In order to ensure the lateral position of the printing material before entering the printing unit, the unit type flexo printing machine often adopts an automatic rectifying device, which can detect the deviation of the lateral position of a certain edge of the printing material and correct it in time, with an accuracy of ±0.5 mm. . Generally, photoelectric sensors are often used for opaque materials such as paper and aluminum foil, and ultrasonic sensors are used for transparent materials such as films. Once the printing material enters the printing area and the die-cut rewinding area, the horizontal position is stabilized, which is ensured by the processing and mounting precision of the machine itself and the parallelism between the rolls.