JP3043453B2 - Control method of injection molding machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a control method for an injection molding machine.

[0002]

2. Description of the Related Art Mold clamping in an injection molding machine is generally performed by a mold clamping ram mechanism which is a hydraulic piston mechanism. Such a ram mechanism often has a structure having a main ram and a boost ram for improving the moving speed thereof. Such a hydraulic type has the feature that high-pressure (high horsepower) and high-speed mold clamping operation is possible, but the operation in the low-speed control region tends to be unstable, and the influence of disturbances such as hydraulic oil temperature There is also a drawback that it is easy to receive and fine position control characteristics cannot be obtained. In particular, the accuracy of the speed switching position cannot be said to be sufficient, and a large impact is likely to occur at the moment when the mating surface of the mold is closed. In an extreme case, there is a problem that the mold is damaged. Further, there is a disadvantage that the hydraulic circuit becomes complicated when performing a composite operation.

For this reason, it has been considered that the mold clamping operation in the mold clamping device is performed by a highly accurate AC servomotor.

[0004]

However, when clamping a large injection molding machine by driving only an AC servomotor, the servomotor has a mold opening / closing speed of 40-50 m / min. Various characteristics such as sufficient mold clamping force and rapid start-up of the mold opening / closing operation are required. In order to satisfy these required characteristics, a servo motor having a very high rating and excellent performance is required. Further, since such a servomotor is expensive, there is a problem that the price of the injection molding machine is increased. In particular, there is no appropriate means in the case where it is necessary to temporarily stop during high-speed operation.
Accordingly, an object of the present invention is to provide a control method of an injection molding machine capable of performing molding with high accuracy while having necessary mold clamping characteristics.

[0005]

According to the present invention, a hydraulic drive unit for pressing and driving a movable base, and a mold fixed to the movable base and used for injection molding via a moving mechanism and a movable plate by the rotation thereof. A servo motor for moving the movable base, and a position scale for detecting the position of the movable base, wherein the high-speed movement is performed by the hydraulic drive unit, and the low-speed movement immediately before mold clamping and a pressure rise at the time of mold clamping are increased by the servo motor. A method for controlling an injection molding machine having a mold clamping device so as to perform, wherein the movable base is advanced by the hydraulic drive to a speed switching position just before a forward limit, and the hydraulic drive is fixed; and A step in which the movable platen is driven by the servomotor to close the mold, a step in which the servomotor is further driven to increase the pressure of the mold to a predetermined value, and a step in which the pressure reaches a predetermined value. Reading the encoder value of the servo motor and setting this value as an auxiliary origin; andremoving the movable platen by the servo motor to open the mold by using a preset mold opening amount based on the auxiliary origin. And a step of performing an injection and a step of performing a compression operation by moving the movable platen forward again by the servomotor when a predetermined compression start command is obtained.

[0006] Whether the compression start command is given in accordance with the screw position or in response to the holding pressure switching signal, the mold clamping pressure at which the compression start command is detected becomes equal to the set pressure. It may be provided at the point of time, or as a signal obtained by delaying them.

[0007]

According to the present invention, a combination of high-speed high-pressure control by hydraulic drive and low-pressure low-speed control by a servomotor is used, and the encoder value of the servomotor once the mold is completely closed is used as an auxiliary origin, and this is used as a reference. After the mold is opened by a predetermined amount and injection is performed, compression is performed again by the servomotor. For this reason, high quality molding is possible.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a partial sectional view showing a mold clamping mechanism of an injection molding machine to which the present invention is applied. This mold clamping mechanism is a tie bar 11
It has a sliding shaft called. The movable platen base 12 and the main movable platen 13 are engaged with the sliding shaft by through holes 12a and 13a provided in the movable platen base 12 and the main movable platen 13, and are slidable with respect to the tie bar 11. The movable platen base 12 is connected to the mold clamping ram 14 by a connecting member 15. The speed control of the mold clamping ram is performed by a control device (not shown).

At the center of the movable platen base 12, a bearing 16 and a substantially cylindrical rotating member 17 having a flange portion which engages with the bearing are provided. The rotating member 17 is held so as to be freely rotatable by a fixed lid 19 and a bearing retainer 18 provided in contact with the inner surface thereof. A concave portion is formed on a surface of the lid body 19 that is in contact with the bearing retainer 18, and a pressure sensor 21 such as a load cell is attached to the concave portion. Has been given. A screw is cut inside a through hole provided at the center of the rotating member 17, and a first gear 22 is provided with a bolt 2 on the end surface of the rotating member 17 on the side of the mold clamping ram.
3 is fixed.

On the other hand, an AC servo motor 26 is fixed to the lower surface of the movable platen base.
A pinion 25 is attached to the rotation shaft 6, and a second gear 24 that engages with the pinion 25 is provided between the pinion 25 and the first gear 22. These gears 22, 2
4, 25 are such that their central axes are on the same straight line,
It is rotatably mounted on an arm (not shown). Note that the AC servomotor used here is 1/6 to 1 / compared to the case where all are driven by the AC servomotor.
A rating of 2 is sufficient. The AC servomotor has a built-in encoder for detecting rotation, and its output is given to a control device (not shown), whereby speed control and torque control are performed. A shaft 27 whose surface is threaded is fixed to the center of the main movable platen 13, and this screw forms a ball screw together with the screw provided in the through hole of the rotating member 17 described above. The movable base 12 is provided with a scale 30 for detecting its position.

By adopting such a structure, A
When the C servo motor 26 is driven, the pinion 25, the second
Gear 24 and the first gear 22 in this order, and the rotating member 1
7 rotates around the shaft 27. As a result,
The main movable platen 13 is moved relatively to the movable platen base 12. The main movable platen 13 is connected to a part of a mold (not shown). The main movable platen 13 is opened and closed by moving the main movable platen 13, and a force is applied to the main movable platen 13. , The pressure will be applied to the mold.

In order to control the mold clamping device having the above structure, the position of the movable platen base 12 is detected by the scale 30, and the relative position of the main movable platen 13 with respect to the movable platen base 12 is determined by the encoder signal of the AC servomotor 26. Is detected by The scale 30 is obtained by setting the origin before driving the mold clamping ram to a scale value 0, and taking a scale value Sc as a position detection value for all strokes in the rightward direction in FIG. The coordinates of the main movable platen 13 are such that the encoder output is set to the origin 0 when the movable platen base 12 and the main movable platen 13 are in close contact with each other, and are negative in the direction in which the movable platen base 12 opens from the main movable platen 13. Is taken as the scale value Sx. That is, the scale value Sx represents the relative position between the main movable platen 13 and the movable platen base 12.

The control operation of the injection molding machine having such a configuration will be described with reference to FIGS. 1, 3 and 4. First, the movable platen base 12 is hydraulically driven by the mold clamping ram 14 to move forward to the speed switching position LS2A just before the forward limit (step S101). In this position, the clamping ram is locked.

Next, the AC servomotor 26 is driven to rotate. As a result, the main movable platen 13 is moved forward by the gear mechanism 22, 24, 25 and the ball screw mechanism 17, 22 to the forward limit LS.
The mold is moved to the position 2 while controlling the speed, and the mold is closed (step S102). When it is confirmed that the main movable platen 13 has reached the forward limit position LS2, a switching signal for switching to pressure control is generated, and the boost operation is shifted. That is,
When the AC servomotor 26 is further driven, the pressure detected by the load cell 21 increases, and the AC servomotor 26 is driven so that the pressure increases to a predetermined value (step S103). This pressure control is performed by feeding back the detection output of the load cell 21. Then, the encoder value of the AC servomotor 26 when the pressure reaches a predetermined value is read, and this value is set as an auxiliary origin (step S104). By setting the origin, the relative position between the main movable platen 13 and the movable platen base 12 can always be recognized.

Subsequently, the AC servomotor 26 is driven to retract the movable platen with reference to the auxiliary origin by a preset mold opening amount to open the mold (step S105) and perform injection (step S106).

Further, when a predetermined compression start command is obtained, the AC servomotor 26 is driven again to move the movable platen 13 forward to perform a compression operation (step S107). Thereby, molding at a high pressure becomes possible, and molding quality can be improved.

The compression start command is issued based on the screw position, the holding pressure switching signal, the fact that the detected mold clamping pressure has become equal to the set pressure, and the like. Further, the signal thus emitted may be delayed, or a timer freely set by the user may be driven, and the compression start timing may be set by the time-up signal.

Next, when the mold is opened, the pressure is reduced by feedback-controlling the AC servomotor 26 using the detection output of the load cell 21 so that the pressure curve in FIG. After a sufficient decrease is confirmed, the flow shifts to speed control by the AC servomotor 26. As a result, the main movable platen 13 is moved to the high-speed mold release start position LS3A which is a position sufficiently distant from the advance limit.
Is reached, the mold ram 14 and the boost are released at a high speed by controlling the speed by hydraulic pressure. By performing such control, high-speed and high-pressure movement by hydraulic pressure and high-precision mold clamping and molding by an AC servomotor can be performed. In particular, accurate position control in a short stroke becomes possible.

In the above embodiment, the movement of the main movable platen and the application of pressure are performed by the gear mechanism and the ball screw. However, the present invention is not limited to this. Any mode may be used as long as pressure and pressure are applied.

Further, the switching from the speed control to the pressure control by the servomotor at the time of mold clamping is performed by satisfying both the conditions of the position and the pressure in the embodiment.
The switching may be performed under only one of the conditions.

[0021]

As described above, according to the present invention, a combination of high-speed and high-pressure control by hydraulic drive and low-pressure and low-speed control by a servomotor is performed. After opening and performing injection, compression is performed again by the servomotor, so that high-quality molding can be performed.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a control method according to the present invention.

FIG. 2 is a partial cross-sectional view showing a configuration of a mold clamping device of an injection molding machine used in the present invention.

FIG. 3 is a graph showing a state of control near a switching point between speed control and pressure control in the control method according to the present invention.

FIG. 4 is a graph showing a state of speed control when the mold is opened.

FIG. 5 is a graph showing a state of switching to pressure control when a detected pressure value reaches a predetermined pressure value.

[Explanation of symbols]

 Reference Signs List 11 tie bar 12 movable plate base 13 main movable plate 14 mold clamping ram 16 bearing 17 rotating member 21 pressure sensor 22 first gear 24 second gear 25 pinion 26 AC servomotor 27 shaft 30 scale

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B29C 45/00-45/84 B22D 17/26

Claims (5)

(57) [Claims] A hydraulic drive unit for pressing and driving a movable base, a servomotor fixed to the movable base, and moved by a rotation thereof to close a mold used for injection molding via a moving mechanism and a movable plate; An injection scale having a position scale for detecting the position of the movable base, wherein a high-speed movement is performed by the hydraulic drive unit, and a low-speed movement immediately before mold clamping and a pressure rise during mold clamping are performed by the servo unit. A method for controlling a molding machine, comprising: moving the movable base body forward to a speed switching position just before a forward limit by the hydraulic drive unit, fixing the hydraulic drive unit, and driving the movable platen by the servo motor. Closing the mold, further driving the servomotor to increase the pressure of the mold to a predetermined value, and encoder value of the servomotor when the pressure reaches a predetermined value. Reading, setting this value as an auxiliary origin, a step of retracting the movable platen by the servomotor to open a mold by a preset mold opening amount based on the auxiliary origin, and a step of performing injection, Moving the movable platen forward again by the servomotor at the time when a predetermined compression start command is obtained, and performing a compression operation. 2. The control method for an injection molding machine according to claim 1, wherein said compression start command is given according to a screw position. 3. The control method for an injection molding machine according to claim 1, wherein said compression start command is given in response to a dwell switching signal. 4. The control method for an injection molding machine according to claim 1, wherein the compression start command is given when the detected mold clamping pressure becomes equal to a set pressure. 5. The control method for an injection molding machine according to claim 2, wherein the compression start command is given as a signal obtained by delaying the given signal.