Incremental printing of symbolic information – Electric marking apparatus or processes – Electrostatic
Reexamination Certificate
2002-01-30
2003-05-06
Pendegrass, Joan (Department: 2852)
Incremental printing of symbolic information
Electric marking apparatus or processes
Electrostatic
C347S132000, C347S900000, C358S001900
Reexamination Certificate
active
06559874
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a printing method and a printing apparatus for developing a latent image on the surface of a photo-conductor drum using liquid toner, to a control device and a control method for controlling a laser output of the printing device, and to a resister control device of the printing device.
2. Description of the Related Art
Heretofore, wet-type electro photographic printing apparatuses have been known in the art, which is provided for forming an image on the surface of a photoconductor drum being rotated at a constant speed by successively overlaying colors such as yellow (Y), magenta (M), cyan (C), and black (K) and then transferring an image formed by overlaying one image on another using a plurality of different color liquid toners onto a sheet of printing paper placed between a transfer roller and a backup roller through the transfer roller. The printing apparatus comprises: charging means for charging the surface of a photoconductor drum having a photosensitivity; exposing means for performing an exposure scan on the photoconductor drum on the basis of drawing data to form a latent image on the photoconductor drum; and developing means for developing the latent image on the photoconductor drum. The developing means includes a plurality of developing rollers that sequentially supply liquid toners of multiple colors on the photoconductor drum.
Furthermore, the exposing means includes a laser-emitting source, a polygon scanner, or the like. A laser beam emitted from the laser-emitting source is incident on the polygon scanner being rotated at a predetermined speed and is then reflected from the polygon scanner. Subsequently, the reflected laser beam passes through an f&thgr; lens and scans the surface of the photoconductor drum to make a latent image.
Conventionally, such a kind of printing apparatus performs the following process.
First, the charging device charges the surface of the photoconductor drum on the basis of an image data. Then, the exposing device forms a latent image on the surface of the photoconductor drum on the basis of a drawing data. Subsequently, the latent image is developed by liquid toner to make an image.
The development with liquid toner is performed by bringing a developing roller partially dipping in the liquid toner close to the photoconductor drum and then revolving it around its axis. On this occasion, meniscus is formed in a comparatively narrow space between the developing roller and the photoconductor drum because the surface of the liquid turner in the space wets them and is provided as a bridge between them. Then, a potential difference is applied on between the exposed surface portion and the remaining surface portion on the photoconductor and the developing roller to permit the electrophoresis movement of liquid toner in the meniscus. As a result, the liquid toner is supplied from the developing roller to the photoconductor roller.
Subsequently, the image formed on the surface of the photoconductor drum is transferred to the surface of a transfer roller. Then, a sheet of printing paper is fed between the transfer roller having the transferred image and the backup roller. Consequently, the image on the transfer roller is transferred on the surface of the printing paper while the paper passes through between the rollers.
In the case of forming an image on the photoconductor drum by supplying liquid toner from the developing roller to the photoconductor drum, an excess amount of the liquid toner may be supplied as a result of capillary phenomenon when the distance between the developing roller and the photoconductor roller becomes closer than the predetermined distance, resulting in an indistinct image. On the other hand, if these rollers are located too far from each other, poor meniscus of the liquid toner can be formed between the rollers. As a result, the liquid toner cannot be transferred from the developing roller to the photoconductor drum, so that the image formation cannot be performed. On the other hand, there are various kinds of customers' needs for printed materials to be obtained by the printing apparatus constructed as described above, such as for different sizes (e.g., A1-, A2-, and B1-sizes) and thicknesses of sheets of printing paper. For printing a multi-color image, in most cases, all of two or more colors to be required are stacked on the same place one after another and a thickness of one area on the recording medium may become different from that of another area depending on the number of colors being stacked on each area. Therefore, printing conditions including the rotation speed of photoconductor drum, the rotation speed of developing roller, the properties of liquid toner, and so on should be adjusted to obtain an appropriate distance between the developing roller and the photoconductor roller for allowing the most clear image every time the customer performs a printing using liquid toner and recording medium which are different from those used in the latest printing.
Conventionally, however, the developing roller and the photoconductor have been kept at a constant distance from each other on the basis of the operator's practical experience and guesswork, so that the resulting image may be subtly deferent from one previously printed every time the image is printed under the different conditions, causing a problem of an undesired effect on the image quality.
Therefore one of the objects of the present invention is to provide a printing apparatus that keeps an excellent image quality by avoiding an influence upon an image to be exerted by the image formation on the surface of photoconductor drum using liquid toner.
In the case of forming an image on the photoconductor drum in an image-on-image fashion, on the other hand, an image development can be performed by causing the migration of charged toner particles when the potential of an area exposed by a beam of laser (i.e., an area on which electrostatic latent image is formed) becomes less than the potential of the developing roller with respect to the potential of charged photoconductor drum. For example, a laser-exposure potential to be defined by the sensitivity for a laser wavelength can be obtained on the surface of photoconductor drum for an image formation of a first color. At the time of forming an image of second color, a laser-exposure potential to be defined by the sensitivity for a laser wavelength can be obtained on another part of the surface of photoconductor drum, which is not exposed in the step of first color, for an image formation of a second color. In this case, however, if the second color is applied on the same area as that of the first color, there is a possibility that a desired laser exposure potential cannot be attained because of the presence of first-color toner on that area. The existing toner absorbs or reflects laser energies, so that the desired laser exposure potential cannot be obtained when the laser's output power is not adjusted. As a result, it becomes difficult to obtain a clear image, causing a problem of an undesired effect on the image quality.
Furthermore, for adjusting the output of laser, a data for each color as a part of output data of laser should be kept to define an output data for printing such a color. Here, if the resolution of the laser output is 256 levels of gradation, for example, 8 bits of data can be required for one dot (one pixel). Therefore, for example, for successively stacking eight colors (e.g., yellow and so on) on an area corresponding to one pixel, 64 bits of data (i.e., 8 bits×8 colors=64 bits) per pixel is required. Thus, the more the size of an image to be printed is increased or the more the resolution increases, the more space for storing laser output data in the large storing device is required.
Therefore, another object of the present invention is to provide a laser-output control device and a method for controlling a laser output, where a clear image can be obtained by controlling
Butsusaka Yoshihiko
Hayashi Makoto
Iida Mitsuhiko
Tanaka Tamihiko
Tsunekawa Junji
Pendegrass Joan
Pillsbury & Winthrop LLP
Toshiba Kikai Kabushiki Kaisha
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