JP3026035B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using an electrostatic transfer process, such as an electrostatic copying machine and a printer.

[0002]

2. Description of the Related Art In a known image forming apparatus in which a process of electrostatically transferring a toner image electrostatically formed on the surface of an image carrier onto a transfer material such as paper is repeated, the transfer material is used for transfer. It is necessary to sufficiently remove the residual toner remaining on the image carrier without transferring to the toner. The toner removing means is such that the edge of a cleaning blade made of an elastic material such as rubber is pressed against the surface of the running image carrier to remove and remove the residual toner. It is well known that it is widely used because it is excellent in function and advantageous in cost.

FIG. 5 is a side sectional view showing a cleaning device of such an image forming apparatus, in which a cleaning device 13 is disposed in parallel with an image carrier 12 running in the direction of arrow A. One edge 10 of the free edge of the elastic cleaning blade 10 attached to the cleaning device
a is pressed against the running direction of the image carrier 12 in the counter direction to scrape and remove residual toner generated at a transfer portion (not shown). In the figure, reference numeral 14 denotes an image formed of fine paper powder, deposits such as rosin and talc generated from paper frequently used as a transfer material, and nitride generated due to the presence of a high-voltage member in the apparatus. A cleaning roller 15 for rubbing and removing substances that cannot be completely removed by the cleaning blade alone, such as foreign substances adhering to the carrier,
Reference numeral denotes a conveying screw for conveying the toner and the like collected and accumulated in the cleaning device to a separately disposed waste toner container.

In the cleaning device in which the cleaning blade is in contact with the image carrier in the counter direction as described above, it is possible to efficiently scrape and remove the toner, but on the other hand, the blade edge and the surface of the image carrier are removed. During operation, the blade edge is turned up in the running direction of the image carrier, and the vibration that returns to the previous position, so-called chatter phenomenon, is liable to occur. There is a possibility that a part or the entirety of the blade is turned over and the blade is turned up.

When the chattering phenomenon occurs, the toner slips through during that time, resulting in poor cleaning. Further, when the blade is turned up, cleaning becomes impossible. A part of the toner arriving at the portion is interposed between the image carrier and the blade edge at the portion to perform a lubricating action, thereby ensuring a smooth cleaning action.

However, when printing a large number of images that consume a small amount of toner, images that use only a part of the image area, and the like, the amount of residual toner naturally decreases, so that the lubricating action is performed as described above. Insufficient toner tends to cause chattering phenomenon and blade turn-up as described above.

Further, a cleaning blade extending in the width direction of the image area usually extends beyond the image area to the outside of the image area in order to reliably clean the image area. In this portion, no development is performed, and the blade edge is always in direct contact with the image carrier even though toner is not supplied.Moreover, portions near both ends of the blade have lower resistance to reversal of the blade edge than the central portion. Therefore, the possibility of occurrence of chattering phenomenon and blade turning increases.

SUMMARY OF THE INVENTION The present invention has been made to cope with such a situation, and an appropriate amount of toner is carried in a non-image area between papers in a running direction of an image area in accordance with the image density in accordance with the image density. By supplying toner to the body as well as to the non-image area outside in the width direction of the image area, the toner is also supplied to the vicinity of both ends of the cleaning blade, and the lubricating property of the entire cleaning blade is suitably improved. An object of the present invention is to provide an image forming apparatus that can maintain the image forming apparatus.

[0009]

To achieve the above object, the present invention provides:
An image carrier, a cleaning blade extending in the axial direction and pressed against the image carrier, and a developer concentration control unit for controlling a toner replenishment amount in accordance with an input image signal; An image forming apparatus for conveying an output patch according to an input image signal to a cleaning device, wherein the output patch is formed up to a non-image area near both ends of the cleaning blade.

With this configuration, even when a large number of images having a low image density or small images are printed, the toner can be constantly and uniformly supplied over the entire length of the cleaning blade. Good quality images can be obtained.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic explanatory view of an image forming apparatus showing an embodiment of the present invention, wherein a surface of a cylindrical image carrier 14 rotating and running in the direction of arrow A is controlled by a primary charger 16. The surface is uniformly charged, and an image signal is applied to the charged surface in a manner described later to form an electrostatic latent image. When the latent image reaches a developing site where the developing device 15 is located, toner is supplied from the developing device to form a toner image.
When the toner image reaches the transfer portion where the transfer charger 17 is present, the transfer bias is applied to the transfer charger, and the toner image on the image carrier side is moved by the action of the electric field formed thereby. The transfer to the transfer material P supplied to the transfer site by this time. Thereafter, the residual toner not transferred to the transfer material is removed by the cleaning device 18, and the residual charge is further removed by the pre-discharge lamp 19, so that the surface of the image carrier is ready for the next image forming step.

With respect to the operation of the apparatus shown in FIG. 1, a process of first transferring toner to a cleaning blade in an image area will be briefly described. An original is read by a CCD, and an A / D conversion 3, a γ conversion 5, and a D / A conversion 9, an image signal input to a comparator 11 and an input to a triangular wave generation circuit 10 form a PWM signal. The output is projected on the charged surface of the image carrier 14 via the scanning means 13 to form an electrostatic latent image.

At the same time, the A / D-converted image signal reaches a video counter 4 where the density level is counted for each pixel and the density level corresponding to one page of the document is integrated. A patch having a density determined by conversion using a table prepared in advance is output to the image carrier. The CPU controls the toner replenishing circuit 7 based on the integrated value to determine the driving time of the toner replenishing device 8 and the developing device 15.
Supply of the toner to the image density.

FIG. 2 shows an example of the table, in which the density level of an image signal per page by the CPU is converted into the density level of an output patch. As shown in the drawing, the patch output is set to be zero (point b in the figure) when a solid black image is input, and to be the maximum (point a in the figure) for a white image. .

[0015] The timing of patch output is preferably a sheet interval between one image signal of the image carrier and the next image signal, or a sheet interval with an appropriate number of image signals. The size of the patch is preferably about 0.5 to 15 mm in the longitudinal direction of the cleaning blade and the running direction of the image carrier.

FIGS. 3A and 3B show another method of controlling patch output in an image area. As shown in "FIG. 3A", when a histogram of the density level viewed in the width direction of the image area, that is, a histogram of the toner amount is created, the toner amount is insufficient at a low value of this, and chatter is likely to occur. As shown in FIG. 3B, a table obtained by inversely converting the histogram is formed, and output patches are set according to the table. As a result, a small amount of toner can be supplied to a portion having a high image density and a large amount of toner can be supplied to a portion having a low image density, so that an appropriate amount of toner can be applied in the longitudinal direction of the cleaning blade.

With the above-described means, it is possible to eliminate the shortage of toner at the blade edge within the range of the image area. However, in practice, chatter vibration occurs in the vicinity of both ends of the cleaning blade, and the blade is turned up due to this. Poor cleaning, inability to clean, and the like often cause problems.

That is, the cleaning blade in contact with the image carrier is generally extended outside the image area so as to be longer than the image area width. For this reason, the toner is not supplied to the blade edge portion which is located outside the image area and abuts on the image carrier, and the action of opposing the reversal of the blade edge is weaker in the vicinity of the blade end than in the center. Often, blade turning occurs from this part.

In order to cope with such a situation, according to the present invention, a patch having a constant density is always output to a portion near the both ends in the length direction of the cleaning blade and outside the image area. As a result, the toner can also be applied to portions near both ends of the cleaning blade, and in particular,
Chatter vibration and blade turn-up that progress from both ends can be effectively prevented, and the cleaning function can be maintained. FIG. 4 shows a longitudinal direction of the cleaning blade where patches are formed outside the output patch in the image area shown in FIG. 3B and near both ends of the cleaning blade.

As described above, by outputting patches at both ends of the cleaning blade, sufficient toner can be applied to the entire blade edge even when a large amount of images having a small image area width or a small toner density are to be printed. can do.

[0021]

As described above, according to the present invention,
In an image forming apparatus that removes residual toner by bringing an edge of a cleaning blade into contact with an image carrier, a toner patch is also output to a non-image area outside both sides of an image area, so that both ends of the cleaning blade are generally removed. Since the toner is applied to a portion to which the toner is not supplied, a good lubricating action can be obtained, and there is a remarkable effect of preventing a cleaning failure caused by chattering vibration, blade turning, and the like, and obtaining a high-quality image.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating the operation of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is an example of a threshold table used in the embodiment;

FIG. 3A is a histogram of the density of an image signal as viewed in the longitudinal direction of a cleaning blade in an image area.

FIG. 3B is a histogram of the same output patch.

FIG. 4 is a histogram of an output patch illustrating an embodiment of the present invention.

FIG. 5 is a schematic side sectional view of a cleaning device used in a known image forming apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 CCD 13 Scanning means 3 A / D conversion circuit 14 Image carrier 4 Video counter 15 Developing device 6 CPU 16 Primary charging device 7 Toner supply circuit 17 Transfer charging device 8 Toner supply device 18 Cleaning device 9 D / A conversion circuit

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) G03G 21/10 G03G 15/00 303 G03G 21/00 370-540

Claims (1)

(57) [Claims] An image carrier, a cleaning blade extending in the axial direction and pressed against the image carrier, and a developer concentration controller for controlling a toner replenishment amount in accordance with an input image signal; An image forming apparatus for conveying an output patch corresponding to an input image signal to a cleaning device in an image forming area, wherein the output patch is formed up to a non-image area near both ends of a cleaning blade.