Disturbance Analysis and Feedforward Compensation Method for Unwinding Tension Control System in Unwinding and Cutting

Abstract

The present invention discloses a disturbance analysis and feedforward compensation method for unwinding tension control system during material feeding and cutting, comprising the following steps: S1. Construct an unwinding tension control system with a controller and equipment. The equipment includes a controlled object, a measuring device and an executing device. During the closed-loop operation of the unwinding tension control system, collect the output signal of the system; S2. According to the given controller model and equipment model, establish a discrete transfer function from the material feeding and cutting disturbance to the output of the unwinding tension control system; S3. According to the system output signal and the discrete transfer function from the material feeding and cutting disturbance to the output of the unwinding tension control system, calculate the equivalent narrow square wave disturbance caused by the material feeding and cutting; S4. Calculate the feedforward compensation amount according to the equivalent narrow square wave disturbance, and add the feedforward compensation amount to the input end of the executing device at the corresponding moment to achieve feedforward compensation. The present invention solves the problem of compensating the tension fluctuation during material feeding and cutting, enables the tension to remain relatively stable, and has small calculation amount, high compensation accuracy and strong robustness.

Description

Technical Field

[0001] The present invention relates to the technical field of automatic control, and specifically, to a method for quantitatively analyzing disturbances caused by unwinding and cutting in a unwind tension control system and a feedforward compensation method for the system. Background Art

[0002] The tension control system mainly refers to a system that maintains a constant tension when the raw material is conveyed on the equipment during the production process of various coils and cables, and has a wide range of applications in industries such as papermaking, textile, printing and packaging. The performance of tension control is directly related to product quality, efficiency, etc., so high-speed and high-precision requirements are also put forward for the tension control system. The unwind tension control system is an important part to ensure continuous feeding during the production process. Generally, the unwind tension control system is divided into two types: indirect tension control and direct tension control. Indirect tension control has no tension detection device and belongs to an open-loop control system, which directly realizes tension control through compensation adjustment. Direct tension control is a feedback control, which consists of the following parts: a tension detection device, a tension controller, a motor and a tension model. The tension detection device is used to measure the tension in real time, and then the feedback controller is used to improve the control accuracy of the system and reduce the steady-state error. During the operation of the unwind system, the coil needs to be replaced. After the old and new coils are replaced, a cutting knife is used for cutting. During this process, it is easy to cause tension fluctuations, thereby affecting product accuracy, quality, etc.

[0003] In the prior art, in addition to improving the mechanical structure and cutting method of the unwind mechanism, a closed-loop control method is often used to solve this problem. By constructing a tension closed-loop system, the output of the motor is controlled to obtain constant tension control. In terms of control algorithms, most of them use PID control or improved PID control. However, when there are disturbances and model uncertainties in the tension control system, the anti-disturbance performance and robustness are relatively insufficient. For the disturbance compensation method caused by unwinding and cutting in the unwind tension control system, the adjustment response speed using closed-loop control is relatively slow, and when the model parameters in the tension control system change, the performance of the controller will decline, resulting in tension fluctuations, thereby affecting the accuracy of the entire production process and causing waste of materials. Summary of the Invention

[0004] The purpose of the present invention is to solve the problem of disturbances caused by unwinding and cutting in the existing unwind tension control system, and to provide a method for analyzing disturbances and feedforward compensation for unwinding and cutting in the unwind tension control system. The calculation method of the present invention is simple, the calculation amount is small, the compensation accuracy is high, and the robustness is strong.

[0005] In order to achieve the above purpose, the technical solutions adopted by the present invention are as follows:

[0006] A disturbance analysis and feedforward compensation method for unwinding and cutting in a unwind tension control system, comprising the following steps:

[0007] S1. Construct an unwind tension control system with a controller and equipment. The equipment includes a controlled object, a measuring device, and an actuator. During the closed-loop operation of the unwind tension control system, collect the output signal of the system;

[0008] S2. According to the given controller model and equipment model, establish a discrete transfer function from the unwind cutting disturbance to the output of the unwind tension control system;

[0009] S3. According to the system output signal and the discrete transfer function from the unwind cutting disturbance to the output of the unwind tension control system, calculate the equivalent narrow square wave disturbance caused by the unwind cutting;

[0010] S4. Calculate the feedforward compensation amount of the system according to the equivalent narrow square wave disturbance, and add the feedforward compensation amount to the input end of the actuator at the corresponding moment to achieve feedforward compensation.

[0011] Further, in step S1, the controller of the unwind tension control system adopts a PI controller, the controlled object is the film tension, the measuring device is a swing arm and a potentiometer, and the actuator is a variable frequency motor.

[0012] Further, the difference between the given tension and the film tension causes the swing arm to deviate from the vertical position to generate a deflection angle, which is measured by the potentiometer, and a voltage signal reflecting the magnitude of the tension error is output and fed back to the PI controller through a computer.

[0013] Further, during the operation of the unwind tension control system, the tension is kept constant through closed-loop PI control. The computer collects the output signal of the swing arm and feeds it back to the PI controller. The PI controller outputs a control quantity to the variable frequency motor, and the variable frequency motor performs an output action according to the control quantity.

[0014] Further, in step S2, according to the given controller model and equipment model, the discrete transfer function from the unwind cutting disturbance to the output of the unwind tension control system is established as:

[0015]

[0016] In the formula, Y(z) is the system output in the Z domain, D(z) is the unwind cutting disturbance in the Z domain, G p (z) is the equipment model in the Z domain, G c (z) is the controller model in the Z domain, G yd (z) is the discrete transfer function from the unwind cutting disturbance in the Z domain to the system output.

[0017] Further, in step S3, according to the discrete transfer function from the system output signal and the feeding and cutting disturbance to the output of the unwinding tension control system, calculate the equivalent narrow square wave disturbance caused by the feeding and cutting. The specific process is as follows:

[0018] S31. According to the discrete transfer function from the feeding and cutting disturbance to the output of the unwinding tension control system, the relationship between the output of the unwinding tension control system and the feeding and cutting disturbance is obtained as:

[0019]

[0020] In the formula, y(k) is the output of the unwinding tension control system at time k, g(k) is the discrete impulse response of the transfer function G yd (z), in the actual system, g(0) = 0, and d(k) is the equivalent narrow square wave disturbance caused by the feeding and cutting at time k;

[0021] S32. According to the relationship between the output of the unwinding tension control system and the feeding and cutting disturbance, and the collected output signal of the unwinding tension control system, obtain the equivalent narrow square wave disturbance of the feeding and cutting as:

[0022]

[0023] In the formula, d(k) is the equivalent narrow square wave disturbance caused by the feeding and cutting at time k, N d is the width of the disturbance, N d The size of is selected according to the response time of the feeding and cutting disturbance, and A is the amplitude size of the equivalent narrow square wave disturbance.

[0024] Further, in step S4, calculate the feedforward compensation amount of the system according to the equivalent narrow square wave disturbance, and add the feedforward compensation amount to the input end of the actuator at the corresponding time to achieve feedforward compensation. The specific process is as follows:

[0025] S41. If the feedforward compensation amount u(i) is added at time M, that is, when i < M, u(i) = 0, the system output after adding the feedforward compensation amount is:

[0026]

[0027] S42. Since g(0) = 0 in the actual system, the feedforward compensation amount u(i) can make the system output equation at the next moment as:

[0028]

[0029] S43. Solve the feedforward compensation amount u(i) according to the system output equation of the unwinding tension control system, and add the feedforward compensation amount u(i) to the input end of the actuator to achieve feedforward compensation.

[0030] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0031] 1. By quantitatively analyzing the disturbance caused by the unwinding and cutting of the unwinding tension control system, the present invention equivalently represents the disturbance caused by the unwinding and cutting as a velocity narrow square wave disturbance, and calculates the feedforward compensation amount according to the narrow square wave disturbance and adds it to the input end of the actuator. This method has the characteristics of simple calculation method, small calculation amount, good compensation effect and high accuracy.

[0032] 2. Compared with the method of using the PID control algorithm or the improved PID control algorithm in the existing unwinding tension control system for closed-loop adjustment to achieve constant tension, the feedforward compensation of the method of the present invention is faster and more accurate, and when the model parameters in the tension control system change, the robustness of this method is stronger.

[0033] 3. The feedforward compensation method in the present invention can solve the disturbance problem in the process of unwinding and cutting, thereby reducing the reject rate and improving the production accuracy and efficiency of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 FIG. is a schematic flow chart of the disturbance analysis and feedforward compensation method for the unwinding and cutting of the unwinding tension control system of the present invention.

[0035] Figure 2 FIG. is a schematic structural diagram of the unwinding tension control system.

[0036] Figure 3 FIG. is a schematic diagram of the output response of the actual system under disturbance.

[0037] Figure 4 FIG. is a schematic diagram of the calculated equivalent narrow square wave disturbance and feedforward compensation amount.

[0038] Figure 5 FIG. is a schematic diagram of the comparison of the system outputs before and after adding the feedforward compensation amount. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0039] The following further describes the disturbance analysis and feedforward compensation method for the unwinding and cutting of the unwinding tension control system of the present invention with reference to the accompanying drawings and specific embodiments.

[0040] Please refer to Figure 1 , the present invention discloses a disturbance analysis and feedforward compensation method for the unwinding and cutting of the unwinding tension control system, including the following steps:

[0041] S1. Construct an unwinding tension control system with a controller and equipment. The equipment includes a controlled object, a measuring device and an actuator, and collect the output signal of the system during the closed-loop operation of the unwinding tension control system.

[0042] S2. Establish a discrete transfer function from the feeding and cutting disturbance to the output of the unwind tension control system according to the given controller model and device model.

[0043] S3. Calculate the equivalent narrow square wave disturbance caused by the feeding and cutting according to the system output signal and the discrete transfer function from the feeding and cutting disturbance to the output of the unwind tension control system.

[0044] S4. Calculate the feedforward compensation amount of the system according to the equivalent narrow square wave disturbance, and add the feedforward compensation amount to the input end of the actuator at the corresponding moment to achieve feedforward compensation.

[0045] Specifically, in step S1, as Figure 2 shown, the controller of the unwind tension control system adopts a PI controller, the controlled object is the film tension, the measuring device is the swing arm and the potentiometer, and the actuator is the frequency conversion motor. The controlled object, the measuring device and the actuator are collectively referred to as the device.

[0046] During the operation of the unwind tension control system, the tension is kept constant through closed-loop PI control. The computer collects the output signal of the swing arm and feeds it back to the PI controller. The PI controller outputs a control quantity to the frequency conversion motor, and the frequency conversion motor performs an output action according to the control quantity. The unwind tension control system adopts computer control, the sampling period is 20 ms, and the output y(k) of the acquisition system is collected.

[0047] The form of the PI controller (i.e., the proportional-integral controller) is The proportional coefficient k p and the integral coefficient k i are designed by the user themselves, and then converted into discrete expressions. The control quantity output by the PI controller is output to the frequency conversion motor. Since the response speed of the motor is very fast, its transfer function is approximately a constant with a gain of 1.

[0048] As Figure 2 shown, the reference speed v0 is the initial speed of the new roll, and the traction speed is the speed of the film driving roller. The tension is generated by the speed difference between the front and rear driving rollers of the film and then according to Hooke's law. The disturbance caused by the feeding and cutting in the unwind tension control system is a sudden change in tension. Therefore, the disturbance caused by the feeding and cutting can be equivalent to a speed narrow square wave disturbance at the input end of the film tension.

[0049] The swing arm measures according to the following principle: The difference between the given tension (i.e., the cylinder thrust) and the film tension causes the swing arm to deviate from the vertical position, thus generating a deflection angle. This deflection angle is measured by the potentiometer, and a voltage signal reflecting the magnitude of the tension error is output and fed back to the PI controller through the computer.

[0050] In step S2, according to the given controller model and device model, the discrete transfer function from the feeding and cutting disturbance to the output of the unwinding tension control system is established as follows:

[0051]

[0052] In the formula, Y(z) is the system output in the Z domain, D(z) is the feeding and cutting disturbance in the Z domain, G p (z) is the device model in the Z domain, G c (z) is the controller model in the Z domain, G yd (z) is the discrete transfer function from the feeding and cutting disturbance to the system output in the Z domain.

[0053] Among them, the device model G p (z) is obtained through identification experiments, and the controller G c (z) is designed by the user himself.

[0054] In step S3, according to the system output signal and the discrete transfer function from the feeding and cutting disturbance to the output of the unwinding tension control system, the equivalent narrow square wave disturbance caused by the feeding and cutting is calculated. The specific process is as follows:

[0055] S31. According to the discrete transfer function from the feeding and cutting disturbance to the output of the unwinding tension control system, the relationship between the output of the unwinding tension control system and the feeding and cutting disturbance is obtained as follows:

[0056]

[0057] In the formula, y(k) is the output of the unwinding tension control system at time k, g(k) is the discrete impulse response of the transfer function G yd (z) at time k. In the actual system, g(0) = 0, and d(k) is the equivalent narrow square wave disturbance caused by the feeding and cutting at time k.

[0058] S32. According to the relationship between the output of the unwinding tension control system and the feeding and cutting disturbance, and the output signal of the collected unwinding tension control system, the equivalent narrow square wave disturbance of the feeding and cutting is obtained as follows:

[0059]

[0060] In the formula, d(k) is the equivalent narrow square wave disturbance caused by the feeding and cutting at time k, N d is the width of the disturbance, and the size of N d is selected according to the response time of the feeding and cutting disturbance, and A is the amplitude size of the equivalent narrow square wave disturbance.

[0061] In step S4, according to the equivalent narrow square wave disturbance, the feedforward compensation amount of the system is calculated, and the feedforward compensation amount is added to the input end of the actuator at the corresponding time to achieve feedforward compensation. The specific process is as follows:

[0062] S41. If the feedforward compensation amount u(i) is added at time M, that is, when i < M, u(i) = 0, the system output after adding the feedforward compensation amount is as follows:

[0063]

[0064] S42. Since g(0) = 0 in the actual system, the feedforward compensation amount u(i) can make the system output equation for the next moment as follows:

[0065]

[0066] S43. Solve for the feedforward compensation amount u(i) according to the system output equation of the unwinding tension control system, and add the feedforward compensation amount u(i) to the input end of the actuator to achieve feedforward compensation.

[0067] Compare the output responses of the system before and after compensation, and observe and adjust the effect of compensation.

[0068] In this embodiment, the equipment model G p (z) is obtained from the identification experiment, and the specific expression of the equipment model G p (z) is as follows:

[0069]

[0070] The parameters k of the PI controller p = 2, k i = 1, and the discrete transfer function of the controller is as follows: The radius of the new roll is 0.2 m.

[0071] Thus, the transfer function from the feeding and cutting disturbance D(z) to the system output Y(z) can be established as follows:

[0072]

[0073] Then, calculate the equivalent narrow square wave disturbance d(k) according to the collected system output y(k):

[0074] y(0) = g(0)d(0)

[0075] y(1) = g(1)d(0) + g(0)d(1)

[0076] y(2) = g(2)d(0) + g(1)d(1) + g(0)d(2)

[0077] ……

[0078] y(k) = g(k)d(0) + … + g(0)d(k)

[0079] Since g(0) = 0, d(0) can only be calculated through y(1) = g(1)d(0) + g(0)d(1). Therefore, the equivalent narrow square wave disturbance d(k - 1) at the previous moment is calculated through y(k).

[0080]

[0081] In this embodiment, the outputs y(1) and y(2) of the first two points are used to obtain d(0) and d(1), and then the average value is obtained. The amplitude A of the disturbance is 8, and the width N of the disturbance d It is selected as 0.4 s according to the response time of the unwinding and cutting disturbance. Then, the feedforward compensation amount u(2) is added at k = 2, and the output after adding the feedforward compensation amount is:

[0082]

[0083] Since g(0) = 0, u(2) can make the output y(3) = 0 at the next moment. When k = 3, the feedforward compensation amount u(3) is added, and the system output after adding the feedforward compensation amount u(3) is:

[0084]

[0085] The system output y(k) after adding the feedforward compensation amount u(k) at the Mth moment is:

[0086]

[0087] From this, the calculation method of the feedforward compensation amount u(k) can be obtained:

[0088]

[0089] Figure 3 The schematic diagram of the output response of the actual system under the disturbance is given, Figure 4 The schematic diagram of the calculated equivalent narrow square wave disturbance and the feedforward compensation amount is given, Figure 5 The comparison schematic diagram of the output (i.e., the tension error) of the unwinding tension control system before and after adding the feedforward compensation amount is given. It can be seen that after adding the feedforward compensation amount, the output of the unwinding tension control system basically remains near 0, that is, the tension error is basically near 0, and the tension remains constant.

[0090] In summary, the present invention has the following advantages and beneficial effects:

[0091] 1. By quantitatively analyzing the disturbance caused by the unwinding and cutting of the unwinding tension control system, the present invention equivalently converts the disturbance caused by the unwinding and cutting into a velocity narrow square wave disturbance, and calculates the feedforward compensation amount according to this narrow square wave disturbance and adds it to the input end of the actuator. This method has the characteristics of simple calculation method, small calculation amount, good compensation effect, high accuracy, etc.

[0092] 2. Compared with the method of using the PID control algorithm or the improved PID control algorithm in the existing unwinding tension control system for closed-loop adjustment to achieve constant tension, the compensation speed of the method of the present invention is faster and more accurate, and when the model parameters in the tension control system change, the robustness of this method is stronger.

[0093] 3. The feedforward compensation method in the present invention can solve the disturbance problem in the process of feeding and cutting, thereby reducing the scrap rate and improving the production accuracy and efficiency of the product.

[0094] The above description is a detailed description of the preferred feasible embodiment of the present invention, but the embodiment is not intended to limit the scope of the patent application of the present invention. Any equivalent changes or modifications made under the technical spirit disclosed by the present invention shall fall within the scope of the patent covered by the present invention.

Claims

1. A disturbance analysis and feedforward compensation method for unwinding tension control system in material feeding and cutting, characterized in that, Including the following steps: S1. Construct a unwind tension control system with a controller and devices. The devices include a controlled object, a measuring device, and an actuating device. During the closed-loop operation of the unwind tension control system, collect the output signal of the system; S2. According to the given controller model and device model, establish a discrete transfer function from the unwind cutting disturbance to the output of the unwind tension control system; S3. According to the system output signal and the discrete transfer function from the unwind cutting disturbance to the output of the unwind tension control system, calculate the equivalent narrow square wave disturbance caused by the unwind cutting; S4. Calculate the feedforward compensation amount of the system according to the equivalent narrow square wave disturbance, and add the feedforward compensation amount to the input end of the actuating device at the corresponding moment to achieve feedforward compensation.

2. The disturbance analysis and feedforward compensation method for unwinding and cutting in the unwinding tension control system according to claim 1, characterized in that, In step S1, the controller of the unwind tension control system adopts a PI controller. The controlled object is the film tension. The measuring device is the swing arm and the potentiometer. The actuating device is the variable-frequency motor; The difference between the given tension and the film tension causes the swing arm to deviate from the vertical position and generate a deflection angle. The deflection angle is measured by the potentiometer, and a voltage signal reflecting the magnitude of the tension error is output and fed back to the PI controller through a computer.

3. The disturbance analysis and feedforward compensation method for unwinding and cutting in the unwinding tension control system according to claim 2, characterized in that, During the operation of the unwind tension control system, the tension is kept constant through closed-loop PI control. The computer collects the output signal of the swing arm and feeds it back to the PI controller. The PI controller outputs a control quantity to the variable-frequency motor, and the variable-frequency motor performs an output action according to the control quantity.

4. The disturbance analysis and feedforward compensation method for unwinding and cutting of the unwinding tension control system according to claim 1, characterized in that In step S2, according to the given controller model and device model, the discrete transfer function from the unwind cutting disturbance to the output of the unwind tension control system is established as: Where, Y(z) is the system output in the Z domain, D(z) is the feeding and cutting disturbance in the Z domain, G p (z) is the equipment model in the Z domain, G c (z) is the controller model in the Z domain, G yd (z) is the discrete transfer function from the feeding and cutting disturbance in the Z domain to the system output.

5. The disturbance analysis and feedforward compensation method for unwinding and cutting in the unwinding tension control system according to claim 4, characterized in that In step S3, according to the system output signal and the discrete transfer function from the unwind cutting disturbance to the output of the unwind tension control system, calculate the equivalent narrow square wave disturbance caused by the unwind cutting. The specific process is as follows: S31. According to the discrete transfer function from the unwind cutting disturbance to the output of the unwind tension control system, obtain the relationship between the output of the unwind tension control system and the unwind cutting disturbance as: where y(k) is the output of the unwinding tension control system at time k, and g(k) is the discrete impulse response of the transfer function G yd (z). In the actual system, g(0) = 0, and d(k) is the equivalent narrow square wave disturbance caused by the material feeding and cutting at time k; S32. According to the relationship between the output of the unwind tension control system and the unwind cutting disturbance, and the collected output signal of the unwind tension control system, obtain the equivalent narrow square wave disturbance of the unwind cutting as: where d(k) is the equivalent narrow square wave disturbance caused by the discharging and cutting at time k, N d is the width of the disturbance, N d is selected according to the response time of the discharging and cutting disturbance, and A is the amplitude of the equivalent narrow square wave disturbance.

6. The disturbance analysis and feedforward compensation method for unwinding and cutting in the unwinding tension control system according to claim 5, characterized in that, In step S4, calculate the feedforward compensation amount of the system according to the equivalent narrow square wave disturbance, and add the feedforward compensation amount to the input end of the actuating device at the corresponding moment to achieve feedforward compensation. The specific process is as follows: S41. If the feedforward compensation amount u(i) is added at time M, that is, when i < M, u(i) = 0, the output of the system after adding the feedforward compensation amount is: S42. Since g(0) = 0 in the actual system, the feedforward compensation amount u(i) can make the system output equation at the next moment as: S43. Solve the feedforward compensation amount u(i) according to the system output equation of the unwind tension control system, and add the feedforward compensation amount u(i) to the input end of the actuating device to achieve feedforward compensation.

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