Wireless shape meter and intelligent shape control system for the whole roll of large cold strip mill

1. Research Background and Issues

The cold-rolled strip steel is a high-end fine steel product, mainly used in high-end automotive and home appliances, electrical and electronics, rail transit and other industries, and the shape (flatness) is an important quality index. Online detection and control of plate shape is the core key technical problem of large-scale cold-rolling mills, an inevitable choice for the production of high-grade cold-rolled strips, and a major demand for the intelligentization of steel manufacturing process equipment in my country.

There are thousands of sets of strip cold rolling mills in my country, of which less than 10% rely on imports to equip the flatness measurement and control system. The imported system is expensive, the maintenance service period is long and the cost is high. Most cold rolling mills rely on workers to feel the shape of the plate by visual inspection and tapping with sticks, and manually adjust the control. The quality of the shape is low and cannot be used in the high-end field.

Cold-rolled strip steel has the characteristics of high speed and heavy load, large aspect ratio, strong coupling of multiple parameters, and nonlinear time-varying properties. The difficulty of strip shape measurement and control technology lies in the dynamic detection and control of the fine distribution of strip length along the width direction through a series of complex and precise electromechanical systems and high-precision high-speed mathematical models at the level of microns and milliseconds. For decades, flatness detection and control has been an international research problem.

 

large strip cold rolling mill

 

The key problems to be solved in cold-rolled strip shape measurement and control technology are:

(1) Develop a shape meter with high detection accuracy, high roll surface quality, reliability and durability.
(2) To develop a flatness control system with multiple flatness control methods coordinated, complete and powerful functions.
(3) Research and develop a high-precision, high-speed flatness control mathematical model.

 

Over the years, the main problems of the internationally popular cold-rolled strip shape measurement and control system are:

(1) The roll surface quality and detection accuracy of the shape meter are not high enough.

There are seams on the roll surface of the segmented piezomagnetic shape meter, which may crush and scratch the strip surface. The sensors of the whole-roll piezoelectric shape meter are arranged in a scattered spiral, which cannot realize the simultaneous measurement of the transverse shape.

(2) The carbon brush slip ring type plate-shaped signal transmission device is susceptible to interference from friction, wear, vibration and electromagnetic temperature, and is difficult to operate and maintain.
(3) There is a channel coupling problem in the whole roll shape meter, which affects the detection accuracy.
(4) Both the shape analysis calculation and the controller design model are static, which cannot realize dynamic prediction and decoupling.
(5) The intelligent degree and calculation accuracy of shape control modelling is low, which affects the performance of the control system.

In order to equip the strip steel cold rolling mill with the self-made flatness measurement and control system and produce high-grade cold-rolled strip steel, the Chinese research team has spent more than 10 years innovating and independently developing the whole roll wireless flatness meter and the intelligent flatness control system, and successfully applied them In Angang 1780mm five-stand tandem cold rolling mill and 12 sets of steel strip, copper strip and aluminium strip cold rolling mills such as Maanshan Iron and Steel 1720 and Hegang 1550, the large-scale application of the large-scale strip steel tandem cold rolling mill flatness measurement and control system has been realized.

 

2. Problem-solving ideas and technical solutions

In order to overcome the fact that the internationally popular segmented piezomagnetic shape meter (slits on the roll surface) may crush and scratch the surface of the strip steel, the whole roll piezoelectric shape meter (sensor scattered spiral arrangement) cannot simultaneously detect the transverse shape, The carbon brush slip ring type plate shape signal transmission device is susceptible to friction and wear, vibration and electromagnetic interference. Simultaneous measurement and precise transmission of shape signals. In order to solve the channel coupling problem of the whole roll shape meter, a mechanism model of channel coupling and signal decoupling is proposed, and then the precise processing of the shape signal is realized through various elimination methods of detection errors.

In order to solve the problem that the flatness analysis and calculation and the static model of the controller design cannot realize dynamic prediction and decoupling, and the intelligence and calculation accuracy of the flatness control modelling are not high, this project combines the roll strip deformation adjustment with the hydraulic system control process The relative gain theory is used to establish a dynamic simulation forecast model for plate shape adjustment and a dynamic decoupling model for control design; a high-precision intelligent control model is established by using the method of synergistic drive between mechanism simulation and measured data.

It consists of a shape meter and a shape control system. The shape meter is composed of a shape detection roller, a shape signal transmission device, and a shape signal processing computer. The shape control system is composed of a control computer, a programmable controller, and a shape control device. The shape control device or means has an inclined roll, work roll bending, intermediate roll bending, intermediate roll traversing, work roll section cooling and other systems.

According to the time and space sequence of technology implementation, the project designed flatness measurement and control technology solutions including flatness setting control technology, flatness online detection technology, and flatness closed-loop control technology. Shape setting control is to design and formulate a shape control scheme before rolling, which lays a good foundation for the closed-loop control of shape. The shape online detection is to use the shape meter to detect the shape in real-time during the rolling process, providing conditions and a basis for the closed-loop control of the shape. The flatness closed-loop control is to perform feedback control according to the deviation between the measured flatness and the target flatness after the flatness is actually measured, so as to further improve the flatness quality.

According to the expression method of flatness lateral distribution, the research methods of the flatness control model include a multi-point method and a component method. The multi-point method achieves the purpose of controlling the overall shape by controlling the shape of many points in the horizontal direction of the strip, and the component method achieves the purpose of controlling the overall shape by controlling the 1st, 2nd, 3rd, 4th and other shape components. Each sub-component of plate shape can be obtained by the pattern recognition method. The multi-point method does not require pattern recognition, but there are many target parameters, the control model is complex, and the amount of calculation is large. The component method has few target parameters, a concise control model, and a small amount of calculation. The purpose of controlling multi-point flatness is achieved by controlling each flatness component. The project adopts the component control method to study the joint control model of the 1st, 2nd, 3rd, and 4th plate shape components such as inclined rolls, work roll bending, intermediate roll bending, and intermediate roll traverse. The multi-point control method is adopted Research on the model of subsection cooling of work rolls to control local shape.

 

cold rolling Mill

 

3. Main scientific and technological innovation achievements

1. Develop the whole roll seamless piezoelectric shape detection roll, improve the quality of the roll surface, and realize the simultaneous measurement of the shape in the width direction; optimize the design of the shape roll structure size, improve the detection accuracy and safety performance, and expand the testing of rolling materials and processes Applicable scope of the equipment.

The shape-detection roller consists of a roller body and a piezoelectric sensor. In the inner part of the roller body near the roller surface, 4 axial precision through holes uniformly distributed along the circumferential direction are processed. In each hole, a series of sensors are arranged in sequence. The width of each sensor in the middle of the detection roller is 52mm, and the width of the sensors at both ends is 26mm to refine the detection of the edge of the strip.

The tension of the strip steel with a certain wrap angle forms pressure on the detection roller, the axial distribution of the pressure is measured by the sensor and then converted into the axial distribution of the tension, and then the strip shape (strip length distribution) can be calculated. After quenching, the surface hardness of the roller body reaches above 60HRC, which is wear-resistant and impact-resistant. The seamless roll surface has high hardness, which avoids pressure damage or colour difference on the strip and maintains the surface quality of the strip. Sensors are densely arranged in the axial direction of the roller to realize synchronous measurement. High-sensitivity piezoelectric sensors and thin edge detection units ensure high-precision detection.

In order to make the sensor work stably in the linear section, it is necessary to apply a certain preload to it by interference fit. During the cold rolling process, due to plastic deformation and contact friction, the temperature of the strip steel can reach 200°C, and there is a certain temperature difference and thermal deformation difference between the outer surface of the detection roll and the inner sensor, which weakens or disappears the interference and pre-pressure of the sensor , causing the detection signal to be distorted. Therefore, the assembly sensor must have sufficient interference and pre-pressure. According to the actual rolling conditions, the thermal-mechanical coupling simulation of the detection roll and the sensor is carried out by using the methods of heat transfer and elastic mechanics, and then the assembly interference of the sensor and the wall thickness of the roll surface is optimally designed. The wall thickness of the roller surface should not only facilitate the transmission of pressure but also ensure a certain amount of grinding roller.

 

2. Using wireless digital communication technology, develop a wireless digital integrated plate shape signal transmission device, which has strong anti-interference, accurate signal transmission and long service life.

The plate-shaped signal transmission device consists of two parts: a rotating head and a fixed cover. The rotating head is connected with the plate shape detection roller and rotates synchronously. The rotating head is equipped with a signal processing chip, a wireless sending chip and an inner magnetic ring. The fixed outer cover is equipped with a wireless receiving chip and an outer magnetic ring.

The working principle is that the plate shape signal detected by the sensor in the detection roller during the rotation process is converted into a high-frequency digital signal after being amplified, filtered, A/D converted, encoded and packaged by the signal processing chip on the rotating head. The signal is output through the wireless sending chip; the wireless receiving chip on the outer cover receives the digital signal in real-time and converts it into a wired digital signal, and transmits it to the plate-shaped signal processing computer at a long distance; the relatively rotating inner and outer magnetic rings are rotated through wireless induction. Power supply for signal processing on the head, sending chip and sensors in the detection roller. This plate-shaped signal transmission device integrates multiple functions such as analogue signal acquisition, analogue-to-digital conversion, digital wireless transmission, and wireless induction power supply. It has strong anti-interference, high stability and reliability, long service life, and is basically “maintenance-free” “.

3. Propose a channel decoupling mechanism model, multiple detection error elimination methods and shape component identification methods, develop an accurate and intelligent processing system for shape signals, and realize accurate measurement and depth perception of shape.

The pressure signal Ni detected by a certain channel of the seamless shape detection roll of the whole roll is not only affected by the surface pressure Fi of the channel but also by the surface pressure Fj of other channels, especially the adjacent channels, that is, there is channel coupling. Using two methods of mechanical calculation and experimental calibration, the channel coupling influence coefficient Aij is determined, and the coupling matrix equation {N}=[A]{F} is established. The coupling matrix equation is reversed to form a decoupling matrix equation {F}=[C]{N}, [C]=[A]-1, which can solve the surface pressure Fi and eliminate the channel interaction.

On the basis of channel decoupling, the elastic mechanics model is applied to comprehensively and accurately compensate for the influence of force deformation and installation error of the detection roller, the temperature difference in the width direction of the strip and the influence of coiling deformation, etc., to improve the accuracy of plate shape detection. Using the Legendre polynomial model and optimization method, the 1st, 2nd, 3rd, and 4th-order flatness components and high-order local flatness are identified for the flatness signal to realize depth perception.

 

4. Propose a dynamic decoupling method and model for shape control, and develop a shape control system that coordinates and decouples multiple means such as inclined rolls, asymmetrical bending rolls, symmetrical bending rolls, traverse rolls, and segmental cooling, ensuring the control function completeness.

For the six-high rolling mill, according to the theoretical calculation of rolling and the actual measurement of the rolling process, and the use of relative gain theory to analyze and prove that the main function of the asymmetrical bending roll of the inclined roll and the work roll is to control the 1st and 3rd asymmetrical shape. The effect of the plate shape component is very small; the main function of the symmetrical bending of the work roll and the intermediate roll, and the traversing of the intermediate roll is to control the 2nd and 4th symmetrical plate shape, and has little effect on other plate shape components; the working rolls are cooled in sections It is suitable for flexible control of high-order local shape.

Therefore, the complex flat shape control system is decomposed into three independent subsystems: (1) the asymmetrical control system of inclined roll and work roll asymmetrical bending control of primary and tertiary flat shape, (2) the asymmetrical control system of work roll and work roll Symmetrical control system for symmetrical roll bending of intermediate rolls, traversing control of intermediate rolls for 2nd and 4th flatness, (3) local control system for segmental cooling of work rolls to control high-order local flatness. The control matrix equations are established separately for the three subsystems, which greatly simplifies the controller design.

The study found that the static control matrix [C] that does not include the transfer function of the hydraulic system can only achieve decoupling at the end of the regulation process, the regulation time is long and the overshoot is large. Therefore, according to the decoupling control theory, a dynamic decoupling control matrix model [D(s)] including the transfer function of the hydraulic system is established to realize decoupling every moment during the control process, shorten the control time, and reduce the overshoot.

 

5. Propose the intelligent collaborative modelling method of flatness control mechanism, the mechanism intelligent model featuring strip element method and neural network, and develop the flatness control system including setting control, predictive control and flatness meter feedback control to achieve high precision Shape control.

According to the deformation mechanism of the roll strip and the measured data of the rolling process, the strip element method mechanism model control scheme and the neural network intelligent model control scheme are respectively established, and then weighted and combined to formulate a collaborative control scheme. With the accumulation of rolling data and the learning of the neural network, the calculation accuracy and generalization ability of the intelligent model are continuously improved, the weight of the intelligent control scheme is increased, and the control accuracy is improved.

In order to compensate for the defect of large time lag in flatness detection, on the basis of setting control and flatness meter feedback control, the mechanism intelligent flatness simulation and prediction model is applied to perform predictive control before the actual measurement of flatness to improve control accuracy and speed.

The above 5 innovative achievements of the project have formed an advanced and perfect plate shape detection and control technology system.

 

4. Application effect

Since 2011, this technology has been applied to Anshan Steel’s 1780mm five-stand continuous cold rolling mill, 1780mm temper mill, 2130mm skin pass mill, Hegang’s 1050mm and 1550mm reversing cold rolling mill, Maanshan Iron and Steel’s 1720mm temper mill, Shandong Guanzhou’s 1500mm, Jiangsu Jiutian Photoelectric Company 750mm, Yanshan University National Cold Rolled Strip Equipment and Process Engineering Technology Research Center 650mm, Taiyuan University of Science and Technology Engineering Research Center of the Ministry of Education 600mm and other reversible cold rolling mills, Anhui Chujiang Copper 800mm copper strip cold rolling mill, Henan Mingtai Aluminum Co., Ltd.’s 1650mm aluminium foil cold rolling mill has a wide range of applications for rolled materials and process equipment. The plate shape detection resolution reaches 0.2I, the plate shape control accuracy reaches 4-6I, and the main technical indicators are better than the foreign advanced level (0.5I, 8-10I).

After this technology is applied to the above-mentioned 12 sets of cold-rolled strip (material) mills, the quality of the plate shape is improved from ordinary precision to advanced precision. Cold-rolled strip steel (material) products are used in automobile and home appliance panels such as Hongqi, Mercedes-Benz, Audi, Gree, Haier, etc., architectural decorative panels such as Beijing Daxing International Airport, Shanghai Hongqiao High-speed Railway Station, etc., Huawei mobile phones, 5G communication equipment and other electrical and electronic panels, COFCO, Walter and other food packaging boards, replacing imports and exporting to the United States, Europe, Japan, South Korea, etc.

This achievement has obtained 20 authorized invention patents, 10 computer software copyrights, presided over the formulation of 2 national standards, and published 80 papers. The overall technology of this achievement has reached the international advanced level, among which the flatness detection channel decoupling model and flatness control dynamic intelligent method has reached the international leading level.

 

Article source: The Chinese Society For Metals – “New Advances in Science and Technology: Wireless Flatness Meter and Intelligent Flatness Control System for Large-scale Continuous Cold Rolling Mills”

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