CANON NP6218
Service Manual

CHAPTER 3 EXPOSURE SYSTEM

I. BASIC OPERATION
A. Varying the Reproduction Ratio
The reproduction ratio across the photosensitive drum is varied by the lens drive system; on the other hand, the ratio around the drum is varied by the scanner drive system. The lens drive system uses a zoom lens; as shown in Figure 3-101, the position and focal distance of the lens are changed to vary the reproduction ratio across the photosensitive drum. The scanner drive system varies the reproduction ratio around the photosensitive drum by moving the No. 1 mirror relatively faster (reduction) or slower (enlargement) than the peripheral speed of the photosensitive drum.
Direct F F'

Reduce F1

F1'

Enlarge F2

F2'

Figure 3-101

II. LENS DRIVE SYSTEM
A. Outline
The lens drive system is driven by the lens motor (M3). The drive of the lens motor is transmitted to the blank exposure unit through a relay gear. (See p. 4-18.) When the lens is moved, the solenoid (SL1) is turned on to engage the relay gear with the lens gear; when the lens motor rotates in the direction of the arrow in this condition, the lens is moved in the direction of enlargement (�) by the work of the relay lens gear and lens cable. The blank exposure shutter, on the other hand, moves according to the distance traveled by the lens for reduction, thereby blanking (whiting) out the areas on both ends of the copy. The copier�s scanner lens home position sensor (PS2) is located at the center of the scanner lens drive rail so that the scanner lens home position may be detected early upon power-on, thereby speeding up the generation of the first copy. In addition, the scanning lens moves to the appropriate position in response to a press on each ratio button, thereby shortening the time it takes to generate the first copy.
COPYRIGHT © 1997 CANON INC. CANON NP6218 REV. 0 MAY 1997 PRINTED IN JAPAN (IMPRIME AU JAPON)

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