JP2853881B2 - Plastic film profile control method - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a profile control method for an average thickness for which the most important quality control is required in a molding process of a plastic film or sheet molded by an extruder. .

[Conventional technology]

In general, the thickness control of this type of plastic film includes the direction of feeding of the plastic film (Machin
e Direction) thickness control (called MD control)
A thickness control (referred to as CD profile control) in a width direction (Cross Direction) of a plastic film is known. Both the MD control and the CD profile control are performed simultaneously using a scanning thickness gauge.

However, profile control for the purpose of equalizing the thickness distribution of the plastic film is performed based on raw data (original waveform) measured by a scanning thickness gauge. In this case, the control target is almost limited to a T-die (die bolt, choke bar).

2. Description of the Related Art Conventionally, as a T-die configured to be able to adjust thickness unevenness in a width direction of a plastic film, a T-die configured to adjust a gap of the die by a movable lip is known. In this type of movable lip type T-die, a fixed lip and a movable lip are opposed to each other, and a gap formed by the lips defines a thickness of a plastic film to be extruded. A plurality of die bolts are provided in the direction, and the lip gap is adjusted by moving the die bolts.

In profile control and die bolt adjustment with such a configuration, a complex profile waveform measured by a scanning thickness gauge is a composite of sinusoidal components of various spatial wavelengths (hereinafter simply referred to as wavelengths) (Fourier series). It is considered that the waveform is analyzed).

Of these, fine wavelength components below a certain limit (wavelength of unevenness of waveform) cannot be corrected by die bolt operation.
For example, profile waveforms such as nylon, PP, PET, and PVA films have conspicuous fine irregularities, and when the operation amount of the die bolt is determined based on such an original waveform, a correction operation targeting a noise component is easily performed. In addition, it is not only impossible to adjust these components by die bolting, but it is rather counterproductive in many cases. In particular, in the case of a thermal displacement type automatic die that controls the amount of heat supplied to each die bolt stepwise, the temperature becomes excessively high or low,
Adjustment becomes impossible.

Therefore, the profile waveform measured by the scanning thickness gauge is inappropriate as profile adjustment data as it is.

Further, in such profile control, it is difficult to monitor and diagnose defects, such as die lines, wrinkles, and noises, caused by factors other than die bolt adjustment.

From such a viewpoint, the relationship between the interval between the lip portion of the T-die and the die bolt and the wavelength component of the profile waveform is examined as follows.

That is, the lip member is formed of an elastic body having high rigidity, and its deformation pattern due to the die bolt has continuity governed by the laws of dynamics, and it is impossible to curve more finely than the limit.

Therefore, the theoretical minimum pitch P _min of the lip deformation pattern
The relationship between the distance and the die bolt distance a is as shown in FIG. 4. In the case of a flexible lip having a special shape (having irregularities on the lip), the following expression is completely satisfied.

P _min = 2a (1) In the case of a standard flexible lip, the minimum pitch P _min of this deformation pattern is substantially P _min = 150 to 200 mm.

Since the relationship is as shown in the equation (1), the smaller the die bolt interval a is, the more the fine unevenness component of the profile waveform can be improved. For this reason, the effect of reducing the die bolt interval is extremely large when the profile waveform includes a small-wavelength unevenness component having a large amplitude.

However, in general, when the minimum wavelength to be corrected among the uneven components included in the profile waveform is λ _min , the required die bolt interval a can be generally regarded as substantially P = λ. Holds.

a ≦ λ _min / 2 (2) This relational expression exactly corresponds to the sampling theorem in digital measurement.

As described above, the profile waveform measured by the scanning thickness gauge as it is is inappropriate for use as profile adjustment data because of the unevenness component that is a noise component. For this reason, a method of removing fine unevenness components, that is, high-frequency components, by using an analog low-pass filter method that has been used for a long time with β-rays or the like, and smoothing the data, or observing very drastically changing data globally. A smoothing method using a digital simple moving average method that is often performed is adopted.

[Problems to be solved by the invention]

However, the smoothing method using the analog low-pass filter method described above smoothes the primary signal through an RC primary delay filter or the like constituted by a resistor and a capacitor. Has the drawback of not being able to grasp the actual state of the profile.

According to the digital simple moving average method (asymmetric type and symmetric type, but the symmetric type is used here), when the bandwidth of a filter for performing the simple moving average calculation is B,
Among the wavelength components included in the film profile, there is a point that the irregularity of the component of the wavelength λ = (0.5 to 1) B is inconsistent with the actual situation, which is very inconvenient in control. Further, there is a problem that there is no base for selecting the optimum bandwidth with respect to the bandwidth of the filter for performing the simple moving average calculation.

Therefore, an object of the present invention is to provide a method for controlling a profile of a plastic film or the like which is continuously molded by an extruder, by selecting an optimum bandwidth with respect to profile data measured by a scanning thickness gauge, thereby making profile control impossible. Possible short wavelength components are attenuated without inversion of unevenness.
Provides a smoothing process that performs optimal data processing that minimizes controllable attenuation of medium- and long-wavelength components that disappears, and provides a plastic film profile control method based on the determined automatic die operation amount. To be.

[Means for solving the problem]

The profile control method for a plastic film according to the present invention measures the profile of a plastic film or the like to be extruded by a scanning thickness gauge, and operates an automatic die based on the obtained profile data to obtain a required thickness. In the method of controlling the profile of a plastic film for forming a film, the profile data is included in the profile data, and when performing a smoothing process for cutting off fine unevenness component data that cannot be adjusted by an automatic die, the profile At least two times symmetrical moving average calculation processing is performed on the data using different averaging bandwidths, and the operation amount of the automatic die is determined based on the average value.

In addition, at least two averaging bandwidths of the moving average calculation processing using the different averaging bandwidths can be performed by setting the second averaging bandwidth to 1 / 1.5 to 1/2 of the first averaging bandwidth. It is suitable.

[Action]

According to the method for controlling the profile of a plastic film according to the present invention, an analog low-pass filter is used for performing a smoothing process for cutting short wavelength components in which profile control is impossible in profile data measured by an operation-type thickness gauge. Since the method does not use the method, there is no drawback due to the phase shift. A new multiple moving average method that performs moving average using at least two different averaging bandwidths is adopted. Can be greatly improved. Furthermore, the optimum bandwidth can be selected so as to attenuate / disappear without the reversal of the unevenness, and based on the operation amount determined by the optimal data processing that minimizes the attenuation of the controllable middle and long wavelength components. Because of the control method, it is possible to form a film of the required thickness with the best quality.

〔Example〕

Next, an embodiment of a method for controlling a profile of a plastic film according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a system configuration diagram showing an embodiment in which the plastic film profile control method of the present invention is applied to a molding process control system of an extruder.

FIG. 1 shows a process for forming a plastic film. Reference numeral 10 denotes an extruder, 12 denotes a film forming T-die, 14 denotes a forming roll unit, 16 denotes a scanning thickness gauge, and 18 denotes a winding machine. Are respectively shown. The scanning thickness gauge 16
Measurement signal from the CPU 22 via the input interface 20
Is input as a profile waveform. The CPU 22 has a memory 24 as storage means and a CRT as input / output means.
A display 26, a keyboard 28, and a printer 30 are connected and arranged.

Then, in the CPU 22, the profile control signal is fed back to the T-die 12 via the power unit 32 as a die bolt operation signal.

Next, the processing operation of the system according to the present invention in the molding process having the above configuration will be described with reference to the flowchart shown in FIG.

First, the forming roll unit is scanned by the scanning thickness gauge 16.
The profile data of the film continuously transmitted from 14 is measured, and the measurement signal is input to the CPU 22 via the input interface 20 and stored in the memory 24.

As described above, when the sampling of the required profile data is achieved, the following data processing is performed by the arithmetic function of the CPU 22.

(1) Creation of a profile waveform (original waveform) (2) Creation of a profile waveform in which the small-wavelength unevenness component of the original waveform is cut off and smoothed (3) Retention of the cut-off data (4) Smoothing Calculation of T-Die Bolt Adjustment Amount Based on Processed Profile Waveform In this manner, each data calculated by CPU 22 is used for CRT display 2 according to the above items (1) to (3).
6 or output to the printer 30.
FIG. 3 shows a display example of the original waveform data and the profile waveform data subjected to the smoothing process. Of course, it is also possible to display cut-off data.

The data relating to the above item (4) is transferred to the power unit 32 as a die bolt control signal, and the die bolt position of the T die 12 is adjusted.

The above processing operation is repeated at a predetermined timing, whereby a smooth operation of the system of the present invention can be achieved.

Here, the smoothing processing according to the present invention in the above item (2) will be described in further detail in comparison with the conventional simple moving average method. As is apparent from FIG. 3, since the original waveform contains noise-like components having fine irregularities, it is necessary to perform a smoothing process for extracting only optimum data for control from the original waveform.

Hereinafter, for simplicity, the model component of the profile is represented as a sine wave, and the continuous function y (x) is analyzed.

y (x) = αsin2π (x / λ) (3) Here, λ is a wavelength, α is a wave height (1/2 of PP), and α = 1 in the above description. Therefore, according to the conventional simple moving average method, the simple moving average of the position x (x)
Is represented by the following equation (symmetric type).

Where B is the bandwidth of the filter.

(4) If the equation is definitely integrated and summarized, Becomes Therefore, the wave height attenuation ratio A is It is expressed as

When the equation (6) is plotted against B / λ, it is as shown in FIG. That is, simply taking a moving average simply results in a negative attenuation ratio A in the range of 1 ≦ (B / λ) ≦ 2 as shown by C in FIG. 6, that is, the phase is shifted by 180 ° and the irregularities are reversed. Phenomenon occurs. This phenomenon is 3 ≦ (B / λ)
The same applies to the range of ≦ 4, but since it can be ignored in practical use, the range C will be discussed below.

As described above, the inversion phenomenon of the concavities and convexities occurs in the conventional simple moving average method because the filter characteristics are not ideal, and it is necessary to improve by performing the optimal selection of the bandwidth B with respect to the wavelength λ. . Therefore, the optimum bandwidth B
Is determined from the filter characteristics shown in FIG. 6 based on the following concept.

Of the wavelength components of the measurement data, if the lip cannot be bent even if it is desired to control it, it is regarded as an extra component and the attenuation ratio A of the controllable component is set to 0.5 or more.

With regard to the above, for a typical flexible lip as described above, the minimum pitch P _min of substantially deformable pattern because it is 150 to 200 mm, here assumed to limit the wavelength lambda _c and 200 mm.

As for B / λ when the damping ratio A is 0.5 from FIG. 6, the bandwidth B is B = 0.6 ×
λ _C = 120 mm is obtained. Actually, since the limit wavelength λ _C is slightly different depending on the shape of the die and the like, it is desirable to treat variable parameters on the system. However, here, for convenience of explanation,
Hereinafter, 120 mm is used as the basic band width.

Regarding the attenuation ratio A of the wave height by the simple moving average method,
When the bandwidth B is fixed to 120 mm and plotted against the wavelength λ, the characteristic curve shown in FIG. 7A is obtained. In this case, the unevenness of the wavelength component of λ = 60 to 120 mm is reversed (the range indicated by C in FIG. 6). The wavelength λ ₁ at which the minimum value occurs is determined in a range where the unevenness is reversed. In equation (6), π (B / λ) = X and the following equation is derived from (∂A / 式 X) = 0.

X−tanX = 0 (7) When this numerical solution is obtained, X = 4.49, and therefore B / λ ₁ = 1.43 (8) is obtained. From this, the wavelength λ at which this minimum occurs
₁ is seen to move in proportion to the band width B. As an example, in the case of the curve shown in FIG. 7A, λ ₁ = 120 / 1.43 = 83.9 mm.

Since the wavelength λ _{1 at} which the minimum value occurs moves in proportion to the bandwidth B, the inversion of the unevenness which occurs when only the conventional simple moving average method is used is canceled out, for example, as shown in FIG. The second bandwidth B ₂ that maximizes the effect of canceling out the minimum value generated by the curve of the attenuation ratio A ₁ shown in a).
It can be understood that it can be improved by selecting and superimposing. That is, the wavelength for the _second bandwidth B ₂ is λ ₂ ,
When the damping ratio in that case and _{A 2, A 2 (λ 2} ) = - A 1 (λ 1) ... may be selected band width B ₂ that satisfies (9).

By using the multiple moving average method based on such a concept, it is possible to perform an optimal smoothing process in which the phenomenon that profile unevenness is reversed in a specific wavelength range is greatly improved. From FIG. 6, the attenuation ratio A (B / λ ₁ ) when B / λ ₁ = 1.43 is A (B / λ ₁ ) = − 0.217, so that A (B / λ) = + 0.217 The satisfying λ is λ _2, which is obtained from FIG. 6 as B / λ ₂ = 0.813 (10). Therefore, λ ₂ = B / 0.813 is obtained.

Considering first band width B ₁ of FIG. 7 is for the case of 120mm curve (a), λ _{1 =} because it is 83.9mm, (10) second to satisfy the equation of the band width B ₂
It is sufficient that the wavelength λ ₂ according to λ ₁ matches λ ₁ according to B ₁ , and B ₂ = 0.813 × 83.9 = 68 mm. Therefore, if the actual sampling pitch is 10mm, the second band width B ₂ is 70mm, and the characteristic curve of the damping ratio A when thereby subjected to simple moving average, a curve shown in FIG. 7 (b )become that way. The characteristic by the double moving average method which takes the average ((A ₁ + A ₂ ) / 2) of the results A ₁ and A ₂ by the simple moving average method using the different bandwidths B ₁ and B ₂ is (c ). Compared to the curves (a) and (b) obtained by the simple moving average method, the wave height of the phase inversion section is reduced to about 1/3 and the peak position is also shifted to the short wavelength side, so that the adverse effect of the inversion phenomenon is greatly affected. It can be seen that it has been improved.

First band width B ₁ described above is 1.5 to 2 times the fifth case of the standard type of flexible lip shown in FIG 70～140Mm, in the case of special flexible lip having a bendable property shown in FIG. 4 die bolt arrangement pitch Is appropriate, and the band width after the second time may be set to 1 / 1.5 to 1/2 in order to perform the multiple moving average.

〔The invention's effect〕

As is apparent from the above-described embodiment, according to the method for controlling the profile of a plastic film of the present invention, the raw data (original waveform) measured by the scanning gage is measured by using different bandwidths for at least two times. A simple moving average is performed, and a control operation (operation amount operation) of the T-die is performed based on the data obtained by the smoothing process using the multiple moving average method of taking the algebraic average. And the profile control for the purpose of making the thickness distribution of the plastic film uniform can be surely achieved. As a result, a film having substantially the best quality is formed.

In particular, when a thermal displacement type automatic die is used, output of an excessive operation amount is prevented, so that stable profile control can be realized.

Although the preferred embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and it goes without saying that various designs can be changed without departing from the spirit of the present invention.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a molding process control system of an extruder showing an embodiment to which a plastic film profile control method according to the present invention is applied, and FIG. 2 executes a control system in the system configuration shown in FIG. FIG. 3 is an operation output waveform diagram when the control method of the present invention is executed by the system configuration shown in FIG. 1, and FIG. 4 is a deformation pattern of a special flexible lip having free bending property in a T-die. FIG. 5 is an explanatory view showing the relationship between the minimum pitch of the die and the die bolt gap, FIG. 5 is an explanatory view showing the relationship between the minimum pitch of the deformation pattern of the standard type flexible lip in the T-die and the die bolt gap, and FIG. Characteristic curve diagram showing wave height attenuation characteristics by
FIG. 7 is a characteristic curve diagram showing the effect of the double moving average method used in the smoothing process according to the present invention as an example. 10 Extruder 12 Film forming T-die 14 Forming roll unit 16 Scanning thickness gauge 18 Rewinder 20 Input interface 22 CPU 24 Memory 26 ... CRT display 28 ... Keyboard, 30 ... Printer 32 ... Power unit

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-61-291120 (JP, A) JP-A-1-95025 (JP, A) JP-A-61-45312 (JP, A) JP-A-61-45312 5916 (JP, A) JP-A-63-272527 (JP, A) JP-A-64-78815 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B29C 47/00-47 / 96

Claims (2)

(57) [Claims] 1. A plastic film for measuring a profile of a plastic film or the like to be extruded by a scanning thickness gauge and operating an automatic die based on the obtained profile data to form a film of a required thickness. In the profile control method, when performing a smoothing process for cutting off fine unevenness component data that is included in the profile data and cannot be adjusted by an automatic die, different averaging is performed on the profile data. A method for controlling a profile of a plastic film, wherein a symmetrical moving average calculation process is performed at least twice using a bandwidth, and an operation amount of an automatic die is determined based on the average value. 2. The averaging bandwidth of at least two times in the moving average calculation processing using different averaging bandwidths is such that the second averaging bandwidth is 1 / 1.5 to 1/2 of the first averaging bandwidth. 2. The method for controlling a profile of a plastic film according to claim 1, wherein: