JPH0464492B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an injection method and apparatus for a molding machine suitable for injection molding ultra-precision molded products.

[Conventional technology]

Generally, the transfer device in an in-line screw type injection molding machine has a hopper at the rear for supplying the molding material, and a heating cylinder with an injection nozzle at the front end.
The screw drive unit includes a screw drive unit that inserts the screw and includes a forward/backward drive unit that controls the advance and retreat of the screw and a rotation drive unit that controls rotation. In the measuring process, by rotating the screw, molten resin is accumulated in front of the screw, and
In the injection process, the accumulated molten resin is injected and filled into the mold cavity by advancing the screw.

By the way, when focusing on drive systems for screws in conventional injection devices of this type, hydraulic systems and electric systems are mainly known. The hydraulic type is a method in which the screw is connected to a ram inside a hydraulic cylinder, and the screw is moved forward and backward by controlling the hydraulic pressure inside the hydraulic cylinder.
In addition, the electric type fixes the nut part of the ball screw mechanism that has the function of changing the direction of movement to the aircraft body, and
In this method, the output shaft of a motor unit including a speed reduction mechanism is connected to the rear end of the threaded part, and the screw is connected to the front end of the threaded part, thereby controlling the rotational speed of the motor unit and moving the screw forward and backward.

[Problem that the invention seeks to solve]

However, the above-mentioned conventional injection devices control the injection speed (transfer pressure) of the screw by controlling the hydraulic pressure of the hydraulic cylinder or the rotational speed of the motor, so they have excellent responsiveness, stability, reproducibility, accuracy, and accuracy. In particular, it was extremely difficult to control at low speeds. For this reason, for ultra-precision molded products, such as optical parts, injection speeds are controlled to extremely low speeds to minimize internal distortions, etc. However, accurate and stable speed control becomes difficult, and as a result, high There was a problem in that it was not possible to obtain molded products with high quality, high precision, and stability.

[Means for solving problems]

The present invention aims to provide an injection method and apparatus for an injection molding machine that solves the problems existing in the conventional techniques described above, and is achieved by the injection method and injection apparatus 1 shown below.

That is, in the transfer method according to the present invention, when the screw 2 is moved forward to inject molten resin, the ball screw shaft 4 and the ball screw nut 5 that constitute the ball screw mechanism section 3 are simultaneously controlled to rotate. Alternatively, the ball screw nut 5 is relatively moved in the axial direction, and the screw 2 is moved forward by this relative movement. At this time, the relative movement amount is set to zero by rotating the ball screw shaft 4 and the ball screw nut 5 in the same direction and at the same speed, and in this state, the speed of at least one of the ball screw shaft 4 or the ball screw nut 5 is changed to make the relative movement Get the amount of movement.

In addition, the injection device 1 that implements the above method includes a screw drive unit 6 that advances the screw 2, a ball screw mechanism unit 3 consisting of a ball screw shaft 4 and a ball screw nut 5, and a first motor that rotationally drives the ball screw shaft 4. part 7 and ball screw nut 5
a second motor section 8 that rotationally drives each motor section 7;
and 8, and a transmission section 10 that applies the relative movement amount of the ball screw shaft 4 or the ball screw nut 5 in the axial direction to the screw 2.

[Effect]

Next, the injection method and injection device 1 according to the present invention
The effect of this will be explained.

Ball screw mechanism section 3 in screw drive section 6
If the ball screw shaft 4 and the ball screw nut 5 are respectively rotated in the same direction and at the same speed (preferably high speed rotation), the amount of relative movement between the two in the axial direction becomes zero. If the speed of at least one of the ball screw shaft 4 or the ball screw nut 5 is relatively varied in this state, the ball screw shaft 4 or the ball screw nut 5 will be relatively moved in the forward or reverse direction. Therefore, it is possible to stably perform ultra-low speed control, and by applying this relative movement amount to the screw 2, it is possible to perform injection molding of ultra-precision molded products.

〔Example〕

Hereinafter, preferred embodiments of the present invention will be described in detail based on the drawings.

First, a schematic configuration of an injection device in an injection molding machine according to the present invention will be described. FIG. 1 is a schematic configuration diagram of the device, and FIG. 2 is a partially longitudinal side view showing the specific main body of the device.

In FIG. 1, the injection device designated by reference numeral 1 has an injection nozzle 21 at its front end, and is equipped with a heating cylinder 20 fixed to a machine stand M (see FIG. 2). A screw 2 is inserted into this heating cylinder 20. On the other hand, the injection nozzle 21 comes into contact with a mold (not shown), and the molten resin inside the heating cylinder 20 is injected and filled into the mold cavity through the injection nozzle 21.

Further, the rear end of the screw 2 is connected to the screw drive section 6, and the screw drive section 6 controls the rotation and movement of the screw 2.

In the screw drive unit 6, 23 indicates the screw 2.
A driven gear 25 is disposed at the rear end of the screw rotating shaft 23 via a spline mechanism 24, and this driven gear 25 is connected to a driving gear 27 attached to the shaft of a metering motor 26.
mesh with. This metering motor 26 can be an inverter motor, for example, and is fixed to the machine base M.

On the other hand, a long cylindrical ball screw shaft 4 is rotatably and coaxially fitted into the outside of the screw rotation shaft 23. Movement of this ball screw shaft 4 in the axial direction with respect to the machine base M is restricted. Further, a driven gear 28 is provided at the rear end of the ball screw shaft 4, and meshes with a drive gear 29 provided on the shaft of an injection servo motor constituting the first motor section 7. A ball screw nut 5 is provided on the outer periphery of the ball screw shaft 4, and the ball screw mechanism section 3 is constituted by both of them. A driven gear 30 is provided on the outer periphery of the ball screw nut 5, and meshes with a drive gear 32 provided on the shaft of an injection servo motor constituting the second motor section 8. The ball screw nut 5 is rotatably disposed on the injection table 34 and axial displacement is restricted, and the second motor section 8 is fixed to the injection table 34. This injection table 34 is arranged to be freely displaceable in the axial direction with respect to the machine stand M. Further, a screw 2 is provided at the front end of the injection table 34.
The rear end is rotatable and axial displacement is restricted. Note that 10 indicates a connecting portion between the screw 2 and the screw rotating shaft 23, that is, a transmission portion that transmits the amount of relative displacement on the ball screw mechanism 3 side to the screw 2 side.

A concrete configuration of such a screw drive section 6 is shown in FIG. In FIG. 2, the same parts as in FIG. 1 are given the same reference numerals to clarify the structure.

In FIG. 2, 35 is a supply path for supplying the molding material into the heating cylinder 20, and communicates with a hopper (not shown). Tie bars 36 and 37 support the injection table 34 so as to be slidable in the axial direction.

Although representative examples are shown in FIG. 2, other examples of changes to the names may be considered. For example, the second motor section 8 may be fixed to the machine base M, and the shaft of the second motor section 8 and the drive gear 32 may be coupled by a spline mechanism.

On the other hand, the control system is configured as follows. In FIG. 1, 50 is a central control section. Central control unit 50
The metering motor 26 is connected to the inverter 51, and the motor sections 7 and 8 are connected to the metering motor 26 through the inverter 51, respectively. Also, there is a screw 2 near the driven gear 25.
A screw tachometer 52 for detecting the number of revolutions is provided, and is connected to a central control unit 50 via an amplifier 53. Each motor section 7, 8 is provided with a tachometer generator 54, 55 for detecting the rotational speed, and is connected to a central control section 50 via amplifiers 56, 57. On the other hand, 58 is a load cell that detects the pressure (resin pressure) applied to the screw 2. The load cell 58 is connected to the central control unit 50 via an amplifier 59. Further, 60 is a position detector attached to the injection table 34, and is connected to the central control unit 50 via an amplifier 61. On the other hand, the central control unit 5
0 is equipped with a setting device 62 for setting various conditions such as injection speed, holding pressure, control switching position, and back pressure.

Next, the operation including the injection method using the device 1 will be explained.

First, when the screw 2 is stopped, the metering motor 26
is generated during the relative rotational movement of each motor section 7 and 8. That is, both motor parts 7 and 8 are moved in the same direction at the same speed (the speed is 1800 rpm).
If the ball screw mechanism section 4 is rotated by the respective motor sections 7 and 8, the ball screw mechanism section 4 will apparently stop.

In the injection process, in such a stopped state, a control command is output from the central control unit 50 to control the ball screw shaft 4.
The rotation speed of the first motor section 7 on the side is increased to be faster than the rotation speed of the ball screw nut 5. Note that by varying the speed on the ball screw shaft 4 side in this way, GD ² (amount of inertia) is smaller than when varying the speed on the ball screw nut 5 side, resulting in better responsiveness. Therefore, a difference in rotational speed occurs between the ball screw shaft 4 and the ball screw nut 5, and the nut 5 side relatively moves forward, causing the screw 2 to move forward together with the injection table 34. That is, injection starts. At this time, the rotational speed of each motor section 7, 8 is detected by a tachometer generator, and feedback control is performed. The injection speed at this time is controlled based on the speed difference between the motor sections 7 and 8, and the forward position of the screw 2 is detected by the position detector 60. Then, if the predetermined forward limit position is detected,
Pressure holding control is performed by switching each motor section 7, 8 to torque control using a torque limiter.

Therefore, by performing such speed control, the startup time of the servo motor itself in each motor section 7, 8 becomes unnecessary. In other words, instantaneous and smooth response can be achieved in the dynamic friction range. Moreover, the backlash included in the gear mechanism does not occur at all because the rotation direction is the same and the gear mechanism receives the same load. Moreover, since no keys are used in other parts, there is no clearance in the rotational or longitudinal directions, maintaining high accuracy, and the servo motor is easy to control, preventing dynamic range and speed ripple. However, it works extremely effectively.

On the other hand, upon completion of the injection process, the process moves to a metering process. In the metering step, the rotational speed of the first motor section 7 is controlled to be reduced to the same speed as the second motor section 8. Note that at this time, torque control is also performed using the torque limiter. If the metering motor 26 is driven in this state, the screw 2 can be rotated via the screw rotation shaft 23. As a result, the molding material is melted and sent forward along the screw groove, and the screw 2 is moved backward by the reaction force at this time. That is, when this reaction force reaches the set value of the torque limiter or more, each motor section 7, 8 slips and the screw 2 retreats, and the back pressure is controlled by the torque limiter. When the screw 2 moves back to a predetermined weighing position, the position detector 60 detects this and the weighing motor 2
6 is stopped. That is, the measurement is stopped. At this time, each motor section 7, 8 continues to rotate at the same speed.

The torque control during pressure holding control and back pressure control may be performed by providing a brake on the shaft of the second motor section 8 to fix it, and then controlling only the first motor section 7 with a torque limiter. These torque controls can be performed by feedback control in which a pressure signal detected by the load cell 58 is fed back to each motor section 7,8.

Although the embodiments have been described above, the present invention is not limited to these embodiments. For example, although an in-line screw type is illustrated, it can be applied to various types of injection devices that generally inject molten resin, such as a plunger type. For example, by replacing the screw with a plunger, it can be implemented in the same way. In addition, although the case where the first motor part and the second motor part are rotated in the same direction and low speed control is performed is shown,
Stop both motor parts, and then
The respective motor sections may be rotated in opposite directions to achieve high-speed control, and in this case, high-speed injection becomes possible. In addition, the detailed configuration, shape, and method may be arbitrarily changed without departing from the gist of the present invention.

〔Effect of the invention〕

As described above, the injection method and device for an injection molding machine according to the present invention moves the ball screw shaft or the ball screw nut relative to each other in the axial direction by simultaneously controlling the rotation of the ball screw shaft and the ball screw nut that constitute the ball screw mechanism. By using relative movement to move the scroll forward, the following effects are obtained.

When controlling injection speed (injection pressure), the speed control range from low speed to high speed can be greatly expanded, and moreover, it can be controlled accurately. As a result, ultra-low speed control (or ultra-high speed control) of the screw can be realized, and in particular, by realizing ultra-low speed control, high-quality molding and high-precision molding of ultra-precision molded products such as chemical parts can be achieved.

Since it is not necessary to start the servo motor, instantaneous control and smooth control can be easily performed, and accuracy, stability, responsiveness, and reproducibility can be dramatically improved.

[Brief explanation of drawings]

FIG. 1: Schematic configuration diagram of a transfer device according to the present invention,
Figure 2: A partially longitudinal side view showing the specific main body of the device. In the drawings, 1: injection device, 2: screw, 3:
Ball screw mechanism section, 4: ball screw shaft, 5: ball screw nut, 7: first motor section, 8: second motor section, 9: control section, 10: transmission section.

Claims (1)

[Claims] 1. When advancing the screw (plunger) to inject molten resin, the ball screw shaft or the ball screw nut is rotated in the axial direction by simultaneously controlling the rotation of the ball screw shaft and the ball screw nut that constitute the ball screw mechanism. An injection method for an injection molding machine, characterized in that the screw (plunger) is moved forward by the relative movement. 2. By rotating the ball screw shaft and the ball screw nut in the same direction and at the same speed, the amount of relative movement in the axial direction is made zero, and in this state, the speed of at least one of the ball screw shaft or the ball screw nut is changed to reduce the relative movement. 2. The injection method for an injection molding machine according to claim 1, wherein: 3. In an injection device for an injection molding machine, which is equipped with a screw drive section that can advance at least a screw (plunger), the screw drive section includes a ball screw mechanism section that includes a ball screw shaft and a ball screw nut, and a ball screw mechanism that rotates the ball screw shaft. A first motor section that drives the ball screw nut, a second motor section that rotationally drives the ball screw nut, a control section that controls each motor section, and a transmission section that gives the screw the amount of relative movement in the axial direction of the ball screw shaft or the ball screw nut. An injection device for an injection molding machine characterized by comprising: