Multi-beam optical scanner

Abstract

A multi-beam optical scanner, in which a lateral magnification beta in a composite system of an optical system between the light source for a multi-beam and the scanned surface satisfies the condition: 2<beta<=8.5, and a plurality of light spots on the scanned surface execute optical scanning of the scanning lines adjacent to each other.

Description

BACKGROUND OF THE INVENTIONThe present invention relates to a multi-beam optical scanner and more particularly to a multi-beam optical scanner realizing a light spot in an appropriate form on a scanned surface and effectively reducing degradation in image quality of a recorded image due to pitch deviation.BACKGROUND OF THE INVENTIONAn optical scanner has been known in relation to an image forming apparatus, such as a digital copying machine, an optical printer, and an optical printing machine or the like. In the optical scanner as described above, there has been proposed a multi-beam optical scanning system for optically and concurrently scanning an image with a plurality of scanning lines for the purpose of speeding up an operation for writing images by way of optical scanning.In the multi-beam optical scanning system, there is sometimes a case where scanning lines for optically and concurrently scanning are not adjacent to each other. There has been proposed, for instance, in Japa...

AI Technical Summary

Benefits of technology

It is an object of the present invention to effectively reduce degradation in image quality in a recorded image due to pitch deviation, in addition, to enable effective reduction of cost of a lengthy lens included in an optical system for converging deflected light fluxes on the scanned surface, and also to effectively suppress contamination of the lengthy lens due to splashed toner.

It is another object of the present invention to realize a multi-beam optical scanner in which a layout of optical arrangement is easy arid which is hardly affected by wavelength deviation in the light source.

The lateral magnification .beta. is made larger than 2, and by employing a "scaling-up type" of composite system, a lengthy lens included in the second image-formation system can effectively be separated from the scanned surface.

Further, by satisfying the conditions, the lengthy lens included in the second image-formation system can effectively be separated from the scanned surface, and in order to realize a pitch between scanning lines of 84.7 .mu.m corresponding to the minimum dot density of 300 dpi required to the optical scanner, a space between light emitting sections in the light source for a multi-beam can be maintained by not less than 10 .mu.m with which thermal crosstalk does not occur.

Problems solved by technology

In the interlace scanning as described above, selection of a signal for modulating each beam is irregular, so that optical scanning is easily complicated, and in addition, scanning lines for optically concurrently scanning are also largely spaced therebetween, so that "a rate of pitch deviation" of optical scanning due to a bend in the scanning lines becomes large, which makes it easy for image quality of a recorded image to degrade.

In the multi-beam optical scanner, there are strict restriction over a magnification in an image-formation system provided in a space between the light source and the surface for scanning due to a relation between pitches of scanning lines, and because of the restrictions over a magnification as described above, a position of an optical system to be provided in a side of the light source from the optical deflector must be closer to the optical deflector, and for this reason, a layout of optical arrangement becomes difficult.

Further, if a "hybrid" combination of two or more LD light emitting sections or LED light emitting sections is employed as a light source having a plurality of light emitting sections used in the multi-beam optical scanner, there occurs a problem of "wavelength deviation" that wavelengths of combined light emitting sections are not identical to each other, and when this wavelength deviation is present therein, constant velocity characteristics of optical scanning or the like may vary for each light emitting section.

HEI 7-111509, but in this optical scanning system a focal length of a lengthy lens for correcting surface offset is as short as 15 mm, and for this reason the lengthy lens is provided at a position close to the scanned surface, which makes larger a length in a direction corresponding to the main scanning as well as cost of the lengthy lens higher, and also toner splashed from a developing device generally provided adjacent to the scanned surface easily makes the lengthy lens contaminated.

Images