Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
1999-04-20
2001-02-27
Allen, Stephone B. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C359S198100, C359S811000, C358S474000
Reexamination Certificate
active
06194713
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a scanning optical device used in an image forming apparatus such as a laser printer or the like.
Generally, a scanning optical device includes a light source which emits a beam and a rotatable polygon mirror which reflects the beam so that the beam scans across a surface of a photo-conductive drum. An f&thgr;-lens is provided between the polygon mirror and the photo-conductive drum, which converges the beam on the surface of the photo-conductive drum. Hereinafter, the direction in which the beam moves according to the rotation of the polygon mirror is referred to as a main scanning direction. The direction perpendicular to the main scanning direction on a mirror surface of the polygon mirror is referred to as an auxiliary scanning direction.
A ‘scanning range’ is set within the actual moving range of the beam caused by the rotation of the polygon mirror. When the beam reaches one end (a starting position) of the scanning range, the scanning optical device starts modulation of the beam, so as to form latent image on the surface of the photo-conductive drum. The modulation of the beam is continued until the beam reaches the other end (an end position) of the scanning range.
In order to detect the beam reaching a proximate position to the starting position of the scanning range, an SOS (start-of-scan) sensor is provided in the scanning optical device. The SOS sensor is so constructed as to receive the beam via an intermediate mirror disposed in the proximity of the f&thgr;-lens.
Since there is a possibility that the rotation axis of the polygon mirror is inclined due to a manufacturing error, the SOS sensor must have a length in the auxiliary n scanning direction. Thus, the SOS sensor uses a PIN photo diode array (as a beam detector)that has a plurality of elongated light receiving surfaces arranged in the main scanning direction. Each light receiving surface of the PIN photo diode array extends in the auxiliary scanning direction.
Further, in order to compensate the deviation of the rotation of the photo-conductive drum, a recently developed optical scanning device has a dynamic prism that is moved so that the beam shifts in the auxiliary scanning direction. It is preferred to dispose the dynamic prism between the light source and the f&thgr;-lens, because the amount of the necessary movement of the dynamic lens can be decreased as the dynamic prism is close to the light source. In such a case, when the dynamic prism is moved, the beam directing toward the SOS sensor is also shifted of the beam in the auxiliary direction.
In such a scanning optical device, if the light receiving surface of the SOS sensor is inclined with respect to the main scanning direction, the following problem may arise.
FIG. 1
shows the light receiving surface PD and a scanning line, that is, the movement of the beam passing through the light receiving surface PD. The scanning line before the dynamic prism is moved (that is, when the dynamic prism is positioned at its original position) is indicated by an arrow ‘a’. The timing when the beam moves across the light receiving surface PD is indicated by Ta. When the dynamic prism is moved, the scanning line shifts in the auxiliary scanning direction as indicated by arrows ‘b’ and ‘c’. If the scanning line shifts as indicated by the arrow ‘b’, the timing when the beam move across the light receiving surface PD is changes to time Tb that is ahead of time Ta. Conversely, if the scanning line shifts as indicated by the arrow ‘c’, the timing when the beam move across the light receiving surface PD is changes to time Tc that behind time Ta. Accordingly, the timing of the beam detection by the SOS sensor is influenced by the movement of the dynamic prism. Conseqently, the detected timing when the light modulating is to be started is influenced by the movement of the dynamic prism.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an optical scanning device wherein timing of beam detection is not influenced by a shifting of a beam in an auxiliary scanning direction.
For the above purpose, according to an aspect of the present invention, there is provided a scanning optical device including a light source which emits a beam, a scanning unit which reflects the beam so that the beam scans in a main scanning direction, a beam detector which detects the beam reaching a predetermined position in the main scanning direction, and a adjustable holder which supports the beam detector. The beam detector has at least one elongated light receiving surface. The adjustable holder is rotatable so that an inclination of the light receiving surface can be varied with respect to the main scanning direction.
As constructed above, an operator is able to adjust the rotational position of the adjustable holder until the longitudinal direction of the light receiving surface is perpendicular to the main scanning direction (while observing the output from the beam detector). With such an adjustment, the timing of the beam detection by the beam detector is not influenced by the shifting of the beam an auxiliary scanning direction.
It is preferred that a rotation axis of the adjustable holder is aligned with a path of the beam directing toward the beam detector.
In a particular arrangement, the scanning optical device further includes a cylindrical support held by a stationary part of the scanning optical device. The adjustable holder has an engaging portion which engages a circumference of the cylindrical support so that the adjustable holder is rotatable about the cylindrical support. The beam proceeds through an interior of the cylindrical support toward the beam detector. An axis of the cylindrical support is aligned with a path of the beam directing toward the beam detector.
In a preferred embodiment, the beam detector further includes an inclination detecting sensor which detects an inclination of the longitudinal direction of the beam detector with respect to the main scanning direction, particularly, the inclination detecting sensor includes a pair of surfaces which are symmetrically disposed with respect to the rotation axis of the adjustable holder.
Advantageously, it is preferred to further provide a converging lens which converges the beam to the beam detector. The converging lens can be mounted in the cylindrical support.
Preferably, the adjustable holder has a positioning part in which the beam detector is positioned. It is preferable to provide a movement prevention arrangement which prevents the movement of the adjustable holder in an axis of the cylindrical support. It is further preferable to provide a rotation restriction member which restricts a range of rotation of the adjustable holder.
REFERENCES:
patent: 4909431 (1990-03-01), Japichino et al.
patent: 4912567 (1990-03-01), Nakajima et al.
patent: 5637852 (1997-06-01), Knowles et al.
patent: 5659432 (1997-08-01), Takashima et al.
patent: 5742326 (1998-04-01), Matsui et al.
patent: 5808774 (1998-09-01), Kawabata
patent: 6008924 (1999-12-01), Ikegame
Allen Stephone B.
Asahi Kogaku Kogyo Kabushiki Kaisha
Greenblum & Bernstein P.L.C.
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