Flexo printing machine In order to keep the tape tension constant, a brake must be set on the coil and the necessary control of this brake must be performed. Most of the web flexographic printing machines use magnetic powder brakes, which can be achieved by controlling the excitation current.

①When the printing speed of the machine is constant, ensure that the tension of the tape is stable at the set number value.

②During machine startup and braking (that is, during acceleration and deceleration), the material belt can be prevented from being overloaded and released at will.

③ During the constant printing speed of the machine, with the continuous reduction of the size of the material roll, in order to keep the tension of the material belt constant, the braking torque is changed accordingly.

Generally speaking, the material roll is not perfectly round, and its winding force is not very uniform. These unfavorable factors of the material itself are generated rapidly and alternately during the printing process, and cannot be eliminated by randomly changing the magnitude of the braking torque. Therefore, on most of the more advanced web flexographic printing presses, a floating roller controlled by a cylinder is often installed. The control principle is: in the normal printing process, the tension of the running material belt is equal to the pressure of the compressed air of the cylinder, resulting in a balance position of the floating roller. Any slight change in tension will affect the extension length of the cylinder piston rod, thereby driving the rotation angle of the phase potentiometer, and changing the excitation current of the magnetic powder brake through the signal feedback of the control circuit, so that the coil braking force can be adjusted according to the material. Belt tension fluctuations are automatically and randomly adjusted. Thus, the first-stage tension control system is formed, which is a closed-loop negative feedback type.