JP3482317B2 - 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 molding machine provided with a plurality of servomotors as an injection drive source for linearly driving a screw in a heating cylinder.

[0002]

2. Description of the Related Art A servomotor (electric servomotor) as a forward / backward drive source of a screw in an in-line screw type injection molding machine, that is, a servomotor for injection, has a resin injection mold filling process ( Accurate speed control during the primary injection process, accurate pressure control during the pressure-holding process that compensates for shrinkage of the resin in the mold by cooling, and process for kneading, plasticizing, and weighing the resin (measurement process) )
At the same time, high load and high precision control such as accurate back pressure control for achieving uniform plasticization of the resin are required.

When an injection molding machine having a servo motor as the injection drive source is to be made large, the injection servo motor is simply made large in response to the increase in size of the machine (the motor capacity is large). If you try to deal with this (by using a servo motor), the outer diameter of the servo motor, the rotary linear motion conversion mechanism, and the bearing will be large, and the moment of inertia will increase, resulting in poor transient response. Since it is expensive, it causes a significant cost increase.

Therefore, by using two or more servo motors having a relatively small capacity and a low cost as an injection drive source, the forces of a plurality of injection servo motors are combined to obtain a large power and the cost is reduced. Various types of injection molding machines have been proposed in which the rise is relatively suppressed and the increase in the moment of inertia is suppressed to obtain good transient response (good rise / fall characteristics).

As a conventional technique of the injection molding machine using the two servo motors as the injection drive source as described above, for example, Japanese Patent Publication No. 3-38100 and Japanese Patent Publication No. 4-736.
89, JP-A-62-48520, JP-A-4.
The technique described in Japanese Patent Publication No. 47917 is cited.

[0006]

As described above, when two injection servo motors are used, if rotation-linear motion conversion mechanisms are provided respectively corresponding to the two servo motors, the rotation-linear motion conversion mechanism is provided. This is advantageous in that the outer diameter of the motion conversion mechanism and the bearing can be reduced (the moment of inertia can be reduced). However, the transmission mechanism such as the individual rotation-linear motion conversion mechanism has dimension and assembly errors within the tolerance, and the servo amplifier (analog servo amplifier) and servo motor also have characteristic variations within the tolerance. If the same command value is input to the two servo motors, it is difficult to guarantee that the same speed or pressure is output to the outputs of the two rotation-linear motion conversion mechanisms. Therefore, conventionally, 2
For each servo motor, the command value given to the analog servo amplifier of one servo motor is used as a reference, and the command value given to the analog servo amplifier of the other servo motor is adjusted and output. It was also necessary to prepare two systems for the servo control calculation unit above the two servo amplifiers (analog servo amplifiers). Therefore, 2
It was pointed out that the hardware of the servo control calculation unit for controlling two servo amplifiers became complicated, or the control software of the servo control calculation unit became complicated, and the construction of the servo control calculation unit was generally troublesome. .

The present invention has been made in view of the above points,
The purpose is to provide an injection molding machine equipped with a plurality of injection servomotors and a rotation-linear motion conversion mechanism for converting the rotation of each servomotor into a linear motion,
It is to provide a machine in which a servo control calculation unit for controlling a servo amplifier can be easily constructed.

[0008]

In order to achieve the above-mentioned object, the present invention has a plurality of injection servo motors and a plurality of rotation-linear motion conversions for converting the rotations of the injection servo motors into linear motions. In an injection molding machine having a mechanism and linearly driving the screw in the heating cylinder by a plurality of injection servomotors through a plurality of rotation-linear motion conversion mechanisms, each injection servomotor is driven. For control, it has a digital servo amplifier provided corresponding to each injection servo motor, and a servo control calculation unit that controls the plurality of digital servo amplifiers in a unified manner. Output the same command value to the servo amplifier,
Each digital servo amplifier responds to the same command value from the servo control calculation unit so that the outputs from each rotation-linear motion conversion mechanism are all equivalent based on the correction data given in advance. Is configured to drive and control the injection servo motor. When the digital servo amplifier is used as described above, the digital servo amplifier can accurately monitor the number of revolutions and torque digitally. By performing adjustments (for example, offset adjustments and gain adjustments) according to the characteristic variations of the above, each digital servo amplifier operates in accordance with each rotation-linear motion conversion mechanism with respect to the same command value from the servo control calculation unit. It is possible to accurately drive and control the corresponding injection servo motors so that the outputs are all equivalent.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a simplified configuration of an injection system in an injection molding machine according to an embodiment of the present invention (hereinafter referred to as the present embodiment).

In FIG. 1, 1 is a screw arranged in a heating cylinder 2 so as to be rotatable and forward / backward, 3 is a connecting member attached to the rear end of the screw,
4 is a slide member that holds the connecting member 3 rotatably,
The slide member 4 is held so that it can be moved back and forth along a guide member (not shown).

Reference numerals 5 and 6 denote a pair of injection servomotors (hereinafter referred to as servomotors) of the same model number, which are the forward and backward drive sources of the screw 1, and 7 and 8 detect the rotational positions of the servomotors 5 and 6. Encoder with counter function, 9, 10
Is a drive pulley attached to the output shaft of each servomotor 5, 6. Further, reference numerals 11 and 12 denote driven pulleys rotatably held by appropriate supporting members.
Between the drive pulleys 9 and 10 and the timing belt 1
3 and 14 are wound around each.

Numerals 15 and 16 are a pair of rotary-linear motion converting mechanisms having the same structure, and ball screw shafts 17 and 19 respectively.
And the nut body 1 screwed onto the ball screw shafts 17 and 19.
8 and 20, and the ball screw shafts 17 and 19
One end of each is integrally coupled to the driven pulleys 11 and 12, respectively. Then, the nut body 18 that moves forward and backward by the rotation of the ball screw 17 is coupled to the slide member 4 via a coupling member 21 having a load cell (pressure sensor) 23,
The nut body 20 which moves forward and backward by the rotation of the ball screw 19 is coupled to the slide member 4 via a coupling member 22 having no load cell.

In the transmission mechanism described above, the rotation of the servomotors 5 and 6 controlled synchronously is such that the drive pulleys 9 and 10 → the timing belts 13 and 14 → the driven pulley 1
1, 12 → ball screw shafts 17 and 19 are transmitted in this order, and the rotation of the ball screw shafts 17 and 19 is converted into forward and backward movement of the nut bodies 18 and 20. The forward / backward movement of the nut bodies 18 and 20 is transmitted to the slide member 4 via the connecting members 21 and 22, and is transmitted from the slide member 4 to the screw 1 via the connecting member 3.

Reference numeral 24 is a system controller for controlling the entire machine (injection molding machine), and 25 is, for example, a color CRT.
A display device composed of a display or the like, 26 is a key input device for an operator to input data and various instructions to the system controller 24, and 27 is a servo control (servo command value output) under the control of the system controller 24. ) Servo control computing unit, 28 is load cell 2
It is an A / D converter that analog-digital converts the output value S4 of No. 3 and outputs it to the servo control calculation unit 27. Also,
Reference numerals 29 and 30 denote a pair of digital servo amplifiers having the same function and configuration. Both of the 29 and 30 are centrally controlled by the servo control calculation unit 27, and one digital servo amplifier 29 is
One servomotor 5 is drive-controlled by feedback control, and the other digital servo amplifier 30 drives-controls the other servomotor 6 by feedback control.

Here, the digital servo amplifiers 29, 30
Although the internal arithmetic control function is completely digitalized, in the current commercial products, the analog input format is still mainstream. In this case, the digital servo amplifiers 29 and 30 are Since it is equipped with an A / D converter for converting an input signal from analog to digital, when such a digital servo amplifier is used, although not shown, the servo control calculation unit 27 A D / A converter that performs digital-analog conversion on the output will be provided. Although the encoders 7 and 8 for detecting the rotational positions of the servo motors 5 and 6 have a counter function, they may be separately provided with encoder counters.

In the present embodiment, the servo control calculation unit 27 has a position set value input unit 27a from the system controller 24, a difference calculation unit 27b, and a speed set value input unit 27c from the system controller 24. When,
Input part 2 of the pressure set value from the system controller 24
7d, a difference calculation unit 27e, and a speed upper limit value control unit 27 for restricting the speed upper limit during pressure feedback control.
f and a switch unit 27g that is switched and controlled by a control signal from the system controller 24, and the switch unit 27g is used during speed feedback control.
Is switched to the a side, and the switch portion 27g is switched to the b side during pressure feedback control.

Further, the digital servo amplifiers 29 and 30 include difference calculation sections 29a and 30a and amplifier sections 29b and 3a.
0b and each digital servo amplifier 2
9 and 30, the same command value S1 is output from the servo control calculation unit 27, and the digital servo amplifier 29 outputs the command value S1 from the servo control calculation unit 27 and the output value from the encoder 7. The servo motor 5 is feedback-controlled by comparing with S2, and the digital servo amplifier 30 compares the command value S1 from the servo control calculating unit 27 with the output value S3 from the encoder 8 and feedbacks the servo motor 6. Control. The output value S2 of the encoder 7 of the one servo motor 5 is also output to the servo control calculation unit 27.

Here, the digital servo amplifiers 29, 30
The amplifier units 29b and 30b of the above-mentioned amplifiers, according to the characteristic variations of the servomotors 5 and 6 respectively driven, the size and assembly error of the transmission mechanism, and the like, output the correction data A1 and A2 at the time of shipping or regular inspection. By giving the offset adjustment and the gain adjustment, the digital servo amplifiers 29 and 30 are provided with the same command value S1 from the servo control calculation unit 27.
The drive currents to the corresponding servomotors 5 and 6 are controlled so that the outputs from the rotation-linear motion conversion mechanisms 15 and 16 become equal. That is, since the digital servo amplifier can accurately monitor the output of the rotation speed and the torque digitally, the output (measurement value of the rotation speed and the torque) by each rotation-linear motion conversion mechanism 15 and 16 at that time.
By contrasting with the above, the above-mentioned adjustment can be made extremely accurate, and its automatic adjustment can be easily realized by software.

In the above-described structure, the switch portion 27g of the servo control calculation portion 27 is switched to the side a in the primary injection stroke in which the resin is injected and filled in the cavity of the mold (switched to the speed feedback control side). Based on the position information controlled by the position feedback control from the difference calculation unit 27b, which compares the output of the position setting value input unit 27a with the output S2 of the encoder 7, the speed setting value input unit 27c The command value S1 corresponding to the current speed target value corresponding to the position information is output to each of the digital servo amplifiers 29 and 30 via the switch unit 27g.

In response to this, the digital servo amplifier 29
Compares the command value S1 with the output value S2 from the encoder 7 to perform feedback control of the servo motor 5, and the digital servo amplifier 30 includes the servo control calculation unit 2
The servo motor 6 is feedback-controlled by comparing the command value S1 from 7 and the output value S3 from the encoder 8. Thereby, each rotation-linear motion conversion mechanism 15, 1
The speeds (forward speeds) output by 6 are the same, and the above-described screw 1 is accurately driven by speed feedback control.

The pressure-holding process following the primary injection process,
Alternatively, in the back pressure control during the measurement process, the switch unit 27g of the servo control calculation unit 27 is switched to the b side (switched to the pressure feedback control side), and the output of the pressure set value input unit 27d Load cell 2
The pressure feedback-controlled pressure information from the difference calculation unit 27e, which is to be compared with the output S4 of No. 3, is used as the command value S1 that is the pressure target value at the present time (current second), the speed upper limit regulating unit 27f, the switch unit. It is output to each digital servo amplifier 29, 30 via 27g.

In response to this, the digital servo amplifier 29
Compares the command value S1 with the output value S2 from the encoder 7 to perform feedback control of the servo motor 5, and the digital servo amplifier 30 includes the servo control calculation unit 2
The servo motor 6 is feedback-controlled by comparing the command value S1 from 7 and the output value S3 from the encoder 8. Thereby, each rotation-linear motion conversion mechanism 15, 1
The pressures output by 6 are the same, and the screw 1 described above
By the pressure feedback control, the holding pressure control or the back pressure control can be performed accurately.

In the above embodiment, a pair of digital servo amplifiers 29 and 30, a pair of servo motors 5 and 6, and a pair of rotation-linear motion conversion mechanisms 15 and 1 are provided.
However, it is needless to say that the present invention can be applied to a configuration using three or more digital servo amplifiers, servo motors, and rotation-linear motion conversion mechanisms.

The present invention is also applicable to a configuration in which the rotations of a plurality of injection servomotors are transmitted to one rotation-linear motion conversion mechanism.

[0025]

As described above, according to the present invention, in an injection molding machine provided with a plurality of injection servomotors and a rotation-linear motion conversion mechanism for converting the rotation of each servomotor into a linear motion, It is possible to provide an injection molding machine in which the servo control calculation unit for controlling the servo amplifier can be easily constructed, and the servo control calculation unit can be simplified. In this type of injection molding machine, its value is great. is there.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a simplified configuration of an injection system in an injection molding machine according to a first embodiment of the present invention.

[Explanation of symbols]

1 screw 2 heating cylinder 3 connecting members 4 Slide member 5,6 Injection servo motor (servo motor) 7,8 encoder 9,10 Drive pulley 11,12 driven pulley 13,14 Timing belt 15, 16 Rotation-linear motion conversion mechanism 17, 19 Ball screw shaft 18,20 Nut body 21 Connecting member with load cell 22 Connecting member without load cell 23 load cell 24 system controller 25 display 26 key input device 27 Servo control calculator 29,30 Digital Servo Amplifier

─────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-1-247128 (JP, A) JP-A-3-199026 (JP, A) JP-B 3-38100 (JP, B2) JP-B 4- 73689 (JP, B2) Japanese Patent Publication No. 7-112711 (JP, B2) Patent 2552549 (JP, B2) (58) Fields investigated (Int.Cl. ⁷ , DB name) B29C 45/00-45/84

Claims (4)

(57) [Claims] 1. A plurality of injection servomotors, and a rotation-linear motion conversion mechanism for converting the rotation of each injection servomotor into a linear motion. A screw in a heating cylinder is provided with a plurality of injection servomotors. In the injection molding machine which is linearly driven through the rotation-linear motion conversion mechanism, the digital servos provided corresponding to the injection servo motors are provided to drive and control the injection servo motors. It has an amplifier and a servo control arithmetic unit that controls the digital servo amplifiers.
The servo control calculation unit outputs the same command value to each of the digital servo amplifiers. 2. The injection molding machine according to claim 1, wherein a plurality of the rotation-linear motion conversion mechanisms are provided corresponding to the plurality of injection servomotors. 3. The digital servo amplifier according to claim 1, wherein each of the digital servo amplifiers responds to the same command value from the servo control calculation unit based on correction data individually given in advance. An injection molding machine characterized by driving and controlling each of the corresponding injection servomotors so that the outputs from the respective rotation-linear motion conversion mechanisms are all equivalent. 4. The rotational position detection information from one of the rotation detection sensors respectively attached to the plurality of injection servomotors according to claim 2 or 3,
Pressure detection information from a pressure sensor attached only to one of the plurality of rotation-linear motion conversion mechanisms is input to the servo control calculation unit as actual measurement position information and actual measurement pressure information. Injection molding machine.