JP2694587B2 - Measuring method of injection molding machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of a weighing method for an injection molding machine.

[0002]

2. Description of the Related Art As a method for supplying pellets, which are a molding material, to an injection cylinder of an injection molding machine, the pellets are stored in a supply hopper connected to the injection cylinder, and the pellets are stored in the injection cylinder by utilizing its own weight. An optional weighing hopper was installed in place of the feeding hopper and the injection hopper of the injection molding machine, and the extension tube from the temperature and humidity controller that stored a large amount of pellets was connected to the weighing hopper and placed in the weighing hopper. A sensor controls the amount of pellets delivered by the temperature and humidity controller to keep the amount of pellets stored in the weighing hopper constant, and the pellets are fed into the injection cylinder from the weighing hopper with a constant pressing force due to its own weight. It is known.

However, in the method in which the pellets are stored and fed into the supply hopper connected to the injection cylinder, the pellet feeding state changes due to a change in the storage amount due to consumption of the pellets, that is, a change in the weight of the entire molding material. ,
In order to keep this constant, there is a problem that manual opening and closing operations of the hopper side shutter must be performed frequently.
Also, if pellets that exceed the plasticizing capacity of the screw are fed without the feeding adjustment work being successful, the resin that has not completely melted will be injected as it is, or the screw will not be able to rotate and the emergency stop function will be activated. May operate, making it impossible to continue the molding operation.

Even when an optional weighing hopper is used, the sensor of the weighing hopper generally detects the storage level of pellets by an optical sensor, and therefore recycled pellets or the like obtained by crashing waste materials such as runners are used. Then, the pellet shape becomes unstable and the density of the molding material as a whole changes, and the storage level (bulk) of the weighing hopper is changed.
Even if the pressure is kept constant, there is no guarantee that the pressing force of the feed will be constant, and it is difficult to keep the wrapping of the molding material constant at the time of weighing and kneading, and the same problem as described above occurs.

Further, there is also an injection molding machine in which a dedicated screw for measurement is provided in parallel with the injection screw to form a pellet feeder, and a predetermined amount of pellets is measured by the rotation of the screw for exclusive use of measurement and supplied into the injection cylinder. It has been known for a long time, but in this case, the control of the pellet feeding amount depends on the driving time (energization time) of the metering screw and the setting operation of the rotation speed of the screw.
The operator must have a certain level of skill to obtain an accurate weighing, and if this setting operation is inappropriate,
After all, problems such as poor plasticization and insufficient measurement occur.

[0006]

SUMMARY OF THE INVENTION Therefore, the object of the present invention is to solve the above-mentioned drawbacks of the prior art, to eliminate the need for complicated manual operation, and regardless of the properties of pellets and the skill level of the operator. An object of the present invention is to provide a weighing method for an injection molding machine, which can repeat an appropriate weighing / kneading operation repeatedly.

[0007]

According to the method of measuring an injection molding machine of the present invention, a pellet feeder is provided between a pellet supply source and an injection cylinder to prevent rotation of an injection screw during a metering / kneading operation. By successively detecting the force and decreasing the feed speed of the pellet feeder with respect to the increase of the reaction force, and increasing the feed speed of the pellet feeder with respect to the decrease of the reaction force to control the pellet supply speed, Was achieved.

Further, a reference value for defining the maximum feed speed of the pellet feeder and an amplification factor for driving control of the pellet feeder are set in advance, and a reaction force that prevents rotation of the injection screw during the weighing / kneading operation is set. The feed rate of the pellet feeder is calculated by multiplying the value subtracted from the reference value by the amplification factor, and by controlling the pellet feeder drive based on this feed rate, the reaction force that prevents rotation of the injection screw can be increased. While decreasing the feed speed of the pellet feeder, the feed speed of the pellet feeder is increased corresponding to the decrease of the reaction force.

In an injection molding machine in which an injection screw is rotationally driven by a servo motor, a torque command value to the servo motor or a speed deviation in the servo motor,
Alternatively, the reaction force that prevents the rotation of the injection screw is detected based on the positional deviation.

[0010]

[Operation] If the pellets are excessively supplied during the weighing / kneading work, the reaction force that prevents the rotation of the injection screw increases due to the interference of the pellets overfilled in the injection cylinder.
When the pellet supply becomes insufficient and the weighing becomes insufficient, the reaction force that hinders the rotation of the injection screw decreases. If the reaction force that hinders the rotation of the injection screw increases, the feed speed of the pellet feeder automatically decreases to suppress the pellet supply, and if the reaction force that hinders the rotation of the injection screw decreases, the feed speed of the pellet feeder automatically decreases. Since the pellet supply is increased to compensate for the insufficient supply of pellets, the amount of resin retained in the injection cylinder and the rotational force of the screw are stabilized, and the metering / kneading operation can be always performed under constant conditions.

[0011]

1 is a block diagram showing a cross section of a main part of an electric injection molding machine according to an embodiment to which the weighing method of the present invention is applied and a control device therefor. Reference numeral 1 in the drawing denotes an injection screw of an injection molding machine, which is slidably and rotatably fitted into an injection cylinder 2 and is axially driven by an injection servomotor M1 and a screw rotation servomotor M2. The screw rotation is designed to be performed independently. Reference numeral 3 is a power transmission mechanism for causing the injection screw 1 to perform an injection operation by using the injection servomotor M1 as a drive source, and the injection cylinder 2 is provided with a heating means (not shown) such as a band heater.

A hopper 4 is provided on the upper surface of the base of the injection cylinder 2 for introducing a pellet, which is a molding material, and the hopper 4 as a pellet supply source and the injection cylinder 2 are provided.
A pellet feeder 5 for supplying the pellets in the hopper 4 to the injection cylinder 2 is provided between and.
The pellet feeder 5 is arranged so as to traverse a communication passage 6 formed between the hopper 4 and the injection cylinder 2, and the rotor 7 with blades as shown in FIG. M3 and a motor drive circuit 8 for controlling the rotation speed of the motor M3. By controlling the rotation speed of the bladed rotor 7, the transfer speed of pellets fed from the hopper 4 to the injection cylinder 2 is adjusted. It has become. It should be noted that, instead of the bladed rotor 7 forming the main part of the pellet feeder 5, the same structure as the conventional screw for measuring and its peripheral part is applied, and the screw for measuring is rotated by the motor M3 to the injection cylinder 2. You may make it send a pellet.

Each of the injection servomotor M1 and the screw rotation servomotor M2 is equipped with a respective pulse coder P1 and P2, and the current position (axial direction) and rotational position (axial rotation) of the injection screw 1 are detected. It has become so.

The control unit 100 of the injection molding machine is a numerical control microprocessor (hereinafter referred to as NCCPU) 11
1 and a microprocessor for programmable machine controller (hereinafter referred to as PMCCPU) 113,
The PMCCPU 113 is connected to a ROM 116 storing a sequence operation of the injection molding machine and a sequence program for controlling the pellet feeder 5, and a nonvolatile PMC RAM 109 and a current value storage RAM 108. The NCCPU 111 is for controlling each part of the injection molding machine as a whole, and for clamping (not shown),
A servo circuit for driving and controlling a servo motor for each axis for ejector (not shown), screw rotation, injection, etc. is connected via a servo interface 110.
In FIG. 1, only the servo circuit 102 for the injection servo motor M1 and the servo circuit 101 for the screw rotation servo motor M2 are shown.

Reference numeral 104 denotes a non-volatile shared RAM composed of a bubble memory, a CMOS memory, etc., which stores a memory unit for storing an NC program for controlling each operation of the injection molding machine and various set values, parameters, macro variables and the like. And a setting memory unit for storing therein various molding conditions and measuring conditions etc. which are set and input by the operator via the CRT display-equipped manual data input device 117 and the operator panel controller 115. It 112
Is a bus arbiter controller (hereinafter referred to as BAC)
Therefore, the BAC 112 has an NCCPU 111 and a PMC.
Each bus of the CPU 113, the shared RAM 104, the input circuit 105, and the output circuit 106 is connected, and the bus used by the BAC 112 is controlled. The injection servomotor M1 is connected to the servo circuit 102, and the torque limit value from the output circuit 106 and the detection output from the pulse coder P1 are input to the servo circuit 102. The current position (axial direction) of the injection screw 1 is always detected. The screw rotation servomotor M2 is connected to the servo circuit 101, and the detection output from the pulse coder P2 is input to the servo circuit 101 to control the position and speed. RA
M103 is a calculation data storage memory for the NCCPU 111.

Then, the output circuit 106 of the control device 100.
Is connected to a motor drive circuit 8 via a D / A converter 9, and the control device 100 is D / A converted by the D / A converter 9.
The motor drive circuit 8 drives and controls the motor M3 in response to the speed command from the rotor, and the bladed rotor 7 of the pellet feeder 5 transfers the pellets in the hopper 4 to the injection cylinder 2 at the feed speed corresponding to the speed command from the control device 100. It is supposed to be supplied.

In the above structure, the NC ROM
NC program or shared RAM 104 stored in 114
Various molding conditions and PMC ROM 116 stored in
By the sequence program etc. stored in
NC113 while PU113 performs sequence control
Reference numeral 111 denotes a drive control of the injection molding machine by pulse-distributing to the servo circuit of each axis of the injection molding machine through the servo interface 110. As far as the injection molding machine main body is concerned, the drive control system of each part is different from the conventional one. Exactly the same.

That is, in the measuring / kneading process, the injection servomotor M1 is drive-controlled in the same manner as the conventional one based on the back pressure preset in the shared RAM 104, and P
NCCP that received the weighing start signal from the MCCPU 113
U111 starts pulse distribution for each predetermined cycle via the servo interface 110 according to the screw rotation speed preset in the shared RAM 104, and is provided with an error register, an F / V converter, an error amplifier, a power amplifier, and the like. The servo circuit 101 performs position, speed, and current loop processes based on the distributed pulse from the NCCPU 111 and the feedback pulse from the pulse coder P2 to output a torque command, so that the rotation speed of the injection screw 1 becomes a set speed. The screw rotation servomotor M2 is controlled.

In FIG. 1, the analog servo circuit 1 is shown.
Since the injection molding machine including 01 is shown, a reaction force that prevents the rotation of the injection screw 1 is detected through a torque command to the screw rotation servomotor M2 or a speed deviation of the screw rotation servomotor M2. In this case, the torque command and the value of the speed deviation detected from the servo circuit 101 are A / D converted and the present value storage RA is performed every predetermined period.
An A / D converter 107 for updating and storing in M108 is required, but a reaction force that prevents rotation of the injection screw 1 is detected from an error register of the servo circuit 101 via a position deviation of the screw rotation servomotor M2. In the case of using a digital servo circuit 101 equipped with a dedicated processor and performing each processing of position, speed and current loop, position deviation, speed deviation, torque command from the servo circuit 101 via the servo interface 110. Since the value of can be directly read out, the A / D converter 107
Is unnecessary.

In the following, the feed speed of the pellet feeder 5 is adjusted by detecting the torque command from the analog servo circuit 101 to the screw rotation servomotor M2 via the A / D converter 107. As an example, the processing operation related to the weighing method of the present embodiment will be described. FIG. 3 is a flow chart showing an outline of the “feed speed adjustment processing” stored in the PMC ROM 116. This processing is performed when the pressure holding is completed and the process shifts to the weighing step.
This is processing executed by the MCCPU 113.

PMCC which started "feed speed adjustment processing"
The PU 113 first sets the value of the reference value α0 for controlling the maximum feed rate of the pellet feeder 5 to the nonvolatile PMC.
Is read from the RAM 109 for storage and stored in the general-purpose register R0 (step S1), and a measurement start signal is output to the NCCPU 111 (step S2) to start rotation speed control of the screw rotation servomotor M2 by the NCCPU 111 and the servo circuit 101, The injection screw 1 is rotated at a metering rotation speed preset in the shared RAM 104 as a molding condition.

At this time, if the reaction force that hinders the rotation of the injection screw 1 is great, the screw rotation servomotor M2 cannot rotate following the distributed pulse which is the movement command from the NCCPU 111, and the servomotor The value of the error register in the circuit 101, that is, the position deviation of the screw rotation servomotor M2 increases, and the value of the speed command obtained by D / A converting the value of the error register also increases. Further, if the reaction force that hinders the rotation of the injection screw 1 is large, the screw rotation servomotor M2 cannot follow the increase of the speed command and accelerate, and the difference between the actual rotation speed and the speed command, that is, the pulse coder. The speed deviation, which is the difference between the actual measurement detection voltage obtained by F / V conversion of the feedback pulse from P2 and the speed command voltage, increases, and the value α of the torque command output in proportion to the speed deviation also increases. , The screw rotation servomotor M2 is strongly driven, and the injection screw 1 is driven at a preset metering rotation speed.
To rotate. If the reaction force that prevents the rotation of the injection screw 1 is small, the screw rotation servomotor M2
Can easily rotate following the distributed pulse which is a movement command from the NC CPU 111.
The injection screw 1 can be rotated at a preset metering rotation speed while the position deviation value, the speed deviation value, and the torque command value α are maintained at small values. During this time, the value α of the torque command from the servo circuit 101 to the screw rotation servomotor M2 is A / D.
The value of the current position storage register, which is digitally converted by the converter 107 every predetermined period, is sequentially updated and stored in the current value storage RAM 108, and the feedback pulse from the pulse coder P2 is cumulatively stored, is set by the NCCPU 111 every predetermined period. It is read from the servo circuit 101 and sequentially updated and stored in the shared RAM 104 as the current position (axial direction) of the injection screw 1.

Therefore, in step S2, the NCCPU
PMCC which started the rotation speed control of the screw rotation servomotor M2 by 111 and the servo circuit 101.
The PU 113 detects the current value α of the torque command stored in the RAM 108 at every predetermined cycle and detects the current value α by the general-purpose register R1.
Is updated and stored in the shared RAM 1 (step S3).
The current position (axial direction) of the injection screw 1 stored in 04 is read out, and a constant set back pressure is maintained according to the increase in the molten resin fed to the tip of the injection cylinder 2 by the metering rotation of the injection screw 1. It is determined whether or not the injection screw 1 which is retracted as it is is retracted to the measurement completion position preset in the shared RAM 104 as a molding condition, that is, whether the measurement completion signal is input from the NCCPU 111 (step S4). ).

When the injection screw 1 has not retracted to the measurement completion position, that is, when the determination result of step S4 is false and it is necessary to continue the measurement and kneading work, the PMCCPU 113 then proceeds. , PMC to a value obtained by subtracting the current value α of the torque command stored in the general-purpose register R1 from the reference value α0 stored in the general-purpose register R0.
The RAM 109 for use is multiplied by a preset amplification value B to obtain the value of the speed command value A to the motor M3 that rotates the rotor 7 with blades of the pellet feeder 5 (step S
5) The speed command value A is output to the motor drive circuit 8 via the output circuit 106 and the D / A converter 9 (step S
6) The rotation speed of the motor M3 is controlled by the motor drive circuit 8 to rotate the bladed rotor 7 at the command rotation speed, and the pellets in the hopper 4 are sent to the injection cylinder 2.

Hereinafter, until the injection screw 1 is retracted to the metering completion position and the completion of the metering / kneading work is detected, the PMCCPU 113 performs steps S3 through S3 in every predetermined cycle.
The processing of step S6 is repeatedly executed, and the general-purpose register R
The reference value α0 stored in 1 and the present value storage RAM 10
Servo motor M2 for screw rotation read from No. 8
A = (α0−) based on the current value α of the torque command of A and each value of the amplification factor B stored in the PMC RAM 109.
The value of the speed command value A to the motor M3 is sequentially calculated by the arithmetic expression of α) · B, and the rotation speed of the rotor 7 with blades of the pellet feeder 5 is controlled via the motor drive circuit 8 so that the pellets in the hopper 4 can be controlled. Is sent to the injection cylinder 2.

During this time, if the amount of pellets sent into the injection cylinder 2 increases more than necessary, the reaction force that hinders the rotational movement of the injection screw 1 that rotates for metering increases, and the torque command value α to the screw rotation servomotor M2 increases. Becomes larger and the value of (α0−α) decreases, the rotation speed of the rotor 7 with blades is automatically reduced to suppress the supply of pellets, and the amount of pellets sent to the injection cylinder 2 is insufficient. Occurs, the reaction force that hinders the rotational movement of the injection screw 1 decreases and the screw rotation servomotor M2
Since the value .alpha. Of the torque command to .alpha. Decreases, the value of (.alpha.0-.alpha.) Increases, and the rotation speed of the bladed rotor 7 is automatically accelerated to increase the pellet supply speed.

In any case, the motor M
The upper limit of the value of the speed command value A to 3 is regulated by the value of the reference value α0, and the value of the speed command value A is not output exceeding α0 · B. Therefore, the injection screw 1 and the injection cylinder 2 and pellets are not fed beyond the plasticizing capacity of the injection molding machine, which is determined by the band heater that constitutes the heating means, and molding defects caused by plasticization defects during weighing and kneading are reliably prevented. To be done. That is, the reference value α0 and the amplification factor B are the rotor 7 with blades when the value of the speed command value A to the motor M3 becomes α0 · B.
The amount of pellets sent to the injection cylinder 2 is a predetermined value so as not to exceed the limit of the plasticizing capacity of the injection molding machine.

In this way, the constant back pressure control by the NCCPU 111 and the servo circuit 102 and the NCCPU 1 are performed.
Constant speed rotation control of the injection screw 1 by 11, and
While the adaptive control of the pellet feeder 5 by the PMCCPU 113 and the motor drive circuit 8 is performed, the shared RAM
When it is detected in the determination processing in step S4 that the injection screw 1 has retracted to the measurement completion position preset as the molding condition in 104, the PMCCPU 113 causes the motor M to operate.
The output of the speed command value to 3 is set to zero output, the rotation of the motor M3 is stopped to stop the pellet feeding by the bladed rotor 7 (step S7), and the driving of the screw rotation servomotor M2 is stopped. The screw rotation for the weighing / kneading process of the one molding cycle is stopped (step S8), and a mold opening start signal is output to the NCCPU 111 to permit the shift to the mold opening process (step S8).
8).

Hereinafter, the PMCCPU 113 is an RO for PMC.
The sequence operation of the injection molding machine is controlled in accordance with the sequence program stored in M116, and the above-mentioned "feed speed adjustment processing" is repeatedly executed every time the pressure holding step after the next one molding cycle is completed. The sequence control other than the measuring / kneading process is exactly the same as that of the conventional injection molding machine, and therefore, will not be described here.

As described above, the pellet is obtained by detecting the torque command (even the substantial drive current of the servomotor M2) from the analog servo circuit 101 to the screw rotation servomotor M2 via the A / D converter 107. The case where the feeding speed of the feeder 5 is adjusted has been described as an example. However, the reaction force that hinders the rotation of the injection screw 1 in the measuring / kneading process is the screw rotation servomotor M.
It is also possible to detect the value based on the value of the position deviation and the value of the speed deviation that occur in step 2.
In the process of 3, the position deviation value α ′ and the speed deviation value α ″ of the screw rotation servomotor M2 are detected instead of the current value α of the torque command, and the bladed rotor 7 is rotated by the same processing as described above. The value of the speed command value A to the motor M3 may be calculated.

In this case, the speed is determined based on the reference value α0 'and the amplification factor B'for calculating the speed command value A based on the position deviation value α', and the speed deviation value α ". The reference value α0 ″ and the amplification factor B ″ for calculating the command value A are rotors with blades when the speed command value A to the motor M3 becomes α0 ′ · B ′ or α0 ″ · B ″. The amount of pellets sent to the injection cylinder 2 by 7 is set to a value that does not exceed the limit of the plasticizing capacity of the injection molding machine and is stored in the control device 100 in advance. In the case where the speed deviation α ″ is detected and the above-mentioned processing is performed in the injection molding machine including the servo circuit 101 of the formula, the speed deviation α ″ of the screw rotation servomotor M2 is calculated by the servo circuit 101 and the A / D converter. 107
The position deviation α ′ is read via the analog servo circuit 101, and the torque command value α and position are read using the digital servo circuit 101. When reading the deviation α ′ and the speed deviation α ″, the A / D converter 107 is not required. In this case, these values are detected from the servo circuit 101 by the processing of the NCCPU 111 in each predetermined cycle and the shared R is calculated.
"Feed speed adjustment process", which is stored in the AM104 in sequence and stored.
In the process of step S3 in step S3, the present value storage RAM 108
Alternatively, these values are read from the shared RAM 104 and the same processing as described above is performed.

Further, the arithmetic expression for obtaining the value of the speed command value A to the motor M3 is not limited to the one shown in step S5, but the torque command value α, the position deviation α ', the speed deviation. The value of the speed command value A is decreased according to the increase of α ″, and the value of the speed command value A is increased according to the decrease of the torque command value α, the position deviation α ′, and the speed deviation α ″. If so, it is possible to use other formulas instead. Also, the screw rotation servo motor M2
Command value α, position deviation α ′, speed deviation α ″ at
The value of the speed command value A may be calculated so that the value of is always constant, and the rotation speed of the motor M3 may be controlled.

[0033]

According to the measuring method of the injection molding machine of the present invention, when the pellets are excessively supplied during the measuring / kneading operation, the feeding speed of the pellet feeder is automatically reduced to suppress the pellet supply. Also, when the pellet supply becomes insufficient, the feed speed of the pellet feeder automatically increases to compensate for the pellet supply shortage, so that the resin retention amount in the injection cylinder and the screw rotating force are stable and complicated. No manual operation is required, and the weighing and kneading operations can be performed under constant conditions regardless of the properties of the pellets and the skill level of the operator. Also, by setting a reference value that prescribes the maximum feed rate in advance, it is possible to set an upper limit on the feed rate of the pellet feeder, so that the pellets will be injected into the injection cylinder beyond the limit of the plasticizing capacity of the injection molding machine. It is not sent, and it is possible to reliably prevent molding defects and the like caused by plasticization defects during weighing and kneading.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a cross section of a main part of an electric injection molding machine of an embodiment to which a weighing method of the present invention is applied and a control device therefor.

FIG. 2 is a cross-sectional view showing a main part of a pellet feeder arranged in the electric injection molding machine of the embodiment.

FIG. 3 is a flowchart showing an outline of a “feed speed adjustment process” by a control device for the electric injection molding machine of the embodiment.

[Explanation of symbols]

 1 Injection Screw 2 Injection Cylinder 4 Hopper 5 Pellet Feeder 6 Communication Passage 7 Bladed Rotor 100 Controller M3 Motor

Claims (5)

(57) [Claims] 1. An injection screw is rotated at a set speed,
In an injection molding machine that plasticizes pellets supplied to a heated injection cylinder to perform weighing / kneading work, a pellet feeder is provided between the pellet supply source and the injection cylinder, and during the weighing / kneading work, Sequentially detecting the reaction force that inhibits the rotation of the injection screw, while decreasing the feed speed of the pellet feeder against the increase of the reaction force, while increasing the feed speed of the pellet feeder against the decrease of the reaction force, the pellet feeding speed Controlling the injection molding machine. 2. A reference value that defines the maximum feed speed of the pellet feeder and an amplification factor for driving control of the pellet feeder are set in advance, and the reaction force detected during the weighing / kneading operation is used as a reference. 2. The weighing method for an injection molding machine according to claim 1, wherein the feed rate of the pellet feeder is calculated by multiplying the value subtracted from the value by the amplification factor, and the pellet feeder is drive-controlled based on the feed rate. 3. The injection according to claim 1, wherein a servomotor is used as a drive source for rotating the injection screw, and a reaction force that prevents rotation of the injection screw is detected by a torque command value to the servomotor. How to measure the molding machine. 4. A servomotor is used as a drive source for rotating the injection screw, and a reaction force that prevents rotation of the injection screw is detected by a deviation between a speed command to the servomotor and a current speed detected by the servomotor. The measuring method for an injection molding machine according to claim 1, wherein 5. A servomotor is used as a drive source for rotating the injection screw, and a reaction force that prevents rotation of the injection screw is detected by a deviation between a movement command to the servomotor and a current position detected by the servomotor. The measuring method for an injection molding machine according to claim 1, wherein