JP2978640B2 - 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 an in-line screw type injection molding machine in which at least the injection power of an injection process is obtained by the driving force of a servomotor.

[0002]

2. Description of the Related Art In-line screw injection molding in which a screw in a heating cylinder is rotated and retracted to plasticize and measure a resin, and the screw is advanced to inject and fill a molten resin into a mold. On the machine,
2. Description of the Related Art Servo motor driven injection molding machines using a servo motor as a drive source for plasticizing / metering operation and injection operation are known. In this conventional injection molding machine driven by a servomotor, a screw rotation servomotor for plasticizing and measuring operation is connected to a screw, the screw is rotated by the screw rotation servomotor, and an injection servomotor for injection operation is also provided. Is generally transmitted to the screw as a linear motion via a rotation-linear conversion mechanism such as a ball screw mechanism.

As is known here, the output torque of a servomotor includes a continuous rated torque that guarantees the torque during continuous use of the motor and a peak torque that allows the use of a large instantaneous torque. The torque can be increased to approximately 400% of the continuous rated torque. In the injection molding machine, during the injection filling step (primary injection step), the molten resin stored at the tip of the screw (at the nozzle side) is rapidly advanced by the screw into the mold in a very short time. Since the injection filling must be performed against the rapidly rising load resin pressure, the specified torque of the injection servomotor is set to the peak torque during the injection filling process. Since it takes a longer time than the injection filling process, the specified torque of the servo motor is a continuous rated torque.) Further, in a servo motor driven injection molding machine, since the speed feedback control is performed in the injection filling process, the output torque of the servo motor in the injection filling process is set to have a force of 200% or more of the continuous rated torque. It is common.

[0004]

As described above, in the injection molding machine driven by the servo motor, the speed feedback control is performed in the injection filling process. 2 during torque operation
Although a force (torque) of at least 00% is provided, when the molten resin is completely filled in the mold at the end of the injection filling process, as shown in FIG. A load resin pressure of 200% or more of (rated resin pressure) occurs. As described above, when a resin pressure that greatly exceeds the rated resin pressure, which is an appropriate resin pressure, is generated in the mold, it causes burrs and the like, and significantly deteriorates the quality of a product (molded product). Therefore, in practice, measures are taken to prevent large resin pressure from acting in the mold, such as by reducing the set speed of the servomotor just before the injection filling is completed, but the injection filling speed is extremely high. In such a case, it is inevitable that a resin pressure larger than an appropriate value occurs in the mold due to factors such as inertia force,
As described above, this is a factor of deteriorating the product (molded product) quality.

[0005] The present invention has been made in view of the above points,
An object of the present invention is to provide an injection molding machine that does not generate a resin pressure larger than an appropriate value in a mold even when an injection filling speed by a servomotor is extremely high.

[0006]

In order to achieve the above-mentioned object, the present invention transmits the rotation of a servomotor to a screw in a heating cylinder as a linear motion via a rotation-linear conversion mechanism, and at least transmits the rotation of the injection step. In an in-line screw type injection molding machine in which the output is obtained by the driving force of a servomotor, a hydraulic cylinder is attached to the headstock holding the heating cylinder, and the piston rod of the hydraulic cylinder can slide back and forth while holding the servomotor A relief valve connected to the hydraulic cylinder is provided along with the motor support member, and when the load pressure applied to the piston of the hydraulic cylinder reaches the relief set pressure of the relief valve due to the reaction force from the resin in the heating cylinder. , Regardless of the firing force generated by the servomotor As to the relief out pressure oil in the cylinder through the relief valve configured.

[0007]

When the molten resin is completely filled in the mold at the end of the injection filling step, the resin pressure in the mold increases, and the resin pressure in the mold, that is, the resin pressure on the tip side of the heating cylinder, increases. The force is applied to a servomotor connected to the screw via a rotation-linear conversion mechanism or the like, that is, a motor support member that holds the servomotor and is slidable back and forth. Here, since the motor support member is connected to the piston rod of the hydraulic cylinder attached to the headstock, the reaction force due to the resin pressure in the heating cylinder is applied to the piston of the hydraulic cylinder, and the hydraulic pressure in the hydraulic cylinder rises. However, since the hydraulic cylinder is connected to the relief valve, when the load pressure applied to the piston of the hydraulic cylinder reaches the relief set pressure, part of the hydraulic oil in the hydraulic cylinder is discharged to the tank via the relief valve. (Relief out). As a result, the reaction force of the resin pressure in the heating cylinder applied to the piston of the hydraulic cylinder causes the piston rod to retreat, retreat the motor support member, and connect with the servomotor on the motor support member via a rotation-linear conversion mechanism or the like. The retreating force acts on the screw thus set, thereby reducing the forward speed of the screw and reliably preventing the generation of a resin pressure larger than an appropriate value in the mold.

That is, by merely setting the relief set pressure of the relief valve connected to the hydraulic cylinder to the rated resin pressure, which is an appropriate resin pressure, it is possible to determine the injection power (rotation speed of the servo motor) generated by the servo motor. Regardless, since the actual advance speed of the screw is reduced so that the resin pressure exceeding the rated resin pressure does not occur, even if the set injection filling speed is extremely high, a resin pressure larger than the appropriate value It will not occur.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to one embodiment shown in FIGS. 1 is a partially cutaway front view of an injection mechanism of an injection molding machine according to the present embodiment, FIG. 2 is a plan view of the same, FIG. 3 is an enlarged view of a main part of FIG. 1, and FIG. FIG. 5 is an enlarged cross-sectional view of a main part showing a portion not shown in the cross section as an enlarged cross section. FIG.

In FIGS. 1 and 2, reference numeral 1 denotes a headstock in which an inlet 1a for a raw material resin is formed;
, A heating cylinder with its rear end held, 3 a nozzle attached to the tip of the heating cylinder 2, 4 a band heater wound around the outer circumference of the heating cylinder 2 (only shown in FIG. 2 for convenience of illustration) Numerals 5 are screws incorporated in the heating cylinder 2 so as to be able to rotate and advance and retreat. 6
Is a connection mechanism including a one-way clutch described later, which connects the rear end side of the screw 5 and the front end side of the drive shaft 7 driven by a motor, and transmits the forward and backward movement of the drive shaft 7 to the screw 5; Further, the rotation of the drive shaft 7 can be selectively transmitted to the screw 5. The position of the head stock 1 is held by a head touch cylinder (hydraulic cylinder) (not shown). In a molding operation state, the tip of the nozzle 3 is pressed against the resin injection port of the mold. The position is assuredly maintained.

Reference numeral 8 denotes a motor support member mounted on a fixed base (not shown) so as to be slidable back and forth, to which a first servomotor 9 and a second servomotor 10 are attached. Reference numeral 11 denotes a first driving rotator rotatably held by the motor support member 8 and is belt-connected to an output pulley 12 fixed to an output shaft of the first servomotor 9 via a timing belt 13. Reference numeral 14 denotes a second driving rotator rotatably held by the motor support member 8, which is belt-connected to an output pulley 15 fixed to an output shaft of the second servomotor 10 via a timing belt 16.

In FIG. 2, reference numeral 21 denotes a hydraulic cylinder whose main body is attached and fixed to the head stock 1.
An end of a piston rod 21b integrally extending from the piston 21a (FIG. 5) is fixed to the motor support member 8. The motor support member 8 is slid back and forth by the hydraulic cylinder 21 as described later. In FIG. 2, the hydraulic cylinder 2
Although the reference numeral 1 is arranged at a position off the center of the headstock 1 and the motor support member 8, it is needless to say that the position of the hydraulic cylinder 21 can be set at an arbitrary position in consideration of the balance of force. No.

As shown in FIG. 3, the first driving rotator 11 is rotatably held at a predetermined position of the support member 8 via radial bearings 17, 17, and the first driving rotator 11 is supported by the first driving rotator 11. The timing belt 13 is wrapped around a pulley portion of the driving rotator 11. The first drive rotating body 11 includes a spline shaft portion 7a of the drive shaft 7.
Are inserted, and the first drive rotating body 11 and the drive shaft 7 are connected to each other by a spline shaft (connected so as to be rotatable integrally but relatively slidable in the axial direction). The spline shaft coupling may be of any configuration. In this embodiment, for example, a ball spline shaft coupling mechanism is used.

As also shown in FIG. 3, the second driving rotator 14 is held rotatably at a predetermined position of the support member 8 via a radial bearing 17 and a thrust bearing 18, and The timing belt 16 is wound around a pulley portion of the second drive rotating body 14 so as to withstand a thrust load. The screw portion 7b of the drive shaft 7 is screwed to the inner peripheral nut portion of the second drive rotary member 14, and the second drive rotary member 14 and the drive shaft 7 are screw-nut coupled. . The screw-nut coupling may have any configuration. In this embodiment, for example, a ball screw mechanism is used.

FIG. 4 shows the structure of the connecting mechanism 6. In the figure, reference numeral 19 denotes a connecting shaft fixed to the rear end of the screw 5. The connecting shaft 19 has a distal end 7c of the drive shaft 7 attached thereto via a radial bearing 18 and a distal end 7c. A thrust bearing 18 is interposed between the drive shaft 7 and the connecting shaft 19 so that the forward and backward movement of the drive shaft 7 can be transmitted to the connecting shaft 19 (that is, the screw 5) without difficulty. A one-way clutch means 20 is provided between the distal end face of the distal end portion 7c of the drive shaft 7 and the outer periphery of the drive shaft 7, and the clutch is turned off when the drive shaft 7 rotates forward (rotation transmission cutoff). State), drive shaft 7
In the reverse rotation of the clutch, the clutch is turned on (rotation can be transmitted). Therefore, only when the drive shaft 7 rotates in the reverse direction and the one-way clutch means 20 is in the ON state, the drive shaft 7 and the connection shaft 19 (that is, the screw 5) rotate integrally.

FIG. 5 shows a hydraulic circuit related to the hydraulic cylinder 21. In FIG. 5, reference numeral 22 denotes a hydraulic pump, 23 denotes an electromagnetic switching valve, 24 denotes an electromagnetic relief valve, and 25 denotes a tank. A hydraulic pump 2 is connected to an oil chamber 21 c of the hydraulic cylinder 21 through an electromagnetic switching valve 23.
2 is connected, and in the molding operation state of the injection molding machine, the oil chamber 21c of the hydraulic cylinder 21 is supplied and filled with a constant pressure (a predetermined pressure less than the rated resin pressure). I have. Also, an electromagnetic relief valve 24 is connected to the oil chamber 21c, and when the oil pressure in the oil chamber 21c exceeds the relief set pressure of the electromagnetic relief valve 24,
The pressure oil in the oil chamber 21c is partially discharged (relief-out) to the tank 25 via the electromagnetic relief valve 24. In the present embodiment, the relief set pressure of the electromagnetic relief valve 24 is set to a value equal to the rated resin pressure determined for each product type. This is set by the system controller of the injection molding machine (not shown) from the driver circuit. To the electromagnetic relief valve 24. The electromagnetic switching valve 23 is also controlled by a system controller of an injection molding machine (not shown) via a driver circuit. In the molding operation state, the electromagnetic switching valve 23 is in an open supply state. In a state where no force equal to or higher than the relief set pressure against the pressure oil is applied to the piston 21a, the piston 21a is set at the forward limit position as illustrated.

Next, the operation based on the above configuration will be described. <Plasticizing / Measuring Step> In the plasticizing / measuring step, the first
Is driven at a relatively low speed in a predetermined direction at a rated torque, and the drive shaft 7 is driven via the output pulley 12, the timing belt 13, and the first drive rotating body 11.
Rotates in the reverse direction. When the drive shaft 7 rotates in the reverse direction, the one-way clutch means 20 is turned on, so that the rotation of the drive shaft 7 is transmitted to the connection shaft 19 via the clutch means 20 and the screw 5 integrated with the connection shaft 19 Rotate in the direction. The rotation direction of the drive shaft 7 at this time is a direction in which the drive shaft 7 is retracted in the screw-nut coupling mechanism described above.

As the molten resin kneaded and plasticized is fed to the front side of the screw with the rotation of the screw 5, the second servo motor 10 is driven to rotate at a very low torque in a predetermined direction. . Second servo motor 1
The rotation of the output pulley 15 and the timing belt 1
The rotation of the second driving rotator 14 is transmitted to the driving shaft 7 by the screw-nut coupling mechanism described above. At this time, the rotation direction of the second driving rotator 14 is the same as the rotation direction of the first driving rotator 11 (that is, the reverse rotation direction shown in FIG. 4), and the driving shaft 7 and the coupling mechanism 6 serves as a force for delaying the retraction of the screw 5 connected via 6 by an appropriate amount. That is, the rotation speed of the second driving rotator 14 is made slightly smaller than the rotation speed of the first driving rotator 11, whereby the screw 5 moves backward while controlling the back pressure.

<Injection Filling Step> In the injection filling step (primary injection step) in the injection step, the first servo motor 9 and the second servo motor 10 are simultaneously driven to rotate at high speed with peak torque specifications. . At this time, the first servomotor 9 is driven to rotate in the direction opposite to that in the plasticizing and measuring step, and the drive shaft 7 rotates forward through the output pulley 12, the timing belt 13, and the first drive rotating body 11. Rotate in the direction. When the drive shaft 7 rotates forward, the one-way clutch 20
Since it is FF, the rotation of the drive shaft 7 is not transmitted to the connection shaft 19. Since the rotating drive shaft 7 is screw-nut-coupled to the second drive rotary member 14 as described above, the drive shaft 7 is rotated forward in the forward rotation direction by this screw-nut coupling mechanism.

In this case, the second servo motor 10
Is also driven to rotate in the same direction as the plasticizing and measuring process,
Of the servo motor 10 is transmitted to the second driving rotator 14 via the output pulley 15 and the timing belt 16, and the second driving rotator 14 is driven by the first driving rotator 11 (that is, the driving shaft 7). It rotates in the direction opposite to the direction of rotation. The rotation of the second drive rotating body 14 is converted into linear motion by the screw-nut coupling mechanism described above and transmitted to the drive shaft 7, and the drive shaft 7 moves forward.

That is, the rotational force of the first servomotor 9 and the rotational force of the second servomotor 10 are both converted into the forward force of the drive shaft 7, and the drive forces of the two servomotors 9 and 10 are added. As a result, the drive shaft 7 is driven forward, whereby the screw 5 is rapidly driven forward (in this case, the one-way clutch means 20 is OFF, so that the screw 5 does not rotate). As described above, at the time of injection filling, the driving force (driving speed) of the two servomotors 9 and 10 is increased while the first and second servomotors 9 and 10 are both operated at the peak torque to ensure a sufficient output torque. By summing up, a very fast screw advance, ie a high-speed injection filling of the molten resin into the mold cavity, can be achieved.

When the molten resin is completely filled in the mold at the end of the injection filling step, the resin pressure in the mold increases, and the reaction force due to the resin pressure in the mold, that is, the heating cylinder 2 The reaction force due to the resin pressure on the tip side holds the first and second servo motors 9 and 10 connected to the screw 5 via a rotation-linear conversion mechanism or the like, that is, slides back and forth while holding the servo motors 9 and 10. The motor support member 8 is enabled. Since the motor support member 8 is connected to the piston rod 21b of the hydraulic cylinder 21 attached to the headstock 1 as described above, the reaction force due to the resin pressure in the heating cylinder 2 is applied to the piston 21a of the hydraulic cylinder 21. The oil pressure in the oil chamber 21c of the hydraulic cylinder 21 increases. Here, since the hydraulic cylinder 21 is connected to the electromagnetic relief valve 24, when the load pressure applied to the piston 21a in the direction indicated by the arrow in FIG. 5 reaches the relief set pressure, a part of the pressure oil in the hydraulic cylinder 21 becomes electromagnetic. Tank 25 via relief valve 24
To be relieved.

As a result, the piston 2 of the hydraulic cylinder 21
1a, the piston rod 21b retreats due to the reaction force of the resin pressure in the heating cylinder 2 and the motor support member 8
And a retreat force is applied to the screw 5 connected to the first and second servo motors 9 and 10 on the motor support member 8 via a rotation-linear conversion mechanism or the like. At this time, a forward force is applied to the screw 5 by the rotation of the first and second servo motors 9 and 10, but the motor 5 is retracted as described above so that the brake is applied to the screw 5. Works, and the forward speed of the screw 5 is reduced.

That is, since the relief set pressure of the electromagnetic relief valve 24 connected to the hydraulic cylinder 21 is set to the rated resin pressure, which is an appropriate resin pressure, the first and second servo motors 9 and 10 generate Regardless of the output,
The actual forward speed of the screw 5 is reduced so that a resin pressure higher than the rated resin pressure is not generated. Therefore, even if the injection filling speed is extremely high, generation of a resin pressure larger than an appropriate value in the mold is reliably prevented.

FIG. 6 is a graph showing the relationship between the injection speed (motor speed, screw speed) and the resin pressure in the mold in this injection filling step. As shown in FIG. In the injection filling process in which the speed feedback control is performed with the torque (force), the actual speed of the screw substantially coincides with the actual speed of the servomotor up to halfway, but the resin pressure in the heating cylinder (load resin pressure) becomes the rated resin pressure. When it reaches, the pressurized oil is released as described above,
As the motor support member 8 retreats, the screw speed decreases rapidly. In other words, the actual speed of the servo motor is maintained at a value corresponding to the set speed, but the actual speed of the screw is reduced, and the screw is reliably controlled so that no resin pressure exceeding the rated resin pressure is generated in the mold. .

<Injection holding pressure step> In the injection holding pressure step following the injection filling step in the injection step, only the first servomotor 9 is driven at a low speed by pressure feedback control with a rated torque specification, and Servo motor 1
0 is stopped. In the injection pressure-holding step, the first servomotor 9 is driven to rotate in the same direction as the injection filling, whereby the drive shaft 7 is rotated forward via the output pulley 12, the timing belt 13, and the first drive rotating body 11. Rotate in the turning direction. Since the rotating drive shaft 7 is screw-nut coupled to the second drive rotating body 14, the drive shaft 7 receives a force that moves forward while rotating in the normal rotation direction. When the drive shaft 7 rotates forward, the one-way clutch means 20 is OFF, so that the rotation of the drive shaft 7 is not transmitted to the connecting shaft 19 and the screw 5, and the screw 5 receives only the forward force. Then, a predetermined holding pressure is applied to the resin in the mold.

[0027]

As described above, according to the present invention, even if the injection filling speed by the servomotor is extremely high, a resin pressure larger than an appropriate value is not generated in the mold.
An injection molding machine that can guarantee good molding can be provided, and its value is enormous.

[Brief description of the drawings]

FIG. 1 is a partially simplified front view of an injection system mechanism of an injection molding machine according to one embodiment of the present invention.

FIG. 2 is a partially simplified plan view of an injection system mechanism of the injection molding machine according to one embodiment of the present invention.

FIG. 3 is an enlarged view of a main part of FIG. 1;

FIG. 4 is an enlarged cross-sectional view of a connecting mechanism part of FIG. 1;

FIG. 5 is a hydraulic circuit diagram showing the hydraulic cylinder of FIG. 2 and a configuration related thereto.

FIG. 6 is an explanatory diagram showing a relationship between an injection speed and a resin pressure during an injection filling step according to one embodiment of the present invention.

FIG. 7 is an explanatory diagram showing a relationship between an injection speed and a resin pressure during an injection filling step by a conventional servo motor driven injection molding machine.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Headstock 2 Heating cylinder 3 Nozzle 5 Screw 6 Connecting mechanism 7 Drive shaft 8 Motor support member 9 1st servo motor 10 2nd servo motor 11 1st drive rotating body 12 Output pulley 13 Timing belt 14 2nd drive Rotating body 15 Output pulley 16 Timing belt 17 Radial bearing 18 Thrust bearing 19 Connecting shaft 20 One-way clutch means 21 Hydraulic cylinder 21a Piston 21b Piston rod 21c Oil chamber 22 Hydraulic pump 23 Electromagnetic switching valve 24 Electromagnetic relief valve 25 Tank

Claims (1)

(57) [Claims] An in-line screw type in which the rotation of a servomotor is transmitted to a screw in a heating cylinder as a linear motion via a rotation-linear conversion mechanism, and at least the injection power of the injection process is obtained by the driving force of the servomotor. In the injection molding machine, a hydraulic cylinder is attached to a headstock holding the heating cylinder, and a piston rod of the hydraulic cylinder is connected to a motor support member that holds the servo motor and is slidable back and forth, A relief valve connected to a cylinder is provided, and when a load pressure applied to a piston of the hydraulic cylinder reaches a relief set pressure of the relief valve due to a reaction force from a resin in a heating cylinder, an emission power generated by the servo motor is reduced. Regardless of the pressure oil in the hydraulic cylinder, Injection molding machine is characterized in that so as to relief out through the relief valve.