KR100508565B1 - Plastic sheet film depth control system by variable P-controller - Google Patents

Abstract

The present invention relates to a lateral thickness control system of plastic sheet / film, wherein the variable P-controller (1) used herein is an outer film thickness control loop (9) in a cascaded dual control structure of the plastic sheet / film thickness control system. It is applied to, characterized in that it comprises a parameter factor that amplifies the absolute value of the error that changes over time.

Therefore, the controller gain value is continuously changed by the absolute value of the error, thereby quickly approaching the target thickness of the plastic sheet / film, and thus has the advantage of shortening the target thickness reaching time.

Description

Plastic sheet film depth control system by variable P-controller

The present invention relates to a lateral thickness control system of a plastic sheet / film, and more specifically, in the present invention, when a polymer having passed through an extruder flows down a cooling roll through a die, the die actuator is adjusted by adjusting the heat bolt. Controls the lateral thickness of the plastic sheet / film. The plastic sheet / film thickness control provides quick access to the target thickness of the plastic sheet / film by using a variable P-controller in the commonly used cascaded dual control structure. It is about the system.

That is, in the plastic sheet / film control system using the selective P-controller according to the prior art shown in FIG. 2, the maximum thickness% (maximum thickness) with respect to the target thickness of the profile in the outer film thickness control loop 9 of the cascade dual control structure. And the thickness error between the difference between the target thickness and the target thickness divided by the target thickness) and the minimum thickness% (the percentage of the difference between the minimum thickness and the target thickness divided by the target thickness), i.e. (maximum thickness-target thickness). ) / Target thickness x 100-(minimum thickness-target thickness) / Target thickness x 100 ms, the variable P-controller according to the present invention is a method in which a predetermined gain value is selected in the selective P-controller 1a. In the plastic sheet / film control system, the gain value is continuously varied according to the thickness range error.

In other words, in the selective control method using the conventional selective P-controller 1a gain, the gain value is determined by the following equation.

K _c1 = Gain1: Limit1 <E _{1 ..........} ⓐ

K _c1 = Gain2: Limit2 ≤ E ₁ ≤ Limit1

K _c1 = Gain3: E ₁ <Limit2

(Here, Gain1, Gain2, Gain3: P-controller gain, Limit1, Limit2: Error boundary value, E ₁ : Thickness range error)

Therefore, in the plastic sheet / film thickness control system using the conventional selective P-controller 1a, the gain of the P-controller 1a is determined to be one of three preset values even if the thickness range error is continuously changed. When using the variable P-controller according to the invention, the gain of the P-controller is continuously changed according to the thickness range error, thereby quickly approaching the target thickness of the plastic sheet / film and shortening the time to reach the target thickness.

In the industrial field, the cascade dual control method is mainly used to control thickness, which is the most basic requirement of plastic sheet / film.

FIG. 2 is a control block diagram showing the structure of a plastic sheet / film thickness control system using a selective P-controller according to the prior art, wherein the internal PID temperature control loop 8 is mainly a temperature mounted on a die 3 heat bolt. By controlling the temperature of the die (3) heat bolts by receiving the temperature from the sensor, the thickness of the plastic sheet / film is controlled by adjusting the gap between the die (3) lip according to the expansion and contraction of the bolt, and the external film thickness control loop (9). ), The actual shrinkage / expansion displacement of the heat bolt calculated on the basis of the profile information of the plastic sheet / film fed back from the scanner is converted into the temperature displacement using the heat expansion coefficient of the heat bolt to obtain the target value of the internal control loop (8). Is entered.

In general cascaded dual control structure, the controller is used in the form of PID controller widely used in the industrial field, mainly P or PI controller in the inner control loop (8), PI or PID controller in the outer film thickness control loop (9) Use However, while the conventional PID temperature control loop (2) is used in the internal PID temperature control loop (8) of the general plastic sheet / film manufacturing process, the non-linearity of the sheet and film manufacturing process (4) is caused in the external film thickness control loop (9). Due to the fact that the selective P-controller (1a) gain is adjusted to some preset fixed value according to the input thickness range error rather than the traditional PID temperature controller (2). In a conventional control system using such a selective P-controller, there is a problem in that it cannot actively cope with an input error.

On the contrary, the selective control method (see equation ⓐ above) has the advantage that the gain value is determined even if the disturbance or noise of the abrupt process is introduced, so that the stability of the disturbance or the amplification of the noise is secured compared to the method using the variable P-controller. Can be.

However, if a variable P-controller is used and the maximum / minimum P-controller gain value is preset and limited, stability will be ensured.

The present invention proposes an active variable P-controller in which the controller gain is continuously changed to compensate for the thickness range error of the plastic film in the cascade dual control structure. As a result, not only can the variable P-controller be used to reduce the number of parameters that must be specified in the controller, but also to actively cope with errors, thereby reducing the time to reach the target thickness of the plastic sheet / film and improving the thickness quality. At the same time can be planned. It is believed that the present invention can be applied to a place where a web thickness control technique such as paper and rolling is required in addition to the plastic sheet / film manufacturing process.

Referring to the configuration and operation of the present invention by the accompanying drawings as follows.

1 is a control block diagram illustrating a state in which a variable P-controller is applied to an outer control loop of a cascade dual control structure for controlling the thickness of a plastic sheet / film according to the present invention, and FIG. 3 is an optional P-controller and a variable P. FIG. 4 is a diagram comparing the process response (film thickness) as a result of applying the controller to the external control loop, and FIG. 4 is a diagram comparing the gain of each controller as a result of applying the selective P-controller and the variable P-controller to the external control loop. 5 is a diagram comparing the outputs of the controllers with the selective P-controller and the variable P-controller applied to the external control loop, and FIG. 6 is the result of applying the selective P-controller and the variable P-controller to the external control loop. 7 is a diagram comparing the process response (film thickness) of each process, and FIG. 7 is a diagram comparing the respective controller gains as a result of applying the selective P-controller and the variable P-controller to the external control loop. 8 is a diagram comparing the outputs of the respective controllers as a result of applying the selective P-controller and the variable P-controller to the external control loop.

On the other hand, in the existing cascaded dual control structure, even if the parameters of the PID temperature controller 2 of the internal PID temperature control loop 8 are properly tuned, there is a limit to shortening the time to reach the target thickness and improving the thickness quality. The control method using the optional P-controller 1a (see Fig. 2) gain for the thickness range input error (see equation ⓐ above) is likely to overset the controller gain for small input errors. There is a possibility that the controller gain is set slightly for the input error.

Therefore, the time required for the thickness to be stabilized after reaching the target thickness can be increased by leading to an inappropriate heat on rate (%) output from the PID temperature controller 2 of the internal PID temperature control loop 8. If a controller gain value for adequately compensating for the thickness range error is calculated in the outer film thickness control loop 9, the number of control operations of the PID temperature controller 2 of the inner PID temperature control loop 8 is reduced to a target value. Not only the time to reach the thickness value is shortened, but also the moderate output of the heat-on rate (%) can prevent the deformation of the die 3 to some extent.

For reference, in the open loop state of the die 3 temperature control system, when the heat on rate (%) is increased instantaneously to understand the dynamic characteristics of the heat bolt temperature, it can be seen that the first linear system is as follows.

.......... ①

K: Gain

τ: Time constant

θ: Time delay

In order to achieve the above object, in the present invention, the existing PID temperature controller 2 is used as it is in the inner control loop of the cascaded dual control structure as shown in the following formula ②, and in the outer control loop, the P controller (see the following formula 3) is used. The P controller gain is not set to the existing optional method (see equation ⓐ above), but is applied to the new plastic sheet / film thickness control method by applying the variable P-controller 1 (see equation ④ below). Suggest)

That is, conceptually briefly describe the internal and external controllers in the cascade control structure, which is a plastic sheet / film thickness control structure, as follows.

PID temperature controller transfer function of internal control loop:

.......... ②

K _c2 : proportional gain

τ _I : integral constant

τ _D : differential constant

E ₂ (s): Current temperature (heat bolt)-Setpoint temperature (heat bolt)

P-controller transfer function for external control loop:

.......... ③

K _c1 : P-controller proportional gain

E ₁ (s): Thickness range error

On the other hand, the error (%) of the thickness range is obtained by the following equation as in the conventional selective P-control scheme.

Thickness range error (%) = (maximum thickness-target thickness) / target thickness × 100

-(Minimum-Target Thickness) / Target Thickness × 100

In contrast, in the selective control scheme using the conventional selective P-controller 1a gain, the gain value is determined by the following equation.

K _c1 = Gain1: Limit1 <E _{1 ..........} ⓐ

K _c1 = Gain2: Limit2 ≤ E ₁ ≤ Limit1

K _c1 = Gain3: E ₁ <Limit2

(Here, Gain1, Gain2, Gain3: P-controller gain, Limit1, Limit2: Error boundary value, E ₁ : Thickness range error)

In the outer film thickness control loop 9 of the cascade dual control structure as shown in FIG. 2, the conventional method of selecting the selective P-controller 1a gain according to the thickness range error (see Equation ⓐ above) is strictly controlled. The controller gain is set so widely that it cannot be considered as the concept of.

In addition, the variable to be set also includes the controller gain Gain1, Gain2, Gain3 In addition, since the limit value of the thickness range error, such as Limit1, Limit2, is five, a great deal of effort and effort are required to obtain an appropriate value of the five variables.

On the other hand, the conventional method (see equation ⓐ above) cannot effectively eliminate sudden disturbances in the process, because the same controller is present if all of the present thickness range errors are within one thickness range error, even if the current thickness range error data is different from the past error data. This is because the gain is set so that the control output C ₁ is output identically.

That is, when E ₁ (n-1) | ≠ | E ₁ (n), Limit2 ≤ E ₁ (n-1) ≤ Limit1 and Limit2 ≤ E ₁ (n) If ≤ Limit1, P-controller gain = K _c1 = Gain2.

In contrast, in the variable control method using the variable P-controller 1 gain according to the present invention, the gain value is determined by the following equation.

K _c1 = K _c0 (1 + β | E ₁ |) .......... ④

(K _c1 : P-controller gain, K _c0 : P-controller when thickness range error is 0

Gain, | E ₁ |: Absolute value of thickness range error, β: Weight range thickness error)

The characteristic of the variable P-controller 1 according to the present invention is that when the maximum and minimum thicknesses of the profile are close to the target thickness, the thickness range error is reduced and the P-controller gain is automatically reduced to reduce the control output C ₁ . Done. In addition, when a disturbance is input to the process or when a setpoint change occurs, the thickness range error increases and the controller gain increases to increase the control output C ₁ .

Therefore, the controller output C ₁ is appropriately increased or decreased in accordance with the change in the thickness error. Also, unlike the conventional selective P-controller 1a gain selection method (see equation ⓐ above), which requires setting five variables, in the variable P-controller 1, only the appropriate values of the two parameters K _c0 and β are available. Get it. Thickness range error | When E ₁ = 0, the P-controller gain is K _c0 . In other words, when the thickness range error is small, the small controller gain eliminates the effect of noise.

Example 1

In the outer film thickness control loop 9, the parameters K _c0 and β of the ④ variable P-controller 1 of the ④ type are set as shown in Table 1, and are set to an arbitrary thickness range error E ₁ . Accordingly, the gain K _c1 and the output value of the variable P-controller 1 are calculated.

Table 1

Control loop parameter Variable P-controller Selective P-controller β Example 1 K _c0 0.3 - β 0.1 - E ₁ (error) 5 - K _c1 0.45 - C ₁ (P-controller output) 2.25 - Comparative Example 1 Limit1 - 10 Limit2 - 0.1 Gain1 - One Gain2 - 0.3 Gain3 - 0.01 E ₁ (error) - 5 K _c1 - 0.3 C ₁ (P-controller output) - 1.5 Example 2 K _c0 , β Same as Example 1 - E ₁ (error) 3 - K _c1 0.39 - C ₁ (P-controller output) 1.17 - Comparative Example 2 Limit1 ~ Gain3 - Same as Comparative Example 1 E ₁ (error) - 3 K _c1 - 0.3 C ₁ (P-controller output) - 0.9 Example 3 K _c0 , β Same as Example 1 - E ₁ (error) 0.5 - K _c1 0.315 - C ₁ (P-controller output) 0.16 - Comparative Example 3 Limit1 to Gain3 - Same as Comparative Example 1 E ₁ (error) - 0.5 K _c1 - 0.3 C ₁ (P-controller output) - 0.15

For example, as in Example 1 of Table 1, the parameters K _c0 and β required for the variable P-controller are set, and the thickness range error E ₁ is inputted as 5 to gain K _c1 of the variable P-controller. And the output value (C ₁ ) is calculated as follows.

Variable P-controller 1:

K _c1 = 0.3 × (1 + 0.1 × 5) = 0.45

C ₁ = K _c1 × E ₁ = 0.45 × 5 = 2.25

That is, in the variable P-controller 1 of the present invention, the controller gain continuously changes as the error E ₁ changes, so that the P-controller output C ₁ is actively adjusted.

Comparative Example 1

In the outer film thickness control loop 9, the parameters of the ⓐ type optional P-controller 1a (see Fig. 2) are set as shown in Table 1 and are set to any thickness range input error E ₁ . Accordingly, the gain K _c1 and the output value of the selective P-controller 1a are calculated.

For example, as shown in Comparative Example 1 of Table 1, the parameters required for the selective P-controller 1a are set, and the thickness range error E ₁ is inputted as 5 to obtain the gain K _c1 and the output value of the selective P-controller ( Calculate C ₁ ) is as follows.

Optional P-controller 1a:

0.1 ≤ E ₁ (= 5.0) ≤ 10

K _c1 = 0.3

C ₁ = K _c1 × E ₁ = 0.3 × 5 = 1.5

In the conventional selective P control method (see Equation described above), even if the thickness range input error is within the same error range, the same P-controller gain value is set as in the first embodiment.

Example 2

As shown in Example 2 of Table 1 carried a parameter (K _c0, β) required for variable-P- controller (1) Example 1 set equal, and the input to the third thickness error range of E _1, the variable P- The gain K _c1 and output value C ₁ of the controller are calculated as follows.

Variable P-controller 1:

K _c1 = 0.3 × (1 + 0.1 × 3) = 0.39

C ₁ = K _c1 × E ₁ = 0.39 × 3 = 1.17

That is, in the variable P-controller 1 according to the present invention, the controller gain continuously changes as the error E ₁ changes, so that the P-controller output C ₁ is actively adjusted.

Comparative Example 2

As in Comparative Example 1, if the gain K _c1 and the output value C ₁ of the selective P-controller 1a were calculated for the arbitrary thickness range error E ₁ under the same conditions as in Comparative Example 2, the same result as in Comparative Example 2 of Table 1 was obtained. Can be obtained.

Optional P-controller 1a:

0.1 ≤ E ₁ (= 3.0) ≤ 10

K _c1 = 0.3

C ₁ = K _c1 × E ₁ = 0.3 × 3 = 0.9

In the conventional selective P control method (Equation ⓐ described above), even if the thickness range input error is included within the same error range, unlike the second embodiment, the same gain value as the P-controller gain value in Comparative Example 1 is set. .

Example 3

As in Example 3 of Table 1, the parameters K _c0 and β necessary for the variable P-controller are set in the same manner as in Example 1, and the thickness range error E ₁ is input as 0.5 to gain the variable P-controller. Calculating K _c1 and output value C ₁ is as follows.

Variable P-controller 1:

K _c1 = 0.3 × (1 + 0.1 × 0.5) = 0.315

C ₁ = K _c1 × E ₁ = 0.315 × 0.5 = 0.16

That is, in the variable P-controller 1 of the present invention, the controller gain continuously changes as the error E ₁ changes, so that the P-controller output C ₁ is actively adjusted.

Comparative Example 3

As in Comparative Example 1, if the gain K _c1 and the output value C ₁ of the selective P-controller 1a were calculated for the arbitrary thickness range error E ₁ under the same conditions as in Comparative Example 3, the same result as in Comparative Example 3 of Table 1 was obtained. Can be obtained.

Optional P-controller 1a:

0.1 ≤ E ₁ (= 0.5) ≤ 10

K _c1 = 0.3

C ₁ = K _c1 × E ₁ = 0.3 × 0.5 = 0.15

In the conventional selective P control method (see Equation described above), even if the thickness range input error is included within the same error range, unlike in Example 3, the same gain value as the P-controller gain value in Comparative Examples 1 and 2 is obtained. Is set.

Example 4

The transfer function of the die 3 temperature system is set to a linear system as shown in equation 5 below, and the transfer function of the sheet and film manufacturing process 4 is also set as shown in equation 6 below.

The temperature system of the die 3 can be easily understood, but since the plastic sheet and film manufacturing process 4 is also highly nonlinear, it is difficult to grasp the dynamic characteristics since the accurate mapping between the die bolt and the film must be preceded. Therefore, even if the plastic sheet and film manufacturing process 4 after the temperature control system is assumed to be a transfer function of a simple linear system as shown in Equation 6 below, it is judged that it will be sufficient to compare / determine the control performance of the P-controller.

As a result, the transfer functions of equations ⑤ and ⑥ are roughly assumed based on the characteristics of the process. Also, since the maximum or minimum thickness of the profile cannot be found in the simulation, the error E ₁ of the external film thickness control structure is simply replaced by the sheet / film thickness measured from the sheet / film thickness meter and the sheet / film target thickness instead of the thickness range error. Assume

Transfer function of die (3) temperature system:

.......... ⑤

Transfer function of sheet and film manufacturing process (4):

.......... ⑥

The parameters of equations ⑥ and ⑦ are summarized in Table 2 below.

1st linear system transfer function:

TABLE 2

Parameter system K τ θ Die temperature 4 300 15 Film process 3 500 30

Under the conditions as shown in Table 2, the die 3 temperature system and the transfer function of the plastic sheet and film manufacturing process 4, the parameters of the ④ variable P-controller 1 in the outer film thickness control loop 9 Set the parameters as shown in Table 3 below and run a simulation to evaluate the performance of the variable P-control scheme.

Parameters of the PID temperature controller 2 of the internal PID temperature control loop 8 (K _c , τ _I , τ _D ,) is an approximate result calculated by the Integral of the time-weighted absolute error (ITAE) tuning method for the transfer function of Table 2. Ultimately, since the purpose is to compare / evaluate the performance of the variable P-controller and the conventional selective P-controller in the outer thickness control loop, the tuning method of the PID temperature controller 2 of the internal PID temperature control loop 8 is the same method. You can use

PID controller transfer function:

TABLE 3

Control loop parameter Variable P-Controller Selective P-Controller Internal PID Temperature Control K _c 3.0 3.0 τ _I 380 380 τ _D 6.0 6.0 External film thickness control K _c0 0.6 - β 0.1 - Limit2 - 6 Limit1 - 15 K _c1 K _c1 value is changed according to IE ₁ I value.    Gain1: 1.3 Gain2: 1.1 Gain3: 0.9

Step input of film thickness target 10 under the conditions of Tables 2 and 3

As a result of the simulation through the change), the response (plastic film thickness) of the sheet and film manufacturing process 4 with time can be obtained as shown in FIG. 3. Therefore, when the variable P-controller 1 is applied to the outer film thickness control loop 9 in the cascaded dual control structure, the selective P-controller 1a in terms of shortening the thickness stabilization time of the plastic sheet and film manufacturing process 4 is applied. The superiority can be seen in FIG. 3.

In FIG. 3, the response of the sheet and film manufacturing process 4 to the step input of the target thickness 10 is not caused to approach 10 as time passes, but the offset is caused by the cascade dual control structure. PI or PID temperature controller 2 is usually used for the outer film thickness control loop 9, but in the plastic sheet / film process according to the present embodiment, the P controller is used for the outer film thickness control loop 9 so that the sheet and film An offset is generated between the response of the manufacturing process 4 and the film thickness target value. In practice, by adjusting the gear hourly flow rate (Kg) of the polymer in a die upstream liquid process, it approaches the sheet / film thickness target (Target) without the sheet / film thickness control action.

[Comparative Example 4]

Under the conditions of Table 2 and Table 3, the simulation was carried out through the step change of the target film thickness (Target) 10, and as a result, the response of the sheet and film manufacturing process (4) over time as shown in FIG. Film thickness) can be obtained. Therefore, applying the selective P-controller 1a to the outer film thickness control loop 9 in the cascaded dual control structure makes the thickness of the plastic sheet and film manufacturing process 4 more stable than when the variable P-controller 1 is applied. It can be seen in FIG. 3 that more time is required.

Example 5

As a result of simulation through a step change of the film thickness target 10 under the conditions of Tables 2 and 3, the gain of the variable P-controller 1 with time (K _c1 ) as shown in FIG. 4. ) Can be obtained. Therefore, when the variable P-controller 1 is applied to the outer film thickness control loop 9 in the dual control structure, it is shown that the controller gain K _c1 is actively changed in response to the change of the error E _{1 with} time. You can find it at

[Comparative Example 5]

As a result of the simulation through the step change of the film thickness target value (Target) 10 under the conditions of Table 2 and Table 3, the gain (K _c1 ) of the selective P-controller 1a according to time as shown in FIG. ) Can be obtained. Therefore, if the conventional selective P-controller 1a is applied to the outer film thickness control loop 9 in the cascaded dual control structure, if the error E ₁ is within the same error range even if it changes with time, the same controller gain K _c1 It can be seen in Figure 4 that is set.

Example 6

The output of the variable P- controller 1 according to Table 2 and Table 3, the film thickness of the target value under the conditions of (Target) of the step input 10 a result of simulation performed through the (Step change), time as shown in FIG. 5 (C _1, ) Can be obtained. Therefore, if the variable P-controller 1 is applied to the outer film thickness control loop 9 in the cascaded dual control structure, when the error E ₁ is large initially, compared with the conventional selective P-controller 1a, If a large control value is output and the error E ₁ is small, the control value is output similarly to the conventional selective P-controller 1a, so that the output value of the variable P-controller 1 is appropriate according to the magnitude of the error E ₁ . It can be seen in Figure 5 that the change.

Comparative Example 6

The output of Table 2 and Table 3, the film thickness of the target value under the conditions of (Target) of the step input 10 a result of simulation performed through the (Step change), optionally with time as shown in FIG. 5 P- controller (1a) (C ₁ ) Can be obtained. If the conventional selective P-controller 1a is applied to the outer film thickness control loop 9 in the cascaded dual control structure, the controller output for error E ₁ (C) compared with the proposed variable P-controller 1 ₁ ) can be over or under output.

Example 7

Under the conditions of Table 2 and Table 4 described below, the simulation was performed through a step change of the film thickness target 10, and the response of the sheet and film manufacturing process 4 with time as shown in FIG. (Plastic film thickness) can be obtained. Therefore, when the variable P-controller 1 is applied to the outer film thickness control loop 9 in the cascaded dual control structure, the P-controller 1a is more effective than the selective P-controller 1a in terms of shortening the thickness stability time of the plastic sheet and film manufacturing process 4. Excellent can be seen in FIG.

Table 4

Control loop parameter β variable P controller Selective P-Controller Internal PID Temperature Control K _c 3.0 3.0 τ _I 380 380 τ _D 6.0 6.0 External film thickness control K _c0 1.25 - β 0.005 - Limit2 - 1.5 Limit1 - 2.0 K _c1 K _c1 value is changed according to IE ₁ I value.      Gain1: 3.0 Gain2: 1.5 Gain3: 1.0

Comparative Example 7

As a result of simulation through a step change of the film thickness target value 10 under the conditions of Tables 2 and 4, the response of the sheet and film manufacturing process 4 with time (plastic) as shown in FIG. Film thickness) can be obtained. Therefore, when the selective P-controller 1a is applied to the outer film thickness control loop 9 in the cascaded dual control structure, the thickness stabilization time of the plastic sheet and film process 4 is greater than when the variable P-controller 1 is applied. This more time can be seen in FIG. 6. In addition, when the selective P-controller 1a is applied, the response (plastic film thickness) of the plastic sheet and film manufacturing process 4 may vibrate depending on the selection of the error limits (Limit1, Limit 2).

Example 8

As a result of simulation through a step change of the film thickness target value (Target) 10 under the conditions of Tables 2 and 4, the gain of the variable P-controller 1 with time (K _c1 ) as shown in FIG. 7. ) Can be obtained. Therefore, applying the variable P-controller 1 to the outer film thickness control loop 9 in the cascaded dual control structure helps to ensure that the controller gain K _c1 is appropriately changed for a change in the error E _{1 over} time. This can be seen in 7.

Comparative Example 8

As a result of the simulation through the step change of the film thickness target value (Target) 10 under the conditions of Table 2 and Table 4, the gain (K _c1 ) of the selective P-controller 1a according to time as shown in FIG. ) Can be obtained. Therefore, as a result of applying the conventional selective P-controller 1a to the outer film thickness control loop 9 in the cascaded dual control structure, as the error E ₁ changes over time, if it is within the same error range, the same controller gain (K _c1) is set by being, it can be seen from Figure 7 that the controller gain (K _c1) may be over-set for a relatively small error E _1.

Example 9

As a result of simulation through a step change of the target film thickness (Target) 10 under the conditions of Table 2 and Table 4, the output of the variable P-controller 1 according to time as shown in FIG. 8 (C ₁ ) Can be obtained. Therefore, when the variable P-controller 1 is applied to the outer film thickness control loop 9 in the cascaded dual control structure, the output value C ₁ of the variable P-controller ₁ is appropriate according to the magnitude of the error E ₁ . It can be seen in Figure 8 that the change.

Comparative Example 9

As a result of the simulation through the step change of the film thickness target value (Target) 10 under the conditions of Table 2 and Table 4, the output of the selective P-controller 1a according to time as shown in FIG. 8 (C ₁ ) Can be obtained. Therefore, if the existing selective P-controller 1a is applied to the outer film thickness control loop 9 in the cascaded dual control structure, the controller output C ₁ for error E ₁ may be excessively or excessively output. It can be seen in FIG.

As described above, the present invention can more effectively compensate the thickness range error of the plastic film by using the active variable P-controller 1 whose controller gain is continuously changed in the external control loop 9 in the cascade dual control structure. Make sure

That is, the β variable P-controller 1 according to the present invention is applied to the outer film thickness control loop in the cascade dual control structure of the plastic sheet / film thickness control system, and amplifies the absolute value of the error that changes over time. A controller (1) characterized in that it comprises a parameter factor, which has the advantage that the controller gain value is continuously changed in accordance with the absolute value of the error, thereby quickly approaching the target thickness of the plastic sheet / film, thereby shortening the target thickness reaching time. Have

1 is a control block diagram showing a state where a variable P-controller is applied to an outer control loop of a cascaded dual control structure for controlling the thickness of a plastic sheet / film according to the present invention;

2 is a control block diagram showing a state where an optional P-controller is applied to an outer control loop of a cascaded dual control structure for controlling the thickness of a plastic sheet / film according to the prior art;

3 is a diagram comparing the process response (film thickness) of each of the results of applying the selective P-controller and the variable P-controller to the external control loop.

4 is a diagram comparing the gains of each controller as a result of applying the selective P-controller and the variable P-controller to an external control loop.

5 is a diagram comparing outputs of respective controllers as a result of applying an optional P-controller and a variable P-controller to an external control loop.

6 is a diagram comparing the process response (film thickness) of each of the results of applying the selective P-controller and the variable P-controller to the external control loop.

7 is a diagram comparing the respective controller gains as a result of applying the selective P-controller and the variable P-controller to an external control loop.

8 is a diagram comparing the outputs of the respective controllers as a result of applying the selective P-controller and the variable P-controller to the external control loop.

* Explanation of symbols on the main parts of the drawings

1: variable P-controller 1a: optional P-controller

2: PID temperature controller 3: die

4: sheet and film manufacturing process 5: film thickness meter

6: temperature sensor 7: sheet thickness meter

8: inner PID temperature control loop 9: outer film thickness control loop

10: outer sheet thickness control loop

Claims (3)

By controlling the temperature of the die (3) heat bolt by receiving the temperature feedback from the temperature sensor mounted on the die (3) heat bolt, the thickness of the plastic sheet / film is adjusted by controlling the gap of the die (3) lip according to the expansion and contraction of the bolt. The actual shrinkage / expansion displacement of the heat bolt calculated by the internal PID temperature control loop 8 to be controlled and the profile information of the plastic sheet / film fed back from the scanner is converted into the temperature displacement by using the thermal expansion coefficient of the heat bolt. In the plastic sheet / film thickness control system of the cascade dual control structure composed of an outer film thickness control loop 9 inputted as a target value of the internal PID temperature control loop 8, Using the variable P-controller, the outer film thickness control loop 9 has a variable-P controller 1 having the gain of the P-controller determined by the absolute value of the thickness range error according to the following equation. Plastic sheet / film thickness control system. Absolute value (%) of thickness range error = ｜ (maximum thickness-target thickness) / target thickness × 100-(minimum Thickness-Target Thickness) / Target Thickness × 100 ｜ 2. The plastic sheet / film thickness control system according to claim 1, wherein the gain of the variable-P controller (1) includes a parameter factor for amplifying the absolute value of the error. The plastic sheet / film thickness control system according to claim 1 or 2, wherein the variable-P controller (1) is configured to satisfy the following equation. K _c1 = K _c0 (1 + β | E ₁ |) (K _c1 : P-controller gain, K _c0 : P-controller when thickness range error is 0 Gain, | E ₁ |: absolute value of the thickness range error, β: weight of the thickness range error)