The unwinding tension control system of ordinary special paper Composite Machine is composed of magnetic powder brake, motor and frequency converter, tension sensor, floating roller device and electrical control system. In the unwinding process, the tension remains constant as the winding diameter decreases.

　　In high-speed special paper Composite Machine, the combination of motor active unwinding coil and floating roller device is often used. This is because when the machine is running at high speed, when the winding diameter is small, even if the output of the magnetic powder brake is 0, the friction of the winding shaft, guide roller, gear, etc., will produce large damping, resulting in the tension higher than the set value; however, if the motor is used to unwind, the friction damping of the winding shaft, gear, guide roller, etc. can be compensated by the active unwinding of the motor. The floating roller can compensate the tension when the tension is unstable (such as roll change, film joint, uneven drawing, etc.).

　　The tension of the compound part is caused by the speed difference between the coating roller and the compound roller. The speed of compound roller is generally 0.05% - 0.1% faster than that of coating roll. By adjusting PID, the drying tension of intermediate part can be adjusted by changing the speed difference of compound roller and coating roller. Because the expansion and thickness of the actual substrate will affect the stability of the clamping force, it is impossible to obtain a completely stable tension. Due to the high temperature and drying section, the setting of tension should consider the influence of drying temperature. The speed of coating roller and compound roller should be controlled by PLC, so as to correct and stabilize the tension in time.