JPH0486209A - Correcting method for mold clamping force in toggle type mold clamping device - Google Patents

Abstract

PURPOSE:To make it possible to easily and surely correct mold clamping force by a method wherein the normality of molds is confirmed by performing mold clamping with the torque slightly larger than the torque value in mold protection process and by detecting foreign matter between the molds with low pressure mold clamping before the detection of the position of a crosshead at the time point of mold closing position. CONSTITUTION:A central controller 14 detects the position of a crosshead at all times on the basis of the signal sent from the sensor 13 of a servo motor 10 so as to judge whether the position of the crosshead 6 under mold clamping control reaches the starting position of mold protection or not so as to output a low pressure mold clamping torque limiting command. When the low pressure mold clamping supervisory timer times out or the arrival of the position of the crosshead to the mold closing position is judged, upon the arrival of the position of the crosshead to the end position of mold protection, the central controller releases the low pressure mold clamping torque limit and outputs the mold closing torque limiting command and, at the same time, starts a mold closing detection timer. However, if the low pressure mold clamping supervisory timer times out before the arrival of a mold to a mold touch position, the central controller issues alarm signal so as to indicate the presence of foreign matter between molds.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for modifying the mold clamping force of a toggle type mold clamping device of an injection molding machine.

[Prior art] It is difficult to detect the clamping force of a toggle type mold clamping device due to the characteristics of its mechanism. When the toggle is fully extended, the amount of extension of the tie bar is adjusted to the set mold clamping force. ing.

In such a case, when the temperature of the mold changes, the mold thickness changes, and the mold clamping force fluctuates. Furthermore, if the mold clamping force is greater than the rated mold clamping force of the machine, there is a risk of overloading the machine and causing damage to the equipment, and if the mold clamping force is lower than the set value, the mold may open. This may cause cracks to occur in the molded product, and may even damage the mold.

Furthermore, the trigger for the mold to open increases the spout of molten metal, causing the mold to open further, and even if the mold clamping force is small, there is a risk that the tie bars will be overloaded and damaged.

For this reason, it is important that the mold clamping force is always normal, and it is necessary to correct it if it differs from the set value. Therefore, as a conventional technology, Patent Publication No. 50-237
Publication No. 0, Japanese Patent Publication No. 6181897, Japanese Patent Application Publication No. 1987
The one described in JP-A-32020 is known.

Although there are differences in the mold clamping force detection methods described in those publications, all of them detect the mold clamping force and feed back the correction amount to the mold thickness adjustment means of the toggle device to keep the mold clamping force constant. The toggle device is driven by a hydraulic cylinder.

[Problems to be Solved by the Invention] In a toggle type mold clamping device, when the temperature of the mold changes, the mold clamping force changes greatly, but the mold thickness usually changes little.

Therefore, it is impossible to finely adjust the mold thickness change by moving the entire toggle device using the mold thickness adjustment means as in the conventional method.
Since the mold thickness adjustment amount is minute, it is not easy and requires experience and time to accurately correct the mold clamping force. Furthermore, when modifying the mold clamping force, it is necessary to temporarily interrupt molding, which poses a problem in terms of productivity.

This invention was devised in order to solve the problems in the toggle type mold clamping device, and its purpose is to use a servo motor as the drive source of the toggle type mold clamping device, and to detect the position of the servo motor and the crosshead. The object of the present invention is to provide a new method for easily and reliably modifying mold clamping force.

[Means for Solving the Problems] The present invention according to the above object is characterized by a toggle type in which rotational motion by a servo motor is converted into linear motion and transmitted to a crosshead of a toggle mechanism, and the movable platen is moved by the toggle mechanism. The servo motor of the mold clamping device is equipped with a control device equipped with a torque limit function that limits the upper limit of output torque, and a sensor that detects the position of the crosshead from the amount of rotation of the servo motor. In addition to detecting the arrival of the head at the mold protection start position and mold protection completion position, the torque value of the servo motor is controlled for each position. Until the mold protection end position is detected, the servo motor is controlled to a low torque according to the torque limit command set to the low pressure mold clamping torque value, and from the detection of the mold protection end position, the torque is slightly larger than the above torque value, Change the torque limit command to a mold closing torque value that is large enough to close the mold, perform mold clamping, detect the position of the crosshead after a certain period of time from the time of the change, and set the position and setting. The forward movement limit position of the crosshead that generates the set mold clamping force is calculated based on the mold clamping force set, and the mold closing torque limit command is canceled to continue mold clamping, and the crosshead is moved forward to the set position above. The purpose is to control positioning at the limit position using a servo motor.

[Function] In the above method, the mold is clamped with a torque slightly larger than the torque value in the mold protection process, and foreign matter between the molds is detected by low-pressure mold clamping before the position of the crosshead at the time of mold closure is detected. Since the mold is confirmed to be normal, damage to the mold due to foreign matter is prevented.

In addition, the torque limit command is changed to the mold closing torque value to clamp the mold, so the crosshead moves further forward at a low speed.
Since the crosshead cannot move forward at the mold closing position where the forces are balanced, the mold closing position can be accurately detected by detecting the crosshead position after a certain period of time has elapsed.

Furthermore, after the mold closing position is detected, the mold closing torque limit is released, and the crosshead is controlled to move forward to the calculated advance limit position, and then positioning is controlled by the servo motor, resulting in highly accurate molding. Tightening force can be obtained.

[In the figure of the embodiment, 1 is a pressure receiving plate, 2 is a fixed plate, and both plates are connected by tie bars 3, 3 provided over the four corners.

A movable plate 4 is provided between the pressure receiving plate 1 and the fixed plate 2 by passing through the tie bars 3, 3, and is connected to the pressure receiving plate 1 by a toggle mechanism 5. A pole nut 7 is installed inside the crosshead 6 at the center of the toggle mechanism 5, and a pressure receiving plate 1
A ball screw shaft 8 is rotatably attached to the holder.

This ball screw shaft 8 and the ball nut 7 are screwed together, and the rotational motion of the ball screw shaft 8 in a fixed position is converted into linear motion by the pole nut 7, and the expansion and contraction of the links 5a+5a due to the movement of the crosshead 6 causes the movable platen to move. 4 moves forward and backward with respect to the fixed platen 2, and opens/closes and clamps a mold 9 attached to opposing sides of the fixed platen 2 and the movable platen 4.

The link mechanism 5 is driven by a servo motor 10 attached to the pressure receiving plate. This servo motor 10 and the ball screw shaft 8 are connected via a drive belt 11, and the servo motor 10 is equipped with a control device 12 that detects the position of the cross head 6 from the amount of rotation of the servo motor. A sensor 13 (encoder) is provided. Furthermore, the sensor 13 and the control device 12 are connected to a central controller 14 .

This central controller 14 is a control device that is equipped with a CRT device as a display equipped with a microcomputer and is in charge of the overall control of the injection molding machine. , M1 It is equipped with an input/output device for controlling the servo motor, and is capable of numerical calculation processing.

Reference numeral 15 designates a die thickness adjusting nut, which is screwed into the threaded portion 3a of each tie bar 3, 3 located on the pressure receiving plate side together with the sprocket 16.

Initial adjustments at the start of molding are performed in the same manner as in the conventional method. To set the mold clamping force, each mold thickness adjustment nut 15 on the ash receiving plate 1 side is rotated synchronously by another motor (not shown) via the sprocket 16. This is done by moving the position of the toggle mechanism 5.

Further, the control device 12 of the servo motor 10 controls the output torque based on a torque limit command from a central controller 14 having a torque limit function that limits the upper limit of the output torque of the servo motor 10 .

The operation of the low-pressure mold clamping process for mold protection is performed by trial or experience as in the conventional method, and the mold protection start position, low-pressure mold clamping torque 'J value, mold touch position, low-pressure mold clamping The setting time of the monitoring timer, etc. are set. Mold closing torque limit=9- The value is an output value of the servo motor 10 that cannot extend the tie bars 3, 3, but is set in advance as an empirical value to a value that can reliably close the mold 9.

In some cases, the mold can be determined from the elongation value of the tie bar 3.3 according to the set mold clamping force (the position of the crosshead 6 at the time of mold closing when mold clamping is normal is calculated from this value and the magnification rate of the toggle). If you calculate the magnification rate of the toggle force at the time of mold closing when tightening is normal and change the setting of the mold closing torque value to a value inversely proportional to the magnification rate, the mold closing force at the time of mold closure detection will always be the same. Since the value is approximately constant, the position of the crosshead 6 at the mold closing time can be detected with accuracy.

In addition, the mold closing point is the low-pressure mold clamping end position (mold touch position, the purpose is to protect the mold, so the mold clamping force is small, and the mold is generally not completely closed. ,
Detection is performed based on the time from when the tie bars 3, 3 are in the mold closed state immediately before they are extended), and the set time of the mold closure detection timer is set based on an empirical value.

10- Since the speed of the crosshead 6 at that time is slow, a fixed time suffices.

When mold clamping is ready and the servo motor 10 is driven to start the mold clamping operation, the central controller 14 constantly detects the position of the crosshead 6 based on the signal from the sensor 13 of the servo motor 10 and performs mold clamping control. It is determined whether or not the position of the crosshead 6 has reached the mold protection start setting position, and a low-pressure mold clamping torque limit command is output. The servo motor 10 is driven by a low-pressure mold clamping torque limit value, and the crosshead 6, movable platen 4, and mold 9 are moved with a weak force.

It is determined whether the low-pressure mold clamping monitoring timer has timed up or the crosshead position has reached the mold closing position, and when it reaches the mold touch position (mold protection end position), the low-pressure mold clamping torque IJ is released. Outputs the mold closing torque limit command and starts the mold closing detection timer. As a result, the servo motor 10 is driven at the mold closing torque limit set value, and the mold 9 is moved with a force greater than the low-pressure mold clamping force but weak enough to extend the tie bars 3, 3.

However, if the low-pressure mold clamping monitoring timer times out before the mold reaches the mold touch position, an alarm signal is generated to indicate that there is a foreign object between the molds. The mold closing position timer, which starts when the crosshead position reaches the mold touch position, reads the position of the crosshead e at the time of time-up, and uses the detected position and the set mold clamping force to determine the setting. The forward limit position of the crosshead 6 that generates mold clamping force is calculated, the mold closing torque command is canceled to continue the mold clamping process, and the servo motor 1
The mold clamping force is controlled by controlling the positioning drive of the crosshead to the forward movement limit position using 0.

FIG. 2 shows the above process as a flowchart.

In addition, when changing the setting of the above-mentioned crosshead advance limit position to correct the mold clamping force, if the amount of correction is within the allowable value, the previous value may be left unchanged, or the previous value may be changed. Even better results can be obtained by adding an operation such as outputting an alarm when the value is outside the corrected allowable range.

[Effects of the Invention] As described above, this invention uses the torque limit function to protect the mold by low-pressure mold clamping, and then uses the l-ru limit function to advance the mold further under low pressure. Detects the mold closing position, calculates the crosshead advance limit position that generates the set mold clamping force from the detected value of the crosshead position at that time, and positions the crosshead at the above position by position control of the servo motor. Since the mold clamping force is controlled, damage to the mold due to foreign matter can be prevented.

Furthermore, since the extension of the tie bars during mold clamping is proportional to the mold clamping force, in order to generate that mold clamping force, it is only necessary to control the extension of the tie bars, so the position of the crosshead when the mold is closed is It is possible to accurately detect l
- Taking into account the magnification rate of the force of the glue mechanism, the forward movement limit position of the crosshead that generates the set mold clamping force can be easily calculated, and the mold clamping force can be adjusted during the mold clamping process. Because it can be done automatically, it is more efficient than traditional methods.
This method has the advantage that it does not require a special device for detecting mold clamping force and can be done with an inexpensive device.

Furthermore, if the magnification rate of the toggle force is calculated from the value of the crosshead position at the time of mold closing, and the setting of the mold closing toggle value is automatically changed to a value that is inversely proportional to the magnification rate. Since the mold closing force (movable platen forward force) at the time of mold closure detection always remains approximately constant, the crosshead position at the time of mold closure can be detected more accurately, making it as accurate as -stage. It has features such as being able to control the mold clamping force.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the mold clamping force correction method of the present invention, and FIG. 2 is a flowchart thereof. 1...... Pressure receiving plate 2......
... Fixed plate 3 ... Tie bar 4
・・・・・・・・・Movable plate 5・・・・・・・・・L・Glue mechanism 6・・・・・・・・・Cross head 7・・・・・・・・・Ball nut 8・・・・・・・・・・Ball screw 9・・・・・・
...Mold 0... Servo motor 11.
...... Drive bell 2 ... Servo motor control device 3 ...... Sensor for detecting crosshead position 4 ......・・Central control 5・・・・・・Mold thickness adjustment nut

Claims (1)

[Claims] A torque that limits the upper limit of the output torque of the servo motor of the toggle type mold clamping device, which converts the rotational motion by the servo motor into linear motion and transmits it to the crosshead of the toggle mechanism, and moves the movable platen by the toggle mechanism. A control device with a limit function and a sensor that detects the position of the crosshead from the rotation amount of the servo motor are installed, and the sensor allows the crosshead to reach the mold protection start position and mold protection completion position. At the same time, the servo motor torque value is controlled for each position, and the servo motor is set to a low-pressure mold clamping torque value from the detection of the crosshead mold protection start position until the detection of the mold protection end position. The torque limit command is then controlled to a low torque, and from the detection of the mold protection end position, the torque limit command is set to a mold closing torque value that is slightly larger than the above torque value and is large enough to close the mold. The crosshead's forward movement limit position is determined by detecting the position of the crosshead after a certain period of time after the change, and generating the set mold clamping force based on that position and the set mold clamping force. The toggle type mold clamping device is characterized in that the mold closing torque limit command is canceled to continue mold clamping, and the crosshead is positioned at the set advance limit position by a servo motor. How to correct mold clamping force.