Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1997-07-01
2002-09-03
Nguyen, Thong (Department: 2872)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S205100
Reexamination Certificate
active
06445483
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an optical scanning apparatus for use with laser printers and the like. More particularly, the invention relates to an optical scanning apparatus of such a type that an optical beam is allowed to be incident on a scanner at an angle with a scanning plane perpendicular to its rotating axis and which is adapted to compensate for the curvature or rotation of the deflected beam such as to prevent the formation of a disfigured beam spot. The invention also relates to an optical scanning apparatus in which an optical beam is allowed to be incident on a scanner twice so that it is deflected and thereafter focused on a surface to be scanned by means of scanning optics in such a way that the optical path of one beam will not interfere with the optical path of the other beam.
Finally, the invention relates to an optical scanning apparatus of the type in which an optical beam is incident twice in succession on the facets of a rotating polygonal mirror while being slanted at angles to a scanning plane perpendicular to the rotating axis of the rotating polygonal mirror. The apparatus prevents a positional variation of a scanning line that is due to a shift of each facet of the rotating polygonal mirror with respect to the rotating axis of the polygonal mirror.
2. Background
Optical scanning apparatus for use with laser beam printers and the like are conventionally adapted to be such that an optical beam emitted from a light source such as a semiconductor laser is passed through shaping optics, deflected by a scanner such as a rotating polygonal mirror and focused by an imaging lens system, typically an f·&thgr; lens system, to form a beam spot on the surface to be scanned. With such optical scanning apparatus, there occurs no particular problem since the optical beam is allowed to be incident within a scanning plane for deflection. However, in the case of an optical scanning apparatus for use with a multi-color laser printer of such a type that optical beams for more than one color are allowed to be incident simultaneously for deflection on the same scanning plane perpendicular to the rotating axis of a rotating polygonal mirror (see Unexamined Published Japanese Patent Application No. 161566/1981), it is necessary to separate the optical beams of the respective colors and, to this end, the beams must be allowed to be incident for deflection by the polygonal mirror at different angles with a scanning plane which is perpendicular to its rotating axis.
Also known in the art is an optical scanning apparatus of such a type that an optical beam is allowed to be incident twice for deflection by the rotating polygonal mirror. This apparatus has also had a problem in that in order to realize a compact system, the optical path for the incident beam must be separated from the optical path for the deflected beam in the first deflection and the second deflection by causing the respective optical beams to be incident on the polygonal mirror at an angle with a scanning plane perpendicular to its rotating axis.
If an optical beam is allowed to be incident on the rotating polygonal mirror at an angle with the scanning plane, the deflected beam becomes curved and the scanning line will draw a conical locus such that the optical beam scanning each end of the scan range is rotated, whereupon a disfigured beam spot is formed on the surface to be scanned, thus making it difficult to form a sharp image.
With the multi-color laser printer proposed in Unexamined Published Japanese Patent Application No. 161566/1981, the optical beams deflected by the reflecting surface are curved and the scanning line formed on the surface to be scanned is not straight. To deal with this problem, an optical scanning apparatus has been disclosed that performs the scanning operation with the aid of a cylindrical lens. However, even in that modified version, the deflected end scanning optical beam is rotated and although the scanning line formed on the surface to be scanned is straight, the resulting beam spot is disfigured so that it is no longer possible to form a satisfactory image.
In order to insure that the position of the scan start point is kept constant, an optical beam carrying a horizontal sync signal is detected. However, if optical beams are allowed to be incident for deflection on the rotating polygonal mirror at an angle with the scanning plane, the beam spot formed by the optical beam carrying a horizontal sync signal becomes disfigured to deteriorate the precision in detection.
The optical scanning apparatus for use with conventional laser beam printers and the like are typically adapted to be such that an optical beam issuing from a light source such as a semiconductor laser is passed through shaping optics and allowed to be incident on a scanner such as a rotating polygonal mirror for single deflection and the thus deflected beam is passed through an imaging lens system, typically an f·&thgr; lens system, to thereby form a beam spot on the surface to be scanned. However, this practice of performing only one deflection has the following problem: the optical beam incident on a reflecting surface of the scanner is so large in the main scanning direction that in order to insure that the entire part of the incident beam will lie in the reflecting surface, the size of individual reflecting surfaces has to be increased. As a result, the scanner becomes bulky and, in addition, the number of reflecting surfaces of the scanner cannot be sufficiently increased to realize a fast operating optical scanning apparatus.
Under the circumstances, various proposals have recently been made to develop a new optical scanning apparatus which is adapted to be such that an optical beam deflected by a first reflecting surface of a scanner such as a rotating polygonal mirror is passed through transfer optics and directed to a second reflecting surface of the same scanner, thereby increasing the angle of the second deflection to produce an optical beam for scanning over the surface to be scanned by means of scanning optics. This type of optical scanning apparatus are claimed to have two major advantages, i.e., compactness and fast operation.
An example of the proposals that have resulted from this approach is the scanning optics capable of self-amplified deflection which is described in Japanese Unexamined Published Patent Application No. 97448/1978. In this system, an optical beam deflected by a first reflecting surface of a scanner is passed through a focal transfer optics so that it is incident on a second reflecting surface, which is different from the first reflecting surface, in a direction parallel to the optical beam from the first reflecting surface. Thus, optical scanning is performed with the optical beam that has been deflected twice by two different reflecting surfaces of the same scanner. The transfer optics is provided in such a way that the optical beam will move in a direction opposite to that in which the scanner is rotated.
The above-described optical scanning apparatus of a dual deflection type has two salient features: the scanning angle can be increased and, in addition, the angle by which the optical beam deflected by the first reflecting surface of the scanner is inclined due to its tilting can be reduced or canceled at the second reflecting surface. However, the scanning optics described in Unexamined Published Japanese Patent Application No. 97448/1978 has the disadvantage that the overall optical scanning apparatus becomes bulky since the optical path of the first deflected optical beam and that of the second deflected optical beam lie in the same plane. In addition, the first and second reflecting surfaces of the scanner must be in diametrically opposite positions and this increases the optical path length of the transfer optics, thereby reducing the latitude in the layout of the optical path of the transfer optics. Further in addition, the transfer optics has to be a focal and to meet this requirement, at least two lens elements are
Hama Takashi
Inoue Nozomu
Nomura Yujiro
Takada Kyu
Cherry Euncha
Nguyen Thong
Seiko Epson Corporation
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