JPH06206244A - Electric injector of injection molding machine - Google Patents

Abstract

PURPOSE:To obtain an electric injector having a screw built-in which is excellent in an injection and pressure-retentive performance by a method wherein a servo motor which is excellent in a response property and an output detector are adopted. CONSTITUTION:A screw 20 having an elongated member 26 at its rear end is provided inside an injection heating cylinder 21. The screw 20 is freely rotatively connected to a support member 25 via the elongated member 26. A screw shaft 30 rotating at a specific position is threaded with a screw box 27 provided to the screw support member 25. A servomotor 35 which advance- drives the screw support member 25 and the screw 20 by rotating the screw shaft 30, is provided. The servo motor 35 is equipped with a current detector which detects a current flowing to the servo motor 35, a current setter for confirming occurrence of an output torque of the servo motor, and a comparator which generates a confirmation signal for coincidence by comparing a detected current of the current detector with a set current of the current setter in a circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection device of an injection molding machine which employs an electric motor as a drive source, and more particularly to an electric injection device in which a screw is installed in an injection heating cylinder.

[0002]

2. Description of the Related Art As an injection device using an electric motor as a drive source, plunger type devices described in JP-B-35-7974 and JP-B-39-10424 are known.

In the electric injection molding machine described in Japanese Utility Model Publication No. 35-7974, a screw shaft is screwed into a nut member that rotates at a fixed position, and a cylindrical connector is provided at the tip of the screw shaft. And the plunger in the heating cylinder is connected, the nut member is rotated by the electric motor through the speed reducer, and the rotational movement is converted into linear movement by the screw shaft to move the plunger forward or backward and to be provided on the connector. The hydraulic cylinder is configured to maintain a constant injection pressure.

In the electric injection device described in Japanese Utility Model Publication No. 39-10424, a pair of tie bars support a sliding plate, and the rear end of the plunger is attached to the front surface of the sliding plate while the sliding plate is mounted. A screw shaft having an axial key groove in the shaft portion is rotatably connected to the rear surface of the rear portion, a pulley that rotates at a fixed position is screwed onto the screw shaft, and a worm wheel is attached to the shaft portion through a key. After meshing and blocking the rotation of the shaft by the worm wheel,
The pulley is rotated by an electric motor, and its rotary motion is converted into a linear motion by a screw shaft to move the plunger forward or backward.

[0005]

In any of the above-mentioned plunger type injection devices, the plunger is moved forward together with the screw shaft for injection, so that a rotation resistance member, a resistance machine or the like for preventing the rotation of the screw shaft is required. Further, since a rotational resistance is given to the screw shaft to convert the rotational movement by the electric motor into the linear movement of the plunger, the resistance at the time of conversion is large, and the reduction gear is also required, so that the transmission efficiency is remarkably poor.

Further, a commonly used ordinary electric motor has drawbacks in starting, stopping, and rapid acceleration / deceleration control of the electric motor, and torque control is also difficult, and a wide range from low speed to rated speed is controlled with high accuracy. For this reason, it has been difficult to use as a drive source for a screw-injection device that requires high-speed response.

Further, in a screw-injection device, unlike any plunger type, a metering process for plasticizing the material resin while rotating the screw is indispensable, unlike the plunger type. This metering is performed accurately by the smooth backward movement of the screw, so the compression by the forward movement of the plunger and the heating cylinder
Even if the transmission mechanism of the plunger type injection device for sequentially plasticizing the material resin in the heating cylinder is applied to the screw internal injection device, it is extremely difficult to achieve the intended purpose.

Further, in the injection device, the injection output and the holding pressure must be detected to control the pressure, and the control can be performed only by the smooth operation of the transmission mechanism and the reliable detection of the output. . Regarding this output detection, in the conventional injection molding machine in which the drive source is hydraulic pressure,
Output detection can be easily achieved by attaching a pressure sensor such as a pressure gauge to each hydraulic actuator such as injection or nozzle touch or a conduit in the vicinity thereof, but when an ordinary electric motor is used as a drive source, It is possible to employ a detection unit that detects the amount of deformation of the transmission member and its supporting member during operation using a strain gauge or the like, converts the amount of deformation into an electric signal, and controls the electric motor.

However, output detection using a strain gauge or the like has problems in mounting space, durability, cost, etc., is weak against environmental changes such as temperature and humidity, and is prone to error, depending on the mounting position and means. It has problems such as difficulty in maintaining accuracy.

The present invention has been conceived in order to solve the problems of the above-mentioned electric injection device, and an object thereof is to be able to smoothly move a screw even in an injection device having a screw inside. It is another object of the present invention to provide an electric injection device that is excellent in injection and pressure holding performance by adopting an electric motor and an output detection device that have good responsiveness.

[0011]

According to the features of the present invention according to the above object, a screw in an injection heating cylinder having an extension member at its rear end, a screw rotatably held through the extension member, and a screw together with the screw are provided. A holding member that moves back and forth,
A screw shaft in a fixed position, which is screwed with a screw receiving member provided on the screw holding member, converts the rotational movement into a linear movement by the screw receiving member to move the screw holding member forward together with the screw, and the extension. A rotation transmission member for screw rotation provided on the member, and a servomotor that rotates the screw shaft to drive the screw holding member and the screw forward. The servomotor supplies a current flowing in the circuit to the servomotor. A current detector for detection, a current setting device for confirming the generation of the output torque of the servo motor, and a detection signal for coincidence are generated by comparing the detection current of the current detector and the setting current of the current setting device. And a comparator.

[0012]

[Operation] In the above configuration, when the servomotor rotates normally, the screw shaft screwed with the screw receiving member on the screw holding member side rotates. Since this screw shaft is located on the axis of the screw and does not move in the axial direction, the screw holding member side moves forward, whereby the screw moves forward in the injection heating cylinder to perform injection.

When a large torque is generated in the servo motor due to the completion of injection and the current flowing through the servo motor rises, the current setter that sets the torque commensurate with the torque and the rising current detected by the current detector are sent to the comparator. When the coincidence confirmation signal is generated, the centralized control device operates and shifts to the pressure holding process.

Since the torque corresponding to the holding pressure is also set in the current setting device, the screw holds the torque by the torque and holds the pressure. In this case as well, as in the case of injection, the current detected by the current detector is compared by the comparator, and it is confirmed by the confirmation signal of coincidence that the predetermined holding pressure has been achieved.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the drawings, 1 is a mold clamping mechanism and 2 is an injection device. The mold clamping mechanism 1 has a tie bar 12 installed on a pair of fixed plates 10 and 11 on the machine base 3, and a movable plate 13 movably attached to the tie bar 12. Molds 14 and 14 are provided on opposing surfaces of the fixed plate 11 and the movable plate 13, respectively, and a screw shaft 15 is provided on the opposite surface of the movable plate 13 so as to project therefrom. The screw shaft 15 is screwed into a rotary plate 16 which is rotatably mounted on the other fixed plate 10, and a gear 17 is attached to the rotary plate 16. When rotated, the screw shaft constitutes a die opening / closing device in which the screw shaft 15 moves together with the movable platen 13 by the screw lead.

The injection device 2 has an injection heating cylinder 21 in which the screw 20 is installed, and a movable housing 22 on the machine base which also serves to hold the injection heating cylinder 21. Inside the housing 22, a rear end portion of the screw 20 and a screw holding member 25 are housed so as to be slidable in the front-rear direction.

An extension shaft 26 having a gear for rotating the screw 20 is connected to the rear end of the screw 20, and the end of the extension shaft 26 is rotatably connected to the screw holding member 25. .

Further, a screw receiving member 27 provided at the rear portion of the screw holding member 25 has a shaft portion 29 rotatably held by the housing wall portion 22a and having an injection gear 28.
A screw shaft 30 integrated with the screw shaft is screwed into the screw shaft 30 to form a force transmission mechanism. The outer end of the shaft portion 29 of the screw shaft 30 is connected to a back pressure control brake 31 fixed to the housing wall portion 22a. This back pressure control brake 31
Has a hysteresis brake inside.

Reference numeral 32 denotes a transmission shaft on the side of the mold clamping mechanism, which is rotatably supported by the lower portions of the fixed plates 10 and 11 and which is in close proximity to the fixed plate 10 and meshes with the gear 17 to form a transmission gear 33.
At the outer end and a key or spline at the inner end. 34 is a transmission shaft on the injection device side,
A drive belt 36 is supported on the lower end of the transmission shaft 2, and is provided around the outer end of the transmission shaft 34 and a servomotor 35 installed on the lower side of the housing. The servomotor 35 rotates the transmission shaft 34. Reference numeral 35a is a tachometer generator.

A joint 37 for connecting the transmission shaft 32 on the mold clamping mechanism side is connected to the inner end of the transmission shaft 34 so as to be freely contactable and separable via an electromagnetically actuated clutch mechanism 38. The joint 37 is formed integrally with the shaft portion rotatably and slidably supported by the housing 22 and the outer end of the shaft portion, and has a key groove or spline for receiving the inner end of the transmission shaft 32 provided inside. A cylinder 37a is provided, and an electromagnetically-operated mold clamping force retainer 39 is provided on the shaft portion. The mold clamping force retainer 39 is composed of a braking plate fixed to the housing wall and an electromagnet that is keyed to the shaft so as to be axially movable, and the electromagnet is coupled with the braking plate by excitation. The mold clamping force is held via the transmission shaft 32.

Reference numeral 40 in the drawing denotes a transmission gear provided on the transmission shaft 34 together with an electromagnetically actuated clutch mechanism 40a, which meshes with the injection gear 28. Reference numeral 41 denotes a transmission gear provided on the transmission shaft 34 together with an electromagnetically actuated clutch mechanism 41a, and meshes with the gear for rotating the screw 24.

FIG. 2 shows a controller, which is a centralized controller 3
4, the servo motor 35 and the tachometer generator 35
A speed setter 45 and a torque setter 46 are provided in parallel with the motor control amplifier 44 connected to a. A current detector 47 provided in the circuit of the servomotor 35 is connected to a current setter 49 via a comparator 48, and the comparator 48 is connected to the central control device 43.

The central control unit 43 includes a clutch mechanism 3
8, the mold clamping force holder 39, the position detector 50, the operation switch 51, and the back pressure control amplifier 52 of the back pressure control brake 31 are connected to each other.

Next, the operation of the injection device using the servo motor 35 as a drive source will be described. While the transmission shafts 32 and 34 are connected by the clutch mechanism 38, the servo motor 3
5 is rotated in the forward direction by a command. At this time, on the injection device 2 side, the transmission gears 40, 41 are kept free by the operation of the clutch mechanisms 40a, 41a.

The rotational force of the servomotor 35 is transmitted to the rotary disc 16 by the transmission shaft 34, the transmission gear 33 and the gear 17, and the screw shaft 15 is sent out by the rotation of the rotary disc 16. As a result, the movable platen 13 moves forward to move the molds 14, 1
4 closes.

When the movable platen 10 is stopped by closing the mold, a large torque is generated and the current increases. At this time, the set torque and the detected current are compared, and when a coincidence confirmation signal is generated, the mold clamping force retainer 39 is excited and the transmission shaft 32 is fixed to the brake housing side. By fixing the transmission shaft 32, the movable platen 13 maintains the mold clamping state.

After the mold is clamped, the clutch mechanism 38 releases the transmission shafts 32 and 34 while the injection device 2 is in nozzle contact with the mold 14, and the clutch 40a is connected to transmit the rotational force of the servo motor 35. It is transmitted to the screw shaft 30 via the gear 40 and the gear 28 for rotating the screw shaft.

Since the screw shaft 30 only rotates at a fixed position by the gear 28, the screw receiving member 27 on the screw holding member side screwed with the screw shaft 30 feeds the screw shaft in the axial direction on the screw shaft. Then, the rotational movement by the servomotor is converted into a linear movement for moving the screw holding member 25 forward. Since an extension shaft 26 at the rear end of the screw is connected to the screw holding member 25, the screw 20 also moves forward together, and the molten resin measured in the injection heating cylinder at the front of the screw is injected into the mold 14. To do.

When the injection is completed, the screw 20 does not move any further, so that a large torque is generated in the servo motor 35 and the current increases. This rising current is detected by the current detector 47, and the detected current is compared with the current setter 49 having a torque setting corresponding to the predetermined torque by the comparator 48, and if a coincidence confirmation signal is generated, the centralized control device 43 is generated. Causes the process to shift to holding pressure.

Since the torque corresponding to the holding pressure is also set in the current setting device 49, the screw 20 is held by the torque to hold the pressure. Also in this case, the detected current in the current detector 47 is compared by the comparator 48 as in the case of injection, and it is confirmed by the coincidence confirmation signal that the predetermined holding pressure is achieved. After that, the process shifts to measuring the molding material.

When the injection is completed, the servo motor 35 is stopped by the command, and at the same time, the clutch mechanism 40a operates in the original free state to cut off the transmission of the rotational force to the gear 28 for rotating the screw shaft. Following this operation, the clutch mechanism 41a in the free state is operated to connect the transmission shaft 34 and the transmission gear 41.

Then, when the servo motor 35 is rotated in the reverse direction,
The rotational force is transmitted to the screw 30 via the transmission gear 41 and the screw rotation gear 24, and the screw 30
Rotates to feed the material resin from the hopper to the front of the screw.

The rotation of the screw 20 plasticizes the material resin to form a molten resin, which is measured in front of the injection heating cylinder 21. Further, the resin pressure in the injection heating cylinder causes a backward force of the screw 20. This retracting force is concentrated on the screw receiving member 27 that is integral with the screw holding member 25 and acts on the screw shaft 30 that is on the same axis as the screw 20, so that the screw shaft 30 moves smoothly in the opposite direction to the screw forward direction. It does not prevent the screw 20 from moving backward.

When the reverse rotation of the screw shaft 30 is braked by the back pressure / back pressure control brake device 31, the screw 2 is rotated.
0 comes to retreat while resisting the acupressure of the tree, and a proper back pressure is measured there.

[0035]

As described above, according to the present invention, the screw in the injection heating cylinder having the extension member at the rear end, and the holding member that rotatably holds the screw via the extension member and moves back and forth together with the screw. And a screw shaft in a fixed position that is screwed into a screw receiving member provided on the screw holding member, converts the rotational movement into a linear movement by the screw receiving member, and moves the screw holding member forward together with the screw. It comprises a rotation transmission member for screw rotation provided on the extension member, and a servomotor that rotates the screw shaft to drive the screw holding member and the screw forward. The servomotor flows in the circuit to the servomotor. The current detector that detects the current, the current setting device for confirming the generation of the output torque of the servo motor, the detection current of the current detector and the setting current of the current setting device It exhibits the following effects since it comprises a comparator for generating a coincidence confirmation signal to compare.

Since the screw holding member side is moved forward by the screw shaft in the fixed position, GD ² can be made smaller than when rotating the screw receiving member side, which enables precise injection control with high response. Becomes

Since the screw holding member side is moved forward by the screw shaft in the fixed position, the rotation preventing member for the screw shaft, which is indispensable for the plunger type injection device moving forward on the screw shaft side, is unnecessary, and the rotation preventing member prevents Since the rotation resistance of the screw shaft is also eliminated, the transmission efficiency is remarkably improved and the screw shaft is smoothly rotated.

The connection between the screw holding member and the screw shaft, which can move back and forth, is performed by screwing the screw receiving member and the screw shaft, and the screw retracting force applied to the screw holding member due to the resin pressure at the time of measuring the material is also used. Since it concentrates on the member, the backward rotation of the screw shaft smoothly occurs due to the retracting force.

The servo motor can perform not only start, stop, and sudden acceleration / deceleration control, but also torque control and speed control over a wide range from a low speed to a rated speed with high accuracy and good response. Since it is possible to meet the requirements for durability against high loads and high-precision adjustment characteristics, etc., in combination with the good transmission efficiency of the screw shaft, the drive source is an electric motor, but it is always stable. Injection of molding material can be performed.

Since the outputs such as the radiation output and the holding pressure can be detected by the current detector provided in the circuit of the servo motor, environmental changes such as temperature and humidity as in the case of using a sensor such as a strain gauge. Moreover, unlike the sensor, the output detector in the circuit does not require a mounting space for a transmission mechanism or the like, so that the structure of the device is simplified and the cost can be reduced.

In the output detection by the current detector in the circuit of the servo motor, the injection output and the holding pressure can be detected without being influenced by the compression amount and the deformation amount applied to the screw, the screw holding member, the transmission member, etc. Also, the holding pressure control can be performed quickly and reliably.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view of an essential part of an injection molding machine equipped with an electric injection device according to the present invention.

FIG. 2 is a block diagram of a control device included in the electric injection device according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Clamping mechanism 2 Injection device 20 Screw 21 Injection heating cylinder 24 Screw rotation gear 25 Screw holding member 26 Extension shaft 27 Screw receiving member 28 Screw shaft rotation gear 29 Screw shaft shaft portion 30 Screw shaft 34 Transmission shaft 35 Servo motor 40 Transmission gear on screw shaft rotation side 43 Centralized control device 47 Current detector 48 Comparator 49 Current setting device

Claims (1)

[Claims] 1. A screw in an injection heating cylinder having an extension member at its rear end, a holding member that rotatably holds the screw through the extension member, and moves forward and backward together with the screw, and the screw holding member. Screw shaft provided in the extension member, which is screwed with the screw receiving member, converts the rotational movement into a linear movement by the screw receiving member, and moves the screw holding member forward together with the screw, and the screw rotation provided in the extension member. And a servomotor for driving the screw holding member and the screw forward by rotating the screw shaft, and the servomotor has a current detector for detecting a current flowing through the servomotor in the circuit. , A current setting device for confirming the generation of the output torque of the servo motor is compared with the detection current of the current detector and the setting current of the current setting device to generate a confirmation signal of agreement. An electric injection device of an injection molding machine, comprising: