JP2002321264A - Back pressure control device of motor-driven injection molding machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To upgrade the metering accuracy of a resin. SOLUTION: This back pressure control device comprises a control mode switching means 50 for switching a control mode from a first control mode to a second control mode at a point of time when an injection screw 4 has reached a specified receding position, a first control means equipped with a screw rotating velocity control means 64 to 66 which are applied to a first control mode and controls a third drive motor 7 so as to make the rotary speed of an injection screw 14 coincide with a target rotary speed and back pressure control means 62, 63 and 59 which control a first and a second drive motor 11A and 11B so as to make a back pressure coincide with a target back pressure and second control means 62, 63 and 66 equipped with metering rate control means 54, 55 and 59 which are applied to a second control mode control and control a first and a second drive motor 11A and 11B so as to make a metering rate coincide with a target metering rate and back pressure control means 62, 63 and 66 which control a third drive motor 7 so as to make the back pressure coincide with a target back pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a back pressure control device for an electric injection molding machine for controlling a back pressure (resin pressure) when measuring a molten resin while retracting an injection screw.

[0002]

2. Description of the Related Art A conventional injection driving device of an electric injection molding machine includes an injection cylinder in which an injection screw is fitted so as to be movable forward and backward.
First and second screw shafts provided symmetrically in parallel and rotatably about the axis of the injection cylinder and first and second drive motors for respectively driving the first and second screw shafts are mounted. And a third drive motor positioned behind the fixed frame, the first and second screw nuts screwed to the first and second screw shafts and the injection screw, respectively. And a moving frame, wherein the moving frame is caused to move straight along with the injection screw by rotation of the first and second screw shafts. In such an injection molding machine, the injection pressure is measured, and the injection speed is controlled so that the servomotor is not overloaded.

On the other hand, in the conventional example disclosed in Japanese Patent Application Laid-Open No. H11-28751, a motion controller drives a master servomotor that operates an injection screw via a master servo amplifier. The master servo amplifier includes a torque command calculation unit that calculates a torque command signal, and the drive command of the master servomotor is commanded by the torque command calculation unit, and at the same time, the drive torque command of the slave servomotor is transmitted to the slave servo amplifier. The slave servo amplifier drives the slave servo motor based on the driving torque command. In this way, the plurality of injection drive motors including the master servomotor and the slave servomotor are tuned.

[0004]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The conventional example disclosed in Japanese Patent No. 751 has a function that enables tuning control of an injection drive motor. However, this conventional example does not have a function of properly controlling the moving speed of the injection screw while appropriately maintaining the resin pressure in the resin measuring step in which the injection screw rotates and retreats. There is a disadvantage that the accuracy of resin measurement is low. Further, in this conventional example, there is a possibility that the screw cannot be smoothly advanced and retracted due to mechanical variations among a plurality of injection drive mechanisms including the screw shaft and its drive motor.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above-described conventional problems, and has as its object to provide a back pressure control device for an electric injection molding machine capable of improving the accuracy of resin measurement. In addition, the present invention corrects an imbalance in operation due to mechanical and electrical variations among a plurality of injection drive mechanisms including a screw shaft and its drive motor,
It is an object of the present invention to provide a back pressure control device of an electric injection molding machine that can smoothly move a screw 4 during weighing.

[0006]

In order to achieve the above object, the present invention provides an injection cylinder in which an injection screw is fitted so as to be able to advance and retreat, and is provided symmetrically parallel and rotatable about the axis of the injection cylinder. A fixed frame to which first and second ball screw shafts and first and second drive motors for driving the first and second ball screw shafts to rotate, respectively;
Movement which is located behind the fixed frame and has first and second ball screw nuts screwed to the first and second ball screw shafts and a third drive motor for rotating and driving the injection screw. A first frame,
The present invention is applied to an electric injection molding machine configured to cause the moving frame to move straight along with the injection screw by rotating the second ball screw shaft. When the injection screw reaches a predetermined retreat position, the control mode is changed to a second mode. Control mode switching means for switching from the first control mode to the second control mode; and the third drive applied to the control of the first control mode so that the rotation speed of the injection screw matches the target rotation speed. A screw rotation speed control means for controlling a motor; and
And a first control means including a back pressure control means for controlling the second drive motor; and the first control means, which is applied to the control of the second control mode, so that the weighing speed matches the target weighing speed. And a second control means comprising: a weighing speed control means for controlling the second drive motor; and a back pressure control means for controlling the third drive motor so that the back pressure matches the target back pressure. Is provided.

In one embodiment, the control mode switching means detects that the injection screw has reached a predetermined retreat position based on the rotational speed of one of the first and second ball screw shafts. .

In an embodiment, the target weighing speed of the weighing speed control means is set such that the weighing speed in the second control mode gradually decreases from the weighing speed in the first control mode.

Further, in the embodiment, as means for detecting the back pressure, a pressure detection sensor for detecting a tensile force acting on the first ball screw shaft, and the first and second pressure sensors from the injection cylinder. Distance to the ball screw shaft of l ₁ and l ₂
And the pressure detected by the pressure sensor is (l ₁ +
calculation means for multiplying by l ₂ ) / l ₁ .

Further, in an embodiment, the first and second ball screw shafts are rotated based on a difference in rotation speed between the first and second ball screw shafts.
And the first and second ball screw nuts are corrected so that the first and second ball screw nuts are corrected for positional deviation based on the positional deviation correction amount.
A means for adjusting the control amount for one of the drive motors is added.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a plan view partially showing an injection drive section of an electric injection molding machine to which a back pressure control device according to the present invention is applied. The injection drive unit 1 has a fixed frame 2 fixedly mounted on a main body (not shown), and a movable frame 6 that moves so as to be able to approach and separate from the fixed frame 2.

The fixed frame 2 has a center hole extending in a horizontal direction, and the base of the injection cylinder 3 penetrates the center hole. The injection cylinder 3 is fixed to the frame 2 by a retaining ring 5 provided on the front side surface of the fixed frame 2, and an injection screw 4 is fitted to the inner periphery of the injection cylinder 4 so as to rotate and move forward and backward. In the fixed frame 2, the injection drive deceleration motors 11A,
11B are mounted respectively, and these motors 1B
Ball screw shafts 8A, 8B parallel to the injection cylinder 3 are arranged inside 1A, 11B.

The ball screw shafts 8A and 8B are located symmetrically with respect to the injection screw 4, and are rotatably supported by the fixed frame 2 via bearings 9A and 9B, respectively.
The bearings 9A and 9B are configured to receive a large thrust load. The driving force of the motors 11A and 11B is transmitted to the ball screw shafts 8A and 8B while being decelerated via power transmission means including a toothed belt 13 and toothed belt pulleys 14 and 15, respectively.

The shaft ends of the ball screw shafts 8A and 8B are provided with encoders 16A and 16A as sensors for detecting their rotation speed.
16B is installed. In addition, a hopper (not shown) for placing resin pellets, which is a raw material for molding, is provided substantially at the center of the upper surface of the fixed frame 2. One side and the other side of the moving frame 6 are provided with a ball screw shaft 8A.
Ball screw nuts 17A and 17B which are screwed to the male ball screws 8a and 8b of the moving screw 6 and 8B are respectively provided. Have been.

The pair of injection drive motors 11A, 11B
Are rotated synchronously, the ball screw shafts 8A and 8B rotate, and their rotational motion is converted into linear motion of the moving frame 6. Then, at the time of injection molding, the injection screw 4 moves forward together with the moving frame 6 by the rotation of the ball screw shafts 8A and 8B. The injection screw 4 is rotationally driven by a screw rotation drive motor 7 attached to the moving frame 6. The injection screw 4 is supported at its drive-side end by a large-capacity thrust bearing (not shown) built in the moving frame 6, so that the injection screw 4 is rotatable even in a state of receiving a large radiation output.

The ball screw nut 17B of the moving frame 6
On the side surface, a pressure detection sensor (for example, a load cell) 1
8 is fixed by means such as bolts. The pressure detection sensor 18 detects an axial force that the ball screw nut 17B receives from the ball screw shaft 8B when the injection screw 4 moves. This pressure detection sensor 18 is connected to the signal line 2
2 is connected to the back pressure calculator 61 of the control device 50 shown in FIG. Note that a dummy 26 having the same shape and made of the same material as the pressure detection sensor is provided between the moving frame 6 and the ball screw nut 17A.

The pressure detected by the pressure detection sensor 18 is
Does not correspond one-to-one with output pressure. However, the ball screw shaft 8
If the rotations of A and 8B are synchronized, the following will be described.
Injection pressure based on the output of the pressure detection sensor 18
Force can be detected. That is, the ball screw shaft 8
The distance from A, 8B to the central axis of the injection screw 4 is
Each one₁, L_Two, The detection pressure of the pressure detection sensor 18
Force (l₁+ L_Two) / L _TwoInjection screw by doubling
Injection pressure can be obtained. Back pressure calculation shown in FIG.
The unit 61 has a means for performing such an operation.
You. Note that, for example, the distance l₁, L_TwoAre equal, (l
₁+ L_Two) / L_TwoIs 2, so the injection pressure at this time
Is calculated as twice the detection pressure of the pressure detection sensor 18.
You.

FIG. 2 shows an example of a control device 50 for controlling the injection driving section 1. In the control device 50, the rotational speed difference calculator 52 includes the encoders 16A and 16A.
The rotational speed difference between the ball screw shafts 8A and 8B is calculated based on the output of B. Further, the position correction calculator 53 calculates a shift correction amount corresponding to the relative position shift amount of the ball screw nuts 17A, 17B based on the rotational speed difference between the ball screw shafts 8A, 8B. The pressure setting device 63 is provided for setting a resin pressure P (injection screw back pressure), and the screw rotation speed setting device 65 is provided for setting a target rotation speed of the injection screw 4.

The screw rotation speed PID control circuit 64
A screw speed control operation amount corresponding to a deviation between the target rotation speed of the injection screw 4 set by the screw rotation speed setting device 65 and the rotation speed of the screw 4 detected by the rotation speed detector 25 is calculated. The back pressure PID control circuit 62 calculates a pressure control operation amount corresponding to a deviation between the target resin pressure Ps (target back pressure) set by the pressure setting device 63 and the actual resin pressure P detected by the pressure detection sensor 18. Calculate.

The weighing speed PID control circuit 54 has a target weighing speed Vs set by the weighing speed setter 55.
And the rotation speed of the ball screw shaft 8A detected by the encoder 16A (corresponding to the moving speed of the injection screw 4, that is, the weighing speed), and corresponds to the deviation between the target weighing speed Vs and the actual weighing speed V. The calculated weighing speed control operation amount is calculated.

The screw position calculator 56 includes the encoder 1
The position of the injection screw 4 is calculated based on the output of 6A. The control switching position setter 58 (with a screw position indicator) switches the position of the injection screw 4 calculated by the screw position calculator 56 from a later-described first-stage control mode to a second-stage control mode. The switch 57 is switched when the position to perform the operation is reached. The changeover switch 57 is provided with a manual lever 57a so that it can be manually operated based on the screw position displayed on the screw position indicator.

In FIG. 1, the solid line indicates a state in which the moving frame 6, the screw rotation drive motor 7, the ball screw nuts 17A and 17B, etc. are at the forward end positions after the injection step. After this state, the resin feeding and plasticizing steps are started. FIG.
, The two-dot chain line indicates the moving frame 6 when the injection screw 4 is stopped after the measurement step of the molten resin is completed.
Screw rotation drive motor 7 and ball screw nut 17
The positions of A and 17B are shown.

In the measuring step in which the resin feeding, plasticizing, and melting processes are performed by the injection cylinder 3 and the injection screw 4, the injection screw 4 is rotated by a screw rotation drive motor 7 to thereby rotate the hopper (not shown). The resin pellets are introduced into the injection cylinder 3 and heated and melt-plasticized while feeding the resin pellets forward with the screw 4. On the other hand, in the resin feeding, plasticizing and melting steps, the ball screw shafts 8A and 8B are simultaneously rotated by the synchronous operation of the injection drive motors 11A and 11B, and the moving frame 6 is retracted together with the injection screw 4. This allows
The molten resin is stored at the tip of the injection screw 4. When one shot of resin for a mold (not shown) is accumulated at the tip of the injection screw 4, the moving frame 6 is stopped at the position shown by the two-dot chain line in FIG. The motor 7 is also stopped.

Next, a mold (not shown) is clamped, and when it is completed, an injection process is started. In this injection step, the pair of injection drive motors 11A and 11B are rotated at a high speed so that the injection screw 4 moves forward at a high speed, whereby the resin accumulated at the tip of the injection screw 4 is transferred to a mold (not shown). Injected into the cavity. At this time, the moving frame 6 is returned to the position indicated by the solid line in FIG. Then, the measuring step and the injection step are repeated as described above.

In the measuring step, as described below, the molten resin pressure is controlled in two stages. FIG. 3 shows the stroke S of the injection screw 4, the rotation speed R of the screw 4, and the speed of the screw 4 based on the two-stage control. The change characteristics of the retreat speed V and the molten resin pressure (back pressure of the injection screw 4) P are illustrated.

The control device 50 includes encoders 16A, 16
The rotation number of the ball screw shafts 8A and 8B is detected based on the output of B, and the resin pressure P in the injection cylinder 3 is detected based on the axial pressure of the ball screw shaft 8B detected by the pressure detection sensor 18. Hereinafter, a control procedure in the measuring step will be described. 1) The injection screw 4 is rotated while the resin outlet of the injection cylinder 3 is closed and the injection drive motors 11A and 11B are stopped (the moving frame 6 is stopped). That is, the screw rotation speed PID control circuit 64
The rotational speed control manipulated variable output from the screw drive output circuit 6 via the contact 57D of the changeover switch 57
6 and as a result, the rotation speed R of the injection screw 4
The screw drive motor 7 is driven such that the speed of the screw 7 coincides with the speed R _S set by the screw rotation speed setting device 65 (see FIG. 3). 3 shows a timing for rotating the screw 4 is indicated by T _1. Since the molten resin is fed into the tip of the injection screw 4 by the rotation of the injection screw 4, the molten resin pressure P increases as shown in FIG. Then, at a timing when the resin pressure P exceeds the target resin pressure P _S (timing indicated by T ₂ in FIG. 3), a start circuit (not shown) sends a signal indicating the back pressure control operation amount from the back pressure PID control circuit 62. Output.

2) The signal indicating the back pressure control operation amount is:
The signal is input to the divider 60 via the contact 57B of the switch 57, and is divided into two here. One and the other of the two divided back pressure control manipulated variables are input to the output circuits 59A and 59B, respectively, and as a result, the injection drive motors 11A and 11B receive one.
A current corresponding to a / 2 back pressure control manipulated variable is supplied. Thereby, the injection screw 4 is retracted so that the resin pressure P is maintained at the target resin pressure P _S. At this time, the retreat speed of the injection screw 4 is V. The above is the back-pressure control according to the first-stage control mode. In the measuring process, the back-pressure control according to the first-stage control mode is executed during most of the period (period A shown in FIG. 3).

3) When the injection screw 4 retreats and its stroke position S reaches the control mode switching stroke position S1 shown in FIG. The switch signal is output, and the switch 57 is switched. As a result, the contacts 57A to 57D of the switch 57 are in a connection state different from that shown in the figure, and the control mode shifts to the second-stage control mode.

In the second stage control mode, the back pressure PID control circuit 62 is disconnected from the output circuits 59A and 59B, and the metering speed PID control circuit 54 is connected to the output circuits 59A and 59B via the switch 57A. You. Therefore, the metering speed PID control circuit 54, output circuit a control operation amount such that the programmed set value V _S (see FIG. 3) in the metering speed V calculated from an output of the encoder 16A is measuring the speed setter 55 Add to 59A and 59B.

On the other hand, in the second stage control mode, the connection between the screw rotation speed PID control circuit 64 and the output circuit 66 is disconnected, and the back pressure PID control circuit 62
It is connected to the output circuit 66 via 7C. This allows
Injection screw rotation driving motor 7, the rotational speed R and output torque is controlled so that the resin pressure P is maintained at the set pressure P _S (ranges refer shown in B in FIG. 3).

4) The target speed value V _S programmed in the metering speed setter 55 is set in a gradually decreasing pattern as shown in FIG. Therefore, the metering speed V gradually decreases according to this pattern, and as a result, the injection screw 4 stops at the predetermined retracted position.

5) The rotational speed difference calculator 52 receives the output signals of the encoders 16A and 16B throughout the entire weighing process, and calculates the rotational speed difference between the ball screw shafts 8A and 8B based on these signals. Then, the position correction computing unit 53
The ball screw nuts 17A, 17A are determined based on the rotation speed difference.
The position shift correction amount of B is calculated, and this is input to the output circuit 59A.

In the first stage control mode, the output circuit 59
At A, the above-described displacement correction amount is added to the output of the divider 60, and as a result, the back pressure P is reduced to the target pressure P while the imbalance of the tensile forces generated by the rotation of the ball screw shafts 8A and 8B is corrected. _S will be enacted. In the second stage control mode, the output circuit 59A adds the deviation correction amount to the output of the metering speed PID control circuit 54, and as a result, each tension generated as the ball screw shafts 8A and 8B rotate. The retreat speed V of the screw 4 is set to the target speed V _S while the imbalance of the forces is corrected.

As described above, according to the back pressure control device for an electric injection molding machine according to this embodiment, the moving speed of the injection screw 4 is appropriately controlled while appropriately maintaining the back pressure (resin pressure). The measurement accuracy of the resin is improved.
In addition, the imbalance in operation due to electrical and mechanical variations among a plurality of injection drive mechanisms including the ball screw shaft and its drive motor can be corrected, and the movement of the screw 4 during weighing can be smoothed. . In addition, the present invention
The present invention is not limited to the above embodiment, and various modifications and changes are possible.

[0035]

According to the present invention, in the resin measuring step,
When the injection screw reaches a predetermined retreat position, the control mode is switched from the first control mode to the second control mode. In the first control mode, the third drive motor for driving the screw is controlled so that the rotation speed of the injection screw matches the target rotation speed, and the back pressure (resin pressure) matches the target back pressure. The first drive motor that drives the first ball screw shaft and the second drive motor that drives the second ball screw shaft are controlled in such a manner. In the first control mode, the first and second drive motors are controlled so that the weighing speed matches the target weighing speed, and the first and second drive motors are controlled so that the back pressure matches the target back pressure. The third drive motor is controlled. Therefore, according to the present invention, it is possible to appropriately control the moving speed of the injection screw 4 while appropriately maintaining the back pressure (resin pressure), thereby improving the accuracy of resin measurement.

Further, according to the present invention, the back pressure is detected by calculating the output of one pressure detection sensor, so that the configuration can be simplified and the cost can be reduced.

Further, according to the present invention, the amount of displacement correction of the first and second ball screw nuts is calculated on the basis of the difference between the rotation speeds of the first and second ball screw shafts, and the displacement is corrected. Since the control amount for one of the first and second drive motors is adjusted so that the displacement of the first and second ball screw nuts is corrected based on the amount, the screw shaft and the drive motor thereof are adjusted. The imbalance in operation due to mechanical and electrical variations among a plurality of injection drive mechanisms including the above can be corrected to facilitate the movement of the screw during weighing.

[Brief description of the drawings]

FIG. 1 is a plan view partially showing a configuration example of an electric injection drive unit of an injection molding machine to which the present invention is applied.

FIG. 2 is a block diagram showing an embodiment of a back pressure control device for an injection molding machine according to the present invention.

FIG. 3 is a graph illustrating control characteristics of an injection stroke, a screw rotation speed, a screw retreat speed, and a molten resin pressure in a measuring process by the control device of FIG. 2;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Injection drive part 2 Fixed frame 3 Injection cylinder 4 Injection screw 6 Moving frame 7 Screw rotation drive motor 8A, 8B Ball screw shaft 16A, 16B Encoder 17A, 17B Ball screw nut 18 Pressure detection sensor, 50 Control device 52 Revolution calculation Unit 53 position correction calculator 54 weighing speed PID control circuit 55 weighing speed setter 56 screw position calculator 57 changeover switch 58 control switching position setter 59A, 59B output circuit 61 back pressure calculator 62 back pressure PID control circuit 63 pressure setting Device 64 Screw rotation speed PID control circuit 65 Screw rotation speed setting device 66 Screw drive output circuit

Claims (5)

[Claims] An injection cylinder in which an injection screw is fitted so as to be able to move forward and backward, first and second ball screw shafts provided symmetrically parallel and rotatable about the axis of the injection cylinder, and the first and second ball screw shafts. A fixed frame to which first and second drive motors respectively rotating and driving the two ball screw shafts are attached; and a second frame located behind the fixed frame and screwed to the first and second ball screw shafts, respectively. A moving frame to which a second ball screw nut and a third drive motor for rotationally driving the injection screw are attached;
The present invention is applied to an electric injection molding machine configured to cause the moving frame to move in a straight line together with the injection screw by rotation of a second ball screw shaft. When the injection screw reaches a predetermined retreat position, the control mode is changed to a second mode. Control mode switching means for switching from the first control mode to the second control mode; and the third drive is applied to the control of the first control mode so that the rotation speed of the injection screw matches the target rotation speed. Screw rotation speed control means for controlling the motor,
And first control means including back pressure control means for controlling the first and second drive motors so that the back pressure matches the target back pressure; and applied to the control of the second control mode. Measuring speed control means for controlling the first and second drive motors so that the weighing speed matches the target weighing speed, and the third drive motor so that the back pressure matches the target back pressure. And a second control means having a back pressure control means for controlling the back pressure control means for the electric injection molding machine. 2. The control mode switching means according to claim 1, wherein said injection screw has reached a predetermined retreat position.
The back pressure control device for an electric injection molding machine according to claim 1, wherein the detection is performed based on the rotation speed of one of the ball screw shafts. 3. The target weighing speed of the weighing speed control means is set such that the weighing speed in the second control mode gradually decreases from the weighing speed in the first control mode. A back pressure control device for an electric injection molding machine according to claim 1. 4. As means for detecting the back pressure,
A pressure detection sensor for detecting a tensile force acting on the first ball screw shaft;
And calculating means for multiplying the pressure detected by the pressure sensor by (l ₁ + l ₂ ) / l _{1 with} distances to the ball screw shaft being l ₁ and l _2. A back pressure control device for an electric injection molding machine as described in the above. 5. A position shift correction amount of the first and second ball screw nuts is calculated based on a rotation speed difference between the first and second ball screw shafts, and based on the position shift correction amount. 2. The apparatus according to claim 1, further comprising a unit that adjusts a control amount for one of the first and second drive motors such that a displacement of the first and second ball screw nuts is corrected. Back pressure control device for electric injection molding machine.