Incremental printing of symbolic information – Electric marking apparatus or processes – Electrostatic
Reexamination Certificate
1999-07-19
2001-02-27
Brase, Sandra (Department: 2852)
Incremental printing of symbolic information
Electric marking apparatus or processes
Electrostatic
C347S133000
Reexamination Certificate
active
06195108
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image formation method for forming an electrostatic latent image on an electrostatically charged photosensitive belt with a laser beam and an image formation apparatus of the same, more particularly to an image forming method which is capable of deciding a position for starting an image writing in a main scanning direction with a laser beam and an image formation apparatus of the same.
2. Description of the Prior Art
A laser printer, a copying machine and like using a photoconductive belt electrostatically charge a photosensitive body by a charger, and then form an electrostatic latent image on the photosensitive belt by scanning a laser beam including image information thereon, thus forming an electrostatic image. Regarding the electrostatic image, the electrostatic image is developed by a developing device and a developed image is formed by attaching toner onto the photosensitive belt. The developed image is transferred onto a recording paper, so as to record the image.
When a belt-shaped photosensitive body is used for the image formation using the laser beam, that is, for the formation of the electrostatic image, an oblique movement of the photosensitive belt or a slip of the photosensitive belt in a main scanning direction laser beam scanning direction) may occur. Therefore, the edge of the photosensitive belt slowly shifts to the main scanning direction. This is because when the photosensitive belt is driven by a roller separated from the belt, a relative positional offset in the main scanning direction by a slippage is apt to occur. Accordingly, there has been a problem that the position for staring the image writing by the laser beam is shifted with the movement of the photosensitive belt.
As a countermeasure to cope with such problem, as is recited in Japanese Patent Laid-open No. 4-274467 which was issued on Sep. 30, 1992, and Japanese Patent Laid-open No. 4-275574 which was issued on Oct. 1, 1992, presented is a method in which an edge portion (side edge) of a photosensitive belt in a main scanning direction is detected by a laser beam scanned during a latent image formation, and a position for stating writing in the main scanning direction is decided based on a detection signal detected by the laser beam.
Furthermore, a technology in which a sensor is disposed at an edge portion of a photosensitive belt in a main scanning direction (hereinafter, referred to a belt edge), and the belt edge is detected by the sensor as a reference position, thus controlling a timing of the main scanning by the laser beam and preventing a color misfit during formation of a color image is disclosed in Japanese Patent Laid-open No. 10-86446 (issued on Apr. 7, 1998), No. 10-86445 (issued on Apr. 7, 1998), No. 6-119571 (issued on May. 18, 1993) and No. 4-16969 (issued on Jan. 21, 1992).
However, there have been the following problems in the foregoing prior arts. Specifically, the photosensitive belt is made of a material with a mechanically low rigidity so that the photosensitive belt possesses an electrostatically charged property, so that such photosensitive belt is apt to be damaged. A non-linearity shape of the belt edge owing to the damage appears in an electrostatic latent image which is written to the photosensitive belt using the belt edge as a reference position.
Accordingly, there is a problem that when it is intended to record one straight line in a sub-scanning direction (driven direction of the photosensitive belt), an actually recorded image takes a jagged line shape similar to that of the belt edge.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an image formation apparatus and an image formation method which are capable of forming a desired latent image of image data at a desired position where formation of the latent image is not influenced by flaws and non-linearity of a belt edge portion of a photosensitive belt.
Another object of the present invention is to provide an image formation method and an image formation apparatus which are capable of achieving a high quality electrostatic latent image formed by scanning a laser beam on a photosensitive belt, which is not influenced by a shape of a belt edge portion, when a color image is formed.
An image formation apparatus of the present invention forms an electrostatic latent image on a moving photosensitive belt by a laser beam of a laser device. The image formation apparatus of the present invention comprises a belt edge detector for detecting by a main scanning of a Laser beam an edge portion (belt edge) of the photosensitive belt in a main scanning direction; a virtual edge detection circuit for generating a virtual edge detection signal which change its generation timing in accordance with a change of a detection timing of the belt edge detected by the belt edge detector, the generation timing of the virtual edge detection signal almost not following the detection timing which changes by flaws and non-linearity of the belt edge and following a slow change of the detection timing; and a driving circuit for driving the laser device so as to start a writing of an image data by the laser beam in synchronization with the virtual edge detection signal.
In the image formation apparatus of the present invention, the slow change of the detection timing is a change produced by an oblique movement of the photosensitive belt or a slip of the belt in the main scanning direction, and a changing time is sufficiently longer than that by flaws and non-linearity of the belt edge.
To be concrete, the belt edge detector detects the belt edge and a reference position which is somewhat apart from the belt edge. Moreover, the virtual edge detection circuit changes the generation timing of the virtual edge detection signal in accordance with a change of a time difference between the detection timing of the reference position and the detection timing of the belt edge.
Another image formation apparatus of the present invention comprises a belt edge detector for detecting by a main scanning for said photosensitive belt an edge portion (belt edge) of a photosensitive belt in a main scanning direction; a lamp signal generator for generating a lamp signal for each main scanning by the laser beam, the lamp signal rising up to a predetermined level; an integrator; a comparator for generating a virtual edge detection signal when a level of the lamp signal and a level of an output signal of the integrator are coincident with each other; a phase comparator for comparing a detection time of the belt edge by the belt edge detector and a generation time of the virtual edge detection signal; and an adjusting circuit for adjusting the level of the output signal of the integrator based on a comparison result. In this case, the adjusting circuit adjusts the level of the output signal of the integrator by a change of the detection timing of the belt edge, and the generation timing of the virtual edge detection signal from the comparator changes.
The adjusting circuit is a charge pump which adjusts the level of the output signal of the integrator by charging/discharging charges of a prescribed amount in/from the integrator.
In the image formation apparatus of the present invention, the photosensitive belt may have a marking for indicating a belt jointing portion. In this case, the image formation apparatus of the present invention further includes a marking detector for detecting the marking, and a charge/discharge processing switching circuit for switching a charge/discharge processing by the charge pump based on the marking detected by the marking detector.
An image formation method for forming an electrostatic latent image on a moving photosensitive belt by a laser beam of a laser device, comprises the steps of
detecting an belt edge portion (belt edge) of the photosensitive belt in a main scanning direction by a main scanning of the laser beam; generating a virtual edge detection signal which change its generation timing in accordance with a
Brase Sandra
Foley & Lardner
NEC Corporation
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