JPH0788946A - Wall thickness control method for parison - Google Patents

Abstract

PURPOSE:To simply and easily conduct a wide-range correction of an existing parison pattern including a local correction by a method wherein a secondary corrected parison pattern is formed to be used for controlling a die gap amount by multiplying a primary corrected parison pattern of a die gap amount obtained from an existing parison pattern by a correction factor only in an arbitrary section of an injection stroke. CONSTITUTION:A set parison pattern is stored in a command signal setting part 11 of a parison wall thickness controller 16. A deviation (e) between a set die gap amount value G1 of an injection cylinder 5 at a position of an injection stroke 3 inputted from a position detector 5b and a measured die gap amount value G2 detected by a die gap detector 9 is evaluated in a deviation operation part 12. A variable condenser cylinder 8 is actuated. in this case, a corrected parison pattern is formed by multiplying an existing set curve A by a factor of alpha, adding a fixed value of a die gap amount G, or synthesizing the gain correction with the offset correction. In addition, a wall thickness change can be corrected so as to be different only in a specified section of an injection stroke S.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the thickness of a parison in a blow molding machine, and in addition to a set parison pattern, a similar parison pattern obtained by modifying an existing parison pattern can be easily created. Then, the present invention relates to a method for controlling the thickness of a parison that immediately restarts the actual operation.

[0002]

2. Description of the Related Art A parison made of a molten resin extruded from a blow molding machine and hung down is not uniform in the longitudinal direction of the parison depending on the intended product shape, and is formed by changing the wall thickness as necessary. . One of the methods conventionally used as a method for controlling the thickness of the parison in this case is to set the parison thickness characteristic curve in which the injection stroke amount (or molding time) and the die gap adjustment amount are preset on the screen on two orthogonal axes. A so-called parison pattern control method is adopted, in which the die gap (in other words, the required wall thickness) setting value for each set point obtained by dividing this molding time into multiple equal parts is taken out and the downward movement of the extrusion plunger is controlled over time. It had been.

[0003]

As described above, in the above-described control method using the parison pattern, the shape of the product is once determined, and the wall thickness is increased or decreased as necessary according to the strength of the product. It is very simple and efficient in the case of mass production of one kind in which a different parison pattern is formed and the same product having the same shape and the same wall thickness variation is repeatedly molded. However, when making a slight correction by looking at the situation of the on-site product or making a slight change to the existing parison pattern due to production reasons to create a product with a new parison pattern, the screen on the two orthogonal axes described above is re-created. He had to remake a new parison pattern from the beginning and start production with the new parison pattern, and he was forced to change all the settings. This parison pattern to be modified is the same as the conventional parison pattern, in which the die gap amount (parison wall thickness) is increased or decreased at the same ratio over the entire length of the injection stroke, or the same amount is added. It has been desired to have a wide range of modifications that can easily change the die gap amount only in a specified section.

[0004]

In order to solve the following problems, in the present invention, the molten resin supplied to the gap formed between the mandrel and the blow head is operated by an injection cylinder to lower the gap. Is a method for controlling the wall thickness of a parison in a blow molding machine that is extruded from a nozzle slit of a nozzle, and is a screen on two orthogonal axes with the injection stroke during molding and the die gap amount of the nozzle slit as axes. The die gap amount is controlled based on the pre-set parison pattern, and the die gap amount corresponding to the already set injection stroke of the existing parison pattern is multiplied by the 1-constant gain constant and the 1-constant offset is set. The first modified parison pattern consisting of the modified set values of the die gap amount obtained by adding the constants Second to obtain a correction factor is calculated based on the function of the injection stroke preset only any designated section of the injection stroke by multiplying the corrected set value
The die gap amount is controlled based on the secondary modified parison pattern formed by the next modified set value.

[0005]

In the present invention, not only is the existing parison pattern multiplied by a certain ratio over the entire injection stroke to change the wall thickness, or a certain amount is added or subtracted to change the wall thickness. Only the required injection stroke section is multiplied by the correction value calculated based on the function specified in advance and the die gap amount in this specified section is multiplied to locally correct the wall thickness to create the desired modified parison pattern. A molded product having a thickness change different from that of the product is obtained.

[0006]

Embodiments of the present invention will be described below in detail with reference to the drawings. 1 to 6 relate to an embodiment of the present invention,
Figure 1 is a block diagram of the parison thickness control device of the blow molding machine,
FIG. 2 is a flow chart showing a procedure for creating a modified parison pattern, and FIGS. 3 to 6 are explanatory views showing examples of the modified parison pattern. As shown in FIG. 1, the blow molding machine 1 is fitted into a mandrel 3A provided in the center of a die 2 including a blow head 2a having a rectangular cross section and a nozzle 2b connected to the blow head 2a. Core 3
The fixed rod 3a is connected to the Parison cylinder 8 so as to be reciprocally movable in the vertical direction, and the molten resin supplied to the resin passage 2c in the die 2 by the extruder 6 is distributed between the core 3 and the nozzle 2b. Nozzle slit 7 formed by a gap
Further, the parison P is formed by pushing downward by the operation of the injection cylinder 5 of the injection device 4. The gap at the lowermost end of the nozzle slit 7 is called a die gap (or die gap amount), and the parison P to be extruded is formed.
Regulate the wall thickness of. Servo valve 10 for supplying hydraulic oil to the Parison cylinder 8 and rod 3 of the Parison cylinder 8
The die gap detector 9 for detecting the movement amount of a and the position detector 5b for detecting the movement amount of the piston rod 5a of the injection cylinder 5 are both connected to the parison thickness control device 16. The parison thickness control device 16 has a built-in command signal setting unit 11 for setting a parison curve, a deviation calculation unit 12, and a PID control calculation setting unit 13, and is connected to a display device 14 and an input device 15 to detect the parison P being discharged. It is constructed so that the wall thickness can be controlled arbitrarily.

Next, the operating procedure of the parison thickness control method according to the embodiment of the present invention will be described. Using the display device 14 and the input device 15, a parison having, for example, a waveform (predetermined curve A) shown in FIG. 3 on a screen on two orthogonal axes with the die gap amount on the vertical axis and the injection stroke S on the horizontal axis. Create a pattern. The procedure for creating the parison pattern is to divide the injection stroke S on the horizontal axis into a plurality of control areas, set the set value of the die gap amount at the start point or the center point of each control area, and then set these points. Interpolate the connected straight lines to form a smooth curve and create a modified curve. This is the set parison pattern, which is stored and stored in the command signal setting unit 11 of the parison thickness control device 16, and in actual operation, the injection stroke S of the injection cylinder 5 input from the position detector 5
A deviation calculator 12 calculates a deviation e between the set value G ₁ of the die gap amount at the position and the measured value G _{2 of} the die gap amount detected by the die gap detector 9. The PID control calculation setting unit 13 performs PID calculation using the obtained deviation e, and outputs the result to the servo valve 10 and the Paris cylinder 8
To operate. By repeating these operations moment by moment, the injection cylinder 5 follows a preset parison pattern.
And the Paris cylinder 8 to operate the die gap G
Is increased or decreased according to the prescribed waveform. The parison P molded in this manner becomes a parison having the same thickness change as the parison pattern set in the longitudinal direction. On the other hand, at the production site where molded products are molded according to these set parison patterns, the wall thickness of all sections in the longitudinal direction of the parison may be thickened or thinned at a constant ratio depending on the condition of the finished product. Sometimes it is necessary to make local corrections that change the wall thickness change only in the designated section than in other sections. Therefore, in the present invention, the complexity of recreating such a new parison pattern from the beginning is alleviated, and a modified parison pattern in which an entire correction or a local correction is added to an existing parison pattern is simply created and is created. It was used to immediately resume production to help improve productivity. The correction procedure will be specifically described below.

The modification shown in FIG. 3 has a modified set value which is α times the existing set value in the entire section of the injection stroke S with respect to the preset curve A which is the existing parison pattern. The modified parison pattern of curve X is shown. Further, what is shown in FIG. 4 is a modified parison pattern of the modified curve Y obtained by uniformly adding the set value of the die gap amount G by a constant value (offset β) in the entire section of the injection stroke S. 5 is a modified curve Z obtained by combining the gain correction shown in FIG. 3 (each set value multiplied by the amplitude ratio α) and the offset correction shown in FIG. 4 (added a constant value offset (steady deviation)). It is a modified parison pattern having. In addition to the corrections common to all sections as described above, there are specific designated sections a to c with the injection stroke S.
When a wall thickness change that is different from other sections is required only during the interval, the function y of the injection stroke S in this specified section is y =
α (S) is defined, and y = 1 at the start point S = a and the end point of this specified section, and y = k (where k is 1 since the point between points a and c (this point is point b)). A function that is a slightly large constant and is usually k = 1.1 to 1.5) is adopted. This function has three points (a, 1), (b, k), (c,
The function may be a second-order or higher function passing through 1), or may be a straight line connecting each two points. The function G = g of the curve having the set value of the die gap amount G corrected between the designated sections a to c using the gain function y = α (S) thus defined.
(S) is the function of the existing parison pattern G = f
If (S), then g (S) = α (S) × f (S). FIG. 6 shows a modified curve W obtained by further locally modifying the modified curve Z of FIG. 5 between designated sections a to c. The gain function y = α (S) described above
In general, it is preferable that the left and right differential coefficients at the start point and the end point between the designated sections a to c are the same or the difference is small so that the appearance of the molded product is smooth. When the above-mentioned linear line is adopted, the difference between the left and right differential coefficients becomes smaller as the value of the designated constant k approaches 1. If the constant k is selected from the above range k = 1.1 to 1.5, there is no practical problem.

As described above, the existing parison pattern is used as a base, and local correction in the entire section of the injection stroke S or in the designated section can be performed to create a modified parison pattern as shown in FIG. The flow chart shown in FIG. 2 shows an example of the procedure for correcting the parison pattern, in which the overall gain correction, the overall offset correction, and the local gain correction are each corrected as required, and then the final corrected parison is corrected. It is designed to create patterns. After the final version of the modified parison pattern created in this way is created via the display device 14 and the input device 15, it is sent to the command signal setting section 11 of the parison thickness control device 16 and the operation procedure as described above is performed. Based on this, it is possible to obtain a desired molded product while adjusting the die gap amount G. As described above, according to the present invention, the original parison pattern is used to easily and easily create the modified parison including the local modification and the overall modification, and the work can be restarted, so that the working time required for changing the molding condition (parison thickness change) is large. Is reduced to.

[0010]

As described above, according to the thickness control method for a parison of the present invention, since it is possible to easily and easily make a correction including a local correction using an existing parison pattern, it is possible to reduce the time required for changing the molding conditions. Also, labor and labor are greatly reduced, and the actual operating rate is increased, so that productivity is improved, product quality is improved, and driving operability is improved.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a parison thickness control device of a blow molding machine according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a procedure for creating a modified parison pattern according to the embodiment of the present invention.

FIG. 3 is an explanatory diagram of a modified parison pattern according to the embodiment of the present invention.

FIG. 4 is an explanatory diagram of a modified parison pattern according to the embodiment of the present invention.

FIG. 5 is an explanatory diagram of a modified parison pattern according to the embodiment of the present invention.

FIG. 6 is an explanatory diagram of a modified parison pattern according to the embodiment of the present invention.

[Explanation of symbols]

1 Blow Molding Machine 2 Die 2a Blow Head 2b Nozzle 2c Resin Passage 3 Core 3A Mandrel 3a Rod 4 Injection Device 5 Injection Cylinder 5a Piston Rod 5b Position Detector 6 Extruder 7 Nozzle Slit 8 Paricon Cylinder 9 Die Gap Detector 10 Servo Valve 11 command signal setting unit 12 deviation calculation unit 13 PID control calculation setting unit 14 display device 15 input device 16 parison thickness control device A preset curve X correction curve Y correction curve Z correction curve W correction curve G die gap amount G ₁ die Gap amount setting value G ₂ Die gap amount measurement value S Injection stroke α Gain constant β Offset constant α (S) Gain function f (S) Original function e Deviation

Claims (1)

[Claims] 1. A method for controlling the thickness of a parison in a blow molding machine, in which molten resin supplied to a gap formed between a mandrel and a blow head is extruded from a nozzle slit at the lower end of the gap by operation of an injection cylinder to perform molding. And the die gap amount is controlled based on a preset parison pattern on a screen on two orthogonal axes with the injection stroke during molding and the die gap amount of the nozzle slit as axes. The first order consisting of the corrected set value of the die gap amount obtained by multiplying the die gap amount corresponding to the injection stroke of the existing parison pattern by the gain constant of 1 constant value and adding the offset constant of 1 constant value. In addition to the modified parison pattern of, the injection stroke box that is preset only in any specified section of the injection stroke Of a parison that controls the die gap amount based on a second-order modified parison pattern formed by a second-order modified set value obtained by multiplying the modified set value by a modified coefficient calculated based on a number. Wall thickness control method.