Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
1998-10-05
2001-12-04
Yockey, David F. (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S243000
Reexamination Certificate
active
06326992
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an image forming apparatus for scanning laser beams and thereby forming a latent image on a image bearing member.
RELATED ART
Heretofore, a large number of image forming apparatuses for forming a static latent image on a image bearing member with a laser beam and for printing the image on a paper at a high speed by a electrophotographic process have been used as output units of computers, facsimile machines, multi-functional copy machines, and so forth. In recent years, there has been an urgent need for improving the output speeds of these apparatuses. Accordingly, the apparatuses have been actively improved.
For example, an image forming apparatus using a rotating polygon mirror type deflecting unit deflects one laser beam with each facet and draws one scanning line. Thus, to increase the number of scanning lines in a particular time period, provided that the number of small mirror surfaces of the rotating polygon mirror is constant, the number of rotations should be increased. On the other hand, provided that the number of rotations is constant, the number of mirror surfaces of the rotating polygon mirror should be increased. To increase the number of rotations of the rotating polygon mirror, a dynamic or static bearing using pneumatic or hydraulic power is required. These bearings are expensive and difficult to handle. Thus, they are difficult to use in conventional laser printers. In contrast, provided that the number of mirror surfaces of the polygon mirror is increased, since the deflection angle becomes small, the length of the optical path following the deflecting unit becomes large. In addition, the diameter of collimated laser beams entering into an image forming optical system becomes large in proportion to the length of the optical path. Thus, the sizes of the lens and the rotating polygon mirror become large. In particular, when a high resolution is required, since the number of scanning lines are increased, the number of rotations of the polygon mirror and the length of optical path should be further increased. This situation also applies to the case where the deflecting unit is not a rotating polygon mirror. In this case, the scanning frequency and the length of the optical path following the deflecting unit increase. To solve these problems, an exposing technique for writing a plurality of scanning lines with a plurality of laser beams in one scanning sequence has been developed. This technique is referred to as a multi-beam exposing technique.
To obtain a plurality of laser beams, a plurality of gas laser (for example, He—Ne) oscillators are used as a light source. In addition, a technique wherein a laser beam generated by one oscillator is time-divided into a plurality of portions by an acousto-optical modulator (AOM) or the like has been developed. As a technique for simplifying the construction of the unit and decreasing the size thereof, for example, as disclosed in Japanese Patent Laid-Open Publication Serial No. SHO 54-7328, a semiconductor laser array where a plurality of light emitting portions for radiating laser beams are integrally disposed on one device is used as a light source.
Next, an image forming apparatus using a semiconductor laser array will be described. An image forming apparatus uses a laser array integrally disposed on one substrate as a light source. A beam radiating point of each light emitting portion is disposed at an edge of a semiconductor device substrate. A plurality of laser beams are collimated by a common collimator lens so that they have a particular diameter. Thereafter, the collimated laser beams are introduced into one facet of the rotating polygon mirror (deflecting unit). As the facet rotates, the laser beams are deflected. Next, the laser beams are spotted as an image through an image forming lens. Then, the image spot exposes the image bearing member and thereby a static latent image is formed. Next, in accordance with the electrophotographic process, the latent image is developed, transferred onto a paper, and then fixed. In addition, as disclosed in Japanese Patent Laid-Open Publication Serial No. SHO 54-158251, to decrease the distance of each adjacent scanning line scanned on the image bearing member at a time, the light emitting portions of the laser array are disposed at particular angles to the scanning plane.
On the other hand, there is still another need of an image forming apparatus using such a semiconductor laser array which can scan laser beams at a high speed and with a high resolution. However, the conventional image forming apparatus has not satisfactorily accomplished a high-speed and high-resolution laser beam scanning technique.
DISCLOSURE OF THE INVENTION
The present invention has been made with consideration of the above described points. An object of the present invention is to provide a compact image forming apparatus for scanning laser beams at a high speed and with a high resolution.
A first feature of the present invention is an image forming apparatus, comprising a image bearing member for forming a static latent image thereon, a charging unit for charging the surface of the image bearing member, a laser beam scanning unit for scanning a plurality of laser beams on the surface of the image bearing member which is charged, and a developing unit for causing a developing agent to adhere on the surface of the image bearing member scanned with the laser beams, wherein the laser beam scanning unit comprises a semiconductor laser array having a plurality of light emitting portions for emitting laser beams, the light emitting portions being formed on a device substrate, and a deflecting unit for deflecting laser beams emitted from the light emitting portions to the surface of the image bearing member, wherein the light emitting portions are disposed two-dimensionally on a surface of the semiconductor laser array, and wherein the lighting and the amount of light of each of the light emitting portions are discretely controlled.
A second feature of the present invention is a laser beam scanning unit, comprising a semiconductor laser array having a plurality of light emitting portions for emitting laser beams, the light emitting portions being formed on a device substrate, and a deflecting unit for deflecting the laser beams emitted from the light emitting portions, wherein the light emitting portions are disposed two-dimensionally on a surface of the semiconductor laser array, and wherein the lighting and the amount of light of each of the light emitting portions are discretely controlled.
A third feature of the present invention is an image forming apparatus, comprising a image bearing member for forming a static latent image thereon, a charging unit for charging the surface of the image bearing member, a laser beam scanning unit for scanning a laser beam on the surface of the image bearing member which is charged, and a developing unit for causing a developing agent to adhere on the surface of the image bearing member scanned with the laser beam, wherein the laser beam scanning unit comprises a semiconductor laser having a light emitting portion for emitting a laser beam, the light emitting portion being formed on a device substrate, and a deflecting unit for deflecting a laser beam emitted from the light emitting portion to the surface of the image bearing member, and wherein the light emitting portion has an optical axis substantially perpendicular to the surface of the device substrate.
A fourth feature of the present invention is a laser beam scanning unit comprising a semiconductor laser having a light emitting portion for emitting a laser beam, the light emitting portion being formed on a device substrate, and a deflecting unit for deflecting the laser beam emitted from the light emitting portion, wherein the light emitting portion has an optical axis substantially perpendicular to a surface of the device substrate.
A fifth feature of the present invention is an image forming apparatus comprising a image bearing member for forming a static late
Inoue Nozomu
Koga Yoshiro
Kurihara Hajime
Takada Kyu
Ladas & Parry
Seiko Epson Corporation
Yockey David F.
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