JPS6127227A - Method of controlling injection molding machine - Google Patents

Abstract

PURPOSE:To enable a nozzle to touch a mold smoothly, by measuring the pressure of a nozzle against the mold, and changing the speed control of the nozzle to the pressure control when the measured pressure reaches a prescribed pressure. CONSTITUTION:A nozzle 5 after clamping is advance with the speed controlled by the driving of a motor 13, and after the nozzle 5 toughes a mold 30, the nozzle is pressed under a prescribed pressure. That is, after the hit of the nozzle 5 against the mold 30 (t2), since the speed (v) decreases and the pressure (p) increases gradually in accordance with the characteristics of the speed control system, the speed control is changed to the pressure control when the actual pressure (p) reaches the command pressure pi that has been set by a setting apparatus, etc. If the command pressure pi is lower than the pressure (p) before the hit, since the pressure (p) decreases in accordance with the speed control system by making the speed command value vi nil after the hit (t2), the control is changed to the pressure control when the command pressure pi is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a method for controlling an injection molding machine for smoothly bringing an injection nozzle of the injection molding machine into contact with a mold for molding a product to perform injection.

(Technical background of the invention and its questions, point B) When designing an injection molding machine, # when automating it, it is necessary to pay attention to improving the quality of molded products, saving energy, and improving productivity. These are particularly important in the weighing process. Among these, from the perspective of improving quality, the quality of molded products is affected by injection speed, pressure, resin temperature, injection amount, etc., and in order to obtain an accurate injection amount with little variation, it is necessary to measure with high precision. Must be.

In addition, from the point of view of energy saving, heat is applied using a heater to make granular resin into a homogeneous molten state, and shearing and kneading is performed using a screw. By effectively controlling the temperature and the like, the energy required for weighing can be minimized, and productivity can be improved by shortening the time required for weighing as much as possible.

FIG. 1 is a diagram showing the measuring mechanism of a conventional injection molding machine.
By the rotation of a rod-shaped screw l with thread grooves on the entire circumference, the resin 4 stored in the hopper 3 is sent to the cylinder 2 along the thread grooves, where it is heated by a heater (not shown). The material is sheared, kneaded, and plasticized by the rotation of the screw 1 while being mixed. In this case, the nozzle 5 provided at the tip of the cylinder 2 is inserted into a mold (
(not shown), the screw l retreats in the Y direction in the figure due to the pressure of the resin 6 that fills the cylinder 2 and fills the mold. In other words, during measurement, the structure is such that the molten resin 6 does not flow out to the outside, and in addition to preventing it from being pulled, back pressure is applied to the screw l by the driving device 100 in order to accurately measure the amount of resin. It will be done. Therefore, the screw 1 is gradually retreated in the direction of the arrow Y due to the difference between the resin pressure generated by the rotation of the screw 1 and the back pressure from the drive device ioo. The rotation speed and back pressure of the screw 1 are set empirically based on the type of resin 4 used, its temperature, etc., and the position of the screw 1, which determines the injection amount, is set by a detection means such as a limit switch.

Note that the mechanism for rotating the screw l, the mechanism for applying back pressure to the screw l, the limit switch, etc. are included in the drive device 10.
Equipped within 0.

The problem here is that the element that directly determines the screw position is the limit switch, and the screw position can only be indirectly controlled by the interaction between rotation speed and back pressure. In other words, if the rotation of the screw l is stopped after the limit switch is activated, the rotation of the screw l is
will overshoot the desired position. Therefore, the only way to prevent overshoot is to gradually reduce the rotation of screw l as it approaches the limit switch, or to set it closer to the limit switch activation point in anticipation of the amount of overshoot. Therefore, in reality, it is necessary to repeatedly determine the weighing process through trial and error, and it not only varies depending on the type of resin 4, the shape of the mold, etc. In view of the fact that changes in the transfer amount, etc. to No. 2 are added as disturbances, it is not only complicated to set the limit switch operating point, but also difficult to obtain an accurate injection amount.
Variations occur in the injection quantity, which inevitably leads to a decline in the quality of the molded product. Furthermore, in this type of system, in order to stop at an accurate position using a limit switch, the rotation speed of the screw L must be reduced to the required amount -H even during steady rotation, which increases the time required for weighing and reduces production. As energy efficiency declined, energy efficiency also declined.

In addition to this problem, when bringing the nozzle into contact with the mold, the nozzle is advanced toward the mold by speed control,
I try to switch to pressure control when the nozzle gets close enough to the mold, but I don't know the position or time to switch speed control to pressure control, and when I switch speed control to pressure control, the speed or pressure changes discontinuously. There was a problem that smooth control could not be achieved.

(Object of the invention) This invention was made under the above circumstances,
The purpose is to provide a control method for an injection molding machine that, in combination with the configuration of the injection molding machine, allows a nozzle to be brought into smooth contact with a mold.

(Summary of the Invention) This invention has a cylinder with a nozzle at its tip, which is equipped with a screw that moves forward and backward as well as rotates.The resin molten inside the cylinder is fed from the norzo to the shape of the product. This relates to a control method for an injection molding machine that injects into a carved mold.The nozzle is moved toward the mold under speed control, the pressure of the nozzle against the mold is measured, and this measured pressure is When the set pressure is reached, the nozzle speed control is switched to pressure control.1. This is to control the nozzle mentioned above so that it is brought into pressure contact with the mold at a set pressure.

(Embodiment of the Invention) In this invention, as shown in FIG. 2, a position command Si for the screw l is input to the control device 15, and the calculated screw back pressure signal Pi is sent to the motor 13 for moving the position of the screw l. The given and calculated screw rotation signal Ri is input to the motor 7 which rotates the screw l by m1. Here, the screw l is rotated by the motor 7 being rotated by the screw rotation signal Ri,
The resin 4 is sent from the hopper 3 to the cylinder 2, and the cylinder 2 is filled with resin 6 which has been sheared, kneaded and plasticized by the screw l, and this pressure causes the screw l to retreat in the direction of arrow N. At this time, back pressure is applied to the screw l in order to accurately measure the amount of resin while preventing air from being sucked into the cylinder 2. This is because the motor 13 is driven by the screw back pressure signal Pi. As the pole screw 11 connected to the motor 13 rotates, the pole screw 12 screwed thereon moves in the direction of the arrow M.
Ball nut to generate directional torque! A red fixed motor 7 mounted on a drive stand 10 connected to 2;
This acts as a back pressure against the force that causes the screw 1 etc. to retreat in the N direction. Here, a rotation speed sensor 8 connected to the motor 7 detects the rotation speed n of the screw l and outputs a screw rotation speed feedback signal Rf, and a position sensor 14 connected to the motor I3 detects the rotation speed n of the screw l. , that is, the position of the screw l, is detected and a screw position feedback signal Sf indicating the back pressure p is inputted to the control device 15, respectively. moreover,
An injection port of a mold 30 for injecting molten resin to mold a product is pressed into contact with the front surface of the nozzle 5.

Next, an example embodying the contents of this control device 15 will be explained in the third section.
To explain this configuration as shown in the figure, the deviation Se between the position command Si and the screw position feedback signal sr is input to the position control element 21, and the signal So calculated to compensate for the characteristics of closed loop control is sent to the speed control element 22. , and outputs the back pressure command (old) and rotational speed command (ki) necessary to control the screw l. Then, the back pressure command old is manually inputted to the back pressure control element 18, and a signal HO calculated to compensate for the characteristics of this closed loop control is sent to the power amplifier 20A.
The signal Pi is input to the motor 13, is power amplified to drive the motor 13, and is input to the motor 13 as a screw back pressure signal Pi. - On the other hand, the rotation number digit Ki is input to the subtracter 24,
The deviation Ke from the screw rotation speed feedback signal R obtained by the subtractor 24 is input to the rotation speed control element 18, and the output Ko calculated to compensate for the characteristics of this closed loop control is input to the power amplifier 20B. The signal is then power amplified and input to the motor 7 as a screw rotation signal Ri in order to drive the motor 7.

FIG. 4 illustrates the operation of the above-mentioned apparatus, with n and the back pressure p of the screw l plotted on the vertical axis, and the moving speeds of the screw l from vO (small) to V4 (large) as parameters.

Here, to describe a series of operations while explaining the metering process, first, the amount of resin 6 to be metered is determined by the position where the screw l stops, so the position command Si input to the control device 15 is This is the amount of resin 6 to be used.

Then, when the screw I moves until the position sensor 14 outputs a screw position feedback signal Sf corresponding to this position command Si, the metering process ends. The process up to the end of this weighing process is shown in FIG. 3. First, when the position control element 21 inputs the deviation Se, it is controlled to have a predetermined frequency characteristic to compensate for this closed-loop characteristic. The signal So is input to the speed control element 22, and this speed control element 22 efficiently outputs the back pressure command old and the rotation speed command Ki by combining them.
And the rotational speed of the screw l is quickly brought to zero. To explain this according to the characteristic diagram in Fig. 4, first, at the start of weighing, the back pressure command and rotation command are p4 and n4, respectively, and the rotational speed n of the screw l is made as high as possible to increase the efficiency of the weighing. Try to get L. That is, the moving speed of the screw I is v4 due to the difference between the speed in the direction of arrow N and the back pressure in the direction of arrow M in FIG. 2, and this moving speed is also quite high. Here, the broken line Ll in FIG. 4 indicates the combination of the rotational speed n and the back pressure p that changes according to the process of the metering process, and this slope can be freely selected and set. As mentioned above, it starts with the combination of 14 and p4 at the beginning of the clear weather forecast, and then sequentially n3 and p3, n2 and p2, and so on. nl and pl change, and finally the moving speed of the screw l becomes vO due to the combination of ns and ps, and the screw l stops and the metering process ends. i.e. screw,
-When approaching the rotational speed ns and screw movement speed VO
These values are almost at a stop, and at the end of this weighing station, it can be smoothly stopped at the correct position relative to the position command Si, so it is possible to weigh at an appropriate value without going too far relative to the position command Si, and at the same time The back pressure p is also an appropriate value p
s can be selected and preparations for the first injection stroke can be made.

Further, if the rotational speed n is high during measurement, the frictional heat generated by this increases, and there is an advantage that the capacity of the heater can be small.

Next 1. The specific structure of an injection molding machine controlled by the above-mentioned principle is shown in FIG. 5 and will be explained.

The motors 7 and 13 are attached to a fixed housing 40 of the injection molding machine, gears 41 and 42 are attached to the rotating shaft 13A of the motor 13, and gears 43 and 44 are attached to the rotating shaft 7A of the motor 7. These gears 41-4
4, transmission of driving force is interrupted and interrupted by clutch mechanisms 45 and 48 provided at each end of the rotating shafts 13A and 7A.

Furthermore, transmission shafts 47A and 48A are mounted on the housing 40, and transmission of driving force is interrupted and interrupted by clutch mechanisms 47 and 48. Gears 48 and 50 are mounted on the transmission shaft 47A, and gear 51 is mounted on the transmission shaft 48A. and 52 are respectively attached. Further, a drive shaft 30^ for moving the mold 30 is mounted on the housing 40, and gears 32 to 32 are connected to each other, and a clutch mechanism 31 provided at the end of the drive shaft 30^ is configured to intermittent transmission of driving force. 34 is mounted within the housing 40, and the drive shaft 30A
is further pivoted on a housing 35 of the mold 30. Housing 35
A gear 36 is attached to the inner drive shaft 30, A, and a gear 37
A rotational force is transmitted to the actuating shaft 38 through the rotating shaft 38, and this rotation causes the mold member 39 to slide on the sliding shafts 38A, 38B, . Furthermore, the housing 40
A shaft IA connected to a screw l is provided inside, a gear 53 is attached to this shaft IA, and a gear 55 is further attached to an operating shaft 54 that is engaged with the inner body of this gear 53 via a bearing. is installed.

In such a configuration, the injection molding machine performs mold clamping to advance the mold member 38 to fit the mold together, pressurization to increase the pressure of the mold, and nozzle advancement to advance the nozzle 5 in the direction of the mold 30. Injection and filling of the molten resin into the mold 30, metering and cooling to plasticize the resin, nozzle retraction to retract the nozzle 5 toward the housing 40, pressure reduction of the mold and mold opening. , the product molded in the mold 30 is repeatedly dropped and stopped. Here, FIG. 5 shows the initial state of the injection molding machine, and when performing mold clamping and pressurization, the motor 13 is driven, and its rotational drive is caused by the rotating shaft 13A→
The gear 41 is transmitted to the drive shaft 30A via the gear gear 33 (not shown), and is transmitted to the operating shaft 3 via the gears 36 and 37.
8 is rotated, the mold member 38 is advanced.

In this way, when the mold member 39 is advanced and stopped at the stop position, and the pressure is increased to a predetermined pressure, the clutch mechanism 9
01 to cut off the transmission from the gear 33 to the gear 3B, and switch the clutch mechanisms 45 and 47 to rotate only the lever 47A, thereby moving the casing 40 in the direction of the mold 30 and keeping it stationary. The nozzle 5 is advanced with respect to the mold 30. Note that the nozzle 5 is moved back by reversing the rotation of the motor 13.

Furthermore, when injecting resin, the motors 7 and 13 are driven, and the clutch mechanisms 45 and 4B are switched so that the gear 41
and the rotation of gear 42 are transmitted to gears 33 and 34, respectively, by gears not shown. Furthermore, by switching the clutch mechanism 31, the rotational drive of the motors 7 and 13 is transmitted to the gear 55, and the rotational drive of the motors 7 and 13 is transmitted to the gear 55.
The screw 1 is moved via A, and the molten resin can be injected into the mold 30 as described above. Further, when measuring resin, only the motor 7 is driven, and this rotational drive is caused by gear 43 → gear not shown → gear 5.
2 → shaft 48A → gear 51 → gear 49 → gear 32 → gear 5
3 to the screw l, which rotates the screw l and drives the motor 1'3, and this rotational drive is transmitted to the gear 42 → gear not shown → gear 33 → clutch 31
-> Gear 55 -> Shaft 54 -> Transmitted to screw 1 via shaft IA, and metering is performed by applying back pressure to screw 1. The mold opening is performed by rotating the motor 13 and retracting the mold member 39 in the opposite manner to the mold clamping described above.

Here, the advance of the nozzle 5 after the mold clamping described above is performed by speed control driven by the motor 13, and after the nozzle 5 contacts the mold 30, it is necessary to press the mold 30 with a predetermined pressure. Therefore, the problem is how to switch the motor 13 from a speed control system for the speed command vi as shown in FIG. 6 to a pressure control system for the pressure command Pi. That is, the speed control system shown in FIG. 6 converts the speed deviation ma into a torque command Ti in a loop system 60 (Gs), and outputs the motor 13 through a power amplifier 61 according to this torque command T1.
7(A).

As shown in (B), the command speed vi from time to to tl
If the pressure is controlled at a constant speed of , and the pressure after time t1 is controlled with a constant pressure of command pressure pi, both the speed V and pressure P become discontinuous at time t1 when the control mode is switched, and injection etc. can be performed smoothly. I can't.

Therefore, in this invention, the nozzle 5 is advanced by speed control, and when the nozzle 5 collides with the mold 30, the moving distance
A collision is detected by utilizing the fact that the speed V becomes 0 as soon as becomes constant, and after the collision is detected, the pressure control is switched to when the actual pressure p becomes the command pressure pi.

FIGS. 8(A) and 8(B) show how the nozzle 5 collides with the mold 30. Since the nozzle 5 is moved at a constant command speed i until time t2, the nozzle 5 travels a distance X also increases linearly, but when the nozzle 5 collides with the mold 30, the velocity V
decreases to 0, and the moving distance X also does not increase = constant value xO
will be retained. Therefore, by detecting the change in the moving distance
can be detected. After the nozzle 5 collides with the mold 30 (time t2), the speed V decreases and the pressure p gradually increases according to the characteristics of the speed control system, so that the actual When the pressure p reaches the command pressure pi set by a setting device or the like (time t3), the control is switched to pressure control. If the command pressure pi is lower than the pressure p before the collision, by setting the speed command value vi to zero after the collision (time t2), the pressure p will gradually decrease according to the characteristics of the speed control system, so the command pressure Switch to pressure control when pi. In this way, speed control at a constant speed is realized by the speed command mi until time t2, and the command pressure pi is prevented from reaching the command pressure pi within a short transient period from time t2 when the nozzle 5 collides with the mold 30. Since the pressure control is switched to the pressure control when the command pressure reaches the command pressure pi (t3), it is possible to smoothly switch from the speed control to the pressure control.

In addition.

The collision of the nozzle 5 with the mold 30 is caused by the collision between the nozzle 5 or the mold 30.
This is done at a speed that does not cause damage.

FIG. 1θ shows an example of a device for realizing the method of the present invention, in which the nozzle 5 and the mold 3 are connected by detecting the drive current of the motor 3 and the number of pulses from the position sensor 14.
A collision detection circuit 70 is provided which detects a collision with 0 and outputs a collision signal CL, and further compares the torque T from the loop system 60 with the command pressure pi from a setting circuit 72 and outputs a switching signal SW.
A torque detection circuit 71 is provided to output the torque. Further, a switch circuit 73 is provided between the loop system 60 and the power amplifier 61 to switch between torque T (contact a) and pressure pi (contact b) in response to a switching signal Sw.

In such a configuration, the collision detection circuit 70 always detects a collision between the nozzle 5 and the mold 30,
When a collision is detected, the collision signal CL is sent to the torque detection circuit 71.
The actual torque T (pressure P) is compared with the command pressure pi set in the setting circuit 72.
When the command pressure pi is lower than the pressure P before the collision, the speed command mi is set to zero when the collision is detected. Then, when the torque T becomes equal to the set pressure pi, a switching signal S- is outputted, and the contact point of the switch circuit 71 is switched from a to b to control the pressure at the command pressure pi.

In addition, in the above description, the rotation speed n of the screw l is detected by the rotation speed sensor 8 connected to the motor 7, but it may be detected via a gear or the like, or the motor current may be detected. , the position of the screw l may also be determined from the position of the drive base 10, the ball nut 12, etc.

Further, the motor may be controlled by direct current or alternating current, and the position of the screw can be moved by a combination of a ball screw and a ball nut, or by driving the screw by driving it on a guide.

(Effects of the Invention) As described above, according to the injection molding machine control method of the present invention, it is possible to switch from speed control to pressure control by simple collision detection or other means. It can be realized. Furthermore, since the speed control is switched to the pressure control when it is detected that the actual pressure has reached the set pressure, the control system can be switched smoothly.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an example of a conventional injection molding machine, Fig. 2 is a diagram showing an embodiment of the injection molding machine to which the present invention can be applied, and Fig. 3 is a block diagram showing an embodiment of its control device. , 4th
The figure is a characteristic diagram showing the relationship between rotation speed and back pressure to explain its operation, 5th Fgi is a configuration diagram showing the specific structure of the injection molding machine, 6th is a block diagram of the speed control system, 7th figure(
A) and (B) are diagrams explaining the discontinuity from speed control to pressure control, Figures 8 (A), (B) and Figure 9 (A
), (B) are diagrams for detailed explanation of this invention, the first
FIG. 0 is a block diagram showing an example of a circuit system according to the present invention. 1... Screw, 2... Cylinder, 3... Hopper, 4, 6... Resin, 5... Nozzle, 7, 13...
・Motor, 8... Rotation speed sensor, 10... Drive base,
11...Ball screw, 12...Ball nut, 14...Position sensor, 15...Control device, 3G
...Mold, 40.35...Casing. 70... Collision detection circuit, 71... Torque detection circuit,
72... Setting circuit, 73... Switch circuit. Applicant's agent Yu Yasugata Sanjo l Figure

Claims (2)

[Claims] (1) A screw that moves forward and backward and rotates is placed inside a cylinder with a nozzle at its tip, and the molten resin inside the cylinder is passed through the nozzle into a metal molded with the shape of the product engraved on it. In a method for controlling an injection molding machine that is configured to inject into a mold, the nozzle is moved toward the mold by speed control, the pressure of the nozzle against the mold is measured, and this measured pressure is the set pressure. 1. A method for controlling an injection molding machine, comprising: switching the speed control of the nozzle to pressure control when the nozzle reaches the set pressure, and controlling the nozzle so as to press the nozzle into contact with the mold at the set pressure. (2) A method for controlling an injection molding machine according to claim 1, wherein the switching time from speed control to pressure control can be freely changed.