Hitachi Koki Co., Ltd.

Ricoh Printing Systems, Ltd.

Hitachi Printing Solutions, Ltd.

Takashi Rokutanda

Takao Umeda

Yukio Otome

Akio Tsujita

Teruaki Mitsuya

Keisuke Kubota

Hiroyuki Mabuchi

Masayoshi Nakayama

Hisao Okada

Nobuyuki Mori

A color image forming apparatus includes a developing unit to which a developing bias with an AC component superposed is applied, wherein the DC voltage of the developing bias is adjusted to set the detected density of a solid image at a specified value, the light amount of radiation for exposing an image area having a width of a few dots adjacent to the white paper is adjusted to set the detected density of an image developed under a peripheral electric field at a specified value, and the gradation density curve is regulated by alternately adjusting the DC voltage, the light amount of radiation for exposing the image area having a width of a few dots adjacent to the white paper, and the amplitude of the AC component until the detected density of a mesh point image having an area ratio from 60 to 80% falls within a specified range.

Color image forming apparatus

A perfecting press apparatus for forming images on both sides of a transfer medium. With respect to a transferring current Ipt of an image forming unit, current Ipc is made large which flows from a charge control instrument for controlling charge polarity of the toner on the transfer medium in the direction of the transfer medium. In particular, in the image forming unit causing retransfer, a de-charging light source is installed between the a developing device and a transferring device for canceling charges other than at a latent image part of an image carrier, so that the relationship between Ipt and Ipc is to be 3&times;Ipc&lE;Ipc&lE;6&times;Ipt, whereby the retransfer is suppressed to minimum for producing satisfied quality of image.

Perfecting press apparatus

An image forming apparatus has an image retaining body which is supported so as to be able to move endlessly, a transfer means which is installed at a specific distance away from the surface of the image retaining body or in contact with the surface of the image retaining body, and a paper guide which is installed upstream and downstream, of or at least upstream or downstream the transfer means along the moving direction of the image retaining body for guiding a sheet of paper between the image retaining body and the transfer means and for pressing the paper onto the surface of the image retaining body. The image forming apparatus is equipped with an adjusting means for adjusting the distance between the paper guide means and the transfer means along the moving direction of the image retaining body, thereby varying the length of the paper wound onto the image retaining body.

Image forming apparatus with adjusting device

A transport roll 1 consists of a metal roll 3 of 40 mm in diameter covered with a conductive PFA tube 2 of 10.sup.10 .OMEGA.cm in volume resistivity and 200 .mu.m in thickness. A DC voltage source 4 is connected to the metal roll. A sheet of paper 5 bearing toner images 6 and 7 on both sides thereof receives a drive force from a paper drive roll, and turns with the movement of the paper. The DC voltage source produces voltage VB1 of the same polarity as the charging polarity (positive) of the toner image 6 being in contact with the transport roll. The voltage VB1 is optimumly controlled so as to prevent the transport roll from being soiled with toner.

Electrostatographic printing machine

There are provided a paper separating mechanism for bringing paper into a state of non-contact with a paper carrying roll; a motor for independently driving the paper carrying roll; and a switch for changing-over the paper carrying roll driving mode between a following mode and an independent driving mode so that the driving mode is changed over to the following mode and independent driving mode at the time of printing and at the time of non-printing, respectively.

Paper carrying device in electrostatic recording apparatus

In an electrostatic printing apparatus, the residual image phenomenon conspicuously observed at low density printing can be eliminated while photo-deterioration of the photosensitive body is being suppressed to a minimum in a high speed printing process. A charging unit, a writing light source, a developing unit, a transfer unit, a first erase lamp, an AC discharging unit and a second erase lamp are arranged around a photosensitive drum. Therein, the light intensity of the erase lamp is strengthened when the density of a printed image is light and is weakened when the density of the printed image is dark. That is, by changing the light intensity of the erase lamps corresponding to a developing bias, the residual image phenomenon can be eliminated while suppressing deterioration of the photosensitive drum to a minimum.

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Ibaraki, Japan

Takashi Rokutanda