JPH05224497A - Image forming device - Google Patents

Abstract

PURPOSE:To effectively avoid defective cleaning and to obtain an excellent image by properly imparting toner to an image carrier at the outside of an image area, supplying it to the edge of a cleaning blade and utilizing it for lubrication. CONSTITUTION:An original is read by a CCD 1 and a PWM signal is generated by a comparator 11 based on an image signal inputted through an A/D conversion circuit 3, a (gamma) conversion circuit 5 and a D/A conversion circuit 9 and a chopping wave generated by a chopping wave generation circuit 10. Besides, an electrostatic latent image is formed on the electrostatic charged surface of the image carrier 14 through a scanning means 13. Simultaneously, the density level of the A/D-converted and inputted image signal is counted every picture element thereof by a video counter 4. Based on the integrated value thereof by a CPU 6, a toner replenishment circuit 7 is controlled and the driving time of a toner replenishment device 8 is decided. Based on it, the supply of the toner to a developing device 15 is adjusted so as to correspond to the density, Then, the toner is rapidly and uniformly supplied in the longitudinal direction of the edge of the blade.

Description

Detailed Description of the Invention

[0001]

[Object of the Invention]

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 that repeats the process of electrostatically transferring a toner image electrostatically formed on the surface of an image carrier to a transfer material such as paper In each case, it is necessary to sufficiently remove the residual toner remaining on the image carrier without being transferred to the transfer material. As the toner removing means, a means for scraping off and removing the residual toner by pressing it against the surface of the image carrier running on the edge of the cleaning blade made of an elastic material such as rubber has a simple structure and has a toner removing function. It is well known that it is widely used because it is excellent in cost and advantageous.

FIG. 5 is a side sectional view showing the main part of such a known cleaning device, in which the cleaning device 13 is arranged parallel to the image carrier 12 traveling in the direction of arrow A. One edge 10a of the free edge of the elastic cleaning blade 10 attached to the cleaning device is
The residual toner generated at the transfer portion (not shown) is scraped off and removed by pressing in the counter direction against the traveling direction of the image carrier 12. In addition, reference numeral 14 in the drawing denotes a paper blank that is often used as a transfer material. Fine paper powder generated in the empty space, precipitates such as rosin and slack, and corona generation such as nitrogen oxides generated due to the presence of a high-pressure member in the apparatus. A cleaning roller that scrapes off substances that cannot be completely removed by the cleaning blade, such as foreign matter adhered to the image carrier by an object. Reference numeral 15 indicates the collected toner accumulated in the cleaning device in a waste toner container provided separately. It is a conveying screw for discharging.

In this type of cleaning device, the edge of the cleaning blade is brought into contact with the surface of the image carrier in the direction (counter direction) as described above, and the toner is efficiently removed by such a method. On the other hand, on the other hand, with a cleaning blade, which is usually made of urethane rubber, etc., the friction between it and the surface of the image carrier is large, so during operation, the blade edge locally moves in the running direction of the image carrier. When it is turned upside down, a vibration that returns to the old position, a so-called chattering phenomenon, is likely to occur, and further, this may develop and a part or the whole of the edge portion of the blade may be reversed to cause upturning of the blade.

If chattering occurs, the toner will rub off during that time, resulting in poor cleaning, and if blade flare occurs, cleaning will be impossible. A part of the toner arriving at the blade edge portion during the cleaning operation is present in the blade edge portion, and the toner is prevented by the action of the lubricant interposed between the image carrier and the blade edge, thereby providing a smooth cleaning function. Execution is secured.

However, when a large number of images with a small toner consumption amount, images using only a part of the image area, and the like are printed, the amount of residual toner is naturally small, so that the lubricant remains on the blade edge. There is not enough toner to perform the action of
A problem arises that blades tend to turn over.

The present invention has been made to cope with such a situation. According to the density of an original, an appropriate amount of toner is applied to a cleaning device by a patch that is output so that an appropriate amount of toner is constantly applied to a blade edge portion. To provide an image forming apparatus capable of supplying a toner and maintaining a small friction between the image carrier and the cleaning blade and performing a good cleaning function without causing the toner shortage at the blade edge portion as described above. It is intended.

[0008]

[Constitution of the invention]

In order to achieve the above object, the present invention provides an image carrier, a cleaning blade in pressure contact with the image carrier, and a developing device whose input changes the toner supply amount according to an image signal. In an image forming apparatus having an agent concentration control means, means for forming a latent image of a patch having a density calculated by an input image signal and developing the latent image, and toner applied to the image carrier by the means are cleaned at a cleaning portion. It is characterized by having means for carrying.

With this configuration, even when a large number of images with a low image density are printed,
A good cleaning function can be maintained by preventing an increase in friction between the cleaning blade and the image carrier.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS "FIG. 1" is a schematic explanatory view of an image forming apparatus schematically showing an embodiment of the present invention. The surface of a cylindrical image carrier 14 rotating in the direction of arrow A is covered by a primary charger 16. It 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 the developing portion where the developing device 15 is located, toner is supplied from the developing device to form a toner image, and further the image carrier 14
When the toner image reaches the transfer portion where the transfer charger 17 is present by rotating and running, a transfer bias is applied to the transfer charger, and the toner image on the image carrier side is Transfer material P supplied to the transfer site by the time
Transfer to. After that, the residual toner that has not transferred to the transfer material is removed by the cleaning device 18, and the residual charge is removed by the pre-electrification lamp 19, so that the surface of the image carrier is ready for the next image forming step.

Next, the formation of the electrostatic latent image and toner image of the above apparatus will be described. An original is read by the CCD 1 and the input image signal A / D-converted 3, γ-converted 5, D / A-converted 9 and a triangular wave are read. A PWM signal is generated by the comparator 11 using the triangular wave generated by the generation circuit 10, and an electrostatic latent image is formed on the charged surface of the image carrier 14 via the scanning means 13. At the same time, the density level of the A / D converted input image signal is counted by the video counter 4 for each pixel, and the toner replenishing circuit 7 is controlled by the integrated value by the CPU 6 to determine the drive time of the toner replenishing device 8. The supply of toner to the developing device 15 is adjusted to match the image density.

In such an image forming apparatus, the A / D
The converted input image signal is counted for each pixel by the video counter 4, and the density level corresponding to one page of the original is integrated, and then the CPU carries out the image carrying of the patch of the density determined by the conversion in the table prepared in advance by the CPU. It shall be output to the body. It is appropriate that the output timing is set to a non-image area between paper sheets between one image signal and an image signal adjacent thereto. Further, it is suitable that the size of the patch is approximately the same length in the longitudinal direction of the cleaning blade and about 0.5 to 15 mm in the running direction of the image carrier. Note that the patch output does not necessarily have to be performed for all the paper intervals, and it is of course possible to output the patch for every several paper intervals.

FIG. 2 shows an example of the threshold table,
The figure shows the relationship between the integrated value of the density level per page and the patch output signal. In the case of a full solid black image, a large amount of toner is supplied to the blade edge, so the patch output is set to zero (point b in the figure). ), If the image is a white image (a
Since there is no toner reaching the blade edge at (dot), the patch output is set to be maximum so as to supply a large amount of toner to the paper interval area.

FIGS. 3A and 3B show another embodiment. As shown in FIG. 3A, the density level, that is, the toner amount, seen in the width direction of the image area and the longitudinal direction of the cleaning blade. When the histogram of the above is created, chattering of the blade edge is likely to occur in a portion where this value is low. Therefore, as shown in FIG. 3B, a table obtained by inversely converting the histogram is configured, and the output in the blade longitudinal direction is generated accordingly. Set the patch.

With this configuration, the toner can be supplied as evenly as possible in the longitudinal direction of the blade edge, and stable cleaning can be performed.

FIG. 4 shows still another embodiment. As is well known, the length of the cleaning blade is usually longer than the image area width on the image carrier side, and there is no toner supply to the blade edge portion that contacts the non-image area. Moreover, the portions near both ends of the blade have a weaker effect against edge reversal than the central portion, so that chattering and blade curling are likely to occur.

For this reason, as shown in the figure, a cleaning function is provided by constantly outputting an appropriate amount of patch to the portion corresponding to the blade edge outside the image area so that the toner can be constantly supplied to the blade edge portion. Can be further stabilized. Further, generally, in this type of image forming apparatus, the length of the cleaning blade is set so as to conform to the maximum transferable width. Therefore, even when a small-width document is given, the above-described configuration is adopted. As a result, good cleaning can always be performed.

[0018]

As described above, according to the present invention, in the image forming apparatus configured to remove the residual toner by the cleaning blade, the toner is timely applied to the image carrier outside the image area such as a sheet interval. Since this is supplied to the edge of the cleaning blade and can be used for lubrication, the friction between the cleaning blade and the image bearing member is extremely large even when printing images with low image density continues. Therefore, it is possible to effectively avoid a situation in which poor cleaning occurs, and always perform good cleaning, which is a remarkable effect in obtaining a high-quality image.

[Brief description of drawings]

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

FIG. 2 is a graph showing an example of a threshold value table used for sympathy

FIG. 3A and

FIG. 3B is a toner distribution and a threshold table corresponding to the toner distribution according to another embodiment.

FIG. 4 is a threshold table showing still another embodiment.

FIG. 5 is a schematic side sectional view showing the configuration of a known cleaning device.

[Explanation of symbols]

 1 CCD 3 A / D Conversion Circuit 4 Video Counter 6 CPU 7 Toner Supply Circuit 8 Toner Supply Device 9 D / A Conversion Circuit 13 Scanning Means 14 Image Carrier 15 Developer 16 Primary Charger 17 Transfer Charger 18 Cleaning Device

Claims (3)

[Claims] 1. An image forming apparatus comprising an image carrier, a cleaning blade in pressure contact with the image carrier, and a developer concentration control means for changing the toner replenishment amount in accordance with the input image signal. An image forming apparatus comprising means for forming a latent image of a patch of density and developing the latent image, and means for conveying the toner applied to the image carrier to the cleaning portion. 2. The image forming apparatus according to claim 1, wherein the patch output is formed in the longitudinal direction of the edge of the cleaning blade. 3. The image forming apparatus according to claim 1, wherein the patch output is formed in a non-image area on the outer side in the longitudinal direction of the cleaning blade.