JPH10119099A - Mold clamping force controller for toggle type motor operated injection molding machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mold clamping force controller for always generating a stable mold clamping force during continuous operation. SOLUTION: The mold clamping force controller comprises a control system for controlling a servo motor 26 based on a speed pattern from a mold clamping speed pattern generator 34, a mold clamping force detector 30 provided at a constituting member of a mold clamping mechanism to sense a strain amount of a constituting member to detect a mold clamping force, and a feedback system for comparing a previously set mold clamping force with an output of the detector 30 to output a stop command of the motor 26 instead of the speed pattern to the control system when the comparison result coincides.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold clamping force control device for an electric injection molding machine having a toggle mold clamping mechanism.

[0002]

2. Description of the Related Art A conventional mold clamping force setting method in a toggle-type mold clamping mechanism is performed by bringing a mold into close contact and driving a toggle support by the amount of extension of a tie bar based on the mold. Therefore, when the mold clamping force is changed, the work of adjusting the mold thickness must be performed again in order to change the reference length of the tie bar.

[0003]

Apart from this, a mold clamping apparatus having a toggle-type mold clamping mechanism has a problem that the mold clamping force is not stable. As a specific example, when the injection molding machine is continuously operated, the temperature of the entire apparatus expands due to the influence of the mold temperature, and it takes several hours until the mold clamping force becomes constant. In addition, if the injection molding machine is operated for a long time, the movable portion may become familiar, the frictional resistance of the movable portion may be reduced, and the initial clamping force may change, and the actual clamping force may change over time. As described above, in the conventional mold clamping device, since the mold clamping force is generated mechanically, there is a problem that the mold clamping force is likely to fluctuate due to various disturbances.

Therefore, in the present invention, a stable mold clamping force can be always generated during continuous operation by detecting the mold clamping force, feeding back the detected value to the injection molding machine, and controlling the mold clamping force itself. It is an object to provide a mold clamping force control device.

[0005]

According to the present invention, there is provided an electric injection molding machine having a servomotor for moving a movable platen back and forth through a toggle type mold clamping mechanism. As a control device, a control system that controls the servomotor based on a speed pattern from a mold closing speed pattern generator, and a mold provided by a component of the mold clamping mechanism to detect a distortion amount of the component, Including a detecting device for detecting a clamping force, when a preset mold clamping force is compared with an output of the detecting device and agrees, a stop command of the servo motor is issued to the control system instead of the speed pattern. And a feedback system for outputting.

The feedback system includes the detecting device, a mold clamping force setting device for setting a mold clamping force in advance, a set clamping force from the mold clamping force setting device, and an output of the detecting device. And a switch that outputs a signal when they match with each other, and a switch that switches between the speed pattern and the stop command of the servomotor based on the output of the comparing unit.

[0007] The detecting device is provided on any one of a tie bar, an arm, a toggle lever, and a toggle support, which are constituent members of the mold clamping mechanism.

[0008]

In a toggle-type mold clamping mechanism having a servomotor, the driving force of the servomotor is transmitted to the crosshead via a ball screw. Then, the movable platen moves forward and backward through a link mechanism connected to the crosshead. When the mold comes into close contact, the tie bar is extended and the mold clamping force starts to rise.

In the case of the conventional toggle-type mold clamping mechanism, when the mold clamping force is changed to generate a set mold clamping force at a predetermined movable platen position, the amount of the toggle support to be driven must be changed. In this case, the mold thickness must be adjusted again.

On the other hand, in the present invention, by providing the mold clamping force detecting device, the mold clamping force is set without performing the operation of adjusting the mold thickness, and the apparatus is stable against disturbances such as temperature and break-in. The mold clamping force is controlled so as to obtain the adjusted mold clamping force.

The detection of the mold clamping force is performed by installing a strain sensor on the tie bar. Alternatively, mold clamping components (arms, movable platens, toggle supports, etc.) other than the tie bars are distorted when the mold clamping force is applied. Therefore, a strain sensor may be installed on them.

When the movable platen advances further due to the close contact of the mold, the mold clamping force rises in accordance with the amplification factor of the force by the toggle-type mold clamping mechanism. At that time, the output of the mold clamping force detecting device is proportional to the mold clamping force. And rise. The position of the movable platen when the detected value of the mold clamping force obtained in this way matches the set mold clamping force is the mold clamping completion position, and by holding at that position, the mold clamping force as set Can be obtained.

If the amount of the toggle support driven at this time is set to the rated clamping force at the conventional clamping completion position, it can be reproduced from 0 to the rated clamping force.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 2, a mold clamping force control device according to the present invention includes a fixed platen 21, a tie bar 22,
Movable platen 23, arm 24, toggle support 2
5, a mold clamping servo motor 26, a ball screw 27,
The present invention is applied to a toggle-type mold clamping mechanism 20 having a crosshead 28 and the like. Reference numeral 10 denotes a mold thickness adjusting device.

The rotational motion of the servo motor 26 is converted into linear motion by a ball screw 27, and the movable platen 23 is moved via a toggle mechanism (comprising a cross head 28, toggle levers 29a and 29b, and an arm 24) connected to the ball screw 27. Move forward and backward. The movable platen 23 advances, and the movable mold contacts a fixed mold (neither is shown),
When the tie bar 22 is further advanced, the tie bar 22 is extended and a mold clamping force is generated.

When a mold clamping force is generated by the mold clamping mechanism 20, the tie bar 22, the movable platen 23, the arm 24, the toggle support 25, and the like are easily elastically deformed and easily distorted. In particular, since the amount of elastic deformation of the tie bar 22 is large, in this example, the mold clamping force detection device 30 is provided at a location that is the tie bar 22 and does not hinder the installation of the mold.
It may be provided on any of the above components. As the mold clamping force detection device 30, for example, a strain sensor is suitable.

Next, a description will be given also with reference to FIG. 1 showing a clamping force control system. In FIG. 1, the clamping force control system obtains a signal indicating the number of rotations of the servo motor 26 by an absolute encoder 31 provided in the servo motor 26, converts the signal into a signal indicating speed through a differentiator 32, and converts the signal into a signal indicating a speed. The position of the crosshead 28, indirectly, the position of the movable platen 23 is controlled by a position control loop that controls the servo motor 26 via the speed control amplifier 33 and the vector control driver 34 based on the speed control amplifier 33. The signal of the absolute encoder 31 is also supplied to the vector control driver 34.

A mold closing speed pattern generator 34 is connected to the above-mentioned position control loop. The speed signal based on the speed pattern output from the mold closing speed pattern generator 34 by the subtracter 35 and the speed from the differentiator 32 are shown. The difference from the signal is calculated, and the control by the position control loop is performed. That is,
The difference between the speed pattern from the mold closing speed pattern generator 34 and the speed signal from the differentiator 32 is calculated by the subtracter 35 and supplied to the speed control amplifier 33. Speed control amplifier 3
3 outputs a signal indicating the position of the crosshead 28 from the signal of the subtracter 35 to the vector control driver 34.

With the above configuration, the position of the crosshead 28 and thus the position of the movable platen 23 are accurately controlled by the position control loop formed by the servo motor 26 and the absolute encoder 31.

In the present invention, a mold clamping force setting device 36 for setting the mold clamping force by an operator in advance, and an amplifier 37 for amplifying a detection signal from the mold clamping force detecting device 30 are provided.
, A comparator 38 for comparing the set mold clamping force with the detected mold clamping force from the amplifier 37, a stop command generator 39 for outputting a stop command, and a mold closing speed according to the comparison result from the comparator 38. A changeover switch 40 is provided for switching between a speed pattern output from the pattern generator 34 and a stop command from the stop command generator 39. The changeover switch 40 is connected to the amplifier 37
When the detected mold clamping force reaches the set mold clamping force, the operation is performed by the output from the comparator 38, and a stop command of the servo motor 26 is given to the position control loop instead of the speed pattern.

The operation of controlling the mold clamping force will be described with reference to FIG. FIG. 3 shows the cross-head position and the time lapse of the mold clamping force after the start of mold clamping. Here, the mold clamping force setting device 36 previously sets two stages of mold clamping forces P1, P2 (P1
<P2) and continuation times t ₁ and t ₂ from the start thereof are set.

When mold clamping is started, the position of the crosshead 28 is detected by the absolute encoder 31 from a position S1 corresponding to the mold opening limit, and when the position reaches a preset deceleration start position S2, the deceleration operation is started. enter.
Thereafter, the movable mold comes into contact with the fixed mold further, so that a mold clamping force is generated and the movable mold rises. Thereafter, when the set mold clamping force P1 is reached at the position S3 which is the first-stage mold clamping completion position,
The changeover switch 40 is switched to the stop command generation section 39, the servomotor 26 stops, and the crosshead position is maintained. At this time the clamping force is maintained from the start to the time t ₁ has elapsed.

When the time t ₁ has elapsed, the mold clamping force setting device 36
Is set to P2, the changeover switch 40 is switched again to the mold closing speed pattern generator 34 side, and the mold clamping force starts to increase. When the set mold clamping force P2 is reached at the position S4, which is the mold clamping completion position of the second stage, the changeover switch 40 is again switched to the stop command generator 39 side, and the servomotor 26 is stopped. Is the time t ₂ from the start
Is held until the time elapses.

[0024]

According to the present invention, since the object to be controlled is the mold clamping force, the mold clamping force can always be generated as set. Therefore, the mold clamping force is stable against disturbances such as a change in frictional resistance due to temperature fluctuations and conformity.
Also, it was difficult to reproduce a low mold clamping force with the conventional setting method due to the influence of the mold touch force.
It is possible to reliably reproduce from a nearby mold clamping force to a rated mold clamping force. Thereby, low pressure molding requiring a low mold clamping force is possible. Further, since the mold clamping force can be freely changed up to the rated mold clamping force without adjusting the mold thickness, a multi-stage mold clamping force can be easily set.

Further, there is a correlation between the clamping force and the weight of the molded product. Therefore, by obtaining a stable mold clamping force, the variation in the weight of the molded product is improved, and the precision moldability of the toggle mold clamping mechanism is improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a mold clamping force control system of an injection molding machine according to an embodiment of the present invention.

FIG. 2 is a diagram showing a structure of a mold clamping device to which the present invention is applied.

FIG. 3 is a characteristic diagram showing behavior of a mold clamping force and a crosshead position during molding according to the present invention.

[Explanation of symbols]

 Reference Signs List 10 mold thickness adjusting device 20 mold clamping mechanism 21 fixed platen 22 tie bar 23 movable platen 24 arm 25 toggle support 26 mold clamping servo motor 27 ball screw 28 crosshead 29a, 29b toggle lever 30 mold clamping force detector 31 absolute encoder

Claims (3)

[Claims] 1. An electric injection molding machine having a servomotor for moving a movable platen forward and backward through a toggle-type mold clamping mechanism, wherein the servomotor is controlled based on a speed pattern from a mold closing speed pattern generator. A control system, including a detection device provided in a component of the mold clamping mechanism and detecting a strain amount of the component to detect a mold clamping force, a preset clamping force and a detection device of the detection device; And a feedback system for outputting a stop command of the servomotor to the control system in place of the speed pattern when the outputs match. The mold clamping force in the toggle-type electric injection molding machine, Control device. 2. The mold clamping force control device according to claim 1, wherein the feedback system comprises: the detection device; a mold clamping force setting device for setting a clamping force in advance; Comparing the set clamping force with the output of the detection device and outputting a signal when they match, and a switch for switching between the speed pattern and the stop command of the servomotor based on the output of the comparison device. A mold clamping force control device in a toggle-type electric injection molding machine. 3. The mold clamping force control device according to claim 1, wherein the detection device is provided on any of a tie bar, an arm, a toggle lever, and a toggle support, which are constituent members of the mold clamping mechanism. A mold clamping force control device for a toggle type electric injection molding machine.