Patent Publication Number: US-2023145021-A1

Title: Injection molding machine

Description:
TECHNICAL FIELD 
     The present invention relates to an injection molding machine. 
     BACKGROUND ART 
     Various methods have been proposed for detecting an abnormality in a mechanical unit of an injection molding machine. In these methods, generally, such an abnormality of the mechanical unit is detected using various sensors and jigs (for example, JP 2010-137542 A). However, installation and setting of the sensors and the jigs are complicated, and it is difficult to detect an abnormality if the sensor or the jig gets out of order. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an injection molding machine capable of relatively easily detecting abnormalities of a mechanical unit. 
     According to an aspect of the present invention, there is provided an injection molding machine including: a stationary platen configured to hold a fixed mold; a rear platen; a tie bar configured to connect the stationary platen and the rear platen to each other; a movable platen that is disposed between the stationary platen and the rear platen and is configured to hold a movable mold in a manner that the movable mold faces the fixed mold and further configured to be movable along the tie bar; a mold clamping mechanism configured to generate a mold clamping force between the fixed mold and the movable mold by moving the movable platen toward the stationary platen and bringing the fixed mold and the movable mold into contact with each other; a drive source configured to drive the mold clamping mechanism; a mold clamping force detection unit configured to detect the mold clamping force; an elongation value detection unit configured to detect an elongation value indicating an elongation amount of the tie bar that is elongated as a result of generation of the mold clamping force; and an abnormality determination unit configured to determine whether there is an abnormality in the injection molding machine, based on a ratio between the mold clamping force and the elongation value. 
     According to the present invention, it is possible to provide an injection molding machine capable of relatively easily detecting an abnormality of a mechanical unit. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a view showing an injection molding machine main body according to an embodiment; 
         FIG.  2    is a functional block diagram of a control device for controlling the injection molding machine main body; 
         FIG.  3    is a flow chart showing a mold closing procedure of the injection molding machine; and 
         FIG.  4    is a graph showing an example of the relationship between the elongation value and the mold clamping force. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     Hereinafter, an injection molding machine according to an embodiment will be described in detail. 
       FIG.  1    is a view showing an injection molding machine main body  12  according to the embodiment. The injection molding machine main body  12  includes a base  14 , a mold clamping device  22  that opens and closes a mold  20 , and an injection device (not shown) that injects a molten resin into the mold  20 . 
     The base  14  is a pedestal for installing the mold clamping device  22  and the injection device. The mold clamping device  22  includes a stationary platen  24 , a rear platen  26 , a movable platen  28 , a toggle mechanism  29 , and a toggle drive mechanism  44 . 
     The stationary platen  24  and the rear platen  26  are disposed on the base  14 , and are connected to each other by four tie bars  32  parallel to each other, the tie bars extending in a direction A so as to penetrate through the movable platen  28 . The movable platen  28  is disposed between the stationary platen  24  and the rear platen  26  on the base  14  via a sliding portion  34 . The sliding portion  34  can move along a guide rail  36  disposed along the direction A on the base  14 . Thus, the movable platen  28  can move toward and away from the stationary platen  24  in the direction A. 
     The mold  20  is provided between the stationary platen  24  and the movable platen  28 . The mold  20  includes a fixed mold  20   a  and a movable mold  20   b.  The fixed mold  20   a  is mounted on a surface of the stationary platen  24  that faces toward the movable platen  28 . The movable mold  20   b  is mounted on a surface of the movable platen  28  that faces toward the stationary platen  24 . 
     The toggle mechanism  29  is provided between the rear platen  26  and the movable platen  28 . The toggle mechanism  29  is driven by the toggle drive mechanism  44 , whereby the toggle mechanism moves the movable platen  28  toward and away from the stationary platen  24 , and opens and closes the mold  20  in the direction A (i.e., in the opening/closing direction). The toggle mechanism  29  amplifies a driving force transmitted from the toggle drive mechanism  44  to a crosshead  40  described later and transmits the amplified driving force to the movable platen  28 . 
     The toggle mechanism  29  includes toggle links  30 , cross links  38 , and a crosshead  40 . The two toggle links  30  and the two cross links  38  are provided on each of the upper side and the lower side, i, e., the four toggle links and the four cross links are provided in total. In the drawing, one upper toggle link, one lower toggle link, one upper cross link, and one lower cross link on the front side are shown, and the two other toggle links and the two other cross links on the back side are hidden behind them. Each of the toggle links  30  contains a first link rod  30   a,  a second link rod  30   b,  a first toggle pin  30   c,  a second toggle pin  30   d,  and a third toggle pin  30   e.    
     One end of the first link rod  30   a  is pivotably connected to the movable platen  28  through the first toggle pin  30   c.  One end of the second link rod  30   b  is pivotably connected to the rear platen  26  through the second toggle pin  30   d.  The other end of the first link rod  30   a  and the other end of the second link rod.  30   b  are pivotably connected to each other through the third toggle pin  30   e.    
     The second link rod  30   b  is connected to the crosshead  40  through the cross link  38 . The crosshead  40  includes arms  42  (an upper arm  42   a  and a lower arm  42   b ) extending upward and downward respectively. The cross link  38  is connected to a distal end portion of the arm  42 . The crosshead  40  can move forward and backward in the direction A by being guided by two guide rods (not shown) that are provided in the rear platen  26  so as to extend in the direction A. 
     The toggle drive mechanism  44  drives the toggle mechanism  29  to open and close the mold  20  in the direction A (opening/closing direction). The toggle drive mechanism  44  includes a mold opening/closing motor  44   a  (drive source), a drive pulley  44   b,  a belt  44   c,  a driven pulley  44   d,  a ball screw  44   e,  and a ball screw nut  44   f.  The ball screw  44   e  is provided along the direction A so as to be parallel to the tie bars  32 . 
     The drive pulley  44   b  is provided so as to be rotatable integrally with the rotary shaft of the mold opening/closing motor  44   a.  The driven pulley  44   d  is provided to be rotatable integrally with the ball screw  44   e.  The belt  44   c  is wound around the drive pulley  44   b  and the driven pulley  44   d,  and transmits the rotational force of the drive pulley  44   b  to the driven pulley  44   d.  The ball screw nut  44   f  is fixed to the crosshead  40  and screw-engaged with the ball screw  44   e.  The ball screw nut  44   f  (crosshead  40 ) moves along the ball screw  44   e  as the ball screw  44   e  rotates. That is, the drive pulley  44   b,  the belt  44   c,  the driven pulley  44   d,  the ball screw  44   e,  and the ball screw nut  44   f  constitute a conversion mechanism  44   g  that converts a rotational motion (rotational force) of the mold opening/closing motor  44   a  into a linear motion (stress) of the crosshead  40  in the direction A. In addition, the conversion mechanism  44   g  and the toggle mechanism  29  function as a mold clamping mechanism that generates a mold clamping force F between the fixed mold  20   a  and the movable mold  20   b.    
     The rotational force (rotational motion) of the mold opening/closing motor  44   a  is converted into stress (linear motion) in the direction A by the conversion mechanism  44   g.  As a result, the crosshead  40  of the toggle mechanism  29  pushes the movable platen  28  in the direction A via the toggle mechanism  29 , and the movable platen  28  moves along the direction A. 
     When the mold opening/closing motor  44   a  is rotated forward, the movable platen  28  moves toward the stationary platen  24 , and the movable mold  20   b  comes into contact with the fixed mold  20   a  (which will be referred to as “a mold touching state”, and at this time, the movable platen  28  is at a mold touching position). When the mold opening/closing motor  44   a  is further rotated forward in the mold touching state, stress (mold clamping force F) acts between the movable mold  20   b  and the fixed mold  20   a.  At this time, the tie bars  32  are elongated between the stationary platen  24  and the rear platen  26  by the mold clamping force F. That is, the elongation value L of the tie bars  32  corresponds to the amount of movement of the movable platen  28  relative to the stationary platen  24  after the mold touching state is established. When the movable mold  20   b  reaches the limit of movement by the toggle mechanism  29 , the mold clamping device  22  is placed into a lock-up state. At this time, the elongation value L of the tie bars  32  and hence the mold clamping force F are sufficiently large. 
     In the lock-up state, a liquid resin material is injected into the mold  20  and solidified. Thereafter, by reversely rotating the mold opening/closing motor  44   a,  the movable platen  28  is moved toward the rear platen  26 , the movable mold  20   b  is separated from the fixed mold  20   a,  and the mold  20  is opened. 
     The mold clamping device  22  has an ejector mechanism (not shown) for ejecting (taking out) a molded product from the movable mold  20   b.  The ejector mechanism is provided on the rear platen  26  side of the movable platen  28 , and pushes the molded product out from the movable mold  20   b  by moving an ejector pin extending in the direction A toward the movable platen  28  in a state where the mold  20  is opened. 
       FIG.  2    is a functional block diagram of a 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 an abnormality of the injection molding machine main body  12 . The injection molding machine  10  is composed of the injection molding machine main body  12  and the control device  50 . 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 the sensors Sf, Sm are input to the control device  50 . 
     The sensors Sf, Sm are installed in the injection molding machine main body  12 , and detect a state of the injection molding machine main body  12 . The sensor Sf detects a quantity (for example, stress, pressure, or strain) relating to the mold clamping force F. The sensor Sm detects a quantity relating to the elongation value L of the tie bar  32  (for example, elongation, strain, position of the rear platen  26 ). 
     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. 
     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 carried out directly or indirectly. 
     As the sensor Sf, for example, a mold clamping force sensor can be used to directly detect the mold clamping force F. As the mold clamping force sensor, a stress sensor (for example, a pressure sensor Sf 1 ) installed in the mold  20  or the tie bars  32  can be used. For example, the stress sensor Sf 1  is provided on at least one of the four tie bars  32  ( FIG.  1    shows the pressure sensor Sf 1  provided between one tie bar  32  and the stationary platen  24  as an example). As the sensor Sf, a strain sensor may be used to detect the mold clamping force F. 
     The elongation value detection unit  54  detects the elongation value L indicating an elongation amount of the tie bar  32  that is elongated as a result of application of the mold clamping force F, based on a signal from the sensor Sm. This detection can be carried out directly or indirectly. 
     For example, a strain sensor Sm 1  can be used as the sensor Sm to directly detect the elongation value L of the tie bar  32 . The strain sensor Sm 1  can be installed on the tie bar  32  to directly detect the elongation value L of the tie bar  32 .  FIG.  1    shows, as an example, a strain sensor Sm 1  provided on a side portion of the tie bar  32 . 
     The elongation value L can be obtained based on the movement amount of the rear platen  26 . That is, when the mold clamping force F is generated in the mold  20 , the rear platen  26  is moved by the reaction force thereof. Therefore, the elongation value L of the tie bar  32  can be detected based on the movement amount of the rear platen  26 . In this case, a position detector Sm 2  (see  FIG.  1   ) that detects the position of the rear platen  26  can be used as the sensor Sm. The elongation value detection unit  54  calculates, as the elongation value L, the amount of change in the position of the rear platen  26  after the fixed mold  20   a  and the movable mold  20   b  have come into contact with each other, based on a signal from the position detector Sm 2 . 
     The abnormality determination unit  56  determines there is an abnormality in the injection molding machine  10 , based on a ratio R between the mold clamping force F and the elongation value L (for example, R=F/L), obtained after the mold touching. That is, when the ratio R of the change ΔF in the mold clamping force F to the change in the elongation value L is smaller than a threshold value Th 0 , it is determined to be abnormal. This determination is made during the mold clamping operation (in particular, between the mold touching position and the lock-up position). 
     Concerning this ratio R, on the basis of not only the elongation value L and the mold clamping force F (i.e., the ratio (R=F/L) between the mold clamping force F and the elongation value L) but also their differential values (infinitesimal change ΔL in the elongation value L, infinitesimal change ΔF in the mold clamping force F), the ratio (R=ΔF/ΔL) may be calculated, and the ratio (R=ΔF/ΔL) may be compared with the threshold value Th 0 . 
     When it is determined to be abnormal, there is a possibility that a crack, a break, or a chip has occurred in the tie bar  32 . In addition, there is a possibility that a crack, a break, or a chip has occurred in a member other than the tie bars  32 , for example, the ball screw  44   e.    
     The motor control unit  58  controls the mold opening/closing motor  44   a  for the mold clamping operation and thereby moves the movable platen  28 . When the abnormality determination unit  56  determines that there is an abnormality during the mold clamping operation, the motor control unit  58  controls the mold opening/closing motor  44   a  to stop the operation of the mold clamping device  22  (mold clamping mechanism) during or after the mold clamping operation. Failure of injection molding can be prevented by stopping the mold clamping operation. 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 there is a possibility that liquid resin material may leak from between the fixed mold  20   a  and the movable mold  20   b.    
       FIG.  3    is a flow chart showing a mold closing procedure of the injection molding machine  10 . The motor control unit  58  controls the mold opening/closing motor  44   a  to start the mold closing operation. That is, the motor control unit  58  forwardly rotates the mold opening/closing motor  44   a  to move the movable platen  28  toward the stationary platen  24 . Accordingly, the movable mold  20   b  comes into contact with the fixed mold  20   a  (reaching the mold touching position, YES in step S 1 ), and the mold clamping force F is generated in the mold  20 . The mold touching can be detected based on, for example, the mold clamping force F calculated by the mold clamping force detection unit  52  (the mold clamping force F starts to change from substantially 0). The mold touching may be detected based on a change in power consumption (or drive current) in the mold opening/closing motor  44   a  (rapid increase in power consumption). 
     Thereafter, the motor control unit  58  continues the forward rotation of the mold opening/closing motor  44   a  until the lock-up state is reached (lock-up position, YES in step S 2 ). During this time, the mold clamping force F increases. The lock-up can be detected based on, for example, a change in power consumption (or drive current) in the mold opening/closing motor  44   a  (the increase in power consumption stops). Further, the lock-up may be detected based on the position of the crosshead  40  or the like. In general, when the mold  20  is exchanged or the like, the die height adjustment is performed on the mold clamping device  22  such that a desired mold clamping force F can be obtained when the crosshead  40  is at a predetermined position (origin). After this adjustment, when the crosshead  40  reaches the origin, the lock-up can be regarded as being detected. The position of the crosshead  40  may be directly measured, or may be determined based on the elongation value L of the tie bar  32  or the like. 
     During a period from the mold touching state to the lock-up state, the elongation value detection unit  54  detects the elongation value L of the tie bars  32  (step S 3 ), and the mold clamping force detection unit  52  detects the mold clamping force F applied to the mold  20  (step S 4 ). 
     The abnormality determination unit  56  calculates a ratio R (=F/L) between the mold clamping force F and the elongation value L (step S 5 ), and compares the ratio R with the threshold value (step S 6 ). When the ratio R is equal to or greater than the threshold value (YES in step S 6 ), it is determined that the injection molding machine  10  is normal, and the mold clamping operation is continued. When the ratio R is smaller than the threshold value (NO in step S 6 ), the injection molding machine  10  is determined to be abnormal (step S 7 ), and the mold clamping operation is interrupted by the motor control unit  58  (step S 8 ). 
       FIG.  4    is a graph showing an example of the relationship between the elongation value L and the mold clamping force F. The horizontal axis represents the elongation value L, and the vertical axis represents the mold clamping force F. The origin O of the elongation value L corresponds to the mold touching position, and the elongation value L 1  corresponds to the lock-up position. As the elongation value L increases, the mold clamping force F also increases. 
       FIG.  4    shows graphs Gs, G 1  and G 2 . The graph Gs is a reference graph in which the ratio of the mold clamping force F to the elongation value L has a reference value Rs (threshold value). The graph G 1  is a graph in which the ratio of the mold clamping force F to the elongation value L is equal to or greater than the reference value Rs (threshold value), and in this case, the mold clamping operation is completed. On the other hand, the graph G 2  is a graph in which the ratio of the mold clamping force F to the elongation value L is smaller than the reference value Rs (threshold value), and in this case, the mold clamping operation is interrupted in the middle. 
     [Modifications] 
     Hereinafter, modifications will be described, 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  44   a  and the amplification factor β p  of the force of the toggle mechanism  29 . In addition, the elongation value detection unit  54  calculates an elongation amount of the tie bars  32  as an elongation value L, based on a rotation amount of the mold opening/closing motor  44   a  (motor) after the fixed mold  20   a  and the movable mold  20   b  has come into contact with each other and the amplification factor of the toggle mechanism  29 . 
     The relationship between the rotation amount M of the mold opening/closing motor  44   a  (motor) and the elongation value L of the tie bars  32  (movement amount of the movable platen  28 ) is expressed by Equation (1). Further, the torque P of the mold opening/closing motor  44   a  (motor) and the mold clamping force have a relationship as shown in Equation (2). 
         L=αm*βm ( M )* M=Am ( M )* M    (1)
 
         F=αp*βp ( M )* P=Ap ( M )* P    (2)
 
     where Am(M)=αm*βm(M), and Ap(M)=αp*βp(M). 
     The rotation amount M is an amount of rotation (number of rotations) of the shaft of the mold opening/closing motor  44   a,  and can be detected by using a rotation detector Sm 3  or the like installed in the mold opening/closing motor  44   a  (see  FIG.  1   ). That is, the sensor Sm can be the rotation detector Sm 3 . The torque P is the rotational force of the shaft of the mold opening/closing motor  44   a,  and can be obtained on the basis of the power consumption or the drive current of the mold opening/closing motor  44   a.  That is, the sensor Sf can be a drive current sensor. 
     The amplification factors αm and αp are the amplification factor of the motion amount and the amplification factor of the stress in the conversion mechanism  44   g,  respectively. That is, the amplification factor αm is a ratio of an output-side motion amount of the conversion mechanism  44   g  (a movement amount of the crosshead  40 ) to an input-side motion amount of the conversion mechanism  44   g  (a rotation amount M in the mold opening/closing motor  44   a ). The amplification factor αp is a ratio of the stress output from the conversion mechanism  44   g  (stress applied to the crosshead  40 ) to the stress input to the conversion mechanism  44   g  (torque P in the mold opening/closing motor  44   a ). The amplification factors αm and αp in the conversion mechanism  44   g  are both constant (not depending on the rotation amount M), but generally have different values. 
     The amplification factors βm(M) and βp(M) are the amplification factor of the motion amount and the amplification factor of the stress in the toggle mechanism  29 , respectively. That is, the amplification factor βm(M) is a ratio of an output-side motion amount of the toggle mechanism  29  (the movement amount of the movable platen  28 ) to an input-side motion amount of the toggle mechanism  29  (the movement amount of the crosshead  40 ). The amplification factor βp (M) is a ratio of the stress (force) output from the toggle mechanism  29  (i.e., applied from the first link rod  30   a  to the movable platen  28 ) to the stress (force) input to the toggle mechanism  29  (i.e., applied from the toggle drive mechanism  44  to the crosshead  40 ). 
     In general, the amplification factors βm(M) and βp(M) (as well as the amplification factors Am(M) and Ap(M)) vary in accordance with the angle θ formed by the toggle link  30  and the second link rod  30   b  (the position of the crosshead  40 , that is, the rotation amount M). For example, the amplification factor βm(M) is relatively large at the mold touching position and relatively small at the lock-up position. The amplification factor βp(M) is relatively small at the mold touching position and relatively large at the lock-up position. As described above, the amplification factors βm(M) and βp(M) (also the amplification factors Am(M) and Ap(M)) depend on the rotation amount M, but the relationship with the rotation amount M (or the position of the crosshead  40 ) after the mold touching has occurred can be obtained in advance by using an analytical or experimental method. If the relationship between the rotation amount M and the amplification factors βm, βp obtained in advance as described above 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 the table. 
     Note that 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 in the conversion mechanism  44   g,  but the amplification factors αm and αp do not necessarily have to be used. That is, since the amplification factors αm and αp are constant values, values L′ and F′ corresponding respectively to the elongation value L and the torque P may be calculated on the basis of the following equations (3) and (4). 
         L′=βm ( M )* M    (3)
 
         F′=βp ( M )* P    (4)
 
     Even in this case, the abnormality determination unit  56  can determine whether there is an abnormality, by obtaining the ratio R (=F′/L′) of the value F′ to the value L′ and comparing the ratio R with a threshold value. The threshold value in this case is determined in consideration of the amplification factors αm and αp. For example, the threshold Th in this case is determined to be “Th 0 *(αp/αm)”. 
     In the above-described method, both the elongation value L and the mold clamping force F are calculated, but this method may be used for calculating only one of the elongation value L and the mold clamping force F, and the other may be obtained by the method described in the embodiment. 
     In other respects, the modification is not substantially different from the embodiment, and detailed description thereof will be omitted. 
     Invention Obtained from the Embodiment 
     Inventions that can be grasped from the above-described embodiment and the modifications thereof will be described below. 
     [1] The injection molding machine  10  includes: the stationary platen  24  configured to hold the fixed mold  20   a;  the rear platen  26 ; the tie bar  32  configured to connect the stationary platen  24  and the rear platen  26  to each other; the movable platen  28  that is disposed between the stationary platen and the rear platen and is configured to hold the movable mold  20   b  such that the movable mold faces the fixed mold and further configured to be movable along the tie bar; the mold clamping mechanism (conversion mechanism  44   g  and toggle mechanism  29 ) configured to generate the mold clamping force F between the fixed mold and the movable mold by moving the movable platen toward the stationary platen and bringing the fixed mold and the movable mold into contact with each other; the drive source (mold opening/closing motor  44   a ) configured to drive the mold clamping mechanism; the mold clamping force detection unit  52  configured to detect the mold clamping force; the elongation value detection unit  54  configured to detect the elongation value L indicating the elongation amount of the tie bar that is elongated as a result of generation of the mold clamping force; and the abnormality determination unit  56  configured to determine whether there is an abnormality in the injection molding machine based on a ratio R between the mold clamping force and the elongation value. With this configuration, the abnormality of the mechanical unit of the injection molding machine can be relatively easily detected based on the ratio between the mold clamping force and the elongation value. 
     [2] The abnormality determination unit determines that there is an abnormality if a ratio of a change in the mold clamping force to a change in the elongation value is smaller than a threshold value Th 0 . By comparing the ratio with the threshold value, it is possible to detect an abnormality in the mechanical unit of the injection molding machine. 
     [3] The mold clamping mechanism is a toggle-type mold clamping mechanism (conversion mechanism  44   g  and toggle mechanism  29 ), the drive source is a motor (mold opening/closing motor  44   a ), and the mold clamping force detection unit calculates the mold clamping force based on a torque of the motor after the fixed mold and the movable mold have come into contact with each other and an amplification factor of the mold clamping mechanism. With this configuration, the abnormality of the mechanical unit of the injection molding machine can be detected without using a mold clamping force sensor. 
     [4] The mold clamping force detection unit calculates the mold clamping force based on a signal from the mold clamping force sensor (Sf, Sf 1 ). With this configuration, it is possible to detect an abnormality in the mechanical unit of the injection molding machine using the mold clamping force sensor. 
     [5] The mold clamping mechanism is a toggle-type mold clamping mechanism (conversion mechanism  44  and toggle mechanism  29 ), the drive source is a motor (mold opening/closing motor  44   a ), and the elongation value detection unit calculates the elongation amount of the tie bar  32  as the elongation value, based on at least a rotation amount of the motor after the fixed mold and the movable mold have come into contact with each other and an amplification factor of the mold clamping mechanism. With this configuration, the abnormality of the mechanical unit of the injection molding machine can be detected without using a position detector or a strain sensor. 
     [6] The elongation value detection unit calculates, as the elongation value, an amount of change in a position of the rear platen after the fixed mold and the movable mold have come into contact with each other, based on a signal from a position detector Sm 2  configured to detect the position of the rear platen. With this configuration, it is possible to easily detect an abnormality in the mechanical unit of the injection molding machine using the position detector. 
     [7] The elongation value detection unit calculates the elongation amount of the tie bar based on a signal from a strain sensor Sm 1 . With this configuration, it is possible to easily detect an abnormality of the mechanical unit of the injection molding machine by using the strain sensor. 
     [8] The injection molding machine further includes a stop control unit (motor control unit  58 ) configured to control the drive source to stop operation of the mold clamping mechanism if the abnormality determination unit determines that there is an abnormality. With this configuration, the operation of the mold clamping mechanism can be stopped to prevent injection molding from failing.