Flatbed imaging is the best solution for aluminum substrates. It is easier to plate and unload the plates on the platesetter in a platform manner. However, it is extremely difficult to perform laser exposure on the platform equipment because when a laser is to be guided through the flat surface, a single beam needs to be rotated around the center point of a polygonal mirror. This polygon mirror reflects the laser beam from a diode or gas laser onto the plate. The advantage of the platform type is that the mechanical structure is simple and stable, the scanning speed is high, the price is relatively cheap, the upper and lower versions are simple and convenient, and can support a variety of punching specifications at the same time, using a single beam laser head. The disadvantage is that it has a large area and is not suitable for large format.
Exposure is the use of the photosensitive drum in the dark when the resistance is large, into the insulator; in the bright place, the resistance is small, the characteristics of the conductor, the photosensitive drum is filled with the light image exposure, use right illumination area (original reflective production points) The surface charge disappears due to the discharge; the area where the light is not irradiated (line and ink portions of the original) is retained, and a process of forming an electrostatic latent image in which the surface potential fluctuates with the brightness and darkness of the image is formed on the photosensitive drum. When the exposure is performed, after the original image is irradiated with light, the image light signal is projected onto the surface of the photosensitive drum through the optical imaging system. The portion of the light guide layer irradiated with light is called a "light area," and there is no natural light "dark area" illuminated by the light. In the bright area, the photoconductive layer generates electron-hole pairs, ie, photogenerated carriers are generated, so that the resistivity of the photoconductive layer is rapidly reduced, and the insulator becomes a good conductor and assumes a conductive state, so that the potential of the photosensitive drum surface is due to the surface of the photoconductive layer. The neutralization of charge and the reverse polarity charge at the interface quickly decays. In the dark area, the photoconductive layer is still in an insulated state, so that the photoconductor surface potential remains substantially unchanged. The level of the electrostatic potential on the surface of the photosensitive drum differs depending on the shade of the original image. The surface potential of the portion corresponding to the dark image on the photosensitive drum is high, and the surface potential of the light portion of the image is low. In this way, an electrostatic latent image with surface potential fluctuation corresponding to the shade of the original image is formed on the surface of the photosensitive drum.