Ricoh FT4215, Service Training Manual

Page: 43 / 208

3.3.3 Lens Positioning
The lens home position sensor [A] informs the main board when the lens is at
full size position (home position). The main board determines the lens stop
position in reduction and enlargement modes by counting the number of
steps the motor makes with reference to the lens home position. When a new
reproduction ratio is selected, the lens [B] moves directly to the selected
magnification position.
The lens home position is registered each time the lens starts from or passes
through the lens home position sensor. As the lens moves from the
enlargement side to the reduction side, the sensor registers the home
position. This occurs when the actuator plate [C] enters the lens home
position sensor.
A small vibration can be observed when the lens moves through home
position from the reduction side to the enlargement side because the lens is
going in the wrong direction to register the home position. The lens
overshoots the home position by only one pulse before going back to register
the home position.
The lens always stops while moving from left to right (as viewed from the
front) to minimize the error caused by mechanical play in the drive gears [D].
[A]
[C]
[D]
[B]
Home Position (100%)
(100%
→
141/155%)
(141/155%
→
71/65%)
(71/65%
→
93%)
(93%
→
71/65%)
(71/65%
→
141/155%)
(141/155%
→
122/129%)
(122/129%
→
141/155%)
(100%
→
71/65%)
(71/65%
→
100%)
Reduction Side Enlargement Side
(141/155%
→
100%)
FT4220/4222 2-12 STM