Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
2001-10-05
2003-10-28
Pham, Hai (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S250000
Reexamination Certificate
active
06639620
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a light beam scanning apparatus for scanning a plurality of laser beams in an image formation apparatus such as a digital copier or a laser printer which forms a single electrostatic latent image on a single photoconductor drum by simultaneously performing scanning and exposure on the photoconductor drum by using the plurality of laser beams.
In recent years, there have been developed various digital copiers according to scanning and exposure using a laser light beam (hereafter referred to as the light beam) and an electrophotographic process.
Recently, a multi-beam digital copier is developed for increasing an image formation speed. The multi-beam system generates a plurality of light beams and simultaneously scans a plurality of lines using these light beams.
Such a multi-beam digital copier is equipped with a semiconductor laser oscillator for generating a plurality of light beams and an optical unit as a light beam scanning apparatus. The optical unit chiefly comprises a rotating polygon such as a polygon mirror, a collimator lens and an f-&thgr; lens for reflecting each light beam from the plurality of laser oscillators toward a photoconductor drum and scanning on a photoconductor drum using each light beam.
Conventionally, the optical unit of the multi-beam digital copier controls scanning direction exposure positions and passage positions of light beams. The scanning direction exposure position control relates to controlling light beam positions in a main scanning direction. The passage position control relates to controlling light beam positions in a sub-scanning direction.
An exemplification of this technology is proposed in U.S. patent application Ser. No. 9/667,317. According to the exemplification, a pair of sensors detect passage points of light beams scanning a photoconductor drum surface in the sub-scanning direction in order to control light beam positions by detecting light beams with high precision in a wide range. The pair of sensors are arranged at a position equivalent to the surface to be scanned. Each of the pair of sensors is formed of a trapezoid pattern, for example. The pair of sensors are arranged symmetrically to each other with a specified interval.
A light beam scanning position is determined by a value obtained by integrating output differences from the pair of sensors. A processing circuit connected to the pair of sensors computes an integration value indicative of the light beam scanning position. The processing circuit comprises a plurality of operational amplifiers and uses an integrator to integrate an electric signal difference detected by each sensor.
U.S. patent application Ser. No. 9/816,773 proposes a pair of sensors comprising two sawtooth patterns for detecting a light beam. Like U.S. patent application Ser. No. 9/667,317, the proposal in Ser. No. 9/816,773 determines a light beam scanning position by using the processing circuit for integrating output differences from the pair of sensors.
In the case of a saturated output from the processing circuit for processing an output signal from the pair of sensors, U.S. patent application Ser. Nos. 9/667,317 or 9/816,773 proposes detection of a light beam scanning position by correcting an output signal from the pair of sensors.
However, there is not provided control to effectively determine a correction amount for correcting an output signal from the pair of sensors. If the light beam excessively deviates from the center position, for example, repeating the correction using a minimum correction amount makes the correction process time-consuming.
Further, an offset voltage exists in the processing circuit for processing an output signal from the pair of sensors. There is the problem that such an offset voltage in the processing circuit affects determination of a light beam passing position.
BRIEF SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a light beam scanning apparatus which can effectively determine a light beam scanning position.
A light beam scanning apparatus according to the present invention comprises: a light emitting device which outputs a light beam; a light beam scanning member which allows a light beam output from this light emitting device to scan toward a scanned face so that the light beam scans the scanned face in a main scanning direction; a pair of sensors which are arranged on the scanned face or a position equivalent thereto, detect a light beam scanned by the light beam scanning member, and output an electric signal; a processing circuit which has a plurality of operational amplifiers, corrects an output from each of the pair of sensors, and integrates a difference between these corrected electric signals; a control section which determines the necessity of correction based on a value integrated by this processing circuit, determines a scanning position of the light beam according to a value integrated by the processing circuit when the necessity of correction is not determined, and sets a correction amount based on a value integrated by the processing circuit and an offset amount present in the processing circuit when the necessity of correction is determined; and a correction signal generation circuit which outputs a correction signal to the processing circuit so as to correct an electric signal output from each of the pair of sensors based on a correction amount set in this control section.
A light beam scanning apparatus according to the present invention comprises: a light emitting device which outputs a light beam; a light beam scanning member which allows a light beam output from this light emitting device to scan toward a scanned face so that the light beam scans the scanned face in a main scanning direction; a pair of sensors which are arranged on the scanned face or a position equivalent thereto, detect a light beam scanned by the light beam scanning member, and output an electric signal; an integrator circuit which integrates a difference between electric signals output from each of the pair of sensors; a first comparator circuit which compares a value integrated in this integrator circuit with a first threshold; a second comparator circuit which compares a value integrated in the integrator circuit with a second threshold smaller than the first threshold; and a control section which specifies first and second thresholds to the first and second comparator circuits, when the comparator circuits yield a normal comparison result, determines an output value of the integrator circuit according to magnitude relation between the first and second thresholds, and, when the comparator circuits yield an abnormal comparison result, determines whether the offset has an effect on the abnormal comparison result based on the predetermined maximum offset amount.
A light beam scanning apparatus according to the present invention comprises: a light emitting device which outputs a light beam; a light beam scanning member which allows a light beam output from this light emitting device to scan toward a scanned face so that the light beam scans the scanned face in a main scanning direction; a pair of sensors which are arranged on the scanned face or a position equivalent thereto, detect a light beam scanned by the light beam scanning member, and output an electric signal; an integrator circuit which integrates a difference between electric signals output from each of the pair of sensors; a first comparator circuit which compares a value integrated in this integrator circuit with a first threshold; a second comparator circuit which compares a value integrated in the integrator circuit with a second threshold smaller than the first threshold; and a decision section which specifies first and second thresholds to the first and second comparator circuits, uses the first and second comparator circuits to repeat comparison among the integrator circuit's output value and the first and second thresholds for a plurality of times, and determines magnitude relation among the integrato
Ishikawa Daisuke
Kawai Koji
Komiya Kenichi
Tanimoto Koji
Foley & Lardner
Kabushiki Kaisha Toshiba
Pham Hai
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