Ricoh D182 Service Training page 86

 At the start of the set, the stapler moves to the center.
 A bracket on the stapler pushes the stopper, and the pawl moves
into the correct position to catch the leading edge of the paper.
 The upper clamp roller holds the stack (see the previous slide).
 When the stack is complete, the stapler moves to the rear-side
position, and the stopper moves away. The upper clamp roller
feeds the stack to the correct position for stapling.
Slide 86
 This diagram is copied from the B793. The mechanism is similar, but the layout
is different, because the stapler tray is at a less steep angle in the D686/D687.
Stoppers for Stapling
Lower Stopper - 2
Pawl
86
OR-C2 Training
Lower Stopper
Bracket