JPS63312128A - Dwelling process control device of injection molder - Google Patents

Abstract

PURPOSE:To perform rational sectional change-over and enhance dimensional accuracy by a method wherein the change-over of dwelling section is automatically done by comparing dwelling speed with a plurality of preset forward speeds of an injection member and the dwelling is brought to an end at the time when the deceleration of the forward speed of the injection member since the application of dwelling pressure exceeds a certain value. CONSTITUTION:Dwelling speed (v) is inputted from data to comparators 28 and 29 and a processor 30. Further, a dwelling first speed critical value V1 and a dwelling second speed critical valve V2 are inputted respectively to the comparators 28 and 29. When the dwelling speed (v) lowers down to the dwelling first speed critical value V1, the trigger pulse sent from the comparator 28 is inputted to a gate 33, in which a dwelling pressure P2 is inputted, resulting in outputting a signal to a comparator 36 so as to control a servo motor 10 in order to make the measured injection pressure (p) equal to P2. Similarly, when the dwelling speed (v) lowers to the dwelling second speed critical value V2, the trigger pulse output sent from the comparator 29 is outputted through a gate 34 to a comparator 37 so as to act and control the servo motor 10 in order to make the injection pressure equal to P3, resulting in setting the dwelling pressure to P3. When the dwelling speed (v) lowers to V3, a stop signal is issued from the processor in order to input to the servo motor 10.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement in a multi-stage control device for holding force in a packing process following an injection filling process of an injection molding machine.

[Conventional technology]

In an injection molding machine, following the injection process in which mixed molten plastic raw materials are filled into a mold cavity, the molten resin, which still maintains fluidity within the cavity, is compressed to the end of the cavity to fill the mold cavity. The pressure holding process begins to finish the plastic molded product according to the shape.

Here, the factors that determine whether the dimensions of the mold cavity are accurately transferred to the molded product, that is, the dimensional accuracy of the molded product, are the temperature of the resin filled in the cavity, the magnitude of the holding force, and this holding force. This is the duration for which pressure is applied.

If sufficient holding pressure is not applied for the necessary time, dimensional accuracy will deteriorate and so-called sink marks and seat shots will occur. However, if the holding force and the duration of applying it are set too high, a so-called overpack condition will occur where compressive strain remains inside the molded product, and even if the molded product accuracy is ensured immediately after opening the mold, it will deteriorate over time. Along with this, warpage and deformation occur, reducing accuracy. In extreme cases, internal strain may cause cranking during use of the molded product. In order to prevent this overpacking, a multi-stage pressure holding method exists as a known technique in which the holding pressure is lowered in several stages during molding.

[Problem that the invention seeks to solve]

FIG. 5 shows the implementation state of the conventional multi-stage pressure holding method described above.

In the same figure, in a conventional injection molding machine, holding pressure 1, holding pressure 2
, holding pressure 3... duration time t1, t2, t3.
...and holding pressure P, ,P! , P2... by manually inputting them through the setting device of the molding machine.
The t6 section is controlled to have a holding pressure of P+, and the Lt section is controlled to a holding pressure of Pg.

In order to achieve the above control, the operator must fully understand the condition of the raw material injected into the cavity and set the optimal holding pressure mtrtt time and holding force for the condition of the raw material. There wasn't. Furthermore, even if the same raw material resin is used, the holding pressure duration and holding pressure will vary considerably depending on the resin temperature during filling injection, the condition of the resin flow path, etc., and the operator must take these conditions into account. input must be made. In other words, in the conventional method, the transition between each section in multi-stage holding pressure is performed based on time, and this is done based on factors that do not necessarily match the state of resin flow in the cavity. This imposes a heavy burden on the operator and may lead to inappropriate operation in some cases.

[Means for solving problems]

The present invention has been constructed in view of the above-mentioned problems. ``During injection molding, even after the holding pressure switching point has passed and the holding pressure step has been entered, the resin in the cavity still has fluidity. It is compressed by the holding force applied to the tip of the screw.For this reason, as the cavity is filled to the finest parts,
This design focuses on the fact that the screw tip continues to move forward, albeit slightly, beyond the pressure retention switching point, and stops completely only after the gate at the cavity entrance cools and solidifies.

Specifically, by detecting the forward speed of the injection member during the pressure holding process (pressure holding speed) and comparing it with the advance speed of multiple injection members set in advance, the switching between multiple holding pressure sections is automatically performed. means for advancing the pressure holding process by applying a plurality of preset holding forces for each of the plurality of holding pressure sections; This device includes a means for determining that the time is gate seal, terminating the pressure holding process, and moving on to the next process.

[Effect]

After starting injection filling, the screw position is input to the control unit using a position sensor such as an encoder, and it is determined whether or not this screw has reached the holding pressure position.If the screw reaches the holding pressure position, the injection filling pressure is Then, switch to the first stage holding pressure, count the number of divided tact pulses for each encoder pulse, and if the counted number, which is inversely proportional to the holding pressure speed, is equal to the set pressure holding speed value, the second stage starts. The holding pressure is set to 1, and when the measured value of the holding pressure speed in the second stage matches the set value, the holding pressure is set to the third stage, and after a predetermined period of time has passed, the holding pressure step is completed and the process moves to the next step.

〔Example〕

First, an overall overview of the configuration of the present invention is as follows.

(1) A means of installing a rack and pinion mechanism that is linked to the forward movement of the injection screw and inputting position signals from a position sensor such as an encoder that operates coaxially with the pinion to the control panel (however, it is not possible to use a recent servo motor The drive injection device uses a ball precision ball screw mechanism that converts the rotational drive of the servo motor into linear motion of the screw, so an encoder is used to detect the rotation angle of the injection drive servo motor without going through the rack and pinion mechanism described above. (2) a counter means for counting the number of tact pulses from the control panel entered between the input position signal pulses; and (3) a counter means calculated by the counter means. The actual value of the holding pressure speed,
a comparator that compares a plurality of preset holding pressure speed settings and outputs a signal when they match; (4) means for switching the holding pressure for injection based on the output signal from the comparator; 5) A means for detecting the point in time when the speed of holding pressure becomes minute and then rapidly increases after entering the final holding pressure section and outputting a signal; (6) This output ends the holding process. This is a control device consisting of means for operating the machine to enter the next process.

Examples of the present invention will be described in detail below.

FIG. 1 shows a state in which the present invention is applied to an injection device driven by a servo motor, which is a three-stage holding pressure switching type device.

A screw 2 is arranged inside the heating cylinder 1 of the injection device, and this screw 2 is connected to a ball screw 6 for driving the screw forward through a servo motor 3 that rotates the screw, a load cell 4, and a thrust bearing 5. It is fixed. A thrust shaft 7 screwed into the ball screw 6 is supported by a bearing 8, and the thrust shaft 7 is driven by a screw advance servo motor 10 via a gear transmission 9.

A bracket 11 is fixed to a member for advancing the screw 2, and a precision rack 12 is fixed to this bracket 11. 13 is a precision pinion that engages with the rack 12;
4 is an encoder that rotates coaxially with this precision pinion 13. The precision of these racks and pinions is appropriately such that, for example, the encoder 14 can transmit about one pulse while the screw 2 moves forward by 0.001 degrees.

In this injection device, the screw forward position signal pulse l from the encoder 14 is transmitted to a control device such as a micro combinator connected to the molding machine. It is branched and input to the comparator 27 and counter 22 via the input interface 21 of 1t20. Of these, the comparator 27 also receives the set value of the holding pressure switching position from the keyboard 31, and the signal pulse l
When the holding pressure switching set value and the holding pressure switching setting value are defeated, a trigger pulse output is outputted to the gate 32, and the set holding pressure PL prepared in the gate 32 is outputted to the comparator 35. The actual measured value p of the injection pressure is input to the comparator 35 as a signal from the load cell 4, for example, and the comparator 35 inputs the measured value p of the injection pressure via the amplifier 38 so that the actual measured value p matches the set holding pressure P1. The servo motor IO is feedback-controlled, thereby accurately maintaining the set holding pressure P1.

On the other hand, every 0.001n of forward movement of the screw 2, between the pulses input to the counter 22, a tact pulse oscillation is generated which is attached to the central processing unit (CPU) 24 of the control device 20 and which determines the tact of M control. Period 1 outputted from the device 25. Count how many pulses of tl (10' seconds) are received. However, since the number of tact pulses is excessive in this cycle, the frequency divider 23 is set to 10-4, for example.
After dividing the frequency into seconds, the counter 22 counts the frequency, and writes the above-mentioned count number into the memory mechanism (RAM) 39 for each input pulse from the encoder 14.

On the other hand, the data (program) corresponding to the control flowchart as shown in FIG.
From the data written in M39, the holding pressure velocity V at that time
is calculated and sent to the comparator 2 via the output interface 26.
8.29 and is input to the processing device 30. This speed V normally slows down as the resin in the cavity solidifies.

The holding pressure 1st speed limit value Vl and the holding pressure 2nd speed limit value Vt inputted from the keyboard 31 are input to the comparators 28 and 29. Here, the holding pressure 1st speed limit value means that the holding pressure speed V gradually slows down, but at what point does it slow down from holding pressure P to holding pressure P?
It means the pressure holding speed at the limit point that determines whether to switch to 8,
Here, as mentioned above, it is written as ■1.

When the pressure holding speed V decreases to the pressure holding first speed limit value V, a trigger pulse output from the comparator 28 is input to the gate 33. The gate 33 has a holding force P set on the keyboard 31.
Since 8 is input, this P! is output to the comparator 36. The servo motor 10 is controlled by the comparator 36 so that the actual measured value p of the injection pressure matches PR, and the holding pressure P!
maintain accurately. In the same way, the holding pressure speed V is changed to holding pressure 2.
When the speed decreases to the speed limit value V2, the trigger pulse output from the comparator 29 is outputted to the comparator 37 via the gate 34, and this comparator 37 is activated, and the servo-motor 1o is activated so that the injection pressure becomes P. control, and the holding pressure is switched from P2 to P. Here, the pressure holding speed V gradually decelerates and suddenly drops to 0 when it reaches the gate seal.
is a device for capturing this, and its configuration is mainly composed of a comparator, and since its judgment criteria are input to the ROM 40, it is connected to the ROM 40 via the CPU 24.

When the pressure holding speed V decreases to the pressure holding speed V1 during gate sealing given by the ROM 40, the servo motor stop signal output from the processing device 30 is directly transmitted to the servo motor l.
0 and completes the pressure holding process.

The above explanation was given using a servo motor driven injection molding machine as an example, but in the case of a hydraulically driven injection molding machine, as shown in Fig. 2,
The only difference from the configuration shown in FIG. 1 is the means for adjusting the holding force.

The specific control state of this hydraulically driven injection molding apparatus is as follows. That is, to explain the difference between FIG. 2 and FIG. 1, reference numeral 15 is a hydraulic cylinder for injection, which is configured to move the screw 2 forward together with a hydraulic motor 3 for rotating the screw. 18 is a hydraulic pump, 19 is a proportional electromagnetic pressure regulating valve, and the magnitude of the holding pressure is switched depending on the pressure specified voltage value P1, Pz%Px.

Reference numeral 17 is a proportional electromagnetic type flow rate adjustment valve, and reference numeral 16 is a direction switching valve.

Next, the operating state of this device will be explained step by step with reference to FIG.

Step 1: Use the keyboard 31 to select the holding pressure switch position,
Holding pressure 1st speed limit vI, holding pressure 2nd speed limit Vt, injection filling pressure P (1
Set % holding pressure I Pl, holding pressure 2p, and holding pressure 3P3, respectively.

Step 2: If the above setting is not 10,000-V, >V, a setting error signal is issued and the setting is corrected again.

Step 3: The program shown in Figure 2 starts automatically when injection filling starts.

Step 4: Convert the position of the paint screw into a pulse l using the encoder 14 and input it to the control device. The pulse interval from the encoder may be, for example, about one pulse per 0°001 m of screw advance.

Step 5.6: Encoder input pulse l to comparator 27
is compared with the holding pressure switching position, and when both signals match, the injection pressure is switched from the filling pressure P0 to the holding pressure 1, P+.

Step 7.8: After entering the pressure holding process, the forward speed of the screw 2 becomes very slow, so use a counter to measure minute time to measure how many tact pulses of the CPU 24 are received between each encoder pulse. do.

Numerical examples of the above count values are shown below.

Encoder pulse interval is 1 pulse per 0.001 crane,
Assuming that the tact pulse period of the CPU is 1 μs and the frequency division ratio of the frequency divider 23 is 1/100, the pressure holding speed v (ms/s)
The relationship between the number of divided tact pulses counted between input pulses from the encoder (hereinafter referred to as "count pulse number n") is as shown in Table 1 below, and as the holding pressure speed V decreases, the number increases. They have this relationship.

Table 1 After converting the small pressure holding speed V into the number n of count pulses that is easy to process as a coefficient as described above, proceed to the next step.

Step 9.10: The holding pressure speed V is the holding pressure 1st speed limit value V.

In actuality, by converting the number of counted pulses to the number of pulses counted on both sides and performing the determination calculation, v=V1.
When the pressure reaches 2, the holding pressure 1 is switched to the holding pressure 2.

Step 11.12: In the same way as in the previous step, the holding pressure speed V is the holding pressure second speed limit value V! When the pressure reaches 3, it switches from holding pressure 2 to holding pressure 3.

Step 13.14: When the area of holding pressure 3 is entered and the gate portion is solidified, the holding pressure speed is rapidly reduced to O, and the count pulse number n rapidly increases.

Note that the ROM stores the pressure holding speed v3 at the time of gate sealing in order to determine that it can be considered as a gate seal if the holding pressure speed decreases to that extent. Similarly to the conversion, this pressure holding speed V
After calculating the number of count pulses N corresponding to , the number of pulses n is compared with N, and if n=N, a signal is sent to the servo motor 10 to end the pressure holding process.

Step 15: Set the holding pressure to O and proceed to the next step of charging.

Figure 6 shows that immediately after the transition from injection filling to the holding pressure process, holding pressure 1 is dropped to almost 0 for a very short period of time, thereby instantly lowering the resin pressure transmitted to the end of the cavity and eliminating minute bursts. The holding pressure 2 and subsequent steps are the regular holding pressure steps, and this is an operation pattern that has been commonly used in the past. In the case of this operation pattern, holding pressure 1 and its application time t1 may be set and operated in a conventional manner, and steps from holding pressure 2 to gate sealing may be performed by the apparatus of the present invention.

〔effect〕

According to Reihachi, in the past, the transition between each section in multi-stage holding pressure was done based on time, which was done using factors that did not necessarily match the state of resin flow inside the cavity. In order to switch between each classification based on actual measurement of the holding pressure speed that accurately reflects the resin flow, the most rational classification switching that automatically takes into account resin temperature, mold structure, etc. is performed, and the dimensional accuracy of the molded product is improved. It is possible to obtain a good product without overpack distortion.

In addition, since the gate sealing point where the holding pressure deceleration rapidly increases is confirmed by actual measurement before moving on to the next process, the holding pressure process does not need to be extended more than necessary, and the molding cycle can be shortened.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a pressure holding process control device connected to a servo motor-driven injection device showing a first embodiment of the present invention, and FIG. 2 is a hydraulic-driven injection device showing a second embodiment of the present invention. 3 is a flowchart of the pressure holding process control device connected to the injection machine of FIGS. 1 and 2, and FIG. 4 is a pressure holding process control device connected to the injection machine of the present invention. A diagram showing the holding pressure stage and changes in pressure and speed during
Fig. 5 is a diagram showing changes in pressure and speed during the pressure holding process in conventional injection molding, and Fig. 6 is a diagram showing changes in pressure and speed during the holding process showing another implementation method of the present invention. It is. 2...Screw 10...Servo motor for screw advancement 14...Encoder 20...Control device Nishiki 4 diagram

Claims (1)

[Claims] Means for actually measuring the forward speed of the injection member during the pressure holding process, and automatic switching between multiple holding pressure sections by comparing the actually measured forward speed of the injection member with a plurality of preset forward speeds of the injection member. means for advancing the pressure holding process by applying a plurality of preset holding forces for each of the plurality of holding pressure sections; 1. A pressure holding process control device for an injection molding machine, comprising means for determining when a gate seal is reached, terminating a pressure holding process, and moving on to the next process.