Image forming apparatus and method

An image forming apparatus comprising:

• a latent image support;
• an optical scanning system configured to form an electrostatic latent image on a circumferential surface of the latent image support, at a first screen angle in a first print mode, and at a second screen angle different from the first screen angle in a second print mode;
• a container configured to hold a binary developer;
• a development roller disposed so as to face the latent image support and form a development area in between, and configured to carry the binary developer from the container to the development area;
• and
• a control circuit configured to rotationally drive the development roller at a first rotation speed during a development process, wherein,
• the development roller has depression portions and land portions on a circumferential surface, the depression portions and the land portions forming oblique grooves in the surface, and
• in the second print mode, the control circuit is configured to rotationally drive the development roller at a second rotation speed different from the first rotation speed, such that a crossing angle approximates 90°, the crossing angle being formed by a screen line in the electrostatic latent image on the circumferential surface of the latent image support and an area where the land portion of the development roller substantially passes over the circumferential surface of the latent image support.

An image forming apparatus comprising:

• a latent image support;
• an optical scanning system configured to form an electrostatic latent image at a predetermined screen angle on a circumferential surface of the latent image support;
• a container configured to hold a binary developer;
• a development roller disposed so as to face the latent image support and form a development area in between, and configured to carry the binary developer from the container to the development area;
• and
• a control circuit configured to rotationally drive the development roller during a development process, wherein,
• the development roller has depression portions and land portions on a circumferential surface, the depression portions and the land portions being created by forming grooves in the surface at a predetermined angle of inclination, and
• the angle of inclination is decided such that a crossing angle approximates 90° while the development roller is rotationally driven, the crossing angle being formed by a screen line in the electrostatic latent image on the circumferential surface of the latent image support and an area where the land portion of the development roller substantially passes over the circumferential surface of the latent image support.

An image forming method for use in an image forming apparatus including a latent image support, an optical scanning system configured to form an electrostatic latent image at a predetermined screen angle on a circumferential surface of the latent image support, a container configured to hold a binary developer, and a development roller that is disposed so as to face the latent image support and form a development area in between, and configured to carry the binary developer from the container to the development area, said method comprising the steps of:

• determining a current print mode from among a plurality of print modes;
• setting a screen angle for the determined print mode, the screen angle varying among the print modes, and
• rotationally driving the development roller at a rotation speed for the screen angle being set, the rotation speed varying among screen angles to be set, wherein,
• the development roller has depression portions and land portions on a circumferential surface, the depression portions and the land portions being created by forming grooves in the surface at a predetermined angle of inclination, and
• the rotation speed of the development roller is decided for each print mode such that a crossing angle approximates 90°, the crossing angle being formed by a screen line in the electrostatic latent image on the circumferential surface of the latent image support and an area where the land portion of the development roller substantially passes over the circumferential surface of the latent image support.