JP2005088501A - Control method of injection molding machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control method for precisely detecting the abnormality of the rotation angle signal of an encoder incapable of being detected heretofore by the conventional checking of the abnormality of communication so as not to exert an effect on the molding operation of an injection molding machine. <P>SOLUTION: The control system 1 of the injection molding machine has a servomotor 12 for driving the actuator of the injection molding machine, a servo amplifier 11 for feeding a drive current to the servomotor 12 and a control device 10 for transmitting an instruction signal 14 for instructing the number of rotations and torque of the servomotor 12 to the servo amplifier 11 and inputting the rotation angle signal 16 from the encoder 13 of the servomotor 12. The control device 10 controls the servomotor 12 by the instruction signal 14 operated on the basis of the rotation angle signal 16 immediately before abnormality at the time of abnormality when the absolute value of the difference of the rotation angle signal 16 from the encoder continuously taken in at every scanning time exceeds a predetermined threshold value. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a control for easily avoiding an abnormality in a rotation angle signal of an encoder when the movement of an actuator of an injection molding machine is detected and controlled by an encoder.

  As shown in Patent Document 1, an injection molding machine using a servo motor transmits rotation angle data from an encoder provided in the servo motor to the control device in various forms, and the control device is closed based on the rotation angle data. Loop calculation controls the rotation and torque of the servo motor. At this time, although not described in Patent Document 1, a known noise countermeasure is applied to the rotation angle data.

  For example, if rotation angle data is transmitted via serial communication, a control field error that checks the parity and delimiter of the control field, and a CRC error that checks all bits except the start bit and delimiter with a predetermined generation formula , A form error that checks the start bit and delimiter logic of all fields after the control field, a short form error in which the received data length after the control field is insufficient for the specified data length, and a predetermined time even if a request is sent Or there is a time-out error that the received data does not return within a predetermined number of times. When these communication abnormalities are detected, the control device does not perform a closed loop calculation using the rotation angle data, and the rotation and torque of the servo motor are not abnormally controlled.

  However, depending on the transmission line on which the noise is superimposed and the situation on which the noise is superimposed, only the numerical value of the rotation angle may change without impairing the appearance of the rotation angle data. In such a case, the communication abnormality signal is not transmitted, and the control device takes in the rotation angle signal as a normal value and performs arithmetic processing, so that the servo motor generates abnormal noise or the actuator suddenly stops or runs away. It becomes.

JP 2002-326267 A (page 1-4, FIG. 1-4)

  The present invention has been made in view of the above circumstances, and accurately detects an abnormality in the rotation angle signal of the encoder that could not be detected by the conventional communication abnormality check, and does not affect the molding operation of the injection molding machine. An object of the present invention is to provide a control method.

  That is, the invention of claim 1 is a servo motor for driving an actuator of an injection molding machine, a servo amplifier for supplying a drive current to the servo motor, and a command signal for instructing the servo amplifier the rotation speed and torque of the servo motor. And a control signal for instructing the state of the control system, and a control system for an injection molding machine having a control device for inputting a rotation angle signal from the encoder of the servo motor, the control device is provided for each scan time. When the absolute value of the difference between the rotation angle signals from the encoders taken in continuously exceeds the predetermined threshold, the servo motor is controlled by a command signal calculated based on the rotation angle signal immediately before the abnormality. The present invention relates to a method for controlling an injection molding machine.

  The invention according to claim 2 relates to the method of controlling an injection molding machine according to claim 1, wherein the threshold value is a rotation angle of the encoder when the actuator moves during one scan time of the control device at the maximum specification speed. .

  According to a third aspect of the present invention, there is provided the method for controlling an injection molding machine according to the first or second aspect, wherein the operation of the actuator is stopped when the abnormality occurs continuously a predetermined number of times.

  According to a fourth aspect of the present invention, the allowable distance of the actuator that does not substantially affect the operation of the actuator even if the predetermined number of times is control based on the rotation angle signal immediately before the abnormality is determined as the maximum of the actuator. The control method for an injection molding machine according to claim 3, which is a value divided by a movement amount during one scan time of the control device at a specified speed.

  According to the first aspect of the present invention, when the absolute value of the difference between the rotation angle signals from the encoder continuously taken in every scan time exceeds the predetermined threshold, the control device rotates immediately before the abnormality. Since the servo motor is controlled by a command signal calculated based on the angle signal, even if an abnormality occurs in the rotation angle signal, the operation of the actuator is not adversely affected.

  In the invention of claim 2, since the threshold value is the rotation angle of the encoder when the actuator moves during one scan time of the control device at the maximum specification speed, the abnormality of the rotation angle signal can be accurately detected.

  According to the third aspect of the present invention, when the abnormality occurs continuously for a predetermined number of times, the operation of the actuator is stopped, so that so-called “choco stop” can be prevented and the production efficiency of the molding operation is improved.

  According to the invention of claim 4, the allowable distance of the actuator that does not substantially affect the operation of the actuator even if the predetermined number of times is control based on the rotation angle signal immediately before the abnormality is determined as the maximum specified speed of the actuator. Since the value divided by the amount of movement during one scanning time of the control device in FIG. 4 is set, the maximum allowable number of times can be set, and the production efficiency is further improved.

Embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a block diagram showing a control system of an injection molding machine embodying the present invention, and FIG. 2 is a flowchart showing a control method of the present invention.

  As shown in FIG. 1, the control system 1 of the injection molding machine includes a control device 10, a servo amplifier 11, a servo motor 12, and an encoder 13. The servo motor 12 drives an actuator of an injection molding machine (not shown) via a ball screw, a ball nut, a belt / pulley, or the like directly. As an actuator, a mold clamping device that opens and closes and presses the mold, an injection device that plasticizes the raw material and injects and fills the molten resin into the mold cavity, an ejector device that releases the molded product from the mold cavity, There is a nozzle shift device that presses the injection device against a mold.

  The control device 10 is a programmable device configured based on a microprocessor, and stores a CPU as a central processing unit, an operation unit for setting and inputting molding conditions and the like, a set value, a constant, and a program. Inputs the rotation angle signal 16 and the like from the RAM / ROM and the servo amplifier 11, and inputs the rotational speed and torque of the servo motor 12 to the servo amplifier 11 and the input unit connected to the thermocouple of the heating cylinder and various manual switches. And a control signal 15 for commanding the state of the control system and an output unit connected to the operation unit. The control device 10 performs a closed-loop operation by comparing the actuator speed and force set values set by the operation unit with the rotation angle signal 16 and a force sensor signal (not shown), and the rotation angle signal 16 and the force sensor signal are obtained. A command signal 14 for controlling the servo motor 12 is output so as to match the set value.

  The servo amplifier 11 supplies a drive current 17 to the servo motor 12 based on feedback of the rotation angle data 19 from the encoder 13 so as to rotate the servo motor 12 in accordance with the command signal 14 accurately. The servo amplifier 11 is a converter that converts a weak command signal 14 into a strong drive current 17, and the ON / OFF of the control loop is controlled from the control device 10 via a control signal 15. The control signal 15 is also used for resetting a communication abnormality of the encoder 13.

  The servo motor 12 is a synchronous type, and a DC servo motor having a brush or an AC servo motor without a brush is employed. The servo motor 12 is characterized in that the response to the drive current 17 is extremely fast, and in the servo motor 12 mounted on the injection molding machine having a mold clamping force of 1800 kN, the time from the stop to the maximum rated rotational speed (1200 rpm) is several tens of milliseconds. It is.

  The encoder 13 is a rotary encoder of absolute value detection that is directly connected to the shaft on the non-drive side of the servo motor 12 and that can detect the rotation angle of the servo motor 12 by multiple rotations. In this embodiment, the rotation angle data 19 is transmitted by serial communication based on the request command 18 substantially synchronized with the scan time from the servo amplifier 11. However, the rotation angle data 19 is transmitted as needed without the request command 18. It is also possible to adopt a method of arbitrarily capturing. Further, the rotation angle data 19 may be based on parallel communication instead of serial communication. The rotation angle data 19 output from the encoder 13 is input to the servo amplifier 11, and the appropriately processed data becomes the rotation angle signal 16. However, the rotation angle data 19 may be used as it is as the rotation angle signal 16. The rotation angle data 19 may be directly input to the control device 10 from the encoder 13.

  Next, based on FIG. 2, the control method of this invention is demonstrated with the action | operation in the control system 1 of an injection molding machine. In the control device 10, the CPU performs a series of processes every unique scan time of about several hundred microseconds. In S1, the counter provided in the control device 10 is reset. In S2, the control device 10 calculates the absolute value A of the difference between the rotation angle signal at the previous scan and the rotation angle signal at the current scan from the encoder that is continuously acquired every scan time.

  In S3, the absolute value A is compared with a predetermined threshold value. Here, the threshold value is the rotation angle of the encoder when the actuator moves during one scanning time of the control device at the maximum specification speed. A specific formula for calculating the threshold is shown in Equation 1.

  In Equation 1, the maximum specification speed of the actuator is the movement speed of the actuator when the servo motor 12 outputs the maximum rated rotational speed. The ball screw pitch means that when the actuator is driven by the servo motor 12 via the ball screw and the ball nut screwed to the ball screw, the actuator moves by one pitch when the ball screw makes one rotation. Is the moving distance. The number of bits of the encoder 13 is the number of pulses output when the encoder 13 makes one revolution, and the larger the number, the higher the resolution.

  In S3, the threshold value is larger than the maximum rotation speed of the servo motor 12 which cannot be achieved by normal control. Therefore, when the absolute value A is smaller than the threshold value, it is determined that the control is normal, and the control device 10 has input. Based on the rotation angle signal 16, the command signal 14 is calculated and output to the servo amplifier 11 (S4).

  In S3, the reason why the absolute value A exceeds the threshold value may be that noise is superimposed on the rotation angle signal 16 or the data of the rotation angle signal 16 is erroneously replaced.

  Examples of the replacement of the data of the rotation angle signal 16 include the following. When noise is superimposed on the transmission line of the control signal 15 and an alarm reset command is erroneously input to the servo amplifier 11, the servo amplifier 11 transmits an alarm reset request command 18 to the encoder 13. Then, the encoder 13 replaces the data in the multi-rotation data area with the value calculated by the CRC error generation formula and outputs it as the rotation angle data 19 in order to confirm reception of the alarm reset. Such an erroneously replaced rotational angle signal makes a large difference from the normal rotational angle signal previously captured, and its absolute value A exceeds the threshold value.

  In S3, when the absolute value A exceeds the threshold value and it is determined that there is an abnormality, 1 is added to the counter (S5). In S6, it is determined whether or not the count value of the counter has reached a predetermined number. When the count value of the counter does not reach the predetermined number, the process returns to S2 to obtain the absolute value A again. When the count value of the counter reaches a predetermined number, a process for stopping the operation of the actuator is performed and an alarm is output (S7). By this control, the actuator is not stopped immediately in the event of an abnormality, but is waited until it reaches a normal value within a range that does not affect the operation of the actuator and thus the molding operation, so that a so-called “choco stop” can be prevented.

  Thus, when the absolute value A exceeds the threshold value in S3 and is determined to be abnormal, the process does not proceed to S4. Therefore, the control device 10 determines the command signal based on the latest rotation angle signal 16 determined to be abnormal. 14 is not calculated. Therefore, while executing a series of processing at the time of abnormality (S5-S6-S2-S3), the control device 10 uses the command signal 14 calculated based on the rotation angle signal 16 immediately before being determined to be abnormal, as a servo motor. 12 control is continued.

  Here, the specific method of obtaining the predetermined number of times will be described by the equation (2).

  In Equation 2, the allowable distance is the allowable distance of the actuator that does not substantially affect the operation of the actuator even if the control is based on the rotation angle signal 16 immediately before the abnormality, and the numerical value is Although it varies depending on the type and size of the actuator, it is approximately 1 millimeter. An example of the predetermined number of times at this time is 6. The denominator means the distance that the actuator moves during one scan time at the maximum specification speed.

  In addition, this invention includes what can be implemented in the aspect which added various change, correction, improvement, etc. based on the knowledge of those skilled in the art. Further, it goes without saying that any of the embodiments to which the above-mentioned changes are added is included in the scope of the present invention without departing from the gist of the present invention.

It is a block diagram which shows the control system of the injection molding machine which implements this invention. It is a flowchart which shows the control method of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Control system of injection molding machine 10 Control apparatus 11 Servo amplifier 12 Servo motor 13 Encoder 14 Command signal 15 Control signal 16 Rotation angle signal 17 Drive current 18 Request command 19 Rotation angle data

Claims (4)

Servo motor that drives the actuator of the injection molding machine, servo amplifier that supplies drive current to the servo motor, control signal that commands the servo amplifier for the rotation speed and torque of the servo motor, and control that commands the status of the control system In a control system of an injection molding machine having a control device that transmits a signal and inputs a rotation angle signal from the encoder of the servo motor,
When the absolute value of the difference between the rotation angle signals from the encoder, which is continuously captured every scan time, exceeds the predetermined threshold, the control device is calculated based on the rotation angle signal immediately before the abnormality. A control method for an injection molding machine, wherein the servo motor is controlled by a command signal.   2. The method of controlling an injection molding machine according to claim 1, wherein the threshold value is a rotation angle of the encoder when the actuator moves during one scan time of the control device at the maximum specification speed.   The method of controlling an injection molding machine according to claim 1 or 2, wherein the operation of the actuator is stopped when the abnormality occurs continuously for a predetermined number of times.   The predetermined number of times is determined based on the allowable distance of the actuator that does not substantially affect the operation of the actuator even if the control is based on the rotation angle signal immediately before the abnormality. The method of controlling an injection molding machine according to claim 3, wherein the control value is a value divided by a moving amount during a scan time.

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