What mechanism is responsible for applying the positive charge to attract toner in a laser printer system?

The transfer roller is responsible for applying a positive charge to attract toner in a laser printer system. During the laser printing process, the imaging drum is first charged and then exposed to a laser, creating a latent image of the document. This image is negatively charged where the laser has written. The transfer roller, which carries a positive charge, then passes through the toner, which has a negative charge. Since opposite charges attract, the positively charged transfer roller attracts the negatively charged toner, effectively transferring the toner from the drum onto the paper.

This process is crucial for achieving a clean and precise transfer of the toner to the print medium. The transfer roller's role is vital to ensure that the toner adheres correctly to the paper before it undergoes fusing. In contrast, the fuser assembly is responsible for permanently bonding the toner to the paper using heat and pressure after the toner has been transferred, while the pickup rollers are involved in feeding the paper into the printer. The imaging drum handles the creation of the image, but it does not attract toner; instead, it provides a surface for toner to adhere once it is transferred.