DETECTION OF LIFE OF PROCESS UNIT

摘要

PURPOSE:To stably detect the life of a process unit with high reliability by judging whether the life of the process unit runs out or not in accordance with a sensor output before the prescribed time elapses after the start of driving of a developing roller upon receipt of the output of a toner concn. sensor. CONSTITUTION:Whether the output of the sensor 65 for detecting the concn. of the toner in a developing device exceeds the prescribed level or not is judged at least before the prescribed time elapses after the start of the driving of the developing roller 14 in the developing device upon receipt of the output of said sensor 65. The operation is shifted to an ordinary image forming operation when the prescribed level or below is attained. Decision is made that the life of the process unit 3 runs out when the output of the sensor 65 exceeds the prescribed level at the point of the time when the prescribed time elapses without attaining the prescribed level or below. The signal for displaying the life is then outputted. The life of the process unit is thereby stably detected without requiring a special device and time. The image formation of always high quality is thus assured and the generation of a trouble such as carrier carry-over is decreased.