JPS61283518A - Mold-clamping force correcting device of injection molder - Google Patents

Abstract

PURPOSE:To enable to maintain the mold-clamping force within the predetermined range at all times under the compensation of the influence of disturbance by a method wherein the strains of tie bar the at the opening of a mold and at its closing are detected and the position of a rear platen is corrected so as to lay the strain within the predetermined range, within which the set mold clamping force is given. CONSTITUTION:The detection output of the strain of a tie bar 5 is issued from a strain detector A attached on the tie bar 5 so as to extract the detection outputs (a) and (b) of the strain at the closing of a mold and at its opening in order to be memorized. A calculating means D calculates the difference a-b between both the outputs (a) and (b) so as to discriminate by a discriminating means E whether the output difference a-b lies within the predetermined range or not. According to the result of discrimination, the correction value L of the position of a rear platen 6 is calculated by a calculating means F on the basis of the calculated difference a-b and further the rear plate 6 is driven in response to the correction value L. Thus, the rear platen 6 is shifted along the tie bars 5 to the position, at which the mold clamping force turns to be the value within the predetermined range. Consequently, if the set mold clamping force oversteps the predetermined range due to the disturbance such as the change of temperature and the like, the deviation can be compensated and the mold clamping force can be maintained within the predetermined range at all times.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a clamping force correction position for an injection molding machine having a toggle type mold clamping device.

In an injection molding machine equipped with a conventional toggle type mold clamping device, the mold clamping force is set according to the thickness of the mold and the injection molding material. However, even if the mold clamping force is once set to a predetermined value by the setting operation, it may deviate from the predetermined range due to external disturbances that affect the set mold clamping force, especially changes in ambient temperature, as the tie bars expand or contract. be. As described above, it is difficult to maintain the mold clamping force within a predetermined range at all times during operation of the injection molding machine.

Problems to be Solved by the Invention The purpose of the present invention is to compensate for the deviation of the set mold clamping force from a predetermined range due to external disturbances such as temperature changes and maintain the mold clamping force within the predetermined range at all times. An object of the present invention is to provide a mold clamping force correction device for an injection molding machine.

Means for Solving the Problems The present invention, as shown in FIG. 1, is an injection molding method that has a toggle type mold clamping device and moves a rear platen along tie bars to reduce mold clamping force. In the device, a strain detector A is attached to the tie bar and detects the strain amount of the tie bar, and strain amount outputs a and b from the strain detector A are provided when the mold clamping device is clamping the mold and opening the mold. Extraction means B for extracting each, storage means C for storing the extracted strain amount outputs a and b at the time of mold closing and mold opening, respectively, and calculation for calculating the difference a-b between the two stored strain suspension outputs. a determining means E for determining whether the calculated difference a-b is within a predetermined range; and a determining means E for determining whether the calculated difference a-b is within a predetermined range;
The present invention has a configuration characterized by comprising a calculation means F for calculating a correction value for the rear platen position based on the correction value b, and a drive means G for driving the aforesaid upplaten in accordance with the correction value.

The strain detector A attached to the tie bar of the toggle type mold clamping device outputs a detection output of the strain amount of the tie bar, and then the strain detection output a when the mold clamping device closes the mold and opens the mold.
b is extracted by extraction means B and stored in storage means C. The calculating means calculates the difference a-b between the outputs a and b, and the determining means E determines whether the difference a-b is within a predetermined range. According to the determination result, the calculation means F calculates three correction values for the rear platen position based on the calculated difference a-b, and the drive means G drives the rear platen according to the correction values. As a result, the rear platen is moved along the tie bars to a position where the mold clamping force is within a predetermined range.

Embodiment FIG. 2 shows a toggle type mold clamping device for an injection molding machine to which an embodiment of the present invention is applied.One mold 1 is mounted on the front platen 2, and the other mold 3 is mounted on the moving platen 4. installed. The front platen 2 is attached to one end of four tie bars 5, and the other end of each tie bar 5 is provided with a rear platen 6. Two sets of toggle links 8, 8' are connected between the rear platen 6 and the moving platen 4. A moving platen 4 is provided with a moving platen 4.
is provided so that it can be driven by the toggle mechanism 7 to slide on each tie bar 5.

A through hole 9 is drilled in the center of the rear platen 6, a pole nut 10 is provided in the through hole 9, and a ball screw 12 is connected to the pole nut 10 with a cross head 11 that bends and extends two sets of toggle links 8, 8'. are screwed together. The pole nut 10 is fixed to the gear 13, and the gear 13
It is provided so that it can be rotated together.

Nuts 15 are provided on the back side of the rear platen 6 to be engaged with screws cut into each tie bar 5, and a sprocket 16 is provided on the nut 15, and a sprocket 16 is provided on the nut 15.
By driving a servo motor Ma for moving the rear platen fixed to the rear platen 6 via a sprocket 7 and a chain 20 provided on the shaft of the servo motor Ma.
．． The nut 15 is rotated via a sprocket 16. One side surface of each nut 15 is formed into a flange shape, and this flange-like protrusion 1
4 engages with a groove 14' provided in the rear platen 6, and thereby each nut 1 driven by the servo motor Ma.
5 rotates and moves on each tie bar 5 to the left and right in FIG. is also moving. The amount of movement of the rear platen 6 is detected by an encoder pa provided on the servo motor Ma as a platen position detection means. Further, on the back surface of the rear platen 6, a toggle drive servo motor Mbb<m is provided which drives a second gear 22 that meshes with the first gear 13 via a shaft 23. Each of the servo motors Mb for driving the toggle is provided with an encoder Pb as a toggle position detecting means for detecting the bending/extending state of the toggle mechanism.

Roughly speaking, an adhesive strain gauge 24 as a strain detector, which is an important part of the present invention, is attached to the circumferential surface of the end of the tie bar 5 on the front platen 2 side. The strain gauge 24 is made of, for example, a conventionally known resistance wire strain gauge, and its resistance changes in accordance with the strain of the tie bar 5 to output an electrical signal representing the strain of the tie bar 5. In addition, four strain gauges 2 are installed at circumferential positions perpendicular to each other on the circumferential surface of the tie bar 5.
4 may be bonded together to form a conventionally known bridge circuit to increase the detection sensitivity.

FIG. 3 shows a control section of the mold clamping device shown in FIG. 2, and 30 is a numerical control device (hereinafter referred to as CNC) having a built-in computer. In the CNC50, 31 is the central processing unit (
32 is a ROM that stores control programs such as mold clamping processing and mold clamping force adjustment, a RAM that is used to temporarily store data in arithmetic processing, and a tie bar 5 that corresponds to the set clamping force. 33 is an input/output circuit whose input side is connected to the strain gauge 24 etc. via the A/D converter 25; 35a and 35b are The pulse generating circuit generates pulses according to the command movement base in response to commands from C; PU 31, and inputs them to reversible counters 34a and '34b, respectively. The outputs of the reversible counters 34a, 34b are converted into analog signals by D/A converters 36a, 36b, respectively, and drive servo motors Ma, Mb via servo circuits 40a, 40b. On the other hand, servo motor M
a.

Encoder Pa provided in Mb, encoder from Pb
3 pulses, the reversible counters 34a, 34b are subtracted, and when the reversible counters 34a, 34b become zero, the servo motors Ma, Mb stop driving.
It is used to move and position the 37 is a manual input device for inputting various commands and various setting values. Note that 38 is a bus.

Therefore, when replacing the molds 1 and 3, etc., the servo motor Ma is driven to move the rear platen 6 to achieve the set tightening force and start molding the product.
After this initial setting, the tie bar 5 expands and contracts under the influence of disturbances such as ambient temperature during the molding operation, and the rear platen position changes, so that the mold clamping force may deviate from a predetermined range.

Therefore, the present invention compensates for the influence of this disturbance.
The operation of this embodiment will be described below with reference to FIG.

First, the mold clamping process (step 81) is performed, and when the toggle link is fully extended and the mold clamping operation is completed, the CPU 31
The output a from the strain gauge 24 is read from the /D converter 25 and stored (step 82).

Next, processes such as injection, holding pressure, and cooling are performed as before (step S3), and then mold opening processing and product ejection processing are performed (
Step 84.85>. When the mold opening is completed, the CPU 31
Then, read the output from the strain gauge 24 from the A/D converter 25 again and store it in step S6). Next, calculate the strain at the time of mold opening from the read strain amount output a from the strain gauges 2 and 4 at the time of mold clamping. The amount output S is subtracted to calculate the difference X (step S7). Next, the strain fiv of the tie bar 5 corresponding to the set tightening force is read from the memory 32, and the above difference X and the strain amount V of the set tightening force are calculated. Compare and judge whether the difference is within the predetermined range ΔV.
8) If it is within the predetermined range, the process from step 81 onwards is repeated again, and the injection molding operation is repeated. Further, if it is outside the predetermined range Δν, the CPU 31 calculates the rear platen position correction ff1L using a theoretically or experimentally obtained formula, for example, 2L
Calculate according to =k(X-v) (step 89). Note that k (>O) is a constant.

Next, the CPU 31 drives the servo motor Ma to correct the position of the rear platen 6 by this correction ff1L, in the direction opposite to the Freon 1 - platen 2 if L>O, and to the front platen 2 side if L<0 (step 5ho). Move on to the next injection molding cycle. In this way, when the strain X of the tie bar 5 becomes larger than the predetermined value V due to changes in the ambient temperature, etc., and the mold clamping force becomes excessive, the rear platen 6 is moved backward, but if the mold clamping force is too low, it is moved forward and next time. The rear platen position is corrected so that the mold clamping force becomes the set value.

In the above embodiment, the correction amount [of the rear platen position] is calculated sequentially, but the correction value is made to correspond to the difference angle between the value of the difference X in the distortion amount output and the distortion amount v corresponding to the set tightening force. Alternatively, the information may be read from a table set in advance.

As described in detail, according to the present invention, the strain amount of the tie bars at the time of mold opening and mold clamping is detected for each injection molding cycle, and the strain amount is determined at a predetermined turning point to provide a set mold clamping force. If not, the rear platen position is corrected so that it falls within the range, so if the tie bar expands or contracts due to disturbances such as changes in atmospheric humidity and the rear platen takes a position where it cannot apply the set mold clamping force. The rear platen position is immediately corrected,
The effects of disturbance can be compensated for, mold clamping force can always be maintained within a predetermined range, and good injection molding processing can be performed.

[Brief explanation of drawings]

Fig. 1 is a diagram showing means for solving the problem, Fig. 2 is a partially sectional side view of a toggle type mold clamping device of an injection molding machine to which an embodiment of the present invention is applied, and Fig. 3 is the above-mentioned A block diagram showing a control section of the mold clamping device and FIG. 4 show an operation flow of the device according to the embodiment. 5... Tie bar, 6... Rear platen, 24...
Strain gauge, 25...Analog-digital converter, 30
...Numerical control device (CNC) with built-in computer, 3
1... Central processing unit (CPU), 32... Memory,
40a, 40b--servo circuit, Ma, Mb
...Servo motor, Pa, Pb...Encoder. Figure 1

Claims (3)

[Claims] (1) In an injection molding apparatus having a toggle type mold clamping device and adjusting mold clamping force by moving a rear platen along a tie bar, a strainer attached to the tie bar and used to detect the amount of strain in the tie bar. a detector, an extraction means for extracting strain amount outputs from the strain detector at the time of mold clamping and mold opening of the mold clamping device, respectively; a storage means for storing, a calculation means for calculating the difference between the stored distortion amount outputs, a determining means for determining whether the calculated difference is within a predetermined range, and a calculating means for determining whether the calculated difference is within a predetermined range; A mold clamping force correction device for an injection molding machine, comprising a calculation means for calculating a rear platen position correction value based on the difference, and a drive means for driving the rear platen according to the correction value. (2) The injection molding according to claim 1, wherein the strain detector comprises an adhesive strain gauge attached to the tie bar, and an analog-to-digital converter interposed between the strain gauge and the extraction means. Machine mold clamping force correction device. (3) Claim 1 or 2, wherein the drive means comprises a servo motor that drives the rear platen, and a servo motor drive means that drives the servo motor in accordance with a correction value for the rear platen position. The mold clamping force correction device for the injection molding machine described above.