Developer unit for electrostatic copier - monitors toner conc. in feed path to developer roller to control toner topping cup

摘要

The developer unit uses a developer roller (5) for application of a mixture of toner and carrier particules to the surface of the imaging drum (100), carrying a latent electrostatic image. The particle mixture is fed to the developer roller (5) via a transport device (16) with a second and third transport device (17, 18) for sucessively feeding the toner mixture. A sensor (AT) provides a toner cone signal, dependent on the ratio of toner contained in the mixture in the circulation path between the second and first transport devices (17, 16), to control a toner topping up deive (20). The latter supplies the toner particles to the circulation path between the third and second transport devices (18, 17). Pref. the toner topping up (20-22) is controlled using a CPU by comparing the obtained toner conc. signal with a threshold value. ADVANTAGE - Maintains required toner conc. level for uniform copy quality.