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 includes a photosensitive drum, a developing section, a voltage applicator, a detector, a calculating section, and an evaluating section. The detector detects values of first and second currents. The first current flows between the photosensitive drum and the developing section during formation of an electrostatic latent image. The second current flows between the photosensitive drum and the developing section when the electrostatic latent image is not being formed. The calculating section calculates a toner charge-to-mass ratio. The evaluating section evaluates reliability of a calculation result of the toner charge-to-mass ratio by comparing the second current value to a reference value. The reference value is of a reference current flowing between the photosensitive drum and the developing section when the electrostatic latent image is not being formed, and indicates a current value detected after adjustment to at least one of the photosensitive drum and the developing section.

An image forming apparatus includes a plurality of image forming portions, an intermediate transfer belt, a belt displacement detector, an attraction force changer, and a controller. The intermediate transfer belt is an endless belt wound around drive and driven rollers. The belt displacement detector detects displacement of the intermediate transfer belt in a rotation axis direction of the driven roller. The attraction force changer is operable to change electrostatic attraction force of the driven roller with respect to the intermediate transfer belt exerted on each of opposite end sides of the driven roller in the rotation axis direction thereof. When the belt displacement detector detects displacement of the intermediate transfer belt, the controller makes the attraction force changer increase the electrostatic attraction force of the driven roller with respect to the intermediate transfer belt exerted on a side opposite to a side toward which the displacement has taken place.

An image forming apparatus includes a power supply board, a driver board, and an engine control board. The driver board includes a plurality of switching elements each configured to supply and shut off a power supply for each of a plurality of distributed power supply voltages supplied from the power supply board. The plurality of switching elements includes a first switching element, to which the power supply voltage is to be applied from the power supply board, and a second switching element, to which the power supply voltage output from the first switching element is to be applied in a distributed manner. The engine control board is configured to performs failure diagnosis of the first switching element when the image forming apparatus is activated, and performs failure diagnosis of the second switching element in a case where an abnormality has occurred in any one of a plurality of loads.

A color imaging device includes a plurality of developer rolls with a common operating point, such as a common operating voltage. To determine the operating point, an acceptable range of color density is determined for each toner, the range being lighter and darker than an optimum color density for that toner. A search range is devised such that values within the range are examined relative to deviations from the optimum color density per each toner. The common operating point is selected as that having the lowest deviation per all toners. Also, if the common operating point corresponds to a color density darker than the acceptable range of color density for any toner, additional halftoning occurs compared to traditional halftoning, such as for continuous tones or solids. In this way, four color developer rolls can be operated from a single power supply, yet still provide acceptable color images.

An image forming apparatus includes an image bearing member, a developing unit to develop an electrostatic latent image formed on the image bearing member with toner, and a detachable toner container in which toner for supplying to the developing unit is contained. A measuring unit measures information relating to an amount of toner in the developing unit, and a determination unit determines an amount of toner in the developing unit based on the measured information. In a case where the determination unit determines that the toner container is empty, a supply operation for supplying toner from the toner container to the developing unit is performed and the measuring unit measures the information relating to an amount of toner in the toner container after the supply operation is performed, and in a case where the information relating to an amount of toner in the toner container measured after the supply operation is performed is within a measurement error range, the determination unit determines that the toner container is empty.

In the first charge amount acquisition operation, based on density of a plurality of toner images for measurement or based on a direct component of a developing current at the time of forming the plurality of toner images in addition to the density of the plurality of toner images for measurement, the charge amount acquisition section acquires a first toner charge amount that is a charge amount of toner included in the toner image for measurement. In the second charge amount acquisition operation, based on the toner density detected at the time of image formation and a relationship between the first toner charge amount and the toner density detected in the first charge amount acquisition operation, the charge amount acquisition section acquires a second toner charge amount that is a charge amount of the toner in the development device.

When, in a state where a developer borne by a developer bearing member is sandwiched by an opposing portion of an image bearing member and the developer bearing member, C denotes capacitance between the image bearing member and the developer bearing member, V denotes a development contrast, Q/S denotes a charge amount per unit area of the developer borne by the developer bearing member, and v denotes a peripheral velocity ratio which is a ratio of a peripheral velocity of the developer bearing member to a peripheral velocity of the image bearing member, a first peripheral velocity ratio is set so that |Q/Sv||CV| is satisfied, and a second peripheral velocity ratio which is larger than the first peripheral velocity ratio is set so that |Q/Sv|>|CV| is satisfied.

A detection apparatus has an alternating-current voltage input unit and a generation circuit. The generation circuit generates a superimposition signal in which information indicating a timing of a zero cross in an alternating-current voltage inputted into the input unit and information indicating a voltage level of the alternating-current voltage are superimposed.

An image forming apparatus includes an image transfer belt; a first transfer member; a second transfer member opposed to the first transfer member with the belt therebetween; an applying device for applying a voltage to at least one of the first and second transfer members; and a controller for controlling the applying device to apply to the at least one transfer member a voltage having the same polarity as a regular polarity of toner and a voltage of the opposite polarity to the first transfer member in a cleaning operation. The controller changes a number of image formations to be carried out from a cleaning operation to a next cleaning operation depending on the kind of the sheet. The number controlled by the controller is different depending on the kind of the sheets in a continuous printing job.