As a direct participant in the whole transfer process of the laser printer, the magnetic roller plays two roles: absorbing toner particles and charging toner; The area with scratches on the surface of the magnetic roller is not sticky, so the relevant area of the printed matter will also appear blank. In addition, when the magnetic roller has printed for three cycles, an aging layer has appeared on its surface, which will also affect the charging effect of the magnetic roller on the toner, thus directly affecting the amount of toner transferred from the magnetic roller to the surface of the photoreceptor drum, and also directly affecting the blackness of the print.

Developing magnetic roller is an important component for carrying toner. The permanent magnetic core is non rotating, and its role is to use magnetism to adsorb toner to the surface of the magnetic roller. A rough graphite layer is sprayed on the surface of the magnetic roller, which makes it form an electronic hole with the toner scraper to facilitate the toner transmission. When the magnetic roller carrying toner rotates out of the scraper position, the toner on the surface of the magnetic roller is charged. In addition, the magnetic field forces it to form a "magnetic spike", that is, "toner fog". Bias pressure is applied to the magnetic roller jacket, so that the magnetic spikes are orderly arranged. The function of the "spacer" of the magnetic roll is to control the effective suction distance between the magnetic spike on the surface of the magnetic roll and the photosensitive drum, which is conducive to improving the "beat imaging" of the toner.