JPH01909A - Optical device in image forming apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Field of Application) The present invention is directed to a laser printer, a copier, or other device that forms an image using a laser beam, in which a plurality of laser beams are directed onto an image carrier. The present invention relates to an improvement in an optical device in an image forming apparatus capable of irradiation.

(Prior Art) In image forming apparatuses such as copying machines and printers, in order to form a multicolor image on a photoreceptor which is an image carrier using a plurality of developers, in recent years, as shown in FIG. A device that forms a plurality of electrostatic latent images on a photoreceptor using a laser beam is often used. That is, this device consists of two
Two laser beams (lla), (llb) (l
lb) is guided to a polygon mirror (12) rotating at high speed via a collimator lens and a beam compressor (not shown). As the polygon mirror (12) rotates, the reflection angles of the laser beams (lla) and (ILb) are changed, and the laser beams (12) are scanned in the longitudinal direction of the photoreceptor (13). On the other hand, from the polygon mirror (12) to the photoreceptor (13)
Until reaching , two laser beams (Ila),
(llb) is provided with a shared imaging lens system (14), and one laser beam (lla) is transmitted to a first lens (15) and a second lens (16a) made of plastic.
) and imaged on the photoreceptor (13), and the other laser beam (llb) is imaged on the photoreceptor (13) by the first lens (15) and the third lens (16b). Ru. However, at this time, two laser beams (lla) are reflected from the polygon mirror (12).

(llb), optical axis (15a) of the first lens (15)
The angle of inclination φ with respect to the angle φ is approximately 2.5 degrees.

However, in such a device, each lens (15), (16a) that constitutes the imaging lens system (14).

(16b) is made of integrally molded plastic, and its characteristics tend to change due to temperature etc., causing distortion and bending on the image formation, and two laser beams (lla), (
llb) is imaged through an optical path formed symmetrically around the optical axis (15a) of the first lens (15),
This occurs due to environmental changes such as the temperature of the first lens (15). The variation of image distortion or curvature over the entire scan line length of the photoreceptor (13) is reversed. That is, as shown in FIG.
If the distortion characteristic of la) is [A], then the distortion characteristic of the other laser beam (llb) is [mouth].1 If the starting point of both laser beams is the same, the maximum difference between the two laser beams (lLa) is This results in a problem of approximately 18 [μ fat] and the entire image is distorted and the image quality is significantly degraded, making it unsuitable for fine images.

(Problem to be Solved by the Invention) Conventionally, the distortion characteristics of imaging due to multiple laser beams passing through optical paths that are symmetrical about the optical axis of the imaging lens system are in opposite directions. The distortions are superimposed, leading to deterioration of image quality and making it impossible to apply to high-definition images.

Therefore, the present invention aims to eliminate the above-mentioned drawbacks. By aligning the distortion characteristics of multiple laser beams in the same direction and minimizing the difference in image distance between each laser beam, the variation in distortion of the entire image is reduced. Resolved.

It is an object of the present invention to provide an optical device in an image forming apparatus that improves image quality and can be applied to high-definition images.

[Structure of the invention]

(Means for Solving the Problems) In order to solve the above problems, the present invention makes it possible to combine a laser beam having distortion characteristics in an arbitrary direction with a laser beam having distortion characteristics in the other direction. A direction changing member is provided within the imaging lens system or between the imaging lens system and the photoreceptor.

(Function) The present invention uses the above-mentioned means to change the direction of a laser beam in an arbitrary direction and align the distortion characteristics of a plurality of laser beams in the same direction, thereby eliminating variations in distortion of the entire image and achieving one image quality. This makes it possible to improve the image quality and, in turn, make it possible to apply it to high-definition images.

(Embodiment) An embodiment of the present invention will be described below with reference to FIGS. 1 to 3. FIG. 1 is a schematic explanatory diagram of an optical device (17) in a non-impact printer (not shown) which is a terminal of a host system such as an electronic computer, and the first laser beam (18a) is composed of a semiconductor laser that oscillates a first laser beam (18a). 1
oscillator (18) and second laser beam (20a)
A second oscillation unit (20) consisting of a semiconductor laser that oscillates
have. Further, (21) is a polygon mirror rotated at 6000 degrees (7 minutes of rotation), and the first oscillation part (18
) and the second oscillating unit (20), the first laser beam (18a) and the second laser beam are focused and deflected through a beam compressor such as a collimator lens and a prism (not shown). (20a) is irradiated. Furthermore, (22) focuses the laser beams (18a) and (20a) reflected by the polygon mirror (21) onto the photoreceptor (23), which is an image carrier, and uniformizes them on the scanning line, which is the elongated direction. This is an imaging lens system for forming an image on - and has a first lens (24), a second lens (26), and a third lens (27) made of integrally molded plastic. Between the first lens (24) and the second lens (26), there is a first mirror (24) which is a direction changing member that deflects the optical path of the first laser beam (18a) and further changes the direction of the image. It has two mirrors: a first lens (28) and a second mirror (30).
4) and the third lens (27) is a direction changing member that deflects the optical path of the second laser beam (20a) and changes the direction of the image, and is located between the third mirror (31) 1
It has only one copy. Note that (24a) is the first lens (24a).
4), the optical axis (32) is the first developing device, (33) is the second developing device, (34) is the first charger, and (36) is the second charger.

When multicolor printing is started in a non-impact printer (not shown) based on information from a host system (not shown), each device is driven, and the photoreceptor (23) is rotated in the direction of arrow X. Each charger (34), (
36) becomes charged, and the developing devices (32) and (33
) can also be developed. In this state, the host system (
Each oscillator (18)
, (20), the first and second laser beams (18a
).

(20a) is oscillated, each laser beam (18a)
.

(20a) are each guided to a polygon mirror (21) via a collimator lens and a beam compressor (not shown), and as they rotate, they are each scanned in the longitudinal direction of the photoreceptor (23) via an imaging lens system (22).

That is, the first laser beam (18a), after being reflected by the polygon mirror (21), passes through the first lens (24).
The laser beam passes through the second lens (26), is inverted and deflected by the first mirror (28), is inverted and deflected again by the second mirror (30), and then passes through the second lens (26). The beam (t8a) is imaged by the first lens (24) and the second lens (26), and is irradiated onto the photoreceptor (23). - The laser beam (20a) of the power tube 2 is reflected on the polygon mirror (21) surface, and then the optical axis (24
It passes through the first lens (24) in an optical path that is symmetrical to the optical path of the first laser beam (18a) centering on a). Therefore, at point A, which has passed through the first lens (24).

The scanning line (a) by the first laser beam (18a) and the scanning line (b) by the second laser beam (20a) are symmetrically distorted as shown in FIG.
The laser beam (20a) is only reversed and deflected by the third mirror (31), passes through the third lens (27), and then passes through the first lens (24) and the third lens (27).
An image is formed and irradiated onto the photoreceptor (23).

That is, the second laser beam (20a) is transmitted through the first lens (20a).
4) After passing, the number of inversions by the mirror is reduced by one compared to the first laser beam (18a), and the imaging lens system (2
At point B in 2), scanning a (a') by the first laser beam (18) and scanning by the second laser beam (20a)
The scanning lines (18a) are distorted in the same direction as shown in FIG.
) and the second laser beam (20a) are irradiated onto the photoconductor (23) under the same conditions, and the scanning lines of both laser beams (18a) and (20a) on the photoconductor (23) are both in the same direction. This will cause distortion. In this state, when scanning of both laser beams (18a) = (20a) is completed and electrostatic latent images are formed, each electrostatic latent image is transferred to the first developing device (32) and the second developing device ( 33).

After that, the developing section using the first laser beam (18a) passes through the second charger (36) and then the second laser beam (20a)
While scanning is performed again by the second laser beam (20a), the developing section using the second laser beam (20a) performs transfer at a transfer section (not shown), and then passes through a cleaning device and a static eliminator to be ready for the next printing.

With this configuration, even if the electrostatic latent images formed by the first laser beam (18a) and the second laser beam (20a) on the photoreceptor (23) are distorted, they will both move in the same direction. Since the distortion between the two beams is constant, there is no variation in distortion across the entire image compared to conventional images in which the distortion is formed symmetrically, making it possible to obtain a good image. Application to high-definition images is also possible.

It should be noted that the present invention is not limited to the above-mentioned embodiments and can be modified in various ways. For example, the incident angle of the laser beam reflected from the polygon mirror to the imaging lens system can be arbitrary, and the direction changing member is not just a mirror. , a prism mirror may be used to adjust the deflection angle of the laser beam. Further, the number of direction changing members in the optical path of each laser beam is completely arbitrary as long as the plurality of laser beams are distorted in the same direction before reaching the image carrier. Furthermore, the number of oscillators is also arbitrary, and for example, as in another modification shown in FIG.
b) , (37c), (37d) are provided, and the first to fourth laser beams (38a), (38b),
(38c) and (38d) may be used to simultaneously scan a photoreceptor (not shown). However, in this case, the first to fourth laser beams (38a)
, (38b), (38c), and (38d), first, after reflection by the polygon mirror (39), the lens (4o) of the tube 1 is aligned with the first optical axis (40a). ) with the third and fourth laser beams (38c
) and (38d), the first and second laser beams (38a) and (38b) passing through optical paths symmetrical to each other are reversed by a first direction changing member (41). first and second laser beams (38a) that are symmetrically incident on the second optical axis (42a);
(38b), after passing through the second lens (42), one of the first laser beams (38a) is reversed by the second direction changing member (43), while the third lens (42)
4), the third and fourth laser beams (38c), (38d) are incident symmetrically around the tip axis (44a).
), after passing through the third lens X (44), one fourth laser beam (38d) is directed to the third direction changing member (
46).

〔Effect of the invention〕

As explained above, according to the present invention, in consideration of saving space and cost, even if the same imaging lens system is shared and multiple laser beams are imaged, the light of the imaging lens system is By reversing one of the multiple laser beams, which pass through an axially symmetrical optical path and have symmetrical distortion characteristics when passing through a lens, using a direction changing member, the direction of the distortion characteristics can be changed, and all laser beams The distortion characteristics of the beam are aligned in the same direction, eliminating the image disturbance caused by variations in the distortion characteristics that existed in the past, and improving the image quality, making it possible to achieve high-definition images with multicolor images. It is possible to expand its functions.

[Brief explanation of drawings]

1 to 3 show an embodiment of the present invention, FIG. 1 is a schematic explanatory diagram thereof, and FIG. 2 is a characteristic of distortion of the scanning line caused by the first and second laser beams at point A in FIG. 1. 3 is a graph showing the distortion characteristics of the scanning line caused by the first and second laser beams at point B in FIG.
The figure is a schematic explanatory diagram showing another modification of the present invention, FIGS. 5 and 6 are schematic explanatory diagrams showing conventional devices, FIG. 5 is a schematic explanatory diagram with a part thereof omitted, and FIG. 3 is a graph showing characteristics of distortion of a scanning line caused by a laser beam. 17... Optical device, 18... First oscillation section. 18a...first laser beam, 20...second
oscillation unit, 20a...second laser beam, 21
... polygon mirror, 22 ... imaging lens system,
23... Photoreceptor, 24... First lens,
24a... Optical axis, 26... Second lens,
27... Third lens, 28... First mirror, 30... Second mirror, 31...
-Third mirror.

Claims (1)

[Claims] 1. Laser beams emitted from a plurality of oscillating units are scanned by the same polygon mirror, and a shared imaging lens system provided between the polygon mirror and the image carrier is used to scan the laser beams on the image carrier. In the system for forming a plurality of electrostatic latent images on a surface, the imaging lens system includes a lens that focuses the plurality of laser beams on optical paths that are symmetrical about the optical axis thereof, and An optical system for an image forming apparatus, comprising a direction changing member that aligns an image of a laser beam passing through one side of a symmetrical optical path in the same direction as an image of a laser beam passing through the other side, up to an image carrier. Device. 2. The image forming apparatus according to claim 1, wherein the direction changing member is made of a mirror, and one laser beam has one more mirror on its optical path than the other laser beam. Optical device in. 3. An optical device in an image forming apparatus according to claim 1 or 2, wherein the direction changing member is provided inside the imaging lens system.