JP3096944B2 - Injection control method for injection molding machine and injection molding machine - Google Patents

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 an injection molding machine , and more particularly to an injection process using a servomotor as a drive source for injection (primary injection process as an injection / filling process). Injection during the process consisting of
Injection control method and injection molding in an injection molding machine that performs a filling step (primary injection step) by speed feedback control
It is about the machine .

[0002]

2. Description of the Related Art In an injection molding machine, control conditions of injection speed and injection pressure are important factors in molding a good product. Injection molding machines in which this injection speed or injection pressure is feedback-controlled are not used. Various proposals have been made. In a conventional injection molding machine that performs feedback control, generally, a primary injection process of injecting and filling a molten resin into a cavity of a mold is performed by controlling an injection speed such that an actual measured speed approaches a set speed value. Feedback control (feedback control giving priority to injection speed) is performed.

In an injection molding machine using a servomotor as a driving source for injection for advancing a screw, the above-mentioned 1 which performs speed feedback control is used.
During the next injection stroke, in order to give priority to speed stability control, the servo motor is generally used in a state where the rated maximum torque can be output (without applying a torque limit).
Feedback control was performed so that the actual measured value always matched the set speed value. 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 in this case. FIG. 3A shows the state of the motor drive current along the time axis. (B) of the figure shows how the speed changes along the time axis. As shown in FIG. 3, in the acceleration region, the motor drive current rises rapidly, and the injection speed rises rapidly to the speed set value. In the deceleration region, the motor drive current falls rapidly, rises again, and the injection speed increases. It falls rapidly to the set value.
However, if the servomotor is used without applying a torque limit, that is, if there is a margin in the output torque of the servomotor so that it can always follow the set speed, the injection speed always matches the set value correctly. Even though the feedback control is performed, the injection pressure corresponding to the motor torque is not constant due to the fluctuation of the resin pressure, which is a load reaction force, and cannot be controlled substantially.

On the other hand, in order to control the injection pressure, for example, as described in Japanese Patent Publication No. 4-58371, the torque (injection pressure) of the servomotor is limited to a predetermined value by applying a torque limit. Techniques are known. FIG.
Is a diagram showing the relationship between the drive current of the servomotor and the injection speed during the primary injection stroke when the control method disclosed in the above-mentioned prior application is applied, and FIG. FIG. 3B shows the state of the motor drive current along the axis, and FIG. 4B shows the state of the speed change along the time axis. As shown in FIG. 4, in the above-mentioned prior application, a torque limit means that operates only in the injection direction is provided. According to the above-mentioned prior application, the reason for this is to prevent breakage due to screw overrun when performing an idling operation (an operation of advancing the screw in a state where there is no reaction force due to resin) by purging or the like. is there.

[0005]

As shown in FIG. 3 and described above, when the injection speed is feedback-controlled without applying a torque limit to the servomotor, the actual measured speed is controlled so as to match the set speed. However, the injection pressure corresponding to the motor torque cannot be controlled. Here, as the set value for the primary injection stroke, the injection speed as a servo target (target of feedback control) is of course set. Since the injection pressure during the injection stroke is also an important factor, this injection pressure is not a servo target but a desirable appropriate value is set as a monitoring index. However,
Under any circumstances, if feedback control is performed so that the injection speed matches the speed setting value (for example, if speed feedback control is performed regardless of the reaction force from the resin, so-called forced feedback control is performed). ), Which can cause the injection pressure to be much higher than appropriate,
A problem arises in that defective products are formed despite the feedback control.

If the method according to the above-mentioned prior application shown in FIG. 4 is applied to control during a molding operation as it is, it gradually rises to a target speed in an acceleration region, so that high-speed response is inferior. A major problem arises in that it cannot be applied to products that require high-speed injection from the beginning.

[0007] The present invention has been made in view of the above points,
The purpose is to achieve good molding without the injection pressure exceeding the proper range even if the primary injection process is executed by speed feedback control using a servomotor.
To make it possible .

[0008]

According to the present invention, in order to achieve the above-mentioned object, an injection screw is advanced by a driving force of a servomotor to perform injection, and a primary injection step during the injection process is performed at a speed. In an injection control method for an injection molding machine executed by feedback control, a torque limiter means capable of limiting a torque of a servomotor is provided, and an acceleration / deceleration region during a primary injection stroke is limited by a torque limiter means for the servomotor. The servo motor is released and the torque is limited by the torque limiter means in the other area than the acceleration / deceleration area during the primary injection stroke. In addition, injection by the driving force of the servo motor
And the speed injection is performed during the primary injection stroke during the injection stroke.
Primary injection in an injection molding machine
The acceleration / deceleration area during the stroke is the torque control for the servo motor.
Limit and cancel other areas other than the acceleration / deceleration area during the primary injection stroke.
The range is the torque limit,
A limiter means is provided.

[0009]

In the acceleration region in the early stage of the primary injection stroke, no torque limit is applied. Therefore, in this acceleration region, the injection speed rapidly rises to the speed set value with a high torque output. After passing through the acceleration region, the servomotor is in a torque-limited state, the output torque of the servomotor is limited so as not to exceed a predetermined value, and the predetermined torque is maintained, in other words, the predetermined injection pressure is reduced. The speed feedback control is performed in this state. For this reason, in the region where the torque limit is applied, even if the speed feedback control is performed, the torque cannot be output to a predetermined value or more.
As a result, the actually measured speed value gradually decreases with respect to the set speed value. In this manner, when the injection speed gradually decreases, that is, when a so-called “natural flow” is achieved, the deviation from the set value of the injection speed is minimized while maintaining the injection pressure at an appropriate value. Injection and filling will be performed, and therefore, injection and filling will be performed while maintaining both the injection speed and the injection pressure at a good level.
Non-defective molding becomes possible. Then, when the vehicle enters the deceleration region at the end of the primary injection stroke, the torque limit for the servo motor is released, and the injection speed falls rapidly to the speed set value in this deceleration region.

By doing so, a high-speed response during acceleration / deceleration is achieved, and both the injection speed and the injection pressure are good in a region other than the acceleration / deceleration region that occupies most of the primary injection stroke. As a result, a good product can be formed at high speed and stably.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One 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.
FIG. 2 is an explanatory diagram showing a feedback control system and the like for the next injection stroke. FIG.
FIG. 7 is an explanatory diagram showing a relationship between a drive current of a servo motor and an injection speed during a next injection stroke period.

In FIG. 1, 1 is a heating cylinder, 2 is a screw disposed in the heating cylinder 1 so as to be able to move forward and backward and rotatable, 3 is a hopper for supplying a raw material (resin material),
4 is a motor for driving the rotation of the screw to which the rear end of the screw 2 is connected, 5 is a servomotor as a driving source for injection, 6
Is a rotation for converting the rotation of the servo motor 5 into a linear motion.
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 is combined with the motor 4 to form the screw 2.
Can move forward and backward.

As is known in the above configuration, the resin material supplied from the hopper 3 is transferred to the tip end 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 the molten resin is removed. Screw 2
As the screw 2 is stored at the front end of the screw 2, the screw 2 moves backward while the back pressure is controlled, and when one shot of the molten resin is stored at the front end of the screw 2 (at the time of completion of the measurement), the screw rotation is stopped. Then, when the injection start timing comes after a lapse of a predetermined time, the screw 2 is driven forward by the driving force of the servo motor 5, and the molten resin is injected and filled into the cavity of the mold (not shown) (primary injection). It is supposed to be. When the injection / filling (primary injection) is completed, the dwelling process starts, and the forward pressure is continuously applied to the screw 2 by the driving force of the servo motor 5, so that the dwelling pressure is continuously applied to the resin in the mold. Is done. In the present embodiment, the injection / injection
The injection speed during the filling (primary injection) process is feedback-controlled by programmed processing by the feedback control block 10 as will be described in detail later.

Reference numeral 7 denotes a rack body which moves forward and backward integrally with the screw 2. An injection stroke sensor 8 composed of, for example, an optical encoder or the like so as to rotate synchronously with a gear (not shown) gear-coupled to the rack body 7. Is provided. Therefore, when the screw 2 moves forward and backward, the injection stroke sensor 8 outputs a corresponding number of detection pulses, which are sent to the feedback control block 10 described later. In the present embodiment, the injection stroke sensor 8 detects, for example, the stroke of the screw 2.
A one-pulse detection signal is generated per 003 mm.

Numeral 10 denotes a feedback control block which controls the servo motor during the primary injection stroke. The arithmetic processing function, storage setting function, etc., which will be described later, are actually realized by processing based on various programs by the microcomputer. However, in this embodiment, for convenience of explanation, 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 made assuming that the motor includes the torque limiter 15, the driver amplifier 16, and the like. In addition, 20
Is a molding condition setting storage unit also embodied by processing in the microcomputer. The molding condition setting storage unit 20 stores setting conditions for operation control of various processes of the injection molding machine including the primary injection process. Have been.

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

The measured speed calculation processing section 13 reads out a predetermined sampling time (period), the count value of the counter 11 and the count value of the PTM 12, and calculates the screw stroke Sn within the sampling period as Sn = (counter 11 previous count value) − (counter 11
Of the sampling period) and the time Tn of the sampling period.
Is measured as Tn = (previous count value of PTM12) − (current count value of PTM12), and based on this, the injection speed Vn within the sampling period is calculated as Vn = Sn / Tn. In this embodiment, the sampling time of the actually measured speed calculation processing unit 13 is, for example, about 3 msec.
The injection speed is set to about 30 msec, and is sent to the feedback output generation processing unit 14 as actual speed value information Vn every time the injection speed is calculated.

As described above, the molding condition setting storage unit 20 stores operating condition set values for various strokes including the primary injection stroke. In the present embodiment, the injection speed condition during the primary injection stroke is set. The injection speed value set corresponding to the screw advance position from the measurement completion point (position) to the pressure holding switching point (position) is stored. During the primary injection stroke, the injection speed value stored in the molding condition setting storage unit 20 is controlled by a memory controller as appropriate to adjust the injection speed according to the current screw position at the timing adjusted to the current screw position. The value is read out, and the read out value is used as the speed output value information Vo.
4 is sent.

In the feedback output generation processing unit 14,
The actually measured speed value Vn calculated by the actually 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 in real time,
A servo motor drive output value is output according to the comparison result. That is, the feedback output generation processing unit 14
If the actual speed value Vn is deviated from the actual speed value Vo, a correction value for bringing the actual speed value Vn closer to the actual speed value Vo is calculated, and a 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 applied motor drive current.

Here, the molding condition setting storage unit 20 stores setting information indicating in which region (in which screw stroke region) the torque limit is to be applied during the primary injection stroke, and the torque for applying the torque limit. The limit value is also stored, and the torque limit condition setting information corresponding to the current screw position is read out at the timing matched with the current screw position by the control of the memory controller as appropriate. It is sent to the torque limiter 15. The torque limiter 15 determines whether or not to apply a torque limit to the output torque of the servomotor 5 based on the input torque limit condition setting information. It is sent to the generation processing unit 14. During the period in which the torque limit value information is input, the feedback output generation processing unit 14 performs a calculation process so that the motor torque becomes the torque limit value, and gives priority to maintaining the torque limit value. And outputs the servo motor drive output value in which the actual speed value Vn is closest to the speed set value Vo within the limited torque value range. Also, during a period in which the torque limit value information is not input (a period in which no torque limit is applied), the feedback output generation processing unit 14 assumes that the rated maximum torque is output, as in the above-described conventional example described with reference to FIG. The priority is given to the speed control, and the servo motor drive output value is output. In the present embodiment, the acceleration / deceleration region during the primary injection stroke is a period in which no torque limit is applied, and the region of the primary injection stroke other than the acceleration / deceleration region (most of the region during the primary injection stroke) is torque. It is 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 when the above-described feedback control method according to the present embodiment 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 at the beginning of the primary injection stroke, the motor drive current is rapidly increased in this acceleration region (the torque of the servo motor 5 is rapidly increased). Launched),
The injection speed is rapidly increased to the set speed by the high power output. After passing through 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), and the predetermined torque is reduced. In other words, in other words, the predetermined injection pressure is maintained, and in this state, the speed feedback control is executed. For this reason, in this torque-limited area,
Even if the speed feedback control is performed, the torque cannot be output beyond the predetermined value. Therefore, usually, the measured speed value gradually decreases with respect to the set speed value due to the reaction force (load resistance) from the resin being filled. In this manner, when the injection speed gradually decreases, that is, when a so-called “natural flow” is achieved, the deviation from the set value of the injection speed is minimized while maintaining the injection pressure at an appropriate value. Injection / filling is performed. Therefore, by performing injection / filling while maintaining both the injection speed and the injection pressure at a favorable level, it is possible to form a good product. Then, when the vehicle enters the deceleration region at the end of the primary injection stroke, the torque limit for the servo motor 5 is released again, and the injection speed is rapidly reduced to the speed set value in this deceleration region.

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 in the region other than the acceleration / deceleration region occupying most of the primary injection stroke. Both can be good, so fast,
In addition, a good product can be formed stably. Also,
It can be applied to products that require high-speed injection from the beginning, such as thin-walled molded products, and thin and small precision molded products can be molded with high precision.

[0024]

As described above, according to the present invention, the injection pressure does not exceed an appropriate range even if the primary injection stroke is executed by speed feedback control using a servomotor. This type of injection molding machine can be applied to products that require high-speed injection from the beginning, such as thin and small precision molded products.
In the, the value is great.

[Brief description of the 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 one embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a relationship between a drive current of a servomotor and an injection speed during a primary injection stroke 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 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 when a control method according to the related art is applied.

[Explanation of symbols]

 2 Screw 5 Servomotor 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 processing unit 14 Feedback output generation processing unit 15 Torque limiter means 16 Driver Amplifier 20 Molding condition setting storage unit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-230917 (JP, A) JP-A-62-207622 (JP, A) JP-A-2-20315 (JP, A) JP-A 62-207 207621 (JP, A) JP-A-2-20316 (JP, A) JP-A-3-213320 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B29C 45/00-45 / 84

Claims (2)

(57) [Claims] 1. A screw for injection subjected to injection is advanced by the driving force of the servo motor, and an injection molding machine to perform injection and filling process in injection stroke (the higher the primary injection line) at a speed feedback control In the injection control method of the above, provided with a torque limiter means capable of limiting the torque of the servo motor, the acceleration / deceleration region during the injection / filling process,
The torque limit of the servo motor by the torque limiter is released, and the torque limiter is applied to the servo motor by the torque limiter in an area other than the acceleration / deceleration area during the injection / filling process. An injection control method for an injection molding machine. 2. Injection is performed by the driving force of a servo motor.
Injection and filling process during the injection process (primary injection process
To the injection molding machine that executes speed feedback control
Oite, acceleration and deceleration regions in the injection-filling stroke, the servomotor
Release the torque limit for the
Other areas than the acceleration / deceleration area of
Torque limiter means
An injection molding machine characterized in that: