Image forming apparatus with control of suction forces in suction fans during sheet conveyance
An image forming apparatus includes a transfer unit, a fixing unit, a conveyance unit, and a control unit. The control unit selectively performs a plurality of modes including a first mode and a second mode. The first mode is a mode in which, when a grammage of a sheet is a first grammage, if a leading edge of the sheet has reached the fixing unit, the control unit controls the first suction unit such that suction force of the first suction unit becomes first suction force. The second mode is a mode in which, when the grammage of the sheet is a second grammage smaller than the first grammage, if a leading edge of the sheet has reached the fixing unit, the control unit controls the first suction unit such that the suction force of the first suction unit becomes second suction force smaller than the first suction force.
1 . An image forming apparatus comprising:
a transfer unit including a transfer nip portion configured to nip and convey a sheet, the transfer unit being configured to transfer a toner image borne on an image bearing member onto the sheet nipped by the transfer nip portion;
a fixing unit including a fixing nip portion configured to nip and convey the sheet, the fixing unit being configured to fix the toner image transferred onto the sheet by the transfer unit on the sheet;
a conveyance unit configured to convey the sheet from the transfer unit toward the fixing unit, the conveyance unit including:
an endless belt configured to convey the sheet supported on a conveyance surface of the endless belt;
a first suction fan configured to suck the sheet onto a first area of the conveyance surface; and
a second suction fan configured to suck the sheet onto a second area of the conveyance surface, the second area being upstream of the first area in a sheet conveyance direction;
a guide configured to guide the sheet conveyed by the endless belt to the fixing unit, the guide being located intersecting with an imaginary plane extending the conveyance surface of the endless belt as viewed in a sheet width direction intersecting with the sheet conveyance direction; and
a control unit configured to control a suction force of the first suction fan and a suction force of the second suction fan so that:
the suction force of the first suction fan is smaller than the suction force of the second suction fan before a leading end of the sheet reaches the fixing nip portion; and
the suction force of the first suction fan remains smaller than the suction force of the second suction fan in a state where the leading end of the sheet reaches the fixing nip portion.
2 . The image forming apparatus according to claim 1 , wherein the conveyance unit further includes:
a first supporting roller configured to support the endless belt; and
a second supporting roller configured to support the endless belt, the second supporting roller being disposed downstream of the first supporting roller in the sheet conveyance direction.
3 . The image forming apparatus according to claim 2 , wherein the conveyance surface of the endless belt is arranged parallel to a common tangent line to the first supporting roller and the second supporting roller.
4 . The image forming apparatus according to claim 1 , wherein the control unit is configured to change the suction force of the first suction fan based on a grammage of the sheet conveyed by the endless belt.
5 . The image forming apparatus according to claim 1 , wherein:
the endless belt is a first endless belt, and the conveyance surface is a first conveyance surface,
the conveyance unit includes a second endless belt located upstream of the first endless belt in the sheet conveyance direction,
the sheet is supported on a second conveyance surface of the second endless belt, and
a downstream end of the second conveyance surface in the sheet conveyance direction is positioned above an upstream, in the sheet conveyance direction, end of the first conveyance surface in a vertical direction.
6 . An image forming apparatus comprising:
a transfer unit including a transfer nip portion configured to nip and convey a sheet, the transfer unit being configured to transfer a toner image borne on an image bearing member onto the sheet nipped by the transfer nip portion;
a fixing unit including a fixing nip portion configured to nip and convey the sheet, the fixing unit being configured to fix the toner image transferred onto the sheet by the transfer unit on the sheet;
a conveyance unit configured to convey the sheet from the transfer unit toward the fixing unit, the conveyance unit including:
an endless belt configured to convey the sheet is supported on an upper surface of the endless belt;
a plurality of supporting portions configured to support the endless belt and including a first supporting portion and a second supporting portion, the first supporting portion being located at the highest position among the plurality of supporting portions, the second supporting portion being located at the second highest position among the plurality of supporting portions;
a first suction fan disposed between the first supporting portion and the second supporting portion in a sheet conveyance direction and configured to suck the sheet onto the upper surface; and
a second suction fan disposed between the first supporting portion and the second supporting portion in the sheet conveyance direction and configured to suck the sheet onto the upper surface, wherein the second suction fan is disposed upstream of the first suction fan; and
a control unit configured to control a suction force of the first suction fan and a suction force of the second suction fan so that:
the suction force of the first suction fan is smaller than the suction force of the second suction fan before a leading end of the sheet reaches the fixing nip portion; and
the suction force of the first suction fan remains smaller than the suction force of the second suction fan in a state where the leading end of the sheet reaches the fixing nip portion.
7 . The image forming apparatus according to claim 6 , wherein:
the first supporting portion is a first supporting roller configured to support the endless belt, and
the second supporting portion is a second supporting roller configured to support the endless belt.
8 . The image forming apparatus according to claim 7 , wherein the upper surface onto which the first suction fan and the second suction fan suck the sheet is arranged parallel to a common tangent line to the first supporting roller and the second supporting roller.
9 . The image forming apparatus according to claim 7 , wherein the control unit is configured to change the suction force of the first suction fan based on a grammage of the sheet conveyed by the endless belt.
10 . The image forming apparatus according to claim 7 , wherein:
the endless belt is a first endless belt, and the upper surface is a first upper surface,
the conveyance unit includes a second endless belt located upstream of the first endless belt in the sheet conveyance direction,
the sheet is supported on a second upper surface of the second endless belt, and
a downstream end of the second upper surface in the sheet conveyance direction is positioned above an upstream, in the sheet conveyance direction, end of the first upper surface in a vertical direction.