| 摘要 |
PROBLEM TO BE SOLVED: To prevent the erroneous recognition of developer amount from being caused by the fault of a contact, for applying developing bias to an electrode pair 60. SOLUTION: The value of detection voltage V12a by detecting toner residual amount is sampled on a fixed condition in an image printing period by a control circuit 407, and its mean value α is calculated and compared with a previously stored compared value β. When a difference ΔV between them is equal to or above a reference value Ref, the circuit 407 discriminates that the fault of the contact is occurred and warns a user through a warning means 412. When the value of ΔV is smaller than the reference value Ref, the circuit 407 discriminates that the contact is in a good state and controls to perform ordinary printing operation. Thereafter, the mean value α is stored in the CPU 407 as the compared value β, and is utilized for next sequence. |
