JPH0448610B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION The present invention relates to a control device for an injection molding machine used for resin injection molding and the like.

Conventional configuration and its problems Traditionally, the injection speed of injection molding machines has been controlled by
There are an open control method using a flow rate regulating valve, a feedback control method using a flow rate regulating valve and a speed sensor, etc., and the latter has been used when accuracy is required.

Hereinafter, a conventional speed control method for an injection molding machine will be explained with reference to the drawings.

FIG. 1 is a block diagram showing a conventional speed control method for an injection molding machine. In FIG. 1, 1 is a heating cylinder for heating and melting the resin, 2 is a screw for kneading and injecting the resin, 3 is a speed sensor that converts the speed of the screw 2 into an electric signal, 4 is a speed signal from the speed sensor 3, 5 is a speed command signal, 6 is a feedback controller that compares the speed signal 4 and speed command signal 5 and performs a feedback calculation, 7 is an amplifier that amplifies the signal from the feedback controller 6, and 8 is a control output from the amplifier 7. signal,
9 is a proportional electromagnetic hydraulic flow control valve; 10 is an injection cylinder whose piston is connected to the screw 2;

In the injection molding machine configured as above,
The speed of the screw 2 is converted into an electrical signal by a speed sensor 3 such as a potentiometer or tachogenerator, and is inputted as a speed signal 4 to a feedback controller 6. The speed command signal 5 is given to the other input of the feedback controller 6, and the difference between the speed command signal 5 and the speed signal 4 is calculated inside the feedback controller 6. PID calculation processing) is performed, and as a result of the processing, a control output signal 8 is output, and this control output signal 8
is applied to the proportional electromagnetic type hydraulic flow control valve 9 to apply a driving force to the injection cylinder 10, and the speed of the screw 2 is controlled to be a speed corresponding to the speed command signal 5.

However, in the above method, if the responsiveness of the feedback controller 6 to changes in the speed command signal 5 after the screw 2 has already started to move is increased (the sensitivity of the PID control is increased),
When the screw 2 starts moving from a stopped state, that is, when it starts, the sensitivity becomes too high, and overshoot may occur in the speed change at the time of start, or it may take a long time before the speed stabilizes due to the vibration of the speed change. It takes time. Furthermore, if the sensitivity of the feedback controller 6 is made to satisfy the characteristics at startup (eliminating overshoot, etc.), the sensitivity of the feedback controller 6 will become too low, and the response to changes in the speed command signal after startup. This has the disadvantage of causing deterioration in performance (increased time to reach the target speed).

Purpose of the Invention In view of the above-mentioned drawbacks, the present invention solves the problem of instability in speed change (overshoot, etc.) when starting the screw without impairing responsiveness to changes in the speed command signal when the screw is already in operation. An object of the present invention is to provide a control device for an injection molding machine that can control

Structure of the Invention In order to achieve this object, the control device for an injection molding machine of the present invention includes, in addition to the components described in the conventional example, a speed detection unit that detects the speed of the injection cylinder, and a settable bias signal. and a switch operated by the speed detecting section, or a digital computer having processing procedures corresponding to these switches.

With this configuration, in the present invention, when the screw starts from a stopped state, when a speed command signal is given from the outside, the injection cylinder is first controlled to open by the settable bias signal by the action of the speed detection section, At the same time, when the injection cylinder starts to move due to the hydraulic pressure, this is detected by the speed detection section, and the switch is switched and the feedback controller starts feedback calculation, thereby shifting from open control to feedback control. At this time, the mechanical system has already started to move, and the effects of static friction and the time for the hydraulic pressure to rise to the injection cylinder, which are the differences in the characteristics of the mechanical system at startup and after startup, have ended, and the feedback controller The response of the mechanical system to the control output signal is already close to the characteristics when it is operating, and the sensitivity of the feedback controller is set to the value with respect to changes in the speed command signal when it is already operating. be able to.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a block diagram showing a method of controlling an injection molding machine in one embodiment of the present invention. In Fig. 2, 1 is a heating tube, 2 is a screw, 3 is a speed sensor, 4 is a speed signal, 5 is a speed command signal, 6 is a feedback controller, 7 is an amplifier, 8 is a control output signal, 9 is a proportional electromagnetic The hydraulic flow control valve 10 is an injection cylinder, and the above structure is the same as that shown in FIG. Furthermore, 11 is a speed detection unit;
12 is a switch operated by the speed detection unit 11; 13 is a bias signal during open control; 1
4 and 15 are contacts of the switch 12, 14 is connected to the bias signal 13, and 15 is connected to the output of the feedback controller 6. 16 is a reset signal for the feedback controller 6.

Regarding the injection molding machine configured as above,
The operation will be explained below.

In FIG. 2, the moving speed of the screw 2 is converted into an electrical signal by a speed sensor 3, and is input as a speed signal 4 to a feedback controller 6 and a speed detecting section 11. The speed command signal 5 is also input to the feedback controller 6 and the speed detection section 11. The feedback controller 6 has a feedback control function (usually controlled by PID calculation) to control the load so that the speed signal 4 becomes equal to the speed command signal 5.

First, when the speed command signal 5 comes from the stopped state, since the screw 2 is not moving yet at this time, the speed signal 4 has a signal indicating the stopped state, and the speed detection unit 11 determines that it is operating at startup. switch 12
is operated to the contact 14 side, the feedback loop is cut off, and the bias signal 13 is inputted to the amplifier 7 to create an open control state, and the proportional electromagnetic type hydraulic flow control valve 9 is operated and a reset signal 16 is sent to the feedback controller 6. and stop the operation. When the hydraulic oil pressure reaches the injection cylinder 10, overcomes the static friction, and the screw 2 begins to move in the desired direction, the speed signal 4 from the speed sensor 3 increases. The speed detection unit 11 is
When this speed signal 4 exceeds the threshold,
The switch 12 is operated to the contact 15 side to form a feedback loop, and the reset signal 16 to the feedback controller 6 is turned off to start feedback control. Thereafter, speed control is performed so that the feedback controller follows changes in the speed command signal 5 as in the past. Note that the bias signal 13
The optimum value is selected and fixed based on the differences between individual injection molding machines or the setting speed of the first injection speed. Further, the feedback controller 6 is reset by connecting a resistor in parallel to the integrating capacitor of the internal PID calculating section to disable the integrating function.

The above operation is shown in a timing diagram as shown in FIG. 3. That is, the speed command signal 6 is input at timing _t1 , the switch 12 is connected to the contact 14 by the operation of the speed detection section 11, and the bias value is set to the open control signal as shown in A in FIG. 3d in the control output signal 8. is output. When the screw 2 begins to move in the desired direction and exceeds the threshold B in FIG. 3b (timing t ₂ ), the switch 12 closes the contact
4 to contact 15, and thereafter the speed is controlled by feedback control. Note that timing _t3 indicates the time at which the speed command signal 5 changes.

FIG. 4 is a block diagram showing a method of controlling an injection molding machine in a second embodiment of the present invention. In FIG. 4, the same numbers as in FIG. 2 indicate the same parts.
A digital computer 17 has a processing procedure for detecting the speed and switching the control state from open control to feedback control.

In the embodiment shown in FIG. 4, the digital computer 17 includes the speed detection section 1 shown in FIG.
1, a switch 12, contacts 14 and 15, a bias signal 13, and a reset signal 16. This is represented by a flowchart as shown in FIG.

The operation of digital computer 17 is as follows. First, in the stopped state, the signal to the proportional electromagnetic hydraulic flow control valve 9 is set to 0 to prevent the screw 2 from moving (step 18). When the speed command signal 5 is input (step 19), the speed signal 4 from the speed sensor 3 is checked (step 20) until a speed equal to or higher than the threshold value in the same direction of movement as the speed command signal 5 is detected. (Step 21), and a bias signal is output under open control without performing feedback calculation (Step 22). Once the speed is detected, feedback control is performed by comparing the speed signal 4 and the speed command signal 5 and performing a feedback calculation (step 23).

As described above, according to the embodiment of the present invention, a bias signal is first output in the open control state to measure the difference in responsiveness between the injection cylinder startup and the mechanical system after startup, and this signal allows the screw to reach the target. By detecting that the robot has begun to move in the direction and switching to feedback control, the responsiveness (sensitivity) of the feedback controller can be adjusted to the state after startup, and there is no overshoot even at startup. , you can get good responsiveness.

Effects of the Invention As described above, the present invention provides a bias signal to the proportional electromagnetic hydraulic flow control valve in an open control state when starting the injection cylinder from a stopped state, so that the bias signal is applied in the same direction as the speed command signal of the injection cylinder. When movement is detected, the entire feedback system is controlled by switching to feedback control using the speed signal from the speed sensor and the speed command signal.
This means that control can be performed in a state where the speed is always high and responsiveness is good, and the practical effect is great because it is not affected by increases in hydraulic pressure at startup, friction when it is stationary, etc.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional injection molding machine control device, FIG. 2 is a block diagram of an injection molding machine control device according to an embodiment of the present invention, and FIG. 3 is an injection molding machine according to an embodiment of the invention. FIG. 4 is a block diagram of the control device for an injection molding machine according to another embodiment of the present invention; FIG. 5 is a diagram showing the control device for an injection molding machine according to another embodiment of the present invention. This is a flowchart of a digital computer. 1...Heating tube, 2...Screw, 3...Speed sensor, 4...Speed signal, 5...Speed command signal,
6... Feedback controller, 7... Amplifier, 8... Control output signal, 9... Proportional electromagnetic hydraulic flow control valve, 10... Injection cylinder, 11...
...Speed detection unit, 12...Switch, 13...Bias signal, 14 and 15...Switch contact, 1
6... Feedback controller reset signal, 17... Digital computer.

Claims (1)

[Scope of Claims] 1. A speed sensor that converts the moving speed of the injection cylinder into an electric signal, a speed detection unit that detects the speed signal from the speed sensor, and a speed command signal and the speed signal from the speed sensor. a feedback controller that receives each of the speed detection signals from the speed detection section as an input signal; a proportional electromagnetic type hydraulic flow control valve controlled by the control output signal of the feedback controller; and the proportional electromagnetic type hydraulic flow control valve. The injection cylinder is connected to the injection cylinder, and when the injection cylinder is started, the speed detection section resets the feedback controller, and at the same time, a predetermined electrical bias is applied to the proportional electromagnetic hydraulic flow control valve, so that the injection cylinder When the speed detecting section detects movement in the same direction as the speed command signal, the feedback controller is set by the speed detecting section, and the output of the feedback controller is applied to the proportional electromagnetic type hydraulic flow control valve. A control device for injection molding machines. 2. The control device for an injection molding machine according to claim 1, wherein the feedback controller and the speed detection section are configured as a digital computer.