Brother MFC990CW Service Manual page 117

Movable platen*
The movable platen has movable ribs that move in synchronization with the leading or trailing
edge of advancing paper. It realizes the following.
- Increased printing speed in borderless printing
- Eliminating paper deflection that could occur in printing on the trailing edge of paper
Synchronization with leading edge of paper
When the leading edge of the paper reaches the movable rib drive position, the head/carriage
unit moves to the left end of its travel and pushes the upper end of the movable platen lever,
releasing its lower end that blocks the rotation of the movable platen cam gear. This triggers
driving the movable platen mechanism.
The mechanism transmits the paper feed motor rotation to the movable ribs. They move from
the home position (center) to the upstream limit of the movable range to wait for the leading
edge of the paper to come. They move in synchronization with the leading edge of the paper
advancing. When they reach the downstream limit, they return to the home position. This is a
sequence of the movable rib operation.
Synchronization with trailing edge of paper
When the registration sensor detects the trailing edge of the paper, the motor further feeds the
paper for the predetermined amount. After that, the head/carriage unit pushes the upper end of
movable platen lever again. Just as for the leading edge of paper, the movable ribs move to the
upstream limit of the movable range to wait for the trailing edge of the paper advancing to come
and then move in synchronization with the trailing edge. When the movable ribs have reached
the downstream limit and the printing operation has completed, they return to the home
position.
Movable platen
Movable platen lever
CR guide rail
Paper feed roller
Upstream limit
Home position
(Center)
Downstream limit
(Front)
3-40
*For models with movable platen
Head/carriage unit
Movable ribs
(3_17_1)
Confidential