JPH055650B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a back pressure control method and device for an electric injection molding machine that uses a servo motor as an injection drive source.

[Prior Art] A general injection molding machine uses an actuator such as a hydraulic cylinder to reciprocate an extrusion tool such as a screw or a plunger, and moves the extrusion tool forward to remove resin from the tip side of the extrusion tool. The structure is such that it is injected into the mold. As a pre-injection process, there is a resin metering process that fills the tip of the extruder with resin.In the metering process, the extruder moves backwards due to the filled resin, but at that time, the extruder The pressure of the resin to be filled, that is, the back pressure, is controlled by applying movement resistance with a hydraulic cylinder or the like. In contrast to the above-mentioned conventional injection molding machines, electric injection molding machines in which the extrusion tool is driven by an electric motor have been developed in recent years. The output is converted into a linear motion output through a screw mechanism such as a screw, and the extrusion tool is moved back and forth by this screw mechanism. The back pressure during the metering process is controlled using an open-loop control method by setting the torque current value of the electric motor to a predetermined value, or by actually measuring the resin pressure and calculating the actual resin pressure. To reach the backpressure setpoint, e.g.
A closed-loop control method that controls the torque current value of the AC servo motor.For example, the resin pressure is actually measured and the measured resin pressure is made to reach the back pressure set value.
A closed-loop control method for controlling the rotational speed of an AC servo motor is known.

[Problems to be Solved by the Invention] However, in the case of the open-loop type control method described above in the electric injection molding machine described above, the torque of the electric motor is transmitted to the extrusion tool via the screw mechanism, so that the screw mechanism cannot be used. This has the disadvantage that the frictional force of ,
Since the measured value and the back pressure set value are repeatedly compared and controlled so that the measured value approaches the set value, there is a drawback that it takes time for the resin pressure to reach the back pressure set value.

The present invention has been made in view of the above circumstances, and provides back pressure control for an electric injection molding machine that can accurately control resin pressure and reach the back pressure set value in a short time. The present invention aims to provide methods and apparatus.

[Means for Solving the Problems] In order to achieve the above object, the present invention converts the rotational motion output of a servo motor into a linear motion output,
This linear motion output causes the resin extrusion tool to reciprocate, and when the extrusion tool moves forward, the resin at the tip of the extrusion tool is injected into the mold, and as a measuring process before injection. In a back pressure control method for an electric injection molding machine, the tip side of an extrusion tool is filled with resin, and at that time, the extrusion tool moving backward is braked by the servo motor to control the pressure of the resin to be filled, In advance, the relationship between the amount of movement of the extrusion tool and the rate of increase in pressure of the resin was investigated with the tip side of the extrusion tool filled with resin, and the amount of movement of the extrusion tool and the rate of increase in pressure of the resin were determined. Set the relationship between the A method is used in which the amount of movement of the extrusion tool is calculated to reach this amount, and the pressure of the resin during the metering process is controlled by moving the extrusion tool by this amount of movement.

In addition, as a device for carrying out the above method, the rotational motion output of a servo motor is converted into a linear motion output, the resin extrusion tool is reciprocated by this linear motion output, and this extrusion tool is moved forward. The extrusion tool has an extrusion tool drive mechanism that injects the resin on the tip side of the extrusion tool into the mold, and is moved backward by the filled resin in the metering process of filling the tip side of the extrusion tool with resin. A back pressure control device for an electric injection molding machine that controls the pressure of the resin by applying braking to the extrusion tool using the servo motor, which includes a pressure detection means for detecting the pressure of the resin; A functional formula representing the relationship between the amount of movement of the extruder and the increase in pressure of the resin when the side is filled is stored, and this functional formula is combined with the actual resin pressure detected by the pressure detection means. A calculation circuit that calculates the amount of movement of the extrusion tool to reach the set value of back pressure by substituting the differential pressure with the set value of back pressure, and the movement of the extrusion tool calculated by this calculation circuit. It is desirable to have a servo amplifier that controls the servo motor so as to move the extrusion tool by the same amount.

[Operation] In the present invention, the amount of movement of the extrusion tool that causes the resin pressure to reach the set value of the back pressure is calculated, and the extrusion tool is moved by this amount of movement. Therefore, the resin pressure changes to the set value of the back pressure in a short time.

[Example] Hereinafter, an example in which the present invention is applied to a pre-plastic electric injection molding machine will be described with reference to FIGS. 1 to 7.

In FIG. 1, reference numeral 1 denotes a frame body, and a stationary platen 2, which is a component of a mold clamping device for opening and closing a mold and clamping the mold, is fixed onto the frame body 1. Also, on the frame body 1,
A movable plate 3 is provided which is movable in the direction toward and away from the fixed platen 2.

The lower part of the movable plate 3 is supported by a guide bar 4 so as to be movable along the guide bar 4. The guide bars 4 are arranged at left and right positions of the frame body 1 (positions shifted from each other in the direction perpendicular to the drawing) with their axes oriented in a direction perpendicular to the fixed platen 2, and both ends of each guide bar It is fixed to the frame main body 1 by a bracket 5 fixed on the main body 1.

Further, the movable plate 3 is provided with an injection device 6. The injection device 6 includes an injection cylinder 7 fixed to the moving plate 3, and this injection cylinder 7.
An injection nozzle 8 provided at the tip of the injection cylinder 7 and an injection plunger (extrusion tool) 9 inserted into the injection cylinder 7.
and a plunger drive mechanism (extruder drive mechanism) 10 that moves and drives the injection plunger 9.

The injection cylinder 7 is inserted into the nozzle introduction hole 2 of the fixed platen 2.
The movable plate 3 is fixed to the movable plate 3 so as to extend toward the fixed plate 2 side, with its axis aligned with the movable plate 3, and a resin inflow hole 7a penetrating upward is provided at the upper side of the peripheral wall at the distal end of the movable plate 3. It is formed. Injection nozzle 8
is for supplying the resin in the injection cylinder 7 into the mold. The injection plunger 9 is fitted into the injection cylinder 7 so as to be movable in the axial direction, and its base end is connected to the plunger drive mechanism 10.

The plunger drive mechanism 10 is installed on the movable plate 3 at a position opposite to the injection cylinder 7, and includes a guide plate 11 that is slidably supported by the guide bar 4 in the axial direction thereof, and this guide plate 11. an injection ball screw rod 12 that is stretched over the moving plate 3; an injection plate 13 that is connected to the injection ball screw rod 12 and moves along the injection ball screw rod 12; It is equipped with an injection ball screw rod rotation drive mechanism 14 that is rotationally driven. The guide plate 11 is formed into a rectangular plate shape, and the left and right portions along the lower side are slidably supported by the guide bar 4. The injection ball screw rod 12 has its axis parallel to the axis of the injection cylinder 7 and is rotatably supported by the moving plate 3 and the guide plate 11.
Centering on the axis of the injection cylinder 7, they are arranged at two or four positions equally distributed at predetermined intervals in the vertical direction and equally distributed at predetermined intervals in the left-right direction. Injection plate 13
is a rectangular injection plate main body 15, injection ball nuts 16 fixed to the four corners of the injection plate main body 15 so as to be screwed onto each of the injection ball screw rods 12, and an axial center of the injection cylinder 7. An injection plunger connecting member 17 is aligned and provided on the injection cylinder 7 side of the injection plate main body 15, and a load converter (pressure detection) is provided between the injection plunger connecting member 17 and the injection plate main body 15. means) 18.

The injection ball screw rod rotation drive mechanism 14 includes an injection AC servo motor 19 attached to the guide plate 11 and an injection first timing pulley 2 fixed to the output shaft of the AC servo motor 19.
0, and each injection ball screw rod 12 protruding from the surface of the guide plate 11 opposite to the moving plate 3.
A second timing pulley 21 for injection fixed to the end of the first timing pulley 20 for injection and a second timing pulley 21 for injection
The injection timing belt 22 is wound around the injection timing belt 22. Furthermore, an injection motor control encoder 23 is connected to the output shaft of the injection AC servo motor 19.

Furthermore, a plasticizing device 31 is attached to the sliding surface 3a formed at the upper end of the moving plate 3.

The plasticizing device 31 includes a plasticizing cylinder 32, a plasticizing cylinder support member 33 which is movably connected to the sliding surface 3a with the base end of the plasticizing cylinder 32 fixed, and the plasticizing cylinder 32. 32, and a plasticizing AC servo motor 35 which is attached to the plasticizing cylinder support member 33 and whose output shaft is connected to the base end of the screw 34. Furthermore, the plasticizing AC servo motor 35 is provided with a plasticizing motor control echoder 36 on its output shaft. In the plasticizing device 31, the distal end of the plasticizing cylinder 32 is connected to the resin inflow hole 7a of the injection cylinder 7 via a cylinder connecting member 41.

The cylinder connecting member 41 is connected to the plasticizing cylinder 32
A communication hole 41a that communicates between the inside and the inside of the injection cylinder 7
is formed in the communication hole 41a,
A backflow prevention mechanism 42 is provided to prevent backflow of resin from the injection cylinder 7 to the plasticizing cylinder 32.

Further, the movable plate 3 is provided with a movable plate moving ball nut (hereinafter abbreviated as a movable ball nut) 51 at its lower end.
This moving ball nut 51 is screwed onto a moving ball screw rod 52 for moving the moving plate (hereinafter abbreviated as moving ball screw rod). The moving ball screw rod 52 has its axial center aligned with the axial direction of the guide bar 4, and both ends thereof are rotatably supported by bearings 53 fixed to the frame body 1. A first timing pulley for moving the moving plate (hereinafter abbreviated as the first timing pulley for moving) 54 is fixed to the end of the moving ball screw rod 52 on the opposite side from the injection cylinder 7. The first timing pulley 54 for moving is connected to the second timing pulley for moving the moving plate (hereinafter referred to as the second timing pulley for moving) fixed to the output shaft of the motor 55 for moving the moving plate (hereinafter abbreviated as the moving motor). Timing pulley) 56, timing belt for moving the moving plate (timing belt for moving) 5
They are connected via 7.

Note that the reference numeral 37 in the figure is a hopper for supplying resin into the plasticizing cylinder 32.

Next, the operation of the pre-plastic electric injection molding machine configured as described above will be explained.

For plasticizing the resin, use AC servo motor 3 for plasticizing.
This is done by rotating the screw 34 at step 5.
At this time, the plasticizing AC servo motor 35 is feedback-controlled based on the rotation speed detected by the plasticization motor control encoder 36, so that the rotation speed of the screw 34 is kept constant. Plasticizing cylinder 32
The plasticized resin inside the cylinder connecting member 41
through the communication hole 41a, the backflow prevention mechanism 42, and the resin inflow hole 7a of the injection cylinder 7, and is pushed out to the tip side of the injection plunger 9 of the injection cylinder 7. Then, the injection plunger 9 is pushed in the backward direction by the pressure of the inflowing resin, and the force pushing the injection plunger 9 is applied to the injection plunger connecting member 17, the load converter 18, and the injection plate main body 1.
5. It is transmitted to the output shaft of the AC servo motor for injection 19 via the injection ball nut 16, the ball screw rod for injection 12, the second timing pulley for injection 21, the timing belt for injection 22, and the first timing pulley for injection 20. , the output shaft rotates. As a result, the injection plunger 9 retreats, and the plasticized resin is stored on the tip side of the injection plunger 9. At that time, a back pressure control device to be described later can generate a predetermined amount of braking torque in the injection AC servo motor 19, thereby providing movement resistance to the injection plunger 9.
It is possible to plasticize the resin while applying back pressure. The injection amount is determined by the injection AC servo motor 19.
Injection motor control encoder 2 attached to
3, the amount of retreat of the injection plunger 9 is calculated from the rotation angle of the injection AC servo motor 19, and the rotation of the screw 34 is stopped when the measurement is completed. For injection, AC servo motor 1 for injection
9 by rotating the resin in the opposite direction (injection direction) from when the resin flows into the injection cylinder 7. That is, when the AC servo motor 19 for injection is rotated in the injection direction, the ball screw rod 12 for injection rotates via the first timing pulley 20 for injection, the timing belt 22 for injection, and the second timing pulley 21 for injection. The injection plate 13 having the injection ball nut 16 screwed onto the injection ball screw rod 12 moves toward the injection cylinder 7, and the injection plunger 9 moves forward within the injection cylinder 7. As a result, the resin on the tip side of the injection plunger 9 is injected from the injection nozzle 8 into the mold. At this time, the backflow prevention mechanism 42 prevents the resin from flowing back from the injection cylinder 7 to the plasticizing cylinder 32. The injection speed is controlled by controlling the rotation speed of the injection AC servo motor 19, and the injection AC servo motor 19 controls the injection speed based on the rotation speed detected by the injection motor control encoder 23. Feedback controlled. Therefore, the injection speed is precisely controlled. In the pressure holding step after injection, the pressure of the resin is controlled by a pressure holding control device, which will be described later. Further, the injection nozzle 8 is moved forward and backward by rotating the moving motor 55, and the moving ball screw rod is moved through the moving second timing pulley 56, the moving timing belt 57, and the moving first timing pulley 54. 52
, thereby rotating the moving ball screw rod 52.
This is done by moving the moving plate 3 having a moving ball nut 51 screwed into the moving ball nut 51 along the moving ball screw rod 52. The injection nozzle 8 is pressed against the sprue bush of the mold by passing a current of a predetermined magnitude through the moving motor 55 and controlling the torque of the moving motor 55.

In the pre-plastic electric injection molding machine configured as described above, the injection plunger 9 and the screw 3 are
Since no hydraulic equipment such as a hydraulic cylinder or a hydraulic motor is used to drive the 4, there is no need to manage hydraulic fluid to operate each hydraulic equipment, and
There is no need to manage the seals used in hydraulic equipment. Moreover, there is no risk of hydraulic oil leaking from hydraulic equipment, and the area around the injection molding machine can be kept clean.

Next, the back pressure control device for the pre-plastic type electric injection molding machine will be explained with reference to FIG. 2.

In this figure, 61 is the main control device of the pre-plastic electric injection molding machine, and this main control device 61 is provided with an arithmetic circuit 62, which includes a load converter 18, a back pressure A setting device 81 and a position counter 65 that detects the position of the plunger 9 by counting the number of pulses 64 from the injection motor control encoder 23 are connected.

The arithmetic circuit 62 compares the actual resin pressure X _p on the tip side of the plunger 9 detected via the load converter 18 with the back pressure set value BP input to the back pressure setting device 81, and calculates the actual resin pressure The movement amount ΔY of the plunger 9 is controlled so that the pressure X _p becomes the back pressure set value BP. When the differential pressure ΔX between the measured resin pressure X _p and the back pressure set value BP is substituted, A functional formula for obtaining the displacement ΔY of the plunger 9 corresponding to the pressure ΔX is programmed. This functional formula is calculated by determining the relationship between the actually measured resin pressure X _p and the position Y _s of the plunger 9 by experiment, depending on the type of resin and the temperature of the resin. Based on the experimental results, a first-order or higher-order formula can be calculated using a simple regression. This is determined by analysis or multiple regression analysis. Therefore, if this functional formula is expressed as a general formula, Y=f(X)...() where X: resin pressure Y: position of plunger. Further, the arithmetic circuit 62 is configured to output a command value 66 of the number of pulses corresponding to the movement amount ΔY of the plunger 9 obtained by the above-mentioned functional formula () to the positioning pulse distributor 67.

The positioning pulse distributor 67 includes a pulse distributor 69 that generates a number of pulses 68 according to the command value 65 for the number of pulses, and a pulse distributor 69 that generates the number of pulses 68 that is generated from the pulse distributor 69 and the number of pulses 68 that are generated from the encoder 23 for controlling the injection motor. The difference is calculated as the pulse frequency deviation amount 7.
a deviation counter 71 that digitally outputs as 0;
A D/A converter 74 converts the frequency deviation amount 70 output from the deviation counter 71 into a D/A converter and outputs a deviation voltage 73 to the servo amplifier 72.

The servo amplifier 72 includes an F-V converter 76 that converts the pulse 64 emitted from the injection motor control encoder 23 into a feedback voltage 75.
and an operational amplifier 78 that amplifies the difference between the feedback voltage 76 and the deviation voltage 73 output from the F-V converter 75 and supplies a voltage 77 for driving the injection AC servo motor 19. .

According to the back pressure control device configured as described above, the injection AC servo motor 19 is controlled at a speed according to the voltage 77, and the injection AC servo motor 19
Since the resin pressure is controlled by repeating the forward and reverse rotation of The influence of the fluctuation width of the movement resistance of the plunger 9 caused by this can be reduced, and the error in the measured resin pressure with respect to the set value of the back pressure can be made extremely small. That is, in the electric injection molding machine, there is a phenomenon in which the frictional force changes due to static friction or dynamic friction in the drive system of the plunger 9, such as between the ball screw rod 12 and the injection ball nut 16, and until the plunger 9 starts to move. The movement resistance is large, and after the movement starts, the movement resistance becomes small, and there is a problem that it is difficult to set the position of the plunger 9 to the target value. In this regard, when controlling the resin pressure using the torque current value, it is greatly affected by the difference in frictional resistance, so there is a drawback that the error in the measured resin pressure with respect to the set value of the back pressure increases.
In the back pressure control device of this embodiment,
Since the AC servo motor 19 repeats forward and reverse rotation,
The drive system of the plunger 9 is always in a state of dynamic friction,
It is not easily affected by changes in the frictional force of the drive system, and the error in the measured resin pressure with respect to the set value of the back pressure can be made extremely small.

In addition, in the case of a closed-loop control method that simply controls the rotational speed of an AC servo motor,
Although there is a drawback that the amplitude of forward and reverse rotation of the servo motor is large and the resin pressure pulsates and cannot be kept at a constant value, in the back pressure control device of this embodiment, the function equation Y=f(X) is Therefore, since the amount of movement of the plunger 9 to reach the set value of the back pressure is predicted and the plunger 9 is moved by the amount of movement, fluctuations in resin pressure can be suppressed to an extremely low level. Furthermore, since the amount of movement of the plunger 9 is predicted and the plunger 9 is moved by that amount at once, it is possible to reduce the resin pressure to the back pressure set value more quickly than when measuring the resin pressure sequentially and performing feedback control. It can change over time.

On the other hand, in the holding pressure control device, in FIG. Other than that, it has the same structure as the back pressure control device.

Also, like the back pressure control device, this pressure holding control device is not easily affected by changes in the frictional force of the drive system of the plunger 9, and it is possible to reduce the error in the measured resin pressure with respect to the setting value of the holding pressure. Furthermore, it is possible to prevent pulsations in the resin pressure and control fluctuations in the resin pressure to be extremely small, and moreover, it is possible to change the resin pressure to the set value of the back pressure in a short time.

Next, a pressure holding control method will be explained with reference to FIGS. 3 to 5.

However, since there is an injection process in which resin is injected into a mold before the pressure holding process, the injection process will be explained first.

As shown in FIG. 3, when an injection start signal is input at step SP1, counting of the total injection time T is started at step SP2. and,
At step SP3, it is determined whether or not the total injection time T has timed up. If the time has not expired, the process moves to step SP4, where it is determined where the plunger position S is. Here, plunger position S
If it is larger than the injection process completion position _S5 of the plunger 9, the process moves to step SP5 and the injection process is continued. In the injection process, as shown in FIG. 4, the plunger position S changes from the injection start position S0 to the injection process completion position _S5 , and during this time the moving speed of the plunger 9 changes from _{V1 to V5} . In order to carry out this injection process, steps SP3, SP4,
SP5 is repeated, and when the plunger position S becomes smaller than the injection process completion position _S5 , step SP6 is executed.
The process moves to the pressure holding process.

In step SP6, it is again determined whether the total injection time T has timed up or not. If the total injection time T has not timed up, counting of the first stage holding pressure time _T1 is started in step SP7, and in step SP8 the first stage pressure holding time T1 is started.
It is determined whether or not the stage holding pressure time T ₁ has timed up. If the first stage holding pressure time T ₁ has not timed up, the process moves to step SP9 and the first stage holding pressure set value HP ₁ and the actual measured resin are determined. By substituting the differential pressure ΔX with the pressure X _p using the functional formula Y=f(X), find the amount of movement of the plunger 9 to increase or decrease the actual resin pressure X _p to the first stage holding pressure set value HP ₁ . Calculate ΔY. Then, in step SP10, a command is given to the injection AC servo motor 19 so that the plunger 9 moves by ΔY, and the process returns to step SP6 again, and the step
SP6, step SP7, step SP8, step
SP9 and step SP10 are repeated, which results in
The measured resin pressure X _p is maintained at the first stage holding pressure set value HP ₁ . Then, when the first stage pressure holding time _T1 times up in step SP8, the process moves to step SP11, and counting of the second stage pressure holding time _T2 starts, and in step SP12, the second stage pressure holding time _T2 times out. A judgment is made as to whether or not the second stage pressure holding time T ₂
If the time is not up, step SP13
Moving on to the second stage holding pressure setting value HP ₂ and the actual resin pressure X _p
Substituting the differential pressure ΔX between the
Movement amount ΔY of plunger 9 to increase or decrease the actual resin pressure X _p to the second stage holding pressure set value HP ₂
Calculate. Then, proceed to step SP10, and adjust the injection AC so that the plunger 9 moves by ΔY.
A command is given to the servo motor 19, and the plunger 9 moves by ΔY. Then step again
Returning to SP6, the control of step SP6, step SP7, step SP8, step SP11, step SP12, step SP13, and step SP10 is repeated.
As a result, the measured resin pressure X _p becomes the second stage holding pressure setting value.
HP remains at ₂ .

Then, when the second stage holding pressure time _T2 times out in step SP12, the process moves to step SP14, and the differential pressure ΔX between the third stage holding pressure set value _HP3 and the actual resin pressure _Xp is determined.
Substituting into the functional formula Y=f(X), the measured resin pressure X _p
The amount of movement ΔY of the plunger 9 to increase or decrease the pressure to the third-stage holding pressure setting value HP ₃ is calculated. Then, move to step SP10, and plunger 9 moves to ΔY.
Injection AC servo motor 19 to move only
A command is given to move the plunger 9 by ΔY. After that, go back to step SP6, step SP6, step SP7, step SP8, step SP11, step SP12, step SP14.
SP10 is repeated, which _results in the actual resin pressure
is maintained at the third stage holding pressure set value HP ₃ .

When the total injection time T times up in step 6, the process moves to step SP15, where the total injection time T, first stage pressure holding time T ₁ , second stage pressure holding time T ₂ , and third stage pressure holding time T ₃ are updated. The timer is reset and the pressure holding process is completed.

With the above control, as shown in _FIG . 5, _the measured resin pressure
2nd stage holding pressure set value HP ₂ and 3rd stage holding pressure set value
As HP ₃ changes, the plunger position S changes from the injection process completion position S ₅ to the pressure holding process completion position S _e .

Also, in step SP3, if the total injection time T times out, the process moves to step SP15, but in this case, the injection process is completed without moving to the pressure holding process.

Like the pressure-holding control device, the above-mentioned pressure-holding control method is also less susceptible to changes in the frictional force of the drive system of the plunger 9, and it is possible to extremely minimize the error in the measured resin pressure with respect to the set value of the holding pressure. Furthermore, it is possible to prevent pulsations in the resin pressure, to control fluctuations in the resin pressure to be extremely small, and to change the resin pressure to the set value for holding pressure in a short time.

Next, a method for controlling back pressure will be explained with reference to FIGS. 6 and 7.

As shown in FIG. 6, in response to the signal to start measuring the resin, it is first determined in step SP1 whether the plunger position S is greater than the metering completion position BS3, and the plunger position S is larger than the metering completion position _BS3 . If it is small, move to step SP2 and screw 34
rotates. As a result, the resin is plasticized and the plasticized resin is sent out to the tip side of the plunger 9. Then, in step SP3, it is determined whether or not the plunger position S is greater than the first stage metering completion position BS1. If the plunger position S is smaller than _the first stage metering completion position _BS1 , step SP3 is performed.
Moving on to SP4, first stage back pressure setting value BP ₁ and actual resin pressure
Substituting the differential pressure ΔX with X _p into the functional formula Y=f(X),
Movement amount ΔY of plunger 9 to increase or decrease the actual resin pressure X _p to the first stage back pressure set value BP ₁
Calculate. Then, in step SP5, a command is given to the injection AC servo motor 19 so that the plunger 9 moves by ΔY, and the process returns to step SP1 again and repeats the steps SP1, SP2, and Step SP2.
SP3, step SP4, step SP5 are repeated,
As a result, the measured resin pressure X _p becomes the first stage back pressure setting value.
Controlled to be BP ₁ .

Then, as the metering of the resin progresses and the plunger 9 moves backwards, and in step SP3 the plunger position S becomes larger than the first stage metering completion position _BS1 , the process moves to step SP6 and the plunger position S changes to the second stage metering completion position. A determination is made whether it is greater than BS ₂ ,
If the plunger position S is smaller than the second stage metering completion position BS2, the process moves to step SP7 and the differential pressure ΔX between the second stage back pressure set value BP ₂ and the measured resin pressure X _p is expressed as a function Y=f(X). By substituting the value, the moving amount ΔY of the plunger 9 to increase or decrease the measured resin pressure _Xp to the second stage back pressure set value _BP2 is calculated. Then, the process moves to step SP5, and after giving a command to the injection AC servo motor position 19 so that the plunger 9 moves by ΔY, the process returns to step SP1 again, and steps SP, SP2, SP3, SP6, SP7, SP5 are executed. is repeated, thereby controlling the actually measured resin pressure _Xp to the second stage back pressure set value _BP2 .

Then, when the plunger 9 moves further backward and the plunger position S becomes larger than the second stage metering completion position _BS2 at step SP6, the step SP8 is reached.
Next, set the 3rd stage back pressure setting value BP ₃ and the measured resin pressure X _p
Substituting the differential pressure ΔX with the function equation Y=f(X),
Movement amount ΔY of plunger 9 to increase or decrease the actual resin pressure X _p to the third stage back pressure set value BP ₃
Calculate. Then, proceed to step SP5, and adjust the injection AC so that the plunger 9 moves by ΔY.
After giving a command to the servo motor 19, the process returns to step SP1 and the steps SP1, SP2, SP3,
SP6, SP8, and SP5 are repeated, thereby controlling the actually measured resin pressure _Xp to the third stage back pressure set value _BP3 .

Then, the plunger position S is the measurement completion position BS ₃
When this is reached, the process moves from step SP1 to step SP9, where the rotation of the screw 34 is stopped and the measurement is completed.

With the above control, as shown in _FIG . 7, _the measured resin pressure
2nd stage back pressure set value HP ₂ and 3rd stage back pressure set value
While changing according to HP ₃ , the plunger 9 moves backward, and the plunger position S changes from the pressure holding completion position S _e to the injection start position S _p .

Like the back pressure control device, the above back pressure control method is also less susceptible to changes in the frictional force of the drive system of the plunger 9, and can extremely minimize the error in the measured resin pressure with respect to the holding pressure set value. Further, pulsation of the resin pressure can be prevented, fluctuations in the resin pressure can be controlled to be extremely small, and the resin pressure can be changed to the set value of the back pressure in a short time.

In the above embodiment, an example was shown in which the present invention was applied to a pre-plastic type electric injection molding machine, but it goes without saying that the present invention may also be applied to an in-line screw type electric injection molding machine.

[Effects of the Invention] As explained above, according to the present invention, the amount of movement of the extrusion tool to reach the set value of back pressure is predicted using a functional formula, and the extrusion tool is moved once by the predicted amount of movement. Therefore, the resin pressure can be changed to the set value of the back pressure in a short time. Moreover, since the resin pressure is measured and controlled so that the measured resin pressure reaches the set value of the back pressure, the resin pressure can be accurately controlled according to the set value of the back pressure.

[Brief explanation of the drawing]

1 to 7 are views showing one embodiment of the present invention, in which FIG. 1 is a cutaway side view of main parts of a pre-plastic electric injection molding machine, and FIG. 2 is a back view of the pre-plastic electric injection molding machine. A block diagram showing the pressure control device and the pressure holding control device, Fig. 3 is a flowchart showing the holding pressure control method, and Fig. 4 is a diagram showing the plunger speed during the injection process and the resin pressure (holding pressure) during the pressure holding process. , Fig. 5 is an enlarged view of circle V in Fig. 4, Fig. 6 is a flowchart showing the back pressure control method, and Fig. 7 is the resin pressure (back pressure) during measurement.
FIG. 9... Plunger (extrusion tool), 10... Plunger drive mechanism (extrusion tool drive mechanism), 18... Load converter (pressure detection means), 19... AC servo motor for injection, 62... Arithmetic circuit, 72 ... Servo amplifier, BP ... Back pressure setting value, X _p ... Actual resin pressure.

Claims (1)

[Claims] 1. Convert the rotational motion output of the servo motor into a linear motion output, and use this linear motion output to reciprocate a resin extrusion tool, and when the extrusion tool is moved forward, the The resin on the tip side of the extrusion tool is injected into the mold, and the resin is filled into the tip side of the extrusion tool in the resin measuring process as a pre-injection step. At this time, the extrusion tool moving backward is In a back pressure control method for an electric injection molding machine that applies braking to control the pressure of the resin being filled, the amount of movement of the extrusion tool and The relationship between the rate of increase in the pressure of the resin is investigated, and the relationship between the amount of movement of the extrusion tool and the rate of increase in the pressure of the resin is set in a functional formula. By substituting the differential pressure between the measured actual resin pressure and the set value of back pressure, calculate the amount of movement of the extrusion tool to reach the set value of back pressure, and move the extrusion tool by this amount of movement. A back pressure control method for an electric injection molding machine, characterized by controlling the pressure of resin during a metering process. 2. Convert the rotary motion output of the servo motor into a linear motion output, use this linear motion output to reciprocate the resin extrusion tool, and when the extrusion tool is moved forward, the resin on the tip side of the extrusion tool The extrusion tool has an extrusion tool drive mechanism that injects the resin into the mold, and in the metering step of filling the tip side of the extrusion tool with resin, the extrusion tool is braked by the servo motor, which moves backward by the filled resin. A back pressure control device for an electric injection molding machine that controls the pressure of the resin by applying pressure to the extrusion tool, comprising: a pressure detection means for detecting the pressure of the resin; and a pressure detection means for detecting the pressure of the resin; A functional formula showing the relationship between the amount of movement of the ejection tool and the increase in resin pressure is stored, and the differential pressure between the actual resin pressure detected by the pressure detection means and the set value of the back pressure is added to this functional formula. By substituting the calculation circuit, a calculation circuit that calculates the amount of movement of the extrusion tool to reach the set value of back pressure, and a calculation circuit that moves the extrusion tool by the amount of movement of the extrusion tool calculated by this calculation circuit. and a servo amplifier for controlling the servo motor.