JPH0576412B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for monitoring and controlling the thickness in the width direction of a plastic film sheet formed by an extrusion molding machine using a T-die at the extrusion opening, and particularly relates to a method for monitoring and controlling the thickness in the width direction of a plastic film sheet formed by an extrusion molding machine using a T-die at the extrusion opening. The present invention relates to a film sheet profile control method for accurately assigning and setting die bolt positions corresponding to measurement points of film sheet profile data measured by a meter. [Prior Art] In general, methods for controlling the average thickness of this type of film sheet include thickness control for the extrusion method of the film sheet (referred to as MD control) and thickness control for the width direction of the film sheet (CD profile control). ) is known. and,
These MD control and CD profile control are performed simultaneously using a sensor (scanning thickness gauge). In this type of film sheet forming process, one of the causes of uneven thickness of the extruded film sheet is that the film sheet extruded from the mold extrusion port (referred to as the T die lip exit) reaches the forming roll. The so-called net-in phenomenon, in which both ends of the film sheet shrink between the two ends, is known. As shown in FIG. 4, the width of the film sheet at the forming roll 12 is narrower than the width of the T die lip outlet 10. This netquin phenomenon is
This is caused by the viscoelasticity of the plastic material, and the amount of shrinkage of the film sheet or its streamline pattern is determined by the type of material and molding conditions [e.g., resin temperature, draw ratio (ratio of take-up speed and outflow speed). ), air gap, roll temperature, etc.). Therefore, in an extrusion molding machine for plastic film sheets, etc., a die forming an extrusion port is used as a T die that can adjust the thickness unevenness in the width direction of the film sheet, with a fixed lip and a movable lip facing each other. The gap between both lips forms the opening gap of the extrusion port,
The thickness of the extruded film sheet is determined by the interval between the openings. In order to do this, a structure is known in which a plurality of die bolts for movably adjusting the movable lip are arranged in the width direction of the lip outlet. In order to properly adjust the lip gap of such a T-die, the measuring head of a scanning thickness gauge is moved back and forth in the width direction of the film sheet to be extruded to measure the thickness, and this measured value is used as a profile. An automatic profile control system is employed in which the die bolt is operated by a power unit, such as a servo motor or a pulse motor, based on aisle data, and the lip gap of the T-die is selected at an appropriate interval. [Problems to be Solved by the Invention] However, in such an automatic profile control system, in order to form a highly accurate film sheet by die bolt operation, the profile data of this film sheet, for example, when the measuring head is Based on the data that there was an abnormality in the thickness of the film sheet measured at what distance from one end of the exit, it was determined by what amount of operation the number die bolt corresponding to this measurement point should be operated. If this is not clear, the thickness of the film sheet cannot be corrected appropriately. For this purpose, it is necessary to accurately assign and set the die bolt positions corresponding to the measurement points of the profile data. In recent years, profile monitoring and control systems using computers have been developing.
Even in this case, the accuracy of allocation of the corresponding die bolts has a great influence on the accuracy of controlling the thickness of the film sheet. This is because the measurement point of the profile data of the film sheet is in the flowing fluid, and it can easily adapt to the amount of net-in that changes every time the molding conditions change.
This is because a simple and accurate method for allocating die bolts has not yet been established. Usually, the actual situation is that a fixed die bolt allocation pattern is applied to all conditions or is determined based on human skill and experience. In addition, attempts have been made to precisely determine the correspondence by manipulating several die bolts through trial and error and measuring changes in thickness with a thickness gauge, but the operation is complicated and complicated. However, it is not practical as it requires a lot of extra time and extra material for the film sheet. From this perspective, the present inventors were able to elucidate the following general characteristics of the process while working on automatic profile control tests. That is, first, regarding the general characteristics of streamlines,
This will be explained with reference to FIG. FIG. 4 is a model diagram showing the net-in phenomenon. Due to this phenomenon, in the streamline pattern from the T-die rip outlet 10 to the forming roll portion 12, the amount of net-in is larger at the ears at both ends.
The streamline 14 is fixed by the forming roll section 12. Note that the black circle indicates the die bolt position 16. (1) The streamline pattern shown in Fig. 4 shows that the corresponding die bolt position 16 on the film sheet varies depending on the type of material and the above-mentioned forming conditions due to the net-in phenomenon, but under certain conditions, the die bolt operation is difficult. Although it fluctuates somewhat depending on the accompanying profile changes, it is almost stable. (2) Streamline 1 corresponding to a specific die bolt position 16
4 is indefinite, but the streamlines 14 never intersect. That is, adjacent streamlines 14 move toward or away from each other, but do not interchange. Therefore, the correspondence between a specific die bolt and a streamline needs to be considered only in a relatively narrow range of the specific die bolt. Next, the general relationship between the die bolt operation amount pattern and the profile change amount pattern is as shown in FIG. In this case, a plurality of die bolt position numbers arranged on the horizontal axis are indicated by 1, 2, . . . i . . . n. In Figure 5a, the vertical axis shows the amount of die bolt operation, and the + side is the direction to loosen the die bolt (the direction to reduce the load).
One side indicates the direction in which the die bolt should be tightened (the direction in which the load should be increased). In FIG. 5b, the vertical axis shows the amount of change in the lip gap, the positive side of which indicates the direction of increasing the lip gap, and the one side thereof indicates the direction of decreasing the lip gap. In FIG. 5c, the vertical axis shows the amount of change in flow rate distribution, with the + side indicating the direction in which the flow rate increases, and the one side indicating the direction in which the flow rate decreases.
In FIG. 5d, the vertical axis represents the amount of profile change, with the + side representing the direction in which the thickness increases, and one side representing the direction in which the thickness decreases. The arrows between the figures in FIG. 5 indicate that when the die bolt operation amount is manipulated, the effect is sequentially exerted on the profile change amount. That is, the die bolt operation amount pattern and the profile change pattern of the film sheet are determined by the mutual interference effect between the die bolt and the lip gap (arrow A), the flow rate characteristics of the streamlines (arrow B), and the network effect (arrow C). In particular, although both ends of the lip exit are considerably deformed, the overall relationship is almost similar. In this way, there is a certain causal relationship between the amount of Diebolt operation and the amount of profile change, so if you record and store as much of both as time series data and examine the cross-correlation between the two at an appropriate time, The point of view of the present invention is that the position where the influence of a particular die bolt operation is the strongest, that is, the case where the correlation coefficient is highest, can be regarded as the corresponding position between the two. Also,
Furthermore, the profile data of the film sheet actually measured by the measuring head of the scanning thickness gauge is
If the length in the width direction of the film sheet is plotted on the horizontal axis and the profile deviation amount is plotted on the vertical axis, a complex profile waveform is obtained as shown in FIG. This waveform is considered to be a composite of sine wave or cosine wave components of various pitches, and among these waveforms, fine pitch components below a certain limit cannot be corrected by die bolt operation, so this is a countermeasure. We found that statistical methods such as the use of filters are required for noise analysis. In addition, as shown in Japanese Patent Application Laid-Open No. 1987-78726, which is the applicant's earlier application,
It is known that when a particular die bolt among multiple die bolts is operated, not only the gap between the lips at the position where that die bolt acts changes, but also other parts are affected (this is called mutual interference). The method is supported by simulations that take this effect into account.
In other words, Fig. 6 shows the simulation results of the correlation between the die bolt operation amount and the lip gap change amount (which is closely related to the profile change amount as shown in Fig. 5), and the horizontal axis shows the die bolt position. , the 0 position indicates the specific die bolt position i, the +1 to +4 positions indicate the die bolt position i+1,
...Indicates die bolt position i+4, -1 to -4
The positions indicate die bolt position i-1, . . . die bolt position i-4. The vertical axis represents the operation amount δi,j at die bolt position i and the lip gap change amount gi-4j, gi-3, j...gi, from i-4 to i+4th equivalent position.
The correlation coefficient between j, g _i+1 , j...gi+4, and j is shown. The curves and curves are taken into consideration with correction values of 1, 0, 1, 2, and 1.4, respectively, depending on the strength of the mutual interference effect between the die bolt and the lip gap, and although there are some differences between these three, a good correlation is established in all of them. are doing. The good agreement between the simulation results and the experimental results is expected based on the numerous experimental results to date. It is judged to be sufficiently effective. Therefore, an object of the present invention is to obtain the amount of profile change from the profile data measured during the film sheet forming process, calculate the die bolt operating amount from this, repeat the process of operating the die bolt, and record the data during this process. Find the correlation coefficient between the die bolt operation amount and the profile change amount, and determine the appropriate die bolt position from the thickness measurement point on the film sheet that can be detected based on this correlation coefficient and the corresponding die bolt position. The objective is to provide the most precise and practical method for setting allocations. [Means for Solving the Problems] The film sheet profile control method according to the present invention includes disposing a plurality of die bolts in the width direction of the mold extrusion port to adjust the opening gap of the mold extrusion port. A film sheet is continuously extruded using an extrusion molding machine, and the profile data of the film sheet is measured by reciprocating the measurement head of a scanning thickness gauge in the width direction of the film sheet. In the film sheet profile control method, the operation amount of the die bolt is calculated based on profile data, and the thickness of the film sheet is controlled by operating the die bolt based on the operation amount, wherein the plurality of die bolts are controlled. Perform the operation a predetermined number of times, record the amount of die bolt operation for each operation, measure and record the amount of profile change at a plurality of thickness measurement points on the film sheet caused by the operation of the die bolt, and record the amount of profile change for each of the predetermined times. Calculating a correlation coefficient between the die bolt operation amount indicating time series data obtained by the operation and the profile change amount, and determining the maximum value from the calculation result,
Detect the thickness measurement point on the film sheet corresponding to this maximum value and the corresponding die bolt position,
The present invention is characterized in that the die bolt position is allocated or corrected by comparing the die bolt detection position and the die bolt setting position. [Function] When using the profile control method of the present invention, the initial data of the die bolt corresponding position is obtained according to the conventional method, and by setting this data, the film sheet is formed at the same time as the film sheet forming process is started. Operation of the die bolt and measurement of profile data are started while maintaining the time interval from the exit of the T die rip to the forming roll section, and then this process is continuously repeated a predetermined number of times. During this time, as shown in FIG. 3, two pieces of time-series data, the amount of operation of the die bolt and the amount of profile change, are stored in the memory. In addition, Figure 3 shows
The horizontal axis shows the number of operations 1, 2, 3...j...N in time series, and the vertical axis shows the die bolt operating amount δ and the profile change amount e. Eventually, the correlation coefficient of these two time-series data is calculated using the following correlation calculation equations (1) to (4). =1/N _N 〓 ^j=1 δi,j and _k =1/N _N 〓 ^j=1 ek,j ……(1)

〔Example〕

Next, an embodiment of the film sheet profile control method according to the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a system configuration diagram showing an example of an extrusion molding process that implements the film sheet profile control method according to the present invention. In FIG. 1, reference numeral 20 is an extrusion molding machine, 22 is a mold (T-die), 24 is an extrusion outlet (rip outlet), 26 is a forming roll unit, 28 is a film sheet, 3
0 is a scanning thickness gauge, 32 is a winding machine, 34 is a measuring head, and 36 is a die bolt. Film sheet 2 measured by the measuring head 34
A measurement signal 52 indicating the thickness of 8 is input to the CPU 40 via the input interface 38 as profile data. A memory 42 as a storage means, a keyboard 44 as an input means, and a CRT display 46 and a printer 48 as output means are connected to the CPU 40 . Said CPU4
0, the die bolt operation amount for controlling the processed profile based on the profile data becomes an operation signal 54 and is input to the power unit 50. The power unit 50 is composed of, for example, a pulse motor, and the operation signal 54 drives the power unit 50 to operate a plurality of die bolts 36 disposed in the mold 22, adjust the opening gap of the extrusion port 24, The thickness of the film sheet 28 to be extruded is controlled. This film sheet 2
8 passes through the forming roll unit 26 and then between the measuring heads 34 of the scanning thickness gauge 30 and is wound up on the winder 32. The new measurement signal 52' detected by the measurement head 34 is input again to the CPU 40 via the input interface 38 as new profile data. The thickness of the film sheet is controlled by a control method using such a feedback loop. Next, processing operations in the CPU 40 will be explained with reference to the flowchart shown in FIG. In FIG. 2, first, in step a, initial data of the bolt corresponding position of the die bolt is obtained by, for example, a conventional method, and this data is written into the memory 42 using the keyboard 44.
Next, in step b, various controls including die bolt operation, correlation analysis conditions, etc. are entered using the keyboard.
4 to the memory 42. In step c, the input profile data is sampled and output and displayed on the CRT display 46 or the printer 48. In step d, a predetermined time is required for the film sheet at the time when the die bolt 36 is operated to reach the position of the measurement head 34 and the profile data is measured. judge whether If this timing is bad, step c
Return to In step e, the operation number (j) of the die bolt is updated. In step f, target lip deviation values indicating target sheet thicknesses at a plurality of predetermined locations of the die bolt, taking into account the above-mentioned mutual interference effect, are set using the initial data of the bolt corresponding positions stored in step a. In step g, the load change amount of each die bolt is calculated based on the deviation (profile change amount e _k,j ) between the profile data input in step c and the lip deviation target value, and this The die bolt operation amount δ _i,j is calculated using the load change amount. That is, control calculations related to the die bolt operation are executed. Step h
Then, the die bolt operation amount is output as the operation signal 34. In step i, the die bolt operation amount δ _i,j and the profile change amount e _{k,j, which are data for correlation analysis, are}
and is transferred to the memory 42 and stored therein. In step j, it is determined whether the data for correlation analysis has been stored until a predetermined operation number is reached. If the predetermined number of operations is not achieved, the process returns to step c.
In step k, the correlation analysis data is read from the memory 42. In step 1, the following formula (1) is used to reach (4) using the die bolt operation amount δ _i,j and the profile change amount e _k,j, which are time series data sufficient to obtain the correlation coefficient. Find the correlation coefficient γ〓 _,e using the correlation calculation formula, and then find its maximum value. =1/N _N 〓 ^j=1 δi,j and _k =1/N _N 〓 ^j=1 e _k,j ……(1)

〔Effect of the invention〕

As is clear from the above-mentioned embodiments, according to the film sheet profile control method according to the present invention, the die bolt operation amount and the profile change amount, which are real-time control data during the film sheet forming process, are used. , the thickness measurement point on the film sheet corresponding to each die bolt and the die bolt position can be detected only by the information processing of calculating these correlation coefficients, and the task of accurately assigning and setting the die bolt position can be avoided, saving extra time. It does not require any materials and can be carried out automatically and with high precision. As a result, the profile control performance under all molding conditions in extrusion molding of this type of film sheet can be improved.

[Brief explanation of the drawing]

FIG. 1 is a system configuration diagram showing an example of an extrusion molding process that implements the film sheet profile control method according to the present invention, and FIG. Figure 3 is a model diagram of two time-series data, Figure 4 is a model diagram showing the net-in phenomenon, and Figure 5 is a waveform diagram showing the similar relationship between the die bolt operation amount pattern and the profile change amount pattern. , FIG. 6 is a characteristic curve diagram showing an example of the calculation result of the correlation coefficient shown in FIG. 5, and FIG. 7 is a waveform chart showing an example of profile data. 10...T die lip outlet, 12...Forming roll, 14...Streamline, 16...Die bolt position, A
... Mutual interference effect, B ... Flow rate characteristics, C ... Network effect, 20 ... Extrusion molding machine, 22 ... Mold, 24 ... Extrusion port, 26 ... Forming roll unit, 28 ... Film sheet, 30... Scanning thickness gauge, 32... Winder, 34... Measuring head, 3
6...Die bolt, 38...Input interface, 40...CPU, 42...Memory, 44...
Keyboard, 46... CRT display, 48... Printer, 50... Power unit, 52... Measurement signal, 54... Operation signal. 1

Claims (1)

[Claims] 1. A film sheet is continuously extruded using an extrusion molding machine equipped with a plurality of die bolts that can adjust the opening width of the mold extrusion ports in the width direction of the mold extrusion ports. Measure the profile data of the film sheet by reciprocating the measurement head of the scanning thickness gauge in the width direction of the film sheet, calculate the operation amount of the die bolt based on this profile data, and perform this operation. In the film sheet profile control method of controlling the thickness of the film sheet by operating the die bolts according to the amount, the plurality of die bolts are operated a predetermined number of times and the die bolt operation amount is recorded for each operation; Measure and record the amount of profile change at a plurality of thickness measurement points on the film sheet caused by the operation of the die bolt, and measure and record the amount of the die bolt operation and the profile showing the time series data obtained by the predetermined number of operations. Calculate the correlation coefficient with the amount of change in the die bolt, find the maximum value from this calculation result, detect the thickness measurement point on the film sheet corresponding to this maximum value and the corresponding die bolt position, and A film sheet profile control method characterized by comparing a detected position and a die bolt setting position and setting or correcting die bolt position allocation.