Automatic image concentration control unit null

摘要

PURPOSE:To always obtain excellent pictures, by determining an optimum developing bias voltage at every selected one of two developing devices. CONSTITUTION:The reference light quantity of the reflecting light from a reference reflecting plate 6 and the light quantity of the reflecting light from an original 5 are detected by a photosensor 17 and respectively converted into digital signals by an AD converter 41. The digital signals are inputted to a CPU 42. The CPU 42 approximately calculates the ground density (mean reflectivity) of the surface of the original from the ratio of the reflecting light quantity of the original to the reference light quantity. If the sensor output detects the A-area, namely, the output of about =80% in the man reflectivity at the time of determining a developing bias voltage V, the CPU 42 judges that the area A is the most approximate to the reflecting density of the ground and fixes the developing bias voltage at the normal central developing bias level of about 300V. When the sensor output detects the B-area, namely, about 60-80% in mean reflectivity, the CPU 42 controls the developing bias voltage so that the optimum one can be applied in accordance with the sensor output.