A developing device includes a magnet roller, a developing sleeve that revolves in a predetermined direction of revolution around the magnet roller, a developer tank having an opening that forms a development region by opening a part of a surface of the developing sleeve in a circumferential direction, a regulating member that regulates a layer thickness of a developer on the surface of the developing sleeve, and a toner residue reduction member that reduces a residue of a toner adhering directly to the surface of the developing sleeve.

A developer device includes a housing having an opening, a developing roller configured to rotate within the housing, the developing roller having a first portion that is exposed through the opening of the housing and a second portion at which developer attached to the developing roller separates from the developing roller, a first airflow passage formed in the housing, and a second airflow passage facing a third portion of the developing roller at a location of the developing roller between the first and second portions and connected to the first airflow passage.

A developing device includes a housing, a developing roller, a developer stirring member, and a layer thickness regulating member. The developing roller includes a stationary magnet and a sleeve. The stationary magnet includes a first magnetic pole having a specific polarity, and a second magnetic pole lying downstream of the first magnetic pole and having the same polarity as the first magnetic pole. In an entire inter-pole region between the first magnetic pole and the second magnetic pole, the stationary magnet produces a magnetic force including a horizontal component that keeps the specific polarity and has a value greater than zero (mT). The inter-pole region includes a flat area where a horizontal magnetic force component having a minimum absolute value exits and the horizontal magnetic force component changes within a range of 0.5 (mT) or less, the flat area extending over a range of 10 degrees or more.

A developing device includes a developing roller which includes: a magnet roller having a plurality of magnetic poles in a circumferential direction; and a developing sleeve rotatably supported along an outer peripheral surface of the magnet roller, and which is configured to supply a toner to an image bearing member. The magnet roller is configured so that the relative position thereof to the developing sleeve is changeable.

A developing device includes a developing container, a developing roller, a supplying roller, a first magnet including a first magnetic pole, a second magnet including second to fifth magnetic poles, and a regulating member. A maximum magnetic flux density of the second magnetic pole is larger in absolute value than a maximum magnetic flux density of the third magnetic pole in a normal direction to the supplying roller, and a maximum magnetic flux density of the third magnetic pole is larger in absolute value than a maximum magnetic flux density of the fourth magnetic pole in the normal direction. With respect to a rotational direction of the supplying roller, an angle between maximum magnetic flux density positions of the second and third magnetic poles is smaller than an angle between maximum magnetic flux density positions of the third and fourth magnetic poles.

A developer roll according to one example embodiment includes a core including at least one permanent magnet forming a magnetized portion of the core. A cylindrical sleeve positioned around the core is rotatable relative to the core about an axis of rotation in an operative rotational direction. A release pole of the permanent magnet is positioned to magnetically attract developer mix to an outer circumferential surface of the sleeve to transport developer mix on the surface of the sleeve in the operative rotational direction when the sleeve rotates relative to the core to a release point where a magnetic field of the permanent magnet is insufficient to retain developer mix against the surface of the sleeve. An axial length of the magnetized portion of the core decreases at both axial ends of the core as the magnetized portion of the core approaches the release point in the operative rotational direction.

A developing device includes a developing container, a developing sleeve, a magnet and grooves provided at a surface of the sleeve and formed along a direction crossing a circumferential direction of the sleeve. In a cross-section, each of the grooves is formed by a flat bottom portion contacting a carrier particle and a pair of side surface portions provided in both sides of the flat bottom portion with respect to the circumferential direction of the sleeve and satisfies the following relationship:

r<w<2r,

2r<L, and

r/2s<2r.

In the above, r is a volume-average particle size of the carrier particles, w is a length of the flat bottom portion, L is a width between the side surface portions at the surface of the sleeve, and s is a depth of each of the grooves.

A developing sleeve includes first groove portions extending in an axial direction of the developing sleeve, wherein each first groove portion satisfies D.sub.12R and W.sub.12R, where 2R is a volume-average particle size of the carrier, D.sub.1 is a maximum depth of each first groove portion and W.sub.1 is a width an opening of each first groove portion with respect to a circumferential direction of the developing sleeve, and second groove portions extending in the axial direction of the developing sleeve, wherein each second groove portion satisfies D.sub.2<2R, where 2R is the volume-average particle size of the carrier and D.sub.2 is a maximum depth of each second groove portion. Each or a plurality of the second groove portions are disposed between the first groove portions with respect to the circumferential direction of the developing sleeve.

A developing device includes a developing container, a developing sleeve, a magnet and grooves provided at a surface of the sleeve and formed along a direction crossing a circumferential direction of the sleeve. In a cross-section, each of the grooves is formed by a flat bottom portion contacting a carrier particle and a pair of side surface portions provided in both sides of the flat bottom portion with respect to the circumferential direction of the sleeve and satisfies the following relationship:
r<w<2r,
2r<L, and
r/2s<2r. In the above, r is a volume-average particle size of the carrier particles, w is a length of the flat bottom portion, L is a width between the side surface portions at the surface of the sleeve, and s is a depth of each of the grooves.

A developer device includes a housing having an opening, a developing roller configured to rotate within the housing, the developing roller having a first portion that is exposed through the opening of the housing and a second portion at which developer attached to the developing roller separates from the developing roller, a first airflow passage formed in the housing, and a second airflow passage facing a third portion of the developing roller at a location of the developing roller between the first and second portions and connected to the first airflow passage.