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Optics Scanning for Copier With Stationary Flat Document Plane

IP.com Disclosure Number: IPCOM000078575D
Original Publication Date: 1973-Feb-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 4 page(s) / 69K

Publishing Venue

IBM

Related People

Queener, CA: AUTHOR

Abstract

Several optics/scanning systems allow the image from a scanned flat original document plane of an electrophotographic copier to be formed on the bottom side (i. e. 6 o'clock position) of a photoreceptor drum in a correct fashion. The system of Fig. 1 combines a moving lens and translating mirrors into one scanning system. Two 45 degree mirrors translate at a velocity which is 1/4 that of the peripheral velocity of the photoreceptor drum, in a plane parallel to the document plane, while the lens is simultaneously being translated in the opposite direction with a velocity equal in magnitude to that of the mirrors.

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Optics Scanning for Copier With Stationary Flat Document Plane

Several optics/scanning systems allow the image from a scanned flat original document plane of an electrophotographic copier to be formed on the bottom side (i. e. 6 o'clock position) of a photoreceptor drum in a correct fashion. The system of Fig. 1 combines a moving lens and translating mirrors into one scanning system. Two 45 degree mirrors translate at a velocity which is 1/4 that of the peripheral velocity of the photoreceptor drum, in a plane parallel to the document plane, while the lens is simultaneously being translated in the opposite direction with a velocity equal in magnitude to that of the mirrors. Thus, imaging of the original document onto the bottom (6 o'clock) position of the photoreceptor drum is accomplished by a total translation displacement of 1/4 the document width, by the lens and each of the two mirrors.

For a scanning system like that in Fig. 1 to form the image on the photoreceptor in a correct fashion, two requisite rules must be obeyed with respect to a light ray emanating from the element on the original document to be imaged and passing through the center of the lens:
1) The ray must intersect the image point of

the photo-receptor at an angle from the

vertical that is identical to the angle from

the vertical, at which it left the document plane.
2) The total path length of the ray on the photoreceptor

side of the lens must equal the path length of the ray

on the document side of the lens.

Fig. 2 illustrates the basic concept of another version and defines some of the geometrical dimensions.
1. This system is a "bottom-imaging" type.
2. Both reflections have been arbitrarily defined as

degrees (right angle) in nature.

For "correct" imaging using two flat mirrors, two "rules" must be obeyed for any given light ray:
1) The angle of incidence to the normal to the

photo-receptor surface must equal the off-axis

angle, alpha, as shown.
2) The path length of any given ray on the photoreceptor

side of the lens must equal that on the document side

(for 1:1 reduction) --i.e. S(1) + S(2) + S(3) =

T over 2 cos alpha.

Taking as a "starting" position the correct position for imaging the on-axis ray
(i. e. mirror surface passing through the point: x = 0, y = 0 with a 45 degree slope), the first (right) mirror "center" moves up the straight line y=(l(2)/2l(1))x by an amount equal to tanalpha(l(1))/cos(arctan l(2)/2l(1)) while simultaneously rotating counterclockwise through an angle alpha, in order to achieve correct imaging for the ray that is off-axis by an angle +alpha. The second (left) mirror moves in an analogous fashion down the line: y=-l(2)/2l(1) (x+l(2)) while rotating clockwise through an angle alpha.

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The mirrors are free to move along fixed slots or rails, the center lines of which are described by the equation y=l(2)/2l(1)x the right (first mirror) rail and y=-l(2)/2l(1) (X+l(2)) for the second (left mirror) rail. The mirror en...