JPH02130117A - Back pressure control method and apparatus of electromotive injection molding machine - Google Patents

Abstract

PURPOSE:To allow the pressure of a resin to reach a set value of back pressure within a short time by calculating the moving quantity of a extrusion jig for allowing the pressure of the resin to reach the set value of the back pressure and moving the extrusion jig by the moving quantity. CONSTITUTION:In the control of back pressure in a pressure holding process, an operation circuit 62 compares the actually measured resin pressure Xp of the leading end side of a plunger 9 through a load converter 18 with the back pressure set value BP inputted to a back pressure setting device 81 to calculate the moving quantity DELTAY of the plunger 9 corresponding to the difference pressure DELTAX between both values according to the functional formula Y=f(X) and the order value 66 of the number of pulses of the moving quantity DELTAY is outputted to a positioning pulse distributor 67. The pulse distributor 67 generate pulses 68 in the number according to the order value 66 and compares the number of these pulses with the number of the pulses 64 emitted from an injection motor controlling encoder 23 to digitally output the difference therebetween as the deviation quantity 70 of pulse frequency while this deviation quantity is converted by a D/A converter to output deviation voltage 73 to a servo amplifier 72. The servo amplifier 72 converts the pulses 64 from the encoder 23 to feedback voltage 75 and amplifies the difference between this voltage 75 and the deviation voltage 73 to move an injection AC servo motor 19.

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 plunger.
By moving this extrusion tool forward, the resin at the tip end of the extrusion tool is injected into the mold. As a pre-injection process, there is a resin metering process in which the tip of the extruder is filled with resin.In the metering process, the extruder moves backwards due to the filled resin, but at this time, the extruder is equipped with a hydraulic cylinder. The pressure of the resin to be filled, that is, the back pressure, is controlled by providing movement resistance. 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. It 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 measuring the actual resin pressure. A closed-loop control method that controls, for example, the torque current value of an AC servo motor so that the pressure reaches the back pressure set value. ■Resin pressure is actually measured and the measured resin pressure is used to set the back pressure. For example, a closed-loop control method is known in which the rotational speed of an AC servo motor is controlled so as to reach the desired value.

[Problems to be Solved by the Invention] However, in the case of the open-loop type control system described in (2) above in the above electric injection molding machine, the torque of the electric motor is transmitted to the extrusion tool via the screw mechanism, so that the screw is unavoidable. The disadvantage is that the frictional force of the mechanism intervenes, increasing the error with respect to the set value of back pressure. It takes a long time for the resin pressure to reach the back pressure setting because the actual measured value is repeatedly compared with the back pressure set value and controlled so that the actual measured value approaches the set value. There are drawbacks.

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, reciprocates a resin extrusion tool using this linear motion output, and When the extrusion tool is moved forward, the resin on the tip side of the extrusion tool is injected into the mold, and as a measuring step before injection, the tip side of the extrusion tool is filled with resin, and at that time, the extrusion tool is moved backward. In a back pressure control method for an electric injection molding machine in which the extrusion tool is braked by the servo motor to control the pressure of the resin being filled, the tip side of the extrusion tool is filled with resin in advance. The relationship between the amount of movement of the extrusion tool and 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, and in this functional formula, By substituting the differential pressure between the actual resin pressure measured directly or via an indirect member and the set value of back pressure, calculate the amount of movement of the extruder to reach the set value of back pressure, and calculate this amount of movement. A method is used in which the pressure of the resin during the metering process is controlled by moving the extruder by the same amount.

In addition, as a device for carrying out the above method, the rotational motion output of the servo motor is converted into a linear motion output, the resin extrusion tool is reciprocated by this linear motion output, and when the extrusion tool is moved forward, It has an extruder drive mechanism that injects the resin on the tip side of the extruder into the mold, and in the metering process of filling the tip side of the extruder with resin, the extruder is moved 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 braking with the servo motor includes 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 representing the relationship between the amount of movement of the extrusion tool and the increase in pressure of the resin in the state of 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 of It is desirable to have a servo amplifier that controls the servo motor so as to control the servo motor.

[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, 1 is a frame body, and a fixed platen 2, which is a component of a mold clamping device that opens and closes the mold and clamps the mold, is fixed on this seven-frame body L. . Furthermore, a movable plate 3 is provided on the frame body 1 and is movable in directions 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 body 1 by a placket 5 fixed on the 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 movable plate 3, an injection nozzle 8 provided at the tip of the injection cylinder 7, an injection plunger (extrusion tool) 9 inserted into the injection cylinder 7, and an injection cylinder 7 fixed to the movable plate 3. The injection plunger 9 is provided with a plunger drive mechanism (extruder drive mechanism) lO that moves and drives the injection plunger 9.

The injection cylinder 7 is 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, with the axes aligned with each other, and a resin inflow hole 71 penetrating upward is formed at the upper side of the peripheral wall at the distal end of the movable plate 3. has been done. The injection nozzle 8 supplies 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 freely movable in the axial direction, and its base end is connected to the granger drive mechanism IO.

The plunger drive mechanism IO is installed at a position opposite to the injection cylinder 7 of the movable plate 3, 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 12 that is passed from the movable plate 3, an injection plate 13 that is connected to this injection pole screw rod 12 and moves along the injection pole screw rod 12, and an injection pole screw rod 12 that is connected to the injection pole screw rod 12. The injection pole threaded rod rotation drive mechanism 14 rotates the injection pole screw rod. 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 pole threaded rod 12 is rotatably supported by the movable plate 3 and the guide plate 11 with its axis parallel to the injection cylinder 7, and is centered on the injection cylinder 7. They are arranged at two or four positions that are evenly distributed at predetermined intervals in the vertical direction and also at predetermined intervals in the left-right direction. The injection plate 13 includes 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 into each of the injection pole screw rods 12, and the injection cylinder 7. An injection plunger connecting member 17 provided on the injection cylinder 7 side of the injection plate main body 15 in a meticulously matched manner, and a load converter provided sandwiched between the injection plunger connecting member 17 and the injection plate main body 15. (pressure detection means) 18.

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

Also, the sliding surface 3 formed at the upper end of the moving grate 3! A plasticizing device 31 is attached to the .

The plasticizing device 31 has a plasticizing cylinder 32 and a base end portion of the plasticizing cylinder 32 fixed, and the sliding surface 3! a plasticizing cylinder support member 33 movably connected to the plasticizing cylinder 32; a screw 34 inserted into the plasticizing cylinder 32;
A plasticizing A that is attached to the plasticizing cylinder support member 33 and has an output shaft connected to the base end of the screw 34.
It is equipped with a C servo motor 35. 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 7& of the injection cylinder 7 via a cylinder connecting member 41.

The cylinder connecting member 41 is formed with a communication hole 411 that communicates the inside of the plasticizing cylinder 32 and the inside of the injection cylinder 7, and the communication hole 41 allows resin to flow from the injection cylinder 7 to the plasticizing cylinder 32. A backflow prevention mechanism 42 is provided to prevent backflow.

Further, the moving plate 3 is provided with a ball nut for moving the moving plate (hereinafter referred to as a moving ball nut) 51 at its lower end, and this moving ball nut 51 is connected to a pole threaded rod for moving the moving plate (hereinafter referred to as a moving ball nut). It is screwed into a ball screw (hereinafter referred to as a ball screw for short) 52. The moving pole threaded 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 referred to as the timing pulley of the moving cylinder 1) 54 is fixed to the end of the moving ball screw rod 52 on the opposite side from the injection cylinder 7. Timing pulley 54 of this moving cylinder 1
The second timing pulley for moving the moving plate (hereinafter referred to as the timing pulley of the moving cylinder 2) 56 fixed to the output shaft of the moving plate moving motor (hereinafter referred to as the moving motor) 55 is connected to the moving plate. They are connected via a moving timing belt (moving timing belt) 57.

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 slip-on type electric injection molding machine configured as described above will be explained.

The resin is plasticized by rotating the screw 34 in the plasticizing AC thermostat 1-35.

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. The resin is plasticized in the plasticizing cylinder 32 and passes through the communication hole 41i of the cylinder connecting member 41, the backflow prevention mechanism 42, and the resin inflow hole 7& of the injection cylinder 7, and reaches the tip of the injection plunger 9 of the injection cylinder 7. pushed to the side. 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, the injection plate main body 15, the injection ball nut 16, and the injection plunger 9. Pole screw 12, timing pulley 21 of injection ring 2. It is transmitted to the output shaft of the injection AC servo motor 19 via the injection timing belt 228 and the timing pulley 20 of the injection ring 1, and 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 this time, a back pressure control device, which will be described later, can generate a predetermined amount of braking torque in the injection AC servo motor 19, which provides movement resistance to the injection plunger 9 and prevents back pressure from being applied to the resin. It can be plasticized in a wet state.

The injection amount is measured by determining the retraction amount of the injection plunger 9 from the rotation angle of the injection AC servo motor 19 using the injection motor control encoder 23 attached to the injection AC servo motor 19. When the measurement is completed, the screw 34 rotation stops.

Injection is performed by rotating the injection AC servo motor 19 in the opposite direction (injection direction) from when the resin flows into the injection cylinder 7. That is, when the injection AC servo motor 19 is rotated in the injection direction, the timing pulley 20 of the injection ring 1 is rotated. An injection ball screw rod 12 rotates via an injection timing belt 22 and a timing pulley 21 of an injection ring 2, and an injection plate 1 has an injection ball nut 16 that is screwed onto the injection pole screw rod 12.
3 moves toward the injection cylinder 7, and the injection plunger 9 moves forward within the injection cylinder 7. As a result, the resin at the tip end 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. In addition, the injection speed is determined by the injection AC servo motor 19.
The injection AC servo motor 19 is feedback-controlled based on the rotation speed detected by the injection motor control encoder 23. Therefore, the injection speed is accurately 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 forward and backward movement of the injection nozzle 8 is achieved by rotating the moving motor 55 via the moving second timing pulley 56, the moving timing belt 57, and the moving first timing pulley 54. The moving ball nut 5 is screwed into the moving pole threaded rod 52 by rotating the moving ball nut 52.
1 to the moving ball screw rod 52.
This is done by moving it along the 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 Bri-Pla type electric injection molding machine configured as described above, hydraulic equipment such as a hydraulic cylinder or a hydraulic motor is not used to drive the injection plunger 9 or the screw 34, so the operation for operating each hydraulic equipment is There is no need to manage oil at all, and there is no need to manage gaskets used in hydraulic equipment.Furthermore, there is no risk of hydraulic oil leaking from hydraulic equipment, and the area around the injection molding machine can be kept clean. can.

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 BRIBRA type electric injection molding machine, and this main control device 61 includes an arithmetic circuit 6.
2, and the calculation circuit 62 includes a position counter that counts the number of pulses 64 from the load converter 18, the back pressure setting device 811, and the injection motor control encoder 23 to detect the position of the granger 9. 65 are connected.

The arithmetic circuit 62 calculates the measured resin pressure x11 on the tip side of the granger 9 detected via the load converter 18 and the back pressure setting device 8.
1, and controls the movement amount ΔY of the plunger 9 so that the measured resin pressure Xp becomes the back pressure set value BP. When substituting the differential pressure ΔX from the pressure setting value BP, the differential pressure ΔX
A functional formula is programmed to obtain the moving amount ΔY of the plunger 9 corresponding to . This functional formula is based on the actual resin pressure xp and the position Ys of the plunger 9, depending on the type of resin and the temperature of the resin.
We experimentally found the relationship between -
The next or higher order equation is determined by multiple regression analysis or multiple regression analysis.

Therefore, if this functional formula is expressed as a general formula, Y−f(X
)...(i) However, X: Resin pressure Y is the position of the nib plunger. Further, the arithmetic circuit 62 outputs 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 (i) to the positioning pulse distributor 67.

The positioning pulse distributor 67 receives the command value 6 of the number of pulses.
a pulse distributor 69 that generates a number of pulses 68 according to 6; and a pulse distributor 69 that generates a number of pulses 68
A deviation counter 7 compares the number 8 with the number of pulses 64 emitted from the injection motor control encoder 23 and digitally outputs the difference as a pulse frequency deviation amount 70.
1, and a D/A converter 74 that performs D/A conversion on the frequency deviation amount 70 output from the deviation counter 71 and outputs a deviation voltage 73 to the servo amplifier 72.

The servo amplifier 72 has an encoder 23 for controlling the injection motor.
An F-V converter 76 converts pulses 64 emitted from the F-V converter 76 into a feedback voltage 75, and a difference between the feedback voltage 76 output from the F-V converter 75 and the deviation voltage 73 is amplified to drive 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, Since the resin pressure is controlled by repeating forward and reverse rotation of the AC servo motor 19 for injection, it is possible to control the resin pressure between the pole threaded rod 12 and the injection ball nut 16, for example, compared to the closed loop method in which the resin pressure is controlled by the torque current value. It is possible to reduce the influence of the fluctuation width of the movement resistance of the plunger 9 caused by static friction and dynamic friction, and it is possible to extremely reduce the error in the measured resin pressure with respect to the set value of the back pressure. 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 pole screw rod 12 and the injection pole nut 16, and the plunger 9 does not move until it starts moving. There is a problem in that the resistance is large, and once the movement starts, the movement resistance becomes small, making it 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 injection AC servo motor 19 repeats forward and reverse rotation,
The drive system of the plunger 9 is always in a state of dynamic friction and is not easily affected by changes in the frictional force of the drive system, making it possible to extremely minimize the error in the measured resin pressure with respect to the set value of the back pressure.

In addition, in the case of a closed loop control method that simply controls the rotational speed of the AC servo motor, there is a drawback that the amplitude of forward and reverse rotation of the AC servo motor is large, and the resin pressure pulsates and cannot be maintained at a constant value. However, in the back pressure control device of this embodiment, the amount of movement of the plunger 9 to reach the set value of the back pressure is predicted by the function equation Y - f (X), and the amount of movement of the plunger 9 is adjusted by the amount of movement. , it is possible to suppress fluctuations in resin pressure to an extremely small level.

Moreover, since the amount of movement of the plunger 9 is predicted and the plunger 9 is moved by that amount at once, it is easier to keep the resin pressure up to the back pressure set value, compared to the case where resin pressure is measured sequentially and feedback control is performed. It can be changed in a short time.

On the other hand, the pressure holding control device includes a back pressure setting device 8 in FIG.
A holding pressure setting device 63 is provided instead of the holding pressure setting device 63, and the structure is the same as that of the back pressure control device except that the holding pressure setting value HP is outputted from the holding pressure setting device 63 to the calculation circuit 61.

Similarly to the back pressure control device, this pressure holding control device is also less susceptible to changes in the frictional force of the drive system of the plunger 9, and the error in the measured resin pressure relative to the holding pressure setting value is reduced. In addition, it is possible to prevent resin pressure pulsations and control resin pressure fluctuations to an extremely low level.
Moreover, the resin pressure can be changed 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 in step SPI, counting of the total injection time T is started in step SP2. And step SP
At '3, it is determined whether the total injection time T has timed up or not. If the time has not timed up, the process moves to step SP4 and it is determined at which position the plunger position S is. Here, the plunger position S is the injection process completion position S of the granger 9.

If it is smaller, 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 vl to V. Then, steps SP3, SF3, and SF3 are repeated to perform this injection process, and when the plunger position S becomes smaller than the injection process completion position S, the process moves to step SP6, and the process moves to a pressure holding process.

In step SP6, it is again determined whether or not the total injection time T is time-amplified. If the total injection time T has not timed up, counting of the first-stage holding pressure time T is started in step SP7, and in step SP8, the first-stage holding pressure time T is started to be counted. It is determined whether or not the stage pressure holding time TI has timed up, and if the first stage pressure holding time T1 has not timed up, step SP
Moving on to step 9, substitute the differential pressure ΔX between the first stage holding pressure set value HP and the measured resin pressure xp into the functional formula Y = f(X), and set the measured resin pressure Xp as the first stage holding pressure set value HP. The amount of movement ΔY of the plunger 9 to increase or decrease the pressure up to , is calculated.

Then, in step 5PIO, 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, and the steps SP6, SP7, SP8, SP9, and 5PIO are repeated. As a result, the actual resin pressure x
p is maintained at the first stage holding pressure set value HP. Then, when the first stage pressure holding time T, times up in step SP8, the process moves to step 5PII, and counting of the second stage pressure holding time T, is started, and in step 5P12, the second stage pressure holding time T,
2 is timed up or not, and the 2nd
If the stage pressure holding time T2 has not timed up, the process moves to step 5P13, and the differential pressure ΔX between the second stage pressure setting value HP and the measured resin pressure xp is substituted into the function equation Y-1(X). The amount of movement ΔY of the plunger 9 to increase or decrease the actual resin pressure Xp to the second-stage holding pressure setting value HP is calculated.

Then, the process moves to step 5 PIO, and the plunger 9 is set to ΔY.
A command is given to the injection AC servo motor 19 to move by ΔY, and the plunger 9 moves by ΔY. After that, return to step SP6 again, step SP6, step SP7, step SP8, step 5PII, step 5P12, step 5P13, step 5PIO
The control described above is repeated, whereby the actually measured resin pressure xp is maintained at the second-stage holding pressure setting value HP.

Then, in step 5P12, the second stage pressure holding time T is determined.

When the time is up, the process moves to step 5P14 and the third
Substitute the differential pressure ΔX between the stage holding pressure set value HP and the measured resin pressure xp into the functional formula Y = I (X), and increase or decrease the actual measured resin pressure Xp to the third stage holding pressure set value HP. The amount of movement ΔY of the plunger 9 for this purpose is calculated.

Then, move to step 5 PIO, Granger 9 is ΔY
A command is given to the injection AC servo motor 19 to move by ΔY, and the plunger 9 moves by ΔY. After that, return to step 5P6J again, step SP6, step SP7, step SP8, step SPI 1,
Step 5P12, Step 5P14, Step 5PI
O is repeated, whereby the measured resin pressure xp is maintained at the third-stage holding pressure set value HPs.

Then, when the total injection time T times up in step 6, the process moves to step 5P15, where the total injection time T1, first stage pressure holding time T1, second stage pressure holding time T3, third stage pressure holding time T,
The timer is reset and the pressure holding process is completed.

With the above control, as shown in Fig. 5, the actual resin pressure
p (holding pressure HP) changes as the first stage holding pressure setting value HP, second stage holding pressure setting value HP2 and third stage holding pressure setting value HP3, and the plunger position S reaches the injection process completion position S. , from the pressure holding process completion position S! changes up to.

Further, in step SP3, when the total injection time T times out, the process moves to step 5P15, but in this case, the injection process is completed without moving to the pressure holding process.

Similarly to the pressure holding control device, the pressure holding control method described above is not easily affected by 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 setting value of 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 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 Figure 6, by the signal to start measuring the resin,
First, in step SPI, it is determined whether the plunger position S is greater than the metering completion position BS3, and the plunger position S is the metering completion position BS! If smaller, step S
Moving to P2, the screw 34 rotates. This results in
As the resin is plasticized, the plasticized resin is sent out to the tip side of the plunger 9. And step S
At P3, it is determined whether the plunger position S is larger than the first stage metering completion position BS1, and if the plunger position S is smaller than the first stage metering completion position BS, step SP
4, substitute the differential pressure ΔX between the first stage back pressure set value BP and the measured resin pressure xp into the function equation Y-1(X), and set the measured resin pressure xp as the first stage back pressure set value BP. The amount of movement ΔY of the plunger 9 to increase or decrease the pressure to , is calculated. 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 SPI again.
P2, step SP3, step SP4, step SP
5 is repeated, thereby controlling the actually measured resin pressure XP to the first stage back pressure set value BP□.

Then, as the measurement of the resin progresses, the plunger 9 moves backward, and in step SP3, the plunger position S becomes the first stage metering completion position BS, and when it becomes larger, the process moves to step SP6, and the plunger position S changes to the second stage metering completion position. A judgment is made as to whether or not it is larger than BS2, and the plunger position Its
Stage measurement completion position BS, if smaller, step SP7
Moving on, the differential pressure ΔX between the second stage back pressure set value BP and the measured resin pressure X9 is substituted into the function equation Y-f(X), and the measured resin pressure The amount of movement ΔY of the granger 9 to increase or decrease the pressure up to this point is calculated.

Then, the process moves to step SP5, and the plunger 9 moves to ΔY.
After giving a command to the injection AC servo motor 19 to move by the amount, the process returns to step SPI again and the steps SPI, SF3, SF3, SF3, SF3, SF3 are repeated. is controlled so that it becomes the second stage back pressure set value BP.

Then, the plunger 9 further moves backward, and in step SP6, the plunger position S changes to the second stage metering completion position BS.
, if it becomes larger, the process moves to step SP8, where the differential pressure ΔX between the third stage back pressure set value BP and the measured resin pressure XP is substituted into the function equation y - t<x The amount of movement ΔY of the plunger 9 to increase or decrease the pressure to the stage back pressure set value BP3 is calculated. And step SP
After moving to step 5 and giving a command to the injection AC servo motor 19 so that the plunger 9 moves by ΔY, the process returns to step spt and steps SPI, SF3, and SF are performed.
3, SF3, SF3, SF3 are repeated, thereby controlling the actually measured resin pressure Xp to the third stage back pressure set value BP.

The plunger position S is the measurement completion position BS.

When the amount is reached, the process moves from step SPI to step SP9, the rotation of the screw 34 is stopped, and the measurement is completed.

With the above control, as shown in Fig. 7, the actual resin pressure
The plunger 9 moves backward while p (back pressure BP) changes as the first stage back pressure setting value HP, the second stage back pressure setting value HP, and the third stage back pressure setting value HP. , the plunger position S changes from the pressure holding completion position SC to the injection start position S. changes up to.

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. 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.

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 functional expression allows
Predict the amount of movement of the extrusion tool to reach the set value of back pressure,
Since the extruder can be moved at once by the predicted movement amount, the resin pressure can be changed to the back pressure set value 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 drawings]

1 to 7 are diagrams showing an embodiment of the present invention, in which FIG. 1 is a cutaway side view of main parts of a plastic-type electric injection molding machine, and FIG. 2 is a back view of a plastic-type 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. , 5th
The figure is an enlarged view of circle V in FIG. 4, FIG. 6 is a flowchart showing a back pressure control method, and FIG. 7 is a diagram showing resin pressure (back pressure) during metering. Fig. 2 9... Plunger (extrusion tool), 10...
・Plunger drive mechanism (extruder 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, xp... Actual resin pressure.

Claims (2)

[Claims] (1) 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 is injected into the mold, and the tip side of the extrusion tool is filled with resin in the resin measuring process as a pre-injection step. At this time, the extrusion tool moving backward is braked by the servo motor to complete the filling process. In a back pressure control method for an electric injection molding machine that controls the pressure of the resin being applied, the amount of movement of the extrusion tool and the rate of increase in the pressure of the resin are determined with the tip side of the extrusion tool filled with resin in advance. By investigating the relationship between By substituting the differential pressure between A back pressure control method for an electric injection molding machine characterized by controlling resin pressure. (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 process 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 includes a pressure detection means for detecting the pressure of the resin, and a pressure detection means for detecting the pressure of the resin; By storing a functional formula showing the relationship between the amount of movement and the resin pressure increase, and substituting the differential pressure between the actual resin pressure detected by the pressure detection means and the set value of the back pressure into this functional formula, , an arithmetic circuit that calculates the amount of movement of the extrusion tool to reach a set value of back pressure, and a control circuit that controls the servo motor to move the extrusion tool by the amount of movement of the extrusion tool calculated by this arithmetic circuit. A back pressure control device for an electric injection molding machine, characterized in that it is equipped with a servo amplifier.