Injection molding machine and method for controlling the same

Abstract

To provide an injection molding machine that can suppress variations in the density of molten resin, and a method for controlling the same.SOLUTION: A control device 53 of an injection molding machine executes a metering operation for transferring a plasticized resin to a tip side E of a cylinder 31 by rotation of a screw 35. In the metering operation, the control device 53 adjusts a position of the screw 35 in a front-rear direction by feedback-controlling a screw driver 36 based on a measured pressure so as to make the measured pressure measured by a load cell 37 into a target pressure. The feedback control includes a first control having a high sensitivity to a measurement pressure, and a second control subsequent to the first control having a low sensitivity to the measurement pressure.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an injection molding machine and a control method thereof. [Background technology]

[0002] Patent Document 1 discloses an example of a conventional injection molding machine. The injection molding machine rotates a screw in a cylinder to plasticize the resin while transferring it forward, and accumulates the molten resin at the tip of the cylinder. The injection molding machine then advances the screw to inject and fill the molten resin into the cavity of a mold.

[0003] Injection molding machines use load cells to measure the backward pressure applied to the screw. During the metering operation, which meters the amount of resin to be injected and filled into the mold cavity, the measured pressure indicates the back pressure applied to the molten resin.

[0004] When the metering operation starts, the injection molding machine rotates the screw. The screw moves backward due to the reaction force of the molten resin transported forward by the rotation of the screw. At this time, the injection molding machine adjusts the forward / backward position of the screw using feedback control so that the measured pressure (back pressure) reaches a specified target value. In this way, the injection molding machine suppresses variations in the density of the molten resin and stabilizes the quality of the molded product. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 9-11289 Summary of the Invention [Problem to be solved by the invention]

[0006] During the metering operation, if a disturbance occurs, such as the resin pellets being caught between the resin inlet of the cylinder and the screw, the measured pressure may temporarily change even though there is no substantial change in the back pressure. This may cause the injection molding machine to change the position of the screw in the front-rear direction, causing the back pressure to fluctuate. Therefore, in order to suppress the fluctuation of the back pressure caused by disturbances occurring during the metering operation, the injection molding machine sets the sensitivity to the measured pressure in the feedback control to be relatively low.

[0007] When the metering operation starts, the screw rotates and the molten resin is transported forward. When the molten resin accumulates at the tip of the cylinder, the back pressure rises rapidly. At this time, the injection molding machine has low sensitivity to the measured pressure in feedback control, so the adjustment of the forward / backward position of the screw in response to changes in the measured pressure is delayed, and an overshoot occurs in which the back pressure greatly exceeds the target value. As a result, a large back pressure is applied to the molten resin, which may cause the density of the molten resin to vary.

[0008] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide an injection molding machine and a control method thereof that can suppress variations in density of molten resin. [Means for solving the problem]

[0009] In order to achieve the above-mentioned object, an injection molding machine according to one embodiment of the present invention is an injection molding machine having a cylinder, a screw housed in the cylinder, a screw drive device that moves the screw in a forward / backward direction, a measuring device that measures the backward pressure applied to the screw, and a control device that controls the screw drive device, wherein, during a metering operation in which plasticized resin is transferred to the tip side of the cylinder by rotating the screw, the control device adjusts the forward / backward position of the screw by feedback controlling the screw drive device based on the measured pressure so that the pressure measured by the measuring device (hereinafter referred to as the "measured pressure") becomes a target pressure, and the feedback control includes multiple controls with different sensitivities to the measured pressure. Effect of the Invention

[0010] According to the present invention, the feedback control includes a plurality of controls with different sensitivities to the measurement pressure. Therefore, during a period in which the measurement pressure changes rapidly and greatly in the metering operation, the position of the screw in the forward and backward directions can be quickly adjusted with respect to the measurement pressure by performing a control with high sensitivity to the measurement pressure. Also, during a period in which the change in the measurement pressure is small in the metering operation, the position of the screw in the forward and backward directions can be prevented from being quickly adjusted with respect to the measurement pressure by performing a control with low sensitivity to the measurement pressure. This enables feedback control according to the state of change in the measurement pressure, and makes it possible to reduce the overshoot of the pressure (back pressure) applied to the resin at the tip side of the cylinder and to suppress the fluctuation of the back pressure caused by disturbances. Therefore, the variation in density of the molten resin can be suppressed. [Brief description of the drawings]

[0011] [Figure 1] 1 is a diagram showing a schematic configuration of an injection molding machine according to an embodiment of the present invention; [Diagram 2] 2 is a diagram showing a schematic configuration of an injection device and a control unit of the injection molding machine of FIG. 1. [Diagram 3] 4 is an example of a graph of the back pressure measured when the metering operation according to the present invention is performed in the injection molding machine of FIG. 1. [Figure 4] 2 is an example of a graph of back pressure measured when a conventional metering operation is performed in the injection molding machine of FIG. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] An injection molding machine according to one embodiment of the present invention will be described below with reference to Figures 1 to 4. An injection molding machine plasticizes a resin, which is a molding material, and injects and fills the resin into a mold cavity to produce a molded product.

[0013] Fig. 1 is a diagram showing a schematic configuration of an injection molding machine according to an embodiment of the present invention. Fig. 2 is a diagram showing a schematic configuration of an injection device and a control unit of the injection molding machine of Fig. 1. Fig. 3 is an example of a graph of the back pressure (measured pressure) measured when the metering operation according to the present invention is performed in the injection molding machine of Fig. 1. Fig. 4 is an example of a graph of the back pressure (measured pressure) measured when the conventional metering operation is performed in the injection molding machine of Fig. 1.

[0014] As shown in FIG. 1, an injection molding machine 1 according to this embodiment includes a mold clamping device 2, an injection device 3, an ejection device 4, a control unit 5, and a base .

[0015] The mold clamping device 2 is disposed on a base 7. The mold clamping device 2 opens, closes, and clamps a fixed-side mold 81 and a movable-side mold 82. The fixed-side mold 81 and the movable-side mold 82 form a cavity 83.

[0016] The mold clamping device 2 has a fixed die plate 21, a movable die plate 22, and a mold clamping drive mechanism 23. A fixed side mold 81 is attached to the fixed die plate 21. A movable side mold 82 is attached to the movable die plate 22. The mold clamping drive mechanism 23 clamps the fixed side mold 81 and the movable side mold 82 in the front-rear direction (left-right direction in FIG. 1) by the fixed die plate 21 and the movable die plate 22 to generate a mold clamping force.

[0017] The injection device 3 is disposed on a base 7. The injection device 3 includes a cylinder 31, a nozzle 32, a resin supply unit 33, a heater 34, a screw 35, a screw driver 36, and a load cell 37.

[0018] The cylinder 31 has a cylindrical shape. The cylinder 31 is arranged along the front-rear direction. The nozzle 32 is attached to the tip of the cylinder 31. The resin supply unit 33 is arranged at the rear end of the cylinder 31. The resin supply unit 33 has a hopper that contains powdered or granular resin. The resin supply unit 33 supplies resin to the cylinder 31. The heater 34 is, for example, a band heater, and is arranged on the outer circumferential surface of the cylinder 31. The heater 34 heats the cylinder 31.

[0019] The screw 35 is housed in the cylinder 31. The screw 35 is rotatable within the cylinder 31 and is movable in the forward and backward directions. The screw 35 has a screw body 35a and a backflow prevention portion 35b. The screw body 35a has a spiral flight. The backflow prevention portion 35b forms a resin flow path for transporting resin from the rear to the front when the screw 35 retracts, and closes the resin flow path when the screw 35 advances.

[0020] The screw driving device 36 rotates and moves the screw 35 in the forward and backward directions. The screw driving device 36 has a metering servo motor 361, a metering timing belt 362, a metering pulley 363, an injection servo motor 364, an injection timing belt 365, a ball screw mechanism 366, a metering encoder 367, and an injection encoder 368.

[0021] The metering servo motor 361 is a drive device for rotating the screw 35. The rotation of an output pulley 361a of the metering servo motor 361 is transmitted to a metering pulley 363 via a metering timing belt 362. The metering pulley 363 is fixed coaxially to the screw 35. The rotation of the metering pulley 363 rotates the screw 35 about its axis.

[0022] The injection servo motor 364 is a drive device for moving the screw 35 in the front-rear direction. The rotation of the output pulley 364a of the injection servo motor 364 is transmitted to the injection pulley 366a via the injection timing belt 365. The injection pulley 366a is coaxially fixed to the screw shaft 366b, and the screw shaft 366b is screwed into the nut portion 366c. The injection pulley 366a, the screw shaft 366b, and the nut portion 366c constitute a ball screw mechanism 366. The rotation of the injection pulley 366a rotates the screw shaft 366b about its axis. The rotation of the screw shaft 366b moves the nut portion 366c in the axial direction (front-rear direction). The movement of the nut portion 366c causes the screw 35 connected to the nut portion 366c to advance or retreat.

[0023] The metering encoder 367 measures the rotational position of the metering servo motor 361 and outputs it as a rotational position output A1. The control device 53 of the control unit 5 obtains the rotational speed R of the screw 35 based on the rotational position output A1.

[0024] The injection encoder 368 measures the rotational position of the injection servo motor 364 and outputs it as a rotational position output A2. The control device 53 of the control unit 5 obtains the front-rear position L and the moving speed V of the screw 35 based on the rotational position output A2.

[0025] The load cell 37 is a measuring device that measures the backward pressure applied to the screw 35 and outputs it as a pressure output A3. The control device 53 of the control unit 5 acquires the measured pressure P based on the pressure output A3. The measured pressure P indicates the pressure applied to the resin at the tip side E of the cylinder 31 (hereinafter also referred to as "back pressure"). The tip side E is in front of the screw 35 in the cylinder 31.

[0026] The ejection device 4 has an ejection mechanism 41. The ejection mechanism 41 drives an ejector pin (not shown) to eject it into the cavity 83, and ejects the molded product from the movable mold .

[0027] The control unit 5 controls the overall operation of the injection molding machine 1. The control unit 5 has a storage device 51, a display operation device 52, a control device 53, a metering servo amplifier 54, and an injection servo amplifier 55.

[0028] The storage device 51 is a rewritable storage medium such as a hard disk drive or a non-volatile memory. The storage device 51 stores condition values ​​for various operations such as a mold closing operation, an injection operation, a metering operation, and a mold opening operation included in a molding operation for forming a molded product. The condition values ​​include, for example, a target value (target rotation speed Rt) of the rotation speed R of the screw 35 used in the metering operation and a target value (target pressure Pt) of the measurement pressure P.

[0029] The display operation device 52 includes, for example, a display device 52a configured with a flat panel display such as a liquid crystal display, and an input device 52b equipped with a touch panel and hardware keys arranged on the display surface of the display device 52a. The display device 52a and the input device 52b may be, for example, a tablet device or a notebook computer connected to the control device 53 by wireless communication.

[0030] The control device 53 is composed of a microcomputer, etc. The control device 53 executes the molding operation.

[0031] Next, an example of the molding operation executed by the control device 53 will be described.

[0032] The control device 53 executes a purge operation and measures the amount of resin to be injected for the first time in preparation for the molding operation.

[0033] In the molding operation, the control device 53 controls the mold clamping drive mechanism 23 to press the movable mold 82 against the fixed mold 81 to clamp the mold (mold closing operation). Next, the control device 53 controls the screw drive device 36 to move the screw 35 forward (injection operation (filling)). This causes the resin at the tip side E of the cylinder 31 to fill the cavity 83. Next, the control device 53 controls the screw drive device 36 to move the screw 35 back and forth so that a predetermined pressure (holding pressure) is applied to the resin in the cavity 83 (injection operation (holding pressure)). In the injection operation (holding pressure), the measured pressure P indicates the holding pressure.

[0034] Next, the control device 53 controls the screw driver 36 to rotate the screw 35 at the target rotation speed Rt to transfer the resin to the tip side E of the cylinder 31 while plasticizing it, and measures the resin required for one injection (measurement operation). The measurement operation is also called a plasticization operation. In the measurement operation, the screw 35 retreats due to the reaction force of the resin transferred to the tip side E, and the control device 53 controls the screw driver 36 to adjust the front-rear position L of the screw 35 so that the target pressure Pt is applied to the resin at the tip side E. In parallel with the measurement operation, the control device 53 waits until the resin in the cavity 83 cools and hardens (cooling operation).

[0035] Then, when the cooling operation is completed, the control device 53 controls the mold clamping drive mechanism 23 to open the fixed side mold 81 and the movable side mold 82 (mold opening operation), and controls the ejection mechanism 41 to remove the molded product from the cavity 83 by the ejector pin (removal operation).

[0036] The steps from the mold closing operation to the removal operation constitute one molding operation. The control device 53 repeatedly executes the molding operation to mold a molded product.

[0037] Next, an example of a measuring operation executed by the control device 53 will be described.

[0038] In the metering operation, the control device 53 adjusts the front-rear position L of the screw 35 by feedback-controlling the screw driver 36 based on the measured pressure P so that the measured pressure P becomes the target pressure Pt.

[0039] The feedback control performed by the control device 53 in the metering operation is PID control including proportional control, integral control, and differential control. This feedback control includes a first control, a second control following the first control, and a third control following the second control. The first control has high sensitivity to the measured pressure P. The second control has lower sensitivity to the measured pressure P than the first control. The third control has lower sensitivity to the measured pressure P than the second control.

[0040] A parameter related to the PID control of the first control is different from a parameter related to the PID control of the second control. For example, the proportional band in the first control is narrower than the proportional band in the second control. The proportional band is a parameter of the proportional control. Also, the integral time in the first control may be shorter than the integral time in the second control. The integral time is a parameter of the integral control. Also, the differential time in the first control may be longer than the differential time in the second control. The differential time is a parameter of the differential control.

[0041] The parameters related to the PID control of the second control are different from the parameters related to the PID control of the third control. For example, the proportional band in the second control is narrower than the proportional band in the third control. Also, the integral time in the second control may be shorter than the integral time in the third control. Also, the differential time in the second control may be longer than the differential time in the third control.

[0042] The control device 53 starts the metering operation at time T0, and controls the screw driver 36 to rotate the screw 35. The screw 35 is at the metering start position at time T0. The control device 53 restricts the screw 35 from moving forward from the metering start position during the metering operation. The rotation speed R of the screw 35 gradually increases, and becomes constant when it reaches the target rotation speed Rt.

[0043] The control device 53 starts the first control from time T0. The screw 35 is at the metering start position at time T0 and is restricted from moving forward from the metering start position. Therefore, the measurement pressure P does not increase until the resin accumulates on the tip side E of the cylinder 31.

[0044] As the screw 35 rotates, the plasticized resin is transferred to the tip side E of the cylinder 31. At time T1, the resin accumulates at the tip side E, and a backward pressure is applied to the screw 35 due to the reaction force of the resin, causing a rapid and large increase in the measured pressure P. Since the first control has high sensitivity to the measured pressure P, when the measured pressure P reaches the target pressure Pt at time T2, the control device 53 quickly adjusts the front-to-rear position L of the screw 35 based on the measured pressure P. This prevents the measured pressure P (back pressure) from exceeding the target pressure Pt by overshooting. The reaction force of the resin transferred to the tip side E causes the screw 35 to start moving backward.

[0045] The control device 53 switches from the first control to the second control at time T3 when a predetermined switching delay time tw has elapsed since time T2. Since the second control has a lower sensitivity to the measured pressure P than the first control, even if the measured pressure P temporarily changes due to a disturbance after time T3, the control device 53 does not quickly adjust the front-rear position L of the screw 35 based on the measured pressure P. This suppresses fluctuations in the back pressure caused by disturbances.

[0046] The control device 53 switches from the second control to the third control at time Ty immediately before the end of the metering operation. In the third control, the control device 53 controls the measured pressure P, the rotation speed R of the screw 35, and the moving speed V of the screw 35 to approach 0 and the screw 35 to stop at the metering completion position. Note that the third control has a lower sensitivity to the measured pressure P than the first control and the second control, and therefore, similar to the second control, fluctuations in the back pressure caused by disturbances are suppressed.

[0047] Then, at time Tz, when the screw 35 reaches the metering completion position and the amount of resin required for one injection is accumulated on the tip side E of the cylinder 31, the control device 53 ends the metering operation.

[0048] FIG. 3 shows an example of a graph of the measured pressure P (back pressure), the rotation speed R of the screw 35, and the moving speed V (retraction speed) of the screw 35 measured when the above-mentioned metering operation is performed in the injection molding machine 1. In this metering operation, the first control is performed from time T0 to time T3, the second control is performed from time T3 to time Ty, and the third control is performed from time Ty to time Tz. As shown in FIG. 3, when the resin accumulates at the tip side E of the cylinder 31 (time T1), the measured pressure P rises rapidly and reaches the target pressure Pt (time T2). However, the measured pressure P does not greatly exceed the target pressure Pt, and remains at a value close to the target pressure Pt until just before the end of the metering operation (time Ty). The third control is performed from time Ty to time Tz when the metering operation ends. As a result, the screw 35 reaches the metering completion position, and the metering operation is completed. The third control has a lower sensitivity than the first control and the second control.

[0049] FIG. 4 shows an example of a graph of the measured pressure P (back pressure), the rotation speed R of the screw 35, and the moving speed V (retraction speed) of the screw 35 measured when a conventional metering operation is performed in the injection molding machine 1. In the conventional metering operation, only the second control is performed from time T0 to time Tz. As shown in FIG. 4, when resin accumulates at the tip side E of the cylinder 31 (time T1), the measured pressure P rises rapidly and reaches the target pressure Pt, greatly exceeding the target pressure Pt. Then, the measured pressure P approaches the target pressure Pt after repeating large fluctuations, and thereafter, remains at a value close to the target pressure Pt until just before the end of the metering operation (time Ty). Then, after the time Ty, the rotation speed R of the screw 35 and the moving speed V of the screw 35 approach 0, the screw 35 stops at the metering completion position, and the metering operation ends (time Tz).

[0050] As described above, the injection molding machine 1 includes the cylinder 31, the screw 35 housed in the cylinder 31, the screw driver 36 for moving the screw 35 in the front-rear direction, the load cell 37 for measuring the rearward pressure applied to the screw 35, and the control device 53 for controlling the screw driver 36. In a measurement operation in which the plasticized resin is transferred to the tip side E of the cylinder 31 by the rotation of the screw 35 and measured, the control device 53 adjusts the front-rear position L of the screw 35 by feedback-controlling the screw driver 36 based on the measured pressure P so that the measured pressure P measured by the load cell 37 becomes the target pressure Pt. The feedback control includes a first control having a high sensitivity to the measured pressure P, and a second control having a low sensitivity to the measured pressure P subsequent to the first control.

[0051] According to the injection molding machine 1, the measured pressure P rises rapidly immediately after the start of the metering operation, but by performing the first control with high sensitivity to the measured pressure P, the position L of the screw 35 in the front-rear direction can be quickly adjusted with respect to the measured pressure P, and an overshoot in the back pressure can be reduced. Furthermore, after the metering operation progresses and the change in the measured pressure P becomes relatively small, the second control with low sensitivity to the measured pressure P can be performed to suppress fluctuations in the back pressure caused by disturbances. Therefore, the injection molding machine 1 can suppress variations in the density of the molten resin.

[0052] Furthermore, the control device 53 switches from the first control to the second control when the switching delay time tw has elapsed since the measured pressure P reached the target pressure Pt. In this manner, the period of the first control and the period of the second control can be easily adjusted according to the configuration of each device and the configuration of the mold. The control device 53 may switch from the first control to the second control when the measured pressure P reaches the target pressure Pt.

[0053] Alternatively, the control device 53 may switch from the first control to the second control when the screw 35 starts to retract from the metering start position, or when the switching delay time tw has elapsed since the screw 35 started to retract from the metering start position.

[0054] Alternatively, the control device 53 may switch from the first control to the second control when the rotational speed R of the screw 35 reaches the target rotational speed Rt, or when the switching delay time tw has elapsed since the rotational speed R of the screw 35 reached the target rotational speed Rt.

[0055] Moreover, the control device 53 may determine the timing of switching from the first control to the second control in accordance with the target rotation speed Rt.

[0056] For example, when the target rotation speed Rt is 100 revolutions per minute or less, the control device 53 switches from the first control to the second control when the measured pressure P reaches the target pressure Pt. When the target rotation speed Rt is greater than 100 revolutions per minute, the control device 53 switches from the first control to the second control when the switching delay time tw has elapsed since the measured pressure P reached the target pressure Pt, and uses a value obtained by dividing the target rotation speed Rt by 300 (tw=Rt / 300 [seconds]) as the switching delay time tw.

[0057] For example, when the target rotation speed Rt is 100 revolutions per minute or less, the control device 53 switches from the first control to the second control when the screw 35 starts to retreat from the metering start position. When the target rotation speed Rt is greater than 100 revolutions per minute, the control device 53 switches from the first control to the second control when the switching delay time tw has elapsed since the screw 35 started to retreat from the metering start position, and uses a value obtained by dividing the target rotation speed Rt by 300 (tw=Rt / 300 [seconds]) as the switching delay time tw.

[0058] For example, when the target rotation speed Rt is 100 revolutions per minute or less, the control device 53 switches from the first control to the second control when the rotation speed R of the screw 35 reaches the target rotation speed Rt. When the target rotation speed Rt is greater than 100 revolutions per minute, the control device 53 uses a value obtained by dividing the target rotation speed Rt by 600 (tw=Rt / 600 [seconds]) as the switching delay time tw when the switching delay time tw has elapsed since the rotation speed R of the screw 35 reached the target rotation speed Rt.

[0059] Furthermore, the feedback control performed in the metering operation includes proportional control, and the proportional band in the first control is narrower than the proportional band in the second control. The feedback control performed in the metering operation includes integral control, and the integral time in the first control is smaller than the integral time in the second control. The feedback control performed in the metering operation includes differential control, and the differential time in the first control is larger than the differential time in the second control. In this manner, the sensitivity to the measured pressure P can be adjusted relatively easily by the parameters used in the PID control. Note that the sensitivity to the measured pressure P may also be adjusted by parameters other than these parameters.

[0060] In the injection molding machine 1, the control device 53 performs feedback control based on the measurement pressure P in the metering operation, which includes a first control having a high sensitivity to the measurement pressure P, and a second control having a low sensitivity to the measurement pressure P following the first control. The feedback control may include a first control having a low sensitivity to the measurement pressure P, and a second control having a high sensitivity to the measurement pressure P following the first control. The feedback control may include a plurality of controls having different sensitivities. In this manner, during a period in which the measurement pressure P changes rapidly and significantly in the metering operation, the position L of the screw 35 in the front-rear direction can be quickly adjusted with respect to the measurement pressure P by performing a control with a high sensitivity to the measurement pressure P. Also, during a period in which the change in the measurement pressure P is small in the metering operation, the position L of the screw 35 in the front-rear direction can be suppressed from being quickly adjusted with respect to the measurement pressure P by performing a control with a low sensitivity to the measurement pressure P. This enables feedback control according to the change in the measured pressure P, making it possible to reduce overshoot of the pressure (back pressure) applied to the resin at the tip side E of the cylinder 31 and suppress fluctuations in the back pressure caused by disturbances. Therefore, it is possible to suppress variations in the density of the molten resin.

[0061] Although the embodiments of the present invention have been described above, the present invention is not limited to these examples. Any addition, deletion, or design change of components by a person skilled in the art to the above-mentioned embodiments, or any combination of features of the embodiments, is also included in the scope of the present invention as long as it does not deviate from the spirit of the present invention. [Explanation of symbols]

[0062] 1... injection molding machine, 2... mold clamping device, 21... fixed die plate, 22... movable die plate, 23... mold clamping drive mechanism, 3... injection device, 31... cylinder, 32... nozzle, 33... resin supply section, 34... heater, 35... screw, 35a... screw body, 35b... backflow prevention section, 36... screw drive device, 361... metering servo motor, 361a... output pulley, 362... metering timing belt, 363... metering pulley, 364... injection servo motor, 364a... output pulley, 365... injection timing belt imprinting belt, 366...ball screw mechanism, 366a...injection pulley, 366b...screw shaft, 366c...nut portion, 367...measuring encoder, 368...injection encoder, 37...load cell, 4...ejection device, 41...ejection mechanism, 5...control unit, 51...storage device, 52...display operation device, 52a...display device, 52b...input device, 53...control device, 54...measuring servo amplifier, 55...injection servo amplifier, 7...base, 81...fixed side mold, 82...movable side mold, 83...cavity, E...tip side

Claims

1. An injection molding machine having a cylinder, a screw housed in the cylinder, a screw drive device that moves the screw in a forward and backward direction, a measuring device that measures a backward pressure applied to the screw, and a control device that controls the screw drive device, the control device, in a metering operation in which the plasticized resin is transferred to the tip side of the cylinder by the rotation of the screw, adjusts the position of the screw in the front-rear direction by feedback-controlling the screw drive device based on the pressure measured by the measuring device (hereinafter referred to as the "measured pressure") so that the pressure becomes a target pressure; 4. The injection molding machine according to claim 1, wherein the feedback control includes a plurality of controls having different sensitivities to the measured pressure.

2. 2. The injection molding machine according to claim 1, wherein the feedback control includes a first control having a high sensitivity to the measurement pressure, and a second control subsequent to the first control having a low sensitivity to the measurement pressure.

3. 2. The injection molding machine according to claim 1, wherein the feedback control includes a first control having a low sensitivity to the measurement pressure, and a second control subsequent to the first control having a high sensitivity to the measurement pressure.

4. 4. The injection molding machine according to claim 2, wherein the control device switches from the first control to the second control when the measured pressure reaches the target pressure, or when a switching delay time has elapsed since the measured pressure reached the target pressure.

5. 4. The injection molding machine according to claim 2, wherein the control device switches from the first control to the second control when the screw starts to retract from a metering start position, or when a switching delay time has elapsed since the screw started to retract from the metering start position.

6. 4. The injection molding machine according to claim 2, wherein the control device switches from the first control to the second control when the rotation speed of the screw reaches a target rotation speed, or when a switching delay time has elapsed since the rotation speed of the screw reached the target rotation speed.

7. A method for controlling an injection molding machine having a cylinder, a screw housed in the cylinder, a screw driving device for moving the screw in a forward and backward direction, and a measuring device for measuring a backward pressure applied to the screw, comprising the steps of: during a metering operation in which the plasticized resin is transferred to the tip side of the cylinder by the rotation of the screw, the screw drive device is feedback-controlled based on the measured pressure so that the pressure measured by the measuring device (hereinafter referred to as the "measured pressure") becomes a target pressure, thereby adjusting the position of the screw in the forward / backward direction; a control method for an injection molding machine, the control method comprising the steps of: performing a plurality of controls having different sensitivities to the measured pressure in the feedback control;

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