Ricoh FW780 Service Manual page 239

EXPOSURE
When the original entrance sensor is turned off by the trailing edge [E] of the
original, the roll paper feed motor turns on and paper feeding starts.
When the trailing edge of the original reaches the original feed start position (26
mm ahead of the original registration sensor [F]), the original feed motor stops to
wait for the copy paper.
The registration clutch is activated after paper feed begins. The copy paper is fed
to the registration roller [G] and the registration clutch turns off when the copy
paper reaches 15 mm ahead of the registration sensor [H]. The voltage is applied
to the charge corona.
At the appropriate time the original feed motor rotates 50 mm/s in opposite
direction and the original is delivered to the exposure glass. The registration clutch
and roll paper feed motor turn on again after the trailing edge of the original passes
the original entrance sensor. The paper feed resumes and the copy paper is
transported to the drum [I].
To measure the original length for synchro-cutting, the copier CPU measures the
time from when the original registration sensor detects the leading edge of the
original until the original entrance sensor detects the trailing edge of the original
(delivering the original to appropriate start position). The copy paper length is
measured by counting the number of steps as the roll paper feed motor (stepper
motor) turns. Just before the cut length of the copy paper is fed, the speed of the
roll paper feed motor is doubled. A paper buckle forms at the trailing edge of the
copy paper. When the copy paper is fed out to the appropriate length, the roll
paper feed motor stops and the cutter unit cuts the paper.
When making duplicate copies, at the appropriate time after the trailing edge of the
original passes at the original registration sensor, the rotation of the original feed
motor changes in the opposite direction and the speed of the original feed motor
changes to 200 mm/s. The roll paper feed motor starts again. The original is
delivered to the original feed start position and roll paper feed starts again. The
above process is repeated. After all the duplicates have been made, the original is
stopped and caught by the original entrance roller (original hold mode: SP16). If
the original hold mode is canceled by SP16, the original is fed out without being
caught in the original entrance roller. During this procedure the original rear sensor
[K] determines the end of the original.
When the original hold mode is selected, the original is fed out when the $ key is
pressed.
SM 2-3 A251/A252