JP5073562B2 - Pressure abnormality detection device for injection molding machine - Google Patents

Description

  The present invention relates to a pressure abnormality detection device that detects an abnormality in injection pressure in an injection molding machine.

  In the injection molding machine, the molten resin in the injection cylinder is injected into the mold clamped by advancing the injection screw, and then holding pressure, cooling, weighing, mold opening, taking out the molded product, mold The process of closing and clamping continues. In this injection process, the molten resin may be clogged in the nozzle portion provided at the tip of the injection cylinder or the injection cylinder due to the influence of the resin temperature or the like, thereby increasing the injection pressure.

  Since excessive pressure rise leads to damage of the mold and injection cylinder / nozzle, control for detecting an abnormality (abnormal pressure increase) by some method and stopping the injection operation has been conventionally performed. For example, in Patent Document 1, during the injection process, the rate of change of the resin pressure with respect to the screw movement distance and the deceleration distance until the injection screw stops are sequentially obtained, and the injection screw stops from the deceleration distance and the pressure change rate. A technique is disclosed in which the amount of pressure change that occurs until then is sequentially obtained, and the injection screw is stopped when the result of adding the current pressure to the pressure change amount exceeds a preset limit pressure.

JP 2006-231749 A

  In the technique disclosed in Patent Document 1 described in the background art, the pressure change amount is calculated and predicted based on the deceleration distance and the pressure change rate. In this prediction, the pressure change amount is calculated on the assumption that the pressure change rate is constant, that is, the pressure increases linearly in proportion to the deceleration distance.

  The actual change in the resin pressure may not be linearly proportional to the deceleration distance (see FIG. 8). In such a case, the technique disclosed in Patent Document 1 uses the predicted pressure change amount and the actual pressure. Deviations from the amount of change may occur.

If the deviation between the predicted pressure change amount and the actual pressure change amount is large, the pressure will exceed the limit value when resin clogging occurs, or conversely, although there is no resin clogging, an error is erroneously detected. There is a risk of doing so.
In particular, in the case of injection molding where the injection speed is high, the pressure rises suddenly even if no resin clogging occurs, so the increase in resin pressure is normal or abnormal. It is difficult to determine if there is any.

  Therefore, an object of the present invention is to further improve the accuracy of predicting the resin pressure based on the deceleration distance until the injection screw stops, the pressure gradient, and the rate of change of the pressure gradient. It is possible to accurately prevent damage to the injection cylinder / nozzle.

  The invention according to claim 1 of the present application is a position detection means for detecting the position of the injection screw, a speed detection means for detecting the speed of the injection screw, and a pressure detection means for detecting an injection pressure generated by the movement of the injection screw. And during the injection process, the deceleration distance until the injection screw stops is sequentially obtained from the current speed obtained from the speed detection means and the machine-specific deceleration of the injection screw obtained in advance, and the position Based on the screw position obtained from the detection means and the pressure obtained from the pressure detection means, the pressure gradient with respect to the screw position is sequentially obtained, and the pressure gradient based on the obtained screw position and the pressure gradient. The rate of change of pressure is calculated sequentially, and the amount of pressure change that occurs until the injection screw stops is calculated based on the deceleration distance, pressure gradient, and rate of change of pressure gradient. An abnormal pressure detecting device for an injection molding machine, wherein the injection screw is stopped when a result obtained by adding the pressure detected by the pressure detecting means to the pressure change amount exceeds a preset limit pressure. It is.

  The invention according to claim 2 includes position detecting means for detecting the position of the injection screw, speed detecting means for detecting the speed of the injection screw, and pressure detecting means for detecting the injection pressure generated by the movement of the injection screw. Storage means for storing a preset rate of change of the machine-specific pressure gradient, and during the injection process, the current speed obtained from the speed detection means and the machine-specific machine for the injection screw obtained in advance. From the deceleration, the deceleration distance until the injection screw stops is sequentially obtained, and the pressure gradient with respect to the screw position is calculated based on the screw position obtained from the position detecting means and the pressure obtained from the pressure detecting means. Based on the deceleration distance, the pressure gradient, and the rate of change of the machine-specific pressure gradient read from the storage means, the injection screw stops until it stops. An injection molding characterized in that an injection screw is stopped when a result of adding a pressure detected by the pressure detecting means to a pressure change amount exceeds a preset limit pressure. This is a pressure abnormality detection device for a machine.

According to a third aspect of the present invention, the amount of change in pressure is calculated by the following formula:
ΔP = α * D ² + β * D
Where ΔP is the amount of pressure change that occurs before the injection screw stops
D: Deceleration distance
α: Change rate of pressure gradient
β: Pressure gradient
*: The pressure abnormality detection device for an injection molding machine according to any one of claims 1 and 2, wherein the multiplication symbol is obtained by sequentially calculating.

  According to the present invention, the prediction accuracy of the resin pressure is further improved on the basis of the deceleration distance until the injection screw stops, the pressure gradient, and the rate of change of the pressure gradient. Nozzle breakage can be prevented accurately.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a principal block diagram of an embodiment in which the present invention is applied to an electric injection molding machine.
A nozzle portion 2 is attached to the tip of the injection cylinder 1, and an injection screw 3 is inserted into the injection cylinder 1. The injection screw 3 is provided with a pressure sensor 5 such as a load cell that detects the pressure applied to the injection screw 3 in order to measure the resin pressure in the injection cylinder 1.
The injection screw 3 is rotated by a screw rotation servomotor M2 via a transmission means 6 composed of a pulley, a belt, or the like. The injection screw 3 is driven by a servo motor M1 for injection via a transmission means 7 including a mechanism for converting a rotary motion of a pulley, belt, ball screw / nut mechanism, etc. into a linear motion, and the shaft of the injection screw 3 Moved in the direction.
Reference numeral Penc1 is a position / speed detector that detects the position and speed of the injection screw 3 in the axial direction by detecting the position and speed of the servo motor M1, and the reference numeral Penc2 is the position and speed of the servo motor M2. This is a position / speed detector that detects the rotation position (rotation angle) and speed of the injection screw 3 by detecting. Reference numeral 4 denotes a hopper that supplies a resin material to the injection cylinder 1.

  An injection molding machine control device 10 having a pressure abnormality detection device of the present invention is a CNC CPU 20 which is a microprocessor for numerical control, a PMC CPU 17 which is a microprocessor for a programmable machine controller, and a microprocessor for servo control. By having the servo CPU 15 and selecting mutual input / output via the bus 26, information can be transmitted between the microprocessors.

  The servo CPU 15 is connected to a ROM 13 that stores a control program dedicated to servo control that executes 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 can detect a pressure signal from the pressure sensor 5 that detects various pressures such as an injection pressure provided on the injection molding machine main body side via an A / D (analog / digital) converter 16. It is connected to the.

  Further, the servo CPU 15 is connected to servo amplifiers 11 and 12 for driving the injection and screw rotation servomotors M1 and M2 connected to the injection shaft and the screw rotation shaft based on a command from the servo CPU 15. Yes. Position / speed detectors Penc 1 and Penc 2 are attached to the servo motors M 1 and M 2, and outputs from the speed detectors Penc 1 and Penc 2 are fed back to the servo CPU 15.

  The rotational position of each servo motor M1, M2 is calculated by the servo CPU 15 based on the position feedback signal from the position / speed detectors Penc1, Penc2, and updated and stored in each current position storage register.

  In FIG. 1, only the servo motors M1 and M2 for driving the injection shaft and the screw rotation shaft, the rotational positions of the servo motors M1 and M2, the position / speed detectors Penc1 and Penc2 for detecting the speed, and the servo amplifiers 11 and 12 are shown. ing. The configuration of each of the shafts, such as a mold clamping shaft for clamping the mold and an ejector shaft for taking out the molded product from the mold, is the same as this, and is not shown in FIG.

  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 that stores an emergency stop processing program that predicts injection pressure and performs an emergency stop in the case of a pressure abnormality, and a RAM 22 that is used for temporary storage of calculation data, etc., connected to the present invention are connected.

  The molding data storage RAM 23 formed of a non-volatile memory is a molding data storage memory for storing molding conditions relating to injection molding work, various set values, parameters, macro variables, and the like.

  A manual input device with LCD (LCD / MDI) 25 is connected to a bus 26 via an LCD display circuit 24, and is provided with a numeric keypad for inputting numeric data and various function keys. In addition, various data input operations can be performed.

  With the above configuration, the PMC CPU 17 controls the sequence operation of the entire injection molding machine, and the CNC CPU 20 instructs the servo motor of each axis to move based on the operating program of the ROM 21 and the molding conditions stored in the molding data storage RAM 23. Servo CPU 15 performs position loop control in the same manner as in the prior art based on the movement command distributed to each axis and the position and speed feedback signals detected by position and speed detectors Penc1 and Penc2. Servo control such as speed loop control and current loop control is performed, so-called digital servo processing is executed, and drive control of the servo motors M1 and M2 is performed.

  The above configuration is the same as the control of the conventional electric injection molding machine, and the pressure abnormality detection device of the present invention is configured by this control device 10. The difference from the control device of the conventional electric injection molding machine is that the ROM 21 stores an emergency stop processing program for predicting the injection pressure and making an emergency stop in case of pressure abnormality, and the CNC CPU 20 executes this emergency stop processing program. By doing so, the pressure abnormality detection device provided in the injection molding machine is configured.

  FIG. 2 is a diagram for explaining the operating principle of the present invention. In FIG. 2, the horizontal axis represents the injection screw position X, and the vertical axis represents the injection speed V and the injection pressure P. In the present specification, the coordinate system is selected so that the injection screw position X increases toward the injection nozzle as shown in FIG. The injection pressure P increases as the injection is started and the resin is filled in the mold. Assume that the injection screw position detected by the position / speed detector Penc1 at a certain sampling time is Xn, the injection speed (injection screw axial movement speed) is Vn, and the injection pressure at that time detected by the pressure sensor is Pn. If the injection screw position at the time of sampling immediately before this sampling is Xn-1, the injection speed is Vn-1, and the injection pressure is Pn-1, the inclination of the injection pressure with respect to the injection screw position at this sampling is , (Pn-Pn-1) / (Xn-1-Xn). As described above, the actual change in the resin pressure may not be completely linearly proportional to the screw movement distance. In the present invention, since the coordinate system of the screw position is defined in the direction in which the screw position decreases with the injection, the screw movement amount during the sampling period is represented by (Xn-1-Xn).

  Therefore, the present invention is characterized in that the amount of pressure change until the injection screw 3 stops is obtained based on the deceleration distance until the injection screw 3 stops, the pressure gradient, and the change rate of the pressure gradient. .

More specifically, in the present invention, the transition of the pressure gradient until the injection screw 3 stops in the subsequent deceleration process is present in the injection cylinder 1 with respect to the pressure gradient (measured value) at the time of sequential detection. Taking into account fluctuations depending on the position of the injection screw 3, a change rate of the detected pressure gradient based on the position of the injection screw 3 is obtained, and the product of the obtained change rate of the pressure gradient and the square of the deceleration distance By calculating the sum of the corrected product of the pressure gradient and the deceleration distance, the amount of pressure change until the injection screw 1 stops is obtained.
First, a first embodiment for obtaining a pressure change amount based on the operation principle of the present invention will be described.

Here, how to obtain the “deceleration distance” (D), “pressure gradient” (β), and “change rate of pressure gradient” (α) will be described.
<How to determine the deceleration distance D>
FIG. 4 is an explanatory diagram of a method for obtaining the deceleration distance D. In FIG. 4, the horizontal axis represents time T, and the vertical axis represents the injection speed V. Symbol A is an absolute value of acceleration in the deceleration direction (hereinafter referred to as “deceleration”), which is obtained in advance as a unique value of the injection molding machine. Assuming that Td is the time from when the rapid deceleration starts from the injection speed Va and the speed becomes zero,

Here, Td is expressed by A and Va from Equation 3 and substituted for Td in Equation 2,

    As a result, the deceleration distance D can be obtained. Note that “*” represents multiplication.

  In determining the deceleration distance D, the deceleration A is set in advance. This deceleration A is a value inherent to the machine, and can be calculated and set theoretically once the injection mechanism of the injection molding machine is determined. it can. However, in order to obtain it simply, an injection operation is performed in the absence of resin in the injection cylinder 1, and the injection operation is interrupted in the middle, and the injection speed at the time of the interruption is Va, and the elapsed time until the speed becomes zero. Td is measured. Based on the injection speed Va and time Td, the deceleration A can be obtained by the calculation of Equation 2 above.

  In the present invention, Va in Formula 3 is used as a variable, and the deceleration distance (hereinafter referred to as “deceleration distance”) until the injection screw stops by the calculation of Formula 4 based on the injection speed and the machine-specific deceleration in the injection process. ) Sequentially (for example, every first predetermined period).

  In Equation 4, “D” represents the deceleration distance until the injection screw stops, “V” represents the screw speed, and “A” represents the machine-specific deceleration.

<Measurement of pressure gradient> will be described.
The screw position and pressure of the injection screw 3 are sequentially detected, and the screw position = (X1, X2, X3,... Xn-2, Xn-1, Xn), injection pressure = (P1, P2, P3,... Pn-2, Pn-1, Pn), Xn: screw position of the nth sample, and Pn: injection pressure of the nth sample. Based on the detected screw position and pressure, the pressure gradient is obtained sequentially (for example, every second predetermined period).

  In Equation 5, “βn” is the pressure gradient of the nth sample, “Xn” is the screw position of the nth sample, and “Pn” is the pressure of the nth sample.

  Using the obtained pressure gradient and the detected screw position, the rate of change of the pressure gradient is obtained sequentially (for example, every third predetermined period).

  In Equation 6, αn is the rate of change in the pressure gradient of the nth sample.

  Using the “deceleration distance” (D), “pressure gradient” (β), and “pressure gradient change rate” (α) obtained as described above, the amount of pressure change until the injection screw stops. ΔP that is (predicted value) can be calculated.

  When the result of adding the obtained pressure change amount (predicted value) ΔP to the current injection pressure P exceeds a preset limit pressure Pmax, the injection screw 3 is stopped. When expressed by a mathematical expression, it is determined whether or not to stop the injection screw based on the mathematical expressions 8 and 9.

In Equations 8 and 9, “P” is the injection pressure at the present time, and “Pmax” is the limit pressure.
The first predetermined period, the second predetermined period, and the third predetermined period may be the same period or different periods. In addition, instead of the first predetermined period, the second predetermined period, and the third predetermined period based on the time, the second predetermined period every time the injection screw advances by the first predetermined distance based on the distance. The above processing may be executed every time the distance advances or every third predetermined distance.

  Here, an arithmetic expression for calculating the pressure change amount ΔP by Expression 7 will be considered. By substituting Equation 5 into Equation 6, which is a calculation equation for sequentially obtaining the change rate α n of the pressure gradient, Equation 10 can be obtained. As can be seen from Equation 10, the rate of change αn of the pressure gradient can be obtained from Pn−2, Pn−1, Pn, and Xn−2, Xn−1, Xn that are sequentially detected.

  The pressure change amount ΔP can be calculated by Expression 11 by substituting Expression 5 and Expression 10 into Expression 7.

  In the above embodiment, the change rate α of the pressure gradient is calculated by sequential calculation, but may be set in advance as a machine-specific parameter. The parameter may store the change rate α of the pressure gradient once calculated.

FIG. 5 is a flowchart showing an algorithm for predicting the injection pressure and making an emergency stop of the injection operation based on the injection pressure. The CNC CPU 20 in the abnormality detection device for an injection molding machine according to the present invention is executed at predetermined intervals. is there. Hereinafter, it demonstrates according to each step.
The CNC CPU 20 reads the machine-specific deceleration A stored in advance in the ROM 21 or the power-backed RAM 22 (step S100).

  Next, the CNC CPU 20 determines whether or not the injection is in progress (when the injection is started, a flag indicating that the injection is in progress is raised by another injection processing program, and when the injection process ends, the flag is lowered. Whether or not injection is in progress is determined based on the flag). If not in injection, the processing in the cycle ends (step S101).

  If it is determined in step S101 that the injection is in progress, the position Xn and the injection speed Vn of the injection screw 3 detected by the position / speed detector Penc1, and the A / D converter 16 detected by the pressure sensor 5 are next detected. The injection pressure Pn input via the CPU is read (step S102).

  Next, from the screw position Xn and injection pressure Pn obtained in this cycle, the screw position Xn-1 detected in the previous cycle stored in the register R (X) and the injection detected in the previous cycle stored in the register R (P) Each of the pressures Pn-1 is subtracted to calculate the movement amount δX and the injection pressure change amount δP of the injection screw 3 in this sampling period (steps S103 and S104). After calculating the movement amount δX and the injection pressure change amount δP, the pressure gradient βn is calculated from the movement amount δX obtained in step S103 and the injection pressure change amount δP obtained in step S104 (step S105), and the register R The pressure gradient βn−1 detected in the previous period stored in (β) is subtracted to calculate δβn (step S106). Then, the change rate αn of the pressure gradient is obtained by dividing δβn by δX (step S107).

Next, the data detected and stored in the previous period stored in the register R (X), the register R (P), and the register R (β) is used as the data of the screw position Xn and the injection pressure Pn detected in the period. Replace (step S108).
In the register, the position X at the start of injection, the injection pressure P, and the change rate of the pressure gradient are set as initial settings at the start of injection.

  Next, the deceleration distance D is calculated based on the preset deceleration A read in step S100 and the injection speed Vn in the period read in step S102 (step S109).

Then, ΔP, which is a pressure change amount (predicted value) until the injection screw 3 is stopped, is calculated by ΔP = αn * D ² + βn * D, which is the equation 7, and the injection at the cycle read in step S102. It is determined whether or not “Pn + ΔP”, which is a value obtained by adding the pressure change amount ΔP calculated in step S110 to the pressure Pn, is larger than Pmax, which is a limit pressure. When the process is completed and Pn + ΔP is larger than Pmax, the injection operation is stopped, and the injection screw 3 is suddenly decelerated and stopped (steps S110 to S112).

  FIG. 6 shows an algorithm of processing executed by the pressure abnormality detection device that obtains the pressure change amount ΔP by the calculation of Equation 11 described above. If it demonstrates according to each step, step T100-step T103 will perform the process similar to the flowchart of the algorithm shown in FIG. Then, the processing of Equation 11 described above is performed, and R (Xn-2), R (Xn-1), R (Pn-2), R (Pn-1) of each register for the calculation in the next cycle. , R (βn-2) and R (βn-1) are stored in different memory contents (step T104 to step 106).

And the process of step T107 and step T108 is the same as the process in step S111 and step S112 of the flowchart shown in FIG.
By executing the processing of the algorithm shown in FIGS. 5 and 6, the divergence between the predicted peak pressure and the actual peak pressure can be eliminated as shown in FIG. 7.
According to the present invention, it is possible to predict the amount of pressure change according to the amount of resin, improve the prediction accuracy of the resin pressure, and accurately prevent damage to the mold and injection cylinder / nozzle due to abnormal injection pressure during the injection process. Is possible.

It is a principal part block diagram of one Embodiment of this invention. It is a figure explaining the principle of operation of the present invention. It is a figure which shows the injection screw position in an injection cylinder. It is explanatory drawing which calculates | requires the deceleration distance used with the pressure abnormality detection apparatus of this invention. It is a flowchart which shows the algorithm for the pressure abnormality detection performed with the pressure abnormality detection apparatus of this invention. It is a flowchart which shows the algorithm for the pressure abnormality detection using Numerical formula 11. It is an example which shows having predicted the predicted peak pressure of this invention with the function of the curve. It is a figure explaining that the predicted peak pressure which is a prior art increases linearly with the movement of an injection screw.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Injection cylinder 2 Nozzle part 3 Injection screw 4 Hopper 5 Pressure sensor 6, 7 Transmission means M1 Injection servomotor M2 Screw rotation servomotor Penc1, Penc2 Position / speed detector 10 Injection molding machine equipped with pressure abnormality detection device Control device 26 Bus A Deceleration D Deceleration distance α Change rate of pressure gradient β Pressure gradient ΔP Pressure change

Claims (3)

Position detection means for detecting the position of the injection screw, speed detection means for detecting the speed of the injection screw, and pressure detection means for detecting the injection pressure generated by the movement of the injection screw,
During the injection process, from the current speed obtained from the speed detection means and the machine-specific deceleration of the injection screw obtained in advance, the deceleration distance until the injection screw stops is sequentially obtained,
Based on the screw position obtained from the position detection means and the pressure obtained from the pressure detection means, the pressure gradient with respect to the screw position is sequentially obtained,
Based on the obtained screw position and the pressure gradient, the rate of change of the pressure gradient is obtained sequentially, and the injection screw is stopped based on the deceleration distance, the pressure gradient, and the rate of change of the pressure gradient. Sequentially determine the amount of pressure change that occurs,
An apparatus for detecting an abnormal pressure in an injection molding machine, wherein an injection screw is stopped when a result of adding a pressure detected by the pressure detecting means to a pressure change amount exceeds a preset limit pressure. Position detection means for detecting the position of the injection screw, speed detection means for detecting the speed of the injection screw, and pressure detection means for detecting the injection pressure generated by the movement of the injection screw,
Storage means for storing a change rate of the pressure gradient inherent to the machine set in advance,
During the injection process, from the current speed obtained from the speed detection means and the machine-specific deceleration of the injection screw obtained in advance, the deceleration distance until the injection screw stops is sequentially obtained,
Based on the screw position obtained from the position detection means and the pressure obtained from the pressure detection means, the pressure gradient with respect to the screw position is sequentially obtained,
Based on the deceleration distance, the pressure gradient, and the rate of change of the machine-specific pressure gradient read from the storage means, the amount of pressure variation that occurs until the injection screw stops is sequentially obtained, and the pressure variation amount is calculated based on the pressure variation amount. An apparatus for detecting a pressure abnormality in an injection molding machine, wherein an injection screw is stopped when a result of applying a pressure detected by a detection means exceeds a preset limit pressure. The amount of pressure change is calculated by the following formula:
ΔP = α * D ² + β * D
Where ΔP is the amount of pressure change that occurs before the injection screw stops
D: Deceleration distance
α: Change rate of pressure gradient
β: Pressure gradient
*: The pressure abnormality detection device for an injection molding machine according to any one of claims 1 and 2, wherein the multiplication symbol is obtained by sequentially calculating a symbol.

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