IMAGE FORMING APPARATUS THAT CORRECTS DEVELOPING BIAS VOLTAGE

摘要

An image forming apparatus that reduces density irregularity caused by SD gap variation. A developing bias voltage for forming a developing electric field between a photosensitive drum and a developing sleeve is applied to the developing sleeve. Current values of an AC component of the developing bias voltage are detected while changing the acquisition timing for each rotation of the photosensitive drum, and detected current values are interpolated and averaged at each same phase with reference to the time of detection by the drum home position sensor HP. From the averaged current values of the variation curves of the developing bias AC current over the plurality of rotations, a correction table for an output control signal of the developing bias voltage is created. The developing bias voltage is controlled based on the created correction table.

主权项

1. An image forming apparatus comprising:
a photosensitive drum configured to be driven for rotation; a developing roller configured to carry toner for developing an electrostatic latent image formed on said photosensitive drum, said developing roller being disposed in a manner opposed to said photosensitive drum and driven for rotation; an application unit configured to apply a developing bias voltage for forming a developing electric field between said photosensitive drum and said developing roller, to said developing roller, formation of the developing electric field causing the electrostatic latent image to be developed with toner carried by said developing roller; a current value detection unit configured to detect a current value corresponding to an electrostatic capacitance between said photosensitive drum and said developing roller; a phase detection unit configured to detect a rotation phase of said photosensitive drum; a storage unit configured to perform operation for sampling a current value detected by said current value detection unit at a fixed time interval, in synchronism with a rotation phase detected by said phase detection unit, a plurality of times while changing detection start timing, and store a current value sampled each of the plurality of times, into a storage section; an interpolated current value calculation unit configured to interpolate current values sampled by said storage unit at each of the plurality of times of sampling to thereby calculate interpolated current values over one rotation of said photosensitive drum, for each time; an average value calculation unit configured to calculate an average value of ones at each same phase of the interpolated current values calculated by said interpolated current value calculation unit over one rotation of said photosensitive drum, for each time; a creation unit configured to create a correction table for correcting the developing bias voltage to be applied by said application unit, using the average value calculated by said average value calculation unit; and an image forming unit configured to control the developing bias voltage based on the correction table created by said creation unit.