Image forming apparatus

Details Image forming apparatus Image forming apparatus

2001-10-02

2002-10-29

Pendegrass, Joan (Department: 2852)

Incremental printing of symbolic information

Electric marking apparatus or processes

Electrostatic

C347S153000, C347S155000, C347S158000

Reexamination Certificate

active

06473107

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus comprising an electric writing device of which a substrate is arranged in elastic contact with a latent image carrier and which forms an electrostatic latent image onto the latent image carrier by writing electrodes disposed on the substrate.
Among conventional known image forming apparatuses, there is a type of using a large number of needle electrodes to form an electrostatic latent image onto a latent image carrier. In an image forming apparatus of this type of using needle electrodes, an electrostatic latent image is formed onto a latent image carrier by discharge from the needle electrodes. The needle electrodes are employed as discharge portion of this image forming apparatus because such a needle electrode can discharge at the lowest possible starting voltage and has an acute tip that is preferable in terms of improving the image resolution. Generally, the needle electrodes are arranged to have a slight space from, i.e. in non-contact with, the latent image carrier and the formation of an electrostatic latent image onto the latent image carrier is conducted by discharge phenomenon.
However, variation of starting voltage for discharge due to fluctuation in the space directly causes the scatter in potential of the electrostatic latent image, leading to major image defects such as linear stains, irregularities, interruption, blur, and/or dusts. Accordingly, to stably keep the space constant, the needle electrodes are required to have high precision and high rigidity and a holding member of positioning and supporting the needle electrodes is also required to have high precision and high rigidity. In addition, the needle electrodes should be precisely positioned on a bus line of the latent image carrier in the circumferential direction of the latent image carrier. If not, the fluctuation in the space should be occurred and thus uniform charge can not be ensured. Further, run-out of the rotational axis of the latent image carrier is sure to cause fluctuation in the space. For this, spacers are provided for controlling the space. However, in case of high-speed printing in which the latent image carrier rotates at a high ratio, it is hard or impossible to keep the space constant due to vibration. As a result, the printing speed should be set at a lower speed.
As a means for solving the aforementioned problems, an image forming apparatus has been proposed in Japanese Patent Publication No. S63-45104 (hereinafter, '104B publication), in which needle electrodes are kept in contact with a latent image carrier coated by an organic glass and lubricant oil is applied to the latent image carrier to prevent wearing or damage of the latent image carrier due to the contact of the needle electrodes.
However, the invention of '104B publication has another problem of wearing of the needle electrodes. The wearing of the needle electrodes causes variation in starting voltage for discharge, leading to change in size of the electrostatic latent image and change in charged potential. Since application of oil to the latent image carrier is necessity for reducing the wearing, developing powder such as toner can not directly deposited so that the latent image carrier can only functions as an intermediate image transferring medium.
As mentioned above, the type of using a large number of needle electrodes has a problem that scatter in potential of an electrostatic latent image is easily caused so that the latent image resolution is varied with time, thus deteriorating the quality of obtained images. Since a holding member and/or a positioning member having high precision are required for holding and positioning the needle electrodes and the latent image carrier and the space therebetween, there is also a problem that the apparatus should be complex and large. There are still problems that the electrodes and the latent image carrier should be damaged for a short period of time due to high contact pressure of needle-type electrodes, that high-speed printing is hardly achieved, and that the apparatus should be large because of the use of the latent image carrier as an intermediate image transferring medium.
To solve these problems, the applicant of this application has proposed an image forming apparatus comprising an electric writing device of which a substrate is arranged in elastic contact with a latent image carrier and which forms an electrostatic latent image onto the latent image carrier by writing electrodes disposed on the substrate. According to this image forming apparatus, the electrodes receive writing signals to form an electrostatic latent image on the latent image carrier. During this, the contact between the substrate and the latent image carrier is stabilized so as to enables homogeneous writing by application of charge, thereby obtaining a high-quality image without image irregularities nor linear stains.
However, the image forming apparatus mentioned above has some problems. As shown in
FIG. 9
as will be described later, in the image forming apparatus, a length L between a distal electrode
3
b
R of the writing electrodes
3
b
and a side edge of the substrate
3
a
is required to be so long as to stabilize the contact of the distal electrode
3
b
R. Without enough length L, the pressing force onto the distal electrode
3
b
R and the writing electrodes near the distal electrode
3
b
R against the latent image carrier
2
should be smaller than that of the writing electrodes located at a middle portion. In this case, homogeneous application of charge for writing can not be achieved. On the other hand, in a cleaning device
7
disposed downstream of a transferring device
6
, it is impossible to completely seal toner at contact boundary faces between a cleaning blade
7
a
and an end seal
7
b
so as to produce leakage toner T which adheres to the latent image carrier
2
. Because of the great length L, however, the leakage toner T passes under the substrate
3
a
so as to adhere to contact portions between the writing electrodes
3
b
and the latent image carrier
2
, causing variation in the gap between the electrodes and the latent image carrier
2
. This variation leads to image irregularities.
As shown in FIG.
11
(A), in a developing device
4
arranged around the periphery of the latent image carrier
2
as well as the electric writing device
3
and the transferring device
6
, it is impossible to completely seal toner at contact boundary faces between a toner control blade
4
c
and an end seal
4
d
to produce leakage toner T which adheres to the latent image carrier
2
as shown in FIG.
11
(B). Because of the great length L, however, the leakage toner T passes under the substrate
3
a
so as to adhere to contact portions between the writing electrodes
3
b
and the latent image carrier
2
, causing variation in the gap between the electrodes and the latent image carrier
2
. This variation leads to image irregularities.
In order to prevent this problem, the width of the electric writing device
3
is set to be smaller than the width of the toner control blade
4
c
as shown in FIG.
13
. In this case, a transferring roller of the transferring device
6
is required to have a width obtained by adding an allowance for the sheet feeding accuracy to the width of the maximum recording sheet size. To prevent the leakage toner T from adhering to the transferring roller, the width of the transferring roller should be smaller than that of the toner control blade
4
c
. The width of the latent image carrier
2
should be the largest among the other components mentioned above to achieve stable contact among the components. When the width dimensions are set in the manner as mentioned above, remainder toner adheres to the transferring roller in a region a between an end of the largest recording sheet and an end of the transferring roller. In addition, even after transfer to the recording sheet, remainder toner exists on the latent image carrier
2
in a region &bgr; between the end of the

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