Developing device, image forming apparatus, magnetic pole position correcting method

A developing device comprising:

• a developing roller disposed to face an image carrier across a predetermined gap and configured to be rotationally driven, the image carrier being configured to keep a toner image formed from supplied toner on an outer circumferential surface of the image carrier;
• and
• a developing magnetic pole provided in an inside of the developing roller, configured to generate a magnetic field in the gap, and configured to be displaced between a first magnetic pole position to generate the magnetic field at a predetermined first position in the gap, and a second magnetic pole position to generate the magnetic field at a second position in the gap, the second position being on an upstream side of the first position in a rotation direction of the developing roller, wherein
• when a blowing amount of air passing through the gap from the second position to the first position is increased, the developing magnetic pole is displaced toward the second magnetic pole position, and when the blowing amount is decreased, the developing magnetic pole is displaced toward the first magnetic pole position.

A magnetic pole position correcting method for correcting a position of a developing magnetic pole provided in an inside of a developing roller, wherein

• the developing magnetic pole is configured to be displaced between a first magnetic pole position to generate a magnetic field at a predetermined first position in a predetermined gap between the developing roller and an image carrier, and a second magnetic pole position to generate a magnetic field at a second position in the gap, the second position being on an upstream side of the first position in a rotation direction of the developing roller,
• the magnetic pole position correcting method comprising:
• a circumferential speed ratio determining step of determining whether or not a circumferential speed ratio of the developing roller to the image carrier has changed;
• and
• a position correcting step of, when the circumferential speed ratio is larger than before the determination by the circumferential speed ratio determining step, displacing the developing magnetic pole toward the second magnetic pole position, and when the circumferential speed ratio is smaller than before the determination by the circumferential speed ratio determining step, displacing the developing magnetic pole toward the first magnetic pole position.

A magnetic pole position correcting method for correcting a position of a developing magnetic pole provided in an inside of a developing roller, wherein

• the developing magnetic pole is configured to be displaced between a first magnetic pole position to generate a magnetic field at a predetermined first position in a predetermined gap between the developing roller and an image carrier, and a second magnetic pole position to generate a magnetic field at a second position in the gap, the second position being on an upstream side of the first position in a rotation direction of the developing roller,
• the magnetic pole position correcting method comprising:
• a blowing amount determining step of determining whether or not a blowing amount of air passing through the gap from the second position to the first position has changed;
• and
• a position correcting step of, when the blowing amount is larger than before the determination by the blowing amount determining step, displacing the developing magnetic pole toward the second magnetic pole position, and when the blowing amount is smaller than before the determination by the blowing amount determining step, displacing the developing magnetic pole toward the first magnetic pole position.