JP2008132685A - Control method of injection molding machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a molded product of high precision and high quality stable in resin pressure by excluding the effect depending on mechanical precision and to more enhance the homogeneity of the molded product (weight) by excluding the effect exerted on resin density (resin amount) at the time of weighing. <P>SOLUTION: A predetermined rotation inhibiting section Zn that inhibits the rotation of a screw 2 from the start of an injection process and a screw angle (reference angle) Qo relatively small in the irregularity R at every shot of resin pressure Pr at the time of advance of the screw 2 are preset. When the injection process is performed, the screw 2 is rotated up to the reference angle Qo after the rotation inhibiting section Zn is elapsed from the start of the injection process and the injection process is subsequently performed while holding the screw 2 to the reference angle Qo. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a control method for an injection molding machine that is suitable for use in performing an injection process by advancing a screw provided with a backflow prevention valve at the tip.

  In general, an in-line screw type injection molding machine has a heating cylinder with a hopper for supplying a molding material at the rear and an injection nozzle provided at the front, and an injection device in which a screw is inserted into the heating cylinder. Yes. In the measuring step, the melted molding material is measured and accumulated in front of the screw by rotating the screw, and in the injection step, the measured molding material is injected and filled into the mold by moving the screw forward. Therefore, in this type of injection molding machine, it is extremely important to accurately control the injection speed, injection pressure (holding pressure), etc., in order to ensure high precision, high quality, and high homogeneity. It becomes.

  By the way, it is known that the influence of the screw angle in the injection process cannot be ignored in order to secure a high-quality and highly uniform molded product. This effect mainly depends on the mechanical accuracy such as the inner diameter accuracy of the heating cylinder and the outer diameter accuracy of the screw (flight part), and the phenomenon that the quality and homogeneity of the molded product differ depending on the screw angle. Arise.

For this reason, conventionally, a control method that considers the screw angle, that is, a control method of an injection molding machine that stabilizes the quality of a molded product, in particular, the weight, by making the posture of the screw the same is also disclosed in Japanese Patent Laid-Open No. 2002-2002. No. 144390. In this control method, a reference angle position is set in advance to the rotation angle position of the screw, and an angle correction operation for correcting the rotation angle position of the screw to match the reference angle position immediately before or after the measuring step is performed at an arbitrary shot interval. It is to be executed in.
JP 2002-144390 A

  However, the conventional method for controlling an injection molding machine disclosed in the above publication has the following problems.

  First, the reference angle position is merely a reference for keeping the screw angle constant, and does not necessarily mean an optimum (best) screw angle in terms of molding. Therefore, it is impossible to eliminate the influence depending on the mechanical accuracy, and there is a limit in securing a high-precision and high-quality molded product stably.

  Second, since the angle correction operation for correcting the rotational angle position of the screw is performed immediately before or after the measuring step, the angle correction result may directly affect the measuring operation. That is, the angle correction is returned, which has a considerable influence on the resin density and the resin amount at the time of weighing, and becomes a factor of lowering the homogeneity in the molded product.

  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.

  In order to solve the above-mentioned problems, the present invention performs the weighing process by rotating the screw 2 provided with the backflow prevention valve 3 at the tip, and when this measuring process is completed, the screw 2 is advanced to perform the injection process. In the control method of the injection molding machine M to be performed, a predetermined rotation prohibition zone Zn for prohibiting the rotation of the screw 2 from the start of the injection process and a variation R of the resin pressure Pr for each shot when the screw 2 moves forward are relatively When a small screw angle (reference angle) Qo is set and the injection process is performed, the screw 2 is rotated to the reference angle Qo after the rotation prohibition zone Zn has elapsed since the injection process started. Is held at the reference angle Qo to perform the injection process.

  In this case, according to a preferred aspect of the invention, the rotation inhibition zone Zn is set based on the zone Zs from when the injection process starts until the backflow prevention valve 3 is closed, specifically, during the injection molding, Can be detected based on the section Zs until the rotation angle Qs of the screw 2 reaches the maximum, and can be set based on the section Zs. In this injection process, it is desirable to perform a servo lock that keeps the screw angle constant. Moreover, the rotation prohibition zone Zn can be set by time t or a screw position (screw moving distance). On the other hand, for the reference angle Qo, during a predetermined period at the time of trial molding, a servo lock that holds at a predetermined screw angle is performed, and the rotational torque Tr at the time of performing this servo lock is detected, and this rotational torque Tr is detected. Is performed for a plurality of different screw angles Qa, Qb, Qc... In one rotation of the screw 2 and set based on the screw angle at which the magnitude of the detected rotational torque Tr is relatively small. it can. The predetermined period can be a period from the end of the injection process to the start of the weighing process, or a period from the end of the measurement process to the start of the injection process. Furthermore, when rotating the screw 2 to the reference angle Qo, the screw 2 can be rotated in the direction opposite to the rotation direction of the measuring step. On the other hand, when the screw angle (start angle) Qi at the start of the injection process is detected and the injection process is completed, the screw 2 is set in the direction opposite to the rotation direction of the metering process so that the screw 2 has the start angle Qi. You may make it rotate.

  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) When performing the injection process, after the rotation prohibition zone Zn for prohibiting the rotation of the screw 2 has elapsed after the injection process has started, the screw 2 is moved by the shot R of the resin pressure Pr during advance. Is rotated to a relatively small reference angle Qo, and thereafter, the injection process is performed with the screw 2 held at the reference angle Qo, so that the influence depending on the mechanical accuracy is eliminated, thereby stabilizing the resin pressure Pr. In addition to obtaining a high-precision and high-quality molded product, the homogeneity of the molded product (weight) can be further improved by eliminating the influence on the resin density (resin amount) during measurement.

  (2) According to a preferred embodiment, if the rotation inhibition zone Zn is set based on the zone Zs from the start of the injection process until the backflow prevention valve 3 is closed, the rotation prevention zone 3 is closed until the backflow prevention valve 3 is closed. Unnecessary movement of the resin through the backflow prevention valve 3 can be prevented, and adverse factors in the zone Zs can be effectively eliminated.

  (3) According to a preferred embodiment, when setting the rotation-inhibited zone Zn, the zone Zs from the start of the injection process until the rotation angle Qs of the screw 2 reaches the maximum is detected during the trial molding. If it sets based on it, the closing point of the backflow prevention valve 3 can be detected easily and reliably.

  (4) According to a preferred aspect, if the servo lock is performed to keep the screw angle constant in the injection process at the time of trial molding, the flow rate of the resin can be stabilized, so that the accurate rotation angle Qs can be detected.

  (5) According to a preferred embodiment, when setting the reference angle Qo, during a predetermined period at the time of trial molding, a servo lock for holding at a predetermined screw angle is performed, and a rotational torque Tr at the time of performing this servo lock is detected. At the same time, the process of detecting the rotational torque Tr is performed for a plurality of different screw angles Qa, Qb, Qc... In one rotation of the screw 2, and the detected rotational torque Tr is relatively small. If the angle is set based on the angle, the reference angle Qo having a relatively small variation R of the resin pressure Pr for each shot when the screw 2 moves forward can be easily set without detecting the actual resin pressure Pr. In addition, the use of an expensive pressure sensor or the like can be eliminated.

  (6) According to a preferred aspect, if a predetermined period at the time of trial molding is a period from the end of the injection process to the start of the weighing process, or a period from the end of the weighing process to the start of the injection process, the injection molding machine A more suitable period can be selected according to the type of the item.

  (7) According to a preferred embodiment, when the screw 2 is rotated to the reference angle Qo, if the screw 2 is rotated in the opposite direction to the rotation direction of the measuring step, the influence on the resin due to the rotation of the screw 2 can be suppressed. it can.

  (8) According to a preferred embodiment, the screw angle (starting angle) Qi at the start of the injection process is detected, and when the injection process is completed, the rotation direction of the measuring process is set so that the screw 2 becomes the start angle Qi. If the rotation is made in the opposite direction, the rotation for each shot can be made quantitatively and qualitatively constant, so that the homogeneity of the molded product can be further improved.

  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 FIG.

  The injection molding machine M shown in FIG. 5 shows only the injection device Mi excluding the mold clamping device. The injection device Mi includes an injection table 11 and a drive table 12 that are separated from each other, and the rear end of the heating cylinder 13 is supported by the front surface of the injection table 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 inside of the heating cylinder 13 at the rear, and the screw 2 is inserted into the heating cylinder 13. The screw 2 includes a backflow prevention valve 3 at the tip. The screw 2 has a conical screw head portion 2h having a pointed tip at the tip, and a relatively small-diameter valve loading shaft portion 2s between the screw head portion 2h and the flight portion 2f side. Then, a cylindrical (ring-shaped) backflow prevention valve 3 is slidably loaded on the valve loading shaft portion 2s. As a result, the backflow prevention valve 3 is slidable over a predetermined stroke in the axial direction (front-rear direction) of the valve loading shaft portion 2s, and the backflow prevention valve 3 moves backward and comes into contact with the valve seat 2r formed on the flight portion 2f side. For example, the resin passage extending from the flight portion 2f side to the screw head portion 2h side is blocked, and when the backflow prevention valve 3 moves forward and moves away from the valve seat 2r, the resin passage is opened. In this case, blocking the resin passage is synonymous with closing the backflow prevention valve 3.

  On the other hand, four tie bars 16 are installed between the injection table 11 and the drive table 12, and a slide block 17 is slidably loaded on the tie bars 16. A rotary block 19 integrally having a driven wheel 18 is rotatably supported at the front end of the slide block 17, and the rear end of the screw 2 is coupled to the center of the rotary block 19. A screw rotating servomotor 20 is attached to the side surface of the slide block 17, and a driving wheel 21 fixed to a rotating shaft of the servomotor 20 is connected to the driven wheel 18 via a rotation transmission mechanism 22. The rotation transmission mechanism 22 may be a gear-type transmission mechanism using a transmission gear or a belt-type transmission mechanism using a timing belt. Further, the servo motor 20 is provided with a rotary encoder 23 for detecting the rotation speed (rotation speed) of the servo motor 20.

  On the other hand, a nut portion 25 is provided coaxially and integrally on the rear portion of the slide block 17, and the front side of the ball screw portion 26 supported rotatably on the drive base 12 is screwed into the nut portion 25. A ball screw mechanism 24 is configured. A driven wheel 27 is attached to the rear end of the ball screw portion 26 protruding rearward from the drive base 12, and a screw motor 28 is attached to the support board 12s attached to the drive base 12. The drive wheel 29 fixed to the rotating shaft of the servo motor 28 is connected to the driven wheel 27 via the rotation transmission mechanism 30. The rotation transmission mechanism 30 may be a gear-type transmission mechanism using a transmission gear or a belt-type transmission mechanism using a timing belt. Further, the servo motor 28 is provided with a rotary encoder 31 for detecting the rotation speed (rotation speed) of the servo motor 28.

  In FIG. 5, 32 is a controller provided in the injection molding machine M, and a series of control (sequence control) in the control method according to the present embodiment can be executed by the stored control program 32p. On the other hand, the servo motors 20 and 28 and the rotary encoders 23 and 31 described above are connected to the controller 32, and a load cell (pressure detector) 33 interposed between the rotary block 19 and the slide block 17 is connected to the controller 32. The pressure (resin pressure) received by the screw 2 by the load cell 33 can be detected. Furthermore, the controller 32 has a data memory 32s that stores various data such as molding conditions.

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

  In the control method according to the present embodiment, a predetermined rotation inhibition zone Zn and a reference angle Qo are set in advance. In this case, the rotation prohibition zone Zn is a zone in which the rotation of the screw 2 is prohibited from the start of the injection process, and is set based on the section Zs from the start of the injection process until the backflow prevention valve 3 is closed. Is set based on a section Zs from the start of the injection process until the rotation angle Qs of the screw 2 reaches the maximum by performing trial molding.

  The reference angle Qo is set to a screw angle with a relatively small variation R of the resin pressure Pr for each shot when the screw 2 moves forward. Specifically, by performing trial molding, a predetermined screw is set in a predetermined period. The servo lock held at the angle is performed, and the rotational torque Tr when the servo lock is performed is detected, and the process of detecting the rotational torque Tr is performed by a plurality of different screw angles Qa, Qb, Qc... Is set based on the screw angle at which the detected rotational torque Tr is relatively small. In the illustrated example, the plurality of screw angles Qa... Are selected in units of 30 [°], that is, 0, 30, 60, 90... 300, 330 [°]. Further, for the variation R, a maximum value-minimum value, a standard deviation, or the like can be used. The screw angle is an angle in the rotation direction of the screw 2. Servo lock is feedback control so that the screw angle is kept constant.

  First, a method for setting the rotation inhibition zone Zn will be described in detail according to the flowchart shown in FIG. 2 with reference to FIGS.

  Since the rotation prohibition zone Zn can be set by performing trial molding, a measurement process is performed using a predetermined molding material (step S11). When the measuring process is completed, the rotation of the screw 2 is fixed, that is, the servo motor 20 is servo-locked (steps S12 and S13). And the injection process which advances the screw 2 from an injection start position is performed (step S14). At this time, the rotation angle Qs of the screw 2 during the injection process is detected by the rotary encoder 23 attached to the servo motor 20 (step S15). The detected rotation angle Qs [°] is shown in FIG. In FIG. 6, the horizontal axis indicates time t [ms] from the start of the injection process, and the vertical axis indicates the rotation angle Qs [°] and the rotational torque when the servo motor 20 is servo-locked by supplying current. Tr [Mm], injection speed (screw advance speed) Vi [mm / s], injection pressure Pi [MPa], and screw position X [mm] are shown.

  As is clear from FIG. 6, during the injection process, the servo lock is performed so that the screw 2 does not rotate. However, when an external force is applied to rotate the screw 2, feedback control for correcting it is performed. Since this is done, the screw 2 rotates slightly. The rotation at this time is about 0.1 [°] at the maximum. Therefore, when the screw 2 is moved forward from the injection start position, the backflow prevention valve 3 is initially open, so that the screw 2 is slightly rotated by applying resin pressure to the screw 2. If the backflow prevention valve 3 is closed thereafter, the resin pressure is not applied to the screw 2, and the screw 2 is returned to the original position (lock position) by feedback control. As described above, when the screw 2 is advanced from the injection start position, a slight rotational behavior in which the rotation angle Qs of the screw 2 reaches the peak (maximum) occurs at the time tr shown in FIG. It can be considered that the backflow prevention valve 3 is closed (closed position Xc).

  FIG. 7 is data showing the relationship between the closing position Xc [mm] for each forming (shot) and the forming quality amount G [g] at the closing position Xc when the peak of the rotation angle Qs is regarded as the closing position Xc. is there. As is apparent from this data, the variation in the molding quality amount G and the variation in the closing position Xc have a clear correlation, and the peak of the rotation angle Qs can be regarded as the closing position Xc. Although it is possible to detect the rotation angle Qs without making the servo motor 20 servo-locked, in this case, the screw 2 rotates greatly by about 0.5 to 3 [°]. Therefore, the reverse flow rate of the resin becomes unstable, and an accurate and stable rotation angle Qs cannot be detected. However, since the flow rate of the resin can be stabilized by servo-locking the servo motor 20 when detecting the rotation angle Qs, the accurate rotation angle Qs can be detected.

  On the other hand, if the rotation angle Qs of the screw 2 is detected, the time tr when the peak rotation angle Qs occurs is taken in and temporarily stored as time data (step S16). Thereafter, the same trial molding is repeated N times, and N pieces of time data are collected (steps S17, S11...). If N pieces of time data have been collected, the time tr that is the average value is calculated (step S18). Since this time tr corresponds to the zone Zs from when the injection process starts until the backflow prevention valve 3 is closed, the rotation inhibition zone Zn is set based on the obtained time tr. In this case, the rotation inhibition zone Zn is a zone for starting screw rotation control after the backflow prevention valve 3 is completely closed. For example, the rotation inhibition zone Zn can be set by adding a predetermined margin time to the time tr. Thus, the end time tsa of the rotation inhibition zone Zn is obtained (step S19).

  Thus, if the rotation inhibition zone Zn is set based on the zone Zs from the start of the injection process until the backflow prevention valve 3 is closed, the backflow prevention valve until the backflow prevention valve 3 is closed. This prevents unnecessary movement of the resin through 3 and effectively eliminates adverse effects in the zone Zs. In particular, the closing point of the backflow prevention valve 3 can be detected easily and reliably by performing the trial molding and setting based on the section Zs from the start of the injection process until the rotation angle Qs of the screw 2 reaches the maximum. There are advantages you can do.

  Next, a method for setting the reference angle Qo will be described in detail according to the flowchart shown in FIG. 3 with reference to FIG.

  Since the reference angle Qo can be set by performing trial molding, a measurement process is performed using a predetermined molding material (step S21). When the measurement is completed, the screw 2 is rotated as it is to the target angle Qa, and when the target angle Qa is reached, the rotation of the screw 2 is stopped (steps S22 and S23). In this case, the initial target angle Qa is 0 [°], and an arbitrary angular position can be selected for this 0 °. When the target angle Qa is reached, the rotation of the screw 2 is fixed, that is, the servo motor 20 is servo-locked and held at the target angle Qa (step S24). This time point is indicated by ta in FIG. Since this time point ta is immediately after weighing (immediately before injection), the resin pressure Pr is applied to the screw 2 and the backflow prevention valve 3 is in an open state. Try to rotate in the opposite direction. Therefore, since the servo motor 20 needs a rotational torque Tr that resists this rotation, the rotational torque Tr at this time (Trd in FIG. 10) is detected and temporarily stored as rotational torque data (step S25).

  Next, a normal injection process for moving the screw 2 forward is performed (step S26). In FIG. 10, the time tb indicates the injection start time. On the other hand, when the injection process is completed, the same trial molding is repeated N times (in the example, 30 times) (steps S27, S21...). As a result, N pieces of rotational torque data are obtained, and the rotational torque Tr serving as the average value is calculated and stored (step S28). The collection of the rotational torque Tr by the above trial molding is similarly performed for the other target angles Qb (steps S29, S21,...). That is, the target angle is changed in the order of Qb (30 [°]), Qc (60 [°]), Qd (90 [°])... Qk (300 [°]), Ql (330 [°]). The same trial molding is performed. When the collection of the rotational torques Tr for all the target angles Qa is completed, the relationship between the target angles Qa and the rotational torques Tr can be represented in the radar chart shown in FIG. This radar chart shows that the rotational torque Tr is smaller toward the outside. In the illustrated example, the screw angle around 30 [°] is relatively the smallest in the rotational torque Tr, so the screw angle of 30 [°] can be set as the reference angle Qo (step S30).

  By the way, the reference angle Qo needs to be set to a screw angle at which the variation R of the resin pressure Pr for each shot when the screw 2 moves forward is relatively small. Therefore, it is necessary to verify whether or not the reference angle Qo set based on the rotational torque Tr described above can be used as a screw angle with a relatively small variation R of the resin pressure Pr for each shot.

  Next, in order to verify this point, the relationship between the variation R of the resin pressure Pr for each shot and the magnitude of the rotational torque Tr will be described in detail according to the flowchart shown in FIG. 4 with reference to FIGS.

  Since the resin pressure Pr is obtained by performing trial molding, a measuring step is performed using a predetermined molding material (step S31). When the measurement is completed, the screw 2 is rotated as it is to the target angle Qa, and when the target angle Qa is reached, the rotation of the screw 2 is stopped (steps S32 and S33). In this case, the initial target angle Qa is 0 [°], and this 0 [°] is made to coincide with the angular position when the above-described rotational torque Tr is detected. When the target angle Qa is reached, the rotation of the screw 2 is fixed, that is, the servo motor 20 is servo-locked and held at the target angle Qa (step S34). Next, a normal injection process for moving the screw 2 forward is performed (step S35). During the injection process, the resin pressure (peak value) Pr is detected and temporarily stored as resin pressure data (step S36). The detection of the resin pressure Pr can be performed by the load cell 33 described above. However, in order to obtain the resin pressure Pr as accurate as possible, the resin pressure Pr is directly detected by a pressure sensor attached to the injection nozzle or the mold for the experiment. It is desirable to detect.

  On the other hand, when the injection process is completed, the same trial molding is repeated N times (in the example, 30 times) (steps S37, S31...). As a result, N pieces of resin pressure data are obtained, and the variation R of the resin pressure Pr is obtained using this resin pressure data. Specifically, the maximum value-minimum value or standard deviation is calculated and stored (step S38). The collection related to the variation R of the resin pressure Pr by the above trial molding is similarly performed for the other target angles Qb (steps S39, S31,...). That is, the target angle is changed in the order of Qb (30 [°]), Qc (60 [°]), Qd (90 [°])... Qk (300 [°]), Ql (330 [°]). The same trial molding is performed. 9 is completed, the relationship between the target angle Qa and the variation R of the resin pressure Pr is represented in the radar chart shown in FIG. it can. The radar chart of FIG. 9 shows that the variation R is larger toward the outer side. In the illustrated example, the screw angle around 30 [°] is relatively smallest.

  Therefore, the reference angle Qo = 30 [°] set based on the radar chart shown in FIG. 8 substantially coincides with the screw angle = 30 [°] having the smallest variation R based on the radar chart shown in FIG. 9 (step S40). . In other words, when the screw angle with a relatively small variation R in the resin pressure Pr for each shot when the screw 2 moves forward is set as the reference angle Qo, the setting is based on the magnitude of the rotational torque Tr of the screw 2 described above. It can be easily set without detecting the actual resin pressure Pr, and the use of an expensive pressure sensor or the like can be eliminated.

  FIG. 11 shows a correlation diagram (scattering chart) of the variation R between the rotational torque Tr and the resin pressure Pr. The variation R between the rotational torque Tr and the resin pressure Pr has a negative correlation, and the correlation coefficient in the example is -0.86. Note that the rotational torque Tr and the resin pressure Pr can be detected at the same time in one trial molding, but in the present embodiment, each is detected by a separate trial molding in order to facilitate understanding of the explanation. Showed the case.

  Next, control in the actual molding process will be described according to the flowchart shown in FIG. 1 with reference to the drawings.

  First, a weighing process is performed using a predetermined molding material (step S1). In the weighing process, the servo motor 20 is driven and controlled in the forward direction, and the screw 2 is rotated in the forward direction to perform weighing. When the measuring process is completed, the rotation of the screw 2 is fixed, that is, the servo motor 20 is servo-locked (steps S2 and S3). Further, the screw angle at this time is detected from the rotary encoder 23 and temporarily stored as the start angle Qi (step S4). Then, the injection process is started (step S5). In the injection process, the servomotor 28 is driven and controlled to advance the screw 2 from the injection start position. In this case, the injection speed target value is given from the data memory 32s, and the screw 2 is driven and controlled to be the injection speed target value.

  On the other hand, timing is started simultaneously with the start of the injection process (step S6). Thereafter, when the set rotation prohibition section Zn has elapsed, that is, when the above-described end time tsa is reached, the servo lock for the servo motor 20 is released, and the screw 2 is rotated to the reference angle Qo. At this time, the screw 2 is rotated in the opposite direction to the rotation direction in the weighing process (steps S7 and S8). Thereby, the influence on resin by rotation of the screw 2 is suppressed. After the rotation inhibition zone Zn has elapsed, the screw 2 is held at the reference angle Qo, that is, the servomotor 20 is servo-locked so as to maintain the reference angle Qo, and the injection process is completed (steps S9, S10). ). When the injection process is completed, the screw 2 is rotated in the opposite direction to the rotation direction of the metering process so that the screw 2 has the start angle Qi, and the screw angle at the end of the injection process is made coincident with the start angle Qi ( Step S11). Thereby, since the rotation for each shot can be made constant quantitatively and qualitatively, the homogeneity of the molded product can be further improved. Further, when the next molding process is continuously performed, a similar molding process is performed (steps S12, S1,...).

  Therefore, according to the control method according to the present embodiment, when the injection process is performed, the screw 2 is moved after the rotation prohibition section Zn for prohibiting the rotation of the screw 2 has elapsed since the injection process started. Depends on the mechanical accuracy because the injection pressure is rotated to the reference angle Qo where the variation R of the resin pressure Pr during advance is relatively small and the screw 2 is held at the reference angle Qo thereafter. By eliminating the influence of the above, it is possible to obtain a high-precision and high-quality molded product having a stable resin pressure Pr, and by eliminating the influence on the resin density (resin amount) during measurement, The homogeneity of (weight) can be further improved.

  As described above, the best embodiment has been described in detail. However, the present invention is not limited to such an embodiment, and the detailed configuration, numerical values, technique, and the like are within the scope not departing from the gist of the present invention. It can be changed, added, or deleted arbitrarily.

  For example, although a ring-shaped valve (ring valve) has been illustrated as the backflow prevention valve 3, it is not necessarily limited to a ring valve. Moreover, although the rotation prohibition zone Zn showed the case where it set with time t, you may set it with a screw position (screw moving distance). Furthermore, although the rotation prohibition zone Zn showed the case where it set based on the zone Zs after the injection process started until the backflow prevention valve 3 closed, it is also possible to set by other conditions, for example, It can be set based on a section related to the speed control area, or a section from the end of the weighing process to the start of the injection process. On the other hand, the reference angle Qo is exemplified by the case where the rotational torque Tr is detected and set, but the resin pressure Pr may be directly detected and set. Moreover, although the case where the period from the end of the measurement process to the start of the injection process is used as the predetermined period for detecting the rotational torque Tr for setting the reference angle Qo, the measurement process starts from the end of the injection process is shown. It is also possible to use a period until time, and a more suitable period can be selected according to the type of the injection molding machine. On the other hand, a method of detecting the start angle Qi when the injection process starts and rotating the screw 2 to the start angle Qi when the injection process is completed is included, but it is not always necessary to include it. .

The flowchart which shows the process sequence of the control method of the injection molding machine which concerns on the best embodiment of this invention, The flowchart which shows the process sequence at the time of setting the rotation prohibition area in the control method, The flowchart which shows the process sequence at the time of setting the reference angle of the screw used for the control method, The flowchart which shows the process sequence at the time of calculating | requiring the variation of the resin pressure used for verification of the control method, Partial cross-sectional plan view of an injection molding machine that can implement the control method, The data figure containing the rotation angle of the screw with respect to time at the time of performing the trial molding which sets a rotation prohibition section by the processing procedure shown in FIG. The data figure which shows the relationship between the closed position of the backflow prevention valve at the time of performing the test molding which sets a rotation prohibition area by the process sequence shown in FIG. A radar chart showing the relationship between the screw angle and the rotational torque used when setting the reference angle of the screw used in the control method, Radar chart showing the relationship between screw angle and resin pressure variation used for verification of the control method, Change characteristic diagram of time vs. various physical quantities when setting the reference angle of the screw in the same control method, Correlation diagram (scatter diagram) showing variation in resin pressure against rotational torque in the same control method,

Explanation of symbols

  2: Screw, 3: Backflow prevention valve, M: Injection molding machine, Zn: Rotation prohibited section, Zs: Section until backflow prevention valve closes, Pr: Resin pressure, Qo: Reference angle, Qs: Screw rotation angle , Qa ...: Screw angle, t: Time, Tr: Rotational torque

Claims (9)

  In the control method of the injection molding machine for performing the injection process by rotating the screw provided with the backflow prevention valve at the tip and performing the injection process when this measurement process is completed, When performing the injection process by setting a predetermined rotation prohibition section for prohibiting the rotation of the screw from the start and a screw angle (reference angle) with a relatively small variation in resin pressure for each shot when the screw moves forward The screw is rotated to the reference angle after the rotation prohibition section has elapsed after the injection process is started, and thereafter, the injection process is performed while the screw is held at the reference angle. Control method of injection molding machine.   2. The method of controlling an injection molding machine according to claim 1, wherein the rotation prohibition section is set based on a section from the start of the injection process to the closing of the backflow prevention valve.   The rotation-inhibiting section detects a section from the start of an injection process to a maximum rotation angle of the screw at the time of trial molding, and is set based on the section. Control method of injection molding machine.   4. The method of controlling an injection molding machine according to claim 3, wherein in the injection step during the trial molding, a servo lock is performed to keep the screw angle constant.   4. The method of controlling an injection molding machine according to claim 1, wherein the rotation prohibition section is set by time or a screw position (screw movement distance).   The reference angle performs a servo lock that is held at a predetermined screw angle during a predetermined period at the time of trial molding, and detects the rotational torque at the time of performing the servo lock, and a process for detecting the rotational torque. 2. The injection molding machine according to claim 1, wherein the rotation is performed on a plurality of different screw angles in one rotation of the screw and is set based on a screw angle at which the magnitude of the detected rotational torque becomes relatively small. Control method.   7. The method of controlling an injection molding machine according to claim 6, wherein the predetermined period is a period from the end of the injection process to the start of the weighing process, or a period from the end of the measurement process to the start of the injection process. .   2. The method of controlling an injection molding machine according to claim 1, wherein when the screw is rotated to the reference angle, the screw is rotated in a direction opposite to a rotation direction of a measuring step.   The screw angle (start angle) at the start of the injection process is detected, and when the injection process is completed, the screw is rotated in the opposite direction to the rotation direction of the metering process so that the start angle is reached. The method of controlling an injection molding machine according to claim 1.

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