JPH0623813A - Injection molding machine - Google Patents

Abstract

PURPOSE:To provide an injection molding machine of the type not causing larger resin pressure than the proper value within the mold even in an extraordinarily high injection speed by a servo-motor. CONSTITUTION:A hydraulic cylinder 21 is attached to a head stock 1 having a heating cylinder retained thereto, and the piston rod 21b of the hydraulic cylinder is connected to a motor support member 8 holding a servo-motor and permitted to be slidable forward and rearward. In connection with this, a relief valve 24 connected to the hydraulic cylinder is provided, and when load pressure exerted on the piston of the hydraulic cylinder reaches the relief setting pressure of the relief valve by the reaction force from resin within the heating cylinder, hydraulic pressure within the hydraulic cylinder is relieved out via the aforesaid relieve valve irrespective of the injection force generated by the servo-motor.

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 an injection output in an injection step is obtained by a driving force of a servo motor.

[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 resin, and the screw is moved forward to inject and fill molten resin into a mold. In the machine
Servo motor driven injection molding machines that use servo motors as drive sources for plasticizing / metering and injection operations are known. In this conventional servomotor-driven injection molding machine, the screw rotation servomotor for plasticizing / metering operation is connected to the screw, the screw is rotated by the screw rotation servomotor, and the injection servomotor for injection operation is also used. It is common to adopt a configuration in which the rotation is 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 servo motor includes a continuous rated torque that guarantees a torque during continuous use of the motor and a peak torque that allows a momentary large torque to be used. The torque can be increased to approximately 400% of the continuous rated torque. Then, in the injection molding machine, during the injection filling process (primary injection process), the molten resin stored on the tip side of the screw (on the nozzle side) is rapidly moved forward into the mold within a very short time. Since it is necessary to perform injection filling against the load resin pressure that rises rapidly, the specified torque of the injection servo motor is set to the peak torque during the injection filling process (Note that the injection pressure holding process and the plasticizing / measuring process are Since it takes a long time compared to the injection filling process, the specified torque of the servomotor is considered to be the continuous rated torque). Further, in an injection molding machine driven by a servo motor, speed feedback control is performed in the injection filling process, so that the output torque of the servo motor in the injection filling process has a force of 200% or more of the continuous rated torque. 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, and during the injection filling process (during operation by the peak torque), the rated value is controlled. 2 during torque operation
Although a force (torque) of not less than 00% is provided, when the molten resin is fully 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 the (rated resin pressure) is generated. In this way, when a resin pressure, which is a proper resin pressure and greatly exceeds the rated resin pressure, is generated in the mold, it causes burrs and the like, which significantly deteriorates the quality of the product (molded product). Therefore, in practice, we are trying to prevent a large resin pressure from working in the mold by lowering the setting speed of the servo motor just before the injection filling is completed, but the injection filling speed is extremely high. In such a case, it is unavoidable that a resin pressure larger than an appropriate value is generated in the mold due to factors such as inertial force.
As described above, it has been a factor that deteriorates the quality of the product (molded product).

The present invention has been made in view of the above points,
An object of the invention is to provide an injection molding machine in which a resin pressure larger than an appropriate value is not generated in a mold even when the injection filling speed by the servo motor 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 through a rotation-linear conversion mechanism, and at least in the injection process. 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 that holds the heating cylinder, and the piston rod of the hydraulic cylinder can be slid back and forth while holding the servomotor. A relief valve connected to the motor support member and connected to the hydraulic cylinder is provided, and when the load pressure applied to the piston of the hydraulic cylinder reaches the relief set pressure of the relief valve by the reaction force from the resin in the heating cylinder. , Regardless of the firing power generated by the servo motor, As to the relief out pressure oil in the cylinder through the relief valve configured.

[0007]

[Function] When the molten resin is fully filled in the mold at the end of the injection filling process, the resin pressure in the mold rises, and the resin pressure in the mold, that is, the resin pressure on the tip side of the heating cylinder, causes a reaction. The force is applied to a servo motor connected to the screw via a rotation-linear conversion mechanism or the like, that is, a motor support member that holds the servo motor 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 pressure oil in the hydraulic cylinder is discharged to the tank via the relief valve. (Relief out). As a result, the reaction force due to the resin pressure in the heating cylinder exerted on the piston of the hydraulic cylinder causes the piston rod to retract and retract the motor support member, so that the motor is connected to the servomotor on the motor support member via a rotation-linear conversion mechanism or the like. The retracted force acts on the screw that has been moved to reduce the forward speed of the screw, and reliably prevents the generation of resin pressure in the mold that is higher than an appropriate value.

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, the injection output (servo motor rotation speed) generated by the servo motor can be determined. Regardless, the actual forward speed of the screw is reduced so that the resin pressure above the rated resin pressure is not generated, so even if the set injection and filling speed is extremely high, a resin pressure larger than the appropriate value will be generated in the mold. 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. FIG. 1 is a partially cutaway front view of an injection system 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. In FIG. 5, an enlarged cross-sectional view of an essential part showing a portion not shown in the cross-section as an enlarged cross-section, and FIG.

In FIGS. 1 and 2, reference numeral 1 is a headstock having a raw resin inlet 1a formed therein, and 2 is a headstock 1.
A heating cylinder whose rear end side is held by 3 is a nozzle attached to the front end side of the heating cylinder 2, and 4 is a band heater wound around the outer circumference of the heating cylinder 2 (only shown in FIG. 2 for convenience of illustration). Reference numeral 5 denotes a screw built in the heating cylinder 2 so as to be rotatable and forward / backward. 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 motor-driven drive shaft 7, and transmits the forward / backward movement of the drive shaft 7 to the screw 5, 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), and in the molding operation state, the tip of the nozzle 3 is pressed against the resin injection port of the mold. The position is surely maintained.

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

In FIG. 2, reference numeral 21 is 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 slidably driven back and forth by the hydraulic cylinder 21 as described later. In FIG. 2, the hydraulic cylinder 2
1 is arranged at a position deviated from the center of the headstock 1 and the motor support member 8, but it goes without saying that the position of the hydraulic cylinder 21 can be set at an arbitrary position in consideration of the balance of forces. Yes.

As shown in FIG. 3, the first drive rotating body 11 is rotatably held at a predetermined position of the support member 8 via radial bearings 17, 17, and the first drive rotating body 11 is rotatable. The timing belt 13 is wound around the pulley portion of the drive rotor 11. The first drive rotor 11 has a spline shaft portion 7a of the drive shaft 7.
The first drive rotor 11 and the drive shaft 7 are spline shaft-coupled (combined so as to be integrally rotatable but relatively slidable in the axial direction). Although any structure can be adopted for this spline shaft coupling, a ball spline shaft coupling mechanism is used in this embodiment, for example.

Similarly, as shown in FIG. 3, the second driving rotary body 14 is rotatably held at a predetermined position of the supporting member 8 via a radial bearing 17 and a thrust bearing 18, and The timing belt 16 is wound around the pulley portion of the second drive rotating body 14 so as to withstand the thrust load. The screw portion 7b of the drive shaft 7 is screwed into the inner peripheral nut portion of the second drive rotor 14, and the second drive rotor 14 and the drive shaft 7 are screw-nut coupled. . It should be noted that this screw-nut coupling can also adopt any configuration, but in this embodiment, for example, a ball screw mechanism is employed.

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, and the distal end 7c of the drive shaft 7 is attached to the connecting shaft 19 via a radial bearing 18, and the distal end 7c is also provided. A thrust bearing 18 is interposed between the connecting shaft 19 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 tip end surface side of the tip 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
During reverse rotation, the clutch is turned on (rotation can be transmitted). Therefore, the drive shaft 7 and the connecting shaft 19 (that is, the screw 5) are integrally rotated only when the drive shaft 7 is reversely rotated and the one-way clutch means 20 is in the ON state.

FIG. 5 shows a hydraulic circuit related to the hydraulic cylinder 21, in which 22 is a hydraulic pump, 23 is an electromagnetic switching valve, 24 is an electromagnetic relief valve, and 25 is a tank. The hydraulic chamber 21c of the hydraulic cylinder 21 has a hydraulic pump 2 through an electromagnetic switching valve 23.
2 is connected, and in a molding operation state of the injection molding machine, the hydraulic chamber 21c of the hydraulic cylinder 21 is supplied with a constant pressure (a predetermined pressure less than the rated resin pressure) of pressure oil to be filled. There is. Further, the electromagnetic relief valve 24 is connected to the oil chamber 21c, and when the hydraulic 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 (relieved out) to the tank 25 via the electromagnetic relief valve 24. In this 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 driver circuit from the system controller of the injection molding machine (not shown). To the electromagnetic relief valve 24 via. Similarly, the electromagnetic switching valve 23 is also controlled by a system controller of an injection molding machine (not shown) via a driver circuit, and in the molding operation state, the electromagnetic switching valve 23 is in an open supply state, and the hydraulic cylinder 21 has As shown in the figure, the piston 21a is located at the forward limit position when the piston 21a is not subjected to a force equal to or higher than the relief set pressure against the pressure oil.

Next, the operation based on the above configuration will be described. <Plasticization / Measurement Process> In the plasticization / measurement process, the first
Servo motor 9 is driven to rotate in a predetermined direction with a rated torque at a relatively low speed, and through the output pulley 12, the timing belt 13 and the first drive rotor 11, the drive shaft 7
Rotates in the reverse direction. When the drive shaft 7 is rotated 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 connecting shaft 19 via the clutch means 20, and the screw 5 integrated with the connecting shaft 19 is predetermined. 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 above-described screw-nut coupling mechanism.

As the kneaded and plasticized molten resin is fed to the front side of the screw 5 as the screw 5 rotates, the second servomotor 10 is rotationally driven in a predetermined direction with extremely low torque. . Second servo motor 1
The rotation of 0 corresponds to the output pulley 15 and the timing belt 1
6 is transmitted to the second drive rotor 14 and the rotation of the second drive rotor 14 is converted into linear motion by the screw-nut coupling mechanism and transmitted to the drive shaft 7. At this time, the rotation direction of the second drive rotor 14 is set to be the same as the rotation direction of the first drive rotor 11 (that is, the reverse direction shown in FIG. 4), and the drive shaft 7 and the connecting mechanism are connected. It works as a force to delay the backward movement of the screw 5 connected via 6 by an appropriate amount. That is, the rotation speed of the second driving rotary body 14 is made slightly smaller than the rotation speed of the first driving rotary body 11, whereby the screw 5 moves backward while controlling the back pressure.

<Injection Filling Step> In the injection filling step (primary injection step) during the injection step, the first servomotor 9 and the second servomotor 10 are simultaneously driven to rotate at high speed with peak torque specifications. . At this time, the first servomotor 9 is rotationally driven in the direction opposite to that in the plasticizing / measuring step, and the drive shaft 7 is rotated in the normal direction via the output pulley 12, the timing belt 13, and the first drive rotor 11. Rotate in the direction. When the drive shaft 7 rotates in the normal direction, the one-way clutch means 20 is set to O.
Since it is FF, the rotation of the drive shaft 7 cannot be transmitted to the connecting shaft 19. Since the rotating drive shaft 7 is screw-nut coupled to the second drive rotating body 14 as described above, the drive shaft 7 advances while rotating in the forward direction by this screw-nut coupling mechanism.

At this time, the second servomotor 10
Is also driven to rotate in the same direction as the plasticizing and weighing process,
The rotation of the servo motor 10 is transmitted to the second drive rotating body 14 via the output pulley 15 and the timing belt 16, and the second drive rotating body 14 is connected to the first drive rotating body 11 (that is, the drive shaft 7). Rotates in the direction opposite to the rotation direction of. 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 advances.

That is, the rotational force of the first servo motor 9 and the rotational force of the second servo motor 10 are both converted into the forward force of the drive shaft 7, and the drive forces of the two servo motors 9 and 10 are added together. Thus, the drive shaft 7 is driven forward, whereby the screw 5 is rapidly driven forward (of course, at this time, the one-way clutch means 20 is OFF, so the screw 5 does not rotate). In this way, at the time of injection filling, the driving force (driving speed) of the two servo motors 9 and 10 is controlled while operating both the first and second servo motors 9 and 10 at the peak torque to ensure a sufficient output torque. By adding them together, very fast screw advancement, that is, high-speed injection filling of the molten resin into the mold cavity can be achieved.

By the way, at the end of the injection filling process, when the mold is filled with the molten resin to a full extent, the resin pressure in the mold rises, 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 slides back and forth while holding the first and second servomotors 9 and 10 connected to the screw 5 via a rotation-linear conversion mechanism or the like, that is, the servomotors 9 and 10. The motor support member 8 is enabled. As described above, since the motor support member 8 is connected to the piston rod 21b of the hydraulic cylinder 21 attached to the head stock 1, 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 hydraulic pressure in the oil chamber 21c of the hydraulic cylinder 21 rises. 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 of the arrow in FIG. 5 reaches the relief set pressure, a part of the pressure oil in the hydraulic cylinder 21 is electromagnetically released. Tank 25 through relief valve 24
Is relieved out.

As a result, the piston 2 of the hydraulic cylinder 21
The reaction force due to the resin pressure in the heating cylinder 2 applied to the la 1a causes the piston rod 21b to retract and the motor support member
Is retracted, and a retracting force is applied to the screw 5 connected to the first and second servomotors 9 and 10 on the motor support member 8 via a rotation-linear conversion mechanism or the like. At this time, the forward force acts on the screw 5 due to the rotation of the first and second servomotors 9 and 10. However, as the motor support member 8 retracts as described above, the screw 5 is braked. The working speed of the screw 5 is reduced.

That is, since the relief setting 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 radiation generated by the first and second servomotors 9 and 10 is generated. Regardless of 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, it is possible to reliably prevent generation of a resin pressure larger than an appropriate value in the mold.

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 process. As shown in FIG. In the injection filling process where the speed feedback control is performed with the torque (force), the actual screw speed is approximately the same as the actual servo motor speed, but the resin pressure in the heating cylinder (load resin pressure) becomes the rated resin pressure. When it reaches, the pressure oil will be reliefed out as described above,
The motor support member 8 retracts and the screw speed rapidly decreases. That is, the actual speed of the servomotor is maintained at a value commensurate with the set speed, but the actual speed of the screw is decelerated and is reliably controlled so that the resin pressure above the rated resin pressure does not occur in the mold. .

<Injection Pressure Holding Step> In the injection pressure holding step subsequent to the injection filling step in the injection step, only the first servomotor 9 is rated torque specification and is driven to rotate at a low speed by pressure feedback control. Servo motor 1
0 is stopped. In this injection pressure-holding step, the first servomotor 9 is rotationally driven in the same direction as the injection filling, so that the drive shaft 7 is positively moved through the output pulley 12, the timing belt 13, and the first drive rotor 11. Rotate in the rolling direction. The rotating drive shaft 7 is screw-nut coupled to the second drive rotating body 14, so that the drive shaft 7 receives a forward force while rotating in the forward rotation direction. Since the one-way clutch means 20 is OFF during the normal rotation of the drive shaft 7, 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. Apply a predetermined holding pressure to the resin in the mold.

[0027]

As described above, according to the present invention, even if the injection filling speed by the servo motor is extremely high, a resin pressure larger than an appropriate value is not generated in the mold.
We can provide an injection molding machine that guarantees good product molding, and its value is enormous.

[Brief description of drawings]

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

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

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

FIG. 4 is an enlarged sectional view of a connecting mechanism portion of FIG.

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 process according to an 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 process by a conventional injection molding machine driven by a servo motor.

[Explanation of symbols]

 1 Headstock 2 Heating Cylinder 3 Nozzle 5 Screw 6 Connection Mechanism 7 Drive Shaft 8 Motor Support Member 9 First Servo Motor 10 Second Servo Motor 11 First Drive Rotator 12 Output Pulley 13 Timing Belt 14 Second 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)

[Claims] 1. An in-line screw type in which rotation of a servo motor is transmitted to a screw in a heating cylinder as a linear motion through a rotation-linear conversion mechanism, and at least an injection output of an injection step is obtained by a driving force of the servo motor. In the injection molding machine, the hydraulic cylinder is attached to the head stock holding the heating cylinder, and the piston rod of the hydraulic cylinder is connected to the motor supporting member that holds the servo motor and is slidable back and forth, A relief valve connected to the cylinder is provided, and when the load pressure applied to the piston of the hydraulic cylinder reaches the relief set pressure of the relief valve by the reaction force from the resin in the heating cylinder, the injection output of the servo motor is increased. Regardless of whether the pressure oil in the hydraulic cylinder is Injection molding machine is characterized in that so as to relief out through the relief valve.