Control device for injection molding machine and control method for injection molding machine

Abstract

A control device (12) of an injection molding machine (10) according to an aspect is provided with: a first motor control unit (90) that moves an injection member (24) in a first direction while gradually reducing a torque of an injection motor (62); a second motor control unit (92) that moves the injection member (24) in a second direction while gradually reducing a torque of the injection motor (62); and a zero-point correction unit (94) that corrects zero point (P0) of a pressure sensor (48) on the basis of a resin pressure generated when movement in the first direction of the injection member (24) stops and a resin pressure generated when movement in the second direction of the injection member (24) stops.

Description

Injection molding machine control device and injection molding machine control method

[0001] The present disclosure relates to a control device for an injection molding machine and a control method for an injection molding machine.

[0002] An injection molding machine includes an injection cylinder, a screw, and a pressure sensor. Resin is supplied to the injection cylinder. The screw is inserted into the injection cylinder. The pressure sensor is used to detect the pressure that the screw applies to the resin in the injection cylinder.

[0003] A method for correcting the zero point of a pressure sensor has been proposed (Japanese Patent Laid-Open Publication No. 9-117946).

[0004] Recently, there has been a demand for a technology that can more efficiently correct the zero point of a pressure sensor.

[0005] A first aspect of the present disclosure is a control device for an injection molding machine including an injection member inserted into an injection cylinder and movable within the injection cylinder, an injection motor that moves the injection member, and a pressure sensor that detects a pressure of a resin within the injection cylinder, the control device including: a first motor control unit that controls the injection motor so that a torque gradually decreases from a first predetermined torque, thereby moving the injection member in a first direction; a second motor control unit that controls the injection motor so that a torque gradually decreases from a second predetermined torque, when movement of the injection member in the first direction stops, thereby moving the injection member in a second direction opposite to the first direction; and a zero point correction unit that corrects a zero point of the pressure sensor based on a first pressure detected by the pressure sensor when movement of the injection member in the first direction stops and a second pressure detected by the pressure sensor when movement of the injection member in the second direction stops.

[0006] A second aspect of the present disclosure is a control device for an injection molding machine including an injection member inserted into an injection cylinder and movable within the injection cylinder, an injection motor that moves the injection member, and a pressure sensor that detects the pressure of resin within the injection cylinder, the control device including: a first motor control unit that controls the injection motor so that torque gradually increases from a first predetermined torque, thereby moving the injection member in a first direction; a second motor control unit that controls the injection motor so that torque gradually increases from a second predetermined torque, thereby moving the injection member in a second direction opposite to the first direction; and a zero point correction unit that corrects a zero point of the pressure sensor based on a first pressure detected by the pressure sensor when the injection member starts to move in the first direction and a second pressure detected by the pressure sensor when the injection member starts to move in the second direction.

[0007] A third aspect of the present disclosure is a control method for an injection molding machine including an injection member inserted into an injection cylinder and movable within the injection cylinder, an injection motor that moves the injection member, and a pressure sensor that detects a pressure of a resin within the injection cylinder, the control method including: a first motor control step of controlling the injection motor so that a torque gradually decreases from a first predetermined torque, thereby moving the injection member in a first direction; a second motor control step that is started when the injection member stops in the first motor control step, and of controlling the injection motor so that the torque gradually decreases from a second predetermined torque, thereby moving the injection member in a second direction opposite to the first direction; and a zero point correction step of correcting a zero point of the pressure sensor based on a first pressure detected by the pressure sensor when movement of the injection member in the first direction stops in the first motor control step, and a second pressure detected by the pressure sensor when movement of the injection member in the second direction stops in the second motor control step.

[0008] A fourth aspect of the present disclosure is a control method for an injection molding machine including an injection member inserted into an injection cylinder and movable within the injection cylinder, an injection motor that moves the injection member, and a pressure sensor that detects a pressure of resin within the injection cylinder, the control method including: a first motor control step of controlling the injection motor so that torque gradually increases from a first predetermined torque, thereby moving the injection member in a first direction; a second motor control step of controlling the injection motor so that torque gradually increases from a second predetermined torque, thereby moving the injection member in a second direction opposite to the first direction; and a zero point correction step of correcting a zero point of the pressure sensor based on a first pressure detected by the pressure sensor when the injection member starts to move in the first motor control step, and a second pressure detected by the pressure sensor when the injection member starts to move in the second motor control step.

[0009] FIG. 1 is an overall configuration diagram of an injection molding system according to one embodiment. FIG. 2 is a schematic diagram showing the configuration of an injection device. FIG. 3 is a block diagram of a control device. FIG. 4A is a number line illustrating the zero point of a pressure sensor, the absolute value of a first pressure, and the absolute value of a second pressure. FIG. 4B is a number line illustrating the zero point, the absolute value of the first pressure, and the absolute value of the second pressure after adjustment by a zero point correction unit. FIG. 5 is a flowchart illustrating a control method for an injection molding machine.

[0010] If the zero point of the pressure sensor that detects the resin pressure is misaligned, it will have a negative impact on the quality of the molded products produced by the injection molding machine. Therefore, it is preferable to correct the zero point of the pressure sensor. Furthermore, the shorter the time required to correct the zero point of the pressure sensor, the better.

[0011] [One embodiment] An injection molding machine control device and an injection molding machine control method according to one embodiment will be described with reference to the drawings. In the following description, components having the same or similar functions will be assigned the same reference numerals. Duplicate descriptions of those components may be omitted.

[0012] Fig. 1 is an overall configuration diagram of an injection molding system SYS according to this embodiment. The direction from the right side of Fig. 1 to the left side of Fig. 1 is referred to as a first direction D1. The direction from the left side of Fig. 1 to the right side of Fig. 1 is referred to as a second direction D2. For convenience of explanation, the left side in Fig. 1 may be referred to as the front side, and the right side in Fig. 1 may be referred to as the rear side.

[0013] The term "injection member" as used herein refers to a member that is inserted into the injection cylinder 22 (see FIG. 2) of the injection molding machine 10 and moves within the injection cylinder 22 to inject resin into the cavity 20c of the mold 20. In this embodiment, the injection member 24 is configured by a screw 24A, but is not limited to this. For example, the injection member 24 may be configured by a plunger (not shown).

[0014] In this application, the term "automatic purging" refers to a predetermined operation that is automatically performed by the injection molding machine 10 to discharge resin from inside the injection cylinder 22. The predetermined operation is, for example, one or more reciprocating motions of the injection member 24 along the axis LA (see FIG. 2) of the injection cylinder 22.

[0015] The injection molding system SYS includes an injection molding machine 10 and a control device 12 .

[0016] The injection molding machine 10 includes a mold clamping device 14 , an injection device 16 , and a machine base 18 .

[0017] The mold clamping device 14 is a device that applies a mold clamping force to the mold 20. The mold clamping device 14 is supported by a machine base 18. The mold clamping device 14 opens and closes the mold 20. The mold clamping device 14 applies a mold clamping force to the mold 20 so that the mold 20 does not open. The mold 20 forms a cavity 20c in a closed state. Figure 1 illustrates the mold 20 in a closed state. A more detailed description of the mold clamping device 14 will be omitted.

[0018] The injection device 16 is a device that plasticizes resin and injects the plasticized resin into the cavity 20c of the mold 20. The injection device 16 is supported by a machine base 18. The injection molding machine 10 produces a molded product by solidifying the resin that has been filled into the cavity 20c by the injection device 16.

[0019] FIG. 2 is a schematic diagram showing the configuration of the injection device 16.

[0020] The injection device 16 includes an injection cylinder 22 , an injection member 24 , a front plate 26 , a rear plate 28 , a pusher plate 30 , and a slide mechanism 32 .

[0021] The injection cylinder 22 is a cylindrical member. The axis LA of the injection cylinder 22 is parallel to the first direction D1 and the second direction D2.

[0022] A nozzle 34 is provided at the front end (tip) of the injection cylinder 22. The nozzle 34 has an injection port 34p. The injection port 34p is an opening for injecting the resin in the injection cylinder 22 into the cavity 20c.

[0023] A hopper 36 is provided at the rear end of the injection cylinder 22. The hopper 36 stores resin. The hopper 36 also supplies the stored resin into the injection cylinder 22.

[0024] In this embodiment, the injection member 24 is constituted by the screw 24A. The screw 24A has a screw head 24a, a flight portion 24b, and a base end portion 24c. The screw head 24a is located at the front end (tip end) of the screw 24A. The flight portion 24b is a spiral portion formed on the body of the screw 24A. The flight portion 24b shears the resin in the injection cylinder 22 in response to the rotation of the screw 24A by the first drive unit 50 described below. The base end portion 24c is located at the rear end of the screw 24A. The axis LA of the injection cylinder 22 coincides with the axis of the injection member 24.

[0025] The front plate 26 is located behind the injection cylinder 22. The front plate 26 supports the injection cylinder 22. The injection member 24 passes through the front plate 26. A base end 24c of the injection member 24 is located rearward of the front plate 26.

[0026] The rear plate 28 is located behind the front plate 26. A predetermined gap is provided between the rear plate 28 and the front plate 26.

[0027] The pusher plate 30 is provided between the front plate 26 and the rear plate 28 .

[0028] The slide mechanism 32 includes a rail 38 and a slider 40. The rail 38 extends in a direction along the axis LA. The slider 40 is movable along the rail 38. The slider 40 supports the pusher plate 30. Therefore, the pusher plate 30 is movable along the rail 38.

[0029] The front plate 26, the rear plate 28, and the slide mechanism 32 are provided on a flat base 42. The front plate 26, the rear plate 28, and the base 42 may be integrally molded.

[0030] The injection unit 16 includes a spline bushing 44 , a screw sleeve 46 , a pressure sensor 48 , a first drive unit 50 , and a second drive unit 52 .

[0031] The spline bushing 44 supports the base end portion 24 c of the injection member 24. For example, the base end portion 24 c of the injection member 24 has a male spline (not shown). In contrast, the spline bushing 44 has a female spline (not shown). The male spline of the base end portion 24 c and the female spline of the spline bushing 44 are fitted together, so that the spline bushing 44 supports the base end portion 24 c of the injection member 24.

[0032] The screw sleeve 46 is provided between the pusher plate 30 and the spline bushing 44. The screw sleeve 46 rotatably supports the spline bushing 44. The screw sleeve 46 also limits relative movement of the spline bushing 44 with respect to the screw sleeve 46 in the direction along the axis LA. The screw sleeve 46 has, for example, a bearing member (not shown). The bearing member rotatably supports the screw sleeve 46 while limiting relative movement of the spline bushing 44 in the direction along the axis LA.

[0033] The pressure sensor 48 detects the pressure inside the injection cylinder 22. The pressure sensor 48 is, for example, a load cell. The pressure sensor 48 is provided, for example, inside the screw sleeve 46. However, the installation location of the pressure sensor 48 may be changed as appropriate.

[0034] The first driving device 50 is a device that rotates the injection member 24 about the axis LA. The first driving device 50 includes a rotation motor 54, a first driving pulley 56, a first belt 58, and a first driven pulley 60.

[0035] The rotation motor 54 is, for example, a servo motor. The rotation motor 54 includes a shaft 54 ​​a. The shaft 54 ​​a rotates when a current is supplied to the rotation motor 54. The shaft 54 ​​a is connected to a first drive pulley 56.

[0036] The first drive pulley 56 rotates in response to the rotation of the shaft 54 ​​a. The first belt 58 is wound around the first drive pulley 56 and the first driven pulley 60. The first belt 58 transmits the rotation of the first drive pulley 56 to the first driven pulley 60.

[0037] The first driven pulley 60 rotates in response to the rotation of the first drive pulley 56, which is transmitted via the first belt 58. In other words, the first driven pulley 60 rotates in response to the rotation of the shaft 54a. The first driven pulley 60 is provided, for example, inside the pusher plate 30. The first driven pulley 60 is connected to the spline bushing 44. The first driven pulley 60 and the spline bushing 44 rotate integrally.

[0038] As described above, the rotation of the shaft 54a rotates the spline bushing 44. The rotation of the spline bushing 44 rotates the injection member 24. In this manner, the first drive unit 50 can rotate the injection member 24 about the axis LA.

[0039] The second drive device 52 is a device that moves the injection member 24 along the axis LA. The second drive device 52 includes an injection motor 62, a second drive pulley 64, a second belt 66, a second driven pulley 68, a ball screw 70, and a nut 72.

[0040] The injection motor 62 is, for example, a servo motor. The injection motor 62 includes a shaft 62a and a rotational position sensor 62b. The shaft 62a rotates when a current is supplied to the injection motor 62. The shaft 62a is connected to a second drive pulley 64. The rotational position sensor 62b detects the rotational position of the shaft 62a.

[0041] The second drive pulley 64 rotates in response to the rotation of the shaft 62a. The second belt 66 is wound around the second drive pulley 64 and the second driven pulley 68. The second belt 66 transmits the rotation of the second drive pulley 64 to the second driven pulley 68.

[0042] The second driven pulley 68 rotates in response to the rotation of the second drive pulley 64 transmitted via the second belt 66. In other words, the second driven pulley 68 rotates in response to the rotation of the shaft 62a.

[0043] The direction of the axis of the ball screw 70 is parallel to the direction of the axis LA of the injection cylinder 22. The ball screw 70 passes through the rear plate 28. The rear plate 28 rotatably supports the ball screw 70 while restricting movement of the ball screw 70 in the direction along the axis LA. For example, the rear plate 28 has a bearing member 74. The bearing member 74 rotatably supports the ball screw 70 while restricting movement of the ball screw 70 in the direction along the axis LA.

[0044] The ball screw 70 is connected to the second driven pulley 68. The ball screw 70 rotates integrally with the second driven pulley 68. Therefore, the ball screw 70 rotates in response to the rotation of the shaft 62a.

[0045] The nut 72 is provided on the rear side of the pusher plate 30. The pusher plate 30 rotatably supports the nut 72. More specifically, the pusher plate 30 rotatably supports the nut 72 using a bearing member (not shown) provided in the pusher plate 30.

[0046] The nut 72 is threaded onto the ball screw 70. The nut 72 moves in the axial direction of the ball screw 70 in response to the rotation of the ball screw 70. That is, the nut 72 moves in the first direction D1 or the second direction D2 in response to the rotation of the shaft 62a. When the nut 72 moves in the first direction D1, the pusher plate 30 moves in the first direction D1 together with the nut 72. When the nut 72 moves in the second direction D2, the pusher plate 30 moves in the second direction D2 together with the nut 72. Because the slide mechanism 32 supports the pusher plate 30, the pusher plate 30 can move smoothly in the first direction D1 or the second direction D2.

[0047] When the pusher plate 30 moves in the first direction D1, the pusher plate 30 pushes the injection member 24 in the first direction D1 via the screw sleeve 46 and the spline bushing 44. When the pusher plate 30 moves in the second direction D2, the pusher plate 30 pulls the injection member 24 in the second direction D2 via the screw sleeve 46 and the spline bushing 44.

[0048] The injection member 24 moves in the first direction D1 or the second direction D2 within the injection cylinder 22 in accordance with the force received from the pusher plate 30. In other words, the injection member 24 is movable along the axis LA of the injection cylinder 22.

[0049] The position of a predetermined portion of the injection member 24 is defined as the position of the injection member 24. For example, the position of the tip of the screw head 24a can be defined as the position of the injection member 24. In this case, the movable range of the tip of the screw head 24a is defined as the movable range of the injection member 24. The front end position of the movable range of the injection member 24 can be referred to as a first end position PE1. The rear end position of the movable range of the injection member 24 can be referred to as a second end position PE2. The first end position PE1 is the frontmost position that can be reached by the tip of the screw head 24a. The second end position PE2 is the rearmost position that can be reached by the tip of the screw head 24a.

[0050] The rotation direction of the shaft 62a when moving the injection member 24 in the first direction D1 is opposite to the rotation direction of the shaft 62a when moving the injection member 24 in the second direction D2. The rotation direction of the shaft 62a when moving the injection member 24 in the first direction D1 is also referred to as the first rotation direction in the following description. The rotation direction of the shaft 62a when moving the injection member 24 in the second direction D2 is also referred to as the second rotation direction in the following description.

[0051] The amount of movement of the injection member 24 correlates with the amount of rotation of the shaft 62a. For example, the amount of movement of the injection member 24 in the first direction D1 correlates with the amount of rotation of the shaft 62a in the first rotational direction. Similarly, the amount of movement of the injection member 24 in the second direction D2 correlates with the amount of rotation of the shaft 62a in the second rotational direction. Because the amount of movement of the injection member 24 correlates with the amount of rotation of the shaft 62a, the rotational position of the shaft 62a detected by the rotational position sensor 62b substantially indicates the position of the injection member 24 in the direction along the axis LA.

[0052] FIG. 3 is a block diagram of the control device 12.

[0053] The control device 12 is an electronic device (computer) that controls the injection molding machine 10. The control device 12 is, for example, a numerical control device. The control device 12 includes a display unit 76, an operation unit 78, a storage unit 80, and a calculation unit 82.

[0054] The display unit 76 is a display device including a display screen 76d, and is, for example, a liquid crystal display or an OEL (Organic Electro-Luminescence) display.

[0055] The operation unit 78 is an input device that accepts information input to the control device 12. The operation unit 78 includes, for example, an operation panel 78a and a touch panel 78b. The touch panel 78b is provided on the display screen 76d. The operation panel 78a may include a keyboard, a mouse, etc. An operator can use the operation unit 78 to instruct the control device 12 to execute, for example, an automatic purge.

[0056] The storage unit 80 may be configured with a volatile memory (not shown) and a non-volatile memory (not shown). Examples of the volatile memory include a random access memory (RAM). Examples of the non-volatile memory include a read-only memory (ROM) and a flash memory. Data and the like are stored in the volatile memory, for example. Programs, data tables, maps, and the like are stored in the non-volatile memory, for example. At least a portion of the storage unit 80 may be provided in a processor, an integrated circuit, or the like, as described below. The storage unit 80 stores a control program 84, first torque information 86, and second torque information 88.

[0057] The control program 84 is a program for causing the control device 12 to execute the control method of this embodiment. The control method will be described in more detail later.

[0058] The first torque information 86 is information indicating a first predetermined torque. The first predetermined torque is an initial target value of torque when rotating the shaft 62 a in the first rotation direction. More specifically, the first predetermined torque is an initial target torque value of the injection motor 62 when a first motor control unit 90 (described later) controls the injection motor 62.

[0059] The second torque information 88 is information indicating a second predetermined torque. The second predetermined torque is an initial target value of torque when rotating the shaft 62 a in the second rotation direction. More specifically, the second predetermined torque is an initial target torque value of the injection motor 62 when a second motor control unit 92 (described later) controls the injection motor 62.

[0060] The first torque information 86 and the second torque information 88 are provided to the user by, for example, the manufacturer of the injection molding system SYS. More specifically, the manufacturer of the injection molding system SYS provides the user with the first predetermined torque and the second predetermined torque, which have been determined, for example, based on experiments. The user can input the first predetermined torque and the second predetermined torque using the operation unit 78. The absolute value of the second predetermined torque and the absolute value of the first predetermined torque may be equal to or different from each other.

[0061] The calculation unit 82 is configured by a processor such as a CPU (Central Processing Unit) or a GPU (Graphics Processing Unit). That is, the calculation unit 82 may be configured by a processing circuitry. The calculation unit 82 includes a first motor control unit 90, a second motor control unit 92, and a zero point correction unit 94.

[0062] The first motor control unit 90, the second motor control unit 92, and the zero point correction unit 94 are realized by the calculation unit 82 executing the control program 84. Note that at least a portion of the first motor control unit 90, the second motor control unit 92, and the zero point correction unit 94 may be realized by an integrated circuit such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field-Programmable Gate Array). Furthermore, at least a portion of the first motor control unit 90, the second motor control unit 92, and the zero point correction unit 94 may be configured by an electronic circuit including discrete devices.

[0063] The first motor control unit 90 controls the injection motor 62 so that the torque in the first rotation direction gradually decreases from the first predetermined torque, thereby moving the injection member 24 in the first direction D1. As described above, the first rotation direction is the rotation direction of the shaft 62a when moving the injection member 24 in the first direction D1. Note that the torque of the injection motor 62 correlates with the amount of current supplied to the injection motor 62. Therefore, the first motor control unit 90 can gradually reduce the torque of the injection motor 62 by controlling the injection motor 62 so that the amount of current supplied to the injection motor 62 gradually decreases.

[0064] As the injection member 24 moves in the first direction D1, it presses the resin in the injection cylinder 22 in the first direction D1. When the torque is relatively large, the force with which the pusher plate 30 pushes the injection member 24 is relatively large. That is, the force that moves the injection member 24 in the first direction D1 is relatively large. Therefore, the injection member 24 can move in the first direction D1. That is, although a resistance force that inhibits the movement of the injection member 24 in the first direction D1 is generated by the resin, the force that moves the injection member 24 in the first direction D1 is sufficiently large, so the injection member 24 can move in the first direction D1.

[0065] As the torque of the injection motor 62 is gradually reduced, the force with which the pusher plate 30 pushes the injection member 24 gradually decreases. That is, the force that moves the injection member 24 in the first direction D1 gradually decreases. Therefore, when the torque of the injection motor 62 decreases to a certain level, the injection member 24 can no longer be moved in the first direction D1. That is, the movement of the injection member 24 in the first direction D1 is stopped by the resin. In this case, the movement of the injection member 24 in the first direction D1 stops before the injection member 24 reaches the first end position PE1, even if the torque of the injection motor 62 in the first rotational direction is greater than zero.

[0066] The detection value of pressure sensor 48 when movement of injection member 24 in first direction D1 has stopped is acquired by calculation unit 82. The pressure detected by pressure sensor 48 when movement of injection member 24 in first direction D1 has stopped is also referred to as first pressure P1 in the following description. Note that first motor control unit 90 determines whether injection member 24 has stopped based on the rotation speed of shaft 62a, which is determined based on information detected by rotational position sensor 62b.

[0067] After the movement of the injection member 24 in the first direction D1 has stopped, control is performed by the second motor control unit 92. The second motor control unit 92 controls the injection motor 62 so that the torque in the second rotation direction gradually decreases from the second predetermined torque, thereby moving the injection member 24 in the second direction D2. As described above, the second rotation direction is the rotation direction of the shaft 62a when moving the injection member 24 in the second direction D2. The second motor control unit 92 controls the injection motor 62 so that the amount of current supplied to the injection motor 62 gradually decreases, thereby gradually reducing the torque of the injection motor 62. The second motor control unit 92 determines whether the injection member 24 has stopped based on the rotation speed of the shaft 62a, which is determined based on information detected by the rotational position sensor 62b.

[0068] When the torque is relatively large, the force with which the pusher plate 30 pulls the injection member 24 is relatively large. That is, the force that moves the injection member 24 in the second direction D2 is relatively large. Therefore, the injection member 24 can move in the second direction D2. That is, although the resin generates a resistance that inhibits the movement of the injection member 24 in the second direction D2, the force that moves the injection member 24 in the second direction D2 is sufficiently large, so the injection member 24 can move in the second direction D2.

[0069] As the torque of the injection motor 62 is gradually reduced, the force with which the pusher plate 30 pulls the injection member 24 gradually decreases. That is, the force that moves the injection member 24 in the second direction D2 gradually decreases. Therefore, when the torque of the injection motor 62 decreases to a certain level, the injection member 24 can no longer be moved in the second direction D2. That is, the movement of the injection member 24 in the second direction D2 is stopped by the resin. In this case, the movement of the injection member 24 in the second direction D2 stops before the injection member 24 reaches the second end position PE2, even if the torque of the injection motor 62 in the second rotational direction is greater than zero.

[0070] The detection value of the pressure sensor 48 when the movement of the injection member 24 in the second direction D2 stops is acquired by the calculation unit 82. The pressure detected by the pressure sensor 48 when the movement of the injection member 24 in the second direction D2 stops is also referred to as the second pressure P2 in the following description.

[0071] 4A is a number line illustrating the zero point P0 of the pressure sensor 48, the absolute value α1 of the first pressure P1, and the absolute value β1 of the second pressure P2. For convenience, in FIG. 4A , the pressure detected by the pressure sensor 48 when the ejection member 24 moving in the second direction D2 stops is represented by a positive number. Also, in FIG. 4A , the pressure detected by the pressure sensor 48 when the ejection member 24 moving in the second direction D2 stops is represented by a negative number.

[0072] As described above, the first pressure P1 is the pressure detected by the pressure sensor 48 when the movement of the injection member 24 in the first direction D1 stops. The second pressure P2 is the pressure detected by the pressure sensor 48 when the movement of the injection member 24 in the second direction D2 stops. The polarity of the first pressure P1 and the polarity of the second pressure P2 are opposite to each other. The magnitudes of the first pressure P1 and the second pressure P2 should be equal to each other, but if the zero point P0 of the pressure sensor 48 is not set correctly, the magnitudes of the first pressure P1 and the second pressure P2 detected by the pressure sensor 48 will not be equal to each other. If the absolute value of the first pressure P1 detected by the pressure sensor 48 is α1 and the absolute value of the second pressure P2 is α2, then if the zero point P0 of the pressure sensor 48 is not set correctly, α1≠β1, as shown in FIG. 4A .

[0073] The zero point correction unit 94 can correct the zero point P0 of the pressure sensor 48. That is, the zero point correction unit 94 corrects the zero point P0 of the pressure sensor 48 based on the first pressure P1 and the second pressure P2. More specifically, the zero point correction unit 94 corrects the zero point P0 of the pressure sensor 48 so that the absolute value of the first pressure P1 and the absolute value of the second pressure P2 become equal. That is, the zero point correction unit 94 corrects the zero point P0 so that the absolute difference between the first pressure P1 and the corrected zero point P0 becomes equal to the absolute difference between the second pressure P2 and the corrected zero point P0.

[0074] 4B is a number line illustrating the zero point P0, the absolute value α2 of the first pressure P1, and the absolute value β2 of the second pressure P2 after adjustment by the zero point correction unit 94. The positive and negative indications in FIG. 4B are the same as those in FIG. 4A.

[0075] As shown in FIG. 4B, the zero point correction unit 94 corrects the zero point P0, so that the absolute value of the first pressure P1 and the absolute value of the second pressure P2 can be made equal.

[0076] FIG. 5 is a flowchart illustrating a method for controlling the injection molding machine 10.

[0077] The control device 12 can execute, for example, the control method shown in Fig. 5. This control method includes a first motor control step S1, a second motor control step S2, and a zero point correction step S3.

[0078] In the first motor control step S1, the first motor control unit 90 controls the injection motor 62 so that the torque in the first rotation direction gradually decreases from a first predetermined torque. In the first motor control step S1, the injection member 24 moves in the first direction D1. When the torque decreases to a certain level, the injection member 24 stops moving in the first direction D1.

[0079] When the movement of the injection member 24 in the first direction D1 stops, the first motor control unit 90 ends the first motor control step S1. In the first motor control step S1, the first pressure P1 is detected by the pressure sensor 48. As described above, the first pressure P1 is the pressure detected by the pressure sensor 48 when the movement of the injection member 24 in the first direction D1 stops.

[0080] It should be noted that there may be a case where the injection member 24 is at the first end position PE1 at the start of the first motor control step S1. In that case, the first motor control unit 90 cannot move the injection member 24 in the first direction D1. In consideration of this problem, the first motor control unit 90 may control the injection motor 62 to adjust the position of the injection member 24 before starting the first motor control step S1.

[0081] In this position adjustment, the first motor control unit 90 moves the injection member 24, for example, to a predetermined initial position that is closer to the second direction D2 than the first end position PE1, thereby allowing the first motor control unit 90 to move the injection member 24 in the first direction D1.

[0082] In the second motor control step S2, the second motor control unit 92 controls the injection motor 62 so that the torque in the second rotation direction gradually decreases from the second predetermined torque. In the second motor control step S2, the injection member 24 moves in the second direction D2. When the torque decreases to a certain level, the injection member 24 stops moving in the second direction D2.

[0083] When the movement of the injection member 24 in the second direction D2 stops, the second motor control unit 92 ends the second motor control step S2. In the second motor control step S2, the second pressure P2 is detected by the pressure sensor 48. As described above, the second pressure P2 is the pressure detected by the pressure sensor 48 when the movement of the injection member 24 in the second direction D2 stops.

[0084] In a zero point correction step S3, the zero point correction unit 94 corrects the zero point P0 of the pressure sensor 48 based on the first pressure P1 and the second pressure P2. The zero point correction unit 94 corrects the zero point P0 of the pressure sensor 48 so that the absolute value of the first pressure P1 and the absolute value of the second pressure P2 become equal. When the zero point correction unit 94 has corrected the zero point P0 of the pressure sensor 48, the control method of FIG. 5 ends.

[0085] The control device 12 can correct the zero point P0 of the pressure sensor 48 so that the first pressure P1 and the second pressure P2, whose detected values ​​are equal in magnitude, are expressed by the same absolute value.

[0086] Moreover, the number of times that the injection member 24 moves in order to correct the zero point P0 of the pressure sensor 48 can be reduced to two: a movement in the first direction D1 by the first motor control unit 90 and a movement in the second direction D2 by the second motor control unit 92. In other words, the control device 12 can correct the zero point P0 of the pressure sensor 48 while reducing the number of times that the injection member 24 moves.

[0087] 5 reduces the number of times that the injection member 24 moves, and therefore reduces the time required to execute the control method. In other words, because the number of times that the injection member 24 moves is reduced, the time required to correct the zero point P0 of the pressure sensor 48 is also reduced.

[0088] Furthermore, by reducing the number of movements of the injection member 24, for example, the risk of air being drawn into the injection cylinder 22 from the injection port 34p due to multiple movements of the injection member 24 is reduced. By reducing the risk of air being drawn into the injection cylinder 22, the risk that the air drawn into the injection cylinder 22 will cause resin burning in the resin inside the injection cylinder 22 is also reduced.

[0089] The timing at which the control device 12 executes the control method of FIG. 5 is not particularly limited, as long as it is within the period during which the resin that applies resistance to the injection member 24 remains in the injection cylinder 22. However, it is preferable that the control device 12 executes the first motor control step S1 and the second motor control step S2 during automatic purging. In other words, it is preferable that the control device 12 also automatically start the control method of FIG. 5 when starting automatic purging. This eliminates the need to delay the start of the molding cycle just to correct the zero point P0 of the pressure sensor 48. It also eliminates the need to interrupt the molding cycle just to correct the zero point P0 of the pressure sensor 48. The automatic purging is executed by appropriately controlling the rotation motor 54, the injection motor 62, etc. by the control device 12.

[0090] [Modifications] Modifications of the above embodiment are described below. However, descriptions that overlap with the above embodiment will be omitted as appropriate in the following description. Elements already described in the above embodiment will be assigned the same reference numerals as in the above embodiment unless otherwise specified.

[0091] (Variation 1) In the above embodiment, the torque of the injection motor 62 is gradually reduced to stop the injection member 24, and the detection value of the pressure sensor 48 is obtained when the movement of the injection member 24 has stopped, but this is not limiting. The torque of the injection motor 62 may be gradually increased, and the detection value of the pressure sensor 48 may be obtained when the movement of the injection member 24 has started.

[0092] In this case, the first predetermined torque, which is the initial setting torque when rotating the shaft 62a in the first rotational direction, is set to a relatively small value. The second predetermined torque, which is the initial setting torque when rotating the shaft 62a in the second rotational direction, is also set to a relatively small value. As described above, the first torque information 86, which is information indicating the first predetermined torque, is stored in the storage unit 80. As described above, the second torque information 88, which is information indicating the second predetermined torque, is also stored in the storage unit 80.

[0093] The first motor control unit 90 controls the injection motor 62 so that the torque in the first rotational direction gradually increases from a first predetermined torque. When the torque is relatively small, the force with which the pusher plate 30 pushes the injection member 24 is relatively small. That is, the force that moves the injection member 24 in the first direction D1 is relatively small. Therefore, the injection member 24 cannot move in the first direction D1. That is, the resistance of the resin that inhibits the movement of the injection member 24 in the first direction D1 is sufficiently large, so the injection member 24 cannot move in the first direction D1. When the torque of the injection motor 62 increases to a certain level, the first motor control unit 90 can move the injection member 24 in the first direction D1. That is, although the resistance of the resin inhibits the movement of the injection member 24 in the first direction D1, the force that moves the injection member 24 in the first direction D1 is sufficiently large, so the injection member 24 can move in the first direction D1. When the injection member 24 starts to move in the first direction D1, the first motor control unit 90 ends control of the injection motor 62.

[0094] The calculation unit 82 acquires the first pressure P1 detected by the pressure sensor 48 when the injection member 24 starts to move in the first direction D1.

[0095] When the first motor control unit 90 ends control of the injection motor 62, the second motor control unit 92 begins control of the injection motor 62. The second motor control unit 92 controls the injection motor 62 so that the torque in the second rotational direction gradually increases from the second predetermined torque. When the torque is relatively small, the force with which the pusher plate 30 pulls the injection member 24 is relatively small. That is, the force moving the injection member 24 in the second direction D2 is relatively small. Therefore, the injection member 24 cannot move in the second direction D2. In other words, the resistance of the resin that inhibits movement of the injection member 24 in the second direction D2 is sufficiently large, so the injection member 24 cannot move in the second direction D2. When the torque of the injection motor 62 increases to a certain level, the second motor control unit 92 can move the injection member 24 in the second direction D2. That is, the resin generates a resistance force that hinders the movement of the injection member 24 in the second direction D2, but the force that moves the injection member 24 in the second direction D2 is sufficiently large, so the injection member 24 can move in the second direction D2.

[0096] The calculation unit 82 acquires the second pressure P2 detected by the pressure sensor 48 when the injection member 24 starts to move in the second direction D2.

[0097] Based on the first pressure P1 and the second pressure P2 thus acquired, the zero point correction unit 94 corrects the zero point P0 of the pressure sensor 48. As in the above embodiment, for example, the zero point correction unit 94 corrects the zero point P0 of the pressure sensor 48 so that the absolute value of the first pressure P1 and the absolute value of the second pressure P2 are equal.

[0098] In this modified example, the zero point correction unit 94 can also correct the zero point P0 of the pressure sensor 48 while minimizing the number of times the injection member 24 moves.

[0099] (Modification 2) The control device 12 may be applied to a pre-plasticization type injection molding machine.

[0100] In a pre-plastication type injection molding machine, the injection member 24 is constituted by a plunger (not shown). The plunger is inserted into the injection cylinder 22. The plunger moves in the first direction D1 and the second direction D2 in response to the driving of the injection motor 62.

[0101] In this modification, the first motor control unit 90 controls the injection motor 62 in the same manner as in the above embodiment, thereby obtaining the first pressure P1 detected by the pressure sensor 48 when the plunger stops moving in the first direction D1.

[0102] In this modification, the second motor control unit 92 controls the injection motor 62 in the same manner as in the above embodiment, thereby detecting the pressure when the plunger stops moving in the second direction D2 as the second pressure P2.

[0103] In this modification, the zero point correction unit 94 can correct the zero point P0 of the pressure sensor 48 based on the first pressure P1 and the second pressure P2, as in the embodiment. Moreover, the zero point correction unit 94 can correct the zero point P0 of the pressure sensor 48 while minimizing the number of times the plunger moves.

[0104] (Combination of Multiple Modifications) The multiple modifications described above may be combined as appropriate within a range that does not cause contradictions.

[0105] [Additional Notes] The following additional notes are disclosed regarding the above-described embodiment and modifications.

[0106] (Supplementary Note 1) A control device (12) of an injection molding machine (10) including an injection member (24) inserted into an injection cylinder (22) and movable within the injection cylinder, an injection motor (62) that moves the injection member, and a pressure sensor (48) that detects the pressure of resin within the injection cylinder, includes a first motor control unit (90) that controls the injection motor so that torque gradually decreases from a first predetermined torque, thereby moving the injection member in a first direction, and a second motor control unit (90) that controls the injection motor so that torque gradually decreases from a first predetermined torque, when movement of the injection member in the first direction stops. a second motor control unit (92) that controls the injection motor so that torque gradually decreases from a second predetermined torque, thereby moving the injection member in a second direction opposite to the first direction, and a zero point correction unit (94) that corrects a zero point (P0) of the pressure sensor based on a first pressure (P1) detected by the pressure sensor when movement of the injection member in the first direction stops and a second pressure (P2) detected by the pressure sensor when movement of the injection member in the second direction stops. This makes it possible to correct the zero point of the pressure sensor while minimizing the number of movements of the injection member.

[0107] (Appendix 2) A control device (12) for an injection molding machine (10) including an injection member (24) inserted into an injection cylinder (22) and movable within the injection cylinder, an injection motor (62) that moves the injection member, and a pressure sensor (48) that detects the pressure of resin within the injection cylinder, includes: a first motor control unit (90) that controls the injection motor so that torque gradually increases from a first predetermined torque, thereby moving the injection member in a first direction; a second motor control unit (92) that controls the injection motor so that torque gradually increases from a second predetermined torque, thereby moving the injection member in a second direction opposite to the first direction; and a zero point correction unit (94) that corrects a zero point (P0) of the pressure sensor based on a first pressure (P1) detected by the pressure sensor when the injection member starts to move in the first direction and a second pressure (P2) detected by the pressure sensor when the injection member starts to move in the second direction. This makes it possible to correct the zero point of the pressure sensor while minimizing the number of times the injection member moves.

[0108] (Supplementary Note 3) In the control device for an injection molding machine according to Supplementary Note 1 or 2, the zero point correction unit may correct the zero point so that an absolute value of the first pressure and an absolute value of the second pressure are equal to each other.

[0109] (Supplementary Note 4) In the control device for an injection molding machine according to any one of Supplementary Notes 1 to 3, the first motor control unit and the second motor control unit may be configured to control the injection motor while the injection molding machine is performing an automatic purge. This allows the zero point of the pressure sensor to be corrected without delaying the start of a molding cycle or interrupting the molding cycle.

[0110] (Supplementary Note 5) A control method for an injection molding machine (10) including an injection member (24) inserted into an injection cylinder (22) and movable within the injection cylinder, an injection motor (62) for moving the injection member, and a pressure sensor (48) for detecting a pressure of resin within the injection cylinder, includes a first motor control step (S1) for controlling the injection motor so that torque gradually decreases from a first predetermined torque to move the injection member in a first direction, and a second motor control step (S2) for controlling the injection motor so that torque gradually decreases from a second predetermined torque to move the injection member in a first direction, which is started when the injection member stops in the first motor control step. and a zero point correction step (S3) of correcting a zero point (P0) of the pressure sensor based on a first pressure (P1) detected by the pressure sensor when the movement of the injection member in the first direction stops in the first motor control step and a second pressure (P2) detected by the pressure sensor when the movement of the injection member in the second direction stops in the second motor control step. This makes it possible to correct the zero point of the pressure sensor while minimizing the number of movements of the injection member.

[0111] (Supplementary Note 6) A control method for an injection molding machine (10) including an injection member (24) inserted into an injection cylinder (22) and movable within the injection cylinder, an injection motor (62) for moving the injection member, and a pressure sensor (48) for detecting a pressure of resin within the injection cylinder, includes a first motor control step (S1) of controlling the injection motor so that torque gradually increases from a first predetermined torque, thereby moving the injection member in a first direction, and a second motor control step (S2) of controlling the injection motor so that torque gradually increases from a second predetermined torque. The method includes a second motor control step (S2) of controlling the injection motor to move the injection member in a second direction opposite to the first direction, and a zero point correction step (S3) of correcting a zero point (P0) of the pressure sensor based on a first pressure (P1) detected by the pressure sensor when the injection member starts to move in the first motor control step and a second pressure (P2) detected by the pressure sensor when the injection member starts to move in the second motor control step. This makes it possible to correct the zero point of the pressure sensor while minimizing the number of movements of the injection member.

[0112] Although the embodiments of the present disclosure have been described in detail, the present disclosure is not limited to the individual embodiments described above. Various additions, substitutions, modifications, partial deletions, etc. are possible in these embodiments without departing from the gist of the invention or the idea and intent derived from the content described in the claims and their equivalents. For example, in the above-described embodiments, the order of each operation or each processing is shown as an example and is not limited to these. The same applies when numerical values ​​or mathematical expressions are used in the description of the above-described embodiments.

[0113] REFERENCE SIGNS LIST 10... injection molding machine 12... control device 22... injection cylinder 24... screw (injection member) 48... pressure sensor 62... injection motor 90... first motor control unit 92... second motor control unit 94... zero point correction unit

Claims

1. A control device for an injection molding machine including: an injection member that is inserted into an injection cylinder and is movable within the injection cylinder; an injection motor that moves the injection member; and a pressure sensor that detects a pressure of a resin within the injection cylinder, a first motor control unit that controls the injection motor so that a torque of the injection motor gradually decreases from a first predetermined torque to move the injection member in a first direction; a second motor control unit that controls the injection motor so that a torque gradually decreases from a second predetermined torque when the movement of the injection member in the first direction is stopped, thereby moving the injection member in a second direction opposite to the first direction; a zero point correction unit that corrects a zero point of the pressure sensor based on a first pressure detected by the pressure sensor when the movement of the ejection member in the first direction is stopped and a second pressure detected by the pressure sensor when the movement of the ejection member in the second direction is stopped; A control device for an injection molding machine comprising:

2. A control device for an injection molding machine including: an injection member that is inserted into an injection cylinder and is movable within the injection cylinder; an injection motor that moves the injection member; and a pressure sensor that detects a pressure of a resin within the injection cylinder, a first motor control unit that controls the injection motor so that a torque gradually increases from a first predetermined torque to move the injection member in a first direction; a second motor control unit that controls the injection motor so that a torque gradually increases from a second predetermined torque to move the injection member in a second direction opposite to the first direction; a zero point correction unit that corrects a zero point of the pressure sensor based on a first pressure detected by the pressure sensor when the ejection member starts to move in the first direction and a second pressure detected by the pressure sensor when the ejection member starts to move in the second direction; A control device for an injection molding machine comprising:

3. The control device for an injection molding machine according to claim 1 or 2, The zero point correction unit corrects the zero point so that an absolute value of the first pressure and an absolute value of the second pressure are equal to each other.

4. The control device for an injection molding machine according to claim 1 or 2, The first motor control unit and the second motor control unit are configured to control the injection motor while the injection molding machine is performing an automatic purge.

5. A control method for an injection molding machine including an injection member that is inserted into an injection cylinder and is movable within the injection cylinder, an injection motor that moves the injection member, and a pressure sensor that detects a pressure of a resin within the injection cylinder, the control method comprising the steps of: a first motor control step of controlling the injection motor so that a torque of the injection motor is gradually decreased from a first predetermined torque to move the injection member in a first direction; a second motor control step that is started when the injection member is stopped in the first motor control step, and that controls the injection motor so that a torque gradually decreases from a second predetermined torque, thereby moving the injection member in a second direction opposite to the first direction; a zero point correction step of correcting a zero point of the pressure sensor based on a first pressure detected by the pressure sensor when the movement of the ejection member in the first direction stops in the first motor control step and a second pressure detected by the pressure sensor when the movement of the ejection member in the second direction stops in the second motor control step; A method for controlling an injection molding machine, comprising:

6. A control method for an injection molding machine including an injection member that is inserted into an injection cylinder and is movable within the injection cylinder, an injection motor that moves the injection member, and a pressure sensor that detects a pressure of a resin within the injection cylinder, the control method comprising the steps of: a first motor control step of controlling the injection motor so that a torque of the injection motor gradually increases from a first predetermined torque to move the injection member in a first direction; a second motor control step of controlling the injection motor so that a torque of the injection motor gradually increases from a second predetermined torque to move the injection member in a second direction opposite to the first direction; a zero point correction step of correcting a zero point of the pressure sensor based on a first pressure detected by the pressure sensor when the ejection member starts to move in the first motor control step and a second pressure detected by the pressure sensor when the ejection member starts to move in the second motor control step; A method for controlling an injection molding machine, comprising: