JP3851618B2 - Injection molding machine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an injection molding machine. In particular, the present invention relates to an injection molding machine that monitors the staying state of resin in a cylinder in an injection molding machine.
[0002]
[Prior art]
In an injection molding machine, a resin, which is a molding material, is heated and melted in a cylinder and injected into a mold. The resin pellets of the molding material are supplied from the screw base portion in the cylinder, and are melted by the shearing heat generated by the rotation of the screw and the heat supplied by the heater provided on the outer periphery of the cylinder. The melted resin is sent to the front of the screw by the screw rotation, and is stored in the cylinder at the tip of the screw. Then, the resin is injected into the mold by moving the screw forward (in the nozzle direction in which the screw is in axial contact with the mold).
[0003]
In the case of continuous molding, the operation of a series of molding cycles such as the above-mentioned resin melt-kneading by screw rotation and metering-kneading process by screw retraction, mold closing process, injection pressure holding process by screw advance, cooling process, mold opening process, etc. Are repeatedly executed continuously. However, when this molding cycle is interrupted, the molten resin is left in the cylinder and stays in the cylinder for a long time, and heating by the heater is continued. Depending on the resin, if the high temperature state is kept for a long time, it decomposes and generates gas, or the resin is burnt and blackened to cause molding defects. This generated gas may cause corrosion of the cylinder or the screw, or may damage the molding machine due to the sudden generation of gas, resulting in a dangerous state for the operator.
[0004]
Therefore, conventionally, the time after the molding cycle is stopped is measured, and if the machine is not operated for a certain period of time, the temperature of the cylinder is lowered or the purge operation is forcibly performed to discharge the resin in the cylinder. Measures to prevent stagnation are taken. For example, when the molding cycle is stopped, the injection nozzle temperature is lowered, and when a predetermined time has elapsed, the screw is rotated to move the resin in the cylinder to prevent resin burning. When the molding is interrupted, the injection nozzle is retracted, and the screw is rotated for a predetermined time each time a set time elapses to move the resin in the cylinder to prevent resin burning. (See Patent Document 1).
[0005]
Also, the resin stagnation monitoring timer is activated simultaneously with the start of metering or injection, and heating to the cylinder by the heater is stopped if it is not possible to shift to injection filling within the allowable resin stagnation time or if injection is not completed. And the method of stopping operation | movement of an injection molding machine is also known (patent document 2). Furthermore, after completion of the temperature rise, if the molding machine is not operated for a certain period of time without being in automatic operation, or if the automatic operation signal cannot be confirmed due to abnormality during automatic operation, the temperature of the cylinder Is also known that is switched to a heat retaining temperature (see Patent Document 3).
[0006]
If a plasticizing signal is generated and the next plasticizing signal is not generated even after a predetermined time has passed, it is assumed that the operation has stopped and the resin is staying in the cylinder, and the temperature of the cylinder is changed. There is also known one that switches to a preset temperature of 2 (see Patent Document 4).
[0007]
[Patent Document 1]
Japanese Patent No. 2981397
[Patent Document 2]
JP 2000-117802 A
[Patent Document 3]
JP-A-10-156908
[Patent Document 4]
Japanese Patent No. 3165602
[0008]
[Problems to be solved by the invention]
As described above, when the molding operation is stopped, the molten resin stays in the cylinder, and the molding operation has been conventionally performed for problems such as resin burning and gas generation caused by heating for a long time. Further, there are a method of measuring the time during which the screw operation is left unattended and reducing the resin temperature when a predetermined time has elapsed, or a method of forcibly purging and removing the resin staying in the cylinder. However, the resin staying in the cylinder is supplied from the cylinder root part, sent to the front of the screw over a fixed time by screw rotation, and discharged by the screw forward movement, so the time staying in the cylinder is Different in each part of the cylinder. That is, the resin near the cylinder root has a short residence time, and the resin near the tip stays long. Here, if the residence time is monitored as a single time, which is the elapsed time after the molding operation, the cylinder base resin has just been supplied into the cylinder, so deterioration can be prevented by the set monitoring time. Since the resin sent up to this point has already stayed in the cylinder for a certain period of time, if the resin is left for the monitoring time of the basic resin, it may start to deteriorate. As described above, it is impossible to accurately monitor the residence time of the resin distributed over the entire screw area by simply monitoring the time during which the molding operation or the screw operation is left in a single time.
[0009]
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an injection molding machine that can more accurately detect the residence time of the resin in the cylinder and more accurately determine the operation timing for preventing the deterioration of the resin in the cylinder.
[0010]
[Means for Solving the Problems]
The present invention divides the resin conveyance path on the screw in the cylinder of the injection molding machine into a plurality of sections, and reduces the resin residence time for each section. Means to seek and , According to the screw operation Sought Increase / decrease residence time Means to do When the dwell time of any section exceeds a predetermined time, the cylinder temperature control is switched to the predetermined temperature. means, Or forcibly drain the resin in the cylinder Means .
This section includes the section in front of the screw. When the screw rotates, the resin residence time in each section before the screw rotation is shifted by the number of sections in which the resin advances by the rotation of the screw. As residence time Desired . When there is no corresponding section before the screw rotation when shifting, the resin residence time is set to 0, and when the screw moves forward and the resin in the section ahead of the screw is discharged, the resin residence time of the section is set to 0. To do. Further, the number of sections in which the resin advances and shifts by the rotation of the screw is obtained based on the number of rotations of the screw and the slip coefficient set for the resin.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a principal block diagram of an injection molding machine according to an embodiment of the present invention. Reference numeral 1 denotes a cylinder of the injection molding machine, reference numeral 2 denotes a nozzle, and reference numeral 3 denotes a screw. The screw 3 is driven in the screw axis direction by an injection servo motor M1 via a drive converter 7 for converting the shaft rotation of the drive source into linear motion in the injection axis direction. Further, the screw 3 is driven to rotate by a screw rotating servo motor M2 via a transmission mechanism 8. The injection servo motor M1 is provided with a pulse coder P1 for detecting the forward / backward position and the moving speed of the screw 3, and the screw rotating servo motor M2 is for detecting the rotational position and speed of the screw 3. A pulse coder P2 is provided.
[0012]
A heater 4 is provided on the outer periphery of the cylinder 1, and electric power is supplied to the heater 4 from a power source by turning on / off the solid state relay 6. In addition, a temperature sensor 5 is attached to the heater 4, and a detection signal from the temperature sensor 5 is input to the control device 10 so that the cylinder temperature is controlled. Reference numeral 9 denotes a hopper that supplies resin pellets to the injection cylinder 1.
[0013]
The control device 10 of the injection molding machine includes a CNC CPU 12 which is a numerical control microprocessor, a PMC CPU 11 which is a programmable machine controller microprocessor, a servo CPU 13 which is a servo control microprocessor, an input / output circuit 14, A molding data storage RAM 15 and a liquid crystal display device 17 are connected by a bus 19 via an interface 16.
[0014]
Connected to the CPU 11 for the PMC are a ROM 21 storing a sequence program for controlling the sequence operation of the injection molding machine, a control program for the resin stay monitoring process in the cylinder of the present invention, and a RAM 22 used for temporary storage of calculation data. Has been. On the other hand, connected to the CNC CPU 12 are a ROM 23 storing a program for controlling the entire injection molding machine and a RAM 24 used for temporary storage of calculation data.
[0015]
The servo CPU 13 is connected to a ROM 25 storing a control program dedicated to servo control and a RAM 26 used for temporary storage of data. Further, the servo CPU 13 is connected to a servo amplifier 27 that drives servo motors for each axis for injection, screw rotation, and the like based on a command from the CPU 13, and the pulse coder P1 and screw provided in the injection servo motor M1. Each of the outputs from the pulse coder P2 arranged in the servo motor M2 for rotation is fed back to the servo CPU 13, and the servo CPU 13 performs feedback control of the position and speed of the screw 3 and speed feedback control of the rotation of the screw 3. In addition, a current position storage register for storing the current position of the screw 3 in the forward / backward direction based on feedback pulses from the pulse coders P1 and P2 and a rotational position storage register for storing the rotational position of the screw are provided.
[0016]
A signal from the temperature sensor 5 is input to the input / output circuit 14 after being converted into a frequency by a VF (voltage / frequency converter) 18, and the temperature of the cylinder 1 is detected by counting the frequency. It has become. The liquid crystal display device 17 can be used to select a monitor display screen and a function menu and input various data, and is provided with a numeric keypad for inputting numeric data, various function keys, and the like. Note that other display devices such as a CRT display device other than the liquid crystal display device may be used as the display device.
[0017]
A molding data storage RAM 15 composed of a non-volatile RAM is a memory for storing molding conditions (injection holding pressure conditions, weighing conditions, etc.) relating to injection molding work, various set values, parameters, macro variables, and the like. Relatedly, the number of sections obtained by dividing the resin conveyance path, the screw advance completion determination position Xmin, the resin retention prevention set time Tmax, the resin slip coefficient Cadj, and the like are set in advance.
[0018]
The CPU 11 for PMC detects the detected temperature from the temperature sensor 5 that detects the temperature of the cylinder 1 through the voltage / frequency converter 18 and the input / output circuit 14 in the same manner as in the past, and PID (proportional / integral / differential) Control processing and the like are performed, and the solid state relay 6 is turned on / off via the input / output circuit 14 to control the temperature of the cylinder. Further, the in-cylinder resin stagnation monitoring process, which is a feature of the present invention, will be described later.
[0019]
In this embodiment, the resin conveyance path on the screw 3 in the cylinder 1 is divided into a plurality of sections, the resin residence time is measured for each section, and the resin residence time in the cylinder can be monitored more accurately. It is what I did. Therefore, first, a resin conveyance path on the screw 3 in the cylinder 1 will be described.
FIG. 2 is an explanatory diagram of functions in the resin conveyance path on the screw 3 in the cylinder 1. The route on the screw 3 is divided into a supply zone 31, a compression zone 32, and a metering zone 33. The resin pellets 30 introduced from the hopper 9 into the supply zone 31 are sent forward (leftward in FIG. 2) by the rotation of the screw 3, and the screw surface and the inner peripheral surface of the cylinder 1 due to the rotation of the screw 3 The resin is gradually melted by the shear heat generated between them and the heat applied from the heater 4 provided on the outer peripheral portion of the cylinder 1. Then, the molten resin is sent further forward and reaches the measurement zone 33. Then, due to the pressure of the molten resin, the screw 3 moves backward, and the amount of the molten resin stored in the cylinder 1 at the tip of the screw 3 increases according to the amount of the backward movement, and the molten resin is measured to the screw retracted position. Will be. After this measurement is completed, the screw 3 is moved forward in the axial direction to perform injection.
[0020]
When the screw 3 makes one rotation, the resin for one section of the screw pitch theoretically moves forward. Therefore, the residence time of the resin in the cylinder varies depending on each section. Therefore, the residence time of the resin is measured for each section. Since the melting of the resin starts from the vicinity of the compression zone 32, the section that divides the resin path is from the compression zone 32 to the section of the metering zone 33. 3-7 is explanatory drawing of the measurement principle of the residence time of the resin of each area in this embodiment. In FIG. 3 to FIG. 7, the section is divided into nine sections, the section at the start of the compression zone is defined as section 0, and the area in front of the screw 3 is defined as section 1, section 2,. Section 8 is set.
[0021]
In general, resin stagnation becomes a problem in the continuation time from the state where the temperature rise of the cylinder is completed, so that the temperature rise by the heater 4 is completed and the cold start prohibition state is released after a predetermined time has elapsed. The accumulated times T (0) to T (8) of all sections are set to “0” as shown in FIG. If the screw 3 does not rotate, the accumulated time of each section is accumulated as time passes. For example, in a state where 60 seconds have passed without the screw 3 rotating after a predetermined time has elapsed after the temperature rise is completed and the cold start prohibition state is canceled, as shown in FIG. T (0) to T (8) are each “60” (seconds).
[0022]
When the screw 3 makes one rotation from the state shown in FIG. 4, the integration time T (1) to T (8) of each section is “60” (seconds) as shown in FIG. The time T (0) is “0”. That is, since the resin moves forward one pitch section by one rotation of the screw 3, the accumulated time of each section (resin time in the cylinder of the resin in each section) is the accumulated time of the previous section ( Dwell time). However, since the first section is the first section of the melting zone and there is no previous section and is the first melting time, the accumulated time is “0”.
[0023]
Then, after 60 seconds have passed in the state of FIG. 5, when the screw 3 rotates twice, the state shown in FIG. 6 is obtained. That is, when 60 seconds elapse in the state of FIG. 5, the accumulated resin residence time in each section becomes T (0) = 60 and T (1) to T (8) = 60 + 60 = 120 seconds. Then, as the screw 3 rotates twice, the resin in each section advances by two pitch sections. Therefore, the accumulated time in each section is shifted by two, and the accumulated time two pitches before becomes the accumulated residence time of the resin in each section. That is, T (N) ← T (N−2), T (8) ← T (6), T (7) ← T (5), T (6) ← T (4), T (5) ← T ( 3), T (4) ← T (2), T (3) ← T (1), T (2) ← T (0), and T (8) = T (7) = T (6) = T (5) = T (4) = T (3) = 120, T (2) = 60, and T (1) = T (0) = 0.
[0024]
As described above, the resin moves through the sections in accordance with the rotation of the screw 3, and the residence time of the resin in the cylinder in each section is determined according to the rotation of the screw 3.
Then, for example, when the screw 3 is moved forward (leftward in FIG. 6) in the state of FIG. 6 and the resin is injected, as shown in FIG. Only the integration time T (8) of the section is set to “0”, and the other sections are the same as the integration time shown in FIG. That is, since the resin accumulated in the section in front of the screw 3 is discharged into the mold or the like by injection, the accumulated time T (8) is assumed that the resin staying in the cylinder 1 is not temporarily in this section. ) Is “0”. However, in the other sections, the screw 3 moves in the axial direction, and the resin moves together with the screw 3. The resin stays in each section. There is no change.
[0025]
As described above, the resin in each section in the cylinder moves along the resin path by the screw rotation, and the movement amount is determined by the screw rotation speed. As a result, the accumulated residence time of the resin also moves with the movement of the resin, and the accumulated residence time of the resin in each section is changed. If the resin in the tip section is discharged from the cylinder by injection or the like, the accumulated time (T (8)) in this section is set to “0”.
[0026]
In the present embodiment, as described above, the resin path of the screw 3 in the cylinder 1 is divided and the accumulated residence time of the resin in the cylinder is obtained for each section, and any one of the accumulated times in each section is set. When the resin retention time has elapsed, the cylinder temperature is lowered to lower the resin temperature, or the forced purge operation is automatically performed, so that the resin is not heated in the cylinder for a long time. It is what I did.
[0027]
FIG. 8 is a flowchart of the in-cylinder resin retention monitoring process performed by the PMC CPU 11 in the control device 10 that controls the injection molding machine. This process may be performed by the CNC CPU 12, or may be performed by a processor having a margin.
[0028]
The power is turned on and the heater 4 is turned on via the input / output circuit 14 and the solid state relay 6 to raise the temperature of the cylinder 1 (step S1). The cylinder temperature is detected by the temperature sensor 5 and input via a VF (voltage / frequency converter) 18 and an input / output circuit 14. Wait until the cylinder temperature reaches the set temperature (step S2). When the cylinder temperature is raised to the set temperature, a cold start timer is started (step S3) and waits until the timer counts the set time (step S4). When the timer expires and the cold start is completed, the resin residence time in the cylinder T (0) to T (0) to each of the divisions n (= 0 to N) dividing the resin conveyance path on the screw 3 in the cylinder 1. The register for integrating T (N) is set to “0”, and the current time Tact is set in the register for storing the residence time measurement time Tset (step S5).
[0029]
Then, the current rotation position Cact stored in the screw rotation position storage register is stored in the register storing the screw reference rotation position C0 (step S6). Next, the screw forward / backward travel current position Xact stored in the current position storage register that stores the forward / backward current position of the screw 3 is smaller than the set screw forward completion completion determination position Xmin, and the screw is further further than the screw forward movement completion determination position Xmin. It is determined whether the vehicle is moving forward (step S7). If Xact> Xmin and the screw does not exceed the screw advance completion judgment position Xmin, the dwell time measurement time Tset is subtracted from the current time Tact and the elapsed time from the previous measurement time (initially the time set in step S5). It is determined whether this elapsed time has exceeded 1 sec (step S8). If 1 sec has not elapsed, the process proceeds to step S16, where it is determined whether or not the temperature of the cylinder has been raised to the set temperature. If not, the process returns to step S1 and the processes in and after step S1 are performed. If the temperature rise is completed, the process returns to step S7, and the processes of step S7, step S8, and step S16 are repeated until 1 second has elapsed.
In this embodiment, the monitoring is performed every second. However, in order to perform more accurate monitoring, the monitoring time may be 1 second or less. In that case, the unit of T (N) is the same as the monitoring time.
[0030]
When 1 sec elapses from the previous measurement, the dwell time measurement time Tset is set as the current time Tact (step S9), and the difference obtained by subtracting the screw reference rotation position C0 from the rotation current position Cact stored in the screw rotation current position storage register is the screw 1 Divide by the rotational movement amount Crev per rotation and set in advance the quotient of the resin slip coefficient (a slip coefficient for correcting the case where the resin does not move forward by one pitch even if the screw rotates once, It is determined whether the value obtained by multiplying the following value) Cadj exceeds 1 (step S10). That is, the determination is made based on the following formula.
[0031]
{(Cact−C0) / Crev} × Cadj> 1
If the screw 3 does not rotate and the determination in step S10 is NO and does not exceed “1”, that is, if the resin has not moved forward by one pitch, the index n indicating the section is set to “0”. (Step S11), it is determined whether the residence time T (n) of the section n has exceeded the set resin retention prevention time Tmax (seconds) (step S12). One second is added to the residence time T (n) (step S13). Then, the index n is incremented by 1 (step S14), and it is determined whether or not the index n has exceeded a number N that is one less than the set residence time monitoring section number (step S15), and if not, the process returns to step S12. The processing from step S12 to step S15 is performed until the index n exceeds the number of the last section N, and it is determined whether the residence time T (n) does not exceed the resin residence prevention set time Tmax in each section.
[0032]
When the index n exceeds the number of the last section N, it is determined whether the temperature raising is completed (step S16). As described above, if it is completed, the process returns to step S7. Return to S1. As described above, when the screw 3 does not rotate or when the screw 3 rotates, the resin does not move forward by one pitch in consideration of the resin slip coefficient Cadj (when step S10 is NO). ), The residence time T (n) of each section continues to be accumulated.
[0033]
Further, when there is rotation of the screw 3 and it is determined YES in step S10, only the integer part of the value of “(Cact−C0) / Crev} × Cadj” obtained in step S10 is screw rotation from the previous measurement. The number Crot is stored (step S17).
Crot = [(Cact−C0) / Crev} × Cadj] integer part
Next, the screw reference rotation position C0 is set to the screw rotation current position Cact (step S18), and the index n is set to a number N corresponding to the final section (step S19). Next, it is determined whether the difference obtained by subtracting the screw rotation number Crot from the previous measurement obtained in step S17 from the index n is negative (less than “0”) (step S20). The fact that this value is negative means that the resin in the zone (supply zone) before the monitoring zone (compression zone and metering zone) has been transported to the area of this section n between the previous measurement and the current measurement. Therefore, the residence time T (n) in the cylinder of the resin is set as “0” (step S21). Further, if the determination in step S20 is “NO” and “n-Crot” is a positive value, the dwell time T (n) in the section n has a previous section (n-Crot) by the number of screw rotation speeds Crot. ) Is stored (step S24). That is, since the screw from the previous measurement is rotated by Crot, it is determined that the resin has advanced by Crot, and it is determined that the resin in the section before Crot has been transferred to the section n. This is defined as a residence time T (n) of the section n.
[0034]
Thus, after the dwell time T (n) of the section n is updated, the index n indicating the section is decremented by 1 (step S22), and it is determined whether the index n is negative. The residence time T (n) of the section is updated. Then, when the index n becomes negative and the update of the residence time of all the sections is completed, the process proceeds to step S11, and the processes after step S11 described above are performed.
[0035]
As described above, the residence time of the resin in each section is measured and updated. Then, when injection or the like is performed and the screw 3 moves forward, and it is determined in step S7 that the current position Xact of the screw forward and backward advance exceeds the screw advance completion determination position Xmin, a section N which is a section in front of the screw 3 This resin is injected, and it can be considered that the remaining resin is gone. Therefore, the residence time T (N) of this section N is set to “0” (step S25), and the process proceeds to step S8.
[0036]
When the residence time T (n) of any section exceeds the set resin residence prevention set time Tmax, this is detected in step S12, and a resin residence alarm is output (step S26). The set temperature is switched to a low temperature (step S27). At this time, the resin may be discharged by performing a forced purge operation.
[0037]
【The invention's effect】
The present invention divides the resin residence time in the resin cylinder into the resin transport route, and sets the resin residence time for each section. Determined and this determined residence time Therefore, it is determined for each section whether the set time for preventing resin stagnation has elapsed, so that it is possible to more accurately prevent overstagnation of the resin.
[Brief description of the drawings]
FIG. 1 is a main part block diagram of an injection molding machine according to an embodiment of the present invention.
FIG. 2 is an explanatory diagram of functions in a resin conveyance path on a screw 3 in a cylinder 1 of an injection molding machine.
FIG. 3 is an explanatory diagram of the principle of measurement of resin residence time in each section in one embodiment of the present invention, and is an explanatory diagram of resin residence time in each section when the screw is not rotating after the temperature rise of the cylinder. is there.
FIG. 4 is an explanatory diagram of a resin residence time in each section after 60 seconds have elapsed since the screw did not rotate after the temperature of the cylinder increased.
5 is an explanatory diagram of a resin residence time in each section when the screw makes one rotation from the state of FIG.
6 is an explanatory diagram of a resin residence time in each section when the screw makes two revolutions after 60 seconds from the state of FIG.
7 is an explanatory diagram of a resin residence time in each section when the screw moves forward and reaches a predetermined position from the state of FIG.
FIG. 8 is a flowchart of in-cylinder resin retention monitoring processing in an embodiment of the present invention.
[Explanation of symbols]
1 cylinder
2 nozzles
3 Screw
4 Heater
5 Temperature sensor
6 Solid state relay
10 Control device
Resin residence time in T (0) -T (N), T (n) section
Tset dwell time measurement time
Tact Current Time
C0 screw reference rotation position
Cact screw rotation current position
Crev Rotation travel per screw rotation
Crot Number of screw rotations since the last measurement
Xact screw current position
Xmin Screw advance completion judgment position
Tmax Resin retention prevention set time
Slip coefficient of Cadj resin

Claims (6)

Means for determining the resin residence time for each section by dividing the resin conveyance path on the screw in the cylinder of the injection molding machine into a plurality of sections, and increasing or decreasing the obtained resin residence time for each section according to the screw operation. injection molding machine characterized by comprising a means for switching the cylinder temperature to a predetermined temperature when the unit, in which a resin residence time of any of the sections has passed a predetermined time. Means for determining the resin residence time for each section by dividing the resin conveyance path on the screw in the cylinder of the injection molding machine into a plurality of sections, and increasing or decreasing the obtained resin residence time for each section according to the screw operation. means and an injection molding machine, characterized in that a means for forcibly discharging the resin in the cylinder if the resin residence time of any of the sections has passed a predetermined time.   The injection molding machine according to claim 1 or 2, wherein the section includes a section in front of the screw. The resin residence time in each section before the screw rotation is obtained by shifting the number of sections in which the resin has advanced by the rotation of the screw and obtained as the resin residence time in each section. Injection molding machine.   When there is no corresponding section before the screw rotation when shifting, the resin residence time is set to 0, and when the screw moves forward and the resin in the section ahead of the screw is discharged, the resin residence time of the section is set to 0. The injection molding machine according to claim 4.   The injection molding machine according to claim 4 or 5, wherein the number of sections in which the resin advances and shifts by the rotation of the screw is obtained based on the number of rotations of the screw and a slip coefficient set for the resin.

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