Injection Molding Metering Control Method

Abstract

To provide a weighing control method for injection molding that can accurately detect fluctuating factors affecting the plasticization melting and melt-mixing properties of the weighing resin and enable stable operation of the weighing process with high accuracy.SOLUTION: In the weighing process, the rotational movement of the screw 15 is performed based on the rotational torque command value RT set in the weighing operation control unit 41, the measured rotational torque value of the screw 15 at that time is measured, the limitation of the backward movement of the screw 15 is performed based on the brake torque command value BT set in the injection operation control unit 42, and the measured brake torque value of the screw 15 at that time is measured. The product of the measured rotational torque and the measured brake torque multiplied together is the control torque value, and torque compensation is started when the control torque value is outside the preset control range KH.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a metering control method for injection molding, which plasticizes and melts a resin material supplied into an injection cylinder by the rotational movement of a screw, transports the molten resin into the injection cylinder in front of the screw, and causes the screw to move backward by the transport of the molten resin, and stops the rotational movement of the screw at a predetermined position to store a predetermined amount of molten resin in the injection cylinder.

[0002] In injection molding using an in-line injection molding machine that simultaneously performs plasticization, storage, and injection of a resin material, the resin material supplied into the injection cylinder is plasticized and melted and transported to the tip of the screw by the shear heat generated by the rotational movement of the screw having spiral flights and the amount of heat from a heater or the like provided in the injection cylinder, and is stored as metered resin in the injection cylinder (referred to as metering control). As the storage of the metered resin increases, the screw moves backward, and the rotational movement of the screw is stopped at a predetermined backward position to hold the screw position. A resistance is applied to the backward movement of the screw to adjust the melt kneadability of the stored metered resin (referred to as back pressure control). Up to this point is called the metering process. The screw is moved forward to inject and fill the molten metered resin into the mold cavity, a holding pressure process for compensating for the cooling and solidification shrinkage of the metered resin, and a cooling process for cooling and solidifying the metered resin in the mold cavity are performed, and then the mold is opened to take out the injection molded product from the mold cavity.

[0003] Also, in injection molding using a pre-plasticizer type injection molding machine in which plasticization of the resin material, storage, and injection are different, metering control and back pressure control are performed in the metering process to store the metered resin, and in the injection process, the metered resin is injected and filled into the mold cavity, and then the process proceeds to the holding pressure process and the cooling process. That is, in both the in-line injection molding machine and the pre-plasticizer type injection molding machine, the metering process is the starting point of injection molding, and the quality of injection molding is determined by the state of the melt kneadability of the metered resin, which is the result of metering control and back pressure control in this metering process. Therefore, it is difficult to correct the state of the metered resin in the injection process and the holding pressure process following the metering process, and many control methods related to the metering process have been proposed.

[0004] Here, in an electric drive type injection device that controls the rotational movement and forward and backward movement of a screw with a servo motor or the like, metering control is performed by adjusting the rotational speed and rotational torque of the servo motor for rotational movement, and back pressure control is performed by adjusting the rotational direction and rotational torque of the servo motor for forward and backward movement. Further, in a hydraulic drive type injection device equipped with a hydraulic motor, a hydraulic cylinder, etc., metering control is performed by adjusting the supply amount and supply pressure of hydraulic pressure to the hydraulic motor, and back pressure control is performed by adjusting the supply pressure of hydraulic pressure to the hydraulic cylinder. Thus, in either the electric drive type or the hydraulic drive type, in the metering process, metering control by the rotational movement of the screw and back pressure control by restricting the backward movement of the screw are performed simultaneously, and as a result, the state of the melt kneadability of the metered resin is determined. Therefore, it is desired to propose a metering control method capable of adjusting metering control and back pressure control simultaneously.

[0005] For example, as shown in Patent Document 1, a first servo motor that performs the forward and backward movement of a screw and a second servo motor that performs the rotational movement of the screw are provided, and using a preset rotational speed command value of the second servo motor and a torque limit command value of the first servo motor according to the position of the screw, a metering and kneading method for controlling the rotational speed and back pressure of the screw has been proposed. Further, as shown in Patent Document 2, a servo motor for screw rotation and a servo motor for screw forward and backward movement are provided, and a torque limit value corresponding to the value obtained by subtracting the frictional force from the rotational torque of the two servo motors, and the rotational speed and rotational direction are preset according to the position of the screw, and it has been proposed to perform the metering process based on this set value.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] Here, as shown in Patent Document 1, it is stated that metering control and back pressure control are performed simultaneously based on the combination conditions of the screw rotation speed command, the torque limit value, and the screw switching position. Further, as shown in Patent Document 2, it is stated that metering control and back pressure control are performed simultaneously based on the combination conditions of the rotation speed, the torque limit value, the rotation direction, and the screw switching position. However, due to variations in the temperature and supply amount of the supplied resin material, variations in the resin material containing additives, variations in the heating temperature of the injection device, variations in the molding cycle, and aging variations such as wear of screw parts and adhesion of stagnant resin, etc., the degree of plasticization and melting of the resin material and the melt kneading property of the metered resin change greatly. However, Patent Document 1 and Patent Document 2 do not describe any of the variation factors at all. Also, due to the backward movement of the screw accompanying the storage of the metered resin, the distance (referred to as the effective screw length) from the supply port (inlet) of the resin material to the storage area (outlet) of the metered resin at the tip of the screw gradually becomes shorter. As a result, the plasticization and melting and the melt kneading property gradually decrease. This phenomenon also changes due to the above-described variation factors. That is, in Patent Document 1 and Patent Document 2, the variation factors cannot be grasped, and it does not satisfy the stabilization of the metering process.

[0008] Therefore, an object of the present invention is to provide a metering control method for injection molding that can accurately detect variation factors affecting the plasticization and melting and the melt kneading property of the metered resin and enables stable operation of a high-precision metering process.

Means for Solving the Problems

[0009] The metering control method for injection molding of the present invention is In an injection molding metering control method in which a resin material supplied into an injection cylinder is plasticized and melted by the rotational movement of a screw, the molten resin is transported into the injection cylinder in front of the screw, and by the transportation of the molten resin, the screw moves backward, and the rotational movement of the screw is stopped at a predetermined position to store a predetermined amount of molten resin in the injection cylinder, Based on the rotational torque command value set in the metering operation control unit, perform the rotational operation of the screw, measure the actual measured value of the rotational torque of the screw at that time, limit the retraction operation of the screw based on the braking torque command value set in the injection operation control unit, measure the actual measured value of the braking torque of the screw at that time, multiply the actual measured value of the rotational torque by the actual measured value of the braking torque, and use the product as the management torque value. When the management torque value deviates from the preset management range, start torque correction. This is the gist of the invention.

[0010] In the metering control method of injection molding of the present invention, When the factor causing the management torque value to deviate from the preset management range is due to the variation of the actual measured value of the rotational torque, the torque correction is preferably to increase or decrease the braking torque command value in the opposite direction with respect to the variation of the actual measured value of the rotational torque.

[0011] Also, in the metering control method of injection molding of the present invention, When the factor causing the management torque value to deviate from the preset management range is due to the variation of the actual measured value of the braking torque, the torque correction is preferably to increase or decrease the rotational torque command value in the opposite direction with respect to the variation of the actual measured value of the braking torque within the allowable range of the screw rotational peripheral speed value calculated from the diameter and rotational speed of the screw.

Effect of the Invention

[0012] According to the present invention, it is possible to accurately detect the variation factors that affect the plasticization and melting and melt kneading properties of the metered resin, and provide a metering control method for injection molding that enables stable operation of a high-precision metering process.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0014] Hereinafter, preferred embodiments for carrying out the present invention will be described with reference to the drawings. Note that the following embodiments do not limit the invention according to each claim. Also, not all combinations of features described in the embodiments are essential for the solution means of the invention according to each claim. Further, in the present embodiment, the scales and dimensions of each component may be exaggerated, or some components may be omitted.

[0015] (Injection molding machine) First, the injection molding machine according to the embodiment of the present invention will be described with reference to FIG. 1. Note that, as the injection molding machine shown in the following description, an in-line type injection molding machine that simultaneously plasticizes, stores, and injects a resin material is used as a base, but it is not limited thereto, and a pre-plasticizing type injection molding machine in which the plasticization, storage, and injection of the resin material are different may be used. Also, a horizontal injection molding machine is used as a base, but a vertical injection molding machine may be used. Further, the injection molding machine in which the rotational operation and the forward and backward movement of the screw are electrically driven is used, but a hydraulic drive type injection molding machine in which the rotational operation of the screw is performed by a hydraulic pump and the forward and backward movement of the screw is performed by a hydraulic cylinder may be used, or a hybrid drive type injection molding machine that combines an electric type and a hydraulic type may be used. Any injection molding machine that plasticizes, stores, and injects a resin material into a mold cavity can be treated as the injection molding machine according to the embodiment of the present invention.

[0016] The injection molding machine 100 shown in FIG. 1 includes an injection device 10, an injection molding die 20, an injection drive unit 30, an injection control unit 40, and a mold clamping control unit 50.

[0017] The injection device 10 includes a cylindrical injection cylinder 11 and a screw 15 disposed within the injection cylinder 11. A plurality of heaters 12 are arranged in the injection cylinder 11 and are heated and controlled to a predetermined temperature pattern by a temperature adjustment device (not shown). The injection control unit 40 operates the injection drive unit 30 to control the rotational movement and the forward and backward movement of the screw 15. Here, regarding the movement of the screw 15, the direction close to the injection mold 20 is defined as the front F, the movement in the forward F direction is defined as the forward movement, the direction away from the injection mold 20 is defined as the rear B, and the movement in the rear B direction is defined as the backward movement.

[0018] The screw 15 is provided with spiral flights 16 extending from the rear B to the front F. The spiral direction and angle of the flights 16 are set so that the resin material supplied from the material hopper 13 at the rear B of the injection cylinder 11 can be rotationally transported forward F with respect to the rotation direction of the screw 15. As shown in FIG. 1, the flights 16 are arranged in a single row at a constant angle at a constant interval, but the present invention is not limited thereto. For example, the interval and angle may be variable, or a plurality of rows may be arranged. Alternatively, only a part of the screw 15 may have a plurality of rows of flights 16 arranged.

[0019] Further, the screw 15 has a conical shape with a gradually increasing diameter from the rear B to the front F. That is, the volume of the gap between the screw 15 and the injection cylinder 11 is set to gradually decrease from the rear B to the front F. As a result, the resin material supplied from the material hopper 13 is transported forward by the rotational movement of the flights 16, and shear heat generation occurs due to the reduction in volume. Due to the synergistic effect of the heat quantity from the heater 12, molten resin is generated (referred to as plasticizing melting). The generated molten resin passes through the screw tip 17 having a backflow prevention function and is stored as metered resin P in the injection cylinder 11. As the metered resin P increases, the screw 15 moves backward toward the rear B side, stops the rotational movement of the screw 15 at a predetermined backward position, and holds the stop position. By restricting the backward movement of this screw 15 (referred to as metering back pressure), the melt-kneading property of the metered resin is adjusted (referred to as back pressure control). This process up to here is called the metering process. In the injection process, the screw 15 is advanced to inject and fill the metered resin P toward the injection molding die 20.

[0020] The injection molding die 20 has a fixed die 21 and a movable die 22 supported by a die clamping device (not shown), and the die clamping device is operated by a die clamping control unit 50. The die cavity 24 is formed by clamping the fixed die 21 and the movable die 22. The metered resin P stored in the injection device 10 is injected and filled into the die cavity 24 via the resin flow path 23. The injected and filled molten resin is cooled, and the product taken out of the die cavity 24 becomes an injection molded product.

[0021] Here, as the resin material used for injection molding, for example, in automotive interior parts, it is common to add colorants such as black, red, and blue to thermoplastic resins such as polypropylene (PP) resin and polyethylene (PE) resin to adjust the color tone of the parts. In addition, plasticizers that impart flexibility to thermoplastic resins, nucleating agents and clarifying agents that control the degree of crystallinity of crystalline resins, flame retardants that suppress combustion, antistatic agents that suppress electrostatic charging, lubricants that improve fluidity and mold release properties, weathering agents and ultraviolet degradation inhibitors that suppress degradation by ultraviolet rays, various additives such as reinforcing agents such as glass fibers and carbon fibers are appropriately selected. In addition, general-purpose resins such as polypropylene (PP) resin and polyethylene (PE) resin, engineering resins such as polyamide (PA) resin and polycarbonate (PC) resin, and thermoplastic resins such as super engineering resins such as polyphenylene sulfide (PPS) resin and polyether ether ketone (PEEK) resin are appropriately selected. The combination of the thermoplastic resin and the additive is called a resin material. Note that instead of the thermoplastic resin, for example, thermosetting resins such as phenol (PF) resin and melamine (MF) resin may be used.

[0022] The injection drive unit 30 is an electric drive type including a metering motor 31 that rotates the screw 15 and an injection motor 34 that moves the screw forward and backward. The rotational movement of the metering motor 31 is transmitted to the screw drive shaft 39 by the rotation transmission mechanism 32. The screw drive shaft 39 and the screw 15 are integrated by a coupling 18. Thereby, the rotational movement of the metering motor 31 is transmitted to the screw 15 via the rotation transmission mechanism 32, the screw drive shaft 39, and the coupling 18, resulting in the rotational movement of the screw 15. In addition, the rotational movement of the injection motor 34 is transmitted to the ball screw mechanism 37 via the rotation transmission mechanism 35. The ball screw mechanism 37 converts the rotational movement into a linear movement to perform the forward and backward movement of the screw 15 via the support member 38 and the screw drive shaft 39. Here, regarding the rotational direction of the metering motor 31, the rotation in which the resin material is transported forward to the F side by the rotation of the screw 15 is defined as the forward rotation, and the rotation in the opposite direction to the forward rotation is defined as the reverse rotation. Also, regarding the rotational direction of the injection motor 34, the rotation in which the screw 15 moves forward is defined as the forward rotation, and the rotation in which the screw 15 moves backward is defined as the backward rotation.

[0023] Here, the metering motor 31 and the injection motor 34 are preferably AC servo motors that can control the rotation direction and rotation speed with high precision. However, for example, an inverter motor that can simply control the rotation speed by operating the supply current with cost priority may also be used. Further, as shown in FIG. 1, the rotation transmission mechanisms (32, 35) are a combination of a pulley and a belt, but are not limited thereto. For example, a combination of a drive gear and a driven gear may be used, or a combination of a chain and a sprocket may be used. Also, although the ball screw mechanism 37 is shown as one for convenience, a plurality of arrangements may be provided vertically, horizontally, or in all directions. Instead of the ball screw mechanism 37, for example, a conversion device combining a rack and a pinion may be used. The arrangements of the metering motor 31 and the injection motor 34 may be arbitrarily changed. Further, a hydraulic motor may be used instead of the metering motor 31, and a hydraulic cylinder may be used instead of the injection motor 34 to form a hydraulic drive type, or a hybrid drive type combining an electric drive type and a hydraulic drive type may be used.

[0024] The injection control unit 40 includes a metering operation control unit 41 that controls the rotation operation of the metering motor 31, an injection operation control unit 42 that controls the rotation operation of the injection motor 34, and an injection metering control unit 43 that is connected to the metering operation control unit 41 and the injection operation control unit 42 and controls the injection process and the metering process. The injection metering control unit 43 is also connected to the mold clamping control unit 50, and injection molding is performed by simultaneously controlling the injection device 10 and the mold clamping device. Encoders (33, 36) for measuring the rotation direction and rotation speed are respectively provided on the metering motor 31 and the injection motor 34, and the detection signals of the encoders (33, 36) are transferred to the metering operation control unit 41 and the injection operation control unit 42. Further, the metering operation control unit 41 and the injection operation control unit 42 are provided with a torque measurement function, and can measure the actual measured value of the rotation torque of the metering motor 31 and the actual measured value of the braking torque of the injection motor 34.

[0025] Based on this, the metering motor 31 is operated (clockwise) according to the set rotational torque command value in the metering operation control unit 41, and metering control of the rotational operation of the screw 15 during the metering process is performed. At that time, the measured rotational torque value of the metering motor 31 is measured by the metering operation control unit 41. Similarly, based on the set braking torque command value in the injection operation control unit 42, the injection motor 34 is operated (counterclockwise), and back pressure control is performed by restricting the backward movement of the screw 15 during the metering process. At that time, the measured braking torque value of the injection motor 34 is measured by the injection operation control unit 42. The detection signals from the encoders (33, 36) are treated as the measured values of the rotational direction and rotational speed of the metering motor 31 and the injection motor 34. At the same time, it is processed by the injection operation control unit 42 as the position of the backward movement of the screw 15 during the metering process.

[0026] Here, the measured rotational torque value and the measured braking torque value shall use the power consumption required for driving the metering motor 31 and the injection motor 34. Note that it is not limited to this. For example, the ratio of the power consumption to the rated power of the metering motor 31 and the injection motor 34 (referred to as the load factor) may be used. In the case of a hydraulic drive type, the supply pressure of the hydraulic pressure to the hydraulic motor is taken as the measured rotational torque value, and the supply pressure of the hydraulic pressure to the hydraulic cylinder is taken as the measured braking torque value. Also, the measurement of the rotational direction and rotational speed of the metering motor 31 and the injection motor 34 may be, for example, by attaching a rotational measurement sensor to each rotational transmission mechanism (32, 38) for measurement, or by attaching a rotational measurement sensor to the screw drive shaft 39 or the ball screw mechanism 37. Also, the position measurement of the forward and backward movement of the screw 15 may be by attaching a position measurement sensor to the screw drive shaft 39 or the ball screw mechanism 37 for measurement.

[0027] (Metering Control Method) Next, the metering control method according to the embodiment of the present invention will be described with reference to FIGS. 2 and 3. First, as shown in FIG. 2, in the metering process, the metering control operates the metering motor 31 in the forward rotation direction based on the rotation torque command value set in the metering operation control unit 41 to control the rotation operation of the screw 15. This rotation torque command is set as the screw rotation speed of the metering control. At that time, the metering operation control unit 41 measures the actual measured value of the rotation torque of the metering motor 31. The resin material supplied from the material hopper 13 is plastically melted by the shear heat generated by the rotation operation of the screw 15 and is rotationally transported to the front F side of the screw 15. During this rotational transportation, the plasticized molten resin is subjected to a kneading action. That is, the rotational kinetic energy of the rotational operation of the screw 15 is consumed as metering control for adjusting plasticization melting, rotational transportation, and kneading action. That is, by measuring the actual measured value of the rotation torque during the metering process, the rotational kinetic energy can be accurately calculated, and the state of the metering control for adjusting plasticization melting, rotational transportation, and kneading action can be grasped.

[0028] Also, in the metering process, the back pressure control operates the injection motor 34 in the reverse rotation direction based on the brake torque command value set in the injection operation control unit 42 to control the restriction of the backward movement of the screw 15 accompanying the storage of the metered resin. At that time, the injection operation control unit 42 measures the actual measured value of the brake torque of the screw 15. When a predetermined positive rotation torque value is loaded on the injection motor 34 and the force of the backward movement of the screw 15 exceeds the positive rotation torque value, the injection motor 34 rotates in the reverse direction so as to maintain the positive rotation torque value, and the screw 15 moves backward (referred to as back pressure control). The positive rotation torque value loaded on the injection motor 34 at this time is the brake torque command value and is set as the back pressure value of the metering process. By the brake torque command value, the backward movement speed of the screw 15 is decelerated, and a speed difference (deceleration energy) is generated. This deceleration energy is consumed as back pressure control for applying pressure to the molten resin rotationally transported to the front F side of the screw 15 to adjust the melt kneadability and resin density of the metered resin. That is, by measuring the actual measured value of the brake torque during the metering process, the deceleration energy can be accurately calculated, and the state of the back pressure control for adjusting the melt kneadability and resin density of the metered resin can be grasped.

[0029] Furthermore, a product obtained by multiplying the measured rotational torque value and the measured braking torque value is used as a management torque value, and the metering control, back pressure control, and evaluation of the state of the metered resin in the metering process are performed using this management torque value. Further, correction of the metering process is performed using the management torque value. The metering process is controlled by multiplying the rotational kinetic energy of the rotational motion of the screw 15 and the deceleration energy of the backward movement speed of the screw 15, and the balance between the two energies is important. Therefore, control of the metering process by the management torque value is suitable.

[0030] In addition, due to factors such as fluctuations in the temperature and supply amount of the supplied resin material, fluctuations in the resin material containing additives, fluctuations in the heating temperature of the injection device, fluctuations in the molding cycle, wear of screw parts, etc., and adhesion of residual resin, the state of plasticization adjustment of plasticization melting, rotational transportation, and kneading action, and the state of resin adjustment of melt kneadability and resin density fluctuate. Further, the backward movement of the screw 15 accompanying the storage of the metered resin shortens the effective screw length indicating the distance from the inlet of the resin material (material hopper 13) to the outlet (metered resin P), and the state of plasticization adjustment and resin adjustment gradually deteriorates during the metering process. These phenomena were difficult to predict in the prior art, but by using the management torque value, fluctuations can be accurately detected, corrected immediately, and stable production of injection molding can be continued.

[0031] When the management torque value is within the preset management range, stable operation of the metering process is guaranteed and injection molding is continued. When the management torque value exceeds the management range, torque correction is immediately started. In that case, if fluctuations in the measured rotational torque value are confirmed, the first torque correction is executed. Also, if fluctuations in the measured braking torque value are confirmed, the second torque correction is executed. For other situations, other corrections are considered.

[0032] As shown in Fig. 3(a), the first torque correction corrects (increases or decreases) the brake torque command value in the opposite direction with respect to the fluctuation (decrease or increase) of the measured rotational torque value. By this correction, the controlled torque value returns within the control range. After confirming the return of the controlled torque value, the first torque correction is completed, and the safe operation of the metering process is resumed. If the controlled torque value does not return within the control range even after correcting the brake torque command value (the dashed line in the figure), the consideration of other corrections is advanced.

[0033] As shown in Fig. 3(b), the second torque correction corrects (decreases or increases) the rotational torque command value in the opposite direction with respect to the fluctuation (increase or decrease) of the measured brake torque value. By this correction, the controlled torque value returns within the control range. In the correction of the rotational torque command value, the product of the screw diameter D (unit: mm) and the screw rotation speed N (unit: rpm) is defined as the screw rotational peripheral speed value DN, and the allowable range is set as this screw rotational peripheral speed value DN = 6000 - 18000. When the screw rotational peripheral speed value DN is 6000 or less, the rotational kinetic energy is too low, and the ability to plasticize and melt the resin material and transport it forward is extremely reduced, and the stable operation of the metering process cannot be ensured. Also, when the screw rotational peripheral speed value DN exceeds 1800, the rotational kinetic energy is excessive, and the shear heat generation becomes excessive, increasing the risk of thermal degradation of the resin material, so the stable operation of the metering process cannot be ensured. Therefore, when the screw rotational peripheral speed value DN is out of the allowable range, the consideration of other corrections is advanced. After confirming that the screw rotational peripheral speed value DN is within the allowable range and the controlled torque value has returned within the control range, the second torque correction is completed, and the safe operation of the metering process is resumed. If the controlled torque value does not return within the control range even after correcting the rotational torque command value (the dashed line in the figure), the consideration of other corrections is advanced.

[0034] (Controlled torque value) Next, the management torque value of the metering control method according to the embodiment of the present invention will be described with reference to FIGS. 4 and 5. FIG. 4 shows a normal state of the management torque value, and FIG. 5 shows an example of an abnormal state of the management torque value. The horizontal axis represents the position of the screw 15 in the metering process. From the metering start position on the left side of the figure towards the metering completion position on the right side, it shows the backward movement of the screw 15 accompanying the storage of the metering resin P, and the metering process ends at the metering completion position. The vertical axis represents the torque command value / measured value of the injection motor 34 and the metering motor 31, and the management torque value.

[0035] First, as shown in FIG. 4(a), the injection operation control unit 42 operates the injection motor 34 in the reverse rotation direction based on the brake torque command value BT to perform back pressure control in the metering process. The measured brake torque value BZ1 is within the range of the upper limit value BTH and the lower limit value BTL, indicating that stable back pressure control is being performed. Here, the upper limit value BTH and the lower limit value BTL are set, for example, within a range where good products can be surely obtained from past injection molding results.

[0036] Next, as shown in FIG. 4(b), the metering operation control unit 41 operates the metering motor 31 in the forward rotation direction based on the rotation torque command value RT to perform metering control in the metering process. The measured rotation torque value RZ1 is within the range of the upper limit value RTH and the lower limit value RTL, indicating that stable metering control is being performed. Here, the upper limit value RTH and the lower limit value RTL are set, for example, within a range where good products can be surely obtained from past injection molding results.

[0037] Since the measured brake torque value BZ1 and the measured rotation torque value RT1 are stable, as shown in FIG. 4(c), the management torque value KZ1 also shows a normal state of a stable metering process. Here, the upper limit value KTH and the lower limit value KTL are set, for example, as a range where good products can be surely obtained from past injection molding results, and set as the management range KH. The reference value KT is the average value of the management range KH.

[0038] Next, the abnormal state of the metering process will be described with reference to FIG. 5. As shown in FIG. 5(a), the measured brake torque value BZ1 is within the range of the upper limit value BTH and the lower limit value BTL, and stable back pressure control is being performed. On the other hand, as shown in FIG. 5(b), the measured rotational torque value RZ2 fluctuates greatly in the latter half of the metering process, deviates from the lower limit value RTL, gradually decreases toward the completion of metering, and indicates an unstable state of the metering control of the screw 15. Such a phenomenon is likely to occur, for example, when the metered resin amount is extremely large, the retraction amount of the screw increases significantly, and the effective length of the screw becomes extremely short. It may also occur when the supply amount of the resin material is unstable due to clogging of the material hopper 13 or the like, or when the resin material clogs on the rear B side of the screw 15 and the rotational transportation decreases.

[0039] Conversely, the measured rotational torque value RZ2 may also increase. For example, it may occur when an additive with a high melting point such as glass fiber accumulates in a large amount in the screw 15 without being rotationally transported. In addition, the measured rotational torque value RZ2 may also have a large amplitude and deviate from the upper limit value RTH or the lower limit value RTL. For example, when resin materials with different melting points are mixed, or in the case of a resin material containing a large amount of an additive with a high melt viscosity in a resin material with a low melt viscosity, the plasticization melting and rotational transportation in the screw 15 fluctuate irregularly, and as a result, the measured rotational torque value RZ2 may show an amplitude. Thus, by measuring the measured rotational torque value RZ2, it is possible to accurately detect the fluctuations in the metering control of the plasticization melting and rotational transportation during the metering process.

[0040] The measured brake torque value BZ1 is in a stable state. However, when the measured rotational torque value RZ2 fluctuates, as shown in Fig. 5(c), the control torque value KZ2 fluctuates. That is, by controlling the control torque value, the states of the metering control and back pressure control during the metering process can be accurately determined. Furthermore, by confirming whether the measured value is fluctuating on the side of the measured brake torque value or the measured rotational torque value, the assumed causes related to the fluctuations during the metering process become clear, and immediate and accurate corrections can be made to return to a normal metering process. Here, the position of the screw 15 where the control torque value KZ2 drops below the lower limit value KTL and deviates from the control range KH is defined as the correction start position SH, and the subsequent metering process is to be corrected.

[0041] (Torque correction procedure) Next, the correction procedure for the metering process using the control torque value according to the embodiment of the present invention will be described with reference to Figs. 6 and 7. Fig. 6 shows the procedure for the first torque correction, and Fig. 7 shows the procedure for the second torque correction. The horizontal axis and the vertical axis are the same as those in Figs. 4 and 5. Also, as shown in Figs. 2 and 3, when the control torque value deviates from the control range KH and the measured rotational torque value fluctuates, the first torque correction is performed, and when the measured brake torque value fluctuates, the second torque correction is performed. In the case shown in Fig. 5, since the measured rotational torque value RZ2 fluctuates, it is the first torque correction as shown in Fig. 6.

[0042] First, as shown in Fig. 6(a), since the measured rotational torque value RZ2 from the start of metering to the correction start position SH is stable, the state is continued as it is. From the correction start position SH towards the completion of metering, the measured rotational torque value RZ2 gradually decreases (fluctuation towards the negative side) outside the lower limit value RTL. At the time of completion of metering, it drops to the measured rotational torque value RZ3, showing a deviation E1 from the rotational torque command value RT. Due to the fluctuation of the measured rotational torque value RZ2, as shown in Fig. 5(c), the control torque value becomes unstable and deviates from the control range KH.

[0043] Therefore, within the range from the correction start position SH to the completion of metering, as shown in FIG. 6(b), the first torque correction is performed. The first torque correction corrects the brake torque command value BT set in the injection operation control unit 42 so that the control torque value returns within the control range KH. For example, a correction is performed by adding a deviation E2 (positive side) that is opposite to the deviation E1 (negative side) to the brake torque command value BT. This correction is continuously performed by subdividing the position of the screw 15 within the range from the correction start position SH to the completion of metering. As a result, the measured brake torque value BZ2 is corrected to the positive side from the correction start position SH toward the completion of metering, and shows the measured brake torque value BZ3 at the completion of metering that is opposite to the measured rotational torque value RZ3. In this way, by performing a positive side correction opposite to the negative side variation, as shown in FIG. 6(c), the control torque value KZ3 returns within the control range KH, and a stable metering process resumes.

[0044] Next, the second torque correction when the measured brake torque value fluctuates will be described with reference to FIG. 7. As shown in FIG. 7(a), the measured brake torque value BZ4 is stable from the start of metering to the correction start position SH, and gradually increases beyond the upper limit value RTH from the correction start position SH toward the completion of metering (variation to the positive side). At the time of completion of metering, it increases to the measured brake torque value BZ5, showing a deviation E3 from the brake torque command value BT. Due to the variation of the measured brake torque value BZ4, the control torque value becomes unstable and deviates from the control range KH.

[0045] Here, the variation in the measured brake torque BZ4 may occur due to, for example, the variation in the heating temperature of the injection cylinder 11 or the rotational speed of the screw 15, which causes the variation in the rotational transport amount of the resin material. Also, due to the temperature variation of the supplied resin material, the states of plasticization melting and rotational transport vary, so the measured brake torque BZ4 is likely to vary. Further, when using a resin material blended with resin materials having different melting points and melt viscosities, or when using a resin material containing a large amount of additives having different specific gravities and melting temperatures, or when using a resin material with varying sizes and shapes, the states of plasticization melting and rotational transport are likely to vary, resulting in the variation of the measured brake torque BZ4. Additionally, it may also vary depending on the adhesion state of the resin material that has stagnated and deteriorated to the screw 15 and the injection cylinder 11.

[0046] Within the range from the correction start position SH to the completion of the holding pressure, as shown in FIG. 7(b), the second torque correction is performed. The second torque correction corrects the rotational torque command value RT set in the metering operation control unit 41 so that the control torque value returns within the control range KH. For example, a correction is performed in which the deviation E4 (minus side) opposite to the deviation E3 (plus side) is subtracted from the rotational torque command value RT. This correction is continuously performed by subdividing the position of the screw 15 in the range from the correction start position SH to the completion of metering. As a result, the measured rotational torque BR4 is corrected to the minus side from the correction start position SH toward the completion of metering, showing the measured rotational torque RZ5 at the completion of metering that is opposite to the measured brake torque BZ5. In this way, by performing the minus-side correction opposite to the plus-side variation, as shown in FIG. 7(c), the control torque value KZ4 returns within the control range KH, and a stable metering process is restarted. Note that the second torque correction is performed within the range of the screw rotational peripheral speed value DN = 6000 to 18000 obtained by multiplying the screw diameter D (unit: mm) by the screw rotational speed N (unit: rpm).

[0047] Here, as described with reference to FIGS. 2 and 3, when the conditions for the first torque correction and the second torque correction are not met, and even if the first torque correction or the second torque correction is performed, and the control torque value does not return within the control range KH, other corrections are performed. For example, the molding cycle may be set longer to increase the residence time in the injection cylinder 11, and sufficient preheating may be given to the resin material to reduce the variation factors of the resin material and mitigate the influence on the metering process. Alternatively, by using a material preheating or drying device or the like to sufficiently preheat or dry the resin material, the temperature variation of the resin material can be reduced. Or, it is also possible to replace the resin material with a resin material having less variation in the amount of additives, replace it with a resin material having uniform size, cleanly remove foreign matters from the resin material, avoid separation of the resin material during the pressure feeding of the resin material using an air transporter, etc., which can reduce the variation of the resin material and suppress the variation in the metering process. Also, large-scale corrections such as replacing the screw 15 with a screw having a different shape, periodically cleaning the screw 15 etc. to remove the residence deteriorated resin, using an injection device with a large capacity, performing maintenance on the injection molding machine including the control device, etc. need to be considered.

[0048] (Effect) In this way, an injection molding metering control method is performed using the control torque value which is the product obtained by multiplying the measured rotational torque value of the metering motor 31 and the measured braking torque value of the injection motor 34. As a result, it is possible to accurately determine the quality state during the metering process, accurately detect the variation factors that affect the plasticization melting and melt kneading property of the metered resin. Furthermore, it is possible to accurately detect an abnormal state during the metering process, clarify the assumed cause, and immediately perform an accurate correction. Thereby, it is possible to quickly return to a normal metering process and provide stable operation of high-quality injection molding without being affected by the variation factors of disturbances.

[0049] As described above, the preferred embodiments of the present invention have been explained, but the technical scope of the present invention is not limited to the scope described in the above embodiments. Various changes or improvements can be made to the above embodiments.

Explanation of Reference Numerals

[0050] 100 Injection molding machine 10 Injection device 11 Injection cylinder 12 Heater 13 Material hopper 15 Screw 16 Flight 17 Screw tip 18 Coupling F Front B Rear P Metered resin 20 Injection mold 21 Fixed mold 22 Movable mold 23 Resin flow path 24 Mold cavity 30 Injection drive unit 31 Metering motor 32, 35 Rotation transmission mechanism 33, 36 Encoder 34 Injection motor 37 Ball screw mechanism 38 Support member 39 Screw drive shaft 40 Injection control unit 41 Metering operation control unit 42 Injection operation control unit 43 Injection metering control unit 50 Mold clamping control unit D Screw diameter N Screw rotation speed DN Screw rotation peripheral speed value BT Brake torque command value BZ1~BZ5 Brake torque measured value BTH, RTH, KTH Upper limit value BTL, RTL, KTL Lower limit value RT Rotation torque command value RZ1~RZ5 Rotation torque measured value KZ1~KZ4 Management torque value KT Reference value KH Management range SH Correction start position Deviations E1 to E4

Claims

1. In an injection molding metering control method, a resin material supplied into an injection cylinder is plasticized and melted by the rotational movement of a screw, the molten resin is transported into the injection cylinder in front of the screw, and due to the transport of the molten resin, the screw moves backward. When the rotational movement of the screw is stopped at a predetermined position and a predetermined amount of molten resin is stored in the injection cylinder, the rotational movement of the screw is performed based on a rotational torque command value set in a metering operation control unit, the actual measured value of the rotational torque of the screw at that time is measured, the backward movement of the screw is restricted based on a brake torque command value set in an injection operation control unit, the actual measured value of the brake torque of the screw at that time is measured, the product obtained by multiplying the actual measured value of the rotational torque and the actual measured value of the brake torque is used as a management torque value, and torque correction is started when the management torque value deviates from a preset management range. A metering control method for injection molding, characterized in that.

2. When the factor causing the management torque value to deviate from the preset management range is due to fluctuations in the actual measured value of the rotational torque, the torque correction is to increase or decrease the brake torque command value in the opposite direction with respect to the fluctuations in the actual measured value of the rotational torque. The metering control method for injection molding according to Claim 1.

3. When the factor causing the management torque value to deviate from the preset management range is due to fluctuations in the actual measured value of the brake torque, the torque correction is to increase or decrease the rotational torque command value in the opposite direction with respect to the fluctuations in the actual measured value of the brake torque within the allowable range of the screw rotational peripheral speed value calculated from the diameter and rotational speed of the screw. The metering control method for injection molding according to Claim 1.

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