An image forming apparatus includes a developing device to contain a developer, the developer including a toner; a developer cartridge to supply the developer to the developing device; a toner concentration sensor to sense a toner concentration of the toner included in the developer contained in the developing device; and a controller. The controller controls, during a non-printing operation a sensor control voltage to adjust an output level of the toner concentration sensor, to control an output of the toner concentration sensor to satisfy a controlling condition, and detects an shape of the output of the toner concentration sensor after the controller controls the sensor control voltage to adjust the output level. The controller adjusts, during a printing operation, the output of the toner concentration sensor, based on the detected shape of the output of the toner concentration sensor, and adjusts supplying the developer from the developer cartridge to the developing device, according to the adjusted output of the toner concentration sensor, to control the toner concentration.

Disclosed is a developing device including a conveying screw and an inductance sensor. The inductance sensor includes a detector detecting magnetic permeability of the developer accommodated in a developing container and has such detection sensitivity that the detection sensitivity with which the detector detects magnetic permeability when a magnetic material is disposed at a position 1 mm away from the detector in a vertical direction is 10% or more of that when magnetic material is disposed at a position which is in contact with the detector. The conveying screw includes a rotary shaft; a blade which is spirally formed on an outer circumference of the rotary shaft; and a rib formed as to protrude outwardly from the outer circumference of the rotary shaft. The rib is disposed opposite the detector with respect to a conveying direction of the conveying screw. The rib is provided with a magnet.

An image forming device to and from which a developing unit in which a developer containing toner is filled is detachable and removable, comprises a hardware processor that: enables the developing unit to perform a stir operation of the developer filled in the developing unit as an initial operation of the developing unit; obtains a reference value of a toner density set in advance in time of a factory shipment of the developing unit at time the stir operation is performed; and compares a toner density received from the developing unit during the stir operation with the reference value to determine a stir condition of the developer.

An image forming apparatus includes a developer container, an agitator, a toner supply, a toner sensor, and a controller. The developer container contains a two-component developer that includes toner and carrier. The agitator stirs the two-component developer. The toner supply replenishes the developer container with additional toner. The toner sensor detects a toner density of the two-component developer in the developer container. The controller calibrates the toner sensor using the two-component developer. The controller compares a first detection value indicating a toner density at a first time with a second detection value indicating a toner density at a second time after a predetermined time period has elapsed since the first time. The controller issues a notification regarding a suitability of calibration based on a comparison result of the first detection value and the second detection value.

An image forming apparatus including a developing unit with a developing container configured to contain a developer including a toner and a carrier, and configured to develop the electrostatic latent image by using the developer in the developing container. A sensor, which is provided on an outer wall of the developing container, is configured to output a pulse signal that changes in frequency depending on a toner concentration of the developer in the developing container. A controller is provided to control supply of the toner to the developing unit by detecting the toner concentration based on the time required for the pulse number to reach a predetermined count number.

An image forming apparatus includes a rotatable image bearing member, a charging member, a rotatable developer carrying member, a developing voltage applying portion, a detecting portion for detecting a first current value and a second current value of currents flowing between the image bearing member and the developer carrying member, and a controller for controlling the applying portion. When a difference between the first current value and the second current value which are detected by the detecting portion exceeds a threshold in a state in which the image bearing member and the developer carrying member are rotated and the developing voltage is applied to the developer carrying member, the controller controls the AC voltage of the developing voltage applied to the developer carrying member.

An image forming apparatus includes: an image forming portion having an image carrying member, a charging device, an exposing device, and a developing device; a developing voltage power supply; a control portion; and an image density sensor. The developing device has a developer carrying member that carries two-component developer and a toner concentration sensor. The control portion senses toner concentration during calibration or during first image formation after calibration for correcting image density based on the sensing result from the image density sensor. If the difference Vtarget−V between the output value V of the toner concentration sensor actually sensed and a target value Vtarget of the toner concentration sensor to be observed when the toner concentration equals a reference concentration is equal to or larger than a predetermined value, the control portion performs calibration again when the amount of toner consumed after calibration reaches a predetermined threshold value.

An example method of controlling the concentration of a printing substance is provided. A layer of printing substance is received on a printing substance receiving member, and a parameter indicative of a current concentration of non-volatile material in the printing substance is measured. The current concentration is compared to a predetermined target concentration. Based on the comparison, a concentration adjustment is determined. The adjustment comprises at least one of (i) an adjustment to a pressure applied to the printing substance receiving member by a pressurizing member, and (ii) an adjustment to a voltage applied to the pressurizing member. The concentration of the printing substance is controlled based on the determination.

An image forming device to and from which a developing unit in which a developer containing toner is filled is detachable and removable, comprises a hardware processor that: enables the developing unit to perform a stir operation of the developer filled in the developing unit as an initial operation of the developing unit; obtains a reference value of a toner density set in advance in time of a factory shipment of the developing unit at time the stir operation is performed; and compares a toner density received from the developing unit during the stir operation with the reference value to determine a stir condition of the developer.

An image forming apparatus includes an image forming section, a controller, and storage. The storage stores therein a coverage rate of a past image specified by a past print job. The controller includes a determining section and a first calculating section. When a new print job is received, the determining section determines whether or not to perform a running-in operation by comparing a coverage rate of a new image specified by the new print job to the coverage rate of the past image stored in the storage. The first calculating section calculates an amount of toner to be supplied from a developing section to a photosensitive drum based on the coverage rate of the new image. The running-in operation is to supply the toner in the amount calculated by the first calculating section from the developing section to the photosensitive drum before the new image is formed on a sheet.