JPH0322288B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an injection molding machine. In particular, the present invention relates to a purge control method for an injection molding machine that uses a servo motor as a drive source for an injection mechanism.

Conventional technology In conventional injection molding machines, the injection mechanism was driven by hydraulic pressure to move the screw in the axial direction to perform injection, so the injection pressure was adjusted by controlling the hydraulic pressure. was completed. On the other hand, an injection molding machine in which an injection mechanism is driven by a servo motor to perform injection has also been developed. When controlling the injection pressure in an injection molding machine that is driven by a servo motor and performs injection, it is necessary to control the output torque of the servo motor. One way to control the torque of a servo motor is to apply a torque limit, which limits the output torque of the servo motor.Generally speaking, when a servo motor is rotated by applying a torque limit, acceleration and deceleration are reduced. Torque limits are sometimes applied, so when accelerating, the speed increases with a gentle rise, but when decelerating, torque limits are applied, so sufficient force may not be generated and the machine may overrun due to inertia, etc. becomes. Figure 3 shows the relationship between the motor current flowing through the armature of the servo motor and the rotational speed of the servo motor when no torque limit is applied.
If it is not applied, the servo motor can be driven to the set position and will not overrun. However, when a torque limit is applied, the motor current I increases to the limit value +
Since it is limited by Ir, −Ir, the speed rises slowly,
It falls slowly even when decelerating. That is, since a torque limit is applied, the deceleration force is weak, and as a result, the motor rotates beyond a set value and overruns. In order to correct this, it is necessary to apply current again in the positive direction (forward direction) and correct the position of the servo motor.

As described above, since it operates when a torque limit is applied, the above-mentioned phenomenon occurs when a torque limit is applied to the servo motor that drives the injection mechanism of an injection molding machine. However, when the molding material is actually injected into the mold for injection molding, the servo motor, that is, the screw, will not overrun due to the reaction force from the molding material. However, when purging is performed, there is no reaction force from the molding material, so as shown in Figure 4, the screw overruns and the tip of the screw collides with the heating cylinder, causing damage to the screw, heating cylinder, nozzle, etc. becomes.

Problems to be Solved by the Invention The present invention aims to provide a purge control system that does not cause screw overrun when purging is performed in an injection molding machine driven by a servo motor.

Means for Solving the Problems In the present invention, a purging operation detection means is provided, and when the purging operation is detected, the screw is moved forward and backward without applying torque restriction.

Function During normal injection molding, torque is limited and controlled by the set injection pressure, but during purging, torque is not limited, so the screw is sufficiently accelerated and decelerated even when there is no resistance from the resin. There is no running.

Embodiment FIG. 1 is a block diagram of an embodiment of the present invention.
M is a servo motor for driving the screw of the injection molding machine to perform injection, P is a detector such as a pulse encoder, 1 is a servo circuit, and the difference from the known servo circuit is that torque limiting means 2 is added. The only difference is that That is, when a position command a composed of a pulse train is input as a drive command for the servo motor M as a movement amount per unit time, this position command a and the movement of the servo motor M detected by a detector P such as a pulse encoder are input. The difference between the quantity b and the
It is converted into an analog voltage as a speed command value c by a converter (referred to as a converter) 4. That is, position command a
If there is a large difference between the movement amount b of the servo motor M from the detector P, a large speed command value c will be output, and if the difference is small and the position command a and the movement amount b approach each other, a small speed command value c will be output. is output as
Furthermore, this servo circuit has speed feedback to improve responsiveness, which is
The signal from the detector P is converted into voltage by the F/V converter 5, and the voltage v corresponding to the actual speed of the servo motor M is subtracted from the speed command value c, and the difference is the command speed c and the actual speed v. The error is amplified by an error amplifier 6 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 M.
In this embodiment, this command torque e is outputted via a buffer amplifier 10 (in a normal servo circuit, this buffer amplifier 10 is not provided, and the command torque e is directly outputted). On the other hand, in order to further improve responsiveness, a voltage f corresponding to the armature current from a current detector 9 that detects the armature current of the servo motor M is fed back, and a feedback signal f of the command torque e and armature current is generated. The error amplifier 7 amplifies the difference, and the power amplifier 8 amplifies the difference, thereby driving the servo motor M.

On the other hand, the torque limiting means 2 converts a torque limiting command value, which is a digital signal from a control device 3 such as a numerical controller, into a current output with a D/A converter 13, and converts it into a command torque limiting value with a current/voltage converter 11. The voltage +Vr corresponding to the command torque limit value is converted by converting the voltage into a corresponding voltage and performing sign conversion by the sign converter 12.
-Vr is input to the buffer amplifier 10 via diodes D1 and D2. The control device 3 is a central processing unit (hereinafter referred to as CPU) for performing overall control.
21. Store control programs, etc.
ROM, used for temporary storage of data, etc.
A memory 22 composed of RAM, a pulse distributor 23 that outputs movement commands to each servo motor (in Fig. 1, only the servo motor M for moving the screw forward and backward) is output, and a manual input device 24. , input/output circuits 25 are interconnected by a bus 26. The manual operation input device 24 is used to input various setting values, etc., and also to select automatic/manual operation switch, and each part of the injection molding machine to be driven during manual operation (for example, mold clamping device, injection unit, screw, etc.). It has a switch and a manual forward and reverse command switch.

Next, the operation of this embodiment will be explained.

First, in the injection cycle during normal automatic operation, a torque limit command is sent from the control device 3 to the D/O via the input/output circuit 25 so as to achieve the target injection pressure.
It is input to the A converter 13 and the diodes D1, D
Limit voltage +Vr, - as torque limit value via 2
Vr is input to the buffer amplifier 10. Then, the position command a is sent to the pulse distributor 23 for injection.
When the speed command value c is input to the servo circuit 1, the D/A converter 4 outputs the speed command value c as a voltage, as described above, and the difference between the voltage c and the voltage v corresponding to the actual speed of the servo motor M. is amplified by the error amplifier 6 and output as a torque command e. This torque command value e is output as a voltage corresponding to the current value to be passed through the armature of the servo motor M. This voltage e is outputted via the buffer amplifier 10, and the electric motor of the servo motor M Detection output f (voltage) from current detector 9 that detects child current
The error amplifier 7 amplifies the difference, which is then amplified by the power amplifier 8, and the servo motor M is driven to move the screw forward and backward to perform the injection operation. on the other hand,
The voltage of the command torque value e from the error amplifier 6 rises and is input via the current-voltage converter 11, sign converter 12, and diodes D1, D2 in response to the torque limit command issued by the control device 3. When the limit voltage exceeds +Vr, -Vr, the diode D1,
D2 is conductive, and the input of the buffer amplifier 10 is at the limit voltage +Vr, -Vr, no matter what value the output e from the error amplifier 6 is above the limit voltage +Vr, -Vr.
Since it is held at Vr, the torque command value is held below this limit voltage. As a result, as shown in FIG. 4, the armature current f(I) of the servo motor M is limited by the limiting voltages +Vr and -Vr and saturates at a constant value.

During normal injection operation, the above-mentioned operation is performed, but when the above-mentioned operation is performed during purging operation, the force from the resin is less, that is, the load is smaller, so the torque limit is ), when the forward movement of the screw is slowed down and stopped, a phenomenon occurs in which the screw overruns and the tip of the screw comes into contact with the heating cylinder, causing damage, as shown in FIG. Therefore, in the present invention, control is performed so that no torque limit is applied during purging, and the operation processing at that time will be explained with reference to the processing flowchart shown in FIG.

When performing purging, use the manual input device 24.
Set the injection molding machine to manual mode and set it to screw movement mode in which the screw moves forward and backward. Therefore, the CPU 21 determines whether these modes are set (steps S1 and S2), and if these modes are set, it determines whether the signal from the nozzle touch detector SE that detects the nozzle touch is off. (Step S3) If the nozzle is not notched in the mold, purging operation processing is possible, so the CPU 21 outputs a signal to turn off the torque limit, and sets the limit voltage +Vr, -Vr. is set to a large value so that the maximum torque of the servo motor M can be output (step S4). Next, manual input device 2
4, it is determined whether a movement command has been input (step S5), and if a movement command has been input, the movement command is output to the servo circuit 1 via the pulse distributor 23 as described above, and the servo motor M is activated. drive (step S6). In this case, since no torque limit is applied, the servo motor M can generate the maximum torque, and when the screw moves to the injection end position and stops (this process is the same as the conventional one) Therefore, it is omitted in the flowchart in Figure 2).
The screw will stop at the set position as shown in FIG. 3 without overrunning as shown in FIG. 4. Also, if no movement command is input (step S5), the torque limit
is turned on to return to the set value (step S7), and this purging process ends.

Effects of the Invention As described above, in an injection molding machine that performs injection control with a torque limit, the torque limit is not applied during purging. This lack of resistance prevents the screw from overrunning.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the main part of an embodiment of the present invention, Fig. 2 is an operation flowchart of the same embodiment, and Fig. 3 is a diagram showing the operation of the servo motor when the servo motor is driven without applying a torque limit. Operation diagram,
FIG. 4 is an explanatory diagram of the operation when a torque limit is applied to the servo motor, which is normally performed. M... Servo motor, P... Pulse encoder, 1... Servo circuit, 2... Torque limiting means, 3... Control device, 9... Current detector, 10... Buffer amplifier, 11... Current-voltage converter, 12... code converter.

Claims (1)

[Claims] 1. An injection device that has a servo motor that drives an injection mechanism and a torque limiting means that limits the output torque of the servo motor, and that during a molding injection operation, the torque is limited by the torque limiting means according to a command from a control device to perform the injection operation. A purge control method for an injection molding machine, wherein the molding machine is provided with a purging operation detection means, and when a purging operation is detected, the torque restriction by the torque limiting means is canceled by a command from the control means to perform a purge operation.