Abstract: A developing apparatus includes a rotatable developer bearing member, a first conveyance screw in a first chamber to convey the developer, and a second conveyance screw in a second chamber to convey the developer. The second conveyance screw includes a first screw portion facing a communication portion between the first and second chambers, a second screw portion downstream of the first screw portion, and a third screw portion downstream of the first screw portion and upstream of the second screw portion and facing the second communication portion. The first screw portion includes a first blade portion formed spirally around a rotation shaft of the second conveyance screw, the second screw portion has a second blade portion formed spirally around the rotation shaft of the second conveyance screw, and the third screw portion comprises no blade portion formed spirally around the rotation shaft of the second conveyance screw.

Abstract: A feeding screw for feeding a developer includes a rotation shaft, and a helical blade provided on the rotation shaft and including a plurality of threads. The feeding screw includes a first blade helically formed with a single thread on the rotation shaft, a second blade helically formed with a single thread on the rotation shaft, and a third blade helically formed with a single thread on the rotation shaft. With respect to a direction along the rotation shaft, a gap is provided between a downstream end portion of the second blade and an upstream end portion of the first blade. The gap is disposed corresponding to a region where the first blade is continuously formed.

Abstract: A feeding screw includes a rotation shaft, and a plurality of blades helically formed with threads on the rotation shaft. The feeding screw includes a section in which a helix angle of each of the blades is not more than 56.5°.

Abstract: A developing device includes a developer carrying member, a first chamber, a second chamber, a first communicating portion, a second communicating portion, and a feeding screw, provided in the second chamber, including a feeding portion having a first helical blade and including a returning portion having a second helical blade in the form of a plurality of threads, the feeding portion and the returning portion being provided so that a boundary portion therebetween opposes the second communicating portion. The first helical blade and the second helical blade satisfy the following relationship: P2?P1, where P1 is a pitch of the first helical blade and P2 is a pitch of the second helical blade.

Abstract: A developing apparatus includes a first screw disposed within a first chamber and conveying developer in a first direction, a second screw disposed within a second chamber and having a conveyance portion conveying the developer in a second direction opposite to the first direction and a return portion provided downstream of a first communication port in a first wall dividing the first and second chambers. A discharge portion in the second chamber, downstream of the return portion, discharges the developer out of the second chamber, and a second wall through which a third communication port is disposed upstream of the discharge portion is defined to deliver the developer from the second chamber to the first chamber. The second wall faces at least a part of the return portion in a view from a horizontal direction such that a lower end of the third communication port is located above a lower end of the first communication port.

Abstract: An image forming apparatus includes first and second image forming portions. A first conveying pipe conveys a first developer discharged from a first developing unit to a collection portion, and a second conveying pipe conveys a second developer discharged from a second developing unit to the collection portion. A first detection unit detects a toner content of the first developer in the first conveying pipe, and a second detection unit detects a toner content of the second developer in the second conveying pipe. The first developing unit can be removed from the image forming apparatus in a state that the first conveying pipe and the first detection unit remain in the image forming apparatus, and the second developing unit can be removed from the image forming apparatus in a state that the second conveying pipe and the second detection unit remain in the image forming apparatus.

Abstract: A developing device includes a first communication portion defining a communication path through which developer in a second chamber is communicated to a first chamber. The communication path has a first area and a second area. The first area is positioned within a range corresponding to a developer coating area of a developer bearing member in a conveyance direction of developer in the collection chamber, while the second area is positioned downstream of the developer coating area in the conveyance direction. A first length of the first area is longer than a second length of the second area. The first length is a maximum length from a bottom surface portion of the communication path to an upper portion of the first area, and the second length is a maximum length from the bottom surface portion of the communication path to an upper portion of the second area.

Abstract: A control portion switches first and second modes based on information which influences a toner charging amount. In the first mode, a driving input to the developer bearing member is stopped in response to image formation completion before or at the same time when a trailing end of a charging area reaches the development position, and an application of the development voltage is stopped after the trailing end reaches the development position. In the second mode, The driving input to the developer bearing member is stopped in response to image formation completion before or at the same time when the trailing end reaches the development position, and the application of the development voltage is stopped at a timing after the trailing end reaches the development position and earlier than that in the first mode, or at the same time when the trailing end reaches the development position.

Abstract: An agitating screw at a first communication port delivering a developer from a collecting chamber to a developing chamber is formed to be a multiple-threaded screw. The use of the multiple-threaded screw makes it possible to increase a developer surface level at the first communication port. If the developer surface level becomes too high within the collecting chamber, an image defect caused by entrainment of the developer by the developing sleeve may occur. Then, an arrangement is made such that the developer surface level does not become so high that may cause the entrainment of the developer by accelerating delivery of the developer at the first communication port. Thus, the use of the multiple-threaded screw makes it possible to accelerate the delivery of the developer and to reduce an image defect otherwise caused by the entrainment of the developer.

Abstract: A developing apparatus is provided with a third communication port downstream of a first communication port of a partition wall. The third communication port is disposed at a position facing a return screw when viewed from a horizontal direction. A lower end of the third communication port is located above a lower end of the first communication port. Because the first communication port is practically enlarged to the return screw, the delivery of the developer from an agitating chamber to a developing chamber is not suppressed even if fluidity of the developer drops. Accordingly, the developer is hardly rotated with a developing sleeve. Still further, because a partition wall prevents the developer from entering the third communication port, the discharge of the developer is hardly suppressed. This arrangement makes it possible to reduce an occurrence of image defect caused by the delivery and discharge of the developer.

Abstract: A developing device including a developer carrying sleeve; a first chamber; a second chamber; a partition having a first opening for relaying the developer from the first chamber into the second chamber and a second opening for relaying back, the partition partitioning between the chambers; a first feeder in the first chamber to feed the developer from the second opening toward the first opening; a second feeder the second chamber to feed the developer in the second chamber from the first opening toward the second opening; a first regulating portion above the second feeder, extended in a direction crossing with the second feeder to regulate movement of the developer fed by the second feeder; and a second regulating portion provided above the second feeder upstream of the first regulating member, extended in a direction crossing with the second feeder to regulate movement of the developer fed by second feeder.

Abstract: An image forming apparatus includes: an image bearing member; a developing unit; a discharge portion which is provided in the developing unit and configured to discharge a developer in the developing unit to the outside of the developing unit; a collection portion which collects the developer discharged from the discharge portion; a conveying pipe which is separable from the developing unit, includes a conveying screw therein, and conveys the developer discharged from the discharge portion to the collection portion; and a toner density sensor which detects toner density in the conveying pipe and of which a detection surface is positioned below a rotational axis of the conveying screw in a vertical direction, wherein the developing unit is removed from the image forming apparatus in a state in which the conveying pipe and the toner density sensor remain in the image forming apparatus.

Abstract: A control portion switches first and second modes based on information which influences a toner charging amount. In the first mode, a driving input to the developer bearing member is stopped in response to image formation completion before or at the same time when a trailing end of a charging area reaches the development position, and an application of the development voltage is stopped after the trailing end reaches the development position. In the second mode, The driving input to the developer bearing member is stopped in response to image formation completion before or at the same time when the trailing end reaches the development position, and the application of the development voltage is stopped at a timing after the trailing end reaches the development position and earlier than that in the first mode, or at the same time when the trailing end reaches the development position.

Abstract: A development device wherein a magnetic force distribution of a developer bearing member in a longitudinal direction at positions at which a magnetic flux density of a low magnetic field area is minimal in the peripheral direction of the developer bearing member is set such that a difference between a maximum magnetic flux density in a range from a maximum position at which an attenuation rate of the magnetic flux density is maximal to a 30 mm distant position toward the center of the developer bearing member and a magnetic flux density on a further center side of the developer bearing member than the range is 3 mT or less, and an absolute value of the magnetic flux density of a further outer side in the longitudinal direction of the developer bearing member than the maximum position is set to 3 mT or less.

Abstract: A development device wherein a magnetic force distribution of a developer bearing member in a longitudinal direction at positions at which a magnetic flux density of a low magnetic field area is minimal in the peripheral direction of the developer bearing member is set such that a difference between a maximum magnetic flux density in a range from a maximum position at which an attenuation rate of the magnetic flux density is maximal to a 30 mm distant position toward the center of the developer bearing member and a magnetic flux density on a further center side of the developer bearing member than the range is 3 mT or less, and an absolute value of the magnetic flux density of a further outer side in the longitudinal direction of the developer bearing member than the maximum position is set to 3 mT or less.

Abstract: An image forming apparatus includes an image bearing member and a developer replenishment device. In addition, a control portion executes a first mode of detecting a first toner image for control by a sensor and controlling an operation of the replenishment device so that a detection result from the sensor attains a first target value, a second mode of detecting a second toner image for control by the sensor and setting a development contrast of a maximum image density so that a detection result attains a second target value, and a third mode of detecting a third toner image for control by the sensor and changing, based on the detection result, at least one of the first target value and a development contrast of the first toner image for control, wherein the control portion executes the third mode according to a timing at which the second mode is executed.

Abstract: An image forming apparatus includes a photosensitive member; a corona charger, provided with an opening, for electrically charging the photosensitive member; a sheet-like shielding member for shielding the opening of the corona charger; a moving device for moving the shielding member in a longitudinal direction of the photosensitive member; a potential sensor for detecting a potential of a portion of the photosensitive member chargeable by the corona charger; and a controller for detecting, on the basis of a result of detection of the potential of the portion of the photosensitive member by the potential sensor, whether or not a charging operation capable of electrically charging the photosensitive member by the corona charger is performed in a state in which the shielding member is located between the opening of the corona charger and the photosensitive member.

Abstract: The image forming apparatus includes a photosensitive drum capable of bearing an electrostatic image, a development device having a developing sleeve capable of bearing a developer and a developer container capable of storing a magnetic toner, and a CPU controlling operation to discharge a developer having polarity opposite to a normally charged polarity to the photosensitive drum by enlarging a restoration electric field to force the developer having a normally charged polarity from the photosensitive drum to the development sleeve during image forming is not performed compared to that during normal image forming is performed, based on a weighted value (p×K) on an edge portion pixel number p of an edge portion of an output image.

Abstract: An image forming apparatus includes an image carrying member, an image forming mechanism, an optical sensor, and a controller. The image forming mechanism performs an image forming operation for forming a reference toner image on the image carrying member under a specific setting associated with the image forming mechanism. The optical sensor is arranged in a vicinity to the image carrying member. The controller performs an optical toner test for checking, by using the optical sensor, optical characteristics of the reference toner image formed on the image carrying member and to adjust the specific setting based on a result of the optical toner test.

Abstract: An image forming apparatus includes a photosensitive member; a corona charger, provided with an opening, for electrically charging the photosensitive member; a sheet-like shielding member for shielding the opening of the corona charger; a moving device for moving the shielding member in a longitudinal direction of the photosensitive member; a potential sensor for detecting a potential of a portion of the photosensitive member chargeable by the corona charger; and a controller for detecting, on the basis of a result of detection of the potential of the portion of the photosensitive member by the potential sensor, whether or not a charging operation capable of electrically charging the photosensitive member by the corona charger is performed in a state in which the shielding member is located between the opening of the corona charger and the photosensitive member.