Abstract: An image forming apparatus having a system speed of from 400 to 1,700 mm/sec, including a latent image bearer; an image developer developing the latent image with two-component developer including a toner and a carrier; a transferer, a toner concentration detector; a toner feeder; and a controller, wherein the toner comprises a release agent and a binder resin including a crystalline polyester resin and an amorphous resin, wherein a ratio (W/R) of a maximum rising peak height (W) of the crystalline polyester resin to a maximum rising peak height (R) of the amorphous resin, which are observed respective infrared absorption spectra when measured by an IR spectroscopy using a Fourier transform infrared spectroanalyzer, is from 0.22 to 0.55.

Abstract: An image forming apparatus is provided. The image forming apparatus includes a developing unit which contains a mixture of toner and carrier, a toner sensor which is disposed in the developing unit, and a controller which determines a control voltage for the toner sensor using change information on a change in a quantity of electric charge which changes according to a time during which the image forming apparatus is used or paused, and drives the toner sensor using the determined control voltage and compensates for an output value of the toner sensor. Accordingly, toner can be prevented from being supplied excessively.

Abstract: A development device includes a developer container for containing developer, a developer bearer to carry by rotation the developer contained in the developer container to a development range facing a latent image bearer, a partition dividing the developer container into an upper compartment and a lower compartment arranged vertically, an upper developer conveyance member disposed in the upper compartment, a lower developer conveyance member disposed in the lower compartment, a communication portion through which the developer moves from the lower compartment to the upper compartment, disposed in a downstream end portion of the lower compartment in a direction in which the lower developer conveyance member transports the developer, and a toner concentration detector to detect a concentration of toner in the developer beneath the communication portion inside the lower compartment.

Abstract: A magnetic permeability detector includes an LC oscillator circuit including a coil and a capacitor; and a resistor connected in series with the coil.

Abstract: The image forming apparatus carries out a monitoring operation in which (i) sensor outputs of the magnetic permeability sensor are periodically sampled, (ii) a time period, corresponding to one (1) circulation period which is required for the developer to be circulated once in the circulation carrying path, is evenly divided into a plurality of blocks, and (iii) an average of the sensor outputs in one (1) block time period corresponding to one (1) block is calculated for each of the plurality of blocks; and determines that toner has run short, in a case where the number of times that the averages of the sensor outputs consecutively exceed a threshold, set to be higher than a reference value of the sensor outputs, becomes not less than the number of the plurality of blocks which correspond to the time period corresponding to one (1) circulation period.

Abstract: A development device includes a development housing, a first developer conveyance member, a developer bearer, and a developer amount detector to detect an amount of developer in the development housing. The developer amount detector includes a light-emitting element, a right-receiving element, a first light guide including a first end from which light enters and a second end disposed inside the development housing, and a second light guide including a first end positioned inside the development housing across a predetermined distance from the second end of the first light guide and a second end from which the light exits. The second end of the first light guide and the first end of the second light guide are arranged in an axial direction of the first developer conveyance member with a light transmission path therebetween partly inside a locus of rotation of the first developer conveyance member.

Abstract: A development device is operable in multiple different speed modes and includes a developer bearer to carry developer, a developer regulator to adjust an amount of developer carried on the developer bearer, and multiple developer conveyance members disposed facing the developer bearer to transport developer in a longitudinal direction to circulate developer inside the development device. The multiple developer conveyance members including a first developer conveyance member to supply developer to the developer bearer and a second developer conveyance member to transport developer collected from the developer bearer. The development device executes developer amount balance adjustment in which a driving velocity of at least the multiple developer conveyance members is increased from a driving velocity in a lower-speed mode for a predetermined period after image development in the lower speed mode is completed and before image development in a higher speed mode is started.

Abstract: Provided are an image forming apparatus that, when a difference between a developing bias in correcting an image density and a reference developing bias has a value not less than a prescribed value that is set preliminarily, replenishes or consumes a toner forcibly, executes correction of the image density again, and controls the developing bias in such a manner that a toner density is controlled to fall within an appropriate range, and an image forming method using the same. When a difference between a developing bias value after correction of the image density and the reference developing bias becomes larger than the prescribed value to the plus side or the minus side, a toner density control portion performs control to consume or replenish a toner forcibly.

Abstract: A developing device includes a developer container, an agitation conveyance member, a toner detection sensor, and a scraper. Agitation conveyance member agitates and conveys a developer in developer container. Toner detection sensor detects a toner concentration or a remaining amount of toner in developer container. Scraper is provided in agitation conveyance member, and cleans a detection surface of toner detection sensor when agitation conveyance member rotates. Scraper includes a first member that comes into contact with detection surface of toner detection sensor when agitation conveyance member rotates forward, and a second member that comes into contact with detection surface of toner detection sensor when agitation conveyance member rotates reversely. First member has a wear resistance higher than that of second member, and a coefficient of friction between second member and detection surface is higher than a coefficient of friction between first member and detection surface.

Abstract: An image forming device includes a toner supplying unit to supply the toner to a storage unit. A mixer supplies developer in the storage unit to a developing roller, and a developer sensor detects the amount of developer on the surface of the developing roller. A toner concentration sensor detects toner concentration in the developer stored in the storage unit, and a control unit adjusts at least one of a developing bias and a rotation speed of the mixer based on a value detected by the developer sensor and a value detected by the toner concentration sensor, such that a printed image has uniform density.

Abstract: A control apparatus includes the following elements. A toner density specifying unit specifies a toner density in a developer stored in a developing device. A toner density controller performs control such that the toner density approximates a predetermined toner density target value. A first calculator calculates a first value corresponding to an image density of an image to be output after a first timing. A correction amount specifying unit specifies a correction amount for the toner density target value at the first timing. When the condition that an absolute value of a difference between the first value and a second value is greater than a predetermined threshold is satisfied, the correction amount specifying unit specifies a smaller correction amount for the toner density target value, compared with when the condition is not satisfied. A correcting unit corrects the toner density target value on the basis of the correction amount.

Abstract: System and methods for controlling toner properties in a two component development system through the toner shape factor. In particular, the present embodiments provide a method for controlling toner concentrations by tailoring the circularity value ranges of the toner particles to prevent dysfunctions and provide a more robust and optimized xerographic system.

Abstract: An image forming apparatus includes an information rewrite unit that rewrites information stored in a storage if an empty detector detects that a toner container is empty and the toner container is at least allowed to be released, and then if the empty detector detects that the toner container is not empty.

Abstract: A developing apparatus includes a development unit configured to supply toner to a photoconductor on which an electrostatic image is formed, a supply unit configured to supply toner to the development unit, a sensor configured to detect a concentration of toner in the development unit, and a control unit. The control unit is configured to, when the detected concentration of the toner is lower than a first value, control the supply unit to perform a toner supply process, control the sensor to detect the concentration of the toner after the toner supply process, count the number of times the sensor detects the concentration of the toner to be higher than a second value that is higher than the first value, and control the supply unit to repeat the toner supply process, when the counted number is less than a predetermined number that is equal to or greater than two.

Abstract: In a new printer, a toner cartridge is mounted in the state where there is no toner in a reserve tank, and toner of the amount of filling toner D therein is supplied with the amount of full accommodation toner E for filling up the reserve tank by a toner supply mechanism. The toner of the amount of remaining surplus toner F remains in the toner cartridge. The amount of toner consumption G is measured by a dot counter during a printing execution. In the case where a toner density sensor detects a toner decreasing, the toner is supplied to a developing unit from the reserve tank. When it becomes G>F, it display-informs a user of “toner cartridge exchange is allowed”. Hereby, it enables to exchange the toner cartridge without stopping operation of the main body of the image forming apparatus using a two-component developer.

Abstract: An image forming apparatus includes a latent image carrier, a container that contains a developer including a toner, developer transport members disposed so that peripheral surfaces thereof face the latent image carrier, a power supply that supplies voltages to the developer transport members, a detector that detects a toner concentration of the developer, and a controller. The controller performs control so that the power supply supplies to the developer transport members, when the toner concentration detected by the detector is higher than a predetermined upper limit, voltages having waveforms that generating a potential difference therebetween that causes the toner concentration of the developer distributed to a most downstream developer transport member to decrease and the toner concentration of the developer distributed to at least one of the developer transport members that is disposed upstream of the most downstream developer transport member to increase.

Abstract: This invention provides a developer concentration adjustment apparatus, a method for concentration adjustment, and an image forming apparatus, in which concentration adjustment is performed by use of a stirring load as a substitute characteristic of viscosity which represents a developer concentration, wherein a trouble of abnormality generation in toner concentration detection due to drying-adhesion of a residual developer on the stirrer is reduced. At the time of finishing the concentration adjustment, a concentration adjustment tank is made to be empty and the stirrer is cleaned by carrier liquid or a liquid developer having a concentration lower than a predetermined concentration. Alternatively, the stirrer is cleaned by empty-stirring operation not being put in a cleaning developer.

Abstract: A controlling system comprising an image forming device and a controlling device for the image forming device, the image forming device having an indicating device which can indicate that a toner cartridge is in a toner near empty state and a communication part for communicating with the controlling device via a communication network, and when the toner near empty state of the toner cartridge is detected, the communication part transmits the information to the controlling device. The controlling device has a controlling condition table in which a controlling condition set for each image forming device to be controlled is recorded, and when a toner near empty signal is received from the image forming device to be controlled, the controlling device refers to the controlling condition of the image forming device recorded in the table, and outputs or does not output a toner near empty indication instruction signal depending on the controlling condition.

Abstract: A toner supply control system for an image forming apparatus includes a supply controller to compute a toner supply amount required for a toner supply operation to cancel a toner concentration fluctuation in the developing agent. The supply controller includes an image-information-based consumption prediction unit to predict toner consumption amount based on image information used for forming an image; a toner-concentration-based consumption prediction unit to predict toner consumption amount based on a detection result of a toner concentration detector; and a toner supply determination unit to determine a toner supply timing and amount and initiate a toner supply operation based on the toner consumption amount predicted by the toner-concentration-based consumption prediction unit right after the toner consumption occurs.

Abstract: In the present invention, for a developing apparatus provided with a sensor for detecting the toner density of a developer, retention of the developer near the sensor face can be suppressed by increasing the force with which the developer present near the sensor face is carried in a shaft direction of a stirring/carrying member.

Abstract: An image forming apparatus prevents printed images from being degraded in image quality due to failure of the toner concentration to fall within a proper range, by correcting the deviations of the amount of toner consumption and the amount of toner supply depending on the individuality of each image forming apparatus and that enables exact identification of the cause of a fault associated with toner concentration, and providing an image forming method using the apparatus. A toner supply device supplies toner to a developing vessel through an opening in accordance with an instruction from a controller. The presence or absence of toner falling is detected based on the variation of the output from a magnetic permeability sensor when toner is supplied. The controller monitors the output voltage level of the magnetic permeability sensor and adjusts the input gain in accordance with the output voltage level to thereby control toner concentration.

Abstract: An image forming apparatus includes a latent image carrier; an image information obtaining unit; a latent image forming unit; a developer carrier; a developing device to develop the latent image by adhering toner onto the latent image carried on a latent image carrier; a toner replenishing device to replenish toner to the developing device; and a controller to adjust a toner replenishment amount by controlling drive of the toner replenishing device based on the image information. When the drive of the developing device is stopped, information relating to unreplenished portion of the toner replenishment amount excluding the already replenished amount from the toner replenishment amount based on the image information is stored in a nonvolatile memory, and the drive of the toner replenishing device is controlled using the stored information relating to the unreplenished portion of the toner replenishment amount when the drive of the developing device is resumed.

Abstract: In the image forming apparatus including a developing device that develops an electrostatic latent image on an image carrying member by using toner, a first toner empty stop condition and a second toner empty stop condition for prohibiting printing because of a lack of the remaining amount in the toner are provided. The first toner empty stop condition and the second toner empty stop condition are switched in response to the state of the device.

Abstract: An image forming apparatus includes an image bearing member on which an electrostatic latent image is to be formed and a developing device for developing the electrostatic latent image by supplying a developer to the image bearing member. The developing device includes a developer container; a rotatable developer carrying member, including a first electrode member; and a developer supplying member, which includes a surface foam layer and a second electrode member. The apparatus further includes a measuring device for measuring a remaining developer amount in the developer container by detecting electrostatic capacity between the first and second electrode members and a replenishing device for replenishing the developer supplying member by rotating the developer supplying member at a speed slower than a speed during image formation. When the measured remaining developer amount is not more than a threshold, the developer is replenished, and thereafter the remaining developer amount is again measured.

Abstract: The developer supplying device supplies a supplementary developer including a toner and a carrier in a predetermined weight ratio. The developer supplying device includes a supplementary developer container containing the supplementary developer, and a supplementary developer feeding passage configured to feed the supplementary developer from the supplementary developer container to a developing device. The supplementary developer container is replaced when the supplementary developer is substantially exhausted. The developer supplying device further includes a carrier concentration determining device provided on the supplementary developer feeding passage to determine the concentration of the carrier in the supplementary developer fed through the supplementary developer feeding passage, and a residual supplementary developer amount estimating device configured to estimate the amount of the supplementary developer remaining in the supplementary developer container.

Abstract: An image forming apparatus includes a two-component developing devices for each of a plurality of photoreceptors and a motor for the developing device. A transmission can assume a coupled state where the transmission transmits driving force of the motor to the developing device and a separated state where the transmission does not transmit the driving force of the motor to the developing device. A toner agitating mechanism stirs toner inside the developing device. A permeability sensor detects permeability inside the developing device and outputs a signal according to a ratio of the toner to the carrier. A coupling judging section judges that the coupling state exists when a variation of a signal value outputted by the permeability sensor equals or exceeds a predetermined value and judges that the separated state exists when the variation of the signal value outputted by the permeability sensor is lower than the predetermined value.

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: A control apparatus includes the following elements. A toner density specifying unit specifies a toner density in a developer stored in a developing device. A toner density controller performs control such that the toner density approximates a predetermined toner density target value. A first calculator calculates a first value corresponding to an image density of an image to be output after a first timing. A correction amount specifying unit specifies a correction amount for the toner density target value at the first timing. When the condition that an absolute value of a difference between the first value and a second value is greater than a predetermined threshold is satisfied, the correction amount specifying unit specifies a smaller correction amount for the toner density target value, compared with when the condition is not satisfied. A correcting unit corrects the toner density target value on the basis of the correction amount.

Abstract: An image forming apparatus includes a developing device having a toner supply sensor, a toner supply device supplying toner to the developing device, a toner supply controller controlling toner supply from the toner supply device to the developing device based on predetermined conditions, a toner empty determiner determining whether toner is present inside the toner supply device. In the image forming apparatus, the toner supply device includes a storage for recording multiple measured values of toner supply detected by the toner supply sensor, and the toner supply controller corrects the amount of toner supply, based on the moving average of multiple measured values of the amount of toner supply.

Abstract: An image forming apparatus capable of stabilizing image density on a long-term basis by compensating for an error in prediction of toner particle charge amount, while reducing variation in image density on a short-term basis by the prediction. A CPU predicts an amount of electrostatic charge of toner particles in a developer container and sets an exposure condition and causes a toner image to be fixed on a recording medium and a pattern image for detecting image density, to be each formed on a photosensitive drum according to the set exposure condition, while performing gradation correction based on the gradation conversion table. The CPU updates the gradation conversion table such that a detected density of the pattern image becomes closer to a target density. The CPU sets the exposure condition based on a result of the prediction such that toner image density becomes constant.

Abstract: In this toner concentration sensor, as the magnetic permeability of a two-component developer 3 containing toner and carrier in a two-component developing unit 1 has changed with changing TC ratio of the two-component developer, the oscillation frequency of a first oscillation circuit 20 having a detection coil 5 changes, on the other hand the oscillation frequency of a second oscillation circuit 30 having a reference coil 6 does not change. While, changes in temperature conditions cause the oscillation frequency of the second oscillation circuit to change in the same way as the oscillation frequency of the first oscillation circuit. Therefore, utilizing a difference between the oscillation frequencies of the first and second oscillation circuits makes it possible to cancel out changes in the temperature conditions so that a value corresponding to only the magnetic permeability of the two-component developer can be obtained.

Abstract: An image forming apparatus includes a latent image holder that holds a latent image; a developing unit that contains developer including toner particles and carrier particles, develops a latent image with the toner particles, and forms a toner image; a voltage applying unit that applies a voltage to the developing unit; a toner concentration detection unit that detects a toner concentration that is a proportion of the toner particles to the developer contained in the developing unit; and a setting unit that sets a setting value of the voltage on the basis of the toner concentration detected by the toner concentration detection unit, the voltage being applied by the voltage applying unit to the developing unit, wherein a difference between an upper limit and a lower limit of the set value increases as the toner concentration increases, the set value being set by the setting unit.

Abstract: A piezoelectric crystal adjacent to a development member in an electrophotographic printer has an electrode on it facing the development member. An AC bias is applied across the crystal while a DC bias is applied between the electrode and the development member to measure toner-mass deposition rate. An AC bias is then applied between the electrode and the development member to measure developer flow rate. The toner concentration of the developer is determined using the measured toner mass-deposition rate and developer flow rate.

Abstract: Developer toner concentration in an electrophotographic system is measured. Two sensors, one before and one after the toning zone in the direction of rotation of the development member, each include respective electrodes that form a respective capacitance between the respective electrode and the development member. A voltage source selectively applies respective AC biases across the sensors and the respective currents across the sensors are measured. A controller causes an electrostatic latent image to be produced on the photoreceptor and causes the development member to rotate and the photoreceptor to move. While the development member is rotating, the processor receives the measured currents and computes toner concentration using the respective received currents and the pixel data. The developer flow rate can be adjusted, or toner added to the developer, in response to the determined toner concentration.

Abstract: An image forming apparatus having a system speed of from 400 to 1,700 mm/sec, including a latent image bearer; an image developer developing the latent image with two-component developer including a toner and a carrier; a transferer, a toner concentration detector; a toner feeder; and a controller, wherein the toner comprises a release agent and a binder resin including a crystalline polyester resin and an amorphous resin, wherein a ratio (W/R) of a maximum rising peak height (W) of the crystalline polyester resin to a maximum rising peak height (R) of the amorphous resin, which are observed respective infrared absorption spectra when measured by an IR spectroscopy using a Fourier transform infrared spectroanalyzer, is from 0.22 to 0.55.

Abstract: An image forming apparatus that includes a latent image carrier, a latent image forming unit, a developing unit, a toner supplier, a toner concentration detector, a prediction calculator, and a toner supply controller. The toner supplier includes a single driving source and supplies toner to a two-component developer at a predetermined supply position by driving a toner supply member with the driving source. The toner concentration detector detects a toner concentration in the developer at a predetermined detection position located upstream of the supply position. The prediction calculator predicts changes in the toner concentration in the developer over time at a prediction position located at the supply position or downstream of the supply position and upstream of a developer feed position to the developer carrier when toner is not supplied. The toner supply controller adjusts an amount of the toner supplied based on the prediction.

Abstract: An image forming apparatus is supplied capable of lowering cost of exchange part. In the image forming apparatus, the exchange part is furnished being attachable and removable, an identification information obtaining process section to obtain identification information of the exchange part from the exchange part, and an operation allowing process section to allow image formation in the case that the identification information obtaining process section can not obtain the identification information, are comprised, so that it is unnecessary to provide an identification information storing portion for storing the identification information to the exchange part of shipment stage.

Abstract: A concentration detection apparatus includes: a light-emitting element that emits light; a light-emitting-element holding unit that holds the light-emitting element; a light-receiving element that receives light emitted from the light-emitting element; a light-receiving-element holding unit that holds the light-receiving element and is provided opposite to the light-emitting-element holding unit with a gap therebetween; a moving unit that can move through or at the gap between the light-emitting-element holding unit and the light-receiving-element holding unit; and a gap adjusting unit that adjusts a value of the gap as a distance between the light-emitting-element holding unit and the light-receiving-element holding unit.

Abstract: A developing device and an image forming apparatus are provided, which prevent the output of the sensor from being destabilized due to the loose aggregation and stagnation of a developer on the detection surface of a permeability sensor and stabilize the output of the permeability sensor so as to enable highly precise toner concentration control. The developing device includes a transport passage, a developing roller that supplies to a photosensitive drum the two-component developer passing through the transport passage, a transport member that stirs the two-component developer in the transport passage and supplies the two-component developer to the developing roller, and the permeability sensor that is disposed in the transport passage to detect a toner concentration of the two-component developer. The developing device also includes an electromagnet located adjacent to the permeability sensor. The electromagnet is supplied with an intermittent flow of current to make the developer active in movement.

Abstract: Methods and systems for facilitating remote access and customization of internally generated printing node status reports. In some embodiments, the methods and systems advantageously facilitate remote access and customization of internally generated printing node status reports by adapting preexisting features that generate local hard copies of printing node status reports in response to locally initiated commands. Such adaptation enables a printing node to receive, process and respond to remotely initiated requests for printing node status reports in a manner that permits remote customization of the style of printing node status reports.

Abstract: Provided is a liquid developer concentration adjusting apparatus and a method so that the concentration can be adjusted easily and efficiently without using time and effort in liquid volume control. Further, the apparatus and method enable the concentration adjustment to be efficiently accomplished in a short period of time with reduced volume of required supply developer to be added for the adjustment independently of the initial concentration of the developer by concurrently measuring the concentration of developer, even if the concentration thereof is high. In the control of the concentration adjustment, the developer is allowed to overflow through an opening of the concentration adjusting container, and the concentration adjustment by using supply developer or the supply speed of the supply developer is started before the start of the overflow.

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: A supply control unit is configured to, in a successive image-forming operation, perform a process of successively generating a driving control pattern for a toner supply device based on image information of each page, and synthesizing an unused portion of the driving control pattern which is obtained by eliminating a portion of the driving control pattern already reflected on a driving control of the toner supply device from the driving control pattern generated based on image information of a previous page with a driving control pattern generated based on a subsequent page.

Abstract: A development device includes a developer container for containing developer, a developer bearer to carry by rotation the developer contained in the developer container to a development range facing a latent image bearer, a partition dividing the developer container into an upper compartment and a lower compartment arranged vertically, an upper developer conveyance member disposed in the upper compartment, a lower developer conveyance member disposed in the lower compartment, a communication portion through which the developer moves from the lower compartment to the upper compartment, disposed in a downstream end portion of the lower compartment in a direction in which the lower developer conveyance member transports the developer, and a toner concentration detector to detect a concentration of toner in the developer beneath the communication portion inside the lower compartment.

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: A developer supplying apparatus can include a first chamber and a second chamber defined within a housing. Each of the first and second chambers may include an agitator disposed therein. A magnetic body may be disposed near the first chamber to receive toner from the first chamber. A controller can determine the level of developer received in the first chamber, and to based on the determined developer level control the operations of one or more of the agitators and the magnetic body in order to ensure sufficient supply of the developer in the first chamber to reduce the occurrences of image defects, such as, for example, auger marks.

Abstract: There is provided an image stabilizing apparatus which is capable of keeping a toner concentration and a printing density constant when toner consumption is small, and further which is systematically simple. The image stabilizing apparatus comprises a control portion for controlling a toner replenishment amount in a toner replenishing apparatus depending on a toner concentration detected by a toner concentration sensor and a print coverage of a document detected by a print coverage detecting portion, and controlling, when the print coverage of the document detected by the print coverage detecting portion is less than a predetermined value and such documents continue, so as to discharge a predetermined amount of toner to the image bearing member by developing forcibly, and then replenish the same amount of toner as the predetermined amount by the toner replenishing apparatus.

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: A developing device using a two-component developing agent including a toner and a carrier. The developing device includes a toner concentration sensor which detects a concentration of a toner contained in the developing agent within the accommodation unit by using electrostatic capacity. The toner concentration sensor includes a frame combined with a housing that forms the accommodation unit, a measuring groove formed in the frame to be concave with respect to an inner surface of the housing so that the developing agent conveyed by the agitator is flowed into the measuring groove, and a pair of opposite electrodes disposed on the measuring groove.

Abstract: An image forming apparatus, comprising, an exposure portion to expose a surface of an image carrier to form an electrostatic latent image; a developing device which includes an agitating roller to agitate developer, a developing roller to transfer toner of the developer on a surface of the image carrier and a toner concentration sensor to detect a toner concentration, said developing device developing the electrostatic latent image formed on the image carrier to form a toner image; a drive source to independently drive to rotate the developing roller and the agitating roller; and a control unit to control the drive source to change a rotational frequency of at least one of the developing roller and the agitating roller depending on the toner concentration detected by the toner concentration sensor.