1. Introduction With the rapid development of materials technology, power electronics technology, control theory technology, computer technology, and microelectronics technology, as well as the gradual improvement of motor manufacturing processes, AC servo technology—AC servo motors and AC servo control systems—has become one of the fundamental technologies for automation in the industrial field and will gradually replace DC servo systems. Currently, intelligent and networked control of AC servo systems are two important development directions for AC servo control. In the Jinan Iron and Steel ASP1700 thin slab continuous casting and rolling project, the continuous casting machine crystallizer width adjustment system adopts a fully digital intelligent AC servo control system based on the PROFIBUS bus, which is currently the world's most advanced servo control technology. 2. Continuous Casting Machine Crystallizer Width Adjustment Process The Jinan Iron and Steel No. 3 Steelmaking Plant's ASP1700 thin slab continuous casting and rolling crystallizer uses a straight crystallizer, consisting of two wide faces and two narrow faces, with a length of 1200mm and a maximum inner cavity thickness of 150mm. The width adjustment range is 100mm～150mm. The narrow faces are movable to adjust the width and taper of the crystallizer during continuous casting machine preparation and pouring (Figure 1). The crystallizer uses a set of tie rods to clamp two wide faces and two narrow faces. The tie rods maintain the clamping force through a spring assembly. The hydraulic cylinder on the tie rod can compress the spring during the width adjustment process, so that the narrow faces can be easily moved and the wide faces can be quickly opened. The hydraulic cylinder pressure can be continuously adjusted to adjust the clamping force according to the width of the slab, achieving soft clamping. Since this pressure does not clamp the wide faces, the spring can maintain the clamping force without danger when the hydraulic pressure fails. [img=397,232]http://www.ca800.com/uploadfile/maga/plc2007-1/mj1.jpg[/img] Figure 1 Mechanical structure of the narrow face of the crystallizer. The crystallizer width adjustment system includes: 4 sets of lead screw mechanisms, 2 sets for each narrow face; 4 sets of AC asynchronous servo motors with rotary transformers, fixed outside the cooling room under the casting platform; 4 universal joints; and 4 sets of AC servo control units. The mechanical structure for controlling the narrow face of the crystallizer width adjustment is shown in Figure 1. Each narrow face uses a servo unit to control the width adjustment motor drive, which can change the width on both sides and the taper of each face. Since the narrow faces of the slab produced during width adjustment are not straight, this means that an air gap will be generated between the copper plate and the slab shell during width adjustment. To avoid steel leakage, the taper must be adjusted simultaneously with the width adjustment. To reduce the stress on the solidified slab shell, the adjustment of the narrow faces should be carried out slowly. To ensure close contact between the slab shell and the copper plate, the crystallizer taper decreases as the width decreases and increases as the width increases. The control system selects different algorithms for the movement of each side during casting based on the steel grade, pouring speed, required taper, and slab length. 3. Crystallizer Width Adjustment Control System The crystallizer width adjustment control system uses a Siemens S7-400 PLC, and the servo unit uses a Siemens MasterDrives MC fully digital motion controller, which features high overload capacity and a wide speed range. It is equipped with a TP270 human-machine interface, which allows for setting and fault monitoring functions. Each servo motor has its own servo unit, employing a three-loop control system (position loop, speed loop, and current loop) for high dynamic response and high precision motion control. The transmission system is connected to the PLC and TP270 via a PROFIBUS bus. The servo motors are Lenz (MDSKARS090-22) three-phase AC asynchronous servo motors with a power of 2.6kW and a rated speed of 2300rpm. Production workers input the crystallizer width and taper settings into the human-machine interface based on the steel grade being produced. This data is transmitted to the width adjustment PLC via the PROFIBUS bus. After calculation, the PLC sends position control signals to each servo unit. The servo unit uses the actual position and speed signals, converted from the servo motor's rotary transformer signal, as position and speed loop feedback signals respectively, achieving three-loop control. This allows the system to quickly and smoothly follow the position settings, ensuring a constant speed difference between the upper and lower motors of the crystallizer and achieving precise positioning of the narrow-face copper plate. The entire control system is a three-loop control structure with the servo motor current loop and motor speed as the inner loop, and the narrow copper plate position as the outer loop. The system has high precision, fast speed response, stable and reliable operation, and accurate positioning. The width adjustment control system structure is shown in Figure 2. [img=397,225]http://www.ca800.com/uploadfile/maga/plc2007-1/mj2.jpg[/img] Figure 2 Crystallizer Width Adjustment Automatic Control System 4 About PROFIBUS Fieldbus 4.1 Definition and Characteristics of Fieldbus According to the definition of the International Electrotechnical Commission (IEC)/SC65C, fieldbus refers to a digital, serial, and multi-point communication data bus installed between field devices in the manufacturing or process area, and between field devices and automatic control devices in the control room. The fully digital control system developed based on fieldbus is called FCS. As a bidirectional digital communication network connecting field-level devices and control equipment in a control system, fieldbus offers significant advantages over traditional DCS systems: enhanced integration of field information; increased anti-interference capability and improved system reliability; convenient installation and good maintainability; openness, interoperability, interchangeability, and integrability; reduced engineering costs; IP67 protection rating for field installation; and automatic fault diagnosis. 4.2 Characteristics of PROFIBUS: PROFIBUS is an international, open fieldbus standard independent of equipment manufacturers. It is widely applicable to manufacturing automation, process industry automation, and automation in other fields such as building automation, transportation, and power automation. Central processing units (such as PLCs/PCs) communicate with distributed field devices (such as I/O, frequency converters, and valves) via a high-speed serial bus, with most data exchanges using a periodic method. PROFIBUS-DP is used for high-speed data transmission at the field device level. The communication medium uses shielded twisted-pair copper cables sharing a single conductor pair. Communication speeds range from 9.6 kbps to 12 Mbps, and communication distances can reach up to 12 km. The PROFIBUS bus boasts strong communication capabilities, allowing for communication of up to 10 words with frequency converters. 4.3 PROFIBUS-DP Data Communication Format The PROFIBUS-DP bus mode enables rapid data exchange between PLCs and drive devices (frequency converters, motion controllers). Access to drive devices is always performed in a master-slave manner; the drive device is always a slave station, and each slave station has a unique address. The message structure for periodic PROFIBUS transmission is shown in Figure 3. [img=397,79]http://www.ca800.com/uploadfile/maga/plc2007-1/mj3.jpg[/img]Figure 3 PROFIBUS-DP message structure 4.4 Available data of PROFIBUS-DP The available data area of ​​the transmission device is divided into two data areas, which transmit data using their respective messages: (1) Process data area (pzd) Control word and set value or status word and actual value; (2) Parameter area (pkw) Used for reading and writing parameters, reading fault information, etc. There are five structural forms of pkw and pzd: ppo1, ppo2, ppo3, ppo4, and ppo5, and their byte length and structural form are different. According to the different tasks of the transmission device in the automation network, ppo should be selected when configuring the communication mode of plc and frequency converter. In the crystallizer width modulation AC servo control system, ppo5 type communication message is used, and its message structure is shown in Figure 4. The symbols in Figure 4 have the following meanings: pkw: parameter identifier; pzd: process data; pke: parameter identifier; ind: index; pwe: parameter value; stw: control word; zsw: status word; hsw: master setpoint; hiw: master actual value. [img=397,165]http://www.ca800.com/uploadfile/maga/plc2007-1/mj4.jpg[/img]Figure 4 PPO message structure[align=center] [/align] 5 Hardware composition of AC servo control system based on PROFIBUS 5.1 PLC system Crystallizer width adjustment PLC system As a subsystem of the continuous casting machine L1 system, its system design follows the principles of reliability, advancement, and openness. Taking into account the system's performance-price ratio, the system structure is as unified as possible according to the process scheme and mechanical equipment conditions, and should be consistent with other L1 level subsystems. The continuous casting L1 level PLC system uses Siemens S7-400 series PLC. According to the performance requirements of the adjustment process, the CPU of the PLC system is selected as S7-414-3. It communicates with L1-level industrial Ethernet through the CP443 communication module, and can also communicate with MC motion controller and TP270 through PROFIBUS-DP interface. 5.2 Human-Machine Interface According to the process characteristics and field environment, the HMI of the crystallizer adjustment is selected as TP270 operation panel. TP270 belongs to the Simatic HMI (human-machine interface) product series and is a text-graphic touch mode operation panel. It has the following performance characteristics: (1) Simple and fast configuration, and the configuration data can be recovered; (2) It can be configured using standard Windows tools; (3) It uses soft keys, function keys or touch mode control, which simplifies the operation and ensures the safety of the operation. It is easy to use; (4) It is perfectly integrated with Siemens PLC, so that the whole system is optimized in both hardware and software, especially the communication supports PROFIBUS-DP bus protocol. 5.3 The MC controller crystallizer width adjustment servo controller selected is the Siemens MasterDrives MC motion controller. This controller is used for high dynamic response cyclic mechanical control and is a fully intelligent control system. The MC controller has the following characteristics: (1) High dynamic response and high overload capacity. The MC driver uses 32-bit DSP digital control technology. The DSP device has powerful hardware computing circuits and special bus structure, and has powerful digital signal processing functions. The MC motion control driver also has an extremely high overload factor and a 300% overload capacity within 250ms. (2) Strong versatility. It can control any type of motor. The modular and pluggable optional encoder function template can complete all driving tasks. There are SBP boards that support pulse encoders (TTL/HTL), SBR2 boards that support rotary transformers, and SBM2 boards that support multi-turn encoders (EQN, EQI, ENDAT/SSI or SIN/COS). All of these can be easily connected to the system. (3) Powerful Communication Capabilities: The MC motion control drive has optional templates that support various fieldbuses. The configuration of these interface templates significantly enhances the interconnection capability between the servo unit and other control devices. Among the various communication templates of the MC motion control drive, there is the CBP2 board that supports the PROFIBUS bus. PROFIBUS-DP is the most successful and popular fieldbus standard in the world today. Communication between modules at the same level is realized on the PROFIBUS CBP2 functional template, which shows its advantages, especially in the system integration of Siemens products. 6. Hardware Configuration of AC Servo Control System In the AC servo control system, the PLC hardware configuration and programming use STEP7 v5.3. STEP7 is the standard software package for configuring and programming SIMATIC programmable logic controllers. The system operation interface TP270 uses ProTool for configuration and programming. ProTool is a simple and high-performance visualization software for visualizing processes, which can run under Windows 95/98 and 2000. 6.1 Configure the PLC master station system (1) Create a new project plc-3 (nwa-ccm1) under the plc project ccm2, right-click, select "insert new object" and then "simatic 400 station" in the pop-up menu, and insert the S7-400 station; (2) Configure the hardware: double-click the "hardware" option to enter the "hw config" window, click the "catalog" icon to open the hardware catalog, and insert the rack, power supply, CPU, communication module, two input and output modules in the order of hardware installation and order number; (3) After inserting the CPU module, the PROFIBUS configuration interface will pop up at the same time. Create a new PROFIBUS named PROFIBUS_PLC3, define the address as 2, click the "properties" button to configure the network properties, select "network settings" to set the network parameters, the PROFIBUS transmission rate is "1.5mbps", and the line rule is "dp"; (4) In the PROFIBUS properties operation mode of the plc, set it to dp master. 6.2 Configuring the PROFIBUS slave station of the MC motion controller (1) Configure the slave station to connect to the MC motion controller on the DP network. Select "motion control plus" and connect to the DP network. Then configure the communication area of ​​the drive, as shown in Figure 5. Define the PROFIBUS station address as station number 3; [img=397,180]http://www.ca800.com/uploadfile/maga/plc2007-1/mj6.jpg[/img]Figure 5 Selecting the MC controller (2) Communication area definition In addition to transmitting set values ​​and control words, the PLC and the MC controller also need to transmit other data. Multiple PZDs need to be selected. Communication requires 9 words. Select PPO-TYP5, PKW+PZD-10/10, as shown in Figure 6. [/align][img=397,213]http://www.ca800.com/uploadfile/maga/plc2007-1/mj7.jpg[/img]Figure 6 MC controller communication area definition (3) Data area definition PKW data area is: piw 512-519 pqw 512-519 PZD data area is: piw 520-539 pqw 520-539 (4) Following the above steps, configure 2#MC, 3#MC, and 4#MC to the DP network respectively. The DP addresses are 4, 5, and 6 respectively. Define the PKW and PZD data of each substation respectively: 2#MC (4# station): PKW data area is: piw 540-547 pqw 540-547 PZD data area is: piw 548-567 pqw 548-567 3#mc (5# station): pkw data area is: piw 568-575 pqw 568-575 pzd data area is: piw 576-595 pqw 576-595 4#mc (6# station): pkw data area is: piw 595-603 pqw 595-603 pzd data area is: piw 604-624 pqw 604-624 6.3 TP270 PROFIBUS slave station configuration (1) Create a new project tp270_moldwidh_adjust under project ccm2, right-click, select "insert new object" under "simatic op" in the pop-up menu, and insert the TP270 station; (2) Double-click the tp270_moldwidth_adjust project to enter the protool programming environment, select the operation panel tp270; (3) Enter the name of the PLC in the width adjustment system, plc_3, and select the Sim-Atic S7-300/400 v6.0 protocol; (4) Click the “parameters” button to set the parameters. The way to connect the OP to the network is to select the plc_3 network, select 1 for the DP address, and use the path method, as shown in Figure 7. [img=397,235]http://www.ca800.com/uploadfile/maga/plc2007-1/mj8.jpg[/img]Figure 7 TP270 Communication Parameter Definition 7 Application of AC Servo Control System Software 7.1 PLC Data PROFIBUS Transmission Programming Step7 v5.3 has two SFC blocks “dprd_dat” and “dpwr_dat”, which are used for data transmission between the PROFIBUS master and slave stations. In the AC servo control system, the DP communication transmission commands “dprd_dat” and “dpwr_dat” are used to transmit data to the PZD data area (PIW) of the MC controller, and at the same time, the PQW value of the PZD data area of ​​the MC controller is read into the DB block of the PROFIBUS-DP transmission. The application program for transmitting PROFIBUS control commands for the #1 MC controller is as follows: `call "dprd_dat" ;` Calls the DP read command `laddr :=w#16#208 ;` Start address `ret_val :="top_left_comdata".recieve_ret` `record :=p#db31.dbx20.0 byte 20 ;` Target data address `call "dpwr_dat" ;` Calls the DP write command `laddr :=w#16#208 ;` Start address `record :=p#db31.dbx0.0 byte 20 ;` Target data address `ret_val :="top_left_comdata".send_ret` 7.2 The MC controller communication parameter definition uses the process data area to realize the transmission of control words and set values ​​(task: master inverter) or status words and actual values ​​(response: inverter master). The transmission of process data is only valid when the control word, set value, and status word actual value are connected according to the path specified in the "process data connection". The application of MC controller communication parameters is divided into two parts: the MC controller receives the control word and set value from the PLC and the MC controller returns the status word and actual value to the PLC. (1) Process data output area In the transmission format of the MC controller, the process data output area pzd1-pzd10 and the register variables k3001-k3010 of the MC controller are in a one-to-one correspondence. Double-byte data can be defined as needed. In the actual application of this system, k3007 and k3008 are used to form a double-byte data, and k3009 and k3010 are used to form a double-byte data. (2) Process data output area in MC controller application In practical applications, the MC controller mainly uses the process data output area to define the following parameters: p554=k3100 Device control word p565.1=k3107 Device reset control u710.003=k3202 Position control signal start u710.004=k3203 Position control signal clear remaining bits u710.026=k3309 Position control signal jog backward u710.027=k3310 Position control signal fast/slow speed selection u710.028=k3311 Position control signal jog forward u710.029=k3312 Position control signal mode selection control 1 u710.030=k3313 Position control signal mode selection control 2 u710.031=k3314 Position control signal mode selection control 3 u710.032=k3315 Position control signal mode selection control 4 u531=k3006 G function MDI enable u532=k3037 Position control signal u533=k3039 Speed ​​control signal (3) Process data input area In the transmission format of the MC controller, the process data input area pzd1-pzd10 and the parameters p734.1-p734.10 of the MC controller are in a one-to-one correspondence. Double-byte data can be defined as needed. In the actual application of this system, p734.2 and p734.3 are used to form a double-byte data, and p734.7 and p734.8 are used to form a double-byte data. (4) Process Data Input Area in MC Controller In practical application, the MC controller mainly defines the following parameters for transmitting process data input area values: p734.1=k32 Device status word p734.2=kk120 Actual position value p734.3=kk120 Actual position value p734.5=k22 Actual current value p734.6=k433 Operation integrated signal p734.7=kk91 Actual speed value p734.8=kk91 Actual speed value 8 Conclusion The successful application of AC servo control in the crystallizer width adjustment system of Jinan Iron and Steel Group's continuous casting machine has realized the requirement of changing the billet cross-section without stopping the Jinan Iron and Steel Group's 1700 continuous casting-rolling system, thus creating conditions for hot charging of billets and direct continuous rolling, fully meeting the requirements of multiple specifications in each unit of steel rolling, greatly improving the production capacity of continuous casting and continuous rolling and increasing the metal yield.