JPH07299849A - In-mold pressure measuring method - Google Patents

Abstract

PURPOSE:To measure the pressure in a cavity without attaching an in-mold pressure sensor to the interior of a mold. CONSTITUTION:In an injection molding machine wherein the mechanism having a member (ejector pin) 8 moved within a mold such as a product ejecting mechanism is driven by a servo motor Me, the moving member 8 is held to a predetermined positioning place during an injection and dwelling process. The moving member 8 is pressed by the rising of the pressure in a cavity due to injection but the servo motor Me outputs output torque so as to keep the predetermind positioning place. The load applied to the servo motor Me is estimated by an observer to measure the pressure in the cavity. Or, the pressure in the cavity is measured on the basis of the drive current value and torque command value (current command value) of the servo motor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring internal pressure of a mold in an injection molding machine.

[0002]

2. Description of the Related Art In an injection molding machine, the pressure inside a mold cavity is monitored, and the result of this monitoring is used as a reference for determining molding conditions, and is also used as a material for finding a molding abnormal portion from the monitor result. (Japanese Patent Laid-Open No. 61-
106219, JP-A-59-224323, etc.). It is also used to monitor the pressure in the cavity and detect the timing of switching from the speed mode to the pressure mode in the injection process.

Conventionally, as a method of detecting the pressure in the cavity, a method of mounting a pressure sensor in the mold inside the cavity to detect the pressure in the cavity is generally used.
For example, as shown in FIG. 5, a mold internal pressure sensor 100 is installed in a mold composed of molds 7 and 7 ', the pressure in the cavity, that is, the resin pressure in the mold is detected, and the detection signal is the mold internal pressure. The sensor amplifier 101 amplifies and detects the cavity pressure. In FIG. 5, 1 is a heating cylinder, 2 is a screw, Me is a projecting servomotor that is a drive source of the product projecting mechanism, Pe is a pulse coder for detecting the position and speed of the servomotor, and 8 is an ejector pin. , 9 are ejector plates.

[0004]

According to the conventional method of mounting the mold internal pressure sensor in the mold to detect the cavity pressure, it is necessary to perform special processing on the mold to mount the mold internal pressure sensor. The mold processing is made expensive accordingly.
Further, an in-mold pressure sensor, an in-mold pressure sensor amplifier, and an A / D converter for converting a detection signal into a digital signal for control by a processor for monitor display are also required. Therefore, the cost of these hardware is high. Therefore, an object of the present invention is to provide a method for measuring the internal pressure of a cavity that can detect the internal pressure of a cavity without providing an internal pressure sensor in the die.

[0005]

SUMMARY OF THE INVENTION The present invention relates to an in-mold moving mechanism having a moving member which is driven by a servomotor and moves in the mold, and particularly to a product ejecting mechanism (ejector mechanism), which drives the mechanism. An observer is provided to estimate the load torque applied to the servo motor that is the source. And
During the injection and pressure holding process, the moving member is held at a predetermined position by the servo motor, the load torque is estimated by the observer at that time, and the cavity pressure is measured by the estimated load torque. In particular, the observer estimates the load torque based on the torque command given to the servo motor and the rotation speed of the servo motor. Further, instead of providing an observer, the pressure inside the cavity is measured by a current command or drive current to the servo motor.

[0006]

The function of ejecting the product is provided with the eject pin that moves in the mold cavity. There is also an injection molding machine and a mold provided with an in-mold moving mechanism having a moving member that moves in the mold other than the product ejecting mechanism. When injection molding is performed by using a servo motor as a drive source of a moving mechanism in a mold having a moving member that moves in such a mold, the ejector pin and the moving member may move the cavity during the injection and pressure holding steps. It is held in place to form. for that reason,
If the pressure in the cavity increases due to injection or the like, the moving member such as the ejector pin tries to retract due to the force due to this pressure. Then, if the moving member moves and retracts from the commanded predetermined position and the position deviation increases,
The drive current of the servo motor is increased, and the output torque is increased so as to eliminate the position deviation and maintain the commanded predetermined position.

That is, the output torque of the servo motor is proportional to the pressure inside the cavity. From this,
It means that the pressure inside the cavity can be measured by the current command (that is, the torque command) to the servo motor or by the value of the actual drive current. Further, more accurately, the load torque applied to the servo motor may be detected. Therefore, the load torque is estimated by an observer, and the pressure in the cavity is measured from the load torque.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a main part of an electric injection molding machine according to an embodiment to which the method for measuring a mold internal pressure according to the present invention is applied. Reference numeral 1 is an injection cylinder of the injection molding machine, and reference numeral 2 is a screw. The screw 2 is driven in the injection axis direction by the injection servomotor Ms, and is also metered and rotated by the screw rotation servomotor Mr via the power transmission mechanism 3 including a timing belt, a toothed pulley, and the like. A pressure detector 4 for detecting a resin reaction force acting in the axial direction of the screw 2 is provided at the base of the screw 2 to detect the injection holding pressure in the injection holding process and the screw back pressure in the measuring and kneading process. It has become so. Furthermore,
The injection servomotor Ms is provided with a pulse coder Ps for detecting the position and moving speed of the screw 2, and the screw rotation servomotor Mr is provided with a pulse coder Pr for detecting the rotation speed of the screw 2. Has been done.

A front platen 6 is fixed to the base of the injection molding machine, and a movable platen 5 slidably mounted on a tie bar fastening the front platen 6 and the rear platen is provided on the rear platen side. It is driven by a motor Mc via a mold clamping mechanism (not shown). The mold clamping servomotor Mc is equipped with a pulse coder Pc for position and speed detection. A movable mold 7 is attached to the movable platen 5, and a fixed mold 7'is attached to the front platen 6.

The movable platen 5 has a movable side mold 7
A product projecting mechanism for projecting the ejector pin 8 to take out the product is provided in the cavity of, and a projecting servomotor Me as a drive source thereof is also provided on the movable platen 5.
The structure of this product ejecting mechanism is similar to that of a conventionally known product ejecting mechanism driven by a servo motor. As shown in FIG.
Is driven to cause the ejector pin 8 attached to the ejector plate 9 to project into the cavity to project the product. The protrusion servo motor Me
A pulse coder Pe for position and speed detection is also provided in the same manner as the servo motor for each axis described above.

The control unit 10 of the injection molding machine includes a CNC CPU 17 which is a numerical control microprocessor, a PMC CPU 16 which is a programmable machine controller microprocessor, a servo CPU 18 which is a servo control microprocessor, and It has a monitor CPU 33 for performing sampling processing of injection holding pressure and screw back pressure via the A / D converter 34,
Information can be transmitted between the microprocessors by selecting mutual input / output via the bus 28.

The PMC CPU 16 is connected to a ROM 20 which stores a sequence program for controlling the sequence operation of the injection molding machine and a RAM 23 which is used for temporary storage of operation data, and the CNC CPU 17
A ROM 21 that stores a program for controlling each axis of the injection molding machine and a RAM 27 that is used for temporary storage of operation data are connected to the. The non-volatile memory 26 connected to the CNC CPU 17 is a molding data storage memory for storing molding conditions and various set values, parameters, macro variables, etc. relating to the injection molding work, and other CPs.
Access from U is also possible.

Each of the servo CPU 18 and the monitoring CPU 33 has a ROM 22 storing a control program dedicated to servo control, a RAM 24 used for temporary storage of data, and a control program relating to sampling processing for obtaining pressure data and the like. ROM that stores
31 and a RAM 32 used for temporary storage of data are connected. Furthermore, a servo CPU 18 (servo C
A plurality of PUs are provided in accordance with the number of axes to be controlled, but they are shown as one block in FIG. 1) based on a command from the CPU 18 for projecting, clamping, screw rotation, and injection. The servo amplifiers 11 to 14 for driving the servo motors of the respective axes are connected via the servo interface 15. Further, each of the outputs from the pulse coders Pe to Ps provided on the servo motors of the respective axes is fed back to the servo CPU 18 via the servo interface 15, and the protrusion of the ejector pin 8 calculated by the servo CPU 18 based on the feedback pulse of the pulse coder. The position, the crosshead position and its moving speed, the current position of the screw 2 and the values of its moving speed and rotation speed are
It is stored in each of the current position storage register and the current speed storage register of the RAM 24.

The input / output circuit 29 is an input / output interface for receiving a signal from a limit switch provided on each part of the injection molding machine or a control panel and transmitting various commands to peripheral equipment of the injection molding machine. In addition, the communication interface 30 is an input / output interface for performing data transmission with a host computer or a cell controller. Manual data input device with display 19
Is connected to the bus 28 via the CRT display circuit 25 so that a monitor display screen, a function menu can be selected and various data can be input. A numeric keypad for inputting numerical data, various function keys and the like are provided. It is provided.

With the above configuration, the CNC CPU 17 distributes pulses to the servo motors of the respective axes based on the control program of the ROM 21 and various set values, and the servo CPU 18 issues the pulse distributed movement commands to the respective axes. Based on the position feedback signal and the speed feedback signal detected by the detectors such as the pulse coders Pe to Ps, servo control such as position loop control, speed loop control and current loop control is performed in the same manner as in the conventional case. Executes digital servo processing.

The monitor CPU 33 monitors the injection pressure holding pressure in the injection pressure holding step input from the pressure detector 4 similar to the conventional one.

FIG. 2 is a block diagram of a servo system in which the servo CPU drives and controls each axis servo motor. In FIG. 2, a position command Mcmd and a pulse coder (Ps, Pr, Pe, P) for the relevant axis distributed from the CNC CPU 17
The position deviation, which is the difference from the actual rotational position of the servo motor detected in c), is obtained, and this position deviation is multiplied by the position loop gain Kp shown by the element 50 to obtain the speed command. The actual speed of the servomotor detected by the pulse coder is subtracted from this speed command to obtain the speed deviation, and the speed command is used for speed loop processing such as proportional-plus-integral control of the element 51 to obtain the torque command (current command) u. Further, although a current loop process is performed on the torque command u to drive the servomotor, the transfer function of the current loop is not shown as "1" in FIG.

Elements 52 and 53 are elements of the transfer function of the servo motor, Kt of the element 52 is the torque constant of the servo motor, and J is the inertia. Note that S is a Laplace operator. For the torque command u, the motor torque constant K
A value obtained by adding the load torque Td to a value multiplied by t is integrated, and a value obtained by dividing the integrated value by the inertia J is obtained as the motor speed y, and this speed y is further integrated by the element 54 to obtain the servo motor. The position of is required.

The servo CPU 1 processes the position loop, velocity loop, and current loop of the servo system shown in FIG.
8 controls the position and speed of each axis servo motor.
In the control of the projecting servomotor Me of the drive source of the product projecting mechanism in the injection and pressure-holding steps, the eject pin 8 is positioned and held at a predetermined position forming the cavity of the mold, Since the ejector pin 8 is pressed by the pressure in the cavity due to the injected resin, this ejecting servo motor M
“E” opposes the force that tries to retract the ejector pin 8 caused by the pressure in the cavity by increasing the torque command u and increasing the drive current so as to hold the commanded positioning position against this pressure. It will generate force (torque). That is, in FIG. 2, the load torque T
d means the force (torque) for retracting the ejector pin due to the cavity pressure. Then, for example, when the ejector pin 8 retracts and the protrusion servomotor Me moves, the deviation position deviation from the commanded position Mcmd increases, and as a result, the speed command output by the position loop processing increases and the speed increases. The torque command u output by the loop processing increases and the eject pin 8 is moved to the command position, and finally held at the positioned position.

From the above, the load torque T applied to the protrusion servomotor Me in the injection and pressure-holding processes.
The pressure inside the cavity can be detected by detecting d. Therefore, in the present embodiment, the load torque Td during the injection and pressure-holding process is estimated by assembling the observer 60 with the protrusion servomotor, and the cavity pressure is detected and measured from the estimated load torque Td. To do. The torque command (current command) u is obtained by the speed loop processing, and the actual speed of the servo motor is also fed back from the pulse coder as speed feedback. Therefore, the load torque Td is determined by the torque command u and the actual motor speed y.
And an observer for estimating the load torque Td is estimated.

FIG. 3 shows the observer 60 used in this embodiment.
It is a block diagram of. In FIG. 3, “b” of the elements 61 and 65 is the estimated ratio of the torque constant Kt and inertia J of this protrusion servomotor. That is, it is an estimated value of (Kt / J). Further, K1 and K2 of the elements 62 and 63 are parameters of this observer, S is a Laplace operator, and element 64 is an integral element.

The block diagram of the observer shown in FIG.
When analyzed as Kt / J, {u · Kt + Td} (1 / J · S) = y (1) {u · (Kt / J) + (y−ya) K1 + (y−ya) (K2 / S)} (1 / S) = ya (2) (where ya is the estimated speed of the output of the integral element 64) From the equation (1), u = (yJS-Td) / Kt (3) ) By substituting the formula (3) into the formula (2) and rearranging, (yJS-Td) / J + (y-ya) K1 + (y-ya) (K2 / S) = yaS (4) S (y-ya) + (y-ya) .K1 + (y-ya) (K2 / S) = Td / J (5) From formula (5), (y-ya) = ( Td / J) .multidot. {1 / [S + K1 + (K2 / S)] (6) From the above equation 6, the integrated value Td1 output from the element 63 is
It is shown by the formula. In Td1 = (y-ya) · (K2 / S) = (Td / J) · {K2 / S 2 + K1 · S + K2} ... (7) 7 formula, selecting the parameters K1, K2 so pole is stabilized , Td1 = Td / J. The reciprocal 1 / of the estimated ratio b is added to the calculated integrated value Td1.
If multiplied by b (= J / Kt) (processing of element 65), Td2 = Td1. (1 / b) = (Td / J). (J / Kt) = (Td / Kt) (8) , Estimated value Td of load torque Td (value proportional to)
2, that is, the value obtained by calculating the load torque Td in units of the torque command (current command) is obtained (if Td is divided by the torque constant, the same dimension as the torque command u is obtained).

In this way, during the injection and pressure-holding steps, the load torque Td applied to the protrusion servomotor Me is obtained by the observer for the protrusion servomotor Me, and the pressure inside the cavity is measured. FIG. 4 shows the servo CPU 18.
Is a flow chart of the processing executed for each speed loop processing cycle for control of the protrusion servomotor Me during the injection and pressure-holding process, and the processing of the observer is mainly described. The parameters K1 and K2 and the estimated ratio b required for this observer processing are set in advance.

The servo CPU 18 executes the processing shown in FIG. 4 for each speed loop processing cycle. First, the pulse coder Pe
The actual speed y (i) of the servo motor sent from the device is read, and the torque command u (i-1) obtained and stored by the speed loop processing of the previous cycle is read (step A1,
A2). Next, the actual speed y (i) read in step A1
Estimated speed ya stored in the register from the previous cycle
A value obtained by multiplying the value obtained by subtracting (i-1) by the parameter K2 as the integral gain of the observer and the velocity loop period Ts is stored in the accumulator until the previous period Td1 (i-1)
And the integrated value Td1 (i) of the observer in the relevant cycle
Ask for. That is, the processing of the element 63 in FIG. 2 is executed to obtain the integrated value Td1 (step A3).

Next, the torque command u (i-1) of the previous cycle stored in the register is multiplied by the estimated ratio b of the above (torque constant / inertia), and the integrated value Td1 obtained in step A3.
(i) Further, a parameter K1 as a proportional gain is obtained by subtracting the estimated speed ya (i-1) obtained in the previous cycle stored in the register from the actual speed y (i) of the cycle read in step A1. The multiplied value is added, and the value obtained by multiplying the added value by the speed loop cycle Ts is added to the estimated speed ya (i-1) obtained in the previous cycle to obtain the estimated speed ya (i) in that cycle ( Step A4). That is, the process of obtaining the estimated speed ya by the element 64 in FIG. 2 is executed.

Then, the integrated value Td1 obtained in step A3
The estimated value Td2 (i) of the load torque is obtained by multiplying (i) by the reciprocal of the estimated ratio b of (torque constant / inertia) (step A5). The estimated value Td2 (i) of the load torque thus obtained is written in the RAM 24 (step A6). Then, the speed command obtained by the position loop processing is read, and the speed command and the actual speed y read in step A1 are read.
By (i), the same speed loop processing as in the conventional case is performed to obtain the torque command u (i), which is stored in the register and also passed to the current loop, and the processing of the speed loop is finished (step A8).

Through the above processing, the RAM 24 stores the estimated load torque Td2 which is proportional to the pressure inside the cavity. When the estimated load torque Td2 stored in this manner is displayed on the CRT screen of the manual data input device 19 with a display device, the monitor CPU reads the estimated load torque Td2 from the RAM 24, and the CRT display circuit 25.
Display on the CRT screen via.

Further, when the injection and the pressure holding process are switched to the pressure holding by the pressure in the detected cavity, the estimated load torque Td2 obtained in step A5 in the above-mentioned flow chart is changed to the pressure holding cavity. It suffices to determine whether or not the set value corresponding to the pressure has been exceeded, and output a switching command to hold pressure when the set value or more has been reached.

The above is the method of detecting the pressure in the cavity by the observer, but since the ejector pin 8 is held at a predetermined position in the injection and pressure holding steps, its movement is small, and the ejecting servomotor is small. Since the movement of Me is small, the protrusion servomotor M
The drive current value of e may be regarded as the force with which the ejector pin 8 is pressed by the pressure in the cavity. Further, since the torque command (current command) u is proportional to the drive current, the torque command (current command) u may be regarded as the force with which the ejector pin 8 is pressed by the pressure in the cavity. Therefore, the cavity internal pressure may be measured from the drive current value or the torque command (current command) value u of the protrusion servomotor Me.

In the above embodiment, the drive current and torque command (current command) of the servomotor of the product ejecting mechanism, and the cavity pressure is measured by forming an observer for the servomotor. In addition to the servo motor of the product ejecting mechanism, when there is a mechanism that drives the moving member that moves in the mold cavity with the servo motor, the servo motor of this mechanism is used instead of the servo motor of the product ejecting mechanism. The pressure in the cavity may be measured by the method. As described above, since the pressure inside the cavity is detected and measured by the control device 10 that controls the injection molding machine, it is not necessary to mount a sensor or the like in the mold, and the sensor for mounting this sensor is not required. Since the mold is not required to be processed and the hardware for measuring the pressure in the cavity is not particularly required, the pressure measurement in the cavity can be obtained at low cost.

[0031]

Industrial Applicability According to the present invention, a metal mold such as a product projecting mechanism having a member such as an ejector pin that moves in a mold by a control device that controls an injection molding machine without providing a mold pressure sensor in the mold. An observer is attached to a servomotor that drives a moving mechanism in a mold having a moving member that moves in the mold so that the pressure in the cavity is detected and measured, or a drive current value of the servomotor or a torque command Since the pressure inside the cavity is detected and measured by the (current command), it is possible to measure the pressure inside the cavity at low cost without requiring extra hardware.

[Brief description of drawings]

FIG. 1 is a block diagram of a main part of an electric injection molding machine that implements a method for measuring a mold internal pressure according to the present invention.

FIG. 2 is a block diagram of a servo system in servo motor control in the embodiment.

FIG. 3 is a block diagram of an observer in the embodiment.

FIG. 4 is a flowchart of processing centered on observer processing for each speed loop processing cycle executed by the servo CPU in the embodiment.

FIG. 5 is an explanatory diagram for explaining pressure measurement in a cab.

[Explanation of symbols]

 7, 7 ′ Mold Me Servo motor for projecting product ejection mechanism Mc Servo motor for clamping 10 Control device 60 Observer

Claims (4)

[Claims] 1. A method for measuring an in-mold pressure in an injection molding machine equipped with an in-mold moving mechanism having a moving member driven by a servo motor to move in the mold, wherein a load torque applied to the servo motor is estimated. An in-mold pressure measuring method in which an observer is provided, the moving member is held at a predetermined position by the servo motor during the injection and pressure holding steps, and the cavity internal pressure is measured by the load torque estimated by the observer. 2. The observer estimates a load torque based on a torque command given to the servo motor and a rotation speed of the servo motor, and measures an intracavity pressure based on the estimated load torque. In-mold pressure measurement method. 3. A method for measuring the internal pressure of an injection molding machine, which comprises an in-mold moving mechanism having a moving member that is driven by a servo motor and moves in the mold, wherein the servo motor is used during the injection and pressure holding steps. Hold the moving member in place,
An in-mold pressure measuring method for measuring a pressure in a cavity by a current command or a drive current to the servo motor. 4. The in-mold pressure measuring method according to claim 1, wherein the in-mold moving mechanism is a product projecting mechanism for projecting a product from inside the mold.