JPS62187318A - Light beam scanning device - Google Patents

Abstract

PURPOSE:To reduce the size of a deflector, to use an ftheta lens in common, and to reduce the size and cost of a device by arranging a light beam expansion optical member between the deflector and an image formation surface, and thus making many beams which are mutually close incident on the deflector. CONSTITUTION:The light beam pitch expansion optical member 7 uses a plane- concave lens 7', etc., having the same sectional shape lengthwise. Light beams B which exit from the deflector closely to each other enter the light beam pitch expansion optical member 7 after passing through the ftheta lens 3 and then reach mirrors 5A and 5B. The beams have their optical paths changed by the mirrors 5A and 5B and pass through correcting lenses 6A and 6B to form images on the photosensitive surfaces of photosensitive bodies 4A and 4B. Conse quently, even when mutually close beams are incident on the deflector, they can be expanded to light-beam pitch large enough to separate the beams, so the deflector 1 is reducible in size, the theta lens is used in common, and the whose device is reduced in size and lowered in price.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a light beam scanning device, and more particularly to a light beam scanning device that scans by inputting a plurality of beams.

(Prior art) A digital color printer using electrophotography and a light beam scanning optical system separates the original into colors, records each color's information on separate photoreceptors, develops it, and transfers it onto the same transfer paper. This is done to prevent it from becoming established.

In the digital color printer as described above, it is effective to scan multiple beams using one deflector in terms of scanning viscosity of each color and cost.

By the way, the light beam scanning optical system generally used in laser beam printers basically consists of a light source, a light beam shaping optical system, a light beam deflector, an fθ correction optical system, and a surface tilt correction optical system. ing.

The optical system as a whole consists of a t+IJ1 stock optical system, and the correction function may be in charge of C other than the optical system. Such a configuration is similar to the light beam scanning optical system of a digital color printer that scans a plurality of light beams and focuses the light onto separate photoreceptors.

As the outline of the optical system is shown in FIG. 6, the light sources (not shown) are gas lasers 11, semiconductor lasers, etc., and the light sources have the same number of light beams B, B... In some cases, one beam may be divided into multiple beams by an RN modulation element, or in the case of a semiconductor laser, an array-like element may be used.

In any case, known light beam shaping means, modulation means,
For example, it has a collimating lens that converts semiconductor laser light into parallel light, an aperture that obtains a horizontally elongated shape, and a modulation circuit that changes the laser drive current by image tanning, and a correction lens that forms part of the tilt correction optical system ( cylindrical lens)
is placed.

As the light beam deflector 1, as shown in the figure, a polygon mirror, a hologram disk rotated at high speed by a scanner motor 2, and a galvanometer mirror are known. B... is scanned within a plane at a constant speed.

Reference numeral 3 denotes the fθ15 characteristic for the isocentrifugal scanning of the light beam B on the imaging planes of the photoreceptors 4A and 4B by 1'T ij
The optical path of the light beam B exiting the θ lens 3 is changed by mirrors 5A and 5B, and the optical path is changed by the correction lens (cylindrical lens > 6A, 6B) which is part of the tilt correction optical system. The light passes through and is imaged on the photosensitive surfaces of photoreceptors 4Δ and 4B.

In this case, it is not necessary for multiple light beams to pass through the same deflector and the same fθ lens, but in order to ensure the same scanning accuracy in digital color printers where color misalignment of each color is a serious problem, The same deflector and the same -fθ lens may be passed through, which is also advantageous from a cost standpoint.

On the other hand, the incident light beams B, B, . . . do not necessarily have to be parallel, but need to be close to each other.

That is, the light beams B, B with respect to the optical axis of the fθ lens 3
The deviation in ... affects the image quality, and the pitch can only be within the permissible limit. Further, as a characteristic of polygon mirrors, the thickness of the mirror is proportional to the cost, so if the beam pitch is widened, the cost will be high.

In the above-mentioned light beam scanning optical system, the pitch between the light beams cannot be expanded after deflection, so the pitch between the beams is set as wide as possible so that the mirrors can be separated after deflection. However, it was difficult to achieve high efficiency and cost reduction.

〔the purpose〕

The present invention has been made with the aim of solving the above-mentioned problems of the prior art, and it is possible to create a pitch between the light beams that is large enough to separate each light beam even when multiple beams that are close to each other are incident on a deflector. This makes the deflector smaller and fθ
It is an object of the present invention to provide a light beam scanning device in which lenses can be shared, optical members can be easily arranged, and the device can be made compact and inexpensive.

〔composition〕

In order to achieve the above object, the present invention provides a light beam scanning device J3 having a light beam generating means for generating a plurality of light beams and a deflector for deflecting the plurality of light beams together. The present invention is characterized by a configuration in which a light beam pitch enlarging optical member for enlarging the pitch between the plurality of beams incident on the deflector is disposed between the deflector and the image forming surface.

Hereinafter, specific embodiments of the present invention will be explained with reference to FIGS. 1 to 5, and the same reference numerals will be used for parts common to those in FIG. 6.

The embodiment shown in FIG. 1 shows a case where an f.theta. lens 3 is provided on the optical path from the deflector 1, and a light beam pitch enlarging optical member 7 is arranged on the output optical path of the f.theta. lens 3.

The optical member 7 has the same cross section in the longitudinal direction, and includes a plano-concave lens 7' shown in FIG. 2 and a cylindrical mirror 7'' shown in FIG. 3, and a beam emitted as shown in FIG. 4. In order to make parallel light, a cylindrical lens group consisting of a combination of a plano-concave lens 7A and a convex-plano lens 7B as shown in Figure 5 is used.Although the illustrated example is for parallel incidence, the shape is As long as the beam has the same cross section in the longitudinal direction, it is not limited to this.
It may be more than a book. Points to note here are the problem of the optical beam width expanding in the sub-scanning direction and the curvature of field, but both of these can be kept within the scope of work in the design of the entire imaging optical system. That's easy.

Therefore, the light beam exiting the deflector 1 passes through the θ lens 3 and enters the beam pitch expanding optical member 7, the beam pitch is expanded by this optical member 7, and reaches the mirrors 5A and 5B.

The optical path of the light is converted at 5B, and the light passes through correction lenses 6Δ and 6B and is imaged onto the photosensitive surfaces of photoreceptors 4A and 4B.

〔effect〕

As explained above, according to the present invention, a light beam pitch enlarging optical member for enlarging the pitch between a plurality of beams incident on the deflector is disposed between the deflector and the image forming surface. It is possible to expand the pitch of the light beams to the extent that even if multiple beams are incident close to each other, each light beam can be separated.This makes it possible to downsize the deflector and also allows the fθ lens to be shared. These make it possible to make the equipment extremely compact, which can greatly contribute to lower prices.

[Brief explanation of drawings]

Figure 1 is a configuration diagram of an embodiment of the present invention, Figures 2 and 3 are
The figure shows an example of the light beam pitch enlarging optical member in Fig. 1. 1. An enlarged explanatory diagram. Fig. 4 is a configuration diagram when the light beam pitch enlarging optical member is a cylindrical lens. Fig. 5 is the same as Fig. 4. FIG. 6 is an enlarged explanatory view showing a cylindrical lens in J3, and FIG. 6 is a configuration diagram of a conventional light beam scanning device. 1... Deflector, 3... fθ lens, 4A, 4B...
・Photoreceptor, 5Δ, 5B...Mirror, 6A, 6B...
Correction lens, 7... optical beam pitch enlarging optical member. Applicant's agent Mr. Sato Figure 1 Figure 30 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] 1. A light beam generating means for generating a plurality of light beams;
In a light beam scanning device having a deflector that deflects a plurality of light beams together, a light beam pitch enlarging optical member that enlarges the pitch between the plurality of beams incident on the deflector between the deflector and an image forming surface. A light beam scanning device characterized in that: 2. The light beam scanning device according to claim 1, wherein the light beam pitch enlarging optical member has the same cross-sectional shape in the longitudinal direction.