An image forming apparatus has a bias controller. The bias controller varies both a charging alternating-current frequency, which is the frequency of a charging alternating-current voltage, and a developing alternating-current frequency, which is the frequency of the developing alternating-current voltage. When the region of the charging and developing alternating-current frequencies in which interference fringes appear in a developed image due to interference between the charging and developing alternating-current frequencies is taken as a variation region and the variation speeds of the charging and developing alternating-current frequencies in the variation region are taken as a first and a second variation speed respectively, the bias controller varies the charging and developing alternating-current frequencies such that one of the first and second variation speeds is a positive-number multiple of the other.

An imaging device includes a photoconductive drum charged by a charge roll and opposed by developer roll. The developer roll adds toner to the drum to develop a latent image on the drum for transfer to media or an intermediate transfer member at a transfer roll. One or more high voltage power supplies communicate with a controller to set voltages on the rolls. During times of non-imaging, but rotation of the drum, the charge roll charges the drum to less than a Paschen breakdown voltage of the drum. A voltage of the transfer roll is determined that corresponds to a temperature and relative humidity of an operating environment of the imaging device and the developer roll is charged based thereon. The charge of the transfer roll is set close to the charge of the drum, but higher in magnitude. A laser may also discharge the drum.

An image forming apparatus includes a photoconductor, a charging roller configured to charge the photoconductor, and a self-excited oscillation circuit. The image forming apparatus includes a transformer including a primary coil and a secondary coil, the transformer being configured to produce, at the secondary coil, a voltage applied to the charging roller, in accordance with the primary coil being driven by the self-excited oscillation circuit. The image forming apparatus includes a controller configured to control, at start-up of the self-excited oscillation circuit, the self-excited oscillation circuit to allow an amount of a current flowing through the primary coil to be larger than an amount of a current flowing from the photoconductor through the secondary coil, via the charging roller.

An imaging device includes a photoconductive drum charged by a charge roll and opposed by developer roll. The developer roll adds toner to the drum to develop a latent image on the drum for transfer to media. One or more high voltage power supplies communicate with a controller to set voltages on the rolls. The controller determines whether imaging of the media is to occur at a time when the drum is rotating. If not, a laser beam discharges the drum and the voltage on the charge roll is decreased to reduce the charge on the drum, but the controller maintains the voltage differential between the drum and the developer roll.

In an image forming apparatus, a bias controller varies one, while keeping the other fixed, of a charging alternating-current frequency, which is the frequency of the charging alternating-current voltage, and a developing alternating-current frequency, which is the frequency of the developing alternating-current voltage. Specifically, in a case where interference fringes appear in a developed image due to interference between the charging and developing alternating-current frequencies, when the recognizable minimum pitch of the interference fringes is A.sub.1 (mm), the width of the variation region of the other frequency is B.sub.1 (Hz), the rotation speed of an image carrying member is C.sub.1 (mm/sec), and the variation speed of the other frequency in the variation region is D.sub.1 (Hz/sec), the bias controller varies the other frequency at a variation speed D.sub.1 that fulfills |D.sub.1|>B.sub.1/(A.sub.1/C.sub.1).

An image forming apparatus has a bias controller. The bias controller varies both a charging alternating-current frequency, which is the frequency of a charging alternating-current voltage, and a developing alternating-current frequency, which is the frequency of the developing alternating-current voltage. When the region of the charging and developing alternating-current frequencies in which interference fringes appear in a developed image due to interference between the charging and developing alternating-current frequencies is taken as a variation region and the variation speeds of the charging and developing alternating-current frequencies in the variation region are taken as a first and a second variation speed respectively, the bias controller varies the charging and developing alternating-current frequencies such that one of the first and second variation speeds is a positive-number multiple of the other.

An image forming apparatus includes a photoconductor, a charging roller configured to charge the photoconductor, and a self-excited oscillation circuit. The image forming apparatus includes a transformer including a primary coil and a secondary coil, the transformer being configured to produce, at the secondary coil, a voltage applied to the charging roller, in accordance with the primary coil being driven by the self-excited oscillation circuit. The image forming apparatus includes a controller configured to control, at start-up of the self-excited oscillation circuit, the self-excited oscillation circuit to allow an amount of a current flowing through the primary coil to be larger than an amount of a current flowing from the photoconductor through the secondary coil, via the charging roller.

An image forming apparatus has a photosensitive member, a plurality of corona chargers configured to charge the photosensitive member by corona discharge, a plurality of charge output circuits configured to output a charging voltage being applied to each of the corona chargers, a plurality of abnormal discharge detection circuits configured to output an abnormal discharge detection signal according to abnormal discharge occurring in each of the corona chargers, and a controller configured to have a common input port connected to the abnormal discharge detection circuits wherein the abnormal discharge detection signal output from each of the abnormal discharge detection circuits is input to the controller through the common input port. Each of the abnormal discharge detection circuits is connected to a corresponding one circuit out of the charge output circuits.

An image forming apparatus provides a configuration capable of suppressing an increase in the resistance of an intermediate transfer belt. The image forming apparatus includes an electrification unit for electrifying an intermediate transfer belt to suppress an increase in resistance of the intermediate transfer belt.

In an example, a method of controlling voltage applied to a print blanket within a printing device includes printing a print job. During the printing, a null cycle trigger is received. In response to the trigger, a print blanket bias voltage is reduced from a print bias level to a null bias level.