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

Abstract

This control device (12) for an injection molding machine (10) comprises: a first motor control unit (90) that moves an injection member (24) in a first direction while maintaining the torque of an injection motor (62) at a prescribed torque; a second motor control unit (92) that moves the injection member (24) in a second direction while maintaining the torque of the injection motor (62) at the prescribed torque; and a zero-point correction unit (94) that corrects a zero point on the basis of a first stop position (PS1) at which the movement of the injection member (24) in the first direction stopped and a second stop position (PS2) at which the movement of the injection member (24) in the second direction stopped.

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 that includes 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 the pressure of resin within the injection cylinder, the control device including: a first motor control unit that controls the injection motor to move the injection member in a first direction so that a torque becomes a predetermined torque; a second motor control unit that controls the injection motor to move the injection member in a second direction opposite to the first direction so that a torque becomes the predetermined torque when the movement of the injection member in the first direction stops; and a zero point correction unit that corrects a zero point of the pressure sensor based on a first stop position of the injection member when the movement of the injection member in the first direction stops and a second stop position of the injection member when the movement of the injection member in the second direction stops.

[0006] A second aspect of the present disclosure is a control method for an injection molding machine that includes 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 including: a first motor control step of controlling the injection motor to achieve a 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 to achieve the 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 stop position of the injection member when the movement of the injection member in the first direction has stopped and a second stop position of the injection member when the movement of the injection member in the second direction has stopped.

[0007] FIG. 1 is a diagram illustrating the overall configuration of an injection molding system according to one embodiment. FIG. 2 is a schematic diagram illustrating the configuration of an injection device. FIG. 3 is a block diagram of a control device. FIG. 4 is a number line illustrating a first stop position, a second stop position, and the midpoint between these two positions. FIG. 5 is a flowchart illustrating a control method for an injection molding machine. FIG. 6 is a block diagram of a control device according to a first modification.

[0008] 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.

[0009] [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.

[0010] 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.

[0011] 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).

[0012] 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.

[0013] The injection molding system SYS includes an injection molding machine 10 and a control device 12 .

[0014] The injection molding machine 10 includes a mold clamping device 14 , an injection device 16 , and a machine base 18 .

[0015] 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.

[0016] 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.

[0017] FIG. 2 is a schematic diagram showing the configuration of the injection device 16.

[0018] 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 .

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] The pusher plate 30 is provided between the front plate 26 and the rear plate 28 .

[0026] 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.

[0027] 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.

[0028] 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 .

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] FIG. 3 is a block diagram of the control device 12.

[0051] 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.

[0052] 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.

[0053] 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. A user can use the operation unit 78 to instruct the control device 12 to perform, for example, an automatic purge.

[0054] 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 and torque information 86.

[0055] 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.

[0056] The torque information 86 is information indicating the magnitude of the predetermined torque. The predetermined torque is a target value of the torque of the injection motor 62. The torque information 86 is provided to the user, for example, by the manufacturer of the injection molding system SYS. More specifically, the manufacturer of the injection molding system SYS provides the user with the predetermined torque determined, for example, based on experiments. The user can input the predetermined torque using the operation unit 78. The magnitude of the predetermined torque is set to be relatively small. More specifically, the magnitude of the predetermined torque is set so that when the injection member 24 is moved in the first direction D1 in the first motor control step S1 described below, the injection member 24 can stop before reaching the first end position PE1.

[0057] 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 position acquisition unit 88, a first motor control unit 90, a second motor control unit 92, and a zero point correction unit 94.

[0058] The position acquisition unit 88, first motor control unit 90, second motor control unit 92, and 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 position acquisition unit 88, first motor control unit 90, second motor control unit 92, and 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 position acquisition unit 88, first motor control unit 90, second motor control unit 92, and zero point correction unit 94 may be configured by an electronic circuit including discrete devices.

[0059] The position acquisition unit 88 acquires the position of the injection member 24 based on the rotational position of the shaft 62a detected by the rotational position sensor 62b. The position acquisition unit 88 can acquire a first stop position PS1 and a second stop position PS2, which will be described later, based on the rotational position of the shaft 62a.

[0060] The first motor control unit 90 controls the injection motor 62 based on the torque information 86 to move the injection member 24 in the first direction D1. In other words, the first motor control unit 90 controls the injection motor 62 so that the magnitude of the torque in the first rotation direction becomes a 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 maintain the torque of the injection motor 62 at a predetermined torque by appropriately adjusting the amount of current supplied to the injection motor 62.

[0061] When the injection member 24 is moved in the first direction D1, a resistance force that inhibits the movement of the injection member 24 in the first direction D1 is generated by the resin or the like. Furthermore, as described above, the torque of the injection motor 62 is set to a predetermined torque that is a relatively small torque. Therefore, when the injection member 24 is moved in the first direction D1 with the torque of the injection motor 62 set to the predetermined torque, the movement of the injection member 24 in the first direction D1 may be stopped due to the inhibition by the resin or the like even before the injection member 24 reaches the first end position PE1.

[0062] Information indicating the position of ejection member 24 when the movement of ejection member 24 in first direction D1 has stopped is acquired by position acquisition unit 88. The position of ejection member 24 when the movement of ejection member 24 in first direction D1 has stopped is also referred to as first stop position PS1.

[0063] It should be noted that there may be cases where the position of the injection member 24 is already at the first end position PE1 when the first motor control unit 90 attempts to move the injection member 24 in the first direction D1. In such cases, the first motor control unit 90 cannot move the injection member 24 in the first direction D1.

[0064] The injection member 24 may be moved in the second direction D2 before being moved in the first direction D1 so that the injection member 24 stops before it reaches the first end position PE1.

[0065] 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 based on the torque information 86 to move the injection member 24 in the second direction D2. In other words, the second motor control unit 92 controls the injection motor 62 so that the torque in the second rotation direction becomes a 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 can maintain the torque of the injection motor 62 at a predetermined torque by appropriately adjusting the amount of current supplied to the injection motor 62.

[0066] When the injection member 24 is moved in the second direction D2, a resistance force that inhibits the movement of the injection member 24 in the second direction D2 is generated by the resin or the like. Furthermore, as described above, the torque of the injection motor 62 is set to a predetermined torque that is a relatively small torque. In this case, if the injection member 24 is moved in the second direction D2 with the torque of the injection motor 62 set to the predetermined torque, the movement of the injection member 24 in the second direction D2 may be stopped due to the inhibition by the resin or the like even before the injection member 24 reaches the second end position PE2.

[0067] Information indicating the position of ejection member 24 when the movement of ejection member 24 in second direction D2 stops is acquired by position acquisition unit 88. The position of ejection member 24 when the movement of ejection member 24 in second direction D2 stops is also referred to as second stop position PS2.

[0068] FIG. 4 is a number line illustrating a first stop position PS1, a second stop position PS2, and the midpoint Pmid between these two positions.

[0069] The first stop position PS1 is a position where the movement of the injection member 24 in the first direction D1 is stopped due to obstruction by resin or the like. The second stop position PS2 is a position where the movement of the injection member 24 in the second direction D2 is stopped due to obstruction by resin or the like. The resistance force of resin or the like when the movement of the injection member 24 in the first direction D1 is stopped is equal to the resistance force of resin or the like when the movement of the injection member 24 in the second direction D2 is stopped. Therefore, if the zero point of the pressure sensor 48 is correctly set, the detection value of the pressure sensor 48 when the injection member 24 is located at the midpoint Pmid should be zero. If the detection value of the pressure sensor 48 is not zero even when the injection member 24 is located at the midpoint Pmid, this means that the zero point of the pressure sensor 48 is misaligned. Furthermore, the detection value of the pressure sensor 48 when the injection member 24 is located at the midpoint Pmid represents the amount of error in the zero point.

[0070] The zero point correction unit 94 corrects the zero point of the pressure sensor 48 so that the detection value of the pressure sensor 48 becomes zero when the injection member 24 is located at the midpoint Pmid between the first stop position PS1 and the second stop position PS2. This makes it possible to correct an error in the zero point of the pressure sensor 48.

[0071] After the position acquisition unit 88 acquires the second stop position PS2, the first motor control unit 90 or the second motor control unit 92 controls the injection motor 62 to move the injection member 24 to the midpoint Pmid. This allows the zero point correction unit 94 to acquire the detection value of the pressure sensor 48 when the injection member 24 is located at the midpoint Pmid.

[0072] FIG. 5 is a flowchart illustrating a method for controlling the injection molding machine 10.

[0073] 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.

[0074] 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 becomes a predetermined torque. In the first motor control step S1, the injection member 24 moves in the first direction D1. After the injection member 24 moves a certain distance, the injection member 24 stops moving in the first direction D1.

[0075] When the movement of injection member 24 in first direction D1 stops, position acquisition unit 88 acquires information indicating first stop position PS1. This ends first motor control step S1. As described above, first stop position PS1 is the position of injection member 24 when the movement of injection member 24 in first direction D1 stops.

[0076] 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 becomes a predetermined torque. In the second motor control step S2, the injection member 24 moves in the second direction D2. After the injection member 24 moves a certain distance, the injection member 24 stops moving in the second direction D2.

[0077] When the movement of injection member 24 in second direction D2 stops, position acquisition unit 88 acquires information indicating second stop position PS2. This completes second motor control step S2. As described above, second stop position PS2 is the position of injection member 24 when the movement of injection member 24 in second direction D2 stops.

[0078] In a zero point correction step S3, the zero point correction unit 94 corrects the zero point of the pressure sensor 48 based on the first stop position PS1 and the second stop position PS2. The zero point correction unit 94 corrects the zero point of the pressure sensor 48 so that the detection value of the pressure sensor 48 becomes zero when the injection member 24 is located at the midpoint Pmid between the first stop position PS1 and the second stop position PS2. When the zero point correction unit 94 corrects the zero point of the pressure sensor 48, the control method of FIG. 5 ends.

[0079] 5, the number of movements of the injection member 24 from the start to the completion thereof can be at least three: movement from a predetermined initial position to the first stop position PS1, movement from the first stop position PS1 to the second stop position PS2, and movement from the second stop position PS2 to the midpoint Pmid. In other words, the control device 12 can correct the zero point of the pressure sensor 48 while limiting the number of movements of the injection member 24.

[0080] 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 of the pressure sensor 48 is also reduced.

[0081] 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.

[0082] The timing at which the control device 12 executes the control method of Figure 5 is not particularly limited. 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 starts the control method of Figure 5 when starting automatic purging. This eliminates the need to delay the start of the molding cycle just to correct the zero point of the pressure sensor 48. It also eliminates the need to interrupt the molding cycle just to correct the zero point of the pressure sensor 48. The automatic purging is executed by the control device 12 appropriately controlling the rotation motor 54, injection motor 62, etc.

[0083] [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.

[0084] (Modification 1) FIG. 6 is a block diagram of the control device 12 (control device 121) according to Modification 1.

[0085] The control device 121 further includes a torque change unit 96. The torque change unit 96 can be realized by the calculation unit 82 executing the control program 84, similar to the position acquisition unit 88 and the like.

[0086] When the injection member 24 reaches the first end position PE1 in the first motor control step S1, the torque change unit 96 edits the torque information 86 to change the predetermined torque to a value smaller than the current setting value.

[0087] If the injection member 24 reaches the first end position PE1 in the first motor control step S1, it is necessary to repeat the first motor control step S1. In this case, by the torque change unit 96 changing the predetermined torque as described above, it is possible to prevent the injection member 24 from reaching the first end position PE1 in the re-executed first motor control step S1.

[0088] Incidentally, even when the injection member 24 reaches the second end position PE2 in the second motor control step S2, the torque change unit 96 edits the torque information 86 to change the predetermined torque to a value smaller than the current setting value.

[0089] If the injection member 24 reaches the second end position PE2 in the second motor control step S2, the second motor control step S2 needs to be repeated. In this case, by the torque change unit 96 changing the predetermined torque as described above, it is possible to prevent the injection member 24 from reaching the second end position PE2 in the re-executed second motor control step S2.

[0090] (Variation 2) The position of the injection member 24 corresponding to the zero point may be a predetermined dividing point located within a predetermined error range with respect to the midpoint Pmid. For example, if a 1% error is allowed for the distance from the first stop position PS1 to the second stop position PS2, the following may be used. That is, in this case, the zero point correction unit 94 may correct the zero point of the pressure sensor 48 so that the detection value of the pressure sensor 48 becomes zero when the injection member 24 is located at a dividing point that divides the first stop position PS1 and the second stop position PS2 at a ratio of 49:51.

[0091] The allowable error range is not limited to a range of 1% of the distance from the first stop position PS1 to the second stop position PS2.

[0092] (Variation 3) During the period when the first motor control step S1 and the second motor control step S2 are being executed, the pressure sensor 48 may successively output a detection value, thereby enabling the zero point correction unit 94 to acquire information indicating the temporal progression of the detection value of the pressure sensor 48 during the period when the first motor control step S1 and the second motor control step S2 are being executed.

[0093] The zero point correction unit 94 can acquire the detection value of the pressure sensor 48 when the injection member 24 is located at the midpoint Pmid, based on the transition of the detection value of the pressure sensor 48 over time.

[0094] The zero point correction unit 94 may correct the zero point of the pressure sensor 48 based on the detection value of the pressure sensor 48 when the injection member 24 was positioned at the midpoint Pmid during the period when the first motor control step S1 and the second motor control step S2 were being executed.

[0095] This eliminates the need to move injection member 24 to midpoint Pmid after second motor control step S2. That is, according to this modification, the number of times injection member 24 is moved is reduced compared to the above embodiment, and therefore the time required to correct the zero point of pressure sensor 48 is also reduced.

[0096] The zero point correction unit 94 does not need to acquire the time transition of the detection value of the pressure sensor 48 during the entire period in which the first motor control step S1 and the second motor control step S2 are executed. The zero point correction unit 94 only needs to acquire the time transition of the detection value of the pressure sensor 48 during the period in which the injection member 24 moves from the first stop position PS1 to the second stop position PS2.

[0097] (Modification 4) The control device 12 may be applied to a pre-plasticization type injection molding machine.

[0098] 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.

[0099] In this modification, the first motor control unit 90 controls the injection motor 62 in the same manner as in the above embodiment. As a result, the position acquisition unit 88 detects the position of the plunger when the plunger stops moving in the first direction D1 as the first stop position PS1.

[0100] In this modification, the second motor control unit 92 controls the injection motor 62 in the same manner as in the above embodiment. As a result, the position acquisition unit 88 detects the position of the plunger when the plunger stops moving in the second direction D2 as the second stop position PS2.

[0101] In this modification, the zero point correction unit 94 can correct the zero point of the pressure sensor 48 based on the first stop position PS1 and the second stop position PS2, as in the embodiment. Moreover, the zero point correction unit 94 can correct the zero point of the pressure sensor 48 while minimizing the number of movements of the plunger.

[0102] (Combination of Multiple Modifications) The multiple modifications described above may be combined as appropriate within a range that does not cause contradictions.

[0103] [Additional Notes] The following additional notes are disclosed regarding the above-described embodiment and modifications.

[0104] (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) for moving the injection member, and a pressure sensor (48) for detecting the pressure of resin within the injection cylinder, includes a first motor control unit (90) that controls the injection motor so that a torque becomes a predetermined torque, and moves the injection member in a first direction, and a second motor control unit (90) that stops the movement of the injection member in the first direction. a second motor control unit (92) that controls the injection motor so that a torque becomes the predetermined torque when the injection motor is in the first direction, 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 of the pressure sensor based on a first stop position (PS1) of the injection member when the movement of the injection member in the first direction stops and a second stop position (PS2) of the injection member when the movement of the injection member in the second direction stops. This makes it possible to correct the zero point of the pressure sensor while reducing the number of movements of the injection member.

[0105] (Supplementary Note 2) In the control device for the injection molding machine according to Supplementary Note 1, the zero point correction unit may correct the zero point based on the detection value of the pressure sensor when the injection member is located at a point that divides the first stop position and the second stop position. This makes it possible to correct the zero point of the pressure sensor while reducing the number of movements of the injection member.

[0106] (Supplementary Note 3) In the control device for an injection molding machine according to Supplementary Note 2, the internal division point may be a midpoint (Pmid) between the first stop position and the second stop position, and the zero point correction unit may correct the zero point so that the detection value of the pressure sensor becomes zero when the injection member is positioned at the midpoint. This makes it possible to correct the zero point of the pressure sensor while reducing the number of movements of the injection member.

[0107] (Supplementary Note 4) In the control device for an injection molding machine according to any one of Supplementary Notes 1 to 3, the injection member may be movable within a predetermined range within the injection cylinder, and the control device may include a torque change unit (96) that changes the predetermined torque to a value smaller than a current setting when the injection member reaches a first end position (PE1) that is an end of the predetermined range in the first direction and when the injection member reaches a second end position (PE2) that is an end of the predetermined range in the second direction, the first stop position being a position closer to the second end position than the first end position, and the second stop position being a position closer to the first direction than the second end position. This makes it possible to correct the zero point of a pressure sensor while reducing the number of movements of the injection member.

[0108] (Supplementary Note 5) In the control device for an injection molding machine according to any one of Supplementary Notes 1 to 4, 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.

[0109] (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 the pressure of resin within the injection cylinder, includes a first motor control step (S1) of controlling the injection motor so that a torque becomes a predetermined torque, thereby moving the injection member in a first direction, and a second motor control step (S2) of detecting the pressure of the resin within the injection cylinder when the injection member has stopped in the first motor control step. and a zero point correction step (S3) of correcting a zero point of the pressure sensor based on a first stop position (PS1) of the injection member when the movement of the injection member in the first direction has stopped and a second stop position (PS2) of the injection member when the movement of the injection member in the second direction has stopped. This makes it possible to correct the zero point of the pressure sensor while reducing the number of movements of the injection member.

[0110] 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.

[0111] REFERENCE SIGNS LIST 10... injection molding machine 12, 121... 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 96... torque change 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 becomes a 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 becomes the 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 stop position of the ejection member when the movement of the ejection member in the first direction stops and a second stop position of the ejection member when the movement of the ejection member in the second direction stops; A control device for an injection molding machine comprising:

2. The control device for an injection molding machine according to claim 1, The zero point correction unit corrects the zero point based on the detection value of the pressure sensor when the injection member is located at a point dividing the first stop position and the second stop position.

3. The control device for an injection molding machine according to claim 2, the internal division point is a midpoint between the first stop position and the second stop position, The zero point correction unit corrects the zero point so that a detection value of the pressure sensor becomes zero when the injection member is positioned at the midpoint.

4. The control device for an injection molding machine according to any one of claims 1 to 3, the injection member is movable within a predetermined range within the injection cylinder, a torque change unit that changes the predetermined torque to a value smaller than a current setting value when the injection member reaches a first end position that is an end of the predetermined range in the first direction and when the injection member reaches a second end position that is an end of the predetermined range in the second direction, the first stop position is a position on the second direction side relative to the first end position, A control device for an injection molding machine, wherein the second stop position is a position on the first direction side of the second end position.

5. The control device for an injection molding machine according to any one of claims 1 to 3, 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.

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, comprising: a first motor control step of controlling the injection motor so that a torque of the injection motor becomes a predetermined torque, thereby moving 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 of the injection motor becomes the 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 stop position of the ejection member when the movement of the ejection member in the first direction is stopped and a second stop position of the ejection member when the movement of the ejection member in the second direction is stopped; A method for controlling an injection molding machine, comprising: