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

Abstract

A control device (12) for an injection molding machine (10) is provided with: a first motor control unit (90) that moves an injection member (24) in each of a first direction and a second direction while reducing a torque of an injection motor (62); a torque setting unit (91) that sets a second prescribed torque on the basis of a control result of the first motor control unit (90); a second motor control unit (92) that controls the injection motor (62) on the basis of a second prescribed torque; and a zero-point correction unit (94) that corrects zero point on the basis of a detection value output by a pressure sensor (48) during control of the second motor control unit (92).

Description

Technical Field

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

Background Art

[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 applied by the screw to the resin in the injection cylinder.

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

Summary of the Invention

[0004] Recently, a technique that can more efficiently correct the zero point of the pressure sensor has been eagerly awaited.

[0005] A first aspect of the present disclosure is a control device for an injection molding machine, comprising: an injection member inserted into an injection cylinder and movable within the injection cylinder; an injection motor for moving the injection member; and a pressure sensor for detecting the pressure of resin in the injection cylinder, wherein the control device performs a first control to move the injection member in a first direction by controlling the injection motor so that the torque gradually decreases from a first predetermined torque, and when the movement of the injection member stops in the first control, it performs a second control to move the injection member in a second direction opposite to the first direction by controlling the injection motor so that the torque gradually decreases from the first predetermined torque, and the torque of the injection motor when the injection member stops in the first control, and when the movement of the injection member stops in the second control. The control device for an injection molding machine comprises: a torque setting unit that sets the smaller of the torque of the injection motor when it is stopped and a second predetermined torque; a second motor control unit that performs a third control to control the injection motor so that the torque becomes the second predetermined torque and the injection member moves in one of the first and second directions, and if the movement of the injection member stops in the third control, it performs a fourth control to control the injection motor so that the torque becomes the second predetermined torque and the injection member moves in the other of the first and second directions; and a zero-point correction unit that corrects the zero point of the pressure sensor based on the detected value output by the pressure sensor during the third control and the detected value output by the pressure sensor during the fourth control.

[0006] A second aspect of the present disclosure is a control method for an injection molding machine comprising: an injection member inserted into an injection cylinder and movable within the injection cylinder; an injection motor for moving the injection member; and a pressure sensor for detecting the pressure of resin in the injection cylinder, the method comprising: a first motor control step of controlling the injection motor so that the torque gradually decreases 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 the torque gradually decreases from the first predetermined torque to move the injection member in a second direction opposite to the first direction; the torque of the injection motor when the injection member stops in the first control; and when the injection member stops in the second control. A control method for an injection molding machine, comprising: a torque setting step of setting the smaller of the torque of the injection motor at the time of injection and a second predetermined torque; a third control step of controlling the injection motor so that the torque becomes the second predetermined torque, thereby controlling the injection member to move in one of the first and second directions; a fourth control step of controlling the injection motor so that the torque becomes the second predetermined torque, thereby controlling the injection member to move in the other of the first and second directions; and a zero-point correction step of correcting the zero point of the pressure sensor based on a detected value output by the pressure sensor during the third control and a detected value output by the pressure sensor during the fourth control. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is an overall configuration diagram of an injection molding system according to one embodiment. [Figure 2] Figure 2 is a schematic diagram showing the configuration of the injection device. [Figure 3] Figure 3 is a block diagram of the control device. [Figure 4] Figure 4A is a graph illustrating the time evolution of the injection motor torque during the first control phase. Figure 4B is a graph illustrating the time evolution of the injection motor torque during the second control phase. [Figure 5]Figure 5 is a flowchart illustrating an example of an injection molding machine control method. [Modes for carrying out the invention]

[0008] If the zero point of the pressure sensor that detects the resin pressure is misaligned, it will negatively affect the quality of the molded products produced by the injection molding machine. Therefore, it is preferable that the misalignment of the pressure sensor's zero point be corrected. Furthermore, it is preferable that the time required to correct the zero point of the pressure sensor be as short as possible.

[0009] [One embodiment] A control device for an injection molding machine and a control method for an injection molding machine 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 denoted by the same reference numerals. Duplication of these components may be omitted.

[0010] Figure 1 is an overall diagram of the injection molding system SYS according to this embodiment. The direction from the right side of Figure 1 to the left side of Figure 1 is referred to as the first direction D1. The direction from the left side of Figure 1 to the right side of Figure 1 is referred to as the second direction D2. For the sake of explanation, the left side of Figure 1 may be referred to as the front side, and the right side of Figure 1 may be referred to as the rear side.

[0011] In this application, "injection member" refers to a member that is inserted into the injection cylinder 22 (see Figure 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 case in which the injection member 24 is composed of a screw 24A is described as an example, but the invention is not limited to this. For example, the injection member 24 may be composed of a plunger (not shown).

[0012] In this application, "automatic purging" refers to a predetermined operation performed automatically by the injection molding machine 10 to discharge resin from the injection cylinder 22. This predetermined operation is, for example, one or more reciprocating movements of the injection member 24 along the axis LA of the injection cylinder 22 (see Figure 2).

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

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

[0015] The clamping device 14 is a device that applies clamping force to the mold 20. The clamping device 14 is supported by the machine base 18. The clamping device 14 opens and closes the mold 20. The clamping device 14 applies clamping force to the mold 20 so that the mold 20 does not open. In the closed state, the mold 20 forms a cavity 20c. Figure 1 shows the mold 20 in the closed state. A more detailed explanation of the clamping device 14 is omitted.

[0016] The injection device 16 is a device that plasticizes the resin and injects the plasticized resin into the cavity 20c of the mold 20. The injection device 16 is supported by the machine base 18. The injection molding machine 10 produces molded products by solidifying the resin that has been filled into the cavity 20c by the injection device 16.

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

[0018] The injection device 16 comprises 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 inside 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. Further, the hopper 36 supplies the stored resin into the injection cylinder 22.

[0022] In the present embodiment, the injection member 24 is constituted by a screw 24A. The screw 24A has a screw head 24a, a flight part 24b, and a base end part 24c. The screw head 24a is located at the front end (tip) of the screw 24A. The flight part 24b is a spiral part formed on the body of the screw 24A. The flight part 24b shears the resin in the injection cylinder 22 as the screw 24A rotates by a first driving device 50 described later. The base end part 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 on the rear side of the injection cylinder 22. The front plate 26 supports the injection cylinder 22. The injection member 24 penetrates the front plate 26. The base end part 24c of the injection member 24 is located behind the front plate 26.

[0024] The rear plate 28 is located behind the front plate 26. A predetermined interval 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 sliding mechanism 32 are mounted on a flat base 42. The front plate 26, the rear plate 28, and the base 42 may be integrally molded.

[0028] The injection device 16 includes a spline bush 44, a screw sleeve 46, a pressure sensor 48, a first drive unit 50, and a second drive unit 52.

[0029] The spline bush 44 supports the base end 24c of the injection member 24. For example, the base end 24c of the injection member 24 has a male spline (not shown). In contrast, the spline bush 44 has a female spline (not shown). The male spline of the base end 24c and the female spline of the spline bush 44 engage, thereby allowing the spline bush 44 to support the base end 24c of the injection member 24.

[0030] The screw sleeve 46 is provided between the pusher plate 30 and the spline bush 44. The screw sleeve 46 rotatably supports the spline bush 44. The screw sleeve 46 also restricts the relative movement of the spline bush 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 restricting the relative movement of the spline bush 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, for example, housed inside the screw sleeve 46. However, the location of the pressure sensor 48 may be changed as appropriate.

[0032] The first drive unit 50 is a device that rotates the injection member 24 about the axis LA. The first drive unit 50 comprises a rotation motor 54, a first drive pulley 56, a first belt 58, and a first driven pulley 60.

[0033] The rotating motor 54 is, for example, a servo motor. The rotating motor 54 includes a shaft 54a. The shaft 54a rotates when current is supplied to the rotating motor 54. The shaft 54a is connected to the first drive pulley 56.

[0034] The first drive pulley 56 rotates in accordance with the rotation of the shaft 54a. The first belt 58 is stretched between 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 accordance with 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 accordance with 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 bush 44. The first driven pulley 60 and the spline bush 44 rotate together as a single unit.

[0036] As described above, the rotation of the shaft 54a causes the spline bush 44 to rotate. The rotation of the spline bush 44 causes the injection member 24 to rotate. In this way, the first drive device 50 can rotate the injection member 24 about the axis LA.

[0037] The second drive unit 52 is a device that moves the injection member 24 along the axis LA. The second drive unit 52 comprises 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 comprises a shaft 62a and a rotational position sensor 62b. The shaft 62a rotates when 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 accordance with the rotation of the shaft 62a. The second belt 66 is stretched between 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, which is transmitted via the second belt 66. In other words, the second driven pulley 68 rotates in accordance with the rotation of the shaft 62a.

[0041] The axis of the ball screw 70 is parallel to 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 its movement 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 and restricts its movement 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 accordance with the rotation of the shaft 62a.

[0043] The nut 72 is located 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 on the pusher plate 30.

[0044] The nut 72 is screwed onto the ball screw 70. The nut 72 moves in the direction of the axis of the ball screw 70 in response to the rotation of the ball screw 70. That is, the nut 72 moves in a first direction D1 or a 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. Since 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 spline bush 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 spline bush 44.

[0046] The injection member 24 moves within the injection cylinder 22 in a first direction D1 or a second direction D2 in response to the force it receives from the pusher plate 30. In other words, the injection member 24 can move along the axis LA of the injection cylinder 22.

[0047] The position of a predetermined part 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 range of motion of the tip of the screw head 24a is defined as the range of motion of the injection member 24. The position of the front end of the range of motion of the injection member 24 may be referred to as the first end position PE1. The position of the rear end of the range of motion of the injection member 24 may be referred to as the second end position PE2. The first end position PE1 is the foremost position that the tip of the screw head 24a can reach. The second end position PE2 is the rearmost position that the tip of the screw head 24a can reach.

[0048] The direction of rotation of the shaft 62a when moving the injection member 24 in the first direction D1 is opposite to the direction of rotation of the shaft 62a when moving the injection member 24 in the second direction D2. The direction of rotation of the shaft 62a when moving the injection member 24 in the first direction D1 is also referred to as the first direction of rotation in the following description. The direction of rotation of the shaft 62a when moving the injection member 24 in the second direction D2 is also referred to as the second direction of rotation 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 rotation 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 rotation direction. Since 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] Figure 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 comprises 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 equipped with a display screen 76d. The display unit 76 is, for example, a liquid crystal display or an OEL (Organic Electro-Luminescence) display.

[0053] The operation unit 78 is an input device that receives 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, mouse, etc. The operator 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 composed of a volatile memory (not shown) and a non-volatile memory (not shown). Examples of volatile memory include RAM (Random Access Memory). Examples of non-volatile memory include ROM (Read Only Memory) and flash memory. Data, for example, is stored in the volatile memory. Programs, data tables, maps, etc., are stored in the non-volatile memory. At least a part of the storage unit 80 may be provided in a processor, integrated circuit, etc., as described later. The storage unit 80 stores a control program 84, first torque information 86, and second torque information 88.

[0055] The control program 84 is a program that causes the control device 12 to execute the control method of this embodiment. A more detailed explanation of the control method will be given later.

[0056] The first torque information 86 is information indicating the magnitude of the first predetermined torque TC. The first predetermined torque TC is the initial target torque value of the injection motor 62 when the first motor control unit 90, which will be described later, controls the injection motor 62.

[0057] The first 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 a first predetermined torque TC determined, for example, based on experiments. The user can input the first predetermined torque TC using the operating unit 78.

[0058] The second torque information 88 is information indicating the magnitude of the second predetermined torque. The second predetermined torque is the target torque value of the injection motor 62 when the second motor control unit 92, which will be described later, controls the injection motor 62. The second torque information 88 is set by the torque setting unit 91, which will be described later.

[0059] The calculation unit 82 is composed of a processor such as a CPU (Central Processing Unit) or a GPU (Graphics Processing Unit). In other words, the calculation unit 82 may be composed of a processing circuit. The calculation unit 82 includes a first motor control unit 90, a torque setting unit 91, a second motor control unit 92, and a zero-point correction unit 94.

[0060] The first motor control unit 90, the torque setting unit 91, 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. At least a portion of the first motor control unit 90, the torque setting unit 91, the second motor control unit 92, and the zero-point correction unit 94 may be realized by integrated circuits such as ASICs (Application Specific Integrated Circuits) and FPGAs (Field-Programmable Gate Arrays). Furthermore, at least a portion of the first motor control unit 90, the torque setting unit 91, the second motor control unit 92, and the zero-point correction unit 94 may be configured by electronic circuits including discrete devices.

[0061] The first motor control unit 90 performs the first control described below. In the first control, the first motor control unit 90 controls the injection motor 62 so that the magnitude of the torque in the first rotation direction gradually decreases from a first predetermined torque TC, thereby moving the injection member 24 in the first direction D1. The first rotation direction is the rotation direction of the shaft 62a when moving the injection member 24 in the first direction D1, as described above. The torque of the injection motor 62 is correlated 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.

[0062] The injection member 24 moves in the first direction D1, thereby pressing 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. In other words, although a resistance force is generated by the resin that would otherwise hinder 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.

[0063] 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. In other words, the force moving 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, it becomes impossible to move the injection member 24 in the first direction D1. That is, the movement of the injection member 24 in the first direction D1 is stopped by the obstruction caused by the resin. In this case, the movement of the injection member 24 in the first direction D1 is stopped even before the injection member 24 reaches the first end position PE1, and even if the torque of the injection motor 62 in the first rotation direction is greater than zero.

[0064] The first motor control unit 90 stores in the storage unit 80 information indicating the torque of the injection motor 62 when the movement of the injection member 24 stops in the first control. For example, the first motor control unit 90 stores in the storage unit 80 information indicating the amount of current supplied to the injection motor 62 when the movement of the injection member 24 stops in the first control. The first motor control unit 90 also determines whether the injection member 24 has stopped based on the rotational position of the shaft 62a detected by the rotational position sensor 62b.

[0065] Figure 4A is a graph illustrating the time progression of the torque of the injection motor 62 during the first control phase. The vertical axis of Figure 4A represents the torque of the injection motor 62 in the first rotational direction. The horizontal axis of Figure 4A represents time.

[0066] Time point t1 in Figure 4A is the point in time when the movement of the injection member 24 in the first direction D1 stops. The torque TA in Figure 4A is the torque of the injection motor 62 in the first rotation direction at time point t1. In this case, the first motor control unit 90 stores information indicating the torque TA in the storage unit 80. In the following description, the torque TA is also referred to as the first acquired torque TA.

[0067] If the movement of the injection member 24 stops in the first control, the first motor control unit 90 further performs the second control described below. In the second control, the first motor control unit 90 controls the injection motor 62 so that the magnitude of the torque in the second rotation direction gradually decreases from the first predetermined torque TC, thereby moving the injection member 24 in the second direction D2. The second rotation direction is the rotation direction of the shaft 62a when moving the injection member 24 in the second direction D2, as described above.

[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. In other words, although a resistance force is generated by the resin that hinders 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. In other words, the force moving 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, it becomes impossible to move the injection member 24 in the second direction D2. That is, the movement of the injection member 24 in the second direction D2 is stopped by the obstruction caused by the resin. In this case, the movement of the injection member 24 in the second direction D2 is stopped even before the injection member 24 reaches the second end position PE2, and even if the torque of the injection motor 62 in the second rotation direction is greater than zero.

[0070] The first motor control unit 90 stores in the storage unit 80 information indicating the torque of the injection motor 62 when the movement of the injection member 24 stops in the second control. For example, the first motor control unit 90 stores in the storage unit 80 information indicating the amount of current supplied to the injection motor 62 when the movement of the injection member 24 stops in the second control.

[0071] Figure 4B is a graph illustrating the time evolution of the torque of the injection motor 62 during the second control. The format of the graph in Figure 4B is the same as that of the graph in Figure 4A.

[0072] Time point t2 in Figure 4B is the point in time when the movement of the injection member 24 in the second direction D2 stops. The torque TB in Figure 4B is the torque of the injection motor 62 in the second rotation direction at time point t2. In this case, the first motor control unit 90 stores information indicating the torque TB in the storage unit 80. In the following description, the torque TB is also referred to as the second acquired torque TB.

[0073] The torque setting unit 91 determines the magnitude of the second predetermined torque using information indicating the first acquired torque TA and information indicating the second acquired torque TB. That is, the torque setting unit 91 creates second torque information 88 using information indicating the first acquired torque TA and information indicating the second acquired torque TB.

[0074] More specifically, the torque setting unit 91 compares the magnitude of the first acquired torque TA with the magnitude of the second acquired torque TB. The torque setting unit 91 sets the smaller of the first acquired torque TA and the second acquired torque TB as the second predetermined torque. If the magnitudes of the first acquired torque TA and the second acquired torque TB are equal, the torque setting unit 91 sets the second predetermined torque based on those magnitudes.

[0075] The second motor control unit 92 performs the third control described below based on the second predetermined torque. In the third control, the second motor control unit 92 controls the injection motor 62 so that the magnitude of the torque in the first rotation direction becomes the second predetermined torque. As a result, the injection member 24 is controlled to move in the first direction D1. The second motor control unit 92 adjusts the amount of current supplied to the injection motor 62 as appropriate to maintain the magnitude of the torque of the injection motor 62 at the second predetermined torque.

[0076] As described above, the second predetermined torque is the smaller of the torque TA when the injection member 24 stops moving in the first direction D1 and the torque TB when the injection member 24 stops moving in the second direction D2. Therefore, if the second motor control unit 92 controls the injection motor 62 so that the magnitude of the torque in the first rotation direction is equal to the second predetermined torque, the injection member 24 will not move in either the first direction D1 or the second direction D2.

[0077] In the third control, the injection member 24 does not move, but an axial force acts on the injection member 24 in a direction parallel to the axis LA. The value detected by the pressure sensor 48 when this axial force acts on the injection member 24 is acquired by the calculation unit 82. Once the calculation unit 82 has acquired the value detected by the pressure sensor 48 when this axial force acts on the injection member 24, the second motor control unit 92 terminates the third control.

[0078] After the third control is completed, the second motor control unit 92 further performs the fourth control described below. In the fourth control, the second motor control unit 92 controls the injection motor 62 so that the magnitude of the torque in the second rotation direction becomes the second predetermined torque. As a result, the injection member 24 is controlled to move in the second direction D2.

[0079] As described above, the second predetermined torque is the smaller of the torque TA when the injection member 24 stops moving in the first direction D1 and the torque TB when the injection member 24 stops moving in the second direction D2. Therefore, if the second motor control unit 92 controls the injection motor 62 so that the magnitude of the torque in the second rotation direction is equal to the second predetermined torque, the injection member 24 will not move.

[0080] In the fourth control, the injection member 24 does not move, but an axial force parallel to the axis LA acts on the injection member 24. The value detected by the pressure sensor 48 when this axial force acts on the injection member 24 is acquired by the calculation unit 82. Once the calculation unit 82 has acquired the value detected by the pressure sensor 48 when this axial force acts on the injection member 24, the second motor control unit 92 terminates the fourth control.

[0081] In the third control, the magnitude of the axial force acting on the injection member 24 correlates with the second predetermined torque. In the fourth control, the magnitude of the axial force acting on the injection member 24 also correlates with the second predetermined torque. Therefore, the magnitude of the axial force acting on the injection member 24 in the third control is equal to the magnitude of the axial force acting on the injection member 24 in the fourth control. Consequently, the magnitude of the detected value output by the pressure sensor 48 in the third control should be equal to the magnitude of the detected value output by the pressure sensor 48 in the fourth control. However, if the zero point of the pressure sensor 48 is not set correctly, the magnitude of the detected value output by the pressure sensor 48 in the third control will not be equal to the magnitude of the detected value output by the pressure sensor 48 in the fourth control.

[0082] The zero-point correction unit 94 can correct the zero point P0 of the pressure sensor 48. Specifically, the zero-point correction unit 94 corrects the zero point of the pressure sensor 48 based on the detected value output by the pressure sensor 48 during the third control and the detected value output by the pressure sensor 48 during the fourth control. More specifically, the zero-point correction unit 94 corrects the zero point of the pressure sensor 48 so that the absolute value of the detected value output by the pressure sensor 48 during the third control is equal to the absolute value of the detected value output by the pressure sensor 48 during the fourth control. In other words, the zero-point correction unit 94 corrects the zero point of the pressure sensor 48 so that the difference between the detected value output by the pressure sensor 48 during the third control and the corrected zero point is equal to the difference between the detected value output by the pressure sensor 48 during the fourth control and the corrected zero point. This corrects the zero-point error of the pressure sensor 48.

[0083] Figure 5 is a flowchart illustrating a control method for the injection molding machine 10.

[0084] The control device 12 can perform, for example, the control method shown in Figure 5. This control method includes a first motor control step S1, a torque setting step S2, a second motor control step S3, and a zero-point correction step S4.

[0085] The first motor control step S1 includes the first control step S11 and the second control step S12.

[0086] In the first control step S11, the first motor control unit 90 performs the first control. More specifically, in the first control step S11, the injection motor 62 is controlled so that the torque in the first rotational direction gradually decreases from a first predetermined torque TC. As a result, the injection member 24 moves in the first direction D1, but when the torque decreases to a certain level, the movement of the injection member 24 in the first direction D1 is stopped by the obstruction of the resin.

[0087] The first motor control unit 90 stores the first acquired torque TA, which occurred when the injection member 24 stopped during the first control, in the storage unit 80. This completes the first control step S11.

[0088] It should be noted that at the start of the first motor control step S1, the injection member 24 may be at the first end position PE1. In that case, the first motor control unit 90 cannot move the injection member 24 in the first direction D1.

[0089] To ensure that the injection member 24 stops before reaching the first end position PE1, the injection member 24 may be moved in the second direction D2 before starting the first motor control step S1.

[0090] In the second control step S12, the first motor control unit 90 performs the second control. More specifically, in the second control step S12, the injection motor 62 is controlled so that the torque in the second rotation direction gradually decreases from the first predetermined torque TC. As a result, the injection member 24 moves in the second direction D2, but when the torque decreases to a certain level, the movement of the injection member 24 in the second direction D2 is stopped by the obstruction of the resin.

[0091] The first motor control unit 90 stores the second acquired torque TB, which was obtained when the injection member 24 stopped in the second control, in the storage unit 80. This completes the second control step S12. When the second control step S12 is completed, the control device 12 starts the torque setting step S2.

[0092] In torque setting step S2, the torque setting unit 91 sets a second predetermined torque. The torque setting unit 91 sets the smaller of the first acquired torque TA and the second acquired torque TB as the second predetermined torque.

[0093] The torque setting unit 91 stores the second torque information 88, which indicates the second predetermined torque, in the storage unit 80. This completes the torque setting step S2. When the torque setting step S2 is completed, the control device 12 starts the second motor control step S3.

[0094] The second motor control step S3 includes the third control step S31 and the fourth control step S32.

[0095] In the third control step S31, the second motor control unit 92 performs the third control. More specifically, in the third control step S31, the second motor control unit 92 controls the injection motor 62 so that the torque in the first rotation direction becomes the second predetermined torque. As described above, the second predetermined torque is the smaller of the first acquired torque TA and the second acquired torque TB. Therefore, the injection member 24 does not move in the first direction D1. If a value detected by the pressure sensor 48 is obtained, the control device 12 terminates the third control step S31.

[0096] In the fourth control step S32, the second motor control unit 92 performs the fourth control. More specifically, in the fourth control step S32, the second motor control unit 92 controls the injection motor 62 so that the torque in the second rotation direction becomes the second predetermined torque. As described above, the second predetermined torque is the smaller of the first acquired torque TA and the second acquired torque TB. Therefore, the injection member 24 does not move in the second direction D2. If a value detected by the pressure sensor 48 is obtained, the control device 12 terminates the fourth control step S32.

[0097] In the zero-point correction step S4, the zero-point correction unit 94 corrects the zero point of the pressure sensor 48. The zero-point correction unit 94 corrects the zero point of the pressure sensor 48 based on the detected value output by the pressure sensor 48 during the third control step S31 and the detected value output by the pressure sensor 48 during the fourth control step S32. The control method shown in Figure 5 is completed when the zero-point correction unit 94 corrects the zero point of the pressure sensor 48.

[0098] According to the control device 12, the zero-point error of the pressure sensor 48 is corrected. Moreover, the number of times the injection member 24 moves to correct the zero-point of the pressure sensor 48 can be as few as two: movement in the first direction D1 when the first control is executed, and movement in the second direction D2 when the second control is executed. In other words, the control device 12 can correct the zero-point of the pressure sensor 48 while minimizing the number of movements of the injection member 24.

[0099] By reducing the number of movements of the injection member 24, the risk of air being drawn into the injection cylinder 22 from the injection port 34p due to the injection member 24 moving multiple times is reduced. By reducing the risk of air being drawn into the injection cylinder 22, the risk of the air drawn into the injection cylinder 22 causing resin burning in the resin inside the injection cylinder 22 is also reduced.

[0100] The control device 12 also reduces the time required to execute the control method shown in Figure 5. In other words, the control device 12 also reduces the time required to correct the zero point of the pressure sensor 48.

[0101] The timing at which the control device 12 executes the control method shown in Figure 5 is not particularly limited, as long as the resin that imparts viscous resistance to the injection member 24 remains in the injection cylinder 22. However, it is preferable that the control device 12 performs the first motor control step S1 and the second motor control step S3 during automatic purging. In other words, it is preferable that the control device 12 automatically starts the control method shown in Figure 5 when it starts automatic purging. This eliminates the need to delay the start of the molding cycle solely to correct the zero point of the pressure sensor 48. It also eliminates the need to interrupt the molding cycle solely to correct the zero point of the pressure sensor 48. The control device 12 executes automatic purging by appropriately controlling the rotary motor 54 and the injection motor 62.

[0102] [Differentiation] The control device 12 may be applied to a pre-plasticized injection molding machine.

[0103] In a pre-plasticized injection molding machine, the injection member 24 is composed of a plunger (not shown). The plunger is inserted into the injection cylinder 22. The plunger moves in a first direction D1 and a second direction D2 in response to the drive of the injection motor 62.

[0104] In this modified example, the first motor control unit 90 can perform the first control and the second control in the same manner as in the above embodiment. As a result, a first acquired torque TA is obtained when the plunger stops moving in the first direction D1, and a second acquired torque TB is obtained when the plunger stops moving in the second direction D2. Therefore, the torque setting unit 91 can set a second predetermined torque based on the first acquired torque TA and the second acquired torque TB, in the same manner as in the above embodiment.

[0105] Furthermore, in this modified example, the second motor control unit 92 can perform the third control and the fourth control, similar to the embodiment described above. Also, the zero-point correction unit 94 can correct the zero point of the pressure sensor 48 based on the detected value output by the pressure sensor 48 during the third control and the detected value output by the pressure sensor 48 during the fourth control, similar to the embodiment described above. Moreover, the zero-point correction unit 94 can correct the zero point P0 of the pressure sensor 48 while minimizing the number of plunger movements.

[0106] [Note] The following additional information is disclosed regarding the above embodiments and modifications.

[0107] (Note 1) The control device (12) of an injection molding machine (10) comprising 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 the resin in the injection cylinder, performs a first control to move the injection member in a first direction by controlling the injection motor so that the torque gradually decreases from a first predetermined torque (TC), and when the movement of the injection member stops in the first control, performs a second control to move the injection member in a second direction opposite to the first direction by controlling the injection motor so that the torque gradually decreases from the first predetermined torque, and the torque of the injection motor when the injection member stops in the first control and the torque of the injection motor when the injection member stops in the second control The system includes a torque setting unit (91) that sets the smaller of the torque of the injection motor when the injection member stops and the torque of the injection motor when the injection member stops as a second predetermined torque; a second motor control unit (92) that performs a third control to control the injection motor so that the torque becomes the second predetermined torque and the injection member moves in one of the first and second directions, and if the movement of the injection member stops in the third control, it performs a fourth control to control the injection motor so that the torque becomes the second predetermined torque and the injection member moves in the other of the first and second directions; and a zero-point correction unit (94) that corrects the zero point of the pressure sensor based on the detected value output by the pressure sensor during the third control and the detected value output by the pressure sensor during the fourth control. This makes it possible to correct the zero point of the pressure sensor while suppressing the number of movements of the injection member.

[0108] (Note 2) The control device for an injection molding machine as described in Appendix 1 may also be a control device for an injection molding machine in which the zero-point correction unit corrects the zero point so that the absolute value of the detected value output by the pressure sensor during the third control is equal to the absolute value of the detected value output by the pressure sensor during the fourth control. This makes it possible to correct the zero point of the pressure sensor while reducing the number of movements of the injection member.

[0109] (Note 3) The control device for an injection molding machine described in Appendix 1 or 2 may be an injection molding machine control device in which the first motor control unit and the second motor control unit control the injection motor while the injection molding machine is performing automatic purging. This eliminates the need to delay the start of the molding cycle solely to correct the zero point of the pressure sensor. It also eliminates the need to interrupt the molding cycle solely to correct the zero point of the pressure sensor.

[0110] (Note 4) A control method for an injection molding machine (10) comprising 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 the resin in the injection cylinder, comprising: a first motor control step (S1) which performs a first control to move the injection member in a first direction by controlling the injection motor so that the torque gradually decreases from a first predetermined torque (TC); a second control to move the injection member in a second direction opposite to the first direction by controlling the injection motor so that the torque gradually decreases from the first predetermined torque; the torque of the injection motor when the injection member stops in the first control; and the torque of the injection motor when the injection member stops in the second control. The method includes: a torque setting step (S2) in which the smaller of the torque of the injection motor when the injection member stops and a second predetermined torque is set; a third control step (S3) in which the injection motor is controlled so that the torque becomes the second predetermined torque and the injection member moves in one of the first and second directions; a fourth control step (S4) in which the injection motor is controlled so that the torque becomes the second predetermined torque and the injection member moves in the other of the first and second directions; and a zero point correction step (S4) in which the zero point of the pressure sensor is corrected based on the detected value output by the pressure sensor during the third control and the detected value output by the pressure sensor during the fourth control. This makes it possible to correct the zero point of the pressure sensor while suppressing the number of movements of the injection member.

[0111] While embodiments of this disclosure have been described in detail, this disclosure is not limited to the individual embodiments described above. These embodiments can be added, replaced, modified, partially deleted, etc., in any way that does not depart from the spirit of the invention or the idea and intent derived from the claims and their equivalents. For example, the order of operations or processes in the embodiments described above are shown as examples only and are not limited thereto. The same applies when numerical values ​​or mathematical formulas are used in the description of the embodiments described above. [Explanation of Symbols]

[0112] 10…Injection molding machine 12…Control device 22…Injection cylinder 24…Injection member 48...Pressure sensor 62...Injection motor 90...First motor control unit 91...Torque setting unit 92...Second motor control unit 94...Zero point correction unit

Claims

1. A control device (12) for an injection molding machine (10) comprising: 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 the resin in the injection cylinder, A first motor control unit (90) performs a first control to move the injection member in a first direction by controlling the injection motor so that the torque gradually decreases from a first predetermined torque (TC), and if the movement of the injection member stops in the first control, it performs a second control to move the injection member in a second direction opposite to the first direction by controlling the injection motor so that the torque gradually decreases from the first predetermined torque, A torque setting unit (91) sets the smaller of the torque of the injection motor when the injection member stops in the first control and the torque of the injection motor when the injection member stops in the second control as the second predetermined torque, A second motor control unit (92) performs a third control to control the injection motor so that the torque becomes the second predetermined torque, thereby controlling the injection member to move in one of the first and second directions, and if the movement of the injection member stops in the third control, it performs a fourth control to control the injection motor so that the torque becomes the second predetermined torque, thereby controlling the injection member to move in the other of the first and second directions. A zero-point correction unit (94) corrects the zero point of the pressure sensor based on the detected value output by the pressure sensor during the third control and the detected value output by the pressure sensor during the fourth control. A control device for an injection molding machine, equipped with the following features.

2. A control device for an injection molding machine according to claim 1, The control device for an injection molding machine, wherein the zero-point correction unit corrects the zero point so that the absolute value of the detected value output by the pressure sensor during the third control is equal to the absolute value of the detected value output by the pressure sensor during the fourth control.

3. A 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 a control device for an injection molding machine that controls the injection motor while the injection molding machine is performing an automatic purge.

4. A control method for an injection molding machine (10) comprising 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 the resin in the injection cylinder, A first motor control step (S1) is performed which involves controlling the injection motor so that the torque gradually decreases from a first predetermined torque (TC) to move the injection member in a first direction, and controlling the injection motor so that the torque gradually decreases from the first predetermined torque to move the injection member in a second direction opposite to the first direction. A torque setting step (S2) is performed in which the smaller of the torque of the injection motor when the injection member stops in the first control and the torque of the injection motor when the injection member stops in the second control is set as the second predetermined torque, A second motor control step (S3) is performed, which involves controlling the injection motor so that the torque becomes the second predetermined torque, thereby controlling the injection member to move in one of the first and second directions, and controlling the injection motor so that the torque becomes the second predetermined torque, thereby controlling the injection member to move in the other of the first and second directions. A zero-point correction step (S4) in which the zero point of the pressure sensor is corrected based on the detected value output by the pressure sensor during the third control and the detected value output by the pressure sensor during the fourth control, A control method for an injection molding machine, including [the specified function / feature].

Images