JPH0142815B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a control device for an electric injection molding machine.

(B) Conventional technology The injection device of conventional injection molding machines includes a fully hydraulic type and a hydraulic/electric type. A fully hydraulic injection device uses a hydraulic motor to rotate the screw for plasticizing the resin material, and a hydraulic cylinder to move the screw for injecting the molten resin. It is.
In addition, a hydraulic/electric injection device uses an electric motor to rotate the screw for plasticizing, and moves the screw for injection using hydraulic pressure.

(c) Problems to be Solved by the Invention However, in the conventional injection device as described above, the screw is caused by the pressure of the molten resin in the cylinder between the end of plasticization and the start of injection, although it is very small. Since the mold moves backward and rotates, the molding conditions for each cycle are not stable, which poses a problem in that it becomes an obstacle when performing precise molding. In other words, the screw is rotated to knead and melt the resin material, and when a predetermined amount of plasticization is completed, the screw waits at that position until the injection process.
During this time, the pressure of the molten resin acts on the screw to push it backward. The pushing force acting on this screw is supported by closing the switching valve of the hydraulic circuit that supplies hydraulic pressure to the injection cylinder, but leakage of hydraulic oil from the switching valve, seal, etc. is completely prevented. Since the screw cannot be stopped, the screw retreats as described above. The amount of retraction of the screw varies with each cycle depending on the degree of kneading of the resin material.
For this reason, the injection operation start position changes every cycle, which impedes precision molding. The present invention aims to solve these problems.

(d) Means for Solving Problems The present invention electrifies plasticization and injection, and changes the operating state of the electric motor to the same state at the end of plasticization from the end of plasticization to the start of the injection operation of the next cycle. By maintaining the condition, the above problem is solved. That is, the control device for an electric injection molding machine according to the present invention includes a first electric motor that can drive the screw in the injection molding machine cylinder in the axial direction, a second electric motor that can rotationally drive the screw, and a rotational position of the first electric motor. a first rotational position detection device that detects the rotational position of the second electric motor; a plasticization end position setting device that can set the screw position at the end of the plasticization stroke; A memory device that stores the detection value of the second rotational position detection device at the end of the stroke, and a plasticization end position setter that stores the detection value of the first rotational position detection device from the end of plasticization to the start of injection operation. The first controller controls the operation of the first electric motor so that the detected value matches the value stored in the memory device, and the detected value of the second rotational position detector from the end of plasticization to the start of injection operation matches the value stored in the memory device. and a second controller that controls the operation of the second electric motor so as to control the operation of the second electric motor.

(E) Function When the first electric motor is set to a free rotation state (or a state where a small driving force is generated) and the second motor is rotated, the screw is rotationally driven, the resin material is plasticized in the cylinder, and the resin pressure is increased. The screw moves backwards. When the screw is retracted to the position set by the plasticization end position setter, a signal from the second rotational position detection device indicating the rotational position of the second electric motor at that time is stored in the memory. Further, at this point, the rotation of the first electric motor and the second electric motor is stopped. If the screw is moved backward by the resin pressure in the cylinder in this state, the actual screw position detected by the first rotational position detector and the screw position set by the plasticization end position setting device are Since a deviation occurs between the two positions, the first controller controls the first controller to eliminate this deviation.
Outputs a signal to drive the motor. This results in
The position of the screw is always maintained at the position set by the plasticization end position setting device. Furthermore, if the screw is rotated by the resin pressure, the amount of rotation is detected by the second rotational position detection device, and the second controller stores the actual rotational position of the second electric motor in the memory. The second value is
Outputs a signal to operate the electric motor. Thereby, the rotational direction position of the screw is always maintained at the rotational direction position at the end of plasticization. By doing this, the axial position and rotational position of the screw are maintained as they were at the end of plasticization from the end of plasticization until the start of the injection process of the next cycle, and the same conditions are maintained for each cycle. Since molding can be performed, more precise molding can be performed.

(F) Embodiments Hereinafter, embodiments of the present invention will be described with reference to Nos. 1 and 2 of the attached drawings.
This will be explained based on the diagram.

As shown in Figure 2, the cylinder 1 of the injection molding machine
A screw 12 is inserted into the 0. A casing 14 is attached to the rear end side of the cylinder 10 (upstream side in the resin flow direction). The casing 14 includes a housing 16 and a cover 18, which define a chamber 20. A rotatable and axially movable intermediate shaft 22 is provided in this chamber 20 . The intermediate shaft 22 has a small diameter shaft portion 24 and a large diameter shaft portion 26 . The tip of the small diameter shaft portion 24 is connected to the screw 12 by a spline. The small diameter shaft portion 24 has sliding bearings 36 and 3 attached to the housing 16.
8 so as to be rotatable and axially movable. On the large diameter shaft portion 26 side of the intermediate shaft 22,
A nut member 5 having a female thread that constitutes a ball screw mechanism 52 together with a male thread 50 provided on the shaft 48
4 is fixed. The shaft 48 on which the male thread 50 is provided is connected to the thrust bearing 5 with respect to the cover 18.
6 and a bearing 58 so as to be rotatable. The shaft 48 is connected to a first electric motor 70 outside the casing 14 . The first electric motor 70 is provided with a first pulse generator 72 (first rotational position detection device). The end of the shaft 48 inside the housing 14 is supported by a linear motion bearing 75 against the inner diameter of the intermediate shaft 22 . A driven gear 8 is attached to the outer periphery of the large diameter shaft portion 26 of the intermediate shaft 22 by a key 81.
2 is attached so as to rotate together with the intermediate shaft 22. The driven gear 82 meshes with a drive gear 83 with a collar 83a, which is connected to the shaft 84 by a sliding key 85. The shaft 84 is rotatably supported by bearings 86 and 87 relative to the housing 16 and cover 18. A portion of the shaft 84 that protrudes to the outside of the casing 14 is connected to the second electric motor 71 . The second electric motor 71 is provided with a second pulse generator 73 (second rotational position detection device).

FIG. 1 shows a device for controlling the first electric motor 70 and the second electric motor 71. As shown in FIG. The device that controls the first electric motor 70 includes a plasticization end position setter 102 that sets the plasticization end position of the screw 12, an AD converter 104 that AD converts a signal from the plasticization end position setter 102, and a first pulse A comparator 106 that compares the signals from the generator 72 and the AD converter 104, a first controller 108 that performs control to eliminate the deviation calculated by the comparator 106, and a signal from the first controller 108. It has a drive circuit 110 that amplifies and outputs the amplified signal to the first electric motor 70. Also, the second
The device that controls the electric motor 71 is the second pulse generator 7 when the screw 12 reaches the plasticization end position set by the plasticization end position setting device 102.
Memory device 112 for storing signals from 3, memory device 1
a comparator 114 that compares the signal from the second pulse generator 73 with the signal from the second pulse generator 73; a second controller 116 that performs control to eliminate the deviation calculated by the comparator 114; It has a drive circuit 118 that amplifies the signal from 116 and outputs it to the second electric motor 71.

Next, the operation of this embodiment will be explained. FIG. 2 shows the state immediately before starting the plasticizing operation after the injection operation has been completed. From this state, the second electric motor 7
1 rotates the shaft 84, the intermediate shaft 22 rotates via the driving gear 83 and the driven gear 82.
When the intermediate shaft 22 rotates, the screw 12 connected to it via a spline moves into the cylinder 1.
The plastic pellet is rotated in the cylinder 10, melts and plasticizes the resin pellets supplied into the cylinder 10 from the material supply port 10a provided with a hopper, and transfers the resin pellets to the front of the cylinder 10 (to the left in FIG. 2). At this time, the shaft 48
If an appropriate torque is applied in the direction of the injection operation by the first electric motor 70, an appropriate plasticizing back pressure is applied and the degree of kneading can be improved. In this way, when the intermediate shaft 22 and the screw 12 move by a preset stroke, that is, when the detected value of the first pulse generator 72 matches the detected value of the plasticization end position setter 102, the plasticizing operation is stopped. . The detected value from the second pulse generator 73 at the time when this plasticizing operation is stopped is stored in the memory 1.
12 is stored. Thereafter, until the injection operation of the next cycle is started, the axial position and rotational position of the screw 12 are maintained at the point at which the plasticizing operation ends by the actions of the first controller 108 and the second controller 116 as described below. will be maintained in the same state. Even at the end of plasticization, the pressure of the molten resin acts on the screw 12 to force it to retreat further.
For example, if the screw 12 retreats without rotation, the intermediate shaft 22 and the nut member 5
Since the shaft 4 also moves backward without rotating, the shaft 48 is rotated. Therefore, the first electric motor 70 is rotated, thereby changing the detected value of the first pulse generator 72. First pulse generator 7
The second detected value is input to the comparator 106, where it is compared with the set value set by the plasticization end position setter 102, and as described above, the first
When the electric motor 70 rotates, the comparator 106 calculates the deviation. The first controller 108 issues a command to rotate the first electric motor 70 to the drive circuit 110 so as to eliminate this deviation. As a result, the screw 12 returns to the position at the end of plasticization. Further, when the screw 12 is retreated and rotated due to the resin pressure, the position in the rotational direction is also returned to the state at the end of plasticization by the action of the second controller 116. That is, the rotation of the second electric motor 71 is detected by the second pulse generator 73, and this detected value and the stored value stored in the storage device 112 (i.e., the rotation of the second pulse generator 73 at the end of plasticization
A comparison is made by the comparator 114 with the detected value of
The rotational position of the second electric motor 71, that is, the rotational position of the screw 12, is returned to the state at the end of plasticization. Note that at this time, the above-described control of the first electric motor 70 by the first controller 108 is also performed at the same time. By controlling the first electric motor 70 and the second electric motor 71 as described above, the axial position and rotational position of the screw 12 are maintained as they were at the end of plasticization until the injection operation of the next cycle is started. be done. Therefore, the screw 1 at the start of the injection operation
The position of 2 does not change with each repeated cycle. Therefore, molding conditions are stable and precise molding is possible.

In this embodiment, a pulse generator is used as the rotational position detecting device of the electric motor, but a tachometer generator may also be used.

(g) Effects of the Invention As explained above, according to the present invention, the rotational positions of the first electric motor and the second electric motor are maintained at the rotational positions at the time of the end of plasticization from the end of the plasticizing operation until the start of the injection operation. As a result, the screw is held in a fixed position during each cycle, stabilizing the molding conditions and enabling more precise molding.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a control device for an electric injection molding machine according to the present invention, and FIG. 2 is a diagram showing the electric injection molding machine. 12... Screw, 70... First electric motor, 7
1... Second electric motor, 72... First pulse generator (first rotational position detection device), 73... Second pulse generator (second rotational position detection device), 102... Plasticization end position setting device , 108...first controller, 11
2...Memory device, 116...Second controller.

Claims (1)

[Scope of Claims] 1. A control device for an electric injection molding machine including a first electric motor capable of driving a screw in an injection molding machine cylinder in an axial direction, and a second electric motor capable of rotationally driving the screw. A first rotational position detection device that detects the rotational position of the electric motor, a second rotational position detection device that detects the rotational position of the second electric motor, and a plasticization end position setting device that can set the screw position at the end of the plasticization stroke. a storage device that stores the detection value of the second rotational position detection device at the end of the plasticizing stroke; and a detection value detected by the first rotational position detection device between the end of plasticization and the start of the injection operation. a first controller that controls the operation of the first electric motor so that the value coincides with the set value of the plasticization end position setter, and a second rotational position detector from the end of plasticization to the start of injection operation. A control device for an electric injection molding machine, comprising: a second controller that controls the operation of the second electric motor so that the detected value matches the stored value stored in the memory device.