Sheet feeding apparatus with mechanism for detecting sheet feeding state and sheet feeding method

An image forming apparatus, comprising:

• a sheet feeding apparatus feeding sheets of paper on a paper feed path on which sheets of paper are fed one by one by a prescribed paper feeder;
• and an image forming unit printing image data on the sheet fed through said paper feed path;
• wherein
• said sheet feeding apparatus includes
• first and second sheet sensors provided in order from upstream to downstream sides in a sheet feeding direction on said paper feed path, each sensor outputting a signal that is on when a sheet is detected and off otherwise, and
• a plurality of sets of sheet conveyor rollers arranged at a plurality of positions along said paper feed path;
• wherein
• two or more sheets may possibly be fed partially overlapped from said paper feeder to said paper feed path;
• said plurality of sets of sheet conveyor rollers include a group of upstream rollers on the upstream side than said first sheet sensor, and a group of downstream rollers on the downstream side than said first sheet sensor;
• said sheet feeding apparatus further comprising:
• a roller controller connected to receive output signals of said first and second sheet sensors, and individually controlling said group of upstream rollers and said group of downstream rollers in accordance with a change in value of said output signals;
• wherein
• said roller controller includes
• an overlapped feeding determining device activated in response to start of paper feeding from said paper feeder to said paper feed path, and outputting a determination signal assuming a first value when overlapped feeding of sheets has occurred and a second value otherwise, in response to a change in values of output signals of said first and second sheet sensors,
• an overlapped feeding eliminating device, temporarily stopping driving of said plurality of sets of sheet conveyor rollers until after the lapse of an idle time to effect print registration of sheets before a register roller positioned at a terminal end of said paper feed path, and after a lapse of the idle time, again driving said group of downstream rollers while driving of said group of upstream rollers is kept stopped, by controlling said roller controller, in response to reception of said determination signal of said first value, and
• a conveyor roller stopping device stopping said group of downstream rollers in response to failure of overlapped feeding elimination the process for eliminating overlapped feeding by said overlapped feeding eliminating device;
• wherein
• said overlapped feeding determining device includes an overlapped feeding occurrence determining device outputting said determination of signal of said first value, when a prescribed time period passed with the output signal from said first sheet sensor kept on, after the output signals from said first and second sheet sensors changed from off to on in this order.

A method of sheet feeding, in a sheet feeding apparatus including first and second sheet sensors provided in order from upstream to downstream sides in a sheet feeding direction on a paper feed path through which sheets of paper are fed one by one by a prescribed paper feeder, each sensor outputting a signal that is on when a sheet is detected and off otherwise, and

• a plurality of sets of sheet conveyor rollers arranged at a plurality of positions along said paper feed path;
• wherein
• two or more sheets may possibly be fed partially overlapped from said paper feeder to said paper feed path;
• said plurality of sets of sheet conveyor rollers include a group of upstream rollers on the upstream side than said first sheet sensor, and a group of downstream rollers on the downstream side than said first sheet sensor;
• and
• said sheet feeding apparatus further includes
• a roller controller connected to receive output signals of said first and second sheet sensors, and individually controlling said group of upstream rollers and said group of downstream rollers in accordance with a change in value of said output signals;
• said sheet feeding method comprising:
• the step, started in response to start of paper feeding from said paper feeder to said paper feed path, of outputting a determination signal assuming a first value when overlapped feeding of sheets has occurred and a second value otherwise, in response to a change in values of output signals of said first and second sheet sensors;
• the step of temporarily stopping driving of said plurality of sets of sheet conveyer rollers until after a lapse of an idle time to effect print registration of sheets before a register roller positioned at a terminal end of said paper feed path, and after the lapse of the idle time, again driving said group of downstream rollers while driving of said group of upstream rollers is kept stopped, by controlling said roller controller, in response to reception of said determination signal of said first value;
• and
• the step of stopping said group of downstream rollers in response to failure of overlapped feeding elimination at said step of driving;
• wherein
• said step of outputting includes the step of outputting said determination signal of said first value, when a prescribed time period passed with the input signal from said first sheet sensor kept on, after the output signals from said first and second sheet sensors changed from off to on in this order.