JP4991646B2 - Control method of injection molding machine - Google Patents

Description

  The present invention relates to a method for controlling an injection molding machine that is suitable for performing a suckback process after the completion of a weighing process and detecting a resin pressure for monitoring.

  In general, in an injection molding machine, in order to improve yield and improve production efficiency, an operation physical quantity during molding is detected, and it is indirectly monitored by monitoring whether the detected operation physical quantity is within a preset allowable range. In addition, the quality of the molded product is determined.

Conventionally, as one of the operation physical quantities used for such monitoring targets, the resin pressure from the end of the measurement process closely related to the molding quality quantity to the start of the injection process is known. As a control device that performs pass / fail discrimination by using, a control device for an injection molding machine disclosed in Patent Document 1 proposed by the present applicant is already known. The control device disclosed by the literature 1 is a control device including a quality determination unit that performs quality determination based on the magnitude of the resin pressure before the start of the injection process, particularly from the end of the weighing process to the start of the injection process. Resin pressure detecting means for detecting resin pressure at two different points in the monitoring section, difference value calculating means for obtaining a difference value between these resin pressures, and pass / fail judgment for determining whether or not the difference value is within an allowable range In this case, as the resin pressure at different locations in the monitoring section, the resin pressure at five locations, that is, the resin pressure at the end of the metering process, the resin pressure during the suckback process, and at the end of the suckback process The resin pressure, the resin pressure between the end of the suck back process and immediately before the start of the injection process, and the resin pressure immediately before the start of the injection process are used.
JP 2007-83431 A

  However, the above-described conventional control device for an injection molding machine has the following problems to be solved.

  First, since the location (timing) of the monitoring section for detecting the resin pressure is set on the assumption of the normal molding operation of the injection molding machine, the viewpoint of obtaining a resin pressure highly correlated with the quality of the molded product Can not exceed the level based on normal molding operations. In other words, if the molding operation is changed from the viewpoint of securing a resin pressure that is highly correlated with the quality of the molded product, it may be possible to determine the quality with higher reliability and accuracy, including the molding operation. There was room for further improvement from the technical point of view.

  Second, although the resin pressure detected in the monitoring section from the end of the weighing process to the start of the injection process is used for quality determination, it is insufficient from the viewpoint of more effectively using the detected data (resin pressure). It becomes. In other words, if it can be used for analysis and control to increase the yield rate of molded products based on the detected resin pressure information, or simplification of the control system (discrimination processing), it will be more useful and effective use of data. There was room for further improvement from the standpoint of planning.

  An object of the present invention is to provide a method for controlling an injection molding machine that solves the problems existing in the background art.

  The control method of the injection molding machine M according to the present invention performs a suck-back process Ss after the completion of the weighing process Sm and solves the above-described problems, and detects the resin pressure Pr for monitoring. After the end of Sm, the resin pressure Pr is detected after the elapse of a preset predetermined interval time Ti, and at least until the detection of the resin pressure Pr is completed, the positioning control for the screw 2 is performed, and thereafter the delay is performed. Further, the present embodiment is characterized in that the suck back process Ss is started.

  In this case, according to a preferred aspect of the invention, the resin pressure Pr can be used for quality determination processing (S7) related to molding. On the other hand, the length of the interval time Ti can be set in accordance with the type of resin and / or the type of molded product, and the interval time Ti has a correlation coefficient C between the resin pressure Pr and the molded product weight W. It can be set to a time that is a predetermined value or more, preferably 1.0 [second] or more.

  According to the control method of the injection molding machine M according to the present invention by such a method, the following remarkable effects are obtained.

  (1) After completion of the weighing step Sm, the resin pressure Pr is detected after the elapse of a predetermined interval time Ti set in advance, and thereafter the suck back process Ss is performed. High resin pressure Pr can be obtained, and can be easily implemented by changing the control method.

  (2) Since highly effective data (resin pressure Pr) regarding the quality of the molded product can be obtained, for example, analysis and control for increasing the yield rate of the molded product based on the information of the detected resin pressure Pr, Alternatively, the control system (discriminating process) can be used more widely and beneficially.

  (3) Since the positioning control on the screw 2 is performed at least until the detection of the resin pressure Pr is completed after the completion of the measuring step Sm, unnecessary error factors can be eliminated for the detection of the resin pressure Pr, and the accuracy is improved. In addition, highly stable detection can be performed.

  (4) According to a preferred embodiment, if the resin pressure Pr is used in the quality determination processing (S7) related to molding, the resin pressure Pr having a high correlation with the quality of the molded product can be secured. Quality) can be performed.

  (5) According to a preferred embodiment, if the length of the interval time Ti is set in accordance with the type of resin and / or the type of molded product, the reliability of the quality determination process and the molding cycle time are balanced. An accurate interval time Ti can be set.

  (6) According to a preferred embodiment, if the interval time Ti is set to a time when the correlation coefficient C between the resin pressure Pr and the molded product weight W is a predetermined value or more, preferably 1.0 [seconds] or more, molding is performed. The resin pressure Pr having a high correlation with the quality of the product can be detected reliably and stably, and the reliability of the quality determination process can be further increased.

  Next, the best embodiment according to the present invention will be given and described in detail with reference to the drawings.

  First, the configuration of an injection molding machine M that can implement the control method according to the present embodiment will be described with reference to FIGS. 2 and 3.

  The injection molding machine M shown in FIG. 2 shows only the injection device Mi excluding the mold clamping device. The injection device Mi includes an injection stand 11 and a drive stand 12 that are spaced apart from each other, and the rear end of the heating cylinder 13 is supported on the front surface of the injection stand 11. The heating cylinder 13 includes an injection nozzle 14 at the front end and a hopper 15 that supplies a molding material to the heating cylinder 13 at the rear, and the screw 2 is inserted into the heating cylinder 13. On the other hand, four tie bars 17 are installed between the injection table 11 and the drive table 12, and a slide block 18 is slidably loaded on the tie bars 17. A rotary block 20 integrally having a driven pulley 19 is rotatably supported at the front end of the slide block 18, and the rear end of the screw 2 is coupled to the center of the rotary block 20. Further, a screw rotating servo motor 21 is attached to the side surface of the slide block 18, and an endless timing belt 23 is bridged between a driving pulley 22 and a driven pulley 19 fixed to a rotating shaft of the servo motor 21 to rotate the screw. The drive mechanism for this is comprised. Reference numeral 21e denotes a rotary encoder that detects the number of rotations of the servo motor 21 and is attached to the rear end of the servo motor 21.

  A nut portion 25 is provided coaxially and integrally on the rear portion of the slide block 18, and the front side of the ball screw portion 26 rotatably supported by the drive base 12 is screwed into the nut portion 25, thereby A screw mechanism 24 is configured. Furthermore, a driven pulley 27 is attached to the rear end of the ball screw portion 26 protruding rearward from the drive base 12, and a screw motor servo 29 is attached to a support board 28 attached to the drive base 12. An endless timing belt 31 is bridged between a drive pulley 30 fixed to the rotating shaft of the servo motor 29 and the driven pulley 27 to constitute a screw advance / retreat drive mechanism. Reference numeral 29e denotes a rotary encoder that detects the rotational speed of the servo motor 29, and is attached to the rear end of the servo motor 29.

  On the other hand, a molding machine controller 32 having a computer function for controlling the whole of the injection molding machine M is provided to execute control processing and arithmetic processing including various sequence controls, and in particular to execute the control method according to the present invention. The control program (processing program) is stored. Servo motors 21 and 29 are connected to the output port of the molding machine controller 32, and rotary encoders 21 e and 29 e are connected to the input port of the molding machine controller 32. A load cell 3 is assembled between the rotary block 20 and the slide block 18, and this load cell 3 is connected to an input port of the molding machine controller 32. The load cell 3 can detect the pressure applied to the screw 2, that is, the resin pressure Pr.

  FIG. 3 shows a specific block configuration of the molding machine controller 32. The figure mainly shows the pressure control system Up. In FIG. 3, reference numeral 29 denotes the servo motor described above, and Mm denotes an injection mechanism including the screw 2 and the ball screw mechanism 24 driven by the servo motor 29. The servo motor 29 is connected to the output part of the servo amplifier 33, and the input part of the servo amplifier 33 is connected to the output part of the pressure control part 35 via the switching function part 34. The load cell 3 described above is connected to the input unit of the processing unit (calculation unit) 36, and the rotary encoder 29 e is connected to the servo amplifier 33 and the processing unit 36. The output unit of the processing unit 36 is connected to the determination unit 37 and the pressure control unit 35, respectively.

  Reference numeral 5 denotes a setting unit that sets various setting values and applies the set values to the corresponding pressure control unit 35, determination unit 37, processing unit 36, and timer unit 4 to be described later. In the setting unit 5, it is possible to set the time from the end of the measuring process until the resin pressure Pr is detected, that is, the interval time Ti. The length of the interval time Ti can be arbitrarily set according to the type of one or both of the resin and the molded product, and this interval time Ti is the resin pressure Pr and the molded product weight W as will be described later. The time when the correlation coefficient C becomes a predetermined value or more, preferably 1.0 [second] or more can be set. Further, 4 is a timer unit, which has a function of measuring at least the interval time Ti and giving the result to the processing unit 36 when the time measurement of the interval time Ti is completed. In addition, Uv indicates a speed control system including a speed control unit 40 and a speed command unit 41. When the speed control is performed by the speed control system Uv, the switching function unit 34 is switched so that the speed control unit 40 is connected to the servo amplifier 33. Is done.

  Next, a control method of the injection molding machine M according to the present embodiment will be described with reference to FIGS.

  As shown in FIG. 4, the basic method of the control method according to the present embodiment is to delay the start of the suck-back process Ss after the end of the weighing step Sm, and after the elapse of a predetermined interval time Ti set in advance. The resin pressure Pr is detected, and thereafter the suck back process Ss is started.

  Initially, the experimental result which verifies the effectiveness of the control method which concerns on this embodiment is demonstrated with reference to FIGS.

  FIG. 5 shows the result of measuring the resin pressure Pr [MPa] with respect to the passage of time [seconds] when the measurement process is completed without leaving a suck-back process. In this case, after the completion of the measurement process, the screw 2 was subjected to positioning control to maintain the end position of the measurement process, and the load cell 3 was used to measure the resin pressure Pr [MPa]. In addition, experiments were conducted on four types of resins. In FIG. 5, (a) is polypropylene (PP), (b) is polybutylene terephthalate (PBT), (c) is polycarbonate (PC), and (d) is The result of polystyrene (GPPS) is shown. 5, in (a) to (d), Tm represents a measuring process section (measuring time), te represents the end point of the measuring process, and Tis represents a leaving section after the end of the measuring process. In any case of FIGS. 5A to 5D, 100 moldings are overwritten.

  As is clear from the results of FIG. 5, the resin pressure Pr immediately after the end of the metering process shows almost no variation in any resin, but the variation in the resin pressure Pr increases with time. And a unique change depending on the type of resin. That is, this phenomenon means that when the measurement process is left as it is, a variation factor related to the resin pressure Pr becomes apparent as time elapses.

  FIG. 6 shows the data regarding the resin pressure Pr [MPa] and the molded product weight W [g] at the time point ts of 4.0 [seconds] shown in FIG. , “Minimum”, “range”, “average”, “σ (standard deviation)”, “variation of molded product weight W (6 CV or R / A)”, “C (phase of molded product weight W and resin pressure Pr) Data) ”. In this case, 6CV is a value obtained by ((6 × σ) / average) × 100 [%], and R / A is a value obtained by (range / average) × 100 [%]. Further, as a comparative example (reference example), “weighing time (plasticization time) Tm [s]” which is another physical quantity (monitoring target) used for pass / fail judgment and weighing torque Fm [N · m] (average value) ) "Was also measured in parallel with the resin pressure Pr. In addition, for the molding (sample molded product), a bar flow mold generally used for testing or the like is used, and if the resin pressure Pr [MPa] is detected at an elapsed time ts of 4.0 [seconds], the suck back is immediately performed. After this, the molded product was molded through a normal molding process.

  As is clear from the results of FIG. 6, a high correlation (correlation coefficient C) was obtained between the resin pressure Pr and the molded product weight W. That is, in FIG. 6, (a) the correlation coefficient C of PP is 0.87, (b) the correlation coefficient C of PBT is 0.82, and (c) the correlation coefficient C of PC is 0.93. Obtained a high correlation coefficient C of 0.8 or more. On the other hand, there was a low correlation (correlation coefficient C) between the measuring time Tm and the molded product weight W measured as a comparative example with respect to the resin pressure Pr, and between the measured torque Fm and the molded product weight W. That is, in the case between the weighing time Tm and the molded product weight W, in FIG. 6, (a) the correlation coefficient C of PP is -0.55, (b) the correlation coefficient C of PBT is -0.22, (c ) The correlation coefficient C of PC is -0.48, and in the case between the measured torque Fm and the molded product weight W, in FIG. 6, the correlation coefficient C of PP is 0.70, and (b) PBT. The correlation coefficient C was 0.69, and (c) the correlation coefficient C of PC was 0.47. Thus, when the correlation (correlation coefficient C) with the molded product weight W is seen, the resin pressure Pr may show a higher correlation than the measurement time Tm and the measurement torque Fm, which are other monitoring targets. I can confirm.

  In FIG. 6, (d) GPPS has a low correlation coefficient C between the resin pressure Pr and the molded product weight W of 0.27. This reason means that 6CV (variation) is small and high quality is already ensured. On the other hand, in FIG. 6, (a) to (c) all mean that 6CV (variation) is large and the quality is not always sufficient, and as a result, the correlation coefficient C becomes high. Therefore, FIG. 6D means that if the variation in the resin pressure Pr is reduced, the molding quality can be improved. If the resin pressure Pr is monitored, optimum molding conditions can be easily set. Thus, highly effective data (resin pressure Pr) regarding the quality of the molded product can be obtained. Thus, since the obtained data (resin pressure Pr) basically has a high correlation with the quality, analysis, control or control for increasing the yield rate of molded products based on the information of the detected resin pressure Pr. The system (discriminating process) can be used more widely and beneficially, for example, a sufficient pass / fail discriminating process can be performed with the resin pressure Pr alone.

  FIG. 7 shows data obtained by calculating the correlation coefficient C between the resin pressure Pr and the molded product weight W at different elapsed times after the end of the weighing process, and FIG. 8 shows the standard deviation σ of the molded product weight W. [G] is data obtained at different elapsed times after the end of the weighing process. In this case, the elapsed time was set to 0.0 [seconds], 1.0 [seconds], and 5.0 [seconds], and PP was used as the resin. As in the case of FIG. 6, a bar flow mold is used for molding (sample molded product), and each elapsed time is 0.0 [second], 1.0 [second], 5.0 [second]. When the resin pressure Pr [MPa] was detected at the elapse of time, a suck-back process was performed immediately thereafter, and thereafter, a molded product was molded through a normal molding process. As is apparent from the results of FIG. 7, the correlation coefficient C between the resin pressure Pr and the molded product weight W increases as the elapsed time becomes longer, and if 1.0 [second] has elapsed. The correlation coefficient C is 0.5 or more. Further, FIG. 8 can confirm the influence on the quality due to different elapsed times, and FIG. 8 shows that the quality of the molded product is not adversely affected by delaying the suck back process by setting the elapsed time. It is shown that.

  Therefore, the control method according to the present embodiment delays the start of the suck-back process Ss after the end of the weighing process Sm based on these verification results, and detects the resin pressure Pr after the elapse of a predetermined interval time Ti. It is what you do. For this reason, in the control method according to the present embodiment, the interval time Ti is set in the setting unit 5 in advance. The length of the interval time Ti can be arbitrarily set in consideration of FIGS. 5 and 6 and corresponding to one or both of the resin and the molded product. The setting in this case may be set to a different interval time Ti that can be selected according to the type of resin or the type of molded product, or one that can be shared in consideration of the assumed type of resin and the type of molded product The interval time Ti may be set. If the length of the interval time Ti is set according to the type of resin and / or the type of molded product, an accurate interval time Ti that balances the reliability of the quality determination process and the molding cycle time is set. can do.

  Further, the interval time Ti can be set to a time during which the correlation coefficient C between the resin pressure Pr and the molded product weight W is not less than a predetermined value, preferably 1.0 [second] or more. 7 and FIG. 8, if the interval time Ti is set to 1.0 [seconds] or more, the correlation coefficient C is 0.5 or more, which can be used as a guideline for setting the interval time Ti. it can. In addition, when the interval time Ti becomes long, the molding cycle time becomes long and there is a possibility that the productivity may be lowered. Therefore, the interval time Ti is usually set to about 1.0 to 5.0 [seconds]. It is desirable to do. Therefore, the control method according to the present embodiment is suitable for forming a thick product in which the cooling time (cooling process) is set long. Thus, if the interval time Ti is set to a time when the correlation coefficient C between the resin pressure Pr and the molded product weight W is equal to or greater than a predetermined value, preferably 1.0 [seconds] or more, the quality of the molded product is determined. The highly correlated resin pressure Pr can be detected reliably and stably, and the reliability of the quality determination process can be further increased.

  Next, a specific control method of the injection molding machine M will be described according to the flowchart shown in FIG. 1 with reference to FIGS.

  Now, it is assumed that the weighing process Sm (FIG. 4) is performed in the injection device Mi (step S1). In the measuring step Sm, the screw 2 is rotated by the operation of the servo motor 21, and the molding material supplied from the hopper 15 is plasticized and melted inside the heating cylinder 13 and accumulated and measured in front of the screw 2. Further, when the screw 2 is retracted by the accumulated measurement of the molten resin and reaches a predetermined measurement end position, the measurement process Sm is ended by stopping the rotation of the screw 2 (step S2). By the end of the measuring step Sm, the position of the screw 2 in the front-rear direction is controlled to the end position, and the rotational direction position of the screw 2 is also fixed (locked) (step S3). Positioning control with respect to the screw 2 is performed at least until the detection of a resin pressure Pr, which will be described later, is completed after the measurement step Sm is completed. If such positioning control for the screw 2 is performed, an unnecessary error factor for the detection of the resin pressure Pr can be eliminated, so that accurate and stable detection can be performed.

  On the other hand, when the measuring step Sm ends, the timer unit 4 measures time (step S4). Note that, normally, a suck back process is performed at the end of the weighing step Sm, but the control method according to the present embodiment does not perform the suck back process at this point. The timer unit 4 measures a preset interval time Ti. Accordingly, when the time measurement by the timer unit 4 is completed, the resin pressure Pr is detected (steps S5 and S6). Since the resin pressure Pr is continuously detected by the load cell 3 and applied to the processing unit 36, the resin pressure Pr is detected by sampling a detection signal applied to the processing unit 36. Sampling (detection of the resin pressure Pr) in this case may be performed once or may be averaged by performing a plurality of times. By using the average value, it is possible to obtain a more accurate resin pressure Pr from which an error factor is eliminated.

  Then, the detected resin pressure Pr is applied to the determination unit 37. Since the determination unit 37 is given a reference value (allowable range) set in advance by the setting unit 5, a pass / fail determination process for determining whether the detected resin pressure Pr does not deviate from the reference value is performed. Performed (step S7). At this time, if it is out of the allowable range, the molding machine controller 32 performs a predetermined defect process. On the other hand, if it is within the allowable range, normal operation continues without performing failure processing. In addition, as a defect process, the process which switches a shooter is performed so that a defect signal may be output, a defect generation | occurrence | production alarm may be activated, for example, and a corresponding molded product may be discharged to a defective container. As described above, if the detected resin pressure Pr is used for the quality determination processing related to molding, the resin pressure Pr having a high correlation with the quality of the molded product can be secured. Therefore, the quality of the reliability (accuracy) is high. A discrimination process can be performed.

  On the other hand, if the above-described detection of the resin pressure Pr (step S6) is performed, the suck back process Ss (see FIG. 4) is started immediately (step S8). Therefore, the suck back process Ss is delayed until the resin pressure Pr is detected. The suck-back process Ss is a process for lowering the resin pressure Pr by operating the servo motor 29 and slightly retracting the screw 2. Thereby, the drawing after completion | finish of the measurement process Sm is prevented. By the end of the suck-back process Ss, the remaining processes (remaining processes) until the next weighing process Sm starts are performed (steps S9 and S10). That is, when the suck back process Ss is completed, a cooling process Sc, a subsequent mold opening process So, a protruding process (mold releasing process), a mold clamping process, and an injection process are performed in parallel. When the next measurement process Sm starts, the measurement process Sm is performed (steps S11, S1,...).

  Therefore, according to such a control method according to the present embodiment, after the completion of the weighing step Sm, the start of the suck back process Ss is delayed, and the resin pressure Pr is detected after a predetermined interval time Ti has elapsed. Then, since the suck back process Ss is started thereafter, the resin pressure Pr having a high correlation with the quality of the molded product can be obtained. And it can implement easily by the change of a control method.

  Although the best embodiment has been described in detail above, the present invention is not limited to such an embodiment, and the detailed configuration, method, and the like can be arbitrarily set within the scope of the present invention. Can be changed, added or deleted. For example, although the case where the suck back process Ss is performed immediately after detecting the resin pressure Pr after the elapse of the interval time Ti, a predetermined delay time is set for the suck back process Ss, and the resin is performed according to the delay time. The detection of the pressure Pr and the suck back process Ss may be performed. The interval time Ti and the delay time may be automatically set (changed) corresponding to the molding cycle. Specifically, the interval time Ti and the delay time are automatically set in conjunction with the set value of the cooling time timer in the cooling process Sc. You may be made to do. Furthermore, when detecting the resin pressure Pr, various pressure detecting means other than the load cell 3 can be used. The resin pressure Pr can be used not only for pass / fail judgment processing but also for various types of monitoring including the exemplified usage modes. On the other hand, the injection molding machine M is an electric injection molding machine, but can be similarly applied to a hydraulic injection molding machine.

The flowchart which shows the process sequence of the shaping | molding process based on the control method which concerns on the best embodiment of this invention, Partial cross-sectional plan view of an injection molding machine that can implement the control method, Block diagram of the main part of the molding machine controller in the same injection molding machine, Process explanatory view showing a part of the molding process based on the control method, Change characteristic diagram of resin pressure over time after the end of the weighing process, A data table regarding the resin pressure at the time point of 4.0 [seconds] shown in FIG. Change characteristic diagram of correlation coefficient between resin pressure and molded product weight for different elapsed time after the end of weighing process, Figure of change characteristics of standard deviation of part weight for different elapsed time after the end of weighing process,

Explanation of symbols

  M: injection molding machine, Sm: weighing process, Ss: suck back process, Pr: resin pressure, Ti: interval time, 2: screw, (S7): pass / fail judgment process, W: molded product weight, C: correlation coefficient

Claims (5)

  In the control method of an injection molding machine that performs a suck back process and detects the resin pressure for monitoring after the end of the measuring step, the resin pressure is measured after a predetermined interval time has elapsed after the end of the measuring step. And controlling the positioning of the screw until at least the detection of the resin pressure is completed, and thereafter starting the delayed suck-back process.   2. The method of controlling an injection molding machine according to claim 1, wherein the resin pressure is used for quality determination processing related to molding.   2. The method of controlling an injection molding machine according to claim 1, wherein the length of the interval time is set corresponding to the type of resin and / or the type of molded product.   The method for controlling an injection molding machine according to claim 1 or 3, wherein the interval time is set to a time when the correlation coefficient between the resin pressure and the weight of the molded product is a predetermined value or more.   5. The method of controlling an injection molding machine according to claim 1, wherein the interval time is set to 1.0 [second] or more.

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