Image forming device

An image forming device which can feed a recording paper sheet of a normal size specified in a recording paper sheet size specifying part or detected by a recording paper sheet size detection part from a recording paper sheet feed part by a paper sheet feed roller unit to a transport roller unit on a next stage located downstream of the paper sheet feed roller unit in a direction of transport of the recording paper sheet;

• can form an image on the recording paper sheet by feeding the recording paper sheet from the transport roller unit to an image forming part;
• and have the paper sheet feed roller unit transport the recording paper sheet in feeding the recording paper sheet from the transport roller unit on the next stage to the image forming part,
• the image forming device comprising a paper sheet transport path which leads the recording paper sheet from the paper sheet feed roller unit to the transport roller unit on the next stage;
• a paper sheet detection sensor disposed downstream of the paper sheet feed roller unit in the direction of transport of the recording paper sheet but upstream of the transport roller unit, facing the paper sheet transport path, the paper sheet detection sensor being capable of detecting the recording paper sheet fed from the paper sheet feed roller unit;
• and
• a size error judgment part which is for detecting a recording paper sheet size error when a small size recording paper sheet is mixed in the recording paper sheets of the normal size, the small size recording paper sheet being possibly expected to be mixed in the recording paper sheets of the normal size in the recording paper sheet feed part and having a length in the direction of transport of the recording paper sheet shorter than that of the normal size recording paper sheet,
• the size error judgment part being so constituted that, in feeding a recording paper sheet from the recording paper sheet feed part, when the recording paper sheet is a recording paper sheet of the normal size and a time period from a point of time the normal size recording paper sheet is started to be fed by the paper sheet feed roller unit until a point of time a rear end of the normal size recording paper sheet completely passes the paper sheet detection sensor is T1, when the recording paper sheet is a small size recording paper sheet and a time period from a point of time the small size recording paper sheet is started to be fed by the paper sheet feed roller unit to a point of time a rear end of the small size recording paper sheet completely passes the paper sheet feed roller unit is T2, the size error judgment part temporarily slows down the paper sheet feed roller unit for a predetermined time period after the time T2 has elapsed from the time the recording paper sheet is started to be fed by the paper sheet feed roller unit but before the time T1 elapses;
• judges that there is a size error which means that a size of the recording paper sheet is not the normal size when the paper sheet detection sensor detects absence of the normal size recording paper sheet from the slowing down of the paper sheet feed roller unit for the predetermined time period;
• judges that there is no size error when the absence of the normal size recording paper sheet is not detected by the paper sheet detection sensor even if the paper sheet feed roller unit is slowed down for the predetermined time period and resumes a normal driving of the paper sheet feed roller unit after the predetermined time period has elapsed.