Image forming method, image forming apparatus and toner image pattern

An image forming apparatus comprising:

• a plurality of image bearing members;
• an exposure unit configured to simultaneously reflect a plurality of light beams from a plurality of light sources by different reflection surfaces of a polygon mirror which has a plurality of reflection surfaces and is rotated in one direction, said plurality of light beams corresponding to a plurality of different colors;
• an image processing unit configured to transform electrostatic latent images formed on each of the plurality of image bearing members into toner images for correction, and to transfer the toner images on each of the image bearing members onto a transfer body that is transported in a transport direction;
• and
• a processing unit configured to calibrate overlapping positions of the toner images based on an optical detection of the toner images on the transfer body,
• wherein the toner images are arranged at positions on the transfer body such that the toner images derived from one of the different reflection surfaces have no overlap with the toner images derived from another one of the reflection surfaces even if the toner images shift in a direction perpendicular to the transport direction due to a color registration error,
• each of the toner images on the transfer body includes a first toner image having a linear portion arranged at an angle greater than 0 and less than 90 degrees with respect to the transport direction, and a second toner image having a linear portion arranged perpendicularly to the transport direction,
• two first toner images simultaneously formed by two corresponding light beams reflected by one reflection surface of the polygon mirror are arranged adjacent to each other in the transport direction, and two second toner images simultaneously formed by said two corresponding light beams reflected by said one reflection surface of the polygon mirror are arranged to sandwich the two first toner images along the transport direction, and
• a distance between two closest-to-each-other first toner images on the transfer body which derive from different reflection surfaces of the polygon mirror is longer than that between first toner images which are positioned so as to be adjacent to each other on the transfer body and derive from a same reflection surface of the polygon mirror.

A toner image pattern for use by an image forming method or apparatus which exposes a plurality of image bearing members by simultaneously reflecting a plurality of light beams from a plurality of light sources by different reflection surfaces of a polygon mirror which has a plurality of reflection surfaces and is rotated in one direction, said plurality of light beams corresponding to a plurality of different colors;

• transforms electrostatic latent images formed on each of the plurality of image bearing members into toner images for correction;
• transfers the toner images on each of the image bearing members onto a transfer body that is transported in a transport direction;
• and calibrates overlapping positions of the toner images based on an optical detection of the toner images on the transfer body, said toner image pattern comprising:
• the toner images arranged at positions on the transfer body such that the toner images derived from one of the different reflection surfaces have no overlap with the toner images derived from another one of the reflection surfaces even if the toner images shift in a direction perpendicular to the transport direction due to a color registration error;
• wherein each of the toner images on the transfer body includes a first toner image having a linear portion arranged at an angle greater than 0 and less than 90 degrees with respect to the transport direction, and a second toner image having a linear portion arranged perpendicularly to the transport direction;
• two first toner images simultaneously formed by two corresponding light beams reflected by one reflection surface of the polygon mirror are arranged adjacent to each other in the transport direction, and two second toner images simultaneously formed by said two corresponding light beams reflected by said one reflection surface of the polygon mirror are arranged to sandwich the two first toner images along the transport direction and
• a distance between two closest-to-each-other first toner images on the transfer body which derive from different reflection surfaces of the polygon mirror is longer than that between first toner images which are positioned so as to be adjacent to each other on the transfer body and derive from a same reflection surface of the polygon mirror.