JPH0231622B2 - SHASHUTSUSOKUDOSEIGYOHOHO - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an injection speed control method in a die casting machine, an injection molding machine, etc.

[Prior art]

FIG. 1 is a diagram schematically showing an injection cylinder and an injection speed control mechanism of a die-casting machine that is considered to be standard. In the figure, a coupling 3 is attached to the piston rod 2 of the injection cylinder 1.
An injection plunger 4 for injecting molten metal into a mold (not shown) is connected thereto. Further, a striker 5 is connected to the piston rod 2 or the coupling ring 3, and the striker 5 controls a limit switch 6a provided at the retraction limit position of the piston rod 2, and a limit switch 6a provided at a position corresponding to the point at which the injection speed is changed. 6b to 6d, and a limit switch 6e provided at the forward end position of the piston rod 2 are turned on and off. On the other hand, the output signals of the limit switches 6a to 6e are input to a signal detector 7. The above-described striker 5, limit switches 6a to 6e, and signal detector 7 constitute a position detector for the injection plunger 4.

The output signal of the signal detector 7 is input to the control signal generator 8, and the control signal generator 8 detects whether the injection stroke of the injection plunger 4 has reached the injection speed change point based on this input signal. .
When the injection stroke reaches the injection speed change point, the control signal generator 8 generates an analog control signal corresponding to the target injection speed preset in the speed setting device 9, and this control signal is used to control the servo control. By supplying the valve 10, its opening degree is controlled. The servo valve 10 is connected to the injection cylinder 1 by a hydraulic circuit 11, and the amount of liquid introduced into the injection cylinder 1 is adjusted according to the opening degree of the servo valve 10. Thereby, the moving speed of the injection plunger 4 connected to the piston rod 2 in the injection cylinder 1 is controlled in accordance with the opening degree of the servo valve 10. That is, the injection speed is controlled to the target speed by a control signal generated at each change point.

FIG. 2 is a graph showing the change pattern of the injection speed that changes due to such control, with the horizontal axis representing the injection stroke st and the vertical axis representing the injection speed v. At injection stroke a where injection starts _at
In the injection stroke b where the limit switch 6b is turned on, the speed is changed toward the target speed v ₂ , and similarly in the injection strokes c and d where the limit switches 6c and 6d are turned on, the target speed v ₃ and v ₄ are changed.
This shows an example of changes toward usually,
The area where the speed reaches from v ₀ to v ₂ is called the sleeve filling area, the area where v ₂ is the gate passing area, and the area from v ₂ to v ₄ and returning to v ₀ is called the cavity filling area. .

By the way, in such an injection speed control mechanism, from the time when the control signal corresponding to the target speed starts to be generated until the injection speed actually starts to change, there are many factors such as the inertia of the mechanical parts and the hydraulic circuit 11, the compressibility of the hydraulic fluid, etc. There is a certain delay time due to Therefore, in consideration of this delay time, the control signal generation start timing, that is, the limit switches 6a to 6
It is necessary to adjust the installation position of e. Therefore, if the installation position is not adjusted, the injection speed change pattern in the cavity filling area will become as shown in Figure 3, and the injection process will end before the final speed _v4 is reached. There is.

To solve this problem, a control pulse train is used as a control signal, and this control pulse train drives a pulse motor to control the opening degree of the flow rate control pulse, thereby increasing the accuracy of the control operation. A method has been proposed in which the installation positions of the limit switches 6a to 6e are adjusted with due consideration to the delay time.

In such a method, the velocity is reduced in sections where the velocity gradient is relatively large, for example in the cavity filling region.
A situation may arise in which two limit switches must be placed in close proximity to change the speed from v ₂ to v ₃ and from v ₃ to v ₄ respectively.

However, if the two limit switches are placed too close together, the control pulse trains pv 3 and ₂ for changing the speed from v ₂ to v ₃ and from speed v ₃ to v ₄ , respectively,
As shown in FIG. 4, pv ₄ may overlap by Δt time. Therefore, control pulse train PV ₄ is normally given priority in such a case, but conventionally, control pulse train PV ₃ was given priority to drive the servo valve without considering the frequency difference between control pulse trains PV ₃ and PV ₄ . Therefore, if the frequency difference between the two pulse trains PV ₃ and PV ₄ is large, the pulse motor will step out of step, resulting in an uncontrollable state.

[Object and structure of the invention]

The present invention has been made to solve these drawbacks, and its purpose is to reliably chain the drives of pulse motors even when control pulse trains generated at adjacent speed change points overlap,
An object of the present invention is to provide an injection speed control method that can reliably complete all injection processes as scheduled.

For this reason, the present invention provides a method for driving a pulse motor by a control pulse train generated in response to a speed change point in the subsequent stage, when the frequency difference between the control pulse train and the control pulse train corresponding to the speed change point in the previous stage becomes less than a predetermined value. It is made to start depending on the condition.

〔Example〕

5 to 10 are graphs showing changes in the frequency of the control pulse train applied to the pulse motor in the present invention, with time on the horizontal axis and pulse frequency (PPS) on the vertical axis. First, the fifth
In the figure, when the control pulse train P _F generated at the speed change point in the previous stage and the control pulse P _B generated at the speed change point in the latter stage overlap after time _t1 , both pulse trains P _F , P _B An example is shown in which the pulse motor is started to be driven by the pulse train P _B by interrupting the subsequent control pulse train P _B at time t ₂ when the pulse frequencies of the pulse trains match. By starting the drive using the control pulse train P _B in the latter stage in this way, it is possible to completely prevent the pulse motor from stepping out when shifting from the pulse train P _F to drive P _B , and furthermore, the injection speed can be increased. You can smoothly transition to a new speed.

Next, similarly in FIGS. 6 and 7,
Pre-stage control pulse train P _F and post-stage control pulse train P _B
This example shows an example in which when the pulse trains P _{F and} P B overlap after time t ₁ , driving by the subsequent pulse train P _B is started at time t ₂ when the pulse frequencies of both pulse trains P F and P _B match. In this case as well, the same advantages as in the example of FIG. 5 can be obtained.

On the other hand, in FIG. 8, the control pulse train in the previous stage
After driving at a constant frequency for a certain period of time Δt from time t ₂ when the pulse frequency of P _F and the pulse frequency of the subsequent control pulse train P _B match, the subsequent control pulse train
An example is shown in which driving by P _B is started.
As a result, it is possible to prevent the pulse motor from stepping out of synchronization, and also to alleviate drastic changes in the injection speed that occur when the injection speed changes from a decelerated state to an accelerated state.

Next, in FIG. 9, the previous stage control pulse train
If the subsequent control pulse train P _B occurs at time t ₁ while the pulse motor is being driven by P _F , the drive by the previous control pulse train P _F is interrupted at time t ₂ and the motor is driven at a constant frequency for Δt ₁ hour. After that, it is decelerated by a pulse train P _C corresponding to the predetermined deceleration characteristics,
At time t ₂ when the pulse frequencies of the pulse train P _C for this deceleration drive and the control pulse train P _B in the latter stage match, the drive is switched to a constant frequency drive, and after Δt ₂ hours have passed, the pulse train P _C in the latter stage is activated. An example is shown in which the transition is made to drive.

Thereby, it is possible to prevent the pulse motor from stepping out of synchronization, and also to quickly reach the target injection speed corresponding to the control pulse P _B of the subsequent stage.

Fig. 10 shows an example in which the control pulse train P B in Fig. 9 occurs after the control pulse train P _B in the previous stage shifts to constant speed driving by the control pulse P _F in the previous stage, and in this case, the same as in the case in Fig. 9 is shown. Deceleration pulse train
After being decelerated by P _C , it is driven at a constant speed for Δt ₂ hours. After this constant speed drive, the drive is shifted to the control pulse train P _B at the subsequent stage.

In addition, in the above explanation, one control pulse train
When shifting from P _F to driving using the other control pulse train P _B , the condition is that the pulse frequencies of both pulse trains match, but the condition is that the frequency difference is within a range where the pulse motor does not step out. It may also be possible to shift to .

FIG. 11 is a block diagram showing an embodiment of an injection speed control mechanism to which the present invention is applied. In the figure, the same parts as in FIG. 1 are given the same reference numerals.

The control pulse generator 8a detects whether the injection stroke has reached the injection speed change point based on the input signal from the signal detector 7, and if it has reached the injection speed change point, the control pulse generator 8a detects whether or not the injection stroke has reached the injection speed change point, and if it has reached the injection speed change point, the control pulse generator 8a detects whether or not the injection stroke has reached the injection speed change point. Outputs a control pulse train with time intervals corresponding to the injection speed. This causes the pulse motor 20 to rotate by an amount proportional to the number of pulses, thereby controlling the opening degree of the flow rate control valve 21. Thereby, the moving speed of the injection plunger 4 is controlled according to the opening degree of the flow rate control valve 21. The control pulse generator 8a performs control as shown in FIGS. 5 to 10.

Next, the structure of the pulse motor 20 and the flow control valve 21 will be explained using FIG. 12.

In FIG. 12, 22 is a valve body having a hydraulic oil inlet 23 from the axial direction and a hydraulic oil outlet 24 perpendicular to the axis, 25 is a spool that moves in the axial direction in the valve body 22, and 26 is a spool 25. A nut shaft 27 is screwed into the inner shaft center of the nut shaft 26 by a ball screw 28, and 29 connects the screw shaft 27 and the shaft of the pulse motor 20. The joint 30 is a key that prevents rotation of the nut shaft 26 and guides its movement in the axial direction.

The spool 25 rotates according to the rotation of the pulse motor 20.
moves back and forth in the axial direction to instantaneously open and close the valve and adjust the opening degree to control the flow rate. As described above, this flow rate control valve 21 has a spool 25 connected to the pulse motor 20 within a cylindrical valve body 22 that has a hydraulic oil inlet 23 on the end surface in the axial direction and a hydraulic oil outlet 24 on the side surface. It is driven in the axial direction by action to control the flow rate.
By rapidly reducing the axial thrust of the spool 25 caused by the hydraulic oil in accordance with the increase in the opening amount and moving speed of the spool 25, the driving force required for high-speed flow rate switching is reduced, and the flow rate control valve 21 can rapidly change the flow rate. This makes it possible to further improve switching performance and reduce driving force.

In this flow rate control valve 21, the spool 2 is controlled by the amount of rotation, that is, the rotation angle, of the pulse motor 20 by the control pulse train from the control pulse generator 8a.
5 is determined, the flow rate to the injection cylinder 1 is controlled, and the rate of change of the flow rate, that is, the rising state of the speed, is determined by the magnitude of the rotational speed of the pulse motor 20 during the rotation. .

In addition, the flow control valve 21 that has such a structure and function is designed so that the time _t1 until the spool 25 actually starts opening after receiving a command to change the speed can be kept to a maximum of 1 millisecond or less. Compared to conventional flow rate control valves, the response is extremely good, and the valve opening/closing operability and operational accuracy are also extremely improved.

A permanent magnet 31 is fixed to a part of the surface of the nut shaft 26, and a magnetic position detector 33 called a zero cross sensor is attached to the permanent magnet 31 and a part of the opposing casing 32, for example. The position detector 33 is constituted by a proximity switch sensitive to the movement of the permanent magnet 31, and can accurately detect the moving distance of the nut shaft 26 and spool 25 in the axial direction, and provide feedback to the control device. Further, the zero position of the spool 25 is electrically detected by the action of the permanent magnet 31 and the position detector 33, and the pulse motor 20 is accurately stopped at that position via the control pulse generator 8a. You can also make it possible.

Note that the position detector 33 has an accuracy of 0.01 m/
m can be used.

In this embodiment, since the flow rate control valve 21 driven by such a pulse motor 20 is used, the inertia is reduced, the responsiveness is improved, and control can be performed reliably and easily.

〔Effect of the invention〕

As explained above, in the present invention, the pulse motor is driven by a control pulse train generated in response to a speed change point in a later stage, so that the frequency difference with the control pulse train corresponding to a speed change point in a previous stage becomes less than a predetermined value. The system is designed to start on the condition that this is the case.

Therefore, even if the control pulse trains generated at adjacent speed change points overlap, the pulse motor can reliably transition from the first injection speed to the second injection speed without stepping out, and the entire injection process can proceed as planned. You can definitely finish it.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an example of the injection speed control mechanism of a die casting machine, Figs. 2 and 3 are graphs showing an example of the relationship between the stroke of the injection cylinder and the injection speed, and Fig. 4 shows the injection speed characteristics. Figures 5 to 10 are diagrams showing the relationship with the control pulse train, Figures 5 to 10 are pulse train frequency characteristic diagrams showing embodiments of the present invention, and Figure 11 is a block diagram showing an embodiment of the injection speed control mechanism to which the present invention is applied. , FIG. 12 is a sectional view showing the structure of the flow control valve. 1...Injection cylinder, 2...Piston rod, 4...
Injection plunger, 6a to 6e... limit switch, 7... signal detector, 8a... control pulse generator,
9a...Speed setter, 20...Pulse motor, 21...
Flow control valve.

Claims (1)

[Claims] 1. An injection speed control method in which a control pulse train corresponding to a target injection speed is generated for each change point in the injection speed, and a pulse motor is driven by this control pulse train to control the injection speed of an injection cylinder to the target speed, The pulse motor is driven by a control pulse train generated corresponding to a subsequent speed change point among the control pulse trains generated at adjacent speed change points, so that the frequency difference between the control pulse train and the control pulse train corresponding to the previous speed change point is determined by a predetermined frequency. An injection speed control method characterized in that the injection speed is started on the condition that the injection speed becomes below a certain value.