JP5113928B2 - Nozzle touch control device for injection molding machine - Google Patents

Description

  The present invention relates to a control device for causing a nozzle attached to the tip of an injection cylinder to touch a mold with a servo motor and generating a predetermined nozzle touch force in an injection molding machine.

  The nozzle attached to the tip of the injection cylinder of the injection unit of the injection molding machine converts the rotational movement of the nozzle forward / backward servomotor fixed on the base of the injection molding machine body into a linear movement using a transmission mechanism such as a ball screw. Performs forward / backward movement by conversion. In the nozzle advancement operation, after the nozzle is advanced by the servo motor and the nozzle is touched, the nozzle forward / reverse motor is further operated to compress the elastic member between the transmission mechanism and the injection unit to generate a predetermined nozzle touch force. Let When a predetermined nozzle touch force is generated, the screw in the injection unit is advanced to inject molten resin into the mold.

  During the continuous molding operation, it is desirable that the nozzle touch force be kept constant so that the molten resin does not leak from the mold and the nozzle portion. However, depending on the structure of the mold, when the mold clamping operation is performed, the nozzle is pushed back in the backward direction, the elastic member is compressed, and the nozzle touch force may increase. At this time, there is no problem as long as the compression amount is equal to or less than the maximum compression amount of the elastic member, but if the compression amount exceeds the maximum compression amount and is pushed back in the nozzle retraction direction, the transmission mechanism of the injection unit and the fixed portion of the servo motor for moving the nozzle back and forth May be damaged due to excessive load. Therefore, it is necessary to control the servo motor for moving the nozzle back and forth so that an excessive load is not generated.

Patent Document 1 discloses a technique in which a predetermined nozzle touch force is generated by controlling the deformation amount of an elastic member.
Patent Document 2 discloses a technique for positioning a servo motor at a position corresponding to a nozzle touch force.
Patent Document 3 discloses a technique for controlling the torque of a motor based on a set nozzle touch force.
In Patent Document 4, when the encoder that detects the compression amount of the elastic member detects that the compression amount of the elastic member exceeds a predetermined amount, the motor is rotated in a direction in which the nozzle moves away from the mold, A technique for releasing a brake that holds a position is disclosed.

JP 2003-351133 A Japanese Patent Laid-Open No. 5-200784 JP-A-63-154320 JP 2006-27248 A

The techniques disclosed in Patent Document 1 and Patent Document 2 described in the Background Art section generate a predetermined nozzle touch force by detecting a displacement amount of an elastic member, or generate a predetermined nozzle touch force. The servo motor is positioned by position. The method of controlling the nozzle touch force with the deformation amount of the elastic member is not affected by the friction of the transmission mechanism as compared with the case of controlling with the torque of the motor as in Patent Document 3, so the predetermined nozzle touch force is accurately There is an advantage that can be generated. However, these prior arts do not disclose any countermeasures for protecting the mechanical unit assuming that an excessive load is applied to the injection unit by the mold clamping operation.
On the other hand, Patent Document 4 discloses that the amount of deformation of the elastic member is detected to rotate the motor or release the brake, but the load is detected and overload avoidance operation such as rotation operation or brake release is performed. For this reason, there is a problem that the avoidance operation is not in time when the load increases instantaneously and suddenly as in the mold clamping operation.
Accordingly, in view of the above-mentioned problems of the prior art, the object of the present invention is that when an excessive load exceeding the torque limit value is generated in the nozzle forward / reverse motor, the motor rotates under the load and the injection unit An object of the present invention is to provide a nozzle touch control device for an injection molding machine in which an excessive load is not applied to a mechanism unit.

  The invention according to claim 1 of the present application includes a servo motor that advances a nozzle for nozzle touching a mold, a transmission mechanism that converts a rotational motion of the servo motor into a linear motion, and a nozzle touch that is connected to the transmission mechanism. An elastic member for generating a force, a positioning control unit for positioning the servomotor at a position compressed by the elastic member in response to a preset nozzle touch force, and while positioning the servomotor, A torque limiting unit that limits torque of the servo motor with a torque limit value that is larger than a set nozzle touch force and smaller than a nozzle touch force corresponding to a maximum compression amount of the elastic member. It is a nozzle touch control device of a molding machine.

  According to the present invention, when an excessive load exceeding the torque limit value is generated, the motor rotates against the load, so that an excessive load is not applied to the mechanism portion of the injection unit. In addition, the torque limiter acts directly on the inner current loop in the motor control loop such as position, speed, and current, so that even if an excessively large load is applied instantaneously, the delay in response can be minimized. The mechanism part can be protected.

It is a block diagram explaining the nozzle touch control apparatus of the injection molding machine to which this invention is applied. It is a figure explaining position and torque control in a nozzle touch state.

FIG. 1 is a block diagram illustrating a nozzle touch control device of an injection molding machine to which the present invention is applied. The injection molding machine M includes a mold clamping part Mc and an injection part Mi on a machine base Mb. The injection part Mi heats and melts a resin material (pellet) and injects the molten resin into the cavity of the mold 31. The mold clamping portion Mc mainly opens and closes the mold 31 (movable side mold 31a, fixed side mold 31b).
The injection part Mi will be described. A nozzle 2 is attached to the tip of the injection cylinder 1. A screw 3 is inserted into the injection cylinder 1. The screw 3 is provided with a resin pressure sensor 5 using a load cell or the like that detects the resin pressure by the pressure applied to the screw 3. The resin pressure sensor output signal output from the resin pressure sensor 5 is converted into a digital signal by the A / D converter 16 and input to the servo CPU 15.

  The screw 3 is rotated by a screw rotating servo motor M2 via a transmission mechanism 6 composed of a pulley, a belt and the like. Further, the screw 3 is driven by a servo motor M1 for moving forward and backward through a transmission mechanism 7 including a mechanism for converting a rotary motion such as a pulley, a belt, a ball screw / nut mechanism, etc. into a linear motion. Moved to. Reference numeral P1 is a position / speed detector that detects the position and speed of the screw 3 in the axial direction by detecting the position and speed of the servo motor M1 for moving forward and backward, and reference numeral P2 is the position of the servo motor M2. The position / speed detector detects the rotational position and speed around the axis of the screw 3 by detecting the speed. Reference numeral 4 denotes a hopper for supplying resin into the injection cylinder 1.

  The injection molding machine M includes a nozzle touch driving device for advancing the injection part Mi toward the mold clamping part Mc in order to press the nozzle 2 against the fixed platen 32 to which the fixed mold 31b is attached (nozzle touch). ing. The nozzle touch drive device includes a nozzle forward / backward servomotor M3 attached to the machine base Mb, one end connected to the load shaft of the nozzle forward / backward servomotor M3, and the other end rotatably supported by the fixed platen 32. Ball screw 34, nut 33 screwed to ball screw 34, first pressure plate 36 fixed to injection unit 39 of injection part Mi, second pressure plate 37 attached to the nut, first pressure plate And a sensor 38 for measuring the distance between the first pressure receiving plate 36 and the second pressure receiving plate 37 and detecting the length of the spring. A position / speed detector P3 is attached to the servo motor M3 for moving the nozzle back and forth. The output signal of the position / velocity detector P3 is fed back to the servo CPU 15 and used for controlling the servo motor M3 for moving the nozzle back and forth.

  The nozzle touch drive device causes the nut 33 to move forward and backward relative to the fixed platen 32 by rotating the nozzle forward / backward servomotor M3 and rotating the ball screw 34. The distance between the first pressure receiving plate 36 and the second pressure receiving plate 37 is adjusted by moving the nut 33 back and forth, and the elastic force of the spring 35 is adjusted. In the case of a mechanism that generates a nozzle pressing force by contracting an elastic body such as the spring 35 shown in FIG. 1, the nozzle pressing force of the nozzle 2 can be detected by measuring the length of the elastic body. . In addition to the spring, rubber can be used as the elastic body. Thereby, the nozzle pressing force (nozzle touch force) to the fixed side die 31b of the desired nozzle 2 can be generated.

An output signal from the sensor 38 that detects the length of the spring 35 is stored in the RAM 22 as the nozzle pressing force of the nozzle 2 via the interface 27. Detection of the nozzle pressing force of the nozzle 2 by the sensor 38 is performed at predetermined time intervals (at each sampling interval).
The mold clamping portion Mc is further moved after the movable platen 30 is advanced in the direction of the fixed platen 32 by a movable platen forward / reverse motor (not shown) and the mold is closed, and the movable platen 31a and the fixed mold 31b are further contacted. 30 is advanced in the direction of the fixed platen 32 to generate a predetermined clamping force. Then, mold opening is performed by moving the movable platen 30 backward. In FIG. 1, only the movable platen 30, the dies 31a and 31b, and the fixed platen 32 are shown as the mold clamping portion Mc.

The control device of the injection molding machine M includes a CNC CPU 20 that is a microprocessor for numerical control, a PMC CPU 17 that is a microprocessor for a programmable machine controller, and a servo CPU 15 that is a microprocessor for servo control. Information is transmitted between the microprocessors by selecting mutual input / output.
The servo CPU 15 is connected to a ROM 13 that stores a control program dedicated to servo control that performs processing of a position loop, a speed loop, and a current loop, and a RAM 14 that is used for temporary storage of data. The servo CPU 15 is connected so as to be able to detect a pressure signal output from the resin pressure sensor 5 provided in the injection molding machine M via an A / D (analog / digital) converter 16.

  Based on a command from the servo CPU 15, the servo CPU 15 drives an injection servo motor M1, connected to the injection shaft, a screw rotation servo motor M2, connected to the screw rotation shaft, and a nozzle forward / reverse servo motor M3. Servo amplifiers 11, 12, and 10 are connected. Further, output signals from position / speed detectors P1, P2, P3 attached to the servo motors M1, M2, M3 are fed back to the servo CPU 15. The rotational positions of the servo motors M1, M2, and M3 are calculated by the servo CPU 15 based on the position feedback signals from the position / speed detectors P1, P2, and P3, and are updated and stored in the current position registers.

A ROM 18 storing a sequence program for controlling the sequence operation of the injection molding machine and a RAM 19 used for temporary storage of calculation data are connected to the PMC CPU 17, and an automatic operation program for overall control of the injection molding machine is connected to the CNC CPU 20. A ROM 21 storing various programs such as these and a RAM 22 used for temporary storage of calculation data are connected.
The molding data storage RAM 23 is a non-volatile memory, and is a molding data storage memory that stores molding conditions relating to injection molding work, various set values, parameters, macro variables, and the like. A display device / MDI (manual data input device) 25 is connected to a bus 26 via an interface (I / F) 24 so that a function menu can be selected and various data can be input. In addition, numeric keys for inputting numeric data, various function keys, and the like are provided. A nozzle touch force set in advance using the display device / MDI unit 25 can be input to the injection molding machine M. The display device may be an LCD (liquid crystal display device), CRT, or other display device.

  With the above-described configuration of the injection molding machine M, the PMC CPU 17 controls the sequence of the entire injection molding machine, and the CNC CPU 20 controls the servo motors of the respective axes based on the molding conditions stored in the operation program of the ROM 21 and the molding data storage RAM 23. The servo CPU 15 distributes the movement command to each axis, and the servo CPU 15 performs the digital servo based on the movement command distributed to each axis and the position and speed feedback signals detected by the position / speed detectors P1, P2, and P3. The process is executed to drive and control the servo motors M1, M2, and M3.

A molding operation using the injection molding machine M will be described.
As described in the background art section, it is desirable that the nozzle touch force (nozzle pressing force) is kept constant so that the molten resin does not leak from the mold and the nozzle portion during the continuous molding operation. However, depending on the structure of the mold, when the mold clamping operation is performed, the nozzle is pushed back in the backward direction, the elastic member is compressed, and the nozzle touch force may increase. At this time, there is no problem as long as the compression amount is equal to or less than the maximum compression amount of the elastic member. May be damaged due to excessive load. Accordingly, in the present invention, the nozzle forward / reverse servomotor is controlled so that an excessive load is not generated.

In the nozzle advance operation, the nozzle 2 is pressed against the fixed mold 31b by the set nozzle touch force, so the servo CPU 15 determines the length of the spring 35 based on the detection signal of the sensor 38 acquired through the interface 27. , The detected nozzle touch force of the nozzle 2 is obtained, and the nozzle forward / reverse servo motor M3 is driven and controlled via the servo amplifier 10 so that the detected nozzle touch force becomes the set nozzle touch force.
More specifically, the movement command for moving the servo motor M3 for moving the nozzle back and forth to a predetermined position is sent from the CUNCPU 20 to the servo CPU 15 at predetermined intervals so that the set nozzle touch force can be obtained by moving the injection unit 39 forward. Is output. Servo CPU15 further sampling period motion command inputted from CNCCPU 20 (position, speed, current loop processing period) is divided into a position command P _CMD of performs position torque control shown in FIG. Then, during the continuous molding operation, the position command P _CMD (see FIG. 2) is output to the servo CPU 15 at each sampling period so that the detected nozzle touch force is maintained at the set nozzle touch force. When the injection unit 39 is positioned at a position where a preset nozzle touch force is obtained, the position command P _CMD becomes a command of zero. The position / torque control performed by the servo CPU 15 will be described later with reference to the drawings.

  Next, mold closing, mold clamping, and mold opening will be described. When a movable platen forward / reverse motor (not shown) of the mold clamping portion Mc is rotated in the forward direction, the ball screw shaft is rotated in the forward direction, the crosshead screwed to the ball screw shaft is advanced, and the toggle mechanism is operated. As a result, the movable platen 30 is advanced toward the fixed platen 32. When the movable mold 31a attached to the movable platen 30 comes into contact with the fixed mold 31b (mold closed state), the mold clamping process is started. In the mold clamping process, a mold clamping force is generated in the mold 31 by driving the movable platen forward / reverse motor further in the forward direction and extending the toggle mechanism.

  Then, the screw servo servo M1 provided in the injection portion Mi is driven to move forward in the axial direction of the screw 3, whereby the cavity space formed in the mold 31 is filled with molten resin. When the mold is opened after the weighing step, the ball screw shaft is rotated in the reverse direction by driving the movable platen forward / reverse motor in the reverse direction. Along with this, the cross head is retracted, the toggle mechanism is operated in a bending direction, and the movable platen 30 is retracted in the direction of the rear platen (not shown).

FIG. 2 is a diagram for explaining the position / torque control of the nozzle forward / reverse servomotor M3 in a state where the nozzle touch force is generated. In FIG. 2, the servo motor 116 corresponds to the nozzle forward / reverse servo motor M3, and the position / speed detector 118 corresponds to the position / speed detector P3.
The nozzle forward / reverse motor M3 is positioned at the position where the nozzle touch force is generated, and the position command _PCMD outputs a command of zero. The torque limit command Tlim _CMD is a torque limit command that is larger than the set nozzle touch force and smaller than the nozzle touch force corresponding to the maximum compression amount of the elastic member.

The position feedback If fed back from the position command P _CMD from the position / speed detector 118 is subtracted by the subtracter 100, and the position deviation is output from the subtracter 100. The position deviation output from the subtracter 100 is input to the position compensator 102, and the position compensator 102 multiplies the position deviation by the position gain to obtain a speed command (position loop control).
The speed feedback Vf fed back from the position / speed detector 118 from the speed command output from the position compensator 102 is subtracted by the subtractor 104 and output as a speed deviation. The speed deviation output from the subtractor 104 is input to the speed compensator 106. The speed compensator 106 obtains a torque command (current command) by performing proportionality and integration based on the speed deviation (speed loop control).

The torque command output from the speed compensator 106 is input to the torque limiter 108. The torque limit value 108 limits the torque command input from the speed compensator 106 by the torque limit command Tlim _CMD , and outputs the torque command to the subtractor 110.
A current feedback If fed back from a current detector (not shown) for detecting the drive current of the servo amplifier 114 is subtracted from the torque command (current command) output from the torque limiter 108 by the subtractor 110, and the subtractor. The current deviation is output from 110 to the current compensator 112. The current compensator 112 generates a PWM signal output to the servo amplifier 114 based on the current deviation input from the subtractor 110 (current loop control). The servo amplifier 114 drives and controls the servo motor 116 based on the PWM signal input from the current compensator 112.

Since the torque command outputted to the current loop is limited by the torque limiting command Tlim _CMD, when an excessive load exceeding a torque limit command Tlim _CMD to the servo motor 116 is generated lost the servo motor 116 is a load rotation To do. That is, since the nozzle forward / backward servomotor M3 of FIG. 1 rotates against the load, an excessive load is not applied to the mechanism portion of the injection portion Mi. In addition, since the torque limiter 108 directly acts on the inner current loop in the motor control loop such as position, speed, and current, the delay in response can be minimized even when an excessive load is momentarily applied. It can be surely protected. That is, the nozzle forward / reverse servomotor M3 can minimize the delay in response even when an excessive load is momentarily applied, and thus can reliably protect the mechanism portion of the injection portion Mi.
In addition, since the position deviation accumulates in the control loop due to the load, it hinders the next operation, so if the accumulated position deviation exceeds the predetermined value, the position deviation is eliminated. It is only necessary to output a command.

DESCRIPTION OF SYMBOLS 100 Subtractor 102 Position compensator 104 Subtractor 106 Speed compensator 108 Torque limiter 110 Subtractor 112 Current compensator 114 Servo amplifier 116 Servo motor 118 Position / speed detector

P _CMD position command Tlim _CMD torque limit command Pf Position feedback Vf Speed feedback If Current feedback

Claims (1)

A servo motor that advances the nozzle for nozzle touching the mold;
A transmission mechanism for converting the rotational movement of the servo motor into a linear movement;
An elastic member connected to the transmission mechanism for generating a nozzle touch force;
A positioning control unit for positioning the servo motor at a position where the elastic member is compressed in response to a preset nozzle touch force;
While positioning the servo motor, a torque limit that limits the torque of the servo motor with a torque limit value that is larger than the set nozzle touch force and smaller than the nozzle touch force corresponding to the maximum compression amount of the elastic member. And
A nozzle touch control device for an injection molding machine.

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