Photocopying – Including fiber optics
Patent
1986-12-12
1988-03-01
Hayes, Monroe H.
Photocopying
Including fiber optics
355 11, 355 66, G03G 1528, G03G 1532, G03B 2770
Patent
active
047289864
DESCRIPTION:
BRIEF SUMMARY
This invention relates to an improved optical scanning system which is inter alia capable of projecting an image onto a moving photoconductive surface as part of a xerographic copying apparatus.
According to one aspect of the invention an optical scanning system for projecting an image onto a moving surface, comprises four reflecting surfaces, a first or scan reflecting surface to deflect an incident light ray into a first direction, second and third reflecting surfaces mutually at right angles which together reflect the ray from the first reflecting surface in a direction opposite to the first direction and displaced laterally therefrom and a fourth or exit reflecting surface to receive the ray reflected from the third reflecting surface and to deflect it parallel to the incident ray onto the moving surface, wherein the scan and exit reflecting surfaces are maintained at right angles to each other as they are translated in opposite directions during a full scan of said image, the second and third reflecting surfaces are translated together in the same direction as the scan reflecting surface, and the translations of the scan and exit reflecting surfaces are effected at respective uniform rates each of which has a fixed ratio to the rate of movement of the moving surface.
Suitably the moving surface on which the scanned image is projected is the surface of a drum, the translations of the scan and exit reflecting surfaces being driven from a drive member of the drum. Conveniently, the translation of the second and third reflecting surfaces is also driven from the drive member of the drum via a motion rate perturbing means.
Conveniently rocking or tipping of the scan and exit reflecting surfaces is effected automatically as a consequence of their translation via a respective cam/cam follower arrangement for each.
The motion rate perturbing means for the second and third reflecting surfaces can be a cam-operated or 4-bar linkage.
Preferably the translations of the scan, linked second and third, and exit reflecting surfaces are in the ratios d.sub.1 :1/2(d.sub.1 -d.sub.3):d.sub.3, where d.sub.1 and d.sub.3 are multiples of even integers.
Possible ratios are 88:31:26 or 54:19:16, but clearly other ratios can be chosen within the ambit of this invention.
The invention will now be more fully described, by way of example, with reference to the accompanying drawings, in which:
FIG. 1 is a schematic plan of how the scanning system operates to scan an image onto a rotating drum,
FIG. 2 shows in greater detail how the scanning unit of FIG. 1 works theoretically.
FIG. 3 shows a practical arrangement for translating the four reflecting surfaces,
FIG. 4 shows how the motion of the ganged second and third reflecting surfaces can be perturbed in the required manner during their translation,
FIG. 5 shows how a system according to this invention is insensitive to the distance of the image forming lens from the scanning device, and
FIG. 6 shows in side elevation how the scan reflecting surface is tipped during its translation.
The principle of operation of a scanning system according to the invention will now be described.
PRINCIPLE OF OPERATION
If an object 1 is imaged by a lens having an optical centre 0 at the plane 2 as shown in FIG. 1, we may imagine a drum 3 rolling along the image plane 2 with constant speed u and the image may then be considered to be wrapped onto the periphery of the drum 3 starting from the point P'.
If, now, an optical mechanism 4 is interposed in the path of projection so that the light rays are deflected to image the point P on a real drum 5 of fixed centre 6 and rotating at a peripheral speed u, the image will be transferred, without distortion on to the surface of the drum 5 if the following conditions are satisfied: for any corresponding point on the image plane 2, instant. and imaginary drums) at any instant, and preferentially is constant.
Note that a slit 7 is placed above the drum 5; this is only required to limit the curved surface of the drum 5 exposed to the image. The greater the dr
REFERENCES:
patent: 3884574 (1975-05-01), Doi et al.
patent: 4023897 (1977-05-01), Clark
patent: 4372670 (1983-02-01), Carpenter et al.
patent: 4462674 (1984-07-01), Nishikawa
IBM Technical Disclosure Bulletin, vol. 15, No. 9 of Feb. 1973: "Optics/Scanning for Copier with Stationary Flat Document Plane", by C. A. Quenner (4 pp.).
IBM Technical Disclosure Bulletin, vol. 15, No. 4 of Sep. 1972: "Scanning System Incorporating Translating and Rotating Mirrors", by M. J. Miller (2 pp.).
Hayes Monroe H.
Striker Michael J.
The Imtec Group plc
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