JPH053814B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention is applicable to injection molding machine injection filling.
This invention relates to the improvement of a multi-stage control device for packing force in the packing process that follows the process. [Prior art] In an injection molding machine, following the injection process in which kneaded and melted plastic raw materials are filled into a mold cavity, the molten resin still retaining fluidity within the cavity is compressed to the end of the cavity. Then, a pressure holding process begins to finish the plastic molded product according to the shape of the mold cavity. 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 pressure, and this holding pressure. 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 short shots will occur. However, if the holding force and the duration of applying it are set too high, a so-called overpacking 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, warping and deformation occur, reducing accuracy. In extreme cases, cracks may occur due to internal strain 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. [Problems to be Solved by the Invention] FIG. 5 shows a state in which the above-described conventional multi-stage pressure holding method is implemented. In the figure, in the conventional injection molding machine, the duration of each process of holding pressure 1, holding pressure 2, holding pressure 3... is t ₁ ,
By manually inputting t ₂ , t _{3 .} . . and holding pressure P ₁ , _{P 2} , _{P 3 .} is controlled such that the holding pressure is _P2 . 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 duration and holding force for the condition of the raw material. Nakatsuta. 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 consideration. 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 is performed using factors that do not necessarily match the state of resin flow in the cavity. This places a heavy burden on the operator and may lead to inappropriate operation in some cases. [Means for Solving the Problems] The present invention has been constructed in view of the above-mentioned problems.
Even after entering the pressure holding process, the resin in the cavity still has fluidity, so it is compressed by the holding pressure applied to the screw tip. For this reason, as the cavity is filled to the smallest detail, the position of the screw tip continues to move forward, albeit slightly, from the pressure retention switching point, and it does not come to a complete stop until the gate at the entrance of the cavity cools and solidifies. It was constructed with a focus on facts. 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. [Operation] After injection filling is started, the screw position is input to the control unit using a position sensor such as an encoder, and it is determined whether or not the screw has reached the holding pressure position. Switch from injection filling pressure to first-stage holding pressure, count the number of divided tact pulses during each encoder pulse, and if the count number, which is inversely proportional to the holding pressure speed, matches the set holding pressure speed value, the The holding pressure is set to two stages, and if the measured value of the holding pressure speed of the second stage matches the set value, the holding pressure is set to the third stage, and the deceleration rate of the forward speed of the screw (injection member) exceeds a certain value. After completing the pressure holding process, proceed to the next process. [Example] First, the overall structure of the present invention will be summarized as follows. (1) A rack-and-pinion mechanism that is linked to the forward movement of the injection screw is installed, and a means for inputting position signals from a position sensor such as an encoder that operates coaxially with the pinion to the control panel (however, recent servo motors Since 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, an encoder is used to detect the rotation angle of the injection drive servo motor without going through the above-mentioned rack-and-pinion mechanism. (2) counter means for counting the number of tact pulses from the control panel that are inserted between the input position signal pulses; (3) calculation by this counter means. (4) A comparator that outputs a signal when the measured value of the holding pressure speed is compared with a plurality of preset holding pressure speed settings, and (4) the output signal from this comparator causes the injection (5) After entering the final holding pressure section and after the holding pressure speed reaches the minute speed Vs, detecting the point in time when the deceleration rate increases rapidly and outputting a signal. (6) means for using this output to complete the pressure holding process and enter the next process. Examples of the present invention will be described in detail below. FIG. 1 is an injection device driven by a servo motor, and shows the state in which the present invention is implemented in a three-stage holding pressure switching type device. A screw 2 is disposed 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 via a servo motor 3 that rotates the screw, a load cell 4, and a thrust bearing 5. It is fixed. The thrust nut 7 screwed into this ball screw 6 is a bearing 8
The thrust nut 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; 14 is this precision pinion 13;
This is an encoder that rotates coaxially with the The precision of the rack and pinion should be such that, for example, the encoder 14 can transmit about one pulse while the screw 2 moves forward by 0.001 mm. In this injection device, the screw advance position signal pulse l from the encoder 14 is branched and input to a comparator 27 and a counter 22 via an input interface 21 of a control device 20 such as a microcomputer connected to the molding machine. Of these, the comparator 27 also receives the setting value L of the pressure-holding switching position from the keyboard 31, and when the signal pulse I and this pressure-holding switching setting value L match, a trigger pulse output is output to the gate 32. The set holding pressure P ₁ prepared in the gate 32 is output 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 compares this actual measured value p with the set holding pressure P ₁
The servo motor 10 is feedback-controlled via the amplifier 38 so that the set holding pressure _P1 is maintained accurately. On the other hand, a tact pulse oscillation device 25 attached to the central processing unit (CPU) 24 of the control device 20 and determining the control tact is generated between the pulses input to the counter 22 every 0.001 mm of advance of the screw 2. Count how many pulses with a period of 1 μs (10 ^-6 seconds) are output from the However, since the number of tact pulses is too large in this period, the frequency is divided by the frequency divider 23 to, for example, 10 ^-4 seconds, and then counted by the counter 22 and the encoder 14
The above-mentioned count number is written into the memory mechanism (RAM) 39 for each input pulse from. On the other hand, data (program) corresponding to the control flowchart shown in Fig. 3 is stored in the ROM 40.
is input in advance, and according to the instructions of the program, the CPU 24 calculates the current holding pressure velocity v from the data written to the RAM 39, and sends it to the comparators 28, 29 and the processing unit 30 via the output interface 26. is input. This speed v normally slows down as the resin in the cavity solidifies. The comparators 28 and 29 receive the holding pressure 1st speed limit value V ₁ and the holding pressure 2nd speed limit value V ₂ input from the keyboard 31. Here, the holding pressure 1st speed limit value is the holding pressure speed at the limit point that determines how slow the holding pressure v becomes when switching from holding pressure P ₁ to holding pressure P ₂ . , and is written here as V ₁ as mentioned above. When the pressure holding speed v decreases to the pressure holding first speed limit value V ₁ , a trigger pulse output from the comparator 28 is input to the gate 33 . Keyboard 3 at gate 33
Since the holding pressure P ₂ set in step 1 has been input, this P ₂ 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 _P2 , thereby accurately maintaining the holding pressure _P2 . Similarly, the holding pressure speed v becomes holding pressure 2.
When the speed decreases to the speed limit value _V2 , the trigger pulse output from the comparator 29 is passed through the gate 34 to the comparator 3.
7, this comparator 37 is activated, and the servo motor 10 is controlled so that the injection pressure becomes _P3 .
Holding pressure switches from P ₂ to P ₃ . Here, the holding pressure speed v gradually decelerates and suddenly drops to 0 when it reaches the gate seal, but the processing device 30 is a device to capture this, and its configuration is mainly composed of a comparator, and its judgment criteria. has been input to the ROM 40, so it is connected to this ROM 40 via the CPU 24. When the pressure holding speed v decreases to the pressure holding speed V _s during gate sealing given by the ROM 40, the servo motor stop signal output from the processing device 30 is directly input to the servo motor 10, and the pressure holding process is completed. . The explanation above has been 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 Figure 2, only the means for adjusting the holding force is different from the configuration shown in Figure 1. Become. The specific control state of this hydraulically driven injection molding apparatus is as follows. That is, in FIG. 2, to explain the difference from 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 pressure specified voltage value P ₁ ,
The magnitude of holding pressure is switched by P ₂ and P ₃ . 17
16 is a proportional electromagnetic flow rate adjustment valve, and 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: Using the keyboard 31, select the holding pressure switching position L, holding pressure 1st speed limit V ₁ , holding pressure 2nd speed limit V ₂ , injection filling pressure P ₀ , holding pressure 1 P ₁ , holding pressure 2 P ₂ , holding pressure 3 P ₃
Set each. Step 2: If V ₁ > V ₂ is not achieved during the above settings, a setting error signal is issued and the settings are corrected again. Step 3: The program shown in Figure 4 starts automatically when injection filling starts. Step 4: Set screw position to encoder 14
It is converted into a pulse l and inputted to the control device. The pulse interval from the encoder is e.g. the screw advance.
Approximately one piece per 0.001mm is sufficient. Steps 5 and 6: The encoder input pulse l is compared with the holding pressure switching position L by the comparator 27, and when both signals match, the injection pressure is switched from the filling pressure P ₀ to the holding pressure 1, P ₁ . Steps 7 and 8: After entering the pressure holding process, the forward speed of the screw 2 becomes very slow, so use a counter to perform minute time measurement to measure how many tact pulses from 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 0.001mm, CPU tact pulse period is 1μs, frequency divider 23
If the frequency division ratio is 1/100, then the holding pressure speed v (mm/
s) and the number of frequency-divided tact pulses counted between the input pulses from the encoder (hereinafter referred to as "count pulse number n"), as shown in Table 1 below, the number increases as the holding pressure speed v decreases. They have an increasing relationship.

〔effect〕

According to the present invention, conventionally, by performing the transition between each section in multi-stage holding pressure based on time,
This was done using factors that did not necessarily match the state of resin flow in the cavity, but in order to switch between each category by actually measuring the holding pressure speed, which accurately reflects the resin flow in the cavity, the resin temperature and metal Automatically takes into account the mold structure, etc., and automatically switches to the most rational classification, improving the dimensional accuracy of the molded product.
Moreover, a good product without overpack distortion can be obtained. 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 hydraulically driven injection device showing a second embodiment. 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 the process,
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 advancing the screw, 14... Encoder, 20... Control device.

Claims (1)

[Claims] 1. Means for actually measuring the forward speed of the injection member during the pressure holding process, and switching between the plurality of 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 automatically carrying out the pressure holding process; means for advancing the holding pressure 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 a gate seal when a gate seal is applied, terminating a pressure holding process, and moving on to the next process.