Abstract: An image forming apparatus includes a developer unit to store two-component developer which includes toner and carrier and develop an electrostatic latent image formed on the image carrier, a toner concentration detector to detect toner concentration in the developer unit, a toner supply unit to supply toner to the developer unit, and a controller to control toner supply amount by controlling the toner supply unit by comparing an output value of the toner concentration detector with a reference value stored in a memory and correcting difference between output values of the toner concentration detector at two or more process linear velocities in accordance with the toner concentration in the developer unit. A compensation amount for correcting difference between output values of the toner concentration detector that differ depending on the process linear velocity is adjustable in accordance with the toner concentration in the development unit.

Abstract: In a device and a method for measuring the concentration of liquid toner, for accurate detection of the concentration of liquid toner, provided are a rotary roller; a toner adhesion portion along the outer circumference of the roller, the toner adhesion portion being configured to hold liquid toner T; a sensor for detecting the concentration of the liquid toner based on the amount of light that is reflected from the liquid toner T adhering at a predetermined thickness to the toner adhesion portion; and a scraping blade for scraping off the liquid toner from the toner adhesion portion after the detection by the sensor, and apply voltage of the same polarity as that of the liquid toner to the toner adhesion portion when the liquid toner is scraped off by the scraping blade.

Abstract: An image forming apparatus and a toner replenishment control method according to the present invention are configured such that a concentration of toner in a developer detected by a toner concentration detection sensor is measured and the measured toner concentration value is stored. These are configured such that regions of image data corresponding to an electrostatic latent image on an image bearing member to be developed by the developer are specified and an amount of toner to be consumed in the developer is predicted based on the image data of the specified regions, then a post-development concentration value of toner in the developer is estimated based on the measured toner concentration value and the predicted toner consumption amount, and control of replenishment of toner to the developer is carried out based on the estimated post-development toner concentration value and a toner setting concentration value that has been set in advance.

Abstract: A solid-concentration measuring apparatus includes an ultrasonic transmitter, an ultrasonic receiver, and a response-time integrator. The ultrasonic transmitter transmits a single-pulse ultrasonic wave to a liquid toner. The ultrasonic receiver receives the single-pulse ultrasonic wave. The ultrasonic transmitter transmits again a single-pulse ultrasonic wave after a predetermined time has passed from when the ultrasonic receiver receives the single-pulse ultrasonic wave. The response-time integrator measures a response time from transmission to reception of each single-pulse ultrasonic wave, and integrates the response time with respect to each set of N pulses (N>1). A solid concentration of the liquid toner is calculated based on the integrated response time.

Abstract: A black developer is conveyed in a first conveyance chamber in a rotation axis direction while agitating with rotation of a first screw member. A black-toner-concentration detecting sensor detects a toner concentration of the black developer by having contact with the black developer conveyed inside the first conveyance chamber. An average of peak amounts of a pressing force on the black developer, which is conveyed inside the first conveyance chamber by the first screw member, with respect to the black toner-concentration detecting sensor is set within a range of 9.8 15 [N/m2] to 9.8 100 [N/m2].

Abstract: An image forming apparatus includes an image carrier on which an electrostatic latent image is formed, a rotary developing device having N developer carriers, where N defines a total number of developer carriers, the N developer carriers carrying developers to develop the electrostatic latent image, and the rotary developing device moves the N developer carriers to a development position opposite to the image carrier, and a toner concentration sensor that measures toner concentrations of the developers carried in the developer carriers. A measurement position of the toner concentration sensor is set on a second virtual straight line with the second virtual straight line having a first angle or an angle that is double the first angle toward a first virtual straight line on a rotation orbit of the rotary device, and the first virtual straight line connects a rotation center of the rotary developing device and the development position.

Abstract: An image forming apparatus in which a predetermined image density can be obtained by correcting a toner density control target value without consuming toner. The toner density of the developer is controlled so that an output value Vt of a magnetic permeability sensor approaches a target output value Vtref. In addition, the target output value Vtref is corrected in accordance with image coverage history information of output images transferred to a transfer paper and image coverage ratio history information of output images determined from the image coverage thereof and the size of the transfer paper. This history information comprises, for example, a cumulative average value of the image coverage or the image coverage ratio per transfer paper. It may also comprise a moving average value of the image coverage or the image coverage ratio per transfer material.

Abstract: An image formation apparatus including a toner cartridge for holding toner, an image supporting unit, on which an electrostatic latent image corresponding to a toner image is formed, a toner development unit for developing the latent image into the toner image with the toner, a detecting unit for detecting toner concentration of the toner image, and a control unit for controlling an amount of toner adhering to the latent image by adjusting a development bias voltage based on an output of the detecting unit. If control by the control unit based on the detection output of the detecting unit is insufficient, and consumption of the toner is out of a predetermined normal range, the control is carried out by estimating one of toner consumption amount and toner recovery amount in a direction that departs from the predetermined normal range.

Abstract: Provided are a method, system and program for checking and conditional processing of a print job printed with multiple transfer media. A print job indicates first print content to print using a first transfer medium and second print content to print using a second transfer medium. The first print content is printed onto a print medium with the first transfer medium. The printed first print content is read to determine whether the printed first print content satisfies a quality requirement. The second print content is printed onto the print medium with the second transfer medium in response to determining that the quality requirement is satisfied. Information is printed indicating an error on the print medium in response to determining that the print quality requirement is not satisfied.

Abstract: A pixel count section calculates a coverage rate corresponding to toner consumption. A control coefficient value setting section determines, based on the coverage rate, a stop threshold value representing reference concentration for toner replenishment and replenishment extension time. A magnetic permeability sensor measures permeability representing toner concentration in a housing portion. A toner concentration control section starts toner replenishment when an output value from the magnetic permeability sensor varies from a value less than a start threshold value to the start threshold value or above, and stops toner replenishment after lapse of replenishment extension time from the time at which an output value varied from a value greater than the stop threshold value to the stop threshold value.

Abstract: A differential sensitivity calculation portion calculates the differential sensitivity D of a toner concentration sensor, using an output voltage V1 and V2 of the toner concentration sensor when a toner chamber is in a state of toner concentration T1 and T2 at the time of initial operation of a printer, or at some other time. A toner replenishment control portion takes as input a current output voltage Vs output from the toner concentration sensor, calculates the toner concentration in the toner chamber using the output voltage Vs and the differential sensitivity D calculated by the differential sensitivity calculation portion, and outputs a control signal to a toner replenishment motor so as to maintain the toner concentration in the toner chamber at an appropriate concentration.

Abstract: A toner-concentration controller includes a controller configured to control a toner supply amount in accordance with a detection result of a toner-concentration of two-component toner, and a sensor unit configured to detect the toner-concentration of two-component toner. The sensor unit includes a correction mechanism to correct an output signal of the sensor unit by changing an external-input voltage, based on relationship data between an output voltage change of the sensor unit and a toner-concentration of unused developer, to control the toner supply amount when the toner-concentration of the two-component toner deviates a predetermined amount from the toner-concentration of the unused developer. The sensor unit is configured to detect the toner-concentration of the unused developer from unused two-component toner based on a change in the external-input voltage.

Abstract: An image-information acquiring unit acquires the image information divided at least in one of a main-scanning direction and a sub-scanning direction. A supply control unit calculates basic-supply patterns of a supply amount of toner and controls the supply amount at a supply point in a developing unit using a toner supply pattern combined with the basic-supply patterns that eliminate temporal variation in toner density of the developer, at the specific point, due to development of the latent image.

Abstract: An image forming apparatus is provided which is capable of forming higher-quality images by detecting a toner concentration with higher accuracy to attain appropriate toner supply and image density. A value obtained by adding a correction value based on a temperature, humidity, a print coverage, or the like to a developer concentration adjustment value is set as a control voltage value Vc which is to be inputted to a toner concentration sensor, and an output value of the toner concentration sensor is detected for each of process speeds. A difference between the output value detected and a value at reference process speed is calculated and based on the difference, a correction value is further calculated. Such another calculation of the correction value with use of the output value detected allows for highly accurate correction.

Abstract: A first developer container having a toner supplying opening is provided in a developing unit. A toner concentration sensor is arranged downstream of the toner supplying opening to detect toner concentration in developer. A supply controlling unit is provided to determine an excess or a shortage in the amount of supplied toner based on image information correspondingly to a detection result by the toner concentration sensor, and to correct the driving amount of a toner supplying unit that has been determined based on the image information correspondingly to the recognized excess or shortage in the amount of supplied toner.

Abstract: An image forming apparatus includes a latent image carrier, a developing unit to develop a latent image on the image carrier with developer including toner and carrier, a developer bearing member, a first detector to detect a toner adhesion amount per unit area of a toner image developed by the developing unit, a second detector to detect humidity, and a controller to calculate an index indicating toner chargeability of the carrier based on detection results of the toner adhesion amount obtained by the first detector and perform a given control process based on calculation results thereof and including a data storage unit to store an algorithm to correct the index to a specific value according to a specific humidity, based on detection results of the humidity obtained by the second detector. The controller corrects the index obtained based on the amount of toner adhesion based on the algorithm.

Abstract: An image forming apparatus 100 includes detection means 116 which detects an image characteristic of an image formed on an image bearing member 103; a first control means which controls a toner concentration in the developer, based on a detection result by the detection means, of an image characteristic of a first reference image for a first control for controlling the toner concentration in the developer; second control means which controls an image parameter, different from the toner concentration in the developer, thereby controlling an image density, based on a detection result by the detection means, of an image characteristic of a second reference image for a second control, different from the reference image for the first control; and correction means 231 which receives detection results of both image characteristics of the first and second reference images, and which, based on the detection result of the image characteristic of either of the reference images for the first and second controls, corrects

Abstract: An image forming apparatus including a latent image bearing member; a developing device configured to develop a latent image on the image bearing member with a two-component developer; a development potential forming device configured to form a development potential; a toner replenishing device configured to supply the toner to the developing device; a toner concentration detecting device configured to detect and output the concentration of the toner in the developer; a toner concentration controlling device configured to compare the toner concentration output with a toner concentration target to control the toner concentration; an information detecting device configured to obtain information to determine the replacement amount of the toner in the developing device in a predetermined period of time; and a development potential correcting device configured to adjust the development potential on the basis of the information obtained by the information detecting device.

Abstract: A control device executes toner concentration control that controls an operation of a developing device such that a value of detection output detected by a concentration detecting device falls within a predetermined range. Moreover, when controlling drive of a first driving device, which drives at least an image carrier, and drive of a second driving device, which drives at least a fuser device, the control device executes operation control that starts the drive of the first driving device before the drive of the second driving device.

Abstract: A digital color copier includes: a toner concentration storage which stores a detected toner concentration of each developer block of multiple developer blocks across an image forming width; a toner consumption predictor for predicting a first predicted toner consumption of toner consumed from developer of every developer block during a first circulation; a toner concentration estimator for estimating, for every developer block, a toner supply point estimate as the toner concentration at a point where toner is supplied, by subtracting the first predicted toner consumption from the associated detected toner concentration and setting up a toner supply target value of the toner to be supplied from a toner supply device to a developing device in accordance with the predicted toner consumption during a second circulation of the developer inside the developing device that follows the first circulation.

Abstract: An image forming apparatus includes an image carrier, a developing unit, a concentration sensor, a toner supplying unit, a developer supplying unit, an ejector, and a condition detector. The image carrier forms a latent image thereon. The developing unit develops the latent image formed on the image carrier with a two-component image developer including toner particles and carrier particles. The concentration sensor detects a toner ratio in the developing unit. The toner supplying unit supplies fresh toner particles to the developing unit. The developer supplying unit supplies fresh image developer to the developing unit. The ejector ejects the image developer to an outside of the developing unit. The condition detector detects a condition of the image developer used for an image forming operation to determine a supply amount of the image developer to supply to the developing unit. The condition includes a degradation level of the image developer.

Abstract: The developing apparatus, having stirring members for conveying and stirring developer-tank-contained developer and a developer holder, comprises a developer replenishing tank; a magnetic-type toner concentration detecting sensor; a trickle-type discharging mechanism; conveying state switching device for temporarily blocking the flow of the developer-tank-contained developer and for temporarily switching the circulating state of the developer-tank-contained developer to the staying state thereof; and a controller for controlling replenishment operation for replenishing the toner and the carrier for replenishment to the developer tank when the toner concentration is lower than a predetermined reference toner concentration, wherein the controller determines the amounts of the toner and the carrier to be replenished on the basis of the calculated toner concentration and the estimated amount of the developer.

Abstract: The developing apparatus, having stirring members for conveying and stirring developer-tank-contained developer and a developer holder, comprises a developer replenishing tank; a toner concentration detecting sensor; a trickle-type discharging mechanism; a developer amount estimating sensor; and a controller for controlling replenishment operation for replenishing the toner and the carrier for replenishment to the developer tank when the toner concentration is lower than a predetermined reference toner concentration, wherein the controller determines the amounts of the toner and the carrier to be replenished on the basis of the calculated toner concentration and the estimated amount of the developer.

Abstract: A plurality of chambers are adapted to accommodate a plurality of cartridges each containing toner to be used for printing. A mode changer is operable to change an operation mode of the printing apparatus in accordance with a combination of respective colors of toner in the cartridges accommodated in the chambers. A first detector is operable to detect a residual amount of toner in each of the cartridges. A second detector is operable to detect the respective colors of toner in the cartridges when the operation mode is changed. A controller is operable to generate an image data including a plurality of first identifiers each indicative of the residual amount of toner in one of the cartridges and a plurality of second identifiers each indicative of one of the colors of toner and associated with one of the first identifiers. A display is adapted to display the image data.

Abstract: The present disclosure provides for an imaging machine having an imaging member including a method for maintaining a toner concentration. The method for maintaining the toner concentration comprises: determining a toner concentration (TC) measurement using a sensor; computing a state estimator output from the TC measurement and a pre-stored estimator gain matrix, Ke; computing an estimated target state from the state estimator and a pre-stored controller gain matrix, K; computing a duty cycle from the estimated target state, pixel count data, and pre-stored target decomposer output; and, updating the duty cycle by repeating the above method for the next TC cycle.

Abstract: An image forming apparatus includes a developing device configured to develop an electrostatic image on an image carrier with developer, and a developer container detachably attachable to the image forming apparatus and configured to store developer to be supplied to the developing device. A developer supply unit is configured to supply the developer from the developer container to the developing device. The developer supply unit includes a developer detector configured to detect the amount of developer in the developer supply unit. The image forming apparatus controls the supply of developer transported via the developer supply unit and disables image formation on the basis of the detection result obtained from the developer detector. After the image formation is disabled, when the completion of the replacement of the developer container is detected, the image forming apparatus canceled the disabled image formation regardless of the detection result obtained from the developer detector.

Abstract: A remaining toner quantity detector includes a detector to detect a projection formed on a toner bottle which is rotated, a counter configured to count the number of rotations of the toner bottle by the detector and integrate the count, and a discriminator configured to discriminate the toner quantity in the toner bottle on the basis of the integrated value by the counter.

Abstract: In accordance with an embodiment of the embodiment of the invention, an image forming apparatus includes: an electrostatic image-bearing member; and a developing device. The developing device includes a developer-carrying member disposed to face the electrostatic image-bearing member, and a developer carried on the developer-carrying member. The developer includes a carrier having a volume-average particle size dc (?m) and a toner having a volume-average particle size dt (?m) of at most 5 ?m and contained at a weight ratio C with respect to the carrier of from 5 to 10% and is controlled so as to provide a surface coverage F of the carrier with the toner of from 30 to 80% as calculated according to Formula (I): F=(¼)×(dc/dt)×(pc/pt)×C, wherein pc denotes a true specific gravity (?) of the carrier, pt denotes a toner absolute specific gravity (?), and C denotes a weight ratio (?) of the toner to the carrier.

Abstract: A black developer is conveyed in a first conveyance chamber in a rotation axis direction while agitating with rotation of a first screw member. A black-toner-concentration detecting sensor detects a toner concentration of the black developer by having contact with the black developer conveyed inside the first conveyance chamber. An average of peak amounts of a pressing force on the black developer, which is conveyed inside the first conveyance chamber by the first screw member, with respect to the black toner-concentration detecting sensor is set within a range of 9.8 15 [N/m2] to 9.8 100 [N/m2].

Abstract: An image forming apparatus includes a developer container that holds a two-component developer, a toner concentration detector that detects toner concentration in the developer, a toner supplying unit configured to supply new toner to a developing unit, a toner supply controlling unit that compares an output of the toner concentration detector and a toner concentration reference value Vtref to control the toner supplying unit. The image forming apparatus detects an output of the toner concentration sensor with respect to a plurality of linear velocities, and calculates linear velocity shift amounts ?Vt1=(Vt1?Vt0) and ?Vt2=(Vt2?Vt0) to be reflected in a toner supply control parameter.

Abstract: An image forming apparatus 100 includes detection means 116 which detects an image characteristic of an image formed on an image bearing member 103; a first control means which controls a toner concentration in the developer, based on a detection result by the detection means, of an image characteristic of a first reference image for a first control for controlling the toner concentration in the developer; second control means which controls an image parameter, different from the toner concentration in the developer, thereby controlling an image density, based on a detection result by the detection means, of an image characteristic of a second reference image for a second control, different from the reference image for the first control; and correction means 231 which receives detection results of both image characteristics of the first and second reference images, and which, based on the detection result of the image characteristic of either of the reference images for the first and second controls, corrects

Abstract: A developer cartridge is provided, which contains developer made of toner and carrier and is detachably mounted in a body of an image formation apparatus. The developer cartridge is configured to include an ID chip in which a carrier content rate of the developer contained in an inner container of the developer cartridge is stored.

Abstract: A developer to be used in an image forming apparatus has a carrier and a toner containing a colorant, a binder resin, a release agent, a charge controlling agent containing Al and Mg, and a conductive inorganic oxide having an intrinsic resistivity of from 1.0×103? to 1.0×1010? in an amount of from 0.2 to 2.0 wt % based on a core toner.

Abstract: To provide a technology that can realize appropriate developer supply processing according to conditions within a developing unit by a simple method. In an image forming apparatus that visualizes an electrostatic latent image formed on a photoconductor with a developing unit, information on an amount of consumption of a developer in the developing unit is acquired, first developer supply information indicating an amount of developer to be supplied to the developing unit is calculated based on the acquired information, information on concentration of the developer contained within the developing unit is acquired, second developer supply information indicating an amount of developer to be supplied to the developing unit is calculated based on the acquired information, and information indicating an amount of developer to be supplied to the developing unit is determined based on the calculated first and second developer supply information.

Abstract: When a two-component developer stored in a developer tank has been replaced, an image forming apparatus performs (a) a first formation step of forming a reference toner image on a photoreceptor, (b) a detection step of detecting an amount of toner of the reference toner image, and (c) a supply step of supplying a predetermined amount of toner to the developer tank when the amount of toner detected in the detection step is less than a threshold. Moreover, the image forming apparatus repeats the first formation step, the detection step, and the supply step until the amount of toner detected in the detection step becomes not less than the threshold. This makes it possible to provide an image forming apparatus that is stable in image quality even immediately after replacement of developers.

Abstract: An image forming apparatus includes a plurality of development units each using a developer including a toner and a carrier, a density detection unit configured to perform a density detection operation for detecting a density of a detection toner image formed by each of the plurality of development units, and a replenishment unit configured to perform a toner replenishment operation based on a result of the detection by the density detection unit. In the image forming apparatus, at least two of the plurality of development units use respective toners having different color depths in the same hue, and a frequency of the density detection operation using the development unit using a lighter color toner is higher than a frequency of the density detection operation using the development unit using a darker color toner.

Abstract: The present invention provides a developing device and an image forming apparatus capable of carrying out excellent image formation for a long period by making the fluctuations in the toner concentration and the volume level of the developer inside a trickle developing device that uses a two-component developer as small as possible.

Abstract: The present invention provides a developing device and an image forming apparatus capable of carrying out excellent image formation for a long period by making the fluctuations in the toner concentration and the volume level of the developer inside a trickle developing device that uses a two-component developer as small as possible.

Abstract: An image forming apparatus includes a first controller for controlling a replenishing operation of a toner replenisher, based on concentration information relating to toner concentration in a developing unit; and a second controller for controlling a correction operation for an image forming condition based on concentration information relating to a concentration control patch formed on an image bearing member. The second controller does not execute the correction operation for the image forming condition, based on the concentration information relating to toner concentration in the developing unit, regardless of the concentration information relating to the concentration control patch, or limits a correction amount for the image forming condition in the correction operation, based on the concentration information relating to the toner concentration in the developing unit.

Abstract: An image forming apparatus includes an image carrier on which an electrostatic latent image is formed, a rotary developing device having N developer carriers, where N defines a total number of developer carriers, the N developer carriers carrying developers to develop the electrostatic latent image, and the rotary developing device moves the N developer carriers to a development position opposite to the image carrier, and a toner concentration sensor that measures toner concentrations of the developers carried in the developer carriers. A measurement position of the toner concentration sensor is set on a second virtual straight line with the second virtual straight line having a first angle or an angle that is double the first angle toward a first virtual straight line on a rotation orbit of the rotary device, and the first virtual straight line connects a rotation center of the rotary developing device and the development position.

Abstract: A method and apparatus for monitoring marking liquid including a carrier liquid having solid particles therein. A transmitter emits an ultrasonic signal into the marking liquid. The ultrasonic signal is received by a receiver and processed by a controller to determine at least one of the temperature of the marking liquid and the concentration of solid particles in the marking liquid.

Abstract: A developer agitation screw is provided with a blade to gather developer onto the sensor surface of a toner concentration sensor. A toner concentration control unit detects the maximum value of the output of the toner concentration sensor within each predetermined period of time, the predetermined period of time being longer than the period in which developer is gathered on the sensor surface of the toner concentration sensor by the blade. The obtained maximum value is used as a characteristic value to control the toner concentration.

Abstract: A developing device including a developer bearing member configured to configured to bear thereon a developer including a toner and a magnetic carrier to develop an electrostatic image on an image bearing member with the developer; a developer container configured to contain and feed the developer to the developer bearing member; a toner concentration sensor configured to detect a concentration of the toner in the developer in the developer container and output a signal depending on the detected toner concentration; and a characteristic information storage device configured to store a characteristic of the toner concentration sensor, wherein the sensor information storage device is separated from the toner concentration sensor. A process unit including an image bearing member and the developing device. An image forming apparatus including an image bearing member, the developing device and a controller.

Abstract: A method for determining printing ink usage efficiency (weight of ink required to print a given area) in a printing process is disclosed where the method is based on the analysis of pigment in the printed ink.

Abstract: An image forming apparatus includes an image carrier on which an electrostatic latent image is formed, a rotary developing device having N developer carriers on a rotation orbit and moving the N developer carriers to a development position opposite to the image carrier, and a toner concentration sensor that measures toner concentrations of the developers. A measurement position of the toner concentration sensor is set on a second virtual straight line having a first angle toward a first virtual straight line that connects a rotation center of the rotary developing device and the development position. The N developer carriers are placed in turn in an order at the same angular interval as the first angle, and an angular interval between the N-th and first developer carriers is set to a second angle greater than the first angle.

Abstract: An image forming apparatus is configured that a developing unit develops a latent image with a toner, which is controlled by a toner-supply control unit based on a deference between a toner-density of the toner that is supplied to the developing unit and a reference-value. A reference-value determining unit determines the reference-value. A condition determining unit determines whether a predetermined condition is satisfied. The reference-value determining unit updates the reference-value with a different reference-value when the condition determining unit determines that the predetermined condition is satisfied.

Abstract: A method of controlling an image forming apparatus having at least one consumption part. The method includes fetching specification information corresponding to the at least one consumption part, detecting whether control information for controlling a printing operation of the image forming apparatus according to the specification information is present in a memory of the image forming apparatus, storing the specification information of the at least one consumption part and the control information about the printing operation into the memory of the image forming apparatus when the control information is not present in the memory, and controlling the printing operation of the image forming apparatus according to the control information stored in the memory of the image forming apparatus.

Abstract: An information attaching unit attaches either one of carrier density information of initial developer and loose apparent density information of toner in the initial developer to a housing of a developing device. A density-information storage unit stores therein either one of the carrier density information and the loose apparent density information as electronic data. At least one of the information attaching unit and the density-information storage unit is provided before shipment of the developing device.

Abstract: An image forming apparatus including an image bearing member; a developing device forming a toner image; a toner supplying device including a toner container, a toner feeding passage, a pump, in which a first member is moved while rubbing a second member to feed a developer supplement including at least the toner, and a residual toner detector detecting the amount of the developer supplement remaining in the toner container. Even after the toner container achieves a near empty state, image forming operations are continued as long as a predetermined condition is satisfied while changing the pump's condition such that the pump is stopped, the ratio of the pump stopping period to the pump driving period is set to be greater than that before the near-empty detection, or the pump stopping period and the pump driving period are set to be longer than those before the near-empty detection.

Abstract: A developing device has stirring members for conveying and stirring a developer-tank-contained developer and a developer holder, and has a developer replenishing tank for replenishing a replenishment developer to a developer tank; a toner concentration detecting sensor; a discharging mechanism for discharging an excessive amount of the developer-tank-contained developer outside the developer tank when the amount of the developer-tank-contained developer inside the developer tank exceeds a predetermined amount; and a control unit for replenishing the developer-tank-contained developer when it is detected that the toner concentration inside the developer tank is lower than a first reference value and for forcibly consuming the toner inside the developer tank and replenishing the replenishment developer when it is detected that the toner concentration inside the developer tank is higher than a second reference value that is higher than the first reference value.