Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
2002-08-29
2004-08-10
Pham, Hai (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S239000
Reexamination Certificate
active
06774925
ABSTRACT:
BACKGROUND
Scanned light beam imaging is employed for various purposes including electrophotographic printing. In such systems used for printing, a light beam generated, for example, by a laser is selectively modulated to vary its amplitude while it is scanned laterally across a moving photoconductor to selectively discharge the photoconductor. Such systems have been binary in nature (“on” or “off”) to accomplish printing of character information by selectively either exposing the photoconductor or leaving it unexposed. To insure complete exposure, adjacent scan lines are usually overlapped slightly. Thus, any slight misalignment of the scans or change in beam size would not be noticed.
This cannot be done if the light beam modulation is other than binary because in any partial exposure, a substantial overlap would appear as a stripe of complete exposure. Alternatively, spacing the scans apart would appear as a stripe that remains unexposed. To attempt to prevent such stripes by substantially eliminating the optical and mechanical tolerances from the system would appear to be prohibitively expensive.
It is therefore an object of the present invention to eliminate the perception of elongated stripes in such optical imaging systems without requiring substantial tightening of allowable optical or electro-mechanical tolerances.
SUMMARY
A method for banding suppression due to vibration in an image forming and/or image receiving apparatus with laser driver utilizes governing equations which relate the on/off time and intensity to velocity and frequency of vibration are disclosed. Using derived formulas, an amplitude and frequency modulation (AM/FM) combination is used to suppress the banding due to vibration. The equation which governs the on/off time (FM) is t
1
+e sin(2&pgr;ft
1
)/v
n
=t
0
. This transcendental equation can be solved for the required on-time t
1
in terms of the nominal on-time t
0
, e (vibration amplitude), v
0
(nominal velocity) and f (vibration frequency). The equation which governs the intensity is H
3
(t)=v(t)/v
0
. H
3
(t) controls the level of irradiance. This method is further extended to multi-temporal vibration frequency and may correct banding due to irradiance modulation.
REFERENCES:
patent: 4180822 (1979-12-01), Hudson et al.
patent: 4251625 (1981-02-01), Sakamoto et al.
patent: 4414583 (1983-11-01), Hooker
patent: 4801978 (1989-01-01), Lama
patent: 4884083 (1989-11-01), Loce et al.
Rahnavard Mohammad H.
Zomorrodi Mehrdad
Pham Hai
Xerox Corporation
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