JP2007021888A - Injection molding machine and injection shaft controlling method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable to stably generate a desired injection speed even in the injection molding condition using a small stroke and a high speed and perform a stable injection molding. <P>SOLUTION: An injection shaft controlling method for an injection molding machine is provided, which, at the time of performing the injection control of the injection process, compares a detected value of the injection speed with a set value and controls the injection shaft so that the deviation becomes zero. The method performs the feedback compensation in response to the speed deviation so that the deviation of the injection speeds becomes zero and performs the feedforward compensation so as for the motor torque to be generated which corresponds with the loading torque estimate that is presumed by the loading torque observer. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an injection molding machine driven by a servo motor and a method for controlling an injection shaft thereof.

  The injection shaft of an injection molding machine that uses an electric motor (servo motor) as the drive mechanism is mainly controlled when the injection speed is controlled (injection process) and when the injection pressure is controlled (pressure holding process and back pressure control). ). The injection speed is controlled by providing a speed sensor for detecting the rotation speed of the injection motor and performing feedback control on the injection speed set value based on the detected value.

  The injection pressure is controlled by detecting the pressure by providing a resin pressure sensor at the load cell or nozzle tip for detecting the reaction force applied to the injection screw, and performing feedback control on the injection pressure set value based on the detected value. It is made by. (For example, refer to Patent Document 1 below).

  As shown in FIG. 3, in the conventional control device, when controlling the injection pressure, the detected value obtained from the load cell 62 that detects the pressure acting on the screw 61 and the holding pressure setting device 63 or the back pressure setting device 64. A given set value is compared by a comparator 65, and the deviation is supplied to a pressure compensation circuit 68 comprising a pressure compensator 66 and an amplifier 67 to obtain a drive control signal, and this drive control signal is supplied to an injection motor drive unit 69. In addition, a feedback control system that controls the deviation to be zero is provided.

In addition, when controlling the injection speed, the detection value obtained from the speed detector 102 (tachometer, pulse generator, etc.) for detecting the rotational speed of the injection motor 71 that injects the screw or drives it in the light direction and the injection speed setting device. A set value given from 100 is compared by a converter 101, and the deviation is supplied to a speed compensation circuit 105 comprising a speed compensator 103 and an amplifier 104 to obtain a drive control signal, and this drive control signal is supplied to an injection motor drive unit 69. And a feedback control system for controlling the deviation to be zero.
Japanese Patent Laid-Open No. 1-263021

  In recent years, the need for thin molded products has increased, and the injection speed has been increased and the injection time has been shortened. In particular, the injection process is completed in a few hundred ms at high speed. In such a case, the pressure change during injection also changes greatly within a few hundred ms, and this pressure change becomes a disturbance to the injection motor, which causes the speed of the injection motor, that is, the injection speed to fluctuate.

  In the control method of the control device shown in FIG. 3 described above, the detected value obtained from the speed detector 102 for detecting the rotation speed of the injection motor 71 and the set value given from the injection speed setting device 100 are compared by the converter 101, The deviation is supplied to a speed compensation circuit 105 including a speed compensator 103 and an amplifier 104 to obtain a drive control signal, and this drive control signal is supplied to the injection motor drive unit 69 to control the deviation to be zero. By performing the feedback control, the injection speed is controlled so as not to fluctuate with respect to the disturbance.

  However, since the injection speed becomes high and the injection time becomes short, the change of the disturbance becomes high. Therefore, when trying to suppress the speed fluctuation with the control configuration as shown in FIG. For this purpose, it was necessary to make the mechanical drive system very rigid.

  As described above, according to the present invention, a change in speed is caused by an increase in injection pressure change due to an increase in injection speed and a reduction in time, and a speed compensator (feedback compensator) is used to suppress the fluctuation. It was made to solve the problem that the drive mechanism with high mechanical rigidity had to be increased for that purpose, and to improve the control algorithm without improving the mechanical rigidity, the high-speed injection was achieved. It is an object of the present invention to provide a corresponding injection molding machine and an injection axis control method thereof.

  An object of the present invention is to provide a control method for an injection molding machine that solves the problems existing in the above-described conventional technology, and is achieved by the following control method.

  The control method of an injection molding machine according to the present invention is a control device and method for comparing the detected values of injection speed during injection control in an injection process and performing control so that the deviation becomes zero, according to the speed deviation. A feedback compensator that operates and a feedforward compensator that operates according to a load torque estimated value of a load torque observer are provided.

  That is, the pressure fluctuation during the injection process acts as a disturbance (load torque) to the injection motor, and changes the injection speed, so that a motor torque corresponding to the magnitude of the load torque detected during the injection process is generated. Thus, by providing the feedforward compensator, it is possible to suppress the speed fluctuation during the injection process.

At the time of injection speed control in the injection process, the change in the injection pressure becomes a factor of fluctuations in the injection speed. This is shown by the following equation of motion.
τ _M = Jdω / dt + τ _L (1)
τ _M : Motor torque τ _L : Load torque (injection pressure)
J: Injection shaft inertia moment (motor shaft conversion)
ω: Motor rotation speed (equivalent to injection speed)

In equation (1), when the motor speed is constant, that is, when dω / dt = 0,
τ _M = τ _L
Is established.
However, if the load torque changes suddenly,
τ _M ≠ τ _L
So that
dω / dt ≠ 0
And
Speed fluctuation occurs.

Therefore, in the present invention, the load torque τ _L is estimated by the load torque observer, and an amount corresponding to the load torque τ _L applied as a disturbance to the injection shaft is fed forward to the motor torque τ _M , thereby changing the τ _L. Since the influence can be canceled theoretically, the speed fluctuation can be suppressed. Therefore, since it is not necessary to increase the gain of the speed compensator more than necessary, it is possible to obtain performance corresponding to high-speed injection molding without improving the mechanical rigidity.

  As described above, according to the present invention, there is an effect that the injection speed does not fluctuate greatly even if the load pressure changes suddenly during the injection process. As a result, a desired injection speed can be stably generated even under a high-speed injection molding condition with a small stroke, so that the effect of enabling stable injection molding is achieved.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram of an electric injection molding machine according to an embodiment of the present invention. Hereinafter, a description will be given based on FIG.

  The screw 2 rotates inside the cylinder 1, kneads and melts (plasticizes) the resin, and pushes out (injects) the melted resin from the tip of the cylinder. In FIG. 1, a drive mechanism for rotating the screw is omitted.

  When the servo motor 9 rotates, the screw injection operation rotates the drive pulley 8 directly connected to the servo motor, and the driven pulley 7 coupled to the drive pulley 8 by the timing belt 11 rotates. The threaded portion 4 of the ball screw is coupled to the driven pulley, and when the threaded portion 4 of the ball screw rotates, the nut portion 6 of the ball screw moves linearly. The thrust in the linear direction generated in the nut portion 6 acts on the slide plate 5, and the slide plate transmits the thrust for moving the screw in the injection direction via the pressure sensor.

  On the other hand, the drive control of the injection shaft is performed by controlling the rotation speed of the servo motor 9 with a servo controller.

  An injection speed command is given to the servo controller from a command generation controller (host controller) 25 at the upper level, while a pulse corresponding to the rotational displacement of the motor is sent from the pulse generator 10 attached to the rotation shaft of the servo motor 9. Generated and converted into a speed detection signal by the speed signal processor 16.

  The adder 18 calculates the difference (speed deviation) between the injection speed command given from the command generation controller 25 and the speed detection signal, and inputs it to the speed controller 17. The speed controller 17 performs an operation such as proportional / integral or differentiation in accordance with the input speed deviation, and generates a current command for the servo motor 9.

  The current command and the current detection value from the current sensor 14 attached to the power line of the servo motor 9 are input to the adder 20.

  The load torque observer (load torque observer) 12 estimates the load torque based on the speed detection value and the current detection value, and generates a motor command according to the estimated load torque. Input to 20.

As a specific observer configuration method, various other configuration methods are conceivable. Basically, the observer is configured by arithmetic means as shown in FIG. In FIG. 2, d / dt is a differential operator, J is movable unit moment of inertia, K _T is a torque constant, K _G feedforward gain, the tau _L shows a load torque estimate.

  Returning to FIG. 1, the adder 20 calculates the current deviation by adding the current command from the speed controller 17 and the current command from the observer 12 and subtracting the detected current value. The current controller 19 generates a voltage command for the voltage source inverter 15 by performing calculations such as proportionality, integration, and differentiation with respect to the calculated current deviation. The voltage source inverter 15 amplifies the voltage command given from the current controller 19 and generates a voltage for driving the servo motor 9. Thus, the rotation of the servo motor 9 is controlled at a speed that matches the speed command from the host controller, and the speed of the injection shaft coupled to the servo motor is controlled.

It is a block diagram which shows embodiment of this invention. It is a block diagram which shows the calculating part in embodiment of this invention. It is a block diagram which shows the structure of the conventional injection molding machine.

Explanation of symbols

  1 cylinder, 2 screw, 3 pressure sensor, 4 ball screw, 5 slide plate, 6 ball screw, 9 servo motor, 10 pulse generator, 11 timing belt, 12 observer (load torque observer), 14 current sensor, 15 voltage type inverter, 16 Speed signal processor, 17 Speed controller, 18, 20 Adder, 19 Current controller, 25 Command generation controller (high-order controller).

Claims (2)

In the injection molding machine that compares the detected value of the injection speed with the set value at the time of injection control in the injection process and performs control so that the deviation becomes zero,
A feedback compensator that operates so that the deviation of the injection speed becomes zero according to the speed deviation;
A feedforward compensator that operates to generate a motor torque according to a load torque estimated value of a load torque observer;
Injection molding machine. An injection shaft control method for an injection molding machine that compares a detected value and a set value of an injection speed at the time of injection control in an injection process, and controls the injection shaft so that the deviation becomes zero,
An injection molding machine that performs feedback compensation so that the deviation of the injection speed becomes zero according to the speed deviation, and performs feedforward compensation so that the motor torque according to the estimated load torque estimated by the load torque observer is generated. Injection axis control method.

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