JPH01238917A - Injecting method and apparatus for injection molder - Google Patents

Abstract

PURPOSE:To carry out a high quality and highly accurate molding of a super- precision molded item by a method wherein the rotations of a ball screw shaft and of a ball screw nut are simultaneously controlled so as to realize the axially relative movement, which is utilized for the advancement of a screw. CONSTITUTION:When both a ball screw shaft 4 and a ball screw nut 5 are respectively rotated in the same direction and at the same speed by means of a central control part 50 controlling a first motor part 7, which rotatingly drives the ball screw shaft 4, and a second motor part 8, which rotatingly drives the ball screw nut 5, then the amount of relative axial movement of both the shaft and the nut becomes zero. When the speed of one of them is changed relative to that of the other, the ball screw shaft 4 or the ball screw nut 5 relatively moved in normal direction or in reverse direction. Accordingly, the stable super-low speed control becomes possible, resulting in realizing the injection molding of a super-precision molded item by working the relative movement on a screw 2.

Description

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

[Conventional technology]

In general, the injection device of an in-line screw injection molding machine has a hopper at the rear for supplying molding material, a screw is inserted into a heating section with an injection nozzle at the front end, and the screw is controlled to move forward and backward. The screw drive unit includes a drive unit and a rotation drive unit that controls the rotation. Then, in the metering 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 the drive methods of the screw in conventional injection devices of this type, the hydraulic type and the electric type are mainly known. The hydraulic type connects a screw to a ram in a hydraulic cylinder, and controls the hydraulic pressure in the cylinder to move the screw forward and backward.In addition, the electric type connects the nut of the ball screw mechanism, which has the function of changing the direction of movement, to the aircraft body. At the same time, by connecting the output shaft of the motor unit including the speed reduction mechanism to the rear end of the threaded part and connecting the screw to the front end of the threaded part, the rotational speed of the motor unit can be controlled and the screw can be moved forward and backward. This is a method of forcing people to do something.

[Problem that the invention seeks to solve]

However, since the conventional injection device described above controls the injection speed (injection pressure) of the screw by controlling the hydraulic pressure of the hydraulic cylinder or the rotational speed of the motor, it has problems in terms of responsiveness, stability, reproducibility, accuracy, and precision. 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 l shown below.

That is, in the injection 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 constituting 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. In addition,
At this time, the relative movement amount is made 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 relative movement amount is changed by changing the speed of at least one of the ball screw shaft 4 or the ball screw nut 5. get.

In addition, the injection device l that implements the above method has a screw 2
The screw drive unit 6 that advances the ball screw mechanism unit 3 consisting of the ball screw shaft 4 and the ball screw nut 5
and a first motor section 7 that rotationally drives the ball screw 11m4.
and a second motor section 8 that rotationally drives the ball screw nut 5.
, a control section 9 for controlling each of the motor sections 7 and 8, and a transmission section IO for imparting a relative movement amount of the ball screw shaft 4 or the ball screw nut 5 in the axial direction to the screw 2.

[For production]

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

If the ball screw shaft 4 and ball screw nut 5 of the ball screw mechanism 3 in the screw drive unit 6 are rotated in the same direction and at the same speed (preferably high speed rotation), then the amount of relative movement between them 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 perform ultra-low speed control stably,
By applying this relative movement m to the screw 2, injection molding of an ultra-precision molded product can be performed.

〔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. Figure 1 is a schematic diagram of the device;
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 unit 6 side, and the screw 2 is controlled to rotate and move back and forth by the screw drive unit 6.

In the screw drive unit 6, 23 is a screw rotation shaft connected to the rear end of the screw 2. A wave gear 25 is arranged at the rear end of the screw rotation shaft 23 via a spline mechanism 24, and this driven gear 25 is It meshes with a drive gear 27 attached to the shaft of a heavy motor 26. This meter firefly motor 2
6 can use, for example, an inverter motor, and is fixed to the machine M.

On the other hand, a long cylindrical ball screw shaft 4 is rotatably and coaxially fitted on the outside of the screw rotating 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,
It 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 3 is constituted by both. A driven gear 30 is provided on the outer periphery of the ball screw nut 5, and a driven gear 30 is provided on the shaft of the injection servo motor that constitutes the second motor section 8.
2. Note that the ball screw nut 5 is disposed on the injection table 34 so as to be rotatable and to restrict displacement in the axial direction, 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, the rear end of the screw 2 is attached to the front end of the injection table 34 so as to be rotatable and to restrict displacement in the axial direction. In addition, 10 is a connecting part between the screw 2 and the screw rotating shaft 23,
That is, it shows a transmission part that transmits the relative displacement amount 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. 2. In FIG. 2, the same parts as in FIG. 1 are given the same reference numerals to clarify the structure.

In FIG. 2, numeral 35 is a supply path for supplying the molding material into the heating cylinder 20, which communicates with a hopper (not shown). 36.37
is a tie bar, which supports the injection table 34 so as to be slidable in the axial direction.

Although a typical example is shown in FIG. 2, various other modifications are possible. 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 Figure 1, 5
0 is the central control unit. The central control unit 50 is connected to the electric motor 26 via an inverter 51, and to the respective motor units 7.8. In addition, wave gear 25
A screw tachometer 52 for detecting the rotational speed of the screw 2 is arranged nearby and connected to the 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 an amplifier 56.
57 to the central control unit 50. 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. In addition, 60 is 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 50 includes 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 same device 1 will be explained.

First, the stopped state of the screw 2 is created by stopping the rotation of the weighing motor 26 and by the relative rotation of each motor section 7 and 8. That is, if both motor sections 7 and 8 are rotated in the same direction and at the same speed (the speed is about 1800 rpm), the ball screw mechanism section 4 rotated by each motor section 7.8 will apparently stop.

In the injection process, in such a stopped state, the central control unit 50
outputs a control command to increase the rotational speed of the first motor section 7 on the ball screw shaft 4 side, and the ball screw nut 5
faster than the rotation speed of

In addition, it is better to vary the speed on the ball screw shaft 4 side in this way than to vary the speed on the ball screw nut 5 side.
(amount of inertia) becomes smaller and responsiveness becomes better. 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. When a predetermined forward limit position is detected, each motor section 7.8 is switched to torque control using a torque limiter, and pressure holding control is performed.

Therefore, by performing such speed control, it becomes unnecessary to start up the servo motor itself in each motor section 7.8. In other words, instantaneous and smooth response can be achieved in the dynamic friction range.

Further, backlash included in the gear mechanism does not occur at all because the gear mechanism rotates in the same direction and 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 precision, and the servo motor is easy to control, making it possible to reduce dynamic range and speed ripple. also 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 by the torque limiter is performed at the same time.

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 reaction force at this time causes the screw 2 to retreat. 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 is retracted to a predetermined total of one position, this is detected by the position detector 60 and the metering motor 26 is stopped. That is, the measurement is stopped. At this time, each motor section 7.8 continues to rotate at the same speed.

Note that 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 pressure signals detected by the load cells 58 are 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 similarly. 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,
Both motor sections may be stopped, and then each motor section may be rotated in opposite directions to perform high-speed control. In this case, high-speed injection is 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. Since the screw is moved forward using relative movement, the following effects are obtained.

■ In controlling injection speed (injection pressure), the speed control range from low speed to high speed has been greatly expanded, and 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 optical parts can be achieved.

■ No need to start the servo motor, allowing instantaneous control and
Smooth control can be easily performed, and accuracy, stability, responsiveness, and reproducibility can be dramatically improved.

[Brief explanation of the drawing]

Fig. 1 2 A schematic configuration diagram of an injection device according to the present invention, Fig. 2:
FIG. 2 is a partially longitudinal side view showing the specific main body of the device. In the drawing, l: 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 unit 10:Transmission unit

Claims (1)

[Scope of Claims] [1] When injecting molten resin by advancing a screw (plunger), the ball screw shaft or the ball screw nut is rotated by simultaneously controlling the rotation of the ball screw shaft and the ball screw nut that constitute the ball screw mechanism section. An injection method for an injection molding machine, characterized in that a screw (plunger) is moved forward by relative movement in an axial direction. [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 2. The injection method for an injection molding machine according to claim 1, wherein movement is caused. [3] In an injection device for an injection molding machine comprising a screw drive section capable of advancing at least a screw (plunger), the screw drive section includes a ball screw mechanism section comprising a ball screw shaft and a ball screw nut, and a ball screw shaft. a first motor section that rotationally drives the ball screw, a second motor section that rotationally drives the ball screw nut, a control section that controls each motor section, and a transmission that imparts relative movement in the axial direction of the ball screw shaft or the ball screw nut to the screw. 1. An injection device for an injection molding machine, comprising: