Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
2001-07-24
2003-07-01
Robinson, Mark A. (Department: 2872)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S212100, C347S256000
Reexamination Certificate
active
06587245
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical scanning device, optical scanning method, and image forming apparatus.
2. Discussion of the Background
There has been proposed an optical scanning method which divides an area to be scanned on a surface to be scanned into n (wherein n≧2) partial scanning portions in the longitudinal direction and uses n light sources corresponding to the partial scanning portions on a one-to-one basis to optically scan the partial scanning portions corresponding to the light fluxes from the n light sources, thereby synthetically optically scanning the area to be scanned (Japanese Unexamined Patent Application Publication No. 7-199098, Japanese Unexamined Patent Application Publication No. 10-213763, etc.).
Such an optical scanning method (hereafter referred to as “segmented scanning”) has the following advantages.
First, increasing the number n of partial scanning portions constituting the area to be scanned allows optical scanning to be performed over extremely wide scanning areas.
Second, each partial scanning portion can be made small, so that in the event of individually providing plural scan imaging optical systems for each partial scanning portion, for example, the angle of each scan imaging optical system does not have to be made unnaturally wide, and the plural scan imaging optical systems and the optical elements constituting the plural scan imaging optical systems can be made small. Further, correction of wave-front aberrations which are correlated with the light spot diameter can be facilitated, and there is less difference in spot diameter due to irregularities in parts and attachment variances, so that the diameter of the light spot can be reduced.
However, on the other hand, dividing the area to be scanned into multiple partial scanning portions results in the optical scanning of the partial scanning portions by separate light fluxes, and in the event that the intensity of light, spot diameter, optical scanning speed, etc., of the light spots irradiating the surfaces to be scanned differ from one partial scanning portion to the next, the latent image written by optical scanning upon developing will show irregularities in concentration as the image density differs from one partial scanning portion to another, e.g., the concentration of band-shaped portions extending in the sub-scanning direction, corresponding to the partial scanning portions, can change cyclically according to the length of the partial scanning portions in the main scanning direction.
A non-uniformity in the intensity of light irradiated on the surface to be scanned from one partial scanning portion to the next can occur due to variances the emitted light intensity between different light sources and the properties of transmittance and reflectance of the optical elements situated between the different light sources and the partial scanning portions.
Also, a non-uniformity in the spot diameter from one partial scanning portion to another can occur due to manufacturing variances in the individual optical elements situated between the different light sources and the partial scanning portions, variances in the precise attachment thereof, and so forth.
Further, a non-uniformity in the optical scanning speed from one partial scanning portion to another can occur due to manufacturing variances in the f&thgr; lens used as the scan imaging optical system, and variances in the precision of attachment thereof.
When there is a difference in image density at image portions corresponding to adjacent partial scanning portions, the image density or concentration changes in steps at the portion corresponding to a seam between the partial scanning portions, and accordingly irregularities in image density tend to be conspicuous.
With the invention described in Japanese Unexamined Patent Application Publication No. 10-213763, the arrangement is such that the amount of light flux optically scanned in each partial scanning portion is uniform near a seam between adjacent partial scanning portions. However, irregularities in concentration can still occur if the spot diameter or optical scanning speed differs from one partial scanning portion to another.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above-discussed and other problems and addresses the above-discussed and other problems.
Accordingly, preferred embodiments of the present invention provide a novel optical scanning device and a novel optical scanning method that effectively reduce the above-described image density or concentration irregularities in optical scanning performed by segmented scanning, and thereby make irregularities in concentration less conspicuous.
According to a preferred embodiment of the present invention, an optical scanning device divides an area to be scanned on a surface to be scanned into n (wherein n≧2) partial scanning portions in the longitudinal direction, and uses n light sources corresponding to the n partial scanning portions on a one-to-one basis to optically scan the n partial scanning portions with respective light fluxes from the n light sources, thereby scanning optically the area to be scanned. The optical scanning device includes a deflecting device and a scan imaging optical device.
The n light sources are each independently capable of modulating the intensity of the emitted light. For example, n solid lasers or gas lasers, n LEDs, etc., may be used. Most practically, n semiconductor lasers may be used.
The n number of light sources is not restricted to those mentioned above. Each light source may have a plurality of light-emitting sources which are each independently capable of modulating the intensity of the emitted light, such as for example articles wherein light fluxes from multiple semiconductor lasers are synthesized with a light flux synthesizing prism, articles wherein light fluxes from multiple semiconductor lasers are mutually given angles and combined, semiconductor laser arrays, etc. Using such light sources for each partial scanning portion allows each partial scanning portion to be optically scanned with the multi-beam scanning method such that multiple lines in the area to be scanned are simultaneously synthetically scanned optically.
The deflecting device deflects the light fluxes from the n light sources, and an appropriate known deflector (e.g., a rotating unifacial mirror, a rotating bifacial mirror, a rotating polygonal mirror, a galvano-mirror, etc.) may be used.
One deflector may be provided for each of the n light sources so that the deflecting device is configured with a total of n deflectors. Alternatively, two or more light sources may share one deflector so that the deflecting device is configured from a number of deflectors which is less than the number n of light sources.
The scan imaging optical device is an optical device for converging each light flux deflected by the deflecting device toward the surface to be scanned, thereby forming a light spot at the partial scanning portion from each light flux.
For example, one set of image scanners (i.e. a scan imaging optical system) may be provided for each of the n light sources, thereby configuring the scan imaging optical device with n sets of image scanners. Alternatively, one set of image scanners which are configured to converge individual light flux from two or more light sources to the respective corresponding partial scanning portions may be utilized, thereby configuring the scan imaging optical device with a number of image scanners which is less than the number n of light sources. Accordingly in this alternate embodiment, when the number of light sources n=2, the scan imaging optical device is configured with only one image scanner.
Each of the image scanners may be configured with one or more lenses, or may be configured with one or more imaging reflectors (reflectors having imaging capabilities), or may be configured with a combination of one or more lenses and one or more imaging reflectors.
The “surface to be
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