1 Overview
The acrylic fiber spinning production line is a continuous production unit. The production process involves over twenty stations where motors operate synchronously with high precision under both static and dynamic conditions. Due to the complexity of the controlled objects in the electrical system, including start-stop and interlock protection for each station, as well as process control such as speed regulation, drawing point position, and relaxation loops for the entire system, the process places high technical demands on the electrical drive system. The production line has twenty stations from the F01 metering pump to the F20 crimping machine. The motors at these twenty stations must start, stop, and operate synchronously with high precision according to a given speed ratio. In particular, the three drawing groups—solvent drawing (F4, F5)—require a draw ratio of 2.5, hot drawing (F13, F14) requires a draw ratio of 4.6, and secondary drawing (F18, F19) requires a draw ratio of 1.4. Furthermore, these draw ratios are adjustable at any time according to production requirements. This means that among these twenty normally operating motors, there are both driving and driven motors. The F01 and its backup frequency converter system is a single frequency converter driving multiple motors. The Siemens 6SE70 frequency converter has complex parameters and many functions. It is necessary to understand the mechanical characteristics of all motors on the production line, master the operating rules of each station, and take effective methods to keep the voltage of the DC bus of the frequency converter within the effective range and avoid overvoltage of the frequency converter.
2. Discussion on the characteristics and technical challenges of the AC variable frequency acrylic fiber production line process system
2.1 Characteristics of Acrylic Fiber Spinning Process and Transmission System
Group control: Multi-motor group coordinated transmission is a feature of acrylic spinning drive system; strong production process continuity, good dynamic synchronization performance; constant draft and constant tension control requirements; constant torque load characteristics; high speed control accuracy required; high speed spinning, large equipment inertia; high and low speed switching.
2.2 Key Control Interlocking Issues in Acrylic Fiber Spinning Drive System
The purpose of setting up interlocks is to promptly prevent danger or take measures to prevent further escalation in the event of an abnormality, accident, or hazard.
Spinning line control interlocks are divided into two categories: one is start-stop interlock, which means the equipment can operate under certain conditions; the other is speed interlock, which means the speed of the preceding and following equipment is tracked proportionally.
Divided by control area, it consists of two independent parts: pre-spinning (F1~F15) and post-processing (F16~F20).
Start-up and shutdown interlocking
Emergency stop at the front spinning mill: Emergency stop buttons on panels E and P, interlocked with F4~F15
The yarn tow washing assembly interlocks: The entire yarn tow washing assembly (F6~F10) is interlocked.
Start-up and stop of the entire spinning unit: Control F6~F14 to start and stop the entire unit.
Oil mist generator interlock: The two oil mist generators are interlocked with the washing machine. Operations F6~F10 can only be started after the oil mist generators are activated.
Hot drawing group interlocking: F12 (clutch roller) and F13~F14 group interlocking: F12, F13 and F14 foot kick switches, F14 star roller winding, relaxation loop high and low limit photoelectric and other actions. After the washing group interlock stops, the hot drawing group will also stop interlocking.
Start-up and stop of the entire hot drawing group: control the start and stop of the entire group by controlling the clutch rollers F12, F13, and F14.
Relaxation loop interlock: After the upper or lower limit exceeds the limit, F12 clutch roller and F13~F15 interlock stop; when the yarn laying head winding roller detection is activated, F15 interlock stops.
Post-processor F16~F20 form a group of interlocks; stopping any one of them will stop all of them.
Stenter interlock: if the inlet is clogged, the inlet roller is wrapped, the outlet exceeds the limit, or the hot water circulation pump stops, all F16~F20 (including the conveyor belt) will stop.
Redrawing machine interlock: The upper and lower limits of the redrawing machine inlet tension roller are exceeded; the upper and lower limits of the oiling inlet tension roller are exceeded.
The speed control before spinning is divided into two groups, A and B. Group A: F1~F12, Group B: F13~F14; Speed F15 is controlled by a relaxation loop. The on-site spinning control panel has acceleration/deceleration switches for F1~F10, allowing individual speed adjustment (fine-tuning) of each station. The on-site hot drafting control panel also has acceleration/deceleration switches for F12~F15, allowing individual speed adjustment (fine-tuning) of each station. The speed interlocks for each station are as follows: F1~F4 interlock: Speeds F2~F3 change proportionally to speed F4; F5~F14 speed interlock: The speed of the subsequent station changes with the speed of the preceding station, ensuring the drafting relationship remains unchanged.
F1~F15 low speed: F1 speed is 1/3.6 of the center speed, F2~F15 speed is 1/3 of the center speed; F13, F14 low speed (drafting): the drafting speed is set by the process personnel on the operation panel; once the spinning speed of each station from F1 to F14 is determined, the speed ratio and draft ratio relationship between them remains unchanged when the speed of the whole group increases or decreases.
The spinning speed at each station is set by the process engineer on the control panel. The on-site acceleration/deceleration switch adjustment range is preset to 20%, and the overall speed adjustment range is preset to 30%. A key switch is provided on the main control cabinet (E) to facilitate disconnecting the acceleration/deceleration circuits of each station after the speeds F1 to F14 have been adjusted. The speed of F15 is determined by the position of the yarn bundle in the relaxation loop.
The post-spinning speed control is divided into the stenter inlet (F16) and the crimping machine (F20). The stenter main control panel (TT panel) has acceleration/deceleration switches for F16~F20 for individual speed adjustment. This group has three spinning speeds: single-machine inching, low speed for the entire group, and high speed for the entire group.
Single-machine jogging: Single-machine jogging buttons are set on the SI, SO, TT, R, and CR control panels on site. Pressing a jogging button prioritizes the jogging speed, which is set by the operator on the control panel (fixed value). Whole-group low speed: Whole-group "low speed-high speed" control switches are set on the SI, SO, TT, R, and CR control panels on site. Setting any one to "low speed" will cause the post-processing group to run at low speed. Whole-group high speed: Setting any one of the whole-group "low speed-high speed" switches to "high speed" will cause the spinning group to run at normal high speed. The speed of F15, controlled by the relaxation loop, is determined by the position of the yarn bundle in the relaxation loop. Four photoelectric switches detect the yarn bundle position to achieve closed-loop speed control. High and low limit positions provide upper and lower limit interlock protection switches, interlocked with the hot drafting group. The two middle photoelectric switches provide speed regulation control, automatically adjusting the speed of the yarn spreader to coordinate with the spinning speed of F14. The software employs a dedicated relaxation loop control module developed using self-learning control technology to ensure stable operation of the wire bundle hanging loop between the two photoelectric sensors. (PLC and drive system)
A PLC-based and fieldbus-based control system is adopted, with the S7-400H as the control core. Distributed I/O slave stations and variable frequency drive equipment are connected via the Profibus fieldbus. The system structure consists of a CPU master station, distributed I/O, operator panels (human-machine interface), and field devices (frequency converters). The CPU master station uses an S7-400H, and signals such as the normal/standby selection switch, the primary and secondary drying circulating fan signals, and the F1 and F2 acquisition signals are directly input to the master station. Each of the field E, P, and TT control panels is equipped with one set of ET200 distributed I/O, which sends the field I/O signals to the CPU master station via the fieldbus. The CPU master station communicates with the ET200, frequency converters, and operator panels via the Profibus fieldbus, and communicates with the DCS host computer via the ModBus protocol.
Operator panel (human-machine interface)
Human-computer interface function
Main screen: Displays key production parameters such as line speed, motor current, and output frequency of each station in a production flow chart format; Setting screen: Allows process engineers to set the normal spinning speed of each station, the yarn drawing speed of the hot drawing group, the jogging speed of the post-processing, and modify the reduction ratio, etc.; Monitoring screen: Monitors the operation status of each station of the acrylic spinning line in real time, displaying the line speed, motor current, and output frequency of each station.
Alarm screen: Displays abnormal conditions in the entire electrical system of acrylic fiber spinning.
3. Development Direction of AC Variable Frequency Technology in the Acrylic Fiber Spinning Industry
Variable frequency drive control systems. The development of variable frequency drive control systems towards a common DC bus design not only reduces the size of the control system but also significantly saves investment costs. This technology is applied to acrylic fiber spinning drive systems, improving their reliability, interchangeability, and anti-interference capabilities.
Redundant control of the communication system. Compared with conventional control systems, the integrated network control system of the acrylic spinning automation control system adopts a redundant control system, which includes a redundant control system, a redundant network system, and a redundant soft-start system. The system consists of a three-level control system, comprising a management computer, a process control system, and a direct control system. The two systems work simultaneously and are mutually redundant. The industrial control computer, PLC, touch screen, and electrical, pneumatic, and hydraulic instrument parameters of the electric drive system can be integrated into the design to achieve intelligent control of spinning and stepless speed regulation throughout the entire spinning process. Even if one system experiences a fault such as PLC input/output module failure or communication interruption, the other system can automatically take over.
Energy feedback control. To address the regenerative energy generated during the regenerative power generation of the acrylonitrile spinning frequency converter system, a four-quadrant voltage-type AC-DC-AC frequency converter or a power regeneration device is used. The active inverter unit is separated from the frequency converter and directly used as an external device, which can be connected in parallel to the DC side of the frequency converter. This feeds the regenerative energy back to the power grid, effectively reducing energy consumption. Integrated intelligent acrylonitrile spinning control system. The acrylic spinning control design fully embodies a human-centered approach, organically integrating equipment operation, display, electrical components, instruments, and computers. The unified design of the mechanical, electrical, and hydraulic control systems meets the requirements of the spinning process. A simple and user-friendly interface and intuitive operation steps further improve operability and efficiency. The spinning field control console transmits field signals and operation commands to the central processing unit of the main station via a network connection, enabling centralized monitoring and automated control. Information collected from the control network and transmitted through the central processing unit of the main station PLC can be provided to the higher-level monitoring system and industrial Ethernet. The VFD room program allows for the setting of frequency converter system fault codes and troubleshooting assistance, providing both near-field and remote technical support to on-site electrical engineers. It adopts a...
An integrated management system, comprised of a management computer, a database management system, and an industrial LAN, manages technical data, establishes a technical archive for acrylonitrile equipment, manages operational status, establishes an acrylonitrile equipment operation database, manages process data, and establishes a database of acrylonitrile spinning process parameters. The software's functional conclusions are as follows: With the development of acrylonitrile spinning technology, higher demands are placed on the reliability of AC variable frequency automated control systems. Further improvements to the coordinated control, redundant control, functional complementarity, safety interlocking, distributed control, and centralized management characteristics of AC variable frequency control systems provide a standard platform for equipment management ERP systems, laying the foundation for the modernization and informatization of acrylonitrile enterprises.
