JPS628118A - Scanning device for plural beams - Google Patents

Abstract

PURPOSE:To eclipse none of a beam even when a small prism is used and to maintain the utilization efficiency at about 100% where cylindrical lenses are arranged by arranging the cylindrical lenses in front of an behind a prism type reflecting mirror and generating a beam waist on the prism in a subscanning direction. CONSTITUTION:Beams from plural independent light sources 1a and 1b which are collimated by collimator lenses 2a and 2b into nearly parallel luminous flux are deflected by the prism 4 and made incident on an optical deflector such as a polygon so that the beams scans on different scanning lines at the same time. This photoscanning device is so constituted that cylindrical lenses 3a and 3b, and 5 which have generating lines in a main-scanning direction, namely, have reflecting power only in a subscanning-directional plane are arranged in front of and behind the prism 4; and the beam are collimated by the collimator lenses 2a and 2b into nearly parallel luminous flux and then the subscanning-directional beam waist is formed on the prism type reflecting mirror 4 through cylindrical lenses 3a and 3b.

Description

[Detailed description of the invention] purpose of invention (Industrial usage total) This invention relates to a laser beam scanning device, special feature K.

The present invention relates to a scanning device for simultaneously scanning beams from a plurality of independent light sources.

(Prior Art) In laser beam scanning devices such as laser printers, attempts have been made to substantially increase the scanning speed by simultaneously scanning the scanning lines of each light source with beams from a plurality of independent light sources. In such devices, beams from a plurality of independent light sources are aligned in the beam propagation direction using a beam splitter, a prism type reflector, or the like.

An example of a typical prism device is shown in FIG. The light beam emitted from the laser light source 6 is converted into an almost consonant beam by the collimating lens 7, and enters the prism 8 whose two chevron-shaped surfaces are used as reflecting mirrors.
As shown in -1, vignetting occurs and the efficiency of light use decreases, and attempts to prevent this have the problem of increasing the size of the prism.

(Problems to be Solved by this Invention) This invention simultaneously scans the light beams from multiple light sources without causing any clutter, and also reduces the size of the prism used to do so, thereby simultaneously achieving cost reductions and increased laser light utilization efficiency. This is what I am trying to do.

Structure of the Invention (Means for Solving the Problems and Their Effects) As shown in FIG. In order to scan different scanning lines at the same time, in an optical scanning device, a beam that has been made into a substantially sub-digit beam by collimating lenses 2m and 2b is deflected by a prism 4 and made to enter an optical deflector such as a polygon. Cylindrical lenses 3m, 3b, and 5 having refractive power only in the main scanning direction and the horizontal plane, that is, in the sub-scanning direction, are arranged before and after the prism 4.

The beams emitted from the laser light sources 1a and Ib are converted into almost consonant beams by collimating lenses 2m and 2b, and then sent to a cylindrical lens 3a.

3bK Therefore, the beam waist t in the sub-scanning direction is a prism type reflection @i! Occurs on 4. At this time, in the main scanning direction, the beam waste)? Of course, this has not happened.

The reflected light is converted into a nearly linear beam again by the cylindrical lens 5, or is focused to form a beam waist at a predetermined position near the optical deflector.

The beam interval t in the sub-scanning direction on the prism is determined by the aperture angle (2θ) of the prism 4 and the distance Δ from the apex to the optical axis of the light beam.
It can be obtained from X as follows.

t=2ΔX tanθ Here, it is assumed that the two beams scan adjacent scanning lines on the surface to be scanned, and the scanning optical system has a function to correct the tilting of the optical deflector. Since the optical deflector is placed in a geometrically optically conjugate relationship, the pitch of the light beam in the sub-scanning direction on the deflector can be determined from the scanning line pitch on the surface to be scanned, and the pitch of the light beam on the above-mentioned prism 4 can be determined from the scanning line pitch on the scanned surface. The focal length of the cylindrical lens 5 can be selected from the beam interval t.

Effects of the Invention In this invention, as described above, cylindrical lenses are placed before and after the prism-type reflecting mirror to create a beam waist in the sub-scanning direction on the prism, so even a small prism does not cause beam clamping. The light utilization efficiency in this part can be approximately 1001 Cff. Moreover, since the prism can be significantly downsized, the device itself does not need to be enlarged and costs can be reduced.

[Brief explanation of drawings]

FIG. 1 is an optical layout diagram in a cross-section in the sub-scanning direction of a light beam scanning device according to the present invention, and FIG. 2 is an optical layout diagram of a conventional one. 1', 1bs 6:'-The light source 2a, 2b, 7: Collimating lens 3a, 3b% 5 Nijilintorical lens 4.8 Nibrism type reflector

Claims (1)

[Claims] In a scanning device in which beams from multiple independent light sources are shaped by a collimating lens, deflected by a prism-type reflecting mirror, and then incident on an optical deflector, the refractive power is adjusted in the plane in the sub-scanning direction. A multiple beam scanning device characterized in that cylindrical lenses having the above-mentioned structure are arranged before and after the prism-type reflecting mirror.