US Patent No. 9,341,993

IMAGE FORMING APPARATUS


Patent No. 9,341,993
Issue Date May 17, 2016
Title Image Forming Apparatus
Inventorship Tohru Nakaegawa, Nagareyama (JP)
Assignee CANON KABUSHIKI KAISHA, Tokyo (JP)

Claim of US Patent No. 9,341,993

1. An image forming apparatus comprising:
an image bearing member;
an electrostatic image forming unit for forming an electrostatic image on said image bearing member;
a developing unit for developing the electrostatic image, formed on said image bearing member, into a toner image;
an intermediary transfer member for carrying and feeding the toner image primary-transferred thereon from said image bearing
member at a primary transfer position;

a rotatable secondary transfer member for secondary-transferring the toner image from said intermediary transfer member onto
a recording material at a secondary transfer position by feeding the recording material by rotation thereof while sandwiching
the recording material between itself and said intermediary transfer member;

a constant voltage element electrically connected between said intermediary transfer member and a ground potential;
a voltage source for applying a voltage to said rotatable secondary transfer member to form a secondary transfer electric
field at the secondary transfer position and for passing a current through said constant voltage element to form a primary
transfer electric field at the primary transfer position,

wherein said apparatus is operable in a lowering mode in which the secondary transfer electric field in a trailing end region
of the recording material passing through the secondary transfer position with respect to a recording material feeding direction
is made lower than the secondary transfer electric field in a region from a leading end to the trailing end region of the
recording material; and

a controller for setting a toner image distance between consecutively formed toner images in an operation in the lowering
mode,

wherein said controller sets the toner image distance so as to be longer than the toner image distance when the operation
in the lowering mode is not performed to prevent a toner image from being primary-transferred in a period in which the secondary
transfer electric field is lowered.