AR-F12 (serv.man4). Saddle stitch unit basic operation - Sharp Copying Equipment Service Manual (repair manual). Page 34

A stack is folded by the action of the paper folding rollers and the paper pushing plate.
The paper pushing plate pushes against the center of a stack toward the roller contact section.

The paper pushing plate starts at its home position and waits at the leading edge position until the
stack has been drawn to the paper folding roller and is gripped for a length of 10 mm. When the paper
folding roller has gripped the stack for a length of about 10 mm, the paper pushing plate motor starts
to rotate once again, and the paper pushing plate returns to its home position. The stack gripped in this
way by the paper folding roller is drawn further by the paper folding roller and then is moved by the
delivery roller to the paper tray.

Half of the peripheral area of the paper folding rollers excluding the center part is punched out.

This punched out area only feeds the paper as the paper feeding roller (lower) contacts the paper
feeding roller (upper) only at the center of the roller to prevent the paper from wrinkling. As the paper
feeding roller (lower) contacts the paper feeding roller (upper) at their entire surfaces on the remain-
ing half of the peripheral area, paper folding starts from this half of the peripheral area, and paper is
fed while it is being folded. The stop position of the paper folding rollers is in this half of the periph-
eral area.

The paper folding start and stop positions on the paper folding rollers is controlled according to

the motor clock signals from the paper folding home position sensor (PI21S).

Paper folding 
roller (lower)

Paper folding 
roller (upper)

Sensor flag

Paper folding home 
position sensor 

(PI21S)

Paper pushing plate top 
position sensor   

(PI15S)

Paper pushing plate home 
position sensor  

(PI14S)

Paper pushing plate

Paper pushing plate motor

Paper folding motor

M2S

M8S

Stack of sheets