Ricoh FT5233 Service Manual page 56

12 February 1992 OPTICS
4.3 LENS DRIVE
[G]
[E]
[D]
[G]
[C]
[B]
[A]
[F]
: Reduction
[H]
: Enlargement
4.3.1 Lens Drive
The lens motor [A] (stepper motor) changes the lens [B] position through the
lens drive wire [C] in accordance with the selected reproduction ratio to
provide the proper optical distance between the lens and the drum surface.
The rotation of the lens drive pulley [D] moves the lens back and forth in
discrete steps. The home position of the lens is detected by the home
position sensor [E]. The main board keeps track of the lens position based on
the number of pulses sent to the lens motor.
4.3.2 Shading Mechanism
The shading plates [F] are installed on the lens housing [G] and are slid open
and shut by the shading cam [H]. This shading mechanism adjusts the
horizontal light intensity, which becomes uneven in reduction mode, when the
light at the sides of the image is more intense. The shading plates close in
reduction mode to even out the light intensity.
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