JP7703999B2 - Injection molding measurement control method - Google Patents

Description

This invention relates to a measurement control method for injection molding in which resin material supplied into an injection cylinder is plasticized and melted by the rotation of a screw, the molten resin is transported into the injection cylinder in front of the screw, the screw moves backwards due to the transport of the molten resin, the rotation of the screw is stopped at a predetermined position, and a predetermined amount of molten resin is stored in the injection cylinder.

Injection molding using an in-line injection molding machine that simultaneously plasticizes, stores, and injects resin material, the resin material supplied to the injection cylinder is plasticized and melted by the shear heat generated by the rotation of the screw with a spiral flight and the heat of a heater or the like installed in the injection cylinder, and is transported to the tip of the screw and stored as metered resin in the injection cylinder (called metering control). As the amount of metered resin stored increases, the screw moves backward, and at a specified backward position, the screw's rotation stops and the screw position is maintained. Resistance is applied to this backward movement of the screw to adjust the melt kneadability of the stored metered resin (called back pressure control). This is called the metering process. The screw moves forward to inject and fill the molten metered resin into the mold cavity in the injection process, the pressure holding process to compensate for the cooling and solidifying shrinkage of the metered resin, and the cooling process to cool and solidify the metered resin in the mold cavity. The mold is then opened and the product is removed from the mold cavity as an injection molded product.

Even in injection molding using a pre-plasticizing injection molding machine, in which the plasticization, storage, and injection of the resin material are different, the metered resin is stored in the metering process by performing metering control and back pressure control, and the metered resin is injected and filled into the mold cavity in the injection process, after which the process proceeds to the pressure holding and cooling processes. In other words, in both in-line injection molding machines and pre-plasticizing injection molding machines, the metering process is the starting point of injection molding, and the quality of the injection molding is determined by the state of the melt kneadability of the metered resin, which is the result of the metering control and back pressure control in this metering process. For this reason, it is difficult to correct the state of the metered resin in the injection process and pressure holding processes that follow the metering process, and many control methods for the metering process have been proposed.

Here, in an electrically driven injection device in which the rotational motion and forward/backward motion of the screw are controlled by a servo motor or the like, metering control is performed by adjusting the rotation speed and rotational torque of the servo motor for rotational motion, and back pressure control is performed by adjusting the rotation direction and rotational torque of the servo motor for forward/backward motion. In a hydraulically driven injection device equipped with a hydraulic motor, hydraulic cylinder, etc., metering control is performed by adjusting the 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 an electrically driven or hydraulically driven type, the metering process simultaneously performs metering control by the rotational motion of the screw and back pressure control by limiting the backward motion of the screw, and the state of melt kneadability of the metered resin is determined as the result. Therefore, it is desired to propose a metering control method that can simultaneously adjust metering control and back pressure control.

For example, as shown in Patent Document 1, a metering and kneading method has been proposed in which a first servo motor for forward and backward movement of the screw and a second servo motor for rotating the screw are provided, and the rotation speed and back pressure of the screw are controlled using a rotation speed command value for the second servo motor and a torque limit command value for the first servo motor, which are preset according to the position of the screw. Also, as shown in Patent Document 2, a servo motor for rotating the screw and a servo motor for forward and backward movement of the screw are provided, and a torque limit value corresponding to the value obtained by subtracting frictional force from the rotation torque of the two servo motors, as well as the rotation speed and rotation direction, are preset according to the position of the screw, and the metering process is performed based on these set values.

Japanese Unexamined Patent Publication No. 61-220817 Special Publication No. 4-6534

Here, as shown in Patent Document 1, metering control and back pressure control are performed simultaneously based on the combined conditions of the screw rotation speed command, the torque limit value, and the screw switching position. Also, as shown in Patent Document 2, metering control and back pressure control are performed simultaneously based on the combined conditions of the rotation speed, the torque limit value, the rotation direction, and the screw switching position. However, the degree of plasticization melting of the resin material and the melt kneading property of the metered resin change significantly due to variable factors such as fluctuations in 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, and aging fluctuations due to wear of screw parts and adhesion of retained resin, but Patent Document 1 and Patent Document 2 do not mention the variable factors at all. Also, due to the retreat of the screw accompanying the storage of the metered resin, the distance (referred to as the effective length of the screw) 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 melting and melt kneading property gradually decrease. This phenomenon also changes due to the above-mentioned variable factors. In other words, Patent Document 1 and Patent Document 2 are unable to grasp the causes of fluctuations and are not sufficient to stabilize the weighing process.

Therefore, the present invention aims to provide a measurement control method for injection molding that can accurately detect variable factors that affect the plasticization and melting and melt-kneading properties of the measured resin, enabling stable operation of a highly accurate measurement process.

The method for controlling injection molding quantity of the present invention comprises the steps of:
A method for controlling injection molding, comprising the steps of: plasticizing and melting a resin material supplied into an injection cylinder by a rotational motion of a screw; transporting the molten resin into the injection cylinder in front of the screw; moving the screw backward by the transport of the molten resin; stopping the rotational motion of the screw at a predetermined position; and storing a predetermined amount of molten resin in the injection cylinder,
The screw is rotated based on a rotational torque command value set in a metering operation control unit, and an actual rotational torque value 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, and an actual brake torque value of the screw at that time is measured. The product of the actual rotational torque value and the actual brake torque value is set as a control torque value. When the control torque value deviates from a preset control range, torque correction is started.

In the injection molding measurement control method of the present invention,
When the cause of the control torque value falling outside the predetermined control range is a fluctuation in the actual rotational torque value, it is preferable that the torque correction be performed by increasing or decreasing the brake torque command value in a direction opposite to the fluctuation in the actual rotational torque value.

In addition, in the injection molding measurement control method of the present invention,
When the cause of the control torque value deviating from the preset control range is due to fluctuations in the actual brake torque value, it is preferable that the torque correction be performed by increasing or decreasing the rotational torque command value in an opposite direction to the fluctuations in the actual brake torque value, within an allowable range of the screw rotational peripheral speed value calculated from the screw diameter and rotation speed.

The present invention provides a method for controlling the measurement of injection molding that can accurately detect fluctuating factors that affect the plasticization and melting properties of the measured resin, enabling stable operation of a highly accurate measurement process.

1 is a conceptual diagram of an injection molding machine according to an embodiment of the present invention. FIG. 2 is a flow diagram showing a metering control method according to an embodiment of the present invention. FIG. 4 is a flowchart showing a procedure for torque correction. FIG. 13 is a diagram showing a normal state of the management torque value. FIG. 11 is a diagram showing an abnormal state of the management torque value. FIG. 11 is a diagram showing a procedure of a first torque correction. FIG. 11 is a diagram showing a procedure of a second torque correction.

Below, 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 inventions according to the claims. Furthermore, not all of the combinations of features described in the embodiments are necessarily essential to the solutions of the inventions according to the claims. Furthermore, in the present embodiments, the scales and dimensions of each component may be exaggerated, and some components may be omitted.

(injection molding machine)
First, an injection molding machine according to an embodiment of the present invention will be described with reference to FIG. 1. The injection molding machine described below is based on an in-line injection molding machine that simultaneously plasticizes, stores, and injects a resin material, but is not limited to this, and may be a pre-plasticization injection molding machine in which the plasticization, storage, and injection of the resin material are different. In addition, although a horizontal injection molding machine is used as a base, a vertical injection molding machine may be used. Furthermore, although the injection molding machine is an electric drive type for rotating and advancing the screw, it may be a hydraulic drive type injection molding machine in which the screw is rotated by a hydraulic pump and the screw is advanced and advanced by a hydraulic cylinder, or it may be a hybrid drive type injection molding machine that combines an electric drive type and a hydraulic drive type. Any injection molding machine that plasticizes and stores a resin material and injects and fills the resin material into a mold cavity can be treated as an injection molding machine according to an embodiment of the present invention.

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

The injection device 10 comprises a cylindrical injection cylinder 11 and a screw 15 arranged inside the injection cylinder 11. A plurality of heaters 12 are arranged in the injection cylinder 11, and heating is 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 forward and backward movement of the screw 15. Here, with regard to the movement of the screw 15, the direction closer to the injection molding die 20 is defined as forward F, the movement toward the forward F is defined as forward movement, the direction away from the injection molding die 20 is defined as backward B, and the movement toward the backward B is defined as backward movement.

The screw 15 has a spiral flight 16 that runs from the rear B to the front F. The spiral direction and angle of the flight 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 rotated and transported to the front F relative to the rotational direction of the screw 15. As shown in FIG. 1, the flight 16 is arranged in a single line at a fixed interval and angle, but is not limited to this. For example, the interval and angle may be variable, or multiple lines may be arranged. Alternatively, the flights 16 may be arranged in multiple lines only in a portion of the screw 15.

The screw 15 is also conical in shape, with the diameter gradually increasing from the rear B to the front F. In other words, 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 rotation of the flight 16, and shear heat is generated by the reduction in volume, and molten resin is generated by the synergistic effect of the heat from the heater 12 (called plasticization melting). The generated molten resin passes through the screw tip 17 equipped with 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 to the rear B side, stops the rotation of the screw 15 at a predetermined backward position, and holds the stopped position. The backward movement of the screw 15 is restricted (called metering back pressure) to adjust the melting and kneading property of the metered resin (called back pressure control). This is called the metering process. In the injection process, the screw 15 is advanced to inject and fill the measured amount of resin P into the injection molding die 20.

The injection molding die 20 has a fixed die 21 and a movable die 22 supported by a clamping device (not shown), which is operated by a clamping control unit 50, and the fixed die 21 and the movable die 22 are clamped to form a die cavity 24. The metered resin P stored in the injection device 10 is injected and filled into the die cavity 24 via a resin flow path 23. The molten resin that has been injected and filled is cooled, and when it is removed from the die cavity 24, it becomes an injection molded product.

Here, as the resin material used in injection molding, for example, in the case of automobile 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, various additives such as plasticizers that give flexibility to thermoplastic resins, nucleating agents and clarifying agents that control the crystallinity of crystalline resins, flame retardants that suppress combustion, antistatic agents that suppress static electricity, lubricants that improve fluidity and releasability, weathering agents and UV degradation inhibitors that suppress deterioration due to ultraviolet rays, and reinforcing agents such as glass fibers and carbon fibers are appropriately selected. In addition, thermoplastic resins such as general-purpose resins such as polypropylene (PP) resin and polyethylene (PE) resin, engineering resins such as polyamide (PA) resin and polycarbonate (PC) resin, and super engineering resins such as polyphenylene sulfide (PPS) resin and polyether ether ketone (PEEK) resin are appropriately selected. Thermoplastic resins and additives are collectively called resin materials. Instead of a thermoplastic resin, a thermosetting resin such as phenol (PF) resin or melamine (MF) resin may be used.

The injection drive unit 30 is an electrically driven type having a metering motor 31 that rotates the screw 15 and an injection motor 34 that moves the screw forward and backward. The rotational motion 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 the connector 18. As a result, the rotational motion of the metering motor 31 is transmitted to the screw 15 via the rotation transmission mechanism 32, the screw drive shaft 39, and the connector 18, resulting in the rotational motion of the screw 15. In addition, the rotational motion 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 motion into linear motion, and the screw 15 moves forward and backward via the support member 38 and the screw drive shaft 39. Here, with regard to the rotation direction of the metering motor 31, the rotation in which the resin material is transported to the forward F side by the rotation of the screw 15 is defined as forward rotation, and the rotation in the opposite direction to the forward rotation is defined as reverse rotation. Also, with regard to the rotation direction of the injection motor 34, the rotation in which the screw 15 moves forward is defined as forward rotation, and the rotation in which the screw 15 moves backward is defined as backward rotation.

Here, the metering motor 31 and the injection motor 34 are preferably AC servo motors capable of controlling the rotation direction and rotation speed with high precision, but may be inverter motors capable of simply controlling the rotation speed by manipulating the supply current with a priority on cost. The rotation transmission mechanism (32, 35) is a combination of a pulley and a belt as shown in FIG. 1, but is not limited to this. For example, it may be a combination of a drive gear and a driven gear, or it may be a combination of a chain and a sprocket. Although the ball screw mechanism 37 is one for convenience, it may be arranged in a plurality of positions above, below, left and right. Instead of the ball screw mechanism 37, for example, a conversion device combining a rack and a pinion may be used. The arrangement of the metering motor 31 and the injection motor 34 may be changed arbitrarily. It may be a hydraulic drive type using a hydraulic motor instead of the metering motor 31 and a hydraulic cylinder instead of the injection motor 34, or it may be a hybrid drive type combining an electric drive type and a hydraulic drive type.

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 unit 10 and the mold clamping unit. The metering motor 31 and the injection motor 34 are each equipped with an encoder (33, 36) that measures the rotation direction and rotation speed, and the detection signal of the encoder (33, 36) is transferred to the metering operation control unit 41 and the injection operation control unit 42. The metering operation control unit 41 and the injection operation control unit 42 are also equipped with a torque measurement function, and can measure the actual rotation torque value of the metering motor 31 and the actual brake torque value of the injection motor 34.

Based on the rotation torque command value set in the metering operation control unit 41, the metering motor 31 is operated (forward rotation) to perform metering control of the rotation operation of the screw 15 during the metering process. The actual rotation torque value of the metering motor 31 at that time is measured by the metering operation control unit 41. Similarly, based on the brake torque command value set in the injection operation control unit 42, the injection motor 34 is operated (reverse rotation) to limit the backward movement of the screw 15 during the metering process and perform back pressure control. The actual brake torque value of the injection motor 34 at that time is measured by the injection operation control unit 42. The detection signal from the encoder (33, 36) is treated as the actual rotation direction and rotation 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.

Here, the measured rotational torque and the measured brake torque are the power consumption required to drive the metering motor 31 and the injection motor 34. It is not limited to this, and for example, the ratio of the power consumption to the rated power of the metering motor 31 and the injection motor 34 (called the load factor) may be used. In the case of a hydraulic drive type, the hydraulic pressure supplied to the hydraulic motor is the measured rotational torque, and the hydraulic pressure supplied to the hydraulic cylinder is the measured brake torque. The rotation direction and rotation speed of the metering motor 31 and the injection motor 34 may be measured, for example, by attaching a rotation measurement sensor to each rotation transmission mechanism (32, 38), or by attaching a rotation measurement sensor to the screw drive shaft 39 or the ball screw mechanism 37. The position of the forward and backward movement of the screw 15 may be measured by attaching a position measurement sensor to the screw drive shaft 39 or the ball screw mechanism 37.

(Metering control method)
Next, a metering control method according to an embodiment of the present invention will be described with reference to FIG. 2 and FIG. 3. First, as shown in FIG. 2, the metering control in the metering process operates the metering motor 31 in the forward rotation direction based on a 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. The actual rotation torque value of the metering motor 31 at that time is measured by the metering operation control unit 41. The resin material supplied from the material hopper 13 is plasticized and melted by shear heat caused by the rotation operation of the screw 15, and is rotated and transported to the front F side of the screw 15. During this rotation transport, the plasticized molten resin is subjected to a kneading action. In other words, the rotational kinetic energy of the rotation operation of the screw 15 is consumed as a metering control that adjusts the plasticization melting, rotational transport, and kneading action. In other words, by measuring the actual rotation torque value during the metering process, the rotational kinetic energy can be accurately calculated, and the state of the metering control that adjusts the plasticization melting, rotational transport, and kneading action can be grasped.

In addition, the back pressure control in the metering process controls the restriction of the backward movement of the screw 15 associated with the storage of the metered resin by operating the injection motor 34 in the reverse rotation direction based on the brake torque command value set in the injection operation control unit 42. The brake torque actual measurement value of the screw 15 at that time is measured by the injection operation control unit 42. A predetermined forward rotation torque value is applied to the injection motor 34, and when the force of the backward movement of the screw 15 exceeds the forward rotation torque value, the injection motor 34 rotates in the reverse direction to maintain the forward rotation torque value, and the screw 15 retreats (called back pressure control). The forward rotation torque value applied to 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. The brake torque command value decelerates the backward speed of the screw 15, generating a speed difference (deceleration energy). This deceleration energy is consumed as back pressure control that applies pressure to the molten resin that is rotated and transported to the front F side of the screw 15 to adjust the melt kneadability and resin density of the metered resin. In other words, by measuring the actual brake torque during the metering process, the deceleration energy can be accurately calculated, and the state of the back pressure control that adjusts the melt-kneadability and resin density of the metered resin can be understood.

Furthermore, the product of the actual measured rotation torque value and the actual measured brake torque value is set as a control torque value, and this control torque value is used to control the metering process and back pressure, and to evaluate the state of the metered resin.Furthermore, the control torque value is used to correct the metering process.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 retreat speed of the screw 15, and the balance between the two energies is important.Therefore, it is preferable to control the metering process using the control torque value.

In addition, the state of plasticization adjustment of the plasticization melting, rotational transport, and kneading action, and the state of resin adjustment of melt kneadability and resin density fluctuate due to factors such as fluctuations in the temperature and supply amount of the resin material supplied, fluctuations in the resin material containing additives, fluctuations in the heating temperature of the injection device, fluctuations in the molding cycle, and fluctuations over time due to wear of screw parts and adhesion of retained resin. In addition, the retreat of the screw 15 accompanying the storage of metered resin shortens the effective screw length, which indicates the distance from the inlet (material hopper 13) to the outlet (metered resin P) of the resin material, and the state of plasticization adjustment and resin adjustment gradually deteriorates from the middle of the metering process. These phenomena were difficult to predict with conventional technology, but by using the control torque value, the fluctuations can be detected with high accuracy, corrections can be made immediately, and stable production of injection molding can be continued.

If the control torque value is within the preset control range, stable operation of the metering process is guaranteed and injection molding continues. If the control torque value exceeds the control range, torque correction is started immediately. In this case, if a fluctuation in the actual rotation torque value is confirmed, the first torque correction is performed. Also, if a fluctuation in the actual brake torque value is confirmed, the second torque correction is performed. For other situations, other corrections are considered.

As shown in Figure 3 (a), the first torque correction corrects (increases or decreases) the brake torque command value in the opposite direction to the fluctuation (decrease or increase) of the actual measured rotational torque value. This correction returns the control torque value to within the control range. After confirming that the control torque value has returned, the first torque correction is completed and safe operation of the weighing process is resumed. Note that if the control torque value does not return to within the control range even after the brake torque command value is corrected (dashed line in the figure), other corrections are considered.

As shown in FIG. 3(b), the second torque correction corrects (lowers or raises) the rotational torque command value in the opposite direction to the fluctuation (increase or decrease) of the brake torque actual measurement value. This correction returns the control torque value to 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 taken as the screw rotational speed value DN, and the allowable range of this screw rotational speed value DN = 6000 to 18000 is set. If the screw rotational 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, making it impossible to ensure stable operation of the metering process. Also, if the screw rotational speed value DN exceeds 1800, the rotational kinetic energy is too excessive, causing excessive shear heat generation and increasing the risk of thermal deterioration of the resin material, making it impossible to ensure stable operation of the metering process. Therefore, if the screw rotational speed value DN falls outside the allowable range, other corrections are considered. After confirming that the screw rotational speed value DN is within the allowable range and that the control torque value has returned to the control range, the second torque correction is completed and safe operation of the metering process is resumed. Note that if the control torque value does not return to the control range even after the rotational torque command value is corrected (dashed line in the figure), other corrections are considered.

(Control torque value)
Next, the control 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 control torque value, and Fig. 5 shows an example of an abnormal state of the control torque value. The horizontal axis shows the position of the screw 15 in the metering process, and indicates the retreating movement of the screw 15 accompanying the storage of the metered resin P from the metering start position on the left side of the figure to the metering completion position on the right side, at which the metering process ends. The vertical axis shows the torque command value/actual measurement value of the injection motor 34 and the metering motor 31, and the control torque value.

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 control the back pressure in the metering process. The brake torque actual measurement value BZ1 falls within the range between 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 to a range in which a non-defective product can be reliably obtained based on, for example, past injection molding results.

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 of the metering process. The measured rotation torque value RZ1 falls within the range between 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 in which a non-defective product can be reliably obtained based on past injection molding results.

Because the brake torque actual measurement value BZ1 and the rotational torque actual measurement value RT1 are stable, as shown in FIG. 4(c), the control torque value KZ1 is also stable, indicating a normal state of the metering process. Here, the upper limit value KTH and the lower limit value KTL are set as the control range KH, for example, within which a non-defective product can be reliably obtained based on past injection molding results. The reference value KT is the average value of the control range KH.

Next, an abnormal state of the metering process will be described with reference to FIG. 5. As shown in FIG. 5(a), the brake torque actual measurement value BZ1 is within the range between the upper limit value BTH and the lower limit value BTL, and stable back pressure control is being performed. In contrast, as shown in FIG. 5(b), the rotation torque actual measurement value RZ2 fluctuates greatly in the latter half of the metering process, deviates from the lower limit value RTL, and gradually decreases toward the completion of metering, indicating an unstable state of metering control of the screw 15. This phenomenon is likely to occur, for example, when the amount of metered resin is extremely large, the amount of retreat of the screw increases significantly, and the effective length of the screw becomes extremely short. It can also occur when the supply amount of resin material is unstable due to clogging of the material hopper 13, or when the resin material is clogged on the rear B side of the screw 15, causing a decrease in rotational transport.

Conversely, the measured rotational torque value RZ2 may also increase. For example, this may occur when a large amount of additives with a high melting point, such as glass fibers, accumulates in the screw 15 without being rotated and transported. The measured rotational torque value RZ2 may also vary greatly 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 when a resin material with a low melt viscosity contains a large amount of additives with a high melt viscosity, the plasticization melting and rotational transport in the screw 15 may fluctuate irregularly, resulting in the measured rotational torque value RZ2 showing fluctuations. In this way, by measuring the measured rotational torque value RZ2, it is possible to accurately detect fluctuations in the measurement control of the plasticization melting and rotational transport during the metering process.

The brake torque actual measurement value BZ1 is stable, but if the rotational torque actual measurement value RZ2 fluctuates, the control torque value KZ2 fluctuates as shown in FIG. 5(c). In other words, by managing the control torque value, the state of the metering control and back pressure control during the metering process can be accurately determined. Furthermore, by checking whether the actual measurement value is fluctuating on the brake torque actual measurement value or the rotational torque actual measurement value, the assumed cause related to the fluctuation during the metering process becomes clear, and appropriate correction can be made immediately to return to a normal metering process. Here, the position of the screw 15 where the control torque value KZ2 falls below the lower limit value KTL and falls outside the control range KH is set as the correction start position SH, and the metering process from this point on is corrected.

(Torque correction procedure)
Next, the correction procedure of the metering process using the management 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 of the first torque correction, and Fig. 7 shows the procedure of the second torque correction. The horizontal and vertical axes are the same as Figs. 4 and 5. As shown in Figs. 2 and 3, when the management torque value deviates from the management range KH and the rotational torque actual measurement value fluctuates, the first torque correction is performed, and when the brake torque actual measurement value fluctuates, the second torque correction is performed. In the case shown in Fig. 5, the rotational torque actual measurement value RZ2 fluctuates, so the first torque correction is performed as shown in Fig. 6.

First, as shown in FIG. 6(a), the rotational torque actual measurement value RZ2 is stable from the start of metering to the correction start position SH, so it is allowed to remain in this state. From the correction start position SH towards the completion of metering, the rotational torque actual measurement value RZ2 leaves the lower limit value RTL and gradually decreases (fluctuations towards the negative side). At the time of completion of metering, it has decreased to the rotational torque actual measurement value RZ3, showing a deviation E1 from the rotational torque command value RT. Due to the fluctuation of the rotational torque actual measurement value RZ2, as shown in FIG. 5(c), the control torque value becomes unstable and deviates from the control range KH.

Therefore, within the range from the correction start position SH to the completion of metering, a first torque correction is performed as shown in FIG. 6(b). The first torque correction corrects the brake torque command value BT set in the injection operation control unit 42 so that the management torque value returns to within the management range KH. For example, a correction is performed in which the deviation E2 (positive side) opposite to the deviation E1 (negative side) is added to the brake torque command value BT. This correction is performed continuously 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 brake torque actual measurement value BZ2 is corrected to the positive side from the correction start position SH toward the completion of metering, and shows the brake torque actual measurement value BZ3 at the completion of metering, which is opposite to the rotational torque actual measurement value RZ3. In this way, by performing a correction on the positive side opposite to the fluctuation on the negative side, the management torque value KZ3 returns to within the management range KH as shown in FIG. 6(c), and a stable metering process is resumed.

Next, the second torque correction when the actual brake torque value fluctuates will be explained with reference to FIG. 7. As shown in FIG. 7(a), the actual brake torque value BZ4 is stable from the start of metering to the correction start position SH, and from the correction start position SH toward the completion of metering, it deviates from the upper limit value RTH and gradually increases (fluctuations toward the positive side). At the completion of metering, it has increased to the actual brake torque value BZ5, showing a deviation E3 from the brake torque command value BT. Fluctuations in the actual brake torque value BZ4 cause the control torque value to become unstable and deviate from the control range KH.

Here, the fluctuation of the brake torque actual value BZ4 may occur, for example, due to the fluctuation of the heating temperature of the injection cylinder 11 or the rotation speed of the screw 15, which causes the amount of rotational transport of the resin material to fluctuate. In addition, the state of plasticization melting and rotational transport fluctuates due to the temperature fluctuation of the resin material being supplied, so the brake torque actual value BZ4 is likely to fluctuate. In addition, when a resin material that is a blend of resin materials with different melting points and melt viscosities is used, when a resin material containing a large amount of additives with different specific gravities and melting temperatures is used, or when a resin material with varying sizes and shapes is used, the state of plasticization melting and rotational transport is likely to fluctuate, resulting in fluctuation of the brake torque actual value BZ4. In addition, it may also fluctuate due to the adhesion state of the resin material that has been retained and deteriorated to the screw 15 and the injection cylinder 11.

Within the range from the correction start position SH to the completion of pressure holding, a second torque correction is performed as shown in FIG. 7(b). The second torque correction corrects the rotational torque command value RT set in the metering operation control unit 41 so that the management torque value returns to the range of the management range KH. For example, a correction is performed in which the deviation E4 (negative side) opposite to the deviation E3 (positive side) is subtracted from the rotational torque command value RT. This correction is performed continuously 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 actual rotational torque value BR4 is corrected to the negative side from the correction start position SH toward the completion of metering, and shows the actual rotational torque value RZ5 at the completion of metering, which is opposite to the actual brake torque value BZ5. In this way, by performing a correction on the negative side opposite to the fluctuation on the positive side, the management torque value KZ4 returns to the management range KH, as shown in FIG. 7(c), and a stable metering process is resumed. The second torque correction is performed within the range of 6000 to 18000, which is the screw rotation peripheral speed value DN obtained by multiplying the screw diameter D (unit: mm) by the screw rotation speed N (unit: rpm).

Here, as explained in FIG. 2 and FIG. 3, if the conditions for the first torque correction and the second torque correction are not met, and the control torque value does not return to the control range KH even after the first torque correction or the second torque correction is performed, other corrections are performed. For example, the molding cycle may be set longer to increase the residence time in the injection cylinder 11, and the resin material may be sufficiently preheated to reduce the fluctuation factors of the resin material and mitigate the impact on the metering process. Alternatively, the resin material may be sufficiently preheated or dried using a material preheating or drying device, etc., to reduce the temperature fluctuation of the resin material. Alternatively, the resin material may be replaced with a resin material with a small amount of additive fluctuation, replaced with a resin material with a uniform size, foreign matter, etc. may be completely removed from the resin material, and separation of the resin material may be avoided when the resin material is pumped using an air transporter, etc., to reduce the fluctuation of the resin material and suppress the fluctuation of the metering process. It is also necessary to consider large-scale corrections such as replacing the screw 15 with one of a different shape, periodically cleaning the screw 15 etc. to remove retained and deteriorated resin, using a larger capacity injection device, and maintaining the injection molding machine including the control device.

(effect)
In this way, the injection molding metering control method uses the product of the measured rotation torque of the metering motor 31 and the measured brake torque of the injection motor 34 to obtain a management torque value. As a result, the pass/fail state during the metering process can be accurately determined, and the fluctuating factors that affect the plasticization, melting, and melt-kneading properties of the metered resin can be accurately detected. Furthermore, an abnormal state during the metering process can be accurately detected, the assumed cause can be clearly identified, and appropriate correction can be immediately performed. This allows the metering process to be quickly restored to a normal state, and stable operation of high-quality injection molding can be provided without being affected by fluctuating factors of disturbance.

The above describes a preferred embodiment of the present invention, but the technical scope of the present invention is not limited to the scope described in the above embodiment. Various modifications and improvements can be made to the above embodiment.

REFERENCE SIGNS LIST 100 Injection molding machine 10 Injection unit 11 Injection cylinder 12 Heater 13 Material hopper 15 Screw 16 Flight 17 Screw tip 18 Connector F Front B Rear P Metered resin 20 Injection molding die 21 Fixed die 22 Movable die 23 Resin flow path 24 Die 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 to BZ5 Actual brake torque value BTH, RTH, KTH Upper limit value BTL, RTL, KTL Lower limit value RT Rotational torque command value RZ1 to RZ5 Actual rotational torque value KZ1 to KZ4 Control torque value KT Reference value KH Control range SH Correction start position E1 to E4 Deviation

Claims (3)

A method for controlling injection molding, comprising the steps of: plasticizing and melting a resin material supplied into an injection cylinder by a rotational motion of a screw; transporting the molten resin into the injection cylinder in front of the screw; moving the screw backward by the transport of the molten resin; stopping the rotational motion of the screw at a predetermined position; and storing a predetermined amount of molten resin in the injection cylinder,
a rotational torque command value set in a metering operation control unit, a rotational torque actual value of the screw at that time is measured, a retreating operation of the screw is limited based on a brake torque command value set in an injection operation control unit, a brake torque actual value of the screw at that time is measured, a product of the rotational torque actual value and the brake torque actual value is set as a control torque value, and a torque correction is initiated when the control torque value deviates from a preset control range. The injection molding measurement control method according to claim 1, wherein when the cause of the control torque value falling outside the preset control range is a fluctuation in the actual rotational torque value, the torque correction increases or decreases the brake torque command value in a direction opposite to the fluctuation in the actual rotational torque value. The injection molding measurement control method according to claim 1, wherein the torque correction, when the cause of the deviation of the control torque value from the preset control range is due to a fluctuation in the brake torque actual measurement value, increases or decreases the rotation torque command value in a direction opposite to the fluctuation in the brake torque actual measurement value within an allowable range of the screw rotation peripheral speed value calculated from the screw diameter and rotation speed.

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