Developing unit and electro-photographic apparatus

A developing unit for developing an electrostatic latent image formed on a photosensitive body by supplying colored particles to a surface of the photosensitive body, comprising:

• first and second developing rollers each having a core and a sleeve, the sleeve accommodating the core, the core having magnetic poles;
• wherein
• the cores of the first and second developing rollers have the same arrangement of the magnetic poles;
• the magnetic pole of the core of one of the first and second developing rollers is placed at an opposing position where first and second developing rollers mutually oppose, while the core of the other one of the first and second developing rollers is disposed such that a intermediate portion between the magnetic poles thereof is placed at the opposing position;
• the sleeve of the first developing roller is driven to rotate in the same direction as a moving direction of the surface of the photosensitive body;
• and
• the sleeve of the second developing roller is driven to rotate in an opposite direction to the moving direction of the surface of the photosensitive body.

An electro-photographic apparatus comprising:

• a photosensitive body;
• a charger for charging a surface of the photosensitive body;
• an exposing unit for exposing the surface of the photosensitive body charged by the charger to form an electrostatic latent image having different potential levels of at least two values on the surface of the photosensitive body;
• a developing unit for forming a visible image on the photosensitive body by supplying colored particles to the surface of the photosensitive body;
• and
• a transfer unit for transferring the visible image onto a recording medium;
• wherein
• the developing unit comprises a plurality of developing rollers each having a core and a sleeve, the sleeve accommodating the core;
• the plurality of developing rollers includes a first developing roller and a second developing roller;
• the sleeve for the first developing roller is rotated to move in the same direction as a moving direction of the surface of the photosensitive body;
• the sleeve for the second developing roller is rotated to move in an opposite direction to the moving direction of the surface of the photosensitive body;
• and
• the core for at least one of the plurality of developing rollers is driven in rotation.

An electro-photographic apparatus, comprising:

• a photosensitive body;
• a charger for charging a surface of the photosensitive body;
• an exposing unit for exposing the surface of the photosensitive body charged by the charger to form an electrostatic latent image having different potential levels of at least two values on the surface of the photosensitive body;
• a developing unit for forming a visible image on the photosensitive body by supplying colored particles to the surface of the photosensitive body;
• and
• a transfer unit for transferring the visible image onto a recording medium;
• wherein
• the developing unit comprises first and second developing rollers each having a core and a sleeve, the sleeve accommodating the core, the core having magnetic poles;
• the cores of the first and second developing rollers have the same arrangement of the magnetic poles;
• the magnetic pole of the core of one of the first and second developing rollers is placed at an opposing position where first and second developing rollers mutually oppose, while the core of the other one of the first and second developing rollers is disposed such that an intermediate portion between the magnetic poles thereof is placed at the opposing position;
• the sleeve of the first developing roller is driven to rotate in the same direction as a moving direction of the surface of the photosensitive body;
• and
• the sleeve of the second developing roller is driven to rotate in an opposite direction to the moving direction of the surface of the photosensitive body.

An electro-photographic printer for forming an image,

• comprising:
• a developing unit having a plurality of developing rolls, each having a cylindrical sleeve and a magnet roll, the magnet roll disposed inside the sleeve;
• wherein
• the plurality of developing rolls include a double rotation developing roll and a sleeve rotation developing roll, the sleeve rotation developing roll disposed in proximity of the double rotation developing roll;
• both of the sleeve and the magnet roll of the double rotation developing roll are rotatable;
• the sleeve of the sleeve rotation developing roll is rotatable while the magnet roll of the sleeve rotation developing roll is fixed;
• a first angle between magnetic poles of the magnet roll of the double rotation developing roll as seen from the center thereof is smaller than a second angle between predetermined magnetic poles of the magnet roll of the sleeve rotation developing roll as seen from the center;
• and
• the predetermined magnetic poles are arranged closer to the double rotation developing roll than the other magnetic poles of the magnet roll of the sleeve rotation developing roll.

An electro-photographic printer for forming an image,

• comprising:
• a developing unit having a plurality of developing rolls, each having a cylindrical sleeve and a magnet roll, the magnet roll disposed inside the sleeve;
• wherein
• the plurality of developing rolls include a double rotation developing roll and a sleeve rotation developing roll, the sleeve rotation developing roll disposed in proximity of the double rotation developing roll;
• both of the sleeve and the magnet roll of the double rotation developing roll are rotatable;
• the sleeve of the sleeve rotation developing roll is rotatable while the magnet roll of the sleeve rotation developing roll is fixed;
• a first distance between magnetic poles on a magnet roll surface of the double rotation developing roll is smaller than a second distance between predetermined magnetic poles on a magnet roll surface of the sleeve rotation developing roll;
• and
• the predetermined magnetic poles are arranged closer to the double rotation developing roll than the other magnetic poles of the magnet roll of the sleeve rotation developing roll.