JPH06246801A - Injection control method for injection molding machine - Google Patents

Abstract

PURPOSE:To provide an injection control method for an injection molding machine capable of molding excellent products wherein injection pressure does not exceed proper range even when a primary injection process is carried out with velocity feedback control by using a servo motor. CONSTITUTION:In an injection control method for an injection molding machine, an injecting screw 2 is made to proceed by driving force of a servo motor 5 so as to carry out an injection, and a primary injection process out of injection processes is carried out by velocity feedback control. A torque limiter means 15 capable of limiting the torque of the servo motor 5 is provided. At an adjustable speed area during the primary injection process, the torque limit for the servo motor 5 by the torque limiter means 15 is released. At other area than the adjustable speed area during the primary injection process, the torque of the servo motor 5 is limited by the torque limiter means 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection control method for an injection molding machine, and more particularly, a servo motor is used as a drive source for injection, and an injection stroke (primary injection stroke and pressure holding stroke as injection / filling stroke). The present invention relates to an injection control method in an injection molding machine for performing an injection / filling process (primary injection process) in a process consisting of (1) and (2) by speed feedback control.

[0002]

2. Description of the Related Art In an injection molding machine, the control conditions of the injection speed and the injection pressure are important factors for molding a good product, and an injection molding machine that controls the injection speed or the injection pressure by feedback control Various proposals have been made. In a conventional injection molding machine that performs feedback control, generally, in the primary injection process of injecting and filling molten resin into the cavity of the mold, the injection speed of the injection speed is set so that the measured speed value approaches the speed setting value. Feedback control (feedback control giving priority to injection speed) is performed.

In an injection molding machine that uses a servomotor as a drive source for injection for advancing the screw, speed feedback control is performed as described above.
During the next injection stroke, in order to give priority to stable speed control, generally use the servo motor in a state where the rated maximum torque can be output (without applying the torque limit).
Feedback control was performed so that the actual speed value would always match the speed setting value. FIG. 3 is a diagram showing the relationship between the servomotor drive current and the injection speed during the primary injection stroke in this case. FIG. 3A shows the state of the motor drive current along the time axis. Part (b) of the figure shows how the velocity changes along the time axis. As shown in FIG. 3, in the acceleration region, the motor drive current rapidly rises and the injection speed rises rapidly to the speed setting value. In the deceleration region, the motor drive current rapidly falls and then rises again, and the injection speed increases. It is designed to quickly fall to the set value.
However, if the servo motor is used without torque limit, that is, if the servo motor output torque has a margin so that it can always follow the set speed, the injection speed will always match the set value correctly. Even if feedback control is performed, the injection pressure corresponding to the motor torque is not constant due to fluctuations in the resin pressure, which is a load reaction force, and is virtually uncontrollable.

On the other hand, in order to control the injection pressure, a torque limit is applied to limit the torque (injection pressure) of the servomotor to a predetermined value, as described in, for example, Japanese Patent Publication No. 4-58371. The method is known. Figure 4
FIG. 3 is a diagram showing the relationship between the drive current of the servo motor and the injection speed during the primary injection stroke period when the control method disclosed in the above-mentioned prior application is applied, and (a) in the same figure is on the time axis. A state of the motor drive current along the time axis is shown, and a state of the speed change along the time axis is shown in FIG. As shown in FIG. 4, in the above-mentioned prior application, a torque limit means that operates only in the injection direction is provided. The reason for doing so is to prevent damage due to screw overrun when performing an idle driving operation (an operation of advancing the screw in a state where there is no reaction force by the resin) by purging or the like, according to the above-mentioned prior application. is there.

[0005]

As shown in FIG. 3 and described above, if the injection speed is feedback-controlled without applying the torque limit to the servomotor, the measured speed value is controlled so as to match the speed set value. , The injection pressure corresponding to the motor torque cannot be controlled. Here, of course, as the set value for the primary injection stroke, the injection speed as the servo target (object of feedback control) is set, but in order to stably mold a good product, the primary injection is performed. Since the injection pressure during the injection stroke is also an important factor, this injection pressure is also set as a monitoring index that is not a servo target but is a desirable proper value. However,
If feedback control is performed so that the injection speed matches the speed setting value under any circumstances (for example, if speed feedback control that is so-called force is performed regardless of reaction force from the resin, etc.) ), Sometimes the injection pressure may greatly exceed the proper value,
Despite the feedback control, there was a problem that a defective product was molded.

If the method according to the above-mentioned prior application shown in FIG. 4 is directly applied to the control during the molding operation, the high speed response is inferior because it slowly rises to the target speed in the acceleration region. There is a big problem that it cannot be applied to products that require high-speed injection from the beginning such as.

The present invention has been made in view of the above points,
The purpose of this is that the injection pressure does not exceed the proper range even if the primary injection process is executed by the speed feedback control using the servo motor, so that good product molding can be realized. It is to provide a control method.

[0008]

In order to achieve the above-mentioned object, the present invention advances an injection screw by a driving force of a servomotor to perform injection, and speeds up a primary injection process during an injection stroke. In the injection control method of the injection molding machine executed by the feedback control, the torque limiter means for limiting the torque of the servo motor is provided, and the acceleration / deceleration region during the primary injection stroke is limited by the torque limiter means for the servo motor. Then, the area other than the acceleration / deceleration area in the primary injection stroke is subjected to torque limitation by the torque limiter means for the servo motor.

[0009]

Since the torque limit is not applied in the acceleration region in the initial stage of the primary injection stroke, the injection speed rapidly rises to the speed set value with a high torque output in this acceleration region. After the acceleration region, the servo motor is in the torque limit state, and the output torque of the servo motor is limited so as not to exceed the predetermined value and the predetermined torque is maintained. In other words, the predetermined injection pressure is maintained. The speed feedback control is executed in this state. For this reason, in the region where the torque limit is applied, the torque cannot be output above the predetermined value even if the speed feedback control is performed, so normally the reaction force (load resistance) from the resin being filled
Therefore, the measured speed value gradually decreases with respect to the set speed value. When the so-called "natural flow" is achieved in which the injection speed gradually decreases in this way, while maintaining the injection pressure at an appropriate value, the amount of deviation from the set value of the injection speed is reduced as much as possible. Injection / filling will be executed, and therefore, injection / filling will be performed while maintaining good injection speed and injection pressure.
Good molding is possible. Then, when entering the deceleration region at the end of the primary injection stroke, the torque limit for the servo motor is released, and in this deceleration region, the injection speed rapidly falls to the speed set value.

By doing so, a high-speed response at the time of acceleration / deceleration is achieved, and both the injection speed and the injection pressure are good in a region other than the acceleration / deceleration region which occupies most of the primary injection stroke. Since it can be made into a good product, it becomes possible to mold a good product at high speed and stably.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 shows an injection molding machine 1 according to this embodiment.
It is explanatory drawing which shows the feedback control system etc. for the next injection stroke, and FIG. 2 is 1 when the control method of this embodiment is applied.
It is explanatory drawing which shows the relationship between the drive current of a servo motor, and injection speed in the following injection stroke period.

In FIG. 1, 1 is a heating cylinder, 2 is a screw arranged in the heating cylinder 1 so as to be able to move forward and backward, and 3 is a hopper for supplying a raw material (resin material).
Reference numeral 4 is a motor for driving the screw rotation in which the rear end of the screw 2 is connected, 5 is a servo motor as a drive source for injection, and 6 is a drive motor.
Is a rotation for converting the rotation of the servomotor 5 into a linear movement-
It is a linear motion conversion mechanism. In the illustrated example, the output of the rotation-linear motion conversion mechanism 6 is transmitted to the casing of the motor 4, and the driving force of the servomotor 5 causes the screw 2 to be integrated with the motor 4.
Is capable of moving forward and backward.

As is well known in the above construction, the resin material supplied from the hopper 3 is transferred to the tip side of the screw 2 while being kneaded and plasticized by the rotation of the screw 2 by the driving force of the motor 4, and is melted. Screw 2
As the screw 2 is stored on the tip side of the screw 2, the screw 2 is retracted while controlling the back pressure, and when one shot of molten resin is stored on the tip side of the screw 2 (at the time of completion of measurement), the screw rotation is stopped. Then, after a lapse of a predetermined time, when the injection start timing is reached, the screw 2 is driven forward by the driving force of the servo motor 5, and the molten resin is injected / filled (primary injection) into the cavity of the mold (not shown). It is supposed to be done. When injection / filling (primary injection) is completed, the pressure-holding process is started, and the forward pressure is continuously applied to the screw 2 by the driving force of the servomotor 5, and the pressure-holding pressure is continuously applied to the resin in the mold. To be done. In this embodiment, the injection by the forward movement of the screw 2 described above
The injection speed during the filling (primary injection) stroke is feedback-controlled by a programmed process by the feedback control block 10 as described in detail later.

Reference numeral 7 denotes a rack body that moves forward and backward together with the screw 2, and an injection stroke sensor 8 composed of, for example, an optical encoder so as to rotate in synchronization with a gear (not shown) gear-connected to the rack body 7. Is provided. Therefore, when the screw 2 moves forward and backward, the injection stroke sensor 8 outputs a number of detection pulses commensurate with this, and the detection pulses are sent to the feedback control block 10 described later. In the present embodiment, the injection stroke sensor 8 is, for example, the stroke 0.
A detection signal of 1 pulse per 003 mm is generated.

Reference numeral 10 is a feedback control block for controlling the servomotor during the primary injection stroke. The arithmetic processing function, memory setting function and the like described later are actually embodied by processing based on various programs by the microcomputer. However, in this embodiment, for convenience of description, the feedback control block 10 includes a counter 11, a programmable timer module (hereinafter referred to as PTM) 12, an actually measured speed calculation processing unit 13, and a feedback output generation processing unit 1.
4, the following description will be given assuming that the torque limiter means 15 and the driver amplifier 16 are provided. 20
Is a molding condition setting storage unit that is also embodied by processing in the microcomputer. The molding condition setting storage unit 20 stores setting conditions for operation control of various strokes of the injection molding machine including the primary injection stroke. Has been done.

The detection pulse of the injection stroke sensor 8 is input to the counter 11, and the counter 11 counts by adding (or subtracting) it. PTM12
A clock of 2 MHz, for example, is input to its clock input terminal, and an internal counter adds (or subtracts) this clock to count a time of 0.5 μsec unit, for example.

The measured speed calculation processing unit 13 reads a predetermined sampling time (at a cycle), the count value of the counter 11 and the count value of the PTM 12 described above, and sets the screw stroke Sn in the sampling period to Sn = (counter 11 previous count value)-(counter 11
Current count value), and the time Tn of the sampling period.
Is calculated as Tn = (previous count value of PTM12) − (current count value of PTM12), and based on this, the injection speed Vn in the sampling period is calculated as Vn = Sn / Tn. The sampling time of the measured speed calculation processing unit 13 is, for example, about 3 msec in this embodiment.
It is set to about 30 msec, and each time the injection speed is calculated, this is sent to the feedback output generation processing unit 14 as speed actual measurement value information Vn.

As described above, the molding condition setting storage unit 20 stores the operating condition setting values for various strokes including the primary injection stroke. In this embodiment, the injection speed conditions for the primary injection stroke are stored. As, the injection speed value set corresponding to the screw forward position from the measurement completion point (position) to the holding pressure switching point (position) is stored. Then, during the primary injection stroke, the injection speed value stored in the molding condition setting storage unit 20 is controlled by the memory controller as appropriate, and the injection speed corresponding to the current screw position is adjusted at the timing matched with the current screw position. The value is read out and used as the speed setting value information Vo as the feedback output generation processing unit 1
4 is sent.

In the feedback output generation processing section 14,
Measured speed value Vn calculated by the measured speed calculation processing unit 13
And the speed setting value Vo at the corresponding position stored in the molding condition setting storage unit 20 are compared in real time,
The servo motor drive output value is output according to the comparison result. That is, the feedback output generation processing unit 14
When the measured speed value Vn deviates from the set speed value Vo, a correction value for bringing the measured speed value Vn closer to the set speed value Vo is calculated, and the servo motor drive output value based on this is output. Then, the output of the feedback output generation processing unit 14 is sent to the driver amplifier 16 via a D / A converter (not shown), and based on this, the driver amplifier 16 responds to the command value from the feedback output generation processing unit 14. The servo motor 5 is driven by the motor drive current.

Here, in the molding condition setting storage unit 20, setting information as to which region (which screw stroke region) in the primary injection stroke the torque limit is applied and the torque when the torque limit is applied are set. The limit value is also stored, and the torque limit condition setting information is also read by torque control condition setting information corresponding to the current screw position at a timing adjusted to the current screw position by the control of the memory controller as appropriate. It is sent to the torque limiter means 15. The torque limiter means 15 judges whether to apply a torque limit to the output torque of the servomotor 5 based on the input torque limit condition setting information. If the torque limit is to be applied, the torque limit value information is fed back as output. It is sent to the generation processing unit 14. The feedback output generation processing unit 14 performs arithmetic processing such that the motor torque becomes the torque limit value during the period in which the torque limit value information is input, and priority is given to maintaining the torque limit value. , The servo motor drive output value where the actual speed value Vn is closest to the speed set value Vo within the limited torque value range is output. Further, in the period in which the torque limit value information is not input (the period in which the torque limit is not applied), the feedback output generation processing unit 14 is assumed to output the rated maximum torque as in the conventional example described in FIG. As a result, the speed control is given the highest priority and the servo motor drive output value is output. In the present embodiment, the acceleration / deceleration area during the primary injection stroke is a period in which no torque limit is applied, and the area of the primary injection stroke other than the acceleration / deceleration area (most of the area during the primary injection stroke) is the torque. It is said to be the area where the limit is applied.

FIG. 2 is an explanatory diagram showing the relationship between the drive current of the servo motor and the injection speed during the primary injection stroke period when the feedback control method according to the present embodiment described above is applied. ) Shows the state of the motor drive current along the time axis, and (b) of the same figure shows the state of the speed change along the time axis.

As shown in FIG. 2, since the torque limit is not applied in the acceleration region in the initial stage of the primary injection stroke, the motor drive current is rapidly raised in this acceleration region (the torque of the servomotor 5 is rapidly increased. Launched),
The high power output causes the injection speed to rise rapidly to the speed setpoint. After the acceleration region, the servo motor 5 is in a torque limited state, and the output torque of the servo motor 5 is limited so as not to exceed a predetermined value (for example, about several tens% of the maximum rated torque). Is maintained, in other words, a predetermined injection pressure is maintained, and the speed feedback control is executed in this state. Therefore, in the area where this torque limit is applied,
Even if the speed feedback control is performed, the torque cannot be output beyond the predetermined value, and therefore the reaction speed (load resistance) from the resin being filled normally causes the measured speed value to gradually decrease with respect to the set speed value. When the so-called "natural flow" is achieved in which the injection speed gradually decreases in this way, while maintaining the injection pressure at an appropriate value, the amount of deviation from the set value of the injection speed is reduced as much as possible. Injection / filling will be executed, and therefore, by performing injection / filling while maintaining both good injection speed and injection pressure, it is possible to mold a good product. Then, when entering the deceleration region at the end of the primary injection stroke, the torque limit for the servomotor 5 is released again, and in this deceleration region, the injection speed is rapidly lowered to the speed set value.

As described above, according to this embodiment, a high-speed response at the time of acceleration / deceleration is achieved, and the injection speed and the injection pressure are increased in the regions other than the acceleration / deceleration region which occupies most of the primary injection stroke. Both can be good, so fast,
In addition, it is possible to stably form a good product. Also,
It can be applied to products that require high-speed injection from the beginning such as thin-walled molded products, and it is possible to accurately mold thin, compact precision molded products.

[0024]

As described above, according to the present invention, the injection pressure does not exceed the proper range even if the primary injection process is executed by the speed feedback control using the servomotor, and the thin-walled molded product or the like is used. It can be applied to products that require high-speed injection from the beginning, and it is possible to provide an injection control method for injection molding machines that can realize good product molding even for thin, small precision molded products, and its value Is a great deal.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a feedback control system and the like for a primary injection stroke of an injection molding machine according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a relationship between a drive current of a servo motor and an injection speed during a primary injection stroke period when a control method according to an embodiment of the present invention is applied.

FIG. 3 is an explanatory diagram showing a relationship between a drive current of a servo motor and an injection speed during a primary injection stroke period when a control method according to a conventional technique is applied.

FIG. 4 is an explanatory diagram showing a relationship between a drive current of a servo motor and an injection speed during a primary injection stroke period when a control method according to a conventional technique is applied.

[Explanation of symbols]

 2 screw 5 servo motor 6 rotation-linear motion conversion mechanism 7 rack body 8 injection stroke sensor 10 feedback control block 11 counter 12 programmable timer module (PTM) 13 actual speed calculation processor 14 feedback output generation processor 15 torque limiter means 16 driver Amplifier 20 Molding condition setting memory

Claims (1)

[Claims] 1. An injection molding machine for performing injection by advancing an injection screw by a driving force of a servomotor, and for performing an injection / filling process (primary injection process) during an injection process by speed feedback control. In the injection control method, a torque limiter means capable of limiting the torque of the servo motor is provided, and the acceleration / deceleration region during the injection / filling stroke is
The torque limit of the servo motor by the torque limiter means is released, and the torque limiter means limits the torque of the servo motor in areas other than the acceleration / deceleration area during the injection / filling stroke. An injection control method for an injection molding machine, comprising: