Image forming apparatus having transfer position changing mechanism

An image forming apparatus comprising:

• a rotatable endless intermediate transfer belt configured to convey a toner image;
• a plurality of tension rollers configured to tension the belt, and including an inner roller and an upstream roller that is disposed adjacent to the inner roller on an upstream side of the inner roller with respect to a rotational direction of the belt;
• an outer roller contacting an outer peripheral surface of the belt and configured to form a transfer portion, where the toner image is transferred from the belt onto a recording material, by nipping said intermediary transfer belt between itself and the inner roller;
• a pressing member configured to come into contact with an inner peripheral surface of the belt on the upstream side of the inner roller and on a downstream side of the upstream roller with respect to a rotational direction of the belt, and press the belt from an inner peripheral surface side to an outer peripheral surface side;
• a first position changing mechanism configured to change a position of the inner roller, and change a position of the transfer portion;
• a second position changing mechanism configured to change a position of the pressing member;
• and
• a controller configured to control the first position changing mechanism and the second position changing mechanism,
• wherein in a cross section substantially orthogonal to a rotational axis direction of the inner roller, a common tangent line of the inner roller and the upstream roller on a side on which the belt is suspended is defined as a reference line LL a straight line passing through a rotation center of the inner roller and being substantially orthogonal to the reference line L1 is defined as an inner roller center line L2, a straight line passing through a rotation center of the outer roller and being substantially orthogonal to the reference line L1 is defined as an outer roller center line L3, and a distance between the inner roller center line L2 and the outer roller center line L3 is defined as an offset amount X (here, a positive value when the outer roller center line L3 is located upstream of the inner roller center line L2 in the rotational direction of the belt),
• the controller controls the second position changing mechanism such that when the offset amount X is a first offset amount X1, the pressing member presses the inner peripheral surface of the belt, and when the offset amount X is a second offset amount X2 (>0) larger than the first offset amount X1, the pressing member separates from the inner peripheral surface of the belt.

An image forming apparatus comprising:

• a rotatable endless intermediate transfer belt configured to convey a toner image;
• a plurality of tension rollers configured to tension the belt, and including an inner roller and an upstream roller that is disposed adjacent to the inner roller on an upstream side of the inner roller with respect to a rotational direction of the belt;
• an outer roller contacting an outer peripheral surface of the belt and configured to form a transfer portion, where the toner image is transferred from the belt onto a recording material, by nipping said intermediary transfer belt between itself and the inner roller;
• a pressing member configured to come into contact with an inner peripheral surface of the belt on the upstream side of the inner roller and on a downstream side of the upstream roller with respect to a rotational direction of the belt, and press the belt from an inner peripheral surface side to an outer peripheral surface side;
• a first position changing mechanism configured to change a position of the inner roller, and change a position of the transfer portion;
• a second position changing mechanism configured to change a position of the pressing member;
• and
• a controller configured to control the first position changing mechanism and the second position changing mechanism,
• wherein in a cross section substantially orthogonal to a rotational axis direction of the inner roller, a common tangent line of the inner roller and the upstream roller on a side on which the belt is suspended is defined as a reference line L1, a straight line passing through a rotation center of the inner roller and being substantially orthogonal to the reference line L1 is defined as an inner roller center line L2, a straight line passing through a rotation center of the outer roller and being substantially orthogonal to the reference line L1 is defined as an outer roller center line L3, and a distance between the inner roller center line L2 and the outer roller center line L3 is defined as an offset amount X (here, a positive value when the outer roller center line L3 is located upstream of the inner roller center line L2 in the rotational direction of the belt),
• the controller controls the second position changing mechanism such that when the offset amount X is a first offset amount X1, an intrusion amount Y of the pressing member with respect to the belt is set to a first intrusion amount Y1, and when the offset amount X is a second offset amount X2 (>0) larger than the first offset amount X1, the intrusion amount Y is smaller than the first intrusion amount Y1.