Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
2000-03-22
2002-07-09
Kim, Robert H. (Department: 2882)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S235000, C250S236000
Reexamination Certificate
active
06417509
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to image forming apparatuses, such as digital copying machines, optical printers and other apparatuses capable forming images, and an optical scanning apparatus included in such image forming apparatuses.
DISCUSSION OF RELATED ART
An optical scanning apparatus is known for use in image forming apparatuses such as digital copying apparatuses, optical printers and other such apparatuses. Optical scanning in an optical scanning apparatus is performed by scanning a beam spot by optically forming the beam spot on a surface to be scanned. The diameter of a beam spot is an important factor influencing the quality of an image generated by the scanning process. In order to produce a good quality image, a scanning beam has to be adequately condensed onto the surface to be scanned. Because an optical scanning apparatus generally includes movable portions such as a rotating polygonal mirror for deflecting a light beam from a light source toward the surface to be scanned, the arrangement conditions of an optical system of the optical scanning apparatus is slightly changed by the influence of vibrations or other external environmental factors over time. Moreover, when an optical system includes a plastic lens or similar lens elements which is easily influenced by temperature and humidity, the characteristics of the optical system slightly fluctuate according to changes in the operating environment of the optical scanning apparatus.
If such optical arrangement deviation and optical characteristic fluctuation occurs, the light condensing position (focusing position) of a scanning beam deviates relative to the surface to be scanned, and thereby, the beam spot diameter increases.
Therefore, several attempts have been made to correct the deviation of the focal position of a scanning beam occurring over time or caused by environmental fluctuations.
For example, Japanese Patent Application Laid-Open No. 10-20225 describes an optical scanning apparatus for condensing a laser beam radiated from a laser beam source into an optical beam spot and linearly scanning a surface to be scanned at a substantially constant velocity with the optical beam spot. The optical scanning apparatus includes a focusing lens for adjusting the condensing position of a laser beam radiated from the laser beam source, a detecting device for detecting the passage of a scanned laser beam to generate a detection signal, a pulse emitting device for allowing the laser beam source to emit a pulse at a predetermined time after the generation of the detection signal, a beam condensed state detecting device located at a position that is substantially optically equivalent to the position of the surface to be scanned for detecting the beam condensed state using a knife edge process, and a control device for driving the focusing lens based on the detection result of the beam condensed state detecting device to adjust the condensed position of the laser beam.
Moreover, another optical scanning apparatus is described in Japanese Patent Publication No. 2761723, which includes a light source for emitting a laser beam, a collimator lens for collimating the laser beam emitted from the light source, a photoelectric converting element for receiving a laser beam passed through the collimator lens, and an adjusting device for adjusting the position of the collimator lens in an optical axis direction in accordance with the output of the photoelectric converting element. The adjusting device adjusts the position of the collimator lens in accordance with a difference between a maximum output value and a minimum output value of the photoelectric converting element when receiving the laser beam flickering in response to an image signal.
In the optical scanning apparatus described in Japanese Patent Application Laid-Open No.10-20225, the laser beam source is allowed to emit a pulse from a pulse emitting device, and the beam condensed state is detected by the beam condensed state detecting device located at a position that is substantially optically equivalent to that of the surface to be scanned. However, a pulse emitting timing of the pulse emitting device actually deviates. Therefore, the detection accuracy of the beam condensed state is decreased when such deviation in pulse emitting timings occurs. Moreover, because the beam condensed state is detected by the beam condensed state detecting device using a knife edge process, the beam condensed state of a main scanning direction can be detected, but the beam condensed state of a sub scanning direction cannot be detected.
There is no apparatus or method for detecting the beam condensed states independently in the main scanning direction and in the sub scanning direction in the conventional art.
Moreover, in the optical scanning apparatus described in the Japanese Patent Application Laid-Open No. 10-20225 or Publication No. 2761723, an adjusting mechanism for adjusting a focal position adjusts the focusing lens or the collimator lens in the optical axis direction. Accuracy is required for the positional relationship between the light source and the focusing lens or the collimator lens. Also, an optical axis deviation or the like occurs when the focusing lens or the collimator lens is displaced for adjusting the focal position. Therefore, it is actually difficult to adjust the focusing lens or the collimator lens.
Furthermore, even when the focusing lens or the collimator lens is adjusted in the optical axis direction, the focal position cannot necessarily be corrected in the main and sub scanning directions at the same time. Particularly, in an optical scanning apparatus, the magnification of an optical system disposed on the optical path leading to a surface to be scanned from a light source often differs in the main scanning direction and in the sub scanning direction, for example, because of surface tilt correction for a rotating polygonal mirror functioning as a deflector for deflecting a light beam from a light source toward a surface to be scanned. In this case, even if the position of a collimating lens is adjusted in the optical axis direction, the focal position deviation of the main scanning direction and sub scanning direction cannot simultaneously be corrected.
The prior art method which includes using a knife edge process can only detect a beam condensed state in the main scanning direction and can not detect the beam condensed state in the sub scanning direction. Also, only a single pulse at a time is detected in the knife edge process so that the detection accuracy is relatively low. Further, the knife edge process requires the use of at least two pixels to achieve detection of the beam condensed state.
The other conventional apparatus which uses a line CCD for detecting a beam condensed state on a surface to be scanned is capable of more accurate detection of the beam condensed state, but is very expensive due to the cost of the line CCD and requires many pixels to achieve the detection. Furthermore, the line CCD can only detect the beam condensed state in the sub scanning direction and can not detect the beam condensed state in the main scanning direction.
Another conventional method uses an area CCD to detect the beam condensed state. Similar to the line CCD, the area CCD is very expensive and requires even more pixels to detect the beam condensed state. Also, the area CCD uses only a single pulse to detect the condensed state of the beam spot which has limited detection accuracy.
SUMMARY OF THE INVENTION
In order to overcome the above-described and other problems, preferred embodiments of the present invention provide a novel optical scanning apparatus which greatly improves the detection accuracy of an image forming state of a light beam.
The preferred embodiments of the present invention further provide a novel optical scanning apparatus which more accurately detects the location of a waist position of a light beam using an inexpensive element.
The preferred embodiments of the present invention further provide a novel optic
Atsuumi Hiromichi
Suzuki Seizo
Greenberg & Traurig, LLP
Kim Robert H.
Ricoh Technology Research Inc.
Rzucidlo Eugene C.
Thomas Courtney
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