How does the development of photography record the micro-world?

Development is the process of converting electrostatic latent image on photosensitive drum into visible toner image with charged toner.

Development includes positive development and reverse development.

In the process of forward development, the polarity of the charge carried by the developing toner is opposite to that of the electrostatic latent image on the surface of the photosensitive drum. When developing, the toner is adsorbed on the photosensitive drum under the action of electrostatic latent image on the surface of the photosensitive drum. The higher the electrostatic latent image potential, the stronger the ability to adsorb toner; The lower the electrostatic latent image potential, the weaker the ability to absorb toner. Corresponding to the difference of electrostatic latent image potential (charge), the amount of adsorbed toner is also different.

In reverse development, the photosensitive drum and toner have the same charge polarity. When developing, the toner is attracted to the exposed area of the photosensitive drum by the electric field between the photosensitive drum and the developing roller. Wherein the potential of the exposed portion is lower than the surface potential of the developing roller and lower than the potential of the unexposed portion of the photosensitive drum.

In this way, the invisible electrostatic latent image on the surface of the photosensitive drum becomes a visible toner image with different gray levels consistent with the original tone. In an electrostatic copier, the charging of toner is usually obtained by friction between the toner and the carrier. After rubbing, the polarity of the ribbon is opposite to that of the carrier (in a one-component developer, there is only toner, and the toner is charged by rubbing with the powder discharging knife).