Abstract: An amount of toner consumption accompanying development of an image corresponding to the image data is calculated based on image data, and a corrected consumption amount is calculated by multiplying the calculated amount of toner consumption by a predetermined correction ratio that is less than 1. Further, toner is supplied based on the calculated corrected consumption amount. As a result, it is possible to prevent excessive supply of toner, and to supply toner without time delay.

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: An image forming apparatus includes an image carrier configured to carry an electrostatic latent image, a developing device configured to develop the electrostatic latent image with a two-component developer including toner and magnetic carrier, a toner supplier configured to supply the toner to the developing device, a toner concentration detector configured to detect toner concentration in the two-component developer inside the developing device, and a controller. The controller is configured to detect first information to determine toner replacement amount in the developing device during a predetermined time period and second information to determine a charge characteristic of the toner in the developing device, change a toner concentration control reference value based on the first information and the second information, and control the toner concentration based on an output from the toner concentration detector and the toner concentration control reference value.

Abstract: To provide a technology capable of realizing high-accuracy detection of toner density. A developing apparatus includes: a partition plate provided within the developing apparatus for partitioning an interior of the developing apparatus into a plurality of space; plural transport mixers each provided in the space within the developing apparatus partitioned by the partition plate and rotating for stirring and transporting a developer including toner and carrier; a density sensor provided in a transport path of the developer in one space of the plurality of space partitioned by the partition plate for detecting toner density of the stirred and transported developer; and retracting part for retracting an amount of the developer more than a predetermined amount into another space than the space in which the toner density is detected by the density sensor so that the amount of developer is constantly equal to or less than the predetermined amount near a toner density detection position by the density sensor.

Abstract: An image forming apparatus having a developer controlling apparatus for a developing roller is provided to uniformly control an amount of developer deposited on the developing roller and a developer controlling method thereof. The apparatus includes a sensing part having a first sensor which senses a conductivity of a liquid developer and a second sensor which senses a density of the liquid developer. A control part controls a voltage applied to the developing roller and/or a deposit roller according to the conductivity and the density sensed by the sensing part.

Abstract: An image forming apparatus includes an image carrying member, a developing unit, an image density detector, a toner concentration detector, a toner concentration controller, and an output adjustment unit. The image carrying member forms a reference latent image pattern. The developing unit develops the reference latent image pattern as a reference image pattern with a two-component developer. The image density detector detects an image density of the reference image pattern. The toner concentration detector detects a toner concentration in the two-component developer. The toner concentration controller controls the toner concentration based on the image density detected by the image density detector. The output adjustment unit adjusts a toner concentration sensing level of the toner concentration detector with a sensor control voltage. The toner concentration is controlled by a target voltage with reference to the image density. The toner concentration range is changed by changing the sensor control voltage.

Abstract: An image forming apparatus includes a toner image forming section including a developing device having a developer tank for storing a two-component developer, a transfer section, a fixing section, a recording medium feeding section, and a discharging section. The image forming apparatus further includes a toner concentration detecting section for detecting the toner concentration in the developer tank, a printing speed switching section, a toner concentration calculating section for correcting a detection result obtained by the toner concentration detecting section according to a speed of printing to calculate the toner concentration, and a toner replenishment control section for replenishing the toner into the developer tank according to a calculation result by the toner concentration calculating section.

Abstract: An image forming apparatus is provided that forms an image using developers of different tone and the same hue. When forming images for measurement for density control, the apparatus performs density control by forming a greater number of density levels of an image for measurement developed using a light developer than the number of density levels of an image for measurement developed using a dark developer. Thus, even if the amount of applied light developer may fluctuate, the fluctuation can be compensated to prevent the occurrence of pseudo-contours that lower image quality.

Abstract: Forced supply of toner(s) from toner hopper(s) to developer storage container(s) is executed while interrupting and/or prohibiting image forming operation(s) so as to prevent consumption of toner(s), toner level(s) within toner hopper(s) being determined to be low and low toner level condition(s) being reported to user(s) when temporal change(s) in value(s) detected by toner sensor(s) is/are small.

Abstract: In an image forming apparatus capable of reducing the number of toner concentration detection errors caused by variation in the volume of a toner below that of the related art, a reverse vane for transferring K developer in an opposite direction to a screw vane as a rotary shaft member rotates protrudes from the rotary shaft member in a region of an entire rotary axis direction region of a first screw member where a gravitational direction lower side faces a bottom wall of a first transfer chamber and two lateral sides that are orthogonal to the rotary axis direction face respective side walls of the first transfer chamber, and a K toner concentration detection sensor is disposed to detect the toner concentration of the K developer as the K developer is transferred between the reverse transfer vane and a location of the screw vane adjacent to the reverse transfer vane.

Abstract: An image forming apparatus includes an image forming portion, a developing apparatus, a developer density detection portion, an image density detection portion, an environment detection portion, and a developer replenishing apparatus. The image forming apparatus further includes a control portion for performing a replenishing operation of the developer replenishing apparatus. The control portion also performs an image density control for controlling an electrostatic image forming condition of the image forming portion. When a detection result by the environment detection portion is changed by a predetermined value or the replenishment developer is renewed, the image forming apparatus advances to a mode of performing the image density control, while performing the replenishing operation by developer replenishing apparatus based on the detection result of the developer density detecting portion.

Abstract: A system, method, and apparatus for adjusting dry ink concentration in a developing station (30) of a printer is disclosed. The adjustment is performed by calculating the thermal drift of a dry ink monitor (40) and applying the result as a compensating factor in calculations in a software algorithm. The dry ink monitor (40) has a sensing port (42) in contact with a dry ink concentration and is connected to a dry ink monitor interface board (10) that houses a temperature sensor (20). The monitor interface board (10) is positioned in proximity to the dry ink monitor (40) to enable the temperature sensor (20) to measure a temperature of the dry ink concentration. The software algorithm is used to adjust the dry ink concentration based on a slope coefficient calculated by the printer based on outputs from the dry ink monitor (40) and the dry ink monitor interface board (10).

Abstract: The present invention generally relates to a digital imaging system or a light lens based imaging system. More specifically, the present invention provides an improved method and apparatus for calculating toner age and, additionally, carrier age using a toner concentration sensor and the amount of material dispensed. Both of these quantities can be used to ensure image quality by anticipating or diagnosing problems in image quality, which may be caused by toner age or carrier age.

Abstract: An image forming apparatus includes a latent image forming portion for forming an electrostatic latent image corresponding to image information on an image bearing member, a developing portion, having a developer container for accommodating a developer containing a toner and a carrier, for developing the electrostatic latent image with the toner, and a toner density detecting portion for detecting a toner density in the developer container, a toner replenishment amount to the developer container being controlled in accordance with a result of detection by the toner density detecting portion, wherein a toner replenishment amount target value used for controlling the toner replenishment is controlled to fall within a restriction range, and the restriction range can be changed according to the image information.

Abstract: An image forming apparatus containing image forming stations Y, M, C, K for respective colors arranged along a transfer belt, each image forming station including an image carrier, a charging means and a developing means disposed around the image carrier. The apparatus further having a housing body in which the image forming stations and the transfer belt are situated, a support frame for supporting a roller around which said transfer belt is laid with some tension, and an image density detecting means which is arranged to face the transfer belt, wherein the support frame is attached to the housing body which allows the support frame to be detachable relative to the housing body by a pivotal movement. The apparatus has a locking device for locking the support frame to the housing body, wherein the image density detecting device is disposed in proximity to the locking device, thereby preventing the deterioration of the detecting accuracy of the image density detecting device.

Abstract: Provided are an image forming apparatus and method of controlling same in which when toner replenishment from a toner accommodating unit has been performed satisfactorily, a no-toner indication can be cancelled without taking more time than necessary, and in which the status of the toner accommodating unit can be reported to the user earlier even if a toner accommodating unit that has no toner or that has malfunctioned has been installed. Whether a toner accommodating unit (5) has toner is determined based upon a detection signal from a toner density sensor (46) that detects the toner density of a developer in a developing unit (4). If it is determined that there is no toner in the toner accommodating unit (5) and the toner accommodating unit (5) is replaced, this is detected and a toner density restoration sequence for restoring the density of toner in the developing unit (4) is executed.

Abstract: This invention relates to an image forming apparatus including a developing unit which develops an electrostatic latent image formed on an image carrier by using a two-component developing agent containing polymerized toner. The developing unit includes a supply/convey member which conveys the two-component developing agent in the axial direction while agitating it and a toner density sensor which detects the toner density of the two-component developing agent. The toner density sensor is placed to be in a non-contact state with respect to the supply/convey member and oppose it with a gap of 0.8 mm or less. The diameter of the supply/convey member is set to 23 mm or more.

Abstract: In an image forming apparatus that is capable of forming an image in a plurality of image forming modes that correspond to frequencies of developing bias, a voltage value that reflects the image forming mode and amount of remaining toner is corrected using a correction quantity that conforms to the image forming mode.

Abstract: An apparatus and method for determining toner concentration of a sample comprised of toner and carrier, including exposing the sample to light; the exposing includes emitting light at a predefined wavelength based upon the color of the toner; detecting the light reflected off the sample with an optical sensor; and determining the toner concentration of the sample base upon the light reflected off the sample.

Abstract: A method for sensing toner concentration in a developer housing with an optical system containing developer material including toner and carrier, the method, including: emitting light with the optical system through a viewing window in the developer housing onto developer material in the housing; sensing the light reflected off the developer material with the optical system; calculating a toner concentration measurement based upon the sensed light reflected off the developer material; and compensating the toner concentration measurement to account for optical variation due to the developer material condition.

Abstract: A developer concentration measuring apparatus of a liquid printer includes a container installed so that developer supplied to a photoreceptor web enters and is exhausted, a roller rotatably installed in the container for forming a film of the developer contained in the container on a surface thereof being exposed while rotating, a roller driving module for driving the roller to rotate at a predetermined speed, a light emitting module for emitting a predetermined amount of light to the surface of the roller where the film is formed, a light-receiving module, installed to detect light emitted from the light emitting module and passing through the film, for transmitting a signal corresponding to the amount of received light, a temperature detector for detecting the temperature of the developer contained in the container; and a concentration measuring module for measuring the concentration of the developer from information on temperature output from the temperature detector and from the signal output from the li

Abstract: This invention relates to an image forming apparatus including a developing unit which develops an electrostatic latent image formed on an image carrier by using a two-component developing agent containing polymerized toner. The developing unit includes a supply/convey member which conveys the two-component developing agent in the axial direction while agitating it and a toner density sensor which detects the toner density of the two-component developing agent. The toner density sensor is placed to be in a non-contact state with respect to the supply/convey member and oppose it with a gap of 0.8 mm or less. The diameter of the supply/convey member is set to 23 mm or more.

Abstract: A developing device of the present invention includes a conveying member for conveying a developer that is a toner and carrier mixture. A sensor senses the toner content of the developer in terms of the permeability of the developer. A preventing member prevents the bulk density of the developer from varying when fresh toner is not replenished. The developing device obviates erroneous toner content sensing when fresh toner is not replenished. An image forming apparatus including the developing device is also disclosed.

Abstract: A permeability detection apparatus configured to stably execute a permeability detection operation for toner concentration and characterized by improved sensitivity. The permeability detection apparatus includes: a detection circuit 22; an oscillation circuit 21 that oscillates a natural frequency to drive the detection circuit; and a phase comparison circuit 23 that extracts signals at an input side of the detection circuit and an end side of the circuit element to perform phase comparison. The detection circuit 22 includes a coil L1, a capacitor C1 connected to the coil in series or in parallel, and a resistance R1 connected to the coil in series or in parallel, and a resistance R1 connected to the coil and the capacitor. The resistance R1 allows the oscillation circuit to eliminate influence from the detection circuit and to oscillate the natural frequency continuously. The coil and the capacitor form a resonant circuit, and a resonant frequency circuit is set approximately equal to the natural frequency.

Abstract: In a detection unit, a measurement electrode member is arranged at a position where it contacts a developer, and has an input electrode for receiving a voltage from an apparatus main body and an output electrode for outputting an electrical signal in accordance with an electrostatic capacitance generated upon application of the voltage. A reference electrode member is arranged at a position where it does not contact the developer, and has an input electrode for receiving a voltage from the apparatus main body and an output electrode for outputting an electrical signal in accordance with an electrostatic capacitance generated upon application of the voltage. The measurement electrode member is adhered to an adhesion member. A lid member is coupled to the adhesion member and covers the reference electrode member. An engaging portion engages with a vessel positioning portion attached to the developer vessel, and positions the detection unit with respect to the developer vessel.

Abstract: An image forming apparatus and method causes a connecting/conveying device to convey a recovered toner from a cleaner part to a recovered toner housing unit to house therein the recovered toner. A controller controls a recovered toner supply unit and new toner supply unit in accordance with a toner concentration ratio in a developing device, which is detected by toner concentration ratio detecting unit, to supply the recovered toner, which is stored in the recovered toner housing unit, and a new toner, which is stored in new toner housing unit, to the developing device.

Abstract: A developing apparatus is provided in which a developer material in a development tank is made to circulate through a developer material storage vessel detachably mounted on the development tank, thereby prolonging the service life of the developer material. In the developing apparatus of the present invention, a predetermined developer material composed of a toner and a carrier stored in a development tank 31 is stirred by a stirring roller 33, and supplied to a latent image formed on a photoreceptor 11 by means of a development roller 32 in the development tank to visualize the latent image. The concentration of the toner consumed in the development tank is detected by a toner concentration sensor 34 so that toner is supplied from a toner storage tank 41 to the development tank so as to maintain the concentration of the toner at a constant level.

Abstract: A toner maintenance system for an electrophotographic developer unit, including a sump for storing a quantity of developer material a sump for storing a quantity of developer material comprised of toner material; a first member for transporting a mixture of developer material and toner particles from the sump, a viewing window, in communication with toner material, in the sump; an optical sensor, device for measuring reflected light off the viewing window and toner material, and generating a signal indicative thereof. A toner concentration controller is adapted to receive a signal from the sensor and to generate an “Add Toner” signal to replenish toner in the sump.

Abstract: An apparatus for controlling toner concentration includes a toner concentration detector, a toner supplier, a wave-former that periodically scrapes off toner from a detecting face of the toner concentration detector and thereby forms a wave of decreasing output of the toner concentration detector, and an about-minimum value detector that detects a minimum of the decreasing output. A toner concentration detection retarder is actuated from the time the minimum is detected. The toner supplier is actuated based on the detected toner concentration after the toner concentration detection retarder is released of action.

Abstract: An image forming apparatus and method cause a connecting/conveying device to convey a recovered toner from a cleaner part to recovered toner housing means to house therein the recovered toner, and cause control means to control recovered toner supply means and new toner supply means in accordance with a toner concentration ratio in a developing device, which is detected by toner concentration ratio detecting means, to supply the recovered toner, which is stored in the recovered toner housing means, and a new toner, which is stored in new toner housing means, to the developing device.

Abstract: A toner maintenance system for an electrophotographic developer unit, including a sump for storing a quantity of developer material comprised of carrier and toner material; a first member for transporting a mixture of developer material and toner particles from the sump, the first member having a voltage applied thereto; a metering blade, positioned closely adjacent to the first member to maintain the compressed pile height of the developer material on first member at a desired level; and a sensor device for measuring the current between the first member and the metering blade, and generating a signal indicative thereof.

Abstract: A developer container for containing a developer includes a detecting member for detecting a developer amount having an electrode member having a pair of input-side and output-side electrodes formed in parallel and in one plane at a predetermined interval and adapted to detect the capacitance between the electrodes, a measurement-side electrode that is in contact with the developer, and a reference electrode that is out of contact with the developer, the detecting member being provided on a side surface of the developer container. The container also includes a developer removing member for removing developer adhering to a detection surface of the detecting member, the developer removing member being attached to the developer conveying member and in contact with the detection surface of the detecting member so as to remove developer on the detection surface of the detecting member.

Abstract: An image forming apparatus has a plurality of image forming devices for forming images in different colors. Each image forming device has an image bearing member, a charging device for charging the image bearing member, a developing device for developing an electrostatic latent image formed on the image bearing member by a developer containing toner and a carrier, and a detecting device for detecting information corresponding to the permeability of the developer in the developing device. The apparatus also has a control device for controlling the amount of the developer supplied to each developing device according to an output from the detecting device and a corresponding target value. Each charging device has magnetic particles which are brought into contact with the image bearing member. The permeability of the magnetic particles is different from the permeability of the carrier. The apparatus also has a correcting device for correcting each of the target values.

Abstract: A cartridge detachably mountable to a main body of an image forming apparatus which has a developing device for developing an electrostatic image formed on an image bearing member with two-component developer includes a toner and a carrier. The developing device has a density detecting portion for detecting toner density of a start agent of the developer and the main body of the apparatus performs a setting operation for setting a control value for controlling the density detecting portion on the basis of a detection result of the density detecting portion and storing device for storing information that the setting operation is performed.

Abstract: A developing device of the present invention includes a conveying member for conveying a developer that is a toner and carrier mixture. A sensor senses the toner content of the developer in terms of the permeability of the developer. A preventing member prevents the bulk density of the developer from varying when fresh toner is not replenished. The developing device obviates erroneous toner content sensing when fresh toner is not replenished. An image forming apparatus including the developing device is also disclosed.

Abstract: A developer density controlling apparatus includes image density detecting device for detecting a target density on the basis of a detected image and, if a difference between a toner density detected by a developer density detecting device and the target density is equal to or greater than a predetermined value, the image density detecting device does not correct the target density.

Abstract: An image forming apparatus is provided with a plurality of developing units containing developer used for supplying the developer to an image bearer. The image forming apparatus also includes a plurality of detectors for detecting densities of the developer in the plurality of developing units, and a replenishing unit for replenishing the plurality of developing units with a developer based on detection results output from the plurality of detectors. The image forming apparatus further includes a plurality of control units for executing a plurality of replenishment operation from the replenishment unit to a developing unit based on the developer density in the plurality of developing units, and a developer-empty state detecting unit for detecting a developer-empty state of the replenishment unit.

Abstract: An image forming apparatus including a developing unit for stocking a developing agent containing toner and forming a toner image on a photosensitive medium with the developing agent, a toner supply unit for supplying the toner to the developing unit, a toner specific concentration detecting unit for detecting the toner specific concentration of the developing agent stocked in the developing unit, a humidity detecting unit for detecting humidity in the neighborhood of the developing unit, a storage unit for storing the humidity information detected by the humidity detecting unit, and a toner specific concentration correcting unit for controlling the toner supply amount of the toner supply unit on the basis of the humidity information stored to correct the toner specific concentration, wherein the toner specific concentration correcting unit compares newly-detected humidity with reference humidity corresponding to the humidity which is detected at the time when the developing agent is stocked into the developi

Abstract: There is provided a toner supply method in a picture image forming system having a plurality of picture image forming parts, each of which is designed to supply a toner from a toner cartridge to a developing part, the toner supply method having the steps of: detecting a cartridge empty when the level of the toner in the toner cartridge of any one of the picture image forming parts becomes an empty level; introducing a toner, which remains in the toner cartridge of each of the plurality of picture image forming parts, from the toner cartridge of a corresponding one of the plurality of picture image forming parts into a reserve tank portion, which is provided so as to correspond to each of the toner cartridges for housing therein a predetermined quantity of toner, when the cartridge empty is detected in any one of the picture image forming parts; detecting a toner empty when the level of the toner in the developing part becomes an empty level in any one of the picture image forming parts; and inspiring to repla

Abstract: The present invention provides a toner concentration control device which can measure the concentration of toner stably in an extended period of time without influenced by the shape of a developer stirring mixer rib and mounting position of a toner concentration detecting censer, with a result the stagnation or adhesion of toner in the proximity of the toner concentration detecting censer is eliminated, by so composing a toner concentration control device having a toner concentration censer for detecting magnetically the concentration of toner mounted facing a developer stirring mixer in a developing vessel, so that a waveform detection means which detects the output of the toner concentration censer for at least over one cycle before a toner supply means is activated, and an about-minimum value judging means which judges the minimum value or its vicinity detected by the waveform detection means are provided, and an about-minimum detection means is activated on the basis of the value judged as minimum or its

Abstract: An image forming apparatus includes a plurality of image forming stations forming images of different colors on a transfer material and is provided along a direction of conveyance of the transfer material by a conveying system, in which a toner replenishing system is operated on the basis of a result of a detected magnetic permeability a detecting device and the developer, which is not transferred to the transfer material but and, which remains on an image bearing member is collected by a developing system.

Abstract: A method for determining whether or not a developer container to contain developer is attached to the main body of an apparatus comprises the steps of detecting information of the magnetic permeability of developer in the developer container; and determining whether or not the developer container is attached to the main body of the image forming apparatus in accordance with an output (or outputs) obtained in the step of detection. With the adoption of this method comprising these steps, there is no need for providing separately any sensor or the like which is dedicated to determining whether or not the developer container is attached to the main body of the image forming apparatus, hence making it possible to implement reducing the costs of an image forming apparatus, and making the image forming apparatus smaller.

Abstract: A toner concentration detecting apparatus, which can accurately detect a toner concentration of a developer without being influenced by ions, is provided. A first electrode and a second electrode are disposed face to face with a developer between the electrodes. First, a voltage of a first power supply is applied to the electrodes. After a designated time, by switching means, a voltage of a second power supply, whose polarity is different from the first power supply, is applied to the electrodes. By using a changing of current flowing between the electrodes caused by the difference between the transferring speed of toner particles and that of ions after switching the polarity of the power supply, a toner concentration calculating means calculates the toner concentration of the developer by using a table showing the relation between a peak value by the toner particles and the toner concentration. With this, the toner concentration can be calculated accurately.

Abstract: A developing device comprises a developer bearing member for bearing and conveying a developer having a toner and a carrier, a first magnetic pole arranged in the developer bearing member, a second magnetic pole arranged in the developer bearing member, a polarity of the second magnetic pole being opposite to a polarity of the first magnetic pole, and the second magnetic pole being adjacent to the first magnetic pole and arranged on a downstream side of the first magnetic pole in a moving direction of the developer bearing member, a regulating member for regulating a layer thickness of the developer borne by the developer bearer, the regulating member being arranged in the vicinity of the second magnetic pole and a concentration detector for detecting a concentration of the toner in the developer.

Abstract: To provide an image forming apparatus provided with a function for forming an image on a recording medium such as a sheet or the like.

Abstract: A developing device mounted on a main body of an electrophotographic image forming apparatus and adapted to develop an electrostatic latent image formed on an electrophotographic photosensitive member includes a developer container having a developing portion with a developer bearing member for containing a developer and feeding the developer to the electrophotographic photosensitive member, and a hopper portion for containing the developer and supplying the developer to the developing portion, in order to develop the electrostatic latent image formed on the electrophotographic photosensitive member, and a developer residual amount detecting electrode pair having first and second electrodes disposed to interpose said developing portion and the hopper portion therebetween in order to detect the residual amount of developer by the main body of the electrophotographic image forming apparatus, wherein the developer residual amount detecting electrode pair are shaped such that a space region defined between the fi

Abstract: A replenisher material of toner particles and carrier particles, wherein a replenisher ratio of the toner particles to the carrier particles in the replenisher is determined as a function of at least one property of the developer and at least one operational property of an apparatus for developing an electrostatic latent image recorded on an image receiving member, and wherein the apparatus includes a housing defining a chamber having a supply of developer comprised of toner particles and carrier particles therein, a donor member spaced from the image receiving member and adapted to transport toner particles of the developer from the chamber to a development zone adjacent the image receiving member, at least one wire positioned in the development zone between the image receiving member and the donor member, a voltage supply for electrically biasing the at least one wire during a developing operation with a current to detach toner particles from the donor member, forming a cloud of toner particles in the devel

Abstract: An image forming apparatus includes an image carrier and a developing device to develop a latent image formed on the image carrier by applying two-component developer, including toner, onto the latent image. The developing device includes a developing part containing the two-component developer and a developer stirring device to stir the two-component developer. A toner supplying device supplies toner to the developing part of the developing device, and a toner density detection device detects a toner density of the two-component developer in the developing device. A toner control device calculates a difference between an output value VT of the toner density detection device and a criterion value VTref for controlling the toner density of the two-component developer and controls the toner supplying device based upon the difference.

Abstract: A toner content control device for an electrophotographic apparatus of the type using a toner and carrier mixture. The control device determines an amount of toner replenishment on the basis of a difference between the toner content of the developer and a reference value, while correcting the reference value in accordance with the condition of a reference pattern formed on a photoconductive element. Although the control device includes a toner content sensor and a pattern density sensor, it omits conventional means for adjusting the toner content sensor. The control device is therefore capable of controlling image density stably with an inexpensive configuration.

Abstract: A developing device having a developer bearing member for carrying thereon a developer having toner and carrier and conveying the developer to a developing area, an agitating member for agitating the developer, a rotation radius R (m) of the agitating member being 5.0.times.10.sup.-3 (m)<R<8.0.times.10.sup.-3 (m), and a density sensor for detecting a density of the toner in the developer, the density sensor detecting any change in the density of the toner as a change in a magnetic permeability of the developer, wherein when a shortest distance between an outermost surface of the agitating member and a detecting surface of the sensor is defined as Dmin (m) and a half length of the detecting surface of the sensor in a plane perpendicular to a rotary axis of the agitating member is defined as r, 0 (m)<Dmin<1.0.times.10.sup.31 3 (m) and 0.4<r/R<0.75.