JPH0142818B2 - - Google Patents

Description

[Detailed Description of the Invention] <Technical Field> The present invention measures the flow of a plastic sheet, etc. (hereinafter simply referred to as a sheet, etc.) discharged from a die and running while displacing a thickness gauge in the width direction of the sheet, etc. This paper relates to an improvement in the thickness control method for sheets, etc. (hereinafter referred to as MD control) that adjusts the thickness in the direction.

<Prior Art> Conventionally, it has been required for product management to measure the thickness distribution in the width direction (usually referred to as profile) of sheets etc. that are continuously manufactured using an extrusion molding machine. For example, in order to measure the profile, we will use a scanning transmission type thickness gauge that is equipped with a measurement head that moves back and forth in the width direction of a part of the product conveyance path. To explain with reference to the drawings, in FIG. 1, reference numeral 10 indicates a sheet etc. that is continuously extruded from a forming die 12 attached to an extruder 11 and manufactured through a forming roll 13 driven by a motor 26. This sheet etc. 1
A transmission type thickness gage 16 is provided in a part of the conveyance path of 0.0 and is equipped with a measurement head consisting of a pair of light emitter 14 and light receiver 15 that move back and forth in the width direction. Further, the transmission type thickness gauge 16 is provided with a scanning motor 17 for reciprocating and scanning the measuring head in the width direction of the sheet etc. 10.
7 is controlled by an external controller to be described later.

However, the external controller that controls the scanning motor 17 includes a speed regulator 18 and a motor controller 1.
9, a position setting device 20, a converter 21 which inputs the measurement head position signal X _S obtained from the transmission type thickness gauge 16, and a comparator 22.
Therefore, in the comparison calculator 22, the converter 2
The feedback position signal _Xs of the measuring head obtained via 1 is compared with the position signal for setting the turning point of the measuring head set by the position setting device 20, and the signal obtained by this comparison calculator 22 and The speed adjustment signal from the speed regulator 18 is input to a motor controller 19 to supply a predetermined motor control signal C _s to the scanning motor 17 .

From the transmission type thickness gauge 16, a thickness signal _ts of the sheet or the like 10 is taken out together with a position signal _Xs of the measurement head. This thickness signal t _s is transferred to the conversion amplifier 2
3. The position data and the thickness data are stored in correspondence with each other in a storage device 25 such as a computer system via the A/D converter 24. The storage device 25 includes a CPU 27, an internal storage device 28,
It is composed of peripheral devices 29, a timer 30, and the like.

In the apparatus shown in FIG. 1, management control of the sheet width direction profile and the average thickness in the sheet flow direction are performed in parallel based on measurement data from the transmission type thickness gauge 16.

Here, the amount of extrusion from the molding die 12 is Qm ³ /
s, the sheet take-up speed of the forming roll 13 is Um/s
Then, the average thickness of the sheet in the machine direction is expressed by the following equation.

=kQ/U...(1) In equation (1), k is a proportionality constant, which is a constant related to the sheet width and the specific weight of the sheet.

The extrusion amount Q in equation (1) gradually decreases as the filter provided at the tip of the screw of the extruder 11 progresses, causing a decrease in the average thickness of the sheet. In addition, there are various disturbance factors that cause the average thickness of the sheet to vary as the extruder Q from the forming die 12 changes due to changes in material properties. For this reason, the thickness in the sheet flow direction is controlled so that the thickness in the sheet width direction is constantly measured, and the average value of the measured values in the sheet width length is taken as the sheet thickness, and the deviation thereof becomes zero.

The screw drive motor 41 of the extruder and the drive motor 26 of the forming roll 13 are objects of this sheet flow direction thickness control. The former is mentioned above
The objective is to obtain a target sheet thickness by controlling the extruder Q while keeping the take-up speed U in equation (1) constant.

The controllability of such a device is governed by the dead time described below. In other words, the smaller the dead time, the
Good control is in place.

The dead time of this device is the sum of the following two types. One of them is the dead time t ₁ depending on the set position of the thickness gauge 16, which is expressed as t ₁ =L/U, where L is the sheet path line length between the forming die 12 and the thickness gauge 16.

The other is the dead time t ₂ associated with scanning the thickness gauge 16 in the width direction, where the scanning stroke is B and the scanning speed is U _s.
Then, it is expressed as t ₂ =B/U _s . This wasted time
t ₂ is the measuring head of the thickness gauge 16, the projector 1
4. This does not occur if the receiver 15 is fixed at a fixed point on the sheet, but as in the present application, it is possible to obtain control data for both the width direction thickness and machine direction thickness of the sheet with one thickness meter. will inevitably occur.

The thickness control method of the present application improves the way in which the values at the measurement points are incorporated into the control amount, and aims to shorten the dead time _t2 as much as possible.

Here, the conventional method of incorporating the value of the measurement point of the sheet machine direction thickness into the control amount will be explained with reference to Fig. 2 A and B. When the thickness changes in the longitudinal direction as shown in graph a, the measurement head changes from A to As the measurement head moves from point B to point C to point D, when it reaches point A, which is the end point of the _S1 zone, the thickness _t1 is calculated as the average thickness of _S1 , and the measurement head reaches _S2. When reaching point B, which is the end point of , calculate t ₂ as the average thickness of zone S ₂ , and do the same to calculate t ₃ ...
Calculate _to . The average thicknesses t ₁ , t _{2 , .} . . t _o appear as a discontinuous step-like graph b. Therefore, the measurement result cannot be determined while the measuring head is moving in the width direction of the sheet, etc., and cannot be determined until it reaches the turning point.

In addition, in the case of relatively rapid changes in thickness, that is, those expressed by high frequencies, the results are not displayed until the measurement head reaches the turning point, so the response is slow, and by the time feedback is given to one phenomenon, it is already reflected in other phenomena. This is a situation where a phenomenon has occurred and another feedback signal is required to compensate for it.

<Objective of the present invention> The present invention solves the above-mentioned problems, and makes it possible to adjust the MD average thickness of sheets, etc. so as to cope with high frequency fluctuations by shortening the dead time as much as possible. The object of the present invention is to provide an MD control method that achieves this.

<Structure of the Invention> In order to accomplish this purpose, the inventors continuously sampled a plastic sheet, etc. discharged from a die and traveling at regular intervals while displacing a thickness gauge in the width direction of the sheet. Based on this measurement data, the thickness distribution in the width direction of the sheet and the average thickness in the machine direction are feedback-controlled in parallel to the automatic die and the drive motor of the extruder or take-up machine. Simultaneous biaxial thickness measurement of sheets, etc. In the control, a plurality of sampling values in the forward process in the sheet width direction of the thickness gauge are input to the moving average calculator, and the most advanced sampling value in the next or several subsequent forward processes is input to the moving average calculator. The method is characterized in that the control amount is calculated at that point by replacing it with the corresponding sampling value within, and is always compared with a preset target setting value, and the deviation is used as the control amount for flow direction average thickness control. An object of the present invention is to provide a method for controlling the thickness of sheets, etc.

<Embodiment> Next, an embodiment of the present invention will be explained with reference to FIGS. 3 and 4. Items having the same numbers as those in FIG. Only the equipment used will be explained. 31 is the third
MD controller 32 and dead time compensation circuit 33 shown in the figure
and a target thickness setting device 34 for setting a predetermined target thickness. 35 is a moving average calculator which inputs the thickness signal t _s detected by the thickness gauge 16 and the detected position signal x _s and causes an output signal to act on the control circuit 31 . Here, the moving average calculator 35 is placed separately from the storage device 25 of the computer system, but is not limited to this.
You can put it in 5. 36 indicates a process, and includes a thickness gauge 16 and a motor 2 for detecting the thickness of a sheet, etc.
A speedometer 26a (not shown) detects the speed of 6.
detect the thickness and speed of the sheet, etc., respectively.

The method of the present invention is constructed as described above, and the operation and action of the method of the present invention will be explained with reference to the flow chart shown in FIG. N
(N ₁ , N ₂ , N ₃ ,...N _o ) and its thickness t (t ₁ ,
t ₂ , t ₃ ...t _o ). Next, the measuring head of the thickness gauge is moved, and it is determined at b whether the position signal N has changed (for example, whether it has changed from N ₁ to N ₂ ), and if YES, the moving average calculator A thickness signal is input at C, and a moving average is calculated at d. For example, calculate the moving average value by adding 1/N of the thickness data just input to the current moving average value and subtracting 1/N of the thickness data from one cycle before, output this new moving average value with e, and then The memory contents not shown are updated by f. At g, the measuring head crosses the width of the sheet, etc., and it is determined whether or not it has passed the turning point in order to cross the width of the sheet, etc. again. At h, it is determined whether the direction in which the measuring head is moving is the opposite of the previous direction. So, at i, the measuring head, which has been progressing 1, 2, 3...n up until now, changes direction and moves to n(n-1)...3, 2, 1.
It is then reversed and returns to b again.

<Effects of the invention> Test results using the control described above,
As shown in Figure 6 A, B, and C, assuming that the thickness changes in the running direction of the sheet, etc. form a sine curve as shown in A, the conventional device has an average thickness of each width as shown in B. It is understood that although the curve changes like a staircase at the turning point in the direction, the method of the present invention can be expressed as a smooth curve as shown in C. Similarly, FIG. 7 shows an example of a high frequency case, where, as in the previous embodiment, the conventional method is represented by a stepped average value, and the method of the present invention is represented by a smooth continuous curve.

In this way, the drawbacks listed at the beginning of the present invention have been removed, the average thickness of the sheet, etc. at each position is expressed as a smooth continuous value, and the dead time is short, allowing highly accurate thickness adjustment control. It became like that.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a thickness adjustment control device according to a conventional method. FIG. 2 is a graph showing the average thickness of sheets, etc., obtained using a conventional device. 3 and 4 are diagrams of an apparatus showing one embodiment for carrying out the method of the present invention, and FIG.
The figure is an overall diagram. Figure 4 is a detailed diagram. FIG. 5 is a flowchart showing the operation in an embodiment of the present invention.
FIGS. 6 and 7 are graphs showing the test results of calculating the average thickness of sheets, etc. using the method according to the present invention.

Claims (1)

[Claims] 1. A thickness gauge is continuously sampled at regular intervals while displacing a plastic sheet, etc. discharged from a die and traveling in the width direction of the sheet, and the width of the sheet is determined based on this measurement data. In simultaneous biaxial thickness control of sheets, etc., in which the thickness distribution in the direction and the average thickness in the machine direction are feedback-controlled in parallel to an automatic die and a drive motor of an extruder or take-off machine, respectively, A plurality of sampled values in the forward process in the width direction are input to the moving average calculator, and the most advanced sampling value in the next or several subsequent forward processes is replaced with the corresponding sampling value in the moving average calculator. At that point, the control amount is calculated and constantly compared with the preset target setting value,
A method for controlling the thickness of a sheet, etc., characterized in that the deviation is used as a control amount for controlling the average thickness in the machine direction.