Toner cartridge Figure 19. Toner cartridge A major portion of the image formation system is contained in the cartridge as shown in figure 19. The toner cartridge is the “heart” of the image formation system. It houses the cleaning, conditioning, and developing steps of the process. The toner cartridge contains the photosensitive drum, primary charging roller, developing roller, toner cavity, and cleaner blade. Including these components that wear, degrade, or are consumed in the replaceable toner cartridge eliminates the need for a service call when replacement is required. EN Chapter 5 Theory of operation 109