JPH0471697B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a back pressure control device for an electric injection molding machine equipped with an injection screw or an injection plunger.

[Conventional technology]

An example of a conventional back pressure control device for an electric injection molding machine is disclosed in Japanese Patent Publication No. 31221/1983.

In this electric injection molding machine, the rotational motion by the electric motor is converted into linear motion through a drive mechanism composed of screws and nuts, and this moves the injection screw or injection plunger (hereinafter referred to as injection screw, etc.) back and forth. ing. In addition, a back pressure control device detects back pressure by detecting the reaction force of an injection screw or the like due to material supply during the metering process with a load sensor, or by detecting the molten resin pressure with a resin pressure sensor. The device controlled the motor using a feedback control circuit that uses the signal as a feedback signal and a motor control device to control the back pressure by feedback control.

[Problem that the invention seeks to solve]

In such a conventional back pressure control device, if the detected value is smaller than the command value of back pressure, the motor is controlled in a direction to increase the back pressure, so that the injection screw or the like moves forward.

In either case, the retraction force during the plasticizing process in the injection screw of an in-line screw type injection molding machine or the injection plunger of a pre-plastic type injection molding machine is generated as the plasticized molten resin accumulates in the heating cylinder. It is something that occurs.

Therefore, at the start of metering, the amount of plasticized molten resin increases at an accelerated rate and works to move the injection screw, etc. in the backward direction, and the back pressure control device causes the amount of molten resin to match the back pressure command value. Since the motor for moving the injection screw back and forth is controlled in the forward direction of the injection screw, that is, in the direction of increasing back pressure, the injection screw moves forward. As a result, the back pressure became larger than the set value, vibration occurred, and it took time to stabilize, making it impossible to perform stable plasticization.

In addition, in an in-line screw type injection molding machine equipped with an open nozzle, when measuring with the nozzle separated from the mold at the start of molding, the detected value is smaller than the back pressure command value, so the injection screw If the machine moves forward and reaches the end of its stroke, the injection screw may be damaged, making it necessary to prepare a separate means to prevent damage to the machine. Furthermore, since the molten material flows out from the nozzle, even if the injection screw moves forward, the back pressure cannot reach the command value, making metering uncertain.

If the back pressure is set low for this measurement, the injection screw will move backward while rotating, but the difference from the back pressure during molding will be too large, and the amount of resin measured will be significantly smaller. Therefore, it was necessary to perform operations such as increasing the initial measurement value.

SUMMARY OF THE INVENTION An object of the present invention is to provide a new back pressure control device for an electric injection molding machine that has good operability and can perform stable metering by preventing wide fluctuations in back pressure during the metering process.

[Means to solve the problem]

The present invention for the above purpose includes a load sensor that detects the reaction force of an injection screw or the like or a resin pressure sensor that detects the pressure of molten resin on the nozzle side of the injection screw or the like, and a back pressure detection signal detected by these sensors and a back pressure sensor. A back pressure feedback control circuit that calculates and operationally amplifies the error with the back pressure command signal of the pressure setting device and outputs a motor control signal for forward and backward movement of the injection screw, etc., and is connected to the output side of the back pressure feedback control circuit. a speed limiter circuit that limits the forward movement of the injection screw, etc., and a forward/reverse motor that controls the rotation speed of the forward/reverse motor of the injection screw, etc. according to the magnitude of the control signal for the forward/reverse motor of the injection screw, etc. and a motor speed control device.

[Effect]

The back pressure feedback control circuit is equipped with a speed limiter circuit that limits the forward movement of the injection screw, etc. During the metering process, the injection screw, etc. can only move to either stop or move backward, and the electric motor is forced to move the injection screw, etc. Never moved forward.

〔Example〕

FIG. 1 is a block diagram showing one embodiment of the back pressure control device of the present invention in an electric injection molding machine equipped with an in-line screw type injection device.

The reaction force of the injection screw 1 is detected by the load sensor 2, and the back pressure during the metering process is detected.

The forward and backward movement of the injection screw 1 is converted into rotational movement by the screw shaft 3, and the injection motor 4 also serves as the electric motor for moving the screw forward and backward, which controls the rotational speed and controls the back pressure during the metering process. , the electric motor 4 consists of a servo motor with a rotation speed detector.

The signal detected by the load sensor 2 is
It is amplified by the amplifier 5 and becomes a back pressure detection signal.
The detection signal inputted to the back pressure feedback control circuit 6 and the back pressure command signal set by the back pressure setting device 7 are compared and calculated by the back pressure feedback control circuit 6, and a motor control signal for forward and backward movement of the screw is output. be done. The control signal is also input to the speed limiter circuit 8.

As shown in FIG. 2, the speed limiter circuit 8 is composed of an operational amplifier 81 and a diode 82, and the + side of the operational amplifier input is grounded.
When the point b (output of the speed limiter circuit) of the speed limiter circuit 8 is at a positive potential, the + point of the operational amplifier input is grounded and at zero potential, so a current flows through the diode 82 to the point a, which is the output point of the operational amplifier 81. The operational amplifier operates so that the current flows and the potential at point b becomes 0.

If the above point b has a negative potential, the operational amplifier operates so that the potential at point a becomes 0 potential, but when point a
The potential is higher than point b and a due to diode 82.
Since the flow of current is blocked at point b, the potential at point b does not change.

In this way, the speed limiter circuit 8 is limited so that when the input voltage is negative, the input voltage is output as is, and when the input voltage is positive, OV is output.

Therefore, the output of the back pressure feedback control circuit 6 becomes a screw motor control signal for forward and backward movement of the screw, which is limited by the speed limiter circuit 8 so that no positive voltage is output, and is input to the electric motor speed control device for forward and backward movement of the screw. The electric motor speed control device for the forward and backward movement of the screw is 0 of the electric motor control signal for the forward and backward movement of the screw.
Or, depending on the magnitude of the negative voltage, the rotational speed of the electric motor for forward and backward movement of the screw (injection screw forward and backward movement speed)
In this embodiment, when the control signal is negative, it acts in the direction of moving the injection screw backward.

As mentioned above, when the back pressure detection signal value is smaller than the back pressure command value, the injection screw is controlled to stop, and when it is larger than the back pressure command value, the injection screw is controlled to move in the backward direction. Feedback control is performed so that the signal value and back pressure command value match, so at the start of the metering process, the screw remains in a stopped state until the molten resin to be plasticized accumulates and reaches the back pressure set value. Since the back pressure is controlled to the set value, the back pressure smoothly matches the set value, allowing stable plasticization.

In the illustrated embodiment, the back pressure is detected using the reaction force at the screw, but the back pressure may also be detected by attaching a resin pressure sensor to the nozzle portion.

In addition, in the embodiment of the present invention, operational amplifiers are used for both the feedback control circuit and the speed limiter circuit, but both the back pressure detection signal and the back pressure command signal are changed to digital signals by an A/D converter, and the CPU, It is also possible to digitally perform calculations using a feedback control device using a microprocessor consisting of RAM, POM, etc., then convert the signal to an analog signal using a D/A converter, and then output the electric control signal for forward and backward movement of the screw. Needless to say.

Furthermore, the present invention can also be implemented in an injection device in which one electric motor is switched between injection and screw rotation drive using a clutch, and is also equipped with a separate back pressure motor, and a pre-plastic injection device equipped with a pre-plasticizing device can be used. Since the present invention can be implemented in the same manner in a metering process using an injection plunger, the present invention is not limited to the electric injection device equipped with the illustrated injection screw.

〔Effect of the invention〕

As described above, the present invention provides a back pressure control device for an electric injection molding machine motor using back pressure feedback control, which includes a speed limiter circuit that sets the value of the motor control signal to 0 when the detected back pressure value is lower than the command value. Therefore, the injection screw etc. will not move forward during the metering process. As a result, the back pressure control characteristics have been improved, making it possible to stably perform high-precision metering, and in the case of in-line screw type injection molding machines, the injection screw will not reach the stroke end. Therefore, it is possible to prevent damage to the screw due to forward movement.

[Brief explanation of the drawing]

The drawings show one embodiment of the invention.
The figure is a block diagram of a back pressure control device in an in-line screw electric injection molding machine, and FIG. 2 is a speed limiter circuit diagram. 1...Injection screw, 2...Load sensor, 3
... Screw shaft, 4 ... Injection motor, 5 ... Amplifier, 6 ... Back pressure feedback control circuit, 7 ...
Back pressure setting device, 8...Speed limiter circuit, 81...
Operational amplifier, 82...Diode, 9...Screw forward and backward movement motor speed control device.

Claims (1)

[Scope of Claims] 1. The forward and backward movement of the injection screw is converted into rotational motion, and the rotational speed is controlled by an electric motor for forward and backward movement of the screw, thereby commanding the back pressure of the screw during the process of measuring the molding material as the screw rotates. In the back pressure control device of an electric injection molding machine equipped with an injection device that performs feedback control to match the injection value, a load sensor that detects the reaction force of the injection screw or a resin pressure sensor that detects the molten resin pressure on the nozzle side of the injection screw is used. sensors, and a back pressure feedback control circuit that calculates and operationally amplifies the error between the back pressure detection signals detected by these sensors and the back pressure command signal of the back pressure setting device, and outputs a motor control signal for forward and backward movement of the screw. , a speed limiter circuit connected to the output side of the back pressure feedback control circuit to limit the forward movement of the injection screw, and a speed limiter circuit that controls the rotational speed of the motor for forward and backward movement of the screw according to the magnitude of the motor control signal for forward and backward movement of the screw. 1. A back pressure control device for an electric injection molding machine, characterized in that it is equipped with a motor speed control device for controlling the forward and backward movement of a screw. 2. The back pressure control device for an electric injection molding machine according to item 1, characterized in that the device includes an injection plunger in place of the injection screw.