JPH04197721A - Method and apparatus for automatically adjusting mold thickness of injection molding machine - Google Patents

Abstract

PURPOSE:To absorb a sudden load based on a movement of a toggle link by detecting a pressure being loaded on a mold by the output of a mold pressure detecting means set on a locking apparatus and performing feedback control of a torque limitation of a locking servo motor so as to make the output to be a set specified value. CONSTITUTION:Even when a toggle link of a toggle mechanism 8 is gradually extended for adjusting mold thickness and just before complete extension, a large force is suddenly provided to a moving platten 5 with the movement, as the force is detected by extension of a tie bar 6 through a strain gauge 22 and an ordered torque limiting value to a servo motor Mb for locking is decreased by this part of the force, only a specified force is loaded to molds 2 and 4 and therefore, loading of a large force to the molds 2 and 4 can be avoided. Therefore, when a rear platten 7 is moved during adjustment of mold thickness, a force pushing the molds 2 and 4 becomes larger and there is no possibility that a large compressive force is loaded on a nut 18 for adjustment of mold thickness and it is avoided to increase suddenly loading on the servo motor Mb for adjustment of mold thickness.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an automatic mold thickness adjustment method and device for an injection molding machine having a toggle type mold clamping device.

[Prior Art] Automatic mold thickness adjustment in a conventional injection molding machine having a toggle type mold clamping device was performed as follows. With the toggle link of the toggle mechanism in the position before it reaches its fully extended state (mouth, Tsukua, Tsubu state), the mold clamping servo motor is rotated to drive the toggle mechanism, and the moving platen is moved to close both molds. to impose. At this time, a torque limit is applied to the mold clamping servo motor, and the pressure applied to the mold is controlled so that the pressure is kept constant. In this way, the mold clamping servo motor continues to apply constant pressure to both molds, while the mold thickness adjustment servo motor is rotated to move the rear platen rearward. Then, the distance between the rear platen and the moving platen increases, and the toggle mechanism moves toward the lock-up state accordingly. Until the lock-up state is reached, the crosshead continues to push the mold by the predetermined torque of the mold clamping servo motor. In this way,
The position where the toggle mechanism finally reaches the lock-up state is detected, and the mold thickness adjustment is then completed by finding the rear platen position where the mold clamping pressure reaches the set value.

[Problem to be solved by the invention] In the conventional automatic mold thickness adjustment method in which the rear platen is moved backward by rotating the mold thickness adjustment motor while applying crosshead pressure using the mold clamping servo motor, this The pressure applied to the crosshead is controlled to be kept constant by a torque limit to the motor, or the force that actually presses the mold is difficult to keep constant due to the toggle mechanism.
In particular, when the toggle link is on the verge of locking up, the force pressing against the mold increases due to the motion characteristics of the toggle. Therefore, if the mold thickness adjustment motor is rotated further in this state, the axial force applied to the mold thickness adjustment nut increases, so the load on the motor increases, and in the case of a chain drive, the chain tooth jump increases. Installation of the motor and motor sometimes caused problems such as destruction of the stand and overheating of the motor.

[Means for solving the problem] In the automatic mold thickness adjustment of an injection molding machine having a toggle type mold clamping device, which is performed by moving the rear platen backward while pressing the mold with the output torque of a mold clamping servo motor. , The pressure applied to the mold is detected by the output of the mold pressure detection means installed in the mold clamping device, and the torque limit of the mold clamping servo motor is feedback-controlled so that the output becomes the set predetermined value, and the mold thickness is adjusted. Prevent excessive pressure from being applied to the mold during adjustment work.

[Operation] While the toggle link of the toggle mechanism is not fully extended, the mold clamping servo motor is rotated to move the moving platen to the stainless platen side and press both molds together. And since the motor does not maintain the pressed state,
Rotate the mold thickness adjustment servo motor to move the rear platen rearward. At this time, a torque limit is applied to the mold clamping servo motor to control the output torque of the mold clamping servo motor. Thus, as the rear platen continues to move rearward while pressing both molds with the set pressure, the toggle link of the toggle mechanism gradually extends. When the toggle link is about to fully extend, the dynamic characteristics of the toggle link cause a sudden pressure to be applied to the mold. However, this sudden pressure is caused by the strain gauge installed on the tie bar, the drive current value of the mold thickness adjustment motor, the tension of the chain driven by the motor, and the strain gauge installed at the foot of the mold thickness adjustment motor. Since the torque limit applied to the mold clamping servo motor is detected by one of them and feedback-controlled, the force for pressing the mold is held constant.

[Example] FIG. 1 schematically shows a mold clamping device 1 in an injection molding machine used in a first example and a numerical control device 30 that controls the injection molding machine. In this figure, one mold 2 in a mold clamping device 1 is attached to a stationary platen 3, and the other mold 4 is attached to a moving platen 5. Stationary platen 3 has four tie bars 6
(Only one tie bar is shown in FIG. 1.) At the other end of each tie bar 6, a rear platen 7 is provided so as to be movable back and forth with respect to the tie bar 6. Two sets of toggle mechanisms 8.8 are provided between the rear platen 7 and the moving platen 5, and the toggle mechanisms 8, 8 are symmetrical with respect to the axis of the ball screw 9 and have the same configuration. A first link 12 is rotatably attached to the rear platen 7 with a pin, a second link 13 in the form of an abbreviation is rotatably attached to the rear platen 7 with a pin, and a second link 13 is rotatably attached with a pin to the crosshead 10. The first link 12 and the second link 13 are rotatably connected with a pin,
Further, the second link 13 and the third link 14 are pivotally connected to each other so as to be rotatable. Also, crosshead 10
has a female thread formed at its center and is screwed into the tip of the hole screw 9. On the other hand, the rear end side of this ball screw 9 is supported by a bearing part 15 fixed to a through hole provided in the center of the rear platen 7, and a connecting part 16 connects a toggle drive servo motor, that is, a mold clamping servo motor. It is fixed to the shaft 17 of the servo motor Mb.

On the back surface of the rear platen 7, nuts 18 for mold thickness adjustment are provided which are screwed into threaded grooves cut in each tie bar 6, and a sprocket 19 is fixed onto the nuts 18. Furthermore, a chain (not shown) is stretched around this sprocket 19.

The sprocket 19 is rotated by a servo motor for moving the rear platen, that is, a servo motor Ma for adjusting mold thickness. As the sprocket 19 rotates, the nut 18 fixed to the sprocket 19 also rotates, pressing the rear platen 7 and moving the rear platen 7 in the left-right direction in FIG.

Note that Pa is a position detector such as a pulse encoder provided on the servo motor Ma for mold thickness adjustment, and similarly, pb
is a position detector such as a pulse encoder provided on the servo motor Mb for mold clamping.

In this embodiment, as shown in FIG. A strain gauge 22 is attached for this purpose.

The mold clamping device 1 is configured as described above, and the rear platen 7
As described above, is moved left and right on the tie bar 6 by the drive of the mold thickness adjusting servo motor Ma. On the other hand, the moving platen 5 acts to press the mold by driving the mold clamping servo motor Mb. This is because the hole screw 9 is rotated by the rotation of the servo motor Mb, and the crosshead 10 screwed into the hole screw 9 is moved left and right, thereby bending and extending the toggle mechanism 8.

When the moving platen 5 moves on the typer 6 by the rotation of the mold clamping servo motor Mb and presses the mold 4 fixed to the platen 5 against the mold 2 of the stationary platen 3, the reaction force is generated. Since a force acts in the direction of stretching the tie bar 6, the magnitude of this force is detected by a strain gauge, amplified by an amplifier 23, and sent to a numerical control device to be described later.

Reference numeral 30 in FIG. 1 is a block diagram showing an example of a numerical control device (hereinafter referred to as an NC device) constituting a control section of an injection molding machine. (referred to as a CPU) 31, and a CPU 32 for a programmable machine controller (hereinafter referred to as PMC).
The PMC CPU 32 is connected to a ROM 35 that stores sequence programs for various injection molding machines, and the NC CPU 31 is connected to a ROM 34 that stores a management program for overall control of the injection molding machine and an injection molding machine. It is connected via a servo interface 37 to a servo circuit of a servo motor that drives various drive devices of the machine. In addition, in the figure, a servo circuit 36a that drives and controls the mold thickness adjustment servo motor M a and the mold clamping servo motor Mb is shown.
, 36b are shown. Further, 38 is a non-volatile shared RAM having a backup power source, which stores various setting values, parameters, etc. of programs for controlling each operation of the injection molding machine. 33 is a bus arbiter controller (hereinafter referred to as BAC), and the BAC 33 has an NC
CPU31 for PMC and CPU32 for PMC. Shared RAM38
．． Input circuit 40. Each bus of the output circuit 4]- is connected,
An operator panel controller (hereinafter referred to as OPC) 39 that connects the CRT/MD I 43 is connected, and the
The bus to be used is controlled by AC33.

Note that 42 is a RAM used for temporary storage of data during various processing by the NC CPU 31.

The output from the strain gauge 22 attached to the tie bar 6 of the mold clamping device 1 is input to the servo circuit 36b of the NC device 1i30.

FIG. 2 shows a servo circuit 3 installed in the NC device 30 of FIG.
6b, in which Mb is a servo motor for mold clamping, and Pb is an incremental pulse encoder. The servo circuit 36b includes torque limiting means 5.
2 has been added.

When a position command a consisting of a pulse train as a movement amount per unit time is input as a drive command for the servo motor Mb from the servo interface 37 in FIG. 1, this position command a and a detector such as a pulse encoder The difference between the amount of movement of the servo motor Mb detected by Pb is converted into an analog voltage as a speed command value C by a digital-to-analog converter (hereinafter referred to as a D/A converter) 54. Furthermore, speed feedback control is performed, which is
The signal from the detector pb is converted into a voltage by the F/V converter 55, and the voltage V corresponding to the actual speed of the servo motor ~1b is subtracted from the speed command value C, and the difference is the command speed C and the actual speed. The error in V is amplified by an error amplifier 56 and output as a command torque e. That is, this command torque e is output as a voltage corresponding to the current value flowing through the armature of the servo motor Mb. This command torque e is outputted via a buffer amplifier 60, and corresponds to the armature current from a current detector 59 that detects the armature current of the servo motor Mb in order to further improve responsiveness to this command torque e. The difference between the command torque e and the armature current feedback signal f is fed back to the error amplifier 5.
7 is amplified, and the power amplifier 58 amplifies the servo motor M.
b.

On the other hand, a D/A converter 53 converts the torque limit command value g, which is a digital signal from the NC device 30, as a current output, and a current-voltage converter 61 converts it into a voltage Vg corresponding to the command torque limit value g. , from the voltage Vg to the strain gauge 2
The subtracter 63 subtracts the voltage Vs corresponding to the output from the torque limiting means 52 and outputs it to the tie motor D side of the torque limiting means 52 as a torque limiting value.

So, when I was adjusting the mold thickness, the toggle link of the toggle mechanism 8 gradually stretched, and just before it was fully extended,
Moving platen 5 suddenly applies a large force as it moves.
Even if the force is applied to the mold clamping servo motor M, the force is detected via the strainer 22 by the extension of the tie bar 6.
Since the command torque limit value for b is lowered by this force, only a predetermined pressure is applied to the mold 2.4, and application of a large force to the mold 2.4 can be avoided.

Therefore, when the rear platen 7 is moved during mold thickness adjustment, the force pressing against the mold 2.4 becomes large, and a large compressive force is no longer applied to the mold thickness adjustment nut 18. It is possible to avoid suddenly increasing the load on the adjustment servo motor Mb.

As described above, in the first embodiment, the output from the strain gauge is input directly to the servo circuit, but in the second embodiment, it is A/'D converted and sent via the input circuit 40 of the NC device 30. and sends it to the CPU 32 for PMC. That is,
In the block diagram of FIG. 2, a subtracter 63 to which the output from the strain gauge 22 is input is not provided between the current-voltage converter 61 and the diode D. And this PMC
The CPU 32 compares the digitally converted outputs from the strain gauges and provides the result to the servo circuit 36b as a command torque limit value. C for this PMC
In the PtJ 32, processing is performed according to the procedure shown in the flowchart of FIG. First, drive the mold thickness adjustment servo motor Ma and the mold clamping servo motor Mb (step S1), and read the current torque value Tr (step S2).
, then compare this with a preset torque value Ts, and add a gain k (a value of 1 or less) to the difference ΔT (=Ts - Tr).
(step S3), and this value (kΔT) is stored in the register to the value To (this value TO is initially set to "0").
is set to . ) (ΔT to To +), store this as a new value To (ΔT to To←To+) in the register (step S4), and output this as the torque limit value g (step S5), then toggle. It is determined whether the link is in a lock-up state (step S6), and if it is not, the process returns to step 2 and the processes from step 2 onwards are repeated. Further, if it is determined that the toggle link is in the lock-up state, both servo motors M a and M b are stopped, and the process moves to mold clamping force setting processing.

In both the first and second embodiments described above, a strain gauge is provided on the tie bar as a means for detecting the pressure applied to the mold. The pressure applied to the mold may be detected by detecting the drive current value, the tension of the chain driven by the motor Ma, or the output of a strain gauge provided at the foot of the mold thickness adjustment motor.

[Effect of the invention] When performing automatic mold thickness adjustment for an injection molding machine having a toggle-type mold clamping device, the force that presses the mold is not controlled to open by limiting the motor torque, but the force that actually presses the mold is controlled. By detecting this, the pressing force is controlled to a set pressure, so that sudden loads caused by the movement of the toggle link can be absorbed. I wanted to,
Since a large load is not applied to the mold thickness adjustment nut, there is no negative effect on the rear platen drive system.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a mold clamping device in an injection molding machine and a numerical control device for controlling the injection molding machine according to the first embodiment. FIG. 2 is a block diagram showing an example of the servo circuit 36b in the numerical control device shown in FIG. Figure 3 shows
FIG. 7 is a block diagram regarding mold thickness adjustment according to the second embodiment. 1... Mold clamping device in an injection molding machine, 2, 4... Mold, 3... Stationary platen, 5... Moving platen, 6... Tie bar, 7... Rear platen, 8...・Toggle mechanism, 18... mold thickness adjustment nut,
22...Strain gauge, 23...Amplifier, 3o.
- Numerical control device, 36a, 36b... Servo circuit, 5
2...Torque limiting means, Ma, Pa...servo motor for mold thickness adjustment and its position detector, Mb, Pb...servo motor for mold clamping and its position detector. Patent applicant FANUC CORPORATION □−〇

Claims (4)

[Claims] (1) In an automatic mold thickness adjustment method for an injection molding machine having a toggle-type mold clamping device, which is performed by moving the rear platen backward while pressing the mold with the output torque of a mold clamping servo motor, the pressure applied to the mold is is detected by the mold pressure detection means installed in the mold clamping device, and the difference between the command value and the output of the detection means is feedback-controlled as the torque limit value of the mold clamping servo motor, and the pressure applied to the mold is maintained at a predetermined level. An automatic mold thickness adjustment method for an injection molding machine, characterized in that the mold thickness is adjusted by moving a rear platen while limiting the pressure to below. (2) An automatic mold thickness adjustment device for an injection molding machine having a toggle type mold clamping device driven by a mold clamping servo motor, wherein the mold pressure detection means for detecting the pressure applied to the mold is installed in the mold clamping device. A torque limiting means is provided in the servo circuit of the mold clamping servo motor, and the difference between the command value output from the numerical control device and the output from the mold pressure detecting means is determined and outputted to the torque limiting means. An automatic mold thickness adjustment device for an injection molding machine that is equipped with a subtractor to maintain the pressure applied to the mold at a predetermined value. (3) An automatic mold thickness adjustment device for an injection molding machine having a toggle type mold clamping device driven by a mold clamping servo motor, wherein the mold pressure detection means for detecting the pressure applied to the mold is installed in the mold clamping device. A torque limiting means is provided in the servo circuit of the mold clamping servo motor, and the output of the mold pressure detection means is input to a control device via an A/D converter, and the control device receives this input. An automatic mold thickness adjustment device for an injection molding machine that performs feedback control by outputting a torque limit value to the torque limit means so that the output becomes a set value. (4) The mold pressure detection means includes a strain gauge installed on the tie bar, a drive current detection means for the mold thickness adjustment motor, a chain tension detection means, and a strain gauge installed at the foot of the mold thickness adjustment motor. An automatic mold thickness adjustment device for an injection molding machine according to claim 2 or 3, characterized in that the device is any one of the following.