Sheet separating apparatus and method

A sheet separating apparatus for a sheet feeder comprising:

• a first nip and a second nip for feeding a series of sheets therebetween;
• said first nip includes a first motor and said second nip includes a second motor for feeding a top sheet from said first nip to said second nip;
• a first sensor for sensing a trailing edge of said top sheet and a second sensor for sensing a leading edge of said top sheet wherein said first sensor is upstream of said first motor and said second sensor is downstream of said second motor;
• an underlying sheet is prevented from feeding with said top sheet by stopping said first motor when said leading edge of said top sheet is sensed by said second sensor while simultaneously said first sensor remains occluded by said underlying sheet;
• said first sensor and said second sensor have a fixed spacing therebetween wherein said spacing is greater than a sheet length;
• wherein said top sheet has a predetermined length;
• and,
• a timer for timing the duration of time between entry of said leading edge and exit of said trailing edge of said top sheet with said second sensor.

A xerographic system, comprising:

• a sheet feeding apparatus having a first nip and an associated first sensor upstream from a second nip and an associated second sensor;
• said first sensor is upstream from said first nip and said second sensor is downstream from said second nip;
• said first nip includes a first motor and said second nip includes a second motor for selectively and independently feeding sheets therebetween;
• said first nip having a feed motion adapted to feed at least a pair of sheets in a feed direction from said first nip toward said second nip during said feed motion;
• said second nip having a feed motion adapted to feed a top sheet from said at least a pair of sheets in said feed direction;
• said first nip adapted to halt said feed motion responsive to said first and second sensors wherein an underlying sheet is stopped at a wait point positioned between said first nip and said second nip until said top sheet clears said second sensor;
• said first sensor and said second sensor have a fixed first spacing therebetween wherein said first spacing is greater than a sheet length;
• and,
• said first nip and said second nip have a fixed second spacing therebetween, wherein said first spacing is greater than said second spacing.

A method of feeding sheets to a printer or a copier, comprising:

• applying a feed force in a feed direction to a top sheet;
• feeding said top sheet from a first nip to a second nip wherein said first nip includes a first motor and said second nip includes a second motor;
• sensing a trailing edge of said top sheet with a first sensor and sensing a leading edge of said top sheet with a second sensor wherein said first sensor is upstream of said first motor and said second sensor is downstream of said second motor;
• preventing an underlying sheet from feeding with said top sheet by stopping said first motor while continuing said second motor, when said leading edge of said top sheet is sensed by said second sensor while simultaneously said first sensor remains occluded by said underlying sheet;
• and,
• said first sensor and said second sensor have a fixed spacing therebetween wherein said spacing is greater than a sheet length.

A method of feeding sheets to a printer or a copier, comprising:

• applying a feed force in a feed direction to a top sheet;
• feeding said top sheet from a first nip to a second nip wherein said first nip includes a first motor and said second nip includes a second motor;
• sensing a trailing edge of said top sheet with a first sensor and sensing a leading edge of said top sheet with a second sensor wherein said first sensor is upstream of said first motor and said second sensor is downstream of said second motor;
• preventing an underlying sheet from feeding with said top sheet by stopping said first motor while continuing said second motor, when said leading edge of said top sheet is sensed by said second sensor while simultaneously said first sensor remains occluded by said underlying sheet;
• said first sensor and said second sensor have a fixed spacing therebetween wherein said spacing is greater than a sheet length;
• wherein said top sheet has a predetermined length;
• wherein said first nip and said second nip have a fixed spacing therebetween:
• wherein said underlying sheet has a leading edge;
• wherein said leading edge of said top sheet is offset and downstream from said leading edge of said underlying sheet;
• comparing a time between sensing said leading edge and said trailing edge of said top sheet by said second sensor with a predetermined time, if said time is substantially equal to said predetermined time, then said underlying sheet becomes the next top sheet;
• and,
• feeding said next top sheet from said first nip to said second nip.

A xerographic system, comprising:

• a sheet feeding apparatus having a first nip and an associated first sensor upstream from a second nip and an associated second sensor;
• said first sensor is upstream from said first nip and said second sensor is downstream from said second nip;
• said first nip includes a first motor and said second nip includes a second motor for selectively and independently feeding sheets therebetween;
• said first nip having a feed motion adapted to feed at least a pair of sheets in a feed direction from said first nip toward said second nip during said feed motion;
• said second nip having a feed motion adapted to feed a top sheet from said at least a pair of sheets in said feed direction;
• said first nip adapted to halt said feed motion responsive to said first and second sensors wherein an underlying sheet is stopped at a wait point positioned between said first nip and said second nip until said top sheet clears said second sensor;
• said underlying sheet is prevented from feeding with said top sheet by stopping said first motor, while continuing said second motor, when said leading edge of said top sheet is sensed by said second sensor while simultaneously said first sensor remains occluded by said underlying sheet;
• and,
• said first sensor and said second sensor have a fixed first spacing therebetween wherein said first spacing is greater than a sheet length.