Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
2001-10-29
2004-02-03
Pham, Hai (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S246000
Reexamination Certificate
active
06686946
ABSTRACT:
CROSS REFERENCE TO A RELATED APPLICATION
This application claims priority under 35 USC §119 to Japanese Patent Application No. 2000-329129 filed on Oct. 27, 2000, the entire contents of which being herein incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to optical writing units which perform optical writing, methods for driving the optical writing unit, image forming apparatuses such as printers, copiers, facsimiles, etc., which employ the optical writing unit, and inspecting apparatuses which inspect the optical writing unit. In particular, the present invention relates to optical writing units capable of suppressing density unevenness in an image formed by the image forming apparatus.
2. Discussion of the Background
Recently, based on the minimization of a digital image output instrument such as a digital copier, a printer, a digital facsimile, etc., an optical writing unit for digital writing use has been necessitated to be minimized. Such digital writing methods can be roughly categorized in to two at the moment. One is a light scanning system that performs scanning a light flux irradiated from a light source such as a semiconductor laser or similar devices using a light deflecting device and forms a light spot by means of a scan imaging lens. The other is a solid writing system that includes and uses an imaging element array so as to form a light spot of a light flux irradiated from a light emitting element array such as one of an light emitting diode (LED) array and an organic EL array made by LEDs aligned.
In the former light scanning system, since the light deflector scans a light, an optical path length becomes longer. In contrast, in the latter solid writing system, since the optical path can extremely be short, there exists an advantage such as compact optical writing unit.
On the other hand, in the solid writing system that includes the light emitting element array having a plurality of light emitting elements and imaging element array, unevenness of a light emitting quantity of the plurality of light emitting elements and that of a shape of the imaging element array may create unevenness of a light spot on an image carrier (e.g. photo-conductive member). Such unevenness can be related to rigidity, a position, and a spot radius. Owing to the unevenness, unevenness of density arises in an image output by an image forming apparatus that employs such an optical writing unit as an exposure unit. As a result, a fine image is hardly obtained.
To obtain a fine image by suppressing the unevenness of the density, a conventional optical writing unit proposes to extend corrections such as any one of light quantity constant correction that enables an emission light irradiated from each light emitting element to the PC member to have a constant value, and spot radius constant correction that enables an optical spot formed on the PC member to have a constant radius at given threshold. For example, Japanese Patent Application Laid Open Nos. 2-62257, 4-305667, and 11-227254 propose such light quantity constant correction and spot radius constant correction, and are known as prior arts.
Among these, the first prior art intends to uniformize an LED light emission quantity by controlling a driving time period for each LED based upon unevenness of a generated light value per each LED dot. The above-described second prior art intends to suppress unevenness of focal depth of a lens array and that of an print density caused by difficulty in packaging of an LED chip with a light quantity adjusted LED head that enables a spot width of an quantity of light to be constant at a given threshold. In addition, it is described in the above-described third prior art that a characteristic point in a light emission intensity distribution of a light emitting element is measured (detected), and light quantity correction data used for energy supply to the light emitting element is determined based upon the characteristic point. Also described is that assumed light quantity correction data is determined based upon unevenness of the light quantity and is corrected based upon the characteristic point, so that the light quantity correction data is determined. In addition, as the characteristic point, changes in a peak position, a peak value, and light emission radius are exemplified.
The light quantity constant correction is a correcting method for measuring an emitted light quantity irradiated from each light emitting element to a PC member with a light quantity measurement device, and changes a current amount supplied to each light emitting element, thereby setting a prescribed supply current amount enabling the emitted light quantity to be constant. The current supply amount is generally controlled by four bits of light quantity correction data, and the light emitting quantity is set at a precision of a few percentages error even admitting that the light quantity is constant in the present circumstances. On the other hand, the spot radius constant correction is a correction method for measuring a light spot radius formed on the PC member with a spot radius measurement device, and changing and setting a prescribed amount of a current that is supplied to each light emitting element and thereby enabling the spot radius to be constant. Since, as same in the above stated light quantity constant correction, the current supply amount is again controlled by four bits, there exists a limit on a controllable amount even admitting that the spot light radius is constant.
In addition, the third prior-art proposes that a light spot radius (Wi) of each light emitting element is measured. Then, it is determined if the light spot radiuses (Wi) represent upward convexity in a graph (not shown) when the light quantity constant correction is only performed using assumed light quantity correction data. The assumed light quantity correction data input to the light emitting element of No. (i) is corrected if the upward convexity appears.
However, the below-described problems generally exist in such a system.
First, assumed light quantity correction data is corrected only in a section that meets the above-described determination. Accordingly, optimization can not be performed over the entire valid image region. Specifically, another section not meeting the determination remains a condition made by the light quantity constant correction.
Second, according to the assumed light quantity correction data correcting system, the assumed light quantity correction data is corrected in accordance with unevenness (Wbi) from the average value (Wave) of (Wi). As a result, it simply performs the spot radius constant correction.
Accordingly, such a proposal shows the light quantity constant correction at a section and the spot radius constant correction at another section, and simply makes combination of light quantity and spot radius constant corrections. In addition, even admitting being constant, there exists a limitation on a controllable value as in the above-described light quantity and spot radius constant corrections.
Thus, according to these light quantity and spot radius constant corrections, each of a light quantity and a spot radius is only converged to a resolution level (i.e., 4 bits) of a current supply amount as correction data. As a result, since it is intended to mostly approximate a prescribed target value, a value obtained after performing one of these constant corrections for each light emitting element should vary at around the prescribed value.
Accordingly, the light quantity or the spot radius of each light emitting element is independently set, and remaining light emitting elements are not taken into account.
Improving a limit of resolution level of correction data can be achieved, for example, from conventional 4 bits to either 6 or 8 bits, to approximate the prescribed value. However, the improvement in the resolution limit causes an increase in data values, and requires increase in data transfer speed, thereby resulting in a cost increase.
SU
Ito Masahiro
Kitao Katsuyuki
Masuda Koji
Ohsugi Tomoya
Saitoh Tetsuro
Oblon, Spivak, McCelland, Maier & Neustadt, P.C.
Pham Hai
Ricoh & Company, Ltd.
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