JP2000006212A - Mold thickness adjusting method and device for injection molder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten a mold thickness adjusting time, execute a mold clamping stable for the change of a mold thickness due to disturbances or the like, and realize the detection of the position of a mold for executing the proper mold clamping by means of the low cost constitution of a device. SOLUTION: The positional relationship between a link housing 38 and a travelling die plate 34 is detected by an encoder 42a provided on a mold clamping servo motor 42. In addition, the amount of movement of a link housing 38 is detected with a rotational frequency detecting sensor 48 through a provided mold thickness adjusting motor 46 for rotatingly driving mold thickness adjusting nuts 39 engaging with threaded parts 36a formed at one end part of tie bar 36. After that, with a positional detecting sensor 50 provided at the retreated position of the link housing is detected so as to set the position of the die plate 34 from a fixed die plate 32 on the basis of the position of the link housing from the fixed die plate 32 through calculation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for adjusting a mold thickness of an injection molding machine having a toggle mold clamping device.

[0002]

2. Description of the Related Art In a toggle-type mold clamping device, when a mold is replaced, the mold clamping force must be adjusted and set by performing a mold thickness adjusting operation according to the thickness of the mold. Therefore, this mold thickness adjustment operation has conventionally been performed by the operator based on experience, but if the mold clamping force is too strong, the tie bar may be damaged due to excessive force, and if the mold clamping force is too weak, injection molding may be smooth. There is a difficulty that can not be.

[0003] From such a viewpoint, there have conventionally been proposed various devices capable of automatically performing mold thickness adjustment in a toggle-type mold clamping device. However, all of these devices have a toggle link that is fully extended. Move the link housing to the state (called lock-up state), close the mold,
Thereafter, the mold clamping force is adjusted. That is, in these devices, the toggle link is extended with the mold opened, the lock-up state is set, the link housing is moved to close the mold, and the mold clamping force is adjusted.

As an automatic mold thickness adjusting means of an injection molding machine having a conventional toggle-type mold clamping device, a position before a toggle link of a toggle mechanism is brought into a lockup state is set, and a mold clamping servomotor is rotated. The toggle mechanism is driven to move the movable die plate to close the mold, and at this time the torque of the mold clamping servomotor is limited so that the pressing pressure applied to the mold is kept constant. are doing. In this way, while the mold clamping servomotor continues to apply a constant pressure to the mold, the mold thickness adjusting servomotor is rotated to move the link housing backward. Due to this movement, the distance between the link housing and the movable die plate is increased, and accordingly, the toggle mechanism moves toward the lockup state. Until the lock-up state is reached, the crosshead keeps pushing the mold with a predetermined torque of the mold-locking servomotor. In this way, it is also known that the position where the toggle mechanism finally locks up is detected, and then the position of the link housing where the mold clamping force becomes the set value is obtained to complete the mold thickness adjustment. I have.

However, as in the above-mentioned conventional automatic mold thickness adjusting means, the link housing is moved backward by rotating the mold thickness adjustment servomotor while applying pressure to the crosshead by the mold clamping servomotor. Although the pressure applied to the crosshead is controlled to be kept constant by limiting the torque to the mold clamping servomotor, the force for actually pressing the mold in the toggle mechanism is difficult to keep constant. In particular, when the toggle link is in a state immediately before lock-up, the force for pressing the mold increases due to the motion characteristics of the toggle mechanism. For this reason, when the mold thickness adjusting motor is further rotated in this state, the axial force applied to the mold thickness adjusting nut is increased, so that the load pressure of the mold thickness adjusting servo motor is increased. When driven via a chain, there is a problem that problems such as jumping of the teeth of the chain, destruction of the mounting base of the servomotor, and overheating of the servomotor occur.

Therefore, as an automatic mold thickness adjusting method for an injection molding machine that can solve many problems described above, the pressure applied to a mold is detected by the output of a mold pressure detecting means provided in a mold clamping device. An automatic mold thickness adjustment method has been proposed in which the torque limit of the mold clamping servomotor is feedback-controlled so that the output becomes a predetermined set value, thereby preventing excessive pressure from being applied to the mold during the mold thickness adjustment work. (Japanese Patent No. 26685)
No. 99).

[0007] The automatic mold thickness adjustment method according to this proposal is shown in FIG.
As shown in (1), the mold clamping servomotor Mb is rotated while the toggle links 11, 11 of the toggle mechanism 8 constituting the mold clamping device 1 are not fully extended, and the movable die plate 5 is moved to the fixed die plate 3 side. Move and close molds 2 and 4.
Then, the ball screw 9 is driven by the mold clamping servomotor Mb.
And presses the crosshead 10 through the dies to maintain the closed state of the molds 2 and 4 while maintaining the mold thickness adjusting servomotor Ma.
Is rotated to move the link housing 7 rearward via the mold thickness adjusting nuts 14 screwed to the tie bars 6, respectively. At this time, a torque limit is applied to the mold clamping servo motor Mb to control the output torque of the mold clamping servo motor Mb. As described above, when the link housing 7 is continuously moved backward while pressing the molds 2 and 4 with the set pressure, the toggle links 11 of the toggle mechanism 8 gradually extend. Immediately before the toggle links 11, 11 are completely extended, a sudden pressure is applied to the mold due to the motion characteristics of the toggle links. However, this sudden pressure is applied to the strain gauge 12 provided on the tie bar 6, the drive current value of the servomotor Ma for adjusting the mold thickness, the tension of the chain driven by the servomotor Ma, and the foot of the servomotor Ma. Of the mold clamping servo motor Mb
Therefore, the torque to be applied when closing the dies 2 and 4 is kept constant. Reference numeral 13 denotes an output amplifier of the strain gauge 12.

In FIG. 4, reference numeral 20 denotes a numerical control device (NC device) constituting a control section of the injection molding machine. The NC device 20 includes a micro processor (CPU) 21 for NC and a programmable controller (CPU). It has a CPU 22 for a machine controller (PMC).
A ROM 25 storing sequence programs of various injection molding machines is connected to the CPU 22 for the NC.
1 includes a ROM 24 storing a management program for controlling the entire injection molding machine, and a servo motor 26a and 26b for a mold thickness adjusting servomotor Ma and a mold clamping servomotor Mb for driving various driving devices of the injection molding machine. It is connected via a servo interface (SSU) 27. In addition,
Reference numeral 28 denotes a nonvolatile shared RAM having a backup power supply, which stores various set values, parameters, and the like such as a program for controlling each operation of the injection molding machine. Reference numeral 23 denotes a bus arbiter controller (BAC).
1 and a PMC CPU 22, a shared RAM 28, an input circuit 15, and an output circuit 16 are connected by buses, respectively, and an operator panel controller (OPC) 29 for connecting a monitor / keyboard (CRT / MDI) 18 is connected and used by the BAC 23. It is configured to control the bus. Further, reference numeral 17 denotes the CPU 2 for NC.
Reference numeral 1 denotes a RAM used for temporarily storing data during various processes.

Therefore, according to the automatic mold thickness adjusting method for an injection molding machine having the above structure, first, the mold thickness adjusting servomotor Ma and the mold clamping servomotor Mb are driven to read the current torque value Tr. Then, this is compared with a preset torque value Ts, the difference ΔT (= Ts−Tr) is multiplied by a gain k, and this value (kΔT) is added to the value T0 stored in the register, and this is added to the new value. Is stored in the register as a value T0, and this is output as a torque limit value g.
Next, it is determined whether or not the toggle links 11 and 11 are in a lock-up state. If not, the process returns to the step of reading the current torque value Tr and the subsequent processing is repeated. When it is determined that the servo motors are in the up state, the two servo motors Ma, M
b is stopped, and the process proceeds to the mold clamping force setting process.

Further, in a mold clamping force setting device for applying a mold clamping force to a pair of dies sandwiched between a fixed platen and a movable platen by using a toggle mechanism, the pair of dies contact each other. Detecting means consisting of an encoder for detecting the thickness of the two dies in a state where they have been moved (that is, the distance of the movable platen from the fixed platen), and keeping the mold clamping force constant based on the detection value obtained by the detecting means. There has been proposed a mold clamping force setting device having means for calculating a correction value of a drive-in amount necessary for the above and a means for driving the toggle mechanism according to the correction value (Japanese Patent Laid-Open No. 1-58521).

[0011]

However, in a mold clamping apparatus using a toggle mechanism, in order to perform proper mold clamping control adapted to a mold, a mold, a fixed die plate, a movable die plate, and a link housing are required. It is important that the positional relationship of each can be accurately grasped. Therefore, when performing automatic mold change, unless the position of the movable die plate is accurately controlled and stopped according to the mold thickness, not only can the mold be automatically changed, but also thermal expansion, shrinkage or When the thickness of the mold changes due to disturbance such as wear of the toggle pin, there is a problem that it is not possible to correct (adjust) the mold to a proper clamping position.

[0012] Regarding these points, the conventional apparatus or the apparatus according to the above-mentioned proposal has still not been satisfactory. That is, in the conventional device,
It takes a lot of time to adjust the mold thickness, the adjustment to perform mold clamping control with a constant mold clamping force is always unstable when the mold thickness changes due to disturbance, and the fixed die plate, movable die plate and link housing There are disadvantages such as an increase in equipment cost of control means using a position detection sensor or the like for detecting a positional relationship.

The inventors of the present invention have conducted intensive studies and as a result, have found that a mold thickness adjusting method for an injection molding machine is set such that a toggle type mold clamping device is driven by a mold clamping servomotor to perform mold thickness adjustment. In the above, the positional relationship between the link housing and the movable die plate, that is, the distance y is detected by an encoder provided on the servomotor for mold clamping, and the mold thickness adjusting nut meshes with the threaded portion formed at one end of the tie bar in the link housing. In addition to this, a mold thickness adjusting motor for driving this is provided, and a moving amount of the link housing, that is, a distance x is detected by a rotation speed detection sensor provided in the mold thickness adjusting motor. By detecting the origin position of the link housing by a position detection sensor provided at the retreat position, the position of the link housing is detected. On the basis of the position of the link housing from the fixed die plate obtained from the point position, ie, the distance L, the position of the moving die plate from the fixed die plate, ie, the distance [L− (y + x)] can be set by calculation. I found it.

Accordingly, an object of the present invention is to provide an injection molding machine having a toggle-type mold clamping device, which can shorten the time required for adjusting the mold thickness and stabilize the mold clamping against a change in the mold thickness due to disturbance or the like. It is an object of the present invention to provide a method and apparatus for adjusting the thickness of an injection molding machine, which can perform a mold position detection for performing proper mold clamping with a low-cost apparatus configuration.

[0015]

In order to achieve the above object, a method for adjusting a mold thickness of an injection molding machine according to the present invention is to adjust a mold thickness by driving a toggle-type mold clamping device by a servomotor for mold clamping. In the method of adjusting the thickness of the injection molding machine set as described above, the positional relationship (distance y) between the link housing and the movable die plate is detected by an encoder provided on the servo motor for mold clamping, and one end of the tie bar is attached to the link housing. A mold thickness adjusting motor for rotating and driving the mold thickness adjusting nut meshing with the formed thread portion is provided,
The amount of movement (distance x) of the link housing is detected by a rotation speed detection sensor provided in the mold thickness adjusting motor, and the origin position of the link housing is detected by a position detection sensor provided at a receding limit position with respect to the link housing. , The position of the moving die plate from the fixed die plate [distance: L− (y + x)] based on the position (distance L) of the link housing from the fixed die plate obtained from the origin position of the link housing. ] Is set by calculation.

A mold thickness adjusting device for an injection molding machine for performing the mold thickness adjusting method is a mold thickness adjusting device for an injection molding machine having a toggle type mold clamping device driven by a mold clamping servomotor. An encoder for detecting the positional relationship (distance y) between the link housing and the movable die plate is provided in the tightening servomotor, and the encoder is rotationally driven with respect to a mold thickness adjusting nut that meshes with a thread formed at one end of the tie bar. A motor for adjusting the thickness of the link is provided in the link housing, and a motor for detecting the moving amount (distance x) of the link housing is provided on the motor for adjusting the thickness of the link. A position detection sensor for detecting an origin position of the link housing; and a fixed die obtained from the origin position detected by the position detection sensor. Position of the link housing from bets based on (a distance L), the position of the movable platen from the stationary die plate [Distance: L- (y + x)] and providing a calculating means for calculating a.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of a method for adjusting a mold thickness of an injection molding machine according to the present invention will be described in detail with reference to the accompanying drawings in relation to an apparatus for performing the method.

FIG. 1 is an explanatory diagram showing a schematic configuration of a mold clamping device for performing a mold thickness adjusting method in an injection molding machine of the present invention and a control system thereof.

In FIG. 1, reference numeral 30 indicates a toggle type mold clamping device, and one mold 31 is a fixed die plate 32.
, And the other mold 33 is attached to a movable die plate 34. Fixed die plate 32
Are attached to one ends of four tie bars 36 (only one is shown in FIG. 1), and the other ends of these tie bars 36 form screw portions 36a, and these screw portions 36a are connected to the link housing. The link tie 38 is inserted through four corners of the tie bar 38 through a mold thickness adjusting nut 39 provided on one side of the tie bar 36.
Is provided so as to be able to move back and forth with respect to.

On the other hand, between the link housing 38 and the movable die plate 34, there is provided a toggle mechanism 40 having toggle links 35 formed of double links. The toggle mechanism 40 is provided with the servo motor 4 for mold clamping.
2 is screwed into a crosshead 44 connected to the toggle links 35, 35 via a ball screw 43 that is rotationally driven by the rotary shaft 2. The ball screw 43 is rotated by driving the mold clamping servo motor 42 to rotate the ball screw 43 so that the crosshead 44 is rotated. Can be moved back and forth to open and close the dies 31, 33. The servomotor 42 for mold clamping is provided with an encoder 42a for detecting the positional relationship (distance y) between the link housing 38 and the movable die plate 34, which will be described later.

However, as means for rotating the mold thickness adjusting nuts 39 provided on one side surface of the link housing 38, gear portions 39a are provided on the outer peripheral portion of the mold thickness adjusting nuts 39, respectively. A motor 46 for adjusting the thickness of the mold is provided with a driving gear 45 meshing with the gear 47, and an interlocking gear 47 for simultaneously rotating the gear 39a.
(See FIG. 2A). For the drive gear 45 that is driven to rotate by the mold thickness adjusting motor 46, the amount of movement (distance x) of the link housing 38 that is moved by the rotation (the number of rotations N) of the drive gear 45 is detected. A rotational speed detection sensor 48 is appropriately provided (see FIG. 2B). In this case, on one side surface of the drive gear 45, a plurality of (four in the illustrated example) detection dogs 49 for detection by the plurality of rotation speed detection sensors 48 are provided at predetermined intervals in the circumferential direction. It can be configured (see FIG. 2C).

Further, in this embodiment, the position detecting sensor 5 for detecting the origin position of the link housing 38 at the retreat limit position with respect to the link housing 38.
0 is appropriately arranged.

Next, a method of adjusting the mold thickness in the toggle-type mold clamping device having the above-described configuration will be described with reference to the control system shown in FIG.
This will be described in relation to the control program shown in FIG.

That is, in FIG. 1, reference numeral 52 denotes a control device for performing mold clamping control and mold thickness adjustment control of the mold clamping device 40. The control device 52 includes a servo control circuit 53 and a CPU 54 for performing mold clamping control on the mold clamping servo motor 42. Further, a sequencer CPU 55 and an input / output unit 56 for performing mold thickness adjustment control for the mold thickness adjustment motor 46 are provided. Reference numeral 57 denotes a display / setting means for performing the mold clamping control and the mold thickness adjustment control. In addition, each of the CPUs
A ROM and a RAM as storage means are connected to the buses 54 and 55, respectively. Further, reference numeral 58
Denotes a switch for controlling the operation and stop of the motor 46 for adjusting the mold thickness.

Therefore, when performing the mold thickness adjustment, first, the key operation of the mold thickness adjustment start provided in the display / setting means 57 of the control device 52 is performed (STEP-1). Thereby, the mold clamping servomotor 42 is driven via the CPU 54 and the servo control circuit 53, and the CPU 54,
Sequencer CPU 55, input / output unit 56 and switch 58
The motor 46 for adjusting the thickness of the mold is driven through the
2). That is, in this case, the mold clamping servomotor 4
2 retracts the crosshead 44 of the toggle mechanism 40 via the ball screw 43 to maintain the positional relationship between the fixed die plate 32 and the movable die plate 34 in the most open state. Then, the positional relationship (distance y) between the link housing 38 and the movable die plate 34 is detected by an encoder 42a provided on the mold clamping servo motor 42 (S
(STEP-3), the detected value is stored in the CPU 54 (STEP-4).

On the other hand, the link housing 38 is retracted by the mold thickness adjusting motor 46. When the link housing 38 reaches the retreat limit position, this state is detected by the position detection sensor 50 as the origin position of the link housing 38 (STEP-5), and the detected value is stored in the sequencer CPUs 55 and 54 (step 5). ST
EP-6). Then, at the retreat limit position of the link housing 38, the drive of the mold thickness adjusting motor 46 is stopped by the action of the sequencer CPU 55 (STEP-
7).

Next, the mold having the mold thickness ML is carried in, and then the mold thickness adjusting operation (STEP-8) is started. At the time of this mold thickness adjustment, the mold thickness adjustment motor 46 is driven so as to advance the link housing 38 (STEP-
9). The rotational speed detecting sensor 48 provided on the mold thickness adjusting motor 46 allows the mold to be clamped with an appropriate mold clamping force, and the movement amount of the link housing 38 in a state where the toggle link 35 is not fully extended. (Distance x) is detected (STEP-10), and this detected value is
5 and at the same time, the drive of the mold thickness adjusting motor 46 is stopped (STEP-11).

Thereafter, the mold clamping servomotor 42 is driven to apply pressure to the cross head 44 of the toggle mechanism 40 via the ball screw 43, and the distance y is detected (S).
TEP-12). Then, in the CPU 54,
Detected distance x, distance y and link housing 3
Based on the position (distance L) of the link housing 38 from the fixed die plate 32 obtained from the origin position of No. 8, the position of the moving die plate 34 from the fixed die plate 32, ie, [distance: L− (y + x)] is calculated. Then, it is confirmed whether or not the distance is within an allowable error with respect to the mold thickness ML, that is, whether or not the distance y is appropriate (STEP-
13).

In this way, the mold thickness adjustment of the toggle mold clamping device 30 can be completed (STEP-14).

Although the preferred embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and many design changes can be made without departing from the spirit of the present invention. It is.

[0031]

As described above, the method for adjusting the mold thickness of the injection molding machine according to the present invention employs an injection molding method in which a toggle type mold clamping device is driven by a mold clamping servomotor to perform mold thickness adjustment. In the method of adjusting the mold thickness of the machine, a positional relationship (distance y) between the link housing and the movable die plate is detected by an encoder provided on the servo motor for mold clamping, and a threaded portion formed at one end of the tie bar in the link housing A mold thickness adjustment motor for rotating the mesh thickness adjustment nut to be engaged is provided, and a movement amount (distance x) of the link housing is detected by a rotation speed detection sensor provided on the mold thickness adjustment motor. The origin of the link housing is detected by detecting the origin of the link housing by a position detection sensor provided at the rearmost position relative to the link housing. Based on the position of the link housing from the fixed die plate obtained from location (distance L), the position of the movable platen from the stationary die plate [Distance:
L- (y + x)] can be set by calculation, so that the mold thickness adjustment time can be shortened and the mold can be stably clamped even when the mold thickness changes due to disturbance or the like. Many excellent advantages are obtained, such as detection of the position of the mold for proper mold clamping, which can be achieved by a low-cost apparatus configuration.

The apparatus for carrying out the method for adjusting the mold thickness of the injection molding machine according to the present invention is a mold thickness adjusting apparatus for an injection molding machine having a toggle-type mold clamping device driven by a mold clamping servomotor. An encoder for detecting the positional relationship (distance y) between the link housing and the movable die plate is provided in the servomotor for mold clamping, and the encoder is attached to the mold thickness adjusting nut which meshes with the screw portion formed at one end of the tie bar. A mold thickness adjusting motor to be driven to rotate is provided in the link housing, and the mold thickness adjusting motor is provided with a rotation speed detecting sensor for detecting a moving amount (distance x) of the link housing. A position detection sensor for detecting an origin position of the link housing, and furthermore, a fixed position obtained from the origin position detected by the position detection sensor. Based on the position of the link housing from the die plate (distance L), the position of the movable platen from the stationary die plate [Distance: L-(y +
x)] is provided so that the mold thickness adjusting function of an injection molding machine having a toggle-type mold clamping device is improved, and this type of mold thickness adjusting device is reduced in cost by a simple configuration. Can be manufactured.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a schematic configuration of a mold clamping device for performing a mold thickness adjusting method of an injection molding machine according to the present invention and a control system thereof.

FIG. 2A is an explanatory view of a main part showing a configuration and arrangement of a mold thickness adjustment nut and a configuration and arrangement of a mold thickness adjustment motor for performing the adjustment drive as viewed from the front of a link housing of the mold clamping device shown in FIG. 1; (B) is a main part side view showing the configuration of the mold thickness adjusting motor of the mold clamping device shown in FIG. 1 and the configuration and arrangement of the rotation speed detection sensor, and (c) is a view of the mold thickness adjusting motor shown in (b). It is a principal part front view which shows the structural arrangement of the detection dog detected by the rotation speed detection sensor of the rotating drive gear.

FIG. 3 is a flowchart showing an embodiment of a control program for implementing a method for adjusting a mold thickness of an injection molding machine according to the present invention.

FIG. 4 is an explanatory diagram showing a schematic configuration of a mold clamping device for performing a mold thickness adjusting method in a conventional injection molding machine and a control system thereof.

[Explanation of symbols]

 Reference Signs List 30 toggle-type mold clamping device 31 fixed mold 32 fixed die plate 33 moving mold 34 moving die plate 36 tie bar 36a screw part 38 link housing 39 mold thickness adjusting nut 39a gear part 40 toggle mechanism 42 mold clamping servo motor 42a encoder 43 Ball screw 44 Cross head 45 Driving gear 46 Die thickness adjusting motor 47 Interlocking gear 48 Rotation speed detection sensor 49 Detection dog 50 Position detection sensor 52 Controller 53 Servo control circuit 54 CPU 55 Sequencer CPU 56 Input / output unit 57 Display / setting Means 58 Switch

Continuing from the front page (72) Inventor Kiyoshi Sasaki 2068-3 Ooka, Numazu-shi, Shizuoka Toshiba Machine Co., Ltd. Numazu Office (72) Inventor Yukio Iimura 3068, Ooka, Numazu-shi, Shizuoka Toshiba Machine Numazu Office (72 ) Inventor Jun Koike 2068-3, Ooka, Numazu-shi, Shizuoka Toshiba Machine Co., Ltd. Numazu Office (72) Inventor Masahiro Tamaki 2068-3, Ooka, Numazu-shi, Shizuoka Toshiba Machine Co., Ltd. 2068-3, Ooka, Numazu City, Fukushima Prefecture Numazu Office F-term (reference) 4F202 AP06 AP08 AQ03 CA11 CB01 CL22 CL32 CL39 CL42 CL46 CR06 4F206 AP067 AP084 AQ03 JA07 JL05 JM02 JM06 JN36 JP13 JQ81

Claims (2)

[Claims] In a method for adjusting a mold thickness of an injection molding machine, wherein a toggle type mold clamping device is driven by a mold clamping servomotor to perform mold thickness adjustment, a positional relationship between a link housing and a movable die plate ( A distance y) is detected by an encoder provided on a mold clamping servomotor, and a mold thickness adjusting motor for rotating a mold thickness adjusting nut meshed with a threaded portion formed at one end of the tie bar in the link housing is driven. In addition, the movement amount (distance x) of the link housing is detected by a rotation speed detection sensor provided on the mold thickness adjusting motor, and the link housing is detected by a position detection sensor provided at a receding limit position with respect to the link housing. By detecting the origin position of the link housing, the link housing from the fixed die plate obtained from the origin position of the link housing Based on the position (distance L), the position [Distance: L- (y + x)] of the movable die plate from the fixed die plate mold thickness adjusting method for an injection molding machine and setting by calculation. 2. A mold thickness adjusting device for an injection molding machine having a toggle type mold clamping device driven by a mold clamping servomotor, wherein the mold clamping servomotor has a positional relationship (a distance y) between a link housing and a movable die plate. ) Is provided, and a mold thickness adjusting motor for rotating and driving a mold thickness adjusting nut meshed with a screw portion formed at one end of the tie bar is provided in the link housing. A motor is provided with a rotation number detection sensor for detecting a moving amount (distance x) of the link housing, and a position detection sensor for detecting an origin position of the link housing corresponding to a retreat limit position of the link housing is provided. Based on the position (distance L) of the link housing from the fixed die plate obtained from the origin position detected by the position detection sensor Position of the moving die plate from the fixed die plate [Distance: L- (y + x)] injection molding machine mold thickness adjusting device and providing a calculating means for calculating a.