valve 56 on the display 63, the set value E set in step S11 is not displayed, but the set pressure value D is displayed. . Thus, the ratio (%) of the pressure that actually acts is indicated to the operator.

The above is the processing when the differential circuit is selected. The processing when the differential circuit is not selected in the measuring step is steps S13 and S14. In the ordinary circuit, the electromagnetic pressure control valve 56 is used. Since the set pressure E and the pressure set value D become the same pressure, the value of the proportional correction coefficient K is set to 1, and the value of the pressure set value D is set as the operating pressure of the electromagnetic pressure control valve. ing.

Next, FIG. 3 is a diagram showing the operation of the embodiment in the filling step and the dwelling step. In the filling step, when the solenoid 52b of the direction switching valve 52 is excited, the pressure oil discharged from the hydraulic pump 50 is supplied to the first cylinder chamber 39 from the B port of the injection cylinder 34 through the direction switching valve 52. You. In the injection cylinder 34, the piston 38 advances, whereby the screw 30 presses the resin in the direction indicated by the arrow to fill the mold.

In the filling step, the switching between the normal circuit and the differential circuit is performed by the direction switching valve 54 in the same manner as in the above-described measuring step. The normal circuit is when the solenoid of the direction switching valve 54 is not excited. When the direction switching valve 54 is excited, the first cylinder chamber 39 and the second
Since the cylinder chamber 40 communicates with the cylinder via the direction switching valve 54, as the piston 38 advances, the pressure oil in the second cylinder chamber 40 flows into the first cylinder chamber 39 as shown by an arrow in the drawing. I have. The pressure of the pressure oil at this time is
The control by the electromagnetic pressure control valve 56 is the same as that of the measuring step. In this case, the pressure set value D is corrected by the correction coefficient K according to the processing of the flowchart of FIG. The electromagnetic pressure control valve 56 is set to the set pressure E so as to be the same as the filling pressure at the set value D. This allows the screw 30 to apply the same filling pressure to the resin, whether or not a differential circuit is selected.

The same applies to the pressure-holding step after the filling step. The operation of the direction switching valves 54 and 52 and the pressure set value D in the measuring step, the filling step, and the pressure-holding step are described above.
Table 1 collectively shows the actual set pressures and display values of the electromagnetic pressure control valve 56 with respect to.

[0036]

[Table 1]

[0037]

As is apparent from the above description, according to the present invention, when the differential circuit is selected, the operation of the electromagnetic pressure control valve is started.
The apparent pressure set value is corrected using the ratio of the piston pressure receiving area of the first cylinder chamber to the piston pressure receiving area of the second cylinder chamber as a correction coefficient, and the pressure setting corresponding to the corrected substantial pressure set value. Since a signal is applied to the electromagnetic pressure control valve to set the operating pressure of the electromagnetic pressure control valve, the screw has the same electromagnetic pressure control valve pressure setting value as when the differential circuit is not selected. In the measuring step, the same movement resistance acts, and in the filling / holding step, the same filling pressure and holding pressure can act. For this reason, it is possible to prevent the wrong setting of the pressure between when the differential circuit is selected and when the differential circuit is not selected, and prevent the actual moving resistance and the filling / holding pressure from being different.

[Brief description of the drawings]

FIG. 1 is a hydraulic circuit diagram at the time of a measuring process in an embodiment of a hydraulic control device according to the present invention.

FIG. 2 is a flowchart showing an operation of a controller of the hydraulic control device.

FIG. 3 is a hydraulic circuit diagram during a filling step and a pressure holding step in one embodiment of the hydraulic control device according to the present invention.

FIG. 4 is a circuit diagram of a conventional hydraulic control device that executes back pressure control using a differential circuit in an injection molding machine.

[Explanation of symbols]

30 screws 32 hydraulic motor 34 Injection cylinder 36 Bearing unit 38 piston 39 1st cylinder chamber 40 Second cylinder chamber 42 small diameter rod 44 Large Diameter Rod 50 hydraulic pump 52 Directional switching valve 54 Directional switching valve 56 Electromagnetic pressure control valve 60 Controller

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-5-169511 (JP, A) JP-A-7-32438 (JP, A) JP-A-5-169512 (JP, A) JP-A-63-163 94811 (JP, A) JP-A-2-147227 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B29C 45/82 B29C 45/50 B29C 45/77

Claims (3)

(57) [Claims] 1. A heating barrel, and a screw rotatably and axially removably inserted into the heating barrel,
A hydraulic motor that rotationally drives the screw, a bearing unit that rotatably supports the screw at its rear end, a first cylinder chamber that is connected to the screw via the bearing unit, and has an injection-side first cylinder chamber therein; In the injection molding machine having a pair of injection cylinders defined by a second cylinder chamber having a pressure receiving area larger than the piston pressure receiving area of the first cylinder chamber through a double rod-shaped piston, the injection cylinder is driven. A direction switching valve capable of selectively switching one of a differential circuit in which a first cylinder chamber and a second cylinder chamber communicate with each other; and a pressure switching value for setting the pressure in the first cylinder chamber to a pressure set value. An electromagnetic pressure control valve for controlling, input means for inputting data necessary for pressure control, a piston pressure receiving area of the first cylinder chamber, and a piston pressure receiving surface of the second cylinder chamber It said electromagnetic the ratio of the product as a correction coefficient
Correct the apparent pressure set value of the pressure control valve, and
When the working circuit is selected, the force acting on the screw is selected.
Calculating means for calculating a substantial set pressure of the electromagnetic pressure control valve so as to be maintained the same as when not selected; and a pressure for outputting a pressure set signal corresponding to the corrected set pressure to the electromagnetic pressure control valve. A hydraulic control device for an injection molding machine, comprising: a setting unit. 2. The injection according to claim 1, wherein the pressure setting means sets an apparent pressure set value as a set pressure of an electromagnetic pressure control valve when a differential circuit is not selected. Hydraulic control device of molding machine. 3. A display device for displaying an operating pressure of the electromagnetic pressure control valve, wherein the display device displays an apparent pressure set value when a differential circuit is selected. 2. The hydraulic control device for an injection molding machine according to 1.