JP2000185339A - Driver for motor operated injection molding machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To largely prolong a life of a ball screw shaft by equivalently distributing a load weight to the shaft by a plurality of nuts. SOLUTION: A plurality of nuts 52, 53 to be engaged with a ball screw shaft 51 rotatably driven by an electric motor are arranged in series with the one shaft. Hydraulic cylinders 54, 55 for transmitting thrusts to a movable member 50 of a motor operated injection molding machine from the nuts 52, 53 are respectively coupled to the nuts to communicate with cylinder chambers of the cylinders 54, 55 through a communicating tube 56.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving device for an electric injection molding machine, and more particularly, to extending a service life of a ball screw by distributing a load evenly to a plurality of nuts. The present invention relates to a drive device for an electric injection molding machine that enables the machine to be electrically driven.

[0002]

2. Description of the Related Art In a conventional injection molding machine, a hydraulic drive mechanism has been mainly used as a drive mechanism for an injection device and a mold clamping device. However, in recent years, a servomotor is used instead of a hydraulic drive mechanism as a drive source. And an electric injection molding machine employing a ball screw for the power transmission mechanism has been developed. This electric injection molding machine has been evaluated for its good controllability and low load on the environment, and has been increasingly used instead of a hydraulically driven one.

FIG. 7 shows an injection device of this type of an electric injection molding machine. 1 is a heating barrel. The plastic material is supplied from the hopper 2 to the heating barrel 1. A screw 3 is rotatably and axially movably inserted into the inner diameter of the heating barrel 1. This screw 1
It is held by an injection bracket 5 via a bearing 4 that supports a radial load and a thrust load. The injection bracket 5 is mounted on the base 6 so as to be movable in the axial direction of the screw 3 by being guided by a guide 7 provided on the base 6.

[0004] Reference numeral 8 denotes a metering motor, and reference numeral 9 denotes an injection motor. Servo motors are used for these electric motors. The measuring motor 8 is attached to the injection bracket 5, and the rotational driving force of the measuring motor 8 is transmitted to the screw 3 by a belt transmission mechanism 10 including a pulley and a timing belt.

On the other hand, the injection motor 9 is installed at the rear end of the base 6 and is connected to a ball screw driven linear positioning mechanism for controlling the linear movement of the injection bracket 5. In this case, the injection motor 9 includes a ball screw 12 horizontally supported via a bearing 11 at the rear of the base 6.
A ball nut 13 connected to the shaft and screwed to the ball screw shaft 12 is fixed to a rear portion of the injection bracket 5. An NC control device (not shown) includes an injection motor 9.
And the weighing motor 8 is controlled.

In the measuring step, the measuring motor 8 rotates the screw 3 to plasticize the resin material supplied to the heating barrel 1. The molten resin material accumulates in front of the screw 3 and retreats the screw 3.

In the injection step, the rotation of the injection motor 9 is controlled by the ball screw shaft 12 and the ball nut 13.
This is converted into a linear forward movement of the injection bracket 5. Thereby, the screw 3 injects the molten resin accumulated in front of the screw 3 in the heating barrel 1 while moving forward (to the left in the figure).

In such an electric injection molding machine, the output of the electric motor is converted into a linear motion by a ball screw mechanism, and the linear motion is directly converted to the screw 3 or the injection bracket 5.
Therefore, by controlling the speed and torque of the electric motor, the injection speed and the injection power can be controlled.

[0009]

However, with regard to the electric injection molding machine, the load capacity of the ball screw is becoming a problem while the electrification of a large machine is gradually studied. When the linear movement of the injection bracket 5 is performed by a ball screw / nut mechanism as in the injection device of FIG.
Acts on the ball screw shaft 12. In order to withstand this force, the ball screw shaft 12 is not suitable for a normal feed mechanism, and a high-strength, large-diameter, expensive ball screw is employed. However, even in the case of a ball screw having a large load capacity, there are many cases in which a long life cannot be ensured for a long time due to a large load, which is a major obstacle to the electrification of large machines.

Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art and to distribute the load applied to the ball screw shaft evenly by a plurality of nuts, thereby shortening the life of the ball screw shaft. An object of the present invention is to provide a drive device for an electric injection molding machine which can be greatly extended.

[0011]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention relates to a driving apparatus for an electric injection molding machine having a ball screw transmission mechanism for converting the rotational motion of an electric motor into a thrust of a movable member. A plurality of ball nuts fitted to a ball screw shaft rotated and driven by the electric motor are arranged in series with respect to one ball screw shaft, and thrust is applied from the ball nut to a movable member of an electric injection molding machine. Are connected to ball nuts, respectively, and the cylinder chambers of each of the hydraulic cylinders are connected by a communication pipe.

FIG. 6 is a diagram showing the principle of load distribution performed by the drive device of the present invention. Reference numeral 50 denotes a movable member such as an injection bracket of the injection device or a movable die plate of the mold clamping device, 51 denotes a ball screw shaft, and 52 and 53 denote ball nuts. The ball nut 52 is connected to the movable member 50 via a hydraulic cylinder 54, and the ball nut 53 is connected to the movable member 50 via a hydraulic cylinder 55.
It is connected to. The respective cylinder chambers of the fluid pressure cylinders 54 and 55 are connected by a communication pipe 56.

The ball screw shaft 51 rotates, and the ball nuts 52 and 53 move to the left in the drawing, and the fluid pressure cylinders 54 and
The thrust is transmitted to the movable member 50 via 55. At this time,
Assuming that the load applied to the movable member is F, the load F is distributed to the ball nuts 52 and 53 via the fluid pressure cylinders 54 and 55. Then, the fluid pressure cylinders 54, 55
When the effective areas are equal and the cylinder chambers communicate with each other, the load F is always equally distributed by 1 / 2F.

In general, the life of a ball screw shaft is inversely proportional to the cube of the load acting on the ball nut.
It is possible to double the length.

According to a preferred embodiment of the present invention, the movable member of the injection molding machine is an injection bracket provided on the base so as to be movable in the axial direction of the screw, and supporting a rear end of the screw. The electric motor comprises an injection motor for advancing a screw in an injection step.

Further, the fluid pressure cylinder has a cylinder chamber having an equal cylinder area on both sides of a flange portion of a ball nut, and a differential pressure sensor for detecting a differential pressure between the pressures of both cylinder chambers is provided. , The net firing force acting on the firing bracket can be detected.

Further, according to the present invention, a plurality of drive devices according to claim 1 are provided so that the ball screw shafts are arranged in parallel, and the communication pipes of the fluid pressure cylinders of the respective sets are further connected to each other. It is characterized by communicating with a pipe,
Furthermore, large-sized machines can be electrically operated.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a drive device for an electric injection molding machine according to the present invention will be described below with reference to the accompanying drawings. First Embodiment FIG. 1 shows a first embodiment in which a driving device according to the present invention is applied to an injection device of an electric injection molding machine. The injection device according to the first embodiment uses the drive device of the present invention for a mechanism that converts the rotational driving force of the injection motor 9 into a thrust and transmits the thrust to the injection bracket 5. 7 are the same as the components of the injection device shown in FIG. 7, and the same reference numerals are given and the detailed description is omitted.

In FIG. 1, two ball nuts 14 and 15 are screwed in series with a ball screw shaft 12 which is driven to rotate by an injection motor 9. These ball nuts 14 and 15 are respectively connected to the injection bracket 5 using hydraulic cylinders.

As shown in FIG. 2, the ball nut 14 on the screw side has a pair of donut-shaped hydraulic cylinders 16a,
16b, which are integrally fastened to the injection bracket 5 by the fastening flange 17. The ball nut 15 on the other side opposite to the screw is similarly connected to a pair of donut-shaped hydraulic cylinders 18a, 18a.
b, and these are integrally clamped flange 1
9 fastened to the injection bracket 5.

The ball nuts 14 and 15 have flange portions 14a and 15a, respectively. this house,
The flange portion 14a is sandwiched between the pistons 20a, 20b of the hydraulic cylinders 16a, 16b. Hydraulic cylinders 16a and 16b have cylinder chambers 21a and 2a, respectively.
1b is formed. In this case, when the ball nut 14 moves forward (leftward in the figure), the force acts on the pressure oil in the cylinder chamber 21a, and when the ball nut 14 moves backward (rightward in the figure), the force is applied to the cylinder chamber 2a.
1b. Hydraulic cylinder 1
Pistons 22a and 22b are fitted into 8a and 18b, respectively, and the flange portion 15a of the ball nut 15 is sandwiched between the pistons 22a and 22b. The hydraulic cylinders 18a, 18b when the ball nut 15 moves
The same applies to the force applied to the pressure oil in the respective cylinder chambers 23a and 23b.

Further, the cylinder chambers 21a, 23 on the forward side to which a force is applied when the ball nuts 14, 15 advance.
a is communicated by the communication pipe 24. Similarly, the cylinder chambers 21b and 23b on the retreating side to which a force is applied when the ball nut retreats are communicated by the communication pipe 25. In addition, each hydraulic cylinder 16a, 16b
The effective areas of the hydraulic cylinders 18a and 18b are equal.

Next, the operation of the injection device according to the present embodiment will be described. In FIG. 1, the rotation of the ball screw shaft 12 driven by the injection motor 9 in the injection process is converted into a thrust for advancing the ball nuts 14, 15, and this thrust is transmitted from the hydraulic cylinders 16a, 18a to the injection bracket 5. It makes this move straight forward. Thereby, the screw 3 injects the molten resin accumulated in front of the screw 3 in the heating barrel 1 while moving forward (to the left in the figure).

During this injection process, the reaction force of the firing force is:
As shown in FIG. 2, a load F acts on the injection bracket 5 in the retreating direction. This load F is applied to the hydraulic cylinders 16a, 1
The ball nuts 14 and 15 are equally distributed and loaded by F / 2 via the ball nuts 8a. That is, the ball nut 1
When the pistons 4 and 15 move forward, the pressure oil in the cylinder chamber 21a is pressurized by the piston 20a and the piston 22a
As a result, the pressure oil in the cylinder chamber 23a is pressurized, and the same thrust as the ejection force acts on the injection bracket 5 via the pressure oil in both the cylinder chambers 21a and 23a. Conversely, the load F, which is the reaction force of the firing force, is distributed to the ball nuts 14 and 15 respectively.
Conveyed to. In this load F distribution, since the two cylinder chambers 21a and 23a communicate with each other through the communication pipe 24, the pressures become equal.
5, the same load of F / 2 is always distributed.

On the other hand, in the measuring step, the resin material melted by the rotation of the screw 3 is accumulated in front of the screw 3 and retreats the screw 3. This screw 3
In both cases, the injection bracket 5 retreats, and during this time, the load F is distributed to the ball nuts 14 and 15 via the cylinders 16b and 18b. Also in this case, the cylinder chamber 21
Since b and 23b communicate with each other by the communication pipe 25, the load F / 2 is equally applied to the ball nuts 14 and 15.

When the ball nuts 14, 15 are fixed directly to the injection bracket 5 without passing through the hydraulic cylinders 16a, 16b, 18a, 18b, the load F is distributed to the ball nuts 14, 15 respectively. The loading is similar, but in this case it is not evenly distributed. This is because the load distribution changes due to a change in the temperature difference between the ball screw shaft 12 and the injection bracket 5 over time.

The life L of the ball screw shaft 12 can be obtained by the following equation.

(Equation 1) Here, C: the dynamic load rating of the ball screw shaft P: the load acting on the ball nut f: the load coefficient From the equation (1), if the load P acting on the ball nut is reduced by half, the life L of the ball screw shaft is increased by 8 times. It turns out that it becomes.

When a larger injection molding machine is electrified, a large load is applied during the injection stroke and the mold clamping stroke, and the moving speed is also high. Therefore, a ball screw having a large dynamic rated load is required. However, in the case of an injection molding machine having a mold clamping force of 400 t or more, even if a ball screw having a large dynamic rated load is employed, the load is too large to secure the life and it is difficult to realize the electrification. Was. However, as described above, the ball nut 14,
By evenly distributing the load to 15, the life is extended eight times, so that a large-sized injection molding machine can be electrically operated.

Next, FIG. 3 shows an example in which a differential pressure sensor 26 is provided to detect the injection power in the injection step. As described above, the load acting on the injection bracket 5 as a reaction force of the shooting power is equally distributed to the ball nuts 14 and 15, so that the net shooting force is used to reduce the net shooting force by using the differential pressure sensor 26.
Is detected by

The force acting on the ball nut 14 from the injection bracket 5 is the difference between the force obtained by multiplying the pressure in the cylinder chamber 21b by the cylinder area and the force obtained by multiplying the pressure in the cylinder chamber 21a by the cylinder area. The force acting on the ball nut 15 is the difference between the force obtained by multiplying the pressure in the cylinder chamber 23b by the cylinder area and the force obtained by multiplying the pressure in the cylinder chamber 23a by the cylinder area. The cylinder areas are equal, the pressure in the cylinder chamber 21b and the pressure in the cylinder chamber 23b is equal to P1, and the pressure in the cylinder chamber 21a and the cylinder chamber 23a is P2.
Is equal to Therefore, if the differential pressure between the pressures P1 and P2 in the cylinder chambers 21a and 21b on both sides of the ball nut 14 is detected by the differential pressure sensor 26 and multiplied by twice the cylinder area, the net emission power can be detected. Can be.

When controlling the firing power based on the firing power detected in this way, the injection bracket 5 and the hydraulic cylinders 16a, 16a, 16b, 16c are used to secure the response characteristics of the control system.
It is necessary to increase the fastening rigidity between b, 18a, 18b and the ball nuts 14, 15. For this purpose, the injection bracket 5-tightening flange 17-hydraulic cylinder 16
It is desirable to preload the internal force loop formed by a-flange portion 14a-hydraulic cylinder 16b-injection bracket 5-hydraulic cylinder 18a-flange portion 15a-hydraulic cylinder 18b-tightening flange 19. Second Embodiment Next, FIG. 4 shows an injection device according to a second embodiment of the present invention. The embodiment shown in FIG.
Is an embodiment in which two driving devices shown in FIG. Regarding the ball screw shaft 12, the ball nuts 14, 15 and the injection motor 9 and other main components, those arranged at the lower stage are given the suffix A, and those arranged at the upper stage are given the suffix B. Distinguish between the two. Other components that are the same as those in FIG. 2 are denoted by the same reference numerals as those in FIG.

FIG. 5 shows the details of the driving device of this embodiment. In each of the upper and lower drive units, the cylinder chambers 21a and 23a of the hydraulic cylinders 16a and 18a on the forward side are communicated by communication pipes 24A and 24B as in the embodiment of FIG. The communication pipes 24 </ b> A and 24 </ b> B of both stages are connected by a pipe 32. Similarly, in both upper and lower stages, the respective cylinder chambers 21b, 2b,
3b communicates with the communication pipes 25A and 25B, respectively.
These are connected by a pipe 34.

Since the respective cylinder chambers are thus communicated with each other, the load F acting on the injection bracket 30 is applied to the ball nuts 14A, 14B, 15A, 15B by the load distribution effect similar to that of the drive device of FIG. Evenly distributed. In this case, since they are arranged in parallel, a load of 荷重 F is distributed to each ball nut.

When the driving devices are arranged in parallel, the injection motors 9A and 9B are controlled to operate synchronously.
It is difficult to completely eliminate out-of-sync. In particular, launch,
There is a risk that undesired movements such as pitching and yawing may occur due to an imbalance of the driving force due to the synchronization deviation at the time of stopping, and a partial overload may act on a specific ball nut.

However, according to the present embodiment, even if a slight deviation occurs between the two injection motors 9A and 9B, the ball screw shafts 12A and 12B and the ball nuts 14A, 14B, 15A and 15B are not affected. Since the load is always evenly distributed, it is possible to avoid imbalance in the driving force and partial overload on a specific ball nut.
For this reason, in addition to extending the life of the ball screw shafts 12A and 12B, it is possible to further solve the problem of the motor being out of synchronization when the driving devices are arranged in parallel.
It is possible to apply the present invention to a larger injection device, which can compensate for the limitation of the load capacity of one ball screw shaft by making it parallel.

Although the present invention has been described with reference to the embodiment in which the present invention is applied to a driving device of an injection device in an injection molding machine, the same effect can be obtained by applying the present invention to a mold clamping device. Further, a hydraulic actuator such as a diaphragm may be used instead of the hydraulic cylinder for distributing the load.

[0037]

As is apparent from the above description, according to the present invention, the applied load can always be evenly distributed to a plurality of ball nuts, so that the applied load per ball nut is reduced. The life of the ball screw can be greatly extended, and large machines can be electrified. Also,
By providing a plurality of drive devices of the present invention in parallel,
Since imbalance of the driving force and partial overload can be avoided, the motorization of a larger machine can be achieved.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment in which the present invention is applied to a driving device of an injection device.

FIG. 2 is an enlarged view of a main part of the driving device of FIG.

FIG. 3 is an enlarged view of a main part of the driving device of FIG. 1 provided with a differential pressure sensor.

FIG. 4 is a schematic configuration diagram showing another embodiment of the present invention.

FIG. 5 is an enlarged view of a main part of the driving device of FIG. 4;

FIG. 6 is a schematic diagram showing the principle of load distribution of the drive device according to the present invention.

FIG. 7 is a schematic configuration diagram of an injection device of a conventional electric injection molding machine.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heating barrel 2 Hopper 3 Screw 5 Injection bracket 6 Base 8 Metering motor 9 Injection motor 10 Belt transmission mechanism 12 Ball screw shaft 14 Ball nut 15 Ball nut 16a, 16b Hydraulic cylinder 18a, 18b Hydraulic cylinder 24 Communication pipe 25 Communication pipe

Claims (4)

[Claims] 1. A driving device for an electric injection molding machine having a ball screw transmission mechanism for converting a rotary motion of an electric motor into a thrust of a movable member, wherein the driving device is fitted to a ball screw shaft which is rotationally driven by the electric motor. A plurality of ball nuts are arranged in series with respect to one ball screw shaft, and fluid pressure cylinders for transmitting thrust from the ball nut to a movable member of an electric injection molding machine are connected to the ball nuts, respectively. A driving device for an electric injection molding machine, wherein a cylinder chamber of a fluid pressure cylinder is communicated with a communication pipe. 2. A movable member of the injection molding machine is an injection bracket which is provided on a base so as to be movable in an axial direction of the screw, and supports a rear end of the screw. 2. The drive device for an electric injection molding machine according to claim 1, wherein the drive device is an injection motor for moving the motor forward. 3. The fluid pressure cylinder has a cylinder chamber having an equal cylinder area on both sides of a flange portion of a ball nut, and a differential pressure sensor for detecting a pressure difference between the two cylinder chambers is provided. The driving device for an electric injection molding machine according to claim 1, wherein: 4. A plurality of drive units according to claim 1, wherein said ball screw shafts are arranged in parallel, and the communication tubes of the fluid pressure cylinders of each group are connected to each other by another communication tube. A drive device for an electric injection molding machine, characterized in that: