Abstract: Packaging is one of the important processes in the cold rolling finishing of steel. This paper starts with advanced unit automatic control, and conducts in-depth analysis and research on system process data processing and high-precision closed-loop control of transmission. It proposes international standard networks, advanced speed control, and advanced high-precision transmission control schemes to improve work efficiency while meeting production requirements.
Keywords: speed control, closed-loop control, data processing
Abstract: Packaging is an important process of cold-rolled. This article start from the automatic control. On the thorough analysis and the research to the system process data processing and high-precision drive closed-loop control, propose the international standard network, advanced speed control and advanced high-precision drive control scheme. On the base of the satisfaction of production request, system enhance the working efficiency.
Keyword: Speed control Closed-loop control Data process
1 Overview
Baosteel's 2030 cold rolling mill added a continuous annealing packaging unit. The entire system is controlled by an S7-400 PLC, with one server and two client computers. The PLC and HMI are connected via an Ethernet network, and the PLC, drive units, remote I/O stations, and encoders use a Profobus-DP control network. The unit's automatic control system is designed to be at an advanced level both domestically and internationally, and has been successfully accepted and put into operation at Baosteel. The system's control components are equipped with safety alarms, and each control panel is equipped with indicator lights and emergency stop buttons. The host computer monitoring uses Siemens Win CC, with interface settings for parameter settings and alarms. Steel coil information is crucial for the automatic packaging control.
To improve control accuracy and safety, the system employs a control scheme that utilizes fiber optic network data transmission and high-precision closed-loop control of the transmission device's length, achieving high-precision and high-quality harmonic control and improving work efficiency.
2 Production Process
2.1 Production Flow Chart
The system first uses a conveyor to move the steel coil from the continuous exit saddle to station #1. Then, at station #2, paper is fed by the #1 paper feed roller for the first packaging. Next, at the next station, the #1 lifting trolley lifts the steel coil, and paper is fed in the reverse direction by the #2 paper feed roller for packaging once more. Then, the #2 lifting trolley lifts the steel coil for edge binding, and the #3 lifting trolley lifts the steel coil to complete the final packaging. Finally, a radial bundling machine bundles the packaged steel coil. The Win CC interface of the production flow diagram is shown in Figure 1.
Figure 1 Overall Flowchart
2.2 System Functions
The control principle of the three lifting trolleys is the same, so we will use one of them as an example. The lifting trolley control box is equipped with a manual/automatic switch, lift/lower, forward/backward, and station completion buttons. When in automatic mode, simply press the automatic lift/lower button to complete the entire process. The paper feeding roller has remote and local control, operated by a forward/reverse switch. The roller on the side with the paper is pressed down by the pressure roller on that side.
The conveyor chain requires high control precision and strict safety and reliability. It is controlled by a Siemens 6SE70 frequency converter. The main control panel has a manual/cycle start switch. In manual mode, it can be operated using forward/reverse buttons. In cycle start mode, simply pressing the cycle start button will automatically complete one cycle, i.e., one workstation. The main control panel has indicator lights for the completion of each workstation, making operation simple.
The CPU processes and judges logic signals from the external system to control the operating status of the system. Additionally, it calculates the steel coil information values sent by the control system and then sends the calculation results to the various actuators in the field to ensure they operate according to process requirements.
2.3 System Network Composition
The control system adopts a server-client model. The HMI and PLC communicate via an Ethernet ring network. Activation or deactivation can be performed on any machine (server or client); if one machine deactivates an activation, all others are deactivated. The server and clients communicate via a fiber optic network, offering very high speeds. The server's fiber optic port 1 connects to the input HMI's fiber optic port 1, the input HMI's fiber optic port 2 connects to the output HMI's port 1, and the output HMI's port 2 connects to the server's port 2, thus forming a ring network.
The fieldbus communication is divided into Profibus (1) and Profibus (2), which are connected by the CPU's DP port and the CP443-5 module, respectively. See Figure 2 for the system automation network configuration diagram. First, Profibus (1) is introduced. All network substations in the electrical room are designed on this network, which includes a transport chain, No. 1 paper feeding roller, No. 2 paper feeding roller, paper feeding swing arm, radial bundling machine, steel coil handling trolley lifting frequency converter and walking frequency converter. See Figure 3 for the network configuration diagram.
The remote I/O station and field encoders are designed on Profibus (2). A DP line is used to connect the CP443-5 module to the DP/fiber optic conversion module, then to the conversion module of the main control console via fiber optic cable, and finally to each network substation via DP line. The substations on this network include the main control console ET station, the radial baler ET station and touch screen, the hydraulic station ET station, the valve station ET station, the No. 3 lifting trolley lifting encoder, the No. 2 lifting trolley lifting encoder, the No. 1 lifting trolley lifting encoder and translation encoder, the steel coil handling control console ET station and its lifting encoder and walking encoder.
Figure 2 System Automation Network Configuration Diagram
Figure 3 PLC network configuration diagram
3. Automation Control Section
3.1 Control System
The automation control of this system mainly focuses on speed control, including the lifting and traversing speed control of the hoisting trolley, the speed control of the conveyor chain and paper feeding rollers, and the speed control of the transmission device, which will be analyzed later. This section mainly introduces the speed control of the hoisting trolley. The trolley speed is first received by the CPU from the operation logic signal and processed, then given to the speed selector, then calculated by the ramp function generator, and finally sent to the analog output control block to convert the data into a standard format. The data is then sent to the analog output module of the remote station to control the servo amplifier to drive the hydraulic valve, and finally the equipment operates according to the process requirements.
3.2 PLC Control
The control unit, consisting of an 18-slot central rack and a control network, comprises: a CPU 416-2DP processor, two DI modules, two DO modules, one CP 443-5 communication module, one CP 443-1 communication module, and one CP 441-2 communication module. PLC control is centralized. The programming software for the Siemens S7-400 PLC is STEP 7.
The system uses S7GRAPH sequential control. S7GRAPH requires SIMATIC_S7_GRAPH_V53_SP5 to be installed. After installation, you can open the program and write sequential control statements. Standard sequential control programming uses a step-by-step block diagram. Sequential control blocks only contain standard language commands and variables, with a limited number of commands and variables. S7GRAPH can only be programmed within a FB (Folded Block), not a FC (Folded Block).
4. Transmission Part
4.1 System Transmission Control
To start the inverter, first close the circuit on the HMI, then operate it on the field control panel by setting the inverter's operating frequency. The motor will then start running. On the drive interface, first select the equipment, then click "Close" or "Open". Multiple inverters can be selected to close or open simultaneously.
The inverter-driven fan starts and stops using the inverter's start command, with a 5-second delay before stopping. It employs Siemens inverter timer nesting technology and cannot use device status word feedback signals because these are output voltages; even when the motor stops, the voltage may still exist, causing the fan to run continuously. The motor's holding brake does not activate during closing and opening; it is only energized when the motor is rotating. The holding brake is energized immediately when the inverter outputs frequency. When a motor stop command arrives, the holding brake does not immediately de-energize and lock; instead, it locks only when the inverter frequency drops to zero.
Figure 4 HMI Drive Control
4.2 High-precision closed-loop control of transmission
The transport chain control requires safety and reliability, and the cycle length control requires high precision, thus the entire transmission control has high requirements. The system design uses an FM350 counting module on the main control console ET, and through encoders and technical modules, completes the hardware conditions for high-precision closed-loop control, so that the control system obtains the closed-loop speed feedback signal.
The calculated length value, when greater than or equal to the set length plus a correction value, and less than or equal to the correction value plus 0.05, represents the actual length of the motor's operation, with an accuracy of 0.025%. The high-precision closed-loop control program is shown below.
5. Summary
In the cold rolling finishing process, packaging is the final highlight, and the effectiveness of its automatic control system directly impacts the product's quality, making it a key technological aspect. Our design, employing state-of-the-art control technology, utilizes fiber optic network data transmission and high-precision closed-loop control of the drive device's length, achieving high-precision, high-quality, and harmonic control, thus improving work efficiency.
The innovations of this paper are: 1) It combines international standard networks for data processing, the advanced nature of fiber optic networks in drive control, and the use of Ethernet optimization strategy for data exchange between multiple HMIs and PLCs.
2) The frequency converter speed control adopts high-precision closed-loop control. In the operation of the packaging unit of Baosteel Cold Rolling Mill, the given length is optimized, meeting both the length requirement and not exceeding it. This solution has good application prospects in steel production.
References:
[1] Cui Jian, Siemens Industrial Network Communication Guide (Volumes 1 & 2), Beijing: Machinery Industry Press, 2004.
[2] Chen Shuihong et al., Analysis and research on a variable parameter PID controller [J] Microcomputer Information, 2005.10, 47-48.
[3] Shi Guanglin, Programmable Logic Controller Communication and Network, Beijing: Machinery Industry Press, 2006.
[4] Liao Changchu, S7-300/400 PLC Application Technology, Beijing: Machinery Industry Press, 2005.
[5] Tianjin Electric Drive Design Institute, ed. Handbook of Electric Drive Automation Technology. Machinery Industry Press. 1992.
About the author: Tang Jianfang (1984~), male, from Xinzhou, Hubei Province, holds a Master of Engineering degree and is an engineer, primarily engaged in the design and practice of electrical drives and automation control. E-mail: [email protected]
Mailing Address: 4th Floor, No. 1000 Pangu Road, Baoshan District, Shanghai, Attn: Tang Jianfang, Tel: 15221907691, 021-36213909-835
