JP2597922B2 - Cold start prevention method for injection molding machine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for preventing a cold start of an injection molding machine.

Conventional technology When the injection screw is driven with a strong force while the injection screw and cylinder remain fixed by the solidified residual resin, excessive stress acts on each part of the injection molding machine, causing breakage and failure. When starting the injection molding operation, it is necessary to at least sufficiently melt the resin in the cylinder so that the injection screw can move freely.

As a method for stopping the cold start, prior to the start of the injection molding operation, the power of the heater of the cylinder is turned on in advance to turn on the warning lamp for the cold start, and the temperature detected by the cylinder temperature detecting means. When the temperature reaches the set temperature range, the cold start prevention timer is activated, and until the set time of the timer elapses, the warning light that is lit when the heater is turned on is continuously lit to give the operator a cylinder. Generally indicates that the sample is in a low temperature state, and calls attention to operation. Normally, the set temperature range that serves as a guide for operating the cold start prevention timer is set within a range of ± 10% of the target melting temperature of the resin, which is the target value. The time from when the cylinder temperature detecting means detects the set temperature range to when the actual temperature inside the cylinder reaches the target value is assumed, and further, the safety factor is set in consideration of a certain safety factor.

Problems to be Solved by the Invention However, the time from when the cylinder temperature detecting means detects the set temperature range to when the actual cylinder temperature reaches the target value is affected by environmental factors such as temperature and humidity. Even if the set time of the cold start prevention timer is set in anticipation of the rate, there is no guarantee that the actual temperature of the cylinder has reached the target value after the set time of the timer has elapsed, and the melting of the resin is insufficient. In some cases, the injection screw is driven as it is.

In addition, there are cases where proper temperature measurement cannot be performed due to failure of the cylinder temperature detecting means itself.If the screw is driven with a strong force at a stage where the temperature of the cylinder is considerably low, a normal injection molding operation cannot be performed. Otherwise, excessive stress may act on each part of the injection molding machine, causing breakage or failure, especially when the tip of the injection screw remains fixed to the cylinder due to the solidified residual resin. Or the like may cause a serious accident such as breakage of a screw tip portion that is vulnerable to torsion.

Accordingly, an object of the present invention is to provide a method for preventing a cold start of an injection molding machine, which can solve the drawbacks of the conventional technology and can surely protect each part of the injection molding machine from damage or failure due to cold start. It is in.

Means for Solving the Problems The cold start prevention method according to the present invention is characterized in that when the temperature detected by the cylinder temperature detection means reaches a set temperature range, time measurement is started, and a very slow reverse command is output with a very small torque for injection. When the position deviation of the injection screw exceeds a predetermined value within a predetermined time period, the driving of the injection screw is stopped. The above object is achieved by enabling the injection molding operation if the value does not exceed the predetermined value.

Further, when the temperature detected by the cylinder temperature detecting means reaches the set temperature range, the timer is operated, and at the same time, the driving of the injection screw is started by outputting a slow reverse command with a small torque, and the timer detects a predetermined time. By this time, every time the position deviation of the injection screw exceeds the set predetermined value, the driving of the injection screw is stopped, the predetermined time is waited, the timing is started again, and the injection screw is output by outputting a slow reverse command with a small torque. May be repeatedly performed, and the injection molding operation may be enabled if the positional deviation of the injection screw does not exceed a predetermined value even when the timer measures a predetermined time.

When the temperature detected by the cylinder temperature detecting means reaches the set temperature range, time measurement is started, and a slight retreat command is output with a small torque to drive the injection screw.

If the positional deviation of the injection screw exceeds a predetermined value within a predetermined time period, the driving of the injection screw is stopped,
In addition, if the positional deviation does not exceed the set predetermined value even if the predetermined time is exceeded, the injection molding operation can be performed.

Therefore, when the positional deviation of the injection screw exceeds the set predetermined value within a predetermined time, that is, the movement of the injection screw is restricted because the injection screw is fixed to the cylinder by the residual resin, Even when the injection screw does not follow the movement command and the positional deviation increases, the injection screw is not driven with a strong force, and damage and failure of each part of the injection molding machine due to cold start are reliably prevented. You.

In addition, the timer is operated to output a slow reverse command with a minute torque to start driving the injection screw, and every time the position deviation of the injection screw exceeds the set predetermined value until the timer detects a predetermined time, Stop the driving of the injection screw, wait for a predetermined time and start timing again, output a slow reverse command with a small torque, repeatedly execute the driving operation of the injection screw, and the timer measures the predetermined time. Even if the position deviation of the injection screw does not exceed the set predetermined value, the injection molding operation is enabled, so that the injection molding operation is automatically permitted at the stage when the obstructive factor that restricts the movement of the injection screw is removed. You.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 2 is a main block diagram of an injection molding machine according to one embodiment of the present invention.

In FIG. 2, reference numeral 1 denotes an injection screw, 2 denotes a cylinder, 3 denotes a servomotor for driving the injection screw 1 in the axial direction, and 4 denotes a rotation of the servomotor 3 to detect the current position of the injection screw 1. It is a pulse coder for detection. The cylinder 2 is divided into a plurality of heating zones, and band heaters B1 to Bn are attached to each heating zone.
B1 to Bn are connected to a power source 6 via switches 7-1 to 7-n to heat the cylinder 2. Further, the temperature sensors S1 to Sn of the temperature converter 5 are arranged in each heating zone, and constitute a cylinder temperature detecting means for detecting the temperature of each heating zone.

Reference numeral 20 denotes a numerical control device (hereinafter, referred to as an NC device) for controlling an injection molding machine. The NC device 20 includes an NC microprocessor (hereinafter, referred to as an NC CPU) 21 and a CPU for a programmable machine controller (hereinafter, referred to as an NC device). , Called CPU for PMC) 2
The RO that stores a sequence program for controlling the sequence operation of the injection molding machine is stored in the PMC CPU 22.
M23 and RAM 24 used for temporary storage of data are connected.

The NC CPU 21 has a ROM 25 storing a management program for controlling the entire injection molding machine, and has a ROM 25 for injection, clamping,
A servo circuit for driving and controlling a servomotor of each axis for rotation of an injection screw, for an ejector, and the like is connected via a servo interface 26. In FIG. 2, the injection servomotor 3 and the servo circuit 27 of the servomotor 3 are shown.
Only the figure is shown. Reference numeral 29 denotes a non-volatile shared RAM composed of a bubble memory and a CMOS memory, a memory section for storing an NC program for controlling each operation of the injection molding machine, and a setting for storing various set values, parameters, and macro variables. And a memory unit.

30 is a bus arbiter controller (hereinafter referred to as BAC)
In the BAC 30, the CPU 21 for NC and the CPU 22 for PMC, the shared RAM 2
9, each bus of the input circuit 31 and the output circuit 32 is connected,
Controls the bus to be used. Reference numeral 34 denotes a BAC3 through the operator panel controller 33.
This is a manual data input device with CRT display device (hereinafter referred to as CRT / MDI) connected to 0, so that various commands and setting data can be input by operating various operation keys such as soft keys and numeric keys. Has become. Note that 28
Is a RAM connected to the bus for the NC CPU 21 and used for temporary storage of data.

The output circuit 32 is connected to the servo circuit 27, and outputs a torque limit value for limiting the output torque of the injection servomotor 3. Further, the switches 7-1 to 7-n
The switches 7-1 to 7-n are turned on and off, and the power supply 6 is connected to the band heaters B1 to Bn to perform on / off control. It is also connected to the temperature converter 5 so that the channel of the temperature sensor unit can be specified.

The output of the temperature converter 5 is input to the input circuit 31.

In the configuration as described above, the NC device 20 includes the shared RAM 29
With the NC program for controlling each operation of the injection molding machine stored in the PC and the parameters such as various molding conditions stored in the setting memory section and the sequence program stored in the ROM 23, the PMC CUP 22 performs the sequence control. , The NC CUP 21 distributes pulses to servo circuits of each axis of the injection molding machine via the servo interface 26 to control the injection molding machine.

FIG. 3 is a block diagram of an example of the temperature converter 5.
In this example, there are six temperature sensor units S1 to S6. In FIG. 3, reference numerals 51-1 to 51-6 denote bridge cold junction compensation circuits for the thermocouples of the temperature sensor units S1 to S6, and output voltages from the circuits are converted by voltage / frequency converters 52-1 to 52-6. The frequency is converted to a frequency and is sequentially connected to a counter 54 via a multiplexer 53.
The output from −6 is counted, and the detected temperature is converted into a digital quantity. Reference numeral 55 denotes a microprocessor which outputs the detected temperature read from the counter 54 via a latch 56.The microprocessor 55 first reads the detected temperature from the counter 54, and sends out the detected temperature to the temperature sensor units S1 to S1 to S5. The channel code CH corresponding to S6 is output to the latch 56, and the read detected temperature data TD is also output to the latch 56.
Thus, after these data are output and held by the latch 56, the ready signal READY is output, and when a predetermined time has elapsed, the ready signal READY is turned off and the detected temperature from the next temperature sensor unit S1 to S6 read from the counter 54 is read. The data and the channel codes representing the temperature sensor units S1 to S6 are output to the latch 56, and the ready signal READY is output again. Hereinafter, the above-described processing is performed in a predetermined cycle, and the temperature sensor units S1 to
The temperature detected in S6 is sequentially circulated and received via the multiplexer 53 and the counter 54, and the detected temperature data received from the temperature sensor units S1 to S6 received by the latch 56 is circulated and transmitted. Then, in order to indicate which temperature sensor unit S1 to S6 the temperature data TD output at that time is from, a channel code CH is simultaneously output, and the channel code CH indicates the temperature sensor unit. For example, the temperature sensor unit S1 has a channel code CH = 1, and the temperature sensor unit S2 has a channel code CH = 2. Hereinafter, the channel codes CH = 3 and CH3 for the temperature sensor units S3, S4, S5 and S6, respectively.
4,5,6, and the channel code CH is 1,
.., 6, 1, 2,... Are sequentially circulated and output, and the temperature data TD detected by the channel of the temperature sensor section is also output at the same time.

Reference numeral 57 denotes a buffer constituting the input circuit, and the NC device 20
When the request signal REQ and the channel code CH ′ are input from the output circuit 32 on the side, the microprocessor 55 reads the detected temperature from the temperature sensor unit corresponding to the input channel code CH ′, and reads the detected temperature via the latch 56. The output is provided to the input circuit 31 of the NC device 20.

Before starting the injection molding operation by the injection molding machine, the operator first heats the cylinder 2 to melt the residual resin that could not be completely discharged in the previous purging operation. setting the heating temperature TS ₁ ~TS _n of bn. In the case of the embodiment, the set temperature range TS _{1 '~TS n'} corresponding to the heating temperature TS ₁ ~TS _n is a target value Atsushi Nobori
It is automatically set at -10% relative to TS ₁ ~TS _n.

Hereinafter, the CN device 20 closes the switches 7-1 to 7-n to start raising the temperature of the band heaters B1 to Bn, and the PMC CPU 22 executes a "cold start prevention process" as shown in FIG. Start.

At the initial stage when the "cold start prevention process" is started, the respective parts of the cylinder 2 heated by the band heaters B1 to Bn have not reached the set temperature widths TS1 _'to TSn _'.
22. First, a warning message of "Cold start prohibition" is displayed on the CRT display screen of the CRT / MD134 to warn the operator that the temperature rise of the cylinder 2 is insufficient (Step S1),
Initialize the temperature raising incomplete flag F and set 1 to the index i indicating the channel code (step S2, step S3),
A loop-like temperature detection process composed of steps S4 to S8 is started.

That is, the PMC CPU 22 outputs the channel code CH ′ corresponding to the index i to the temperature converter 5 via the output circuit 32 together with the request signal REQ at predetermined intervals, and outputs the temperature of the channel code CH ′ corresponding to the index i. Input circuit 31 for data TD _i
Through reading from temperature transducer 5 (step S4), and temperature data TD _i is determined whether or not reached the set temperature range TS _{i 'which} is set to correspond to the heating zone (step S
5) If the set temperature range TS _{i '} has not been reached, the temperature rise incomplete flag F is set, the fact that the heating zone not reaching the set temperature range remains, and the index i is incremented (step S6, Step S7) Thereafter, the temperature detection processing of steps S4 to S8 is repeatedly executed until it is determined in step S8 that the value of the index i has reached the value of the band heater number n.

Each time the temperature detection process is completed, the PMC CPU 22 determines whether or not the temperature raising incomplete flag F is set, that is, whether or not a heating zone that has not reached the set temperature width remains in the cylinder 2. Then, if a heating zone that has not reached the set temperature width remains (Step S9), the temperature rise incomplete flag F is initialized and the index i indicating the channel code is set to 1 (Step S2, Step S3). The temperature detection process is repeatedly executed.

When all the heating zones in the cylinder 2 reach the set temperature range and the determination result in step S9 becomes true,
PMC for CPU22 sets the cold start prevention time T _w1 timer is started (step S10), and the band heater B1~B
Apply power to continue to each n, internal JitsuAtsushi heating zones each part of the cylinder 2 enters a standby state to wait for reaching the target value TS _i of heating temperature (step S11).

If heating continues all by the set temperature more cold start prevention time after reaching the width T _w1 heating zones under normal conditions, the internal JitsuAtsushi of heating temperature of the heating zones each unit definitive cylinder 2 target value TS _i However, since the temperature rise of the cylinder 2 depends on environmental factors such as temperature and humidity, there is no guarantee that the actual temperature of the cylinder has reached the target value after the elapse of the set time of the timer. Further, when a failure occurs in the temperature sensor units S1 to S6 and the like, it may be difficult to detect an appropriate temperature.

Therefore, PMC for CPU22 sets the minute torque limit value T _min to a torque limit circuit of a servo circuit 27 for injection through the output circuit 32 (step S12), the predetermined time Tw ₂ for position deviation detection The timer is set and started (step S13), and the servo circuit 2 of the injection servomotor 3 is set.
A low-speed retreat command for retreating the injection screw 1 at a very low speed is output to 7, and pulse distribution at a very low speed is started (step S14). A command retreat position of the injection screw 1 by the low-speed retreat command and a current position of the injection screw 1 detected by feedback from the pulse coder 4 are input to the servo circuit 27 of the injection servomotor 3.
The position deviation Sd of the injection screw 1 is detected as a value of an error register in the servo circuit 27.

The PMC CPU 22 reads the position deviation Sd of the injection screw 1 from the error register of the servo circuit 27 (step S1).
5) It is determined whether or not the absolute value | Sd | of the position deviation exceeds the range of the allowable maximum value Ss of the position deviation previously set and stored in the shared RAM 29 (step S16). Since the pulse distribution of the speed is executed, | Sd |> Ss does not immediately occur even in the case where the melting of the resin is incomplete and the movement of the injection screw 1 is restricted.
Therefore, in the process of step S17, the timer setting predetermined time Tw ₂
Until the elapsed time is detected, or the absolute value | Sd |
Step S1 at predetermined intervals until it is determined that Ss has been exceeded.
The position deviation detection processing from step 5 to step S17 is repeatedly executed.

If it is determined that the absolute value | Sd | of the position deviation of the screw 1 has exceeded the allowable maximum value Ss before the elapse of the predetermined time Tw ₂ of the timer is detected, it is determined that the melting of the resin is incomplete. Since the movement of the injection screw 1 is impeded for some reason, the PMC CPU 22 proceeds to step S18 to stop the pulse distribution to the servo circuit 27, and waits for a predetermined time Tw to wait for the resin to melt. Set ₃ as a timer and start, and wait for the required time (step S19, step S2
0). Then a predetermined time Tw ₂ for position deviation detection proceeds to step S13 to start by setting the timer, after outputting a slow retraction command by the processing of step S14, step S
The position deviation detection processing from step 15 to step S17 is repeatedly executed.

If the resin melts while such a process is repeatedly performed while raising the temperature of the cylinder 2, the constraint of the injection screw 1 is removed, and the screw 1 is moved toward the command retreat position. Absolute value of position deviation of | S
d | so becomes less than the allowable maximum value Ss of the positional deviation, the result of the determination at step S16 in the position deviation detecting process is always true, the step S21 in step CPU22 for the PMC detects a lapse of the timer setting predetermined time Tw ₂ Then, the pulse distribution to the servo circuit 27 is stopped, the maximum injection pressure _Tmax is reset in the torque limit circuit of the servo circuit 27, and the normal injection molding operation requiring a strong force to drive the screw 1 is performed. "Cold start prohibited" from the CRT / MDI34 CRT display screen
Is released, and the operator is notified that the injection molding operation can be performed (step S2).
2).

Note that the value of the error register may be reset when the pulse distribution is stopped in the process of step S18.

Further, when the resin does not melt due to improper setting of the heating temperature TS _i and the set temperature width TS _{i ′} , it is a waste of time to repeatedly execute such processing, so that the step is not performed.
After the cold start prevention time T _w1 has elapsed in S11, if the value of the position deviation Sd does not decrease even after a certain period of time has elapsed, or if the screw 1 is left with a position deviation equal to or more than the allowable maximum value Ss. If the system gradually retreats and reaches the retreat limit, the setting is considered to be inappropriate and CRT / MDI3
An error message may be displayed on the CRT display screen of 4, and the “cold start prevention processing” may be automatically terminated.
However, the phenomenon that the screen 1 gradually retreats to reach the retreat limit while leaving a position deviation equal to or more than the allowable maximum value Ss is caused by alternately outputting the low-speed retreat command and the low-speed forward command in the processing of step S14. Can be avoided.

As described above, the embodiment in which the torque limit is automatically released at the stage when the injection screw 1 can freely move to enable the injection molding operation has been described. You may make it input manually. For example, after setting the torque limit T _{min. In} the process of step S12 of the embodiment shown in FIG _.
Display the message "Screw fine movement possible" on the CRT display screen of the RT / MDI34, allow the operator to operate the key for fine movement of the screw retreat, detect the key operation by the operator, and then detect the position deviation in the process of step S13. the predetermined time Tw ₂ is started by setting the timer for, for PMC
The processing from step S15 can be automatically executed by the CPU 22. In this case, since the low-speed retraction command of the injection screw 1 is input by the operator, the processing of Steps S19 to S20 is not necessarily required. It is also possible to enter a standby state waiting for the operation of the movement key. The waiting time for waiting for the resin to melt is determined by the operator. When the operator manually inputs the low-speed retreat command, it is assumed that the injection screw 1 is rotated (extrud) due to an erroneous operation. Therefore, in step S12 of the embodiment shown in FIG. In the processing corresponding to the above, the rotation of the screw 1 that is vulnerable to torsion should be prohibited by, for example, setting a very small torque limit in the screw rotation servo circuit.

However, it is a matter of setting the torque limit whether or not the screw 1 is damaged by transmitting the rotational driving force to the injection screw 1 at a stage where the resin is not sufficiently melted.
Theoretically, it is possible to detect the molten state of the resin based on the positional deviation during the rotation of the screw 1 instead of the backward movement of the screw 1.

Effect of the Invention The cold start prevention method of the present invention prevents cold start by detecting the position deviation of the injection screw and confirming the restrained state of the screw, so that the screw remains locked. In this state, no strong driving force is applied, and each part of the injection molding machine can be reliably protected from damage or failure due to cold start.

[Brief description of the drawings]

FIG. 1 is a flow chart showing the outline of "cold start prevention processing" in one embodiment of the present invention, FIG. 2 is a block diagram showing the main part of the injection molding machine of the embodiment, and FIG. It is a block diagram showing a temperature converter of an injection molding machine. 1 ... Screw, 2 ... Cylinder, B1-Bn ... Band heater, S1-Sn ... Temperature sensor unit, 5 ... Temperature converter,
6 ... power supply, 7-1 to 7-n ... switch, 20 ... NC device.

 ──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-2-169224 (JP, A) JP-A-2-62220 (JP, A) JP-A-62-1332 (JP, A) 142017 (JP, U)

Claims (2)

(57) [Claims] When the temperature detected by the cylinder temperature detecting means reaches a set temperature range, time measurement is started, and at the same time, a slow retreat command is output with a very small torque to drive an injection screw, and within a predetermined time measured time. When the position deviation of the injection screw exceeds a predetermined value, the driving of the injection screw is stopped, and the injection molding operation can be performed if the position deviation does not exceed the predetermined value even if the predetermined time is exceeded. A cold start prevention method for an injection molding machine. 2. When the temperature detected by the cylinder temperature detecting means reaches a set temperature range, a timer is operated, and a very slow reverse command is output with a small torque to start driving the injection screw. Each time the position deviation of the injection screw exceeds the set value before detecting
Stop the driving of the injection screw, wait for a predetermined time and start timing again, output a slow retreat command with a small torque, repeatedly execute the driving operation of the injection screw, and the timer measures the predetermined time. Even if the position deviation of the injection screw does not exceed a predetermined value, the injection molding operation can be performed.