1 Introduction In the nonwoven fabric equipment process, after the fibers are mixed and opened, they can be fed into the feeding system. The selection of the feeding system should be adapted to the fiber type and the form of the web forming machine. Generally, trough-type feeding machines are used for fine denier fibers with a length of less than 60mm, while longer fibers or coarse denier fibers should use a feeding box with a vibrating trough—a pneumatic vibrating feeding box. The pneumatic vibrating feeding box, which is the focus of this project, has been developed and put into normal production. 2 Introduction and Control Requirements of Pneumatic Vibrating Feeding Box 2.1 Vibrating Feeding Box The pneumatic vibrating feeding box is an important process equipment between the opening and cleaning system and the carding system, as shown in Figure 1. The raw material enters the feeding box from the upper conveying pipe. By controlling the airflow pressure in the upper and lower boxes, a continuous and balanced feeding rate is ensured. At the same time, through the vibration of the vibrating plate, the feeding box forms a uniform cotton slick, which is output from the lower part of the feeding box and fed into the next web forming machine. As far as web forming machine is concerned, the balanced and stable output of cotton by the cotton feeding system is crucial to the quality of the web (weight per unit area and unevenness of long and short segments, etc.). [align=center][img=397,458]http://www.ca800.com/uploadfile/maga/plc2008-7/tt-1.jpg[/img] Figure 1 Pneumatic vibrating cotton feeding box[/align] 2.2 Design requirements It is required to establish a complete automatic control system, use advanced automation technology and process parameters to monitor and automatically adjust the cotton feeding box in real time, so that the equipment and process production are kept in the optimal operating state and the operating efficiency of the equipment is improved. The main points include the following: (1) PID and continuous feeding automatic control system, by setting appropriate process parameters such as: upper and lower box pressure, upper and lower limit pressure alarm and PID proportional coefficient p and integral coefficient i, the feeding speed is continuously guaranteed, so that the upper and lower box pressure is kept constant. (2) High-speed counting: The PLC uses special high-speed counting points to monitor the speed of the hand roller in real time, so as to make appropriate treatment in time before the raw material blockage occurs. (3) Real-time monitoring of the operating status of many process parameters and equipment, such as monitoring the material level of the cotton storage box, so as to ensure the stability of the pressure in the cotton feeding box; real-time monitoring of the pressure of the upper and lower boxes, so as to deal with the problem in time when the cotton is stuck or the cotton supply is insufficient, and to ensure the continuity and stability of production. (4) Establish a centralized control system, and issue centralized start and stop commands through the computer to quickly and accurately complete the automatic start or stop of the production equipment, and to effectively interlock and protect all equipment. (5) Setting and implementation of MPI communication: Communication problems can be solved simply and quickly through communication settings. 3 Technical solutions and implementation methods Siemens S7-200CN series PLC is selected according to the control requirements and the actual number of control points required. CPU224 main unit plus EM223 extended I/O unit, and Siemens TP170B touch screen is selected for the human machine interface to achieve a high configuration cost performance. Except for two reserved points, all other PLC points are fully utilized in the design. The TP170B is a monochrome 5.7" screen, which saves costs and can intuitively display the required work screen content with both graphics and text. The specific control principle is shown in Figure 2. In engineering practice, the most widely used regulator control law is PID control or PID regulation, which is the most effective control algorithm for common weakly coupled single-loop low-order feedback systems. The pressure setpoints of the upper and lower boxes of the cotton feeding box are determined by the process. The pressure values ​​of the upper and lower boxes are set according to different raw materials and output requirements, and the PI algorithm is selected. In actual debugging, an empirical value k1 and k2 are first roughly set through the human-machine interface, and then the parameter values ​​are modified according to the adjustment effect. At the same time, the feeding speed value can be adjusted by PI to achieve continuous cotton feeding. The fluctuation of continuous cotton feeding is vividly represented by a bar graph in the interface, as shown in Figure 3. [align=center][img=397,248]http://www.ca800.com/uploadfile/maga/plc2008-7/tt-2.jpg[/img] Figure 2 System Control Principle Block Diagram [img=567,408]http://www.ca800.com/uploadfile/maga/plc2008-7/tt-3.jpg[/img] Figure 3 Continuous Cotton Glue Feeding Diagram[/align] 3.1 Real-time Monitoring of Beater Roller Speed ​​The speed of the beater roller is monitored in real time using a special high-speed counting point of the PLC, so as to take appropriate measures in time before the raw material blockage occurs. Utilizing the dedicated high-speed counting points of the S7-200 CPU224, there are six independent high-speed counters (100kHz). HSC0-HSC5 require defining the counter and its mode before their dynamic parameters can be programmed. Each high-speed counter has a control byte. This program uses SMB37 as an example; for SMB37.7-SMB37.0D7-D0, 11001000 is converted to hexadecimal as 16#C8, using HSC0, mode0, corresponding to the high-speed counting point i0.0. A counting device is installed on the machine body, emitting one pulse per revolution. The number of pulses per second is assigned to VD5000, simultaneously resetting HSC0 once. VD5000 is multiplied by 60 to convert the counting unit to rpm/min (see attached table). [img=402,87]http://www.ca800.com/uploadfile/maga/plc2008-7/tt-b1.jpg[/img] Program Listing: main network 10 ld sm0.5 eu lps movd hc0, vd5000 aeno *d +60, vd5000 lpp hsc 0 subrutine network 1 ld sm0.0 // Enable counter; movb 16#c8, smb37 // Update current value, do not update preset value, set counting direction to increment; // Set start and reset to high level; // Set to 1× mode; hdef 0, 0 movd +0, smd38 // Clear current value of hsc0; hsc 0 // Program hsc0; 3.2 A centralized control and real-time process parameter monitoring system is established. The control panel features jog, automatic, and linkage selection switches. In jog mode, individual motors can be started and stopped; in automatic mode, individual machines can be started; and in linkage mode, the system is centrally started and stopped, simultaneously issuing associated interlock start/stop signals, interlock alarm signals, and emergency stop signals to upstream and downstream connected equipment. Centralized start follows process requirements, starting the fan first, then the individual machine actuators, and finally the individual machine feeders; centralized stop follows the reverse sequence. Communication scheme settings: communication between the PC and the S7-200 PLC follows the PC/PPI protocol, while communication between the HMI and the PLC uses MPI. [align=center][img=510,357]http://www.ca800.com/uploadfile/maga/plc2008-7/tt-4.jpg[/img] Figure 4 Process Parameter Screen[/align] On the TP170B interface, there are manual screen, automatic screen, alarm screen, password management screen and parameter setting screen. In particular, there is a screen in the automatic screen that displays the normal working screen, as shown in Figure 4 below, which displays in real time: (1) The working status (0 or 1), rotation direction and speed (hz or rpm or m/min) of each roller; (2) The photoelectric switch controls the material level. The photoelectric blocking light dims and the exposed light brightens; (3) The real-time pressure value of the upper and lower boxes, in Pa. This allows users to monitor equipment operation in real time using only this one screen during normal operation. If an alarm is detected, the interface automatically displays the alarm screen and information for timely troubleshooting. Simultaneously, an alarm bell sounds, with different ringtones programmed for different alarm types (stopping the equipment or not stopping it), facilitating fault identification and troubleshooting by on-site operators. 4. Conclusion : The S7-200CN series is an economical, small, high-performance PLC with a compact structure and extremely high cost-effectiveness. Its powerful structured programming language provides strong engineering advantages. This system operates stably and reliably. Other process sections in the project, such as the opening machine, roughing and finishing opening machines, large-warehouse cotton blending machine, cotton storage box, cotton feeding box, and some needle punching machines and lap forming machines, are all using the S7-200CN control system. In future applications, we plan to use the S7-200CN more extensively and deeply to win over users with even better cost-effectiveness.