injection molding machine

Abstract

The injection molding machine (10) comprises: a mold clamping mechanism (a conversion mechanism (44g) and a toggle mechanism (29)), which moves a fixed pressure plate (24) holding a fixed mold (20a) toward a fixed pressure plate holding a fixed mold, so that the fixed mold contacts the movable mold and a mold clamping force (F) is generated therebetween; a driving source (a mold opening and closing motor (44a)), which drives the mold clamping mechanism; a mold clamping force detection unit (52), which detects the mold clamping force; an elongation value detection unit (54), which detects an elongation value (L) indicating an elongation amount of a pull rod (32) elongated as the mold clamping force is generated; and an abnormality determination unit (56), which determines an abnormality of the injection molding machine based on a ratio of the elongation value to the mold clamping force.

Description

Technical Field

[0001] The present invention relates to an injection molding machine. Background Art

[0002] Various methods have been proposed to detect abnormalities in the mechanical components of injection molding machines. These methods generally use various sensors and fixtures to detect abnormalities in the mechanical components (for example, Japanese Patent Application Laid-Open No. 2010-137542). However, the installation and configuration of sensors and fixtures are complex, and if a sensor or fixture malfunctions, abnormality detection becomes difficult. Summary of the Invention

[0003] An object of the present invention is to provide an injection molding machine capable of detecting an abnormality in a mechanism portion relatively easily.

[0004] An injection molding machine according to one embodiment includes: a fixed pressure plate that holds a fixed mold; a rear pressure plate; a tie rod that connects the fixed pressure plate and the rear pressure plate; a movable pressure plate that is arranged between the fixed pressure plate and the rear pressure plate, holds the movable mold in a manner opposite to the fixed mold, and is movable along the tie rod; a clamping mechanism that moves the movable pressure plate toward the fixed pressure plate to bring the fixed mold into contact with the movable mold, thereby generating a clamping force between the fixed mold and the movable mold; a drive source that drives the clamping mechanism; a clamping force detection unit that detects the clamping force; an elongation value detection unit that detects an elongation value indicating an elongation amount of the tie rod that is elongated as the clamping force is generated; and an abnormality determination unit that determines an abnormality of the injection molding machine based on a ratio of the elongation value to the clamping force.

[0005] According to the present invention, it is possible to provide an injection molding machine capable of detecting an abnormality in a mechanism portion relatively easily. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 It is a diagram showing an injection molding machine main body according to the embodiment.

[0007] Figure 2 This is a functional block diagram of the control device that controls the main body of the injection molding machine.

[0008] Figure 3 This is a flowchart showing the mold closing sequence of an injection molding machine.

[0009] Figure 4 This is a graph showing an example of the relationship between the elongation value and the mold clamping force. DETAILED DESCRIPTION

[0010] Hereinafter, the injection molding machine according to the embodiment will be described in detail.

[0011] Figure 11 is a diagram showing an injection molding machine body 12 according to an embodiment. The injection molding machine body 12 includes a base 14, a mold clamping device 22 for opening and closing a mold 20, and an injection device (not shown) for injecting molten resin into the mold 20.

[0012] The base 14 is a base for installing the mold clamping device 22 and the injection device. The mold clamping device 22 includes a fixed platen 24, a rear platen 26, a movable platen 28, a toggle mechanism 29, and a toggle drive mechanism 44.

[0013] The fixed platen 24 and rear platen 26 are mounted on the base 14 and connected by four parallel tie bars 32 that extend through the movable platen 28 and in the A-direction. The movable platen 28 is positioned between the fixed platen 24 and rear platen 26 on the base 14 via a slide 34. The slide 34 is movable along a guide rail 36 disposed along the base 14 in the A-direction. This allows the movable platen 28 to advance and retract in the A-direction relative to the fixed platen 24.

[0014] The mold 20 is provided between the fixed platen 24 and the movable platen 28. The mold 20 is composed of a fixed mold 20a and a movable mold 20b. The fixed mold 20a is attached to the movable platen 28 side of the fixed platen 24. The movable mold 20b is attached to the fixed platen 24 side of the movable platen 28.

[0015] The toggle mechanism 29 is disposed between the rear platen 26 and the movable platen 28. Driven by the toggle drive mechanism 44, the toggle mechanism 29 advances and retracts the movable platen 28 relative to the fixed platen 24, thereby opening and closing the mold 20 in the A direction (opening and closing direction). The toggle mechanism 29 amplifies the driving force transmitted from the toggle drive mechanism 44 to the crosshead 40 (described later) and transmits it to the movable platen 28.

[0016] The toggle mechanism 29 includes a toggle link 30, a cross link 38, and a crosshead 40. Two toggle links 30 and two cross links 38 are provided at the top and bottom, respectively, for a total of four. Here, one is shown near the top and bottom, with the two further links hidden behind them. The toggle link 30 includes a first link 30a, a second link 30b, a first toggle pin 30c, a second toggle pin 30d, and a third toggle pin 30e.

[0017] One end of the first link 30a is rotatably connected to the movable platen 28 via a first toggle pin 30c. One end of the second link 30b is rotatably connected to the rear platen 26 via a second toggle pin 30d. The other end of the first link 30a and the other end of the second link 30b are rotatably connected to each other via a third toggle pin 30e.

[0018] The second link 30b is connected to the crosshead 40 via a transverse link 38. The crosshead 40 has arms 42 (upper arm 42a, lower arm 42b) extending upward and downward. The transverse link 38 is connected to the front end of the arm 42. The crosshead 40 is mounted on the rear platen 26 and is guided by two guide rods (not shown) extending in the A direction, thereby enabling it to advance and retreat in the A direction.

[0019] The toggle drive mechanism 44 drives the toggle mechanism 29 to open and close the mold 20 in the A direction (opening and closing direction). The toggle drive mechanism 44 includes a mold opening and closing motor 44a (drive source), a drive pulley 44b, a conveyor belt 44c, a driven pulley 44d, a ball screw 44e, and a ball screw nut 44f. The ball screw 44e is arranged along the A direction so as to be parallel to the tie rod 32.

[0020] The driving pulley 44b is configured to rotate integrally with the rotating shaft of the mold opening and closing motor 44a. The driven pulley 44d is configured to rotate integrally with the ball screw 44e. The conveyor belt 44c is mounted on the driving pulley 44b and the driven pulley 44d to transmit the rotational force of the driving pulley 44b to the driven pulley 44d. The ball screw nut 44f is fixed to the crosshead 40 and screwed with the ball screw 44e. The ball screw nut 44f (crosshead 40) moves along the ball screw 44e as the ball screw 44e rotates. That is, the driving pulley 44b, the conveyor belt 44c, the driven pulley 44d, the ball screw 44e and the ball screw nut 44f constitute a conversion mechanism 44g that converts the rotational motion (rotational force) of the mold opening and closing motor 44a into the linear motion (stress) of the crosshead 40 in the A direction. Furthermore, the conversion mechanism 44g and the toggle mechanism 29 function as a mold clamping mechanism that generates a mold clamping force F between the fixed mold 20a and the movable mold 20b.

[0021] The conversion mechanism 44g converts the rotational force (rotational motion) of the mold opening / closing motor 44a into stress (linear motion) in the A direction. As a result, the crosshead 40 of the toggle mechanism 29 presses the movable platen 28 in the A direction via the toggle mechanism 29, and the movable platen 28 moves in the A direction.

[0022] When the mold opening / closing motor 44a rotates forward, the movable platen 28 moves toward the fixed platen 24, causing the movable mold 20b to abut against the fixed mold 20a (a mold-contact state, at which point the movable platen 28 is at the mold-contact position). While in this contact state, further forward rotation of the mold opening / closing motor 44a applies stress (the mold clamping force F) between the movable mold 20b and the fixed mold 20a. At this point, the tie rod 32 is extended between the fixed platen 24 and the rear platen 26 by the mold clamping force F. In other words, the extension value L of the tie rod 32 corresponds to the amount of movement of the movable platen 28 relative to the fixed platen 24 after the mold contact state is achieved. When the movable mold 20b's movement, caused by the toggle mechanism 29, reaches its limit, the mold clamping device 22 enters a locked state. At this point, the extension value L of the tie rod 32, and therefore the mold clamping force F, is sufficiently large.

[0023] In the locked state, liquid resin material is injected into the mold 20 and solidified. Thereafter, by reversing the mold opening and closing motor 44a, the movable platen 28 moves toward the rear platen 26, the movable mold 20b separates from the fixed mold 20a, and the mold 20 opens.

[0024] The mold clamping unit 22 also includes an ejector mechanism (not shown) for removing the molded product from the movable mold 20b. The ejector mechanism is located on the rear platen 26 side of the movable platen 28. When the mold 20 is open, the ejector pins extending in the A direction are moved toward the movable platen 28, thereby extruding the molded product from the movable mold 20b.

[0025] Figure 2 This is a functional block diagram of the control device 50 that controls the injection molding machine main body 12. The control device 50 opens and closes the mold 20, controls the injection molding machine main body 12 to generate the mold clamping force F, and detects abnormalities in the injection molding machine main body 12. The injection molding machine main body 12 and the control device 50 constitute the injection molding machine 10. The control device 50 includes a mold clamping force detection unit 52, an elongation value detection unit 54, an abnormality determination unit 56, and a motor control unit 58. Detection signals from sensors Sf and Sm are input to the control device 50.

[0026] Sensors Sf and Sm are installed in the injection molding machine body 12 to detect the state of the injection molding machine body 12. Sensor Sf detects quantities related to the mold clamping force F (e.g., stress, pressure, strain). Sensor Sm detects quantities related to the elongation value L of the tie rod 32 (e.g., elongation, strain, position of the rear platen 26).

[0027] The mold clamping force detection unit 52 , the elongation value detection unit 54 , the abnormality determination unit 56 , and the motor control unit 58 can be configured by a processor (for example, a CPU: Central Processing Unit) and a program.

[0028] The mold clamping force detection unit 52 detects the mold clamping force F applied to the mold 20 based on the signal from the sensor Sf. This detection can be performed directly or indirectly.

[0029] As the sensor Sf, for example, a mold clamping force sensor can be used to directly detect the mold clamping force F. The mold clamping force sensor can be a stress sensor (for example, a pressure sensor Sf1) provided on the mold 20 or the tie rod 32. The stress sensor Sf1 is provided on, for example, at least one of the four tie rods 32 ( Figure 1 , as an example, a pressure sensor Sf1 is shown which is provided between the tie rod 32 and the fixed platen 24. Alternatively, a strain sensor may be used as the sensor Sf to detect the mold clamping force F.

[0030] The extension value detection unit 54 detects an extension value L indicating the extension amount of the tie bar 32 that extends in accordance with the mold clamping force F, based on a signal from the sensor Sm. This detection can be performed directly or indirectly.

[0031] As the sensor Sm, for example, a strain sensor Sm1 can be used to directly detect the elongation value L of the tie rod 32. The strain sensor Sm1 is provided on the tie rod 32 and can directly detect the elongation value L of the tie rod 32. Figure 1 , a strain sensor Sm1 provided on a side portion of the tie rod 32 is shown as an example.

[0032] The elongation value L can be obtained based on the amount of movement of the rear platen 26. That is, when the mold clamping force F is generated in the mold 20, the rear platen 26 moves due to its reaction force. Therefore, the elongation value L of the tie rod 32 can be detected based on the amount of movement of the rear platen 26. In this case, as the sensor Sm, a position detector Sm2 (see Figure 1 The elongation value detecting unit 54 calculates the amount of change in the position of the rear platen 26 after the fixed mold 20a and the movable mold 20b come into contact as the elongation value L based on the signal from the position detector Sm2.

[0033] The abnormality determination unit 56 determines an abnormality in the injection molding machine 10 based on the ratio R between the elongation value L and the mold clamping force F after mold contact (e.g., R = F / L). Specifically, an abnormality is determined when the ratio R, representing the change ΔF in the mold clamping force F relative to the change in the elongation value L, is less than a threshold value Th0. This determination is made during the mold clamping operation (particularly, from the mold contact position to the locked position).

[0034] This ratio R is not only based on the elongation value L and the clamping force F, that is, the ratio of the elongation value L and the clamping force F themselves (R=F / L), but can also be calculated based on their differential amounts (small changes ΔL in the elongation value L, small changes ΔF in the clamping force F) to compare it with the threshold value Th0.

[0035] If it is determined to be abnormal, cracks, fissures, or chips may occur in the tie rod 32. In addition, cracks, fissures, or chips may occur in components other than the tie rod 32, such as the ball screw 44e.

[0036] The motor control unit 58 controls the mold opening and closing motor 44a for the mold clamping operation to move the movable platen 28. When the abnormality determination unit 56 determines that an abnormality occurs during the mold clamping operation, the motor control unit 58 controls the mold opening and closing motor 44a to stop the operation of the mold clamping device 22 (mold clamping mechanism) in the middle of or after the mold clamping operation. The mold clamping operation can be stopped to prevent the failure of the injection molding. If the mold clamping operation and the subsequent injection molding are performed when it is determined to be abnormal, the mold clamping force F during the injection molding becomes insufficient, and the liquid resin material may leak from between the fixed mold 20a and the movable mold 20b.

[0037] Figure 3 : is a flowchart showing the mold closing sequence of the injection molding machine 10. The motor control unit 58 controls the mold opening and closing motor 44a to start the mold closing action. That is, the motor control unit 58 rotates the mold opening and closing motor 44a in the forward direction to move the movable platen 28 toward the fixed platen 24. As a result, the movable mold 20b abuts against the fixed mold 20a (mold contact position, step S1), and a mold clamping force F is generated in the mold 20. In addition, mold contact can be detected based on the mold clamping force F calculated by the mold clamping force detection unit 52, for example (the mold clamping force F changes substantially from zero). In addition, mold contact can also be detected based on a change in the power consumption (or drive current) in the mold opening and closing motor 44a (a sharp increase in power consumption).

[0038] Afterwards, the motor control unit 58 continues the forward rotation of the mold opening and closing motor 44a until it becomes locked (locked position, step S2). During this period, the mold clamping force F increases. In addition, regarding locking, for example, it can be detected based on the change in the power consumption (or driving current) in the mold opening and closing motor 44a (the increase in power consumption stops). In addition, locking can also be detected based on the position of the crosshead 40, etc. Usually, when the mold 20 is replaced, the mold clamping device 22 is adjusted for mold thickness, and when the crosshead 40 is at a predetermined position (origin), the desired mold clamping force F can be obtained. After this adjustment, the crosshead 40 reaches the origin, and it can be regarded as having detected locking. The position of the crosshead 40 can be measured directly, but it can also correspond to the elongation value L of the tie rod 32, etc.

[0039] From the mold contact state to the locked state, the extension value detector 54 detects the extension value L of the tie bar 32 (step S3 ), and the mold clamping force detector 52 detects the mold clamping force F applied to the mold 20 (step S4 ).

[0040] The abnormality determination unit 56 calculates the ratio R (=F / L) of the elongation value L to the mold clamping force F (step S5) and compares this ratio R with a threshold value (step S6). If the ratio R is greater than the threshold value (yes in step S6), the injection molding machine 10 determines that it is normal and the mold clamping operation continues. If the ratio R is less than the threshold value (no in step S6), the injection molding machine 10 determines that it is abnormal (step S7) and the motor control unit 58 interrupts the mold clamping operation (step S8).

[0041] Figure 4 This graph shows an example of the relationship between elongation value L and mold clamping force F. The horizontal axis represents elongation value L, and the vertical axis represents mold clamping force F. The origin O of elongation value L corresponds to the mold contact position, and elongation value L1 corresponds to the locked position. As elongation value L increases, mold clamping force F also increases.

[0042] Figure 4 Graphs Gs, G1, and G2 are shown. Graph Gs is a reference graph in which the ratio of the mold clamping force F to the elongation value L is at a reference value Rs (threshold value). Graph G1 is a graph in which the mold clamping operation is terminated when the ratio of the mold clamping force F to the elongation value L is at or above the reference value Rs (threshold value). Graph G2, on the other hand, is a graph in which the ratio of the mold clamping force F to the elongation value L is less than the reference value Rs (threshold value). In this case, the mold clamping operation is interrupted midway.

[0043] (Variation)

[0044] The following describes a modified example. Here, the mold clamping force detection unit 52 calculates the mold clamping force F based on the torque (rotational force) P of the mold opening / closing motor 44a and the force amplification factor βp of the toggle mechanism 29. Furthermore, the extension value detection unit 54 calculates the extension of the tie rod 32 as the extension value L based on the rotation amount of the mold opening / closing motor 44a (motor) after the fixed mold 20a and movable mold 20b come into contact and the amplification factor of the toggle mechanism 29.

[0045] The rotation amount M of the mold opening and closing motor 44a (motor) and the extension value L of the tie rod 32 (the movement amount of the movable platen 28) are related as shown in equation (1). In addition, the torque P of the mold opening and closing motor 44a (motor) and the mold clamping force F are related as shown in equation (2).

[0046] L=αm*βm(M)*M=Am(M)*M……(1)

[0047] F=αp*βp(M)*P=Ap(M)*P……(2)

[0048] Here, Am(M)=αm*βm(M) and Ap(M)=αp*βp(M).

[0049] The rotation amount M is the amount (number of rotations) by which the shaft of the mold opening and closing motor 44a has rotated, and can be detected using a rotation detector Sm3 or the like provided in the mold opening and closing motor 44a (see Figure 1 ). That is, the sensor Sm can be a rotation detector Sm3. In addition, the torque P is the rotational force of the shaft of the mold opening and closing motor 44a, and can be obtained based on the power consumption or drive current of the mold opening and closing motor 44a. That is, the sensor Sf can serve as a drive current sensor.

[0050] The amplification factors αm and αp are the amplification factors of the motion and stress in the conversion mechanism 44g, respectively. Specifically, the amplification factor αm is the ratio of the motion on the output side of the conversion mechanism 44g (the movement of the crosshead 40) to the motion on the input side of the conversion mechanism 44g (the rotation M of the mold opening and closing motor 44a). Furthermore, the amplification factor αp is the ratio of the stress output from the conversion mechanism 44g (the stress applied to the crosshead 40) to the stress input to the conversion mechanism 44g (the torque P of the mold opening and closing motor 44a). The amplification factors αm and αp in the conversion mechanism 44g are both constant (independent of the rotation M), but their values generally differ.

[0051] The amplification factors βm(M) and βp(M) are the amplification factors of the motion and stress, respectively, in the toggle mechanism 29. Specifically, the amplification factor βm(M) is the ratio of the motion on the output side of the toggle mechanism 29 (the amount of movement of the movable platen 28) to the motion on the input side of the toggle mechanism 29 (the amount of movement of the crosshead 40). Furthermore, the amplification factor βp(M) is the ratio of the stress (force) output from the toggle mechanism 29 (applied from the first link 30a to the movable platen 28) to the stress (force) input to the toggle mechanism 29 (applied from the toggle drive mechanism 44 to the crosshead 40).

[0052] Typically, the magnifications βm(M) and βp(M) (magnifications Am(M) and Ap(M)) also vary depending on the angle θ formed between the toggle link 30 and the second link 30b (which is the position of the crosshead 40 and, as a result, the amount of rotation M). For example, the magnification βm(M) is relatively large at the mold contact position and relatively small at the locked position. Furthermore, the magnification βp(M) is relatively small at the mold contact position and relatively large at the locked position. Thus, the magnifications βm(M) and βp(M) (magnifications Am(M) and Ap(M) as well) depend on the amount of rotation M, but the relationship between the amount of rotation M (or the position of the crosshead 40) after contact with the mold can be determined in advance using analytical or experimental methods. If the relationship between the amount of rotation M and the magnifications βm and βp determined in advance is stored as a table in a memory or the like, the elongation value L and the mold clamping force F can be calculated using this table.

[0053] In the above equations (1) and (2), the elongation value L and the mold clamping force F are calculated using the amplification factors αm and αp of the conversion mechanism 44g. However, the amplification factors αm and αp do not necessarily need to be used. In other words, the amplification factors αm and αp are fixed values. Therefore, the values L' and F' corresponding to the elongation L and the torque P can be calculated based on the following equations (3) and (4).

[0054] L'=βm(M)*M……(3)

[0055] F'=βp(M)*P……(4)

[0056] In this case, abnormality determination unit 56 also determines the ratio R of value F' to value L' (=F' / L') and compares this ratio R with a threshold value to detect an abnormality. The threshold value in this case takes into account the amplification factors αm and αp. For example, threshold value Th in this case is set to "Th0*(αp / αm)."

[0057] In the above method, both the elongation value L and the mold clamping force F are calculated. However, this method can also be used to calculate only one of the elongation value L and the mold clamping force F, and the other can be obtained by the method described in the embodiment.

[0058] In other respects, the modification example does not differ substantially from the embodiment, and therefore detailed description thereof will be omitted.

[0059] (Invention derived from embodiment)

[0060] Hereinafter, inventions that can be grasped based on the above-described embodiment and modified examples will be described.

[0061] [1] The injection molding machine 10 comprises: a fixed platen 24 that holds the fixed mold 20a; a rear platen 26; a tie rod 32 that connects the fixed platen 24 and the rear platen 26; a movable platen 28 that is arranged between the fixed platen and the rear platen and holds the movable mold 20b in a manner opposite to the fixed mold and is movable along the tie rod; a mold clamping mechanism (a switching mechanism 44g and a toggle mechanism 29) that moves the movable platen toward the fixed platen to allow the movable platen to move toward the fixed platen. The fixed mold contacts the movable mold, generating a mold clamping force F between them; a drive source (mold opening / closing motor 44a) that drives the mold clamping mechanism; a mold clamping force detector 52 that detects the mold clamping force; an elongation value detector 54 that detects an elongation value L indicating the amount of elongation of the tie rod as the mold clamping force is generated; and an abnormality determination unit 56 that determines an abnormality in the injection molding machine based on a ratio R between the elongation value and the mold clamping force. Thus, abnormalities in the mechanical components of the injection molding machine can be detected relatively simply based on the ratio between the elongation value and the mold clamping force.

[0062] [2] The abnormality determination unit determines that an abnormality is present when the ratio of the change in the mold clamping force to the change in the elongation value is less than a threshold value Th0. By comparing the ratio with the threshold value, an abnormality in the mechanism of the injection molding machine can be detected.

[0063] [3] The mold clamping mechanism is a toggle-type mold clamping mechanism (conversion mechanism 44g and toggle mechanism 29), the drive source is an electric motor (mold opening and closing motor 44a), and the mold clamping force detection unit calculates the mold clamping force based on the torque from the motor after the fixed mold and the movable mold come into contact and the amplification factor of the mold clamping mechanism. This makes it possible to detect abnormalities in the mechanical components of the injection molding machine without using a mold clamping force sensor.

[0064] [4] The mold clamping force detection unit calculates the mold clamping force based on the signal from the mold clamping force sensor (Sf, Sf1). This allows the mold clamping force sensor to be used to detect abnormalities in the mechanism of the injection molding machine.

[0065] [5] The mold clamping mechanism is a toggle-type mold clamping mechanism (the toggle drive mechanism 44 and the toggle mechanism 29), the drive source is a motor (the mold opening and closing motor 44a), and the elongation value detection unit calculates the elongation of the tie rod 32 as the elongation value based on at least the amount of rotation of the motor after the fixed mold and the movable mold come into contact and the amplification factor of the mold clamping mechanism. This makes it possible to detect abnormalities in the mechanical components of the injection molding machine without using a position detector or strain sensor.

[0066] [6] The elongation value detection unit calculates the elongation value as the change in position of the rear platen after the fixed mold and the movable mold contact, based on a signal from the position detector Sm2 that detects the position of the rear platen. This makes it possible to easily detect abnormalities in the mechanical components of the injection molding machine using the position detector.

[0067] [7] The elongation value detection unit calculates the elongation of the tie rod based on the signal from the strain sensor Sm1. This makes it possible to easily detect abnormalities in the mechanism of the injection molding machine using the strain sensor.

[0068] [8] The injection molding machine includes a stop control unit (motor control unit 58) that controls the drive source to stop the operation of the mold clamping mechanism when the abnormality determination unit determines that an abnormality has occurred. This can stop the operation of the mold clamping mechanism and prevent injection molding failure.

Claims

1. An injection molding machine (10), characterized in that The injection molding machine (10) comprises: A fixed pressing plate (24) which holds the fixed die (20a); rear pressing plate (26); a pull rod (32) connecting the fixed pressure plate and the rear pressure plate; A movable pressing plate (28) is arranged between the fixed pressing plate and the rear pressing plate, holds the movable mold (20b) in a manner opposite to the fixed mold, and is movable along the pull rod; a mold clamping mechanism (44g, 29) which moves the movable platen toward the fixed platen to bring the fixed mold into contact with the movable mold, thereby generating a mold clamping force (F) between the fixed mold and the movable mold; a driving source (44a) for driving the mold clamping mechanism; a mold clamping force detection unit (52) for detecting the mold clamping force during a period from a mold contact state in which the movable mold is moved by the movable platen and abuts against the fixed mold to a locked state in which the limit of movement of the movable mold is reached by the mold clamping mechanism; an elongation value detecting section (54) for detecting an elongation value (L) indicating an elongation amount of the tie rod elongated as the mold clamping force is generated during a period from the mold contact state to the locked state; as well as An abnormality determination unit (56) calculates a ratio of the elongation value to the mold clamping force and determines an abnormality of the injection molding machine (10) based on the ratio.

2. The injection molding machine according to claim 1, characterized in that The abnormality determination unit determines that an abnormality has occurred when a ratio of a change in the mold clamping force to a change in the elongation value is smaller than a threshold value.

3. The injection molding machine according to claim 1, wherein The mold clamping mechanism is a toggle-type mold clamping mechanism (44g, 29), The driving source is an electric motor (44a), The mold clamping force detection unit calculates the mold clamping force based on the torque (P) of the motor and the amplification factor (αm, βm) of the mold clamping mechanism after the fixed mold and the movable mold come into contact.

4. The injection molding machine according to claim 1, wherein The mold clamping force detection unit calculates the mold clamping force based on a signal from a mold clamping force sensor (Sf, Sf1).

5. The injection molding machine according to any one of claims 1 to 4, characterized in that The clamping mechanism is a toggle clamping mechanism, The driving source is an electric motor, The extension value detection unit calculates the extension amount of the tie rod as the extension value based on at least the rotation amount (M) of the motor after the fixed mold and the movable mold come into contact and the amplification factor of the mold clamping mechanism.

6. The injection molding machine according to any one of claims 1 to 4, characterized in that The elongation value detecting section calculates, as the elongation value, an amount of change in the position of the rear platen after the fixed mold and the movable mold come into contact, based on a signal from a position detector (Sm2) that detects the position of the rear platen.

7. The injection molding machine according to any one of claims 1 to 4, characterized in that The elongation value detection unit calculates the elongation of the tie rod based on a signal from a strain sensor (Sm1).

8. The injection molding machine according to any one of claims 1 to 7, characterized in that The injection molding machine includes a stop control unit (58) which controls the driving source to stop the operation of the mold clamping mechanism when the abnormality determination unit determines that an abnormality has occurred.

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